Browsing by Author "Chang, Wen-Thong"

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Adaptive Parameter Adaptation in 802.11e
(2015)
Chang, Wen-Thong
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Din, Yin-Tin
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電機學院
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College of Electrical and Computer Engineering
IEEE 802.11e is an extension for media access control in wireless network. It is used for different Quality of Service requirement for different transmission application. But it assumes that all terminals operate in the same transmission speed. But when terminals use different transmission speeds, the access mechanism, EDCA, can not perform to its design purposes. Because the parameters designed for the four different categories can not be adapted according to the transmission speed. For high priority application, it is given a fixed transmission time, this will make the terminal with low speed difficult to achieve the required QoS due to insufficient time to transmit large packet. However, for low priority application, the system will be occupied by terminal with slow transmission speed when transmitting a long packet. This will affect the real time requirement of the QoS service and eventually reduce the total system performance. This paper will address the above two issues and try to purpose methods to improve it. First, a method is used to reduce the time that a low speed terminal will take when transmitting low priority data. Secondly, another method is used to enhance the QoS for all terminals with different transmission speed. With those two methods, we can obtain better throughput and better QoS for the WiFi system.
Clock Synchronization by Phase Difference in Timing Estimation
(2015)
Chang, Wen-Thong
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Synchronization has been an important task in communication. Many signal processing algorithms focus on the issues of carrier estimation, phase estimation and timing estimation. In this paper, we focus on the issue of timing synchronization. The basic timing synchronization problems involving a time shift and many related research results have been reported. This time shift operation is based on the assumption that the clocks on both sides of communication are synchronous. In such a condition, timing estimation is just a problem of offset estimation. If the two clocks are not synchronized, the symbol periods measured in the two sides will be different. Uniform sampling rate in the receiver will not be able to probe the optimum point for decision. Here, we propose a simple procedure to estimate the symbol period in the transmitter side such that the incommensurate of the clock rate can be compensated.
Computationally efficient algorithm for sub-carrier, bit, and power allocation
(2006)
Chang, Wen-Thong
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Chang, Chi-Wei
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電信工程研究所
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Institute of Communications Engineering
An adaptive subcarrier assignment and bit loading strategy for multiple users in an orthogonal-frequency division multiplexing-based wireless systern is considered. Based on the channel condition for each user, the algorithm minimizes the system total transmit power while satisfying each user's transmission rate constraint under a given bit error rate requirement. The minimization is attained by an optimal weighting for each user during the compete for the subcarrier. The problem of joint allocation is divided into two steps. First subcarrier assignment based on channel condition is performed. After that, the modulation level on each subcarrier is determined. Both the carrier assignment and bit allocation are iteratively adjusted by properly adjusting the weighting factor for each user until all the transmit constraints for all the users are satisfied. The purpose of such iteration is to ensure that total system power is minimized. During the iterative search, efficient estimation of the weighting factor is proposed.
Design of a downlink power control scheme in multi-code CDMA mobile medicine system
(2006)
Lin, Chin-Feng
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Chang, Wen-Thong
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Lee, Hsin-Wang
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Hung, Shih-Ii
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交大名義發表
In this paper, we proposed a downlink power control scheme to apply in the multi-code CDMA mobile medicine system. The mobile medicine system contains (i) blood pressure and body temperature measurement value, (ii) medical signals measured by the electrocardiogram device, (iii) mobile patient\'s history, (iv) G.729 audio signal and MPEG-4 CCD sensor video signal. By the help of the multi-code CDMA spread spectrum communication system with downlink power control strategy to make it possible for transmission media in this system to meet the quality of service of mobile medicine system, and achieve the purpose of the maximum resource utilization. In different media, the power is controlled according to the demand for bit error rate. Higher transmission power is given to the media requesting lower bit error rate. Numerical analysis shows that the ratio of transmission power of voice, video and data virtual channels are approximately 1:2:13 when the bit error rates for the voice, video, and data are set at 10(-3), 10(-4) and 10(-7). It is similar to the ratio of SNIR of voice, video and data transmission requirement. Meanwhile, we also test related mobile medical signal transmission and simulation.
Downlink power control in multi-code CDMA for mobile medicine
(2006-05-01)
Lin, Chin-Feng
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Chang, Wen-Thong
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Lee, Hsin-Wang
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Hung, Shih-Ii
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電信工程研究所
In this paper, we propose a downlink power-control mechanism to be applied in a multi-code code division multiple access (CDMA) mobile medicine system. The mobile medicine system can provide (i) measured blood pressure and body temperature, (ii) medical signals measured by the electrocardiogram (ECG) device, (iii) mobile patient's history, (iv) G. 729 audio signals, (v) Joint Photographic Experts Group 2000 Medical images and Moving Picture Experts Group 4 charge-coupled device sensor video signals. By utilizing a multi-code CDMA spread spectrum communication system with downlink power-control strategy, it is possible for this system to meet the quality of service requirements of a mobile medicine network. In addition, such a system can maximize the resource utilization. For different messages to be sent, the power is controlled according to the requisite bit error rate (BER). Higher transmission power is given to the media with lower BER requirement. Numerical analysis shows that the ratios of transmission power for voice, video, and data virtual channels is approximately 1: 2: 13 when the BERs for voice, video, and data are 10 boolean AND(- 3), 10 boolean AND(- 4), and 10 boolean AND(- 7), respectively. This power ratio is similar to the ratio of signal-to-noise plus interference power ratio for voice, video, and data during transmission. For the purpose of verifying the proposed argument, a simulation has been done and the results match the derivation very well.