How Much Does Transmit Correlation Affect the Sum-Rate of MIMO Downlink Channels?
Abstract
This paper considers the effect of spatial correlation between transmit antennas on the sum-rate capacity of the MIMO broadcast channel (i.e., downlink of a cellular system). Specifically, for a system with a large number of users n, we analyze the scaling laws of the sum-rate for the dirty paper coding and for different types of beamforming transmission schemes. When the channel is i.i.d., it has been shown that for large n, the sum rate is equal to M log log n + M log P/M + o(1) where M is the number of transmit antennas, P is the average signal to noise ratio, and o(1) refers to terms that go to zero as n rarr infin. When the channel exhibits some spatial correlation with a covariance matrix R (non-singular with tr(R) = M), we prove that the sum rate of dirty paper coding is M log log n + M log P/M + log det(R) + o(1). We further show that the sum-rate of various beamforming schemes achieves M log log n + M log P/M + M log c + o(1) where c les 1 depends on the type of beamforming. We can in fact compute c for random beamforming proposed in M. Sharif et al. (2005) and more generally, for random beamforming with preceding in which beams are pre-multiplied by a fixed matrix. Simulation results are presented at the end of the paper.
Additional Information
© Copyright 2006 IEEE. Reprinted with permission. Publication Date: July 2006. Posted online: 2006-12-26. The work of T. Y. Al-Naffouri has been supported by King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia. Their work is supported in part by NSF under grant no. CCR-0133818 and CCR-0326554, by David and Lucy Packard Foundation, and by Caltech Lee Center for Advanced Networking.Files
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- 9700
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- CaltechAUTHORS:NAFisit06
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