• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.11C
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• pp.1067-1075
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• 2009

In this paper, we propose an adaptive companding scheme to effectively reduce PAPR (Peak-to-Average Power Ratio) of the OFDM (Orthogonal Frequency Division Multiplexing) signals, while considering both complexity and BER (Bit Error Rate) performance of systems. The proposed scheme adaptively alters the compression function in the transmitter and the expanding function in the receiver to simultaneously take into account the BER performance and the PAPR reduction. In this paper, we also measure in-band and out-of-band spectra of the proposed scheme, and observe the BER performance after applying the filtering to reduce the out-of-band radiation. As compared to the conventional companding algorithm, simulation results reveal that the proposed scheme achieves more reliable BER performance in all the cases of with and without the filtering, and has a good spectrum characteristic with effective PAPR reduction.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.359-369
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• 2021

In underwater communications, to compensate performance degradation induced from rapidly changing channel transfer characteristic, multi-band communication method which allocate the same data to different frequency bands is used. However, the multi-band configuration may have worse performance than the single-band one because performance degradation in a particular band affects the output from the entire bands. This problem can be solved through a receiving end that analyzes error rates of each band, sets threshold values and allocates lower weights to inferior bands. Therefore, this paper proposed a weighting algorithm based on estimated Bit Error Rate (BER) which analyzes reliability of received data based on the performance difference between demodulated and decoded data. Employing turbo codes with coding rate of 1/3, we evaluate the performance of the proposed weighted multi-band transmission model in real underwater environments based on optimal simulation parameters. Through the sea trial experiment, we confirmed error performance was improved by applying the proposed weighting algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.10
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• pp.987-993
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• 2013

Chaos communication system has characteristics of non-periodic, non-predictability, broadband signal and easy implementation. Also, chaos communication system is sensitive to the initial value, because completely another signal is generated when initial value of chaos equation is changed subtly. By these characteristics, security of chaos communication system is generally evaluated better than other digital communication systems. However, BER(Bit Error Rate) performance is worse than other digital communication systems, because transmitter and receiver of existing chaos communication system are strongly influenced by reference signal and noise. So, studies in order to improve the BER performance of chaos communication system is continuously performed. In this paper, We will propose a new CDSK (Correlation Delay Shift Keying) receiver in order to improve the BER performance. After we compare to the performance of existing receiver and proposed receiver, BER performance of proposed receiver evaluate. A novel receiver has characteristic that BER performance is better than existing receiver. However, if existing transmitter is used, existing receiver is possible to recover information bits even though BER performance is bad. Therefore, we propose a novel CDSK transmitter in order to improve the security of proposed receiver. When information bits are transmitted by using proposed transmitter, existing receiver is impossible to recover information bits, and proposed receiver is possible to recover information bits.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.2
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• pp.113-118
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• 2011

In this paper, we develop a speaker gender classification technique using collaborative sensor fusion for use in a wireless sensor network. The distributed sensor nodes remove the unwanted input data using the BER(Band Energy Ration) based voice activity detection, process only the relevant data, and transmit the hard labeled decisions to the fusion center where a global decision fusion is carried out. This takes advantages of power consumption and network resource management. The Bayesian sensor fusion and the global weighting decision fusion methods are proposed to achieve the gender classification. As the number of the sensor nodes varies, the Bayesian sensor fusion yields the best classification accuracy using the optimal operating points of the ROC(Receiver Operating Characteristic) curves_ For the weights used in the global decision fusion, the BER and MCL(Mutual Confidence Level) are employed to effectively combined at the fusion center. The simulation results show that as the number of the sensor nodes increases, the classification accuracy was even more improved in the low SNR(Signal to Noise Ration) condition.

• Proceedings of the IEEK Conference
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• 2003.11c
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• pp.15-19
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• 2003

In this paper, the bit error rate (BER) performance of the fast frequency hopping/M-ary frequency shift keying system using the clipper receiver is analyzed by using the characteristic function (CF) technique in the presence of n=1 band multitone jamming and additive white Gaussian noise environment. The CFs of the clipper receiver outputs are derived as a infinite series representation using Gamma function and Marcum's Q -function. The analytical results are validated with various simulation results. Performance comparisons with linear combining receiver are shown that the BER performance of the clipper receiver is much better than that of the linear combining receiver In addition, as the clipping level approaches to infinity, it is shown that the clipper receiver simply performs a linear combining without clipping and there exists an optimum value of diversity level (the number of hops per symbol) that maximizes the worst case BER performance of the clipper receiver.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1821-1827
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• 2007

In this paper, an analytic transfer channel modeling function by impulse signal propagation effects in indoor power-line network are analysed. The modeled channel parameters of power line channel including background noise is applied to the OFDM system and we analysis BER for QPSK and 16-QAM modulation signals with simulation. By the representation of gain for OFDM modulation, we can estimate the characteristic parameters of OFDM in Broadband power line communication.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.3
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• pp.265-270
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• 2004

This paper addresses the effect of group delay in satellite communication system. Phase of signal is distorted by the non-constant group delay. Group delay can be modeled as linear, parabolic and cubic type according to the polynomial characteristic. We investigate BER performance of satellite communication system with each 3 kinds of group delay. As signal bandwidth becomes wider, group delay makes more influence on the signal. BNR performance of satellite communication system is found when data rates are 1Mbps, 4Mbps and 8Mbps. Convolution coding with the code rate of 1/2 or 7/8 is used. At BER =10$\^$-5/, system with group delay needs more SNR of minimum 0.3㏈ to maximum 4.4㏈ than system without group delay. The worst case of BER performance happens in the linear group delay, 7/8 punctured convolution coding and 8 Mbps. The required SNR is increased by 4.4㏈ at this worst case.

• Journal of Navigation and Port Research
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• v.34 no.10
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• pp.769-774
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• 2010

The performance of underwater communication system is influenced on channel characteristic. Delay spread cause by reverberation and multi-path happen the ISI (Inter Symbol Interference) and reduces the communication performance. In this paper, we analyze the performance of acoustic communication experiment in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for overcome the reverberation and multi-path. As a result, we acquired the BER of modulation techniques. The BER of 2kbps data rate is $1.22{\times}10^{-1}$ and BER of 4 kbps data rate is $2.47{\times}10^{-2}$.

• The Journal of the Acoustical Society of Korea
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• v.37 no.6
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• pp.404-411
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• 2018

This paper proposes a dolphin whistle mimicking underwater communication method using FSK (Frequency Shift Keying) and method to improve BER (Bit Error Rate) performance by using multipath gain combining. The proposed method divides whistle sound into short time intervals and transmits FSK modulated signal that ensures orthogonality of the symbol. Multipath gain can be obtained by using characteristic of mimicked signal frequency that varies with time. To demonstrate the performance of the proposed method, computer simulations and lake experiments were conducted. Computer simulation results show that an additional multipath gain is obtained by multipath. From lake experiments, when symbol length is 20 msec and modulation band is 900 Hz, the proposed FSK method with multipath combining gain obtains BER of 0.002, which is better than CSS (Chirp Spread Spectrum) with BER of 0.185. he proposed based on FSK method has higher imitation degree than the CSS method by analyzing mean cross-correlation value in the time - frequency domain of the imitated signal and actual whistle signal.

• Journal of Internet Computing and Services
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• v.8 no.5
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• pp.125-132
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• 2007

Transmission mechanisms that include an available bandwidth estimation algorithm and a packet loss differentiation scheme, in general, exhibit higher TCP performance in wireless networks. TCP New Jersey, known as the best existing scheme in terms of goodput, improves wireless TCP performance using the available bandwidth estimation at the sender and the congestion warning at intermediate routers. Although TCP New Jersey achieves 17% and 85% improvements in goodput over TCP Westwood and TCP Reno, respectively, we further improve TCP New Jersey by exploring improved available bandwidth estimation, retransmission timeout, and recovery mechanisms. Hence, we propose TCP New Jersey PLUS (shortly TCP NJ+), showing that under 1% packet loss rate, it outperforms 3% by TCP New Jersey and 5% by TCP Wes1wood. In 5% packet loss rate, a characteristic of high bit-error-rate wireless network, it outperforms other TCP variants by 19% to 104% in terms of goodput even when the network is in bi-directional congestion.