 
Summary: How Much Does Transmit Correlation Affect the
SumRate of MIMO Downlink Channels?
TAREQ Y. ALNAFFOURI, MASOUD SHARIF and BABAK HASSIBI
Abstract This paper considers the effect of spatial correlation
between transmit antennas on the sumrate 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 sumrate 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 . When the channel exhibits some
spatial correlation with a covariance matrix R (nonsingular 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
