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Analysis of multiple-antenna wireless links at low SNR

Rao, Chaitanya and Hassibi, Babak (2004) Analysis of multiple-antenna wireless links at low SNR. IEEE Transactions on Information Theory, 50 (9). pp. 2123-2130. ISSN 0018-9448. http://resolver.caltech.edu/CaltechAUTHORS:RAOieeetit04

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Abstract

Wireless channels with multiple transmit/receive antennas are known to provide a high spectral efficiency both when the channel is known to the receiver, and when the channel is not known to the receiver if the signal-to-noise ratio (SNR) is high. Here we analyze such systems at low SNR, which may find application in sensor networks and other low-power devices. The key point is that, since channel estimates are not reliable, it is often not reasonable to assume that the channel is known at the receiver at low SNR. In this unknown channel case, we show that for sensible input distributions, in particular all practical modulation schemes, the capacity is asymptotically quadratic in the SNR, /spl rho/, and thus much less than the known channel case where it exhibits a linear growth in /spl rho/. We show that under various signaling constraints, e.g., Gaussian modulation, unitary space-time modulation, and peak constraints, that mutual information is maximized by using a single transmit antenna. We also show that at low SNR, sending training symbols leads to a rate reduction in proportion to the fraction of training duration time so that it is best not to perform training. Furthermore, we show that the per-channel use mutual information is linear in both the number of receive antennas and the channel coherence interval.


Item Type:Article
Additional Information:©2004 IEEE. Reprinted with permission. Manuscript received March 10, 2003; revised February 1, 2004. [Posted online: 2004-08-30] This work was supported in part by the National Science Foundation under Grant CCR-0133818, by the Office of Naval Research under Grant N00014-02-1-0578, and by Caltech’s Lee Center for Advanced Networking. Communicated by G. Caire, Associate Editor for Communications.
Subject Keywords:Low-signal-to-noise ratio; Rayleigh fading; SNR; multiple-antenna systems; noncoherent channels; regime
Record Number:CaltechAUTHORS:RAOieeetit04
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:RAOieeetit04
Alternative URL:http://dx.doi.org/10.1109/TIT.2004.833369
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2634
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:13 Apr 2006
Last Modified:26 Dec 2012 08:50

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