# User QoS-Based Optimized Handover Algorithm for Wireless Networks
## 2 Related Work  
The handover procedure of wireless networks is an important issue. The processing flow of the handover procedure is shown in Figure 1. Before the handover process is executed, the system will enter the detection phase to start. In this process, the AP will detect the signal strength of the connection with the UE that it is currently connected to. If the signal quality of the connection between the UE and the AP is poor, the AP will notify the UE to start looking for nearby APs that it can hand over the right of network service provision to. After that, it will enter the second phase of the handover: the discovery and scanning phase. The UE will start to actively search for beacons sent by nearby APs, and further measure the signal strength of these connectable APs as a basis for the UE to select the best handover AP. The last stage is the effective handover. At this stage, after the UE selects the target AP for handover, it will verify and connect/reconnect with the AP. The handover procedure will be completed when all three of the above handover phases are completed. Handover is divided into soft handover and hard handover [4]. In soft handover, the UE can still connect to the currently connected AP before the new connection with the target handover AP is established, which is usually performed via IEEE 802.11 wireless local area network (WLAN). In hard handover, which is used by 4G [5] mobile phone mobile communication technology, the UE must disconnect from the currently connected AP before the connection with the target handover AP can be established. In addition, handover can also be separated into vertical handover [6] and horizontal handover [4]. Vertical handover is also known as heterogeneous network handover; it refers to the behavior of the UE switching the connection between APs under two different network communication technologies. Horizontal handover is also known as homogeneous network handover. This handover method refers to when the UE switches between two APs with the same network communication technology. The goal of our research is to achieve optimized handovers between APs based on homogeneous networks. In recent years, there have been many papers focusing on the design of handover algorithms. When designing handover methods, the handover threshold must be precisely designed, otherwise the connection between the UE and the AP will become unstable. There are three main handover decision methods: the received signal strength indicator (RSSI) threshold method, the dwell timer method, and the time prediction for staying method. The RSSI threshold method [7] is the most commonly used and the simplest goal for designing this kind of handover decision. It involves setting a threshold as the criterion for judging whether to perform the handover, which is called the \"single-threshold handover judgment method\" [8]. Although this method is easily applicable to various handover algorithms, it may cause frequent ping-pong effects and make wireless network connections unstable. The dwell timer method [9] adds a countdown timer on the basis of the \"single-threshold handover judgment method\". When the signal strength between the nearby AP and the UE is stronger than the signal strength between the AP to which the UE is currently connected and the UE, the system will start a countdown timer (the countdown timer can be set by the user). When the countdown timer ends, it means that the signal fluctuation effect caused by an unstable signal between the UE and the nearby APs that can be handed over to is eliminated, meaning that the handover procedure can be executed. This method can reduce the probability of unnecessary handovers, but if the handover decisions of multiple connections are executed at the same time, multiple countdown timers will start at the same time, resulting in a high computational burden of the system.