01 RA21611EN10GLS0 Channel Configuration

Channel configuration and allocation strategy

Contents

1 Channel configuration overview 3

1.1 Control channel configuration 14

1.2 Dedicated channel 14

1.3 Smooth Channel Modification 16

1.4 Random access channel 21

1.5 Paging, Access Grant and Notification channels 28

1.6 CCCH load 32

1.7 Additional ASCI service related parameters 36

2 Extended channel mode 49

3 Adaptive Multirate AMR 53

3.1 Basic 54

4 Channel allocation strategy 67

4.1 Basic 68

4.2 Multi Service Layer Support 70

5 Exercises 79

6 Solutions 91

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© 2008 Nokia Siemens Networks


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© 2008 Nokia Siemens Networks2


1 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 DCS1800

876 - 880 MHz GSM-R

1850 - 1910 MHz PCS1900

Downlink DL BTS-MS

869 - 894 MHz GSM850

935 - 960 MHz P-GSM900 (primary band)

925 - 960 MHz E-GSM900 (extended band)

1805 - 1880 MHz DCS1800

921 - 925 MHz GSM-R

1930 - 1990 MHz 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 900 Fu(n) = 890 + 0.2 n 0< n < 124 Fd(n) = Fu(n) + 45

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Fu(n) = 890 + 0.2 x (n -1024) 975 < n < 1023

DCS1800 Fu(n) = 1710.2 + 0.2 x (n -512) 512 < n < 885 Fd(n) = Fu(n) + 95

GSM-R Fu(n) = 876.2 + 0.2 x (n -955) 955 < n < 974 Fd(n) = Fu(n) + 45

PCS1900 Fu(n) = 1850.2 + 0.2 x (n -512) 512 < n < 810 Fd(n) = Fu(n) + 80

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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.

Fig. 2 Radio frequency channels RFC on Um

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Fig. 3 Logical channel types

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Fig. 4 Broadcast control channel

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Fig. 5 Common control channel

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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) + SACCH/H (0, 1)

2 half rate subscriber (speech or data)

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c) FCCH + SCH + BCCH + CCCH uplink: 800 000 RACH slots per hdownlink: 140 000 CCCH blocks per h

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

uplink: 400 000 RACH slots per hdownlink: 46 000 CCCH blocks per h+ dedicated signaling channels for4 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 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

TCH/H (0) + FACCH/H (0) + SACCH/H (0) + TCH/H (1) ) + FACCH/H (1) + SACCH/H (1)

TCHF_HLF

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

BCBCH

7 (SDCCH + SACCH) + CBCH SCBCH

BCCH + CCCH CCCH

TCH/H(0,1) + FACCH/H(0,1) + SACCH/H(0,1) orTCH/F + FACCH/F + SACCH/TF orSDCCH/8 + SACCH/C8

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 as shown in figures 7 and 8.

The timeslots 1 to 7 run in the 26 frame organization as shown in figure 9.

:

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 TCH/F + FACCH/F + SACCH/F

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or

Timeslot 0 8 (SDCCH + SACCH)

Timeslot 1...7 TCH/F + FACCH/F + SACCH/F

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Fig. 7 Multiframe for channel combination MAINBCCH

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B BCCHC CCCHD SDCCHF frequency correction burstR RACHS synchronized burstI idle

Fig. 8 Multiframe for channel combination MBCCHC (2xMBCCH makes SACCHBCCH multiframe =2x 235.38 msec)

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T: Traffic Channel (TCH) Burst for subscriber 1t: Traffic Channel (TCH) Burst for subscriber 2A: Slow Associated Control Channel (SACCH) for subscriber 1a: Slow Associated Control Channel (SACCH) for subscriber 2

Fig. 9 Time organization for one TCH Multiframe

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1.1 Control channel configuration

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.

1.2 Dedicated channel

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.

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At the following page an example for a channel configuration of the 2carriers cell is given using the above assumptions.

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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

Cell with 2 TRX: 16 channels

Configuration A Configuration B

1 comb. CCCH/SDCCH 4 SDCCH

15 TCH

uncomb. CCCH

1 SDCCH/8 8 SDCCH

14 TCH

offered TCH load at 1 % blocking8.11 Erl Subscriber 8.11 / 0.025 = 324

offered TCH load at 1 % blocking7.35 Erl Subscriber: 7.35 / 0.025 = 294

offered SDCCH load at 1 % blocking0.87 Erl Subscriber 0.87 / 0.004 = 218

offered SDCCH load at 1 % blocking3.13 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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1.3 Smooth Channel Modification

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.

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, etc.) 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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Fig. 10 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 sub-channels 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

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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. 11 The process triggered by an SDCCH request

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Parameters for Channel Configuration:

Specification Name

DB Name Object Range

(default)

Meaning

CH_TYPE

GSM 04.08

GSM 05.01

GSM 05.02

CHTYPE CHAN TCHFULLSDCCHMAINBCCHMBCCHCCCCHSCBCHBCBCHTCHF_HLFTCHSD

Type of Channel combination

CH_POOL_ TYPE

CHPOOLTYP CHAN TCHPOOLSDCCHPOOLTCHSDPOOLNULL

(NULL)

Channel Pool Typemust be defined if CH_TYPE=TCHSD

SDCCH_ CONGESTION_ THRESHOLD

SDCCHCONGTH BTS 70 ... 100[ % ]

(70)

SDCCH Congestion Threshold

GUARD_ TIMER_ TCHSD

TGUARDTCHSD BSC SEC00

SEC10 (default)

SEC11SEC12SEC13SEC14SEC15

Guard Timer TCHSD

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1.4 Random access channel

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 2340000 RACH slots per hour(not in BR2.1)

uncombined: timeslot 0,2,4,6 3120000 RACH slots per hour(not in BR2.1)

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

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1.4.1 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.

Until BR9, 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. But now, since BR10, the value is spelt into two which are RACHBT for the channel request and FACHBT for HO access.

With this feature it is now possible to set up optimal threshold values for discrimination of access bursts on RACH and on TCHs as well (with only one threshold for both cases before, it was necessary to find a compromise for the threshold value). Thus phantom RACH access bursts can be avoided efficiently while TCH access bursts (e.g. to access the target cell / BTS in case of inter-cell handover) are accepted even in case of low receive power level. As a consequence the RACH load in the BTS and the rejection of inter-cell handovers (or even call drops) can be kept low simultaneously.

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:

NSLOTST value 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

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GSM value 3 4 5 6 7 8 9 10 11 12 14 16 20 25 32 50

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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 2 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)

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.

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Fig. 12 Retransmission of CHANNEL_REQUEST

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Immediate Assignment Procedure

The procedure is specified in GSM 04.08, chapter 3.3.1.2:

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Fig. 13 Immediate assignment procedure

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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:

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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

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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

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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.

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1.5 Paging, Access Grant and Notification channels

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.

1.5.1 PCH/AGCH Control Parameters

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 (NFRAMEPG 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

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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.

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Fig. 14 Number of multiframes between paging

1.5.2 NCH Control Parameters

In all cells where the ASCI (Advanced Speech Call Item) service is

enabled, an downlink logical channel belonging to CCCH is defined, Notification Channel (NCH). An MS which is VBS/VGCS (Voice Broadcast Service /Voice Group Call Service) 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 is 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.

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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.

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1.5.3 Improved CCCH handling between AGCH and PCH

To make the CCCH block management more flexible, in BR8.0 a new

mechanism was introduced which observes the current filling state (load) of the AGCH queue. The mechanism dynamically priorities the AGCH message higher then the paging messages if the detected AGCH queue load requires that and features the preemption of unreserved CCCH blocks (i.e. blocks that are shared between PCH and AGCH) for AGCH procedures even if also paging messages are queued for transmission in the BTS paging queues.

Improvements

16 instead of 4 Immediate Assignment entries can be queued

two Immediate Assignment Command can be combined within one AGCH

modification of the priority for ''not reserved'' CCCH blocks by defining three signaling loads (NORMAL, MEDIUM and HIGH) for AGCH queue

The priority of PCH messages before AGCH messages depends on the current AGCH queue filling state.

The AGCH queue load is assumed NORMAL when less then 12 out of 16 AGCH queuing places are used. This implies that the IMMEDIATE ASSIGNMENT (REJ) messages waiting for delivery in the AGCH queue are delivered on a non-reserved block only if no PAGING REQUEST message is pending in the paging queue (see picture below).

The AGCH queue load is assumed MEDIUM when there are still less then 12 IMMEDIATE ASSIGNMENT (REJ) messages in the queue but some are in danger of being delayed too much if not quickly delivered over the Um interface. Under these conditions, the preemption takes place only on those paging queues that are completely empty or half full, but not already preempted during the last CCCH cycle (e.g. IMMEDIATE ASSIGNMENT (REJ) message is sent if in the previous cycle PAGING REQUEST was sent from the queue).

The AGCH queue load is assumed HIGH when there are more then 12 IMMEDIATE ASSIGNMENT (REJ) messages in the queue. In this case AGCH blocks have absolute precedence over PCH ones until the number of AGCH pending in queue drops again below 12.

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There is no parameter to enable improved handling of CCCH mechanism.

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Fig. 15 Common control channel handling

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1.6 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

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Example

Calculate the number of subscribers that can be served in a cell regarding CCCH load if the traffic model described with the following values is used

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

Consider both possible configurations for the CCH.

Solution

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)

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20000 subscriber (uncombined CCCH)

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Parameters for Common Control Channel Configuration

Specification Name


(default)

Meaning

RACH_BUSY_ THRES

RACHBT BTS 0...127

(109)

Threshold for the received signal level (RXLEV) during RACH access.

An access burst signal is assumed as valid (not noise), if the receive level exceeds this threshold.

Step : 1 dbm

FACH_Busy_THRES

FACHBT BTS 0…127

(109)

Threshold for the received signal level (RXLEV) during handover access and ASCI uplink access. An access burst signal is assumed as valid (not noise), if the receive level

exceeds this threshold.

Step : 1 dbm

MAX_RETRANS

GSM 04.08

GSM 05.08

MAXRETR BTS ONE,TWO, FOUR, SEVEN

(FOUR)

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

TX_INTEGER

GSM 04.08

NSLOTST BTS 0...15

(10)

Number of RACH slots to spread re-transmission of channel request; also fixing he deterministic part of wait time0... 15 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, 16, 20, 25, 32, 50

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BS_AG_BLKS_ RES

GSM 04.08

GSM 05.02

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

(1)

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

BS_PA_MFRMS

GSM 04.08

GSM 05.02

GSM 05.08

NFRAMEPG BTS 2...9

(2)

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

NCH_FIRST_ BLOCK

NOCHFBLK BTS 1...7

(1)

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

NCH_BLOCK_ NUMBER

NOCHBLKN BTS 1...4

(1)

number of downlink CCCH blocks to be used for NCH

TIMER_NCH TNOCH BTS 1...254

(1)

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

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1.7 Additional ASCI service related parameters

ASCI service is enabled via parameter ASCISER

This service introduced in the SBS BR5.5 has been improved since BR6.0 with a number of procedures that are defined with a number of additional parameters.

Uplink reply procedure

Uplink reply procedure delays the assignment of common broadcasted (TCH) channel until required by a mobile "interested" in that ASCI call. In that way the traffic channel resources in the cell belonging to the Group Call Area but without ASCI listening subscribers are saved. Notification messages are sent without the VBS/VGCS channel description in that cell.

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).

Description

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 assumes that no listening ASCI MS is present in the cell and initiates the de-allocation 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.

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ASCI one channel model and Talker Change Procedure

Even the Notification without Channel Description and Uplink Reply procedure allows saving of the resources on the air interface, still remains the problem, that both sides, the talker and the listeners, have assigned different duplex connections each for his own, not using the DL in case of the talker and the UL in case of the listeners.

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With the ASCI one channel model feature the group call channel may be

used both by the talker and by the listeners: The UL will be occupied by the talker, if present in

the cell, the DL by the listeners. This way no separate dedicated TCH is necessary for the talker. In a cell with only listeners the UL of the group call channel is unused. In a cell without talker and listeners no group call channel will be allocated at all.

In case of an already allocated VGCS common channel one of the listener mobile stations may want to become talker (subsequent talker). The MS is sending Uplink Access messages to the BTS. BTS reacts by sending a VGCS Uplink Grant message to the requesting mobile station and a Talker Detection message to the BSC.

After the VGCS Uplink Grant message has been sent to the mobile station wanting to become talker, the respective task within BTS ignores any further Uplink Access message on the VGCS common channel.

This way it is always guaranteed that in case of competitor talkers belonging to the same VGCS group there may be only one talker per cell at a time to which the VGCS common channel uplink has been granted by the BTS.

The call-initiating talker can not become a ‘subsequent’ talker with an originator reconfiguration. For this very first talker only an intra- or intercell HO to a dedicated TCH is possible. Obviously, this call-initiating talker can subsequently become a talker again after he has left the uplink and he can try the talker change procedure later on.

A subsequent talker may gain access to the uplink of a VGSC only through a Talker Change procedure.

For the BSC the parameter ASCIONECHMDL has to be set to true to enable the ASCI one channel mode.

In case of setting the parameter ASCIONECHMDL to false BSC assigns a new TCH to the subsequent talker, this is also called 1,5 channel mode.

Late entry notification for VGC listeners

When a VGCS/VBS group call is established with a priority level equal to or higher than the level set by the operator (defined by the NOTFACCH parameter), FACCH notifications (Fast Associated Control Channel) are periodically sent on the common channels of all other ongoing voice group (VGCS) and broadcast calls (VBS) in that cell.

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This notification is sending as long as the relevant high priority call lasts, and will be repeated at a rate indicated by a new PNOFACCH O&M parameter.

With this solution, mobile stations in the group receive mode are informed about ongoing high-priority calls, irrespective of whether the call is a late entrant to a cell, or whether there is another ongoing ASCI call, or irrespective of a group transmit mode of a late entrant in that cell due to the handover of the subsequent talker (one-channel model).

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Fig. 16 Advanced speech call items - principle

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Group call broadcast point in BSS

ASCI services, as specified in the relevant standards, require for each cell in the service area of a call one common broadcast channel where the listeners in the cell are able to receive the speech of the talker. Therefore, for each cell of the ASCI call a dedicated channel is required that is assigned on the A interface between MSC and BSS and on the Asub interface between TRAU and BSC.The feature “ASCI: Group call broadcast point in BSS” supports the 3GPP definedA-Interface link sharing, which shifts the voice broadcast point of ASCI calls – both for circuits and signaling – into the BSS. Within the BSS, the BSC works as a multicast so that it is possible to reduce the amount of channels on the A and Asub interfaces to only one common channel for group calls from the MSC to each BSS that control the cells in the service area of the ASCI call.The feature “ASCI: Group call broadcast point in BSS” can be enabled/disabled bynetwork operators per BSC.

It is expected that the number of cells for ASCI services increase considerably whenASCI services are used by technical emergency organizations such as fire brigades,ambulances etc. The high number of cells that have to be served by each ASCI callwould lead to a very high number of channels carrying the same signal over the same route, thereby wasting line and transport resources on A and Asub interfaces. If there are, for example, 5 ASCI calls with a service area of 400 cells each, they require 2000 circuits on the A/Asub interface.

By shifting the voice broadcast point of ASCI calls into the BSS, the feature “ASCI:Group call broadcast point in BSS” establishes only one terrestrial resource and oneSCCP resource connection on the A and Asub interfaces for all cells of an ASCI call controlled by a given BSC. Saving the number of circuits reduces substantially the network operators' costs for leased lines.

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Fig. 17 Group call broadcast point in BSS for BSC1

Fig. 18 Group call broadcast point in BSS for eBSC

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Reactivation of VGCS/VBS channels after service unavailability

Up to now, if an ongoing ASCI call (VGCS/VBS) is released in one of the cells of theservice area due to BSS generated reasons (e.g. HW failure of radio channels) resulting in the release of the resources and stop of transmitting the notifications for the ASCI call, it is not possible to re-establish the ASCI call in this cell after the cause for the release has been overcome. Similarly, if an ASCI call establishment fails in a cell, e.g. because of cell congestion, and the request is rejected for this cell, no further attempts are undertaken to connect the ASCI subscribers in this cell to the ASCI call. Eventually, if a shutdown command affects the VGCS/VBS channel in a cell, the related ASCI connections are released without trying to reconfigure the VGCS/VBS channel, because a reconfiguration report to the MSs in that cell was not provided.

The feature “ASCI: Reactivation of VGCS/VBS Channels After Service Unavailability”offers the (re-)establishment of an ASCI call in the involved cells automatically by theBSC, as soon as the reasons for the release/rejection have been overcome. Also areconfiguration of VGCS/VBS Channels in case of shutdown commands and appropriate reconfiguration reports are provided.

The “ASCI: Reactivation of VGCS/VBS Channels After Service Unavailability” featuregenerates the following benefits for the customer:

• Since a congestion situation, shutdown of radio resources or a hardware failure in acell inhibits a call connection only for a short time usually, an ASCI subscriber in thiscell is excluded from an ASCI call only for this time period. Thus ASCI messages arebroadcast in a reliable way even in case of a temporary connection failure.

• There is no effort to re-establish the ASCI connection after a temporary interruptionany more and other participants of the group call in other cells which operate wellare not disturbed during the re-establishment process. Without this feature, theusual way to have the “lost” subscribers participate again was to stop the completeASCI call and re-establish it again.

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Fig. 19 ASCI Call Re-Establishment after Failure of the VGCS/VBS Channel

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Ciphering for Voice Group Call Services

In all previous SBS releases the implementation of ASCI service supports no confidentiality protection, e.g. no encryption/decryption is performed during a VGCS/VBS call.

In BR9.0, ciphering is introduced for both ASCI call types (VBS and VGCS) to allow radio interface integrity also for group calls. This is done by defining per cell basis the new parameter ASCICIPH.

For those ASCI subscribers that use a dedicated channel (i.e. originator of a VGCS call or the ‘subsequent talker’), the usual ciphering procedure as known for CS calls (IMSI related ciphering based on a subscriber-individual Kc) is applied in any case.

Special conditions apply, however, for all other subscribers participating in a group call. The overall (not talker-related) ciphering of a group call is not based on an individual ciphering key Kc but on the broadcast ciphering key V_ Kc.

Within different cells, different Voice group or Broadcast ciphering keys V_Kc must be used. This means that in case of cell change of an MS also the Group Ciphering Key V_Kc changes. On another hand the lifetime of the same V_Kc shall not be longer than the TDMA frame number cycle (which is equal to 3 hours and 28 minutes period).

In the BSS and MS, the ciphering key V_ Kc is calculated using the so-called ‘Key Modification Function’ (KMF) each time

a new ASCI group call is set up in a cell and

after each TDMA frame number cycle (which is equal to 3 hours and 28 minutes period).

The input parameters of KMF are:

VSTK_RAND: a 128 bits Short Term Key, forwarded from the BSC to the BTS

CGI: the cell global identifier which identifies a cell world-wide uniquely

CELL_GLOBAL_COUNT: counter value used for a mechanism that ensures the change of the V_Kc in regular time periods (the time period is the length of a complete TDMA frame number cycle).

The output of KMF is the ciphering key:

V_Kc: 128 bit encryption key that is to be used for the VGCS call in this cell in this time period.

The 'Ciphering on Voice Group Call Services' feature introduces the KMF in the BTS independently on the BTS platform, e.g. the feature if enabled can run in the BTSone as well as in the BTSplus.

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CS data transmission during active voice group call

Advanced Speech Call Items (ASCI) offer customers the possibility to establish a call in several cells that form the so-called service area of a Voice Group Call Service (VGCS) or Voice Broadcast Service (VBS). Within this service area one subscriber speaks and several subscribers in the various cells listen to the speech. In case of VGCS the speaker can change. Up to now, such group communication is implemented as a pure voice service within today's mobile radio systems.This feature, also called “Enhanced Push-to-Talk”, is an extension of ASCI services and provides an additional point-to-multipoint data service for an ongoing VGCS call: Each participant of the voice group call – the talker and the listeners as well – can send a small amount of application data to the other participants without interrrupting or releasing the active voice group call.

The feature "CS Data Transmission During Active Voice Group Call" offers the following functionality:

• Short application data can be sent during an ongoing voice group call without interrupting the group call.

• Any subscriber (listener or talker) is able to send short application data to all otherparticipants of the ongoing VGCS call. In case it is a listener who sends data, hisidentity is included. The transmission of short application data is triggered bypressing the push-to-send key on the MS.

• Any subscriber (listener or subsequent talker) is able to confirm the receipt of databy sending an acknowledgement regardless if someone is currently talking or not.Confirmation is done by pressing the push-to-confirm key on the MS.

• The transmission time of the short application-specific data from pressing the pushto- send key at the sender's terminal to displaying the data at the receiver's mobiles does not exceed 500 ms.

The basic ideas to avoid interrupting of an ongoing group call while sending and distributing short data are the following:

– Short CS application data is usually sent and distributed on air interface via FACCH.– The ASCI 1.5 channel mode shall be used providing one common DL channel andtwo UL channels (one is the counterpart of the common DL channel, the other is anadditional allocated dedicated UL channel). In case a listener sends data, one ULchannel is still used for the UL VGCS call, the other for sending CS data. The ASCI 1.0 channel mode – only one UL channel, which is the counterpart of the common DL channel – also allows additional transmitting of short data, but with performancedegradation.

– Application data is short enough to fit in one SABM frame.

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Specification Name

DB Name Object

Range

(default)

Meaning

ASCI_SERVICE ASCISER BTS ENABLED,

DISABLED (DISABLED)

Enables or disables ASCI service on a cell basis.

ASCI_UPLINK_ REPLY

ASCIULR BTS ULRDISABLE

VBSENABLE

VGCSENABLE

VBS_VGCSENABLE

(ULRDISABLE)

The ASCI Uplink Reply parameter enables or disables the uplink reply procedures for both VGCS and VBS

TIMER_UPLINK_ REPLY

TUPLREP BTS 5..60 s

(20)

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

NOTIFICATION_ FACCH

NOTFACCH BSC NO SUPP,

ALWAYS,

EQA, HIGHEQB, HIGHEQx, x=0…4

(NOSUPP)

Indicates for which mobile priorities the NOTIFICATION FACCH messages are sent on the FACCH belonging to the TCH seized by one ASCI subscriber.

TIMER_GRANT TGRANT BTS 1-254

unit 10ms

(4)

This timer determines the period in which BTS waits for a correctly decoded message from MS as an answer to the sent message VGCS UL GRANT.

Enable_ EnhancedPush- ToTalk

EPTT BSC TRUE/(FALSE) The “Enhanced Push-to_Talk” feature can be enabled/disabled by this

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attribute

VGShort_Data_ DistributionByBSC

VGSDBB BSC TRUE/(FALSE) This attribute allows to distribute the short data to be transmitted within the group call area by control of the BSC in case only one BSC covers this area; otherwise the MSC is involved which causes a certain time delay

timer3151 T3151 BTS 1 ... 9 s

(3s)

This attribute determines the repetition time for the UPLINK BUSY message in the cell

Number_Of_Enhanced_PushToTalk_Repetitions

NEPTTREP BTS (0 )... 3 This attribute determines the number of repetitions of the application-specific data transmissions

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Specification Name


(default)

Meaning

VG_UPINK_ FREE

VGRULF BTS 1-254

(1)

This parameter is used for the repetition of the UPLINK FREE message during the Talker Change procedure to inform all MS that UL is free.

ASCI_ONE_CH_ MODEL

ASCIONE-

CHMDL

BSC TRUE,FALSE

(FALSE)

Determines whether the ASCI "one channel model" is enabled or not.

ENABLE _NCH_ REPET

ENPERNOTDE BTS TRUE, FALSE

(FALSE)

This attribute enables the repetition of notifications on dedicated channels.

REPET_PER_ FACCH

PNOFACCH BTS 1, 1.5 …5

unit 0,5s

(5)

This attribute defines the duration of the repetition period for the FACCH notification of a given ASCI call.

ASCI_ CIPHERING

ASCICIPH BTS TRUE, FALSE

(FALSE)

This parameter indicates whether the ciphering for ASCI calls is enabled.

Enable_ASCI_CallReEstablish

EASCICRE BTS TRUE/FALSE

(FALSE)

The “ASCI Reactivation of

VGCS/VBS Channels ... ” feature can be enabled/disabled by this attribute

Bsc_Timer14_Public

BSCT14PUB BTS TunitType:

(HLFSEC) /

SEC5

TvalueType:

0 –(16)- 254

The queuing timer for the ASCI calls in the “public” ASCI re-establishment buffer. When the queuing timer expires, a call in the ASCI re-establishment buffer is released. The “public” queue is used for ordinary subscribers.

Bsc_Timer14_WPS

BSCT14WPS BTS TunitType:

(HLFSEC) / SEC5

TvalueType:

0 –(16)- 254

The WPS queue is used for prioritized subscribers.

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2 Extended channel mode

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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

Name


(default)

Meaning

CELL_TYPE CELLTYP BTS STDCELL

(def.)

Maximum range35 km a cell covering,

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EXTCELL

DBSTDCELL

Maximum range 100 km a cell covering,

Dual Band Standard Cell.

EXTENDED_MODE EXTMODE CHAN TRUEFALSE

(FALSE)

Defines if a channel is used in extended mode or not.

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Fig. 17 Extended Cell

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3 Adaptive Multirate AMR

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3.1 Basic

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 speech codecs FR, EFR and 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 full-rate 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.

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Fig. 18 AMR principle

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Fig. 19 AMR codecs

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Fig. 20 Family of curves (clean speech in full rate) acc. to ETSI study

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Fig. 21 AMR performance curves (full rate with street noise) acc. to ETSI study

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Fig. 22 Family of curves (clean speech in half rate) acc. to ETSI study

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Fig. 23 AMR capacity gain acc. to ETSI study

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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 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 and 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.

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AMR Codec Modes

The AMR codec operates at different codec mode bit-rates (4.75 kbit/s - 12.2 kbit/s). Each codec mode performs differently under changing channel quality (C/I). The following table provides an overview on the codecs used.

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AMR Codec Mode Bitrate (kbit/s)

Designation

(Full Rate / Half Rate Mode)

Support by BTSplus

Support by BTSone

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 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. An algorithm to determine 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.

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VAD/DTX

Signaling and measurement reporting for codec mode changes are transmitted in-band on the radio interface.

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3.2 AMR wideband TCH/WFS

Most speech coding systems in use today are based on a speech sampling rate of 8 kHz deploying a typical bandwidth of speech between approx. 200-300 and 3400 Hz only which limits the speech quality. Such speech codecs are used in today's wireline and mobile networks and include usual AMR codecs (narrowband adaptive multiratecodecs).

This feature introduces wideband AMR coding as specified by 3GPP and ITU-T. Thesampling rate is increased to 16 kHz, the deployed bandwidth is extended and ranges from 50 to 7000 Hz. AMR wideband is based on a family of new speech codecs.

AMR wideband significantly improves the speech quality compared to today’s narrowband solutions. The “tin can” sound experienced with narrowband communication is replaced by a more face-to-face like sound sensation creating a greater sense of privacy, discretion and comfort. More in detail, the increase of the high frequency range of the audio signals improves intelligibility (such as differentiation between “s”, “f” and “th”) and the separation of speech from background noise. Additionally, speech sounds more natural easing speaker recognition and giving a feeling of transparent communication. The increase of the low frequency range of the audio signals mainly affects speech naturalness.

The increased intelligibility and naturalness of speech allows for mobile applicationsrequiring high quality audio parts. Such applications can be e.g. enhanced automaticvoice recognition, improved voice mail, audio teleconferencing, program broadcasting, drive information services. Also wireless communication regarding multimedia content and Internet applications can be pushed. Such applications are e.g. network based language learning, distribution of narrative content, streaming services, real-time collaboration, virtual reality scenarios.

Since the quality of wideband AMR speech surpasses that of today’s fixed networks,users of fixed networks might be attracted by appropriate mobile services and mightbecome new costumers. Positive changes in calling patterns are expected, generating substantially more mobile traffic, both in terms of number and duration of calls.

Wideband AMR is adopted by both 3GPP and ITU-T, thus the same codec can beapplied for wireless and wireline services. The implementation of wideband voice applications and services across a wide range of communication systems and platforms will be simplified.

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Implementation

Application of wideband AMR affects all network elements of the radio access network including TRAUs. The different network elements are in charge for the main functional parts of wideband AMR as described in the following topics.

TRAU

Two TRAUs are affected in case of an MS-MS call, one on the originating side, one on the terminating side of the connection. These TRAUs activate and control the “tandem free operation” (TFO) mode required for the transparent transmission of speech encoded (thereby compressed) wideband AMR speech data in the core network. The TRAUs decide, if TFO is possible. They handle the TFO protocol and continuously monitor the tandem free operation. This includes the handling of TFO frames (packing/unpacking in uplink/downlink direction) and of in-band control information (contained in the downlink TFO frames).

BSC

– Channel allocation for wideband AMR usage– Database handling for the new attributes

BTS

– Channel coding/decoding (DL/UL) for GMSK modulated wideband AMR codecs– Pre-processing for handover and power control– Link adaptation

MS

– Measurements for DL link adaptation– Channel coding/decoding (UL/DL) for GMSK modulated wideband AMR codecs– Speech coding/decoding (UL/DL)

AMR Wideband Codec Modes

AMR wideband for Nokia Siemens Networks comprises three speech codec modes with bit rates of 12.65, 8.85 and 6.6 kbit/s. The speech codecs utilize the Algebraic Code Excited Linear Prediction (ACELP) technology, which is also employed in the AMR narrowband and EFR speech codecs. Table 1 and Table 2 show the characteristics of the wideband AMR codecs. The encoding is done block by block (one block comprises data for one TFO frame and 4 radio bursts). The speech bits are grouped in the two classes 1a and 1b. Class 1a bits are protected by CRC and convolutional coding, class 1b bits are protected by convolutional coding only.

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Characteristics of AMR Wideband Codec Modes for CRC Encoding

Characteristics of AMR Wideband Codec Modes for Convolution Coding

The information about the AMR wideband codec is carried by the “Multirate Configuration” Information Element. This Information Element is present in the following messages within the radio access network:

– CHANNEL ACTIVATION (Abis)– MODE MODIFY REQUEST (Abis)– ASSIGNMENT COMMAND (Um)– HANDOVER COMMAND (Um)– CHANNEL MODE MODIFY (Um)– DTM ASSIGNMENT COMMAND (Um)

Further aspects of the wideband AMR feature comprise:

– Integration in the Service Dependent Channel Allocation– Codec Selection at Call Setup– Tandem Free Operation– Codec Mode Adaptation– Switching Between Wideband AMR and Narrowband AMR (exceptional cases)

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3.2.1 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 and HR2 (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, etc.)

3.2.2 TRAU pooling

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

Parameter Object Range

(default)

Meaning

DEFPOOLTYP PCMA NOT_DEFINED, POOL_1,…, POOL_48

(NOT_DEFINED)

Default pool type, this parameter is only relevant if the feature ‘pooling of A-interface TCH resources’ (the parameter EPOOL in command SET BSC) is enabled and defines the default type of pool assigned to every TSLA of the given PCMA.

POOLTYP TSLA NOT_DEFINED, POOL_1,…, POOL_48

(NOT_DEFINED)

Pool type, this parameter defines the type of pool assigned to the TSLA.

3.2.3 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 dynamic changes between AMR codecs is done according to an adaptation algorithm without notification or intervention by the BSC. This algorithm is called AMR

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Link Adaptation. It 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).

For the AMR link adaptation DL the thresholds and the associated hysteresis are administrable by the parameters given in the following table.

For the AMR link adaptation UL so called reference thresholds for the transition between the possible codec modes are hard-coded.

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3.2.4 BSC Database Parameters

The tables below contain parameters concerning basic AMR settings

(used codec modes, threshold - hysteresis for the active codecs and initial coding mode). In the BSC DB there are two sets of these parameters with the same meaning but configured independently. One set is applied for AMR subscribers allocated on hopping and another on non hopping traffic channels (e.g. FHAMRFRC1 and AMRFRC1 respectively).

Since release BR9.0 the AMR feature has to be enabled generally on BSC level.

Parameter Object Range (Default) Meaning

EAMR BSC TRUE, FALSE (TRUE) The parameter enables AMR speech in the BSC. When it is set to TRUE, the BSC generally allows the use of AMR speech codecs in the BSC when the BSC receives TCH request messages.

EAMRWB BSC TRUE/FALSE (FALSE) This attribute generally enables/disables

the “AMR wideband” feature.

AMRFRC1,

AMRFRC2,

AMRFRC3,

AMRFRC4

and

FHAMRFRC1,

FHAMRFRC2,

FHAMRFRC3,

FHAMRFRC4

BTS 1:RATE_01 (4.75 kbit/s),

2:RATE_02 (5.15 kbit/s),

3:RATE_03 (5.90 kbit/s),

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)

AMR Full Rate Codec no. 1,




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AMRFRTH23

and

FHAMRFRTH23

BTS Threshold: 0 ... 63; Default: 12 (6 dB)

Hysteresis: 0 ..15 (7.5dB) Default: 4 ( 2dB)

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

AMRFRTH34

and

FHAMRFRTH34

BTS Threshold: 0 ... 63; Default: 23 (11,5 dB)

Hysteresis: 0 ..15 (7.5dB) Default: 4 ( 2dB)

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

AMRHRC1

AMRHRC2,

AMRHRC3,

AMRHRC4

and

FHAMRHRC1

FHAMRHRC2,

FHAMRHRC3,

FHAMRHRC4

BTS 1:RATE_01 (4.75 kbit/s),

2:RATE_02 (5.15 kbit/s),

3:RATE_03 (5.90 kbit/s),

4:RATE_04 (6.70 kbit/s),

5:RATE_05 (7.40 kbit/s)

AMR Half Rate Codec no. 1,




AMR Half Rate Codec no. 5

AMRACMRDL HAND 1…31 ,

Unit=CMR

(5 CMR)

Size of averaging window for Codec Mode Requests (CMR)

AMRHRTH12

and

FHAMRHRTH12

Threshold 0..63

Default: 19 (9,5 dB)

Hysteresis 0..15

Default:4 (2 dB)

"Threshold-Hysteresis" related to the active codecs specified in the AMRHRC1 and AMRHRC2

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AMRHRTH23

and

FHAMRHRTH23

Threshold: 0 ... 63

Default: 24 (12 dB)

Hysteresis: 0 ... 15

Default:4 (2 dB)


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Parameter Object

Range (Default) Meaning

AMRHRTH34

and

FHAMRHRTH34

BTS Threshold: 0 ... 63

Default: 30(15 dB)

Hysteresis: 0 ... 15

Default:4 (2 dB)

Null (BTS One)


For BTS One family these two values should be set as NULL

AMRFRIC

and

FHAMRFRIC

BTS 0:START_MODE_FR,

1:CODE_MODE_01,

2:CODE_MODE_02,

3:CODE_MODE_03,

4:CODE_MODE_04

Default:0

Initial FR codec mode (i.e. start mode among the ACS)

AMRHRIC

and

FHAMRHRIC

BTS 0:START_MODE_HR,

1:CODE_MODE_01,

2: CODE_MODE_02,

3:CODE_MODE_03,

4:CODE_MODE_04

Default:0

Initial HR codec mode

AMRLKAT BTS Range: 0..200

0 = -10dB,

100 = 0dB,

200 = +10dB

unit: 0.1dB

Default: 100

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 signal-to-noise ratios. A value lower than the

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default has the opposite effect. Adaptation of AMR HR and AMR FR is affected simultaneously.

AMRWBFGTH12 BTS threshold:

0 … 63

hysteresis:

0 … 15

Lower threshold for switching between codec 2 and 1 and hysteresis value to obtain the higher threshold for switching between codec 1 and 2.

FHAMRWBFGTH12

BTS threshold:0 … 63(0 … 31.5 dB)hysteresis:0 … 15

(0 … 7.5 dB)

Lower threshold in case of frequency hopping for switching between codec 2 and 1 and hysteresis value to obtain the higher threshold for switching between codec 1 and 2.

AMRWBFGTH23

BTS threshold:0 … 63(0 … 31.5 dB)hysteresis:0 … 15(0 … 7.5 dB)

Lower threshold for switching

between codec 3 and 2 and hysteresis value to obtain the higher threshold for switching between codec 2 and 3.

FHAMRWBFGTH23

BTS threshold:0 … 63(0 … 31.5 dB)hysteresis:0 … 15(0 … 7.5 dB)

Lower threshold in case of frequency hopping for switching between codec 3 and 2 and hysteresis value to obtain the higher threshold for switching between codec 2 and 3.

AMRLKATWFS BTS 0 … 200(-10 … 10 dB)

This attribute allows to favour either more robust AMR codec or wideband AMR codec in uplink direction.

AMRWBFGIC BTS 0 ... 3 This attribute determines the initial wideband AMR codec for GMSK modulated full rate TCHs.

FHAMRWBFGIC BTS 0 ... 3 This attribute determines the initial wideband AMR codec for GMSK modulated full rate TCHs in case of frequency hopping.

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The thresholds and hysteresis values indicated in the table (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 Meaning 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)

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Fig. 24 Threshold and hysteresis determine the switching "up" and "down" between codec modes in downlink

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If the EAMR attribute of BSC is set to FALSE then the TRAU

DEFPOOLTYP attribute (CREATE PCMA) cannot be equal to POOL_23 or POOL_46.

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Thresholds and Hysteresis for AMR Link Adaptation Uplink

For the AMR link adaptation in the uplink so-called Reference Thresholds for the transition between the possible CODEC modes are hard-coded. However, the effective thresholds are not fixed, but they are calculated for each call, depending on the used ACS and the value of the tuning parameter AMRLKAT.

As a basis for this calculation, the BTS uses a table of 'reference values'.

Fig. 25 Default values for the AMR Full/Half Rate Thresholds for AMR Link Adaptation Uplink

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The AMR Link Adaptation is based on the quality of a connection. Since a

finer scale is needed than the one RXQUAL offers, C/I is used. The approach to consider C/I values for AMR calls was basically used to achieve a higher resolution of quality values for AMR link adaptation. To harmonize and simplify the Handover and Power Control Quality Threshold parameters the C/I values are since BR9.0 used for all service types.

PC and HO decisions however are still based on RXQUAL values which are then mapped into C/I values within the BTS.

The following mapping between C/I values and RXQUAL values is applied:

RXQUAL C/I

6.88 ... 7.00 1

6.76 ... 6.87 2

6.38 ... 6.75 4

6.13 ... 6.37 5

5.88 ... 6.12 6

5.63 ... 5.87 7

5.38 ... 5.62 8

5.13 ... 5.37 8

4.88 ... 5.12 9

4.63 ... 4.87 10

4.13 ... 4.62 11

3.88 ... 4.12 12

3.38 ... 3.87 13

2.88 ... 3.37 14

2.63 ... 2.87 15

2.13 ... 2.62 16

1.63 ... 2.12 17

1.13 ... 1.62 18

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0.38 ... 1.12 19

0.00 ... 0.37 20

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4 Channel allocation strategy

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4.1 Basic

Allocation of the radio channels is not only based on the best interference

band as it was in early SBS releases (e.g. BR5.5) but is a service dependant.

The Service Dependant Channel Allocation Strategy (SDCA) applied on Um interface offers the possibility to decide the call policy for resource allocation (data calls preferably on BCCH carrier and speech calls on non BCCH carriers or vice versa) and the downgrading strategy (parameter DGRSTRGY) for multislot data calls in case of congestion.

Cell Load Dependent Activation of Half Rate allocates half rate channels only during high traffic peaks in the cell, when additional capacity is needed. The feature can be enabled with the parameter EHRACT within a cell which is configured for dual rate channels. A threshold HRACTT1 for standard cells and HRACTT2 for extended and concentric cells is implemented.

If the cell traffic load exceeds the percentage defined by HRACTT1, all incoming calls or incoming handovers, for which HR in the info element (IE) is indicated as supported speech version, are forced to HR. If the cell load is below the percentage defined by HRACTT1, all incoming calls are forced to FR.

The allocation of half rate channels according to the current cell load is also provided for AMR half rate codecs with the parameters EHRACTAMR, HRACTAMRT1, HRACTAMRT2 (see chapter 3, section 4.5.3).

Enhanced pairing of HR channels, parameter EPA set on the BSC basis, implies automatically triggered forced intracell handovers that fill up dual rate TCHs, carrying only one HR call, with another HR call.

Enhanced pairing due to Um radio TCH load is triggered if the percentage of dual rate TCHs or full rate TCHs in the BTS in usage state ''idle'' drops below a definable threshold. This thresholds are based on the parameters EPAT1 in case of standard cell, complete area of a concentric cell and far area of an extended cell, and EPAT2 in case of inner area of a concentric cell and near area of an extended cell.

In addition, for circuit switched (CS) services Service Dependant Handover and Power Control was introduced to offer higher flexibility for handover and power control algorithms (parameters SGxHOPAR and SGxPCPAR discussed in chapters 3 and 6 respectively).

Further step to improve the Channel Allocation Strategy (SDCA) was done in the SBS BR8.0 by introducing the feature “Multi Service Layer Support''.

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Fig. 26 SDCA history

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4.2 Multi Service Layer Support

Operators can split-up the frequency spectrum of their networks to supply

a variety of services based on the marketing forecast for them.

In order to be able to supply the quality required for a variety of services the network has to be designed with different frequency reuse patterns. That means that a cell may consist of one or more service layers that, in turn, may comprise one or more TRXs with the same reuse pattern and that provide the same mean quality in terms of C/I.

The “Multi Service Layer Support” feature enables operators to assign the required number of TRXs to the different service layers. This feature distinguishes between up to nine different types of services having different quality demands. These service types can be assigned to the respective service layers.

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Service Type Description

Signaling Signaling services only use the Stand Alone Dedicated Control Channel (SDCCH) for signaling purposes, e.g. call setups, Short Message Service, location updates, Location Services, etc.

CS Speech EFR/FR/HR

Denotes circuit switched single slot speech services that use the following codecs: Enhanced Full Rate (EFR), Full Rate (FR) or Half Rate (HR).

CS Speech AMR FR Denotes circuit switched single slot speech services that use the Adaptive Multi-Rate Full Rate codec (AMR FR)

CS Speech AMR HR Denotes circuit switched single slot speech services that use the Adaptive Multi-Rate Half Rate codec (AMR HR)

CS Data Performs circuit switched single slot data transfers using rates up to 9.6 kbit/s or up to 14.4 kbit/s

HSCSD Denotes circuit switched single slot or multislot data transfers that carry High Speed Circuit Switched Data Services (HSCSD).

GPRS Denotes packet switched single slot or multislot data transfers that carry General Packet Radio Services (GPRS) on the Packet Data Traffic Channels (PDTCH) that are either embedded alone or multiplexed in dynamically allocated Packet Data Channels (PDCH)

EGPRS Denotes packet switched single slot or multislot data transfers that carry Enhanced General Packet Radio Services (EGPRS) in Packet Data Traffic Channels (PDTCH) that are either embedded alone or multiplexed in dynamically allocated Packet Data Channels (PDCH).

ASCI The Voice Broadcast Services (VBS) of Advanced Speech Call Items (ASCI) allocate specific channels; e.g. GSM-Railway subscribers (GSM-R) use common voice group broadcast channels for Voice Group Call Services (VGCS).

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Two new concepts have been introduced to provide flexible resource

allocation - the Service Layer that a transceiver belongs to and the Service List SL.

The Service List is a collection of all of the service types supported within a cell and defines the mapping of the service types onto the Service Layer Lists (SLL). The Service Layer List is a logical entity, i.e. it is not an O&M parameter that includes all of the Service Layers, but one or more, assigned to a particular service and listed in decreasing order of their priority. A certain level of mean radio quality, as a result of radio network planning characterizes a service ‘Layer’ - referred to as ‘Layer’ (LY) in this document.

The Service List has to be configured per cell. Modification or deletion of the priority layers within the SLL can be done for CS service types without interrupting service provisioning, but for PS service types the service is interrupted because the PTPPKF object has to be locked.

In order to avoid blocking on a layer as long as unused resources are available, it is recommended to assign the layers to several Service Layer Lists.

NOTE

Please note that service types not included in the SL are not supported in the cell. The system checks network consistencies such as hardware support before enabling or disabling services, i.e. before modifying the ‘Service List’.

Separate Service Lists must be maintained per area in case of dual area cells, i.e. concentric cells using single/dual bands or extended cells. The Service List of the complete or far area is referred to as the Service List of the Primary Area. The Service List of the inner or near area is referred to as the Service List of the Complementary Area.

For dual band standard cells, a Service List of the Primary Area belongs to the area that supports the radio frequency band using the BCCH.

Please note that GPRS is not available in specific cell areas, e.g. in the inner areas of concentric cell structures, although both dual band standard cell areas support it.

EGPRS needs transceivers that are capable of satisfying its service requirements.

Resource allocation

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On receiving a request for a particular service, the system reads the SL of the cell to check its resources. If it contains the relevant service type, the system searches through the resources in the first layer of the relevant SLL. If there are no resources available in the highest priority layer, the system checks the next layer of that SLL and so forth. Thus, services may be temporarily allocated on a layer other than the highest prior layer.

Therefore, a resource reallocation procedure is periodically triggered to move such CSC calls into a more appropriate layer as soon as possible.

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Fig. 27 Allocation example

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4.2.1.1 Service Layer List

The Service Layer List contains radio channels of one or several TRXs

with expected the same quality and the same characteristics. Each TRX in the BTS will be associated to a layer via O&M. The selection of the appropriate layer LYn and grouping layers in the SLL for each service will be performed on the Radio Network planning and customer consideration basis.

SLL0 is default for signaling services. SLL1 is created for data services requiring higher quality. SLL2 is designed for less demanding services.

After creation of SL and SLL, resources assignment table can be created.

By default LY0 is reserved for signaling services.

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4.2.1.2 Parameters related to the Multi Service Layer Support and some changes in the BSC DB

In the BSC DB object (SET) BTS the attributes xLLPRM and xLLCOM

related to the Service List Primary and Complementary respectively (x stands in this document for different services like S for signaling, AMRFR, AMRHR, SCRTSWD for circuit switched data, CRTSWSPE speech, EDGE, GPRS and HSCSD) are introduced.

In the BSC DB object TRX a new attribute LAYER ASSIGNED (LYn where n=0…11) is introduced.

GSUP parameter in TRX is no longer supported.

CPOLICY is also no longer supported as the service layer concept is introduced.

DGRSTRGY is from the BSC object moved to the BTS object.

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4.2.2 BSC Database parameters


DGRSTRGY-BCNT

BSC ENABLED,DISABLED

(DISABLED)

Downgrade strategy busy counting enables/disables the functionality that considers the setting of the parameter DGRSTRGY.

If DGRSTRGYBCNT is set to ENABLED, the BSC considers the setting of the DGRSTRGY parameter in the

-Radio TCH load calculation and

-Abis TCH load calculation

as in the previous SBS releases.

If DGRSTRGYBCNT is DISABLED

the BSC considers all (non-reserved) TCHs which are currently busy due to GPRS traffic (PDCH) as 'busy' (like any other TCH currently seized by a CS call) no matter what the setting of DGRSTRGY is.

DGRSTRGY BTS HSCSD_FIRST_ DOWNGRADE, GPRS_FIRST_ DOWNGRADE, DOWNGRADE_HSCSD_ONLY, DOWNGRADE_GPRS_ONLY, NO_DOWNGRADE

(GPRS_FIRST_ DOWNGRADE)

Downgrade strategy for multislot data calls.

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<x>LLPRM BTS NULL (def.),

LY_00,

LY_01…

LY_11

Primary Service List for the corresponding service.

x = AMRFR, AMRHR, AMRWBFR, ASCI, S, CRTSWD, CRTSWSPE, E, G, HSCSD.

Multiple selection is possible.

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<x>LLCOM BTS NULL (def.),

LY_00,

LY_01…

LY_11

Complementary Service List for the corresponding service.

x = AMRFR, AMRHR, AMRWBFR, CRTSWD, CRTSWSPE, E, G, HSCSD.

Multiple selection is possible.

LAYERID TRX NULL (def.),

LY_00,

LY_01 …

LY_11

Specification of the group of the radio resources the TRX belongs to.

EPA BSC TRUE (def.),

FALSE

Enable HR channels pairing.

EPAT1 BTS 0…10000,

Unit:0,01%

(4000)

Enhanced pairing threshold 1 indicates the percentage of busy TCHs in a standard cell or complete area of a concentric cell or far area of an extended cell.

EPAT2 BTS 0…10000,

Unit:0,01%

(4000)

Enhanced pairing threshold 2 indicates the percentage of busy TCH of the inner area of a concentric cell or near area of an extended cell.

EHRACT BTS TRUE (def.), FALSE Enable cell load dependent HR activation.

HRACTT1 BTS 0 ... 10000

(6000)

Threshold 1 for HR activation: percentage of busy TCH in a standard cell or complete area of a concentric cell or far area of an extended cell.

HRACTT2 BTS 0 ... 10000 Threshold 2 for HR activation: percentage of busy TCH for the

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(6000) inner area of a concentric cell or near area of an extended cell.

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t

5 Exercises

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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.

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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.

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Exercise 3

Title: Determining the highest "Trunking Gain" for the system

Task

By using Erlang B-traffic model table (chapter 9, page 45) compare the "Trunking gain" in the operator's network composed of:

an Erlang B system with 36 trunks

2 Erlang B systems with 18 trunks each

4 Erlang B systems with 9 trunks each

Which solution gives the highest offered traffic (trunking gain) if 1% blocking is assumed in all cases?

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Exercise 4

Title: SS7 signaling load per BSC and needed number of CCSS7 links per BSC

Task

Assume the standard profile subscriber that makes signaling load of 900byte, BSC system of 3500Erlang traffic capacity and traffic load per subscriber 25mErlang.

Calculate the total signaling load in the system and the number of needed CCSS7 links.

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Exercise 5

Title: Configuration of the Multi Service Layer in the given BTS

Task

Given an standard cell with 3carriers. TRX0 is the BCCH carrier

The BTS should support Signaling, CS speech, GPRS and HSCSD.

Create the service list for the given services in the BTS.

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6 Solutions

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Solution 1

Title: Creation of a RFC in the SBS

CREATE TRX:NAME=BTSM:0/BTS:0/TRX:1, TRXFREQ=CALLF05, PWRRED=0, RADIOMR=OFF, RADIOMG=254, MOEC=TRUE, TRXAREA=NONE, LPDLMN=0,; TRXMD=GSM; LAYERID=LY_02; USFGRAN=DISABLED;

The parameters are specified as following:

BTSM: BTS site manager number 0 ... 199

BTS: Number of sectors/site 0 ... 23

TRX: TRX number to the related cell 0 ... 23

TRXFREQ: TRX-frequency - ARFCN BCCHFREQ,CALLF01,

CALLF02, :CALLF63

PWRRED: Power reduction [0...18 dB in steps of 2 dB] fordecrease max. transmit power

0 ... 9

RADIOMR: Radio measurement reports from TRXto the BSC ON / OFF

RADIOMG: Granularity of radio measurement reports insteps 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 ... 10

TRXMD TRX is associated to the GSM or EDGE CU GSM / EDGE

USFGRAN Flexible USF granularity ENABLED/

DISABLED

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Solution 2

Title: Dimensioning control channels of an extended cell

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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Solution 3

Title: Determining the highest "Trunking Gain" for the operator's system

The offered traffic for the given number of trunks and blocking is:

25.51 Erlang if the operator uses only 1 system with 36 trunks

2x 10.44=20.88Erlang if the operator uses 2 systems with 18 trunks each

4x3.78=15.12 Erlang if the operator uses 4 systems with 9 trunks each.

Obviously the highest trunking gain is obtained by using the available number of trunks in one system only.

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Solution 4

Title: SS7 signaling load per BSC and needed number of CCSS7 links per BSC

Number of the subscriber in the system is defined as:

Number of subscribers=Traffic capacity of the system/traffic per subscriber

Thus for the given values the number of subscribers is:

Number of subscribers=3500Erlang/25mErlang=140 000.

Total signaling load made by all subscribers is in 1h observation period is:

Total signaling load=Number of subscribes*signaling load per subscriber/1h, i.e.

Total signaling load=140 000*900byte/3600s= 35kbyte/s.

CCSS7 link single capacity is 64kbit/s=8kbyte/s.

Thus needed number of signaling links to handle offered signaling load is 5 as obtained from:

35kbyte/s : 8kbyte/s=4,37 .

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Solution 5

Title: Configuration of the Multi Service Layer in the given BTS

The first step is to define in the TRX object the layers.

BCCH TRX should be defined as LY0 (best expected quality)

The other two TRXs we define as LY1 (normal quality).

Therefore three available TRXs are building 2 Layers:

LY0 (BCCH TRX)

LY1 (TRX1, TRX2)

Then SLL can be created. The position of the service in the service list corresponds to the service priority:

SLL0 (LY0)

SLL1 (LY0, LY1)

SLL2 (LY1, LY0)

It means that for SLL0 services will be allocated on BCCH TRX only.

For SLL1 system will look for a channel on BCCH TRX, and in case of channel congested will search for a TCH of TRX1 and TRX2.

For SLL2 the services allocation will take place on TCHs of TRX2 and TRX1 and in case of congestion on BCCH TRX.

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Fig. 28 Service List and Service Layer List

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Fig. 29 Services supported in the cell by available TRXs

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Fig. 30 Database entry example

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Documents

01 RA21611EN10GLS0 Channel Configuration