Existing capacity constrained cellular networks that operate in fixed spectrum bands can be enhanced with capacity-on-demand services using the Coordinated Dynamic Spectrum Access (CDSA) model. In this model, a centralized spectrum broker coordinates access to spectrum in a given region and assigns short term spectrum leases to competing wireless service providers and/or end users. In contrast to existing multi-year cellular spectrum licenses that span large regions, a spectrum broker can grant spectrum leases that are for small regions (e.g.: per base station) and valid for short durations (e.g.: tens of minutes). Fast spectrum allocation algorithms are crucial to the design of scalable spectrum brokers that can provide such real-time spectrum access. In this paper, we address this challenge. Specifically, we formulate the spectrum allocation problem as two optimization problems: first with the objective of maximizing the overall demand (Max-Demand) satisfied among the various base stations and the second with the objective of minimizing the overall interference in the network (Min-Interference) when all the demands of the base stations are satisfied. We show that the optimization problems are NP-hard and design efficient algorithms to solve them. Our simulation results on sample network topologies show that our algorithms scale very well for large network sizes.
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