Abstract— Cognitive radio networks (CRNs) have a greatpotential in supporting time-critical data delivery among theInternet of Things (IoT) devices and for emerging applicationssuch as smart cities. However, the unique characteristics ofdifferent technologies and shared radio operating environmentcan significantly impact network availability. Hence, in thispaper, we study the channel assignment problem in time-criticalIoT-based CRNs under proactive jamming attacks. Specifically,we propose a probabilistic spectrum assignment algorithm thataims at minimizing the packet invalidity ratio of each cognitiveradio (CR) transmission subject to delay constrains. We exploitthe statistical information of licensed users’ activities, fadingconditions, and jamming attacks over idle channels. Simulationresults indicate that network performance can be significantlyimproved by using a security- availability- and quality-awarechannel assignment that provides communicating CR pair withthe most secured channel of the lowest invalidity ratio.