Managing the challenge of cognitive radio

The paper presents the evolution trends and challenges of cognitive radio as well as the radio RF circuits. Cognitive radio challenges are unconventional and interdisciplinary in nature ( RF, analog, digital, signal processing etc.). Spectrum access condition based on different technique: sensing technique/geo-location/beacon involves RF design, robust signal processing, pattern recognition. Cognitive radio transmit spectrum is very challenging and need to combine different techniques. Consider reducing output power to relax ACLR and allow aggregation.