Rx-tx time difference generation, measurement and reporting with neighboring base stations
A method performed by a first base station for positioning in a cellular communication system includes receiving, at the first base station, a signal transmitted by a second base station and estimating a Time of Arrival (TOA) of the received signal at the first base station according to a clock of the first base station. The method further includes determining a delta value that is a function of an amount of time between the TOA of the received signal at the first base station and a time reference at the first base station and performing either, (a) providing the delta value to a positioning estimation entity within the cellular communications system or (b) using the delta value at the first base station to reduce a time synchronization error between the first base station and the second base station, or (c) passing the delta value to a User Equipment (UE).
1. A method performed by a first base station in a radio access network of a cellular communications system, the method comprising:
receiving, at the first base station, a signal transmitted by a second base station;
estimating a Time of Arrival (TOA) of the received signal at the first base station according to a clock of the first base station;
determining a delta value that is a function of an amount of time between the TOA of the received signal at the first base station according to the clock of the first base station and a time reference at the first base station; and
either:
(a) providing the delta value to a positioning estimation entity within the cellular communications system; or
(b) using the delta value at the first base station to reduce a time synchronization error between the first base station and the second base station; or
(c) passing the delta value to a User Equipment (UE).
2. The method of claim 1 , wherein receiving the signal comprises receiving the signal via a Line of Sight (LOS) propagation path.
3. The method of claim 2 , wherein the signal is a Positioning Reference Signal (PRS).
4. The method of claim 2 , wherein the signal is a data signal.
5. The method of claim 2 , wherein a propagation delay between the first base station and the second base station via the LOS propagation path is known a priori.
6. The method of claim 1 , wherein receiving the signal comprises receiving the signal via a first arrived path of an identifiable reflected or diffracted path between the first base station and the second base station.
7. The method of claim 6 , wherein a propagation delay between the first base station and the second base station via the first arrived path is known a priori.
8. The method of claim 1 , wherein the signal is transmitted from the first base station using transmit beamforming.
9. The method of claim 1 , wherein receiving the signal comprises receiving the signal using receive beamforming.
10. The method of claim 1 , comprising providing the delta value to a positioning estimation entity within the cellular communications system.
11. The method of claim 10 , wherein the positioning estimation entity is a location server.
12. The method of claim 10 , wherein the positioning estimation entity is a wireless communication device.
13. The method of claim 10 , wherein determining the delta value comprises determining the delta value in accordance with an original timing of the first base station.
14. The method of claim 1 , comprising using the delta value at the first base station to reduce the time synchronization error between the first base station and the second base station.
15. The method of claim 14 , wherein determining the delta value comprises setting the delta value to a value that reduces a time synchronization error between the first base station and the second base station.
16. The method of claim 1 , wherein the time reference at the first base station is a time of transmission of a transmitted signal by the first base station according to the clock of the first base station.
17. The method of claim 16 , wherein the delta value is a difference between the time of transmission of the transmitted signal by the first base station according to the clock of the first base station and the TOA of the received signal at the first base station according to the clock of the first base station.
18. The method of claim 1 , wherein the time reference at the first base station is a start of a downlink radio frame at the first base station, a start of a downlink subframe at the first base station, a start of a downlink slot at the first base station, or a start of a downlink symbol at the first base station.
19. A first base station for a radio access network of a cellular communications system, the first base station comprising:
processing circuitry in communication with a transceiver, the processing circuitry configured to cause the first base station to:
receive, at the first base station, a signal transmitted by a second base station;
estimate a Time of Arrival, (TOA) of the received signal at the first base station according to a clock of the first base station;
determine a delta value that is a function of an amount of time between the TOA of the received signal at the first base station according to the clock of the first base station and a time reference at the first base station; and
either (a) provide the delta value to a positioning estimation entity within the cellular communications system or (b) use the delta value at the first base station to reduce a time synchronization error between the first base station and the second base station or (c) pass the delta value to a User Equipment (UE).
20. A method performed by a positioning estimation entity in a cellular communications system for determining an estimate of a position of a wireless communication device, the method comprising:
receiving, from a plurality of base stations in a radio access network of the cellular communications system, a plurality of delay values each being a delay value for a different pair of base stations (BS i, BS j), wherein for each pair of base stations (BS i, BS j) the corresponding delay value is a function of an amount of time between a Time of Arrival, TOA, of a signal received at BS i from BS j according to a clock of BS i and a time reference at BS i;
obtaining Time Difference of Arrival, TDOA, (TDOA) measurements for different pairs of base stations (BS i, BS j) made by the wireless communication device; and
computing an estimate of the position of the wireless communication device based on: (a) the TDOA measurements, (b) the delay values received for the different pairs of base stations (BS i, BS j) for which the TDOA measurements were made, and (c) known propagation delays for the different pairs of base stations (BS i, BS j) for which the TDOA measurements were made.
21. The method of claim 20 , wherein computing the estimate of the position of the wireless communication device comprises:
for each of the TDOA measurements, adjusting the TDOA measurement based on the delay value received for the corresponding pair of base stations (BS i, BS j) and the known propagation delay for the corresponding pair of base stations (BS i, BS j); and
computing the estimate of the position of the wireless communication device using the adjusted TDOA measurements.
22. The method of claim 21 , wherein adjusting the TDOA measurement comprises subtracting the delay value received for the corresponding pair of base stations (BS i, BS j) and the known propagation delay for the corresponding pair of base stations (BS i, BS j) from the TDOA measurement.
23. The method of claim 20 , wherein the known propagation delays are known Line of Sight, LOS, (LOS) propagation delays for the different pairs of base stations (BS i, BS j) for which the TDOA measurements were made.
24. The method of claim 20 , wherein the known propagation delays are known first arrived path propagation delays for the different pairs of base stations (BS i, BS j) for which the TDOA measurements were made.