• Journal of the Institute of Convergence Signal Processing
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• v.3 no.2
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• pp.53-57
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• 2002

Recently, digital communication system becomes high speed, as communication demand dose not only increases sharply, but an image, voice various kinds data also comes multimedia. In transmitting data at a high speed, the main problem is fading by multipath. A linear or nonlinear distortion arise In multipath channel fading from ISI(Intersymbol Interference). For restoring this distorted signal, A lot of equalizer and adaptive algorithm is introduced. This paper compares and analysises, for improving communication quality in channel which is long delay spread, performance of decision feedback equalizer by RLS algorithm, a channel estimation by RLS-MLSE and viterbi equalizer Particularly, there Is exactly channel estimation of impluse response and excellent property of equalization about channel, which delay spread is long impluse response comparatively and is property of non-minimun phase.

• Journal of Communications and Networks
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• v.6 no.1
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• pp.19-25
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• 2004

In this paper, we present a trellis-based blind channel estimation and equalization technique coupling two kinds of adaptive Viterbi algorithms. First, the initial blind channel estimation is accomplished by incorporating the list parallel Viterbi algorithm with the least mean square (LMS) updating approach. In this operation, multiple trellis mappings are preserved simultaneously and ranked in terms of path metrics. Equivalently, multiple channel estimates are maintained and updated once a single symbol is received. Second, the best channel estimate from the above operation will be adopted to set up the whole trellis. The conventional adaptive Viterbi algorithm is then applied to detect the signal and further update the channel estimate alternately. A small delay is introduced for the symbol detection and the decision feedback to smooth the noise impact. An automatic switch between the above two operations is also proposed by exploiting the evolution of path metrics and the linear constraint inherent in the trellis mapping. Simulation has shown an overall excellent performance of the proposed scheme in terms of mean square error (MSE) for channel estimation, robustness to the initial channel guess, computational complexity, and channel equalization.

• Journal of Advanced Navigation Technology
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• v.6 no.3
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• pp.203-210
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• 2002

In this paper, the BER performance of IEEE 802.11a OFDM WLAN system is obtained by simulation and it is shown that the proposed modified channel estimation algorithm improves the channel estimation performance of the system. The wireless channel used in channel simulation includes AWGN and delay spread channel implemented by TDL model. At first, the performance of OFDM WLAN system according to data rate and coding rate defined in standard is evaluated in AWGN channel. Then, imperfect channel estimation in indoor wireless channel is considered. After the performance of conventional channel estimation scheme using only two long training symbols is evaluated, and that of proposed modified channel estimation scheme using additional 8 short training symbol is compared with it. From the simulation results, it is shown that modified channel estimation scheme provides reduced channel estimation error and improves the channel estimation performance due to noise averaging effect with the same preamble format as defined in specification.

• Journal of Advanced Navigation Technology
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• v.8 no.2
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• pp.136-144
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• 2004

In this paper, we present an improved channel estimation method for orthogonal frequency division multiplexing systems using pilot-symbol-aided parameter estimation. Conventional linear minimum mean square error(LMMSE) channel estimation method uses only pilot symbols for channel estimation. So, as the fading channel varies rapidly, a performance is decreased. We proposed a channel estimation method, which estimates channel attenuation in the middle of pilots using pilot symbols and then estimates the whole channel attenuation with pilots and estimated channel attenuation. Compared with conventional LMMSE channel estimation method, the proposed method is significantly robust in a rapid fading channel with high Doppler frequency and delay spread.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.869-872
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• 2001

Blind identification and equalization of communication channel is important because it does not need training sequence, nor does it require a priori channel information. So, we can increase the bandwidth efficiency. The linear prediction error method is perhaps the most attractive in practice due to the insensitive to blind channel estimator and equalizer length mismatch as well as for its simple adaptive algorithms. In this paper, we propose method for fractionally spaced blind equalizer with arbitrary delay using one-step forward prediction error filter from second-order statistics of the received signals for SIMO channel. Our algorithm utilizes the forward prediction error as training sequences for data estimation and desired signal for channel estimation.

• Journal of Communications and Networks
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• v.4 no.3
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• pp.189-198
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• 2002

Precoder has been shown to be able to provide source diversity and design flexibility. In this paper we employ precoding techniques for block transmission based on a multirate filterbank structure. To accommodate multiuser communication with variable data rates, different precoders with corresponding coefficients and up/down sampling rates are used. However, due to unknown multipath distortion, different interferences may exist in the received data, such as multiuser interference, intersymbol interference and interblock interference. To estimate channel parameters for a desired user, we employ all structured signature waveforms associated with different symbols of that user and apply subspace techniques. Therefore better performance of channel estimator can be achieved than the conventional subspace method based only on the signature of the current symbol. The delay for that user can also be jointly estimated. Channel identifiability conditions and asymptotic channel estimation error are investigated in detail. Numerical examples are provided to justify the proposed method. gest either multicode (MC) or multiple processing gain (MPG) mechanism [2], while requiring data rates to be integral multiples of some basic low-rate. In order to support variable rate transmission however, a comprehensive scheme needs to be investigated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11C
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• pp.1100-1106
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• 2006

In downlink of mobile communication systems, the feedback delay between channel estimation and actual transmission causes inaccuracy in channel-state-information (CSI) and this results in performance degradation. In order to overcome this phenomenon, channel prediction is inevitable. In this paper, an adaptive transmission scheme based on channel prediction is proposed and its performance is evaluated. From simulation results, it is shown that the performance degradation due to the feedback delay is successfully mitigated by using the proposed scheme.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.8
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• pp.1-7
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• 2004

The effect of the sub-optimal beam-forming and the fading channel correlation on the closed loop transmit antenna diversity(CTD) system is investigated in frequency flat Rayleigh fading channels. The fast channel fading prevents the perfect channel estimation at a mobile station, hence the imperfect weight is applied to the antenna branch of transmitter. The weight causes sub-optimalbeam-forming and aggravates the performance of CTD system. The fading correlation or a wireless channel also is one of the factors decreasing the diversity gain. A bit error rate expression for the CTD system is analytically derived as a function of the channel estimation error, the channel correlation coefficient the feedback delay, and fading index. It is shown that the channel estimation error gives more severe effect to the system performance than the channel correlation.

• International Journal of Computer Science & Network Security
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• v.23 no.5
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• pp.121-127
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• 2023

A 500 km/h linear motor high speed terrestrial transportation service is planned to launch 2027 in Japan. In order to support 5G service in the train, the Sub-carrier spacing frequency of 30 kHz is planned to be used instead of common 15 kHz sub-carrier spacing to mitigate Doppler effect in such high-speed transportation. In addition, to increase the cell size of 5G mobile system, plural Base Station antenna will transmit the identical Down Link (DL) signal to form the expanded cell size along the train rail. In this situation, forward and backward antenna signals will be Doppler shifted by reverse direction respectively and the receiver in the train might suffer to estimate accurate Channel Transfer Function (CTF) for its demodulation. In this paper, Delay and Doppler Profiler (DDP) based Channel Estimator is proposed and it is successfully implemented in signal processing simulation system. Then the simulated performances are compared with the conventional Time domain linear interpolated estimator. According to the simulation results, QPSK modulation can be used even under severe channel condition such as 500 km/h, 2 path reverse Doppler Shift condition, although QPSK modulation can be used less than 200 km/h with conventional Channel estimator.

• Journal of Broadcast Engineering
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• v.21 no.4
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• pp.552-561
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• 2016

In OFDM system, frequency-domain sub-carriers of a symbol generally consist of data sub-carriers and scattered pilot sub-carriers and in the receiver, channel is estimated through time-axis interpolating pilot sub-carriers of several OFDM symbols. However, time-axis interpolation fails to keep track of rapid channel variation caused by fast moving receiver. Although symbol by symbol channel estimation without time-axis interpolation enables fast estimation, the performance is severely degraded for a long delay spread channel in a single frequency networks (SFNs) because of insufficient pilot sub-carriers. In this paper, a channel estimation scheme for OFDM receiver in a fast mobile SFN channel is proposed. The proposed scheme is applied to DVB-T receiver to improve the Doppler mobile performance in SFN channel.