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 Space Alignment for Cognitive Transmission in MIMO Uplink Channels | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2010 Article ID 465157 6 pages doi 2010 465157 Research Article Space Alignment for Cognitive Transmission in MIMO Uplink Channels loannis Krikidis Department of Electrical and Computer Engineering University of Cyprus 1678 Nicosia Cyprus Correspondence should be addressed to Ioannis Krikidis krikidis@ Received 5 July 2010 Revised 14 September 2010 Accepted 2 November 2010 Academic Editor George Karagiannidis Copyright 2010 Ioannis Krikidis. 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. This paper investigates a new transmission technique for cognitive access in multiple-input multiple-output MIMO uplink channels with waterfilling power allocation- WPA- based primary transmission. The proposed technique allows a cognitive node to access the common destination simultaneously with the primary node without affecting the MIMO primary performance. By using an appropriate precoding design the cognitive node aligns its transmitted signal to the unused primary eigenmodes and ensures an orthogonality between the primary and the cognitive links. In order to overcome the limitation of the conventional WPA at high signal-to-noise ratios a modified WPA enables the primary node to release some eigenmodes in order to provide a positive cognitive rate for all the cases. 1. Introduction Cognitive radio CR is introduced as an efficient technique in order to use the radio spectrum more efficiently 1 . It is characterized by the capability of the cognitive radios secondary or unlicensed nodes to coexist with the spectrum owners primary or licensed nodes and share the same frequency band in an opportunistic fashion. The opportunistic access enables the cognitive nodes to use the spectrum when it is idle spectrum
