Low-Complexity Coordinated Beamforming for Downlink Multicell SDMA/OFDM Systems

Coordinated beamforming (CBF) or coordinated scheduling is regarded as an effective means of mitigating the intercell interference (ICI) in orthogonal frequency-division multiplexing (OFDM) systems. In this paper, a new CBF scheme is presented based on leakage-controlled minimum-mean-square-error (LC-MMSE) precoding. We use a regularized factor to maximize the signal-to-interference-plus-noise-ratio (SINR) of LC-MMSE and analyze its achievable throughput loss compared with the conventional minimum-mean-square-error (MMSE) scheme. The results show that the upper bound of the achievable throughput loss increases as the number of serving users grows. A joint frequency and spatial coordination scheme is proposed as an effort to simplify the design of transmit beamforming weights by separating the objective functions that maximize the expected signal strength and minimize the interference leakage in different resource groups. System-level simulation results demonstrate that the proposed scheme can significantly reduce the ICI, and it performs well even with imperfect channel-state information (CSI) at the transmitter.