WO2015117537A1 - 由辅基站和主基站执行的通信方法以及相应的基站 - Google Patents

由辅基站和主基站执行的通信方法以及相应的基站 Download PDF

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Publication number
WO2015117537A1
WO2015117537A1 PCT/CN2015/070788 CN2015070788W WO2015117537A1 WO 2015117537 A1 WO2015117537 A1 WO 2015117537A1 CN 2015070788 W CN2015070788 W CN 2015070788W WO 2015117537 A1 WO2015117537 A1 WO 2015117537A1
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WIPO (PCT)
Prior art keywords
base station
data transmission
downlink data
pdcp pdu
status message
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PCT/CN2015/070788
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English (en)
French (fr)
Inventor
肖芳英
刘仁茂
Original Assignee
夏普株式会社
肖芳英
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Application filed by 夏普株式会社, 肖芳英 filed Critical 夏普株式会社
Priority to JP2016548148A priority Critical patent/JP2017508364A/ja
Priority to EP15745793.8A priority patent/EP3104632B1/en
Priority to US15/116,761 priority patent/US10355826B2/en
Publication of WO2015117537A1 publication Critical patent/WO2015117537A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/1607—Details of the supervisory signal
    • H04L1/1621—Group acknowledgement, i.e. the acknowledgement message defining a range of identifiers, e.g. of sequence numbers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/1607—Details of the supervisory signal
    • H04L1/1614—Details of the supervisory signal using bitmaps
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/1607—Details of the supervisory signal
    • H04L1/1642—Formats specially adapted for sequence numbers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1867—Arrangements specially adapted for the transmitter end
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1809—Selective-repeat protocols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1829—Arrangements specially adapted for the receiver end
    • H04L1/1848—Time-out mechanisms
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00—Arrangements for detecting or preventing errors in the information received
    • H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
    • H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
    • H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
    • H04L1/1829—Arrangements specially adapted for the receiver end
    • H04L1/1864—ARQ related signaling
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W80/00—Wireless network protocols or protocol adaptations to wireless operation
    • H04W80/02—Data link layer protocols
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/02—Hierarchically pre-organised networks, e.g. paging networks, cellular networks, WLAN [Wireless Local Area Network] or WLL [Wireless Local Loop]
    • H04W84/04—Large scale networks; Deep hierarchical networks
    • H04W84/042—Public Land Mobile systems, e.g. cellular systems

Definitions

  • the present invention relates to mobile communications, and in particular, to a method for reporting a downlink data transmission state by a secondary base station to a primary base station, a method for deleting a packet data convergence protocol protocol data unit PDCP PDU by a primary base station as early as possible, and corresponding primary and secondary base stations.
  • the Layer 2 User-Plane Protocol Stack of the 3GPP Partnership (3GPP) Long Term Evolution (LTE) system consists of three sub-layers, from high to low: Packet Data Convergence Protocol (Packet Data Convergence Protocol, PDCP) layer, Radio Link Control (RLC) layer, and Media Access Control layer.
  • Packet Data Convergence Protocol Packet Data Convergence Protocol
  • RLC Radio Link Control
  • Media Access Control layer Media Access Control
  • a Service Data Unit (SDU) is received from a higher layer to provide services for the layer
  • PDU Protocol Data Unit
  • the RLC layer receives packets from the PDCP. These packets are PDCP PDUs for the PDCP layer but RLC SDUs for the RLC layer.
  • the process is reversed, with each layer sending an SDU to the upper layer and the upper layer receiving it as a PDU.
  • the PDCP SDU is mapped to a PDCP PDU after IP header compression (Header Compression), encryption, and addition of a PDCP Header.
  • the RLC SDU is mapped into RLC PDUs by performing segmentation and/or concatenates according to the size specified by the MAC layer and adding an RLC header (RLC Header).
  • the PDCP SDU is identified by a PDCP sequence number (SN), the PDCP SDU has the same sequence number as the corresponding PDCP PDU and the RLC SDU, and the RLC PDU is identified by the RLC sequence number.
  • each radio bearer has a PDCP entity and an RLC entity.
  • Each base station also known as a NodeB or evolved NodeB (eNB)
  • each user equipment has one MAC entity.
  • the RLC entity in the base station or the user equipment sends the RLC PDU corresponding to each segment of the RLC SDU
  • the PDCP PDU is sent to the PDCP entity in the same base station or the user equipment.
  • the PDCP entity deletes the corresponding PDCP PDU, and releases the retransmission buffer of the PDCP entity to receive more PDCP SDUs from the upper layer.
  • the user equipment can be a user Terminal, user node, mobile terminal or tablet.
  • the 3GPP LTE Release 12 standard under development includes standardization work for user equipments having dual connectivity capabilities, a primary base station (Master eNB, MeNB), and a secondary base station (Secondary eNB, SeNB).
  • the primary base station is responsible for maintaining the Radio Resource Management (RRM) measurement configuration of the user equipment and requesting the secondary base station to provide additional equipment for the user equipment based on the received measurement report or traffic conditions or bear type. Resources (the coverage of the secondary base station is called the serving cell serving cells of the user equipment).
  • RRM Radio Resource Management
  • the secondary base station After receiving the request from the primary base station, the secondary base station configures the serving cell for the user equipment or rejects the request due to insufficient resources.
  • the option 3C shown in FIG. 1 has the following features: (1) the primary base station communicates with the Serving Gateway (S-GW) through the S1-U interface; (2) the bearer is separated in the primary base station; (3) for the separated bearer (split bearer), there are corresponding RLC entities in the primary base station and the secondary base station.
  • the RLC entity located at the secondary base station interacts with the upper layer (ie, the PDCP entity located at the primary base station) through the X2 interface.
  • the PDCP entity and the RLC entity are in the same base station, and after the RLC SDU is successfully transmitted, the PDCP SDU and the PDCP PDU corresponding to the successfully transmitted RLC SDU may be deleted at the same time, where the process is internal to the base station.
  • the PDCP entity corresponding to the split bearer and one of the RLC entities are located in the primary base station, and the other RLC entity is located in the secondary base station.
  • the existing non-dual-connection deployment solution cannot solve the problem of deleting the corresponding PDCP PDU and the PDCP SDU in the primary base station when the PDCP PDU successfully transmitted in the secondary base station is deleted, so that the successfully transmitted PDCP SDU and PDCP PDU are in the retransmission buffer. It is saved for a long time until the deletion timer (discardtimer) of the PDCP SDU expires, which causes the storage space to be wasted.
  • the PDCP SDU and PDCP PDUs that have been successfully transmitted in the retransmission buffer occupy a large amount of storage space for a long time.
  • the rate of sending PDCP SDUs is higher, the PDCP retransmission buffer is successfully sent but not expired.
  • the PDCP SDU is full, and the newly arrived PDCP SDU is discarded, thereby affecting the reliability of the wireless link.
  • the present invention aims to provide a mechanism for enabling a primary base station to delete a PDCP PDU that has been successfully transmitted by a secondary base station.
  • a first aspect of the present invention provides a communication method performed by a secondary base station, comprising the steps of: a secondary base station transmitting a PDCP PDU from a primary base station to a user equipment; and a secondary base station transmitting a downlink data transmission to the primary base station.
  • the status message, the downlink data transmission status message includes a sequence number of at least one PDCP PDU that has been successfully transmitted.
  • the method according to the first aspect of the present invention may further include the step of: determining, by the secondary base station, whether to send a downlink data transmission status message to the primary base station based on whether at least one condition is met.
  • the at least one condition includes: the number of successfully sent PDCP PDUs reaches a set value; the set timer expires; and the difference between the maximum and minimum sequence numbers of the successfully transmitted PDCP PDUs is greater than or equal to the set value Bitmap length.
  • a second aspect of the present invention provides a secondary base station, including a data transmitting unit and a downlink data transmission status message transmitting unit.
  • the data sending unit is configured to send a PDCP PDU.
  • the downlink data transmission status message sending unit is configured to send a PDCP PDU to the primary base station to send a downlink data transmission status message after the at least one PDCP PDU is successfully sent, where the downlink data transmission status includes at least one successfully sent PDCP PDU. serial number.
  • the secondary base station may further include a determining unit.
  • the determining unit is configured to determine whether to send a downlink data transmission status message to the primary base station according to whether the following at least one condition is met: the number of successfully sent PDCP PDUs reaches a set value; the set timer expires; And the difference between the maximum and minimum sequence numbers of the successfully transmitted PDCP PDU is greater than or equal to the set bitmap length.
  • a third aspect of the present invention provides a method performed by a primary base station, comprising the steps of: a primary base station receiving a downlink data transmission status message from a secondary base station; and a primary base station deleting the primary base station according to the downlink data transmission status message PDCP PDU.
  • a fourth aspect of the present invention provides a primary base station, including a downlink data transmission status message receiving unit and a PDCP PDU deleting unit.
  • the downlink data transmission status message receiving unit is configured to receive a downlink data transmission status message from the secondary base station, where the downlink data transmission status message includes a sequence number of at least one successfully transmitted packet data convergence protocol protocol data unit PDCP PDU.
  • the PDCP PDU deleting unit is configured to delete the PDCP PDU stored in the primary base station according to the downlink data transmission status message.
  • the primary base station can delete the corresponding PDCP PDU as soon as possible, thereby saving the storage space of the primary base station to receive more service data units from the upper layer.
  • 1 is a schematic diagram of a dual connectivity deployment option 3C given in 3GPP TR 36.842;
  • FIG. 2 is a sequence diagram showing a communication procedure for enabling a primary base station to delete a secondary base station that has successfully transmitted a PDCP PDU according to the present invention
  • FIG. 3 is a flow chart showing a method for reporting a downlink data transmission state by a secondary base station to a primary base station according to the present invention
  • FIG. 4 is a flow chart showing a method of deleting a PDCP PDU by a primary base station as early as possible according to the present invention
  • FIG. 5 is a flowchart illustrating a method of reporting a downlink data transmission state by a secondary base station to a primary base station according to an exemplary embodiment of the present invention
  • FIG. 6 is a flowchart illustrating a method of reporting a downlink data transmission state by a secondary base station to a primary base station according to another exemplary embodiment of the present invention
  • FIG. 7 is a schematic diagram showing a bitmap included in a downlink data transmission status message
  • FIG. 8 is a flowchart illustrating a method of reporting a downlink data transmission state by a secondary base station to a primary base station according to still another exemplary embodiment of the present invention.
  • FIG. 9 is a block diagram showing an example structure of a secondary base station according to the present invention.
  • Figure 10 is a block diagram showing an example structure of a primary base station according to the present invention.
  • the following is an example application of the LTE Rel-12 mobile communication system and its subsequent evolved version. Environment, various embodiments in accordance with the present invention are specifically described. However, it should be noted that the present invention is not limited to the following embodiments, but can be applied to more other wireless communication systems, such as future 5G cellular communication systems.
  • the implementation example of the technical solution of the present invention is described herein only for the case where the primary base station and one secondary base station cooperate to provide communication services for the user equipment, the technical solution of the present invention will be equally applicable to the primary base station and one. The above secondary base station cooperates to provide a communication service for the user equipment.
  • step 210 the secondary base station transmits a PDCP PDU from the primary base station to the user equipment.
  • step 220 the secondary base station sends a downlink data transmission status message to the primary base station through the X2 interface, where the downlink data transmission status message includes a sequence number of at least one successfully transmitted PDCP PDU.
  • step 230 the primary base station deletes the PDCP PDU stored in the primary base station according to the received downlink data transmission status message.
  • the primary base station determines whether the PDCP PDU and/or the corresponding PDCP SDU indicated in the downlink data transmission status message are still stored locally, if the PDCP PDU and/or the corresponding PDCP SDU indicated in the downlink data transmission status message. Also stored locally, the PDCP PDU and/or the corresponding PDCP SDU are deleted.
  • the downlink data transmission status message may only include one PDCP PDU sequence number. In this case, whenever the secondary base station successfully transmits a PDCP PDU from the primary base station, an indication message containing the serial number of the PDCP PDU is sent to the primary base station.
  • the secondary base station can determine whether the primary base station is satisfied.
  • the condition for transmitting the downlink data transmission status message avoids sending the downlink data transmission status message to the primary base station too frequently.
  • the condition that the secondary base station sends the downlink data transmission status message to the primary base station includes at least one of the following: the number of successfully sent PDCP PDUs reaches a set number; the set timer Expired; or the difference between the maximum and minimum sequence numbers of PDCP PDUs that have been successfully sent reaches the set bitmap length.
  • the set number of PDCP PDUs, the timer period of the timer, or the bitmap length may be determined according to factors such as a transmission rate of the radio link, a processing capability of the primary base station, and a timing period of a PDCP SDU deletion timer in the primary base station.
  • the indication message that the PDCP PDU is successfully sent may include one or more successfully transmitted PDCP PDU sequence numbers and/or bitmaps, and the bitmap length may be a fixed length or a variable length.
  • step 310 the secondary base station transmits the PDCP PDU from the primary base station to the user equipment.
  • step 320 the secondary base station sends a downlink data transmission status message to the primary base station, where the downlink data transmission status message includes a sequence number of at least one successfully transmitted PDCP PDU.
  • the primary base station receives a downlink data transmission status message from the secondary base station, where the downlink data transmission status message includes at least one successfully transmitted.
  • the sequence number of the packet data convergence protocol protocol data unit PDCP PDU is the sequence number of the packet data convergence protocol protocol data unit.
  • the primary base station deletes the PDCP PDU stored in the primary base station according to the downlink data transmission status message.
  • FIG. 5 is a schematic flowchart diagram of an embodiment in which the secondary base station determines the number of successfully transmitted PDCP PDUs and the downlink data transmission status message includes multiple successfully transmitted PDCP PDU sequence numbers.
  • the secondary base station sets the SN-number value to 0 and starts the first timer.
  • the SN-number indicates the number of PDCP PDUs from the primary base station that have been successfully sent.
  • the value of the first timer may be configured in the RLC entity of the secondary base station by using the inter-base station radio resource control message, and may be according to the wireless link.
  • the transmission rate, the processing capability of the primary base station, and the timing period of the PDCP SDU deletion timer in the primary base station are determined.
  • step 503 the secondary base station determines whether the SN-number value is equal to the set number of PDCP PDUs to be successfully transmitted. If it is equal to the set number of PDCP PDUs to be successfully sent, Then step 504 is performed, otherwise step 506 is performed.
  • the secondary base station sends a downlink data transmission status message to the primary base station through the X2 interface, where the downlink data transmission status message includes the sequence number of the successfully transmitted PDCP PDU.
  • the downlink data transmission status message further includes the number of PDCP PDUs that have been successfully sent.
  • step 505 the secondary base station determines whether the PDCP PDUs from the primary base station have all been transmitted. If the transmission is not completed, step 501 is executed to continue to send the PDCP PDU. End if it has been sent.
  • step 506 the secondary base station determines whether the first timer expires. If the first timer expires, step 504 is performed; otherwise, step 507 is performed.
  • step 507 the secondary base station determines whether the PDCP PDUs from the primary base station have all been transmitted. If not, the process proceeds to step 502 to continue transmitting the PDCP PDU. If the transmission has been completed, step 508 is executed to send a downlink data transmission status message to the primary base station.
  • the secondary base station instructs the primary base station to delete the PDCP PDU whenever the set number of PDCP PDUs is successfully transmitted.
  • FIG. 6 is a schematic flowchart diagram of an embodiment in which a secondary base station uses a set timing period as a judgment condition and the downlink data transmission status message includes a plurality of successfully transmitted PDCP PDU sequence numbers.
  • the secondary base station starts a second timer.
  • the value of the second timer may be configured in an RLC entity of the secondary base station by using an inter-base station radio resource control message, and may be based on a transmission rate of the radio link, a processing capability of the primary base station, and a PDCP SDU deletion timer in the primary base station. Factors such as the timing period are determined.
  • step 602 the secondary base station successfully sends a PDCP PDU from the primary base station, and locally stores the serial number of the successfully transmitted PDCP PDU.
  • step 603 the secondary base station determines whether the second timer expires. If the second timer expires, step 604 is performed; otherwise, step 606 is performed.
  • the secondary base station sends a downlink data transmission status message to the primary base station through the X2 interface.
  • the downlink data transmission status message includes a sequence number of the successfully transmitted PDCP PDU.
  • the downlink data transmission status message further includes the number of PDCP PDUs that have been successfully sent.
  • step 605 the secondary base station determines whether the PDCP PDUs from the primary base station have all been sent. Finished. If the transmission is not completed, step 601 is executed to continue to send the PDCP PDU. End if it has been sent.
  • step 606 the secondary base station determines whether the PDCP PDUs from the primary base station have all been transmitted. If the transmission is not completed, step 602 is performed to continue to send the PDCP PDU. If the transmission has been completed, step 607 is executed to send a downlink data transmission status message to the primary base station through the X2 interface.
  • the secondary base station instructs the primary base station to delete the PDCP PDU whenever the second timer expires.
  • Figure 7 illustrates an example embodiment of a bitmap structure.
  • the length of the bitmap shown in Figure 7 can be fixed or variable.
  • a bitmap indication bit value of 1 indicates that the corresponding PDCP PDU has been successfully transmitted, and a value of 0 indicates that the corresponding PDCP PDU was not successfully transmitted.
  • All the bits corresponding to the PDCP PDUs sent by the primary base station RLC entity have a value of 0.
  • 10 PDCP SDUs in the primary base station need to be sent, and PDCP SDUs with sequence numbers 1, 2, 5, 7, and 9 are sent to the RLC entity located at the primary base station, and the sequence is 0, 3, 4, and 6.
  • the PDCP SDU of 8 is sent to the RLC entity located at the secondary base station.
  • the bitmap in the downlink data transmission status message can be as shown in FIG. 7.
  • the sequence numbers of the successfully transmitted PDCP PDUs corresponding to the bitmap shown in FIG. 7 are 4 and 6, respectively.
  • the PDCP SDU with sequence number 5 is sent by the RLC entity in the primary base station. Therefore, the value of the bitmap indication bit corresponding to the PDCP PDU with sequence number 5 is zero.
  • the PDCP PDU sequence number with sequence number 3 has been listed in the Minimum Sequence Number field of the successfully transmitted SDU in the header of the Downstream Data Transfer Status message and therefore need not be indicated in the bitmap.
  • the value of the bitmap indication bit can be any two distinguishable values, including but not limited to ⁇ 0, 1 ⁇ , ⁇ True, False ⁇ .
  • the embodiment of the downlink data transmission status message includes a variable length bitmap and the implementation of the downlink data transmission status message shown in FIG. 6 includes multiple successfully transmitted PDCP PDU sequence numbers.
  • the flowchart of the example is the same (that is, the condition of determining whether to send the indication message is still determined by the set timing period), but the downlink data transmission status message sent in step 604 includes: the minimum sequence number of the successfully transmitted PDCP PDU and the indication Whether the PDCP PDU following the minimum sequence number PDCP PDU is successfully transmitted by the secondary base station.
  • the bitmap is generated according to the sequence number of the successfully transmitted PDCP PDU saved in step 602. Specifically, the bitmap indication bit corresponding to the successfully transmitted PDCP PDU saved locally by the secondary base station is 1, and the other bitmap indication bits are 0.
  • the downlink data transmission status message includes a bitmap length degree.
  • FIG. 8 shows a flow diagram of an example embodiment of a fixed length bitmap in the downlink data transmission status message.
  • the secondary base station starts a third timer and sets the minimum and maximum sequence numbers of the successfully transmitted PDCP PDUs to initial values.
  • the value of the third timer may be configured in an RLC entity of the secondary base station by using an inter-base station radio resource control message, and may be based on a transmission rate of the radio link, a processing capability of the primary base station, and a PDCP SDU deletion timer in the primary base station. The timing period and other factors are determined.
  • the initial value is a special value different from the serial number of the PDCP PDU to be transmitted, for example, -1, infinity, infinity.
  • step 8002 the secondary base station successfully transmits a PDCP PDU from the primary base station, locally stores the sequence number of the successfully transmitted PDCP PDU, and updates the values of the minimum and maximum sequence numbers of the successfully transmitted PDCP PDU.
  • the minimum sequence number of the successfully transmitted PDCP PDU is an initial value
  • the minimum sequence number of the successfully transmitted PDCP PDU is set to the locally saved successfully transmitted PDCP PDU sequence number. If the minimum sequence number of the successfully transmitted PDCP PDU is greater than the locally saved successfully transmitted PDCP PDU sequence number, the minimum sequence number of the successfully transmitted PDCP PDU is updated to the locally saved successfully sent SDU. serial number. If the maximum sequence number of the successfully transmitted PDCP PDU is the initial value or the maximum sequence number of the successfully transmitted PDCP PDU is smaller than the locally saved successfully transmitted PDCP PDU sequence number, the maximum sequence number of the successfully transmitted PDCP PDU is updated to local save. The PDCP PDU sequence number has been successfully sent.
  • step 8003 the secondary base station determines whether the difference between the maximum and minimum sequence numbers of the PDCP PDUs that have been successfully transmitted is equal to the set bitmap length. If it is equal to the set bitmap length, step 8004 is performed, otherwise step 8006 is performed.
  • the secondary base station sends a downlink data transmission status message to the primary base station through the X2 interface.
  • the downlink data transmission status message includes: a minimum sequence number of the successfully transmitted PDCP PDU, and a bitmap indicating whether the PDCP PDU after the minimum sequence number PDCP PDU is successfully transmitted by the secondary base station.
  • the bitmap is generated according to the sequence number of the successfully transmitted PDCP PDU saved in step 8002. Specifically, the bitmap indication bit corresponding to the successfully transmitted PDCP PDU saved locally by the secondary base station is 1, and the other bitmap indication bits are 0.
  • step 8005 the secondary base station determines whether the PDCP PDU from the primary base station is all Send it. If not, the process proceeds to step 8001 to continue transmitting the PDCP PDU. End if it has been sent.
  • step 8006 the secondary base station determines whether the difference between the maximum and minimum sequence numbers of the PDCP PDUs that have been successfully transmitted is greater than the set bitmap length. If it is greater than the set bitmap length, step 8009 is performed, otherwise step 8007 is performed.
  • step 8007 the secondary base station determines whether the third timer expires. If the third timer expires, step 8004 is performed; otherwise, step 8008 is performed.
  • step 8008 the secondary base station determines whether the PDCP PDUs from the primary base station have all been transmitted. If not, the process proceeds to step 8002 to continue transmitting the PDCP PDU. End if it has been sent.
  • the secondary base station sends a downlink data transmission status message to the primary base station through the X2 interface.
  • the downlink data transmission status message includes: a minimum sequence number of the successfully transmitted PDCP PDU, and a bitmap indicating whether the PDCP PDU after the minimum sequence number PDCP PDU is successfully transmitted by the secondary base station.
  • the bitmap is generated according to the sequence number of the successfully transmitted PDCP PDU saved in step 8002. Specifically, the bitmap indication bit corresponding to the successfully transmitted PDCP PDU saved locally by the secondary base station is 1, and the other bitmap indication bits are 0.
  • the secondary base station also restarts the timer, deletes the locally saved PDCP PDUs other than the recently transmitted PDCP PDU, and sets the maximum and minimum sequence numbers of the successfully transmitted PDCP PDUs.
  • the serial number of the PDCP PDU was successfully transmitted recently.
  • step 8010 the secondary base station determines whether the PDCP PDUs from the primary base station have all been transmitted. If the transmission is not completed, step 8002 is performed to continue to send the PDCP PDU; otherwise, step 8011 is performed.
  • the secondary base station sends a downlink data transmission status message to the primary base station through the X2 interface.
  • the downlink data transmission status message includes a minimum sequence number of the successfully transmitted PDCP PDU.
  • the downlink data transmission status message further includes a bitmap, where each indicator bit of the bitmap is 0.
  • the bitmap length may be configured for the secondary base station RLC entity via the X2 interface by using a radio resource control message between the base stations.
  • the RRC message may be sent in a request message sent by the primary base station to the secondary base station to allocate additional resources to the user equipment or sent as an independent message.
  • the maximum number of PDCP PDUs that have been successfully sent The difference between the minimum sequence number and the minimum sequence number reaches the set bitmap length, and the secondary base station instructs the primary base station to delete the PDCP PDU.
  • FIG. 9 is a block diagram showing the schematic configuration of the secondary base station 900.
  • the secondary base station 900 includes a data transmitting unit 910 and a downlink data transmission status message transmitting unit 930.
  • the data sending unit 910 is configured to send a PDCP PDU to the user equipment.
  • the downlink data transmission status message sending unit 930 is configured to send a downlink data transmission status message to the primary base station, where the downlink data transmission status message includes a sequence number of at least one successfully transmitted PDCP PDU.
  • the secondary base station 900 may further include a determining unit 920.
  • the determining unit 920 is configured to determine, according to whether the following at least one condition is met, whether to send a downlink data transmission status message to the primary base station: the number of successfully sent PDCP PDUs reaches a set value; the set timer expires; And the difference between the maximum and minimum sequence numbers of the successfully transmitted PDCP PDU is greater than or equal to the set bitmap length.
  • FIG. 10 is a block diagram showing the schematic configuration of the primary base station 1000.
  • the primary base station 1000 includes a downlink data transmission status message receiving unit 1010 and a PDCP PDU deleting unit 1020.
  • the downlink data transmission status message receiving unit is configured to receive a downlink data transmission status message from the secondary base station, where the downlink data transmission status message includes a sequence number of at least one successfully transmitted packet data convergence protocol protocol data unit PDCP PDU.
  • the PDCP PDU deleting unit is configured to delete the PDCP PDU stored in the primary base station according to the downlink data transmission status message.
  • the primary base station can delete the corresponding PDCP PDU as soon as possible, thereby saving the storage space of the primary base station to receive more service data units from the upper layer.

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Abstract

本申请公开了一种由辅基站向主基站报告下行数据传输状态的方法。所述方法包括：辅基站向用户设备发送来自主基站的PDCP PDU；以及辅基站向主基站发送下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU序列号。本申请还公开了一种由主基站尽早删除PDCP PDU的方法，包括：主基站从辅基站接收下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU的序列号；以及主基站根据所述下行数据传输状态消息，删除主基站中存储的分组数据汇聚协议协议数据单元PDCP PDU。本申请还公开了相应的主基站和辅基站。

Description

由辅基站和主基站执行的通信方法以及相应的基站 技术领域
本发明涉及移动通信，具体地，涉及由辅基站向主基站报告下行数据传输状态的方法、由主基站尽早删除分组数据汇聚协议协议数据单元PDCP PDU的方法以及相应的主基站和辅基站。
背景技术
在第三代伙伴计划(3GPP)长期演进(LTE)系统的层2(layer 2)用户平面协议栈(User-Plane Protocol Stack)由3个子层组成，从高到低依次为：分组数据汇聚协议(Packet Data Convergence Protocol，PDCP)层、无线链路控制(Radio Link Control，RLC)层和媒体接入控制(Media Access Control)层。在发送端，从高层接收服务数据单元(Service Data Unit，SDU)，为该层提供业务，并向低层输出协议数据单元(Protocol Data Unit，PDU)。例如：RLC层接收来自PDCP的分组(packet)。这些分组对PDCP层来说是PDCP PDU，但对RLC层来说是RLC SDU。在接收端，该过程是相反的，每层向上层发送SDU，上层作为PDU接收。PDCP SDU经IP报头压缩(Header Compression)、加密并附加PDCP分组头(PDCP Header)后映射成为PDCP PDU。RLC SDU按照MAC层指定的大小进行分块/串联(segments and/or concatenates)并增加RLC包头(RLC Header)后映射为RLC PDU。PDCP SDU由PDCP序列号(sequence number，SN)标识，PDCP SDU与对应的PDCP PDU和RLC SDU具有相同的序列号，RLC PDU由RLC序列号标识。
3GPP LTE版本11中，每一无线承载(bearer)有一个PDCP实体(entity)和一个RLC实体。每个基站(也称为NodeB或演进NodeB(eNB))和每个用户设备(UE)均有一个MAC实体。基站或用户设备中的RLC实体将RLC SDU的各个片段(segment)对应的RLC PDU发送成功后，向位于同一基站或用户设备中的PDCP实体发送PDCP PDU发送成功的指示。当PDCP实体接收到所述PDCP PDU发送成功的指示后，删除对应的PDCP PDU，释放PDCP实体的重传缓冲区(retransmission buffer)以便从上层接收更多的PDCP SDU。这里，用户设备可以是用户 终端，用户节点，移动终端或平板电脑。
正在制定中的3GPP LTE版本12标准中，包含关于具有双连接(dual connectivity)能力的用户设备、主基站(Master eNB，MeNB)、辅基站(Secondary eNB，SeNB)的标准制定工作。主基站负责维护用户设备的无线资源管理(Radio Resource Management，RRM)测量配置并且基于接收到的测量报告或流量状况(traffic conditions)或承载类型(bear type)向辅基站请求为用户设备提供额外的资源(该辅基站的覆盖范围称为用户设备的服务小区serving cells)。辅基站接收到主基站的请求后为用户设备配置服务小区或因没有足够的资源而拒绝所述请求。
基于承载分离(bearer split)的不同方式和用户平面协议栈的不同，在3GPP TSG-RAN2第83bis次会议上，确定1A和3C两种用户平面架构(User-plane Architecture)作为双连接部署方式的标准化选项。图1示出的选项3C具有如下特征：(1)主基站通过S1-U接口与业务网关(Serving Gateway，S-GW)通信；(2)承载在主基站中分离；(3)对于分离承载(split bearer)，在主基站和辅基站中都有对应RLC实体(entity)。在选项3C中，位于辅基站的RLC实体与上层(即位于主基站的PDCP实体)通过X2接口进行交互。
在非双连接部署方案中，由于PDCP实体和RLC实体处于同一基站中，当RLC SDU发送成功后，可同时删除所述成功发送的RLC SDU对应的PDCP SDU和PDCP PDU，所述流程为基站内部实现，无需标准化。但是，在双连接部署方案选项3C中，分离承载对应的PDCP实体和其中一个RLC实体位于主基站中，而另一个RLC实体位于辅基站中。现有非双连接部署方案无法解决在删除辅基站中成功发送的PDCP PDU时，删除主基站中对应PDCP PDU和PDCP SDU的问题，从而使得已经发送成功的PDCP SDU和PDCP PDU在重传缓冲区长时间保存，直至所述PDCP SDU的删除计时器(discardtimer)到期才被删除，导致存储空间浪费。此外，因已经发送成功的PDCP SDU和PDCP PDU在重传缓冲区长时间保存占用大量存储空间，当上层发送PDCP SDU的速率较高时，PDCP重传缓冲区被已经发送成功但未到期的PDCP SDU占满，导致新到达的PDCP SDU被丢弃，从而影响无线链路的可靠性。
发明内容
鉴于现有技术中存在的以上问题，本发明旨在提供一种机制，使得主基站能够删除辅基站已成功发送的PDCP PDU。
为实现上述目的，本发明的第一方面提供了一种由辅基站执行的通信方法，包括以下步骤：辅基站向用户设备发送来自主基站的PDCP PDU；以及辅基站向主基站发送下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU的序列号。
可选地，根据本发明第一方面的方法还可以包括以下步骤：辅基站基于是否满足至少一项条件，来判断是否向主基站发送下行数据传输状态消息。所述至少一项条件包括：已成功发送的PDCP PDU个数达到设定的值；设定的计时器到期；以及已成功发送的PDCP PDU的最大和最小序列号之差大于等于设定的位图长度。
本发明的第二方面提供了一种辅基站，包括数据发送单元和下行数据传输状态消息发送单元。所述数据发送单元用于发送PDCP PDU。所述下行数据传输状态消息发送单元用于在成功发送了至少一个PDCP PDU后，向主基站发送PDCP PDU发送下行数据传输状态消息，所述下行数据传输状态包括至少一个已成功发送的PDCP PDU的序列号。
可选地，根据本发明第二方面的辅基站还可以包括判断单元。所述判断单元用于基于是否满足以下至少一项条件，来判断是否向主基站发送下行数据传输状态消息：已成功发送的PDCP PDU个数达到设定的值；设定的计时器到期；以及已成功发送的PDCP PDU的最大和最小序列号之差大于等于设定的位图长度。
本发明的第三方面提供了一种由主基站执行的方法，包括以下步骤：主基站从辅基站接收下行数据传输状态消息；以及主基站根据所述下行数据传输状态消息，删除主基站中存储的PDCP PDU。
本发明的第四方面提供了一种主基站，包括下行数据传输状态消息接收单元和PDCP PDU删除单元。所述下行数据传输状态消息接收单元用于从辅基站接收下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的分组数据汇聚协议协议数据单元PDCP PDU的序列号。所述PDCP PDU删除单元用于根据所述下行数据传输状态消息，删除主基站中存储的PDCP PDU。
通过采用本发明提出的技术方案，在辅基站成功发送PDCP PDU之后，主基站能够尽早删除对应的PDCP PDU，从而能够节省主基站的存储空间，以从上层接收更多的服务数据单元。
附图说明
通过下文结合附图的详细描述，本发明的上述和其它特征将会变得更加明显，其中：
图1为3GPP TR36.842中给出的双连接部署选项3C的示意图；
图2是示出了根据本发明的使得主基站能够删除辅基站已成功发送PDCP PDU的通信过程的序列图；
图3是示出了根据本发明的由辅基站向主基站报告下行数据传输状态的方法的流程图；
图4是示出了根据本发明的由主基站尽早删除PDCP PDU的方法的流程图；
图5是示出了根据本发明一示例实施例的由辅基站向主基站报告下行数据传输状态的方法的流程图；
图6是示出了根据本发明另一示例实施例的由辅基站向主基站报告下行数据传输状态的方法的流程图；
图7是示出了下行数据传输状态消息中包含的位图的示意图；
图8是示出了根据本发明又一示例实施例的由辅基站向主基站报告下行数据传输状态的方法的流程图；
图9为根据本发明的辅基站的示例结构的框图；以及
图10为根据本发明的主基站的示例结构的框图。
具体实施方式
下面，通过结合附图对本发明的具体实施例的描述，本发明的原理和实现将会变得明显。应当注意的是，本发明不应局限于下文所述的具体实施例。另外，为了简便起见，省略了对与本发明没有直接关联的公知技术的详细描述，以防止对本发明的理解造成混淆。
下文以LTE Rel-12移动通信系统及其后续的演进版本作为示例应用 环境，具体描述了根据本发明的多个实施例。然而，需要指出的是，本发明不限于以下实施例，而是可适用于更多其它的无线通信系统，例如今后的5G蜂窝通信系统。另外，虽然此处仅针对主基站和一个辅基站协同为用户设备提供通信服务的情形描述了本发明技术方案的实现示例，本领域技术将意识到本发明的技术方案同样适用于主基站和一个以上的辅基站协同为用户设备提供通信服务的情形。
首先，参照图2，描述根据本发明的使得主基站能够删除辅基站已成功发送的PDCP PDU所对应的PDCP PDU的通信过程。如图所示，起初，在步骤210，辅基站向用户设备发送来自主基站的PDCP PDU。接着，在步骤220，辅基站通过X2接口向主基站发送下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU的序列号。最后，在步骤230，主基站根据接收到的下行数据传输状态消息，删除主基站中存储的PDCP PDU。具体地，主基站判断本地是否还在存储所述下行数据传输状态消息中所指示的PDCP PDU和/或对应的PDCP SDU，如果下行数据传输状态消息中指示的PDCP PDU和/或对应的PDCP SDU还在本地存储，则删除所述PDCP PDU和/或对应的PDCP SDU。
在具体实现中，所述下行数据传输状态消息可能仅可包含一个PDCP PDU序列号。在该情况下，每当辅基站成功发送一个来自主基站的PDCP PDU，就向主基站发送包含该PDCP PDU的序列号的指示消息。
在下行数据传输状态消息能够承载更多信息(例如，多个PDCP PDU的序列号和/或将于稍后参照图7详细说明的位图)的情况下，辅基站可以判断是否满足向主基站发送下行数据传输状态消息的条件，避免过于频繁地向主基站发送下行数据传输状态消息。
在本发明的实施例中，所述辅基站向主基站发送下行数据传输状态消息的条件包括以下至少一项：已成功发送的PDCP PDU的个数达到设定的个数；设定的计时器到期；或已成功发送的PDCP PDU的最大和最小序列号之差达到设定的位图长度。所述设定的PDCP PDU个数、计时器的计时周期或位图长度可以根据无线链路的传输速率、主基站的处理能力、主基站中PDCP SDU删除计时器的计时周期等因素来确定，并且通过基站间无线资源控制消息(inter-node RRC message)经由X2接口 进行配置。所述PDCP PDU发送成功的指示消息可以包含一个或多个已发送成功的PDCP PDU序列号和/或位图，所述位图长度可以是固定长度或可变长度。
图3和图4分别示出了在图2所示的通信过程中由辅基站和主基站执行的方法的流程图。如图3所示，在由辅基站执行的向主基站报告下行数据传输状态的方法中，起初，在步骤310，辅基站向用户设备发送来自主基站的PDCP PDU。在步骤320，辅基站向主基站发送下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU的序列号。
如图4所示，在由主基站执行的尽早删除PDCP PDU的方法中，在步骤410，主基站从辅基站接收下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的分组数据汇聚协议协议数据单元PDCP PDU的序列号。接着，在步骤420，主基站根据所述下行数据传输状态消息，删除主基站中存储的PDCP PDU。
以下，参照图5至8，详细描述根据三个示例实施例的由辅基站向主基站报告下行数据传输状态的方法，其中，辅基站判断是否满足向主基站发送下行数据传输状态消息的条件，并且在每个实施例中采用不同的判断条件。
图5示出了辅基站以设定的发送成功的PDCP PDU个数为判断条件且所述下行数据传输状态消息中包含多个已成功发送的PDCP PDU序列号的实施例的流程示意图。
如图所示，在步骤501中，辅基站将SN-number值设置为0，并启动第一计时器。所述SN-number表示已成功发送的来自主基站的PDCP PDU个数，所述第一计时器的值可通过基站间无线资源控制消息配置到辅基站的RLC实体中，并且可以根据无线链路的传输速率、主基站的处理能力、主基站中PDCP SDU删除计时器的计时周期等因素来确定。
在步骤502中，辅基站成功发送一个来自主基站的PDCP PDU，本地保存所述成功发送的PDCP PDU的序列号，并使SN-number增1(即，SN-number＝SN-number+1)。
在步骤503中，辅基站判断SN-number值是否等于设定的需成功发送的PDCP PDU个数。如果等于设定的需成功发送的PDCP PDU个数， 则执行步骤504，否则执行步骤506。
在步骤504中，辅基站通过X2接口向主基站发送下行数据传输状态消息，所述下行数据传输状态消息中包含已成功发送的PDCP PDU的序列号。可选地，所述下行数据传输状态消息还包含已成功发送的PDCP PDU的个数。
在步骤505中，辅基站判断来自主基站的PDCP PDU是否已全部发送完。如果未发送完，则执行步骤501，继续发送PDCP PDU。如果已发送完，则结束。
在步骤506中，辅基站判断第一计时器是否到期。如果第一计时器到期，则执行步骤504；否则，执行步骤507。
在步骤507中，辅基站判断来自主基站的PDCP PDU是否已全部发送完。如果未发送完，则执行步骤502，继续发送PDCP PDU。如果已发送完，则执行步骤508，向主基站发送下行数据传输状态消息。
通过采用如图5所示的方法，每当成功发送了所设定个数的PDCP PDU，辅基站指示主基站删除PDCP PDU。
图6示出了辅基站以设定的计时周期为判断条件且所述下行数据传输状态消息中包含多个已成功发送的PDCP PDU序列号的实施例的流程示意图。
如图所示，在步骤601中，辅基站启动第二计时器。所述第二计时器的值可通过基站间无线资源控制消息配置到辅基站的RLC实体中，并且可以根据无线链路的传输速率、主基站的处理能力、主基站中PDCP SDU删除计时器的计时周期等因素来确定。
在步骤602中，辅基站成功发送一个来自主基站的PDCP PDU，本地保存所述成功发送的PDCP PDU的序列号。
在步骤603中，辅基站判断第二计时器是否到期。如果第二计时器到期，则执行步骤604；否则，执行步骤606。
在步骤604中，辅基站通过X2接口向主基站发送下行数据传输状态消息。所述下行数据传输状态消息中包含已成功发送的PDCP PDU的序列号。可选地，所述下行数据传输状态消息还包含已成功发送的PDCP PDU的个数。
在步骤605中，辅基站判断来自主基站的PDCP PDU是否已全部发 送完。如果未发送完，则执行步骤601，继续发送PDCP PDU。如果已发送完，则结束。
在步骤606中，辅基站判断来自主基站的PDCP PDU是否已全部发送完。如果未发送完，则执行步骤602，继续发送PDCP PDU。如果已发送完，则执行步骤607，通过X2接口向主基站发送下行数据传输状态消息。
通过采用如图6所示的方法，每当第二计时器到期，辅基站就指示主基站删除PDCP PDU。
图7示出了位图结构的示例实施例。图7所示位图的长度可以是固定或可变的。位图指示位值为1表示对应的PDCP PDU已发送成功，值为0表示对应的PDCP PDU未发送成功。所有通过主基站RLC实体发送的PDCP PDU对应的位取值均为0。举例来说，在主基站中有10个PDCP SDU需要发送，其中序列号为1、2、5、7、9的PDCP SDU发送给位于主基站的RLC实体，序列为0、3、4、6、8的PDCP SDU发送给位于辅基站的RLC实体。假设已发送成功的PDCP PDU的序列号最小为3，则下行数据传输状态消息中的位图可如图7所示。具体地，图7所示位图对应的已成功发送的PDCP PDU的序列号分别为4、6。因序列号为5的PDCP SDU通过主基站中的RLC实体发送，故序列号为5的PDCP PDU对应的位图指示位的值为0。序列号为3的PDCP PDU序列号已在下行数据传输状态消息的消息头中的已成功发送SDU的最小序列号字段中列出，故不需要在位图中指示。位图指示位的值可以是任意两个可区分的值，包括但不限于{0，1}、{True、False}。
在一实施例中，所述下行数据传输状态消息中包含可变长度位图的实施例与图6所示的所述下行数据传输状态消息中包含多个已成功发送的PDCP PDU序列号的实施例的流程图相同(即，仍以设定的计时周期为判断是否发送指示消息的条件)，但步骤604中发送的下行数据传输状态消息包含：已发送成功的PDCP PDU的最小序列号以及指示该最小序列号PDCP PDU之后的PDCP PDU是否由辅基站成功发送的位图。所述位图根据步骤602中保存的已成功发送PDCP PDU的序列号生成。具体地，辅基站本地保存的已成功发送PDCP PDU对应的位图指示位为1，其他位图指示位为0。可选地，所述下行数据传输状态消息包括位图长 度。
图8示出了所述下行数据传输状态消息中包含固定长度位图的示例实施例的流程图。
如图所示，在步骤8001中，辅基站启动第三计时器，并将已成功发送的PDCP PDU的最小和最大序列号设置为初始值。所述第三计时器的值可通过基站间无线资源控制消息配置到辅基站的RLC实体中，并且可可以根据无线链路的传输速率、主基站的处理能力、主基站中PDCP SDU删除计时器的计时周期等因素来确定。所述初始值为不同于待发送PDCP PDU序列号的特殊值，例如，为-1、无穷大，无穷小。
在步骤8002中，辅基站成功发送一个来自主基站的PDCP PDU，本地保存所述成功发送的PDCP PDU的序列号，并更新已成功发送的PDCP PDU的最小和最大序列号的值。
具体地，如果已成功发送的PDCP PDU的最小序列号为初始值，则将已成功发送的PDCP PDU的最小序列号置为所述本地保存的已成功发送PDCP PDU序列号。如果已成功发送的PDCP PDU的最小序列号大于所述本地保存的已成功发送的PDCP PDU序列号，则将已成功发送的PDCP PDU的最小序列号更新为所述本地保存的已成功发送的SDU序列号。如果已成功发送PDCP PDU的最大序列号为初始值或已成功发送PDCP PDU的最大序列号小于本地保存的已成功发送PDCP PDU序列号，则将已成功发送PDCP PDU的最大序列号更新为本地保存的已成功发送PDCP PDU序列号。
在步骤8003中，辅基站判断已成功发送的PDCP PDU的最大和最小序列号的差值是否等于设定的位图长度。如果等于设定的位图长度，则执行步骤8004，否则执行步骤8006。
在步骤8004中，辅基站通过X2接口向主基站发送下行数据传输状态消息。所述下行数据传输状态消息中包含：已成功发送的PDCP PDU的最小序列号、以及指示该最小序列号PDCP PDU之后的PDCP PDU是否由辅基站成功发送的位图。所述位图根据步骤8002中保存的已成功发送PDCP PDU的序列号生成。具体地，辅基站本地保存的已成功发送PDCP PDU对应的位图指示位为1，其他位图指示位为0。
在步骤8005中，辅基站判断来自主基站的PDCP PDU是否已全部 发送完。如果未发送完，则执行步骤8001，继续发送PDCP PDU。如果已发送完，则结束。
在步骤8006中，辅基站判断已成功发送的PDCP PDU的最大和最小序列号的差值是否大于设定的位图长度。如果大于设定的位图长度，则执行步骤8009，否则执行步骤8007。
在步骤8007中，辅基站判断第三计时器是否到期。如果第三计时器到期，则执行步骤8004；否则，执行步骤8008。
在步骤8008中，辅基站判断来自主基站的PDCP PDU是否已全部发送完。如果未发送完，则执行步骤8002，继续发送PDCP PDU。如果已发送完，则结束。
在步骤8009中，辅基站通过X2接口向主基站发送下行数据传输状态消息。所述下行数据传输状态消息中包含：已成功发送的PDCP PDU的最小序列号、以及指示该最小序列号PDCP PDU之后的PDCP PDU是否由辅基站成功发送的位图。所述位图根据步骤8002中保存的已成功发送PDCP PDU的序列号生成。具体地，辅基站本地保存的已成功发送PDCP PDU对应的位图指示位为1，其他位图指示位为0。在步骤8009中，辅基站还重启计时器，删除本地保存的除最近发送成功的PDCP PDU之外的其他已发送成功的PDCP PDU，并将已成功发送PDCP PDU的最大和最小序列号置为所述最近成功发送PDCP PDU序列号。
在步骤8010中，辅基站判断来自主基站的PDCP PDU是否已全部发送完。如果未发送完，则执行步骤8002，继续发送PDCP PDU；否则，执行步骤8011。
在步骤8011中，辅基站通过X2接口向主基站发送下行数据传输状态消息。所述下行数据传输状态消息中包含已成功发送的PDCP PDU的最小序列号。可选地，所述下行数据传输状态消息中还包含位图，所述位图各指示位均为0。
在本发明实施例中，所述位图长度可通过基站间的无线资源控制消息经由X2接口为辅基站RLC实体配置。所述无线资源控制消息可以携带在主基站向辅基站发送的为用户设备分配额外资源的请求消息中发送或作为独立的消息发送。
通过采用如图8所示的方法，每当已成功发送的PDCP PDU的最大 和最小序列号之差达到所设定的位图长度，辅基站就指示主基站删除PDCP PDU。
与上述由辅基站向主基站报告下行数据传输状态的方法相对应地，本发明还提出了相关的辅基站900。图9示出了该辅基站900的示意结构方框图。
如图9所示，根据本发明的辅基站900包括数据发送单元910和下行数据传输状态消息发送单元930。所述数据发送单元910用于向用户设备发送PDCP PDU。所述下行数据传输状态消息发送单元930用于向主基站发送下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU的序列号。
备选地，辅基站900还可以包括判断单元920。该判断单元920用于基于是否满足以下至少一项条件，来判断是否向主基站发送下行数据传输状态消息：已成功发送的PDCP PDU个数达到设定的值；设定的计时器到期；以及已成功发送的PDCP PDU的最大和最小序列号之差大于等于设定的位图长度。
与上述由主基站尽早删除PDCP PDU的方法相对应地，本发明还提出了相关的主基站1000。图10示出了该主基站1000的示意结构方框图。
如图10所示，根据本发明的主基站1000包括下行数据传输状态消息接收单元1010和PDCP PDU删除单元1020。所述下行数据传输状态消息接收单元用于从辅基站接收下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的分组数据汇聚协议协议数据单元PDCP PDU的序列号。所述PDCP PDU删除单元用于根据所述下行数据传输状态消息，删除主基站中存储的PDCP PDU。
通过采用本发明提出的技术方案，在辅基站成功发送PDCP PDU之后，主基站能够尽早删除对应的PDCP PDU，从而能够节省主基站的存储空间，以从上层接收更多的服务数据单元。
尽管以上已经结合本发明的优选实施例示出了本发明，但是本领域的技术人员将会理解，在不脱离本发明的精神和范围的情况下，可以对本发明进行各种修改、替换和改变。因此，本发明不应由上述实施例来限定，而应由所附权利要求及其等价物来限定。

Claims (19)

  1. 一种由辅基站执行的通信方法，包括以下步骤：
    辅基站向用户设备发送来自主基站的分组数据汇聚协议协议数据单元PDCP PDU；以及
    辅基站向主基站发送下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU的序列号。
  2. 根据权利要求1所述的方法，还包括以下步骤：
    辅基站基于是否满足以下至少一项条件，来判断是否向主基站发送下行数据传输状态消息：
    已成功发送的PDCP PDU个数达到设定的值；
    设定的计时器到期；以及
    已成功发送的PDCP PDU的最大和最小序列号之差大于等于设定的位图长度。
  3. 根据权利要求1所述的方法，其中，
    辅基站判断已成功发送的PDCP PDU个数是否达到设定的值；
    如果达到设定的值，则向主基站发送下行数据传输状态消息；
    如果未达到设定的值，辅基站进一步判断第一计时器是否到期；
    如果第一计时器到期，则辅基站向主基站发送下行数据传输状态消息。
  4. 根据权利要求3所述的方法，其中，如果第一计时器未到期，辅基站进一步判断PDCP PDU是否已全部发送完；
    如果PDCP PDU已全部发送完，则辅基站向主基站发送下行数据传输状态消息；
    否则，辅基站不向主基站发送下行数据传输状态消息。
  5. 根据权利要求3或4所述的方法，其中，所述下行数据传输状态消息包括：已成功发送的PDCP PDU的序列号。
  6. 根据权利要求3或4所述的方法，其中，所述设定的值和所述第一计时器的计时周期携带在主基站向辅基站发送的为用户设备请求额外资源的请求消息中或通过节点间无线资源配置消息由主基站发送至辅基 站。
  7. 根据权利要求2所述的方法，其中，
    辅基站判断第二计时器是否到期；
    如果第二计时器到期，则辅基站向主基站发送下行数据传输状态消息。
  8. 根据权利要求7所述的方法，其中，如果第二计时器未到期，辅基站进一步判断PDCP PDU是否已全部发送完；
    如果PDCP PDU已全部发送完，则辅基站向主基站发送下行数据传输状态消息；
    否则，辅基站不向主基站发送下行数据传输状态消息。
  9. 根据权利要求7或8所述的方法，其中，所述下行数据传输状态消息包括：已成功发送的PDCP PDU的序列号；或者已发送成功的PDCPPDU的最小序列号以及指示该最小序列号PDCP PDU之后的PDCP PDU是否由辅基站成功发送的位图。
  10. 根据权利要求7或8所述的方法，其中，所述第二计时器的计时周期携带在主基站向辅基站发送的为用户设备请求额外资源的请求消息中或通过节点间无线资源配置消息由主基站发送至辅基站。
  11. 根据权利要求2所述的方法，其中，
    辅基站判断已成功发送的PDCP PDU的最大和最小序列号之差是否大于等于设定的位图长度；
    如果所述差大于或等于设定的位图长度，则辅基站向主基站发送下行数据传输状态消息；
    否则，辅基站进一步判断第三计时器是否到期；
    如果第三计时器到期，则辅基站向主基站发送下行数据传输状态消息。
  12. 根据权利要求11所述的方法，其中，如果第三计时器未到期，辅基站进一步判断PDCP PDU是否已全部发送完；
    如果PDCP PDU已全部发送完，则辅基站向主基站发送下行数据传输状态消息；
    否则，辅基站不向主基站发送下行数据传输状态消息。
  13. 根据权利要求11或12所述的方法，其中，所述下行数据传输 状态消息包括：已成功发送的PDCP PDU的最小序列号；以及指示该最小序列号PDCP PDU之后的PDCP PDU是否由辅基站成功发送的位图。
  14. 根据权利要求11或12所述的方法，其中，如果所述差大于设定的位图长度，则辅基站还判断PDCP PDU是否已全部发送完；
    如果PDCP PDU已全部发送完，则辅基站向主基站发送下行数据传输状态消息，该下行数据传输状态消息包括最近一次成功发送的PDCP PDU的序列号；
    否则，辅基站不向主基站发送下行数据传输状态消息。
  15. 根据权利要求11或12所述的方法，其中，所述位图长度携带在主基站向辅基站发送的为用户设备请求额外资源的请求消息中或通过节点间无线资源配置消息由主基站发送至辅基站。
  16. 一种辅基站，包括：
    数据发送单元，用于向用户设备发送来自主基站的分组数据汇聚协议协议数据单元PDCP PDU；以及
    下行数据传输状态消息发送单元，用于向主基站发送下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的PDCP PDU的序列号。
  17. 根据权利要求16所述的辅基站，还包括：判断单元，基于是否满足以下至少一项条件，来判断是否向主基站发送下行数据传输状态消息：
    已成功发送的PDCP PDU个数达到设定的值；
    设定的计时器到期；以及
    已成功发送的PDCP PDU的最大和最小序列号之差大于等于设定的位图长度。
  18. 一种由主基站执行的通信方法，包括以下步骤：
    主基站从辅基站接收下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的分组数据汇聚协议协议数据单元PDCP PDU的序列号；以及
    主基站根据所述下行数据传输状态消息，删除主基站中存储的PDCP PDU。
  19. 一种主基站，包括：
    下行数据传输状态消息接收单元，用于从辅基站接收下行数据传输状态消息，所述下行数据传输状态消息包括至少一个已成功发送的分组数据汇聚协议协议数据单元PDCP PDU的序列号；以及
    PDCP PDU删除单元，用于根据所述下行数据传输状态消息，删除主基站中存储的PDCP PDU。
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