A Comparison Between Co-Located and Distributed MIMO Deployments in OFDM-ISAC Networks

TL;DR

This paper compares cell-free and multi-cell massive MIMO architectures in OFDM-ISAC networks, showing that cell-free deployments generally offer superior sensing performance due to their distributed nature.

Contribution

It provides a unified analysis of OFDM-based ISAC in both architectures, deriving sensing detectors and evaluating how network configurations impact sensing performance.

Findings

Cell-free MIMO offers more robust sensing performance.

Distributed antennas improve sensing accuracy.

Performance benefits are consistent across various network configurations.

Abstract

This paper investigates network-level integrated sensing and communication (ISAC) under two fundamentally different topology configurations: cell-free massive MIMO (CF-mMIMO) and multi-cell massive MIMO (MC-mMIMO). A unified OFDM-based waveform is adopted for both architectures as the key enabler for ISAC functionalities. The CF system exploits distributed access points (APs) and a scalable user-target-centric operation, whereas the MC system relies on co-located transmit-receive arrays with conventional cell-centric deployment. For both architectures, we derive a GLRT-based sensing detector and the corresponding sensing SNR expressions. We then examine a series of case studies investigating how the number of OFDM subcarriers, the transceiver allocation strategy, and the antenna/node distribution across the network affect the sensing performance. The results consistently demonstrate that CF-mMIMO provides more robust and higher sensing performance across most tested scenarios, particularly when transmit resources or antenna elements are spatially distributed. These findings highlight the inherent advantages of CF deployments for next-generation ISAC networks.