Code timing acquisition using an antenna array for asynchronous DS-CDMA systems in a near-far environment

An adaptive near-far resistant detector using multiple antennas for acquiring synchronization of an asynchronous DS-CDMA system is presented. The only requirement is the prior knowledge of the user-spreading sequence of interest. Also, there is no need of a training sequence and a training period. Synchronization acquisition of asynchronous DS-CDMA signals is treated as a binary-hypothesis test. Under the binary hypotheses, an adaptive generalized maximum likelihood ratio test (GLRT) is developed to acquire the multipath code timings of a single desired user in both a fading and a near-far interference environment. The synchronization is obtained by sliding a search window in a sample-by-sample manner to perform the adaptive GLRT with the non-constrained maximum likelihood estimator (MLE) of direction-of-arrival (DOA) during the symbol interval. The acquisition performance of the proposed detector is illustrated by computer simulations of an asynchronous BPSK DS-CDMA system and is shown to have potential against multipath fading and the problems of near-far interference.