  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.
