CDMA/OTFS Sensing Outperforms Pure OTFS at the Same Communication Throughput

TL;DR

This paper demonstrates that CDMA/OTFS sensing outperforms pure OTFS in sensing accuracy while maintaining similar communication throughput, making it a promising approach for integrated sensing and communication systems.

Contribution

The study characterizes and compares the sensing and communication performance of various CDMA/OTFS configurations against pure OTFS, highlighting its advantages in multi-user ISAC applications.

Findings

Zadoff-Chu Dl-CDMA/OTFS and DD-CDMA/OTFS outperform pure OTFS in sensing.

CDMA/OTFS maintains similar communication throughput as pure OTFS.

Lower demodulation complexity compared to some other OTFS multi-user methods.

Abstract

There is a dearth of publications on the subject of spreading-aided Orthogonal Time Frequency Space (OTFS) solutions, especially for Integrated Sensing and Communication (ISAC), even though Code Division Multiple Access (CDMA) assisted multi-user OTFS (CDMA/OTFS) exhibits tangible benefits. Hence, this work characterises both the communication Bit Error Rate (BER) and sensing Root Mean Square Error (RMSE) performance of CDMA/OTFS, and contrasts them to pure OTFS. Three CDMA/OTFS configurations are considered: Delay Code Division Multiple Access OTFS (Dl-CDMA/OTFS), Doppler Code Division Multiple Access OTFS (Dp-CDMA/OTFS), and Delay Doppler Code Division Multiple Access OTFS (DD-CDMA/OTFS), which harness direct sequence spreading along the delay axis, Doppler axis, and DD domains respectively. For each configuration, the performance of Gold, Hadamard, and Zadoff-Chu sequences is investigated. The results demonstrate that Zadoff-Chu Dl-CDMA/OTFS and DD-CDMA/OTFS consistently outperform pure OTFS sensing, whilst maintaining a similar communication performance at the same throughput. The extra modulation complexity of CDMA/OTFS is similar to that of other OTFS multi-user methodologies, but the demodulation complexity of CDMA/OTFS is lower than that of some other OTFS multi-user methodologies. CDMA/OTFS sensing can also consistently outperform OTFS sensing whilst not requiring any additional complexity for target parameter estimation. Therefore, CDMA/OTFS is an appealing candidate for implementing multi-user OTFS ISAC.