# Handover Management for D2D Communication in 5G Networks
## 4 Proposed Approach
### Choosing Handover Target
simulated environment--that is, the average behavior of D2D pairs. Also, both of the aforementioned mobility models--FD and RPGM--would be examined. Subsequently, for the second part, in contrast to the first part, by observing the moving process of a single instance of D2D pair, we can thus analyze its performance from a micro point of view. ### Macro View of Numerical Results

For the performance evaluation of the macro view of the system, we consider the following performance indicators: total number of handovers, the utility value measured using (8), and the satisfaction ratio which is assessed according to the predefined RSRP threshold \(\varphi\). We observe the change in system performance by varying essential parameter settings, such as the number of D2D pairs and moving speed. Both mobility models--the FD model and the RPGM model--are included in our simulations. Four approaches, namely Standard, D-A3, DP, and DTDP, are compared in our study to examine their relative merits and limitations. Figure 4a shows the total number of handovers with respect to a different number of D2D pairs in the system. We can see that the proposed method has the fewest number of handovers compared to the other methods for both mobility models. Since the conventional standard only considers the received signal condition of a single cellular user, there is a high probability that the two DUEs of the same D2D pair will not simultaneously hand over to the same target when they are moving around in the area overlapped with multiple eNBs. This results in an additional number of handovers in the system. For the D-A3 method, both DUEs of the same pair will choose the same target eNB first and hand over to the target together when both of them have satisfied A3 events. DP only considers the received signal conditions of both DUEs, which does not take into account their movements. This will result in an additional number of handovers. On the other hand for the proposed DTDP, attributing to the \(D_{counter}\) and the utility function, which accounts for both DUEs' movements and their received signal conditions, the better handover decision of a D2D pair to their preferred eNB can be realized. Now we examine the effects of different mobility models. Unlike FD which maintains a fixed distance (30 m) between both DUEs for each pair, the range between two devices of a D2D pair in RPGM is varied between 0 to 30 m. Thus FD may have less probability to synchronously hand over both DUEs of the same pair. This lack results in about 16% to 21% more handovers than RPGM. The impacts of the number of D2D pairs on the average utility value per D2D pair and the average satisfied ratio are shown in Figure 4b,c. The satisfied-D2D pair-ratio, simply referred to as the satisfied ratio hereafter, is defined as the ratio of D2D pairs that the RSRPs of both DUEs of that pair can attain the predefined threshold \(\varphi\). The conventional standard may connect DUEs of a D2D pair to different eNBs. The average utility value per D2D pair and the satisfied ratio are calculated based on the received signal conditions for both DUEs when they are connecting to the same eNB. Therefore, the conventional standard is not included in the comparisons. As we can see from Figure 4b,c, the number of D2D pairs in the system and the type of mobility models do not significantly affect the result of average utility and satisfied ratio. This can be a result of the independence of D2D pairs and the sufficiency of resources in the network. We can still observe that the average utility value per D2D pair does really affect the result of satisfied ratio in the system. There is a trend that the higher the value of average utility per D2D pair, the better the satisfied ratio. The reason behind this phenomenon is that the eNB with a better received signal condition will be chosen using the proposed utility function (8). Moreover, the D-A3 method only chooses the target eNB that has the best RSRP to either one of the DUEs of the same pair.