Coordinated SINR balancing methods for multi-cell downlink systems

In this paper, we consider coordinated beamforming techniques where multiple base stations jointly design a transmission strategy by sharing channel state information. Particularly, we tackle the signal-to-interference-plus-noise ratio (SINR) balancing problem to maximize the worst-user rate for multi-cell downlink systems. To solve this problem, both symmetric complex (SC) and asymmetric complex (AC) signaling methods are investigated. First, we present the SINR balancing algorithm with the SC signaling. Due to residual interference, the worst-user rate in the SC signaling is saturated at high signal-to-noise ratio (SNR). To alleviate this issue, we also propose the SINR balancing technique based on the AC signaling which combines both interference alignment and power control methods. Simulation results confirm that the AC signaling outperforms the SC signaling scheme over all SNR range.