CN110495211B

CN110495211B - Apparatus in wireless communication system and buffer control method thereof

Info

Publication number: CN110495211B
Application number: CN201880023557.3A
Authority: CN
Inventors: 金东建; 金成勋; 张宰赫
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2017-03-31
Filing date: 2018-04-02
Publication date: 2023-05-02
Anticipated expiration: 2038-04-02
Also published as: CN110495211A; KR102293999B1; KR20180111413A

Abstract

A 5G communication system or pre-5G communication system for supporting a higher data rate than that of a super 4G communication system such as LTE is provided. A method for controlling a buffer by an apparatus in a wireless communication system includes storing information related to a packet in at least one of a first buffer or a second buffer, transmitting data generated based on the packet, and discarding the information when an acknowledgement signal is received for the data.

Description

Apparatus in wireless communication system and buffer control method thereof

Technical Field

The present disclosure relates to operations of a terminal and a base station in a next generation mobile communication system, and more particularly, to a method for efficiently managing buffers by a terminal and a base station, and a method and apparatus capable of accelerating retransmission during retransmission.

Background

In order to meet the demand for wireless data services that have increased since the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Therefore, a 5G or pre-5G communication system is also referred to as a "super 4G network" or a "LTE-after-system".

The 5G communication system is considered to be implemented in a higher frequency (millimeter wave) band, for example, a 60GHz band, in order to achieve a higher data rate. In order to reduce propagation loss of radio waves and increase transmission distance, beamforming, massive Multiple-Input Multiple-Output (MIMO), full-Dimensional Multiple-Input Multiple-Output (FD-MIMO), array antennas, analog beamforming, and large-scale antenna techniques are discussed in 5G communication systems.

Further, in the 5G communication system, development of system network improvement is performed based on advanced small cells, cloud radio access networks (Radio Access Network, RAN), ultra dense networks, device-to-Device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, coordinated multipoint (Coordinated Multi-Points, coMP), reception-side interference cancellation, and the like.

In 5G systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (Sliding Window Superposition Coding, SWSC) as advanced code modulation (Advanced Coding Modulation, ACM) have been developed, as well as filter bank multicarrier (Filter Bank Multi Carrier, FBMC), non-orthogonal multiple access (Non-Orthogonal Multiple Access, NOMA) and sparse code multiple access (Sparse Code Multiple Access, SCMA) as advanced access techniques. On the other hand, in the next generation mobile communication system, a method for a base station to efficiently manage a buffer and a method capable of accelerating retransmission are required.

The above information is presented merely as background information to aid in the understanding of the present disclosure. No determination is made, nor is an assertion made, as to whether any of the above information is applicable as prior art with respect to the present disclosure.

Disclosure of Invention

Technical problem

Aspects of the present disclosure address at least the above problems and/or disadvantages and provide at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide a method for efficiently managing buffers and an implementation method thereof in different buffer structures. Furthermore, the present disclosure proposes a method for accelerating retransmission and efficiently managing buffers in a next generation mobile communication system, and an implementation method thereof in a different buffer structure.

Problem solution

According to an aspect of the present disclosure, there is provided a method for controlling a buffer by an apparatus in a wireless communication system. The method comprises the following steps: storing information related to the packet in at least one of the first buffer or the second buffer; transmitting data generated based on the packet; and discarding the information when an acknowledgement signal is received for the data.

According to another aspect of the present disclosure, a method for controlling a buffer by an apparatus in a wireless communication system is provided. The method comprises the following steps: storing first information related to the first packet in a third buffer; storing second information related to the second packet in a fourth buffer, wherein the second information is generated by preprocessing the first packet before acquiring resource information for transmitting the first packet; identifying mapping information between the position information of the third buffer and the position information of the fourth buffer; and transmitting data corresponding to the second packet based on the resource information when the resource information is received.

According to another aspect of the present disclosure, an apparatus in a wireless communication system is provided. The apparatus includes a transceiver and at least one processor configured to: storing information related to the packet in at least one of the first buffer or the second buffer; transmitting data generated based on the packet; and discarding the information when an acknowledgement signal is received for the data.

According to another aspect of the present disclosure, an apparatus in a wireless communication system is provided. The apparatus includes a transceiver and at least one processor configured to: storing first information related to the first packet in a third buffer; storing second information in a fourth buffer, the second information being related to a second packet generated by preprocessing the first packet before acquiring resource information for transmitting the first packet; identifying mapping information between the position information of the third buffer and the position information of the fourth buffer; and transmitting data corresponding to the second packet based on the resource information when the resource information is received.

Advantageous effects of the invention

According to the embodiments of the present disclosure, it is possible to improve efficiency of buffer management of a terminal and increase a data rate.

Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the disclosure.

Drawings

The foregoing and other aspects, features, and advantages of certain embodiments of the disclosure will become more apparent from the following description, taken in conjunction with the accompanying drawings, in which:

fig. 1 is a diagram illustrating a structure of a long term evolution (Long Term Evolution, LTE) system according to an embodiment of the present disclosure;

fig. 2 is a diagram illustrating a radio protocol structure of an LTE system according to an embodiment of the present disclosure;

fig. 3 is a diagram illustrating a structure of a next generation mobile communication system according to an embodiment of the present disclosure;

fig. 4 is a diagram illustrating a radio protocol structure of a next generation mobile communication system according to an embodiment of the present disclosure;

fig. 5A and 5B are diagrams illustrating a data processing structure in an LTE system according to an embodiment of the present disclosure;

fig. 6 is a diagram illustrating a first embodiment of an efficient buffer management method applicable when an LTE system terminal operates in a radio link control (Radio Link Control, RLC) acknowledged mode (Acknowledged Mode, AM) according to an embodiment of the present disclosure;

Fig. 7 is a diagram illustrating a mapping table and corresponding operations of an efficient buffer management method when an LTE system terminal operates in RLC AM mode according to an embodiment of the present disclosure;

fig. 8A and 8B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure;

fig. 9A and 9B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLC unacknowledged mode (Unacknowledged Mode, UM) according to an embodiment of the present disclosure;

fig. 10A and 10B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure;

fig. 11A and 11B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in RLC UM mode according to an embodiment of the present disclosure;

fig. 12 is a diagram illustrating a mapping table and a buffer management method applicable when an LTE system terminal operates in RLC AM mode according to an embodiment of the present disclosure;

fig. 13A and 13B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure;

Fig. 14A and 14B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in RLC UM mode according to an embodiment of the present disclosure;

fig. 15A and 15B are diagrams illustrating a data processing structure in a next generation mobile communication system according to an embodiment of the present disclosure;

fig. 16 is a diagram illustrating a mapping table and a retransmission acceleration method applicable when a next generation mobile communication system terminal is operated in an RLC AM mode, proposed according to an embodiment of the present disclosure;

fig. 17A and 17B are diagrams illustrating an operation of a terminal in which a next generation mobile communication system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure;

fig. 18A and 18B are diagrams illustrating an operation of a terminal in which a next generation mobile communication system terminal manages a buffer in RLC UM mode according to an embodiment of the present disclosure;

fig. 19 is a block diagram of a terminal according to an embodiment of the present disclosure;

fig. 20 is a block diagram of a transmission and reception point (Transmission and Reception Point, TRP) in a wireless communication system according to an embodiment of the disclosure; and is also provided with

Fig. 21 is a diagram illustrating a method for preprocessing data of a multi-connection terminal according to an embodiment of the present disclosure.

Throughout the drawings, it should be noted that like reference numerals are used to depict the same or similar elements, features and structures.

Detailed Description

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of the various embodiments of the disclosure defined by the claims and their equivalents. It includes various specific details to aid understanding, but these are merely to be considered exemplary. Accordingly, one of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to written meanings, but are used only by the inventors to enable a clear and consistent understanding of the disclosure. Accordingly, it will be apparent to those skilled in the art that the following descriptions of the various embodiments of the present disclosure are provided for illustration only and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.

It will be understood that the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "component surface" includes reference to one or more of such surfaces.

In describing the present disclosure, well-known functions or configurations incorporated herein will not be described in detail in order to determine that the related well-known functions or configurations incorporated herein obscure the subject matter of the present disclosure in unnecessary detail. Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings.

Hereinafter, for convenience of explanation, terms for identifying connection nodes, terms for referring to network entities, terms for referring to messages, terms for referring to interfaces between network entities, and terms for referring to various identification information as used in the following description are exemplified. Accordingly, the present disclosure is not limited to terms that will be described later, but other terms for referring to objects having equivalent technical meanings may be used.

Hereinafter, for convenience of explanation, terms and headings defined in the third generation partnership project Long Term Evolution (LTE) standard are used in the present disclosure. However, the present disclosure is not limited by the terms and headings, but may be equally applied to systems that conform to other standards.

In the next generation mobile communication system, it is necessary to support a peak data rate of 20Gbps in the downlink and a peak data rate of 10Gbps in the uplink, and a considerably short delay response time is required. Therefore, in the case of a service terminal in the next generation mobile communication system, a considerably high transmission/reception data processing speed is necessary. Therefore, a method for accelerating data processing of a terminal is important. Furthermore, in order to support high data rates and to speed up data processing, efficient buffer management is also important. One of the biggest reasons for greatly reducing the data rate in a mobile communication system is a delay due to retransmission. Therefore, in order to support a high data rate in the next generation mobile communication system, it is necessary to accelerate retransmission.

The LTE system has a data processing structure different from that of the next generation mobile communication system. In particular, in the LTE system, a Radio Link Control (RLC) layer performs an RLC concatenation function, and thus a terminal cannot perform some data pre-processing until it receives uplink transmission resources from a network. If an uplink transmission source is received, the terminal generates and transmits an RLC PDU through concatenation of PDCP Packet Data Units (PDUs) transmitted from a Packet Data convergence protocol (Packet Data Convergence Protocol, PDCP) layer to a medium access control (Media Access Control, MAC) layer to continue Data transmission.

In contrast, in the next generation mobile communication system, the RLC layer does not have an RLC concatenation function, and thus the terminal has a data processing structure capable of generating and transmitting RLC PDUs to the MAC layer by processing PDCP PDUs transmitted from the PDCP layer through the RLC layer before receiving uplink transmission resources, and pre-generating MAC subheaders and MAC service data units (Service Data Unit, SDUs).

Therefore, it is necessary to implement a method for efficiently managing a buffer and a method for accelerating retransmission in different methods according to different data processing structures.

Fig. 1 is a diagram illustrating a structure of an LTE system according to an embodiment of the present disclosure.

Referring to fig. 1, as shown, a Radio Access Network (RAN) of the LTE system is composed of Evolved Nodes (ENBs) 105, 110, 115, and 120 (also referred to as base stations), a mobility management entity (Mobility Management Entity, MME) 125, and a Serving-GateWay (S-GW) 130. A terminal or User Equipment (UE) 35 accesses an external network through the ENBs 105 to 120 and the S-GW 130.

In fig. 1, the ENBs 105 to 120 correspond to existing node bs of UMTS (Universal Mobile Telecommunications System ). The ENB connects to the UE 135 on a radio channel and plays a more complex role than the existing node B. In the LTE system, since all user traffic includes real-time services such as voice over internet protocol (Internet Protocol, IP) (voice over internet protocol, voIP) serviced on a shared channel, a device that performs scheduling by combining state information such as a buffer state, an available transmission power state, and a channel state of each UE is necessary, and the ENBs 105 to 120 correspond to such scheduling devices. Typically, one ENB controls a plurality of cells. For example, in order to implement a transmission speed of 100Mbps, the LTE system uses orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) in, for example, a 20MHz bandwidth as a radio access technology. In addition, the LTE system employs an Adaptive Modulation and Coding (AMC) scheme that determines a modulation scheme and a channel Coding rate to match the channel state of a terminal. The S-GW 130 provides data bearers and generates or removes data bearers under control of the MME 125. The MME controls mobility management and various control functions of the terminal and is connected to a plurality of base stations.

Fig. 2 is a diagram illustrating a radio protocol structure of an LTE system according to an embodiment of the present disclosure.

Referring to fig. 2, in a UE or ENB, a radio protocol of an LTE system is composed of PDCP 205 or 240,

RLC

210 or 235, and

MAC

215 or 230. PDCP 205 or 240 is responsible for IP header compression/decompression operations. The main functions of PDCP are summarized as follows.

Header compression and decompression: robust header compression only (RObust Header Compression, ROHC)

Delivery of user data

-in-order delivery of upper layer PDUs during PDCP re-establishment of radio resource control (Radio Resource Control, RRC) Acknowledged Mode (AM)

-for split bearers (RLC AM only) in dual connectivity (Dual Connectivity, DC): PDCP PDU routing for transmission and PDCP PDU reordering for reception

Duplicate detection of lower layer SDUs during PDCP re-establishment of RLC AM

Retransmission of PDCP SDUs at handover for split bearers in DC and PDCP PDUs during PDCP data recovery for RLC AM

-encryption and decryption

Timer based SDU discard in uplink

The

RLC

210 or 235 reconfigures PDCP PDUs having an appropriate size and performs an automatic repeat request (Automatic Repeat Request, ARQ) operation, etc. The main functions of RLC are summarized as follows.

Delivery of upper layer PDUs

Error correction by ARQ (for AM data transfer only)

Concatenation, segmentation and reassembly of RLC SDUs (for UM and AM data transfer only)

Re-segmentation of RLC data PDU (for UM and AM data transfer only)

Reordering of RLC data PDUs (for UM and AM data transfer only)

Duplicate detection (for UM and AM data delivery only)

Protocol error detection (for AM data transfer only)

RLC SDU discard (for UM and AM delivery only)

RLC re-establishment

The

MAC

215 or 230 is connected to several RLC layer devices configured in one terminal, and performs multiplexing/de-multiplexing RLC PDUs into/from MAC PDUs. The main functions of the MAC are summarized as follows.

Mapping between logical channels and transport channels

Multiplexing/de-multiplexing a MAC SDU belonging to one or different logical channels as Transport Block (TB) delivered to/from the physical layer on a Transport channel

Scheduling information reporting

Hybrid automatic repeat request (Hybrid Automatic Repeat Request, HARQ) function (error correction by HARQ)

Priority handling between logical channels of a UE

Priority handling between UEs by dynamic scheduling

-multimedia broadcast multicast service (Multimedia Broadcast Multicast Service, MBMS) service identification

Transport format selection

-filling

The

physical layer

220 or 225 performs channel coding and modulation of upper layer data to configure and transmit OFDM symbols to a radio channel, or performs demodulation and channel decoding of OFDM symbols received on the radio channel to deliver the demodulated and channel decoded data to an upper layer.

Fig. 3 is a diagram illustrating a structure of a next generation mobile communication system according to an embodiment of the present disclosure.

Referring to fig. 3, as shown, the RAN of the next generation mobile communication system (NR or 5G) is composed of a new radio node B (NR gNB or NR ENB) 310 and a new radio core network (new radio core network, NR CN) 305. A new radio user equipment (NR UE or terminal) 315 accesses the external network through NR gNB 310 and NR CN 305.

In fig. 3, NR gNB 310 corresponds to an ENB of an existing LTE system. The NR gNB is connected to the NR UE 315 on a radio channel, so it can provide a service superior to that of the existing node B. Since all user traffic is served on a shared channel in the next generation mobile communication system, a device that performs scheduling by combining state information such as a buffer state, an available transmission power state, and a channel state of each UE is necessary, and the NR gNB 310 is responsible for this. One NR gNB typically controls multiple cells. To implement ultra-high speed data transmission compared to existing LTE, an NR gNB or cell may have an existing maximum bandwidth or more, and may additionally include a beamforming technique in consideration of OFDM as a wireless connection technique. In addition, an AMC scheme that determines a modulation scheme and a channel coding rate to match the channel state of the UE is employed.

The NR CN 305 performs the functions of mobility support, bearer configuration, and quality of service (Quality Of Service, qoS) configuration. The NR CN is responsible for terminal mobility management and various control functions, and is connected to a plurality of ENBs. Further, the next generation mobile communication system may also be configured to communicate with existing LTE systems within the area 320, and the NR CN is connected to the MME 325 through a network interface. The MME is connected to an ENB 330 as an existing base station.

Fig. 4 is a diagram illustrating a radio protocol structure of a next generation mobile communication system according to an embodiment of the present disclosure.

Referring to fig. 4, in the UE or the NR ENB, a radio protocol of the next generation mobile communication system is composed of

NR PDCP

405 or 440,

NR RLC

410 or 435, and

NR MAC

415 or 430. The main functions of the

NR PDCP

405 or 440 may include part of the following functions.

Header compression and decompression: ROHC only

Delivery of user data

In-order delivery of upper layer PDUs

Reordering of PDCP PDUs for reception

Duplicate detection of lower layer SDUs

Retransmission of PDCP SDUs

-encryption and decryption

Timer based SDU discard in uplink

As described above, reordering the NR PDCP devices may mean reordering PDCP PDUs received from a lower layer based on a PDCP Sequence Number (SN). The reordering may include delivering data to an upper layer in a reordered order, recording lost PDCP PDUs by reordering status reports for the lost PDCP PDUs to a transmitting side, and a retransmission request for the lost PDCP PDUs.

The main functions of

NR RLC

410 or 435 may include part of the following functions.

Delivery of upper layer PDUs

In-order delivery of upper layer PDUs

Out-of-order delivery of upper layer PDUs

Error correction by ARQ

Concatenation, segmentation and reassembly of RLC SDUs

Re-segmentation of RLC data PDUs

Reordering of RLC data PDUs

-repeated detection

Protocol error detection

RLC SDU discard

RLC re-establishment

As described above, the in-order delivery of RLC NR devices may mean in-order delivery of RLC SDUs received from a lower layer to an upper layer. In case one RLC SDU is segmented into several RLC SDUs to be received, the in-sequence delivery of the NR RLC device may comprise reassembly and delivery of RLC SDUs. Further, the in-order delivery of the NR RLC device may include reordering RLC PDUs based on RLC SNs or PDCP SNs, recording missing RLC PDUs by reordering, performing status reporting for the missing RLC PDUs to the transmitting side, and a retransmission request for the missing PDCP PDUs. Further, the in-order delivery of NR RLC devices may include: if there is a missing RLC SDU, only RLC SDUs immediately preceding the missing RLC SDU are delivered to an upper layer in sequence; if a specific timer has expired despite the presence of missing RLC SDUs, all RLC SDUs received before the timer starts its operation are delivered to an upper layer in sequence; or if the timer has expired, all RLC SDUs received so far are delivered to the upper layer in order, although there are missing RLC SDUs. Further, the NR RLC layer can process RLC PDUs in the order in which they are received (in the order in which they arrive regardless of the sequence number), and can deliver RLC PDUs to the PDCP device in an out-of-order delivery manner. In case the packet is segmented, the segment stored in the buffer or to be received later is received and reconfigured to a complete RLC PDU to be processed and delivered to the PDCP device. The NR RLC layer may not include a concatenation function, and the function may be performed by the NR MAC layer or may be replaced by a multiplexing function of the NR MAC layer.

As described above, out-of-order delivery of the NR RLC device means a function of directly delivering RLC SDUs received from a lower layer to an upper layer in an out-of-order delivery manner. If one RLC SDU is segmented into several RLC SDUs to be received, out-of-order delivery may include reassembly and delivery of RLC SDUs, and recording missing RLC SDUs by storing and ordering RLC SN or PDCP SN of RLC PDUs.

The

NR MAC

415 or 430 may be connected to several NR RLC layer devices configured in one terminal, and a main function of the NR MAC may include part of the following functions.

Mapping between logical channels and transport channels

Multiplexing/demultiplexing of MAC SDUs

Scheduling information reporting

HARQ functionality (error correction by HARQ)

Priority handling between logical channels of a UE

Priority handling between UEs by dynamic scheduling

MBMS service identity

Transport format selection

-filling

NR

physical layer

420 or 425 may perform channel coding and modulation of upper layer data to configure and transmit OFDM symbols to a radio channel, or may perform demodulation and channel decoding of OFDM symbols received on a radio channel to deliver the demodulated and channel decoded data to an upper layer.

Fig. 5A and 5B are diagrams illustrating a data processing structure in an LTE system according to an embodiment of the present disclosure.

Referring to fig. 5A and 5b, the lte system performs PDCP layer and RLC layer data processing for a logical channel. That is, logical channel 1 505 and logical channel 2 510 have different PDCP layers and RLC layers, and perform independent data processing. In addition, the LTE system delivers RLC PDUs generated from the RLC layers of the respective logical channels to the MAC layer to configure one MAC PDU, and transmits the MAC PDU to the receiving end. In the LTE system, the PDCP layer, RLC layer, and MAC layer may include the functions described above with reference to fig. 2, and may perform operations corresponding to the functions.

In the LTE system, the RLC layer may concatenate PDCP PDUs. Further, in the LTE system, in the PDCP PDU structure denoted by reference numeral 525, all MAC subheaders are located at the front of MAC PDUs, and a MAC SDU part is located at the rear of MAC PDUs. Due to the above features, in the LTE system, the RLC layer cannot pre-perform or prepare data processing until the terminal receives the uplink grant.

As shown in fig. 5A and 5B, if an uplink grant 530 is received, the terminal generates RLC PDUs by concatenating PDCP PDUs received from the PDCP layer to match the uplink grant. After the MAC layer 520 receives the uplink grant from the base station, the terminal performs logical channel prioritization (Logical Channel Prioritization, LCP) and divides the uplink grant for each logical channel. That is, the uplink grant 530 is an uplink transmission resource allocated from the base station to the MAC layer 520. If the size of the PDCP PDU to be concatenated does not match the size of the uplink grant, the RLC layer 515 performs a segmentation procedure such that the PDCP PDU matches the uplink grant. The terminal may perform the above procedure for the respective logical channels, and each RLC device may configure an RLC header using concatenated PDCP PDUs, and may transmit the completed RLC PDUs to the MAC device.

As described above, the MAC device may configure RLC PDUs (MAC SDUs) received from the respective RLC layers as one MAC PDU to transmit the MAC PDU to the physical device. If the RLC device performs a segmentation operation and includes segmentation information in the RLC header during configuration of the RLC header, it is possible to include length information of each concatenated PDCP PDU in the header (this is to reassemble them at the receiving end).

As described above, the LTE system is characterized in that the overall data processing of the RLC layer, MAC layer, and physical layer is made to start from the time when the uplink grant is received.

In the LTE system, the RLC layer may operate in RLC AM, RLC Unacknowledged Mode (UM), and RLC Transparent Mode (TM).

In the RLC AM mode, the RLC layer supports an ARQ function, and the transmitting side may receive an RLC status report from the receiving side. In addition, the transmitting end may perform retransmission of unacknowledged RLC PDUs through the status report. Therefore, reliable data transmission without errors can be ensured, and thus RLC AM mode is suitable for services requiring high reliability.

In contrast, in RLC UM mode, ARQ functionality is not supported. Therefore, in RLC UM mode, the transmitting end does not receive RLC status report and does not perform retransmission function. In RLC UM mode, if an uplink grant is received, the RLC layer of the transmitting end serves to concatenate PDCP PDUs (RLC SDUs) received from an upper layer and continuously deliver the concatenated PDCP PDUs to a lower layer. Therefore, continuous data transmission without transmission delay becomes possible, and thus RLC UM mode is useful for a service sensitive to transmission delay. In RLC mode, the RLC layer directly transmits PDCP PDUs received from an upper layer to a lower layer without performing any processing. That is, in the TM mode of the RLC layer, data from an upper layer is transparently transferred from the RLC layer to a lower layer. Therefore, when system information or a paging message transmitted through a Common CHannel such as a Common Control CHannel (CCCH) is transmitted, the RLC TM mode can be effectively used.

In the present disclosure, the PDCP layer and the RLC layer process an efficient buffer management method and retransmission acceleration method, and thus an RLC AM mode and an RLC UM mode excluding a mode (such as an RLC TM mode) in which the RLC layer does not perform any processing will now be described in detail.

Separate buffer structure of LTE system.

Fig. 6 is a diagram illustrating an efficient buffer management method applicable when an LTE system terminal operates under RLC AM according to an embodiment of the present disclosure.

Referring to fig. 6, a detailed mapping table and corresponding operations according to a first embodiment of an efficient buffer management method when an LTE system terminal operates in RLC AM mode, as set forth in the present disclosure.

Referring to fig. 6, the terminal has a first buffer 610 and a second buffer 620 for respective logical channels, and the MAC layer has a third buffer 635. The first, second and third buffers of the logical channel may be physically divided buffers or physically identical but logically divided buffers. In the present disclosure, when actually implemented, the buffers include physically or logically partitionable buffer structures, and are divided into, for example, first to third buffers according to their roles. Preferably, the first buffer may be a PDCP buffer, the second buffer may be an RLC buffer, and the third buffer may be a MAC buffer.

The first buffer 610 may store an IP packet (PDCP SDU) 605 that enters the PDCP layer, generate a header of the PDCP SDU, and generate PDCP PDUs 620 by configuring the header with the PDCP SDU to store the PDCP PDUs therein. Further, the generated PDCP PDU may be transferred to the second buffer 625.

If an uplink grant is received from the base station, the terminal distributes the uplink grant to each logical channel by reflecting the priority or QoS of each logical channel. If an uplink grant is received, each logical channel concatenates PDCP PDUs (RLC SDUs) in the RLC layer, inputs length information of each PDCP PDU (RLC SDU) to a header of the RLC PDU, and configures RLC PDU 630. The RLC layer may perform a segmentation operation if the sizes of RLC SDUs are not exactly identical to each other when the RLC SDUs are concatenated to an uplink grant. If segmentation is performed for the RLC SDU, the RLC layer inputs segmentation information to the header of the RLC PDU. In addition, the RLC layer may transmit the completed RLC PDU to the MAC layer.

The MAC layer may configure one MAC PDU 640 by multiplexing RLC PDUs received from different logical channels, and may transmit the MAC PDU to the physical layer. Further, for HARQ processing, the MAC layer may store the MAC PDU and may perform retransmission until an acknowledgement is received (ACKnowledgement, ACK).

Further details may be described below with reference to fig. 7.

Fig. 7 is a diagram illustrating a mapping table and corresponding operations of an efficient buffer management method when an LTE system terminal operates in an RLC AM mode according to an embodiment of the present disclosure.

Referring to fig. 7, if PDCP PDUs (RLC SDUs) are received from the layer, the RLC layer may store them in a second buffer 710. In addition, the RLC layer may not store PDCP PDUs (RLC SDUs) in the second buffer 710, but may record a storage address of the PDCP PDUs for reference.

If the size of the uplink grant is received, the RLC layer can configure one RLC PDU through concatenation of PDCP PDUs (RLC SDUs). Once the RLC PDU is configured as described above, the RLC layer may configure a mapping table 735 based on the RLC sequence number and includes a storage address 740 of the second buffer, a storage address 745 of the first buffer, segmentation information 750, ACK/Non-acknowledgement (Non-ACKnowledgment, NACK) information 755, and PDCP sequence number 760. For example, an address of a second buffer in which RLC PDUs corresponding to RLC sequence number 1 are stored may be recorded, and a storage address 745 of a first buffer of concatenated PDCP PDUs to record information about PDCP PDUs concatenated to the RLC PDUs may be recorded. The addresses of the buffers may be managed as a start link and an end link of the memory address. In addition, if the RLC layer has performed a segmentation operation, segmentation information 750 may be recorded in the mapping table 735. In the segmentation information, if a portion excluding a header of the RLC SDU, i.e., a payload, is identical to a forefront portion of the RLC SDU, a "0" may be recorded as a first bit of the FI field, and if the payload is not identical to the forefront portion, a "1" may be recorded as a second bit of the FI field, as compared to the original RLC SDU. As described above, the segment information may be recorded. Further, the RLC layer of the transmitting side may recognize ACK/NACK results of the respective RLC sequence numbers after receiving the RLC status report from the RLC layer of the receiving side, and may record ACK/NACK information 755 of the respective RLC sequence numbers. Further, information about what PDCP PDUs are concatenated to RLC PDUs corresponding to the respective RLC sequence numbers may be recorded. That is, information indicating that

PDCP sequence numbers

1 and 2 and a portion of PDCP sequence number 3 are concatenated to RLC sequence number 1 may be recorded. In case of performing a segmentation operation in the RLC layer, information on each segment may be marked on the last segment. The reason for marking the last segment is to identify what PDCP sequence number can be considered an ACK when an ACK is received for a certain RLC sequence number. That is, if an ACK for RLC sequence number 2 is received after transmitting RLC sequence number 2 to which the last segments of PDCP sequence number 3 and PDCP sequence number 4 are concatenated, the RLC layer can receive an ACK for the last segment of PDCP sequence number 3, and thus can consider that it has received an ACK for PDCP sequence number 3 and PDCP sequence number 4.

The RLC layer can generate RLC PDUs through concatenation and segmentation of PDCP PDUs every time an uplink grant is received, to transmit the RLC PDUs to a lower layer. In addition, the RLC layer may transmit and store RLC PDUs in an appropriate order such as 715, 720, and 725, and may record the stored information as mapping table information such as mapping table 735. If a NACK is received for RLC sequence number 1 in an RLC status report received from the RLC layer of the receiving end, the RLC layer of the transmitting end prepares for retransmission. In this case, if the uplink grant for retransmission is smaller than the uplink grant at the beginning of operation 715, the RLC layer of the transmitting end performs re-segmentation, newly configures a header for the segmented RLC PDU, transmits the configured RLC PDU, and separately records corresponding information.

The operation of the first buffer and the second buffer is as follows.

If an IP packet is received from an upper layer, the PDCP layer may store the respective IP packets in the

first buffers

610 and 705 by assigning a storage address to the IP packet, and may drive and manage a PDCP discard timer 615 for each IP packet. The timer value may be configured by the network. For example, when the terminal configures the RRC connection, the timer value may be configured by the network through an RRC message. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the first buffer.

If the PDCP PDU corresponding to the timer is transferred to the RLC layer, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer. The discard indicator may indicate a memory address of the PDCP PDU transferred to the RLC layer of the second buffer, a PDCP sequence number, or mapping information about the PDCP PDU. Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the first buffer, and if an unexpired timer corresponding to the discarded PDCP PDUs exists, it may stop and discard the timer.

If the PDCP PDU corresponding to the discard indicator received from the PDCP layer has not been part of or mapped onto the RLC PDU in the RLC layer, the RLC layer discards the corresponding information. That is, the RLC layer discards PDCP PDUs (RLC SDUs) and related information transferred to and stored in the RLC layer, and mapping information from the second buffer. If the PDCP PDU indicated by the discard indicator has become a part of the RLC PDU, the RLC layer does not discard the PDCP PDU and related information from the second buffer. This is because if PDCP PDUs that have become part of RLC PDUs are discarded, gaps occur in RLC sequence numbers, resulting in transmission delay. That is, the receiving end cannot distinguish whether the corresponding RLC sequence number is lost during transmission or discarded by the discard indicator in the transmitting end.

Further, if an RLC status report is received from the RLC layer of the receiving end, the RLC layer may recognize an ACK/NACK result for each RLC sequence number. Further, in case of acknowledged RLC PDUs, the RLC layer may discard RLC PDUs from the second buffer and may discard related mapping information. In addition, the RLC layer prepares retransmissions for negatively acknowledged RLC PDUs. The RLC layer may immediately perform retransmission if uplink grant is sufficient in case that RLC PDU for retransmission is stored in the second buffer during the performance of retransmission. Further, if the uplink grant is insufficient, the RLC layer may perform re-segmentation to transmit RLC PDUs at operation 730. If the RLC PDU for retransmission is not stored in the second buffer, and previously generated information (header information and information on the concatenated PDCP PDU) and mapping information are recorded, the RLC layer of the transmitting end may dynamically regenerate the RLC PDU based thereon to perform retransmission.

The RLC layer can identify the result of ACK/NACK for RLC sequence number through RLC status report, identify mapping table 735, and determine the ACK/NACK result for corresponding PDCP sequence number 760. If the ACK of the PDCP sequence number is recognized, the RLC layer may transfer ACK information of the PDCP sequence number to the PDCP layer. The PDCP layer may recognize ACK information and may record ACK/NACK information of the PDCP sequence number. The ACK information for the PDCP sequence number may be used during a handover operation. That is, when a terminal handover occurs, the PDCP layer may perform retransmission to the handover target base station starting from the acknowledged PDCP sequence number after the lowest PDCP sequence number in the order of sequence numbers. The PDCP layer may retransmit only negative-acknowledged PDCP PDUs to the target base station of the handover if the network supports selective retransmission during the handover.

Fig. 8A and 8B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure.

Referring to fig. 8A, if an IP packet is received from an upper layer, the terminal PDCP layer operates at operation 801, receives the IP packet at operation 805, and may store the respective IP packets in a first buffer by assigning a storage address to the IP packet at operation 810. Further, the terminal PDCP layer may drive and manage a PDCP discard timer for each IP packet at operation 815. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the first buffer at operation 820. If the PDCP PDU corresponding to the timer is transferred to the RLC layer at operation 825, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 830. The discard indicator may indicate a memory address of the PDCP PDU transferred to the RLC layer of the second buffer, a PDCP sequence number, or mapping information about the PDCP PDU. Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the first buffer, and if there is an unexpired timer corresponding to the discarded PDCP PDUs, the PDCP layer may stop and discard the timer at operation 820.

Referring to fig. 8B, the terminal layer RLC operates at operation 835. If a discard indicator is received from the PDCP layer at operation 840, the terminal RLC layer may determine whether to discard information at operation 840. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer at operation 845, the terminal RLC layer discards the corresponding information at operation 855. The contents of the discard indicator are delivered to the RLC layer, and the terminal RLC layer discards the stored PDCP PDU (RLC SDU), information related thereto, and mapping information from the second buffer. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU (845), the terminal RLC layer 835 does not discard the PDCP PDU and related information from the second buffer at operation 850.

If an RLC status report is received from the RLC layer of the receiving end, the RLC layer can recognize an ACK/NACK result for each RLC sequence number. Further, in case of the acknowledged RLC PDU at operation 860, the RLC layer discards the RLC PDU from the second buffer and discards the related mapping information at operation 865. Further, the RLC layer prepares a retransmission for the negatively acknowledged RLC PDU at operation 875. The RLC layer may immediately perform retransmission if uplink grant is sufficient in case that RLC PDU for retransmission is stored in the second buffer during the performance of retransmission, and may perform re-segmentation to transmit RLC PDU if uplink grant is insufficient. If the RLC PDU for retransmission is not stored in the second buffer, and previously generated information (header information and information on the concatenated PDCP PDU) and mapping information are recorded, the RLC layer may dynamically regenerate the RLC PDU based thereon to perform retransmission.

The RLC layer may identify the result of ACK/NACK for the RLC sequence number through the RLC status report, identify mapping table information at operation 870, and determine the ACK/NACK result for the corresponding PDCP sequence number. If the ACK of the PDCP sequence number is recognized, the RLC layer may pass ACK information of the PDCP sequence number to the PDCP layer. The PDCP layer may recognize ACK information and may record ACK/NACK information of the PDCP sequence number.

A first embodiment of an efficient buffer management method applicable when an LTE system terminal operates in an RLC AM mode according to the present disclosure has proposed a method in which a PDCP layer independently manages a first buffer through a PDCP discard timer and an RLC layer independently manages a second buffer through an RLC ACK.

A first embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC UM mode according to the present disclosure is as follows.

When operating in RLC UM mode, the terminal according to the present disclosure has a structure as shown in fig. 6 and operates in a similar manner as described above with reference to fig. 7. However, unlike the RLC AM mode, the ARQ function is not supported in the RLC UM mode, and thus retransmission is not performed. Furthermore, RLC status reporting is not performed. Therefore, for retransmission, it is not necessary to record RLC PDUs already transmitted or information related thereto and mapping table information. This is the largest difference between RLC UM mode and RLC AM mode.

In the present disclosure, a first embodiment of a method in which an LTE system terminal in RLC UM mode efficiently manages buffers is as follows.

first buffers

610 and 705 by assigning a storage address to the IP packet. In addition, the PDCP layer may drive and manage a PDCP discard timer for each IP packet. The timer value may be configured by the network. That is, when the terminal configures the RRC connection, the timer value may be configured by the network through an RRC message. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the first buffer.

The RLC layer may discard information if a discard indicator is received from the PDCP layer. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer, the RLC layer discards the corresponding information. The contents of the discard indicator are delivered to the RLC layer, and the RLC layer discards the stored PDCP PDU (RLC SDU), information related thereto, and mapping information from the second buffer. If the PDCP PDU indicated by the discard indicator has become a part of the RLC PDU, the RLC layer does not discard the PDCP PDU and related information from the second buffer. This is because if PDCP PDUs that have become part of RLC PDUs are discarded, gaps occur in RLC sequence numbers, resulting in transmission delay. That is, the receiving end cannot distinguish whether the corresponding RLC sequence number is lost during transmission or discarded by the discard indicator in the transmitting end.

In addition, the RLC layer may receive an uplink grant and may configure RLC PDUs through concatenation and segmentation of PDCP PDUs. Further, after the RLC PDU is completed and transferred to the MAC layer, the RLC layer discards the RLC PDU from the second buffer, and discards the related information and the mapping information. Therefore, in RLC UM mode, the RLC layer transmits RLC PDUs and then discards them together with related information without directly storing them in the second buffer. This is because the ARQ function is not supported in the RLC UM mode, and thus it is not necessary to record information for retransmission.

A first embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC UM mode according to the present disclosure has proposed a method in which a PDCP layer independently manages a first buffer through a PDCP discard timer and an RLC layer independently manages a second buffer according to whether RLC PDUs are transmitted.

Fig. 9A and 9B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLCUM mode according to an embodiment of the present disclosure.

Referring to fig. 9A, if an IP packet is received from an upper layer, the terminal PDCP layer may operate at operation 901, the PDCP layer may receive the IP packet at operation 905, and the terminal may store the respective IP packets in a first buffer by assigning a storage address to the IP packet at operation 905. Further, the terminal PDCP layer may drive and manage a PDCP discard timer for each IP packet at operation 915. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the first buffer at operation 920. If the PDCP PDU corresponding to the timer is transferred to the RLC layer at operation 925, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 930. The discard indicator may indicate a memory address of the PDCP PDU transferred to the RLC layer of the second buffer, a PDCP sequence number, or mapping information about the PDCP PDU. Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the first buffer, and if there is an unexpired timer corresponding to the discarded PDCP PDUs, the PDCP layer may stop and discard the timer at operation 920.

Referring to fig. 9B, the terminal RLC layer may operate at operation 935. If a discard indicator is received from the PDCP layer at operation 940, the terminal RLC layer 935 may discard information. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer at operation 945, the terminal RLC layer discards the corresponding information at operation 955. The contents of the discard indicator are delivered to the RLC layer, and the terminal RLC layer discards the stored PDCP PDU (RLC SDU), information related thereto, and mapping information from the second buffer. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU at operation 945, the terminal RLC layer does not discard the PDCP PDU and related information from the second buffer at operation 950.

The RLC layer may receive the uplink grant and may configure RLC PDUs through concatenation and segmentation of PDCP PDUs. After completing the RLC PDU and passing it to the MAC layer at operation 940, the RLC layer discards the RLC PDU from the second buffer and discards the related information and mapping information. That is, in the RLC UM mode, the RLC layer transmits RLC PDUs and then discards them together with related information at operation 960 without directly storing them in the second buffer. This is because the ARQ function is not supported in the RLC UM mode, and thus it is not necessary to record information for retransmission.

According to the first embodiment of the efficient buffer management method applicable when the LTE system terminal operates in the RLC AM mode and the first embodiment of the efficient buffer management method applicable when the LTE system terminal operates in the RLC UM mode, which are proposed in the present disclosure, the PDCP layer independently manages the first buffer and the RLC layer independently manages the second buffer. Thus, the implementation is simple and uncomplicated. However, in order to support high data rates, a more optimized buffer management method should be considered. For example, if the first buffer is not being emptied quickly at a high data rate, a large buffer size may be required to prevent buffer overflow due to the high data rate. If a small timer value is configured to prevent buffer overflow, data may be lost before being transmitted, resulting in a decrease in data throughput.

Hereinafter, a second embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC AM mode and a second embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC UM mode are presented.

In a second embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC AM mode, the first buffer is not independently managed by the PDCP layer but is managed by reflecting RLC ACK results of the RLC layer. Further, in the second embodiment of the efficient buffer management method, which is applicable when the LTE system terminal operates in RLC UM mode, the first buffer is not independently managed by the PDCP layer but is managed by reflecting whether to transmit RLC PDUs in the RLC layer.

If an RLC status report is received from the receiving end RLC device in RLC AM mode and an ACK for the RLC PDU is received, it is no longer necessary for the RLC device to have an acknowledged RLC PDU, information corresponding thereto and any further mapping table information, and it is reasonable for the RLC device to discard them from the second buffer. Furthermore, if PDCP PDUs concatenated to RLC PDUs that have received an ACK exist in the first buffer, even such information is not used for retransmission, and thus the RLC layer is no longer necessarily provided with them even if the PDCP discard timer has not expired. Accordingly, in a second embodiment of an efficient buffer management method applicable when an LTE system terminal according to the present disclosure operates in RLC AM mode, the RLC layer may discard RLC PDUs from the second buffer, which have received RLC ACK. Further, if the RLC layer informs the PDCP layer of PDCP PDUs concatenated to the RLC PDU, the corresponding PDCP PDU is discarded from the first buffer, and information corresponding to the discarded PDCP PDU and the timer is released and discarded.

In contrast, in RLC UM mode, the ARQ function is not supported, and thus it is not necessary to store corresponding information after RLC PDU is transmitted for retransmission. Therefore, after transmitting the RLC PDU, the RLC layer does not store the corresponding RLC PDU in the second buffer, but discards the related information, if any. Furthermore, once the RLC PDU is transmitted, the RLC layer no longer has to have PDCP PDUs concatenated to the RLC PDU even though the PDCP discard timer has not expired. Therefore, in the second embodiment of the efficient buffer management method applicable when the LTE system terminal according to the present disclosure operates in RLC UM mode, after transmitting RLC PDUs, the RLC layer does not store the corresponding RLC PDUs in the second buffer, but discards the related information, if any. Further, if information on PDCP PDUs concatenated to the RLC PDU is transferred to the PDCP layer, the PDCP layer immediately discards the information on PDCP PDUs from the first buffer even though the PDCP discard timer has not expired.

Fig. 10A and 10B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure.

Referring to fig. 10A, if an IP packet is received from an upper layer, the terminal PDCP layer may operate at operation 1001, may receive the IP packet at operation 1005, and may store the respective IP packets in a first buffer by allocating a storage address to the IP packet at operation 1005. Further, the terminal PDCP layer may drive and manage a PDCP discard timer for each IP packet at operation 1015. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the first buffer at operation 1020. If the PDCP PDU corresponding to the timer is transferred to the RLC layer at operation 1025, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 1030. The discard indicator may indicate a memory address of the PDCP PDU transferred to the RLC layer of the second buffer, a PDCP sequence number, or mapping information about the PDCP PDU.

Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the first buffer. Further, if there is an unexpired timer corresponding to the discarded PDCP PDU, the PDCP layer may stop and discard the timer at operation 1020. Further, the PDCP layer may receive information about PDCP PDUs concatenated to RLC PDUs having received RLC ACK from the RLC layer. Since PDCP PDUs mean that they have been successfully delivered to the receiving end, it is no longer necessary to store them in the first buffer, and the PDCP layer discards them, the correspondence information, and the mapping table information. If there is an unexpired timer, the PDCP layer may stop and discard the timer at operation 1020. In case of managing the first buffer based on RLC ACK, it is important to manage the first buffer differently according to PDCP layer operation of the terminal during handover.

As a first case, the terminal may perform PDCP layer operation using a network configuration in which the PDCP layer should retransmit PDCP PDUs again to a handover target base station during handover after the lowest PDCP sequence number has been successfully delivered in order so far. In this case, if information on PDCP PDUs concatenated to RLC PDUs having received RLC ACK is received, the PDCP layer should store the lowest PDCP sequence number in which all ACKs have been received in the order of PDCP sequence number. In addition, for PDCP sequence numbers higher than the lowest PDCP sequence number, the PDCP layer should not discard RLC ACKs even though they have been received by the RLC layer. That is, PDCP PDUs that have been identified as being successfully delivered based on the RLC ACK can only be discarded in the order of their PDCP sequence numbers. For example, even if it is recognized that

PDCP sequence numbers

1, 2, 3, 4, 5, 9, and 10 have been successfully transferred from RLC ACKs of the RLC layer,

PDCP sequence numbers

1, 2, 3, 4, and 5, and information related to corresponding PDCP PDUs and mapping information can be discarded from the first buffer.

As a second case, the terminal may perform PDCP layer operation using a network configuration in which the PDCP layer should selectively retransmit PDCP PDUs which have not been successfully delivered so far to the handover target base station. In this case, if information on PDCP PDUs concatenated to RLC PDUs having received RLC ACK is received, the PDCP layer may discard information corresponding to the PDCP PDUs and mapping information from the first buffer, and may separately store information on PDCP sequence numbers having received ACK in order to use the information during handover.

Referring to fig. 10B, the terminal RLC layer operates at operation 1035. If a discard indicator is received from the PDCP layer at operation 1040, the terminal RLC layer may discard information corresponding to the discard indicator. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer at operation 1045, the terminal RLC layer discards the corresponding information at operation 1055. The contents of the discard indicator are delivered to the RLC layer, and the terminal RLC layer discards the stored PDCP PDU (RLC SDU), information related thereto, and mapping information from the second buffer. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU (1045), the terminal RLC layer does not discard the PDCP PDU and related information from the second buffer at operation 1050.

If an RLC status report is received from the RLC layer of the receiving end at operation 1040, the RLC layer may recognize an ACK/NACK result for each RLC sequence number. Further, in case of the acknowledged RLC PDU at operation 1060, the RLC layer discards the RLC PDU from the second buffer and discards the related mapping information at operation 1065. At operation 1075, the RLC layer prepares a retransmission for the negatively acknowledged RLC PDU. The RLC layer may immediately perform retransmission if uplink grant is sufficient in case that RLC PDU for retransmission is stored in the second buffer during the performance of retransmission, and may perform re-segmentation to transmit RLC PDU if uplink grant is insufficient. If the RLC PDU for retransmission is not stored in the second buffer, and previously generated information (header information and information on the concatenated PDCP PDU) and mapping information are recorded, the RLC layer may dynamically regenerate the RLC PDU based thereon to perform retransmission.

The RLC layer may identify the result of ACK/NACK for the RLC sequence number through the RLC status report, identify mapping table information at operation 1070, and determine the ACK/NACK result for the corresponding PDCP sequence number. If the ACK of the PDCP sequence number is recognized, the RLC layer may pass ACK information of the PDCP sequence number to the PDCP layer. The PDCP layer may identify ACK information and may discard corresponding PDCP PDUs from the first buffer using the ACK information.

Therefore, in a second embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC AM mode, characterized in that the RLC layer discards RLC PDUs for which RLC ACK has been received from a second buffer, notifies PDCP layer of PDCP PDUs concatenated to RLC PDUs, discards corresponding PDCP PDUs from a first buffer, and releases and discards corresponding information and timer. Therefore, even if the first buffer is quickly emptied with a small-sized buffer, the buffer can be efficiently managed, and thus efficiency can be maximized.

Fig. 11A and 11B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in RLC UM mode according to an embodiment of the present disclosure.

Referring to fig. 11A, if an IP packet is received from an upper layer, the terminal PDCP layer may operate at operation 1101, the PDCP layer may receive the IP packet at operation 1105, the terminal may store the respective IP packets in a first buffer by assigning a storage address to the IP packet at operation 1110, and a PDCP discard timer of each IP packet may be driven and managed at operation 1115. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the first buffer at operation 1120. If the PDCP PDU corresponding to the timer is transferred to the RLC layer at operation 1125, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 1130. The discard indicator may indicate a memory address of the PDCP PDU transferred to the RLC layer of the second buffer, a PDCP sequence number, or mapping information about the PDCP PDU. Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the first buffer, and if there is an unexpired timer corresponding to the discarded PDCP PDUs, the PDCP layer may stop and discard the timer at operation 1120. Further, if RLC PDUs are transmitted from the RLC layer and the RLC layer delivers information about PDCP PDUs concatenated to the transmitted RLC PDUs to the PDCP layer, the PDCP layer may discard information about the transmitted PDCP PDUs from the first buffer, and if the corresponding timer has not expired, the PDCP layer may release and discard the timer.

Referring to fig. 11B, the terminal RLC layer may operate at operation 1135. If a discard indicator is received from the PDCP layer at operation 1140, the terminal RLC layer 1135 may discard information corresponding to the discard indicator. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer at operation 1145, the terminal RLC layer discards the corresponding information at operation 1155. The contents of the discard indicator are delivered to the RLC layer, and the terminal RLC layer discards the stored PDCP PDU (RLC SDU), information related thereto, and mapping information from the second buffer. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU at operation 1145, the terminal RLC layer does not discard the PDCP PDU and related information from the second buffer at operation 1150.

The RLC layer may receive the uplink grant and may configure RLC PDUs through concatenation and segmentation of PDCP PDUs. After the RLC PDU is completed and delivered to the MAC layer at operation 1140, the RLC layer discards the RLC PDU from the second buffer and discards the related information and mapping information at operation 1160. That is, in the RLC UM mode, the RLC layer transmits RLC PDUs and then discards them together with related information without directly storing them in the second buffer. This is because the ARQ function is not supported in the RLC UM mode, and thus it is not necessary to record information for retransmission. Further, at operation 1165, the RLC layer may determine information about PDCP PDUs concatenated to the transmitted RLC PDUs and pass it to the PDCP layer, and may use the information to manage the first buffer.

Therefore, in a second embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC UM mode, it is characterized in that after transmitting RLC PDUs, the RLC layer does not store the corresponding RLC PDUs in the second buffer, but discards related information (if any), and transmits information about PDCP PDUs concatenated to the RLC PDUs to the PDCP layer. Even if the PDCP timer does not expire, the PDCP layer immediately discards information about the PDCP PDU from the first buffer.

Shared buffer structure of LTE system.

Fig. 12 is a diagram illustrating a mapping table and a buffer management method applicable when an LTE system terminal operates in an RLC AM mode, and illustrates a detailed mapping table and corresponding operations according to an embodiment of the present disclosure.

Referring to fig. 12, the terminal has a fourth buffer for each logical channel. The fourth buffer may be an integrated buffer in which the first buffer and the second buffer as shown in fig. 6 and 7 are shared. Preferably, the fourth buffer may be a shared buffer. Therefore, by using a shared buffer, the buffer can be managed more efficiently. The fourth buffer of the logical channel may be a physically divided buffer or a physically identical but logically divided buffer. In this disclosure, a buffer includes a physically or logically partitionable buffer structure when actually implemented.

The fourth buffer 1205 may store IP packets (PDCP SDUs) 1210 that enter the PDCP layer, generate a header of the PDCP SDU, and generate PDCP PDUs 1215 by configuring the header with the PDCP SDU to store the generated PDCP PDUs therein. Further, if an uplink grant is received from the base station, the terminal distributes the uplink grant to each logical channel by reflecting the priority or QoS of each logical channel. If an uplink grant is received as described above, the RLC layer concatenates PDCP PDUs (RLC SDUs) in the fourth buffer to respective logical channels, inputs length information of the respective PDCP PDUs (RLC SDUs) to a header of the RLC PDU, and dynamically configures the RLC PDU 630. The RLC layer may perform a segmentation operation if the size of the RLC SDU is not exactly identical to the uplink grant when the RLC SDU is concatenated to the uplink grant. If segmentation is performed for the RLC SDU, the RLC layer inputs segmentation information to the header of the RLC PDU. In addition, the RLC layer may transmit the completed RLC PDU to the MAC layer.

In addition, the MAC layer may configure one MAC PDU by multiplexing RLC PDUs received from different logical channels, and may transmit the MAC PDU to the physical layer. Further, for HARQ processes, the MAC layer may store MAC PDUs and may perform its retransmissions until an ACK is received.

If the size of the uplink grant is known, the fourth buffer may configure one RLC PDU through concatenation of PDCP PDUs (RLC SDUs). In a third embodiment of the efficient buffer management method proposed in the present disclosure, which is applicable when the LTE system terminal operates in RLC AM mode, RLC PDUs may not be stored for retransmission after the RLC PDUs are configured and transmitted. Thus, in the third embodiment, the storage address, segmentation information, and header information of the concatenated PDCP PDUs during the configuration of the RLC PDUs in the fourth buffer are recorded in the mapping table, and if retransmission is necessary, the RLC PDUs are dynamically reconfigured and transmitted with reference to the recorded information.

Once the RLC PDU is configured as described above, the RLC layer may configure the mapping table 1220 based on the RLC sequence number. For example, in order to record information about PDCP PDUs concatenated to the RLC PDU corresponding to RLC sequence number 1, the RLC layer may record a storage address of a fourth buffer of the concatenated PDCP PDUs. The address of the buffer may be composed of a start link and an end link of the memory address. Further, if the RLC layer has performed a segmentation operation, segmentation information may be recorded. In the segmentation information, if a portion excluding a header of the RLC SDU, i.e., a payload, is identical to a forefront portion of the RLC SDU, a "0" may be recorded as a first bit of the FI field, and if the payload is not identical to the forefront portion, a "1" may be recorded as a first bit of the FI field, as compared to the original RLC SDU. In contrast to the original RLC SDU, if the payload is consistent with the last part of the RLC SDU, a "0" may be recorded as the second bit of the FI field, and if the payload is inconsistent with the last part, a "1" may be recorded as the second bit of the FI field. The RLC layer may record segmentation information as described above.

Further, the RLC layer of the transmitting side may recognize ACK/NACK results of respective RLC sequence numbers after receiving the RLC status report from the RLC layer of the receiving side, and may record ACK/NACK of respective RLC sequence numbers. In addition, the RLC layer may record information about what PDCP PDUs are concatenated to RLC PDUs corresponding to the respective RLC sequence numbers. That is, information indicating that

PDCP sequence numbers

1 and 2 and a portion of PDCP sequence number 3 are concatenated to RLC sequence number 1 may be recorded. In case of performing a segmentation operation in the RLC layer, information on each segment may be marked on the last segment.

The reason for marking the last segment is to identify what PDCP sequence number can be considered an ACK when an ACK is received for a certain RLC sequence number. That is, if an ACK for RLC sequence number 2 is received after transmitting RLC sequence number 2 to which the last segments of PDCP sequence number 3 and PDCP sequence number 4 are concatenated, the RLC layer can receive an ACK for the last segment of PDCP sequence number 3, and thus can consider that it has received an ACK for PDCP sequence number 3 and PDCP sequence number 4.

The RLC layer can generate RLC PDUs through concatenation and segmentation of PDCP PDUs every time an uplink grant is received, to transmit the RLC PDUs to a lower layer. In addition, the RLC layer may transmit and store RLC PDUs in an appropriate order. For example, the RLC layer may record the information as mapping table information such as the mapping table 1220. If a NACK is received for RLC sequence number 1 in an RLC status report received from the RLC layer of the receiving end, the RLC layer prepares for retransmission. In this case, if the uplink grant for retransmission is smaller than the uplink grant at the beginning, the RLC layer performs re-segmentation, newly configures a header for the segmented RLC PDU, and transmits the configured RLC PDU. Further, the RLC layer may separately record information about the retransmitted RLC PDU at operation 1225.

The fourth buffer operates as follows.

If the IP packets are received from the upper layer, the PDCP layer may store the respective IP packets in the fourth buffer by assigning storage addresses to the respective IP packets. In addition, the PDCP layer may drive and manage a PDCP discard timer for each IP packet. The timer value may be configured by the network. That is, when the terminal configures the RRC connection, the timer value may be configured by the network through an RRC message. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the fourth buffer. If the PDCP PDU corresponding to the timer is transferred to the RLC layer, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer. The discard indicator may indicate a PDCP PDU sequence number or mapping information of PDCP PDUs transmitted to the RLC layer. Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the fourth buffer, and if an unexpired timer corresponding to the discarded PDCP PDUs exists, it may stop and discard the timer. Further, the PDCP layer may receive information about PDCP PDUs concatenated to RLC PDUs having received RLC ACK from the RLC layer. Since PDCP PDUs mean that they have been successfully delivered to the receiving end, it is no longer necessary to store them in the fourth buffer. Thus, the information stored in the fourth buffer may be discarded. Specifically, information corresponding to PDCP PDUs successfully delivered to the receiving end and mapping table information may be discarded, and if there is an unexpired timer, the timer may also be stopped and discarded. In case of managing the fourth buffer based on RLC ACK, it is important to manage the fourth buffer differently according to PDCP layer operation of the terminal during handover.

PDCP sequence numbers

1, 2, 3, 4, and 5, and information related to corresponding PDCP PDUs and mapping information can be discarded only from the fourth buffer.

As a second case, the terminal may perform PDCP layer operation using a network configuration in which the PDCP layer should selectively retransmit PDCP PDUs which have not been successfully delivered so far to the handover target base station. In this case, if information on PDCP PDUs concatenated to RLC PDUs having received RLC ACK is received, the PDCP layer may discard information corresponding to the PDCP PDUs and mapping information from the fourth buffer, and may separately store information on PDCP sequence numbers having received ACK in order to use the information during handover.

If the discard indicator is received from the PDCP layer, the RLC layer may discard the corresponding information in a state where the PDCP PDU corresponding to the discard indicator has not been part of the RLC PDU or has not been mapped thereon. Specifically, the RLC layer discards information related to PDCP PDUs (RLC SDUs) delivered to and stored in the RLC layer, as well as mapping information. If the PDCP PDU indicated by the discard indicator has become a part of the RLC PDU, the RLC layer does not discard the PDCP PDU and related information. This is because if PDCP PDUs that have become part of RLC PDUs are discarded, gaps occur in RLC sequence numbers, resulting in transmission delay. The receiving end cannot distinguish whether the corresponding RLC sequence number is lost during transmission or discarded by the discard indicator in the transmitting end.

If an RLC status report is received from the RLC layer of the receiving end, the RLC layer can recognize an ACK/NACK result for each RLC sequence number and discard mapping information related thereto in case of an acknowledged RLC PDU. The RLC layer prepares retransmissions for negatively acknowledged RLC PDUs. If the uplink grant is sufficient in case of performing retransmission, the RLC layer may dynamically regenerate and retransmit the RLC PDU using the mapping table information, and if the uplink grant is insufficient, the RLC layer may perform re-segmentation and dynamically regenerate and transmit the RLC PDU at operation 1225.

The RLC layer can recognize the result of ACK/NACK of the RLC sequence number through the RLC status report, recognize the mapping table information 1220, and determine the ACK/NACK result of the corresponding PDCP sequence number. If the ACK of the PDCP sequence number is recognized, the RLC layer may pass ACK information of the PDCP sequence number to the PDCP layer. The PDCP layer may identify ACK information and may record ACK/NACK information for each PDCP sequence number. The ACK information for the PDCP sequence number may be used during handover. When a terminal handover occurs, the PDCP layer may perform retransmission to the target base station of the handover, starting with the PDCP sequence number after the lowest PDCP sequence number where all ACKs have been received in the sequence of sequence numbers. The PDCP layer may retransmit only negative-acknowledged PDCP PDUs to the target base station of the handover if the network supports selective retransmission during the handover.

In a fourth embodiment of the efficient buffer management method applicable when the LTE system terminal operates in RLC AM mode according to the present disclosure, the fourth buffer is not independently managed by the PDCP layer but is managed by reflecting RLC ACK results of the RLC layer. Further, in a fourth embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC UM mode, it is characterized in that the fourth buffer is not independently managed by the PDCP layer but is managed by reflecting whether RLC PDUs in the RLC layer are transmitted or not.

If an RLC status report is received from the receiving-end RLC apparatus in the RLC AM mode and an ACK for the RLC PDU is received, it is no longer necessary for the RLC apparatus to have information corresponding to the acknowledged RLC PDU and mapping table information, and it is reasonable for the RLC apparatus to discard them from the fourth buffer. Furthermore, if PDCP PDUs concatenated to RLC PDUs that have received an ACK exist in the fourth buffer, even such information is not used for retransmission, and thus the RLC layer is no longer necessarily provided with them even if the PDCP discard timer has not expired.

Therefore, in a third embodiment of an efficient buffer management method applicable when an LTE system terminal according to the present disclosure operates in RLC AM mode, characterized in that the RLC layer discards information on RLC PDUs for which RLC ACK has been received from a mapping table, informs the PDCP layer of PDCP PDUs concatenated to the RLC PDUs, discards corresponding PDCP PDUs from a fourth buffer, and releases and discards the corresponding information and timer.

A third embodiment of an efficient buffer management method applicable when an LTE system terminal having a structure as shown in fig. 12 operates in RLC UM mode is as follows.

When operating in RLC UM mode, the terminal according to the present disclosure has a structure as shown in fig. 12 and operates in a similar manner as described above with reference to fig. 12. However, unlike the RLC AM mode, the ARQ function is not supported in the RLC UM mode, and thus retransmission is not performed. Furthermore, RLC status reporting is not performed. Therefore, it is not necessary to record RLC PDUs or related information that have been transmitted, and mapping table information for retransmission. This is the largest difference between RLC UM mode and RLC AM mode.

In the present disclosure, a third embodiment of a method in which an LTE system terminal in RLC UM mode efficiently manages buffers is as follows.

If an IP packet is received from an upper layer, the PDCP layer may store the respective IP packets in the fourth buffer 1205 by assigning a storage address to the IP packet. In addition, the PDCP layer may drive and manage a PDCP discard timer for each IP packet. The timer value may be configured by the network. For example, when the terminal configures the RRC connection, the timer value may be configured by the network through an RRC message. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the fourth buffer. If the PDCP PDU corresponding to the timer is transferred to the RLC layer, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer. The discard indicator may indicate a storage address of the PDCP PDU transferred to the RLC layer or mapping information about the PDCP PDU.

Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the fourth buffer, and if an unexpired timer corresponding to the discarded PDCP PDUs exists, it may stop and discard the timer.

If the discard indicator is received from the PDCP layer, the RLC layer may discard information corresponding to the discard indicator. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer, the RLC layer discards the corresponding information. The contents of the discard indicator are delivered to the RLC layer, and the RLC layer discards information related to the stored PDCP PDU (RLC SDU) and mapping information.

If the PDCP PDU indicated by the discard indicator has become a part of the RLC PDU, the RLC layer does not discard the related information. This is because if PDCP PDUs that have become part of RLC PDUs are discarded, gaps occur in RLC sequence numbers, resulting in transmission delay. That is, the receiving end cannot distinguish whether the corresponding RLC sequence number is lost during transmission or discarded by the discard indicator in the transmitting end.

The RLC layer may receive the uplink grant and may configure RLC PDUs through concatenation and segmentation of PDCP PDUs. In addition, after the RLC PDU is completed and transferred to the MAC layer, the RLC layer discards information related to the RLC PDU and mapping information. In RLC UM mode, the RLC layer transmits RLC PDUs and then discards them together with related information without storing them. This is because the ARQ function is not supported in the RLC UM mode, and thus it is not necessary to record information for retransmission.

In RLC UM mode, the ARQ function is not supported, and thus it is not necessary to store corresponding information after RLC PDU is transmitted for retransmission. Therefore, after transmitting the RLC PDU, the RLC layer does not store the corresponding RLC PDU in the fourth buffer, but discards the related information, if any. Furthermore, once the RLC PDU is transmitted, the RLC layer no longer has to concatenate the PDCP PDU to the RLC PDU even though the PDCP discard timer has not expired.

Accordingly, in the third embodiment of the efficient buffer management method applicable when the LTE system terminal according to the present disclosure operates in the RLC UM mode, after transmitting the RLC PDU, the RLC layer may not store the corresponding RLC PDU in the fourth buffer and the mapping table. Further, if related information exists, the RLC layer discards the information and may transmit information on PDCP PDUs concatenated to the RLC PDU to the PDCP layer. If information about PDCP PDUs is received, the PDCP layer immediately discards the information about PDCP PDUs from the fourth buffer even though the PDCP discard timer has not expired.

Fig. 13A and 13B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure.

Referring to fig. 13A, if an IP packet is received from an upper layer, the terminal PDCP layer may operate at operation 1301, may receive the IP packet at operation 1305, and may store the respective IP packets in a fourth buffer by allocating a storage address to the IP packet at operation 1310. Further, the terminal PDCP layer may drive and manage a PDCP discard timer for each IP packet at operation 1315. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the first buffer at operation 1320. If the PDCP PDU corresponding to the timer is transmitted to the RLC layer at operation 1325, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 1330. The discard indicator may indicate a PDCP PDU sequence number transmitted to the RLC layer, or mapping information about the PDCP PDU.

Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the fourth buffer. Further, if there is an unexpired timer corresponding to the discarded PDCP PDU, the PDCP layer may stop and discard the timer at operation 1320. Further, the PDCP layer may receive information about PDCP PDUs concatenated to RLC PDUs having received RLC ACK from the RLC layer. Since PDCP PDUs mean that they have been successfully delivered to the receiving end, it is no longer necessary to store them in the fourth buffer, and the PDCP layer may discard them.

In addition, the PDCP layer discards information corresponding to the discarded PDCP PDU and mapping table information. If there is an unexpired timer, the PDCP layer may stop and discard the timer at operation 1320. In case of managing the fourth buffer based on RLC ACK, it is important to manage the fourth buffer differently according to PDCP layer operation of the terminal during handover.

PDCP sequence numbers

Referring to fig. 13B, the terminal RLC layer may operate at operation 1335. If a discard indicator is received from the PDCP layer at operation 1340, the terminal RLC layer may discard information corresponding to the discard indicator. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer at operation 1345, the terminal RLC layer discards the corresponding information at operation 1355. The contents of the discard indicator are delivered to the RLC layer, which discards information related to the stored PDCP PDU (RLC SDU) and mapping information. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU at operation 1345, the terminal RLC layer does not discard information related to the PDCP PDU at operation 1350.

If an RLC status report is received from the RLC layer of the receiving end at operation 1340, the RLC layer may recognize an ACK/NACK result for each RLC sequence number. Further, in case of the acknowledged RLC PDU at operation 1360, the RLC layer discards the related mapping information at operation 1365. At operation 1375, the RLC layer prepares a retransmission for the negatively acknowledged RLC PDU. The RLC layer may dynamically regenerate and retransmit RLC PDUs based on mapping information of the RLC PDUs and header information if uplink grants for the retransmissions are sufficient during the execution of the retransmissions. Further, if the uplink grant is insufficient, the RLC layer may perform re-segmentation to dynamically generate and transmit RLC PDUs at operation 730. The RLC layer may identify the result of ACK/NACK for the RLC sequence number through the RLC status report, identify mapping table information at operation 1370, and determine the ACK/NACK result for the corresponding PDCP sequence number. If the ACK of the PDCP sequence number is recognized, the RLC layer may pass ACK information of the PDCP sequence number to the PDCP layer. The PDCP layer may identify ACK information and may discard corresponding PDCP PDUs from the fourth buffer using the ACK information.

Accordingly, in the third embodiment of the efficient buffer management method applicable when the LTE system terminal operates in the RLC AM mode according to the present disclosure, the RLC layer may discard information on RLC PDUs for which RLC ACK has been received, as well as mapping table information. Further, if the RLC layer informs the PDCP layer of PDCP PDUs concatenated to the RLC PDU, the PDCP layer discards the corresponding PDCP PDU from the fourth buffer and releases and discards the corresponding information and the timer. Therefore, even if the fourth buffer is quickly emptied with a small-sized buffer, the buffer can be efficiently managed, and thus efficiency can be maximized.

Fig. 14A and 14B are diagrams illustrating an operation of a terminal in which an LTE system terminal manages a buffer in RLC UM mode according to the disclosure of the embodiment.

Referring to fig. 14A, if an IP packet is received from an upper layer, the terminal PDCP layer may operate at operation 1401, may receive the IP packet at operation 1405, and may store the respective IP packets in a fourth buffer by allocating a storage address to the IP packet at operation 1410. Further, the terminal PDCP layer may drive and manage a PDCP discard timer for each IP packet at operation 1415. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the fourth buffer at operation 1420. If the PDCP PDU corresponding to the timer is transmitted to the RLC layer at operation 1425, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 1430. The discard indicator may indicate a PDCP PDU sequence number transmitted to the RLC layer or mapping information regarding PDCP PDUs.

Further, if ACK/NACK information regarding PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the fourth buffer, and if there is an unexpired timer corresponding to the discarded PDCP PDUs, the PDCP layer may stop and discard the timer at operation 1420. Further, if RLC PDUs are transmitted from the RLC layer and the RLC layer delivers information about PDCP PDUs concatenated to the transmitted RLC PDUs to the PDCP layer, the PDCP layer may discard information about the transmitted PDCP PDUs from the fourth buffer, and if the corresponding timer has not expired, the PDCP layer may release and discard the timer.

Referring to fig. 14B, the terminal RLC layer may operate at operation 1435. If a discard indicator is received from the PDCP layer at operation 1440, the terminal RLC layer 1435 may discard information corresponding to the discard indicator received at operation 1440. Specifically, if the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer at operation 1445, the terminal RLC layer discards the corresponding information at operation 1455. The contents of the discard indicator are delivered to the RLC layer, and the terminal RLC layer discards information related to the stored PDCP PDU (RLC SDU) and mapping information. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU at operation 1445, the terminal RLC layer does not discard information related to the PDCP PDU at operation 1450.

The RLC layer may receive the uplink grant and may configure RLC PDUs through concatenation and segmentation of PDCP PDUs. After the RLC PDU is completed and delivered to the MAC layer at operation 1440, the RLC layer discards the information related to the RLC PDU and the mapping information at operation 1460. In RLC UM mode, the RLC layer transmits RLC PDUs and then discards the related information, if any, without storing them. This is because the ARQ function is not supported in the RLC UM mode, and thus it is not necessary to record information for retransmission. Further, at operation 1465, the RLC layer may determine and pass information about PDCP PDUs concatenated to the transmitted RLC PDUs to the PDCP layer, and may use the information to manage the fourth buffer.

Accordingly, in a third embodiment of an efficient buffer management method applicable when an LTE system terminal operates in RLC UM mode, the RLC layer transmits RLC PDUs and then discards related information, if any, without storing the corresponding RLC PDUs. In addition, the RLC layer may transmit information about PDCP PDUs concatenated to the RLC PDUs to the PDCP layer. Even if the PDCP timer does not expire, the PDCP layer immediately discards information about the PDCP PDU from the fourth buffer.

Buffer structure and retransmission acceleration of the next generation mobile communication system.

In the preamble of the present disclosure, a method for efficiently managing buffers in an LTE system has been proposed and described. In the remainder of the present disclosure, structures and methods for efficiently managing buffers and accelerating retransmissions in a next generation mobile communication system are presented.

Fig. 15A and 15B are diagrams illustrating a data processing structure in a next generation mobile communication system according to an embodiment of the present disclosure.

Referring to fig. 15A and 15B, the next generation mobile communication system performs PDCP layer and RLC layer data processing for a logical channel. That is, logical channel 1 1505 and logical channel 2 1510 have different PDCP layers and RLC layers, and perform independent data processing. Further, the next generation mobile communication system delivers RLC PDUs generated from the RLC layer 1515 of each logical channel to the MAC layer 1520 to configure one MAC PDU, and transmits the MAC PDU to the receiving end. In the next generation mobile communication system, the PDCP layer, RLC layer, and MAC layer may include the functions described above with reference to fig. 4, and may perform operations corresponding to the functions.

In the next generation mobile communication system, the RLC layer does not concatenate PDCP PDUs. Further, in the next generation mobile communication system, a MAC PDU structure such as reference numeral 1525 is characterized by having a structure having a MAC sub-header for each MAC SDU, in other words, a structure in which the MAC sub-header is repeated in units of MAC SDUs. Accordingly, in the next generation mobile communication system, at operation 1530, data preprocessing may be performed before receiving the uplink grant.

For example, if the PDCP layer receives an IP packet, a terminal of the next generation mobile communication system may perform PDCP processing (ciphering) and integrity protection on the received IP packet before receiving an uplink grant, and may generate a PDCP PDU by generating a PDCP header. In addition, the terminal may configure the RLC header by delivering the PDCP PDU to the RLC layer, and may pre-configure the MAC sub-header and the MAC SDU by delivering the RLC PDU to the MAC layer.

If the terminal receives an uplink grant at operation 1530, it may configure the MAC PDU by causing the MAC subheader and the MAC SDU to the extent that they match the size of the uplink grant. In contrast, if the uplink grant is insufficient, the terminal may perform a segmentation operation in order to fill and efficiently use transmission resources. At operation 1540, the terminal may update an RLC header (segmented information or length information) and a MAC header (L field, length change) corresponding to the segmented data. Thus, if it is assumed that uplink grants such as operation 1530 and operation 1545 are received at the same time, the next generation mobile communication system may have a large gain in processing time such as reference numeral 1535, compared to the LTE system. The RLC layer and PDCP layer may use one common sequence number if needed or if configured in the network.

The preprocessing may be performed for each logical channel, and the RLC PDU preprocessed for each logical channel may be preprocessed again into a MAC SDU and a MAC sub-header by the MAC layer. Further, if the MAC layer receives an uplink grant at operation 1530, the terminal may multiplex the pre-generated MAC SDUs and MAC subheaders by assigning an uplink grant to each logical channel.

After the MAC layer receives the uplink grant from the base station, the terminal may perform LCP and may divide the uplink grant for each logical channel. In addition, the terminal may configure one MAC PDU by multiplexing the MAC SDU and the MAC subheader generated for each logical channel and deliver the MAC PDU to the physical layer. Segmentation may be requested for the RLC layer if the uplink grant allocated to each logical channel is insufficient. Accordingly, if the RLC layer performs a segmentation operation, segmentation information included in the header may be updated. In addition, if the RLC layer delivers updated information to the MAC layer again, the MAC layer may update a corresponding MAC header. As described above, the next generation mobile communication system has a feature that data processing of the PDCP layer, RLC layer, and MAC layer is started before an uplink grant is received.

Since the next generation mobile communication system has the above-described structure, several RLC PDUs can be entered into one MAC PDU. In the LTE system, since the RLC layer has a concatenation function, several PDCP PDUs are concatenated to generate one RLC PDU to be transferred to the MAC layer, and one MAC PDU generally includes as many RLC PDUs as the number of logical channels (the number of logical channels is generally about 2 to 4 in the LTE system).

However, in the next generation mobile communication system, the RLC layer does not have an RLC concatenation function, and thus one PDCP PDU is generated as one RLC PDU. Thus, one MAC PDU may include RLC PDUs whose number corresponds to the number of IP packets (PDCP PDUs) multiplied by the number of logical channels. Through simple arithmetic calculation, one MAC PDU may include at most about 4 RLC PDUs in the LTE system, and one MAC PDU may include not less than 500 RLC PDUs in the next generation mobile communication system. Therefore, in the next generation mobile communication system, if one MAC PDU is lost, it is necessary to retransmit hundreds of RLC PDUs. Therefore, the RLC layer should retransmit hundreds of RLC PDUs, which may cause serious transmission delay. Accordingly, in the present disclosure, a structure and method capable of accelerating retransmission in a next generation mobile communication system are proposed.

In the next generation mobile communication system, the RLC layer may operate in an RLC acknowledged mode (RLC AM), an RLC unacknowledged mode (RLC UM), and an RLC transparent mode (RLC TM). In the RMC AM mode, the RLC layer supports an ARQ function, the transmitting side may receive an RLC status report from the receiving side, and the transmitting side may retransmit a negatively acknowledged RLC PDU using the status report. Thus, reliable data transmission without errors is ensured. Therefore, the RLC AM mode is suitable for services requiring high reliability.

In contrast, in RLC UM mode, ARQ functionality is not supported. Therefore, in RLC UM mode, the transmitting end does not receive RLC status reports from the receiving end and does not perform retransmission functions. In RLC UM mode, if an uplink grant is received, the RLC layer of the transmitting end serves to concatenate PDCP PDUs (RLC SDUs) received from an upper layer and continuously deliver the concatenated PDCP PDUs to a lower layer. Therefore, continuous data transmission without transmission delay becomes possible, and thus RLC UM mode is useful for a service sensitive to transmission delay. In RLC TM mode, the RLC layer directly transmits PDCP PDUs received from an upper layer to a lower layer without performing any procedure. In the TM mode of the RLC layer, data from an upper layer is transparently transferred from the RLC layer to a lower layer. Therefore, when system information or a paging message transmitted through a common channel such as CCCH is transmitted, RLC TM mode can be effectively used.

Buffer structure under RLC AM/TM for next generation mobile communication systems and retransmission acceleration.

Fig. 16 is a diagram illustrating a mapping table and a retransmission acceleration method applicable when a next generation mobile communication system terminal operates in an RLC AM mode according to an embodiment of the present disclosure.

Referring to fig. 16, the terminal has a fifth buffer and a sixth buffer for respective logical channels. For convenience, fig. 16 illustrates one logical channel. The fifth and sixth buffers of the logical channel may be physically divided buffers or physically identical but logically divided buffers. Preferably, the fifth buffer may be a PDCP buffer, and the sixth buffer may be a MAC buffer. In this disclosure, a buffer includes a physically or logically partitionable buffer structure when actually implemented.

The terminal may store an IP packet (PDCP SDU) 1610 into the PDCP layer and may generate a header of the PDCP SDU. Further, the terminal may generate PDCP PDUs 1615 by configuring the generated header together with PDCP SDUs to store them in the fifth buffer 1605. Furthermore, the terminal may perform data preprocessing before receiving an uplink grant from the base station. Specifically, the terminal may configure the RLC PDU 1620 by generating an RLC header for the PDCP PDU in the fifth buffer, configure a MAC sub-header for an RLC PDU (MAC SDU), and store the MAC SDU and the MAC sub-header together in the sixth buffer 1630 at operation 1625. However, if all PDCP PDUs are pre-processed into MAC SDUs and MAC subheaders, the sixth buffer may require a large capacity. Thus, in the present disclosure, data preprocessing of PDCP PDUs may be performed only up to a maximum Transport Block (TB) size supported by a terminal and a network.

For example, the terminal may pre-process the data until a time when the sum of the sizes of the MAC SDU and the MAC sub-header of the data pre-process exceeds the maximum TB size (because the size of the PDECP PDU is variable, and thus the sum of the sizes of the MAC SDU and the MAC sub-header may not coincide with the maximum TB size). Furthermore, the terminal may pre-process the data only to a degree close to the maximum TB size. For example, if the size of the MAC SDU and the MAC sub-header (stored for transmission to the sixth buffer) of the data pre-processing is close to the maximum TB size, the terminal may not perform the data pre-processing any more.

If an RLC PDU is generated during data preprocessing, the terminal may allocate an RLC sequence number, preprocess a PDCP PDU constituting the RLC PDU at a storage address 1655 of the fifth buffer and MAC SDUs and MAC subheaders corresponding to the RLC PDU, and store a storage address 1660 of the sixth buffer in the mapping table 1650. The terminal may store the corresponding PDCP sequence number if necessary. However, in the next generation mobile communication system, if the PDCP sequence number and the RLC sequence number are the same, the PDCP sequence number or the RLC sequence number may be omitted. In addition, in the next generation mobile communication system, even though the PDCP layer and the RLC layer use one common sequence number, the PDCP sequence number or the RLC PDCP sequence number may be omitted.

If an uplink grant is received, the terminal distributes the uplink grant to each logical channel by reflecting the priority or QoS of each logical channel. If an uplink grant 1635 is received, the terminal configures a portion of the MAC PDU 1645 by causing data to correspond to the extent of the uplink grant in units of MAC subheader and MAC SDU from the sixth buffer. In addition, for other logical channels, the terminal may complete one MAC PDU 1645 by multiplexing the MAC sub-header 1640 and the MAC SDU received through the above-described procedure, and may transmit the MAC PDU to the physical layer.

If the sizes of the MAC sub-header and the MAC SDU are not exactly identical to each other when data is added to the uplink grant in units of the MAC sub-header and the MAC SDU for each logical channel, the RLC layer may perform a segmentation operation for the last RLC SDU that becomes inconsistent with the size. If segmentation is performed for the RLC SDU, the RLC layer can newly input and update segmentation information to the header of the RLC PDU. Further, the MAC layer may newly update a new MAC subheader for the completed RLC PDU, and may configure the MAC subheader and the MAC SDU to match the uplink grant.

If the RLC layer performs the segmentation operation as described above, information on a header field for the segmentation operation may be recorded in a mapping table at operation 1665. However, such recording may be omitted if not necessary. The RLC SDU segmentation operation as described above is characterized in that the segmented RLC PDU is provided with a segmentation information field indicating whether the segmented segment is the first segment, the middle segment or the last segment in a state where the segmented RLC PDU maintains the same RLC sequence number, and a field including an offset indicating where the segment corresponds to the original RLC SDU.

If an ACK/NACK is identified through an RLC status report received from the RLC layer of the receiving end, the terminal may record the information in a mapping table at operation 1670. If it is necessary to retransmit the negatively acknowledged RLC PDU, the RLC layer of the transmitting end can immediately perform retransmission by accessing the memory address of the MAC SDU and the MAC sub-header previously generated and transmitted corresponding to the RLC PDU using the memory address information of the sixth buffer in the mapping table 1650. If the uplink grant is large enough to include all RLC PDUs for which retransmission should be performed, retransmission may be performed using the MAC SDU and MAC subheader stored in the sixth buffer. In contrast, if the uplink cannot include all RLC PDUs for which retransmission should be performed, the RLC layer performs a segmentation operation for the last MAC SDU (RLC PDU), and the RLC header and MAC layer perform a procedure of updating the MAC header to perform retransmission. In addition, if several consecutive RLC PDUs need to be retransmitted at a time, the terminal can perform fast retransmission with a small memory access by using the memory address of the sixth buffer in the mapping table 1650. For example, the MAC PDU may be configured by introducing several RLC PDUs at a time from the sixth buffer by referring to a start link of a first RLC PDU and an end link of a last RLC PDU among several consecutive RLC PDUs. For example, if retransmission of RLC sequence numbers 1 to 6 is required, the terminal may recognize the memory address 1655 of the sixth buffer from the mapping table 1650 and perform retransmission using the memory addresses 0 to m of the sixth buffer with reference to the start link p of the sixth buffer for RLC sequence number 1 and the end link m of RLC sequence number 6.

In a fourth embodiment of the efficient buffer management method and retransmission acceleration method, which are applicable when a terminal of the next generation mobile communication system proposed in the present disclosure operates in the RLC AM mode, the terminal may store in the sixth buffer a MAC subheader and a MAC SDU for which data preprocessing of the PDCP PDU stored in the fifth buffer has been performed, and may configure a mapping table based on the RLC sequence number to manage them. Further, in the fourth embodiment, if it is necessary to perform retransmission, it is characterized in that retransmission is immediately performed using the mapping table information that has been pre-generated and stored in the sixth buffer without regenerating the RLC header and the MAC sub-header.

Therefore, even if it is necessary to perform retransmission of hundreds of RLC PDUs in the next generation mobile communication system, the terminal can rapidly retransmit RLC PDUs which are data-preprocessed and stored in the sixth buffer using the mapping table information without newly configuring hundreds of RLC headers and MAC subheaders. If a segmentation operation is necessary for each logical channel, it is sufficient to update only one RLC header and one MAC header corresponding to the last MAC SDU, and thus the transmission delay is greatly reduced.

The fifth buffer and the sixth buffer operate as follows.

If an IP packet is received from an upper layer, the PDCP layer may store the respective IP packets in the fifth buffer 1605 by assigning a storage address to the IP packet. In addition, the PDCP layer may drive and manage a PDCP discard timer for each IP packet. The timer value may be configured by the network. For example, when the terminal configures the RRC connection, the timer value may be configured by the network through an RRC message. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the fifth buffer. If the PDCP PDU corresponding to the timer is transmitted to the RLC layer, the PDCP layer transmits a discard indicator corresponding to the PDCP PDU to the RLC layer. The discard indicator may indicate a PDCP PDU sequence number transmitted to the RLC layer or mapping information regarding PDCP PDUs.

Further, if ACK/NACK information for the PDCP PDU is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDU from the fifth buffer. In addition, if an unexpired timer corresponding to the discarded PDCP PDU exists, it may stop and discard the timer. Further, the PDCP layer may receive information about PDCP PDUs corresponding to RLC PDUs having received RLC ACK from the RLC layer. Since PDCP PDUs mean that they have been successfully delivered to the receiving end, it is no longer necessary to store them in the fifth buffer. Accordingly, the correspondence information and the map information may be discarded, and if there is an unexpired timer, the timer may also be stopped and discarded. In case of managing the fifth buffer based on the RLC ACK, it is important to manage the fifth buffer differently according to the PDCP layer operation of the terminal during handover.

As a first case, the terminal may perform PDCP layer operation using a network configuration in which the PDCP layer should retransmit PDCP PDUs again to a handover target base station during handover after the lowest PDCP sequence number has been successfully delivered in order so far. In this case, if information on PDCP PDUs corresponding to RLC PDUs for which RLC ACKs have been received is received, the PDCP layer should store the lowest PDCP sequence number for which all ACKs have been received in the order of PDCP sequence numbers. In addition, for PDCP sequence numbers higher than the lowest PDCP sequence number, the PDCP layer should not discard RLC ACKs even though they have been received by the RLC layer. That is, PDCP PDUs that have been identified as being successfully delivered based on RLCACK can only be discarded in the order of their PDCP sequence numbers. For example, even if it is recognized that

PDCP sequence numbers

1, 2, 3, 4, 5, 9, and 10 have been successfully transferred from RLC ACK of the RLC layer,

PDCP sequence numbers

1, 2, 3, 4, and 5, and information related to corresponding PDCP PDUs and mapping information can be discarded only from the fifth buffer.

As a second case, the terminal may perform PDCP layer operation using a network configuration in which the PDCP layer should selectively retransmit PDCP PDUs which have not been successfully delivered so far to the handover target base station. In this case, if information on PDCP PDUs concatenated to RLC PDUs having received RLC ACK is received, the PDCP layer may discard information corresponding to the PDCP PDUs and mapping information from the fifth buffer, and may separately store information on PDCP sequence numbers having received ACK in order to use the information during handover.

If the discard indicator is received from the PDCP layer, the RLC layer may discard the corresponding information in a state in which the PDCP PDU corresponding to the discard indicator has not been part of the RLC PDU, data pre-processing has not been performed using the MAC PDU and the MAC sub-header, or the PDCP PDU has not been mapped thereto. For example, the RLC layer discards information related to PDCP PDUs (RLC SDUs) delivered to and stored in the RLC layer, as well as mapping information. If the PDCP PDU indicated by the discard indicator has become a part of the RLC PDU, the RLC layer does not discard information related to the PDCP PDU in case data pre-processing has been performed using the MAC SDU and the MAC sub-header. This is because if PDCP PDUs that have become part of RLC PDUs are discarded, gaps occur in RLC sequence numbers, resulting in transmission delay.

The receiving end cannot distinguish whether the corresponding RLC sequence number is lost during transmission or discarded by the discard indicator in the transmitting end. If an RLC status report is received from the RLC layer of the receiving end, the RLC layer can recognize an ACK/NACK result for each RLC sequence number. In addition, in the case of acknowledged RLC PDUs, the RLC layer may discard the mapping table 1650 associated therewith. The RLC layer delivers information on PDCP PDUs corresponding to the acknowledged RLC PDUs, and discards the corresponding MAC subheader and MAC SDU from a sixth buffer storing the acknowledged pre-processed RLC PDUs.

In case of a negatively acknowledged RLC PDU, the RLC layer prepares for its retransmission. If uplink grant is sufficient in case of performing retransmission, the RLC layer may perform retransmission with reference to the MAC subheader and the MAC SDU from the sixth buffer using the mapping table information. Further, if the uplink grant is insufficient, the RLC layer may perform re-segmentation for the MAC sub-header in the sixth buffer and the last RLC SDU among the MAC SDUs, and may update and retransmit the RLC header and the MAC header.

The RLC layer can identify the result of ACK/NACK for RLC sequence number through RLC status report, identify mapping table information (1670), and determine the ACK/NACK result for corresponding PDCP sequence number. If the ACK of the PDCP sequence number is recognized, the RLC layer may pass ACK information of the PDCP sequence number to the PDCP layer. The PDCP layer may recognize ACK information, record ACK/NACK information for each PDCP sequence number, and discard PDCP PDUs of the fifth buffer using the ACK information. The ACK information for the PDCP sequence number may be used during handover. When a terminal handover occurs, the PDCP layer may perform retransmission to the target base station of the handover, starting with the PDCP sequence number after the lowest PDCP sequence number where all ACKs have been received in the sequence of sequence numbers. The PDCP layer may retransmit only negative-acknowledged PDCP PDUs to the target base station of the handover if the network supports selective retransmission during the handover.

In a fourth embodiment of the efficient buffer management method and retransmission acceleration method, which are applicable when a terminal of the next generation mobile communication system proposed in the present disclosure operates in RLC AM mode, characterized in that the fifth buffer is not independently managed by the PDCP layer, but the fifth buffer and the sixth buffer are managed by reflecting RLC ACK results of the RLC layer. Further, in a fourth embodiment of an efficient buffer management method and retransmission acceleration method applicable when a terminal of a next generation mobile communication system operates in RLC UM mode, characterized in that the fifth buffer is not independently managed by the PDCP layer, but the fifth buffer and the sixth buffer are managed by reflecting whether RLC PDU in the RLC layer is transmitted or not.

If an RLC status report is received from the receiving-end RLC apparatus in the RLC AM mode and an ACK for the RLC PDU is received, it is no longer necessary for the RLC apparatus to have information corresponding to the acknowledged RLC PDU and mapping table information, and it is reasonable for the RLC apparatus to discard them from the fifth buffer. Further, if PDCP PDUs corresponding to RLC PDUs for which ACK has been received exist in the fifth buffer and MAC SDUs and MAC subheaders for data pre-processing exist in the sixth buffer, such information is not used for retransmission, and thus the RLC layer is not necessary to have them even though the PDCP discard timer has not expired. Accordingly, in a fourth embodiment of an efficient buffer management method and retransmission acceleration method, which are applicable when a terminal of a next generation mobile communication system according to the present disclosure operates in an RLC AM mode, characterized in that the RLC layer discards information on RLC PDUs for which RLC ACKs have been received from a mapping table, informs the PDCP layer of PDCP PDUs corresponding to the RLC PDUs, discards the corresponding PDCP PDUs from a fifth buffer, discards a data-pre-processed MAC sub-header and MAC SDU from a sixth buffer, and releases and discards the corresponding information and timer.

A fourth embodiment of an efficient buffer management method applicable when a terminal of a next generation mobile communication system according to the present disclosure having a structure as shown in fig. 16 operates in RLC UM mode is as follows.

When operating in RLC UM mode, the terminal according to the present disclosure has a structure as shown in fig. 16, and operates in a similar manner as described above with reference to fig. 16. However, unlike the RLC AM mode, the ARQ function is not supported in the RLC UM mode, and thus retransmission is not performed. Furthermore, RLC status reporting is not performed. Therefore, the transmitting end does not have to record RLC PDUs or related information that have been transmitted, and mapping table information for retransmission. This is the largest difference between RLC UM mode and RLC AM mode. That is, in case of completing transmission, it is not necessary to store RLC PDU through data pre-processing of PDCP PDU, MAC SDU and MAC sub-header for retransmission.

In the present disclosure, a fourth embodiment of a method in which a terminal of a next generation mobile communication system in RLC UM mode efficiently manages buffers is as follows.

If an IP packet is received from an upper layer, the PDCP layer may store the respective IP packets in the fifth buffer 1605 by assigning a storage address to the IP packet. In addition, the PDCP layer may drive and manage a PDCP discard timer for each IP packet. The timer value may be configured by the network. For example, when the terminal configures the RRC connection, the timer value may be configured by the network through an RRC message. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the fifth buffer. If the PDCP PDU corresponding to the timer is transmitted to the RLC layer, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer. The discard indicator may indicate a PDCP PDU sequence number transmitted to the RLC layer or mapping information regarding PDCP PDUs. Further, if ACK/NACK information for the PDCP PDU is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDU from the fifth buffer. Further, if an unexpired timer corresponding to the discarded PDCP PDU exists, the PDCP layer may stop and discard the timer.

If the discard indicator is received from the PDCP layer, the RLC layer may discard the corresponding information in a state where the PDCP PDU corresponding to the discard indicator has not been a part of the RLC PDU in the RLC layer or has not been mapped thereto. For example, the RLC layer discards information related to PDCP PDUs (RLC SDUs) delivered to and stored in the RLC layer, as well as mapping information. If the PDCP PDU indicated by the discard indicator has become a part of the RLC PDU, the RLC layer does not discard information related to the PDCP PDU indicated by the discard indicator. This is because if PDCP PDUs that have become part of RLC PDUs are discarded, gaps occur in RLC sequence numbers, resulting in transmission delay. The receiving end cannot distinguish whether the corresponding RLC sequence number is lost during transmission or discarded by the discard indicator in the transmitting end.

The RLC layer may configure RLC PDUs by preprocessing data of PDCP PDUs before receiving an uplink grant, and complete the RLC PDUs and pass them to the MAC layer to store MAC subheaders and MAC SDUs in the sixth buffer. After the RLC PDU is completed and delivered to the MAC layer, the RLC layer discards information related to the RLC PDU, mapping information, MAC subheader, and MAC SDU. In other words, in RLC UM mode, the RLC layer transmits RLC PDUs and then discards them together with related information, if any, without storing them. This is because the ARQ function is not supported in the RLC UM mode, and thus it is not necessary to record information for retransmission.

In RLC UM mode, the ARQ function is not supported, and thus it is not necessary to store corresponding information for retransmission after RLC PDU is transmitted. Therefore, after transmitting the RLC PDU, the RLC layer does not store the corresponding RLC PDU, MAC sub-header, MAC SDU and related mapping information in the sixth buffer, but discards the related information, if any. In addition, once RLC PDUs are transmitted, the RLC layer no longer has to have PDCP PDUs corresponding to the RLC PDUs even though the PDCP discard timer has not expired.

Accordingly, in the fourth embodiment of the efficient buffer management method applicable when the LTE system terminal according to the present disclosure operates in RLC UM mode, after transmitting RLC PDUs, the RLC layer may not store the corresponding RLC PDUs, MAC subheaders, and MAC SDUs in the sixth buffer and mapping table, but may discard related information and mapping information, if any. Further, information on PDCP PDUs corresponding to RLC PDUs is transferred to the PDCP layer, and the PDCP layer discards the information on PDCP PDUs from the fifth buffer even though the PDCP timer has not expired.

Terminal data preprocessing and retransmission.

The embodiments of the present disclosure as described above may apply the data preprocessing procedure to the next generation mobile communication system. The data preprocessing procedure may be performed as large as the amount of data that can be maximally transmitted in one TTI or one transmission. That is, the data preprocessing may be performed as much as the maximum allowed UL grant or the maximum UL grant. Further, the time at which the data preprocessing is performed may include one or more of the following.

1. Data preprocessing may be performed if the amount of data currently preprocessed becomes less than the maximum allowed UL grant as described above.

2. The data preprocessing may be periodically performed based on a specific time.

3. Data preprocessing may be performed when the MAC layer configures MAC PDUs using uplink grants and passes data to the physical layer.

4. After the new data is sent, data preprocessing may be performed.

5. If an indicator to perform data preprocessing is received from the lower layer, data reception may be performed.

At one of the above time points, the terminal may perform data preprocessing. Further, the terminal may perform data preprocessing according to several points of time as described above, if necessary.

In the case where RLC controls a PDU dynamically generated in the RLC layer, for example, in the case where an RLC status report (RLC status PDU) is generated, the terminal may first generate the RLC status report at the time when data preprocessing is performed, and may perform data preprocessing for the RLC status report in preference to other general RLC PDUs. In addition, the terminal may also perform data preprocessing preferentially for RLC PDUs to be retransmitted.

That is, at the time when the above data preprocessing is performed, the terminal may perform the data preprocessing in the order of RLC status report, retransmitted data RLC PDU, and data RLC PDU.

The terminal segment executing method.

In the above-described procedure, it is necessary to further designate the terminal to perform the procedure of segmentation. That is, if an uplink grant is received in a state in which the terminal stores a data-pre-processed MAC SDU and MAC subheader for each logical channel, the terminal may perform an LCP procedure in consideration of logical channel priority, priority bit rate (Priority Bit Rate, PBR), numerology, and TTI values, and may allocate an uplink grant for each logical channel. Segmentation may be necessary if an integer of the sum of the MAC SDU and the MAC subheader unit of the data pre-processing exceeds the uplink grant when the uplink grant is allocated for each logical channel.

The first embodiment of the segmentation is as follows.

In the first embodiment, the RLC layer may store RLC PDUs transferred to the MAC layer for segmentation. The MAC layer may compare the uplink grant allocated for each logical channel with an integer of the sum of the data-pre-processed MAC SDU and the MAC sub-header unit, and if the uplink grant is insufficient, the MAC layer may transfer information on an RLC sequence number corresponding to the last MAC SDU (RLC PDU) to the RLC layer. The RLC layer may perform segmentation for RLC PDUs corresponding to the transferred RLC sequence numbers, and may transfer the segmented RLC PDU segments to the MAC layer.

The MAC layer may configure a MAC subheader for the delivered RLC PDU segments and may perform data multiplexing or concatenation to match the uplink grant. The RLC layer may perform data preprocessing and segmentation according to uplink grants, and in this case, performs segmentation in consideration of the size of the RLC header (in consideration of added fields that may be added to the RLC header, such as a segmentation offset (Segmentation Offset, SO) field) and the size of a MAC subheader to be updated later, to match the size of the uplink grant allocated for each logical channel.

A second embodiment of segmentation is as follows.

In the second embodiment, the RLC layer may not store RLC PDUs transferred to the MAC layer for segmentation. The MAC layer may compare the uplink grant allocated for each logical channel with an integer of the sum of the data-pre-processed MAC SDU and the MAC sub-header unit, and if the uplink grant is insufficient, the MAC layer may transfer information on an RLC sequence number corresponding to the last MAC SDU (RLC PDU) to the RLC layer. The RLC layer may dynamically regenerate RLC PDUs corresponding to the delivered RLC sequence numbers based on the PDCP PDUs using the mapping table information, perform segmentation for the generated RLC PDUs, and deliver the segmented RLC PDU segments to the MAC layer. The MAC layer may configure a MAC subheader for the delivered RLC PDU segments and may perform data multiplexing or concatenation to match the uplink grant. The RLC layer may perform data preprocessing and segmentation according to uplink grants, and in this case, performs segmentation in consideration of the size of the RLC header (in consideration of an added field that may be added to the RLC header, such as an SO field) and the size of a MAC subheader to be updated later to match the size of the uplink grant allocated for each logical channel.

A third embodiment of segmentation is as follows.

In the third embodiment, the RLC layer may not store RLC PDUs transferred to the MAC layer for segmentation. The MAC layer may compare the uplink grant allocated for each logical channel with an integer of the sum of the data-pre-processed MAC SDU and the MAC sub-header unit, and if the uplink grant is insufficient, the MAC layer may pass the last MAC SDU (RLC PDU) to the RLC layer. The RLC layer may then perform segmentation for the delivered RLC PDU, and may deliver the segmented RLC PDU segments to the MAC layer. The MAC layer may configure a MAC subheader for the delivered RLC PDU segments and may perform data multiplexing or concatenation to match the uplink grant. The RLC layer may perform data preprocessing and segmentation according to uplink grants, and in this case, performs segmentation in consideration of the size of the RLC header (in consideration of an added field that may be added to the RLC header, such as an SO field) and the size of a MAC subheader to be updated later to match the size of the uplink grant allocated for each logical channel.

A fourth embodiment of the segmentation is as follows.

In the fourth embodiment, the RLC layer may not store RLC PDUs transferred to the MAC layer for segmentation. The MAC layer may compare the uplink grant allocated for each logical channel with an integer of the sum of the data-pre-processed MAC SDU and the MAC sub-header unit, and if the uplink grant is insufficient, the MAC layer may transfer mapping information (e.g., a memory address) of the last MAC SDU (RLC PDU) to the RLC layer using a mapping table. The RLC layer may then use the mapping information to introduce stored RLC PDUs, perform segmentation for the RLC PDUs, and may pass the segmented RLC PDU segments to the MAC layer. The MAC layer may configure a MAC subheader for the delivered RLC PDU segments and may perform data multiplexing or concatenation to match the uplink grant.

The RLC layer may perform data preprocessing and segmentation according to uplink grants, and in this case, performs segmentation in consideration of the size of the RLC header (in consideration of an added field that may be added to the RLC header, such as an SO field) and the size of a MAC subheader to be updated later to match the size of the uplink grant allocated for each logical channel.

A fifth embodiment of the segmentation is as follows.

In the fifth embodiment, the RLC layer may not store RLC PDUs transferred to the MAC layer for segmentation. The MAC layer may compare the uplink grant allocated for each logical channel with an integer of the sum of the data-pre-processed MAC SDU and the MAC sub-header unit, and if the uplink grant is insufficient, the MAC layer may transfer mapping information (e.g., a memory address) of the last MAC SDU (RLC PDU) to the RLC layer using a mapping table. The RLC layer may then regenerate RLC PDUs based on the PDCP PDUs using the transferred mapping information, perform segmentation for the RLC PDUs, and may transfer the segmented RLC PDU segments to the MAC layer. The MAC layer may configure a MAC subheader for the delivered RLC PDU segments and may perform data multiplexing or concatenation to match the uplink grant.

A terminal data preprocessing execution method for multiple connections.

In order to perform data preprocessing in a multi-connection or dual-connection environment, a terminal should be able to determine in advance whether a primary cell group or a secondary cell group is to transmit data of the PDCP layer. That is, since RLC sequence numbers need to be allocated in the data preprocessing, what cell group should perform transmission should be determined in advance in order to perform data preprocessing. In the dual connectivity environment, the method for pre-allocating PDCP layer data to the primary cell group and the secondary cell group is as follows.

1. The first allocation method at operation 2101: if the data amount of the PDCP layer is less than a predetermined threshold value, the terminal does not pre-allocate the data of the PDCP layer to the primary cell group and the secondary cell group. Data within the threshold is only pre-processed in the primary cell group (or secondary cell group). Further, if the data amount of the PDCP layer becomes greater than the threshold, the terminal does not perform data pre-processing for data whose amount is greater than the threshold, but performs buffer status reporting for the primary cell group and the secondary cell group for the current data amount of the PDCP layer. Further, if an uplink grant is received for each cell group, the terminal may allocate PDCP layer data to the primary cell group and the secondary cell group according to the uplink grant, and may perform data preprocessing to transmit the data. The threshold may be assigned a value capable of indicating a low data rate or small data, and may be configured when the network (or base station) performs RRC connection configuration.

2. The (1-1) allocation method at operation 2102: if the data amount of the PDCP layer is less than a predetermined threshold value, the terminal does not pre-allocate the data of the PDCP layer to the primary cell group and the secondary cell group. Data within the threshold is only pre-processed in the primary cell group (or secondary cell group). Further, if the data amount of the PDCP layer becomes greater than a threshold, the terminal may pre-process as much data as the threshold only for the primary cell group, and may perform buffer status reporting for the primary cell group and the secondary cell group for data exceeding the threshold. Further, if an uplink grant is received for each cell group, the terminal may allocate PDCP layer data to the primary cell group and the secondary cell group according to the uplink grant, and may perform data preprocessing to transmit the data. The threshold may be assigned a value capable of indicating a low data rate or small data, and may be configured when the network (or base station) performs RRC connection configuration.

3. The (1-2) th allocation method at operation 2103: if the data amount of the PDCP layer is less than a predetermined threshold value, the terminal does not pre-allocate the data of the PDCP layer to the primary cell group and the secondary cell group. Data within the threshold is only pre-processed in the primary cell group (or secondary cell group). Further, if the data amount of the PDCP layer becomes greater than the threshold, the terminal may pre-process as much data as the threshold for the primary cell group and may pre-process as much data exceeding the threshold for the secondary cell group as the size of the uplink grant that can be maximally allocated for the secondary cell group. Further, for the remaining data, the terminal may perform buffer status reporting, and if an uplink grant is received for each cell group, the terminal may allocate PDCP layer data to the primary cell group and the secondary cell group according to the uplink grant, and may perform data preprocessing to transmit the data. The threshold may be assigned a value capable of indicating a low data rate or small data, and may be configured when the network (or base station) performs RRC connection configuration.

4. A second allocation method at operation 2104: if the data amount of the PDCP layer is less than a predetermined threshold value, the terminal does not pre-allocate the data of the PDCP layer to the primary cell group and the secondary cell group. Data within the threshold is only pre-processed in the primary cell group (or secondary cell group). Further, if the data amount of the PDCP layer becomes greater than the threshold, the terminal may pre-allocate the current overall data of the PDCP layer to the primary cell group and the secondary cell group according to a specific split ratio configured by the network or the base station (or perform data pre-processing on the primary cell group for as much data as the threshold and perform data pre-processing for data exceeding the threshold after pre-allocating the data to the primary cell group and the secondary cell group according to the specific split ratio). Further, for pre-allocated data, the terminal may perform data pre-processing on each cell group before it is allocated with an uplink grant. The threshold may be configured to a value capable of indicating a low data rate or small data when RRC connection configuration is performed by the network (or base station), and a specific ratio may be configured when the network (or base station) performs RRC connection configuration in consideration of network and base station resource conditions.

In the present disclosure, a terminal in a dual connectivity environment may perform data preprocessing by applying one of the four methods as described above.

The process in which the PDCP layer of the terminal determines the amount of data based on a threshold and pre-allocates the data to the primary and secondary cell groups may begin at one or more points in time as described below.

1. When data preprocessing is intended to be performed in a state where the amount of data currently preprocessed becomes smaller than the uplink grant amount that can be maximally allocated

2. Periodically based on constant time

3. Configuring a MAC PDU using uplink grants at the MAC layer and at a time when data is transferred to the physical layer

4. After transmitting the new data

5. When an indicator for performing data preprocessing is received from a lower layer and data preprocessing is intended to be performed

6. Whenever new data is received in PDCP layer

7. When receiving an indicator for performing data allocation on a primary cell group and a secondary cell group from a lower layer

8. When the data amount becomes greater than a specific threshold in the PDCP layer

The data amount of the PDCP layer may be calculated every time the data amount of the PDCP layer is compared with a threshold value by the following method.

1. The first calculation method comprises the following steps: the method calculates a size of overall data corresponding to a sum of a data amount of a PDCP data layer that is not transmitted and is not preprocessed, a data amount that is not transmitted and is preprocessed in a primary cell group, and a data amount that is not transmitted and is preprocessed in a secondary cell group, and compares the calculated value with a threshold value.

2. The second calculation method is as follows: the method calculates a size of a data amount of the PDCP data layer that is not transmitted and is not preprocessed, and compares the calculated value with a threshold.

3. The third calculation method is as follows: the method calculates the size of the amount of data that is not transmitted and excludes the data calculated when compared to the previous threshold and the amount of data that is newly received, and compares the calculated value to the threshold.

4. A fourth calculation method: the method calculates a size of overall data corresponding to a sum of an amount of data not transmitted but preprocessed in the primary cell group and an amount of data not transmitted but preprocessed in the secondary cell group, and compares the calculated value with a threshold value.

Using one of the four methods described above, the size of data of the PDCP layer to be compared with a threshold by a terminal in a dual connectivity environment can be calculated.

Terminals in a dual connectivity environment may have as a rule the assignment of consecutive PDCP sequence numbers such that when data of the PDCP layer is pre-assigned to a primary cell group and a secondary cell group, the respective cell groups maximally have them. If the PDCP sequence numbers are not separated to the respective cell groups but allocated to groups of consecutive PDCP sequence numbers, processing time and load occurring when the PDCP layer of the receiving side rearranges the order of the PDCP sequence numbers can be reduced.

In the method for performing data preprocessing of the terminals in the dual connection environment, the data preprocessing may be performed by applying the method for performing data preprocessing of the terminals in the single connection environment to each cell group. That is, when data preprocessing is performed in each cell group, the terminal may perform data preprocessing as much as the maximum transport block size, the maximum allowed UL grant, or the size of the maximum transmittable data in one TTI. That is, although the data preprocessing is performed as much as the above-described size, the maximum data preprocessing gain for the next data transmission can be obtained.

In a method for performing data preprocessing of a terminal in a dual connectivity environment, a threshold or a specific split ratio may be configured from a base station to the terminal through an RRC message (RRCConnectionSetup or RRCConnectionReconfiguration), or may be dynamically reconfigured through an RRC message (RRCConnectionReconfiguration). Furthermore, in order to dynamically allocate a threshold or a specific split ratio, the threshold or the specific split ratio may be updated using a newly defined PDCP control PDU.

In a method for performing data preprocessing of a terminal in a dual connectivity environment, it is necessary for a base station to configure a threshold so that the threshold becomes larger than a maximum transport block size of a primary cell group, a maximum allowed UL grant, or a maximum transmittable data size in one TTI. This is because the maximum data preprocessing gain for the next data transmission can be obtained by configuring the threshold such that it becomes larger than the maximum transport block size, the maximum allowed UL grant, or the maximum transmittable data size in one TTI.

In the dual connectivity environment as described above, the terminal may configure data of the PDCP layer to transmit them to different cell groups through packet duplication, and the configuration may be activated or deactivated through RRC messages or newly defined PDCP control PDUs.

Fig. 17A and 17B are diagrams illustrating an operation of a terminal in which a next generation mobile communication system terminal manages a buffer in an RLC AM mode according to an embodiment of the present disclosure.

Referring to fig. 17A, if an IP packet is received from an upper layer, the terminal PDCP layer may operate at operation 1701, may receive the IP packet at operation 1705, and may store the respective IP packets in a fifth buffer by allocating a storage address to the IP packet at operation 1710. Further, at operation 1715, the terminal PDCP layer may drive and manage a PDCP discard timer for each IP packet. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the fifth buffer at operation 1720. If the PDCP PDU corresponding to the timer is transmitted to the RLC layer at operation 1725, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 1730. The discard indicator may indicate a PDCP PDU sequence number transmitted to the RLC layer, or mapping information regarding PDCP PDUs. Further, if ACK/NACK information for the PDCP PDU is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDU from the fifth buffer. Further, if there is an unexpired timer corresponding to the discarded PDCP PDU, the PDCP layer may stop and discard the timer at operation 1720.

Further, the PDCP layer may receive information about PDCP PDUs concatenated to RLC PDUs having received RLC ACK from the RLC layer. Since PDCP PDUs mean that they have been successfully delivered to the receiving end, it is no longer necessary to store them in the fifth buffer, and the PDCP layer may discard them. At operation 1720, the PDCP layer discards information corresponding to the discarded PDCP PDU and mapping table information, and if there is an unexpired timer, the PDCP layer may stop and discard the timer. In case of managing the fifth buffer based on the RLC ACK, it is important to manage the fifth buffer differently according to the PDCP layer operation of the terminal during handover.

PDCP sequence numbers

Referring to fig. 17B, the terminal RLC layer operates at operation 1735. If a discard indicator is received from the PDCP layer at operation 1740, the terminal RLC layer may discard the corresponding information when the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer at operation 1745. That is, the terminal RLC layer discards information related to PDCP PDUs (RLC SDUs) delivered to and stored in the RLC layer, as well as mapping information. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU at operation 1745, the terminal RLC layer does not discard information related to the PDCP PDU at operation 1750.

If an RLC status report is received from the RLC layer of the receiving end at operation 1740, the RLC layer may identify an ACK/NACK result for each RLC sequence number. Further, in case of the acknowledged RLC PDU at operation 1760, the RLC layer discards mapping information, MAC subheader and MAC SDU related to the acknowledged RLC PDU from a sixth buffer where the RLC PDU/PDCP PDU is preprocessed and stored at operation 1765. In contrast, for a negative acknowledged RLC PDU, the RLC layer prepares for retransmission at operation 1775.

The RLC layer may rapidly perform retransmission using the MAC subheader and the MAC SDU data-preprocessed by the sixth buffer based on the mapping information of the RLC PDU if uplink grant for retransmission is sufficient during the performance of retransmission. In contrast, if the uplink grant is insufficient, the RLC layer may perform re-segmentation for the last MAC sub-header and MAC SDU to update the RLC header and MAC sub-header, and may perform retransmission. The RLC layer may identify the result of ACK/NACK for the RLC sequence number through the RLC status report, identify mapping table information at operation 1770, and determine the ACK/NACK result for the corresponding PDCP sequence number. If the ACK information of the PDCP sequence number is recognized, the RLC layer may pass the ACK information of the PDCP sequence number to the PDCP layer. The PDCP layer may identify ACK information and may discard corresponding PDCP PDUs from the fifth buffer using the ACK information.

Accordingly, in the fourth embodiment of the efficient buffer management method and retransmission acceleration method applicable when the terminal of the next generation mobile communication system according to the present disclosure operates in the RLC AM mode, the RLC layer can discard information on RLC PDUs for which RLC ACK has been received and MAC subheaders and MAC SDUs of mapping table information/data pre-processing, and PDCP PDUs corresponding to RLC PDUs for which the RLC layer has notified the PDCP layer, from the fifth buffer, and release and discard the corresponding information and timer. Therefore, even with a small size for quickly emptying the fifth buffer and the sixth buffer, the buffers can be efficiently managed, and thus efficiency can be maximized and retransmission can be accelerated.

Fig. 18A and 18B are diagrams illustrating an operation of a terminal in which a next generation mobile communication system terminal manages a buffer in RLC UM mode according to an embodiment of the present disclosure.

Referring to fig. 18A, if an IP packet is received from an upper layer, the terminal PDCP layer may operate at operation 1801, may receive the IP packet at operation 1805, and may store the respective IP packets in a fifth buffer by allocating a storage address to the IP packet at operation 1810. Further, the terminal PDCP layer may drive and manage a PDCP discard timer for each IP packet at operation 1815. If the timer expires, the terminal discards the PDCP PDU or PDCP SDU corresponding to the timer from the fourth buffer at operation 1820. If the PDCP PDU corresponding to the timer is transmitted to the RLC layer at operation 1825, the PDCP layer may transmit a discard indicator corresponding to the PDCP PDU to the RLC layer at operation 1830. The discard indicator may indicate a PDCP PDU sequence number transmitted to the RLC layer or mapping information regarding PDCP PDUs. Further, if ACK/NACK information regarding the PDCP PDUs is received from the PDCP layer of the receiving end through the PDCP status report, the PDCP layer may discard the acknowledged PDCP PDUs from the fifth buffer, and if there is an unexpired timer corresponding to the discarded PDCP PDUs, the PDCP layer may stop and discard the timer at operation 1820. Further, if RLC PDUs are transmitted from the RLC layer and the RLC layer delivers information about PDCP PDUs concatenated to the transmitted RLC PDUs to the PDCP layer, the PDCP layer may discard information about the transmitted PDCP PDUs from the fifth buffer, and if the corresponding timer has not expired, the PDCP layer may release and discard the timer.

Referring to fig. 18B, the termination layer operates at operation 1835. If a discard indicator is received from the PDCP layer in operation 1840, the terminal RLC layer may discard the corresponding information in case that the PDCP PDU corresponding to the discard indicator has not been part of or mapped onto the RLC PDU in the RLC layer in operation 1845. That is, the terminal RLC layer discards information related to PDCP PDUs (RLC SDUs) delivered to and stored in the RLC layer, as well as mapping information, at operation 1855. If the PDCP PDU indicated by the discard indicator has become part of the RLC PDU at operation 1845, the terminal RLC layer does not discard information related to the PDCP PDU at operation 1850.

The RLC layer may configure RLC PDUs through data pre-processing of PDCP PDUs before receiving the uplink grant, and may complete the RLC PDUs and pass them to the MAC layer to store MAC subheaders and MAC SDUs in the sixth buffer. Further, if RLC PDU transmission is completed by receiving the uplink grant, the RLC layer discards the RLC PDU-related information, mapping information, MAC subheader, and MAC SDU (discarded from the sixth buffer) at operation 1860. In other words, in RLC UM mode, the RLC layer transmits RLC PDUs and then discards related information, if any, without storing RLC PDUs. This is because the ARQ function is not supported in the RLC UM mode, and thus it is not necessary to record information for retransmission. Further, at operation 1865, the RLC layer may determine information about PDCP PDUs corresponding to the transmitted RLC PDUs and pass it to the PDCP layer, and may use the information to manage the fifth buffer.

Accordingly, in a fourth embodiment of an efficient buffer management method when a terminal of the next generation mobile communication system operates in RLC UM mode, the RLC layer transmits RLC PDUs, and then may discard the related information in the sixth buffer and the corresponding data-pre-processed MAC subheader and MAC SDU (if any) without storing the corresponding RLC PDUs. Further, in the fourth embodiment, the RLC layer may transmit information about PDCP PDUs corresponding to the transmitted RLC PDUs to the PDCP layer, and the PDCP layer immediately discards the information about PDCP PDUs from the fifth buffer even though the PDCP timer has not expired.

The first to fourth embodiments of the present disclosure propose a buffer structure and a retransmission acceleration method when a terminal transmits data. In the present disclosure, when a terminal receives data, the RLC layer may have a separate buffer for storing RLC PDUs. RLC PDUs can only indicate segmented RLC PDU segments, but not complete RLC PDUs (non-segmented RLC PDUs or RLC PDUs that are not segmented). That is, if the RLC layer receives complete RLC PDUs when the terminal receives data, it may directly transfer them to an upper layer without storing them, whereas if RLC PDU segments are received, the RLC layer stores them in a separate buffer for reassembly, and if a specific condition is satisfied, it combines RLC PDU segments into one complete RLC PDU to transfer the complete RLC PDU to the upper layer. RLC PDU segments that have not been combined into one complete RLC PDU may all be discarded. The specific condition may be a case where a timer for reassembly has expired or a case where a window based on RLC layer sequence numbers moves to trigger reassembly.

Fig. 19 is a block diagram of a terminal according to an embodiment of the present disclosure.

Referring to fig. 19, the terminal includes a Radio Frequency (RF) processor 1910, a baseband processor 1920, a memory 1930, and a controller 1940.

The RF processor 1910 performs functions for transmitting and receiving signals over radio channels, such as signal band conversion and amplification. That is, the RF processor 1910 performs up-conversion of the baseband signal supplied from the baseband processor 1920 to the RF band signal to transmit the converted signal to the antenna, and performs down-conversion of the RF band signal received through the antenna to the baseband signal. For example, the RF processor 1910 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a Digital-to-Analog Converter (DAC Digital-to-Analog Converter), and an Analog-to-Digital Converter (ADC). Although only one antenna is shown in the drawings, the terminal may be provided with a plurality of antennas. Further, the RF processor 1910 may include multiple RF chains. In addition, the RF processor 1910 may perform beamforming. For beamforming, the RF processor 1910 may adjust the phase and size of signals transmitted or received through multiple antennas or antenna elements. Further, the RF processor may perform MIMO, and may receive several layers during the performance of MIMO operations. The RF processor 1910 may perform receive beam scanning through appropriate configuration of multiple antennas or antenna elements under control of a controller, or may control the direction and beam width of a receive beam so that the receive beam is synchronized with a transmit beam.

The baseband processor 1920 performs conversion between baseband signals and bit strings according to the physical layer standard of the system. For example, during data transmission, the baseband processor 1920 generates complex symbols by encoding and modulating the transmitted bit string. Further, during data reception, the baseband processor 1920 restores the received bit string by demodulating and decoding the baseband signal supplied from the RF processor 1910. For example, in case of following the OFDM method, during data transmission, the baseband processor 1920 generates complex symbols by encoding and modulating the transmitted bit string, performs mapping of the complex symbols on subcarriers, and then configures the OFDM symbols through inverse fast fourier transform (Inverse Fast Fourier Transform, IFFT) operation and Cyclic Prefix (CP) interpolation. Further, during data reception, the baseband processor 1920 divides the baseband signal supplied from the RF processor 1910 in units of OFDM symbols, restores the signal mapped on the subcarrier by a Fast Fourier Transform (FFT) operation, and then restores the received bit string by demodulation and decoding.

The baseband processor 1920 and the RF processor 1910 transmit and receive signals as described above. Thus, the baseband processor 1920 and the RF processor 1910 may be referred to as a transmitter, receiver, transceiver, or transceiver. Further, to support different radio connection technologies, at least one of the baseband processor 1920 and the RF processor 1910 may include a plurality of communication modules. Further, at least one of the baseband processor 1920 and the RF processor 1910 may include different communication modules in order to process signals of different frequency bands. For example, different radio connection technologies may include LTE networks and NR networks. Further, the different frequency bands may include an ultra-high frequency (Super High Frequency, SHF) (e.g., 2.5GHz or 5 GHz) band and a millimeter wave (mmWave) (e.g., 60 GHz) band.

The memory 1930 stores therein data of basic programs, application programs, and configuration information for the operation of the terminal. Memory 1930 provides stored data upon request from controller 1940.

The controller 1940 controls the entire operation of the terminal. For example, the controller 1940 transmits and receives signals through the baseband processor 1920 and the RF processor 1910. In addition, the controller 1940 records data in the memory 1930 or reads data from the memory 1930. To this end, controller 1940 may include at least one processor that executes instructions to implement multi-connectivity processor 19, wherein multi-connectivity processor 19 executes instructions to implement multi-connectivity processor 204242. For example, the controller 1940 may include a communication processor (Communication Processor, CP) that performs control for communication and an application processor (Application Processor, AP) that controls upper layers, such as an application program.

Fig. 20 is a block configuration of Transmission and Reception Points (TRP) according to an embodiment of the disclosure.

Referring to fig. 20, the base station includes an RF processor 2010, a baseband processor 2020, a transceiver 2030, a memory 2040 and a controller 2050.

The RF processor 2010 performs functions for transmitting and receiving signals over a radio channel, such as signal band conversion and amplification. That is, the RF processor 2010 performs up-conversion of the baseband signal supplied from the baseband processor 2020 to an RF band signal to transmit the converted signal to the antenna, and performs down-conversion of the RF band signal received through the antenna to the baseband signal. For example, RF processor 2010 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC. Although only one antenna is shown in the drawings, the first connection node may be provided with a plurality of antennas. In addition, the RF processor 2010 may include a plurality of RF chains. In addition, RF processor 2010 may perform beamforming. For beamforming, the RF processor 2010 may adjust the phase and magnitude of signals transmitted or received through multiple antennas or antenna elements. Further, the RF processor may perform a MIMO operation through transmission of one or more layers.

The baseband processor 2020 performs conversion between baseband signals and bit strings according to a physical layer standard of a first radio connection technology. For example, during data transmission, baseband processor 2020 generates complex symbols by encoding and modulating a transmitted bit string. Further, during data reception, the baseband processor 2020 recovers the received bit string by demodulating and decoding the baseband signal supplied from the RF processor 2010. For example, in case of following the OFDM method, during data transmission, the baseband processor 2020 generates complex symbols by encoding and modulating a transmitted bit string, performs mapping of the complex symbols on subcarriers, and then configures OFDM symbols through FFT operation and CP interpolation. Further, during data reception, the baseband processor 2020 divides a baseband signal supplied from the RF processor 2010 in units of OFDM symbols, restores a signal mapped on subcarriers through an FFT operation, and then restores a received bit string through demodulation and decoding. The baseband processor 2020 and the RF processor 2010 transmit and receive signals as described above. Accordingly, baseband processor 2020 and RF processor 2010 may be referred to as a transmitter, receiver, transceiver, or wireless transceiver.

The transceiver 2030 provides an interface for performing communications with other nodes in the network.

The memory 2040 stores therein data of basic programs, application programs, and configuration information for the operation of the main base station. Specifically, the memory 2040 may store information on bearers allocated to the connection terminals and measurement results reported from the connection terminals. Further, the memory 2040 may store information that underlies a determination of whether to provide or suspend multiple connections to the terminal. In addition, the memory 2040 provides stored data according to a request from the controller 2050.

The controller 2050 controls the entire operation of the master base station. For example, the controller 2050 transmits and receives signals through the baseband processor 2020 and the RF processor 2010 or through the transceiver 2030. Further, the controller 2050 records data in the memory 2040 or reads data from the memory 2040. To this end, the controller 2050 may include at least one processor that executes instructions to implement the multi-connection processor 2052.

In the drawings explaining the method according to the present disclosure, the order of explanation does not necessarily correspond to the order of execution, and the processes may be executed in reverse order or in parallel.

Further, in the drawings explaining the method according to the present disclosure, only a portion of the constituent elements may be included, and other portions of the constituent elements may be omitted without departing from the subject matter of the present disclosure.

Although preferred embodiments of the present disclosure have been described in the specification and drawings, and specific language has been used, these are used in a generic sense only to help those of ordinary skill in the art to obtain a full understanding of the disclosure, and do not limit the scope of the disclosure. It is apparent to those skilled in the art to which the present disclosure pertains that various modifications are possible based on the technical concept of the present disclosure in addition to the embodiments disclosed herein.

While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.

Claims

1. A method for controlling a buffer for handover by a device in a wireless communication system, the method comprising:

storing information of a packet data convergence protocol PDCP protocol data unit PDU in a first buffer;

obtaining a Radio Link Control (RLC) Protocol Data Unit (PDU) corresponding to the PDCP PDU;

storing information about a media access control MAC service data unit SDU and a MAC subheader corresponding to the RLC PDU in a second buffer;

Transmitting the RLC PDU;

in case positive acknowledgement information is received for RLC PDU:

discarding information of at least one PDCP PDU of PDCP PDUs corresponding to the RLC PDU for which the positive acknowledgement information is received, wherein the at least one PDCP PDU has a consecutive sequence number starting with a lowest sequence number for which corresponding information is stored in the first buffer; and

the information included in the second buffer is discarded.

2. The method of claim 1, wherein the information of the at least one PDCP PDU is discarded in an order of sequence numbers of the at least one PDCP PDU.

3. The method of claim 1, wherein discarding the information further comprises:

stopping a timer associated with the at least one PDCP PDU; and

the information about the timer is discarded.

4. The method of claim 1, further comprising:

based on the mapping information between the first buffer and the second buffer, RLC PDUs for which negative acknowledgement information is received are retransmitted.

5. An apparatus for controlling a buffer for handover in a wireless communication system, the apparatus comprising:

a transceiver; and

At least one processor configured to:

information of a packet data convergence protocol PDCP protocol data unit PDU is stored in a first buffer,

obtaining a radio link control RLC protocol data unit PDU corresponding to the PDCP PDU,

information on a medium access control MAC service data unit SDU and a MAC sub-header corresponding to the RLC PDU is stored in a second buffer,

the RLC PDU is transmitted in a state that,

in case positive acknowledgement information is received for RLC PDU:

the information included in the second buffer is discarded.

6. The apparatus of claim 5, wherein the information of the at least one PDCP PDU is discarded in an order of sequence numbers of the at least one PDCP PDU.

7. The apparatus of claim 5, wherein the at least one processor is further configured to: stopping a timer associated with the at least one PDCP PDU; and

The information about the timer is discarded.

8. The apparatus of claim 6, wherein the at least one processor is further configured to: