Transceiver Design for MIMO-DFRC Systems Cai Wen 1,2 and Timothy N. Davidson 2 1. School of Information Science and Technology, Northwest University, Xi’an, China. 2. Department of Electrical and Computer Engineering, McMaster University, Hamilton, Canada. (wencai@nwu.edu.cn); (davidson@mcmaster.ca) ABSTRACT This paper addresses joint design of the transmitting waveform and the receivers of a dual-function radar-communication (DFRC) sys- tem that enables both multiple-input multiple-output (MIMO) ra- dar sensing and multi-user multiple-input single-output (MU- MISO) communications. The proposed approach incorporates the design of the communication receiving (Rx) coefficients, in addi- tion to the radar Rx filters. We seek to maximize the minimum ra- dar signal-to-interference-plus-noise ratio (SINR) over multiple targets, subject to per-antenna power constraints, peak-to-average- power ratio (PAPR) constraints and a communication SINR con- straint for each user. A successive convex approximation algorithm is developed to find a good solution for the resultant nonconvex design problem. Numerical results show that by incorporating the communication Rx coefficients into the joint design, the radar and communication capabilities of the DFRC system can be signifi- cantly enhanced over the state-of-the-art designs. Index Terms—Dual-function radar-communication systems, MIMO radar, MU-MISO communication. 1. INTRODUCTION Dual-functional radar and communication (DFRC) systems, in which radar sensing and communication functions share a common Tx platform, have been recognized as a promising architecture to address the problem of spectrum congestion [1]-[4]. In this paper, we consider a DFRC system with multiple antennas that provides both MIMO radar sensing and MU-MISO communication func- tionalities. Since the objectives and intrinsic requirements of sig- naling for radar and communication systems are inherently differ- ent [2], the key design question for MIMO-DFRC systems is how to effectively and efficiently leverage the available information and the degrees-of-design-freedom (design DOFs) in the transmitter and the radar/communication receivers to improve the performance tradeoffs between the radar and communication functions. While there are several strategies that can be adopted for DFRC transceiver design, e.g., [5]-[13], [20]-[24], directly designing the Tx waveform for each communication/radar data block has the ad- vantage that it enables us to explicitly control the deterministic waveform properties, e.g., [5]-[13]. For example, in [9] the prob- lem of joint Tx waveform and radar Rx filter design is considered on the basis of nonlinear precoding. A constant-envelope con- straint is incorporated into the problem of minimizing the weighted sum of multiuser communication interference (MUI), radar SINR and waveform similarity, and a design methodology based on al- ternating optimization and gradient projection is proposed. How- ever, in literature so far, the transceiver designs for DFRC systems have only focused on a simple scenario, in which a single target is present in the observation scene [9], [11]. In practice, it is quite common that multiple targets appear concurrently. Moreover, the existing designs overlook the fact that conventional MU-MISO communication receivers operate coherently, and hence can scale and rotate the received signal using a complex-valued equalization coefficient; e.g., [14]. Motived by the above observations, in this paper we propose a generalized transceiver design for the joint MIMO radar and MU- MISO communication system, where the Tx waveform, the radar Rx filters and the communication Rx coefficients will be jointly de- signed via block-level nonlinear precoding. The communication Rx coefficients represent additional design DOFs over existing sys- tems, and hence offer the potential to improve performance tradeoffs. We will focus on the scenario in which multiple radar targets coexist with arbitrarily located signal-dependent interfer- ence and multiple single-antenna communication users. To guaran- tee the communication quality-of-service (QoS) and obtain good radar performance, we consider maximizing the minimum radar target SINR, subject to communication SINR, per-antenna power and PAPR constraints. The resultant design problem is an NP-hard nonconvex problem, and we propose a customized iterative algo- rithm based on successive convex approximation (SCA) [25] and the feasible point pursuit (FPP) technique [15]. Numerical exam- ples indicate that the designed transceiver is able to provide supe- rior performance tradeoffs compared with the existing techniques. 2. SYSTEM MODEL AND PROBLEM FORMULATION 2.1 Signal Model and Performance Metrics As depicted in Fig. 1, we consider a MIMO-DFRC system that can simultaneously realize monostatic MIMO radar sensing and MU-MISO downlink communication functionalities. The shared Tx aperture is an N-element uniform linear array (ULA), and the Rx antenna used for radar sensing is an M-element ULA. We will consider a scenario with Q radar targets, K single-antenna commu- nication users and significant signal-dependent clutter. In the communication side, we consider a standard coherent downlink MU-MISO transmission scenario wherein the received data block of K users is expressed as Shared Tx array 1 2 N : Radar target Single-antenna comm. user Radar Rx array 1 2 M Signal-dependent interference Dual-use Tx waveform Rx signal processing Control center : : Fig. 1. MIMO-DFRC system model. ICASSP 2023 - 2023 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) | 978-1-7281-6327-7/23/$31.00 ©2023 IEEE | DOI: 10.1109/ICASSP49357.2023.10096008