Modeling and Analysis of Ambient RF Energy Harvesting in Networks with Secrecy Guard Zones

This paper studies the secrecy performance in wireless networks (primary network) overlaid with an ambient RF energy harvesting network (secondary network). The nodes in the secondary network are assumed to be solely powered by ambient RF energy harvested from transmissions of the primary network. We assume that the secondary nodes can eavesdrop on the primary transmissions due to which the primary network uses secrecy guard zones. The primary transmitter goes silent if any secondary receiver is detected within its guard zone. Using tools from stochastic geometry, we first derive the optimal guard zone radius that minimizes the probability of going silent while ensuring a predefined minimum secure connection probability. Clearly, when more secondary nodes are deployed, more primary transmitters will remain silent for a given guard zone radius, thus impacting the amount of energy harvested by the secondary network. This introduces an interesting coupling between the performance of the two networks. We study this coupling using tools from game theory and propose an algorithm that can assist the two networks to converge to Nash equilibrium. Our results demonstrate the convergence of the proposed algorithm to the Nash equilibrium in finite number of iterations. Overall, this work forms one of the few concrete works that symbiotically merge tools from stochastic geometry and game theory.