• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.635-643
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• 2007

In this paper, a decision-directed expectation maximization (DEM) algorithm is proposed to improve the performance of channel estimation in OFDM-based cellular systems. The DEM algorithm enables a mobile station (MS) with multiple antennas, located at the cell boundary, to increase the performance of channel estimation using transmit data, without decreasing spectral efficiency. Also, DEM algorithm can apply fast fading without loss of channel estimation performance because that includes channel variation factor in a group. It is verified by computer simulation that the DEM algorithm can reduce computational complexity significantly while improving the performance of channel estimation in fast fading channels, compared with the expectation maximization (EM) algorithm.

• Proceedings of the KIEE Conference
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• 2003.04a
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• pp.402-404
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• 2003

Radio frequency identification (RF-ID) is an automatic data capture (ADC) technology that comprises small data-carrying device(is called Tag) and fixed or mobile device(is called reader). Tags are attached or deattached device. Readers may be installed at locations where data capture is required, and may also be in the form of portable readers. In this paper, we are proposing an application for the subway station using the RF-ID system and a system for the gateless fare collection passing through the booth in only carrying the card. In this system that RF-ID system and Bluetooth are applied. We designed two wireless communication channels. One is the 125kHz communication channel by FSK and PSK for power supplying on the card and identification and the other is 2.4GHz channel for the collection.

• Journal of the Korea Society of Computer and Information
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• v.7 no.2
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• pp.130-135
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• 2002

In this paper, it is designed mobile communication base station module type bandpass filter which is recently used coplanar waveguide in many way because of structural merit. Using Conductor-Backed Coplanar waveguide of Itoh, it is determined the value of impedance which had capable impedance value with selected H in 2.4 and proved the impedance of each sections. It use the commensurate line of $\lambda$/4, fixed a space of between two ground line and calculated the width of signal line. Because designed filter less than microstrip filter in space, it obtained excellent characteristic of 15dB throughout all passband and sharp cut-off characteristic.

• Journal of Korea Society of Digital Industry and Information Management
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• v.15 no.4
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• pp.85-92
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• 2019

This paper presents a SDR-based Long Term Evolution Advanced (LTE-A) Physical Downlink Shared Channel (PDSCH) decoder using a multicore Digital Signal Processor (DSP). For decoder implementation, multicore DSP TMS320C6670 is used, which provides various hardware accelerators such as turbo decoder, fast Fourier transformer and Bit Rate Coprocessors. The TMS320C6670 is a DSP specialized in implementing base station platforms and is not an optimized platform for implementing mobile terminal platform. Accordingly, in this paper, the hardware accelerator was changed to the terminal implementation to implement the LTE-A PDSCH decoder supporting the multi-antenna and the functions not provided by the hardware accelerator were implemented through core programming. Also pipeline using multicore was implemented to meet the transmission time interval. To confirm the feasibility of the proposed implementation, we verified the real-time decoding capability of the PDSCH decoder implemented using the LTE-A Reference Measurement Channel (RMC) waveform about transmission mode 2 and 3.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.36S no.9
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• pp.27-35
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• 1999

In this paper, we propose an error detection scheme of phase offsets for binary sequences including PN (Pseudo Noise) sequences based on the number theoretical approach. It is important to know phase offsets of spreading sequences in the CDMA (Code Division Multiple Access) mobile communication systems because phase offsets of the same spreading sequence are used to achieve the acquisition and are used to distinguish each base station. When the period of the sequence is not very long, the relative phase offset between the sequence and its shifted replica can be found by comparing them, but as the period of the sequence increases it becomes difficult to find the phase offset. The error detection failure probability of the proposed method is derived, and it is confirmed by the simulation results. We also discuss the circuit realization of the proposed method and show it can be easily implemented.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.27-35
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• 2010

In wireless packet networks, energy and wireless resource efficiency is critical issue to addressed for wide deployment. To achieve the both goals of saving the mobile station's energy and increasing the wireless capacity, transmission power control is introduced to wireless packet networks. In the transmission power controled networks, it is not deeply studied on unfairness among transmissions with different power levels that reaches starvation. Through the performance analysis, this paper explains the throughput unfairness of high power transmission with the unfair media access probability owing to the contending node number difference and proposes a simple PHY-MAC cross layer approach.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1113-1120
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• 2003

It is expected in the future that the demand of optical subcarrier multiplexing system, in which a number of small size base stations with only antenna and RF transmission are connected to central station using optical fiber, will be increased in the CDMA digital cellular mobile communication network. In this paper, in order to analysis the performance of optical SCM system fur CDMA RF signal transmission, MZ modulator is modelled as a non-linear transfer function with cubic operation. The performance degradation due to multipath signals and other user signals through MB modulator is analyzed and the performance is improved using the Rake receiver.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2018.10a
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• pp.565-567
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• 2018

The rover acquires its own position information using satellites signals provided by several satellites(at least four or more). For the present, GNSS systems are widely used in various fields. However, there are many factors that cause accuracy errors in positioning between rovers and GNSS satellites. Due to satellite time error, orbit error, ionospheric & convective refraction, multipath, etc., rover can't acquire precise position. Differential GPS(DGPS) and Real-Time Kinematic(RTK) have been developed as compensation techniques to reduce such errors. In this paper, we intend to develop a terminal with RTK technique to acquire precise position information of mobile station.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.8
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• pp.1952-1962
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• 1998

Radio interference ahs been occurred in TRS service on the south seashore in Korea from 1994. After monitoring the radio signal interference, it is found that the main reasons of radio interference are due to the source stations located at Fukuoka and Yamaguchi in Japan. However, Japan didn't agree about this fact, based on the their technique evaluationof the radio signal; since the distance (about 240-300km) of the radio station between Fukuoka and Pusan is enough to separate from the interference, the radio signal from Digital Mobile Phone is Japan cannot be reached to Pusan area in Korea. In this paper, we verified that the main sources of radio interference are a ducting propagation generated from Japan area by using the computer simulation technique and the measuring data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7C
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• pp.666-674
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• 2005

A hybrid multicarrier CDMA/FDM system with a truncated adaptive transmission scheme is analyzed in forward link based on the feedback information from the mobile station. In the single cell environment, the prop(mea scheme outperforms the adaptive FH/DS system as well as the MC DS/CDMA system when orthogonal signature sequences are used. In the multiple cell environment also, the proposed scheme has better performance characteristics than the adaptive FH/DS system when orthogonal and random codes are used as spreading sequences.