Date Added: Jan 2012
Spectrum overcrowding continues to present is a fundamental challenge for both military and commercial communications. Recent studies suggest that spectrum congestion is primarily due to inefficient usage rather than spectrum availability. Dynamic Spectrum Access (DSA) and Cognitive Radio (CR) are two techniques being considered to improve spectrum efficiency and utilization. Interest in Cognitive Radio (CR) remains strong as the communications community strives to solve the spectrum congestion problem. In conventional CR implementations, interference to primary users is minimized using either overlay waveforms that exploit unused (white) spectrum holes or underlay waveforms that spread their power density over an ultra-wide bandwidth.