 
Summary: IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 57, NO. 2, FEBRUARY 2009 1
How Much Does Transmit Correlation Affect the
SumRate Scaling of MIMO Gaussian
Broadcast Channels?
Tareq Y. AlNaffouri, Masoud Sharif, Senior Member, IEEE, and Babak Hassibi
Abstract This paper considers the effect of spatial correlation
between transmit antennas on the sumrate capacity of the
MIMO Gaussian 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
