• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.12
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• pp.2812-2817
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• 2013

In this paper, an outage probability for the best relay selection in decode-and-forward relaying systems in the presence of interference is analyzed over Rayleigh fading channels. Based on the outage performance results, we propose a method to determine effective relay candidates for the best relay selection, where the effective relay candidates represent the relays except for relays that make no contribution to improving the performance. in all possible relays given in the system. By determining the effective relay candidates, the feedback overhead of channel state information and the energy consumption of relays can be significantly reduced while minimizing the performance degradation. In this paper, we provide important parameters that affect the determination of the effective relay candidates.

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1997.11a
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• pp.211-220
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• 1997

체비셰프 삽입손실법을 이용하여 선택도가 높은 대역 여파기를 설계한다. 체비셰프 방식은 차단주파수 근방 곡선의 경사가 버터워쓰에 비해 급격하게 떨어지는 특징을 가진다. 인접 채널의 간섭을 최소화 하기위해 차단 대역의 감쇄를 70db이상으로 유지한다. 중심주파수는 885MHz에서 통과대역폭 10MHz의 여파기를 제작하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.370-377
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• 2004

In this paper, we present an adaptive modulation technique for orthogonal frequency division multiplexing (OFDM) for broadband wireless communications. Also, using improved channel prediction, we enhance the performance of adaptive OFDM in high mobility environments. Adaptive modulation technique has been shown to achieve reliable high-rate data transmission over frequency-selective fading channel when OFDM is employed. This scheme requires the accurate channel information between two stations for a better performance. In an outdoor high mobility environment, most of adaptive OFDM systems have to be given the channel information transmitted from the receiver. Even if it is possible, there is some delay. Moreover, the channel impulse response between two stations is very rapidly varied. If the channel information is obsolete at the time of transmission, then poor system performance will result. In order to solve this problem, we propose adaptive OFDM with improved channel predictor. The proposed bit allocation algorithm has a lower complexity and the proposed scheme mitigates the effect of channel delay. Robust approach is less sensitive to outdated channel information. Performance results show that the proposed scheme can achieve considerable performance enhancement.

• The KIPS Transactions:PartC
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• v.12C no.7 s.103
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• pp.1025-1030
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• 2005

Cooperative communications among users in multiple access wireless environments is an efficient way to obtain the powerful benefits of multi-antenna systems without the demand for physical arrays. This paper proposes a solution to optimize the weights of partnering users' signals for the minimum error probability at the output of maximum likelihood (ML) detector under the transmit power constraints by taking advantage of channel state information (CSI) feedback from the receiver to the transmitter. Simulation programs are also established to evaluate the performance of the system under flat Rayleigh fading channel plus AWGN (Additive White Gaussian Noise).

• Journal of Convergence Society for SMB
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• v.2 no.1
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• pp.25-31
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• 2012

Recently Wireless Communication technologies are widely used in Small And Medium Business fields. Wireless mesh networks have been studied as the next generation technology to solve problem of conventional wireless networks. Wireless mesh network uses a 802.11 when make up of network. mesh clients occurs Hard handover moving between ones. This increases the handover latency of the network mobility is a very great issues. Consequently, this paper propose a channel information previously methods to reduce the handover latency selective channels. Proposed scheme accounts for more than 90% of the probe delay to minimize the client had to move the mesh based on the old channel to retrieve information. Through simulation, the proposed scheme had shorter handover delay time than transitional full scan and selective scan. Through results of evaluation, the suggest PCISS scheme more fast 6.5% than transitional scheme.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.135-139
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• 2016

본 연구에서는 동역학적 격자기반 대정준 Monte Carlo (Kinetic Lattice Grand Canonical Monte Carlo, KLGCMC) 모의실험 방법을 이용하여 모델 이온채널 내에서 KCl과 HCl의 이온 전류를 시간의 함수로 구하였다. KLGCMC 모의실험 계산 결과로부터 이온채널의 양이온 선택성이 더 큰 것을 확인 할 수 있었다. 또한 모의실험 결과를 통해 각 이온의 확산계수가 전류에 미치는 영향을 확인 할 수 있었다. $H^+$ 이온은 농도가 매우 작음에도 확산계수가 커 전체 전류에 큰 영향을 미쳤다. 반면에 확산계수가 작은 $K^+$ 이온은 이온채널 안에서 쉽게 흐르지 못하고 정체 되며, $H^+$ 이온의 전류흐름을 방해하는 것을 확인 할 수 있었고, 이로 인해 이온전류의 패턴이 시간에 따라 변화함을 알 수 있었다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.6B
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• pp.579-585
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• 2002

The investigation into the effect of various feedback errors on system performance can help the robust feedback channel design and transmission of exact feedback channel information as well. In this paper, we address the algorithm that determines space combining weight vector maximizing received signal power at mobile on frequency flat fading channel and investigate the performance degradation by feedback channel delay in the FDD/CDMA systems employing transmit beamforming. We observe the effect of feedback channel delay corresponding to the number of transmit antennas and the temporal/spatial correlation of channel. The results show that performance is more sensitive to feedback delay with the larger number of antennas when fadings at transmit antennas are not spatially correlated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.905-911
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• 2005

We propose an efficient adaptive subcarrier selection scheme, in which the active subcarriers and their modulation and coding schemes (MCSs) are selected at the receiver, and subsequently conveyed to the transmitter using limited feedback We theoretically show that capacity maximization can be achieved by selecting subcarriers with highest signal-to-noise ratios (SNRs) and adapting the number of active subcarriers according to channel environments. Furthermore, an ordering based adaptive subcarrier selection algorithm is proposed to select the optimal active subcarriers with low complexity. Numerical results show that the proposed adaptive subcarrier selection scheme provides higher capacity than that obtained by water-filling approaches, even with limited feedback.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.143-149
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• 2022

In this paper, we evaluate the underwater frequency diversity communication performance of Selective Combination (SC) using Maximum Likelihood Estimation (MLE). In an underwater multipath frequency selective channel, destructive interference fading due to delay spread of a received signal affects the increase in error and Signal to Noise Ratio (SNR) variability of an underwater acoustic communication. Selective Combination frequency diversity using a single sensor is applied as a transmission performance improvement technique according to the frequency selectivity of a channel. In the sea experiment applying MLE for SC decision value extraction, we evaluate the performance of SC frequency diversity and MLE-SC frequency diversity. In experiment result, we confirm through experiment that the Bit Error Rate (BER) is relatively lower when the decision value extracted through MLE-SC is applied than when the SC decision value is fixed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.11
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• pp.1050-1057
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• 2012

Super Wi-Fi is a newly emerging wireless Internet technology, which constitutes Wi-Fi networks using TV white space. A key technical challenge in the Super Wi-Fi applications is how to provide a seamless Internet service even when a Super WiFi user should give up the channel in use to the active incumbent user which is activated in the same service area, preventing from the service continuity in Super Wi-Fi. In this paper, we propose a channel handover method to support service continuity of Super Wi-Fi, in which an AP selects a new operational channel and provides the channel information for MSs. Therefore, the AP and the MSs can carry out seamless handover for Super Wi-Fi service. A performance evaluation shows that the proposed scheme is superior to the conventional Wi-Fi in channel mobility delay.