We consider spectrum sharing between a limited set of operators having similar rights for accessing spectrum. A coordination protocol acting on the level of the Radio Access Network (RAN) is designed. The protocol is noncooperative, but assumes an agreement to a set of negotiation rules. The signaling overhead is low, and knowledge of competitor's channel state information is not assumed. No monetary transactions are involved; instead, spectrum sharing is based on a RAN-internal virtual currency. The protocol is applicable in a scenario of mutual renting and when the operators form a spectrum pool. The protocol is reactive to variations in interference and load of the operators, and shows gains in a simulated small cell scenario compared to not using any coordination protocol.

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Inter-operator spectrum sharing is expected to play a key role in fulfilling the predicted spectrum demand for future wireless systems. In this work, we propose an adaptive co-primary shared access scheme between co-located Radio Access Networks (RANs) owned by different operators. In the literature, the main focus is on orthogonal spectrum sharing. In this work, the spectrum is adaptively partitioned into private and non-orthogonally shared frequency sub-bands with the aim of maximizing inter-RAN sum rate. The non-orthogonally shared frequency sub-band is simultaneously used by all the RANs, with inter-RAN interference minimized. A zero-forcing precoder is used to serve the users scheduled in the private frequency subband. With the exchange of inter-RAN channel state information, a sparse precoder is used as inter-RAN precoder to serve the users scheduled in the shared frequency sub-band. Using a heuristic algorithm based on user grouping, spectrum partitioning and user scheduling are optimized. Based on simulation results, the proposed adaptive spectrum sharing approach outperforms conventional approaches of orthogonal and full-band non-orthogonal spectrum sharing.

User Equipment (UE) paging and location tracking are influenced by the underling state handling model. There are recent proposals to introduce a new RRC state called RRC Inactive as a main state for inactive UEs in 5 th Generation (5G) cellular systems. One of the characteristics of the new state is that the interface between the Radio Access Network (RAN) and Core Network (CN) is kept. Considering this characteristic, there are proposals for a RAN controlled paging and location tracking schemes for RRC Inactive UEs. In this paper, we show that this approach is not always beneficial, especially for high mobility UEs. Instead, we propose a hybrid paging and location tracking scheme where both RAN and CN are involved in the paging and location tracking of RRC Inactive UEs. This is done transparently to the UE. We further propose a hierarchical paging and location tracking scheme to reduce the signaling overhead from paging and location tracking updates. The scheme is applicable to both RAN based and CN based paging and location tracking schemes.

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