UAV-Assisted Free Space Optical Communication System With Decode-and-Forward Relaying

Free space optical (FSO) relay communication systems based on unmanned-aerial-vehicle (UAV) play an important role in various communication scenarios. In this paper, a UAV-assisted FSO relay system with a decode-and-forward (DF) relaying scheme is analyzed. We examine the effects of path loss, atmospheric turbulence, nonzero boresight pointing errors, angle-of-arrival (AoA) fluctuations, and other parameters on the performance of the system. Using Málaga distribution as the atmospheric turbulence model, closed-form expressions are derived for channel fading coefficient probability density function (PDF), outage probability, bit error rate (BER) and other parameters. Based on the closed-form expression, numerical results are then utilized in order to determine the optimal values for various tunable parameters to maximize system performance. The results indicate that the performance metrics are strongly dependent on tunable parameters, such as beamwidth, UAV's position and receiver's field-of-view (FoV) angle, the optimal UAV's position is highly correlated with the beamwidth at the receiver of destination. Moreover, when using DF relaying, we observe that the end-to-end system performance is dependent on the link with inferior performance. Therefore, when other tunable parameters are already determined, the UAV's position should be adjusted to balance the performance of two links for the purpose of improving the end-to-end system performance.