Contention-sensing and dynamic spectrum co-use in secondary user Cognitive Radio societies

Emerging standards in Cognitive Radio seek to alleviate the problem of spectrum scarcity by leveraging spectrum under-utilization through dynamic spectrum access (DSA). Unlicensed users ('secondary') may opportunistically make use of channels during times when the licensed ('primary') user is absent. The 'open access' paradigm proposed by FCC mandates the study of primary-secondary dynamics, as well as secondary-secondary dynamics to better understand the implications of uncoordinated competition for limited number of resources between secondary users. In this paper, we consider long term etiquette between secondary users engaged in spectrum co-use. In order to maximize throughput, by avoiding over-crowded channels, we propose a novel approach wherein secondary users have the ability to 'sense' very approximate contention levels at a single spectrum band at each point in time. System performance under the contention-sensing paradigm is compared to two schemes: first, a previously defined non-cooperative game model; second, a new model which allows for spectrum foraging, but without providing secondary users the ability to sense contention in a band. Through simulation experiments, we show that the contention-sensing paradigm results in significantly better co-use of spectrum resources. Additionally, our experiments demonstrate that the proposed contention-sensing paradigm continues to outperform when the ratio of secondary users to spectrum bands is increased. Thus, the new schemes described here may be of critical importance in a future where we expect the number of secondary users to grow exponentially and thus require a scalable mechanism for opportunistic scavenging of unused spectrum.