Spectral efficiency and aggregate capacity in cognitive radio networks- An application study

Cognitive radio could help to overcome the spectrum shortage by having an opportunistic system sharing a licensed spectrum with primary users. One of the main difficulties in the analysis of cognitive radio systems is to model the interference. Various works presented this modeling for two pairs of wireless users, one primary and one cognitive. Others consider two random overlaid networks. The approaches usually consider variations in densities, distances and power transmission (specially) of the cognitive users. However, the alternatives to implement such systems can lead to some disadvantages inherent in the procedures adopted. This work presents an analysis of a scenario where a cognitive radio network shares the spectrum with a primary network, searching always to opportunities to take advantage of any possibility to increase its capacity. The network users (primary and cognitive) are distributed according to a Poisson Point Process (PPP), and use M-QAM modulation schemes. This first approach considers a cognitive system that can work using different modulation schemes, increasing or decreasing its M-QAM modulation level according the better or the worse noise channel conditions respectively, searching for the optimum performance for its traffic demand without disturbing the primary users.