• Journal of the Institute of Convergence Signal Processing
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• v.1 no.2
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• pp.169-176
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• 2000

Deadbeat property is well established in digital control system design in time domain. But in continuous time system, deadbeat is impossible because of it's ripples between sampling points inspite of designs using the related digital control system design theory. But several researchers suggested delay elements. A delay element is made from the concept of finite Laplace Transform. From some specifications such as internal model stability, physical realizations as well as finite time settling, unknown coefficents and poles in error transfer functions with delay elements can be calulted so as to satisfy these specifications. For the application to the real system, robustness property can be added. In this paper, error transfer function is specified with 1 delay element and robustness condition is considered additionally. As the criterion of the robustness, a weighted sensitive function's $H_{infty}$ norm is used. For the minimum value of the criterion, error transfer function's poles are calculated optimally. In this sense, optimal design of the continuous time deadbeat controller is obtained.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.7
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• pp.45-51
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• 2009

We have presented a routing mechanism that selects a route by considering channel statuses in order to fast transfer delay-sensitive data in WSNs (Wireless Sensor Networks). The existing methods for real-time data transfer select a path whose latency is the shortest or the number of hops is the smallest. An algorithm to select a real-time transfer path based on link error rates according to the characteristic of wireless medium was also suggested. However, the propagation delay and retransmission timeout affected by link error rates are shorter than channel assessment time and backoff time. Therefore, the mechanism proposed in this paper estimated the time spent in using a clear channel and sending out a packet, which is based on channel backoff rates. A source node comes to select a route with the shortest end-to-end delay as a fast transfer path for real-time traffic, and sends data along the path chosen. We found that this proposed mechanism improves the speed of event-to-sink data transfer by performing experiments under different link error and channel backoff rates.

• International Journal of Computer Science & Network Security
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• v.23 no.9
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• pp.8-16
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• 2023

In Japan, high-speed ground transportation service using linear motors at speeds of 500 km/h is scheduled to begin in 2027. To accommodate 5G services in trains, a subcarrier spacing frequency of 30 kHz will be used instead of the typical 15 kHz subcarrier spacing to mitigate Doppler effects in such high-speed transport. Furthermore, to increase the cell size of the 5G mobile system, multiple base station antennas will transmit identical downlink (DL) signals to form an expanded cell size along the train rails. In this situation, the forward and backward antenna signals are Doppler-shifted in opposite directions, respectively, so the receiver in the train may suffer from estimating the exact Channel Transfer Function (CTF) for demodulation. In a previously published paper, we proposed a channel estimator based on Delay and Doppler Profiler (DDP) in a 5G SISO (Single Input Single Output) environment and successfully implemented it in a signal processing simulation system. In this paper, we extend it to 2×2 MIMO (Multiple Input Multiple Output) with spatial multiplexing environment and confirm that the delay and DDP based channel estimator is also effective in 2×2 MIMO environment. Its simulation performance is compared with that of a conventional time-domain linear interpolation estimator. The simulation results show that in a 2×2 MIMO environment, the conventional channel estimator can barely achieve QPSK modulation at speeds below 100 km/h and has poor CNR performance versus SISO. The performance degradation of CNR against DDP SISO is only 6dB to 7dB. And even under severe channel conditions such as 500km/h and 8-path inverse Doppler shift environment, the error rate can be reduced by combining the error with LDPC to reduce the error rate and improve the performance in 2×2 MIMO. QPSK modulation scheme in 2×2 MIMO can be used under severe channel conditions such as 500 km/h and 8-path inverse Doppler shift environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.265-270
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• 2004

This paper addresses the effect of group delay in satellite communication system. Phase of signal is distorted by the non-constant group delay. Group delay can be modeled as linear, parabolic and cubic type according to the polynomial characteristic. We investigate BER performance of satellite communication system with each 3 kinds of group delay. As signal bandwidth becomes wider, group delay makes more influence on the signal. BNR performance of satellite communication system is found when data rates are 1Mbps, 4Mbps and 8Mbps. Convolution coding with the code rate of 1/2 or 7/8 is used. At BER =10$\^$-5/, system with group delay needs more SNR of minimum 0.3㏈ to maximum 4.4㏈ than system without group delay. The worst case of BER performance happens in the linear group delay, 7/8 punctured convolution coding and 8 Mbps. The required SNR is increased by 4.4㏈ at this worst case.

• Journal of Broadcast Engineering
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• v.10 no.4 s.29
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• pp.548-556
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• 2005

In wireless network environments, wireless channels are characterized by time-varying fading and interference conditions, which may lead to burst packet corruptions and delay variation. This can cause severe quality degradation of streaming media. To guarantee successful transmission of media over the hostile wireless networks, where channel conditions are highly fluctuating, a flexible and network-adaptive transport method is required. Thus, we propose a network-adaptive transport error control consisting of packet-level interleaved FEC and delay-constrained ARQ, which acts as an application-level transport method of streaming media to alleviate burst packet losses while adapting to the changing channel condition in wireless networks. The performances of the proposed network-adaptive transport error control, general error control schemes, and hybrid schemes are evaluated by a developed simulator at the transport-level and video quality of streaming media. Simulation results show that the proposed mechanism provides the best overall performance among compared other schemes in terms of the transport-level performance of error control and the performance of video quality for streaming media.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.2
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• pp.75-82
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• 2000

In this Paper, a new type of feedforward linearizer using a delay line which controls the phase characteristics of the correction amplifier block is proposed. The extra delay line provides the control-ability of IM signals so that the IM rejection is accomplished without the conventional pilot tone. The error signal loop consists of several key components such as phase shifter and attenuator, subtractor. These key components are replaced by new designs in order to obtain better linearization characteristics without the pilot tone generator which is indispensable in the conventional linearizer designs. The proposed linearizer was designed at Korean PCS band and combined with 35W HPA manufactured by KMW inc., and tested with two-tone signals separated 0.6MHz apart at the center frequency of 1855MHz. The experimental results show C/l improvement by 16.9 ~ 24.6 dB over 15 dB dynamic range(30 ~45 dBm) which gave IMD of 58.5~63.2 dBc for the designed LPA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1876-1883
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• 2016

The new channel model for high data rate common data link(CDL) is proposed. The Two-ray channel, which is composed of the reflected signals on the front ground of the receiver, is considered in this paper. This channel arises due to the curvature of the earth when the altitude of the transmitter is tens of kilometers and distance between the transmitter and the receiver is hundreds of kilometers. The Two-ray channel is modeled by estimating the maximum delay profile and the power delay profile, depending on the transmitting and receiving beamforming angle and the radiation pattern of antenna. The power delay profile has a larger effect on the bit error rate(BER) over signal to noise ratio(SNR) than the maximum delay profile, because the distance range is too long in the proposed channel model.

• Convergence Security Journal
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• v.7 no.2
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• pp.17-25
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• 2007

In this paper, an algorithm that provisions proportional differentiation of packet delays is proposed with an objective for enhancing quality of service (QoS) in future packet networks. It features an adaptive scheme that adjusts the target delay every time slot to compensate the deviation from the target delay which is caused by the prediction error on the traffic to be arrived in the next time slot. It predicts the traffic to be arrived at the beginning of a time slot and measures the actual arrived traffic at the end of the time slot. The difference between them is utilized to the delay control operation for the next time slot to offset it. As it compensates the prediction error continuously, it shows superior adaptability to the bursty traffic as well as the exponential rate traffic. It is demonstrated through simulations that the algorithm meets the quantitative delay bounds and shows superiority to the traffic fluctuation in comparison with the conventional non-adaptive mechanism. The algorithm is implemented with VHDL on a Xilinx Spartan XC3S1500 FPGA and the performance is verified under the test board based on the XPC860P CPU.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.6
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• pp.879-888
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• 1999

A Study on the ARQ scheme of data error control is important for more reliable information transmission. Since performance difference is large by the long transmission delay time in satellite communication, the performances of SR ARQ and conventional type-I hybrid ARQ with fixed code rate are investigated by using the parameters of packet length, channel capacity, BER, and transmission delay time especially. BCH code is used in type-I hybrid ARQ for FEC method. This paper presents the throughput analyses according to such various parameters as BCH code rate, window size, data rate and round-trip delay time. Especially we derive a performance equation of type-I hybrid ARQ with the factor of the transmission delay time using the equation of SAW ARQ. Also, the performance of type-I hybrid ARQ specially considering transmission delay time is analyzed through numerical analysis and computer simulation so we can get a important characteristics variation.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.1
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• pp.13-21
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• 2005

This paper presents a fuzzy model-based approach for synchronization of time-delay chaotic system with input saturation. Time-delay chaotic drive and response system is respectively represented by Takagi-Sugeno (T-S) fuzzy model. Specially, the response system contains input saturation. Using the unidirectional linear error feedback and the parallel distributed compensation (PDC) scheme, we design fuzzy chaotic synchronization system and analyze local stability for synchronization error dynamics. Since time-delay in the transmission channel always exists, we also take it into consideration. The sufficient condition for the local stability of the fuzzy synchronization system with input saturation and time-delay is derived by applying Lyapunov-Krasovskii theory and solving linear matrix inequalities (LMI's) problem. A numerical example is given to demonstrate the validity of the proposed approach.