Precision time protocol link time error calibration using over-the-air synchronization

1 . A method by a network node comprising:

determining a timing error associated with a closed loop comprising at least one radio link between two radio points, the timing error determined based on at least one timing measurement associated with the at least one radio link; and

adjusting timing information carried over a timing protocol link based on the timing error associated with the closed loop comprising the at least one radio link;

wherein determining the timing error associated with the closed loop comprises:

obtaining a PTP network topology associated with a first set of radio points, T, that includes the at least two radio points;

obtaining an Over-the-Air Synchronization (OAS) network topology associated with a second set of radio points, R, that includes the at least two radio points; and

selecting a set of network elements, N, that is an intersection of the first set of radio points, T, and the second set of radio points, R, and

wherein the PTP network topology and the OAS network topology form a connected graph.

2 . The method of claim 1 , wherein the timing protocol link comprises a Precision Time Protocol, PTP, link.

3 . The method of claim 1 , further comprising:

for an edge in the PTP network topology:

selecting an edge in the PTP network topology, the edge comprising a link between the two radio points;

determining a shortest path between the two radio points in the OAS network topology; and

calculating a PTP link time error for the edge based on a signed sum of the at least one timing error measurement associated with the shortest path in the OAS network between the two radio points.

4 . The method of claim 3 , further comprising determining at least one additional path between the two radio points in the OAS network and wherein the PTP link time error is calculated as a mean of the at least one timing error measurements associated with the shortest path and the at least one additional path.

5 . The method of claim 4 , further comprising repeating the step of determining at least one additional path between the two radio points in the OAS network for all edges in the PTP network topology.

6 . The method of claim 1 , further comprising:

defining all possible loops in the connected graph; and

determining at least one equation for each loop defined for the connected graph, wherein each one of the at least one equations expresses at least one unknown value associated with the PTP network topology in terms of the timing error determined based on at least one timing measurement associated with the at least one radio link.

7 . The method of claim 6 , wherein the possible loops comprises a plurality of loops, and the PTP link time error is calculated as a mean of each of the at least one unknown values expressed by the at least one equations.

8 . The method of claim 6 , further comprising determining that a matrix comprised of each of the at least one equations satisfies at least one condition for a solution of the at least one unknown value associated with the PTP network topology.

9 . The method of claim 2 , wherein adjusting the PTP link based on the timing error comprises:

configuring a PTP link asymmetry compensation on at least one edge of the PTP network topology.

10 . The method of claim 1 , wherein the PTP network topology is obtained from a transport network.

11 . The method of claim 10 , wherein the transport network comprises a fronthaul transport network or an backhaul transport network.

12 . The method of claim 1 , wherein the OAS network topology is received from a RAN network.

13 . The method of claim 1 , wherein the closed loop comprises a plurality of radio links between a plurality of radio points.

14 . A network node adapted to:

determine a timing error associated with a closed loop comprising at least one radio link between two radio points, the timing error determined based on at least one timing measurement associated with the at least one radio link; and

adjust timing information carried over a timing protocol link based on the timing error associated with the closed loop comprising the at least one radio link;

wherein, when determining the timing error associated with the closed loop, the network node is adapted to:

obtain a PTP network topology associated with a first set of radio points, T, that includes the at least two radio points;

obtain an Over-the-Air Synchronization (OAS) network topology associated with a second set of radio points, R, that includes the at least two radio points;

select a set of network elements, N, that is an intersection of the first set of radio points, T, and the second set of radio points, R, and

wherein the PTP network topology and the OAS network topology form a connected graph.

15 . The network node of claim 14 , wherein the timing protocol link comprises a Precision Time Protocol, PTP, link.

16 . The network node of claim 14 , further adapted to:

for an edge in the PTP network topology:

select an edge in the PTP network topology, the edge comprising a link between the two radio points;

determine a shortest path between the two radio points in the OAS network topology; and

calculate a PTP link time error for the edge based on a signed sum of the at least one timing error measurement associated with the shortest path between the two radio points.

17 . The network node of claim 16 , further adapted to determine at least one additional path between the two radio points in the OAS network, and wherein the PTP link time error is calculated as a mean of the at least one timing error measurements associated with the shortest path and the at least one additional path.

18 . The network node of claim 14 , further adapted to:

define all possible loops in the connected graph; and

determine at least one equation for each loop defined for the connected graph, wherein each one of the at least one equations expresses at least one unknown value associated with the PTP network topology in terms of the timing error determined based on at least one timing measurement associated with the at least one radio link.

19 . The network node of claim 18 , wherein the possible loops comprises a plurality of loops, and wherein the PTP link time error is calculated as a mean of each of the at least one unknown values expressed by the at least one equations.

20 . The network node of claim 18 , further adapted to determine that at least one condition for a solution of the at least one unknown value associated with the PTP network topology is satisfied.

21 . The network node of claim 14 , wherein, when adjusting the PTP link based on the timing error, the network node is adapted to:

configure a PTP link asymmetry compensation on at least one edge of the PTP network topology.

22 . The network node of claim 14 , wherein the PTP network topology is obtained from a transport network.

23 . The network node of claim 22 , wherein the transport network comprises a Centralized-Radio Access Network (C-RAN) transport network or an Elastic-Radio Access Network (E-RAN) transport network.

24 . The network node of claim 14 , wherein the OAS network topology is received from a RAN network.