Method and apparatus for radio link failure recovery in a wireless communications network
In a wireless network, for example, an LTE network, the context information relating to a mobile terminal UE is transmitted to a plurality of network nodes eNB 2, 3 and 4 from a source network node, eNB 1 . One of the eNB 2 is a handover target node and also reserves resources for the UE in anticipation of receiving it after handover. The other eNBs 3 and 4 do not reserve resources. In the event of radio link failure, the UE may attach to one of the designated eNBs 3 and 4 that have not reserved resources, but that do recognize the UE because they have received its context. The method reduces the likelihood of the UE needing to go via the time consuming IDLE state while only reserving resources at a handover target eNB.
1. A method for radio link failure recovery in a wireless communications network, including the steps of:
selecting a network node as a handover target in the event of handover of a mobile terminal from a source network node;
sending to the handover target network node context information for said mobile terminal and an indication to the handover target network node to reserve resources for said mobile terminal, the indication being a handover request message including an indicator which is set to indicate that resources should be reserved for the mobile terminal;
designating a network node as a handover candidate in the event of failure of a radio link between the mobile terminal and the source network node; and
sending to the designated handover candidate network node context information for said mobile terminal and an indication to the designated handover candidate network node not to reserve resources for said mobile terminal, the indication being a handover request message including an indicator which is set to indicate that resources should not be reserved for the mobile terminal.
2. The method as claimed in claim 1 and wherein the act of designating includes designating a plurality of network nodes as handover candidate network nodes in the event of failure of the radio link between the mobile terminal and the source network node and wherein the act of sending includes sending context information for said mobile terminal to each designated handover candidate network node and wherein the indication is sent to each designated handover candidate network node not to reserve resources for said mobile terminal.
3. The method as claimed in claim 1 further including following radio link failure, when the mobile terminal attaches to a network node, the network node to which the mobile terminal is attached requesting the source network node to release resources.
4. The method as claimed in claim 3 and further including the source network node requesting those network nodes, except that network node to which the mobile terminal is attached, that have reserved resources to release them.
5. The method as claimed in claim 1 and including the handover target network node that has reserved resources releasing them after a predetermined period of time following the request to it to reserve resources.
6. The method as claimed in claim 1 and including a network node that has stored context information discarding it after a predetermined period of time.
7. The method as claimed in claim 1 further including following radio link failure and attachment of the mobile terminal to a network node, the source network node informing other network nodes of the attachment.
8. The method as claimed in claim 1 further including following radio link failure and attachment of the mobile terminal to a network node, other nodes discarding the context information of the mobile terminal.
9. The method as claimed in claim 1 further including sending a request message to network nodes with an indicator which is set to indicate that resources should, or should not, be reserved for the mobile terminal.
10. The method as claimed in claim 1 wherein the network is in accordance with Long Term Evolution (LTE) specifications.
11. The method as claimed in claim 10 further including sending a request message to network nodes with an indicator which is set to indicate that resources should, or should not, be reserved for the mobile terminal, the request message being a Handover_Request message and the indicator being an allocation bit included in the Handover_Request message.
12. The method as claimed in claim 11 further including sending a Handover_Request_ack message in response to the Handover_Request message only by network nodes that have reserved resources.
13. The method as claimed in claim 10 further including following radio link failure and attachment of the mobile terminal to a network node, the network node to which the mobile terminal is attached sending a Release_Resource message to the source network node and the source network node sending a Free_Resource message to all other network nodes that have sent a Handover_Request_ack message.
14. A wireless communications network comprising
a plurality of nodes, a node being designated as a handover candidate to accept a mobile terminal in the event of failure of a radio link between the mobile terminal and a source network node; and
wherein the designated handover candidate network node is arranged to receive context information for said mobile terminal and an indication not to reserve resources for said mobile terminal, the indication being a handover request message including an indicator which is set to indicate that resources should be reserved for the mobile terminal.