Application and tasks

The Underwater Internet of Things system is designed to provide access to autonomous underwater tools: various sensors, actuators, AUV / ROV directly from the Internet. The system is designed to solve the problems of remote data collection and control of various underwater mechanisms, data transfer from autonomous underwater sensors without the need for pre-setting or coordination in the changing composition and position of agents.

System concept

The Underwater Internet of Things system is a set of specialized devices and a stack of network protocols, originally developed considering their use in hydroacoustic channel conditions: complex hydrological conditions, low information transfer rate, and low signal propagation rate in the medium, narrow available frequency band.

The basis of the system includes three types of devices:

• multi-mode sonar modems that provide reliable data transmission through the sonar channel and support a specialized protocol stack, starting from the physical layer;
• two-medium floating access points that provide access to the underwater network infrastructure from the Internet via cellular and/or satellite communications, as well as passive positioning of the underwater network elements;
• universal interface devices with open circuitry and source code, which provide an informational interface of various sensors and instruments with sonar modems.

The main problem faced by the developers of such projects is the occurrence of collisions of acoustic signals at the receiving point while using relatively high-speed (and calculated over short distances – up to hundreds of meters) methods of data transmission. A bet is made on complicating the routing methods, but practice shows that this approach is unjustified for the following reasons: in a real hydroacoustic channel, rapidly changing, where the probability of message delivery may be significantly less than one, data transmission through the repeater chain is extremely inefficient not only because of the ever-increasing with the number of repeaters the probability of error, but also because of unacceptable delay and overhead costs for routing.

In our Headen system is applied a completely different approach, which, thanks to the specialized protocol stack, ensures the complete absence of collisions on the receiver side and data transmission without intermediaries-repeaters. The control commands and the transfer of small amounts of data are carried out using fixed-length code parcels, the transfer of data from autonomous underwater nodes takes place only at the request of a surface two-medium access point, which, having information about the location (and therefore possible propagation delays) of the underwater nodes, polls them optimally using time and bandwidth. In addition, this system uses methods that initially provide data transmission over long distances (up to 8 km between the transmitter and receiver), which eliminates the need to use repeaters. The fixed length of messages allows you to maximize the system’s energy efficiency and, as a result, increase autonomy. Moreover, to the separation in time, the system uses the code division of subscribers at the physical level, which is an integral part of the specialized protocol stack.

Under this system, underwater sites are divided into three types:

• nodes with dynamic addressing that do not require pre-configuration and can be included in an existing network automatically. One two-medium access point can simultaneously work with 256 such nodes. Each of these nodes is equipped with built-in pressure and temperature sensors. Using an interface device, the device can transmit up to 8 integer values from 0 to 999, up to 7 combined values, consisting of 24-bit integer and 32-bit, to a floating access point, real number, and a byte array of up to 128 bytes. An open architecture interface with source code processes various user sensors and transmits them directly to the modem, which, upon request from a two-medium access point, transmits them to the top, where they are accessible from the Internet;
• nodes for controlling actuators of the first type with a fixed address. The two-medium access point can work with 250 such devices. Each node can accept 4 different commands address and/or broadcast with the ability to confirm;
• nodes to control the second type of actuators with a fixed address; The two-medium access point can work with 49 such devices. Each node can receive 20 different commands address and/or broadcast with the ability to confirm.

So, in total, one access point can simultaneously serve up to 555 different nodes, in the water area with a radius of up to 8 kilometers.

All nodes support remote configuration of power saving modes in a wide range. At the same time, the mode is controlled by a modem, which, before going to sleep mode, signals this to the interface device, and on waking up, it also awakens the interface device connected to it.

Modems use modern highly reliable and noise-resistant digital hydroacoustic communication technology, which allows them to work steadily in a wide range of hydrological conditions and has proven itself well both in marine conditions and in extremely complex shallow water bodies.

High versatility of the system is complemented by passive positioning, which is provided by the following technical solutions:

• when using three or more floating access points, receiving signals from nodes and fixing the time of their arrival is performed simultaneously on all user access points, which, being equipped with satellite navigation system receivers, form a long navigation base, allowing to determine their geographical location;
• when using a specialized access point equipped with a phased antenna array, the horizontal angle of arrival of the signal from underwater nodes is determined, which, along with their known depth (all nodes are equipped with depth sensors), which is also transmitted upon request from the access point, allows to determine their relative location.

Development Stages

The development of the system is supposed to be carried out in the following stages.

Stage 1. Implementation of basic functionality. Long basic positioning system + physical protocol. Planned completion dates – the beginning of 2018.

Stage 2. Implementation of a two-frequency system of interaction. Increasing the frequency of data exchange with nearby devices should lead to the unloading of the main low-frequency channel, as well as to a significant increase in the speed of information exchange. The planned deadlines for the implementation of the stage are 2018.

Stage 3. Implementation of two-medium buoys with phased antenna arrays. Ensuring the operation of the communication system and navigation all on one buoy. The planned deadlines for the implementation of the stage are 2019.