Channel Estimation Method for OTFS System Based on Pilot Sharing
In Orthogonal Time Frequency Space (OTFS) systems, in order to support high-speed mobility and multi-user compatibility, and to reconstruct the entire two-dimensional delay-Doppler (DD) channel response from limited observations in strong interference environments, pilot structures with extensive guard intervals are required for channel estimation. This leads to high pilot overhead and low information transmission efficiency. To address this issue, a pilot-sharing-based channel estimation method for OTFS systems is proposed. This method targets high-speed railway long-tunnel scenarios and leverages the correlation between adjacent users’ channels to enable cooperative sharing and reuse of pilot information, thereby effectively reducing the overall system pilot overhead. Firstly, a correlation-based shared pilot structure is designed, allowing the saved delay-Doppler resource grid elements under low pilot overhead to be reallocated for data transmission. Then, a decision-feedback-based channel estimation algorithm is designed, which significantly enhances the overall resource utilization and effective data transmission rate of the system while ensuring channel estimation accuracy. Simulation results demonstrate that, in a delay-Doppler domain grid of $32\times 32$ with a subcarrier spacing of 15 kHz and under Quadrature Phase Shift Keying (QPSK) modulation, the proposed method reduces the pilot overhead of the considered two-user system by 50% compared to existing approaches while keeping the bit error rate (BER) at a low level. This results in a relative increase of 19.05% in the system’s throughput. Moreover, at a mean square error (MSE) of $1.5\times 10^{-4}$ , the proposed algorithm achieves a performance gain of about 2 dB compared to conventional schemes.