Multiple Access Performance of FH/NCMFSK with List Decoding

Multiple Access (MA) performance of list metric decoding is evaluated for frequency hopped (FH), noncoherent M-ary frequency shift keying (NCMFSK). In a list decoding receiver, the demodulator constructs an energy-ordered list of the channel symbols, and the decoder then awards each symbol a score based on its ranking in this list. We considered two cases: in one, the decoder assigns the same set of scores on each use of the channel; in the other, the decoder is adaptive and assigns metrics which award one of M sets of scores depending on how many energy detector outputs were believed to have contained user signals. We show that in a fading environment a list decoding system can accommodate five times more users than the best hard decision system, and that an adaptive metric doubles the capacity of the static list metric.