Cognitive radios and flexible spectrum use provide an efficient way to exploit underutilized radio spectrum by allowing secondary users to access licensed frequencies in an agile manner. This means that a secondary user may access the licensed frequency when its transmission will not interfere the primary receiver.
In order to identify such spectral opportunities secondary users have to sense the radio spectrum and decide whether it is free or not. In this work a cooperative spectrum sensing policy employed by spatially displaced multiple cognitive radios is developed. The policy enables sensing multiple potentially discontinuous frequency bands simultaneously while facilitating the use of spatial diversity to mitigate the effects of shadowing and fading on spectrum sensing. The design of the sensing policy is converted into designing and allocating pseudorandom frequency hopping patterns with desired Hamming correlation properties. The method allows for dealing with multiple discontinuous bands of different bandwidths and priorities in a straightforward manner. Moreover, we characterize the diversity order in cooperative sensing under fading channels. In order to optimize the sensing policy under time-frequency-location varying channels a greedy machine learning algorithm to prioritize the cooperative sensing over multiple frequency bands is proposed. We show that even such a suboptimal method is able to significantly increase the obtained throughput by the secondary network.
Visa Koivunen (IEEE Fellow) is Academy professor at Aalto University, Finland (formerly known as Helsinki Univ of Technology). He is one of the Principal Investigators in the SMARAD (Smart Radios and Wireless Systems) Center of Excellence in Radio and Communications Engineering nominated by the Academy of Finland. He has also been an Adjunct Full Professor at the University of Pennsylvania, Philadelphia and currently visiting fellow at Princeton University (2009-). During his sabbatical leave in 2006-2007, he was a Visiting Fellow at Nokia Research Center, as well as Princeton University. His research interests include statistical, communications, and sensor array signal processing. He has published more than 350 papers in international scientific conferences and journals. Dr. Koivunen received the Primus Doctor (best
graduate) Award among the doctoral graduates in the years 1989 to 1994. He co-authored the papers receiving the Best Paper Award in IEEE PIMRC 2005, EUSIPCO 2006, and EuCAP 2006. He has been awarded the IEEE Signal Processing Society Best Paper Award for 2007 (co-authored with J. Eriksson). He served as an Associate Editor for IEEE SIGNAL PROCESSING LETTERS, the Signal Processing Journal and the Journal of Wireless Communication and Networking. He is a member of the editorial board for the IEEE TRANSACTIONS ON SIGNAL PROCESSING. He is also a member of the IEEE Sensor Array Multichannel Signal Processing Technical Committee. He is also serving at the industrial liaison board of the IEEE SP society.