Notification of relay capabilities for UE-to-network relay functions

1. An apparatus comprising:

relay User Equipment (UE) enabled for UE-to-network relay and configured to announce relay capabilities during a synchronization process, the relay UE comprising:

a radio interface; and

a controller configured to scan for a reference signal from a synchronization source during the synchronization process, and to synchronize timing of the radio interface to the reference signal;

wherein the controller is further configured to generate, during the synchronization process, synchronization signals for synchronizing timing of the radio interface with other UEs in proximity for device-to-device (D2D) communication, to determine relay capabilities of the relay UE to act as a relay to re-transmit traffic between a remote UE and a network, and to insert an indication of the relay capabilities of the relay UE into the synchronization signals; and

wherein the radio interface is configured to transmit the synchronization signals over-the-air to the other UEs.

2. The apparatus of claim 1 wherein:

the controller is configured to insert the indication of the relay capabilities in a parameter of the synchronization signals, wherein the indication is selected from:

direct relay where the relay UE is in-coverage of a base station;

indirect relay where the relay UE is out-of-coverage of a base station but has D2D communication with another relay UE that is in-coverage of a base station; and

no relay where the relay UE is out-of-coverage of a base station, and does not have D2D communication with another relay UE that is in-coverage of a base station.

3. The apparatus of claim 1 wherein:

the controller is configured to determine a number of hops between the relay UE and the network over at least one of the other UEs, and to insert an indicator of the number of hops in the synchronization signals.

4. The apparatus of claim 1 wherein:

the controller is configured to determine a signal strength between the relay UE and the other UEs in proximity, and to insert an indicator of the signal strength in the synchronization signals.

5. The apparatus of claim 1 wherein:

the synchronization signals comprise D2D Synchronization Signals (D2DSS).

6. The apparatus of claim 1 wherein:

the controller is configured to receive the synchronization signals from the other UEs, to process the synchronization signals to identify the relay capabilities of the other UEs, and to store the relay capabilities of the other UEs.

7. A method of operating relay User Equipment (UE) enabled for UE-to-network relay to announce relay capabilities of the relay UE during a synchronization process, the method comprising:

scanning, by the relay UE, for a reference signal from a synchronization source;

synchronizing timing of a radio interface in the relay UE to the reference signal;

generating synchronization signals by the relay UE for synchronizing timing of the radio interface with other UEs in proximity for device-to-device (D2D) communication;

determining relay capabilities of the relay UE to act as a relay to re-transmit traffic between a remote UE and a network;

inserting an indication of the relay capabilities of the relay UE in the synchronization signals; and

transmitting the synchronization signals from the radio interface of the relay UE over-the-air to the other UEs.

8. The method of claim 7 wherein inserting an indication of the relay capabilities of the relay UE in the synchronization signals comprises:

inserting the indication of the relay capabilities in a parameter of the synchronization signals, wherein the indicator is selected from:

direct relay where the relay UE is in-coverage of a base station;

indirect relay where the relay UE is out-of-coverage of a base station but has D2D communication with another relay UE that is in-coverage of a base station; and

no relay where the relay UE is out-of-coverage of a base station, and does not have D2D communication with another relay UE that is in-coverage of a base station.

9. The method of claim 7 further comprising:

determining a number of hops between the relay UE and the network over at least one of the other UEs; and

inserting an indicator of the number of hops in the synchronization signals.

10. The method of claim 7 further comprising:

determining a signal strength between the relay UE and the other UEs in proximity; and

inserting an indicator of the signal strength in the synchronization signals.

11. The method of claim 7 wherein:

the synchronization signals comprise D2D Synchronization Signals (D2DSS).

12. The method of claim 7 further comprising:

receiving the synchronization signals from the other UEs;

processing the synchronization signals to identify the relay capabilities of the other UEs; and

storing the relay capabilities of the other UEs.

13. An apparatus comprising:

originating User Equipment (UE) enabled for UE-to-network relay, the originating UE comprising:

a controller configured to receive synchronization signals from a plurality of relay UEs for synchronizing the originating UE with the relay UEs in preparation for device-to-device (D2D) communication, wherein the controller is further configured to employ the synchronization signals to synchronize timing of radio resources between the originating UE and the relay UEs for the D2D communication, and

wherein the controller is further configured to process the synchronization signals to identify relay capabilities of the relay UEs to act as relays to re-transmit traffic between the originating UE and a network, and to determine a route for traffic toward the network based on the relay capabilities of the relay UEs in proximity; and

a radio interface configured to transmit the traffic toward the network over the route.

14. The apparatus of claim 13 wherein:

the controller is configured to determine the route for the traffic based on a number of hops from each of the relay UEs to the network.

15. The apparatus of claim 13 wherein:

the controller is configured to determine the route for the traffic based on a signal strength between each of the relay UEs and the originating UE.

16. A method of operating originating User Equipment (UE) enabled for UE-to-network relay, the method comprising:

receiving synchronization signals in the originating UE from a plurality of relay UEs for synchronizing the originating UE with the relay UEs prior to device-to-device (D2D) communication, wherein the originating UE and the relay UEs are configured to use the synchronization signals to synchronize timing of radio resources between the originating UE and the relay UEs for the D2D communication;

processing the synchronization signals to identify relay capabilities of the relay UEs to act as relays to re-transmit traffic between the originating UE and a network;

determining a route for traffic toward the network based on the relay capabilities of the relay UEs in proximity; and

transmitting the traffic toward the network over the route.

17. The method of claim 16 wherein determining the route for the traffic comprises:

determining the route for the traffic based on a number of hops from each of the relay UEs to the network.

18. The method of claim 16 wherein determining the route for the traffic comprises:

determining the route for the traffic based on a signal strength between each of the relay UEs and the originating UE.