The goal of this chapter is to introduce the novel concept of cognitive radio (CR) for wireless telecommunications. Cognitive radios are a new type of radio devices that include cognition and reconfigurability features. The raising number of studies in different areas of research shows their potential and the expectation created among the telecommunications community. In this chapter, the authors first introduce the reader to the new paradigm that cognitive radio networks have created; more specifically, they explain in detail the new next generation networks. Given that our intention is to introduce cognitive radio, the authors focus on the challenges in PHY layer and MAC sublayer and the most relevant studies in these fields. Finally, the integration of game theory and cognitive radio creates a new paradigm where the advantages of both technologies merge to solve complex problems.
As mentioned in the introduction, the term cognitive radio is credited to Mitola III and Maguire (1999). They introduced cognitive radio as a radio device with cognition functions. Before explaining in detail the concept of cognitive radio, it is useful to introduce the precedent technology, Software Defined Radio (SDR). SDR is defined as (FCC, 2005) “any radio that includes a transmitter in which the operating parameters of frequency range, modulation type or maximum output power can be altered by making a change in software without making any changes to hardware components that affect the radio frequency emissions”. In other words, by using software the transmit power, adaptive modulation and transmission frequency, among other transmission parameters and features, may be changed.
Nevertheless, cognitive radio goes a step further than SDR, empowering the radio to change the transmission parameters based on interaction with the environment of operation. Among the wireless scientific community a widely accepted definition of cognitive radio is provided by Haykin (2005); he considers a cognitive radio as “an intelligent wireless communication system that is aware of its surrounding environment”, with the ability of adapting its states to environmental changes. In other works, a cognitive radio can be described as a SDR endowed with a “brain” which not simply reacts to external changes but also “thinks” about the actions to take. Two key characteristics must then be associated to any cognitive radio: cognitive capability and reconfigurability.
However, what is exactly contained in the cognition part of these radios? Citing again (Haykin, 2005), three major tasks make up the cognitive capability:
Radio-scene analysis, in charge of the detection of spectrum holes and the estimation of interference.
Channel identification, which carries out the estimation of both channel state information (CSI) and channel capacity.
Power and spectrum management.
Figure 1 provides how these three tasks are connected. In practice, cognitive capability may reduce to signal processing or machine learning algorithms for implementation purposes.
Reconfigurability seems to be easier to characterize than cognition capability. This functionality is provided by a SDR platform, which carries out the suitable actions to change the radio parameters values and to adapt the transmitted signal to the new environment. Consequently, the design of SDRs for cognitive radios must consider the dialog between the cognitive part of the radio and the software radio component.