KR102425660B1 - Method and Apparatus for managing a congestion in a wireless communication system - Google Patents

Abstract

The present disclosure relates to a 5G or pre-5G communication system that will support a higher data rate after a 4G communication system such as LTE.
According to an embodiment of the present invention, in a method for controlling congestion of a base station in a wireless communication system, the steps of determining whether congestion control for uplink is required, and determining whether congestion control for uplink is necessary, congestion control application target terminal It is possible to provide a method comprising the steps of determining , and performing congestion control on the terminal determined as the congestion control application target terminal.

Description

Method and apparatus for managing congestion in a wireless communication system {Method and Apparatus for managing a congestion in a wireless communication system}

The present invention relates to a method and apparatus for managing congestion in a wireless communication system. In addition, the present invention relates to a method and apparatus for improving a downlink transmission speed degradation in an uplink congestion situation in a wireless communication system.

In general, a mobile communication system has been developed to provide a voice service while ensuring user activity. However, the mobile communication system has gradually expanded its scope not only to voice but also to data services, and has now developed to the extent that it can provide high-speed data services. Unlike the voice service, the data service determines the amount of data to be transmitted and the resources that can be allocated according to the channel condition. Accordingly, in a wireless communication system such as a mobile communication system, the scheduler manages to allocate transmission resources in consideration of the amount of resources to be transmitted, the channel condition, and the amount of data. This is also done in the latest mobile communication system, long term evolution (LTE), and the scheduler located in the base station manages and allocates radio transmission resources.

LTE is largely divided into two types: FDD and TDD. FDD stands for Frequency Division Duplex and TDD stands for Time Division Duplex. FDD uses uplink and downlink frequencies respectively when uploading/downloading data. TDD divides uplink and downlink at the same frequency with a time difference. Since the TDD method is advantageous in efficiently processing asymmetric transmission/reception data, it is very suitable for the current wireless data traffic usage situation where the proportion of data reception is overwhelmingly high. In the present invention, the TDD scheme is referred to as TD-LTE.

Efforts are being made to develop an improved 5G communication system or pre-5G communication system in order to meet the increasing demand for wireless data traffic after commercialization of the 4G communication system. For this reason, the 5G communication system or the pre-5G communication system is called a system after the 4G network (Beyond 4G Network) communication system or the LTE system after (Post LTE).

In order to achieve a high data rate, the 5G communication system is being considered for implementation in a very high frequency (mmWave) band (eg, such as a 60 gigabyte (60 GHz) band). In order to alleviate the path loss of radio waves and increase the propagation distance of radio waves in the very high frequency band, in the 5G communication system, beamforming, massive MIMO, and Full Dimensional MIMO (FD-MIMO) are used. ), array antenna, analog beam-forming, and large scale antenna technologies are being discussed.

In addition, for network improvement of the system, in the 5G communication system, an evolved small cell, an advanced small cell, a cloud radio access network (cloud radio access network: cloud RAN), an ultra-dense network (ultra-dense network) , Device to Device communication (D2D), wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP), and interference cancellation Technology development is underway.

In addition, in the 5G system, the advanced coding modulation (ACM) methods FQAM (Hybrid FSK and QAM Modulation) and SWSC (Sliding Window Superposition Coding), and advanced access technologies FBMC (Filter Bank Multi Carrier), NOMA (non orthogonal multiple access), and sparse code multiple access (SCMA) are being developed.

It is an object of the present invention to provide an improved congestion management method and apparatus.

Another object of the present invention is to provide a method and apparatus for overcoming a phenomenon in which a downlink transmission speed is lowered in an uplink congestion situation in a wireless communication system.

According to an embodiment of the present invention, in a method for controlling congestion of a base station in a wireless communication system, the steps of determining whether congestion control for uplink is required, and determining whether congestion control for uplink is necessary, congestion control application target terminal It is possible to provide a method comprising the steps of: determining and performing congestion control on the terminal determined as the congestion control application target terminal.

In addition, according to an embodiment of the present invention, in a base station for congestion control in a wireless communication system, a communication unit transmitting and receiving signals and determining whether congestion control is required for uplink and uplink congestion control are required If it is determined that it is, it is possible to provide a base station comprising a control unit that determines a congestion control application target terminal, and controls the terminal determined as a congestion control application target terminal to perform congestion control.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. will be able

According to an embodiment of the present invention, it is possible to provide an improved method and apparatus for managing congestion.

In addition, according to an embodiment of the present invention, it is possible to provide a method and an apparatus for overcoming a phenomenon in which a downlink transmission speed is lowered in an uplink congestion situation in a wireless communication system.

In addition, according to an embodiment of the present invention, it is possible to improve the phenomenon that the throughput (throughput) is lowered due to the lack of uplink resources despite the availability of downlink resources.

1 is a diagram illustrating the structure of an LTE system to which the present invention is applied.
2 is a diagram illustrating a radio protocol structure of a data plane in an LTE system to which the present invention is applied.
3 is a diagram for explaining carrier aggregation in a terminal to which the present invention is applied.
4 is a diagram for explaining an uplink resource and a downlink resource according to an embodiment of the present invention.
5 is a diagram for explaining a congestion control method according to an embodiment of the present invention.
6 is a view for explaining the determination of whether congestion control is necessary and the determination of a target terminal according to an embodiment of the present invention.
7 is a view for explaining a method of performing congestion control through packet discard according to an embodiment of the present invention.
8 is a diagram for explaining whether congestion control is required and determination of a target terminal according to another embodiment of the present invention.
9 is a view for explaining a method of performing congestion control using congestion marking according to an embodiment of the present invention.
10 is a view for explaining a base station according to an embodiment of the present invention.
11 is a diagram illustrating a terminal according to an embodiment of the present invention.

Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings. In this case, it should be noted that in the accompanying drawings, the same components are denoted by the same reference numerals as much as possible. In addition, detailed descriptions of well-known functions and configurations that may obscure the gist of the present invention will be omitted. In the following description, only parts necessary for understanding the operation according to various embodiments of the present invention will be described, and it should be noted that descriptions of other parts will be omitted so as not to obscure the gist of the present invention.

In the following embodiments of the present invention, a method and apparatus for improving a congestion situation in a wireless communication system will be described. In addition, an embodiment of the present invention describes a method and apparatus for overcoming a shape in which a downlink transmission speed is lowered in an uplink congestion situation. In addition, an embodiment of the present invention describes a method and apparatus for controlling a traffic transmission amount of a TCP uplink session in order to improve downlink throughput by efficiently using insufficient uplink resources. In the present invention, through this, a phenomenon in which throughput is lowered due to lack of uplink resources even though downlink resources are available is improved.

In an embodiment of the present invention, an operation in an LTE system will be described as an example for convenience of description. However, the embodiment of the present invention is not limited to the LTE system and may be applied to various communication systems capable of controlling congestion through traffic management.

Hereinafter, in an embodiment of the present invention, a base station is a subject that performs resource allocation of a terminal, and may be at least one of an eNode B, a Node B, a BS (Base Station), a radio access unit, a base station controller, or a node on a network. The terminal may include a user equipment (UE), a mobile station (MS), a cellular phone, a smart phone, a computer, or a multimedia system capable of performing a communication function. In the present invention, downlink (DL) is a wireless transmission path of a signal transmitted from a base station to a terminal, and uplink (UL) means a wireless transmission path of a signal transmitted from a terminal to a base station. In addition, although an embodiment of the present invention will be described below using an LTE or LTE-A system as an example, the embodiment of the present invention may be applied to other communication systems having a similar technical background or channel type. In addition, the embodiments of the present invention may be applied to other communication systems through some modifications within the scope of the present invention as judged by a person having skilled technical knowledge.

In an embodiment of the present invention, the terminal is a mobile station (MS), user equipment (UE), user terminal (UT), wireless terminal, access terminal (AT), terminal, subscriber unit (Subscriber Unit), subscriber may be referred to as a Subscriber Station (SS), a wireless device, a wireless communication device, a Wireless Transmit/Receive Unit (WTRU), a mobile node, a mobile, or other terms. Various embodiments of the terminal include a cellular phone, a smart phone having a wireless communication function, a personal digital assistant (PDA) having a wireless communication function, a wireless modem, a portable computer having a wireless communication function, and a digital camera having a wireless communication function. device, gaming device with wireless communication function, music storage and playback home appliance with wireless communication function, connected drive with wireless communication function, mobile means with wireless communication function, Internet home appliance that enables wireless Internet access and browsing but also portable units or terminals incorporating combinations of such functions.

In an embodiment of the present invention, download may mean transmission of a data packet from the base station to the terminal, and upload may mean transmission of a data packet from the terminal to the base station. A downlink session and a download session may be used as the same meaning, and an uplink session and an upload session may be used as the same meaning.

In an embodiment of the present invention, traffic may mean an amount of data flowing within a predetermined time on a specific transmission path. Also, it may mean a load applied to any communication device or system.

In an embodiment of the present invention, traffic may mean a packet of a transmission control protocol/internet protocol (TCP/IP). TCP/IP is a communication protocol governing packet switching.

1 is a diagram illustrating the structure of an LTE system to which the present invention is applied.

In FIG. 1 , the eNBs 105 to 120 correspond to the existing Node B of the UMTS system. The eNB is connected to the UE 135 through a radio channel and performs a more complex role than the existing Node B. In the LTE system, all user traffic, including real-time services such as VoIP (Voice over IP) through the Internet protocol, are serviced through a shared channel, so status information such as buffer status, available transmission power status, and channel status of UEs A device for scheduling is required, and the eNBs 105 to 120 are responsible for this. One eNB typically controls multiple cells. For example, in order to implement a transmission rate of 100 Mbps, the LTE system uses, for example, Orthogonal Frequency Division Multiplexing (hereinafter referred to as OFDM) as a radio access technology in a 20 MHz bandwidth. In addition, an Adaptive Modulation & Coding (AMC) method that determines a modulation scheme and a channel coding rate according to the channel state of the terminal is applied. The S-GW 130 is a device that provides a data bearer, and creates or removes a data bearer under the control of the MME 125 . The MME is a device responsible for various control functions as well as the mobility management function for the UE, and is connected to a number of base stations.

2 is a diagram illustrating a radio protocol structure in an LTE system to which the present invention is applied.

Referring to FIG. 2, the radio protocol of the LTE system consists of Packet Data Convergence Protocol (PDCP) 205 and 240, RLC (Radio Link Control 210, 235), and MAC (Medium Access Control 215 and 230) in the UE and ENB, respectively. PDCP (Packet Data Convergence Protocol) (205, 240) is in charge of operations such as IP header compression / restoration, radio link control (Radio Link Control, hereinafter referred to as RLC) (210, 235) PDCP PDU (Packet Data Unit) ) to an appropriate size. The MACs 215 and 230 are connected to several RLC layer devices configured in one terminal, and perform an operation of multiplexing RLC PDUs into MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The physical layers 220 and 225 channel code and modulate upper layer data, make OFDM symbols and transmit them over a wireless channel, or demodulate and channel decode OFDM symbols received through the wireless channel and deliver them to higher layers. . In addition, the physical layer uses HARQ 　 (Hybrid ARQ) for additional error correction. This is called HARQ ACK/NACK information. Downlink HARQ ACK/NACK information for uplink transmission is transmitted through a Physical Hybrid-ARQ Indicator Channel (PHICH) physical channel, and uplink HARQ ACK/NACK information for downlink transmission is PUCCH (Physical Uplink Control Channel) or PUSCH (Physical Uplink Shared Channel) It may be transmitted through a physical channel.

3 is a diagram for explaining carrier aggregation in a terminal.

Referring to FIG. 3 , in one base station, multi-carriers are generally transmitted and received over several frequency bands. For example, when a carrier wave 315 having a center frequency of f1 and a carrier wave having a center frequency of f3 (310) are transmitted from the base station 305, one terminal uses one carrier among the two carriers in the prior art. was sent and received. However, a terminal having carrier aggregation capability can transmit and receive data from multiple carriers at the same time. The base station 305 may increase the transmission speed of the terminal 330 by allocating more carriers depending on the situation to the terminal 330 having the carrier aggregation capability.

In a traditional sense, when one forward carrier and one reverse carrier transmitted and received from one base station constitute one cell, carrier aggregation may be understood as a terminal transmitting and receiving data through multiple cells at the same time. will be. Through this, the maximum transmission rate is increased in proportion to the number of integrated carriers.

Hereinafter, in describing the present invention, that a terminal receives data through an arbitrary forward carrier or transmits data through an arbitrary reverse carrier means a control channel provided by a cell corresponding to the center frequency and frequency band characterizing the carrier and It has the same meaning as transmitting and receiving data using a data channel. In addition, an embodiment of the present invention will be described below assuming an LTE system for convenience of description, but the present invention may be applied to various wireless communication systems supporting carrier aggregation.

Most of Internet traffic such as data download, file sharing, and video uses TCP. TCP is a connection-based protocol for connecting and communicating sessions. In TCP, to ensure reliability, the receiving end that has received data transmits an acknowledgment packet (ACK packet) to notify the transmitting end. Therefore, a certain percentage of uplink resources are required even when downloading. That is, when uplink resources are insufficient, transmission/reception speed may be reduced even when resources for downlink are sufficient. Both the data packet of the TCP upload session and the ACK packet of the TCP download session use uplink resources. Since the uplink transmission resource is limited, when many resources are used for upload data transmission, the amount of resources for transmitting the ACK packet for the download may be relatively insufficient. The ACK packet for the download session is information indicating whether the download data received by the receiving end has been successfully received.

The uplink congestion situation is a case in which resources for uplink transmission are insufficient. When insufficient uplink resources are used a lot for upload data transmission, the ACK packet for the download session cannot be sufficiently transmitted. In this case, a phenomenon in which throughput is lowered may occur despite the availability of downlink resources. That is, in TCP transmission, the transmitting end transmitting download data must transmit the next information after receiving the ACK information for the previously transmitted download data. When ACK transmission is delayed, a phenomenon in which throughput is lowered may occur even though downlink resources are available. If uplink resources become scarce due to the influence of voice over LTE (VoLTE), signaling message, etc., which have a high processing priority in the base station, the downlink throughput degradation phenomenon may be further aggravated.

Therefore, there is a need for a method to prevent a decrease in throughput by controlling the ACK packet for the download session to be transmitted sufficiently to prevent a decrease in throughput due to inability to utilize the downlink resource even though there is a spare. In an embodiment of the present invention, when it is determined that uplink congestion control is necessary, a congestion control target terminal is determined, and congestion control is performed on the determined terminal to secure uplink resources for transmitting an ACK packet for a download session. can do.

4 is a diagram for explaining an uplink resource and a downlink resource according to an embodiment of the present invention.

Referring to FIG. 4 , resources of the downlink 110 and the uplink 130 are allocated. The downlink 110 may be divided into an ACK packet 111 of a TCP upload session, a data packet 113 of a TCP download session, and downlink traffic 115 other than the TCP packet. The uplink 130 may include a data packet 131 of a TCP upload session, an ACK packet 133 of a TCP download session, and uplink traffic 135 other than the TCP packet.

The ACK packet 111 of the TCP upload session is information indicating whether the data packet 131 of the TCP upload session is received. The data packet 113 of the TCP download session is a TCP data packet transmitted from the base station to the terminal. The downlink traffic 115 other than the TCP packet is a data packet transmitted from the base station to the terminal except for the TCP packet, and may include a VoLTE packet, a packet used for signaling, a user datagram protocol (UDP) packet, and the like. The data packet 131 of the TCP upload session is a TCP data packet transmitted from the terminal to the base station. The ACK packet 133 of the TCP download session is information indicating whether the data packet 131 of the TCP download session is received. The uplink traffic 135 other than the TCP packet is a data packet transmitted from the terminal to the base station except for the TCP packet, and may include a VoLTE packet, a packet used for signaling, a UDP packet, and the like.

In TCP, to ensure reliability, the receiving end that has received data transmits an ACK packet (a packet indicating whether or not it has been received) to notify the transmitting end. Therefore, a certain percentage of uplink resources are required even when downloading. For example, in FIG. 4 , a resource for the ACK packet 133 of a TCP download session of a certain ratio is required for download. Similarly, a certain percentage of downlink resources are required for uploading. For example, in FIG. 4 , ACK packets 111 of a TCP upload session of a certain percentage are required for upload.

When delayed ACK (delay ACK) is used, one ACK packet is transmitted per n data packets. For transmission of TCP data packet size * n byte, the opposite direction resource is required as much as ACK packet size byte. For convenience of explanation, this ratio is defined as C.

Among the uplink 110 resources, A is the resource amount occupied by the data packet 131 of the TCP upload session, B 133 the resource amount occupied by the ACK packet of the TCP download session, and the resource 135 occupied by the upload packet other than the TCP packet. can be defined as Ua. The units of A, B, and Ua may be Mbps. In the uplink congestion situation, the amount of uplink resources used for A + B + Ua may be 100% of the cell uplink resources. Therefore, in order to secure the resource B in the congestion situation, it is required to adjust the resource of A or the resource of Ua.

In this case, the maximum throughput of the downlink becomes A*C + B/C + Da. Here, when B is low, downlink resources cannot be efficiently used because there is no download data to be transmitted due to delay of ACK reception despite the availability of downlink resources. Therefore, in order to efficiently use the downlink resource, it is required to maintain the amount of resource B not to fall below a certain level.

Ua and Da cannot be adjusted by the base station. Therefore, in order to increase downlink resource utilization, B must be increased, and in order to increase B, the base station must adjust adjustable A. You can adjust A to increase B or keep it above a certain level.

An embodiment of the present invention may use a TCP flow control operation and a congestion control operation for this purpose. The TCP flow control operation is an operation that limits the maximum amount of data (window) that can be transmitted without ACK so as not to transmit too many packets to the network. The TCP congestion control operation is an operation of reducing the window size when the transmitter recognizes congestion. When the window size of the uplink session is reduced, the uplink data transmission request is reduced, which may lead to a reduction in the amount of data resources A used for data transmission. Through this, the amount of resource B can be maintained above a certain level and the amount of resource B can be increased.

The UE may recognize congestion through reception of a packet indicating packet loss or a packet with congestion marking. In an embodiment of the present invention, the base station selectively discards uplink data packets transmitted by a specific terminal or performs congestion marking to instruct the terminal for congestion control. The UE, recognizing the congestion situation, reduces the amount of data in the uplink session, and as a result, more ACK packets of the downlink session may be transmitted in the cell. Through this, it is possible to overcome the problem of a decrease in downlink throughput due to a lack of resources for transmitting the ACK packet of the download session. That is, in an embodiment of the present invention, A can be reduced by selectively discarding packets, recognizing a congestion situation using congestion marking, and reducing the amount of uplink data by adjusting the window size in the congestion situation. This allows B to be maintained or increased above a certain level.

Specifically, by restricting the traffic transmission of the upload session in the uplink congestion situation through the following method, it is possible to control the ACK packet of the download session to be transmitted well.

For convenience of description, parameters are defined as follows.

- cell_threshold: a reference point for determining whether a cell is congested

- p: probability of performing congestion control

- UE_threshold: a reference point for determining a UE to be subjected to congestion control

- packet_size_threshold: a reference point for determining which packets are subject to congestion control

Each of the parameters may be preset in the base station.

5 is a diagram for explaining a congestion control method according to an embodiment of the present invention.

Referring to FIG. 5 , the base station may determine whether congestion control is required in operation 510 . The base station may determine whether congestion control is required by using cell_threshold. For example, it may be determined whether the cell_threshold is satisfied using a buffer status report (BSR) received from the terminal. The buffer size of each terminal can be confirmed through the BSR transmitted by the terminal. The base station may determine whether congestion control is required based on whether the sum of the buffers of the terminals in the cell exceeds cell_threshold for every transmission time interval (TTI). In the LTE system, the TTI may be a subframe. The criterion for determining cell_thereshold is not limited to the buffer state of the terminal. The number of terminals in the RRC connection state of the base station may be set to cell_threshold. When each condition set as cell_threshold is satisfied, the base station may determine that congestion control is required.

If the Cell_threshold is not satisfied, the base station may determine that congestion control is not required and terminate the operation for congestion control in the corresponding TTI. If the cell threshold is satisfied, the base station proceeds to operation 520 .

In operation 520, the base station may select a congestion control target terminal. The base station may randomly select a terminal whose buffer is greater than the UE_threshold among terminals scheduled in the corresponding TTI. For example, the base station may select one terminal from among the terminals whose buffer is greater than the UE_threshold. The base station may select n terminals. The base station may know the buffer state of each terminal through the BSR, and UE_threshold may be preset. Meanwhile, for efficiency, the base station may exclude a terminal transmitting a scheduling request and a retransmitting terminal from the congestion control target terminal. When the scheduling request or retransmission terminal is selected as the congestion control target terminal, the efficiency of achieving the purpose of securing resources for the ACK packet of the TCP download session may be reduced. can be excluded. The base station may check the packet received from the terminal to determine whether it is a scheduling request terminal or a terminal that has transmitted a retransmission packet. The base station may select a terminal with a large amount of buffer with a higher probability when determining a terminal to be congestion control.

The base station may perform congestion control probabilistically. For example, it is possible to determine whether to perform actual congestion control for the probabilistically selected terminal using a preset parameter p. Since the probability of P determines whether the terminal performs congestion control, it may be determined to perform congestion control on the selected terminal, or it may be determined not to perform congestion control on the selected terminal. When it is determined not to perform congestion control on the selected terminal, the following operation is not performed and the operation for congestion control in the corresponding TTI is terminated. When it is determined to perform congestion control on the selected terminal, the base station performs an actual congestion control operation based on the following operation. For example, when p is 10%, congestion control for the actually selected terminal is performed with a probability of 10% among cases in which the base station determines that congestion control is necessary. The probability p may be a preset fixed parameter or a variable parameter according to the load of the cell.

The base station may manage the terminal selected as the congestion control target by distinguishing it from other terminals. For example, the base station may use a congestion control identifier. The congestion control identifier may be a congestion control flag. The identifier may be 1-bit information. For example, a congestion control terminal may be indicated as 1, and a congestion control exclusion terminal may be indicated as 0. The base station may use a congestion control table as shown in Table 1 to allow each terminal to manage a congestion control target terminal.

terminal Congestion Control Flag A 0 B One C 0 ... ...

In Table 1, terminals A and C are not congestion control target terminals, and terminal B is a congestion control target terminal.

Meanwhile, operations 510 and 520 may be performed for each TTI. That is, the base station may determine whether congestion control is required for each TTI or each subframe, and may determine a UE to which congestion control is applied.

Thereafter, the base station performs congestion control in operation 530 . Operation 530 may be applied to every packet received by the base station. The base station may discard the upload data packet of the selected terminal (discard). Discarding (discarding) the packet means that the base station does not transmit the received packet to an upper layer of the base station after receiving the packet from the terminal. The upper layer of the base station may treat it as not receiving the corresponding packet. When an acknowledgment (ACK) packet for a specific packet is not received, the terminal may perform congestion control. The terminal may reduce the window size that the terminal can transmit without receiving an ACK through congestion control. When the terminal reduces the window size, the amount of resources used by the terminal for transmission of uplink data traffic may be reduced, and if this operation is repeated, as a result, the amount of resources for transmitting the ACK packet for downlink reception can be secured. can

The base station may perform congestion marking for congestion control. Upon receiving the packet marked with congestion, the terminal may perform congestion control. The terminal may reduce the window size that the terminal can transmit without receiving an ACK through congestion control. When the terminal reduces the window size, the amount of resources used by the terminal for transmission of uplink data traffic may be reduced, and if this operation is repeated, as a result, the amount of resources for transmitting the ACK packet for downlink reception can be secured. can

If the amount of resources for transmitting the ACK packet for downlink reception is sufficiently secured through this operation, the base station can smoothly receive the ACK packet for the download data transmitted by the base station to the terminal, and even if the downlink resource is sufficient In spite of this, it is possible to solve the problem of delay in downlink transmission due to the delay in receiving the ACK packet for the reception of download data.

The base station may discard the packet received from the selected terminal or update the congestion control table after performing congestion marking. The base station may change the terminal in which the congestion flag is set to 1 to 0.

In operation 530 , the base station may discard packets or perform congestion marking only for packets exceeding a packet size threshold (packet_size_threshold). The preset packet size threshold may be determined based on the size of an ACK packet for download data reception (ACK packet of a TCP download session). In general, the size of the ACK packet for download data reception is smaller than the size of the upload data packet (upload TCP data packet). If a packet larger than the ACK packet size for download data reception is set as the packet size threshold, the base station may discard the packet or not perform congestion marking on the ACK packet for the download data reception packet, and only for the upload data packet. Packets may be discarded or congestion marking may be performed. This allows you to control the window size of the TCP upload session.

Each operation described with reference to FIG. 5 may be performed in the same layer or may be performed in different layers. When the operation is performed in different layers, a control message for congestion control between protocol layers may be used.

Each operation of FIG. 5 may be controlled by the control unit of the base station. The control unit of the base station may include a congestion control necessity determining unit, a congestion control target terminal determining unit, and a congestion control performing unit. Operation 510 may be performed by the congestion control necessity determining unit of the control unit, operation 520 may be performed by the congestion control target terminal determining unit of the control unit, and operation 530 may be performed by the congestion control performing unit of the base station. .

6 is a diagram for explaining congestion control determination and determination of a target terminal according to an embodiment of the present invention.

In operation 610, the base station may determine whether congestion control is required. The base station may determine whether congestion control is required by using cell_threshold. The base station may check whether the sum of the buffers of the UE in the cell exceeds cell_threshold for every TTI. The buffer size of each terminal can be confirmed through the BSR transmitted by the terminal. It may also be determined whether congestion control is required through another embodiment described in operation 510 .

If the sum of the buffers of the UE in the cell does not exceed Cell_threshold, the base station may determine that congestion control is not required and terminate the operation for congestion control in the corresponding TTI. If the sum of the buffers of the UE in the cell exceeds the cell threshold, the base station proceeds to operation 621 .

In operation 621, the base station may select a congestion control target terminal. The base station may select a terminal whose buffer is greater than the UE_threshold among terminals scheduled in the corresponding TTI. The base station may randomly select a specific terminal from among the terminals satisfying the above conditions. The base station may select one terminal. The base station may select a plurality of terminals if necessary. . Meanwhile, for efficiency, the base station may exclude a terminal transmitting a scheduling request and a retransmitting terminal from the congestion control target terminal.

In operation 623, the base station determines whether to actually perform congestion control with p probability. That is, the congestion control operation is not always performed on the terminal selected in operation 621 , and congestion control may be performed on the selected terminal with a probability of p. The probability p may be a preset fixed parameter or a variable parameter according to the load of the cell. Actual congestion control may be performed for the terminal selected with a probability of P. If actual congestion control is not performed on the terminal based on the P probability, the following operation may be terminated. When it is determined to perform actual congestion control for the selected terminal based on the probability of P, the following congestion control operation may be performed. Through this operation, an actual congestion control application target terminal may be determined.

If it is determined to perform actual congestion control for the selected terminal, the process proceeds to operation 625 . The base station performs a congestion control operation for the selected terminal. The base station may manage the terminal selected as the congestion control target by distinguishing it from other terminals. For example, the base station may use a congestion control identifier. The congestion control identifier may be a congestion control flag. The identifier may be 1-bit information. For example, a congestion control terminal may be indicated as 1, and a congestion control exclusion terminal may be indicated as 0. The base station may use a congestion control table as shown in Table 1 to allow each terminal to manage a congestion control target terminal. For example, a congestion control table may be managed as shown in Table 1.

Operations 621 to 625 may be performed for every TTI. The base station may determine whether congestion control is required for each TTI or each subframe, select a congestion control application target terminal, and determine whether to actually perform congestion control on the selected terminal. In addition, the congestion control table may be managed according to the determination result to distinguish and manage the determined terminal from other terminals. The series of operations may be performed by the control unit of the base station. For example, operation 610 may be performed by the congestion control determiner of the base station. Operations 621, 623, and 625 may be performed by the congestion control target terminal determiner of the base station.

Thereafter, an actual congestion control operation of the base station may be performed through the process of FIG. 7 .

7 is a diagram for explaining a method of performing congestion control through packet discard according to an embodiment of the present invention.

Referring to FIG. 7 , in operation 731 , the base station may check the size of a packet received from the terminal for which actual congestion control is determined. The base station may compare the size of the received packet with a preset packet size threshold. When the size is less than or equal to a preset threshold, the congestion control operation for the corresponding packet is terminated. If the size exceeds a preset threshold value, operation 733 may be performed. The preset packet size threshold may be determined based on the size of an ACK packet for download data reception (ACK packet of a TCP download session). The base station may exclude the ACK packet for download data reception from the congestion control target packet.

In operation 733, the base station may check whether the terminal that has transmitted the packet is an actual congestion control target terminal. For example, the base station may check whether the terminal that transmitted the packet is an actual congestion control target terminal using the congestion control table. When the terminal is not an actual congestion control target terminal, the base station may terminate the congestion control operation for the corresponding terminal. When the terminal is an actual congestion control target terminal, the base station may perform a congestion control operation in operation 735 .

Meanwhile, the order of operation 731 and operation 733 is interchangeable. That is, after determining whether the terminal that transmitted the received packet is a congestion control target terminal, the size of the corresponding packet may be checked. In addition, after checking the size of the corresponding packet, if the packet size exceeds a preset threshold value, it is determined whether the terminal transmitting the corresponding packet is a congestion control target, and the following operation may be performed.

In operation 735, the base station may perform a congestion control operation on the corresponding packet.

The base station may discard the packet received from the terminal when conditions 731 and 733 are satisfied. That is, the base station may discard the packet received from the terminal without transmitting it to a higher layer. The base station may treat the corresponding packet as not receiving it. Also, the base station may transmit information indicating that the terminal does not receive an uplink packet to the terminal. Thereafter, the base station may update the congestion control table. For a terminal that has performed congestion control, a flag may be changed from 1 to 0 or updated.

When an acknowledgment (ACK) packet for a specific packet is not received, the terminal may perform congestion control. The terminal may reduce the window size that the terminal can transmit without receiving an ACK through congestion control. When the terminal reduces the window size, the amount of resources used by the terminal for transmission of uplink data traffic may be reduced, and if this operation is repeated, as a result, the base station increases the amount of resources for transmitting the ACK packet for downlink reception. can be obtained When the amount of resources for transmitting the ACK packet for downlink reception is sufficient, the base station can smoothly receive the ACK packet for the download data transmitted by the base station to the terminal, and is It is possible to solve the problem of delay in downlink transmission according to the delay in receiving the ACK packet.

Operations 731 to 735 may be performed by the control unit of the base station. For example, it may be performed by the congestion control performing unit of the base station control unit.

Each operation described with reference to FIGS. 6 and 7 may be performed in the same layer or may be performed in different layers. When the operation is performed in different layers, a control message for congestion control between protocol layers may be used.

8 is a diagram for explaining congestion control determination and determination of a target terminal according to another embodiment of the present invention.

In operation 810, the base station may determine whether congestion control is required. The base station may determine whether congestion control is required by using cell_threshold. The base station may check whether the sum of the buffers of the UE in the cell exceeds cell_threshold for every TTI. The buffer size of each terminal can be confirmed through the BSR transmitted by the terminal. It may also be determined whether congestion control is required through another embodiment described in operation 510 .

If the sum of the buffers of the UE in the cell does not exceed Cell_threshold, the base station may determine that congestion control is not required and terminate the operation for congestion control in the corresponding TTI. When the sum of the buffers of the UE in the cell exceeds the cell threshold, the base station proceeds to operation 821.

The base station may perform the following operations for the terminal scheduled in the corresponding TTI.

In operation 821, the base station may select a congestion control target terminal. The base station may select a terminal whose buffer is greater than the UE_threshold among terminals scheduled in the corresponding TTI. The base station may randomly select a specific terminal from among the terminals satisfying the above conditions. The base station may select one terminal. The base station may select a plurality of terminals if necessary.

The base station may manage the congestion control table using operations 823 and 825. When the condition of 821 is satisfied, the base station may proceed to operation 823 to determine the congestion control terminal of the corresponding terminal and set the congestion control flag to 1. If the condition of 821 is not satisfied, the base station may determine the terminal as a congestion control exclusion terminal and set the congestion control flag to 0. Meanwhile, for efficiency, the base station may exclude a terminal transmitting a scheduling request and a retransmitting terminal from the congestion control target terminal. That is, even when the condition of 821 is satisfied, the terminal transmitting the scheduling request and/or the retransmitting terminal may be excluded from the congestion control target. Also, based on the probability p, a congestion control target terminal may be determined and the congestion control table may be updated.

In operation 830, the base station may share congestion control table information. The control unit of the base station may transmit congestion control table information to the congestion control performing unit.

The series of operations may be performed by the control unit of the base station. For example, operation 810 may be performed by the congestion control necessity determining unit of the base station. Operations 821, 823, 825, and 830 may be performed by the congestion control target terminal determiner of the base station. The congestion control target terminal determining unit of the base station may transmit congestion control table information to the congestion control performing unit.

Thereafter, an actual congestion control operation of the base station may be performed through the process of FIG. 9 .

9 is a diagram for explaining congestion control using congestion marking according to an embodiment of the present invention.

Referring to FIG. 9 , in operation 931 , the base station may check the size of a packet received from the terminal. The base station may compare the size of the received packet with a preset packet size threshold. When the size is less than or equal to a preset threshold, the congestion control operation for the corresponding packet is terminated. If the size exceeds a preset threshold value, operation 933 may be performed. The preset packet size threshold may be determined based on the size of an ACK packet for download data reception (ACK packet of a TCP download session). The base station may exclude the ACK packet for download data reception from the congestion control target packet.

In operation 933, the base station may check whether the terminal that has transmitted the packet is an actual congestion control target terminal. For example, the base station may check whether the terminal that transmitted the packet is an actual congestion control target terminal using the congestion control table. When the terminal is not an actual congestion control target terminal, the base station may terminate the congestion control operation for the corresponding terminal. When the terminal is an actual congestion control target terminal, the base station may proceed to operation 935 to perform a congestion control operation.

Meanwhile, the order of operation 931 and operation 933 is interchangeable. That is, after determining whether the terminal that transmitted the received packet is a congestion control target terminal, the size of the corresponding packet may be checked. In addition, after checking the size of the corresponding packet, if the packet size exceeds a preset threshold value, it is determined whether the terminal transmitting the corresponding packet is a congestion control target, and the following operation may be performed.

In operation 935, the base station may perform a congestion control operation on the corresponding packet.

The base station may perform congestion marking for congestion control. Upon receiving the packet marked with congestion, the terminal may perform congestion control. The terminal may reduce the window size that the terminal can transmit without receiving an ACK through congestion control. When the terminal reduces the window size, the amount of resources used by the terminal for transmission of uplink data traffic may be reduced, and if this operation is repeated, as a result, the base station increases the amount of resources for transmitting the ACK packet for downlink reception. can be obtained

When the amount of resources for transmitting the ACK packet for downlink reception is sufficiently secured, the base station can smoothly receive the ACK packet for the download data transmitted by itself to the terminal, and it is difficult to receive the download data even though the downlink resource is sufficient. It is possible to solve the problem of delay in downlink transmission according to the delay in receiving the ACK packet.

Thereafter, the base station may update the congestion control table. For a terminal that has performed congestion control, a flag may be changed from 1 to 0 or updated.

Operations 931 to 935 may be performed by the control unit of the base station. For example, it may be performed by the congestion control performing unit of the base station control unit.

Each operation described with reference to FIGS. 8 and 9 may be performed in the same layer or may be performed in different layers. When the operation is performed in different layers, a control message for congestion control between protocol layers may be used.

10 is a view for explaining a base station according to an embodiment of the present invention.

Referring to FIG. 10 , the base station 1000 may include a communication unit 1010 and a control unit 1030 . The communication unit 1010 may transmit and receive signals. The communication unit 1010 may include a transmitter and a receiver. The controller 1030 may control the overall operation of the base station 1000 . In addition, the controller 1030 may control the operation of the base station 1000 for performing an embodiment of the present invention.

The control unit 1030 may include a congestion control necessity determining unit, a congestion control target terminal determining unit, and a congestion control performing unit. For the operation of each unit, refer to the description of FIGS. 5 to 9 . Operations performed by the congestion control necessity determination unit, the congestion control target terminal determination unit, and the congestion control performing unit included in the control unit 1030 may be integrally performed by the control unit 1030 .

According to an embodiment of the present invention, the controller 1030 determines whether congestion control for uplink is required, and when it is determined that congestion control for uplink is required, determines a congestion control application target terminal, and congestion control application target terminal It is possible to control to perform congestion control for the terminal determined as .

Also, the controller 1030 may control to determine congestion control for the uplink based on buffer information received from a plurality of terminals within the cell of the base station and a cell buffer threshold value. Also, the controller 1030 may control to determine congestion control for the uplink based on the number of radio resource control (RRC) connected terminals in the cell of the base station.

In addition, the controller 1030 may control to determine the congestion control application target terminal based on the buffer status information (BSR, buffer status report) received from the terminal and the terminal buffer threshold value. Also, the controller 1030 may control a terminal having a large amount of buffer among a plurality of terminals in the cell to be determined as the congestion control application target terminal. Also, the controller 1030 may control to determine one or less terminals as the congestion control application target terminals in units of uplink TTI (transmission time interval).

In addition, the controller 1030 may control to determine the congestion control application target terminal from among terminals other than the terminal that has transmitted the scheduling request and the terminal that is being retransmitted in a medium access control (MAC) layer. Also, the controller 1030 may control to discard packets exceeding a preset threshold packet size among packets received from the terminal determined as the congestion control application target terminal.

In addition, the control unit 1030 may control to discard packets except for high-priority signaling and guaranteed bit rate (GBR) bearers among packets received from the terminal determined as the congestion control application target terminal.

Also, in order to prevent retransmission in a radio link control (RLC) layer, the controller 1030 may control to discard a packet in a packet data convergence protocol (PDCP) layer or an upper layer of the PDCP layer after RLC layer processing. Also, the controller 1030 may control to discard packets exceeding a preset size among packets received from the terminal determined as the congestion control application target terminal or to perform congestion marking.

11 is a diagram illustrating a terminal according to an embodiment of the present invention.

Referring to FIG. 11 , the terminal 1100 may include a communication unit 1110 and a control unit 1130 . The terminal may transmit and receive a signal using the communication unit 1110 . The communication unit 1110 may include a transmitter and a receiver. The controller 1130 may control the overall operation of the terminal 1100 . In addition, the controller 1130 may perform an operation of the terminal for performing the embodiment. In particular, in an embodiment of the present invention, the controller 1130 may perform a congestion control operation according to a congestion control instruction from the base station. The controller 1130 may control to secure resources for transmitting an ACK packet for downlink reception by reducing the window size and reducing the amount of resources for uplink TCP packets.

In addition, the embodiments disclosed in the present specification and drawings are merely provided for specific examples to easily explain the contents of the present invention and help understanding, and are not intended to limit the scope of the present invention. Therefore, the scope of the present invention should be construed as including all changes or modifications derived based on the technical spirit of the present invention in addition to the embodiments disclosed herein are included in the scope of the present invention.

Claims (22)

A method for controlling congestion of a base station in a wireless communication system, the method comprising:
determining whether congestion control for uplink is required;
determining a congestion control application target terminal among a plurality of terminals in a cell of the base station based on a determination that congestion control for uplink is necessary; and
Comprising the step of performing congestion control by transmitting a congestion-marked packet to a terminal determined as a congestion control application target terminal,
The congestion control application target terminal is determined based on a buffer status report (BSR) and a terminal buffer threshold value received from each of a plurality of terminals in the cell of the base station, and
Among the plurality of terminals, a terminal that has transmitted a scheduling request and a terminal that is being retransmitted in a medium access control (MAC) layer are excluded from the congestion control application target terminal. According to claim 1,
It is characterized in that it is determined whether congestion control for the uplink is required at every transmission time interval (TTI) based on whether the sum of the buffer sizes of the plurality of terminals checked through the buffer status report exceeds a cell buffer threshold value. how to do it with According to claim 1,
A method for determining whether congestion control is required for the uplink based on the number of terminals in a radio resource control (RRC) connection state in the cell of the base station. According to claim 1,
Based on the performed congestion control, the amount of uplink resources occupied by a data packet of a transmission control protocol (TCP) upload session received from the terminal determined as the congestion control application target terminal is reduced. The method of claim 1, wherein a terminal having a large amount of data stored in a buffer among a plurality of terminals in a cell of the base station is determined as the congestion control application target terminal. The method of claim 1, wherein one or less terminals are determined as the congestion control application target terminal in units of uplink TTI (transmission time interval). The method of claim 1, wherein the congestion control application target terminal and the congestion control exclusion terminal are distinguished from among a plurality of terminals in the cell of the base station by using the congestion control identifier. The method of claim 1, wherein performing the congestion control comprises:
Discarding a packet exceeding a preset threshold packet size among packets received from the terminal determined as the congestion control application target terminal,
The preset threshold packet size is determined based on an acknowledgment (ACK) packet size of a transmission control protocol (TCP) download session. The method of claim 1, wherein performing the congestion control comprises:
and discarding packets excluding high-priority signaling and guaranteed bit rate (GBR) bearers among packets received from the terminal determined as the congestion control application target terminal. The method of claim 1, wherein performing the congestion control comprises:
A method characterized in that the packet is discarded in a packet data convergence protocol (PDCP) layer or an upper layer of the PDCP layer after processing the RLC layer to prevent retransmission in the radio link control (RLC) layer. The method of claim 1, wherein performing the congestion control comprises:
and performing congestion marking on packets exceeding a preset size among packets received from the terminal determined as the congestion control application target terminal. A base station for congestion control in a wireless communication system, comprising:
a communication unit for transmitting and receiving signals; and
Determining whether congestion control for uplink is necessary, and determining a congestion control application target terminal among a plurality of terminals in a cell of the base station based on the determination that congestion control for uplink is necessary, and congestion control application target A control unit for controlling to perform congestion control by transmitting a congestion-marked packet to a terminal determined as a terminal,
The congestion control application target terminal is determined based on a buffer status report (BSR) and a terminal buffer threshold value received from each of a plurality of terminals in the cell of the base station, and
A base station, characterized in that, among the plurality of terminals, a terminal that has transmitted a scheduling request and a terminal that is being retransmitted in a medium access control (MAC) layer are excluded from the congestion control application target terminal. The method of claim 12, wherein the control unit,
Control to determine whether congestion control for the uplink is required at every transmission time interval (TTI) based on whether the sum of the buffer sizes of the plurality of terminals checked through the buffer status report exceeds a cell buffer threshold value A base station, characterized in that. The method of claim 12, wherein the control unit,
Base station, characterized in that the control to determine whether congestion control for the uplink is necessary based on the number of terminals in a radio resource control (RRC) connection state in the cell of the base station. 13. The method of claim 12,
Based on the performed congestion control, the amount of uplink resources occupied by a data packet of a TCP (transmission control protocol) upload session received from the terminal determined as the congestion control application target terminal is reduced. The method of claim 12, wherein the control unit,
Base station, characterized in that the control to determine a terminal with a large amount of data stored in a buffer among a plurality of terminals in the cell of the base station as the congestion control application target terminal. The method of claim 12, wherein the control unit,
The base station, characterized in that the control to determine one or less terminals as the congestion control application target terminal in an uplink transmission time interval (TTI) unit. The method of claim 12, wherein the control unit,
A base station, characterized in that, by using a congestion control identifier, control to distinguish between a congestion control application target terminal and a congestion control exclusion terminal among a plurality of terminals in the cell of the base station. The method of claim 12, wherein the control unit,
Controls to discard packets exceeding a preset threshold packet size among packets received from the terminal determined as the congestion control application target terminal,
The preset threshold packet size is determined based on an acknowledgment (ACK) packet size of a transmission control protocol (TCP) download session. The method of claim 12, wherein the control unit,
The base station, characterized in that the control so as to discard packets except for signaling and guaranteed bit rate (GBR) bearers of high priority among packets received from the terminal determined as the congestion control application target terminal. The method of claim 12, wherein the control unit,
In order to prevent retransmission in a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer or an upper layer of the PDCP layer after processing the RLC layer, characterized in that the base station controls to discard the packet. The method of claim 12, wherein the control unit,
and controlling to perform congestion marking on packets exceeding a preset size among packets received from the terminal determined as the congestion control application target terminal.

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