Software Radio Technology (SRT) Announce New AIS Products

[jimh]

Software Radio Technology in the United Kingdom (SRT) have announced several new products for the automatic identification system (AIS) market.

HF-AIS
SRT has coined a new acronym: HF-AIS, which means high-fidelity automatic identification system. HF-AIS is described as new technology in reception and demodulation of AIS radio signals into their data content. SRT says that HF-AIS is a decoder technology "more commonly found in high-end communication devices such as 4G mobile phones where very high data rates are required. [HF-AIS] ensures reliable decoding and processing of all AIS messages in real time--which in turn ensures that the end user sees everything. When combined with SRT's superior radio reception sensitivity, the difference for the user can be dramatic."

The choice of HF for use in the acronym to mean high fidelity is a bit awkward. Because AIS is a radio based protocol, one would generally think HF refers to high-frequency, not high-fidelity.

Concurrent with the announcement of the new receiver-demodulator technology of HF-AIS, SRT has also introduced new products that utilize the method.

Artemis Class-B SOTDMA Transponder
SRT has introduced a new Class-B transponder product, the Artemis. The Artemis is an enhanced Class-B device, using a 5-Watt transmitter power and capable of participating in the self-organizing time-division multiple access (SOTDMA) protocol used by Class-A AIS Transponders. Typical Class-B AIS transponders only use a 2-Watt transmitter and use a different protocol, called carrier-sense time-division multiple-access (CSTDMA) to participate in AIS communications.

Apollo Class-A Transponder
While unlikely to be applicable for use in small boats, SRT has also introduced an improved Class-A AIS transponder, the Apollo model. It is said to based on an entirely new hardware design. The use of HF-AIS demodulator methods is presumed to be included.

AIS Changing Role
The automatic identification system (AIS) was conceived and designed to be a safety device: a collision avoidance system. Commercial vessels with AIS would be able to see other AIS vessels, know their identity, course, speed, and other data, and make use of this information to avoid collisions. AIS has now changed from that initial collision-avoidance purpose and has become a global vessel tracking system. A white paper from SRT discusses this changing role for AIS.

A good summary of the differences between Class-A, Class-B SOTDMA, and Class-B CSDTMA AIS transponders can be found at the website of the Coast Guard of the USA.

[jimh]

SRT has published two new papers on their enhanced AIS transceivers with their High-Fidelity or HF AIS. A three-page PDF file is available directly from

http://www.srt-marine.com/wp-content/up ... HF-AIS.pdf

SRT explains that when AIS traffic density increases, the reception and decoding of AIS transmissions becomes much more difficult:

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.

Radio communication loading problems 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.

A longer and power-point-type presentation on HF AIS can also be downloaded from the SRT website.