Performance analysis of spatially multiplexed MIMO-OFDM free space optical communication system

In this paper, we present the performance analysis of spatially multiplexed Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) Free Space Optical Communication system over turbulence induced fading channels MIMO is used with OFDM to enhance the performance and the capacity of the FSO system. The use of spatial multiplexing yields an impressive increase in the capacity of the system. The capacity of the system at higher values of signal power increases from 2 bits/sec/Hz to 16 bit/sec/Hz for 2×2 and 8×8 MIMO systems, respectively for a 3 dB increase in E_b/N₀. We have used QPSK, 8 QAM and 16 QAM modulation formats and it is found that the performance of QPSK is superior among these schemes We also show the effect of different antenna configuration on the bit error rate with QPSK modulation technique. To reduce the system complexity V-BLAST is used for the detection. The atmospheric turbulence is modeled using the Gamma Gamma (G-G) distribution function. The focus of the work is upon evaluation of capacity with spatial multiplexing and bit error rate for different atmospheric turbulence strength, modulation techniques and various antenna configurations.