Mode selection map-based vertical handover in D2D enabled 5G networks

One of the promising features of 5G networks is device-to-device (D2D) communication that enables direct transmission between D2D user equipments (UEs). Besides the traditional cellular transmission mode, UEs can select between the reuse and dedicated modes. In this study the authors consider a scenario where a communicating D2D pair and a cellular UE that communicates with an evolved Node-B can use the same spectrum. It is assumed that the cellular UE can move in the network while the D2D UEs are static. The movement of the cellular UE can affect the quality of the communication between the D2D pair. Therefore, the transmission mode between the D2D UEs might change to keep the best quality. In this study the authors propose a new mobility management and vertical handover algorithm that handles the transmission mode transition during the D2D connection to maximise the overall throughput. The algorithm uses distance from the border and critical direction set as mobility variables that are analytically determined. These variables are calculated using a mode selection map that is derived analytically when pathloss and fading models are used. Finally, in order to analyse the performance of the proposed handover algorithm, the authors analytically calculate handover rate and sojourn time metrics.