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In the modern era of wireless communications, radios are becoming increasingly more cognitive. As the complexity and robustness of friendly communications increases, so do the abilities of adversarial jammers. The potential uses and threats of these jammers directly pertain to fourth generation (4G) communication standards, as well as future standards employing similar physical layer technologies. This paper investigates a number of threats to the technologies utilized by 4G and future systems, as well as potential improvements to the security and robustness of these communications systems. The work undertaken highlights potential attacks at both the physical layer and the multiple access control (MAC) layer along with improvements to the technologies which they target. This work presents a series of intelligent, targeted jamming attacks against the orthogonal frequency division multiplexing (OFDM) synchronization process to demonstrate some security flaws in existing 4G technology, as well as to highlight some of the potential tools of a cognitive electronic warfare attack device. Performance analysis of the OFDM synchronization process are demonstrated in the presence of the efficient attacks, where in many cases complete denial of service is induced. A method for cross ambiguity function (CAF) based OFDM synchronization is presented as a security and mitigation tactic for 4G devices in the context of cognitive warfare scenarios. The method is shown to maintain comparable performance to other correlation based synchronization estimators while offering the benefit of a disguised preamble. Sync-amble randomization is also discussed as a combinatory strategy with CAF based OFDM synchronization to prevent cognitive jammers for tracking and targeting OFDM synchronization. Finally, this work presents a method for dynamic spectrum access (DSA) enabled radio identification based solely on radio frequency (RF) observation. This method represents the framework for which both the cognitive jammer and anti-jam radio would perform cognitive sensing in order to utilize the intelligent physical layer attack and mitigation strategies previously discussed. The identification algorithm is shown to be theoretically effective in classifying and identifying two DSA radios with distinct operating policies. / Ph. D.

Li Ning. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (leaves 52-55). / Abstracts in English and Chinese. / Acknowledgments --- p.ii / Abstract --- p.iii / 哲學碩士論文摘要 --- p.iv / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Research Background --- p.2 / Chapter 1.2 --- Contributions of the Thesis --- p.5 / Chapter 1.3 --- Organization of the Thesis --- p.6 / Chapter Chapter 2 --- Properties of OVSF Codes --- p.7 / Chapter 2.1 --- Tree-Structured Generation of OVSF Codes --- p.7 / Chapter 2.2 --- OVSF Codes Assignment --- p.10 / Chapter Chapter 3 --- Support Delayable Traffic in Wireless Networks --- p.14 / Chapter 3.1 --- System Model --- p.15 / Chapter 3.2 --- Scheduling Algorithm with Burst Adaptation --- p.17 / Chapter 3.3 --- Performance Analysis --- p.22 / Chapter 3.4 --- Simulation Results --- p.24 / Chapter Chapter 4 --- Allocate OVSF Codes with Joint Design --- p.30 / Chapter 4.1 --- Combine Number of Active Users and Error-Control Coding Scheme --- p.31 / Chapter 4.1.1 --- System Model --- p.31 / Chapter 4.1.2 --- Scheduling Algorithm Description --- p.33 / Chapter 4.1.3 --- Simulation Results --- p.35 / Chapter 4.2 --- Combine Power Adaptation and Error-Control Coding Scheme --- p.39 / Chapter 4.2.1 --- System Model --- p.39 / Chapter 4.2.2 --- Scheduling Algorithm Description --- p.41 / Chapter 4.2.3 --- Simulation Results --- p.44 / Chapter Chapter 5 --- Conclusion --- p.50 / Bibliography --- p.52

Thesis (Ph.D.)--University of Florida, 2005. / Title from title page of source document. Document formatted into pages; contains 102 pages. Includes vita. Includes bibliographical references.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2002. / Thesis advisor(s): John C. McEachen, R. Clark Robertson, Daniel M. Rosser. Includes bibliographical references (p. 73-75). Also available online.

Thesis (Ph.D.)--University of Melbourne, Dept. of Electrical and Electronic Engineering, 2007. / Typescript. Includes bibliographical references (leaves 141-156).

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2002. / Thesis advisor(s): R. Clark Robertson, Roberto Cristi. Includes bibliographical references (p. 93-94). Also available online.

Thesis (M.S.)--University of Florida, 2005. / Title from title page of source document. Document formatted into pages; contains 80 pages. Includes vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Florida, 2005. / Title from title page of source document. Document formatted into pages; contains 150 pages. Includes vita. Includes bibliographical references.

Wireless cellular networks, which serve a large area by geographically partitioning users, suffer from interference from adjacent cells transmitting in the same frequency band. This interference can theoretically be completely mitigated via transceiver cooperation in both the uplink and downlink. Optimally, base stations serving the users can utilize high-capacity backbones. to jointly transmit and receive all the data in the network across all the base stations. In reality, the backbone connecting the base stations is of finite capacity, limiting joint processing to localized clusters. Even with joint processing on a small scale, the overhead involved in sharing data between multiple base stations is large and time-sensitive. Other forms of cooperation have been shown to require less overhead while exhibiting much of the performance benefit from interference mitigation. One particular strategy, called interference alignment (IA), has been shown to exploit all the spatial degrees of freedom in the channel provided data cannot be shared among base stations. Interference alignment was developed for the multi-user interference channel to exploit independent channel observations when all of the links in the network have high signal-to-noise ratio, and assumes all the nodes utilizing the physical resources are participating in the cooperative protocol. When some or all of the links are at moderate signal-to-noise ratio, or when there are non-cooperating users, IA is suboptimal. In this dissertation, I take three approaches to addressing the drawbacks of IA. First, I develop cooperative transmission strategies that outperform IA in various operationg regimes, including at low-to-moderate SNR and in the presence of non-cooperating users. These strategies have the same complexity and overhead as IA. I then develop algorithms for network partitioning by directly considering the overhead of cooperative strategies. Partitioning balances the capacity gains of cooperation with the overhead required to achieve them. Finally, I develop the shared relaying model, which is equivalent to the interference channel but with a single multi-antenna relay mediating communications between transceivers. The shared relay requires less overhead and cooperation than interference alignment but requires added infrastructure. It is shown to outperform conventional relaying strategies in cellular networks with a fixed number of total relay antennas. / text