Local Decoding of Walsh Codes to Reduce CDMA Despreading ComputationCDMA Cell Sites Are Power-HungrySuboptimal Walsh Decoder with FeedbackTest SetupBit Error Rate and Power Usage Walsh Decoder FHTFHT Recombine AlgebraLocal Decoding of Walsh Codes to Reduce CDMA Despreading ComputationMatthew DohertyCDMA 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)Suboptimal Walsh Decoder with FeedbackWalshDecoderBit Error RateDetector• Exploit structure of Walsh codes to estimate bits using fewer symbols• Use feedback to choose number of symbols to use and maintain bit error rateSymbols BitsBERTest SetupTest Vectors in Block RAMWalshDecoderBER DetectorVGAFeedback PathSyncDCMControl Buffer BufferEnablerBufferBit Error Rate and Power Usage Source: http://finance.yahoo.com/q/bc?s=%5eIXIC&t=1d&c=Walsh Decoder FHTSame algorithm as FFT but with real (1 or -1) coefficientsSource: http://grus.berkeley.edu/~jrg/ngst/fft/timedeca.htmlFHT Recombine AlgebraSource: http://en.wikipedia.org/wiki/Butterfly_diagram• FFT butterfly structurey0 = x0 + x1y1 = x0 −
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