Dynamic frequency broker and Cognitive Radio

Traditional frequency allocation and assignment are relatively slow processes that are inadequately suited for satisfying and exploiting the dynamic spectrum needs of various communication and broadcast systems. This leads to poor average utilization of the spectrum, yet with the demand for assigned spectrum in some bands and locations exceeding availability. Cognitive radio (CR) attempts to increase the spectrum utilization by sensing and reusing available spectrum bands, e.g. in the 802.22 standard the CR system attempts to reuse spectrum bands allocated to TV transmitters. A fundamental problem is, however, that although the CR does not detect any transmitter in a specific band, e.g. due to how the CR is located in the terrain, it may still create disturbance for a receiver, commonly known as a ´hidden node´ problem. To allow improved utilization of the spectrum resources, but at the same time avoiding that this improvement comes at the expense of interfering hidden nodes, we describe the dynamic frequency broker (DFB) system. The DFB acts as a local computerized frequency coordination authority. It keeps a complete list of frequency assignments within an area and keeps an updated terrain propagation path loss model of its area. It assigns frequencies on a temporary basis based upon transmitted signal power, spectral density, receive and transmitter antenna properties and the required received signal to interference level. It receives by Internet and radio, information about the active transmitters, and revokes permissions to transmit if they are idle over a certain period.