Drones swarm free space optical communication with pointing error

Abstract

Drones are one of the Unmanned Arial Vehicles (UAV) used for short-length and low-altitude applications. Applying Free Space Optical (FSO) technology is modern in drone communication systems. The FSO technology has significant features such as high security due to narrow beamwidth, insusceptible to interferences, free license, landline connection is not appropriate, etc. The proposed system took the V-shape configuration and simulated it using MATLAB 2020. The V-shape configuration is one topology of networking topologies used in communication systems. The system has three subsystems: two Single-Input Single-Output (SISO) topologies and one Multiple-Input single-output (MISO) topology, connected by an optical beam and flying in weak atmospheric turbulence. The optical beam modulates using the PPM technique and faces many obstacles that affect the system's performance, such as the attenuation and turbulence of the atmospheric channel and misalignment. The obstacles represented by the channel gain H consist of three factors: the pointing error factor HP, the atmospheric attenuation Ha, and the atmospheric turbulence Hf. Hp is a significant factor that may be happening in the transmitter, receiver, or optical beam. The related parameters to Hp are the pointing error angle θr, the link distance Z, and the beamwidth wz. The pointing error angle θr must be < 10−4 rad for long distances (inter-satellite application). The goal of this dissertation is to measure the allowable range of the pointing error angles θr that is > 10−4 rad at specific link distance Z where the system gets high performance, and determine the link distance Z where the system failed at a specific pointing error angle θr. The results showed that high system performance happens at SNR ≥ 10 dB. For pointing error angle θr=10−2 rad, the values of the applicable link distances Z are nearly 10% of the link distances Z values for θr=10−3 rad. The same percent when increasing the pointing error angle θr to 10−1 rad. Also, the results showed that the best performance was at Z≤ 8500 m. Therefore, the system's highest altitude h system can reach ≤ 8500 m, depending on the drone's characteristics. Each subsystem can be considered an independent system and used in another configuration.