19. Bursts Frequency Bursts: All 148 bits(142+6) are coded with 0. The output of GMSK Modulator is a fixed frequency signal exactly 67.7 Khz above the BCCH carrier frequency. Thus the MS on receiving this fixed frequency signal fine tunes to the BCCH frequency and waits for the Sync burst to arrive after 1 TDMA Frame .i.e =15/26*8=4.615ms
20. Bursts Synchronization Bursts: This burst is used for time synchronization of the MS 39Bit x 2=78 Bits :Are decoded to arrive 25-SCH control bits and that contains the information of the NCC ,BCC & TDMA FN 64 Bits : Long training seq. of 64 Bits are identical for all BTS
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22. Bursts Dummy Bursts: To enable the BCCH frequency to be transmitted with a constant power level, dummy burst are inserted. This burst is transmitted on CHGR=0 when no other type of burst is to be sent. Thus it makes possible for MS to perform the power measurement on the BTS in order to determine which BTS to use for initial access or which to use for HO CCCH is replaced by the dummy page, when there is no paging message to transmit. 58Bits: Coded with pseudo random bit seq. to prevent confusion with Freq correction burst
23. Mapping of Logical Channel Method of transmitting logical channels onto physical channel is called Mapping FCCH+SCH+BCCH+CCCH: An idle MS search for the FCH. When MS finds the frequency correction burst it knows that this is TS 0 on CHGR=0 The cycle means F,S,B repeats after the Idle frame I.e. at Frame no 50. Cycle=51TS
24. Mapping of Logical Channel SDCCH+SACCH: Cycle=102 TS This sequence is repeated after last idle frame. The Uplink & Downlink pattern are time shifted, so SDCCH sub channel is sent in frame 0-3 on downlink and in frame 15-18 on uplink. The reason for this is to achieve efficient communication, by giving MS time to calculate its answer to the request received on down link SDCCH
25. Mapping of Logical Channel TCH+SACCH: 0&2 used by control channels. This leaves TS-1and 3-7 free for the use by TCHs. Repetition time (Cycle) =26 Frames .i.e. =26*8*(15/26)=120ms Every 13 th TS contains SACCH. Downlink contains TA value and Uplink contains measuring report.
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27. Possible Configurations SDCCH/8 : 8 Sub channels for signaling are mapped on 1 TS, this results 1 less TCH for the cell. SDCCH/4 (Combining BCCH and SDCCH) :4 Sub channels for signaling are mapped on BCCH TS. As a result Paging capacity on BCCH is reduced by 1/3. CBCH : If CBCH is active 1 sub channel of SDCCH is replaced by 1 CBCH channel. Limitations : SDCCH/8 in a cell = Number of TRX’s
31. SDCCH Holding Time Normal Location Updating = 3.5 Sec Periodic Registration = 3.5 Sec IMSI Attach = 3.5 Sec IMSI Detach = 2.9 Sec (IMSI detach Indication message sent to NW, no authentication is performed (which normally takes 0.6Sec) & no ack is sent to MS.) Call Setup = 2.7 Sec (MOC) = 2.9 Sec (MTC) Short Message Service(SMS) = 6.2 Sec (Vary depending the length of SMS) Fax Transmission = 2.7 Sec (MOC) = 2.9 Sec (MTC) False Access = 1.8 Sec (when Channel req is rec’d by system ,as SDCCH is allocated by sending Imm Ass message, and the system waits a certain time before performing disconnection.)
32. SDCCH Traffic Estimations Normal Location Update : Mean Holding time =3.5 Sec No of Location update =1.0 per sub and BH AC: Avg No of Location updates =1000X(1 X 3.5)/3600=0.972 mE/Sub IC : No Location updating at all =1000X(0 X 3.5)/3600=0 mE/Sub BC: 3 times the Avg no of Location updates =1000X(3 X 3.5)/3600=2.916mE/Sub SMS : Mean Holding time =6.2 Sec No of SMS submitted =1.0 per Sub and BH Traffic : 1000 X (1.0 X 6.2) / 3600 =1.7 mE/sub Call Setup : Mean Holding time =2.7 Sec(MOC) & 2.9 Sec(MTC) Mob Originating Traffic (Incl B Ans) =0.8 BHCA Mob Terminating Traffic (Incl B Ans) =0.4 BHCA Traffic : 1000 X {(0.8 X 2.7)+(0.4 X 2.9)} / 3600 =0.9 mE/sub
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39. SDCCH Dimensioning Immediate Assignment on TCH : In case of this feature on the channel administration assigns TCH for signaling instead of an SDCCH, based on 7 different channels allocation strategies (CHAPs) TCH first strategy : Decreases the SDCCH load and enable to use SDCCH/4 in all the cells Traffic load on TCH will in this case increases substantially so this strategy is not recommended. SDCCH first strategy : SDCCH is always allocated first if available, otherwise signaling is performed on TCH.
40. SDCCH Dimensioning Example : ASSUME: CELL=3TRX ,SDCCH Traffic =4 Erlang, Bcchtype=NCOMB.No CBCH GOS: SDCCH/4 = 1%, SDCCH/8 =0.5% & TCH % =2% 1> When Immediate Assignment on TCH not used Erlang B Table :To maintain 0.5 % GOS & 4 Erlang min 13 Subchannels reqd 2SDCCH/8 => TCH=(3TRX*8TS) –(1BCCH)-(2SDCCH/8)=21TCH’s 21TCH’s with 2 % GOS => 14.04 Erlang 2> When Immediate Assignment on TCH used If we use 1SDCCH/8 only than 4 Erlangs with 8 sub channels GOS=>3 % Congested Erlang will be =4 Erlang x 3 %=0.12Erlang 1SDCCH/8 => TCH=(3TRX*8TS) –(1BCCH)-(1SDCH/8)=22TCH’s 22TCH’s with 2 % GOS => 14.9 Erlang Actual TCH Capacity=14.9 – 0.12 = 14.7 Erlang TCH Capacity in the cell is increased with 0.7 Erlang
43. SDCCH Dimensioning HALF RATE CAPACITY CALCULATION Half rate will affect SDCCH dimensioning since more signaling will be req’d when no of TCH is increased. Important dimensioning factor is therefore the Half rate penetration .i.e.the % of Half rate mobile in a NW. Example: 2 TRX Cell, Half Rate Penetration =10 %, 1 SDCCH/8 TCH/F =14 support 14 Subscriber Penetration 10% of 14 is 1.4 = 2 Subscribers (Req’d 2 Half Rate TCH/H) Total 13 TCH/F+2TCH/H = 15 TCH required Capacity : Erlang B Table: 15 TCH @ 2% GOS => 9.0096 Erlang
44. SDCCH Dimensioning Max Allowed SDCCH/TCH Load Ratio (Half Rate) AC : Average Cells BC : Border Cells IC : Inner Cells
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46. Parameters MFRMS :This parameter defines period of transmission for PAGING REQUEST messages to the same paging subgroup. T3212 : Is the periodic registration timer ACCSTATE : Activate/Deactivate the Adaptive config of logical channel feature per cell basis CHAP :Selecting Channel Allocation profile per cell. SLEVEL: The attempt to increase the number of SDCCH/8 will take place when allocation of an SDCCH has failed due to congestion. STIME : Parameter STIME determines how long the system waits before the number of SDCCH/8 added by this function is decreased when the demand for signalling channels has returned to a low level BTDM : Implicit detach supervision should be equal or longer than T3212 in BSC. GTDM : is an extra Gurad time in minutes before the subscriber is set to detach. RLINKT : Radio link time-out This parameter defines the time before an MS disconnects a call due to failure in decoding SACCH messages. The parameter is given as number of SACCH periods (480ms).
48. STS Counters CCALLS : Call attempt counter CCONGS : Congestion counter CTRALACC : Traffic level accumulator. CNSCAN : Number of accumulations of SDCCH traffic level counter. CNDROP : Dropped connections due to Failure. CNUCHCNT : Number of defined channels. CAVAACC : Available channels accumulator. CMSESTAB : Successful MS channel establishment on SDCCH s. CTCONGS : S DCCH congestion time ( Sec)
49. Formulas No. of SDCCH Attempts CCALLS SDCCH Congestion (%) 100 X { CCONGS / CCALLS } No. of SDCCH Connections CMSESTAB SDCCH Establishments No Congestion (%) 100 X {CMSESTAB / (CCALLS - CCONGS)} SDCCH Time Congestion (%) 100 X { CTCONGS / (RPL * 60)} SDCCH Drop (%) 100 X { CNDROP / CMSESTAB } SDCCH Mean Holding Time (Sec.) RPL X 60 X {(CTRALACC/CNSCAN) / CMSESTAB } SDCCH Traffic (Erlang) CTRALACC / CNSCAN SDCCH/TCH Ratio (CTRALACC/CNSCAN) / ((TFTRALACC/TFNSCAN)+(THTRALACC/THNSCAN))
52. Call Setup-Mobile Terminating Call 1>Paging(LAI+IMSI/TMSI) 2>Paging Command Imsi/Tmsi+PG+TRX+CG+TN 3>Paging Req(Imsi on PCH) 4>Channel Req(On RACH) 5>Channel Reqd (Access Delay) 6>Channel Actn (MSPwr,BSPwr,TA) 7>Channel Activation Ack 8>Imm Assign Cmd(On AGCH , Freq +TS+ SDCCH SubChannel No+TA 8>Immediate Assign 9>Estblish Ind (Paging Resp) IMSI+MS Class 9>Conn Req (Paging Resp: BSC add CGI) 10>Auth Req (128 bit RAND+ 3bit CKSN) 10>Auth Req (128 bit RAND+3bitCKSN) 10>Auth Req (128 bit RAND+3bitCKSN) 11>Auth Response (MS Calculate SRES & Kc with its own Ki stored in SIM by appling algorithm A3&A8) 11>Auth Response (SRES) 11>Auth Response (SRES) SABM (Paging Resp:IMSI/MS Class) UA(Paging Resp) Unnumbered Ack Frame which confirms only 1 MS is using Sig Channel PCH RACH AGCH SDCCH SDCCH Next.. MS BTS BSC MSC
53. Call Setup-Mobile Terminating Call 14>Setup (Req for Services I.e. Speech/Data/Fax etc) 15>Call Confirmed 17>Channel Activation (BSC Allocated Idle TS for Traffic) 20>Assign Comp (MS tune to TCH and send Ind that Chan is Seized) 14>Setup 14>Setup 15>Call Confirmed 15>Call Confirmed 16>Assignment Req (MSC send CIC to BSC) 18>Channel Activation Ack 19>Assignment Cmnd (BSC send message on SDCCH to MS telling to go TCH) 19>Assignment Cmnd (BSC send message on SDCCH to MS telling to go TCH) 20>Assign Comp (MS tune to TCH and send Ind that Chan is Seized) 20>Assign Comp (MS tune to TCH and send Ind that Chan is Seized) 21>RF Chann Realease 21>RF Chann Realease Ack 22>Alert (MS Send Alert to MSC as soon as the ringing is started in MS) 22>Alert (MS Send Alert to MSC as soon as the ringing is started in MS) 22>Alert (MS Send Alert to MSC as soon as the ringing is started in MS) 23>Connect ( When MS Sub Answer the Conn message sent to MSC) 23>Connect (When MS Sub Answer the Conn message sent to MSC) 23>Connect (When MS Sub Answer the Conn message sent to MSC) 24>Connect Ack 24>Connect Ack 24>Connect Ack SDCCH SDCCH SDCCH TCH TCH TCH TCH Exit.. MS BTS BSC MSC
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