KR20100002111A - Method for retransmitting data unit using delivery status information from a peer entity - Google Patents

Abstract

PURPOSE: A method for retransmitting data unit using delivery status information from a peer entity is provided to prevent the unnecessary retransmission of the already received RLC data PDU and to improve The usage efficiency of the radio resource. CONSTITUTION: Data unit is transmitted to the peer receiving automatic repeat request entity. The delivery failure indication about data unit is received from the transmitting hybrid automatic repeat request entity. The delivery status indication about data unit previously received from the reception ARQ entity is determined. The data unit is selectively retransmitted.

Description

Method for Retransmitting Data Unit using Delivery Status Information from a Peer Entity}

The present invention relates to a Long Term Evolution (LTE) system, and more particularly, a hybrid automatic repeat request (HARQ) transmission failure notification provided by a medium access control (MAC) of an LTE system. The present invention relates to a method in which an acknowledgment mode radio link control (AM RLC) retransmits a protocol data unit (PDU) using a failure notification.

1 is a diagram illustrating a network structure of an LTE system, which is a conventional mobile communication system. The LTE system has evolved from the existing Universal Mobile Telecommunications System (UMTS) system and is currently being standardized by the 3rd Generation Partnership Project (3GPP).

As can be seen in Figure 1, LTE network can be largely divided into Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) and Core Network (CN). The E-UTRAN is composed of a user equipment (UE), a base station (Evolved NodeB; eNB), and an access gateway (aGW) located at an end of a network and connected to an external network.

The aGW may be divided into a part that handles user traffic and a part that handles control traffic. In this case, a new interface may be used to communicate with each other between the aGW for processing new user traffic and the aGW for controlling traffic.

One or more cells may exist in one eNB. In addition, an interface for transmitting user traffic or control traffic may be used between eNBs. The CN may be configured as a node for aGW and user registration of the UE. On the other hand, an interface for distinguishing between E-UTRAN and CN may be used.

2 and 3 illustrate a structure of a radio interface protocol between a user equipment (UE) and an E-UTRAN based on a radio access network standard of 3GPP.

The wireless interface protocol consists of a physical layer, a data link layer, and a network layer horizontally, and a user plane (U-plane) for transmitting data information vertically. ) And a control plane (C-plane) for transmitting control signals.

The protocol layers of FIGS. 2 and 3 are based on the lower three layers of the Open System Interconnection (OSI) reference model, which are well known in the field of communication systems, based on the lower three layers of the first layer (L1) and the second layer (L2). ), And the third layer L3. These radio protocol layers exist in pairs in the user terminal and the E-UTRAN, and are responsible for data transmission in the radio section.

Hereinafter, each layer of the wireless protocol control plane (C-plane) of FIG. 2 and the wireless protocol user plane (U-plane) of FIG. 3 will be described.

A physical layer (PHY) layer, which is a first layer, provides an information transfer service to a higher layer by using a physical channel. The PHY layer is connected to the upper Medium Access Control (MAC) layer through a transport channel, and data between the MAC layer and the PHY layer moves through this transport channel. At this time, the transport channel is largely divided into a dedicated transport channel and a common transport channel according to whether the channel is shared. In addition, data is moved between different PHY layers, that is, between PHY layers of a transmitting side and a receiving side through a physical channel using radio resources.

There are several layers in the second layer. First, the Medium Access Control (MAC) layer is responsible for mapping various logical channels to various transport channels, and also for logical channel multiplexing to map multiple logical channels to one transport channel. It also plays a role. The MAC layer is connected to the upper layer RLC layer by a logical channel, and the logical channel is a control channel that transmits information of a control plane (C-Plane) according to the type of information to be transmitted. And a traffic channel for transmitting information of a user plane (U-Plane).

The Radio Link Control (RLC) layer of the second layer segments and concatenates the data received from the upper layer, thereby adjusting the data size so that the lower layer is suitable for transmitting data to the radio section. It plays a role in controlling. In addition, transparent mode (TM), un-acknowledged mode (UM) to ensure the various quality of service (QoS) required by each radio bearer (RB) ), And an acknowledgment mode (AM). In particular, the AM RLC performs a retransmission function through an Automatic Repeat Request (ARQ) function for reliable data transmission.

The Packet Data Convergence Protocol (PDCP) layer of the second layer provides a relatively large and unnecessary control information in order to efficiently transmit in a wireless bandwidth having a small bandwidth during IP packet transmission such as IPv4 or IPv6. Header Compression is used to reduce the size of the IP packet header.

This transmits only the necessary information in the header portion of the data, thereby increasing the transmission efficiency of the radio section. In addition, in the LTE system, the PDCP layer also performs a security function, which is composed of encryption (Ciphering) to prevent data interception and third party data manipulation integrity (Integrity protection).

The radio resource control (RRC) layer located at the bottom of the third layer is defined only in the control plane, and the configuration, re-configuration, and release of radio bearers (RBs) are performed. It is responsible for controlling logical channels, transport channels and physical channels. Here, RB means a logical path provided by the first layer and the second layer of the radio protocol for data transmission between the user terminal and the UTRAN.

In general, the establishment of the RB refers to a process of defining characteristics of a radio protocol layer and a channel required to provide a specific service, and setting each specific parameter and operation method. In addition, RB is divided into SRB (Signaling RB) and DRB (Data RB). SRB is used as a path for transmitting RRC messages in control plane (C-plane) and DRB is user plane (U-plane). ) Is used as a channel for transmitting user data.

Conventionally, when an AM RLC entity receives a NACK (Negative acknowledgment) from a HARQ delivery failure notification for a specific RLC data PDU, the sequence number of the corresponding RLC data PDU Check and retransmit the corresponding RLC data PDU.

In some cases, however, a HARQ delivery failure notification may be received for an RLC data PDU that has previously received an acknowledgment (ACK) from an RLC STATUS PDU. This case may occur when an ACK-to-NACK error occurs in the HARQ operation.

In addition, in the related art, when an HARQ delivery failure notification is received for an RLC data PDU already received an ACK from an RLC STATUS PDU, the RLC data PDU is retransmitted immediately.

However, this is a waste of radio resources because retransmission is unnecessarily caused by an ACK-to-NACK error in HARQ operation. In addition, if the RLC deletes the RLC data PDU received the ACK from the RLC STATUS PDU in the transmission buffer, the RLC protocol is deadlocked because the retransmission cannot be performed even if the HARQ delivery failure notification is received. There is a problem of missing (deadlock).

Accordingly, the present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is when an AM RLC receives a HARQ delivery failure notification for a specific RLC data PDU from HARQ of a MAC. By not retransmitting the RLC data PDUs immediately and retransmitting only if they have not received an ACK from the RLC STATUS PDU previously, it prevents unnecessary retransmission of the already received RLC data PDUs, thereby preventing waste of radio resources and It is to improve the efficiency of use.

In addition, another object of the present invention, if the RLC deletes the RLC data PDU received the ACK from the RLC STATUS PDU in the transmission buffer, the RLC protocol cannot be retransmitted even if receiving a HARQ delivery failure notification It is to prevent this deadlock.

In order to achieve the above object, the present invention provides a method for retransmitting a data unit in a wireless communication system, the method comprising: transmitting a data unit to a receiving peer entity; Receiving a delivery failure indication for the data unit from a lower layer of a transmitting entity; Determining whether a delivery status indication for the data unit was previously received from the receiving peer entity; And selectively retransmitting the data unit on the basis of the determination result.

Advantageously, selectively retransmitting the data unit further comprises: if the transmission status indication from the receiving peer entity indicates a successful transmission, the transmission failure indication from a lower layer of the transmitting entity is ignored and the The data unit is not retransmitted. More preferably, selectively retransmitting the data unit further comprises: retransmitting the data unit to the receiving peer entity if the transmission status indication from the receiving peer entity indicates a transmission failure or does not exist. do.

Also preferably, the lower layer of the transmitting entity is Medium Access Control (MAC). More preferably, the medium access control (MAC) performs the operation of the transmission failure indication.

On the other hand, the receiving peer entity is a receiving peer RLC entity. More preferably, the transmitting entity is a transmitting RLC entity.

Also preferably, the transmission failure indication is a HARQ delivery failure notification. More preferably, the transmission status indication is a status PDU (STATUS Protocol Data Unit).

According to the present invention, when an AM RLC receives a HARQ delivery failure notification for a specific RLC data PDU from HARQ of a MAC, it does not immediately retransmit the RLC data PDU and receives an ACK from an RLC STATUS PDU. By retransmitting only if it is not, it is possible to prevent unnecessary retransmission of the already received RLC data PDU to prevent the waste of radio resources and improve the use efficiency of the radio resources.

In addition, according to the present invention, if the RLC deletes the RLC data PDU received the ACK from the RLC STATUS PDU in the transmission buffer, even if the HARQ delivery failure notification is received, the retransmission cannot be performed and the RLC protocol deadlocks. It can prevent you from falling into a deadlock.

The present invention is applied to 3GPP communication technology, in particular UMTS (Universal Mobile Telecommunications System) system, communication device and communication method. However, the present invention is not limited thereto and may be applied to all wired and wireless communication to which the technical spirit of the present invention can be applied.

A basic concept of the present invention is a method of retransmitting a data unit in a wireless communication system, the method comprising: transmitting the data unit to a peer receiving Automatic Repeat Request entity; Receiving a delivery failure indication for the data unit from a transmitting HARQ entity (transmitting Hybrid Automatic Repeat Request entity); Determining whether a delivery status indication for the data unit was previously received from the peer receiving ARQ entity; And selectively retransmitting the data unit based on the determination result, and a method of retransmitting a data unit using transmission state information of a peer entity, and a wireless mobile communication terminal capable of performing such a method; Suggest a network.

A method of retransmitting a data unit in a wireless communication system, the method comprising: transmitting the data unit to a receiving peer entity; Receiving a delivery failure indication for the data unit from a lower layer of a transmitting entity; Determining whether a delivery status indication for the data unit was previously received from the receiving peer entity; And selectively retransmitting the data unit based on the determination result, and a method of retransmitting a data unit using transmission state information of a peer entity, and a wireless mobile communication terminal capable of performing such a method; Suggest a network.

Hereinafter, with reference to the accompanying drawings an embodiment according to the present invention will be described in detail.

In the LTE system, HARQ (Hybrid Automatic Repeat Request) operation is performed in the MAC layer for efficient data transmission, and a detailed process of the uplink HARQ operation is as follows.

(1) The user terminal first receives uplink scheduling information (hereinafter, referred to as 'UL scheduling information') through a physical downlink control channel (PDCCH) control channel from the eNB in order to transmit data to the eNB in a HARQ scheme. .

(2) The received UL scheduling information includes a terminal identifier (for example, a Cell Radio Network Temporary Identity (C-RNTI) or Semi-Persistent Scheduling C-RNTI), and a location of an allocated radio resource. block assignment, transmission parameters (e.g., modulation, coding scheme and redundancy version), new data indicator, and the like.

(3) The user terminal has eight HARQ processes, and the HARQ processes operate in synchronization with a Transmission Time Interval (TTI). That is, in 1 TTI, HARQ process # 1, in 2 TTI, HARQ process # 2, ..... 8 In TTI, HARQ process # 8 is used, and again in 9 TTI, HARQ process # 1, and in 10 TTI, HARQ process # 1. Assigned in order of 2, ...

In addition, since the HARQ processes are synchronously allocated, a HARQ process connected to a TTI that receives a PDCCH for initial transmission of specific data is used for transmission of the data. For example, assuming that the terminal receives the PDCCH including the UL scheduling information in the Nth TTI, the user terminal transmits data in the N + 4th TTI. In other words, the HARQ process allocated in the N + 4th TTI is used for the data transmission.

That is, the user terminal monitors the TTI and PDCCH control channels every time, checks the UL scheduling information coming to the user, and transmits data to the eNB through the PUSCH (Physical Uplink Shared Channel) according to the UL scheduling information.

(4) When the eNB receives the data, it stores it in a soft buffer and attempts to decrypt the data. In this case, the eNB transmits an acknowledgment (ACK) signal when the decoding succeeds, and transmits a negative acknowledgment (NACK) signal to the base station when the decoding fails.

(5) When the user terminal receives the ACK signal, it detects that the data transmission to the eNB was successful and transmits the next data. When the user terminal receives the NACK signal, it detects that data transmission to the eNB has failed and retransmits the same data in the same format or a new format.

In this case, HARQ retransmission of the user terminal may operate in a non-adaptive manner. That is, initial transmission of specific data is possible only by receiving a PDCCH including UL scheduling information, but retransmission is possible even without receiving a PDCCH. The non-adaptive HARQ retransmission retransmits the data using the same UL scheduling information as the initial transmission in the TTI to which the corresponding HARQ process is next assigned without the PDCCH.

In addition, HARQ retransmission of the user terminal may operate in an adaptive manner. In this case, a transmission parameter for retransmission is received through a PDCCH control channel, and UL scheduling information included in the PDCCH may be different from initial transmission according to channel conditions. For example, if the channel condition is better than the initial transmission, the transmission may be instructed at a high bit rate. On the contrary, if the channel condition is bad, the transmission may be instructed at a lower bit rate than the initial transmission. .

If the UE receives the UL scheduling information through the PDCCH, the determination of whether the data to be transmitted at this time is initial transmission data or whether to retransmit previous data should be performed in the new data in the PDCCH. This can be seen by looking at the New Data Indicator (NDI) field. The NDI field is a 1-bit field and toggles from 0-> 1-> 0-> 1-> ... whenever new data is transmitted, and has the same value as the initial transmission for retransmission. . Accordingly, the user terminal may know whether the data is retransmitted by comparing whether the NDI field is equal to a previously transmitted value.

(6) The user terminal counts the number of transmissions (CURRENT_TX_NB) each time data is transmitted once in the HARQ scheme. When the number of transmissions (CURRENT_TX_NB) reaches the maximum number of transmissions set in the RRC layer, the transmission of the data in the HARQ buffer is canceled and the related RLC layer is notified.

(7) On the other hand, when the eNB receives the retransmitted data, it attempts to decode again by combining this data with the data stored in the soft buffer in various ways without failing the previous decoding. If the decoding is successful, the ACK signal is transmitted. If the decoding is unsuccessful, the NACK signal is transmitted to the base station. The eNB repeats the process of transmitting the NACK signal and receiving the retransmission until successful decoding of the data.

An example of the operation method of the HARQ as described above is shown in FIG. 4 is a diagram illustrating an operation method of HARQ between a user terminal and an eNB.

In such HARQ operation, data retransmission of the transmitter is based on feedback information transmitted from the receiver. That is, when the HARQ NACK is received from the receiver, the transmitter performs data retransmission, and when the HARQ ACK is received from the receiver, the transmitter stops transmitting the data and prepares to transmit new data. The transmission of new data is performed when data to be transmitted remains in the transmission buffer and a radio resource capable of transmitting the data is allocated from the scheduler.

As such, in the HARQ operation, appropriate feedback is required from the receiving side to the transmitting side. However, unlike the data transmission of other upper channels, the HARQ ACK signal or the HARQ NACK signal is error-prone because the contents are simple and other additional protection devices cannot be applied. For example, although one HARQ entity transmits an ACK signal, the other HARQ entity may receive the NACK signal or vice versa. This makes the transmitting HARQ entity unable to perform optimal operation.

If the receiving side transmits the HARQ NACK signal but the transmitting side receives the HARQ ACK signal (NACK-to-ACK error), the transmitting side no longer performs data transmission, resulting in loss of the data. The receiving side sends a NACK signal and waits for retransmission of data. At this time, when the transmitting side transmits new data instead of retransmitting data, the receiving side determines that a NACK-to-ACK error has occurred at the transmitting side. The data is discarded as a decryption failure and an attempt is made to decrypt new data. If the HARQ entity fails to decode the data, the error correction function may be recovered by retransmission if there is a layer having an error correction function thereafter, but the data is lost if the error correction function is not present in the upper layer.

On the contrary, if the receiving side transmits the HARQ ACK signal but the transmitting side receives the HARQ NACK signal (ACK-to-NACK error), the transmitting side determines that the receiving side has not successfully received the data and retransmits the data. do. In this case, there is no loss of data. However, since the transmitting side retransmits the data already received successfully by the receiving side, radio resources are unnecessarily wasted.

That is, the receiver side receives data successfully and transmits HARQ ACK signal to wait for new data. If the transmitter side retransmits the previous data, the receiver side determines that an ACK-to-NACK error has occurred. do. The receiving side discards the received retransmission data and transmits an HARQ ACK signal back to the transmitting side to prevent further unnecessary retransmission.

Next, the response mode radio link control (AM RLC) of the LTE system will be described.

First, the biggest feature of AM RLC is the retransmission function. AM RLC aims to ensure error-free data transmission through retransmission. For this purpose, AM RLC is mainly responsible for the transmission of non-real-time packet data such as TCP / IP in the PS domain in the user plane, and the acknowledgment response is required among the RRC messages transmitted to specific terminals in the cell in the control plane. Responsible for sending RRC messages.

The complexity of AM RLC is due to the retransmission function. In order to manage retransmission, AM RLC has a retransmission buffer in addition to the transmit / receive buffer, use of the transmit / receive window for flow control, polling and receiving that the sender requests status information to the receiver of peer RLC entity. The side performs various functions such as a status report for reporting its buffer status to the sender of the peer RLC entity and a status pdu for carrying status information. In addition, AM RLC also requires various protocol parameters, state variables, and timers to support these functions.

PDUs used for control of data transmission in AM RLC, such as Status Report or Status PDU, are called RLC Control PDUs, and are used to deliver user data. The PDUs used are called data PDUs. On the other hand, PDUs used to transmit actual data are called RLC data PDUs, which are specifically divided into AMD PDUs and AMD PDU segments.

The AMD PDU segment has some of the data belonging to the AMD PDU. In the LTE system, the maximum size of the data block transmitted by the user terminal changes variably each time. Therefore, when a transmitting AM RLC entity constructs and transmits an AMD PDU having a size of 200 bytes at some point and receives a NACK signal from a receiving AM RLC, the transmitting side receives the AMD PDU. If the maximum size of the data block that can be actually transmitted when attempting to retransmit is 100 bytes, the AMD PDU cannot be retransmitted in that state.

In this case, the AMD PDU segment is used, and the AMD PDU segment means that the corresponding AMD PDU is divided into small units. In the above process, the transmitting AM RLC entity divides the AMD PDU into AMD PDU segments and transmits them over several hours, and the receiving AM RLC entity transmits the received AMD PDU segments. Restore AMD PDU from.

The receiving side AM RLC informs the sending side AM RLC if there is data that it did not receive properly and requests retransmission. This is called a status report and is transmitted using a STATUS PDU, which is one of control PDUs.

The STATUS PDU structure used in the current LTE system is shown in FIG. Description of each field of the RLC STATUS PDU of FIG. 5 is as follows.

(1) D / C (Data / Control) indicates whether the corresponding RLC PDU is an RLC Data PDU or an RLC Control PDU.

(2) Control PDU Type (CPT) indicates what type of Control PDU is. Currently, only STATUS PDUs are defined in the RLC Control PDU.

(3) ACK_SN (Acknowledgement Sequence Number) is the RLC Sequence Number (SN) of the first PDU whose STATUS PDU does not contain information. When the sender receives this STATUS PDU, all of the PDUs corresponding to (ACK_SN-1) are correctly received by the receiver except for the PDU corresponding to NACK_SN or NACK_SN, SOstart, SOend, or a part thereof. To judge.

(4) E1 (Extension 1) indicates whether there is another NACK_SN element after this NACK_SN element (that is, NACK_SN or NACK_SN, SOstart, SOend).

(5) A NACK_SN (Negative Acknowledgment Sequence Number) is an RLC SN of an AMD PDU or AMD PDU segment that failed to receive.

(6) E2 (Extension 2) indicates whether there are SOstart and SOend fields corresponding to this NACK_SN.

(7) SOstart (Segment Offset Start) and SOend (Segment Offset End) are used when only a portion of the PDU corresponding to NACK_SN is required for the NACK signal. The first byte of the portion corresponds to SOstart and the last byte corresponds to SOend.

Retransmission in the AM RLC is not randomly performed by the AM RLC, but only when certain conditions are satisfied. This is called a retransmission trigger, and the following triggers are defined in the current LTE system.

(1) NACK (Negative acknowledgment) by STATUS PDU from peer AM RLC

When the sending AM RLC entity receives a STATUS PDU from the receiving side of its peer AM RLC entity, the receiving side does not receive the RLC data PDU (ie, AMD PDU or AMD PDU segment). Retransmit). At this time, in order to prevent waste of radio resources, the receiving side retransmits only for the RLC data PDU to which the NACK signal is transmitted.

(2) HARQ delivery failure notification from MAC

When a transmitting AM RLC entity delivers RLC data PDUs to a lower layer MAC for wireless transmission of data, the MAC segments or concatenates the RLC data PDUs received from several RLC entities. concatenation) to configure one MAC PDU and then transmit to the receiver using HARQ.

At this time, if HARQ transmission of the MAC PDU continues to fail and reaches a reference value set by RRC, the MAC considers HARQ delivery failure, and considers the RLC data PDU included in the MAC PDU. Notify all delivered RLC entities.

The transmitting side AM RLC entity determines that the transmission of the RLC data PDU included in the MAC PDU has failed when the MAC notifies HARQ delivery failure, and retransmits the RLC data PDU. . At this time, in order to prevent waste of radio resources, retransmission is performed only for the RLC data PDU in which the MAC notifies HARQ delivery failure.

When one of the two trigger conditions described above occurs, the AM RLC checks whether the corresponding RLC data PDU has not been successfully transmitted or whether the PDU has performed the transmission attempt. As a result of the check, in the case of a PDU that attempts to transmit but has not been successfully transmitted yet, the AM RLC retransmits the RLC data PDU. This can be expressed as the following procedure text.

When receiving a negative acknowledgment for an AMD PDU or a portion of an AMD PDU by a STATUS PDU from its peer AM RLC entity, the transmitting side of the AM RLC entity shall:

if the SN of the corresponding AMD PDU falls within the range VT (A) <= SN <VT (S):

   -consider the AMD PDU or the portion of the AMD PDU for which a negative acknowledgment was received for retransmission.

When receiving a negative acknowledgment for an AMD PDU or a portion of an AMD PDU by HARQ delivery failure notification from the transmitting MAC entity, the transmitting side of the AM RLC entity may:

if the SN of the corresponding AMD PDU falls within the range VT (A) <= SN <VT (S):

   -consider the AMD PDU or the portion of the AMD PDU for which a negative acknowledgment was received for retransmission.

Here, VT (A) and VT (S), which are state variables on the transmitting side, will be described in detail.

VT (A) is an acknowledgment state variable, which is the SN of the AMD PDU that must receive the next in-sequence ACK. That is, it is the SN of the first AMD PDU which determines that the transmitting AM RLC has not yet succeeded in transmission. Corresponds to the start of the transmission window. The initial value is 0. If an ACK signal corresponding to SN = VT (A) is received, it is updated to SN of an AMD PDU, which should receive the first ACK signal after SN = VT (A).

On the other hand, VT (S) is a send state variable (Send state variable), which is the SN of the first AMD PDU of the new AMD PDU to be transmitted next. The initial value is 0, which is increased by 1 each time the AMD PDU corresponding to SN = VT (S) is transmitted.

As described above, when the MAC receives a NACK from a HARQ delivery failure notification for a specific RLC data PDU, the receiving AM RLC entity indicates that the SN of the RLC data PDU is VT (A) ≤ It checks whether SN < VT (S) is satisfied, and if so, retransmits the RLC data PDU.

In some cases, however, a HARQ delivery failure notification may be received for an RLC data PDU that has previously received an ACK from the RLC STATUS PDU. This case may occur when an ACK-to-NACK error occurs in the HARQ operation as shown in FIG. 6. FIG. 6 is a diagram for explaining a case where RLC STATUS PDUs and HARQ transmission information indicate different state information.

In the present invention, the Acknowledgment Mode Radio Link Control (AM RLC) is configured for a specific RLC data PDU (PDU) from a Hybrid Automatic Repeat Request (HARQ) of Medium Access Control (MAC). In case of receiving a HARQ delivery failure notification, a method of selectively retransmitting the corresponding RLC data PDU after additionally performing the inspection process described below is proposed.

When the contents of the present invention are expressed in procedure text, they may be as follows.

When receiving a negative acknowledgment for an RLC data PDU by HARQ delivery failure notification from the transmitting MAC entity, the transmitting side of the AM RLC entity shall:

if the SN of the corresponding RLC data PDU falls within the range VT (A) <= SN <VT (S):

   if the RLC data PDU is already acknowledged by a previous STATUS PDU:

ignore the HARQ delivery failure notification, i.e., RLC does not perform retransmission of the RLC data PDU;

   else if the RLC data PDU has not been acknowledged by a previous STATUS PDU:

consider the RLC data PDU for which a negative acknowledgment was received for retransmission;

else if the SN of the corresponding RLC data PDU falls outside of the range VT (A) <= SN <VT (S):

   ignore the HARQ delivery failure notification, i.e., RLC does not perform retransmission of the RLC data PDU.

That is, in the method of the present invention, in order to determine whether the AM RLC retransmits the RLC data PDU having received the HARQ delivery failure notification, the SN of the RLC data PDU is VT (A) ≤ SN <VT It checks whether (S) is satisfied, that is, a PDU that has attempted transmission but has not yet succeeded in transmission.

As a result of the test, the AM RLC performs retransmission only when VT (A) ≤ SN <VT (S) is satisfied and ACK is not received by the STATUS PDU. If VT (A) ≤ SN <VT (S) is not satisfied or if an ACK has been previously received from the STATUS PDU, the received HARQ delivery failure notification is ignored and the RLC data PDU is ignored. Does not retransmit.

7 is a flowchart illustrating the above procedure. 7 is a flowchart illustrating a PDU retransmission method using HARQ delivery failure notification according to the present invention.

Meanwhile, in the present invention, when receiving an ACK from a STATUS PDU for a specific RLC data PDU and subsequently receiving a HARQ delivery failure notification, that is, a NACK, the present invention ignores the HARQ delivery failure notification and retransmits. I do not want to.

However, in the opposite case, that is, a HARQ delivery successful notification, that is, an ACK and a NACK from a STATUS PDU may occur after a specific RLC data PDU. In this case, the present invention retransmits the RLC data PDU as NACK without ignoring the received STATUS PDU.

The reason for this retransmission in the present invention is that HARQ delivery notification is information provided by the transmitting MAC to the transmitting RLC, and HARQ errors such as ACK-to-NACK errors or NACK-to-ACK errors may occur. Because there is a possibility. In other words, since information provided by a peer entity, such as an RLC STATUS PDU, is more reliable than information provided by its lower layer, success of reception for a specific RLC data PDU is primarily determined by the RLC STATUS PDU. It is based on judgment.

Accordingly, in the present invention, when the RLC STATUS PDU and the HARQ delivery notification for different RLC data PDUs transmit different status information, the AM RLC entity is determined as shown in Table 1 below.

 First Receive Information  Second received information  Judgment result  HARQ delivery = success  STATUS PDU = NACK  NACK  HARQ delivery = N / A  STATUS PDU = NACK  NACK  HARQ delivery = failed  STATUS PDU = ACK  ACK  HARQ delivery = N / A  STATUS PDU = ACK  ACK  STATUS PDU = ACK  HARQ delivery = failed  ACK  STATUS PDU = N / A  HARQ delivery = failed    NACK Estimation (ACK-to-NACK Error Estimation)  STATUS PDU = NACK  HARQ delivery = success ACK estimation (NACK-to-ACK error estimation in HARQ)  STATUS PDU = N / A  HARQ delivery = success ACK estimation (NACK-to-ACK error estimation in HARQ)

As can be seen from Table 1, in the present invention, when the AM RLC receives the RLC STATUS PDU, ACK or NACK is first determined based only on the information of the RLC STATUS PDU regardless of previous HARQ transmission information. On the other hand, upon receiving a HARQ transmission failure notification, it checks whether there is information previously received from the STATUS PDU, and if there is information previously received from the STATUS PDU, it determines whether to ACK or NACK by considering the STATUS PDU and HARQ transmission information together. It is.

That is, in the present invention, the HARQ transmission result may have meaning only when there is no previously received STATUS PDU or when the STATUS PDU previously informed NACK, even in this case, an ACK-to-NACK error or NACK-to- The RLC operates in consideration of an ACK error.

According to the present invention as described above, when the AM RLC receives the HARQ delivery failure notification from the HARQ of the MAC, by retransmitting only if not previously received an ACK from the RLC STATUS PDU, the already received RLC data PDU Can be unnecessarily retransmitted to prevent waste of radio resources and improve the efficiency of use of radio resources. In addition, when the RLC deletes the RLC data PDU received from the RLC STATUS PDU in the transmission buffer, the RLC protocol cannot be deadlocked even when receiving a HARQ delivery failure notification. Can be prevented.

Although the preferred embodiment of the present invention has been described above by way of example, the scope of the present invention is not limited to this specific embodiment. The invention may be modified, changed or improved in various forms within the scope of the spirit and claims of the invention.

1 is a diagram illustrating a network structure of an LTE system, which is a conventional mobile communication system.

2 is a diagram illustrating a control plane structure of a radio interface protocol used between a conventional user terminal (UE) and an E-UTRAN.

3 is a diagram illustrating a user plane structure of a radio interface protocol used between a conventional user terminal (UE) and an E-UTRAN.

4 is a diagram illustrating a HARQ operation method between a user terminal and an eNB.

5 is a view showing a STATUS PDU structure used in the current LTE system.

FIG. 6 is a diagram illustrating a case where RLC STATUS PDUs and HARQ transmission information indicate different state information.

7 is a flowchart illustrating a data unit retransmission method using transmission status information of a peer entity according to the present invention.

Claims (16)

A method for retransmitting a data unit in a wireless communication system, Sending the data unit to a peer receiving Automatic Repeat Request entity; Receiving a delivery failure indication for the data unit from a transmitting HARQ entity (transmitting Hybrid Automatic Repeat Request entity); Determining whether a delivery status indication for the data unit was previously received from the peer receiving ARQ entity; And And selectively retransmitting the data unit based on the determination result. The method of claim 1, wherein selectively retransmitting the data unit comprises: If the transmission status indication from the peer receiving ARQ entity indicates successful transmission, the transmission failure indication from the transmitting HARQ entity is ignored and the data unit is not retransmitted. How to retransmit data units. The method of claim 1, wherein selectively retransmitting the data unit comprises: If the transmission status indication from the peer receiving ARQ entity indicates a transmission failure or does not exist, the data unit is retransmitted to the peer receiving ARQ entity; Way. The method according to any one of claims 1 to 3, And the peer receiving ARQ entity is a receiving peer RLC entity (peer radio link control entity). The method according to any one of claims 1 to 3, The transmitting HARQ entity is a transmitting side RLC entity (Radio Link Control entity), characterized in that the data unit retransmission method using the transmission status information of the peer entity. The method according to any one of claims 1 to 3, The transmission failure indication is a HARQ delivery failure notification (HARQ delivery failure notification) characterized in that the data unit retransmission method using the transmission status information of the peer entity. The method according to any one of claims 1 to 3, The transmission status indication is a status PDU (status Protocol Data Unit) characterized in that the data unit retransmission method using the transmission status information of the peer entity. A method for retransmitting a data unit in a wireless communication system, Transmitting the data unit to a receiving peer entity; Receiving a delivery failure indication for the data unit from a lower layer of a transmitting entity; Determining whether a delivery status indication for the data unit was previously received from the receiving peer entity; And And selectively retransmitting the data unit based on the determination result. The method of claim 8, wherein selectively retransmitting the data unit comprises: If the transmission status indication from the receiving peer entity indicates successful transmission, the transmission failure indication from the lower layer of the transmitting entity is ignored and the data unit is not retransmitted. Data unit retransmission method using information. The method of claim 8, wherein selectively retransmitting the data unit comprises: If the transmission status indication from the receiving peer entity indicates a transmission failure or does not exist, the data unit is retransmitted to the receiving peer entity, wherein the data unit retransmission using the transmission status information of the peer entity Way. The method of claim 8, The lower layer of the transmitting entity is a medium access control (MAC) layer, characterized in that the data unit retransmission method using the transmission status information of the peer entity. The method of claim 11, The medium access control (MAC) layer is a data unit retransmission method using the transmission status information of the peer entity, characterized in that for performing the operation of the transmission failure indication. The method according to any one of claims 8 to 12, And the receiving peer entity is a receiving peer RLC entity. The method according to any one of claims 8 to 12, The transmitting entity is a data unit retransmission method using the transmission status information of the peer entity, characterized in that the transmitting RLC entity. The method according to any one of claims 8 to 12, The transmission failure indication is a HARQ delivery failure notification (HARQ delivery failure notification) characterized in that the data unit retransmission method using the transmission status information of the peer entity. The method according to any one of claims 8 to 12, The transmission status indication is a status PDU (STATUS Protocol Data Unit), characterized in that the data unit retransmission method using the transmission status information of the peer entity.

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