Doctor of Philosophy, The Ohio State University, 2014, Electrical and Computer Engineering

The rapid growth in wireless communication systems has provided a flexibility of communication and content that has had a transformative impact to all aspects of society. However, the broadcast nature of the wireless medium makes these systems vulnerable to passive attacks in which the adversary attempts to eavesdrop on the transmitted messages, and to active attacks in which the adversary can intelligently manipulate legitimate transmissions, both of which can jeopardize a myriad of critical wireless services. Hence, it is imperative to design wireless networks with safeguards in place to ensure their resilience to attacks. To that end, this dissertation provides various perspectives in the domain of information theoretic secrecy and authentication, which provably guarantees security, regardless of the computational capabilities of the adversary. We strive to bridge the gap between the information theory of security and the practically implementable protocols within this paradigm. We first consider point to point secure communication over flat fading wireless channels under delay constraint. We extend the definition of outage capacity to account for the secrecy constraint and obtain sharp characterizations of the corresponding fundamental limits under different assumptions on the transmitter channel state information (CSI). The capacity achieving scheme relies on opportunistically exchanging private keys between the legitimate nodes. These keys are stored in a key buffer and used to secure delay sensitive data. We also characterize the optimal power control policies and analyze the effect of key buffer overflow on the overall outage probability. Next, we focus on investigating additional sources for generating secret key bits in mobile wireless networks. We propose an algorithm for secret key generation based on the observations of the relative locations between a pair of nodes. We test our algorithm in a vehicular setting based on observations made (open full item for complete abstract)

Committee: Can Emre Koksal (Advisor); Hesham El Gamal (Advisor); Ness Shroff (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2007, Electrical Engineering

The central theme of this dissertation is the impact of feedback on the performance of wireless networks. Wireless channels offer a multitude of new challenges and opportunities that are uncharacteristic of wireline systems. We reveal the crucial role of feedback in exploiting the opportunities and in overcoming the challenges posed by the wireless medium. In particular, we consider three distinct scenarios and demonstrate the different ways in which feedback helps improve performance. We first consider cellular multicast channels and show that the availability of feedback allows for the cross-layer design of efficient multicast schedulers. Here we focus on two types of feedback scenarios: perfect channel state information (CSI) feedback and automatic repeat request (ARQ) feedback. We propose low-complexity multicast schedulers that achieve near-optimal asymptotic throughput-delay tradeoffs for both feedback scenarios. We further propose a cooperative multicast scheduler, requiring perfect CSI feedback, that achieves the optimal asymptotic scaling of both throughput and delay with the number of users. Next, we consider fading eavesdropper channels and reveal the importance of feedback in establishing secure communications. We characterize the secrecy capacity of such channels under the assumptions of full CSI and main (legitimate) channel CSI knowledge at the transmitter, and propose optimal rate and power allocation strategies. Interestingly, we show that the availability of CSI feedback enables one to exploit the time-varying nature of the wireless medium and achieve a perfectly secure non-zero rate even when the eavesdropper channel is more capable than the legitimate receiver channel on the average. We also propose a low-complexity on/off power allocation strategy and establish its asymptotic optimality. We then consider a minimal ARQ feedback scenario and propose transmission schemes that leverage the ARQ feedback to achieve non-zero perfect secrecy rates. Fina (open full item for complete abstract)

Committee: Hesham El Gamal (Advisor) Subjects: