• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6A
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• pp.547-554
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• 2010

Recently, the multi-band orthogonal frequency division multiplexing(MB-OFDM) system, one of UWB system, can satisfy the requirement and can be applied to various wireless communication services because ultra-wideband(UWB) is a wireless communication technique that supports high data rate with low power. In this paper, the method applying Alamouti's space time block code(STBC) and cyclic delay diversity(CDD) is proposed. The proposed method can be easily applied with arbitrary number of relays and only needs two time slots of quasi stationary assumption. And it is applied to the MB-OFDM system. Second, an optimal relaying scheme based on decode-and-forward(DF) method is proposed which is provides good error performance compared to conventional schemes.

• Proceedings of the Korea Contents Association Conference
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• 2004.05a
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• pp.423-428
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• 2004

In this paper, STBC (Space Time Block Code) is applied to the WB system and frequency repeated diversity is used to get the 4-th order space time diversity gain. The performance of が STDB-OFDM system is analyzed by computer simulation. As a result of simulation, proposed W system can reduce the complexity that is introduced by increasing number of transmit antenna and show the same performance of 4 antennas with only using 2. Proposed system shows the enhancement of 7.1 dB compared to the general UWB OFDM and 1.9 dB compared to UWB STBC-OFDM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.11C
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• pp.673-681
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• 2011

In this paper, we design multiple antenna relay transmission schemes of low complexity to enhance the spatial diversity in orthogonal frequency division multiplexing (OFDM) systems. The relay scheme underlined, can provide space time block coding (STBC) of OFDM signals in the time domain without IFFT and FFT operations with much reduced complexity. In this paper, we modify the conventional low-complexity STBC-OFDM relaying scheme to be compatible to the existing OFDM systems. In addition, we extend the proposed scheme for multiple antenna relays and provide performance enhancement strategies according to the channel quality information available at the relay. The proposed scheme is shown to improve the diversity and thereby to reduce the outage probability and coded bit error rate. Therefore, the proposed scheme will be promising for service quality improvement or coverage extension based on OFDM like wireless LANs and maritime communications.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.239-252
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• 2008

For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response, resulting in a loss of bandwidth efficiency. In this paper, we describe a new technique to restore the cyclicity of the received signal when the CP is not sufficient for OFDM systems. The proposed technique efficiently restores the cyclicity of the current received symbol by adding the weighted next received symbol to the current received symbol. Iterative CP reconstruction (CPR) procedure, based on the residual intersymbol interference cancellation (RISIC) algorithm, is analyzed and compared to the RISIC. In addition, we apply the CPR method to Alamouti space-time block coded (STBC) OFDM system. It is shown that in the STBC OFDM, tail cancellation as well as cyclic reconstruction of the CPR procedure should be repeated. The computational complexities of the RISIC, the proposed CPR, the RISIC with STBC, and the proposed CPR with STBC are analyzed and their performances are evaluated in multipath fading environments. We also propose an iterative channel estimation (CE) method for OFDM with insufficient CP. Further, we discuss the CE method for the STBC OFDM system with the CPR. It is shown that the CPR technique with the proposed CE method minimizes the loss of bandwidth efficiency due to the use of CP, without sacrificing the diversity gain of the STBC OFDM system.

• Journal of Korea Society of Industrial Information Systems
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• v.20 no.6
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• pp.1-10
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• 2015

In this paper, we propose a spectral efficient orthogonal frequency division multiple access(OFDMA) transmission system using multiple relays for a shadow area. The performance of the proposed OFDMA system in a shadow area can be improved by applying space-frequency(SF) block code over relaying multi-path channels. A simple channel cyclicity restoration method is also added in the proposed OFDMA system without cyclic prefix(CP) to recover the destruction of channel cyclicity due to the lack of CP. Simulation results show that the proposed OFDMA system without CP is almost same as that of the conventional OFDMA system with sufficient CP, which increases the spectral efficiency of the system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.8
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• pp.1643-1648
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• 2005

MIMO system takes advantage of the spatial diversity obtained by spatially separated antennas for high- performance and high-capacity broadband wireless access. In this paper, we propose Carrier Interferometry coded MIMO-OFDM system (MIMO-CI/OFDM) which provides frequency and spatial diversity. One combined diversity gains featly improve the performance of OFDM systems. To perform a performance analysis, we have used SPW platform that provides an easy tool to analyze the performance. The results show that the performance of MIMO-CI/OFDM shows an approximately 4dB gain over the MIMO-OFDM even in highly frequency selective fading channels.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.11a
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• pp.247-250
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• 2008

본 논문에서는 다중안테나-직교 주파수 분할 다중화(multiple input multiple output orthogonal frequency division multiplexing, MIMO-OFDM)시스템 중 공간 다중화와 전송 다이버시티 이득을 동시에 얻기 위해 제안된 double space-time block code(D-STBC) OFDM 시스템에 대해 기존 수신 기법인 그룹단위 간섭 제거 기법의 문제점을 보완하는 새로운 간섭 제거 기법을 제안한다. 또한 STBC의 다이버시티 이득을 극대화 할 수 있는 컴포넌트 인터리버 구조를 송수신단에 추가함으로써 수신 성능을 크게 향상시킨다. 이동방송 수신을 고려한 빠른 시변 채널환경에서의 전산 모의 실험을 통해 STBC의 부호직교성 상실로 인한 성능열화 현상이 개선됨을 보이고 다비어시티 이득에 의해 수신 성능 향상을 확인한다.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.3 s.345
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• pp.1-9
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• 2006

In this paper, we propose a MIMO-OFDMA (Multi Input Multi Output-Orthogonal Frequency Division Multiple Access) system based on beamforming for performance improvement of downlink real-time traffic transmission in harsh channel conditions with low CIR (Carrier-to-Interference Ratio). In the proposed system, we first consider the M-GTA-SBA (Modified-Grouped Transmit Antenna-Simple Bit Allocation) using effective CSI (Channel State Information) calculation procedure based on spatial resource grouping, which is adequate for the combination of MRT (Maximum Ratio Transmission) in the transmitter and MRC (Maximum Ratio Combining) in the receiver. In addition, to reduce feedback information for the beamforming, we also apply QEGT (Quantized Equal Gain Transmission) based on quantization of amplitudes and phases of beam weights. Furthermore, considering multi-user environments, we propose the P-SRA (Proposed-Simple Resource Allocation) algorithm for fair and efficient resource allocation. Simulation results reveal that the proposed MIMO-OFDMA system achieves significant improvement of spectral efficiency in low CRI region as compared to a typical open-loop MIMO-OFDMA system using pseudo-orthogonal space time block code and H-ARQ IR (Hybrid-Automatic Repeat Request Incremental Redundancy).

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.4 s.95
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• pp.351-358
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• 2005

In this paper, STBC(Space Time Block Code) is applied to the UWB system and frequency repeated diversity is used to get the 4-th order space time diversity gain. The performance of UWB STBC-OFDM system is analyzed by computer simulation. As a result of analysis, proposed UWB system can reduce the complexity that is introduced by increaing number of radiator and show the same performance of 4 antennas with that only using 2 radiator. This system at the $10^{-4}$ also shows the enhancement of $7.1\;\cal{dB}$ to the general UWB OFDM and $1.9\;\cal{dB}$ to UWB STBC-OFDM.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.144-154
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• 2004

In this paper we apply the space-time block codes (STBCs), the key technologies for the 4th generation mobile communication systems, to the OFDM system and analyze their performances. First, we derive the signal models for representative STBC schemes and demodulation procedures for each scheme. We also select the parameters for OFDM system considering mobile cellular environments and assign adequate modulation schemes to STBC-OFDM schemes according to the transmission rate from 2bps/Hz to 4bps/Hz. We finally compare and analyze the performances of STBC-OFDM schemes for the selected transmission rates through computer simulations, together with performance comparison when the same modulation scheme being adopted.