channel_configuration.pdf

Channel configuration

Siemens


Contents 1 2 2.1 2.2 2.3 2.4 3 4 4.1 4.2 4.3 5 6

Channel configuration overview Control channel configuration Dedicated channels Random access channel Paging / access grant and notification-channel CCCH load Extended channel mode Adaptive Multirate AMR General SBS implementation Database parameters Exercises Solutions

MN1789EU10MN_0002 © 2004 Siemens AG

3 13 14 21 28 30 33 35 36 42 43 47 53

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1

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Channel configuration overview


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On the radio interface Um two subbands for the BTS-MS duplex connection are specified: Uplink UL

MS-BTS

824 -

849 MHz

GSM850

890 -

915 MHz

P-GSM900 (primary band)

880 -

915 MHz

E-GSM900 (extended band)

1710 - 1785 MHz 876 -

880 MHz

1850 - 1910 MHz Downlink DL

DCS1800 GSM-R PCS1900

BTS-MS

869 -

894 MHz

GSM850

935 -

960 MHz

P-GSM900 (primary band)

925 -

960 MHz

E-GSM900 (extended band)

1805 - 1880 MHz 921 -

925 MHz

1930 - 1990 MHz

DCS1800 GSM-R PCS1900

The radio frequency channel spacing in 200 kHz, allowing 124 RFC in P-GSM, 174 RFC in E-GSM, 374 in DCS, 20 RFC in GSM-R and 299 in PCS1900. Within the database or within the protocol messages a carrier frequency is characterized by its absolute radio frequency channel number (ARFCN). Using the abbreviation n = ARFCN, there is the following relation between ARFCN and the frequency in MHz in the uplink Fu [MHz] and the downlink Fd [MHz]. GSM850

Fu(n) = 824.2 + 0.2 (n – 128)

128 < n < 251

Fd(n) = Fu(n) + 45

P-GSM900 Fu(n) = 890 + 0.2 n

1 < n < 124

Fd(n) = Fu(n) + 45

E-GSM 960 Fu(n) = 890 + 0.2 n

0< n < 124

Fd(n) = Fu(n) + 45

Fu(n) = 890 + 0.2 x (n -1024) DCS1800 GSM-R PCS1900

4

975 < n < 1023

Fu(n) = 1710.2 + 0.2 x (n -512) 512 < n < 885

Fd(n) = Fu(n) + 95

Fu(n) = 876.2 + 0.2 x (n -955)

955 < n < 974

Fd(n) = Fu(n) + 45

Fu(n) = 1850.2 + 0.2 x (n -512) 512 < n < 810

Fd(n) = Fu(n) + 80


Siemens


(880) 890 Mhz 1710 MHz

960 Mhz GSM 900 1880 MHz DCS 1800

(925) 935 Mhz 1805 MHz

915 Mhz 1785 MHz

UPLINK (UL)

DOWNLINK (DL)

Transmit band of the mobile station

Transmit band of the base station

Duplex Distance 45 MHz resp. 95 MHz 25 (35) MHz 75 MHz

25 (35) MHz 75 MHz

Guard band not used C 124 (174) 374

C C C 1 2 3

C 124’ (174’) 374

C C C 1’ 2’ 3’

C = radio frequency channel (RFC)

200 kHz

512...............885

975....1024 01...............124

DCS1800

ARFCN (Absolute RF channel number)

GSM900 E-GSM900

Fig. 1 Radio frequency channels RFC on Um

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Each RFC offers 8 physical channels a time division multiplex access TDMA. The physical channels are subdivided into logical channels, divided in traffic channels and control channels according GSM 04.03.

200 kHz

0

1

2

4 3

5

6

0 7

Time

1

2

4 3

4.615 msec = 8 • 577 µs

Fig. 2 Radio frequency channels RFC on Um

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Speech Channels (Full/Half) Traffic Channels TCH Data Channels (Data Rate) Logical Channels Broadcast Control Channel BCCH

Control Channels CCH

Common Control Channel CCCH

Dedicated Control Channel DCCH

Fig. 3 Logical channel types

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Frequency Correction Channel FCCH

Synchronization Channel SCH

identification of BCCH frequency, MS frequency synchronization

frame (time) synchronization, identification of neighbour cells (handover)

Broadcast Control Channels BCCH Broadcast Control Channel BCCH

Cell Broadcast Channel CBCH

system information: cell identifier, cell parameter, channel configuration, cell frequencies, broadcast frequencies of neighbour cells

broadcast of short messages: traffic, weather, date, ... (no mobile system info)

Fig. 4 Broadcast control channel

Random Access Channel RACH

MS requests a dedicated channel from network

Access Grant Channel AGCH

answer to a random access, assignment of dedicated signaling channel

Paging Channel PCH

paging of a MS in all cells of a location area for a mobile terminating call

Common Control Channel CCCH

Notification Channel NCH

paging of MS‘s in all cells of a voice group call area to perform ASCI (Advanced Speech Call Items)

Fig. 5 Common control channel

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Stand Alone Dedicated Control Channel SDCCH

Dedicated Control Channel DCCH

“out of band” signaling channel for: call setup signaling, short message service (SMS), location update (LUP), IMSI attach/detach

Slow Associated Control Channel SACCH

“in band” signaling channel (periodic): downlink: system info, power command, TA; uplink: measurements (level quality), short messages service

Fast Associated Control Channel FACCH

“in band” signaling channel (sporadic): handover signaling channel mode modify: speech → data

Fig. 6 Dedicated control channel

Multiplexing of Logical Channels 1 physical channel (time slot) can carry one of the following logical channel combinations: Channel Combination

Capacity

a) TCH/F + FAACH/F + SACCH/F

1 full rate subscriber

b) TCH/H (0, 1) + FACCH/H (0, 1) 2 half rate subscriber (speech or data) + SACCH/H (0, 1) c) FCCH + SCH + BCCH + CCCH

uplink: downlink:

800 000 RACH slots per hour 140 000 CCCH blocks per hour

d) FCCH + SCH + BCCH + CCCH + SDCCH/4 (0..3) + SACCH/4 (0..3)

uplink: 400 000 RACH slots per hour downlink: 46 000 CCCH blocks per hour + dedicated signaling channels for 4 subscribers

e) SDCCH/8 (0..7) + SACCH/8 (0..7) ...

dedicated signaling channels for 8 subscribers

1 RACH slot:

1 channel request message of 1 subscriber.

1 CCCH block (4 slots):

1 paging message for 1..4 subscribers or 1 access grant message for 1..2 subscribers.


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Channel Organization in a Cell In SBS BR2.1 the following channel combinations are allowed: TCH/F + FACCH/F + SACCH/F

TCHFULL

FCCH + SCH+ BCCH+ CCCH (AGCH + PCH + RACH)

MAINBCCH

FCCH + SCH + BCCH + CCCH + 4 (SDCCH + SACCH)

MBCCHC

SDCCH/8 + SACCH/C8

SDCCH

Additional channel combinations in SBS BR3.0: TCH/H (0) + FACCH/H (0) + SACCH/H (0) + TCH/H (1)

TCHF_HLF

FCCH + SCH + BCCH + CCCH + 3 (SDCCH + SACCH) + CBCH

BCBCH

7 (SDCCH + SACCH) + CBCH

SCBCH

BCCH + CCCH

CCCH

New channel type in SBS BR6.0: TCH/H(0,1) + FACCH/H(0,1) + SACCH/H(0,1)

TCH/F + FACCH/F + SACCH/TF SDCCH/8 + SACCH/C8

or or

TCHSD

In a cell with a single RFC the allocation should be the following: Timeslot 0

→ FCCH+SCH + BCCH + CCCH + 4 (SDCCH + SACCH)

Timeslot 1...7

→ TCH/F + FACCH/F + SACCH/F

The timeslot 0 runs in the 51 frame organization:

1.

F S 0 1

BCCH 2 3 4 5

CCCH F S CCCH CCCH F S SDCCH0 SDCCH1 F S SDCCH2 SDCCH3 F S SACCH0 SACCH1 I 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

2.

F S 0 1

BCCH 2 3 4 5

CCCH F S CCCH CCCH F S SDCCH0 SDCCH1 F S SDCCH2 SDCCH3 F S SACCH2 SACCH3 I 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

‘downlink’ BCCH + CCCH + 4 SDCCH / 4, F = FCCH, S = SCH

1.

SDCCH3 0 1 2 3

R R SACCH2 4 5 6 7 8 9

SACCH3 R R R R R R R R R R R R R R R R R R R R R R R SDCCH0 SDCCH1 R R SDCCH2 10 11 1213 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

2.

SDCCH3 0 1 2 3

R R SACCH0 4 5 6 7 8 9

SACCH1 R R R R R R R R R R R R R R R R R R R R R R R SDCCH0 SDCCH1 R R SDCCH2 10 11 1213 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

‘uplink’ R = RACH + SDCCH / 4 Fig. 7 1 SACCHBCCH multiframe = 235,38 msec

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The timeslots 1...7 run in the 26 frame organization

1 Full Rate TCH

T T T T T T T T T T T T A T T T T T T T T T T T T 26 frames = 120 ms T t T t T t T t T t T t A t T t T t T t T t T t T a

T: t: A: a:

2 Half Rate TCH

Traffic Channel Burst for subscriber 1 Traffic Channel Burst for subscriber 2 Slow Associated Control Channel for subscriber 1 Slow Associated Control Channel for subscriber 2

Fig. 8 Time organization for one TCH

In a cell with 2 RFC there are more possibilities, depending on the used traffic model [SDCCH dimensioning], for example: RFC-0

see cell with 1 TRX

RFC-1

Timeslot 0...7


or


Timeslot 0

→ 8 (SDCCH + SACCH)

Timeslot 1...7


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2

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Control channel configuration


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Introduction: In a MOC, MTC, LU the MS has to request an SDCCH using the RACH. There is a time delay between the request and the SDCCH allocation due to the traffic load. If there is a free SDCCH, it is allocated using the AGCH. The SDCCH is used for the authentication, transmission of cipher parameters and call initialization. Next a traffic channel is requested and allocated, if available. After this, the SDCCH is released. The MS acknowledges the allocation on the FACCH. The TCH with its FACCH and SACCH is occupied until the end of the call. So the blocking probability is a function of availability of SDCCH availability of TCH waiting time in TCH queue, if queuing performed (BTS parameter) time for connection establishment.

2.1

Dedicated channels

If we evaluate a given traffic model, we find a certain traffic load per subscriber. Additionally we have to calculate the SDCCH load per subscriber. According to the traffic model given in appendix-C, there are four values to be considered: call attempts per subscriber per hour

1.1

time for MOC/MTC setup signaling

3 sec

time for Location Update

5 sec

location updates per subscriber per hour

2.2.

The SDCCH load per subscriber is calculated as follows: (1.1 * 3 sec + 2.2 * 5 sec) / 3600 sec = 0.004 Erl. Furthermore we have for the TCH: 25 mErl. At the following page an example for a channel configuration of a 2 carrier cells is given using the assumptions above.

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Example for Channel Configuration Assumptions:

25 mErl TCH Load per subscriber 4 mErl SDCCH load per subscriber no load problem on CCCH (refer to chapter 1.2.4)

Cell with 2 TRX: 16 channels Configuration A

Configuration B

1 comb. CCCH/SDCCH → 4 SDCCH

uncomb. CCCH

15 TCH

1 SDCCH/8 → 8 SDCCH 14 TCH

offered TCH load at 1 % blocking 8.11 Erl → Subscriber 8.11 / 0.025 = 324

offered TCH load at 1 % blocking 7.35 Erl → Subscriber: 7.35 / 0.025 = 294

offered SDCCH load at 1 % blocking 0.87 Erl → Subscriber 0.87 / 0.004 = 218

offered SDCCH load at 1 % blocking 3.13 Erl → Subscriber: 3.13 / 0.004 = 782

→ SDCCH limited: 218 subscriber

→ TCH limited: 294 subscriber

→ Configuration B is the better one for this scenario.


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Smooth Channel Modification BR 6.0 The control channel configuration up to BR5.5 is a static definition of the channel type (TCH or SDCCH) independent of the dynamic variations of the SDCCH traffic load in the network. The new feature in BR6.0 'Smooth Channel Modification' offers an automatic change of the channel type (e.g. between TCH and SDCCH/8) without operator interaction. If the SDCCH load is higher than a settable threshold, an additional SDCCH is automatically used instead of an idle TCH. In case of unexpected high SDCCH load (SMS traffic, LCS, specific areas as airports or PLMN borders, ...) a blocking of SDCCH is avoided. This results in saving of resources on Um interface, since a further SDCCH does not have to be configured permanently. Flexible channels used as TCH or SDCCH are created as channel type 'TCHSD'. To provide full flexible channel configuration, a radio frequency pool concept is introduced. The customer selects and configures the channels to be used as TCH or SDCCH for each carrier. This can be done when new versions or new cells are introduced to the network or new carriers are added to a cell. These channels are created using the new TCH_SD channel type. When the BSC selects a TCHSD channel for a specific service, the operational mode notifies the BTS on a call-by-call basis using a channel activation message. The system can then dynamically use the timeslot as either a TCH or a SDCCH without further service interruption. A radio frequency pool of resources in the BSC allows flexible allocation of radio frequency resources. Each TCH, SDCCH and TCHSD is assigned to a specific pool, TCH and SDCCH are assigned permanently to their related pools, and each TCHSD is assigned by the operators using the new specific object attribute CHPOOLTYP. This attribute can be changed using a SET command.

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TS 0

TS 1

TS 3

TS 2

TS 6

TS 5

TS 4

TS 7

assignment In case of SDCCH request SDCCH_POOL

TCH_POOL

TCH/SD_POOL

SDCCH_BACKUP _POOL

Traffic Channel / SDCCH Request Fig. 9 Pooling concept for smooth channel modification

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SDCCH Allocation Strategy In case of SDCCH request the BSC first tries to get one SDCCH sub-channel from the SDCCH_POOL. If the SDCCH_POOL and the SDCCH_BACKUP_POOL are empty or congested (i.e. all sub-channels are busy) the BSC moves eight subchannels with best quality from TCH_SD_POOL to SDCCH_BACKUP_POOL and uses one sub-channel to satisfy the request. If also in the TCH_SD_POOL there is no resource available and the service request is MOC and MTC, the direct assignment procedure is tried. If the requested services are Location Update Procedure LUP-SMS or SDCCH/SDCCH-H/O the service is rejected. Additionally a configurable SDCCH congestion threshold on cell basis is implemented in order to move a sub-channel from TCH_SD_POOL to SDCCH_BACKUP_POOL when the sub-channel occupation (i.e. the sum of SDCCH_POOL and SDCCH_BACKUP_POOL) is higher than this threshold for two seconds. The range of the SDCCH congestion threshold can be set by the operator. Due to peak load traffic (e.g. SMS) at different times, the system can then automatically share resources between signaling and speech without configuration changes thus reducing blocking probability in signaling phase. SDCCH Release Strategy When a SDCCH sub-channel is released and coming from the SDCCH_POOL the sub-channel is returned to that pool. If the sub-channel to be released is coming from the SDCCH_BACKUP_POOL and is not the last sub-channel busy in the TCH_SD, the sub-channel is returned in the SDCCH_BACKUP_POOL. If the sub-channel to be released is coming from the SDCCH_BACKUP_POOL and is the last sub-channel busy in the TCH_SD, the decision of the destination pool is based on a configurable attribute. This attribute is cell based and specifies the guard timer for return of the TCH_SD channel to the TCH_SD_POOL. This timer is implemented to avoid oscillation between TCH_SD_POOL and SDCCH_BACKUP_POOL.

TCH Allocation Strategy In case of TCH full request, the BSC uses the TCH with the best quality from the TCH_POOL. In case of TCH half request the BSC first tries to use unpaired channels. If TCH_POOL is empty or congested, the BSC tries to get one TCH_SD from the TCH_SD_POOL. If both pools are empty or congested, a directed retry procedure is attempted for new MOC or MTC. In case of handover, the target cell list is scanned in order to find a target cell not congested. TCH Release At TCH release the TCH is returned to the original pool.

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Fig. 10 The process trigger by an SDCCH request


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Parameters for Channel Configuration:

20

Specification Name

Object

DB Name

Range

Meaning

CH_TYPE

CHAN

CHTYPE

TCHFULL SDCCH MAINBCCH MBCCHC CCCH SCBCH BCBCH TCHF_HLF TCHSD

Type of Channel combination

CH_POOL_TYPE

CHAN

CHPOOLTYP

TCHPOOL Channel Pool Type SDCCHPOOL must be defined if TCHSDPOOL CH_TYPE=TCHSD

SDCCH_CONGESTION_ BTS THRESHOLD

SDCCHCONGTH 70 ... 100

[%] SDCCH Congestion Threshold

GUARD_TIMER_TCHSD BSC

TGUARDTCHSD SEC00 SEC10 SEC11 SEC12 SEC13 SEC14 SEC15

Guard Timer TCHSD


Siemens


2.2

Random access channel

RACH Capacity of the RACH The RACH is used by the MS to request a dedicated channel, the SDCCH. The channel request needs one RACH timeslot. The cause for the channel request can be a paging response in MTC, an emergency call, a MOC, LU or IMSI attach/detach. According to the traffic model from appendix-C there are about 4 RACH activities per subscriber per hour. Configuration of the RACH The RACH is configured only uplink, his frequency corresponds to the downlink BCCH frequency. The RACH may be combined with the uplink part of the SDCCH. In the combined case, the RACH is multiplexed onto 27 timeslots 0 out of 51 of a BCCHcombined. These 27 RACH are spread over the multiframe as follows: SSSSRRSSSSSSSSRRRRRRRRRRRRRRRRRRRRRRRSSSSSSSSRRSSSS with S = SDCCH/SACCH and R = RACH. The RACH can also be configured uncombined on all timeslots 0, 2, 4, 6. This gives the following capacities, the frame duration is 4.6 ms (period between two successive timeslots 0): combined:

27/51 of all timeslots 0

=>

400000 RACH slots per hour

uncombined:

timeslot 0

=>

800000 RACH slots per hour

uncombined:

timeslot 0,2

=>

1560000 RACH slots per hour (not in BR2.1)

uncombined:

timeslot 0,2,4

=>


uncombined:

timeslot 0,2,4,6

=>


In a cell with 5000 subscriber normally there are about 20 000 RACH activities per hour only!!


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RACH Control Parameter RACH busy threshold, defines a threshold for the signal level during the RACH bursts. The BTS measures the signal level on each RACH timeslot and determines whether a channel request is successfully received or not: If the received signal level is greater than or equal to the value of RACHBT then the RACH burst in question will be indicated as busy (one or more mobile stations have tried to access the network). The purpose of this parameter is to avoid unnecessary load on the BSS by normal noise signals being decoded as RACH bursts (followed by seizure of SDCCH) by mistake. However, to be on the safe side the BTS does not only evaluate the RACH level but additionally decodes the Synch sequence bits of the RACH burst. Note:

The value entered for this parameter is not only relevant for the CHANNEL REQUEST message on the RACH but also for the HANDOVER ACCESS message on the FACCH!

The MS receives the RACH control parameters from the base station on the BCCH: Maximum number of retransmission (max_retrans) MAXRETR = 1, 2, 4, 7.

If a channel request is not acknowledged by the base station, the MS repeats the request until the given value of MAXRETR. Number of slots to spread transmissions (tx_integer) NSLOTST = 0,..15

representing the real values according to the following table:

22

NSLOTST value

0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15

GSM value

3

4

5

6

7

8

9

10 11 12 14 16 20 25 32 50


Siemens


The NSLOTST value determines the time period between sending of two channel requests. This period is measured in RACH slots and is the sum of a deterministic part td and a random part tr: MS

tx_integer

td (RACH slots, combined)

td (RACH slots, uncombined)

Phase 1

-----

41 (0.35 sec)

55 (0.25 sec)

3, 8, 14, 50

41 (0.35 sec)

55 (0.25 sec)

4, 9, 16

52 (0.45 sec)

76 (0.35 sec)

5, 10, 20

58 (0.50 sec)

109 (0.50 sec)

6, 11, 25

86 (0.75 sec)

163(0.75 sec)

7, 12, 32

115 (1.00 sec)

217(1.00 sec)

Phase 2

Deterministic part td of retransmission period as a function of tx_integer

The random part tr is an integer between 1 and tx_integer where the probability of choosing a certain time slot i is given by: p ( tr = i ) = 1 / tx_integer for i = 1...tx_integer.

retransmission

td = 163 slots

first transmission with a collision

tr = tx_integer = 6

Fig. 11 Retransmission of CHANNEL_REQUEST


23

Siemens


Immediate Assignment Procedure: The procedure is specified in GSM 04.08, chapter 3.3.1.2:

IMMEDIATE ASSIGNMENT PROCEDURE Select RACH slot for first transmission number of retransmissions = 0 Send CHANNEL REQUEST msg.

no.of retransmissions = max_retrans

Y

set timer T3126 wait for grant

N

GRANT during Sup. time Y

N Select RACH slot for next transmission, wait for grant

CELL RESELECTION

immediate assignment

Y

Rejection

Y

N number of retransmissions + 1

N SDCCH Allocation

WAIT T3122

Fig. 12 Immediate assignment procedure

24



Siemens

Evaluation of Immediate Assignment Procedure for different parameter values Traffic Load/RACH Activities per Hour The relative traffic load is the average number of initiated immediate assignment procedures or RACH activities in a timeslot: traffic load = total number of immediate assignment procedures / total number of RACH slots. The absolute number of RACH activities per hour is obtained by multiplying this relative load with the number of RACH slots per hour. Blocking The blocking shows the percentage of not successful immediate assignment procedures initialized by the MS. blocking [%] = (number of unsucc. imm. ass. proc. / total number of imm. ass. Proc. ) * 100. Throughput The channel throughput is the average number of successful transmissions per time slot. throughput = number of successful transmissions/number of simulated time slots. throughput = ( 1 - blocking ) * traffic load. Wait Time The wait time is the time between the initiation of the immediate assignment procedure and the arrival of the immediate assignment message. For the waiting time it is useful to consider the 90% quantile of the wait time: for 90% of the immediate assignment procedures, the wait time is less than the time t90. The blocking and the 90% (95%) quantile for different values of the RACH control parameters is shown in the following tables for a combined RACH/SDCCH:


25

Siemens


tx_integer

max_retrans

blocking(%)

90% quantile(s) 95% quantile(s)

3

1

2.9

< 0.1

0.35

3

2

1.1

< 0.1

0.35

3

4

0.2

< 0.1

0.35

3

7

< 0.01

< 0.1

0.4

7

1

1.6

< 0.1

1.0

7

2

0.4

< 0.1

1.0

7

4

0.1

< 0.1

1.0

7

7

< 0.01

< 0.1

1.0

14

1

0.9

< 0.1

0.4

14

2

0.1

< 0.1

0.4

14

4

< 0.01

< 0.1

0.4

14

7

< 0.01

< 0.1

0.4

25

1

0.6

< 0.1

0.8

25

2

< 0.1

< 0.1

0.8

25

4

< 0.01

< 0.1

0.8

25

7

< 0.01

< 0.1

0.8

50

1

0.5

< 0.1

0.5

50

2

0.1

< 0.1

0.5

50

4

< 0.01

< 0.1

0.5

50

7

< 0.01

< 0.1

0.5

Values for 25000 RACH activities per hour

26


Siemens


tx_integer

max_retrans

blocking(%)

90% quantile(s) 95% quantile(s)

3

1

6.1

0.35

3

2

2.8

0.35

0.75

3

4

0.6

0.35

0.75

3

7

0.1

0.35

0.75

7

1

3.6

1.0

1.1

7

2

1.0

1.0

1.1

7

4

0.1

1.0

1.1

7

7

< 0.1

1.0

1.1

14

1

2.6

0.4

0.45

14

2

0.5

0.4

0.45

14

4

< 0.1

0.4

0.45

14

7

< 0.01

0.4

0.45

25

1

2.0

0.8

0.9

25

2

0.4

0.8

0.9

25

4

< 0.01

0.8

0.9

25

7

< 0.01

0.8

0.9

50

1

1.8

0.5

0.7

50

2

0.2

0.5

0.7

50

4

< 0.01

0.5

0.7

50

7

< 0.01

0.5

0.7

Values for 50000 RACH activities per hour.

The results of these studies show, that even the RACH minimal configuration (combined RACH/SDCCH is able to serve 50000 RACH activities per hour at a low blocking (< 0.5%) with an acceptable wait time. An uncombined RACH is able to serve twice the traffic load with the same grade of service. The minimum blocking for the considered traffic load is achieved by the following setting of parameters: max_retrans = 7, tx_integer = 50. Though a combined RACH can serve the expected traffic load, another RACH configuration may have to be chosen. The RACH is only the uplink part of the CCCH. The downlink parts (AGCH,PCH) may need a higher capacity. Therefore, the configuration of CCCH is determined by the capacity needed by the downlink channels, the RACH configuration is uncritical.


27

Siemens

2.3


Paging / access grant and notification-channel

PCH/AGCH The paging channel and the access grant channel share the same TDMA frame mapping (modulo 51) when combined onto a basic physical channel. The channels are shared on a block by block basis. The information within each block allows the MS to determine if it is a paging or an access grant message. Every paging channel can be used by the system as access grant channel but it is not allowed to the system to use access grant channels as paging channels. However, to ensure a mobile a satisfactory access to the system, there is a control parameter to define a fixed number of access grant blocks in the 51 multiframe. The number of blocks reserved for AGCH is broadcasted on the BCH. The number of available paging blocks is reduced by this number. Paging channels may be used as access grant channels but not vice versa. Therefore it is useful to set the parameter BS_AG_BLKS_RES to the smallest value and let the system organize the use of channels. In case of MOC more AGCH are needed, in case of MTC more PCH are needed. In average the number of MOC is higher than the number of MTC. If the BS_AG_BLKS_RES value is set too high with the result of a PCH shortage, a overload indication for the PCH may arise in high traffic time. In GSM traffic model the paging per subscriber per hour is 0.93. The second parameter to be set is called BS_PA_MFRMS (value = 2..9, number of multiframes between paging). It indicates the number of TDMA multiframes between transmission of paging messages to the same paging subgroup. The MS gets the information on BCH, to which paging groups it should listen to. By this way the MS can save battery because it only listens to its own paging group. If the value is too high so that the time between two blocks of the same paging sub-channel is high, the time for setting up an MTC is high. In a medium cell the common channel pattern on timeslot 0 on one of the TRX can use the following combination downlink (in uplink all channels are used as RACH): FSBBBBPPPPFSPPPPPPPPFSPPPPPPPPFSPPPPPPPPFSPPPPPPPP F = FCCH S = SCH B = BCCH P = PACH/AGCH. An example for the load and the servable number of subscribers is given at the following pages.

28



Siemens

NCH In all cells where the ASCI service is enabled, a new logical channel belonging to CCCH is defined, this new downlink channel is the Notification Channel (NCH). An MS which is VBS/VGCS* subscriber, besides the paging blocks, monitors also the Notification Channel. This logical channel is mapped onto contiguous blocks reserved for access grants, the position and the number of blocks are defined by the two parameters NCH_FIRST_BLOCK and NCH_BLOCK_NUMBER. Service subscribers are notified of the VBS/VGCS call in each cell via notification messages that are broadcasted on the Notification Channel; these messages don’t use individually TMSI/IMSI but the group identity and service area identity. The process of broadcasting messages on NCH is carried out throughout the call in order to provide late entry facility. The repetition time is defined by the parameter TIMER_NCH. * Voice Broadcast Service / Voice Group Call Service ASCI Uplink Reply is only relevant if ASCI is enabled. The parameter ASCIULR is used to enable or disable the uplink reply procedure for VGCS calls only (VGCSENABLE), VBS calls only (VBSENABLE) or both at the same time (VBS_VGCSENABLE). When an ASCI group call (VBS or VGCS) is set up in a cell and simultaneously an ASCI common TCH was activated, the BTS broadcasts the group call reference and the Channel Description data of the ASCI common TCH via the NCH in the cell. In this situation, the BSC may initiate the release of the activated ASCI common TCH, if no listening ASCI MSs are available in the cell. To check whether or not ASCI MSs are present in the cell, the BTS sends the UPLINK FREE message via the FACCH associated to the ASCI common TCH and waits for an UPLINK ACCESS message. This UPLINK ACCESS message is sent on the ASCI common TCH and is the response from the ASCI MSs, if they have previously received the UPLINK FREE message with the IE ‘Uplink Access Request’ included. For the supervision of this procedure, the BTS uses 2 timers: TWUPA (timer to wait for uplink access, hardcoded in the BTS) and the administrable timer TUPLREP which are both started when the UPLINK FREE message is sent. The BTS periodically repeats the sending of the abovementioned UPLINK FREE message (containing IE ‘Uplink Access Request’) via the FACCH of the ASCI common TCH. The time period between two consecutive transmissions of the UPLINK FREE message is determined by the timer TUPLREP. When no UPLINK ACCESS message was received from any ASCI MS before timer TWUPA expires, the BTS assumes that no listening ASCI MS is present in the cell and initiates the deallocation of the ASCI common TCH in this cell by sending the VBS/VGCS CHANNEL RELEASE INDICATION towards the BSC, which in turn releases the channel by sending CHANNEL RELEASE, DEACTIVATE SACCH, RF CHANNEL RELEASE etc..


29

Siemens

2.4

30


CCCH load

paging messages per hour:

SUBSCR * LA_size * MTC_ph * REPET/ subscr_per_pag_message

random messages per hour:

SUBSCR * (MTC_PR_ph + MOC_ph + LU_ph + IMSI_ph + SMS_ph)

access grant messages per hour:

SUBSCR * (MTC_PR_ph + MOC_ph + LU_ph + IMSI_ph + SMS_ph) / subscr_per_agch_message

SUBSCR

number of subscribers within the cell

LA_size

number of cells on the location area

MTC_ph

mobile terminating calls per subscriber per hour (with and without paging response)

REPET

mean number of repetitions of a paging message (no paging response to first paging)

MTC_PR_ph

mobile terminating calls per subscriber per hour with paging response to first paging)

MOC_ph

mobile originating calls per subscriber per hour

LU_ph

location updates per subscriber per hour

IMSI_ph

IMSI attach/detach per subscriber per hour

SMS_ph

short message service requests per subscriber per hour


Siemens


CCCH Load (Example) paging messages per hour:

SUBSCR * LA_size * MTC_ph * REPET/ subscr_per_pag_message

access grant messages per hour:

SUBSCR * (MTC_PR_ph + MOC_ph + LU_ph + IMSI_ph + SMS_ph) / subscr_per_agch_message

random messages per hour:

SUBSCR * (MTC_PR_ph + MOC_ph + LU_ph + IMSI_ph + SMS_ph)

SUBSCR:

?

LA_size:

20

MTC_ph:

0.46

REPET:

1.33

MTC_PR_ph

0.30

MOC_ph

0.64

LU_ph

2.2

IMSI_ph

1.0

SMS_ph

-

subscr_per_pag_message = 2 subscr_per_agch_message = 1.0 paging messages per hour = SUBSCR * 20 * 0.46 * 1.33/2

∼ SUBSCR * 6/h

access grant messages per hour

∼ SUBSCR * 4/h

→ paging + access grant messages per hour

∼ SUBSCR * 10/h

→ ∼ 4600 subscriber (combined CCCH) → ∼ 14000 subscriber (uncombined CCCH) random access messages per hour

∼ SUBSCR * 4 / h (at 10 % load)

→ ∼ 10000 subscriber (combined CCCH) → ∼ 20000 subscriber (uncombined CCCH)


31

Siemens


Parameters for Common Control Channel Configuration Specification Name

Object

DB Name

Range

Meaning

RACH_BUSY_THRES

BTS

RACHBT

0...127

RACH busy threshold defined in steps of -1 dBm

MAX_RETRANS

BTS

MAXRETR

ONE TWO FOUR SEVEN

maximum number of allowed retransmissions of a channel request on the RACH

TX_INTEGER

BTS

NSLOTST

0...15

number of RACH slots to spread re-transmission of channel request; also fixing the deterministic part of wait time 0 ... 15 = 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 20, 25, 32, 50

BS_AG_BLKS_RES

BTS

NBLKACGR 0...7 0...2 for comb. CCCH

number of common control blocks per multiframe used for access grant exclusively

BS_PA_MFRMS

BTS

NFRAMEPG 2...9

number of multiframes between paging blocks belonging to the same paging sub-channel

ASCI_SERVICE

BTS

ASCISER

TRUE, FALSE enables or disables ASCI service on a cell basis

ASCI_UPLINK_REPLY

BTS

ASCIULR

ULRDISABLE, the ASCI Uplink Reply parameter enables or disables VBSENABLE the uplink reply procedures for VGCSENABLE both VGCS and VBS VBC_VGCSEN ABLE

NCH_FIRST_BLOCK

BTS

NOCHFBLK 1...7

indicates the first block of downlink CCCH to be used for NCH

NCH_BLOCK_NUMBER

BTS

NOCHBLKN 1...4

number of downlink CCCH blocks to be used for NCH

TIMER_NCH

BTS

TNOCH

1...254

repetition period for notification messages defined in steps of one multi-frame period – 235 ms

TUPLREP

5..60 s

This timer determines the period between transmissions of the Uplink Free message in the uplink reply procedure.

TIMER_UPLINK_REPLY BTS

32



3

Siemens

Extended channel mode


33

Siemens


In a normal GSM standard cell the maximum MS-BTS distance is 35 km; this is the limit given by the maximum TA (timing advance 0...63 bit) which is possible on one radio timeslot. Distance calculation: Dist = TA * bit-period * light-speed / 2 bit-period = 48/13 (3.69) µs light-speed = 300000 km/s. The feature ‘Extended Cells’ supports a larger distance between MS and BTS by using two subsequent radio timeslots to compensate the longer delay of the bursts. The first timeslot of a double timeslot has always an even number (0,2,4,6), the following corresponding channel must not be created. For a double timeslot the maximum propagation delay can be 219 bit ( 120 km), but note that the maximum distance which can be configured by O&M is 100 km. The BTS splits the propagation delay into two values: timing advance (TA), covering the first 63 bit delay timing offset (TO), used for extended cells as an offset to TA for delays greater 63

bit (the propagation delay is the algebraic sum of TA and TO). When activating the SDCCH and later the TCH for that corresponding MS, the evaluated initial TA value forms part of the layer 1 header downlink, the initial TO is used BTS-internally. If the average of the deviation exceeds 1 bit period (48/13 µs) in comparison to the TA confirmed by the MS (contained in every uplink SACCH header information), the previously ordered TA is incremented/decremented by one and sent as new ordered TA in the layer 1 header downlink to MS. As previously mentioned TA cannot exceed 63 bit. TO is used internally for processing further delay in case of extended cells. Note that TO may only be greater then 0 when TA has the maximum value 63. In extended cells all control and signaling channels must be defined in extended (double) mode. Specification

Object

DB Name

Range

Meaning

BTS

CELLTYPE STDCELL EXTCELL

maximum range 35 km a cell covering other cells maximum range 100 km

EXTMODE

defines if a channel is used in extended mode or not

Name CELL_TYPE

EXTENDED_MODE CHAN

34

TRUE FALSE



4

Siemens

Adaptive Multirate AMR


35

Siemens

4.1


General

The Adaptive Multi Rate Speech Codec (AMR) is made up of a set of speech codec modes at different bit rates. Each codec mode provides a different level of error protection on the air interface, obtained by varying the balance between source (i.e. speech) coding bit rate and radio channel coding bit rate. All modes may be mapped to full rate channels, only the lower bit rate modes may be mapped to half rate channels. The currently available speech codecs (FR, EFR, HR) show several constraints. They operate at constant source and channel coding bit rate and at constant error protection. The quality of FR and HR is not high enough to cope with wireline speech, EFR is not robust enough against bad radio conditions. The flexibility of AMR provides important benefits: Improved speech quality in both half-rate and full-rate modes by means of codec mode adaptation, i.e. varying the balance between speech and channel coding for the same gross bit-rate. Ability to trade speech quality and capacity smoothly and flexibly by a combination of channel and code mode adaptation. Improved robustness to channel errors under bad radio signal conditions in fullrate mode. This increased robustness to errors and hence to interference may be used to increase capacity by operating a tighter frequency re-use pattern. This allows the optimization of networks for high quality or high capacity. Use of certain modes for special applications, e.g. wireline quality half-rate for indoor with low channel errors In full-rate mode only, the robustness to high error levels is substantially increased such that the quality level of EFR at a C/I of 10 dB is extended down to a C/I of 4 dB. This gives additional coverage in noise limited scenarios.

36


Siemens


Traffic Channel Full: Gross rate 22.8 kbit/s

Flexible

Channel Coding

Speech Coding

balance

Fig. 13 AMR principle

22,8 kbit/s channel coding FR channel coding HR speech coding

11,4 kbit/s

0 FR 1

FR 2

FR 3 / HR 1

FR 4 / HR 2

FR 5 / HR 3

FR 6 / HR 4

FR 7 / HR 5

FR 8 / HR 6

Fig. 14 AMR codecs


37

Siemens


MOS 5.0

4.0

3.0 EFR 12.2 10.2 7.95 7.4 6.7 5.9 5.15 4.75

2.0

1.0

No Errors

C/I=16 dB

Conditions C/I=13 dB

C/I=10 dB

C/I= 7 dB

C/I= 4 dB

4.01

3.65

3.05

1.53

EFR

4.01

12.2

4.01

4.13

3.93

3.44

1.46

10.2

4.06

3.96

4.05

3.80

2.04

7.95

3.91

4.01

4.08

3.96

3.26

7.4

3.83

3.94

6.7

3.77

5.9

4.06

C/I= 1 dB

1.43

3.98

3.84

3.11

1.39

3.80

3.86

3.29

1.87

3.72

3.69

3.59

2.20

5.15

3.50

3.58

3.44

2.43

4.75

3.50

3.52

3.43

2.66

Fig. 15 Family of curves (clean speech in full rate) acc. to ETSI study

DMOS 5.0

4.0

3.0

2.0

Sel. Requir. AMR-FR EFR FR G.729 Conditions

1.0 No Errors

C/I=16 dB

C/I=13 dB

C/I=10 dB

C/I= 7 dB

C/I= 4 dB

C/I= 1 dB

Fig. 16 AMR performance curves (full rate with street noise) acc. to ETSI study

38


Siemens


5.0

MOS

4.0

3.0

EFR 7.95 7.4 6.7 5.9 5.15 4.75 FR HR

2.0

Conditions

1.0 No Errors

C/I=19 dB

C/I=16 dB

C/I=13 dB

C/I=10 dB

C/I= 7 dB

C/I= 4 dB

4.21

3.74

3.34

1.58

3.37

2.53

1.60

EFR

4.21

7.95

4.11

4.04

7.4

3.93

3.93

3.95

3.52

2.74

1.78

6.7

3.94

3.90

3.53

3.10

2.22

1.21

5.9

3.68

3.82

3.72

3.19

2.57

1.33

5.15

3.70

3.60

3.60

3.38

2.85

1.84

4.75

3.59

3.46

3.42

3.30

3.10

2.00

FR

3.50

HR

3.35

3.96

3.50

3.14

2.74

1.50

3.24

2.80

1.92

Fig. 17 Family of curves (clean speech in half rate) acc. to ETSI study

Capacity Improvement as a function of the AMR Handset Penetration (Parameter: Half Rate Operating Threshold) 120.0%

HR Only

Capacity Improvement

100.0%

15 dB

80.0% 60.0%

20 dB

40.0%

25 dB

20.0% 0.0% 50%

AMR Penetration 60%

70%

80%

90%

100%

Fig. 18 AMR capacity gain acc. to ETSI study


39

Siemens


Most speech codecs including the existing GSM codecs (FR, HR and EFR) operate at a fixed coding rate. Channel protection against errors is added also at a fixed rate. The coding rates are chosen as a compromise between best clear channel performance and robustness to channel errors. The AMR system exploits this performance compromise by adapting the speech and channel coding rates according to the quality of the radio channel resulting in better quality and increased robustness against errors. The new radio resource algorithm, enhanced to support AMR operation, allocates a half-rate or full-rate channel according to channel quality and the traffic load on the cell in order to obtain best balance between quality and capacity. The channel measurement reports and any other information for the codec mode adaptation are transmitted in-band in the traffic channel. In addition the channel mode of the codec can be switched in order to increase channel capacity while maintaining the speech quality to operator specified limits. These variations are carried out by means of AMR modifications and handovers. The allocation of AMR FR or AMR HR codecs can also be related to the current traffic load in the network. The operator sets the threshold for the traffic dependent allocation of HR channels (c.f. "Cell Load Dependent Activation of Half Rate"). Principles Channel state information is derived in MS and BTS. BTS/BSC decide which AMR codec mode is used based on channel state

information. Quality/robustness of AMR modes depend on division of the gross bit-rate into

speech and channel coding. In-band signaling is provided over the air interface to switch rapidly between the

different modes (within full-rate or half-rate modes) in order to adapt to the channel conditions. Switching between codec modes is seamless. AMR can also be operated in "HR only" mode. The speech quality perceived by

the subscriber is similar to present FR quality. AMR "HR only" mode is even better in respect to clean speech and channel errors. In case of background noise and channel errors the performance is lower. AMR Codec Modes The AMR codec operates at different codec mode bit-rates (4.75 kbit/s to 12.2 kbit/s) including GSM EFR. Each codec mode performs differently under changing channel quality (C/I). The following table provides an overview on the codecs used.

40


Siemens


AMR Codec Mode Bitrate (kbit/s)

Designation

Support by (Full Rate / Half Rate BTSplus (BR6.0) Mode)

Support by BTSone (BR6.0)

12.2

FR 1 ("Enhanced FR") Yes

Yes

10.2

FR 2

Yes

Yes

7.95

FR 3 / HR 1

FR 3 only

FR 3 only

7.40

FR 4 / HR 2

Yes

FR 4 only

6.70

FR 5 / HR 3

Yes

FR 5 only

5.90

FR 6 / HR 4

Yes

Yes

5.15

FR 7 / HR 5

Yes

Yes

4.75

FR 8 / HR 6

Yes

Yes

AMR FR channels are mapped on 16 kbit/s TRAU frames on the Abis interface while AMR HR channels are mapped on 8 kbit/s TRAU frames. (GSM standards, however, map HR1 codec, 7.95 kbit/s source bit rate, to 16 kbit/s TRAU frames.) Radio Interface The AMR codec and its control operate without any changes to the air-interface channel multiplexing. Conventional TCH/F and TCH/H channels are used for full-rate and half-rate channel modes of the AMR codec. Channel Mode Handover Channel mode handovers (AMR HR AMR FR) are executed in the same way as existing intra cell handovers. A new algorithm for determination when and whether to perform an AMR handover is applied. Code Mode Signaling Signaling and measurement reporting for codec mode changes (e.g. AMR FRi AMR FRj) are transmitted in-band on the radio interface. VAD/DTX Signaling and measurement reporting for codec mode changes are transmitted inband on the radio interface.


41

Siemens

4.2


SBS implementation

Both BTSplus and BTSone support all FR codecs. However, not all AMR HR codecs are supported: Due to static alignment of HR channels on 8 kbit/s TRAU frames, AMR HR codec HR1 (for BTSplus) and AMR HR codecs HR1, HR2 and HR3 (for BTS1) are not supported. The TRAU equipped with TRAC V7 modules supports all codecs (FR/HR/EFR speech, data, AMR full rate, AMR half rate, …)

4.2.1

TRAU pooling

For the TRAU pools can be defined for the timeslots of a PCMA: Parameter

Object

Range

Description

DEFPOOLTYP

PCMA

0 .. 143

Default pool type

POOLTYP

TSLA

POOL_NOTDEF, Pool type for TSLA (different from POOL_1,…, DEFPOOLTYP) POOL_48

4.2.2

AMR codec adaptation

AMR codec adaptation is done within a restricted set of codec modes (using half-rate or full-rate). This set is called Active Code Set ACS and can be composed of up to four codec modes. The changes between codecs is done according to an adaptation algorithm without notification or intervention by the BSC. This algorithm is based on channel quality measurements performed in the BTS and MS (Quality Indicator is defined in terms of carrier to interference ratio C/I).

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Siemens


4.3

Database parameters

Parameter

Object

Range

Description

AMRFRC1,

BTS,

1:RATE_01 (4.75 kbit/s),

AMR Full Rate Codec no. 1,

AMRFRC2,

FHSY

2:RATE_02 (5.15 kbit/s),


AMRFRC3,

3:RATE_03 (5.90 kbit/s),


AMRFRC4

4:RATE_04 (6.70 kbit/s),


5:RATE_05 (7.40 kbit/s), 6:RATE_06 (7.95 kbit/s), 7:RATE_07 (10.2 kbit/s), 8:RATE_08 (12.2 kbit/s) AMRFRTH12

Threshold: 0 (0.0 dB)... 63 "Threshold-Hysteresis" related (31.5 dB), step is 0.5 dB; to the active codecs specified in the AMRFRC1 and Hysteresis: 0 (0.0 dB)... AMRFRC2 15 (7.5 dB) (Threshold default value: 30 (15.0 dB) for BTSP family and for BTSE family; hysteresis default value: 0 (0.0 dB)

AMRFRTH23

Threshold: 0 ... 63; Hysteresis: 0 ... 15

AMRFRTH34

Hysteresis: 0 ... 15

"Threshold-Hysteresis" related to the active codecs specified in the AMRFRC3 and AMRFRC4

AMRHRC1

1:RATE_01 (4.75 kbit/s),

AMR Half Rate Codec no. 1,

AMRHRC2,

2:RATE_02 (5.15 kbit/s),


AMRHRC3,

3:RATE_03 (5.90 kbit/s),


AMRHRC4

4:RATE_04 (6.70 kbit/s),


5:RATE_05 (7.40 kbit/s)

AMR Half Rate Codec no. 5


Threshold: 0 ... 63;

"Threshold-Hysteresis" related to the active codecs specified in the AMRFRC2 and AMRFRC3

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Siemens


AMRHRTH12

Threshold 0..63 (0.5 dB step size); hysteresis 0..15 (0.5 dB step size)

AMRHRTH23


AMRHRTH34

BTS


AMRFRIC

BTS, FHSY

0:START_MODE_FR, 1:CODE_MODE_01,

"Threshold-Hysteresis" related to the active codecs specified in the AMRHRC1 and AMRHRC2 (threshold default value: 24 (12.0 dB); hysteresis default value: 0 (0.0 dB) "Threshold-Hysteresis" related to the active codecs specified in the AMRHRC2 and AMRHRC3 "Threshold-Hysteresis" related to the active codecs specified in the AMRHRC2 and AMRHRC3 Initial FR codec mode (i.e. start mode among the ACS)

2:CODE_MODE_02, 3:CODE_MODE_03, 4:CODE_MODE_04 AMRHRIC

BTS, FHSY

START_MODE_HR,

Initial HR codec mode

CODE_MODE_01, CODE_MODE_02, CODE_MODE_03, CODE_MODE_04

AMRLKAT

BTS

Range: 0..200 0 = -10dB, 100 = 0dB, 200 = +10dB unit: 0.1dB Default: 100

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The AMR link adaptation tuning parameter is used by the AMR Uplink Codec Mode Adaptation in the BTS. It tunes the transition between CODEC modes determined by internal thresholds. A value higher than the default shifts the transition towards higher carrier-to-interferer or signalto-noise ratios. A value lower than the default has the opposite effect. Adaptation of AMR HR and AMR FR is affected simultaneously.


Siemens


The thresholds and hysteresis values (for HR and FR codec modes, see above) must fulfill the following conditions: Thr_1 ≤ Thr_2 ≤ Thr_3 Thr_1 + Hys_1 ≤ Thr_2 + Hys_2 ≤ Thr_3 + Hys_3 Parameter

Description

Range

Thr_1 / 2 / 3

Thr_i gives the "downward" threshold for switching to mode i (from mode i+1)

0 (0.0 dB)... 63 (31.5 dB)

Hys_1 / 2 / 3

Hys_i determines the "upward" threshold for switching to mode i+1 (from i, the switch occurs at Thr_i+Hyst_i)

0 (0.0 dB)... 15 (7.5 dB)

Codec_Mode_4

Carrier-tointerference ratio C/I

Thr_3 + Hyst_3 = Thr_Mx_Up (3) Thr_3

= Thr_Mx_Down (4)

Codec_Mode_3 Thr_2 + Hyst_2 = Thr_Mx_Up (2) Thr_2

= Thr_Mx_Down (3)

Codec_Mode_2 Thr_1 + Hyst_1 = Thr_Mx_Up (1) Thr_1

= Thr_Mx_Down (2)

Codec_Mode_1 Thr Hyst

Threshold Hysteresis

Fig. 19 Threshold and hysteresis determine the switching "up" and "down" between codec modes in downlink


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Siemens


The AMR link adaptation works based on the quality of the connection. Since a finer scale is needed than the one RXQUAL offers, C/I is used. The following table is used for the mapping between C/I values and RXQUAL values:

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RXQUAL

C/I

RXQUAL

C/I

6.88 ... 7

1

3.13 ... 3.37

14

6.63 ... 6.87

2

2.88 ... 3.12

14

6.38 ... 6.62

4

2.63 ... 2.87

15

6.13 ... 6.37

5

2.38 ... 2.62

16

5.88 ... 6.12

6

2.13 ... 2.37

16

5.63 ... 5.87

7

1.88 ... 2.12

17

5.38 ... 5.62

8

1.63 ... 1.87

17

5.13 ... 5.37

8

1.38 ... 1.62

18

4.88 ... 5.12

9

1.13 ... 1.37

18

4.63 ... 4.87

10

0.88 ... 1.12

19

4.38 ... 4.62

11

0.63 ... 0.87

19

4.13 ... 4.37

11

0.38 ... 0.62

19

3.88 ... 4.12

12

0.13 ... 0.37

20

3.63 ... 3.87

13

0 ... 0.12

20

3.38 ... 3.62

13



Siemens

t

5

Exercises


47

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48



Siemens


Exercise 1 Title:

Creation of a RFC in the SBS

Task The object in the SBS configuration language specifying a RFC is called TRX (transceiver). Take the UMN: BSC-CML (User Manual: BSC command manual) and check the required input parameters.


49

Siemens

50



Siemens


Exercise 2 Title:

Dimensioning control channels of an extended cell

Task Given an extended cell with 2 carriers. In this cell, 3 channels with extended_mode = true are required. Assume Erlang B and the following values: Typical SDCCH load per subscriber and hour: 8 mErl. Typical TCH load per subscriber and hour: 25 mErl. Blocking probability 1%. Determine the control channel configuration which offers highest capacity.


51

Siemens

52




6

Siemens

Solutions


53

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54



Siemens


Solution 1 Title:

Creation of a RFC in the SBS

Task CREATE TRX:NAME=BTSM:0/BTS:0/TRX:1, TRXFREQ=CALLF05, PWRRED=0, RADIOMR=OFF, RADIOMG=254, MOEC=TRUE, TRXAREA=NONE, LPDLMN=0, GSUP=FALSE;

The parameters are specified as following: BTSM:

BTS site manager number

0 ... 199

BTS:

Number of sector

0 ... 23

TRX:

TRX number to the related cell

0 ... 23

TRXFREQ:

TRX-frequency - ARFCN

BCCHFREQ, CALLF01, CALLF02, : CALLF63

PWRRED:

Power reduction [0...12 dB in steps of 2 dB] for decrease max. transmit power

0 ... 6

RADIOMR:

Radio measurement reports from TRXto the BSC

ON / OFF

RADIOMG:

Granularity of radio measurement reports in steps of 1 SACCH multiframe

0 ... 254

MOEC

Member of emergency configuration

TRUE / FALSE

TRXAREA:

Configuration of concentric cells

NONE / COMPLETE / INNER

LPDLM

Number of LAPD link

0 ... 7

GSUP

TRX supports GPRS

TRUE / FALSE


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Siemens

56



Siemens


Solution 2 Title:

Dimensioning control channels of an extended cell

Task

Example configuration A: 1 BCCH combined (containing 4 SDCCH subslots), extmode must be true! 3 TCH_full, extmode = true 2 carriers NTCH = 11, ATCH = 5.16 Erl, B = 0.01 ⇒ 206 subscribers NSDCCH = 4, ASDCCH = 0.87 Erl, B = 0.01 ⇒ 108 subscribers ⇒ Configuration A is SDCCH limited to 108 subscribers. Example configuration B: 1 BCCH uncombined, extmode must be true! 1 SDCCH timeslot (containing 8 SDCCH subslots), extmode must be true! 3 TCH_full, extmode = true 2 carriers NTCH = 9, ATCH = 3.78 Erl, B = 0.01 ⇒ 151 subscribers NSDCCH = 8, ASDCCH = 3.13 Erl, B = 0.01 ⇒ 391 subscribers ⇒ Configuration B is TCH limited to 151 subscribers.

⇒ Configuration B offers higher capacity.


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58



channel_configuration.pdf

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