Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Achievable Rates and Scaling Laws for Cognitive Radio Channels | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2008 Article ID 896246 12 pages doi 2008 896246 Research Article Achievable Rates and Scaling Laws for Cognitive Radio Channels Natasha Devroye Mai Vu and Vahid Tarokh School of Engineering and Applied Sciences Harvard University Cambridge MA 02138 USA Correspondence should be addressed to Natasha Devroye natasha@ Received 30 May 2007 Accepted 23 October 2007 Recommended by Ivan Cosovic Cognitive radios have the potential to vastly improve communication over wireless channels. We outline recent information theoretic results on the limits of primary and cognitive user communication in single and multiple cognitive user scenarios. We first examine the achievable rate and capacity regions of single user cognitive channels. Results indicate that at medium SNR 0-20 dB the use of cognition improves rates significantly compared to the currently suggested spectral gap-filling methods of secondary spectrum access. We then study another information theoretic measure the multiplexing gain. This measure captures the number of point-to-point Gaussian channels contained in a cognitive channel as the SNR tends to infinity. Next we consider a cognitive network with a single primary user and multiple cognitive users. We show that with single-hop transmission the sum capacity of the cognitive users scales linearly with the number of users. We further introduce and analyze the primary exclusive radius inside of which primary receivers are guaranteed a desired outage performance. These results provide guidelines when designing a network with secondary spectrum users. Copyright 2008 Natasha Devroye et al. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited. 1. INTRODUCTION Secondary spectrum usage is of current .
