Green communications and positioning by integration of adaptive and distributed beam-forming technologies in cognitive radio systems

Abstract

Cognitive radio (CR) concepts were introduced by J. Mitola in 1999/2000. It is an approach with high potential to allow most-intensive usage of the precious natural source spectrum. CR is capable of sensing the communication environments and of adapting to its environment by adjusting the radio parameters. With beam-forming techniques, CR can direct its main beam towards CR users while creating nulls to licensed users (LU's) in up-link in order to share the same spectrum with LU's without disturbing them. Adaptive beam-forming (AB) techniques are used for interference reduction by null broadening (NB) of the beam patterns of a CR base station in down-link operations. In this way by steering those NB angular sectors towards selected regions the LU's will experience less interference. Distributed Beam-forming (DB) is a new concept to form beams by distributed wireless sensors in order to transmit signals over a long distance with less transmit power. At IRCTR of Delft University cognitive radio concepts receive broad attention in the Radio Advanced Technology and Systems (RATS) program. Several MSc's and PhD's participate in this program. In this invited paper the latest IRCTR results on AB and DB are overviewed. Furthermore, our Intelligent-WiMAX (I-WiMAX) initiative is summarized with some focus on adaptive OFDM and on applications for green communications and positioning.