• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.8B
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• pp.1532-1539
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• 1999

In this paper, we propose a bit synchronizer which is suitable for frequency hopping systems. The proposed bit synchronizer is an ADPLL in which the digial loop filter is combined with an error symbol detecting circuit using an adaptive window. Suppressing the tracking process when hop mute and impulse noises are detected improves the performance of the digital loop filter and enhances the probability of the frequency hopping system. The simulation results demonstrate an improved performance of the proposed bit synchronizer compared with existing ones.

• Journal of electromagnetic engineering and science
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• v.4 no.4
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• pp.175-182
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• 2004

When the M-ary signal experiences the Rayleigh fading, the diversity schemes can reduce the effect of fading since the probability that all the signals components will fade simultaneously is reduced considerably. The symbol error probabilities for various M-ary signals, such as MDPSK(M-ary DPSK) and MPSK(M-ary PSK), are mathematically derived for the Selection Combining 2(SC-2) and Selection Combining 3(SC-3) demodulation system which requires a less complex receiver than Maximum Ratio Combining(MRC). The propagation model used in this paper is the frequency-nonselective slow Rayleigh fading channel corrupted by the Additive White Gaussian Noise(AWGN). The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• Journal of electromagnetic engineering and science
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• v.7 no.4
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• pp.183-189
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• 2007

When the M-ary signal experiences the Rayleigh fading, the diversity schemes can reduce the effect of fading since the probability that all the signals components will fade simultaneously is reduced considerably. The symbol error probabilities for various M-ary signals, such as MDPSK(M-ary DPSK) and MPSK(M-ary PSK), are mathematically derived for the Selection Combining 2(SC-2) and Selection Combining 3(SC-3) demodulation system which requires a less complex receiver than maximum ratio combining(MRC). The propagation model used in this paper is the frequency-nonselective slow Rayleigh fading channel corrupted by the additive white gaussian noise(AWGN). The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• Journal of electromagnetic engineering and science
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• v.7 no.4
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• pp.201-206
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• 2007

When the M-ary signal experiences the Rayleigh fading, the diversity schemes can reduce the effects of fading since the probability that all the signals components will fade simultaneously are reduced considerably. The symbol error probabilities for various M-ary signals, such as MDPSK, MPSK and MQAM, are mathematically derived for the SC-2(Selection Combining 2) demodulation system, whereby the two signals with the two largest amplitudes are coherently combined among the L branches. On the other hand, maximum ratio combining(MRC) requires the individual signals from each path to be time-aligned, cophased, optimally weighted by their own fading amplitude, and then summed. The propagation model used in this paper is the frequency-nonselective slow Rayleigh fading channel corrupted by the Additive White Gaussian Noise(AWGN). The numerical results presented in this paper are expected to provide information for the design of radio system using M-ary modulation method for above mentioned channel environment.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2001.06a
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• pp.1-4
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• 2001

In this paper, we develop a blind adaptive multiuser detector for synchronous CDMA with a noise-whitened filter. To Improve the symbol error probability performance, Decision-Feedback Blind Adaptive Multiuser Detector(DFBD) is proposed and compared with Blind Adaptive Multiuser Detector(BD). The proposed DFBD is slightly improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.220-225
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• 2002

MUD(Multiuser detection) technology which locates desired signal and removes interference signal from multiple access signals increases system capacity and decreases multiple access effect. In this paper, we develop a blind adaptive multiuser detector for synchronous CDMA with a noise-whitened filter. To improve the symbol error probability performance, DFBD (Decision-Feedback Blind Adaptive Multiuser Detector) is proposed and compared with BD(Blind Adaptive Multiuser Detector). The proposed DFBD is slightly improved.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.12
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• pp.2696-2705
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• 1997

An exact experssion for the average symbol error rate(SER) of L-order selection diversity for MPSK signals in a frequency-nonselective slowy m-distributed Nakagami fading and additive white Gaussian noise(AWGN) is determs of finite sums is obtained. To derive the SER of MPSK signals with selection combining, the new expression of pdf is introduced and many other mathmatical methods are used. When fading index m is 1, the derived exppression lead to those of MPSK with selection combining in Rayleight fading channels. The results show that the error probability decreases as the order of diversity increases.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.39 no.1
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• pp.66-75
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• 2002

For the theoretical performance analysis of Viterbi Decoder for wireless LAN with data rate 12Mbps, code rate 1/2 and constraint length 7 defined in IEEE 802.11a, the transfer function is derived using Cramer's rule and the first-event error probability and bit error probability is derived under the AWGN. In the design process, input symbol is quantized into 16 steps for 4 bit soft decision and register exchange method instead of memory method is proposed for trace back, which enables the majority at the final decision stage. In the implementation, the Viterbi decoder based on parallel architecture with pipelined scheme for processing 12Mbps high speed data rate and AWGN generator are implemented using FPGA chips. And then its performance is verified in real time.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1373-1392
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• 2017

WiFi Direct (WD) is a state of the art technology for a Device-to-Device (D2D) communication in 802.11 networks. The performance of the WD system can be significantly affected by some key factors such as the type of application, specifications of MAC and PHY layer parameters, and surrounding environment etc. It is, therefore, important to develop a system model that takes these factors into account. In this paper, we focus on investigating the design parameters of the PHY layer that could maximize the efficiency of the WD 802.11 system. For this purpose, a basic theoretical model is formulated for a WD network under a 2x2 Multiple In Multiple Out (MIMO) TGn channel B model. The design level parameters such as input symbol rate and antenna spacing, as well as the effects of the environment, are thoroughly examined in terms of path gain, spectral density, outage probability and Packet Error Rate (PER). Thereafter, a novel adaptive algorithm is proposed to choose optimal parameters in accordance with the Quality of Experience (QoE) for a targeted application. The simulation results show that the proposed method outperforms the standard method thereby achieving an optimal performance in an adaptive manner.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.1
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• pp.83-88
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• 2009

Selection relaying(SR) is usually based on signal-to-noise ratio(SNR) to decide whether or not to forward recovered symbols. However, instantaneous noise at relay is ignored, leading to the risk of erroneous retransmission induced by the relay that can be detrimental to the eventual detection of symbols at destination. To overcome this problem, we propose using new symbol error probability(SEP) related directly to reliability of received symbols instead of SNR. Simulation results show that the proposed SEP-based SR is considerably better than the conventional SNR-based SR under any relay position and threshold.