NDA chip synchronization for bandlimited DS/SS M-PSK signals using CDMA with unequal power levels on nonselective fading channels

Derives two maximum-likelihood (ML) oriented nondecision-aided (NDA) chip synchronization algorithms for bandlimited direct-sequence spread spectrum (DS/SS) M-PSK signals transmitted over a nonselective fading channel. The authors also investigate their tracking performance in the presence of multi-user interference in a code-division multiple access (CDMA) system where the users have unequal power levels. The performance of the non-channel aided (NCA) algorithm was found to be independent of the fading characteristics, whereas the channel aided (CA) algorithm is influenced by the carrier-to-multipath ratio C/M, but not by the fading bandwidth. For practical E_s/N₀, the NCA algorithm outperforms the CA algorithm, whose performance degrades with decreasing C/M. The performance of both algorithms is better for synchronous than for asynchronous CDMA. For large signal-to-noise ratio, the tracking error variances approach asymptotic values that are inversely proportional to the ratio of the reference user power to the total power of the multi-user interference