A Novel ISAC Transmission Framework based on Spatially-Spread Orthogonal Time Frequency Space Modulation

TL;DR

This paper introduces a new ISAC transmission framework using SS-OTFS modulation, enabling efficient radar sensing and communication through spatially-spread discretization and tailored estimation, detection, and power allocation schemes.

Contribution

The paper proposes the innovative SS-OTFS modulation with angular domain discretization, simplifying radar and communication models, and designs novel estimation, detection, and power allocation strategies for integrated sensing and communication.

Findings

Effective beam tracking and angle estimation methods developed.

Communication performance analyzed via pair-wise error probability.

Power allocation strategies favoring radar sensing demonstrated.

Abstract

In this paper, we propose a novel integrated sensing and communication (ISAC) transmission framework based on the spatially-spread orthogonal time frequency space (SS-OTFS) modulation by considering the fact that communication channel strengths cannot be directly obtained from radar sensing. We first propose the concept of SS-OTFS modulation, where the key novelty is the angular domain discretization enabled by the spatial-spreading/de-spreading. This discretization gives rise to simple and insightful effective models for both radar sensing and communication, which result in simplified designs for the related estimation and detection problems. In particular, we design simple beam tracking, angle estimation, and power allocation schemes for radar sensing, by utilizing the special structure of the effective radar sensing matrix. Meanwhile, we provide a detailed analysis on the pair-wise error probability (PEP) for communication, which unveils the key conditions for both precoding and power allocation designs. Based on those conditions, we design a symbol-wise precoding scheme for communication based only on the delay, Doppler, and angle estimates from radar sensing, without the a priori knowledge of the communication channel fading coefficients, and also introduce the power allocation for communication. Furthermore, we notice that radar sensing and communication requires different power allocations. Therefore, we discuss the performances of both the radar sensing and communication with different power allocations and show that the power allocation should be designed leaning towards radar sensing in practical scenarios. The effectiveness of the proposed ISAC transmission framework is verified by our numerical results, which also agree with our analysis and discussions.