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

TL;DR

This study evaluates the energy efficiency of uplink cell-free massive MIMO systems using measured propagation data, comparing power control algorithms and antenna configurations to identify optimal strategies for high EE.

Contribution

It provides a comprehensive analysis of uplink energy efficiency considering real-world channel measurements, comparing multiple power control algorithms and antenna setups.

Findings

Max-min EE power control significantly improves energy efficiency.

Fully-distributed antenna systems perform better in energy efficiency.

Channel conditions greatly influence the effectiveness of power control algorithms.

Abstract

Cell-free massive MIMO (CF-mMIMO) provides wireless connectivity for a large number of user equipments (UEs) using access points (APs) distributed across a wide area with high spectral efficiency (SE). The energy efficiency (EE) of the uplink is determined by (i) the transmit power control (TPC) algorithms, (ii) the numbers, configurations, and locations of the APs and the UEs, and (iii) the propagation channels between the APs and the UEs. This paper investigates all three aspects, based on extensive (~30,000 possible AP locations and 128 possible UE locations) channel measurement data at 3.5 GHz. We compare three different TPC algorithms, namely maximization of transmit power (max-power), maximization of minimum SE (max-min SE), and maximization of minimum EE (max-min EE) while guaranteeing a target SE. We also compare various antenna arrangements including fully-distributed and semi-distributed systems, where APs can be located on a regular grid or randomly, and the UEs can be placed in clusters or far apart. Overall, we show that the max-min EE TPC is highly effective in improving the uplink EE, especially when no UE within a set of served UEs is in a bad channel condition and when the BS antennas are fully-distributed.