Cell-free massive MIMO Channels in an Urban Environment -- Measurements and Channel Statistics

TL;DR

This paper presents extensive urban environment measurements for cell-free massive MIMO channels at 3.5 GHz, providing key statistics and insights essential for system design and modeling.

Contribution

It introduces a comprehensive measurement campaign and data analysis for CF-mMIMO channels, including a novel virtual AP technique and detailed channel statistics.

Findings

Pathloss coefficients of 2.9 (LOS) and 10.4 (NLOS)

Shadowing standard deviations of 5.1 dB (LOS) and 16.6 dB (NLOS)

RMS delay spreads of -80.6 dB (LOS) and -72.6 dB (NLOS)

Abstract

Cell-free massive MIMO (CF-mMIMO), where each user equipment (UE) is connected to multiple access points (APs), is emerging as an important component for 5G and 6G cellular systems. Accurate channel models based on measurements are required to optimize their design and deployment. This paper presents an extensive measurement campaign for CF-mMIMO in an urban environment. A new "virtual AP" technique measures channels between 80 UE locations and more than 20,000 possible microcellular AP locations. Measurements are done at 3.5 GHz carrier frequency with 350 MHz bandwidth (BW). The paper describes the measurement setup and data processing, shows sample results and their physical interpretation, and provides statistics for key quantities such as pathloss, shadowing, delay spread (DS), and delay window. We find pathloss coefficients of 2.9 and 10.4 for line-of-sight (LOS) and non line-of-sight (NLOS), respectively, where the high LOS coefficient is mainly because larger distance leads to more grazing angle of incidence and thus lower antenna gain in our setup. Shadowing standard deviations are 5.1/16.6 dB, and root mean squared (RMS) DSs of -80.6/-72.6 dBs. The measurements can also be used for parameterizing a CUNEC-type model, which will be reported in future work.