Unitary isotropically distributed inputs are not capacity-achieving for large-MIMO fading channels
Paper i proceeding, 2012

We analyze the capacity of Rayleigh block-fading multiple-input multiple-output (MIMO) channels in the noncoherent setting and prove that unitary space-time modulation (USTM) is not capacity-achieving when the total number of antennas exceeds the coherence time of the fading channel. This situation is relevant for MIMO systems with large antenna arrays (large-MIMO systems). Our result settles a conjecture by Zheng & Tse (2002) in the affirmative. The capacity-achieving input signal, which we refer to as Beta-variate space-time modulation (BSTM), turns out to be the product of a unitary isotropically distributed random matrix, and a diagonal matrix whose nonzero entries are distributed as the eigenvalues of a Beta-distributed random matrix of appropriate size. Numerical results illustrate that using BSTM instead of USTM in large-MIMO systems yields a rate gain as large as 13% for SNR values of practical interest.


Wei Yang

Chalmers, Signaler och system, Kommunikation, Antenner och Optiska Nätverk

Giuseppe Durisi

Chalmers, Signaler och system, Kommunikation, Antenner och Optiska Nätverk

Erwin Riegler

Technische Universität Wien

2012 IEEE International Symposium on Information Theory, ISIT 2012. Cambridge, MA,1 - 6 July 2012

1717-1721 6283571
978-146732579-0 (ISBN)


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