An array processing approach to joint PN (pseudo-noise) code acquisition and DOA (direction-of-arrival) estimation in asynchronous direct-sequence code-division multiple access (DS-CDMA) systems is proposed. This problem is traditionally treated as a 2-D search problem in the space-time domain. Our approach transforms the 2-D space-time matrix data from the antenna output to several time domain vectors using a set of beams steering to different directions. Then, the acquisition process searches from these 1-D temporal vectors to provide soft information for the next stage, i.e. DOA estimation. Our algorithm is a blind approach, where the training sequence is not needed. 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 process. Numerical simulations are presented to demonstrate that the proposed solution is resistant to the near-far effect and robust to the change of the fading environment.
KEYWORDS: Antennas, Signal to noise ratio, Phased arrays, Optical correlators, Interference (communication), Signal detection, Receivers, Data modeling, Signal processing, Mobile communications
The problem of PN code acquisition at base stations in asynchronous direct-sequence code-division multiple access (DS-CDMA) systems equipped with antenna arrays is investigated in this work. Both the fading and the near-far interference effects of the communication channel are considered. The antenna system in the base station is a one-dimensional (1D) linear beamforming array. After formulating the acquisition problem, we propose several methods for its solution. They include: the least squares method, the constrained optimization method, the weighted eigenvectors method and the generalized likelihood ratio test method. The system parameters such as the fading gain, the direction of arrival (DOA) and transmitted data symbols from each active mobile user are assumed to be unknown but deterministic in our model. The only knowledge is the spreading code of the desired user. It is demonstrated by simulation results that our proposed solutions are resistant to the near-far effect and robust to the change of the fading environment.
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