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
Collections
Source
IEEE Transactions on Communications
Type
Journal article