Our society relies more and more on wireless communication technologies while most of the RF spectrum has already been allocated by the states. As a result, un-licensed bands are becoming crowded which makes it difficult to create a reliable network without using more spectrum than really necessary. Allowing radio nodes to seamlessly switch between different frequency bands without prior synchronisation would allow the creation of a truly resilient radio network capable of avoiding the frequency bands used by nodes that are not part of the network. In this paper, we propose using software-defined radios in order to sense the surrounding RF environment to find the most suitable bands for communication. We also propose a PHY-layer and a MAC-layer signalling protocols to provide a seamless way of discovering other nodes and selecting the parameters that will be used for communicating with them. Our first experimentation results are very promising towards defining a resilient cognitive radio network.