  Cognitive radio networks (CRNs) have emerged as an essential technology to
enable dynamic and opportunistic spectrum access which aims to exploit
underutilized licensed channels to solve the spectrum scarcity problem. Despite
the great benefits that CRNs offer in terms of their ability to improve
spectrum utilization efficiency, they suffer from user location privacy issues.
Knowing that their whereabouts may be exposed can discourage users from joining
and participating in the CRNs, thereby potentially hindering the adoption and
deployment of this technology in future generation networks. The location
information leakage issue in the CRN context has recently started to gain
attention from the research community due to its importance, and several
research efforts have been made to tackle it. However, to the best of our
knowledge, none of these works have tried to identify the vulnerabilities that
are behind this issue or discuss the approaches that could be deployed to
prevent it. In this paper, we try to fill this gap by providing a comprehensive
survey that investigates the various location privacy risks and threats that
may arise from the different components of this CRN technology, and explores
the different privacy attacks and countermeasure solutions that have been
proposed in the literature to cope with this location privacy issue. We also
discuss some open research problems, related to this issue, that need to be
overcome by the research community to take advantage of the benefits of this
key CRN technology without having to sacrifice the users' privacy.
