Title :
Multiple-antenna capacity in correlated Rayleigh fading with channel covariance information
Author :
Jafar, Syed Ali ; Goldsmith, Andrea
Author_Institution :
Electr. Eng. & Comput. Sci., Univ. of California, Irvine, CA, USA
fDate :
5/1/2005 12:00:00 AM
Abstract :
We analyze a mobile multiple input multiple output wireless link with M transmit and N receive antennas operating in a spatially correlated Rayleigh flat fading environment. Only the correlations between the channel coefficients are assumed to be known at the transmitter and the receiver. The channel coefficients are correlated in space and uncorrelated in time from one coherence interval to another. These coefficients remain constant for a coherence interval of T symbol periods after which they change to another independent realization according to the spatial correlation model. For this system we characterize the structure of the input signal that achieves capacity. The capacity achieving transmit signal is expressed as the product of an isotropically distributed unitary matrix, an independent nonnegative diagonal matrix and a unitary matrix whose columns are the eigenvectors of the transmit fade covariance matrix. For the case where the number of transmit antennas M is larger than the channel coherence interval T, we show that the channel capacity is independent of the smallest M-T eigenvalues of the transmit fade covariance matrix. In contrast to the previously reported results for the spatially white fading model where adding more transmit antennas beyond the coherence interval length (M>T) does not increase capacity, we find that additional transmit antennas always increase capacity as long as their channel fading coefficients are spatially correlated with the other antennas. We show that for fast hopping or fast fading systems (T=1) with only channel covariance information available to the transmitter and receiver, transmit fade correlations are beneficial. Mathematically, we prove this by showing that capacity is a Schur-convex function of the vector of eigenvalues of the transmit fade correlation matrix. We also show that the maximum possible capacity gain due to transmitter fade correlations is 10logM dB.
Keywords :
MIMO systems; Rayleigh channels; antenna arrays; channel capacity; eigenvalues and eigenfunctions; matrix algebra; mobile radio; receiving antennas; transmitting antennas; channel covariance information; correlated Rayleigh flat fading environment; distributed unitary matrix; eigenvectors; mobile multiple input multiple output wireless link; multiple antenna capacity; nonnegative diagonal matrix; receive antennas; receivers; spatial correlation model; transmit antennas; transmit fade correlation matrix; transmitter; Channel capacity; Coherence; Covariance matrix; Eigenvalues and eigenfunctions; Fading; MIMO; Rayleigh channels; Receiving antennas; Transmitters; Transmitting antennas; Antenna correlation; channel capacity; channel state information (CSI); multielement antenna arrays; wireless communications;
Journal_Title :
Wireless Communications, IEEE Transactions on
DOI :
10.1109/TWC.2005.847029