It802 d mobilecommunicationspart4

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

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It802 d mobilecommunicationspart4

  1. 1. IT 802DMobile CommunicationsPart 4<br />Debasis Das<br />
  2. 2. Radio Interface-1<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />2<br />890 MHz to 915 MHz, 200 KHz each<br />MS to BTS , reverse links<br />Channels assigned<br />In pairs, 45 MHz gap<br />Possible channels,<br />124 are used<br />45 MHz gap<br />935 to 960 MHz, 200 KHz each<br />BTS to MS, forward links<br />Absolute Radio Frequency Channel number (ARFCN) – 0 to 124 and 975 to 1023<br />
  3. 3. Radio Interface-2Physical Channel<br />3/24/2011<br />3<br /> 124 channels, 935-960 MHz<br />124 channels, 890-915 MHz<br />TS0<br />TS<br />1<br />TS<br />2<br />.<br />.<br />.<br />.<br />TS7<br />GSM TDMA Frame<br />4.615 ms<br />Guard<br />space<br />t<br />User<br />data<br />User<br />data<br />S<br />S<br />Training<br />t<br />Guard<br />space<br />GSM time slot.<br /> Normal burst<br />3<br />57<br />57<br />3<br />1<br />1<br />26<br />546.5 micro S<br />577 micro S<br />Debasis Das Mallabhum Institute of Technology<br />Time<br />
  4. 4. Up/Down links<br />Channels 1 & 124 not used in GSM 900<br />32channels for organizational data<br />90 channels for users<br />One BTS handles 1 organizational channel and up to 10 user data channels.<br />Each of 248 (124 x 2 Up and down), separated by GSM time frame<br />Each GSM time frame slot has a fixed pattern<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />4<br />
  5. 5. GSM Time Slot<br />Data transmitted in small portions, bursts<br />Burst is 546.5 micro sec long and contains 148 bits<br />Remaining 30.5 micro sec slot is used as guard spaces<br />Avoids multipath overlaps, gives transmitter time to switch on and off<br />156.25 bits in 577 micro sec leads to a data rate of 33.8 Kbps, 270 kbps over a radio carrier<br />All 3 bits of tail is set to 0<br />Training sequence adapts receiver to current propagation conditions and select the strongest signal in multipath situation<br />S- flag indicating user data or network control data<br />4 more busts are defined<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />5<br />
  6. 6. Types of bursts<br />Frequency correction bursts, helps MS to correct the LO frequency<br />Synchronization burst wit extended training sequence, help sync MS with BTS<br />Access burst set up initial connection with BTS<br />Dummy burst, when no data is available for a slot<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />6<br />
  7. 7. Simplification of Transmitter Hardware<br />Up and downlinks are separated in frequency by 45 MHz in GSM 900 and 95 MHz in GSM 1800<br />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<br />Thus MS does not need a full duplex transmitter<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />7<br />
  8. 8. Point to Note<br />As solution to frequency selective fading, sometimes a slow frequency hopping sequence is sometimes prescribed<br />MS and BTS may change carrier frequency after each frame based on a common hopping sequence<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />8<br />
  9. 9. Logical Channels & Frame HierarchyPhysical & logical Channels<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />9<br />1<br />2<br />3<br />8*124 Duplex channels<br />4<br />4.615 ms<br />5<br />C1C2xC2C1C2xC2C1<br />6<br />7<br />8<br />
  10. 10. Logical Channels & Frame HierarchyTraffic & Control Channels-1<br />Traffic Channels (TCH)<br />Available<br />Full rate TCH (TCH/F), 22.8 kbps data rate<br />Half rate TCH (TCH/H), 11.4 kbps data rate<br />Beginning of GSM<br />TCH/F- 13 kbps, TCH/FS (22.8-13=9.8 kbps)<br />TCH/H + TCH/HS may not give the right voice quality<br />Full rate codecs<br />FR-13 kbps, HR-5,6 kbps<br />Enhanced full rate (EFR), better voice quality at 12.2 kbps, given low transmission errors<br />Adaptive multi rate (AMR) is used in 3G<br />Other TCH/F4.8 and TCH/F14,4,coding, error correction differ<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />10<br />
  11. 11. Logical Channels & Frame HierarchyTraffic & Control Channels-2<br />Control Channel<br />Broadcast control channel (BCCH) ( info carried are cell id, options available, frequencies in the cell and neighboring cells)<br />Frequency control channel (FCCH) , Synchronization channel (SCCH)<br />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.<br />Dedicated control channel (DCCH) (bi directional)<br />Stand alone dedicated control channel ( SDCCH), low rate, 782 bps for signaling, authentication, registration, etc. data<br />Slow associated dedicated control channel (SACCH), associated with each TCH and SDCCH<br />Fast associated dedicated control channel ( FACCS), uses TCH time channel for fast data transfer, such as handover time<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />11<br />
  12. 12. Logical Channels & Frame HierarchyTraffic & Control Channels-3<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />12<br />No arbitrary transmission of channels, fixed patterns<br />Speech multi-frame, 26 TDMA frames<br />Slow signaling slot<br />Blank slot/S<br />TCH frames<br />Normal burst-114 bits every 4.615 ms=24.7 kbps<br />24 of 26 TCH is used, effective rate then= 22.8 kbps<br />Pattern repeats<br />
  13. 13. GSM Logical Channel Types<br />Traffic channels (TCH)<br />Carries digital user speech or data, identical on both forward and reverse links<br />Control channels (CCH)<br />Carries signaling and synchronizing commands between base station and mobile station, some CCH may defined for only the forward or the reverse links<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />13<br />
  14. 14. Traffic Channels (TCH)<br />Full rate TCH (22.8 kbps)<br />Full rate speech channel (TCH/FS)<br />Full rate data channel ,9600 bps (TCH/F9.6)<br />Full rate data channel, 4800 bps (TCH/F4.8)<br />Full rate data channel, 2400 bps (TCH/F2.4)<br />Half rate TCH (11.4 kbps)<br />Half rate speech channel (TCH/HS)<br />Half rate data channel, 4800 bps (TCH/H4.8)<br />Half rate data channel, 2400 bps (TCH/H2.4)<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />14<br />
  15. 15. Control Channels(CCH)<br />Each control channel consists of several logical channels, distributed in time<br />Control channel types<br />Broadcast channel (BCH)<br />Common control channel (CCCH)<br />Dedicated control channel (DCCH)<br />BCH and CCCH are allocated in TS0 slots only, broadcast only during certain frames in the 51 frame control Superframe and designated ARFCNs (34).<br />DCCH can be sent any time slot, frame<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />15<br />
  16. 16. Control Channel Types- BCH<br />Broadcast channels (BCH)<br />Broadcast control channel (BCCH)<br />Works as a TDMA beacon, helps synchronize MSs in a cell, broadcasts on TS0 only<br />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<br />Frequency control channel (FCCH): special pattern every 10th frame for synchronizing LO frequency in MS<br />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<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />16<br />
  17. 17. Control Multi-frame<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />17<br />F: FCCH burst, S: SCH burst, B: BCCH burst, all three BCH<br />C: PCH/AGCH burst (CCCH), I: idle<br />F<br />B<br />S<br />B<br />B<br />B<br />C<br />C<br />C<br />C<br />F<br />S<br />C<br />C<br />C<br />F<br />S<br />C<br />C<br />F<br />S<br />C<br />C<br />I<br />C<br />Control channel multi-frame, forward link, TS0<br />0<br />R<br />2<br />R<br />1<br />R<br />49<br />R<br />50<br />R<br />R: Reverse RACH burst (CCCH)<br />Control channel multi-frame, reverse link, TS0<br />
  18. 18. Control Channel Types- CCCH<br />Uses TS0 if BCH is not using it or the idle frame<br />Paging channel (PCH), forward link only<br />Broadcasts IMSI number of incoming call, request to acknowledge on RACH, used to broadcast text messages as part of SMS feature of the GSM<br />Random access channel (RACH), a slotted ALOHA channel, reverse link only, <br />Acknowledge a call, initiate a call by MS, during TS0, base assigns a SDCCH for call establishment, connection confirmed over AGCH<br />Access grant channel (AGCH), forward link only<br />Instructs a MS to operate in a physical link and ARFCN<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />18<br />
  19. 19. Control Channel Types- DCCH<br />Bi directional, any TDM slot & ARFCN except TS0<br />Standalone dedicated control channel (SDCCH)<br />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<br />Slow associated control channel (SACCH)<br />Sends & receives regular control information such as transmit power level instruction and specific timing<br />Fast associated control channel (FACCH)<br />Fast control requirements such as handover, steal frames from TCH<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />19<br />
  20. 20. Call From Within GSM-1<br />Subscriber should be synchronized to the local base<br />After receiving FCCH, SCH and BCCH, subscriber will get on to appropriate BCH<br />Subscriber dials the number and hits send<br />Sends a RACH using the same ARFCN on which it was locked<br />Base sends AGCH on CCCH and assigns a SDCCH<br />Mobile unit gets time slot and ARFCN assignment through AGCH and tune to it, wait for SACCH for time advance and transmitter power commands<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />20<br />
  21. 21. Call From Within GSM-2<br />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.<br />Base station command via SDCCH about TS and ARFCN assignments for a specific TCH<br />Transferred to TCH to and fro transfers start and SDCCH is vacated<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />21<br />
  22. 22. Call from PSTN<br />Page is responded by the MS, replies with RACH<br />Base uses AGCH and CCCH to assign a new SDCCH and a SACCH while network and base are connected<br />MS does timing advance and authentication on SDCCH, base issues a new physical channel assignment and the TCH assignment is made<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />22<br />
  23. 23. Traffic Multi-frame<br />3/24/2011<br />Debasis Das Mallabhum Institute of Technology<br />23<br />Hyperframe<br />3 h, 28 m, 53.76 s<br />2,715,647 frames<br />0<br />1<br />2<br />……..<br />2045<br />2046<br />2047<br />6.12 sec<br />Superframe<br />0<br />1<br />2<br />……..<br />51<br />0<br />1<br />2<br />……..<br />25<br />traffic multi-frame, 120 ms<br />0<br />1<br />2<br />……..<br />7<br />4.615 ms<br />Burst<br />577 micro sec<br />Slot<br />

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