# Handover Management for D2D Communication in 5G Networks
## 4 Proposed Approach
### Choosing Handover Target
Particularly, the first one assumes that the fixed distance (30 m) is preserved between two DUEs of the same D2D pair during their movement. Also, they possess the same moving direction and velocity, while the moving direction would be changed every 3 s. For this scenario, we name it as the fixed distance (FD) model. For the second scenario, we refer to the reference point group mobility (RPGM) model in [PERSON] et al. [23]. It assumes that the movement of a group of users is mainly decided by the moving behavior of a central point in that group. Note that the moving direction of each user

Figure 3: Network topology considered in the simulation. would be changed every 3 s. Mathematically, the moving direction for a group member \(l\) at time slot t can be expressed by

\[SNR_{k}^{m}=\frac{RSRP_{k}^{m}}{P_{noise}} \tag{5}\]0

where \(V_{group}^{\rightarrow}(t)\) and \(R\overset{\rightarrow}{M_{l}}(t)\) indicate the moving vector of the central point and a random biased vector with respect to the central point, respectively. In our simulation, when RPGM is used as the mobility model, each D2D pair \(i\) would be viewed as a group. \(DUE_{i}^{1}\) would be regarded as the central point of this group, and \(DUE_{i}^{2}\) can move around in the circular area around the central point with a radius of 30 m.

Moreover, in this section, we also make comparisons among three methods. The first one is the conventional LTE-A handover standard in which the handover decision of a single cellular user is made according to the A3 event, which is referred to as the \"standard\" in our discussion. The second one is the method proposed in [PERSON] et al. (2019), with which two DUEs of the same D2D pair find out the target eNB first, then both users jointly hand over to the target if both of them meet A3 event. However, if only one of them meets the A3 event, the satisfied one hands over to the target first, while the other stays with the original eNB until it meets the A3 event. The second method is referred to as \"D-A3\" in our discussion. The third scheme under consideration is our method. Our approach considers users' movements together with the received signal conditions for both DUEs of the same D2D pair. In order to evaluate the effect of individual mechanism, we conduct experiments considering only utility function as well as experiments considering both utility function and \(D_{counter}\). The former is referred to as \"D2D pairing (DP),\" and the latter is referred to as \" direction-counter-triggered D2D pairing (DTDP)\" in our discussion. The signaling cost can be substantially reduced if both parties of a D2D pair connected the same eNB, DTDP and DP are therefore designed to let both parties of a D2D pair to handover together. For the sake of a fair comparison, the above-mentioned D-A3 will act the same in our simulations. We will use the total number of handover, utility, satisfied ratio and average interruption time as our performance metrics for the comparative studies under different scenarios. In the following sections, we will analyze the numerical results in great detail. Particularly, the numerical results can be further divided into two parts. For the first part, the analysis is focused on the macro view of the \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Bandwidth & 10 MHz \\ Number of RBs & 50 \\ Number of eNBs & 19 \\ Number of D2D pairs & 1–6 per eNB \\ Radius of eNB & 500 m \\ Transmit power of eNB & 46 dBm \\ Transmit power of UE & 23 dBm \\ Path loss model [22] & eNB to UE: 128.1+36.7 log \(d\), \(d\) in km; UE to UE: 148+40 log \(d\), \(d\) in km \\ Shadow fading deviation & 8 dB \\ Distribution of D2D pair & Uniform \\ UE mobility model & Random direction \\ Speed of UE & 3, 30, 60, 90, 120 km/h \\ Distance between DUEs & 5–30 m \\ \(\varphi\) & \(-80\) dBm \\ \(\rho\) & 60 \\ A3 event margin & 3 dB \\ Time-to-Trigger (TTT) & 160 ms \\ Simulation rounds & 30 \\ Simulation time & 40 s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters.