JP2013034048A - Radio communication device and retransmission control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio communication device and a retransmission control method which efficiently use radio resources and improve a system throughput restraining wasteful retransmission in retransmission control employing an RLC system.SOLUTION: An RLC transmission management unit 123 determines whether a time interval obtained based on the reception time of a STATUS-PDU received from a receiving side RLC which is a communication partner and the transmission time when data was re-transmitted immediately before is larger than the RTT. If the time interval is smaller than the RTT, the RLC transmission management unit 123 determines the communication partner, the receiving side RLC, had transmitted the status-PDU before the data re-transmitted immediately before arrived at the communication partner, the receiving side RLC, and ignores its NACK.

Description

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

  Currently, a 3GPP (3rd Generation Partnership Project) TSG RAN (Technical Specification Group Radio Access Network) is studying LTE (Long Term Evolution) which is a next generation mobile communication system. In 3GPP LTE, a mobile terminal device (hereinafter referred to as UE: User Equipment) is connected to an E-UTRAN (Enhanced Universal Terrestrial Radio Access Network) configured by a plurality of base station devices (hereinafter referred to as eNodeB: Evolved Node B). Connect and send and receive user data.

  FIG. 1 is a diagram showing a network architecture used in the LTE communication system.

  As shown in FIG. 1, the UE is connected to an E-UTRAN composed of a plurality of base stations (e NodeBs), and transmits / receives user data to / from the E-UTRAN.

  Here, user data between the UE and the eNodeB is controlled by a layer 1 (physical layer) and a layer 2 (data link layer) of a communication protocol used in 3GPP LTE. Layer 2 includes a MAC (Medium Access Control) sublayer that performs radio resource allocation control, an RLC (Radio Link Control) sublayer that controls radio links, data encryption / decryption, and packets during handover This is divided into a PDCP (Packet Data Convergence Protocol) sublayer that performs order control and the like.

  FIG. 2 is a diagram showing the arrangement of the user data control system protocol stack.

  As shown in FIG. 2, user data between the UE and the eNodeB is controlled by LTE communication protocol layer 1 and layer 2 (MAC / RLC / PDCP). A radio bearer is set in the RLC / PDCP sublayer of each of the UE and eNodeB at the start of communication. Multiple radio bearers can be activated. An RLC / PDCP entity corresponding to each UE and eNodeB is generated for each radio bearer, and control information for transmission / reception data passing through the radio bearer is held.

  Radio bearers are roughly classified into three. That is, a signaling radio bearer (SRB) that transmits / receives a layer 3 (RRC / NAS) communication control message, and a data radio bearer (DRB-AM) that retransmits the user data until delivery confirmation is obtained in the RLC sublayer. Data Radio Bearer-Acknowledged Mode), which is a data radio bearer (DRB-UM: Data Radio Bearer-Unacknowledged Mode) that does not perform delivery confirmation in the RLC sublayer. DRB-AM and DRB-UM are collectively referred to as DRB.

  As a retransmission control method, non-patent document 1 and non-patent document 2 disclose radio link control defined by 3GPP E-UTRAN. The RLC retransmission control method in E-UTRAN disclosed in Non-Patent Document 1 will be described below with reference to FIG.

  In FIG. 3, in step (hereinafter abbreviated as “ST”) 11, data is transmitted from the transmitting RLC to the receiving RLC in the order of SN (Sequence Number). Here, it is assumed that the transmission side RLC transmits SN = 1 to 3, and the reception side RLC can normally receive the data of SN = 1, 3, but cannot receive the data of SN = 2 normally. And

  In ST12, the receiving side RLC includes information (NACK) indicating that the data of SN = 2 could not be normally received (not received) in the STATUS-PDU (Protocol Data Unit) and transmits the information to the transmitting side RLC. In ST13, the transmission side RLC retransmits the data of SN = 2 notified as not received (NACK).

  The receiving-side RLC waits until the STATUS-PDU transmission period timer (Timer_Status_Periodic) (hereinafter simply referred to as “timer”) expires for retransmission of the data (SN = 2) notified as unreceived. If there is no retransmission until the timer expires, in ST14, the receiving side RLC transmits the NACK of SN = 2 to the transmitting side RLC again.

3GPP TS25.322 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Radio Link Control (RLC) protocol specification 3GPP TS36.322 Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Link Control (RLC) protocol specification (Release 8) 3GPP TS36.300 Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 8)

  However, in the above-described RLC retransmission control method, as shown in FIG. 3, when the arrival of retransmission data in ST13 is late, a NACK may be transmitted again in ST15. In this case, the transmission side RLC judges that the retransmission data of ST13 was successfully received by the reception side RLC, but did not reach the reception side RLC, and was notified as not received (NACK). The data of SN = 2 will be retransmitted again. As a result, the data of SN = 2 that has been retransmitted again has already been normally received by the receiving RLC in the previous retransmission, and is discarded as useless data.

  Thus, if a retransmission request is made before the arrival of retransmission data, radio resources are wasted and system throughput is reduced.

  An object of the present invention is to provide a wireless communication apparatus and a retransmission control method that suppress unnecessary retransmission in RLC scheme retransmission control, efficiently use radio resources, and improve system throughput.

  The wireless communication apparatus according to the present invention includes a receiving unit that receives a NACK transmitted from a communication partner, a reception time of the received NACK, and a time determined based on a transmission time of data retransmitted immediately before the reception of the NACK. When the interval is smaller than RTT (Round Trip Time), the transmission management means for discarding the NACK is adopted.

  According to the retransmission control method of the present invention, the time interval obtained based on the reception time of the received NACK and the transmission time of data retransmitted immediately before the reception of the NACK is received as an RTT. If it is smaller than (Round Trip Time), the NACK is discarded.

  According to the present invention, it is possible to suppress unnecessary retransmissions in the RLC retransmission control, to efficiently use radio resources and to improve system throughput.

The figure which shows the network architecture used by the LTE communication system Diagram showing the layout of the user data control protocol stack Sequence diagram for explaining the retransmission control method of the RLC method in E-UTRAN disclosed in Non-Patent Document 1 1 is a block diagram showing a configuration of a wireless communication apparatus according to Embodiment 1 of the present invention. FIG. 4 is a sequence diagram showing a retransmission control procedure between the wireless communication apparatus shown in FIG. 4 and a communication partner. The figure which uses for description of the processing delay in the transmission side RLC and the communication side reception side RLC FIG. 2 is a block diagram showing a configuration of a wireless communication apparatus according to Embodiment 2 of the present invention. FIG. 7 is a sequence diagram showing a retransmission control procedure between the wireless communication apparatus shown in FIG. 7 and a communication partner. The figure which uses for description of the processing delay in the reception side RLC and the transmission side RLC of the communicating party

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, in the embodiment, components having the same function are denoted by the same reference numerals, and redundant description is omitted.

(Embodiment 1)
FIG. 4 is a block diagram showing a configuration of radio communication apparatus 100 according to Embodiment 1 of the present invention. Hereinafter, the configuration of the wireless communication apparatus will be described with reference to FIG. FIG. 4 particularly shows the configuration of the RLC sublayer.

  The RLC sublayer 120 stores the PDCP PDU transmitted from the upper layer 110 in the transmission buffer 121. The PDCP PDU stored in the transmission buffer 121 is managed by the RLC transmission management unit 123 described later.

  The RLC PDU generation unit 122 extracts data from the transmission buffer 121 in accordance with the instruction from the RLC transmission management unit 123, and includes an RLC sublayer including information for identifying each data, data size, information for order control, and the like Is added to the extracted data to generate an RLC PDU. The generated RLC PDU is transmitted to the communication partner via the lower layer 130 (MAC / PHY).

  In addition, when the lower layer 130 (MAC / PHY) receives data transmitted from a communication partner and receives an RLC PDU, the lower layer 130 transmits the RLC PDU to the RLC PDU analysis unit 125 of the RLC sublayer 120.

  The RLC PDU analysis unit 125 determines whether the data transmitted from the lower layer 130 is STATUS-PDU (CONTROL PDU) or PDCP DATA PDU (user data). When it is determined that the received data is a PDCP DATA PDU, the RLC PDU analysis unit 125 stores the PDCP DATA PDU in the RLC reception buffer unit 126. On the other hand, when it is determined that the received data is a STATUS-PDU, the RLC PDU analysis unit 125 transmits the STATUS-PDU to the RLC transmission management unit 123.

  The RLC transmission management unit 123 sets the SN (sequence number) for order control, the setting of data to be transmitted in the transmission buffer 121, and the reception side RLC of the communication partner to the RLC PDU generation unit 122. It instructs the setting of the poll bit for requesting transmission of STATUS-PDU.

  The RLC transmission management unit 123 holds transmission time information of the transmitted RLC PDU, and measures RTT (Round Trip Time) when receiving STATUS-PDU from the receiving-side RLC sublayer of the communication partner. This measurement may be performed at the beginning of communication, and thereafter, the measurement value may be used as an RTT fixed value, or may be measured each time during communication to dynamically update the value.

  Further, the RLC transmission management unit 123 holds the transmission time information of the retransmitted data, and then, when the NACK of the same data as the retransmitted data is included in the STATUS-PDU received from the communication partner, It is determined whether the time interval is larger than the RTT from the reception time of the STATUS-PDU and the transmission time of the data retransmitted immediately before this.

  When the time interval is smaller than the RTT, the RLC transmission management unit 123 transmits the STATUS-PDU before the data retransmitted immediately before receiving the STATUS-PDU arrives at the receiving RLC of the communication partner. NACK is discarded. On the other hand, when the time interval is larger than the RTT, the RLC transmission management unit 123 determines that the data retransmitted immediately before the reception of the STATUS-PDU has not reached the receiving RLC of the communication partner, and the data for which the NACK notification has been received Resend again.

  Next, a retransmission control procedure between radio communication apparatus 100 shown in FIG. 4 and the communication partner will be described with reference to FIG. In FIG. 5, the wireless communication device 100 illustrated in FIG. 4 is referred to as a transmission side RLC, and a communication partner is referred to as a reception side RLC.

  In FIG. 5, in ST201, data is transmitted from the transmission side RLC to the reception side RLC in the SN order. Here, it is assumed that the transmission side RLC transmits SN = 1 to 3, and the reception side RLC can normally receive the data of SN = 1, 3, but cannot receive the data of SN = 2 normally. And

  In ST202, the receiving side RLC includes information indicating that the SN = 2 data has not been normally received (not received), that is, a retransmission request (NACK) in the STATUS-PDU and transmits the information to the transmitting side RLC. At this time, the transmitting side RLC measures the RTT from the Poll bit transmission to the STATUS-PDU reception.

  In ST203, the transmission side RLC retransmits the data of SN = 2 notified as not received (NACK). At this time, the transmitting side RLC holds the transmission time information of the retransmitted data.

  In ST204, when there is a NACK notification of the same data as the data retransmitted in ST203 in the STATUS-PDU received from the receiving side RLC of the communication partner, the reception time of the STATUS-PDU and the transmission of the data retransmitted immediately before this From the time, it is determined whether the time interval is larger than the RTT.

  If the time interval is smaller than the RTT, it is determined that the receiving RLC is transmitting the STATUS-PDU before the data retransmitted immediately before receiving the STATUS-PDU arrives at the receiving RLC of the communication partner. NACK is discarded. Thereby, even when the receiving side RLC has performed NACK notification accompanying the expiration of the timer before the retransmission data reaches the receiving side RLC of the communication partner, it is possible to suppress useless retransmission. On the other hand, if the time interval is larger than the RTT, it is determined that the data retransmitted immediately before the reception of the STATUS-PDU did not reach the receiving side RLC of the communication partner, and the data with the NACK notification is retransmitted again.

  Thus, according to Embodiment 1, it is obtained based on the reception time of the STATUS-PDU (NACK) received from the receiving side RLC of the communication partner and the transmission time of the data retransmitted immediately before the reception of this NACK. When the time interval is smaller than the RTT, it is determined that the communication partner receiving side RLC is transmitting STATUS-PDU (NACK) before the data retransmitted immediately before receiving the NACK arrives at the communication partner receiving side RLC. The NACK is discarded. As a result, even if the receiving side RLC has made a NACK notification due to the expiration of the timer before the retransmit data arrives at the receiving side RLC of the communication partner, the NACK is discarded, so that unnecessary retransmission is suppressed. Can do. As a result, efficient use of radio resources and improvement of system throughput can be achieved.

  In the present embodiment, the RTT is obtained by measuring the time from when the transmitting side RLC transmits the Poll bit until receiving the STATUS-PDU, but the present invention is not limited to this. For example, you may define RTT as follows. The transmission side RLC exchanges information regarding processing delay with the communication partner RLC at the start of communication (connection setup), and defines the RTT. As specific processing delays, first, transmission / reception delays (Tx-delay, Rx-delay) in the MAC / PHY layer and delays from receiving the poll bit of the receiving side RLC of the communication partner to STATUS-PDU transmission (STATUS-Tx-delay) is defined. The transmission side RLC and the communication side reception side RLC exchange information regarding these processing delays at the time of connection setup.

As can be seen from FIG. 6, the RTT corresponding to the transmission from the poll bit to the reception of the STATUS-PDU can be determined by the following equation (1).
RTT =
Tx-delay of transmitting RLC + Rx-delay of receiving RLC + STATUS-Tx-delay of receiving RLC
+ Receiver RLC Tx-delay + Transmitter RLC Rx-delay (1)

  In equation (1), the delay in the radio line is not included, but if the system can also estimate the radio line delay, the accuracy can be further improved by adding the delay in the radio line.

(Embodiment 2)
In the first embodiment, a case has been described in which transmission-side RLC determines whether or not transmission of STATUS-PDU, which is retransmission data, is possible. A case where the transmission timing of the STATUS-PDU including the NACK indicating ACK is adjusted is described.

  FIG. 7 is a block diagram showing a configuration of radio communication apparatus 300 according to Embodiment 2 of the present invention. However, FIG. 7 differs from FIG. 4 in that the RLC reception management unit 301 is added and the RLC transmission management unit 123 is changed to the RLC transmission management unit 302.

  The RLC reception management unit 301 manages the SN of the data stored in the RLC reception buffer 126, the setting of the Poll bit, and the reception time information. The RLC reception management unit 301 notifies the RLC transmission management unit 302 of a STATUS-PDU transmission request when it is determined that there is a loss in the SN of the received data and a retransmission request (NACK) should be transmitted to the transmission side RLC.

  The RLC transmission management unit 302 instructs the RLC PDU generation unit 122 to transmit the STATUS-PDU according to the STATUS-PDU transmission request notified from the RLC reception management unit 301. In addition, the RLC transmission management unit 302 notifies the RLC reception management unit 301 of the transmission time information of the STATUS-PDU.

  Next, a retransmission control procedure between radio communication apparatus 300 shown in FIG. 7 and the communication partner will be described with reference to FIG. In FIG. 8, the radio communication apparatus 300 shown in FIG. 7 is referred to as a reception side RLC, and the communication partner is referred to as a transmission side RLC.

  In FIG. 8, in ST401, data is transmitted from the transmission side RLC to the reception side RLC in the SN order. Here, it is assumed that the transmission side RLC transmits SN = 1 to 3, and the reception side RLC can normally receive the data of SN = 1, 3, but cannot receive the data of SN = 2 normally. And

  In ST402, the reception side RLC includes information indicating that the SN = 2 data has not been received normally (not received), that is, a retransmission request (NACK), in the STATUS-PDU and transmits the information to the transmission side RLC.

  In ST403, the transmission side RLC retransmits the data of SN = 2 notified as not received (NACK), and the reception side RLC receives the retransmitted data. At this time, the receiving side RLC measures the RTT from the transmission of the STATUS-PDU in ST402 to the reception of retransmission data. The receiving side RLC sets the timer to a value larger than the measured RTT. Here, it is assumed that the receiving side RLC has successfully received retransmission data of SN = 2.

  In ST404, the receiving side RLC confirms the expiration of the timer, and transmits the STATUS-PDU to the transmitting side RLC. Here, since retransmission data is normally received in ST403, the receiving side RLC includes ACK in the STATUS-PDU.

  As described above, according to the second embodiment, the receiving side RLC sets the timer to a value larger than the RTT, and waits for the timer to expire before transmitting the STATUS-PDU. The receiving side RLC does not perform NACK notification before the retransmitted data arrives, and unnecessary retransmission can be suppressed. As a result, efficient use of radio resources and improvement of system throughput can be achieved.

  In the present embodiment, the RTT is obtained by measuring the time from when the receiving side RLC transmits STATUS-PDU until it receives retransmission data, but the present invention is not limited to this. For example, you may define RTT as follows. The transmission side RLC exchanges information regarding processing delay with the communication partner RLC at the start of communication (connection setup), and defines the RTT. As specific processing delays, first, transmission / reception delay (Tx-delay, Rx-delay) in the MAC / PHY layer and NACK notification of the communication side transmitting side RLC are received, and then data based on the NACK notification is received. Defines the delay (STATUS-Tx-delay) before resending. The transmission side RLC and the communication side reception side RLC exchange information regarding these processing delays at the time of connection setup.

As can be seen from FIG. 9, the RTT corresponding to the time from the reception side RLC transmitting the STATUS-PDU to the reception of the retransmission data can be determined by the following equation (2).
RTT =
Rx-delay of receiving RLC + Rx-delay of transmitting RLC
+ Retransmit-Tx-delay of transmitting RLC + Tx-delay of transmitting RLC
+ Rx-delay of receiving RLC (2)

  In the expression (2), the delay in the radio line is not included, but if the system can also estimate the radio line delay, the accuracy can be further improved by adding the delay of the radio line.

  The radio communication apparatus and the retransmission control method according to the present invention can be applied to a radio communication terminal apparatus, a radio communication base station apparatus, and the like in a mobile communication system.

100, 300 Wireless communication apparatus 110 Upper layer 120 RLC sublayer 121 Transmission buffer 122 RLC PDU generation unit 123, 302 RLC transmission management unit 125 RLC PDU analysis unit 126 RLC reception buffer 130 Lower layer 301 RLC reception management unit

Claims (4)

Receiving means for receiving NACK transmitted from the communication partner;
A transmission management means for discarding the NACK when the time interval obtained based on the reception time of the received NACK and the transmission time of the data retransmitted immediately before the reception of the NACK is smaller than RTT (Round Trip Time);
A wireless communication apparatus comprising:   The radio communication apparatus according to claim 1, wherein the transmission management unit measures, as an RTT, a time from when a poll bit is transmitted to when a STATUS-PDU is received.   The radio communication apparatus according to claim 1, wherein the transmission management unit measures RTT based on a reception delay and a transmission delay in each of the own apparatus and the communication partner. Receives a NACK sent from the communication partner,
When the time interval obtained based on the received time of the received NACK and the transmission time of the data retransmitted immediately before the reception of the NACK is smaller than RTT (Round Trip Time), the NACK is discarded.
Retransmission control method.

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