2023_programme: Experimental demonstration of equalization against Doppler shifts of multipath signals on underwater acoustic communications

• Session: 19. Underwater Communications and Networking
  Organiser(s): Charalampos Tsimenidis, Paul Mitchell and Konstantinos Pelekanakis
• Lecture: Experimental demonstration of equalization against Doppler shifts of multipath signals on underwater acoustic communications [invited]
  Paper ID: 1903
  Author(s): Deguchi Mitsuyasu, Kida Yukihiro, Shimura Takuya
  Presenter: Deguchi Mitsuyasu
  Abstract: In general, the Doppler shifts and multipath signals with large amplitudes and lags severely affect underwater acoustic communication (UWAC). Furthermore, the Doppler shift of each signal can be different from those of the other signals due to difference in the direction of arrival. The Doppler shifts of multipath signals including to the direct signal are still obstacle for UWAC. \nA decision feedback equalizer (DFE) has been utilized in UWAC for decades. Although it is still a powerful tool for robust UWAC, it is difficult to suppress degradation of the Doppler shifts in cases with multipath signals and the severe Doppler shifts, including mobile UWAC between small surface and underwater vehicles. \nTo suppress degradation caused by the Doppler shifts, the modified versions of the DFE have been proposed for several years. \nAgainst the Doppler shift of the direct signal, an adaptive digital down converter (ADDC) has been proposed. The ADDC adaptively adjust the digitized timing according to an estimated phase shift of the direct signal by the DFE. On the other hand, against the Doppler shifts of multipath signals other than the direct signal, the equalization with additional digital phase lock loops (DPLLs) has been recently proposed. The DPLLs compensate for phase shifts which the Doppler shifts of the signals individually cause. Both equalizers have reportedly improved demodulation performance through UWAC simulations with small surface and underwater vehicles.\nIn this study, it is investigated that the equalizers against the Doppler shifts can improve demodulation performance by application to data received in an at-sea experiment with a small autonomous surface vehicle (ASV). Consequently, the equalizer with the additional DPLLs greatly improved demodulation performance, whereas the ADDC-DFE offers improvement at a certain extent. The results show that the equalizers against the Doppler shifts validly work for actual data, not only simulation data.
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• Corresponding author: Dr Mitsuyasu Deguchi
  Affiliation: Japan Agency for Marine-Earth Science and Technology
  Country: Japan
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