• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.16-24
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• 2011

The sound speed of seawater can be calculated by the empirical formula as a function of temperature, salinity and pressure. It is little affected by salinity because the average salinity is 34 psu and varies within a few psu seasonally and spatially in the ocean. Recently, low-salinity water of 24 psu flows into the western sea area of Jeju Island due to the flood of the Yangtze River in China during summer, affecting sound speed profile. In this paper, it was analyzed how environmental changes affected to the underwater communication - the sound speed of low-salinity water was calculated, and the communication channel was estimated by the simulated acoustic rays while the transmitting and receiving depth and the range were varied with and without the low-salinity layer. And The BER (Bit error rate) was calculated by BPSK(Binary phase shift key) modulation and the effects of the low-salinity water on the BER was investigated. The sound speed profile was changed to have positive slope by the low-salinity layer at the sub-surface up to 20 m of depth, forming acoustic wave propagation channel at the sub-surface resulting in the decrease of most of the BER Consequently, this paper suggests that it is important to consider changes of the ocean environment for correctly analyzing the underwater communication and the detection capability.

• The Journal of the Acoustical Society of Korea
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• v.22 no.5
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• pp.367-374
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• 2003

In this paper, we propose an audio watermarking method using the attribute of tonal masker. First, the attribute of tonal masker as an audio watermarking attribute is analyzed. According to existing researches, it is possible to be imperceptible modulation for the energies of the frequencies that compose a tonal masker. And when the relation between the tone energy and the left or right frequency energy after various signal processing is compared with the one before the processing, very few changes are showed. We propose an audio watermarking method using these attributes of tonal masker. A watermark bit is embedded by the modulation of the difference between the two neighboring frequency energies of a tone. In the detection, the modulated the tonal masker is searched using the key wed in the embedding without original audio and the embedded watermark bit is detected. After each attack of noise insertion, band-pass filtering, re-sampling, compression, echo transform and equalization, the detection error ratios of the proposed method were average 0.11%, 1.26% for Classics and Pops. And the SDG(Subjective Diff-Grades) scale evaluation of the sound quality of the watermarked audio result in the average SDG -0.31.

• The Journal of the Acoustical Society of Korea
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• v.38 no.1
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• pp.82-95
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• 2019

In this study, we analyzed the beam time series of ocean reverberation which was conducted in the eastsouthern region of East Sea, Korea during the August, 2015. The reverberation data was gathered by moving research vessel towing LFM (Linear Frequency Modulation) source and triplet receiver array. After signal processing, we analyzed the variation of ocean reverberation level according to the seafloor bathymetry, source/receiver depth and sound speed profile. In addition, we used the normalized data by using cell averaging algorithm and identified the statistical characteristics of seafloor scatterer by using moment estimation method and estimated shape parameter. Also, we analyzed the coincidence of data with Rayleigh and K-distribution probability by Kolmogorov-Smirnov test. The results show that there is range dependency of reverberation according to the bathymetry and also that the time delay and the intensity level change depend on the depths of source and receiver. In addition, we observed that statistical characteristics of similar Rayleigh probability distribution in the ocean reverberation.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.9-15
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• 2011

Communication environments in the context of underwater channel are characterized to be bad by the characteristics of multipath. Multipaths are affected by various factors e.g. the temperature and the salinity of the ocean. In this paper, the representative sound speed profiles were calculated in the southern part of Baengnyeoung island so that the eigen-ray paths with the channel impulse responses were determined using the average sound speed profile of last decade. The performance of underwater communication was analyzed using the BPSK modulation and time reversal method. The significant differences of results were shown according to the change of season and carrier frequency by using computer simulation. In addition, improved performance is obtained using preprocess channel impulse response for the better comparison of two cases of summer and autumn.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2002.05a
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• pp.163-166
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• 2002

The underwater acoustic communication has been widely applied to various objects such as ocean exploration-development and military affairs. And recently for embodiment of the communication system that is installed in a submarine and underwater work system, many studies have been progressing. This scope of the main studies in the meantime. It made it possible for a diver and a scuba diver who arc difficult to notice the situation of the outside because of staying in the water to hear a sound through a small speaker by using a ultra sound transducer that a central frequency is 32KHz after modulation of a voice to give the information of the outside. Also in case of happening an emergency to a diver in the water, it made him/her ask for help to a person in the outside by pressing a key and send a letter data to a person in the outside by using a keyboard. Through this system, it is possible to send a voice or data between the underwater and the outside and it is available to a diver or skin scuba diver.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.227-234
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• 2022

Covert Underwater Communication (CUC) signals should not be detected by other unintended users. Similar to the method used in Radio Frequency (RF), covert communication technique sending information underwater is designed in consideration of the characteristics of Low Probability of Detection (LPD) and Low Probability of Intercept (LPI). These conventional methods, however, are difficult to be used in the underwater communications because of the narrow frequency bandwidth. Unlike the conventional methods of reducing transmission power or increasing the modulation bandwidth, a method of mimicking the acoustic signal of an underwater mammal is being studied. The biomimetic underwater acoustic communication mainly mimics the click or whistle sound produced by dolphin or whale. This paper investigates biomimetic communication method and introduces research trends to understand the potential for the development of such biomimetic covert underwater acoustic communication and future research areas.

• Korean Journal of Audiology
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• v.18 no.3
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• pp.105-111
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• 2014

Assistive listening devices (ALDs) refer to various types of amplification equipment designed to improve the communication of individuals with hard of hearing to enhance the accessibility to speech signal when individual hearing instruments are not sufficient. There are many types of ALDs to overcome a triangle of speech to noise ratio (SNR) problems, noise, distance, and reverberation. ALDs vary in their internal electronic mechanisms ranging from simple hard-wire microphone-amplifier units to more sophisticated broadcasting systems. They usually use microphones to capture an audio source and broadcast it wirelessly over a frequency modulation (FM), infra-red, induction loop, or other transmission techniques. The seven types of ALDs are introduced including hardwire devices, FM sound system, infra-red sound system, induction loop system, telephone listening devices, television, and alert/alarm system. Further development of digital wireless technology in hearing instruments will make possible direct communication with ALDs without any accessories in the near future. There are two technology solutions for digital wireless hearing instruments improving SNR and convenience. One is near-field magnetic induction combined with Bluetooth radio frequency (RF) transmission or proprietary RF transmission and the other is proprietary RF transmission alone. Recently launched digital wireless hearing aid applying this new technology can communicate from the hearing instrument to personal computer, phones, Wi-Fi, alert systems, and ALDs via iPhone, iPad, and iPod. However, it comes with its own iOS application offering a range of features but there is no option for Android users as of this moment.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.4
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• pp.505-513
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• 2017

Cavitation is a phenomenon caused by vapour cavities that is produced in rapid pressure changes. When the cavitation happened, the sound pressure level of a underwater radiated noise is increased rapidly. As a result, it can increase the probability of the identification or classification of a our warship's acoustic signature by an enemy ship. However, there is a problem that it is hard to precisely detect the occurrence of a cavitation noise. Therefore, this paper presents recent improvements in terms of the cavitation noise measurement by using continuous wavelet transform and DEMON(Detection of Envelope Modulation on Noise) signal processing. Then, we present that the suggested scheme is more suitable for detecting the cavitation than existing algorithms.

• The Journal of the Acoustical Society of Korea
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• v.37 no.1
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• pp.31-38
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• 2018

Based on the measured data in the south western sea of Jeju Island during the SAVEX15(Shallow Water Acoustic Variability EXperiment 2015), the effect of internal waves on the PPD (Predictive Probability of Detection) of a sonar system was analyzed. The southern west sea of Jeju Island has complex flows due to internal waves and USC (Underwater Sound Channel). In this paper, sonar performance is predicted by probabilistic approach. The LFM (Linear Frequency Modulation) and MLS (Maximum Length Sequence) signals of 11 kHz - 31 kHz band of SAVEX15 data were processed to calculate the TL (Transmission Loss) and NL (Noise Level) at a distance of approximately 2.8 km from the source and the receiver. The PDF (Probability Density Function) of TL and NL is convoluted to obtain the PDF of the SE (Signal Excess) and the PPD according to the depth of the source and receiver is calculated. Analysis of the changes in the PPD over time when there are internal waves such as soliton packet and internal tide has confirmed that the PPD value is affected by different aspects.

• Journal of Broadcast Engineering
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• v.24 no.4
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• pp.670-675
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• 2019

AM radio broadcasting has the advantage that the sound quality is lower than that of FM radio but the service area is wide and at night it can be transmitted even to overseas due to ionospheric reflection. AM radio broadcasts usually transmit large amounts of several tens to several hundreds of kilowatts (KW), requiring a lot of power, which is a financial burden on broadcasters. Recently, it is required to introduce a way to reduce the power of AM radio broadcasting in Korea. Therefore, it is possible to save a certain amount of power compared to the conventional AM radio broadcasting, and it is possible to maintain the existing license service area and sound quality, and what policies are needed to introduce the technology. In this paper, we predict the reduction of transmission power when a high efficiency transmission system is applied to existing AM radio broadcasting transmission system. As a result of the research, AMC adopting the high efficiency transmission method instead of the conventional AM radio transmission method, and when the modulation ratio of AM radio is 70%, if -3 dB companding is applied, the annual transmission power charge is decreased from 5,185,838,160Won to 3,528,900,086Won with saving of 32.0%, When -6 dB companding is applied, it is expected to be reduced to 2,608,378,934Won, which is 49.7% savings.