Location Privacy of Primary Users in Geolocation Database-Driven Spectrum Sharing

The use of geolocation databases for enabling spectrum sharing in the TV bands has been mandated by the Federal Communications Commission (FCC), and it is very likely to be adopted for other spectrum sharing applications as well. Although using geolocation databases is a practical approach for enabling spectrum sharing, it poses a potentially serious privacy problem. Secondary users (queriers), through seemingly innocuous queries to the database, can determine the types and locations of incumbent systems operating in a given region of interest, and thus compromise the incumbents’ operational privacy. When the incumbent systems are commercial systems, this is not a critical issue. However, if the incumbents are federal government systems, including military systems, then the information revealed by the databases can pose a serious breach of operational privacy. In this report, we show that a group of malicious queriers can infer the location of the incumbent systems even though the database’s responses to the queries do not directly reveal the locations. We propose a countermeasure that can be employed by a database to make an appropriate tradeoff between protecting the incumbents’ location privacy and enabling efficient spectrum utilization. The countermeasure uses a Bayes filter to estimate the amount of knowledge accumulated by the malicious queriers, and then generates false positive responses when needed. Our results indicate the efficacy of our countermeasure for both stationary and mobile incumbent users. To the best of our knowledge, this is the first study that investigates the problem of incumbents’ privacy in database-driven spectrum sharing.