Over-the-air synchronization of radio nodes in a radio access network

1. A method for synchronizing timing in phase and frequency of clocks associated with a plurality of radio nodes (RNs) in a small cell radio access network (RAN) having an access controller operatively coupled to each of the RNs, comprising:

generating, for each given RN in the RAN, a donor list representing an ordered list of potential wireless access points that are able to serve as a source of a wireless sync signal for the given RN;

distributing the donor lists to the respective RNs; and

selecting, by each of the RNs, an access point from their respective donor lists to use as a sync signal source, each of the RNs synchronizing their respective clocks in phase and frequency using wireless sync signals received from the respective selected access points.

2. The method of claim 1 wherein the generating and distributing of the donor list are performed by the access controller.

3. The method of claim 2 further comprising, receiving, at the access controller, information concerning a current sync status of the RNs.

4. The method of claim 1 further comprising assigning a score to each sync signal source included on the donor lists, the scores ranking a quality of the access points when used as a sync signal source.

5. The method of claim 1 wherein generating the donor list includes generating a network topology.

6. The method of claim 5 wherein generating the network topology includes generating a directed graph having nodes corresponding to the RNs in the RAN.

7. The method of claim 6 wherein generating the directed graph includes expanding the directed graph using data obtained from REM scans to obtain a sync tree.

8. The method of claim 7 further comprising expanding the directed graphs using a minimum spanning tree algorithm.

9. The method of claim 8 further comprising expanding the directed graph to minimize a depth of the sync tree from a root node serving as a master synchronization source to any child node, the depth of the sync tree being measured in units of hops from the root node to any given child node.

10. The method of claim 9 wherein minimizing the depth of the sync tree includes assigning weights to edges in the minimum spanning tree algorithm, the weights being a function of signal quality and a logical distance in units of hops.

11. The method of claim 9 wherein the master synchronization source is a macro cell.

12. The method of claim 7 further comprising coordinating a boot order of the RNs in the RAN in accordance with the sync tree such that radio nodes nearest to the root node of the sync tree in units of hops are instructed to boot up first and radio nodes most remote from the root node in units of hops are instructed to boot up last.

13. The method of claim 7 further comprising coordinating a muting pattern such that a radio node is prevented from transmitting when attempting to obtain a sync signal or when ancestor nodes of the radio node in the sync tree are listening for the synch signal.

14. The method of claim 1 wherein the RNs periodically provide the access controller with information concerning their current sync status.

15. The method of claim 1 further comprising selecting, by a given one of the radio nodes, another access point from the donor list to use as a sync signal source when synchronization to a previously selected access point is lost.

16. The method of claim 1 where the access points include macrocells and RNs in the RAN.