Optimization Methodology Using GSM Forte

Optimization Methodology Using GSM Forté

Optim pt imiz iza ation ti on Method th odol olog ogy y Us i n g GSM GSM Fo r t é


Table of Contents 1

Introduction.............................................................................................. 3

2

Project Workflow for Single Band Market.................................................. 4

3

Project Workflow for Dual Band Markets................................................... 5

4

MS Recording Creation .............................................................................. 6 4.1 Pre-project Neighbor Optimization.....................................................................6 4.2 BSIC Check ...................................................................................................6 4.3 Recording Implementation ...............................................................................6 4.3.1 Recording Length..................................................................................6 4.3.2 Shadow-Breaking..................................................................................7 4.3.3 Conclusion ...........................................................................................9

5

Neighbor Optimization ............................................................................ 10

6

Frequency Planning................................................................................. 11 6.1 Available Frequency Planning Strategy............................................................. 11 6.1.1 Theoretical Background of Frequency Hopping ........................................ 11 6.1.2 Frequency Hopping ............................................................................. 11 6.2 Hopping Method ........................................................................................... 12 6.3 BCCH Planning for SFH .................................................................................. 13 6.4 Taking Advantages of Forté Planning Capabilities .............................................. 14

7

Parameter Optimization .......................................................................... 16 7.1 Dual Band Parameter Optimization .................................................................. 16 7.2 Feature Activation......................................................................................... 16


1

Introduction

This document presents the methodology for optimizing any GSM network (single band or dual band markets – GSM900/DCS1800 or GSM850/PCS1900) using Schema’s GSM Forté’s optimization tool.

The complete optimization cycle includes: •

Preliminary analysis

•

Set-up Recording

•

Neighbor Optimization

•

Frequency Planning

•

Parameter Optimization (traffic management between bands, feature activation)

This document offers a general approach to the optimization process, and is not meant to replace the existing training document used for each vendor (Seven Basic Steps to Optimize an Ericsson Market…).


2

Project Work flo w for Sing le Band Market

PRE-PROJECT KPIs COLLECTION

NEIGHBOR DELETION/ BSIC CHECK

INITIAL RECORDING (OPTIONNAL)

INITIAL RETUNE (OPTIONNAL)

FINAL RECORDING


3

Project Work flo w for Dual Band Markets

PRE-PROJECT KPIs COLLECTION

NEIGHBOR DELETION/ BSIC CHECK

INITIAL GSM 900 RECORDING

INITIAL GSM 900 RETUNE

DCS 1800 RECORDING (optional)

INITIAL DCS 1800 RETUNE (optional)


4

MS Reco rd in g Creati on

The MS recording process must be performed carefully to minimize the length of the project, especially with regard to Siemens, Alcatel, Motorola, Huawei, or Nortel, where the BA list cannot be modified by the user, but only through the creation of fake neighbors.

4.1

Pre-pr oject Neigh bor Optim ization

Before starting the MS recording, an analysis of the neighbor list should be performed using Forté in order to identify all cells with more than 25 neighbors. Based on this analysis, a list should be created with neighbors to be deleted, using only Handover Statistics, (as a model is not yet available) based on the following workflow: 1. Identify all cells in the optimization set that have more than 25 neighbors. 2. Rank each neighbor relation by descending number of handover attempts. 3. Delete 6 of the last 12 neighbor relation by targeting inter-band HO relations first (in case of dual band market)

4.2

BSIC Chec k

Before beginning recording, the Forté BCCH-BSIC Reuse report should be checked to


Markets using free BCCH/TCH planning (with or without Base band hopping) may require several recording sessions per cell when more than 30 BCCHs are used.

Dual Band Markets

The length of recordings varies for each band, based on the number of BCCHs to measure and on the vendor. Since the DCS1800 (PCS1900) layer is normally the capacity layer with more available spectrum, it uses more potential BCCH. On average, it takes twice as long to record the DCS layer as it does to record the GSM layer. In theory, cross band measurements are only needed: •

•

If a network has a mixed configuration of Common BCCH or CBCCH (e.g., BCCH on band 850/900 and TCH on band 1900/1800– within the same sector) and Multiple BCCH or MBCCH (e.g., two co-sited sectors, one with 850/900 BCCH and one with 1900/1800 BCCH); all sectors should consider measuring interferences from both bands (mandatory). If cross-band HO optimization is required: The C/I between sectors belonging to different bands must be available for the user to optimize the handovers between bands. Therefore, measurement recording on both bands should be activated. If this not possible (as in siemens), Forté can estimate cross-band measurements in the model by using intra-band measurements, and applying an attenuation value based on the difference in propagation between the bands.


be estimated except if measurements can be collected before and after the BCCH have been changed. Shadow breaking may be required when the number of BCCHs used is limited (below 20) In most cases, an initial retune is recommended for the GSM layer. Check the following for shadowing: •

•

The BCCH reuse report before a project shows the number of close BCCH reuses below 5 km may indicate poor BCCH planning and high shadowing A low correlation with an under-predicted model may indicate a high level of shadowing (but the first recording session must be finished before it is possible to see the shadowing).

If an initial BCCH retune is performed for shadow-breaking, the Reveal shadowing option must be used in the initial plan. That option should not be used for the second and final plan. Note: the initial BCCH retune goal, also called mini-BCCH retune, is not to improve

the network statistics, but simply to reveal shadowed impacts (and eventually clean up the BSIC plan). It is recommended to that Forté change all the BCCHs in the retune area. Otherwise, the Minimum change option can be used to allow only a predetermined number of changes. If no initial BCCH reuse is performed, the user may or may not use that option in the Frequency plan.


4 .3 .3 C o n c l u s i o n An initial retune is recommended for markets having less than 20 BCCHs. MS statistics should be recorded before and after the retune. In dual band markets, the capacity layer (DCS 1800) does not always require a shadow-breaking retune. Since twice the recording time is required, only one retune (one set of recordings) should be implemented for that layer. The recordings should be made after dual-band parameter optimization is implemented, if possible. If additional time is available, inter-band (cross-band) measurements could be recorded.


5

Neigh bor Opti mizatio n

Neighbor optimization should be prepared with a shadow-free model, if possible, and implemented before the final retune. The main goal of the neighbor optimization is to decrease the constraints on the BCCH plan, not to improve network statistics (HO Success Rate), since most customers already have a reasonable HO list. Forté uses neighbor relations as logical constraints when planning BCCH to avoid using co-channel BCCHs between neighbors, which is usually not permitted in the OSS. A large number of intra-band neighbors, creates many logical constraints (not physical constraints), which are NOT based on measured interference from MS. The Handover optimizer should be run on the layer with the most frequency planning constraints. Minimizing the number of neighbor relations improves the quality of Forté’s BCCH FP output. Optimizing inter-band HO for dual band markets reduces the length of the recording process, but does not necessarily improve performance. If cross-band MS cannot be recorded because of the extra length associated with it, Forté should not be used to optimize inter-band HO relations, since those relations are only based on HO Statistics (not measured interference). The DCS1800 to 1800 Handover relations can be optimized along with GSM900 to 900, but this will usually not result in significant improvement in the performance or quality of the Forté 1800 BCCH plan because of the high number of available BCCH


6

Frequency Planni ng

Frequency plans can be prepared separately for both bands, according to the Forté methodology.

6.1

Av ailable Frequency Plannin g Strategy

Several frequency planning strategies are available to operators, which involve BCCH vs. TCH planning, hopping vs. non-hopping strategy, and base band hopping vs. synthesized hopping. Activating frequency hopping will maximize improvement to the network.

6 .1 .1 T h e o r e t i c a l B a c k g r o u n d o f Fr e q u e n c y H o p p i n g GSM networks evolve with the goals of providing better quality of service and more system capacity. Frequency hopping helps to achieve these goals. Cellular systems are limited by interference. Multiple co-channel interference, though controlled, is normal, and determines the limits of the service area. The higher the interference level, the harder it is to reuse available frequencies within the smallest area. Since quality of service depends on the carrier/interference ratio (C/I) more than on the signal/noise ratio, the system can tolerate the trade-off between quality and capacity.


The following factors affect SFH performance: 1. Number of Hopping Frequencies A higher number of hopping frequencies improves system performance by increasing frequency diversity. It is not helpful to use more than eight hopping frequencies since the GSM interleaving period consists of eight bursts. 2. Hopping frequencies separation A larger frequency separation between hopping frequencies, improves system performance as the effects of propagation become more uncorrelated. Frequency spacing directly affects Fast Fading. A separation of three to five channels between hoppers provides the maximum gain. 3. System load Since a low system load results in lower interference probability in each hopping frequency, this directly affects SFH performance. The choice of frequency hopping strategy depends on each network’s optimization level and available spectrum.

6.2

Hoppi ng Metho d

Frequency hopping should be activated before using any frequency planning methodology. The choice of one method over another (Base band vs. SFH) depends on the available spectrum, the system load (number of TRXs and EFL), and the maturity of the market (either fast growing or mature with very few new site activations). The

Optimization Methodology Using GSM Forté •

•

•

A specific number of frequencies must be reserved for BCCH planning only (between 12 and 21), potentially affecting the quality of the BCCH plan. The traffic TS on the BCCH TRX will not hop. Without frequency planning, the random collisions between cells cannot be controlled.

The main advantage of SFH is that it does not requires extensive planning, so that TRX or new sites can easily be added to the network, which is especially good for fast-growing markets. In addition, SFH brings the quality gain of hopping even to cells with low number of TRXs, since the number of hoppers is much greater than the number of TRXs. 3. SFH Ad Hoc is a different version of SFH that allows planning a specific MAL (with a different frequency and length) for each sector, instead of a fixed MAL used by all sectors (SFH 1:1). MAL length is based on the number of TRXs in each cell. Normally, a minimum of three or four hoppers is used for each cell with a MAL length equal to the number of TRXs+1. SFH Ad Hoc planning reintroduces frequency planning within SFH, and keeps SFH quality gain even for cells with few TRXs. Random collisions are avoided through the Interference matrix that Forté creates.

6.3

BCCH Plannin g for SFH

Two dedicated groups of frequencies for BCCH and TCH should be used with SFH


Example 1 1 TCH 2 TCH 3 BCCH 4 BCCH 5 TCH 6 TCH 7 BCCH 8 BCCH 9 TCH 10 TCH 11 BCCH 12 BCCH 13 TCH 14 TCH 15 BCCH 16 BCCH 17 TCH 18 TCH 19 BCCH 20 BCCH 21 TCH 22 TCH 23 BCCH 24 BCCH

Example 2 1 TCH 2 BCCH 3 TCH 4 BCCH 5 TCH 6 BCCH 7 TCH 8 BCCH 9 TCH 10 BCCH 11 TCH 12 BCCH 13 TCH 14 BCCH 15 TCH 16 BCCH 17 TCH 18 BCCH 19 TCH 20 BCCH 21 TCH 22 BCCH 23 TCH 24 BCCH

Optimization Methodology Using GSM Forté •

•

Base band hopping for markets with many TRXs/ cells (3 or more TRX/cells), including free BCCH/ TCH planning. SFH Ad Hoc planning, preferably with dedicated BCCH and TCH channels (blocked or staggered to increase frequency diversity) for markets with limited spectrum or few TRX/cell (2 TRX/cells average).

Both methods have advantages and disadvantages, but also significantly increase network performance and capacity.


7

Parameter Opti mi zati on

7.1

Dual Band Parameter Optim ization

This topic is covered in a separate document that deals only with Dual band markets.

7.2

Feature Act iv ation

GSM Forté easily checks the activation status of the major GSM features, including Intra cell Handover, Power control, DTX, and TCH allocation strategy. When the environment is exported to Schema format, it can be checked, regardless of vendor, using the Sector and Channel Group.txt files. The Sector.txt file includes the Intra-cell Handover activation status and the TCH allocation strategy used in the network. •

•

Intra-cell Handover should be activated for Non-hopping or SFH (since it is irrelevant when base band is used). The TCH allocation priority should be set to TCH first in the case of SFH (which is irrelevant when base band is used) since hopping gain provides better quality on the TCH layer.

The Channel group.txt file includes the DTX and Power control activation status: •

DTX Uplink should always be activated (downlink may provide some benefit, but also results in voice quality distortions).


8

Project Planni ng

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Optimization Activit ies Project Preparation and Logistic Kickoff meeting NBR Clean-up MS Statistic s Coll ection (900 ) (*)

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Network Modeling/Planning Dual-band Parameters Optim ization Frequency plan implementation MS Statistics Collection (1800 cross b and) (**)

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MS Statistics Collection (900 and 1800) (***)

N1 N2 N3 N4 N5

Network Modeling/Analysis Neighbor list impl ementation Frequency Plan Implementation Fine tuning of fP and parameters BB Hopping Activation Performance collection/analysis Performance Benchmarking Before Performance Benchmarking After Final Report Preparation

(*) N1 to N3 for 900 (N1 to N5 for 1800 optional) (**) N1 and N2 for 1800 measuring 900 BCCH (optional)

Schema Confidential & Proprietary

May 2008

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Optimization Methodology Using GSM Forte

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