• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7B
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• pp.1296-1304
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• 1999

In this paper, we propose an enhanced usage parameter control algorithm, which is one of the preventive traffic control method in ATM networks. Proposed algorithm is based on the cell loss priority bit in the ATM cell header. This algorithm can eliminate the measurement phasing problem in cell conformance testing in ATM networks. Proposed algorithm can minimize the cell loss ratio of high priority cell(CLP = 0) and resolve the burstiness of cells which may be introduced in traffic multiplexing and demultiplexing procedure. For the performance evaluation, we simulate the proposed algorithm with discrete time input traffic model, the results show that the performance of proposed algorithm is better than that of ITU-T usage parameter control algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.2A
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• pp.130-136
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• 2002

It is required to control the picture quality among video sources when the multiple video sources are together transmitted through the channel of fried bandwidth such as satellite and terrestrial broadcasting. This paper presents a control method to keep the uniform picture quality among the video sources. We first find a model of distortion and titrate far the multiplexing system of multiple sources. Then we allocate the bitrate to each source for uniformly divided picture quality among the sources by using the distortion-bitrate relationship for the real-time implementation without time delay. It is shown by simulation that the proposed quality control method can keep almost uniform picture quality among the sources in comparison to the conventional control method.

• ETRI Journal
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• v.37 no.1
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• pp.11-20
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• 2015

This paper deals with optimal power allocation for channel estimation of orthogonal frequency-division multiplexing uplinks in time-varying channels. In the existing literature, the estimation of time-varying channel response in an uplink environment can be accomplished by estimating the corresponding channel parameters. Accordingly, the optimal power allocation studied in the literature has been in terms of minimizing the mean square error of the channel estimation. However, the final goal for channel estimation is to enable the application of coherent detection, which usually means high spectral efficiency. Therefore, it is more meaningful to optimize the power allocation in terms of capacity. In this paper, we investigate capacity with imperfect channel estimation. By exploiting the derived capacity expression, an optimal power allocation strategy is developed. With this developed power allocation strategy, improved performance can be observed, as demonstrated by the numerical results.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.3
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• pp.434-439
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• 2002

본 연구는 파장 분할 다중화(WDM：Wavelength Division Multiplexing) 방식 전송 시스템 (Transmission System)에 사용되는 어븀 첨가 광섬유 증폭기(EDFA : Erbium-Doped Fiber Amplifier)의 이득 제어(Gain Control) 방법에 관한 것으로 어븀 첨가 광섬유에서 상호 이득 포화(Cross Gain Saturation) 현상, 이득 비동질 (Gain In-homogeneity) 특성, 그리고 어븀 이온의 밀도 반전(Population Inversion)의 변화 에 의해 출력되는 다 파장 광 신호들의 광 세기가 각기 다르게 출력되는 현상을 고출력을 내도록 구성된 어븀 첨가 광섬유 증폭기와 고속 제어기를 구성하여 위 현상들을 억제하며 이득을 제어하기 위한 레이저 다이오드(Laser Diode : LD)의 제어전압 조사하고, 얻어진 결과들을 토대로 이득 제어에 적합한 방법을 제시하고 제어기를 설계한다.

• Journal of Astronomy and Space Sciences
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• v.12 no.1
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• pp.54-65
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• 1995

We present a design study for a remote sensing camera system which can be operated in multi-channel mode simultaneously with several bandpass filters. The camera control electronics is based on the multiplexed driving concept, which can provide a variety of flexibility for system control parameters and its individual optimisation. The design can also be applied to any system with linear sensors or frame sensors according to its functional requirements. The system design parameters have been examined, including modification of driving waveforms for different types of sensors, waveforms for low-nosie readout circuit in analog chain, and synchronisation with other signal processing.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.55 no.5
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• pp.199-204
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• 2006

To develop a safety-critical network in nuclear power plants that puts more stringent requirements than the competitive commercial ones do, we establish four design criteria - deterministic communication, explicit separation/isolation structure, reliability, verification & validation. According to those design criteria, the fundamental design elements are chosen as follows - a star topology, point-to-point physical link, connection-oriented link control and fixed allocation access control. After analyzing the design elements, we also build a communication architecture with TDM (Time Division Multiplexing) bus switching scheme. Finally, We develop a DDCNet (Deterministic Data Communication Network) based on the established architecture. The DDCNet is composed of 64 nodes and guarantees the transmission bandwidth of 10Mbps and the delay of 10 msec for each node. It turns out that the DDCNet satisfies the aforementioned design criteria and can be adequately utilized for our purpose.

• Journal of information and communication convergence engineering
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• v.1 no.4
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• pp.194-198
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• 2003

Recently, the use of TCP/IP protocols over wireless LANs poses significant problems. In this paper, we have analyzed transmission control protocol (TCP) packet transmission time for mobile IP over wireless local area networks (LANs) using a proposed a new random backoff scheme. We call it as a proxy backoff scheme. It is considered the transmission time of TCP packet on the orthogonal frequency division multiplexing (OFDM) in additive white gaussian noise (AWGN) channel. From the results, a proposed proxy backoff scheme produces a better performance than an original random backoff in mobile IP over wireless LANs environment. Also, in OFDM/quadrature phase shift keying (QPSK) medium access control (MAC), we have obtained that the transmission time in wireless channel decreases as the TCP packet size increases.

• Proceedings of the KIEE Conference
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• 2004.07d
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• pp.2610-2612
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• 2004

The polyphase filter-based orthogonal frequency division multiplexing (PF-OFDM) is proposed in [1]. It provides more efficient data transmission mechanism than the classical OFDM method. However, the channel estimation mechanism in the classical OFDM system such as the cyclic prefix can not be applied straightforwardly, since the received signal contains unpredictable terms. Therefore, the PF-OFDM system requires a complicated channel estimation scheme when it works on the multipath fading communication channel. In this paper, we proposed a pilot-symbol aided channel estimation algorithm suitable for the PF-OFDM system which efficiently deals with the unpredictable terms and verified its performance through a series of computer simulations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.6
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• pp.1101-1112
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• 2011

The Multiuser Eigenmode Transmission (MET) has generated significant interests in literature due to its optimal performance in linear precoding systems. The MET can simultaneously transmit several spatial multiplexing eigenmodes to multiple users which significantly enhance the system performance. The maximum number of users that can be served simultaneously is limited due to the constraints on the number antennas, and thus an appropriate user selection is critical to the MET system. Various algorithms have been developed in previous works such as the enumerative search algorithm. However, the high complexities of these algorithms impede their applications in practice. In this paper, motivated by the necessity of an efficient and effective user selection algorithm, a low complexity recursive user selection algorithm is proposed for the MET system. In addition, the fairness of the MET system is improved by using the combination of the proposed user selection algorithm and the adaptive Proportional Fair Scheduling (PFS) algorithm. Extensive simulations are implemented to verify the efficiency and effectiveness of the proposed algorithm.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.293-297
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• 2002

본 연구는 파장 분할 다중화(WDM： Wavelength Division Multiplexing) 방식 전송 시스템 (Transmission System)에 사용되는 어븀 첨가 광섬유 증폭기(EDFA： Erbium-Doped Fiber Amplifier)의 이득 제어(Cain Control) 방법에 관한 것으로 어븀 첨가 광섬유에서 상호 이득 포화 (Cross Cain Saturation) 현상, 이득 비동질(Cain In-homogeneity) 특성, 그리고 어븀 이온의 밀도. 반전(Population Inversion)의 변화에 의해 출력되는 다 파장 광 신호들의 광세기가 각기 다르게 출력되는 현상을 고출력을 내도록 구성된 어븀 첨가 광섬유 증폭기와 고속 제어기를 구성하여 위 현상들을 억제하며 이득을 제어하기 위한 레이저 다이오드(Laser Diode : LD)의 제어전압 조사하고, 얻어 진 결과들을 토대로 이득 제어에 적합한 방법을 제시하고 제어기를 설계한다.