  TV white spaces refer to the allocated but locally unused TV spectrum and can
be used by unlicensed devices as secondary users. Thanks to their lower
frequencies (e.g., 54 -- 698 MHz in the US), communication over the TV spectrum
has excellent propagation characteristics over long distances and through
obstacles. These characteristics along with their wide availability make the TV
white spaces a great choice and alternative to many existing wireless
technologies, especially the ones that need long range and high bandwidth
communication. In the last decade, there have been numerous efforts from
academia, industries, and standards bodies for exploiting the potentials of the
TV white spaces for several applications including wireless broadband Internet
access. Their characteristics and features also hold potentials for many new
applications including sensing and monitoring, Internet of Things, wireless
control, smart utility, location-based services, and transportation and
logistics. In this paper, we perform a retrospective review and comparative
study of existing work on networking in the TV white spaces. Additionally, we
discuss the associated research challenges such as dealing with the
interference between primary and secondary TV spectrum users, TV white space
temporal and spatial variations and fragmentation, antenna design, mobility,
and security. We also describe the future research directions to handle the
above challenges. To the best of our knowledge, this is the first comprehensive
survey on the literature of TV white space networking research.
