Link budget for a terrestrial FSO link and performance of space time block codes over FSO channels

Abstract

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 about two decades but have not gained widespread acceptance and popularity. This is primarily due to a major drawback of the FSO systems. Changing the environmental conditions (atmospheric turbulence and fog) can drastically affect their throughput and reliability. Atmospheric turbulence can affect the FSO link in a manner similar to the impairments introduced by multi-path propagation (signal fading) in a wireless channel. 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. 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. FSO systems have the potential to provide high data-rate communication with the advantages of quick deployment times, high security, and no frequency regulations. These features have resulted in FSO becoming a unique technology within the domain of wireless communication.