Asymptotic coding gains in multiuser systems


In this work the asymptotic multiuser coding gain (AMCG) as well as asymptotic multiuser efficiency (AME) are found for K coded asynchronous users and a variety of multiuser detectors, including optimum (MLS), multistage, decorrelated and conventional detectors. Since the direct sequence can be viewed as a special kind of block repetition codes, it gives zero (dB) coding gain in power-limited application. It is shown that some block encoding schemes with (n, k), k > 1 can provide direct-sequence spread-spectrum modulation and give positive coding gain. These systems combined with the narrow-band signature waveforms are shown to outperform their conventional approachs with the same bandwidth expansion constraint.