Method and apparatus for bidirectional demodulation of digitally modulated signals

A system for bidirectionally demodulating data symbols transmitted through a communication channel comprising:

• means for sequentially receiving a first plurality of known data symbols, a second plurality of unknown data symbols, and a third plurality of known data symbols;
• means for storing the first plurality of known data symbols, the second plurality of unknown data symbols and the third plurality of known data symbols;
• means for forward-demodulating a first block of the second plurality of unknown data symbols received nearer said first plurality of known data symbols;
• means for backward-demodulating a second block of the second plurality of unknown data symbols received nearer said third plurality of known data symbols;
• means for determining quality values indicative of demodulation qualities in the forward-demodulated first block and the backward-demodulated second block of the unknown data symbols, said quality values including a plurality of figure-of-merits each based upon at least one of noise power, signal power, and a combination of signal power plus noise power;
• means for comparing the quality values to produce a best direction indication;
• and
• means for selecting either the means for forward-demodulating or the means for backward-demodulating to demodulate subsequent blocks of unknown data symbols based on the comparison of the quality values.