# A Hybrid User Mobility Prediction Approach for Handover Management in Mobile Networks
## 3 The Proposed Predictive Handover Management Approach
### Predictive Handover Procedure  
_Objective:_ Given the user future trajectory, we want to reduce the number HO signaling messages needed when handover is triggered. In this section, we investigate the conventional (i.e., non-predictive) and predictive handover signaling procedures. More specifically, we analyze the impact of trajectory prediction on handover signaling flow and compare it with the non-predictive handover scenario. A conventional handover procedure has three main steps including handover preparation, execution, and completion [23]. In the preparation step, target gNB is selected by the source gNB. The target gNB completes admission control. In the execution step, the user device attaches to the target gNB. In the last step, HO completion, the data path is switched to the new gNB and the handover steps are completed. However, if the network has reliable information on the user's future locations (i.e., path), it can effectively perform some of the HO procedure steps before handover triggers. With correct prediction of the user future trajectory, we can complete the HO preparation phase in advance and when user requires a handover, it will start the execution phase. However, with a wrong prediction, even more signaling messages are required compared to the conventional HO. In the following, we elaborate on the impact of prediction on HO signaling in both horizontal and vertical handovers in a 5G architecture. Figure 3 shows a 5G intra-AMF-UPF handover signaling process where we predicted the target base station. AMF and UPF in 5G architecture, respectively, refer to access and mobility management function (AMF) and user plane function (UPF). We considered both the cases of right and wrong predictions regarding a target gNB. As we can see in the figure, when the target gNB is correctly predicted, it is equal to the actual next base station (highlighted in green). However, with a wrong prediction, the predicted target base station is not the same as the actual next base station (highlighted in red). In this case, the source base station should send a message to the wrongly predicted base station and cancel the HO request. Therefore, there are three cases including (1) non-predictive HO (i.e., conventional HO), (2) predictive HO with right prediction, and (3) predictive HO with wrong prediction. For the first case, we need to perform all of the HO preparation, execution, and completion steps. According to Figure 3, signaling messages from numbers 3 to 14 need to be exchanged (i.e., parts 2 and 3). For the second case, when we predict the next base station correctly, the preparation steps can be performed in advance. When HO is triggered, the procedure starts with the execution phase. Thus, we need signaling messages from numbers 8 to 14 (i.e., part 3). Lastly, for the third case with a wrong prediction, signaling messages from numbers 1 to 14 are needed to complete the HO. First, resources at the wrongly predicted gNB should be released (part 1). Next, the non-predictive HO is applied to communicate with the actual next base station (parts 2 and 3). Similarly, Figure 4 shows an inter-radio access (RAT) handover signaling diagram from 5G next generation core (5G NGC) to evolved packet system (EPS). Similar to the  
Figure 2: The proposed VAR-GRU mobility model. procedure in the Figure 3, we investigated the HO signaling procedure for right and wrong predictions regarding the next target gNB. There are three cases here as well. We note that the prediction accuracy has a vital role in the success of reducing HO signaling costs. An accurate prediction can reduce the signaling noticeably. On the other hand, as is evident, wrong predictions lead to even more signaling messages. Therefore, it is important to give undivided attention to the mobility predictor accuracy performance. Figure 4: Inter-RAT handover signaling diagram (from 5G NGC to EPS). Figure 3: Intra-AMF-UPF handover signaling diagram.