WO2017149361A1

WO2017149361A1 - Handover notification

Info

Publication number: WO2017149361A1
Application number: PCT/IB2016/051237
Authority: WO
Inventors: Jun Wang
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2016-03-04
Filing date: 2016-03-04
Publication date: 2017-09-08

Abstract

The present disclosure provides a method and system for handover notification between a source and a target node in a wireless communication network to facilitate a handover procedure for a User Equipment (UE). According to a broad aspect, the source node (112) monitors for a random access detect message from the target node (114) indicating that the UE initiated a random access procedure with the target node. When a random access detect message is received (136), the source node (112) can assume the UE has left the source cell and in response, take certain actions, e.g. terminate UE scheduling, initiate data forwarding toward the target node) to make the handover procedure more efficient.

Description

HANDOVER NOTIFICATION

TECHNICAL FIELD

[0001]The present disclosure relates to handover procedures and more particularly to methods and systems for handover notification during a handover procedure for a wireless device.

BACKGROUND

[0002] In a cellular radio system (such as, by way of non-limiting example, 3GPP, LTE, 3G and 4G), wireless terminals (also known as mobile stations and/or User Equipment units (UEs)) communicate via a radio access network (RAN) to one or more Core Networks (CNs) such as, by way of non-limiting example, the Evolved Packet Core (EPC) network. [0003] UEs may be (by way of non-limiting example) mobile telephones ("cellular" telephones), desktop computers, laptop computers, tablet computers, and/or any other devices with wireless communication capability to communicate voice and/or data with a RAN. In order to gain access to a CN service, the UE first selects an access node (e.g. an eNodeB or eNB) in the RAN to communicate with and then goes through an attach procedure to establish a connection with the Core

Network. Once connected, the UE sends periodic measurement reports to enable the serving eNB to determine whether and when the UE should be handed over to a different eNB in the RAN for continued access to CN services. [0004] In a Long Term Evolution (LTE) network, the serving eNB (also referred to as the source eNB) initiates the handover procedure based on measurements reports received from the UE. The handover procedure is specified in section 10.1.2.1 of 3GPP Technical Specification (TS) 36.300, Evolved Universal

Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2, version 12.8.0 dated January 2016, hereinafter referred to as "TS 36.300" and incorporated herein by reference in its entirety. [0005] Figure 1 shows an example of a conventional handover procedure for a UE 10 from a source eNB 12 to another eNB 14 (the "target" eNB). The procedure begins at step 20 with the source eNB 12 sending a handover request to the target eNB 14 selected by the source eNB 12 based on, for example, channel quality measurement report(s) between the UE and neighboring eNBs. The handover request typically includes the necessary context and configuration information (e.g. the UE X2, S1 signaling contexts, and as well as the E-RAB context) for the UE 10 to prepare the handover. If the request is accepted, the target eNB 14 sends a handover request acknowledgment at step 24 to the source eN B 12, for example, after performing admission control or determining that sufficient resources can be allocated to the UE at step 22. The handover request acknowledgement message typically includes the handover command to be sent by the source eNB 12, a new cell Radio Network Temporary Identifier (C-RNTI), an optional non-contention or dedicated Random Access Channel (RACH) preamble as well as other parameters (e.g. target eNB security algorithm identifiers, SIBs, etc.) which may be used by the UE 10 to access the cell served by the target eNB 14. At step 26, the source eN B 12 sends the handover command (e.g. an RRC Connection Reconfiguration message) to the UE 10. The source eNB 12 also sends a Sequence Number (SN) Status Transfer to the target eNB 14 conveying the uplink (PDCP) SN receiver status and the downlink PDCP SN transmitter status if appropriate, for example, for each E-RAB where status preservation applies.

[0006] Once the handover command has been sent and/or a handover request acknowledgement has been received, the source eNB 12 suspends all user-plane data transmissions to the UE 10 and begins forwarding UE data (either uplink or downlink data) to the target eNB 14. The target eNB 14 buffers the data forwarded until it can delivered either to the UE or the Serving Gateway (S-GW) 18 once proper Radio Resource Control (RRC) and S1 connections have been established. [0007]After leaving the source cell (step 28), the UE 10 attempts to synchronize with the target eNB 14 at step 36 following a contention-free procedure and using a dedicated RACH preamble or following a contention-based procedure if a dedicated RACH preamble is not available. For a contention-free procedure (the example shown in Figure 1), the UE 10 sends to the target eNB 14 the dedicated RACH preamble included in the handover command it received from the source eNB 12. At step 37, the target eNB 14 responds with an initial uplink (UL) grant and Timing Advance (TA) information to enable the UE 10 to send an RRC Connection Reconfiguration message back to the eNB 14 at step 38 to confirm the handover. At steps 39, 40, the target eNB 14 can begin to deliver (to the UE 10 or S-GW 18) the data forwarded from the source eNB 12 as well as scheduling resources for the UE 10 to send any new UL data it might have.

[0008]At step 42, the target eNB 14 sends a path switch request to the MME 16 to switch the UE's user plane (U-plane) data path at the S-GW 18. If successful, the MME 16 responds with a path switch request acknowledgement message at step 46 acknowledging the path switch. In response, the target eNB 14 sends a UE Context Release message at step 48 to notify the source eNB 12 that the handover requested was successfully completed and to trigger the source eN B 12 to release its UE resources (shown as step 50).

[0009] In order to avoid delaying the execution of the handover procedure, it is common for UEs to leave the source cell immediately upon receipt of the handover command and not wait to deliver an acknowledgement response (e.g. HARQ/ARQ) back to the source eNB. However, if the handover command is not acknowledged, the source eNB is unware of whether the UE has successfully received the command and will remain in that state until it receives the UE Context Release message from the target eNB confirming completion of the handover. From transmitting the handover command until it receives a UE Context Release message (also known as a "transient window"), the source eNB does not know whether the handover has been successfully received and acted upon and may continue to re-schedule the handover command (e.g. using Signaling Radio Bearer 1 or SRB1 ) and prioritize its retransmission over user-plane data it might have pending. In scenarios where the UE has already left the cell, the handover command retransmission(s) may unnecessarily increase the interference to neighboring cells and consume valuable radio resources which otherwise could have been allocated to other UEs in the cell, particularly if the UE channel conditions are poor (e.g. at the cell edge).

[0010] Another issue with the current handover notification scheme between the target eNB and the source eNB is the impact on user traffic. In some

implementations, the source eNB is configured to suspend the scheduling of user- plane data and begin data forwarding to the target eNB as soon as possible e.g. when a handover acknowledgement request message is received (step 24 in Figure 1 ). However, in scenarios where the UE is still present in the source cell and capable of sending and/or receiving data, early suspension and data forwarding may be premature and prevent the UE from acknowledging

transmissions made after the handover command, which in turn may cause unnecessary retransmissions and latency in the target cell.

[001 1] To guard against possible delays in receiving the UE Context Release message confirming successful completion of the handover procedure and/or handover failures, the source eNB uses a timer TX2_RELocoveraii (hereinafter referred to as the TX2 timer)). In current implementations, the value of the TX2 timer is sufficiently large (e.g. 5 seconds) to provide ample time for the source eNB to receive the message. If a UE Context Release message is not received before the timer TX2 expires, the source eNB (assuming a handover failure has occurred at that point) will stop re-scheduling the handover command and suspend any data forwarding to the target eNB. In addition, the source eNB may also release its UE resources and notify the MME to allow the UE to access another target cell.

[0012] One issue with the TX2 timer is that it is difficult to select a timer value that is appropriate for both success and failure scenarios. As noted above, it is generally desirable to set the TX2 to a large value to ensure successful handovers can be confirmed to the source eNB but in failure scenarios, a large value may be inefficient. For example, if the UE leaves the source cell rapidly but fails to synchronize with the target eNB and attempts to access another cell, the source eNB, unware of the state of the handover, may re-schedule the handover command (if it was unacknowledged) and perform data forwarding to the target eNB until the TX2 timer expires. A large TX2 value may also cause the MM E to reject attempts by the UE to re-establish the UE's RRC connection at a new eNB while the TX2 timer is running, since the source eNB typically does not notify the MME of its release of the UE Context until after the TX2 timer expires.

[0013] Accordingly, to address some or all of the drawbacks noted above, there is a need for an improved handover notification scheme to facilitate the handover procedure for a UE.

SUMMARY

[0014] The present disclosure provides an efficient method and system for handover notification between a source and a target node in a wireless communication network to facilitate a handover procedure for a wireless device such as a User Equipment (UE).

[0015] ln a broad aspect of the disclosure, there is provided a handover notification method for a source node configured for a UE handover in a wireless network from the source node to a target node. The method includes monitoring for a random access detect message from the target node where the random access message indicates a random access procedure for the U E initiated with the target node. The method also includes terminating UE scheduling when a random access detect message has been received from the target node and releasing the one or more resources associated with the UE in response to receiving a release message from the target node after a downlink path for the UE has been switched from the source node to the target node.

[0016] In this aspect, in some embodiments, the method includes comprising starting forwarding UE data to the target node when a random access detect message has been received from the target node. In yet some other

embodiments, the UE scheduling includes scheduling of a handover command for the UE, the one or more resources include one or more of a UE context, a radio resource and a control plane resource. In yet some other embodiments, the method further includes sending a context for the UE to the target node when the random access detect message includes a request indication for a UE context.

[0017] In yet some other embodiments, the monitoring for a random access detect message from the target node includes setting a random access timer upon transmission of a handover command to the UE and wherein the terminating includes terminating the UE scheduling when either a random access detect message has been received from the target node or the random access timer has expired. In yet some other embodiments, the method further includes setting a resource release timer when either a random access detect message has been received from the target node or the random access timer has expired where the releasing includes releasing the one or more resources associated with the UE when either a release message has been received from the target node or the resource release timer has expired. In yet some other embodiments, the random access procedure is one of a CFRA procedure and a CBRA procedure and/or each of the source and target nodes comprises an eNB.

[0018] In yet another broad aspect of the disclosure, there is provided a source node configured for a UE handover in a wireless network from the source node to a target node, where the source node includes circuitry containing instructions which, when executed, cause the source node to perform any of the method embodiments described above for a source node. [0019] In yet another broad aspect, there is provided a non-transitory computer readable memory configured to store executable instructions for a source node configured for a UE handover in a wireless network from the source node to a target node. The executable instructions when executed by a processor cause the source node to perform any of the method embodiments described above for a source node.

[0020] In yet another broad aspect, there is provided a source node configured for a UE handover in a wireless network from the source node to a target node. The source node includes a transceiver, a processor and a memory containing a random access monitoring module configured to monitor for a random access detect message from the target node where the random access message indicates a random access procedure for the UE initiated with the target node. The memory also includes a scheduling module configured to terminate UE scheduling when a random access detect message has been received from the target node and a resource release module configured to release the one or more resources associated with the UE in response to receiving a release message from the target node after a downlink path for the UE has been switched from the source node to the target node.

[0021] In this aspect, in some embodiments, the memory also includes a data forwarding module configured to starting forwarding UE data to the target node when a random access detect message has been received from the target node. In other embodiments, the memory also includes a context transmission module configured to send a context for the UE to the target node when the random access detect message includes a request indication for a UE context.

[0022] In yet another broad aspect of the present disclosure, there is provided a handover notification method for a target node configured for a UE handover in a wireless network from a source node to the target node. The method includes sending a random access detect message to the source node in response to receiving a random access related message from the UE where the random access detect message is indicative of a random access procedure for the UE initiated with the target node. The method also includes sending a release message to the source node to release one or more resources associated with the UE after a downlink path for the UE has been switched from the source node to the target node.

[0023] In this aspect, in some embodiments, the method further includes receiving UE data forwarded from the source node only after the random access detect message has been sent to the source node. In other embodiments, the random access detect message causes the source node to stop UE scheduling. In yet other embodiments, sending the random access detect message includes sending the random access detect message to the source node prior to receiving an RRC Connection Reconfiguration Complete message from the UE. In yet other embodiments, the random access detect message is sent with a request indication for a UE context when the random access message includes an RRC Connection Re-establishment Request message. In yet other embodiments, the random access procedure is one of a CFRA procedure and a CBRA procedure. In yet other embodiments, the random access message includes one of a non- contention random access preamble and an RNTI associated with the UE.

[0024] According to another broad aspect of the disclosure, there is provided a target node configured for a UE handover in a wireless network from a source node to the target node, where the target node includes circuitry containing instructions which, when executed, cause the target node to perform any of the handover notification method embodiments described above for a target node. .

[0025] In yet another broad aspect, there is provided a non-transitory computer readable memory configured to store executable instructions for a target node configured for a UE handover in a wireless network from a source node to the target node. The executable instructions when executed by a processor cause the target node to perform any of the method embodiments described above for a target node.

[0026] In yet another broad aspect, there is provided a target node configured for a UE handover in a wireless network from a source node to the target node. The target node includes a transceiver, a processor and a memory containing a random access notification module configured to send a random access detect message to the source node in response to receiving a random access related message from the UE where the random access detect message is indicative of a random access procedure for the UE initiated with the target node. The memory also includes resource release notification module configured to send a release message to the source node to release one or more resources associated with the UE after a downlink path for the UE has been switched from the source node to the target node.

[0027] In this aspect, in some embodiments, the memory also includes a data reception module configured to receive UE data forwarded from the source node only after the random access detect message has been sent to the source node. In other embodiments, the memory also includes a context request module configured to include a request indication for a UE context in the random access detect message when the random access message includes an RRC Connection Re-establishment Request message.

[0028] In other implementations, a target node sends a first message to the source node when a radio connection between the UE and the target node (e.g. a physical, Medium Access Control (MAC and /or Radio Resource Control (RRC) connection) is initiated or established for the UE. In yet other implementations, the target node also sends a second message to the source node when a data connection or path for UE data connectivity is initiated / established between the target node and a node in a Core Network (CN) or a Radio Access Network (RAN). The first and second messages may respectively be indicative of the initiation / establishment of the radio and data connections. In some implementations, by using two separates messages, e.g. one indicative of a radio connection from the UE to a target node and the other indicative of the data connection for UE data connectivity (e.g. from the target node to a node in the RAN or CN), a source node can distinguish between the two types of connection events and in response, take one or more of the actions described above (e.g. terminate UE control (or SRB) scheduling and/or initiate data forwarding) or any other action it might deem appropriate for a more efficient handover procedure.

[0029] In one specific implementation the first message is a random access detect message from the target node indicating that the UE initiated a random access procedure with the target node and the second message is a UE Context Release message indicating the UE data path or connection has been switched from the source node to the target node. Other possibilities exist for the first and second messages.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Example embodiments of the present disclosure will now be described by reference to the following figures, in which identical reference numbers in different figures indicate identical elements, and in which:

[0031] Figure 1 is a signaling diagram of a conventional handover procedure for a User Equipment (UE) from a source eNodeB (eNB) to a target eNB in a Long Term Evolution (LTE) Radio Access Network (RAN);

[0032] Figure 2 is a signaling diagram of a handover procedure example for a UE from a source eNB to a target eNB in an LTE RAN, in accordance with the principles described herein; [0033] Figure 3 is a signaling diagram of another handover procedure example for the UE in the LTE RAN of Figure 2, in accordance with the principles described herein; [0034] Figure 4 is a signaling diagram of yet another handover procedure example for the UE in the LTE RAN of Figure 2, in accordance with the principles described herein;

[0035] Figure 5 shows a signaling diagram of yet another handover procedure example for the UE in the LTE RAN of Figure 2 showing use of timers for controlling retransmissions, data forwarding and UE resources at the source eNB in accordance with the principles described herein;

[0036] Figure 8 shows an example method for a target eNB for a handover procedure for the UE in the LTE RAN of Figure 1 , in accordance with the principles described herein;

[0037] Figure 7 shows an example method for a source eNB for a handover procedure for the UE in the LTE RAN of Figure 1 , in accordance with the principles described herein;

[0038] Figure 8A, 8B show a block diagram of an exemplary embodiment of a source node and a target node configured in accordance with the principles described herein; and

[0039] Figure 9A, 9B show a block diagram of another exemplary embodiment of a source node and a target node configured in accordance with the principles described herein. DETAILED DESCRIPTION

[0040] The present disclosure provides an efficient method and system for handover notification between a source and a target node in a wireless communication network to facilitate a handover procedure for a wireless device.

[0041] Generally, the present disclosure applies to a handover procedure for a wireless device (also known as a User Equipment or UE in 3GPP) in a wireless communication network. The procedure is normally carried out between two access nodes in the wireless network i.e, a first access node which may be a serving node or more generally a node with which the UE is connected or attached (also known as the source node) and a second access node to which the UE is to be handed over (also known as the target node). The handover procedure is normally performed with the assistance of one or more control node(s) in a core network such as for example, a Mobility Management Entity (MME) node, although it is conceivable that in some implementations, the handover is performed without such assistance e.g. only by the access nodes involved. The source and target nodes may be a Node B (NB), evolved Node B (eNB), base station, wireless access point (AP), base station controller (BSC), radio network controller (RNC), relay, donor node controlling relay, base transceiver station

(BTS), transmission point, transmission node, remote RF unit (RRU), remote radio head (RRH), etc.

[0042] The wireless device or UE may be any type of device capable of at least communicating through wireless communication, for example a wireless terminal (also known as a mobile stations, a mobile phone ("cellular" phone), a desktop, laptop, netbook, and/or tablet computer, a laptop embedded equipment (LEE), laptop mounted equipment (LME), or a portable device such as an e-book reader, watch, digital music and/or video player, camera, game controller and/or device but also may be a computing-like device such as a hart monitoring implant, biochip transponder, automobile, sensor, modem, thermostat, and/or other home or car appliance generally referred to as an Internet of Things (loT) device, a machine type communication (MTC) device (also known as a machine-to-machine (M2M) or device-to-device (D2D) device).

[0043] The following description will now be presented in the context of a Long Term Evolution (LTE) Radio Access Network (RAN) infrastructure but it is to be understood that it is not limited as such and the concepts presented herein may be applied to other 4^th Generation (4G), 5^th Generation (5G) or other future generations of a 3GPP communication network infrastructure. More generally, the present disclosure applies to any current or future wireless and core network infrastructures configured to handover, transition or transfer a wireless device or a connection of the wireless device from a first access node (e.g. a source node) to a second access node (e.g. the target node).

[0044] The present disclosure is directed to provide a more efficient handover notification scheme for the source eNB to have a better sense of the progress or state of the handover procedure. In 3GPP, the conventional handover procedure is specified in section 10.1.2.1 of 3GPP Technical Specification (TS) 36.300, Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2, version 12.8.0 dated January 2016, hereinafter referred to as "TS 36.300" and incorporated herein by reference in its entirety.

[0045] Although the embodiments provided below are based on the TS 36.300 handover procedure, it is important to note that the principles described herein are not limited as such and could also be applied to a modified version of the procedure (with additional or fewer steps, some of which may be as described in TS 36.300) or an entirely different handover or transfer procedure between access nodes. [0046] Figure 2 shows an example of a handover procedure for a UE 110 in an LTE RAN from a first access node (the source eNB 1 12 - in this case, the eNB serving the UE 1 10) to a second node (the target eNB 14), according to one embodiment of the present disclosure. The procedure begins at step 120 with the source eNB 1 12 sending a handover request to the target eNB 1 14 the source eNB 112 selected based on, for example, channel quality measurement report(s) between the UE 110 and neighboring eNBs. The handover typically includes the necessary context and configuration information (e.g. the UE X2, S1 signaling contexts, and as well as the E-RAB context) for the UE 10 to prepare the handover. If the request is accepted, the target eNB 114 sends a handover request acknowledgment to the source eNB 1 12 at step 124, for example, after performing admission control or determining that sufficient resources can be allocated to the UE 1 10 at step 122. The handover request acknowledgement message typically includes the handover command to be sent by the source eNB 112, a new cell Radio Network Temporary Identifier (C-RNTI), an optional non- contention or dedicated Random Access CHannel (RACH) preamble as well as other parameters (e.g. target eNB security algorithm identifiers, SIBs, etc.) which may be used by the UE 110 to access the cell served by the target eNB 114. At step 126, the source eNB 112 sends a handover command (e.g. an RRC

Connection Reconfiguration message in this case) to the UE 1 10, which typically is not acknowledged, making the source eNB 1 12 unaware of whether or not the UE has successfully received the command.

[0047] After leaving the source cell at step 132, the UE 10 attempts to synchronize with the target eNB 1 14 and follows a Contention-Free Random Access (CFRA) procedure to gain access to the target cell. The procedure begins at step 134 with the UE 110 sending the dedicated random access or RACH preamble included in the handover command it received from the source eNB 112. At step 138, the target eNB 1 14 responds with an initial uplink (UL) grant and Timing Advance (TA) information to enable the UE 1 10 to send an RRC Connection Reconfiguration message to the target eNB 114 at step 140 to confirm the handover from the UE's perspective.

[0048] According to principles of the present disclosure, once the handover command has been sent or once a handover request acknowledgement message has been received from the target eNB 1 14, instead of immediately initiating data forwarding to the target eNB 1 14, the source eNB is configured to delay that operation (step 142) until after it receives a confirmation or an indication (e.g. a random access detect message) at step 136 that the UE 1 10 has initiated a random access procedure with the target eNB 1 14. By delaying the data forwarding (step 142) to the target eNB 1 14 until after a random access indication is received, the source eNB 1 12 may reduce unnecessary traffic over the X2 interface and retransmissions in the target cell, particularly in scenarios where the UE 1 10 is still present in the source cell and capable of acknowledging or carrying out transmissions before leaving the cell.

[0049] In one implementation, after sending the handover command (step 126), the source eNB 1 12 suspends or terminates data scheduling for the UE (over Data Radio Bearers (DRBs)) at step 128 and buffers in-transit packets (step 130), which, as noted above, may be forwarded to the target eNB 1 14 after receiving an indication (step 136) that the UE 1 10 has initiated a random access procedure with another eNB (e.g. the target eNB 1 14). In another implementation, the source eNB 1 12 suspends data (or DRB) scheduling but continues to schedule the handover command (and other control signaling) over Signaling Radio Bearers (SRBs) until it receives the random access indication confirming that the handover command was successful at which point the UE control or SRB scheduling (including the scheduling of the handover command) can be terminated.

[0050] According to principles of the present disclosure, the target eNB 1 14 sends the random access indication (step 136) to the source eNB 1 12 in response to receiving a random access related message from the UE 1 10 (step 134). In the example of Figure 2, the random access indication is a random access detect message and the random access related message is the dedicated RACH preamble sent by the UE 1 10 at step 134. Upon receipt of the random access detect message, the source eNB 1 12 can safely assume the UE 1 10 has left the source cell and in response, take one or more of the actions described above (e.g. terminate SRB scheduling (e.g. the handover command), and/or initiate data forwarding toward the target eNB 114, etc.) to make the handover procedure more efficient.

[0051] There are many other possibilities for the random access indication. In some implementations, the random access indication indicates random access initiation or completion at the target eNB 1 14. In other implementations, the random access indication message can be sent either as part of another (X2) message from the target eNB 14 to the source eNB 112 (for example as an Information Element (IE)) or as a stand-alone message. In one implementation, the random access indication is a stand-alone message structured as shown in table A below.

TABLE A

[0052] In this example, the random access indication is a random access detect message that includes a message type IE identifying the message as a random access detect message, a first eNB UE ID identifying the old or source eNB, a second eNB UE ID identifying the new or target eNB and a fetch UE Context IE identifying a request for a UE context by the target eNB. But other possibilities exist for the random access detect message, for example, additional or different lEs could be included to provide more information related to the random access procedure initiated or completed. [0053] Referring again to the handover procedure of Figure 2, in some

implementations, the source eNB 1 12 sends a Sequence Number (SN) Status Transfer message to the target eNB 1 14 at step 141 conveying the uplink Packet Data Convergence Protocol (PDCP) SN receiver status and the downlink PDCP SN transmitter status if appropriate, for example, for each Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB) where status preservation applies. With that information, the target eNB 1 14 can begin to deliver the data forwarded from the source eNB 1 12 (to the U E 1 10 or the S-GW 1 18 - steps 144, 146) as well as scheduling resources for the UE 1 10 to enable it send any new UL data it might have.

[0054] At step 148, the target eNB 1 14 sends a path switch request to the MME 1 16 to switch the UE's user plane (U-plane) data connection or path at the S-GW 1 18 from the source eNB 1 12 to the target eNB 1 14. In some implementations, the UE data path is a (Downlink - DL) path or a U-plane General Packet Radio System (GPRS) Tunneling Protocol (GTP) or GTP-U tunnel. At step 152, after a path switch request acknowledgement message has been received from the MME 1 16 acknowledging the path switch (shown as step 150), the target eNB 1 14 sends a UE Context Release message at step 154 to notify the source eNB 1 12 that the handover requested was successfully completed (and indicating by reference that the UE data path or connection has been switched from the source node to the target node) and to trigger the source eNB 1 12 to release its UE resources (shown as step 156). [0055] There are many possibilities for the target eNB 1 14 to determine when to send an indication confirming the UE 1 10 has initiated or completed a random access procedure. In some implementations, the target eNB 1 14 sends the indication as soon as it can unequivocally determine the UE 1 10 has initiated / completed a random access procedure so that the source eNB 1 12 can take the actions described above (e.g. terminate the UE control or SRB scheduling (e.g. of the handover command) and begin the data forwarding) as soon as possible. In the example of Figure 2, the target eNB 1 14 uses the first random access related message (i.e. the dedicated RACH preamble (step 136)) but other possibilities exist. The target eNB 1 14 could, for example, send the random access indication in response to receiving the RRC Connection Reconfiguration Complete from the UE 1 10 confirming completion of the handover from the UE's perspective.

[0056] Figure 3 shows another possibility where the random access indication from the target eNB 1 14 is sent in response to yet another random access related message from the UE 1 10 (further details below). In this example, the U E 1 10 uses a Contention-Based Random Access (CBRA) procedure to access the target cell. The signaling leading up to the handover command is similar to the signaling shown in the example of Figure 2 and includes the source eNB 1 12 sending a handover request to the target eNB 1 14 at step 120, the target eNB 1 14 performing admission control or determining that sufficient resources can be allocated to the UE 1 10 at step 122, and sending a handover request

acknowledgment to the source eNB 1 12 at step 124 that includes the handover command to be sent by the source eNB 1 12, a new cell Radio Network Temporary Identifier (C-RNTI), as well as other parameters (e.g. target eNB security algorithm identifiers, System Information Blocks (SIBs), etc.) which may be used by the UE 1 10 to access the cell served by the target eNB 1 14. At step 126, the source eNB 1 12 sends the handover command (e.g. an RRC Connection Reconfiguration message in this case) to the UE 1 10, which typically is not acknowledged, making the source eNB unaware of whether or not the UE has successfully received the command. [0057] The CBRA procedure begins at step 160 with the UE 1 10 sending a random access preamble message containing a random access preamble selected from one or more groups of preambles. At step 162, the target eNB 1 14 responds with an initial UL grant (i.e. a random access response) that includes timing advance and other information to complete the random access procedure. The UE 1 10 replies with an initial or first uplink transmission to the target eNB 1 14 at step 164 that includes the C-RNTI identifier provided to the UE 1 10 in the handover command as well as an optional uplink buffer status report. The rest of the CBRA procedure includes the target eNB 1 14 sending a contention resolution message at step 168 which includes an uplink grant to enable the UE 1 10 to send an RRC Connection Reconfiguration Complete message to the target eNB 1 14 at step 170 to confirm the handover from the UE's perspective.

[0058] According to principles of the present disclosure, the target eNB 1 14 sends a random access detect message to the source eNB 1 12 at step 166 after determining that the UE 1 10 has initiated the CBRA procedure (e.g. in response to the UE's initial uplink transmission at step 164). However, other possibilities exist and, for example, the target eNB 1 14 could rely on a different random access related message from the U E (e.g. the RRC Connection Reconfiguration message) to trigger transmission of the random access detect message.

[0059] Upon receipt of the random access detect message, the source eNB 1 12 can safely assume the UE 1 10 has left the source cell and take one or more of the actions described above (e.g. terminate the scheduling of UE control signaling over SRBs (e.g. the handover command), and/or initiate data forwarding toward the target eN B 1 14, etc.) to make the handover procedure more efficient. [0060] In the example of Figure 3, the source eNB 1 12 is configured to delay the data forwarding (step 172) until after it receives the random access detect message (step 166). In one implementations, after sending the handover command (step 126), the source eNB 1 12 also suspends data (or DRB) scheduling for the UE 1 10 and buffers in-transit packets at step 130, which, as noted above, may be forwarded to the target eNB 1 14 (step 172) in response to or after a random access detect message has been received at step 166. In another implementation, the source eNB 1 12 suspends data (or DRB) scheduling but continues to schedule the handover command (and other control signaling) over SRBs until it receives the random access detect message confirming that the handover command was successful at which point the SRB scheduling can be terminated. [0061] In some embodiments, the source eNB 112 sends an SN Status Transfer message to the target eNB 114 at step 171 conveying the uplink (PDCP) SN receiver status and the downlink PDCP SN transmitter status if appropriate, for example, for each E-RAB where status preservation applies. With that information, the target eNB 1 14 can begin to deliver the data forwarded from the source eNB 1 12 (to the UE 110 or the S-GW 1 18 - steps 174, 176,) as well as scheduling resources for the UE 1 10 to enable it send any new uplink data it might have. [0062] At step 178, the target eNB 114 sends a path switch request to the MME

116 to switch the UE's U-plane data connection or path at the S-GW 1 18. In some implementations, the UE data path is a (DL) path or a GTP-U tunnel. At step 182, after a path switch request acknowledgement message has been received from the MME 116 acknowledging the path switch, the target eNB 114 sends a UE Context Release message at step 184 to notify the source eNB 112 that the handover requested was successfully completed (and indicating by reference that the UE data path or connection has been switched from the source eNB 1 12 to the target eNB 1 14) and to trigger the source eNB 1 12 to release its UE resources (shown as step 186).

[0063] The principles described therein also apply to scenarios where the UE 110 handovers to a different eNB after a failed attempt with the target eNB 1 4. As an example, Figure 4 shows a signaling diagram of a portion of a failed handover procedure between the source and target eNBs 1 12, 114 and a subsequent random access procedure the UE 110 attempts with a third eNB 115.

[0064] In this example, the signaling leading up to the handover command is similar to the signaling shown in the examples of Figures 2 and 3 and includes the source eNB 1 12 sending a handover request to the target eNB 1 14 at step 120, the target eNB 114 performing control at step 122, and sending a handover request acknowledgment to the source eNB 112 at step 124 that includes the handover command to be sent by the source eNB 1 12, a new C-RNTI identifier, an optional dedicated RACH preamble as well as other parameters (e.g. target eNB security algorithm identifiers, SI Bs, etc.) which may be used by the UE 1 10 to access the cell served by the target eNB 1 14. At step 126, the source eN B 1 12 sends the handover command (e.g. an RRC Connection Reconfiguration message) to the UE 1 10, which as noted above is not typically acknowledged, making the source eNB 1 12 unaware of whether or not the UE 1 10 has successfully received the command.

[0065] To gain access to the target cell, the UE 1 10 initiates a CFRA procedure by sending a synchronization message to the target eNB 1 14 (e.g. the dedicated RACH preamble received in the handover command). If the target eNB 1 14 receives the synchronization message, it responds with a synchronization response (e.g. a Random Access Response (RAR) message) containing an initial UL grant and TA information. If received successfully, the UE 1 10 sends an RRC Connection Reconfiguration Complete message to the target eN B 1 14 to reestablish its RRC connection. The example of Figure 4 shows that if either the synchronization message or the synchronization response is not transmitted successfully or if the RRC Connection Reconfiguration Complete message fails, the UE 1 10 attempts another CFRA procedure to connect with eNB 1 15 upon expiry of a UE timer (e.g. T₃₀₄). Specifically, the UE 1 10 send a synchronization message to the eNB 1 15 at step 196 which responds with an initial UL grant and TA information at step 198. The UE 1 10 then proceeds to send an RRC

Connection Reestablishment Request message to the eN B 1 15 at step 200. Based on the RRC Connection Reestablishment Request message received, the eNB 1 15 re-establishes the U E's RRC connection at step 202.

[0066] According to principles of the present disclosure, after determining that the UE 1 10 has initiated a random access procedure and requested reestablishment of the RRC connection (e.g. with the RRC Connection Reestablishment Request message), the eNB 1 15 sends a random access detect message to the source eNB 1 12 at step 204. Upon receipt of the random access detect message, the source eNB 204 can safely assume the UE 1 10 has left the source cell and in response, take one or more of the actions described above (e.g. terminate the scheduling of UE control signaling over SRBs (e.g. the handover command), and/or initiate data forwarding toward the eNB 1 15, etc.) to make the handover procedure more efficient. Although not shown, the eNB 1 15 completes the handover procedure by sending a UE Context Release message (after path switch) to notify the source eNB 1 12 the handover requested was successfully completed (indicating by reference that the UE data path or connection has been switched from the source eNB 1 12 to the target eNB 1 14) and to release its resources assigned to the UE 1 10.

[0067] In some implementations, the random access detect message includes a request or an indication for the UE context. In those implementations, upon receiving such request / indication, the source eNB 1 12 sends a message to the eNB 1 15 that includes the UE context requested to enable the eNB 1 15 to complete the handover. In other implementations, the source eNB 1 12 is configured to send the UE context to the eNB 1 15 autonomously upon receipt of the random access detect message (e.g. without a specific request or indication). Other possibilities exist for requesting and/or sending the UE context to the eNB 1 15 to complete the handover procedure.

[0068] Figure 5 shows a signaling diagram of another handover procedure example where, instead of suspending data (or DRB) scheduling for the U E 1 10 and buffering in-transit packets, the source eNB 1 12 continues to schedule data for the UE 1 10 (step 1 19) until it receives a random access detect message at step 212 confirming the UE 1 10 has left the source cell. In yet another implementation, in addition to the continued scheduling of data (step 1 19), the source eNB 1 12 may also continue to schedule the handover command over SRBs (as Radio Link Control (RLC) retransmissions - step 126) until it receives the random access detect message at which point the UE control (or SRB) scheduling can be terminated. [0089] Similarly to the examples described above in relation to Figures 2-4, the handover notification scheme used by the target eNB 114 toward the source eNB 112 includes the random access detect message sent when a random access message (e.g. a dedicated RACH preamble or MSG3 with specific C-RNTI) is received from the UE 110 and a release message (e.g. a UE context release message) sent after a data path for the UE 1 10 has been switched from the source node eNB 1 12 to the target eNB 1 14. However, other possibilities exist. In some implementations, the target eNB 114 sends a first message to the source eNB 112 when a radio connection between the UE 110 and the target eNB 1 14 (e.g. a Physical, MAC and /or RRC connection) is initiated or established. In other implementations, the target eNB 1 14 also sends a second message to the source eNB 1 12 when a data connection or path for UE data connectivity is initiated / established between the target eNB 1 14 and the S-GW 1 18 or some other node / device in the RAN or CN (e.g. a General Packet Radio System (GPRS) Tunneling Protocol (GTP) tunnel to the S-GW 118 for user plane connectivity and/or an S1-AP connection to the MME 116 for control plane connectivity). The first and second messages may respectively be indicative of the initiation / establishment of the radio and data connections. In some implementations, by using two separates messages, e.g. one indicative of a radio connection from the UE to a target access node and the other indicative of a data connection or path for UE data connectivity (e.g. from the target node to the S-GW 118 or to some other node / device in the RAN or CN), a source node can distinguish between the two types of connection events and in response, take one or more of the actions described above (e.g. terminate UE control (or SRB) scheduling and/or initiate data forwarding) or any other action it might deem appropriate for a more efficient handover procedure.

[0070] Figure 5 also shows the use of timers at the source eNB 1 2 to guard against possible delays or failures. In this example, a first timer T_RA 220 guards against delays / failure cases related the random access detect message. The

T_RA timer 220 is started when the source eNB 1 12 sends a handover command to the UE 110. The T_RA timer is set to a value such that the target eNB 1 14 has sufficient time to detect the UE's random access procedure and send a random access detect message to the source eNB 1 12. However, if it does not receive a random access detect message before the timer T_RA 220 expires, the source eNB 1 12 (determining a random access failure at the target eNB 1 14) is configured to stop scheduling retransmissions of the handover command and refrain from forwarding any buffered data to the target eNB 1 14. Because it guards against delays / failures related to random access detect message (and hence related to the initiation of a random access procedure at the Target eNB 1 14) and not against delays / failures related to the UE Context Release request (and hence related to the entire handover procedure), the T_RA 220 timer can be set to a shorter time period which, in some implementations, may reduce the number of handover command retransmissions at the source eNB 1 12 and/or prevent unnecessary data forwarding traffic over the X2 interface in the event of a random access failure at the target eN B 1 14. It is to be understood that if the U E 1 10 returns to the source eNB 1 12 (e.g. initiates a random access procedure) before the source eNB 1 12 receives a random access detect message or before expiry of timer T_RA 220, the source eNB 1 12 may stop the T_RA 220 timer and continue to serve the UE 1 10. [0071] In some implementations, a second timer T_rei_ease 222 is also used to guard against delays / failure cases related to the UE Context Release message. In those implementations, the T_rei_ease timer 222 is started when the source eNB 1 12 receives a random access detect message from the target eNB 1 14 (or another eNB) or when the T_RA timer expires, whichever is earlier. The T_reiease timer value is such that the target eNB 1 14 has sufficient time to request a path switch for the UE 1 10 and send a UE Context Release message to the source eNB 1 12.

However, if it does not receive a UE Context Release message from the before timer Treiease 222 expires, the source eNB 1 12 (determining a handover failure) stops data forwarding, releases its UE resources at timer expiry and/or notifies the MME 1 16 to allow the UE 1 10 to access another target cell, if necessary. [0072] Figure 6 shows an example method 300 for a target node (e.g. the target eNB 14) for a UE handover from a source node (e.g. the source eNB 12) in accordance with the principles described herein. The method begins at step 302 where the target node sends a random access detect message to the source eNB in response to receiving a random access message from the UE. The random access detect message (e.g. a random access preamble) is indicative of a random access procedure (e.g. a CFRA or CBRA procedure) the UE initiated or completed with the target eNB and may include one of a non-contention random access preamble and an RNTI associated with the UE. In some implementations at step 304, the target node optionally receives UE data forwarded from the source node after (e.g. in response to) sending the random access detect message. In other implementations, the random access defect message causes the source node to stop scheduling data and/or control signaling (over SRBs) for the UE including, for example, scheduling retransmissions of a handover command for the UE. In yet other implementations, the source node sends the random access detect message when it can determine the UE has initiated a random access procedure, for example, prior to receiving an RRC Connection Reconfiguration Complete message from the UE. [0073] In yet other implementations, the target node optionally sends a request indication for a UE context to the source node at step 308. The request indication may be sent as a stand-alone message or may be included in the random access detect message, for example, as a fetch UE Context IE. Finally at step 308, the target node sends a release message to the source node to release one or more UE resources after a UE downlink path has been switched from the source node to the target node.

[0074] Figure 7 shows an example method 400 for a source node (e.g. the source eNB 12) for a UE handover to a target node (e.g. the target eNB 14) in

accordance with the principles described herein. The method begins at step 402 where the source node monitors for a random access detect message from the target node indicative of a random access procedure for the UE (e.g. a CFRA or CBRA procedure) initiated with the target node. When a random access detect message is received, the source node terminates scheduling data (over DRBs) and/or control signaling (over SRBs) for the UE at step 404 including, for example scheduling retransmissions of a handover command for the UE. In some implementations, the monitoring for a random access detect message from the target node includes setting a random access timer upon transmission of a handover command to the UE. In those implementations, the source node terminates the (UE) scheduling when either a random access detect message has been received from the target node or the random access timer has expired.

[0075] In some implementations (for example, where the target node does not have yet the UE context), the source node may determine at step 406 whether the random access detect message includes a request or fetch indication for the UE context and if so, send the UE context to the target node at step 408. After receiving a random access detect message and optionally sending the UE context to the target node if requested, the source node may start forwarding UE data to the target node at step 410. At step 412, the source node releases one or more resources associated with the UE (e.g. a UE context, a radio resource and/or a control plane resource) in response to receiving a release message from the target node after a downlink path for the UE has been switched from the source node to the target node.

[0076] In some implementations, the source node sets a resource release timer when either a random access detect message has been received from the target node or the random access timer has expired. In those implementations, the source node releases the one or more resources associated with the UE when either a release message has been received from the target node or the resource release timer has expired. Other examples [0077] Figures 8A-B are block diagrams of exemplary embodiments of respectively a source node 600 (e.g. the source eNB 12) and a target node 700 (e.g. the target eNB 14) configured for a UE handover in accordance with the principles of the present disclosure.

[0078] As illustrated in Figure 8A, the source node 600 includes a transceiver 602, one or more processor(s) 604, memory 606 which includes one or more of a random access monitoring module 608, a scheduling module 610, a data forwarding module 612, a context transmission module 614 and a resource release module 616. In one embodiment, the transceiver 602 may be replaced by a transmitter and a receiver (not shown). The random access monitoring module 608 is configured to perform the random access monitoring functionality described above which includes monitoring for a random access detect signal from a target node. The scheduling module 610 is configured to perform the scheduling functionality described above, which includes terminating or suspending the scheduling of control and/or user data for the UE when a random access detect message has been received from a target node. The data forwarding module 612 is configured to perform the data forwarding functionality described above which includes starting forwarding (UE) data to the target node when a random access detect message has been received from the target node. The context

transmission module 614 is configured to perform the context transmission functionality described above, which includes sending the UE context to the target node when the random access detect message includes a request indication for the U E context. The resource release module 616 is configured to perform the resource releasing function described above which includes releasing the resources associated with the UE in response to receiving a release message from the target node.

[0079] Depending on the implementation and the functionality desired, not all of the random access monitoring, scheduling, data forwarding, context transmission and/or resource release functions need to be performed and as such, some of the modules described above may be optional. For example, in implementations where the random access detect message does not include a request for a UE context, the memory 606 only includes the random access monitoring module 608, the scheduling module 610, the data forwarding module 614 and the resource release module 616 respectively performing the functions described above. In other implementations, where, for example, no data needs to be forwarded by the source node, and the random access detect message does not include a request for a UE context, the memory 606 only includes the random access monitoring module 608, the scheduling module 610, and the resource release module 616 respectively performing the functions described above. Other module

combinations are possible.

[0080] The random access monitoring module 608, scheduling module 610, data forwarding module 614, context transmission module and resource release module 616 are implemented at least partially in the memory 606 in the form of software or (computer-implemented) instructions executed by the processor(s)

604 within the source node 600 or distributed across two or more nodes (e.g. , the source node 600 and another node or device). In another example, the

processor(s) 604 includes one or more hardware components (e.g. , Application Specific Integrated Circuits (ASICs)) that provide some or all of the random access monitoring, scheduling, data forwarding, context transmission and/or resource release functionality described above. In another embodiment, the processor(s) 604 include one or more hardware components (e.g., Central Processing Units (CPUs)), and some or all of the random access monitoring, scheduling, data forwarding, context transmission and/or resource release functionality described above is implemented in software stored in, e.g. , the memory 606 and executed by the processor 604. In yet another embodiment, the processor(s) 604 and memory 606 form processing means (not shown) configured to perform the random access monitoring, scheduling, data forwarding, context transmission and/or resource release functionality described above.

[0081]As illustrated in Figure 8B, the target node 700 includes a transceiver 702, one or more processor(s) 704, and memory 706 which includes one or more of a random access notification module 708, a data reception module 710, a context request module 712, and a resource release notification module 714. In one embodiment, the transceiver 702 may be replaced by a transmitter and a receiver (not shown). The random access notification module 708 is configured to perform the random access notification functionality described above which includes sending a random access detect message to the source node when a random access procedure initiated by the UE has been detected (e.g. when a random access message from the UE has been received). The data reception module 710 is configured to perform data reception functionality described above, which includes receiving (UE) data from the source node after (e.g. in response to) sending the random access detect message to the source node. The context request module 712 is configured to perform the context requesting functionality described above which includes sending a request indication for a UE context to the source node. The resource release notification module 714 is configured to perform the resource release notification functionality described above which includes sending a release message to the source node to release one or more UE resources after a UE downlink path has been switched from the source node to the target node. [0082] Depending on the implementation and the functionality desired, not all of the random access notification, data reception, context requesting and/or resource release notification functions need to be performed and as such, some of the modules described above may be optional. For example, in implementations where the target node does not need to request the UE context (for e.g. if provided in the handover command), the memory 606 only includes the random access notification module 708, the data reception module 710, and the resource release notification module 716 respectively performing the functions described above. In other implementations where the target node is the node initially identified for the handover by the source node and no (UE) data is forwarded by the source node, the memory 606 only includes the random access notification module 708 and the resource release notification module 716 respectively performing the functions described above. Other module combinations are possible. [0083] The random access notification module 708, data reception module 710, context request module 712, and resource release notification module 714 are implemented at least partially in the memory 706 in the form of software or (computer-implemented) instructions executed by the processor(s) 704 within the target node 700 or distributed across two or more nodes (e.g. , the target node 700 and another node or device). In another example, the processor(s) 704 includes one or more hardware components (e.g. , Application Specific Integrated Circuits (ASICs)) that provide some or all of the random access notification, data reception, context requesting and/or resource release notification functionality described above. In another embodiment, the processor(s) 704 include one or more hardware components (e.g., Central Processing Units (CPUs)), and some or all of the random access notification, data reception, context requesting and/or resource release notification functionality described above is implemented in software stored in, e.g., the memory 706 and executed by the processor(s) 704. In yet another embodiment, the processor(s) 704 and memory 706 form

processing means (not shown) configured to perform the random access notification, data reception, context requesting and/or resource release notification functionality described above.

[0084] Figures 9A-B show a variant for each of the source node and target node examples of Figures 8A-B, denoted respectively as source node 800, and target node 900. Each of the nodes 800, 900 includes a transceiver 802, 902 and circuitry containing (computer-implemented) instructions which when executed by one or more processor(s) 804, 804 cause their respective node 800, 900 to perform some or all of the functionality described above in relation to source and target nodes 600, 700. In yet another variant, the circuitry includes a respective memory 806, 906 and processor(s) 804, 904 which, may be implemented in many different ways. In one example, the memories 806, 906 contain instructions which, when executed, cause the respective node 800, 900 to perform some or all of the functionality described above in relation to the source and target nodes 600, 700. Other implementations are possible. [0085]The following is also noted in accordance with other contemplated embodiments. [0086] In a broad aspect of the disclosure, there is provided a handover notification method for a source node configured for a UE handover in a wireless network from the source node to a target node. The method includes monitoring for a random access detect message from the target node where the random access message indicates a random access procedure for the UE initiated with the target node. The method also includes terminating UE scheduling when a random access detect message has been received from the target node and releasing the one or more resources associated with the UE in response to receiving a release message from the target node after a downlink path for the UE has been switched from the source node to the target node.

[0087] In this aspect, in some embodiments, the method includes comprising starting forwarding UE data to the target node when a random access detect message has been received from the target node. In yet some other

embodiments, the UE scheduling includes scheduling of a handover command for the UE, the one or more resources include one or more of a UE context, a radio resource and a control plane resource. In yet some other embodiments, the method further includes sending a context for the UE to the target node when the random access detect message includes a request indication for a UE context. [0088] In yet some other embodiments, the monitoring for a random access detect message from the target node includes setting a random access timer upon transmission of a handover command to the UE and wherein the terminating includes terminating the UE scheduling when either a random access detect message has been received from the target node or the random access timer has expired. In yet some other embodiments, the method further includes setting a resource release timer when either a random access detect message has been received from the target node or the random access timer has expired where the releasing includes releasing the one or more resources associated with the UE when either a release message has been received from the target node or the resource release timer has expired. In yet some other embodiments, the random access procedure is one of a CFRA procedure and a CBRA procedure and/or each of the source and target nodes comprises an eNB.

[0089] In yet another broad aspect of the disclosure, there is provided a source node configured for a UE handover in a wireless network from the source node to a target node, where the source node includes circuitry containing instructions which, when executed, cause the source node to perform any of the method embodiments described above for a source node.

[0090] In yet another broad aspect, there is provided a non-transitory computer readable memory configured to store executable instructions for a source node configured for a UE handover in a wireless network from the source node to a target node. The executable instructions when executed by a processor cause the source node to perform any of the method embodiments described above for a source node. [0091] In yet another broad aspect, there is provided a source node configured for a UE handover in a wireless network from the source node to a target node. The source node includes a transceiver, a processor and a memory containing a random access monitoring module configured to monitor for a random access detect message from the target node where the random access message indicates a random access procedure for the UE initiated with the target node. The memory also includes a scheduling module configured to terminate UE scheduling when a random access detect message has been received from the target node and a resource release module configured to release the one or more resources associated with the UE in response to receiving a release message from the target node after a downlink path for the UE has been switched from the source node to the target node. [0092] In this aspect, in some embodiments, the memory also includes a data forwarding module configured to starting forwarding UE data to the target node when a random access detect message has been received from the target node. In other embodiments, the memory also includes a context transmission module configured to send a context for the UE to the target node when the random access detect message includes a request indication for a UE context.

[0093] In yet another broad aspect of the present disclosure, there is provided a handover notification method for a target node configured for a UE handover in a wireless network from a source node to the target node. The method includes sending a random access detect message to the source node in response to receiving a random access related message from the UE where the random access detect message is indicative of a random access procedure for the UE initiated with the target node. The method also includes sending a release message to the source node to release one or more resources associated with the UE after a downlink path for the UE has been switched from the source node to the target node.

[0094] In this aspect, in some embodiments, the method further includes receiving UE data forwarded from the source node only after the random access detect message has been sent to the source node. In other embodiments, the random access detect message causes the source node to stop UE scheduling. In yet other embodiments, sending the random access detect message includes sending the random access detect message to the source node prior to receiving an RRC Connection Reconfiguration Complete message from the UE. In yet other embodiments, the random access detect message is sent with a request indication for a UE context when the random access message includes an RRC Connection Re-establishment Request message. In yet other embodiments, the random access procedure is one of a CFRA procedure and a CBRA procedure. In yet other embodiments, the random access message includes one of a non- contention random access preamble and an RNTI associated with the UE. [0095] According to another broad aspect of the disclosure, there is provided a target node configured for a UE handover in a wireless network from a source node to the target node, where the target node includes circuitry containing instructions which, when executed, cause the target node to perform any of the handover notification method embodiments described above for a target node. .

[0096] In yet another broad aspect, there is provided a non-transitory computer readable memory configured to store executable instructions for a target node configured for a UE handover in a wireless network from a source node to the target node. The executable instructions when executed by a processor cause the target node to perform any of the method embodiments described above for a target node.

[0097] In yet another broad aspect, there is provided a target node configured for a UE handover in a wireless network from a source node to the target node. The target node includes a transceiver, a processor and a memory containing a random access notification module configured to send a random access detect message to the source node in response to receiving a random access related message from the UE where the random access detect message is indicative of a random access procedure for the UE initiated with the target node. The memory also includes resource release notification module configured to send a release message to the source node to release one or more resources associated with the UE after a downlink path for the UE has been switched from the source node to the target node.

[0098] In this aspect, in some embodiments, the memory also includes a data reception module configured to receive UE data forwarded from the source node only after the random access detect message has been sent to the source node. In other embodiments, the memory also includes a context request module configured to include a request indication for a UE context in the random access detect message when the random access message includes an RRC Connection Re-establishment Request message. [0099] In other implementations, a target node sends a first message to the source node when a radio connection between the UE and the target node (e.g. a physical, Medium Access Control (MAC and /or Radio Resource Control (RRC) connection) is initiated or established for the UE. In yet other implementations, the target node also sends a second message to the source node when a data connection or path for UE data connectivity (e.g. a GTP tunnel or an S1-AP connection) is initiated / established between the target node and a node in a Core Network (CN) or a Radio Access Network (RAN). The first and second messages may respectively be indicative of the initiation / establishment of the radio and data connections. In some implementations, by using two separates messages, e.g. one indicative of a radio connection from the UE to a target node and the other indicative of the data connection for UE data connectivity (e.g. from the target node to a node in the RAN or CN), a source node can distinguish between the two types of connection events and in response, take one or more of the actions described above (e.g. terminate UE control (or SRB) scheduling and/or initiate data forwarding) or any other action it might deem appropriate for a more efficient handover procedure. [00100] In one specific implementation the first message is a random access detect message from the target node indicating that the UE initiated a random access procedure with the target node and the second message is a UE Context Release message indicating the UE data path or connection has been switched from the source node to the target node. Other possibilities exist for the first and second messages.

[00101] It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described herein above. A variety of modifications and variations are possible in light of the above teachings and as defined by the following claims.

Claims

1 . A source node (1 12) configured for a User Equipment (UE) handover in a wireless network from the source node (1 12) to a target node (1 14), the source node (1 12) comprising circuitry containing instructions which, when executed, cause the source node (1 12) to:

monitor for a random access detect message (136, 166) from the target node (1 14), the random access detect message being indicative of a random access procedure for the UE initiated with the target node (1 14),

terminate UE scheduling when a random access detect message (136,

166) has been received from the target node (1 14), and

release the one or more resources associated with the U E in response to receiving a release message (154, 184) from the target node (1 14) after a downlink path for the UE has been switched from the source node (1 12) to the target node (1 14).

2. The source node (1 12) of claim 1 , wherein the instructions further cause the source node (1 12) to start forwarding UE data to the target node (1 14) when a random access detect message (136, 166) has been received from the target node (1 14).

3. The source node (1 12) of claim 1 wherein the UE scheduling comprises scheduling of a handover command for the UE. 3. The source node (1 12) of claim 1 , wherein the one or more resources comprise one or more of a UE context, a radio resource and a control plane resource.

4. The source node (1 12) of claim 1 , wherein the instructions further cause the source node (1 12) to send a context for the UE to the target node (1 14) when the random access detect message (136, 166) includes a request indication for a UE context.

5. The source node (1 12) of claim 1 , wherein the instructions further cause the source node (1 12) to monitor for a random access detect message (136, 166) from the target node (1 14) by setting a random access timer (220) upon transmission of a handover command to the UE and to terminate UE scheduling when either a random access detect message (136, 166) has been received from the target node (1 14) or the random access timer (220) has expired.

6. The source node (1 12) of claim 5, wherein the instructions further cause the source node (1 12) to set a resource release timer (222) when either a random access detect message (136, 166) has been received from the target node (1 14) or the random access timer (220) has expired and to release the one or more resources associated with the UE when either a release message (154, 184) has been received from the target node (1 14) or the resource release timer (222) has expired.

7. The source node (1 12) of claim 1 , wherein the random access procedure is one of a Contention-Free Random Access (CFRA) procedure and a Contention- Based Random Access (CBRA) procedure.

8. The source node (1 12) of claim 1 wherein each of the source and target nodes (1 14) comprises an Evolved Universal Terrestrial Access Network Node B (eNB).

9. A handover notification method for a source node (1 12) configured for a

UE handover in a wireless network from the source node (1 12) to a target node

(1 14), method comprising:

monitoring (400) for a random access detect message (136, 166) from the target node (1 14), the random access detect message (136, 166) being indicative of a random access procedure for the UE initiated with the target node

(1 14), terminating (404) UE scheduling when a random access detect message (136, 166) has been received from the target node (1 14), and

releasing (412) the one or more resources associated with the UE in response to receiving a release message (154, 184) from the target node (1 14) after a downlink path for the UE has been switched from the source node (1 12) to the target node (1 14).

10. The method of claim 9 further comprising starting (410) forwarding UE data to the target node (1 14) when a random access detect message (136, 166) has been received from the target node (1 14).

1 1 . The method of claim 9 wherein the UE scheduling comprises scheduling of a handover command for the UE.

12. The method of claim 9 wherein the one or more resources comprise one or more of a UE context, a radio resource and a control plane resource.

13. The method of claim 9 further comprising sending (408) a context for the UE to the target node (1 14) when the random access detect message (136, 166) includes a request indication for a UE context.

14. The method of claim 9, wherein monitoring (402) for a random access detect message (136, 166) from the target node (1 14) comprises setting a random access timer (220) upon transmission of a handover command to the U E and wherein the terminating comprises terminating the U E scheduling when either a random access detect message (136, 166) has been received from the target node (1 14) or the random access timer (220) has expired.

15. The method of claim 14 further comprising setting a resource release timer (222) when either a random access detect message (136, 166) has been received from the target node (1 14) or the random access timer (220) has expired and wherein the releasing comprises releasing the one or more resources associated with the UE when either a release message (154, 184) has been received from the target node (1 14) or the resource release timer (222) has expired.

16. The method of claim 9, wherein the random access procedure is one of a CFRA procedure and a CBRA procedure.

17. The method of claim 9 wherein each of the source and target nodes (1 14) comprises an eNB.

18. A target node (1 14) configured for a UE handover in a wireless network from a source node (1 12) to the target node (1 14), the target node (1 14) comprising circuitry containing instructions which, when executed, cause the target node (1 14) to:

send a random access detect message (136, 166) to the source node

(1 12) in response to receiving a random access related message (134, 164) from the UE, the random access detect message (136, 166) being indicative of a random access procedure for the UE initiated with the target node (1 14), and send a release message (154, 184) to the source node (1 12) to release one or more resources associated with the UE after a downlink path for the UE has been switched from the source node (1 12) to the target node (1 14).

19. The target node (1 14) of claim 18, wherein the instructions further cause the target node (1 14) to receive UE data forwarded from the source node (1 12) only after the random access detect message (136, 166) has been sent to the source node (1 12).

20. The target node (1 14) of claim 18, wherein the random access detect message (136, 166) causes the source node (1 12) to stop UE scheduling.

21 . The target node (1 14) of claim 18, wherein the instructions further cause the target node (1 14) to send the random access detect message (136, 166) to the source node (1 12) prior to receiving an RRC Connection Reconfiguration Complete message from the UE.

22. The target node (1 14) of claim 1 , wherein the instructions further cause the target node (1 14) to send the random access detect message (136, 166) with a request indication for a UE context when the random access message includes an RRC Connection Re-establishment Request message.

23. The target node (1 14) of claim 1 , wherein the random access procedure is one of a CFRA procedure and a CBRA procedure.

24. The target node (1 14) of claim 1 wherein the random access message comprises one of a non-contention random access preamble and an RNTI associated with the UE.

25. A handover notification method for a target node (1 14) configured for a UE handover in a wireless network from a source node (1 12) to the target node (1 14), the method comprising:

sending a random access detect message (136, 166) to the source node (1 12) in response to receiving a random access related message (134, 164) from the UE, the random access detect message (136, 166) being indicative of a random access procedure for the UE initiated with the target node (1 14), and sending a release message (154, 184) to the source node (1 12) to release one or more resources associated with the UE after a downlink path for the UE has been switched from the source node (1 12) to the target node (1 14).

26. The target node (1 14) of claim 26, further comprising receiving UE data forwarded from the source node (1 12) only after the random access detect message (136, 166) has been sent to the source node (1 12).

27. The target node (1 14) of claim 18, wherein the random access detect message (136, 166) causes the source node (1 12) to stop UE scheduling.

28. The target node (1 14) of claim 26, wherein sending the random access detect message (136, 166) comprises sending the random access detect message (136, 166) to the source node (1 12) prior to receiving an RRC

Connection Reconfiguration Complete message from the UE.

29. The target node (1 14) of claim 26, wherein the random access detect message (136, 166) is sent with a request indication for a UE context when the random access message includes an RRC Connection Re-establishment Request message.

30. The target node (1 14) of claim 26, wherein the random access procedure is one of a CFRA procedure and a CBRA procedure.

31 . The target node (1 14) of claim 26 wherein the random access message comprises one of a non-contention random access preamble and an RNTI associated with the UE.