Power-Bandwidth Tradeoff in Dense Multi-Antenna Relay Networks

TL;DR

This paper analyzes the energy and spectral efficiency tradeoff in dense multi-antenna relay networks, proposing distributed beamforming schemes that improve performance and approach theoretical limits in large networks.

Contribution

It introduces linear distributed multi-antenna relay beamforming schemes and characterizes their optimal power-bandwidth tradeoff in large multi-user relay networks.

Findings

Distributed relay beamforming enhances energy and spectral efficiency.

The schemes approach the cutset bound in large networks.

Optimal power scaling of K^{-1} achieved asymptotically.

Abstract

We consider a dense fading multi-user network with multiple active multi-antenna source-destination pair terminals communicating simultaneously through a large common set of $K$ multi-antenna relay terminals in the full spatial multiplexing mode. We use Shannon-theoretic tools to analyze the tradeoff between energy efficiency and spectral efficiency (known as the power- bandwidth tradeoff) in meaningful asymptotic regimes of signal-to-noise ratio (SNR) and network size. We design linear distributed multi-antenna relay beamforming (LDMRB) schemes that exploit the spatial signature of multi-user interference and characterize their power-bandwidth tradeoff under a system wide power constraint on source and relay transmissions. The impact of multiple users, multiple relays and multiple antennas on the key performance measures of the high and low SNR regimes is investigated in order to shed new light on the possible reduction in power and bandwidth requirements through the usage of such practical relay cooperation techniques. Our results indicate that point-to-point coded multi-user networks supported by distributed relay beamforming techniques yield enhanced energy efficiency and spectral efficiency, and with appropriate signaling and sufficient antenna degrees of freedom, can achieve asymptotically optimal power-bandwidth tradeoff with the best possible (i.e., as in the cutset bound) energy scaling of $K^{-1}$ and the best possible spectral efficiency slope at any SNR for large number of relay terminals.