Costas array-based OTFS HF channel estimation for high-speed platforms

High-Frequency (HF) communication on high-speed platforms offers advantages such as flexibility, wide coverage, and long-distance transmission, but faces significant challenges in achieving efficient and reliable communication due to multipath propagation and high-Doppler fading induced by high-speed motion. Recognizing Orthogonal Time-Frequency Space (OTFS) as a promising solution to multipath and Doppler challenges, this paper focuses on leveraging its inherent channel sparsity to advance HF mobile channel estimation. To address the high Peak-to-Average Power Ratio (PAPR) and limited estimation accuracy of traditional pilot patterns, we design a two-dimensional Costas array pilot and investigate both high-accuracy embedded and high-spectral-efficiency superimposed structures. Leveraging the correlation characteristics of Costas array, an innovative Orthogonal Matching Pursuit (OMP) algorithm combined with sidelobe interference cancellation is proposed. With modest computational overhead, the proposed Costas array pilot outperforms the impulse pilot by 5 dB in PAPR and is superior to the sequence pilot in Normalized Mean Square Error (NMSE), with no apparent floor effect. At a Pilot-to-Data Ratio (PDR) of 25 dB, both the embedded and superimposed Costas array pilots demonstrate superior performance in PAPR, NMSE, and Bit Error Rate (BER).