  The so-called `TV white spaces' (TVWS) - representing unused TV channels in
any given location as the result of the transition to digital broadcasting -
designated by U.S. Federal Communications Commission (FCC) for unlicensed use
presents significant new opportunities within the context of emerging 4G
networks for developing new wireless access technologies that meet the goals of
the US National Broadband Plan (notably true broadband access for an increasing
fraction of the population). There are multiple challenges in realizing this
goal; the most fundamental being the fact that the available WS capacity is
currently not accurately known, since it depends on a multiplicity of factors -
including system parameters of existing incumbents (broadcasters), propagation
characteristics of local terrain as well as FCC rules. In this paper, we
explore the capacity of white space networks by developing a detailed model
that includes all the major variables, and is cognizant of FCC regulations that
provide constraints on incumbent protection. Real terrain information and
propagation models for the primary broadcaster and adjacent channel
interference from TV transmitters are included to estimate their impact on
achievable WS capacity. The model is later used to explore various trade-offs
between network capacity and system parameters and suggest possible amendments
to FCC's incumbent protection rules in the favor of furthering white space
capacity.
