2023_programme: A Demonstration of Frequency-Based Modulation for Underwater Optical Wireless Communication

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  • Session: 19. Underwater Communications and Networking
    Organiser(s): Charalampos Tsimenidis, Paul Mitchell and Konstantinos Pelekanakis
  • Lecture: A Demonstration of Frequency-Based Modulation for Underwater Optical Wireless Communication [invited]
    Paper ID: 2006
    Author(s): Chen Jianhui, Geldard Callum, Popoola Wasiu
    Presenter: Chen Jianhui
    Abstract: This paper presents experimental comparison of frequency-shift chirp modulation (FSCM), and frequency-shift keying implemented with subcarrier intensity modulation (FSK-SIM) for underwater optical wireless communications (UOWC), in a range of channel conditions. Due to the nature of the UOWC, its channel poses difficulties in designing a reliable link in real-world water conditions. These channel effects include turbidity and turbulence, caused by suspended particles and channel inhomogeneities within the UOWC channel, respectively. Turbidity results in photon scattering and absorption while turbulence causes fluctuation and fading in the received signal amplitude. Encoding data on the frequency of the transmitted signal, as in FSCM and FSK-SIM, can protect data from these channel effects. The two techniques use different signal structures to implement frequency-based modulation. In FSK-SIM, data is encoded on the subcarrier frequencies of a SIM-modulated signal. Whereas in FSCM, data is carried within a chirp pulse encompassing a range of frequencies. In this paper, the performance of FSCM and FSK-SIM is evaluated in three different water conditions, these are: clear tap water; turbid water; and turbulent water, where both temperature inhomogeneity and air bubble induced turbulence effect are considered. The UOWC channel is first characterised to understand the effect of the various channel conditions on the propagating optical signal. Secondly, the power spectral density (PSD) is used to demonstrate how the frequency characteristics of the signal are affected by different channel conditions. Finally, the data performance of the two modulation schemes is compared in terms of the bit error rate (BER) and maximum achieved data rate. Experimental results show that both FSCM and FSK-SIM have resilience against the effect of turbulence and provide good performance in low signal-to-noise ratio underwater channel conditions. Further, it is shown that in the channel conditions considered, FSCM can achieve a higher maximum data rate compared to FSK-SIM.
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  • Corresponding author: Mr Jianhui Chen
    Affiliation: University of Edinburgh
    Country: United Kingdom
    e-mail:

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