Numerous researches have been performed in UAV communication relay scheme. In the conceptual study of UAV based military communication relays, Pinckney et al. described a multi-year airborne communication range extension program plan which was primarily used to support the Battlefield Information Transmission System. The main objective of the program was to provide the beyond line of sight (BLOS) communications capabilities without the help of scarce satellite resources. Their range of coverage can vary from 50 to 100 miles for UAVs of interest. Rangel et al. developed a multipurpose aerial platform using a UAV for tactical surveillance of maritime vessels. They concluded that the communication relay using a UAV system is a low-cost application which could provide air dominance with satisfied communication range with lost cost resources. In Orphans et al. the use of the self-organizing paradigm to design efficient UAV relay networks to support military operations was proposed.
Abundant previous studies have focused on the algorithms for vehicle position assignment and network configuration. Choi et al. developed guidance laws to optimize the position of a Micro-UAV which relayed communication and video signals when the other UAV is out of radio contact range with the base. Zhan et al. investigated a communication system in which UAVs were used as relays between ground terminals and a network base station. Their work mainly focused on developing the algorithm for optimizing the performance of the relay system. In , Cetin and coworkers proposed a novel dynamic approach to the relay chain concept to maintain communication between vehicles in the long-range communication relay infrastructure. Their path planning method was based on the artificial potential field.