Communication-Sensing Region for Cell-Free Massive MIMO ISAC Systems

TL;DR

This paper introduces the communication-sensing (C-S) region for Cell-Free massive MIMO ISAC systems, analyzing the trade-offs and designing beamforming strategies considering target location uncertainties.

Contribution

It defines the C-S region for Cell-Free MIMO ISAC systems and develops novel beamforming methods for sensing, communication, and combined operation under location uncertainties.

Findings

The C-S region illustrates the trade-off between sensing and communication performance.

Cell-Free MIMO offers advantages over traditional systems for radar sensing.

The proposed beamforming scheme outperforms zero-forcing and maximum ratio transmission methods.

Abstract

This paper investigates the system model and the transmit beamforming design for the Cell-Free massive multi-input multi-output (MIMO) integrated sensing and communication (ISAC) system. The impact of the uncertainty of the target locations on the propagation of wireless signals is considered during both uplink and downlink phases, and especially, the main statistics of the MIMO channel estimation error are theoretically derived in the closed-form fashion. A fundamental performance metric, termed communication-sensing (C-S) region, is defined for the considered system via three cases, i.e., the sensing-only case, the communication-only case and the ISAC case. The transmit beamforming design problems for the three cases are respectively carried out through different reformulations, e.g., the Lagrangian dual transform and the quadratic fractional transform, and some combinations of the block coordinate descent method and the successive convex approximation method. Numerical results present a 3-dimensional C-S region with a dynamic number of access points to illustrate the trade-off between communication and radar sensing. The advantage for radar sensing of the Cell-Free massive MIMO system is also studied via a comparison with the traditional cellular system. Finally, the efficacy of the proposed beamforming scheme is validated in comparison with zero-forcing and maximum ratio transmission schemes.