1. Overview of GSM Cellular Network and Operations Ganesh Srinivasan NTLGSPTN

7. The GSM Radio Interface

9. GSM uses paired radio channels 0 124 0 124 890MHz 915MHz 935MHz 960MHz UPLINK DOWNLINK

16. GSM uses paired radio channels 0 124 0 124 890MHz 915MHz 935MHz 960MHz UPLINK DOWNLINK

18. Various Access Method

19. Cells

21. Representation of Cells Ideal cells Fictitious cells

25. The K factor and Frequency Re-Use Distance i j 1 2 3 4 5 6 7 Frequency re-use distance is based on the cluster size K The cluster size is specified in terms of the offset of the center of a cluster from the center of the adjacent cluster K = i 2 + ij + j 2 K = 2 2 + 2*1 + 1 2 K = 4 + 2 + 1 K = 7 D =  3K * R D = 4.58R 1 2 3 5 6 7 D R

26. The Frequency Re-Use for K = 4 K = i 2 + ij + j 2 K = 2 2 + 2*0 + 0 2 K = 4 + 0 + 0 K = 4 D =  3K * R D = 3.46R i D R

27. The Cell Structure for K = 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 2 1 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7

28. Cell Structure for K = 4 1 2 3 4 1 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 4 3 2

29. Cell Structure for K = 12 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6 7 7 7 7 8 8 8 8 9 9 9 9 10 10 10 10 11 11 11 11 12 12 12 12

32. Tri-Sector antenna for a cell

33. Cell Distribution in a Network Highway Town Suburb Rural

35. Re-use of the frequency One Cell = 288 traffic channels 72 Cell = 1728 traffic channels 246 Cell = 5904 traffic channels 8 X 36 = 288 8 X (72/12 X 36) = 1728

37. GSM uses paired radio channels 0 124 0 124 890MHz 915MHz 935MHz 960MHz UPLINK DOWNLINK

38. GSM delays uplink TDMA frames Uplink TDMA Frame F1 + 45MHz Downlink TDMA F1MHz The start of the uplink TDMA is delayed of three time slots TDMA frame (4.615 ms) Fixed transmit Delay of three time-slots T1 T2 T3 T5 T6 T7 T4 T8 R T R T R1 R2 R3 R5 R6 R7 R4 R8

39. GSM - TDMA/FDMA 935-960 MHz 124 channels (200 kHz) downlink 890-915 MHz 124 channels (200 kHz) uplink frequency time GSM TDMA frame GSM time-slot (normal burst) guard space guard space 1 2 3 4 5 6 7 8 higher GSM frame structures 4.615 ms 546.5 µs 577 µs tail user data Training S S user data tail 3 bits 57 bits 26 bits 57 bits 1 1 3

40. LOGICAL CHANNELS TRAFFIC SIGNALLING FULL RATE Bm 22.8 Kb/S HALF RATE Lm 11.4 Kb/S BROADCAST COMMON CONTROL DEDICATED CONTROL FCCH SCH BCCH PCH RACH AGCH SDCCH SACCH FACCH FCCH -- FREQUENCY CORRECTION CHANNEL SCH -- SYNCHRONISATION CHANNEL BCCH -- BROADCAST CONTROL CHANNEL PCH -- PAGING CHANNEL RACH -- RANDOM ACCESS CHANNEL AGCH -- ACCESS GRANTED CHANNEL SDCCH -- STAND ALONE DEDICATED CONTROL CHANNEL SACCH -- SLOW ASSOCIATED CONTROL CHANNEL FACCH -- FAST ASSOCIATED CONTROL CHANNEL DOWN LINK ONLY UPLINK ONLY BOTH UP & DOWNLINKS

45. DEFINITION OF TIME SLOT - 156.25 BITS 15/26ms = 0.577ms TAIL BIT ENCRYPTION BIT GUARD PERIOD TRAINING BITS MIXED BITS SYNCHRONISATION BITS FIXED BITS FLAG BITS 3 57 1 26 1 57 3 8.25 NORMAL BURST - NB 3 142 3 8.25 FREQUENCY CORRECTION BURST - FB 3 3 8.25 39 64 39 SYNCHRONISATION BURST - SB 3 6 41 36 68.25 ACCESS BURST - AB

46. 0 1 2 3 4 5 6 2043 2044 2045 2046 2047 0 1 2 24 25 0 1 2 3 24 25 1 HYPER FRAME = 2048 SUPERFRAMES = 2 715 648 TDMA FRAMES ( 3 H 28 MIN 53 S 760 MS ) 1 SUPER FRAME = 1326 TDMA FRAMES ( 6.12 S ) LEFT (OR) RIGHT 1 MULTI FRAME = 51 TDMA FRAMES (235 .4 ms ) 1 SUPER FRAME = 26 MULTI FRAMES 1 SUPER FRAME = 51 MULTI FRAMES 1 MULTIFRAME = 26 TDMA FRAMES ( 120 ms ) TDMA FRAME NO. 0 1 0 1 HIERARCHY OF FRAMES 1 2 3 4 155 156 1 TIME SLOT = 156.25 BITS ( 0.577 ms) (4.615ms) (4.615 ms) 1 bit =36.9 micro sec TRAFFIC CHANNELS SIGNALLING CHANNELS 0 1 2 3 4 48 49 50 0 1 2 3 4 48 49 50 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0

47. GSM Frame Full rate channel is idle in 25 SACCH is transmitted in frame 12 0 to 11 and 13 to 24 Are used for traffic data Frame duration = 120ms Frame duration = 60/13ms Frame duration = 15/26ms 0 1 2 3 4 5 6 7 3 57 1 26 1 57 3 8.25 0 1 2 12 24 25

49. LOGICAL CHANNELS TRAFFIC SIGNALLING FULL RATE Bm 22.8 Kb/S HALF RATE Lm 11.4 Kb/S BROADCAST COMMON CONTROL DEDICATED CONTROL FCCH SCH BCCH PCH RACH AGCH SDCCH SACCH FACCH FCCH -- FREQUENCY CORRECTION CHANNEL SCH -- SYNCHRONISATION CHANNEL BCCH -- BROADCAST CONTROL CHANNEL PCH -- PAGING CHANNEL RACH -- RANDOM ACCESS CHANNEL AGCH -- ACCESS GRANTED CHANNEL SDCCH -- STAND ALONE DEDICATED CONTROL CHANNEL SACCH -- SLOW ASSOCIATED CONTROL CHANNEL FACCH -- FAST ASSOCIATED CONTROL CHANNEL DOWN LINK ONLY UPLINK ONLY BOTH UP & DOWNLINKS

50. Location update from the mobile Mobile looks for BCCH after switching on RACH send channel request AGCH receive SDCCH SDCCH authenticate SDCCH switch to cipher mode SDCCH request for location updating SDCCH authenticate response SDCCH cipher mode acknowledge SDCCH allocate TMSI SDCCH acknowledge new TMSI SDCCH switch idle update mode

51. Call establishment from a mobile Mobile looks for BCCH after switching on RACH send channel request AGCH receive SDCCH SDCCH do the authentication and TMSI allocation SDCCH require traffic channel assignment SDCCH send call establishment request SDCCH send the setup message and desired number FACCH switch to traffic channel and send ack (steal bits) FACCH receive alert signal ringing sound FACCH acknowledge connect message and use TCH TCH conversation continues FACCH receive connect message

52. Call establishment to a mobile Mobile looks for BCCH after switching on Receive signaling channel SDCCH on AGCH Receive alert signal and generate ringing on FACCH Receive authentication request on SDCCH Generate Channel Request on RACH Answer paging message on SDCCH Authenticate on SDCCH Receive setup message on SDCCH FACCH acknowledge connect message and switch to TCH Receive connect message on FACCH Receive traffic channel assignment on SDCCH Mobile receives paging message on PCH FACCH switch to traffic channel and send ack (steal bits)

53. GSM speech coding

54. Transmit Path BS Side 8 bit A-Law to 13 bit Uniform RPE/LTP speech Encoder To Channel Coder 13Kbps 8 K sps MS Side LPF A/D RPE/LTP speech Encoder To Channel Coder 13Kbps 8 K sps, Sampling Rate - 8K Encoding - 13 bit Encoding (104 Kbps) RPE/LTP - Regular Pulse Excitation/Long Term Prediction RPE/LTP converts the 104 Kbps stream to 13 Kbps

56. GSM Frame Full rate channel is idle in 25 SACCH is transmitted in frame 12 0 to 11 and 13 to 24 Are used for traffic data Frame duration = 120ms Frame duration = 60/13ms Frame duration = 15/26ms 0 1 2 3 4 5 6 7 3 57 1 26 1 57 3 8.25 0 1 2 12 24 25

60. GSM Protocol Suite

61. BTS Radio interface HLR MSC VLR BSC RR MM + CM SS

65. BSC BTS A-Bis Interface Um Base Station System GSM Functional Architecture and Principal Interfaces HLR AC EIR VLR MSC Q.921 Radio Interface Q.931 Q.921 MAP TCAP CCS7 MTP CCS7 SCCP Mobile Application Part Q931 BSSAP SCCP CCS7 MTP A Interface

66. GSM protocol layers for signaling CM MM RR MM LAPD m radio LAPD m radio LAPD PCM RR’ BTSM CM LAPD PCM RR’ BTSM 16/64 kbit/s U m A bis A SS7 PCM SS7 PCM 64 kbit/s / 2.048 Mbit/s MS BTS BSC MSC BSSAP BSSAP

70. LAPDm Message structure ADDRESS CONTROL INFORMATION 0-21 OCTETS SAPI N(S) N(R)

75. LAPD message structure FLAG ADRESS CONTROL INFORMATION 0 – 260 OCT FCS FLAG SAPI TEI N(S) N(R)

77. Presentation of the A-ter interface

78. BSC TRAU MSC OMC OAM Transcoding LAPD TS1 Speech TS CCS7 TS X.25 TS2 Speech TS CCS7 TS X.25 TS2 PCM LINK PCM LINK

80. Presentation of the A interface

81. Signaling Protocol Model

83. Inter MSC presentation

84. O A M L A P D BTS MTP2 SCCP MTP3 L A P D O A M R R D T A P B S S M A P BSSAP BSC MTP1 MTP3 MTP2 SCCP MTP2 MTP3 SCCP BSSAP DTAP/ BSSMAP T C A P MM CM M A P NSS R R MM CM MS LAPDm LAPDm RADIO RADIO PCM PCM PCM E1 T1 ISUP/TUP Um Interface A bis Interface A Interface

85. SCCP Ref=R2 TRX:TEI=T1 Channel ID = N1 SCCP Ref=R1 DTAP DLCI: SAPI=3 DLCI: SAPI=0 Channel=C1 Link: SAPI=3 Link: SAPI=0 PD=CC TI=a TI=b PD=MM PD=RR TI=A MS BSC MSC Channel=C2 Channel ID = N1 Radio Interface Abis Interface A Interface PD: protocol discriminator TI: Transaction Identifier for RIL3-CC protocol DLCI: Data Link connection Identifier SAPI: Service Access Point Identifier on the radio Interface TEI: Terminal Equipment Identifier on the Abis I/F

90. Thank You