23295351 01 Mn1789eu11mn 0001 Channel Configuration

Channel configuration and allocation strategy Siemens

MN1789EU11MN_0001 © 2005 Siemens AG

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Contents 1 Channel configuration overview 3 1.1 Control channel configuration 13 1.2 Dedicated channel 14 1.3 Smooth Channel Modification 16 1.4 Random access channel 21 1.5 Paging / access grant and notification channel 28 1.6 CCCH load 29 1.7 Additional ASCI service related parameters 32 2 Extended channel mode 37 3 Adaptive Multirate AMR 41 4 Channel allocation strategy 55 4.1 Basic 56 4.2 Multi Service Layer Support 58 4.3 Database parameters 63 5 Exercises 65 6 Solutions 77

Channel configuration and allocation strategy

Siemens Channel configuration and allocation strategy

MN1789EU11MN_0001© 2005 Siemens AG

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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 960 Fu(n) = 890 + 0.2 n Fu(n) = 890 + 0.2 x (n -1024)

0< n < 124 975 < n < 1023

Fd(n) = Fu(n) + 45

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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25 (35) MHz75 MHz

UPLINK (UL)

915 Mhz1785 MHz

(880) 890 Mhz1710 MHz

Transmit band of themobile station

C124

(174)374

C3

C2

C1

200 kHz

DOWNLINK (DL)

GSM 900DCS 1800

960 Mhz1880 MHz

01...............124512...............885 975....1024

ARFCN(Absolute RF channel number)

C = radio frequency channel (RFC)

Guard bandnot used

(925) 935 Mhz1805 MHz

Transmit band of the basestation

C124’

(174’)374

C3’

C2’

C1’

25 (35) MHz75 MHz

Duplex Distance 45 MHz resp. 95 MHz

E-GSM900

GSM900DCS1800

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 kHzTime

0

4321

0765

4321

4.615 msec= 8 • 577 µs

Fig. 2 Radio frequency channels RFC on Um



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Speech Channels(Full/Half)

DataChannels

(Data Rate)

Control ChannelsCCH

Traffic Channels TCH

Logical ChannelsBroadcast Control

Channel BCCH

Dedicated ControlChannel DCCH

Common ControlChannel CCCH

Fig. 3 Logical channel types



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Broadcast ControlChannel BCCH

Cell BroadcastChannel CBCH

SynchronizationChannel SCH

FrequencyCorrection Channel

FCCH

Broadcast ControlChannels BCCH

system information:cell identifier, cell parameter, channelconfiguration, cell frequencies,broadcast frequencies of neighbourcells

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

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

identification of BCCH frequency, MSfrequency synchronization

Fig. 4 Broadcast control channel

Paging ChannelPCH

Notification ChannelNCH

Access GrantChannel AGCH

Random AccessChannel RACH

Common ControlChannel CCCH

paging of a MS in all cells of alocation area for a mobileterminating call

paging of MS‘s in all cells of avoice group call area to performASCI (Advanced Speech Call Items)

answer to a random access,assignment of dedicatedsignaling channel

MS requests a dedicatedchannel from network

Fig. 5 Common control channel



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Fast AssociatedControl Channel

FACCH

Slow AssociatedControl Channel

SACCH

Stand AloneDedicated ControlChannel SDCCH

DedicatedControl

Channel DCCH

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

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

“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) + SACCH/H (0, 1)

2 half rate subscriber (speech or data)

c) FCCH + SCH + BCCH + CCCH

uplink: 800 000 RACH slots per hour downlink: 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 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) or TCH/F + FACCH/F + SACCH/TF or SDCCH/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 or Timeslot 0 → 8 (SDCCH + SACCH) Timeslot 1...7 → TCH/F + FACCH/F + SACCH/F



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F0

S1

BCCH2 - 5

CCCH6 - 9

F10

S11

CCCH12 - 19

F20

S21

CCCH22 - 29

F30

S31

CCCH32 - 39

F40

S41

CCCH42 - 49

I50

DL: F = FCCH, S = SCH, B = BCCH, C = CCCH, (PCH, AGCH), I = idle

UL: R = RACH

R0

R1

R10

R11

R20

R21

R30

R31

R40

R41

R50

Fig. 7 Multiframe for channel combination MAINBCCH

F S B C F S C C F S D0 D1 F S D2 D3 F S A0 A1 I

51 TDMA Frame = 235,38 ms

DOWNLINK: Broadcast Control Channel (BCCH), Common Control Channel (CCCH)+4 Stand Alone Dedicated Control Channels (SDCCH/4)

UPLINK: Common Control Channel (CCCH)+4 Stand Alone Dedicated Control Channels (SDCCH/4)

D3 R R A2 A3 R R R R R R R R R R R R R R R R R R R R R R R R RD0 D1 D2

D3 R R A0 A1 R R R R R R R R R R R R R R R R R R R R R R R R RD0 D1 D2

F S B C F S C C F S D0 D1 F S D2 D3 F S A2 A3 I

B BCCH C CCCH D SDCCH F frequency correction burst R RACH S synchronized burst I idle Fig. 8 Multiframe for channel combination MBCCHC (2xMBCCH makes SACCHBCCH multiframe =2x 235,38 msec)



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TT TT TT TT TT TT A TT TT TT TT TT -TT

t 2 Half Rate TCH

1 Full Rate TCH

26 frames = 120 ms

T tT tT tT tT tT A Tt Tt Tt Tt Tt aTt

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



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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.

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. 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

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 % 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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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, ...) 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 2 TS 3 TS 4 TS 5 TS 6 TS 7

SDCCH_POOL TCH_POOL TCH/SD_POOL

SDCCH_BACKUP_POOL

assignment

In case ofSDCCH request

Traffic Channel / SDCCH Request

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 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 trigger by an SDCCH request



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Parameters for Channel Configuration: 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 SDCCHPOOLTCHSDPOOLNULL (default)

Channel Pool Type must be defined if CH_TYPE=TCHSD

SDCCH_CONGESTION_ THRESHOLD

BTS SDCCHCONGTH 70 ... 100

(70)

[ % ] SDCCH Congestion Threshold

GUARD_TIMER_TCHSD BSC TGUARDTCHSD SEC00, (default)

SEC10 SEC11 SEC12 SEC13 SEC14 SEC15

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. 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:

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



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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 1 ----- 41 (0.35 sec) 55 (0.25 sec)

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.

tr = tx_integer = 6

retransmission

td = 163 slots

first transmissionwith a collision

Fig. 12 Retransmission of CHANNEL_REQUEST



24

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

set timer T3126wait for grant

WAITT3122

SDCCHAllocation

N

Y

Y

N

N

Y

number of retransmissions + 1

number ofretransmissions = 0

Select RACH slotfor first transmission

IMMEDIATEASSIGNMENTPROCEDURE

no.of retransmissions= max_retrans

immediate assignment

Send CHANNELREQUEST msg.

GRANT during Sup. time

Rejection

CELLRESELECTION

N

Y

Select RACH slot for next transmission,

wait for grant

Fig. 13 Immediate assignment procedure



25

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:



26

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



27

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.



28

1.5 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.

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 (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.



29

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 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.

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



30

CCCH Load

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)

→ ∼ 20000 subscriber (uncombined CCCH)



31

Parameters for Common Control Channel Configuration Specification Name Objec

t DB Name Range Meaning

RACH_BUSY_THRES BTS RACHBT 0...127

(109)

RACH busy threshold defined in steps of -1 dBm

MAX_RETRANS BTS MAXRETR ONE TWO

FOUR (default)SEVEN

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

TX_INTEGER BTS NSLOTST 0...15

(10)

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 for uncomb.

0...2 for comb. CCCH

(0)

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

BS_PA_MFRMS BTS NFRAMEPG 2...9

(2)

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

NCH_FIRST_BLOCK BTS NOCHFBLK 1...7

(1)

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

NCH_BLOCK_NUMBER BTS NOCHBLKN 1...4

(1)

number of downlink CCCH blocks to be used for NCH

TIMER_NCH BTS TNOCH 1...254

(16)

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



32

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 with a number of procedures since BR6.0 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. 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. 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



33

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

Cell A

Cell 1 Cell 2 Cell 3

common downlinkcommon downlink

common downlinkuplink

Fig. 14 Advanced speech call items - principle



34

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. This notification is sent as long as the relevant high priority call lasts, and will be repeated at a rate indicated by a new PERNOTFACCH 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).



35

Specification Name Obje

ct DB Name Range Meaning

ASCI_SERVICE BTS ASCISER ENABLED/

DISABLED (d)

enables or disables ASCI service on a cell basis

ASCI_UPLINK_REPLY BTS ASCIULR ULRDISABLE,

VBSENABLE

VGCSENABLE

VBC_VGCSENABLE

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

TIMER_UPLINK_REPLY BTS TUPLREP 5..60 s

(20)

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

NOTIFICATION_ FACCH BCS NOTFACCH NO SUPP,

ALWAYS,

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 BTS TGRANT 1-254

unit 10ms

(4)

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

VG_UPINK _FREE BTS VGRLUF 1-254

(2)

This parameter is used for the repetition of the UPLINK FREE message during the Talker Change procedure

ASCI_ONE _CH_MODEL BSC ASCIONE- CHMDL

TRUE/FALSE

(FALSE)

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

ENABLE _NCH_REPET

BTS ENPERNOTDE

TRUE, FALSE

(FALSE)

This attribute enables the repetition of notifications on dedicated channels

REPET_PER_FACCH BTS PERNOTFACCH

2,…10

(5)

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



36



37

2 Extended channel mode



38

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

Object DB Name Range Meaning

CELL_TYPE BTS CELLTYPE STDCELL EXTCELL DBSTDCELL

maximum range 35 km a cell covering, other cells maximum range 100 km, dual band standard cell

EXTENDED_MODE CHAN EXTMODE TRUE FALSE

defines if a channel is used in extended mode or not



39

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

Max 100 km

Max 35 km

BTS

0 42 3 51 6 7 TRX in Extended Cell(for near and far area)

EXTMODE=TRUE EXTMODE=FALSE

Fig. 15 Extended Cell



40



41

3 Adaptive Multirate AMR



42

3.1.1 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 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.



43

Channel Coding Speech Coding

Traffic Channel Full: Gross rate 22.8 kbit/s

Flexible

balance

Fig. 16 AMR principle

11,4 kbit/s

22,8 kbit/s

0 FR1 FR2 FR3 FR4 FR5 HR2 HR5 HR6

channel coding FR

channel coding HR

speech coding

FR6 FR7 FR8 HR1 HR4HR3

Fig. 17 AMR codecs



44

1.0

2.0

3.0

4.0

5.0

Conditions

MOS

EFR12.210.27.957.46.75.95.154.75

EFR 4.01 4.01 3.65 3.05 1.53

12.2 4.01 4.06 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 1.43

7.4 3.83 3.94 3.98 3.84 3.11 1.39

6.7 3.77 3.80 3.86 3.29 1.87

5.9 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

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

1.0

2.0

3.0

4.0

5.0

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

Conditions

DMOS

Sel. Requir.AMR-FREFRFRG.729

Fig. 19 AMR performance curves (full rate with street noise) acc. to ETSI study



45

1.0

2.0

3.0

4.0

5.0

Conditions

MOS

EFR7.957.46.75.95.154.75FRHR

EFR 4.21 4.21 3.74 3.34 1.58

7.95 4.11 4.04 3.96 3.37 2.53 1.60

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 3.50 3.14 2.74 1.50

HR 3.35 3.24 2.80 1.92

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

Fig. 20 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)

0.0%

20.0%

40.0%

60.0%

80.0%

100.0%

120.0%

50% 60% 70% 80% 90% 100%

AMR Penetration

Capa

city

Impr

ovem

ent 15 dB

20 dB

25 dB

HR Only

Fig. 21 AMR capacity gain acc. to ETSI study



46

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.



47

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 FR 5 only

5.90 FR 6 / HR 4 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 in-band on the radio interface.



48

3.1.2 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, …)

3.1.3 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_1,…, POOL_48

Pool type for TSLA (different from DEFPOOLTYP)

3.1.4 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 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.



49

3.1.5 Database parameters This table contains 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 this parameters with the same meaning that can be configured independently. One set is applied for AMR subscribers allocated on hopping and another on non hopping channels (e.g. FHAMRFRC1 and AMRRFC1 respectively). Parameter Object Range Description

AMRFRC1,

AMRFRC2,

AMRFRC3,

AMRFRC4

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,




AMRFRTH12 Threshold: 0 (0.0 dB)... 63 (31.5 dB), step is 0.5 dB;

Default: 7(3,5dB)

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

"Threshold-Hysteresis" related to the active codecs specified in the AMRFRC1 and AMRFRC2

AMRFRTH23 Threshold: 0 ... 63; Default: 12(6 dB)

Hysteresis: 0 ... 15(7,5dB Default: 4(2 dB)5


AMRFRTH34 Threshold: 0 ... 63; Default: 23(11,5 dB)

Hysteresis: 0... 15 (7,5dB) Default: 4 ( 2dB)


AMRHRC1

AMRHRC2,

AMRHRC3,

AMRHRC4

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…63 , Unit=CMR

(5 CMR)

Size of averaging window for Codec Mode Requests (CMR)



50

Parameter Object Range Description

AMRHRTH12 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

AMRHRTH23 Threshold: 0 ... 63

Default: 24 (12 dB)

Hysteresis: 0 ... 15

Default:4 (2 dB)


AMRHRTH34 BTS Threshold: 0 ... 63

Default: 26(13 dB)

Hysteresis: 0 ... 15

Default:4 (2 dB)

Null (BTS One)


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

AMRFRIC BTS 0:START_MODE_FR,

1:CODE_MODE_01,

2:CODE_MODE_02,

3:CODE_MODE_03,

4:CODE_MODE_04

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

Default:2

AMRHRIC BTS 0:START_MODE_HR,

1:CODE_MODE_01,

2: CODE_MODE_02,

3:CODE_MODE_03,

4:CODE_MODE_04

Initial HR codec mode

Default:2 for BTS Plus

Default:1 for BTS One

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



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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 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)

Carrier-to-interferenceratio C/I

Codec_Mode_4

Codec_Mode_3

Codec_Mode_2

Codec_Mode_1

Thr_3 + Hyst_3 = Thr_Mx_Up (3)

Thr_3 = Thr_Mx_Down (4)





Thr ThresholdHyst Hysteresis

Fig. 22 Threshold and hysteresis determine the switching "up" and "down" between codec modes in downlink



52

Complete table of Thresholds and Hysteresis for Link Adaptation AMR FULL RATE

Rate

1 (4.75 Kb/s)

2 (5.15 Kb/s)

3 (5.90 Kb/s)

4 (6.70 Kb/s)

5 (7.40 Kb/s)

6 (7.95 Kb/s)

7 (10.2 Kb/s)

8 (12.2 Kb/s)

1 (4.75 Kb/s) 4.0 3.5 5.0 5.5 5.0 6.5 7.5 2 (5.15 Kb/s) 3.0 5.0 5.5 5.0 6.5 8.0 3 (5.90 Kb/s) 6.0 6.5 6.0 7.0 8.5 4 (6.70 Kb/s) 7.0 6.0 7.5 9.5 5 (7.40 Kb/s) 3.5 8.0 10.5

6 (7.95 Kb/s) 10.0 11.5

7 (10.2 Kb/s) 11.0 8 (12.2 Kb/s)

Table: Default values for the AMR Full Rate Thresholds attributes, table units are in dB so each entry value has to be doubled to obtain the corresponding parameter unit value.

AMR HALF RATE

Rate

1 (4.75 Kb/s)

2 (5.15 Kb/s)

3 (5.90 Kb/s)

4 (6.70 Kb/s)

5 (7.40 Kb/s)

6 (7.95 Kb/s)

1 (4.75 Kb/s) 9.5 11.0 12.0 12.5 13.5 2 (5.15 Kb/s) 12.0 12.5 13.5 14.0 3 (5.90 Kb/s) 13.0 14.5 15.0 4 (6.70 Kb/s) 14.5 15.0 5 (7.40 Kb/s) 16.0 -

Table: Default values for the AMR Half Rate Thresholds attributes, table units are in dB so each entry value has to be doubled to obtain the corresponding parameter unit value



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The AMR link adaptation is based on the quality of the 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. PC and HO decisions however are still based on RXQUAL values which are then mapped into C/I values. The following mapping between C/I values and RXQUAL values is applied:

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



54



55

4 Channel allocation strategy



56

4.1 Basic Allocation of the radio channels is not only based on the best interference band as it was in early SBS releases but is 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) has been done in the SBS BR8.0 by introducing the feature “Multi Service Layer Support'.



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

BR6.0

BR7.0

BR8.0

Service dependent Channel Allocation Strategy (SDCA)

BCCH TRX Packet Switchedtraffic

Downgrade Strategy: HSCSD first

Service dependent Power Control and Handover

Service Group 1Service Group 2

Service Group 14

Thresholds

Enable / Disable

BTS

Service List:• CS speech• Signaling• GPRS...

Layer 1Layer 2

Fig. 23 SDCA history



58

4.2 Multi Service Layer Support Operators can split-up the frequency spectrum of their network to supply a variety of services based on their 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.



59

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).



60

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, 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, an 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: 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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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Service List

Service 1(e.g. signaling)

Service 2(e.g. GPRS)

Service 3(e.g. cs data)

Service 4(e.g. cs speech)

Layer 1

Layer 2

Layer 3

TRX 0

TRX 1

TRX 2

TRX 3

TRX 4

TRX 5

List of all orselected of the 9 service types

Service layer list defined per service, e.g.

signaling -> LY1

GPRS -> LY1, LY2

cs data -> LY2, LY1

cs speech -> LY3, LY2, LY1

TRX with same expected C/I are assigned to layers, e.g.

LY 1 -> TRX 0

LY 2 -> TRX 1, TRX 2

LY 3 -> TRX 3, TRX 4, TRX 5

Fig. 24 Allocation example



62

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.

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

In the BSC DB object (SET) BTS the new 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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4.3 Database parameters

Parameter Object Range Description DGRSTRGY BTS HSCSD_FIRST_DOWN

GRADE, GPRS_FIRST_DOWNGRADE, DOWNGRADE_HSCSD_ONLY, DOWNGRADE_GPRS_ONLY, NO_DOWNGRADE (default)

Downgrade strategy

<x>LLPRM BTS LY_00, LY_01,… LY_11, (NULL)

Primary Service List for the corresponding service. X = AMRFR, AMRHR, ASCI, S, CRTSWD,CRTSWSPE, E, G, HSCSD.

Multiple selection possible

<x>LLCOM BTS LY_00, LY_01,… LY_11, (NULL)

Complementary Service List for the corresponding service. X = AMRFR, AMRHR, ASCI, S, CRTSWD,CRTSWSPE, E, G, HSCSD.

Multiple selection possible

LAYERID TRX LY_00, LY_01,… LY_11, (NULL)

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

EMANPRESPRIM

PTPPKF

0-190 (0)

Number of channels that are reserved for EGPRS

EPA BSC TRUE, FALSE (FALSE) Enable HR channels pairing

EPAT1 BTS 0…10000, unit:0,01% (6000)

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



64

Parameter Object Range Description EPAT2 BTS 0…10000,

unit:0,01% (6000)

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, FALSE (default) Enable cell load dependent HR activation

HRACTT1 BTS 0 ... 10000 (default 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 (default 6000)

Threshold 2 for HR activation: percentage of busy TCH for the 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 HSCSH. 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

Task 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 sector/site 0 ... 11, 23 Pico

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 ... 11

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

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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Solution 3 Title: Determining the highest "Trunking Gain" for the operator's

system

Task 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

Task 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

Task

The first step is to define in the TRX object the layers. BCCH TRX is defined as LY0 (best quality) The other two are defined as LY1 (normal quality). Therefore three available TRX are building 2 Layers:

• LY0 (BCCH)

• LY1 (TCH1, TCH2) 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 only. SLL1 system will look for resources on BCCH, and in case of channel congested will move to TCHs of TRX1. For SLL2 the services allocation will take place on TCHs of TRX2 and in case of congestion on BCCH.



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HSCSD4

GPRS3

CS speech2

Signaling (SDCCH)1

Service TypePriority

SLL2 (LY1, LY0)HSCSD4

SLL1 (LY0, LY1)GPRS3

SLL2 (LY1, LY0)CS speech2

SLL0 (LY0)Signaling (SDCCH)1

SLLService TypePriority

Fig. 25 Service List and Service Layer List



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TRX:NAME=BTSM:0/BTS:0/TRX:0,TRXFREQ=BCCHFREQ,PWRRED=0,RADIOMR=ON,RADIOMG=2,MOEC=TRUE,TRXAREA=NONE,LPDLMN=0,TRXMD=GSM,MAIO=<NULL>,FHSYID=<NULL>,LAYERID=LY_00,USFGRAN=DISABLED;

TRX:NAME=BTSM:0/BTS:0/TRX:1,TRXFREQ=CALLF01,PWRRED=0,RADIOMR=ON,RADIOMG=2,MOEC=TRUE,TRXAREA=NONE,LPDLMN=0,TRXMD=GSM,MAIO=<NULL>,FHSYID=<NULL>,LAYERID=LY_01,USFGRAN=DISABLED;

TRX:NAME=BTSM:0/BTS:0/TRX:2,TRXFREQ=CALLF02,PWRRED=0,RADIOMR=ON,RADIOMG=2,MOEC=TRUE,TRXAREA=NONE,LPDLMN=0,TRXMD=GSM,MAIO=<NULL>,FHSYID=<NULL>,LAYERID=LY_01,USFGRAN=DISABLED;

BTS:NAME=BTSM:0/BTS:0, SLLPRM=LY_00, CRTSWSPELLPRM=LY_01&LY_00,GPRSLLPRM= LY_00&LY_01,HSCSDLLPRM=LY_01& LY_00…;

Fig. 26 Database entry example



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Documents

23295351 01 Mn1789eu11mn 0001 Channel Configuration