• Information and Communications Magazine
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• v.14 no.6
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• pp.109-122
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• 1997

본 고에서는 통과 대역 DMT ADSL 시스템의 등화기 구조를 설계하고 이를 포함하는 DMT ADSL 시스템 성능 모델을 제시하였다. CSA 지역에서 다중 반송파 변조 방식(multicarrier modulation)을 전송방식으로 하는 6Mb/s급의 ADSL 서비스를 위하여 가입자 루프 및 전송신호 특성을 고려한 노이즈 모델을 고찰하고 DMT ADSL 시스템에서 성능예측을 위한 시뮬레이션 모델을 제시하였다. 그리고 기존에 설치되어 있는 일반 전화선(unshilided twisted pair copper wire)를 이용하여 ATM 환경에서 가입자에게 주문형 비디오(video on demand) 서비스, 화상전화회의 서비스, 고속 인터넷 접속 서비스를 제공하기 위한 서비스 망 구조를 제시하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.6
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• pp.512-519
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• 2013

In this paper, we propose a novel unambiguous correlation function for composite binary offset carrier (CBOC) signal tracking. First, we observe that a sub-carrier of CBOC signal is seen as a sum of four partial sub-carriers, and generate four partial-correlations composing the CBOC autocorrelation. Then, we obtain an unambiguous correlation function with a sharp main-peak by re-combining the partial correlations. From numerical results, we confirm that the proposed unambiguous correlation function offers a better tracking performance than the conventional correlation functions in terms of the tracking error standard deviation and multipath error envelope.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.2
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• pp.6-12
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• 2008

In uplink cable modem link operated in time-division multiple access mode, it is crucial to employ a suitable preamble pattern enabling frame detection, coarse timing/carrier recovery. Preamble pattern based on the constant envelope zero autocorrelation sequence is proposed for the uplink cable modem compliant to the data over cable service interface specification. Frame detection, coarse/fine timing and carrier recovery algorithms suitable for the proposed preamble pattern are also proposed. We check up the performances using numerical results.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2015.07a
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• pp.301-302
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• 2015

케이블 방송망에서 멀티-Gbps(Giga bit per second) 초고속 인터넷 서비스 제공을 위해 최근 북미에서 DOCSIS 3.1(Data over Cable Service Interface Specifications Version 3.1) 표준을 발표하였다. DOCSIS 3.1 은 최대 10Gbps 하향 데이터 전송과 최대 2Gbps 의 상향 데이터 전송을 목표로 한다. DOCSIS 3.1 이 이전 DOCSIS 표준들과 다른 점은 전송 효율을 높이기 위해 물리계층 전송 방식에 큰 변화를 주었다는 점이다. 기존 6MHz 대역폭의 단일 반송파 전송 방식에서 최대 192MHz 광역 채널의 다중 반송파 전송 방식으로 변경하였다. 또한 채널 오류정정 방식으로 BCH(Bose, Chaudhuri, and Hocquenghem)와 LDPC(Low Density Parity Check) 연접부호를 적용하여, 이로 인한 SNR 성능 이득 통해 4096-QAM 의 고차 변조를 지원한다. 본 논문에서는 최대 192MHz 의 광역 채널로 전송되는 약 2Gbps 의 전송 데이터에 대한 채널 오류 정정을 위해 고속의 LDPC 복호기 구현 방법을 제시한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.2
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• pp.295-302
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• 2014

OFDM technique uses multiple sub-carriers for the data transmission. Therefore, inter carrier interference is generated because of nonlinear high power amplifier and carrier frequency offset. Wireless OFDM transmission over Doppler fading channels also causes inter carrier interference. The interference increases the bit error rate in receiver. Sub-carrier allocation methods in LTE and WiMAX standards are different. The performance of OFDM systems using different sub-carrier allocation, gauged by the bit error rate, is analyzed considering the nonlinear high power amplifier, carrier frequency offset and Doppler fading channels.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.2
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• pp.280-286
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• 2007

In this paper, the phase noise effects of OFDM transceiver diversity systems were analyzed. Since OFDM communication system is very sensitive to phase noise, the system performance may degrade seriously due to the increase of subcarrier interferences and system noise. Therefore, the phase noise model was suggested and its distribution and power were varied to investigate the effects of phase noise on the system performance. The degree of the system performance degradation depends on the specific diversity structures of transceiver systems. Here, the performances of OFDM systems with two antennas transceiver diversity were analyzed and compared with that of systems with only transmission diversity and without diversity as the phase noise characteristics varied.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.1
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• pp.29-37
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• 2005

One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can Provide another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1349-1355
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• 2016

It should guarantee high reliability and ultra low latency communication. Additionally, it should support connection between massive devices. As one of estimated scenarios for 5G mobile communication, mobile devices and sensors using low data rate wireless communication will increase. For communication of these devices, single-carrier system can be considered. In order to satisfy these requirements, in this paper, we propose CDMA (Code Division Multiple Access) system using complex spreading and Multi-level BPSK(Binary Phase Shift Keying). The proposed system spread transmit symbol by using chip code consisted of real and imaginary number. As simulation results, we can confirm that although the proposed system has 3dB lower BER (Bit Error Rate) performance than conventional CDMA system, the proposed system can support 2 times more users in comparison with conventional CDMA system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.2
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• pp.294-301
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• 2013

OFDM technique uses multiple sub-carriers for the data transmission. Therefore, bit error rate increases because of inter-carrier interference caused by nonlinear high power amplifier and carrier frequency offset. Wireless OFDM transmission over multi path fading channels is characterized by small transmission gain in multiple sub-carrier frequency interval. Therefore bit error rate increases because of burst errors. Inter-leaver and convolution error control coding are effective for the reduction of this burst error. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of this convolution coding OFDM systems using inter-leaver, gauged by the bit error rate, is analyzed considering the nonlinear high power amplifier, carrier frequency offset and channel estimation error.

• Proceedings of the Korea Contents Association Conference
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• 2003.11a
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• pp.289-302
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• 2003

In this paper, the performance of a multicarrier CDMA system applying adaptive modulation and adaptive subchannel allocation scheme is analyzed in wireless environment. In case of the proposed system, total subchannels is 4 and data is transmitted over 2 subchannels with the biggest fading, Threshold of each channels is 5.2 ㏈, 9 ㏈, 13.2 ㏈ and 8.4 ㏈, 12.2 ㏈, 16.3 ㏈. The BER of 10-3 is 8.1 ㏈. This is increased 12.9 ㏈ in comparison with the existing system. The BPS according to average channel is needed average E$_{b}$ N$_{o}$ of about 15 ㏈ in 7 bit.t.