Comparison of alamouti & MRC schemes over various channels for Free Space Optics

Free Space Optic (FSO) Communication systems are ideal for setting up high speed short distance (a few kilometers) communication links. They have been in existence for more than two decades but have not gained widespread acceptance and popularity. This is primarily because they suffer from a serious handicap. It is well known that the random variation of signal strength due to fading in a communication channel can result in severe bit-error-rate (BER) performance degradation and an increase in the outage probability. This is a major challenge in all wireless communication systems and FSO Communication is not an exception. A number of receiver combining schemes and Space Time Block Codes (STBCs) have been designed to improve the performance of wireless communication systems over fading channels. In our study, we have conducted numerical studies to determine the performance of the most widely used STBC (namely Alamouti code) over FSO channels perturbed by atmospheric turbulence. At the receiving end, the signals received from multiple paths are weighted and summed in accordance with MRC scheme which provides maximum performance improvement by maximizing the SNR of the FSO system.