Iterative Turbo Receiver for FTN Based on Semi-Definite Relaxation

Faster-than-Nyquist (FTN) technology, as a transmission technique that can improve spectrum efficiency, has received widespread attention. However, it introduces severe Inter-Symbol Interference (ISI), leading to increased complexity in symbol detection at the receiver end. An FTN detector based on Semidefinite Relaxation (SDR) exhibits good performance and low complexity. In this paper, an iterative FTN detector based on soft-output SDR is proposed. In traditional turbo receivers, forward error correction codes are only used at the decoder. However, the SDR detector proposed in this paper outputs external information to the decoder with higher reliability. By simplifying the SDR Turbo receiver, this approach solves only one SDR problem for each codeword instead of multiple SDR problems in the iterative turbo processing, thus reducing the time complexity of the SDR turbo receiver while maintaining the original error performance.