Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2001-02-02
2003-02-18
Nguyen, Lee (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S065000, C342S357490, C342S450000
Reexamination Certificate
active
06522890
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to mobile radio-frequency communication systems, and in particular to improvements in positioning and tracking systems for mobile radio-frequency transceivers such as cellular telephones. In a further aspect the invention concerns a method of finding the position of a mobile radio-frequency transceiver in a communications system.
BACKGROUND ART
Two important concepts in understanding the modes of operation of a positioning system are “remote-positioning” and “self-positioning”. In remote-positioning, a central station works out the location of the mobile. In self-positioning, the mobile works out its own location using data supplied by the station.
Two important modes of operation are radial remote-positioning and hyperbolic self-positioning.
Radial remote-positioning uses measurements of round trip time between a number of base stations and a mobile telephone. The distance between each base station and the mobile telephone can then be calculated by using the fact that radio waves propagate at the speed of light. There are a number of ways of measuring the round trip time, one way being the standard timing advance measurements made by base stations operating with the Global System Mobile (GSM) mobile telephony standard.
In operation the time-delay measurements from two base stations are transmitted via a radio link or fixed communication lines to a central station. From the time delays distances can be calculated, and using the distances it is possible to generate circles corresponding to loci of possible positions. The intersection of these loci establishes the position of the mobile telephone. There are two possible intersection points. Any ambiguity can be often resolved from a priori information. If this is not possible, a measurement from a third base station will resolve the issue. The third measurement will also allow a higher level of accuracy for the position measurement. Measurements from more than three base stations can also be combined, using standard techniques, to give more accurate measurements.
In the hyperbolic self-positioning system, the mobile telephone will compare the time of arrival of signals from three different base stations. The difference in time of arrival from two of the base stations will define one hyperbola, the time difference between another pair of stations will generate another hyperbola. The intersection of the two hyperbolas will define the location of the mobile telephone. In some cases there will be two intersections raising possible ambiguity. This can be resolved by the use of a fourth base station. This fourth base station will also allow a higher level of accuracy for the position measurement. Measurements from more than four base stations can also be combined to give more accurate measurements.
A combination of other modes is also possible. For example the round trip times could be measured at the mobile, so producing a radial self-positioning system. Alternatively the round trip time measurements could be made at the base stations, but sent to the mobile, which would then make the position calculations; an indirect radial self-positioning system. Alternatively, the base stations could co-operate to measure the time difference of arrival of the signals from a single mobile; a direct remote hyperbolic positioning system.
There are many possible uses for a system that allows accurate location of mobile telephones. These include locating people who are in distress, efficient dispatching of fleets, providing navigational guidance, recovery of stolen telephones, and giving geographically referenced information such as the location of the nearest restaurant. There have already been some attempts at implementation of systems for locating mobile phones. However, as yet there has not been a widespread commercial implementation. The major reason for this is that current solutions have technical deficiencies in the areas of coverage, accuracy, and cost.
DISCLOSURE OF THE INVENTION
In a first aspect the invention provides a mobile radio-frequency communications system, comprising: a network of at least two base stations arranged to transmit/receive signals to at least one mobile radio-frequency transceiver; a reference receiver located at a known distance from the base stations and including measuring means to measure the times of arrival of signals transmitted from the base stations; determination means to use the known distances and measured times to determine the relative time offsets of transmissions from each base station; and location means to use the determined relative time offsets to calculate the position of a mobile transceiver in the network area using hyperbolic positioning techniques.
The invention may be applied to any communications system that uses multiple sites, including cellular telephone systems, personal communications systems, and orbiting mobile telephone systems. It is an advantage of at least some embodiments of the invention to improve the accuracy and coverage, and reduce the cost of locating mobile telephones. Another advantage is the small number of changes required to a cellular system in order to implement some embodiments of the invention.
The position information could be derived remotely by the network or locally by the mobile transceivers.
Such a system could measure the actual propagation time of the signal transmitted from each base station to the reference receiver, compare the actual propagation time with a reference propagation time, and provide the selected mobile transceivers with time-difference measurements. The time difference measurements may include differences introduced by synchronisation errors, and by propagation delays.
Alternatively, the reference radio-frequency receiver may include signal processing means to measure the actual propagation time of the signal transmitted from each base station to the reference receiver and compare the actual propagation time with a reference propagation time. The reference receiver may also communicate the time difference measurements to a control means through its nearest base station, and the control means in turn could forward the time-difference measurements to the base stations for transmission to the selected receivers. In this case the determination means may be situated within the reference receiver, in which case the reference receiver transmits the relative time offsets back to the system.
In a self-positioning system the location means may be situated within the mobile transceiver. Alternatively, in a remote positioning system the location means may be associated with a central site remote from the mobile. For a remote system, the central station could use the information derived from the reference receiver in order to make the position determination.
The location means may receive information from the reference receiver by means of a landline rather than by means of a broadcast transmission. The location means may also receive data concerning at least one of base station oscillator stability, basestation location or the phase difference between two signals having different frequencies that have been transmitted by the same base station, by means of the landline.
Only a parameter of the signal (the epoch difference) needs to be transmitted, not the whole signal which is bandwidth efficient, and also means that it is not essential to compare exactly the same epochs. In many applications, the use of a reference receiver is more efficient, as it does not detract from system capacity and can be set up without any modification to the infrastructure of the cellular system.
A selector means may be operationally associated with the determination means to selectively prevent information concerning the position of a mobile transceiver from being available to that receiver. The base stations or the transceivers, or both, may be modified to ensure that only selected transceivers have available the position information. Non-selected transceivers may still be able to use the system to communicate, but wil
Drane Christopher R.
MacNaughtan Malcolm D.
Scott Craig A.
Cambridge Positioning Systems Ltd.
Nguyen Lee
Roylance Abrams Berdo & Goodman L.L.P.
LandOfFree
Location and tracking system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Location and tracking system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Location and tracking system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3172161