Altitude and power optimization for vertical heterogeneous networks

Due to the growth of the traffic demand in mobile networks, vertical heterogeneous networks (VHetNet) are proposed which consist of unmanned aerial vehicles (UAVs) and terrestrial base station (TBS) to enhance the downlink performance and quality of service of the network. In these networks, the terrestrial and aerial vehicles coexist and serve their corresponding users. However, there is interference between the terrestrial and aerial communication links. In other words, the efficient deploying of UAVs for balancing of their traffic load is a very important challenge in these networks. In this case, the user association to each UAV can balance the demand traffic of UAVs. Therefore, a user association strategy is proposed for maximizing the downlink sum data-rate of the network by UAVs’ transmission power and altitude setting while load balancing is achieved between UAVs. The problem is solved using the convex optimization method and based on Karush–Kuhn–Tucker (KKT) conditions, an iterative algorithm is proposed to allocate proper users to each UAV and adjust the transmission power and altitude of each UAV. Simulation results indicate effectiveness of the proposed algorithm for data-rate improvement and balancing the traffic load for different number of users and UAVs in comparison with the benchmark algorithms According to the results, the data rate of the network is increased up to 500 bps/Hz compared to the benchmark algorithms.