ISAC MIMO Systems with OTFS Waveforms and Virtual Arrays

TL;DR

This paper introduces a novel ISAC MIMO system using OTFS waveforms and virtual arrays to enhance high-mobility sensing and communication efficiency, balancing resolution and bandwidth.

Contribution

It proposes a new virtual array construction method and a low-complexity target estimation technique for high-mobility ISAC systems.

Findings

Virtual array enables higher target resolution than physical array.

Small number of private bins achieves significant sensing gains.

System remains robust under high Doppler shifts.

Abstract

A novel Integrated Sensing-Communication (ISAC) system is proposed that can accommodate high mobility scenarios while making efficient use of bandwidth for both communication and sensing. The system comprises a monostatic multiple-input multiple-output (MIMO) radar that transmits orthogonal time frequency space (OTFS) waveforms. Bandwidth efficiency is achieved by making Doppler-delay (DD) domain bins available for shared use by the transmit antennas. For maximum communication rate, all DD-domain bins are used as shared, but in this case, the target resolution is limited by the aperture of the receive array. A low-complexity method is proposed for obtaining coarse estimates of the radar targets parameters in that case. A novel approach is also proposed to construct a virtual array (VA) for achieving a target resolution higher than that allowed by the receive array. The VA is formed by enforcing zeros on certain time-frequency (TF) domain bins, thereby creating private bins assigned to specific transmit antennas. The TF signals received on these private bins are orthogonal, enabling the synthesis of a VA. When combined with coarse target estimates, this approach provides high-accuracy target estimation. To preserve DD-domain information, the introduction of private bins requires reducing the number of DD-domain symbols, resulting in a trade-off between communication rate and sensing performance. However, even a small number of private bins is sufficient to achieve significant sensing gains with minimal communication rate loss. The proposed system is robust to Doppler frequency shifts that arise in high mobility scenarios.