Cognitive Radio Systems: Multicarrier Modulation and Power Allocation Challenges

Radio spectrum is a scarce resource and its demand is growing rapidly to meet high data rate end user demands. Current static frequency allocation leads to insufficient usage of limited spectrum resources and urges the regulatory bodies to review their policy and inquire communication technologies that can exploit spectrum in a more flexible and intelligent fashion. For example, spectrum occupancy measurements conducted by Ofcom in different areas of UK, show underutilization of spectrum in significant periods of time. Similarly, according to FCC, in New York City and downtown Washington DC only 13.1% and 35% of spectrum utilization has been reported, respectively, below 3 GHz [1]. These studies clearly suggest that physical spectrum shortage is mainly due to the inflexible spectrum licensing scheme.