JP6670294B2 - Network device and base station - Google Patents

Description

  The present invention relates to a network device and a base station used in a mobile communication system.

  In 3GPP (3rd Generation Partnership Project) which is a standardization project of a mobile communication system, discontinuous reception (DRX) is defined as an intermittent reception technique for reducing power consumption of a wireless terminal. The wireless terminal in the DRX state monitors the downlink control channel intermittently. The period for monitoring the downlink control channel is called a “DRX cycle”.

  The wireless terminal and the base station for which the DRX setting has been performed in the idle mode calculate the system frame number (SFN) of the paging frame (PF), which is the timing at which the paging message can be transmitted, based on the DRX cycle. The base station transmits a paging message at the timing, and the wireless terminal receives the paging message at the timing.

  In recent years, attention has been paid to machine type communication (MTC) in which a wireless terminal performs communication without human intervention in a mobile communication system. From such a background, it has been studied to newly introduce an extended DRX (extended DRX) cycle longer than the existing DRX cycle to further reduce power consumption (for example, see Non-Patent Document 1). DRX that uses the extended DRX cycle is called extended DRX.

3GPP contribution "RP-141994"

  The network device according to the first feature is capable of communicating with a wireless terminal whose position is registered in a predetermined tracking area. The network device includes a transmitting unit that notifies a paging message to the wireless terminal, and a control unit that detects that the wireless terminal has received the paging message. The control unit, when detecting that the wireless terminal has received the paging message, for a base station that manages a cell belonging to the predetermined tracking area, for the base station to release the paging message Send a release message.

  The base station according to the second feature is capable of communicating with a wireless terminal whose position is registered in a predetermined tracking area. The base station includes: a storage unit that stores a paging message received from an upper node, and a control unit that notifies the wireless terminal of the paging message. The storage unit discards the paging message in response to receiving a message for releasing the paging message from the upper node or a base station that manages a cell belonging to the predetermined tracking area.

FIG. 1 is a configuration diagram of the LTE system. FIG. 2 is a block diagram of the UE. FIG. 3 is a block diagram of the eNB. FIG. 4 is a block diagram of the MME. FIG. 5 is a protocol stack diagram. FIG. 6 is a configuration diagram of a radio frame. FIG. 7 is a diagram for explaining the operation according to the embodiment. FIG. 8 is a sequence diagram for explaining the operation according to the embodiment. FIG. 9 is a diagram for explaining an operation according to a modification of the embodiment.

[Overview of Embodiment]
Since the transmission timing of the paging message is based on the DRX cycle, the base station may have to hold the paging message addressed to the wireless terminal to which the long DRX cycle is applied for a long time. In particular, since the extended DRX cycle is longer than the existing DRX cycle, the base station is likely to hold the paging message for a long time. As a result, the resources (memory) of the base station may be squeezed.

  Therefore, the embodiment provides a network device and a base station that can suppress resource pressure on the base station based on holding of a paging message.

  The network device (for example, MME, eNB) according to the embodiment can communicate with a wireless terminal whose position is registered in a predetermined tracking area. The network device includes a transmitting unit that notifies a paging message to the wireless terminal, and a control unit that detects that the wireless terminal has received the paging message. The control unit, when detecting that the wireless terminal has received the paging message, for a base station that manages a cell belonging to the predetermined tracking area, for the base station to release the paging message Send a release message.

  In an embodiment, the base station that manages a cell belonging to the predetermined tracking area is a base station other than the base station that transmitted the paging message received by the wireless terminal.

  In an embodiment, when the extended DRX using a second DRX cycle longer than the first DRX cycle is set for the wireless terminal in an idle mode, the control unit transmits the release message. Transmit to the base station.

  In an embodiment, when the base station is a base station that retransmits a paging message, the control unit transmits the release message to the base station.

  In an embodiment, the control unit transmits the release message to the base station including information for releasing a plurality of paging messages in the release message.

  The base station according to the embodiment can communicate with a wireless terminal whose position is registered in a predetermined tracking area. The base station includes: a storage unit that stores a paging message received from an upper node, and a control unit that notifies the wireless terminal of the paging message. The storage unit discards the paging message in response to receiving a message for releasing the paging message from the upper node or a base station that manages a cell belonging to the predetermined tracking area.

  In an embodiment, the control unit stops transmitting the paging message in response to receiving the release message.

[Embodiment]
Hereinafter, an embodiment in which the present invention is applied to an LTE system will be described.

(System configuration)
FIG. 1 is a configuration diagram of the LTE system according to the embodiment. As illustrated in FIG. 1, the LTE system according to the embodiment includes a UE (User Equipment) 100, an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 10, and an EPC (Evolved Packet Core) 20.

  The UE 100 corresponds to a user terminal. The UE 100 is a mobile communication device, and performs wireless communication with a connected cell (serving cell). The configuration of the UE 100 will be described later.

  E-UTRAN10 is equivalent to a radio access network. E-UTRAN10 includes eNB200 (evolved Node-B). eNB 200 corresponds to a base station. The eNBs 200 are mutually connected via an X2 interface. The configuration of the eNB 200 will be described later.

  The eNB 200 manages one or a plurality of cells, and performs wireless communication with the UE 100 that has established a connection with the own cell. The eNB 200 has a radio resource management (RRM) function, a user data routing function, a measurement control function for mobility control and scheduling, and the like. “Cell” is used not only as a term indicating the minimum unit of the wireless communication area, but also as a term indicating a function of performing wireless communication with the UE 100.

  EPC 20 corresponds to a core network. The E-UTRAN 10 and the EPC 20 configure an LTE system network (LTE network). EPC 20 includes an MME (Mobility Management Entity) / S-GW (Serving-Gateway) 300 and an OAM (Operation and Maintenance) 400. The MME performs various mobility controls on the UE 100 and the like. The S-GW controls transfer of user data. MME / S-GW 300 is connected to eNB 200 via an S1 interface.

  The OAM 400 is a server device managed by an operator, and performs maintenance and monitoring of the E-UTRAN 10.

  FIG. 2 is a block diagram of the UE 100. As shown in FIG. 2, the UE 100 includes an antenna 101, a radio transceiver 110, a user interface 120, a GNSS (Global Navigation Satellite System) receiver 130, a battery 140, a memory 150, and a processor 160. The memory 150 corresponds to a storage unit, and the processor 160 corresponds to a control unit. The UE 100 may not have the GNSS receiver 130. Further, the memory 150 may be integrated with the processor 160, and this set (that is, a chip set) may be referred to as a processor 160 '.

  The antenna 101 and the wireless transceiver 110 are used for transmitting and receiving wireless signals. The wireless transceiver 110 converts a baseband signal (transmission signal) output from the processor 160 into a wireless signal and transmits the wireless signal from the antenna 101. The wireless transceiver 110 converts a wireless signal received by the antenna 101 into a baseband signal (received signal) and outputs the baseband signal to the processor 160.

  The user interface 120 is an interface with a user having the UE 100, and includes, for example, a display, a microphone, a speaker, and various buttons. The user interface 120 receives an operation from the user, and outputs a signal indicating the content of the operation to the processor 160. The GNSS receiver 130 receives a GNSS signal and outputs the received signal to the processor 160 in order to obtain position information indicating a geographical position of the UE 100. Battery 140 stores power to be supplied to each block of UE 100.

  The memory 150 stores a program executed by the processor 160 and information used for processing by the processor 160. Processor 160 includes a baseband processor that performs modulation / demodulation and encoding / decoding of a baseband signal, and a CPU (Central Processing Unit) that executes various programs by executing a program stored in memory 150. . The processor 160 may further include a codec for encoding / decoding audio / video signals. The processor 160 executes various processes and various communication protocols described below.

  FIG. 3 is a block diagram of the eNB 200. As shown in FIG. 3, the eNB 200 includes an antenna 201, a wireless transceiver 210, a network interface 220, a memory 230, and a processor 240. Note that the memory 230 may be integrated with the processor 240, and this set (that is, a chip set) may be referred to as a processor 240 '.

  The antenna 201 and the wireless transceiver 210 are used for transmitting and receiving wireless signals. The wireless transceiver 210 converts a baseband signal (transmission signal) output from the processor 240 into a wireless signal and transmits the wireless signal from the antenna 201. The wireless transceiver 210 converts a wireless signal received by the antenna 201 into a baseband signal (received signal) and outputs the baseband signal to the processor 240.

  The network interface 220 is connected to the adjacent eNB 200 via the X2 interface, and is connected to the MME / S-GW 300 via the S1 interface. The network interface 220 is used for communication performed on the X2 interface and communication performed on the S1 interface.

  The memory 230 stores a program executed by the processor 240 and information used for processing by the processor 240. Processor 240 includes a baseband processor that performs modulation / demodulation and encoding / decoding of a baseband signal, and a CPU that executes programs stored in memory 230 to perform various processes. The processor 240 executes various processes and various communication protocols described below.

  FIG. 4 is a block diagram of the MME 300. As shown in FIG. 4, the MME 300 includes a network interface 320, a memory 330, and a processor 340. The memory 330 may be integrated with the processor 340, and this set (that is, a chip set) may be used as the processor.

  The network interface 320 is connected to the eNB 200 via the S1 interface. The network interface 320 is used for communication performed on the S1 interface.

  The memory 330 stores a program executed by the processor 340 and information used for processing by the processor 340. The processor 340 includes a baseband processor that performs modulation / demodulation and encoding / decoding of a baseband signal, and a CPU that executes a program stored in the memory 330 to perform various processes. The processor 340 executes various processes and various communication protocols described below.

  FIG. 5 is a protocol stack diagram of a radio interface in the LTE system. As shown in FIG. 5, the wireless interface protocol is divided into first to third layers of the OSI reference model, and the first layer is a 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 an RRC (Radio Resource Control) layer.

  The physical layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Between the physical layer of the UE 100 and the physical layer of the eNB 200, user data and control signals are transmitted via a physical channel.

  The MAC layer performs data priority control, retransmission processing using hybrid ARQ (HARQ), and the like. Between the MAC layer of the UE 100 and the MAC layer of the eNB 200, user data and control signals are transmitted via a transport channel. The MAC layer of the eNB 200 includes a transport format (transport block size, modulation / coding scheme) for uplink and downlink, and a scheduler for determining (scheduling) resource blocks to be allocated to the UE 100.

  The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and the physical layer. Between the RLC layer of the UE 100 and the RLC layer of the eNB 200, user data and control signals are transmitted via logical channels.

  The PDCP layer performs header compression / expansion and encryption / decryption.

  The RRC layer is defined only in the control plane that handles control signals. Control signals (RRC messages) for various settings are 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 according to 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 the RRC connected mode (connected mode). Otherwise, the UE 100 is in the RRC idle mode (idle mode).

  A NAS (Non-Access Stratum) layer located above the RRC layer performs session management, mobility management, and the like.

  FIG. 6 is a configuration diagram of a radio frame used in the LTE system. In the LTE system, Orthogonal Frequency Division Multiple Access (OFDMA) is applied to the downlink (DL), and SC-FDMA (Single Carrier Frequency Multiple Access) is applied to the uplink (UL).

  As shown in FIG. 6, the radio frame is composed of ten subframes arranged in the time direction. Each subframe is composed of two slots arranged in the time direction. Each subframe has a length of 1 ms, and each slot has a length of 0.5 ms. Each subframe includes a plurality of resource blocks (RBs) in a frequency direction and a plurality of symbols in a time direction. Each resource block includes a plurality of subcarriers in the frequency direction. A resource element is configured by one subcarrier and one symbol. Of the radio resources allocated to the UE 100, the frequency resources are configured by resource blocks, and the time resources are configured by subframes (or slots).

(Overview of DRX operation)
Hereinafter, a DRX (Discontinuous Reception) operation in the RRC idle mode will be described.

  The UE 100 can perform a DRX operation to save battery power. The UE 100 performing the DRX operation monitors the PDCCH intermittently. Usually, the PDCCH in a subframe carries scheduling information (information on radio resources and transport format) of the PDSCH in the subframe.

  UE 100 in the RRC idle mode performs a DRX operation of intermittently monitoring the PDCCH in order to receive a paging message notifying that there is an incoming call. The UE 100 decodes the PDCCH (CCE) using the paging group identifier (P-RNTI), and acquires paging channel assignment information (PI). The UE 100 acquires a paging message based on the allocation information. The PDCCH monitoring timing in the UE 100 is usually determined based on the identifier of the UE 100 (IMSI: International Mobile Subscriber Identity). The calculation of the PDCCH monitoring timing will be specifically described.

  The PDCCH monitoring timing (PDCCH monitoring subframe) in the DRX operation in the RRC idle mode is called Paging Occlusion (PO).

  The UE 100 (and the eNB 200) calculates a paging occasion (PO) and a paging frame (PF) which is a radio frame that can include the paging occasion as follows.

  The system frame number (SFN) of the PF is obtained from the following equation (1).

    SFN mod T = (T div N) * (UE_ID mod N) (1)

  Here, T is a DRX cycle of the UE 100 for receiving the paging message, and is represented by the number of radio frames. 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 determined by “IMSI mod 1024”.

  Of the PFs thus obtained, the subframe number of the PO is obtained as follows. First, an index i_s is obtained by the following equation (2).

    i_s = floor (UE_ID / N) mod Ns (2)

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

  Next, the PO corresponding to Ns and the index i_s is obtained from Table 1 or Table 2. Table 1 applies to the LTE FDD system, and Table 2 applies to the LTE TDD system. In Tables 1 and 2, N / A means not applicable.

  As described above, UE 100 and eNB 200 determine the timing at which the paging message can be transmitted.

  Next, the extended DRX will be described. According to the extended DRX, an extended DRX cycle longer than the existing DRX cycle can be set.

  The extended DRX may be defined by extending a value range of a paging cycle (defaultPagingCycle) in an existing PCCH setting (PCCH-Config.) Broadcasted to the UE 100 by the SIB2. The paging cycle is used as an (extended) DRX cycle.

  Alternatively, it may be defined as an information element different from the existing “DRX-Config”. For example, “Idle-eDRX-Config” which is setting information of the extended DRX in the idle mode may be defined. The “Idle-eDRX-Config” may be able to set, for example, a range of “... Rf512, rf1024,...” As an extended DRX cycle.

(Operation according to the embodiment)
Next, an operation according to the embodiment will be described with reference to FIGS. FIG. 7 is a diagram for explaining the operation according to the embodiment. FIG. 8 is a sequence diagram for explaining the operation according to the embodiment.

  As illustrated in FIG. 7, the UE 100 is located in a cell managed by the eNB 200-1. Further, the description will proceed on the assumption that the UE 100 is in the RRC idle mode and the extended DRX in the RRC idle mode is set.

  Each of eNB 200-1, eNB 200-2, and eNB 200-3 manages a cell, and each cell belongs to the same tracking area (TA). Each eNB 200 is connected to the MME 300 via the S1 interface.

  The MME 400 knows the tracking area where the UE 100 exists by registering the location of the UE 100. On the other hand, since the UE 100 is in the RRC idle mode, the cell (eNB 200) in which the UE 100 is located is unknown.

  Hereinafter, since the eNB 200-3 performs the same operation as the eNB 200-2, the description of the eNB 200-3 will be omitted.

  As illustrated in FIG. 8, in step S10, the MME 300 transmits a paging message addressed to the UE 100 to each eNB 200 (eNB 200-1 and eNB 200-2) that manages a cell in a TA where the UE 100 exists.

  Each eNB 200 receives the paging message and holds (stores) the paging message until it reaches the timing of transmitting the paging message.

  In step S20, the eNB 200-1 transmits the paging message by reaching the timing of transmitting the paging message.

  The UE 100 monitors the PDCCH when it reaches the timing of monitoring the PDCCH according to the setting of the extended DRX, and receives a paging message from the eNB 200-1. Specifically, the UE 100 decodes the PDCCH (CCE) using the paging group identifier (P-RNTI), and acquires paging channel assignment information (PI). The UE 100 acquires a paging message based on the allocation information.

  On the other hand, the eNB 200-2 keeps holding the paging message because the timing for transmitting the paging message has not been reached.

  In step S30, the UE 100 executes a random access procedure for the eNB 200-1 that manages a cell in which the UE 100 is located.

  In step S40, after ending the random access procedure, the UE 100 notifies the MME 300 of a NAS message for requesting a service via the eNB 200-1. The MME 300 receives the NAS message via the eNB 200-1. MME 300 detects that UE 100 has received the paging message in response to receiving the NAS message. Here, for example, the UE 100 may include the identifier of the eNB 200-1 in the NAS message notified to the MME 300. Thereby, the MME 300 may detect that the UE 100 has received the paging message from the eNB 200-1 (or that the UE 100 is located in a cell managed by the eNB 200-1).

  In step S50, when detecting that the UE 100 has received the paging message, the MME 300 transmits, to the eNB 200-2, a release message (Release message) for the eNB 200-2 to release the paging message. Specifically, the MME 300 transmits a release message to at least one or more eNBs 200 other than the eNB 200-1 through which the NAS message from the UE 100 has passed. The release message for releasing the paging message may be a discard message for discarding the paging message or a stop message for stopping transmission of the paging message.

  Here, the MME 300 may notify the release message in the following cases.

  First, when extended DRX is set in the UE that is the transmission destination of the paging message, the MME 300 can transmit a release message. For example, when the MME 300 has notified the UE 100 of the setting of the extended DRX by the NAS message, the MME 300 notifies the release message. Alternatively, when the MME 300 has received a notification from the UE 100 by the NAS message that the extended DRX setting has been applied, the MME 300 notifies the release message. Here, the setting of the extended DRX applied to the UE 100 may be notified from the MME 300 or may be notified from the eNB 200.

  This is because the paging message addressed to the UE 100 in which the extended DRX is set is likely to be held in the eNB 200 for a long time.

  Note that, when the paging message is addressed to the UE 100 in which the normal DRX is set, the MME 300 does not have to transmit the release message to any of the eNBs 200.

  Second, the MME 300 can transmit a release message to the eNB 200 that retransmits the paging message. MME 300 may hold a list of eNBs 200 that retransmit the paging message. MME 300 can transmit a release message to eNB 200 that retransmits the paging message based on the list.

  This is because the eNB 200 that retransmits the paging message holds the paging message for retransmission even after transmitting the paging message once.

  Note that MME 300 may not need to transmit a release message to eNB 200 that does not retransmit the paging message.

  Further, MME 300 may transmit one release message corresponding to one paging message, or may transmit one release message corresponding to a plurality of paging messages to eNB 200. Specifically, when detecting that each of the plurality of paging messages has been received by each UE 100, the MME 300 transmits one release message to each eNB 200 instead of transmitting a plurality of release messages. be able to. The one release message includes information (for example, an identifier of each UE 100) for releasing a plurality of paging messages.

  The eNB 200-2 receives the release message from the MME 300. The eNB 200-2 discards the paging message in response to receiving the release message. Specifically, eNB 200-2 deletes the paging message from memory 230. Thereby, based on a paging message, it can control that the resource of eNB200-2 is pressed.

  When the release message includes information for releasing a plurality of paging messages, the eNB 200-2 discards the plurality of paging messages specified by the information. Since one release message includes information for releasing a plurality of paging messages, signaling from the MME 300 to each eNB 200 is reduced. As a result, the load on the MME 300 can be reduced. This is particularly effective when a large number of wireless terminals in the TA are executing the extended DRX operation.

  In addition, before transmitting the paging message, the eNB 200-2 stops transmitting the paging message in response to receiving the release message. As a result, radio resources for transmitting the paging message can be saved.

(Example of change)
Next, a modification of the embodiment will be described with reference to FIG. FIG. 9 is a diagram for explaining an operation according to a modification of the embodiment. The following description focuses on portions that are different from the above-described embodiment, and similar portions are omitted as appropriate.

  In the above embodiment, the MME 300 transmitted the release message. In the present modification, the eNB 200 transmits a release message.

  As shown in FIG. 9, the operating environment is similar to that of the above-described embodiment. Here, after transmitting the paging message to UE 100, eNB 200-1 receives the signaling from UE 100. Thereby, eNB 200-1 detects that UE 100 has received the paging message. For example, eNB 200-1 detects that UE 100 has received a paging message in response to reception of signaling (for example, message 3) in a random access procedure. Specifically, eNB 200-1 detects that UE 100 has received the paging message by comparing the identifier (ID) included in the paging message from MME 300 with the identifier (ID) included in message 3. I do. For example, when the S-TMSI (SAE Temporary Mobile Station Identifier) matches, the eNB 200 detects that the UE 100 has received the paging message.

  As illustrated in FIG. 9, the eNB 200-1 transmits a release message to each of the eNB 200-2 and the eNB 200-3 according to the detection. For example, the eNB 200-1 transmits a release message via the X2 interface.

  The eNB 200-1 may hold a list of each eNB 200 that manages each cell in the TA to which the own cell belongs. The eNB 200-1 may transmit a release message to each eNB 200 based on the list. Alternatively, the eNB 200-1 may transmit a release message to each adjacent eNB 200 that manages a cell adjacent to the own cell.

  Since the eNB 200 can receive the signaling from the UE 100 earlier than the MME 300, the eNB 200 can transmit the release message earlier. As a result, before the other eNB 200 notifies the UE 100 of the paging message, the release message can be transmitted to the other eNB 200. As a result, radio resources for transmitting the paging message can be saved.

  Each eNB 200 that has received the release message from the eNB 200-1 may transfer (transmit) the release message to another eNB 200 that manages a cell in the same TA. For example, the eNB 200-2 can transfer the release message to another eNB 200 that is not connected to the eNB 200-1 via the X2 interface.

[Other Embodiments]
In the above-described embodiment, the UE 100 in which the extended DRX is set has been described as an example, but is not limited thereto. Even when the paging message is a paging message to the UE 100 in which the normal DRX is set, each eNB 200 and the MME 300 may execute the same operation.

  In the above-described modification, the eNB 200-1 may transmit a release message to the MME 300 when detecting that the UE 100 has received the paging message. The MME 300 that has received the release message can transmit the release message to another eNB 200 as in the embodiment.

  In the embodiment described above, the LTE system is described as an example of the cellular communication system. However, the present invention is not limited to the LTE system, and the present invention may be applied to a system other than the LTE system.

[Cross Reference]
The entire contents of Japanese Patent Application No. 2015-041864 (March 3, 2015) are incorporated herein by reference.

  The present invention is useful in the communication field.

Claims (6)

A network device capable of communicating with a wireless terminal whose location is registered in a predetermined tracking area,
A transmitting unit that notifies a paging message to the wireless terminal,
A control unit that detects that the wireless terminal has received the paging message,
With
The control unit, when detecting that the wireless terminal has received the paging message, for a base station that manages a cell belonging to the predetermined tracking area, for the base station to release the paging message sends a release message,
The control unit, when the extended DRX using the second DRX cycle longer than the first DRX cycle is set for the wireless terminal in the idle mode, the release message to the base station Network device to send to .   The network device according to claim 1, wherein the base station that manages a cell belonging to the predetermined tracking area is a base station other than the base station that transmitted the paging message received by the wireless terminal.   The network device according to claim 1, wherein the control unit transmits the release message to the base station when the base station is a base station that retransmits a paging message.   The network device according to claim 1, wherein the control unit transmits the release message to the base station including information for releasing a plurality of paging messages in the release message. A base station capable of communicating with a wireless terminal whose location is registered in a predetermined tracking area,
A storage unit for holding a paging message received from an upper node,
A control unit that transmits the paging message to the wireless terminal,
With
The storage unit, from the base station that manages the cell belonging to the higher-level node or the predetermined tracking area, in response to receiving a message for releasing the paging message, discard the paging message ,
The control unit, when the extended DRX using the second DRX cycle longer than the first DRX cycle is set for the wireless terminal in the idle mode, the paging message from the upper node. Base station that receives the message to release the . The base station according to claim 5 , wherein the control unit stops transmitting the paging message in response to receiving the release message.

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