Exploiting Known Interference as Green Signal Power for Downlink Beamforming Optimization

TL;DR

This paper introduces a novel data-aided beamforming scheme for MISO downlink channels that exploits constructive interference to reduce transmit power while maintaining QoS, outperforming traditional methods.

Contribution

It proposes a new precoding scheme leveraging data and CSI to exploit constructive interference, reducing power consumption compared to conventional beamforming.

Findings

Significant power savings in small-scale MISO channels

Enhanced SINR balancing with lower transmit power

Robust beamforming with imperfect CSI maintains QoS

Abstract

We propose a data-aided transmit beamforming scheme for the multi-user multiple-input-single-output (MISO) downlink channel. While conventional beamforming schemes aim at the minimization of the transmit power subject to suppressing interference to guarantee quality of service (QoS) constraints, here we use the knowledge of both data and channel state information (CSI) at the transmitter to exploit, rather than suppress, constructive interference. More specifically, we design a new precoding scheme for the MISO downlink that minimizes the transmit power for generic phase shift keying (PSK) modulated signals. The proposed precoder reduces the transmit power compared to conventional schemes, by adapting the QoS constraints to accommodate constructive interference as a source of useful signal power. By exploiting the power of constructively interfering symbols, the proposed scheme achieves the required QoS at lower transmit power. We extend this concept to the signal to interference plus noise ratio (SINR) balancing problem, where higher SINR values compared to the conventional SINR balancing optimization are achieved for given transmit power budgets. In addition, we derive equivalent virtual multicast formulations for both optimizations, both of which provide insights of the optimal solution and facilitate the design of a more efficient solver. Finally, we propose a robust beamforming technique to deal with imperfect CSI, that also reduces the transmit power over conventional techniques, while guaranteeing the required QoS. Our simulation and analysis show significant power savings for small scale MISO downlink channels with the proposed data-aided optimization compared to conventional beamforming optimization.