Hybrid Index Modulation for Dual-Functional Radar Communications Systems

Abstract

Dual-functional radar communications (DFRC) systems, which jointly design radar and communication functionalities on one common platform, have been recognized as an attractive approach for leveraging the scarce spectral efficiently in diverse applications, such as autonomous driving. Index modulation (IM), a promising communication technique with high energy utilization and spectral efficiency, has been successfully integrated into DFRC systems. Most existing IM-based DFRC schemes utilize the degrees of freedom (DoFs) from one or two domains for separate information embedding, without utilizing the full diversity of the integrated waveform. In this paper, we propose a novel DFRC scheme, referred to as hybrid index modulation (HIM), operating on frequency hopping multiple-input multiple-output (FH-MIMO) radar. The HIM embeds communication information into the index of the 3-tuples in the hybrid dictionary, which is the outer product of DoFs from the frequency, phase, and antenna index of the integrated waveform. Since the HIM entwines waveform diversities from different domains, it increases the communication rate by multiples. We also apply the HIM to the non-orthogonal FH-MIMO radar to improve spectral efficiency, in addition to the conventional orthogonal case. Furthermore, we propose a constrained HIM scheme to enhance the radar detection performance, where the FH pattern has been optimized in terms of ambiguity function. System performance is evaluated both theoretically and experimentally in metrics of communication rate, ambiguity function and symbol error rate.