Open Access Research Article

Space Alignment for Cognitive Transmission in MIMO Uplink Channels

Ioannis Krikidis

Author Affiliations

Department of Electrical and Computer Engineering, University of Cyprus, 1678 Nicosia, Cyprus

EURASIP Journal on Wireless Communications and Networking 2010, 2010:465157  doi:10.1155/2010/465157

Published: 3 November 2010

Abstract

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.