Student Conference on Research and Development

Để đo lường các vật liệu dielectrics, chúng tôi đã phát triển một hệ thống đo lường không gian tự do trong khoảng tần số từ 8 - 12,5 GHz. Các thành phần chính của hệ thống đo lường gồm có một cặp ăng-ten giác hội tụ hình phễu, máy phân tích mạng và cáp đồng trục. Trong dự án này, mục tiêu là phân tích và đo lường các hệ số phản xạ phức tạp của các vật liệu dielectrics như các tấm cao su silicon tải sắt carbonyl và PVC bằng cách sử dụng phương pháp mạch ngắn và mạch hở ở tần số vi sóng. Kỹ thuật hiệu chuẩn thru, reflect và line 2 (LRL) đã được sử dụng để loại bỏ các hiệu ứng phản xạ không mong muốn. Bằng cách thực hiện một thuật toán được suy diễn từ mạch hở và mạch ngắn, được xác định từ các phương trình đường truyền, các hằng số dielectrics và độ từ thẩm phức tạp đã được tính toán từ các hệ số phản xạ đã đo được.

Solving large systems of Boolean equations is a hard combinatorial problem. It can be greatly facilitated by preliminarily reducing the number of roots in separate equations which, in turn, leads to a reduction in the number of variables, equations and time complexity. This can have a significant effect upon the physical space and connectivity of electronic logic circuits when these are implemented using actual electronic devices or components. In this paper, we review various representation techniques, Boolean function manipulation issues and problems that are used in a practical design environment for digital systems design.

This paper presents a dynamic channel allocation scheme for wireless asynchronous transfer mode (WATM) satellite systems. Handoff schemes of WATM are utilized to deal with handoff issues in a WATM mobile satellite system. Here we investigate and simulate a dynamic channel allocation scheme for handoff in WATM mobile satellite networks, which improves the network resource utilization, by measuring the network performance in terms of new call blocking probability (NCBP) and handoff call blocking probability (HCBP). Arriving calls are given channels based on their priority and calls are subdivided into real time and non real time calls. Highest priority is given to real time handoff calls, followed by non real time handoff calls, then real time new calls and finally non real time new calls.

This paper describes a new method for classification of transient disturbance via fuzzy logic incorporated with wavelet processing. The transient is one of the major causes of power quality issues that have been experienced by the utility and consumer parties. The ability of a wavelet to detect the transient disturbance is being exposed. Finally, the fuzzy logic MATLAB is being proposed as a classification tool to differentiate between oscillatory and impulsive transient. This paper is an initial step towards auto-detecting the real-time power quality classification in a real time monitoring system.

The General Packet Radio Service (GPRS) is a complex data network which upgrades current second generation GSM networks, offering true high-speed Internet (IP) and X.25 network connectivity over existing GSM cellular networks. The key benefits of GPRS are better use of radio and network resources and completely transparent IP support. The increasing population of mobile users leads to congestion problems in these systems, and motivates the development of more efficient management schemes. Although GPRS offers a major improvement in spectrum efficiency, the capability and functionality compared with today's non-voice mobile services, there are still some key limitations with GPRS such as the transit delay, speeds which are much lower in reality and limited modem of operation. This paper overviews radio resource and mobility management such as location management and handoff management and discusses some of the key problems and method of overcoming these limitation and management problems in the GPRS network. A simulator based on Matlab which can study the location updating was developed in this GPRS system. The initial simulation shows the updating based on cell distance with various speeds.

This paper presents the development of a simple 1.5 kW single-phase sinusoidal pulse width modulation (PWM) inverter. This inverter is designed to be either a stand-alone or grid connected inverter from a direct supply of photovoltaic (PV) cells. The developed inverter unit converts the DC input supply from the PV cells into a clean sinusoidal voltage output. This power inverter is also capable of being a grid-connected PV system where the electricity produced by PV, which exceeds the load consumption, can be fed back to the grid. The inverter is of a full-bridge topology using a step-up transformer. The PWM signals, which feed the bridges, are generated by a dual ended PWM modulator, and isolated with the isolated gate driver. The L-C filter is implemented after the step-up transformer before the load to attenuate the harmonics component. The 1.5 kW designed prototype of the inverter was tested with the resistive loads and a fluorescent lamp and the total harmonic distortion (THD) for all load is about 2.7%.

TDD graph-based representation is actually a natural extension of the binary decision diagram (BDD) to the three-valued case. This paper describes a method of defining, analyzing, and implementing the Boolean function using a ternary decision diagram (TDD). This diagram representation enables us to evaluate a Boolean function. We investigate the characteristics of different types of TDDs in order to develop an efficient general software package associated with efficient manipulation algorithms that leads to simpler Boolean functions. We define and discuss the data structure and reduction algorithms of the developed package. The performance of this software package is finally demonstrated by subjecting practical circuits, LGSynth93 standard benchmarks, to it.

In a network where geographically dispersed replicated servers offer the same service to a large number of clients, requests tend to concentrate at only a few of these servers, causing congestion in the network around them. A server load balancing method based on the active anycast service has been proposed to alleviate the problem. In this method, an anycast address is used to represent the group of servers and active networking provides the means to select and deliver requests to the selected server with the overall objective of balancing the load on each server. Active networking allows a router to make decisions in selecting the appropriate server based on load information of all servers and by subsequently changing the anycast address to the unicast address of the selected server. This paper presents preliminary performance results which give an idea of the efficiency of the proposed service.

The mobile community is currently gearing towards third-generation (3G) and beyond, promising upgraded and seamless integration of a wide variety of communication services for consumers worldwide. 3G systems have been implemented in some European and Asian countries but the development in Malaysia is still in its infancy. The 3G system is based on the wideband code division multiple access (WCDMA) air interface platform which is backward compatible with the second-generation (2G) global system for mobile communications (GSM) networks. Therefore, a simple user-friendly WCDMA simulator has been built; it is deemed necessary and invaluable for research purposes involving the performance of the 3G system. This paper investigates the simulated performance of the WCDMA system at both the forward and reverse channels for different channel conditions in a multiuser environment. Simple matched filtering and RAKE diversity combining is implemented at the receiver. Performance improvement due to error correction coding is also shown.

In this paper, we evaluate the performance of multicasting in a single-hop local lightwave network based on a broadcast-and-select system. We use an approximate analytical solution and Markov model to show the effect of tuning time on the average packet delay and offered load. We also show the trade-off between the average packet delay and the number of wavelengths for the network.