Method of estimating the position of a user device

1. A method of estimating the position of a user device comprising the steps of:

at each of a plurality of measurement points of known position within a zone, scanning for electromagnetic signal sources of known position, obtaining and storing measurements of the strength of the signal received from the scanned electromagnetic signal sources, to thereby obtain measurements of the strength of the signal received from a plurality of electromagnetic signal sources at a plurality of measurement points within the zone;

processing the stored data, the positions of the plurality of measurement points and the positions of the electromagnetic signal sources and, for each of the electromagnetic signal sources, fitting the measurements of received signal strength to a function of received signal strength with distance between the respective measurement point and the respective electromagnetic signal source, thereby obtaining parameters of the fitted function, the fitted function comprising as variables the received signal strength from the respective electromagnetic signal source and the distance between the respective measurement point and the respective electromagnetic signal source, the variables being related to each other by the parameters;

for each of the electromagnetic signal sources, storing the parameters of the fitted function; and

subsequently calculating the position of a user device by scanning for electromagnetic signal sources of known position, measuring the received signal strength from the scanned electromagnetic signal sources, retrieving the parameters of the function stored for the zone with reference to the scanned electromagnetic signal sources, using the function, the retrieved parameters and the received signal strengths measured by the user device to estimate the distance of the user device from each of the scanned electromagnetic signal sources; and

estimating the position of the user device from the estimated distances from the scanned electromagnetic signal sources and the known positions of the electromagnetic signal sources.

2. A method according to claim 1 , wherein the method comprises carrying out measurements in a plurality of zones, storing parameters for each zone and then using the parameters for the zone in which the user device is present to estimate the position of the user device.

3. A method according to claim 2 , wherein the method comprises determining in which zone the user device is located from the measured signal strengths, retrieving the parameters of the function stored with reference to that respective zone and using the parameters stored with reference to that respective zone to estimate the position of the user device.

4. A method according to claim 2 , wherein the method comprises storing measurements of the strength of the signal received from a plurality of electromagnetic sources for at least one measurement location in each zone.

5. A method according to claim 1 , wherein the parameters of the function are stored with reference to the respective zone.

6. A method according to claim 5 , wherein measurements are taken at a plurality of measurement points in each zone and parameters are calculated and stored with reference to each of a plurality of zones.

7. A method according to claim 1 , wherein the function is a linear function of a logarithm of received signal strength with distance from the respective electromagnetic signal source.

8. A method according to claim 1 , wherein the function is a non-linear function of a logarithm of received signal strength with distance from the respective electromagnetic signal source.

9. A method according to claim 1 , wherein the method comprises updating the stored parameters, in response to making further measurements, or detecting a new electromagnetic signal source, or that an electromagnetic signal source has moved, or detection that an electromagnetic signal source has stopped operating or due to a change or correction in a map of the building or the boundaries of zones.

10. A method according to claim 1 , wherein the method comprises making further measurements of the strength of the signal received from a respective electromagnetic signal source at a known position, recalculating the parameters for the respective electromagnetic signal source and updating the stored parameters.

11. A method according to claim 1 , wherein the function of received signal strength with distance from an electromagnetic signal source is different for different electromagnetic signal sources, in at least some cases.

12. A method according to claim 1 , wherein the function of received signal strength with distance from an electromagnetic signal source is different for the same electromagnetic signal source for different zones, in at least some cases.

13. A method according to claim 1 , wherein the method comprise changing the function which is to be used for a particular electromagnetic signal source, and for a particular zone where appropriate, in response to making further measurements or detecting a new electromagnetic signal source, or that an electromagnetic signal source has moved or responsive to detection that an electromagnetic signal source has stopped operating or due to a change or correction in a map of the building or the boundaries of zones.

14. A non-transitory computer readable medium storing a database comprising the parameters obtained by the method of claim 1 .

15. A method of storing data useful to estimate the position of a user device comprising the steps of:

at each of a plurality of measurement points of known position within a zone, scanning for electromagnetic signal sources of known position, obtaining and storing measurements of the strength of the signal received from the scanned electromagnetic signal sources, to thereby obtain measurements of the strength of the signal received from a plurality of electromagnetic signal sources at a plurality of measurement points within the zone;

processing the stored data, the positions of the plurality of measurement points and the positions of the electromagnetic signal sources and, for each of the electromagnetic signal sources, fitting the measurements of received signal strength to a function of received signal strength with distance between the respective measurement point and the respective electromagnetic signal source, thereby obtaining parameters of the fitted function the fitted function comprising as variables the received signal strength from the respective electromagnetic signal source and the distance between the respective measurement point and the respective electromagnetic signal source, the variables being related to each other by the parameters; and

for each of the electromagnetic signal sources, storing the parameters of the fitted function.

16. A method according to claim 15 , wherein the parameters are stored with reference to the respective zone and the method is repeated for each of a plurality of zones.

17. A computing device comprising a processor and a memory storing program code which, when executed by the processor, causes the processor to carry out the method of claim 15 .

18. A non-transitory computer readable medium storing a database comprising the parameters obtained by the method of claim 15 .

19. A method of estimating the position of a user device comprising the steps of: at each of a plurality of measurement points of known position within a zone, scanning for electromagnetic signal sources of known position, obtaining and storing measurements of the strength of the signal received from the scanned electromagnetic signal sources, to thereby obtain measurements of the strength of the signal received from a plurality of electromagnetic signal sources at a plurality of measurement points within the zone;

processing the stored data, the positions of the plurality of measurement points and the positions of the electromagnetic signal sources and, for each of the electromagnetic signal sources, fitting the measurements of received signal strength to a function of received signal strength with distance between the respective measurement point and the respective electromagnetic signal source, thereby obtaining parameters of the fitted function, the fitted function comprising as variables the received signal strength from the respective electromagnetic signal source and the distance between the respective measurement point and the respective electromagnetic signal source, the variables being related to each other by the parameters;

for each of the electromagnetic signal sources, storing the parameters of the fitted function; and

subsequently estimating the position of a user device by scanning for electromagnetic signal sources of known position, measuring the received signal strength from the scanned electromagnetic signal sources, retrieving the parameters of the function stored for the zone with reference to the scanned electromagnetic signal sources and using the retrieved parameters, the received signal strengths measured by the user device and the known positions of the electromagnetic signal sources to estimate the position of the user device.

20. A method according to claim 19 comprising:

at each of a plurality of measurement points of known position within each of a plurality of zones, scanning for electromagnetic signal sources of known position, obtaining and storing measurements of the strength of the signal received from the scanned electromagnetic signal sources, to thereby obtain measurements of the strength of the signal received from a plurality of electromagnetic signal sources at a plurality of measurement points within each of the zones;

for each zone, processing the stored data, the positions of the plurality of measurement points and the positions of the electromagnetic signal sources and, for each of the electromagnetic signal sources, fitting the measurements of received signal strength to a function of received signal strength with distance between the respective measurement point and the respective electromagnetic signal source, thereby obtaining parameters of the fitted function, the fitted function comprising as variables the received signal strength from the respective electromagnetic signal source and the distance between the respective measurement point and the respective electromagnetic signal source, the variables being related to each other by the parameters; and

for each zone, for each of the electromagnetic signal sources, storing the parameters of the fitted function;

wherein the step of estimating the position of the user device comprises scanning for electromagnetic signal sources of known position, measuring the received signal strength from the scanned electromagnetic signal sources, retrieving the parameters of the function stored for each of the zones with reference to the scanned electromagnetic signal sources and using the retrieved parameters, the received signal strengths measured by the user device and the known positions of the electromagnetic signal sources to estimate the position of the user device.

21. A method according to claim 20 comprising estimating the position of the user device by determining a zone in which the user device is located from the plurality of zones using the retrieved parameters for each of the zones, the received signal strengths measured by the user device and the known positions of the electromagnetic signal sources.