Asymptotic coding gains in multiuser systems

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 maximum likelihood sequence (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 a power-limited application. It is shown that some block encoding schemes with (n,κ), κ>1 can provide direct-sequence spread-spectrum modulation and give a positive coding gain. These systems combined with the narrow-band signature waveforms are shown to outperform the conventional approaches with the same bandwidth expansion constraint