GB2367618A

GB2367618A - Acoustic / electromagnetic mobile telephone location system

Info

Publication number: GB2367618A
Application number: GB0023861A
Authority: GB
Inventors: John Joseph Spicer
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 2000-09-29
Filing date: 2000-09-29
Publication date: 2002-04-10
Anticipated expiration: 2020-09-29
Also published as: GB0023861D0; GB2367618B

Abstract

A mobile telecommunications system which provides position information for a mobile telephone 50 forming part of the system. The system comprises a network 60 associated with the mobile telephone 50 which provides electromagnetic timing signals for the telephone 50 and an audio system 70 for providing audio signals from which the position of the telephone 50 can be determined. The mobile telephone 50 receives radio signals from its network 60 to provide an absolute time reference and acoustic signals from the audio system 70 to determine its position. The signal information may be processed by either the mobile telephone 50 or the network 60 in order to determine the position of the mobile telephone.

Description

IMPROVEMENTS IN OR RELATING TO MOBILE TELECOMMUNICATIONS The present invention relates to improvements in or relating to mobile telecommunications, and is more particularly concerned with object location.

Mobile telecommunications utilises a plurality of telecommunications cells, each cell having one or more base stations provided for communicating with a plurality of mobile units located within the cell. Each base station effectively controls mobile units in its cell so that each unit can be connected for transmission and reception when required. Transmission of voice and data services between the base station and a mobile unit is termed the 'downlink'and between the mobile unit and the base station is termed the 'uplink'. Control signals are provided from the base station in the downlink connections which may include timing signals and other information. The telecommunications cells are arranged so that substantially unbroken coverage is provided for the mobile units as they move from location to location, control of each mobile unit being handed over to another base station as the unit leaves its current cell and enters another adjacent cell so that communication can be maintained.

With the development of more sophisticated systems, the use of mobile telecommunications has extended beyond the mere provision of voice and data services. One area of particular interest is that of wide area location.

This can be achieved using either the timing embedded in the control signals from the base station or an independent system such as global positioning system (GPS).

However, GPS can be expensive to implement and the control signals from a base station are usually distributed to the whole of the telecommunications cell in which the base station is located.

Navigation using external broadcast signals has been implemented in many commercial and military systems now in use. In such systems, a receiving platform can determine its position by using relative time of arrival signals from a multiplicity of synchronised sources whose locations are known.

It is therefore an object of the present invention to provide an improved method of providing accurate positional information for a receiver.

In accordance with one aspect of the present invention, there is provided a method of determining the position of a mobile unit comprising the steps of :- a) determining an absolute time reference for the unit using a first type of transmission; and b) determining the position of the unit using a second type of transmission.

In accordance with another aspect of the present invention, there is provided a mobile telecommunications system for providing position information for a mobile unit, the system comprising: a network for receiving signals from and transmitting signals to the mobile unit; an audio system for providing audio signals to the mobile unit; and means for processing the audio signals to provide position information for the mobile unit.

For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which: Figure 1 illustrates one embodiment of a location system in accordance with the present invention; and Figure 2 illustrates a further embodiment of a location system in accordance with the present invention.

The method of the present invention utilises absolute time of arrival signals from a multiplicity of synchronised broadcast sources to enable a receiver to calculate its position. The receiver must have access to an absolute time reference in order to be able to calculate its position, the absolute time reference being provided by a second broadcast signal set that uses a transmission medium with a different wave velocity.

Referring now to Figure 1, a system 10 for calculating the position of a receiving platform 20 is shown. The receiving platform 20 may be a mobile unit in a mobile telecommunications system. Six broadcast sources 30,32, 34,36, 38,40 are located around the receiving platform 20. Three of the sources 30,34, 38 are of a first type transmitting a wave velocity V, and are located at respective distances D, a D1 b and Dl c from the receiving platform 20. The other three sources 32,36, 40 are of a second type

transmitting a wave velocity Vz and are located at respective distances D a, D band D2 ,.

The wave velocity values of V, and Vu are different and the larger of the two values is used to determine the absolute time reference and the smaller of the two values is used to determine the position information.

In the case where V, > V2, then the transmissions from the first type sources 30,34, 38 are used to calculate the local absolute time reference for

the receiving platform 20. Transmission from the second type sources 32, 36, 40 are used to calculate the position of the receiving platform 20.

In the embodiment illustrated in Figure 1, the sources 30,34, 38 are synchronised so that they transmit signals at the same time to the receiving platform 20. Moreover, as the positions of these broadcast sources 30,34, 38 are also known, then respective time of arrival of signals from these sources 30, 34, 38 at the receiving platform 20 can be determined. As the wave velocity V, and the respective distances DI, D1,b and D1,c of the sources from the receiving platform 20 are known, the times of arrival, tl, t1,b and t1,c of

respective signals from sources 30, 34, 38 can be expressed as (DI, a) NI, (D, b) NI and (D, NI respectively. These times of arrival, t, t, b and t, are then used to provide a local absolute time reference for the receiving platform 20.

Having determined local absolute time reference using the times of arrival of signals of the first type of transmission, the broadcast sources 32, 36, 40 are used to determine the position of the receiving platform 20. This is achieved by sending signals of the second type of transmission from the broadcast sources 32,36, 40 at a known time. As the time of transmission of the second type of transmissions is known, the receiving platform 20 knows the initiation time of the transmission and measures the times of arrival, tz, a, t2, band of the transmissions from each of the three broadcast sources 32, 36, 40 at the receiving platform. The times of arrival, t2, t2,b and t2,c, of these signals are then used to determine the distances, D2, a, D2,b and D2,c, of the

receiving platform 20 from each of these sources 32, 36, 40 using the wave velocity V2, that is, Da, D2, b and Dz, c can be expressed as V z x al V2 X tu and V2 x Tue respectively.

It will readily be understood that the first type and second type transmissions can be interchanged.

Although the operation of the present invention is described with six broadcast sources, it will readily be understood that the number of broadcast sources is not critical to the operation of the invention and that any suitable number of broadcast sources can be used.

When the velocities or the time of flight (V/D) are of the same order of magnitude, an iterative process is required. The time is calculated from the first type transmissions, then the position is calculated from the second type transmissions. The position is then used to recalculate the time from the first type transmissions, which in turn is used to recalculate the position from the second type transmissions.

In the case where Vt V, or more particularly (V,/D,) > > (V2/D2) for all the broadcast sources to be used, then the position calculation may be made using two independent calculations as above.

A particular implementation of the present invention is shown in Figure 2. Here, the receiving platform 20 of Figure 1 comprises a mobile telephone 50 having specially installed software. The mobile telephone 50 includes a speaker 52, a microphone 54 and an antenna or aerial 56 as is conventional. The mobile telephone 50 is arranged to receive signals from and to transmit signals to a cellular network, shown generally as 60, via its antenna or aerial 56 in accordance with its normal use for the reception and transmission of voice and/or data signals.

As will be readily understood, signals to and from the network 60 comprise radio signals and therefore have a wave velocity at the speed of light, that is, 3 x 1 O8ms-\ and therefore the network 60 provides the first type of transmissions providing local time reference information either from

timing information inherent in the cellular standard for that network or from a special signal transmitted specifically for location. The mobile telephone 50 uses its normal radio reception capability to receive such signals.

The second type of transmissions are received from a distributed speaker system 70. The system 70 comprises two loudspeakers 72,74 which are spaced apart and which are connected to a control unit 76 which generates the second type of transmissions. The signals provided by the loudspeakers 72,74 are suitable for navigation. The loudspeakers 72,74 may form part of an existing installation, for example, a tannoy system, or could be specially installed for providing signals suitable for navigation. The mobile telephone 50 uses its microphone 54 to receive the signals from the loudspeakers 72,74 which are then processed internally.

It will readily be understood that the signals produced by the loudspeakers are acoustic signals having a velocity of around 300mis-'. Due to the very large ratio between the speed of light and the speed of sound, a single iteration for the position calculation is required.

The mobile telephone 50 in the system illustrated and described with reference to Figure 2 has special software which enables the processing of the acoustic signals to provide the positional information of the mobile telephone 50.

In an alternative method of operation, the mobile telephone 50 still receives the audio signals from the loudspeakers 72, 74 and transmits a representation of the audio signals received therefrom to its base station (not shown) located in the network 60 for the position determination to be carried out. The position information is then be transmitted down to the mobile telephone 50 from the base station over the cellular radio link.

The network 60 may be a GSM or a DECT system, but it will be understood that any radio system could be employed. For operation of the present invention, a tie up between the radio system and the audio system is required. Signals are sent from the radio system or network 60 to the mobile telephone 50 and the control unit 76 of the audio or speaker system 70 at a given point in time-the signals to the mobile telephone 50 providing instructions for receiving the audio signals at the given point in time and those to the speaker system 70 indicating that the acoustic signals are to be delivered by the loudspeakers 72,74.

The present invention is not limited to use with mobile telephones, but could also be used with specially designed pagers having an audio input and means for transmitting signals back to the network.

The system of the present invention can be used in many applications where it is required to find the position of a mobile unit. For example, the system can be used in an airport where it desired to find the user of a mobile telephone. In this case, the network to which the mobile telephone is connected provides the radio signal for the absolute time reference. The tannoy system at the airport is used as the acoustic source so that the position of the mobile telephone in the airport can be determined. The system of the present invention can also be used to locate guests in the VIP lounge.

As mentioned above, the present invention can be used to determine the position of a mobile unit in an area having a speaker system and may form part of a tiered system. For example, having located a general position of a mobile unit in a building, the position can be narrowed down to the room in the building and then to the exact position using a repetitive process.

Claims

CLAIMS: 1. A method of determining the position of a mobile unit comprising the steps of :- a) determining an absolute time reference for the unit using a first type of transmission; and b) determining the position of the unit using a second type of transmission.
2. A method according to claim 1, wherein step a) comprises receiving signals from a network associated with the mobile unit.
3. A method according to claim 2, wherein the signals received from the network comprise timing information inherent in network transmissions.
4. A method according to claim 2, wherein the signals received from the network comprise specifically transmitted signals.
5. A method according to any one of the any one of the preceding claims, wherein step b) comprises receiving audio signals from a distributed loudspeaker system comprising at least two loudspeakers the positions of which are known.
6. A method according to claim 5, wherein the distributed loudspeaker system comprises a tannoy system.
7. A method according to claim 5 or 6, wherein the mobile unit processes the received audio signals to provide the position information.
8. A method according to claim 5 or 6, wherein the mobile unit transmits a representation of the received audio signals to the network for determination of the position information.
9. A method according to claim 8, wherein the network transmits the position information to the mobile unit via a radio link.
10. A mobile telecommunications system for providing position information for a mobile unit, the system comprising: a network for receiving signals from and transmitting signals to the mobile unit; an audio system for providing audio signals to the mobile unit; and means for processing the audio signals to provide position information for the mobile unit.
11. A system according to claim 10, wherein the means for processing the audio signals is provided in the mobile unit.
12. A system according to claim 10, wherein the means for processing the audio signals is provided by the network.
13. A system according to claim 12, wherein the mobile unit provides representations of the received audio signals to the network for processing, the position information being transmitted back to the mobile unit when determined.
14. A system according to any one of claims 10 to 13, wherein the mobile unit comprises a mobile telephone.
15. A method of determining the position of a mobile unit substantially as hereinbefore described with reference to the accompanying drawings.
16. A mobile telecommunications system for providing position information for a mobile unit substantially as hereinbefore described with reference to the accompanying drawings.