Secure and Spectrally-Efficient Channel Access in Multi-Channel Wireless Networks

Abstract

Wireless services have become an indispensable part of our social, economic, and everyday activities. They have facilitated and continue to facilitate rapid access to information and have created a highly-interconnected web of users who are untethered to particular locations. In fact, it is expected that in the very near future, the number of users that access the Internet through their mobile devices will surpass those access the Internet from the fixed infrastructure. Aside from mobile Internet access, wireless technologies enable many critical applications such as emergency response, healthcare and implantable medical devices, industrial automation, tactical communications, transportation networks, smart grids, smart homes, navigation, and weather services. The proliferation and wealth of wireless applications has created a soaring demand for ubiquitous broadband wireless access. This demand is further fueled by the richness of the information accessed by users. Low-bit rate voice communications and text have been replaced with graphics, high-definition video, multi-player gaming, and social networking. Meeting the growing traffic demand poses many challenges due to the spectrum scarcity, the cost of deploying additional infrastructure, and the coexistence of several competing technologies. These challenges can be addressed by developing novel wireless technologies, which can efficiently and securely manage multi-user access to the wireless medium. The multi-user access problem deals with the sharing of the wireless resource among contending users in an efficient, secure, and scalable manner. To alleviate contention and interference among the multiple users, contemporary wireless technologies divide the available spectrum to orthogonal frequency bands (channels). The availability of multiple channels has been demonstrated to substantially improve the performance and reliability of wireless networks by alleviating contention and interference. Multi-channel networks, whether cellular, sensor, mesh, cognitive radio, or heterogeneous ones, can potentially achieve higher throughput and lower delay compared to single-channel networks. However, the gains from the existence of orthogonal channels are contingent upon the efficient and secure coordination of channel access. Typically, this coordination is implemented at the medium access control (MAC) layer using a multi-channel MAC (MMAC) protocol. MMAC protocols are significantly more sophisticated than their single-channel counterparts, due to the additional operations of destination discovery, contention management across channels, and load balancing. A significant body of research has been devoted to designing MMAC protocols. The majority of solutions negotiate channel assignment every few packet transmissions on a default control channel. This design has several critical limitations. First, it incurs significant overhead due to the use of in-band or out-of-band control channels. Second, from a security standpoint, operating over a default control channel constitutes a single point of failure. A DoS attack on the control channel(s) would render all channels inoperable. Moreover, MMAC protocols are vulnerable to misbehavior from malicious users who aim at monopolizing the network resources, or degrading the overall network performance. In this dissertation, we improve the security and spectral efficiency of channel access mechanisms in multi-channel wireless networks. In particular, we are concerned with MAC-layer misbehavior in multi-channel wireless networks. We show that selfish users can manipulate MAC-layer protocol parameters to gain an unfair share of network resources, while remaining undetected. We identify possible misbehavior at the MAC-layer, evaluate their impact on network performance, and develop corresponding detection and mitigation schemes that practically eliminate the misbehavior gains. We extend our misbehavior analysis to MAC protocols specifically designed for opportunistic access in cognitive radio networks. Such protocols implement additional tasks such as cooperative spectrum sensing and spectrum management. We then discuss corresponding countermeasures for detecting and mitigating these misbehavior. We further design a low-overhead multi-channel access protocol that enables the distributed coordination of channel access over orthogonal channels for devices using a single transceiver. Compared with prior art, our protocol eliminates inband and out-of-band control signaling, increases spatial channel reuse, and thus achieves significant higher throughput and lowers delay. Furthermore, we investigate DoS attacks launched against the channel access mechanism. We focus on reactive jamming attacks and show that most MMAC protocols are vulnerable to low-effort jamming due to the utilization of a default control channel. We extend our proposed MMAC protocol to combat jamming by implementing cryptographic interleaving at the PHY-layer, random channel switching, and switching according to cryptographically protected channel priority lists. Our results demonstrate that under high load conditions, the new protocol maintains communications despite the jammer's effort. Extensive simulations and experiments are conducted to evaluate the impact of the considered misbehaviors on network performance, and verify the validity of the proposed mechanisms.