A Hybrid I/O Relation Estimation Scheme for Zak-OTFS Receivers

2025-10-10

AI Summary

In Zak-OTFS systems, channel estimation in the delay-Doppler (DD) domain suffers from inaccurate modeling of out-of-support-channel responses due to the limited support of pulse-shaping filters, degrading detection performance—especially under fractional DD shifts. Method: This paper proposes a hybrid DD-domain channel estimation scheme that synergistically integrates the low-complexity advantage of model-agnostic methods with the wide-support modeling capability of model-based approaches. By jointly leveraging the Zak transform and pulse-shaping filter analysis, it explicitly estimates physical channel parameters and supports both pilot-dedicated and embedded pilot structures. Contribution/Results: Simulation results under representative vehicular (Vehicular-A) and tapped-delay-line (TDL-A/C) channels demonstrate that the proposed method significantly outperforms purely model-agnostic schemes—achieving up to one-order-of-magnitude BER reduction in fractional DD scenarios—thereby enhancing robustness and detection accuracy.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Intelligent Robots: State Estimation
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

In this paper, we consider the problem of estimating the delay-Doppler (DD) domain input-output (I/O) relation in Zak-OTFS modulation, which is needed for signal detection. Two approaches, namely, model-dependent and model-free approaches, can be employed for this purpose. The model-dependent approach requires explicit estimation of the physical channel parameters (path delays, Dopplers, and gains) to obtain the I/O relation. Such an explicit estimation is not required in the model-free approach, where the I/O relation can be estimated by reading off the samples in the fundamental DD period of the received pilot frame. Model-free approach has the advantage of acquiring fractional DD channels with simplicity. However, the read-off in the model-free approach provides an estimate of the effective channel only over a limited region in the DD plane but it does not provide an estimate for the region outside, and this can affect the estimation performance depending on the pulse shaping characteristics of the DD pulse shaping filter used. A poorly localized DD pulse shape leads to an increased degradation in performance. Motivated by this, in this paper, we propose a novel, yet simple, I/O relation estimation scheme that alleviates the above issue in the model-free approach. We achieve this by obtaining a coarse estimate of the effective channel outside the model-free estimation region using a novel model-dependent scheme and using this estimate along with the model-free estimate to obtain an improved estimate of the overall I/O relation. We devise the proposed estimation scheme for both exclusive and embedded pilot frames. Our simulation results using Vehicular-A, TDL-A and TDL-C channel models with fractional DDs show that the proposed hybrid estimation approach achieves superior performance compared to the pure model-free approach.

Problem

• Estimating delay-Doppler input-output relation for Zak-OTFS receivers
• Improving model-free channel estimation using hybrid approach
• Addressing performance degradation from poorly localized DD pulse shapes

Innovation

• Hybrid model-dependent and model-free estimation scheme
• Coarse channel estimate outside model-free region
• Improved overall I/O relation estimation performance