Technique for acquiring timing and frequency synchronization for modem utilizing known (non-data) symbols as part of their normal transmitted data format

For use in a communications system wherein signals transmitted over a communication channel are formatted as successive frames of symbols, each frame containing a block of a first prescribed member of unknown information symbols to be recovered and a block of a second prescribed number of known reference symbols, so that for successive frames of symbols the blocks of unknow information symbols are interleaved with blocks of known reference symbols, the distribution of said interleaved blocks of known reference symbols among said blocks of unknown information symbols being predetermined, said known symbols being employed at a receiver for providing compensation for distortion-introducing characteristics of a channel over which received signals have been transmitted, a method of operating said receiver to enable said receiver to recover said unknown information symbols comprising the steps of:

• (a) correlating a sequentially generated replica of said block of known symbols with sequences of received symbol-representative signals, each sequence covering the span of a frame of symbols, and causing said replica of said block of known symbols to be generated in synchronism with the blocks of known symbols contained in the received signals, whose distribution among said blocks of unknown information symbols is predetermined, in accordance with the correlation of said generated replica with said sequences of received symbol-representative signals;
• and
• (b) causing the distortion-introducing characteristics of the channel to be compensated in accordance with the contents of the received signals corresponding to the known blocks of symbols in successive frames of symbols.

For use in a communications system wherein signals transmitted over a communication channel are formatted as successive frames of symbols, each frame containing a block of a first prescribed number of unknown information symbols to be recovered and a block of a second prescribed number of known reference symbols, so that for successive frames of symbols the blocks of unknown information symbols are interleaved with blocks of knwon reference symbols, the distribution of said interleaved blocks of known reference symbols among said blocks of unknown information symbols being predetermined, said known symbols being employed at a receiver for providing compensation for distortion-introducing characteristics of a channel over which received signals have been transmitted, a signal processing apparatus for enabling said received to recover said unknown information symbols comprising:

• first means for correlating a sequentially generated replica of said block of known symbols with sequences of received symbol-representative signals, each seqeunce covering the span of a frame of symbols, and causing said replica of said block of known symbols to be generated in synchronism with the blocks of known symbols contained in the received signals, whose distribution among said blocks of unknown information symbols is predetermined, in accordance with the correlation of said generated replica with said sequences of received symbol-representative signals;
• and
• second means, coupled to said for means, for causing the distortion-introducing characteristics of the channel to be compensated in accordance with the contents of the received signals corresponding to the known blocks of symbols in successive frames of symbols.

For use in a communications receiver wherein signals received thereby contain successive data symbols between which are interleaved sequences of prescribed known symbols, the distribution of said interleaved sequences of prescribed known symbols among said data symbols being predetermined, said known symbols being employed in said receiver for providing compensation for distortion-introduced characteristics of a channel over which signals received have been transmitted, a method of operating said receiver to enable said receiver to detect said data symbols comprising the steps of:

• (a) selectively combining a replica of said known symbols with received symbol-representative signals until the timing of the occurence of said interleaved sequences of prescribed known symbols in said received signals has been identified;
• (b) adjusting the timing at which said replica of said known symbols is generated in order to maintain a prescribed time alignment between said replica of said known symbols and a received known symbol sequence;
• (c) generating a frequency for tuning the receiver to a modulation frequency for said symbols and adjusting said frequency;
• and
• (d) causing the distortion-introducing characteristics of the channel to be compensated in accordance with the contents of received signals including those the timing of occurence of which within the received signals corresponds to that of the interleaved prescribed known symbols identified in step (a).

For use in a communications receiver wherein signals received thereby contain successive data symbols between which are interleaved sequences of prescribed known symbols, the distribution of said interleaved sequences of prescribed known symbols among said data symbols being predetermined, said known symbols being employed in said receiver for providing compensation for distortion-introducing characteristics of a channel over which signals received have been transmitted, a signal processing apparatus for enabling said receiver to detect said data symbols comprising, in combination;

• first means for combining a replica of said known symbols with received symbol-representative signals until the timing of the occurence of said interleaved sequences of prescribed known symbols in said received signal has been identified;
• second means, responsive to the operation of said first means, for adjusting the timing at which said replica of said known symbols is generated in order to maintain a prescribed time alignment between said replica of said known symbols and a received known symbol sequence;
• third means, responsive to the operation of said first and second means means, for generating a frequency for tuning the receiver to a modulation frequency for said symbols and adjust said frequency;
• and
• fourth means for causing the distortion-introducing characteristics of the channel to be compensated in accordance with the contents of received signals including those the timing of occurence of which within the received signals corresponds to that of the interleaved prescribed known symbols identified by said first means.