Abstract
Two emerging technologies, cognitive radio (CR) and free-space optical (FSO) communication, have created much interest both in academia and industry recently as they can fully utilize the spectrum while providing cost-efficient secure communication. In this article, motivated by the mounting interest in CR and FSO systems and by their ability to be rapidly deployed for civil and military applications, particularly in emergency situations, we propose a CR enabled radio frequency (RF)/FSO communication model for an aerial relay network. In the proposed model, CR enabled RF communication is employed for a ground-to-air channel to exploit the advantages of CR, including spectrum efficiency, multi-user connectivity, and spatial diversity. For an air-to-air channel, FSO communication is used, since the air-to-air path can provide perfect line-of-sight connectivity, which is vital for FSO systems. Finally, for an air-to-ground channel, a hybrid RF/FSO communication system is employed, where the RF communication functions as a backup for the FSO communication in the presence of adverse weather conditions. The proposed communication model is shown to be capable of fully utilizing the frequency spectrum, while effectively dealing with RF network problems of spectrum mobility and underutilization, especially for emergency conditions when multiple unmanned aerial vehicles (UAVs) are deployed.
Highlights
Over the past few years, there has been a mounting interest in the efficient use of the frequency spectrum as wireless data traffic has been increasing at a tremendous rate due to the proliferation of user equipment
URNs can be deployed at an altitude of up to 300 m, whereas high-altitude platform station (HAPS) systems can be located in the stratosphere at 17–22 km above the surface [9]
Even though HAPS communications have attracted considerable interest in academia and industry, HAPS systems can be vulnerable to the harsh weather conditions of stratosphere, where temperatures drop to −90◦C and wind speeds reach up to 100 km per hour
Summary
Over the past few years, there has been a mounting interest in the efficient use of the frequency spectrum as wireless data traffic has been increasing at a tremendous rate due to the proliferation of user equipment. Compared to its RF counterpart, FSO communication can boost the overall performance of wireless systems by enabling high data rates, lower delay, inherent security, and easy deployment. On account of this potential, FSO systems are expected to be used in many areas including campus connectivity, video surveillance, and monitoring. We propose to use a CR enabled RF transmission for the ground-to-air (GtA) channel to create spectrally efficient multi-user connectivity, whereas FSO communication is used at the air-to-air (AtA) link, where a continuous LOS connection is available with the aid of acousto-optic and electro-optic FSO transceivers [7]. For the air-to-ground (AtG) channel, hybrid RF/FSO communication is used, where the RF communication functions as a backup for the FSO communication, creating continuous connectivity without any performance loss
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