Advanced core AIS technology innovation

HF-AIS™ is an advanced DSP core technology which enables an AIS transceiver to reliably and accurately receive and decode every AIS transmission in real time, even in very busy areas where there are hundreds, perhaps thousands of transmissions every minute.

This means that you do not miss targets and see everything that there is to see.

From BusinessWire & SRT Marine

High Fidelity AIS (HF-AIS™) technology is another innovation from the global leaders in Automatic Identification System ‘AIS’ technology research and development - SRT Marine Technology. HF-AIS™ is advanced core technology which ensures that, even in increasingly busy areas, all AIS transmissions are received and decoded and thus displayed.
Not all AIS transceivers are the same, and HF-AIS™ defines a meaningful performance difference.

AIS transceivers constantly receive and then process hundreds, perhaps thousands of transmissions from other transceivers in real time.
Successful processing of AIS transmissions and therefore display of targets and data is often taken for granted by the end user.

But, if a transmission is not successfully received and processed, that data is not displayed.

The user may think they are seeing everything but that may not be the case. 

The ultimate determining factor of how well any AIS transceiver works in the field is determined by the core technology – its ability to receive, transmit and process thousands of messages in real time simultaneously.

HF-AIS is a turbo-decoder technology more commonly found in high-end communication devices such as 4G mobile phones where very high data rates are required.
It ensures reliable decoding and processing of all AIS messages in real time – which in turn ensures that the end user sees everything.

As more commercial and leisure vessels use AIS transceivers, the number of transmissions that your AIS transceiver must cope with is increasing exponentially.

Your transceiver must receive and decode (extract the information in the AIS transmission) each and every transmission in real time with absolute accuracy for you to see the target on your display.
This receive and decoding performance goes unseen, but sits at the heart of every AIS transceiver and defines the difference in performance between different AIS products.

Since AIS is an international maritime technology standard it is often assumed that the core performance [the receiving and transmitting of messages] of every AIS transceiver, and associated accessory, is the same and that the only variation between products are physical attributes such as size or user related functionali- ty such as connectivity options.

However, this is not the case.

The baseline functionality and radio operating protocol of all AIS devices are defined in the formal AIS product specification documents issued and maintained by the IEC and ITU committees under the auspices of the IMO.

However these do not define the actual operational real world performance of the core radio transceivers which do all AIS message communication work within every AIS device—and if the radio transceiver performance is compromised, so are the targets and data displayed.

This means targets may be present, but your AIS transceiver is not decoding them.

HF-AISTM ensures that every AIS message is received, decod- ed and displayed in real time.

 How AIS works :
AIS technology is optimized for real time terrestrial operation
using a sophisticated TDMA based radio communications protocol. 

Every AIS transmission is a standard structure as defined in the IEC & ITU, but the content (payload) of each message is different.

The content of every message is made up of static data such as MMSI, name, dimensions and dynamic (constantly changing) data such as position, speed, course, status etc.

AIS transceivers are continuously transmitting and receiving AIS messages between each other and the information seen on any display medium such as a chart plotter, ECDIS and or PC is ultimately determined by the ability of the radio transceiver to receive and decode each message and provide the static and dynamic data contained within each message.

[Decode?? When a radio transmission is received, the information contained within it needs to be ex- tracted and converted into a format which can be used such as NMEA0183 or NMEA2000. This process is called decoding.]

In very quiet areas, where there are perhaps only a few AIS transmissions the core radio transceiver technology may only have to decode 15 to 20 messages per minute.

However as the use of AIS has massively in- creased across leisure and commercial boats and now includes new active transmitting AIS devices such as AtoN, MOB, SART, Coast Stations and additional functionality and content such as weather, text messaging and satellite AIS an AIS transceiver must receive and decode a relentless stream of transmissions in real time—perhaps over 2,000 transmissions per minute: every minute.

Every transmission needs to be ’cleanly’ received and then accurately decoded and the information outputted in the correct data format to the selected display platform.

The process of decoding is complex and one which is relatively easy to achieve when the transmit loading is low, but becomes exponentially challenging as the transmit loading increases.

The result is that errors are made at the receive point and the decode point—which means transmissions are lost and therefore the content contained within not seen.

Example of AIS targets display (courtesy of Weather 4D 2.0)

Radio communication loading issues are not new and are encountered in all radio communication systems.

It is therefore a major challenge and area of specific expertise for the developers of all core communications technology—GSM, GPRS, 3G, 4G, WiFi etc.

The normal way for technology to manage this is through a combination of high performance technology (software & hardware) and to regulate the data rates between two entities so as not to overload the devices and or to request lost data is resent.

This regulating is unseen by the user, who may experience the device ’freezing’ or slowing, or in some cases, the data not coming through.

However AIS is a real time communication system and so it is not possible to regulate transmission rates.

Every transmission is unique and if not received and decoded the first time is lost.

Therefore when an AIS transceiver has sub optimal core technology as loading increases, transmissions will be simply be lost and targets and other information not seen—without the user being aware.

HF-AISTM uses advanced radio communications decoding technology known as ‘Turbo Decoding’ which, through a combination of advanced DSP (Digital Signal Processing) software and high quality hardware, en- sures that every message received is decoded.

The concept and technology fundamentals of Turbo Decoding originates in the cell-phone technology space where huge leaps in data rates were required, whilst at the same time devices were expected to be smaller and more power efficient.

The practical development and implementation of turbo decoding technology is highly specialist and exceptionally challenging.

DSP software capable of handling large amounts of data in real time without error needs to be developed which can operate to the required performance levels on hardware processors which meet the size and power consumption parameters for the overall product—one works against the other. Equally it is important that performance is achieved without overstressing hardware as this creates long term reliability and performance issues.

AIS is a sophisticated VHF radio based maritime tracking and data communications system.

Multiple independent entities such as vessels, buoys and coast stations automatically transmit and receive messages to and from each other.

HF-AIS turbo decoding technology is an ultra efficient DSP technology operating on a single high performance processor.

This streamline architecture means that the real time processing of all AIS messages at even the highest loading level is achieved whilst at the same time the size of the core transceiver module is minimized along with power consumption and heat generation.

For the user of an AIS transceiver with HF-AIS technology it means peace of mind that all targets and information will be received and decoded and available to display.

Links :

• GeoGarage blog : Concern over 'high seas security loophole' / Space station keeps watch on world's sea traffic / Google can track ships at sea ; detailed maps planned of sea bottom / Space station keeps watch on world's sea traffic / AIS vessel tracking experimentation in the Marine GeoGarage / AIS vessel tracking for 'la Solitaire du Figaro'