TABLE OF CONTENTS Spectrum is the "lifeblood" of RF communications.
The wireless designer's adaptation of the classic New England weather observation could be "Everyone complains about spectrum availability (or at least the lack of it), but no one does anything about it!" Cognitive radio, however, offers the opportunity to do something about it. Spectrum aware radios offer the opportunity to fundamentally change how we manage interference, and thus transit the allocation and utilization of spectrum from a command and control structure dominated by decade-long planning cycles, assumptions of exclusive use, conservative worst-case analysis, and litigious regulatory proceedings to one that is embedded within the radios, each of which individually and collectively, implicitly or explicitly, cooperates to optimize the ability of the spectrum to meet the needs of all the using devices. As this chapter looks at this opportunity, it investigates solutions that range from local brokers that "deal out" spectrum, to totally autonomous systems that operate completely independently of any other structures. In its ultimate incarnation, it is possible to actually use spectrum awareness and adaptation to relax the hardware physical (PHY) layer performance requirements by avoiding particularly stressing spectrum situations. As such, a cognitive radio could ultimately be of lower cost than a less intelligent, and more performance stressed, conventional one.
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Before discussing a cognitive spectrum process, let us consider the classical spectrum management and assignment...
