Grant: Strategic Projects - Group

Free-space optical (FSO) communication refers to the transmission of information via modulated visible or infrared (IR) optical band emissions through the atmosphere. FSO is particularly interesting for last-mile broadband connectivity as it can virtually extend the high speed fiber backbone network to the subscriber's premises at comparatively low cost. There is a large demand for this type of connectivity since, for example, approximately 75% of commercial buildings in the US are within 1 km of a major fiber trunk, but only 5% of these are connected to that trunk. However, FSO is also favorably applied as fiber back up, in meteropolitan area networks, and in space communications. When compared to more conventional RF wireless links, FSO enables significantly higher data rates, is not affected by co- or adjacent-channel interference, and offers inherent security due to the high directivity of the light beam. Furthermore, FSO systems are lightweight and rapidly deployable, do not require expensive spectrum licensing, and are inexpensive compared to fiber or RF systems. Despite these advantages and a growing interest in this technology from both industry and academia, widespread deployment of FSO faces three primary challenges: (1) For reliable communication the FSO transmitter has to directly illuminate the FSO receiver. Misalignment between transmitter and receiver leads to large fluctuations in the received signal intensity. (2) Atmospheric turbulence causes fading in FSO links. This leads to signal intensity fluctuations in both space and time. (3) Adverse weather conditions such as fog, heavy rain, and heavy snow can severely attenuate FSO links. The overall goal of the proposed research project is to develop new intelligent signal processing techniques that can overcome these challenges and facilitate the widespread deployment of FSO technology. This requires fundamental research on (a) the modeling of urban FSO channels, (b) coding and modulation for FSO systems, (c) multiple-input multiple-output (MIMO) FSO systems, and (d) signal design for hybrid FSO-RF systems.