Influence of primary network structure and dynamics on achievable performance of cognitive wireless networks

We study the influence of the structure and dynamics of the primary network on occurrence and quality of transmit opportunities of the secondary network. In order to obtain accurate results, we develop a framework for performance evaluation that allows detailed modeling of the networks involved, while still enabling general conclusions to be drawn. The approach and results are applicable to diverse application scenarios, such as use of dynamic spectrum access techniques for femtocell deployments within operator networks. The techniques presented here can also be applied beyond dynamic spectrum access based networks for studying the performance of more general heterogeneous wireless systems as well. We use a combination of actual node location data sets and carefully selected node location models in order to obtain reliable results, while still allowing general conclusions to be made. The results show that even in dense primary networks significant opportunities for secondary use can arise. These originate either from the temporal dynamics of the primary, or in spatial domain from frequency reuse, provided that the primary network is active at most 30-50% of the time. For higher activity levels there are almost no useful spectrum opportunities even if the primary network is rather sparsely deployed. The results also show that the spatial structure of the deployment of the secondary network has significant influence on the capacity that can be achieved by using the arising spectrum opportunities.