Spectrum sharing between radar and communication systems: Can the privacy of the radar be preserved?

As the demand for mobile data traffic continues to increase, regulatory bodies have proposed to allow radar and communication systems to co-exist in the same frequency band. The success of co-existence would depend on how well the interference which one system exerts to the other can be controlled. Recently proposed co-existence approaches use a precoder at the communication and/or radar system, with the precoding matrices optimally designed to control the interference to the radar. However, this could potentially pose a security risk for the radar, as the precoding matrix assigned to the communication system contains implicit information about the radar. This paper is a first step towards understanding whether the signaling scheme of a smartphone co-existing with a radar could be used by an adversary to infer radar information, for example, the radar location. Different precoder matrices are considered, and the likelihood of the adversary estimating the angle at which the radar is located is computed based solely on the observed precoder. We simulate an adversary inference attack and show that such a breach to the radar's privacy does pose a reasonable risk.