On the Design of Capacity-Approaching Iterative Soft Cancellation for Coded OTFS

Orthogonal time-frequency-space (OTFS) modulation is able to improve the performance of the wireless communication system in a high-speed environment. This paper proposes an iterative soft cancellation receiver with element-wise extrinsic information for coded OTFS system. In calculating the soft estimates that are fed back to the iterative soft cancellation, the existing full extrinsic information based method subtracts the entire a priori information from the a posteriori probability (APP) outputs from the decoder. In the proposed element-wise extrinsic information method, only the a priori information w.r.t the specific path (a single-element from the observation) in OTFS system is subtracted from the decoder's APP outputs. We show that the proposed approach outperforms existing a posteriori probability and full extrinsic information based iterative detection by 2 dB and 1 dB, respectively. Further, we apply extrinsic information transfer chart curve-fitting technique to optimize the code profile of the proposed scheme. We demonstrate that the proposed scheme performs within 0.5 dB of the capacity limit of OTFS.