Thesis (M.S. in Systems Engineering)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Tri T. Ha. Includes bibliographical references (p. 68). Also available online.

Thesis (M.S. in Electrical Engineering and M.S. in Systems Engineering)--Naval Postgraduate School, March 2004. / Thesis advisor(s): Clark Robertson. Includes bibliographical references (p. 143). Also available online.

Thesis (M.S. in Computer Science)--Naval Postgraduate School, March 2003. / Thesis advisor(s): Bert Lundy, Richard Riehle. Includes bibliographical references (p. 77-79, 81). Also available online.

Thesis (M.S. in Computer Science)--Naval Postgraduate School, March 2003. / Thesis advisor(s): Geoffrey Xie, John Gibson. Includes bibliographical references (p. 171-172). Also available online.

Thesis (M.S. in Information Technology Management)--Naval Postgraduate School, March 2003. / Thesis advisor(s): Norman F. Schneidewind, Douglas E. Brinkley. Includes bibliographical references (p. 67). Also available online.

With the proliferation of wireless-enabled devices, the information being transmitted on the wireless spectrum has increased manifolds. This explosive growth of wireless traffic has created spectrum crisis. Further, combined with the inherently lossy wireless medium, it is imperative to develop techniques that can significantly improve wireless spectrum efficiency. This dissertation develops three complementary techniques to enhance spectrum efficiency: (i) sending more information per transmission, (ii) sending more transmissions per spectrum, and (iii) selecting the right spectrum for transmission. More specifically, in (i), we observe that network coding allows us to send more information per transmission by combining (coding) multiple packets together in a single transmission and letting multiple receivers extract different information from the same transmission. However, wireless networks are inherently prone to loss and how to harness network coding gain under such conditions poses a significant challenge. To this end, we develop a novel routing protocol, called O3, which jointly optimizes network coding, opportunistic routing, and rate limiting. Multi-antenna devices (MIMO) dramatically increase wireless network capacity by sending multiple transmissions simultaneously. However, most existing work focuses on MIMO in single hop wireless networks, and how to effectively extend MIMO benefits to multihop wireless networks remain an open problem. In (ii), we propose a new routing protocol, called DM+, which is the first practical distributed MIMO routing protocol. It optimizes spatial multiplexing, routing, and rate limiting in the presence of interference. Using simulation and testbed experiments, we show it out-performs state-of-the-art shortest part routing and opportunistic routing protocols. Finally, in (iii), we examine spectrum selection at two different granularities: (a) selecting an appropriate channel to transmit a frame, and (b) selecting a subcarrier (within a channel) to transmit a symbol of the frame. In (a), we propose LBRH, a novel channel hopping algorithm that allows different nodes converge to a fair and efficient channel hopping sequence in a completely distributed fashion. In (b), we develop Smart-Fi, a series of techniques to harness the frequency diversity of the channel while transmitting the current frame. We demonstrate the effectiveness of both approaches using simulation and testbed experiments. / text

In a Wireless Mesh Network (WMN) exists mobile nodes which have an unpredictable behaviour, i.e. they can join, leave and free move around the network. For this reason, a static network configuration is not proper for them. A distributed Dynamic Host Configuration Protocol (DHCP) is needed due to the unavailability of a centralized server in a network placed over a vast extension. This report shows a Distributed DHCP for WMNs using IPv6 (Internet Protocol version 6). It is fault tolerant, robust and durable. The algorithm was created using counters Bloom filters as data structure. After, a complete simulation of the system was done. The simulations showed that using 24 servers with 16Mbits of memory each one is possible to manage around 9000000 clients without adding an excessive network load. Therefore, the DDHCPv6 could be in a near future the host configuration protocol in WMN.

WiFi networks have become ubiquitous. However, due to the nature of the radio-wave medium, the performance of 802.11 is unpredictable and highly dependent on the environment. This problem is fundamental to 802.11's decentralized, signal-based airspace arbitration mechanism. When devices have incomplete and inconsistent channel conditions for an overlapping interference domain, their signals alone cannot ensure a fair competition for airspace. As a result, competing flows may suffer from unfair bandwidth distribution if the shared airspace is congested. A useful tool to visualize and diagnose problematic wireless networks is the set of devices interfering with each other at a given time. We say two devices a and b interfere when one of two possible situations occur. First, a is able to sense b's radio signals, though not necessarily decode them, resulting in a unable to send data. Second, a and b aren't in radio range, but their destination devices are, resulting in packet collisions. We call such a set of mutually interfering devices the interference neighbourhood. We present wypy, an online system which merges trace-files and produces a map of interfering devices contained within the trace. wypy is able to identify pairs of devices exhibiting either hidden or exposed terminal interference using a pipeline that consists of trace merging and reconstruction, filtering of simultaneously sending devices, throughput and delay signal calculations, and a test for interference correlation. We evaluate wypy using an in-lab testbed set up in known interference scenarios.

WiFi networks have become ubiquitous. However, due to the nature of the radio-wave medium, the performance of 802.11 is unpredictable and highly dependent on the environment. This problem is fundamental to 802.11's decentralized, signal-based airspace arbitration mechanism. When devices have incomplete and inconsistent channel conditions for an overlapping interference domain, their signals alone cannot ensure a fair competition for airspace. As a result, competing flows may suffer from unfair bandwidth distribution if the shared airspace is congested. A useful tool to visualize and diagnose problematic wireless networks is the set of devices interfering with each other at a given time. We say two devices a and b interfere when one of two possible situations occur. First, a is able to sense b's radio signals, though not necessarily decode them, resulting in a unable to send data. Second, a and b aren't in radio range, but their destination devices are, resulting in packet collisions. We call such a set of mutually interfering devices the interference neighbourhood. We present wypy, an online system which merges trace-files and produces a map of interfering devices contained within the trace. wypy is able to identify pairs of devices exhibiting either hidden or exposed terminal interference using a pipeline that consists of trace merging and reconstruction, filtering of simultaneously sending devices, throughput and delay signal calculations, and a test for interference correlation. We evaluate wypy using an in-lab testbed set up in known interference scenarios.

Thesis (M Info Tech) -- Auckland University of Technology, 2004. / Also held in print (100 leaves, 30 cm.) in Wellesley Theses Collection (T 004.68 LIA)