Radio bearer dependent forwarding for handover
View Patent ↗This invention employs an inherent tradeoff in a radio bearer dependent data handling method for intra-E-UTRA handoffs. For user equipment using real time data, the source node forwards to the target node not yet acknowledged real time service data units and disconnects. This makes the handoff latency short at the expense of data traffic between nodes. For user equipment not needing real time data, the source node continues to receive user equipment acknowledgements during a time out period and only forwards service data units acknowledged during the time out period. This reduces X2 interface traffic between the source and target nodes but extends the handoff latency.
1. A method of handoff of user equipment between a source node and a target node comprising the steps of:
determining to handoff the user equipment from the source node to the target node;
determining if the user equipment is employing real time data;
if the user equipment is employing real time data
forwarding from the source node to the target node all real time service data units not yet acknowledged by the user equipment,
disconnecting the user equipment from the source node, and
connecting the user equipment to the target node; and if the user equipment is not employing real time data
continuing to receive acknowledgement from the user equipment at the source node for a predetermined time out period,
following the time out period forwarding from the source node to the target node all service data units not yet acknowledged by the user equipment,
disconnecting the user equipment from the source node, and
connecting the user equipment to the target node.
2. The method of claim 1 , wherein:
said steps of forwarding from the source node to the target node all real time service data units not yet acknowledged by the user equipment employs transmission via an X2 interface.
3. The method of claim 1 , further comprising:
transmitting a handoff indicator message from the source node to the user equipment following determining to handoff the user equipment, the handoff indicator message containing relevant system information for the user equipment to connect to the target node.
4. The method of claim 3 , further comprising:
simultaneously with transmitting the handoff indicator message, transmitting handoff request message from the source node to the target node.
5. The method of claim 4 , further comprising:
upon receiving a handoff request acknowledgement at the source node from the target node
ceasing downlink data transmission from the source node to the user equipment, and
forwarding downlink data destined for the user equipment and not yet transmitted from the source node to the target node.
6. The method of claim 4 , further comprising:
following determining to handoff the user equipment, transmitting a handoff command from the source node to the user equipment;
following determining if the user equipment is employing real time data, determining if the user equipment is employing transmission control protocol data;
if the user equipment is employing transmission control protocol data and a radio link control status report had been not received before the time out, re-transmitting handoff command from the source node to the target node; and
if the user equipment is not employing transmission control protocol data
disconnecting the user equipment from the source node, and
connecting the user equipment to the target node.
7. The method of claim 6 , wherein:
said step of transmitting a handoff command employs a low modulation and coding scheme signal on a downlink synchronization channel.