[Paper Review] Rate-Splitting Multiple Access for Multi-Antenna Joint Radar and Communications

Chengcheng Xu, Bruno Clerckx+3 more|arXiv (Cornell University)|Mar 14, 2021

Radar Systems and Signal Processing37 references160 citations

TL;DR

This paper proposes a Rate-Splitting Multiple Access (RSMA)-assisted multi-antenna dual-functional radar-communication (DFRC) system that jointly optimizes communication rate and radar beampattern matching. By exploiting the common stream in RSMA to manage interference among users and between radar and communication, the framework achieves superior tradeoff performance between weighted sum rate (WSR) and beampattern approximation MSE—outperforming SDMA-based DFRC with or without a dedicated radar sequence—while eliminating the need for an additional radar sequence and SIC, thus simplifying system architecture without performance loss.

ABSTRACT

Dual-Functional Radar-Communication (DFRC) system is an essential and promising technique for beyond 5G. In this work, we propose a powerful and unified multi-antenna DFRC transmission framework, where an additional radar sequence is transmitted apart from communication streams to enhance radar beampattern matching capability, and Rate-Splitting Multiple Access (RSMA) is adopted to better manage the interference. RSMA relies on multi-antenna Rate-Splitting (RS) with Successive Interference Cancellation (SIC) receivers, and the split and encoding of messages into common and private streams. We design the message split and the precoders of the radar sequence and communication streams to jointly maximize the Weighted Sum Rate (WSR) and minimize the radar beampattern approximation Mean Square Error (MSE) subject to the per antenna power constraint. An iterative algorithm based on Alternating Direction Method of Multipliers (ADMM) is developed to solve the problem. Numerical results first show that RSMA-assisted DFRC achieves a better tradeoff between WSR and beampattern approximation than Space-Division Multiple Access (SDMA)-assisted DFRC with or without radar sequence, and other simpler radar-communication strategies using orthogonal resources. We also show that the RSMA-assisted DFRC frameworks with and without radar sequence achieve the same tradeoff performance. This is because that the common stream is better exploited in the proposed framework. The common stream of RSMA fulfils the triple function of managing interference among communication users, managing interference between communication and radar, and beampattern approximation. Therefore, by enabling RSMA in DFRC, the system performance is enhanced while the system architecture is simplified since there is no need to use additional radar sequence and SIC. We conclude that RSMA is a more powerful multiple access for DFRC.

Motivation & Objective

• Address the challenge of spectrum scarcity in 5G and beyond by enabling integrated sensing and communication (ISAC) through dual-functional radar-communication (DFRC) systems.
• Overcome the limitations of existing DFRC approaches based on Space-Division Multiple Access (SDMA), which struggle with interference management between radar and communication functions and among communication users.
• Develop a unified transmission framework that jointly maximizes weighted sum rate (WSR) and minimizes radar beampattern approximation mean square error (MSE) under per-antenna power constraints.
• Demonstrate that RSMA can replace the need for a dedicated radar sequence by leveraging the common stream to fulfill multiple roles: interference management, radar beampattern shaping, and communication multiplexing.

Proposed method

• Propose a novel RSMA-based DFRC architecture where messages are split into common and private streams, and the common stream is used to shape the radar beampattern.
• Design precoders for the radar sequence, common stream, and private streams jointly to optimize WSR and MSE, subject to per-antenna power constraints.
• Utilize Rate-Splitting (RS) with Successive Interference Cancellation (SIC) at the receiver to decode the common stream and cancel interference selectively.
• Formulate a non-convex optimization problem combining WSR maximization and MSE minimization, solved via an Alternating Direction Method of Multipliers (ADMM) algorithm.
• Integrate the SIC receiver to manage interference not only between radar and communication but also among communication users, leveraging the common stream's dual-purpose capability.
• Enable the common stream to serve as a virtual radar waveform, replacing the need for a separate radar sequence while maintaining or improving beampattern accuracy.

Experimental results

Research questions

• RQ1 Can RSMA be effectively applied to multi-antenna DFRC to improve the tradeoff between communication rate and radar beampattern accuracy compared to conventional SDMA-based DFRC?
• RQ2 Does the common stream in RSMA uniquely enable the simultaneous management of interference among communication users and between radar and communication, thereby eliminating the need for a separate radar sequence?
• RQ3 How does the performance of RSMA-assisted DFRC compare to SDMA-assisted DFRC with and without a dedicated radar sequence, especially when SIC is used?
• RQ4 Can the SIC receiver in RSMA be leveraged for dual interference management—between communication users and between radar and communication—thereby simplifying system design?
• RQ5 What is the impact of the common stream's role in beampattern approximation, and does it achieve performance parity with a dedicated radar sequence?

Key findings

• RSMA-assisted DFRC without a dedicated radar sequence achieves the same WSR-beampattern MSE tradeoff performance as RSMA-assisted DFRC with a radar sequence, demonstrating that the common stream can fully replace the radar sequence.
• The common stream in RSMA performs a triple function: managing interference among communication users, managing interference between radar and communication, and shaping the radar beampattern.
• RSMA outperforms SDMA-assisted DFRC with or without a radar sequence and SIC, particularly in the tradeoff between WSR and MSE, with performance gains observed for α < 0.78.
• The SIC receiver in RSMA is effectively used for dual-purpose interference cancellation—among users and between radar and communication—enabling better spectral efficiency and system simplification.
• Numerical results confirm that the ADMM-based algorithm converges in approximately ten iterations, indicating efficient and stable optimization of the non-convex problem.
• The absence of a dedicated radar sequence in RSMA-based DFRC simplifies system architecture without sacrificing performance, as the common stream subsumes the role of the radar sequence.