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The mysterious underwater phone: How it could change the future of ocean communications?
Underwater acoustic communication is a technology for sending and receiving messages in water. With the advancement of technology, this field has slowly revealed its potential. However, the challenges of communicating underwater are clear, with factors including multipath propagation, channel time variations, small bandwidth availability, and strong signal attenuation, especially when transmitting over long distances. Underwater communication is characterized by lower data speeds than terrestrial communication because it uses sound waves rather than electromagnetic waves.
Despite its challenges, underwater communication technology continues to evolve.
In the early 20th century, some ships began communicating via underwater clocks and using the system for navigation. Submarine signals at the time were competing in primitive maritime radio navigation. With the invention of the Fesden oscillator, there was a new breakthrough in the form of submarine communication.
Modulation types for underwater acoustic communication
There are many modulation methods used in Underwater Acoustic Communications (UAC), most of which are adapted from radio communications. However, due to the needs of special underwater channels, some modulation schemes are more suitable for underwater acoustic communication. The following are some modulation methods commonly used in UAC:
Modulation technologies include frequency shift keying (FSK), phase shift keying (PSK), orthogonal frequency division multiplexing (OFDM) and continuous phase modulation (CPM).
Frequency shift keying (FSK)
FSK is the earliest form of modulation used for underwater acoustics, typically using two different frequencies to modulate data. Although this is a relatively simple modulation method, one of the challenges it faces is the multipath reflection present in UAC, which may cause confusion at the receiving end and limits its use in vertical channels.
Phase shift keying (PSK)
Phase shift keying (PSK) is a digital modulation scheme that transfers data by varying (modulating) the phase of a reference signal. This technology is widely used in wireless LAN and Bluetooth communications.
Orthogonal frequency division multiplexing (OFDM)
OFDM is a digital multi-carrier modulation technology that can transmit information on multiple parallel data channels and is extremely advantageous in resisting interference from underwater frequency-selective channels.
Continuous Phase Modulation (CPM)
Continuous phase modulation (CPM) is a modulation technology with continuously changing phases, which can suppress multipath propagation effects in underwater environments and maintain signal integrity. Its high spectral efficiency makes it suitable for underwater bandwidth-limited situations. Be an excellent choice.
The use of vector sensors
Compared with scalar pressure sensors that are common underwater, vector sensors, which can measure the velocity of acoustic particles, have been widely studied in the past few decades. The application of vector sensors under water has extended to fields such as sonar and target detection. The company is also developing communication receivers and equalizers related to vector sensors.
Application
Underwater Telephone and JANUS System
Introduced by the U.S. Navy in 1945, the Underwater Telephone (UQC) is a two-way communication system that has been widely used on active submarines and surface ships. In addition, the JANUS system launched by NATO in 2017 is designed to transmit digital information using sound waves and has been used in military and civilian fields to help improve the efficiency and popularity of underwater communications.
Underwater messaging technology
Commercial hardware products have been designed to support two-way messaging between scuba divers, and researchers are also exploring how to use smartphones for underwater communication. This not only improves the convenience of underwater communication, but also provides new opportunities for diving activities. possibility.
As technology advances, how will the development of underwater communications materials impact the future of ocean exploration and conservation? This issue may become the direction we must think about.
