This paper considers the problem of simultaneous multiuser downlink beamforming. The idea is to employ a transmit antenna array to create multiple "beams" directed toward the individual users, and the aim is to increase throughput, measured by sum capacity. In particular, we are interested in the practically important case of more users than transmit antennas, which requires user selection. Optimal solutions to this problem can be prohibitively complex for online implementation at the base station and entail so-called Dirty Paper (DP) precoding for known interference. Suboptimal solutions capitalize on multiuser (selection) diversity to achieve a significant fraction of sum capacity at lower complexity cost. We analyze the throughput performance in Rayleigh fading of a suboptimal greedy DP-based scheme proposed by Tu and Blum. We also propose another user-selection method of the same computational complexity based on simple zero-forcing beamforming. Our results indicate that the proposed method attains a significant fraction of sum capacity and throughput of Tu and Blum's scheme and, thus, offers an attractive alternative to DP-based schemes.
Bibliographical noteFunding Information:
Manuscript received May 12, 2004; revised November 26, 2004. This work was supported in part by the European Research Office (ERO) of the U.S. Army under Contract N62558-03-C-0012 and in part by the Army Research Laboratory under Cooperative Agreement DADD19-01-2-0011. Any opinions, findings and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of ERO and ARL of the U.S. Army. U.S.–Greek exchange supported in part by a GSRT collaborative exchange grant. An earlier version of part of this work appears in Proc. IEEE ICASSP 2004, May 17-21, 2004, Montréal, QC, Canada. The associate editor coordinating the review of this manuscript and approving it for publication was Dr. Vikram Krishnamurthy.
- Multiuser diversity