Performance Analysis of Communication Systems over Mimo Free Space Optical Channels

The global telecommunications network has seen massive expansion over the last few years. Optical communication through clear atmosphere provides a means for high data rate communication over relatively short distances (e.g. 2km). However, the turbulence in the atmosphere leads to fades of varying depths, some of which may lead to heavy loss of data. Free space optical communication system using multi-input multi-output with QPPM is described in this thesis. We use spatial diversity at both the transmitter and receiver as a means to mitigate the channel fading. Using direct detection receivers and QPPM modulation, we derive the symbol error probability of MIMO systems that use ML detection and equal gain combining with and without background radiation. We demonstrate that for faded channels, performance gains are seen as the number of transmitters and receivers increases. Full transmitter and receiver diversity is obtained and observed by analyzing the Rayleigh fading case. We also show that multipulse QPPM is superior to PPM with respect to bandwidth efficiency, and exhibits superior symbol error performance when the system is peakpower-limited. Hence, we conclude that MIMO systems can be used effectively as a technique for atmospheric optical channels.