MIMO Free Space Optical Communication Systems with Low Complexity QR-OSIC Detector

Abstract

In this paper, we investigate the performance of QR based Ordered Successive Interference Cancellation (OSIC) detectors for free space optical (FSO) communication system over spatial multiplexing (SM) multiple-input multiple-output (MIMO) scenario. The spatial multiplexing MIMO links are introduced in FSO systems in order to achieve high capacity gain. The performance of FSO system is deteriorated by the pessimistic effects of atmospheric turbulence and pointing errors. To mitigate the fading effects of atmospheric turbulence we achieve spatial diversity by utilizing MIMO technique in FSO systems. The maximum likelihood (ML) detector being the optimum detector suffers from high computational complexity for SM-MIMO FSO systems. On the other hand, the use of other low complexity linear detectors like zero forcing (ZF) and minimum mean square error (MMSE) results in the poor performance. Our aim is to investigate the practical interest of this scheme by taking into account the receiver performance and its computational complexity. The proposed QR-OSIC detector for SM-MIMO FSO systems is a nonlinear detector which is a low complexity detector and achieves performance close to that ML detectors. The results show the BER performance over $N_{t}\times N_{r}$ MIMO systems using QPSK, 16-QAM modulation. It is deduced by the simulation results that, the QR-OSIC detectors achieves higher performance gain over ZF, MMSE detectors for MIMO FSO systems while keeping the computational complexity low compared to ML detector. Further, we also present the complexity analysis of all the detection techniques discussed in this paper.