System for determining a physical metric such as position

1. A system for determining a physical metric comprising:

a local signal generator configured to provide a local signal;

a receiver configured to receive a signal having properties corresponding to those in a signal transmitted by a trusted remote source;

a motion module configured to provide a measured or assumed movement of the receiver, wherein the assumed movement is based on movement of the receiver in previous epochs;

a correlation unit configured to provide a correlation signal by correlating the local signal with the received signal;

a motion compensation unit configured to provide motion compensation of at least one of the local signal, the received signal, and the correlation signal based on the measured or assumed movement to thereby generate a motion-compensated correlation signal, wherein the motion compensation is based on a sequence of phasors that are indicative of amplitude and/or phase changes introduced into the received signal by the measured or assumed movement of the receiver;

a signal analysis unit configured to determine whether the received signal includes a component received in a direction that is different to a line-of-sight direction between the receiver and the trusted remote source, wherein the determination is based on a signal strength of the received signal and a signal to noise ratio of the motion-compensated correlation signal; and

a metric determination unit configured to determine a physical metric associated with the receiver based on the determination made by the signal analysis unit, and wherein the metric determination unit is configured to determine whether or not to use the received signal in the determination of the physical metric, based on the determination made by the signal analysis unit.

2. The system of claim 1 , wherein the signal analysis unit is configured to determine whether the received signal includes a component that is received from the trusted remote source, following at least one reflection.

3. The system of claim 1 , wherein the signal analysis unit is configured to determine the direction in which the component is received, based on the correlation signal.

4. The system of claim 1 , wherein the receiver comprises or is coupled to a single antenna.

5. The system of claim 1 , wherein the motion compensation unit is configured to provide motion compensation of at least one of the local signal, the received signal, and the correlation signal based on the measured or assumed movement in the direction of the line-of-sight between the receiver and the trusted remote source.

6. The system of claim 1 , wherein the motion compensation unit is configured to provide motion compensation of at least one of the local signal, the received signal, and the correlation signal based on the measured or assumed movement in a direction in which the component is received.

7. The system of claim 1 , wherein, if the received signal includes a component received in a direction that is different to the line-of-sight direction between the receiver and the trusted remote source, the component is substantially attenuated in the determination of the physical metric by the metric determination unit.

8. The system of claim 1 , wherein the metric determination unit is configured to determine the physical metric associated with the receiver based on the determination made by the signal analysis unit and a topographic map.

9. The system of claim 1 , wherein the motion compensation unit is configured to provide motion compensation of at least one of the local signal, the received signal, and the correlation signal based on the measured or assumed movement in a plurality of directions.

10. The system of claim 9 , wherein the plurality of directions are distributed across all possible directions in which a signal can be received at the receiver.

11. The system of claim 9 , wherein the motion compensation unit provides a phase difference for signals received at different respective times in order to provide motion compensation in the plurality of different directions.

12. The system of claim 1 , wherein the signal analysis unit is configured to determine whether the received signal includes a component from a counterfeit remote source.

13. A method of determining a physical metric, using a positioning system, comprising the steps of:

providing a local signal with a local signal generator;

receiving a signal having properties corresponding to those in a signal transmitted by a trusted remote source;

providing a measured or assumed movement of the receiver, wherein the assumed movement is based on movement of the receiver in previous epochs;

providing a correlation signal by correlating the local signal with the received signal;

providing motion compensation of at least one of the local signal, the received signal, and the correlation signal based on the measured or assumed movement to thereby generate a motion compensated correlation signal, wherein the motion compensation is based on a sequence of phasors that are indicative of amplitude and/or phase changes introduced into the received signal by the measured or assumed movement of the receiver;

determining whether the received signal includes a component received in a direction that is different to a line-of-sight direction between the receiver and the trusted remote source, wherein the determination is based on a signal strength of the received signal and a signal to noise ratio of the motion-compensated correlation signal; and

determining a physical metric associated with the receiver based on the determination made by the signal analysis unit, wherein determining the physical metric comprises determining whether or not to use the received signal in the determination of the physical metric, based on the determination of whether the received signal includes a component received in a direction that is different to a line-of-sight direction between the receiver and the trusted remote source.

14. A non-transitory computer program product comprising executable instructions which when executed on a computer cause the computer to carry out steps comprising:

providing a local signal with a local signal generator;

receiving a signal having properties corresponding to those in a signal transmitted by a trusted remote source;

providing a measured or assumed movement of the receiver, wherein the assumed movement is based on movement of the receiver in previous epochs;

providing a correlation signal by correlating the local signal with the received signal;

providing motion compensation of at least one of the local signal, the received signal, and the correlation signal based on the measured or assumed movement to thereby generate a motion compensated correlation signal, wherein the motion compensation is based on a sequence of phasors that are indicative of amplitude and/or phase changes introduced into the received signal by the measured or assumed movement of the receiver;

determining whether the received signal includes a component received in a direction that is different to a line-of-sight direction between the receiver and the trusted remote source, wherein the determination is based on a signal strength of the received signal and a signal to noise ratio of the motion-compensated correlation signal; and

determining a physical metric associated with the receiver based on the determination made by the signal analysis unit, wherein determining the physical metric comprises determining whether or not to use the received signal in the determination of the physical metric, based on the determination of whether the received signal includes a component received in a direction that is different to a line-of-sight direction between the receiver and the trusted remote source.