Patent Publication Number: US-2023140487-A1

Title: Base station, communication method, and communication program

Description:
TECHNICAL FIELD 
     An embodiment relates to a base station, a communication method, and a communication program. 
     BACKGROUND ART 
     A wireless LAN base station and a terminal apparatus access a channel using CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to transmit wireless signals. In CSMA/CA, the base station and the terminal apparatus stand by for an amount of time defined by an access parameter, and transmit wireless signals upon having confirmed by carrier sensing that the channel is not in use by another terminal apparatus or the like. 
     A primary channel that is used foremostly when transmitting wireless signals, and a secondary channel that is usable in conjunction with the primary channel, are installed in the base station. Ina case in which confirmation is made by carrier sensing that neither the primary channel nor the secondary channel is in use, the base station can transmit wireless signals using both the primary channel and the secondary channel in conjunction. 
     CITATION LIST 
     Non Patent Literature 
     
         
         NPL 1: IEEE Std 802.11-2016, “10.22.2.5 EDCA channel access in a VHT or TVHT BSS”, 7 Dec. 2016 
       
    
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, in a case in which the same channel is set as the primary channel among a plurality of base stations, a base station that fails to acquire a transmission right for the primary channel does not transmit wireless signals, regardless of whether or not the secondary channel is in use. Thus, in a case in which the same channel is set as the primary channel in a plurality of base stations, there is a possibility that the secondary channel will not be used even if usable. That is to say, there is room for consideration regarding efficiently using channels among of plurality of base stations. 
     The present invention has been made in view of the foregoing, and it is an object thereof to provide a wireless communication environment in which channels can be efficiently used among a plurality of base stations. 
     Means for Solving the Problem 
     In one aspect, a base station serving as a second base station includes a wireless signal processing unit capable of using a first channel held in common with another base station serving as a first base station. The wireless signal processing unit is configured to execute first cooperative processing in a case of the first base station acquiring a transmission right for the first channel that is a primary channel. The first cooperative processing includes, on the basis of the second base station acquiring a transmission right for a second channel that is a secondary channel of the second base station, deciding to transmit by the second channel. 
     Effects of the Invention 
     According to the embodiment, a wireless communication environment can be provided in which channels can be efficiently used among a plurality of base stations. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a block diagram illustrating a configuration of a communication system according to an embodiment. 
         FIG.  2    is a block diagram illustrating a hardware configuration of a base station according to the embodiment. 
         FIG.  3    is a block diagram illustrating a hardware configuration of a terminal apparatus according to the embodiment. 
         FIG.  4    is a conceptual diagram showing a cooperative base station management table stored in the base station according to the embodiment. 
         FIG.  5    is a flowchart showing negotiation processing executed between base stations according to the embodiment. 
         FIG.  6    is a conceptual diagram showing a cooperative base station management table generated by negotiation processing executed between base stations according to the embodiment. 
         FIG.  7    is a flowchart showing transmission processing of data executed among a plurality of base stations according to the embodiment. 
         FIG.  8    is a timing chart showing a case of cooperative transmission processing being executed, out of the transmission processing of data executed among the plurality of base stations according to the embodiment. 
         FIG.  9    is a timing chart showing a case of the cooperative transmission processing not being executed, out of the transmission processing of data executed among the plurality of base stations according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment will be described below with reference to the Figures. Note that in the description below, components that have the same functions and configurations are denoted by common reference signs. Also, in a case of distinguishing a plurality of components having common reference signs, distinguishment will be made by further reference signs added following the common reference signs (e.g., a hyphen and numeral, such as “-1” or the like). 
     1. Embodiment 
     1.1 Configuration 
     A configuration of a wireless communication system according to the embodiment will be described. 
     1.1.1 Wireless Communication System 
       FIG.  1    is a block diagram illustrating an example of the configuration of the wireless communication system according to the embodiment. 
     The wireless communication system  1  is provided with a plurality of base stations  10 - 1 ,  10 - 2 , and  10 - 3 , and a terminal apparatus  20 , as illustrated in  FIG.  1   . The plurality of base stations  10 - 1  to  10 - 3  each connects a network NW and the terminal apparatus  20 , and functions as an access point for the terminal apparatus  20  to access the network NW. Each of the plurality of base stations  10 - 1  to  10 - 3  has a service area that is set in advance, and is capable of communicating with terminals within this service area. 
     Also, the plurality of base stations  10 - 1  to  10 - 3  are capable of communicating with each other, and can execute cooperative data transmission in a frequency domain, by sharing information of frequency bands (channels) and so forth used for communication. Details of cooperative transmission processing of data in the frequency domain will be described later. 
     The terminal apparatus  20  is a wireless terminal apparatus such as a smartphone, PC (Personal computer), or the like, for example. The terminal apparatus  20  is configured to be capable of exchanging data with the network NW via the plurality of base stations  10 - 1  to  10 - 3 . The example in  FIG.  1    illustrates a case of the terminal apparatus  20  belonging to the service areas of all of the plurality of base stations  10 - 1  to  10 - 3 . 
     1.1.2 Base Station 
       FIG.  2    and  FIG.  3    are block diagrams illustrating an example of a hardware configuration and a functional configuration of the base station according to the embodiment, respectively. Note that the plurality of base stations  10 - 1  to  10 - 3  in  FIG.  1    may have the same configuration.  FIG.  2    and  FIG.  3    exemplify the configuration of any one of the plurality of base stations  10 - 1  to  10 - 3  as the base station  10 . 
     First, the hardware configuration of the base station  10  will be described with reference to  FIG.  2   . 
     As illustrated in  FIG.  2   , the base station  10  is provided with a processor  11 , a ROM (Read only memory)  12 , a RAM (Random access memory)  13 , a wireless module  14 , and a router module  15 . 
     The processor  11  is a processing device that controls the entire base station  10 . The processor  11  is a CPU (Central processing unit), for example, but is not limited to this, and an ASIC (Application specific integrated circuit) or the like may be used instead of a CPU. The ROM  12  is a nonvolatile semiconductor memory, for example, and holds firmware and various types of programs necessary for operation of the base station  10 . The RAM  13  is a volatile semiconductor memory, for example, and is used as a work area for the processor  11 . 
     The wireless module  14  is a circuit used for exchange of data by wireless signals, and is connected to an antenna. The router module  15  is provided for the base station  10  to communicate with a server that is omitted from illustration within the network NW, for example. 
     Next, the functional configuration of the base station  10  will be described with reference to  FIG.  3   . 
     As illustrated in  FIG.  3   , the base station  10  functions as a computer provided with a data processing unit  101  and a wireless signal processing unit  102 . The data processing unit  101  and the wireless signal processing unit  102  are functional blocks for performing data communication on the basis of the OSI (Open systems interconnection) reference model. Communication functions in the OSI reference model are divided into seven layers (Layer 1: physical layer, Layer 2: data link layer, Layer 3: network layer, Layer 4: transport layer, Layer 5: session layer, Layer 6: presentation layer, Layer 7: application layer). The data link layer includes an LLC (Logical Link Control) layer and a MAC (Media access Control) layer. In the present specification, Layer 3 to Layer 7 will be referred to as “higher layers”, with the data link layer that is Layer 2 as a reference. 
     The data processing unit  101  executes processing corresponding to the LLC layer and higher layers on input data. For example, the data processing unit  101  outputs data input from the network NW to the wireless signal processing unit  102 . The data processing unit  101  also outputs data input from the wireless signal processing unit  102  to the network NW. 
     The wireless signal processing unit  102  executes MAC layer and physical layer processing with regard to the input data, and exchanges data between the base station  10  and the terminal apparatus  20 , or between the base station  10  and other base stations  10 , using wireless communication. For example, the wireless signal processing unit  102  creates wireless frames using data input from the data processing unit  101 , converts the wireless frames into wireless signals, and sends the wireless signals out to the terminal apparatus  20  or another base station  10  via the antenna. The wireless signal processing unit  102  also converts wireless signals received via the antenna into wireless frames, and outputs the data included in the wireless frames to the data processing unit  101 . 
     Now, the wireless signal processing unit  102  may perform control in accordance with a degree of priority in transmission, by allocating wireless frames to a plurality of transmission queues. For example, the wireless signal processing unit  102  may have a plurality of transmission queues AC_LL, AC_VO, AC_VI, AC_BE, and AC_BK, for each access category (AC). The transmission queue AC_LL is a queue for holding wireless frames categorized into LL (Low latency). The transmission queue AC_VO is a queue for holding wireless frames categorized into VO (Voice). The transmission queue AC_VI is a queue for holding wireless frames categorized into VI (Video). The transmission queue AC_BE is a queue for holding wireless frames categorized into BE (Best effort). The transmission queue AC_BK is a queue for holding wireless frames categorized into BK (Background). The wireless signal processing unit  102  inputs the wireless frames into the corresponding transmission queues, in accordance with the category of the data recorded in the wireless frames. 
     The wireless signal processing unit  102  confirms by carrier sensing, for each access category, that there is no transmission of wireless signals by other base stations or the like on the channel to be used, and waits for transmission in accordance with an amount of time defined by access parameters set for each access category. The access parameters are assigned such that transmission of wireless signals are prioritized in a relative manner in the order of LL, VO, VI, BE, and BK, for example. If there is no transmission of wireless signals by another base station or the like while waiting for transmission, the wireless signal processing unit  102  assumes that the own station has acquired the transmission right for the channel, takes the wireless frame out of the corresponding transmission queue, and thereafter converts the wireless frame into wireless signals on the basis of the predetermined channel and performs transmission thereof. 
     Note that in a case of having acquired the transmission right for a particular channel, the wireless signal processing unit  102  can transmit wireless signals using this particular channel and another channel regarding which the transmission right has been further acquired, in conjunction. In the following description, the above-described “particular channel” and “other channel” will be referred to as “primary channel” and “secondary channel”, respectively, and will be distinguished as necessary. 
     The wireless signal processing unit  102  includes a cooperative transmission control unit  103 . The cooperative transmission control unit  103  controls cooperative transmission processing in the frequency domain that is carried out between the base station  10  that is the own station, and other base stations  10 , on the basis of a cooperative base station management table  104 . Cooperative transmission processing is processing in which, among a plurality of base stations regarding which the same channel is set as the primary channel, a base station that succeeded in acquisition of the transmission right for the primary channel (master station) and a base station that failed in acquisition of the transmission right (slave station) use channels of different bands from each other to cooperative execute OFDMA (Orthogonal Frequency Division Multiple Access). 
     Specifically, prior to transmission processing of data to the terminal apparatus  20 , the cooperative transmission control unit  103  executes negotiation processing with other base stations  10  capable of communication (cooperation candidate base stations), and decides a base station  10  capable of executing cooperative transmission processing (cooperative base station). Information regarding cooperation candidate base stations and cooperative base stations is stored in the cooperative base station management table  104  within the base station  10 , for example. 
     Also, when the own station becomes the master station, the cooperative transmission control unit  103  generates an invite signal requesting a slave station to participate in cooperative transmission processing, on the basis of the cooperative base station management table  104 . Conversely, in a case in which the own station becomes a slave station, upon receiving an invite signal from the master station, the cooperative transmission control unit  103  determines whether or not to participate in the cooperative transmission processing requested from the master station, and generates response signals including the determination results thereof. 
       FIG.  4    is a conceptual diagram showing a cooperative base station management table stored in a base station according to the embodiment.  FIG.  4    showing a conceptual diagram of a cooperative base station management table  104 - 1  in the base station  10 - 1 , as an example of the cooperative base station management table  104 . 
     As illustrated in  FIG.  4   , identification information of cooperation candidate base stations, the primary channel and the secondary channel used by the cooperation candidate base stations, and a negotiation success flag, are stored in the cooperative base station management table  104 - 1  in a cooperative manner. The negotiation success flag is information indicating whether or not negotiation with the cooperation candidate base station was successful (whether or not the cooperation candidate base station was registered as a cooperative base station as a result of the negotiation processing). 
     In the example in  FIG.  4   , the first row stores that the base station  10 - 1  that is the own station uses channel CH2 as the primary channel and uses channel CH1 as the secondary channel. 
     The second row stores that the base station  10 - 2  uses channel CH2 as the primary channel and uses channel CH3 as the secondary channel. Also stored in the negotiation success flag column is that negotiation with the base station  10 - 2  was successful, and information indicating that the base station  10 - 2  has been registered as a cooperative base station of the base station  10 - 1  (indicated by a “circle” in  FIG.  4   ). 
     The third row stores that the base station  10 - 3  uses channel CH3 as the primary channel and uses channel CH4 as the secondary channel. Also stored in the negotiation success flag column is that negotiation with the base station  10 - 3  was not successful, and information indicating that the base station  10 - 3  has not been registered as a cooperative base station of the base station  10 - 1  (indicated by a “cross” in  FIG.  4   ). 
     By referencing the cooperative base station management table  104 - 1  in which information such as described above is stored, the cooperative transmission control unit  103  of the base station  10 - 1  can recognize that the object of cooperation in the cooperative transmission processing is the base station  10 - 2 . 
     1.2 Operations 
     Next, operations of the wireless communication system according to the embodiment will be described. 
     1.2.1 Negotiation Processing 
     Negotiation processing among base stations according to the embodiment will be described by way of a flowchart shown in  FIG.  5    and a conceptual diagram shown in  FIG.  6   . 
     In the example in  FIG.  5   , an example of a case of executing negotiation processing between the base station  10 - 1  and the base station  10 - 2  is shown.  FIG.  6    shows the cooperative base station management table  104 - 1  in the base station  10 - 1 , and a cooperative base station management table  104 - 2  in the base station  10 - 2 , updated by the negotiation processing shown in  FIG.  5   . 
     Negotiation processing is executed in advance, prior to execution of the cooperative transmission processing. 
     As shown in  FIG.  5   , in step ST10, the base station  10 - 2  transmits a beacon. The beacon includes, for example, the address of the own station (base station  10 - 2 ), information indicating the primary channel and the secondary channel of the base station  10 - 2 , and information indicating whether or not the base station  10 - 2  handles cooperative transmission processing (cooperative transmission handleability flag). 
     In step ST11, upon receiving the beacon transmitted from the base station  10 - 2  in step ST10, the base station  10 - 1  determines whether or not cooperation with the base station  10 - 2  that is the transmission source of the beacon is possible. Specifically, in a case in which the cooperative transmission handleability flag included in the beacon indicates handling cooperative transmission processing, and the primary channel of the base station  10 - 2  is the same as the primary channel of the base station  10 - 1 , for example, the base station  10 - 1  determines that cooperation with the base station  10 - 2  is possible. Conversely, in a case in which the cooperative transmission handleability flag indicates not handling cooperative transmission processing, or the primary channel of the base station  10 - 2  is different from the primary channel of the base station  10 - 1 , for example, the base station  10 - 1  determines that cooperation with the base station  10 - 2  is not possible. In a case of determining that cooperation with the base station  10 - 2  is possible (step ST11; yes), the processing of the base station  10 - 1  advances to step ST12, and a case of determining that cooperation with the base station  10 - 2  is not possible (step ST11; no), the processing of the base station  10 - 1  skips step ST12 and advances to step ST15. 
     In step ST12, the base station  10 - 1  generates a cooperation request signal, and performs transmission thereof to the base station  10 - 2 . The cooperation request signal corresponds to a type of management frame, and the request signal includes, for example, information indicating the primary channel and the secondary channel of the base station  10 - 1 , and information of the channel that the base station  10 - 1  uses for transmission of an invite signal. Any channel is selectable for the channel that the base station  10 - 1  uses for transmitting the invite signal, but the primary channel common to the base station  10 - 1  and the base station  10 - 2  may be selected, for example. 
     In step ST13, the base station  10 - 2  determines whether or not the cooperation request signal has been received. In a case in which the cooperation request signal has been received (step ST13; yes), the processing of the base station  10 - 2  advances to step ST14. Conversely, in a case in which the cooperation request signal has not been received (step ST13; no), the processing of the base station  10 - 2  skips steps ST14 and ST16 and ends. 
     In step ST14, the base station  10 - 2  generates a response signal to the received cooperation request signal, and performs transmission thereof to the base station  10 - 1 . The response signal to the cooperation request signal corresponds to a type of management frame, and this response signal includes, for example, a negotiation success flag and information of the channel that the base station  10 - 2  uses for transmission of the invite signal. Any channel is selectable for the channel that the base station  10 - 2  uses for transmitting invite signal, but the primary channel common to the base station  10 - 1  and the base station  10 - 2  may be selected, for example. 
     In step ST15, the base station  10 - 1  updates the cooperative base station management table  104 - 1 . 
     Specifically, the base station  10 - 1  stores information indicating the primary channel and the secondary channel of the base station  10 - 2  in the cooperative base station management table  104 - 1 , on the basis of the information in the beacon received in step ST10. 
     Also, in a case of determining in step ST11 that cooperation with the base station  10 - 2  is not possible (step ST11; no), or in a case in which the negotiation success flag indicates failure in negotiation in step ST14, the base station  10 - 1  sets the negotiation success flag correlated with the base station  10 - 2  in the cooperative base station management table  104 - 1  to a “cross”. Conversely, in a case in which the negotiation success flag indicates success in negotiation in step ST14, the base station  10 - 1  sets the negotiation success flag correlated with the base station  10 - 2  in the cooperative base station management table  104 - 1  to a “circle”. 
     Accordingly, the results of negotiation processing with the base station  10 - 2  are stored in the cooperative base station management table  104 - 1  of the base station  10 - 1 . 
     In step ST16, the base station  10 - 2  updates the cooperative base station management table  104 - 2 . Specifically, in a case of transmitting a negotiation success flag indicating failure of negotiation processing in step ST14, the base station  10 - 2  sets a “cross” to the negotiation success flag correlated with the base station  10 - 1  in the cooperative base station management table  104 - 2 . Also, in a case of transmitting a negotiation success flag indicating success of negotiation in step ST14, the base station  10 - 2  sets a “circle” to the negotiation success flag correlated with the base station  10 - 1  in the cooperative base station management table  104 - 2 . 
     Accordingly, the results of the negotiation processing with the base station  10 - 1  are stored in the cooperative base station management table  104 - 2  of the base station  10 - 2 . 
     Thus, the negotiation processing ends. 
     As illustrated in  FIG.  6   , upon negotiation succeeding between the two base stations  10 - 1  and  10 - 2 , the base station  10 - 2  is registered as a cooperative base station in the cooperative base station management table  104 - 1  in the base station  10 - 1 , and the base station  10 - 1  is registered as a cooperative base station in the cooperative base station management table  104 - 2  in the base station  10 - 2 . 
     Note that the cooperative base station management tables  104 - 1  and  104 - 2  do not store which of the base stations  10 - 1  and  10 - 2  is the master station (or slave station). That is to say, the relation of the base stations  10 - 1  and  10 - 2  is that of equals in the period during the negotiation processing and after the negotiation processing ends, until one of the base stations  10 - 1  and  10 - 2  acquires the transmission right for the primary channel. 
     In the flowchart shown in  FIG.  5   , a case has been described in which the base station  10 - 1  transmits a cooperation request signal on the basis of the beacon that the base station  10 - 2  transmits, but this is not limiting. That is to say, the base stations  10 - 1  and  10 - 2  are configured to be able to alternate the roles of each other shown in  FIG.  5    in the negotiation processing. 
     1.2.2 Transmission Processing 
     Next, transmission processing of data by a plurality of base stations according to the embodiment will be described with reference to the flowchart shown in  FIG.  7   .  FIG.  7    shows an example of a case in which the base station  10 - 1  is the master station and the base station  10 - 2  is the slave station. 
     As shown in  FIG.  7   , in step ST20, the base stations  10 - 1  and  10 - 2  perform carrier sensing. 
     In step ST21, the base station  10 - 1  acquires the transmission right for the primary channel. The base station  10 - 2  that was not able to acquire the transmission right for the primary channel continues carrier sensing. From step ST21 onward, the base station  10 - 1  functions as the master station, and the base station  10 - 2  functions as the slave station. 
     In step ST22, the base station  10 - 1  references the cooperative base station management table  104 - 1 , and determines whether or not there is a base station regarding which negotiation has already been successful. In a case in which there is a base station regarding which negotiation has already been successful (step ST22; yes), the processing advances to step ST23, and in a case in which there is no base station regarding which negotiation processing has already been successful (step ST22; no), the processing advances to step ST31. 
     In step ST23, the base station  10 - 1  generates an invite signal requesting participation in cooperative transmission processing, and performs transmission thereof, by a control frame for example, to the base station  10 - 2  regarding which determination is made that negotiation processing has already been successful. The invite signal includes, for example, time tw in which the base station  10 - 1  waits for a response from the base station  10 - 2 . Also, the invite signal may include information indicating at least the primary channel, as information indicating the channel that the base station  10 - 1  will use for the cooperative transmission processing. 
     Also, in step ST24, in a case of having acquired the transmission right for the secondary channel of the base station  10 - 1 , the base station  10 - 1  executes reservation processing for a TXOP (Transmission opportunity) period Ts_master to perform transmission using this secondary channel. The TXOP period Ts_master may be aligned with a TXOP period Tp regarding the primary channel. Specifically, the base station  10 - 1  transmits a CTS-to-self (Clear to Send) signal in which its own address is specified as the destination (CTS-to-self processing), for example. Thus, an NAV (Network Allocation Vector) can be set to the secondary channel of the base station  10 - 1 , and other base stations  10  and so forth in the service area of the base station  10 - 1  can be suppressed from using the secondary channel of the base station  10 - 1 . Note that the period reserved in the above-described reservation processing may be a period from the transmission of the invite signal until transmission of data. 
     Note that the base station  10 - 1  may execute the processing according to steps ST23 and ST24 in reverse order, or may perform execution thereof simultaneously. 
     Upon receiving the invite signal, in step ST25, the base station  10 - 2  determines whether or not participation in the cooperative transmission processing can be performed. Specifically, the base station  10 - 2  determines whether or not data awaiting transmission is present in the transmission queue. In addition, the base station  10 - 2  further determines whether or not the transmission right for the secondary channel of the base station  10 - 2  has been acquired as a result of the carrier sensing which has being continued from step ST20. Note that in this determination, even if a random backoff period remains at the time of receiving the invite signal, the base station  10 - 2  may assume the transmission right for the secondary channel to have been acquired if the secondary channel of the base station  10 - 2  is in an available state at that point in time. In a case in which there is data awaiting transmission, and the transmission right for the secondary channel of the base station  10 - 2  has been acquired (step ST25; yes), the processing of the base station  10 - 2  advances to step ST25. Conversely, in a case in which there no data awaiting transmission, or the transmission right for the secondary channel of the base station  10 - 2  has not been acquired (step ST25; no), the processing of the base station  10 - 2  skips steps ST26, ST27, and ST30, and ends. 
     In step ST26, the base station  10 - 2  generates a signal including information to the effect of participating in the cooperative transmission processing, as a response signal to the invite signal, and performs transmission thereof to the base station  10 - 1 . 
     Also, in step ST27, the base station  10 - 2  executes reservation processing for TXOP period Ts_slave for performing transmission using the secondary channel of the base station  10 - 2 . The TXOP period Ts_slave may be aligned with the TXOP period Tp and the Ts_master. Specifically, for example, the base station  10 - 2  can set a NAV to the secondary channel of the base station  10 - 2  by executing CTS-to-self processing. Thus, other base stations  10  and so forth in the service area of the base station  10 - 2  can be suppressed from using the secondary channel of the base station  10 - 2 . Note that the period reserved in the above-described reservation processing may be a period from the transmission of the response signal to the invite signal until transmission of data. 
     Note that the base station  10 - 2  may execute the processing according to steps ST26 and ST27 in reverse order, or may perform execution thereof simultaneously. 
     In step ST28, the base station  10 - 1  determines whether or not the response signal to the invite signal has been received within the wait time tw from the transmission of the invite signal. In a case in which the response signal to the invite signal has been received within the wait time tw (step ST28; yes), the processing of the base station  10 - 1  advances to step ST29, and a case in which the response signal to the invite signal has not been received within the wait time tw (step ST28; no), the processing of the base station  10 - 1  advances to step ST31. 
     In a case in which the processing advances to step ST29, the base station  10 - 1  transmits a cooperative transmission start signal including information to the effect of starting cooperative transmission processing with the base station  10 - 2 , to the base station  10 - 2 . 
     In step ST30, the base stations  10 - 1  and  10 - 2  execute cooperative transmission processing of data. Specifically, the base station  10 - 1  and the base station  10 - 2  cooperate with each other in the frequency domain to transmit data by the primary channels of each and the secondary channel of the base station  10 - 2 , respectively. 
     Conversely, in a case in which the processing advances to step ST31, the base station  10 - 1  executes transmission of data using the primary channel thereof, independent from the base station  10 - 2 . 
     Thus, transmission processing of data ends. 
       FIG.  8    and  FIG.  9    are timing charts for describing transmission processing of data by a plurality of base stations according to the embodiment. In  FIG.  8    and  FIG.  9   , operations on the three channels CH1, CH2, and CH3 by the base stations  10 - 1  and  10 - 2  in the flowchart described in  FIG.  7    are shown on a time axis.  FIG.  8    shows a timing chart in a case of executing cooperative transmission processing of data (step ST30 in  FIG.  7   ).  FIG.  9    shows a timing chart in a case of not executing cooperative transmission processing of data, and transmission processing is executed by the master station alone (step ST31 in  FIG.  7   ). Note that  FIG.  8    and  FIG.  9    show examples of cases in which the cooperative base station management tables  104 - 1  and  104 - 2  shown in  FIG.  6    are stored in the respective base stations  10 - 1  and  10 - 2 . 
     First, a case in which cooperative transmission processing is executed will be described with reference to  FIG.  8   . 
     As shown in  FIG.  8   , carrier sensing of channels CH1 and CH2 by the base station  10 - 1 , and carrier sensing of channels CH2 and CH3 by the base station  10 - 2 , are executed. 
     At time point T1, the base station  10 - 1  acquires the transmission rights for the channel CH2 that is the primary channel, and the channel CH1 that is the secondary channel of the base station  10 - 1 . In conjunction with this, the base station  10 - 1  uses channel CH2 to transmit an invite signal to the base station  10 - 2 , and also executes reservation processing of the channel CH1 by CTS-to-self processing. The base station  10 - 1  sets in advance a reservation period Ts_master for the secondary channel, aligned with the TXOP period Tp of the primary channel, for example, and includes this in the CTS signal. Accordingly, the channel CH1 can be suppressed from being used for other communication until the cooperative transmission processing of the data is executed. 
     At time point T2, the base station  10 - 2  assumes that the transmission right for the channel CH3 that is the secondary channel of the base station  10 - 2  will be acquired, or that the transmission right has been acquired. In conjunction with this, the base station  10 - 2  uses the channel CH2 to transmit the response signal to the invite signal to the base station  10 - 1 , and also executes reservation processing of the channel CH3 by CTS-to-self processing. The base station  10 - 2  sets the TXOP period Ts_slave for reservation of the channel CH3 in the CTS signal, on the basis of information indicating the TXOP period Ts_master included in the CTS signal transmitted at the time of the reservation processing of the channel CH1 by the base station  10 - 1 . Accordingly, the channel CH3 can be suppressed from being used for other communication until the cooperative transmission processing of the data is executed. 
     Note that in the example in  FIG.  8   , the base station  10 - 2  transmits the response signal to the invite signal to the base station  10 - 1 , within the wait time tw from the transmission of the invite signal. Accordingly, the base station  10 - 1  can determine that cooperative transmission processing is possible with the base station  10 - 2 , and can transmit a cooperative transmission start signal to the base station  10 - 2 . 
     The base stations  10 - 1  and  10 - 2  start cooperative transmission processing of data at a time point T3 following a SIFS (Short Inter Frame Space) after exchange of the cooperative transmission start signal is completed, for example. Specifically, data transmission processing by the base station  10 - 1  using the channels CH1 and CH2 in conjunction, and data transmission by the base station  10 - 2  using the channel CH3, are executed cooperatively in the frequency domain. 
     Next, a case in which cooperative transmission processing is not executed will be described with reference to  FIG.  9   . 
     As shown in  FIG.  9   , the acquisition of transmission rights, and transmission processing of the invite signal and the CTS signal by the base station  10 - 1  are the same as in the case of  FIG.  8   , and accordingly description will be omitted. 
     Meanwhile, in  FIG.  9   , at the time point (T2+Δ) at which the wait time tw from the transmission of the invite signal has elapsed, the base station  10 - 2  has not acquired the transmission right for the channel CH3 of the base station  10 - 2 , or cannot assume that the transmission right has been acquired, unlike as in  FIG.  8   . In conjunction with this, the base station  10 - 2  does not transmit the response signal to the invite signal to the base station  10 - 1 . Accordingly, at time point (T2+Δ), the base station  10 - 1  abandons cooperative transmission processing with the base station  10 - 2 , and decides to execute data transmission alone. Specifically, the base station  10 - 1  executes data transmission processing using the channels CH1 and CH2 in conjunction after SIFS from the time point (T2+Δ), for example. 
     1.3 Effects According to Present Embodiment 
     In a case in which the base station  10 - 1  does not acquire the transmission right for the primary channel CH2, in order for the base station  10 - 2  to use the secondary channel CH3 and transmit wireless signals, the base station  10 - 2  is required to acquire the transmission right for this secondary channel CH3, and also acquire the transmission right for the primary channel CH1. This is because acquisition of the transmission right for the primary channel set in advance is required in the channel bonding specifications for transmitting wireless signals using a plurality of channels in conjunction. Thus, in a case in which the base station  10 - 1  does not acquire the transmission right for the primary channel CH2, the base station  10 - 2  cannot transmit wireless signals in a state in which the base station  10 - 2  has not acquired the transmission right for the primary channel CH2. 
     According to the present embodiment, in a case in which the base station  10 - 1  that is a cooperative base station of the base station  10 - 2  acquires the transmission right for the primary channel CH2, the base station  10 - 2 , on the basis of acquiring the transmission right for the secondary channel CH3 of the base station  10 - 2 , decides to transmit wireless signals using this secondary channel CH3. Accordingly, the base station  10 - 2  can transmit wireless signals over the secondary channel CH3 cooperatively with the base station  10 - 1 , in a state in which the transmission right for the primary channel CH2 is not acquired. Thus, channels can be efficiently used between the base stations  10 - 1  and  10 - 2 . 
     Also, the base station  10 - 1  receives wireless signals including information indicating the primary channel of the base station  10 - 2 , and transmits wireless signals including information indicating the primary channel of the base station  10 - 1  to the base station  10 - 2 . Accordingly, the base stations  10 - 1  and  10 - 2  can recognize that each other will use the same channel CH2 as the primary channel, prior to the cooperative transmission processing. Thus, when one base station out of the base stations  10 - 1  and  10 - 2  acquires the transmission right for the primary cannel CH2, an invite signal can be transmitted to the other base station, requesting participation in the cooperative transmission processing. 
     Note that generally, when transmission on the primary channel and reception on the secondary channel occur at the same time, power cross-leaking occurs with each other, and reception fails. According to the present embodiment, the TXOP period Ts_master and Ts_slave that the base stations  10 - 1  and  10 - 2  use for reservation periods of the secondary channel when the base stations  10 - 1  and  10 - 2  are a master station and a slave station respectively, are aligned with the TXOP period Tp on the primary channel. Thus, the problem of power cross-leaking does not occur, since the two channels are used for transmission at the same time at the master station side, and the possibility of reception occurring on the primary channel at the slave station side is also eliminated, and therefore occurrence of power cross-leaking can be suppressed. 
     2. Modifications, Etc 
     Note that various modifications can be made of the above-described embodiment. 
     For example, although a case of the two stations of the base station  10 - 1  and the base station  10 - 2  registering each other as cooperative base stations has been described in the above embodiment, this is not limiting, and three or more stations may register each other as cooperative base stations. In this case, the master station that has acquired the transmission right for the primary channel transmits invite signals to each of the plurality of slave stations. Each of the plurality of slave stations that have received the invite signals can determine whether or not to participate in the cooperative transmission processing on the basis of acquiring the transmission right for the secondary channel that each uses. 
     Now, in a case of the plurality of slave stations each using different secondary channels from each other, each of the plurality of slave stations can decide whether or not to participate in the cooperative transmission processing, independent of each other. Accordingly, the master station can execute cooperative transmission processing with at least one slave station that transmits a response signal to the invite signal to the master station. 
     Conversely, in a case in which the plurality of slave stations each using the same secondary channel, only one station out of the plurality of slave stations can acquire the transmission right for this secondary channel. Accordingly, the master station can execute the cooperative transmission processing with just the one slave station from which a response signal to the invite signal is received. Note that as described above, the wireless signal processing unit  102  can have a plurality of transmission queues including the transmission queue AC_LL. Accordingly, a slave station that has data awaiting transmission in a transmission queue to which access parameters with a higher degree of priority are set can more readily participate in cooperative transmission processing. 
     Note that in a case of three or more stations registering each other as cooperative base stations, the reservation period for the secondary channel may be set for a period prior to transmitting data with priority, rather than the TXOP period. Accordingly, in a case of reservations signals for the secondary channel being transmitted from a plurality of slave stations, for example, reservation signals of slave stations that were not able to acquire transmission rights can be suppressed from obstructing communication of other base stations. 
     Each of the processing in the embodiment described above can also be stored as a program that can be executed by a processor that is a computer. Additionally, storage thereof in a storage medium of an external storage device such as a magnetic disk, an optical disk, semiconductor memory, and so forth, may be performed, and distribution may be performed. The processor can then execute the above-described processing by reading in the program stored in the storage medium of the external storage device, and actions thereof being controlled by the program read in. 
     Note that the present invention is not limited to the above embodiment, and various modifications can be made at the stage of carrying out without departing from the essence thereof. Also, the embodiments may be combined and carried out as appropriate, and in this case, combined effects are obtained. Further, the above embodiment includes various types of inventions, and various inventions can be extracted by combination of selected sets of a plurality of disclosed components. For example, in a case in which the problem can be solved and effects can be obtained even though several components are omitted from all components shown in the embodiment, the configuration in which these components are omitted can be extracted as an invention. 
     REFERENCE SIGNS LIST 
     
         
           1  Wireless communication system 
           10 - 1 ,  10 - 2 ,  10 - 3  Base station 
           11  Processor 
           12  ROM 
           13  RAM 
           14  Wireless module 
           15  Router module 
           20  Terminal apparatus 
           101  Data processing unit 
           102  Wireless signal processing unit 
           103  Cooperative transmission control unit 
           104  Cooperative base station management table