DocumentCode :
824736
Title :
Randomly spread CDMA: asymptotics via statistical physics
Author :
Guo, Dongning ; VerdÚ, Sergio
Author_Institution :
Dept. of Electr. Eng., Princeton Univ., NJ, USA
Volume :
51
Issue :
6
fYear :
2005
fDate :
6/1/2005 12:00:00 AM
Firstpage :
1983
Lastpage :
2010
Abstract :
This paper studies randomly spread code-division multiple access (CDMA) and multiuser detection in the large-system limit using the replica method developed in statistical physics. Arbitrary input distributions and flat fading are considered. A generic multiuser detector in the form of the posterior mean estimator is applied before single-user decoding. The generic detector can be particularized to the matched filter, decorrelator, linear minimum mean-square error (MMSE) detector, the jointly or the individually optimal detector, and others. It is found that the detection output for each user, although in general asymptotically non-Gaussian conditioned on the transmitted symbol, converges as the number of users go to infinity to a deterministic function of a "hidden" Gaussian statistic independent of the interferers. Thus, the multiuser channel can be decoupled: Each user experiences an equivalent single-user Gaussian channel, whose signal-to-noise ratio (SNR) suffers a degradation due to the multiple-access interference (MAI). The uncoded error performance (e.g., symbol error rate) and the mutual information can then be fully characterized using the degradation factor, also known as the multiuser efficiency, which can be obtained by solving a pair of coupled fixed-point equations identified in this paper. Based on a general linear vector channel model, the results are also applicable to multiple-input multiple-output (MIMO) channels such as in multiantenna systems.
Keywords :
Gaussian channels; MIMO systems; channel capacity; channel coding; code division multiple access; decoding; fading channels; least mean squares methods; matched filters; multiuser detection; radio receivers; radiofrequency interference; spread spectrum communication; statistical mechanics; CDMA; MAI; MIMO; MMSE; arbitrary input distribution; channel capacity; code-division multiple access; coupled fixed-point equation; decorrelator; deterministic function; flat fading; hidden Gaussian statistic; linear minimum mean-square error detector; linear vector channel model; matched filter; multiple-access interference; multiple-input multiple-output channel; multiuser channel; multiuser detection; posterior mean estimator; single-user decoding; statistical mechanic; statistical physic; Decoding; Degradation; Detectors; Fading; MIMO; Matched filters; Multiaccess communication; Multiple access interference; Multiuser detection; Physics; Channel capacity; code-division multiple access (CDMA); free energy; multiple-input multiple-output (MIMO) channel; multiuser detection; multiuser efficiency; replica method; statistical mechanics;
fLanguage :
English
Journal_Title :
Information Theory, IEEE Transactions on
Publisher :
ieee
ISSN :
0018-9448
Type :
jour
DOI :
10.1109/TIT.2005.847700
Filename :
1435646
Link To Document :
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