JP7050721B2 - Wireless communication device and control method - Google Patents

Description

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

Conventionally, various measures have been taken to increase the transmission capacity (hereinafter referred to as "system capacity") in a wireless communication system. For example, in 3GPP LTE (3rd Generation Partnership Project Radio Access Network Long Term Evolution), discussions are being held on technologies for increasing system capacity by utilizing small cells (small cells) in addition to macro cells. Here, the cell refers to a range covered by a wireless base station for a wireless terminal to transmit and receive a wireless signal. The macro cell is a cell of a base station having a relatively high transmission power and a relatively large radio wave reach. Further, the small cell is a cell of a base station having a relatively low transmission power and a relatively small radio wave reach.

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. Then, a technique for connecting a mobile station to a macro cell and a small cell at the same time is being studied. In addition, a technique for connecting two small cells having different mobile stations at the same time is being studied. In this way, the communication carried out by the mobile station connected to two different cells at the same time is sometimes called dual connectivity.

When a mobile station connects to a macro cell and a small cell at the same time, for example, a signal on the control plane containing layer 3 control information such as transmission path setting and handover control is a macro cell base station (hereinafter referred to as "macro base station"). It is sent and received to and from). Further, for example, a data plane signal including user data is transmitted to and received from both a macro base station and a small cell base station (hereinafter referred to as "small base station"). Here, the control plane may be referred to as a control plane (Control Plane: C plane) or SRB (Signaling Radio Bearer). The data plane is also called a user plane (User Plane: U plane) or a DRB (Data Radio Bearer).

On the other hand, when the mobile station is connected to two different small cells at the same time, for example, the signal of the control plane is transmitted to and received from one small base station, and the signal of the data plane is connected to the other small base station. It is sent and received by. Data plane signals may be sent to and received from both small base stations.

In such a dual connection, the base station to which the control plane is connected may be referred to as a primary base station. Further, a base station that communicates in cooperation with the primary base station and is connected to the data plane may be called a secondary base station. Further, these base stations may also be referred to as an anchor radio base station and an assisting radio base station, or a master radio base station and a slave radio base station. In the latest trend of LTE-A, they are 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.

Regarding the division of functions between the primary base station and the secondary base station in the dual connection, various configurations have been proposed depending on which layer the data plane signal is branched. For example, there is a configuration in which a data plane signal is branched before the PDCP (Packet Data Convergence Protocol) layer. Further, 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. Further, 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 limited to these, it is also possible to branch the signal of the data plane in each layer. Further, for example, it is possible to allocate some functions of the PDCP layer to the primary base station and the remaining functions of the PDCP layer to the secondary base station. This also applies to the functions of the RLC layer and the MAC layer. In the latest trend of LTE-A, the configuration for branching the signal of the data plane between the PDCP layer and the RLC layer (Architecture 3C), and the PDCP layer, RLC layer, and MAC layer for each of the master base station and the small base station, respectively. It is supposed to adopt the configuration (Architecture 1C) that it has.

The primary base station and the secondary base station that share functions in this way are connected to each other by a wired or wireless link. Then, the signal of the data plane 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 during the implementation of the dual connection, it is conceivable that the dual connection will be canceled and the connection will be switched to the one. Be done. That is, if there is a change in the communication state between the mobile station and the small base station when the mobile station is connected at the same time as the macro base station and the small base station, the dual connection is canceled and the mobile station becomes the macro base station. It is conceivable that it will communicate with only. Examples of changes in the communication state include the occurrence of problems and errors related to data communication and deterioration of wireless quality.

However, since the data plane signal is transmitted from both the macro base station and the small base station during the implementation of the dual connection, duplication of user data in the mobile station when switching to the dual connection occurs. Or defects may occur. That is, when a switch from a dual connection to a primary connection occurs, the macro base station duplicately transmits the user data transmitted from the small base station, or the user data not transmitted from the small base station. May be deleted without sending.

Further, 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 implementation of the dual connection, the mobile station transmits the user data to both the macro base station and the small base station, but after switching to the primary connection, the mobile station transmits the user data only to the macro base station. do. At this time, since the mobile station does not know whether or not the user data transmitted to the small base station has been transferred to the macro base station, the user data is transferred to the macro base station without excess or deficiency after switching to the unified connection. It is difficult to send to. Similarly, even when the mobile station has a multiple access of 3 or more elements, inconsistency in user data transmitted and received after switching to the 1-element connection may occur.

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

The wireless communication device disclosed in the present application is, in one embodiment, a wireless communication device capable of dually connecting and communicating with a first communication device and a second communication device, and the first communication device during the dual connection. The first signal transmitted from the communication device of No. 1 is received via the first path, and the second signal transmitted from the first communication device is received via the second path via the second communication device. A control unit capable of communication control that changes the connection between the reception unit and the first communication device to a unified connection, and a control unit that has received or has not been received by the reception unit when the communication control is performed. It has a transmission unit that transmits the first reception state information for specifying the signal of the above to the first communication device via the first path, and the reception unit has the first reception unit during the binary connection. Information about a packet lost between the second communication device and the first communication device can be acquired from the second communication device, and is transmitted from the first communication device according to the information. The RRC reconfiguration message, which is an RRC reconfiguration message instructing to switch from the binary connection to the primary connection , and communication to the first communication device via the second communication device at the time of the dual connection. This is the second reception status information transmitted by the first communication device when the problem of the above occurs, and the received or unreceived signal is specified by the first communication device as the unreceived signal. The second reception state information including the signal of data loss between the first communication device and the second communication device is received, and the control unit responds to the RRC reconfiguration message received by the reception unit. While performing the communication control, the packet transmitted to the first communication device is controlled according to the second reception state information .

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

FIG. 1 is a diagram showing a configuration example of a wireless communication system according to the first embodiment. FIG. 2 is a block diagram showing a configuration of a wireless communication system according to the first embodiment. FIG. 3 is a block diagram showing a layer configuration of the wireless communication system according to the second embodiment. FIG. 4 is a diagram showing a specific example of the PDCP SR format. 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 chart 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 a hardware configuration of a base station. FIG. 10 is a block diagram showing a hardware configuration of a mobile station.

Hereinafter, embodiments of the wireless communication device and the control method disclosed in the present application will be described in detail with reference to the drawings. The present invention is not limited to this embodiment. Needless to say, the following embodiments may be combined as appropriate. Hereinafter, embodiments relating to downlink communication and uplink communication are described, and since the dual connection is often used in bidirectional communication in which both downlink communication and uplink communication are performed, each embodiment is described. It is clear that they may be carried out in combination.

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

The mobile station 300 connects to the macro base station 100 as a primary base station. Therefore, the mobile station 300 is connected to the macro base station 100 by the control plane represented by the solid arrow in FIG. 1 and the data plane represented by the broken line arrow. Further, the mobile station 300 connects 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 a data plane.

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

The macro base station 100 has 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 device 4, and wireless communication with the mobile station 300.

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

The transmission unit 13 wirelessly transmits control data addressed to the mobile station 300 to the mobile station 300. Further, the transmission 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 according to the instruction of the control unit 14.

The control unit 14 collectively 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 according to the communication state. When switching from the binary connection to the primary connection, the mobile station 300 refers to the reception status information received from the mobile station 300 to ensure data consistency with the mobile station 300.

As an example of switching to a unified 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). Subsequently, the small base station 200 remains set, but the data may be transmitted only to the macro base station 300 and not to the small base station 200 (RRC reconfiguration). In addition, the setting of the small base station 200 is erased (RRC reconfiguration including the SeNB removal).

In the above, the timing at which the macro base station 100 receives the reception status information from the mobile station 300 includes, for example, the following examples.
(First example)
When the macro base station 100 switches from the binary connection to the primary connection, the mobile station 300 is notified of the setting change by RRC (Radio Resource Control) signaling. Similarly, the small base station 200 is also notified of the setting change. This RRC signaling can include instructions for reporting reception status information. When the mobile station 300 receives the RRC signaling including the instruction to report the reception status information, the mobile station 300 notifies the 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 transmits the reception state information to the macro base station 100 using the detection as a trigger. The report of the reception status information may be set in advance by RRC signaling. Here, the change in the communication state corresponds to, for example, the following cases. First, 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, or This is the case when the desired data is not received in the mobile station 300 due to a transmission failure in the wireless link (such as transmission failure) (detection is possible when the timer in the PDCP layer expires). Secondly, in the RLC layer of the small base station 200, the retransmission of the desired data transmission fails and the radio link quality deterioration (Radio Link Failure) is detected (at the counter of exceeding the maximum number of retransmissions in the RLC layer). Can be detected). In this case, not only the downlink transmission but also the acknowledgment corresponding to the downlink transmission (RLC STATUS REPORT for transmitting ACK and NACK, or TCP acknowledgment if the downlink communication is TCP (Transmission Control Protocol) communication). There is a high possibility that transmission will also fail. Therefore, when the uplink communication fails, Radio link Failure is detected in the RLC layer of the mobile station 300. Summarizing the above, it is an example of a change in the communication state that a communication problem occurs in the transmission path via the small base station 200 at the time of dual connection.

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 in the mobile station 300 (the state change of the wired link and the wireless link can be detected), and the second trigger is the downlink communication in the small base station 200. It is the detection of the state change (the state change of the wireless link can be detected), and the third trigger is the detection of the change of the uplink communication state in the mobile station 300 (the state change of the wireless link can be detected).

(Third example)
It is a combination of the above examples. Specifically, in the second example, when at least one of the three changes in the communication state described in the second example is notified to the macro base station 100 and the macro base station receives the notification, the RRC The mobile station 300 is notified of the setting change by signaling. At that time, the macro base station 100 can include an instruction to report the reception status information in the RRC signaling. In this way, the macro base station 100 collectively controls the transmission timing of the reception status information, so that the trigger by the above-mentioned "detection of change in downlink communication status" and the trigger by "detection of change in uplink communication status" can be obtained. Therefore, it is possible to prevent the mobile station 300 from reporting the reception status information at the same time.

In order to ensure data integrity, the control unit 14 refers to the reception status information so that the mobile station 300 does not transmit unreceived user data and the mobile station 300 does not transmit received user data. In addition, it controls transmission after switching to a unified connection.

Here, as a method for the mobile station 300 to transmit unreceived user data, the control unit 14 may transmit the data held in the macro base station 100 as it is, or the 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 whose delivery has not been confirmed) and data that the macro base station 100 continues to receive (X2). Data being transmitted on the interface, may be referred to as fresh data) may be transmitted.

As described above, according to the present embodiment, when switching from the dual connection to the single connection, the macro base station identifies the unreceived packet and the received packet received from the mobile station. To receive. At that time, the mobile station transmits the unreceived packet by referring to the reception status information, and the mobile station does not transmit the received packet. Therefore, even when the connection is switched, the macro base station can transmit the packet according to the reception state to the mobile station, and the data consistency can be ensured.

In the first embodiment, the downlink communication from the macro base station 100 to the mobile station 300 has been described, but 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 problem occurs in the transmission path of the uplink via the small base station 200 at the time of binary connection, the macro base station 100 may transmit the reception status information to the mobile station 300. As a result, even when switching to the unified connection occurs, the packet can be transmitted from the mobile station 300 to the macro base station 100 according to the reception state, and the data consistency can be ensured.

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

[Wireless communication system configuration]
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 will be omitted.

The macro base station 100 has 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 has a reception unit 12 and a transmission unit 13. The receiving unit 12 receives control data and user data from the upper layer communication device 4. Then, the receiving unit 12 outputs the received control data and user data to the transmitting unit 13.

Further, when the small base station 200 detects an error (communication failure), the receiving unit 12 receives an error detection notification from the small base station 200. Then, when the error detection notification is received, the receiving unit 12 wirelessly receives the reception status information for specifying the received user data and the unreceived user data from the mobile station 300. Then, the receiving unit 12 outputs the received error detection notification and the reception status information to the control unit 14. The timing at which the receiving unit 12 receives the reception status information and the content of the reception status 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. Further, the transmission 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 according to the instruction of the control unit 14.

The control unit 14 collectively 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 determines to temporarily cancel the dual connection and switch to the single connection. Then, when switching to the unified connection, the control unit 14 refers to the reception status information output from the receiving unit 12 and determines the user data to be transmitted to the mobile station 300 after switching to the unified connection. Specifically, the control unit 14 refers to the reception status information and makes a unified connection so that the mobile station 300 does not transmit unreceived user data and the mobile station 300 does not transmit received user data. Controls transmission after switching to.

The small base station 200 has 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 wireless communication with the mobile station 300.

Specifically, the communication unit 21 has 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 receiving unit 22 outputs the received user data to the transmitting unit 23.

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

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

The mobile station 300 has a communication unit 31 and a control unit 34, and the communication unit 31 communicates with the macro base station 100 and the small base station 200. That is, the communication unit 31 is dually connected to the macro base station 100 and the small base station 200, and performs wireless communication at the same time as both base stations.

Specifically, the communication unit 31 has 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 a part of the user data transmitted from the macro base station 100 from the macro base station 100, and the small base station 200 receives the remaining part of the user data transmitted from the macro base station 100. Receive via.

Further, when an error is detected in communication with the small base station 200, the receiving unit 32 receives user data received from the macro base station 100 and the small base station 200 by the mobile station 300 and user data not received. Generates reception status information that identifies. Then, the receiving unit 32 outputs the generated reception state information to the control unit 34.

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

The control unit 34 collectively controls the operation of the communication unit 31 including the reception unit 32 and the transmission unit 33. Further, 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 the desired user data is not received even after a predetermined time has elapsed after receiving the user data from the small base station 200, or the number of times the user data is retransmitted becomes a predetermined maximum number of retransmissions. Such as an error to reach. Then, when the control unit 34 detects an error in the reception unit 32, the control unit 34 acquires the reception status information generated by the reception unit 32 and outputs it to the transmission unit 33.

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

Further, 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, the RLC layer defines a retransmission (Automatic Repeat Request) control, and retransmission is performed for user data in which an error has occurred in wireless transmission. If the retransmission is successful within a predetermined number of times, it is determined that the reception is successful, but if the number of retransmissions exceeds the predetermined number of times, an error is determined. In this case, conventionally, it is determined that RLF (Radio Link Failure) has occurred, and RRC reconnection (RRC Connection Re-establishment) is carried out. Further, in the dual connection, especially when RLF occurs on the small base station 200 side, RRC reconnection is not performed, but a communication failure (RLC failure) in the RLC layer is notified to the macro base station 100. As described in the first embodiment, the communication defect 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, the reception status information is transmitted from the mobile station 300 to the macro base station 100. Therefore, for example, the reception status information can be transmitted to the macro base station 100 earlier than the technology in which the reception status information is transmitted when the retention amount in the buffer of the mobile station 300 exceeds a predetermined threshold value. It will be possible. When a large amount of loss of user data is detected in the PDCP layer, the timer expires for each lost packet and the reception status information is transmitted, which increases the signaling overhead. Therefore, for example, a prohibit timer may be set separately so that the reception status information is not frequently transmitted. Specifically, it is determined by using the prohibition timer whether or not a certain period has elapsed since the previous transmission of the reception status information, and the reception status information is not transmitted again while the certain period has not elapsed. Is also good.

[Processing of wireless communication system]
Next, the 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. These macro base station 100, small base station 200, and mobile station 300 communicate using a link layer protocol corresponding to a plurality of 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, or the like is used. FIG. 3 is a block diagram showing a layer configuration of the wireless communication system according to the second embodiment.

Here, first, the processing of the macro base station 100 regarding the transmission / 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. The RLC layer 102 is a downlink RLC layer, and the RLC layer 103 is an uplink RLC layer. 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, 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 an odd number to the packet output to the RLC layer 102, and assigns an even number to the packet transmitted to the small base station 200, for example. This sequence number is also used, for example, in the case of handover. Further, the communication unit 11 performs header compression, security check, and encryption on the user data in the PDCP layer 101.

Then, the communication unit 11 outputs the packet to which the odd number is assigned from the PDCP layer 101 to the RLC layer 102. Further, the communication unit 11 transmits a packet to which an even number is assigned to the small base station 200 via a wired connection. As a result, 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.

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

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

After that, 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 in the MAC layer 104 using the RLC packet. That is, for example, the RLC packet is divided or integrated as needed, and a header of the MAC layer is added to generate a packet of the MAC layer (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 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. 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 order of the data using the header of the RLC layer in the RLC layer 103, and outputs the user data from the RLC layer 103 to the PDCP layer 101.

Next, the processing of the macro base station 100 when the 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 the error detection notification transmitted from the small base station 200 in the PDCP layer 101. Further, the communication unit 11 acquires reception status information transmitted from the mobile station 300 and via the MAC layer 104 and the RLC layer 103 in the PDCP layer 101. The reception status information includes information that allows the mobile station 300 to identify received packets and unreceived packets 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 binary connection with the mobile station 300 and switch to the single connection. Then, the control unit 14 transmits a dual connection cancellation notification indicating that the dual connection is canceled to the small base station 200 and the mobile station 300 via the communication unit 11. Further, the control unit 14 refers to the reception status information received by the communication unit 11 and notifies the PDCP layer 101 of the packet 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 unreceived packet by the mobile station 300 indicated by the reception status information, and also sets the sequence number of the received packet as the sequence number of the packet that does not need to be transmitted. Notify PDCP layer 101.

Then, the communication unit 11 outputs the unreceived packets from the PDCP layer 101 to the RLC layer 102 in ascending order of the sequence number, while excluding the packets that have been received by the mobile station 300 and no longer need to be transmitted. Then, the communication unit 11 generates an RLC packet at the RLC layer 102, generates a MAC packet at the MAC layer 104, and transmits the MAC packet to the mobile station 300. As a result, the mobile station 300 can receive the packet without duplication and loss even after switching from the binary connection to the primary connection.

Next, the processing of the small base station 200 regarding the transmission / 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. The RLC layer 201 is a downlink RLC layer, and the RLC layer 202 is an uplink RLC layer. The small base station 200 may have a layer (not shown) such as a PHY layer.

The communication unit 21 receives the packet transmitted from the PDCP layer 101 of the macro base station 100 via the wired connection in the RLC layer 201. As described above, even numbers are assigned to this packet. Then, the communication unit 21 generates an RLC packet by dividing or integrating the packet in the RLC layer 201 as necessary and adding a header of the RLC layer.

After that, 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 in the MAC layer 203 using the RLC packet. That is, for example, the RLC packet is divided or integrated as needed, and the header of the MAC layer is added to generate the MAC packet. 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. Then, the communication unit 21 reconstructs (reassembles) the received user data in the MAC layer 203, and divides or integrates the received user data in the RLC layer 202. Further, the communication unit 21 corrects the order of the data using the header of the RLC layer in the RLC layer 202, and transmits the user data from the RLC layer 202 to the macro base station 100.

Next, the 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 for measuring 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, the reception confirmation (ACK) is not received by the time the timer expires. Therefore, if the reception confirmation (ACK) is not received by the time the timer expires, the control unit 24 detects that an error has occurred.

Further, the control unit 24 may monitor the number of data retransmissions 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 after receiving the packet from the macro base station 100 via the 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.

After that, when the macro base station 100 determines to disconnect the binary connection, the communication unit 21 receives the binary connection disconnection notification from the macro base station 100. After receiving the dual connection disconnection notification, the wireless communication between the small base station 200 and the mobile station 300 is no longer executed, so that the communication unit 21 stops transmitting and receiving data.

Next, the processing of the mobile station 300 regarding the transmission / 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 PDCP layer 307. Since the mobile station 300 has a function of receiving user data from two base stations at the same time, the MAC layer and the RLC layer are provided corresponding to the respective base stations. That is, the MAC layer 301, the RLC layer 303, the RLC layer 304, and the PDCP layer 307 are used for transmitting and receiving user data to and 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 or integrates the received user data in the RLC layer 303. Further, the communication unit 31 corrects the order of the data using the header of the RLC layer in the RLC layer 303, and outputs the user data from the RLC layer 303 to the PDCP layer 307. Then, the communication unit 31 performs decoding, security check, and decompression of the header for the user data in the PDCP layer 307.

Similarly, the communication unit 31 receives user data (MAC packet) from the small base station 200 at 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 the data using the header of the RLC layer in the RLC layer 305, and outputs the user data from the RLC layer 305 to the PDCP layer 307. Then, the communication unit 31 performs decoding, security check, and decompression of the header for 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 a part of the packet from the PDCP layer 307 to the RLC layer 304, and outputs the remaining packet 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 adds the header of the RLC layer to generate the packet of the RLC layer (hereinafter referred to as “RLC packet”). do.

After that, 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 the RLC packet. That is, for example, the RLC packet is divided or integrated as needed, and the header of the MAC layer is added to generate the 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, respectively, via the PHY layer (not shown) and the like according to the scheduling.

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

The control unit 34 monitors the reception of user data in the communication unit 31, for example, in the PDCP layer 307, even if a predetermined time elapses after receiving the packet to which the sequence number is assigned, the sequence before this packet. Detects that an error has occurred when there are unreceived packets with numbers. Further, the control unit 34 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. Then, when an error is detected in the data reception from the small base station 200, the control unit 34 instructs the communication unit 31 to generate the 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 the sequence number assigned by 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 the PDCP layer 307, indicating whether or not a predetermined number of packets to which a sequence number after this sequence number is assigned and the smallest sequence number among the sequence numbers of the unreceived packets are received. Generate state information. Specifically, for example, packets of sequence numbers # 1, # 3, # 5, and # 7 are transmitted from the macro base station 100, and packets of sequence numbers # 2, # 4, # 6, and # 8 are transmitted from the small base station 200. Consider the case of being sent. Here, for example, it is assumed that the packet of 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, the packets of sequence numbers # 1, # 3, # 5, and # 7 transmitted from the macro base station 100 are received by the mobile station 300, and the packets of sequence numbers # 2, # 4, # 6, and # 8 are. Not received by mobile station 300.

Therefore, in the PDCP layer 307, reception status information indicating whether or not the packet having the smallest sequence number # 2 among the sequence numbers of the unreceived packets and the packets of the sequence numbers # 3 to # 8 are received is generated. Therefore, here, reception status information indicating that the packets of sequence numbers # 3, # 5, and # 7 have been received and the packets of sequence numbers # 4, # 6, and # 8 have not been received is generated. .. This reception status information needs to be transmitted from the macro base station 100 again after the sequence numbers # 2, # 4, # 6, and # 8 have not been received by the mobile station 300 and are switched to the unified connection. It is shown that.

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

When the reception status information is generated in the PDCP layer 307, the communication unit 31 transmits the reception status information to the macro base station 100. Therefore, 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 disconnecting the dual connection and switching to the primary 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 the communication between the small base station 200 and the mobile station 300, the reception status information is transmitted from the mobile station 300 to the macro base station 100. As the 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 PDCP SR format. The PDCP SR400 shown in the upper part of FIG. 4 is a PDCP SR for a 12-bit sequence number. The PDCP SR410 shown in the middle of FIG. 4 is a PDCP SR for a 15-bit sequence number. Further, the PDCP SR420 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 sent and received. Specifically, for example, in VoIP (Voice of Internet Protocol), a 7-bit sequence number may be used. Therefore, each PDCP SR400, 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 the unreceived packets is stored.

That is, for example, in the PDCP SR400, the FMS field 401 stores 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 mobile station 300. In other words, the FMS field 401 stores the sequence number of the packet that should be received earliest among the packets of user data that have not arrived from the small base station 200. In the following, 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”.

Further, in the fields of Bitmap ₁ to Bitmap _N of PDCP SR400, 410 and 420, the presence / absence of reception for the packet after the FMS packet is stored, respectively. Specifically, for example, for the 1st to Nth (N is an integer of 1 or more) th packet after the FMS packet, if it is 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 above example, the packets of sequence numbers # 1, # 3, # 5, and # 7 are transmitted from the macro base station 100, and the packets of sequence numbers # 2, # 4, # 6, and # 8 are small. Consider the case where the packet is transmitted from the base station 200. Here, if the packet of sequence number # 2 is not received by the mobile station 300 and an error is detected, the subsequent packets of sequence numbers # 4, # 6, and # 8 are also not received from the small base station 200. Therefore, in the mobile station 300, the packets of sequence numbers # 1, # 3, # 5, and # 7 have been received, and the packets of sequence numbers # 2, # 4, # 6, and # 8 have not been received.

In this case, since the FMS packet is the packet of sequence number # 2, the sequence number # 2 is stored in the FMS fields 401, 411 and 412 of PDCP SR400, 410 and 420. As for the packets after the FMS packet, the packets of sequence numbers # 3, # 5, and # 7 have been received, and the packets of 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.

Further, in the PDU Type field of PDCP SR400, 410 and 420 shown in FIG. 4, information regarding the type of PDU (Protocol Data Unit) used as PDCP SR400, 410 and 420 is stored. 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 the bit "000" is stored in the PDU Type field, it indicates that this PDU is a PDCP status report such as PDCP SR400, 410 and 420.

On the other hand, when the bit "001" is stored in the PDU Type field, it means that this PDU is an Interspersed ROHC feedback packet. The scattered ROHC feedback packet contains feedback information for the PDU of the PDCP layer transmitted from the receiving side.

Further, the bits "010" to "111" that can be stored in the PDU Type field are left as reserved bits. Therefore, in the present 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 the binary connection to the single connection according to the second embodiment will be described with reference to the sequence diagram shown in FIG.

When the mobile station 300 is dually connected to the macro base station 100 and the small base station 200, a 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 given a sequence number indicating the order of data in the communication unit 11 of the macro base station 100. For example, a packet to which an odd number is given is directly from the macro base station 100 to the mobile station 300. Packets 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), the control unit 24 of the small base station 200 detects an error (step S103). This error is detected, for example, when the reception confirmation (ACK) for the packet wirelessly transmitted from the small base station 200 is not returned from the mobile station 300. Further, when the number of retransmissions with the mobile station 300 reaches a predetermined maximum number of retransmissions, or when a packet is received from the macro base station 100 and the next packet is not received even after a predetermined time has elapsed. , The error is detected by the control unit 24 of the small base station 200.

On the other hand, when the packet from the small base station 200 is not received, the 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 before this packet even after a predetermined time has elapsed after receiving a packet with a sequence number from the small base station 200. Will be done. Further, even when the number of retransmissions with the small base station 200 reaches a predetermined maximum number of retransmissions, the control unit 34 of the mobile station 300 detects an error.

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 status information includes the sequence number of the packet whose order is closest to the beginning among the packets not received by the mobile station 300, and whether or not a predetermined number of packets after this packet have been received. Then, the generated reception status 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, upon receiving the error detection notification transmitted from the small base station 200, the control unit 14 determines to temporarily cancel the dual connection and switch to the single 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 directly transmits all the user data to the mobile station 300. Then, the communication unit 11 transmits a binary connection cancellation notification indicating that the dual connection is canceled to the small base station 200 (step S107). After receiving the dual connection disconnection notification, the small base station 200 stops transmitting user data to the mobile station 300.

The dual connection disconnection notification is also transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S108). After receiving the dual connection disconnection notification, the mobile station 300 receives all the user data from the macro base station 100.

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

As described above, in the present embodiment, when an error is detected in the user data transmission path via the small base station 200, the reception status information is transmitted from the mobile station 300 to the macro base station 100. Then, the macro base station 100 cancels the dual connection, and the mobile station 300 transmits the unreceived user data to the mobile station 300 without excess or deficiency with reference to the reception status information. Therefore, even when switching from the dual connection to the single connection occurs, it is possible to prevent duplication and loss of user data received by the mobile station 300.

[Specific example of mobile station processing when an 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 at the time of binary connection will be described with reference to the flow chart shown in FIG. 7.

The control unit 34 of the mobile station 300 monitors the 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 or not there is an unreceived packet with a sequence number before this packet. do. Then, if there is an unreceived packet, a predetermined timer is started to determine whether or not the unreceived packet is received before the predetermined time elapses. As a result of these determinations, if there are no unreceived packets or if the packets are correctly received before the lapse of a predetermined time, it is assumed that no error is detected (step S201No), and the control unit 34 continues to monitor the communication. ..

Then, when an error is detected (step S201Yes), the control unit 34 instructs the communication unit 31 to generate PDCP SR, which is reception status 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 the reception / absence of a predetermined number of packets after this packet. (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 the binary connection disconnection notification from the macro base station 100 that has decided to temporarily disconnect the dual connection (step S204). After receiving the dual connection disconnection notification, the communication unit 31 starts a unified connection with the macro base station 100 (step S205), and receives all the 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 in just proportion, the communication unit 31 does not overlap or lack user data from the macro base station 100. To 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 dual connection, the mobile station identifies unreceived packets and received packets. Sends reception status information to the macro base station. Then, the macro base station cancels the dual connection and switches to the primary connection, and at the same time, the mobile station transmits an unreceived packet by referring to the reception status information. Therefore, even when the connection is switched, the packet can be transmitted from the macro base station to the mobile station in just proportion, 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, but the error detection notification is transmitted from the mobile station 300 to the macro base station 100. You can 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 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 dual connection may be temporarily canceled and switched to the single connection. Therefore, in the third embodiment, a connection switching method when an error is detected in the uplink will be described.

Since the configuration of the wireless communication system according to the present embodiment is the same as that of the second embodiment, the description thereof will be omitted. The present embodiment is different from the second embodiment in that an error is detected in which the packet transmitted from the mobile station 300 via the small base station 200 is not received by the 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 is dually connected to the macro base station 100 and the small base station 200, a part of the user data is directly connected to the macro base station 100 from the communication unit 31 of the mobile station 300. 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.

A sequence number is assigned to these user data packets by the communication unit 31 of the mobile station 300. For example, a packet to which an odd number is assigned is wirelessly transmitted directly to the macro base station 100 and an even number is assigned. The packet is transmitted to the macro base station 100 via the small base station 200.

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

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 not received by the macro base station 100, and whether or not a predetermined number of packets after this packet have been received. Then, the generated reception status information is transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S304).

Further, in the macro base station 100, since an error is detected by the control unit 14, it is determined to temporarily cancel the dual connection and switch to the single connection. That is, it is determined that the reception of user data via the small base station 200 is temporarily stopped, and all the 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 disconnection notification indicating that the dual connection is disconnected to the small base station 200 (step S305). After receiving the dual connection disconnection notification, the small base station 200 stops receiving the user data from the mobile station 300.

The dual connection disconnection notification is also transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S306). After receiving the dual connection disconnection notification, the mobile station 300 wirelessly transmits all the user data directly to the macro base station 100.

After switching to the one-way connection, when the mobile station 300 transmits the 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 packet of the notified sequence number is sequentially transmitted from the communication unit 31 to the macro base station 100.

As described above, in the present embodiment, when an error is detected in the user data transmission path via the small base station 200, the reception status information is transmitted from the macro base station 100 to the mobile station 300. Then, after the macro base station 100 disconnects the dual connection, the mobile station 300 refers to the reception status information and transmits the unreceived user data to the macro base station 100 without excess or deficiency. Therefore, even when switching from the binary connection to the primary connection occurs, it is possible to prevent duplication and loss of user data received by the macro base station 100.

As described above, according to the present embodiment, when an error is detected in the transmission path via the small base station during dual connection, the macro base station identifies unreceived packets and received packets. Send the reception status information to the mobile station. Then, when the macro base station cancels the binary connection and switches to the one-way connection, the mobile station refers to the reception status information and transmits the unreceived packet by the macro base station. Therefore, even when the connection is switched, the packet can be transmitted from the mobile station to the macro base station in just proportion, and duplication and loss of user data can be prevented.

In the third embodiment, the error is detected by the macro base station 100, but the error may be detected by, for example, the small base station 200 or the mobile station 300. Then, the small base station 200 or the mobile station 300 that has detected the error may notify the macro base station 100 that the 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. Further, the mobile station 300 detects an error when the 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, a dual connection in which the mobile station 300 connects to two base stations of the macro base station 100 and the small base station 200 at the same time has been described as an example, but there are three or more mobile stations 300. Similar processing is possible for multiple access that connects to the base station at the same time. That is, when an error is detected in the transmission path via any of the base stations, the mobile station on the receiving side transmits the reception status information to the primary base station to which the control plane is connected. Then, the primary base station can cancel the multiple access and switch to the primary connection, refer to the reception status information, and transmit the 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 cancel the binary connection and switch to the single connection. bottom. However, the macro base station 100 does not necessarily have to switch to the unified connection when an error is detected. Even if the connection is not switched to the primary connection, the receiving side mobile station 300 or the macro base station 100 transmits the reception status information to the transmitting side macro base station 100 or the mobile station 300, so that the transmitting side receives the packet on the receiving side. It is possible to check the reception status of.

Further, in each of the above embodiments, when an error is detected in the transmission path via the small base station 200, the binary connection is canceled and the connection is switched to the single connection, but the connection is switched. 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 the small base station to be connected is changed, it is conceivable to temporarily cancel the binary connection and switch to the single connection. Even in such a case, by transmitting the reception status information to the transmission side, it is possible to prevent duplication and loss of user data when connection switching occurs.

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 do not necessarily have to be the same as the block diagrams shown in FIGS. 2 and 3. Therefore, a specific example of the hardware configuration 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 showing a hardware configuration of a base station. The base station shown in FIG. 9 corresponds to, for example, a macro base station 100 and a small base station 200, and has 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, for example, the functions of the control unit 14 of the macro base station 100 and the control unit 24 of the small base station 200.

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

The CPU 505, the memory 504, and the RF circuit 503 realize, for example, 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, various programs such as a program for realizing the function of the communication unit 11 or the communication unit 21 are stored in the memory 504. Then, the CPU 505 reads out the program stored in the memory 504 and cooperates with the RF circuit 503 or the like to realize the function of the communication unit 11 or the communication unit 21.

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 has an antenna 511, a control unit 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, the memory 514, and the RF circuit 513 realize, for example, the function of the communication unit 31 of the mobile station 300. That is, for example, various programs such as a program for realizing the function of the communication unit 31 are stored in the memory 514. Then, the CPU 515 reads the program stored in the memory 514 and cooperates with the RF circuit 513 or the like to realize the function of the communication unit 31.

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 (3)

In a wireless communication device capable of wireless communication with a first communication device that is dually connected to its own device and a second communication device.
The first signal destined for the first communication device that is dually connected is transmitted via the first path, and the second signal destined for the first communication device is transmitted via the second communication device. And the transmitter that transmits via the second route
Information on packets lost between the second communication device and the own device during the binary connection is acquired from the second communication device, and the connection with the first communication device is made one from the binary connection. A control unit that can control the communication control that changes to a connection,
When the communication control is performed, the first communication device has a receiving unit for receiving reception state information for specifying a received or unreceived signal via the first path.
The transmitter is
A wireless communication device characterized in that an RRC reconfiguration message instructing switching from the binary connection to the primary connection is transmitted to the first communication device in response to the acquisition of the information by the control unit. .. The wireless communication device according to claim 1 , wherein the control unit determines data to be transmitted from the transmission unit via the first path according to the reception state information received by the reception unit. .. A wireless communication system having a first base station device, a second base station device, and a mobile station device capable of dually connecting and communicating with the first base station device and the second base station device. There,
The first base station device is
The first signal addressed to the mobile station device that is dually connected is transmitted via the first path, and the second signal addressed to the mobile station device is transmitted via the second base station device. The first transmitter that transmits via route 2 and
Information indicating that a packet loss has occurred between the first base station device and the second base station device during the dual connection is acquired from the second base station device, and the mobile station is used. It has a first control unit capable of performing communication control for changing the connection with the device from the binary connection to the single connection.
The second base station device is
A detector that detects packet loss between the first base station device and the second base station device, and
It has a notification unit for notifying the first base station device of information indicating that a packet loss has occurred.
The mobile station device is
A receiving unit that receives the first signal via the first path and receives the second signal via the second path during the dual connection.
A second control unit that changes the connection with the first base station device to a unified connection in response to communication control by the first base station device.
A second transmission unit that transmits reception status information that identifies signals that have been received or not received by the reception unit to the first base station apparatus via the first path when changing to the primary connection. A wireless communication system characterized by having and.

Images