TABLE OF CONTENTS Generally speaking, a cognitive radio is a radio system that can intelligently adapt its behavior or operational characteristics in response to changes in the radio's internal state or external environment. This ability to adapt promises a range of functional capabilities, including making the radio systems more "personal", as suggested by Mitola [1]. Some examples of internal states that may alter the operational behavior of the radio are:
Low Battery Power: A reduction in available power may result in the inability to support multiple waveforms simultaneously. The radio may select and disable a low-priority waveform in order to conserve power or maintain operation of a mission-critical waveform.
Component Failure: The radio may reroute around a failure point; it may provide an alternative service possibly at a lower data rate, or it may terminate a lower priority service in favor of a mission-critical communication.
Some examples of external influences that can affect the operational behavior include:
Co-Site Interference: Use of the same radio frequency (RF) by multiple radios or a radio attempting to exercise multiple frequencies through a single set of RF equipment will diminish or negate successful communications. The radio may select an alternate operating frequency or change other characteristics of the waveform.
Background Noise: Normal RF background noise can impede the effectiveness of communications on a given channel or frequency. Again, the radio may sense the level of background noise and alter the frequency, initiate frequencyhopping, or take other adaptive...
