Code timing estimation in a near-far environment for direct-sequence code-division multiple-access

Abstract

An adaptive receiver structure is considered for obtaining timing information for a direct-sequence code-division multiple-access (CDMA) communication network operating in a near-far environment. The receiver consists of a chip matched filter followed by an adaptive equalizer. By using a simple channel-access protocol, the timing information for a new system user can be extracted from the weights of the adaptive equalizer. In order to obtain this timing information, the receiver only requires knowledge of the spreading code of the new user. A maximum-likelihood (ML) estimation algorithm is given based on several simplistic assumptions on the statistical properties of the adaptive filter tap weights. Several different CDMA environments were simulated, and the performance of the ML estimation algorithm is presented. These results show that even though simplistic assumptions were used in the derivation of the ML estimation algorithm, this receiver structure is applicable to extracting timing information for a direct-sequence CDMA system operating in a near-far environment. >