Positioning system for determining the location of a device

1. A wireless device having a physical location, the wireless device comprising:

a wireless interface for communicating with a network of reference nodes, each being located at a respective set of physical coordinates; and

a location module configured to obtain a measurement of a respective signal communicated between the wireless interface and each of a plurality of said reference nodes, and to be supplied with a respective set of transformed time-varying coordinates for each of said plurality of reference nodes, transformed relative to the physical coordinates;

wherein the location module is configured, using said signal measurements and the transformed time-varying coordinates of said plurality of reference nodes, to submit information indicative of a transformed location of the wireless device to an interpretation function, and to thereby access functionality relating to the physical location of the wireless device, and

wherein the location module is configured to receive a respective identifier from each of said plurality of reference nodes, and to be supplied with the transformed time-varying coordinates from a server by submitting the identifiers to the server and receiving the respective sets of transformed coordinates back in response.

2. The wireless device of claim 1 , wherein the location module is configured to perform a calculation at the wireless device to determine the transformed location based on said signal measurements and transformed time-varying coordinates, and the information submitted to the interpretation function comprises the transformed location.

3. The wireless device of claim 2 , wherein said interpretation function comprises a transform function and the wireless device is configured to submit the transformed location to the transform function to be transformed to the physical location, thereby accessing said functionality relating to the physical location.

4. The wireless device of claim 1 , wherein the interpretation function is implemented on a server, the location module of the wireless device being configured to submit said information to the server over a network.

5. The wireless device of claim 1 , wherein said functionality comprises the physical location being provided to the wireless device.

6. The wireless device of claim 5 , wherein the physical location is provided to the wireless device in a signed form.

7. The wireless device of claim 1 , wherein said functionality comprises a location-based service, access to which is conditional on the physical location of the wireless device.

8. The wireless device of claim 6 , wherein said functionality comprises a location-based service and the location module is configured to submit the signed form of the physical location to the location based-service, access to which is conditional on the physical location of the wireless device and on verifying the signed form of the physical location submitted by the wireless device.

9. The wireless device of claim 1 , wherein the location module is configured to obtain said signal measurements by performing the measurements at said wireless device.

10. The wireless device of claim 1 , wherein the location module is configured to be supplied with the transformed time-varying coordinates by receiving the respective sets of transformed time-varying coordinates from each of said plurality of reference nodes.

11. The wireless device of claim 1 , wherein the transformed time-varying coordinates map to the physical coordinates according to a time varying mapping.

12. A server for use in a location system in which measurements of signals communicated between a wireless device and each of a plurality of reference nodes are used to determine a physical location of the wireless device, the server comprising:

a mapping between a respective set of physical coordinates at which each of the reference nodes is located and a respective set of transformed time-varying coordinates allocated to each of the reference nodes;

an interface configured to receive information indicative of a transformed location of the wireless device, submitted from the wireless device based on said signal measurements and the transformed time-varying coordinates of said plurality of reference nodes; and

a transform function configured to determine the physical location of the wireless device from said information in accordance with said mapping,

wherein the server supplies the wireless device with respective sets of the transformed time-varying coordinates after receiving a respective identifier associated with each of said plurality of reference nodes.

13. A location system comprising:

a wireless device having a physical location to be determined;

network of reference nodes of a location system, each being located at a respective set of physical coordinates; and

a server comprising a mapping between a respective set of physical coordinates at which each of the reference nodes is located and a respective set of transformed time-varying coordinates allocated to each of the reference nodes;

wherein the wireless device is configured to obtain a measurement of a respective signal communicated between the wireless interface and each of a plurality of said reference nodes, and to be supplied with the respective set of transformed time-varying coordinates for each of said plurality of reference nodes; and

wherein the wireless device is further configured, using said signal measurements and the transformed time-varying coordinates of said plurality of reference nodes, to submit information indicative of a transformed location of the wireless device; and

the server is configured to transform the transformed location into the physical location, the system thereby providing access to functionality relating to the physical location,

wherein the wireless device is further configured to receive a respective identifier from each of said plurality of reference nodes, and to be supplied with the transformed time-varying coordinates from the server by submitting the identifiers to the server and receiving the respective sets of transformed coordinates back in response.