# Handover Management for D2D Communication in 5G Networks
## 4 Proposed Approach
### Choosing Handover Target
It implies that the signaling cost of ID-A3 will be higher than that of DP and DTDP. Figure 6: Average handover time and average throughput versus the distance between two device-to-device user equipment (DUEs) of the same pair, and the cumulative distribution function (CDF) analysis of transmission delay and average throughput of the system. (**a**) Performance of average handover time and average throughput. (**b**) CDF of transmission delay and average throughput. Figure 7: Ratio of D2D pairs having parties connected to the same eNB. Previous simulations present the system dynamics in the control plane, so now we turn our attention to the data plane. For 76 D2D pairs moving at a speed of 3 km/h, we vary the transmission power of UEs and observe the change in system throughput. Figure 8 shows that the system throughput is correlated to the UE transmission power. For the same distance between two UEs, the higher transmission power at the sender implies the higher received signal strength at the receiver. As indicated in Equations (3) and (4), the higher received signal strength will result in the higher system capacity and, therefore, the higher system throughput. It is worth noting that the change in UE transmission power will not affect the number of handovers, utility function, and satisfaction ratio. That is because, for those handover management schemes that we considered, the selection of handover target and the timing of handover rely on the RSRP in the control plane rather than the UE transmission power in the data-plane. ### Micro View of Numerical Results

The numerical results described above are evaluated from a macro view of our simulations. In this section, we will focus on the micro view of our system. In other words, we will look into the detailed behavior of a single instance of the D2D pair. The first pair of D2D users in the system is chosen as the object of observation, and the comparisons between various methods are made based on the performance of this particular D2D pair. Figure 9a shows the number of handovers for the first pair of D2D users versus their moving speed. As mentioned in the previous section, when the moving speeds of both users increase, there is a higher probability for the D2D pair to pass the overlapped areas of multiple eNBs. This results in more number of handovers. Additionally, the results of comparison among different methods are the same as before. DTDP chooses a single eNB as the handover target of the D2D pair and makes the handover decision weighing both DUEs' movements and their received signal conditions. Doing so can greatly reduce unnecessary handovers. In Figure 9b,c, the utility value and the average satisfied ratio for the first D2D pair in the system versus its moving speed are given. As discussed in the previous section, with the increasing of the speeds of both DUEs, the received signal conditions of both users become more unstable. Thus, it may be possible for a rapid-moving pair of users to start their handover process before they have left the original serving eNB's coverage. This will give a lower utility value. The utility value is correlated to the satisfied ratio. With the increasing speeds of both DUEs, the satisfied ratio will decrease accordingly. For the comparison between various methods, DP only depends on received signal conditions so as to have the highest utility value and satisfied ratio among all the methods. However, extra handovers may also degrade the performance. For D-A3, since it only chooses the target eNB that has the best RSRP to either one of the DUEs, the other DUE may have inferior RSRP to the target. This behavior results in the worst utility and satisfied ratio compared with other methods. As for DTDP, with the

Figure 8: System throughput versus user equipment (UE) transmission power. considerations of received signal conditions for both DUEs and their movements, its utility value and satisfied ratio are a little bit worse than DP.