Energy-Efficient Precoding for Multiple-Antenna Terminals

TL;DR

This paper investigates energy-efficient precoding for multi-antenna terminals in MIMO channels, highlighting optimal strategies at low power and in special cases, with numerical analysis showing the impact of antenna count.

Contribution

It introduces the problem of energy-efficient precoding in MIMO systems, providing solutions for specific scenarios and analyzing the effect of antenna numbers on energy efficiency.

Findings

Energy efficiency maximized at low transmit power.

Optimal precoding is complex for slow fading channels but solved in special cases.

Number of antennas significantly affects energy efficiency.

Abstract

The problem of energy-efficient precoding is investigated when the terminals in the system are equipped with multiple antennas. Considering static and fast-fading multiple-input multiple-output (MIMO) channels, the energy-efficiency is defined as the transmission rate to power ratio and shown to be maximized at low transmit power. The most interesting case is the one of slow fading MIMO channels. For this type of channels, the optimal precoding scheme is generally not trivial. Furthermore, using all the available transmit power is not always optimal in the sense of energy-efficiency (which, in this case, corresponds to the communication-theoretic definition of the goodput-to-power (GPR) ratio). Finding the optimal precoding matrices is shown to be a new open problem and is solved in several special cases: 1. when there is only one receive antenna; 2. in the low or high signal-to-noise ratio regime; 3. when uniform power allocation and the regime of large numbers of antennas are assumed. A complete numerical analysis is provided to illustrate the derived results and stated conjectures. In particular, the impact of the number of antennas on the energy-efficiency is assessed and shown to be significant.