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7 Advantages of VDES vs. AIS in Maritime Satellite Communications

Advantages of VDES vs. AIS in Maritime Satellite Communications

VDES services are set to transform maritime satellite communications. In the maritime sector, there is major interest in making the connection between ships and ports as seamless as possible. For this purpose, the AIS (Automated Identification System) is currently the communications benchmark, but the emergence of the VDES (VHF Data Exchange System) standard may change this scenario in the coming years.

What is the difference between VDES and AIS? In this article we have selected the main advantages of VDES vs. AIS and some of the practical implications this transition may have for maritime satellite communications. Let's start.

1. VDES enables two-way communication

Satellite AIS services are unidirectional, which means that it is not possible to send messages to AIS terminals from space. This is one of the main innovations when it comes to VDES vs. AIS services, as the new standard has the capability to allow two-way maritime satellite communications.

Today, other services partially address this AIS problem in two ways: satellite connectivity through systems such as Iridium or Inmarsat (at a high cost and requiring specialised equipment) or through 2G and 3G cellular network connections for vessels not many kilometres from the coast.

Instead, the VDES service implements true two-way communication through ship-to-ship and ship-to-port data transmissions in both directions. Furthermore, the communication will be based on an international standard, without having to use equipment tied to a particular service provider.

These new communication capabilities not only provide accurate knowledge of the position, course, speed and status of vessels, but also enable the sending of relevant information. For example, for alerts on sightings of drifting objects, indications of fishing zones, pollution spots, possible delays in port arrival time and other possible incidents.

VDES also incorporates relay mechanisms that ensure the delivery of information.

2. VDES provides encryption for communications

A common practice for fishing vessels is to deactivate AIS equipment when they are about to make catches, so that nearby vessels and monitoring stations cannot know their exact location. This avoids revealing information about fishing grounds and fishing zones to their competitors, as the information transmitted by AIS is not encrypted and can be received by all members of the network.

These practices become a security issue for AIS communications, as other vessels in the area no longer receive information about that vessel, which may lead to collision risks or false sinking alerts.

Unlike AIS, VDES communications are encrypted. In this way, fishermen (and other vessels) can be confident that their fishing grounds will not be known to competitors and can keep their VDES equipment operational so that rescue and maritime control agencies can be aware of the location and status of all vessels.

3. VDES has been designed to operate via satellite (VDE-SAT)

In recent years, some initiatives have emerged to improve AIS services through the use of satellites, which allow the tracking of vessels on the high seas and in areas where terrestrial networks cannot provide service. The main difficulty is that AIS is not designed to be received from satellites. In fact, there is no specific standard for these types of transmissions, which creates problems of confidence in the reception of the signals and complicates the provision of this service from space, as well as the lost opportunity of one-way communications.

Unlike AIS, VDES has space in its DNA. In addition to the terrestrial component (VDE-T), this system has had the satellite component (VDE-SAT) in mind from the beginning. VDE-SAT waveforms and protocols are being defined to operate over satellite channels and take into account their peculiarities and specific needs. The result is a much more robust and digitised maritime satellite communications service.

The in-orbit communication needs of VDES services can be further complemented by ISL (Inter-satellite Link) systems for sending information between satellites in the same constellation and HDR (High Data Rate) transmitters for high-speed links to the ground.

4. AIS becomes saturated in areas with a high concentration of ships

In certain areas with a high concentration of ships, such as the Strait of Gibraltar, the English Channel or some ports, AIS has saturation problems due to the high number of users. Sometimes the maximum capacity for which the system was designed is reached. This results in dangerous situations, because the network is not able to report information from all vessels in these areas.

This problem is expected to increase in the coming years. At present, not all ships are required to have AIS equipment: only ships over 500 tonnes (over 300 tonnes for international voyages) and any type of passenger carrying vessel. The point is that the recommendations of the International Maritime Organization (IMO), a UN agency, are increasingly aiming for more ships to be equipped with technology to ensure communications and improve safety.

These saturation situations have been taken into account in the development of VDES, which has up to 32 times more bandwidth than current AIS services. Furthermore, through intelligent algorithms, it is possible to make an automatic selection of the communication system (VDE-T, VDE-SAT and other possible integrations, such as 5G), depending on the location of the ship, the coverage, the saturation level of the different systems, and the size and priority of the data being sent.

5. AIS only has a horizontal reach of 40 nautical miles

One of the challenges of maritime communications with today's technology is maintaining connectivity at long distances from shore. AIS transponder signals have a horizontal range of about 40 nautical miles (about 74 kilometres), which means that all AIS traffic information is only available in coastal areas or in areas where ship-to-ship communication is possible under ECDIS (Electronic Chart Display and Information System) detection capability. This translates into 47% of vessels being out of range of shore-based transceivers.

While there have been initiatives in recent years to address this problem through the use of small satellite constellations, there is still no AIS standard for providing maritime satellite communications, as we have seen in this article. For this reason, the reception of AIS messages from space is not fully guaranteed.

Another advantage of VDES vs. AIS is that it has been designed so that a terrestrial and a satellite component can coexist from the outset. VDE-SAT provides a global and robust service from space, guaranteeing accurate monitoring of each ship at all times, even at sea or on transoceanic voyages, without the risk of loss of communication information.

6. VDES allows for the integration of other communication systems

Beyond their terrestrial (VDE-T) and satellite (VDE-SAT) components, VDES services also allow the integration of new transmission channels to ensure their responsiveness to the emergence of a growing number of new players in the maritime sector.

In areas closer to the coast, for example, the demand for connectivity can be complemented by cellular networks, especially 5G. There are already projects working with 5G smart modules that can act as redundant and back-up links for VDES communications.

7. VDES facilitates the rollout of autonomous navigation systems

The transformation of maritime satellite communications implies a huge qualitative leap for the shipping industry in terms of digitalisation and autonomy.

With the help of VDES and its ability to handle two-way communication, which allows real-time two-way information transmission, e-Navigation solutions can be fostered and the emergence of unmanned autonomous vessels in the maritime sector can be encouraged.

The information provided by VDES will also lead to an optimisation of maritime traffic, leading to a reduction in emissions and fuel consumption.


These advantages of VDES vs. AIS point to a future in which maritime satellite communications can offer a more robust, secure, reliable and efficient service. This revolution also means a relatively simple transition for vessels, as VDES technology only requires a change of transponder, with no need to replace the antenna or ECDIS.

If you need advice on how to implement a project in the maritime sector that requires the use of VDES or AIS technology, please contact us. We will answer all your questions.

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