GSM FRAME STRUCTURE.pptx

GSM Frame Structure

1. GSM Frame structure, VoLTE Call Procedure & WiFi - Off Loading Presnted by - Rohit Soni

2. GSM - RADIO INTERFACE IN THIS PRESENTATION Frequency Bands & Specifications Multiple Access Method: FDMA & TDMA FDMA /TDMA Frame Representation Logical Channels: Traffic & Control

3. Communication - Mobile Telephone Exchange Subscriber Line (2W) Inter-Exchange Junction Mobile Switching Centre (MSC) BSC BTS MS

4. GSM Uplink & Downlink Frequency Bands GSM 900 Mhz DCS 1800 MHz B T S UPLINK DOWNLINK

5. GSM - MULTIPLE ACCESS GSM uses both FDMA & TDMA Freq Mhz. 890.2 1 890.4 2 890.6 3 890.8 4 891.0 5 6 91 4.8 124 FDMA Access along Frequency axis ……...

6. Digital Voice Transmission - In GSM speech coding a block of 20 ms is encoded in one set of 260 bits. - This calculates as 50X 260 = 13 kbps. Thus GSM speech coder produces a bit rate of 13 kbps per subscriber. - This provides speech quality which is acceptable for mobile telephony and comparable with wire-line PSTN phones. Speech Coding

7. Speech Coding Parameters like tone, length of tone, pitch are transmitted Sampling=50 times/sec instead of 8000 of 260 bits each overall bit rate= 50x260x8 subs=104kbps

8. GSM Digital Voice Transmission - It uses 260 bits from speech coding as input and outputs 456 encoded bits. - In one burst one block of 57 bits from one sample and another block from another sample are sent together. - These 456 bits for every 20 ms of speech are interleaved forming eight blocks of 57 bits each. Channel Coding Interleaving

9. GSM Digital Voice Transmission To counteract the problems encountered in radio path: Burst Formatting - Additional bits as training sequence added to basic speech/data. - Total of 136 bits added, bringing overall total to 592 bits. - Each TS of TDMA frame is 0.577 ms long and during this time 156.25 bits are transmitted. - One burst contains only 148 bits. Rest of the space, 8.25 bits time, is empty and is called Guard Period ( GP ). - GP enables MS/BTS to “ramp up” and “ ramp down”.

10. 8.25 3 57 1 26 1 57 3 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 D D D D D D D D D D D D D D D D 456 bits Sample 1 456 bits Sample 2 Normal Burst Stream of Time Slots Interleaving & Burst Formatting 1 st Sample of 20 ms speech 2 nd Sample of 20 ms speech

11. 4 GSM SPEECH CHANNEL INTERLEAVING ( Diagram ) 1 2 3 5 6 4 456 bits 5 456 bits 6 456 bits Full rate encoded speech blocks from a single conversation Bursts TDMA Frames Frame 1 Frame 2 Frame 3 Frame 4 INTERLEAVING

12. FREQUENCY CORRECTION BURST 1 2 3 4 5 6 7 1 2 3 4 5 6 7 142 bits 3 3 FRAME1(4.615ms) FRAME2 Fixed Data Tail Bits Tail Bits Guard Period Guard Period 0.546ms 0.577ms Carries FCCH channel. Made up of 142 consecutive zeros. Enables MS to correct its local oscillator locking it to that of the BTS. CHANNEL CONCEPT

13. SYNCHRONISATION BURST 1 2 3 4 5 6 7 1 2 3 4 5 6 7 39 bits 3 3 FRAME1(4.615ms) FRAME2 Synchronisation Sequence Tail Bits Tail Bits Guard Period Guard Period 0.546ms 0.577ms 64 bits 39 bits Encrypted Bits Encrypted Bits Carries SCH chann e l. Enables MS to synchronise its timings with the BTS. Contains BSIC and TDMA Frame number. CHANNEL CONCEPT

14. DUMMY BURST 1 2 3 4 5 6 7 1 2 3 4 5 6 7 57 bits 57 bits 26 bits 3 3 FRAME1(4.615ms) FRAME2 Training sequence Data Data Tail Bits Tail Bits Flag Bit Flag Bit Guard Period Guard Period 0.546ms 0.577ms Transmitted on the unused timeslots of the BCCH carrier in the downlink. CHANNEL CONCEPT

15. A CCESS BURST 1 2 3 4 5 6 7 1 2 3 4 5 6 7 41 bits 68.25 bits 8 FRAME1(4.615ms) FRAME2 Tail Bits Tail Bits Guard Period 0.577ms 36 bits Synchronisation Sequence Encrypted Bits 3 Carries RACH. Has a bigger guard period since it is used during initial access and the MS does not know how far it is actually from the BTS. CHANNEL CONCEPT

16. NORMAL BURST 1 2 3 4 5 6 7 1 2 3 4 5 6 7 57 bits 57 bits 26 bits 3 3 FRAME1(4.615ms) FRAME2 Training sequence Data Data Tail Bits Tail Bits Flag Bit Flag Bit Guard Period Guard Period 0.546ms 0.577ms Carries traffic channel and control channels BCCH, PCH, AGCH, SDCCH, SACCH and FACCH. CHANNEL CONCEPT

17. GSM-- TDMA STRUCTURE TDMA 8 Time Slots / RF Channel Time slot duration 0.577m sec or 15 / 26 m sec Frame 8 Burst Periods ( Time Slots) = 8  15/26 = 4.615 m sec Multi Frame Traffic 26  4.615 = 120 msec Control 51  4.615 = 235.365 m sec Super Frame 51  Traffic Multi frames 26  Control Multi frames Hyper Frame 2048 Super Frames = 3 28 52.76 hr min sec

18. 1 1 2 2045 2046 2047 1 Hyperframe = 2048 superframes = 2,715,648 TDMA frames 3h 28min 53s 760ms 1 Superframe = 1326 TDMAframes = 51(26 fr) 0r 26(51 fr) multiframes 1 2 3 49 48 47 50 1 24 25 1 2 23 24 25 48 1 2 49 50 2 3 4 5 6 7 6.12s 235.38ms 120ms Control 51 - Frame Multiframe Traffic 26 - Frame Multiframe 4.615ms TDMA Frame HYPERFRAME AND SUPERFRAME STRUCTURE CHANNEL CONCEPT

19. GSM Radio Interface - CYCLES 2047 Hyperframe = 2048 Superframes 3 Hours 28 Minutes 53 Seconds and 760 milliseconds 50 25 Superframe = 26 × 51 multiframes 6.12 Seconds 51 Multiframe Approx 235 mS 26 Multiframe 120 mS 25 24 2 1 50 49 48 1 7 6 5 4 3 2 1 TDMA frame 4.615 mS

20. Organisation of Speech & Data 24 25 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 BP 7 BP 6 BP 5 BP 4 BP 3 BP 2 BP 1 BP 0 8.25 3 57 1 26 1 57 3 Frames 0-11 : TCH Frames 12 : SACCH Frames 13-24 : TCH Frames 25 : Unused 26 – frame multiframe Duration: 120 ms TDMA frame Duration: 60/13 ms =4.615 ms Tail bits Data bits Stealing bit Training sequence Stealing bit Data bits Tail bits Guard bits Normal burst Duration 15/26 ms

21. Physical channel - Each timeslot on a carrier is referred to as a physical channel. Per carrier there are 8 physical channels. Logical channel - Variety of information is transmitted between the MS and BTS. There are different logical channels depending on the information sent. The logical channels are of two types Traffic channel Control channel Downlink Uplink CHANNELS CHANNEL CONCEPT

22. Logical Channels Logical Channels Traffic Channels Control Channels TCH/F TCH/H Common Control Channels Dedicated Control Channels Broadcast Channels SDCCH SACCH FACCH RACH PCH AGCH FCCH SCH BCCH

23. BCH Channels BCCH( Broadcast Control Channel ) Downlink only Broadcasts general information of the serving cell called System Information BCCH is transmitted on timeslot zero of BCCH carrier Read only by idle mobile at least once every 30 secs. SCH( Synchronisation Channel ) Downlink only Carries information for frame synchronisation. Contains TDMA frame number and BSIC . FCCH( Frequency Correction Channel ) Downlink only. Enables MS to synchronise to the frequency. Also helps mobiles of the ncells to locate TS 0 of BCCH carrier. CHANNEL CONCEPT

24. CCCH Channels RACH( Random Access Channel ) Uplink only Used by the MS to access the Network. AGCH( Access Grant Channel ) Downlink only Used by the network to assign a signalling channel upon succes s full decoding of access bursts. PCH( Paging Channel ) Downlink only. Used by the Network to contact the MS. CHANNEL CONCEPT

25. DCCH Channels SDCCH( Standalone Dedicated Control Channel ) Uplink and Downlink Used for call setup, location update and SMS. SACCH( Slow Associated Control Channel ) Used on Uplink and Downlink only in dedicated mode. Uplink SACCH messages - Measurement reports. Downlink SACCH messages - control info. FACCH( Fast Associated Control Channel ) Uplink and Downlink. Associated with TCH only. Is used to send fast messages like handover messages. Works by stealing traffic bursts. CHANNEL CONCEPT

26. Logical Channels Configuration Non Combined Mode TS0 = BCCH and CCCH/9. Combined Mode TS0 = BCCH, SDCCH/4 + SACCH/2 and CCCH/3. SDCCH not on TS0 TS2 = SDCCH/8 + SACCH/4.

27. T 15 T 5 T 9 T 10 T 11 S 12 T 13 T 14 T 6 T 7 T 8 T T 1 T 2 T 3 T 4 T 16 T 17 T 18 T 19 T 20 T 21 T 22 T 23 T 24 I 25 1 2 3 4 5 6 7 1 2 3 4 5 6 7 1 2 3 4 5 6 7 120 msec 4.615 msec 26 FRAME MULTIFRAME STRUCTURE Logical Channels Configuration

28. Multiplexing of BCHs and CCCHs onTS0 Non-Combined Time Slot 0

29. Multiplexing of BCHs and SDCCH onTS0 0 5 9 15 19 F S B B B B C C C C F S C 1 C 1 C 1 C 1 C 2 C 2 C 2 C 2 20 25 31 35 39 F S D 1 1 1 F S D 2 D 2 D 2 D 2 D 3 D 3 D 3 D 3 1 40 45 49 F S A A A A A 2 A 2 A 2 A 2 I D D D D D D D Combined Time Slot 0

30. Multiplexing of SDCCHs and SACCHs on TS2

31. SUMMARY Radio Interface Frequency Bands & Specifications Multiple Access Method FDMA & TDMA FDMA /TDMA Frame Representation Logical Channels Traffic & Control