# Handover Management for D2D Communication in 5G Networks
## 4 Proposed Approach
### Choosing Handover Target
As mentioned before, the objective of this work is to reduce the unnecessary handovers caused by possible ping-pong effect and to ascertain both users of the same D2D pair to be with the same eNB. Since the latter and part of the former are achieved by choosing a single handover target eNB for each pair of D2D users and by jointly taking into account their movements and received signal conditions. In this section, we will make the handover decision for each D2D pair by factoring in the RSRPs of both users of a D2D pair so as to further reduce the unnecessary handovers and to ensure the stability of a connection. As we have each user report its RSRPs received from all eNBs, we can thus examine the RSRPs received from the current serving eNB and the likely target eNB for the D2D pair. Specifically, for \(i\)-th pair of D2D users, since we have got \(RSRP_{DUL_{i}^{1}}^{\textit{SeNB}}\), \(RSRP_{DUL_{i}^{2}}^{\textit{SeNB}}\), \(RSRP_{DUL_{i}^{1}}^{\textit{TeNB}}\), \(RSRP_{DUL_{i}^{2}}^{\textit{TeNB}}\), and a predefined threshold of the minimum requirement of connection \(\varphi\). Thus with the joint consideration of decreasing inappropriate handovers and raising the stability of the connection, we can make the decision on whether or not to hand over the D2D pair to the target eNB. In this aspect, for \(i\)-th pair of D2D users, we first categorize the level of satisfaction regarding the serving eNB into the following three classes: (1) both users are satisfied with the minimum requirement of connection (i.e., \(RSRP_{DUL_{i}^{1}}^{\textit{SeNB}}\geq\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{SeNB}}\geq\varphi\)), (2) either one of them has attained the minimum requirement of connection, but the other has not (i.e., \(RSRP_{DUL_{i}^{1}}^{\textit{SeNB}}\geq\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{SeNB}}<\varphi\), or \(RSRP_{DUL_{i}^{1}}^{\textit{SeNB}}<\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{SeNB}}\geq\varphi\)), and (3) neither one of them has reached the minimum requirement of a connection (i.e., \(RSRP_{DUL_{i}^{1}}^{\textit{SeNB}}<\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{SeNB}}<\varphi\)). For the first class, both users of the same D2D pair can sustain their stability of connection by connecting to the original serving eNB. For the sake of bringing down redundant handovers, it is not suggested to hand over to the target eNB. For the second class, if connecting both users of \(i\)-th D2D pair to the target eNB, we can further sort it into the following three subclasses: (1) both users can satisfy their minimum requirement of connection (i.e., \(RSRP_{DUL_{i}^{1}}^{\textit{TeNB}}\geq\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{TeNB}}\geq\varphi\)), (2) either one of them can satisfy the minimum requirement of connection but the other cannot (i.e., \(RSRP_{DUL_{i}^{1}}^{\textit{TeNB}}\geq\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{TeNB}}<\varphi\), or \(RSRP_{DUL_{i}^{1}}^{\textit{TeNB}}<\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{TeNB}}\geq\varphi\)), and (3) neither one of them can satisfy the minimum requirement of connection (i.e., \(RSRP_{DUL_{i}^{1}}^{\textit{TeNB}}<\varphi\) and \(RSRP_{DUL_{i}^{2}}^{\textit{TeNB}}<\varphi\)). Specifically, for the first subclass, since the target eNB is better than the original serving eNB in terms of satisfaction, we then hand over both users to the target eNB to advance their stability. For the second subclass, the satisfaction is the same for the D2D pair with regard to its target eNB and its original serving eNB. In order to determine which eNB is better in terms of stability of connection for both users of the D2D pair, we make the comparison according to their \(D_{counter}\) values. Since whatever the D2D pair connects to, the unsatisfied user's received signal condition would probably not be too disparate from the satisfied one because of the short distance between the two users.