Method of and apparatus for transmitting and receiving coded digital signals

摘要

A system for transmitting digital information such as audio or video over a lossy or dispersive medium. The digital information is of the type where certain bits are more important than others and hence the less important bits can suffer a greater bit error rate. Accordingly, the most important bits are encoded into a (7,k) 8-ary Reed Solomon code where 7 is the length of the code and k is the dimension of the code. The less important bits are then respectively encoded into a (7,k+1) or a (7,k+2) 8-ary Reed Solomon code. The code words are modulated onto a plurality of tones or subcarriers. The decoding is effected by initially demodulating the subcarriers and generating a candidate set of code words from each 7-tuple of demodulated 8-ary symbols corresponding to a transmitted code word. The decoding of each transmitted code word is completed by making the statistical decision that the transmitted code word is the member of the associated group of candidate code words maximizing an adaptive maximum likelihood test statistic.