• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.11
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• pp.33-38
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• 2004

In this paper, we review a trellis-coded orthogonal frequency division multiplex (TC-OFDM) system, which combines OFDM with trellis-coded modulation, for overcoming the frequency selective and multipath fading of time dispersive channels. We simulate and analyse the BER performance of rate 2/3 trellis coded 8DPSK-OFDM over time dispersive channels. Design of the trellis codes at different carrier numbers of OFDM is discussed. Results show that TC-OFDM system can provide 6 dB coding gain at a BER of 10$^{-3}$ compared with OFDM system without coding.

• 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.

• Proceedings of the IEEK Conference
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• 2002.06a
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• pp.339-342
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• 2002

In this paper, the structure of OFDM system is studied, and causes of inter carrier interference (ICI) are analyzed. Based on analysis, this paper shows a technique to prevent a distortion due to nonlinearity of high Power amplifier. The proposed scheme is a predistorter for high power amplifier linearization in orthogonal frequency division multiplexing (OFDM) system used in wireless local area network(WLAN). This is verified by comparing BER characteristics of OFDM system, between used PD and not used PD.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2606-2609
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• 2001

We propose a robust channel equalization algorithm. which is called a 1-tap additional coefficient decision feedback equalizer(ACDFE), to improve the Doppler shift performance for the OFDM receiver. The algorithm is based on the frequency domain DFE with additional coefficients which are independent of the OFDM subcarriers. Test results on OFDM-16QAM signals confirm that the proposed ACDFE is robust against fading channel due to Doppler shifts and outperforms the conventional DFE in terms of SER, MSE, and convergence speed.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.11
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• pp.9-16
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• 2011

We need to establish standard for the ICT based on train control system. In order to solve the ISI problem, this paper evaluate the performance of OFDM and FDE system. We seem that OFDM system is better than FDE system. In order to solve ISI problem, SC System is needed a equalizer. And another method is OFDM System. If system is used SC with a equalizer, It is better than OFDM in terms of PAPR, but this system is not easy to use Multi-Antenna technique, i.e., beam-forming and MIMO-multiplexing. And If system is used high-order modulation, BER performance is worse than OFDM. If we think about in terms of PAPR problem, considerations are considered not significant because the size of relays is not considered in the communication between trains and ground.

• Proceedings of the KSR Conference
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• 2010.06a
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• pp.2089-2094
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• 2010

The importance of broadband wireless communication implemented at subway tunnels is growing up. At 18GHz wireless video transmission system, the transmitter requires a digital modulation method. At subway tunnel, A 18GHz's influence of the multi-pass padding is strong. OFDM digital modulation that is strong for multi-pass padding is recommended. In this paper, Suitable to a subway wireless video transmission OFDM receiver is designed. OFDM receiver system has 6dB gaion because uses diversity of space diversity and MRC(Maximum Ratio Combining) diversity. The transmitter system use C&ITechnologies's transmitter board. IF frequency of receiver is 480MHz. OFDM modulation parameter is as follow, The bandwidth is 8MHz, The numuber of carrier if 2,000, The modulation methode is QAM16, The guard interval is 1/32.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.5 s.335
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• pp.55-62
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• 2005

In this paper, we propose an efficient symbol detection algorithm for space-frequency OFDM (SF-OFDM) transmit diversity scheme and present the implementation results of the SF-OFDM WLAN baseband processor with the proposed algorithm. When the number of sub-carriers in SF-OFDM scheme is small, the interference between adjacent sub-carriers may be generated. The proposed algorithm eliminates this interference in a parallel manner and obtains a considerable performance improvement over the conventional detection algorithm. The bit error rate (BER) performance of the proposed detection algorithm is evaluated by the simulation. In the case of 2 transmit and 2 receive antennas, at $BER=10^{-4}$ the proposed algorithm obtains about 3 dB gain over the conventional detection algorithm. The packet error rate (PER), link throughput, and coverage performance of the SF-OFDM WLAN with the proposed detection algorithm are also estimated. For the target throughput at $80\%$ of the peak data rate, the SF-OFDM WLAN achieves the average SNR gain of about 5.95 dB and the average coverage gain of 3.98 meter. The SF-OFDM WLAN baseband processor with the proposed algorithm was designed in a hardware description language and synthesized to gate-level circuits using 0.18um 1.8V CMOS standard cell library. With the division-free architecture, the total logic gate count for the processor is 945K. The real-time operation is verified and evaluated using a FPGA test system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.8
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• pp.16-21
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• 2009

OFDM is a key technology for 4G cellular systems in the future. But when OFDM is used in cellular system environment, it has severe inter-cell interference problems. In this paper, we propose an ICIC scheme that can reduce inter-cell interference for OFDM-based 4G cellular systems. and we analyze the efficiency of the proposed scheme. Simulation is carried out according to the simplified 3GPP LTE system level simulation parameters. We have confirmed the improvement of Geometry efficiency about 4dB at the results.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.23-31
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• 2008

This paper addresses relationships between diversity techniques and channel coding rates for OFDM and SC-FDE systems. In OFDM systems it is important to select proper channel coding rates according to multi-path channel profiles and low channel coding rates are required with cyclic delay diversity compared to the case of space time coding. On the other hand, it is not necessary to use low channel coding rates for SC-FDE systems where DFT spreading is applied to OFDM and relatively high channel coding rates can be used regardless of diversity techniques.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12A
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• pp.1198-1204
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• 2006

In this paper, we extend SVR-MMSE detection scheme which is proposed in MIMO system to MIMO-OFDM system, and evaluate performance of the system in frequency selective fading channel. First of all, we explain about typical MIMO-OFDM system and detection scheme of constant modulus signals in this system. And compare proposed SVR-MMSE with Zero Forcing, Minimum Mean Square Error which is conventional detection scheme. we identify that the performance of the proposed system is shown different by varying doppler frequency in frequency selective fading channel using jakes channel model. The result of detection performance by the proposed SVR-MMSE in this simulation, it shows that proposed algorithm have a good performance in MIMO-OFDM systems.