Browsing by Author "Dr. Wenye Wang, Committee Member"

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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).
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.
Mobile Movement Patterns and Applications in Wireless Networks
(2008-08-21) Feng, Fang; Dr. Arne A. Nilsson, Committee Member; Dr. Douglas S. Reeves, Committee Chair; Dr. Wenye Wang, Committee Member; Dr. Matthias Stallmann, Committee Member
In a real-life wireless network, the logical movements of mobile nodes are not purely random. Movements of individual mobile nodes have intrinsic patterns determined by regular activities of individual persons. Regularities in people's group activities also introduce patterns in co-location behavior of multiple mobile nodes. Mobile nodes are able to predict their future behavior using history information, and prediction results can be used to expedite network management processes and reduce the required overhead. Our research focus on characterization and applications of movement and co-location patterns. echanism with movement prediction for wireless IP networks. Each mobile node records movement history information, and predicts its next subnet before the actual movement. It explicitly notifies the current foreign agent to duplicate and forward packets to the predicted subnet. Simulation with real-life wireless network trace shows that the latency of network-layer handoff and the amount of packet loss are greatly reduced, only with a limited overhead in packet duplication and forwarding. The topology matching issue for mobile peer-to-peer networks is also investigated, and a Local Topology Cache mechanism is designed to expedite topology matching for overlay topology optimization and reduce the associated overhead. As mobile nodes have patterns in their movement and interaction, the physical network topology nearby might be similar for a mobile node's two consecutive visits to a subnet. The mobile node caches the information of topologically matched P2P neighbors and reuses them when returning to the subnet, without probing the network again. We simulate this scheme with a real-life wireless network trace, and found the caching mechanism can greatly reduce network probing overhead, while achieving similar efficiency of P2P overlay topology. We further investigate the co-location behavior of multiple mobile nodes. People's regular interactions determine that co-location of mobile nodes has regularities. Using real-life wireless network traces, we measure the characteristics of mobile nodes' co-location, and show that co-location has patterns and is repetitive, which provides the basis of co-location prediction. A Markov-family model is used to dynamically model the co-location behavior, and a fully distributed co-location prediction method only using a mobile node's own movement trace and co-location history is proposed. The effectiveness of this co-location prediction method is demonstrated with simulations based on real-life wireless network activity traces. We also utilize the co-location prediction method in the construction of the peer-to-peer overlay in a wireless network, and show that it can construct a peer-to-peer overlay as efficient as topology matching techniques, without probing the physical network. This demonstrates that co-location prediction can indeed expedite network management and reduce the associated overhead.
Performance Evaluation of iSCSI Protocol for Mirroring Application.
(2008-11-25) Godbole, Chaitanya Umesh; Dr. Michael Devetsikiotis, Committee Chair; Dr. Wenye Wang, Committee Member; Dr. Khaled Harfoush, Committee Member
FC SAN has been the work-horse of the storage industry for quiet sometime now. It has prevailed and prospered in the enterprise-level storage environment due to its high performance and reliability. Data mirroring for disaster management and data recovery is gaining immense importance as the amount of data being stored increases exponentially. FC has been the default transport protocol for mirroring due to its performance advantages. But now with the demand for mirroring solutions for small & medium sized businesses being on the rise, the high acquisition and maintenance costs of FC have propelled iSCSI to be a cost-effective and viable alternative to FC. Traditionally iSCSI has been deemed unfit for delay sensitive applications due to its slow nature and lower throughput. In this thesis, we attempt to evaluate the performance of mirroring over iSCSI and show that it can be performed satisfactorily and economically, without requiring the costlier FC option. This study involves the use of a customized caching algorithm deployed on a SAN in order to exploit any performance enhancements when it comes to the response time for an application running on iSCSI. The cache tries to reduce the response-time for a write request for mirroring by deploying a two-level primary cache with a faster, smaller backup cache or a faster primary cache with a two-level backup cache. A comparative study of the results obtained for mirroring after deploying these caches over FC and iSCSI show that iSCSI provides adequate performance and reliability for a successful deployment of the mirroring application over it.
QoS Provisioning and Pricing in Multiservice Networks: Optimal and Adaptive Control over Measurement-based Scheduling
(2005-08-14) Xu, Peng; Dr. Michael Devetsikiotis, Committee Chair; Dr. George Michailidis, Committee Member; Dr. Peng Ning, Committee Member; Dr. Wenye Wang, Committee Member; Dr. Ioannis Viniotis, Committee Member
In order to ensure efficient performance under inherently and highly variable traffic in multiservice networks, we propose a generalized adaptive and optimal control framework to handle the resource allocation. Even though this framework addresses rigid Quality of Service concerns for the deterministic delay-bound classes by reserving part of the link capacity and employing appropriate admission control and traffic shaping schemes, our research actually emphasizes the adaptive and optimal control of the shared resources for the flexible delay-bound classes. Therefore, the resource allocation is delivered by a subsystem of this generalized framework, the measurement-based optimal resource allocation (MBORA) system. By applying a simple threshold policy, we first validate the advantages of the adaptivity of our proposed framework through extensive simulation results. Then we introduce a generalized profit-oriented formulation inside decision module of MBORA system, that supplies the network provider with criteria in terms of profit, by leveraging the utility charge revenue and delay-incurred cost. The optimal resource allocation will be affected by the various types of pricing models together with the different levels of service guarantee constraints. As a case study, we investigate this generalized profit-oriented formulation under generalized service models. Combining further with a linear pricing model subject to average queue delay constraints, we propose a fast algorithm for online dynamic and optimal resource allocation under this specific scenario. Finally, we propose a delay-sensitive nonlinear pricing model for the generalized profit-oriented formulation, that realizes two-tier delay differentiation. By better understanding the fluid queueing model, we propose a generalized solution strategy for linear, nonlinear or mixed pricing models that is free of the dimensionality problem and amenable to online implementation.
QoS Provisioning in Wi-Fi Networks: Capacity Modeling and Resource Control
(2005-11-09) Hui, Jie; Dr. Arne Nilsson, Committee Member; Dr. Wenye Wang, Committee Member; Dr. Michael Devetsikiotis, Committee Chair; Dr. Steve Roberts , Committee Member
The ubiquitous Wireless Fidelity (Wi-Fi) networks, and their increasing quality of service (QoS) requirements for emerging applications, motivate extensive studies of QoS provisioning in such networks. Two tasks, namely, capacity modeling and resource control, are crucial in solving the problem: A performance model is first needed to predict the network QoS metrics from the network settings. We propose a new unified analytical model to study the saturation throughput and delay performance of 802.11e Enhanced Distributed Coordination Function (EDCA), which is easier to apply than the most current ones. In order to find usable mathematical models for most cases where analytical models are not feasible, we first advocate the application of metamodeling techniques to Wi-Fi performance studies and formulate a general metamodeling framework for such purpose. The results in three case studies support the validity of our methodology: our saturation capacity metamodel for 802.11 Distributed Coordination Function (DCF) displays an interesting log-linear relationship between capacity and number of users; our voice over Wi-Fi admission capacity metamodel gives a much tighter bound than bounds existing in the literature; and, finally, our throughput metamodel for a simple ad-hoc network, for the first time, characterizes the cross-layer effects between MAC and network layer. Our work, therefore, points out a new direction for future performance studies of Wi-Fi networks. Then, based on the performance models we derive, control schemes of input parameters can be designed to achieve certain level of QoS outputs in some cases. For example, we are able to design a Weighted Round Robin (WRR) scheduler at the MAC layer to control the share of the radio resources, by applying our analytical model to a special case of EDCA configuration. Furthermore, based on our fitted metamodel for the capacity of voice over Wi-Fi, a more practical admission control scheme is composed.
Radio Resource Management in UMTS-WCDMA Systems.
(2005-12-28) Subramaniam, Kamala; Dr. Wenye Wang, Committee Member; Dr. George Rouskas, Committee Member; Dr. Ioannis Viniotis, Committee Member; Dr. Arne A. Nilsson, Committee Chair
Universal Mobile Telecommunications System (UMTS) is a Third Generation (3G) cellular technology representing an evolution of a heterogenous mix of services and increased data speeds from today's second generation mobile networks. UMTS uses Wideband Code Division Multiple Access (WCDMA) as its radio air interface. The main advantage of this is its flexibility in resource management. The implementation of WCDMA is a technical challenge because of its complexity and versatility. Billions of dollars have been spent procuring these air interfaces. To exploit the flexibility of the air interface, development of 'Radio Resource Management (RRM)' schemes are imperative. RRM is comprised of power control, handover control, load control and resource allocation algorithms. These ensure optimum network coverage, maximize the system throughput and , guarantee Quality of Service (QoS) requirements to users having different requirements. This research investigates mainly the resource allocation and power control algorithms with which the load control and handover control are intertwined. The state of the art is studied and their pros and cons are discussed, which lays the foundation for the need for more efficient RRM schemes that are eventually presented in this research. The two main schemes considered here are:1)Adaptive Call Admission Control (ACAC) scheme for resource allocation where the system is mathematically modeled as a multi-rate system with priority. Further, a tier based analytical model pertaining to the hierarchical hexagonal cell structure is analyzed and mobility is given importance. 2) Adaptive Uplink Power Control (AUPC) scheme for power control is analyzed where Monte Carlo simulations are used to fine-tune WCDMA link budget parameters. Finally, Location Update (LU) procedures in cellular networks using Bloom Filters is studied where bandwidth gain is given importance. Various performance metrics are observed and two key metrics are given the most importance: the Call Blocking and Call Dropping probabilities. Simulation results are compared to the existing schemes and further strengthened by comparing them to analytical results which validate the entirety of this research.