# Handover Management for D2D Communication in 5G Networks
## 4 Proposed Approach
### Choosing Handover Target
The other DUE may have a worse RSRP value with respect to the target. Thus, the average utility of D-A3 is inferior to our method. As for the performance difference between DTDP and DP, DTDP firstly considers \(D_{counter}\) values rather than the utility values in the selection of the target eNB. This renders the average utility of DTDP slightly worse than that of DP, which only counts utility values in the handover mechanism. Figure 5a shows the impact of the moving speed of D2D users on the total number of handovers under both mobility models, FD and RPGM. As the moving speed of D2D users increases, there is a higher chance for D2D pairs to pass the areas overlapped with multiple eNBs. This results in a higher number of handovers. The conventional standard has the most number of handovers. It only considers the RSRP of each user, which may lead to different handover targets for the two DUEs of the same pair. For the DA-3 method, although the same target eNB is chosen by a pair of D2D users, the selected eNB might not be the best in minimizing the number of handovers. Thus additional handover times may still be generated. The proposed DTDP takes into account users' movement angels for the handover

Figure 4: Total number of handover, utility, and satisfied ratio versus the number of device-to-device (D2D) pairs under different mobility models. The charts on the left and the charts on the right correspond to the fixed distance (FD) model and reference point group mobility (RPGM) model, respectively. (**a**) Total number of handovers; (**b**) utility; (**c**) satisfied ratio. target choice while DP does not. With DTDP, there is a higher probability for each pair of D2D users to correctly determine whether to hand over to the new eNB or stay at current eNB. Therefore, the total number of handovers of DP is about 18% to 20% more than that of DTDP. The distance between two DUEs of the same D2D pair for RPGM is shorter than in FD. The total number of handovers of FD may be more than that of RPGM due to a considerably more difference in the RSRP values between two DUEs of the same pair. This causes more unstable received signal conditions for D2D pairs with respect to their connecting eNBs. Figure 5: Total number of handovers, utility, and satisfied ratio versus the moving speed of each D2D user under different mobility models. The charts on the left and the charts on the right correspond to the FD model and RPGM model, respectively. (**a**) Total number of handovers; (**b**) utility; (**c**) satisfied ratio. Figure 5b,c shows the average utility value per D2D pair and the satisfied ratio of the system vs. different speeds of users. Here, we can observe that there is a close correlation between the average utility value per D2D pair and the satisfied ratio of the system, as mentioned before. In addition, the average utility value and the satisfied ratio decrease with the increase of the user velocity. This is due to the fact that, as users move rapidly, the frequent handovers caused by unstable RSRPs may happen for each D2D pair, which leads to the lower average utility value. For the comparison of various methods, as mentioned before, since the D-A3 method only chooses the target eNB that has the best RSRP to either one of the DUEs of the same pair. The other DUE may have a worse RSRP value to the target, which results in worse utility than both of the proposed methods (DP and DTDP). DP only considers the utility values for choosing the target eNB and making the handover decision. Consequently, DP incurs additional handovers and generates a longer latency. However, the performance of DP would be better than DTDP in terms of average utility and the satisfied ratio of the system.