• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1A
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• pp.24-33
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• 2007

In this paper, two different dynamic cell coordination strategies for frequency flat and selective fading are proposed for efficient subcarrier allocation in the joint consideration of adaptive modulation and variable frequency reuse in the channel-aware OFDMA downlink multicellular environment. Compared to a conventional OFDMA system without cell coordination, where system throughput may become degraded due to the persistent interference from other cells, the proposed system dynamically allows RNC to apply different reuse factors on each subchannel and scheduling in consideration of channel and interference conditions of individual users so as to increase the system throughput and guarantee QoS of each user. In a frequency flat fading, the dynamic scheme with the proposed scheduling achieves on average three times larger throughput than the conventional dynamic scheme [8]. In a selective fading channel, the proposed schemes showed 2.6 times as large throughput as that of a single reuse factor of one for all subchannels.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.5 no.1 s.9
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• pp.45-54
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• 2006

The UWB signal distortion in frequency selective channel has made it difficult to implement the channel estimator and the synchronizer of the UWB receiver. In this paper, we examine the performances of TR(Transmitted Reference) and DTR(Differential TR) UWB which use either reference pulse or differential method to estimate the channels. we also propose a FSK-based PRM(Pulse Repetition Modulation) UWB system as an another form of UWB system which is advantageous in frequency selective channel. Finally, resorting to statistical analysis, we examine the noise effect due to noisy reference at an auto-correlation(AcR) receiver. moreover, SNR dependance of the integration length in the AcR receiver is also investigated.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.116-120
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• 2008

The conventional channel selection method for a ZigBee communication network basically detects the energy values in all channels. In the ISM band, no license is required to use channels in this band, so there may exist various interference factors in this band. It is well known that WLAN is the major interference factor degrading the performance of ZigBee in the ISM band. In this paper, we propose an efficient channel selection algorithm which uses the pattern of WLAN channel uses as the a priori information. By using the proposed algorithm, we may save the time required to select channels for the ZigBee communications.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.2
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• pp.235-243
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• 2012

In this paper, we propose a method to improve performance of pilot symbol assisted modulation(PSAM) channel estimation method for OFDM systems over frequency selective channel. When channel values are estimated, the low pilot density used for channel estimation increases not only the effective data rate but also power efficiency. Thus, the lower pilot density which is used for channel estimation is better for OFDM system. At first, we estimate the channel values which are located at the middle of adjacent pilots, and then all of the possible channel values are estiamted by using original pilot values and previously estimated pilot values. Furthermore, the error of estimated channel values is reduced by introducing guard interval which is designed acccording to maximum channel delay. Performance achieved with the proposed method is illustrated by simulation experiments in comparison with the existing methods in terms of mean squared error(MSE).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7A
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• pp.710-716
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• 2007

In this paper, a new scheme of downlink co-channel interference (CCI) cancellation in OFDM cellular networks is introduced for users at the cell-edge. Coordinated symbol transmission between base stations (BS) is operated where the same symbol is transmitted from different BS on different sub-carriers. At the mobile station (MS) receiver, we introduce a soft decision maximum likelihood CCI canceler and a modified maximum ratio combining (M-MRC) to obtain an estimate of the transmitted symbols. Weights used in the combining method are derived from the channels coefficients between the cooperated BSs and the MS. Simulations show that the proposed scheme works well under frequency-selective channels and frequency non-selective channels. A gain of 9 dB and 6 dB in SIR is obtained under multipath fading and flat-fading channels, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.3C
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• pp.153-157
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• 2005

Frequency selective fading occurs due to the Doppler Effect in mobile communication systems. The performances of the systems are rapidly reduced due to effect of multiuser interference under frequency selective channels at DS-CDMA systems. To overcome these problems, we adopted the multi-carrier modulation techniques, and it is able to solve the frequency selective channel effects by means of these modulation techniques, and interference problems due to multiuser access are solved by means of multiuser detection techniques. In this paper, we proposed the blind MOE/PIC multiuser detection method which is composed of both the blind multiuser detection technique and parallel interference canceller. Thus, simulation results show that the proposed method performs better than conventional methods.

• Proceedings of the Korean Information Science Society Conference
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• 1999.10c
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• pp.253-255
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• 1999

주파수 선택적 페이딩을 통하여 무선통신에서 등화기로 결합된 다중 채널을 이용하여 성능을 평가하고 가우시간 잡음 상태와 독립적인 페이딩의 환경화에서 심볼간의 간섭과 데이터 이동 전송에서 발생되는 페이딩을 최소화하고 분산된 페이딩을 역변환하여 샘플링하고, 신호벡터의 특성을 이용하여 시뮬레이션을 통해 성능을 분석한다.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2003.06a
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• pp.292-295
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• 2003

블루투스 전송 기술은 2.4㎓ 의 ISM(Industrial Scientific Medicine)밴드에서 주파수 호핑 방식을 사용한다. 주파수 호핑율은 연결 상태에서 초당 1600회, 조회 또는 호출 상태에서 초당 3200회의 호핑을 한다. Hop 채널 선택은 블루투스 표준안에서 제시한 5개의 호핑 시퀸스 중 하나를 선택하고 호핑 주파수에 따라 이를 매핑 함으로써 이루어진다. 본 논문에서는 6개의 상태에 따라 다르게 실행되는 채널 계산을 효율적으로 제어하고 필요한 연산모듈의 수를 줄이기 위해 9비트 프로세서를 이용해 Hop 선택 모듈을 설계하고 구현한다. 설계된 모듈은 레지스터 파일, 마이크로프로그램 제어장치, 가산, 치환(permutation), Modulo 계산을 위한 3개의 연산장치로 구성된다. Hop 채널 계산 중 가장 클럭 소요가 큰 Modulo 연산은 SRT나눗셈 알고리즘을 사용하여 음수 값 계산 및 연산 속도 향상을 꾀하였다. 제시된 Hop 선택 모듈은 하드웨어 묘사언어인 VHDL로 설계하고 시뮬레이션 및 테스트는 Xilinx FPGA를 이용해 검증하였다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.5
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• pp.1031-1037
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• 2011

Pilot symbol assisted modulation (PSAM) can be used for the channel estimation in orthogonal frequency division multiplexing (OFDM) transmission systems. However, imperfect channel estimates in PSAM systems degrade the bit error rate (BER) performance. I derive the BER of PSAM OFDM systems over time dispersive fading channels. The BER performance of OFDM systems with SFBC antenna diversity are analyzed, where data is transmitted over time and frequency selective Rayleigh fading channel. The performance of this PSAM SFBC OFDM systems, gauged by the average bit error rate, is analyzed considering the channel estimation error.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.2B
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• pp.176-183
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• 2011

In this paper, we propose the implementation and performance analysis of power line communication based on SISO/MIMO-OFDM which focuses on high speed data transmission in smart grid and future power line grid. We employ Zimmermann frequency model and Middleton Class A model as the multipath power line fading channel and impulse noise channel, respectively. In this paper, in order to improve the three-phase or single-phase PLC performance, we introduce a new MRC (called a&f-MRC) which effectively sums up multiple antenna diversity gain and multipath fading diversity gain. Via simulation, we prove the performance advantage over existing SISO/MIMO systems. In addition, we offer the tradeoff on system design through comparing with MRC, EGC and SC.