• 인터넷정보학회논문지
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• 제8권4호
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• pp.41-49
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• 2007

EPON(Ethernet Passive Optical Network)는 적은 비용으로 고품질 서비스를 제공하기 위한 차세대 기술로써, EPON을 구성하는 모든 ONU(Optical Network Unit)들은 한정된 업링크 채널을 나누어 사용한다. 대용량 LAN에 사용자들의 대역폭 요구를 충족시키기 위해서, OLT(Optical Line Terminal)는 효과적인 방법으로 업링크 채널의 시간슬롯을 각 ONU에게 분할 할당한다. 본 논문에서는 효율적인 업링크 채널의 시간슬롯 분배(대역폭 할당)를 위해 기존 연구 IPACT(Interleaved Polling with Adaptive Cycle Time)와 SLICT(Sliding Cycle Time)방식에 대해 살펴보고, 새로운 대역폭 할당 방식인 DRSM(Dynamic Right Sizing of Maximum-windows)을 제안한다. 이 방식은 과거 모든 ONU에게 할당된 대역폭 정보를 기반으로 다음 구간에서 ONU에 할당 가능한 최대 대역폭을 계산하고, 계산된 최대 전송 가능 대역폭과 ONU의 대역폭 요구량으로 각 ONU의 전송 윈도우의 크기를 결정한다. 제안한 방식은 모든 ONU의 대역폭 요구를 허용 범위 내에서 최대한 충족시키고, ONU들간 균등한 대역폭 할당을 추구한다.

• Journal of Communications and Networks
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• 제12권1호
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• pp.52-66
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• 2010

Since large objects consume substantial resources, web proxy caching incurs a fundamental trade-off between performance (i.e., hit-ratio and latency) and overhead (i.e., resource usage), in terms of caching and relaying large objects to users. This paper investigates how and to what extent the current dedicated-server based web proxy caching scheme is affected by large file transfers in a high bandwidth campus network environment. We use a series of trace-based performance analyses and profiling of various resource components in our experimental squid proxy cache server. Large file transfers often overwhelm our cache server. This causes a bottleneck in a web network, by saturating the network bandwidth of the cache server. Due to the requests for large objects, response times required for delivery of concurrently requested small objects increase, by a factor as high as a few million, in the worst cases. We argue that this cache bandwidth bottleneck problem is due to the fundamental limitations of the current centralized web proxy caching model that scales poorly when there are a limited amount of dedicated resources. This is a serious threat to the viability of the current web proxy caching model, particularly in a high bandwidth access network, since it leads to sporadic disconnections of the downstream access network from the global web network. We propose a peer-to-peer cooperative web caching scheme to address the cache bandwidth bottleneck problem. We show that it performs the task of caching and delivery of large objects in an efficient and cost-effective manner, without generating significant overheads for participating peers.

• IEIE Transactions on Smart Processing and Computing
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• 제6권4호
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• pp.276-280
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• 2017

This paper presents computationally efficient image compression for wireless transmission of high-definition video, to adaptively utilize available channel bandwidth and improve image quality. The method indirectly predicts an unknown available channel bandwidth by monitoring encoder buffer status, and adaptively controls a quantization parameter to fully utilize the bandwidth. Experimental results show that the proposed method is robust to variations in channel bandwidth.

• Journal of electromagnetic engineering and science
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• 제13권3호
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• pp.178-185
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• 2013

This paper introduces a high-efficiency, high-gain, broadband quasi-Yagi antenna, and its four-element array for use in 60-GHz wireless communications. The antenna was fed by a microstrip-to-slotline transition consisting of a curved microstripline and a circular slot to allow broadband characteristics. A corrugated ground plane was employed as a reflector to improve the gains in the low-frequency region of the operation bandwidth, and consequently, to reduce variation. The single antenna yielded an impedance bandwidth of 49 to 69 GHz for $|S_{11}|$ <-10dB and a gain of >12.0 dBi while the array exhibited a bandwidth of 52 to 68 GHz and a gain greater than 15.0 dBi. Both proposed designs had small gain variations (${\pm}0.5$ dBi) and high radiation efficiency (>95%) in the 60-GHz bands. The features of the proposed antenna were validated by designing, fabricating, and testing a scaled-up configuration of the single antenna at the 15-GHz band. The measurements resulted in an impedance bandwidth of 13.0 to 17.5 GHz for $|S_{11}|$ <-10dB, a gain of 10.1 to 13.2 dBi, and radiation efficiency in excess of 88% within this bandwidth. Additionally, the 15-GHz antenna yielded quite symmetric radiation profiles in both E- and H-planes, with a high front-to-back ratio.

• 한국음향학회지
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• 제23권6호
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• pp.481-487
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• 2004

본 논문에서는 대역폭 계층 구조의 광대역 음성 부호화기 구조와 이를 위한 상위 대역 부호화기를 제안한다. 상위 대역 부호화기는 상위 대역 신호를 다수의 주파수 밴드로 분할하고, 각 밴드 신호를 DCT 변환하여 양자화한다. DCT 계수는 크기와 부호로 분리하여 독립적으로 처리하며, 각각의 특성에 적합한 양자화 방법을 개발하여 성능을 향상시킨다. 또한, 하위 대역의 부호화된 이득 파라미터를 상위 대역의 양자화에 이용함으로써 부호화 성능을 향상시키는 방법을 제안한다. G.729E로 하위 대역을 부호화하고 제안한 부호화기로 상위 대역을 처리하는 대역폭 계층 구조의 광대역 음성 부호화기를 개발하였고, 주관적 음질을 측정하여 24kbps G.722.1보다 우수한 음질을 가지는 것을 확인하였다.

• 한국통신학회논문지
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• 제25권5A호
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• pp.593-601
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• 2000

다중 대역 확산 CDMA 시스템에서 확산 대역폭과 레일리 페이딩 채널의 지연 확산에 대한 다중 선택 결합 RAKE 수신기의 성능을 분석하여, 지연 확산이 다른 여러 채널 환경에서 RAKE 수신기 차수에 따른 전체 수신 에너지와 다중 경로 다이버시티 이득간의 상호 관계를 규명하였다. 분석 결과, 지역 확산이 작은 환경에서의 광대역 확산을 이용하여 확산 대역폭을 증가시키는 것이 더 좋은 성능을 나타냈다. 높은 차수와 낮은 차수의 선택 결합기간의 성능 비교 결과, 확산 대역폭이 증가할수록 그 성능 차가 더 크게 나타났다. 또한, 확산 대역폭을 일정수준 이상으로 증가시킬 경우 수신 성능이 저하되었으며, 각 채널 환경에서의 최적 확산 대역폭은 채널의 지연 확산이 증가할수록 감소하였다.

• 한국통신학회논문지
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• 제36권4A호
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• pp.380-387
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• 2011

While mobile IPTV services are supported through the mobile WiMAX networks, there must need some guaranteed bandwidth for the IPTV services especially if IPTV and non-IPTV services are simultaneously supported by the mobile WiMAX networks. The quality of an IPTV service definitely depends on the allocated bandwidth for that channel. However, due to the high quality IPTV services and to support of huge non-IPTV traffic over mobile WiMAX networks, it is not possible to guarantee the sufficient amount of the limited mobile WiMAX bandwidth for the mobile IPTV services every time. A Service Level Agreement (SLA) between the mobile IPTV service provider and mobile WiMAX network operator to reserve sufficient bandwidth for the IPTV calls can increase the satisfaction level of the mobile IPTV users. In this paper, we propose a SLA negotiation procedure for mobile IPTV users over mobile WiMAX networks. The Bandwidth Broker controls the allocated bandwidth for IPTV and non-IPTV users. The proposed dynamically reserved bandwidth for the IPTV services increases the IPTV user's satisfaction level. The simulation results state that, our proposed scheme is able to provide better user satisfaction level for the IPTV users.

• International Journal of Control, Automation, and Systems
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• 제6권6호
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• pp.948-953
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• 2008

In high dynamic situations, the GPS carrier tracking loop requires a wide bandwidth to track a carrier signal because the Doppler frequency changes more rapidly with time. However, a wide bandwidth allows noises within the bandwidth of the tracking loop to pass through the loop filter. As these noises are used in the numerical controlled oscillator(NCO), the carrier tracking loop of a GPS receiver shows a degraded performance in high dynamic situations. To solve this problem, an adaptive two-stage Kalman filter, which offers the NCO a less noisy phase error, can be used. This filter is based on a carrier phase dynamic model and can adapt to an incomplete dynamic model and a quickly changed Doppler frequency. The performance of the proposed tracking loop is verified by several simulations.

• 한국전기전자재료학회논문지
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• 제17권7호
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• pp.770-775
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• 2004

Although $High-T_c $superconducting HTS antennas have high efficiency and high gain, narrow bandwidth due to the high Q is the major limitation for application of satellite communication and mobile communication. Defining bandwidth as the frequency range over which standing wave ratio (SWR) is 2:1 or less, HTS antenna bandwidths are typically less than 1 %. Thus considerable effort has been focused on developing HTS antennas for broadband operation. In this work the HTS antenna array, using the bipin antenna which consisted of two triangle-radiation patches, was designed and fabricated using a ${YBa}_2{Cu}_3{O}_7x (YBCO)$ superconducting thin film on a MgO substrate for broadband operation. Also gold antennas with the same dimension as our HTS antennas were fabricated on the MgO substrate for the comparison. Experimental results for both antennas were reported in terms of radiation patterns, return losses, bandwidths and other various characteristics. The center frequency of HTS antennas was 20.28 GHz and the bandwidth obtained was significant 10 %.

• ETRI Journal
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• 제34권6호
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• pp.942-945
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• 2012

A high-speed traveling-wave photodetector (TWPD) with an InGaAs absorber is designed and realized. The bandwidth of the TWPD is measured using electro-optic sampling techniques. The bandwidth is 410 GHz, which shows that the RC limitation is overcome. While the TWPD shows a low responsivity of 0.06 A/W at 1,550 nm, this value can be improved through further optimization of the structure without a sacrifice in bandwidth.