Communication control method, base station and system

Abstract

To provide a base station and a wireless terminal used in a mobile communication system, which reduce network load accompanying signaling.SOLUTION: In a mobile communication system, a base station eNB200-1 included in a RAN paging area includes: a reception unit that receives, from a wireless terminal UE100 in a specific state, a message indicating departure from the RAN paging area; and a transmission unit that, in accordance with receipt of the message, transmits paging area information pertaining to updating the RAN paging area to a mobility management entity MME300C. The specific state is a state in which a base station in the RAN paging area maintains an S1 connection for the wireless terminal and a state in which the RAN paging area is set to the wireless terminal.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a base station and a wireless terminal used in a mobile communication system. [Background technology]

[0002] In recent years, with the spread of wireless terminals such as smartphones capable of executing a large number of applications, the frequency with which wireless terminals connect to networks and the frequency with which networks page wireless terminals are increasing.

[0003] As a result, the network load associated with signaling is increasing in mobile communication systems. In light of this situation, 3GPP (3rd Generation Partnership Project) (registered trademark; the same applies hereinafter), a standardization project for mobile communication systems, is studying technologies to reduce signaling. Summary of the Invention

[0004] The radio terminal includes a receiving unit that receives an RRC Connection Release message from a network, the RRC Connection Release message including a Light Connected indicator that instructs the radio terminal to transition to a Light Connected state, which is one state of the RRC Connected mode, and a control unit that performs a cell reselection operation in the Light Connected state after receiving the RRC Connection Release message. The control unit performs an operation of transitioning from the RRC Connected mode to an RRC Idle mode when a cell that does not support the Light Connected state is reselected in the cell reselection operation.

[0005] The RRC Connection Release message may include information indicating a RAN paging area. The wireless terminal may further include a transmitter configured to transmit an RRC Connection Resume Request message including RAN paging area update information to the network when the user terminal leaves the RAN paging area. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a diagram illustrating a configuration of an LTE system according to an embodiment. [Figure 2] 1 is a diagram illustrating a configuration of a UE (wireless terminal) according to an embodiment. [Figure 3] FIG. 2 is a diagram illustrating a configuration of an eNB (base station) according to the embodiment. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a protocol stack of a radio interface in an LTE system according to an embodiment. [Figure 5] 1 is a diagram illustrating a configuration of a radio frame used in an LTE system according to an embodiment. [Figure 6] FIG. 10 is a diagram illustrating an outline of an operation related to a transition to a light connected state (specific state) according to the embodiment. [Figure 7] FIG. 1 is a diagram illustrating an operation pattern 1 according to an embodiment. [Figure 8] FIG. 10 is a diagram illustrating an operation pattern 2 of the embodiment. [Figure 9] FIG. 1 illustrates an operation for determining a RAN paging area according to an embodiment. [Figure 10] FIG. 4 is a diagram illustrating an example of operation according to the first embodiment. [Figure 11] FIG. 10 is a diagram illustrating an example of operation according to the second embodiment. [Figure 12] FIG. 10 is a diagram illustrating an operation according to the third embodiment. [Figure 13] FIG. 10 is a diagram showing an operation pattern 1 of the fourth embodiment. [Figure 14] FIG. 10 is a diagram showing an operation pattern 2 of the fourth embodiment. [Figure 15] FIG. 13 is a diagram illustrating an example of operation according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Mobile communication system] (Configuration of a mobile communication system) The configuration of a mobile communication system according to an embodiment will be described below. Fig. 1 is a diagram showing the configuration of an LTE (Long Term Evolution) system, which is a mobile communication system according to an embodiment. The LTE system is a mobile communication system based on the 3GPP standard.

[0008] As shown in FIG. 1, the LTE system includes a radio terminal (UE: User Equipment) 100, a radio access network (E-UTRAN: Evolved-UMTS Terrestrial Radio Access Network) 10, and a core network (EPC: Evolved Packet Core) 20.

[0009] The UE 100 is a mobile communication device, and performs wireless communication with the eNB 200 that manages a cell (serving cell) in which the UE 100 is located.

[0010] E-UTRAN 10 includes base stations (eNBs: evolved Node-Bs) 200. The eNBs 200 are connected to each other via an X2 interface. Each eNB 200 manages one or more cells and performs wireless communication with a UE 100 that has established a connection with its own cell. The eNB 200 has a radio resource management (RRM) function, a routing function for user data (hereinafter simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. The term "cell" is used not only to indicate the smallest unit of a wireless communication area, but also to indicate a function or resource for performing wireless communication with a UE 100.

[0011] The EPC 20 includes a mobility management entity (MME) 300C and a serving gateway (S-GW) 300U (see FIG. 6, etc.). The MME 300C performs various mobility controls for the UE 100. The MME 300C manages information about the tracking area (TA) in which the UE 100 resides by communicating with the UE 100 using NAS (Non-Access Stratum) signaling. A tracking area is an area consisting of multiple cells. The S-GW 300U controls data forwarding. The MME 300C and the S-GW 300U are connected to the eNB 200 via an S1 interface.

[0012] 2 is a diagram showing the configuration of the UE 100 (wireless terminal). As shown in FIG. 2, the UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit .

[0013] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130.

[0014] The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0015] The control unit 130 performs various controls in the UE 100. The control unit 130 includes at least one processor and a memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor that performs modulation / demodulation and encoding / decoding of baseband signals, and a CPU (Central Processing Unit) that executes programs stored in the memory and performs various processing. The processor executes the processing described below.

[0016] 3 is a diagram showing the configuration of the eNB 200 (base station). As shown in FIG. 3, the eNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240.

[0017] The transmission unit 210 performs various transmissions under the control of the control unit 230. The transmission unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna.

[0018] The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 230.

[0019] The control unit 230 performs various controls in the eNB 200. The control unit 230 includes at least one processor and a memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor that performs modulation / demodulation and encoding / decoding of baseband signals, and a CPU that executes programs stored in the memory to perform various processing. The processor executes the processing described below.

[0020] The backhaul communication unit 240 is connected to a neighboring eNB via an X2 interface and is connected to the MME / S-GW 300 via an S1 interface. The backhaul communication unit 240 is used for communication over the X2 interface and communication over the S1 interface.

[0021] The MME 300C has a control unit and a network communication unit. The control unit performs various controls in the MME 300C. The control unit includes at least one processor and a memory. The memory stores programs executed by the processor and information used in processing by the processor. The processor may include a baseband processor that performs modulation / demodulation and encoding / decoding of baseband signals, and a CPU that executes programs stored in the memory to perform various processing. The processor executes the processing described below. The network communication unit is connected to the eNB 200 via the S1 interface. The network communication unit is used for communication over the S1 interface.

[0022] Fig. 4 is a diagram showing the configuration of a radio interface protocol stack in an LTE system. As shown in Fig. 4, the radio interface protocol is divided into first to third layers of the OSI reference model, with the first layer being the physical (PHY) layer. The second layer includes a medium access control (MAC) layer, a radio link control (RLC) layer, and a packet data convergence protocol (PDCP) layer. The third layer includes a radio resource control (RRC) layer. The PHY layer, MAC layer, RLC layer, PDCP layer, and RRC layer form an access stratum (AS) layer.

[0023] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the UE 100 and the PHY layer of the eNB 200 via a physical channel.

[0024] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of eNB 200 via a transport channel. The MAC layer of eNB 200 includes a scheduler that determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resource blocks to be allocated to UE 100.

[0025] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the eNB 200 via logical channels.

[0026] The PDCP layer performs header compression / decompression and encryption / decryption.

[0027] The RRC layer is defined only in the control plane that handles control information. RRC signaling for various settings is transmitted between the RRC layer of the UE 100 and the RRC layer of the eNB 200. The RRC layer controls logical channels, transport channels, and physical channels in accordance with the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of the UE 100 and the RRC of the eNB 200, the UE 100 is in RRC connected mode; otherwise, the UE 100 is in RRC idle mode.

[0028] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the MME 300C. Note that the UE 100 has functions such as an application layer in addition to the radio interface protocol.

[0029] FIG. 5 is a diagram showing the configuration of a radio frame used in an LTE system. As shown in FIG. 5, a radio frame is composed of 10 subframes on the time axis. Each subframe is composed of two slots on the time axis. The length of each subframe is 1 ms, and the length of each slot is 0.5 ms. Each subframe includes multiple resource blocks (RBs) on the frequency axis and multiple symbols on the time axis. Each resource block includes multiple subcarriers on the frequency axis. Specifically, one RB is composed of 12 subcarriers and one slot. One resource element (RE) is composed of one symbol and one subcarrier. Furthermore, of the radio resources (time-frequency resources) allocated to UE 100, frequency resources can be identified by resource blocks, and time resources can be identified by subframes (or slots).

[0030] In the downlink, the first few symbols of each subframe are used as a Physical Downlink Control Channel (PDCCH) for transmitting downlink control information, and the remaining part of each subframe is used as a Physical Downlink Shared Channel (PDSCH) for transmitting downlink data.

[0031] Basically, the eNB 200 transmits downlink control information (DCI) to the UE 100 using a PDCCH and transmits downlink data to the UE 100 using a PDSCH. The DCI carried by the PDCCH includes uplink scheduling information, downlink scheduling information, and a TPC command. The uplink scheduling information is scheduling information (UL grant) related to allocation of uplink radio resources, and the downlink scheduling information is scheduling information related to allocation of downlink radio resources. The TPC command is information instructing an increase or decrease in uplink transmission power. In order to identify the UE 100 to which the DCI is to be transmitted, the eNB 200 includes CRC bits scrambled with an identifier (RNTI: Radio Network Temporary ID) of the UE 100 to which the DCI is to be transmitted, in the DCI. Each UE 100 descrambles DCI that may be addressed to itself with its own UE's RNTI and then performs a CRC check, thereby performing blind decoding of the PDCCH and detecting the DCI addressed to itself. The PDSCH carries downlink data using downlink radio resources (resource blocks) indicated by the downlink scheduling information.

[0032] In the uplink, both ends of each subframe in the frequency direction are regions that are mainly used as a Physical Uplink Control Channel (PUCCH) for transmitting uplink control information, and the remaining part of each subframe is a region that is mainly used as a Physical Uplink Shared Channel (PUSCH) for transmitting uplink data.

[0033] Basically, the UE 100 transmits uplink control information (UCI) to the eNB 200 using the PUCCH, and transmits uplink data to the eNB 200 using the PUSCH. The UCI carried by the PUCCH includes a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), a scheduling request (SR), and a HARQ ACK / NACK. The CQI is an index indicating downlink channel quality and is used to determine the MCS to be used for downlink transmission, etc. The PMI is an index indicating a precoder matrix that is desirable to be used for downlink transmission. The RI is an index indicating the number of layers (number of streams) that can be used for downlink transmission. The SR is information requesting allocation of PUSCH resources. The HARQ ACK / NACK is acknowledgement information indicating whether downlink data has been correctly received.

[0034] (specific conditions) A specific state according to the embodiment will be described below. The specific state is a state in which the S1 connection for the UE 100 is maintained while signaling for the UE 100 is suppressed. The S1 connection may be referred to as an S1 bearer. The S1 connection is a connection established between the eNB 200 and the EPC 20 over an S1 interface. The S1 interface includes an S1-U interface for the user plane and an S1-MME interface for the control plane. The S1 connection may include an S1-U connection established between the eNB 200 and the S-GW 300U over the S1-U interface and an S1-MME connection established between the eNB 200 and the MME 300C over the S1-C interface.

[0035] The specific state may be one state of the RRC connected mode or one state of the RRC idle mode. Alternatively, the specific state may be an RRC state different from the RRC idle mode and the RRC idle mode. In operation pattern 1 of the embodiment, the specific state is one state (substate) of the RRC connected mode. In contrast, in operation pattern 2 of the embodiment, the specific state is one state (substate) of the RRC connected mode. According to the specific state, signaling is reduced compared to the general RRC connected mode. Furthermore, according to the specific state, the UE 100 can start data communication more quickly compared to the general RRC idle mode. Hereinafter, the specific state will be referred to as a "Light Connected state (Light Connected substate)."

[0036] Fig. 6 is a diagram showing an overview of operations related to transition to a Light Connected state (specific state). In the initial state of Fig. 6, the UE 100 is in an RRC connected mode, and an RRC connection is established between the UE 100 and the eNB 200. An S1-MME connection is also established between the eNB 200 and the MME 300C. An S1-U connection is also established between the eNB 200 and the S-GW 300U. The UE 100 performs data communication with the eNB 200.

[0037] As shown in FIG. 6, in step S1, the eNB 200 transmits to the UE 100 a transition instruction (Request to Light Conn.) instructing the UE 100 to transition to the Light Connected state.

[0038] In step S2, in response to receiving the transition instruction, the UE 100 transmits an acknowledgement (Ack) message to the eNB 200. However, step S2 is not essential and may be omitted.

[0039] In step S3, the UE 100 and the eNB 200 maintain or release the RRC connection. Specifically, in operation pattern 1 of the embodiment, the UE 100 and the eNB 200 maintain the RRC connection. In contrast, in operation pattern 2 of the embodiment, the UE 100 and the eNB 200 release the RRC connection.

[0040] In step S4, the eNB 200 and the MME 300C maintain the S1-MME connection. In step S5, the eNB 200 and the S-GW 300U maintain the S1-U connection. In step S6, the UE 100 transitions to a Light Connected state and suspends data communication with the eNB 200.

[0041] The eNB 200 maintains the context information (UE context) of the UE 100 that has transitioned to the Light Connected state without discarding it. The UE context includes information related to various settings and capabilities of the UE 100. The various settings include an AS (Access Stratum) setting.

[0042] The UE 100 in the Light Connected state can resume data communication with the eNB 200 with less signaling by utilizing the maintained S1 connection and UE context.

[0043] The UE 100 that has transitioned to the Light Connected state in the cell of the first eNB 200 may move from the cell of the first eNB 200 to the cell of the second eNB 200. When the UE 100 resumes data communication in the cell of the second eNB 200, the second eNB 200 may acquire the UE context of the UE 100 from the first eNB 200 over the X2 interface and use the acquired UE context for data communication with the UE 100.

[0044] In the embodiment, RAN paging is applied to the UE 100 in the light connected state. RAN paging is performed in units of a predetermined paging area where paging is controlled by the E-UTRAN 10 (eNB 200). The predetermined paging area is an area smaller than a tracking area. By introducing the predetermined paging area, the number of cells that perform paging for one UE 100 can be reduced, and therefore signaling can be reduced. Hereinafter, such a predetermined paging area is referred to as a "RAN paging area."

[0045] As an example, the RAN paging area (predetermined paging area) is composed of the cell of a specific eNB200 that maintains an S1 connection for the UE100 in the Light Connected state and the cells of other eNBs200 surrounding the specific eNB200. The surrounding eNB200 may be an eNB200 having an X2 interface with the specific eNB200. When the specific eNB200 receives data or NAS signaling addressed to the UE100 in the Light Connected state from the MME / S-GW300, the specific eNB200 determines to perform RAN paging and pages the UE100 together with the surrounding eNB200. The paging may be performed by transmitting an RRC paging message or by transmitting data addressed to the UE100 as a paging message. The specific eNB200 may be referred to as an anchor eNB.

[0046] (Operation pattern 1) Operation pattern 1 of the embodiment will be described below.

[0047] In operation pattern 1, UE 100 in RRC connected mode receives a message from eNB 200 instructing a change in the settings of the RRC connection, and changes the settings in response to the reception of the message. As an example, the message is an RRC Connection Reconfiguration message. As another example, the message is a message different from the RRC Connection Reconfiguration message. In operation pattern 1, a case is assumed in which the message is an RRC Connection Reconfiguration message. eNB 200 changes the RRC settings of UE 100 by transmitting the RRC Connection Reconfiguration message to UE 100.

[0048] The eNB200 causes the UE100 to transition to the Light Connected state by including information instructing the transition to the Light Connected state in an RRC Connection Reconfiguration message. The UE100 transitions to the Light Connected state in response to the information instructing the transition to the Light Connected state being included in the RRC Connection Reconfiguration message. In operation pattern 1, the Light Connected state is a state in which the RRC connection is maintained, but at least one function of the UE100 that generates signaling with the eNB200 is deactivated.

[0049] Here, the plurality of features may include a data (user data) transmission / reception function, a scheduling request (SR) transmission function, a channel state information (CSI) transmission (i.e., CSI feedback) function, a sounding reference signal (SRS) transmission function, a carrier aggregation function, a dual connectivity function, a semi-persistent scheduling (SPS) function, a WLAN aggregation function, a radio link monitoring (RLM) function, a notification function (e.g., in-device Coexistence Indication UE Assistance information, MBMS Interest Indication, Sidelink UE Information), an idle mode discontinuous reception (DRX) function, and a WLAN interworking function using broadcast signaling. However, in the light connected state, at least one of the cell reselection function, the connected mode DRX function, and the WLAN interworking function using dedicated signaling may remain activated without being deactivated. For details of these functions, see, for example, 3GPP technical specification "TS36.300 V13.4.0."

[0050] Fig. 7 is a diagram showing operation pattern 1 of the embodiment. In the initial state of Fig. 7, the UE 100 is in the RRC connected mode and is performing data communication with the eNB 200. Note that the processes indicated by dashed lines in Fig. 7 are not essential and can be omitted.

[0051] As shown in FIG. 7, in step S101, the UE 100 detects that data communication with the eNB 200 has been interrupted.

[0052] The interruption of data communication may be a case where downlink (DL) data is not received (or there is no prospect of receiving it) and / or uplink (UL) data is not transmitted (or there is no prospect of transmitting it). Here, the "prospect" may be a state where it is predicted that no data will be generated for a certain period of time. The certain period of time may be set by the eNB 200. The setting from the eNB 200 to the UE 100 is performed by RRC signaling. The RRC signaling may be UE-specific signaling (e.g., an RRC Connection Reconfiguration message) or broadcast signaling (e.g., a system information block (SIB)).

[0053] As an example, the RRC layer of the UE 100 detects an interruption of data communication with the eNB 200 based on information of a layer higher than the RRC layer (for example, an application layer). As an example, the RRC layer of the UE 100 may detect an interruption of data communication in response to a shutdown of an application that currently communicates most frequently. As another example, the RRC layer of the UE 100 may detect an interruption of data communication in response to a communication restriction imposed by an operation system (OS), a disappearance of an application running in the foreground (i.e., only background processing), or a determination by the OS that a data communication interruption state has occurred.

[0054] In step S102, the UE 100 transmits a notification indicating the suspension of data communication to the eNB 200. The UE 100 may transmit the notification by RRC layer signaling. The RRC layer signaling may be a UE Assistance Information message or another message. When the notification indicating the suspension of data communication is transmitted in the UE Assistance Information message, the notification may be referred to as an Extended Power Preference Indicator (Extended PPI).

[0055] In step S103, in response to receiving the notification indicating the interruption of data communication, the eNB 200 determines to transition the UE 100 to the light connected state.

[0056] In step S104, the eNB 200 transmits an RRC Connection Reconfiguration message (or another message) including information instructing the UE 100 to transition to the Light Connected state to the UE 100. In other words, the eNB 200 transmits an instruction to transition to the Light Connected state as a setting change of the RRC connection.

[0057] The information instructing a transition to the Light Connected state is, for example, "Light Connected=Setup." The RRC Connection Reconfiguration message may also include information specifying which of the above-described functions to deactivate. As an example, the eNB 200 includes a list of active functions or a list of deactivated functions in the RRC Connection Reconfiguration message to individually specify which functions to deactivate.

[0058] In step S105, in response to receiving the RRC Connection Reconfiguration message including information instructing transition to the Light Connected state, the UE 100 deactivates predetermined functions among the above-mentioned plurality of functions. When the functions to be deactivated are specified by the RRC Connection Reconfiguration message, the UE 100 deactivates only the specified functions.

[0059] In step S106, even if the UE 100 deactivates a predetermined function, the UE 100 holds the setting information (AS Context) of the predetermined function. In other words, even when the UE 100 transitions to the Light Connected state, the UE 100 does not discard but maintains the setting information of the function to be deactivated.

[0060] In step S107, the UE 100 transitions to a light connected state. In operation pattern 1, the light connected state is one state (substate) of the RRC connected mode. The UE 100 in the light connected state performs processing for receiving a paging message transmitted within the RAN paging area.

[0061] Thereafter, in step S108, the UE 100 in the Light Connected state detects a predetermined event in the UE 100. The predetermined event is either reception of a paging message from the eNB 200 or generation of UL data to be transmitted to the eNB 200. The predetermined event may be generation of UL data and the amount of the UL data being equal to or greater than a threshold. The threshold may be set in the UE 100 by the eNB 200.

[0062] In step S109, in response to detecting a predetermined event, the UE 100 in the Light Connected state transmits an activation request (RRC Activation Request) to the eNB 200, requesting activation of a deactivated function.

[0063] The activation request may request activation of all of the inactive functions, or may request activation of some of the inactive functions. When requesting activation of all of the inactive functions, the activation request may be a request to discontinue the Light Connected state (i.e., a request to transition to the normal RRC Connected mode). On the other hand, when requesting activation of all of the inactive functions, the activation request may include a list of functions to be activated, or may include a list of functions to be maintained in the inactive state.

[0064] In step S110, the eNB 200 determines whether to accept the activation request in response to receiving the activation request. Here, the description will proceed assuming that the eNB 200 has determined that the request is acceptable. Note that if the eNB 200 has determined that the request is unacceptable, the eNB 200 may transmit a negative acknowledgement (Nack) or a rejection notification (Reject) to the UE 100.

[0065] In step S111, the eNB 200 transmits an acknowledgment (RRC Activation Acknowledge) in response to the activation request to the UE 100. The eNB 200 may determine whether to accept the activation request for each function. In this case, the eNB 200 may include a list of functions for which activation is permitted and / or a list of functions for which activation is denied in the acknowledgment (RRC Activation Acknowledge). Alternatively, an RRC Connection Reconfiguration message may be used instead of the acknowledgment.

[0066] In step S112, the UE 100 determines whether to activate the deactivated function based on the content of the response received from the eNB 200. When the UE 100 receives the acknowledgement, the UE 100 activates the permitted function. The UE 100 activates the function from the time (subframe) when the UE 100 receives the acknowledgement. Alternatively, the UE 100 may activate the function within a certain period (for example, within 8 subframes) after receiving the acknowledgement.

[0067] (Operation pattern 2) In the following, the operation pattern 2 of the embodiment will be described, focusing mainly on the differences from the operation pattern 1.

[0068] In operation pattern 2, UE 100 in the RRC connected mode receives an RRC connection release message from eNB 200 instructing the release of the RRC connection, and releases the RRC connection in response to receiving the RRC connection release message. The RRC connection release message includes a field (Release Cause) indicating the reason for releasing the RRC connection. UE 100 transitions to the Light Connected state in response to information instructing the transition to the Light Connected state (e.g., RRC-LightConnected) being included in the field. eNB 200 transitions UE 100 to the Light Connected state by including information instructing the transition to the Light Connected state in the field. Alternatively, the Light Connected state may be a state in the network (i.e., the eNB and MME / S-GW). In this case, the RRC state of UE 100 becomes idle. However, eNB 200 may cause the UE to retain context (configuration information). In this case, the eNB 200 sets the Release Cause of the RRC Connection Release to rrc-Suspend, and notifies the UE 100 of a Resume ID (resumeIdentity) that is an identifier corresponding to the set Release Cause, such that the RRC connection is suspended. This state may be referred to as a state in which the RRC connection is suspended.

[0069] In the operation pattern 2, the light connected state is a state in which the RRC connection is released and an S1 connection for the UE 100 is maintained between the eNB 200 and the core network (EPC 20). In the operation pattern 2, the light connected state may further be a state in which at least some of the above-described functions are deactivated.

[0070] Fig. 8 is a diagram showing operation pattern 2 of the embodiment. In the following, differences from operation pattern 1 shown in Fig. 7 will be mainly described, and overlapping descriptions will be omitted.

[0071] As shown in FIG. 8, steps S201 to S203 are the same as those in operation pattern 1.

[0072] In step S204, the eNB 200 transmits an RRC Connection Release message including, as a Release Cause, information instructing the UE 100 to transition to the Light Connected state. The RRC Connection Release message may include information specifying which of the above-mentioned functions to deactivate. In this case, the handling of the deactivated function is the same as in operation pattern 1. The RRC Connection Release message may include a restoration identifier (Resume ID). The eNB 200 stores the UE context in association with the restoration identifier.

[0073] In step S205, in response to receiving the RRC Connection Release message including, as a Release Cause, information instructing transition to the Light Connected state, the UE 100 releases the RRC connection with the eNB 200.

[0074] In step S206, the UE 100 transitions to a light connected state. In operation pattern 2, the light connected state is a substate of the RRC idle mode. The UE 100 in the light connected state performs processing for receiving a paging message transmitted within the RAN paging area.

[0075] After that, in step S207, the UE 100 in the light connected state detects a predetermined event in the UE 100.

[0076] In step S208, in response to detecting a predetermined event, the UE 100 in the Light Connected state transmits an RRC connection resume request to the eNB 200, requesting restoration of the RRC connection. The RRC connection resume request may include information requesting activation of a deactivation function. The RRC connection resume request may include a restoration identifier.

[0077] In step S209, in response to receiving the RRC connection reestablishment request, the eNB 200 determines whether or not to accept the request. Here, the description will proceed assuming that the eNB 200 determines that the request is acceptable.

[0078] In step S210, the eNB 200 transmits an RRC Connection Resume message to the UE 100. The eNB 200 may include a list of functions that are permitted to be activated and / or a list of functions that are denied to be activated in the RRC Connection Resume message.

[0079] In step S211, the UE 100 restores the RRC connection based on the RRC connection restoration message received from the eNB 200. The eNB 200 resumes use of the UE context based on the restoration identifier.

[0080] (Movement status information) In operation patterns 1 and 2, the notification indicating the interruption of data communication may include movement state information related to the movement speed of UE 100. eNB 200 receives the movement state information related to the movement speed of UE 100 from UE 100, and determines the range of the RAN paging area corresponding to UE 100 based on the movement state information.

[0081] Alternatively, the UE 100 may transmit the mobility state information to the eNB 200 at any of the following timings.

[0082] First, the UE 100 transmits the mobility state information triggered by updating a tracking area or a RAN paging area. In this case, the UE 100 may include the mobility state information in a tracking area update message or a RAN paging area update message.

[0083] Second, the UE 100 transmits the mobility state information by using cell reselection as a trigger. In this case, the UE 100 may include the mobility state information in a cell update message.

[0084] Thirdly, the UE 100 transmits the mobility state information in response to an inquiry from the eNB 200 .

[0085] Fourth, the UE 100 periodically transmits the mobility state information. The period may be set to the UE 100 by the eNB 200.

[0086] FIG. 9 illustrates operations for determining a RAN paging area.

[0087] 9, in step S301, the UE 100 generates mobility status information. The mobility status information includes at least one of the following information:

[0088] 1) The number of handovers or cell reselections within a certain period of time. The certain period of time may be set by the eNB 200 to the UE 100.

[0089] 2) Average moving speed within a certain period of time. The moving speed can be obtained from location information of the UE 100. It is not limited to a direct value of the moving speed (for example, xxx km / h), but may also be an index of the moving speed (for example, High / Mid / Low). The certain period of time may be set to the UE 100 by the eNB 200.

[0090] 3) A one-bit identifier indicating whether the moving speed exceeds a threshold. Here, the moving speed may be the above 1) or 2). The threshold may be set in the UE 100 by the eNB 200.

[0091] 4) Cell history information of UE 100. The cell history information includes a plurality of combinations of cell IDs and residence times in the cells.

[0092] In step S302, the UE 100 transmits a message including the mobility state information to the eNB 200. The UE 100 may further include its own location information in the message. The UE 100 may further include its own category (UE category) in the message.

[0093] In step S303, the eNB 200 determines the range of the RAN paging area based on the mobility state information, and may notify the MME 300C of a list of cells (and eNBs) belonging to the determined RAN paging area.

[0094] For example, the eNB 200 sets a wider RAN paging area for the UE 100 moving at a high speed in order to prevent the UE 100 from missing a paging message, whereas the eNB 200 sets a narrower RAN paging area for the UE 100 moving at a low speed in order to reduce the number of signalings due to paging messages.

[0095] As another example, the eNB 200 may set a wider RAN paging area for the UE 100 of category M1 to save power. Category M1 is a UE category for machine-type communication that requires power-saving operation. This can reduce the number of RAN paging area update messages required when the UE 100 leaves the RAN paging area.

[0096] [First embodiment] A first embodiment will be described below on the premise of the above-mentioned LTE system. The first embodiment is an embodiment relating to mobility in a light connected state.

[0097] Here, the basic operation of mobility in the Light Connected state will be described.

[0098] The S1 connection of the UE 100 in the Light Connected state is maintained and active with the "anchor eNB." The anchor eNB may be the eNB 200 that transitioned the UE 100 to the Light Connected state. If the UE 100 moves to another RAN paging area, the anchor eNB may be switched.

[0099] For the UE 100 in the Light Connected state, paging (RAN paging) can be initiated by the RAN (E-UTRAN 10). RAN paging may be initiated by the anchor eNB.

[0100] Paging process (RAN paging) is controlled by the anchor eNB.

[0101] RAN paging area can be configured specifically for the UE.

[0102] The UE 100 in the Light Connected state performs a cell reselection mechanism similar to that in the RRC idle mode.

[0103] The context information (UE AS context) of the UE 100 in the Light Connected state is held by both the UE and the anchor eNB.

[0104] The Light Connected state is an EPS Connection Management (ECM) connected state from the network's perspective. The ECM indicates the connection state between the UE 100 and the core network (MME 300C).

[0105] When the UE 100 in the Light Connected state detects paging or starts data transmission, the UE 100 restores the connection with the eNB 200. Alternatively, the UE 100 may transition to the RRC connected mode.

[0106] The UE 100 transitions to the Light Connected state by RRC signaling.

[0107] A UE-specific RAN paging area is configured to the UE 100 by the eNB 200 through dedicated signaling or broadcast signaling. The RAN paging area is specified by a list of cells or a paging area ID.

[0108] · A UE 100 in Light Connected state notifies the network when it moves outside the configured RAN paging area.

[0109] A RAN paging area consists of one or more cells, which may be managed by different eNBs.

[0110] The UE 100 in the light connected state performs DRX operation using parameters similar to those of the DRX operation in the RRC idle mode. The parameters for determining the paging occasion may include the ID of the UE (e.g., IMSI, S-TMSI, Resume ID, etc.).

[0111] The eNB200 according to the first embodiment is an eNB200 included in the RAN of a mobile communication system. The eNB200 includes a receiver 220 that receives a message indicating that the UE 100 has left the RAN paging area from the UE 100 in the Light Connected state, and a transmitter (backhaul communication unit 240) that transmits paging area information related to updating the RAN paging area to the MME 300C (mobility management entity) in response to receiving the message. The Light Connected state is a state in which an anchor eNB in ​​the RAN paging area maintains an S1 connection for the UE 100, and a state in which the RAN paging area is set for the UE 100.

[0112] In the eNB 200 according to the first embodiment, the transmission unit (backhaul communication unit 240) may transmit a switching request message including paging area information to the MME 300C. The switching request message is a message for requesting switching of the S1 connection to the eNB 200 itself.

[0113] Furthermore, the paging area information may include information indicating a new RAN paging area for the UE 100. The new RAN paging area includes the area (cell) of the eNB 200 itself.

[0114] Fig. 10 is a diagram showing an example of operation according to the first embodiment. In the initial state of Fig. 10, the UE 100 is in RRC connected mode (S1001). Furthermore, the connection state between the UE 100 and the core network (MME 300C) is ECM Connected, and an S1 connection (S1-MME connection) for the UE 100 exists between the eNB 200 and the MME 300C. Although not shown in the figure, an S1 connection (S1-U connection) for the UE 100 also exists between the eNB 200 and the S-GW 300U.

[0115] 10 , in step S1003, the anchor eNB 200-1 transmits a transition instruction (Light Connection Instruction) to the UE 100 to instruct the UE 100 to transition to the Light Connected state. As described above, the transition instruction is transmitted in an RRC Connection Reconfiguration message or an RRC Connection Release message. The anchor eNB 200-1 may set a RAN paging area specific to the UE 100 for the UE 100.

[0116] In step S1004, in response to the reception of the transition instruction from the cell (serving cell) of the anchor eNB 200-1, the UE 100 transitions to the Light Connected state.

[0117] In step S1005, the UE 100 detects that it has moved outside the RAN paging area set for itself, for example, based on a cell identifier or a paging area ID transmitted by the eNB 200-2 outside the RAN paging area. Note that the eNB 200-2 does not need to have an X2 interface with the anchor eNB 200-1.

[0118] In step S1006, the UE 100 transmits to the eNB 200-2 a message indicating that the UE 100 has moved out of the RAN paging area set for the UE 100. The message may be a message indicating an update of the RAN paging area (Paging Area Update). The message may be a message requesting recovery from the Light Connected state (RRC Connection Boot request). The message may be an RRC Connection Resume Request message.

[0119] The message may include a Resume ID, a Short Resume MAC-I, and a Resume Cause.

[0120] Alternatively, instead of the Resume ID, an identifier consisting of a combination of a cell identifier (cell ID) and a Cell-Radio Network Temporary Identifier (C-RNTI) may be used. The cell ID may be an E-UTRAN Cell Global Identifier (ECGI), an E-UTRAN Cell Identifier (ECI), or a Physical Cell Identifier (PCI). The cell ID and / or the C-RNTI may not be explicitly provided in an instruction to transition to Light Connected (e.g., RRC Connection Release). When receiving the instruction to transition to Light Connected, the UE 100 may store the cell ID of the cell and the currently assigned C-RNTI. When resuming, the UE 100 reads out this value and notifies the eNB 200.

[0121] The ECGI is a combination of an ECI and a PLMN ID. That is, the ECI does not have a PLMN ID. Therefore, when the ECI is used as a cell identifier, the identifier formed by this combination may be valid only within the same PLMN (Public Land Mobile Network).

[0122] When the PCI is used as the cell identifier, the eNB 200 may find the specific eNB (anchor eNB) by using the PCI received from the UE 100 and a neighbor cell list (Neighbor Relation Table) that the eNB 200 has.

[0123] The combination of identifiers that UE 100 should notify may be specified by eNB 200. For example, eNB 200 may broadcast, via SIB, a notification of an identifier that is a combination of ECI and C-RNTI. Alternatively, eNB 200 may individually set the identifier for UE 100.

[0124] Also, although not shown in the figure, even when ECI and PCI are used, eNB200 can identify the specific eNB (anchor eNB), and therefore eNB200 can obtain the UE context (configuration information) from the specific eNB using the X2 or S1 interface.

[0125] Although not shown in the figure, the identifier formed by this combination may be used to identify the calling UE in paging. When UE 100 receives a paging message, it reads out the identifier and determines that it is being called if the identifier matches the identifier in the paging message. In this case, UE 100 may start an operation to establish an RRC connection (for example, sending an RRC Connection Request).

[0126] Furthermore, instead of Resume Cause, Boot Cause relating to recovery from Light Connected may be used, or a new value such as LightConnected-Access relating to recovery from Light Connected may be defined as Resume Cause.

[0127] In step S1007, in response to receiving the message from UE 100, eNB 200-2 transmits a message (S1 Path Switch Request) to MME 300C over the S1 interface to request switching of the S1 connection to eNB 200-2. The message (S1 Path Switch Request) includes the ID address of the E-RAB for which path switching is to be performed, the source MME UE S1AP ID, a cell ID, etc. The eNB 200-2 includes paging information (PA info.) indicating a new RAN paging area for UE 100 in the message (Path Switch Request). The paging information (PA info.) may be a list of cells (Recommended Cell List) included in the new RAN paging area.

[0128] In step S1008, the MME 300C ascertains or determines a new RAN paging area for the UE 100 based on the message (Path Switch Request) received from the eNB 200-2. That is, the MME 300C can manage the RAN paging area in which the UE 100 is located based on the paging information (PA info.). The MME 300C also performs a process of switching the S1 connection for the UE 100 from the anchor eNB 200-1 to the eNB 200-2.

[0129] Note that this sequence assumes that there is no X2 interface between anchor eNB200-1 and eNB200-2. However, if there is an X2 interface between anchor eNB200-1 and eNB200-2, eNB200-2 may transmit UE Context Release or UE Context Retrieve to anchor eNB200-1 over the X2 interface in response to receiving a message from UE100. UE Context Release is a message for requesting the release of context information of UE100. UE Context Retrieve is a message for acquiring context information of UE100. eNB200-2 may include paging information (PA info.) in these messages. Anchor eNB200-1 may forward the paging information (PA info.) received from eNB200-2 to MME300C.

[0130] [Second embodiment] The second embodiment will be described below, focusing mainly on the differences from the first embodiment. The second embodiment is an embodiment related to the operation of the eNB 200 performing RAN paging.

[0131] The eNB200 according to the second embodiment includes a control unit 230 that performs RAN paging on the UE 100 in the Light Connected state and determines whether the RAN paging is successful, and a transmission unit (backhaul communication unit 240) that transmits a failure notification indicating the failure of the RAN paging to the MME 300C in response to a failure of the RAN paging. The RAN paging is an operation in which the RAN performs paging on the UE 100 in units of RAN paging areas. The failure notification may be a message that causes the MME 300C to perform paging based on the tracking area in which the UE 100 resides. Therefore, even if the RAN paging fails, the MME 300C can perform normal paging.

[0132] The eNB 200 according to the second embodiment may include a receiver (backhaul communication unit 240) that receives information regarding whether or not paging has been successful for another eNB 200 within the RAN paging area from the other eNB 200. The controller 230 determines that RAN paging has failed in response to paging failures for both the eNB 200 itself and the other eNB 200.

[0133] Fig. 11 is a diagram showing an example of operation according to the second embodiment. In Fig. 11, anchor eNB200-1 and eNB200-2 belong to the same RAN paging area. Anchor eNB200-1 and eNB200-2 may be connected via an X2 interface. In the initial state of Fig. 11, UE100 is in RRC connected mode (S2001, S2002). Note that the operations indicated by dashed lines in Fig. 11 are not essential.

[0134] As shown in FIG. 11, the operations in steps S2003 and S2004 are the same as those in the first embodiment.

[0135] In step S2005, the anchor eNB 200-1 receives data (DL data) addressed to the UE 100 from the S-GW 300U via the S1 connection for the UE 100. In response to the reception of the data, the anchor eNB 200-1 determines to start paging of the UE 100.

[0136] In step S2006, the anchor eNB 200-1 transmits, to the eNB 200-2, a paging request requesting execution of paging (RAN paging) of the UE 100. The paging request may include information for specifying paging timing (see the third embodiment).

[0137] In step S2007, the anchor eNB 200-1 starts a timer when it determines to start paging or when it transmits a paging request. The anchor eNB 200-1 may stop the timer when it receives a paging response from the UE 100 or a paging success notification from the eNB 200-2.

[0138] In step S2008, anchor eNB 200-1 and eNB 200-2 transmit a paging message (Ran paging) addressed to UE 100 within the RAN paging area set for UE 100. Here, the description will proceed assuming that UE 100 fails to receive the paging message (Ran paging).

[0139] In step S2009, the eNB 200-2 transmits a failure notification (Paging Failure) indicating that paging of the UE 100 (RAN paging) has failed to the anchor eNB 200-1.

[0140] In step S2010, the anchor eNB 200-1 determines whether the timer has expired and / or whether a failure notification (Paging Failure) has been received. Here, the description will proceed assuming that the timer has expired and / or a failure notification (Paging Failure) has been received.

[0141] In step S2011, the anchor eNB 200-1 transmits a failure notification (RAN Paging Failure) indicating a failure of RAN paging to the MME 300C over the S1 interface. The failure notification (RAN Paging Failure) includes an identifier (e.g., eNB UE S1AP ID) that allows the MME 300C to identify the UE 100. The failure notification (RAN Paging Failure) may include the MME UE S1AP ID, a Cause (e.g., RAN Paging Failed), and the like. Note that instead of the failure notification (RAN Paging Failure), a paging request (Paging Request) requesting the execution of paging may be used.

[0142] In step S2012, in response to receiving a failure notification (RAN Paging Failure) from anchor eNB200-1, MME300C transmits a paging message (PAGING) to each eNB200 belonging to the tracking area in which UE100 is located. Each eNB200 belonging to the tracking area in which UE100 is located transmits the paging message within its own cell. However, instead of transmitting the paging message to all eNB200 belonging to the tracking area in which UE100 is located, MME300C may transmit the paging message only to some of the eNB200 belonging to the tracking area.

[0143] In step S2013, in response to receiving the paging message (PAGING), the UE 100 transmits a message (RRC Connection Boot request) requesting recovery from the Light Connected state to the eNB 200 (for example, the anchor eNB 200-1).

[0144] [Third embodiment] The third embodiment will be described below, focusing mainly on the differences from the first and second embodiments. The third embodiment is an embodiment related to the DRX operation of the UE 100 in the light connected state.

[0145] First, a general idle mode DRX operation will be described. To reduce power consumption, discontinuous reception (DRX) may be configured in the UE 100. In the DRX operation, the UE 100 in the RRC idle mode monitors paging messages at paging reception opportunities (Paging Occasions) that occur at predetermined time intervals (DRX cycles). In the DRX operation, the UE 100 discontinuously monitors the PDCCH to receive paging. The UE 100 decodes the PDCCH using a paging identifier (P-RNTI: Paging Radio Network Temporary Identifier) ​​to acquire paging channel allocation information. The UE 100 acquires the paging message based on the allocation information. The PDCCH monitoring timing in the UE 100 is determined based on the identifier (IMSI: International Mobile Subscriber Identity) of the UE 100. The PDCCH monitoring timing (PDCCH monitoring subframe) in the DRX operation is called a Paging Occasion (PO). The PO corresponds to a paging reception opportunity.

[0146] The UE 100 and the eNB 200 calculate a Paging Occasion (PO) and a Paging Frame (PF), which is a radio frame that may include a Paging Occasion, as follows.

[0147] The system frame number (SFN) of the PF is calculated using the following formula (1).

[0148] SFN mod T = (T div N) * (UE_ID mod N) …(1)

[0149] where T is the DRX cycle of UE 100 for monitoring paging, and is expressed as the number of radio frames. T is the smaller of the default DRX value broadcast by eNB 200 using an SIB (System Information Block) and the UE-specific DRX value set in UE 100 using an NAS message. If a UE-specific DRX value is not set, UE 100 applies the default DRX value. N is the minimum value of T and nB. nB is a value selected from 4T, 2T, T, T / 2, T / 4, T / 8, T / 16, and T / 32. UE_ID is a value calculated using "IMSI mod 1024".

[0150] Among the PFs thus obtained, an index i_s is obtained by the following equation (2), and the subframe number of the PO corresponding to the index i_s is obtained.

[0151] i_s = floor(UE_ID / N) mod Ns …(2)

[0152] Here, Ns is the maximum value between 1 and nB / T.

[0153] Next, a description will be given of the operation according to the third embodiment, with reference to Fig. 12, which is a diagram showing the operation according to the third embodiment.

[0154] A UE 100 according to operation pattern 1 of the third embodiment includes a receiver 110 that receives a transition instruction from a serving cell to instruct the UE 100 to transition to the Light Connected state, and a controller 130 that transitions to the Light Connected state in the serving cell and performs DRX operation in the RRC connected mode. That is, as shown in FIG. 12(a), the UE 100 continues the DRX operation in the RRC connected mode while the UE 100 is present in the serving cell at the time of transition to the Light Connected state. As shown in FIG. 12(b), the controller 130 of the UE 100 suspends the DRX operation in the RRC connected mode in response to the UE 100 moving from the serving cell to another cell within the RAN paging area. The controller 130 of the UE 100 suspends the DRX operation in the RRC connected mode and starts operation based on the DRX operation in the RRC idle mode. The operation based on the DRX operation in the RRC idle mode is an operation of determining a paging frame (PF) and a paging occasion (PO) using a calculation formula for the PF and the PO in the DRX operation in the RRC idle mode or a calculation formula adapted from the calculation formula. As shown in Fig. 12(c), the control unit 130 of the UE 100 performs a notification when the UE 100 moves to a different RAN paging area.

[0155] Alternatively, even if the UE 100 according to operation pattern 2 of the third embodiment moves from the serving cell at the time of transition to the Light Connected state to another cell, the UE 100 continues the DRX operation in the RRC connected mode as long as the other cell belongs to the same RAN paging area. In this case, as shown in FIGS. 12(a) and 12(b), the UE 100 can continue the DRX operation in the RRC connected mode within the same RAN paging area. That is, even if the UE 100 moves to another cell, the UE 100 performs a reception operation in accordance with the connected mode DRX. As will be described later, a setting value (DRX Config) of the connected mode DRX may be transferred to the eNB 200-2 in the paging request.

[0156] Here, such an operation may be performed on a per eNB 200 basis. That is, in operation patterns 1 and 2 of the third embodiment, the "serving cell" may be read as the "serving eNB" or the "anchor eNB", and the "other cell" may be read as the "other eNB".

[0157] In the operation patterns 1 and 2 of the third embodiment, UEs 100 other than the anchor eNB do not necessarily hold the context information of the UE 100. Therefore, it is desirable that other eNBs within the same RAN paging area obtain information for determining the timing of paging from the anchor eNB.

[0158] The eNB 200-2 (see FIG. 11 ) according to the third embodiment includes a control unit 230 that performs RAN paging for the UE 100 in the Light Connected state. The control unit 230 acquires information for determining the timing of transmitting a paging message for RAN paging to the UE 100 from the anchor eNB 200-1 (see FIG. 11 ). The information for determining the timing includes at least one of identification information of the UE 100 (e.g., IMSI, S-TMSI, Resume ID, etc.) and a DRX setting in the RRC connected mode. The anchor eNB 200-1 may include such information in a paging request and transmit it to the eNB 200-2 (see step S2006 in FIG. 11 ).

[0159] In the third embodiment, the identification information for determining the timing of paging may be an E-UTRAN Cell Global Identifier (ECGI) and a Cell-Radio Network Temporary Identifier (C-RNTI). The anchor eNB200-1 may assign the identification information to the UE 100 when transitioning the UE 100 to the light connected state.

[0160] [Fourth embodiment] The fourth embodiment will be described below, focusing mainly on differences from the first to third embodiments. The fourth embodiment is an embodiment related to a message for transitioning the UE 100 to the light connected state.

[0161] 13 is a diagram illustrating operation pattern 1 of the fourth embodiment. In operation pattern 1 of the fourth embodiment, UE 100 includes: a receiving unit 110 that receives an RRC Connection Reconfiguration message from a serving cell; a transmitting unit 120 that transmits an RRC Connection Reconfiguration Complete message, which is a response message to the RRC Connection Reconfiguration message, to the serving cell when the RRC Connection Reconfiguration message does not include a transition instruction instructing the UE to transition to a Light Connected state; and a control unit 130 that cancels transmission of the RRC Connection Reconfiguration Complete message when the RRC Connection Reconfiguration message includes a transition instruction. Here, the transition instruction may be setting information related to a Light Connection. According to operation pattern 1, UE 100 does not transmit an RRC Connection Reconfiguration Complete message when a Light Connection is set up in the RRC Connection Reconfiguration. This makes it possible to reduce signaling.

[0162] FIG. 14 is a diagram illustrating an operation pattern 2 of the fourth embodiment. In the operation pattern 2 of the fourth embodiment, the UE 100 includes a receiver 110 that receives an RRC Connection Release message from a serving cell, a controller 130 that stops transmitting a response message to the RRC Connection Release message when the RRC Connection Release message does not include a transition instruction for transitioning to the Light Connected state, and a transmitter 120 that transmits an RRC Connection Release Complete message, which is a response message, to the serving cell when the RRC Connection Release message includes a transition instruction. Here, the transition instruction may be configuration information related to the Light Connection. The controller 130 of the UE 100 transitions to the Light Connected state when it is confirmed, for example, based on an HARQ ACK, that the RRC Connection Release Complete message has been delivered. According to the operation pattern 2, the UE 100 transmits the RRC Connection Release Complete message when a transition to the Light Connected state is instructed in the RRC Connection Release. This allows the eNB 200 to more reliably confirm that the UE 100 has transitioned to the Light Connected state.

[0163] [Fifth embodiment] The fifth embodiment will be described below, focusing on differences from the first to fourth embodiments. The fifth embodiment is an embodiment related to a message for the UE 100 to recover from the light connected state.

[0164] The UE 100 according to the fifth embodiment includes a transmitter 120 that transmits information indicating recovery from the light connected state to a serving cell, and a controller 130 that recovers from the light connected state without receiving an RRC connection reconfiguration message from the serving cell. The information indicating recovery from the light connected state is, for example, the above-mentioned RRC activation request, RRC connection resume request, RRC connection boot request, etc.

[0165] FIG. 15 is a diagram illustrating an example of operation according to the fifth embodiment.

[0166] 15(a), according to the legacy approach, UE 100 in the light connected state transmits a request to recover from the light connected state to eNB 200. Next, UE 100 receives an RRC connection reconfiguration message from eNB 200 and transmits an RRC connection reconfiguration complete message to eNB 200, thereby recovering from the light connected state (transitioning to RRC connected mode).

[0167] As shown in Fig. 15(b), according to the first approach (One-step approach) of the fifth embodiment, the UE 100 in the Light Connected state recovers from the Light Connected state (transitions to the RRC connected mode) simply by transmitting an indication indicating recovery from the Light Connected state to the eNB 200. The indication may include information requesting allocation of radio resources (scheduling request) and / or information reporting an uplink buffer status (buffer status report). If the UE 100 cannot confirm that the indication has been delivered based on an HARQ ACK or the like, the UE 100 may either maintain the Light Connected state or transition to the RRC idle mode.

[0168] As shown in FIG. 15(c), according to the second approach (two-step approach) of the fifth embodiment, the UE 100 in the light connected state transmits a request (Request) to the eNB 200 to recover from the light connected state, and recovers from the light connected state (transitions to the RRC connected mode) simply by receiving an acknowledgement (Acknowledge) in response to the request from the eNB 200. The request (Request) may include information requesting allocation of radio resources (scheduling request) and / or information reporting an uplink buffer status (buffer status report). The eNB 200 may transmit a negative acknowledgement to the request (Request) to the UE 100. If the UE 100 receives the negative acknowledgement, the UE 100 may either maintain the light connected state or transition to the RRC idle mode. Whether to maintain the light connected state or transition to the RRC idle mode may be specified in the negative acknowledgement.

[0169] Therefore, according to the fifth embodiment, it is possible to reduce signaling compared to conventional approaches. The reason why RRC Connection Reconfiguration is not necessary is as follows. Specifically, assuming that the Light Connected state is a state similar to the RRC Connected mode, the eNB200 does not need to prepare new resources (i.e., there is no reason to reject). Also, the UE does not need to apply new settings (i.e., there is no setting failure). Furthermore, there is no RRC state transition, and the eNB200 and the UE100 do not need to match their recognition. For example, if the UE100 operates according to DRX in the RRC Connected mode, the reception timing of the UE100 is the same in both the Light Connected state and the RRC Connected mode, so data communication is not disabled.

[0170] However, the UE 100 may perform the operation according to the fifth embodiment only when the UE 100 is present in the cell at the time of transition to the Light Connected state. The UE 100 may perform the operation according to the conventional approach when the UE 100 moves from the cell at the time of transition to the Light Connected state to another cell within the same RAN paging area.

[0171] An indication and a request according to the fifth embodiment may be transmitted to the eNB 200 during a random access procedure. As an example, the indication and the request may be transmitted from the UE 100 to the eNB 200 in Msg1 (random access preamble / PRACH transmission) or Msg3 (scheduled transmission) of the random access procedure. Furthermore, an acknowledgement or a negative acknowledgement may be transmitted from the eNB 200 to the UE 100 in Msg2 (random access response) or Msg4 (contention resolution) of the random access procedure.

[0172] [Sixth embodiment] The sixth embodiment will be described below, focusing mainly on the differences from the first to fifth embodiments. The sixth embodiment is an embodiment relating to a notification (Extended PPI) indicating an interruption of data communication.

[0173] As described above, when data communication is not occurring (or is not expected to occur), the UE 100 transmits the notification (Extended PPI) to the eNB 200. In contrast, in the sixth embodiment, the notification (Extended PPI) is improved as follows.

[0174] The UE 100 according to the sixth embodiment includes a control unit 130 that detects an interruption of data communication with a serving cell (eNB 200), and a transmission unit 120 that, in response to detecting the interruption of data communication (Data inactive), transmits a notification (Extended PPI) indicating the interruption of data communication to the serving cell. The control unit 130 estimates an expected time for the interruption of data communication. The transmission unit 120 transmits the notification (Extended PPI) including the expected time.

[0175] The UE 100 (control unit 130) may predict the interruption time of data communication based on information from the application layer, as described above. Specifically, the time notified from the application layer may be used as the predicted time. Alternatively, the prediction may be made by the UE 100 (on the AS side) using information from the application layer, such as which applications are running and which applications have been shut down, and whether the user is currently performing an operation (or whether foreground communication is expected or only background communication is expected). The AS (Access Stratum) consists of each protocol below the RRC layer. For example, the AS side collects traffic generation patterns in advance, and performs traffic prediction and estimates the predicted time using information from the application layer, etc. as needed.

[0176] In the sixth embodiment, the notification (Extended PPI) may be a direct notification of a desire to enter the light connected state or a direct notification that it is possible to enter the light connected state.

[0177] In the sixth embodiment, the eNB200 may explicitly or implicitly configure the UE100 as to whether or not to transmit a notification (Extended PPI). For example, when the UE100 broadcasts an identifier indicating that transmission of the notification (Extended PPI) is permitted in the SIB, or when the eNB200 has set up transmission of the notification (Extended PPI), the UE100 determines that transmission of the notification (Extended PPI) is permitted. Furthermore, whether the notification (Extended PPI) is 1) determined based on a past state (i.e., no data has occurred), 2) determined based on a future prediction (i.e., there is no possibility of occurrence), or 3) determined based on both the past and future may be configured by the eNB200 to the UE100. Furthermore, a prohibit timer value and / or a report period of the notification (Extended PPI) may be configured by the eNB200 to the UE100. The prohibit timer is a timer that defines the time until the UE 100 is enabled to transmit the next notification (Extended PPI) after transmitting the notification (Extended PPI).

[0178] In the sixth embodiment, the notification (Extended PPI) may include a recommended or desired DRX cycle for Light Connection DRX. The UE 100 (control unit 130) may determine the desired DRX cycle based on the above-described expected time of interruption of data communication. Specifically, the UE 100 determines an appropriate DRX cycle based on its own situation and transmits the DRX cycle in the notification (Extended PPI). The UE 100 may apply the notified DRX cycle at the time of sending the notification. Alternatively, the UE 100 may set the DRX cycle in response to a response (such as RRC connection reconfiguration) from the eNB 200. When the notification is sent and a DRX cycle is applied, the application may be considered to have resulted in a transition to Light Connected.

[0179] Note that the eNB 200 may set (for example, by broadcast or unicast) a timer value for the UE 100 until the UE 100 transitions to the Light Connected state. The UE 100 resets (restarts) the timer when data communication is performed, and transitions to the Light Connected state when the timer expires. The UE 100 may notify the eNB 200 of the data interruption when the data communication is interrupted while the timer is running (for example, when the predicted time is later than the timer expiration).

[0180] [Seventh embodiment] The seventh embodiment will be described below, focusing mainly on differences from the first to sixth embodiments. The seventh embodiment is an embodiment related to a cell reselection operation of the UE 100 in the light connected state.

[0181] The UE 100 according to the seventh embodiment includes a control unit 130 that performs a cell reselection operation in the light connected state. In the cell reselection operation, the control unit 130 preferentially selects a cell that supports recovery from the light connected state as a serving cell for the UE 100.

[0182] A typical cell reselection operation is an operation of selecting an appropriate cell based on a ranking based on the priority of the frequency to which the cell belongs and the radio quality of the cell.

[0183] In the cell reselection operation according to the seventh embodiment, the UE 100 (control unit 130) may set a cell that supports Light Connected as the highest priority. The UE 100 (control unit 130) may set a cell that does not support Light Connected as the lowest priority. Here, Highest / Lowest means a priority (for example, "8" or "-1") higher / lower than the priority (CellReselectionPriority: 0 to 7) broadcast from the eNB 200 or the value obtained by adding the priority and a sub-priority (CellReselectionSubPriority: 0.2, 0.4, 0.6, 0.8).

[0184] Alternatively, in the cell reselection operation according to the seventh embodiment, the UE 100 (control unit 130) may prioritize cells that support Light Connected by introducing an offset into the ranking. For example, a positive offset may be added to a cell that supports Light Connected, and / or a negative offset may be added to a cell that does not support Light Connected. The offset value may be a predefined value or may be a value set by the eNB 200. When set by the eNB 200, the eNB 200 may broadcast the offset value or may set the offset value individually for each UE by dedicated signaling.

[0185] In the seventh embodiment, the eNB 200 may configure the UE 100 as to whether or not to perform priority control of a cell that supports recovery from the light connected state. This configuration may be configured when transitioning to the light connected state. This configuration may be included in RRC connection reconfiguration or RRC connection release.

[0186] Each eNB 200 (each cell) may broadcast information indicating whether it supports the light connected state (specifically, recovery from the light connected state). As an example, the eNB 200 transmits the information by an SIB. Such information may be implicit information. For example, the UE 100 may consider a cell transmitting an identifier of a RAN paging area as a cell that supports the light connected state.

[0187] In the seventh embodiment, the UE 100 may transition to the RRC idle mode in response to a case where a cell that supports recovery from the light connected state and satisfies a predetermined radio quality criterion (for example, S criterion) is not detected. As an example, the UE 100 may transition to the RRC idle mode in a case where the only cell that satisfies the S-criterion is a legacy cell (that is, a cell that does not support the light connected state).

[0188] [Other embodiments] The above-described embodiments may be implemented not only independently but also in combination with two or more embodiments. For example, some operations according to one embodiment may be added to another embodiment. Alternatively, some operations according to one embodiment may be replaced with some operations according to another embodiment.

[0189] In the above-described embodiment, no particular mention is made of a case in which the UE 100 receives or is interested in receiving a Multimedia Broadcast Multicast Service (MBMS). However, the eNB 200 may determine whether to transition the UE 100 to the Light Connected state based on the reception status of the Multimedia Broadcast Multicast Service (MBMS) at the UE 100, etc. As an example, if Single-cell Point-to-Multipoint (SC-PTM) reception is not performed in the Light Connected state (for example, if SC-PTM reception is not permitted or the UE capability is insufficient), the eNB 200 does not transition the UE 100 to the Light Connected state. As another example, if the MBMS Interest Indication indicates interest in MBMS service reception (for example, SC-PTM reception), the eNB 200 does not transition the UE 100 to the Light Connected state. Furthermore, some UEs 100 cannot receive MBMS in the RRC Connected state. If the UE 100 is capable of receiving MBMS in the Light Connected state, the eNB 200 may transition the UE 100 to the Light Connected state in response to the UE 100 indicating an interest in receiving the MBMS service (for example, SC-PTM reception).

[0190] In the above-described first embodiment, an example has been described in which an identifier formed by a combination of a cell ID and a C-RNTI is included in a paging message.

[0191] However, even when high-priority MT data (an incoming call to UE 100) occurs, the current paging does not have a means for indicating this situation. Therefore, when paging occurs for UE 100 that prioritizes MBMS reception (for example, SC-PTM reception), there is a risk that it will not be possible to appropriately determine whether to continue MBMS reception or to interrupt MBMS reception and prioritize RRC connection.

[0192] Therefore, by adding priority information to the paging message, it becomes possible to make an appropriate decision. The priority information may be a value of Establishment Cause (e.g., high priority access), an identifier indicating that the incoming call is of high priority, a numerical value indicating the priority (e.g., 0 to 7), or a bearer identifier associated with the incoming call. The priority information may also be provided by a list, and each entry of the list may correspond to each entry of a list of UE identifiers in the paging message (Paging Record List). Alternatively, the priority information may be incorporated into an entry of the Paging Record List (i.e., a Paging Record). The priority information may be determined by the eNB200 or the MME300C.

[0193] The UE 100, which has received the paging message including the priority information, determines whether or not an RRC connection initiation process (e.g., RRC Connection Request transmission) is necessary, using the priority information. When starting the RRC connection process, the UE 100 may notify the eNB 200 that the process is based on the priority information (e.g., "prioritized MT call") in a message for the RRC connection process, and the notification may be included in an Establishment Cause.

[0194] On the other hand, when the UE 100 prioritizes MBMS reception over a paging message including priority information, the UE 100 does not need to respond to the paging message.

[0195] In each of the above-described embodiments, an example has been described in which the occurrence of a predetermined event is used as a trigger to terminate the Light Connected state. The Light Connected state may be valid only during a period in which a timer set in the UE 100 by the eNB 200 is operating. In this case, the predetermined event may be expiration of the timer. Alternatively, the Light Connected state may be valid only during a period in which the UE 100 exists within a predetermined frequency. For example, the UE 100 that has received an instruction to enter the Light Connected state in a certain cell may terminate the Light Connected state in response to moving to a cell using a frequency different from the frequency to which the cell belongs.

[0196] In each of the above-described embodiments, the LTE system has been exemplified as a mobile communication system. However, the present invention is not limited to the LTE system. The present invention may also be applied to systems other than the LTE system.

[0197] (Appendix 1) (1. Introduction) RAN2#95 agreed on the basic functions / characteristics of Light Connected as follows:

[0198] Agreement: Light Connected UE capabilities include:

[0199] The S1 connection is maintained and active in the "anchor eNB".

[0200] -Support for RAN initiated paging.

[0201] The paging process is controlled by an "anchor NB".

[0202] - eNB-controlled RAN-based paging area.

[0203] RAN-based paging area update mechanism: The RAN-based paging area may be configurable as UE-specific.

[0204] -Implement cell reselection-based mobility, which is the same cell reselection mechanism as in RRC idle.

[0205] The UE's AS context is maintained on both the UE and the "anchor eNB" side.

[0206] -The ECM state is ECM connected from the network's perspective. The state from the UE's perspective needs further consideration.

[0207] (Lightly Connected) When the UE is paged (via RAN initiated paging) or any MO data / signaling is triggered, the UE returns to connect to the eNB. The related procedures require further study.

[0208] -UE is "lightly connected" via RRC signaling. Details need further study.

[0209] This appendix provides details about Light Connected.

[0210] (2. Consideration) (2.1. Modeling principles) (2.1.1. RRC States and Substates) LTE has two RRC states: RRC Connected and RRC Idle. Even when the RRC Connection Suspend / Resume procedure was introduced in Release 13, the two-state modeling was maintained. A UE that has suspended its RRC connection is in RRC Idle from a state perspective, i.e., it is a "sub-state" of an Idle UE that remembers the AS context and resume ID. The two-state modeling works well to simplify the state transitions and these states, which are somewhat complex in legacy systems. Therefore, RAN2 should stick to the RRC modeling even with the introduction of Light Connected. That is, it should be defined as a Light Connected "sub-state" that is part of RRC Connected or Idle, with specific functionality added or restricted depending on the desired behavior determined by RAN2.

[0211] Proposal 1: RAN2 should stick to the existing two-state modeling, i.e., RRC Connected and Idle, where Light Connected is defined in RRC.

[0212] (2.1.2. Baseline Condition) If Proposal 1 is acceptable, the Light Connected "sub-state" will be built on top of RRC Connected or RRC Idle.

[0213] In RAN2#95, it was suggested that RRC Suspended / Resume is the baseline for Light Connected. Light Connected combines the ability to suspend the RRC connection from the UE's perspective with a new capability to actively maintain the S1 connection from the CN's perspective. While still beneficial for S1, eliminating the UE context suspend / resume request / response is still beneficial, as the UU does not benefit in terms of signaling and latency reduction in Release 14 compared to Release 13 due to its reliance on Release 13 procedures. Furthermore, there may be an ECM state mismatch between the NW and a Light Connected UE. That is, from the network's perspective, the ECM state is ECM Connected, but from the UE's perspective, it is ECM Idle, since the UE is in RRC Idle while the RRC connection is suspended. It is unclear whether this mismatch will be accepted by other WGs.

[0214] Observation 1: RRC suspend-based light connected may not provide any gain in terms of reducing Uu signaling / latency.

[0215] Observation 2: It is unclear whether the mismatch in ECM state between NW and light-connected UEs is acceptable.

[0216] Meanwhile, a method based on RRC Connected has also been proposed. The greatest benefit of RRC Connected is low access latency for MO and MT calls. Potentially, paging is not required for MT calls, but the introduction of "RAN-initiated paging support" for Light Connected has already been agreed upon. Furthermore, ECM states are naturally synchronized between the network and the UE. Therefore, RRC Connected-based Light Connected has the potential to improve Uu signaling and latency without unnecessary impact on upper layers, i.e., the NAS. However, simply keeping the UE in legacy RRC Connected mode clearly results in poor UE power consumption. In other words, the solution fails to achieve the goal of "making UE power consumption equivalent to that of RRC Idle." Therefore, if RRC Connected-based Light Connected is necessary, some optimizations are required.

[0217] Consideration 3: RRC Connected-based Light Connected requires standardization efforts in RAN2 to minimize UE power consumption, but has the potential to improve Uu signaling overhead and access latency without unnecessary impact on higher layers.

[0218] The first statement of the WI goal is that the purpose of this work item is to reduce radio and network interface signaling overhead and improve UE access latency and UE power consumption for all device types, i.e., not only MTC UEs but also regular LTE UEs such as smartphones. Regarding MTC-type traffic, this was already optimized by RRC Connection Suspend / Resume in Release 13, which of course also applies to regular LTE UEs. Therefore, Release 14 work should focus on regular LTE UEs such as smartphone traffic.

[0219] Observation 4: Light Connected must be efficient not only for MTC-type traffic, which is already optimized in Release 13, but also for regular LTE traffic such as smartphones, which is a major challenge for Release 14.

[0220] Considering the above considerations, i.e., ECM state mismatch, as well as optimization of signaling / latency and adaptation for smartphone traffic, RAN2 needs to take the RRC Connected state as the baseline for the Light Connected "sub-state".

[0221] Proposal 2: RAN2 should use the RRC Connected state as the baseline for Light Connected.

[0222] (2.2. RRC Signaling) (2.2.1. Transition to Light Connected) RAN2#95 agreed that "UE enters 'Light Connected' by RRC signaling. Details require further study. If Proposal 2 is reasonable, it is straightforward to use the RRC Connection Reconfiguration message to establish Light Connected, since RRC connection release due to RRC connection interruption transitions the UE to RRC Idle.

[0223] Proposal 3: RAN2 should use the RRC Connection Reconfiguration message to set up Light Connected.

[0224] However, one drawback of the RRC Connection Reconfiguration message is that it requires a handshake in the RRC Connection Reconfiguration Complete, which is not required in the RRC Connection Release. From the perspective of signaling reduction, it is preferable for the UE not to send the RRC Connection Reconfiguration Complete. However, without an acknowledgement, as in the case of the RRC Connection Release message, the probability of a state mismatch between the serving cell and the UE would increase. In contrast, if the RRC Connected-based Light Connected state is already a substate of the RRC Connected state, issues involving state transition mismatch are not a significant concern. Therefore, the RAN2 should discuss whether an RRC Connection Reconfiguration Complete is required when transitioning the UE to Light Connected.

[0225] Proposal 4: RAN2 should discuss whether an acknowledgement from the UE, such as RRC connection re-establishment completion, is required when the UE transitions to Lightly Connected.

[0226] It is also worth considering whether to allow autonomous transition to Light Connected: the serving cell could set an "inactivity" timer for the UE via broadcast / dedicated signaling, and once the timer expires, the UE could autonomously proceed to "Light Connected". This could further reduce the overhead of Light Connected control for the Uu.

[0227] Proposal 5: RAN2 should discuss whether to allow autonomous entry into Light Connected, for example using an "inactivity timer", to further reduce signaling.

[0228] (2.2.2. Moving away from Light Connected) It has been agreed that when a "Lightly Connected" UE is paged (via RAN initiated paging) or any MO data / signaling is triggered, the UE will return to being connected to the eNB. The related procedures require further study. Therefore, it is worth considering how to return from Lightly Connected to RRC Connected.

[0229] In the conventional approach, the handshake to obtain an RRC connection requires three steps: (1) RRC Connection Resumption Request, (2) RRC Connection Resumption, and (3) RRC Connection Resumption Complete ((b) and (c) in Figure 15). On the other hand, if the handshake is minimized, signaling and latency can be reduced ((b) and (c) in Figure 15).

[0230] For example, a one-step approach with instructions from the UE, such as that shown in Figure 15(b), is beneficial for minimizing signaling and latency. Regarding the state mismatch problem discussed in Proposal 4, from the perspective of message reachability, only DL is an issue due to UE radio issues (i.e., reception errors during T310 execution are only visible to the UE, not the serving cell). Therefore, the one-step approach is technically feasible.

[0231] If Proposal 2 is reasonable, i.e., in the RRC Connected-based "substate," the serving cell can consider whether to reject a UE returning to RRC Connected, as shown in Figure 15(c). Since a Lightly Connected UE is already part of RRC Connected, it seems unnecessary to send a rejection message. If for some reason the number of RRC connections needs to be reduced, the serving cell can initiate an RRC connection release at any time.

[0232] Therefore, we prefer the one-step approach, but RAN2 should discuss whether to optimize signaling during the transition from Light Connected to RRC Connected.

[0233] Proposal 6: RAN2 should consider minimizing the handshake for transitioning from Light Connected to RRC Connected.

[0234] (2.2.3. Recognizing Inactivity During RRC Connected) Because the UE enters Light Connected mode via RRC signaling, the serving cell should determine when to enter Light Connected. One possible implementation is for the serving cell to monitor traffic behavior and enter Light Connected when the UE has not sent or received packets for a certain period of time. Because this depends on the predicted traffic behavior, an inaccurate prediction could actually increase signaling overhead. For example, frequent switching between Light Connected and RRC Connected, or a failure to transition to Light Connected. While MTC-type traffic is somewhat easy to predict, LTE-type traffic and smartphone traffic behavior may not be easy for the network to predict. Therefore, since the UE has better knowledge / control of its traffic behavior, it may be necessary for the UE to provide some assistance information. Therefore, it is worth considering whether the serving cell should configure the UE to provide assistance information to trigger Light Connected.

[0235] Proposal 7: RAN2 should discuss whether the serving cell can configure the UE to provide assistance information to decide to put the UE into Light Connected mode via RRC signaling.

[0236] If Proposal 7 is acceptable, the assistance information may have some similarities with the existing Power Preference Indicator (PPI) and / or MBMS Interest Indication (MII). Using the PPI, the UE can signal low power consumption if its power consumption is preferred to be optimized, e.g., by a longer DRX cycle. The MII is used to signal MBMS frequencies of interest and priority between unicast and MBMS, e.g., when handover to a frequency is preferred. In this case, the UE can signal the possibility of entering Light Connected to the serving cell. In other words, the UE can transmit assistance information when data transmission / reception has already been or will be inactive for a certain period of time. The details and necessity of additional assistance require further study, such as the expected inactivity time of the UE.

[0237] Proposal 8: RAN2 should consider whether the UE should transmit assistance information when data is inactive.

[0238] (2.3. Activities during Light Connected) (2.3.1. Paging Monitoring) Since RAN2#95 has agreed to support RAN initiated paging, the UE should monitor while light connected in the subframes determined as the baseline where Release 13 legacy PO / PF calculations are used for RAN initiated paging.

[0239] Meanwhile, as shown in FIG. 12, when the UE returns to RRC Connected, which is related to the UE's mobility, three scenarios can be considered.

[0240] Scenario 1: The UE remains in the same cell where it entered Light Connected.

[0241] This scenario occurs frequently, assuming a smartphone. If Light Connected is part of RRC Connected, i.e., Proposal 2, the C-RNTI is still active and valid and can still be reused to page the UE. Therefore, the UE can monitor for paging at the opportunities determined by the existing Connected Mode DRX (C-DRX).

[0242] Scenario 2: The UE is in a different cell within the same RAN paging area (PA) that has entered Light Connected.

[0243] In a different cell, the C-RNTI is no longer valid since it is a cell-specific ID. Therefore, other IDs may be needed to page the UE, such as (a) the NAS UE ID (i.e., S-TMSI), (b) the Release 13 UE Resume ID, (c) the new RAN UE ID, or (d) the IMSI mode. However, the "paging occasion" is still determined by the C-DRX if the DRX-Config is transferred to the target cell, for example, within "X2 paging".

[0244] Scenario 3: The UE is outside the RAN paging area and enters Light Connected there.

[0245] In this case, the Lightly Connected UE is required to notify the network. The UE may be instructed to enter Lightly Connected in the cell where the notification is sent. Therefore, this scenario has the same conditions as Scenario 1 and does not need to be considered further.

[0246] Regarding UE paging occasions in Light Connected, the C-DRX mechanism can be reused, even taking into account UE mobility. In this approach, from the RAN2 perspective, the Release 13 legacy PO / PF calculation is the baseline used for RAN-initiated paging, but no impact on the specification is foreseen for this approach. The input parameters for the PO / PF calculation can be changed as needed, which implies some impact and complexity. Therefore, RAN2 should reuse the baseline for PF / PO calculation.

[0247] Proposal 9: RAN2 should decide to reuse the existing connected mode DRX mechanism for paging occasions.

[0248] If Proposal 9 is agreeable, the agreement to "Define UE ID for paging calculation, e.g. (a) NAS UE ID (i.e. S-TMSI), (b) Release 13 UE Resume ID, (c) new RANUE ID or (d) IMSI mode" is no longer necessary, since C-DRX does not need to input ID to calculate OnDuration.

[0249] Proposal 10: If Proposal 9 is agreeable, RAN2 should not use the ID in calculating paging occasions.

[0250] Regarding the ID for paging the UE, C-RNTI is used in Scenario 1 but not in Scenario 2. Therefore, especially in Scenario 2, it is necessary to "define the UE ID carried in the paging message." The UE ID should be selected from (a) NAS UE ID (i.e., S-TMSI), (b) Release 13 UE Resume ID, (c) new RAN UE ID, or (d) IMSI mode. If Light Connected needs to be as transparent as possible to the CN, the ID should be selected from IDs that can be managed by the RAN. Therefore, the candidates are "(b) Release 13 UE Resume ID" or "(c) new RAN UE ID." The Resume ID is used by the eNB to obtain the UE context from the "anchor NB," but the exact content of the Resume ID is invisible to the UE. In other words, only the bit size is defined.

[0251] The UE can be identified by an ID consisting of the ECGI (i.e., Cell Global Id EUTRA in the "anchor eNB") and the C-RNTI (assigned by the cell with the ECGI). To minimize the message size, it is also possible to use either the ECI (i.e., Cell Identity or "eNBID+PCI") or the PCI (i.e., PhysCellId) instead of the ECGI. These optimizations should assume that the ID is valid within the PLMN.

[0252] If the contents of the ID are explicitly specified, the UE uses it to determine whether it has been paged even if the ID has not been explicitly assigned via RRC signaling (e.g., RRC connection reconfiguration or release when the UE enters Light Connected).

[0253] Proposal 11: RAN2 should define "ECGI+C-RNTI", "ECI+C-RNTI" and / or "PCI+C-RNTI" as new RAN IDs in "Paging Message".

[0254] Proposal 12: If proposal 11 is agreeable, then when the UE enters Light Connected, the ID does not need to be explicitly assigned by the cell in the "anchor eNB".

[0255] (2.3.2. UE-based mobility) RAN2 agreed to "implement the same cell reselection mechanism in RRC Idle, cell reselection-based mobility." Therefore, the UE behavior follows the idle mode procedure in terms of cell reselection, and as long as all eNBs in the network support reversion from Lightly Connected to RRC Connected, there is no problem for Lightly Connected UEs. Although it depends on the network implementation, Release 13 does not assume that all eNBs in the network support new features (eDRX Permission for eDRX, voiceServiceCauseIndication for VoLTE establishment, Up-CIoT-EPS-Optimization and CIoT-EPS Optimization for cp-RRC Connection Resumption). Therefore, it is debatable whether it can be assumed that all eNBs in the network support Lightly Connected.

[0256] Proposal 13: RAN2 should discuss whether it can be assumed that all eNBs in the network support Light Connected.

[0257] If some eNBs do not support Light Connected, the UE may become unreachable from RAN paging, so the question is how the UE should behave. One possibility is for the UE to prioritize cells that support Light Connected as much as possible. Another possibility is for the UE to transition to RRC Idle when reselecting a cell that does not support Light Connected. RAN2 should take into account the specifics of UE-based mobility during Light Connected.

[0258] Proposal 14: If one or more eNBs do not support Light Connected, RAN2 should discuss the details of UE-based mobility during Light Connected, e.g. whether cells should be de-prioritized during cell reselection and whether the UE should transition to RRC Idle when such a cell is reselected.

[0259] (Appendix 2) 1. The paging may optionally contain some priority information for each UE.

[0260] A) The priority information can be:

[0261] · EstablishmentCause value.

[0262] A 1-bit flag that identifies this paging as a priority call (such as MT Voice).

[0263] · The number indicates the priority of the MT call (e.g., 0-7, like the absolute priority of cell reselection).

[0264] · The bearer ID associated with this paging.

[0265] B) The priority information is formed as a list, with each entry in the list pointing to a corresponding entry in the PagingRecordList in the paging.

[0266] Priority information can be integrated within an existing PagingRecord.

[0267] C) The priority information may be determined by the eNB (eg in the case of an eVoLTE MT video call) or the MME (eg via the existing paging priority IE in S1 paging).

[0268] 2. Upon receiving the paging priority in the paging, the UE: A) It is used to decide whether to initiate an RRC connection request (or one for Light Connected), i.e., the UE implementation, or B) If the priority information indicates a high priority call, initiate an RRC connection request (or one for Right Connected).

[0269] The establishment cause of the request can be matched with priority information, for example "prioritized MT call".

[0270] [Cross reference] This application claims priority to U.S. Provisional Application No. 62 / 397,453 (filed September 21, 2016), the entire contents of which are incorporated herein by reference.

Claims

1. A communication control method in a mobile communication system, comprising: A base station sets a predetermined area for performing RAN paging to a user equipment; The base station transmits a paging request to a neighbor base station within the predetermined area, the paging request requesting that paging be performed on the user equipment for which the predetermined area is set; receiving, by the base station, a message from the neighboring base station indicating that the neighboring base station has failed the paging; The paging request includes a DRX setting for the user equipment. Communication control method.

2. A base station, a control unit that sets a predetermined area for performing RAN paging in a user device; the control unit transmits a paging request to a neighbor base station within the predetermined area, the paging request requesting that paging be performed on the user equipment for which the predetermined area is set; the control unit receives a message from the neighboring base station indicating that the neighboring base station has failed the paging; The paging request includes a DRX setting for the user equipment. Base station.

3. A base station, a receiving unit that receives a paging request from a neighboring base station within a predetermined area, the paging request requesting paging of a user equipment in which a predetermined area for performing RAN paging is set; a transmitter that transmits a message indicating that the previous base station has failed in the paging to the neighboring base station, The paging request includes a DRX setting for the user equipment. Base station.

4. A mobile communication system comprising the base station according to claim 2 and an adjacent base station.

Images