• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4C
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• pp.397-402
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• 2009

Accurate estimation of time-selective fading channel is a difficult problem in OFDM(Orthogonal Frequency Division Multiplexing) system. There are many channel estimation algorithms that are very weak in noisy channel. For solving this problem, we use EM (Expectation-Maximization) algorithm for iterative optimization of the data. We propose an EM-LPC algorithm to estimate the time-selective fading. The proposed algorithm improves of the BER performance compared to EM based channel estimation algorithm and reduces the iteration number of the EM loop. We simulated the uncoded system. If coded system use the EM-LPC algorithm, the performance are enhanced because of the coding gain. The EM-LPC algorithm is able to apply to another communication system, not only OFDM systems. The image processing of the medical instruments that the demand of accurate estimation can also use the proposed algorithm.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.16 no.2
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• pp.61-68
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• 2023

Multi-band method which allocate the same data to different frequency bands, improves performance by compensating Doppler spreading and selective fading in underwater communications. The drawback of multi-band configuration may have worse performance because performance degradation in a particular band affects the output from the entire bands. It is very important to find which band is superior or inferior band in order to improve performance. Therefore this paper analyzes performance prediction algorithms of each band. This paper proposes three kinds of prediction methods. Through the ocean tests, this paper confirms utilizing the preamble error rates is most efficient algorithm among of them.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.12B
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• pp.1483-1490
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• 2009

Orthogonal frequency division multiplexing (OFDM) has been investigated as an enabling technology for future wireless communications such as ad hoc, mesh and sensor networks. However, prior works on bit-loading lack consideration of the constraints on energy and computing facility in sensor networks. In this paper, we suggest an adaptive bit allocation algorithm for a frequency selective fading channel environment which exploits channel state information obtained through a feedback channel. The proposed algorithm significantly reduces computational complexity and satisfies the power budget. Also, its throughput is comparable to the optimum solution. Simulation results support the claim stated.

• Journal of Broadcast Engineering
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• v.18 no.6
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• pp.927-934
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• 2013

This paper aims to realize a Signal to Noise Ratio Estimator which constitutes a critical index of the broadcasting system in OFDM system with a synchronized type based on ISDB-T system. Of the elements which are comprising OFDM segments of ISDB-T system using the MSE algorithm suitable for ASIC design owing to its low complexity among a diverse SNR estimation methods, SNR estimation method using the broadcasting information data and the SNR estimation method using scattered pilot signal were realized by RTL. These two methods were compared in terms of their performance through simulation test not only in the AWGN channel which is an ideal channel, but also in SFN channel and frequency selective fading channel, which are distorted channels. Complexity of two methods were also compared through RTL realization. As a result of this comparison analysis, it was concluded that the SNR estimation method using scattered pilot signal shows more excellent performance and easiness in realization.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.2
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• pp.176-187
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• 2002

The digital Audio Broadcasting (DAB) system adopts Coded OFDM(COFDM) for channel coding. The COFDM is a combined technique of multicarrier transmission(OFDM) and punctured convolutional coding with viterbi error correction. Because the channel coding is an important topic for OFDM systems, this paper proposes a new turbo coded OFDM system that replaces the existing RCPC codec by a turbo codec without modifying the puncturing procedure and puncturing vectors defined in the standard DAB system for compatibility. The performance of a new system is compared to that of the conventional system under the frequency selective Rician fading channel and the frequency selective Rayleigh fading channel in conjunction with DAB transmission mode I suitable for the terrestrial single frequency network(SFN) broadcasting. The standard system's performance was improved with the aid of turbo codec.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.370-377
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• 2004

In this paper, we present an adaptive modulation technique for orthogonal frequency division multiplexing (OFDM) for broadband wireless communications. Also, using improved channel prediction, we enhance the performance of adaptive OFDM in high mobility environments. Adaptive modulation technique has been shown to achieve reliable high-rate data transmission over frequency-selective fading channel when OFDM is employed. This scheme requires the accurate channel information between two stations for a better performance. In an outdoor high mobility environment, most of adaptive OFDM systems have to be given the channel information transmitted from the receiver. Even if it is possible, there is some delay. Moreover, the channel impulse response between two stations is very rapidly varied. If the channel information is obsolete at the time of transmission, then poor system performance will result. In order to solve this problem, we propose adaptive OFDM with improved channel predictor. The proposed bit allocation algorithm has a lower complexity and the proposed scheme mitigates the effect of channel delay. Robust approach is less sensitive to outdated channel information. Performance results show that the proposed scheme can achieve considerable performance enhancement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2A
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• pp.34-42
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• 2005

In orthogonal frequency-division multiple access (OFDMA) uplink environments, asynchronously received signals can cause multiple access interference (MAI). This paper focuses on the performance degradation due to the MAI over frequency-selective fading channels. We first introduce the timing misalignment, which is defined as the relative timing difference between asynchronous timing error of uplink user and reference time of the base station, and analytically derive the MAI using the power delay profile of wide-sense stationary uncorrelated scattering (WSSUS) channel model. Then, the effective signal-to-noise ratio (SNR) and the average symbol error probability (SEP) are derived. The proposed analytical results are verified through simulations with respect to the region of the timing misalignment and the number of asynchronous users.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.12
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• pp.28-33
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• 2007

We present a space-time trellis coded OFDM system in flow fading channels. Generalized principal ratio combining (GPRC) is also analyzed theoretically in frequency domain. The analysis show that the decoding metric of GPRC include the metrics of maximum likelihood (ML) and PRC. The computer simulations with M-PSK modulation are obtained in frequency flat and frequency selective lading channels. The decoding complexity and simulation running times are also evaluated among the decoding schemes.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.3
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• pp.564-571
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• 2009

In this paper, we propose out-of -band collaborative spectrum sensing scheme in the cognitive radio (CR) base station operated by the multiple frequency channels. Also this paper presents the signal detection results for ATSC digital TV signal as an incumbent signal and derives signal detection probability and false alarm probability for the out-of-band collaborative spectrum sensing scheme in frequency selective Rayleigh fading channel. Numerical results demonstrate that the sensing performance is improved by the out-of-band collaborative spectrum sensing in the case that the incumbent signal powers measured by the CR terminals of the multiple frequency channels are almost similar.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.201-204
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• 2000

In this paper, a new multiuser detector combining multicarrier and decorrelating detection schemes is proposed and analyzed in a frequency selective Rayleigh fading channel. The bit error probability is derived and compared with that of the conventional decorrelating detector. From the numerical results, it is shown that the proposed detector achieves better BER performance and lower computational complexity than those of the conventional decorrelating detector.