Towards the Mobility Issues of 5G-NOMA Through User Dissociation and Re-association Control

Non-Orthogonal Multiple Access (NOMA) system is considered as core enabler for the Fifth-Generation (5G) of the wireless cellular networks, contributing to the improvement of spectral efficiency. NOMA groups users into clusters, based on the maximum channel gain-difference. However, user mobility continuously changes the channel gain and requires re-clustering, depending on the percentage of mobile users and the environment in which they operate. In this paper, we propose a set of re-clustering methods: arbitrary, one-by-one and simultaneous, that expedite link re-establishment and keep the clusters interference-free, taking into account the mobility of users. The methods are applied to dissociate identified users within clusters, when the gain-difference is lower than a given threshold, followed by re-association procedure, which integrates users into different clusters, maintaining an appropriate gain-difference. The proposed methods are based on mathematical formulation and algorithms and address many technical and computational challenges associated with the clustering techniques. Numerical and experimental investigation has been carried out to test their performance and the results show that the simultaneous method can provide lower number of clusters, making it more suitable in dense and highly mobile scenarios. Our findings also demonstrate that this method has the potential to minimize the number of reclustering, improving resource utilization and lowering signaling loads.