The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
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Multipath combining method for frequency shift keying underwater communications mimicking dolphin whistle

돌고래 휘슬음을 모방한 frequency shift keying 수중통신기법의 다중경로결합 수신 방법

  • Received : 2018.09.04
  • Accepted : 2018.11.22
  • Published : 2018.11.30
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Abstract

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.

본 논문은 수중에서 은밀성을 확보하기 위해 FSK(Frequency Shift Keying)를 이용하여 돌고래 휘슬음을 모방하는 통신 기법과 다중경로 결합 이득을 이용하여 BER(Bit Error Rate) 성능을 높이는 방법을 제안한다. 제안하는 방법은 휘슬음을 짧은 시간 구간으로 나누고 그 구간에 심볼의 직교성을 보장하는 FSK 변조신호를 만든다. 그리고 휘슬음을 모방할 때 다중경로 채널에서 심볼간의 ISI(Inter Symbol Interference)가 줄어드는 특징을 이용하여 다중경로 결합 이득을 얻는 방법이다. 제안한 방법의 성능을 보이기 위해 전산모의실험과 실제 호수실험을 진행하였다. 전산모의실험을 통해 다중경로에 의해 추가적인 다중경로 결합 이득이 발생함을 보였다. 호수 실험에서는 제안된 FSK 방법이 20 msec의 심볼 길이와 900 Hz의 변조 대역을 갖는 경우 다중경로 결합 이득을 얻어 0.002의 BER갖고 0.185의 BER을 갖는 CSS(Chirp Spread Spectrum)보다 우수함을 보였다. 그리고 모방한 신호와 실제 휘슬 신호의 시간-주파수 영역에서 평균 상호 상관 값을 통해 모방도를 분석하여 제안된 FSK방법이 CSS방법에 비해 높은 모방도를 보였다.

Keywords

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Fig. 1. Spectrogram of dolphin whistle.

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Fig. 2. Dolphin whistle mimicking communication signal spectrogram, (a) large K, (b) small K.

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Fig. 3. Dolphin whistle biomimicking communication signal structure.

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Fig. 4. Multipath gain combiner.

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Fig. 5. Non-coherent FSK demodulator.

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Fig. 6. Path combining vs BER gain.

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Fig. 7. Channel delay (a) and sound speed profile (b).

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Fig. 8. Simulation BER result, (a) 10 msec, (b) 20 msec.

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Fig. 9. Lake experiment configuration.

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Fig. 10. Received signal spectrogram (a) and time delay spread (b) of Kyungchun lake experiment.

Table 1. BER results of Kyugchun lake experiments.

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Table 2. Correlation coefficient average.

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