Communication device, communication method, and computer-readable storage medium

A communication device that forms a first Basic Service Set (BSS) communicates a radio frame including a preamble and a data field of a physical layer (PHY). The preamble includes an Extremely High Throughput (EHT) Signal Field (EHT-SIG-A). The EHT-SIG-A includes a subfield for setting a BSS color, and if the communication device and a first other communication device are to cooperatively transmit the radio frame to a second other communication device, a value of this subfield is set, without changing the BSS color used in a first BSS, based on the BSS color of a second BSS to which the second other communication device belongs.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a communication device, a communication method, and a computer-readable storage medium and, more particularly, to a communication control technique in a wireless LAN.

Background Art

As a communication standard concerning a wireless LAN (Wireless Local Area Network), the IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard is known. In the IEEE802.11ax standard that is the latest standard of the IEEE802.11 standard series, not only a high peak throughput but also improvement of a communication speed under a congestion situation is implemented using OFDMA (Orthogonal Frequency-Division Multiple Access) (see PTL 1).

Currently, in order to further improve throughput, a study group called IEEE802.11EHT (Extremely High Throughput) has been formed as a successor standard of IEEE802.1 lax. In the EHT, to achieve throughput improvement, a Multi-AP Coordination configuration in which a plurality of access points (APs) arranged while being spatially distributed cooperatively transmit data to a single STA (Station) has been examined.

CITATION LIST

Patent Literature

In the IEEE802.11ax standard, use of identification information called BSS (Basic Service Set) color is defined. If a communication device receives a radio frame in which the same BSS color as the BSS color of an AP connected to the self-device is set, the radio frame is handled as a frame of Intra-BSS. On the other hand, in the IEEE802.11EHT, use of the Multi-AP Coordination configuration has been examined, as described above. How to set the BSS color in this case is not clear yet.

SUMMARY OF THE INVENTION

The present invention provides a technique of appropriately executing a setting for causing a plurality of access points to concurrently transmit data to a terminal.

According to one aspect of the present invention, there is provided a communication device that forms a first Basic Service Set (BSS), and transmits a radio frame including a preamble and a data field of a physical layer (PHY), characterized in that the preamble includes a Legacy Short Training Field (L-STF), a Legacy Long Training Field (L-LTF) arranged immediately after the L-STF in the radio frame, a Legacy Signal Field (L-SIG) arranged immediately after the L-LTF in the radio frame, an Extremely High Throughput (EHT) Signal Field (EHT-SIG-A) arranged after the L-SIG in the radio frame, an EHT Short Training Field (EHT-STF) arranged after the EHT-SIG-A in the radio frame, and an EHT Long Training Field (EHT-LTF) arranged immediately after the EHT-STF in the radio frame, the EHT-SIG-A includes a subfield for setting a BSS color, and if the communication device and a first other communication device are to cooperatively transmit the radio frame to a second other communication device, a value of the subfield is set, without changing the BSS color used in a first BSS, based on the BSS color of a second BSS to which the second other communication device belongs.

DESCRIPTION OF THE EMBODIMENTS

FIG.1shows an example of the configuration of a wireless communication network according to this embodiment. This wireless communication network is configured to include access points (an AP102and an AP104) and terminals (an STA103and an STA105), which are IEEE802.11EHT (Extremely High Throughput) devices. In the following description, in a case in which a specific device is not referred to or the like, the access point may be referred to as “AP” and the station may be referred to as “STA” without reference numerals. Note that inFIG.1, the wireless communication network including two APs and two STAs is shown as an example, but the numbers of communication devices may be, for example, three or more. InFIG.1, the communicable area of the network formed by the AP102and the AP104is indicated by a circle101. Note that this communicable area may cover a larger area, or may cover only a smaller area. In addition, althoughFIG.1shows STAs complying with the IEEE802.11EHT standard, an STA that supports only a standard (legacy standard) of a generation before the IEEE802.11EHT standard may exist. Note that it may be understood that EHT is an acronym of Extreme High Throughput.

Note that in this example, each of the AP102and the AP104can receive a signal transmitted from the other AP. Note that the connection form is not particularly limited, and the AP102and the AP104may be connected by a wire or wirelessly. The AP102and the AP104support the Multi-AP Coordination configuration of the IEEE802.11EHT and can cooperatively concurrently transmit data to one STA. For example, the STA105can concurrently transmit/receive radio frames to/from the AP102and the AP104, which cooperatively operate. The STA105can be configured to, for example, include a plurality of wireless LAN control units and transmit/receive radio frames to/for a plurality of APs using different radio channels. Note that the STA105may include one physical control unit capable of processing a plurality of frames concurrently received via a plurality of radio channels. That is, the STA105has a configuration capable of logically concurrently processing a plurality of wireless communications physically using one or a plurality of control devices.

FIG.2shows the hardware configuration of each of the APs (the AP102and the AP104) and the STAs (the STA103and the STA105). The communication device includes, as an example of its hardware configuration, a storage unit201, a control unit202, a function unit203, an input unit204, an output unit205, a communication unit206, and an antenna207.

The storage unit201is formed by both of a ROM and a RAM or one of them, and stores programs for performing various kinds of operations to be described later and various kinds of information such as communication parameters for wireless communication. Note that other than the memories such as a ROM and a RAM, a storage medium such as a flexible disk, a hard disk, an optical disk, a magnetooptical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, or a DVD may be used as the storage unit201.

The control unit202is formed by, for example, a processor such as a CPU or an MPU, an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like. Here, CPU is an acronym of Central Processing Unit, and MPU is an acronym of Micro Processing Unit. The control unit202executes the programs stored in the storage unit201, thereby controlling the entire device. Note that the control unit202may control the entire device by cooperation of the programs stored in the storage unit201and an OS (Operating System).

In addition, the control unit202controls the function unit203to execute predetermined processing such as image capturing, printing, or projection. The function unit203is hardware used by the device to execute predetermined processing. For example, if the device is a camera, the function unit203is an image capturing unit and performs image capturing processing. For example, if the device is a printer, the function unit203is a printing unit and performs print processing. For example, if the device is a projector, the function unit203is a projection unit and performs projection processing. Data to be processed by the function unit203may be data stored in the storage unit201, or may be data communicated with another AP or STA via the communication unit206to be described later.

The input unit204accepts various kinds of operations from a user. The output unit205performs various kinds of outputs for the user. Here, the output by the output unit205includes, for example, at least one of display on a screen, audio output by a loudspeaker, vibration output, and the like. Note that both the input unit204and the output unit205may be implemented by one module, like a touch panel.

The communication unit206controls wireless communication complying with the IEEE802.11 standard series, or controls IP communication. In this embodiment, the communication unit206can execute processing complying with at least the IEEE802.11EHT standard. In addition, the communication unit206controls the antenna207to transmit and receive radio signals for wireless communication. The device communicates contents such as image data, document data, or video data with another communication device via the communication unit206. The antenna207is an antenna that can transmit and receive signals in at least any one of, for example, a sub-GHz band, 2.4 GHz band, 5 GHz band, and 6 GHz band. Note that the frequency band (and a combination of frequency bands) to which the antenna207is adaptable is not particularly limited. The antenna207may be one antenna, or may be a set of two or more antennas to perform MIMO (Multi-Input and Multi-Output) transmission/reception.FIG.2shows one antenna207, but the antenna may include two or more antennas (two or more sets of antennas) that are adaptable to different frequency bands. The antenna207is configured to be adaptable to communication of Distributed Coordination of the IEEE802.11EHT standard. For example, the AP has a configuration capable of transmitting D-MIMO (Distributed MIMO) for JTX (Joint Transmission).

Note that JTX is one element used to implement the Multi-AP Coordination function that is expected to be newly introduced from the IEEE802.11EHT, and indicates that a plurality of APs cooperatively concurrently transmit data to one STA. The Multi-AP Coordination function is a function of making a plurality of APs cooperatively operate to improve transmission/reception throughput or signal strength on the STA side. As a wireless technology at this time, D-MIMO can be used. D-MIMO is a technique of causing a plurality of APs to communicate with one STA at the same time and same frequency channel (for example, in the same RU (Resource Unit) of OFDMA (Orthogonal Frequency-Division Multiple Access)). According to D-MIMO, since the space use efficiency is improved, high-speed communication can be implemented. The minimum configuration of D-MIMO includes an M-AP (master AP), an S-AP (slave AP), and an STA. In this case, under the control of the M-AP, the two APs, that is, the M-AP and the S-AP cooperatively concurrently (simultaneously) transmit radio frames to one STA.

FIG.3shows an example of the functional configuration of each of the communication devices (the AP102and the AP104). As an example, the AP includes a wireless LAN control unit301, a frame generation unit302, a BSS color setting unit303, a UI control unit304, a storage unit305, and an antenna306.

The wireless LAN control unit301is configured to include circuits that transmit/receive radio signals to/from another wireless LAN device (for example, another AP or STA), and programs configured to control these. The wireless LAN control unit301executes communication control of wireless LAN such as transmission of a frame generated by the frame generation unit302and reception of a radio frame from another wireless LAN device in accordance with the IEEE802.11 standard series. The frame generation unit302generates a radio frame to be transmitted by the wireless LAN control unit301based on, for example, data that is received from another AP and should be transmitted to an STA. In addition, the frame generation unit302generates, for example, a radio frame including data that another AP should transmit to an STA or a trigger frame (JTX TF) for instructing the timing of transmitting the radio frame including the data to the STA.

The BSS color setting unit303sets the BSS color of a radio frame. For example, when the self-device (the AP102or the AP104) forms a BSS (Basic Service Set), the BSS color setting unit303sets a BSS color to be used in the BSS. The BSS color setting unit303sets the value of the BSS color for a radio frame to be transmitted to the STA connected to the self-device. On the other hand, when performing data transmission by JTX to an STA connected to another AR the BSS color setting unit303sets a BSS color used in the BSS formed by the other AP for the radio frame to be transmitted to the STA. That is, when transmitting a radio frame to an STA connected to another AP different from the self-device by JTX, the BSS color setting unit303uses not the BSS color used in the BSS formed by the self-device but the BSS color of the other AP. According to this, a plurality of radio frames received by the STA can be handled as radio frames in which the BSS color used in the BSS connected to the STA is set. For this reason, the STA can handle all of a plurality of radio frames received from a plurality of APs as Intra-BSS frames. On the other hand, since the BSS color setting unit303sets the BSS color of the BSS formed by the self-device for a radio frame other than JTX, the STA connected to the other AP can handle the radio frame as an Inter-BSS frame. Note that the STA can execute different control processes depending on whether a received radio frame is an Intra-BSS frame or an Inter-BSS frame. For example, if the reception power of a radio frame does not exceed a predetermined value, the STA can transmit the radio frame. A predetermined value concerning the Inter-BSS frame can be set to a value higher than a predetermined value concerning an Intra-BSS frame. According to this, even if a radio frame is received by power more than the predetermined value concerning an Intra-BSS frame, the STA may have a transmission opportunity if the radio frame is a radio frame of Inter-BSS. For this reason, when the AP uses a BSS color different from that of another AP at time other than JTX, the communication opportunity of the STA connected to the other AP can be increased, and the frequency use efficiency of the entire system can be improved.

The UI control unit304is configured to include hardware concerning user interfaces (UIs) such as a touch panel and buttons configured to accept an operation on the AP by the user (not shown) of the AP, and programs configured to control these. Note that the UI control unit304also has a function of, for example, presenting information to the user, such as display of an image or the like or audio output. The storage unit305is configured to include a storage device such as a ROM (Read Only Memory) or a RAM (Random Access Memory) configured to store programs to be executed by the communication device and various kinds of data.

Note that the STA has the functions of a general STA. The STA can have a function of receiving a radio frame transmitted by the Multi-AP Coordination configuration.

An example of the structure of a PPDU (Physical Layer (PHY) Protocol Data Unit) complying with the IEEE802.11EHT standard will be described with reference toFIGS.4to6.FIG.4shows an example of an EHT SU (Single User) PPDU that is a PPDU for single-user communication, andFIG.5shows an example of an EHT MU (Multi User) PPDU for multi-user communication.FIG.6shows an example of an EHT ER (Extended Range) PPDU for long distance transmission. The EHT ER PPDU is used when the communication area should be extended in communication between an AP and a single STA. Note that the fields of the PPDU need not always be arranged in the orders shown inFIGS.4to6, and may include new fields that are not shown inFIGS.4to6.

The PPDU includes fields including an STF (Short Training Field), an LTF (Long Training Field), and a SIG (Signal Field). As shown inFIG.4, the head portion of the PPDU includes an L (Legacy)-STF401, an L-LTF402, and an L-SIG403for ensuring backward compatibility with the IEEE802.11a/b/g/n/ax standards. Note that each of frame formats shown inFIGS.5and6includes an L-STF (L-STF501or L-STF601), an L-LTF (L-LTF502or L-LTF602), and an L-SIG (L-SIG503or RL-SIG603). Note that the L-LTF is arranged immediately after the L-STF, and the L-SIG is arranged immediately after the L-LTF. Note that each of the structures shown inFIGS.4to6further includes an RL-SIG (Repeated L-SIG, an RL-SIG404, RL-SIG504, or RL-SIG604) arranged immediately after the L-SIG In the RL-SIG field, the contents of the L-SIG are repeatedly transmitted. The RL-SIG is used to enable a receiver to recognize that this PPDU complies with a standard after the IEEE802.11ax standard, and may be omitted in IEEE802.11EHT in some cases. In addition, a field for enabling the receiver to recognize that this PPDU complies with the IEEE802.11EHT may be provided in place of the RL-SIG

The L-STF401is used for detection of a physical layer (PHY) frame, AGC (Automatic Gain Control), timing detection, or the like. The L-LTF402is used for highly accurate frequency/time synchronization, obtainment of propagation channel information (CSI: Channel State Information), or the like. The L-SIG403is used for transmitting control information including information such as a data transmission rate and a PHY frame length. A legacy device complying with the IEEE802.11a/b/g/n/ax standards can decode the above-described various kinds of legacy fields.

Each PPDU further includes an more EHT-SIG (EHT-SIG-A405, EHT-SIG-A505, EHT-SIG-B506, or EHT-SIG-A605) arranged immediately after the RL-SIG and used for transmitting control information for EHT. Each PPDU further includes an STF for EHT (EHT-STF406,507, or606) and an LTF for EHT (EHT-LTF407,508, or607). Each PPDU includes, after these controlling fields, a data field408,509, or608and a Packet extension field409,710, or609. The portion including the fields from the L-STF to the EHT-LTF of each PPDU is referred to as a PHY preamble.

Note that each ofFIGS.4to6shows the PPDU that can ensure the backward compatibility as an example. However, if it is unnecessary to ensure the backward compatibility, for example, the legacy fields may be omitted. In this case, for example, the EHT-STF and EHT-LTF are used in place of the L-STF and the L-LTF to establish synchronization. In this case, the EHT-STF and one of the plurality of EHT-LTFs after the EHT-SIG field can be omitted.

The EHT-SIG-A405and605included in the EHT SU PPDU and the EHT ER PPDU include an EHT-SIG-A1and an EHT-SIG-A2necessary for reception of the PPDU, respectively, as shown in Tables 1 and 2 below. A 6-bit “BSS color” subfield is included in the EHT-SIG-A1. Also, the EHT-SIG-A505of the EHT MU PPDU shown inFIG.5includes an EHT-SIG-A1and an EHT-SIG-A2necessary for reception of the PPDU as shown in Tables 3 and 4 below. In the PPDU as well, a 6-bit “BSS color” subfield is included in the EHT-SIG-A1. Note that the configurations of Tables 1 to 4 are merely examples, and information other than the information shown in these tables may be included in the EHT-SIG field, and some of the pieces of information shown in these tables may be excluded from the EHT-SIG field.

TABLE 1BitSub-BitPositionfieldCountDescriptionEHT-B0Format1“1” is set for an EHT PPDU and anSIG-EHT ER PPDU to distinguish themA1from an EHT TB PPDU.B1Beam1“1” is set if the pre-EHT of the PPDUChangeis arranged in a space different from thefirst symbol of the EHT-LTF, or “0” isset if the pre-EHT is mapped similarlyto the first symbol.B2UL/DL1This subfield indicates whether thePPDU is for UL or DL, and has thesame value as TXVECTORUPLINK_FLAGB3-MCS4This subfield indicates the value ofB6the Modulation and Coding Scheme.In a case of an EHT SU PPDU, n = 0,1, 2, . . . , 11 (12 to 15 are reserved).In a case of an EHT ER SU PPDU andBandwidth = 0, n = 0, 1, 2 (3 to 15 arereserved areas).In a case of an EHT ER SU PPDU andBandwidth = 1, n = 0 for MCS0 (1 to 15 are reserved areas).B7DCM1This subfield indicates whether DualCarrier Modulation is applied to thedata field.If “0” is set in the STK field, “1” is set.(If both the DCM and STBC fieldsare “1”, neither of them is applied)If DCM is not applied, “0” is set.B8-B13BSS66-bit number for identifying the BSSColorB14Re-1Reserved fieldservedB15-Spatial4This subfield indicates whether SpatialB18ReuseReuse is allowed during transmissionof this PPDU.The value of Spatial Reuse field encod-ing shown in the separate table is set.B19-Band-2In a case of an EHT SU PPDU:B20width“0” is set for 20 MHz, “1” is set for40 MHz, “2” is set for 80 MHz, or“3” is set for 160 MHz (80 + 80 MHz).In a case of an EHT ER SU PPDU:“0” is set for 242-tone RU, or “1” isset for upper 106-tone RU of 20 MHz.B21-G1 +2This subfield indicates the GuardB22LTFInterval period and the EHT-LTF size.Size“0” is set for 1 × EHT-LTF and 0.8 μsGI, “1” is set for 2 × EHT-LTF and0.8 μs GI, “2” is set for 2 × EHT-LTFand 1.6 μs GI, “3” is set if both theDCM and STBC fields are “1” andfor 4 × EHT-LTF and 0.8 μs GI, or“3” is set for 4 × EHT-LTF other thanthe above case and 3.2 μs GI.B23-NSTS2This subfield indicates the number ofB25Andspace-time streams and the midambleMid-period for frame synchronization.ambleIf the Doppler field is “0”, “(thePerio-number of space-time streams)—1” isdicityset.If the Doppler field is “1”, B23 andB24 indicate the number of space-time streams.B25 is “0” if the midamble period is10, or “1” if the midamble period is 20.

TABLE 3BitSub-BitPositionfieldCountDescriptionEHT-B0UL/DL1This subfield indicates whether theSIG-PPDU is for UL or DL, and has theA1same value as TXVECTORUPLINK_FLAGB1-B3SIGB3This subfield indicates the MCS ofMCSthe EHT-SIG-B field. “0” is set forMCS 0, “1” is set for MCS 1, “2” isset for MCS 2, “3” is set for MCS 3,“4” is set for MCS 4, or “5” is setfor MCS 5. “6” and “7” are reservedareas.B4SIGB1“1” is set if the HT-SIG-B field isDCMmodulated using DCM.B5-B10BSS66-bit number for identifying the BSSColorB11-Spatial4This subfield indicates whether SpatialB14ReuseReuse is allowed during transmissionof this PPDU. The value of SpatialReuse field encoding shown in theseparate table is set.B15-Band-3“0” is set for 20 MHz, “1” is set forB17width40 MHz, or “3” is set for 160 MHz(80 + 80 MHz).When the SIGB Compression fieldis “0”, “4” is set if only the secondary20 MHz is puncturing in 80 MHzpreamble puncturing,“5” is set if two 20 MHz of thesecondary 40 MHz are puncturingin 80 MHz preamble puncturing.“6” is set if only the secondary 20MHz is puncturing in 160 (or 80 +80) MHz preamble puncturing, or“7” is set if only the secondary 40MHz is puncturing in 160 (or 80 +80) MHz preamble puncturing.If the SIGB field is “1”, the valuebetween “4” to “7” means “reserved”.B18-Number4When the SIGB Compression field isB21of EHT-“0”, this subfield indicates the numberSIG-Bof OFDMA symbols in the EHT-SIG-SymbolsB.or MU-If the number of OFDM symbols inMIMOthe EHT-SIG-B is smaller than 16, theUsersnumber obtained by subtracting 1 fromthe number of OFDM symbols in theEHT-SIG-B is set. If at least one re-ceiving terminal has set the capabilityof supporting the number of EHT SIG-B OFDM symbols larger than 16 to“0”, “15” is set to indicate that thenumber of OFDM symbols in theEHT-SIG-B is 16. If all the receivingterminals have set the capability ofsupporting the number of EHT SIG-B OFDM symbols larger than 16 to“0” and the data rate of the EHT-SIG-B is smaller than MCS 4 which doesnot use DCM, “15” is set to indicatethat the number of OFDM symbolsin the EHT-SIG-B is equal to orlarger than 16. When the SIGB Com-pression field is “1”, the value sethere means the number obtained bysubtracting 1 from the number of MU-MIMO users.B22SIG1“1” is set if a Common field exists inCom-the EHT-SIG-B.pressionB23-Gi +2This subfield indicates the GuardB24LTFInterval period and the EHT-LTF size.Size“0” is set for 4 × EHT-LTF and 0.8 μsGI, “1” is set for 2 × EHT-LTF and 0.8μs GI, “2” is set for 2 × EHT-LTE and1.6 μs GI, or “3” is for 4 × EHT-LTEand 3.2 μs GI.B25Doppler1“1” is set if either of the followingconditions is met:the number of OFDM symbols in thedata field is larger than “the value in-dicated by the midamble period + 1”,and a midamble exists, andthe number of OFDM symbols in thedata field is equal to or smaller than“the value indicated by the midambleperiod + 1”, no midamble exists, andthe channel changes rapidly.

TABLE 4BitSub-BitPositionfieldCountDescriptionEHT-B0-B6TXOP1Transmission OpportunitySIG-If TXOP_DURATION of TXVECTORA2is UNSPECIFIED and there is no periodinformation, 127 is set.If TXOP_DURATION of TXVECTORis smaller than 512, a value smaller than127 is set to set NAV. At this time, if B0is “0”, FLOOR of TXOP_DURATION/8(round down) is set in B1 to B6. If B0 is“1”, FLOOR of (TXOP_DURATION—512)/8 is set in B1 to B6.B7Re-1Reserved fieldservedB8-B10Number3This subfield indicates the number ofof EHT-EHT-LTFs.LTF“0” is set for one EHT-LTF, “1” is setSymbolsfor two EHT-LTFs, “2” is set for fourAndEHT-LTFs, “3” is set for six EHT-Mid-LTFs, or “4” is set for eight EHT-LTFs.ambleWhen the Doppler field is “1”, B8 andPerio-B9 indicate the number of EHT-LTFdicitysymbols, and B10 indicates themidamble period.B11LDPC1This subfield indicates the presence/Extraabsence of an extra OFDM symbolSymbolsegment for LDPC.SegmentB12STBC1When the number of users of each RU(Resource Unit) is not larger than 1, “1”is set to indicate that STBC is used forencoding.B13-Pre-FEC2“0” is set if the Pre-FEC Padding FactorB14Paddingis 4, “1” is set if the Pre-FEC PaddingFactorFactor is 1, “2” is set if the Pre-FECPadding Factor is 2, or “3” is set if thePre-FEC Padding Factor is 3.B15PE1Disambiguity field of Packet ExtensionDisam-biguilyB16-CRC4The CRC of the EHT-SIG-A (26 bits ofB19A1 and 16 bits up to B15 of A2, that is,42 bits in total) field up to here.B20-Tail6An area to set “0” to indicate the endB25portion to a trellis convolution decoder.
(Procedure of Processing)

Examples of the procedure of processing executed by an AP as described above and the procedure of processing executed by a wireless communication network will be described next with reference toFIGS.7and8.FIG.7shows an example of the procedure of processing in the wireless communication network, andFIG.8shows an example of the procedure of processing executed by the AP102and the AP104.

First, the AP102forms a first BSS (BSS1) (F701, step S801). Note that in this embodiment, a setting for using BSS color1is done in the BSS1. Also, the AP104forms a second BSS (BSS2) (F702, step S801). Here, in this embodiment, a setting for using BSS color2different from BSS color1is done in the BSS2. Each AP notifies Beacon of IEEE802.11 at a predetermined period and accepts a connection request from the STA, thereby setting a state in which the AP mediates communication between the STA and another STA or between the STA and a DS (Distribution System).

The AP102executes a connection procedure with the STA103and transitions to a connected state (F703). Similarly, the AP104executes a connection procedure with the STA105and transitions to a connected state (F704). With this connection procedure, the AP notifies the STA of the information of the operation state, as in IEEE802.11ax. The information of the operation state includes the value of the BSS color. The BSS color is 6-bit information for identifying the BSS included in the preamble of the physical layer (PHY), as described above. Based on the value of the BSS color, the STA can ascertain whether a received radio frame is a frame of a BSS (intra-BSS) to which the STA belongs or a frame of a BSS (inter-BSS) to which the STA does not belong.

The AP102can transmit a radio frame to the STA103(F705). This radio frame is a PPDU shown in one ofFIGS.4to6, and a value indicating BSS color1used in the BSS1is stored in the BSS color subfield. Similarly, the AP104can transmit a radio frame to the STA105(F706). This radio frame is a PPDU shown in one ofFIGS.4to6, and a value indicating BSS color2used in the BSS2is stored in the BSS color subfield. In a case of an EHT SU PPDU or EHT ER PPDU, the BSS color subfield is formed by the ninth to 14th bits (B8to B13) of EHT-SIG-A1, as shown in the above-described table. In a case of an EHT MU PPDU, the BSS color subfield is formed by the sixth to 11th bits (B5to B10) of EHT-SIG-A1.

After that, the AP102and the AP104decide to cooperatively concurrently perform data transmission to a common STA. For example, upon detecting that there exists an enormous amount of data to be transmitted to the STA105, the AP104can decide to transmit the data to the STA105cooperatively with the AP102that is another AP existing on the periphery. Also, even if there does not exist a plan of a mass data communication to a specific STA, the AP102or the AP104may decide to prepare for cooperative transmission with another AP in preparation for occurrence of mass data communication in the future. If it is decided to perform cooperative transmission by a plurality of APs or make a preparation for that, the AP102and the AP104perform a negotiation for JTX (Joint Transmission) (F707, step S802). Note that the negotiation for JTX will sometimes simply be referred to as “negotiation” hereinafter. In the negotiation, the AP that executes the negotiation can decide whether to operate as an M-AP or an S-AP. Here, the AP102decides to operate as an M-AP (F708, YES in step S803), and the AP104decides to operate as an S-AP (F709, NO in step S803). Additionally, in this negotiation, which AP should be associated with the STA as the target of JTX may be decided.

After the end of the negotiation, the AP104serving as the S-AP notifies the AP102serving as the M-AP of the information of the STA105connected to the self-device and the information of BSS color2used in the BSS2formed by the self-device (F710, steps S804and S811). Here, the information of the STA can include the information of the MAC (Medium Access Control) address of the STA, and the like. Note that these pieces of information may be notified from the S-AP to the M-AP at another timing such that, for example, the pieces of information are exchanged between the APs at the time of negotiation. Also, the AP102may notify the AP104of the information of the STA103connected to the self-device and the information of BSS color1used in the BSS1formed by the self-device. Furthermore, if the AP102and the AP104perform JTX to transmit data to a specific STA, the AP connected to the STA may notify the other AP of the information of the STA and the information of the BSS color. However, since the M-AP can designate the STA as the data transmission target and the BSS color in transmission of transmission target data or a JTX trigger frame to be described later, the information need not always be provided from the M-AP to the S-AP.

After that, the AP102notifies the AP104operating as the S-AP of the start of the JTX mode (F711, steps S805and S812). After that, when transmission target data to the STA105is generated (YES in step S806), the transmission target data is transmitted from the AP102to the AP104(F712, steps S807and S813). Instead of immediately transmitting the received data to the STA105, the AP104temporarily holds the received data because it is operating in the JTX mode.

Note that at the time of transmission of the transmission target data from the M-AP to the S-AP, the information of the BSS color to be used may be notified from the M-AP to the S-AP. In this embodiment, since the data is transmitted by JTX to the STA105, BSS color2used in the AP104connected to the STA105can be notified as the information of the BSS color to be used. Note that if the BSS color to be used matches the BSS color used in the S-AP, or the BSS color to be used by JTX is known in advance, the information of the BSS color need not be notified from the M-AP to the S-AP. That is, if the data is transmitted by JTX to the STA connected to the S-AP, or the information of the BSS color is exchanged with the STA as the data transmission target of JTX, the M-AP need not notify the S-AP of the information of the BSS color. Note that, for example, when performing data transmission to the STA103by JTX, the AP102can notify the AP104of BSS color1as the information of the BSS color to be used. Note that if data is transmitted by the above-described PPDU, the information of the BSS color to be used is notified because the PPDU includes a PHY preamble for notifying the BSS color. In this case, the S-AP receives a radio frame for which a BSS color different from the BSS color used by the self-device is set. However, since the S-AP is operating in the JTX mode, the data in the radio frame is not discarded.

After transmission/reception of the transmission target data, the AP102transmits a JTX trigger frame (TF) to the AP104to cause the AP104to transmit a radio frame including the transmission target data (F713, steps S808and S814). By the JTX TF, the AP102can instruct the AP104to transmit the radio frame to the STA105and designate the timing of transmission. For example, at the timing designated by the JTX TF (YES in step S809), the AP102and the AP104concurrently transmit the data to the STA105(F714, F715, step S810). Note that the transmission timing can be a timing after the elapse of a predetermined time (SIFS, Short Inter Frame Space) from transmission/reception of the JTX TF. In this case, the transmission timing is instructed by transmission/reception itself of the JTX TF. In this case, the JTX TF can be transmitted at a timing according to the timing when the AP102and the AP104should transmit the radio frame to the STA105. Alternatively, information for designating the transmission timing may be included in the frame of the JTX TF. In this case, using the designated transmission timing and a timer or clock in the self-device, the AP102and the AP104can decide when the radio frame should be transmitted. As described above, using the JTX TF, the AP102and the AP104can synchronously transmit the radio frame.

Note that in the data transmission at this time, the BSS color used in the BSS (the AP connected to the STA) to which the STA as the data transmission target belongs is set in the PHY preamble in the radio frame. In the example shown inFIG.7, BSS color2used in the BSS2to which the STA105as the data transmission target belongs is set in the radio frame. That is, the AP104transmits the radio frame directly using BSS color2used in the self-device, and the AP102transmits the radio frame using BSS color2different from BSS color1used in the self-device. The BSS color of the BSS1formed by the AP102is not changed from BSS color1. That is, the AP102does not change the BSS color of the BSS formed by the self-device. However, to transmit data by JTX, the AP102sets, in the radio frame, the BSS color used in the BSS to which the STA as the transmission destination of the data belongs and transmits the data. At this time, the AP102can transmit the data to the STA (STA103) connected to the self-device even if the AP102is operating in the JTX mode. In this case, the AP102can set, in the radio frame, BSS color1used in the BSS1formed by the self-device and transmit the data. That is, during the operation in the JTX mode, the AP102sets the BSS color of the BSS to which the STA belongs in the radio frame and transmits the data. This also applies to the AP104. That is, the AP104uses BSS color2in the BSS2formed by the self-device. However, for example, if the AP102instructs to transmit data by JTX to the STA103, the AP104can transmit a radio frame for which BSS color1is set to the STA103. Note that at this time, the AP104does not change the BSS color of the BSS2.

Since each AP does not change the BSS color in the BSS formed by the self-device, the connected STA is never instructed to change the BSS color. For this reason, the setting of the STA is never unnecessarily changed, and, for example, an increase in the power consumption of the STA can be suppressed. On the other hand, in JTX, since the BSS color in the PHY preamble of the radio frame is set in accordance with the BSS to which the STA belongs, the STA can receive the radio frame without changing the setting of the BSS color in JTX.

According to the present invention, it is possible to appropriately execute a setting for causing a plurality of access points to concurrently transmit data to a terminal.

OTHER EMBODIMENTS