Optimization of beam width, bit error rate and availability for free-space optical links

The design of free-space optical (FSO) communication links based on beam width optimization is investigated. Bit error rate (BER) and link availability for on-off keying (OOK) and pulse position modulations (PPM) are analyzed. For a required BER and fixed transmitted optical power, optimizing the transmitted beam width maximizes link availability. The combined effects of atmospheric turbulence and pointing errors are considered. Different weather conditions are considered and three scenarios are investigated: adaptive, semi-adaptive and fixed beam width over weather conditions. The performance-complexity tradeoff is analyzed in the design. Beam width adaptation for subsets of weather conditions as a sub-optimum solution shows a remarkable performance improvement over the fixed beam scenario. In all cases, significant performance in link availability is shown when employing PPM over widely used OOK signaling at a cost of more bandwidth.