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IS95: 2G CDMA DIGITAL CELLULAR STANDARD

IS95: 2G CDMA DIGITAL CELLULAR STANDARD. CDMA FORWARD LINK. 20 ms frame. CC(2,1,9). User Data 9,6 kbps 4,8 kbps 2,4 kbps 1,2 kbps. 2,4 kbps 4,8 kbps 9,6 kbps 19,2 kbps. Power Control Bits. Walsh Code. 19,2 kbps. Modulo-2 Adding. MUX. Symbol Repetition. Block Interleaver. Traffic Data.

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IS95: 2G CDMA DIGITAL CELLULAR STANDARD

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  1. IS95: 2G CDMA DIGITAL CELLULAR STANDARD

  2. CDMA FORWARD LINK 20 msframe CC(2,1,9) User Data9,6 kbps4,8 kbps2,4 kbps1,2 kbps 2,4 kbps4,8 kbps9,6 kbps19,2 kbps Power Control Bits Walsh Code 19,2 kbps Modulo-2Adding MUX SymbolRepetition BlockInterleaver Traffic Data 19,2 kbps 19,2 kbps 1 4 Long CodeGenerator Decimator Decimator Long Code for use n(43 bits) 800 Hz 1,2288 Mcps BasebandFilter Forward CDMA (IS-95) Channel PN I If power control=1 MS reduces power by 1dB power control=0 MS increases power by 1dB PN Q BasebandFilter Q channel short PN code(15 bit-SR)

  3. WC (8-31,33-63) Convert toIQ-PNSpreading T Traffic Channel  I WC 0 Convert toIQ-PNSpreading P Pilot Channel WC 32 Convert toIQ-PNSpreading S Sync Channel  Q WC 1 to 7 Convert toIQ-PNSpreading PG Paging Channel FORWARD LINK LOGICAL CHANNELS cosWct FIR FIR S(t) Transmitted forward link signal from the BS FIR FIR sinWct QPSK modulation

  4. Public Mask permuted ESN 32 bits 1100011000 31 Private Mask 0 1 WALSH AND PN CODES Walsh Codes Long PN sequence (period 242-1) ESN electronic serail number MIN mobile station ID number All CDMA calls are initiated using the public mask. Transition to the private mask is carried out after authentication is performed Long code mask format for IS-95

  5. Functions of Walsh and PN Codes • Forward Link (Downlink) • Walsh: for user separation and orthogonal modulation (sending of different logical channels at the same time) • Short PN: for BS identification • Long PN: for data scrambling • Reverse Link (Uplink) • Walsh : for orthogonal modulation (i.e., sending one of the rows of Walsh matrix with length 64 according to 6 bits) • Short PN : for user speration • Long PN : for data scrambling

  6. CDMA POWER CONTROL Power Control Subchannel 20 ms= 16 Power Control Groups 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Base station:1) measure signal strenght2) converts measurement to power control bit3) transmits power control bit Round TripDelay 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Long code bits usedfor scrambling Power Control Bit(two modulation symbols) Transmitted Value=11=PowerControl Bit Position 0 1 1 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Not used for power control bits 1.25 ms= 24 modulation symbols Randomization of power control bit positions in a IS-95 forward traffic channel

  7. CDMA REVERSE LINK Long code mask for user n Long CodeGenerator 20msframe group of 6 bits 1,22 Mcps 64-aryWalshModulator Data Bits Randomizer Vocoder CC(3,1,9) SymbolRepetition information bits9,6 kbps (192 bits)4,8 kbps2,4 kbps1,2 kbps 307,2 kbps 28,8 kbps(576 bits) Transmits one of 64 rows depending on decimal value at 6-bits data BasebandFilter I I channel short PN code PN I cosWct  S(t) Q channel short PN code PN Q Transmitted signal from the MS BasebandFilter Tc/2 Q sinWct Tc= Chip period Offset QPSK modulation

  8. Multipath Delay 2 1 3 1 2 3 RAKE RECEIVER C(t): PN code C(t-1) Output C(t-2) C(t-3)

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