Uplink Energy Efficiency of Cell-Free Massive MIMO With Transmit Power Control in Measured Propagation Channels

TL;DR

This paper evaluates uplink energy efficiency in cell-free massive MIMO systems using real-world channel measurements, comparing power control algorithms to optimize battery life while maintaining spectral efficiency.

Contribution

It introduces and tests three transmit power control algorithms on measured propagation data, highlighting the effectiveness of max-min EE in practical scenarios.

Findings

Max-min EE algorithm significantly improves uplink energy efficiency.

Performance gains are higher with more APs and lower circuit power.

Effectiveness depends on maximum UE transmit power and number of APs.

Abstract

Cell-free massive MIMO (CF-mMIMO) is expected to provide reliable wireless services for a large number of user equipments (UEs) using access points (APs) distributed across a wide area. When the UEs are battery-powered, uplink energy efficiency (EE) becomes an important performance metric for CF-mMIMO systems. Therefore, if the "target" spectral efficiency (SE) is met, it is important to optimize the uplink EE when setting the transmit powers of the UEs. Also, such transmit power control (TPC) method must be tested on channel data from real-world measurements to prove its effectiveness. In this paper, we compare three different TPC algorithms using zero-forcing reception by applying them to 3.5 GHz channel measurement data featuring ~30,000 possible AP locations and 8 UE locations in a 200mx200m area. We show that the max-min EE algorithm is highly effective in improving the uplink EE at a target SE, especially if the number of single-antenna APs is large, circuit power consumption is low, and the maximum allowed transmit power of the UEs is high.