• Journal of Communications and Networks
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• 제18권2호
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• pp.246-260
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• 2016

A major challenge achieving scalable access control for a large number of subscribers in a public broadcast is to distribute key update messages reliably to all stateless receivers. However, in a public broadcast, the rekeying messages can be dropped or compromised during transmission over an insecure broadcast channel, or transmitted to receivers while they were off-line. In this study, we propose a novel group key management scheme. It features a mechanism to allow legitimate receivers to recover the current group key, even if they lose key update messages for long-term sessions. The scheme uses short hint messages and member computation. Performance analysis shows that the proposed scheme has the advantages of scalability and efficient rekeying compared to previous reliable group key distribution schemes. The proposed key management scheme targets a conditional access system in a media broadcast in which there is no feedback channel from receivers to the broadcasting station.

• ETRI Journal
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• 제44권6호
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• pp.925-935
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• 2022

In this study, we propose a limited feedback-based frequency divided group beamforming with sparse space-frequency transmit diversity coded orthogonal frequency division multiplexing (OFDM) system for ultrareliable low latency communication (URLLC) scenario. The proposed scheme has several advantages over the traditional hybrid beamforming approach, including not requiring downlink channel state information for baseband precoding, supporting distributed multipoint transmission structures for diversity, and reducing beam sweeping latency with little uplink overhead. These are all positive aspects of physical layer characteristics intended for URLLC. It is suggested in the system to manage the multipoint transmission structure realized by distributed panels using a power allocation method based on cooperative game theory. Link-level simulations demonstrate that the proposed scheme offers reliability by achieving both higher diversity order and array gain in a nonline-of-sight channel of selectivity and limited spatial scattering.

• 전자공학회논문지S
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• 제35S권10호
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• pp.42-51
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• 1998

본 논문은 CL (ConnectionLess) 가입자와 CL 서버간, CL 서버간, 그리고 종단간 CL가입자간 궤한 루프와 CL서버의 헤더 변환 테이블을 이용하여CL 중첩망의 폭주 제어 방안을 제안한다. ITU-T(International Telecommunication Union-Telecommunication)에 의하여 정의된 CBDS(Connectionless Broadhand Data Service)을 위한 CL 중첩망은 프레임을 라우팅해 주는 CL 서버와 CL 가입자와 CL서버 또는 CL 서버를 연결해주는 링크들로 구성된다. 이와 같은 CL 중첩망에서, 두 종류의 폭주, 즉. CL 링크 폭주와 CL 서버폭주가 일어날 수 있다. 본 논문에서 두 종류의 폭주를 해결할 수 있는 방안을 제시한다. 링크-바이-링크 방법[18]은 CL가입자와 CL서버간 또는 CL 서버간 ATM 계층의 ABR(Available Bit Rate) 궤환 루프와 CL 서버의 헤더 변환 테이블을 이용한다. 그러나 이 방법은 출력 가상 채널의 폭주 발생시 링크를 통해 전송되는 모든 트래픽에 영향을 주게 되어 폭주에 관여하지 않은 트래픽에게도 영향을 주어 이 트래픽이 출력되는 출력 가상 채널의 링크 이용도가 떨어지게 된다. 이와 같은 단점을 보완하기 위하여 본 논문에서 제한한 하이브리드 방법은 링크-바이-링크 방법의 ABR 궤환 루프, CL 계층의 종단의 CL 가입자간 궤환 루프, 그리고 헤더 변환 테이블을 이용한 폭주 상태표를 이용한다. 이 방안은 링크-바이-링크 루프와 헤더 변환 테이블을 이용하여 폭주에 즉시 대처하고, 다음에 종단간 루프를 이용하여 실제 폭주에 관여한 CL 가입자의 전송속도를 조절하는 것이다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 추계종합학술대회 논문집(1)
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• pp.381-384
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• 2000

In this paper, we designed and fabricated a low noise amplifier which can be used in W-CDMA. For improving input VSWR and stability an emitter inductance series feedback was used, and for acquiring higer linearity at low current DC bais by-passing method was used. Fabricated low noise amplifier had 15.33 ㏈ power gain, 2.17 ㏈ NF, -9.53 ㏈ $S_{11}$ and -35.91 ㏈ $S_{22}$ at 2.16 GHz, and +5.34 ㏈m II $P_{ 3}$ at 10 MHz channel spacing.g.g.g.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.3-5
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• 2007

This paper presents decision feedback equalizers using a recurrent neural network trained algorithm using extended Kalman filter(EKF) and sigma-point Kalman filter(SPKF). EKF is propagated, analytically through the first-order linearization of the nonlinear system. This can introduce large errors in the true posterior mean and covariance of the Gaussian random variable. The SPKF addresses this problem by using a deterministic sampling approach. The features of the proposed recurrent neural equalizer And we investigate the bit error rate(BER) between EKF and SPKF.

• 제어로봇시스템학회지
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• 제17권2호
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• pp.27-35
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• 2011

This paper presents the state of the art of control strategies for bilateral teleoperation systems under time delays. In the bilateral teleoperation that has force feedback, the time delay in the communication channel is the main source of instability. To cope with this problem. a number of control methods have been proposed. Among many control strategies. key aspects of the recent passivity-based methods are mainly summarized for approaches with wave variables. PO/PC (passivity observer/passivity controller), simple PD, and energy bounds.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 ITC-CSCC -3
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• pp.1920-1923
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• 2002

This paper proposes an impulse response shortening algorithm applicable to decision feedback equalization of single carrier wideband signal. When he impulse response shortening methods for narrowband signaling are applied to single carrier wideband signals, they result in noise enhancement problem, significantly deterioriting the receiver performance. This problem can be alleviated by educing the eigenvalue spread ratio of the impulse response, which can be achieved by adding additive white noise with small variance to the impulse response of the channel. The performance of the proposed scheme is verified by computer simulation.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2006년도 하계종합학술대회
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• pp.143-144
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• 2006

This paper presents an adaptive OFDM system with multistep predictor to effectively compensate multiple feedback delays. The proposed scheme adaptively changes the modulation order per subcarrier based on the predicted CSI to improve data capacity and system performance.

• Journal of Communications and Networks
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• 제9권3호
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• pp.213-218
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• 2007

Methods for symbol-by-symbol channel feedback and adaptation of symbol durations have been recently proposed. In this paper, we quantitatively analyze the gain in error-constrained data throughput due to such an extremely rapid adaptation of symbol durations to fast-time-varying channels. The results show that a symbol-by-symbol adaptation can achieve a throughput gain by orders of magnitude over a frame-by-frame adaptation.

• 한국자기학회지
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• 제5권5호
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• pp.395-398
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• 1995

For the core loss measurement under arbitrary waveform of magnetic induction, we have constructed a single sheet core loss measuring system which consists of yoke apparatus for single sheet of $10\;cm{\times}10\;cm$, arvitrary waveform synthesizer, B-feedback system, and two channel transient recorder. Using the constructed measuring system, we can measure core loss including higher harmonics up to 2 kHz. Core loss of non-oreinted electrical steel was increased exponentially when higher harmonic frequency was increased or amplitude of harmonic induction was increased.