Index Modulation with Circularly-Shifted Chirps for Dual-Function Radar and Communications

TL;DR

This paper introduces a novel index modulation scheme using circularly-shifted chirps for dual-function radar and communication systems, enhancing spectral efficiency, autocorrelation properties, and estimation bounds.

Contribution

It proposes a new CSC-IM scheme that encodes information via CSC indices and PSK symbols, with theoretical analysis and practical advantages for DFRC systems.

Findings

Improved spectral efficiency through index separation

Derived bounds for error rate and estimation accuracy

Validated scheme effectiveness via comprehensive comparisons

Abstract

In this study, we propose index modulation (IM) with circularly-shifted chirps (CSCs) (CSC-IM) for dual-function radar and communication (DFRC) systems. The proposed scheme encodes the information bits with the CSC indices and the phase-shift keying (PSK) symbols. It allows the receiver to exploit the frequency selectivity naturally in fading channels by combining IM and wideband CSCs. It also leverages the fact that a CSC is a constant-envelope signal to achieve a controllable peak-to-mean envelope power ratio (PMEPR). For radar functionality, CSC-IM maintains the good autocorrelation (AC) properties of a chirp by ensuring that the transmitted CSCs are separated apart sufficiently in the time domain through index separation (IS). We investigate the impact of IS on spectral efficiency (SE) and obtain the corresponding mapping functions. For theoretical results, we derive the union bound (UB) of the block error rate (BLER) for arbitrary chirps and the Cramer-Rao lower bounds (CRLBs) for the range and reflection coefficients for the matched filter (MF)-based estimation. We also prove that complementary sequences (CSs) can be constructed through CSCs by linearly combining the Fourier series of CSCs. Finally, through comprehensive comparisons, we demonstrate the efficacy of the proposed scheme for DFRC scenarios.