Joint User Selection and Beamforming Schemes for Inter-Operator Spectrum Sharing

We consider the downlink of an inter-operator spectrum sharing scenario where two operators share the same piece of spectrum and use it simultaneously. A base station of one operator cooperates with a base station of the other operator in order perform joint user selection and beamforming using a central unit. Optimal scheduling, in the sense of maximizing sum-rate or proportional fairness, is in many cases impractical due to high computational complexity. Therefore, we propose a heuristic algorithm that schedules users based on simple beamforming techniques. Once the users are scheduled, we compute the optimal beamforming vectors for them. This method still performs an exhaustive user search. Therefore, we also propose a greedy user selection scheme. From numerical evaluations, we notice that these schemes perform close to the optimal selection. Also, we use our proposed methods to identify when spectrum sharing provides extra gains over the non-sharing scenario.