Systems and methods for joint handover of user equipment and secondary cell group in 3GPP LTE dual connectivity
Systems and methods provide a joint handover process wherein a user equipment (UE) and at least one secondary node remain connected to each other and are handed over together from a first master node to a second master node. Thus, a re-establishment procedure with the at least one secondary node is avoided.
1. An Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Node B (eNB) comprising:
a wireless transceiver to communicate with a user equipment (UE);
a processor configured to:
establish a connection as a serving master eNB (MeNB) through the wireless transceiver to the UE, the UE in dual connectivity with the serving MeNB and a secondary eNB (SeNB);
determine to handover the UE from the serving MeNB to a target MeNB; and
in response to the determination, handover both the UE and the SeNB to the target MeNB,
wherein to handover the SeNB to the target MeNB, the processor:
sends a handover request to the target MeNB, the handover request to instruct the target MeNB to keep a secondary cell group (SCG) corresponding to the SeNB, and
sends a command to the SeNB comprising a list of cells to keep in the SCG and instructions to change the SeNB to a master cell group (MCG) corresponding to the target MeNB.
2. The eNB of claim 1 , wherein the wireless transceiver is configured to receive a measurement report from the UE indicating at least a strength of signals received by the UE from the eNB, and wherein the processor is further configured to:
process the measurement report to determine that the UE is moving from a first cell coverage area corresponding to the serving MeNB to a second cell coverage area corresponding to the target MeNB; and
in response, make the determination to handover the UE from the serving MeNB to the target MeNB.
3. The eNB of claim 2 , wherein the measurement report comprises a reference signal received power (RSRP) or reference signal received quality (RSRQ).
4. The eNB of claim 1 , wherein to handover both the UE and the SeNB to the target MeNB, the processor is further configured to:
send a radio resource control (RRC) connection reconfiguration message to the UE through the wireless transceiver, the RRC connection reconfiguration message including a field indicating the list of cells to keep in the SCG.
5. The eNB of claim 1 , wherein the processor is further configured to:
receive, from the SeNB, a response to the command;
send a sequence number status transfer and data forwarding message to the target MeNB; and
receive, from the target MeNB, a UE context release message.
6. The eNB of claim 1 , wherein the serving MeNB is configured to communicate with the SeNB and the MeNB through a non-ideal backhaul interface (X2).