Low Complexity Unitary Approximate Message Passing Based Equalization for OTFS System

Orthogonal time frequency space (OTFS) modulation is a new promising two-dimensional (2D) modulation technique for future wireless communication systems over high-mobility channels. To achieve the performance gain promised by OTFS, the unitary approximate message passing (UAMP) based detector is widely used due to its robustness, low complexity and superior performance. However, the complexity of the UAMP-based detector is high in the case of more practical waveforms, such as the rectangular waveform, which hinders its practical implementation. In this work, we propose a low complexity UAMP-based detector which inserts null symbols in the last few rows of the delay-Doppler domain according to the max delay of the time-varying channel, and exploits the circulant property of the equivalent channel matrix to simplify the calculation process of the UAMP detector. Simulation results show that the proposed detector has similar bit error rate (BER) performance as compared with the original UAMP detector, but exhibits much lower complexity.