Low Complexity Detectors for Spectral and Energy Efficient GQSM-OTFS System

Abstract

Orthogonal time frequency space (OTFS) is a novel modulation scheme that offers robustness against multipath fading and Doppler shifts. For future generation green communication systems, generalized quadrature spatial modulation (GQSM) is an enhancement of traditional quadrature spatial modulation (QSM) that reduces the number of transmit antennas for same spectral efficiency (SE) and improves the energy efficiency (EE) of wireless communication systems. In this paper, we propose a GQSM based OTFS (GQSM-OTFS) system to enhance SE, EE, and transmission reliability of wireless communication systems in high mobility scenarios. Further, we find the expression of the upper-bound and lower-bound on SE and validate it by the simulation results. Then, we propose low-complexity detectors, i.e., energy greedy detector (EGD), modified EGD (MEGD), and improved EGD with log-likelihood ratio (IEGD-LLR). The EGD provides lesser complexity than the minimum mean squared error based maximum likelihood (MMSE-ML) detector with minor degradation ( $\leq 1$ dB) of system performance. MEGD performs same as MMSE-ML detector with reduction in computational complexity. IEGD-LLR is proposed based on the LLR, which performs same as the MMSE-ML detector with significant reduction in computational complexity. Moreover, we discuss the discrete-input continuous-output memoryless channel (DCMC) capacity of the GQSM-OTFS system. Finally, simulation results demonstrate that the proposed GQSM-OTFS system outperforms the conventional spatial modulation (SM) based OTFS systems.