Primary user activity is a major bottleneck for existing routing protocols in cognitive radio networks. Typical routing protocols avoid areas that are highly congested with primary users, leaving only a small fragment of available links for secondary route construction. In addition, wireless links are prone to channel impairments such as multipath fading; which renders the quality of the available links highly fluctuating. In this paper, we investigate using cooperative communication mechanisms to reveal new routing opportunities, enhance route qualities, and enable true coexistence of primary and secondary networks. As a result, we propose Undercover: a cooperative routing protocol that utilizes the available location information to assist in the routing process. Specifically, our protocol revisits a fundamental assumption taken by the state of the art routing protocols designed for cognitive radio networks. Using Undercover, secondary users can transmit in the regions of primary users activity through utilizing cooperative communication techniques to null out transmission at primary receivers via beamforming. In addition, the secondary links qualities are enhanced using cooperative diversity. To account for the excessive levels of interference typically incurred due to cooperative transmissions, we allow our protocol to be interference-aware. Thus, cooperative transmissions are penalized in accordance to the amount of negatively affected secondary flows. We evaluate the performance of our proposed protocol via NS2 simulations which show that our protocol can enhance the network goodput by a ratio reaches up to 250 compared to other popular cognitive routing protocols with minimal added overhead.
Our previous work @cite_32 considered using beamforming in the routing layer. However, we only proposed a route maintenance mechanism to alleviate the need for route re-establishment upon the detection of a PU which limits the usefulness of beamforming. In this paper, we consider cooperative beamforming a foundation for building successful cognitive radio routing protocols. We understand the true potential of employing cooperative beamforming, mitigate its introduced interference effects, and provide practical mechanisms for efficient cooperative group construction.
@cite_32
2064503103
We consider a cognitive radio setting in which a relay-assisted secondary link employs cooperative beamforming to enhance its throughput and to provide protection to the primary receiver from interference. We assume the presence of infinite buffers at both the primary and secondary transmitters and characterize the maximum stable throughput region exactly using the dominant system approach. Numerical examples are provided to give insights into the impact of power control on the stability region.