Method of providing communication over a mobile communication network

1. A method of providing communication over a mobile communication network comprising two or more fixed nodes each operating a fixed radio cell for serving one or more user equipments via a first radio interface, wherein each of the fixed radio cells is identified by a physical cell ID, selected out of a set of N physical cell IDs, and one or more mobile relay nodes served by the two or more fixed nodes via a second radio interface, the one or more mobile relay nodes each operating a mobile radio cell for serving one or more user equipments via a third radio interface, wherein each of the mobile radio cells is identified by a physical cell ID selected out of the set of N physical cell IDs, wherein the method comprises:

dynamically assigning a physical cell ID of the set of N physical cell IDs to the one or more mobile radio cells,

measuring a signal strength of a serving fixed radio cell and a signal strength of surrounding fixed radio cells by a mobile relay node,

if the signal strength of a surrounding fixed radio cell exceeds the signal strength of the serving fixed radio cell, sending a handover request to the serving fixed node by the mobile relay node and executing a handover acceptance procedure between the serving fixed node and a target fixed node, and

if the handover is accepted, then assigning a new physical cell ID of the set of N physical cell IDs to a mobile radio cell operated by the mobile relay node.

2. The method according to claim 1 , wherein the method comprises:

providing by a fixed node of the two or more fixed nodes an internal list which stores information about a physical cell ID of the set of N physical cell IDs currently assigned to a fixed radio cell operated by the fixed node, and information about a physical cell ID of the set of N physical cell IDs currently assigned to a surrounding fixed radio cell operated by a surrounding fixed node, and/or information about a physical cell ID of the set of N physical cell IDs currently assigned to a mobile radio cell operated by a mobile relay node, in particular a mobile relay node served by the fixed node, and

wherein dynamically assigning the physical cell ID comprises selecting by the fixed node a physical cell ID of the set of N physical cell IDs which according to the internal list is not yet currently assigned.

3. The method according to claim 2 , wherein the method comprises:

receiving by the fixed node from a surrounding fixed node information about a physical cell ID of the set of N physical cell IDs currently assigned to a surrounding fixed radio cell operated by the surrounding fixed node and/or information about a physical cell ID of the set of N physical cell IDs currently assigned to a surrounding mobile radio cell operated by a surrounding mobile relay node served by the surrounding fixed node, and updating the internal list by means of the received information.

4. The method according to claim 2 , wherein the method comprises:

storing, by the mobile relay node, information about physical cell IDs of the surrounding fixed and/or mobile radio cells,

sending the information to the fixed node and updating the internal list by means of the received information.

5. The method according to claim 1 , wherein the method comprises:

transmitting the new physical cell ID from the serving fixed node or the target fixed node to the mobile relay node and

switching from an old physical cell ID to the new physical cell ID by using the new physical cell ID by the mobile relay node to identify the mobile radio cell operated by said mobile relay node.

6. The method according to claim 5 , wherein the new physical cell ID of the mobile radio cell operated by said mobile relay node is transmitted from the target fixed node by means of a RRC message to the mobile relay node via a UE if interface of the second radio interface.

7. The method according to claim 5 , wherein the new physical cell ID of the mobile radio cell operated by said mobile relay node is transmitted from the target fixed node by means of a X2 message to the mobile relay node via a Un interface of the second radio interface.

8. The method according to claim 1 comprising:

switching from an old physical cell ID to the new physical cell ID by using the new physical cell ID by the mobile relay node to identify the mobile radio cell operated by said mobile relay node,

detecting by the user equipment that the mobile radio cell identified by the new physical cell ID is the strongest radio cell,

sending by the user equipment a handover request to the mobile relay node operating the mobile radio cell identified by the new physical cell ID and executing a handover procedure to the mobile radio cell identified by the new physical cell ID.

9. The method according to claim 1 comprising:

switching from an old physical cell ID to the new physical cell ID by using the new physical cell ID by the mobile relay node to identify the mobile radio cell operated by said mobile relay node,

detecting by the user equipment that the old physical cell ID is not longer transmitted, whereby the user equipment suffers a radio link failure,

after detection of the radio link failure transmitting a RRC connection re-establishment request by the user equipment to the mobile relay node, and

transmitting a RRC connection re-establishment message from the mobile relay node to the user equipment via the third radio interface.

10. The method according to claim 1 comprising:

switching from an old physical cell ID to the new physical cell ID by using the new physical cell ID by the mobile relay node to identify the mobile radio cell operated by said mobile relay node and

sending a RRC connection reconfiguration message to all active user equipments served by the mobile radio cell identified by the old physical cell ID, the RRC connection reconfiguration message forcing the user equipments to connect to the mobile radio cell identified by the new physical cell ID.

11. The method according to claim 10 , wherein the method comprises:

sending the RRC connection reconfiguration message before switching from the old physical cell ID to the new physical cell ID,

triggering a handover timer of the user equipment based on the reception of said RRC connection reconfiguration message and

connecting the user equipment to the mobile radio cell identified by the new physical cell ID as soon as the handover timer expires or as long as the handover timer is still running.

12. The method according to claim 1 , wherein the method comprises:

switching at a specific time stamp from an old physical cell ID to the new physical cell ID by using the new physical cell ID by the mobile relay node to identify the mobile radio cell operated by said mobile relay node and

transmitting a broadcast message comprising the new physical cell ID and the time stamp towards the user equipment served by the mobile radio cell identified by the old physical cell ID.

13. A mobile relay node being provisioned to:

operate a mobile radio cell for serving one or more user equipments via a third radio interface, wherein the mobile radio cell is identified by a physical cell ID selected out of a set of N physical cell IDs,

communicate via a second radio interface with one or more fixed nodes each operating a fixed radio cell for serving one or more user equipments via a first radio interface, wherein each of the fixed radio cells is identified by a physical cell ID selected out of the set of N physical cell IDs,

on assignment of a physical cell ID of the set of N physical cell IDs as new physical cell ID of the mobile radio cell, switch from an old physical cell ID to the new physical cell ID,

measure a signal strength of a serving fixed radio cell and a signal strength of surrounding fixed radio cells,

if the signal strength of a surrounding fixed radio cell exceeds the signal strength of the serving fixed radio cell, send a handover request to the serving fixed node such that a handover acceptance procedure is executed between the serving fixed node and a target fixed node, and

if the handover is accepted, then a new physical cell ID of the set of N physical cell IDs is assigned to a mobile radio cell operated by the mobile relay node.