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Detection of digital signals received from multipath channels

  • US 5,005,189 A
  • Filed: 01/23/1989
  • Issued: 04/02/1991
  • Est. Priority Date: 01/23/1989
  • Status: Expired due to Fees
First Claim
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1. For any positive integers N, M, and K with N=K+2M, a method for detection or demodulation of a phase-and-amplitude-shift-keyed signal having a block format wherein each block has N symbols and is comprised of a known fixed pattern of M symbols preceding and following K symbols of data, where said signal is transmitted through a channel that may have multiple propagation paths and may add interfering noise, said method comprising the steps of:

  • a. obtaining from a received waveform complex samples of its complex-envelope at a rate which is an integer multiple of its symbol rate;

    b. establishing block synchronization and symbol synchronization for said complex samples;

    c. down-sampling to the symbol rate, and buffer-storing the N complex samples of the block to be detected and the first M complex samples of the next subsequent block;

    d. computing the M-point fast Fourier transform (FFT) of the first M complex samples of said block to be detected, and computing the M-point FFT of the first M complex samples of said next subsequent block, where an M-point FFT is an efficient algorithm for evaluating an M-point discrete Fourier transform;

    e. computing a weighted average of the two FFT'"'"'s computed in step d;

    f. computing the quotient of said average formed in step e divided component-by-component by the precomputed M-point FFT of said known fixed pattern;

    g. obtaining a complex vector that is an estimate of the multipath-structure of the channel by computing the M-point inverse fast Fourier transform (IFFT) of said quotient formed in step f, and subjecting the components of said IFFT to a threshold;

    h. computing the N-point FFT of said estimate of the multipath-structure of the channel obtained in step g padded with K+M zeros;

    i. scaling up the small components of said N-point FFT computed in step h and replacing any zero by a non-zero number;

    j. computing the N-point FFT of said block to be detected;

    k. dividing component-by-component said N-point FFT formed in step j by the result of step i;

    l. forming analog estimates of said data symbols and pattern symbols by computing the IFFT of the result of step k;

    m. detection of said analog estimates of said data symbols formed in step 1 by an operation appropriate for detection of a signal of the same modulation transmitted over a noisy channel having but a single propagation path.

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