Signal phase-based location of network nodes

1. A method of determining the physical position of an unknown node in a wireless network, comprising:

sending a first signal from a first transmitting reference node having a known position to a first receiving reference node having a known position and the unknown node, the first transmitting reference node and the first receiving reference node forming a first pair of reference nodes;

receiving the first signal in the unknown node and sending a second signal from the unknown node to the first receiving reference node in phase with the first signal;

receiving the first signal and the second signal in the first receiving reference node and comparing the phase of the received first and second signals;

sending a third signal from a second transmitting reference node having a known position, different from the first transmitting reference node, to a second receiving reference node having a known position, different from the first receiving reference node, and the unknown node, the second transmitting reference node and the second receiving reference node forming a second pair of reference nodes;

receiving the third signal in the unknown node and sending a fourth signal from the unknown node to the second receiving reference node in phase with the third signal;

receiving the third signal and the fourth signal in the second receiving reference node and comparing the phase of the received third signal and the received fourth signal;

determining the position of the unknown node based on the phase difference between the received first and second signals and on the phase difference between the received third and fourth signals;

wherein the first transmitting reference node, the first receiving reference node, the second transmitting reference node, and the second receiving reference node are positioned such that a line between the first transmitting reference node and the first receiving reference node is orthogonal to a line between the second transmitting reference node and the second receiving reference node;

wherein the wireless network is a mesh network.

2. The method of determining the physical position of a movable node in a network of claim 1 , wherein determining the position of the unknown node comprises determining the position as one of two points on a plane defined by the first transmitting reference node, the first receiving reference node and the unknown node.

3. The method of determining the physical position of a movable node in a network of claim 1 , further comprising repeating the method using two or more signal frequencies to resolve position ambiguity where signal wavelength is small relative to distances between nodes.

4. The method of determining the physical position of a movable node in a network of claim 1 , wherein the network nodes comprise at least one of a Zigbee or a DigiMesh.

5. The method of determining the physical position of a movable node in a network of claim 1 , wherein one or more of the first transmitting reference node and first receiving reference node comprise a mobile or unknown node whose location has already been determined.

6. A wireless network, comprising:

a first transmitting reference node having known positions and a first receiving reference node having known positions and forming a first pair of reference nodes;

a second transmitting reference node having known positions and a second receiving reference node having known positions and forming a second pair of reference nodes, wherein the first transmitting reference node is operable to send a first signal; and

an unknown node operable to receive the first signal from the first transmitting reference node and send a second signal to the first receiving reference node in phase with the first signal;

wherein the second transmitting reference node is operable to send a third signal;

wherein the unknown node is operable to receive the third signal from the second transmitting reference node and send a fourth signal to the second receiving reference node in phase with the third signal;

wherein the first receiving reference node is operable to receive and compare the phase of the first signal and second signal;

wherein the second receiving reference node is operable to receive and compare the phase of the third signal and the fourth signal;

wherein the position of the unknown node is determined based on the phase difference between the received first and second signals and on the phase difference between the received third and fourth signals;

wherein the first transmitting reference node, the first receiving reference node, the second transmitting reference node, and the second receiving reference node are positioned such that a line between the first transmitting reference node and the first receiving reference node is orthogonal to a line between the second transmitting reference node and the second receiving reference node;

wherein the wireless network is a mesh network.

7. The wireless network of claim 6 , wherein determining the position of the unknown node comprises determining the position as one of two points on a plane defined by the first transmitting reference node, the first receiving reference node and the unknown node.

8. The wireless network of claim 6 , the second reference node further operable to receive and compare signal phases using two or more signal frequencies to resolve position ambiguity where signal wavelength is small relative to distances between nodes.

9. The wireless network of claim 6 , wherein the network nodes comprise at least one of a Zigbee or a DigiMesh.

10. The wireless network of claim 6 , wherein one or more of the first transmitting reference node and the first receiving reference node comprise a mobile or unknown node whose location has already been determined.