Cambridge Positioning Systems Limited

Robert Willem Rowe

Peter James Duffett-Smith

Malcolm David MacNaughtan

Murray Robert Jarvis

John Christopher Clarke

Simon David Hern

Ben J Tarlow

Nicolas Guy Albert Graube

Anthony Richard Pratt

Christopher R Drane

Christopher John Clarke

A method and apparatus are disclosed for determining the position, or change in the position, of a mobile terminal. The terminal has a receiver for receiving the signals from one or more transmission sources at unknown positions and an independent positioning device able to find, when operative, the position of the mobile terminal. The method uses the independent positioning device to measure the position of the mobile terminal at one or more first locations. A respective first set of time or phase offset values of signals received from the transmission sources relative to each other or to a reference in the mobile terminal is measured in the mobile terminal, at each first location. A second set of time or phase offset values are measured in the mobile terminal at a second terminal location where the independent positioning device is not operative and a second set of time or phase offset values of the signals received from the transmission sources, relative to each other or to a reference in the mobile terminal is measured. The values and said first measured terminal position or positions are combined, to thereby calculate the position of the mobile terminal at the second location, or the change in position of the mobile terminal between a first location and the second location.

Finding the position of a mobile terminal

A method of determining the location of a mobile receiver is provided. The method works within a radio system in one or more dimensions, the radio system includes a network of transmitters the positions of which are known. The method comprises the steps of: compiling a list of the signals detected by the receiver, sending said list to a calculation device; constructing a position function which relates to the probability that the receiver is at a given location, which position function has components corresponding to each member of the list, each component including a predetermined probability function that depends on mobile receiver position; and evaluating said position function to determine a position that corresponds to the highest probability of location, and defining that position to be the location of the mobile receiver.

Method and system for locating a mobile radio receiver in a radio system with multiple transmitters

To determine whether a mobile terminal of a communications system has moved outside a locale, the terminal measures relative time offsets of signals received by the terminal from transmitters of the network, relative to each other or a reference. At a first time when the terminal is within a given locale, the time of receipt of signals received by the terminal from a plurality of the transmitters relative to a reference or each other are measured to create a first set of receive time offsets. At a second time, a second set of receive time offsets is measured. Change(s) in receive  time offsets is/are calculated, and change(s) between the first and second times in transmission time offsets of the signals transmitted by at least one transmitter is/are obtained to determine movement indicators that are compared with threshold valuets to determine whether the mobile terminal has moved outside the locale.

Method and apparatus for determining whether a mobile terminal has moved outside a given locale

A method of processing received satellite radio signals is disclosed in which signals are received the signals from plural satellites through a common antenna. The received signals are digitised to produce a time-series of digitised signal samples and a plurality of replicas representing the signals of each of the plurality of satellites are obtained. At least one sample is selected from each of the replicas and the elements of a register are set equal to the selected replica samples. Thereafter, in turn, for each one of said digitised signal samples, the value of the digitised signal sample is combined with each of the values of the elements of the register to produce corresponding modified values; and the modified values corresponding to each of said register elements are accumulated.

Processing received satellite radio signals

In a terminalhaving a receiverfor receiving the signals from plural transmission sources-whose positions and transmission time offsets are unknown within the terminal, a method is provided for determining the change in the time (elapsed time) at the terminal between two instants. At a first position of the terminal a first set of measurements, aligned to a first instant, of a signal parameter representative of the time or phase of receipt of said signals from said plural transmission sources relative to one or more of them, or to a reference, or to a terminal clock is obtained. Then at a second position of the terminal a corresponding second set of measurements, aligned to a second instant, of a signal parameter representative of the time or phase of receipt of said signals from said plural transmission sources relative to one or more of them, or to the reference, or to the terminal clock is also obtained. The aligned measurements of the first and second sets are combined, and the time elapsed between the first and second instants is calculated from the change in the combined aligned measurements of the first and second sets.

Determining the change in time at a mobile terminal

The present invention sets out to overcome the hearability problem in CDMA communications networks in which positioning services are provided, by using a separate sampling devicefor each transmitter, which sends to the computing devicea representation of the signals transmitted only by that transmitter. A cross-correlation of the representation sent back by the mobile terminalwith the representation sent back by the sampling device in the brightest transmitter is performed in the computing device, and a blurred estimate of that brightest signal is subtracted from a blurred version of the representation sent back by the mobile terminalin order to reduce its effect on the remaining signals as far as possible. The cross-correlation and subtraction steps are iterated until no useful signals remain to be extracted.

Radio positioning systems

The invention provides a method of estimating the time offsets between signals transmitted by plural transmitters of a communications network and received by a receiver attached to a terminal. In the method a section of a representation of the signals from the plural transmitters received by the receiver at the terminal (a 'terminal section') is created as are a first section of a representation of the signal transmitted by a first of said transmitters and a second section of a representation of the signal transmitted by a second of said transmitters. Each of the first and second sections overlaps in time with the terminal section. Using the first section, the second section and a set of signal parameters, including initial estimates of the time offsets between the first section and the terminal section and between the second section and the terminal section, a model of a section of a representation of the composite signal received by the receiver from the first and second transmitters is created. Thereafter, the model is compared with the terminal section and the set of signal parameters including the time offset estimates is refined to minimize the difference between the model and the terminal section. The time offsets in the refined parameter set used to minimize the difference between said model and the terminal section, are adopted as the estimated time offsets between the first section and the terminal section and between the second section and the terminal section.

The present invention sets out to overcome the hearability problem in CDMA communications networks in which positioning services are provided, by using a separate sampling device () for each transmitter (), which sends to the computing device () a representation of the signals transmitted only by that transmitter. A cross-correlation of the representation sent back by the mobile terminal () with the representation sent back by the sampling device in the brightest transmitter is performed in the computing device (), and an estimate of that brightest signal is subtracted from the representation sent back by the mobile terminal () in order to reduce its effect on the remaining signals as far as possible. The cross-correlation and subtraction steps are iterated until no useful signals remain to be extracted.

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Cambridge, United Kingdom

Robert Willem Rowe