Donghui Yu

Data forwarding based on sensor device constraints in wireless multimedia sensor networks

A variety of data forwarding schemes have been proposed for wireless multimedia sensor networks where energy awareness and reliability are essential design issues. This paper proposes a data forwarding mechanism based on sensor device constraints in wireless multimedia sensor networks. A dynamic path cost function is defined considering the constraints and characteristics of wireless multimedia sensor networks. The cost function is applied to ZigBee mesh routing, and the performance of the proposed method is evaluated using a QualNet network simulator.

Embedded System Design for Network Time Synchronization

Every computer needs a timer mechanism to keep track of current time and also for various accounting purposes such as calculating the time spent by a process in CPU utilization, disk I/O, and so on, so that the corresponding user can be charged properly. In a distributed system, an application may have processes that concurrently run on multiple nodes of the system. For correct results, several such distributed applications require that the clocks of the nodes are synchronized with each other. Nowadays, time synchronization has been a compulsory thing as distributed processing and network operations are generalized. A network time server obtains, keeps accurate and precise time by synchronizing its local clock to a standard reference time source and distributes time information through a standard time synchronization protocol. This paper describes design issues and implementation of an embedded system for network time synchronization especially based on a clock model. Our system uses GPS (Global Positioning System) as a standard reference time source and offers UTC (Coordinated Universal Time) through the NTP (Network Time Protocol). Implementation results and performance evaluation are also presented.

Attribute-based routing for home automation networks

This paper proposes an attribute-based routing mechanism for home automation networks. A dynamic path cost function is defined considering the constraints and characteristics of home automation networks. The cost function is applied to ZigBee mesh routing, and the performance of the proposed method is evaluated using a QualNet network simulator.

A Stable Estimation Model for Time Synchronization on the Internet Using Kalman Filtering

We propose a time synchronization model on the Internet using kalman filtering to provide the stability to time synchronization. To verify the new stable time synchronization model, we introduce the characteristics of the Internet transmission delays and present the comparison results with SNTP(Simple Network Time Protocol) time offset model. SNTP has been widely used as a time synchronization method on the Internet. While SNTP provides a very simple usage, SNTP may not provide the stable services, since SNTP does not consider the several essential error factors of the Internet. In order to overcome the instability of SNTP, we analyze the process of time estimation of SNTP and the premise. To verify and apply the proposed model, we present the measurement results and analysis.

An Internet Time Synchronization Model using Dynamic Linear Model

We propose a new Interet time synchronization model using danamic linear model and introduce the characteristics of internet transmission delays. SNTP(Simple Network Time Protocol) has been widely used as a time synchronization method on the Internet. While SNTP provides a very simple usage, SNTP may not provide the stable services, since SNTP does not consider the several essential error factors. In order to overcome the instabitily of SNTP, we analyze the process of time estimation of SNTP and find the difference between forward transmission delay and backward transmission delay operates the main error on the estimation of an time offset.