Maximum-likelihood code-timing acquisition of DS-CDMA signals for multipath channels

Abstract

Future CDMA systems may be required to operate with a low processing gain in order to accommodate high rate users. The resulting increase in channel dispersion will have a detrimental impact on code-timing acquisition. Two maximum-likelihood code-timing acquisition algorithms are proposed for multipath channels: a multiuser estimator and a single-user estimator. Multipath diversity is exploited in the estimators via maximum ratio combining to increase the signal-to-interference ratio. In addition, correlations between signals from different paths are explicitly incorporated in the test statistics of both estimators. Both help to improve the estimation accuracy and decrease mean acquisition time. Extensive simulations indicate that the estimators are robust to near-far power ratio and channel dispersion. Moreover, the gain achieved by incorporating channel dispersion in estimator design is significant.