media access, TDMA structure etc. of GSM and the sequence of actions during a call.

1. IT 802DMobile CommunicationsPart 4 Debasis Das

2. Radio Interface-1 3/24/2011 Debasis Das Mallabhum Institute of Technology 2 890 MHz to 915 MHz, 200 KHz each MS to BTS , reverse links Channels assigned In pairs, 45 MHz gap Possible channels, 124 are used 45 MHz gap 935 to 960 MHz, 200 KHz each BTS to MS, forward links Absolute Radio Frequency Channel number (ARFCN) – 0 to 124 and 975 to 1023

3. Radio Interface-2Physical Channel 3/24/2011 3 124 channels, 935-960 MHz 124 channels, 890-915 MHz TS0 TS 1 TS 2 . . . . TS7 GSM TDMA Frame 4.615 ms Guard space t User data User data S S Training t Guard space GSM time slot. Normal burst 3 57 57 3 1 1 26 546.5 micro S 577 micro S Debasis Das Mallabhum Institute of Technology Time

4. Up/Down links Channels 1 & 124 not used in GSM 900 32channels for organizational data 90 channels for users One BTS handles 1 organizational channel and up to 10 user data channels. Each of 248 (124 x 2 Up and down), separated by GSM time frame Each GSM time frame slot has a fixed pattern 3/24/2011 Debasis Das Mallabhum Institute of Technology 4

5. GSM Time Slot Data transmitted in small portions, bursts Burst is 546.5 micro sec long and contains 148 bits Remaining 30.5 micro sec slot is used as guard spaces Avoids multipath overlaps, gives transmitter time to switch on and off 156.25 bits in 577 micro sec leads to a data rate of 33.8 Kbps, 270 kbps over a radio carrier All 3 bits of tail is set to 0 Training sequence adapts receiver to current propagation conditions and select the strongest signal in multipath situation S- flag indicating user data or network control data 4 more busts are defined 3/24/2011 Debasis Das Mallabhum Institute of Technology 5

6. Types of bursts Frequency correction bursts, helps MS to correct the LO frequency Synchronization burst wit extended training sequence, help sync MS with BTS Access burst set up initial connection with BTS Dummy burst, when no data is available for a slot 3/24/2011 Debasis Das Mallabhum Institute of Technology 6

7. Simplification of Transmitter Hardware Up and downlinks are separated in frequency by 45 MHz in GSM 900 and 95 MHz in GSM 1800 TDM frames are shifted in time by three slots. If BTS send data on t0 in slot 1 on the downlink then the MS will access slot 1 of uplink in t0+3.577 micro sec Thus MS does not need a full duplex transmitter 3/24/2011 Debasis Das Mallabhum Institute of Technology 7

8. Point to Note As solution to frequency selective fading, sometimes a slow frequency hopping sequence is sometimes prescribed MS and BTS may change carrier frequency after each frame based on a common hopping sequence 3/24/2011 Debasis Das Mallabhum Institute of Technology 8

9. Logical Channels & Frame HierarchyPhysical & logical Channels 3/24/2011 Debasis Das Mallabhum Institute of Technology 9 1 2 3 8*124 Duplex channels 4 4.615 ms 5 C1C2xC2C1C2xC2C1 6 7 8

10. Logical Channels & Frame HierarchyTraffic & Control Channels-1 Traffic Channels (TCH) Available Full rate TCH (TCH/F), 22.8 kbps data rate Half rate TCH (TCH/H), 11.4 kbps data rate Beginning of GSM TCH/F- 13 kbps, TCH/FS (22.8-13=9.8 kbps) TCH/H + TCH/HS may not give the right voice quality Full rate codecs FR-13 kbps, HR-5,6 kbps Enhanced full rate (EFR), better voice quality at 12.2 kbps, given low transmission errors Adaptive multi rate (AMR) is used in 3G Other TCH/F4.8 and TCH/F14,4,coding, error correction differ 3/24/2011 Debasis Das Mallabhum Institute of Technology 10

11. Logical Channels & Frame HierarchyTraffic & Control Channels-2 Control Channel Broadcast control channel (BCCH) ( info carried are cell id, options available, frequencies in the cell and neighboring cells) Frequency control channel (FCCH) , Synchronization channel (SCCH) Common control channels ( CCCH)(info regarding MS and BS; BTS to MS uses paging channel (PCH), MS to BTS uses random access channel (RACH). MS uses access grant channel (AGCH) to tell MS that it can use a TCH or a SCCH for further set up. Dedicated control channel (DCCH) (bi directional) Stand alone dedicated control channel ( SDCCH), low rate, 782 bps for signaling, authentication, registration, etc. data Slow associated dedicated control channel (SACCH), associated with each TCH and SDCCH Fast associated dedicated control channel ( FACCS), uses TCH time channel for fast data transfer, such as handover time 3/24/2011 Debasis Das Mallabhum Institute of Technology 11

12. Logical Channels & Frame HierarchyTraffic & Control Channels-3 3/24/2011 Debasis Das Mallabhum Institute of Technology 12 No arbitrary transmission of channels, fixed patterns Speech multi-frame, 26 TDMA frames Slow signaling slot Blank slot/S TCH frames Normal burst-114 bits every 4.615 ms=24.7 kbps 24 of 26 TCH is used, effective rate then= 22.8 kbps Pattern repeats

13. GSM Logical Channel Types Traffic channels (TCH) Carries digital user speech or data, identical on both forward and reverse links Control channels (CCH) Carries signaling and synchronizing commands between base station and mobile station, some CCH may defined for only the forward or the reverse links 3/24/2011 Debasis Das Mallabhum Institute of Technology 13

14. Traffic Channels (TCH) Full rate TCH (22.8 kbps) Full rate speech channel (TCH/FS) Full rate data channel ,9600 bps (TCH/F9.6) Full rate data channel, 4800 bps (TCH/F4.8) Full rate data channel, 2400 bps (TCH/F2.4) Half rate TCH (11.4 kbps) Half rate speech channel (TCH/HS) Half rate data channel, 4800 bps (TCH/H4.8) Half rate data channel, 2400 bps (TCH/H2.4) 3/24/2011 Debasis Das Mallabhum Institute of Technology 14

15. Control Channels(CCH) Each control channel consists of several logical channels, distributed in time Control channel types Broadcast channel (BCH) Common control channel (CCCH) Dedicated control channel (DCCH) BCH and CCCH are allocated in TS0 slots only, broadcast only during certain frames in the 51 frame control Superframe and designated ARFCNs (34). DCCH can be sent any time slot, frame 3/24/2011 Debasis Das Mallabhum Institute of Technology 15

16. Control Channel Types- BCH Broadcast channels (BCH) Broadcast control channel (BCCH) Works as a TDMA beacon, helps synchronize MSs in a cell, broadcasts on TS0 only Broadcast control channel (BCCH): cell & network id, operating characteristics of cell (current control channel structure, channel availability, congestion, etc.), list of channels in use during frames 2 to 5 of control multi frame Frequency control channel (FCCH): special pattern every 10th frame for synchronizing LO frequency in MS Synchronization channel (SCH): serving base station is identified by base station identity code(BSIC) and frame number (FN), following FCCH and repeated every 10th frame 3/24/2011 Debasis Das Mallabhum Institute of Technology 16

17. Control Multi-frame 3/24/2011 Debasis Das Mallabhum Institute of Technology 17 F: FCCH burst, S: SCH burst, B: BCCH burst, all three BCH C: PCH/AGCH burst (CCCH), I: idle F B S B B B C C C C F S C C C F S C C F S C C I C Control channel multi-frame, forward link, TS0 0 R 2 R 1 R 49 R 50 R R: Reverse RACH burst (CCCH) Control channel multi-frame, reverse link, TS0

18. Control Channel Types- CCCH Uses TS0 if BCH is not using it or the idle frame Paging channel (PCH), forward link only Broadcasts IMSI number of incoming call, request to acknowledge on RACH, used to broadcast text messages as part of SMS feature of the GSM Random access channel (RACH), a slotted ALOHA channel, reverse link only, Acknowledge a call, initiate a call by MS, during TS0, base assigns a SDCCH for call establishment, connection confirmed over AGCH Access grant channel (AGCH), forward link only Instructs a MS to operate in a physical link and ARFCN 3/24/2011 Debasis Das Mallabhum Institute of Technology 18

19. Control Channel Types- DCCH Bi directional, any TDM slot & ARFCN except TS0 Standalone dedicated control channel (SDCCH) Carries signaling data after a connection is made with base station and before a TCH assignment is made, lets MS and base remain connected as MSC verifies subscriber and allocates resources Slow associated control channel (SACCH) Sends & receives regular control information such as transmit power level instruction and specific timing Fast associated control channel (FACCH) Fast control requirements such as handover, steal frames from TCH 3/24/2011 Debasis Das Mallabhum Institute of Technology 19

20. Call From Within GSM-1 Subscriber should be synchronized to the local base After receiving FCCH, SCH and BCCH, subscriber will get on to appropriate BCH Subscriber dials the number and hits send Sends a RACH using the same ARFCN on which it was locked Base sends AGCH on CCCH and assigns a SDCCH Mobile unit gets time slot and ARFCN assignment through AGCH and tune to it, wait for SACCH for time advance and transmitter power commands 3/24/2011 Debasis Das Mallabhum Institute of Technology 20

21. Call From Within GSM-2 While MS and base finish authentication and user validation, MSC locates and establishes a connection with th4 called party in the PSTN, MSC switches the speech path to the serving base station. Base station command via SDCCH about TS and ARFCN assignments for a specific TCH Transferred to TCH to and fro transfers start and SDCCH is vacated 3/24/2011 Debasis Das Mallabhum Institute of Technology 21

22. Call from PSTN Page is responded by the MS, replies with RACH Base uses AGCH and CCCH to assign a new SDCCH and a SACCH while network and base are connected MS does timing advance and authentication on SDCCH, base issues a new physical channel assignment and the TCH assignment is made 3/24/2011 Debasis Das Mallabhum Institute of Technology 22

23. Traffic Multi-frame 3/24/2011 Debasis Das Mallabhum Institute of Technology 23 Hyperframe 3 h, 28 m, 53.76 s 2,715,647 frames 0 1 2 …….. 2045 2046 2047 6.12 sec Superframe 0 1 2 …….. 51 0 1 2 …….. 25 traffic multi-frame, 120 ms 0 1 2 …….. 7 4.615 ms Burst 577 micro sec Slot