Recovering from an unsuccessful handover in a LTE system

[0001] The present invention relates to wireless communication systems. In particular, the present invention relates to a method and a system for realizing a long term evolution (LTE) link switching.

BACKGROUND [0002] In the LTE system for a fourth generation (4G) system, the development of a new radio interface and a radio network architecture is currently under consideration, which provides high data transfer rates, low latency, packet optimization, and improved system performance and coverage. For the LTE system, instead of using code division multiple access (CDMA), which is currently used in the 3G system, it is proposed to use orthogonal frequency division multiple access (OFDMA) and multi-access with division frequencies (frequency division multiple access) (FDMA) in transmissions, respectively, downlink and uplink links. As a result of changing many aspects of the LTE system,

[0003] User equipment (UE) mobility management in LTE_ACTIVE mode handles all necessary steps for smooth switching of the LTE system connection, such as making decisions to switch the interconnection within LTE on the source network side (i.e., control and evaluation of measurements EU equipment and evolved Node-B node (evolved Node-B) (eNode-B) with restrictions

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, The provision of radio resources on the side of the target network, the recommendation that the UE equipment be connected to new radio resources, the release of radio resources on the source network side, and the like. The EU Equipment Mobility Management mechanism also supports the transfer of context data between the involved nodes, and the updating of nodes relations in the control plane (C-plane) and the user plane (U-plane).

[0004] FIG. 1 is a signaling diagram of a call switching process 100 currently being proposed for an LTE system. The UE equipment 152 and the source node eNode-B 154 perform measurements and exchange measurement reports (step 102). The source node eNode-B 154 decides to switch the connection based on the measurement reports (step 104). The source node eNode-B 154 then sends a request to switch the connection to the target node eNode-B 156 (step 106). The decision to switch the connection and subsequent procedures before the connection switching is completed are performed without engaging the mobility management unit / user plane unit (MME / UPE) 158 (i.e. the switch preparation preparations are directly exchanged between the source eNode-B 154 and the target eNode -B 156).

[0005] The target node eNode-B 156 performs admission control for UE 152 (step 108). If the target node eNode-B 156 can accept the UE equipment 152, the target node eNode-B 156 sends a call switch response to the source node eNode-B 154 (step 110). The source node eNode-B 154 sends a command to switch the connection to the UE 152 (step 112). For smooth connection switching, a user plane tunnel (U-plane) is established between the source node eNode-B 154 and the target node eNode-B 156.

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[0006] The UE 152 and the target node eNode-B 156 then exchange the signaling of layers 1 and 2 (L1 / L2) (step 114). During the connection handover, the user data may be forwarded from the source node eNode-B 154 to the target node eNode-B 156. Forwarding may be a service dependent and implementation-specific method. The transfer of user data from the source node eNode-B 154 to the target node eNode-B 156 should take place as long as the packets are received at the source node eNode-B 154 from the unit UPE 158.

[0007] After establishing the connection to the target node eNode-B 156, the UE provides a termination message for switching the call to the target node eNode-B 156 (step 116). The target node eNode-B 156 sends a call completion end message to the MME / UPE unit 158 ​​(step 118). The MME / UPE 158 unit then sends an acknowledgment (ACK) of the termination of the call switching to the target node eNode-B 156 (step 120). After the MME / UPE 158 has been informed by the target node eNode-B 156 that the UE 152 has accessed at the target node eNode-B 156 via the termination handover message, the plane path (U-plane) is switched by the unit from the source node eNode- B 154 to the target user MME / UPE 158 of the eNode-B 156 node.

[0008] The release of radio resources at the source node eNode-B 154 is triggered by the resource release message sent by the target node eNode-B 156 (step 122). Upon receiving the resource release message from the target node eNode-B 156, the source node eNode-B 154 releases radio resources for the UE 152 equipment (step 124). The UE 152 equipment updates the location (location update) with the MME / UPE 158 unit (step 126).

[0009] In the document "3GPP TR R3.018 V0.4.0 3rd Generation Partnership Project; Technical Specification Group Radio

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Access Network; Evolved UTRA and UTRAN; Radio Access Architecture and Interfaces (Release 7), 3GPP Draft; TR R3.018 V040, 3RD Generation Partnership Project (3GPP), Mobile Competence Center; 650, Route Des Lucioles; F-06921 Sophia-Antipolis Cedex; France, vol. RAN WG3, 19 May 2006 (2006-05-19), XP050423646 ", a connection switching error is described, wherein the UE equipment that has been disconnected from the source by a call switch command is unable to establish communication with the intended cell target. One possible consequence is that the EU equipment will attempt to retreat to the source cell.

[0010] The above LTE interphone switch routine 100 does not provide details about the call switch command (such as UE UE 152 configurations based on the eNode-B target requirement), or details about the operation of the UE after the UE has received the toggle command. connections, (such as data transmission between the source node eNode-B 154 and the node UE 152 and radio link control (RLC) and re-setting the hybrid automatic repeat request (HARQ) and identifying the number slot sequential (SN) packet data convergence protocol (PDCP) by UE 152).The above LTE connection switch routine 100 also does not provide details regarding the timing of UE equipment for synchronous and asynchronous eNode-B nodes, nor details for efficient resource scheduling of the target eNode-B for transmission of UE equipment.

BEING

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[0011] The present invention relates to a method and a system for performing call switching in an LTE system. The source node eNode-B decides to switch the connection based on measurements, and sends a request to switch the connection to the target node eNode-B. The target eNode-B sends a response to the source node eNode-B indicating that the connection should be switched. The source node eNode-B then sends a command to switch the connection to the wireless transceiver unit (WTRU). The connection switch command includes at least one of the reconfiguration information, time control information, relative time difference between the source node eNode-B and the target node eNode-B, information about the initial planning process at the target eNode-B node and measurement information for the target eNode-B node. The WTRU then accesses the target node eNode-B and exchanges the layer signaling 1/2 to perform downlink synchronization, timing, and uplink and downlink resource allocation based on the information contained in the switch-over command.

[0012] The object of the present inventive idea is to provide an improved method of returning to operation after an unsuccessful call switching. Another object is to provide a WRTU in which the method may be implemented, and an eNode-B, which may communicate with the WTRU.

[0013] According to a first aspect of the invention, there is provided a method of returning to operation after an unsuccessful call switching. The method includes: the WTRU determines that the procedure for switching the connection of the WTRU from the source cell to the target cell has been unsuccessful; and the WTRU initiates the radio link failure procedure in response to determining that the procedure for the handover

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It is characterized by the fact that the WTRU sends a cell identification indication, ID, a source cell with a temporary radio network identifier, RNTI, during a radio link failure procedure.

[0014] According to a second aspect of the invention, a WTRU is provided including a transceiver configured to transmit and receive data and a controller connected to the transceiver. The WTRU is configured to determine that the procedure for switching the connection of the WTRU from the source cell to the target cell was unsuccessful, and initiating the radio link failure procedure in response to determining that the procedure for switching the connection was unsuccessful and that the WTRU is in addition, to send the cell ID indication for the source cell with the RNTI identifier during the radio link failure procedure.

[0015] According to a third aspect of the invention, an eNode-B is provided including a transceiver configured to transmit and receive data and a controller connected to the transceiver. The eNode-B is configured to send a call switch command to the WTRU, the call switch instructs has made the call switch handled by the eNode-B to the target cell, characterized in that the eNode-B is further configured to receive the ID identification indication. the cell for the source cell with the RNTI identifier during the radio link failure procedure initiated in response to the unsuccessful call transfer.

wherein the WTRU unit command is from the source cell

BRIEF DESCRIPTION OF THE DRAWINGS

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[0016] A more detailed understanding of the invention may take place from the following description of a preferred embodiment, provided in the form of an example and conceivable in conjunction with the accompanying drawings, in which:

Figure 1 is a signal flow diagram of a connection switching process currently proposed for an LTE system; and

Figure 2 is a signaling diagram of an LTE connection switching process in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0017] In further references, the term "WTRU" includes, but is not limited to, providing the UE, a mobile station, a stationary or a mobile subscriber, a pager, a cellular telephone, a personal digital assistant (PDA), a computer, or any other type of user equipment capable of operating in a wireless environment. In further references, the term "eNode-B" includes, but is not limited to, a base station, a Node-B node, a site controller, an access point (AP), or any other type of interface device capable of operating in a wireless environment.

[0018] The present invention provides detailed procedures for signaling and operations in the WTRU and the source and target eNode-B when switching the connection inside the LTE for both the case of successful call switching and the case of a switchover error. In the case of a successful connection switching, new information elements (IE) are added in both the switch switching command message and in the call switch completion message. In case of switching error

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As a result of this connection, new signaling messages are exchanged between the source eNode-B and the target node eNode-B.

[0019] Figure 2 is a signaling diagram of a LTE connection switching process 200 in accordance with the present invention. Both the WTRU 252 and the source node eNode-B 254 perform at least one measurement and the WTRU 252 sends the measurement report to the source node eNode-B 254 (step 202). The source node eNode-B 254 decides to switch the connection based on the measurement report and the result of its own measurement (step 204). The source node eNode-B 254 then sends a request to switch the connection to the target node eNode-B 256 (step 206). The target node eNode-B 256 performs admission control for the WTRU 252 unit (step 208). If the target node eNode-B 256 can accept the WTRU 252, the target node eNode-B 256 sends to the source node eNode-B 254 a call switch response indicating that the connection should be switched (step 210). The source node eNode-B 254 then sends a command to switch the connection to the WTRU 252 (step 212).

[0020] The connection switch command should contain at least one of the reconfiguration information for radio resource control (RRC), radio link control (RLC), media access control (MAC) and physical layer ( PHY), time control information when transferring a call from the source node eNode-B 254 to the target node eNode-B 256, (i.e. whether the WTRU 252 should implement the time control autonomously or using the random access channel procedure) ) (RACH), if the RACH channel is to be used, whether a random access or dedicated access signature, or the like), the relative time difference between the eNode-B nodes (or cells) will be used for

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The autonomous timing, information regarding the initial procedure for scheduling radio resources at the target node eNode-B 256, measurement information for the target node eNode-B 256, and the like. The information about the initial planning routine at the target node eNode-B 256 indicates whether the RACH access procedure should be used for a resource assignment request, or the target node eNode-B 256 can schedule resources for the WTRU 252 without receiving an explicit resource allocation request from the unit WTRU 252. Alternatively, measurement information and other configuration information may be sent to the WTRU 252 by the target node eNode-B 256 upon receipt of the termination of the handover message from the WTRU 252 in step 226.

[0021] For a smooth connection switching, the user plane tunnel (U-plane) is established between the source node eNode-B 254 and the target node eNode-B 256. After sending the switch-call command, the source node eNode-B 254 can transfer user data to the the target node eNode-B 256. The handover may occur in a service-specific manner and implementation-specific.

[0022] Upon receipt of a call switch command from the source node eNode-B 254, the WTRU 252 may continue to transmit and receive data to and from the source node eNode-B 254. The data transmission process depends on whether a synchronized call switch or a synchronization is used. unsynced connection switching.

[0023] When the synchronized connection switching procedure is used (i.e., the source eNode-B 254 and the target node eNode-B 256 are synchronized or the relative time difference is known to the WTRU 252), the source node eNode-B 254 and the WTRU 252 they can continue transmitting and receiving data after receiving the command to switch the connection up to a specified time (tHO)

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Switching through

Broadcast connection, which is signaled for the connection switching commands. the data after the reception of the connection switch command is preferably limited to the incomplete service data units (SDUs), (i.e. units other types of SN numbers of the received data service unit's SDUs (PDUs) of the RLC control data (PDUs), transmitted before a switch command has been sent. connections. The RLC control message is sent to the WTRU 252 to indicate the sequence number (SN) of the successfully received SDUs (SDUs) and the slot of the SDU. The SN number may be the SN number of the PDCP protocol, or be the SN number common to successfully (SDUs) and the unsuccessfully received SDUs (SDUs) may be included in the RLC control message.

[0024] When the non-synchronized connection switching procedure is used (ie, the source eNode-B 254 and the target eNode-B 256 are not synchronized or the relative time difference is not known to the WTRU 252), the source node eNode-B 254 stops the transmission once the source node eNode-B 254 sends a command to toggle the connection to the WTRU 252. The WTRU 252 also stops transmitting data packets to the source node eNode-B 254 when only the WTRU 252 receives the call switch command. Alternatively, the source node eNode-B 254 may continue to transmit data packets until the WTRU 252 switches to the target node eNode-B 254.

[0025] Upon receipt of the call switch command, the WTRU 252 accesses the target node eNode-B 256 and exchanges the signaling layer 1/2 (L1 / L2) with the target node eNode-B 256 to perform downlink synchronization, timing control, (i.e. uplink link synchronization) and uplink and link resource allocation

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The downlink is based on the information contained in the connection switch command.

[0026] For time control (i.e. uplink synchronization), the WTRU 252 performs one of two options. Preferably, the network decides which option to use.

[0027] According to a first option, the WTRU 252 autonomously performs timing based on the relative time difference between the source node eNode-B 254 (or cell) and the target node eNode-B 256 (or cells) (step 214a). The relative time difference information is preferably included in the connection switch command.

[0028] According to a second option, a conventional RACH channel access procedure is used for timing (step 214b). The WTRU sends the preamble of the RACH to the target node eNode-B, and the target node eNode-B computes the time offset based on the transmitted preamble of the RACH channel and sends the time shift information to the WTRU for uplink synchronization. [0029] A plurality of RACH preamble signatures with different orthogonality and different priority may be used, and among the multiple preamble signatures of the RACH channel, a RACH preamble flag with higher orthogonality, higher priority and / or higher power may be used for switching purposes.

[0030] A specific (dedicated) RACH preamble flag may be reserved for switching purposes to indicate that the sender is a WTRU subject to a call switch (i.e., a WTRU subject to the call switching process). This dedicated RACH preamble signature is indicated in the connection switch command. Upon receipt of the reserved RACH preamble signature, the target node eNode-B 256 recognizes that the sender is a WTRU subject to a call switch and may prioritize the entity.

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WTRU subject to connection switching. Thanks to this, you can avoid the random access process, which causes a long break time when switching the connection. Alternatively, the RACH channel message following the preamble of the RACH channel may clearly indicate that the sender is a WTRU entity to be switched over. The WTRU subject to a call switching preferably has a higher priority assigned to access to the node eNode-B (cells) than the WTRU not subject to connection switching due to the change of state. The RACH channel procedure using the reserved RACH preamble signature may be used in either the synchronized or non-synchronized connection of the eNode-B (or cell) node.

[0031] The random access procedure may be used for various purposes. The random access procedure may be used to initiate communication between the WTRU and the network, which requires a change of state from the LTE_idle state to the LTE_active state. The random access procedure can be used for timing when switching a connection and then for requesting access to a new cell. When the random access procedure is used when the connection is switched, the delay triggered by the random access procedure should be minimized. Therefore, there should be differences (eg prioritizing the WTRU subject to switching the connection),

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Idle on the LTE-Active status in the absence of a call switch.

[0032] After receiving the RACH preamble signature from the WTRU, the target node eNode B estimates the time control value and sends this value back to the WTRU (step 216).

[0033] Once the time control has been implemented (either autonomously or via the RACH preamble transmission), the WTRU 202 may send a radio resource assignment request to the target node eNode-B 256 (step 218). The request is preferably sent via the RACH channel message following the preamble of the RACH channel. The target node eNode-B 256 then schedules the downlink and uplink resources for the WTRU 252 (step 220). Alternatively, the target node eNode-B 256 may schedule resources for the WTRU 252 without receiving an explicit request from the WTRU 252. Resource planning may occur any time after the target node 256 of the WTRU has allowed the eNode-B 256 to the WTRU in step 208. For example, for the procedures of synchronized connection switching,

[0034] The target node eNode-B 256 sends an uplink resource assignment to the WTRU 252 (step 222). This uplink resource is used to send the end call switch termination message in step 226, and not for data transmission. The WTRU 252 preferably re-sets the RLC and HARQ parameters after receiving the uplink resource assignment from the target node eNode-B 256 (step 224). Alternatively, the WTRU 252 may reset the RLC and HARQ parameters after receiving and processing the call switch command in step 212.

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These parameters related to the transmission to the target node eNode-B 256 (or cells) are included in the connection switch command.

[0035] The WTRU 252 sends a termination of the handover message to the target node eNode-B 256 (step 226). The WTRU 252 preferably includes an initial SN number of the PDCP protocol to be transmitted in the termination of the handover message. Optionally, the WTRU 252 may send an RLC control message to the target node eNode-B 256 after the end of the handover message to indicate successfully transmitted SDUs and the SDU slot.

[0036] The target eNode-B 256 sends uplink uplink and downlink uplink information information for data transmission and an RRC message to the WTRU (step 228). The RRC message includes at least one of the radio access bearer (RAB) reconfiguration information, the initial SNCP number of the PDCP on the downlink, the control message RLC and the information regarding the measurements. Some or all of the above information may optionally be sent as part of a switch command of the first packet connection from the target node eNode-B 256.

[0037] The target node eNode-B 256 sends a call completion end message to the MME / UPE unit 258 to inform that the WTRU 252 has accessed at the target node eNode-B 256 (step 230). The MME / UPE unit 258 then sends a confirmation of the end of the call switch (ACK) to the target node eNode-B 256 and switches the path of the user plane data (U-plane) from the source node eNode-B 254 to the target node eNode-B 256 (step 232) . The release of radio resources at the source node eNode-B 254 is triggered by the resource release message sent by the target node eNode-B 256 (step 234). After

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When receiving a message from the target node eNode-B 256, the source node eNode-B 254 releases radio resources for the WTRU 252 (step 236).

[0038] The case of call switching error is explained below with reference to figure 2. When the WTRU 252 is not able to successfully make a call transfer, the WTRU 252 may resort to a radio link failure (RL) or to the cell reselection procedure. If the connection toggle command fails in step 212, the source node eNode-B 254 informs the target node eNode-B 256 of such a failure. The target node eNode-B 256 schedules any uplink and downlink resources to the WTRU 252 after step 208. When performing cell reselection in the event of a connection fail error, the WTRU 252 may first attempt to access the originally connected cell at the source node eNode- B 254. If it fails, the WTRU 252 may attempt to access other cells in the source node eNode-B. If this also fails, the WTRU 252 may attempt to access other cells not included in the source node eNode-B based on the measurement result.

[0039] The source node eNode-B 254 maintains a timer for exceeding the dwell time if the end of the handover message is not received after a predetermined time after the call switch fails. The source node eNode-B 254 can reset the RRC context, the PDCP context, the RLC and HARQ parameters related to the WTRU 252, if the connection switch timing timer completes the countdown. The source node eNode-B then releases radio resources for the WTRU 252.

[0040] When the cell reselection is performed by the WTRU 252 unit, the identification (ID) of the source cell or

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The eNode-B (ID) node is sent by the WTRU 252 to any eNode-B as part of the temporary radio network LTE (RNTI) information to detect whether the WTRU 252 gains access to the original cell or to the any other cells. At the source node eNode-B, the MAC layer of the source node eNode-B informs its RRC layer of the connection switchover error if the MAC layer detects an unsuccessful transmission of a switchover command.

[0041] Although the features and elements of the present invention are described in preferred embodiments in particular combinations, each feature or element may be used alone without other features and elements of preferred embodiments or in various combinations with or without other features and elements of the present invention. . The methods or flow charts provided in the present invention may be implemented in a computer program, software or firmware actually included on a computer readable storage medium for execution by a general-purpose computer or processor. Examples of computer readable storage media include read-only memory (ROM), random access memory (RAM), register, cache memory, semiconductor memory devices, magnetic carriers,

Suitable processors include, for example, a general-purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors in combination with a DSP core, controller, microcontroller, integrated circuits for special applications (ASIC), directly programmable systems

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Gateway array (FPGA), any other type of integrated circuit (IC) and / or state machine.

[0043] The processor in conjunction with the software may be used to implement a radio frequency transceiver for use in a wireless transceiver (WTRU), user equipment (UE), terminal, base station, radio network controller (RNC) or any computer. home. The WTRU unit can be used in conjunction with modules implemented in hardware and / or software, such as a camera, video camera module, videophone, hands-free system, vibrating device, speaker, microphone, television transceiver, headset, keyboard, Bluetooth module ®, frequency modulated radio unit (FM), liquid crystal display (LCD), display unit with organic light emitting diodes (OLED), digital music player,

InterDigital Technology Corporation Plenipotentiary:

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