WO2015080039A1 - 通信制御方法及び基地局 - Google Patents
通信制御方法及び基地局 Download PDFInfo
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- WO2015080039A1 WO2015080039A1 PCT/JP2014/080886 JP2014080886W WO2015080039A1 WO 2015080039 A1 WO2015080039 A1 WO 2015080039A1 JP 2014080886 W JP2014080886 W JP 2014080886W WO 2015080039 A1 WO2015080039 A1 WO 2015080039A1
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- 238000004891 communication Methods 0.000 title claims abstract description 48
- 238000000034 method Methods 0.000 title claims abstract description 47
- 230000010261 cell growth Effects 0.000 claims abstract description 15
- 238000010295 mobile communication Methods 0.000 claims abstract description 11
- 230000000295 complement effect Effects 0.000 claims description 11
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- 239000013589 supplement Substances 0.000 abstract description 17
- 238000010586 diagram Methods 0.000 description 14
- 238000012546 transfer Methods 0.000 description 11
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- 230000004044 response Effects 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 5
- 230000006870 function Effects 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 238000012986 modification Methods 0.000 description 5
- 230000004048 modification Effects 0.000 description 5
- 238000012545 processing Methods 0.000 description 5
- 230000011664 signaling Effects 0.000 description 3
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- 230000008859 change Effects 0.000 description 2
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/16—Performing reselection for specific purposes
- H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
- H04W16/02—Resource partitioning among network components, e.g. reuse partitioning
- H04W16/06—Hybrid resource partitioning, e.g. channel borrowing
- H04W16/08—Load shedding arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/16—Performing reselection for specific purposes
- H04W36/165—Performing reselection for specific purposes for reducing network power consumption
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/24—Reselection being triggered by specific parameters
- H04W36/247—Reselection being triggered by specific parameters by using coverage extension
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W52/00—Power management, e.g. TPC [Transmission Power Control], power saving or power classes
- H04W52/02—Power saving arrangements
- H04W52/0203—Power saving arrangements in the radio access network or backbone network of wireless communication networks
- H04W52/0206—Power saving arrangements in the radio access network or backbone network of wireless communication networks in access points, e.g. base stations
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W36/00—Hand-off or reselection arrangements
- H04W36/0005—Control or signalling for completing the hand-off
- H04W36/0055—Transmission or use of information for re-establishing the radio link
- H04W36/0069—Transmission or use of information for re-establishing the radio link in case of dual connectivity, e.g. decoupled uplink/downlink
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Definitions
- the present invention relates to a communication control method and a base station used in a mobile communication system.
- 3GPP 3rd Generation Partnership Project
- a power saving (energy saving) technology for reducing power consumption of a network is introduced (for example, see Non-Patent Document 1).
- the cell managed by the base station is turned off (Deactivate) at night when communication traffic is low.
- improved energy saving technology will be introduced after Release 12. For example, when one cell is turned off, the transmission power of other neighboring cells is increased. Thereby, the coverage of the other cell can be expanded (cell expansion), and the coverage of the cell to be turned off can be complemented (that is, area complementation).
- the user terminal may be handed over again from the off-target base station to the extension target base station that performs cell expansion.
- an object of the present invention is to provide a communication control method and a base station that can improve the efficiency of handover when energy saving technology is introduced.
- a communication control method includes: a mobile having an off-target base station that intends to turn off its own cell; and an expansion-target base station that should perform cell expansion to complement the cell of the off-target base station Used in communication systems.
- the communication control method includes a step of receiving a handover request requesting acceptance of a user terminal before the off-target base station turns off its own cell, and the off-target base station accepts the handover request. And a step of transmitting a pre-handover request for requesting the extension target base station to perform connection setting necessary for establishing a connection with the user terminal.
- the base station includes a mobile communication having an off-target base station that intends to turn off its own cell, and an extension-target base station that should perform cell expansion to complement the cell of the off-target base station In the system, this corresponds to the off-target base station.
- the base station Before the base station turns off its own cell, when receiving the handover request for requesting acceptance of the user terminal and accepting the handover request, the base station, for the extension target base station, And a transmitter that transmits a pre-handover request for requesting execution of connection settings necessary for establishing a connection with the user terminal.
- a communication control method includes a mobile communication system having an off target base station that intends to turn off its own cell, and an expansion target base station that is to perform cell expansion to complement the cell of the off target base station. Used in The communication control method includes a step of receiving a handover request requesting acceptance of a user terminal before the off-target base station turns off its own cell, and the off-target base station accepts the handover request. And a step of transmitting a pre-handover request for requesting the extension target base station to perform connection setting necessary for establishing a connection with the user terminal.
- the communication control method includes the step of executing the connection setting when the extension target base station that has received the preliminary handover request approves the preliminary handover request, and relates to the connection setting. Transmitting a prior handover acknowledgment including connection setting information from the extension target base station to the off target base station.
- the connection setting performed in the extension target base station includes C-RNTI allocation to the user terminal.
- the connection setting information includes the C-RNTI assigned to the user terminal.
- the communication control method is configured such that the off-target base station that has received the pre-handover acknowledgment has received the pre-connection including the connection setting information after the user terminal is handed over to the off-target base station.
- the method further includes the step of transmitting a notification to the user terminal.
- the communication control method includes a step in which the extension target base station starts the cell extension when the cell of the off target base station is turned off, and the user terminal that has received the pre-connection notification And switching the connection to the expansion target base station by synchronizing with the expansion target base station that has started the cell expansion based on the connection setting information.
- a data path pre-switching request for data path pre-switching to the user terminal is transmitted from the off-target base station.
- Data for transmitting to the extension target base station, and data for setting the data path between the extension target base station and the core network by the extension target base station that has received the data path advance switching request Transmitting a path switching request to the core network.
- the communication control method includes a step of transmitting an off-notification notification indicating that the off-target base station intends to turn off its own cell to the extension target base station;
- the extension target base station that has received the signal further starts a first timer for estimating the timing to turn off the cell of the off target base station.
- the extension target base station starts the cell extension.
- the extension target base station that has received the off notice notice starts a second timer for determining a timing to release the connection setting; and And releasing the connection setting when the user terminal has not switched the connection to the extension target base station when the timer expires.
- a base station is a mobile communication system having an off-target base station that intends to turn off its own cell, and an extension-target base station that should perform cell expansion to complement the cell of the off-target base station. Corresponds to the off-target base station. Before the base station turns off its own cell, when receiving the handover request for requesting acceptance of the user terminal and accepting the handover request, the base station, for the extension target base station, And a transmitter that transmits a pre-handover request for requesting execution of connection settings necessary for establishing a connection with the user terminal.
- FIG. 1 is a configuration diagram of an LTE system according to the embodiment.
- the LTE system according to the embodiment includes a UE (User Equipment) 100, an E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) 10, and an EPC (Evolved Packet Core) 20.
- UE User Equipment
- E-UTRAN Evolved-UMTS Terrestrial Radio Access Network
- EPC Evolved Packet Core
- the UE 100 corresponds to a user terminal.
- the UE 100 is a mobile communication device, and performs radio communication with a cell (serving cell).
- the configuration of the UE 100 will be described later.
- the E-UTRAN 10 corresponds to a radio access network.
- the E-UTRAN 10 includes an eNB 200 (evolved Node-B).
- the eNB 200 corresponds to a base station.
- the eNB 200 is connected to each other via the X2 interface. The configuration of the eNB 200 will be described later.
- the eNB 200 manages one or a plurality of cells and performs radio 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 / scheduling, and the like.
- RRM radio resource management
- Cell is used as a term indicating a minimum unit of a radio communication area, and is also used as a term indicating a function of performing radio communication with the UE 100.
- the EPC 20 corresponds to a core network.
- the E-UTRAN 10 and the EPC 20 constitute an LTE system network.
- the EPC 20 includes an MME (Mobility Management Entity) / S-GW (Serving-Gateway) 300.
- the MME performs various mobility controls for the UE 100.
- the S-GW controls user data transfer.
- the MME / S-GW 300 is connected to the eNB 200 via the S1 interface.
- FIG. 2 is a block diagram of the UE 100.
- the UE 100 includes a plurality of antennas 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.
- the processor 160 (and the memory 150) constitutes a control unit.
- the UE 100 may not have the GNSS receiver 130.
- the memory 150 may be integrated with the processor 160, and this set (that is, a chip set) may be used as the processor 160 '.
- the plurality of antennas 101 and the wireless transceiver 110 are used for transmitting and receiving wireless signals.
- the radio transceiver 110 converts the baseband signal (transmission signal) output from the processor 160 into a radio signal and transmits it from the plurality of antennas 101. Further, the radio transceiver 110 converts radio signals received by the plurality of antennas 101 into baseband signals (received signals) and outputs the baseband signals to the processor 160.
- the user interface 120 is an interface with a user who owns 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 UE location information (longitude, latitude, etc.) indicating the geographical location of the UE 100.
- the battery 140 stores power to be supplied to each block of the UE 100.
- the memory 150 stores a program executed by the processor 160 and information used for processing by the processor 160.
- the processor 160 includes a baseband processor that modulates / demodulates and encodes / decodes a baseband signal, and a CPU (Central Processing Unit) that executes programs stored in the memory 150 and performs various processes. .
- the processor 160 may further include a codec that performs encoding / decoding of an audio / video signal.
- the processor 160 executes various processes and various communication protocols described later.
- FIG. 3 is a block diagram of the eNB 200.
- the eNB 200 includes a plurality of antennas 201, a radio transceiver 210, a network interface 220, a memory 230, and a processor 240.
- the memory 230 corresponds to a storage unit.
- the processor 240 (and the memory 230) constitutes a control unit.
- the plurality of antennas 201 and the wireless transceiver 210 are used for transmitting and receiving wireless signals.
- the radio transceiver 210 converts a baseband signal (transmission signal) output from the processor 240 into a radio signal and transmits the radio signal from the plurality of antennas 201.
- the radio transceiver 210 converts radio signals received by the plurality of antennas 201 into baseband signals (reception signals) and outputs the baseband signals to the processor 240.
- the network interface 220 is connected to the neighboring 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.
- the processor 240 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 230 and performs various processes.
- the processor 240 executes various processes and various communication protocols described later.
- FIG. 4 is a protocol stack diagram of a radio interface in the LTE system. As shown in FIG. 4, the radio interface protocol is divided into the first to third layers of the OSI reference model, and the first layer is a physical (PHY) layer.
- the second layer includes a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, and a PDCP (Packet Data Convergence Protocol) 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 UE100 and the physical layer of eNB200, user data and a control signal are transmitted via a physical channel.
- the MAC layer performs data priority control, retransmission processing by 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 scheduler that determines an uplink / downlink transport format (transport block size, modulation / coding scheme) and an allocation resource block 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 a logical channel.
- the PDCP layer performs header compression / decompression 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 the logical channel, the transport channel, and the physical channel according to establishment, re-establishment, and release of the radio bearer.
- RRC connection 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 a connected state (RRC connected state), and otherwise, the UE 100 is in an idle state (RRC idle state).
- the NAS (Non-Access Stratum) layer located above the RRC layer performs session management and mobility management.
- FIG. 5 is a configuration diagram of a radio frame used in the LTE system.
- OFDMA Orthogonal Frequency Division Multiple Access
- SC-FDMA Single Carrier Division Multiple Access
- the radio frame is composed of 10 subframes arranged in the time direction.
- Each subframe is composed of two slots arranged in the time direction.
- the length of each subframe is 1 ms, and the length of each slot is 0.5 ms.
- Each subframe includes a plurality of resource blocks (RB) in the frequency direction and includes a plurality of symbols in the time direction.
- Each resource block includes a plurality of subcarriers in the frequency direction.
- a resource element is composed of one subcarrier and one symbol.
- frequency resources are configured by resource blocks
- time resources are configured by subframes (or slots).
- a communication control method relates to an improved energy saving (ES) technology. Specifically, when one cell is turned off to perform ES, the transmission power of other neighboring cells is increased. Thereby, the coverage of the other cell can be expanded (cell expansion), and the coverage of the cell to be turned off can be complemented (that is, area complementation).
- ES energy saving
- ESeNB off target eNB
- area supplement eNB area supplement eNB
- the handover from the ES eNB to the area supplement eNB may not be in time, and there is a possibility that the UE 100 may be disconnected. Further, the repetition of handover as described above causes an increase in signaling accompanying the handover. Therefore, in the embodiment, the efficiency of handover when ES technology is introduced is improved by the following method.
- FIG. 6 is a diagram for explaining the outline of the communication control method according to the embodiment.
- the eNB 200-2 corresponds to the ES eNB that intends to turn off its own cell (cell 2).
- the eNB 200-3 corresponds to an area supplement eNB that performs cell expansion of its own cell (cell 3).
- the UE 100-1 is connected to the cell 1 of the eNB 200-1 (connected state).
- C-RNTI Cell-Radio Network Temporary Identifier 1 which is a temporary UE identifier in cell 1 is assigned to UE 100-1 from eNB 200-1.
- the eNB 200-1 controls communication with the UE 100-1 using C-RNTI1.
- the UE 100-1 is located in a region where the coverage of the cell 1 and the coverage of the cell 2 overlap, and the eNB 200-1 determines a handover for switching the serving cell of the UE 100-1 from the cell 1 to the cell 2.
- the eNB 200-2 allocates the C-RNTI2 in the cell 2 to the UE 100-1 at the time of the handover of the UE 100-1 to the cell 2.
- the UE 100-1 is connected to the cell 2 of the eNB 200-2.
- the eNB 200-3 assigns the C-RNTI 3 in the cell 3 to the UE 100-1.
- the UE 100-1 establishes an RRC connection corresponding to C-RNTI2 with the eNB 200-2 and establishes an RRC connection corresponding to C-RNTI3 with the eNB 200-3.
- the eNB 200-2 moves to the ES state when the cell 2 is turned off, and the eNB 200-3 expands the cell 3 to perform area complementation. Since the UE 100-1 has already established an RRC connection corresponding to C-RNTI3 with the eNB 200-3, connection processing in a lower layer (such as a physical layer and a MAC layer), specifically, with the eNB 200-3 By synchronizing, communication with the eNB 200-3 becomes possible. Note that such a connection process for only the lower layer is denoted as “re-synchronization” in the drawing.
- FIG. 7 is a diagram showing an operation sequence according to the communication control method described above.
- the eNB 200-1 has decided to turn off its own cell (cell 2) after a predetermined time, and is in the process of shifting to the ES state of turning off its own cell (cell 2).
- step S101 a data path is set between the UE 100-1 and the MME / S-GW 300, and data is transmitted / received via the data path.
- the UE 100-1 transmits a Measurement Report indicating measurement results of the serving cell (cell 1) and the neighboring cell (cell 2) to the eNB 200-1.
- the eNB 200-1 that has received the Measurement Report determines the handover of the UE 100-1 to the cell 2 based on the received Measurement Report.
- step S103 the eNB 200-1 transmits a Handover Request (handover request) requesting acceptance of the UE 100-1 to the eNB 200-2.
- handover Request handover request
- step S104 the eNB 200-2 that has received the Handover Request performs connection setting necessary for establishing a connection with the UE 100-1 with respect to the eNB 200-3 when the eNB 200-2 accepts the received Handover Request.
- Send the requested PreHandover Request (pre-handover request).
- the eNB 200-3 that has received the PreHandover Request performs connection setting when accepting the PreHandover Request.
- the connection setting performed in the eNB 200-3 includes assignment of C-RNTI 3 to the UE 100-1.
- step S105 the eNB 200-3 transmits a PreHandover Request Ack (pre-handover acknowledgment) including the connection setting information (such as CRNTI3) related to the connection setting to the eNB 200-2.
- the eNB 200-2 that has received the PreHandover Request Ack transmits a Handover Request Ack (handover acknowledgment) to the eNB 200-1.
- the eNB 200-1 that has received the Handover Request Ack transmits a handover command including information necessary for the handover to the cell 2 to the UE 100-1.
- step S108 the eNB 200-1 transmits an SN Status Transfer related to transmission / reception data with the UE 100-1 to the eNB 200-2.
- step S109 the eNB 200-2 that has received the SN Status Transfer transfers the received SN Status Transfer to the eNB 200-3.
- step S110 the eNB 200-1 transmits Data Forwarding including untransmitted data to the UE 100-1 to the eNB 200-2.
- step S111 the eNB 200-2 that has received the Data Forwarding transfers the received Data Forwarding to the eNB 200-3.
- the UE 100-1 performs a non-contention based random access procedure for establishing a connection with the eNB 200-2 based on the handover command. Specifically, in step S112, the UE 100-1 transmits the random access preamble designated by the handover command to the eNB 200-2 on the random access channel (Rach). In step S113, the eNB 200-2 that has received the random access preamble transmits a random access response including an uplink timing correction value, C-RNTI2, and the like to the UE 100-1. The UE 100-1 that has received the random access response transmits a connection request (so-called Msg3) requesting establishment of an RRC connection to the eNB 200-2. As a result, an RRC connection is established between the UE 100-1 and the eNB 200-2, and the handover is completed.
- Msg3 connection request
- step S115 the eNB 200-2 transmits a Pass Switch Notice (data path pre-switching request) for pre-switching of the data path to the UE 100-1 to the eNB 200-3.
- step S116 the eNB 200-3 that has received the Pass Switch Notice issues a Path Switch Request (data path switching request) for setting a data path between the eNB 200-3 and the MME / S-GW 300. Send to.
- the MME / S-GW 300 that has received the Path Switch Request from the eNB 200-3 does not switch the data path for the UE 100-1 from the eNB 200-1 to the eNB 200-2, but switches from the eNB 200-1 to the eNB 200-3.
- a data path passing through the eNB 200-2 and the eNB 200-3 is set between the UE 100-1 and the MME / S-GW 300.
- step S117 data is transmitted / received via the data path.
- the eNB 200-2 transmits a pre-connection notification including the connection setting information (C-RNTI3 or the like) of the eNB 200-3 to the UE 100-1.
- the pre-connection notification further includes the cell ID of cell 3 corresponding to C-RNTI3.
- step S119 the eNB 200-2 transitions to the ES state by turning off the own cell (cell 2), that is, stopping the wave. Further, when turning off the cell 2, the eNB 200-3 starts cell expansion of the cell 3. The UE 100-1 cannot detect the reference signal of the cell 2 and detects the reference signal of the cell 3.
- step S120 the UE 100-1 switches to the RRC connection with the eNB 200-3 by synchronizing with the cell 3 (eNB 200-3) based on the connection setting information (C-RNTI 3) of the eNB 200-3.
- the same procedure as steps S112 to S114 is performed from the UE 100-1 to establish a communication connection.
- the UE 100-1 switches the serving cell from the cell 2 to the cell 3.
- step S121 the eNB 200-3 transmits a notification indicating that the synchronization with the UE 100-1 is completed to the eNB 200-2.
- step S122 the eNB 200-2 that has received the notification transmits the SN Status Transfer to the eNB 200-3.
- a data path that passes through the eNB 200-3 is set between the UE 100-1 and the MME / S-GW 300 without passing through the eNB 200-2.
- step S123 data is transmitted / received via the data path.
- Steps S105 to S123 are operations performed when the eNB 200-3 can accept the UE 100-1, but when the eNB 200-3 cannot accept the UE 100-1, the eNB 200 that has received the PreHandover Request. 3 transmits a PreHandover Preparation failure indicating that the PreHandover Request is rejected to the eNB 200-2 (Step S124).
- the eNB 200-2 that has received the PreHandover Preparation failure transmits a Handover Preparation failure indicating that the handover is rejected to the eNB 200-1 (step S125).
- FIG. 8 is an operation flowchart of the eNB 200-2 at the time of receiving a Handover Request from the eNB 200-1.
- the eNB 200-2 receives the Handover Request (Step S1201), and determines whether or not to accept the Handover Request (Step S1202). When the Handover Request is not accepted (Step S1202; NO), the eNB 200-2 transmits the Handover Preparation failure to the eNB 200-1 (Step S1203).
- the eNB 200-2 determines whether or not the transition to the ES state is in progress (step S1204). When the transition to the ES state is not in progress (step S1204; NO), the eNB 200-2 transmits a Handover Request Ack to the eNB 200-1 (step S1205).
- the eNB 200-2 transmits a PreHandover Request to the eNB 200-3 that is the area complementary eNB (step S1211) and receives a response from the eNB 200-3. (Step S1212).
- the eNB 200-2 transmits a Handover Preparation failure to the eNB 200-1 (Step S1214).
- the eNB 200-2 transmits the Handover Request Ack to the eNB 200-1 (step S1215).
- FIG. 9 is an operation flow diagram of the eNB 200-3 at the time of receiving a PreHandover Request from the eNB 200-2.
- the eNB 200-3 receives the PreHandover Request (Step S1301), and determines whether or not to accept the PreHandover Request (Step S1302).
- the eNB 200-3 transmits the PreHandover Preparation failure to the eNB 200-2 (step S1303).
- the eNB 200-3 transmits the PreHandover Request Ack to the eNB 200-2 (step S1304).
- FIG. 10 is an operation flowchart of the eNB 200-2 at the time of handover failure.
- the eNB 200-2 detects the handover failure of the UE 100-1 to the own cell (cell 2) (step S1221; YES)
- the PreHandover Request Ack from the eNB 200-3 (area supplement eNB) Whether or not has been received (step S1222).
- the eNB 200-2 transmits a PreHandover Cancel indicating handover cancellation to the eNB 200-3 (step S1223).
- FIG. 11 is an operation flowchart of the eNB 200-3 at the time of handover failure.
- the eNB 200-3 receives the PreHandover Cancel from the eNB 200-2 (step S1311), and determines whether there is a resource (C-RNTI3, etc.) reserved for the UE 100-1. (Step S1312). If the resource exists (step S1312; YES), the eNB 200-3 releases the resource (step S1313).
- a resource C-RNTI3, etc.
- the eNB 200-2 transmits a PreHandover Request to the plurality of area complementary eNBs. To do.
- the PreHandover Request may be transmitted only to the area supplement eNB that is likely to be connected to the UE 100-1 among the plurality of area supplement eNBs.
- FIG. 12 is a diagram illustrating an operation sequence when a plurality of area supplement eNBs (eNB 200-3 and eNB 200-4) are set. Here, differences from the operation sequence (FIG. 7) according to the above-described embodiment will be described.
- the eNB 200-2 transmits a PreHandover Request to the eNB 200-3 and the eNB 200-4 (step S104).
- the eNB 200-3 and the eNB 200-4 approves the PreHandover Request
- the eNB 200-3 and the eNB 200-4 transmit the PreHandover Request Ack to the eNB 200-2.
- the eNB 200-2 transmits the SN Status Transfer to the eNB 200-3 and the eNB 200-4 (Step S109), and the Data Forwarding is performed. It transmits to eNB200-3 and eNB200-4 (step S111).
- the eNB 200-2 transmits the Pass Switch Notice only to one of the eNB 200-3 and the eNB 200-4 (here, the eNB 200-3) (step S115). As a result, a data path is set between the eNB 200-3 and the MME / S-GW 300.
- the eNB 200-4 determines that the UE 100- 1 is transmitted to the eNB 200-2 indicating that the synchronization with 1 is completed (step S121).
- the eNB 200-2 transmits the SN Status Transfer to the eNB 200-4 (step S122), and transmits the Pass Switch Notice to the eNB 200-4 (step S201).
- the eNB 200-4 that has received the Pass Switch Notice transmits a Path Switch Request to the MME / SGW 300 (step S202).
- the MME / S-GW 300 that has received the Path Switch Request from the eNB 200-4 switches the data path for the UE 100-1 from the eNB 200-3 to the eNB 200-4 (step S123).
- the eNB 200-4 transmits a notification indicating that the synchronization with the UE 100-1 is completed not only to the eNB 200-2 but also to the eNB 200-3.
- the eNB 200-3 that has received the notification transmits an SN Status Transfer to the eNB 200-4.
- the eNB 200-4 that has received the SN Status Transfer transmits a Path Switch Request to the MME / S-GW 300.
- the MME / S-GW 300 switches the data path for the UE 100-1 from the eNB 200-3 to the eNB 200-4.
- FIG. 13 is a diagram illustrating an operation sequence according to the third modification.
- UE 100-1 to UE 100-3 are UEs that perform handover from eNB 200-1 (cell 1) to eNB 200-2 (cell 2).
- step S301 the eNB 200-2 transmits to the eNB 200-3 an ES Request (off notice notice) indicating that the own cell (cell 2) is scheduled to be turned off.
- ES Request off notice notice
- Step S302 the eNB 200-3 that has received the ES Request transmits the ES Request Ack to the eNB 200-2.
- step S303 the eNB 200-3 releases the timer t1 for estimating the timing for turning off the cell 2 of the eNB 200-2 (hereinafter referred to as “off timing”) and the timing for releasing the connection setting (C-RNTI3, etc.)
- off timing the timing for turning off the cell 2 of the eNB 200-2
- C-RNTI3 the timing for releasing the connection setting
- release timing a timer t2 for determining “release timing”.
- the ES Request may include a value t1 (timer value, time, etc.) indicating the off timing or the cell expansion start timing.
- the eNB 200-3 sets the value t1 to the timer t1, and starts the timer t1.
- ES Request may include a value t2 (timer value, time, etc.) indicating release timing.
- t2 timer value, time, etc.
- the eNB 200-3 sets the value t2 to the timer t2, and starts the timer t2.
- the ES Request may include a value t3 (timer value, time, etc.) indicating the timing to end cell expansion.
- the eNB 200-3 sets the value t3 to the timer t3 and starts the timer t3.
- the UE 100-1 to the UE 100-3 establish an RRC connection with the eNB 200-2 (and the eNB 200-3) by the operation sequence according to the above-described embodiment.
- the eNB 200-2 transmits a pre-connection notification including the connection setting information (C-RNTI3 or the like) of the eNB 200-3 to the UE 100-1 to the UE 100-3
- the eNB 200-2 sets a value t2 indicating the release timing. You may notify UE100-1 thru
- step S306 the eNB 200-3 starts cell 3 expansion (area expansion) when the timer t1 expires.
- steps S308 and S309 the UE 100-1 and the UE 100-2 switch to the RRC connection with the eNB 200-3 by synchronizing with the eNB 200-3 (cell 3).
- step S310 when the timer t2 expires, the eNB 200-3 releases the connection setting (C-RNTI3 or the like) for the UE 100-3 that has not switched the connection to the eNB 200-3. Similarly, the UE 100-3 releases the connection setting (C-RNTI3, etc.).
- the LTE system has been described as an example of the mobile communication system.
- 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.
- the present invention is useful in the field of wireless communication such as mobile communication.
Abstract
Description
実施形態に係る通信制御方法は、自セルをオフしようとするオフ対象基地局と、前記オフ対象基地局のセルを補完するためのセル拡張を行うべき拡張対象基地局と、を有する移動通信システムにおいて用いられる。前記通信制御方法は、前記オフ対象基地局が、自セルをオフするよりも前において、ユーザ端末の受け入れを要求するハンドオーバ要求を受信するステップと、前記オフ対象基地局が、前記ハンドオーバ要求を了承する場合に、前記拡張対象基地局に対して、前記ユーザ端末との接続を確立するために必要な接続設定の実施を要求する事前ハンドオーバ要求を送信するステップと、を備える。
以下において、本発明をLTEシステムに適用する場合の実施形態を説明する。
図1は、実施形態に係るLTEシステムの構成図である。図1に示すように、実施形態に係るLTEシステムは、UE(User Equipment)100、E-UTRAN(Evolved-UMTS Terrestrial Radio Access Network)10、及びEPC(Evolved Packet Core)20を備える。
以下において、実施形態に係る通信制御方法について説明する。
実施形態に係る通信制御方法は、改良されたエナジーセービング(ES)技術に関する。具体的には、ESを行うために一のセルをオフする場合に、近隣の他セルの送信電力を上昇させる。これにより、当該他セルのカバレッジを拡張(セル拡張)し、オフされるセルのカバレッジを補完(すなわち、エリア補完)することができる。
図7は、上述した通信制御方法に係る動作シーケンスを示す図である。図7の初期状態において、eNB200-1は、所定時間後に自セル(セル2)をオフすることを決定しており、自セル(セル2)をオフするES状態へ移行する途中である。
次に、上述した動作シーケンスに係る各eNB200の動作フローを説明する。
上述した実施形態では、eNB200-1(セル1)からeNB200-2(セル2)へのUE100-1のハンドオーバが失敗するケースについて触れなかったが、ハンドオーバ失敗時には以下のように動作する。
上述した実施形態では、エリア補完eNBが複数存在するケースについて触れなかったが、複数のエリア補完eNBが設定されている場合、eNB200-2は、当該複数のエリア補完eNBに対してPreHandover Requestを送信する。或いは、複数のエリア補完eNBのうちUE100-1が接続する可能性が高いエリア補完eNBに対してのみPreHandover Requestを送信してもよい。
変更例3では、エリア補完eNBであるeNB200-3がセル拡張を行うタイミング等を決定するための方法について説明する。図13は、変更例3に係る動作シーケンスを示す図である。図13において、UE100-1乃至UE100-3は、eNB200-1(セル1)からeNB200-2(セル2)へのハンドオーバを行うUEである。
上述した実施形態では、ハンドオーバ元eNBがエリア補完eNBであるケースを考慮していなかった。しかしながら、ハンドオーバ元eNBがエリア補完eNBであるケースでは、上述した実施形態に係る動作を次のように変更する。具体的には、図6において、ハンドオーバ元eNB(セル1)におけるC-RNTI1とエリア補完eNB(セル3)におけるC-RNTI3とがあるが、エリア補完eNB=ハンドオーバ元eNB(セル3=セル1)となる場合には、C-RNTI3=C-RNTI1と読み替える。この場合、ESeNB(セル2)からのHandover Requestに対して、Handover Request AckでC-RNTI1を返してもよい。
Claims (9)
- 自セルをオフしようとするオフ対象基地局と、前記オフ対象基地局のセルを補完するためのセル拡張を行うべき拡張対象基地局と、を有する移動通信システムにおいて用いられる通信制御方法であって、
前記オフ対象基地局が、自セルをオフするよりも前において、ユーザ端末の受け入れを要求するハンドオーバ要求を受信するステップと、
前記オフ対象基地局が、前記ハンドオーバ要求を了承する場合に、前記拡張対象基地局に対して、前記ユーザ端末との接続を確立するために必要な接続設定の実施を要求する事前ハンドオーバ要求を送信するステップと、を備えることを特徴とする通信制御方法。 - 前記事前ハンドオーバ要求を受信した前記拡張対象基地局が、前記事前ハンドオーバ要求を了承する場合に、前記接続設定を実施するステップと、
前記接続設定に係る接続設定情報を含んだ事前ハンドオーバ肯定応答を前記拡張対象基地局から前記オフ対象基地局に対して送信するステップと、をさらに備えることを特徴とする請求項1に記載の通信制御方法。 - 前記拡張対象基地局で実施する前記接続設定は、前記ユーザ端末に対するC-RNTIの割り当てを含み、
前記接続設定情報は、前記ユーザ端末に対して割り当てられた前記C-RNTIを含むことを特徴とする請求項2に記載の通信制御方法。 - 前記事前ハンドオーバ肯定応答を受信した前記オフ対象基地局が、前記オフ対象基地局への前記ユーザ端末のハンドオーバ後において、前記接続設定情報を含んだ事前接続通知を前記ユーザ端末に対して送信するステップをさらに備えることを特徴とする請求項2に記載の通信制御方法。
- 前記オフ対象基地局のセルをオフする際に、前記拡張対象基地局が前記セル拡張を開始するステップと、
前記事前接続通知を受信した前記ユーザ端末が、前記接続設定情報に基づいて、前記セル拡張を開始した前記拡張対象基地局との同期をとることにより前記拡張対象基地局へ接続を切り替えるステップと、をさらに備えることを特徴とする請求項4に記載の通信制御方法。 - 前記オフ対象基地局への前記ユーザ端末のハンドオーバの際に、前記ユーザ端末に対するデータパスの事前切り替えのためのデータパス事前切り替え要求を前記オフ対象基地局から前記拡張対象基地局に対して送信するステップと、
前記データパス事前切り替え要求を受信した前記拡張対象基地局が、前記拡張対象基地局とコアネットワークとの間に前記データパスを設定するためのデータパス切り替え要求を前記コアネットワークに対して送信するステップと、をさらに備えることを特徴とする請求項1に記載の通信制御方法。 - 前記オフ対象基地局が、前記拡張対象基地局に対して、自セルをオフする予定であることを示すオフ予告通知を送信するステップと、
前記オフ予告通知を受信した前記拡張対象基地局が、前記オフ対象基地局のセルをオフするタイミングを推定するための第1のタイマを起動するステップと、をさらに備え、
前記第1のタイマの満了時に、前記拡張対象基地局が前記セル拡張を開始することを特徴とする請求項1に記載の通信制御方法。 - 前記オフ予告通知を受信した前記拡張対象基地局が、前記接続設定を解放するタイミングを決定するための第2のタイマを起動するステップと、
前記第2のタイマの満了時に、前記ユーザ端末が前記拡張対象基地局への接続切り替えを行っていない場合に、前記接続設定を解放するステップと、をさらに備えることを特徴とする請求項7に記載の通信制御方法。 - 自セルをオフしようとするオフ対象基地局と、前記オフ対象基地局のセルを補完するためのセル拡張を行うべき拡張対象基地局と、を有する移動通信システムにおいて、前記オフ対象基地局に該当する基地局であって、
自セルをオフするよりも前において、ユーザ端末の受け入れを要求するハンドオーバ要求を受信する受信部と、
前記ハンドオーバ要求を了承する場合に、前記拡張対象基地局に対して、前記ユーザ端末との接続を確立するために必要な接続設定の実施を要求する事前ハンドオーバ要求を送信する送信部と、を備えることを特徴とする基地局。
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