An overview of Cognitive Radio for satellite communications

The present scarcity of frequency spectrum allocated to radio communications has motivated the search for technologies able to alleviate it by adapting the transmission to changing environmental and network-usage conditions. Cognitive Radio is one of the most promising among these technologies. Three paradigms for its application have emerged. With “interweaving,” the secondary (unlicensed) users are able to occupy the portions of the spectrum left temporarily free by the primary (licensed) users. In the “underlay” paradigm, the secondary transmitter overlaps in frequency with the primary user, after making sure that the interference level it causes is below a given threshold. The “overlay” paradigm uses the secondary user's knowledge of the primary users transmission scheme and of the channel to choose a transmission scheme that causes an acceptable amount of interference. In this paper we briefly review the basic concepts underlying Cognitive Radio, and examine their applications to satellite communications.