• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.4
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• pp.699-705
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• 2001

It is considered DPSK modulation and the channel is modeled as multipath Nakagami fading type which has been recently taken as a general model in the communication environments in this paper. Most paper assumed that Nakagami fading index(m) of each branch of Rake receiver was fixed the same value in recent years. However, Nakagami fading index(m) of each branch of Rake receiver takes several value through communication environments. In this case, the branch ,which takes a small Nakagami fading index(m), exclude. So we can improve performance. We are considered phase error and analyzed wideband DS/CDMA cellular system. When nakagami fading index(m) takes voluntary value, we analyze BER of wideband DS/CDMA cellular system. Finally, When the branch, which takes a small Nakagami fading index(m), exclude, we analyze BER of wideband DS/CDMA cellular system.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.4
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• pp.70-79
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• 2012

For an aerodynamic test facility, it is very important to get the precise measurement data of pressure, temperature and mass flow rate at the upstream to the test article. Hence, a new measurement method using a bellmouth and rakes was studied for the large scale system of which the corrected mass flow is between 5 kg/s and 8 kg/s. The bellmouth was designed by ISO standard for 0.5% accuracy, and the rakes were designed by using the equal area method. From the results of 9 test trials, it is found that the Reynolds number of rakes and the mass flow rate ratio can be simply formulated by an one-dimensional equation. The mass flow rate of rakes was calibrated by this equation. By the result of calibration, The maximum error rate was -0.507%, and the average error rate was -0.000274%.

• Journal of the Korean Society of Propulsion Engineers
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• v.17 no.4
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• pp.63-72
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• 2013

A Mach 5 nozzle and a diffuser of the Scramjet Engine Test Facility (SETF) were made for a hydrocarbon-fueled scramjet engine. SETF, attached with a diffuser guide, started with a model of 60% blockage, though the model engine could not start by over expansion of the facility nozzle. The model was moved into the nozzle to escape the shock generated from the nozzle exit, both SETF and the engine could start. The pitot rake experiments (blockage of 2.3%) were done for measuring the core flow in the test section. From the pitot experiments, the core flow was expanded by an under expansion. It means that the core flow in the test section was related with a model blockage. SETF and the engine with a blockage of 33% work normally. From a series of experiments, SETF started with a normal shock efficiency of 58%, regardless of a blockage ratio.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.6
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• pp.1030-1035
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• 2021

Diving fishermen are demanding permission to use an inspirator that can efficiently catch Manila clam; however, coastal fishermenargue that the use of inspirator devastates the seabed and depletes fishery resources. Therefore, the aim of this study was to evaluate the fishing power of diving gears and its effect on coastal fishing grounds. The average time taken to fish in the seabed (4 m²) with a rake, water gun, and an inspirator was 11.17 min, 13.33 min and 7.81 min, respectivelyThe values of catch per unit time with a rake, water gun, and an inspirator were 3.35 kg/min, 2.26 kg/min, and 3.83 kg/min, respectively. Suspended sediments were observed the most in the water gun fishing area, and were observed more in April when fishing was not carried out than in February when fishing was carried out. However, the difference in the amount of sediment deposited in the fishing area using the three-fishing gears was very small. For an accurate analysis of the impact of the fishing gears on the seabed, supplementary tests such as grain size analysis and changes in benthic organisms need to be conducted.

• Geomechanics and Engineering
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• v.31 no.3
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• pp.249-263
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• 2022

The specially-shaped Polycrystalline Diamond Compact (PDC) cutter is widely used in drill bit design due to its advantages of high rock cutting efficiency, strong impact resistance and long service life in hard and abrasive formation drilling. A detailed understanding of rock cutting behavior of worn specially-shaped PDC cutter is essential to improve the drilling efficiency and decrease the drilling costs. In this paper, the theoretical models of two new principles (loading performance (LP) and cutting performance (CP)) are derived for evaluating the cutting process of worn specially-shaped cutter, the theoretical models consider the factors, such as cutter geometry, aggressiveness, stress state, working life, and rock cutting efficiency. Besides, the numerical model of heterogeneous granite is developed using finite element method combined with Voronoi tessellation, the LP and CP of 12 kinds of worn specially-shaped PDC (SPDC) cutters are analyzed. The results found that the mechanical specific energy (MSE) of worn cutters first increase and then decrease with increasing the cutting depth, and the MSE increase with the increase of back rake angle except for Conical cutter and Wedge-shaped cutter. From the perspective of CP, the worn PDC cutters are more suitable for the smaller cutting depths, and the back rake angle has little effect on the CP of the specially-shaped worn PDC cutters. Conical cutter, Saddle-shaped cutter and Ellipse-shaped cutter have the highest CP value, while Rhombus-shaped cutter, Convex cutter and Wedge-shaped cutter have the lowest value in selecting cutters. This research leads to an enhanced understanding of rock-breaking mechanisms of worn SPDC cutters, and provides the basis to select of specially-shaped PDC cutters for the specific target formation.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.873-881
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• 2002

In this paper, a on-line estimation method of the radial immersion angle using cutting force is presented. The ratio of cutting forces in feed and cross-feed directions acting on the single tooth at the immersion angle is a function of the immersion angle and the ratio of radial to tangential cutting force. It is found that the ratio of radial to tangential cutting force is not affected by cutting conditions and axial rake angle, which implies that the ratio determined by one preliminary experiment can be used regardless of the cutting conditions for a given tool and workpiece material. Using the measured cutting force during machining and predetermined ratio, the radial immersion ratio is estimated in process. Various experimental results show that the proposed method works within 5% error range.

• Journal of Communications and Networks
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• v.5 no.4
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• pp.374-385
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• 2003

The growing interest towards ultra-wideband (UWB) communications stems from its unique features such as baseband operation, ample multipath diversity, and the potential of enhanced user capacity. But since UWB has to overlay existing narrowband systems, multiple access has to be achieved in the presence of narrowband interference (NBI). However, existing baseband spreading codes for UWB multiple access are not flexible in handling NBI. In this paper, we introduce two novel spreading codes that not only enable baseband UWB multiple access, but also facilitate flexible NBI cancellation. We construct our codes using a single carrier or multiple carriers (SC or MC), which can be implemented with standard discrete-cosine transform (DCT) circuits. With our SC/MC codes, NBI can be avoided by simply nulling undesired digital carriers. Being digital, these SC/MC codes give rise to multiband UWB systems, without invoking analog carriers. In addition, our SC/MC codes enable full multipath diversity, and maximum coding gains. Equally attractive is their capability to reduce the number of interfering users, with simple matched filter operations. Comprehensive simulations are also carried out to corroborate our analysis.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.5A
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• pp.836-845
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• 2001

본 논문에서는 시간 선택성 다중경로 이동 무선 채널을 다양한 방법으로 모델링 하고 그에 따른 여러 가지 특성평가를 제시하였다. 모델링 방법에는 Jakes 방식과 시간 영역에서 독립적인 두 개의 가우시안 잡음 발생기와 정형필터(shaping filter)를 사용하는 방식 및 주파수 영역에서 필터링 하는 방식이 있다. 이 세 가지 모델링 방법의 성능을 진폭의 자기상관함수, 상호상관함수, 누적분포함수(Cumulative Distribution Function), 레벨 교차율(Level Crossing Rate), 평균 페이딩 지속 시간(Average Duration of Fades), 위상차의 확률 밀도, 위상차의 자기상관함수 등의 측면에서 시뮬레이션하고 그 결과치와 이론치 간의 특성 비교를 제시하였다. 특히, 확산 대역 시스템을 고려했을 때 이상적인 채널 추정을 가정한 레이크 수신기에서의 BER 성능을 다중경로 개수에 따라 보임으로써 여러 가지 채널 모델링 중에서 주파수 영역에서 필터링 하는 방식이 이동 무선 채널을 모델링 하는데 있어 가장 적합하다는 것을 보였다. 마지막으로 비대칭 도플러(Doppler) 스펙트럼을 모델링 하는 것도 주파수 영역에서 필터링 하는 방식이 편리하다.

• Journal of information and communication convergence engineering
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• v.9 no.6
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• pp.652-656
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• 2011

In this paper, a transmitter-based multipath processing and inter-channel interference (ICI) cancellation scheme for a ultra-wideband (UWB) spatial multiplexing (SM) multiple input multiple output (MIMO) system is presented. It consists of taps delayed lines and zero-forcing (ZF) filters in the transmitter and correlators in the receiver. For a UWB SM MIMO system with N transmit antennas, M receive antennas, and Q resolvable multipath components, the BER performance of a linear transmit ZF scheme is analyzed in a log-normal fading channel and also compared with that of a receiver-based ICI rejection approach. It is found that when M ${\leq}$ N, the transmit ZF processing approach outperforms the ZF receiver while making the mobile units low-cost and low-power.

• ETRI Journal
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• v.29 no.2
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• pp.237-239
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• 2007

Interference from IEEE 802.11a systems affects ultra-wideband (UWB) systems significantly. In this letter, we suggest a novel narrow-band interference (NBI) suppression technique based on the singular value decomposition (SVD) algorithm in time-hopping pulse amplitude modulation (TH-PAM) UWB systems. The SVD algorithm is used to approximate the interference which then is subtracted from the received signals. In contrast to the conventional notch filter and rake receiver, our method is more effective and the receiver complexity can be greatly reduced.