Downlink beamforming in small cells with scalar information exchange

Multi-input single-output (MISO) beamforming techniques are addressed in the downlink small cells environment, where a small cell base station (BS) has multiple antennas while a user has a single antenna. Two-types of extreme beamforming schemes at small cell base stations (BSs) are considered based on local channel state information (CSI) at transmitter: i) maximizing the desired channel gain and ii) minimizing the interference generated by each small cell base station (BS). Then, we propose a beamforming scheme that minimizes weighted generating-interference in pursuit of enhancing the achievable rate. In particular, an additional scalar information exchange is assumed between the BSs via a low-rate interface such as the X-2 interface in the 3GPP standards. By carefully choosing the weight coefficients based on the signal-to-interference-and-noise-ratios (SINRs), the scheme balances between these two philosophies - egoism and altruism. Simulation results show that there exists a trade-off between the amount of CSI knowledge and the achievable rate.