Codes to unmask spectrum violators in cognitive radio systems

The advent of frequency-agile radios holds the potential for improving the utilization of spectrum by allowing wireless systems to dynamically adapt their spectral footprint based on the local conditions. The gains result from shifting some responsibility for avoiding harmful interference from the static ldquoregulatory layerrdquo to layers that can adapt at runtime. However, this leaves open the major problem of how to enforce/incentivize compliance. We propose a ldquolight-handedrdquo regulation framework where we examine this and focus on assigning liability by detecting the culprits. The key idea is to have the identity of the guilty parties revealed when their signatures appear in the interference pattern. Previously, we only considered a simplistic deterministic scenario. In this paper, we extend the analysis to a more realistic scenario to account for probabilistic collisions, background wireless losses as well as adversarial non deterministic transmission of the guilty parties. We derive converse and achievable bounds on the total system capacity and quantify the fundamental tradeoffs between the various system parameters. The quality of regulatory guarantees is expressed by the time required to convict the guilty, the number of potential cognitive systems that can be supported, the number of simultaneously guilty parties that can be resolved and the potential average utilization provided for the secondary systems. We also quantify the tradeoff between stealthiness and actual utilization when culprits purposely trade their utilization to make it harder for the primary system to identify them.