Downlink Beamforming with Imperfect Channel Information for a TDD-Based OFDMA System

Eunchul YOON  Joontae KIM  

IEICE TRANSACTIONS on Communications   Vol.E92-B   No.9   pp.2967-2971
Publication Date: 2009/09/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E92.B.2967
Print ISSN: 0916-8516
Type of Manuscript: LETTER
Category: Wireless Communication Technologies
downlink beamforming,  interference suppression,  OFDMA,  imperfect channel information,  

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The beamforming weights which can suppress the interfering signal toward out-of-cell mobile stations in downlink are designed for a time division duplexing based OFDMA system when the channel information is not perfect. The derived beamforming weights do not improve the average SINR performance monotonously with the increased transmit SNR if the inverse of the transmit SNR is used as the regularization factor of the beamforming weights and the channel information obtained by the BS to design the BF weights is not perfect. Therefore, we suggest a simple scheme to select the regularization factor. The proposed beamforming weights improve the performance monotonously with the increased transmit SNR and achieve near-optimal performance. The performance achieved by applying the beamforming weights used in uplink to downlink beamforming is also investigated.