• ETRI Journal
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• 제37권4호
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• pp.677-684
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• 2015

Recently, orthogonal frequency-division multiplexing (OFDM) was applied to VLC systems owing to its high rate capability. On the other hand, a real-valued unipolar OFDM signal for VLC significantly reduces bandwidth efficiency. For practical implementation, channel estimation is required for data demodulation, which causes a further decrease in spectral efficiency. In addition, the large fluctuation of an OFDM signal results in poor illumination quality, such as chromaticity changes. This paper proposes a spectrally efficient method based on a hidden-pilot-aided precoding technology for VLC with less flickering than a conventional OFDM-based method. This approach can obtain channel information without any loss of bandwidth efficiency while ensuring illumination quality by reducing the flickering effect of an OFDM-based VLC. The simulation results show that the proposed method provides a 6.4% gain in bandwidth efficiency with a 4% reduction in flicker compared to a conventional OFDM-based method.

• 한국광학회:학술대회논문집
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• 한국광학회 2005년도 제16회 정기총회 및 동계학술발표회
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• pp.160-161
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• 2005

A critical issue in implementing efficient Ethernet passive optical network(EPON) System is the bandwidth allocation algorithm. The overall goal of bandwidth allocation is to effectively and fairly perform scheduling of time slots between ONUs in EPON System. We propose a new algorithm of dynamic bandwidth allocation for improved bandwidth efficiency in EPON system.

• 전기전자학회논문지
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• 제22권4호
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• pp.1019-1024
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• 2018

In this paper, we suggest a combined cost function to find out the optimal operation of an envelope tracking system, and evaluated its performance with Quadrature Amplitude Modulation (QAM) waveform, with which envelope tracking coefficients for the peak drain efficiency and the bandwidth of power amplifiers are determined. Based on the classical envelope tracking theory, the operation of the supply modulator, which is a key part of the envelope tracking process, is modeled and analyzed mathematically. Then characteristics of the modulator by setting envelope shaping function as a cubic polynomial and sweeping the coefficients of this function was analyzed. By sweeping the coefficients, efficiency and bandwidth at each condition with 64-QAM signal was used to obtain optimal point of the supply modulator. Compared to the conventional shaping functions, the optimized function showed the bandwidth reduction by 12.7 percent point while the efficiency was maintained.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 통신소사이어티 추계학술대회논문집
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• pp.149-152
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• 2003

In this paper, we propose a scheme that applies to the VoIP application based on H.323 protocol to enhance the bandwidth efficiency. We multiplex the audio and video stream. In this scheme, audio frame is carried with video stream. And we applies not only multiplexing but also (in header compressing to the real audio/video stream to increase the bandwidth efficiency. With the multiplexing and RTP header compressing, we gain the bandwidth efficiency. In the finite network environment, We can assign bandwidth to other users who want to use other service. and other VoIP users. If we can apply the real time network situation to the our VoIP application, we can get more efficient performance.

• 한국멀티미디어학회논문지
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• 제10권12호
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• pp.1632-1644
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• 2007

Wireless Mesh Networks aim to attain large connectivity with minimum performance degradation, as network size is increase. As such, scalability is one of the main characteristics of Wireless Mesh Networks that differentiates it from other wireless networks. This characteristic creates the need for bandwidth efficiency strategies to ensure that network performance does not degrade as the size of the network increase. Several researches have been done to realize mesh networks. However, the researches conducted were mostly focused on a per TCP/IP layer basis. Also, the studies on bandwidth efficiency and bandwidth improvement are usually dealt with as separate issues. This paper aims to simultaneously study bandwidth efficiency and improvement. Aside from optimizing the bandwidth given a fixed capacity, the capacity is also increased using results of physical layer studies. In this paper, the capacity is improved by using the concept of non-overlapping channels for wireless communication. A channel allocation scheme is conceptualized to choose the transmission channel that would optimize the network performance parameters with consideration of chosen Quality of Service (QoS) parameters. Network utility maximization is used to optimize the bandwidth after channel selection. Furthermore, a routing scheme is proposed using the results of the network utilization method and the channel allocation scheme to find the optimal path that would maximize the network gain.

• 한국통신학회논문지
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• 제30권6A호
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• pp.455-464
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• 2005

본 논문에서는 OFDMA, TDD 전송방식을 채택한 WiBro 시스템 표준의 resource 할당 알고리듬을 시뮬레이션을 통해 구현하였고, bandwidth efficiency를 보다 더 높이기 위한 알고리듬을 제안하였다. 제안하는 알고리듬은, 변조지수를 최대로 하여 채널 이득이 큰 subchannel부터 작은 subchannel 순서로 비트를 할당한다. 이 때 subchannel의 수를 증가시킴으로 인해 전송되어야 할 power가 증가하는데, 이 power가 available power를 넘는 순간에 할당되는 subchannel의 변조지수를 조정하여 available power를 넘지 않게 하는 방법이다. 기존의 greedy algorithm이나 WiBro 시스템과 비교하였을 때, 제안하는 알고리듬을 적용할 경우 power가 제한되어 있는 것으로 인해 사용되는 subchannel의 수가 현저히 작아져서 bandwidth efficiency 측면에서는 좋은 성능을 나타내게 한다. 하지만 channel attenuation이 큰 환경에서는 최대 throughput이 떨어지는 문제점이 발생하는데, 타 시스템에서 지원하는 만큼의 throughput을 보장하는 문제 역시 중요하기 때문에, 이를 극복하기 위해 이 경우에는 available power를 추가 할당하여 사용되는 subchannel수를 증가시켰다. 이 경우, 기존 시스템과 비슷한 throughput을 보장하면서 bandwidth 이득은 더 높게 얻을 수 있음을 확인하였다.

• 한국산학기술학회논문지
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• 제10권7호
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• pp.1601-1607
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• 2009

일반적으로 무선 통신에 널리 사용되는 직교 변조 (Orthogonal Modulation) 방식은 대역폭 효율 (Bandwidth Efficiency)이 지나치게 떨어져 대용량의 데이터를 전송하기에는 부적절하다. 따라서 본 논문에서는 기존의 직교 변조방식의 대역폭 효율을 증가시키기 위해 다중 부호 전송 개념을 트랜스 직교 변조 방식에 적용하여 대용량 데이터를 전송하는 다중 부호 트랜스 (이진) 직교 변조 (Multi-Code Trans-(Bi-)Orthogonal Modulation) 방식을 제안한다. 제안된 다중 부호 트랜스 (이진) 직교 변조는 직교 변조에 비해 대역폭 효율 측면에서 2배 이상의 개선을 얻을 수 있고 수신기의 복잡도 측면에 있어서도 2배 이상의 개선을 얻을 수 있다. 제안된 다중 부호 트랜스 (이진) 직교 변/복조 방식은 고속 데이터 율을 제공해야 하는 디지털 무선 통신 시스템 (멀티미디어 통신 시스템, 고속 무선 개인 영역 네트워크)의 물리층으로 사용될 수 있다.

• 한국IT서비스학회지
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• 제7권1호
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• pp.131-149
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• 2008

Bandwidth Trading(BT) represents a potential market with over 1 trillion USD across the world and high growth potential. BT is also likely to accelerate globalization of the telecommunications industry and massive restructuring driven by unbundling rush. However, systematic researches on BT remain at an infant stage. This study starts with structure analysis of the Internet industry, and discusses significance of Internet interconnection with respect to BT Issues. We also describe the bandwidth commoditization trends and review technical requirements for effective Internet interconnection with BT capability. Taking a step further, this study explores the possibility of improving efficiency of network providers and increasing user convenience by developing an architectural prototype of Hub-&-Spoke interconnection model required to facilitate BT. The BT market provides an Innovative base to ease rigidity of two-party contract and Increase service efficiency. However, as fair, efficient operation by third party is required, this research finally proposes an exchanging hub named NIBX(New Internet Business eXchange).

• Journal of electromagnetic engineering and science
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• 제16권1호
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• pp.52-56
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• 2016

This paper suggests a class-F power amplifier with split open-end stubs to provide a broadband high-efficiency operation. These stubs are designed to have wide bandwidth by splitting wide open-end stubs into narrower stubs connected in shunt in an output matching network for class-F operation. In contrast to conventional wideband class-F designs, which theoretically need a large number of matching lines, this method requires fewer transmission lines, resulting in a compact circuit implementation. In addition, the open-end stubs are designed with slant ends to achieve additional wide bandwidth. To verify the suggested design, a 10-W class-F power amplifier operating at 1.7 GHz was implemented using a commercial GaN transistor. The measurement results showed a peak drain efficiency of 82.1% and 750 MHz of bandwidth for an efficiency higher than 63%. Additionally, the maximum output power was 14.45 W at 1.7 GHz.

• 한국정보통신학회논문지
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• 제10권7호
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• pp.1214-1221
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• 2006

헤더 압축 기술은 기존의 일반적인 패킷 데이터의 비효율적인 오버 헤드를 줄이기 위한 방안으로 제안되었다. 특히 음성과 같은 실시간 미디어 스트림 경우에는 더욱 큰 오버헤드율을 보이게 되는데, 헤더 압축을 통해 보다 높은 대역폭 효율을 얻을 수 있다. 본 논문에서는 PHR(periodic Header Refresh) 방법과 HR(Header Request) 방법 의 두가지 에러 복구 기법 에 관하여 각각 성능 분석을 실시하였다. 그 결과로 Overhead Rate, Bandwidth Gain, 그리고 Bandwidth Efficiency 등의 분석 결과가 제시되었다.