Universal Shipborne Automatic Identification System (AIS) Transponder

What is an AIS? Picture a shipboard radar display, with overlaid electronic chart data, that includes a mark for every significant ship within radio range, each as desired with a velocity vector (indicating speed and heading). Each ship "mark" could reflect the actual size of the ship, with position to GPS or differential GPS accuracy. By "clicking" on a ship mark, you could learn the ship name, course and speed, classification, call sign, registration number, MMSI, and other information. Maneuvering information, closest point of approach (CPA), time to closest point of approach (TCPA) and other navigation information, more accurate and more timely than information available from an automatic radar plotting aid, could also be available. Display information previously available only to modern vessel traffic service operations centers could now be available to every AIS-equipped ship.

With this information, you could call any ship over VHF radiotelephone by name, rather than by "ship off my port bow" or some other imprecise means. Or you could dial it up directly using GMDSS equipment. Or you could send to the ship, or receive from it, short safety-related email messages.

The AIS is a shipboard broadcast system that acts like a transponder, operating in the VHF maritime band, that is capable of handling well over 4,500 reports per minute and updates as often as every two seconds. It uses Self-Organizing Time Division Multiple Access (SOTDMA) technology to meet this high broadcast rate and ensure reliable ship-to-ship operation.

How Does it Work?

Each AIS system consists of one VHF transmitter, two VHF TDMA receivers, one VHF DSC receiver, and a standard marine electronic communications link (IEC 61162/NMEA 0183) to shipboard display and sensor systems. Position and timing information is normally derived from an integral or external global navigation satellite system (e.g. GPS) receiver, including a medium frequency differential GNSS receiver for precise position in coastal and inland waters. Other information broadcast by the AIS, if available, is electronically obtained from shipboard equipment through standard marine data connections. Heading information and course and speed over ground would normally be provided by all AIS-equipped ships. Other information, such as rate of turn, angle of heel, pitch and roll, and destination and ETA could also be provided.

The AIS transponder normally works in an autonomous and continuous mode, regardless of whether it is operating in the open seas or coastal or inland areas. Transmissions use 9.6 kb GMSK FM modulation over 25 or 12.5 kHz channels using HDLC packet protocols. Although only one radio channel is necessary, each station transmits and receives over two radio channels to avoid interference problems, and to allow channels to be shifted without communications loss from other ships. The system provides for automatic contention resolution between itself and other stations, and communications integrity is maintained even in overload situations.

Each station determines its own transmission schedule (slot), based upon data link traffic history and knowledge of future actions by other stations. A position report from one AIS station fits into one of 2250 time slots established every 60 seconds. AIS stations continuously synchronize

themselves to each other, to avoid overlap of slot transmissions. Slot selection by an AIS station is randomized within a defined interval, and tagged with a random timeout of between 0 and 8 frames. When a station changes its slot assignment, it pre-announces both the new location and the timeout for that location. In this way new stations, including those stations which suddenly come within radio range close to other vessels, will always be received by those vessels.

The required ship reporting capacity according to the IMO performance standard amounts to a minimum of 2000 time slots per minute, though the system provides 4500 time slots per minute. The SOTDMA broadcast mode allows the system to be overloaded by 400 to 500% through sharing of slots, and still provide nearly 100% throughput for ships closer than 8 to 10 NM to each other in a ship to ship mode. In the event of system overload, only targets further away will be subject to drop-out, in order to give preference to nearer targets that are a primary concern to ship operators. In practice, the capacity of the system is nearly unlimited, allowing for a great number of ships to be accommodated at the same time.

The system coverage range is similar to other VHF applications, essentially depending on the height of the antenna. Its propagation is slightly better than that of radar, due to the longer wavelength, so it’s possible to “see” around bends and behind islands if the land masses are not too high. A typical value to be expected at sea is nominally 20 nautical miles. With the help of repeater stations, the coverage for both ship and VTS stations can be improved considerably.

The system is backwards compatible with digital selective calling systems, allowing shore-based GMDSS systems to inexpensively establish AIS operating channels and identify and track AIS-equipped vessels, and is intended to fully replace existing DSC-based transponder systems.

What is broadcast by AIS

A Class A AIS unit broadcasts the following information every 2 to 10 seconds while underway, and every 3 minutes while at anchor at a power level of 12.5 watts. The information broadcast includes:

MMSI number - unique referenceable identification Navigation status - not only are "at anchor" and "under way using engine" currently defined, but "not under command" is also currently defined. Rate of turn - right or left, 0 to 720 degrees per minute Speed over ground - 1/10 knot resolution from 0 to 102 knots. Position accuracy - differential GPS or other and an indication if RAIM processing is being used Longitude - to 1/10000 minute and Latitude - to 1/10000 minute Course over ground - relative to true north to 1/10th degree True Heading - 0 to 359 degrees derived from gyro input Time stamp - The universal time to nearest second that this information was generated

In addition, the Class A AIS unit broadcasts the following information every 6 minutes:

MMSI number - same unique identification used above, links the data above to described vessel IMO number - unique referenceable identification (related to ship's construction) Radio call sign - international call sign assigned to vessel, often used on voice radio Name - Name of ship, 20 characters are provided Type of ship/cargo - there is a table of possibilities that are available Dimensions of ship - to nearest meter Location on ship where reference point for position reports is located Type of position fixing device - various options from differential GPS to undefined Draught of ship - 1/10 meter to 25.5 meters [note "air-draught" is not provided] Destination - 20 characters are provided Estimated time of Arrival at destination - month, day, hour, and minute in UTC

Types of AIS

ITU-R Recommendation M.1371-1 describes the following types of AIS:

Class A

Shipborne mobile equipment intended for vessels meeting the requirements of IMO AIS carriage requirement, and is described above.

Class B

Shipborne mobile equipment provides facilities not necessarily in full accord with IMO AIS carriage requirements. IEC has begun work on a Class B certification standard, which should be completed by 2003. The Class B is nearly identical to the Class A, except the Class B:

Has a reporting rate less than a Class A (e.g. every 30 sec. when under 14 knots, as opposed to every 10 sec. for Class A)

Does not transmit the vessel’s IMO number or call sign

Does not transmit ETA or destination

Does not transmit navigational status

Is only required to receive, not transmit, text safety messages

Is only required to receive, not transmit, application identifiers (binary messages)

Does not transmit rate of turn information

Does not transmit maximum present static draught

Search and Rescue Aircraft

Aircraft mobile equipment, normally reporting every ten seconds.

Aids to Navigation

Shore-based station providing location of an aid to navigation. Normally reports every three minutes. This may eventually replace the racon.

AIS base station.

Shore-based station providing text messages, time synchronization, meteorological or hydrological information, navigation information, or position of other vessels. Normally reports every ten seconds.

AIS Frequencies

The International Telecommunications Union World Radio Conference in 1997 designated two VHF radio frequencies: 161.975 MHz (AIS1, or channel 87B) and 162.025 MHz (AIS2, or channel 88B) for AIS. In the US, the first channel is owned by MariTEL, a public coast station operator, and the second by the federal government. The USCG signed a Memorandum of Agreement with MariTEL for use of AIS 1, and has authority from the National Telecommunications and Information Administration to use both AIS1 and AIS 2 US-wide for AIS operation. The USCG has asked the Federal Communications Commission to authorize any US vessel to operate AIS on these two channels under its existing ship station license. The FCC released a Notice authorizing operation of AIS under a ship's existing station license.

IMO Carriage Requirement

The 73rd Session of the IMO's Maritime Safety Committee decided the following ships will be required to carry AIS equipment:

All ships of 300 gross tonnage and upwards engaged on international voyages and cargo ships of 500 gross tonnage and upwards not engaged on international voyages and passenger ships irrespective of size shall be fitted with AIS, as follows:

ships constructed on or after 1 July 2002; ships engaged on international voyages constructed before 1 July 2002; in the case of passenger ships, not later than 1 July 2003; in the case of tankers, not later than the first "safety equipment survey" after 1 July 2003; in the case of ships, other than passenger ships and tankers, of 50,000 gross tonnage and upwards, not later than 1 July 2004; in the case of ships, other than passenger ships and tankers, of 10,000 gross tonnage and upwards but less than 50,000 gross tonnage, not later than 1 July 2005; in the case of ships, other than passenger ships and tankers, of 3,000 gross tonnage and upwards but less than 10,000 gross tonnage, not later than 1 July 2006; in the case of ships, other than passenger ships and tankers, of 300 gross tonnage and upwards but less than 3,000 gross tonnage, not later than 1 July 2007; and in the case of ships not engaged on international voyages constructed before July 2002.

The United States Coast Guard will also require AIS on certain vessels not subject to SOLAS under a forthcoming rulemaking.

IMO Resolution MSC.74(69), Annex 3, Recommendation on Performance Standards for an Universal Shipborne Automatic Identification Systems (AIS)

This standard defines the basic performance requirements for AIS equipment, and was used by ITU and IEC in developing technical and test standards. It can be downloaded at no charge as an annex to the MSC 69 final report.

ITU-R Recommendation M.1371-1, Technical Characteristics for a Universal Shipborne Automatic Identification System Using Time Division Multiple Access in the Maritime Mobile Band

The International Telecommunications Union Sector for Radiocommunications formally adopted this standard in August 2001. This is the standard that defines in detail how the AIS works, and as such is the primary AIS standard. It can be purchased electronically from ITU. ITU gave IALA the responsibility of maintaining technical guidelines for AIS design, and is available from them as "IALA Technical Clarifications on Recommendation ITU-R M.1371-1".

IEC 61993-2 Ed.1, Maritime navigation and radiocommunication requirements - Automatic identification systems (AIS) - Part 2: Class A shipborne equipment of the universal automatic identification system (AIS) - Operational and performance requirements, methods of test and required test results

The International Electrotechnical Commission formally adopted this standard in November 2001, and a published version is available from IEC. This standard defines the certification test requirements for Class A shipborne AIS equipment.

IALA Recommendation on AIS Shore Stations and Networking Aspects Relating to the AIS Service, Edition 1.0, September 5, 2002

This 159-page document is available from IALA.

Certification of AIS equipment in the U.S.

In June 2002, the FCC released a Notice entitled "Applications For Equipment Authorization Of Universal Shipborne Automatic Identification Systems To be Coordinated with U.S. Coast Guard To Ensure Homeland Security". Pending completion of FCC rulemaking, the FCC Laboratory will coordinate review of applications for certification of AIS equipment with the United States Coast Guard to ensure that the equipment meets all applicable international standards and requirements. Essentially, AIS manufacturers must the requirements of the FCC's regulations for equipment authorization, 47 CFR 2 Subpart J (beginning 2.901), and the Coast Guard's Navigational and Vessel Inspection Circular (NVIC) 8-01, Approval of Navigation Equipment for Ships. NVIC 8-01 describes the certification process for AIS and other navigation equipment described under the newly adopted SOLAS V. The Federal Communications Commission has requested comments on how its rules should be amended to accommodate AIS certification, in a further Notice of Proposed Rulemaking under Docket PR 92-257. Until these FCC rules are finally adopted, the procedures described in the FCC Notice and the NVIC should apply.

Product & Services

C.N.S. Systems provides transponder solutions for any type of ship or application in accordance with IMO requirements and IEC specifications:

• Mobile Transponders Transponders for ships required to meet IMO and IEC standards.

Mobile transponders for Helicopters and SAR-aircraft

• Base Stations Supplies from stripped down stations to full configuration including 3 receivers, server and dual transponders in hot standby.

• System Solutions - Fleet Management

Costal Surveillance

- Harbour/Port management - VTM, Vessel Traffic Management - Solutions for the Offshore Industry

• Services

- Ground station cell planning - System planning and set to work

Base Stations

C.N.S. Systems carries a complete range of Ground Stations.

The base line offer, the VDL M/GS I, is intended for local applications in a Port or at a VTS station. The flexible design allows for an easy future upgrade to fit into a future network. The Ground Station comprises a UAIS sub segment, a GNSS reference receiver, a power supply and a data Control Unit all built into a 19 " rack with lockable doors.

The Ground Station VDL M/GS III offers full network functionality. This unit is suitable for example nationwide costal surveillance network. The Ground Stations core module is the Data Management Unit that handles communication to and from the station. This includes control, monitoring and configuration both remotely and by local access.

Coastal Surveillance

A Coastal Surveillance System is a difficult task to accomplish. Many parameters have to be considered, the present information needs as well as what the future demands has to be thought through.

C.N.S. Systems offers a solution that leaves room for the future as well as takes care of the current needs. The approach used is taken from many years of experience with ground networks within the aviation industry.

To accomplish the task of a system that provides surveillance of a coastline a Ground Station with high reliability and availability should be used. The ground station shall not only provide information on vessels within radio coverage instead it should form part of a logical entity providing services from a competent authority shore to ship as well as in the reverse direction.

With the field proven experiences from the field of aviation C.N.S. Systems can offer the following system solution:

A decentralised processing configuration

Methods to provide different services for various parts of the network, i.e. VTS specific services, for example Port ARPA targets, contrary to network wide services for example “Notice to Mariners”

Methods to provide filtering at lowest level, i.e. directly in the physical ground station

Methods to provide geographical service areas

Separation of AIS targets between physical ground stations

Handle data conversion of local services

Remote control and monitoring of functions as well as software changes and upgrades

Addition of a local non networked station at a minimum cost

Support increase of data traffic over time

Support customer application protocols at a certain service level

Log incoming and outgoing of data traffic through Ground Station

With the above criteria as guidelines CNSS manufactures and develops the VDL M/GS II

The VDL M/GS III consist of 3 major components

- The AIS subsystem

- The GNSS reference receiver subsystem

- The Data Management Subsystem, DMS.

The most vital part of a coastal surveillance system is the DMS that handles network traffic. The DMS system manages all incoming and outgoing traffic.

The DMS handles:

Remote Monitoring and Control

Network management

Data logging including statistics for reports etc.

Addition of services and conversion of protocols to AIS format such as

ARPA targets

Information services, wind, current, tidal, wave etc

RDF

VTM information, remote pilotage etc

AToNs

The DMS further allows specific network entities to subscribe to specific data. This can be a National Administration wanting to know the number of vessels passing through a channel during a certain time interval or a VTS station with information requirements on all AIS traffic received.

Addition of local application services

In order to reduce the cost for our customers a solution to the possibility of unnecessarily increasing data traffic over the network due to that two or more Ground stations sees the same AIS target has to be introduced.

The DMS subsystem has the advantage of handling all targets within radio coverage as IP addresses. The IP addresses are a shared database with other physical Ground Stations. In this way we get a twofold advantage, first only one Ground station is responsible for monitoring the target and secondly we can achieve true point-to-point communication by using the IP address as the recipient of messages originating from within the network.

Further by introducing geographical service areas for the physical Ground stations the network can be optimised further both in number of stations but also in radio coverage.

Ground Station coverage sectors

The GNSS reference receiver has the capability to provide local corrections using the VDL. CNSS has also introduced means to monitor and control the reliability of the corrections. The system is called PIMs and uses the position sent out over the link that the system correlates with a known geographical position. With this method an early warning system for erroneous positions can be achieved.

Port Management

With the introduction of AIS as a tool for surveillance at sea, a tool for development of data flow in port operations has emerged.

Any cargo operation is associated with a number of events, for which there are electronic systems available today. However the systems installed/sold often solve only a small portion of the problem.

With focus on the flow of data instead of flow of paper and by using the capacity of potentially existing systems a general operational system can be constructed.

A system for port operations should include, mobile units such as forklifts and trailers, stationary cargo, vessels, trucks and trains and of course also an electronic version of the paper work.

Port Organiser

In order to create an efficient and cost effective tool for a Port, a number of different functions have to be included and considered. It is easiest to describe the flow of data by using the loading of a container as an example. Of course the system is not restricted to this but can manage any cargo operation.

We need to make the flow through the port more efficient. Therefore there are some areas that have to be considered:

Arrival of container and paper work

Positioning of container

Arrival of ship

Pick up of container

Loading and unloading of ship

Departure of ship

The AIS data link together with standard software methods, such as optimising software, can support throughput increase in a port and at the same time support activities in mobile units such as vessels and forklifts.

Vessel Traffic Management

Cost-Benefits

The UAIS systems have cost-benefits for many actors in the marine markets.

Both cost reductions and income can be generated from implementing the system.

The major cost savings that can be achieved by adopting UAIS are:

• Reduced piloting expenses

• More efficient fairway management through;

o Remote position and performance monitoring of Aids to Navigation

o Reduction of the overall number of navigation marks

• Less standby time for port services, tugs, etc.

The above cost savings will also lead to greater revenues for the port by making it more cost attractive for shippers. The system can also be used for generating revenues by making available Internet based portal services to third parties.

System description Built around the UAIS data link concept and with experience gathered from Air Traffic Control and Management the UAIS offers complete flexibility and real cost savings.

Overview of UAIS network

The VDL M/GS III supports functions such a:

Remote pilotage;

Sea corridors;

Virtual transponders;

Performance/positioning monitoring of navigation marks;

Conflict detection;

Way point negotiating;

Differential GPS corrections

Text messaging (SMS);

Information services, ARPA, weather, tidal, current etc;

Customer specific protocols.

Remote pilotage

02-Dec-03

Without elaboration this is the most essential part of the introduction of AIS. By using an approach with experience gathered from Air Traffic Control a cost effective and safe system can be arranged.

Conflict detection

By using the concept of conflict detection the VTM station at an early stage, can get warnings on possible hazardous situations that may occur in the near future.

Identification of conflict zone with screen for text messages

The conflict detection system has the capability to advise on actions within limits of the sea corridor and other restraining factors.

ARPA target broadcast.

Any radar-acquired target can be broadcast over the data link. By allowing conversion of data formats to be internal in the AIS ground station the concept can cost effectively be achieved.

The broadcasted targets can be accompanied by a text message to specific vessels concerned, so-called safety related message.

Waypoints

A designated route can be sent to a specific vessel by using waypoints. The route is predetermined by the VTM authority and selected with consideration to the type of vessel that needs to be guided.

The UAIS data link allows for broadcast of virtual transponders. Such transponders are not physically in the channel but they will appear for the receiving stations as if they were sent from for example a Racon.

A virtual transponder is an extremely cheap way of organizing the fairway. Cost savings are high when complete marks can be withdrawn and replaced with broadcast of data over the link.

Position and performance monitoring

Any navigation mark may be equipped with a transponder. This allows for a cost effective tool for surveillance of position. By using differential corrections from the base station and a zone within which the mark is allowed to move, the mark can always tell if it keeps station.

Compared to satellite and radar surveillance this method allows for a very short pay off time.

To further enhance the cost efficiency the transponder can be equipped with interfaces to for example:

• Wind direction and speed;

• Tidal water level;

• Any technical issue with the mark, for example battery voltage, current draw;

• All other customer specific information.