• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.8C
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• pp.742-749
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• 2009

In this paper, we propose mitigation techniques using time-domain shortening filter (TSF) and frequency-domain shortening filter (FSF) to overcome inter-block interference (IBn and inter-carrier interference (ICn due to the time difference of arrival (TDoA) and carrier frequency offset (CFO) between downlink and uplink signals from access point (AP) and subscriber station (SS) in synchronous digital duplexing (SDD)/orthogonal frequency division multiple access (OFDMA) systems for indoor wireless communication. The proposed TSF and FSF maximize SIR for shortening in time (SIRST) and SINR for shortening in frequency (SINRSF), respectively, by using channel impulse responses and timing information among stations, obtained from mutual ranging procedure. It is verified by computer simulation that the proposed TSF and FSF reduce effectively the effects of IBI and ICI in the SDD/OFDMA systems.

• Journal of Korea Society of Industrial Information Systems
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• v.16 no.4
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• pp.27-35
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• 2011

Multicarrier-Direct Sequence/Code Division Multiple Access(MC-DS/ CDMA) which is a combination of Orthogonal Frequency Division Multiplexing(OFDM) and DS/CDMA has been of significant interest as a means to take such advantages as bandwidth efficiency, high bit rate and robustness against multipath fading. In this paper we study a reduced-complexity multiuser detection aided multirate MC-DS/CDMA with time(T)-domain and frequency(F)-domain spreading. The one- dimensional orthogonal variable spreading factor(1D OVSF) code extracted from 2D OVSF code are used as a spreading code in T/F-domain. The proposed system will use code grouping interference cancellation(CGIC) receiver to reduce Multiuser Interference(MUI). The CGIC receiver uses code grouping by the correlation properties of 1D OVSF code and dose not requires the code information and activity of other user. The multiuser detector with CGIC receiver will be analyzed in Time- and Frequency-domain separately(jointly). The system performance is analytically derived in Additive White Gaussian Noise(AWGN) channel and we also compare the system performance between proposed system and T/F spreaded single(multi) rate multiuser MC-DS/CDMA system. In the computer simulation results, the proposed receiver of demonstrated huge performance improvement over conventional matched filter receiver.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.108-111
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• 2009

In this paper, the development of unmanned vehicle systems to analysis applicable communications and alternative IEEE 802.11a. IEEE 802.11b/g uses the 2.4GHz. So, using the 5GHz OFDM in IEEE 802.11a interference phenomenon better. IEEE 802.11a has a maximum speed of 54Mbps. Indoors and apartment parking on experiment to soft roaming, hard roaming. Test equipments are AP four units(RSU), reliable results for the AP one unit Bridge, Switch one unit, one server notebook, one notebook(OBU), one car. Use Softwares are Wireshark, Jperf, Ping and million second transfer was used to develop the program. So the actual car was similar to the environment. With the results of the experiment for the unmanned vehicle systems will provide the best method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9C
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• pp.826-833
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• 2007

In this paper, we present an adaptive transmission system model to establish the baseline for wireless adaptive transmission using CR (Cognitive Radio) systems, and propose an adaptive transmission scheme based on IT (Interference Temperature) cognition for CR systems in the presented system environment. The proposed CR adaptive transmission scheme is the method that provides the CR user with the maximum transmit power in the range of not causing any interference to the incumbent user and guaranteeing the optimal throughput by applying CR-AMC (CR-Adaptive Modulation and Coding) in the given channel state. Simulation results show that in case of using the proposed CR adaptive transmission scheme, there is little degradation of BER performance, while causing no interference to the incumbent user. At the same time, the proposed scheme guarantees the optimal throughput to the CR user in the given channel state.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.3
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• pp.27-33
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• 2008

In this paper, we propose a cognitive beamforming scheme for coexistence of CR (Cognitive Radio) and IR (Incumbent Radio) systems. In order to maintain the priority of the IR in spectrum utilization the proposed cognitive beamforming scheme needs to have the CR not cause any interference to the IR systems occupying the same frequency band at the same time. In addition the proposed scheme has to provide maximum channel gain to the CRU (CR User) in a boundary of satisfying the former criterion. For this purpose, the proposed scheme does not cause any interference to the IRU (IR User), while the CRU is served without additional radio resource consumption. From simulation, we confirmed that when using the proposed scheme the CRU does not interfere with the IRU and there is little bit error rate performance degradation of the CRU as compared to that of the ideal beamforming system, which does not consider the IR priority.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.5
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• pp.27-36
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• 2012

We propose a new scheme combining the calibration of the path imperfections and the compensation of HPA nonlinearity in the downlink OFDM smart antenna systems. We use a two term third-order polynomial (without second-order term) and the indirect learning architecture for calibration and compensation, to make each path of the antenna array have equal characteristics. We test our scheme with computer simulations. The result shows that, with the addition of only one third-order term, the adverse nonlinear effects as well as the those of linear imperfections can be effectively compensated.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.63-66
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• 2010

본 논문은 차세데 3D-TV 방송을 위해 수정된 ATSC (Modified Advanced Television Systems Committee) 시스템 [1]에서 파일럿 (Pilot)을 이용한 채널 추정 대신, PN 시퀀스 (Pseudo-Noise Sequence)를 이용한 채널 추정 방식의 문제점에 대하여 2가지 방법으로 연구하였다. PN 시퀀스를 이용하여 채널을 추정하는 TDS-OFDM (Time Domain Synchronous - Orthogonal Frequency Division Multiplexing)시스템은 QAM (Quadrature Amplitude Modulation) 변조 방식을 사용하기 때문에 수신측 PN 시퀀스의 위상 변화가 일어나지 않는다. 하지만 수정된 ATSC 시스템에서 사용하는 VSB (Vestigial Side Band)변조 방식에서 직교위상 (Quadrature) 채널을 통해 전송되는 값은 동위상 (In-Phase) 채널을 통해 전송되는 값의 단순한 힐버트 변환 (Hilbert Transform)에 의해 생성되어 불규칙한 위상 변화가 발생한다. 따라서 수정된 ATSC 시스템에서 채널 추정을 위해 PN 시퀀스를 사용하게 된다면 상관 (Correlation) 특성을 잃어버릴 것이며 올바른 채널 임펄스 응답 (Channel Impulse Response)을 얻을 수 없다.

• ETRI Journal
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• v.40 no.4
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• pp.537-545
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• 2018

In this paper, we present a comprehensive analytical study of the symbol error rate (SER) of single-carrier frequency-division multiple access (SC-FDMA) with zero-forcing frequency domain equalization (ZF-FDE) over a Rayleigh fading channel. SC-FDMA is considered as a potential waveform candidate for fifth-generation (5G) radio access networks (RANs). First, the $N_C$ fold convolution of the noise distribution of an orthogonal frequency-division multiplexing (OFDM) system is computed for each value of the signal-to-noise ratio (SNR) in order to determine the noise distribution of the SC-FDMA system. $N_C$ is the number of subcarriers assigned to a user or the size of the discrete Fourier transform (DFT) precoding. Here, we present a simple alternative method of calculating the SER by simplifying the $N_C$ fold convolution using time and amplitude scaling properties. The effects of the $N_C$ fold convolution and SNR over the computation of the SER of the SC-FDMA system has been separated out. As a result, the proposed approach only requires the computation of the $N_C$ fold convolution once, and it is used for different values of SNR to calculate the SER of SC-FDMA systems.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2014.06a
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• pp.126-128
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• 2014

디지털 방송기술의 비약적인 발전으로 기존 HD(High Definition) 화질의 4~16배까지 지원 가능한 UHD(Ultra High Definition) 방송 서비스가 제공되는 새로운 시대를 맞이하게 되었다. UHD 방송은 초고선명 비디오와 22.2 채널 오디오 서비스가 가능한 차세대 실감방송 기술이다. 이러한 UHD 서비스를 제공하기 위해서는 고압축 영상 코덱 기술인 HEVC(High Efficiency Video Coding), OFDM(Othogonal Frequency Division Multiplexing) 기반 대용량 전송기술과 다양한 멀티미디어 부가서비스 가능한 전송 프로토콜이 필수적으로 요구된다. 최근 UHD 방송 전송 프로토콜로 표준화 추진 중인 MMT(MPEG Media Transport)는 이기종망에서 적용할 수 있으며, 양방향 전환이 가능하여 시청자의 요구사항을 실시간으로 반영할 수 있다는 장점을 지닌다. 한편, 지상파 UHD 방송 서비스를 빠르고 효과적으로 수신하기 위해 필요한 정보인 NIT(Network Information Table), RRT(Rating Region Table) 및 SDT(Service Description Table)가 MMT 시그널링 프로토콜에서는 포함되어 있지 않다. 따라서 본 논문에서는 지상파 UHD 방송 서비스의 효과적 수신이 가능한 MMT 기반 지상파 UHD 방송을 위해 NIT, RRT 및 SDT 정보가 포함된 서비스 시그널링 구조을 제안한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.11
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• pp.3008-3025
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• 2012

In this paper, the downlink resource allocation of OFDMA system with decode-and-forward (DF) relaying is investigated. A non-convex optimization problem maximizing system throughput with users' satisfaction constraints is formulated with joint relay selection, subcarrier assignment and power allocation. We first transform it to a standard convex problem and then solve it by dual decomposition. In particular, an Optimal resource allocation scheme With Time-sharing (OWT) is proposed with combination of relay selection, subcarrier allocation and power control. Due to its poor adaption to the fast-varying environment, an improved version with subcarrier Monopolization (OWM) is put forward, whose performance promotes about 20% compared with that of OWT in the fast-varying vehicular environment. In fact, OWM is the special case of OWT with binary time-sharing factor and OWT can be seen as the tight upper bound of the OWM. To the best of our knowledge, such algorithms and their relation have not been accurately investigated in cooperative OFDMA networks in the literature. Simulation results show that both the system throughput and the users' satisfaction of the proposed algorithms outperform the traditional ones.