Diversity Transmission of M-Ary Orthogonal Signals in a Hostile Environment

This paper discusses some aspects of the problem of making good decisions when the signals are M-ary (M = 2^K) orthogonal waveforms transmitted over a channel that may include intentional jamming. The diversity may be simple as with fast frequency hopping or more complex as with error correction coding. Optimal processing with constant wideband Gaussian noise is presented to give a reference. Performance of this processor is also evaluated with optimized partial band (or time) noise jamming. Departing from optimality, two techniques that operate on the k individual bits associated with an M-ary symbol are discussed and performance is evaluated for the jamming environments mentioned previously. A ratio-threshold quantization technique with a corresponding recombination rule is presented. Finally, an example application of 8-ary FSK modulation combined with rate 1/2, constraint length 7 convolutional coding is used to illustrate the utility of this sub-optimal processing technique.