Random Leader: A distributed-centralized spectrum sharing scheme in Cognitive Radios

In Cognitive Radio (CR) networks, Primary Users (PUs) can share their idle spectrums with Secondary Users (SUs) under certain mechanisms. Centralized schemes and market-driven mechanisms are two major considerations in solving the spectrum sharing problems in the multiple-PU scenario. Centralized schemes can achieve the social optimal spectrum allocation among multiple PUs and multiple SUs but require a central control entity, which is impractical in the CR environment due to its distributed nature. Market-driven mechanisms can be implemented in a distributed manner but are hard to obtain the social optimal spectrum utilization in the multiple-PU scenario. Furthermore, many market-driven mechanisms are not economic-robust (Incentive Compatible, Individual Rational, etc). In this paper, we propose a distributed-centralized spectrum sharing scheme based on contracts for the multiple-PU scenario, which introduces a Random Leader who is elected randomly among SUs or PUs. The distributed aspect of our scheme lies in that our scheme requires no central control entities, which can be independently implemented within a distributed spectrum market. The centralized aspect is that the leader draws up and assigns the social optimal spectrum allocation contracts as well as the payment contracts for all PUs and SUs in a centralized manner. The former contracts maximize the spectrum utilization of the whole network, and the latter contracts help attain the economic robustness of our scheme. Under the leadership of the Random Leader, those non-cooperative SUs and PUs behave in a cooperative manner, which mitigates the complexity and time overhead needed for information exchange.