Modul 4 signalling dimensioning

GSM-GPRS Operation
Signalling Dimensioning
Module 4

kris.sujatmoko@gmail.com 2
Outline
 Channel Configuration
 SDCCH Capacity
 Paging Capacity
 LA Size

GSM-GPRS Operation
Channel Configuration

4
Hierarchy Of Channel
kris.sujatmoko@gmail.com

5
MS Mode
Search for Frequency Correction Burst
Search for Synchronisation sequence
Read System Informations
listen for Paging
send Access burst
wait for signalling channel allocation
Call setup
traffic channel is assigned
Conversation
Call release
FCCH
SCH
BCCH
PCH
RACH
AGCH
SDCCH
FACCH
TCH
FACCH
idle mode
“off” state
dedicated
mode
idle mode

6
0 7
ts0=bcch/pch/agchts1=sdcch/8
0 7
ts0=bch/sdcch/4/pch/agch
Combined Configuration
Time slot 0 contains 1 BCCH, 3 CCCH and 4
SDCCH
0 7
ts0=bcch/pch/agch/sdcch/4
ts1=sdcch/8
Non-Combined Configuration
Time slot 0 contains 1 BCCH, 9 CCCH
Time Slot x (<>0 of BCCH TRX) contains 8
SDCCH
Hybrid Configuration
Time slot 0 contains 1 BCCH, 3 CCCH, and 4
SDCCH
Time Slot x (<>0 of BCCH TRX) contains additional
8 SDCCH
Configuration of Signalling Channels

7
Configuration Of Signalling Channels – CCH Downlink

8
Configuration Of Signalling Channels – CCH Downlink

9
Configuration Of Traffic Channel - TCH

10
r r rr r r r fr rr r r r r r rr r r rr fr r r r r rr r r r fr r r r rr r r rr fr r r r rr r rr
Uplink
f s bb bbc fc fc scccc cc ccfc fscccc cc cc f fcccc cc cc fs fcccc cc ccs
Downlink 51 TDMA frames = 235ms
r
Time Slot 0
CHANNELS f = FCCH b = BCCH r = RACH
s = SCH/SACCH c = CCCH t = SDCC
Non-Combined Configuration
BCCH/CCCH Multiframe

11
CHANNELS t = SDCCH/8 s = SACCH/8
t t tt t t t ft tt t t t t t tt t t tt ft t t t t tt t t t fssss ss s ss fssssss
ss ss sss fs ss s t tt t t ts ft t t t t tt t t t ft t t t tt t t tt ft t t t tt t tt
Downlink
Uplink
t
t
51 TDMA frames = 235 ms
s
1. 2. 3. 5. 6. 7. 8.4.
Time Slot 1
Non-Combined SDCCH/8 Multiframe

12
Channel Combination
 The following combinations of logical channel types are
allowed for the radio timeslots and specified by GSM
(Rec. 05.02):
 TCH/F + FACCH/F + SACCH/TF
 TCH/H + FACCH/H + SACCH/TH
 SDCCH/8 + SACCH/C8
 FCCH + SCH + BCCH + CCCH (TS 0)
 FCCH + SCH + BCCH + CCCH + SDCCH/4 + SACCH/C4 (TS 0)
 BCCH + CCCH
 SDCCH/8 + SACCH/8 + CBCH
 FCCH + SCH + BCCH + CCCH + SDCCH/4 + SACCH/C4 + CBCH (TS
0)

13
Channel Configuration - Combined

14
Channel Configuration - Separated

15
Channel Configuration - Hybrid

16
SDCCH Dimensioning
 SDCCH used for:
 Call setup signalling
 Short message service (SMS)
 Location update (LU)
 IMSI attached/detached

17
SDCCH Dimensioning (2)

18
SDCCH Dimensoning (2)
 TCH load per subscriber = [ # of call attempts per sub per hour*
%MOC
+ # of call attempts per sub per call*%MTC*(1-%no response)*(1-%
no answer)*%MTC success] * mean call duration / 3600
= [ 1.1 * 60% + 1.1 * 40% * (1-32.5%) * (1-13.5%) * 54%] *
115/3600
= 0.026 Erlang
 SDCCH load per subscriber = [number of call attempts*setup
signalling + #LU per sub per hour*duration for loc update] / 3600
= [1.1 * 3 + 2.2 * 5] / 3600
= 0.004 Erlang

19
 A cell with 2 TRXs
 Combined SDCCH
 1 comb. CCCH/SDCCH →4 SDCCH
 15 TCH
 Offered TCH load at 2% blocking
 9.01 Erlangs  9.01/0.026=346 subscribers
 Offered SDCCH load at 1% blocking
 4 SDCCH blocks for combined configuration
 Thus from Erlang B table, lookup 4 channels at 1%
blocking
 0.87 Erlangs  0.87/0.004=217 subs
 SDCCH limited: 217 subscribers

20
 Non-combined SDCCH
 1 SDCCH/8 →8 SDCCH
 14 TCH
 Offered TCH load at 2% blocking
 8.20 Erlangs  8.20/0.026=315 subscribers
 Offered SDCCH load at 1% blocking
 8 SDCCH blocks for non-combined configuration
 Thus from Erlang B table, lookup 8 channels at 1%
blocking
 3.13 Erlangs  3.13/0.004=782 subs
 TCH limited: 315 subscribers
 This configuration is preferred as it is TCH limited

GSM-GPRS Operation
Parameters Related To Channel

22
Common Control Channel Load

23
Common Control Channel Load (2)

24
 CCCH Capacity
 Calculation (non-combined):
 Uplink : 51*3600/(51*0.004615) = 780000 RACH slots per
hour
 downlink : 36*3600/(51*0.004615) = 137658 CCH blocks per
hour

25
 CCCH Capacity
 Calculation (combined):
 Uplink : 27*3600/(51*0.004615) = 413000 RACH slots per
hour
 downlink : 12*3600/(51*0.004615) = 45886 CCH blocks per
hour

26
 CCCH Capacity
 1 RACH slot : a channel message for 1
subscriber
 1 CCCH block (4 slots): 1 paging message for 1..4
subscribers* or
 1 access grant message for 1..2 subscribers
* Depends on IMSI(2) or TMSI(4) paging

27
Common Control Channel Load (6) - RACH
 Used by MS to request a dedicated channel
(SDCCH)
 The causes for the channel request can be:
 A paging response in MTC
 An emergency call
 A MOC
 LU or
 IMSI attach/detach
 Parameters related to RACH
 maxNumberOfRetransmission (1, 2, 4 or 7)
 numberOfSlotsSpreadTrans (3 ... 12, 14, 16, 20, 25, 32,
50)

28
 The combination of maxNumberOfRetransmission and
numberOfSlotsSpreadTrans values determine the time period
between sending of two channels requests.
 This period is measured in RACH slots and is the sum of a
deterministic part S and a random part tr. (refer to GSM 04.08)
 RACH can be configured in combined and non-combined case
 Combined: all 27 timeslot0 out of 51 timeslots
 Non-combined: all timeslot0,2,4,6

29
 values for 50000 RACH activities per hour

30
 The minimum blocking is achieved by the following
setting of parameters: maxNumberOfRetransmission =
7, numberOfSlotsSpreadTrans = 50
 The configuration of CCCH is mainly determined by the
capacity needed by the downlink channels, the RACH
configuration is uncritical

31
Common Control Channel Load (10) - PCH
 PCH may be used as AGCH but not vice-versa
 MOC requires AGCH and MTC requires PCH
 Typical network will have MOC higher than MTC
 Strategy: to dimension the AGCH to a smaller value
and let the system organise the use of channels
 Parameter related to PCH:
 noOfMultiframesBetweenPaging (2 ... 9)
 It indicates the number of TDMA multiframes between
transmission of paging message to the same paging sub-
group
 It impacts on the MS battery life and MTC setup time
 Higher value will save battery life but longer call setup time
and vice versa
 Recommended value is 5

32
Common Control Channel Load (11) - AGCH
 Parameter related to AGCH:
 NumberOfBlocksForAccessGrant (0 ... 7)
 It defines the number of blocks reserved for
access grant messages from the CCCH during
the 51 TDMA frame (a multiframe)
 Recommended value is 1 for combined and 2 for
non-combined configuration
 Note that if the AGCH is insufficient, PCH can be
used as AGCH

33
Common Control Channel Load (12) - Example

34
Common Control Channel Load (12) –
Example Cont..
 Analysis:
 DL CCCH (PCH and AGCH) is the limiting factor
 The usage for PCH and AGCH is almost equal
For MOC, response to paging in MTC, LU and IMSI attached/detached, thus 4
RACH
activities per sub per hour

35
Common Control Channel Load (12) – Paging
Capacity
 Paging demand is a function of:
 Number of MTC
 Number of subscribers in the LAC
 Paging repetition
 PCH can be configured as combined or non-combined :
 Combined: both BCCH and SDCCH occupy the TS0
 12 out of 51 slots per multiframe form 3 PCH/AGCH,
each block consists of 4 slots

36
Capacity
 PCH can be configured as combined or non-combined:
 Non-combined: BCCH occupies TS0 and SDCCH occupies TS1
 36 out of 51 slots per multiframe form 9 PCH/AGCH, each block
consists of 4 slots
 Split of blocks between PCH and AGCH: the available blocks in 51
multiframe is splitted between PCH and AGCH and it is set by
parameter NumberOfBlocksForAccessGrant

37
Capacity
 IMSI/TMSI paging:
 IMSI: 2 mobiles can be paged with each page
message occupying 4 slots
 TMSI: 4 mobiles can be paged with each page
message occupying 4 slots
 Paging capacity calculation:
 PCH per second

38
Capacity
 What does the table mean?
 CCCH can be used for both AGCH and PCH
 Example for combined configuration, 3 CCCH blocks are
available
 If u reserve 0 blocks for AGCH, all 3 CCCH blocks will be used
for PCH
 If u reserve 2 blocks for AGCH, only 1 CCCH blocks will be used
for PCH

39
Capacity
 For combined BCCH:
 Making sense out of the table:
 Number of MS that can be paged in a
second:
 Depends on IMSI or TMSI paging and
 Number of blocks reserved for AG

40
Capacity
 For Combined BCCH
 Example: if u reserved 1 block for AG, then u
have 2 blocks for PCH
 If u decide TMSI paging, I.e. 4 MS can be paged
with 1 block of PCH
 Thus; (number of PCH blocks*number of pages
per block)/(51*one TDMA frame period);
 =(2*4) / (51*0.004615) = 34
 34 MS can be paged in a second (using TMSI
paging)

41
Capacity
 For Combined BCCH

42
Capacity
 For Non Combined BCCH
 Making sense out of the table:
 3 blocks reserved for AG, remaining 6 blocks used for PCH
 Number of MS can be paged in a second (TMSI paging)
 = (6*3)/(51*0.004615) = 76 MS/second

43
Capacity
 For Non Combined BCCH

GSM-GPRS Operation
Location Area Design

45
Location Area Design
 What is Location Area?
 A location area is an area in which MSs may
roam without updating the location registers
 A location area consists of one or more cells
 What information you need?
 Traffic model
 • What is next?
 Calculate SDCCH traffic
 Determine paging capacity
 Calculate LA size (in term of number of cells)

46
LA Size – SDCCH Traffic calculation

47
LA Size – SDCCH Traffic calculation (2)

48
LA Size – Paging Capacity

49
LA Size – Paging And AG Traffic Demand

GSM-GPRS Operation
End of Section 4
Signalling Dimensioning

Modul 4 signalling dimensioning

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