The Journal of the Acoustical Society of Korea (한국음향학회지)

The Acoustical Society of Korea (한국음향학회)
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Performance analysis of OFDM and CDMA communication methods in underwater acoustic channel

수중 채널 환경에서 OFDM 및 CDMA 통신 방식별 성능 분석

  • 김길용 (호서대학교 해양IT융합기술연구소) ;
  • 김민상 (호서대학교 해양IT융합기술연구소) ;
  • 고학림 (호서대학교 정보통신공학과) ;
  • 임태호 (호서대학교 해양IT융합기술연구소)
  • Received : 2018.10.01
  • Accepted : 2019.01.23
  • Published : 2019.01.31
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Abstract

In recent years, researches on various communication methods have been conducted, particularly on OFDM (Orthogonal Frequency Division Multiplexing) and CDMA (Code Division Multiple Access) methods, as the use of underwater communication increases. While OFDM is, in general, advantageous in that it is resistant to Doppler in the water and it enables a high-speed communication, CDMA is resistant to frequency selective fading in the water and it can reduce energy consumption. Therefore, in this paper, we performed experiments in the shallow water in Western Sea of Korea to analyze the performance of OFDM and CDMA communication systems in the underwater channel environment. The maximum delay spread and Doppler spread were drawn by using the data obtained from the real sea area in order to analyze the underwater channel environment characteristics of the shallow water in Western Sea of Korea. The communication performances of OFDM and CDMA are shown as coded BER (Bit Error Rate) according to the variation of the maximum delay spread and the Doppler spread, respectively. The result of the analysis show that the OFDM method has more resistant performances to the underwater channel environment changes than the CDMA method.

최근 수중 통신을 활용하는 사례가 많아짐에 따라 여러 가지 통신 방식에 대한 연구가 진행되고 있으며, 그 중에서 OFDM(Orthogonal Frequency Division Multiplexing) 방식과 CDMA(Code Division Multiple Access) 방식에 대한 연구 사례가 증가하고 있다. 일반적으로 OFDM은 수중에서 도플러에 강하고 고속 통신이 가능하다는 장점이 있으며, CDMA는 수중에서 주파수 선택적 페이딩에 강하고 에너지 소모를 줄일 수 있는 등의 장점이 있다. 따라서 본 논문에서는 수중 채널 환경에서 OFDM과 CDMA 통신 방식의 성능 분석을 위해 서해 천해역에서 실험을 수행하였다. 서해 천해역의 수중 채널 환경 특성을 분석하기 위해 실해역에서 취득한 데이터를 사용하여 최대 지연 확산과 도플러 확산을 도출하였으며, 최대 지연 확산과 도플러 확산의 변화에 따른 OFDM과 CDMA 방식의 통신 성능을 coded BER(Bit Error Rate)로 나타내었다. 분석 결과 OFDM 방식이 CDMA 방식에 비해 수중 채널 환경 변화에 강인한 통신 성능을 보임을 확인하였다.

Keywords

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Fig. 1. Block diagram of the OFDM system used in this study.

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Fig. 2. Frame structure of OFDM system.

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Fig. 3. Block diagram of the CDMA system used in this study.

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Fig. 4. Frame structure of CDMA uplink system.

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Fig. 5. Experimental location.

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Fig. 6. Experimental environment.

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Fig. 7. Transmitting transducers (L) and receiving hyd-rophones (R).

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Fig. 8. Transceive systems.

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Fig. 9. Performance comparison by pilot spacing when frequency repetition is maximum (a) and time repetition (b) is maximum.

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Fig. 10. Performance comparison with maximum excess delay spread and doppler spread when time repetition is fixed.

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Fig. 11. Performance comparison by pilot spacing with maximum excess delay spread and doppler spread when frequency repetition is fixed.

Table 1. Parameters of OFDM uplink system.

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Table 2. Parameters of CDMA uplink system.

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Table 3. Spreading code.

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