Low-Complexity Code Acquisition Method in DS/CDMA Communication Systems: Application of the Maximum Likelihood Method to Propagation Delay Estimation

Nobuoki ESHIMA  Tohru KOHDA  

IEICE TRANSACTIONS on Communications   Vol.E91-B   No.5   pp.1472-1479
Publication Date: 2008/05/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e91-b.5.1472
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
code acquisition,  complexity,  DS/CDMA system,  efficiency,  maximum likelihood method,  sign-matched filter,  

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Code acquisition performance in the Direct-Sequence Code-Division Multiple-Access (DS/CDMA) communication system is strongly related to the quality of the communication systems. The performance is assessed by (i) code acquisition time; (ii) precision; and (iii) complexity for implementation. This paper applies the method of maximum likelihood (ML) to estimation of propagation delay in DS/CDMA communications, and proposes a low-complexity method for code acquisition. First, a DS/CDMA system model and properties of outputs with a passive matched-filter receiver are reviewed, and a statistical problem in code acquisition is mentioned. Second, an error-controllable code acquisition method based on the maximum likelihood is discussed. Third, a low-complexity ML code acquisition method is proposed. It is shown that the code acquisition time with the low-complexity method is about 1.5 times longer than that with the original ML method, e.g. 13 data periods under 4.96 dB.