KR20090132503A - Method of delivering a pdcp data unit to an upper layer - Google Patents

Abstract

PURPOSE: A method for delivering a successively received PDCP(Packet Data Convergence Protocol) data unit to an upper layer is provided to reduce a data transmission delay time by delivering successively received data units to an upper layer when a PDCP data unit is received. CONSTITUTION: A method for transmitting data comprises the following steps: a step for receiving a data unit including a sequence number from a lower layer; a step for storing the received data unit to a buffer; a step for determining identity of the sequence number of the received data unit and a sequence number+1 of a last delivered data unit; and a step for successively delivering all stored data units having successively connected sequence numbers more than the sequence number of the received data unit based on the determined result.

Description

METHOOD OF DELIVERING A PDCP DATA UNIT TO AN UPPER LAYER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system and a terminal for providing a wireless communication service. The present invention relates to a PDCP SDU delivery method of a Packet Data Convergence Protocol (PDCP) layer.

1 is a diagram illustrating a network structure of an LTE system, which is a mobile communication system to which the present invention and the present invention are applied. The LTE system is an evolution from the existing UMTS system and is currently undergoing basic standardization in 3GPP.

The LTE network can be roughly divided into an E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) and a CN (Core Network). The E-UTRAN consists of a User Equipment (UE), an 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 aGW for handling new user traffic and aGW for controlling traffic. One or more cells may exist in one eNB. An interface for transmitting user traffic or control traffic may be used between eNBs. The CN may be configured as a node for user registration of the aGW and other UEs, and the like. 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 UE and an E-UTRAN based on the 3GPP radio access network standard. The wireless interface protocol consists of a physical layer, a data link layer, and a network layer horizontally, and vertically, a user plane and a U-plane for data information transmission. ) And control plane (C-plane) for signal transmission. 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 communication systems, and include L1 (first layer), L2 (second layer), L3 (third layer) can be divided. These radio protocol layers exist in pairs in the UE and the E-UTRAN, and are responsible for data transmission in the radio section.

Hereinafter, each layer of the wireless protocol control plane of FIG. 2 and the wireless protocol user 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 transferred 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 serves to map various logical channels to various transport channels, and also logical channel multiplexing to map several logical channels to one transport channel. Plays the role of. The MAC layer is connected to the upper layer RLC layer in a logical channel, and the logical channel includes a control channel for transmitting information of a control plane according to the type of information to be transmitted. It is divided into a traffic channel that transmits user plane information.

The Radio Link Control (RLC) layer of the second layer adjusts the data size so that the lower layer is suitable for transmitting data to the radio section by segmenting and concatenating data received from the upper layer. It plays a role. In addition, TM (Transparent Mode), UM (Un-acknowledged Mode), and AM (Acknowledged Mode,) to ensure the various QoS required by each radio bearer (RB) Response mode). In particular, the AM RLC performs a retransmission function through an automatic repeat and request (ARQ) function for reliable data transmission.

The Packet Data Convergence Protocol (PDCP) layer of the second layer is an IP containing relatively large and unnecessary control information for efficient transmission in a wireless bandwidth where bandwidth is small when transmitting an IP packet such as IPv4 or IPv6. Header Compression, which reduces the packet header size. 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 third-party data interception and integrity protection (Integrity protection) to prevent third-party data manipulation.

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 refers to a logical path provided by the first and second layers of the radio protocol for data transmission between the terminal and the UTRAN, and in general, the RB is set to mean that the radio protocol layer and channel required to provide a specific service are provided. The process of defining characteristics and setting each specific parameter and operation method. RB is divided into SRB (Signaling RB) and DRB (Data RB). SRB is used as a path for transmitting RRC messages in C-plane, and DRB is used as a path for transmitting user data in U-plane. do.

In the prior art, the receiving PDCP stores the PDCP SDUs received through RLC (Radio Link Control) re-establishment in the receiving buffer without reordering and reorders them. The PDCP SDUs stored in the reception buffer are transferred to the upper layer according to the SN comparison result when a new PDCP SDU is received after the RLC reestablishment.

In the prior art, retransmission of PDCP SDUs by the transmitting PDCP is based on the RLC status report rather than the RLC reestablishment. Therefore, in many cases, the PDCP may receive all missing PDCP SDUs through a large number of the RLC resets. For example, if a plurality of handovers occur within a predetermined time period, the probability of receiving all the lost PDCP SDUs is high because the plurality of handovers causes a plurality of RLC resets. However, overlapping retransmission of all the lost PDCP SDUs during the plurality of RLC resetting processes causes loss of radio resources or unnecessary time delay.

In addition, as mentioned above, in the prior art, since PDCP SDUs received through RLC re-establishment are stored in the reception buffer without being transferred to the upper layer, reordering is performed, which causes unnecessary delay time for data transmission. In addition, if the PDCP SDU received through RLC re-establishment is the last packet in the data stream, there is no more data to receive, so there is no deadlock. Occurs until

This continuous RLC re-establishment is caused by frequent handover when using a mobile terminal in a high-speed automobile. The prior art PDCP SDU delivery method is used in such high-speed driving. Since the performance of the mobile terminal is greatly reduced, there is a need for a solution.

Accordingly, an object of the present invention is that when PDLC receives PDCP SDU from RLC due to RLC re-establishment due to handover or the like, PDCP SDUs received continuously and in-sequence are delivered to the upper part, It is to reduce the delay time of data transmission.

In order to solve the above problems of the present invention, a data transmission method in a wireless communication system, comprising: receiving a data unit having a sequence number from a lower layer; Storing the received data unit in a buffer; Determining whether the serial number of the received data unit is the same as the serial number +1 of the last delivered data unit; And sequentially delivering all stored data units having serially connected serial numbers greater than or equal to the serial number of the received data unit based on the determining step.

Preferably, the lower layer is a Radio Link Control (RLC) layer.

Preferably, the determining step and the forwarding step are performed in a Packet Data Convergence Protocol (PDCP) entity.

Preferably, the data unit is characterized in that the PDCP Service Data Unit (PDCP SDU).

Preferably, the data unit is characterized in that received through the RLC re-establishment.

Preferably, header decompression or deciphering is performed between the receiving step and the storing step.

Preferably, the serial number +1 of the last delivered data unit represents the serial number immediately following the serial number of the last delivered data unit.

Preferably, the serial number +1 of the last delivered data unit represents the next serial number from the serial number of the last delivered data unit.

Preferably, the method further comprises setting the serial number of the last data unit delivered to the upper layer as 'LAST'.

In the prior art, when the RLC re-establishment occurs due to a handover or the like, the PDCP SDUs delivered to the PDCP are waited in the PDCP reception buffer even though they can be transferred upward. In the present invention, the PDCP SDU received through the RLC re-establishment is also proposed a method of performing the SN check as soon as possible to deliver to the upper level. This approach reduces latency in data transmission and also prevents deadlocks in the protocol for end of data streams.

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 idea of the present invention can be applied.

The basic concept of the present invention is a data transmission method in a wireless communication system in order to reduce the delay time of data transmission when delivering PDCP SDUs to a higher layer, having a sequence number from a lower layer. Receiving a data unit; Storing the received data unit in a buffer; Determining whether the serial number of the received data unit is the same as the serial number +1 of the last delivered data unit; And sequentially transferring all stored data units having serially connected serial numbers greater than or equal to the serial number of the received data unit based on the determining step. A wireless mobile communication terminal capable of performing the method is proposed.

Hereinafter, the configuration and operation of the embodiments according to the present invention will be described with reference to the accompanying drawings.

First, look at the PDCP entity in detail. The PDCP entity is connected to the RRC layer or user application at the top and to the RLC layer at the bottom.

4 is an exemplary diagram illustrating a PDCP entity structure to which the present invention is applied. 4 may be different from actual implementations as functional blocks.

First, the PDCP entity is composed of a transmitting side and a receiving side as shown in FIG. The PDCP entity of the sender configures peer PDCP entities by configuring a service data unit (SDU) received from an upper layer or control information generated by the PDCP entity itself as a protocol data unit (PDU). The PDCP entity on the receiving side serves to extract PDCP SDU or control information from the PDCP PDU received from the transmitting side of the peer PDCP entity.

As described above, there are two types of PDUs generated by the transmitting side of the PDCP entity, a Data PDU and a Control PDU. First, the PDCP data PDU is a data block that PDCP processes and processes the SDU received from the upper layer, and the PDCP control PDU is a data block that PDCP generates for itself to deliver control information to the peer entity.

The PDCP data PDU is generated in both a user plane and a radio bearer (RB) of a control plane. Some functions of the PDCP are selectively applied according to the plane used. That is, the header compression function is applied only to user plane data, and the integrity protection among security functions is only applied to control plane data. In addition to the integrity protection function, the security function also includes a ciphering function for maintaining data security. The encryption function is applied to both user plane (U-plane) and control plane (C-plane) data.

The PDCP control PDU is generated only in the U-plane RB. There are two types of PDCP control PDUs: a PDCP Status Report for informing the sender of PDCP reception buffer status and a Header Compression Feedback packet for informing the Header Compressor of the status of the Header Decompressor. have.

The data processing performed by the transmitter PDCP of FIG. 4 is as follows. First, for a received PDCP SDU, the PDCP layer stores it in a transmission buffer and assigns a sequence number to each PDCP SDU. (S1) If the configured radio bearer is an RB of the U-plane, that is, a data radio bearer (DRB), the PDCP layer performs header compression on the PDCP SDU. (S2) On the other hand, if the configured radio bearer is an RB of the C-plane, that is, a signaling radio bearer (SRB), the PDCP layer performs integrity protection on the PDCP SDU. After S3, the PDCP layer performs encryption on the data blocks generated as a result of step 2 or step 3. (S4) In addition, through step 4, for the data blocks to which encryption is applied, the PDCP layer configures a PDCP PDU with an appropriate header, and then delivers the configured PDCP PDU to the RLC layer.

The data processing performed by the receiving PDCP of FIG. 4 is as follows. First, for the received PDCP PDU, the PDCP layer removes the header. After S1, the PDCP layer performs de-ciphering on the PDCP PDU from which the header is removed. (S2) If the configured radio bearer is an RB of the U-plane, that is, a DRB (Data Radio Bearer), the PDCP layer performs header de-compression on the PDCP PDU which has been de-ciphered. . (S3) On the other hand, if the configured radio bearer is an RB of a C-plane, that is, a signaling radio bearer (SRB), the PDCP layer performs integrity verification on the PDCP PDUs that have undergone the de-ciphering process. Thereafter, the PDCP layer transfers the data blocks, that is, PDCP SDUs, received through the third or fourth process to the upper layer. (S5) If the configured radio bearer is a DRB (Data Radio Bearer) using RLC (Radio Link Control) AM (Acknowledged Mode), if necessary, after storing in the receive buffer and performing reordering (S6), To the layer.

In this case, when the configured radio bearer is a DRB (Data Radio Bearer) using RLC AM (Acknowledged Mode), reordering is necessary in step 6 of the receiving side. This is because the DRB using the RLC AM mainly transmits traffic sensitive to error of data, and performs retransmission to minimize the error in the radio section. That is, reordering function is required for PDCP to in-order delivery PDCP SDUs to upper layers in consideration of retransmitted PDCP SDUs. Therefore, for the DRB using the RLC AM, the PDCP receiver ensures in-sequence delivery to the PDCP PDU received with various state variables as follows.

First, state variables can be defined as follows:

RSN (Received Sequence Number): Sequence Number (SN) of the received PDCP SDU.

LAST (Last Submitted PDCP SDU SN): The sequence number of the last PDCP SDU delivered among the higher PDCP SDUs.

NEXT (Next expected PDCP SDU SN): The SN of the next PDCP SDU of the PDCP SDU having the largest SN among the received PDCP SDUs. That is, Highest PDCP SDU SN + 1.

When the PDCP receiving side receives the PDCP SDU with SN = RSN using the state variable as described above, the PDCP SDU processes the PDCP SDU as follows. For simplicity, all state variables and mathematical comparisons and calculations assume modulo operations. That is, all values have a value between 0 and 4095, and the smallest value is NEXT-2048.

First, when a PDCP SDU having a SN lower than a PDCP SDU previously delivered to a higher level is received, the received PDCP SDU is discarded because it is an outdate PDCP SDU. This process can be represented by the following procedure text.

if NEXT-2048 <= RSN <= LAST

decipher

-decompress

-discard

If a PDCP SDU corresponding to the PDCP SDU received between the last delivered PDCP SDU and the PDCP SDU having the largest SN value among the received PDCP SDUs is received, the received PDCP SDU is duplicated. Save it. This process can be represented by the following procedure text.

if LAST <RSN <NEXT

decipher

-decompress

-if not duplicate, store in the reception buffer

-if duplicate, discard

If a PDCP SDU having a larger SN than a PDCP SDU having the largest SN among the received PDCP SDUs is received, the received PDCP SDU is a new SDU and is stored in a reception buffer and NEXT is updated to RSN + 1. . This process can be represented by the following procedure text.

if NEXT <= RSN <NEXT + 2048

decipher

-decompress

-store in the reception buffer

-set NEXT to RSN + 1

When the received PDCP SDU is processed and stored in the reception buffer by using the above process, the PDCP then transfers the stored PDCP SDU to the upper part by the following process. This process can be represented by the following procedure text.

-if the PDCP SDU received by PDCP is not due to the RLC re-establishment:

deliver to upper layer in ascending order of the associated SN value:

all stored PDCP SDU (s) with an associated SN <RSN;

all stored PDCP SDU (s) with consecutively associated SN value (s)> = RSN;

-set LAST to the SN of the last PDCP SDU delivered to upper layers.

That is, the PDCP SDU delivery is performed only when the PDCP SDU is received in a general situation rather than an RLC reestablishment situation. In other words, PDCP SDUs received in an RLC re-establishment situation perform reordering while the PDCP is stored in a buffer rather than forwarded to the upper layer.

In a general situation, since PDCP receives PDCP SDUs in order without missing PDCP SDUs from RLC AM, PDCP also delivers them in order without reordering. However, when the RLC is re-established like a handover, the RLC transfers only the PDCP SDUs that have been successfully received to the PDCP in SN order, except for PDCP SDUs that have not been received. Therefore, there is a missing PDCP SDU. These missing PDCP SDUs can be recovered after RLC reestablishment by retransmitting PDCP SDUs not received by the PDCP by the peer PDCP entity. In this case, since the transmitting PDCP retransmits the PDCP SDU based on the most recent RLC status report before the RLC re-establishment occurrence, the PDCP SDU already successfully received may be retransmitted. Therefore, the SN value of the received PDCP SDU is discarded by comparison with LAST and NEXT or stored in the reception buffer.

However, some PDCP SDUs may be lost while performing RLC reestablishment. This occurs mainly when forwarding PDCP SDUs between eNBs due to handover. In other words, since some PDCP SDUs may not be retransmitted forever, PDCP SDUs with SNs smaller than the SNs of the received PDCP SDUs, even if they are not contiguous, are stopped by reordering them. To convey. That is, PDCP performs delivery without reordering if the received PDCP SDU is not an SDU received from the RLC reestablishment.

As described above, in the method of PDCP SDU delivery, all PDCP SDUs having an SN value smaller than RSN are transferred upward, and PDCP SDUs having an SN value larger than RSN are forwarded only PDCP SDUs having a consecutive SN after RSN. It is. After the possible PDCP SDUs are delivered to the upper level, the LAST value is set to the sequence number of the last PDCP SDU delivered among the PDCP SDUs transferred higher. 5 is a flowchart illustrating a process of delivering a PDCP data unit described above.

As shown in FIG. 5, a PDCP Protocol Data Unit (PDU) including a PDCP Service Data Unit (SDU) having a serial number is first received. The serial number is defined by the state variable 'RSN'. Thereafter, the PDCP SDU is stored in the PDCP buffer after header decompression and deciphering. Then, if the RSN is greater than or equal to the state variable 'NEXT', the NEXT is set to RSN + 1. Then, it is determined whether the received PDCP SDU has been received due to RLC re-establishment, and if so, the PDCP SDU delivery process is terminated immediately, if not, sequentially all stored PDCP SDUs having an associated serial number smaller than the RSN to higher layer. To pass. In addition, it sequentially delivers all stored PDCP SDUs with consecutively associated serial numbers greater than or equal to the RSN to a higher layer. Thereafter, the serial number of the last PDCP SDU delivered to the upper layer is set to the state variable 'LAST', and the PDCP SDU delivery process is terminated.

6 is an exemplary diagram illustrating a reordering and transferring process of a PDCP data unit. For convenience of explanation, it is assumed that one PDCP PDU is included in one RLC PDU. In addition, it is assumed that one PDCP PDU includes one PDCP SDU without considering the PDCP Control PDU.

As shown in FIG. 6, first, the receiving RLC sequentially receives up to RLC PDU = 13 and delivers them to the upper receiving PDCP, and at the same time, successfully receives up to RLC PDU = 13 through the RLC status report to the transmitting RLC. Inform. The receiving PDCP sequentially receives up to PDCP SDU = 22 and transfers them to the upper level. The transmitting PDCP may know from the RLC status report that the receiving PDCP has successfully received PDCP SDU = 22.

Immediately before the RLC reestablishment occurred, the transmitting RLC transmitted RLC PDU = 20 at RLC PDU = 14, but among them, RLC PDU = 16, 17, and 19 failed to transmit. The receiving side RLC sequentially receives the RLC PDUs up to RLC SN = 15 and delivers them to the upper PDCP, and the PDCP sequentially receives the PDCP SDUs included in the RLC PDU up to PDCP SN = 24 and delivers them to the upper layer. . LAST = 24, NEXT = 25 with PDCP SN = 24 up. RLC PDU 18 and RLC PDU 20 have been successfully received, but since the previous RLC PDUs were not received, these RLC PDUs are stored in the RLC receive buffer. The receiving RLC should inform the sending RLC of the situation through the RLC status report, but RLC reestablishment occurs before sending the RLC status report. (S1)

When the RLC reestablishment occurs due to a handover, etc., the RLC transmits the RLC PDUs stored in the buffer to the upper PDCP because the RLC successfully received but did not receive the previous PDU. In this example, RLC PDU = 18 and RLC PDU = 20 are delivered upstream. PDCP stores PDCP SDUs received due to RLC reestablishment in the PDCP receive buffer. Here, PDCP SDU = 27 and PDCP SDU = 29 are stored in the PDCP buffer. Since PDCP determines whether the PDCP SDU is successfully transmitted based on the most recent RLC status repot, it is determined that PDCP SDU = 22 was successfully transmitted, and PDCP SDU = 23-29 was not successful. do. (S2)

When the RLC re-establishment ends, the RLC initializes all state variables and resumes data transfer again. The sending PDCP retransmits PDCP SDUs that the receiving PDCP did not receive successfully before the RLC reestablishment. In this case, some PDCP SDUs may be lost, and the transmitting PDCP sequentially retransmits only PDCP SDUs that can be transmitted.

The transmitting PDCP retransmits PDCP SDUs that were not successfully transmitted before RLC reestablishment based on the most recent RLC status report. In this example, the sending PDCP retransmits PDCP SDU = 23 ~ 29. Since RLC becomes re-establishment, these PDCP SDUs are transmitted via RLC PDU = 0-6. When the receiving RLC receives these RLC PDUs, the receiving RLC sequentially transfers the received RLC PDUs to the upper receiving PDCP. Upon receipt of these, the receiving PDCP discards PDCP SDUs = 23, 24 since SN is less than or equal to LAST, and discards PDCP SDUs received since PDCP SDUs = 27, 29 are already stored. The receiving PDCP sequentially delivers PDCP SDU = 25 ~ 29. After the receiving PDCP delivers the deliverable PDCP SDU, it is updated to LAST = 29 and NEXT = 30. (S3-1)

In handover, the source eNB forwards PDCP SDUs that have not been successfully transmitted before handover to the target eNB, and data loss may occur at an interface between networks. In this example, the source eNB forwarded PDCP SDU = 23-29 to the target eNB, but PDCP SDU = 23-27 is lost. Accordingly, the transmitting PDCP transmits the PDCP SDUs in the order of RLC PDUs 0 to 3 in the order of 28, 29, 30, and 31. When the receiving RLC receives these RLC PDUs, the receiving RLC sequentially transfers the received RLC PDUs to the upper receiving PDCP. Upon receipt of these, the receiving PDCP discards PDCP SDUs = 23, 24 since SN is less than or equal to LAST, and discards PDCP SDUs received since PDCP SDUs = 27, 29 are already stored. The receiving PDCP sequentially delivers PDCP SDU = 25 ~ 29. When receiving PDCP SDU = 28 included in RLC PDU = 0, the receiving PDCP forwards PDCP SDU = 27 having a smaller SN. In addition, PDCP SDU = 28 and subsequent sequential PDCP SDU = 29 is also delivered to the upper level. After the receiving PDCP delivers the deliverable PDCP SDU, it is updated to LAST = 29 and NEXT = 30. (S3-2)

FIG. 7 is an exemplary diagram illustrating a process in which a PDCP data unit is not sequentially transmitted even when sequentially received.

As shown in FIG. 7, first, the receiving side RLC sequentially receives up to RLC PDU = 13 and delivers them to the upper receiving PDCP, and at the same time, successfully receives up to RLC PDU = 13 through the RLC status report to the transmitting RLC. Inform. The receiving PDCP sequentially receives up to PDCP SDU = 22 and transfers them to the upper level. The transmitting PDCP may know from the RLC status report that the receiving PDCP has successfully received PDCP SDU = 22.

Immediately before the RLC reestablishment occurred, the transmitting RLC transmitted RLC PDU = 20 at RLC PDU = 14, but among them, RLC PDU = 16, 17, and 19 failed to transmit. The receiving side RLC sequentially receives the RLC PDUs up to RLC SN = 15 and delivers them to the upper PDCP, and the PDCP sequentially receives the PDCP SDUs included in the RLC PDU up to PDCP SN = 24 and delivers them to the upper layer. . LAST = 24, NEXT = 25 with PDCP SN = 24 up. RLC PDU 18 and RLC PDU 20 have been successfully received, but since the previous RLC PDUs were not received, these RLC PDUs are stored in the RLC receive buffer. The receiving RLC should inform the sending RLC of the situation through the RLC status report, but RLC reestablishment occurs before sending the RLC status report. (S1)

When the RLC reestablishment occurs due to a handover, etc., the RLC transmits the RLC PDUs stored in the buffer to the upper PDCP because the RLC successfully received but did not receive the previous PDU. In this example, RLC PDU = 18 and RLC PDU = 20 are delivered upstream. PDCP stores PDCP SDUs received due to RLC reestablishment in the PDCP receive buffer. Here, PDCP SDU = 27 and PDCP SDU = 29 are stored in the PDCP buffer. Since PDCP determines whether the PDCP SDU is successfully transmitted based on the most recent RLC status repot, it is determined that PDCP SDU = 22 was successfully transmitted, and PDCP SDU = 23-29 was not successful. do. (S2)

After the first RLC re-establishment, all of the RLC PDUs containing missing PDCP SDUs were successfully received, but the RLC PDUs containing the PDCP SDUs that were already successfully received were not received and the successfully received RLC PDUs are stored in the RLC buffer. (S3) When another RLC re-establishment occurs, the receiving PDCP can successfully receive all missing PDCP SDUs through the second RLC re-establishment. However, as shown in FIG. 7, even in this case, sequentially received PDCP SDUs may not be delivered to a higher layer. (S4)

As mentioned above, an object of the present invention is that when PDLC receives PDCP SDU from RLC due to RLC re-establishment due to handover, PDCP SDUs received continuously and in-sequence are transferred upward. It is to reduce the delay time of data transmission.

To this end, in the present invention, when the PDCP receives the PDCP SDU from the RLC and stores it in a buffer through deciphering / decompression, the present invention proposes to deliver the PDCP to the upper layer using the following procedure text.

if RSN = LAST + 1:

deliver to upper layer in ascending order of the associated SN value:

all stored PDCP SDU (s) with consecutively associated SN value (s)> = RSN;

set LAST to the SN of the last PDCP SDU delivered to upper layers;

-else if the PDCP SDU received by PDCP is not due to the RLC re-establishment:

deliver to upper layer in ascending order of the associated SN value:

all stored PDCP SDU (s) with an associated SN <RSN;

all stored PDCP SDU (s) with consecutively associated SN value (s)> = RSN;

-set LAST to the SN of the last PDCP SDU delivered to upper layers.

That is, even if PDCP receives the PDCP SDU through RLC re-establishment, the PDCP SDU is not stored in the receiving buffer unconditionally, but the received PDCP SDU serial number is LAST (the last PDCP SDU delivered among the higher PDCP SDUs). Sequentially checks if the received PDCP SDU is LAST + 1, and if the received PDCP SDUs have sequential PDCP SDUs with a subsequent serial number (SN) To pass to the parent. In other words, when a PDCP receives a PDCP SDU in any path, it must check if it is a PDCP SDU that should be delivered to the next (in-sequence) of the last PDCP SDU delivered to the upper level, and then immediately forward it. If the PDCP SDU is correct, the PDCP SDUs and subsequent PDCP SDUs having SNs sequentially in-sequence are transferred directly to the upper part without waiting in the reception buffer.

8 is an exemplary view illustrating a PDCP data unit delivery process according to the present invention.

As shown in FIG. 8, a PDCP Protocol Data Unit (PDU) including a PDCP Service Data Unit (SDU) having a serial number is first received. The serial number is defined by the state variable 'RSN'. Thereafter, the PDCP SDU is stored in the PDCP buffer after header decompression and deciphering. Then, if the RSN is greater than or equal to the state variable 'NEXT', the NEXT is set to RSN + 1. Then, according to the method of the present invention described above, it is determined or checked whether the serial number of the received PDCP SDU, that is, the RSN is LAST (SN of the last PDCP SDU delivered from the higher PDCP SDU) + 1. If the RSN is LAST + 1, the received PDCP SDUs and subsequent PDCP SDUs having a serial number (SN) that are sequentially in-sequence are sequentially transmitted to the upper part. Thereafter, the serial number of the last PDCP SDU delivered to the upper layer is set to the state variable 'LAST', and the PDCP SDU delivery process is terminated. If the RSN is not LAST + 1, it is determined whether the received PDCP SDU has been received due to RLC re-establishment, and if so the PDCP SDU delivery process is terminated immediately, if not the associated serial number smaller than the RSN to the higher layer. All stored PDCP SDUs are delivered sequentially. In addition, it sequentially delivers all stored PDCP SDUs with consecutively associated serial numbers greater than or equal to the RSN to a higher layer. Thereafter, the serial number of the last PDCP SDU delivered to the upper layer is set to the state variable 'LAST', and the PDCP SDU delivery process is terminated.

The procedure of comparing the SN of the PDCP SDU received above with LAST + 1 and the procedure of checking whether the PDCP SDU is received through RLC reestablishment are mutually exclusive. Therefore, first, the PDCP SDU may check whether it is received through RLC re-establishment, and when receiving it through RLC re-establishment, RSN may be compared with LAST + 1. If the SN of the received PDCP SDU is LAST + 1, the PDCP SDUs having the received PDCP SDUs and subsequent SNs having an in-sequence thereafter are sequentially delivered in the same manner as the above method. In other words, even if the two tests are reversed, the result is the same, so the following procedure text is possible.

-if the PDCP SDU received by PDCP is not due to the RLC re-establishment:

deliver to upper layer in ascending order of the associated SN value:

all stored PDCP SDU (s) with an associated SN <RSN;

all stored PDCP SDU (s) with consecutively associated SN value (s)> = RSN;

-set LAST to the SN of the last PDCP SDU delivered to upper layers.

else if RSN = LAST + 1:

deliver to upper layer in ascending order of the associated SN value:

all stored PDCP SDU (s) with consecutively associated SN value (s)> = RSN;

set LAST to the SN of the last PDCP SDU delivered to upper layers;

9 is another exemplary diagram illustrating a PDCP data unit delivery process according to the present invention.

As shown in FIG. 9, first, a PDCP Protocol Data Unit (PDU) including a PDCP Service Data Unit (SDU) having a serial number is received. The serial number is defined by the state variable 'RSN'. Thereafter, the PDCP SDU is stored in the PDCP buffer after header decompression and deciphering. Then, if the RSN is greater than or equal to the state variable 'NEXT', the NEXT is set to RSN + 1. Then, it is determined whether the received PDCP SDU has been received due to RLC re-establishment, and if so, the serial number of the received PDCP SDU, that is, the RSN is LAST (SN of the last PDCP SDU delivered higher) + 1 Judge or examine cognition. Here, if the RSN is LAST + 1, the received PDCP SDUs and PDCP SDUs having an in-sequence serial number (SN) successively are sequentially transmitted upward. Thereafter, the serial number of the last PDCP SDU delivered to the upper layer is set to the state variable 'LAST', and the PDCP SDU delivery process is terminated. If the RSN is not LAST + 1, the PDCP SDU delivery process ends immediately. If it is determined that the received PDCP SDU has not been received due to RLC re-establishment, it sequentially transmits all stored PDCP SDUs having an associated serial number smaller than the RSN to a higher layer, and also transmits to a higher layer than the RSN. All stored PDCP SDUs with successive associated serial numbers greater than or equal to are delivered sequentially. Thereafter, the serial number of the last PDCP SDU delivered to the upper layer is set to the state variable 'LAST', and the PDCP SDU delivery process is terminated.

In the present invention, the aforementioned PDCP SN may be included in the COUNT format. That is, the COUNT value may consist of a Hyper Frame Number (HFN) and a PDCP SN. The length of the PDCP SN may be set by a higher layer. The use of the COUNT value or PDCP SN may be used to avoid wrap around problems.

Hereinafter, a terminal according to the present invention will be described.

The terminal according to the present invention includes all types of terminals that can use a service that can exchange data with each other over the air. That is, the terminal according to the present invention is a mobile communication terminal capable of using a wireless communication service (for example, user equipment (UE), mobile phone, cellular phone, DMB phone, DVB-H phone, PDA phone, and PTT phone, etc.) It is a comprehensive meaning including laptops, laptops, laptops, digital TVs, GPS navigation, handheld game consoles, MP3s, and other consumer electronics.

The terminal according to the present invention may include a basic hardware configuration (transmitter / receiver, processor or controller, storage, etc.) required to perform functions and operations for efficient system information reception illustrated in the present invention.

The method according to the invention described thus far can be implemented in software, hardware, or a combination thereof. For example, the method according to the present invention may be stored in a storage medium (eg, internal memory of a mobile terminal or base station, flash memory, hard disk, etc.) and may be stored in a processor (eg, mobile terminal or base station). Code or instructions within a software program that can be executed by an internal microprocessor).

In the above, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary and will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a network structure of E-UTRAN, which is a mobile communication system to which the present invention and the present invention are applied.

Figure 2 is an exemplary view showing a control plane structure of a radio interface protocol between the terminal and the E-UTRAN in the prior art.

3 is an exemplary diagram illustrating a user plane structure of a radio interface protocol between a terminal and an E-UTRAN in the prior art.

4 is an exemplary diagram illustrating a PDCP entity structure to which the present invention is applied.

5 is a flowchart illustrating a PDCP data unit delivery process.

6 is an exemplary diagram illustrating a reordering and transferring process of a PDCP data unit.

FIG. 7 is an exemplary diagram illustrating a process in which a PDCP data unit is not sequentially transmitted even when sequentially received.

8 is an exemplary view illustrating a PDCP data unit delivery process according to the present invention.

9 is another exemplary diagram illustrating a PDCP data unit delivery process according to the present invention.

Claims (9)

As a data transmission method on a wireless communication system, Receiving a data unit with a sequence number from a lower layer; Storing the received data unit in a buffer; Determining whether the serial number of the received data unit is the same as the serial number +1 of the last delivered data unit; And  And sequentially delivering all stored data units having serially connected serial numbers greater than or equal to the serial number of the received data unit based on the determining step. The method of claim 1, wherein the lower layer is a Radio Link Control (RLC) layer. 2. The method of claim 1, wherein said determining and forwarding step is performed at a Packet Data Convergence Protocol (PDCP) entity. The method of claim 1, wherein the data unit is a PDCP Service Data Unit (PDCP SDU). The method of claim 1, wherein the data unit is received through RLC re-establishment. 2. The method of claim 1, wherein header decompression or deciphering is performed between the receiving and storing steps. The method of claim 1, wherein a serial number +1 of the last delivered data unit indicates a serial number immediately after the serial number of the last delivered data unit. The method of claim 1, wherein the serial number +1 of the last delivered data unit represents a next serial number from the serial number of the last delivered data unit. 2. The method of claim 1, further comprising setting a serial number of the last data unit delivered to a higher layer as 'LAST'.

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