• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.10
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• pp.2247-2255
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• 2015

In very shallow water acoustic communication channel, underwater acoustic (UWA) communication signal is observed as frequency selective fading signal due to time-varying multipath. This induces a time and frequency dependent inter-symbol-interference (ISI) and degrades the UWA system performance. There is no study about how the performances of the error correction codes are related to a multipath fading statistics in very shallow water. In this study, the characteristics of very shallow water multipath fading channel is analyzed and the performances of two different forward error correction (FEC) codes are compared. The convolution code (CC) and Reed-Solomon (RS) code are adopted. Sea experimental results show that RS code is better choice than CC in frequency selective channel with fading.

• The Journal of the Acoustical Society of Korea
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• v.33 no.6
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• pp.407-412
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• 2014

In this paper, we propose an underwater acoustic communication of FH-MFSK(Frequency-Hopped Multiple Frequency Shift Keying) system with multiple orthogonal property. Generally, the processing of FSK(Frequency Shift Keying) method is simple, but it is vulnerable to ISI (Inter-Symbol Interference) caused by multipath transmission. In this paper, the orthogonal codes are generated with the same number of transmitting symbols, and these codes are corresponding to multiple frequencies. We used m-sequence to generate multiple orthogonal codes. We compared the performance of proposed method with conventional MFSK method via the experiment. As a result, we confirmed that the proposed method shows 6~10 % lower error rate at 100 bps than conventional method.

• The KIPS Transactions:PartC
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• v.13C no.3 s.106
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• pp.369-374
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• 2006

This paper related with the performance improvement of adaptive equalizer that is a based on the tricepstrum eqalization algorithm by using the received signal. Adaptive equalizer used for the improvement of communication performance, like as high speed, maintain of synchronization, BER, at the receive side in the environment of communication channel of the presence of the aditive noise, phase distortion and frequency selective fading, mainly. It's characteristics are nearly same as the inverse characterstics of the communication channel. In this paper, the TEA algorithm using the HOS and the 16-QAM which is 2-dimensional signaling method for being considered signal was used. For the precoding of 16-QAM singnal in the assignment of the signal costellation, Gray code was used, and the improvement of performance was gained by computer simulation in the residual intersymbol interence and mean squared error which is representive measurement of adaptive equalizer.

• The Journal of the Acoustical Society of Korea
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• v.38 no.6
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• pp.678-686
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• 2019

Underwater communication performance is degraded by the influence of Inter-Symbol Interference (ISI) due to multipath. Passive time reversal processing is the most effective technique for mitigating multipath, and the diversity combining method can be used to improve its performance. This paper analyzed communication performance using the beam diversity combining method, which combines signals obtained through the beam steering to various angles. Directions of arrival were estimated through the beam-time migration, which, in turn, was estimated from probe signals received by a vertical line array. The performance was analyzed based on the number and type of combinations among the estimated angles. In this paper, the data obtained from the Biomimetic Long range Acoustic Communications 2018 (BLAC18) experiment, which was conducted in the East sea, ~50 km east of Pohang, in October 2018, were used for the analysis. The output Signal to Noise Ratio (SNR) was used as communication indicators.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.184-193
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• 2012

In this paper, a 5-bit 2-GS/s 2-way time interleaved pipeline ADC for high-speed serial link receiver is demonstrated. Implemented as a current-mode amplifier, the stage ADC simultaneously processes the tracking and residue amplification to achieve higher sampling rate. In addition, each stage incorporates a built-in 1-tap FIR equalizer, reducing inter-symbol-interference (ISI）without an extra digital post-processing. The ADC is designed in a 110nm CMOS technology. It comsumes 91mW from a 1.2-V supply. The area excluding the memory block is $0.58{\times}0.42mm^2$. Simulation results show that when equalizer is enabled, the ADC achieves SNDR of 25.2dB and ENOB of 3.9bits at 2.0GS/s sample rate for a Nyquist input signal. When the equalizer is disengaged, SNDR is 26.0dB for 20MHz-1.0GHz input signal, and the ENOB of 4.0bits.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.4
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• pp.7-13
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• 2012

The performance of blind equalization algorithm ISCA was compared with MSCA that is used for the minimization of the inter symbol interference which occurs in the time dispersive communication channel for digital transmission. Because of the non-linearities of a magnitude and phase transfer characteristics of a communication channel, the transmitting signal will be received that band limited and time dispersived. Therefore the distortion was compensated by using the self adaptive equalizer at the receiving side, then passing through the detector for the decision of "1" or "0". At this time the Constellation Dependent Constant is played an important role in the adaptive equalizer used on the receiver. In order to calculation of this constant, the ISCA and MSCA was used the second order statistics. The ISCA and MSCA which are possible to compensation of mensioned transfer function simulataneously, are improved the performance of original SCA algorithm and then was compared the performance by computer simulation. For this, the recovered constellation, residual isi and MSE was used, and a result of performance comparison, the ISCA algorithm has better than the MSCA in every performance index. But on the steady state of equalizer, the variation of performance due to the CME terms in the MSCA equalization algorithm was less than the ISCA, so MSCA has better stability.