To realize high-speed and high-capacity 5G mobile networks, secondary users (SUs) may opportunistically use licensed spectrum allocated to primary users (PUs). This paper presents a framework to deal with the situation that occurs when a PU suffers harmful interference caused by the secondary use of the spectrum allocated to it. Here, the PU is assumed to be a radar system. In our proposed framework, the PU informs the database that it is suffering harmful interference. Receiving this information, the database updates the primary exclusive region (PER), where SUs are prohibited from using the licensed spectrum. The updated PER depends on the current knowledge of the SUs, which is stored in the database. We assume a circular PER centered at the primary receiver (PR) and derive its optimal radius using stochastic geometry. For each type of SU knowledge stored in the database, we evaluate the optimal PER radius for a target probability at which the PU suffers harmful interference. The results show that more detailed knowledge of the SU density and transmission powers leads to a smaller updated PER radius. Hence, a more efficient spatial reuse of the licensed spectrum is achieved.
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