# User QoS-Based Optimized Handover Algorithm for Wireless Networks
## 2 Related Work
The time prediction for staying method [10] calculates the distance that the UE travels from the preset AP coverage boundary to the coverage boundary of the single handover threshold when the UE moves at a constant speed, to calculate the time that the UE travels within the coverage of the target handover AP. If the movement time of the UE calculated by the aforementioned method is higher than the right to delay time of the handover, the network service provision right will be transferred to the target handover AP. Although this method can reduce the generation of the ping-pong effect, like the dwell countdown timer method, the time estimation for staying needs to continue calculating, resulting in a high computational burden of the system. In addition to the design of a handover algorithm with a fixed threshold, the \"dynamic threshold\" approach was proposed [11]. In this approach, the available spectrum is allocated to the UE newly connected to the AP by setting dynamic thresholds. The \"dynamic threshold\" changes its value as the environment changes, so it can be considered the best solution in a changing environment. In this way, the flexibility of the system and its applicability to various environments will be further improved. Although this method should have good performance, it should be dynamically adjusted to the best handover parameters according to the environment; otherwise, it will still cause a ping-pong effect and reduce the stability of the user's network service. Figure 1: Wireless network handover procedure. In order to alleviate the ping-pong effect, in [12], the \"time prediction for staying method\" was used, and whether the target handover AP could provide users with sufficient throughput was used as a handover decision indicator to reduce the overall number of handovers and improve network service efficiency. In [13], the author decided whether an AP could be selected as the target handover AP by checking whether the UE was facing it. After all nearby APs that can be handed over to are included in the target handover candidate list, one of the APs with the best signal strength between it and the UE will be selected as the target handover AP. At the same time, the signal strength between the selected target handover AP and the UE must be greater than the handover threshold to ensure that this AP can truly provide good network services to the UE. Another way to deal with ping-pong effects is to use hysteresis margins (HMs) [14]. HMs are like a buffer space added to the handover threshold, so that the new handover threshold will increase the value of HMs to the original threshold. After adding this parameter to the handover algorithm, if the signal strength between the UE and the currently connected AP is lower than the original threshold, the handover that should have been performed before the HM was added will not be performed, because the signal strength between the UE and its currently connected AP is not bad enough. The handover procedure will only be executed after the handover condition is met. Therefore, when considering the long-term disconnection caused by the ping-pong effect, which results from the user's wandering between two APs and further causing the UE to continuously switch service providers between APs, the use of HMs can greatly reduce the probability of the ping-pong effect and reduce network service interruption. In [14], a handover algorithm based on a double threshold and a double hysteresis margin was proposed. From the experimental results, although the method proposed by the author can achieve 100% PDR, more than double the expected number of handovers occurred in the experiment. It was found that the value of certain parameters in the handover algorithm, such as the handover threshold and HM, must be accurately designed; otherwise, this may cause unnecessary handovers and is not conducive to providing high-QoS network services. In addition, in the handover process of a wireless network, it is also important to consider the factors of QoS to meet the needs of users.