Integrated Approach to Free Space Optical Communications in Strong Turbulence

摘要

The propagation of a free space optical communication signal through atmospheric turbulence experiences random fluctuations in intensity, including signal fades which negatively impact the communications link performance. This research develops an analytical probability density function (PDF) to model the best case scenario of using multiple independent beams to reduce the intensity fluctuations. The PDF was further developed to account for partially correlated beams, such as would be experienced by beams having finite separation. The PDF was validated with results obtained from digital simulations as well as lab experiments. The research showed that as the number of transmitted beams increases the probability of fade decreases. While fade probability is reduced by adding more beams, using more than four transmitters does little to improve the overall performance. Additionally, the use of pulse position modulation (PPM) provided significant improvement over traditional fixed threshold on/off keying with the impact of signal fading reduced. Combining PPM with multiple transmitters produced the best overall bit error rate results.