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Modul 4 signalling dimensioning

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Explain 2G signalling and dimensioning of it.

Explain 2G signalling and dimensioning of it.

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  • Depending on the capacity requirements , we can define the signaling channels in two different ways.They have trade offs! Paging and the immediate assignment processes use the same resources on the signaling channels, CCCHs. There can be different strategies in defining their priorities to escjh other. PCH has in normal case priority to AGCH.
  • Channels can be configured with different parameters. There are parameters directly related to PCH, AGCH, FACCH and RACH. Parameter noOfMultiframesBetweenPaging (2 ... 9) tells how often paging messages are sent to Mobile Stations. There is a direct influence on the battery saving of a Mobile Station. The Mobile Station will only need to listen the paging sub-group it belongs to (Discontinuous Reception, DRX), which will make the mobile spend less power. However this makes the call assignment time longer. The mobile unit listens for a possible incoming paging message once every noOfMultiframesBetweenPaging, therefore min. every 0.47 seconds and max. every 2.1 seconds when the noOfMultiframesBetweenPaging is 9. This means that if in average it takes 2 paging messages to page a mobile, it’ll take from 1 to 4 seconds. NumberOfBlocksForAccessGrant (0 ... 7) is a parameter for reserving the number of CCCH blocks for AGCH (figure 6). CCCH blocks are used either for PCH or for AGCH. The configuration of RACH takes two parameters; maxNumberOfRetransmission (1, 2, 4 or 7) and numberOfSlotsSpreadTrans (3 ... 12, 14, 16, 20, 25, 32, 50 . NumberOfSlotsSpreadTrans describes a window when Mobile Station tries to send random access to Base Station. MaxNumberOfRetransmission describes the maximum amount of times the Mobile Station can send random access to the Base Station, whenever the previous time failed. So if MaxNumberOfRetransmission is set to "2", the MS will try a first time to send the message within the window defined within a first 51-TDMA RACH multiframe. Then if no reply comes from the network, the MS will try a second time (or as many times as needed till a maximum as specified in the MaxNumberOfRetransmission parameter) within a window of another 51-TDMA RACH multiframe. All the above mentioned parameters belong to the GSM phase 1. The last parameters used for channel configurations are newEstabCallSupport (Yes/No) and facchCallSetup (0 ... 4), which are used only in GSM phase 2 . The parameter itself contains information concerning the possibility to use FACCH in call assignment procedure as SDCCH or not.
  • Transcript

    • 1. GSM-GPRS Operation Signalling Dimensioning Module 4
    • 2. kris.sujatmoko@gmail.com 2 Outline  Channel Configuration  SDCCH Capacity  Paging Capacity  LA Size
    • 3. GSM-GPRS Operation Channel Configuration
    • 4. 4 Hierarchy Of Channel kris.sujatmoko@gmail.com
    • 5. 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 kris.sujatmoko@gmail.com
    • 6. 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 kris.sujatmoko@gmail.com
    • 7. 7 Configuration Of Signalling Channels – CCH Downlink kris.sujatmoko@gmail.com
    • 8. 8 Configuration Of Signalling Channels – CCH Downlink kris.sujatmoko@gmail.com
    • 9. 9 Configuration Of Traffic Channel - TCH kris.sujatmoko@gmail.com
    • 10. 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 kris.sujatmoko@gmail.com
    • 11. 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 kris.sujatmoko@gmail.com
    • 12. 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) kris.sujatmoko@gmail.com
    • 13. 13 Channel Configuration - Combined kris.sujatmoko@gmail.com
    • 14. 14 Channel Configuration - Separated kris.sujatmoko@gmail.com
    • 15. 15 Channel Configuration - Hybrid kris.sujatmoko@gmail.com
    • 16. 16 SDCCH Dimensioning  SDCCH used for:  Call setup signalling  Short message service (SMS)  Location update (LU)  IMSI attached/detached kris.sujatmoko@gmail.com
    • 17. 17 SDCCH Dimensioning (2) kris.sujatmoko@gmail.com
    • 18. 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 kris.sujatmoko@gmail.com
    • 19. 19 SDCCH Dimensioning (3)  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 kris.sujatmoko@gmail.com
    • 20. 20 SDCCH Dimensioning (4)  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 kris.sujatmoko@gmail.com
    • 21. GSM-GPRS Operation Parameters Related To Channel
    • 22. 22 Common Control Channel Load kris.sujatmoko@gmail.com
    • 23. 23 Common Control Channel Load (2) kris.sujatmoko@gmail.com
    • 24. 24 Common Control Channel Load (3)  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 kris.sujatmoko@gmail.com
    • 25. 25 Common Control Channel Load (4)  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 kris.sujatmoko@gmail.com
    • 26. 26 Common Control Channel Load (5)  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 kris.sujatmoko@gmail.com
    • 27. 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) kris.sujatmoko@gmail.com
    • 28. 28 Common Control Channel Load (7) - RACH  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 kris.sujatmoko@gmail.com
    • 29. 29 Common Control Channel Load (8) - RACH  values for 50000 RACH activities per hour kris.sujatmoko@gmail.com
    • 30. 30 Common Control Channel Load (9) - RACH  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 kris.sujatmoko@gmail.com
    • 31. 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 kris.sujatmoko@gmail.com
    • 32. 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 kris.sujatmoko@gmail.com
    • 33. 33 Common Control Channel Load (12) - Example kris.sujatmoko@gmail.com
    • 34. 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 kris.sujatmoko@gmail.com
    • 35. 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 kris.sujatmoko@gmail.com
    • 36. 36 Common Control Channel Load (12) – Paging 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 kris.sujatmoko@gmail.com
    • 37. 37 Common Control Channel Load (13) – Paging 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 kris.sujatmoko@gmail.com
    • 38. 38 Common Control Channel Load (14) – Paging 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 kris.sujatmoko@gmail.com
    • 39. 39 Common Control Channel Load (15) – Paging 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 kris.sujatmoko@gmail.com
    • 40. 40 Common Control Channel Load (16) – Paging 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) kris.sujatmoko@gmail.com
    • 41. 41 Common Control Channel Load (17) – Paging Capacity  For Combined BCCH kris.sujatmoko@gmail.com
    • 42. 42 Common Control Channel Load (18) – Paging 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 kris.sujatmoko@gmail.com
    • 43. 43 Common Control Channel Load (19) – Paging Capacity  For Non Combined BCCH kris.sujatmoko@gmail.com
    • 44. GSM-GPRS Operation Location Area Design
    • 45. 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) kris.sujatmoko@gmail.com
    • 46. 46 LA Size – SDCCH Traffic calculation kris.sujatmoko@gmail.com
    • 47. 47 LA Size – SDCCH Traffic calculation (2) kris.sujatmoko@gmail.com
    • 48. 48 LA Size – Paging Capacity kris.sujatmoko@gmail.com
    • 49. 49 LA Size – Paging And AG Traffic Demand kris.sujatmoko@gmail.com
    • 50. GSM-GPRS Operation End of Section 4 Signalling Dimensioning