A wireless optical communication (WOC) system is similar to a fixed wireless (microwave or RF) system except that information is carried by optical or infrared beam rather than by a microwave or RF carrier. They are also referred to as Free Space Optical or Infrared communications systems. Like fixed wireless, WOC requires a direct line of sight between locations. Optical networks remain an ideal medium for ultra-high bandwidth communications (>Gbps) for the transmission of data, voice, and multimedia across telecommunications networks. There are two distinct types of optical communications: fiber optics cable and free space optics (FSO). Like fiber optics cable, FSO uses lasers to transmit data, but instead of enclosing the data stream in a glass fiber, it is transmitted through the air.
FSO enables optical transmission speeds which are not possible using existing fixed wireless radio frequency (RF) technology and obviates the need to buy expensive spectrum. This clearly distinguishes FSO from fixed wireless technologies, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11, Local Multi-point Distribution Services (LMDS), and Multi-channel Multi-point Distribution System (MMDS). For long-haul ultra-high bandwidth networks, nothing is better than fiber optics cable. Fixed wireless RF technologies provide installation cost advantages and rapid deployment, but at lower bandwidth.
The main aim then was to develop communication between satellites and submarines beneath the surface of the sea. During the last 40 years, WOC has expanded to include deep space mission and terrestrial networks connected to nodes with a distance separation of 100 or 200 m at rates up to 10 Gbps. It uses light beams propagated through the atmosphere or space to carry information. WOC provides unique alternative technology options to meet the growing and seemingly insatiable bandwidth demand for short distance applications and will be the focus of this paper.
Wireless optical communication, WOC (FSO) systems are not worry-free and the technology has its limitations that affect link performance. At a given desired data rate, WOC systems performance can be characterized by four main parameters: Total transmitter power Transmitting beamwidth Receiving optics collecting area Receiver sensitivity Probably the single most significant parameter in describing the performance on an FSO link is the link margin. Basically, this is the amount of light received by a terminal over and above what is required to keep the FSO link active. This definition eliminates misleading claims from some vendors who provide performance numbers based on power coming out of the transmitter, which is generally larger, but does not include atmospheric attenuation.