The No. 81 lecture of Tsinghua Information Forum was successfully held in Room 1-415 of FIT building on Dec. 26, 2011. Dr. Wei Zhang, from the University of New South Wales in Australia, was invited by Prof. Zhisheng Niu to present his current research, and the topic is “Spectrum Sharing in Multihop Cognitive Relay Networks”. Due to the scarcity but underutilization of spectrum resource, Cognitive Radio was proposed and is one of current hot topics. One typical application of Cognitive Radio is that unlicensed cognitive users can access the radio spectrum together with the licensed primary users (PU) when the spectrum is not occupied by Pus. Based on this, Dr. Wei Zhang, proposes a novel “Whispering Radio” technique by utilizing multihiop relay techniques and smart power control to take full advantage of the “grey space” of the licensed spectrum. The proposed “Whispering Radio” can maximize the spectrum utilization efficiency by allowing cognitive radios to access the licensed band even when the PUs are in operation. This lecture was hosted by Prof. Zhisheng Niu, and more than 30 faculty members and students attended this lecture.