A review on pointing, acquisition, and tracking approaches in UAV-based fso communication systems

Abstract

The challenge of tracking unmanned aerial vehicles (UAVs) is arising out of increasing their market and spread usage in many applications. Miscuing UAVs can lead to potential threats as they are considered an essential part of national security. One of the major issues in communication with UAVs is the enormous amount of data generated by UAVs that requires a high data rate link, making the free space optics (FSO) communication, with very high bandwidth, an appropriate choice. Consequently, current developments in UAVs have provided new horizons for establishing UAV-based FSO links. However, FSO is a narrow line of sight (LoS) technology that is highly affected by the misalignment between the transmitter and receiver. So, tracking mechanisms are of vital importance when considering UAV-based FSO communication systems. This paper addresses coarse to fine pointing, acquisition, and tracking (PAT) approaches and the recently developed tracking approaches to establish a reliable link for communication. Also, the various approaches are discussed and compared for precise alignment between the ground station and its associated UAV, highlighting their advantages and limitations. Current challenges and future research directions are addressed and integrated by combining different ideas.

A Comprehensive Review of UAV-Assisted FSO Relay Systems

“…These may include Azimuth/Elevation (AZ-EL) gimbals, a Machine Vision Camera (MV CAM) that could either be visual or thermal cameras, and Near Infrared (NIR) cameras for coarse pointing, while the fine-tracking apparatus typically includes options such as Spatial Light Modulators (SLMs), Fast Steering Mirrors (FSMs), AZ-EL gimbals, Position Sensing Detectors (PSDs), MV CAMs, and NIR cameras. In a review of PAT approaches for UAV-assisted FSO relays, the author of [49] identifies conventional and asymmetric approaches, whereby in the conventional approach, the OGS and aerial platform both require mechanical gimbals to actively align the link, implying heavy hardware onboard the UAV, a setup better suited for larger platforms such as HAPs. Conversely, in an asymmetric approach, the UAV adheres to strict SWaP constraints and uses lightweight compact payload modules, thereby transferring the heavier mechanical gimbals and other PAT apparatus to the OGS.…”

Underwater Wireless Laser-Based Communications Using Optical Phased Array Antennas

“…This type of system is particularly well-suited for setups that require a large angular range. However, the heavy weight of gimbals, primarily due to the servo motors, makes them unsuitable for vehicles with strict weight restrictions [3], [4]. Another disadvantage of this approach is the low pointing resolution, which results in large angular steps, which is challenging especially at long ranges.…”

“…Conversely, the receiver is aligned with the direction of the incoming beam during acquisition. Tracking plays an important role in maintaining alignment and acquisition by continuously tracking the position of the mobile transceiver so that data transmission can be kept stable [4].…”

Review on UAV-based FSO links: recent advances, challenges, and performance metrics

“…An optical signal is vulnerable to many impairments that degrade the performance of the system 16 . Attenuation due to rain, fog, dust particles, haze and snow, turbulence-induced fading mainly due to scintillation, 17 , 18 pointing errors because of the misalignment, 19 , 20 and angle-of-arrival (AoA) fluctuations are the major causes of signal degradation while propagating through the atmosphere. Out of the four channel deterioration effects, atmospheric loss is assumed to be deterministic and remaining three are considered as independent random events.…”