Browsing by Author "Wang, BC"

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Adaptive fuzzy power control for CDMA mobile radio systems
(1996-05-01)
Chang, PR
;
Wang, BC
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
This paper introduces a new application of fuzzy-logic control (FLC) theory to the power control in a direct-sequence, code-division multiple-access (DS/CDMA) cellular system over the mobile fading radio channels. Power control is essential in DS/CDMA to compensate for the differing received powers due to both the slowly varying long-term and fast varying short-term fading processes and co-channel interference. The conventional feedback power control algorithms allow the base station to send a power command to either raise or lower each user transmitting signal power level by a fixed power step and then keep the received powers almost equal. The fixed-step approach is actually an integral control whose power increment is determined according to the bang-bang-like control policy. However, this control scheme suffers from poor system stability, large overshoot, and long rise time. To tackle this difficulty, a fuzzy proportional-plus-integral (PI) control, whose input variables are the received power error and error change, is introduced to determine each user's transmitting power in order to maintain simultaneously all users' signal power received at the base station nearly equal and to achieve better system stability and control performance. The derivation of the fuzzy PI control has been carried out by analyzing both the closed-loop steady state behavior and transient response of the system with a priori knowledge of the dynamics of the CDMA mobile fading channels. In fuzzy control, linguistic descriptions of actions in controlling a process are represented as fuzzy rules. This fuzzy-rule base is used by an inference mechanism in conjunction with some knowledge of the states of process in order to determine control actions. These control actions would lead to the fast rise time, minimum overshoot, and small root-mean-squared (rms) tracking error. Furthermore, the additional advantages of fuzzy PI control over conventional control theories are increased robustness despite interference and the ability to handle the time-delay process without system degradation since there is usually a latency between each user and base station. Simulation results show that the fuzzy PI power control provides much smaller rms tracking error and better traffic capacity performance compared with the fixed-step control, especially in poor co-channel interference conditions.
Adaptive fuzzy proportional integral power control for a cellular CDMA system with time delay
(1996-12-01)
Chang, PR
;
Wang, BC
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
In this article, we investigate the use of fuzzy logic control techniques for adaptive power control in a direct-sequence code-division multiple-access (DS/CDMA) cellular system over the mobile fading radio channels with propagation time delay, A fuzzy PI (proportional-plus-integral) control whose input variables are the received power error and error change is introduced to determine each user transmitting power in order to simultaneously equalize all users' signal powers received at the base station and achieve better System stability and control performance, This control strategy can ensure long loop transmission delays without causing the system to become unstable, According to the well-known phase-plane method, the derivation of the fuzzy PI control has been carried out by analyzing the response areas, cross-over, and extreme points of the system step response with apriori knowledge of the dynamics of the CDMA mobile fading channels, For a long time-delay fading process, a methodology is developed to modify the rule base to contain the delay information for reducing the deadtime effects of the process, Moreover, the additional advantages of fuzzy PI control over conventional control theories are: increased robustness in spite of interference and the ability to handle the time-delay process whose parameters are not accurately known, Simulation results show that a good performance can he achieved both in rms tracking error and traffic capacity by use of fuzzy PI power control, especially in poor interuser interference and long time delay conditions.
Design and investigation of calamitic liquid crystals with low aspect-ratios: rigid y-shaped 1,2,4-tris(4-alkoxyphenylethynyl)benzenes
(2005-12-07)
Hsu, HF
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Chen, HC
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Kuo, CH
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Wang, BC
;
Chin, HT
The synthesis and characterization of triynylbenzenes, 1-iodo-2,4,5-tri(4-alkoxyphenyl-ethynyl)benzenes (1), are reported, and their structure-mesomorphism relationship is investigated. These compounds possess a y-shaped geometry with rigid linear spacers and a stable nematic phase that was achieved by lengthening the alkoxy chains or replacing the iodo group with a smaller atom. The low aspect ratios and identified calamitic nature of these rigid y-shaped liquid crystals, make them suitable as potential candidates to be used in the liquid crystal layer of liquid crystal display devices for improving viewing angles. In addition, the geometry of I was modified stepwise from a rigid y-geometry to a rigid rectangle for realization of the unstable nematic behaviors of the previously reported board-like 1,2,4,5-tetrakis(4-tridecyloxyphenyl-ethynyl)benzene that was expected to potentially show biaxial nematic phases. The sizes of the fourth side-arm and hence the aspect ratios of these tetra-substituted benzenes are ascribed to the less liquid crystallinity.
Heuristic PAC model for hybrid MTO and MTS production environment
(2003-09-11)
Chang, SH
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Pai, PF
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Yuan, KJ
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Wang, BC
;
Li, RK
Two distinct types of semiconductor plants in Taiwan are integrated device manufacturing (IDM) plants and foundry plants. Most IDM plants are make-to-stock (MTS) operations, focusing on throughput and machine utilization. However, foundry plants are make-to-order (MTO) operations, focusing on due date and cycle time. Besides the challenge of different process technology, the mode of hybrid operation (a combination of MTO and MTS operations) is also a formidable task for these plants. This study develops a heuristic production activity control model to achieve the two different criteria in a hybrid wafer production environment. (C) 2003 Elsevier B.V. All rights reserved.
Spread spectrum multiple-access with DPSK modulation and diversity for image transmission over indoor radio multipath fading channels
(1996-04-01)
Wang, BC
;
Chang, PR
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
As demand for networked multimedia applications is increasing rapidly, it is important to provide the ubiquitous accessibility for these services in wireless communication environment, Such access allows users to share novel multimedia applications without any geographical restrictions. In this paper, we investigate the application of the well-known antimultipath spread spectrum code-division multiple access (SS-CDMA) techniques to image transmission related to the development of next-generation multimedia wireless local area networks within a building, SS-CDMA is particularly well suited to a subband coding scheme that divides the image information into multiple parallel data streams using an analysis filter bank, each of which is multiplied by its unique spreading code, All the product signals are then transmitted at the same time in the same radio channel, even though the total bandwidth of all the signals may exceed the channel bandwidth. Each received signal is independently recovered at the decoder by multiplying its spreading code and all the recovered subbands are then reassembled by a synthesis filter bank into a close reproduction to the original image, A forward error correction (FEC) scheme based on convolutional codes with interleaving is proposed to minimize the effect of bursty channel errors on the picture duality degradation, Better image quality can be achieved by using the predetection diversity combining in order to combat the indoor multipath distortion, In this paper, the image quality of subband image transmission via SS-CDMA indoor fading channels with differential phase shift keying (DPSK) modulation is evaluated and examined, Simulation results show that the image peak signal-to-noise (PSNR) ratio is inversely related to a logarithmic function of bit error rate when each subband employs equal protection channel coding.
Spread spectrum multiple-access with DPSK modulation and diversity for image transmission over indoor radio multipath fading channels
(1996-01-01)
Wang, BC
;
Chang, PR
;
電信工程研究所
;
Institute of Communications Engineering