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Multi User Detection for CDMA

Multi User Detection for CDMA. Group Members: -Bhushan G. Jagyasi -Himanshu Soni. Multiple Access Interference(MAI). Conventional Detector. Modula- tion. Modula- tion. b 1 (.). b^ 1 (.). Decision. AWGN. g1. g1. b^ 2 (.). b 2 (.). Decision. g2. g2. r(t).

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Multi User Detection for CDMA

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  1. Multi User Detection for CDMA Group Members: -Bhushan G. Jagyasi -Himanshu Soni

  2. Multiple Access Interference(MAI) • Conventional Detector Modula- tion Modula- tion b1(.) b^1(.) Decision AWGN g1 g1 b^2(.) b2(.) Decision g2 g2 r(t) Noisy Channel b^n(.) Decision bn(.) gn gn Reciever / Detector Received signal , r(t) = b1g1f1+ b2g2f2+ ……bngnfn + n(t) After detector y(t)=b^1(t) = b1.g1.g1. f1+ b2.g2.g1.f2+ ……bn.gn.g1.fn + no.g1 y(t) = b1 f1 + MAI + zk

  3. Actual Problem y(t) = b1. f1 + MAI + zk • Total Interference (Includes interference due to other cells also) I = IMAI + f IMAI where f= Ratio of other cell MAI / IMAI • Near Far Problem in CDMA • Difficulty to implement more sophisticated algo at receiver because of limitations of size, cost, weight of handset. • Solutions to all such problems is Multi-user detection 0

  4. Genre of Multi-user detctors • NonBlind Multiuser detection algorithm • Detectors Available • Linear Detector (LMS based) • Subtractive interference canceller • Requires following information • Spreading waveform of desired signal • Spreading waveform of interfering signal • Timing (pd) of desired signal • Timing (pd) of interfering signal • Training data for every active user • Drawback • More Computational complexity. • Requires much more information.

  5. Genre of Multi-user detctors • Blind multiuser detection algorithm • Detectors Available • Kalman based • Requires following information • Spreading waveform of desired signal • Timing (pd) of desired signal • Turbo MUD: • Joint channel decoding and MUD using iterative exchange of information between two processes.

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