In this paper, we examine a cognitive spectrum access scheme in whichsecondary users exploit the primary feedback information. We consider anoverlay secondary network employing a random access scheme in which secondaryusers access the channel by certain access probabilities that are function ofthe spectrum sensing metric. In setting our problem, we assume that secondaryusers can eavesdrop on the primary link's feedback. We study the cognitiveradio network from a queuing theory point of view. Access probabilities aredetermined by solving a secondary throughput maximization problem subject to aconstraint on the primary queues' stability. First, we formulate our problemwhich is found to be non-convex. Yet, we solve it efficiently by exploiting thestructure of the secondary throughput equation. Our scheme yields improvedresults in, both, the secondary user throughput and the primary user packetdelay. In addition, it comes very close to the optimal genie-aided scheme inwhich secondary users act upon the presumed perfect knowledge of the primaryuser's activity.
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