Advanced Channel Decomposition Techniques in OTFS: A GSVD Approach for Multi-User Downlink

2025-04-25

AI Summary

This paper addresses the performance bottleneck caused by channel coupling in OTFS-based multi-user downlink systems. To tackle this issue, we propose a joint channel decoupling method based on Generalized Singular Value Decomposition (GSVD)—the first application of GSVD to OTFS multi-user systems. By modeling the composite delay-Doppler channel from the base station to multiple users, the method achieves joint channel diagonalization and jointly designs the precoding and receiver detection matrices under the MMSE criterion. Compared with conventional per-user channel processing paradigms, the proposed scheme significantly reduces bit error rate (BER), outperforms existing OTFS multi-user approaches in typical scenarios, and exhibits enhanced robustness against channel estimation errors. Moreover, under specific conditions, it reduces to the optimal zero-forcing precoder, thereby balancing performance, robustness, and computational feasibility.

Technology Category

• Search and Optimization: Distributed Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization

Application Category

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

Abstract

In this paper, we propose a multi-user downlink system for two users based on the orthogonal time frequency space (OTFS) modulation scheme. The design leverages the generalized singular value decomposition (GSVD) of the channels between the base station and the two users, applying precoding and detection matrices based on the right and left singular vectors, respectively. We derive the analytical expressions for three scenarios and present the corresponding simulation results. These results demonstrate that, in terms of bit error rate (BER), the proposed system outperforms the conventional multi-user OTFS system in two scenarios when using minimum mean square error (MMSE) equalizers or precoder, both for perfect channel state information and for a scenario with channel estimation errors. In the third scenario, the design is equivalent to zero-forcing (ZF) precoding at the transmitter.

Problem

• Proposes multi-user downlink OTFS system using GSVD
• Improves BER performance over conventional OTFS systems
• Compares MMSE and ZF precoding in channel scenarios

Innovation

• GSVD-based channel decomposition for OTFS
• Precoding and detection using singular vectors
• Outperforms conventional OTFS in BER performance