Interference resistant blind code synchronization for DS-CDMA systems

In this paper, we present a novel blind code synchronization algorithm, referred to as the Capon algorithm, for direct-sequence (DS) code division multiple access (CDMA) systems. The idea is to design a bank of filters, each of which passes one user signal of interest without distortion (unit-gain), meanwhile suppressing the overall interference as much as possible. The only required knowledge of the proposed scheme is the spreading code of the desired user; therefore, it is appealing to a decentralized implementation. The Capon algorithm is able to mitigate not only interference signals originated within the same cell (i.e., intra-cell interference), but also unknown interference of various origins, such as unmodeled inter-cell interference and narrowband interference in cellular overlay systems. It can be readily implemented using standard adaptive schemes, making it amenable to both acquisition and tracking. An additional advantage enjoyed by Capon is that it does not need to know the number of active transmissions, a knowledge usually indispensable for some blind algorithms to function properly. Numerical simulations are presented to illustrate the performance of the proposed Capon scheme.