• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1214-1222
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• 2006

In this paper, an efficient direction-r)f-arrival based adaptive beamforming algorithm for orthogonal frequency-division multiple-access smart antenna systems is proposed. The proposed algorithm provides a high performance by steering main beams to the directions of a desired signal, whereas steering nulls to the directions of the interference, using the estimated directions. The beamforming outputs obtained by steering the main beams to the distinct directions of resolvable multipath signals are combined in a maximal ratio manner to exploit angular diversity gain. The performance elf the proposed algorithm is finally evaluated in cellular mobile environments to verify its efficiency and is compared with that of least-squares beamforming algorithm, by taking the WiBro system as a target system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.7 no.3
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• pp.201-210
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• 1996

In this paper, we analyzed performance of a symbol timing recovery scheme for 16QAM Radio system. As a symbol timing recovery scheme, both maximum amplitude method(MAM) and wave difference method(WDM) are analyzed employing a pulse shaping filter, such as raised cosine filter(RCF) and nonlinear filter(NLF). Simulation result shows that the jitter performance of MAM or WDM using NLF is better than that using square root RCF. In order to estimate and compensate for the Rayleigh fading PSAM(Pilot Symbol Assisted Modulation) and space diversity are also employed. Consequently, BER performance of about $10^{-4}$ is obtained for $E_b/N_o$= 20 dB.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.10C
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• pp.949-957
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• 2003

This paper presents a gradient ON-OFF algorithm of which the performance is very robust even when the angle spread increases in the mobile communication environments. The proposed method getting the diversity gain by utilizing the primary and secondary eigenvector, which corresponds to the largest and the second largest eigenvalue of the autocovariance matrix of the received signal vector, outperforms the method which just utilizes one eigenvector. By applying the proposed method to IS-2000 1X signal environments, it is observed that the proposed method shows excellent performance compared to a typical beamforming method using just one eigenvector, which considerably degrades the receiving performance as the angle spread increases.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7B
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• pp.878-885
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• 2011

Due to reflect at surface of the water and limit bandwidth, it is difficult to design underwater acoustic communication systems with high-reliability and high transmission rate. Therefore the trends of underwater communication is transformed from single sensor to multiple sensor studies. However, underwater MIMO communication techniques have a high correlation value between multiple sensors on transmitters and receivers in underwater environments, it is difficult to expect space diversity gain on muli-path channels. Therefore, this paper proposed the MISO communications system with two transmit sensors and single receiver sensor, and analyzed its performance using the LDPC codes and channel compensation algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.5A
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• pp.305-310
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• 2012

This paper proposes a selection combined hybrid sequential deconvolution and single carrier modulation with a zero forcing frequency domain equalizer for single carrier transmission system in order to enhance performance. Selection combining method is an algorithm of antenna space diversities, the receiver can choose the best channel environment only with the increase of the number of antennas, but a baseband structure is the same as the traditional receiver architecture. Simulation results show that the proposed algorithm has a better performance rather than the traditional single carrier transmission with a frequency domain equalizer.

• Journal of Satellite, Information and Communications
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• v.7 no.1
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• pp.7-12
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• 2012

In this paper, we proposed spectrum sensing using cooperative relay to solve problem of sensing performance degradation due to CPE (Customer-Primise equipments) which causes low SNR (signal-to-noise ratio) problem. In cooperative communication system, AF (amplify-and-forward) and DF (decoded-and-forward) is widely used for relay mechanism. Also, it is expected that cooperative relay scheme guarantees the high sensing performance by its diversity gain. Based on these backgrounds, in this paper, we apply to cooperative relay scheme to the CR (cognitive radio) system, and simulation results show comparison of the sensing performance between AF and DF.

• Journal of Satellite, Information and Communications
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• v.6 no.2
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• pp.117-124
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• 2011

In this paper, we present more effective throughput enhancement technique to improve the data rate and reliability by using the multiple antenna technique. The conventional spatial diversity scheme is limited in according with the interference from each antenna channel status, and the orthogonality of spreading codes and subcarriers are destroyed due to the frequency selectivity. Proposed system is considered MC-CDMA system with 4 transmit antennas and 1 receive antenna. Proposed system based on SVD with the MS-RLS MMSE subcarrier combining method in order to achieve better performance with low computational complexity. Via computer simulation, we confirm that the proposed system is able to improve the BER performance by suppressing the interference of other antenna signals.

• Journal of Advanced Navigation Technology
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• v.14 no.3
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• pp.328-335
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• 2010

In this paper, an efficient algorithm and area-efficient hardware architecture have been proposed for $2{\times}2$ MIMO-OFDM based WLAN baseband modem with two transmit and two receive antennas. To enhance the performance of the receiver, the efficient timing synchronization algorithm and symbol detector based on MML algorithm are presented. Also, by sharing the hardware block with multi-stage pipeline structure and using the complex multiplier based on polar-coordinate, the complexity of the proposed architecture is dramatically decreased. The proposed area-efficient hardware design was designed in hardware description language (HDL) and synthesized to gate-level circuits using 0.13um CMOS standard cell library. As a result, the complexity of the proposed modem receiver is reduced by 56% over the conventional architecture.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.4 s.346
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• pp.31-38
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• 2006

In this paper, we propose an efficient preceding scheme for STBC-Spatial Muiltiplexing OFDM systems. In MIMO systems, the precoder is designed on the assumption that feedback channel information is perfectly known to transmitter and receiver. However, feedback delay and link errors in real environment make the transmitter use the incorrect channel information and consequently cause the performance degradation. The proposed precoder is designed to compensate for the performance degradation by the diversity gain provided by STBC. At the transmitter, the precoder for each subcarrier is constructed by using the index of codebook, subcarrier correlation, and auto correlation of channel. From the simulation results, STBC-spatial multiplexing OFDM outperforms the preceded-spatial multiplexing OFDM at $SER=10^{-3}$ when the Doppler frequency is greater than 60Hz.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.1044-1053
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• 2010

Transmitting correct train control information is important in a train control system which demands safety. The train control information includes the maximum speed of trains, position of preceding trains, incline of tracks and curve sections etc. A radio frequency-communication based train control system is influenced by the noise and interference because the train control information is transmitted by wireless between a on-board system and wayside system. The radio frequency-communication based train control system is a mobile communication system due to moving trains. The inter symbol interference(ISI) occurs by the multipath fading in the mobile ommunication system. As signal-to-noise ratio(SNR) is decreased by the ISI, the train control information is not received correctly. In case of tunnel section, numerous reflected waves exist. Therefore, the power density of receiver is decreased by difference among the received times, magnitudes, phases through the multipath. So, the train suddenly is stopped by the fail-safe operation in the train control system on account of decreasing the power density of receiver. In this paper, a line of sight model-(Additive White Gaussian noise(AWGN) channel), rayleigh and rician fading model are presented. Probability density functions which are related to the SNR are derived from the models. The fading phenomenon severely occurs as a result of analyzing the probability density functions. So, the space diversity method is used in order to reduce the fading effect and it is demonstrated by using Matlab program.