Fundamental CRB-Rate Tradeoff in Multi-antenna Multicast Channel with ISAC

TL;DR

This paper explores the fundamental limits of multi-antenna multicast channels with integrated sensing and communication, deriving optimal transmit strategies to balance data rate and sensing accuracy.

Contribution

It introduces a semi-closed form solution for optimal transmit covariance that balances communication and sensing performance in ISAC systems.

Findings

Optimal transmit covariance is full rank, combining information and sensing signals.

Derived the outer bound of the CRB-Rate (C-R) region for ISAC.

Numerical results demonstrate the effectiveness of the proposed beamforming strategies.

Abstract

This paper studies the multi-antenna multicast channel with integrated sensing and communication (ISAC), in which a multi-antenna base station (BS) sends common messages to a set of single-antenna communication users (CUs) and simultaneously estimates the parameters of an extended target via radar sensing. We investigate the fundamental performance limits of this ISAC system, in terms of the achievable rate for communication and the estimation Cram\'er-Rao bound (CRB) for sensing. First, we derive the optimal transmit covariance in semi-closed form to balance the CRB-rate (C-R) tradeoff, and accordingly characterize the outer bound of a so-called C-R region. It is shown that the optimal transmit covariance should be of full rank, consisting of both information-carrying and dedicated sensing signals in general. Next, we consider a practical joint information and sensing beamforming design, and propose an efficient approach to optimize the joint beamforming for balancing the C-R tradeoff. Numerical results are presented to show the C-R region achieved by the optimal transmit covariance and the joint beamforming, as compared to other benchmark schemes.