GB2448715A

GB2448715A - Wireless asset tracking system

Info

Publication number: GB2448715A
Application number: GB0707945A
Authority: GB
Inventors: Bruce William Henry Harbon; Christopher James French
Original assignee: Airbus DS Ltd
Current assignee: Airbus DS Ltd
Priority date: 2007-04-24
Filing date: 2007-04-24
Publication date: 2008-10-29
Also published as: GB0707945D0

Abstract

A system is disclosed for determining the position of a mobile unit 4. The system comprises a mobile unit 4 and a plurality of transmitters 8,10,12 whereby each transmitter sends a signal to the mobile unit 4, with each signal being sent in phase, wherein the mobile unit 4 comprises a processing means adapted to determine the difference in phase between signals received from each of said plurality of transmitters 8,10,12 in order to determine the position of said mobile unit 4 relative to the positions of said transmitters 8,10,12. The system is particularly suited to determining the location of the mobile unit 4 within a building 6 whereby each of the transmitters 8,10,12 may be located close to the building at known positions.

Description

-1-2448715 Wireless Tracking System This invention relates to wireless

tracking systems, such as wireless asset tracking systems.

S

There are many circumstances in which it is desirable to know the absolute position of one or more assets. For example a courier company may need to know the current position of each of its delivery units at all times and an ambulance controller may need to know the current position of the ambulances under his or her control.

One method of providing positional information is to make use of a satellite Positioning systems, such as the well-known Global Positioning System (OPS). Each of a number of mobile units can be provided with a receiver, such as a OPS receiver, which receives satellite signals that can be used to provide an absolute position of the mobile unit. That data can be transmitted to a central server, for example at an ambulance control centre, for use in monitoring the position of all ambulances under its control.

A problem with GPS and similar systems is that they are not usable in all locations. For example, GPS systems are less effective in city centres having many large buildings. Furthermore, if the mobile unit is inside a building, GPS is often ineffective.

An alternative process by which the location of a mobile asset can be determined is dead reckoning. Dead reckoning provides an estimate of a current position based on a known starting position and information relating to the movements of the mobile unit since it was at that starting position. By their nature, positions estimated using a dead reckoning systems include uncertainties and the uncertainties increase over time.

The performance of dead reckoning systems can be improved by providing regular positional information, for example using a GPS or similar system.

The present invention seeks to provide a tracking system that addresses at least some of the problems identified above.

A first aspect of the present invention provides a system comprising a mobile unit and a plurality of transmitters, wherein each transmitter transmits a signal to the mobile unit, with each signal being transmitted in phase, wherein the mobile unit comprises a processing means adapted to determine the difference in phase between signals received from each of said plurality of transmitters in order to determine the position of said mobile unit relative to the Positions of said transmitters.

The first aspect of the invention also provides a method of determining the position of a mobile unit, the method comprising the steps of: receiving at a mobile unit a signal from each of a plurality of transmitters, wherein the phases of the signals when transmitted are the same; determining the relative phases of the signals at the mobile unit; and determining the position of the mobile unit relative to the transmitters using triangulation.

The method may further comprise the step of providing the said plurality of transmitters and transmitting the said signals.

The present invention makes use of the fact that the speed at which signals travel from the transmitters to the receivers is substantially constant, such that the phase of a signal received at the receiver is related to the distance between the transmitter and the receiver.

By providing a plurality of transmitted signals, triangulajo can be used to determine the position of the receiver relative to the Positions of the transmitters The system and method of the first aspect of the invention have the advantage that they are able to work in areas where satellite Positioning systems, such as GPS, provide poor reception, such as when the mobile unit is is inside a building, or when the system is being used in a City centre having lots of tall buildings.

In one form of the invention, the position of each transmitter is known such that the absolute position of the mobile unit can be determined. The position of one or more of the transmitters may be determined, for example using a satellite Positioning Systems.

Alternatively or in addition, the Position of one or more of the transmitters may be fixed and therefore known.

In one form of the invention, each transmitter comprises a receiver for receiver a plurality of satellite signals for use in determining the position of that transmitter.

In one form of the invention, the position of each transmitter is determined using the well known Global Positioning System.

The present invention may allow the phase of the signals output by each of said plurality of transmitters to be synchronjsed. By way of example, in one embodiment of the invention, each transmitter comprises a synchronising means having an input for receiving an externally provided timing signal. The said externally provided signal may be a nationally recognised time signal.

A second aspect of the present invention provides a mobile unit comprising a receiver for receiving a signal from each of a plurality of transmitters, wherein said transmitted signals are in phase when transmitted, wherein the mobile unit further comprises a processing means adapted to determine the difference in phase between signals received from each of said plurality of transmitters in order to determine the position of said mobile unit relative to the positions of said transmitters.

A third aspect of the present invention provides a * transmitter for transmitting a signal to a mobile unit, wherein said transmitter is one a plurality of transmitters arranged to transmit signals in phase, wherein the transmitter comprises a synchronising means for synchronising the phase of the signals output by said plurality of transmitters.

A fourth aspect of the present invention provides a kit of parts comprising a mobile unit and a plurality of transmitters, wherein: said mobile unit comprises a receiver for receiving a signal from each of a plurality of transmitters and a processing means adapted to determine the difference in phase between signals received from each of said plurality of transmitters in order to determine the position of said mobile unit relative to the positions of said transmitters; and each of said plurality of transmitters is arranged to transmit a signal in phase with the signal transmitted by the other transmitters in the plurality. Each of said transmitters may comprise a synchronising means for synchronising the phase of the signals output by said plurality of transmitters.

Of course, any of the features of the first aspect of the invention described above may be incorporated in the second, third or fourth aspects of the invention.

Devices and methods in accordance with the invention will now be described, by way of example only, with reference to the accompanying schematic drawing.

Figure 1 is a plan view of a situation in which the present invention may be used. The plan, indicated generally by the reference numeral 2, shows a mobile unit 4 located within a building 6. The building is such that known satellite-based positioning systems, such as the well-known GPS system, cannot reliably determine the position of the mobile unit 4.

The plan view 2 also shows a first transmitter 8, a second transmitter 10 and a third transmitter 12 located close to the building 6. Each transmitter transmits a signal having the same phase to the mobile unit 4. The mobile unit receives each signal and, from the difference in phase between those signals, determines the position of the mobile unit relative to the transmitters 8, 10 and 12.

If the positions of the transmitters 8, 10 and 12 are known, then the absolute position of the mobile unit 4 can be determined. In one form of the invention, the transmitters 8, 10 and 12 are permanently installed in known positions. Thus, the absolute positions of the transmitters can be given to a high degree of accuracy.

In an alternative form of the invention, the absolute position of the transmitters 8, 10 and 12 is determined using a satellite-based Positioning system, such as GPS.

It is noted that in the arrangement of Figure 1, the transmitters 8, 10 and 12 are located outside the building 6. Accordingly, the problems associated with determining the Position of the mobile unit 4 using a GPS system do not apply to the transmitters. In most implementations of the invention, there will usually be a certain amount of flexibility regarding the location of the transmitters; accordingly, the position of the transmitters can often be chosen to ensure that the Positioning system works well.

Since the position of the mobile unit 4 relative to the Positions of the transmitters 8, 10 and 12 is determined by the phases of the signals received at the mobile unit, it is important that the phase of the signals transmitted by the transmitters is the same. This can be achieved by providing an external control signal that is used to synchronise each transmitter. One simple manner of achieving this is to use a nationally recognised time signal. In the United Kingdom, the National Physical Laboratory time signal (also known as the "Rugby Clock" or "The Time from NPL") provides a suitable clock reference that the transmitters can all use to ensure that the phase of the transmitted signals is the same.

There are many potential applications of the tracking system of the present invention, including those described below.

Application 1 In some situations, fire fighters are required to work in a building in which smoke makes orientation and navigation around the building difficult. The present invention enables the position of individuals within the building to be accurately monitored.

On arrival at the scene of a fire, a number of transmitters, such as transmitters 8, 10 and 12 described above with reference to Figure 1, can be positioned around the building such that the absolute positions of the transmitters can be determined using GPS. Each fire fighter entering the building can be provided with a receiver, such as the mobile unit 4 described above. The mobile unit 4 can be used to determine the absolute position of each fire fighter within the building.

Application 2 Stadiums when used, for example, for sporting events, can present difficulties for communication and positioning systems. it can be difficult to monitor the position of people and equipment in and around a stadium, especially if GPS and/or mobile telephone connections are unreliable.

The present invention enables transmitters, such as transmitters 8, 10 and 12 to be positioned near the stadium in positions where a reliable GPS signal can be achieved. Alternatively, the transmitters can located in a known position such that a GPS signal is not required.

The transmitters 8, 10 and 12 can then be used to transmit signals to mobile units 4 within and around the stadium and the positions of those mobile units can be monitored from a central control room. By way of example, the position of individual police officers and stewards on duty at the stadium can readily be monitored in this way.

The present invention has been described with reference to a number of embodiments. The skilled person would, of course, be aware of many variants to the embodiments described. For example, although the arrangement 2 described above includes three transmitters, more transmitters may be provided.

Claims

CLAIMS: 1. A system comprising a mobile unit and a plurality of

transmitters, wherein each transmitter transmits a signal to the mobile unit, with each signal being transmitted in phase, wherein the mobile unit comprises a processing means adapted to determine the difference in phase between signals received from each of said plurality of transmitters in order to determine the position of said mobile unit relative to the positions of said transmitters.
2. A system as claimed in claim 1, further comprising a means for determining the absolute position of the mobile unit from said relative position of the mobile unit and the absolute positions of the transmitters.
3. A system as claimed in claim 1 or claim 2, wherein each transmitter comprises a receiver for receiver a plurality of satellite signals for use in determining the position of that transmitter.
4. A system as claimed in any one of claims 1 to 3, further comprising a synchronising means for syncl-ironising the phase of the signals output by each of said plurality of transmitters.
5. A system as claimed in claim 4, wherein said synchronjsjng means comprises an input for receiving an externally provided timing signal.
6. A method of determining the position of a mobile unit, the method comprising the steps of: receiving at a mobile unit a signal from each of a plurality of transmitters, wherein the phases of the signals when transmitted are the same; determining the relative phases of the signals at the mobile unit; and determining the position of the mobile unit relative to the transmitters using triangulation.
7. A method as claimed in claim 6, further comprising the step of providing the said plurality of transmitters and transmitting the said signals.
8. A method as claimed in claim 6 or claim 7, further comprising the step of determining the absolute position of the mobile unit from said relative Position of the mobile unit and the absolute Positions of the transmitters.
9. A method as claimed in claim 8, further comprising the step of determining the absolute positions of said transmitters using a satellite Positioning system.
10. A method system as claimed in any one of claims 6 to 9, further comprising the step of synchronisjng the phase outputs of the transmitters.
11. A method as claimed in claim 10, wherein said transmitters are synchronised relative to an external clock.
12. A mobile unit comprising a receiver for receiving a signal from each of a plurality of transmitters, wherein said transmitted signals are in phase when transmitted, wherein the mobile unit further comprises a processing means adapted to determine the difference in phase between signals received from each of said plurality of transmitters in order to determine the position of said mobile unit relative to the positions of said transmitters.
13. A transmitter for transmitting a signal to a mobile unit, wherein said transmitter is one a plurality of transmitters arranged to transmit signals in phase, wherein the transmitter comprises a synchronisLing means for synchroni.sing the phase of the signals output by said plurality of transmitters.
14. A kit of parts comprising a mobile unit and a plurality of transmitters, wherein: said mobile unit comprising a receiver for receiving a signal from each of a plurality of transmitters and a processjng means adapted to determine the difference in phase between signals received from each of said plurality of transmitters in order to determine the position of said mobile unit relative to the Positions of said transmitters; and each of said plurality of transmitters is arranged to transmit a signal in phase with the signals transmitted by the other transmitters in the plurality.
15. A kit as claimed in claim 14, wherein each of said transmitters comprises a synchronising means for synchroriising the phase of the signals output by said plurality of transmitters.