Cognitive Radio Systems: State of the art

Cognitive radio has been introduced by Mitola in 1999 as an extension to software radio [1] (Stevens USA). Cognitive radio extends the software radio with radio-domain model-based reasoning about etiquettes (set of RF bands, air interfaces, protocols, and spatial and temporal patterns that moderate the use of the radio spectrum). Cognitive radio enhances the flexibility of personal services through a Radio Knowledge Representation Language (RKRL). This language represents knowledge of radio etiquette, devices, software modules, propagation, networks, user needs, and application scenarios in a way that supports automated reasoning about the needs of the user. This empowers software radios to conduct expressive negotiations among peers about the use of radio spectrum across fluents of space, time, and user context. With RKRL, cognitive radio agents may actively manipulate the protocol stack to adapt known etiquettes to better satisfy the user’s needs. This transforms radio nodes from blind executors of predefined protocols to radio-domain-aware intelligent agents that search out ways to deliver the services the user wants even if that user does not know how to obtain them. Software radio provides an ideal platform for the realization of cognitive radio. More detail can be found in his disseration [2]. In [3] (FCC USA), the federal commission on communications concludes that more flexibility is needed in today’s wireless networks. In [4] (McMaster CA), Haykin addresses three fundamental tasks in cognitive radio: radio-scene analysis, channel-state estimation and predictive modeling, transmit-power control and dynamic spectrum management. In his article, the following definition of cognitive radio is given: “Cognitive radio is an intelligent wireless communication system that is aware of its surrounding environment (i.e., outside world), and uses the methodology of understanding-by-building to learn from the environment and adapt its internal states to statistical variations in the incoming RF stimuli by making corresponding changes in certain operating parameters (e.g., transmit-power, carrier-frequency, and modulation strategy) in real-time, with two primary objectives in mind: