Cognitive radio is an agile radio technology which has the potential of dealing with the stringent requirement and scarcity of the radio spectrum by opportunistically utilizing licensed spectrum. In this talk, a “whispering radio” technique is focused to enable cognitive radio sharing licensed band with primary users and improving spectrum utilization. An overview of cognitive radio technology is first provided and the current research advance and challenges are discussed. Then, a cognitive relay based spectrum sharing approach, referred to as “whispering radio” is presented to address the problem of spectrum under-utilization. In particular, power control and routing for cognitive relay networks are discussed. Finally, performance benefits of the “whispering radio” are shown.