Multiple UAVs as Relays: Multi Hop Single Link Versus Multiple Dual Hop Links
Unmanned aerial vehicles (UAVs) have found many important applications in communications. They can serve as either aerial base stations or mobile relays to improve the quality of services. In this paper, we study the use of multiple UAVs in relaying. Considering two typical uses of multiple UAVs as relays that form either a single multi hop link or multiple dual hop links, we first optimize the placement of the UAVs by maximizing the end to end signal to noise ratio for three useful channel models and two common relaying protocols. Based on the optimum placement, the two relaying setups are then compared in terms of outage and bit error rate. Numerical results show that the dual hop multi link option is better than the multi hop single link option when the air to ground path loss parameters depend on the UAV positions. Otherwise, the dual hop option is only better when the source to destination distance is small. Also, decode and forward UAVs provide better performances than the amplify and forward UAVs. The investigation also reveals the effects of important system parameters on the optimum UAV positions and relaying performances to provide useful guidelines.
IEEE Transactions on Wireless Communications