• 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.32 no.2C
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• pp.95-112
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• 2007

Spatial Multiplexing techniques, which is a kind of Multiple antenna techniques, provide high data transmission rate by transmitting independent data at different transmit antenna with the same spectral resource. OFDM (Orthogonal Frequency Division Multiplexing) is applied to MIMO (Multiple-Input Multiple-Output) system to combat ISI (Inter-Symbol Interference) and frequency selective fading channel, which degrade MIMO system performance. But, orthogonality between subcarriers of OFDM can't be guaranteed under high-mobility condition. As a result, severe performance degradation due to ICI is induced. In this paper, both ICI and CAI (Co-Antenna Interference) which occurs due to correlation between multiple antennas, and performance degradation due to both ICI and CAI are analyzed. In addition to the proposed CIR (Channel Impulse Response) estimation method for avoiding loss in data transmission rate, HIC (Hybrid Interference Cancellation) approach for guaranteeing QoS of MIMO-OFDM receiver is proposed. We observe the results on analytical performance degradation due to both ICI & CAI are coincide with the simulation results and performance improvement due to HIC are also verified by simulation under SCM-E Sub-urban Macro MIMO channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12B
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• pp.1728-1735
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• 2011

In this paper, satellite data link waveform is proposed which is based on the waveform of Link-16 but LDPC code is studied instead of CCSK code in order to be optimized to satellite nonlinear channel environment and transmission characteristics. And the DSM (Demux, Selective CH switch, and Mux) transponder structure is suggested which can remove all of the jamming signal out of the transmission signal band and convert uplink hopping frequency to desired ones of downlink. The results of BER and anti-jamming performance analysis shows that the required Eb/No and processing gain in the worst case partial band jammer of the proposed waveform are 2.5dB and 52dB respectively and the anti-jamming capacity improvement of DSM transponder is maximum 2dB.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.59-60
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• 2005

OFDM communication system is effective for the high data rate transmission in the frequency selective fading channel. Since OFDM has high PAPR, OFDM signal may be distorted by the nonlinear HPA. In this paper, we propose an combined SLM and PTS method for reducing the PAPR in OFDM communication system. Proposed method increased some system complex in comparison with exiting method..

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.481-484
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• 2003

OFDM(Orthogonall Frequency Division Multiplexing) is an efficient transmission techniques for the frequency selective fading wireless channel where conventional modulations suffer from severe performance degradation. Recently, more efficient techniques for the OFDM are paid much attention such as adaptive modulation for each subcarrier, since more bit rate has been required for the wireless data network [1-3]. The proposed system employs the adaptive modulation between transmitter and receiver in each subcarrier, where the bit and power is properly allocated. Also multiple antenna system called MIMO is considered, which result in robustness in channel delay, improved power efficiency and improved bit SNR for the given BER.

• Proceedings of the IEEK Conference
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• 2000.07a
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• pp.73-76
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• 2000

In the basic continuous ARQ schemes (Go-Back-N or Selective Repeat ARQ), each block is continuously transmitted without interruptions. Only when the transmitter receives NAK from the receiver side, the transmitter stops sending current data block and retransmit the erroneous block (Naked block). When channel error rate increases and become sufficiently high, there exists a point at which each block of message is transmitted, on average, more than once. Under such conditions, it will be more efficient to send continuously two or more copies(generally $\ell$ copies) of each block from the first transmission over noisy channel. A request for repeat will be made again only when none of $\ell$ duplicates are received correctly. By this way, the proposed scheme yields a better throughput efficiency and holds nearly constant throughput as compared to others continuous A.R.Q schemes under wide error rate variations (0 < P < 0.3).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.11A
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• pp.1841-1847
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• 2001

A novel decision-feedback equalization technique for a generalized filter bank based orthogonal frequency division multiplexing data transmission system operating in a frequency selective multipath fading channel is presented in this paper. At the cost of relatively increased computational complexity in comparison to the conventional OFDM systems, the proposed system achieves a better performance in trims 7f bit error rates. The simulation results confirm of superiority and robustness of our method, particularly, in the low SNR channel environments.

• Proceedings of the Korea Information Processing Society Conference
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• 2009.04a
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• pp.1300-1302
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• 2009

인간 생활의 질적인 향상을 위해, 각종 시스템이 연구되고 있다. 특히 작고 설치가 용이한 센서를 중심으로 Ubiquitous 분야가 발달하고 있으며, 센서 네트워크에 대한 연구가 활발히 진행되고 있다. 특히 일반적인 생활에는 물론 의료, 노약자의 보호, 위험 감지 등의 중요한 분야에까지 센서 네트워크가 활용됨으로써 데이터 전송의 정확성과 신뢰성은 중요한 문제로 대두되었다. 이에 본 논문에서는, 센서의 특성과 무선 통신의 특징을 고려하여 에너지 효율성 및 데이터 전송의 신뢰성을 향상시키기 위한 방법을 제시하고자 한다. 특히 RSSI 신호와 채널 에러율을 함께 이용하여 각 노드 경로별 신뢰도를 계산하고, 이에 따라 선택적으로 Acknowledgement를 사용하며 오버히어링 문제를 역으로 이용하여, 묵시적 Acknowledgement로 사용함으로써 에러율이 높고 에너지가 한정되어있는 무선 센서 네트워크에서 계속적인 ACK/NACK 사용으로 인한 에너지 소비 및 트래픽 낭비를 줄이고자 한다.

• ETRI Journal
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• v.44 no.1
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• pp.125-134
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• 2022

Visible light communication (VLC) systems incorporate ambient lighting and wireless data transmission, and the experienced channel in indoor VLC is a major topic that should be examined for reliable communication. In this study, it is realized that multiple transmitters in classical alignment are the forceful factors for channel characteristics. In the frequency band, fluctuations with sudden drops are observed, where the fluctuation shape is related to the source layout and receiver location. These varying frequency-selective channels need solutions, especially for mobile users, because sustained channel estimation and equalization are necessary as the receiver changes its location. It is proven that using light-emitting diodes (LEDs) with highly directional beams as sources or using a detector with a narrow field of view (FOV) in the receiver may help partially alleviate the problem; the frequency selectivity of the channel reduces in some regions of the room. For flat fading channel characteristics all over the room, LEDs should be aligned in hexagonal cellular structure, and detector FOV should be arranged according to the cell dimension outcomes.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.1
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• pp.40-47
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• 2015

We propose a method to provide a selective VoD service during live streaming sessions. In the proposed method, each peer joined the live streaming session receives video stream packets with P2P manner and stores the packets to provide a VoD service. To mitigate the overhead of each peer node to store the video stream packets, the proposed scheme categorizes peers into three different groups based on their link types. To increase data gathering speed and reduce the network load, we also proposes the P2P transmission scheme within the same AP network for the peers with Wi-Fi link. To evaluate the performance of the proposed method, we implement computer simulator using NS-3. Simulation results show that the proposed method reduces the overhead about 66% and increases the P2P data gathering speed about 50% compared to the conventional schemes.