• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.47 no.8
• /
• pp.9-15
• /
• 2010

This paper presents an analysis of asynchronous multicarrier-code division multiple access (MC-CDMA) uplink systems over frequency-selective multipath fading channels when the frequency offsets (FOs) of all users are random variables and the frequency offset for the desired user is compensated. The effect of a residual frequency offset(RFO) on the average bit error rate (BER) is evaluated by the semi-analytical method, then the approximated BER performance is obtained as a closed-form expression. Moreover, the signal to noise ratio (SNR) loss caused by RFO is evaluated. Derived results show that the performance degradation due to RFO is negligible if the estimation error of RFO for the desired user is less than the normalized value of 0.1.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.46 no.4
• /
• pp.277-282
• /
• 2018

In this study, the accuracy and efficiency of a composite rotor blade cross-section analysis program, Ksec2d-AE, which is available at an educational web-based platform called EDISON-CSD, are assessed for possible use in undergraduate structural analysis projects. To this purpose, the convergence of cross-sectional constants by varying the number of finite elements in the cross-section of a wind turbine blade is investigated. The stiffness constants along with the cross-sectional engineering offsets obtained using Ksec2d-AE are validated against a 3D finite element analysis program MSC NASTRAN.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.9
• /
• pp.1699-1709
• /
• 2015

Moving terminals like high-speed-train undergo high Doppler frequency shift, and this leads to carrier frequency offsets that have to be compensated to avoid degradation of communication performance. In multiple access mechanism like OFDMA, base-stations need complex hardware to compensate the uplink frequency offset. In this paper, we propose a method, which can reduce burden of the base-station and makes frequency offset estimation and compensation simple. This method contains transmitting new synchronization signal, estimating frequency offsets in base-station, transmitting feedback information to terminal, and compensating the offset in uplink transmission. Simulation results show the proposed method operates well in high Doppler frequency shift conditions of 500 km/h which is the requirements of 5G mobile communication.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.3
• /
• pp.253-260
• /
• 2016

In this paper, the optimal seismic design method for inducing the beam-hinge collapse mechanism of steel moment frames is presented. This uses the non-dominated sorting genetic algorithm II(NSGA-II) as an optimal algorithm. The constraint condition for preventing the occurrence of plastic hinges at columns is used to induce the beam-hinge collapse mechanism. This method uses two objective functions to minimize the structural weight and maximize the dissipated energy. The proposed method is verified by the application to nine story steel moment frame example. The minimum column-to-beam strength ratio to induce the beam-hinge collapse mechanism are investigated based on the simulation results. To identify the influence of panel zone on the minimum column-to-beam strength ratio, three analytic modeling methods(nonlinear centerline model without rigid end offsets, nonlinear centerline model with rigid end offsets, nonlinear model with panel zones) are used.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.9B
• /
• pp.1624-1630
• /
• 1999

Code division multiple access (CDMA) is a promising air interface technique for cellular systems. When an MS (Mobile Station) moves to an adjacent cell, the handoff between the serving cell and the target cell is needed. Compared with the hard handoffs, the soft handoffs between two CDMA channels with the identical frequency assignments and frame offsets can provide a better quality of service by minimizing the undesirable ping pong phenomenon of back-and forth handoffs between two adjacent cells in conventional hard handoffs. For the soft handoff of a call to an adjacent cell to be successful, the adjacent cell should assign to the call the same frame offset as that being used in the original cell by the call. In this paper, considering the assignment states of the frame offsets of the adjacent cells, a frame offset assignment algorithm for the originated call is proposed. And analytic method for the handoff blocking probability due to the lack of the frame offset capacity is also presented to show the advantage of the proposed algorithm with respect to the soft handoff blocking probability.

• Proceedings of the KSRS Conference
• /
• 2008.10a
• /
• pp.277-280
• /
• 2008

Enhancing the positioning precision is the primary pursuit of GPS users. To achieve this goal, most studies have focused on the relationship between GPS receiver clock errors and GPS positioning precision. This study utilizes undifferentiated phase data to calculate GPS clock errors and to compare with the frequency of cesium clock directly, thus verifying estimated clock errors by the method used in this paper. The relative frequency offsets from this paper and from National Standard Time and Frequency Laboratory of Taiwan match to $1.5{\times}10^{12}$ in the frequency instability, suggesting that the proposed technique has reached a certain level of quality. The built-in quartz clocks in the GPS receivers yield relative frequency offsets that are 3 to 4 orders higher than those of rubidium clocks. The frequency instability of the quartz clocks is on average two orders worse than that of the rubidium clock. Using the rubidium clock instead of the quartz clock, the horizontal and vertical positioning accuracies were improved by 26-78% (0.6-3.6 mm) and 20-34% (1.3-3.0 mm), respectively, for a short baseline. These improvements are 7-25% (0.3-1.7 mm) and 11% (1.7 mm) for a long baseline. Our experiments show that the frequency instability of clock, rather than relative frequency offset, is the governing factor of positioning accuracy.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2003.11a
• /
• pp.581-584
• /
• 2003

It is important to know phase offsets of PN (Pseudo Noise) sequences in spread spectrum communications since the acquisition is equivalent to make a phase offset between a receiving PN sequence and a PN sequence of local PN generator be identical. In this paper, a phase offset enumeration method for PN sequences with error detection, and its application to the synchronization are proposed. The phase offset enumeration far an n-tuple PN sequence and its error detection are performed when one period of the sequence is received. Once the phase offset of the receiving sequence is calculated, we can easily accomplish the synchronization by initializing shift registers of a local PN generator according to the phase offset value. The mean acquisition time of the proposed synchronization method is derived analytically, and we see that the method acquires very fast acquisition in the high SNR (Signal-to- Noise Ratio) environment.

• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.35S no.10
• /
• pp.1-10
• /
• 1998

It is important to know phase offsets of a spreading code in the code division multiple access(CDMA) mobile communication systems because different phase offsets of the same spreading code are used to distinguish each base station. When the period of the code is not that long, the relative phase offset between the code and its shifted code can be found by comparing them, but as the period of the code increases it becomes difficult to find the phase offset. This paper describes a method to calculate the phase offset of a binary code based on the number theoretical approach. We define an accumulator function which plays a central role in this paper, and relationships between the functions are clarified. This number theoretical approach and their results show that this method is very easy for the phase offset calculation. Its application to the CDMA system and circuit realization of the phase offset calculation are also discussed.

• Geomechanics and Engineering
• /
• v.21 no.2
• /
• pp.111-122
• /
• 2020

In most cases in urban areas, construction of divergence tunnel should take into account proximity to existing tunnel in operation. This inevitably leads to deformation of adjacent structures and surrounding ground. Preceding researches mainly dealt with reinforcing of the diverging section for the stability including the pillar. This has limitations in investigating the interactive effects between existing structures and surrounding ground due to the excavation of the divergence tunnel. In this study, the complex interactive behavior of pile, the operating tunnel, and the surrounding ground according to horizontal offsets between the two adjacent tunnels was quantitatively analyzed based on conditions diverged from operating tunnel in urban areas. The effects on ground structures confirmed by analyzing the ground surface settlements, pile settlements, and the axial forces of the pile. The axial forces of lining in operating tunnel investigated to estimate their impact on existing tunnel. In addition, in order to identify the deformation of the surrounding ground, the close range photogrammetry applied to the laboratory model test for confirming the underground displacements. Two-dimensional finite element numerical analysis was also performed and compared with the results. It identified that the impact of excavating a divergence tunnel decreased as the horizontal offset increased. In particular, when the horizontal offset was larger than 1.0D (D is the diameter of operating tunnel), the impact on existing structures further reduced and the deformation of surrounding ground was concentrated at the top of the divergence tunnel.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.4C
• /
• pp.241-253
• /
• 2011

In this paper, a CFNC (Complex Field Network Coding) scheme is presented, which focuses on improving transmission efficiency by reducing time slots that are needed to exchange data frames. Conventional CFNC scheme has the advantage of minimizing the number of time slots required for information exchanges. However, there exists serious performance deterioration because the transmit signals are interfered with each other. Moreover, when CFNC scheme is applied, the estimation and compensation performance of fine frequency offset severely deteriorates due to the multiple frequency offsets in received signal of relay node. In order to overcome these critical problems, we propose an improved CFNC scheme with modified maximum likelihood decision method which uses uplink transmit diversity. Also, we propose an enhanced fine frequency offset estimation method and a corresponding compensation method to deal with the multiple frequency offsets. Corresponding simulation results verify that the proposed methods are able to effectively solve the problems of CFNC scheme.