JP2023144042A - Radio communication device and radio communication method - Google Patents

Abstract

To prevent inconsistency of user data that is transmitted and received.SOLUTION: A radio communication device includes: a reception unit that receives a part of data transmitted from a first communication device, via a first path including a radio channel between the radio communication device and the first communication device and that receives another part of data transmitted from the first communication device, via a second path that goes through a second communication device; a control unit that performs communication control in accordance with a state of data communication via the second path; and a transmission unit that transmits, to the first communication device via the first path by using control by the control unit according to the state of the data communication via the second path, reception state information that identifies data that has been received or data that has not been received by the reception unit.SELECTED DRAWING: Figure 2

Description

The present invention relates to a wireless communication device and a wireless communication method.

Conventionally, various efforts have been made to increase the transmission capacity (hereinafter referred to as "system capacity") in wireless communication systems. For example, in 3GPP (registered trademark) LTE (3rd Generation Partnership Project Radio Access Network Long Term Evolution), discussions are underway regarding technology for increasing system capacity by utilizing small cells in addition to macro cells. Here, a cell refers to a range covered by a wireless base station for wireless terminals to transmit and receive wireless signals. A macro cell is a base station cell with relatively high transmission power and a relatively large radio coverage area. Furthermore, a small cell is a cell of a base station with relatively low transmission power and a relatively small radio coverage area.

In 3GPP (registered trademark) LTE-Advanced (LTE-A), a configuration in which a plurality of small cells are included in a macro cell, for example, is being considered as a wireless communication system configuration. Techniques are being considered in which a mobile station connects to a macro cell and a small cell simultaneously. Other technologies are being considered in which a mobile station connects to two different small cells at the same time. Communication performed by a mobile station by simultaneously connecting to two different cells in this manner is sometimes referred to as dual connectivity.

When a mobile station connects to a macro cell and a small cell at the same time, control plane signals containing layer 3 control information such as transmission path settings and handover control are sent to the macro cell base station (hereinafter referred to as the "macro base station"). ). Further, 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 is sometimes called a control plane (Control Plane: C plane), SRB (Signaling Radio Bearer), or the like. Further, the data plane is also called a 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, control plane signals are transmitted and received with one small base station, and data plane signals are transmitted and received with the other small base station. sent and received. Data plane signals may be transmitted and received between both small base stations.

In such a binary connection, the base station to which the control plane is connected is sometimes called a primary base station. Further, a base station to which a data plane is connected and communicates in cooperation with a primary base station may be referred to as a secondary base station. Further, these base stations are sometimes called an anchor radio base station and an assisting radio base station, or a master radio base station and a slave radio base station. Note that in the latest trends in LTE-A, these are respectively called a master base station and a secondary base station. In this application, they may be referred to as a first communication device and a second communication device, respectively.

Regarding the division of functions between a primary base station and a secondary base station in a dual connection, various configurations have been proposed depending on at which layer data plane signals are to be branched. For example, there is a configuration in which data plane signals are branched before a PDCP (Packet Data Convergence Protocol) layer. Furthermore, for example, there is a configuration in which data plane signals are branched between a PDCP layer and an RLC (Radio Link Control) layer. Furthermore, for example, there is a configuration in which data plane signals are branched between an RLC layer and a MAC (Medium Access Control) layer. The configuration is not limited to these, and a configuration in which data plane signals are branched within each layer is also possible. Furthermore, for example, a configuration is also possible in which some functions of the PDCP layer are assigned to the primary base station, and the remaining functions of the PDCP layer are assigned to the secondary base station. This also applies to the functions of the RLC layer and MAC layer. The latest trends in LTE-A include a configuration in which data plane signals are branched between the PDCP layer and the RLC layer (Architecture 3C), and a configuration in which the master base station and small base station each split the PDCP layer, RLC layer, and MAC layer. Architecture 1C is to be adopted.

The primary base station and secondary base station that share functions in this way are connected to each other by a wired or wireless link. Then, the 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, if the communication status changes, for example in the communication between the secondary base station and the mobile station, while a two-way connection is in progress, it is possible that the two-way connection will be canceled and switched to a one-way connection. It will be done. In other words, if there is a change in the communication status between the mobile station and the small base station while the mobile station is connected to a macro base station and a small base station at the same time, the dual connection is canceled and the mobile station connects to the macro base station. It is conceivable that the system will only communicate with Examples of changes in communication status include, for example, occurrence of problems or errors related to data communication, and deterioration of wireless quality.

However, during dual connection, data plane signals are transmitted from both the macro base station and the small base station, so when switching to single connection occurs, user data may be duplicated at the mobile station. There is a risk that damage or loss may occur. In other words, when switching from a two-way connection to a one-way connection occurs, the macro base station may redundantly transmit user data that has already been transmitted from the small base station, or transmit user data that has not yet been transmitted from the small base station. may be lost without being sent.

Furthermore, 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. In other words, while performing a dual connection, the mobile station transmits user data to both the macro base station and the small base station, but after switching to a single connection, the mobile station transmits user data only to the macro base station. do. At this time, the mobile station does not know whether or not the user data already transmitted to the small base station has been transferred to the macro base station. It is difficult to send to. Similarly, even when a mobile station has three or more multiple accesses, inconsistencies in user data transmitted and received may occur after switching to single access.

The disclosed technology has been made in view of this point, and aims to provide a wireless communication device and a wireless communication method that can prevent inconsistencies in transmitted and received user data.

In one aspect, a wireless communication device disclosed in the present application receives a portion of data transmitted from a first communication device via a first path including a wireless line with the first communication device. and a receiving unit that receives another part of the data transmitted from the first communication device via a second path passing through a second communication device, and the data via the second path. A control section that performs communication control according to a communication state, and a control section that controls communication according to a state of data communication via the second path, so that data already received or unreceived by the reception section is transmitted. and a transmitter that transmits the specified reception state information to the first communication device via the first path.

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

FIG. 1 is a diagram illustrating a configuration example of a wireless communication system according to a first embodiment. FIG. 2 is a block diagram showing the configuration of the wireless communication system according to the first embodiment. FIG. 3 is a block diagram showing a layer configuration of a wireless 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 showing a connection switching method according to the second embodiment. FIG. 7 is a flow diagram showing the processing of the mobile station according to the second embodiment. FIG. 8 is a sequence diagram showing a connection switching method according to the third embodiment. FIG. 9 is a block diagram showing the hardware configuration of the base station. FIG. 10 is a block diagram showing the hardware configuration of the mobile station.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a wireless communication device and a wireless communication method disclosed in the present application will be described in detail with reference to the drawings. Note that the present invention is not limited to this embodiment. Furthermore, it goes without saying that the following embodiments may be implemented in combination as appropriate. Embodiments related to downlink communication and uplink communication are described below, and since dual connections are often used in bidirectional communication where both downlink communication and uplink communication are performed, each embodiment It is clear that the methods may be implemented in combination.

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

Mobile station 300 connects to macro base station 100 as a primary base station. Therefore, the mobile station 300 is connected to the macro base station 100 through a control plane represented by a solid arrow in FIG. 1 and a data plane represented by a broken arrow. Furthermore, the mobile station 300 connects to the small base station 200 as a secondary base station. Therefore, mobile station 300 is connected to small base station 200 via the data plane.

[Wireless communication system configuration]
FIG. 2 is a block diagram showing the 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 device 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.

Macro base station 100 includes a communication section 11 and a control section 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 device 4, and performs wireless communication with the mobile station 300.

Specifically, the communication section 11 includes a receiving section 12 and a transmitting section 13. The receiving unit 12 receives control data and user data from the upper layer communication device 4 . The receiving unit 12 then outputs the received control data and user data to the transmitting unit 13. Note that the control data may be data generated by the macro base station 100 itself.

The transmitter 13 wirelessly transmits control data addressed to the mobile station 300 to the mobile station 300. Furthermore, according to instructions from the control unit 14, the transmitting unit 13 wirelessly transmits a part of the 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.

The control unit 14 centrally controls the operation of the communication unit 11 including the reception unit 12 and the transmission unit 13. Further, the control unit 14 controls data communication depending on the communication state. When switching from a two-way connection to a one-way connection, data consistency with the mobile station 300 is ensured by referring to reception status information received from the mobile station 300.

Note that, as an example of switching to one-way connection, there are the following cases, for example. First, there is a case where the communication partner is switched from the current small base station 200 to another small base station (RRC reconfiguration including the SeNB change). Next, there is a case where the small base station 200 remains configured, but data is transmitted only to the macro base station 300 and not to the small base station 200 (RRC reconfiguration). This is also a case where the configuration of the small base station 200 is deleted (RRC reconfiguration including the SeNB removal).

In the above, the timing at which the macro base station 100 receives reception status information from the mobile station 300 includes, for example, the following example.
(1st example)
When the macro base station 100 switches from a dual connection to a single connection, the mobile station 300 is notified of the setting change by RRC (Radio Resource Control) signaling. Note that, similarly, the small base station 200 is also notified of the setting change. This RRC signaling can include an instruction to report reception status information. When mobile station 300 receives RRC signaling including an instruction to report reception status information, mobile station 300 notifies macro base station 100 of the reception status information.

(Second example)
When the mobile station 300 detects a change in the communication state, the mobile station 300 uses the detection as a trigger to transmit reception state information to the macro base station 100. Reporting of reception status information may be set in advance by RRC signaling. Here, the change in communication status corresponds to, for example, the following cases. First, there is data loss in the transmission path (X2 interface and wireless link) via the small base station 200 (packet loss in the X2 interface, data discard due to buffer overflow caused by traffic congestion in the small base station, (a transmission failure in a wireless link, etc.) occurs, and desired data is not received at the mobile station 300 (this can be detected by the expiration of a timer in the PDCP layer). Second, in the RLC layer of the small base station 200, retransmission of desired data transmission fails and radio link quality deterioration (Radio Link Failure) is detected (the counter for exceeding the maximum number of retransmissions in the RLC layer detection is possible). In this case, not only the downlink transmission but also the acknowledgment corresponding to the downlink transmission (RLC STATUS REPORT for sending ACK and NACK, TCP acknowledgment if the downlink communication is TCP (Transmission Control Protocol) communication) There is a high possibility that the transmission will also fail. Therefore, if uplink communication fails, Radio link Failure is detected in the RLC layer of the mobile station 300. To summarize the above, the occurrence of a communication problem in the transmission path via the small base station 200 during dual connection is an example of a change in the communication state.

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

(Third example)
This 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 mobile station 300 is notified of the setting change through signaling. At that time, macro base station 100 can include an instruction to report reception status information in RRC signaling. In this way, the macro base station 100 collectively controls the transmission timing of reception state information, so that the above-mentioned trigger due to "detection of change in downlink communication state" and trigger due to "detection of change in uplink communication state" Accordingly, it is possible to avoid the mobile station 300 from reporting reception status information at the same time.

In order to ensure data consistency, the control unit 14 refers to reception status information and prevents the mobile station 300 from transmitting unreceived user data and not transmitting already received user data. In addition, it controls transmission after switching to a one-way connection.

Here, as a method for the mobile station 300 to transmit unreceived user data, the control unit 14 may cause the macro base station 100 to transmit the data held as is, or the control unit 14 may transmit the data held in the macro base station 100 as is, or the control unit 14 may transmit the data held in the macro base station 100 as is, or the 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 received confirmation of delivery), and data that the macro base station 100 continues to receive (X2 Data currently being transmitted on the interface (also referred to as fresh data) may be transmitted.

As described above, according to the present embodiment, when switching from a two-way connection to a one-way connection, the macro base station receives reception status information that identifies unreceived packets and received packets received from a mobile station. receive. At this time, the mobile station refers to the reception status information to transmit packets that have not been received by the mobile station, and prevents the mobile station from transmitting packets that have already been received. Therefore, even if connection switching occurs, packets can be transmitted from the macro base station to the mobile station according to the reception state, and data consistency can be ensured.

Note that in the first embodiment described above, downlink communication from macro base station 100 to mobile station 300 has been described, but similar processing is performed for uplink communication from mobile station 300 to macro base station 100. be able to. That is, for example, if a communication problem occurs in the uplink transmission route via the small base station 200 during dual connection, the macro base station 100 may transmit reception status information to the mobile station 300. As a result, even if switching to a one-way connection occurs, packets can be transmitted from the mobile station 300 to the macro base station 100 according to the reception state, and data consistency can be ensured.

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

[Wireless communication system configuration]
The configuration of the wireless communication system according to the second embodiment is the same as that of the first embodiment (FIG. 2), so a detailed explanation of the same parts as the first embodiment will be omitted.

Macro base station 100 includes a communication section 11 and a control section 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 section 11 includes a receiving section 12 and a transmitting section 13. The receiving unit 12 receives control data and user data from the upper layer communication device 4 . The receiving unit 12 then outputs the received control data and user data to the transmitting 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 malfunction). When the error detection notification is received, the receiving unit 12 wirelessly receives reception status information from the mobile station 300 that specifies user data that the mobile station 300 has received and user data that has not been received. The receiving unit 12 then outputs the received error detection notification and reception status information to the control unit 14. Note that 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 transmitter 13 wirelessly transmits control data addressed to the mobile station 300 to the mobile station 300. Furthermore, according to instructions from the control unit 14, the transmitting unit 13 wirelessly transmits a part of the 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.

The control unit 14 centrally controls 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 decides to temporarily cancel the two-way connection and switch to the one-way connection. Then, when switching to the one-way connection, the control unit 14 refers to the reception status information output from the reception 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 and establishes a one-way connection so that the mobile station 300 transmits unreceived user data and the mobile station 300 does not transmit received user data. Controls transmission after switching to .

Small base station 200 includes a communication section 21 and a control section 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 wireless communication with the mobile station 300.

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

The transmitter 23 wirelessly transmits the user data addressed to the mobile station 300 output from the receiver 22 to the mobile station 300. Furthermore, when an error is detected in communication with the mobile station 300, the transmitter 23 transmits an error detection notification to the macro base station 100. Errors detected here include, for example, an error in which a user data reception confirmation (ACK) is not received from the mobile station 300 even after a predetermined period of time has passed after transmitting the user data to the mobile station 300, and the number of retransmissions of user data. Errors such as reaching a predetermined maximum number of retransmissions. Note that the transmitter 23 may also transmit an error detection notification to the macro base station 100 when an error is detected in communication with the macro base station 100.

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

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

Specifically, the communication section 31 includes a receiving section 32 and a transmitting section 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 transmits the remaining part of the user data transmitted from the macro base station 100 to the small base station 200. Receive via.

In addition, when an error is detected in communication with the small base station 200, the receiving unit 32 allows the mobile station 300 to receive user data that has been received from the macro base station 100 and the small base station 200 and user data that has not been received yet. Generate reception status information that specifies the The receiving unit 32 then outputs the generated reception state information to the control unit 34.

The transmitter 33 acquires the reception status information generated by the receiver 32 via the controller 34 . Then, the transmitter 33 wirelessly transmits the acquired reception state information to the macro base station 100.

The control unit 34 centrally controls the operation of the communication unit 31 including the reception unit 32 and the transmission unit 33. Furthermore, the control unit 34 monitors the reception unit 32 and detects errors that occur in communication with the small base station 200. Errors detected here include, for example, an error in which desired user data is not received even after a predetermined period of time has passed after receiving user data from the small base station 200, or an error in which the number of retransmissions of user data has reached a predetermined maximum number of retransmissions. Such as the error that is reached. When the control unit 34 detects an error in the reception unit 32 , the control unit 34 acquires reception status information generated by the reception unit 32 and outputs it to the transmission unit 33 .

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

Furthermore, an error in which the number of retransmissions of user data reaches a predetermined maximum number of retransmissions can be detected, for example, in the RLC layer. Specifically, retransmission (Automatic Repeat Request) control is defined in the RLC layer, and retransmission of user data in which an error has occurred in wireless transmission is performed. If retransmission is successful within a predetermined number of times, reception is determined to be successful, but if the number of retransmissions exceeds a predetermined number of times, it is determined to be an error. In this case, conventionally, it is determined that RLF (Radio Link Failure) has occurred, and RRC Connection Re-establishment is performed. In addition, in a dual connection, especially if RLF occurs on the small base station 200 side, RRC reconnection is not performed, but a communication failure in the RLC layer (RLC failure) is notified to the macro base station 100. Note that, as described in Embodiment 1, a communication failure in the RLC layer can be detected by the RLC on the downlink transmitting side and the RLC on the downlink receiving side.

In this embodiment, when these errors are detected, reception status information is transmitted from mobile station 300 to macro base station 100. For this reason, it is possible to transmit reception status information to the macro base station 100 earlier than, for example, a technique in which reception status information is transmitted when the amount of retention in the buffer of the mobile station 300 exceeds a predetermined threshold. It becomes possible. Note that when a large amount of user data loss is detected in the PDCP layer, a timer expires and reception status information is transmitted for each lost packet, resulting in an increase in signaling overhead. Therefore, for example, a prohibition timer may be separately set so that reception status information is not transmitted frequently. Specifically, a prohibition timer is used to determine whether a certain period of time has elapsed since the previous transmission of reception status information, and the reception status information is not sent again until the specified period has elapsed. Also good.

[Wireless communication system processing]
Next, the processing of macro base station 100, small base station 200, and mobile station 300 in the wireless communication system configured as described above will be explained. These macro base station 100, small base station 200, and mobile station 300 communicate using a link layer protocol that supports multiple link layers. That is, for example, a link layer protocol 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, etc. is used. FIG. 3 is a block diagram showing a layer configuration of a wireless communication system according to the second embodiment.

Here, first, processing of the macro base station 100 regarding transmission and reception of user data will be described. As shown in FIG. 3, the communication unit 11 of the macro base station 100 has a PDCP layer 101, an RLC layer 102, an RLC layer 103, and a MAC layer 104. RLC layer 102 is a downlink RLC layer, and 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, for example.

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

The communication unit 11 then outputs the odd numbered packets from the PDCP layer 101 to the RLC layer 102. Furthermore, the communication unit 11 transmits the even-numbered packets to the small base station 200 via a wired connection. As a result, for example, packets assigned sequence numbers #1, #3, #5, #7, etc. are output to the RLC layer 102, and packets assigned sequence numbers #2, #4, #6, #8, etc. are output to the RLC layer 102. is transmitted to the small base station 200.

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

The communication unit 11 acquires packets assigned odd numbers from the PDCP layer 101 in the RLC layer 102 . Then, the communication unit 11 generates an RLC layer packet (hereinafter referred to as "RLC packet") by dividing or integrating the packet as necessary in the RLC layer 102 and adding an RLC layer header.

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. The communication unit 11 then assembles data for transmission in the MAC layer 104 using RLC packets. That is, for example, a MAC layer packet (hereinafter referred to as a "MAC packet") is generated by dividing or integrating an RLC packet as necessary and adding a MAC layer header. 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 the scheduling.

On the other hand, when receiving user data from the mobile station 300, the communication unit 11 receives the user data from the mobile station 300 in the MAC layer 104. The communication unit 11 then 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 order of data 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, the processing of the macro base station 100 when receiving an error detection notification 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. The communication unit 11 also acquires reception status information transmitted from the mobile station 300 and passed through the MAC layer 104 and the RLC layer 103 at the PDCP layer 101 . The reception status information includes information that allows mobile station 300 to identify packets that have been received and packets that have not been received at the time when an error is detected.

When the error detection notification is received by the communication unit 11, the control unit 14 decides to cancel the two-way connection with the mobile station 300 and switch to the one-way connection. Then, the control unit 14 transmits a binary connection cancellation notification to the small base station 200 and the mobile station 300 via the communication unit 11, indicating that the binary connection is to be canceled. Furthermore, the control unit 14 refers to the reception status information received by the communication unit 11 and notifies the PDCP layer 101 of packets to be transmitted to the mobile station 300. That is, the control unit 14 notifies the PDCP layer 101 of the sequence number of the packet that the mobile station 300 has not received, which is indicated by the reception state information, and also uses the sequence number of the received packet as the sequence number of the packet that does not need to be transmitted. The PDCP layer 101 is notified.

Then, the communication unit 11 outputs packets that have not been received by the mobile station 300 from the PDCP layer 101 to the RLC layer 102 in order of decreasing sequence number, while excluding packets that have been received by the mobile station 300 and no longer need to be transmitted. The communication unit 11 then 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 packets without duplication or loss even after switching from a two-way connection to a one-way connection.

Next, processing of the small base station 200 regarding transmission and reception of user data will be described. As shown in FIG. 3, the communication unit 21 of the small base station 200 has an RLC layer 201, an RLC layer 202, and a MAC layer 203. RLC layer 201 is a downlink RLC layer, and 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, for example.

The communication unit 21 receives, at the RLC layer 201, a packet transmitted from the PDCP layer 101 of the macro base station 100 via a wired connection. As mentioned above, this packet is given an even number. Then, in the RLC layer 201, the communication unit 21 generates an RLC packet by dividing or combining the packets as necessary and adding an RLC layer header.

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. The communication unit 21 then assembles data for transmission in the MAC layer 203 using RLC packets. That is, for example, MAC packets are generated by dividing or integrating RLC packets as necessary and adding a MAC layer header. Then, the communication unit 21 transmits the MAC packet from the MAC layer 203 to the mobile station 300 via a PHY layer (not shown) or the like according to the scheduling.

On the other hand, when receiving user data from the mobile station 300, the communication unit 21 receives the user data from the mobile station 300 in the MAC layer 203. The communication unit 21 then 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 RLC layer header in the RLC layer 202, and transmits user data from the RLC layer 202 to the macro base station 100.

Next, the processing of 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 a reception confirmation (ACK) from the mobile station 300. At this time, if the MAC packet is not correctly received by the mobile station 300, the reception confirmation (ACK) will not be received before the timer expires. Therefore, the control unit 24 detects that an error has occurred if the reception confirmation (ACK) is not received before the timer expires.

Further, the control unit 24 may monitor the number of retransmissions of data between the mobile station 300 and detect that an error has occurred when the number of retransmissions reaches a predetermined maximum number of retransmissions. Furthermore, the control unit 24 may detect that an error has occurred if a desired packet is not received even after a predetermined period of time has passed 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 the macro base station 100 decides 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 no longer performed, so the communication unit 21 stops transmitting and receiving data.

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

The communication unit 31 receives user data (MAC packets) from the macro base station 100 in the MAC layer 301 . The communication unit 31 then 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 RLC layer header 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 header decompression on the user data in the PDCP layer 307 .

Similarly, the communication unit 31 receives user data (MAC packets) from the small base station 200 at the MAC layer 302. The communication unit 31 then 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 RLC layer header 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 header decompression 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 the user data in the PDCP layer 307 .

Then, the communication unit 31 outputs some of the 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 generates RLC layer packets (hereinafter referred to as "RLC packets") by dividing or integrating the packets as necessary in the RLC layers 304 and 306, and adding an RLC layer header. do.

Thereafter, the communication unit 31 outputs RLC packets from the RLC layers 304 and 306 to the MAC layers 301 and 302, respectively, according to the scheduling in the MAC layers 301 and 302. Then, the communication unit 31 assembles data for transmission in the MAC layers 301 and 302 using RLC packets. That is, for example, MAC packets are generated by dividing or integrating RLC packets as necessary and adding a MAC layer header. Then, the communication unit 31 transmits the MAC packets from the MAC layers 301 and 302 to the macro base station 100 and the small base station 200, respectively, via a PHY layer (not shown), etc., according to the scheduling.

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

The control unit 34 monitors the reception of user data in the communication unit 31, and for example, in the PDCP layer 307, even if a predetermined period of time has elapsed after receiving a packet to which a sequence number has been assigned, the control unit 34 monitors reception of user data in the communication unit 31. Detects that an error has occurred if there is a numbered packet that has not been received. The control unit 34 also monitors the number of data retransmissions 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 so. Then, 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 status 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 each packet is assigned a sequence number assigned at the PDCP layer 101 of the macro base station 100, the sequence number assigned by the macro base station 100 is acquired at the PDCP layer 307. Then, in the PDCP layer 307, the communication unit 31 determines the sequence number of the unreceived packet from the acquired sequence number.

Then, in the PDCP layer 307, the communication unit 31 receives information indicating the smallest sequence number among the sequence numbers of unreceived packets and whether or not a predetermined number of packets with sequence numbers after this sequence number have been 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, it is assumed that the 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 macro base station 100 are received by mobile station 300, and packets with sequence numbers #2, #4, #6, and #8 are received by mobile station 300. Not received by mobile station 300.

Therefore, the PDCP layer 307 generates reception status 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 have been received. Therefore, reception status information is generated here 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 indicates that sequence numbers #2, #4, #6, and #8 have not been received by the mobile station 300, and needs to be transmitted from the macro base station 100 again after switching to a single connection. It is shown that.

Note that the above description is based on the assumption that consecutive sequence numbers are assigned to packets in ascending order in the PDCP layer 101. However, as described above, in the PDCP layer 101, sequence numbers do not necessarily need to be added to packets. If another identifier is assigned to a 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 unreceived packets. . Further, the reception status information in this case includes whether or not a predetermined number of packets after the packet closest to the beginning of the entire user data have been received.

When receiving state information is generated in the PDCP layer 307, the communication unit 31 transmits this receiving state information to the macro base station 100. Therefore, the macro base station 100 can grasp the reception state of packets at the mobile station 300, including packets passing through the small base station 200. As a result, even after canceling the dual connection and switching to the single connection, the macro base station 100 can transmit just enough packets to the mobile station 300, 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 small base station 200 and mobile station 300, reception status information is transmitted from mobile station 300 to macro base station 100. As this reception status information, for example, a PDCP status report (hereinafter abbreviated as "PDCP SR") can be used.

FIG. 4 is a diagram showing a specific example of the format of PDCP SR. The PDCP SR 400 shown in the upper part of FIG. 4 is a PDCP SR for a 12-bit sequence number. Further, the PDCP SR 410 shown in the middle part of FIG. 4 is a PDCP SR for a 15-bit sequence number. Furthermore, the 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 to be transmitted and received. Specifically, for example, in VoIP (Voice of Internet Protocol), a 7-bit sequence number may be used. Therefore, 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, respectively. The FMS fields 401, 411, and 421 are fields in which the sequence number of the packet closest to the beginning of the entire user data among unreceived packets is stored.

That is, for example, in the PDCP SR 400, the FMS field 401 stores 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 mobile station 300. In other words, the FMS field 401 stores the sequence number of the packet that is supposed to be received earliest among the user data packets that have not arrived from the small base station 200. Hereinafter, packets in which sequence numbers are stored in the FMS fields 401, 411, and 421 may be referred to as "FMS packets."

Further, in fields Bitmap ₁ to Bitmap _N of the PDCP SRs 400, 410, and 420, whether or not a packet subsequent to the FMS packet is received is stored. Specifically, for example, if the 1st to Nth (N is an integer greater than or equal to 1) packets after the FMS packet have been received by the mobile station 300, "1" is stored; If not, "0" is stored.

For example, as in the above 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 as small packets. Consider the case where the signal is transmitted from the base station 200. Here, if the packet with sequence number #2 is not received by mobile station 300 and an error is detected, subsequent packets with sequence numbers #4, #6, and #8 are also not received from 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 have not been received.

In this case, since the FMS packet is a packet with sequence number #2, sequence number #2 is stored in FMS fields 401, 411, and 412 of PDCP SRs 400, 410, and 420. Regarding 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 fields of Bitmap ₁ to Bitmap ₆ , respectively.

Furthermore, information regarding the type of PDU (Protocol Data Unit) used as the PDCP SRs 400, 410, and 420 is stored in the PDU Type fields of the PDCP SRs 400, 410, and 420 shown in FIG. Specifically, as shown in FIG. 5, for example, a bit representing the type of this PDU is stored in the PDU Type field. That is, when bit "000" is stored in the PDU Type field, this PDU represents a PDCP status report such as PDCP SR400, 410, and 420.

On the other hand, when bit "001" is stored in the PDU Type field, this PDU represents an interspersed ROHC feedback packet. The interspersed ROHC feedback packet includes feedback information for the PDCP layer PDUs transmitted from the receiving side.

Furthermore, 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 the normal PDCP SR may be assigned to the reception status information transmitted from the mobile station 300 when an error is detected, and this bit may be stored in the PDU Type field. It is possible.

[Connection switching method]
Next, a connection switching method from a two-way connection to a one-way connection according to the second embodiment will be described with reference to the sequence diagram shown in FIG. 6.

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

If the 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 passed after receiving a packet from the macro base station 100, etc. , an error is detected by the control unit 24 of the small base station 200.

On the other hand, if the 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 a predetermined period of time has passed after receiving a packet with a sequence number from the small base station 200, and there is still an unreceived packet with a sequence number earlier than this packet. be done. Further, an error is also detected by the control unit 34 of the mobile station 300 when the number of retransmissions with the small base station 200 reaches a predetermined maximum number of retransmissions.

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, the communication unit 31 generates reception status information. The reception state information includes the sequence number of the packet closest to the beginning among the packets that have not been received by the mobile station 300, and whether or not a predetermined number of packets after this packet have been received. The generated reception state information is then 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, upon receiving the error detection notification transmitted from the small base station 200, the control unit 14 decides to temporarily cancel the two-way connection and switch to the one-way connection. That is, it is decided that the transmission of user data via the small base station 200 will be temporarily stopped and the macro base station 100 will directly transmit all user data to the mobile station 300. Then, the communication unit 11 transmits a binary connection cancellation notification to the small base station 200 indicating that the binary connection is to be canceled (step S107). After receiving the binary connection release notification, the small base station 200 stops transmitting user data to the mobile station 300.

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 received the binary connection release 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 packets with the notified sequence number are sequentially transmitted from the communication unit 11 to the mobile station 300.

As described above, in this embodiment, when an error is detected in the transmission path of user data via small base station 200, reception status information is transmitted from mobile station 300 to macro base station 100. Then, the macro base station 100 cancels the binary connection, and transmits user data that has not been received by the mobile station 300 to the mobile station 300 in just the right amount with reference to the reception status information. Therefore, even if switching from a two-way connection to a 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 error is detected]
Next, the processing of the mobile station 300 when an error is detected in the transmission path via the small base station 200 during dual connection will be described with reference to the flowchart shown in FIG. 7.

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 an error has occurred (step S201). That is, when a packet assigned a sequence number is received from the small base station 200, the control unit 34 determines whether there is an unreceived packet assigned a sequence number earlier than this packet. do. If there is an unreceived packet, a predetermined timer is started, and it is determined whether the unreceived packet is received before a predetermined time elapses. As a result of these determinations, if there is no unreceived packet or if a packet is correctly received before the elapse of a predetermined period of time, it is assumed that no error has been detected (No in step S201), and the control unit 34 continues to monitor communication. .

If an error is detected (step S201 Yes), the control unit 34 instructs the communication unit 31 to generate PDCP SR, which is reception status information. Upon receiving this instruction, the communication unit 31 generates a PDCP SR that includes the sequence number of the packet closest to the beginning of the entire user data among unreceived packets and whether or not a predetermined number of packets after this packet have been received. (Step S202). Then, the communication unit 31 transmits the generated PDCP SR to the macro base station 100 (step S203).

After that, the communication unit 31 receives a binary connection cancellation notification from the macro base station 100 that has decided to temporarily cancel the binary connection (step S204). After receiving the binary connection release notification, the communication unit 31 starts a single 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, the macro base station 100 refers to the PDCP SR and transmits user data that has not been received by the mobile station 300 without excess or deficiency, so the communication unit 31 transmits the user data from the macro base station 100 without duplication or loss. receive.

As described above, according to the present embodiment, when an error is detected in the transmission route via a small base station during dual connection, the mobile station identifies unreceived packets and received packets. Send reception status information to the macro base station. Then, the macro base station cancels the dual connection and switches to the single connection, and refers to the reception status information and transmits the packets that the mobile station has not received. Therefore, even if connection switching occurs, packets can be transmitted from the macro base station to the mobile station in just the right amount, and duplication and loss of user data can be prevented.

Note that 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. You can also do it. In this case, the error detection notification may be transmitted to the macro base station 100 together with the reception status information.

(Embodiment 3)
In the second embodiment, a connection switching method when an error is detected in the downlink from macro base station 100 and small base station 200 to 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 dual connection may be temporarily canceled and switched to a single connection. Therefore, in Embodiment 3, a connection switching method when an error is detected in the uplink will be described.

The configuration of the wireless communication system according to this embodiment is the same as that of Embodiment 2, so the description thereof will be omitted. This embodiment differs from the second embodiment in that an error is detected in which a packet transmitted from mobile station 300 via small base station 200 is not received by macro base station 100.

FIG. 8 is a sequence diagram showing a connection switching method according to the third embodiment. As shown in FIG. 8, when the mobile station 300 has a dual connection with 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 to the macro base station 100. The information is wirelessly transmitted to (step S301). Further, the remaining user data is transmitted to the macro base station 100 via the small base station 200.

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

Then, if the 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 occurs when, for example, a predetermined period of time elapses after receiving a packet assigned a sequence number from the mobile station 300 via the small base station 200, but an unreceived packet assigned a sequence number earlier than this packet remains unreceived. Detected when there is a This error detection can be performed, for example, in the PDCP layer, as described above. Further, this error detection can also be performed, for example, in the RLC layer, and when performed in the RLC, it is also possible to detect the error by the small base station 200 or the mobile station 300. When an error is detected by the small base station 200 or the mobile station 300, the macro base station 100 may be notified of the occurrence of the error.

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

Furthermore, in the macro base station 100, since an error has been detected by the control unit 14, it is decided to temporarily cancel the dual connection and switch to a single connection. That is, it is decided to temporarily stop receiving user data via small base station 200 and to transmit all user data from mobile station 300 directly to macro base station 100. Then, the communication unit 11 transmits a binary connection cancellation notification to the small base station 200 indicating that the binary connection is to be canceled (step S305). The small base station 200 that received the binary connection release notification thereafter stops receiving user data from the mobile station 300.

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 S306). The mobile station 300 that received the binary connection release notification thereafter wirelessly transmits all user data directly to the macro base station 100.

After switching to the one-way connection, when the mobile station 300 transmits user data to the macro base station 100, the control unit 34 refers to the reception status information received from the macro base station 100. Then, the sequence number of the 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 packets with the notified sequence number are sequentially transmitted from the communication unit 31 to the macro base station 100.

As described above, in this embodiment, when an error is detected in the transmission path of user data via small base station 200, reception status information is transmitted from macro base station 100 to mobile station 300. Then, after the macro base station 100 cancels the dual connection, the mobile station 300 refers to the reception state information and transmits user data that has not been received by the macro base station 100 to the macro base station 100 in just the right amount. Therefore, even if switching from a dual connection to a single 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 route via a small base station during dual connection, the macro base station identifies unreceived packets and received packets. The mobile station transmits reception status information to the mobile station. Then, when the macro base station cancels the dual connection and switches to the single connection, the mobile station refers to the reception status information and transmits the packet that the macro base station has not received. Therefore, even if connection switching occurs, packets can be transmitted from the mobile station to the macro base station in just the right amount, and duplication and loss of user data can be prevented.

Note that in the third embodiment, the error is detected by the macro base station 100, but 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 mobile station 300 that has detected the error may notify the macro base station 100 of the occurrence of the error. 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. Furthermore, the mobile station 300 detects an error when a reception confirmation (ACK) of the user data is not received from the small base station 200 even after a predetermined period of time has passed since the mobile station 300 transmitted the user data to the small base station 200.

Note that in each of the above embodiments, the explanation has been given using a binary connection in which the mobile station 300 connects to two base stations, the macro base station 100 and the small base station 200, as an example. Similar processing is possible in multiple access where multiple base stations are connected simultaneously. That is, if an error is detected in a transmission path via any base station, the receiving mobile station transmits reception status information to the primary base station to which the control plane is connected. Then, the primary base station can cancel multiple access and switch to single access, refer to the reception state information, and transmit user data to the mobile station in just the right amount.

Furthermore, in each of the above embodiments, when an error is detected in the transmission route via the small base station 200, the macro base station 100 decides to cancel the dual connection and switch to the single connection. did. However, the macro base station 100 does not necessarily need to switch to a single connection when an error is detected. Even if the connection is not switched to a one-way connection, the mobile station 300 or macro base station 100 on the receiving side sends reception status information to the macro base station 100 or mobile station 300 on the sending side, so that the sending side can It becomes possible to check the reception status of the .

Furthermore, in each of the above embodiments, when an error is detected in the transmission route via the small base station 200, the dual connection is canceled and switched to the single connection, but the connection switching occurs. This is not limited to when an error is detected. That is, for example, even when the mobile station 300 moves and the macro base station or small base station to which it is connected is changed, it is conceivable to temporarily cancel the two-way connection and switch to the one-way connection. Even in such a case, by having the receiving side transmit reception status information to the transmitting side, it is possible to prevent duplication and loss of user data when connection switching occurs.

The physical configurations of macro base station 100, small base station 200, and mobile station 300 in each of the above embodiments do not necessarily have to be the same as the block diagrams shown in FIGS. 2 and 3. Therefore, specific examples of the hardware configurations of the macro base station 100, the small base station 200, and the mobile station 300 will be explained.

FIG. 9 is a block diagram showing the hardware configuration of the base station. The base station shown 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 realizes 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 other base stations through a wired connection. For example, macro base station 100 and small base station 200 are connected by wire via network interface 506.

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, for example. That is, for example, the memory 504 stores various programs such as programs for realizing the functions of the communication unit 11 or the communication unit 21. Then, the CPU 505 reads the program stored in the memory 504 and implements the functions of the communication unit 11 or 21 by cooperating with the RF circuit 503 and the like.

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

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

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

11, 21, 31 communication section 12, 22, 32 reception section 13, 23, 33 transmission section 14, 24, 34 control section 101, 307 PDCP layer 102, 103, 201, 202, 303, 304, 305, 306 RLC layer 104, 203, 301, 302 MAC layer

Claims (10)

a communication unit capable of wirelessly connecting with a first communication device and a second communication device to perform wireless communication;
a control unit capable of controlling the connection change of the wireless communication when the communication unit receives first information instructing the change of the wireless connection from the first communication device;
The control unit performs control to execute processing according to reception status information received by the communication unit in response to the connection change,
The reception status information is information that identifies received data or unreceived data among the data transmitted to the first communication device or the second communication device,
A wireless communication device characterized by: The communication department includes:
The wireless communication device according to claim 1, wherein the reception status information can be received after the connection change. The communication department includes:
The wireless communication device according to claim 1, wherein the wireless communication device is capable of receiving an RRC (Radio Resource Control) signal including the first information. The communication department includes:
It is possible to transmit data to which an identifier indicating the order of the data is assigned,
The above information includes an identifier assigned to the first unreceived data, and information indicating whether a predetermined number of data assigned an identifier indicating that the data is received after the identifier has been received. The wireless communication device according to claim 1, wherein the wireless communication device is capable of receiving reception status information. The communication unit can transmit first data on a first path between the first communication device and the wireless communication device, and can transmit first data on a first path between the second communication device and the wireless communication device. 2. The wireless communication device according to claim 1, wherein the second data can be transmitted over a path. The first information includes changing the wireless connection from a two-way connection connecting the first communication device and the second communication device to a one-way connection connecting the first communication device. This is information that instructs
The wireless communication device according to claim 1, wherein the communication unit receives the reception status information from the first communication device. a communication unit that is connected to a first communication device and a second communication device and can perform wireless communication with the first communication device;
a control unit capable of controlling wireless connection with the first communication device;
The communication unit may transmit first information instructing a connection change to the first communication device, and may transmit reception status information in response to the connection change of the first communication device. I can do it,
The wireless communication device, wherein the reception status information is information that specifies received data or unreceived data among the data transmitted from the first communication device or the second communication device. The communication department includes:
first data transmitted from the first communication device can be received via a first path between the first communication device and the wireless communication device; 8. The wireless communication device according to claim 7, wherein the second data can be received via a second path passing through the second communication device. The first information changes the wireless connection of the first communication device from a two-way connection connecting the wireless communication device and the second communication device to a one-way connection connecting the wireless communication device. 8. The wireless communication device according to claim 7, wherein the information is an instruction to change. a first communication device;
a second communication device;
comprising the first communication device and a wireless communication device capable of wirelessly connecting with the second communication device and performing wireless communication;
The first communication device includes:
first information instructing to change the wireless connection can be transmitted to the wireless communication device;
The wireless communication device includes:
When the first information is received, the wireless communication connection change can be controlled;
The wireless communication device includes:
Performing control to execute processing according to reception status information received in response to the connection change,
The reception status information is information that identifies received data or unreceived data among the data transmitted to the first communication device or the second communication device.
A wireless communication system characterized by:

Images