IEEE Communications Letters,
vol. 10, no. 6, pp. 471-473, Jun. 2006.
Sum Capacity of MIMO Gaussian Broadcast Channels
with Channel Frobenius Norm Constraints
Jeffrey G. Andrews,
Brian L. Evans
Wireless Networking and
The University of Texas at Austin,
Austin, TX 78712 USA
The motivation of this paper is to find the class
of channels that provides the best sum capacity of a MIMO
Gaussian broadcast channel with both transmit power and
channel energy constraints when
Nt ≥ K Nr,
here Nt, Nr, and
K denote the number of transmit antennas, the number of receive
antennas, and the number of users in the system, respectively.
The best sum capacity is achieved when the user channels are
mutually orthogonal to each other.
For each individual user, equal energy is distributed to all
non-zero spatial eigenmodes.
Further, we optimize the number of non-zero eigenmodes for all
users and the optimal power distribution among users.
Although, we only study the case of
Nt ≥ K Nr in this paper,
we conjecture that similar results still hold for
Nt < K Nr.
The characteristics of the optimal channels can be used to direct
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