Simulative Investigation of MIMO-OFDM-FSOC System over Modified Malaga Distributed Composite Atmospheric Channel

In this research work, we propose a novel design for a multiple aperture based Free-Space Optical Communication (FSOC) system where the Low Density Parity Check (LDPC)-coded, M-independent parallel Quadrature Amplitude Modulation (QAM)-OFDM multiplexed data streams are transmitted over a composite Malaga atmospheric channel by selecting any one of the switching transmission schemes: diversity, hybrid, or spatial multiplexing based on channel conditions, to yield the maximum average channel capacity while satisfying the reliable Average Bit Error Rate (ABER). In diversity switching, the coded data stream is transmitted to extract diversity gains, whereas in hybrid switching, a compromise between diversity and multiplexing gains is sought to achieve the maximum outage capacity by maintaining the reliable ABER. The performance of each switching scheme is evaluated under the power-series represented Malaga distributed composite channel which comprise of losses due to turbulence-induced fading and pointing error. In this work, a closed loop approximated mathematical expressions for the Average Channel Capacity (ACC) and ABER for each transmission mode is also derived. Apart from this, a Look-Up Table (LUT) consists of threshold Signal-to-Noise Ratio (SNR) corresponding to different channel conditions is also constructed to select the optimal switching transmission scheme. The extensive simulation results clearly demonstrate that the proposed switched mode transmission based MIMO-OFDM-FSOC system has a significant improvement in ACC compared with each stand-alone system.