Interference Management Through Exclusion Zones in Two-Tier Cognitive Networks

The transmission capacity of wireless networks is limited by the intensity of the interference received from concurrent transmissions. Interference causes serious performance degradation, particularly when no centralized controller within the network exists. Cognitive radio (CR) is a promising solution for distributed interference management as users with CR capabilities can acquire local activity and position information to achieve spatial reuse while limiting interference to neighboring users. Considering a two-tier network consisting of a licensed primary network overlaid by an unlicensed secondary tier, this paper proposes CR-based spectrum access schemes for secondary users (SUs). Acquiring the activity information of nearby users, the SUs are activated only when they are outside the exclusion zone of primary receivers. Additionally, the active secondary transmitters are separated from each other by forming secondary exclusion zones around themselves. Using stochastic geometry, primary and secondary exclusion zone sizes that maximize the transmission capacity under per-tier outage constraints are calculated. Analytical results supported by numerical simulations, suggest primary exclusion zones reduce predominantly the cross-tier interference while the secondary exclusion zone size is critical in mitigating the interference among SUs.