Abstract: Recently, the cognitive radio networks (CRNs) has emerged as an intelligent, flexible, and efficient spectrum accessing based wireless networks to increase the spectrum efficiency by enabling the secondary users (unlicensed users) to opportunistically utilize the vacant spectrum which is not used by the primary users (licensed users). This talk will start with investing the motivations and reviewing the state-of-the-art of CRN, including its fundamental theories and key techniques, classification of different spectrum sensing and sharing modes. Then, we will focus on the main challenges of cognitive radio MAC for QoS provisioning in synchronous CRNs, which is critical to many delay-, reliability-, and/or throughput-sensitive QoS-driven CRNs. The problem is challenging in that the QoS performance of the secondary users is not only affected by the time-varying wireless channels, but also constrained by the uncertain incumbency of the primary users. Finally, we will concentrate on our newly developed cognitive radio MAC and its modeling techniques for QoS-driven CRNs with emphasis on PHY and MAC cross-layer optimization. Specifically, we will present the cognitive radio MAC protocols design, its channel sensing policies, and M/G^Y/1 queuing modeling techniques for packet delay analysis and control. We will conclude the talk by discussing the potential future research directions in CRNs. Biography: Xi Zhang received the B.S. and M.S. degrees from Xidian University, Xi�an, China, the M.S. degree from Lehigh University, Bethlehem, PA, all in electrical and computer science, and the Ph.D. degree in electrical engineering and computer science (Electrical Engineering-Systems) from The University of Michigan, Ann Arbor. Prof. Zhang is currently an Associate Professor and the Founding Director of the Networking and Information Systems Laboratory, Department of Electrical and Computer Engineering, Texas A&M University, College Station. He was an Assistant Professor and the Founding Director of the Division of Computer Systems Engineering, Department of Electrical Engineering and Computer Science, Beijing Information Technology Engineering Institute, China, from 1984 to 1989. He was a Research Fellow with the School of Electrical Engineering, University of Technology, Sydney, Australia, and the Department of Electrical and Computer Engineering, James Cook University, Australia, under a Fellowship from the Chinese National Commission of Education. He was with the Networks and Distributed Systems Research Department, AT&T Bell Laboratories, Murray Hills, NJ, and with AT&T Laboratories Research, Florham Park, NJ. He has published more than 200 research papers in the areas of wireless networks and communications systems, mobile computing, network protocol design and modeling, statistical communications, random signal processing, information theory, and control theory and systems. Prof. Zhang received the U.S. National Science Foundation CAREER Award in 2004 for his research in the areas of mobile wireless and multicast networking and systems. He is an IEEE Communications Society Distinguished Lecturer. He received the Best Paper Awards in the IEEE WCNC 2010, IEEE GLOBECOM 2009, and the IEEE GLOBECOM 2007, respectively. He also received the TEES Select Young Faculty Award for Excellence in Research Performance from the Dwight Look College of Engineering at Texas A&M University, College Station, in 2006. He is currently serving as an Editor for the IEEE Transactions on Communications, an Editor for the IEEE Transactions on Wireless Communications, an Associate Editor for the IEEE Transactions on Vehicular Technology, a Guest Editor for the IEEE Journal on Selected Areas in Communications (J-SAC) for the special issue on �Broadband Wireless Communications for High Speed Vehicles�, a Guest Editor for the IEEE Journal on Selected Areas in Communications (J-SAC) for the special issue on �Wireless Video Transmissions�, an Associate Editor for the IEEE Communications Letters, a Guest Editor for the IEEE Communications Magazine for the special issue on �Advances in Cooperative Wireless Networking�, a Guest Editor for the IEEE Wireless Communications Magazine for the special issue on �next generation of CDMA versus OFDMA for 4G wireless applications�, an Editor for the John Wiley�s Journal on Wireless Communications and Mobile Computing, an Editor for the Journal of Computer Systems, Networking, and Communications, an Associate Editor for the John Wiley�s Journal on Security and Communication Networks, an Area Editor for the Elsevier Journal on Computer Communications, and a Guest Editor for John Wiley�s Journal on Wireless Communications and mobile computing for the special issue on �next generation wireless communications and mobile computing�. He has frequently served as the Panelist on the U.S. National Science Foundation Research-Proposal Review Panels. Prof. Zhang is serving or has served as the Technical Program Committee (TPC) Co-Chair for IEEE INFOCOM 2013, the TPC Chair for IEEE GLOBECOM 2011, TPC Area Chair for IEEE INFOCOM 2012, General Co-Chair for INFOCOM 2012 � Workshop on Communications and Control for Sustainable Energy Systems: Green Networking and Smart Grids, TPC Co-Chair for IEEE ICC 2012 � Workshop on Green Communications and Networking, General Co-Chair for IEEE INOFOCOM 2011 - Workshop on Green Communications and Networking, General Chair for IEEE ICC 2011 - Workshop on Advanced Networking Technologies for Smart-Services Based Clouding Computing, TPC Co-Chair for the IEEE ICDCS 2011 - Workshop on Data Center Performance, Panel/Demo/Poster Chairs for ACM MobiCom 2011, TPC Vice-Chair for IEEE INFOCOM 2010, General Chair for ACM QShine 2010, TPC Co-Chair for IEEE INFOCOM 2009 Mini-Conference, TPC Co-Chair for IEEE GLOBECOM 2008 - Wireless Communications Symposium, TPC Co-Chair for IEEE ICC 2008 - Information and Network Security Symposium, Symposium Chair for IEEE/ACM International Cross-Layer Optimized Wireless Networks Symposium 2006, 2007, and 2008, respectively, Demo/Poster Chair for IEEE INFOCOM 2008, Student Travel Grants Chair for IEEE INFOCOM 2007, General Chair for ACM QShine 2010, Panel Co-Chair for IEEE ICCCN 2007, Poster Chair for IEEE/ACM MSWiM 2007 and IEEE QShine 2006, Executive Committee Co-Chair for QShine, Publicity Chair for IEEE/ACM QShine 2007 and IEEE WirelessCom 2005, and Panelist on Cross-Layer Optimized Wireless Networks and Multimedia Communications at IEEE ICCCN 2007 and WiFi-Hotspots/WLAN and QoS Panel at IEEE QShine 2004. He has served as the TPC members for more than 100 IEEE/ACM conferences, including IEEE INFOCOM, IEEE GLOBECOM, IEEE ICC, IEEE WCNC, IEEE VTC, IEEE/ACM QShine, IEEE WoWMoM, IEEE ICCCN, among many others. For more details for Prof. Xi Zhang�s background, please visit his home website at: https://www.ece.tamu.edu/~xizhang/.