JP2019146274A - Wireless communication device and control method - Google Patents

Abstract

To prevent mismatching of user data that is sent and received.SOLUTION: A wireless communication device capable of performing communication of a first communication device and a second communication device in binary connection includes a reception section configured to receive a first signal transmitted from the first communication device via a first path in the binary connection and receive a second signal transmitted from the first communication device via a second path through the second communication device, a control section capable of performing communication control to receive a notification from the second communication device in the binary communication and change a connection with the communication device to a one-way connection according to control of the first communication device capable of acquiring information about a packet lost between the second communication device and the first communication device, and a transmission section configured to transmit reception state information identifying a signal that has been received or not received by the reception section to the first communication device via the first path when performing communication control.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a wireless communication apparatus and a control method.

  Conventionally, various devices have been devised to increase the transmission capacity (hereinafter referred to as “system capacity”) in a wireless communication system. For example, 3GPP LTE (3rd Generation Partnership Project Radio Access Network Long Term Evolution) discusses a technique for increasing a system capacity by utilizing a small cell (small cell) in addition to a macro cell. Here, the cell refers to a range covered by the radio base station in order for the radio terminal to transmit and receive radio signals. The macro cell is a cell of a base station that has a relatively high transmission power and a relatively large radio wave reachable range. A small cell is a cell of a base station that has a relatively low transmission power and a relatively small radio wave reachable range.

  In 3GPP LTE-Advanced (LTE-A), as a configuration of a wireless communication system, for example, a configuration in which a plurality of small cells are included in a macro cell is being studied. And the technique in which a mobile station connects to a macro cell and a small cell simultaneously is examined. In addition, a technique in which a mobile station is simultaneously connected to two different small cells has been studied. In this way, communication performed by a mobile station connected to two different cells at the same time is sometimes referred to as dual connectivity.

  When a mobile station is connected to a macro cell and a small cell at the same time, for example, a control plane signal including layer 3 control information such as transmission path setting and handover control is transmitted from the macro cell base station (hereinafter referred to as “macro base station”). Sent / received). In addition, for example, a data plane signal including user data is transmitted and received between both a macro base station and a small cell base station (hereinafter referred to as a “small base station”). Here, the control plane may be referred to as a control plane (Control Plane: C plane) or an SRB (Signaling Radio Bearer). The data plane is also called a user plane (User Plane: U plane) or DRB (Data Radio Bearer).

  On the other hand, when a mobile station connects to two different small cells at the same time, for example, a control plane signal is transmitted / received to / from one small base station, and a data plane signal is transmitted / received to / from the other small base station. Sent and received. Data plane signals may be transmitted and received between both small base stations.

  In such a two-way connection, the base station to which the control plane is connected may be referred to as a primary base station. Also, a base station that communicates in cooperation with the primary base station and is connected to the data plane may be referred to as a secondary base station. In addition, these base stations may be called an anchor radio base station and an assisting radio base station, a master radio base station, and a slave radio base station. In addition, in the latest trend of LTE-A, it is called a master base station and a secondary base station, respectively. In the present application, they may be referred to as a first communication device and a second communication device, respectively.

  Various functions have been proposed for function sharing to the primary base station and the secondary base station in the two-way connection depending on which layer the signal of the data plane is branched. For example, there is a configuration in which a data plane signal is branched before the PDCP (Packet Data Convergence Protocol) layer. For example, there is a configuration in which a data plane signal is branched between a PDCP layer and an RLC (Radio Link Control) layer. For example, there is a configuration in which a data plane signal is branched between an RLC layer and a MAC (Medium Access Control) layer. Not only these but the structure which branches the signal of a data plane within each layer is also possible. Further, for example, a configuration in which a part of the functions of the PDCP layer is allocated to the primary base station and the remaining functions of the PDCP layer are allocated to the secondary base station is also possible. The same applies to the functions of the RLC layer and the MAC layer. In addition, in the latest trend of LTE-A, the configuration (Architecture 3C) for branching the data plane signal between the PDCP layer and the RLC layer, and the master base station and the small base station respectively have the PDCP layer, the RLC layer, and the MAC layer. The structure (Architecture 1C) is to be adopted.

  The primary base station and the secondary base station that share functions in this way are connected to each other via a wired or wireless link. A data plane signal branched at the primary base station is transmitted to the secondary base station via this link.

3GPP TS 36.300 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 3GPP TS36.211 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation 3GPP TS36.212 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding 3GPP TS36.213 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures 3GPP TS36.321 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification 3GPP TS36.322 V11.0.0 (2012-09), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Link Control (RLC) protocol specification 3GPP TS 36.323 V11.2.0 (2013-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Packet Data Convergence Protocol (PDCP) specification 3GPP TS36.331 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification 3GPP TS36.413 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) 3GPP TS36.423 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access Network (E-UTRAN); X2 Application Protocol (X2AP) 3GPP TR36.842 V12.0.0 (2013-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Study on Small Cell enhancements for E-UTRA and E-UTRAN; Higher layer aspects

  By the way, when the communication state changes in the communication between the secondary base station and the mobile station during the two-way connection, the two-way connection is canceled and the switch to the one-way connection may occur. It is done. That is, when the mobile station is connected to the macro base station and the small base station at the same time, if there is a change in the communication state between the mobile station and the small base station, the two-way connection is released, and the mobile station It may be possible to communicate with only. As an example of the change in the communication state, for example, a problem or error relating to data communication, deterioration of radio quality, and the like can be cited.

  However, since data plane signals are transmitted from both the macro base station and the small base station during the two-way connection, the user data is duplicated in the mobile station when switching to the one-way connection occurs. There is a risk of damage. That is, when switching from two-way connection to one-way connection occurs, the macro base station transmits user data that has already been transmitted from the small base station, or user data that has not been transmitted from the small base station. May be lost without sending.

  This problem occurs not only in the downlink from the base station to the mobile station, but also in the uplink from the mobile station to the base station. That is, during the two-way connection, the mobile station transmits user data to both the macro base station and the small base station, but after switching to the one-way connection, the mobile station transmits the user data only to the macro base station. To do. At this time, since the mobile station does not know whether or not the user data that has been transmitted to the small base station has been transferred to the macro base station, the user data can be transmitted without excess or shortage after switching to the one-way connection. Difficult to send to. Similarly, even when the mobile station has multiple access of three or more elements, inconsistency of user data transmitted and received after switching to the one-way connection may occur.

  The disclosed technology has been made in view of the above point, and an object thereof is to provide a wireless communication device and a control method capable of preventing mismatch of user data transmitted and received.

  In one aspect, a wireless communication device disclosed in the present application is a wireless communication device capable of performing a two-way connection with a first communication device and a second communication device. The first signal transmitted from the first communication device is received via the first route, and the second signal transmitted from the first communication device is received via the second route via the second communication device. Receiving a notification from the second communication device during the two-way connection, and obtaining information on a packet lost between the second communication device and the first communication device In response to the control of the first communication device capable of communication, a control unit capable of communication control for changing the connection with the first communication device to a one-way connection, and when performing the communication control, Reception status information that identifies signals received or not received by the receiver Via the serial first path and a transmission unit for transmitting to the first communication device.

  According to one aspect of the wireless communication device and the control method disclosed in the present application, it is possible to prevent inconsistency between user data transmitted and received.

FIG. 1 is a diagram illustrating a configuration example of a radio communication system according to the first embodiment. FIG. 2 is a block diagram showing a configuration of the wireless communication system according to the first embodiment. FIG. 3 is a block diagram showing a layer configuration of the radio communication system according to the second embodiment. FIG. 4 is a diagram showing a specific example of the format of PDCP SR. FIG. 5 is a diagram showing a list of PDU types. FIG. 6 is a sequence diagram illustrating a connection switching method according to the second embodiment. FIG. 7 is a flowchart showing processing of the mobile station according to the second embodiment. FIG. 8 is a sequence diagram illustrating a connection switching method according to the third embodiment. FIG. 9 is a block diagram illustrating a hardware configuration of the base station. FIG. 10 is a block diagram illustrating a hardware configuration of the mobile station.

  Hereinafter, embodiments of a wireless communication apparatus and a control method disclosed in the present application will be described in detail with reference to the drawings. In addition, this invention is not limited by this embodiment. Needless to say, the following embodiments may be combined as appropriate. In the following, embodiments related to downlink communication and uplink communication are described. Since two-way connection is often used in bidirectional communication in which both downlink communication and uplink communication are performed, each embodiment is described. Obviously, it may be implemented in combination.

(Embodiment 1)
FIG. 1 is a diagram illustrating a configuration example of a radio communication system according to the first embodiment. The wireless communication system illustrated in FIG. 1 includes a macro base station 100, a small base station 200, and a mobile station 300.

  The mobile station 300 is connected to the macro base station 100 as a primary base station. Accordingly, the mobile station 300 is connected to the macro base station 100 by a control plane represented by a solid arrow and a data plane represented by a broken arrow in FIG. The mobile station 300 is connected to the small base station 200 as a secondary base station. Therefore, the mobile station 300 is connected to the small base station 200 by the data plane.

[Configuration of wireless communication system]
FIG. 2 is a block diagram showing a configuration of the wireless communication system according to the first embodiment. As shown in FIG. 2, the macro base station 100 is connected to the upper layer communication apparatus 4, and the macro base station 100 and the small base station 200 are connected by wire using, for example, an X2 interface. Then, the macro base station 100 and the small base station 200 perform wireless communication with the mobile station 300.

  The macro base station 100 includes a communication unit 11 and a control unit 14. The communication unit 11 communicates with the small base station 200, the mobile station 300, and the upper layer communication device 4. That is, the communication unit 11 performs wired communication with the small base station 200 and the upper layer communication apparatus 4 and performs wireless communication with the mobile station 300.

  Specifically, the communication unit 11 includes a reception unit 12 and a transmission unit 13. The receiving unit 12 receives control data and user data from the upper layer communication apparatus 4. Then, the reception unit 12 outputs the received control data and user data to the transmission unit 13. The control data may be data generated by the macro base station 100 itself.

  The transmission unit 13 wirelessly transmits control data addressed to the mobile station 300 to the mobile station 300. In addition, the transmission unit 13 wirelessly transmits a part of user data addressed to the mobile station 300 to the mobile station 300 and transmits the remaining user data to the small base station 200 according to the instruction of the control unit 14.

  The control unit 14 performs overall control of the operation of the communication unit 11 including the reception unit 12 and the transmission unit 13. The control unit 14 controls data communication according to the communication state. When switching from the two-way connection to the one-way connection, the mobile station 300 is referred to the reception state information received from the mobile station 300 to ensure data consistency with the mobile station 300.

  Examples of switching to a one-way connection include the following cases. First, the communication partner is switched from the current small base station 200 to another small base station (RRC reconfiguration including the SeNB change). Subsequently, the small base station 200 remains set, but the data is transmitted only to the macro base station 300 and not transmitted to the small base station 200 (RRC reconfiguration). Moreover, it is a case where the setting of the small base station 200 is erase | eliminated (RRC reconfiguration including the SeNB removal).

In the above, the timing at which the macro base station 100 receives the reception state information from the mobile station 300 includes, for example, the following examples.
(First example)
When the macro base station 100 switches from the two-way connection to the one-way connection, the mobile station 300 is notified of the setting change by RRC (Radio Resource Control) signaling. Similarly, the small base station 200 is notified of the setting change. This RRC signaling can include an instruction to report reception status information. When the mobile station 300 receives RRC signaling including an instruction to report reception state information, the mobile station 300 notifies the macro base station 100 of the reception state information.

(Second example)
When the mobile station 300 detects a change in the communication state, the mobile station 300 transmits the reception state information to the macro base station 100 using the detection as a trigger. The report of reception status information may be set in advance by RRC signaling. Here, the change in the communication state corresponds to the following case, for example. First, data loss or loss of data in the transmission path (X2 interface and radio link) via the small base station 200 (packet loss at the X2 interface or buffer overflow caused by traffic congestion at the small base station) This is a case where the mobile station 300 does not receive desired data (such as transmission failure in the radio link) (detection is possible when the timer in the PDCP layer expires). Second, in the RLC layer of the small base station 200, retransmission of desired data transmission fails and radio link failure (Radio Link Failure) is detected (in the counter of exceeding the maximum number of retransmissions in the RLC layer). Can be detected). In this case, not only downlink transmission but also an acknowledgment corresponding to downlink transmission (RLC STATUS REPORT for transmitting ACK and NACK, and TCP acknowledgment if downlink communication is TCP (Transmission Control Protocol) communication). Transmission is also likely to fail. Therefore, when uplink communication fails, Radio link Failure is detected in the RLC layer of the mobile station 300. To summarize the above, it is an example of a change in the communication state that a communication failure occurs in the transmission path via the small base station 200 during two-way connection.

  To summarize this example, there are three triggers for the mobile station 300 to transmit the reception state information. That is, the first trigger is detection of a change in the downlink communication state in the mobile station 300 (can detect a change in the state of the wired link and the wireless link), and the second trigger is a downlink communication in the small base station 200. The state change is detected (a change in the state of the radio link can be detected), and the third trigger is a change in the uplink communication state in the mobile station 300 (a change in the state of the radio link can be detected).

(Third example)
It is a combination of the above examples. Specifically, in the second example, at least one of the three communication state changes described in the second example is notified to the macro base station 100, and when the macro base station receives the notification, the RRC The change of setting is notified to the mobile station 300 by signaling. At this time, the macro base station 100 can include an instruction to report reception status information in the RRC signaling. As described above, the macro base station 100 collectively controls the transmission timing of the reception state information, so that the trigger by the “detection of change in the downlink communication state” and the trigger by “detection of the change in the uplink communication state” described above Thus, it can be avoided that the mobile station 300 reports the reception status information at the same time.

  In order to ensure data consistency, the control unit 14 refers to the reception state information so that the mobile station 300 transmits unreceived user data and the mobile station 300 does not transmit the received user data. The transmission after switching to the one-way connection is controlled.

  Here, as a method of transmitting unreceived user data by the mobile station 300, the control unit 14 may transmit the data held in the macro base station 100 as it is or data sent back from the small base station 200. Data that has not been transmitted to the mobile station 300 (data that has not been transmitted by the packet scheduler and data that has been transmitted by the packet scheduler but has not been acknowledged), and data that the macro base station 100 continues to receive (X2 Data being transmitted on the interface or may be referred to as fresh data) may be transmitted.

  As described above, according to the present embodiment, when switching from the two-way connection to the one-way connection, the macro base station receives the reception state information for identifying the unreceived packet and the received packet received from the mobile station. Receive. At that time, the mobile station transmits an unreceived packet with reference to the reception state information, and the mobile station does not transmit a received packet. For this reason, even when connection switching occurs, a packet according to the reception state can be transmitted from the macro base station to the mobile station, and data consistency can be ensured.

  Although the downlink communication from the macro base station 100 to the mobile station 300 has been described in the first embodiment, the same processing is performed for the uplink communication from the mobile station 300 to the macro base station 100. be able to. That is, for example, when a communication failure occurs in the uplink transmission path via the small base station 200 at the time of two-way connection, the macro base station 100 may transmit the reception state information to the mobile station 300. As a result, even when switching to the one-way connection occurs, a packet corresponding to the reception state can be transmitted from the mobile station 300 to the macro base station 100, and data consistency can be ensured.

(Embodiment 2)
Since the configuration example of the radio communication system according to the second embodiment is the same as that of the first embodiment (FIG. 1), description thereof is omitted. Such a configuration of a wireless communication system is often employed for traffic offloading and reducing the number of handovers.

[Configuration of wireless communication system]
Since the configuration of the wireless communication system according to the second embodiment is the same as that of the first embodiment (FIG. 2), detailed description of the same parts as those of the first embodiment is omitted.

  The macro base station 100 includes a communication unit 11 and a control unit 14. The communication unit 11 communicates with the small base station 200, the mobile station 300, and the upper layer communication device 4. Specifically, the communication unit 11 includes a reception unit 12 and a transmission unit 13. The receiving unit 12 receives control data and user data from the upper layer communication apparatus 4. Then, the reception unit 12 outputs the received control data and user data to the transmission unit 13.

  Further, the receiving unit 12 receives an error detection notification from the small base station 200 when the small base station 200 detects an error (communication failure). When the error detection notification is received, the receiving unit 12 wirelessly receives from the mobile station 300 reception status information that identifies user data that has been received by the mobile station 300 and user data that has not been received. Then, the reception unit 12 outputs the received error detection notification and reception state information to the control unit 14. The timing at which the receiving unit 12 receives the reception state information and the contents of the reception state information will be described in detail later.

  The transmission unit 13 wirelessly transmits control data addressed to the mobile station 300 to the mobile station 300. In addition, the transmission unit 13 wirelessly transmits a part of user data addressed to the mobile station 300 to the mobile station 300 and transmits the remaining user data to the small base station 200 according to the instruction of the control unit 14.

  The control unit 14 performs overall control of the operation of the communication unit 11 including the reception unit 12 and the transmission unit 13. Further, when the error detection notification is output from the receiving unit 12, the control unit 14 determines to temporarily cancel the two-way connection and switch to the one-way connection. When switching to the one-way connection, the control unit 14 refers to the reception state information output from the receiving unit 12 and determines user data to be transmitted to the mobile station 300 after switching to the one-way connection. Specifically, the control unit 14 refers to the reception state information, so that the mobile station 300 transmits unreceived user data and the mobile station 300 does not transmit received user data. Control transmission after switching to.

  The small base station 200 includes a communication unit 21 and a control unit 24. The communication unit 21 communicates with the macro base station 100 and the mobile station 300. That is, the communication unit 21 performs wired communication with the macro base station 100 and performs wireless communication with the mobile station 300.

  Specifically, the communication unit 21 includes a reception unit 22 and a transmission unit 23. The receiving unit 22 receives user data from the macro base station 100 via a wired connection. Then, the reception unit 22 outputs the received user data to the transmission unit 23.

  The transmission unit 23 wirelessly transmits the user data addressed to the mobile station 300 output from the reception unit 22 to the mobile station 300. Further, the transmission unit 23 transmits an error detection notification to the macro base station 100 when an error is detected in communication with the mobile station 300. The error detected here is, for example, an error that the user data reception confirmation (ACK) is not received from the mobile station 300 even after a predetermined time has passed since the user data was transmitted to the mobile station 300, or the number of times of user data retransmission. Is an error that reaches a predetermined maximum number of retransmissions. The transmission unit 23 may transmit an error detection notification to the macro base station 100 even when an error is detected in communication with the macro base station 100.

  The control unit 24 performs overall control of the operation of the communication unit 21 including the reception unit 22 and the transmission unit 23.

  The mobile station 300 includes a communication unit 31 and a control unit 34. The communication unit 31 communicates with the macro base station 100 and the small base station 200. That is, the communication unit 31 performs a binary connection with the macro base station 100 and the small base station 200, and performs wireless communication simultaneously with both base stations.

  Specifically, the communication unit 31 includes a reception unit 32 and a transmission unit 33. The receiving unit 32 wirelessly receives control data and user data from the macro base station 100. At the same time, the receiving unit 32 wirelessly receives user data from the small base station 200. That is, the receiving unit 32 directly receives part of the user data transmitted from the macro base station 100 from the macro base station 100 and receives the remaining part of the user data transmitted from the macro base station 100 from the small base station 200. Receive via.

  In addition, when an error is detected in the communication with the small base station 200, the reception unit 32 receives user data and unreceived user data that the mobile station 300 has received from the macro base station 100 and the small base station 200. The reception status information for identifying is generated. Then, the reception unit 32 outputs the generated reception state information to the control unit 34.

  The transmission unit 33 acquires the reception state information generated by the reception unit 32 via the control unit 34. Then, the transmission unit 33 wirelessly transmits the acquired reception state information to the macro base station 100.

  The control unit 34 performs overall control of the operation of the communication unit 31 including the reception unit 32 and the transmission unit 33. In addition, the control unit 34 monitors the reception unit 32 and detects an error that occurs in communication with the small base station 200. The error detected here is, for example, an error in which desired user data is not received even after a predetermined time elapses after receiving user data from the small base station 200, or the number of retransmissions of user data is a predetermined maximum number of retransmissions. Such as an error to reach. When the control unit 34 detects an error in the reception unit 32, the control unit 34 acquires the reception state information generated by the reception unit 32 and outputs the reception state information to the transmission unit 33.

  Here, an error in which desired user data is not received can be detected in the PDCP layer, for example. Specifically, when the reception order of user data is lost, that is, when there is unreceived user data (also called out-of-order delivery), it waits for the arrival of the first unreceived packet. A timer is started. If the packet is received before the timer expires, it is determined that reception is successful, but if it is not received, it is determined that an error occurs. Thereafter, the same processing is performed for the next unreceived packet.

  An error in which the number of retransmissions of user data reaches a predetermined maximum number of retransmissions can be detected in, for example, the RLC layer. Specifically, retransmission (Automatic Repeat Request) control is defined in the RLC layer, and retransmission related to user data in which an error has occurred in wireless transmission is performed. If the retransmission succeeds within the predetermined number of times, it is determined that the reception is successful, but if the number of retransmissions exceeds the predetermined number of times, it is determined that there is an error. In this case, conventionally, it is determined that RLF (Radio Link Failure) has occurred, and RRC connection re-establishment is performed. In the two-way connection, particularly, when RLF occurs on the small base station 200 side, the RRC reconnection is not performed, but a communication failure (RLC failure) in the RLC layer is notified to the macro base station 100. Note that, as described in the first embodiment, communication failure in the RLC layer can be detected by the RLC on the downlink transmission side and the RLC on the downlink reception side.

  In the present embodiment, when these errors are detected, reception status information is transmitted from mobile station 300 to macro base station 100. For this reason, for example, it is possible to transmit the reception status information to the macro base station 100 at an early stage as compared with a technique in which the reception status information is transmitted when the retention amount in the buffer of the mobile station 300 exceeds a predetermined threshold. It becomes possible. When a large amount of user data loss is detected in the PDCP layer, the timer expires for each lost packet, and reception status information is transmitted, increasing signaling overhead. Therefore, for example, a prohibit timer may be separately set so that the reception state information is not frequently transmitted. Specifically, whether or not a certain period has elapsed since the previous transmission of the reception state information is determined using a prohibit timer, and the reception state information is not transmitted again while the certain period has not elapsed. Also good.

[Processing of wireless communication system]
Next, processing of the macro base station 100, the small base station 200, and the mobile station 300 in the wireless communication system configured as described above will be described. The macro base station 100, the small base station 200, and the mobile station 300 communicate using a link layer protocol corresponding to a plurality of link layers. That is, for example, link layer protocols corresponding to a PDCP (Packet Data Convergence Protocol) layer, an RLC (Radio Link Control) layer, a MAC (Medium Access Control) layer, a PHY (Physical) layer, and the like are used. FIG. 3 is a block diagram showing a layer configuration of the radio communication system according to the second embodiment.

  Here, first, processing of the macro base station 100 related to transmission / reception of user data will be described. As illustrated in FIG. 3, the communication unit 11 of the macro base station 100 includes a PDCP layer 101, an RLC layer 102, an RLC layer 103, and a MAC layer 104. The RLC layer 102 is a downlink RLC layer, and the RLC layer 103 is an uplink RLC layer. Note that the macro base station 100 may have a layer (not shown) such as a PHY layer.

  The communication unit 11 receives user data from the upper layer communication device 4. Then, in the PDCP layer 101, the communication unit 11 assigns a sequence number to the received user data packet. At this time, for example, the communication unit 11 assigns an odd number to a packet output to the RLC layer 102 and assigns an even number to a packet transmitted to the small base station 200. This sequence number is also used at the time of handover, for example. In addition, the communication unit 11 performs header compression, security check, and encryption on user data in the PDCP layer 101.

  Then, the communication unit 11 outputs the packet assigned with the odd number from the PDCP layer 101 to the RLC layer 102. Moreover, the communication part 11 transmits the packet with which the even number was provided to the small base station 200 via wired connection. Thus, for example, packets with sequence numbers # 1, # 3, # 5, # 7,... Are output to the RLC layer 102, and packets with sequence numbers # 2, # 4, # 6, # 8,. Is transmitted to the small base station 200.

  Note that the number assigned to the packet does not necessarily have to be an ascending sequence number. That is, as long as each packet can be identified and the identifier indicates the order of the packets in the entire user data, other numbers may be given to the packets. In the following, the description will be continued assuming that consecutive sequence numbers in ascending order are given to the packet.

  The communication unit 11 acquires, from the PDCP layer 101, a packet to which an odd number is assigned in the RLC layer 102. Then, the communication unit 11 divides and integrates the packets as necessary in the RLC layer 102 and adds an RLC layer header to generate an RLC layer packet (hereinafter referred to as “RLC packet”).

  Thereafter, the communication unit 11 outputs the RLC packet from the RLC layer 102 to the MAC layer 104 according to the scheduling in the MAC layer 104. Then, the communication unit 11 assembles data for transmission using the RLC packet in the MAC layer 104. That is, for example, RLC packets are divided or integrated as necessary, and a MAC layer header is added to generate a MAC layer packet (hereinafter referred to as “MAC packet”). Then, the communication unit 11 transmits the MAC packet from the MAC layer 104 to the mobile station 300 via a PHY layer (not shown) or the like according to scheduling.

  On the other hand, when receiving user data from the mobile station 300, the communication unit 11 receives user data from the mobile station 300 in the MAC layer 104. Then, the communication unit 11 reconstructs (reassembles) the received user data in the MAC layer 104, and divides and integrates the received user data in the RLC layer 103. Further, the communication unit 11 corrects the data order using the RLC layer header in the RLC layer 103, and outputs user data from the RLC layer 103 to the PDCP layer 101.

  Next, processing of the macro base station 100 when an error detection notification is received from the small base station 200 will be described.

  When an error is detected in the small base station 200, the communication unit 11 acquires an error detection notification transmitted from the small base station 200 in the PDCP layer 101. In addition, the communication unit 11 acquires reception state information transmitted from the mobile station 300 and passed through the MAC layer 104 and the RLC layer 103 in the PDCP layer 101. The reception state information includes information that allows the mobile station 300 to identify a packet that has been received and a packet that has not been received when an error is detected.

  When the error detection notification is received by the communication unit 11, the control unit 14 determines to cancel the two-way connection with the mobile station 300 and switch to the one-way connection. Then, the control unit 14 transmits, to the small base station 200 and the mobile station 300, a two-way connection release notification indicating that the two-way connection is released through the communication unit 11. Further, the control unit 14 refers to the reception state information received by the communication unit 11 and notifies the PDCP layer 101 of a packet to be transmitted to the mobile station 300. That is, the control unit 14 notifies the PDCP layer 101 of a sequence number of a packet that has not been received by the mobile station 300 indicated by the reception status information, and sets a sequence number of a received packet as a sequence number of a packet that does not require transmission. The PDCP layer 101 is notified.

  Then, the communication unit 11 outputs packets not received by the mobile station 300 from the PDCP layer 101 to the RLC layer 102 in ascending order of sequence numbers while excluding packets that have been received by the mobile station 300 and are no longer required to be transmitted. Then, the communication unit 11 generates an RLC packet in the RLC layer 102, generates a MAC packet in the MAC layer 104, and transmits the MAC packet to the mobile station 300. Thereby, the mobile station 300 can receive a packet without duplication and loss even after switching from a two-way connection to a one-way connection.

  Next, processing of the small base station 200 related to transmission / reception of user data will be described. As illustrated in FIG. 3, the communication unit 21 of the small base station 200 includes an RLC layer 201, an RLC layer 202, and a MAC layer 203. The RLC layer 201 is a downlink RLC layer, and the RLC layer 202 is an uplink RLC layer. Note that the small base station 200 may have a layer (not shown) such as a PHY layer.

  The communication unit 21 receives a packet transmitted from the PDCP layer 101 of the macro base station 100 via a wired connection in the RLC layer 201. As described above, an even number is assigned to this packet. And the communication part 21 produces | generates a RLC packet by performing the division | segmentation and integration of a packet in the RLC layer 201 as needed, and providing the header of a RLC layer.

  Thereafter, the communication unit 21 outputs the RLC packet from the RLC layer 201 to the MAC layer 203 according to the scheduling in the MAC layer 203. Then, the communication unit 21 assembles data for transmission using the RLC packet in the MAC layer 203. In other words, for example, RLC packets are divided or integrated as necessary, and a MAC layer header is added to generate a MAC packet. Then, the communication unit 21 transmits the MAC packet from the MAC layer 203 via a PHY layer (not shown) or the like to the mobile station 300 according to scheduling.

  On the other hand, when receiving user data from the mobile station 300, the communication unit 21 receives user data from the mobile station 300 in the MAC layer 203. Then, the communication unit 21 reconstructs (reassembles) the received user data in the MAC layer 203, and divides and integrates the received user data in the RLC layer 202. Further, the communication unit 21 corrects the order of data using the header of the RLC layer in the RLC layer 202 and transmits user data from the RLC layer 202 to the macro base station 100.

  Next, processing of the small base station 200 when an error is detected will be described.

  When the MAC packet is transmitted from the MAC layer 203 to the mobile station 300, the control unit 24 starts a timer that measures a predetermined time and waits for reception confirmation (ACK) from the mobile station 300. At this time, if the MAC packet is not correctly received by the mobile station 300, an acknowledgment (ACK) is not received until the timer expires. For this reason, the control unit 24 detects that an error has occurred when a reception confirmation (ACK) is not received before the timer expires.

  The control unit 24 may monitor the number of retransmissions of data with the mobile station 300 and detect that an error has occurred when the number of retransmissions reaches a predetermined maximum number of retransmissions. Further, the control unit 24 may detect that an error has occurred when a desired packet is not received even after a predetermined time has elapsed since the packet was received from the macro base station 100 via a wired connection. . When the control unit 24 detects an error, the communication unit 21 transmits an error detection notification to the macro base station 100 via a wired connection.

  Thereafter, when it is determined by the macro base station 100 to cancel the binary connection, the communication unit 21 receives a binary connection cancellation notification from the macro base station 100. After receiving the binary connection release notification, wireless communication between the small base station 200 and the mobile station 300 is not executed, and the communication unit 21 stops data transmission / reception.

  Next, processing of the mobile station 300 regarding user data transmission / reception will be described. As illustrated in FIG. 3, the communication unit 31 of the mobile station 300 includes MAC layers 301 and 302, RLC layers 303 to 306, and a PDCP layer 307. Since the mobile station 300 has a function of simultaneously receiving user data from two base stations, the MAC layer and the RLC layer are provided corresponding to each base station. That is, the MAC layer 301, the RLC layer 303, the RLC layer 304, and the PDCP layer 307 are used for transmitting / receiving user data to / from the macro base station 100. Further, the MAC layer 302, the RLC layer 305, the RLC layer 306, and the PDCP layer 307 are used for transmitting and receiving user data to and from the small base station 200. The RLC layers 303 and 305 are downlink RLC layers, and the RLC layers 304 and 306 are uplink RLC layers. The mobile station 300 may have a layer (not shown) such as a PHY layer.

  The communication unit 31 receives user data (MAC packet) from the macro base station 100 in the MAC layer 301. Then, the communication unit 31 reconstructs (reassembles) the received user data in the MAC layer 301, and divides and integrates the received user data in the RLC layer 303. Further, the communication unit 31 corrects the order of data using the header of the RLC layer in the RLC layer 303, and outputs user data from the RLC layer 303 to the PDCP layer 307. Then, the communication unit 31 performs decryption, security check, and release of header compression on the user data in the PDCP layer 307.

  Similarly, the communication unit 31 receives user data (MAC packet) from the small base station 200 in the MAC layer 302. Then, the communication unit 31 reconstructs (reassembles) the received user data in the MAC layer 302 and divides and integrates the received user data in the RLC layer 305. Further, the communication unit 31 corrects the order of data using the header of the RLC layer in the RLC layer 305, and outputs user data from the RLC layer 305 to the PDCP layer 307. Then, the communication unit 31 performs decryption, security check, and release of header compression on the user data in the PDCP layer 307.

  On the other hand, when transmitting user data to the macro base station 100 and the small base station 200, the communication unit 31 assigns a sequence number to the user data packet in the PDCP layer 307. Further, the communication unit 31 performs header compression, security check, and encryption on user data in the PDCP layer 307.

  Then, the communication unit 31 outputs some packets from the PDCP layer 307 to the RLC layer 304 and outputs the remaining packets from the PDCP layer 307 to the RLC layer 306. Then, the communication unit 31 divides and integrates the packets as necessary in the RLC layers 304 and 306, and generates an RLC layer packet (hereinafter referred to as "RLC packet") by adding an RLC layer header. To do.

  Thereafter, the communication unit 31 outputs the RLC packet from the RLC layers 304 and 306 to the MAC layers 301 and 302 according to the scheduling in the MAC layers 301 and 302, respectively. Then, the communication unit 31 assembles data for transmission using RLC packets in the MAC layers 301 and 302. In other words, for example, RLC packets are divided or integrated as necessary, and a MAC layer header is added to generate a MAC packet. Then, the communication unit 31 transmits the MAC packet from the MAC layers 301 and 302 to the macro base station 100 and the small base station 200 through the PHY layer (not shown) according to the scheduling, respectively.

  Next, processing of the mobile station 300 when an error is detected will be described.

  The control unit 34 monitors reception of user data in the communication unit 31. For example, in the PDCP layer 307, even after a predetermined time has elapsed after receiving a packet with a sequence number, the sequence preceding this packet When there is an unreceived packet assigned a number, it is detected that an error has occurred. In addition, the control unit 34 monitors the number of retransmissions of data between the macro base station 100 and the small base station 200, and detects that an error has occurred when the number of retransmissions reaches a predetermined maximum number of retransmissions. You may do it. When an error is detected in data reception from the small base station 200, the control unit 34 instructs the communication unit 31 to generate reception state information.

  Upon receiving the instruction, the communication unit 31 acquires the sequence number assigned to the received packet in the PDCP layer 307. That is, since the sequence number assigned in the PDCP layer 101 of the macro base station 100 is assigned to each packet, the sequence number assigned by the macro base station 100 is acquired in the PDCP layer 307. Then, the communication unit 31 determines the sequence number of the unreceived packet from the acquired sequence number in the PDCP layer 307.

  Then, the communication unit 31 receives, in the PDCP layer 307, the smallest sequence number among the sequence numbers of unreceived packets and reception indicating whether or not a predetermined number of packets to which a sequence number subsequent to this sequence number has been received are received. Generate state information. Specifically, for example, packets with sequence numbers # 1, # 3, # 5, and # 7 are transmitted from the macro base station 100, and packets with sequence numbers # 2, # 4, # 6, and # 8 are transmitted from the small base station 200. Consider the case where it is sent. Here, for example, it is assumed that a packet with sequence number # 2 transmitted from the small base station 200 is not received by the mobile station 300 and an error is detected. In this case, packets with sequence numbers # 1, # 3, # 5, and # 7 transmitted from the macro base station 100 are received by the mobile station 300, and packets with sequence numbers # 2, # 4, # 6, and # 8 are received. It is not received by the mobile station 300.

  Therefore, in the PDCP layer 307, reception state information indicating the smallest sequence number # 2 among the sequence numbers of unreceived packets and whether or not packets with sequence numbers # 3 to # 8 are received is generated. Therefore, here, reception state information is generated indicating that packets with sequence numbers # 3, # 5, and # 7 have been received, and packets with sequence numbers # 4, # 6, and # 8 have not been received. . This reception status information is not received by the mobile station 300 with sequence numbers # 2, # 4, # 6, and # 8, and after switching to a one-way connection, the macro base station 100 needs to transmit again. It is shown that.

  The above explanation is based on the premise that sequence numbers that are consecutive in ascending order in the PDCP layer 101 are given to packets. However, as described above, in the PDCP layer 101, the sequence number does not necessarily have to be given to the packet. When another identifier is added to the packet in the PDCP layer 101, the reception status information includes the identifier of the packet (the first unreceived packet) whose order is closest to the beginning of the entire user data among the unreceived packets. . Also, the reception state information in this case includes the presence / absence of reception of a predetermined number of packets after the packet closest to the head of the entire user data.

  When the reception state information is generated in the PDCP layer 307, the communication unit 31 transmits the reception state information to the macro base station 100. For this reason, in the macro base station 100, it is possible to grasp the reception state of the packet in the mobile station 300 including the packet passing through the small base station 200. As a result, the macro base station 100 can transmit packets to the mobile station 300 without excess or deficiency even after canceling the two-way connection and switching to the one-way connection, preventing duplication and loss of user data. can do.

[Specific example of reception status information]
As described above, when an error is detected in communication between the small base station 200 and the mobile station 300, reception state information is transmitted from the mobile station 300 to the macro base station 100. For example, a PDCP status report (hereinafter abbreviated as “PDCP SR”) can be used as the reception status information.

  FIG. 4 is a diagram showing a specific example of the format of PDCP SR. PDCP SR 400 shown in the upper part of FIG. 4 is a PDCP SR for a 12-bit sequence number. 4 is a PDCP SR for a 15-bit sequence number. Further, PDCP SR 420 shown in the lower part of FIG. 4 is a PDCP SR for a 7-bit sequence number.

  As shown in these figures, in PDCP SR, the size of the sequence number differs depending on the data transmitted and received. Specifically, for example, a 7-bit sequence number may be used in VoIP (Voice of Internet Protocol). For this reason, each PDCP SR 400, 410, and 420 shown in FIG. 4 has FMS (First Missing Sequence number) fields 401, 411, and 421 of different sizes. The FMS fields 401, 411, and 421 are fields in which the sequence numbers of the packets closest to the head of the entire user data among the unreceived packets are stored.

  That is, for example, in the PDCP SR 400, the FMS field 401 stores the sequence number of the packet closest to the beginning of the entire user data among the packets not received by the mobile station 300. In other words, the FMS field 401 stores the sequence number of the packet that should be received earliest among the user data packets that have not arrived from the small base station 200. Hereinafter, a packet in which a sequence number is stored in the FMS fields 401, 411, and 421 may be referred to as an “FMS packet”.

In addition, in the Bitmap ₁ to Bitmap _N fields of the PDCP SRs 400, 410, and 420, the presence / absence of reception regarding a packet after the FMS packet is stored. Specifically, for example, if the 1st to Nth packets (N is an integer of 1 or more) after the FMS packet are received by the mobile station 300, “1” is stored and received by the mobile station 300. If not, “0” is stored.

  For example, as in the example described above, packets with sequence numbers # 1, # 3, # 5, and # 7 are transmitted from the macro base station 100, and packets with sequence numbers # 2, # 4, # 6, and # 8 are small. Consider the case of transmission from the base station 200. Here, if the mobile station 300 does not receive the packet with the sequence number # 2 and an error is detected, the subsequent packets with the sequence numbers # 4, # 6, and # 8 are not received from the small base station 200. Therefore, in mobile station 300, packets with sequence numbers # 1, # 3, # 5, and # 7 have been received, and packets with sequence numbers # 2, # 4, # 6, and # 8 are not received.

In this case, since the FMS packet is the packet with the sequence number # 2, the sequence number # 2 is stored in the FMS fields 401, 411, and 412 of the PDCP SRs 400, 410, and 420. For packets after the FMS packet, packets with sequence numbers # 3, # 5, and # 7 have been received, and packets with sequence numbers # 4, # 6, and # 8 have not been received. Therefore, “1”, “0”, “1”, “0”, “1”, and “0” are stored in the Bitmap ₁ to Bitmap ₆ fields, respectively.

  Also, information regarding the type of PDU (Protocol Data Unit) used as the PDCP SRs 400, 410, and 420 is stored in the PDU Type field of the PDCP SRs 400, 410, and 420 shown in FIG. Specifically, for example, as shown in FIG. 5, a bit representing the type of the PDU is stored in the PDU Type field. That is, when bit “000” is stored in the PDU Type field, this indicates that the PDU is a PDCP status report such as PDCP SRs 400, 410, and 420.

  On the other hand, when the bit “001” is stored in the PDU Type field, this PDU indicates a scattered ROHC feedback packet. The scattered ROHC feedback packet includes feedback information for the PDU of the PDCP layer transmitted from the receiving side.

  Further, bits “010” to “111” that can be stored in the PDU Type field are left as reserved bits. Therefore, in this embodiment, a bit different from normal PDCP SR is assigned to the reception status information transmitted from mobile station 300 when an error is detected, and this bit may be stored in the PDU Type field. Is possible.

[Connection switching method]
Next, a connection switching method from two-way connection to one-way connection according to Embodiment 2 will be described with reference to the sequence diagram shown in FIG.

  When the mobile station 300 is two-way connected to the macro base station 100 and the small base station 200, a part of user data is wirelessly transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300. The remaining user data is transmitted to the small base station 200 via a wired connection (step S101), and wirelessly transmitted from the communication unit 21 of the small base station 200 to the mobile station 300. These user data packets are given sequence numbers indicating the order of data in the communication unit 11 of the macro base station 100. For example, packets with odd numbers are directly transmitted from the macro base station 100 to the mobile station 300. The packet to which the even number is assigned is wirelessly transmitted to the mobile station 300 via the small base station 200.

  Then, when a packet wirelessly transmitted from the small base station 200 is not received by the mobile station 300 (step S102), an error is detected by the control unit 24 of the small base station 200 (step S103). This error is detected, for example, when a reception confirmation (ACK) for a packet wirelessly transmitted from the small base station 200 is not returned from the mobile station 300. Also, when the number of retransmissions with the mobile station 300 reaches a predetermined maximum number of retransmissions or when the next packet is not received even after a predetermined time has elapsed after receiving a packet from the macro base station 100 An error is detected by the control unit 24 of the small base station 200.

  On the other hand, when a packet from the small base station 200 is not received, an error is also detected by the control unit 34 of the mobile station 300 (step S104). This error is detected, for example, when there is an unreceived packet with a sequence number prior to this packet even after a predetermined time has elapsed after receiving a packet with a sequence number from the small base station 200. Is done. Further, when the number of retransmissions with the small base station 200 reaches a predetermined maximum number of retransmissions, an error is detected by the control unit 34 of the mobile station 300.

  When an error is detected by the control unit 24 of the small base station 200, an error detection notification is transmitted to the macro base station 100 (step S105). Further, when an error is detected by the control unit 34 of the mobile station 300, reception state information is generated by the communication unit 31. The reception status information includes the sequence number of the packet whose order is closest to the top of the packets that have not been received by the mobile station 300 and the presence / absence of reception of a predetermined number of packets after this packet. Then, the generated reception state information is transmitted from the communication unit 31 of the mobile station 300 to the macro base station 100 (step S106).

  In the macro base station 100, the error detection notification transmitted from the small base station 200 is received, and the control unit 14 determines to temporarily cancel the two-way connection and switch to the one-way connection. That is, it is determined that the transmission of user data via the small base station 200 is temporarily stopped, and the macro base station 100 transmits all user data directly to the mobile station 300. Then, the communication unit 11 transmits a two-way connection release notification indicating that the two-way connection is released to the small base station 200 (step S107). The small base station 200 that has received the binary connection release notification stops transmission of user data to the mobile station 300 thereafter.

  Further, the binary connection release notification is also transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S108). The mobile station 300 that has received the two-way disconnection notification thereafter receives all user data from the macro base station 100.

  When the macro base station 100 transmits user data to the mobile station 300 after switching to the one-way connection, the control unit 14 refers to the reception state information received from the mobile station 300. Then, the sequence number of the packet that has not been received by the mobile station 300 is notified from the control unit 14 to the communication unit 11, and the packet with the notified sequence number is sequentially transmitted from the communication unit 11 to the mobile station 300.

  Thus, in the present embodiment, when an error is detected in the transmission path of user data via small base station 200, reception state information is transmitted from mobile station 300 to macro base station 100. Then, the macro base station 100 cancels the two-way connection and refers to the reception state information, and the mobile station 300 transmits user data that has not been received to the mobile station 300 without excess or deficiency. For this reason, even when switching from two-way connection to one-way connection occurs, duplication and loss of user data received by the mobile station 300 can be prevented.

[Specific example of mobile station processing when an error is detected]
Next, processing of the mobile station 300 when an error is detected in the transmission path via the small base station 200 at the time of two-way connection will be described with reference to the flowchart shown in FIG.

  The control unit 34 of the mobile station 300 monitors communication between the small base station 200 and the mobile station 300, and determines whether or not an error has occurred (step S201). That is, when a packet with a sequence number is received from the small base station 200, the control unit 34 determines whether there is an unreceived packet with a packet with a sequence number prior to this packet. To do. If there is an unreceived packet, a predetermined timer is started, and it is determined whether an unreceived packet is received before the predetermined time elapses. As a result of these determinations, if there is no unreceived packet or if the packet is correctly received before the predetermined time has elapsed, it is assumed that no error is detected (No in step S201), and the control unit 34 continues to monitor communication. .

  When an error is detected (Yes in step S201), the control unit 34 instructs the communication unit 31 to generate PDCP SR that is reception state information. In response to this instruction, the communication unit 31 generates a PDCP SR including the sequence number of the packet closest to the beginning of the entire user data among the unreceived packets and whether or not a predetermined number of packets are received after this packet. (Step S202). Then, the communication unit 31 transmits the generated PDCP SR to the macro base station 100 (step S203).

  Thereafter, the communication unit 31 receives a binary connection release notification from the macro base station 100 that has decided to temporarily release the binary connection (step S204). After receiving the two-way connection release notification, the communication unit 31 starts one-way connection with the macro base station 100 (step S205), and receives all user data addressed to the mobile station 300 from the macro base station 100. At this time, since the macro base station 100 refers to the PDCP SR and the mobile station 300 transmits unreceived user data without excess or deficiency, the communication unit 31 transmits user data from the macro base station 100 without duplication and loss. Receive.

  As described above, according to the present embodiment, when an error is detected in the transmission path via the small base station at the time of two-way connection, the mobile station identifies an unreceived packet and a received packet. Transmit reception status information to the macro base station. Then, the macro base station releases the two-way connection and switches to the one-way connection, and the mobile station transmits an unreceived packet with reference to the reception state information. For this reason, even when connection switching occurs, packets can be transmitted from the macro base station to the mobile station without excess or deficiency, and duplication and loss of user data can be prevented.

  In the second embodiment, the error detection notification is transmitted from the small base station 200 to the macro base station 100. However, the error detection notification is transmitted from the mobile station 300 to the macro base station 100. Anyway. In this case, the error detection notification may be transmitted to the macro base station 100 together with the reception state information.

(Embodiment 3)
In the second embodiment, the connection switching method when an error is detected in the downlink from the macro base station 100 and the small base station 200 to the mobile station 300 has been described. However, even when an error is detected in the uplink from the mobile station 300 to the macro base station 100 and the small base station 200, the two-way connection may be temporarily released and switched to the one-way connection. Therefore, in Embodiment 3, a connection switching method when an error is detected on the uplink will be described.

  Since the configuration of the radio communication system according to the present embodiment is the same as that of the second embodiment, description thereof is omitted. The present embodiment is different from the second embodiment in that an error that a packet transmitted from the mobile station 300 via the small base station 200 is not received by the macro base station 100 is detected.

  FIG. 8 is a sequence diagram illustrating a connection switching method according to the third embodiment. As shown in FIG. 8, when the mobile station 300 is two-way connected to the macro base station 100 and the small base station 200, part of the user data is directly transmitted from the communication unit 31 of the mobile station 300. (Step S301). The remaining user data is transmitted to the macro base station 100 via the small base station 200.

  These user data packets are given sequence numbers in the communication unit 31 of the mobile station 300. For example, packets with odd numbers are directly transmitted to the macro base station 100 and even numbers are given. The packet is transmitted to the macro base station 100 via the small base station 200.

  Then, when a packet transmitted via the small base station 200 is not received by the macro base station 100 (step S302), an error is detected by the control unit 14 of the macro base station 100 (step S303). This error is caused by, for example, an unreceived packet to which a sequence number before this packet is assigned even after a predetermined time has elapsed after receiving a packet to which a sequence number is assigned from the mobile station 300 via the small base station 200. Detected when there is. This error detection can be performed, for example, in the PDCP layer as described above. Also, this error detection can be performed, for example, in the RLC layer. When the error detection is performed in the RLC, the small base station 200 or the mobile station 300 can detect the error. When an error is detected by the small base station 200 or the mobile station 300, the macro base station 100 may be notified that an error has occurred.

  When an error is detected by the control unit 14 of the macro base station 100, reception state information is generated by the communication unit 11. The reception status information includes the sequence number of the packet that is closest to the beginning of the entire user data among the packets that have not been received by the macro base station 100, and the presence / absence of reception of a predetermined number of packets after this packet. Then, the generated reception state information is transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S304).

  In the macro base station 100, since an error is detected by the control unit 14, it is determined to temporarily cancel the two-way connection and switch to the one-way connection. That is, it is determined that reception of user data via the small base station 200 is temporarily stopped and all user data is transmitted directly from the mobile station 300 to the macro base station 100. Then, the communication unit 11 transmits a binary connection release notification indicating that the binary connection is released to the small base station 200 (step S305). The small base station 200 that has received the binary connection release notification stops receiving user data from the mobile station 300 thereafter.

  The binary connection release notification is also transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S306). The mobile station 300 that has received the binary connection release notification thereafter wirelessly transmits all user data directly to the macro base station 100.

  When the mobile station 300 transmits user data to the macro base station 100 after switching to the one-way connection, the control unit 34 refers to the reception state information received from the macro base station 100. Then, the sequence number of a packet that has not been received by the macro base station 100 is notified from the control unit 34 to the communication unit 31, and the packet with the notified sequence number is sequentially transmitted from the communication unit 31 to the macro base station 100.

  Thus, in the present embodiment, when an error is detected in the user data transmission path via small base station 200, reception state information is transmitted from macro base station 100 to mobile station 300. Then, after the macro base station 100 cancels the two-way connection, the mobile station 300 refers to the reception state information and transmits the user data not received by the macro base station 100 to the macro base station 100 without excess or deficiency. For this reason, even when switching from a two-way connection to a one-way connection occurs, duplication and loss of user data received by the macro base station 100 can be prevented.

  As described above, according to the present embodiment, when an error is detected in the transmission path via the small base station at the time of two-way connection, the macro base station identifies an unreceived packet and a received packet. The reception status information to be transmitted is transmitted to the mobile station. When the macro base station cancels the two-way connection and switches to the one-way connection, the mobile station refers to the reception state information and transmits a packet that has not been received by the macro base station. For this reason, even when connection switching occurs, packets can be transmitted from the mobile station to the macro base station without excess or deficiency, and duplication and loss of user data can be prevented.

  In the third embodiment, the macro base station 100 detects an error. However, the error may be detected by the small base station 200 or the mobile station 300, for example. Then, the small base station 200 or the mobile station 300 that has detected the error may notify the macro base station 100 that an error has occurred. The small base station 200 detects an error when, for example, the number of retransmissions with the mobile station 300 in the RLC layer reaches a predetermined maximum number of retransmissions. In addition, the mobile station 300 detects an error when a user data reception confirmation (ACK) is not received from the small base station 200 even after a predetermined time has elapsed since the user data was transmitted to the small base station 200.

  In each of the above embodiments, the two-way connection in which the mobile station 300 is simultaneously connected to the two base stations of the macro base station 100 and the small base station 200 has been described as an example, but there are three or more mobile stations 300. The same processing can be performed in multiple access that is simultaneously connected to the base stations. That is, when an error is detected in the transmission path via any one of the base stations, the receiving-side mobile station transmits the reception state information to the primary base station to which the control plane is connected. Then, the primary base station can cancel the multiple connection and switch to the single connection and refer to the reception state information to transmit user data to the mobile station without excess or deficiency.

  Further, in each of the above embodiments, when an error is detected in the transmission path via the small base station 200, the macro base station 100 determines to release the two-way connection and switch to the one-way connection. did. However, the macro base station 100 does not necessarily have to switch to a one-way connection when an error is detected. Even when the mobile terminal 300 or the macro base station 100 on the receiving side transmits the reception state information to the macro base station 100 or the mobile station 300 on the transmitting side even when switching to the one-way connection is not performed, the transmitting side Can be confirmed.

  Further, in each of the above embodiments, when an error is detected in the transmission path via the small base station 200, the two-way connection is canceled and the first connection is switched. However, the connection is switched. This is not limited to the case where an error is detected. That is, for example, even when the mobile station 300 moves and the connection destination macro base station or small base station is changed, it is conceivable to temporarily cancel the two-way connection and switch to the one-way connection. Even in such a case, the reception side transmits the reception state information to the transmission side, so that duplication and loss of user data when connection switching occurs can be prevented.

  The physical configurations of the macro base station 100, the small base station 200, and the mobile station 300 in each of the above embodiments are not necessarily the same as the block diagrams shown in FIGS. Therefore, specific examples of hardware configurations of the macro base station 100, the small base station 200, and the mobile station 300 will be described.

  FIG. 9 is a block diagram illustrating a hardware configuration of the base station. The base station illustrated in FIG. 9 corresponds to, for example, the macro base station 100 and the small base station 200, and includes an antenna 501, a control unit 502, an RF (Radio Frequency) circuit 503, a memory 504, a CPU 505, and a network interface 506.

  The control unit 502 implements the functions of the control unit 14 of the macro base station 100 and the control unit 24 of the small base station 200, for example.

  The network interface 506 is an interface for connecting to another base station by wired connection. For example, the macro base station 100 and the small base station 200 are connected by wire through the network interface 506.

  For example, the CPU 505, the memory 504, and the RF circuit 503 realize the functions of the communication unit 11 of the macro base station 100 and the communication unit 21 of the small base station 200. That is, for example, the memory 504 stores various programs such as a program for realizing the function of the communication unit 11 or the communication unit 21. Then, the CPU 505 reads the program stored in the memory 504 and realizes the function of the communication unit 11 or the communication unit 21 by cooperating with the RF circuit 503 or the like.

  FIG. 10 is a hardware configuration diagram of the mobile station. The mobile station illustrated in FIG. 10 corresponds to the mobile station 300, for example, and includes an antenna 511, a control unit 512, an RF circuit 513, a memory 514, and a CPU 515.

  The control unit 512 implements the function of the control unit 34 of the mobile station 300, for example.

  For example, the CPU 515, the memory 514, and the RF circuit 513 realize the function of the communication unit 31 of the mobile station 300. That is, for example, the memory 514 stores various programs such as a program for realizing the function of the communication unit 31. Then, the CPU 515 reads the program stored in the memory 514 and realizes the function of the communication unit 31 by cooperating with the RF circuit 513 and the like.

11, 21, 31 Communication unit 12, 22, 32 Reception unit 13, 23, 33 Transmission unit 14, 24, 34 Control unit 101, 307 PDCP layer 102, 103, 201, 202, 303, 304, 305, 306 RLC layer 104, 203, 301, 302 MAC layer

Claims (11)

In a wireless communication device capable of communicating by performing a binary connection with a first communication device and a second communication device,
During the two-way connection, the first signal transmitted from the first communication device is received via the first path, and the second signal transmitted from the first communication device is received as the second communication. A receiver for receiving via a second path through the device;
Receiving the notification from the second communication device during the two-way connection, and obtaining information on a packet lost between the second communication device and the first communication device; A control unit capable of communication control for changing the connection with the first communication device to a one-way connection in accordance with the control of the communication device;
A transmission unit that transmits reception state information specifying a signal that has been received or not received by the reception unit to the first communication device via the first path when the communication control is performed. A wireless communication device. The receiver is
Receive data with an identifier indicating the order of the data,
The transmitter is
An identifier assigned to the first unreceived data, and information indicating whether or not a predetermined number of data assigned with an identifier indicating that the order is later than the identifier has been received by the receiving unit; The wireless communication apparatus according to claim 1, further comprising: receiving state information including: The receiving unit receives an RRC reconfiguration message instructing switching from the two-way connection to the one-way connection from the first communication device;
The wireless communication apparatus according to claim 1, wherein the control unit performs the communication control according to the RRC reconfiguration message.   The RRC reconfiguration message includes information for switching the second communication device to a third communication device, information for performing the communication control while maintaining a connection relationship with the second communication device, or the second communication device. 4. The wireless communication apparatus according to claim 3, wherein any of the information for deleting the connection setting is included.   The control unit receives a notification from the second communication device during the two-way connection, and acquires information on the lost packet and information on a packet that has not been transmitted to the mobile station. The wireless communication apparatus according to claim 1, wherein the communication control is performed in accordance with control of the first communication apparatus that can perform the operation.   The information on a packet that has not been transmitted to the mobile station includes information indicating a packet for which the second communication apparatus has not received a response confirmation signal for the second signal. 5. The wireless communication device according to 5. The first signal includes a part of data transmitted from the first communication device, and the second signal includes another data transmitted from the first communication device. Part data,
The wireless communication according to any one of claims 1 to 6, wherein the reception state information that specifies a received or unreceived signal is reception state information that specifies received or unreceived data. apparatus. In a wireless communication device capable of communicating by performing a binary connection with a first communication device and a second communication device,
A first signal addressed to the first communication device connected in two ways is transmitted via the first path, and a second signal addressed to the first communication device is transmitted via the second communication device. A transmitter for transmitting via the second path;
Receives a notification from the second communication device during the two-way connection, obtains information on a packet lost between the second communication device and the own device, and establishes a connection with the first communication device. A control unit capable of controlling communication control for changing from two-way connection to one-way connection;
When the communication control is performed, a reception unit that receives reception state information that specifies a signal that the first communication device has received or has not received via the first path;
A wireless communication apparatus comprising:   9. The wireless communication apparatus according to claim 8, wherein the control unit determines data to be transmitted from the transmission unit via the first path according to reception state information received by the reception unit. .   The wireless communication device according to claim 8 or 9, wherein the transmission unit transmits an RRC reconfiguration message instructing switching from the two-way connection to the one-way connection to the first communication device. In a control method of a wireless communication device capable of performing a two-way connection with a first communication device and a second communication device,
A first signal transmitted from the first communication device is received via a first path including a wireless line with the first communication device and transmitted from the first communication device. Receiving a second signal via a second path;
The first communication device capable of receiving a notification from the second communication device during the two-way connection and acquiring a lost packet between the second communication device and the first communication device In accordance with the control, the communication control is performed to change the connection with the first communication device to a one-way connection,
A control method for controlling a process of transmitting reception state information for specifying a received or unreceived signal to the first communication device via the first path when the communication control is performed. .

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