Power Efficient Downlink Beamforming Optimization by Exploiting Interference

We propose a new beamforming scheme for the multi- user multiple-input-single-output (MISO) downlink channel. While conventional beamforming aims at the minimization of the transmit power subject to suppressing interference to guarantee quality of service (QoS) constraints, here we exploit, rather than suppress, the constructive part of interference. By exploiting the power of constructively interfering symbols, the proposed scheme achieves the required QoS at lower transmit power. In addition, we derive an equivalent virtual multicast formulation for the proposed optimization to facilitate the design of a more efficient solver. Our simulation and analysis show significant power savings for small scale MISO downlink channels with the proposed optimization compared to conventional beamforming optimization.

I. Introduction

Transmit beamforming schemes for power minimization have become particularly relevant for the downlink channel, in-line with the global initiative to improve the power efficiency of communication systems. Highly complex capacity-achieving dirty paper coding (DPC) techniques [1] have been proposed for pre-subtracting interference prior to transmission. Their suboptimal low-complexity counterparts [2]–[9] offer a complexity reduction at a comparable performance. Linear precoding schemes based on channel inversion [10]–[14] offer the least complexity, but their performance is far from achieving the optimum maximum likelihood bound for small scale MIMO systems, while the contrary has been shown for large scale MIMO [15]–[17].