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
36. 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
39. 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
40. 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
41. 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
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46. 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
48. 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
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50. 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
51. 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
52. 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
53. 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)
55. 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
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57. 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
66. 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
67. 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
85. 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
86. 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
270.833 kb/s per carrier GMSK with a time bandwidth product BT =0.3 Slow frequency hoping 217/hops/second. Synchronization compensation for up to 233micro seconds absolute delay Block and convolutional channel coding copuled with interleaving to combat channel perturbations- overall channel rate of 22.8 kb/s Full rate channel 13 kb/s voice coder rate using regular pulse excitation/linear predictive coding RPE/LPC, half rate channel 6.5 kb/s using Vector coder rate using vector sum excited linear predictivie coding VSELP Overall full rate channel bit rate of 22.8 kb/s. Each cell can have from 1 to 16 pairs of carriers.
The system capacity depends on : The total number of radio channels The size of the cell The frequency re-use factor or distance The minimum distance which allows the same frequencies to be re-used will depend on many factors, The number of co-channel cells in the vicinity of the center cell The geography of the terrain, The antenna height The transmitted power within each cell
Due to assumptions 1MHz carrier 5 radio frequencies(radio channels) 5X200 kHz. Each radio frequency carries 8 traffic channels = 40 traffic channels/MHz Without cell splitting, traffic channels = 7.2MHzX40 = 288 traffic channels With 72 cells, 72/12(kfactor = 12) = 6 paterns(all spectrum may be used in a pattern), traffic channels = 6X288 = 1728 traffic channels With 246 cells, 246/12(K factor = 12) we will get 20 sectors + 6 cells, for 20 patterns and 6/12 we get 20X288 + 6/12*288 = 5904 traffic channels. For the same channels spacing and re-use pattern, the number of re-used channels is increased when cell radius are reduced.
The start of the uplink TDMA frame is delayed with respect to downlink by a fixed period of three timeslots. Why ? Staggering TDMA frames allows the same timeslot number to be used in both the down and uplink while avoiding the requirement for mobile to transmit and receive simultaneously. Between T and R the MS is in the IDLE mode, makes measurement of signal strength of neighboring cells.
Because of natural and man-made electromagnetic interference, the encoded speech or data signal transmitted over the radio interface must be protected from errors. GSM uses convolutional encoding and block interleaving to achieve this protection. The exact algorithms used differ for speech and for different data rates. The method used for speech blocks will be described below. Recall that the speech codec produces a 260 bit block for every 20 ms speech sample. From subjective testing, it was found that some bits of this block were more important for perceived speech quality than others. The bits are thus divided into three classes: Class Ia 50 bits - most sensitive to bit errors Class Ib 132 bits - moderately sensitive to bit errors Class II 78 bits - least sensitive to bit errors Class Ia bits have a 3 bit Cyclic Redundancy Code added for error detection. If an error is detected, the frame is judged too damaged to be comprehensible and it is discarded. It is replaced by a slightly attenuated version of the previous correctly received frame. These 53 bits, together with the 132 Class Ib bits and a 4 bit tail sequence (a total of 189 bits), are input into a 1/2 rate convolutional encoder of constraint length 4. Each input bit is encoded as two output bits, based on a combination of the previous 4 input bits. The convolutional encoder thus outputs 378 bits, to which are added the 78 remaining Class II bits, which are unprotected. Thus every 20 ms speech sample is encoded as 456 bits, giving a bit rate of 22.8 kbps. To further protect against the burst errors common to the radio interface, each sample is interleaved. The 456 bits output by the convolutional encoder are divided into 8 blocks of 57 bits, and these blocks are transmitted in eight consecutive time-slot bursts. Since each time-slot burst can carry two 57 bit blocks, each burst carries traffic from two different speech samples. Recall that each time-slot burst is transmitted at a gross bit rate of 270.833 kbps. This digital signal is modulated onto the analog carrier frequency using Gaussian-filtered Minimum Shift Keying (GMSK). GMSK was selected over other modulation schemes as a compromise between spectral efficiency, complexity of the transmitter, and limited spurious emissions. The complexity of the transmitter is related to power consumption, which should be minimized for the mobile station.
Normal burst 148 bits + 8.25 guard bits Frequency correction burst 148 bits + 8.25 guard bits Synchronizing burst 148 bits + 8.25 guard bits Access burst 88 bits +68.25 guard bits used to access a cell for the first time in case of a call set up or handover The data structure within a normal burst consists of 148 bits transmitted at a rate of 270.833 kb/s. Each burst in GSM system modulates one of the carriers assigned to a particular cell using GMSK.
Speech in GSM is digitally coded at a rate of 13 kbps, so-called full-rate speech coding. This is quite efficient compared with the standard ISDN rate of 64 kbps. One of the most important Phase 2 additions will be the introduction of a half-rate speech codec operating at around 7 kbps, effectively doubling the capacity of a network. This 13 kbps digital stream (260 bits every 20 ms) has forward error correction added by a convolutional encoder. The gross bit rate after channel coding is 22.8 kbps (or 456 bits every 20 ms). These 456 bits are divided into 8 57-bit blocks, and the result is interleaved amongst eight successive time slot bursts for protection against bursty transmission errors. Each time slot burst is 156.25 bits and contains two 57-bit blocks, and a 26-bit training sequence used for equalization. A burst is transmitted in 0.577 ms for a total bit rate of 270.8 kbps, and is modulated using Gaussian Minimum Shift Keying (GMSK) onto the 200 kHz carrier frequency. The 26-bit training sequence is of a known pattern that is compared with the received pattern in the hope of being able to reconstruct the rest of the original signal. Forward error control and equalization contribute to the robustness of GSM radio signals against interference and multipath fading. The digital TDMA nature of the signal allows several processes intended to improve transmission quality, increase the mobile's battery life, and improve spectrum efficiency. These include discontinuous transmission, frequency hopping and discontinuous reception when monitoring the paging channel. Another feature used by GSM is power control, which attempts to minimize the radio transmission power of the mobiles and the BTS, and thus minimize the amount of co-channel interference generated.
The full rate TCH uses 24 out of the 26 available in the multiframe The duration of the multiframe is therefore 26X60/13ms = 120ms At the 900 MHz range, radio waves bounce off everything - buildings, hills, cars, airplanes, etc. Thus many reflected signals, each with a different phase, can reach an antenna. Equalization is used to extract the desired signal from the unwanted reflections. It works by finding out how a known transmitted signal is modified by multipath fading, and constructing an inverse filter to extract the rest of the desired signal. This known signal is the 26-bit training sequence transmitted in the middle of every time-slot burst. The actual implementation of the equalizer is not specified in the GSM specifications.
Distinct training sequences will therefore be allocated to channels using the same frequencies in cells which are close enough to interfere with one another.
When a mobile station is first switched on it is necessary to read the BCCH in order to determine its orientation within the network. The mobile must first synchronize in frequency and then in time. The FCCH, SCH and BCCH are all transmitted on the same carrier frequency which has a higher power density than any of the other channels in a cell because steps are taken to ensure that it is transmitted information at all times. The mobile scans around the available frequencies, picks the strongest and then selects the FCCH. Fc+67.7kHz
The full rate TCH uses 24 out of the 26 available in the multiframe The duration of the multiframe is therefore 26X60/13ms = 120ms At the 900 MHz range, radio waves bounce off everything - buildings, hills, cars, airplanes, etc. Thus many reflected signals, each with a different phase, can reach an antenna. Equalization is used to extract the desired signal from the unwanted reflections. It works by finding out how a known transmitted signal is modified by multipath fading, and constructing an inverse filter to extract the rest of the desired signal. This known signal is the 26-bit training sequence transmitted in the middle of every time-slot burst. The actual implementation of the equalizer is not specified in the GSM specifications.
The GSM group studied several speech coding algorithms on the basis of subjective speech quality and complexity (which is related to cost, processing delay, and power consumption once implemented) before arriving at the choice of a Regular Pulse Excited -- Linear Predictive Coder (RPE--LPC) with a Long Term Predictor loop. Basically, information from previous samples, which does not change very quickly, is used to predict the current sample. The coefficients of the linear combination of the previous samples, plus an encoded form of the residual, the difference between the predicted and actual sample, represent the signal. Speech is divided into 20 millisecond samples, each of which is encoded as 260 bits, giving a total bit rate of 13 kbps. This is the so-called Full-Rate speech coding. Recently, an Enhanced Full-Rate (EFR) speech coding algorithm has been implemented by some North American GSM1900 operators. This is said to provide improved speech quality using the existing 13 kbps bit rate.
Mike
The first one of them Msa is the only one where all the levels of detail are given: The mobile station has two calls in progress (TI=a and b on PD=CC, on SAPI=0) And one SMS transaction (TI=A on SAPI=3).