Waveform Index Modulation for Backscatter Communications in RIS-Based MIMO Radars

TL;DR

This paper introduces a novel waveform index modulation scheme for RIS-assisted MIMO radars that enables simultaneous radar operation and low-complexity backscatter communication without changing the beampattern.

Contribution

It proposes a new modulation technique that encodes information via subset selection of orthogonal codes, enhancing communication efficiency in RIS-based radar systems.

Findings

Effective backscatter communication demonstrated through numerical results.

Low-complexity detection at the reader without channel state information.

RIS partitioning enables simultaneous radar and communication functionalities.

Abstract

This paper studies a symbiotic system in which a reconfigurable intelligent surface (RIS) assists a radar transmitter while conveying information to a reader via backscattering. The RIS is partitioned into subarrays that redirect the radar signal toward the angular sector under inspection and superimpose a slow-time modulation using orthogonal phase codes, thereby implementing MIMO radar functionalities. Communication is achieved by encoding information in the selection of an unordered subset of orthogonal codewords, without altering the RIS transmit beampattern. At the reader, the proposed index modulation scheme enables low-complexity detection without requiring channel state information. Numerical results demonstrate the effectiveness of the proposed backscatter communication approach.