Optimal Design of OTFS Systems for Fractional Inter-Doppler Interference Suppression

Orthogonal Time Frequency Space (OTFS) modulation, a two-dimensional delay-Doppler (DD) domain modulation technique, has been widely studied in recent years to address challenges in high-speed mobile communication environments. In this work, we propose an optimized design for OTFS systems, in which a Kaiser (KS) window is employed in the time domain of the transmitter (Tx), to significantly enhances the sparsity of the DD domain channel and effectively suppresses fractional inter-Doppler interference (IDI) without requiring additional spectral overhead. Furthermore, the impacts of the roll-off factor of the Root Raised Cosine (RRC) pulse shaping on the system's Bit Error Rate (BER) in fractional delay channels is investigated, and a detailed matrix derivation of the input-output relationship of the proposed system in the context of fractional delay and Doppler shift channels is given. Simulation results show that, compared to traditional OTFS systems using a Dolph-Chebyshev (DC) window in the time-frequency (TF) domain, the proposed design not only reduces computational complexity by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2NM\log_{2}M$</tex> but also achieves an approximate performance gain of 3 dB.