GB2575673A - Improvements in and relating to maritime communication systems - Google Patents

Abstract

A communication system comprises a steerable antenna 12 and an automatic identification system (AIS) signal receiver and a control system to steer the antenna 12 based on information derived from a received AIS signal. The communication system may be on-board a maritime vessel 10 and/or at a ground based station 20. The antenna 12 may be steered mechanically or electronically using heading or other positional and/or locational information derived from the AIS signals received. The system may provide a high capacity radio link between a ship 10 and shore 20 via a highly directional narrow communication beam signal 32.

Description

Improvements in and relating to maritime communication systems

The present invention relates to systems for providing communication to/from a shore-based transceiver and a vessel-based transceiver. In particular, the invention makes use of existing the Automated Identification System (AIS) available on many or most vessels, to assist in setting up and managing the link between the vessel and the shore. In the remainder of this description, the term ‘ship’ will be used to refer to any maritime vessel of any size, class and use.

It is desirable to provide a high capacity radio link between ship and shore. In order to provide the desired capacity, it is preferable to provide a highly directional narrow beam, so that spatial diversity can allow frequency re-use in a given area. This helps to optimise the use of a limited frequency spectrum in often crowded waterways.

However, a problem exists in that it is not always possible to know the exact position coordinates of a ship. Positional co-ordinates, in this context, refers to not only the instantaneous position of the ship (i.e. latitude, longitude, altitude) but also its compass heading.

It is generally possible to determine the latitude, longitude and altitude by means of a GPS system, but it is harder to determine an accurate value for the ship’s heading.

In order to steer a radio beam from the shore to a moving ship, it is necessary to know not only where it is at any given time, but where it is going to. This is determined based on the heading of the ship. The true heading is difficult to determine on board a ship as the ship is a large metal body and a magnetic compass will not always give a true reading.

Steering a beam from a moving ship to the shore experiences additional problems related to the angular degrees of freedom (tilt, roll and heading). Essentially, since the ship could be at a fixed location, but still rolling on the waves, the antenna requires continual adjustment to maintain a direction.

Embodiments of the present invention aim to address shortcomings with prior art ship to shore radio links and to provide a high capacity directional link.

According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

According to a first aspect of the present invention, there is provided an onboard transceiver, for use on a maritime vessel, comprising: a steerable antenna, operable to produce a directional beam for communication with a remote antenna; a receiver operable to intercept an AIS transmission from the maritime vessel; a control system operable to steer the directional beam of the steerable antenna towards the remote antenna on the basis of information derived from the AIS transmission.

In an embodiment, a receiver operable to intercept an AIS transmission from the maritime vessel comprises an antenna arranged to receive the AIS transmission.

In an embodiment, the steerable antenna is steerable electronically or mechanically. The mechanical steering may be achieved by means of a robotic head unit operable to move the antenna physically. Electronic steering may be achieved by means of beam-steering techniques such as a phased array antenna.

In an embodiment, the information intercepted from the AIS transmission comprises True Heading information. This information is included as a field in AIS messages. It is to be distinguished from Course over Ground (COG).

In an embodiment, the information further comprises one or more of latitude, longitude, altitude, rate of turn and direction of turn. In practice, altitude, longitude and altitude are likely to be derived from a GPS receiver, since this will give more instantaneous results. However, in principle, these parameters could be derived from AIS information.

In an embodiment, the direction of the directional beam is determined based on at least a present location of the vessel and a known location of the ground station. The direction may be determined on the basis of a simple geometrical calculation.

According to a second aspect of the present invention, there is provided a ground station transceiver comprising: a steerable antenna, operable to produce a directional beam for communication with a remote maritime vessel; a receiver operable to receive an AIS transmission from the vessel; and a control system operable to steer the directional beam of the steerable antenna towards the vessel on the basis of information derived from the AIS transmission.

In an embodiment, the steerable antenna is steerable electronically or mechanically.

According to a third aspect of the present invention, there is provided a communication system comprising the onboard transceiver of the first aspect and the ground station transceiver of the second aspect.

According to a fourth aspect of the present invention, there is provided a method of steering a directional radio beam from a maritime vessel to a ground station comprising the steps of: transmitting from the vessel AIS information; receiving on the vessel the AIS information; determining on the basis of the received AIS information a direction in which to steer the radio beam towards the ground station; steering the radio beam in the determined direction.

According to a fifth aspect of the present invention, there is provided a method of steering a directional radio beam from a ground station to a maritime vessel comprising the steps of: receiving from the vessel, transmitted AIS information; determining on the basis of the received AIS information a direction in which to steer the radio beam towards the vessel; steering the radio beam in the determined direction.

Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

Figure 1 shows a directional radio link between ship and shore, according to a first embodiment of the present invention;

Figure 2 shows details of an onboard control system according to an embodiment of the present invention.

Embodiments of the present invention provide a system which allows a highly directional, high performance narrow radio beam to be pointed or steered towards a moving vessel, offshore. This requires the creation of a directional beam from the ship to the shore and vice-versa.

In order to accomplish this, use is made of signals broadcast from the ship’s Automated Identification System (AIS), which is typically provided on most, if not all, vessels. Certainly, all large vessels are obliged to operate AIS Class A telemetry systems so that collisions may be avoided between such vessels.

The position of the ground station is fixed and known to the ship but, of course, the ship moves and so its position changes continuously. Embodiments of the invention utilise information from the AIS data transmitted by the ship to allow the ground station to locate the ship and direct a beam in its direction. Furthermore, the ship uses its own AIS data to provide positional information which may be used to accurately steer a corresponding beam in the direction of the ground station. The problems faced in each instance are similar, but there are some differences which will be described in the following paragraphs.

The ship transmits, via AIS, its location (latitude and longitude) and also its heading. Sensors provided on the ship are also provided capture roll, tilt and rotation of the ship. By use of these parameters, transmitted via AIS, it is possible for the ship to accurately point a narrow high performance radio beam directly at the ground station.

The radio beam is generated in an antenna which is steered as required to point directly at the ground station. The steering may be achieved mechanically by means of a robotic unit which physical moves the antenna as required. Alternatively, beam-steering may be achieved by means such as a phased array of antenna elements which allows the beam to be steered entirely electronically with no moving parts.

Embodiments of the invention are able to achieve a 1° beamwidth.

The AIS Class A telemetry system referred to above is taken advantage of to derive certain signals which may be used in embodiments of the invention, both in the onboard system and in the ground station. In AIS systems, a number of different signals are transmitted periodically from a ship, with messages being transmitted typically between every 2 and 6 seconds, if the ship is moving.

Of the various message types which may be transmitted, on of the most common and which is most useful to embodiments of the present invention is termed a class 1,2, 3 message (these messages are identical).

The following table indicates various parameters which are transmitted from a ship in various AIS messages.

	L&ss			T	Visits.·
o-5	6	Message Type	type	u	Constant: 1-3
6-7	2	Repeat Indicator	repeat	u	Message repeat count
8-37	30	MMSI	mmsi	u	9 decimal digits
38-41	4	Navigation Status	status	e	See. ’Tvavigation Status
42-49	8	Rate of Turn (ROT)	tuns	13	See below
50-59	IO	Speed Over Ground (SOG)	speed	Ui	See below
6Q-0Q	1	Position Accuracy	accuracy	b	See below
61-88	28	Longitude	Ion	14	Minutes; ΐαοοϋ (.see below)
89-115	27	Latitude	lat	14	Minutes/lGOQQ (see below)
116-127	12.	Coarse Over Ground (COG)	course	L’l	Relative to true noidi. to o.i degree precision
128-136	O	True Heading (HDG)	heading	a	0 to 359 degrees, 511 = not available.
Ι37-Ι4Ξ	6	Time Stamp	second	u	Second of UTC timestamp
I43-I44	2	Maneuver Indicator	maneuver	e	See ’’Maneuver Indicator”
I45-I47	3	Spare		X	Not used
I48-I48	1	RAIM flag	raim	b	See below
149-167	19	Radio status-	radio	U	See below

From these messages, it is possible to identify the ship, its location, speed, course overground, true heading and rate of turn. These parameters are utilised in embodiments of the present invention.

By use of at least some of these parameters, it is possible to inform the ground station of the current position of the ship along with enough other information for the expected future position to be calculated. This information is then used at the ground station to create a narrow radio beam between the ship and the ground station.

The AIS data transmitted from the ship is not guaranteed to arrive, since it is a broadcast signal, with no acknowledgement or handshaking. As such, it should be regarded as an irregular but frequent transmission.

It is assumed that the ship will not make major rapid movements in a relatively short period of time (say, 30 seconds) and so it is possible to extrapolate from the current location to an expected future location to a high degree of accuracy to ensure that the beam from the ground station is always directed accordingly. Of course, as the current location and other parameters change overtime, the expected future location is adjusted on the basis of actual data.

Figure 1 shows a typical scenario with a ship 10 at sea. The ship is provided with an antenna 12 for providing a directional data link 32 to a complementary antenna 22 at the ground station

20. The antenna 12 is further connected to a ship-board transceiver for transmitting and receiving data over the data link 32.

The ship is also provided with an AIS antenna 14 which broadcasts AIS messages 34 according to a schedule, or as required. The AIS system on the ship is transmit only and there is no mechanism to receive data over this link. The AIS data 34 is received by a complementary antenna 24 at the ground station 20.

At the ground station 20, AIS messages 34 are received, which include parameters signifying latitude, longitude, speed, heading and course over ground (COG). These parameters allow the ground station 20 to identify the current location and to predict the future location.

Therefore, purely on the basis of information 34 provided by the ship 10, the ground station 20 is able to calculate the current and expected future position of the ship and so steer a highly directional beam in its direction.

The system aboard the ship faces different challenges. The location of the ground station is fixed and known. However, the ship is in motion and has six degrees of freedom. These are spatial: latitude, longitude and altitude; and angular: tilt, roll and heading.

Figure 2 shows a representation of how the ship’s AIS transmissions 34 are utilised to assist in the creation of the directional beam from ship antenna 12 to the ground station antenna 22. The high capacity data link 32 is transmitted from the ship via antenna 12. The input to the associated transceiver is data link 36, derived from an onboard cabled link.

An onboard AIS receiver antenna 60 is provided to effectively receive the ship’s own AIS transmissions. This should be carefully positioned so as not to be overloaded by the transmitted signal. Importantly, the antenna 60 does not in any way intrude on the transmitted signal 34 and is entirely non-invasive. It may be possible to sample the transmitted AIS signal in some other way provided this is non-invasive and does not interfere with the ship’s safetycritical systems. One possible way includes sampling the transmitted signal from a feed to antenna 12 by some form of inductive coupling. However, the preferred technique uses a separate antenna 60

A beam control system 70 is provided to point the beam from antenna 12 towards antenna 22. As mentioned previously, this control system can be mechanical and actually move the antenna or it can be electronic and steer the beam using e.g. a phased array.

The control system 100 of Figure 2 requires information on all six parameters referred to above (latitude, longitude, altitude, tilt, roll and heading) in order to point antenna 12 towards antenna

22. Latitude and longitude can be easily obtained from GPS signals readily available onboard. Altitude can be similarly obtained or may be fixed depending on the position ofthe antenna 12 on the ship’s superstructure. Tilt and roll can be derived from standard accelerometers and provided to the control system

However, heading information is much more difficult to determine. Compass-based systems do not function well on ships, in the presence of large motors and steel structures. As such, without extensive calibration, compass readings cannot be relied upon, particularly, as in this case, accuracy and a timely response are required.

In order to provide heading information, embodiments of the present invention capture, via computer 26, suitable details from the ships own AIS data 34, which is transmitted from the ship, using AIS receiver antenna 60. The AIS data includes the calibrated heading data from the ship’s calibrated and accurate compass. The actual direction of the beam from the ship can be determined based on the ships location and the known, fixed, location of the ground station.

AIS data 34 sent from the ship is not typically intercepted by the ship itself, since its intended use is remote from the ship. However, embodiments ofthe present invention make use ofthe availability of this information in order to provide the directional link between ship and shore.

Embodiments of the invention allow the interception of the AIS data 34 without requiring any physical connection to safety-critical systems on the ship. It would not typically be desirable, let alone permissible, to interfere with safety-critical signals onboard the ship. By using the AIS data, an unobtrusive means is provided to gather the data that is required. This avoids any form of tampering with a safety-critical system.

It should be noted that the heading information is provided by the message field “True Heading (HDG)” and not “Course over ground (COG)”. The latter differs from the former due to water currents.

The heading information provided by the AIS is accurate to 1°. The ship also provides rate of turn information and direction of turn information which can be used to provide a still more accurate prediction of heading and so future location. This can be repeatedly calibrated against the accurate but less precise AIS data.

The rate of turn information can also be used to calibrate the rotational sensors on accelerometers, which are sensitive and reactive to small changes in orientation, but can drift in value and required frequent correction.

Embodiments of the present invention are thus able to offer high performance radio links by means of directional antenna beams provided between a ground station 20 and a ship 10. The directional control of the beam in each direction is provided by making use of data included in the ship’s ASI signalling 34. This is provided in the prior art to offer information on a vessel and its course. Its primary function is collision-avoidance. However, embodiments of the present invention re-purpose that data and utilise it to provide a directional data link.

As such, a high capacity reliable radio communication link is available which would otherwise be difficult and/or expensive to provide. This re-use of an existing system offers excellent value for money and minimises expenditure on new equipment.

At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as ‘component’, ‘module’ or ‘unit’ used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims (10)

1. An onboard transceiver, for use on a maritime vessel, comprising:

a steerable antenna, operable to produce a directional beam for communication with a remote antenna;

a receiver operable to intercept an AIS transmission from the maritime vessel;

a control system operable to steer the directional beam of the steerable antenna towards the remote antenna on the basis of information derived from the AIS transmission.

2. The onboard transceiver as claimed in claim 1 wherein the steerable antenna is steerable electronically or mechanically.

3. The onboard transceiver of claim 1 or 2 wherein the information intercepted from the AIS transmission comprises True Heading information.

4. The onboard transceiver of claim 3 wherein the information further comprises one or more of latitude, longitude, altitude, rate of turn and direction of turn.

5. The onboard transceiver of any preceding claim wherein the direction of the directional beam is determined based on at least a present location of the vessel and a known location of the ground station.

6. A ground station transceiver comprising:

a steerable antenna, operable to produce a directional beam for communication with a remote maritime vessel;

a receiver operable to receive an AIS transmission from the vessel; and a control system operable to steer the directional beam of the steerable antenna towards the vessel on the basis of information derived from the AIS transmission.

7. The ground station of claim 6 wherein the steerable antenna is steerable electronically or mechanically.

8. A communication system comprising the onboard transceiver of any of claims 1 to 5 and the ground station transceiver of claims 6 or 7.

9. A method of steering a directional radio beam from a maritime vessel to a ground station comprising the steps of:

transmitting from the vessel AIS information;

receiving on the vessel the AIS information;

determining on the basis of the received AIS information a direction in which to steer the radio beam towards the ground station;

steering the radio beam in the determined direction.

5

10. A method of method of steering a directional radio beam from a ground station to a maritime vessel comprising the steps of:

receiving from the vessel, transmitted AIS information;

determining on the basis of the received AIS information a direction in which to steer the radio beam towards the vessel;

10 steering the radio beam in the determined direction.

Intellectual Property Office