Discrete Exclusion Zone for Dynamic Spectrum Access Wireless Networks

Abstract

The implementation of a geographic exclusion zone (GEZ) has been a scheme in regulations developed to protect a primary user (PU) in dynamic spectrum access wireless networks, where secondary users (SUs) can transmit only outside the exclusion zone region centered at the PU receiver. After determining the radius of the GEZ, the number of operable nodes in actual deployment is quite uncertain due to the random location of nodes. This poses certain difficulty for SU spectrum sharing planning. In this paper, we propose an alternative PU protection scheme called the discrete exclusion zone (DEZ), which is shapeless. The PU protection is achieved by switching off the first k -1 nearest neighboring SUs surrounding the PU. Building on the stochastic geometry of wireless node locations, the conditions under which the mean and the variance of the aggregate interference from SUs to the PU exist are obtained. These conditions define the minimum size of the DEZ. Then, we obtain the closed-form expressions for the mean and the variance as a function of the DEZ size k for a given number of SUs N, including N → ∞. Since it is challenging to obtain a closed-form expression of the density function, we resort to the Gamma distribution to approximate the distribution of the aggregate interference, which is validated by simulations. Finally, the performances of the GEZ and DEZ are investigated in terms of the number of operable SUs outside the GEZ and DEZ, respectively, for achieving a given PU protection requirement. The results show that the DEZ gives a fixed number of operable nodes in the presence of topology randomness associated with the actual SU network deployment.

Keywords

• Cognitive radio system (CRS)
• dynamic spectrum access (DSA)
• coexistence
• aggregate interference
• exclusion zone
• stochastic geometry