Communication device, control method for the same, and program

Abstract

To provide an efficient sounding procedure in multi-AP cooperative configurations.SOLUTION: A communication device functions as a master AP in a multi-AP (access point) cooperative configuration that complies with the IEEE 802.11 series of standards. The communication device is configured to select from a plurality of sounding method a sounding method, which is a sending method for a null data packet (NDP) of the AP to receive CSI reports as feedback from a terminal device connected to the communication device and send the NDP according to the selected sounding method.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wireless LAN communication technology. [Background technology]

[0002] The IEEE802.11 series of standards are known as communication standards for wireless local area networks (WLANs). The IEEE802.11ax standard uses OFDMA to achieve high peak throughput as well as improved communication speeds under congested conditions. OFDMA stands for Orthogonal Frequency-Division Multiple Access, and is also known as orthogonal frequency division multiple access.

[0003] Currently, in order to further improve throughput, the 802.11be TG (Task Group) is working on the successor standard to the IEEE 802.11ax standard, after going through a study group (SG) called IEEE 802.11 EHT (Extreme or Extremely High Throughput).

[0004] As one of the measures for improving throughput aimed at by this TG, a multi-AP coordination configuration in which multiple APs (access points) work in coordination is being considered. In order to efficiently operate this multi-AP coordination configuration, a sounding procedure is generally performed between an access point (AP) and a terminal (STA). The sounding procedure is a procedure in which a STA receives NDPs (Null Data Packets) from multiple APs as "sounding packets" and transmits feedback packets including channel state information (CSI) to each AP (Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2016-526856 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the conventional sounding procedure, the procedure for multiple APs operating in cooperation to transmit sounding frames has not been clarified. In addition, in the conventional technology, the time overhead of the sounding procedure and the heavy load on the STA have been mainly proposed to reduce the amount of CSI information transmitted by the STA (reducing the amount of feedback). However, reducing the amount of CSI information makes the estimation of the wireless medium inaccurate, and the effects of inefficiency of medium utilization and slower speeds caused by the inaccuracy can be significant, especially in a multi-AP cooperative configuration.

[0007] The present invention has been made in consideration of the above problems, and has an object to provide an efficient sounding procedure in a multi-AP cooperative configuration. [Means for solving the problem]

[0008] As one means for achieving the above object, a communication device of the present invention has the following configuration: That is, a communication device that functions as a master AP in a multi-AP (access point) cooperative configuration conforming to the IEEE 802.11 series of standards has a selection means for selecting, from a plurality of sounding methods, a sounding method that is a transmission method of a null data packet (NDP) of an AP for receiving a CSI report as feedback from a terminal device connected to the communication device, and a transmission means for transmitting the NDP in accordance with the sounding method selected by the selection means. Effect of the Invention

[0009] An efficient sounding procedure in a multi-AP cooperative configuration is provided. [Brief description of the drawings]

[0010] [Figure 1] 1 illustrates an example of a system configuration according to an embodiment. [Diagram 2] 2 illustrates an example of a hardware configuration of an AP according to an embodiment. [Diagram 3] 2 shows an example of the functional configuration of an AP (a) and an example of the functional configuration of a STA (b) in an embodiment. [Figure 4] 11 is a flowchart of a process executed when starting a connection with a STA. [Diagram 5] 11 is a flowchart of a process executed when data to be transmitted to a STA occurs. [Figure 6] 13 is a flowchart of a process for selecting a sounding method. [Figure 7] The structure of a MAC frame is shown below. [Figure 8] The configuration of the trigger frame (TF) is shown. [Figure 9] The structure of the CSI report field is shown. [Figure 10] The configuration of the MIMO control field is shown. [Figure 11] This is a sequence diagram of "from connection between AP and STA to selection of sounding method". [Figure 12] This is a sequence diagram for "NDP simultaneous transmission (without BFRP TF)". [Figure 13] This is a sequence diagram for "NDP simultaneous transmission (with BFRP TF)". [Figure 14] This is a sequence diagram for "NDP sequential transmission". DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0012] [System configuration] FIG. 1 shows an example of a system configuration in this embodiment. AP102 and AP105 are access points equipped with a function (multi-AP cooperation function) capable of realizing a multi-AP cooperative configuration. The multi-AP cooperation function is a function that cooperates with other APs and realizes faster or more stable communication for a connected terminal than when there is only one AP. Here, the stable state is, for example, a state of any combination of a good signal-to-noise ratio, low interference, low delay, and low jitter. There are various methods for realizing such a stable state. For example, JTX (Joint Transmission) using D-MIMO (Distributed Multiple Input Multiple Output), null steering, Coordinated OFDMA, and Fractional Coordinated OFDMA are listed. When the multi-AP cooperation function is not being executed, AP102 and AP105 manage only the network of BSS (Basic Service Set) 101 and only the network of BSS 104, respectively.

[0013] The AP 102 and the AP 105 are connected by a network (backhaul) 100. The network 100 is a communication means for interconnecting a BSS (Basic Service Set) with other networks when the AP constructs a DS (Distributions System). The network 100 is realized by wired communication such as Ethernet (registered trademark) or a telephone line, or by wireless communication such as LTE (Long-Term Evolution) or WiMAX (Worldwide Interoperability for Microwave Access). Furthermore, the network 100 may be a wireless LAN conforming to the IEEE802.11 series standard. In this case, the network 100 may be the same as or different from the wireless channel used between the AP and the STA.

[0014] STA103 and STA106 are wireless LAN terminals. These STAs are capable of data communication with multiple APs. The data communication includes the communication in the sounding procedure described above. In detail, this includes reception of an NDPA (NDP Announement) and an NDP, transmission of a frame including a CSI Report field, and reception of an NFRP TF (NDP Feedback Report Poll Trigger Frame).

[0015] [Configuration of communication devices (AP, STA)] 2 shows an example of a hardware configuration of an AP (AP 102, AP 105) in this embodiment. As an example of the hardware configuration, the AP has a storage unit 201, a control unit 202, a function unit 203, an input unit 204, an output unit 205, a communication unit 206, and an antenna 207. The storage unit 201 is configured with memories such as ROM and RAM, and stores various information such as programs for performing various operations described later and communication parameters for wireless communication. As the storage unit 201, in addition to memories such as ROM and RAM, a storage medium such as a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a non-volatile memory card, a DVD, etc. may be used. The storage unit 201 may also include a plurality of memories, etc.

[0016] The control unit 202 is configured with, for example, one or more processors 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 for Central Processing Unit, and MPU is an acronym for Micro Processing Unit. The control unit 202 controls the AP by executing a program stored in the storage unit 201. The control unit 202 may control the AP in cooperation with the program stored in the storage unit 201 and an OS (Operating System). The control unit 202 may also be configured to be composed of multiple processors such as a multi-core processor and control the AP. The control unit 202 may also control the function unit 203 to execute a predetermined process such as an AP function, imaging, printing, or projection. The function unit 203 is hardware for the AP to execute a predetermined process.

[0017] The input unit 204 receives various operations from the user. The output unit 205 outputs various information to the user. Here, the output by the output unit 205 includes at least one of display on a screen, audio output by a speaker, vibration output, and the like. Note that both the input unit 204 and the output unit 205 may be realized by one module, such as a touch panel.

[0018] The communication unit 206 controls wireless communication conforming to the IEEE 802.11 series standard, wireless communication conforming to Wi-Fi (registered trademark), and IP (Internet Protocol) communication. Furthermore, the communication unit 206 controls the antenna 207 to transmit and receive wireless signals for wireless communication. The antenna 207 supports communication for multi-AP cooperative configuration. For example, the AP is capable of transmitting D-MIMO (Distributed Multiple Input Multiple Output) for JTX (Joint Transmission). In the figure, only one antenna 207 is shown for simplification, but multiple antennas may be used. In general, the number of antennas 207 (elements) corresponds to the number of streams. In addition to the 2.4 and 5 GHz bands, the frequency bands supported by the antenna 207 are the 6 GHz band that is scheduled to be introduced from 802.11ax.

[0019] The STAs (STA103, STA106) also have the same hardware configuration as the AP shown in Fig. 2. In this case, the control unit 202 controls the function unit 203 to execute predetermined processing such as the STA function.

[0020] FIG. 3(a) shows an example of the functional configuration of an AP. The AP includes, as an example of its functional configuration, a communication control unit 301, a CSI processing capability setting unit 302, a memory management unit 303, a UI (user interface) control unit 304, a multi-AP configuration control unit 305, a sounding method determination unit 306, and a sounding processing unit 307. The communication control unit 301 performs control for transmitting and receiving wireless signals with other wireless LAN devices (e.g., other APs and STAs) via the communication unit 206. The communication control unit 301 performs wireless LAN communication control such as frame generation and frame transmission, and reception of wireless frames from other wireless LAN devices, in accordance with the IEEE802.11 standard series. The CSI processing capability setting unit 302 sets (the value of) the CSI processing capability of the STA based on information exchanged with the STA. The memory management unit 303 performs memory control and management for the memory unit 201. The UI control unit 304 transmits a control signal in response to an input operation by a user (not shown) to the input unit 204 to each component. The multi-AP configuration control unit 305 selects a multi-AP configuration method according to the presence of surrounding APs, the capabilities of the surrounding APs, and the connection state between the surrounding APs and the STAs, and executes the multi-AP configuration function. The sounding method determination unit 306 determines whether to perform sounding processing in an explicit method or an implicit method described below. The sounding processing unit 307 performs sounding processing according to the method determined by the sounding method determination unit 306. In this embodiment, the sounding processing is performed based on the CSI processing capabilities of the STAs.

[0021] 3(b) shows an example of the functional configuration of the STA. As an example of its functional configuration, the STA has a communication control unit 311, a UI control unit 312, a CSI processing capability determination unit 313, and a CSI calculation unit 314. The communication control unit 311 and the UI control unit 312 are similar to the communication control unit 301 and the UI control unit 304. The CSI processing capability determination unit 313 determines the CSI processing capability of the STA itself. The CSI calculation unit 314 performs CSI calculation processing.

[0022] [Processing flow] Next, the processing flow of the AP having the above configuration will be described with reference to the drawings. The following processing can be started when the AP starts the BSS or at any timing during the operation of the BSS.

[0023] <Connection processing between AP and STA> Figure 4 is a flowchart of the processing executed when AP102 starts a connection with STA103. In S401, the communication control unit 301 of AP102 exchanges the capability information and operation information of each other when connecting to STA103. This is realized by exchanging Management frames including Information Elements (IEs). The information elements have been newly defined in correspondence with the progress of IEEE802.11 standardization. For example, in IEEE802.11n, it is the HT Capability element, in IEEE802.11ac, it is the VHT Capability element, in IEEE802.11ax, it is the HE Capabilities element, and in IEEE802.11be, it is the EHT Capabilities element. Note that HT is an acronym for High Throughput, VHT is an acronym for Very High Throughput, HE is an acronym for High Efficiency, and EHT is an acronym for Extremely High Throughput. Also, Management frames are MAC (Medium Access Control) frames such as Beacon, Probe Request / Response, Association Reqest / Response, Authentiation Request / Response. The multi-AP cooperation function is a function introduced from the IEEE802.11be standard. Therefore, the capability information for this function is included in the EHT Capabilities element.

[0024] 7 shows the configuration of a MAC frame defined in the IEEE802.11 standard. A MAC frame 700 includes various fields. Frame Control 701 includes subfields 721 to 731. An information element (IE) of a Frame Body 710 includes subfields 741 to 747. Address 1 703, Address 2 704, Address 3 704, and Address 4 707 are set with addresses such as BSSID, source, and destination depending on the MAC frame type (Type 722). In addition, the MAC frame 700 includes Duration / ID 702, Sequence Control 706, QoS Control 708, and FCS (Frame Check Sequence) 711, but detailed description will be omitted.

[0025] HT Control 709 is defined in the IEEE802.11ax standard as follows: When the first bit is 0, it is for HT (IEEE802.11n), when the first two bits are 10, it is for VHT (IEEE802.11ac), and when the first two bits are 11, it is for HE (IEEE802.11ax). The definition of HTControl 709 for EHT (IEEE802.11be) has not yet been determined.

[0026] In Frame Control 701, Protocol Version 721 is a 2-bit number indicating the protocol version, and is "0" for IEEE802.11 frames. Type 722 is a 2-bit number indicating the frame type, indicating either Management, Control, or Data. Subtype 723 is a 4-bit number indicating the frame subtype, and is used to further classify the types of Management, Control, and Data. To DS 724 indicates that the destination of the frame is a DS (Distribution System). Frame Control 701 also includes From DS 725, More Fragment 726, Retry 727, Power Management 728, More Data 729, Protected Frame 730, and +HTC 731, but detailed explanations will be omitted.

[0027] In the Frame Body 710, subfields 741 to 747 are the configuration of the EHT Capabilities element for IEEE 802.11be. The value of Element ID 741 related to EHT in IEEE 802.11be follows the value of the HE Capabilities element of IEEE 802.11ax, and is 255. Length 742 is the length of the information element. In Element ID Extension 743, the EHT Capabilities element related to capability information or the EHT Operation element related to operation information is defined. EHT MAC Capabilities Information 744, EHT PHY Capabilities Information 745, Supported EHT-MCS and NSS Set 746, and PPE (Physical layer Packet Extension) Thresholds 747 are the same configuration as in the case of IEEE 802.11ax (HE Capabilities element).

[0028] In this embodiment, a subfield (CSI processing capability subfield) indicating the capability for calculating CSI by the STA (CSI processing capability / CSI calculation capability) is defined in the EHT MAC Capabilities Information 744. The CSI processing capability can be determined by the CSI processing capability determination unit 313 in the STA. A first example of the CSI processing capability subfield is a 1-bit number indicating "high" / "low" CSI processing capability. A second example of the CSI processing capability subfield is a 1-bit number indicating "able to respond to multiple sounding packets within SIFS (Short Inter Frame Space)" / "not able to respond". A third example of the CSI processing capability subfield is a time conversion value calculated from an equation consisting of the "number of transmitting / receiving antennas", "number of streams" and "arbitrary coefficient" of the AP and the STA. In this case, it is not limited to the 1-bit number. That is, it may be two or more values. A fourth example of the CSI processing capability subfield is a value similar to the expression format of the processing capability of the CPU. In this case, it is also not limited to the 1-bit number.

[0029] Note that the means for reporting the CSI processing capability is not limited to the above-mentioned CSI processing capability subfield. As another example, the HE Capabilities element may be used instead of the EHT Capabilities element. In this case, the capability representation value is 1 bit. This 1-bit restriction is due to the fact that 1 bit is reserved out of the 48-bit HE Capabilities element in the IEEE 802.11ax standard.

[0030] Another example of a method for reporting CSI processing capabilities is to use a new Action frame defined in the IEEE 802.11 standard. In this case, the capability representation of the reported information can be expressed in any number of bits.

[0031] Returning to the explanation of FIG. 4, in S401, the communication control unit 301 of the AP 102 exchanges capability information and the like with the STA 103, and then in S402, the CSI processing capability setting unit 302 of the AP 102 judges whether the CSI processing capability of the STA 103 has been acquired. If the CSI processing capability of the STA 103 has been acquired (Yes in S402), the process proceeds to S403. In S403, the memory management unit 303 sets a value indicating the acquired CSI processing capability in the STA management table. Here, the STA management table is an area that holds capability information and status of the STA required when the AP manages a BSS (Basic Service Set), and exists in the memory unit 201. If the CSI processing capability of the STA 103 has not been acquired in S402 (No in S402), the process proceeds to S404. In S404, the CSI processing capability setting unit 302 of the AP 102 judges whether the MinTrigProcTime of the STA 103 has been acquired. If the MinTrigProcTime of the STA 103 has been acquired (Yes in S404), the process proceeds to S405. The determination in S404 has the significance of confirming whether an index that serves as a substitute for a value indicating the CSI processing capability itself has been acquired.

[0032] Here, the value indicated by MinTrigProcTime will be explained. This value corresponds to the value of Trigger Frame MAC Padding Duration in the HE MAC Capabilities Information of IEEE802.11ax. This subfield is a 2-bit number, with 0 / 1 / 2 corresponding to 0 (zero) μsec / 8 μsec / 16 μsec of MinTrigProcTime, respectively. The name MinTrigProcTime comes from the "minimum value of preparation time for transmission using an RU (Resource Unit) specified by a Trigger Frame (TF)."

[0033] FIG. 8 shows the configuration of a trigger frame (Trigger Frame (TF)). The trigger frame is a frame newly introduced in IEEE 802.11ax, and is a frame for indicating the start timing and wireless channel information using the frame necessary for multiple STAs (users) to simultaneously transmit frames to an AP. The trigger frame 800 in FIG. 8 includes various fields. Frame Control 801 is a field common to the IEEE 802.11 series, and in this embodiment, a value indicating that it is an IEEE 802.11ax trigger frame is entered. Common Info 805 indicates information common to multiple STAs (terminals) that are the destinations of this trigger frame, and includes subfields 811 to 813. Per User Info 806 indicates individual information for the destination of this trigger frame. Padding 807 is for giving a time grace to the STAs that receive this trigger frame. The AP determines the time grace (i.e., the length of Padding 807) from the MinTrigProcTime of each STA. Generally, the length (value) of padding that corresponds to the maximum value of MinTrigProcTime among the STAs that are the destinations of the trigger frame is used. In addition, the trigger frame 800 includes Duration 802, RA (Receiver Address) 803, TA (Transmitter Address) 804, and FCS (Frame Check Sequence) 808, but detailed description is omitted.

[0034] In Common Info 805, the value indicated by Trigger Type 811 (Trigger Type subfield value) and the description corresponding to the value are shown in the table at the bottom of Fig. 8. For example, when Trigger Type 811 is 7, it indicates NFRP (NDP Feedback Report Poll) TF. Common Info 805 also includes Length 812 and Trigger Type Dependent 813, but detailed description is omitted.

[0035] Returning to the description of FIG. 4 again, in S405, the CSI processing capability setting unit 302 of the AP102 sets a value obtained by multiplying MinTrigProcTime by a predetermined coefficient as the value of the CSI processing capability, and the process proceeds to S403. Note that instead of multiplying MinTrigProcTime by a predetermined coefficient (multiplication), a predetermined constant may be subtracted. In any case, the smaller the value of MinTrigProcTime, the higher the CSI capability is treated.

[0036] In S404, if the MinTrigProcTime of the STA103 has not been obtained (No in S404), the process proceeds to S406. In S406, the CSI processing capability setting unit 302 of the AP102 sets the value of the CSI processing capability to a default value. For example, in the case of 1 bit number, this default value is a value meaning "low" or "unable to respond within SIFS for a plurality of sounding packets". The reason for estimating the CSI processing capability of an STA with unknown CSI processing capability to be low in this way is to surely execute the subsequent required processes regardless of the capability of the STA.

[0037] Note that if the STA103 does not notify the AP102 of the CSI processing capability in S401, the AP102 may inquire the STA103 about the CSI processing capability in S402.

[0038] <Data Generation to STA> FIG. 5 is a flowchart of the process executed when data to be transmitted to the STA103 is generated in the AP102. The data includes data from the STA106 to the STA103, data from an STA (not shown) in the BSS to the STA103, data from a terminal of the network 100 to the STA103, data from the AP102 to the STA103, and the like.

[0039] In S501, the communication control unit 301 of the AP 102 judges whether to transmit the generated data in a multi-AP cooperative configuration. If the data is to be transmitted in a multi-AP cooperative configuration (Yes in S501), the process proceeds to S502. In S502, the multi-AP configuration control unit 305 of the AP 102 executes a multi-AP cooperative function with the surrounding APs. Next, in S503, the AP 102 judges whether the AP itself operates as a Master-AP or a Slave-AP in the multi-AP cooperative configuration as a result of executing the multi-AP cooperative function. Here, the Master-AP is an AP that manages the multi-AP cooperative configuration, and the Slave-AP is an AP that operates under the control of the Master-AP. If the AP operates as a Master-AP (Yes in S503), the process proceeds to S507. The process of S507 will be described later with reference to FIG. 6. If the AP operates as a Slave-AP (No in S503), the process proceeds to S506.

[0040] If the answer is No in S503, this corresponds to the case in this embodiment where the Slave-AP is AP102 and the Master-AP is AP 105. In S506, the communication control unit 301 of AP102 transmits the CSI processing capability of the STA 103 to the Master-AP (i.e., AP 105). In the following S508, the sounding processing unit 307 of AP102 performs sounding processing of the Slave-AP.

[0041] If it is determined in S501 that transmission is not to be performed in a multi-AP cooperative configuration, the process proceeds to S505, and the AP 102 performs Single-AP transmission processing. This Single-AP transmission processing does not include any characteristic operation of the present invention, and therefore a description thereof will be omitted.

[0042] In this embodiment, it is assumed that the AP 102 that has performed the connection process with the STA 103 becomes the Master-AP, but on the other hand, the AP 102 may execute a multi-AP cooperative configuration function for the STA 106 that has performed the connection process with the Slave-AP (AP 105). In this case, after the process of S503, the AP 102 performs a process of receiving information transmitted by the AP 105 in the process of S506.

[0043] <Selection of Sounding Method for Master-AP> Next, the process of S507 in FIG. 5 will be described with reference to FIG. 6. In S601, the sounding method determination unit 306 of AP102 makes a selection as to whether to perform the sounding process in an explicit manner or an implicit manner. This selection can be made based on the capability information exchanged with STA103, the input information to the input unit 204 by the user, or a predetermined setting or the like.

[0044] Here, the explicit method and the implicit method will be described. In the explicit method, first, the AP (beamformer) transmits an NDP (Null Data Packet) as a sounding packet. The STA (beamformee) that receives the NDP calculates the CSI from the NDP and feeds it back to the AP. Thereby, the AP estimates the reception status of the packet it transmits at the STA.

[0045] In the implicit method, first, the STA transmits an NDP as a sounding packet, and the AP that receives the NDP estimates the status of the STA from the reception state of the packet. Thus, in the implicit method, the STA only needs to transmit the NDP at the specified timing, and compared with the explicit method, the processing load on the STA is less because the CSI calculation process is not required. Therefore, when the implicit method is selected in S601 (No in S601), the problem of an increase in the processing burden on the STA does not occur. Therefore, the description of the processing of the implicit method (S607) is omitted.

[0046] When the explicit mode is selected in S601 (Yes in S601), the process proceeds to S602. In S602, the subsequent process branches according to the value of the CSI processing ability of STA103. In the process of S403 in FIG. 4, when the value registered in the STA management table is a single bit number, it corresponds to "high" and "low". That is, when the value of the CSI processing ability is represented by two values indicating two levels of "high" / "low", the process branches to S603 or S606. When the resolution of the registered value is greater than 1 bit, it corresponds to "high", "medium", and "low". That is, when the value of the CSI calculation ability is represented by three or more values indicating three levels of "high" / "medium" / "low", the process branches to any of S603, S604, and S606.

[0047] When the CSI processing ability is "high", the process proceeds to S603. In S603, AP102 performs "NDP simultaneous transmission (without BFRP TF ((BeamForming Report Poll Trigger Frame))) processing". When the CSI processing ability is "medium", the process proceeds to S604. In S604, AP102 determines the length (time) of Padding in BFRP TF. This determination process is a process of shortening the CSI Padding time as the CSI processing ability increases for the same CSI processing ability classified as "medium". Next, in S605, AP102 performs "NDP simultaneous transmission (with BFRP TF) processing". When the CSI processing ability is "low", the process proceeds to S606. In S606, AP102 performs "NDP sequential transmission processing". The details of the processes of S603, S605, and S606 will be described later with reference to FIGS. 12 to 14 respectively. After the sounding process (any of S603, S605, and S606), data transmission processing is performed (S608).

[0048] <CSI calculation> Next, the CSI report field in the CSI frame generated (calculated) and transmitted by the STA will be described with reference to Fig. 9. Fig. 9 shows the configuration of the CSI report field. The CSI frame is, for example, an Action frame whose category is HT in the IEEE 802.11 standard, or an Action No Ack frame. This CSI frame is for notifying the beamformer of channel state information. Note that the Action frame is a frame in which Type 722 in Fig. 7 has a value of 00 and Subtype 723 has a value of 1101.

[0049] In FIG. 9, SNR in receive chain 1 901 is an 8-bit number, which is the signal-to-noise ratio (SN) of the receive chain of the STA that transmits the CSI report. Here, the receive chain is an entity that performs necessary signal processing on the received data. This signal processing includes filtering, amplification, down-conversion, and sampling. CSI Matrix for carrier 902 is a matrix derived from CHAN_MAT of RXVECTOR. Here, RXVECTOR is a set of parameters related to the reception of the physical layer of the 802.11 frame, and CHAN_MAT is one of the parameters. This CHAN_MAT indicates whether the frame includes CSI matrices or beamforming feedback matrices. Note that FIG. 9 shows the configuration of the CSI report field when the operating band is 20 MHz, but when the operating band is 40 MHz, CSI Matrix for carrier 902 becomes "-58 to -2" and "2 to 58". 9, Nb, Nc, and Nr are values ​​specified in a MIMO control field. Here, the MIMO control field is used to exchange channel state information or manage the transmission of beamforming feedback information.

[0050] FIG. 10(a) and FIG. 10(b) show the configurations of the MIMO control field before IEEE802.11ax and IEEE802.11ax, respectively. Note that the MIMO control field of IEEE802.11ax is also used in IEEE802.11be. Here, Nb is a number determined by the Coefficient Size field 1003 of the MIMO control field. Nc is the number of columns in the CSI Matrix determined by the Nc Index field 1001 of the MIMO control field. Nr is the number of rows in the CSI Matrix determined by the Nr Index field 1002 of the MIMO control field.

[0051] Meanwhile, the simultaneous transmission of sounding packets (NDP) by multiple APs in a multi-AP cooperative configuration is equivalent to an increase in the number of antennas on the transmitting side for the receiving side. Here, the amount of calculation of the CSI matrix increases according to the number of transmitting antennas, so the simultaneous NDP transmission increases the amount of CSI matrix calculation compared to the method of sequentially transmitting each NDP. Therefore, when executing the simultaneous NDP transmission method, in order to feedback the CSI report for the NDP within the SIFS time, the processing capacity per unit time in the STA must be higher than the processing capacity per unit time for the sequential method.

[0052] In consideration of this, in this embodiment, the AP 102 changes the sounding process according to the processing capacity of the STA 103, as in the branch of S602 in Fig. 6. This allows the feedback of CSI reports to all NDPs to be completed within a period based on a predetermined time (e.g., SIFS).

[0053] <Sequence diagram> Next, the operation sequence of AP 102 and STA 103 will be described with reference to Fig. 11 to Fig. 14. Fig. 11 is a sequence diagram of "from connection between AP and STA to selection of sounding method". In F1101, connection processing is performed between AP 102 and STA 103 (S401). This connection processing corresponds to the exchange of management frames such as Probe Request / Response, Association Request / Response, and Authentication Request / Response frames. In F1102, AP 102 checks whether it has acquired the CSI processing capability of STA 103 (S402). In F1103, AP 102 determines the CSI processing capability of STA 103. This processing includes calculating the CSI processing capability from MinTrigProcTime, requesting the CSI processing capability if it has not been acquired, and setting the CSI processing capability to a default value (S404 to S406). At F1104, AP102 registers its CSI processing capability in the STA management table (S403). At F1105, AP102 recognizes the generation of data addressed to STA103. At F1106, AP102 determines whether to establish a multi-AP cooperative configuration and transmit data (S501). At F1107, a multi-AP cooperative function is executed between AP102 and AP105 to establish a multi-AP cooperative configuration (S502). In this example, AP102 is assumed to be the Master-AP. At F1108, AP102 starts operating as the Master-AP. At F1109, AP105 starts operating as the Slave-AP. At F1110, AP102, which is the Master-AP, selects and determines whether the sounding method should be the explicit method or the implicit method (S601). In this example, the explicit method is selected. In F1111, the AP 102 checks the CSI processing capability of the STA 103 (S602). This is performed by referring to the STA management table. In F1112, the AP 102 selects a sounding method according to the CSI processing capability of the STA 103 (S602).

[0054] Next, the operation sequences of AP102 and STA103 in each sounding method selected in F1112 will be described with reference to FIGS. 12 to 14.

[0055] <NDP Simultaneous Transmission (without BFRP TF)> FIG. 12 shows a sequence when the CSI processing ability of STA103 is determined to be "high" (at "high" in S602), and the sounding method selected in F1112 of FIG. 11 is the case of "NDP simultaneous transmission (without BFRP TF)" (S603). At F1201, the AP102 transmits a sounding TF to AP105. This sounding TF is a frame used for the Master-AP and Slave-AP to transmit NDPs simultaneously. It is transmitted to the Slave-AP from the Master-AP. Although this sounding TF does not exist in the IEEE802.11ax standard, it can be realized by a frame in the same format as the trigger frame 800 in FIG. 8. In this case, the value of Trigger Type811 is any one of "8" to "15" which are reserved. At F1202, the AP102 transmits an NDPA (NDP Announcement) to STA103. This NDPA contains the STA Info List (STA information list) of the terminals to receive NDPs. This individual STA Info List is composed of an Association ID (AID12) in 12-bit format, a Feedback Type indicating whether it is SU (Single User) or MU (Multi User), and an Nc Index. At F1203, the AP105 transmits an NDPA to STA103. Here, F1202 and F1203 are performed after the SIFS has elapsed from F1201. At F1204, the AP102 transmits an NDP to STA103. At F1205, the AP105 transmits an NDP to STA103. Here, F1204 and F1205 are performed after the SIFS has elapsed from F1202 (F1203).

[0056] At F1206, the CSI calculation unit 314 of STA103 calculates the CSI. At F1207, STA103 transmits a frame including the CSI report field 900 of FIG. 9 to AP102. At F1208, AP102 shares CSI information with AP105. Note that this sharing may be performed when sharing data to STA103 between AP102 and AP105, or immediately before transmitting data to STA103. Note that the transmission in F1201 and F1203 may not be performed, and the transmission in F1202 may be performed. In this case, AP105 can control the destination and timing for NDP transmission in F1205 based on the content of the sounding TF in F1201 from AP102.

[0057] <NDP Simultaneous Transmission (with BFRP TF)> FIG. 13 shows a sequence when the CSI processing capability of STA103 is determined to be "medium" (at "medium" in S602), and the sounding method selected in F1112 of FIG. 11 is the case of "NDP simultaneous transmission (with BFRP TF)" (S604, S605). The processing from F1201 to F1205 is the same as that in the case of "NDP simultaneous transmission (without BFRP TF)" in FIG. 12.

[0058] The difference from FIG. 12 is that in F1301, the AP 102 transmits a BFRP TF (Beam Forming Report Poll Trigger Frame) to the STA 103. This BFRP TF can be realized by a frame of the same format as the trigger frame 800 in FIG. 8. In this case, the value of Trigger Type 811 is "7". Furthermore, the AP 102 determines CSI padding (S604). As described above, the AP 102 determines the CSI padding time for the same CSI processing capability classified as "medium" so that the CSI padding time is shorter as the CSI processing capability is higher. This means that the number of bits of the padding 807 in FIG. 8 is further increased. The padding 807 is data whose bit string is all 1. The STA (terminal) analyzing the structure of the trigger frame shown in FIG. 8 can determine that the Per User Info 806 has ended based on the data whose bit string is all 1. This determination is based on the IEEE802.11ax standard.

[0059] Furthermore, this termination decision allows the STA to allocate the computational resources of the control unit 202 from the analysis of the trigger frame to other processes. Note that the CSI calculation by the STA 103 at F1302 in Fig. 13 starts halfway through the CSI padding, which is a schematic representation of this. Here, in this sequence diagram, time passes from top to bottom. Also, the vertical length of F1302 is longer than the vertical length of F1206, which indicates that the CSI calculation capability of the STA 103 is low.

[0060] With such a BFRP TF configuration, the STA 103 can transmit CSI in F1207 after SIFS has elapsed from the end of the Padding 807 including the CSI padding. The processing in F1208 is the same as that in the case of “NDP simultaneous transmission (without BFRP TF)” in FIG. 12.

[0061] Note that in FIG. 13, after receiving the BFRP TF at F1301, STA103 starts CSI calculation at F1302. The flow of this process is an example. STA103 may start CSI calculation after receiving the NDP at F1204 and F1205, interrupt once when receiving the BFRP TF at F1301, and resume after the end determination of Per User Info806.

[0062] <NDP Sequential Transmission> FIG. 14 shows the sequence when the CSI processing ability of STA103 is determined to be "low" (at S602, "low") and the sounding method selected at F1112 in FIG. 11 is the case of "NDP Sequential Transmission" (S606). The processing of F1201 is the same as that in the case of "NDP Simultaneous Transmission (without BFRP TF)" in FIG. 12. At F1401, AP102 transmits an NDPA (NDP Announcement) to STA103. At F1402, AP105 transmits an NDPA to STA103. At F1403, AP102 transmits an NDP to STA103. At F1404, STA103 calculates and holds the CSI. At F1405, AP105 transmits an NDP to STA103. Thus, in the case of "NDP Sequential Transmission", AP102 (Master-AP) and AP105 (Slave-AP) transmit NDPs to STA103 at individual timings (F1403, F1405).

[0063] At F1406, STA103 calculates and holds the CSI. At F1407, AP102 transmits a BFRP TF to STA103. The CSI padding included in the BFRP TF transmitted by AP102 at F1301 in FIG. 13 is not added to this BFRP TF. The reason is based on the premise that in STA103, CSI calculation for one NDP can be completed within the SIFS time. The processing of F1207 and F1208 is the same as that in the case of "NDP Simultaneous Transmission (without BFRP TF)" in FIG. 12.

[0064] Although the above embodiment is applied to the general Multi-AP Coordination configuration, the use case may be limited to JTX (Joint Transmission) using D-MIMO (Distributed Multiple Input Multiple Output) or null steering.

[0065] In any of the cases of FIGS. 12 to 14, after AP 102 and AP 105 receive the CSI report, data transmission to STA 103 is performed under the control of AP 102 (S608).

[0066] As explained above, by performing sounding processing using a method determined according to the STA's CSI processing capability, each AP can obtain CSI from the STA at the desired timing without reducing the amount of information. This makes it possible to realize high-speed, high-efficiency, and stable wireless communication through a multi-AP cooperative configuration. In addition, by performing sounding without reducing the CSI information, it is possible to achieve the improvements in the usage efficiency of the wireless medium, the overall system and individual communication speed, and stability that the IEEE 802.11be standard aims for.

[0067] [Other embodiments] The present invention can also be realized by a process in which a program for implementing one or more of the functions of the above-described embodiments is supplied to a system or device via a network or a storage medium, and one or more processors in a computer of the system or device read and execute the program. The present invention can also be realized by a circuit (e.g., ASIC) that implements one or more of the functions.

[0068] The invention is not limited to the above-described embodiments, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0069] 101, 104 BBS (Basic Service Set), 102, 105 AP (Access Point), 103, 106 STA (Terminal Device)

Claims

1. A communication device that functions as a master AP in a multi-AP (access point) cooperative configuration that complies with the IEEE 802.11 series of standards, A selection means for selecting a sounding scheme, which is a transmission scheme of a null data packet (NDP) of an AP for receiving a CSI report as feedback from a terminal device connected to the communication device, from among a plurality of sounding schemes; A communication device comprising: a transmitting means for transmitting an NDP in accordance with the sounding method selected by the selecting means.

2. The communication device described in claim 1, characterized in that the selection means selects from among a plurality of sounding methods including at least a first sounding method in which the communication device and a slave AP in the multi-AP cooperative configuration simultaneously transmit an NDP, and a second sounding method in which the communication device and the slave AP transmit the NDP at individual timings.

3. 2. The communication device according to claim 1, wherein the selection means selects from among a plurality of sounding methods including at least a first sounding method in which the communication device and a slave AP in the multi-AP cooperative configuration simultaneously transmit an NDP, and a second sounding method in which the communication device transmits a BeamForming Report Poll Trigger Frame (BFRP TF) after the communication device and the slave AP simultaneously transmit the NDP.

4. The communication device according to claim 1, characterized in that the selection means selects from among a plurality of sounding methods including at least a first sounding method in which the communication device transmits a BeamForming Report Poll Trigger Frame (BFRP TF) after the communication device and the slave AP simultaneously transmit the NDP, and a second sounding method in which the communication device and the slave AP transmit the NDP at individual timings.

5. receiving means for receiving a predetermined frame including capability information related to sounding from the terminal device; 2. The communication device according to claim 1, wherein said selection means selects a sounding method based on said capability information regarding sounding.

6. The communication device according to claim 5 , wherein the sounding capability information is represented by two or more values.

7. The communication device according to claim 5 , wherein the sounding capability information is indicated by a value of Trigger Frame MAC Padding Duration.

8. The communication device according to claim 5 , wherein the capability information regarding the sounding is indicated by a Capabilities element in an information element in the predetermined frame.

9. 6. The communication device according to claim 5, wherein the predetermined frame is any one of a beacon, a probe request / response, an association request / response, and an authentication request / response frame.

10. A method for controlling a communication device that functions as a master AP in a multi-AP (access point) cooperative configuration conforming to the IEEE 802.11 series of standards, comprising the steps of: A selection step of selecting a sounding scheme, which is a transmission method of a null data packet (NDP) of an AP for receiving a CSI report as feedback from a terminal device connected to the communication device, from among a plurality of sounding schemes; A control method comprising: a transmitting step of transmitting an NDP in accordance with the sounding method selected in the selection step.

11. The control method described in claim 10, characterized in that in the selection process, a sounding method is selected from among a plurality of sounding methods including at least a first sounding method in which the communication device and a slave AP in the multi-AP cooperative configuration simultaneously transmit an NDP, and a second sounding method in which the communication device and the slave AP transmit the NDP at individual timings.

12. 11. The control method according to claim 10, characterized in that in the selection step, the sounding method is selected from among a plurality of sounding methods including at least a first sounding method in which the communication device and a slave AP in the multi-AP cooperative configuration simultaneously transmit an NDP, and a second sounding method in which the communication device transmits a BFRP TF (BeamForming Report Poll Trigger Frame) after the communication device and the slave AP simultaneously transmit the NDP.

13. 11. The control method according to claim 10, characterized in that in the selection step, a first sounding method is selected from among a plurality of sounding methods including at least a first sounding method in which the communication device transmits a BeamForming Report Poll Trigger Frame (BFRP TF) after the communication device and the slave AP simultaneously transmit the NDP, and a second sounding method in which the communication device and the slave AP transmit the NDP at individual timings.

14. The method further includes a receiving step of receiving a predetermined frame including capability information related to sounding from the terminal device; 11. The control method according to claim 10, wherein in the selection step, a sounding method is selected based on the capability information regarding sounding.

15. The control method according to claim 14, wherein the sounding capability information is represented by two or more values.

16. The method of claim 14, wherein the sounding capability information is represented by a value of Trigger Frame MAC Padding Duration.

17. The method according to claim 14, wherein the capability information regarding the sounding is indicated by a Capabilities element in an information element in the predetermined frame.

18. 15. The control method according to claim 14, wherein the predetermined frame is any one of a beacon, a probe request / response, an association request / response, and an authentication request / response frame.

19. A storage medium storing a program for causing a computer to function as the communication device according to any one of claims 1 to 9.

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