Handover method and apparatus in a wireless communications network
View Patent ↗A method for handover in a wireless communications network includes the step of communicating information between a target network node and a source network node to enable the source network node to identify and to distinguish types of failures prior to, during or after handover. The information may relate to: “Handover command not received” due to RLF prior to handover or Handover command failure experienced in the source cell; or “Handover failure” where “Handover command received” is followed by Access failure in the target cell. The method is applicable, for example, to networks in accordance with LTE.
1. A method for handover in a wireless communications network, comprising:
at a selected network node, receiving a re-establishment cause from a mobile terminal during call re-establishment of the mobile terminal with the selected network node; and
at the selected network node, sending the re-establishment cause to a source network node to enable the source network node to identify failures related to an attempted handover of the mobile terminal from the source network node to a target network node.
2. The method as claimed in claim 1 wherein different values for the re-establishment cause enable the source network node to identify and distinguish handover failure types occurring i) prior to the attempted handover, ii) during the attempted handover and prior to a successful handover command, and iii) during the attempted handover and after the handover command.
3. The method as claimed in claim 1 wherein the handover failure relates to a Radio Link Failure (RLF) prior to the attempted handover and the re-establishment cause is a value indicative of the RLF failure.
4. The method as claimed in claim 1 , wherein the handover failure relates to a handover command failure in a source cell associated with the source network node and the re-establishment cause is a value indicative of the handover command failure.
5. The method as claimed in claim 1 , wherein the handover failure relates to an access failure in a target cell associated with the target network node and the re-establishment cause is a value indicative of the access failure.
6. The method as claimed in claim 1 wherein the re-establishment cause is received in a request message from the mobile terminal.
7. The method as claimed in claim 1 wherein the re-establishment cause is sent in a release message to the source network node.
8. The method as claimed in claim 1 wherein the network is implemented in accordance with LTE standards.
9. The method as claimed in claim 8 wherein the re-establishment cause is included in an X2 interface message and the X2 interface message has an additional purpose.
10. The method as claimed in claim 9 wherein the re-establishment cause is included in an extension of an X2 interface UE Context Release message.
11. The method as claimed in claim 1 wherein the re-establishment cause is used to adapt handover parameters for a subsequent attempted handover.
12. A network node in a wireless communications network, comprising
a receiver configured to receive a re-establishment cause from a mobile terminal during call re-establishment of the mobile terminal with the network node; and
a transmitter configured to send the re-establishment cause to a source network node to enable the source network node to identify failures related to an attempted handover of the mobile terminal from said source network node to a target network node.
13. The network node as claimed in claim 12 wherein the handover failure relates to a Radio Link Failure (RLF) prior to the attempted handover and the re-establishment cause is a value indicative of the RLF failure.
14. The network node as claimed in claim 12 wherein different values for the re-establishment cause enable the source network node to identify and distinguish handover failure types occurring i) prior to the attempted handover, ii) during the attempted handover and prior to a successful handover command, and iii) during the attempted handover and after the handover command.
15. The network node as claimed in claim 12 wherein the handover failure relates to a handover command failure in a source cell associated with the source network node and the re-establishment cause is a value indicative of the handover command failure.
16. The network node as claimed in claim 12 wherein the handover failure relates to an access failure in a target cell associated with the target network node and the re-establishment cause is a value indicative of the access failure.
17. The network node as claimed in claim 12 wherein the re-establishment cause is received in a request message from the mobile terminal.
18. The network node as claimed in claim 12 wherein the re-establishment cause is sent in a release message to the source network node.
19. A method for performing a handover in a wireless communications network, comprising:
receiving a request message from a mobile terminal at a selected network node during call re-establishment of the mobile terminal with the selected network node, the request message including a re-establishment cause; and
sending a release message from the selected network node to a source network node in conjunction with the call re-establishment, the release message including the re-establishment cause to enable the source network node to identify failures related to an attempted handover of the mobile terminal from the source network node to a target network node.
20. The method as claimed in claim 19 wherein different values for the re-establishment cause enable the source network node to identify and distinguish handover failure types from i) a Radio Link Failure (RLF) associated with the source network node prior to the attempted handover, ii) a handover command failure associated with the source network node during the attempted handover, and iii) an access failure associated with the target network node during the attempted handover.