• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.12A
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• pp.1161-1167
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• 2005

In this Paper, a concept of virtual smart antenna (SA) is introduced for orthogonal Sequency division multiplexing (OFDM)-based cellular systems with a frequency reuse factor equal to 1. The OFDM-based cellular system is robust to multipath channels but has a disadvantage that the intercell interference (ICI) caused by adjacent base stations is large at the edge of a cell. In this paper, after deriving the symbol timing offset estimation scheme for the OFDM signal received from multiple base stations in a quasi-static fading channel, the ICI cancellation method based on virtual smart antenna is proposed using the steering vector formed by the symbol timing offset of the desired signal and interference signals.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6C
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• pp.444-449
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• 2008

Selected mapping is well-known scheme for peak to average power ratio(PAPR) reduction in orthogonal frequency multiplexing(OFDM) systems. In this paper, we proposed a new scheme for generating a set of candidate transmission sequences. In conventional SLM, candidate sequences were generated by rotating the phases of the frequency domain OFDM M-ary symbols but in proposed scheme, candidate sequences are generated by multiplying the m-sequences with data in bit format of OFDM signals. Computer simulation results show that, as compared to the conventional SLM scheme, the proposed approach has better PAPR reduction performance and especially in case of OFDM systems which has small number of subcarriers has better performance than large ones.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.5 no.3 s.11
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• pp.29-39
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• 2006

In this paper, we propose an efficient method to detect the signal and evaluate performance of the system in frequency selective fading channel. We combine proposed system with OFDM (Orthogonal Frequency Division Multiplexing) to improve performance of the system. First, we study the SOSTTC-OFDM system using two transmit antenna and one receive antenna, and compare performance of the proposed space-time coded OFDM with that of previous system. We expand this system to the system using four transmit antennas with the proposed decoding method. Simulation results show that the proposed decoding method can detect the signal efficiently, and we identify that the performance of the proposed system is shown with varying doppler frequency in frequency selective fading channel.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1996.06a
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• pp.55-59
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• 1996

In this paper, we first analyze the influence of interference due to the time variation and delay spread of the mobile channel on an orthogonal frequency division multiplexing (OFDM) system. With the result, we obtain the bit error rate performance of the 16-QAM OFDM system. Second, we investigate the performance of the Reed-Solomon (RS) coded 16-QAM OFDM system when the number of subcarriers varies. In the investigation, we assume that the information transmission rate and the total bandwidth expansion due to coding, guard interval, and the number of subcarriers are fixed. Under this condition, it is observed that there are optimum numbers of subcarriers that minimize the post decoding symbol error probability of RS code for various channel states.

• Journal of Communications and Networks
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• v.12 no.6
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• pp.533-543
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• 2010

This paper proposes an orthogonal frequency division multiplexing (OFDM) waveform for the forward link of a fixed broadband satellite system. We focus on the synchronization tasks in the receiver. Our objective is to minimize the required overhead, in order to improve the spectral efficiency with regard to a single carrier waveform system. A non pilot aided algorithm is used for fine synchronization. It is preceded by a coarse synchronization stage, which relies on a limited overhead (short cyclic prefix associated to some pilots). The performance of the proposed receiver is assessed through simulation results.

• Journal of Communications and Networks
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• v.14 no.3
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• pp.257-266
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• 2012

A decode-and-forward two-way relay system benefits from orthogonal frequency division multiplexing (OFDM) and relay transmission. In this paper, we consider a decode-and-forward two-way relay system over OFDMwith two strategies: A joint subcarrier matching algorithm and a power allocation algorithm operating with a total power constraint for all subcarriers. The two strategies are studied based on average capacity using numerical analysis by uniformly allocating power constraints for each subcarrier matching group. An optimal subcarrier matching algorithm is proposed to match subcarriers in order of channel power gain for both transmission sides. Power allocation is defined based on equally distributing the capacity of each hop in each matching group. Afterward, a modified water-filling algorithm is also considered to allocate the power among all matching groups in order to increase the overall capacity of the network. Finally, Monte Carlo simulations are completed to confirm the numerical results and show the advantages of the joint subcarrier matching, power allocation and water filling algorithms, respectively.

• Journal of Communications and Networks
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• v.8 no.3
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• pp.323-329
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• 2006

For orthogonal frequency division multiplexing (OFDM), the discrete Fourier transform (DFT)-based processing at the receiver has been perceived equivalent to the matched filter (MF)-based processing. In this paper, we revisit the equivalence and mathematically show that when the guard interval is insufficient, the well-known DFT-based processing inherently causes more intersymbol and interchannel interference (ISI/ICI) than the MF-based processing. Then, with the adverse increase of interference, analytical expressions for the link performance are derived in terms of bit error rate (BER). Numerical results from computer simulation and analysis are presented to justify our claims.

• ETRI Journal
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• v.44 no.1
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• pp.105-116
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• 2022

In this study, a novel group-indexed orthogonal frequency division multiplexing index modulation (OFDM-IM) scheme is proposed to achieve a tradeoff between spectral efficiency (SE) and bit-error-rate (BER) performance. In the proposed scheme, the total subcarriers in a group are divided into subgroups, and additional bits are transmitted by subgroup indexing, unlike the conventional OFDM-IM scheme, which uses index bits to select active subcarriers. With the proposed scheme, the additional degree of freedom provided by the number of active subgroups selected provides a tradeoff between spectral efficiency and BER performance. Decoding is performed in steps to reduce computional complexity in the decoder design. Simulaton results show that the number of active subgroups selected influences the proposed scheme's performance in terms of energy efficiency, spectral efficiency, and BER performance.

• Proceedings of the KIEE Conference
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• 2004.11c
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• pp.277-279
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• 2004

In this paper, we propose an channel estimation method for Multi-Input Multi-Output-Orthogonal frequency Division Multiplexing (MIMO-OFDM). The proposed method estimates uniquely all channel frequency responses needed in space-frequency block coded OFDM systems using "comb-type" pilot symbols. To reduce the computational complexity of the proposed method, least square(LS) and linear minimum mean square error(LMMSE) are used in the frequency-domain. The performance of the proposed approach is evaluated by computer simulation for rayleigh fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8C
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• pp.613-616
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• 2008

In this paper, a fine residual frequency offset estimation scheme is proposed for multiband orthogonal frequency division multiplexing ultra-wideband (MB-OFDM UWB) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols carry the identical information in the MB-OFDM UWB system, thus removing the need of pilot symbols. The mean square error of the synchronization scheme is evaluated and simulation results are used to verify the effectiveness of the proposed estimator. When compared to the pilot-aided conventional estimator, the proposed estimator has a lower estimation error.