151 research outputs found
A novel oscillating plane jet : its effect on ejector thrust augmentation
Full text linkA plane subsonic turbulent jet was excited by a special oscillating nozzle.
Its overall performance compares favorably with that of the vane excited
jet investigated earlier. The nozzle when installed in an ejector system
yielded a thrust augmentation ratio of 1.6 at an excitation frequency of
20 Hz. The dynamics of the oscillating flow was examined in the light of
the Korst theory.N0001485WR41005The work reported herein was carried out at the Department of
Aeronautics, Naval Postgraduate School. This research activity is based on
the proposal submitted by the first author to the National Research Council,
Washington, DC, under the NRC Associateship Program. Dr. M. A. Badri
Narayanan is a Professor of Aerospace Engineering, Indian Institute of
Science, Bangalore, India, now visiting the Naval Postgraduate School.http://archive.org/details/noveloscillating00bad
Ad Hoc Positioning System (APS)
No full textMany ad ho network protools and appliations assume the knowledge of geographi loation of nodes. The absolute loation of eah networked node is an assumed fat by most sensor networks whih an then present the sensed information on a geographial map. Finding loation without the aid of GPS in eah node of an ad ho network is important in ases where GPS is either not aessible, or not pratial to use due to power, form fator or line of sight onditions. Loation would also enable routing in suÆiently isotropi large networks, without the use of large routing tables. We are proposing APS { a distributed, hop by hop positioning algorithm, that works as an extension of both distane vetor routing and GPS positioning in order to provide approximate loation for all nodes in a network where only a limited fration of nodes have self loation apability.Technical report DCS-TR-43
Multi-resolution state retrieval in sensor networks
No full textLarge-scale sensor networks require mechanisms to extract topology information that can be used for various aspects of sensor network management. It is critical for any topology discovery algorithm in sensor networks to adhere to the resource constraints of bandwidth and energy. In this paper, we describe a distributed parameterized algorithm for Sensor Topology Extraction at Multiple Resolutions (STEM), which makes a tradeoff between topology details and resource expended. The algorithm retrieves network state at multiple resolutions at a proportionate communication cost. We also define various classes of topology queries and show how the parameters in the algorithm can be used to support queries specific to sensor networks. We show that the topology determined, albeit at a low resolution, is sufficient for approximating actual network properties. Finally we show how STEM can be used for generalpurpose multi-resolution information retrieval in sensor networks.Technical report DCS-TR-47
Ad hoc positioning system (APS) using AoA
No full textAoA (Angle of Arrival) is a well known method used for positioning in providing services such as E911, and for other military and civil radio-location applications, such as sonars and radars. Although devices such as GPS receivers and digital compasses provide good positioning and orientation outdoors, there are many applications requiring the same facilities indoors, where line of sight access to satellites is unavailable, or earth magnetic readings are unreliable. We propose a method for all nodes to determine their orientation and position in an ad hoc network where only a fraction of nodes have the positioning capabilities, under the assumption that each node has the AoA capability.Technical report DCS-TR-46
Trajectory based forwarding and its applications
No full textTrajectory based forwarding (TBF) is a novel method to forward packets in a dense ad hoc network that makes it possible to route a packet along a predefined curve. It is a generalization of source based routing and Cartesian forwarding in that the trajectory is set by the source, but the forwarding decision is based on the relationship to the trajectory rather than the final destination. The fundamental aspect of TBF is that it decouples path naming from the actual path, thereby providing a common framework for applications such as: flooding, unicast, multicast and multipath routing, and discovery in ad hoc networks. TBF requires that nodes know their position relative to a coordinate system. While a global coordinate system afforded by a system such as GPS would be ideal, in this paper we propose Local Positioning System (LPS), a method that only positions the nodes along the trajectory, by making use of other node capabilities, such as angle of arrival or range estimations, compasses and accelerometers. We explore several forwarding strategies that are appropriate for these node capabilities.Technical report DCS-TR-48
Optimization based bandwidth allocation in mobile cellular networks
No full textEfficient bandwidth allocation strategy with simultaneous fulfillment of QoS requirement of a user in a mobile cellular network is still a critical and an important practical issue. We explore the problem of minimizing the amount of time for which bandwidth has to be allocated in a cell while meeting the QoS constraint. With the knowledge about the the arrival and residence time distribution of a user in a cell, the above problem can be optimally solved using a dynamic programming based approach in polynomial time. To be able to use the solution, we provide a mechanism for constructing the arrival/residence time distribution based on the measurement of hand-off events in a cell. The above solution allows us to propose an optimal time based bandwidth reservation and call admission scheme. By being scalable and distributed, the proposed scheme justifies for practical implementation. Simulations results are also presented to show the effectiveness of the scheme to achieve the target QoS level and optimal bandwidth utilization.Technical report DCS-TR-45
An Edge Router Based Protocol for Fault Tolerant Handling of Advance Reservations
No full textTo provide quality of service guarantees, resource reservation schemes have to maintain reservation states at the nodes along the path of a flow. Advance reservation schemes have to maintain these states for a long period of time. The loss of reservation state caused by node failures, makes advance reservation schemes highly susceptible to node failures. In this paper, we argue that a domain-by-domain reservation approach is inherently more fault tolerant than the traditional hop-by-hop approach. We propose a novel domain-based protocol for handling advance reservations. It requires support only at the edge routers and no changes are required at the core routers. We describe various factors which determine whether a flow’s advance reservation is handled properly by a network in event of router failures. We use simulations to show that our protocol is highly fault tolerant. Our protocol allows the best effort flows to utilize the remaining bandwidth without any static partitioning of bandwidth among reserved and best effort flows.Technical report DCS-TR-43
ReInForM: Reliable Information Forwarding using Multiple Paths in Sensor Networks
No full textSensor networks are meant for sensing and disseminating information about the environment they sense. The criticality of a sensed phenomenon determines it’s importance to the end user. Hence data dissemination in a sensor network should be information-aware. Such information-awareness is essential firstly to disseminate critical information more reliably and secondly to consume network resources proportional to criticality of information.
In this paper, we describe a protocol called ReInForM to support information awareness in sensor networks. Using ReInForM, data can be delivered at desired levels of reliability at proportional cost, in spite of the presence of significant channel errors. It uses the concept of dynamic packet state in context of sensor networks to control the number of paths required for the desired reliability using only local knowledge of channel error rates and does not require any prior computation or maintenance of these multiple paths. We also show that for uniform unit disk graphs, multiple edge-disjoint paths numbering as many as the average node degree, exist between any source and sink with very high probability. These paths exist in a thin band between source and sink having low deviation from the optimal path. ReInForm utilizes this property in its randomized forwarding mechanism which results in use of all possible paths in this band. Thus as a side effect ReInForM leads to load balancing as well.Technical report DCS-TR-49
STREAM: Sensor Topology Retrieval at Multiple Resolutions
No full textLarge-scale dense sensor networks require mechanisms to extract topology information that can be used for various aspects of sensor network management. Many network properties can be inferred from a relatively low-resolution representation of topology. Different topology resolutions suffice for different management applications to perform at a desired level. In these cases, it is an overkill to retrieve the entire topology of large-scale dense networks particularly because sensor nodes are energy constrained. In this paper, we describe a distributed parameterized algorithm for Sensor Topology Retrieval at Multiple Resolutions (STREAM), which makes a tradeoff between topology details and resources expended. The algorithm retrieves network state at multiple resolutions at proportionate communication cost by adaptive spatial sampling. We also define various classes of topology queries and show how the parameters in the algorithm can be used to support queries specific to sensor networks. We show that the topology determined, albeit at a low resolution, is sufficient to approximate actual network properties.Technical report DCS-TR-51
SBone: Personal Device Sharing Using Social Networks
No full textPeople own a number of personal devices whose state and resources might be of interest to others. Owners of these devices may be willing to selectively share them with their family, friends, and colleagues, but there exists no easy and secure mechanism to do so. In this paper, we propose SBone, an architecture that allows personal devices to share their resources and state with each other, seamlessly and securely, using a social network for authentication, naming, discovery and access control. The sharing mechanism is derived from the inter-personal relationships that exists among owners by virtue of their presence in online social networks. We present a case study of how SBone can be used to share internet connectivity resource between devices.Technical report DCS-TR-66
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