Management of a Shared-Spectrum Network in Wireless Communications

We consider a band of the electromagnetic spectrum with a finite number of identical channels shared by both licensed and unlicensed users. Such a network differs from most many-server, two-class queues in service systems, including call centers, because of the restrictions imposed on the unlicensed users to limit interference to the licensed users. We first approximate the key performance indicators-namely the throughput rate of the system and the delay probability of the licensed users under the asymptotic regime, which requires the analysis of both scaled and unsealed processes simultaneously using the averaging principle. Our analysis reveals a number of distinctive properties of the system. For example, sharing does not affect the level of service provided to the licensed users in an asymptotic sense even when the system is critically loaded. We then study the optimal sharing decisions of the system to maximize the system throughput rate while maintaining the delay probability of the licensed users below a certain level when the system is overloaded. Finally, we extend our study to systems with time-varying arrival rates and propose a diffusion approximation to complement our fluid one.