On the interference due to cooperative cognitive radios in the presence of multiple low-power primary users

We analyze a cognitive radio network where the low-power primary users and cognitive radio (CR) devices are distributed according to two independent homogeneous Poisson processes over the k- dimensional space, where k = 1, 2, 3. The CRs cooperate among themselves in detecting the beacons transmitted by the primary users, to ensure that they cause reduced interference at the primary users. A range of cooperative sensing schemes including the no (NC), partial (PC) and full cooperation (FC) scenarios are analyzed. Using the concepts of stochastic geometry, we assess the impact of the presence of the multiple primary users on the distribution of the signal-to-interference-plus-noise ratio (SINR) at a given primary user, for each cooperation scheme. Further, we characterize the improvement in the spectrum usage due to the CR operation in the licensed frequency band in terms of the probability, denoted by rho, that a CR is able to operate within the k-dimensional space. Using our calculations of the SINR at the primary user and rho, it is shown that the PC scheme achieves enhanced spectrum usage vis-a-vis the FC scheme and an improved SINR as compared to the NC scheme. Moreover, the PC scheme can be tuned in such a way that any desired value for spectrum usage and SINR is achievable.