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Approved for public release; distribution is unlimited / Orthogonal frequency division multiplexing (OFDM) is being used by wireless local area network (WLAN) standards, such as IEEE 802.11a, and wireless metropolitan area network (MAN) standards, such as IEEE 802.16a. OFDM is a very efficient communications scheme for wireless ADHOC networks. However, the wireless environment causes inter-symbol interference (ISI) and inter-carrier interference (ICI). Estimating the starting point of an OFDM symbol must be handled efficiently and effectively to reduce the errors. OFDM must be time synchronized to prevent inter-symbol interference (ISI) and inter-carrier interference (ICI). Many techniques exist to realize timing synchronization in OFDM systems. In this thesis, the need for timing synchronization, the timing errors, and the performance of different techniques under a variety of mobile channel models (indoor and outdoor) are investigated, and simulation performance results for each technique under different channel models are presented. / First Lieutenant, Turkish Army

Thesis (M.S. in Electrical Engineering and M.S. in Applied Physics)--Naval Postgraduate School, June 2004. / Thesis advisor(s): Tri T. Ha, Brett H. Borden. Includes bibliographical references (p. 107-109). Also available online.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Murali Tummala, Roberto Cristi. Includes bibliographical references (p. 127-129). Also available online.

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Frank E. Kragh. Includes bibliographical references (p. 151-153). Also available online.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (p. 87-96).

Conventional data networks are based on a layered architecture, in which a layer implements some aspect of the network while hiding the detailed implementation from the other layers. The introduction of wireless networks has created a need to violate this layered discipline to create cross-layer designs or adaptations. Such cross-layer adaptations optimize the performance of wireless networks by using information from any layer in the network. The key problem is that ad-hoc implementations of cross-layer adaptations introduce complex interactions between layers and thus reduce the level of modularity and abstraction in the network's implementation. This gives rise to a significant increase in complexity. We demonstrate that a new software architecture is able to provide a systematic framework that helps us to implement a wide variety of cross-layer adaptations while preserving to a significant degree the modularity found in the existing network's implementation. To develop such an architecture, we first create a taxonomy of possible cross-layer adaptations. The taxonomy allows a precise description of a wide variety of cross-layer adaptations. Thus our taxonomy can serve as a framework for developing a cross-layer architecture. We develop the software architecture by creating two architectures, a conceptual one and a concrete one. We first develop a conceptual architecture, which shows the key mechanisms that are required to implement cross-layer adaptations. This architecture helps us to understand how we can implement cross-layer adaptations by using our architectural framework. We then develop a concrete architecture, which shows how we can implement such a conceptual architecture on real wireless systems. This architecture addresses more detailed implementation issues. We design the concrete architecture for Hydra, which is a flexible wireless network testbed. We then show that our architecture is generic enough to allow us to support a wide set of cross-layer architectures. We evaluate the proposed architecture by performing three case studies, each of which implements a cross-layer adaptation within Hydra based on the concrete architecture. The case studies allow us to implement and evaluate the key mechanisms provided by our architectural framework. We also implement each cross-layer adaptation by using a conventional approach, in which one layer performs the cross-layer adaptation directly communicating with other layers and other nodes. Comparing both the implementation techniques allows us to evaluate how our architectural framework supports a wide variety of cross-layer adaptations while reducing the complexity of implementation of cross-layer adaptations. / text

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