• Journal of Power System Engineering
• /
• v.19 no.2
• /
• pp.33-39
• /
• 2015

In conducting indoor positioning by code division multiple access using spread spectrum ultrasonic waves, it is required to detect signals under the influence of near-far problem occurred by difference on signal power, caused by distance between transmitter and receiver. For discussing robustness to the problem, we verified measuring accuracy on distance from an experiment on a real space with a hardware device where our proposed method is mounted. The proposed method performs automatic signal detection by setting threshold level dynamically. As an experimental result, measurable distance were improved by the proposed method, and measurement errors were up to 50mm in distances from 1000mm to 6000mm; therefore, enough accuracy to realize self-localization or navigation for autonomous mobile robot or human was obtained.

• Journal of The Korean Astronomical Society
• /
• v.46 no.3
• /
• pp.125-131
• /
• 2013

We present the relation between the genus in cosmology and the Betti numbers for excursion sets of three- and two-dimensional smooth Gaussian random fields, and numerically investigate the Betti numbers as a function of threshold level. Betti numbers are topological invariants of figures that can be used to distinguish topological spaces. In the case of the excursion sets of a three-dimensional field there are three possibly non-zero Betti numbers; ${\beta}_0$ is the number of connected regions, ${\beta}_1$ is the number of circular holes (i.e., complement of solid tori), and ${\beta}_2$ is the number of three-dimensional voids (i.e., complement of three-dimensional excursion regions). Their sum with alternating signs is the genus of the surface of excursion regions. It is found that each Betti number has a dominant contribution to the genus in a specific threshold range. ${\beta}_0$ dominates the high-threshold part of the genus curve measuring the abundance of high density regions (clusters). ${\beta}_1$ dominates the genus near the median thresholds which measures the topology of negatively curved iso-density surfaces, and ${\beta}_2$ corresponds to the low-threshold part measuring the void abundance. We average the Betti number curves (the Betti numbers as a function of the threshold level) over many realizations of Gaussian fields and find that both the amplitude and shape of the Betti number curves depend on the slope of the power spectrum n in such a way that their shape becomes broader and their amplitude drops less steeply than the genus as n decreases. This behaviour contrasts with the fact that the shape of the genus curve is fixed for all Gaussian fields regardless of the power spectrum. Even though the Gaussian Betti number curves should be calculated for each given power spectrum, we propose to use the Betti numbers for better specification of the topology of large scale structures in the universe.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.7
• /
• pp.32-41
• /
• 1999

In this study, a new knocking control algorithm was developed using the knock threshold value auto-correction algorithm. This algorithm uses the Fast Fourier Transform9FFT) method by measuring cylinder block vibration signals of a 1498 cc four-cylinder spark ignition engine. The experimental results show the proposed knock control algorithm provides improved performance compared to existing methods. The results also show that the proposed FFT algorithm provides real-time adjustment of the knock threshold value.

• Journal of Communications and Networks
• /
• v.16 no.6
• /
• pp.627-638
• /
• 2014

In this paper, we study the joint price and power allocation in spectrum sharing macro-femtocell networks. The proposed game theoretic framework is based on bi-level Stackelberg game where macro base station (MBS) works as a leader and underlaid femto base stations (FBSs) work as followers. MBS has fixed data rate and imposes interference price on FBSs for maintaining its data rate and earns revenue while FBSs jointly adjust their power for maximizing their data rates and utility functions. Since the interference from FBSs to macro user equipment is kept under a given threshold and FBSs compete against each other for power allocation, there is a need to determine a power allocation strategy which converges to Stackelberg equilibrium. We consider two cases for MBS power allocation, i.e., fixed and dynamic power. MBS can adjust its power in case of dynamic power allocation according to its minimum data rate requirement and number of FBSs willing to share the spectrum. For both cases we consider uniform and non-uniform pricing where MBS charges same price to all FBSs for uniform pricing and different price to each FBS for non-uniform pricing according to its induced interference. We obtain unique closed form solution for each case if the co-interference at FBSs is assumed fixed. And an iterative algorithm which converges rapidly is also proposed to take into account the effect of co-tier interference on interference price and power allocation strategy. The results are explained with numerical simulation examples which validate the effectiveness of our proposed solutions.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.6 no.8
• /
• pp.1894-1912
• /
• 2012

This paper proposes a system called Wireless Link based on Global Communication Channel (WLGCC) to enhance the spectrum sharing between digital broadcasting (DB) services and the cognitive radio (CR) system in the licensed band of 470-790 MHz. The WLGCC aims to enhance the spectrum sensing and geolocation database (GLD) spectrum sharing methods in the CR system. Spectrum sensing can be enhanced by receiving the status of the used frequencies from the WLGCC, thereby eliminating the need for a low detection threshold (i.e., avoiding the hidden node problem). In addition, the GLD can be enhanced by providing a reliable communication link between the database and the CR device in the form of an unused TV white space that is reserved as the proposed Global Communication Channel (GCC). This paper analyzes the coexistence of the new WLGCC system and the DB service in terms of avoiding additional interference. Specifically, we mathematically determine the WLGCC parameters, such as the in-band and out-of-band power levels, and operation coverage, and verify them using Monte Carlo simulation. The results show that WLGCC does not degrade the existing DB service and reliably transmits information of the vacant (or used) frequency bands to the CR.

• ETRI Journal
• /
• v.38 no.6
• /
• pp.1153-1162
• /
• 2016

This paper addresses the resource allocation (RA) problem in multi-cell cognitive radio networks. Besides the interference power threshold to limit the interference on primary users PUs caused by cognitive users CUs, a proportional fairness constraint is used to guarantee fairness among multiple cognitive cells and the impact of imperfect spectrum sensing is taken into account. Additional constraints in typical real communication scenarios are also considered-such as a transmission power constraint of the cognitive base stations, unique subcarrier allocation to at most one CU, and others. The resulting RA problem belongs to the class of NP-hard problems. A computationally efficient optimal algorithm cannot therefore be found. Consequently, we propose a suboptimal RA algorithm composed of two modules: a subcarrier allocation module implemented by the immune algorithm, and a power control module using an improved sub-gradient method. To further enhance algorithm performance, these two modules are executed successively, and the sequence is repeated twice. We conduct extensive simulation experiments, which demonstrate that our proposed algorithm outperforms existing algorithms.

• Journal of Oral Medicine and Pain
• /
• v.23 no.4
• /
• pp.433-445
• /
• 1998

본 연구는 정상인의 저작근에서 지속적인 등척성 수축후 근전도 power spectrum과 압력통각 역치의 회복 특성을 구명하기위해 시행되었다. 악안면 영역의 동통과 긴으장애의 벙력 및 현증이 ㅇ벗고 정상적인 교합관계를 가진 26명의 정상인(남자 14명, 여자 12명) 을 대상으로 최대근활성도의 70% 수준에서 인내가능 할 때까지의 등척성 수축과 수축후 회복기 동안의 근전도 power spectrum과 압력통각 역치를 컴퓨터를 이용한 근전도 시스텀과 전자식 압력통각계를 사용하여 분석한 결과 다음과 같은 결론을 얻었다. 1. 지속적인 등척성 수축 시작 시점의 중간주파수에서 남녀간에는 통계적으로 유의한 차이가 관철되지 않았지만, 근육간 비교에서는 전측두근에서 교근보다 유의하게 높게 나타났다(p<0.05). 2. 지속적인 등척성 수축전 암력통각 역치는 전축두근에서 교근보다 유의하게 높았고(p<0.001), 남성에서 여성보다 유의하게 높게 나타났다(p<0.05). 3. 지속적인 등척성 수축시 중간주파수와 압력통각 역치의 변화량은 성별간, 근육간에 우의한 차이가 관찰되지 않았다. 4. 지속적인 등척성 수축말기 중간주파수는 수축초기에 비하여 유의하게 감소하였으며(p<0.001), 이의 회복은 모든 근육에서 60초와 120초 사이에서 이루어 졌다. 5. 지속적인 등척성 수축후 압력통각역치는 수축전에 비해 유의하게 감소하였으며(p<0.001), 수축전 수준으로의 회복은 여자군의 전측두근과 교근에서는 30분후에 남자구느이 전측두근과 교근에서는 50분 후에 이루어졌다. 6. 지속적인 등척성 수축후 주관적인 동통이 소실된 시각은 여자군의 전축두근에서는 28분, 교근에서는 42분으로 남자군의 전측두근에서는 30분, 교근에서는 40분으로 나타났다.

• Current Optics and Photonics
• /
• v.8 no.1
• /
• pp.65-71
• /
• 2024

We present a Yb-doped narrow-linewidth polarization-maintaining all-fiber amplifier that achieves a high mode-instability (MI) threshold, high output power, and 9.7-GHz spectral linewidth. Six wavelength-multiplexed laser diodes are used to pump this amplifier. First, we construct a high-power fiber amplifier based on a master oscillator-power amplifier configuration for experiments. Subsequently, we examine the MI threshold by individually pumping the amplifier with wavelengths of 976, 974, 981, 974, and 981 nm respectively. The experimental results demonstrate that the amplifier exhibits a high MI threshold (>3.5 kW) when pumped with a combination of wavelengths at 974 and 981 nm. Afterward, we inject an optimized phase-modulated seed with a nearly flat-top spectrum into this amplifier. Ultimately, laser output of 3.2 kW and 9.7 GHz are obtained.

• Proceedings of the KIEE Conference
• /
• 2011.07a
• /
• pp.1850-1851
• /
• 2011

The faults of a electric motor cause to rise the maintenance and repair cost and to reduce the reliability of the electric power system. In this paper, the auto fault detection system for a induction motor is developed using the torque signal spectrum analysis. The spectrum of motor torque signal is used for finding a bearing fault feature frequency. A threshold value, for detecting the motor bearing fault is set by the difference of torque signal spectrum(FFT signal) between normal condition and faulted condition of the motor.

• Journal of Oral Medicine and Pain
• /
• v.32 no.4
• /
• pp.403-411
• /
• 2007

This investigation was carried out to evaluate the effect of Transcutaneous Electric Nerve Stimulation (TENS) to experimentally induced masticatory muscle pain and muscular fatigue. Twenty-nine healthy volunteers (18 men and 11 women, aged $26.1{\pm}4.7$ years) without past history or present symptoms of temporomandibular disorders were participated in this study. All of the subjects were randomly assigned to experimental group and control group, after at least 3 days interval, two groups were reassigned conversely. Subjects assigned to experimental group were received TENS and others assigned to control group were received sham-TENS therapy for 45 minutes, respectively. The changes of Visual Analogue Scale (VAS), Pressure Pain Threshold (PPT), and EMG power spectrum were measured on the masseter muscle both before and after sustained fatiguing contraction in each group. The major findings of this study are as follows : 1. PPTs and median frequencies of masseter muscles were significantly decreased after sustained isometric contraction resulting in muscular fatigue. 2. In experimental group received TENS therapy, PPTs measured both before and after occurrence of experimentally induced muscular fatigue were significantly increased. 3. In experimental group received TENS therapy, the changes of PPTs during sustained isometric contraction resulting in muscular fatigue were significantly decreased. 4. In experimental group received TENS therapy, VAS measured after occurrence of experimentally induced muscular fatigue was significantly decreased. 5. Although there were not statistical significances, endurance time was increased in experimental group received TENS therapy and decreased in control group received sham-TENS therapy. 6. In experimental group received TENS therapy, the changes of median frequencies were the less decreased and the slope of median frequency shift was the more increased during endurance time than in control group, however, there were not statistical significances.