Multi-Objective Optimization-Based Waveform Design for Multi-User and Multi-Target MIMO-ISAC Systems

Integrated sensing and communication (ISAC) opens up new service possibilities for sixth-generation (6G) systems, where both communication and sensing (C&S) functionalities co-exist by sharing the same hardware platform and radio resource. In this paper, we investigate the waveform design problem in a downlink multi-user and multi-target ISAC system under different C&S performance preferences. The multi-user interference (MUI) may critically degrade the communication performance. To eliminate the MUI, we employ the constructive interference mechanism into the ISAC system, which saves the power budget for communication. However, due to the conflict between C&S metrics, it is intractable for the ISAC system to achieve the optimal performance of C&S objective simultaneously. Therefore, it is important to strike a trade-off between C&S objectives. By virtue of the multi-objective optimization theory, we propose a weighted Tchebycheff-based transformation method to re-frame the C&S trade-off problem as a Pareto-optimal problem, thus effectively tackling the constraints in ISAC systems. Finally, simulation results reveal the trade-off relation between C&S performances, which provides insights for the flexible waveform design under different C&S performance preferences in MIMO-ISAC systems.

I. Introduction

Due to the dual capability of communication and radar sensing, integrated sensing and communication (ISAC) has inspired enormous academic and industrial enthusiasm [2], [3]. The appealing concept stems from the fact that communication and radar systems share many similarities in terms of devices, waveform, and signal processing algorithms [4]. What’s more, the overlapping of radar and communication frequency bands developing towards higher frequency such as millimeter wave, terahertz and visible light, promotes the interoperability of communication and sensing (C&S) with existing wireless infrastructure [5]. Consequently, ISAC has been identified as a promising technique to alleviate the exacerbated spectrum scarcity for the upcoming sixth-generation (6G) wireless systems. Triggered by benefits from ISAC, a unified theoretical framework for ISAC resource allocation is likely to drive a paradigm innovation for future cellular architecture and networking protocols.