Communications: directive radio wave systems and devices (e.g. – Directive – Position indicating
Reexamination Certificate
2000-02-17
2002-01-29
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Position indicating
C342S463000
Reexamination Certificate
active
06342854
ABSTRACT:
FIELD OF THE INVENTION
This application is 371 or PCT/GB 96/02308 filed Sep. 16, 1996.
This invention relates to a position determining system using radio or other broadcast transmissions. More particularly, it relates to a system using the Global System for Mobile Communications (GSM) or other digital transmission systems.
BACKGROUND OF THE INVENTION
In our European Patent EP-B-0 303 371 we describe a radio navigation and tracking system, now known as ‘CURSOR’, which uses the spatial coherence of the signals from several radio transmitters to determine the position of a roving receiver. Its principles are explained in the above patent specification where it is shown how the signals received directly by the roving receiver (rover) are compared with those received by a fixed base station whose location is known (base) to determine their phase difference, and hence the difference in range of the base and rover from each transmitter. Three such measurements made on independent transmitters are needed for navigation and tracking in two dimensions to fix the position of the rover relative to the base station and network of transmitters. The unknown quantities calculated for each new position are the spatial x and y co-ordinates of the rover together with the phase offset between the local oscillators in the equipment of the two receivers. A further patent specification, WO 94/28432, shows how the same principles may be applied in tunnels and other shielded spaces such as underground car parks. Duffett-Smith and Woan (Journal of Navigation, 45, 157, 1992) describe a particular implementation of the phase-measuring system in which the signals from three or more medium-wave AM public broadcast stations are used to track the position of a vehicle in and around Cambridge, UK, at speeds up to 110 km h
−1
, with a precision of about 5 m. Once of the advantages of such a system lies in the fact that no additional costly infrastructure of coherent radio transmitters needs to be set up for CURSOR operation. On the contrary, CURSOR is able to use the signals from any independent radio transmitters set up for any purpose.
EP-B-0 303 371 also explains how the wider bandwidth signals of modulated transmissions may be used to measure the time difference between the signals received from each transmitter at the base station and the rover. In this case, the position of the peak in the cross correlation can be used as an estimator of the time difference between the two received signals, and hence the difference in distance from the transmitter of the base and rover. As with the phase-measuring system, three such measurements made on three widely-spaced transmitters suffice to calculate the spatial x and y co-ordinates of the rover together with the time offset between the oscillators in the two receiving stations.
Mobile telephones are increasingly using GSM and other digital techniques, and it would be an advantage to add time-measuring CURSOR positioning technology to provide additional services for users. However, signals radiated by digital telephone transmitters are complex and therefore there are problems to be overcome in attempting to combine the technologies.
SUMMARY OF THE INVENTION
According to the present invention there is provided a position determining system, for receiving broad band signals transmitted by a number of transmission sources equal at least to the number of dimensions in which the movement of a roving object is to be monitored, the system comprising
a pair of receiving stations, in use the first of the receiving stations being at a known position and the second being located on the roving object;
a position determining processor;
means for passing a link signal from each of the receiving stations to the position determining processor, the link signal containing information about the signals received at the receiving station from the transmission sources;
wherein each of the receiving stations is arranged to receive the signals from the respective transmission sources substantially simultaneously, and the position determining processor is arranged to compare the information received from the one receiving station about the signals received at the one receiving station from the transmission sources with the information received from the other receiving station about the signals received at the other receiving station from the transmission sources, and to determine the time delay between the respective signals received at both receiving stations in order to determine the position of the roving object.
The receiving stations may receive the signals from the respective transmission sources sequentially and in the same sequence as each other.
The invention also includes a method of determining the position of a roving object, the method comprising transmitting a broadband signal from a number of transmission sources equal at least to the number of dimensions in which the movement of a roving object is to be monitored; receiving the signals at a pair of receiving stations, in use a first of the receiving stations being at a known position and a second being located on the roving object, each of the receiving stations being arranged to receive the signals from the respective transmission sources substantially simultaneously; passing link signals from each of the receiving stations to a position determining processor, the link signals containing information about the signals received at the respective receiving station from the transmission sources; comparing the information received at the position determining processor from the one receiving station about the signals received at the one receiving station from the transmission sources with the information received from the other receiving station about the signals received at the other receiving station from the transmission sources; and determining the time delay between the respective signals received at both receiving stations in order to determine the position of the roving object.
Additionally, the invention includes a method of estimating the offset in time of receipt of a broadcast signal received at two locations, where the signal received at the one location may have been subject to corruption by multipath effects, the method comprising auto-correlating the signals received at the one location; auto-correlating the signals received at the other location; cross-correlating the signals received at the one and other locations; constructing a template comprising that portion of the auto-correlation of the signals received at the other location corresponding to the negative time axis, and that portion of the auto-correlation of the signals received at the one location corresponding to the positive time axis; and measuring the offset at which the template best fits the measured cross-correlation of the signals received at the one and other locations as an estimate of the time offset between the signals received at the two locations.
In some systems, each of the receiving stations is also arranged to receive a second signal from one or more of the transmitters, said second signal being used to enable compensation for changes in equipment offsets during receipt of the sequentially received signals.
The position determining processor may be co-located with one of the receiving stations or may be located remotely.
In one embodiment, the link signal from one of the receiving stations is passed to the other receiving station and from the other receiving station to the position determining processor.
Preferably, for locating purposes, a signal providing information about the position of the roving object is passed from the position determining processor to at least one of the receiving stations.
The system may further comprise one or more monitoring stations and a signal providing information about the position of the roving object may then be passed from the position determining processor to one or more of the monitoring stations.
To provide enhanced functionality, a database server may be connected to the position determini
Duffett-Smith Peter James
Grainge Keith James Bruno
Blum Theodore M.
Cambridge Positioning Systems Ltd.
Roylance Abrams Berdo & Goodman LLP
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