• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5A
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• pp.441-449
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• 2011

Sample timing offset (STO) and carrier frequency offset (CFO) are caused by inter-symbol interference (ISI), inter-carrier interference (ICI) and phase error in orthogonal frequency division multiplexing (OFDM) system. OFDM characteristic is sensitive about STO and CFO. So when ICI occurs, compensation is hard and complex equalizer is needed. In this paper, we propose an effective correction method using feedback process with pilot and synchronization symbol. After feedback with estimated value in frequency domain, STO and CFO are corrected by control sample & and holder and oscillator. As a result of simulation, we confirm that STO and CFO can be corrected without equalizer through feedback.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.26 no.12A
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• pp.1978-1982
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• 2001

In a Multi-carrier modulation system, CP (Cyclic prefix) is inserted in the transmit tame in order to eliminate the ISI (Intersymbol Interference) and ICI (Interchannel Interference) caused by delay spread of a received signal, which in rum degrades the throughput of the system. TEQ (Time-domain equalizer) improves the system throughput by shortening the CIR (Channel Impulse Response) time and maintaining the CP length to the minimum regardless of the channel condition. In this paper, a new MMSE (Minimum Mean Square Error) TEQ algorithm is proposed and its performance is analyzed in order to speed up computing the optimum tap coefficients of the equalizer by employing Newton method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8A
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• pp.1187-1194
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• 1999

In general wireless mobile channel is modeled as complex random processes having a narrowband spectrum. In this paper, a real-time feneration of fading signals using a DSP chip is described. Real-time simulator is designed so that simulation parameters such as mobile terminal speed, carrier frequency, power ratio of line-of-sight component versus multipath, and variance of received power can be chosen in the window. Design algorithms for the generation of ideal fading signals with a minimum DSP computation and trade-offs are investigated. The accuracy of the statistical characteristics is verified through the comparison of measured results with the theoretical prediction.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.12 s.91
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• pp.1199-1206
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• 2004

In this paper, we analyzed the orthogonal MC DS-CDMA system and no-overlapping MC DS-CDMA System, which were divided by the normalized spacing between adjacent subcarrier over Nakagami-m fading channels. In order to reduce the number of selective paths occurring in the MC system, the Hybrid SCMRC technique was applied, which was compared with the case when the MRC technique was used. As a result of simulations, it was found that the Hybrid SC/MRC method could be replaced by the MRC method and if the number of subcarriers was increased when the given bandwidth was fixed, the interval between subcarriers increased and bigger bandwidths were required. an, the number or subcarriers should be selected in consideration or given bandwidth.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.12
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• pp.1303-1312
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• 2008

Satellite WiBro system has high PAPR characteristics in addition to the nonlinear characteristics of the power amplifier. These characteristics reduce amplifying efficiency of the power amplifier and also cause high error rate and interference with adjacent channels. This paper proposed satellite WiBro based system to reduce input signal's IBO of TWTA remarkably by adapting simultaneously PAPR reduction techniques, active-constellation extension technique and pre-distortion technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.9C
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• pp.643-651
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• 2008

In this paper, we propose a method to determine the optimal cyclic delay value of cyclic delay diversity(CDD) in orthogonal frequency division multiplexing(OFDM) systems. As the cyclic delay value increases, we can get signal to interference and noise ratio(SINR) gain by diversity effect, while SINR loss increases because of channel estimation errors. If the optimal delay value obtained by the proposed method is applied to CDD scheme, we can minimize the required SINR for a given FER(frame error rate) under the above mentioned trade-off.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.4
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• pp.240-246
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• 2013

In heterogeneous networks, the almost blank subframes (ABS) for inter-cell interference coordination (ICIC), which can be protected from the CCI due to unutilized subframes (i.e., ABS) is proposed. However, the analytical model for ABS-based systems has not been fully studied yet. In this paper, we derive a new analytical model to evaluate the performance of ABS-based systems. In an analytic model, we assume that each carrier in multicarrier systems, such as in OFDMA, is subject to large-scale fading, which is independent of other carriers. As a performance measure, we present the cumulative distribution function (CDF) for the effective SINR. We show the accuracy of the analytical model via simulation results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.1A
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• pp.70-75
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• 2005

The efficient hardware design of the the algorithm is important in wide variety of DSP. One example is OFDM(Orthogonal Frequency Division Multiplexing) based WLAN(Wireless Local Area Network) systems which place high requirements on throughput and power consumption on FFT. The output RAM is composed of two banks of $64{\times}W.$ The banks are swapped immediately following the falling edge or the start signal strobe. This bank swapping allows 64-Point FFT to continue Processing samples and to continue filling the alternative bank, without affecting the data flow outputs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.7C
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• pp.554-561
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• 2008

For the tone reservation (TR) scheme in orthogonal frequency division multiplexing (OFDM), there exists a trade-off between peak to average power ration (PAPR) reduction performance and data transmission rate. While PRT set is fixed in the conventional TR scheme, the proposed scheme adaptively select the PRT set according to the PAPR of the input OFDM symbol. It is shown that the PAPR reduction performance of the proposed scheme is better than that of the conventional scheme when the data transmission rate is the same.

• Journal of IKEEE
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• v.20 no.1
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• pp.26-30
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• 2016

In this paper, an inter-orthogonal frequency division multiplexing (OFDM) sub-carrier distortion due to fiber chromatic dispersion is investigated. The fiber chromatic dispersion induces phase difference among OFDM sub-carriers, resulting in non-symmetric peak to average power ratio (PAPR) inducing inter-OFDM distortion. Experiments to confirm the fiber dispersion are performed in a direct-detection optical front-haul link. Quadrature phase shift keying (QPSK) encoded OFDM symbols at 25 Gbit/s are transmitted over 100 km fiber and the resulting error vector magnitude (EVM) of 40 % is observed.