• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.11 no.10
• /
• pp.1968-1976
• /
• 2007

This paper proposes a hybrid pseudo-noise (PN) code acquisition scheme for Multicarrier Direct Sequence - Code Division Multiple Access (MC DS-CDMA) mobile communication systems on the code acquisition performance for Nakagami-m fading channel. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time (MAT) slightly inferior to that of the total parallel acquisition. The closed-form expressions of the detection and false-alarm probabilities are derived.

• Structural Engineering and Mechanics
• /
• v.51 no.4
• /
• pp.531-546
• /
• 2014

In this paper the extension of a recently established energy-based pushover procedure in order to include the higher mode contributions to the seismic response of structures is presented and preliminary evaluated. The steps of the proposed methodology in its new formulation are quite similar to those of the well-known Modal Pushover Analysis. However, the determination of the properties of the 'modal' equivalent single-degree-of-freedom systems is achieved by a rationally founded energy-based concept. Firstly, the theoretical background and the assumptions of the proposed methodology are presented and briefly discussed. Secondly, the sequence of steps to be followed for its implementation along with the necessary equations is systematically presented. The accuracy of the methodology is evaluated by an extensive parametric study which shows that, in general, it provides better results compared to those produced by other similar procedures. In addition, the main shortcoming of the initial version of the methodology now seems to be mitigated to a large extent.

• Journal of Astronomy and Space Sciences
• /
• v.38 no.3
• /
• pp.165-173
• /
• 2021

Apophis is a near-Earth object with a diameter of approximately 340 m, which will come closer to the Earth than a geostationary orbit in 2029, offering a unique opportunity for characterizing the object during the upcoming encounter. Therefore, Korea Astronomy and Space Science Institute has a plan to propose a space mission to explore the Apophis asteroid using scientific instruments such as a laser altimeter. In this study, we evaluate the performance metrics of a laser altimeter using a pseudorandom noise modulation technique for the Apophis mission, in terms of detection probability and ranging accuracy. The closed-form expression of detection probability is provided using the cross correlation between the received pulse trains and pseudo-random binary sequence. And the new ranging accuracy model using Gaussian error propagation is also derived by considering the sampling rate. The operation range is significantly limited by thermal noise rather than background noise, owing to not only the low power laser but also the avalanche photodiode in the analog mode operation. However, it is demonstrated from the numerical simulation that the laser altimeter can achieve the ranging performance required for a proximity operation mode, which employs commercially available components onboard CubeSat-scale satellites for optical communications.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.15 no.6
• /
• pp.2240-2254
• /
• 2021

We investigate the channel allocation problem in an ultra-dense device-to-device (D2D) enabled cellular network in underlaying mode where multiple D2D users are forced to share the same channel. Two kinds of low complexity solutions, which just require partial channel state information (CSI) exchange, are devised to resolve the combinatorial optimization problem with the quality of service (QoS) guaranteeing. We begin by sorting the cellular users equipment (CUEs) links in sequence in a matric of interference tolerance for ensuring the SINR requirement. Moreover, the interference quota of CUEs is regarded as one kind of communication resource. Multiple D2D candidates compete for the interference quota to establish spectrum sharing links. Then base station calculates the occupation of interference quota by D2D users with partial CSI such as the interference channel gain of D2D users and the channel gain of D2D themselves, and carries out the channel allocation by setting different access priorities distribution. In this paper, we proposed two novel fast matching algorithms utilize partial information rather than global CSI exchanging, which reduce the computation complexity. Numerical results reveal that, our proposed algorithms achieve outstanding performance than the contrast algorithms including Hungarian algorithm in terms of throughput, fairness and access rate. Specifically, the performance of our proposed channel allocation algorithm is more superior in ultra-dense D2D scenarios.

• Korean Journal of Optics and Photonics
• /
• v.31 no.5
• /
• pp.223-230
• /
• 2020

In this paper, we have studied the characteristics of stimulated Brillouin scattering (SBS) and mode instability (MI) in a ytterbium-doped polarization-maintaining fiber laser with master oscillator power amplifier configuration. We measured the laser output power and back-reflection spectrum for a variety of ytterbium-doped fibers and seed lights, to investigate the power-scaling limits of fiber lasers. By optimizing the laser structure, we demonstrated an all-fiber high-power polarization-maintaining fiber laser with near-diffraction-limited beam quality. The output power of 1.5 kW was achieved with a linewidth of 10 GHz, generated by pseudo-random binary sequence (PRBS) phase modulation. The beam quality M² was about 1.15 at the maximum output power. The polarization extinction ratio (PER) was greater than 17 dB.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.26 no.1A
• /
• pp.191-203
• /
• 2006

The vibration characteristics of composite stiffened laminated plates with stiffener is presented using the assumed natural strain 9-node shell element. To compare with previous research, the stiffened plates are composed of carbon-epoxy composite laminate with a symmetric stacking sequence. Also, the result of the present shell model for the stiffener made of composite material is compared with that of the beam model. In the case of torsionally weak stiffener, a local buckling occurs in the stiffener. In this case, the stiffener should be idealized by using the shell elements. The current investigation concentrates upon the vibration analysis of rectangular stiffened and unstiffened composite plates when subjected to the in-plane compression and shear loads. The in-plane compression affect the natural frequencies and mode shapes of the stiffened laminated composite plates and the increase in magnitude of the in-plane compressive load reduces the natural frequencies, which will become zero when the in-plane load is equal to the critical buckling load of the plate. The natural frequencies of composite stiffened plates with shear loads exhibit the higher values than the case of without shear loads. Also, the intersection, between the curves of frequencies against in-plane loads, interchanges the sequence of some of the mode shapes as a result of the increase in the inplane compressive load. The results are compared with those available in the literature and this result shows that the present shell model for the stiffened plate gives more accurate results. Therefore, the magnitude, direction type of the in-plane shear and compressive loads in laminated composite stiffened plates should be selected properly to control the specific frequency and mode shape. The Lanczos method is employed to solve the eigenvalue problems.

• Steel and Composite Structures
• /
• v.19 no.5
• /
• pp.1095-1113
• /
• 2015

In order to determine the mechanical behavior of the curved laminates in practical applications, three right-angled composite brackets with different lay-ups were investigated both experimentally and numerically. In the experimental, quasi-static tests on both unidirectional and multidirectional curved composite brackets were conducted to study the progressive failure and failure modes of the curved laminates. In the numerical modeling, three-dimensional finite element analysis was used to simulate the mechanical behavior of the laminates. Here, a strength-based failure criterion, namely the Ye criterion, was used to predict the delamination failure in the composite curved laminates. The mechanical responses of the laminate subjected to off-axis tensile loading were analyzed, which include the progressive failure, the failure locations, the load-displacement relationships, the load-strain relationships, and the stress distribution around the curved region of the angled bracket. Subsequently, the effects of stacking sequence and thickness on the load carrying capacity and the stiffness of the laminates were discussed in detail. Through the experimental observation and analysis, it was found that the failure mode of all the specimens is delamination, which is initiated abruptly and develops unstably on the symmetric plane, close to the inner surface, and about $29^{\circ}$ along the circumferential direction. It was also found that the stacking sequence and the thickness have significant influences on both the load carrying capacity and the stiffness of the laminates. However, the thickness effect is less than that on the curved aluminum plate.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.23 no.4
• /
• pp.23-28
• /
• 2023

In a wireless smart utility network communication system, an asynchronous low power MAC is standardized and used according to IEEE 802.15.4e. An asynchronous MAC called RIT (Receiver Initiated Transmission) has a characteristic in which delay time and power consumption are greatly affected by a check-in interval (RIT period). By waking up from sleep every check-in interval and checking whether there is data to be received, power consumption in the receiving end can be drastically reduced, but power consumption in the transmitting end occurs due to an excessive wakeup sequence. If an excessive wake-up sequence is reduced by shortening the check interval, power consumption of the receiving end increases due to too frequent wake-up. In the RIT asynchronous MAC technique, power consumption performance according to traffic load and operation of check-in interval is analyzed and applied to Wi-SUN construction.

• Journal of Broadcast Engineering
• /
• v.16 no.3
• /
• pp.510-519
• /
• 2011

Intra mode decision is a useful coding tool in Distributed Video Coding (DVC) for improving DVC coding efficiency for video sequences having fast motion. A major limitation associated with the existing intra mode decision methods, however, is that its efficiency highly depends on user-specified thresholds or modeling parameters. This paper proposes an entropy-based method to address this problem. The probabilities of intra and Wyner?Ziv (WZ) modes are determined firstly by examining correlation of pixels in spatial and temporal directions. Based on these probabilities, entropy of the intra and the WZ modes are computed. A comparison based on the entropy values decides a coding mode between intra coding and WZ coding without relying on any user-specified thresholds or modeling parameters. Experimental results show its superior rate-distortion performance of improvements of PSNR up to 2 dB against a conventional Wyner?Ziv coding without intra mode decision. Furthermore, since the proposed method does not require any thresholds or modeling parameters from users, it is very attractive for real life applications.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.19 no.12
• /
• pp.2963-2967
• /
• 2015

The pump-probe scheme is used to analyze the cross-phase modulation penalty of a single-mode fiber in a WDM system. The pump signal is assumed to be a periodically modulated input like a raised sinusoidal. The periodic signal models an alternating bit sequence, and leads to an analytical expression of CPM penalty which is measured by EOP. The derived expression shows good agreement with numerical results in conventional single-mode fiber systems over a wide range of channel spacing, ${\Delta}f$. In dispersion-shifted fiber systems when ${\Delta}f$ < 100GHz, the derived expression shows increased discrepancy with the numerical results due to the increased FWM. This is not a surprising because the pump-probe scheme is used to analyze system performance degradation due to CPM.