P). The March 2006 edition of Scientific American magazine describes how such technology, called cognitive radio (CR), will work (www.sciam.com/article.cfm?chanID=sa006&articleID=000C7B72-2374- 13F6-A37483414B7F0000&pageNumber=1&catID=2). CR is the next step in the evolution of SDR. It starts with SDR's ability to adapt to changing communications protocols and frequency bands and adds the ability to perceive the world around it and learn from experience. The term cognitive radio describes a smart system in which a radio device and its antenna can adapt their spectrum use in response to their operating environment, including the radio fre- quency spectrum, user behavior, and network state. CR detects temporarily unused spectrum segments, such as amateur radio and paging frequencies, and jumps into and out of them without interfering with the transmissions of the authorized users of those segments. There are several types of CR: Full CR (also known as Mitola radio)-With this type of CR, every possi- ble parameter is taken into account, including radio frequency spectrum, network state, and user behavior. Spectrum-sensing CR-This type of CR considers only the radio frequency parameter. Licensed band CR-This type of CR is capable of using unlicensed bands as well as bands assigned to licensed users. Unlicensed band CR-This type of CR can use only the unlicensed parts of the radio frequency spectrum. The majority of research is currently focused on spectrum-sensing CR, particularly on the utilization of TV bands for communication. CR introduces a unique design problem: interference temperature. A CR device must know its location and sense the interference it may cause to nearby radios, and Mobile IP it must also know exactly which air interfaces are available for it to use at any given moment, regardless of the band. Debate continues on how to best resolve the prob- lem of interference temperature. Most of the interest in CR to date has come from the military and public-sector emergency services, but the commercial se