Recently, using unmanned aerial vehicles (UAVs) as Relay in communication networks have attracted attention due to advantages of extending coverage and improving connectivity for long-range communications. The main point of using a UAV as a relay, which is that its location could changing according to the terms of the network. In applications that ground nodes are mobile, and may be due to existence of mountainous terrain or urban, the possibility of sending information directly to each other, using a UAV with Appropriate-altitude flight can be guaranteed continuous connection between the ground nodes and avoid network outage. An important issue in the field to determine the optimal path for the appropriate location in the UAV placement at any moment relative to the other network nodes in order to provide the best performance. In this thesis we've considered a relay communication network consisting of two ground nodes as source and destination information and as well as a UAV in the role of relay which operates in Amplify and Forward (AF) protocol. In this network, all nodes are movable and have multiple antenna. Our goal is providing optimal algorithm to determine the UAV path by maximization data rate via the maximization SNR signal received at the destination. The proposed algorithm simulation results suggest increasing the number of antennas at each node and transmit power source or relay can have a great impact on the UAV path and improve network efficiency. The results of the proposed algorithm compared with exhaustive search method to determine the path indicates the proposed method is acceptable, while exhaustive search method is more complex and requires more processing. Keywords: Unmanned Aerial Vehicles, path planning, Cooperative communication, Beamforming, Space-Time Code.
