Patent Publication Number: US-2023137775-A1

Title: Base station, wireless communication system, and wireless communication method

Description:
TECHNICAL FIELD 
     The present invention relates to a base station, a wireless communication system, and a wireless communication method. 
     BACKGROUND ART 
     Some of wireless communication systems establish connection by using TCP (Transmission Control Protocol) and implement highly reliable communication between a wireless terminal (client) and a server. 
     Examples of a wireless terminal used in the such wireless communication systems include a cellular phone and a smartphone. For example, the wireless terminal communicates with components such as a content server which provides content via a base station. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         Non-Patent Literature 1: Takeshita, Takafumi and three others, “masutaringu TCP/IP nyumon hen” (mastering TCP/IP: elementary level), 5th ed., Ohmsha, Ltd., Feb. 25, 2012, p. 230-256 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     For example, in TCP communication, an algorithm called slow start is used at the start of communication in order to prevent a client, such as a wireless terminal, from transmitting massive data to a server from the beginning to cause an excess over the capacity of a network. 
     Slow start has parameters, such as a congestion window (CW) and a slow start threshold (SST). 
     The amount of data to be transmitted by a wireless terminal depends on a CW. For the wireless terminal, an initial value for the CW is set to be small. Upon receipt of a positive acknowledgment (ACK) from a server, the wireless terminal exponentially increases a value of the CW. 
     In TCP communication, a wireless terminal can only transmit data, the amount of which is dependent on a CW, until the wireless terminal receives an ACK. A round trip time (RTT) thus largely affects throughput. 
     A base station allocates communication resources (a band) for a wireless terminal on the basis of a buffer amount notification transmitted by the wireless terminal. For this reason, the wireless terminal may suffer from an increase in delay and a reduction in throughput, depending on a band allocated by the base station and a time period taken for the base station to allocate the band. 
     An object of the present invention is to provide a base station, a wireless communication system, and a wireless communication method capable of enhancing throughput of a wireless terminal even when the wireless terminal establishes connection with a server to perform communication. 
     Means for Solving the Problem 
     A base station according to one aspect of the present invention is a base station which performs relaying between a wireless terminal and a server, the wireless terminal and the server establishing connection with each other, including a request detection unit which detects a connection establishment request transmitted to the server by the wireless terminal, a response detection unit which detects an acknowledgment transmitted to the wireless terminal by the server on the basis of the connection establishment request detected by the request detection unit, and a band allocation unit which, if the response detection unit detects the acknowledgment, performs allocation so as to expand a band over which the wireless terminal is capable of transmission to the server, regardless of presence or absence of a buffer amount notification from the wireless terminal. 
     A wireless communication system according to one aspect of the present invention is a wireless communication system including a server and a base station which performs relaying between a wireless terminal and the server, the wireless terminal and the server establishing connection with each other, wherein the base station includes a request detection unit which detects a connection establishment request transmitted to the server by the wireless terminal, a response detection unit which detects an acknowledgment transmitted to the wireless terminal by the server on the basis of the connection establishment request detected by the request detection unit, and a band allocation unit which, if the response detection unit detects the acknowledgment, performs allocation so as to expand a band over which the wireless terminal is capable of transmission to the server, regardless of presence or absence of a buffer amount notification from the wireless terminal. 
     A wireless communication method according to one aspect of the present invention is a wireless communication method for performing relaying between a wireless terminal and a server, the wireless terminal and the server establishing connection with each other, including a request detection step of detecting a connection establishment request transmitted to the server by the wireless terminal, a response detection step of detecting an acknowledgment transmitted to the wireless terminal by the server on the basis of the detected connection establishment request, and a band allocation step of, if the acknowledgment is detected, performing allocation so as to expand a band over which the wireless terminal is capable of transmission to the server, regardless of presence or absence of a buffer amount notification from the wireless terminal. 
     Effects of the Invention 
     According to the present invention, it is possible to enhance throughput of a wireless terminal even when the wireless terminal establishes connection with a server to perform communication. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram showing an example of a configuration of a wireless communication system. 
         FIG.  2    is a functional block diagram showing an outline of functions which a base station has. 
         FIG.  3    is a sequence chart showing an example of operation of the wireless communication system including the base station. 
         FIG.  4    is a functional block diagram showing an outline of functions which a base station according to one embodiment has. 
         FIG.  5    is a sequence chart showing an example of operation of a wireless communication system including the base station according to the one embodiment. 
         FIG.  6    is a diagram showing an example of a hardware configuration of the base station according to the one embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A background against which the present invention has been made will be described first.  FIG.  1    is a diagram showing an example of a configuration of a wireless communication system  1 . As shown in  FIG.  1   , the wireless communication system  1  has, for example, n wireless terminals  10 - 1  to  10 - n , a base station  20 , and a server  30 . Note that the numbers of base stations  20  and servers  30  are not limited. 
     The wireless terminals  10 - 1  to  10 - n  are each, for example, a cellular phone or a smartphone, and establish, for example, TCP connection with the server  30  via the base station  20  and perform communication. Note that if any of a plurality of components, such as the wireless terminals  10 - 1  to  10 - n , is not specified, each wireless terminal will simply be referred to as a wireless terminal  10  or the like hereinafter. 
     The base station  20  is connected to the server  30  via a wired or wireless network and performs wireless communication with each of the wireless terminals  10 - 1  to  10 - n . The server  30  is, for example, a content server. Note that the server  30  only needs to be a device which establishes connection with the wireless terminal  10  and performs communication and may be, for example, a PC (personal computer) or the like. 
       FIG.  2    is a functional block diagram showing an outline of functions which the base station  20  has. As shown in  FIG.  2   , the base station  20  has, for example, a transmit-receive switch unit  200 , an uplink signal processing unit  202 , a higher layer processing unit  204 , a band allocation unit  206 , and a downlink signal processing unit  208 . 
     The transmit-receive switch unit  200  has a function as a wireless communication unit which performs wireless communication with the wireless terminal  10  and switches between uplink communication and downlink communication with the wireless terminal  10 . For example, the transmit-receive switch unit  200  receives an uplink signal which is transmitted by the wireless terminal  10  and outputs the uplink signal to the uplink signal processing unit  202 . The transmit-receive switch unit  200  also transmits a downlink signal which is processed by the downlink signal processing unit  208  to the wireless terminal  10 . 
     The uplink signal processing unit  202  performs predetermined processing on an uplink signal which is input from the transmit-receive switch unit  200  and outputs the processed uplink signal to the higher layer processing unit  204 . The uplink signal processing unit  202  also outputs buffer information indicating a capacity of a transmit-receive buffer which each wireless terminal  10  includes to the band allocation unit  206 . Note that the buffer information of the wireless terminal  10  is transmitted as an uplink signal. 
     The higher layer processing unit  204  has a function as a network interface which performs, for example, U-plane wireless protocol processing and performs uplink communication and downlink communication with the server  30 . 
     For example, the higher layer processing unit  204  performs processing (higher layer processing), such as MAC (Media Access Control) layer processing and RLC/PDCP (Radio Link Control/Packet Data Convergence Protocol) layer, on an uplink signal which is processed by the uplink signal processing unit  202  and transmits the processed uplink signal to the server  30 . 
     The higher layer processing unit  204  receives a downlink signal which is transmitted by the server  30 , performs the higher layer processing on the downlink signal, and outputs the downlink signal to the band allocation unit  206  and the downlink signal processing unit  208 . 
     The band allocation unit  206  allocates respective communication resource amounts (bands) for the wireless terminals  10  on the basis of pieces of buffer information which are input from the uplink signal processing unit  202  and a downlink signal subjected to the higher layer processing by the higher layer processing unit  204  and outputs pieces of band information indicating the allocated bands to the downlink signal processing unit  208 . 
     The downlink signal processing unit  208  performs signal processing such that a downlink signal subjected to the higher layer processing by the higher layer processing unit  204  is arranged in bands which are allocated by the band allocation unit  206  and outputs the processed downlink signal to the transmit-receive switch unit  200 . 
       FIG.  3    is a sequence chart showing an example of operation of the wireless communication system  1  including the base station  20 . As shown in  FIG.  3   , the wireless terminal  10  first requests a band for connection by the base station  20  in order to request establishment of connection with the server  30  (S 100 ). 
     The base station  20  makes a response of intent to allocate a band for connection to the wireless terminal  10 (S 110 ). 
     The wireless terminal  10  transmits a SYN packet for establishing TCP connection by using a band which is allocated by the base station  20  to the server  30  via the base station  20  (S 120 ). 
     The server  30  transmits a response (ACK) to the SYN packet transmitted from the wireless terminal  10  to the wireless terminal  10  via the base station  20  (S 130 ). 
     Note that a time period from when the wireless terminal  10  transmits a SYN packet to the server  30  to when the wireless terminal  10  receives a response (ACK) from the server  30  is a round trip time (RTT). 
     The wireless terminal  10  sets a congestion window (CW) to 1 MSS (Maximum Segment Size) and tries to start communication with the server  30 . Even though the wireless terminal  10  has created data to be transmitted, no band for connection has yet been allocated. For this reason, the wireless terminal  10  temporarily stores the data in the buffer and makes a band request (buffer amount notification) based on an amount by which the buffer is occupied to the base station  20  (S 140 ). 
     Note that the congestion window (CW) is a value which is passed in a connection establishment request and a response thereto and is expressed as n×MSS. As to an initial value for the congestion window (CW), although n is set at 1 in  FIG.  3   , n is defined as 4 in RFC 2581, and n is defined as 10 in RFC 6928. 
     The base station  20  makes a response of intent to allocate a band for connection to the wireless terminal  10  (S 150 ). 
     The wireless terminal  10  transmits the data to the server  30  via the base station  20  by using an allocated band (S 160 ). Here, let T 1  be a time period from when the wireless terminal  10  receives a response (ACK) from the server  30  to when the wireless terminal  10  transmits data to the server  30 . 
     The server  30  transmits a response (ACK) to the data transmitted with the CW of 1 MSS from the wireless terminal  10  to the wireless terminal  10  via the base station  20  (S 170 ). 
     The wireless terminal  10  then sets the CW to 2 MSS and requests a band for connection by the base station  20  (S 180 ). 
     The base station  20  makes a response of intent to allocate a band for connection to the wireless terminal  10  (S 190 ). 
     The wireless terminal  10  transmits data to the server  30  via the base station  20  by using an allocated band (S 200 ). 
     The server  30  transmits a response (ACK) to the data transmitted with the CW of 2 MSS from the wireless terminal  10  to the wireless terminal  10  via the base station  20  (S 210 ). 
     Next, a base station  20   a  according to one embodiment will be described.  FIG.  4    is a functional block diagram showing an outline of functions which the base station  20   a  according to the one embodiment has. The base station  20   a  is replaced by the base station  20  shown in  FIG.  1    to constitute a wireless communication system  1 . The base station  20   a  performs relaying between a wireless terminal  10  and a server  30  which establish connection with each other by, for example, TCP. 
     As shown in  FIG.  4   , the base station  20   a  has a transmit-receive switch unit  200   a , an uplink signal processing unit  202   a , a request detection unit  210 , a higher layer processing unit  204   a , a response detection unit  212 , a band allocation unit  206   a , and a downlink signal processing unit  208   a.    
     The transmit-receive switch unit  200   a  has a function as a wireless communication unit which performs wireless communication with the wireless terminal  10  and switches between uplink communication and downlink communication with the wireless terminal  10 . For example, the transmit-receive switch unit  200   a  receives an uplink signal which is transmitted by the wireless terminal  10  and outputs the uplink signal to the uplink signal processing unit  202   a . The transmit-receive switch unit  200   a  also transmits a downlink signal which is processed by the downlink signal processing unit  208   a  to the wireless terminal  10 . 
     The uplink signal processing unit  202   a , for example, performs predetermined processing on an uplink signal which is input from the transmit-receive switch unit  200   a  and outputs the processed uplink signal to the request detection unit  210  and the higher layer processing unit  204   a . The uplink signal processing unit  202   a  also outputs buffer information indicating a capacity of a transmit-receive buffer which each wireless terminal  10  includes to the band allocation unit  206 . Note that the buffer information of the wireless terminal  10  is transmitted as an uplink signal. 
     The request detection unit  210  detects a connection establishment request which is transmitted to the server  30  by the wireless terminal  10  on the basis of, for example, a processed uplink signal which is input from the uplink signal processing unit  202   a  and outputs information indicating the transmission of the connection establishment request to the server  30  by the wireless terminal  10  and a destination address to the band allocation unit  206   a  and the response detection unit  212 . 
     For example, the request detection unit  210  detects a SYN packet for establishing TCP connection which is transmitted to the server  30  by the wireless terminal  10  and outputs information indicating the detection and a communication partner (transmission information and a destination address) to the band allocation unit  206   a  and the response detection unit  212 . 
     The higher layer processing unit  204   a  has a function as a network interface which performs, for example, U-plane wireless protocol processing and performs uplink communication and downlink communication with the server  30 . 
     For example, the higher layer processing unit  204   a  performs processing (higher layer processing), such as MAC layer processing and RLC/PDCP layer, on an uplink signal which is processed by the uplink signal processing unit  202   a  and transmits the processed uplink signal to the server  30 . 
     The higher layer processing unit  204   a  receives a downlink signal which is transmitted by the server  30 , performs the higher layer processing on the downlink signal, and outputs the downlink signal to the response detection unit  212 , the band allocation unit  206   a , and the downlink signal processing unit  208   a.    
     The response detection unit  212  detects an acknowledgment (ACK) which is transmitted to the wireless terminal  10  by the server  30  on the basis of, for example, information which is input from the request detection unit  210  and a downlink signal subjected to the higher layer processing by the higher layer processing unit  204   a . The response detection unit  212  outputs information indicating the transmission of the acknowledgment (ACK) to the wireless terminal  10  by the server  30 , a predetermined instruction (to be described later), and the like to the band allocation unit  206   a.    
     Note that, after information is input from the request detection unit  210 , the response detection unit  212  waits for a fixed time period for an acknowledgment (ACK) which is a communication opposite in transmission information and destination address to an uplink signal. The fixed time period is set to a length equal to or more than a time period (a retransmission time-out time period) taken for a transmitting side (the wireless terminal  10 ) to retransmit data. 
     For example, if the response detection unit  212  detects an acknowledgment (ACK) within the fixed time period, since a CW is expected to be increased in later TCP communication, the response detection unit  212  instructs the band allocation unit  206   a  to allocate a band wider than last time. 
     The band allocation unit  206   a  allocates respective communication resource amounts (bands) for the wireless terminals  10  on the basis of pieces of buffer information which are input from the uplink signal processing unit  202   a , a downlink signal subjected to the higher layer processing by the higher layer processing unit  204   a , information which is input from the request detection unit  210 , information which is input from the response detection unit  212 , and the like and outputs pieces of band information indicating the allocated bands to the downlink signal processing unit  208   a.    
     For example, if the response detection unit  212  detects an acknowledgment (ACK), the band allocation unit  206   a  performs allocation so as to expand a band over which the wireless terminal  10  is capable of transmission to the server  30 , regardless of presence or absence of a buffer amount notification to be transmitted by the wireless terminal  10 . 
     In the presence of a buffer amount notification transmitted by the wireless terminal  10 , the band allocation unit  206   a  may allocate a band over which the wireless terminal  10  is capable of transmission to the server  30 , regardless of the magnitude of a buffer amount in question. That is, the band allocation unit  206   a  may be configured to ignore a buffer amount notification in question if the wireless terminal  10  transmits the buffer amount notification. 
     In normal TCP communication, a congestion window (CW) increases exponentially. In contrast, the band allocation unit  206   a  performs band allocation, for example, on the assumption that a congestion window (CW) is twice wider than last time. Note that a band to be allocated by the band allocation unit  206   a  is not limited to an amount twice a width of a most recently allocated band if the response detection unit  212  detects an acknowledgment. 
     For example, the band allocation unit  206   a  may allocate a band on the assumption that the congestion window (CW) increases to a maximum value for a standard. Alternatively, the band allocation unit  206   a  may perform band allocation for the congestion window (CW) having an initial value after a SYN packet for establishing TCP connection is detected, and a first ACK packet is received. 
     The band allocation unit  206   a  may determine the initial value on the basis of the fact that n=4 in RFC 2581, the fact that n=10 in RFC 6928, or the like. Alternatively, the band allocation unit  206   a  may monitor uplink traffic thus far, learn how wide a band is needed as an initial value, and allocate a band. For example, if the response detection unit  212  detects an acknowledgment, the band allocation unit  206   a  may perform allocation so as to expand a band on the basis of statistics obtained by learning traffic amounts after past acknowledgment detection by the response detection unit  212 . 
     The downlink signal processing unit  208   a  performs signal processing such that a downlink signal subjected to the higher layer processing by the higher layer processing unit  204   a  is arranged in bands which are allocated by the band allocation unit  206   a  and outputs the processed downlink signal to the transmit-receive switch unit  200   a.    
     An example of operation of the wireless communication system  1  including the base station  20   a  will be described.  FIG.  5    is a sequence chart showing the example of the operation of the wireless communication system  1  including the base station  20   a  according to the one embodiment. As shown in  FIG.  5   , the wireless terminal  10  first requests a band for connection by the base station  20   a  in order to request establishment of connection with the server  30  (S 300 ). 
     The base station  20   a  makes a response of intent to allocate a band for connection to the wireless terminal  10  (S 310 ). 
     The wireless terminal  10  transmits a SYN packet for establishing TCP connection by using a band which is allocated by the base station  20  to the server  30  via the base station  20   a  (S 320 ). 
     At this time, in the base station  20   a , the request detection unit  210  detects a connection establishment request which is transmitted to the server  30  by the wireless terminal  10  (S 325 ). 
     The server  30  transmits a response (ACK) to the SYN packet transmitted from the wireless terminal  10  to the wireless terminal  10  via the base station  20   a  (S 330 ). 
     At this time, in the base station  20   a , the response detection unit  212  detects the acknowledgment (ACK) transmitted to the wireless terminal  10  by the server  30  on the basis of the connection establishment request detected by the request detection unit  210  (S 335 ). 
     Note that a time period from when the wireless terminal  10  transmits a SYN packet to the server  30  to when the wireless terminal  10  receives a response (ACK) from the server  30  is a round trip time (RTT). 
     If the response detection unit  212  detects the acknowledgment (ACK), the base station  20   a  performs allocation so as to expand a band over which the wireless terminal  10  is capable of transmission to the server  30 , regardless of presence or absence of a buffer amount notification to be transmitted by the wireless terminal  10  (S 355 ). 
     Even without the wireless terminal  10  requesting band allocation by the base station  20   a , the base station  20   a  expands and allocates the band in the process in S 355 . Thus, the wireless terminal  10  sets the CW to, for example, 1 MSS and transmits data to the server  30  via the base station  20   a  (S 360 ). 
     Here, let T 2  be a time period from when the wireless terminal  10  receives a response (ACK) from the server  30  to when the wireless terminal  10  transmits data to the server  30 . The time period T 2  shown in  FIG.  5    is shorter than the time period T 1  shown in  FIG.  3   . This is because a time period taken for the wireless terminal  10  to request a band by the base station  20   a  is unnecessary. 
     The server  30  transmits a response (ACK) to the data transmitted with the CW of 1 MSS from the wireless terminal  10  to the wireless terminal  10  via the base station  20   a  (S 370 ). 
     At this time, in the base station  20   a , the response detection unit  212  detects the acknowledgment (ACK) transmitted to the wireless terminal  10  by the server  30  on the basis of a connection establishment request which is detected by the request detection unit  210  (S 375 ). 
     If the response detection unit  212  detects the acknowledgment (ACK), the base station  20   a  performs allocation so as to expand the band, over which the wireless terminal  10  is capable of transmission to the server  30 , regardless of presence or absence of a buffer amount notification to be transmitted by the wireless terminal  10  (S 385 ). 
     Even without the wireless terminal  10  requesting band allocation by the base station  20   a , the base station  20   a  expands and allocates the band in the process in S 385 . Thus, the wireless terminal  10  sets the CW to, for example, 2 MSS and transmits data to the server  30  via the base station  20   a  (S 400 ). 
     The server  30  transmits a response (ACK) to the data transmitted with the CW of 2 MSS from the wireless terminal  10  to the wireless terminal  10  via the base station  20   a  (S 410 ). 
     At this time, in the base station  20   a , the response detection unit  212  detects the acknowledgment (ACK) transmitted to the wireless terminal  10  by the server  30  on the basis of a connection establishment request which is detected by the request detection unit  210  (S 415 ) and continues predetermined communication. 
     As described above, if the base station  20   a  detects a TCP-based connection establishment request which is transmitted by the wireless terminal  10  and detects an acknowledgment which is transmitted by the server  30 , the base station  20   a  performs allocation so as to expand a band over which the wireless terminal  10  is capable of transmission, regardless of presence or absence of a buffer amount notification to be transmitted by the wireless terminal  10 . For this reason, the base station  20   a  can reduce a time period required for band allocation and enhance throughput of the wireless terminal  10 . 
     Note that a part or the whole of each of functions which the wireless terminal  10 , the base station  20 , the base station  20   a , and the server  30  have may be implemented by hardware or may be implemented as a program to be executed by a processor, such as a CPU. 
     That is, the wireless communication system  1  according to the present invention can be implemented by using a computer and a program, and the program can be recorded on a storage medium or can be provided through a network. 
       FIG.  6    is a diagram showing an example of a hardware configuration of the base station  20   a  according to the one embodiment. As shown in  FIG.  6   , for example, an input unit  500 , an output unit  510 , a communication unit  520 , a CPU  530 , a memory  540 , and an HDD  550  are connected via a bus  560 , and the base station  20   a  has functions as a computer. The base station  20   a  is configured to be capable of inputting and outputting data from and to a storage medium  570 . 
     The input unit  500  is, for example, a keyboard or a mouse. The output unit  510  is, for example, a display device, such as a display. The communication unit  520  is, for example, a wireless or wired network interface. 
     The CPU  530  controls the units constituting the base station  20   a  and performs the above-described processing. The memory  540  and the HDD  550  store data. The storage medium  570  is configured to be capable of storing, e.g., a wireless communication program which causes execution of the functions that the base station  20   a  has. Note that architecture of the base station  20   a  is not limited to the example shown in  FIG.  6   . The wireless terminal  10  and the server  30  may have the same configurations as the base station  20   a.    
     REFERENCE SIGNS LIST 
     
         
         
           
               1  Wireless communication system 
               10 - 1  to  10 - n  Wireless terminal 
               20 ,  20   a  Base station 
               30  Server 
               200 ,  200   a  Transmit-receive switch unit 
               202 ,  202   a  Uplink signal processing unit 
               204 ,  204   a  Higher layer processing unit 
               206 ,  206   a  Band allocation unit 
               208 ,  208   a  Downlink signal processing unit 
               210  Request detection unit 
               212  Response detection unit 
               500  Input unit 
               510  Output unit 
               520  Communication unit 
               530  CPU 
               540  Memory 
               550  HDD 
               560  Bus 
               570  Storage medium