30 CHAPTER 2 Radio frequency spectrum and regulation spectrum or control certain types of cognitive devices or implement different rules for devices with different cognitive capabilities. Beacon Reception This approach requires the transmission of a signal from some appropriate infra- structure providing information on which frequencies are available for cognitive use in the vicinity. Cognitive devices tune to this channel and use the information provided to select their preferred frequency. This can be thought of as centralizing the database described in the previous section and setting the location to that reachable from the specific transmission source. If the cognitive device is unable to find a beacon, it is safest for it not to transmit, since it may be within the area covered by the beacon but shielded from receiving it. Hence, if it were to transmit on a randomly selected channel it could cause interference. While this resolves the sensing problem at the cognitive device it raises many other problems: Who provides the beacon signal? What are the commercial arrangements, and if there is only one provider, are there competition concerns? How is the information the beacon transmits kept up to date, especially where the licensed services are changing rapidly? What spectrum is used for the beacon? What technical parameters and protocols are used by the beacon transmitter? How to prevent the beacon signal from being received outside its intended coverage area and as a result being applied incorrectly, and conversely how to make sure that it is available to all cognitive devices in the target area? Should there be separate beacons for separate frequency bands or one beacon for all the bands into which cognitive access is allowed? Is it acceptable for the use of cognitive devices to be denied access if the beacon fails or is taken off-air for any reason? In part based on these questions, the beacon reception approach has not generated much interest in the regulatory community to date and hence few, if any, of these questions have been explored at a regulatory level. 2.5.4 Regulatory Developments to Date At the time of writing, in July 2009, on a global basis a number of regulators have given serious consideration to cognitive access in general. Most notably in November 2008 the FCC published its Report and Order enabling cognitive access in the white space in the TV broadcast spectrum [63]. Furthermore, in July 2009, Ofcom published a statement on "Licence-Exempting Cognitive Devices Using Interleaved Spectrum" [64], following a public consultation on this topic, which was released in February 2009. The FCC concluded that sensing alone was insufficiently proven for cognitive access. They noted that devices provided on trial often failed to identify wireless