Challenges to Implement Cognitive Radio
As mentioned earlier, the research on cognitive radio technology has a very short history, which
spans less than 10 years. We have to get over many technical hurdles before cognitive radios can
be deployed on a mass commercial application scale. Many challenges need to be overcome to
implement a cognitive radio system for practical applications. Cognitive radio is a methodology for the
opportunistic utilization of fallow spectrum. This technology can be categorized into two broad classes:
• Unlicensed cognitive radios operating in the unlicensed bands;
• Unlicensed cognitive radios operating in the licensed bands.
Each class has unique challenges to ensure its successful operation. The implementation of the
second class of cognitive radios is in particular challenging since there are many parts of the radio
spectra that are used by passive receivers such as radio astronomy where very weak distant objects are
being observed. A typical signal power in radio astronomy is less than a trillionth of a watt. Detecting
and avoiding these passive receivers is an extremely difficult issue and one method of solving this
problem is to require any device operating in this band to be able to determine its location and avoid
utilizing that part of the spectrum once in the proximity of this sensitive receiver.
Future research areas in cognitive radio include, but are not limited to: (1) New concepts and
algorithms for agile radio and spectrum etiquette protocols; (2) Architecture and design of adaptive
wireless networks based on cognitive radios; (3) Detailed evaluation of large-scale cognitive
radio systems using alternative methods; (4) Spectrum measurement and field validation of proposed
methods; and (5) Cognitive radio hardware and software platforms.
User-level field trials of emerging cognitive radios and related algorithms/protocols may also
be useful in gaining experience, including: (1) controlled test bed experiments comparing different
methods; (2) large-scale spectrum server trial for 802.11x coordination; (3) experimental deployments
in the proposed US FCC cognitive radio band.
It has to be admitted that there exists a huge gap between what we expect a cognitive radio
to do and what we can use to implement a prototyping cognitive radio. Without doubt, success
with the development of cognitive radio technologies should lead to major improvements in spectrum
efficiency, performance, and in the interoperability of different wireless networks as a whole. The wide
application of cognitive radio technologies will also bring a fundamental change to the philosophy in
global radio spectrum allocation and specification across different frequency bands.