Common BCCH Control

GSM/EDGE BSS, Rel. RG10(BSS), Operating Documentation, Issue 08

Feature description

BSS10016 and BSS10118: Common BCCH Control DN0176501 Issue 9-2 Approval Date 2010-12-15

Confidential

BSS10016 and BSS10118: Common BCCH Control

The information in this document is subject to change without notice and describes only the product defined in the introduction of this documentation. This documentation is intended for the use of Nokia Siemens Networks customers only for the purposes of the agreement under which the document is submitted, and no part of it may be used, reproduced, modified or transmitted in any form or means without the prior written permission of Nokia Siemens Networks. The documentation has been prepared to be used by professional and properly trained personnel, and the customer assumes full responsibility when using it. Nokia Siemens Networks welcomes customer comments as part of the process of continuous development and improvement of the documentation. The information or statements given in this documentation concerning the suitability, capacity, or performance of the mentioned hardware or software products are given "as is" and all liability arising in connection with such hardware or software products shall be defined conclusively and finally in a separate agreement between Nokia Siemens Networks and the customer. However, Nokia Siemens Networks has made all reasonable efforts to ensure that the instructions contained in the document are adequate and free of material errors and omissions. Nokia Siemens Networks will, if deemed necessary by Nokia Siemens Networks, explain issues which may not be covered by the document. Nokia Siemens Networks will correct errors in this documentation as soon as possible. IN NO EVENT WILL Nokia Siemens Networks BE LIABLE FOR ERRORS IN THIS DOCUMENTATION OR FOR ANY DAMAGES, INCLUDING BUT NOT LIMITED TO SPECIAL, DIRECT, INDIRECT, INCIDENTAL OR CONSEQUENTIAL OR ANY LOSSES, SUCH AS BUT NOT LIMITED TO LOSS OF PROFIT, REVENUE, BUSINESS INTERRUPTION, BUSINESS OPPORTUNITY OR DATA,THAT MAY ARISE FROM THE USE OF THIS DOCUMENT OR THE INFORMATION IN IT. This documentation and the product it describes are considered protected by copyrights and other intellectual property rights according to the applicable laws. The wave logo is a trademark of Nokia Siemens Networks Oy. Nokia is a registered trademark of Nokia Corporation. Siemens is a registered trademark of Siemens AG. Other product names mentioned in this document may be trademarks of their respective owners, and they are mentioned for identification purposes only. Copyright © Nokia Siemens Networks 2011. All rights reserved

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The same text in German:

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DN0176501 Issue 9-2


Table of contents This document has 71 pages. Summary of changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1

Overview of Common BCCH Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2 2.1 2.2 2.3 2.4 2.5

Technical description of Common BCCH Control . . . . . . . . . . . . . . . . . Common BCCH frequency bands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mobile station capabilities with Common BCCH Control . . . . . . . . . . . . Intra-segment resource usability estimation . . . . . . . . . . . . . . . . . . . . . Inter-segment resource usability estimation . . . . . . . . . . . . . . . . . . . . . Segment environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11 11 12 13 13 14

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10

System impact of Common BCCH Control . . . . . . . . . . . . . . . . . . . . . . Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Restrictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact on transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact on BSS performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . User interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact on Network Switching Subsystem (NSS) . . . . . . . . . . . . . . . . . . Impact on NetAct products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact on mobile terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Impact on interfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interworking with other features. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

16 16 17 18 18 19 25 25 26 26 26

4 4.1 4.2 4.3 4.4

Common BCCH Control system information messages . . . . . . . . . . . . Common BCCH Control Cell Allocation. . . . . . . . . . . . . . . . . . . . . . . . . Several cell allocations in one band. . . . . . . . . . . . . . . . . . . . . . . . . . . . Common BCCH Control Mobile Allocation . . . . . . . . . . . . . . . . . . . . . . Common BCCH Control BCCH allocation . . . . . . . . . . . . . . . . . . . . . . .

35 35 35 36 36

5 5.1 5.2

Radio resource management and Common BCCH Control . . . . . . . . . 37 SDCCH allocation in Common BCCH segment. . . . . . . . . . . . . . . . . . . 37 TCH allocation in Common BCCH segment environment . . . . . . . . . . . 39

6 6.1 6.2 6.3 6.4

Handover algorithm and Common BCCH Control . . . . . . . . . . . . . . . . . 44 SDCCH resource usability evaluation in Common BCCH . . . . . . . . . . . 44 TCH resource usability evaluation in Common BCCH. . . . . . . . . . . . . . 47 Extended call set-up in Common BCCH segment . . . . . . . . . . . . . . . . . 52 SDCCH handover based on reservation duration and Common BCCH Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Load-based TCH handover and Common BCCH Control . . . . . . . . . . . 53 Intra-segment handover from non-BCCH layer based on signal level. . 54 Power budget handover and Common BCCH Control . . . . . . . . . . . . . 55 IUO handover and Common BCCH Control . . . . . . . . . . . . . . . . . . . . . 56 Channel allocation criteria based on the minimum acceptable C/N ratio and Common BCCH Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Optimisation of the MS power level in handover and in call set-up and Common BCCH Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

6.5 6.6 6.7 6.8 6.9 6.10

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7 7.1 7.2 7.3

Planning Common BCCH . . . . . . . . . . . . . . . . . Common BCCH and handover . . . . . . . . . . . . . Common BCCH and channel allocation . . . . . . SDCCH dimensioning with Common BCCH . . .

8

Implementing Common BCCH Control overview . . . . . . . . . . . . . . . . . . 71


....... ....... ....... .......

...... ...... ...... ......

. . . . . . 65 . . . . . . 65 . . . . . . 67 . . . . . . 70

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List of figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12

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GSM 900 / GSM 1800 Common BCCH configuration . . . . . . . . . . . . . . . 8 High level view of a SEG containing three frequency bands . . . . . . . . . 11 Segment and BTS object in Common BCCH . . . . . . . . . . . . . . . . . . . . 14 Example of SEG radio network objects . . . . . . . . . . . . . . . . . . . . . . . . . 15 IUO frequency groups in GSM 900 / GSM 1800 Common BCCH network 28 IUO frequency groups in GSM 800 / GSM 1900 Common BCCH network 28 Possible handover directions on a segment . . . . . . . . . . . . . . . . . . . . . 29 Hopping groups in a segment with GSM 900 and GSM 1800 resources (BCCH on PGSM 900). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Hopping groups in a segment with GSM 800 and GSM 1900 resources (BCCH on GSM 800) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Different interference levels with BSC recommendation 2 and without recommendation when searching for full-rate TCHs. . . . . . . . . . . . . . . . . . 41 Intra-segment handover from non-BCCH frequency layer to BCCH frequency layer of the segment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 PBGT HO decision when non-BCCH layer has less coverage . . . . . . . 55


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List of tables Table 1 Table 2 Table 3 Table 4 Table 5 Table 6

6

Required additional or alternative hardware or firmware . . . . . . . . . . . . 16 Required software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Impact of Common BCCH Control on BSC units . . . . . . . . . . . . . . . . . . 18 Counters of Handover Measurement related to Common BCCH Control . 22 Counters of BSC Level Clear Code (PM) Measurement related to Common BCCH Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Counters of Non-BCCH Layer Offset Measurement related to Common BCCH Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24


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Summary of changes

Summary of changes Changes between document issues are cumulative. Therefore, the latest document issue contains all changes made to previous issues. Changes made between issues 9-2 and 9–1 Section Several Cell Allocations in one band is added to the chapter Common BCCH Control system information messages. Changes made between issues 9-1 and 9–0 Information on InSite BTS has been removed. Changes made between issues 9-0 and 8–0 The NetAct Radio Access Configurator (RAC) changed to NetAct Configurator. Changes made between issues 8-0 and 7–1 The name of the document has been changed from Common BCCH Control in BSC to Common BCCH Control. Sections System impact of Common BCCH and Implementing Common BCCH have been added. Information related to PGSM 900 and EGSM 900 frequencies when regarded as a single BTS objects has been removed from chapters Overview of Common BCCH Control, System impact of Common BCCH and Common BCCH Control system information messages. Sections Requirements for Common BCCH Control in BSC and User interface of Common BCCH Control in BSC have been removed. Changes made between issues 7–1 and 7–0 Information on frequency hopping in an EGSM - PGSM BTS has been added in chaptersTechnical description of Common BCCH Control in BSC and Common BCCH Control system information messages. Changes made between issues 7–0 and 6–2 In Overview of Common BCCH Control, a list of related topics has been added. In Technical description of Common BCCH Control in BSC, a short reference to Dual Transfer Mode (DTM) has been added. In Requirements for Common BCCH Control in BSC, Flexi EDGE BTS has been added to the list software requirements for Common BCCH Control in BSC. The figure Example of SEG radio network objects has been improved.

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Overview of Common BCCH Control


1 Overview of Common BCCH Control Common BCCH Control allows the integration of resources from different frequency bands into one cell. TRXs of different frequency bands can be configured in the same cell by letting them share a common BCCH that has been allocated from one frequency band used in the cell. A common broadcast control channel (BCCH) of a cell is configured in only one of the bands of operation when resources across all bands are co-located and synchronised.

Cell 1 GSM900 (BCCH) / GSM1800

/



Cell 1

BTS-900

BTS-1800

Cell 2

BTS-900

BTS-1800

Cell 3

BTS-900 Synch.

BTS-1800

GSM900

GSM1800

BSC O&M O&M

Abis interface Figure 1

GSM 900 / GSM 1800 Common BCCH configuration

Common BCCH Control enhances the functionality of a cell to offer service to multiband user equipment in all the frequency bands which they support. It also provides improved trunking gain, tighter reuse of carriers, better quality because the number of handovers decreases, and improved spectral efficiency. The basic implementation of Common BCCH Control is based on the segment concept where the different frequency bands are separate BTS objects in the segment.

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The BSC supports Common BCCH Control for Talk-family, UltraSite, Flexi EDGE, and MetroSite base stations. Benefits of Common BCCH Control Using Common BCCH Control gives you the following benefits: • • •

• • • • •

improved trunking gain optimised use of signalling channels by sharing them between bands the absence of a BCCH channel (in non-BCCH frequency band) leads to a reduction of the overall interference and allows more freedom in frequency allocation with improved quality reduced number of cells in the network reduced number of Location Area Codes (LAC) reduced number of neighbouring cells multi-layer network simplified into one-layer network quality improvement due to decreased number of handovers between frequency layers; calls directed to an appropriate layer in call set-up

Other related topics •

• •

• •

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Activate • Radio Network Performance • Activating and testing BSS10016 and BSS10118: Common BCCH Control for GSM Administer • Radio Network Administration Reference • Commands • MML commands • EA - Adjacent Cell Handling • EE - Base Station Controller Parameter Handling in BSC • EH - Handover Control Parameter Handling • EQ - Base Transceiver Station Handling in BSC • EU - Power Control Parameter Handling • Counters/Performance indicators • Call Control Measurements (CS) • 4 Handover Measurement • 51 BSC Level Clear Code (PM) Measurement • 92 Non-BCCH Layer Offset Measurement • Parameters • BSS Radio Network Parameter Dictionary Troubleshoot • Base Station Alarms (7000–7999) Functional Area Descriptions • Radio Network Performance • Radio Channel Allocation • RF Power Control and Handover Algorithm • Traffic Reason Handover in BSC • Operability


9


•

10


• Radio Network Supervision in BSC Feature Descriptions • Existing Features • Radio Network Performance • Advanced Multilayer Handling • Direct Access to Desired Layer/Band (DADL/B) • Directed Retry in BSC • Dual Band Network Operation • Enhanced Coverage by Frequency Hopping • Enhanced Speech Codecs: AMR and EFR • FACCH Call Set-up • Frequency Hopping • Intelligent Underlay-Overlay • PGSM 900 - EGSM 900 BTS in BSC • Packet Switched Data • GPRS System Feature Description • HSCSD and 14.4 kbit/s Data Services in BSC • Macrocellular • Extended Cell • Handover Support for Coverage Enhancements • Multi BCF Control in BSC • Value added services • Radio Resource Pre-emption and Queuing • Trunk Reservation


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Technical description of Common BCCH Control

2 Technical description of Common BCCH Control 2.1

Common BCCH frequency bands The following frequency band combinations are supported: • • • • •

PGSM 900 / EGSM 900 PGSM 900 / GSM 1800 PGSM 900 / EGSM 900 / GSM 1800 EGSM 900 / GSM 1800 GSM 800 / GSM 1900

The BCCH carrier is allowed in any of the supported frequency bands. Note that if you combine the resources of several base stations into one segment, you must have Multi BCF Control activated.

GSM 1800 EGSM 900

SEG

PGSM 900

BTS

Figure 2

High level view of a SEG containing three frequency bands

A common BCCH segment must contain a "serving layer". It is the frequency band, which contains the TRX with the BCCH channel, and any other combination of TRXs from other frequency bands. The band where the BCCH carrier is in the common BCCH controlled segments must be the same throughout the whole network. This ensures that the support for single band mobile stations remains in at least one of the frequency bands of operation. It is also possible that there are single band cells, possibly on different frequency bands, in the network simultaneously with the multiband common BCCH segments and the service to mobile stations is offered via these single band cells as well. The need for dividing GSM 900 resources into two different bands in Common BCCH Control comes from the different capabilities of the terminals. Specifications state that the EGSM 900 band includes both the primary GSM 900 frequencies and the extension band. This means that BTSs and mobile stations supporting EGSM 900 support also the PGSM 900 frequencies. In the segment solution, however, an EGSM 900 BTS contains only the extended band GSM 900 frequencies that are outside the primary GSM 900 band. Using this division the BSC can make sure that only terminals supporting EGSM 900 are directed to the EGSM 900 frequencies. In addition to the varying capabilities of terminals in supporting different frequency bands, the BCCH frequency band and the non-BCCH frequency band have to be kept as separate resources because of the different propagation properties of these two

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bands. To ensure proper operation of the network, you should take into account issues related to the difference of propagation when performing cell planning. The above discussion about the different propagation properties refers to the resource division between GSM 900 and GSM 1800 and also between GSM 800 and GSM 1900. Because the division between PGSM 900 and EGSM 900 resources exists only because of the different capabilities of the terminals, the BSC regards these two bands as equal from the radio properties' point of view. If, for example, the BCCH of a segment is in a PGSM 900 BTS, and there is also an EGSM 900 BTS in the segment, the resources of this latter BTS are regarded usable whenever the resources of the BCCH BTS are regarded usable, if only the MS in question supports EGSM 900.

2.2

Mobile station capabilities with Common BCCH Control In each frequency combination environment, Mobile Stations (MS) may support one or more of the frequency bands specified in the GSM specifications. An MS which supports more than one frequency band and the functionality described in the following paragraph is defined as a multiband MS [3GPP 43.026]. The multiband MS has the functionality to perform handover, channel assignment, cell selection and cell re-selection between all its bands of operation within a PLMN when one PLMN code is used in all bands. Additionally, it has the functionality to make a PLMN selection, in manual or automatic mode, in all its bands of operation. The multiband MS will meet all requirements specified for each individual band. In addition, it will meet the extra functional requirements for multi band MSS. Selection of the frequency band in a common BCCH segment is based on the resource situation on each band and the frequency capabilities of the mobile station. The BCCH carrier is configured in the same frequency band in the whole area of the network. Consequently, the mobile stations which have service in the common BCCH network can be distinguished as follows: Single Band MS MS supports one frequency band. Multi Band MS MS supports two or more frequency bands. In a network where cells with resources from different frequency bands are controlled by a common BCCH on one of those bands, the access to the network is limited to the mobile stations that support the BCCH frequency band of the network. Thus, the MSS, single band or multiband, supporting the BCCH frequency band have access to the services of the common BCCH network. MS Classmarks Different classes of mobile stations can be defined according to their frequency capabilities. .The information of the mobile station's frequency capabilities is included in two information elements (IEs): •

12

Mobile Station Classmark 2 IE, which includes information on the possible EGSM 900 capability of the mobile station. The network receives this IE in the ESTABLISH INDICATION message.


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Mobile Station Classmark 3 IE, which defines all the frequency bands supported by the MS and the MS power capabilities in each supported frequency band. The network receives this IE in the CLASSMARK CHANGE message.

The BSC receives both of these messages while the related mobile station is on a dedicated signalling channel (SDCCH). Controlled early classmark sending In early classmark sending, the MS sends a Classmark Change message as early as possible after accessing the network to provide the additional classmark information. An MS which carries out the "Controlled early classmark sending" option, performs the early classmark sending if the network explicitly accepts it, as indicated in the last reception of the System Information type 3 message in the accessed cell. An MS which carries out one of the "Multiple band support" options also carries out the "Controlled Early Classmark Sending" option. An MS which carries out the "Controlled early classmark sending" option indicates it in the Mobile Station Classmark 2 (ES IND = Establishment Indication bit). The MS also sends the Classmark Change message containing the Mobile Station Classmark 2 and Mobile Station Classmark 3 information elements on the first occasion if the network accepts it.

2.3

Intra-segment resource usability estimation When the BSC has received information on both the MS frequency band capability and on the downlink received BCCH signal level (measurement report), it defines the usability of the segment's different resource types. For formulas for non-BCCH layer resource usability estimation used (in intra-segment SDCCH-SDCCH handovers and TCH allocations for call set-up, or intra-segment TCH-TCH handovers), see SDCCH resource usability evaluation in Common BCCH. If the MS is on a BCCH layer channel, the RXLEV_DL is the terminal received signal level on the channel. If the MS is using a non-BCCH layer channel, the RXLEV_DL is the downlink signal level of the BCCH carrier of the segment. If the RX level based TCH access is in use, the TCH usability in call set-up and intrasegment TCH-TCH handover is determined with the following formula: RXLEV_DL - non BCCH layer offset >= C/N + DL noise level + 110 where carrier-to-noise ratio (C/N) is a user-defined BSC-level parameter separate for each call type and DL noise level a user-defined BTS-level parameter. For a list of the user-defined BSC-level C/N parameters, see BSC radio network object parameters in BSC parameters.

2.4

Inter-segment resource usability estimation When the BSC has defined a need for an inter-segment (SDCCH-SDCCH or TCH-TCH) handover based on the measurements of the serving channel, the usability of the different resource types of each candidate segment is decided using the BCCH measurement results for the segment and the values of parameter non BCCH layer offset for different resource types in the segment. For more information on the criteria used, see TCH resource usability evaluation in Common BCCH. RxLevMinCell(n) is the level which the signal level in the adjacent segment must exceed for the handover to the adjacent segment to become possible.

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If the RX level based TCH access is in use, the TCH usability in inter-segment TCH-TCH handover is determined with the following formula: AV_RXLEV_NCELL(n) - non BCCH layer offset >= C/N + DL noise level + 110 where C/N is a user-defined BSC-level parameter separate for each call type and DL noise level a user-defined BTS-level parameter. For a list of the BSC-level C/N parameters, see BSC radio network object parameters in BSC Parameters. In a handover between two BSCs, the radio link measurements related to the target segment are available on the source side BSC only. It is therefore not possible to use the radio link measurements to define the usability of the non-BCCH layer resources on the target side. In this case the decisions are based on the non BCCH layer offset parameter. If the non-BCCH layer is regarded as a layer with less coverage (as indicated by the positive value of the non BCCH layer offset parameter), only BCCH frequency band resources are used in channel allocation for external handovers. For more information, see Radio Channel Allocation.

2.5

Segment environment Multi BCF Control and Common BCCH Control use an architecture and radio network object called segment (SEG). The properties of a segment are the following: • • • • •

A segment is essentially the same as a telecom cell. A segment may consist of several BTS objects. BTSs of a segment are co-located and synchronised. The maximum number of BTSs in a segment is 32. The maximum number of TRXs in a segment is 36.

The BTS object in a segment must consist of TRXs of the same • •

frequency band (PGSM 900, EGSM 900, GSM 1800, GSM 800, GSM 1900 separated) base station site type (Talk-family, UltraSite, Flexi EDGE, and MetroSite separated)

BTS specific parameters

Segment specific parameters BTS

SEGMENT

14

BTS

EGSM 900

GSM 1800

PGSM 900 PGSM 900 BCCH

Figure 3

BTS

Segment and BTS object in Common BCCH


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Figure Segment and BTS object in Common BCCH shows a typical BTS configuration in Common BCCH. When considering Common BCCH, segment-specific and BTSspecific parameters should be taken into account. In many cases the BTS and the frequency band are the same. However, sometimes they are different. For example, PGSM 900 Talk-family and PGSM 900 UltraSite must be configured as separate BTSs. Segment-specific, BTS-specific, and frequency-band-specific parameters need to be considered in this case. The allocation of a dedicated channel (SDCCH or TCH) inside a multiband segment (that is, with BTSs from different frequency bands) is based on: • • •

the frequency capabilities of the mobile station the prevailing radio conditions of the mobile station the resource situation on each band.

The second condition is evaluated for the secondary frequency band using the BTS parameter non BCCH layer offset. The possibility to use the segment structure is not restricted to Multi BCF Control or Common BCCH Control software, but it is an option of its own. You can, for example, create multiple hopping groups in a cell by gathering TRXs of one hopping group into one BTS object and have several such BTSs in a segment. The common BCCH segment is seen as one single cell even though parameterisation and management has been partly separated between the segment object and the BTSs of the segment. The MS also sees the segment as one BCCH frequency band cell and many SEGs as one BCCH frequency band network because it has no knowledge of the other frequency bands in a segment because these bands have no BCCH.

BCF-1

BCF-2

BTS-1

BTS-2

BTS-3

TRX-1

TRX-2

SEG-1

BCCH

TRX-4

SEG-2 BTS-4 BCCH Figure 4

TRX-3

= GSM 900 = GSM 1800

Example of SEG radio network objects

For an overview of Multi BCF Control, see Multi BCF Control.

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System impact of Common BCCH Control


3 System impact of Common BCCH Control The system impacts of BSS10016: Tri-Band GSM/EDGE Common BCCH, ETSI and BSS30045: GSM/EDGE Common BCCH, ANSI are specified in the sections below.

3.1

Requirements Hardware requirements Network element

HW/FW required

BSC

No requirements

BTS

RF units are band specific, and correct RF units are needed for the supported frequency bands.

TCSM

No requirements

SGSN

No requirements

Table 1

Required additional or alternative hardware or firmware

Software requirements Table Required software shows the earliest version that supports Common BCCH Control. Network element

Software release required

BSC

S11.5

Flexi EDGE BTSs

EP1.0

UltraSite EDGE BTSs

CX4.0

MetroSite EDGE BTSs

CXM4.0

Talk-family BTSs

DF6.0 Does not support 800/1900 Common BCCH.

MSC

No requirements

NetAct

OSS3.1 ED1 (Enhancement Delivery)

NetAct Planner

4.0

SGSN

No requirements

Table 2

Required software

Frequency band support for Common BCCH Control The BSC supports Common BCCH on the following frequency bands: •

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• • •

3.2


GSM 900 GSM 1800 GSM 1900

Restrictions The use of Common BCCH Control and the segment environment causes restrictions for the functionality of the following operating softwares. Configuration with Common BCCH Control The band where the BCCH carrier is in the common BCCH controlled segments must be the same throughout the whole network. BCCH Allocation and Common BCCH Control In Common BCCH, the BCCH frequency of the segment is added among the BCCH frequencies that the MS should measure when the MS is active on the non-BCCH band of the segment. This leads to the following restrictions: • •

There can be only 31 frequencies in adjacent cell and BA lists. Only 5 of the strongest neighbours are included in the adjacent cell measurements.

GSM-WCDMA Interworking and Common BCCH Control If GSM-WCDMA Interworking and Common BCCH Control are used together, the maximum amount of adjacent cells and frequencies in a BA list is 30. SDCCH allocation and Common BCCH Control In a multiband Common BCCH segment, the initial SDCCH channel for a call setup is always allocated in the frequency band where also the segment's BCCH is. Note that when the BCCH is on the EGSM 900 band, then all the GSM 900 resources of the segment can be regarded as being of the EGSM 900 frequency band and the segment's possible PGSM 900 resources are also available for the initial SDCCH allocation of a call. When an SDCCH is allocated for an external handover in a multiband Common BCCH segment the search may be restricted among the BCCH frequency band resources of the segment. This depends on the frequency band the BCCH is using. If the non-BCCH layer is regarded as a layer with less coverage (as indicated by the positive value of the non BCCH layer offset parameter) then only BCCH frequency band resources are used in the SDCCH allocation for an external handover. TCH allocation and Common BCCH Control Since a FACCH setup takes place as a response to an SDCCH allocation request the same restrictions as for SDCCH allocation represented in the previous chapter apply. In a multiband common BCCH segment the TCH for a FACCH setup is always allocated in the BCCH frequency band of the segment. When a segment's BCCH carrier is on EGSM 900 band then the segment's possible PGSM 900 resources are also available for the FACCH setup. When a TCH is allocated for an external handover in a multiband common BCCH segment the search may be restricted among the BCCH frequency band resources of the segment. This depends on the frequency band the BCCH is using. If the non-BCCH layer is regarded as a layer with less coverage (as indicated by the positive value of the

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non BCCH layer offset parameter) then only BCCH frequency band resources are used in TCH allocation for external handover. Dynamic SDCCH allocation and Common BCCH Control The dynamic SDCCH RTSLs can be utilised only in the BCCH frequency band in a common BCCH cell. This is because of the fact that the multiband capabilities of an accessing MS are not known at the time of the initial SDCCH allocation. When a segment's BCCH carrier is on EGSM 900 band then the segment's possible PGSM 900 resources are also available for the dynamic SDCCH allocation. Extended cell range and Common BCCH Control In the segment environment, only BCCH BTS can have extended area TRXs. Intelligent Underlay Overlay (IUO) and Common BCCH Control The super-reuse layer of a BTS in a segment with several BTSs can be accessed only via the regular layer of the BTS. The handover from super-reuse resources back to the regular layer is not restricted totally inside source BTS. But it is limited among the segment's BTSs that can be regarded as stronger than or equal to the source BTS (as indicated by the values of the respective non BCCH layer offset parameters). Frequency Hopping and Common BCCH Control The multiband MS and the multiband network support Frequency Hopping within each band of operation. Frequency Hopping between the bands of operation is not supported. Cell broadcast and Common BCCH Control You can give definitions with the ECS command only for the BCCH BTS.

3.3

Impact on transmission No impact.

3.4

Impact on BSS performance OMU signalling No impact. TRX signalling No impact. Impact on BSC units BSC unit

Impact

MCMU

No impact

BCSU

No impact

PCU

No impact

Table 3

18

Impact of Common BCCH Control on BSC units


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Impact on BTS units No impact.

3.5

User interface BSC MMI The following MML programs are used for handling Common BCCH Control: • • • • •

Adjacent Cell Handling: EA Base Station Controller Parameter Handling in BSC: EE Base Transceiver Handling in BSC: EQ Handover Control Parameter Handling: EH Power Control Parameter Handling: EU

For more information, see MML commands. BTS MMI Common BCCH Control cannot be managed with BTS MMI. BSC parameters Most of the parameters related to Common BCCH Control are defined per segment object. Parameters related to Common BCCH Control in Adjacent Cell Handling, Handover Control Parameter Handling, and Power Control Parameter Handling are all defined as common values for the BTSs of one segment. In the Base Transceiver Station Handling command group most of the parameters are segment level parameters, but there are also BTS-specific parameters with the possibility to define separate values for different BTS objects of a segment. For the parameter division between BTS and segment objects in Base Transceiver Station Handling, see BSS Radio Network Parameter Dictionary. Adjacent GSM Cell (ADJC/ADCE) radio network object parameters • • • •

MS txpwr max gsm MS txpwr max gsm1x00 GPRS MS txpwr max cch GPRS MS txpwr max cch1x00

The parameters MS txpwr max gsm (PMAX1) and MS txpwr max gsm1x00 (PMAX2) are used regardless of whether the Common BCCH Control options are enabled or not. MS txpwr max gsm (PMAX1) is used in the GSM 900 and the GSM 800 frequency bands, and MS txpwr max gsm1x00 (PMAX2) is used on the GSM 1800 and the GSM 1900 frequency bands. The parameters MS txpwr max CCH1x00 (TXP2) and GPRS MS TX pwr max CCH1x00 (GTXP2) are used regardless of whether the Common BCCH Control options are enabled or not. These new parameters are used in cells where the BCCH is either on the GSM 1800 or on GSM 1900 frequency band. The parameters MS txpwr max CCH (TXP1) and GPRS MS TX pwr max CCH (GTXP1) are used in cells where the BCCH is either on the GSM 900 or GSM 800 frequency band. Base Station Controller (BSC) radio network object parameters • •

DN0176501

intra segment SDCCH HO guard RX level based TCH access


19


• • • • •

soft soft soft soft soft

blocking blocking blocking blocking blocking


C/N C/N C/N C/N C/N

FR HR AMR FR AMR HR 14.4

The parameter intra segment SDCCH HO guard (ISS) is used for controlling the transfer of SDCCH reservations out of the BCCH resource layer in the segments under the control of the BSC. Base Transceiver Station (BTS) radio network object parameters • • • • •

BTS load non BCCH GPRS non GPRS non DL noise

in SEG layer offset BCCH layer rxlev lower limit BCCH layer rxlev upper limit level

The BTS-specific parameter non BCCH layer offset (NBL) is used for estimating the signal level of the non-BCCH layer resources and BTS load in SEG (LSEG) is used for controlling the traffic load in different BTSs of a segment. The parameter non BCCH layer offset (NBL) is used to indicate how much weaker the signal level of a BTS is when compared to that of the BCCH BTS. Because of this the value of the parameter must always be set to value 0 in the BCCH BTS. A positive value of NBL in a BTS indicates a signal level that is lower than in the BCCH BTS and prevents the SDCCH allocation for call set-ups and TCH allocation in external handovers in that BTS. The band-specific parameters bs tx pwr max (PMAX1) and bs tx pwr max 1x00 (PMAX2) have an effect on setting the parameter non BCCH layer offset (NBL). Frequency-band-specific BTS radio network object parameters • • • • • •

GPRS MS txpwr max cch GPRS MS txpwr max cch1x00 MS txpwr max cch MS txpwr max cch1x00 MS txpwr max gsm MS txpwr max gsm1x00

Handover Control (HOC) radio network object parameters • • • •

non non non non

BCCH BCCH BCCH BCCH

layer layer layer layer

access threshold exit threshold exit threshold Px exit threshold Nx

The parameter non BCCH layer access threshold (LAR) is used for the usability evaluation of the weaker frequency band in a segment with resources from different frequency bands. The parameters non BCCH layer exit threshold (LER), non BCCH layer exit threshold px (LEP), and non BCCH layer exit threshold nx (LEN) are used to decide whether the MS's downlink signal level is good enough on the weaker frequency band. Power Control (POC) radio network object parameters

20


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When radio frequency power control (POC) is created, the BSC selects the ALPHA and GAMMA default values according to the BCCH frequency band of the segment. If there is no BCCH TRX in the segment, and there is more than one frequency band in use in the segment when POC is created, then GSM 900 default values are used if there exists at least one GSM 900 or GSM 800 BTS in the segment. The different radio propagation properties of the different frequency bands of a multiband segment result in different radio coverages of the two bands. The maximum transmission power for the different frequency bands of a multiband segment needs to be adjusted separately in order to better maintain connection to MSS in the segment. Matching the radio coverage to the same size on both bands of a multiband segment is done by adjusting the maximum transmission power for the bands separately with band specific power controlling parameters BS TX pwr max and BS TX pwr max1x00. SEG-specific Base Transceiver Station (SEG-BTS) radio network object parameters • • •

direct GPRS access BTS SEG identification SEG name

For more information on radio network parameters, see BSS Radio Network Parameter Dictionary. Alarms The segment object is invisible to the BSC alarm system. The alarms are focused on the same radio network objects regardless of whether the segment architecture is used or not. All the cell and BTS-specific alarms are given per BTS object also in the segment environment. With the alarms that focus on the cell object, the alarm is given via the BCCH BTS of a multi BTS segment. The BSC generates alarm 7767 BCCH MISSING only for the BTSs having a BCCH configured. The congestion supervision for alarm 7746 CH CONGESTION IN BTS ABOVE DEFINED THRESHOLD is made in the BCCH BTS concerning the whole segment. The supervision for alarm 7746 CH CONGESTION IN BTS ABOVE DEFINED THRESHOLD is based on the relation between received and rejected resource requests in a cell. It is a general view of the cell's capability to serve mobile subscribers in its coverage area. In the multiband segment environment the rejection of a service request does not necessarily mean that all the segment's resources are occupied. Because of the different capabilities of terminals and the difference between the propagation properties of frequency bands the resources that are applicable to individual resource requests vary case by case. A rejection in a segment means that all the resources that could be applied for a request at that moment are occupied. Depending on the case this can mean all the resources of a segment or only part of them. In any case the congestion supervision gives a good idea how the supply meets the demand for radio channel resources in a cell. Measurements and counters The introduction of Common BCCH Control has not affected the basic structure of statistics. The measurements are still collected per BTS in the segment environment. In addition, the network service and management system NetAct offers the possibility to have frequency band-specific statistics and segment-specific statistics based on the BTS-specific measurements.

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The introduction of the segment concept and the possibility to have several BTS objects in one cell causes changes in the data collection of some cell level activities and in the BTS-specific counter interpretation in the segment environment. Common BCCH Control introduces some counters for the supervision of intra-segment TCH handover based on load, intra-segment handover from non-BCCH layer based on signal level, and inter-segment handovers that take place between separate BTSs of a segment. These are implemented in Handover Measurement and BSC Level Clear Code (PM) Measurement. The non-BCCH layer offset measurement collects data of the signal level differences between the BTSs of the BCCH frequency band and the non-BCCH frequency band. Based on the collected information, you can verify the accuracy and tune the values of the non BCCH layer offset (NBL) parameters of the non-BCCH layer BTSs. Common BCCH Control traffic measurement When a BTS-specific statistical counter is updated in a procedure where an entire segment is the target, the respective attempt counter is updated for the BCCH BTS of the segment. In traffic measurement this means that all incoming channel allocation attempts are included in the statistics of the BCCH BTS of the target segment. If an allocation attempt is not successful, the rejection of the resource request is updated according to the capabilities of the MS requesting the resource. Whenever the MS could accept a channel from a non-BCCH frequency band, the resource request rejection is updated for a non-BCCH frequency band BTS of the target segment, if there is one. If the request reject cannot be updated in a BTS of any other resource type, it will be updated for the BCCH BTS of the cell. In case of an unsuccessful channel allocation attempt for an internal intercell handover, the attempt and the resource request rejection are updated in the first segment of the handover candidate list. When the channel allocation succeeds, the procedure is updated in a counter of the BTS where the channel was allocated. In this case the attempt counter is updated for the BCCH BTS of the selected segment. Common BCCH Control handover measurement In the handover measurement, as well as in all other measurements collecting statistics on handovers, the counters that have been describing intra-cell handovers inside a BTS are in segment environment showing the handovers inside a segment. These include both handovers between a segment's BTSs and handovers within single BTSs. On the other hand the counters of inter-cell handovers that used to give information on all handovers between BTSs of a BSC are in segment environment collecting information of handovers that take place between BTSs of different segments. Handover measurement introduces Common BCCH Control specific counters to separate the intra-cell handovers in which calls move from one BTS to another from the ones in which calls only change channels within a BTS. The following 4 Handover Measurement counters are related to Common BCCH Control: Name

Number

INTRA CELL SUCCESS SDCCH HO BETWEEN BTSS

004131

INTRA CELL SUCCESS TCH HO BETWEEN BTSS

004132

Table 4

22

Counters of Handover Measurement related to Common BCCH Control


DN0176501



Name

Number

HO ATTEMPT INTER BAND SDCCH

004133

INTRA CELL SUCCESS SDCCH HO BETWEEN BANDS

004134

HO ATTEMPT INTER BAND TCH

004135

INTRA CELL SUCCESS TCH HO BETWEEN BANDS

004136

SUCCESSFUL HO INTER BAND TCH

004159

UNSUCCESSFUL HO INTER BAND TCH

004161

HO ATTEMPT INTER BAND DUE LEVEL

004163

UNSUCC HO INTER BAND DUE LEVEL

004164

SUCC HO INTER BAND DUE LEVEL

004165

INTER SEGMENT SUCCESS SDCCH HO BETWEEN BANDS

004166

INTER SEGMENT SUCCESS TCH HO BETWEEN BANDS

004168

Table 4

Counters of Handover Measurement related to Common BCCH Control

For more information, see 4 Handover Measurement. General counters In an intra-cell handover between BTSs inside a segment, the handover attempt counter is updated for the source BTS of the handover. This makes it possible to gather information on the origin of intra-cell handovers with the counters that were defined before the segment concept was introduced. When the intra-cell handover fails, the failure of the handover is also updated for the source BTS of the handover. In the successful case the update of the success counter is made for the BTS from which the channel is allocated. On the target side of an inter-cell handover with only one candidate cell and in external handovers between BSCs, the BSC updates the appropriate attempt counter for the BCCH BTS of the target segment. If the BSC is unable to allocate a channel for the handover, it also updates the failure for the BCCH BTS of the target segment. In a successful case the BSC updates the appropriate success counter for the BTS in which the allocation has been made. In addition, if the handover fails after the channel has been allocated, the failure is updated for the selected target BTS. In inter-cell handovers with several candidate cells, the object for the handover counter update on the target side varies depending on the success of channel allocation. If the BSC is able to allocate a channel for the handover, the counter updates on the target side are made for the BTS from where the channel has been allocated. In an unsuccessful channel allocation case the counters are updated for the BCCH BTS of the first SEG on the target cell list of the handover. Common BCCH Control specific counters The Common BCCH Control specific handover measurement counters include attempt counters that are updated for the source BTS of a handover. Other special counters for segment environment mainly collect information on completed handovers of certain types and are updated at the target BTS of the intra-segment handover. Common BCCH Control and BSC Level Clear Code (PM) Measurement Following the established practice with the handover attempt causes and the related handover measurement counters there are the respective success counters in the BSC

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Level Clear Code (PM) Measurement. The following counters are related to the interband handover attempts that are indicated by the Handover measurement counters 004133, 004135, and 004169. The following 51 BSC Level Clear Code (PM) Measurement counters are related to Common BCCH Control: Name

Number

INTRA INTER BAND TCH HANDOVER

051135

INTRA INTER BAND SDCCH HANDOVER

051136

INTRA INTER BAND DUE LEV

051153

Table 5

Counters of BSC Level Clear Code (PM) Measurement related to Common BCCH Control

For more information, see 51 BSC Level Clear Code (PM) Measurement. Common BCCH Control and Non-BCCH Layer Offset measurement The non-BCCH layer offset measurement collects data on how much weaker the signal level of a BTS on the non-BCCH layer is compared to that of the BCCH BTS. The measurement includes counters for absolute difference values from -40 to +40 dB in 1 dB steps. All the samples that are below -40 dB are collected into a separate counter. In addition, the samples that indicate a difference greater than 40 dB are collected in a counter of their own. The negative values are for the cases where the signal level of the non-BCCH layer is actually stronger than that of the BCCH BTS. The measurement samples are collected at the SACCH signalling rate from each MS with an ongoing call in a non-BCCH frequency band BTS. When defining the signal level differences between the bands, the BSC takes into account the used power levels in order to establish an accurate value of the difference between the two frequency bands. The non-BCCH layer offset statistics are collected BTS-specifically in every BTS that is on the non-BCCH frequency band of a segment using Common BCCH Control. The operator can use the results of the measurement to verify the accuracy of the non BCCH layer offset (NBL) parameters of the non-BCCH layer BTSs. The following 92 Non-BCCH Layer Offset Measurement counters are related to Common BCCH Control: Name

Number

OFFSET SAMPLE BELOW -40

092000

OFFSET SAMPLE OF ZERO

092001

OFFSET SAMPLE OF +1

092002

OFFSET SAMPLE OF +40

092041

OFFSET SAMPLE ABOVE +40

092042

OFFSET SAMPLE OF -40

092043

OFFSET SAMPLE OF -1

092082

Table 6

24

Counters of Non-BCCH Layer Offset Measurement related to Common BCCH Control


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For more information, see 92 Non-BCCH Layer Offset Measurement.

3.6

Impact on Network Switching Subsystem (NSS) No impact.

3.7

Impact on NetAct products NetAct support for Common BCCH Control and Multi BCF Control is available from OSS3.1 ED1 onwards. If this release is not available, it is not recommended to activate Common BCCH Control and Multi BCF Control in the network. Otherwise the whole management of radio network in the sites where Common BCCH Control and Multi BCF Control are available will not work. NetAct Administrator NetAct Administrator offers full support for Common BCCH Control and Multi BCF Control administration tasks, for example: • • •

Fast download and activation of Common BCCH Control and Multi BCF Control software to BTSs via NetAct tools Expandable software archives Storages for multiple software configurations

NetAct Monitor Standard NetAct monitoring applications are also used for monitoring Common BCCH Control and Multi BCF Control. NetAct Optimizer Optimizer supports BSS Common BCCH Control and Multi BCF Control. Internally Optimizer creates cell objects based on segment ID and Master BTS flag information. In geographical map view Common BCCH Control and Multi BCF Control cells (segments) are visible entirely; non-segment BTSs are available normally. Two views are available in Topology view: new cell (segment) view and old common object model view (BSCBCF-BTS). Adjacency, Power Control, and Handover Control objects are linked to Master BTS in cell (segment). NetAct Planner NetAct Planner release 4.1 includes a set of radio network and planning features for Common BCCH Control and Multi BCF Control. This allows visibility of Common BCCH Control and Multi BCF Control in radio network planning: creation of Multi BCF master BTSs and Common BCCH allocations. Plans can be completed with the Configurator. NetAct Configurator NetAct Configurator provides network wide access and tools to configure Common BCCH Control and Multi BCF Control. The related BTS radio parameters can be managed from Configurator. In BSC, Common BCCH Control and Multi BCF Control management is handled via segment. In the Configurator the segment management is done using a master BTS definition., see Maintaining Multi-BCF Sites in NetAct Product Documentation.

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NetAct Reporter Reporting for Common BCCH Control and Multi BCF Control is done by common NetAct reporting tools. NetAct Reporter can be used to create reports from measurements related to Common BCCH Control. The segment replaces in many cases BTSs in reporting: • • •

presenting raw counters or KPIs result in segment ID level instead of BTS level with the current ReportBuilder defining the object (for example, segment ID, BTS, etc.) aggregation method on top of the time aggregation formula in the Formula wizard with ReportBuilder selecting the segment ID as hierarchy and segment ID as summary level in the dimension selection for report properties

Note that the BTS level is still applicable in some cases, although it is in many cases replaced by segment. NetAct Tracing No impact.

3.8

Impact on mobile terminals Common BCCH Control requires a multiband capable terminal.

3.9

Impact on interfaces No impact.

3.10

Interworking with other features Wideband AMR When Wideband AMR is enabled in BSC and WB-AMR FR is set as the most preferred speech codec, BSC selects channel primarily from Wideband AMR capable BTS and TRX. PGSM 900 - EGSM 900 BTS If you are using the GSM 900 frequency band, the PGSM 900 and EGSM 900 resources do not necessarily have to be configured as separate BTS objects. It is also possible to have both the PGSM 900 and EGSM 900 TRXs in a single BTS object, which enables BCCH recovery between the TRXs. There are restrictions when the BCCH is on PGSM 900 frequency in a PGSM 900 EGSM 900 BTS., see PGSM 900 - EGSM 900 BTS in BSC. BCCH allocation In Common BCCH, the BCCH frequency of the segment is added among the BCCH frequencies that the MS should measure when the MS is active on the non-BCCH band of the segment. This leads to the following restrictions: • •

26

There can be only 31 frequencies on adjacent cell frequency list and BCCH Allocation frequency list. Only 5 of the strongest neighbours are included in the adjacent cell measurements.


DN0176501



SDCCH allocation In a multiband Common BCCH segment, the Initial SDCCH channel for a call set-up is always allocated in the frequency band where also the segment's BCCH is located. An exception to this rule is when the segment's BCCH carrier is on EGSM 900 band. When the BCCH carrier is on EGSM 900 band, the possible PGSM 900 resources of the segment are also available for the initial SDCCH allocation of a call. When an SDCCH is allocated for an external handover in a multiband Common BCCH segment, the search may be restricted among the BCCH frequency band resources of the segment. This depends on the frequency band the BCCH is using. If the non-BCCH layer is regarded as a layer with less coverage (as indicated by the positive value of the non BCCH layer offset parameter), only BCCH frequency band resources are used in SDCCH allocation for external handovers. Dynamic SDCCH allocation The dynamic SDCCH RTSLs can be utilised only in the BCCH frequency band in a Common BCCH cell. This is due to the fact that the multiband capabilities of an accessing MS are not known at the time of the initial SDCCH allocation. When the segment's BCCH carrier is on EGSM 900 band, the possible PGSM 900 resources of the segment are also available for the dynamic SDCCH allocation. Queuing Queuing is applied at the segment level. There is no priority between different mobile types; therefore the mobiles supporting all frequency bands are more likely to be allocated a channel. There is no specific reason to vary the values of the parameters time limit call and time limit handover with respect to the one-layer network setting. The value of the parameter max queue length has to be reset, considering that the percentage is evaluated on the total number of TRXs (including all BTSs of the segment) and the resulting number should be lower than the number of available SDCCH channels on the BCCH serving layer band. This is because some capacity must be left to services that run on SDCCH only (for example, SMS). Some mobiles may be put into a queue even though all the TCH resources of the segment are not fully utilised (this is the case when the mobile in the queue does not support the available capacity). In this case it is very important to make sure that SDCCH capacity is still available for further requests from mobiles supporting the available TCH capacity. For this reason the margin between max queue length and the number of SDCCH channels on the BCCH serving layer band should be greater than before. GPRS/EDGE Each BTS object in a segment has its own GPRS terrritory. The parameters that are used to define the size of GPRS territory are adjusted in each BTS. When comparing the TCH load of a segment's BTS with the parameter BTS load in SEG, the BSC interprets RTSLs in GPRS territory as busy channels (excluding dedicated GPRS resources). This interpretation prevents the GPRS territory of a single BTS from shrinking unnecessarily, if there are other BTSs in the segment to which CS calls could be transferred from the BTS in question. Note that you must define GPRS territory to the BCCH frequency band in a common BCCH cell in which more than one frequency band is in use. Otherwise GPRS does not

DN0176501


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work properly in the cell. The reason for this requirement is that in cases when the MS RAC of the GPRS mobile is not known by the BSC the TBF must be allocated on the BCCH frequency band first. During the first TBF allocation the GPRS mobile indicates its frequency capability to BSC. After that other frequency bands of the cell can be used for the GPRS mobile accordingly. The interactions between the circuit switched radio resource management of a segment and GPRS are explained in detail in TCH allocation in Common BCCH segment environment. For the effects of the segment concept on the radio resource management of the packet switched services in the PCU, see GPRS in BSC. Every GPRS BTS in a segment has to be connected to the same PCU. For more information about GPRS territories, see GPRS/EDGE in BSC . Pre-emption When the segment architecture is used, Pre-emption is a segment level function. In a segment with several BTSs of different properties it is possible that a TCH request cannot be served even though all the TCH resources in a segment are not fully utilised. However, pre-emption is possible if permitted by the related parameters. The candidate for the forced actions is selected among the resource types that are indicated as reasonable in the resource request that initiates these actions. In the candidate selection the criterion of the lowest possible priority is the most important one. When searching for the lowest priority call the different resource types are preferred so that the BTSs that use same frequency band as BCCH BTS are the most preferred ones. Intelligent Underlay-Overlay In the segment environment, the use of Intelligent Underlay-Overlay is a BTS-specific functionality. Each BTS in a segment can have its own regular and super-reuse layers. The super-reuse layer of a BTS can be accessed only via the regular layer of the BTS. P reg

P super

E reg

E super

D reg

D super

P GSM 900

super

E GSM 900

super

GSM 1800

super

regular TRXs

TRXs

regular TRXs

TRXs

regular TRXs

TRXs

Figure 5

IUO frequency groups in GSM 900 / GSM 1800 Common BCCH network

GSM 800 regular TRXs

Figure 6

GSM 800 super TRXs

GSM 1900 regular TRXs

GSM 1900 super TRXs

IUO frequency groups in GSM 800 / GSM 1900 Common BCCH network

The target for a super-reuse TCH request is always one BTS (a few TRXs within the BTS) and not the whole segment as in resource requests in general. The handover from regular resources to super-reuse resources in a BTS is the same regardless of whether segment architecture is used or not. When an IUO handover from a super-reuse TRX to the regular resources of a BTS is performed, the information on the usability of different resource types in the segment is decided based on the values of the parameter non BCCH layer offset in the differ-

28


DN0176501



ent BTSs of the segment. As a target, the BSC accepts the BTSs whose non BCCH layer offset value is less than or equal to the value of the BTS where the handover was initiated. This is indicated in the figure Possible handover directions on a segment with dashed-line arrows going from the super-reuse layer of one BTS to the regular layer of another BTS in a segment. The child cell concept is not supported in the BSC in which the segment option is enabled. Direct Access to super-reuse layer is only supported inside the BTS object with the initial SDCCH, which must be in the BCCH band. To get an accurate estimation of the C/I value of the Common BCCH segment's nonBCCH frequency band layer, the estimation is based on the measurement of the BCCH frequency in the segment. The C/I calculation is modified so that the segment's BCCH measurement result is used instead of the serving TCH measurement result.

BTS1

BTS2

Regular area

Regular area

Super-reuse area

Super-reuse area

Figure 7

Possible handover directions on a segment

For more information, see Intelligent Underlay-Overlay. Multi BCF Control When Common BCCH Control is combined with Multi BCF Control, you are allowed to configure to one segment both BTSs of different frequency bands and BTSs of different base station types. For more information, see Multi BCF Control . Frequency Hopping The multiband MS and the multiband network support Frequency Hopping within each band of operation. Frequency Hopping between the bands of operation is not supported. Frequency Hopping is managed by a BTS when the segment concept is in use. In a PGSM 900 - EGSM 900 BTS, Frequency Hopping is possible on only one of the two bands. However, there is a feature called Single MA list for EGSM 900 and PGSM 900 that allows combined frequency hopping with PGSM 900 and EGSM 900 and this feature is licence key controlled. In the segment architecture the resources of different types are grouped as separate BTSs. All the resource types have the hopping parameters and the hopping groups of their own.

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BB hopping PGSM 900 BTS, two hopping groups

EGSM 900 BTS, two hopping groups

GSM 1800 BTS, two hopping groups

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

0

1

2

3

4

5

6

7

RF hopping PGSM 900 BTS, one hopping group

EGSM 900 BTS, one hopping group

GSM 1800 BTS, one hopping group

0

1

2

3

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Hopping groups in a segment with GSM 900 and GSM 1800 resources (BCCH on PGSM 900)

BB Hopping GSM 800 BTS Two hopping groups

GSM 1900 BTS Two hopping groups

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RF Hopping GSM 1900 BTS One hopping group

GSM 800 BTS One hopping group

Figure 9

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Hopping groups in a segment with GSM 800 and GSM 1900 resources (BCCH on GSM 800)

The segment architecture enables having BTSs without a BCCH TRX. This reduces the amount of hopping groups in the regular area of a BTS, because there is no need for a separate group for the BCCH TRX in RF hopping. In baseband hopping there is also no need for separating TSL0 from the other TSLs in BTSs that do not contain a BCCH TRX. However, the separation between TSL0 and other TSLs remain and these are regarded as two different hopping groups. The user gives one set of parameters for the TSL0 group and another for the other TSLs. A similar set of parameters can be given for both.

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The segment model offers the opportunity to have several hopping groups even though there are only resources for one band in a segment. The operator can form hopping groups by gathering the needed TRXs into one BTS and have several BTSs of the same band. Each BTS has hopping parameters of its own. For more information, see Frequency Hopping. High Speed Circuit Switched Data (HSCSD) From the point of HSCSDthe effects of the segment structure appear mainly when allocating TCHs for HSCSD requests. The basic principles that apply for the TCH allocation in general are also valid in HSCSD cases. This means that the HSCSD resource allocation is made according to the capabilities of an MS considering the radio conditions and the loads of different resource types. Among the resource types that the BSC defines as reasonable, the TCH search is performed in a way that an HSCSD channel configuration that best fulfills the request is selected. Within a segment the HSCSD allocation is made in a BTS that has no restrictions based on the HSCSD load parameters rather than in a BTS where the allocation is restricted to include only one TCH. The user can control the HSCSD traffic load between BTSs of a segment by using BTS specific HSCSD load parameters HSCSD TCH capacity minimum,HSCSD cell load upper limit, HSCSD cell load lower limit and HSCSD regular cell load upper limit. If necessary, in the segment environment one HSCSD downgrade per segment per received request is made. When the received request leads to TCH allocation, the need for an HSCSD downgrade is examined in the BTS of the allocation. In case a free TCH cannot be found, the candidate for the HSCSD downgrade is selected among the segment's BTSs that are defined as appropriate targets for the request. A round robin method is used to direct separate downgrade attempts to different BTSs in the segment. In each BTS the downgrade decision is based on the HSCSD parameters of the particular BTS. For more information, see HSCSD and 14.4 kbit/s Data Services in BSC. Enhanced Coverage by Frequency Hopping and Handover Support for Coverage Enhancements Enhanced Coverage by Frequency Hopping and Handover Support for Coverage Enhancements can be used in the BCCH BTS of common BCCH controlled cells. For more information, see Handover Support for Coverage Enhancement and Enhanced Coverage by Frequency Hopping. Extended Cell, Extended Cell Range In a segment environment, only BCCH BTSs can have extended area TRXs. For more information, see Extended Cell. Directed Retry Directed Retry or Intelligent Directed Retry can be triggered even if all resources of a segment are not completely in use. It requires that all the resources that an accessing MS could utilise under the current conditions are unavailable. Since the Directed Retry procedure reduces SDCCH capacity, the Directed Retry timers should not be set too high and SDCCH capacity should be dimensioned with the proper

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margin, to avoid SDCCH blocking (due to the DR procedure) for any mobile supporting the available TCH capacity. For more information, see Directed Retry in BSC. Direct Access to Desired Layer/Band The purpose of Direct Access to Desired Layer/Band is to direct traffic in the call setup phase from the SDCCH of a macrocell/GSM 900/800 cell to a TCH of a micro cell/GSM 1800/1900 cell whenever possible. In the segment environment, DADL/B can be used to direct traffic between segments. The loads are evaluated per segment, adjacency definitions are between segments, and DADL/B handovers are made between segments. For more information, see Direct Access to Desired Layer/Band (DADL/B) . Trunk Reservation and Common BCCH Control The control of Trunk Reservation is removed from the BTS level to the segment level. The defining of the number of the available TCHs in a segment is made according to the capabilities of the accessing MS. In case of PGSM 900 MS only the respective resources are examined. In case of a multi band terminal both BCCH frequency band and non-BCCH frequency band resources are included in calculations. Non-BCCH frequency band resources are included even though the MS cannot utilise them immediately because of bad radio conditions. However, the MS can be handed over to the nonBCCH frequency band as the conditions improve. For more information, see Trunk Reservation . Advanced Multilayer Handling The BSC-controlled traffic-reason handover is a segment level procedure, including the related parameters. The loads are evaluated per segment, and the idea is that the power budget margin is dynamically changed to direct the MSS at the segment border to less loaded adjacent segments. Nevertheless, if each segment is dimensioned to handle the needed capacity (as it should be with Common BCCH Control, considering that three different bands can be used and up to 36 TRX objects are allowed in a segment), the traffic should be smoothed out among the BTSs within a segment, rather than directed to adjacent segments. Therefore, when Common BCCH Control is active and the segments are multiband, the Advanced Multilayer Handling is less beneficial. For more information, see Advanced Multilayer Handling, Intelligent Underlay-Overlay and Dual Band Network Operation and RF Power Control and Handover Algorithm. Minimum acceptable C/N ratio in channel allocation If the value of the parameter CN threshold varies between the BTSs of the same resource type, the BSC selects the highest value for calculation. The recommendation for a certain resource type in the segment is disabled when the value is not used even in one of the BTSs of the same resource type. MS power level optimisation in handover and call setup If the value of the parameter optimum Rx lev UL varies between the TRXs of the BTSs of the same resource type, the BSC selects the highest value for calculation. The optimum uplink RF signal level for a certain resource type in the segment is disabled

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when the value is not used even in one of the TRXs of the BTSs of the same resource type. MSC controlled TRHO & resource indications with Common BCCH Control The MSC controlled traffic reason handover and the related resource indications are segment level procedures. In the spontaneous resource indication method the segment level parameter BTS load threshold is used when defining the need to send the resource indication. In selecting the candidate call for the traffic reason handover the BCCH BTS is preferred. If there are not enough of suitable candidates in the BCCH BTS, the candidates are selected from other BTSs of the segment. The other BTSs of the segment are preferred according to their frequency band in the following way: •

BTSs using BCCH frequency band are preferred to BTSs using other than BCCH frequency band.

Note that when the BCCH is on the EGSM 900 band then also the PGSM 900 resources of the segment can be regarded as belonging to the EGSM 900 frequency band. When there are three frequency bands (PGSM 900, EGSM 900 and GSM 1800) in use in Common BCCH segment the preference between the two non-BCCH frequency bands is made in the following way: • •

If BCCH is on PGSM 900 frequency band EGSM 900 is preferred to GSM 1800. If BCCH is on GSM 1800 frequency band PGSM 900 is preferred to EGSM 900.

For more information, see Traffic Reason Handover in BSC . Radio network supervision The congestion supervision for alarm 7746 CH CONGESTION IN CELL ABOVE DEFINED THRESHOLD is monitored on the segment level since the target for a channel request is a segment. In a segment with several BTSs, the channel congestion supervision is made in the BCCH BTS for the whole segment. And a possible alarm on congestion, even if it is identified with the BCCH BTS, describes the congestion level of the whole segment. For more information, see Radio Network Supervision in BSC . FACCH Call Setup In the FACCH call setup the SDCCH phase during which the capability information of an accessing terminal are received is totally skipped and the call is put directly to a TCH channel, so there is no information on the usability of the possible other resource types than that of the segment's BCCH TRX at the time the TCH is allocated. Because of this a TCH for an FACCH setup is allocated within the resource type that the BCCH TRX of the segment represents. As an exception to the rule, when the segment's BCCH carrier is on EGSM 900 band, the possible PGSM 900 resources of the segment are also available for the FACCH Call Setup. Adaptive Multi-rate speech codec (AMR) and Common BCCH Control Decisions on the need for packing AMR full rate (FR) calls to half rate (HR) AMR calls is based on the load situation of each individual BTS also in the segment environment. If FR AMR calls in a certain BTS should be packed is decided based on the load of that

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BTS only. Furthermore, the intra-cell handovers that perform the actual packing of calls are implemented as BTS internal events. For more information, see Enhanced Speech Codecs: AMR and EFR.

External handover When a TCH is allocated for an external handover in a multiband Common BCCH segment, the search may be restricted among the BCCH frequency band resources of the segment. This depends on the frequency band BCCH is using. If the non-BCCH layer is regarded as a layer with less coverage (as indicated by the positive value of the non BCCH layer offset parameter), only BCCH frequency band resources are used in TCH allocation for external handovers. TRX prioritisation in TCH allocation The possibility to favour or avoid the BCCH TRX in call assigning has been maintained to some extent in the segment environment. This is examined after the BTSs of a segment have been compared on the basis of their loads and their respective load parameters. Shutdown with forced handover When locking a single BTS of a segment, an intra-cell handover is possible. If a BCCH BTS of the segment is in the state LOCKED when another BTS in the SEG is shut down, only an inter-cell handover is possible. The same applies when the BCCH BTS itself is shutting down. Dual Band Common BCCH Control replaces Dual Band. However, Dual Band is available for cases where BTS site and cell definitions still use separate BCCHs for each of the bands. Use Common BCCH if possible. GSM-WCDMA Inter-System Handover and GSM - TD-SCDMA Interworking If GSM-WCDMA Inter-System Handover and GSM - TD-SCDMA Interworking are used together with Common BCCH Control the maximum number of adjacent cells and frequencies in a BA list is 30. Dual Transfer Mode The BSC decides the usability of a segment’s BTSs for a Dual Transfer Mode (DTM) call by using the RX-level based traffic channel (TCH) access control. on DTM, see Dual Transfer Mode. Energy Optimised TCH Allocation TCH is allocated primarily among those BTSs that have appropriate resources with same interference level as interference recommendation is present on the TCH request. It is possible that interference recommendation is not present for BCCH BTS hence, TRX for TCH allocation may be selected from non-BCCH BTSs.

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Common BCCH Control system information messages

4 Common BCCH Control system information messages 4.1

Common BCCH Control Cell Allocation Cell Allocation (CA) is a subset of radio frequency channels that is allocated to each common BCCH segment. One of Cell Allocation's radio frequency channels is used to carry synchronisation information and the BCCH. This is known as the BCCH carrier. The subset of the Cell Allocation frequencies that is allocated to a particular MS is known as the Mobile Allocation. The MS uses the CA list to decode Mobile Allocation when frequency hopping is applied. The multi-band MS and multi-band network support frequency hopping within each band of operation. Frequency hopping between the bands of operation is not supported. Although frequencies of several bands can be in use in a segment, they are kept apart by having separate Cell Allocation and Mobile Allocation lists for each frequency band of the segment. It is not certain whether all mobile stations can cope with CA lists including frequencies that the MS itself does not support in a common BCCH environment. In addition, combining the frequencies of different bands in one frequency list restricts the number of frequencies that can be included in frequency hopping. This is because of the limitations of the absolute radio frequency number (ARFCN) encoding in the system information messages. An exception to the above-mentioned rule is when the BCCH of a segment is on the EGSM 900 frequency band and there are also PGSM 900 resources in the segment. In this case, a common CA list for all the GSM 900 frequencies in the segment is used. From the point of view of the MS's capabilities, it is safe to have a common CA list because all the accessing GSM 900 mobile stations in the segment support both of the GSM 900 frequency bands. However, the number of frequencies on such a common CA list is limited to 16 (17, if ARFCN 0 is included) because of the needed ARFCN number encoding method used in this case. The broadcast of the CA list to the MSS in the System Information 1 message includes only the segment's frequencies of the band on which the BCCH carrier is.If the BCCH carrier of a segment is on PGSM 900, then PGSM 900 and EGSM 900 are regarded as separate frequency bands. If the BCCH carrier of a segment is on EGSM 900, all the GSM 900 resources of the segment can be regarded as belonging to the BCCH frequency band, that is, the EGSM 900 frequency band. During the call set-up and handover procedures each MS is informed on the frequencies of the band the MS is going to use next with either Assignment Command or Handover Command.

4.2

Several cell allocations in one band With the Several cell allocations in one band feature the BSC can build a separate cell allocation (CA) list for each BTS object in a segment instead of a common CA list for the whole band. The BSC also uses the BTS object specific CA list for the respective BTS objects.

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Common BCCH Control system information messages


A wider frequency spectrum allocation is possible when each BTS object in the segment uses a CA list of its own. The spectrum is divided to sub-bands which can be used for frequency hopping in one segment. This feature works together with all type of frequency hopping modes used in the BSC. CA list per BTS enabled (CABE) A segment level parameter CA List Per BTS Enabled defines if separate CA lists are built. If parameter value is 0 (CA List per BTS is disabled), then common frequency band specific CA list functionality is used in segment. When any of the frequency hopping modes is in use on a CA List Per BTS Enabled activated segment, only BCCH BTS resources are available for the initial SDCCH allocation, Dynamic SDCCH allocation or FACCH setup in the segment.

4.3

Common BCCH Control Mobile Allocation Mobile Allocation is the subset of the Cell Allocation allocated to a particular MS. The purpose of the Mobile Allocation information is to provide the MS with the Cell Allocation RF channels, which are used in the mobile hopping sequence. The MA list indicated to the MS in the Assignment Command and the Handover Command is a band-specific list formed according to the frequency band the MS is directed to. In the Immediate Assignment Command, the MA list of the band containing the segment's BCCH is always included. When a segment's BCCH carrier uses an EGSM 900 frequency, the CA list in the System Information 1 message also includes the possible PGSM 900 frequencies of the segment. This enables the use of both PGSM 900 and EGSM 900 frequencies in the MA frequency list already in the Immediate Assignment procedure. Having both PGSM and EGSM requires an additional feature, Single MA list for EGSM 900 and PGSM 900. When the segment's BCCH carrier uses a PGSM 900 frequency, the CA list in the System Information 1 message includes only PGSM 900 frequencies, which prevents the use of the possible EGSM 900 frequencies of the segment in the MA list at the Immediate Assignment phase.

4.4

Common BCCH Control BCCH allocation The sending of BCCH Allocation and system information in the common BCCH networks is mainly similar to those used in the traditional networks of single BTS cells. The adjacency information sent to the MS is based on the BCCH frequency of a common BCCH segment. Other frequency layers in the segment are invisible to the MSS. However, in order for the BSC to be able to make reasonable decisions on certain handovers for an MS on the non-BCCH frequency layer of a segment, the BCCH frequency of the segment itself is added among the BCCH frequencies the MS should measure when on the non-BCCH frequency band. A modified BA list is sent to an MS on the nonBCCH frequency layer in System Information type 5 message on the SACCH. When the MS is on a segment's non-BCCH frequency layer, there can only be 31 frequencies in the adjacent cell and BA lists. Only five of the strongest neighbours are included in the adjacent cell measurements as the BCCH of the serving segment itself is added among the frequencies to be measured. For an overview, see Overview of Common BCCH Control.

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Radio resource management and Common BCCH Control

5 Radio resource management and Common BCCH Control 5.1

SDCCH allocation in Common BCCH segment Stand-alone dedicated control channels (SDCCHs) are allocated for signalling purposes, immediate assignments, intra-BSC handovers, and inter-BSC handovers. The channel allocation algorithm in the BSC selects the SDCCH in all these situations. SDCCH allocation from a segment with BTSs from different frequency bands is based on the frequency capability information of the accessing MS and the usability of the radio resources. The accessing MS sends frequency capability information to the BSC in the Classmark information message. The usability of the radio resources in different frequency bands for the accessing MS is defined by the power control and handover algorithm in the BSC. Selection of BTSs in Common BCCH segment Immediate assignment Even though there are resources of several frequency bands in a common BCCH segment, the initial SDCCH must always be allocated from the BCCH frequency band. This is because the multiband capabilities of an accessing mobile station are not known at the time of the initial SDCCH allocation. Even if the capabilities of an accessing MS were known already in the beginning, it would not be possible to define the usability of the non-BCCH frequencies of the segment. This is because the MS starts sending measurement reports only after it has been moved to a dedicated channel. Because of these restrictions the SDCCH for immediate assignment must be selected among the BTSs using the BCCH frequency band of the segment. BTSs using other frequencies are not allowed to be used. The channel allocation algorithm selects the BTSs using the BCCH frequency band as targets for an SDCCH selection. An exception to the above-mentioned rules is when the segment's BCCH carrier is on EGSM 900 band. In that case the segment's possible PGSM 900 resources are also available for the initial SDCCH allocation because an MS supporting the EGSM 900 band is always capable of supporting the PGSM 900 frequency band and because these two bands are regarded as equal from the radio properties' point of view. Intra-BSC handover In intra-BSC handover the channel allocation algorithm receives the information about the frequency capability of the accessing MS and the usability of radio resources in different frequency bands. The usability of radio resources in different frequency bands is calculated by the power control and handover algorithm. Based on this information the channel allocation algorithm selects certain BTSs of the segment as targets of SDCCH selection. Inter-BSC handover In inter-BSC handover the channel allocation algorithm in the target BSC receives the information about the accessing MS's frequency band capability. The usability of radio resources in different frequency bands is defined based on the value of the parameter non BCCH layer offset (NBL). If the MS is capable of using the BTS's frequency

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band and the parameter non BCCH layer offset (NBL) of the BTS is less than or equal to zero, the BTS is selected as the target for SDCCH allocation.

Selection of TRX, RTSL and channel in Common BCCH Control Having selected the BTSs from which the SDCCH can be allocated, the channel allocation algorithm selects TRX, RTSL, and the channel to be used. The principles of selecting the TRX, RTSL, and the channel are described below. The channel allocation algorithm divides the BTSs into groups according to their frequencies: • • •

BTSs using the BCCH frequency band form one group. BTSs using other frequency band than BCCH form one group. If the BCCH is on EGSM 900 band, the BTSs using PGSM 900 belong to the group of BCCH frequency band.

The channel allocation algorithm calculates the SDCCH load of each BTS group. In SDCCH load calculation only the static SDCCH resources are taken into account. If there are idle static SDCCH resources in some group, the load of the group is the most decisive factor in TRX/RTSL/channel selection. The channel is allocated from the BTS group which has the lowest load. The TRX/RTSL/channel selection from the TRXs of the selected BTS group is made according to the following principles: The channel allocation algorithm selects a suitable (TRX, RTSL) pair by using the TRXspecific resource information. If possible, the pair to be selected is not the last seized pair. There are two methods for selecting (TRX, RTSL) pairs among static SDCCH resources depending on the hopping method and TRX prioritisation in the cell. The method used in radio frequency (RF) hopping BTSs with RF hopping TRX prioritisation: •

•

• •

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In the first phase all SDCCH TRXs, except BCCH TRX, are examined up to the starting TRX. The TRX that has the least channel load (busy traffic and signalling channels) is selected. Within the selected TRX, the RTSL which has the highest number of idle SDCCH channels left is selected. However, if a signalling channel was last allocated from the same TRX, another RTSL than last time is allocated, if possible. The SDCCH channel from the BCCH TRX is allocated only if there are no idle SDCCHs in other TRXs at all. The method used in cells without RF hopping or without RF hopping TRX prioritisation: In the first phase all SDCCH TRXs are examined up to the starting TRX. The TRX that has the least channel load (busy traffic and signalling channels) is selected. Within the selected TRX, the RTSL which has the highest number of idle SDCCH channels left is selected. However, if a signalling channel was last allocated from the same TRX, another RTSL than the last time is allocated, if possible. If there are no idle static SDCCH resources in the BTSs, dynamic SDCCH resources are searched for. All the TRXs in every BTS group including free dynamic SDCCH


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resources are examined. From the TRXs, the RTSL which has the least idle dynamic SDCCH channels is selected. If there are no idle static or dynamic SDCCH resources in the BTSs, an idle TCH time slot is configured as a new temporary SDCCH resource. Dynamic SDCCH reconfiguration is applied only in the immediate assignment phase, not during handovers. After the channel allocation algorithm has found a suitable (TRX, RTSL) pair, it allocates the next free SDCCH subchannel from the RTSL. In the case of an intra-BTS handover, the SDCCH allocation differs from the basic procedure. If the TRX where the call is maintained is currently not blocked, the search procedure differs from the basic one in the following ways: • • •

5.2

The search procedure starts only if another SDCCH RTSL than the serving one is defined in the BTS. The call-serving TRX is accepted only if other TRXs containing free SDCCH channels are not available. Channel in the call-serving RTSL is never selected. If the call-serving TRX is blocked, the basic search procedure is used.

TCH allocation in Common BCCH segment environment The basic difference between TCH allocation in a common BCCH-controlled segment and a single BTS cell is that the target of a TCH request in a segment is a set of BTSs instead a single BTS. In addition, in a BSC internal inter-cell handover the target cell list contains segments instead of BTSs. For TCH allocation algorithm the segment concept brings some issues to be taken into account when selecting a free TCH resource for a service request, for example, the loads of the BTSs and the possibility of separate interference recommendations for different frequency bands. Basically, all existing rules for selecting a TCH in a single BTS cell (see Radio Channel Allocation) are valid also between BTSs in a segment. RX level based TCH resource usability evaluation The channel allocation algorithm can perform RX level based TCH resource usability evaluations depending on the value of the parameter RX level based TCH access (RXTA). If the RX level based TCH access method is in use, the resource usability information set by the power control and handover algorithm is bypassed. The values of the RX level based TCH access parameter have the following impact: • •

if the value is 1, the RX level based TCH access method is used in the call set-up. if the value is 2, the RX level based TCH access method is used in the call set-up and handovers.

When the RX level based TCH access method is applied, the usability of resources can be determined on a BTS basis. Whereas if the resource usability evaluation set by the power control and handover algorithm is used, resource usability can be determined only on frequency band and BTS site type basis. For more information on RX level based TCH resource usability evaluation, see Radio Channel Allocation.

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Search of a single slot TCH and Common BCCH Control The BSC starts the TCH search procedure by selecting the BTSs to be examined according to the frequency bands that the MS supports and according to the allowed frequency bands because of radio conditions. In a call set-up and BSC internal handover the allowed frequency bands are defined based on the measurement result of the BCCH layer of the target segment. For the non-BCCH frequency band resource usability decision, an estimate for the non-BCCH layer is used. The estimate is derived from the BCCH layer measurement with the BTS-specific non BCCH layer offset (NBL) parameter. This estimate is further compared to a threshold parameter. In a call set-up and intra-cell handover the threshold parameter is non BCCH layer access threshold (LAR) of the cell where the call is at that moment. In inter-cell handover the parameter is non BCCH layer access threshold (LAR) of the target cell. When the BCCH carrier is on the GSM 1900 band in the GSM 800/ GSM 1900, the resource usability estimation is done for the BCCH band resources. In a BSC external handover the estimate of the non-BCCH frequency band cannot be obtained because of the missing measurement information in the target BSC. The decision on the usability of non-BCCH frequency resources is made based on the value of the parameter non BCCH layer offset (NBL). If the parameter is less than or equal to zero it means that the non-BCCH frequency layer is at least as strong as the BCCH frequency layer and can be safely used for the incoming call. After the applicable frequency bands have been defined, the selection between the remaining candidate BTSs is made by the BSC according to the following criteria and order: 1. Load of a BTS according to parameter BTS load in SEG (LSEG) 2. The interference band of an idle channel, TRX prioritisation in TCH allocation and the channel type 3. The circuit switched territory load of a BTS 4. Round robin of the BTSs. The load of a BTS is based on load conditions in the BTS and on the parameter BTS load in SEG (LSEG) of each BTS. The principle is to keep the load of a BTS within the limit that the parameter BTS load in SEG (LSEG) defines. For channel search the BSC divides the BTSs into different load groups: 1. The BTSs with load under BTS load in SEG (LSEG). 2. The BTSs with load between BTS load in SEG (LSEG) and the highest BTS load in SEG value in the segment. 3. The BTSs with load above the highest BTS load in SEG (LSEG) value of the segment. The primary target for the allocation is the first group. After the BTS's load limit has been reached, the BSC aborts the TCH allocation to that BTS, if possible, until the load limits in all the other BTSs have been reached. The equal filling continues in all those BTSs where the load limit has not yet been reached. Finally, when each BTS has reached its load limit the allocation continues in the BTSs where the load is less than the highest load threshold value among the BTSs. The load in these BTSs is increased so that the load in every BTS gradually approaches the highest limit value among the BTSs. This continues until the load in all the BTSs is at least on the level of the highest load threshold value among the BTSs. After that the general rule is that the non-BCCH frequency band is preferred to BCCH frequency band.

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When three frequencies (PGSM 900, EGSM 900, and GSM 1800) are used in the common BCCH segment, an extension to this general rule is needed. The preference between the two non-BCCH frequency layers is made in the following way: • •

if BCCH is on the PGSM 900 frequency band GSM 1800 is preferred to EGSM 900 if BCCH is on the GSM 1800 frequency band EGSM 900 is preferred to PGSM 900.

By preferring the non-BCCH frequency band resources, the resources on the BCCH frequency band are saved and the possibility of single band mobile stations to get service in the Common BCCH network is increased. By applying the above-mentioned rules, either one or more BTSs can be defined as the primary target group for TCH allocation. The next thing to be examined within these BTSs is the possible interference level recommendations and the respective interference levels of idle channels. For a BTS for which the BSC has defined a recommendation of the acceptable interference the TCHs on the acceptable levels are ranked as the best choices for allocation by values starting from 1. However, in BTSs for which no recommendation is present the levels are also ranked so that the best possible level (0) has the ranking value 1. The following table gives an example of the ranking of different interference bands with and without interference level recommendation.

Interference level

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Figure 10

Different interference levels with BSC recommendation 2 and without recommendation when searching for full-rate TCHs

If there are still several candidate BTSs after you have applied the TRX prioritisation in TCH allocation (see TRX prioritisation in TCH allocation), or when no prioritisation is defined, the final selection between BTSs is made according to the circuit switched territory load in them. The BSC selects the one with the lowest load using the round robin method so that the BTS that was allocated the previous time is the last choice. TRX prioritisation in TCH allocation The possibility to favour or avoid the BCCH TRX in call assignment is maintained to some extent in the segment environment. This is examined after the BTSs have been compared based on their loads and their respective load parameters. In the segment environment there can be both BTSs with and without BSC defined interference level recommendation in a TCH request. If the recommendation is present for the BCCH BTS and the BCCH TRX is preferred in TCH allocation and the allocation can be made in the BCCH TRX according to the recommendation (interference less or equal to recommendation), it will also be made there. If this is not possible, a TCH ranked as the best according to its interference level is allocated among the BTSs that were defined as best targets based on their loads.

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If the BCCH TRX is preferred in TCH allocation but no recommendation is present for the BCCH BTS, a TCH ranked as the best according to its interference level is allocated among the target BTSs. If a TCH with the selected interference level is found in the BCCH TRX it is the primary choice. In addition, in cases where the non-BCCH TRXs are preferred the allocation is made primarily according to the interference level ranking and secondarily according to the defined TRX prioritisation. Combined usage of Common BCCH Control and Multi BCF Control When Multi BCF Control is used together with Common BCCH Control and both Talkfamily BTS and UltraSite/MetroSite BTSs are in use in a segment, the number of BTS types to be taken into account in TCH search extends. The priority order between the BTS types in TCH search when the load in all the BTSs has reached the highest load value of the segment is: 1. 2. 3. 4.

Talk-family BTS on non-BCCH frequency band UltraSite/MetroSite BTS on non-BCCH frequency band Talk-family BTS on BCCH frequency band UltraSite/MetroSite BTS on BCCH frequency band

When there are three different frequency bands (PGSM 900, EGSM 900, GSM 1800) in use in a segment, an extension to the preference rule is needed. The preference between the two non-BCCH frequency layers is made in the following way: 1. if the BCCH is on the PGSM 900 frequency band GSM 1800 is preferred to EGSM 900 2. if the BCCH is on the GSM 1800 frequency band EGSM 900 is preferred to PGSM 900. UltraSite and MetroSite BTSs have a better link budget than a Talk-family BTS. This is the reason why a Talk-family BTS, rather than a UltraSite/MetroSite BTS, is used when the preference between BTSs cannot be decided based on other criteria. This is done to save the better UltraSite/MetroSite resources for MSS on the cell border area. GPRS GPRS is a BTS-specific feature in the segment environment and therefore there are independent GPRS territories in the BTSs. In TCH search the actions on GPRS territories are avoided if possible. This means that a TCH for a circuit switched service is not allocated in the GPRS territory of a BTS if there is an available TCH in the CS territory of another BTS in the segment. Likewise, if there is another candidate where the allocation can be made in the CS territory without any effect on the GPRS territory, TCH allocation is skipped in a BTS where it would cause a GPRS territory downgrade based on the defined safety margins. When all the CS resources that the MS can use in the whole segment are busy, the channel is allocated in the GPRS territory taking into account the following criteria and in the following order: 1. 2. 3. 4.

GPRS territory type according to PCU recommendation Load according to parameter BTS load in SEG (LSEG) Dedicated GPRS territory size Default GPRS territory size

When both GPRS and EGPRS territories are used in a segment, the PCU is aware of the usage and loads of different type of GPRS territories and recommends usage of the one with the lower load.

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The GPRS channels are handled as occupied channels for the load comparison with the BTS load in SEG (LSEG) parameter. If the load of a BTS is above the highest BTS load in SEG (LSEG) value of the segment and the highest BTS load in SEG (LSEG) is under 100 %, the TCH search follows the BTS band order, that is, the nonBCCH frequency band is preferred to the BCCH frequency band. If there are still several candidate BTSs left after selecting between GPRS and EGPRS and comparing loads of the BTSs of the chosen band, the selection of the BTS is made according to the GPRS territory sizes of the BTSs. In this case the BTS with the smallest dedicated GPRS territory and after that the smallest default GPRS territory is chosen. This is done, because it is reasonable to save a few larger territories for GPRS rather than several smaller ones. Multi-slot allocation and Common BCCH Control In multi-slot allocation for HSCSD call requests, multiple TCH/Fs in a TRX can be allocated. HSCSD call configurations of up to four TCH/Fs are possible. In this allocation method the applied principles differ somewhat from those in single-slot allocation, but basically the same segment-specific rules are valid as in a single-slot TCH allocation. This means that the HSCSD resource allocation is made according to the capabilities of the MS considering the radio conditions and the loads of different resource bands. For the HSCSD control to be efficient, the HSCSD load parameters are on the BTS level. This also means a better way of controlling the HSCSD traffic load between the BTSs of a segment. HSCSD search in the segment environment is performed by the BSC using the following segment-specific rules: 1. HSCSD allocation is made in a BTS that has no restrictions based on the HSCSD load parameters rather than in a BTS where the allocation is restricted to include only one TCH. 2. Among the resource types that the BSC defines as reasonable, the TCH search is performed by selecting the best HSCSD channel configuration fulfilling the request. 3. Load according to BTS load in SEG (LSEG) (see Search of a single slot TCH and Common BCCH Control) 4. If there are both BTSs with and BTSs without the BSC interference band recommendation, the ranking of the BTSs is: • A TSL gap without any interference in a BTS that has no interference band recommendation and a TSL gap within the recommendation in a BTS where the interference band recommendation is present, are both ranked as the best choices. • A secondary choice is a TSL gap with some interference in a BTS without interference band recommendation set by the BSC. • The last choice is a TSL gap that does not meet the interference band recommendation set by the BSC. 5. The circuit switched territory load of a BTS 6. Round robin method of the BTSs.

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Handover algorithm and Common BCCH Control


6 Handover algorithm and Common BCCH Control The following terms are used in this section: • • • • • •

6.1

AV_RXLEV_DL = Averaged received downlink signal strength of the serving channel AV_RXLEV_NCELL(n) = Averaged received downlink signal strength of the BCCH in the adjacent cell (n) AV_RXLEV_NCELL (serving BCCH) = Averaged received downlink signal strength of the BCCH in the serving segment BS_TXPWR = Downlink output power level used on the serving channel RXLEV_NCELL (serving BCCH) = Latest received downlink signal strength of the BCCH in the serving segment RXLEV_DL = Latest received signal strength on the serving channel

SDCCH resource usability evaluation in Common BCCH Common BCCH carrier on GSM 800, GSM 900 and GSM 1800 Immediate assignment When the initial SDCCH channel is allocated for call set-up, the accessing mobile station (MS) has not yet indicated its multiband capabilities. Because the BSC has no knowledge of the mobile station's support for the non-BCCH band, the initial SDCCH channel has to be allocated among the BCCH band resources and evaluation of the non-BCCH band resources is not needed. Intra-cell SDCCH handover In cases where the BSC starts an intra-segment SDCCH handover because of the traditional criterion, the usability of different frequency bands of the segment are evaluated based on the signal level and the non BCCH layer offset (NBL) parameters of different BTSs in the segment. If the MS is initially on a BCCH frequency band SDCCH, the usability of resources is evaluated based on the average measurement results of the serving SDCCH. The serving resource type on the BCCH frequency band is automatically considered usable. The other resource type on the BCCH frequency band is usable when AV_RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) - non BCCH layer offset (NBL) (target resource) >= rxlev access min (RXP). The non-BCCH frequency band of a segment is usable when AV_RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) - non BCCH layer offset (NBL) (target resource)>= non BCCH layer access threshold (LAR). If the initial SDCCH has been allocated from a non-BCCH frequency BTS, the usability of the BCCH band resources is evaluated based on the average BCCH measurement results. The serving resource type on a non-BCCH frequency band is automatically considered usable. The other resource type on the non-BCCH frequency band is usable when

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AV_RXLEV_NCELL (serving BCCH) - non BCCH layer offset (NBL) (target resource) >= non BCCH layer access threshold (LAR). The BCCH frequency band in the segment is usable when AV_RXLEV_NCELL (serving BCCH) - non BCCH layer offset (NBL) (target resource)>= rxlev access min (RXP). If the mobile does not report adjacent cell measurement from the serving cell, the BCCH frequency band is usable when AV_RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) + non BCCH layer offset (NBL) (source resource) - non BCCH layer offset (NBL) (target resource) >= rxlev access min (RXP). Internal inter-cell SDCCH handover When the BSC has defined a need for an inter-cell handover based on the measurements of the serving SDCCH channel, the usability of the non-BCCH band of each candidate segment is decided using the BCCH measurement results for the segment, the non BCCH layer offset (NBL) parameter for the segment's non-BCCH band and the segment's non BCCH layer access threshold (LAR) parameter. The nonBCCH band frequencies in the target segment are usable when AV_RXLEV_NCELL(n) - non BCCH layer offset (NBL) (target resource) (n) >= non BCCH layer access threshold(n) (LAR). The BCCH band of a candidate segment is automatically regarded as usable because the segment has already been selected as a valid handover candidate based on its BCCH measurement results. External SDCCH handover In a handover between two BSCs, the usability of the non-BCCH frequency band resources is defined on the target side based on the value of the parameter non BCCH layer offset (NBL). If the MS is capable of using the frequency band of the BTS and the non BCCH layer offset (NBL) of the BTS is less than or equal to zero, the BTS can be used for the incoming call. Common BCCH carrier on GSM 1900 Immediate assignment When the initial SDCCH channel is allocated for call set-up, the accessing mobile station has not yet indicated its multiband capabilities. Because the BSC has no knowledge of the mobile station's support for the non-BCCH band, the initial SDCCH channel has to be allocated among the BCCH band resources, and evaluation of the non-BCCH band resources is not needed. Intra-cell SDCCH handover Resources that are on the same frequency band and of the same BTS site type as the serving BTS (from where the handover is initiated) are always considered usable. The BCCH frequency band resources are evaluated against the non BCCH layer access threshold (LAR) parameter. If the MS is on a non-BCCH frequency band, BCCH frequency resources are considered usable when AV_RXLEV_NCELL (serving BCCH) - non BCCH layer offset (NBL) (target resource) > non BCCH layer access threshold (LAR).

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When the MS is on a BCCH frequency band or when the MS does not report the adjacent cell measurement from the serving cell on a non-BCCH frequency band, the BCCH frequency resources are usable when AV_RXLEV_DL + non BCCH layer offset (NBL) (source resource) + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) - BS_TXPWR) - non BCCH layer offset (NBL) (target resource) > non BCCH layer access threshold (LAR). When the MS is on a non-BCCH frequency band and the non-BCCH frequency resource has weaker coverage than the BCCH resource type (non BCCH layer offset (NBL)> 0) then non-BCCH frequency band resources are evaluated against the rxlev access min (RXP) parameter. AV_RXLEV_NCELL (serving BCCH) - non BCCH layer offset (NBL) (target resource) > rxlev access min (RXP). When the MS is on a BCCH frequency band or when the MS does not report the adjacent cell measurement from the serving cell on the non-BCCH frequency band, the non-BCCH frequency resources are usable when AV_RXLEV_DL + non BCCH layer offset (NBL) (source resource) + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) - BS_TXPWR) - non BCCH layer offset (NBL) (target resource) > rxlev access min (RXP).

t

If the non-BCCH frequency resource has coverage that is better than or the same as the BCCH resource type (non BCCH layer offset (NBL) =< 0), the non-BCCH frequency resource type is always considered usable. Note that for GSM 1900 single band mobiles, resources that are on the same frequency band and on the same resource BTS site type as the serving BTS (from where the HO is initiated) are always considered usable. The other BTS site type resources on the segment's BCCH frequency layer are evaluated against the non BCCH layer access threshold (LAR) parameter. The other site type resource is usable when AV_RXLEV_DL + non BCCH layer offset (NBL) (source resource) + (BS TX pwr max1x00 (PMAX2) - BS_TXPWR) - non BCCH layer offset (NBL) (target resource) > non BCCH layer access threshold (LAR). Internal inter-cell SDCCH handover BCCH frequency band resources are evaluated against the non BCCH layer access threshold (LAR) parameter. The BCCH frequency resources are usable when AV_RXLEV_NCELL(n) - non BCCH layer offset (NBL) (target resource)> non BCCH layer access threshold(n) (LAR). If a non-BCCH frequency resource has weaker coverage than the BCCH resource type (non BCCH layer offset (NBL) (target resource > 0), the non-BCCH frequency band resources are evaluated against the rxlev access min(n) (RXP)parameter. The non-BCCH frequency resource is usable when AV_RXLEV_NCELL(n) - non BCCH layer offset (NBL) (target resource) > rxlev access min(n) (RXP).

t

46

If a non-BCCH frequency resource has coverage that is better than or the same as the BCCH resource type (non BCCH layer offset (NBL) =< 0), the non-BCCH frequency resource type is always considered usable.


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Note that for GSM 1900 single band mobiles, resources that are on the same frequency band and on the same BTS site type as the BCCH BTS are always considered usable. The other BTS site type resources on the target segment's BCCH frequency layer are evaluated against the non BCCH layer access threshold (LAR) parameter. The other site type resource is usable when AV_RXLEV_NCELL(n) - non BCCH layer offset (NBL) (target resource type) > non BCCH layer access threshold (LAR). External SDCCH handover In a handover between two BSCs, the usability of the non-BCCH frequency band resources is defined on the target side based only on the value of the parameter non BCCH layer offset (NBL). If the MS is capable of using the frequency band of the BTS and the non BCCH layer offset (NBL) of the BTS is less than, or equal to zero, the BTS can be used for the incoming call. If the common BCCH is on the GSM 1900 band, the GSM 800 non-BCCH band is always preferred for a GSM 800/GSM 1900 Dual Band mobile.

6.2

TCH resource usability evaluation in Common BCCH Common BCCH carrier on GSM 800, GSM 900 and GSM 1800 The algorithm that performs the TCH resource usability evaluation depends on the value of the parameter RX level based TCH access (RXTA). The handover algorithm performs the TCH resource usability evaluation during the call set-up only when the parameter has the value 0. When the value of the parameter is 1, the TCH resource usability evaluation is made by the power control and handover algorithm in handover cases. If the parameter value is 2, the handover algorithm does not make a TCH resource usability evaluation; the evaluation is performed by the channel allocation algorithm. Call set-up If the SDCCH has been allocated from a BTS that uses the same frequency band as the BCCH BTS, the usability evaluation is based on the latest measurement report of the serving SDCCH. The serving resource type on the BCCH frequency band is automatically considered usable. The other resource type on the BCCH frequency band is usable when RXLEV_DL - non BCCH layer offset (NBL) (target resource)>= rxlev access min (RXP). The non-BCCH frequency band of a segment is usable when RXLEV_DL - non BCCH layer offset (NBL) (target resource)>= non BCCH layer access threshold (LAR). If the SDCCH has been allocated from a non-BCCH frequency BTS, the usability of resources is evaluated based on the latest BCCH measurement results. The serving resource type on the non-BCCH frequency band is automatically considered usable. The other resource type on the non-BCCH frequency band is usable when RXLEV_NCELL (serving BCCH) -non BCCH layer offset (NBL) (target resource) >= non BCCH layer access threshold (LAR). If the MS does not report adjacent cell measurement from the serving cell, the BCCH frequency band is usable when

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RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) + non BCCH layer offset (NBL) (source resource) -non BCCH layer offset (NBL) (target resource) >= non BCCH layer access threshold (LAR). A segment's BCCH frequency band is usable when RXLEV_NCELL (serving BCCH) - non BCCH layer offset (NBL) (target resource) >= rxlev access min (RXP). If the MS does not report adjacent cell measurement from the serving cell, the BCCH frequency band is usable when RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) + non BCCH layer offset (NBL) (source resource) - non BCCH layer offset (NBL) (target resource) >= rxlev access min (RXP). Intra-cell TCH handover When a call is on a BCCH frequency band TCH channel, the BSC defines the usability of the non-BCCH frequency band based on the average measurements of the serving TCH. The serving resource type on the BCCH frequency band is automatically considered usable. The other resource type on the BCCH frequency band is considered usable when AV_RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) - non BCCH layer offset (NBL) >= rxlev access min (RXP). A segment's non-BCCH frequency band is usable when AV_RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) -non BCCH layer offset (NBL) (target resource)>= non BCCH layer access threshold (LAR). When the call is on a non-BCCH frequency band TCH channel, the usability of the BCCH band resources is evaluated based on the averaged BCCH measurement results. The serving resource type on a non-BCCH frequency band is automatically considered usable. The other resource type on the non-BCCH frequency band is usable when AV_RXLEV_NCELL(serving BCCH) - non BCCH layer offset (NBL) (target resource) >= non BCCH layer access threshold (LAR). The BCCH frequency band in the segment is usable when AV_RXLEV_NCELL(serving BCCH) - non BCCH layer offset (NBL) (target resource) >= rxlev access min (RXP). If the MS does not report adjacent cell measurement from the serving cell, the BCCH frequency band is usable when AV_RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) + non BCCH layer offset (NBL) (source resource) -non BCCH layer offset (NBL) (target resource) >= rxlev access min (RXP). Internal inter-cell TCH handover When a call is on a BCCH frequency band, the need for an inter-cell handover is based on the measurements of the serving TCH and the measurements of the BCCHs of the adjacent cells. When a call is on a non-BCCH frequency, the need for an inter-cell handover is based on the measurements of the serving TCH channel. However, in Power Budget (PBGT)

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handover and Umbrella handover the decision is made by comparing the average measurements of the segment's own BCCH and the BCCHs of the adjacent cells. When the BSC has defined the need for an inter-cell handover and selected the candidate segments for the handover, the BSC evaluates the usability of the different frequency bands in the target segments. The usability of the non-BCCH frequency band of a candidate segment is decided using the averaged BCCH measurement results of the candidate segment, the parameter non BCCH layer offset (NBL) (target resource) of the candidate segment and the parameter non BCCH layer access threshold (LAR) of the candidate segment: AV_RXLEV_NCELL (n) - non BCCH layer offset(n) (NBL) (target resource) >= non BCCH layer access threshold(n) (LAR). The usability of the BCCH frequency band of each candidate segment is decided by comparing the average BCCH measurement results for the segment to the RX lev min cell (SL) parameter. AV_RXLEV_NCELL(n) >= RX lev min cell(n) (SL). External TCH handover In a handover between two BSCs, the usability of the non-BCCH frequency band resources is defined on the target side based on the value of the parameter non BCCH layer offset (NBL). If the MS is capable of using the frequency band of the BTS and the non BCCH layer offset (NBL) of the BTS is less than, or equal to zero, the BTS can be used for the incoming call. Common BCCH carrier on GSM 1900 The algorithm that performs the TCH resource usability evaluation depends on the value of the parameter RX level based TCH access (RXTA). The handover algorithm performs the TCH resource usability evaluation during the call set-up only when the parameter has the value 0. When the value of the parameter is 1, the TCH resource usability evaluation is made by the power control and handover algorithm in handover cases. If the parameter value is 2, the handover algorithm does not make a TCH resource usability evaluation; the evaluation is performed by the channel allocation algorithm. Call set-up BCCH frequency band resources are evaluated against the non BCCH layer access threshold (LAR) parameter. When the MS is on a BCCH frequency band or the MS does not report adjacent cell measurement from the serving cell on the non-BCCH frequency band, BCCH frequency band resources are usable when RXLEV_DL + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) BS_TXPWR) +non BCCH layer offset (NBL) (source resource) - non BCCH layer offset (NBL) (target resource) > non BCCH layer access threshold (LAR). If the MS is on a non-BCCH frequency band, the BCCH frequency resources are usable when RXLEV_NCELL(serving BCCH) - non BCCH layer offset (NBL) (target resource) > non BCCH layer access threshold (LAR). If a non-BCCH frequency resource has weaker coverage than the BCCH resource type (non BCCH layer offset (NBL) > 0), the non-BCCH frequency band resources are evaluated against the rxlev access min (RXP)parameter.

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When the MS is on a BCCH frequency band or the mobile does not report adjacent cell measurement from the serving cell on the non-BCCH frequency band, the non-BCCH frequency band resources are usable when RXLEV_DL + (BS TX pwr max1x00 (PMAX2) - BS_TXPWR) + non BCCH layer offset (NBL) (source resource) -non BCCH layer offset (NBL) (target resource)> rxlev access min (RXP). When the MS is on a non-BCCH frequency band, the non-BCCH frequency band resources are usable when RXLEV_NCELL(serving BCCH) - non BCCH layer offset (target resource) > rxlev access min (RXP).

t

If a non-BCCH frequency resource has coverage that is better than or the same as a BCCH resource type (non BCCH layer offset (NBL) =< 0), the non-BCCH frequency resource type is always considered usable. Note that for GSM 1900 single band mobiles, resources that are on the same frequency band and on the same resource type as the serving BTS (from where the handover is initiated) are always considered usable. The other resources on the segment's BCCH frequency layer are evaluated against the non BCCH layer access threshold (LAR) parameter. The other resource is usable when RXLEV_DL + (BS TX pwr max1x00 (PMAX2) - BS_TXPWR) - non BCCH layer offset (NBL) (target resource) > non BCCH layer access threshold (LAR). Intra-cell TCH handover Resources that are on the same frequency band and on the same resource type as the serving BTS (from where handover is initiated) are always considered usable. The BCCH frequency band resources are evaluated against the non BCCH layer access threshold (LAR) parameter. If the MS is on a non-BCCH frequency band, BCCH frequency resources are usable when AV_RXLEV_NCELL(serving BCCH) - non BCCH layer offset (NBL) (target resource) > non BCCH layer access threshold (LAR). When the MS is on a BCCH frequency band or when the MS does not report adjacent cell measurement from the serving cell on the non-BCCH frequency band, the BCCH frequency resources are usable when AV_RXLEV_DL + non BCCH layer offset (NBL) (source resource) + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) - BS_TXPWR) - non BCCH layer offset (NBL) (target resource)> non BCCH layer access threshold (LAR). If the MS is on a non-BCCH frequency band and the non-BCCH frequency resource has weaker coverage than the BCCH resource type (non BCCH layer offset (NBL)> 0), the non-BCCH frequency band resources are evaluated against the rxlev access min (RXP) parameter. AV_RXLEV_NCELL(serving BCCH) - non BCCH layer offset (NBL) (target resource) > rxlev access min (RXP). When the MS is on a BCCH frequency band or when the MS does not report adjacent cell measurement from the serving cell on a non-BCCH frequency band, the non-BCCH frequency resources are usable when

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AV_RXLEV_DL + non BCCH layer offset (source resource) + (BS TX pwr max (PMAX1) or BS TX pwr max1x00 (PMAX2) - BS_TXPWR) -non BCCH layer offset (NBL) (target resource) > rxlev access min (RXP).

t

If a non-BCCH frequency resource has coverage that is better than or the same as the BCCH resource type (non BCCH layer offset (NBL) =< 0), the non-BCCH frequency resource type is always considered usable. Note that for GSM 1900 single band mobiles, resources that are on the same frequency band and on the same resource type as the serving BTS (from where handover is initiated) are always considered usable. The other resources on the BCCH frequency band layer in the segment are evaluated against the non BCCH layer access threshold (LAR) parameter. The other resource is usable when AV_RXLEV_DL + non BCCH layer offset (NBL) (serving resource) + (BS TX pwr max1x00 (PMAX2) - BS_TXPWR) - non BCCH layer offset (NBL)(target resource) > non BCCH layer access threshold (LAR). Internal inter-cell TCH handover BCCH frequency band resources are evaluated against the non BCCH layer access threshold(n) (LAR) parameter. The BCCH frequency band resources are usable when AV_RXLEV_NCELL(n) - non BCCH layer offset(n) (NBL) (target resource)> non BCCH layer access threshold(n) (LAR). If a non-BCCH frequency band resource has weaker coverage than a BCCH resource type (non BCCH layer offset(n) (NBL) > 0), the non-BCCH frequency band resources are evaluated against the rxlev access min(n) (RXP) parameter. A non-BCCH frequency band resource is usable when AV_RXLEV_NCELL(n) - non BCCH layer offset(n) (NBL) (target resource) >rxlev access min(n) (RXP).

t

If a non-BCCH frequency resource has coverage that is better than or the same as the BCCH resource type (non BCCH layer offset (NBL)(n) =< 0), the non-BCCH frequency resource type is always considered usable. Note that for GSM 1900 single band mobiles, resources that are on the same frequency band and on the same resource type as the BCCH BTS are always considered usable. The other resource type resources on the BCCH frequency band in the target segment are evaluated against the non BCCH layer access threshold (LAR) parameter. The other resource is usable when AV_RXLEV_NCELL(n) -non BCCH layer offset(n) (NBL)(target resource) >non BCCH layer access threshold(n) (LAR). External TCH handover In a handover between two BSCs the usability of the non-BCCH frequency band resources is defined on the target side based only on the value of the parameter non BCCH layer offset (NBL). If the MS is capable of using the frequency band of the BTS and the non BCCH layer offset (NBL) of the BTS is less than or equal to zero, the BTS can be used for the incoming call. If the common BCCH is on the GSM 1900 band, the GSM 800 non-BCCH band is always preferred for a GSM 800/GSM 1900 Dual Band mobile station.

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6.3


Extended call set-up in Common BCCH segment To improve the usability of a secondary frequency band during call set-up, an enhancement has been implemented in the BSC. This assures that a valid measurement report from the MS is available for the BSC to evaluate the usability of non-BCCH frequency resources of the segment during call set-up. If there is a secondary frequency band in a segment and the accessing MS supports the secondary band, the BSC extends its call set-up procedure to wait for a valid measurement report from the MS. If a valid measurement report is received before the waiting period ends the call set-up proceeds immediately. If a valid measurement report is not received during the waiting period, the secondary frequency band resources cannot be used during call set-up. The length of the waiting period can be adjusted by changing the value of a UTPFIL parameter. For instructions, see Technical Note No. 773 (Delaying call set-up to ensure MS measurement report availability in a segment environment). The UTPFIL parameter defines how many SACCH multiframe periods the BSC is allowed to wait for a valid measurement report. The default value of the parameter is 3 and the value range is 1…4.

t

The averaging of radio link measurements in the BTS decreases the probability of the BSC to receive a valid measurement report in time and consequently diminishes the usability of the cell's secondary frequency band resources during call set-up. Therefore, it is recommended to deny the measurement averaging in a Common BCCH controlled cell by having the parameter BTS measure average (BMA) in its default value 1.

6.4

SDCCH handover based on reservation duration and Common BCCH Control Because of the possibility for long lasting SDCCH reservations, an intra-segment interband SDCCH handover is implemented to reduce the SDCCH pressure on the BCCH resource layer. The need for an intra-segment SDCCH handover out of the initial resource layer is defined based on the length of an SDCCH reservation and on the configuration of the segment. If the timer set according to the parameter intra segment SDCCH HO guard (ISS) for an MS expires (or irrespective of the timer, if intra segment SDCCH HO guard (ISS)= 0), there are resources outside the BCCH band, and if the MS has the required capability, the BSC defines the possibility for an interband SDCCH handover. If a handover possibility exists only from PGSM 900 to EGSM 900, the BSC can start an intra-segment handover attempt for a call on an SDCCH in the PGSM 900 area without further examinations. If it is possible to make a handover between two different frequency bands, the BSC searches for a candidate BTS for which the following criteria is fulfilled: •

RXLEV_DL - non BCCH layer offset (NBL)>= non BCCH layer access threshold (LAR).

RXLEV_DL is the terminal's reported signal level on the initial SDCCH. This is decreased by the BTS-specific offset of a BTS on non-BCCH frequency layer to get an estimation for that band. This estimate is then compared to a threshold parameter non BCCH layer access threshold (LAR). If the BSC ends up in a conclusion that the MS could survive on a non-BCCH layer of the segment, the BSC starts an intra-segment handover attempt.

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In case the intra-segment SDCCH handover fails an interval timer for intra-segment SDCCH handovers is set. Interval time is adjusted by the handover parameter min int between unsucc HO attempt (MIU).

t

Interval timer also concerns the load-based handovers in the segment.

6.5

Load-based TCH handover and Common BCCH Control The BSC tries to allocate traffic channels in a segment to spread the load evenly among the BTSs and also to keep the load of a single BTS below the BTS-specific parameter BTS load in SEG (LSEG). However, the load cannot necessarily be kept within the set limits because not all terminals support all the resource types. In addition, because of propagation properties, resources of different frequency bands may not be available in all TCH allocation cases. If a call cannot be directed to the frequency layer that the load balancing criteria initially call for in the call set-up or in a handover from another cell, the BSC can later initiate a handover to balance the load between the different frequency bands. The BSC bases the decision on the need for balancing the load on the BTS level parameter BTS load in SEG (LSEG). BTS load in SEG (LSEG) is used as such in deciding if a new call is allowed to enter a BTS. When deciding on initiating a handover to balance the load between BTSs of a segment the triggering load limit L is defined with the following formula: L = (BTS load in SEG (LSEG) + 100) / 2 Thefore the limit for triggering the load-based handover in a BTS is higher than the limit based on which the BTS can be avoided in TCH allocation. The limit for triggering the handover is in the middle between the value of BTS load in SEG (LSEG) and 100%. Note that if value 0 is set to parameter BTS load in SEG (LSEG), the L is not defined by using the formula, but value 0 is also applied to L. For example, if value 0 is set to parameter BTS load in SEG (LSEG) in BCCH-BTS, the BSC tries to hand over all calls that fulfill the signal strength criteria from the BCCH-BTS to the non-BCCH layer. This results in that the resources on the BCCH layer are kept free as long as possible. Separating the load limit that controls the access to a BTS inside a segment from the one that triggers the load-based handover to another BTS is necessary to avoid a situation where most of the incoming calls enter the segment via a TCH of the BCCH layer. The BSC checks the load of the segment's BTSs every time it receives a TCH request for the segment in question. When the BSC selects target BTSs for the load-based intracell handover it accepts as target only BTSs whose load is below the respective BTS load in SEG (LSEG) value. Load-based TCH handover in GSM 900/GSM 1800 Common BCCH In the GSM 900/GSM 1800 environment the main purpose of the handover is to move TCH load from the GSM 900 BCCH frequency band to the non-BCCH frequency band. However, in a segment with resources from three frequency bands (PGSM 900, EGSM 900, GSM 1800) it is also possible to start load-based handover between the two nonBCCH frequency bands. In the GSM 900/GSM 1800 environment, load-based handovers are never made to the BCCH frequency band of the segment. In case the BCCH is on the EGSM 900 band,

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the GSM 1800 band is the only possible target for the load-based TCH handover in the segment. If an intra-segment TCH handover to a non-BCCH frequency band is possible, the BSC has to search for a candidate MS which supports non-BCCH frequencies and which fulfils the following criteria: AV_RXLEV_DL + (BS TX pwr max (PMAX1) - BS_TXPWR) - non BCCH layer offset (NBL) >= non BCCH layer access threshold (LAR). AV_RXLEV_DL is the terminal's reported signal level on the current TCH. This is decreased by the BTS-specific offset of a BTS on the non-BCCH frequency layer to get an estimation for that band. This estimate is then compared to an existing threshold parameter non BCCH layer access threshold (LAR). If the MS is already on non-BCCH frequency layer, AV_RXLEV_DL is the downlink signal level of the BCCH carrier of the segment. If the call is on a non-BCCH resource, the non-BCCH resource is set to always available. If the handover is possible only from PGSM 900 to EGSM 900, the BSC can start an intra-segment handover attempt for a call on a TCH on the PGSM 900 band without any further examinations if only the MS in question supports the EGSM 900 frequencies. Load-based TCH handover in GSM 800/GSM 1900 Common BCCH In the GSM 800/GSM 1900 environment, when the common BCCH is on GSM 1900, the load-based TCH handover is also possible from the non-BCCH band GSM 800 BTS towards the GSM 1900 BCCH BTS. In this case, if the MS on the GSM 800 BTS has reported adjacent cell measurement from the serving cell, the following criterion has to be fulfilled: AV_RXLEV_NCELL(serving BCCH) >= non BCCH layer access threshold (LAR). If the MS has not reported adjacent cell measurement from the serving cell, the used criterion is AV_RXLEV_DL + (BS TX pwr max (PMAX1) - BS_TXPWR) + non BCCH layer offset (NBL) >= non BCCH layer access threshold (LAR).

6.6

Intra-segment handover from non-BCCH layer based on signal level As described in Load-based TCH handover and Common BCCH Control, the BSC has means to direct traffic from the BCCH frequency band to the other bands in a segment. A mechanism to direct traffic in the opposite way has also been implemented. When the downlink signal level in the serving non-BCCH frequency TCH decreases, the BSC starts a handover to the BCCH frequency layer of the segment. This handover type is applicable only in networks where the BCCH frequency layer has more coverage than the non-BCCH frequency layer (that is, the BCCH is on the GSM 900 frequency band or on the GSM 800 frequency band).

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Non BCCH freq. layer BCCH freq. layer

Figure 11

BCCH freq. layer

Intra-segment handover from non-BCCH frequency layer to BCCH frequency layer of the segment

The BSC bases the decision on the need for moving a call from non-BCCH frequency layer to BCCH frequency layer on a threshold parameter non BCCH layer exit threshold (LER). The parameters non BCCH layer exit threshold px (LEP) and non BCCH layer exit threshold nx (LEN) have also been introduced to allow the operator to fine tune the triggering of the handover. For more information on the parameters, see BSS Radio Network Parameter Dictionary. As the signal level on the non-BCCH frequency layer channel decreases below the threshold non BCCH layer exit threshold (LER), an intra-SEG handover is initiated. The purpose of the handover is to move calls away from the non-BCCH frequency layer of the segment so that a channel in the non-BCCH frequency layer is never allocated for this type of handover. Only channels on the BCCH frequency layer can be used. Note that when the BCCH is on the GSM 1900 frequency band, the intra-segment handover that is based on the signal level is made from the BCCH frequency band with a weaker coverage to the non-BCCH frequency band with a stronger coverage. The counters that are related to this handover are shortly presented in Measurements and counters. For more information on the counters, see 4 Handover Measurement.

6.7

Power budget handover and Common BCCH Control There are two different ways of making a decision on the power budget (PBGT) handover if an MS is on the non-BCCH frequency layer of the multiband common BCCH segment. Whenever the MS has reported the measurement results for the serving segment's BCCH frequency the PBGT decision is made based on that information. If the measurement of the serving segment's BCCH frequency is not included in the results reported by the MS, the PBGT decision is made based on the measurement results of the serving TCH.

Adj. BCCH

Own BCCH

Server

Figure 12

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PBGT HO decision when non-BCCH layer has less coverage


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Whenever a call is on a BCCH frequency layer TCH of a common BCCH segment, measurements of the serving TCH are always used, and the used PBGT handover criterion is: PBGT(n) = (B - AV_RXLEV_DL_HO - (BS TX pwr max (PMAX1) - BS_TXPWR)) - (A - AV_RXLEV_NCELL(n)) where the measurements of the serving and an adjacent segment are compared to determine the superiority between them. A = MS txpwr max gsm (PMAX1) (ADJ)(n) if adjacent cell is GSM 900 or GSM 800. A = MS txpwr max gsm1x00 (PMAX2) (ADJ)(n) if adjacent cell is GSM 1800 or GSM 1900. B = MS txpwr max gsm (PMAX1) (BTS) if serving cell is GSM 900 or GSM 800. B = MS txpwr max gsm1x00 (PMAX2) (BTS) if serving cell is GSM 1800 or GSM 1900. For a call on a non-BCCH frequency layer TCH of a common BCCH segment, measurements of the serving BCCH are used whenever available, and the used PBGT handover criterion is: PBGT(n) = (B - AV_RXLEV_NCELL(serving BCCH)) - (A - AV_RXLEV_NCELL(n)). The measurements of the serving TCH are used for PBGT calculation for an MS on the non-BCCH frequency layer only if the signal level of the serving BCCH is not reported by the MS. PBGT(n) = (B - AV_RXLEV_DL_HO - (BS TX pwr max (PMAX1) - BS_TXPWR) - non BCCH layer offset (NBL)) - (A - AV_RXLEV_NCELL(n)).

6.8

IUO handover and Common BCCH Control Each BTS in a segment can have its own regular and super-reuse layers. The superreuse layer of a BTS can be accessed only via the regular layer of the BTS. When the MS is camped on a non-BCCH frequency band in the common BCCH environment, the carrier-to-interference ratio (C/I) estimation is always performed between serving segment's BCCH measurement and BCCH measurement of an interfering cell. The child cell concept is not supported when the segment option is in use.

6.9

Channel allocation criteria based on the minimum acceptable C/N ratio and Common BCCH Control When the traffic channel allocation criteria based on the minimum acceptable carrier-tonoise (C/N) ratio are employed, the BSC ensures that: • •

the uplink signal coming from the MS can overcome the uplink interference the uplink interference level on the TCH to be allocated is not unnecessarily low when compared to the uplink signal level.

The channel allocation criteria based on the minimum acceptable C/N ratio are controlled with the parameter C/N threshold (CNT) administered on a BTS-by-BTS basis in a segment by O&M. C/N threshold (CNT) gives a recommendation on the minimum acceptable C/N ratio when a time slot to be allocated in a call or in a handover attempt is selected. The range is from 1 dB to 63 dB.

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If the value of the parameter C/N threshold (CNT) varies between the BTSs of the same resource type, the BSC selects the greatest value for the calculation. The recommendation for a certain resource type in the segment is disabled when the value is 'not used' even in one of the BTSs of the same resource type. Maximum acceptable interference level The BSC first calculates the maximum acceptable interference level MAX_INTF_LEV for each existing resource type in the segment. It is calculated in the following ways depending on the handover type and whether the software optimisation of the MS power level in handover and call set-up is used: 1. Call set-up and intra-cell HO; optimisation of the MS power level in call set-up and in intra-cell HO is not employed:

MAX_INTF_LEV = RXLEV_UL + ( MsTxPwrMaxGSM(BTS) - MS_TXPWR ) - CNThreshold if serving BTS is GSM 800 or GSM 900 and calculation is performed for resource type of GSM 800 or GSM 900 MAX_INTF_LEV = RXLEV_UL + ( MsTxPwrMaxGSM1x00(BTS) - MS_TXPWR ) - CNThreshold if serving BTS is GSM 1800 or GSM 1900 and calculation is performed for resource type of GSM 1800 or GSM 1900 MAX_INTF_LEV = RXLEV_UL + ( MsTxPwrMaxGSM1x00(BTS) - CORR_MS_TXPWR ) - CNThreshold if serving BTS is GSM 900 and calculation is performed for resource type of GSM 1800 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 5 dBm to 33 dBm CORR_MS_TXPWR = 36 dBm if MS_TXPWR is from 35 dBm to 39 dBm MAX_INTF_LEV = RXLEV_UL + ( MsTxPwrMaxGSM(BTS) - CORR_MS_TXPWR ) - CNThreshold if serving BTS is GSM 1800 and calculation is performed for resource type of GSM 900 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 6 dBm to 36 dBm CORR_MS_TXPWR = 5 dBm if MS_TXPWR is from 0 dBm to 4 dBm MAX_INTF_LEV = RXLEV_UL + ( MsTxPwrMaxGSM1x00(BTS) - CORR_MS_TXPWR ) - CNThreshold if serving BTS is GSM 800 and calculation is performed for resource type of GSM 1900 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 5 dBm to 31 dBm CORR_MS_TXPWR = 33 dBm if MS_TXPWR is from 33 dBm to 39 dBm MAX_INTF_LEV = RXLEV_UL + ( MsTxPwrMaxGSM(BTS) - CORR_MS_TXPWR ) - CNThreshold if serving BTS is GSM 1900 and calculation is performed for resource type of GSM 800

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CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 6 dBm to 32 dBm CORR_MS_TXPWR = MS_TXPWR if MS_TXPWR is 33 dBm CORR_MS_TXPWR = 5 dBm if MS_TXPWR is from 0 dBm to 4 dBm

RXLEV_UL is the current uplink signal level and it is measured during the initial signalling period of a call set-up or just before the handover attempt. MS txpwr max gsm (PMAX1) (BTS) - MS_TXPWR or MS txpwr max gsm1x00 (PMAX2) (BTS) - MS_TXPWR depending on a frequency band is the difference between the maximum RF power that an MS is permitted to use on a channel in the segment and the actual transmitting power of the mobile station. CORR_MS_TXPWR is the corrected MS_TXPWR value which is used when the BSC calculates MAX_INTF_LEV for the resource type different from the serving one. 2. Call set-up and intra-cell HO; optimisation of the MS power level in call set-up and in intra-cell HO is employed: MAX_INTF_LEV = MAX( MIN(RXLEV_UL+(MsTxPwrMaxGSM(BTS)-MS_TXPWR), OptimumRxLevUL), RXLEV_UL-(MS_TXPWR-MsTxPwrMin) ) - CNThreshold if serving BTS is GSM 800 or GSM 900 and calculation is performed for resource type of GSM 800 or GSM 900 MAX_INTF_LEV = MAX( MIN(RXLEV_UL+(MsTxPwrMaxGSM1x00(BTS)-MS_TXPWR), OptimumRxLevUL), RXLEV_UL-(MS_TXPWR-MsTxPwrMin) ) - CNThreshold if serving BTS is GSM 1800 or GSM 1900 and calculation is performed for resource type of GSM 1800 or GSM 1900 MAX_INTF_LEV = MAX( MIN(RXLEV_UL+(MsTxPwrMaxGSM1x00(BTS)-CORR_MS_TXPWR), OptimumRxLevUL), RXLEV_UL-(CORR_MS_TXPWR-MsTxPwrMin) ) - CNThreshold if serving BTS is GSM 900 and calculation is performed for resource type of GSM 1800 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 5 dBm to 33 dBm CORR_MS_TXPWR = 36 dBm if MS_TXPWR is from 35 dBm to 39 dBm MAX_INTF_LEV = MAX( MIN(RXLEV_UL+(MsTxPwrMaxGSM(BTS)-CORR_MS_TXPWR), OptimumRxLevUL), RXLEV_UL-(CORR_MS_TXPWR-MsTxPwrMin) ) - CNThreshold if serving BTS is GSM 1800 and calculation is performed for resource type of GSM 900 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 6 dBm to 36 dBm CORR_MS_TXPWR = 5 dBm if MS_TXPWR is from 0 dBm to 4 dBm MAX_INTF_LEV = MAX( MIN(RXLEV_UL+(MsTxPwrMaxGSM1x00(BTS)-CORR_MS_TXPWR), OptimumRxLevUL), RXLEV_UL-(CORR_MS_TXPWR-MsTxPwrMin) ) - CNThreshold if serving BTS is GSM 800 and calculation is performed for resource type of GSM 1900

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CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 5 dBm to 31 dBm CORR_MS_TXPWR = 33 dBm if MS_TXPWR is from 33 dBm to 39 dBm MAX_INTF_LEV = MAX( MIN(RXLEV_UL+(MsTxPwrMaxGSM(BTS)-CORR_MS_TXPWR), OptimumRxLevUL), RXLEV_UL-(CORR_MS_TXPWR-MsTxPwrMin) ) - CNThreshold if serving BTS is GSM 1900 and calculation is performed for resource type of GSM 800 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 6 dBm to 32 dBm CORR_MS_TXPWR = MS_TXPWR if MS_TXPWR is 33 dBm CORR_MS_TXPWR = 5 dBm if MS_TXPWR is from 0 dBm to 4 dBm MS_TXPWR -MS txpwr min (PMIN) is the difference between the actual transmitting power of the MS and the minimum RF power that an MS is permitted to use on a channel in the certain resource type BTS. The parameter optimum RX level uplink (LEV) indicates the optimum uplink RF signal level which ensures adequate speech/data quality but does not cause uplink interference.

t

If the value of the parameter optimum RX level uplink (LEV) varies between the TRXs of the BTSs of the same resource type, the BSC selects the greatest value for the calculation. The optimum uplink RF signal level for the certain resource type in the segment is disabled when the value is 'not used' even in one of the TRXs of the BTSs of the same resource type. If the value of the parameter MS txpwr min (PMIN) varies between the BTSs of the same resource type, the BSC selects the greatest value for the calculation.

3. Inter-cell handover; optimisation of the MS power level in handover is not employed: MAX_INTF_LEV = AV_RXLEV_NCELL(n) — nonBcchLayerOffset(n) — RxLevBalance - CNThreshold(n) AV_RXLEV_NCELL(n) is the averaged downlink signal level of the target (adjacent) segment (n). The parameter RX level balance (RXBAL) indicates the difference between the uplink signal level and the downlink signal level within the BSC coverage area. The range is from 0 dB to 20 dB and, for example, the value 5 dB indicates that the downlink signal is 5 dB stronger than the uplink signal. The parameter is set for the BSC. The parameter non BCCH layer offset(n) indicates the estimated difference between the signal levels of the BCCH layer and the nonBCCH layer resource in the target segment (n). 4. Inter-cell handover; optimisation of the MS power level in handover is employed: MAX_INTF_LEV = MAX( MIN(AV_RXLEV_NCELL(n) — nonBcchLayerOffset(n) - RxLevBalance,MsPwrOptLevel(n) + nonBcchLayerOffset(n) - RxLevBalance), (AV_RXLEV_NCELL(n) — nonBcchLayerOffset(n) - RxLevBalance) (MsTxPwrMaxGSM(BTS)(n) - MsTxPwrMin(n)) ) - CNThreshold(n) if calculation is performed for adjacent segments GSM 800 or GSM 900 resource type MAX_INTF_LEV = MAX( MIN(AV_RXLEV_NCELL(n) — nonBcchLayerOffset(n)

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- RxLevBalance,MsPwrOptLevel(n) + nonBcchLayerOffset(n) - RxLevBalance), (AV_RXLEV_NCELL(n) — nonBcchLayerOffset(n) - RxLevBalance) (MsTxPwrMaxGSM1x00(BTS)(n) - MsTxPwrMin(n)) ) - CNThreshold(n) if calculation is performed for target segments GSM 1800 or GSM 1900 resource type MS txpwr max gsm(BTS)(n) - MS txpwr min(n) or MS txpwr max gsm1x00(BTS)(n) - MS txpwr min(n), depending on a frequency band, is the difference between the maximum RF power that an MS is permitted to use on a certain resource type traffic channel in the target segment(n) and the minimum RF power which an MS is permitted to use on a certain resource type traffic channel in the target segment(n). The parameter MS pwr opt level(n) (set independently for each adjacent segment) indicates the optimum uplink RF signal level on a channel in the adjacent segment after a handover. The range is from -110 dBm to 47 dBm. The optimisation of the MS power level in handover is disabled when the value is 'no optimisation'.

t

When the BSC calculates the optimised RF power level of the MS, it presumes that the uplink signal level is equal to the downlink signal level, measured by the MS, within the coverage area of the adjacent segment. If the downlink signal is, for example, 5 dB stronger than the real uplink signal, the value for the parameter MS pwr opt level (POPT) should be selected 5 dB higher than the desirable uplink signal level. Correspondingly, if the downlink signal is weaker than the real uplink signal, the value of the parameter MS pwr opt level (POPT) should be lower than the desirable uplink signal level. Interference band recommendation Interference band recommendation is used in the traffic channel allocation in a call and in an intra-BSC handover attempt. The BSC is able to calculate an interference band recommendation for each existing resource type in the segment by using the minimum acceptable C/N ratio (parameter C/N threshold (CNT)), the radio link measurements reported by the MS/BTS and the boundary limits for the interference bands (parameter averaging period (AP)). The parameter averaging period (AP) is used for calculating averaged values from the interference level in the active/unallocated time slots for the traffic channel allocation procedure (see Extended Cell Range): •

•

averaging period is the number of SACCH multiframes from which the averaging of the interference level in the active/unallocated time slots is performed. The range is from 1 to 32. Boundary1 - Boundary5 are the limits of the five interference bands for the active/unallocated time slots. The range is from -110 dBm to -47 dBm.

The BSC then compares the maximum acceptable interference level MAX_INTF_LEV of each existing resource type to 5 interference bands. The comparison indicates the interference band recommendation which is used in the channel allocation procedure. Note that the limits of five interference bands are looked from that resource type BTS for which resource type the interference band recommendation is calculated. Example:

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An MS is on the GSM 900 band and the BSC calculates recommendation for the GSM 900 band. CNThreshold = 20 dB

Interference band 0 -110 ... -105 dBm

RXLEV_UL = -78 dBm

Interference band 1 - 104... - 100 dBm Interference band 2 - 99 ... - 95 dBm Interference band 3 - 94 ... - 90 dBm Interference band 4 - 89 ... - 47 dBm

MAX_INTF_LEV = -78 dBm - 20 dB = -98 dBm => Interference band recommendation for GSM 900 is band 1

The interference band is always a resource type-associated recommendation for a target segment. In a handover attempt where there are several target segments, the interference band recommendation does not change the order of preference of the target segments. The BSC allocates for a call or for an intra-BSC handover attempt primarily a TCH whose uplink interference level is within the recommended interference band. For more information, see Radio Channel Allocation.

6.10

Optimisation of the MS power level in handover and in call set-up and Common BCCH Control Optimisation of the MS power level in a handover and in a call set-up is a software in the BSC. If this option is not enabled, the MS uses the maximum RF power permitted on a certain resource type. If the serving BTS is GSM 800 or GSM 900, the maximum RF power is defined by the parameter MS txpwr max gsm (PMAX1). If the serving BTS is GSM 1800 or GSM 1900, the maximum RF power is defined by the parameter MS txpwr max gsm1x00 (PMAX2). Note that the interference band recommendation is essential for the optimisation of the MS power level in a handover and in a call set-up. Channel allocation criteria based on the minimum acceptable C/N ratio eliminate the possibility of handover and call set-up failures because of power optimisation. If channel allocation criteria based on the minimum acceptable C/N ratio is not employed for that resource type or there are no such idle TCHs available whose uplink interference level is better than or within the recommended interference band, the BSC cannot perform the optimisation for that resource type. For more information, see Radio Channel Allocation. Optimisation of the MS power level in call set-up and Common BCCH Control When optimisation of the MS power level in a call set-up is employed, the BSC determines the RF power level which the MS uses as the initial RF power on the traffic channel of certain resource type in the segment so that the RF power level corresponds to the radio link properties of that resource type in the segment. The crucial principle is that the better the radio link properties are the lower the initial MS power level can be. In other words, if the radio link properties of a certain resource type in the segment are good, the MS may use a lower RF power level than the maximum level when accessing the traffic channel. The optimised RF power level MS_TXPWR_OPT is calculated in the following way:

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MS_TXPWR_OPT = MsTxPwrMaxGSM(BTS) - MAX( 0,( RXLEV_UL - OptimumRxLevUL )) if calculation is performed for resource type of GSM 800 or GSM 900 MS_TXPWR_OPT = MsTxPwrMaxGSM1x00(BTS) - MAX( 0,( RXLEV_UL - OptimumRxLevUL )) if calculation is performed for resource type of GSM 1800 or GSM 1900 RXLEV_UL is the uplink signal level when the MS is transmitting at the maximum RF power that an MS is permitted to use on a channel in the serving segment's BCCH resource type. RXLEV_UL is measured during the initial signalling period of call set-up. The parameter optimum RX level uplink (LEV) indicates the optimum uplink RF signal level which both ensures adequate speech/data quality and does not cause uplink interference. The range of the parameter is from -109 dBm to -47 dBm. The use of the parameter is disabled when the value is 'not used'.

t

To enable the optimisation of the MS power level for the resource type in a call set-up, set theoptimum RX level uplink (LEV) parameter for every TRX of the same resource type BTSs in the segment. Note that if the value of the parameter optimum RX level uplink (LEV) varies between the TRXs of the same resource type BTSs in the segment, the BSC selects the greatest value for the calculation. Optimisation of the MS power level in intra-BSC handover and Common BCCH Control When optimisation of the MS power level in a handover is employed, the BSC determines, in case of a BSC-controlled handover, the RF power level which the MS that has been handed over uses as the initial RF power in the certain resource type of the target segment so that the RF power level corresponds to the radio link properties of that resource type in the target segment. The crucial principle is that the better the radio link properties are the lower the initial MS power level can be. That is, if the radio link properties of certain resource type in the segment are good, the MS may use a lower RF power level than the maximum level when accessing the target cell. When optimisation of the MS power level in a handover is not employed, the initial MS power level in the target segment is the maximum RF power an MS is permitted to use on a channel in the target segment (parameter MS TX pwr max gsm (PMAX1) (BTS) if the serving BTS is GSM 800 or GSM 900 and parameter MS TX pwr max gsm1x00 (PMAX2) (BTS) if serving BTS is GSM 1800 or GSM 1900). When the handover to be performed is an inter-cell handover, the optimisation is controlled by the parameter MS pwr opt level(n) (POPT). If the handover to be performed is an intra-cell handover, the optimisation is controlled by the parameter optimum RX level uplink (LEV). The optimised RF power level MS_TXPWR_OPT is calculated in the following two ways depending on whether the case is an inter-cell handover or an intra-cell handover: Inter-cell handover

MS_TXPWR_OPT(n) = MsTxPwrMaxGSM(ADJ)(n) - MAX(0,((AV_RXLEV_NCELL(n) NonBcchLayerOffset(n)) - MsPwrOptLevel(n))) if calculation is performed for adjacent segments GSM 800 or GSM 900 resource type

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MS_TXPWR_OPT(n) = MsTxPwrMaxGSM1x00(ADJ)(n) - MAX(0,((AV_RXLEV_NCELL(n) — nonBcchLayerOffset(n)) - (MsPwrOptLevel(n) + nonBcchLayerOffset(n)))) if calculation is performed for adjacent segments GSM 1800 or GSM 1900 resource type AV_RXLEV_NCELL(n) is the averaged downlink signal level of the adjacent segment(n). The parameter MS TX pwr max gsm (PMAX1) (ADJ)(n) or the parameter MS TX pwr max gsm1x00 (PMAX2) (ADJ)(n) depending on a frequency band (set for each adjacent segment) is the maximum RF power that an MS is permitted to use on a channel in the adjacent segment(n). The parameter MS pwr opt level(n) (POPT) (set for each adjacent segment) indicates the optimum uplink RF signal level on a channel in the adjacent segment(n) after the handover. The range is from -110 dBm to -47 dBm. The optimisation of the MS power level in handover is disabled when the value is 'no optimisation'.

t

When the BSC calculates the optimised RF power level of the MS, it presumes that the uplink signal level is equal to the downlink signal level within the coverage area of the adjacent segment. If the downlink signal is, for example, 5 dB stronger than the uplink signal, the value for the parameter MS pwr opt level(n) (POPT) should be selected 5 dB higher than the desirable uplink signal level. Correspondingly, if the downlink signal is weaker than the uplink signal, the value of the parameter MS pwr opt level(n) (POPT) should be lower than the desirable uplink signal level. Example: Optimum uplink RF signal level after a handover on a channel in the adjacent segment(n) is -70 dBm.

1. If the uplink signal level equals the downlink signal level within the coverage area of the adjacent segment(n), the value of the parameter MS pwr opt level(n) (POPT) should be -70 dBm. 2. If the downlink signal is 5 dB stronger than the uplink signal within the coverage area of the adjacent segment(n), the value of the parameter MS pwr opt level(n) (POPT) should be -65 dBm. 3. If the downlink signal is 5 dB lower than the uplink signal within the coverage area of the adjacent segment(n), the value of the parameter MS pwr opt level(n) (POPT) should be -75 dBm. MS_TXPWR_OPT = MsTxPwrMaxGSM(BTS) MAX( 0,(AV_RXLEV_UL_HO+(MsTxPwrMaxGSM(BTS)-MS_TXPWR)-OptimumRxLevUL) ) if serving BTS is GSM 800 or GSM 900 and calculation is performed for resource type of GSM 800 or GSM 900 MS_TXPWR_OPT = MsTxPwrMaxGSM1x00(BTS) MAX( 0,(AV_RXLEV_UL_HO+(MsTxPwrMaxGSM1x00(BTS)-MS_TXPWR)-OptimumRxLevUL) ) if serving BTS is GSM 1800 or GSM 1900 and calculation is performed for resource type of GSM 1800 or GSM 1900 MS_TXPWR_OPT = MsTxPwrMaxGSM1x00(BTS) MAX( 0,(AV_RXLEV_UL_HO+(MsTxPwrMaxGSM1x00(BTS)-CORR_MS_TXPWR)-OptimumRxLevUL) ) if serving BTS is GSM 900 and calculation is performed for resource type of GSM 1800

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CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 5 dBm to 33 dBm CORR_MS_TXPWR = 36 dBm if MS_TXPWR is from 35 dBm to 39 dBm MS_TXPWR_OPT = MsTxPwrMaxGSM(BTS) MAX( 0,(AV_RXLEV_UL_HO+(MsTxPwrMaxGSM(BTS)-CORR_MS_TXPWR)-OptimumRxLevUL) ) if serving BTS is GSM 1800 and calculation is performed for resource type of GSM 900 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 6 dBm to 36 dBm CORR_MS_TXPWR = 5 dBm if MS_TXPWR is from 0 dBm to 4 dBm MS_TXPWR_OPT = MsTxPwrMaxGSM1x00(BTS) -MAX( 0,(AV_RXLEV_UL_HO+(MsTxPwrMaxGSM1x00(BTS)-CORR_MS_TXPWR)-OptimumRxLevUL) ) if serving BTS is GSM 800 and calculation is performed for resource type of GSM 1900 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 5 dBm to 31 dBm CORR_MS_TXPWR = 33 dBm if MS_TXPWR is from 33 dBm to 39 dBm MS_TXPWR_OPT = MsTxPwrMaxGSM(BTS) -MAX( 0,(AV_RXLEV_UL_HO+(MsTxPwrMaxGSM(BTS)-CORR_MS_TXPWR)-OptimumRxLevUL) ) if serving BTS is GSM 1900 and calculation is performed for resource type of GSM 800 CORR_MS_TXPWR = MS_TXPWR + 1 if MS_TXPWR is from 6 dBm to 32 dBm CORR_MS_TXPWR = MS_TXPWR if MS_TXPWR is 33 dBm CORR_MS_TXPWR = 5 dBm if MS_TXPWR is from 0 dBm to 4 dBm Intra-cell handover MS TX pwr max gsm (PMAX1) (BTS) - MS_TXPWR or MS TX pwr max gsm1x00 (PMAX2) (BTS) - MS_TXPWR depending on a frequency band is the difference between the maximum RF power that an MS is permitted to use on a certain resource type channel in the segment and the actual transmitting power of the mobile station. The parameter optimum RX level uplink (LEV) indicates the optimum uplink RF signal level which ensures adequate speech/data quality and does not cause uplink interference. The range of the parameter is from -109 dBm to -47 dBm. The use of the parameter is disabled when the value is 'not used'. CORR_MS_TXPWR is the corrected MS_TXPWR value which is used when the BSC calculates optimum power level for the resource type different from the serving one.

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To enable the optimisation of the MS power level for a certain resource type in an intracell handover, set the optimum RX level uplink (LEV) parameter for every TRX of the same resource type BTSs in the segment. Note that if the value of optimum RX level uplink (LEV) varies between the TRXs of the same resource type BTSs in the segment, the BSC selects the greatest value for the calculation.

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Planning Common BCCH

7 Planning Common BCCH 7.1

Common BCCH and handover In a Common BCCH segment environment, an inter-BTS intra-segment handover, that is, a handover between different BTSs inside a segment has been introduced. The interBTS handover can occur within the same frequency band or between different frequency bands Handover causes •

•

Power budget handover The standard power budget (PBGT) calculation is applied to an MS on the BCCH layer. If an MS is on the non-BCCH frequency layer of the multiband Common BCCH segment, the decision on the PBGT handover is based on the measurement of the segment's own BCCH frequency that the MS measures when on the nonBCCH frequency band. The BCCH measurements are compared with each other to determine the superiority between the serving and adjacent segment. Load-based TCH handover In addition to the standard TCH–TCH handovers, the BSC can command an additional handover to balance the load between different frequency bands when Common BCCH is active. During the call set-up procedure the load cannot necessarily be kept under the BTS load in SEG limit for each BTS, because not all terminals support all the resource types. Furthermore, due to their propagation properties, the GSM 1800/1900 resources may not be available in all TCH allocation cases. When deciding on initiating a handover to balance the load between the BTSs of a segment, the triggering load limit L is defined with the formula: L = (BTS load in SEG + 100) / 2 If the BTS load in SEG parameter is set to the value 1%..100%, the load limit is calculated according to the formula above. The value 0 of the parameter BTS load in SEG, however, is a special case. When the operator has set the value to be 0, the BSC tries to hand over all calls that meet the signal strength criteria from the BCCH layer BTS to the non BCCH layer. This results in the resources on the BCCH layer being kept free for as long as possible. In most cases the main purpose of the handover is to move TCH load from the BCCH band to the other band to free BCCH band traffic channels for single-band mobile stations. The BSC checks the load of BTSs in a multiband segment every time it receives a TCH request for the segment in question. When the BSC selects target BTSs for a load-based intra-cell handover, it only accepts BTSs whose load is below the respective BTS load in SEG value.

SDCCH handover In addition to the standard SDCCH–SDCCH handovers, an inter-band (intra-segment) SDCCH handover has been implemented to avoid long SDCCH reservations. It reduces the SDCCH pressure on the BCCH resource layer. This handover is triggered when the length of an SDCCH reservation on the BCCH layer equals the value of the intra segment SDCCH HO guard parameter.

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Planning Common BCCH


The handover is performed if there are available SDCCH resources outside the BCCH band and the mobile station has the required capability.

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7.2

Common BCCH and channel allocation SDCCH allocation procedure In the case of an SDCCH-SDCCH intra-BSC handover, the general process of SDCCH selection takes place in the following way: •

•

•

BTS selection: The BTSs where the SDCCH can be allocated are filtered based on the information on the frequency capability of the accessing MS and on the usability of radio resources in different frequency bands. The BTSs are divided into groups according to their frequency band (BTSs using the BCCH frequency band form one group and BTSs using a frequency other than the BCCH frequency band form another group). The SDCCH load of each BTS group is calculated by taking into account only the static SDCCH resources. The channel is allocated from the BTS group that has the lowest load. TRX selection: Within the selected BTS(s), the TRX that has the lowest channel load (busy traffic and signalling channels) is selected. In RF hopping, in the BTSs with a non-BCCH TRX prioritisation, the priority is given to RF hopping TRXs. The SDCCH channel from the BCCH TRX is allocated only if there are no idle SDCCHs at all in other TRXs. RTSL selection: The RTSL that has the highest number of idle SDCCH channels left is selected. However, if a signalling channel was last allocated from the same TRX, another RTSL than last time is allocated, when possible. If there are no idle static SDCCH resources in the BTSs, dynamic SDCCH resources are searched for in every BTS group. From all TRXs, the RTSL which has the least idle dynamic SDCCH channels is selected.

SDCCH assignment (Immediate Assignment) In a multiband Common BCCH segment, the initial SDCCH channel for a call set-up is always allocated in the layer where the segment's BCCH resides. This is because the capabilities of an accessing MS are not known when the MS sends the ESTABLISH INDICATION message. It is not possible to define the usability of the non-BCCH frequencies of the segment, as the MS only starts sending measurement reports after it has been moved to a dedicated channel. An exception to the rule is when the segment's BCCH carrier is on EGSM 900 band. In that case the segment's possible PGSM 900 resources are also available for the initial SDCCH allocation because an MS supporting the EGSM 900 band is always capable of supporting the PGSM 900 frequency band and because the two frequency bands are regarded as equal from the radio properties point of view. Within the BCCH frequency band, the SDCCH to be allocated is selected according to the algorithm described above. If there are no idle static or dynamic SDCCH resources in the BTSs, an idle TCH timeslot is configured as a new temporary SDCCH resource. Dynamic SDCCH reconfiguration is only applied in the Immediate Assignment phase, not in handovers.

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SDCCH external handover During inter-BSC handovers, the usability of radio resources in different frequency bands than the BCCH cannot be defined in the target BSC. If the non-BCCH layer is regarded as a layer with less coverage, as indicated by the positive value of the non BCCH layer offset parameter, only BCCH frequency band resources are used in the SDCCH allocation for an external handover. If the BCCH is on PGSM 900, the EGSM 900 band can also be used according to the MS capabilities. If the BCCH is on EGSM 900, the PGSM 900 band can also be used. If the non-BCCH layer is regarded as a layer with equal or greater coverage, as indicated by the zero or negative value of the non BCCH layer offset parameter, the non-BCCH layer resources can also be used in the SDCCH allocation for an external handover according to the MS capabilities. SDCCH-SDCCH intra-BTS handover In the case of an intra-BTS handover, the SDCCH allocation differs from the basic procedure. The SDCCH is trying to be allocated in a TRX other than the call serving TRX. The channel in the call-serving RTSL is never selected (therefore the search procedure is started only if a SDCCH RTSL other than the serving one is defined in the BTS). If the call-serving TRX is blocked, the basic search procedure is used. TCH assignment The basic difference between TCH allocation in a Common BCCH controlled segment and a single BTS cell is that the target of a TCH request in a segment is a set of BTSs instead of a single BTS. Basically, all existing rules for selecting a TCH in a single BTS cell are also valid between BTSs in a segment cell. The general process for TCH selection is as follows: •

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BTS selection: The BTSs where a TCH can be allocated are filtered on the basis of the information on the frequency capability of the accessing MS and on the usability of radio resources in different frequency bands. The BTSs are filtered according to their load. The load calculation is based on the BTS-specific parameter BTS load in SEG. TCHs are assigned from the BTSs whose load is less than the BTS load in SEG value. For more information, see Search of a single slot TCH and Common BCCH Control. When each BTS has reached its load limit, the allocation continues in those BTSs where the load is less than the highest load threshold value among the BTSs. When the load in all the BTSs has reached the level of the highest load threshold value among the BTSs, the general rule is that the non-BCCH frequency band is preferred to the BCCH frequency band. An extension to this general rule is needed when there are three frequencies (PGSM 900, EGSM 900, and GSM 1800) in use in the common BCCH segment. The preference between the two non-BCCH frequency layers is made in following way: • if BCCH is on the PGSM 900 frequency band, GSM 1800 is preferred to EGSM 900 • if BCCH is on the GSM 1800 frequency band, EGSM 900 is preferred to PGSM 900 By preferring the non-BCCH frequency band resources the resources on the BCCH frequency band are saved and the possibility of single band mobiles to get service in the Common BCCH network is increased.


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RTSL selection: After the primary target group of BTSs for TCH allocation has been selected, all the idle RTSLs are ranked according to their interference level and to the interference level recommendation defined in the BTS they belong to. If there are several candidate RTSLs with the same interference level, the TRX prioritisation in TCH allocation is applied: the RTSL is allocated from the BCCH TRX or from a non-BCCH TRX according to the defined prioritisation. If several candidate RTSLs exist after applying the TRX prioritisation in TCH allocation, the RTSL is allocated from the BTS with the lowest circuit-switched load by using the round robin method so that the BTS allocated the previous time is the last choice.


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7.3

SDCCH dimensioning with Common BCCH Consider the multi-band mobile and the following two scenarios: Case 1: GSM network with separated cells GSM 900/800 and GSM 1800/1900 Case 2: Common BCCH GSM network (GSM 900/800 and GSM 1800/1900 BTSs colocated).

Case 1

• • •

• • •

Case 2

2 TRXs/cell (1% blocking), 8.11 Erl/cell Traffic density 25 mErl/subs, 325 subs/cell Call establishment time: SDCCH reservation time 7 sec/call, 1.94 mErl/call, 325 calls/hour/cell x 1.94 mErl/call = 0.631 Erl/cell (SDCCH) Location update (once in 60 minutes), 325 subs/cell x 1.94 mErl/call = 0.631 Erl/cell (SDCCH) SDCCH capacity = 0.631 + 0.631 =1.262 Erl/cell Number of SDCCH channels/cell = 5

5 SDCCH channels are necessary for each BTS. So a separated channel configuration is needed for each BTS (TS0 is dedicated for the BCCH channel and TS1 for SDCCH channels).

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• • •

•

• •

4 TRXs in a segment (1% blocking), 20.33 Erl/cell Traffic density 25 mErl/subs, 813 subs/cell Call establishment time: SDCCH reservation time 7 sec/call, 1.94 mErl/call, 813 calls/hour/cell x 1.94 mErl/call = 1.58 Erl/Call (SDCCH) Location update (1.4 times in 60 minutes due to smaller location area compare with 2 TRXs/cell), 813 calls/cell x 1.4 x 1.94 mErl/call = 2.2 Erl/Cell (SDCCH) SDCCH capacity = 1.58 Erl/Cell + 2.2 Erl/Cell = 3.8 Erl/Cell Number of SDCCH channels = 10

A separated configuration is needed, with two timeslots for SDCCH on the BCCH layer.


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Implementing Common BCCH Control overview

8 Implementing Common BCCH Control overview Common BCCH Control can be activated/disabled with the WOA command. For detailed implementation instructions of Common BCCH Control, see Activating and testing BSS10016 and BSS10118: Common BCCH Control for GSM. Further information Implementing Parameter Plans in NetAct Product Documentation gives instructions on how to plan and prepare parameter changes, for example when activating new features in the GSM and WCDMA networks.

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