Trusted cooperative transmissions: Turning a security weakness into a security enhancement

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Since the invention of wireless telegraphy, the effort to improve wireless channel capacity has never stopped. In the last decade, significant advancement has been made and this advancement has featured two milestones. The first milestone is Multiple-Input-Multiple-Output (MIMO) techniques, which create spatial diversity by taking advantage of multiple antennas and improves the wireless channel capacity by an amount on the order of the number of antennas on a wireless device. The second milestone is cooperative transmission. Instead of relying on the installation of multiple antennas on one wireless device, cooperative transmission achieves spatial diversity through physical layer cooperation. In cooperative transmission, when the source node transmits a message to the destination node, the nearby nodes that overhear this transmission will "help" the source and destination by relaying the replicas of the message, and the destination will combine the multiple received waveforms so as to improve the link quality. In other words, cooperative transmission techniques utilize nearby nodes as virtual antennas, and mimic the effects of MIMO in achieving spatial diversity. It is well-documented that cooperative transmission can improve channel capacity significantly and has a great potential to improve wireless network capacity [1-5]. Cooperative transmission departs from the traditional point-to-point link abstraction. Whereas early work on cooperative transmission focused on understanding the design choices and performance gain of this new communication technique, recent work is moving towards building the network support required to attain the associated performance gains. The research community is exploring integrating cooperative transmission into cellular, WiMAX, WiFi, Bluetooth, ultra-wideband (UWB), and ad hoc and sensor networks. Cooperative transmission is also making its way into standards; e.g., IEEEWiMAX standards body for future broadband wireless access has established the 802.16j Relay Task Group to incorporate cooperative relaying mechanisms [6]. The majority of work on cooperative transmission focuses on communication efficiency, including capacity analysis, protocol design, power control, relay selection, and cross layer optimization. In those studies, all network nodes are assumed to be trustworthy. Security threats are not taken into consideration in the process of design, protocol development, and performance evaluation. • It is well known that malicious nodes can enter many wireless networks by merely transmitting or through node compromise. In cooperative transmission, malicious nodes have the opportunity to serve as relays (i.e., the nodes helping the source node by forwarding messages). One means to subvert cooperative communications would involve malicious relays sending arbitrary information to the destination as opposed to correct information. • Cooperative transmission can also suffer from selfish behavior. When wireless nodes do not belong to the same network or have the same network authority, some nodes may refuse to cooperate with others, e.g., by not working as relay nodes, as a means to preserve their own resources. • In cooperative transmissions, channel information is often required to perform signal combination and relay selection at the destination. Malicious relays can provide false channel state information, hoping that they will be selected as relays or that the destination will combine the received messages inadequately. This chapter is dedicated to studying the security issues related to cooperative transmission for wireless communications. Particularly, we will discuss the vulnerabilities of cooperation transmission schemes, evaluate potential network performance degradation due to these vulnerabilities, present an effective way to strengthen the security of cooperative transmission through jointly managing trust and channel estimation, and finally investigate possible advantages of utilizing cooperation transmission to assist other network security protocols. © 2010 Springer Science+Business Media, LLC.

Publication Title

Securing Wireless Communications at the Physical Layer