• Proceedings of the Acoustical Society of Korea Conference
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• spring
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• pp.429-432
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• 2000

수중에서 AUV신호나 화상데이터의 정확한 고속 전송 등을 위해 수중 데이터 통신에 대한 많은 연구가 진행되어 왔다. 수중 데이터 통신에서 잔향과 배경 잡음 등의 해양 환경 특성을 극복하는 것은 신뢰성 있는 통신 환경을 이룩하는데 중요하다. 특히 해면과 해저로 이루어진 천해 환경에서 해면과 해저 반사파에 의한 영향은 수중 데이터 통신의 성능을 좌우하는 중요한 요소 중의 하나로 알려져 있다. 이러한 환경적 영향을 최소화하여 높은 성능의 통신 환경을 제공하기 위해 다중경로의 영향을 적게 받는 변조방식을 선택하는 것이다. 수중 데이터 통신에서 일반적으로 사용되는 변조방식은 FSK, PSK, DPSK 등이 있다. 본 연구에서는 해면$\cdot$해저로 이루어진 해양 통신 채널에서 세 가지 변조방식의 성능을 수치모의실험을 통하여 비교$\cdot$분석하였다. 수치모의실험에서 해면 해저로 이루어진 천해의 해양 통신 채널은 음원 영상법을 적용하여 구성하였으며 각 변조방식의 성능은 BER(Bit Error Ratio)로 나타내었다.

• Information and Communications Magazine
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• v.33 no.8
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• pp.63-70
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• 2016

본고에서는 최근 활발하게 연구되고 있는 수중 음향통신을 위한 물리계층 기술에 대하여 알아 본다. 수중음향통신은 지상의 전파를 이용한 무선 통신 기술과 달리 음파를 이용한다. 음파는 수중에서 약1500m/s로 매우 저속이고 시간에 따른 다중 경로와 해수면과 해저면에서의 반사가 발생한다. 또한 수온, 염분, 수압, 해류와 해저지형 등에 의해 신호의 왜곡 및 손실이 일어나기 때문에 수중음향통신은 지상에서 전파를 이용한 통신에 비하여 매우 어려운 일이다. 본고에서는 이러한 수중음향채널의 특성을 살펴보고 링크버짓 계산을 한다. 그리고 수중음향통신을 위한 물리계층 변조기법을 살펴본다. 특히 OFDM 변조기법에 대하여 자세히 설명하고 실해역 측정을 통한 수중채널 특성을 기반으로 채널을 모델링하고 OFDM 변조기법을 위한 파라미터 선정 및 성능비교를 하였다.

• The Journal of the Acoustical Society of Korea
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• v.34 no.4
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• pp.295-302
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• 2015

Acoustic channels are characterized by long multipath spreads that cause inter-symbol interference. The way in which this fact influences the design of the receiver structure is considered. To satisfy performance and throughput, we presented consecutive iterative BCJR (Bahl, Cocke, Jelinek, Raviv) equalization to improve the performance and throughput. To achieve low error performance, we resort to powerful BCJR equalization algorithms that iteratively update probabilistic information between inner decoder and outer decoder. Also, to achieve high throughput, we divide long packet into consecutive small packets, and the estimate channel information of previous packets are compensated to next packets. Based on experimental channel response, we confirmed that the performance is improved for long length packet size.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.6 no.1
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• pp.29-36
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• 2013

The inter-symbol interference(ISI) is one of the main obstacles to reliable high-rate data communication in the shallow underwater acoustic channel. This paper studies on the simulation of adaptive equalizer used as a means of mitigating the ISI in the shallow underwater acoustic communication system. The underwater channel is modeled as a superposition of multiple paths, whose lengths and relative delays are calculated from the channel geometry. Based on this channel model, computer simulations are carried out to investigate the performance of adaptive equalizer in the shallow underwater acoustic channel.

• Journal of the Institute of Convergence Signal Processing
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• v.18 no.2
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• pp.37-42
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• 2017

In this paper, we study on symbol error rate(SER) performance of frequency domain decision feedback equalization for modelled underwater channel. Underwater channel is generated by Bellhop model. Simulation results show that proposed method is efficient for underwater acoustic communication.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.143-149
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• 2022

In this paper, we evaluate the underwater frequency diversity communication performance of Selective Combination (SC) using Maximum Likelihood Estimation (MLE). In an underwater multipath frequency selective channel, destructive interference fading due to delay spread of a received signal affects the increase in error and Signal to Noise Ratio (SNR) variability of an underwater acoustic communication. Selective Combination frequency diversity using a single sensor is applied as a transmission performance improvement technique according to the frequency selectivity of a channel. In the sea experiment applying MLE for SC decision value extraction, we evaluate the performance of SC frequency diversity and MLE-SC frequency diversity. In experiment result, we confirm through experiment that the Bit Error Rate (BER) is relatively lower when the decision value extracted through MLE-SC is applied than when the SC decision value is fixed.

• Journal of the Institute of Convergence Signal Processing
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• v.20 no.4
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• pp.177-185
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• 2019

In this paper, we propose and evaluate a FDE combined with STBC transmission structure to cancellation of ISI in underwater acoustic communication. To achieve this purpose, underwater acoustic channels are modeled and the simulation results are presented. In case of STBC-FDE, the transmission rate is less about 4% than STBC-OFDM, but the SER performance is better than STBC-OFDM that is larger from 4.4% to 16.8% at the SNR of 15dB than STBC-OFDM.

• Journal of Navigation and Port Research
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• v.38 no.4
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• pp.349-356
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• 2014

In the underwater communication, the performance of system is reduced because of the inter-symbol interference occur by the multi-path. In the recent years, to deal with poor channel environment and improve the throughput, the efficient concatenated structure of equalization, channel codes and Space Time Codes has been studied as MIMO system in the underwater communication. Space Time Codes include Space Time Block Codes and Space Time Trellis Codes in underwater communication. Space Time Trellis Codes are optimum for equalization and channel codes among the Space Time Codes to apply in the MIMO environment. Therefore, in this paper, turbo pi codes are used for the outer code to efficiently transmit in the multi-path channel environment. The inner codes consist of Space Time Trellis Codes with transmission diversity and coding gain in the MIMO system. And Zero Forcing method is used to remove inter-symbol interference. Finally, the performance of this model is simulated in the underwater channel.

• Journal of the Institute of Convergence Signal Processing
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• v.19 no.3
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• pp.139-146
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• 2018

Underwater acoustic communication can be applied to various area such as scientific, commercial and military survey using Autonomous Underwater Vehicles and Unmanned Underwater Vehicles. Underwater communication is studying very actively by advanced country like United States. But differ from wireless communication in the air, underwater acoustic communication has some difficult problems, ISI(Inter Symbol Interference) due to multipath and limit of transmission bandwidth due to slow propagation of sound wave. In this paper, SC-FDE and OFDM transmission system for the cancellation of ISI in conjunction with underwater acoustic channel modeling are applied to the underwater simulation of communication. The performance of these methods in the simulation guide to possibility of adopting in underwater acoustic communication algorithm. For this purpose, we compare SER performance of SC-FDE with that of OFDM for modelled underwater channel. Underwater channel is generated by Bellhop model. Simulation results show above 5dB SNR gain at 10-3 SER. And it demonstrate SC-FDE is efficient method for underwater acoustic communication.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7B
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• pp.878-885
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• 2011

Due to reflect at surface of the water and limit bandwidth, it is difficult to design underwater acoustic communication systems with high-reliability and high transmission rate. Therefore the trends of underwater communication is transformed from single sensor to multiple sensor studies. However, underwater MIMO communication techniques have a high correlation value between multiple sensors on transmitters and receivers in underwater environments, it is difficult to expect space diversity gain on muli-path channels. Therefore, this paper proposed the MISO communications system with two transmit sensors and single receiver sensor, and analyzed its performance using the LDPC codes and channel compensation algorithm.