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Title
Abstract
Figures
Introduction
Experimental Tests and Results
Streaming Video Results
Conclusions
References
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Computer Science
Media Technology

Underwater acoustic modem with streaming video capabilities

Profile image of A. Fernando RibeiroA. Fernando Ribeiro

2015, OCEANS 2015 - Genova

Abstract

Oceans have shown tremendous importance and impact on our lives. Thus the need for monitoring and protecting the oceans has grown exponentially in recent years. On the other hand, oceans have economical and industrial potential in areas such as pharmaceutical, oil, minerals and biodiversity. This demand is increasing and the need for high data rate and nearreal-time communications between submerged agents became of paramount importance. Among the needs for underwater communications, streaming video (e.g. for inspecting risers or hydrothermal vents) can be seen as the top challenge, which when solved will make all the other applications possible. Presently, the only reliable approach for underwater video streaming relies on wired connections or tethers (e.g. from ROVs to the surface) which presents severe operational constraints that makes acoustic links together with AUVs and sensor networks strongly appealing. Using new polymer-based acoustic transducers, which in very recent works have shown to have bandwidth and power efficiency much higher than the usual ceramics, this article proposes the development of a reprogrammable acoustic modem for operating in underwater communications with video streaming capabilities. The results have shown a maximum data-rate of 1Mbps with a simple modulation scheme such as OOK, at a distance of 20 m.

Figures (8)
TABLE I: MECHANICAL AND PIEZOELECTRIC CHARACTERISTICS OF PVDF [9]. The emitter transducer was mounted in a structure with two PVDF layers of 110 um thickness with 20 mm diameter, where it was glued to a stainless steel mass and the outside surface was isolated with a thin silicone layer to protect it from water. The layers were connected in parallel to the excitation circuit, thus each layer is independently excited with the maximum voltage. By bonding reversed polarization layers, the electrodes between the glue have the same electrical potential and there is no current between them. This consequently reduces the power consumption once the parasite capacitance was disabled. To operate up to 1 MHz the maximum thickness cannot exceed 225 um as it was presented in Eq. 4, and to increase the pressure wave output it was selected a multilayer structure with 2 layers of 110 um. Table I shows the main physical properties of PVDF to the proposed application, according to equations | to 5:
TABLE I: MECHANICAL AND PIEZOELECTRIC CHARACTERISTICS OF PVDF [9]. The emitter transducer was mounted in a structure with two PVDF layers of 110 um thickness with 20 mm diameter, where it was glued to a stainless steel mass and the outside surface was isolated with a thin silicone layer to protect it from water. The layers were connected in parallel to the excitation circuit, thus each layer is independently excited with the maximum voltage. By bonding reversed polarization layers, the electrodes between the glue have the same electrical potential and there is no current between them. This consequently reduces the power consumption once the parasite capacitance was disabled. To operate up to 1 MHz the maximum thickness cannot exceed 225 um as it was presented in Eq. 4, and to increase the pressure wave output it was selected a multilayer structure with 2 layers of 110 um. Table I shows the main physical properties of PVDF to the proposed application, according to equations | to 5:
From the developer point of view, the system is divided into three main layers, namely: application layer, hardware layer and physical layer, as it is presented in Fig. 2. Fig. 2. System archietcture: application layer, hardware layer and physical layer.
From the developer point of view, the system is divided into three main layers, namely: application layer, hardware layer and physical layer, as it is presented in Fig. 2. Fig. 2. System archietcture: application layer, hardware layer and physical layer.
Fig. 1. Transducer frequency response and power consumption. As it is possible to verify the transducer shows a flat response between 500 kHz and | MHz and only varies 5 dB between 100 kHz and 500 kHz. The transducer also displays low power consumption at 1 MHz since it only consumes 2.3 W.
Fig. 1. Transducer frequency response and power consumption. As it is possible to verify the transducer shows a flat response between 500 kHz and | MHz and only varies 5 dB between 100 kHz and 500 kHz. The transducer also displays low power consumption at 1 MHz since it only consumes 2.3 W.
As the base for the hardware layer a ZTEX USB-FPGA Module 1.15d was selected, provided with a microcontroller Cypress CY7C68013A EZ-USB FX2 and a Xilinx Spartan 6 FPGA. An instrumentation board was developed and mounted on this module as shown in Fig. 3. Fig. 3. System impelementation: control unit and instrumentation.
As the base for the hardware layer a ZTEX USB-FPGA Module 1.15d was selected, provided with a microcontroller Cypress CY7C68013A EZ-USB FX2 and a Xilinx Spartan 6 FPGA. An instrumentation board was developed and mounted on this module as shown in Fig. 3. Fig. 3. System impelementation: control unit and instrumentation.
Fig. 4. H-Bridge Power Amplifier PCB Board.
Fig. 4. H-Bridge Power Amplifier PCB Board.
Fig. 5. Flowcharts of video sender (left) and video receiver (right). In order to provide video streaming, two algorithms were developed based on the Open Source Computer Vision library also known as OpenCV. The flowcharts of Fig. 5 illustrate the algorithm steps for sending and receiving the video data.
Fig. 5. Flowcharts of video sender (left) and video receiver (right). In order to provide video streaming, two algorithms were developed based on the Open Source Computer Vision library also known as OpenCV. The flowcharts of Fig. 5 illustrate the algorithm steps for sending and receiving the video data.
Fig. 6. Original captured image (top), 25% quality (middle), 5% quality (below). On the sender side, a video frame is acquired from a camera and then compressed using the JPEG algorithm (cvEncodeImage function) provided by the OpenCV library. The compression quality is adjustable and it should provide the best compromise between image quality and compression ratio. This in turn allows different frame rates to be achieved. A higher compression ratio results in a lower quality image and hence in a higher frame rate (and vice-versa) as shown in Figure 6.
Fig. 6. Original captured image (top), 25% quality (middle), 5% quality (below). On the sender side, a video frame is acquired from a camera and then compressed using the JPEG algorithm (cvEncodeImage function) provided by the OpenCV library. The compression quality is adjustable and it should provide the best compromise between image quality and compression ratio. This in turn allows different frame rates to be achieved. A higher compression ratio results in a lower quality image and hence in a higher frame rate (and vice-versa) as shown in Figure 6.

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Related topics

  • Engineering
  • Computer Science
  • Underwater Acoustics
  • Underwater Communication
  • Adaptive Video Streaming
  • Video Streaming
  • Acoustic communications
  • Acoustic Streaming
  • Streaming Video
  • OCEANS Conference
  • Underwater Acoustic Communication
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