Flexible Quadrature Spatial Modulation: Transmission, Detection, and Implementation

Abstract

In the conventional spatial modulation schemes, such as spatial modulation (SM) and quadrature SM (QSM), the number of the transmit antennas must be an integer power of 2, which limits the spectral efficiency and raises the hardware cost. To overcome the antenna limitation, a new modulation method, namely flexible QSM (FQSM), is proposed in this paper. Computer simulation results show that in contrast to the existing SM-like schemes, the proposed FQSM can provide better bit error rate (BER) performance under the same bit per channel use (bpcu). To further make the implementation of the FQSM systems feasible, a low-complexity symbol detection algorithm with matrix merging, group-based Givens rotation, candidate searching, symbol estimation, and likelihood estimation (LE) is introduced. Furthermore, the corresponding very-large-scale integration (VLSI) architecture is also proposed. Finally, the results of simulation and computational complexity reveal that the proposed symbol detection algorithm can offer the near-optimal BER performance with lower computational complexity, compared to other related detection methods. The results of the VLSI architecture implemented under the TSMC 90-nm CMOS technology at an operating frequency of 625 MHz show that the proposed hardware requires 554.37 KGEs and performs a 1562.5 Mbps detection throughput.