Performance analysis of MIMO FSO adaptive mode switching in Malaga turbulent channels with pointing error

MIMO FSO (Free Space Optical) systems can provide high data rates through spatial multiplexing or improve transmission reliability using spatial diversity, but atmospheric turbulence is a bottleneck that restricts communication performance. Adaptive transmission technology can effectively suppress the influence of turbulence and improve communication performance. In this paper, switching between spatial multiplexing and diversity is proposed as an adaptive transmission technology for MIMO links to improve the diversity performance of spatial multiplexing of FSO systems. The switching criterion is based on the Minimum Euclidean Distance (MED) of the spatial mapping scheme. The MED expressions for two spatial modes at the receiver are derived, and the bit error rate (BER) approximations are provided, respectively. We evaluate the BER performance of spatial multiplexing and spatial diversity schemes, respectively, taking into account the joint effects of turbulence strengths, pointing error and path loss. To choose the optimal adaptive switching strategy for the system in different signal-to-noise ratio (SNR) ranges, a lookup table for the adaptive switching statistical SNR threshold was created based on the BER curve corresponding to the minimal Euclidean distance. The results show that compared with fixed spatial mode systems, adaptive spatial mode switching systems can achieve significant BER performance gains. The Demmel condition number of matrix channels is considered to provide a sufficient condition for spatial multiplexing to be superior to spatial diversity.