Bandwidth Exchange: A Framework for Enhancing the Performance of Cognitive Radio Networks
This project develops a framework called bandwidth exchange (BE) as a means of providing flexible and incentivized spectrum allocation in cognitive radio networks. Using analytical methods, numerical software and testbed experimentations, the BE framework is being developed as a practical implementable system to provide the following advantages in a tactical wireless network:
- Increase data rates and provide better quality of service
- Reduce outage probability
- Reduce total transmission power and extend the battery life
Cognitive radios in their simplest embodiment (which are by no means simple yet to implement) have the ability to recognize transmissions received by them and adjust their frequencies, waveforms and protocols. These radios will be able to manage their power, time and bandwidth resources in ways that share the available spectrum more efficiently. In a network setting, along with cooperative techniques they hold the promise of promoting efficient and robust operation that is required in tactical wireless networks. These techniques are in themselves diverse, and include collaborative signal processing, cooperative coding, relaying and forwarding.
Cooperation, however, involves significant costs that have to be reconciled with, especially in the context of tactical networks supporting critical applications in a dynamic environment. Existing cooperative forwarding mechanisms rely on incentivizing nodes using reputation based mechanisms, credit based incentives, network assisted pricing mechanisms and mechanisms based on forwarding games. These prior techniques often mimic the operation of a complex economy and their efficient operation requires such enablers as a stable currency, a system of credit or a shared understanding of what things are worth. In real economies, these enablers are achieved over long periods of time, and even with experience, the overall functioning of such economies is difficult to predict. Moreover, even if there were no added cost in terms of energy or delay, such cooperative schemes will need to be provided with additional degrees of freedom to adapt to changing conditions so as to meet mission critical goals. In this ONR funded project, we study means of providing flexible and incentivized spectrum allocation in cognitive radio networks.
The approaches taken here have a strong theoretical focus and we validate our results by numerical simulation and real-time prototypes. Fundamentally, Shannon theory expounds how the two basic transmit resources of transmit power and transmission bandwidth can be traded off for performance. We will build on this and propose cooperative strategies where transmission bandwidth can be explicitly used as a resource that can significantly alleviate many of the costs associated with cooperative forwarding in wireless networks. Specifically, we develop a protocol framework called Bandwidth Exchange (BE) where the available bandwidth in a network is flexibly apportioned across the transmissions of the various nodes to enhance cooperative network performance without increasing either the total bandwidth or the total transmit power. This framework is ideally suited to networks of cognitive radios with the ability to perform noncontiguous multicarrier modulation and use Orthogonal Frequency Division Multiple Access (OFDMA) where a number of noncontiguous subcarriers can be flexibly assigned across nodes. Further, the ability to assign noncontiguous portions of spectrum to a wireless node in a tactical network in a dynamic/opportunistic manner provides robustness against variations due to electromagnetic propagation, networks dynamics as well as adversarial conditions such as attacks.
The results to date have been disseminated through conference papers and journal papers in preparation. Future directions include implementation of adaptive modulation based rate control using a GNU-radio based USRP2 platforms realized on the ORBIT testbed. We plan to extend this work to investigate joint relay, rate and modulation selection in a N-node BE environment.