Wen Ouyang

Graph Model for OVSF Code Placement

The orthogonal variable-spreading-factor (OVSF)-CDMA systems can support multimedia applications with different bandwidth requirements. Code management schemes, including code placement and replacement, significantly impact the code utilization of the system. Many researches have studied these two closely related problems and are solving them independently. For replacement, the optimality concerns the minimization of the reassignment number. There is no definition about the placement optimality yet. We formally define the placement optimality for code placement schemes and presented a novel graph model, constrained independent dominating set problem (CIDP), which is proved to be NP-complete for general graphs. A unified algorithm is provided to firstly address both OVSF code placement and replacement issues at the same time which achieves placement optimality in linear time complexity. This demonstrated that OVSF code placement optimality problem is in P. Another simple and practical unified solution is presented and is shown to be reasonably effective.

Safe Path Planning Strategy for Bike Net

Biking has gained much popularity recently due to its unique characteristics. It is simultaneously a sport, a leisure activity, and a means of transportation. It has low negative environmental impact and it conserves energy. It can be a solo or a group activity and it applies to all ages. Path planning is essential for all tour activities, including biking. However, most path planning services focus on the shortest path finding when other qualities of service also deserve attention. Among them, safety is always the first priority for any type of activity. There are tools which help people plan for biking tour paths. However, safety is not a major concern in these. This work proposes an innovative and practical safe path planning strategy which addresses the issue with the concept of safety factors and a safety recurrence relation. A dynamic programming solution is provided accordingly. The idea is illustrated using real site data to demonstrate the result of the strategy.

Tracers placement for IP traceback against DDoS attacks

This paper explores the tracers deployment problem for IP traceback methods how many and where the tracers should be deployed in the network to be effective for locating the attack origins. The minimizing the number of tracers deployment problems depended on locating the attack origins are defined. The problem is proved to be NP-complete. A heuristic method which can guarantee that the distance between any attack origin and its first met tracer be within an assigned distance is proposed. The upper bound for the probability of an undetected attack node can be calculated in advance and used to evaluate the number of tracers needed for the proposed heuristic method. Extended simulations are performed to study the performance of the tracers deployment.

Wireless Charging Scheduling Algorithms in Wireless Sensor Networks

Wireless sensor nodes are commonly deployed in outdoor or hazardous environments. Due to limited resources and power consumption required to perform tasks, these nodes may experience power shortages and thus lead to the disconnection of the whole wireless sensor network. To prolong the lifetime of the network, new technologies are developed to wirelessly recharge the sensor nodes via mobile machines. Previous works have considered applying wireless charging to elevate the network lifetime without defining performance optimization. In addition, the effect of the speed of the mobile machines, the chargingspeed, and the possibility of more than one mobile machine to charge one sensor node is discussed. Another interesting issue is the effective utilization of the network once it is disconnected. This work is the first one which formally defines the wireless charging problem in wireless sensor networks by converting it into a job scheduling optimization problem and provides an algorithm for it using multiple mobile charging machines. Two more algorithms are further provided to locate the sensors whose failure can easily jeopardize network connectivity and to solve the charging machine scheduling problems by protecting these weak sensors first. From simulation results, our methods outperform previous methods in the sense of lifetime and number of received messages in sink.

High-Accuracy Indoor Personnel Tracking System with a ZigBee Wireless Sensor Network

The fast advancement of Wireless Sensor Network (WSN) technologies has initiated different perspectives for applications from traditional wireless networks and wire networks. For example, they can be set up in indoor environments which integrate varieties of sensors with network capabilities to provide indoor environment monitoring or personnel location monitoring. Zig Bee is a commonly used transmission technology of indoor positioning. However, the accuracy of Zig Bee positioning is usually far from satisfactory due to the strength and interference of signals. In this paper, we strive to improve the accuracy of Zig Bee positioning and implement an indoor personnel tracking system. Two methods, Neighbor Area Majority Vote Priority Correction and Environment Parameter Correction, are proposed to promote the accuracy of Zig Bee positioning. The experiment results prove that our methods can largely increase accuracy of Zig Bee positioning and provide useful personnel tracking technology.

A Comprehensive Real-Time High-Performance Object-Tracking Approach for Wireless Sensor Networks

Besides sensing the environment variables and detecting the events in the deployment area, tracking of objects has gained much attention in the wireless sensor network research fields. Unlike the other range-free localization schemes which are not effective in real time performance, we propose a mechanism based on the received signal strength to develop real time object-tracking strategy, which determines the location of the moving object according to dynamically changing signal strength. Moreover, to improve the tracking accuracy and to be more practical, we consider a comprehensive approach, called CAUSS (Comprehensive Algorithm Using Signaling Strength), which can be applied in deployment which may result in various anchor node coverage. Simulation results demonstrated that our algorithm is more effective in the sense of real time tracking scheme compared with previous results.

Station Decision Problem in Bicycle Ad Hoc Networks

Biking has been more and more popular recently where public bicycle systems have been adopted in many cities around the world. However, to develop and design a successful public bicycle system is challenging. This work proposes a novel problem called Station Decision Problem for Bicycle Ad Hoc Networks. The problem is to find minimum number of stations while satisfying reach ability and richness conditions. A station decision (SD) algorithm using graph theory is provided with simulation conducted to prove the effectiveness of this method. A real site data is also plugged in to check the result of the SD algorithm.

Optimum Partition for Distant Charging in Wireless Sensor Networks

Wireless sensor nodes are commonly deployed in outdoor or hazardous environments. Due to limited resources and power consumption required to perform tasks, these nodes may experience power shortages and thus lead to the disconnection of the whole wireless sensor network. To prolong the lifetime of the network, new technologies are developed to wirelessly recharge the sensor nodes via mobile machines. Previous works have considered applying wireless charging to elevate the network lifetime without defining performance optimization. An interesting issue is the effective partitioning of the network for more than one charging machine to patrol over. In this work, we aim to design and analyse three network partition methods, namely the tier-based partition, the sector-based partition, and the mixed partition, for charging scheduling with mobile charging machines so that the resulting sub-networks exhibits approximately the same total energy consumption rate. To the best of our knowledge, no optimal partition method has been proposed before. Moreover, we show that the largest diameter of the partitioned areas from the mixed partition is shorter than those from the tier-based partition and the sector-based partition. This indicates that the delay time can be reduced when a mobile charging machine runs for a dying sensor using the mixed partition method.

Graph model for optimal OVSF code placement strategies

The code utilisation of OVSF-CDMA systems are significantly impacted by the code placement and replacement schemes which have been studied by many researchers as independent problems. We formally define the placement optimality and present a novel graph model, CIDP, which is proved to be NP-complete for general graphs where the CIDP graphs reduced from the OVSF code placement problem are trivial perfect graphs. A unified algorithm UCMS-1, provided to firstly address both OVSF code placement and replacement jointly, achieves placement optimality in linear time complexity. It shows that OVSF code placement optimality problem is in P.

Entropy-Based Distributed Fault-Tolerant Event Boundary Detection Algorithm for Wireless Sensor Networks

Wireless sensor networks observe the occurrences of concerned events by the collaboration between sensor nodes via wireless communication. Sensors are usually prone to errors due to the unstable conditions they are exposed to. The goal is to solve event boundary detection with faulty sensors (EBDF) problem which is to successfully identify the sensor nodes close to the event boundary when faulty sensors exist in wireless sensor networks. Some previous works proposed solutions based on 0/1 decision predicate for which only values 0 or 1 (true or false) are used to represent the sensing values which may ignore local variations. Others require centralized mechanism to retrieve the threshold or it may not be applied to dynamic situation efficiently. A novel distributed event boundary detection algorithm, EBD_Entropy, using entropy is proposed which applies system entropy concept from both thermodynamics and information theory points of view. EBD_Entropy accepts scalar values as input. Its also distributed and localized and thus is scalable. Simulation results show that EBD Entropy is effective in enhancing the performance of boundary detection and can be applied to more dynamic environments.