1. A cellular communication system based on a plurality of radio-based communication units, said communication system comprising: a central main communication unit; a primary-cell radio-based communication unit interconnected to said central main unit; a number of secondary-cell radio-based communication units, each of which is connected to said primary-cell radio-based communication unit via a respective wireless optical link and provided as a remote radio unit forming a distributed radio base station together with said central main unit, said distributed radio base station having radio transceiver functionality divided between said remote secondary-cell radio unit and said central main unit; means for measuring the quality of at least one of said wireless optical links; and means for re-directing radio traffic, if the measured wireless optical link quality associated with a secondary-cell communication unit is insufficient, from the secondary-cell communication unit to another one of said communication units within said cellular communication system.