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Analysis of SIRBased Downlink Beamforming
Holger BOCHE Martin SCHUBERT
Publication
IEICE TRANSACTIONS on Communications
Vol.E85B
No.6
pp.11601168 Publication Date: 2002/06/01 Online ISSN:
DOI: Print ISSN: 09168516 Type of Manuscript: PAPER Category: Antenna and Propagation Keyword: mobile communication, smart antenna, multiuser downlink beamforming, power control,
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Summary:
Transmit beamforming is a promising way to increase the downlink capacity of wireless networks. Since all users are coupled via their radiation patterns, the beamforming vectors must be optimized along with power control. It is necessary to balance the signaltointerference levels according to individual QoS requirements. This problem leads back to the minimization of the infinitynorm of a certain vector and has first been studied by Gerlach and Paulraj in [1]. It has been assumed that the optimum solution can be obtained by minimizing the 1norm instead, thereby leading to a new problem, which is generally easier to handle. The analytical and numerical results in this paper, however, indicate that this conjecture is generally not valid. We characterize the case where the 1norm solution also solves the infinitynorm problem. In particular, it is shown that for the special case of a 2user scenario, both optimization problems are indeed equivalent and a closedform solution can be given. The analytical results provide new insights into the problem of coupled downlink beamforming and offer a useful approach to the design of efficient and reliable algorithms.

