Optimal Transmit Beamforming for Secrecy Integrated Sensing and Communication

TL;DR

This paper develops optimal transmit beamforming strategies for a secrecy integrated sensing and communication system, balancing confidential communication, target sensing, and eavesdropper confusion, with solutions ranging from globally optimal to sub-optimal methods.

Contribution

It introduces a joint optimization framework for information and sensing beamforming in ISAC systems, including a globally optimal solution and practical sub-optimal approaches.

Findings

Proposed globally optimal beamforming algorithm using SDR and 1D search.

Designed low-complexity zero-forcing and separate beamforming solutions.

Achieved effective tradeoffs among communication secrecy, sensing accuracy, and eavesdropper confusion.

Abstract

This paper studies a secrecy integrated sensing and communication (ISAC) system, in which a multi-antenna base station (BS) aims to send confidential messages to a single-antenna communication user (CU), and at the same time sense several targets that may be suspicious eavesdroppers. To ensure the sensing quality while preventing the eavesdropping, we consider that the BS sends dedicated sensing signals (in addition to confidential information signals) that play a dual role of artificial noise (AN) for confusing the eavesdropping targets. Under this setup, we jointly optimize the transmit information and sensing beamforming at the BS, to minimize the matching error between the transmit beampattern and a desired beampattern for sensing, subject to the minimum secrecy rate requirement at the CU and the transmit power constraint at the BS. Although the formulated problem is non-convex, we propose an algorithm to obtain the globally optimal solution by using the semidefinite relaxation (SDR) together with a one-dimensional (1D) search. Next, to avoid the high complexity induced by the 1D search, we also present two sub-optimal solutions based on zero-forcing and separate beamforming designs, respectively. Numerical results show that the proposed designs properly adjust the information and sensing beams to balance the tradeoffs among communicating with CU, sensing targets, and confusing eavesdroppers, thus achieving desirable transmit beampattern for sensing while ensuring the CU's secrecy rate.