Spectrum access policy reasoning for policy-based cognitive radios
Cognitive radio (CR) is one of the key enabling technologies for opportunistic spectrum sharing. In such a spectrum sharing paradigm, radios access spectrum opportunistically by identifying the under-utilized spectrum and then transmitting waveforms in that spectrum that are compliant to relevant spectrum access policies. Implementing such a flexible scheme requires changes in the current static spectrum management approach. As a result, declarative spectrum management through policy-based dynamic spectrum access has garnered significant attention recently. Policy-based spectrum access decouples spectrum access policies and Policy Processing Components from the radio platform. The Policies define conditions under which the radios are allowed to transmit in terms of frequencies used, geographic locations, time etc. The Policy Processing Components include a reasoning engine called the Policy Reasoner, which is responsible for enforcement, analysis and processing of the policies, as well as resolving policy conflicts. This paper describes the design and implementation of a novel policy reasoner that processes spectrum access policies efficiently by reframing the policy reasoning problem as a graph-based Boolean function manipulation problem. The proposed policy reasoner has the capability to respond to either under-specified or invalid transmission requests (sent by the system strategy reasoner) by returning multiple sets of opportunity constraints that prescribe different ways of modifying transmission parameters in order to make them policy compliant.