A UAV network composed of multiple UAVs allows a wide operating radius and various tasks to be performed. However, a UAV network mostly suffers from high probability of transmission failure due to interference or mobility. Also, nodes connected to the network often experience connection loss and segment loss caused by frequent node mobility and routing update. Since congestion is not the only cause of data loss in UAV networks, the TCP congestion control should not be run if there is a possibility of transient link instability unless a reduction in transmission speed is required. For this reason, we propose an algorithm to improve the transmission performance of UAV network through TCP with Slow-Start threshold (Ssthresh) value adjusted. The adjustment algorithm is called Adaptive Ssthresh Reviser for flying Ad hoc Network (ASRAN) that quickly restores unnecessary decrease of transmission speed in UAV network.
IntroductionWith the development of wireless network devices, it has become possible to collect a wide range of information and form flexible topologies through various small network devices. However, due to the wide range of activities or mobility, it is difficult for all equipment to be directly connected to the Internet's backbone. In environments where it is difficult to connect directly to the Internet, many devices can connect to the Internet with a wireless ad hoc network. There are various techniques based on wireless multi-hop environments; for example, Unmanned aerial vehicle (UAV)-based network system [1-3], multiple Internet of Things (IoT) devices [4,5], 5G network with small mesh networks for fast data transmission speed [6], VANET technology for vehicles [7,8], and MANET technology [9,10]. However, various wireless multi-hop networks including UAV network (e.g., flying ad hoc network) often suffers from segment loss [11]. UAVs have an unstable network because they are difficult to load high-performance device due to limited payload size and moves around frequently to carry out various tasks. As a result, UAV networks often suffer from segment losses due to unstable networks. In this situation, since the formation information and the control message necessary for UAV must be received, the transmission control protocol (TCP), which is a reliable communication protocol, is used to recover the segment loss [12]. Based on this observation, this paper suggests an improvement technique of TCP to enhance the performance of the overall UAV network.If the segment loss occurs, TCP considers the network to be congested and decreases the congestion window (CWND) to reduce the transmission speed. The reason for reducing the transmission speed is that segment losses are caused by heavy traffic exceeding link capacity in most of wired environment. However, in wireless multi-hop environments such as UAV networks, segment losses are caused by not only buffer overflow but also transient link instability. For example, if power