Cognitive radio and advanced spectrum management

Conventional fixed spectrum allocation cannot successfully cope with today’s scarcity of radio frequency spectrum. Therefore, regulation of spectrum will undergo revolutionary changes in the future, allowing a less restricted and more flexible access to radio spectrum. Intelligent mobile radios, or the so-called cognitive radios, will improve the spectrum utilization by seeking and opportunistically utilizing radio resources in time, frequency and space domains on a real time basis. The cognitive radio technology poses many new technical challenges, and overcoming these issues becomes even more challenging due to nonuniform spectrum and other radio resource allocation policies, economic considerations, the inherent transmission impairments of wireless links and user mobility. Cognitive radio technology advances are based on interdisciplinary research, including among others: signal processing, information theory, computer science, communications engineering, artificial intelligence, game theory and economics. Cognitive radios are self-aware communication systems, which autonomously coordinate the usage of spectrum. They identify unused radio spectrum, the so-called ‘spectrum opportunities’ or ‘white spaces’, while observing their radio environment, and follow regulatory rules, which are known or are to be learnt. The classification of spectrum as being unused and the way it is used involves regulation, as this spectrum might be originally assigned to a licensed communication system. Cognitive radios will share spectrum either horizontally with distributed spectrum access such as ‘listen-before-talk’ and equal rights to access the radio spectrum, or vertically, where the so-called primary radio systems have higher priority to access the radio spectrum than secondary radio systems (i.e. cognitive radio systems). Advanced spectrum management can refer to the implementation of centralized means for coordinating dynamic spectrum access. Such a centralized approach has the advantage of facilitating the regulators’ control of spectrum usage, and to allow them directing how the spectrum is used. Such a control is of particular interest in vertical spectrum sharing. Contrary, the decentralized paradigm of cognitive radio allows for a more flexible spectrum access, which is especially helpful in horizontal spectrum sharing scenarios. Joint efforts of academia, regulators, infrastructure suppliers and telecom operators are required to establish trust in cognitive radio technologies and to enable a sustainable go-to-market. The introduction of cognitive radios will be rather a smooth evolution than a radical revolution of communication technology. Standardization, spectrum regulation, confidence in business opportunities and a commercialization of products based on cognitive radio technologies will most likely be incremental on a step-by-step basis. The standardization efforts on cognitive radio, advanced spectrum management and its enablers by the IEEE in SCC41/P1900, 802.11y and 802.22 are an example of this. Cognitive radio technologies as those discussed in this special issue have the potential to considerably change the wireless communication market as barriers for new market entries are essentially lowered. This special issue presents one invited and seven peer-reviewed papers written by experts from academia and industry.