Bradford G. Nickerson

Communicating and Displaying Real-Time Data with WebSocket

Internet communication provides a convenient, hyperlinked, stateless exchange of information, but can be problematic when real-time data exchange is needed. The WebSocket protocol reduces Internet communication overhead and provides efficient, stateful communication between Web servers and clients. To determine whether WebSocket communication is faster than HTTP polling, the authors built a Web application to measure the one-way transmission latency of sending real-time wind sensor data at a rate of 4 Hz. They implemented a Jetty servlet to upgrade an HTTP connection to a WebSocket connection. Here, they compare the WebSocket protocol latency to HTTP polling and long polling.

ON THE DISCRETE UNIT DISK COVER PROBLEM

Given a set of n points and a set of m unit disks on a 2-dimensional plane, the discrete unit disk cover (DUDC) problem is (i) to check whether each point in is covered by at least one disk in or not and (ii) if so, then find a minimum cardinality subset such that the unit disks in cover all the points in . The discrete unit disk cover problem is a geometric version of the general set cover problem which is NP-hard. The general set cover problem is not approximable within , for some constant c, but the DUDC problem was shown to admit a constant factor approximation. In this paper, we provide an algorithm with constant approximation factor 18. The running time of the proposed algorithm is . The previous best known tractable solution for the same problem was a 22-factor approximation algorithm with running time .

The Cascade Vulnerability Problem

A network of computers is vulnerable to the cascading problem when data of a security level d can be passed to a user with a lower security clearance u elsewhere on the network, without having to defeat any single component of the system that has an accreditation range great enough to allow users of level u and data of level d on a single system. An algorithm of time complexity order O(an3) and space complexity O(an2) is given to solve the cascade detection problem, where a is the number of security levels for data, and n is the number of nodes in the network. Also, the cascade correction problem, to remove all cascading paths from a network for a given cost, under restrictive conditions is shown to be NP-complete.

On the discrete unit disk cover problem

Given a set P of n points and a set D of m unit disks on a 2-dimensional plane, the discrete unit disk cover (DUDC) problem is (i) to check whether each point in P is covered by at least one disk in D or not and (ii) if so, then find a minimum cardinality subset D* ⊆ D such that unit disks in D* cover all the points in P. The discrete unit disk cover problem is a geometric version of the general set cover problem which is NP-hard [14]. The general set cover problem is not approximable within c log |P|, for some constant c, but the DUDC problem was shown to admit a constant factor approximation. In this paper, we provide an algorithm with constant approximation factor 18. The running time of the proposed algorithm is O(n log n+m log m+mn). The previous best known tractable solution for the same problem was a 22-factor approximation algorithm with running time O(m2n4).

A sensor Web language for mesh architectures

A sensor Web language (SWL) for mesh architectures is presented. The mesh SWL architecture was extended from a hierarchical structure to provide a more robust environment to deploy, maintain and operate sensor networks. Alerts, direct sensor node communication, multiple gateway nodes and dynamic configuration are realized. With mesh architecture support in SWL, multiple sensor networks are provided with greater flexibility, more reliable operation and machinery to better support self-diagnosis and inferencing with sensor data.

A language for wireless sensor webs

A language for wireless sensor webs called the sensor web language (SWL) is presented. SWL is especially useful for transmitting information over low power wireless networks with relatively low bandwidth. The language has been designed for automated translation into three software layers. SWL compilers translate SWL statements into server, browser, gateway and sensor node software components of a wireless sensor web. Our approach provides flexibility and efficiency to wireless sensor web developers. Sensor webs can be readily deployed or modified (e.g. adding new sensors, recalibrating sensors) by a straightforward recompilation of the SWL statements. A prototype wireless sensor web for environmental applications that uses SWL is discussed. An example SWL program is presented that describes a sensor web with a cellular telephone gateway, two sensor nodes, four sensors and a Linux server base station.

A fuzzy control framework for wireless sensor networks

We present a novel framework that can be used to dynamically control the operation of sensors embedded in a Wireless Sensor Network WSN. Fuzzy logic incorporating temporal reasoning is used as the basis of our framework, permitting WSNs to automatically adapt to their changing environment. This makes WSNs more responsive and potentially more energy efficient. A fuzzy rule based, object-oriented programming language for WSNs called fuzzy Sensor Web Language fuzzy SWL is implemented as the front end of our framework. A proof-of-concept field test with two rules incorporating air temperature, rainfall, and water level demonstrates the feasibility of our fuzzy control approach for environmental monitoring. A novel aspect of this research is the addition of time factors in fuzzy rules. Time factors permit the fuzzy control system to effectively adapt to changing environmental conditions.

A User Friendly Toolkit for Building Robust Environmental Sensor Networks

Wireless sensor network research is growing rapidly, but building and deploying real-world wireless sensor network applications still requires the assistance of technology experts. We present a user friendly toolkit that simplifies the process of building robust and extensible wireless sensor networks, with our first target application being long-term environmental sensor networks. This project includes a programing language called the sensor Web language (SWL), an Eclipse-based graphical user interface for writing SWL programs, and a compiler for generating a complete stack of deployable sensor network code. Currently we target Mica2 and Mica2dot motes, MDA300 sensor boards, Linux- based servers for base stations, Java clients, and gateways using embedded Linux and cellular network modems.

Efficient search of moving objects on a planar graph

We present a dynamic spatio-temporal data structure called the Graph Strip Tree (GStree) for indexing objects constrained to move on a graph. The GStree is designed to efficiently answer range queries about the current or past positions of moving objects. To test the efficiency of our data structure, a road network of 66,437 roads was used. Average search times for random queries to find moving objects indexed by a GStree were compared to average search times for the same queries on moving objects indexed by a MON-tree. Results indicate that the GStree is up to 24 times faster than the MON-tree for internal memory searching, and visits between 3.6 and 38 times fewer nodes. Analysis indicates the GStree will be significantly faster for external memory search where the search time is dominated by the number of disk I/Os.

Data structures for fast searching of SEG-Y seismic data

Abstract An index structure for seismic data was designed using a modified PR quadtree data structure and implemented in the C++ computer language. To test the software and to evaluate the implementation of the structures, experiments were carried out with data from a marine seismic survey in the Mid-Pacific Ocean. The section of the survey used spanned 6 days, consisted of ten seismic lines (total of 1904 line kilometres) with a total of 39,720 traces. The seismic data (in SEG-Y format) required 335.8 Mbyte storage on disk. Experimental results of range searching (in two dimensions) with varying query window sizes shows that less than 0.1 s is required to determine which seismic lines intersect the query window. The index structure occupies 9.19 Mbyte (about 2.74% of the original data size) and requires 34.5 s to build using a UNIX® workstation. The modified PR quadtree index structure was compared to a standard PR quadtree index structure, and found to require less time (by up to 67%) to perform a 2D range search.