POSITIONING METHOD FOR A MOBILE TELEPHONE RECEIVER

Abstract: A method for accurately locating the position of a mobile telephone receiver uses a timing signal sent out from base station transmitters and these signals are decoded by the receiver. By accurate synchronisation of the timing signals and by accurate measurement by the receiver the precise location of the receiver can be determined.

Description: POSITIONING METHOD FOR A MOBILE TELEPHONE RECEIVER The present invention relates to a method for identifying the position of a person or object. Global satellite positioning (GSP) is known in which the position of a receiver on a map or grid is identified by means of timing signals sent out by satellites and received by receiver so that, if the relative location of the satellites are known, and the difference in time it takes for the signal received from each satellite measured it is possible to identify the location of the receiver on the map or grid. The timing signal sent out by each satellite has to be exactly synchronised and this is done with reference to a master clock which synchronises clocks on all the satellites. The precision of location will depend on the accuracy of the clocks and the number and closeness of transmitters in the satellites and on interference and other external factors. In maritime, country, non-urban and less densely built up areas a degree of precision easily obtainable by existing systems is adequate for most purposes and a location of 30 metres is satisfactory. However in towns a more precise location of a user is needed and a precision of less than a metre or even a few centimetres is required for many purposes e.g. location of services such as water and gas pipes, electricity cables. In order to increase the precision of location using existing equipment, refinements to the timing systems, analysis of the signals and decoding software have been devised and used. However, in built up areas, inaccuracies can be caused by external factors such as satellite visibility and multipath interference which are difficult to overcome. In addition, for satellite systems, transmission through the ionosphere is a major source of uncertainty. We have devised a positioning system which reduces these problems. According to the invention there is provided a method for locating the position of a receiver, which method comprises transmitting a timing signal from a plurality of mobile telephone base stations transmitters using a frequency in the bandwidth of the mobile phone receiver, decoding the timing signals at the receiver and identifying the location of the receiver. The receiver can conveniently be incorporated in, or added to the mobile telephone receiver. By knowing the relative location of the base stations, and the time of transmitting the signal from each base station and accurately decoding the timing signal from two or more base stations at the receiver the location of the receiver can be accurately determined. In practice the precise location of each base station as well as their relative locations will be known. The receiver needs to include a means to decode the timing signal so the time taken from the separate base stations is measured and conventional hardware and software, as is used in existing satellite systems, is widely available and can be used. The invention also provides a mobile telephone receiver which can be used in the method of the invention which incorporates a decoding means adapted to decode and measure timing signals transmitted from a plurality of separate base stations. The decoding means should be able to measure the time difference between the timing signals received from these different base stations. It is a feature of the invention that the timing signal can be sent out from each base station along with the telephone signal so that a separate network of base stations and transmitters do not need to be set up. Each base station should incorporate a clock of the requisite accuracy and the clocks at each base station need to be synchronised so that the receiver can be located with adequate accuracy. As in satellite systems, the more accurate the clocks the more precisely the location of a receiver can be detected. In addition the closer the base stations are together the greater the accuracy that can be obtained. In mobile telephone systems, the density of the base stations is greater in more densely populated areas, such as urban areas, and these are the same areas in which greater precision of location is required and where satellite systems are less effective. In practice it should always be possible to receive signals from at least three base stations and so the precise location of a receiver should be possible. The clock to be used to generate the timing signal at the base station should be sufficiently accurate and well synchronised to enable the requisite degree of precision to be achieved, for example location to within thirty centimetres would require a timing accuracy of the receiver to be of less than 2 nanoseconds e.g. of the order of 1 nanosecond or less and so the clocks in the transmitters would need to be synchronised to this accuracy and to be able to maintain this degree of synchronisation between each re-synchronisation. As a receiver with a timing accuracy of ~ 1 nanosecond or less is preferred the accuracy of the clocks should be of comparable accuracy and this should be maintained over the period between resynchronisation of the clocks. The resynchronisation of the clocks can be carried out using known methods using a master clock. For convenience resynchronisation of the clocks could take place once every twenty four hours and the clock accuracy required would range from 1 in 10 8 for a measuring time of 0. Is to 1 in 10 14 for the measurement of time corresponding to the maximum delay following a resynchronisation sequence. The resynchronisation is not restricted to once every twenty-four hours and it is preferable if resynchronisation is carried out at shorter time intervals than twenty-four hours. At this accuracy a suitable clock would be cryogenic (~60K) sapphire resonator based clock. These clocks require the provision of cryogenic equipment at the base station, but the third generation UMTS specifications for mobile telephones have been said to require the provision of cryofilters to provide the filters which would be required to receive and transmit functions at the base stations so this equipment would be available. The invention is not restricted to the use of sapphire as the resonator and other single crystal materials such as, but not restricted to, titanium oxide, lanthanum aluminate, might also be used. The clock might also be based on sintered materials, for example sintered materials such as, but not restricted to, barium magnesium tantalate or zirconium tin titanate might be used. For lower accuracy clocks ambient temperature operation would be possible. The present invention provides a method for improved accuracy of location, particularly in urban areas, which would make use of existing mobile telephone network of base stations and which could be used as part of or in conjunction with a mobile telephone. The invention is illustrated with reference to the accompanying drawing which shows diagrammatically a simplified system. In the drawing each of the three mobile telephone transmitter base stations (la), (lb) and (lc) transmit a timing signal in their spare bandwidth. These signals are received by a receiver at (2) which decodes the timing signals and, by comparing the signal received from each of the transmitters and, knowing the location of the base stations, a precise location of the transmitter can be identified. This can be displayed as an image on a map or grid (3) or as co-ordinates. As the mobile telephone facilities are utilised, this location can be transmitted, if requested, directly to emergency or rescue services at (4) without the user needing to know his precise location.

Claims: Claims 1. A method for locating the position of a receiver, which method comprises transmitting a timing signal from a plurality of mobile telephone base stations transmitters using a frequency in the bandwidth of the mobile phone receiver, decoding the timing signals at the receiver and identifying the location of the receiver. 2. A method as claimed in claim 1 in which the receiver is incorporated in, or added to a mobile telephone receiver 3. A method as claimed in claim 1 or 2 in which the timing signal is sent out from each base station along with a telephone signal. 4. A method as claimed in any one of the preceding claims in which each base station incorporates a clock and the clocks at each base station are synchronised. 5. A method as claimed in claim 4 in which the timing accuracy of the receiver is less than 2 nanoseconds and the clocks in the transmitters are synchronised to this accuracy and are able to maintain this degree of synchronisation between each re- synchronisation. 6. A method as claimed in claim 5 in which the timing accuracy of the receiver is less than 1 nanosecond 7. A method as claimed in claim 4, 5 or 6 in which the accuracy of clock resynchronisation is 1 in 10 8 for a measuring time of 0.1s to 1 in 10 14 for the measurement of time corresponding to the maximum delay following a resynchronisation sequence. 8. A method as claimed in any one of claims 4 to 7 in which a single crystal material resonator clock is used. 9. A method as claimed in claim 8 in which the clock is a cryogenic sapphire resonator based clock. 10. A mobile telephone receiver which incorporates a decoding means adapted to decode and measure timing signals transmitted from a plurality of separate base stations. 11. A mobile telephone receiver as claimed in claim 10 in which the decoding means can measure the time difference between the timing signals received from different base stations. 12. A mobile telephone receiver as claimed in claim 10 or 11 in which the decoding means can measure time differences to an accuracy of less than 1 nanosecond.

Inventors: ALFORD NEIL MCNEILL, GALLOP JOHN CHARLES, ALFORD, NEIL, MCNEILL, GALLOP, JOHN, CHARLES
Applicants: ALFORD NEIL MCNEILL, GALLOP JOHN CHARLES, SOUTH BANK UNIV ENTPR LTD, ALFORD, NEIL, MCNEILL, GALLOP, JOHN, CHARLES, SOUTH BANK UNIVERSITY ENTERPRISES LTD.
Application year: 2001
Main classification: H04Q7
IPC codes: G01S5, H04W64