Our work includes new analysis methods and the development
of new software architectures and applications, in addition to
work on the core concepts and architectures underlying
cognitive radios and cognitive networks. This paper describes
these contributions and points towards critical future work that
remains to fulfill the promise of cognitive radio. We briefly
describe the history of work on cognitive radios and networks
at Virginia Tech and then discuss our contributions to the core
cognitive processing underlying these systems, focusing on our
cognitive engine. We also describe developments that support
the cognitive engine and advances in radio technology that
provide the flexibility desired in a cognitive radio node. We
consider securing and verifying cognitive systems and examine
the challenges of expanding the cognitive paradigm up the
protocol stack to optimize end-to-end network performance.