CMA-based Code Acquisition Scheme for DS-CDMA Systems

Date

2000

Authors

Cheung, P
Rapajic, P

Journal Title

Journal ISSN

Volume Title

Publisher

Institute of Electrical and Electronics Engineers (IEEE Inc)

Abstract

In direct-sequence code-division multiple access, a code synchronization must take place before the multiuser detector. As the initial synchronization stage, code acquisition scheme is used to estimate the relative timing phase for the desired transmission within one chip interval. In this paper, a blind code acquisition scheme using adaptive linear filtering based on a linearly constrained constant modulus algorithm (CMA) is proposed. The uncertainty of a desired user's delay is initially discretized and translated into a number of hypotheses. The lock convergence property of CMA is exploited, where the filter at the steady state can lock onto the desired user while nulling all other interfering users (i.e., a decorrelator). For each delay hypothesis, the filter is initialized as the corresponding shifted spreading sequence of the desired user. It is shown that lock convergence always occurs for the correct hypothesis, while all incorrect hypotheses will be hovered around some saddle regions, given sufficiently small step sizes. Then, the correct hypothesis is the one which has the converged filter to yield the maximum lock onto the desired user, or a maximum output energy.

Description

Keywords

Keywords: Adaptive filtering; Algorithms; Code division multiple access; Maximum likelihood estimation; Signal interference; Signal to noise ratio; Spurious signal noise; Synchronization; White noise; Blind adaptation; Code acquisition; Constant modulus algorithm;

Citation

Source

IEEE Transactions on Communications

Type

Journal article

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