# Energy-Efficient Multi-User Routing in a Software-Defined Multi-Hop Wireless Network
## 1 Introduction  
With the increasing scale and complexity of networks, people's requirements for the quality of network service are increasing. During data transmission, we need to not only develop a transmission strategy for multiple users at the same time, but also provide better QoS service and a wider transmission range. Traditional wireless networks allow nodes to exchange data directly within the transmission range, but this approach is severely limited by distance. As mobile communication technology develops rapidly, the utilization of mobile devices becomes more widespread and novel mobile applications emerge continuously. In order to solve the problem of traditional networks, a multi-hop wireless network (MWN) architecture has been proposed to reasonably utilize the idle resources of the mobile devices to process and forward data, thus extending the coverage of the network. In a multi-hop wireless network, the node forwards the data packet to the destination through the intermediate mobile nodes in a multi-hop manner, so MWN belongs to the infrastructure-less networks [1]. Unfortunately, although MWN provides a wider transmission range for data transmission technology, it still faces some crucial problems [2; 3; 4]. Firstly, since nodes can move arbitrarily, the network topology is always changing while the flexibility of the network is increasing. Therefore, the location of nodes should be acquired in real time to complete data forwarding. Secondly, MWN is self-organizing and distributed, resulting in that nodes only store a local network topology. In theabsence of central control, it is difficult to modify the network topology dynamically and develop the global optimal data transmission strategy. Finally, since MWN is composed of battery-powered mobile nodes, we should consider the specific energy consumption of nodes and ensure that they do not lose too much power, so as to extend the life of the network. Moreover, without any central control, managing the energy consumption of the network is arduous. Recently, the development of software-defined network (SDN) technology has brought new solutions to these problems [5; 6]. The main idea of SDN is to separate data and control by separating the data plane and control plane [7]. Data routing and network traffic can be controlled by programming in a logical centralized controller, which centralizes decentralized routing information. Therefore, the SDN architecture can be applied to a multi-hop wireless network to compensate for the lack of centralized control, namely a software-defined multi-hop wireless network (SDMWN) [8]. In SDMWN, the SDN controller is responsible for centralized management of wireless nodes. Once the network topology changes, users can design the routing algorithm in the controller on the basis of their needs to implement the data transmission. The software-defined multi-hop wireless network has the following advantages [9]:  
**Node mobility management:** Mobility management means that once mobile nodes move, it is necessary to obtain the real-time location of the nodes and update the network topology in time. SDMWN adds centralized management to MWN, in which each node sends its location information to the logical centralized controller in real time. The logical centralized controller can get the global view of the network and dynamically adjust the current routing strategy. **Energy:** In SDMWN, all routing strategies are decided by the logical centralized controller. Nodes in the network only receive and transmit data, which reduces the energy consumption of mobile devices. **Quality of service:** Real time is the most significant feature of SDMWN. Nodes periodically send their current state to the logical centralized controller, such as energy remaining, network bandwidth and delay, etc. Then, the controller makes corresponding routing adjustments according to the collected information, so that the whole network can provide better service.