RF chirp signal propagation delay measurement

1. A method of estimating a distance between two radio frequency devices, comprising:

transmitting a plurality of spread spectrum chirp signals frequency offset from one another from a first radio frequency device;

receiving the plurality of spread spectrum chirp signals in a second radio frequency device;

evaluating the received plurality of spread spectrum chirp signals for relative phase shifts between the plurality of spread spectrum chirp signals; and

deriving a fine propagation time between the first and second devices using the phase shifts between the spread spectrum chirp signals.

2. The method of estimating a distance between two radio frequency devices of claim 1 , further comprising determining a coarse propagation time established by propagation delay of at least one of the plurality of chirp signals plus known processing delays, and combining the coarse propagation delay and the fine propagation time to establish an accurate propagation time.

3. The method of estimating a distance between two radio frequency devices of claim 1 , further comprising shifting a frequency domain despreading window in the receiver to reduce the influence of time-delayed near multipath signals in receiving the plurality of spread spectrum chirp signals.

4. A radio frequency ranging system, comprising:

a first device operable to transmit a plurality of spread spectrum chirp signals frequency offset from one another;

a second device operable to receive the plurality of spread spectrum chirp signals, the second device further operable to evaluate the received plurality of spread spectrum chirp signals for relative phase shifts between the plurality of spread spectrum chirp signals and derive a fine propagation time between the first and second devices using the phase shifts between the spread spectrum chirp signals.

5. The radio frequency ranging system of claim 4 , the receiver further operable to determine a coarse propagation time established by propagation delay of at least one of the plurality of chirp signals plus known processing delays, and combine the coarse propagation delay and the fine propagation time to establish an accurate propagation time.

6. The radio frequency ranging system of claim 4 , the receiver further operable to shift a frequency domain despreading window in the receiver to reduce the influence of time-delayed near multipath signals in receiving the plurality of spread spectrum chirp signals.

7. A method of estimating a distance between two radio frequency devices, comprising:

receiving a plurality of spread spectrum chirp signals transmitted from a transmitting radio frequency device frequency offset from one another;

evaluating the received plurality of spread spectrum chirp signals for relative phase shifts between the plurality of spread spectrum chirp signals; and

deriving a fine propagation time between the first and second devices using the phase shifts between the spread spectrum chirp signals.

8. The method of estimating a distance between two radio frequency devices of claim 7 , further comprising determining a coarse propagation time established by propagation delay of at least one of the plurality of chirp signals plus known processing delays, and combining the coarse propagation delay and the fine propagation time to establish an accurate propagation time.

9. The method of estimating a distance between two radio frequency devices of claim 7 , further comprising shifting a frequency domain despreading window in the receiver to reduce the influence of time-delayed near multipath signals in receiving the plurality of spread spectrum chirp signals.

10. A radio frequency device, comprising:

a radio frequency receiver operable to receive a plurality of spread spectrum chirp signals frequency offset from one another transmitted from a transmitting radio device; and

processing logic operable to evaluate the received plurality of spread spectrum chirp signals for relative phase shifts between the plurality of spread spectrum chirp signals and derive a fine propagation time between the first and second devices using the phase shifts between the spread spectrum chirp signals.

11. The radio frequency device of claim 10 , the processing logic further operable to determine a coarse propagation time established by propagation delay of at least one of the plurality of chirp signals plus known processing delays, and combine the coarse propagation delay and the fine propagation time to establish an accurate propagation time.

12. The radio frequency device of claim 10 , the processing logic further operable to shift a frequency domain despreading window to reduce the influence of time-delayed near multipath signals in receiving the plurality of spread spectrum chirp signals.

13. A method of estimating a distance between two radio frequency communication devices, comprising:

wirelessly transmitting a plurality of spread spectrum chirp signals frequency offset from one another from a first radio frequency communication device to a second radio frequency communication device, the plurality of spread spectrum chirp signals transmitted with a known phase relationship between signals;

evaluating, at the second radio frequency communication device, the received plurality of spread spectrum chirp signals for relative phase shifts between the plurality of spread spectrum chirp signals;

deriving a fine propagation time between the first and second devices using the phase shifts between the spread spectrum chirp signals; and

determining a location of the second radio frequency communication device based, at least in part, on the derived fine propagation time between the first and second radio frequency communication devices.