C/U Split Multi-Connectivity in the Next Generation New Radio System

The next generation mobile network is foreseen as a heterogeneous network comprising not only the evolved existing systems but also the new radio (NR) spanning over the whole spectrum. Multi-connectivity (MC), where a UE aggregates the radio resources from multiple cells, provides an efficient way to fulfill the diverse 5G requirements. In 3GPP, Dual connectivity (DC) and carrier aggregation (CA) have been specified in LTE to boost the capacity, and similar MC operations were agreed to be developed for the NR. Since the solutions have been targeting the user plane performance, the cells delivering the highest through-put, normally small cells, are likely selected. This leads to the frequent change of MC associated cells and degrades the control plane performance in terms of service interruption, signaling overhead, connection failure, etc. It is therefore suggested to use the macro cells as the anchoring point, however, they cannot contribute much to the overall data transmission due to its lower available bandwidth and meanwhile decreases the access opportunities for the single connectivity UEs in its coverage. In this paper, it is proposed to manage the UP and CP transmission of a multi-connectivity session separately, which is named as CP/UP (C/U) split MC. In line of the proposal, we elaborate the design principles, the radio protocol architecture and the UE operation in the context of the new radio architecture. The performance is further evaluated in contrast with legacy LTE dual connectivity where the benefits in terms of UE throughput are clearly observed in different scenarios.