Joint PN code acquisition and DOA estimation in asynchronous DS-CDMA systems
A technique that combines temporal filtering and spatial beamforming for joint PN (pseudonoise) code acquisition and DOA (direction-of-arrival) estimation in asynchronous direct-sequence code-division multiple access (DS-CDMA) systems with antenna arrays is proposed in this research. Traditionally, the joint code acquisition and DOA estimation is a 2-D search problem in the space-time domain. In this work, we apply window-based spatial filtering to antenna outputs to result in a set of temporal vectors, and then perform PN code acquisition on these vectors. Search results from several 1-D temporal vectors are combined to determine delay positions. Once delay positions are determined, the soft information provided by the acquisition process can be fully exploited by the next stage, i.e. DOA estimation. The proposed algorithm is a blind approach, which means that the training sequence is not necessary. Besides, the number of antennas required can be much less than that of the incoming signals, and the DOA search range can be largely reduced based on the soft information from the acquisition phase. Numerical simulations are given to demonstrate that the proposed solution is resistant to the near-far effect and robust to the change of the fading environment.