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

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.