Spectrum sharing in multi-rat radio base stations

A radio base station for allocating a radio resource to be used for communication in a radio communications network, which radio base station is configured to serve a first cell of a first radio access technology and a second cell of a second radio access technology, which first cell and second cell are comprised in the radio communications network, and which radio base station is arranged to support communication over a frequency band, wherein the frequency band comprises a first frequency band dedicated to the first radio access technology, a second frequency band dedicated to the second radio access technology, and a third frequency band allowed to be allocated to either one of the first and the second radio access technology, which first, second and third frequency bands are separated in frequency, wherein the radio base station comprises:

• a determining circuit configured to determine a load in at least one of the first cell and the second cell, and
• an allocating circuit configured to allocate a radio resource supporting the third frequency band to the first radio access technology of the first cell or the second radio access technology of the second cell based on the determined load.