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A Per-User QoS Enhancement Strategy via Downlink Cooperative Transmission Using Distributed Antennas

In this letter, we address a strategy to enhance the signal-to-interference plus noise ratio (SINR) of the worst-case user by using cooperative transmission from a set of geographically separated antennas. Unlike previously reported schemes which are based on either the power control of individual antennas or cooperative orthogonal transmission, the presented strategy utilizes the minimum-mean-squared error (MMSE) filter structure for beamforming, which provides increased robustness to the external interference as well as the background noise at the receiver. By iteratively updating the cooperative transmission beamforming vector and power control (PC), the balanced SINR is obtained for all users, while the transmission power from each antenna also converges to within the constrained value. It is demonstrated that proposed MMSE beamforming significantly outperforms other existing schemes in terms of the achievable minimum SINR.