A Cyclic Shift Embedded Pilot based Channel Estimation for Multi-User MIMO-OTFS systems with fractional delay and Doppler

2025-12-02

AI Summary

To address the high pilot overhead and low channel estimation accuracy in high-mobility multi-user MIMO-OTFS systems, this paper proposes a novel pilot structure leveraging the cyclic-shift orthogonality of Zadoff-Chu (ZC) sequences, coupled with a multidimensional decoupled channel estimation algorithm. The proposed structure enables inter-user pilot reuse via cyclic shifts, reducing pilot overhead by over 30%. The algorithm jointly exploits path-domain decoupling, grid offset compensation, subspace-based angle estimation, and spatial projection for interference suppression, integrated with compressed sensing to achieve high-precision fractional delay–Doppler joint estimation. Simulation results demonstrate that the method significantly improves channel estimation accuracy and bit error rate performance while simultaneously reducing computational complexity—thereby achieving an effective trade-off among pilot overhead, estimation accuracy, and algorithmic complexity.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Distributed Search
• Intelligent Robots: State Estimation

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Experiences and lessons learnt from Web-based algorithms and system deployments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Security and Privacy: Large-scale security measurements

Abstract

Orthogonal time frequency space (OTFS) modulation has been proposed to meet the demand for reliable communication in high-mobility scenarios for future wireless networks. However, in multi-user OTFS systems, conventional embedded pilot schemes require independent pilot allocation for each user, leading to linearly increasing pilot overhead. To address these issues, in this paper, we investigate the uplink channel estimation and pilot design for multi-user multiple-input multiple-output (MIMO)-OTFS systems. We propose a multi-dimensional decomposition-based channel estimation algorithm. Specifically, the proposed algorithm first estimates the angles of arrivals (AoAs) via subspace decomposition-based method. A spatial projection matrix, constructed from the estimated AOAs, decouples the received signal by propagation path subspace, effectively mitigating inter-path interference. The remaining fractional delay and Doppler can be obtained by a compressed sensing (CS)-based off-grid channel estimation method. Furthermore, to reduce the pilot overhead in multi-user OTFS systems, this paper proposes a novel cyclic shift embedded pilot (CSEP) structure, which can reuse users through cyclic shift-orthogonality of Zadoff-Chu (ZC) sequences. Compared with conventional embedded pilot structures, the CSEP structure can save over 30% of pilot overhead. Finally, an imporved channel estimation method based on the CSEP structure is proposed. Simulation results demonstrate that it achieves superior performance in channel estimation. Moreover, the proposed CSEP structure and channel estimation algorithm achieve a favorable balance between computational complexity, estimation accuracy, and bit error rate (BER) performance.

Problem

• Estimates uplink channels in multi-user MIMO-OTFS systems with fractional delay/Doppler.
• Reduces pilot overhead via cyclic shift embedded pilot structure using ZC sequences.
• Mitigates inter-path interference and improves estimation accuracy with low complexity.

Innovation

• Subspace decomposition for AoA estimation and interference mitigation
• Compressed sensing for off-grid delay and Doppler estimation
• Cyclic shift embedded pilot structure using ZC sequences