How Much Does Transmit Correlation Affect the Sum-Rate of MIMO Broadcast Channels?

In this talk, we consider 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 (DPC) and for different types of beamforming transmission schemes. When the channel is i.i.d., it has been shown that for large number of users n, the sum rate is equal to M*loglog(n) + M*log SNR where M is the number of transmit antennas.

When the channel exhibits some spatial correlation with a covariance matrix R, we show that this results in an SNR hit that depends on 1) the multiuser broadcast technique and 2) on the eigenvalues of the correlation matrix R. In this talk, we quantify the hit resulting from spatial correlation to the sum-rate of DPC, beam-forming with channel whitening, random beam-forming, and deterministic beam-forming.

This is a joint work with Masoud Sharif (Boston University) and Babak Hassibi (California Institute of Technology)