Double-differential round trip time measurement

1. A method of operating a position estimation entity, comprising:

obtaining a first differential round trip time (RTT) measurement based on a first RTT measurement between a user equipment (UE) and a first wireless node and a second RTT measurement between the UE and a second wireless node;

obtaining a second differential RTT measurement based on a third RTT measurement between a third wireless node and the first wireless node and a fourth RTT measurement between the third wireless node and the second wireless node; and

determining a positioning estimate of the UE based at least in part on the first differential RTT measurement and the second differential RTT measurement.

2. The method of claim 1 , wherein the first differential RTT measurement is triggered by the position estimation entity separately from the second differential RTT measurement.

3. The method of claim 1 ,

wherein the first differential RTT measurement is triggered at a first frequency or based on a first triggering event, and

wherein the second differential RTT measurement is triggered at a second frequency or based on a second triggering event.

4. The method of claim 3 ,

wherein the determination of the positioning estimate of the UE comprises measuring the first differential RTT measurement, and

wherein calibrating a hardware group delay of the first wireless node, the second wireless node, or both comprises measuring the second differential RTT measurement.

5. The method of claim 1 , wherein the first wireless node, the second wireless node and the third wireless node are associated with respective known locations before the determination of the position estimate.

6. The method of claim 1 , wherein the first wireless node, the second wireless node and the third wireless node comprise one or more base stations, one or more anchor user equipments (UEs), or a combination thereof.

7. The method of claim 6 , wherein the first wireless node, the second wireless node and the third wireless node each correspond to a respective base station.

8. The method of claim 7 ,

wherein the third RTT measurement is based on one or more positioning reference signals (PRSs) exchanged between the first wireless node and the third wireless node on one or more fixed beams, or

wherein the fourth RTT measurement is based on at least one PRS exchanged between the second wireless node and the third wireless node on at least one fixed beam, or

a combination thereof.

9. The method of claim 6 , wherein the first wireless node, the second wireless node and the third wireless node each correspond to a respective UE.

10. The method of claim 6 , wherein the first wireless node and the second wireless node correspond to base stations and the third wireless node corresponds to an anchor UE associated with a known location.

11. The method of claim 10 , wherein positioning resources allocated for determination of a location of the anchor UE are greater than positioning resources used for determination of the positioning estimate of the UE.

12. The method of claim 1 , wherein the first wireless node, the second wireless node and the third wireless node comprise one or more positioning reference units (PRUs).

13. The method of claim 1 , wherein the third RTT measurement is based on a first positioning reference signal (PRS) from the third wireless node to the first wireless node and a second PRS from the first wireless node to the third wireless node.

14. The method of claim 13 , wherein the first PRS and the second PRS are associated with the same PRS type.

15. The method of claim 13 , wherein the first PRS and the second PRS comprise at least one single symbol PRS, at least one multi-symbol PRS, or a combination thereof.

16. The method of claim 13 , wherein the fourth RTT measurement is based on a third PRS from the third wireless node to the second wireless node and a fourth PRS from the second wireless node to the third wireless node.

17. The method of claim 16 ,

wherein the first PRS corresponds to the third PRS, or

wherein the first PRS and the second PRS are different.

18. The method of claim 13 , further comprising:

transmitting a message to the first wireless node and the third wireless node, the message indicating whether the first PRS follows the second PRS or whether the second PRS follows the first PRS.

19. The method of claim 13 , further comprising:

transmitting a message to the first wireless node and the third wireless node, the message indicating a PRS resource to be used for an initial PRS of the third RTT measurement.

20. The method of claim 1 , wherein the first, second, third and fourth RTT measurements and/or the first differential RTT measurement and the second differential RTT measurement are received at the position estimation entity via one or more measurement reports.

21. The method of claim 20 , wherein the one or more measurement reports each indicate, for a respective measurement, a transmission reception point (TRP) identifier a positioning reference signal (PRS) source identifier, a PRS resource set ID, a frequency layer ID, a time stamp, or a combination thereof.

22. The method of claim 1 ,

wherein the first differential RTT measurement is based on at least one additional RTT measurement between the UE and at least one additional wireless node,

wherein the second differential RTT measurement is based on one or more additional RTT measurements between the third wireless node and one or more additional wireless nodes, or

a combination thereof.

23. The method of claim 1 , further comprising:

obtaining a third differential RTT measurement based on a fifth RTT measurement between a fourth wireless node and the first wireless node and a sixth RTT measurement between the fourth wireless node and the second wireless node; and

using the third differential RTT measurement to determine the positioning estimate.

24. The method of claim 1 , further comprising:

receiving, from the first wireless node, the second wireless node, or both, an indication of a first hardware group delay calibration capability,

wherein the second differential RTT measurement is triggered in response to the first hardware group delay calibration capability.

25. The method of claim 24 , wherein the first hardware group delay calibration capability is a dynamic indication or a static or semi-static indication.

26. The method of claim 24 , wherein another positioning estimate for another UE is determined based on a single differential RTT measurement based on wireless nodes involved with the another positioning estimate being associated with a second hardware group delay calibration capability that is more accurate than the first hardware group delay calibration capability.

27. The method of claim 1 , further comprising:

receiving, from the first wireless node, the second wireless node, or both, a request to trigger the second differential RTT measurement for hardware group delay calibration.

28. The method of claim 1 , further comprising:

selecting the third wireless node for hardware group delay calibration of the first wireless node and the second wireless node via the second RTT differential measurement based on one or more parameters.

29. The method of claim 28 , wherein the one or more parameters comprise channel conditions between the third wireless node and the first wireless node and the second wireless node.

30. The method of claim 29 ,

wherein the selection of the third wireless node is predetermined if each of the first wireless node, the second wireless node and the third wireless node are stationary nodes, and

wherein the selection of the third wireless node is dynamic if one or more of the first wireless node, the second wireless node and the third wireless node are mobile nodes.

31. A position estimation entity, comprising:

a memory;

at least one transceiver; and

at least one processor communicatively coupled to the memory and the at least one transceiver, the at least one processor configured to:

obtain a first differential round trip time (RTT) measurement based on a first RTT measurement between a user equipment (UE) and a first wireless node and a second RTT measurement between the UE and a second wireless node;

obtain a second differential RTT measurement based on a third RTT measurement between a third wireless node and the first wireless node and a fourth RTT measurement between the third wireless node and the second wireless node; and

determine a positioning estimate of the UE based at least in part on the first differential RTT measurement and the second differential RTT measurement.

32. The position estimation entity of claim 31 , wherein the first differential RTT measurement is triggered by the position estimation entity separately from the second differential RTT measurement.

33. The position estimation entity of claim 31 ,

wherein the first differential RTT measurement is triggered at a first frequency or based on a first triggering event, and

wherein the second differential RTT measurement is triggered at a second frequency or based on a second triggering event.