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Local Decoding of Walsh Codes to Reduce CDMA Despreading Computation

Local Decoding of Walsh Codes to Reduce CDMA Despreading Computation. Matthew Doherty. CDMA Cell Sites Are Power-Hungry. Code Division Multiple Access Moves multiple access problem to DSP Computation uses more power than other standards (TDMA, GSM, etc.).

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Local Decoding of Walsh Codes to Reduce CDMA Despreading Computation

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  1. Local Decoding of Walsh Codes to Reduce CDMA Despreading Computation Matthew Doherty

  2. CDMA Cell Sites Are Power-Hungry • Code Division Multiple Access • Moves multiple access problem to DSP • Computation uses more power than other standards (TDMA, GSM, etc.) Orthogonal coding functions(Source: wikipedia.org/Cdma)

  3. Exploit structure of Walsh codes to estimate bits using fewer symbols Use feedback to choose number of symbols to use and maintain bit error rate Suboptimal Walsh Decoder with Feedback WalshDecoder Bit Error RateDetector Symbols Bits BER

  4. Test Setup Test Vectors in Block RAM Sync Control Buffer Buffer Buffer WalshDecoder BER Detector VGA DCM Enabler Feedback Path

  5. Bit Error Rate and Power Usage Source: http://finance.yahoo.com/q/bc?s=%5eIXIC&t=1d&c=

  6. Walsh Decoder FHT Same algorithm as FFT but with real (1 or -1) coefficients Source: http://grus.berkeley.edu/~jrg/ngst/fft/timedeca.html

  7. FHT Recombine Algebra • FFT butterfly structure y0 = x0 + x1 y1 = x0 − x1 Source: http://en.wikipedia.org/wiki/Butterfly_diagram

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