Runhua
Chen, Zukang Shen, Jeffrey G. Andrews, Robert W. Heath, Jr.
Submitted to IEEE Transactions on Signal Processing,
November 2006
We propose a low-complexity multi-mode
transmission technique for downlink multiuser MIMO systems with block diagonalization (BD). The proposed technique adaptively
adjusts the number of data streams for each user, switching between
single-stream beamforming and multi-stream spatial
multiplexing, as a means to exploit the multi-mode switching diversity.
Multi-mode transmission is studied in the multiuser context,
where there are more mobile users than the base station can serve
simultaneously, therefore a subset of users need to be selected. Joint user and
antenna selection has been proposed as a multiuser multi-mode switching
technique, where theoptimal subset of receive
antennas and users are chosen to maximize the sum throughput. The brute-force
search, however, is prohibitively complicated and impractical due to the
computational demand. In this paper, we propose two low-complexity near-optimal
user/antenna selection algorithms. The first algorithm aims at maximizing a
capacity lower bound, derived in terms of the effective channel energy, while
the second algorithm greedily maximizes the sum capacity. We analytically
evaluate the complexity of our proposed algorithms and show that it is orders
of magnitude lower than the exhaustive search. Simulation results demonstrate
that the proposed algorithms achieve up to 98% of the sum throughput of the
exhaustive search, for most system configurations, while the complexity is
substantially reduced.
This preprint is available via email.