Method and apparatus for determining desired buffer size (DBS) in wireless communication system

Abstract

A method performed by a subordinate base station including a radio link control (RLC) layer in a wireless communication system, according to one embodiment of the present disclosure, may comprise the steps of: receiving, from a superordinate base station including a packet data convergence protocol (PDCP) layer, a first downlink (DL) delay determined on the basis of a DL delay measurement value for a bearer from the superordinate base station up to the subordinate base station, which is measured by the superordinate base station; determining a second DL delay on the basis of the first DL delay; determining a target buffering time on the basis of the second DL delay and a downlink data delivery status (DDDS) interval; determining a desired buffer size (DBS) on the basis of the target buffering time; and transmitting a DDDS including the DBS to the superordinate base station.

Description

Method and device for determining DBS (desired buffer size) in a wireless communication system

[0001] The present disclosure relates to a wireless communication system, and more particularly, to a method and apparatus for determining a desired buffer size (DBS) in a wireless communication system.

[0002] In a dual connectivity (DC) environment or a separated base station environment, a buffer of a lower base station can be managed through flow control between a base station including a PDCP (packet data convergence protocol) stack (e.g., a centralized unit (CU), hereinafter referred to as an "upper base station") and a base station including a radio link control (RLC) stack (e.g., an eNode B (eNB) or a distributed unit (DU), hereinafter referred to as a "lower base station"). Specifically, the data flow between the upper base station and the lower base station can be controlled by having the lower base station transmit the amount of data to be received to the upper base station at regular intervals (e.g., downlink data delivery status, DDDS interval) so as to prevent the data transmission rate of the upper base station from exceeding the processing rate of the lower base station. The amount of data to be received per second can be expressed as a desired buffer size (DBS).

[0003] A lower base station can request the amount of data to be downloaded from the upper base station by transmitting a downlink data delivery status (DDDS) message containing information about the DBS to the upper base station. Conventionally, lower base stations determine the target buffering time based on the nru-delay value set as the default value for the interface between the upper and lower base stations, and determine the DBS based on the target buffering time determined in this way.

[0004] If a higher-order base station transmits more data than a lower-order base station can handle, an increasing amount of data may be buffered, and in a dual-connectivity environment where link stability is not guaranteed, data loss (e.g., PDCP loss) may occur. If a higher-order base station transmits less data than a lower-order base station can handle, less data is scheduled than available resources, resulting in reduced throughput. Therefore, a lower-order base station needs to determine a DBS that accurately reflects its actual processing capacity. However, a DBS determined based on the nru-delay value set at the base station cannot accurately reflect the actual processing capacity of the lower-order base station.

[0005] To improve DBS accuracy and flow control performance, a method of measuring downlink delay values ​​in real time and calculating DBS based on this data could be considered. However, this method, in which the operator measures downlink delay values ​​in real time and inputs them as parameters for lower-level base stations, is not economically feasible.

[0006] The present disclosure can provide a feasible method and device for determining a reliable DBS based on real-time downlink delay measurements and improving flow control performance.

[0007] According to the method and device of the present disclosure, in flow control, it is possible to solve the problem of data loss or throughput degradation due to determining DBS based on an nru-delay value preset at a base station.

[0008] In one embodiment, a method performed by a lower base station including an RLC (radio link control) layer in a wireless communication system may include the steps of: receiving, from an upper base station including a PDCP (packet data convergence protocol) layer, a first downlink (DL) delay determined based on a DL delay measurement value for a bearer from the upper base station to the lower base station, the DL delay measured by the upper base station; determining a second DL delay based on the first DL delay; determining a target buffering time based on the second DL delay and a DDDS (downlink data delivery status) interval; determining a DBS (desired buffer size) based on the target buffering time; and transmitting a DDDS including the DBS to the upper base station.

[0009] In a wireless communication system according to one embodiment, a lower base station including an RLC (radio link control) layer includes a transceiver; and a control unit connected to the transceiver, wherein the control unit receives, from an upper base station including a PDCP (packet data convergence protocol) layer, a first downlink (DL) delay determined based on a DL delay measurement value for a bearer from the upper base station to the lower base station measured by the upper base station, determines a second DL delay based on the first DL delay, determines a target buffering time based on the second DL delay and a DDDS (downlink data delivery status) interval, determines a DBS (desired buffer size) based on the target buffering time, and controls transmission of a DDDS including the DBS to the upper base station.

[0010] In one embodiment, a method performed by an upper base station including a PDCP (packet data convergence protocol) layer in a wireless communication system includes the steps of: measuring a downlink (DL) delay for a bearer from the upper base station to a lower base station including a radio link control (RLC) layer; determining a first DL delay based on the DL delay measurement value; transmitting the first DL delay to the lower base station; and receiving a downlink data delivery status (DDDS) including a DBS (desired buffer size) from the lower base station, wherein the DBS is determined based on a target buffering time, the target buffering time is determined based on a second DL delay and a DDDS interval, and the second DL delay can be determined based on the first DL delay.

[0011] In a wireless communication system according to one embodiment, an upper base station including a PDCP (packet data convergence protocol) layer includes a transceiver; and a control unit connected to the transceiver, wherein the control unit measures a downlink (DL) delay for a bearer from the upper base station to a lower base station including a radio link control (RLC) layer, and determines a first DL delay based on the measured DL delay value, transmits the first DL delay to the lower base station, and controls receiving a downlink data delivery status (DDDS) including a DBS (desired buffer size) from the lower base station, wherein the DBS is determined based on a target buffering time, the target buffering time is determined based on a second DL delay and a DDDS interval, and the second DL delay can be determined based on the first DL delay.

[0012] According to one embodiment of the present disclosure, DBS for bearers can be determined based on downlink (DL) delay measurements for the bearer from an upper base station including a packet data convergence protocol (PDCP) layer to a lower base station including a radio link control (RLC) layer.

[0013] According to one embodiment of the present disclosure, since DBS can be determined based on a measured DL delay value, throughput or flow control for a data radio bearer (DRB) can be improved even in a dual connectivity environment or a separated base station when the delay between upper and lower base stations is long.

[0014] FIG. 1 illustrates an interface of an NR gNB including a PDCP layer and an NR gNB including an RLC layer according to one embodiment of the present disclosure.

[0015] FIG. 2 illustrates an interface between an NR gNB including a PDCP layer and an eNB including an RLC layer according to one embodiment of the present disclosure.

[0016] FIG. 3 illustrates a DDDS (downlink data delivery status) transmission procedure between an upper base station and a lower base station according to one embodiment of the present disclosure.

[0017] FIG. 4 is a flowchart of a process for obtaining information of a lower base station performed by an upper base station according to one embodiment of the present disclosure.

[0018] FIG. 5 illustrates a frame format of the NR-U protocol according to one embodiment of the present disclosure.

[0019] FIG. 6 is a flowchart of a process for transmitting information of a lower base station to an upper base station performed by a lower base station according to one embodiment of the present disclosure.

[0020] FIG. 7 illustrates a time delay that occurs when multiple downlink user data (DUD) packets are transmitted through multiple bearers according to one embodiment of the present disclosure.

[0021] FIG. 8 is a flowchart illustrating a process by which a lower base station determines a DBS based on a minimum value among a plurality of first DL delays according to one embodiment of the present disclosure.

[0022] FIG. 9 is a flowchart of a process for storing a minimum value among a plurality of first DL delays by a lower base station according to one embodiment of the present disclosure.

[0023] FIG. 10 is a flowchart of a method for determining a target buffering time or DBS based on the value of one of the first DL delays when a lower base station receives a plurality of first DL delays according to one embodiment of the present disclosure.

[0024] FIG. 11 illustrates the structure of a lower base station according to one embodiment of the present disclosure.

[0025] FIG. 12 illustrates the structure of an upper base station according to one embodiment of the present disclosure.

[0026] As higher frequency bands are used in 4G (4th generation), 5G (5th generation) and / or later communication systems, and the cell radius of base stations decreases, the number of base stations to cover a specific area has increased, and the burden of installation costs on operators for installing the increased number of base stations has increased. To minimize base station installation costs, a structure has been proposed in which the base station's DU and RU are separated, one or more RUs are connected to a single DU via a wired network, and one or more RUs are geographically distributed to cover a specific area.

[0027] Furthermore, a base station structure implemented in a distributed deployment according to a centralized unit (CU) configured to perform functions of upper layers of an access network (e.g., PDCP (packet data convergence protocol, RRC)) and a distributed unit (DU) configured to perform functions of lower layers has been proposed. At this time, the distributed unit (DU) may include a digital unit (DU) and a radio unit (RU). Between a core (e.g., 5GC (5G core) or NGC (next generation core)) network and a radio network (RAN), the base station may be implemented in a structure in which the CU, DU, and RU are deployed in that order. The interface between the CU and the distributed unit (DU) may be referred to as an F1 interface.

[0028] A centralized unit (CU) can be connected to at least one DU and can be responsible for functions at a higher layer than the DU. For example, the CU can be responsible for functions at the RRC (radio resource control) or SDAP (service data adaptation protocol) and PDCP (packet data convergence protocol) layers, while the DU and RU can be responsible for functions at lower layers. The DU can perform some functions (high PHY) of the RLC (radio link control), MAC (media access control), and PHY (physical) layers, and the RU can be responsible for the remaining functions (low PHY) of the PHY layer. In addition, for example, a DU (digital unit) can be included in a DU (distributed unit) depending on the implementation of a distributed deployment of a base station. Hereinafter, unless otherwise defined, the operations of DU (digital unit) and RU are described, but various embodiments of the present disclosure can be applied to both a base station deployment including a CU and a deployment in which a DU is directly connected to a core network without a CU (i.e., a deployment in which the CU and DU are integrated into one entity).

[0029] FIG. 1 illustrates an interface of an NR gNB including a PDCP layer and an NR gNB including an RLC layer according to one embodiment of the present disclosure.

[0030] Referring to FIG. 1, an NR1 gNB (101) and an NR2 gNB (102) are illustrated. Each of the NR1 gNB (101) and the NR2 gNB (102) may be connected to a 5G core (100) via an NG interface. An NR base station (NR base station) may be divided into two parts: a central unit (gNB-CU) and one or more distributed units (gNB-DU). For example, an NR1 gNB (101) may be divided into an NR1 gNB CU (120) and two NR1 gNB DUs (140, 150).

[0031] NR1 gNB (101) and NR2 gNB (102) illustrate CU / DU separated base stations. In the case of separated gNBs, RRC, PDCP, and SDAP protocol entities may be placed in the gNB-CU, and protocol entities such as RLC, MAC, and PHY may be placed in the gNB-DU.

[0032] The F1 interface may refer to an information exchange interface connecting a gNB-CU and a gNB-DU of a separate gNB. For example, the F1 interface may connect an NR1 gNB CU (120) and an NR1 gNB DU (140 or 150) in an NR1 gNB (101), as shown in FIG. 1.

[0033] The Xn interface connects different NR base stations, for example, the Xn interface may connect an NR1 gNB CU (120) and an NR2 gNB CU (130), or may connect an NR1 gNB CU (120) and an NR2 gNB DU (160). In the present disclosure, the Xn interface between an upper base station and a lower base station may mean an interface between a gNB-CU of a separate base station or a PDCP stack of an integrated base station and a gNB-DU of a separate base station or an RLC stack of an integrated base station.

[0034] FIG. 2 illustrates an interface between an NR gNB (202) including a PDCP layer and an eNB (201) including an RLC layer according to one embodiment of the present disclosure.

[0035] Referring to FIG. 2, an NR1 gNB (202) and an eNB (201) are illustrated. The eNB (201) can be connected to an Evolved Packet Core (EPC) (200) via an S1 interface.

[0036] The X2 interface may refer to an interface connecting base stations for information exchange between base stations in an LTE system. In the present disclosure, the X2 interface between an upper base station and a lower base station may refer to an interface between a CU of a separate gNB or a PDCP stack of an integrated gNB and an RLC stack of an LTE eNB. For example, in FIG. 2, the X2 interface may connect an NR1 gNB CU (220) and an eNB (201).

[0037] In the dual connectivity (e.g., EN-DC (EUTRA-NR dual connectivity) or NR-DC, etc.) environment of the present disclosure or the CU / DU separated base station environment, a base station including a PDCP stack may be referred to as an upper base station, and a base station including an RLC stack may be referred to as a lower base station. For example, in the NR-DC environment of FIG. 1, the upper base station may refer to an NR1 gNB CU (120) or an NR2 gNB CU (130) including a PDCP stack. In the present disclosure, an upper base station including a PDCP stack may be expressed as an upper base station including a PDCP layer or an upper base station including a PDCP entity. Similarly, a lower base station including an RLC stack may be expressed as a lower base station including an RLC entity or a lower base station including an RLC layer.

[0038] In FIG. 1, the upper base station, NR1 gNB CU (120), can exchange information with the lower base station, NR2 gNB DU (160) via the Xn interface. Alternatively, the upper base station, NR2 gNB CU (130), can exchange information with the lower base station, NR2 gNB DU (160) or NR2 gNB DU (170) via the F1 interface. Specifically, the UP (user plane) of the upper base station, CU (130), can exchange user data with the lower base station, NR2 gNB DU (160) or NR2 gNB DU (170) via the F1-U interface. Alternatively, in FIG. 2, the upper base station, NR1 gNB CU (220), can exchange information with the lower base station, eNB, via the X2 interface, or can exchange information with the lower base station, NR1 gNB DU (240) or NR1 gNB DU (250).

[0039] An upper base station can measure the downlink delay when sending data traffic to a lower base station. For example, the upper base station can transmit a PDCP Service Data Unit (SDU) to the lower base station on the PDCP layer over the interface with the lower base station (e.g., F1-U, Xn-U, or X2-U) and measure the time it takes for the same packet to be received by the lower base station (or the time delay incurred).

[0040] A method performed by an upper base station or a lower base station according to one embodiment can perform flow control between the upper base station and the lower base station and manage a buffer of the lower base station. Specifically, the upper base station can measure a downlink delay for the lower base station and transmit the measured information to the lower base station. The lower base station can determine a Desired Buffer Size (DBS) based on the information about the downlink delay received from the upper base station. The lower base station can manage the buffer of the lower base station by transmitting DBS information to the upper base station to transmit a request for the amount of data to be downloaded to the upper base station.

[0041] FIG. 3 illustrates a DDDS (downlink data delivery status) transmission procedure between an upper base station and a lower base station according to one embodiment of the present disclosure.

[0042] Referring to FIG. 3, a lower base station may perform a DDDS transmission procedure to provide feedback information related to data flow control to an upper base station. The upper base station (302) may be expressed as a node hosting NR PDCP. The lower base station may interact with the node hosting NR PDCP for flow control, serve user equipment (UE) based on DRB, and may be expressed as a corresponding node.

[0043] Referring to FIG. 3, a lower base station (304) can transmit a DDDS to an upper base station (302). By transmitting the DDDS to the upper base station (302), the lower base station (304) can provide feedback for controlling the downlink user data flow for each bearer. Using the provided feedback, the upper base station (302) can successfully transmit downlink data to the lower base station (304).

[0044] Specifically, as soon as the lower base station (304) identifies a successful random access channel (RACH) of the UE for the bearer (or bearers), the lower base station (304) may transmit an initial DDDS frame to the upper base station (302). The DDDS frame may also include a last frame indication when this frame is the last DL status report. Upon receiving the last frame indication, the upper base station may expect that no further UL or DL ​​data will be transmitted between the lower base station and the UE.

[0045] The DDDS frame may also include information about a radio link interruption or radio link resumption for the corresponding DRB. When the radio link is interrupted, the upper base station may receive the information about the radio link interruption and determine that traffic forwarding via the data radio bearer configured for the UE is not available to the lower base station in both the UL and DL. When the radio link is resumed, the upper base station may receive the information about the radio link resumption included in the DDDS frame and determine that traffic forwarding via the data radio bearer configured for the UE is available to the lower base station in both the UL and DL. When the UL or DL ​​radio link is interrupted, the upper base station may receive the interruption information and determine that traffic forwarding via the data radio bearer configured for the UE is not available to the lower base station in both the UL and DL. When the UL or DL ​​radio link is resumed, the upper base station may determine that traffic forwarding via the DRB configured for the UE is available to the lower base station in the UL or DL ​​based on the received resumption information.

[0046] Also specifically, when the upper base station (302) receives a DDDS frame, it can determine at least one of the DBS or data rate included in the DDDS frame as the amount of data to be transmitted from the upper base station. If the DBS value received by the upper base station is 0, the upper base station can stop data transmission per bearer. If the DBS value received by the upper base station is greater than 0, the upper base station can transmit an amount of data corresponding to the DBS value per bearer.

[0047] Information about DBS or data rate included in any DDDS frame received by an upper base station may be valid until the upper base station receives the next DDDS frame.

[0048] FIG. 4 is a flowchart of a process for obtaining information of a lower base station performed by an upper base station according to one embodiment of the present disclosure.

[0049] In step 410, the upper base station may measure the DL delay for the bearer from the upper base station to the lower base station. Alternatively, the upper base station may measure the DL delay for the interface between the lower base stations. If multiple bearers are configured in the upper base station, the upper base station may measure the DL delay for at least one of the configured bearers. For example, the upper base station may measure the DL delay for all configured bearers.

[0050] The upper base station can measure DL delay at regular intervals. For example, the upper base station can measure DL delay at one-minute intervals. The upper base station can measure DL delay when transmitting data traffic to the lower base station.

[0051] In this way, the upper base station can periodically or repeatedly measure DL delay for multiple bearers and obtain the latest DL delay information.

[0052] At step 420, the upper base station can determine the first DL delay based on the DL delay measurement value.

[0053] For example, the upper base station can determine the value of the first DL delay by discarding the decimal point below the millisecond (ms) level in the DL delay measurement value.

[0054] According to one embodiment, when the measured DL delay value exceeds the maximum value of nru-delay, the upper base station may determine the maximum value, instead of the measured DL delay value, as the value of the first DL delay and transmit it to the lower base station. nru-delay is a base station parameter related to the nru protocol used by the interface (e.g., F1, Xn, or X2 interface) between the upper base station and the lower base station. For example, the maximum value of the base station parameter nru-delay may be, for example, 50 ms. In this case, when the measured DL delay value exceeds 50 ms, the upper base station may transmit 50 ms, instead of the measured DL delay value. In other words, the maximum value of nru-delay may mean an upper limit value of the first DL delay that the upper base station may determine.

[0055] According to one embodiment, the value of the first DL delay determined by the upper base station based on this DL delay measurement value can be expressed by [Mathematical Formula 1].

[0056]

[0057] For example, if the maximum value of nru-delay is 50ms and the DL delay measurement value is 55ms, the upper base station can transmit 50ms to the lower base station as information about the DL delay measurement value. For example, if the maximum threshold value of nru-delay is 50ms and the DL delay measurement value is 5.5ms, the upper base station can transmit 5ms to the lower base station as information about the DL delay measurement value.

[0058] At step 430, the upper base station may transmit a first DL delay to the lower base station.

[0059] In one embodiment, an upper base station may select and use at least one of PDU Types 3 to 15 reserved for future PDU type extensions among PDU Types to transmit the first DL delay to a lower base station. For example, the upper base station may include the first DL delay in the field of PDU Type 15 and transmit it to the lower base station.

[0060] Through steps 420 to 430, the upper base station may transmit a frame of the NR-U protocol (e.g., one of PDU Type 3 to PDU Type 15 frames) including a first DL delay determined based on a DL delay measurement value.

[0061] Meanwhile, each step described in the flowchart of the present disclosure may be omitted or replaced with a different configuration as needed, and since the purpose of the present disclosure is to transmit information about the DL delay measurement value measured by the upper base station to the lower base station in order to determine an accurate DBS, the description of step 420 does not exclude an embodiment in which the upper base station transmits the DL delay measurement value to the lower base station. Accordingly, in step 430, the upper base station may transmit the DL delay measurement value to the lower base station, and at this time, the lower base station may perform steps according to an embodiment based on the DL delay measurement value.

[0062] In step 440, the upper base station can receive a DDDS including a DBS from the lower base station. The upper base station can receive the DDDS from the lower base station to obtain feedback information related to data flow control or the buffer of the lower base station. The upper base station can determine the DBS included in the DDDS received from the lower base station as the amount of data to be transmitted to the lower base station (see FIG. 3) and transmit downlink data based on the DBS. Since the DBS received by the upper base station from the lower base station is determined based on information about the DL delay measurement value transmitted by the upper base station to the lower base station, the upper base station can manage the buffer of the lower base station by utilizing the latest delay information.

[0063] FIG. 5 illustrates a frame format of the NR-U protocol according to one embodiment of the present disclosure.

[0064] Referring to FIG. 5, information on a DL delay measurement value measured by an upper base station (e.g., the first DL delay in FIG. 4) can be included in an NR-U PDU frame and transmitted to a lower base station. Specifically, the upper base station can transmit a PDU (protocol data unit) including the first DL delay to the lower base station.

[0065] According to one embodiment, a higher base station may select at least one of PDU types 3 to 15 reserved for future PDU type extensions and transmit the same to a lower base station (510). A PDU for first DL delay transmission may include a first field (530) including a delay result and a second field (520) including a delay indicator.

[0066] The first field (530) may include information about the delay measurement result value (delay result) obtained by the upper base station. For example, the upper base station may include information about the DL delay measurement value (e.g., the first DL delay of FIG. 4) in the first field (530) of the PDU.

[0067] The second field (520) may indicate whether the first field includes the first DL delay. For example, if the second field value is 0, it may indicate that the first field does not include information about the delay measurement value, and if the second field value is 1, it may indicate that the first field includes information about the delay measurement value.

[0068] FIG. 6 is a flowchart of a process for transmitting information of a lower base station to an upper base station performed by a lower base station according to one embodiment of the present disclosure.

[0069] In step 610, the lower base station may receive a first DL delay from the upper base station. The first DL delay received by the lower base station may be determined based on a DL delay measurement value measured by the upper base station (step 420 of FIG. 4). Alternatively, as described above, the lower base station may also receive a DL delay measurement value measured by the upper base station.

[0070] More specifically, the lower base station may receive a PDU including a first DL delay. Referring to FIG. 5, the PDU received by the lower base station may include a first field (530) that may include a first DL delay and a second field (520) that indicates whether the first field includes the first DL delay.

[0071] The lower base station can determine whether to check the first DL delay of the first field (530) based on the information indicated by the second field (520). For example, if the second field (520) indicates that 'the first field includes the first DL delay', the lower base station can check the first DL delay of the first field (530). Alternatively, as in the example of FIG. 5, if the second field (520) is set to 0, the lower base station may not check the first field (530). In this way, the lower base station can obtain information about the DL delay measurement value indicated by the first field (530) (e.g., the first DL delay) based on the information indicated by the second field (520).

[0072] In step 620, the lower base station may determine the second DL delay based on the first DL delay. Based on the first DL delay value received from the upper base station, an additional operation such as [Mathematical Formula 2] may be performed to determine (or obtain) the second DL delay value.

[0073]

[0074] Using [Mathematical Formula 2], the lower base station can obtain a value of the second DL delay that falls within a certain range greater than or equal to the minimum value of nru-delay and less than or equal to the maximum value of nru-delay. In the present disclosure, the range greater than or equal to the minimum value of nru-delay and less than or equal to the maximum value of nru-delay can be expressed as the range of the base station parameter nru-delay. In [Mathematical Formula 2], a margin can be added to obtain a value of the second DL delay that is higher than the minimum value of the nru-delay parameter set in the lower base station.

[0075] For example, the range of the nru-delay parameter may be 5 ms or more and 50 ms or less, and the margin may be 5 ms. If the first DL delay received by the lower base station is '3' ms, which is less than 5 ms, the lower base station may obtain 5 ms as the second DL delay value according to [Mathematical Formula 2]. Alternatively, if the range of the nru-delay parameter is 5 ms or more and 50 ms or less, and the first DL delay received by the lower base station is '55' ms, which is greater than 50 ms, the lower base station may obtain '50' ms as the second DL delay value according to [Mathematical Formula 2].

[0076] According to one embodiment, a lower base station can obtain a second DL delay that does not exceed the range of the nru-delay parameter by determining the second DL delay based on [Mathematical Formula 2].

[0077] In other words, the maximum value of nru-delay in step 620 may mean an upper limit value of the second DL delay that can be determined based on the first DL delay received by the lower base station. The minimum value of nru-delay may mean a lower limit value of the second DL delay that can be determined based on the first DL delay received by the lower base station. In other words, if the value of the first DL delay is greater than or equal to the minimum value of nru-delay and less than or equal to the maximum value, the value of the first DL delay can determine a significant second DL delay. Therefore, the maximum value of nru-delay may be referred to as a maximum threshold value of the effective range of the first DL delay. The minimum value of nru-delay may be referred to as a minimum threshold value of the effective range of the first DL delay.

[0078] According to [Mathematical Formula 2], the second DL delay may be determined as a maximum threshold value if a value obtained by adding a predetermined margin to the first DL delay is greater than a maximum threshold value of the effective range of the first DL delay. The second DL delay may be determined as a minimum threshold value if a value obtained by adding a predetermined margin to the first DL delay is less than a minimum threshold value of the effective range of the first DL delay. The second DL delay may be determined as a value obtained by adding a predetermined margin to the first DL delay if a value obtained by adding a predetermined margin to the first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value.

[0079] In step 610, the DL delay measurement value or the first DL delay value received by the lower base station may be too small or too large due to an error occurring in the DL delay measurement process or the process of determining the first DL delay value. In step 620, the lower base station can correct the DL delay measurement value or the first DL delay value that is too small or too large by determining the second DL delay that has a meaningful value that falls within the range of nru-delay set as a base station parameter. Even if the lower base station receives the DL delay measurement value or the first DL delay value that is too small or too large in step 610, the lower base station can correct the value so that it does not go beyond the range of the base station parameter nru-delay in step 620, and as a result, the lower base station can obtain the second DL delay value, which is meaningful information about the DL delay measurement value.

[0080] In step 630, the lower base station may determine a target buffering time based on the second DL delay and the DDDS interval. The target buffering time may refer to the time that a data packet remains in the buffer of the lower base station.

[0081] Since the lower base station can transmit DDDS (feedback) to the upper base station at every DDDS interval and receive data based on the DBS included in the DDDS, the target buffering time can be determined by [Mathematical Formula 3] as follows.

[0082]

[0083] According to [Mathematical Formula 3], the lower base station can determine the target buffering time by adding the DDDS interval to a multiple of the nru-delay value. The multiple of the nru-delay value can mean the sum of the time the lower base station transmits the DDDS to the upper base station and the time the upper base station transmits data to the lower base station based on the DBS included in the DDDS.

[0084] According to one embodiment, a lower base station may use a value of a second DL delay determined based on a DL delay measurement value measured by an upper base station, instead of the nru-delay value of [Mathematical Formula 3]. This can be expressed as in [Mathematical Formula 4].

[0085]

[0086] The lower base station can determine the target buffering time based on a multiple of the second DL delay and the DDDS interval, according to [Equation 4]. For example, DDDS can be transmitted whenever a specific condition is satisfied.

[0087] According to one embodiment, a lower base station may, if necessary, determine a target buffering time using the nru-delay parameter value as in [Mathematical Formula 3]. Specifically, when transmitting DDDS without receiving a DL delay measurement value from an upper base station, the lower base station may determine the target buffering time using the value of the base station parameter nru-delay. For example, if an upper base station can measure DL delay at a regular cycle of 1 minute and the DDDS transmission interval is 10 ms, the lower base station may have to transmit DDDS before the upper base station measures the DL delay. In this case, the lower base station may determine the target buffering time according to [Mathematical Formula 3].

[0088] In step 640, the lower base station may determine the DBS based on the target buffering time. The lower base station may determine the DBS by comprehensively considering the buffer status of the lower base station, the target buffering time, and the estimated average throughput.

[0089] Additionally, the sub-base station can estimate the average throughput of the bearer. The sub-base station can estimate the average throughput of the bearer and determine the DBS according to [Mathematical Formula 5].

[0090]

[0091] α can mean a weight factor for the buffer status.

[0092] Remaining size can mean the amount of data currently remaining in the buffer.

[0093] α and remaining size can each represent the buffer status of the lower base station.

[0094] The lower base station can determine the amount (amount of data) corresponding to the target buffering time by multiplying the current throughput and the target buffering time according to [Mathematical Formula 5], and determine the DBS by considering the buffer status of the lower base station.

[0095] In step 650, the lower base station can transmit a DDDS including a DBS to the upper base station. The operation of the lower base station transmitting the DDDS to the upper base station can be understood as an operation of requesting an amount of data corresponding to the DBS. As shown in Fig. 4, by transmitting the DDDS to the upper base station, the lower base station can provide the upper base station with feedback related to the buffer of the lower base station for data flow control. Since the DBS transmitted by the lower base station to the upper base station is determined based on information about the DL delay measurement value transmitted by the upper base station to the lower base station, the lower base station can manage the buffer of the lower base station by utilizing the latest delay information.

[0096] FIG. 7 illustrates a time delay that occurs when multiple PDCP PDUs are transmitted via multiple bearers according to an embodiment of the present disclosure. PDCP PDUs can be transmitted via the NR-U protocol, and PDCP PDUs can be transmitted by being included in a DUD (downlink user data) frame defined in the NR-U protocol. A DUD packet can include a PDCP PDU. Therefore, FIG. 7 can be understood as illustrating multiple DUD packets being transmitted via multiple bearers, and PDCP PDUs being included in the DUD packets and transmitted.

[0097] Referring to FIG. 7, DUD 1 transmitted from an upper base station (702) at t1 can be received at a lower base station (704) at t2. PDCP PDU 1 included in DUD 1 can be received at the lower base station (704) at t2. The DL delay of DUD 1 can be determined as t2-t1 (711). The DL delay of PDCP PDU 1 included in DUD 1 can be determined as t2-t1 (711). In addition, DUD 2 transmitted from an upper base station (702) at t3 can be received at a lower base station (704) at t3. PDCP PDU 2 included in DUD 2 can be received at the lower base station (704) at t3. The DL delay of DUD 2 including PDCP PDU 2 can be determined as t4-t3 (712). The DL delay of DUD 3 containing PDCP PDU 3 can be determined as t6-t5 (713).

[0098] Referring to step 410 of FIG. 4, when multiple bearers are set up in an upper base station, the upper base station can measure DL delay for the multiple set bearers. Referring to FIG. 7, the upper base station (702) can periodically or repeatedly measure DL delay for the multiple bearers by measuring the DL delay of each DUD for the multiple bearers. For example, the upper base station (702) can measure DL delay t2-t1 (711) for the bearer corresponding to DUD 1. Alternatively, the upper base station (702) can measure DL delay t4-t3 (712) for the bearer corresponding to DUD 2.

[0099] As shown in Fig. 7, since the upper base station (702) measures the DL delay for each bearer while transmitting data, the DL delay measurement value measured by the upper base station (702) may have been affected by congestion time.

[0100] The upper base station (702) can transmit DL delays (711 to 717) for multiple bearers to the lower base station (704). The upper base station (702) can determine a first DL delay based on the DL delay measurement values ​​(711 to 717) for each bearer, and can include the first DL delay in a PDU and transmit it to the lower base station (704) (see FIG. 5).

[0101] According to one embodiment, a lower base station may store a minimum value among a plurality of first DL delays received from an upper base station, in order to exclude as much as possible the congestion time that may be included in the first DL delay.

[0102] FIG. 8 is a flowchart illustrating a process by which a lower base station determines a DBS based on a minimum value among a plurality of first DL delays according to one embodiment of the present disclosure.

[0103] Referring to FIG. 8, the upper base station (802) can measure DL delay for multiple bearers and transmit a first DL delay value determined based on the DL delay measurement value to the lower base station (804). For example, in step 811, the upper base station (802) can transmit a first DL delay A determined based on the DL delay measurement value for the first bearer to the lower base station (804). In step 812, the upper base station (802) can transmit a first DL delay B determined based on the DL delay measurement value for the second bearer to the lower base station (804).

[0104] In step 822, the lower base station (804) may determine the second DL delay based on the minimum value among the plurality of first DL delays.

[0105] According to one embodiment, the lower base station (804) can determine the second DL delay based on the first DL delay value stored as the minimum value among a plurality of first DL delays. Since the lower base station (804) determines the second DL delay based on the minimum first DL delay value, it can exclude congestion time that may be included in the delay value as much as possible, determine the propagation delay of the interface itself, and estimate the propagation delay of the changed path when the routing path is changed.

[0106] If the value obtained by adding a predetermined margin to the minimum first DL delay is greater than the maximum threshold, the second DL delay may be determined as the maximum threshold. If the value obtained by adding a predetermined margin to the minimum first DL delay is less than the minimum threshold, the second DL delay may be determined as the minimum threshold. If the value obtained by adding a predetermined margin to the minimum first DL delay is greater than or equal to the minimum threshold and less than or equal to the maximum threshold, the second DL delay may be determined as the value obtained by adding a predetermined margin to the minimum first DL delay.

[0107] According to one embodiment, a lower base station (804) may store a minimum first DL delay among a plurality of first DL delays received from an upper base station for a predetermined period of time, and determine a second DL delay based on the first DL delay value stored as the minimum value. The predetermined period of time may be a time corresponding to an integer multiple of a DDDS interval.

[0108] The predetermined time may be a time corresponding to a DDDS interval. For example, the lower base station (804) may check the minimum value stored in the lower base station when deciding to transmit DDDS and perform steps 830 to 850. Alternatively, the minimum first DL delay value stored in the lower base station for the predetermined time may refer to the minimum value stored in the lower base station when transmitting DDDS or the minimum value stored in the lower base station when deciding to transmit DDDS.

[0109] The predetermined time may be a time corresponding to an integer multiple of the DDDS interval. For example, when the lower base station (804) transmits the first DDDS, the DBS may be determined using the minimum value among the plurality of first DL delay values ​​received during a time corresponding to the DDDS interval. Thereafter, when the lower base station (804) transmits the second DDDS, the DBS may be determined using the minimum value among the plurality of first DL delay values ​​received during a time corresponding to two DDDS intervals.

[0110] In step 830, the lower base station (804) may determine a target buffering time based on the second DL delay and the DDDS interval. In step 840, the lower base station (804) may determine a DBS based on the target buffering time. In step 850, the lower base station (804) may transmit a DDDS including the DBS to the upper base station (802).

[0111] Regarding the operation of the upper base station and lower base station of Fig. 8, descriptions that overlap with those of Figs. 4 and 6 may be omitted.

[0112] FIG. 9 is a flowchart of a process for storing a minimum value among a plurality of first DL delays by a lower base station according to one embodiment of the present disclosure.

[0113] Referring to FIG. 9, a lower base station can store a minimum first DL delay value by storing at least one first DL delay among a plurality of first DL delays received from an upper base station as a minimum value. The lower base station can update information about the minimum value of the first DL delay whenever it receives at least one first DL delay among a plurality of first DL delays from an upper base station.

[0114] According to one embodiment, a lower base station may store a first DL delay A received for the first time as a minimum value. For subsequent first DL delays received, if a first DL delay B among the subsequently received first DL delays is smaller than the stored minimum value, the lower base station may store the first DL delay B as a minimum value. If the first DL delay B is equal to or greater than the stored minimum value, the lower base station may maintain the stored minimum value. The lower base station may store a minimum first DL delay among a plurality of first DL delays determined for a plurality of different bearers received from an upper base station.

[0115] Specifically, a case in which a lower base station receives a first DL delay A, a first DL delay B, a first DL delay C, and a first DL delay D in alphabetical order from an upper base station will be described. The lower base station may receive the first DL delay A from the upper base station (step 911) and store the value of the first DL delay A as a minimum value (step 912). The first DL delay A may be the first DL delay that the lower base station receives for the first time. Alternatively, the first DL delay A may be the first DL delay that the lower base station receives for the first time after the minimum value of the first DL delay stored in the lower base station is initialized.

[0116] Hereinafter, for convenience of explanation, the value of the first DL delay stored as the minimum value may be expressed as a 'stored minimum value'. After step 912, the minimum value stored in the lower base station may be the value of the first DL delay A.

[0117] Thereafter, when the lower base station receives the first DL delay B from the upper base station (step 913), it can determine whether the value of the first DL delay B is smaller than the stored minimum value (step 914). The lower base station can compare the stored minimum value (i.e., the value of the first DL delay A) with the value of the first DL delay B and store the smaller value as the minimum value. Alternatively, if the value of the first DL delay B received in step 914 is smaller than the stored minimum value, the lower base station can store the value of the first DL delay B as the minimum value and update the stored minimum value (step 915). If the value of the first DL delay B received in step 914 is larger than or equal to the stored minimum value, the lower base station may not update the stored minimum value. However, FIG. 9 is merely an example for explaining an operation of storing a smaller value among two first DL delay values ​​to be compared, and is not intended to limit the operation of the lower base station so that the lower base station cannot update the minimum value when the two values ​​are the same. Accordingly, step 914 may be set to perform step 915 when the value of the first DL delay B is less than or equal to the stored minimum value, and according to this setting, the lower base station may update the stored minimum value by storing the value of the first DL delay B as the minimum value even when the value of the first DL delay B is equal to the stored minimum value.

[0118] In step 916, the lower base station may receive the first DL delay C from the upper base station, and in step 917, the lower base station may compare the value of the first DL delay C with the stored minimum value. If the value of the first DL delay C is less than the stored minimum value in step 917, the lower base station may store the first DL delay C as the minimum value in step 918 and update the stored minimum value. If the value of the first DL delay C is greater than or equal to the stored minimum value in step 917, the lower base station may not update the stored minimum value.

[0119] Again, at step 919, the lower base station may receive the first DL delay D from the upper base station, and may compare the stored minimum value with the value of the first DL delay D to determine whether to update the stored minimum value.

[0120] After receiving the first DL delay A, the first DL delay B, the first DL delay C, and the first DL delay D from the upper base station, the lower base station may receive additional first DL delays and may or may not update the stored minimum value using the method according to steps 911 to 919.

[0121] The lower base station, which was updating the latest information on the minimum value according to the method in steps 911 to 919, can determine the value of the second DL delay based on the stored minimum value in step 922. When the lower base station decides to transmit DDDS to the upper base station, the lower base station can check the minimum value stored in the lower base station and determine the target buffering time and DBS based on the value of the first DL delay stored as the minimum value (steps 930 and 940).

[0122] Regarding the operation of the lower base station of Fig. 9, any description overlapping with that of Figs. 6 and 8 may be omitted.

[0123] In a method for storing a minimum first DL delay among a plurality of first DL delays determined for a plurality of bearers by a lower base station according to one embodiment, the stored minimum value may be valid for a first time period. In other words, the stored minimum value may be initialized after a certain period of time. If the routing path between the upper base station and the lower base station changes, the value originally stored as the minimum delay value may no longer be valid. The lower base station may initialize the minimum value at regular intervals or periodically to respond to the change in the routing path. The lower base station may delete the minimum value received and stored from the upper base station. For a detailed description, see FIG. 10.

[0124] FIG. 10 is a flowchart of a method for determining a target buffering time or DBS based on the value of one of the first DL delays when a lower base station receives a plurality of first DL delays according to one embodiment of the present disclosure.

[0125] Referring to FIG. 10, a plurality of bearers are set for a plurality of cells managed by an upper base station (1002), and the upper base station (1002) measures DL delay for the plurality of bearers and can transmit a plurality of first DL delays determined based on the DL delay measurement value to a lower base station.

[0126] The lower base station (1004) may first receive the first DL delay in step 1011 and store the value of the first DL delay, "10," as the minimum value in step 1012. Descriptions of steps 1011 and 1012 that overlap with steps 911 and 912 of FIG. 9 may be omitted.

[0127] For the first DL delays received thereafter, the lower base station may store the first DL delay received as the minimum value or maintain the originally stored minimum value. Alternatively, the lower base station may store at least one first DL delay that satisfies the condition among the plurality of first DL delays received thereafter as the minimum value.

[0128] In steps 1013 and 1014, the lower base station (1004) may receive first DL delays consecutively. The lower base station (1004) may compare the value "11" (unit: ms, omitted hereinafter) of the first DL delay received in step 1013 with the stored minimum value "10" according to the determination method illustrated in FIG. 9 and may not update the stored minimum value. Thereafter, the lower base station (1004) may compare the value "12" of the first DL delay received in step 1014 with the stored minimum value "10" and may not update the stored minimum value. In steps 1013 and 1014, the lower base station receives the first DL delay, but may not update the stored minimum value and may maintain the stored minimum value.

[0129] The lower base station (1004) may receive the first DL delay of step 1015, compare the value "6" of the first DL delay with the stored minimum value "10", and store "6" as the minimum value (step 1016). The lower base station may update the stored minimum value to "6".

[0130] If the lower base station does not receive a first DL delay having a value less than "6" before determining the second DL delay in step 1022, the minimum value stored in step 1022 may be "6". For example, if the lower base station decides to transmit DDDS, it may check the minimum value stored in the lower base station when it decides to transmit DDDS.

[0131] In step 1030, the lower base station (1004) may determine a target buffering time based on the second DL delay and the DDDS interval. For example, if the DDDS interval is 10 ms, the target buffering time may be determined as a multiple of the second DL delay value plus 10 ms (see [Mathematical Formula 4]).

[0132] In step 1040, the lower base station (1004) may determine the DBS based on the target buffering time. For example, the DBS may be determined based on [Mathematical Formula 5].

[0133] At step 1050, the lower base station (1004) can transmit a DDDS including the DBS to the upper base station.

[0134] In steps 1017 and 1018, the lower base station (1004) may sequentially receive the first DL delays. The lower base station (1004) may compare the value "8" of the first DL delay received in step 1017 with the stored minimum value "6" according to the determination method illustrated in FIG. 9, and may not update the stored minimum value because the stored minimum value "6" is smaller. In step 1018, the lower base station may compare the value "5" of the received first DL delay with the stored minimum value "6", and may determine that "5" is smaller than the stored minimum value, and may thus store "5" as the minimum value in step 1019, thereby updating the stored minimum value.

[0135] In this way, the lower base station can check and use the most recently updated minimum value as needed, such as in steps 1022 to 1050, while repeating whether to update or not update the stored minimum value whenever the first DL delay is received during the first time period.

[0136] When the first time period ends and the second time period starts, the lower base station can delete the stored minimum value and initialize the stored minimum value. Therefore, the lower base station (1004) that receives the first DL delay for the first time in step 1020 after initialization can store the value "8" of the first DL delay as the minimum value in step 1021. The value "8" of the first DL delay received in step 1020 is the same as the value of the first DL delay received in step 1017, but since the minimum value originally stored in the lower base station exists during the first time period, the condition that it is less than the stored minimum value can be satisfied only in order to store "8" as the minimum value. Step 1021 may refer to step 911 or step 1012 of FIG. 9.

[0137] For example, the lower base station (1004) may delete the stored minimum value every hour to prevent the originally stored minimum value from becoming meaningless when the routing path between the upper base station and the lower base station changes.

[0138] FIG. 11 illustrates the structure of a lower base station (1100) according to one embodiment of the present disclosure.

[0139] As illustrated in FIG. 11, the lower base station (1100) of the present disclosure may include a control unit (control unit) (1130), a transceiver (1110), and a storage unit (memory) (1120). However, the components of the lower base station (1100) are not limited to the examples described above. For example, the lower base station (1100) may include more or fewer components than the components described above. In addition, the control unit (1130), the transceiver (1110), and the storage unit (1120) may be implemented in the form of a single chip. The control unit (1130) of FIG. 11 may include at least one processor or controller. The lower base station (1100) of FIG. 11 may correspond to the NR1 gNB DU (140), NR1 gNB DU (150), NR2 gNB DU (160), NR2 gNB DU (170) of FIG. 1, the NR1 gNB DU (240), NR1 gNB DU (250), eNB of FIG. 2, and the lower base stations (304, 704, 804, 1004) of FIGS. 3, 7, 8, and 10.

[0140] The control unit (1130) can control a series of processes so that the base station can operate according to the above-described embodiment of the present disclosure. For example, the control unit (1130) can control the components of the base station to perform a method for scheduling a terminal according to whether the base station mode is the base station energy saving mode or the base station normal mode according to the embodiment of the present disclosure. There can be one or more control units (1130), and the control units (1130) can perform a method for scheduling a terminal according to whether the base station mode of the above-described present disclosure is the base station energy saving mode or the base station normal mode by executing a program stored in the storage unit (1120).

[0141] The transceiver (1110) can transmit and receive signals with the terminal. The signals transmitted and received with the terminal can include control information and data. The transceiver (1110) can be configured with an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, an RF receiver that low-noise amplifies the received signal and down-converts the frequency, etc. However, the transceiver (1110) is only one embodiment, and the components of the transceiver (1110) are not limited to the RF transmitter and RF receiver. In addition, the transceiver (1110) can receive a signal through a wireless channel and output it to the control unit (1130), and transmit a signal output from the control unit (1130) through the wireless channel.

[0142] According to one embodiment, the storage unit (1120) can store programs and data required for the operation of the lower base station (1100). In addition, the storage unit (1120) can store control information or data included in signals transmitted and received by the lower base station (1100). The storage unit (1120) can be configured as a storage medium or a combination of storage media, such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD. In addition, the storage unit (1120) can be provided in multiple numbers. According to one embodiment, the storage unit (1120) can store a program for performing a method for scheduling a terminal depending on whether the base station mode of the embodiments of the present disclosure described above is a base station energy saving mode or a base station normal mode.

[0143] FIG. 12 illustrates the structure of an upper base station (1200) according to one embodiment of the present disclosure.

[0144] As illustrated in FIG. 12, the upper base station (1200) of the present disclosure may include a control unit (control unit) (1230), a transceiver (1210), and a storage unit (memory) (1220). However, the components of the upper base station (1200) are not limited to the examples described above. For example, the upper base station (1200) may include more or fewer components than the components described above. In addition, the control unit (1230), the transceiver (1210), and the storage unit (1220) may be implemented in the form of a single chip. The control unit (1230) of FIG. 12 may include at least one processor or controller. The upper base station (1200) of FIG. 12 may correspond to the NR1 gNB CU (120), NR2 gNB CU (130) of FIG. 1, the NR1 gNB CU (220) of FIG. 2, and the upper base stations (302, 702, 802, 1002) of FIGS. 3, 7, 8, and 10.

[0145] The control unit (1230) can control a series of processes so that the base station can operate according to the above-described embodiment of the present disclosure. For example, the control unit (1230) can control the components of the base station to perform a method for scheduling a terminal according to whether the base station mode is the base station energy saving mode or the base station normal mode according to the embodiment of the present disclosure. There can be one or more control units (1230), and the control units (1230) can perform a method for scheduling a terminal according to whether the base station mode of the above-described present disclosure is the base station energy saving mode or the base station normal mode by executing a program stored in the storage unit (1220).

[0146] The transceiver (1210) can transmit and receive signals with the terminal. The signals transmitted and received with the terminal can include control information and data. The transceiver (1210) can be configured with an RF transmitter that up-converts and amplifies the frequency of a transmitted signal, an RF receiver that low-noise amplifies the received signal and down-converts the frequency, etc. However, the transceiver (1210) is only one embodiment, and the components of the transceiver (1210) are not limited to the RF transmitter and RF receiver. In addition, the transceiver (1210) can receive a signal through a wireless channel and output it to the control unit (1230), and transmit a signal output from the control unit (1230) through the wireless channel.

[0147] According to one embodiment, the storage unit (1220) can store programs and data required for the operation of the upper base station (1200). In addition, the storage unit (1220) can store control information or data included in signals transmitted and received by the upper base station (1200). The storage unit (1220) can be configured as a storage medium or a combination of storage media such as a ROM, a RAM, a hard disk, a CD-ROM, and a DVD. In addition, the storage unit (1220) can be provided in multiple numbers. According to one embodiment, the storage unit (1220) can store a program for performing a method for scheduling a terminal depending on whether the base station mode of the above-described embodiments of the present disclosure is a base station energy saving mode or a base station normal mode.

[0148] The upper base station (1200) can measure the DL delay for the bearer from the upper base station (1200) to the lower base station (1100), determine the first DL delay based on the DL delay measurement value, transmit the first DL delay to the lower base station (1100), and receive a DDDS including a DBS from the lower base station (1100).

[0149] The lower base station (1100) can receive a first DL delay from the upper base station (1200), determine a second DL delay based on the first DL delay, determine a target buffering time based on the second DL delay and a DDDS interval, determine a DBS based on the target buffering time, and transmit a DDDS including the DBS to the upper base station (1200).

[0150] The methods according to the embodiments described in the claims or specification of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software.

[0151] When implemented in software, a computer-readable storage medium storing one or more programs (software modules) may be provided. The one or more programs stored in the computer-readable storage medium are configured for execution by one or more processors within an electronic device. The one or more programs include instructions that cause the electronic device to execute methods according to the embodiments described in the claims or specification of the present disclosure.

[0152] These programs (software modules, software) may be stored in random access memory, non-volatile memory including flash memory, read only memory (ROM), electrically erasable programmable read only memory (EEPROM), magnetic disc storage device, compact disc ROM (CD-ROM), digital versatile discs (DVDs) or other forms of optical storage device, magnetic cassette. Or, they may be stored in a memory configured as a combination of some or all of these. In addition, each configuration memory may be included in multiple numbers.

[0153] Additionally, the program may be stored on an attachable storage device that is accessible via a communication network, such as the Internet, an intranet, a local area network (LAN), a wide local area network (WLAN), a storage area network (SAN), or a combination thereof. Such a storage device may be connected to a device performing an embodiment of the present disclosure via an external port. Additionally, a separate storage device on the communication network may be connected to a device performing an embodiment of the present disclosure.

[0154] In the specific embodiments of the present disclosure described above, components included in the invention are expressed in the singular or plural form, depending on the specific embodiment presented. However, the singular or plural expressions are selected to suit the presented situation for convenience of explanation, and the present disclosure is not limited to singular or plural components. Components expressed in the plural form may be composed of singular elements, or components expressed in the singular form may be composed of plural elements.

[0155] Meanwhile, the embodiments of the present disclosure disclosed in this specification and drawings are only specific examples to easily explain the technical contents of the present disclosure and help understand the present disclosure, and are not intended to limit the scope of the present disclosure. In other words, it will be apparent to those skilled in the art that other modifications based on the technical idea of ​​the present disclosure are possible. In addition, each embodiment can be combined and operated with each other as needed. For example, parts of one embodiment of the present disclosure and parts of another embodiment can be combined with each other to operate a base station and a terminal. For example, parts of the first embodiment and the second embodiment of the present disclosure can be combined with each other to operate a base station and a terminal. In addition, although the embodiments have been presented based on an FDD LTE system, other modifications based on the technical idea of ​​the embodiments can be implemented with other systems such as a TDD LTE system, 5G, or NR system.

[0156] Meanwhile, the order of description in the drawings explaining the method of the present invention does not necessarily correspond to the order of execution, and the order of precedence may be changed or executed in parallel.

[0157] Alternatively, the drawings illustrating the method of the present invention may omit some components and include only some components within a scope that does not harm the essence of the present invention.

[0158] In addition, the method of the present invention may be implemented by combining some or all of the contents included in each embodiment within a scope that does not harm the essence of the invention.

[0159] Various embodiments of the present disclosure have been described above. The foregoing description of the present disclosure is for illustrative purposes only, and the embodiments of the present disclosure are not limited to the disclosed embodiments. Those skilled in the art will appreciate that the present disclosure can be readily modified into other specific forms without altering the technical spirit or essential characteristics of the present disclosure. The scope of the present disclosure is indicated by the claims below rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present disclosure.

[0160] In one embodiment, a method performed by a lower base station including an RLC (radio link control) layer in a wireless communication system may include the steps of: receiving, from an upper base station including a PDCP (packet data convergence protocol) layer, a first downlink (DL) delay determined based on a DL delay measurement value for a bearer from the upper base station to the lower base station, the DL delay measured by the upper base station; determining a second DL delay based on the first DL delay; determining a target buffering time based on the second DL delay and a DDDS (downlink data delivery status) interval; determining a DBS (desired buffer size) based on the target buffering time; and transmitting a DDDS including the DBS to the upper base station.

[0161] The second DL delay may be determined as: a value obtained by adding a predetermined margin to the first DL delay is greater than a maximum threshold value of an effective range of the first DL delay, determined as a maximum threshold value; a value obtained by adding the predetermined margin to the first DL delay is less than a minimum threshold value of an effective range of the first delay, determined as a minimum threshold value; and a value obtained by adding the predetermined margin to the first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value.

[0162] The method performed by the lower base station further includes the step of storing, during a first time period, a minimum first DL delay among a plurality of first DL delays determined for a plurality of bearers from the upper base station to the lower base station, received from the upper base station, and wherein the second DL delay is: if a value obtained by adding a predetermined margin to the minimum first DL delay is greater than a maximum threshold value of an effective range of the first DL delay, it is determined as the maximum threshold value; if a value obtained by adding the predetermined margin to the minimum first DL delay is less than a minimum threshold value of the effective range of the first DL delay, it is determined as the minimum threshold value; and if a value obtained by adding the predetermined margin to the minimum first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value, it is determined as a value obtained by adding the predetermined margin to the minimum first DL delay, and the first time period may correspond to a multiple of the DDDS interval.

[0163] The step of storing a minimum first DL delay among the plurality of first DL delays determined for the plurality of bearers includes the step of storing at least one first DL delay among the plurality of first DL delays as a minimum value, and the stored minimum value can be updated when the at least one first DL delay is received.

[0164] The step of storing a minimum first DL delay among the plurality of first DL delays determined for the plurality of bearers may include the step of storing a first received first DL delay A as a minimum value; and the step of performing the following operations on the first DL delays received after the first DL delay A: if the first DL delay B among the first DL delays received after the first DL delay A is smaller than the stored minimum value, the operation of storing the first DL delay B as a minimum value; and if the first DL delay B is equal to or greater than the stored minimum value, the operation of maintaining the stored minimum value.

[0165] The above stored minimum value can be deleted after the second time has elapsed.

[0166] The step of receiving the first DL delay may include: receiving a protocol data unit (PDU) including a first field including the first DL delay and a second field indicating whether the first field includes the first DL delay; and confirming the first DL delay of the first field based on whether the second field indicates that the first field includes the first DL delay.

[0167] The method performed by the lower base station may further include a step of estimating an average throughput of the plurality of bearers, and the step of determining the DBS based on the target buffering time may include a step of determining the DBS based on a buffer status of the lower base station, the target buffering time, and the average throughput.

[0168] The step of determining the target buffering time based on the second DL delay and the DDDS interval may include the step of determining the target buffering time based on a multiple of the second DL delay.

[0169] In a wireless communication system according to one embodiment, a lower base station including an RLC (radio link control) layer includes a transceiver; and a control unit connected to the transceiver, wherein the control unit receives, from an upper base station including a PDCP (packet data convergence protocol) layer, a first downlink (DL) delay determined based on a DL delay measurement value for a bearer from the upper base station to the lower base station measured by the upper base station, determines a second DL delay based on the first DL delay, determines a target buffering time based on the second DL delay and a DDDS (downlink data delivery status) interval, determines a DBS (desired buffer size) based on the target buffering time, and controls transmission of a DDDS including the DBS to the upper base station.

[0170] In one embodiment, a method performed by an upper base station including a PDCP (packet data convergence protocol) layer in a wireless communication system includes the steps of: measuring a downlink (DL) delay for a bearer from the upper base station to a lower base station including a radio link control (RLC) layer; determining a first DL delay based on the DL delay measurement value; transmitting the first DL delay to the lower base station; and receiving a downlink data delivery status (DDDS) including a DBS (desired buffer size) from the lower base station, wherein the DBS is determined based on a target buffering time, the target buffering time is determined based on a second DL delay and a DDDS interval, and the second DL delay can be determined based on the first DL delay.

[0171] The second DL delay may be determined as: a value obtained by adding a predetermined margin to the first DL delay that is greater than a maximum threshold value of an effective range of the first DL delay, determined as a maximum threshold value; a value obtained by adding the predetermined margin to the first DL delay that is less than a minimum threshold value of an effective range of the first DL delay, determined as a minimum threshold value; and a value obtained by adding the predetermined margin to the first DL delay that is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value.

[0172] The method performed by the upper base station comprises: a step of measuring a plurality of DL delays for a plurality of bearers from the upper base station to the lower base station; a step of determining a plurality of first DL delays based on the plurality of DL delay measurement values; And further comprising a step of transmitting the plurality of first DL delays to the lower base station, wherein for a minimum first DL delay among the plurality of first DL delays received by the lower base station during a first time, the second DL delay: if a value obtained by adding a predetermined margin to the minimum first DL delay is greater than a maximum threshold value of an effective range of the first DL delay, the second DL delay is determined as the maximum threshold value, if a value obtained by adding the predetermined margin to the minimum first DL delay is less than a minimum threshold value of the effective range of the first DL delay, the second DL delay is determined as the minimum threshold value, and if a value obtained by adding the predetermined margin to the minimum first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value, the second DL delay is determined as a value obtained by adding the predetermined margin to the minimum first DL delay, and the first time may correspond to a multiple of the DDDS interval.

[0173] At least one first DL delay among the plurality of first DL delays is stored as a minimum value in the lower base station, and the minimum value stored in the lower base station can be updated when the at least one first DL delay is received by the lower base station.

[0174] The above stored minimum value may be deleted after the second time has elapsed.

[0175] The step of transmitting the first DL delay may include a step of transmitting the first DL delay by including it in a PDU (protocol data unit), and the PDU may include a first field including the first DL delay and a second field indicating that the first field includes the first DL delay.

[0176] The above DBS can be determined based on the buffer status of the lower base station, the target buffering time, and the estimated average throughput of the plurality of bearers.

[0177] The above target buffering time can be determined based on a multiple of the second DL delay.

[0178] In a wireless communication system according to one embodiment, an upper base station including a PDCP (packet data convergence protocol) layer includes a transceiver; and a control unit connected to the transceiver, wherein the control unit measures a downlink (DL) delay for a bearer from the upper base station to a lower base station including a radio link control (RLC) layer, and determines a first DL delay based on the measured DL delay value, transmits the first DL delay to the lower base station, and controls receiving a downlink data delivery status (DDDS) including a DBS (desired buffer size) from the lower base station, wherein the DBS is determined based on a target buffering time, the target buffering time is determined based on a second DL delay and a DDDS interval, and the second DL delay can be determined based on the first DL delay.

[0179] The control unit measures a plurality of DL delays for a plurality of bearers from the upper base station to the lower base station, determines a plurality of first DL delays based on a plurality of DL delay measurement values, and further controls to transmit the plurality of first DL delays to the lower base station, and for a minimum first DL delay among the plurality of first DL delays received by the lower base station during a first time, the second DL delay is: if a value obtained by adding a predetermined margin to the minimum first DL delay is greater than a maximum threshold value of an effective range of the first DL delay, it is determined as the maximum threshold value; if a value obtained by adding the predetermined margin to the minimum first DL delay is less than a minimum threshold value of the effective range of the first DL delay, it is determined as the minimum threshold value; and if a value obtained by adding the predetermined margin to the minimum first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value, it is determined as a value obtained by adding the predetermined margin to the minimum first DL delay, and the first time is determined as a value obtained by adding the predetermined margin to the minimum first DL delay, and the second ... It can correspond to the drain.

Claims

1. A method performed by a lower base station including an RLC (radio link control) layer in a wireless communication system, A step of receiving, from an upper base station including a PDCP (packet data convergence protocol) layer, a first DL (downlink) delay determined based on a DL delay measurement value for a bearer from the upper base station to the lower base station measured by the upper base station; A step of determining a second DL delay based on the first DL delay; A step of determining a target buffering time based on the second DL delay and DDDS (downlink data delivery status) interval; A step of determining DBS (desired buffer size) based on the target buffering time; and A method comprising the step of transmitting a DDDS including the DBS to the upper base station.

2. In claim 1, the second DL delay is: If the value obtained by adding a predetermined margin to the above first DL delay is greater than the maximum threshold value of the effective range of the above first DL delay, it is determined as the maximum threshold value, If the value obtained by adding the predetermined margin to the first DL delay is smaller than the minimum threshold value of the effective range of the first delay, it is determined as the minimum threshold value, and A method wherein the value obtained by adding the predetermined margin to the first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value, and the value is determined as the value obtained by adding the predetermined margin to the first DL delay.

3. In claim 1, Further comprising a step of storing a minimum first DL delay among a plurality of first DL delays determined for a plurality of bearers from the upper base station to the lower base station, received from the upper base station during a first time period, The above second DL delay is: If the value obtained by adding a predetermined margin to the minimum first DL delay is greater than the maximum threshold value of the effective range of the first DL delay, it is determined as the maximum threshold value. If the value obtained by adding the predetermined margin to the minimum first DL delay is smaller than the minimum threshold value of the effective range of the first DL delay, it is determined as the minimum threshold value, and If the value obtained by adding the predetermined margin to the minimum first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value, the value is determined as the value obtained by adding the predetermined margin to the minimum first DL delay, A method wherein the first time period corresponds to a multiple of the DDDS interval.

4. In claim 3, The step of storing the minimum first DL delay among the plurality of first DL delays determined for the plurality of bearers is: A step of storing at least one of the plurality of first DL delays as a minimum value, A method wherein the stored minimum value is updated upon receiving at least one first DL delay.

5. In claim 3, The step of storing the minimum first DL delay among the plurality of first DL delays determined for the plurality of bearers is: A step of storing the first DL delay A received for the first time as a minimum value; and Steps for performing the following operations on the first DL delays received after the first DL delay A: An operation of storing the first DL delay B as the minimum value when the first DL delay B among the first DL delays received after the first DL delay A is smaller than the stored minimum value; and If the first DL delay B is greater than or equal to the stored minimum value, the operation of maintaining the stored minimum value is included. A method in which the above stored minimum value is deleted after the second time has elapsed.

6. In claim 1, the step of receiving the first DL delay comprises: A step of receiving a PDU (protocol data unit) including a first field including the first DL delay and a second field indicating whether the first field includes the first DL delay; and A method comprising: verifying the first DL delay of the first field based on the second field indicating that the first field includes the first DL delay.

7. In claim 6, Further comprising a step of estimating the average throughput of the above bearer, The step of determining the DBS based on the target buffering time is: A method comprising the step of determining the DBS based on the buffer status of the lower base station, the target buffering time, and the average throughput.

8. In a lower base station including an RLC (radio link control) layer in a wireless communication system, Transmitter and receiver; and A control unit connected to the above transceiver, wherein the control unit: Receive a first DL delay determined based on a DL (downlink) delay measurement value for a bearer from the upper base station to the lower base station, which is measured by the upper base station, from an upper base station including a PDCP (packet data convergence protocol) layer, The second DL delay is determined based on the first DL delay above, Determine the target buffering time based on the second DL delay and DDDS (downlink data delivery status) interval, Based on the above target buffering time, the DBS (desired buffer size) is determined. A lower base station that controls to transmit a DDDS including the DBS to the upper base station.

9. A method performed by an upper base station including a PDCP (packet data convergence protocol) layer in a wireless communication system, A step of measuring a DL (downlink) delay for a bearer from the upper base station to a lower base station including an RLC (radio link control) layer; A step of determining a first DL delay based on a DL delay measurement value; A step of transmitting the first DL delay to the lower base station; and A step of receiving a downlink data delivery status (DDDS) including a desired buffer size (DBS) from the above lower base station, The above DBS is determined based on the target buffering time. The above target buffering time is determined based on the second DL delay and DDDS interval, A method in which the above second DL delay is determined based on the above first DL delay.

10. In claim 9, the second DL delay is: If the value obtained by adding a predetermined margin to the above first DL delay is greater than the maximum threshold value of the effective range of the above first DL delay, it is determined as the maximum threshold value, If the value obtained by adding the predetermined margin to the first DL delay is smaller than the minimum threshold value of the effective range of the first DL delay, it is determined as the minimum threshold value, and A method wherein the value obtained by adding the predetermined margin to the first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value, and the value is determined as the value obtained by adding the predetermined margin to the first DL delay.

11. In claim 9, A step of measuring multiple DL delays for multiple bearers from the upper base station to the lower base station; A step of determining a plurality of first DL delays based on a plurality of DL delay measurement values; and Further comprising a step of transmitting the plurality of first DL delays to the lower base station, For a minimum first DL delay among the plurality of first DL delays received at the lower base station during the first time, the second DL delay is: If the value obtained by adding a predetermined margin to the minimum first DL delay is greater than the maximum threshold value of the effective range of the first DL delay, it is determined as the maximum threshold value. If the value obtained by adding the predetermined margin to the minimum first DL delay is smaller than the minimum threshold value of the effective range of the first DL delay, it is determined as the minimum threshold value, and If the value obtained by adding the predetermined margin to the minimum first DL delay is greater than or equal to the minimum threshold value and less than or equal to the maximum threshold value, the value is determined as the value obtained by adding the predetermined margin to the minimum first DL delay, A method wherein the first time period corresponds to a multiple of the DDDS interval.

12. In claim 11, At least one of the plurality of first DL delays is stored as a minimum value in the lower base station, The minimum value stored in the above lower base station is updated when at least one first DL delay is received at the above lower base station, A method in which the above stored minimum value is deleted after the second time has elapsed.

13. In claim 9, the step of transmitting the first DL delay comprises: Including a step of transmitting the above first DL delay by including it in a PDU (protocol data unit), A method wherein the PDU comprises a first field including the first DL delay and a second field indicating that the first field includes the first DL delay.

14. In claim 13, A method in which the above DBS is determined based on the buffer status of the lower base station, the target buffering time, and the estimated average throughput of the bearer.

15. In a wireless communication system, in an upper base station including a PDCP (packet data convergence protocol) layer, Transmitter and receiver; and A control unit connected to the above transceiver, wherein the control unit: Measure the DL (downlink) delay for a bearer from the upper base station to the lower base station including the RLC (radio link control) layer, and The first DL delay is determined based on the DL delay measurement value. To the above lower base station, transmit the first DL delay, Control to receive DDDS (downlink data delivery status) including DBS (desired buffer size) from the above lower base station, The above DBS is determined based on the target buffering time. The above target buffering time is determined based on the second DL delay and DDDS interval, The upper base station, wherein the above second DL delay is determined based on the above first DL delay.

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