New five-user collaborative codes with improved performance

In this paper, we present two new 5-user collaborative codes that offer better performance than published ones, especially those by Chang and Weldon [Coding for T-user multiple access channels. IEEE Trans Info Theory 1979;25(6):684–91]. Using BPSK modulation for each individual user, the resulting output symbols set to the channel is an M-ary ASK signal. Constellation size is reduced to 5-ary ASK {−5,−3,−1,+1,+3} for the new codes instead of 6-ary {−5,−3, −1,+1,+3,+5} for the published (Chang et al.) codes. As a result, new codes offer a gain of 1.5 dB at 10−4 probability of symbol error. New codes also require 28.6% less transmitter power.