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Method of determining a collision between a plurality of transmitting stations in a frame-based communications network

  • US 6,898,204 B2
  • Filed: 04/04/2001
  • Issued: 05/24/2005
  • Est. Priority Date: 04/07/2000
  • Status: Expired due to Term
First Claim
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1. A method of determining that a collision between two or more transmitting stations occurred at one of the transmitting stations on a frame-based communications network, the method comprising:

  • providing a header format for the transmitted frame, the header format including a cyclic preamble, destination address field, source address field and fixed guard field, the destination address field and the source address field immediately following the preamble and the fixed guard field following the source address field, the cyclic preamble having a cyclic preamble format wherein a plurality of identical copies of a preamble symbol sequence are transmitted sequentially;

    computing a least-squares channel estimate of an echo channel between a station transmitter and a station receiver from a received sample sequence and a transmitted preamble;

    computing an estimate of received samples of the source address field of the transmitted frame by linear convolution of the least-squares channel estimate and an upsampled and zero-filled sequence of destination address, source address, and fixed guard;

    subtracting the estimate of received samples of the source address field of the transmitted frame from actual received samples corresponding to the source address field to produce a source field error vector low-pass filtered signal;

    computing an (L2) norm of each term of the source field error vector;

    computing an estimate of received samples of second and third copies of the cyclic preamble by linear convolution of the least-squares channel estimate and upsampled and zero-filled second and third copies of the cyclic preamble;

    computing an estimate of received samples of third and fourth copies of the cyclic preamble by linear convolution of the least-squares channel estimate and upsampled and zero-filled known third and fourth copies of the cyclic preamble;

    computing an estimate of error power in the second and third copies of the preamble by subtracting actual received samples of the second and third copies of the preamble from the estimate of the received samples of the second and third copies of the cyclic preamble, then squaring a norm of a first resulting vector and dividing by length of one copy of the cyclic preamble;

    computing an estimate of error power in the third and fourth copies of the cyclic preamble by subtracting actual received samples of the third and fourth copies of the preamble from the estimate of the received samples of the third and fourth copies of the cyclic preamble, then squaring a norm of a second resulting vector and dividing by the length of one copy of the cyclic preamble; and

    declaring a collision if;

    an absolute value of an estimate of 10*log 10 of the error power in the second and third copies of the preamble minus 10*log 10 of the estimate of the error power in the third and fourth copies of the preamble exceeds a first threshold;

    or a 20*log 10 of a maximum value of the norm of each term of a source field error vector minus 10*log 10 of a greater of the estimate of the error power in the second and third copies of the cyclic preamble and the estimate of the error power in the third and fourth copies of the preamble exceeds a second threshold.

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