Periodic Reporting for period 1 - WABCom (Water-to-Air Backscatter Communications)
Berichtszeitraum: 2020-10-01 bis 2022-09-30
Over 70% of the Earth’s surface is covered by water, while the majority of the underwater areas are unexplored yet. Owing to growing underwater activities, e.g. undersea oil & gas exploration, and Internet of underwater things (IoUT), which are expected to connect various underwater sensors and autonomous underwater vehicles (AUVs) to the outside world, reliable water-to-air wireless communications are urgently needed by the industry, military, and scientific communities. However, it is difficult to communicate across a water-air interface using a single type of wireless signal, e.g. acoustic, radio frequency (RF), or optical. RF signals decay exponentially in water. Although acoustic and optical signals can travel over long distances underwater, they both suffer from severe reflections off the water surface and hence cannot transmit smoothly across the water-air interface. To overcome the water-air barrier, most existing water-to-air communications rely on sonobuoys, which are floating devices that receive acoustic signals from underwater transmitters and then RF-transmit them to receivers on/above the water surface. Presently, battery-powered sonobuoys use magnesium/silver chloride or lithium primary batteries, which are full of toxic metals and tend to vent toxic fumes during discharging. As they might not be retrieved from remote, hostile areas of the ocean, battery-powered sonobuoys are posing a great threat to the marine environment. Although energy-harvesting technologies (e.g. solar, wave, or seawater semi-fuel cell) have been developed for sonobuoys to charge onboard energy storage systems, the challenge of miniaturizing and incorporating these technologies into the sonobuoy volume constraint remains a dominant issue. Large sonobuoys would require complex mooring systems, thus limiting their wide deployment for water-to-air communications.
Miniature/lightweight battery-free sonobuoys, which can be flexibly deployed (e.g. air-dropped by unmanned aerial vehicles (UAVs)) where and when needed and are disposable with a minimum impact on the marine environment, are in high demand for many ocean applications, such as underwater search and rescue (SAR), IoUT, oil spill monitoring, and scientific exploration. Since RF communication is the major source of energy consumption for sonobuoys, a battery-free design of sonobuoy can leverage backscatter communications, which allow a device to communicate at near-zero power by reflecting an existing RF signal, thus leading to novel water-to-air backscatter communications (WABCom).
The project validates the feasibility of the proposed WABCom system through a comprehensive approach that includes mathematical simulations, prototyping, and extensive experimentation. The results demonstrate the potential of the proposed system, and the innovation activities of the project can lead to the development of new products, services, reference materials, processes, or methods that can be launched into the market. These developments have significant benefits for various industries and government agencies involved in underwater IoT, underwater detection, marine biology research, oil exploration, and emergency rescue.
Miniature/lightweight battery-free sonobuoys, which can be flexibly deployed (e.g. air-dropped by unmanned aerial vehicles (UAVs)) where and when needed and are disposable with a minimum impact on the marine environment, are in high demand for many ocean applications, such as underwater search and rescue (SAR), IoUT, oil spill monitoring, and scientific exploration. Since RF communication is the major source of energy consumption for sonobuoys, a battery-free design of sonobuoy can leverage backscatter communications, which allow a device to communicate at near-zero power by reflecting an existing RF signal, thus leading to novel water-to-air backscatter communications (WABCom).
The project validates the feasibility of the proposed WABCom system through a comprehensive approach that includes mathematical simulations, prototyping, and extensive experimentation. The results demonstrate the potential of the proposed system, and the innovation activities of the project can lead to the development of new products, services, reference materials, processes, or methods that can be launched into the market. These developments have significant benefits for various industries and government agencies involved in underwater IoT, underwater detection, marine biology research, oil exploration, and emergency rescue.
The main works and results of the project are listed below.
1) Efficient energy harvesting for a battery-free buoy: The project has successfully developed and implemented efficient energy harvesting techniques that can harvest enough power from an in-air RF transceiver to operate a buoy without the need for a battery. The development of these techniques involved the integration of rectifier design, RF impedance matching, high-frequency circuit design, simulation, and fabrication.
2) Water-to-Air Backscatter Communication: The project has also achieved a breakthrough in the development of water-to-air backscatter communication technology, which allows for low-cost and low-power communication in marine environments. This involves transmitting data from an underwater acoustic transmitter to the buoy, and from the buoy to an aerial receiver.
3) Optimization of the buoy’s circuit: The project has successfully optimized the buoy’s circuit to increase the amount of energy harvested from the RF signals while ensuring high signal-to-noise ratio (SNR) water-to-air backscatter communications. This required careful selection of components and tuning of the circuit to match the impedance of the energy source and make a trade-off between the SNR of the water-to-air backscatter communications and the energy harvesting efficiency.
4) Enhanced robustness: The project has designed and tested the battery-free buoy to withstand dynamic marine environments. The project studied the relationship between the buoy's motion and water surface movement and developed a pilot-based channel estimation and equalization method to reduce the impact of the dynamic water surface on the backscatter communication channel.
5) Real-World testing: The project has built a prototyping for the battery-free buoy and implemented a test bed to evaluate and validate the buoy's performance on a wavy water surface. This involved testing the buoy in a controllable wave tank and measuring its performance under different wave patterns to identify any design flaws in the buoy's shape, the proposed backscatter communication technology, and the channel estimation and equalization methods. These results will help refine the technology for future practical applications.
1) Efficient energy harvesting for a battery-free buoy: The project has successfully developed and implemented efficient energy harvesting techniques that can harvest enough power from an in-air RF transceiver to operate a buoy without the need for a battery. The development of these techniques involved the integration of rectifier design, RF impedance matching, high-frequency circuit design, simulation, and fabrication.
2) Water-to-Air Backscatter Communication: The project has also achieved a breakthrough in the development of water-to-air backscatter communication technology, which allows for low-cost and low-power communication in marine environments. This involves transmitting data from an underwater acoustic transmitter to the buoy, and from the buoy to an aerial receiver.
3) Optimization of the buoy’s circuit: The project has successfully optimized the buoy’s circuit to increase the amount of energy harvested from the RF signals while ensuring high signal-to-noise ratio (SNR) water-to-air backscatter communications. This required careful selection of components and tuning of the circuit to match the impedance of the energy source and make a trade-off between the SNR of the water-to-air backscatter communications and the energy harvesting efficiency.
4) Enhanced robustness: The project has designed and tested the battery-free buoy to withstand dynamic marine environments. The project studied the relationship between the buoy's motion and water surface movement and developed a pilot-based channel estimation and equalization method to reduce the impact of the dynamic water surface on the backscatter communication channel.
5) Real-World testing: The project has built a prototyping for the battery-free buoy and implemented a test bed to evaluate and validate the buoy's performance on a wavy water surface. This involved testing the buoy in a controllable wave tank and measuring its performance under different wave patterns to identify any design flaws in the buoy's shape, the proposed backscatter communication technology, and the channel estimation and equalization methods. These results will help refine the technology for future practical applications.
The prject make multiple contributions to the state of the art.
1) Development of a new architecture that supports water-to-air backscatter communications. Compared with existing solutions for water-to-air communications, the proposed architecture has the feature of low cost and battery-free, which improves the scalability and feasibility of large-scale underwater IoT sensor networks.
2) Development of a new water-to-air backscatter communication technology that outperforms existing technologies in terms of less power consumption of the buoy to over the water-air barriers.
3) Development of a channel estimation and equalization method to address the impact of the dynamical water surface on the proposed communication technology.
4) Development of a test bed to validate the proposed architecture in a controllable wave tank.
5) The research on battery-free buoy and low-power communication technology meets the European policy objectives of sustainable development and promoting energy efficiency and renewable energy sources.
1) Development of a new architecture that supports water-to-air backscatter communications. Compared with existing solutions for water-to-air communications, the proposed architecture has the feature of low cost and battery-free, which improves the scalability and feasibility of large-scale underwater IoT sensor networks.
2) Development of a new water-to-air backscatter communication technology that outperforms existing technologies in terms of less power consumption of the buoy to over the water-air barriers.
3) Development of a channel estimation and equalization method to address the impact of the dynamical water surface on the proposed communication technology.
4) Development of a test bed to validate the proposed architecture in a controllable wave tank.
5) The research on battery-free buoy and low-power communication technology meets the European policy objectives of sustainable development and promoting energy efficiency and renewable energy sources.