Reacting to the interference field

Introduction Wireless technology is proliferating rapidly, and the vision of pervasive wireless networking, computing, and communications offers the promise of many industrial and individual benefits. This explosion of wireless applications creates an ever-increasing demand for more radio spectrum. However, most easily usable spectrum bands have been allocated, although many measurements, nevertheless, show that at any specific time and location, these spectrum bands are significantly underutilized and significant amounts of energy are wasted. The presence of high priority primary users and the requirement that the cognitive users should cause only limited interference with them define an access paradigm called cognitive access. Cognitive access control is relevant to both the cognitive radio and the coexistence community. Cognitive access control protocols play an important role to exploit the spectrum opportunities, manage the interference to primary users, and coordinate the spectrum access amongst cognitive users. Spectrum access as a game In the absence of primary users, the secondary or cognitive users can opportunistically share the spectrum in a distributed and autonomous manner. However, simultaneous transmissions will generate an aggregate interference that could be potentially high and thus reduces users’ performance. This falls down clearly in a strategic decision-making problem, also called game, where the decision is on when to transmit and with which transmit power. The decision policy is based on location, queue, remaining energy, channel state, and resource availability. In this chapter we study multiple access problems in cognitive radio networks. We specially examine the large-scale interaction between secondary users as a reaction to an evolving interference called the interference field.