• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.5
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• pp.971-980
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• 1994

The need increased capacity in the cellular system has resulted in the adoption of digital technology with CDMA as the channel access method. It has been recognized that the distinction of the base station is important for its performance in CDMA, since the same spreading sequences are used by the all base stations. Time offset of the pseudo-random noise binary code are used to distinguish signals received at a mobile station from different base station. But the start of the zero offset PN sequence is chosen arbitrary without the background of the systematic and mathematical elaboration. This paper proposes a mothed that define the start of the zero offset PN sequence mathematically. This paper also discusses a method that can easily calculate the time offset of the received spreading sequence with respect to the zero offset PN sequence.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.556-562
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• 2006

In this paper, macro diversity coding methods are proposed to efficiently transmit broadcast packet data over mobile cellular networks based on OFDM. In the method, cells are divided into multiple cell groups which transmit one of two orthogonal branches in a transmit diversity code. Furthermore, a coded packet is partitioned into the subblocks for which different cell group combinations are assigned to transmit two different branches. The methods extend the cell coverage at the same transmit power due to the transmit diversity of each symbol and coding diversity obtained through different fading statistics over the subblocks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.10A
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• pp.1159-1166
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• 2004

This paper follows up the previous work on the linearly constrained, modified minimum mean-squared error(MMSE) detection for direct-sequence code-division multiple-access DS-CDMA) systems in fading channels. We find a condition to avoid the breakdown of joint modified MMSE detection and pilot symbol-aided channel estimation (PSACE). The linearly constrained, modified MMSE solution is theoretically shown to be robust against time variations in Rayleigh fading channels. This fact is consistent with the simulation results. We also show that under some conditions the linearly constrained, modified MMSE detection maximizes the output signal-to-interference-plus-noise ratio.(SINR)

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.3175-3180
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• 2008

A metal-fueled pool-type liquid metal fast reactor (LMFR) provides large margins to sodium boiling and fuel damage under accident conditions. The favorable passive safety results are obtained by both a reactivity feedback mechanism in the core and a passive decay heat removal system. Among the various reactivity feedbacks, the ones by a thermal expansion of a radial dimension of the core and by the control rod drivelines are strongly dependent on the flow conditions in the core and the hot pool, respectively. The effects of multidimensional thermal hydraulic characteristics on these reactivity feedbacks are investigated by the system-wide safety analysis code SSC-K with advanced thermal hydraulics models. Particularly a detailed three dimensional thermal hydraulics reactor core model is integrated into SSC-K for use in a whole system analysis of the passive safety aspects of LMR designs. The model provides fuel and cladding temperatures for every fuel pin in a reactor and coolant temperatures for every coolant sub-channel in the reactor.

• Journal of the Korea Society for Simulation
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• v.22 no.1
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• pp.41-51
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• 2013

This tutorial paper presents the design methodology of system-level simulators targeted for code division multiple access (CDMA) cellular standards such as EV-DO (Evolution-Data Only) and broadcast multicast service (BCMCS). The basic structure and simulation flow of system-level simulators are delineated, following the procedure of cell layout, mobile drops, channel modeling, received power calculation, scheduling, packet error prediction, and traffic generation. Packet data transmissions on the forward link of CDMA systems and EV-DO BCMCS systems are considered for modeling simulators. System-level simulators for cellular standards are modeled and developed with high-level languages and utilized to evaluate and predict air interface performance metrics including capacity and coverage.

• ETRI Journal
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• v.32 no.4
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• pp.493-502
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• 2010

The operation time of an encoder is one of the critical implementation issues for satisfying the timing requirements of Long Term Evolution (LTE) systems because the encoder is based on binary operations. In this paper, we propose a design and implementation of a latency efficient encoder for LTE systems. By virtue of 8-bit parallel processing of the cyclic redundancy checking attachment, code block (CB) segmentation, and a parallel processor, we are able to construct engines for turbo codings and rate matchings of each CB in a parallel fashion. Experimental results illustrate that although the total area and clock period of the proposed scheme are 19% and 6% larger than those of a conventional method based on a serial scheme, respectively, our parallel structure decreases the latency by about 32% to 65% compared with a serial structure. In particular, our approach is more latency efficient when the encoder processes a number of CBs. In addition, we apply the proposed scheme to a real system based on LTE, so that the timing requirement for ACK/NACK transmission is met by employing the encoder based on the parallel structure.

• Journal of Industrial Technology
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• v.30 no.A
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• pp.17-23
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• 2010

Recently, a large number of open-pit mines are planning to change their mining method to underground types because the environmental concerns and legal regulations are increased with a rise in the standard of living. The K silica mine, which is one of them and located in Kyunggi province, is planning the establishment of a vertical shaft which will be used for ore-pass channel in their new glory hole mining method. This vertical shaft will be designed to join with a horizontal gangway excavated from the ground level. In this new mining system, the excavated ore particles will be stored inside a shaft and transported out with a help of a conveyor belt. Therefore the hang-up of ore particles in a shaft, the control of gate at the bottom of a shaft, the installation of dog-leg at the gate should be investigated identically. In this study, the PFC-2D code which is one of the discrete element numerical methods has been applied to simulate the particle flow mechanism in a shaft, and the optimum mine design has been proposed to maximize the productivity and to minimize the system damage.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.4
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• pp.195-201
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• 2011

Cognitive radio (CR), which is proposed as a technology that utilizes the frequency resources effectively, has studied to relive scarcity of the frequency resources. CR provides opportunistically under-utilize licensed frequency to the secondary user. However, in the wireless channels, due to the effect of fading and shadowing environments, spectrum sensing performance is compromised. Besides, to detect and classify various CR systems, a novel spectrum sensing algorithm is needed. Therefore, in this paper, we proposed the spectrum sensing algorithm with water marking scheme.

• Nuclear Engineering and Technology
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• v.36 no.1
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• pp.36-46
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• 2004

The ISAAC fission product release calculation is based on detailed FPRAT models developed by Jaycor. For volatile fission product release calculations, either the Cubicciotti steam oxidation correlation or the NUREG-0772 correlation is used. In this study, evaluation is carried out for these volatile fission product release models. As a result, in the case of early release, the IDCOR model with an in-vessel Te release option shows the most conservative results and for the late release case, the NUREG-0772 model shows the most conservative results. Considering both early and late release, the IDCOR model with an in-vessel Te bound option is evaluated to show mitigated conservative results. In addition, a sensitivity study on detailed core nodalization is performed. In the study, 380 horizontal fuel channels in the Wolsong plant are nodalized into 12 (6 channels per loop, $3{\times}3$ Core Pass) representative channels and detailed by 16/20/24 channels. For reference accidents, LOAH and large LOCA are selected as representing high and low pressure sequences, respectively. According to the results, the original 12 channel approach with $3{\times}3$ core passes is evaluated to be sufficient as an optimal scheme.

• Nuclear Engineering and Technology
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• v.37 no.6
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• pp.575-586
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• 2005

In a CANDU (CANada Deuterium Uranium) reactor, fuel channel integrity depends on the coolability of the moderator as an ultimate heat sink under transient conditions such as a loss of coolant accident (LOCA) with coincident loss of emergency core cooling (LOECC), as well as normal operating conditions. This study presents assessments of moderator thermal-hydraulic characteristics in the normal operating conditions and one transient condition for CANDU-6 reactors, using a general purpose three-dimensional computational fluid dynamics code. First, an optimized calculation scheme is obtained by many-sided comparisons of the predicted results with the related experimental data, and by evaluating the fluid flow and temperature distributions. Then, using the optimized scheme, analyses of real CANDU-6 in normal operating conditions and the transition condition have been performed. The present model successfully predicted the experimental results and also reasonably assessed the thermal-hydraulic characteristics of a real CANDU-6 with 380 fuel channels. A flow regime map with major parameters representing the flow pattern inside a calandria vessel has also proposed to be used as operational and/or regulatory guidelines.