Radio communication device and radio communication method

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

[Technical Field]

[0001] The present invention relates to a wireless communication device and a wireless communication method. [Background technology]

[0002] 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 on technology to increase system capacity by utilizing small cells in addition to macro cells. Here, a cell refers to an area covered by a wireless base station so that wireless terminals can transmit and receive wireless signals. A macro cell is a cell of a base station with relatively high transmission power and a relatively large radio wave coverage area. A small cell is a cell of a base station with relatively low transmission power and a relatively small radio wave coverage area.

[0003] In 3GPP (registered trademark) LTE-Advanced (LTE-A), for example, a configuration in which a macrocell includes multiple small cells is being considered as a configuration of a wireless communication system. Furthermore, a technology in which a mobile station simultaneously connects to a macrocell and a small cell is being considered. Another technology in which a mobile station simultaneously connects to two different small cells is also being considered. This type of communication in which a mobile station simultaneously connects to two different cells is sometimes called dual connectivity.

[0004] When a mobile station is simultaneously connected to a macro cell and a small cell, for example, control plane signals including Layer 3 control information for setting transmission paths and controlling handovers are transmitted and received between the mobile station and the macro cell base station (hereinafter referred to as a "macro base station"). Furthermore, data plane signals including user data are transmitted and received between the mobile station and both the macro base station and the small cell base station (hereinafter referred to as a "small base station"). Here, the control plane is sometimes called the control plane (C-plane) or SRB (Signaling Radio Bearer). Furthermore, the data plane is sometimes called the user plane (U-plane) or DRB (Data Radio Bearer).

[0005] On the other hand, when a mobile station connects to two different small cells simultaneously, for example, control plane signals are transmitted and received to and from one small base station, and data plane signals are transmitted and received to and from the other small base station. Data plane signals may also be transmitted and received to and from both small base stations.

[0006] In such a dual connection, a base station to which the control plane is connected may be called a primary base station. Also, a base station to which the data plane is connected and which communicates in cooperation with the primary base station may be called a secondary base station. Also, these base stations may be 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, they are called a master base station and a secondary base station, respectively. In this application, they may be called a first communication device and a second communication device, respectively.

[0007] Regarding the division of functions between the primary base station and the secondary base station in a dual-mode connection, various configurations have been proposed, depending on at which layer the data plane signal is split. For example, there is a configuration in which the data plane signal is split before the Packet Data Convergence Protocol (PDCP) layer. Another configuration, for example, is a configuration in which the data plane signal is split between the PDCP layer and the Radio Link Control (RLC) layer. Another configuration, for example, is a configuration in which the data plane signal is split between the RLC layer and the Medium Access Control (MAC) layer. In addition to these, configurations in which the data plane signal is split within each layer are also possible. For example, a configuration in which some PDCP layer functions are assigned to the primary base station and the remaining PDCP layer functions are assigned to the secondary base station. The same applies to the RLC layer and MAC layer functions. The latest trends in LTE-A include a configuration in which the data plane signal is split between the PDCP layer and the RLC layer (Architecture 3C), and a configuration in which the master base station and small base station each have a PDCP layer, an RLC layer, and a MAC layer (Architecture 1C).

[0008] The primary base station and secondary base station, which share functions in this way, are connected to each other by a wired or wireless link. Data plane signals branched at the primary base station are transmitted to the secondary base station via this link. [Prior art documents] [Non-patent literature]

[0009] [Non-Patent Document 1] 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 [Non-Patent Document 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 [Non-Patent Document 3] 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 [Non-Patent Document 4] 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 [Non-Patent Document 5] 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

Non - Patent Document 6

Non - Patent Document 7

Non - Patent Document 8

[0010] Meanwhile, if the communication state changes, for example, in communication between a secondary base station and a mobile station while a two-way connection is being implemented, it is conceivable that the two-way connection will be released and switched to a single connection. That is, if a change occurs in the communication state between the mobile station and the small base station while the mobile station is simultaneously connected to a macro base station and a small base station, the two-way connection will be released and the mobile station will communicate only with the macro base station. Examples of changes in the communication state include, for example, the occurrence of a malfunction or error in data communication, and deterioration of wireless quality.

[0011] However, since data plane signals are transmitted from both the macro base station and the small base station during dual connectivity, there is a risk that user data will be duplicated or lost in the mobile station when switching to single connectivity occurs. In other words, when switching from dual connectivity to single connectivity occurs, the macro base station may duplicate user data that has already been transmitted from the small base station, or may not transmit user data that has not yet been transmitted from the small base station, causing the data to be lost.

[0012] 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. That is, while two-way access is being performed, the mobile station transmits user data to both the macro base station and the small base station, but after switching to single access, the mobile station transmits user data only to the macro base station. At this time, the mobile station does not know whether the user data already transmitted to the small base station has been transferred to the macro base station, so it is difficult to transmit the exact amount of user data to the macro base station after switching to single access. Similarly, even when the mobile station is performing three-way or more multiple access, inconsistencies in the user data transmitted and received after switching to single access may occur.

[0013] The disclosed technology has been made in consideration of the above points, and aims to provide a wireless communication device and a wireless communication method that can prevent inconsistencies in transmitted and received user data. [Means for solving the problem]

[0014] In one aspect, the wireless communication device disclosed in the present application has a receiving unit that receives a portion of data transmitted from a first communication device via a first route including a wireless line between the first communication device and the first communication device, and receives another portion of the data transmitted from the first communication device via a second route that passes through a second communication device; a control unit that performs communication control in accordance with the state of data communication via the second route; and a transmitting unit that transmits reception status information identifying data that has been received or data that has not been received by the receiving unit to the first communication device via the first route by control by the control unit in accordance with the state of data communication via the second route. [Effects of the Invention]

[0015] According to one aspect of the wireless communication device and wireless communication method disclosed in the present application, it is possible to prevent inconsistencies in transmitted and received user data. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a wireless communication system according to the first embodiment. [Figure 2] FIG. 2 is a block diagram showing a configuration of a wireless communication system according to the first embodiment. [Figure 3] FIG. 3 is a block diagram showing a layer configuration of a wireless communication system according to the second embodiment. [Figure 4] FIG. 4 is a diagram showing a specific example of the format of the PDCP SR. [Figure 5] FIG. 5 is a diagram showing a list of PDU types. [Figure 6] FIG. 6 is a sequence diagram showing a connection switching method according to the second embodiment. [Figure 7] FIG. 7 is a flowchart showing processing performed by the mobile station according to the second embodiment. [Figure 8] FIG. 8 is a sequence diagram showing a connection switching method according to the third embodiment. [Figure 9] FIG. 9 is a block diagram showing the hardware configuration of the base station. [Figure 10] FIG. 10 is a block diagram showing the hardware configuration of a mobile station. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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 these embodiments. It goes without saying that the following embodiments may be implemented in appropriate combination. The following describes embodiments relating to downstream communication and upstream communication. Since two-way connectivity is often used in bidirectional communication in which both downstream communication and upstream communication are performed, it is clear that the embodiments may be implemented in combination.

[0018] (Embodiment 1) 1 is a diagram showing an example of the configuration of a radio communication system according to embodiment 1. The radio communication system shown in FIG.

[0019] 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 arrows and the data plane represented by the dashed arrows in Fig. 1. The mobile station 300 also 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 the data plane.

[0020] [Wireless communication system configuration] Fig. 2 is a block diagram showing the configuration of a radio communication system according to embodiment 1. As shown in Fig. 2, the macro base station 100 is connected to an upper layer communication device 4, and the macro base station 100 and the small base station 200 are wired connected using, for example, an X2 interface. The macro base station 100 and the small base station 200 then perform radio communication with the mobile station 300.

[0021] 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. In other words, 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.

[0022] Specifically, the communication unit 11 has a receiving unit 12 and a transmitting 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. Note that the control data may be data generated by the macro base station 100 itself.

[0023] The transmitter 13 wirelessly transmits control data addressed to the mobile station 300 to the mobile station 300. Furthermore, in accordance with instructions from the control unit 14, the transmitter 13 wirelessly transmits 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.

[0024] The control unit 14 controls the overall operation of the communication unit 11, which includes the receiving unit 12 and the transmitting unit 13. The control unit 14 also controls data communication according to the communication state. When switching from two-way connection to one-way connection, the control unit 14 ensures data consistency with the mobile station 300 by referring to reception state information received from the mobile station 300.

[0025] Note that examples of switching to a single connection include the following cases. First, there is the 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 the 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). There is also the case where the configuration of the small base station 200 is erased (RRC reconfiguration including the SeNB removal).

[0026] In the above, the timing at which the macro base station 100 receives the reception state information from the mobile station 300 is, for example, as follows. (First example) When the macro base station 100 switches from two-way connectivity to one-way connectivity, 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 an instruction to report reception state information. When the mobile station 300 receives the RRC signaling including an instruction to report reception state information, it notifies the macro base station 100 of the reception state information.

[0027] (Second example) When the mobile station 300 detects a change in the communication state, the detection serves as a trigger to transmit reception state information to the macro base station 100. The reporting of the reception state information may be set in advance by RRC signaling. Here, the change in the communication state corresponds to, for example, the following cases. First, a data loss (packet loss in the X2 interface, data discard due to buffer overflow caused by traffic congestion in the small base station, or transmission failure in the radio link, etc.) occurs in the transmission path (X2 interface and radio link) via the small base station 200, and the desired data is not received by the mobile station 300 (this can be detected by the expiration of a timer in the PDCP layer). Second, a retransmission of the desired data fails in the RLC layer of the small base station 200, and deterioration in radio link quality (Radio Link Failure) is detected (this can be detected by a counter for exceeding the maximum number of retransmissions in the RLC layer). In this case, there is a high possibility that not only the downlink transmission will fail, but also the transmission of the acknowledgment response corresponding to the downlink transmission (the RLC STATUS REPORT for transmitting ACK and NACK, or the TCP (Transmission Control Protocol) acknowledgment response if the downlink communication is TCP communication). Therefore, if the uplink communication fails, a Radio link Failure is detected in the RLC layer of the mobile station 300. In summary, the occurrence of a communication problem in the transmission path via the small base station 200 during two-way connectivity is an example of a change in the communication state.

[0028] To summarize this example, there are three triggers for the mobile station 300 to transmit reception status information. That is, the first trigger is detection of a change in downlink communication status in the mobile station 300 (capable of detecting status changes in wired and wireless links), the second trigger is detection of a change in downlink communication status in the small base station 200 (capable of detecting status changes in wireless links), and the third trigger is detection of a change in uplink communication status in the mobile station 300 (capable of detecting status changes in wireless links).

[0029] (Third example) This is a combination of the above examples. Specifically, in the second example, at least one of the three changes in communication state described in the second example is notified to the macro base station 100, and when the macro base station receives the notification, it notifies the mobile station 300 of the setting change by RRC signaling. At this time, the macro base station 100 can include an instruction to report the reception state information in the RRC signaling. In this way, by the macro base station 100 collectively controlling the transmission timing of the reception state information, it is possible to prevent the mobile station 300 from reporting the reception state information simultaneously, triggered by the above-mentioned "detection of a change in the downlink communication state" and "detection of a change in the uplink communication state."

[0030] In order to ensure data consistency, the control unit 14 refers to the reception status information and controls transmission after switching to the single connection so that the mobile station 300 transmits user data that has not yet been received and does not transmit user data that the mobile station 300 has already received.

[0031] Here, as a method for transmitting user data that has not yet been received by the mobile station 300, the control unit 14 may cause the macro base station 100 to transmit the data that has been held in the macro base station 100 as is, or may cause the macro base station 100 to transmit data that has been returned from the small base station 200 but 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 for which delivery confirmation has not been obtained), and data that the macro base station 100 continues to receive (data that is being transmitted on the X2 interface, which may also be referred to as fresh data).

[0032] As described above, according to the present embodiment, when switching from dual connection to single connection, the macro base station receives reception status information that identifies unreceived packets and received packets from the mobile station. At that time, the macro base station refers to the reception status information to transmit packets that the mobile station has not received, and does not transmit packets that the mobile station has received. Therefore, even when the connection is switched, packets according to the reception status can be transmitted from the macro base station to the mobile station, and data consistency can be ensured.

[0033] In the above-described first embodiment, the downlink communication from the macro base station 100 to the mobile station 300 has been described, but similar processing can be performed for the uplink communication from the mobile station 300 to the macro base station 100. That is, for example, when a communication problem occurs in the uplink transmission path via the small base station 200 during two-way connectivity, the macro base station 100 may transmit reception status information to the mobile station 300. This makes it possible to transmit packets according to the reception status from the mobile station 300 to the macro base station 100, even when switching to one-way connectivity occurs, and data consistency can be ensured.

[0034] (Embodiment 2) An example of the configuration of a wireless communication system according to the second embodiment is the same as that of the first embodiment (FIG. 1), and therefore a description thereof will be omitted. Such a wireless communication system configuration is often adopted to offload traffic and reduce the number of handovers.

[0035] [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), and therefore detailed description of the same parts as those of the first embodiment will be omitted.

[0036] 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 receiving unit 12 and a transmitting 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.

[0037] Furthermore, when the small base station 200 detects an error (a communication problem), the receiver 12 receives an error detection notification from the small base station 200. Then, when an error detection notification is received, the receiver 12 wirelessly receives from the mobile station 300 reception status information that identifies user data that has been received by the mobile station 300 and user data that has not yet been received. The receiver 12 then outputs the received error detection notification and reception status information to the control unit 14. The timing at which the receiver 12 receives the reception status information and the contents of the reception status information will be described in detail later.

[0038] The transmitter 13 wirelessly transmits control data addressed to the mobile station 300 to the mobile station 300. Furthermore, in accordance with instructions from the control unit 14, the transmitter 13 wirelessly transmits 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.

[0039] The control unit 14 performs overall control of the operation of the communication unit 11, which includes the receiving unit 12 and the transmitting unit 13. Furthermore, when an error detection notification is output from the receiving unit 12, the control unit 14 determines to temporarily release the two-way connection and switch to a one-way connection. When switching to a one-way 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 one-way connection. Specifically, the control unit 14 refers to the reception status information and controls transmission after switching to the one-way connection so that the mobile station 300 transmits user data that has not yet been received and does not transmit user data that the mobile station 300 has received.

[0040] 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. In other words, the communication unit 21 performs wired communication with the macro base station 100 and wireless communication with the mobile station 300.

[0041] Specifically, the communication unit 21 has a receiving unit 22 and a transmitting 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.

[0042] 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, if 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. The detected error here is, for example, an error in which an acknowledgement (ACK) of the user data is not received from the mobile station 300 even though a predetermined time has elapsed since the user data was transmitted to the mobile station 300, or an error in which the number of retransmissions of the user data reaches a predetermined maximum number of retransmissions. Note that the transmitter 23 may also transmit the error detection notification to the macro base station 100 if an error is detected in communication with the macro base station 100.

[0043] The control unit 24 controls the overall operation of the communication unit 21 including the receiving unit 22 and the transmitting unit 23 .

[0044] The mobile station 300 has a communication unit 31 and a control unit 34. The communication unit 31 communicates with the macro base station 100 and the small base station 200. In other words, the communication unit 31 establishes a dual connection with the macro base station 100 and the small base station 200, and performs radio communication with both base stations simultaneously.

[0045] Specifically, the communication unit 31 has a receiving unit 32 and a transmitting unit 33. The receiving unit 32 receives control data and user data wirelessly from the macro base station 100. At the same time, the receiving unit 32 receives user data wirelessly from the small base station 200. In other words, the receiving unit 32 receives part of the user data transmitted from the macro base station 100 directly from the macro base station 100, and receives the remaining part of the user data transmitted from the macro base station 100 via the small base station 200.

[0046] Furthermore, when an error is detected in communication with the small base station 200, the receiver 32 generates reception status information that identifies user data that has been received and user data that has not yet been received by the mobile station 300 from the macro base station 100 and the small base station 200. Then, the receiver 32 outputs the generated reception status information to the control unit 34.

[0047] The transmitter 33 acquires the reception state information generated by the receiver 32 via the controller 34. Then, the transmitter 33 transmits the acquired reception state information to the macro base station 100 by radio.

[0048] The control unit 34 performs overall control over the operation of the communication unit 31, which includes the receiving unit 32 and the transmitting unit 33. The control unit 34 also monitors the receiving unit 32, and detects errors that occur in communications 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 time has passed since receiving user data from the small base station 200, or an error in which the number of retransmissions of user data reaches a predetermined maximum number of retransmissions. When the control unit 34 detects an error in the receiving unit 32, it acquires reception status information generated by the receiving unit 32 and outputs it to the transmitting unit 33.

[0049] Here, an error in which desired user data is not received can be detected, for example, in the PDCP layer. Specifically, when it is detected that user data has been received out of order, that is, that there is unreceived user data (also called out-of-order delivery), a timer is started to wait for the arrival of the first unreceived packet. If the packet is received before the timer expires, it is determined that reception was successful, but if it is not received, it is determined that there is an error. Thereafter, the same process is performed for the next unreceived packet.

[0050] 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 is performed for user data in which an error has occurred in wireless transmission. If retransmissions are successful within a predetermined number of retransmissions, it is determined that reception is successful, but if the number of retransmissions exceeds the predetermined number, it is determined that an error has occurred. In this case, conventionally, it is determined that an RLF (Radio Link Failure) has occurred, and an RRC connection re-establishment is performed. Furthermore, in a two-way connection, if an RLF occurs particularly on the small base station 200 side, an 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 the first embodiment, 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.

[0051] In this embodiment, when such an error is detected, reception status information is transmitted from the mobile station 300 to the macro base station 100. Therefore, compared to a technique in which reception status information is transmitted when the amount of data remaining in the buffer of the mobile station 300 exceeds a predetermined threshold, it is possible to transmit the reception status information to the macro base station 100 earlier. Note that when a large amount of user data loss is detected in the PDCP layer, a timer expires for each lost packet, causing reception status information to be transmitted, which increases signaling overhead. Therefore, for example, a prohibit timer may be separately set to prevent the reception status information from being transmitted frequently. Specifically, the prohibit timer may be used to determine whether a certain period has elapsed since the previous transmission of the reception status information, and the reception status information may not be transmitted again until the certain period has elapsed.

[0052] [Wireless communication system processing] Next, the processing of the macro base station 100, small base station 200, and mobile station 300 in the wireless communication system configured as above will be explained. These macro base station 100, small base station 200, and mobile station 300 perform communication using link layer protocols corresponding to a plurality of link layers. That is, for example, link layer protocols corresponding to a PDCP (Packet Data Convergence Protocol) layer, an RLC (Radio Link Control) layer, a MAC (Medium Access Control) layer, and a PHY (Physical) layer are used. Fig. 3 is a block diagram showing the layer configuration of a wireless communication system according to embodiment 2.

[0053] Here, first, processing of the macro base station 100 related to 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. The RLC layer 102 is an RLC layer for the downlink, and the RLC layer 103 is an RLC layer for the uplink. Note that the macro base station 100 may also have layers not shown, such as a PHY layer.

[0054] The communication unit 11 receives user data from the upper layer communication device 4. Then, the communication unit 11 assigns sequence numbers to packets of the received user data in the PDCP layer 101. At this time, the communication unit 11 assigns odd numbers to packets to be output to the RLC layer 102, for example, and assigns even numbers to packets to be transmitted to the small base station 200. These sequence numbers are also used, for example, during handover. Furthermore, the communication unit 11 performs header compression, security check, and encryption on the user data in the PDCP layer 101.

[0055] Then, the communication unit 11 outputs the packets assigned odd numbers from the PDCP layer 101 to the RLC layer 102. Also, the communication unit 11 transmits the packets assigned even numbers to the small base station 200 via a wired connection. As a result, packets assigned sequence numbers #1, #3, #5, #7, ... are output to the RLC layer 102, and packets assigned sequence numbers #2, #4, #6, #8, ... are transmitted to the small base station 200.

[0056] Note that the numbers assigned to packets do not necessarily have to be sequence numbers in ascending order. In other words, other numbers may be assigned to packets as long as they are identifiers that can identify each packet and indicate the order of the packets in the entire user data. In the following, the explanation will be continued assuming that consecutive sequence numbers in ascending order are assigned to packets.

[0057] The communication unit 11 acquires packets with odd numbers assigned in the RLC layer 102 from the PDCP layer 101. Then, in the RLC layer 102, the communication unit 11 divides or combines the packets as necessary and assigns an RLC layer header to generate RLC layer packets (hereinafter referred to as "RLC packets").

[0058] Thereafter, the communication unit 11 outputs the RLC packets from the RLC layer 102 to the MAC layer 104 in accordance with the scheduling in the MAC layer 104. Then, the communication unit 11 assembles data for transmission in the MAC layer 104 using the RLC packets. That is, for example, the RLC packets are divided and combined as necessary, and MAC layer headers are added to generate MAC layer packets (hereinafter referred to as "MAC packets"). Then, the communication unit 11 transmits the MAC packets from the MAC layer 104 to the mobile station 300 via a PHY layer (not shown) and the like in accordance with the scheduling.

[0059] 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 reassembles the received user data in the MAC layer 104, and divides and combines the received user data in the RLC layer 103. Furthermore, the communication unit 11 corrects the order of data using the RLC layer header in the RLC layer 103, and outputs the user data from the RLC layer 103 to the PDCP layer 101.

[0060] Next, the processing of the macro base station 100 when an error detection notification is received from the small base station 200 will be described.

[0061] When an error is detected in the small base station 200, the communication unit 11 acquires, in the PDCP layer 101, an error detection notification transmitted from the small base station 200. The communication unit 11 also acquires, in the PDCP layer 101, reception status information transmitted from the mobile station 300 and passed through the MAC layer 104 and the RLC layer 103. The reception status information includes information that enables the mobile station 300 to identify packets that have been received and packets that have not yet been received at the time the error is detected.

[0062] When the communication unit 11 receives the error detection notification, the control unit 14 decides to release the two-way connection with the mobile station 300 and switch to one-way connection. Then, the control unit 14 transmits a two-way connection release notification indicating that the two-way connection will be released to the small base station 200 and the mobile station 300 via the communication unit 11. The control unit 14 also references 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 numbers of packets that have not yet been received by the mobile station 300 and that are indicated by the reception status information, and also notifies the PDCP layer 101 of the sequence numbers of packets that have been received as sequence numbers of packets that do not need to be transmitted.

[0063] Then, communication unit 11 excludes packets that have been received by mobile station 300 and no longer need to be transmitted, and outputs packets that have not yet been received by mobile station 300 from PDCP layer 101 to RLC layer 102 in ascending order of sequence numbers. Communication unit 11 then generates RLC packets in RLC layer 102, generates MAC packets in MAC layer 104, and transmits the MAC packets to mobile station 300. This allows mobile station 300 to receive packets without duplication or loss, even after switching from dual connectivity to single connectivity.

[0064] Next, the processing of the small base station 200 relating to the 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. The RLC layer 201 is the RLC layer for the downlink, and the RLC layer 202 is the RLC layer for the uplink. Note that the small base station 200 may also have layers not shown, such as a PHY layer.

[0065] The communication unit 21 receives, in the RLC layer 201, packets transmitted from the PDCP layer 101 of the macro base station 100 via a wired connection. As described above, these packets are assigned even numbers. Then, in the RLC layer 201, the communication unit 21 divides and combines packets as necessary and adds an RLC layer header to generate RLC packets.

[0066] Thereafter, the communication unit 21 outputs the RLC packets from the RLC layer 201 to the MAC layer 203 in accordance with the scheduling in the MAC layer 203. Then, the communication unit 21 assembles data for transmission in the MAC layer 203 using the RLC packets. That is, for example, the RLC packets are divided and aggregated as necessary, and MAC layer headers are added to generate MAC packets. Then, the communication unit 21 transmits the MAC packets from the MAC layer 203 to the mobile station 300 via a PHY layer (not shown) and the like in accordance with the scheduling.

[0067] 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 reassembles the received user data in the MAC layer 203, and divides and combines the received user data in the RLC layer 202. Furthermore, the communication unit 21 corrects the order of data using the RLC layer header in the RLC layer 202, and transmits the user data from the RLC layer 202 to the macro base station 100.

[0068] Next, the processing of the small base station 200 when an error is detected will be described.

[0069] When a 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 an acknowledgement (ACK) from the mobile station 300. If the MAC packet is not correctly received by the mobile station 300, the acknowledgement (ACK) will not be received by the time the timer expires. Therefore, if the acknowledgement (ACK) is not received by the time the timer expires, the control unit 24 detects that an error has occurred.

[0070] The control unit 24 may also monitor the number of retransmissions of data with the mobile station 300, and detect that an error has occurred when the number of retransmissions reaches a predetermined maximum number of retransmissions. Furthermore, the control unit 24 may detect that an error has occurred when a desired packet is not received even after a predetermined time has elapsed since the packet was received from the macro base station 100 via a wired connection. When the control unit 24 detects an error, the communication unit 21 transmits an error detection notification to the macro base station 100 via the wired connection.

[0071] Thereafter, when the macro base station 100 decides to release the two-way connection, the communication unit 21 receives a two-way connection release notification from the macro base station 100. After receiving the two-way connection release notification, wireless communication between the small base station 200 and the mobile station 300 is no longer performed, and therefore the communication unit 21 stops transmitting and receiving data.

[0072] Next, processing by 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. Because the mobile station 300 has the function of receiving user data from two base stations simultaneously, a MAC layer and an RLC layer are provided corresponding to each base station. That is, the MAC layer 301, the RLC layer 303, the RLC layer 304, and the PDCP layer 307 are used to transmit and receive user data to and from the macro base station 100. The MAC layer 302, the RLC layer 305, the RLC layer 306, and the PDCP layer 307 are used to transmit and receive user data to and from the small base station 200. The RLC layers 303 and 305 are RLC layers for the downlink, and the RLC layers 304 and 306 are RLC layers for the uplink. The mobile station 300 may also have layers not shown, such as a PHY layer.

[0073] The communication unit 31 receives user data (MAC packets) from the macro base station 100 in the MAC layer 301. Then, the communication unit 31 reassembles the received user data in the MAC layer 301, and divides and combines the received user data in the RLC layer 303. Furthermore, the communication unit 31 corrects the order of data using the RLC layer header 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 decrypts, checks security, and decompresses the header of the user data in the PDCP layer 307.

[0074] Similarly, the communication unit 31 receives user data (MAC packets) from the small base station 200 in the MAC layer 302. Then, the communication unit 31 reassembles the received user data in the MAC layer 302, and divides and combines the received user data in the RLC layer 305. Furthermore, the communication unit 31 corrects the order of data using the RLC layer header 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 decrypts, checks security, and decompresses the header of the user data in the PDCP layer 307.

[0075] 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. Furthermore, the communication unit 31 performs header compression, security check, and encryption on the user data in the PDCP layer 307.

[0076] Then, communication unit 31 outputs some of the packets from PDCP layer 307 to RLC layer 304, and outputs the remaining packets from PDCP layer 307 to RLC layer 306. Then, communication unit 31 divides and combines packets as necessary in RLC layers 304 and 306, and adds RLC layer headers to generate RLC layer packets (hereinafter referred to as "RLC packets").

[0077] Thereafter, the communication unit 31 outputs the RLC packets from the RLC layers 304 and 306 to the MAC layers 301 and 302, respectively, in accordance with the scheduling in the MAC layers 301 and 302. Then, the communication unit 31 assembles data to be transmitted using the RLC packets in the MAC layers 301 and 302. That is, for example, the RLC packets are divided and integrated as necessary, and MAC layer headers are added to generate MAC packets. 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, in accordance with the scheduling, via a PHY layer (not shown) and the like.

[0078] Next, the processing of the mobile station 300 when an error is detected will be described.

[0079] The control unit 34 monitors the reception of user data in the communication unit 31, and detects that an error has occurred if, for example, a predetermined time has elapsed since a packet with an assigned sequence number was received in the PDCP layer 307 and there is still an unreceived packet with an earlier sequence number assigned to that packet. The control unit 34 may also monitor the number of data retransmissions between the macro base station 100 and the small base station 200, and detect that an error has occurred when the number of retransmissions reaches a predetermined maximum number of retransmissions. 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 reception status information.

[0080] 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 by the PDCP layer 101 of the macro base station 100, 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.

[0081] Then, in the PDCP layer 307, the communication unit 31 generates reception status information indicating the smallest sequence number among the sequence numbers of unreceived packets and whether a predetermined number of packets assigned sequence numbers subsequent to this sequence number have been received. Specifically, consider a case where 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. Here, assume 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, the packets with sequence numbers #1, #3, #5, and #7 transmitted from the macro base station 100 are received by the mobile station 300, but the packets with sequence numbers #2, #4, #6, and #8 are not received by the mobile station 300.

[0082] Therefore, the PDCP layer 307 generates reception status information indicating the smallest sequence number #2 among the sequence numbers of unreceived packets and whether packets with sequence numbers #3 to #8 have been received. Therefore, in this example, reception status information is generated indicating that packets with sequence numbers #3, #5, and #7 have been received and packets with sequence numbers #4, #6, and #8 have not been received. This reception status information indicates that sequence numbers #2, #4, #6, and #8 have not been received by the mobile station 300 and will need to be transmitted again from the macro base station 100 after switching to single-access connectivity.

[0083] The above explanation is based on the premise that consecutive sequence numbers are assigned to packets in ascending order in the PDCP layer 101. However, as mentioned above, sequence numbers do not necessarily have to be assigned to packets in the PDCP layer 101. If other identifiers are assigned to packets in the PDCP layer 101, the reception status information includes the identifier of the packet (first unreceived packet) that is closest in order to the beginning of the entire user data among the unreceived packets. In this case, the reception status information also includes whether a predetermined number of packets after the packet closest to the beginning of the entire user data have been received.

[0084] When the PDCP layer 307 generates reception status information, the communication unit 31 transmits this reception status information to the macro base station 100. This allows the macro base station 100 to grasp the reception status of packets at the mobile station 300, including packets passing through the small base station 200. As a result, even after the macro base station 100 releases the two-way connectivity and switches to the one-way connectivity, it is still possible to transmit packets to the mobile station 300 without excess or deficiency, and it is possible to prevent duplication and loss of user data.

[0085] [Examples of reception status information] As described above, when an error is detected in communication between the small base station 200 and the mobile station 300, reception status information is transmitted from the mobile station 300 to the macro base station 100. As this reception status information, for example, a PDCP Status Report (hereinafter abbreviated as "PDCP SR") can be used.

[0086] Figure 4 shows a specific example of a PDCP SR format. PDCP SR 400 shown in the upper part of Figure 4 is a PDCP SR for a 12-bit sequence number. PDCP SR 410 shown in the middle part of Figure 4 is a PDCP SR for a 15-bit sequence number. PDCP SR 420 shown in the lower part of Figure 4 is a PDCP SR for a 7-bit sequence number.

[0087] As shown in these figures, in a PDCP SR, the size of the sequence number varies depending on the data being transmitted and received. Specifically, for example, in VoIP (Voice of Internet Protocol), a 7-bit sequence number may be used. For this reason, PDCP SRs 400, 410, and 420 shown in Fig. 4 each have an FMS (First Missing Sequence number) field 401, 411, and 421 of a different size. FMS fields 401, 411, and 421 are fields that store the sequence number of the packet that is closest to the beginning of the entire user data among the unreceived packets.

[0088] 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 all the user data among the packets that have not yet been received by the mobile station 300. In other words, the FMS field 401 stores the sequence number of the packet that is to be received earliest among the packets of user data that have not yet arrived from the small base station 200. Hereinafter, packets whose sequence numbers are stored in the FMS fields 401, 411 and 421 may be referred to as "FMS packets".

[0089] Also, Bitmap1 to Bitmap of PDCP SR400, 410 and 420 N The fields store whether or not packets after the FMS packet have been received. Specifically, for example, for the 1st to Nth packets (N is an integer equal to or greater than 1) after the FMS packet, if the packets have been received by the mobile station 300, "1" is stored, and if the packets have not been received by the mobile station 300, "0" is stored.

[0090] For example, consider the case where 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, as in the example described above. Here, if the packet with sequence number #2 is not received by the mobile station 300 and an error is detected, the subsequent packets with sequence numbers #4, #6, and #8 are also not received from the small base station 200. Therefore, the mobile station 300 has already received the packets with sequence numbers #1, #3, #5, and #7, but has not yet received the packets with sequence numbers #2, #4, #6, and #8.

[0091] In this case, the FMS packet is the packet with sequence number #2, so sequence number #2 is stored in FMS fields 401, 411, and 412 of PDCP SRs 400, 410, and 420. Furthermore, of the packets following the FMS packet, packets with sequence numbers #3, #5, and #7 have already been received, and packets with sequence numbers #4, #6, and #8 have not yet been received. Therefore, the fields of Bitmap1 to Bitmap6 store "1", "0", "1", "0", "1", and "0", respectively.

[0092] 4 stores information about the type of PDU (Protocol Data Unit) used as the PDCP SRs 400, 410, and 420. Specifically, as shown in FIG. 5, bits indicating the type of this PDU are stored in the PDU Type field. That is, when bits "000" are stored in the PDU Type field, this indicates that this PDU is a PDCP status report such as PDCP SRs 400, 410, and 420.

[0093] On the other hand, if the PDU Type field contains bits "001", this indicates that the PDU is an interspersed ROHC feedback packet. The interspersed ROHC feedback packet contains feedback information for the PDU of the PDCP layer transmitted from the receiving side.

[0094] Furthermore, bits "010" to "111" that can be stored in the PDU Type field are left as reserved bits. Therefore, in this embodiment, it is possible to assign bits different from those used in normal PDCP SR to reception status information transmitted from mobile station 300 when an error is detected, and store these bits in the PDU Type field.

[0095] [Connection switching method] Next, a method for switching connection from a dual connection to a single connection according to the second embodiment will be described with reference to a sequence diagram shown in FIG.

[0096] When the mobile station 300 is in a two-way connection with the macro base station 100 and the small base station 200, part of the user data is transmitted wirelessly from the communication unit 11 of the macro base station 100 to the mobile station 300. The remaining user data is transmitted to the small base station 200 via a wired connection (step S101), and then transmitted wirelessly 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 the data by the communication unit 11 of the macro base station 100. For example, packets assigned odd numbers are transmitted wirelessly from the macro base station 100 directly to the mobile station 300, and packets assigned even numbers are transmitted wirelessly to the mobile station 300 via the small base station 200.

[0097] Then, if the packet transmitted wirelessly 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 the mobile station 300 does not return an acknowledgement (ACK) for a packet transmitted wirelessly from the small base station 200. The control unit 24 of the small base station 200 also detects an error 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 passed.

[0098] On the other hand, if a packet is not received from the small base station 200, an error is also detected by the control unit 34 of the mobile station 300 (step S104). This error is detected, for example, when, after a packet with a sequence number assigned thereto is received from the small base station 200, even after a predetermined time has elapsed, there is an unreceived packet with an earlier sequence number assigned thereto. The control unit 34 of the mobile station 300 also detects an error when, for example, the number of retransmissions with the small base station 200 reaches a predetermined maximum number of retransmissions.

[0099] When the control unit 24 of the small base station 200 detects an error, it transmits an error detection notification to the macro base station 100 (step S105). Furthermore, when the control unit 34 of the mobile station 300 detects an error, the communication unit 31 generates reception status information. The reception status information includes the sequence number of the packet closest to the beginning of the packets that the mobile station 300 has not yet received, and whether 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).

[0100] 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 release the two-way connection and switch to one-way connection. That is, it decides to temporarily stop transmission of user data via the small base station 200 and for the macro base station 100 to transmit all user data directly to the mobile station 300. Then, the communication unit 11 transmits a two-way connection release notification indicating that the two-way connection will be released to the small base station 200 (step S107). Having received the two-way connection release notification, the small base station 200 thereafter stops transmitting user data to the mobile station 300.

[0101] The dual connection release notification is also transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S108). Upon receiving the dual connection release notification, the mobile station 300 receives all user data from the macro base station 100 thereafter.

[0102] After switching to the single connectivity, when the macro base station 100 transmits 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 control unit 14 notifies the communication unit 11 of the sequence numbers of packets that have not yet been received by the mobile station 300, and the communication unit 11 sequentially transmits the packets with the notified sequence numbers to the mobile station 300.

[0103] As described above, in the present embodiment, when an error is detected in the transmission path of user data via the small base station 200, reception status information is transmitted from the mobile station 300 to the macro base station 100. Then, the macro base station 100 releases the two-way connection and, by referring to the reception status information, transmits to the mobile station 300 the exact amount of user data that has not yet been received by the mobile station 300. Therefore, even when switching from two-way connection to one-way connection occurs, it is possible to prevent duplication and loss of user data received by the mobile station 300.

[0104] [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 during dual connectivity will be described with reference to the flow diagram shown in FIG.

[0105] 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 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 that is assigned a sequence number earlier than this packet. If there is an unreceived packet, the control unit 34 starts a predetermined timer and determines whether the unreceived packet will be received before a predetermined time has elapsed. If these determinations show that there is no unreceived packet or that a packet has been correctly received before the predetermined time has elapsed, it is determined that no error has been detected (step S201 No), and the control unit 34 continues to monitor the communication.

[0106] If an error is detected (Yes in step S201), control unit 34 instructs communication unit 31 to generate a PDCP SR, which is reception status information. In response to this instruction, communication unit 31 generates a PDCP SR that includes the sequence number of the packet that is closest to the beginning of the entire user data among the unreceived packets, and information on whether a predetermined number of packets after this packet have been received (step S202). Communication unit 31 then transmits the generated PDCP SR to macro base station 100 (step S203).

[0107] Thereafter, the communication unit 31 receives a dual connection release notification from the macro base station 100 that has decided to temporarily release the dual connection (step S204). After receiving the dual 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 the user data that has not yet been received by the mobile station 300 without any excess or deficiency, so that the communication unit 31 receives the user data from the macro base station 100 without any duplication or loss.

[0108] As described above, according to the present embodiment, when an error is detected in a transmission path via a small base station during dual connection, the mobile station transmits reception status information that identifies unreceived packets and received packets to the macro base station. Then, the macro base station cancels the dual connection and switches to a single connection, and transmits the packets that the mobile station has not received by referring to the reception status information. Therefore, even when a connection switch occurs, it is possible to transmit packets from the macro base station to the mobile station without excess or shortage, and it is possible to prevent duplication and loss of user data.

[0109] In the above-mentioned 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 may be transmitted from the mobile station 300 to the macro base station 100. In this case, the error detection notification may be transmitted to the macro base station 100 together with reception state information.

[0110] (Embodiment 3) In the second embodiment, a connection switching method has been described for the case where an error is detected in the downlink from the macro base station 100 and the small base station 200 to the mobile station 300. However, even when an error is detected in the uplink from the mobile station 300 to the macro base station 100 and the small base station 200, the two-way connection may be temporarily released and switched to a single connection. Therefore, in the third embodiment, a connection switching method for the case where an error is detected in the uplink will be described.

[0111] The configuration of the radio communication system according to the present embodiment is the same as that of embodiment 2, and therefore description thereof will be omitted. This embodiment differs from embodiment 2 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.

[0112] Fig. 8 is a sequence diagram showing a connection switching method according to embodiment 3. As shown in Fig. 8, when the mobile station 300 is in a dual connection with the macro base station 100 and the small base station 200, part of the user data is wirelessly transmitted directly from the communication unit 31 of the mobile station 300 to the macro base station 100 (step S301). The remaining user data is transmitted to the macro base station 100 via the small base station 200.

[0113] These user data packets are assigned sequence numbers by the communication unit 31 of the mobile station 300, and for example, packets assigned odd numbers are wirelessly transmitted directly to the macro base station 100, and packets assigned even numbers are transmitted to the macro base station 100 via the small base station 200.

[0114] 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 is detected, for example, when, after a packet to which a sequence number is assigned is received from the mobile station 300 via the small base station 200, a packet to which a sequence number earlier than this packet is assigned remains unreceived even after a predetermined time has elapsed. This error detection can be performed, for example, in the PDCP layer, as described above. This error detection can also be performed, for example, in the RLC layer, and when performed in the RLC, it is also possible for the small base station 200 or the mobile station 300 to detect the error. When an error is detected by the small base station 200 or the mobile station 300, the occurrence of the error can be notified to the macro base station 100.

[0115] When the control unit 14 of the macro base station 100 detects an error, the communication unit 11 generates reception status information. The reception status information includes the sequence number of the packet that is closest to the beginning of all user data among the packets that the macro base station 100 has not yet received, and information on whether a predetermined number of packets after this packet have been received. The generated reception status information is then transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S304).

[0116] Furthermore, in the macro base station 100, since the control unit 14 has detected an error, it decides to temporarily release the two-way connection and switch to one-way connection. That is, it decides to temporarily stop receiving user data via the small base station 200 and to have all user data transmitted directly from the mobile station 300 to the macro base station 100. Then, the communication unit 11 transmits a two-way connection release notification indicating that the two-way connection will be released to the small base station 200 (step S305). Having received the two-way connection release notification, the small base station 200 thereafter stops receiving user data from the mobile station 300.

[0117] The dual connection release notification is also transmitted from the communication unit 11 of the macro base station 100 to the mobile station 300 (step S306). Upon receiving the dual connection release notification, the mobile station 300 thereafter wirelessly transmits all user data directly to the macro base station 100.

[0118] After switching to the single connectivity, when the mobile station 300 transmits user data to the macro base station 100, the control unit 34 refers to the reception state information received from the macro base station 100. Then, the control unit 34 notifies the communication unit 31 of the sequence numbers of packets that have not yet been received by the macro base station 100, and the communication unit 31 sequentially transmits the packets with the notified sequence numbers to the macro base station 100.

[0119] As described above, in the present embodiment, when an error is detected in the transmission path of user data via the small base station 200, reception status information is transmitted from the macro base station 100 to the mobile station 300. Then, after the macro base station 100 releases the two-way connectivity, the mobile station 300 refers to the reception status information and transmits to the macro base station 100 just the right amount of user data that has not yet been received by the macro base station 100. Therefore, even when switching from two-way connectivity to one-way connectivity occurs, it is possible to prevent duplication and loss of user data received by the macro base station 100.

[0120] As described above, according to the present embodiment, when an error is detected in a transmission path via a small base station during dual connection, the macro base station transmits reception status information that identifies unreceived packets and received packets to the mobile station. Then, when the macro base station releases the dual connection and switches to single connection, the mobile station refers to the reception status information and transmits packets that the macro base station has not received. Therefore, even when a connection switch occurs, it is possible to transmit packets from the mobile station to the macro base station just enough, and it is possible to prevent duplication and loss of user data.

[0121] In the above third embodiment, an error is assumed to be detected by the macro base station 100, but the error may also 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 detects the error may notify the macro base station 100 that an error has occurred. The small base station 200 detects an error, for example, when the number of retransmissions with the mobile station 300 in the RLC layer reaches a predetermined maximum number of retransmissions. The mobile station 300 also detects an error when, for example, an acknowledgement (ACK) of the user data is not received from the small base station 200 even when a predetermined time has elapsed since the mobile station 300 transmitted user data to the small base station 200.

[0122] Note that, in the above-described embodiments, a dual access in which the mobile station 300 is simultaneously connected to two base stations, the macro base station 100 and the small base station 200, has been described as an example, but similar processing is also possible for a multiple access in which the mobile station 300 is simultaneously connected to three or more base stations. That is, when an error is detected in a transmission path via any of the base stations, the receiving mobile station transmits reception status information to the primary base station to which the control plane is connected. The primary base station then cancels the multiple access and switches to a single access, and, by referring to the reception status information, is able to transmit just the right amount of user data to the mobile station.

[0123] Furthermore, 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 decides to release the two-way connection and switch to a one-way connection. However, the macro base station 100 does not necessarily have to switch to a one-way connection when an error is detected. Even if the macro base station 100 does not switch to a one-way connection, the mobile station 300 or macro base station 100 on the receiving side transmits reception status information to the macro base station 100 or mobile station 300 on the transmitting side, thereby enabling the transmitting side to check the reception status of packets on the receiving side.

[0124] Furthermore, in each of the above embodiments, the two-way connection is released and switched to a single connection when an error is detected in the transmission path via the small base station 200, but the connection switching does not have to occur only when an error is detected. That is, for example, when the mobile station 300 moves and changes the macro base station or small base station to which it is connected, it is also possible to temporarily release the two-way connection and switch to a single connection. And even in such a case, by the receiving side transmitting reception status information to the transmitting side, it is possible to prevent duplication and loss of user data when the connection switching occurs.

[0125] The physical configurations of the 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 Figures 2 and 3. Therefore, a specific example of the hardware configuration of the macro base station 100, small base station 200 and mobile station 300 will be explained below.

[0126] 9 is a block diagram showing the hardware configuration of a 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.

[0127] 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.

[0128] The network interface 506 is an interface for connecting to other base stations via a wired connection. For example, the macro base station 100 and the small base station 200 are connected via a wired connection via the network interface 506.

[0129] The CPU 505, memory 504, and 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, the memory 504 stores various programs such as a program for realizing the functions of the communication unit 11 or the communication unit 21. The CPU 505 then reads out the programs stored in the memory 504 and realizes the functions of the communication unit 11 or the communication unit 21 by cooperating with the RF circuit 503 and the like.

[0130] 10 is a diagram showing the hardware configuration of a mobile station. The mobile station shown in FIG. 10 corresponds to, for example, mobile station 300, and includes antenna 511, control unit 512, RF circuit 513, memory 514, and CPU 515.

[0131] The control unit 512 implements the functions of the control unit 34 of the mobile station 300, for example.

[0132] The CPU 515, memory 514, and RF circuit 513 implement, for example, the functions of the communication unit 31 of the mobile station 300. That is, for example, the memory 514 stores various programs, such as a program for implementing the functions of the communication unit 31. The CPU 515 then reads out the programs stored in the memory 514 and implements the functions of the communication unit 31 by cooperating with the RF circuit 513 and the like. [Explanation of symbols]

[0133] 11, 21, 31 Communications Department 12, 22, 32 Receiver 13, 23, 33 Transmitter 14, 24, 34 Control section 101, 307 PDCP layer 102, 103, 201, 202, 303, 304, 305, 306 RLC layers 104, 203, 301, 302 MAC layer

Claims

1. a communication unit that is wirelessly connected to a first communication device and a second communication device and is capable of performing wireless communication; a control unit that controls a change of the wireless communication connection when the communication unit receives a Radio Resource Control (RRC) signal including first information instructing a change of the wireless connection from the first communication device, The control unit controls transmission of first reception state information when second information instructing a report of reception state information is included in the RRC (Radio Resource Control) signal; the first reception status information is information that identifies received data or unreceived data among data transmitted from the first communication device or the second communication device; A wireless communication device comprising:

2. The communication unit 2. The wireless communication device according to claim 1, wherein the reception status information can be received from the first communication device after the connection change.

3. The wireless communication device according to claim 1, characterized in that the control unit can control a change in the wireless communication connection when the communication unit receives the RRC (Radio Resource Control) signal in response to an error detection notification sent from the second communication device to the first communication device when data loss occurs in a network interface between the first communication device and the second communication device.

4. the first information is information instructing to change the wireless connection from a dual connection connecting the first communication device and the second communication device to a single connection connecting to the first communication device, 2. The wireless communication device according to claim 1, wherein the communication unit transmits the first reception status information to the first communication device.

5. the control unit performs control to execute processing according to second reception status information when the communication unit receives the second reception status information in response to the connection change; the second reception status information is information that identifies received data or unreceived data among data transmitted to the first communication device or the second communication device; 2. The wireless communication device according to claim 1.

6. A wireless communication device, a communication unit that is connected to a first communication device and a second communication device and that can perform wireless communication with the first communication device; a control unit capable of performing control related to a wireless connection with the first communication device, the communication unit is capable of transmitting, to the first communication device, a Radio Resource Control (RRC) signal including first information instructing a connection change and second information instructing a report of first reception state information; the communication unit receives, from the first communication device, the first reception state information transmitted from the first communication device in response to the second information; A wireless communication device characterized in that the first reception status information is information that identifies received data or unreceived data among data transmitted from the wireless communication device or the second communication device to the first communication device.

7. The wireless communication device according to claim 6, characterized in that the control unit can control the transmission of the RRC (Radio Resource Control) signal in response to an error detection notification transmitted from the second communication device to the wireless communication device when data loss occurs in a network interface between the wireless communication device and the second communication device.

8. the control unit performs control to execute a process of transmitting second reception status information via the communication unit in response to the connection change; the second reception status information is information that identifies received data or unreceived data among data transmitted to the first communication device or the second communication device; 7. The wireless communication device according to claim 6.

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