TFRC-CR: An equation-based transport protocol for cognitive radio networks

Data delivery in a dynamically changing spectrum environment continues to remain an unsolved problem, with existing TCP based implementations falling short owing to their inability to react swiftly to spectrum changes. This paper proposes the first equation-based transport protocol, based on the TCP Friendly Rate Control (TFRC) protocol, which uses the recent FCC mandated spectrum database information instead of relying on any intermediate node feedback. Not only does this approach maintain the strict end to end property required at this layer of the protocol stack, but also allows fine adjustment of the transmission rate through continuous adaptation. We explore interesting directions on how to limit repeated queries to the spectrum database and yet allow the source to control the rate effectively; when to re-start the transmissions; and how to interpret possible spectrum changes in the intermediate nodes correctly without mistaking it for normal network congestion, among others. Our extension to the ns-2 simulator enables thorough testing of various aspects of our protocol adapted for cognitive radio, called as TFRC-CR. We show through simulation an improvement of over 33% in the end to end throughput when compared with the classical TFRC.