Maximum-likelihood synchronization of a single user for code-division multiple-access communication systems

Code-division multiple access (CDMA) has emerged as an access protocol well-suited for voice and data transmission. One significant limitation of the conventional CDMA system is the near-far problem where strong signals interfere with the detection of a weak signal. Multiuser detectors assume knowle...

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Bibliographic Details
Published in:IEEE transactions on communications 1998-03, Vol.46 (3), p.392-399
Main Authors: Bensley, S.E., Aazhang, B.
Format: Article
Language:English
Subjects:
Access protocols
Data communication
Detectors
Interference elimination
Maximum likelihood detection
Maximum likelihood estimation
Multiaccess communication
Multiple access interference
Multiuser detection
Yield estimation
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Summary:Code-division multiple access (CDMA) has emerged as an access protocol well-suited for voice and data transmission. One significant limitation of the conventional CDMA system is the near-far problem where strong signals interfere with the detection of a weak signal. Multiuser detectors assume knowledge of all of the modulation waveforms and channel parameters, and exploit this information to eliminate multiple-access interference (MAI) and to achieve near-far resistance. A major problem in practical application of multiuser detection is the estimation of the signal and channel parameters in a near-far limited system. We consider maximum-likelihood estimation of users delay, amplitude, and phase in a CDMA communication system. We present an approach for decomposing this multiuser estimation problem into a series of single-user problems. In this method the interfering users are treated as colored non-Gaussian noise. The observation vectors are preprocessed to be able to apply a Gaussian model for the MAI. The maximum-likelihood estimate (MLE) of each user's parameters based on the processed observation vectors becomes tractable. The estimator includes a whitening filter derived from the sample covariance matrix which is used to suppress the MAI, thus yielding a near-far resistant estimator.
ISSN:0090-6778
1558-0857
DOI:10.1109/26.662645