• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.45-54
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• 2010

This paper studies the design of a multiuser multiple-input multiple-output (MIMO) system, where a base station (BS) transmits independent messages to multiple users. The remarkable "dirty paper coding (DPC)" result was first presented by Costa that the capacity does not change if the Gaussian interference is known at the transmitter noncausally. While several implementable DPC schemes have been proposed recently for single-user dirty-paper channels, DPC is still difficult to implement directly in practical multiuser MIMO channels. In this paper, we propose a network channel matrix triangulation (NMT) algorithm for utilizing interference known at the transmitter. The NMT algorithm decomposes a multiuser MIMO channel into a set of parallel, single-input single-output dirty-paper subchannels and then successively employs the DPC to each subchannel. This approach allows us to extend practical single-user DPC techniques to multiuser MIMO downlink cases. We present the sum rate analysis for the proposed scheme. Simulation results show that the proposed schemes approach the sum rate capacity of the multiuser MIMO downlink at moderate signal-to-noise ratio (SNR) values.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3C
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• pp.153-157
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• 2005

Frequency selective fading occurs due to the Doppler Effect in mobile communication systems. The performances of the systems are rapidly reduced due to effect of multiuser interference under frequency selective channels at DS-CDMA systems. To overcome these problems, we adopted the multi-carrier modulation techniques, and it is able to solve the frequency selective channel effects by means of these modulation techniques, and interference problems due to multiuser access are solved by means of multiuser detection techniques. In this paper, we proposed the blind MOE/PIC multiuser detection method which is composed of both the blind multiuser detection technique and parallel interference canceller. Thus, simulation results show that the proposed method performs better than conventional methods.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.7 s.337
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• pp.1-4
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• 2005

A four-channel photoreceiver ways have been realized in a 0.8$\mu$m Si/SiGe HBT technology for the applications of parallel optical interconnects. The receiver array includes four-channel transimpedance amplifiers (TIAs) and p-i-n photodiodes, where the TIAs exploit a common-emitter (CE) input configuration. Measured results demonstrate that the four-channel CE TIA array provides 3.9GHz bandwidth, 62dB$\Omega$ transimpedance gain, 7.5pA/sqrt(Hz) average noise current spectral density, and less than -25dB crosstalk between adjacent channels with 40mW power dissipation.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.37 no.5
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• pp.85-92
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• 2000

In this paepr, a multicode CDMA scheme with serial and parallel structure as the transmission scheme of wireless LAN which can transmit high speed data under an indoor channel environment is modeled and optimal values of several parameters needed for implementing wireless LAN modern system are derived through computer simulation. it is verified that given the transmission bandwidth and maximum data rate, the system performance is improved if increasing spreading gain anf the number of channels or decreasing the data rate of each channel. Especially the parallel structure makes not only the system performance much more improved but also the hardware implementation easier than serial structure under the same condition because the effective chip rate is decreased.

• Journal of Korea Multimedia Society
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• v.16 no.7
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• pp.897-904
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• 2013

The recursive circulant network G(N,d) can be widely used in the design and implementation of parallel processing architectures. It consists of N identical nodes, each node is connected through bidirectional, point-to-point communication channels to different neighbors by jumping $d^i$, where $0{\leq}i{\leq}{\lceil}{\log}_dN{\rceil}$ - 1. In this paper, we investigate the routing of a message on $G(2^m,4)$, a special kind of RCN, that is key to the performance of this network. On $G(2^m,4)$ we would like to transmit k packets from a source node to k destination nodes simultaneously along paths on this network, the $i^{th}$ packet will be transmitted along the $i^{th}$ path, where $1{\leq}k{\leq}m-1$, $0{{\leq}}i{{\leq}}m-1$. In order for all packets to arrive at a destination node quickly and securely, we present an $O(m^4)$ routing algorithm on $G(2^m,4)$ for generating a set of one-to-many node-disjoint and nearly shortest paths, where each path is either shortest or nearly shortest and the total length of these paths is nearly minimum since the path is mainly determined by employing the Hungarian method.

• 한국전산유체공학회:학술대회논문집
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• 2006.05a
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• pp.395-397
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• 2006

Air interlacing serves to protect the yarn against damage, strengthens inter-filament compactness or cohesion, and ensures fabric consistency. The air interlacing nozzle is used to introduce intermittent nips to a filament yarn so as to improve its performance in textile processing. The effect of various interlacing nozzle geometries on the interlacing process was studied. The geometries of interlacing nozzles with single or multiple air inlets located across the width of yarn channels are investigated. The basis case is the yarn channel, with a perpendicular main air inlet in the middle. Other cases have main air inlets, slightly inclined double sub air inlets, The yarn channel cross sectional shapes are either semicircular or rectangular shapes. The compressed impinging jet from the main air inlet hole hits the opposing bottom wall of the yarn channel, is divided into two branches, joins with the compressed air coming out from sub air inlet at the bottom and creates two free jets at both ends of the yarn channel. The compressed air movement in the cross-section consists of two opposing directional vortices. The CFD-FASTRAN flow parallel solver was used to perform steady simulations of impinging jet flow inside of the interlace nozzles. The vortical structure and the flow pattern such as pressure contour, particle traces, velocity vector plots inside of interlace nozzle geometry are discussed in this pater.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.5
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• pp.493-502
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• 2009

In this paper, we compare the performance of initial timing acquisition in direct sequence ultra-wideband(DS-UWB) systems with different transmit pulse shaping filters through extensive computer simulations. Simulation results show that the timing acquisition performance of the DS-UWB system, whose chip rate is 1.32 Gchip/s, employing a rectangular transmit filter is similar to that employing a square root raised cosine(SRRC) filter with an interpolation factor of 4 in the realistic UWB channels(CM1 and CM3) as well as the additive white Gaussian noise(AWGN) channel. Additionally, we present both a 24-parallel digital correlator structure and a 24-parallel processing searcher operating at a 55 MHz system clock, and then briefly discuss the initial timing acquisition procedure. Because we can adopt an 1.32 Gsample/s digital-to-analog(D/A) converter and an 1.32 Gsample/s analog-to-digital(AID) converter in the DS-UWB system by employing the rectangular transmit filter, we have a realistic solution for the DS-UWB chipset development.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.4 s.316
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• pp.55-60
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• 2007

In high field (> 3 T) MR imaging, the magnetic field inhomogeneity in the target object increases due to the nonuniform electro-magnetic characteristics of the relatively high RF frequency. Especially in the body imaging, the effect causes more serious problems resulting in locally high SAR(Specific Absorption Ratio). In this paper, we propose an optimized parallel-transmission RF coil and show the utility of the coil by FDTD simulations to overcome the unwanted effects. Three types of TX coil elements are tested to maximize the efficiency and their driving patterns(amplitude and phase) optimized to have adequate field homogeneity, proper SAR level, and sufficient field strength. For the proposed coil element of $25cm{\times}8cm$ loop structure with 12 channels for a 3.0 T body coil, the field non-uniformity of more than 70% without optimization was reduced to about 26 % after the optimization of driving patterns. The experimental as well as simulation results show that the proposed parallel driving scheme is clinically useful for (ultra) high field MRI.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.7B
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• pp.944-950
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• 2001

현재 상용화된 CDMA (code division multiple access) 방식은 사용자가 증가함에 따라 다중 사용자 간섭에 의해 통화품질 향상 및 가입자 수용 용량 증대에 한계를 가지고 있다. 이러한 문제를 극복하기 위해 다양한 형태의 다중 사용자 검파 알고리즘이 제안되었다. 본 논문에서는 여러 형태의 알고리즘들 가운데, 역상관 (decorrelating) 검파기와 병렬 간섭 제거 (parallel interference cancellation, PIC) 검파기, 연속 간섭 제거 (successive interference cancellation, SIC) 검파기와 PIC 검파기, zero-forcing decision-feedback (ZF-DF) 검파기와 PIC 검파기를 하이브리드 형태로 구성하는 방법을 제시하였고, Rayleigh 페이딩 환경에서 성능분석 및 컴퓨터 시뮬레이션을 통한 성능 비교를 하였다. 컴퓨터 모의실험 결과, 본 논문에서 제안한 세 가지 하이브리드 검파기 모두 기존 검파기에 비하여 우수한 성능을 보였다.

• Journal of information and communication convergence engineering
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• v.14 no.3
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• pp.163-170
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• 2016

Because of rapid technological advancements, increased data rate support has become the key criterion for future communication medium selection. Multimode optical fibers and multicore optical fibers are well matched to high data rate throughput requirements because of their tendency to support multiple modes through one core at a time, which results in higher data rates. Using the numerical mode solver OptiFiber, we have designed a concentric core fiber by investigating certain design parameters, namely core diameter (µm), wavelength (nm), and refractive index profile, and as a result, the number of channels, material losses, bending losses, polarization mode dispersion, and the effective nonlinear refractive index have been determined. Space division multiplexing is a promising future technology that uses few-mode fibers in parallel to form a multicore fiber. The experimental tests are conducted using the standard second window wavelength of 1,550 nm and simulated results are presented.