| Free-space optical (FSO) communication links are susceptible to a tremendous amount of variability and offer a real challenge for efficient, robust system design. Whether changes in link margin are predictable (i.e. weather conditions or mission profiles) or truly random (i.e. atmospheric turbulence induced scintillation or boundary layer induced tracking errors), FSO communication systems will experience a large dynamic range of performance through most mission scenarios. Recent system designs within commercial, academic, and military organizations have focused on leveraging COTS technology from the fiber optic telecommunications industry. These systems are typically based on fixed designs that use set data rates and modulation formats. Utilizing such modalities in a mobile free-space environment can lead to systems that are either overly conservative or have a high rate of failure. To maximize overall system efficiency, we propose a transceiver architecture with rate and modulation agility. The presented transceiver is built with COTS components, supports data rate adjustability, and can switch modulation formats between Differential Phase-Shift Keying (DPSK), Binary Pulse-Position Modulation (BPPM), and On-off-Keying (OOK). A prototype system illustrating adaptive operation is presented and experimental results are shown. |