[Paper Review] On the Energy-Spectral Efficiency Trade-off of the MRC Receiver in Massive MIMO Systems with Transceiver Power Consumption

Sudarshan Mukherjee, Saif Khan Mohammed|arXiv (Cornell University)|Apr 11, 2014

Advanced MIMO Systems Optimization8 references9 citations

TL;DR

This paper investigates the energy-spectral efficiency trade-off in massive MIMO systems using a Maximum Ratio Combining (MRC) receiver, accounting for transceiver circuit power consumption. It shows that by adaptively increasing the number of base station antennas (M) and users (K) with spectral efficiency R, energy efficiency converges to a positive constant as R→∞, unlike fixed (M,K) configurations where it tends to zero.

ABSTRACT

We consider the uplink of a multiuser massive MIMO system wherein a base station (BS) having $M$ antennas communicates coherently with $K$ single antenna user terminals (UTs). We study the energy efficiency of this system while taking the transceiver power consumption at the UTs and the BS into consideration. For a given spectral efficiency $R$ and fixed transceiver power consumption parameters, we propose and analyze the problem of maximizing the energy efficiency as a function of $(M,K)$. For the maximum ratio combining (MRC) detector at the BS we show that with increasing $R$, $(M,K)$ can be adaptively increased in such a way that the energy efficiency converges to a positive constant as $R ightarrow \infty$ ($(M,K)$ is increased in such a way that a constant per-user spectral efficiency $R/K$ is maintained). This is in contrast to the fixed $(M,K)$ scenario where the energy efficiency is known to converge to zero as $R ightarrow \infty$. We also observe that for large $R$, the optimal $(M,K)$ maximizing the energy efficiency is such that, the total power consumed by the power amplifiers (PA) in all the $K$ UTs is a small fraction of the total system power consumption.

Motivation & Objective

• To analyze the energy efficiency of massive MIMO systems with MRC combining while accounting for transceiver circuit power consumption at both base station and user terminals.
• To investigate how energy efficiency scales with increasing spectral efficiency R when M and K are adaptively increased.
• To compare the optimal energy efficiency of MRC and ZF receivers under realistic power consumption models.
• To determine the optimal (M,K) pair that maximizes energy efficiency for a given spectral efficiency R and fixed power consumption parameters.

Proposed method

• Formulates a system model for uplink massive MIMO with M-antenna base station and K single-antenna users, incorporating power amplifier (PA), receiver, and transceiver circuit power consumption.
• Derives a closed-form expression for total system power consumption, including PA, receiver, and circuit power at both BS and UTs.
• Proposes an optimization problem to maximize energy efficiency (bits/Joule) with respect to (M,K) for a fixed spectral efficiency R.
• Analyzes the asymptotic behavior of optimal energy efficiency as R→∞, showing convergence to a positive constant when M and K scale such that per-user spectral efficiency R/K is maintained.
• Uses asymptotic approximations and numerical simulations to validate analytical results, particularly in the large-R regime.
• Compares MRC with ZF receivers by evaluating their optimal energy efficiency under identical system parameters and assumptions.

Experimental results

Research questions

• RQ1 Can energy efficiency be maintained at a positive constant as spectral efficiency R→∞ when M and K are adaptively increased in an MRC-based massive MIMO system with transceiver power consumption?
• RQ2 How does the optimal (M,K) pair scale with increasing R, and what is the resulting energy efficiency behavior in the large-R regime?
• RQ3 How does the MRC receiver's optimal energy efficiency compare to that of the ZF receiver when transceiver power is considered?
• RQ4 What fraction of total system power is consumed by user terminal power amplifiers at optimal (M,K) for large R?
• RQ5 How sensitive is the optimal energy efficiency to variations in transceiver power consumption parameters?

Key findings

• For the MRC receiver, energy efficiency converges to a positive constant as R→∞ when M and K are increased such that per-user spectral efficiency R/K is held constant, unlike the fixed (M,K) case where energy efficiency tends to zero.
• The optimal energy efficiency of the MRC receiver is strictly lower than that of the ZF receiver for large R, confirming that ZF achieves better energy efficiency under the same conditions.
• For large R, the total power consumed by power amplifiers in all K user terminals constitutes only a small fraction of the total system power, indicating that energy efficiency is primarily limited by circuit power at the BS and UTs.
• The optimal (M,K) pair increases with R, and the approximation of optimal energy efficiency becomes tight when both M and K are sufficiently large.
• The optimal energy efficiency decreases with increasing transceiver power consumption parameters (ρr, ρd, ρs), showing sensitivity to hardware power profiles.
• Numerical results confirm that the analytical approximation of optimal energy efficiency is tight for large R, validating the asymptotic analysis.