• Journal of Broadcast Engineering
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• v.11 no.3 s.32
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• pp.302-310
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• 2006

ITU-R B.O. 1130-4 Digital System E adopted for Korean satellite DMB service is a multimedia broadcasting system based on DS-CDM-QPSK technique which broadcasts audio and video contents via the satellite or terrestrial gap-filler. However, Digital System E can not provide full loading services because the multi-channel interference (MCI) is increased due to the loss of orthogonality between signature waveforms in multipath fading channels. In this paper a chip equalizer using tap selection algorithm that enhances the receiving performance is proposed and compared to the conventional rake receiver for the satellite DMB system.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.10
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• pp.45-52
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• 2004

This Paper presents a modified hard decision Viterbi decoder with an error prediction circuit enhancing performance for the burst error inputs. Viterbi decoder employs the maximum likelihood decoding algorithm which shows excellent error correction capability for the random error inputs. Viterbi decoders, however, suffer poor error correction performance for the burst error inputs under the fading channel. The proposed error prediction algorithm increases error correction capability for the burst errors. The algorithm estimaties the burst error data area using the maximum path metric for the erroneous inputs, It calculates burst error intervals based on increases in the maximum values of a path metric. The proposed decoder keeps a performance the same as the conventional decoders on AWGN channels for the IEEE802.l1a WLAN system. It shows performance inproving 15% on the burst error of multi-path fading channels, widely used in mobile systems.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.1
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• pp.69-74
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• 2003

In this paper, we propose the synchronization recovery algorithm which is suitable to wireless Multimedia of wireless channel situation which is being used OFDM signaling method. The basic of the suggested clock synchronization. restoration Algorithm is to getting the shock response of channel or getting the multipath strength profile through IFTT after the getting the frequency, response of deducted channel from channel deducted of receiver and to trace the location in the channel energy concentrated area of timing area. And it also analysis the start point of 64-QAM and 16-QAM if the sampling clock offset has the sample of ${\pm}$ 1-3, and we identified the occurance of performance deterioration when occures more than 2 samples of offset to compare with star point and BER performance in optimum sampling point result of BER performance checking, and we know that the recovery algorithm proposed algorithm also provide excellent synchronization characteries under frequency, selecting fading channel as result of simulation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.53-60
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• 2005

In this paper, we analyze the performance of UWB MC-CDMA system and compareit with DS-CDMA and OFDM systems, which have been drafting in standardization even now. Too many Rake Fingers are needed in the DS-CDMA system to separate multi-path signals, which results in highsystem complexity. OFDM radio power fails to qualify for FCC certification unless frequency hopping. From this reason, MC-CDMA system considered is proposed in this paper. It has lower complexity compared with DS-CDMA and shows good performance against frequency selective fading. In addition, for a wide-band communication, less radio power per spectrum is allowed in the MC-CDMA system than in an OFDM system. Simulation result show that the DS-CDMA system has better performance with single user, but MC-CDMA system shows best performance in case of multi user environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.1C
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• pp.77-86
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• 2010

In this paper, we present a noncoherent IR-UWB (Impulse Radio-Ultra Wide Band) ranging system with an AFE (Analog Front End) composed of a simple integrator and an 1-bit ADC (Analog-to-Digital Converter), and define AFE characteristics affecting the ranging performance. This system is realistic and easy to implement, since the integrator simply accumulates signal energies and the simple 1-bit ADC is applied instead of the multi-bit ADCs for coherent IR-UWB systems. On the other hand, its ranging accuracy is largely affected channel environments such as noise, multipath fading and so on, since the noncoherent receiver simply squares and integrates the received signals. However, despite these practical importances, there are few conventional researches on the performance analysis according to AFE characteristics in IR-UWB ranging systems. To this end, we analyze in this paper ranging performance according to AFE characteristics for the noncoherent IR-UWB ranging system in various wireless channel environments, and through these results we also present system parameters to be considered in UWB hardware designs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.11A
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• pp.1154-1163
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• 2007

For orthogonal frequency division multiplexing (OFDM), cyclic prefix (CP) should be longer than the length of channel impulse response. In order to prevent a loss of bandwidth efficiency due to the use of a CP, residual intersymbol interference cancellation (RISIC) method has recently been developed. In this paper, we first apply the RISIC algorithm to the space-time block coded (STBC) OFDM and the space-frequency block coded (SFBC) OFDM with insufficient CP. It is shown that in the STBC OFDM, tail cancellation as well as cyclic restoration of the RISIC should be repeated. Second, we propose iterative channel estimation method for the RISIC in the STBC OFDM system with insufficient CP. Based on the expectation-maximization (EM) algorithm, the proposed estimation method exploits the extrinsic probabilities of the channel decoder iteratively. The performance of the proposed method is evaluated by computer simulation in a multipath fading environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.10C
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• pp.1017-1026
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• 2005

In burst OFDM system, the frame synchronization should be performed first for the acquisition of received frame and the estimation of the correct FFT-window position. The conventional frame synchronization algorithms using design features of the preamble symbol, the repetition pattern of the OFDM symbol by pilot sub-carrier allocation rule and Cyclic Prefix(CP), has difficulty in the detection of precise frame timing because its correlation characteristics would increase and decrease gradually. Also, the algorithm based on the correlation between the reference signal and the received signal has performance degradation due to frequency offset. Therefore, we adopt a differential correlation method that is robust to frequency offset and has the clear peak value at the correct frame timing for frame synchronization. However, performance improvement is essential for differential correlation methods, since it usually shows multiple peak values due to the repetition pattern. In this paper, we propose an enhanced frame synchronization algorithm based on the differential correlation method that shows a clear single peak value by using differential correlation between samples of identical repeating pattern. We also introduce a normalization scheme which normalizes the result of differential correlation with signal power to reduce the frame timing error in the high speed mobile channel environments.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.164-167
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• 2005

Recently, STC techniques have been considered to be candidate to support multimedia services in the next generation mobile radio communications and have been developed the many communications systems in order to achieve the high data rates. In this paper, we propose the Trellis-Coded Differential Space Time Modulation system with multiple symbol detection. The Trellis-code performs the set partition with unitary group codes. The Viterbi decoder containing new branch metrics is introduced in order to improve the bit error rate (BER) in the differential detection of the unitary differential space time modulation. Also, we describe the Viterbi algorithm in order to use this branch metrics. Our study shows that such a Viterbi decoder improves BER performance without sacrificing bandwidth and power efficiency.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2A
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• pp.103-109
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• 2006

OFDM system has a disadvantage of sensitiveness about the effect of the frequency offset caused by the discord of oscillators in transmitter and receiver. The frequency offset can be divided into integral part and decimal part. Although the frequency offset of integral part do not effect orthogonality between subcarriers, it makes the bit error probability become to 0.5 because of circular transient among transmitted data symbols. This paper proposes a new estimation scheme of the frequency offset of integral part by Maximum Likelihood (ML) demanding only one training symbol in multipath fading channel environment. This proposed scheme not only can reduce the number of training symbol but do not increase the complexity and it shows the better performance by simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7B
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• pp.660-666
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• 2004

Overall TCP performance represented by end-to-end throughput is largely dependent upon its loss recovery performance. In particular non-congestion packet losses caused by transmission errors degrade TCP performance seriously. Using Markov process, we analyze TCP loss recovery performance for correlated packet losses caused by multipath fading. The results show that loss recovery performance can be severely affected by burstiness in packet losses, even if overall packet loss ratio is very low.