Cognitive Radio and Dynamic Spectrum Sharing Systems

The vision behind software radio (SR) is to realize the communication specific signal processing of a radio as far as possible on programmable hardware. An ideal SR samples the received signal directly at the antenna, and its hardware consists of a general purpose processor that is connected with analog-to-digital and with digital-to-analog converters. A radio that uses an analog radio frontend for signal conditioning and employs digital signal processors as well as field programmable gate arrays is referred to as software defined radios (SDRs). Cognitive radios (CRs) are self-learning, intelligent SDRs that are able to monitor their environment and to adapt to actual conditions like available base stations (standards) or channel properties. Most important CR properties are, for example, self-location, spectrum awareness, transmission power control, or radio signal analysis. By extending cognitive radio principles to a network layer, a concept of cognitive networks arises. Cognitive networks can adapt their topology and parameters in self-configurable and dynamic manner according to the any sort of relevant changes. With an increased demand for mobile communications and new wireless applications, the efficient usage of the available spectrum resources gains importance. Due to the currently practiced static assignment of spectrum to specific users by regulatory bodies, the actual demand for transmission resources often exceeds the available band-width. Promising approaches to overcome static spectrum assignments are given by dynamic spectrum sharing systems. Important examples of these technologies are overlay systems in which the spectral resources left idle by the primary (licensed) users are offered to secondary users. Obviously, the terminals in the secondary systems must be able to detect an emerging primary user immediately as well as reliably. At this point, the strong connection between cognitive radio and dynamic spectrum sharing systems becomes apparent. With this relation in mind, the present special issue presents twelve papers written by well-known experts from academia and industry. The first (invited) paper " Achievable rates and scaling laws for cognitive radio channels, " by N. Devroye et al. outlines recent information theoretic results on the limits of possible primary and cognitive user communication in single and multiple cognitive user scenarios. The authors first consider the achievable rate and capacity regions of single user cognitive channels and then consider a different information theoretic measure: the multiplexing gain. Furthermore, a cognitive network setting with a single primary user and multiple cognitive users is studied and it is shown that, with single-hop transmission, …