Physical layer non-line-of-sight path discrimination based on polarization

1. A method at a wireless device of determining a line-of-sight (LOS) path between a transmitter and the wireless device, comprising:

receiving, from the transmitter, a first reference signal transmitted on a first antenna port and a second reference signal transmitted on a second antenna port, the first reference signal having a first polarization and the second reference signal having a second polarization with known difference to the first polarization;

comparing multi-path channels estimated from reception of the first reference signal and the second reference signal to multi-path channels expected from the first reference signal and the second reference signal when transmitted along the LOS path between the transmitter and the wireless device; and

determining which path of the estimated multi-path channels corresponds to the LOS path between the transmitter and the wireless device based on the comparison.

2. The method of claim 1 , wherein the comparing comprises:

comparing a receive power of the first reference signal and a receive power of the second reference signal to expected receive powers of the first reference signal and the second reference signal.

3. The method of claim 2 , wherein the determining comprises:

determining whether the receive power of the first reference signal and the receive power of the second reference signal matches the expected receive powers of the first reference signal and the second reference signal.

4. The method of claim 1 , wherein the first polarization and the second polarization are rotated relative to previous polarizations of the first reference signal and the second reference signal.

5. The method of claim 4 , wherein the previous polarizations of the first reference signal and the second reference signal are rotated by the transmitter randomly or uniformly.

6. The method of claim 4 , further comprising:

receiving an indication from the transmitter of how the first polarization and the second polarization are rotated; and

determining an expected polarization of each of the first and second reference signals based on the indication.

7. The method of claim 6 , wherein the determining comprising:

determining, based on the first polarization matching the expected polarization of the first reference signal, that the first reference signal followed the LOS path.

8. The method of claim 7 , wherein the determining further comprises:

determining, based on the second polarization not matching the expected polarization of the second reference signal, that the second reference signal is a reflection.

9. The method of claim 6 , wherein the indication is received over Layer 1 signaling, higher layer signaling, downlink control information (DCI) signaling, or radio resource control (RRC) signaling.

10. The method of claim 1 , wherein the comparing comprises:

comparing a first vector measurement of a measurement of the first reference signal and a second vector measurement of a measurement of the second reference signal to expected vector measurements of the first reference signal and the second reference signal.

11. The method of claim 10 , wherein the first and second vector measurements comprise first and second amplitude measurements, respectively, of the first reference signal and the second reference signal.

12. The method of claim 10 , wherein the measurements of the first reference signal and the second reference signal comprise first and second time of arrival (ToA) measurements, respectively, of the first reference signal and the second reference signal.

13. The method of claim 10 , wherein the determining comprises:

determining which of the first vector measurement and the second vector measurement of the second reference signal matches the expected vector measurements of the first reference signal and the second reference signal.

14. The method of claim 1 , further comprising:

reporting, to a positioning entity, a ToA of the first reference signal, the first polarization, a ToA of the second reference signal, and the second polarization to enable the positioning entity to determine whether the first reference signal or the second reference signal reflected off of a ground surface near the wireless device based on the ToA of the first reference signal, the first polarization, the ToA of the second reference signal, and the second polarization.

15. The method of claim 1 , wherein the determining comprises:

determining whether the first reference signal or the second reference signal reflected off of a ground surface near the wireless device based on a ToA of the first reference signal, the first polarization, a ToA of the second reference signal, and the second polarization.

16. The method of claim 1 , further comprising:

sending, to the transmitter, an indication that the wireless device is capable of determining a polarization of a reference signal.

17. The method of claim 1 , further comprising:

receiving, from the transmitter, an indication that the first and second reference signals are quasi-co-located (QCL) across different polarizations.

18. The method of claim 1 , further comprising:

reporting, to the transmitter, a ToA of the path of the estimated multi-path channels that corresponds to the LOS path.

19. The method of claim 1 , wherein the comparing comprises:

calculating, for each of the first reference signal and the second reference signal, a round-trip-time (RTT) between the transmitter and the receiver using an RTT positioning procedure.

20. The method of claim 1 , wherein the first reference signal is transmitted on a first bandwidth segment and the second reference signal is transmitted on a second bandwidth segment.

21. The method of claim 1 , wherein:

the wireless device comprises a user equipment and the transmitter comprises a gNode B,

the wireless device comprises a first gNode B and the transmitter comprises a second gNode B, or

the wireless device comprises a first gNode B and the transmitter comprises a user equipment.

22. The method of claim 1 , further comprising:

estimating a location of the wireless device based on a ToA of the path of the estimated multi-path channels that corresponds to the LOS path between the transmitter and the wireless device.

23. A method at a wireless device, comprising:

receiving, from a transmitter, at least a first reference signal and a second reference signal, the first reference signal transmitted on a first antenna port with a first transmitted polarization and the second reference signal transmitted on a second antenna port with a second transmitted polarization; and

estimating at least a first received polarization of the first reference signal and a second received polarization of the second reference signal to determine whether the first reference signal, the second reference signal, or both followed a line of sight (LOS) path between the transmitter and the wireless device.

24. The method of claim 23 , further comprising:

comparing the first received polarization to an expected received polarization associated with the LOS path.

25. The method of claim 24 , further comprising:

determining that the first reference signal is a non-line of sight (NLOS) signal based on the comparing.

26. The method of claim 24 , further comprising:

determining that the first reference signal is an LOS signal based on the comparing.

27. The method of claim 23 , further comprising:

determining a time of arrival (ToA) of the first reference signal.

28. The method of claim 23 , further comprising:

determining a ToA for the first reference signal and a ToA for the second reference signal; and

transmitting, to a network apparatus, at least the ToA for the first reference signal, the ToA for the second reference signal, the first received polarization, and the second received polarization.

29. A wireless device, comprising:

a memory;

at least one transceiver; and

at least one processor, the at least one processor configured to:

receive, from a transmitter device via the at least one transceiver, a first reference signal transmitted on a first antenna port and a second reference signal transmitted on a second antenna port, the first reference signal having a first polarization and the second reference signal having a second polarization with known difference to the first polarization;

compare multi-path channels estimated from reception of the first reference signal and the second reference signal to multi-path channels expected from the first reference signal and the second reference signal when transmitted along a line-of-site (LOS) path between the transmitter and the wireless device; and

determine which path of the estimated multi-path channels corresponds to the LOS path between the transmitter and the wireless device.

30. The wireless device of claim 29 , wherein:

the at least one processor being configured to compare comprises the at least one processor being configured to compare a receive power of the first reference signal and a receive power of the second reference signal to expected receive powers of the first reference signal and the second reference signal, and

the at least one processor being configured to determine comprises the at least one processor being configured to determine whether the receive power of the first reference signal and the receive power of the second reference signal matches the expected receive powers of the first reference signal and the second reference signal.

31. The wireless device of claim 29 , wherein the at least one processor being configured to compare comprises the at least one processor being configured to:

compare a first vector measurement of a measurement of the first reference signal and a second vector measurement of a measurement of the second reference signal to expected vector measurements of the first reference signal and the second reference signal.

32. The wireless device of claim 29 , wherein the at least one processor being configured to determine comprises the at least one processor being configured to:

determine whether the first reference signal or the second reference signal reflected off of a ground surface near the wireless device based on a ToA of the first reference signal, the first polarization, a ToA of the second reference signal, and the second polarization.

33. The wireless device of claim 29 , wherein the at least one processor is further configured to:

estimate a location of the wireless device based on a ToA of the path of the estimated multi-path channels that corresponds to the LOS path between the transmitter and the wireless device.

34. A wireless device, comprising:

a memory;

at least one transceiver; and

at least one processor, the at least one processor configured to:

receive, from a transmitter device via the at least one transceiver, at least a first reference signal and a second reference signal, the first reference signal transmitted on a first antenna port with a first transmitted polarization and the second reference signal transmitted on a second antenna port with a second transmitted polarization; and

estimate at least a first received polarization of the first reference signal and a second received polarization of the second reference signal to determine whether the first reference signal, the second reference signal, or both followed a line of sight (LOS) path between the transmitter and the wireless device.

35. The wireless device of claim 34 , wherein the at least one processor is further configured to:

compare the first received polarization to an expected received polarization associated with the LOS path.

36. The wireless device of claim 34 , wherein the at least one processor is further configured to:

determine a ToA for the first reference signal and a ToA for the second reference signal; and

cause the at least one transceiver to transmit, to a network apparatus, at least the ToA for the first reference signal, the ToA for the second reference signal, the first received polarization, and the second received polarization.