Inter-system interference in communications

An inter-system interference estimation method is disclosed for both primary and secondary radio systems. In the case of a primary system (such as a GSM system), inter-system interference estimation is based on a comparison of cell level measurement statistics before and after secondary spectrum usage in neighboring cells. In the case of a secondary system (such as an LTE system), inter-system interference estimation is based on a measurement on secondary spectrum before starting transmission on the secondary spectrum. Based on both of the above mentioned inter-system inter-cell interference estimations, a cell-level decision on the secondary spectrum usage is made, and optimization of radio resource allocation inside the systems may be carried out.