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Adaptive modem for varying communication channel

  • US 5,127,051 A
  • Filed: 06/13/1988
  • Issued: 06/30/1992
  • Est. Priority Date: 06/13/1988
  • Status: Expired due to Term
First Claim
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1. An adaptive modem system for a communication channel exhibiting multipath dispersion, which has a channel response characterized by an anticipated multipath delay time length, comprising:

  • transmitting means for transmitting signals over the communication channel representing a packet of data made up of a plurality of frames in series, wherein each frame is composed of two adjacent training blocks in series with a data sequence of unknown symbols, which symbols are unknown as containing data to be received and which symbols become known only when received and decoded with respect to an accurate estimate of said channel response and wherein a second of the two training blocks is made up of M known symbols, and a first of the two training blocks has a time length longer than the multipath delay time length and separates the second training block from the data sequence; and

    receiving means for receiving the transmitted signals, demodulating the data packet therefrom, and processing each frame thereof, including;

    (a) source means for storing and generating the sequence of M known symbols;

    (b) channel estimate means for correlating the sequence of M known symbols from said source means with the received M known symbols of the second training block and obtaining an estimate of said channel response as would be associated with an anticipated multipath delay time length in each frame of the data packet, wherein said second training block is isolated by the time length of said first training block so as to be substantially unaffected by any multipath dispersion from the data sequence; and

    (c) decision means for decoding the unknown symbols of the data sequence in each frame using the estimate of said channel response as obtained.

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