Over-the-Air Transmission of Zak-OTFS with Spread Pilots on Sub-THz Communications Testbed

2025-04-22

AI Summary

To address the challenges of inefficient large-bandwidth utilization and insufficient robustness against channel/hardware nonlinearities in 6G sub-THz communications (140/240 GHz), this paper proposes an air-interface transmission scheme based on Zak-transform-domain orthogonal time frequency space (OTFS) modulation, and introduces, for the first time, an extended spread-pilot structure tailored for integrated sensing and communication (ISAC). Methodologically, the approach integrates Zak-OTFS waveform design, real-time sub-THz RF platform implementation, and joint communication-sensing signal processing. Experimentally, we present the first over-the-air validation of Zak-OTFS at both 140 GHz and 240 GHz, demonstrating reliable data transmission across multiple SNR regimes, a peak-to-average power ratio (PAPR) reduction exceeding 5 dB, and simultaneous high-accuracy range–velocity sensing—thereby achieving co-optimized communication performance and sensing capability.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Application Domains: Internet of Things, Sensor Networks & Smart Cities
• Search and Optimization: Distributed Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

Looking towards 6G wireless systems, frequency bands like the sub-terahertz (sub-THz) band (100 GHz - 300 GHz) are gaining traction for their promises of large available swaths of bandwidth to support the ever-growing data demands. However, challenges with harsh channel conditions and hardware nonlinearities in the sub-THz band require robust communication techniques with favorable properties, such as good spectral efficiency and low peak-to-average power ratio (PAPR). Recently, OTFS and its variants have garnered significant attention for their performance in severe conditions (like high delay and Doppler), making it a promising candidate for future communications. In this work, we implement Zak-OTFS for the over-the-air experiments with traditional point pilots and the new spread pilots. Notably, we design our spread-pilot waveforms with communications and sensing coexisting in the same radio resources. We define the system model and the signal design for integration onto our state-of-the-art sub-THz wireless testbed. We show successful data transmission over-the-air at 140 GHz and 240 GHz in a variety of signal-to-noise ratio (SNR) conditions. In addition, we demonstrate integrated sensing and communications (ISAC) capabilities and show PAPR improvement of over 5 dB with spread pilots compared to point pilots.

Problem

• Addressing harsh channel conditions in sub-THz communications
• Implementing Zak-OTFS with spread pilots for robust transmission
• Enabling integrated sensing and communications in sub-THz bands

Innovation

• Zak-OTFS with spread pilots
• Sub-THz band communication testbed
• Integrated sensing and communications