• Title/Summary/Keyword: low bandwidth

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Clock Synchronization in Wireless Embedded Applications (무선 임베디드 환경에서의 시간 동기화)

  • No, Jin-Hong;Hong, Young-Sik
    • Journal of KIISE:Information Networking
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    • v.32 no.6
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    • pp.668-675
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    • 2005
  • With the proliferation of wireless network and the advances of the embedded systems, the traditional distributed systems begin to include the wireless embedded systems. Clock synchronization in the distributed systems is one of the major issues that should be considered for diverse Purposes including synchronization, ordering, and consistency. Many clock synchronization algorithms have been proposed over the years. Since clock synchronization in wireless embedded systems should consider the low bandwidth of a network and the poor resources of a system, most traditional algorithms cannot be applied directly. We propose a clock synchronization algorithm in wireless embedded systems, extending IEEE 802.11 standard. The proposed algorithm can not only achieve high precision by loosening constraints and utilizing the characteristics of wireless broadcast but also provide continuous time synchronization by tolerating the message losses. In master/slave structure the master broadcasts the time information and the stave computes the clock skew and the drift to estimate the synchronized time of the master. The experiment results show that the achieved standard deviation by the Proposed scheme is within the bound of about 200 microseconds.

Implementation of 10 Gb/s 4-Channel VCSELs Driver Chip for Output Stabilization Based on Time Division Sensing Method (시분할 센싱 기법 기반의 출력 안정화를 위한 10 Gb/s 4채널 VCSELs 드라이버의 구현)

  • Yang, Choong-reol;Lee, Kang-yoon;Lee, Sang-soo;Jung, Whan-seok
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.40 no.7
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    • pp.1347-1353
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    • 2015
  • We implemented a 10 Gb/s 4-channel vertical cavity surface emission lasers (VCSEL) driver array in a $0.13{\mu}m$ CMOS process technology. To enhance high current resolution, power dissipation, and chip space area, digital APC/AMC with time division sensing technology is primarily adopted. The measured -3 dB frequency bandwidth is 9.2 GHz; the small signal gain is 10.5 dB; the current resolution is 0.01 mA/step, suitable for the wavelength operation up to 10 Gb/s over a wide temperature range. The proposed APC and AMC demonstrate 5 to 20 mA of bias current control and 5 to 20 mA of modulation current control. The whole chip consumes 371 mW of low power under the maximum modulation and bias currents. The active chip size is $3.71{\times}1.3mm^2$.

The Effect of Clipping on the Spectrum and BER of IFDMA Signal with Pulse Shaping (파형정형된 IFDMA 신호에서 클리핑이 스펙트럼과 BER에 미치는 영향)

  • Park, Seung-Yong;Kim, Jeong-Goo
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.11C
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    • pp.1106-1112
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    • 2009
  • The SC-FDMA(single carrier-frequency division multiple access) was recently adopted as the uplink multiple access scheme from 3GPP LTE(3rd Generation Partnership Project Long Tenn Evolution) due to its low PAPR (Peak-to-averaged power ratio). The bandwidth of IFDMA(interleaved FDMA), one of the sub-carrier mapping methods of SC-FDMA, gets narrower as the roll-off factor of RRC(root raised cosine) filter decreases from 1 to 0, whereas its PAPR can increase significantly. In practice, to increase the power efficiency of an amplifier, signals with high PAPR undergo the process of clipping. Clipping of signals may cause regeneration of high-frequency components as well as distortion of signals. The current paper deals with the effect of clipping on the spectrum and BER of IFDMA signals with RRC filters.

Hybrid Detection Algorithm for Spatial Multiplexing MIMO-OFDM System (공간 다중화 MIMO-OFDM 시스템을 위한 Hybrid 검출 기법)

  • Won, Tae-Yoon;Kim, Seung-Hwan;Lee, Jin-Yong;Kim, Young-Lok
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.6C
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    • pp.539-546
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    • 2010
  • In next generation wireless communication systems based on OFDM, multiple-input multiple-output (MIMO) technique is adopted in order to achieve high data throughput with limited bandwidth. As one of MIMO techniques, spatial multiplexing scheme needs high performance data detection algorithm that can be performed with low computational complexity. In this paper, we propose an algorithm that can compute QRM-MLD with reduced complexity. Also, hybrid detection technique is proposed, which can reduce the complexity by selecting between MMSE and QRM-MLD according to the channel condition. The proposed algorithm provides the trade-off between performance and complexity. The computer simulations for downlink transmission in 3GPP LTE system show that less than 0.1dB performance degradation can be achieved at 0.1% BER with 59% reduction on computational complexity compared with the conventional QRM-MLD algorithm.

Low Phase Shift Attenuator Using the Half-Moon Radial Stub (반달 모양의 방사형 동조 스터브를 이용한 저위상 변화 감쇠기의 설계)

  • 윤종만;양기덕;김민택;박익모;신철재
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.8 no.5
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    • pp.452-461
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    • 1997
  • In this paper, we present a computer-aided design(CAD) technique for minimizing the phase shift in microstrip PIN diode attenuators due to the junction capacitance in the equivalent circuit model of PIN diode. Microstrip PIN diode attenuators use the characteristics which the reactance of microstrip line changes from inductive to capacitive as the frequency sweeps across the band. Microstrip PIN diode attenuator designed utilizes the quarter-wavelength transmission line terminating with the half-moon radial stub, which is designed for negligible phase shifting effect over the intersted bandwidth. The attenuator has similar phase shift at 0 dB and 10 dB of attenuation within average $1.27^{\circ}$ between 1.2GHz and 1.9GHz. The input and output return losses between 1.4 GHz and 1.9 GHz are less than 10 dB over the attenuation range of 0 dB and 10 dB.

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A Power Plane Using the Hybrid-Cell EBG Structure for the Suppression of GBN/SSN (GBN/SSN 억제를 위한 이종 셀 EBG 구조를 갖는 전원면)

  • Kim, Dong-Yeop;Joo, Sung-Ho;Lee, Hai-Young
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.18 no.2 s.117
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    • pp.206-212
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    • 2007
  • In this paper, a novel power/ground plane using the hybrid-cell electromagnetic band-gap(EBG) structure is proposed for the wide-band suppression of the ground bound noise(GBN) or simultaneous switching noise(SSN). The -30 dB stopband of the proposed structure starts from a few hundred MHz where the GBN/SSN energy is dominant. The distinctive features of this new structure are the thin spiral strip line and hybrid-cells. They realize the enhanced inductance and the shorter period of the EBG lattice. As a result, the lower cut-off frequency and bandwidth of the -30 dB stopband becomes lower and wider, respectively. In addition, the proposed structure has smaller number of resonance modes between power/ground planes and performs a low EMI behavior compared with the reference board.

Operation Scheme of Aerial Relay Networks and the Analysis of Its Effectiveness against Failures of Terrestrial Tactical Networks (지상 전술망 장애에 대비한 공중중계망 운용 방안 및 이의 효과도 분석)

  • Ghil, Joon-ho;Lee, Gyu-min;Lee, Seungwoon;Roh, Byeong-hee;Kim, Jae-hyun;Kim, Donghyun;Lee, Jaemoon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.42 no.1
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    • pp.172-180
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    • 2017
  • Korean army has been trying to construct a future tactical network in collaboration with TICN at the ground level and the next-generation military satellite system in the space level. However, due to the low bandwidth and high operational cost, the satellite system has the limitation to exchange all kind of tactical information through it. To overcome the limitation, there have been several researches to construct airborne networks. In this paper, we propose an effective interworking architecture and operation scheme between terrestrial tactical networks and aerial relay networks to counteract against the communication breaks of terrestrial terminals. And, we also propose a way to analyze its effectiveness. The experimental results show that the interworking of aerial relay networks can manage the failure situations in terrestrial tactical networks very effectively.

Highly Efficient Trans-Reflective Color Filters Incorporating TiO2-MgF2 Multilayer Stacks

  • Shrestha, Vivek Raj;Park, Chul-Soon;Koirala, Ishwor;Lee, Sang-Shin;Choi, Duk-Yong
    • Journal of the Optical Society of Korea
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    • v.19 no.6
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    • pp.566-574
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    • 2015
  • We report for the first time highly efficient trans-reflective color filters capable of demonstrating coloration in both transmission and reflection modes by taking advantage of a multilayer stack consisting of MgF2 and TiO2 used respectively as the low and high index materials. In order to enable such trans-reflective performance, securing an optimal stop band assuming an appropriate bandwidth within the visible regime is pivotal, which was realized by tailoring the thicknesses and the numbers of TiO2-MgF2 bi-layers. Three devices were designed through rigorous simulations and developed via e-beam evaporation to demonstrate vivid blue, green, and red colors in the reflection mode, and yellow, magenta, and cyan colors in the transmission mode, featuring an enhanced efficiency exceeding 90% under normal incidence. The color performance of the filters was examined by referring to the chromaticity coordinates of the transmission and reflection spectra, alongside photographed color images. The dependence of the performance on the angle of incidence was explored with respect to incident polarization, indicating that a transmission surpassing 60% could be stably maintained up to an angle of 75°. Polarization independent transfer characteristics were especially achieved for the normal incidence. The proposed devices may be readily extended to other spectral regimes by adjusting the thicknesses of the films.

A DCT Adaptive Subband Filter Algorithm Using Wavelet Transform (웨이브렛 변환을 이용한 DCT 적응 서브 밴드 필터 알고리즘)

  • Kim, Seon-Woong;Kim, Sung-Hwan
    • The Journal of the Acoustical Society of Korea
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    • v.15 no.1
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    • pp.46-53
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    • 1996
  • Adaptive LMS algorithm has been used in many application areas due to its low complexity. In this paper input signal is transformed into the subbands with arbitrary bandwidth. In each subbands the dynamic range can be reduced, so that the independent filtering in each subbands has faster convergence rate than the full band system. The DCT transform domain LMS adaptive filtering has the whitening effect of input signal at each bands. This leads the convergence rate to very high speed owing to the decrease of eigen value spread Finally, the filtered signals in each subbands are synthesized for the output signal to have full frequency components. In this procedure wavelet filter bank guarantees the perfect reconstruction of signal without any interspectra interference. In simulation for the case of speech signal added additive white gaussian noise, the suggested algorithm shows better performance than that of conventional NLMS algorithm at high SNR.

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A Study On The Bending Characteristics of Ribbon Cable Unit (리본광케이블 유니트의 구부림 특성 연구)

  • 이병철;이영탁;김미경
    • Korean Journal of Optics and Photonics
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    • v.6 no.4
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    • pp.379-384
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    • 1995
  • In order to construct B-ISDN, it is inevitable to introduce optical fiber of low loss and wide bandwidth. Coincidently, high count optical fiber cable is solely important to form optical subscriber network. The best structure of high count optical fiber cable to achieve multi-splicing as well as high density at the same time is the one of taking optical ribbon as a unit of accomodation. However, since optical ribbon has its own width. optical loss due to length difference during the bending of ribbon cable unit occurs in relatively easy way. Therefore, care should be taken during its manufacturing and storage. In t\1::; paper, strain, bending radius and lateral pressure of each fiber in ribbon due to the bending of ribbon cable unit are caculated theoretically. Hence, we have measured optical loss of each fiber as function of unit bending radius, when we bent the ribbon cable unit on the various reel. We found that the result accords well with the theoretical analysis. The result shows the importance to determine proper radius of reel used in ribbon cable manufacturing and storage. orage.

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