Browsing by Author "Dr. Mihail L. Sichitiu, Committee Chair"

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DCAP: A Multichannel Protocol for Single Interface 802.11 Wireless Mesh Networks
(2006-12-15) Lee, Michael E; Dr. Mihail L. Sichitiu, Committee Chair; Dr. Wenye Wang, Committee Member; Dr. Alexander G. Dean, Committee Member
Wireless ad hoc networks are gaining popularity as quick and inexpensive methods of connecting computers. In particular, Wireless Mesh Networks (WMNs) are becoming a viable method of offering Internet access to entire neighborhoods. One reason WMNs are attractive is because of their use of inexpensive 802.11 wireless hardware. However, using 802.11 standard compliant hardware has a major limitation: the 802.11 standard does not support the use of multiple channels in the same network. Because of this limitation, wireless 802.11 networks are not able to achieve the traffic throughput possible when utilizing all the available channels. To increase the throughput in WMNs, this paper proposes a novel protocol allowing the use of multiple channels with a single wireless 802.11 interface. This protocol, Distributed Channel-switching Accessory Protocol, or DCAP, requires no modifications to the 802.11 MAC layer. DCAP defines the methods wireless nodes use to send and receive traffic across multiple channels with a single wireless interface. The key concept of our approach is Home Channels. A node's Home Channel is the only wireless channel on which the node receives data. By requiring the sender to change to the receiver's Home Channel to transmit a packet, all nodes know on which channel to transmit each packet. Once on the receiver's Home Channel, the transmission of the packet follows the 802.11 standard. In this work, DCAP is implemented in the ns-2 event simulator to evaluate its performance. DCAP is implemented as a separate protocol immediately above the 802.11 MAC layer in ns-2. The implementation of DCAP makes no modifications to the 802.11 MAC protocol. A series of performance evaluation tests are performed to compare DCAP's performance against a single channel 802.11 network. These tests compare the throughput of the two networks in a variety of different network traffic conditions and network topologies. The simulation results show the network with the DCAP protocol achieves significantly higher throughputs than the single channel 802.11 network (up to four times in a network with three channels).
Directed Waypoint Model: A Hybrid Approach to Realistic Mobility Modeling in Mobile Ad-hoc Networks
(2005-08-08) Aia, Mahesh; Dr. Rudra Dutta, Committee Member; Dr. Yannis Viniotis, Committee Member; Dr. Mihail L. Sichitiu, Committee Chair
Researchers are highly dependent on simulations to compare and evaluate the performance of Mobile Ad-hoc networking protocols. Mobility modeling plays a very important role in simulation-based studies of MANET protocols, since the mobility of nodes is the limiting factor in the performance of such protocols. Currently, simulations of MANET protocols rely on simplistic, purely stochastic models such as the random waypoint. These models do not reflect the motion of real world MANET nodes, which may be deployed in diverse scenarios. At the present time, the only available alternative to these models is fine-grained detailed simulations based on extensive surveys of actual node behavior, or extensive sets of real world traces. This work proposes an alternative hybrid mobility model that extracts scenario-specific information from real traces and generates realistic node movements for particular scenarios. The distinguishing features of our model are its ability to reproduce spatial-temporal node movement properties from sample traces and its general adaptability to traces from any real-life scenario. We develop a framework for our model and apply it to reference traces from several realistic scenarios. The hybrid model is then evaluated for accuracy by comparing the performance of MANET routing protocols using random waypoint with realistic parameters and our model against the original reference traces used by our model. The results show the relevance of accounting for spatial and temporal aspects of node movements in mobility models.
Distributed Robust Geocast: A Multicast Protocol for Inter-Vehicle Communication
(2007-08-30) Joshi, Harshvardhan P.; Dr. Yannis Viniotis, Committee Member; Dr. Mihail L. Sichitiu, Committee Chair; Dr. Rudra Dutta, Committee Member
Localization in Wireless Sensor Networks with Inaccurate Range Measurements
(2004-09-03) Ramadurai, Vaidyanathan; Dr. Mihail L. Sichitiu, Committee Chair; Dr. Wenye Wang, Committee Member; Dr. Arne A. Nilsson, Committee Member; Dr. Douglas S. Reeves, Committee Member
We refer to localization as the problem of estimating the spatial coordinates of wireless nodes in an ad-hoc network. Wireless sensor network is an example of such a network, where localization as a problem has been a challenging topic for several years. The position of sensor nodes can be either manually configured before deployment or a GPS receiver can be built into each of these nodes. The former approach is very tedious and error-prone while the latter is a costly proposition in terms of volume, money and power consumption. In this thesis, we consider the problem of determining the positions of wireless nodes using range measurements from multiple, sparsely located, beacon stations with known locations. Clusters of unknown nodes collaborate among themselves in estimating their positions with the help of beacon stations. The major problem is overcoming range measurement inaccuracies. We propose a simple position estimation algorithm that features robustness with respect to range measurement inaccuracies, has low complexity and distributed implementation using only local information. We analyze the performance of the algorithm based on rigorous simulation and theory. We then extend the simple algorithm to a probabilistic algorithm that overcomes some of the drawbacks present in the simple algorithm. The algorithm was designed and implemented in a wireless test-bed consisting of IEEE 802.11 based iPAQs to study its performance. Most of the current localization systems are based on multiple beacons assisting unknown nodes. In an attempt to eliminate some of the drawbacks present in such systems, we also propose and study a single mobile beacon based localization method where a mobile beacon assists unknown nodes in estimating their positions. An implementation of this method in a wireless testbed was used to evaluate the performance.
Power Adaptive, Spatial Distributed MAC (PowSD-MAC):A Long Distance Media Access Protocol for Air-to-Air (A2A) Communication
(2008-08-17) Prabhu, Manjunath Madhava; Dr. Mihail L. Sichitiu, Committee Chair
This thesis focuses on an Airplane-to-Airplane (A2A) communication system. We propose an airplane black box data replication application that aims to replicate all black box data to nearby airplanes, thereby avoiding the use of expensive black boxes. We review existing MAC protocols for long distance communication involving high-mobility nodes. In these conditions, it has been shown that contention based protocols are inefficient due to increased packet collisions. In this thesis, we propose a media access protocol called Spatial Distributed MAC (SD-MAC) based on Time Division Multiple Access (TDMA). This protocol allocates slots for packet transmission and provides acknowledgments for reliable communication. SD-MAC also provides adaptive power control for increased spatial re-use, which significantly improves the performance of the protocol. The protocol with adaptive power control is called PowSD-MAC. We compare SD-MAC and PowSD-MAC with tuned-up versions of IEEE 802.11 for varying topologies using different airplane cruise speeds, airplane density, offered load conditions and packet sizes. We evaluate the performance of the proposed protocol in terms of efficiency, reliability and scalability by implementing these protocols in OMNeT++, an event-based network simulator. The results show that PowSD-MAC outperforms IEEE802.11 for a large range of parameters and performance metrics. This material is based upon work supported by the National Science Foundation under Grant No. 0553247.
RaPTEX: Rapid Prototyping Tool for Embedded Communication Systems
(2007-05-17) Lim, Jun Bum; Dr. Laurie Williams, Committee Member; Dr. Injong Rhee, Committee Member; Dr. Mihail L. Sichitiu, Committee Chair
Advances in microprocessors, memory, and radio technology have enabled the emergence of embedded systems that rely on communication systems to exchange information and coordinate their activity in spatially distributed applications. Developing embedded communication systems that are efficient and reliable, is a challenge due to the trade-offs imposed by the conflicts between application requirements and hardware constraints. In this thesis, we present RaPTEX, an integrated development environment (IDE) for embedded communication systems. RaPTEX consists of three major subsystems: a graphical module to facilitate component composition, code generation with access to component-level parameters, and a performance evaluation framework for allowing system designers to explore what-if scenarios and clearly expose the trade-offs of their choices. We also present two case studies of developing wireless sensor network applications using RaPTEX.
Wireless MAC Protocol Design and Analysis
(2009-06-01) Jang , Beakcheol; Dr. Mihail L. Sichitiu, Committee Chair; Dr. David Thuente, Committee Member; Dr. Khaled Harfoush, Committee Member; Dr. Rudra Dutta., Committee Member
Wireless networks are becoming very common due to their advantages such as rapid deployment and support for mobility. In this dissertation, we design and analyze the Medium Access Control (MAC) protocol for two popular wireless networks: Wireless Sensor Networks (WSNs) and Wireless Local Area Networks (WLANs). For WSNs, we design and analyze an energy efficient MAC protocols. Energy efficiency is a key design factor of a MAC protocol for WSNs. Existing preamble-sampling based MAC protocols have large overheads due to their preambles and are inefficient at large wakeup intervals. Synchronous scheduling MAC protocols minimize the preamble by combining preamble sampling and scheduling techniques; however, they do not prevent energy loss due to overhearing. In this dissertation, we present an energy efficient MAC protocol for WSNs, called AS-MAC, that avoids overhearing and reduces contention and delay by asynchronously scheduling the wakeup time of neighboring nodes. We also provide a multi-hop energy consumption model for AS-MAC. To validate our design and analysis, we implement the proposed scheme on the MICAz and TELOSB platforms. Experimental results show that AS-MAC considerably reduces energy consumption, packet loss and delay when compared with other energy efficient MAC protocols. For WLANs, we present a saturation throughput model for IEEE 802.11, the standard of WLAN, for a simple infrastructure scenario with hidden stations. Despite the importance of the hidden terminal problem, there have been a relatively small number of studies that consider the effect of hidden terminals on IEEE 802.11 throughput. Moreover, existing models are not accurate for scenarios with the short-term unfairness. In this dissertation, we present a new analytical saturation throughput model for IEEE 802.11 for a simple but typical infrastructure scenario with small number of hidden stations. Simulation results are used to validate the model and show that our model is extremely accurate. Lastly, we provide a saturation throughput model for IEEE 802.11 for the general infrastructure scenario with hidden stations. Simulation results show that this generalized model is reasonably accurate.