Low Complexity Path Layer Message Passing Detector for CP-OTFS Systems in Dual Fractional Channels

Orthogonal Time Frequency Space (OTFS) modulation is a promising candidate for improving the communication reliability in high-mobility environments. However, in practical scenarios, the delay-Doppler (DD) domain resolution is not fine enough due to bandwidth limitations, resulting in dual fractional channels that bring higher complexity to signal detection. In this letter, we reformulate the DD domain input-output relationship in matrix form for dual fractional Cyclic Prefix-OTFS (CP-OTFS) systems, and prove that the path layer channel matrix is orthogonal under arbitrary waveform. Based on this property, we propose a low complexity path layer message passing detector. This algorithm effectively increase the received signal power and channel sparsity by equalizing the DD domain received signals, and converts the factor graph into a point-to-point transmission scheme based on path layer signal, ensuring timely update of messages. Simulation results show that the proposed algorithm has lower computational complexity and faster convergence speed compared to the baseline algorithm, and has similar bit error rate (BER) performance as the message passing (MP) algorithm.