Access point device and communication method

Abstract

Provided is an access point device that communicates with a station device in cooperation with another access point, the access point device comprising a control unit that performs carrier sensing and acquires a transmission opportunity (TXOP), and a transmission unit that transmits a control frame to the other access point device. The control frame is used in order to share the acquired TXOP with the other access point device, and the length of the TXOP that can be acquired changes depending on whether the length of the TXOP aligns with the other access point device.

Description

Access point device and communication method

[0001] The present application claims priority to Japanese Patent Application No. 2024-109653, filed on July 8, 2024, the contents of which are incorporated herein by reference.

[0002] The Institute of Electrical and Electronics Engineers Inc. (IEEE) is continuously working on updating the specifications of IEEE 802.11, the wireless LAN (Local Area Network) standard, to achieve faster wireless LAN communication speeds, improved frequency utilization efficiency, highly reliable communication, and low latency communication. In next-generation wireless LANs, there is a growing demand for applications with advanced requirements, and access point (AP) cooperation is attracting attention as a way to achieve this. AP cooperation is being considered to share transmission opportunities (TXOPs) between APs to increase efficiency and to avoid or suppress interference with neighboring access points. AP cooperation is described in Non-Patent Document 1.

[0003] James Yee et al, “Multi AP Coordination and Residential Wi-Fi”, 11-22-1512r0, Sep. 2022.

[0004] However, since wireless LANs are systems that operate in unlicensed bands, it is necessary to consider the impact on existing communication devices. The present invention has been made in light of these circumstances, and its purpose is to provide an access point device and a communication method that improve throughput and frequency utilization efficiency while taking into consideration the impact on existing communication devices.

[0005] The access point device and communication method according to the present invention for solving the above-mentioned problems are as follows.

[0006] That is, an access point device according to one embodiment of the present invention is an access point device that communicates with a station device in cooperation with other access point devices, and is equipped with a control unit that performs carrier sensing and acquires a transmission opportunity (TXOP), and a transmission unit that transmits a control frame to the other access point devices, wherein the control frame is used to share the acquired TXOP with the other access point devices, and the length of the TXOP that can be acquired changes depending on whether or not the access point device cooperates with other access point devices.

[0007] In addition, in the access point device according to one aspect of the present invention, the TXOP length that can be acquired is limited depending on the number of cooperating access point devices.

[0008] In the access point device according to an aspect of the present invention, the number of cooperating access point devices is the number of members registered through negotiation between the access point devices.

[0009] In addition, in the access point device according to one aspect of the present invention, the number of access point devices that can cooperate is limited for each access category.

[0010] In addition, in an access point device according to one aspect of the present invention, the number of access points that can share the acquired TXOP is determined depending on the length of the acquired TXOP.

[0011] In addition, a communication method according to one embodiment of the present invention is a communication method in an access point device that communicates with a station device in cooperation with other access point devices, comprising the steps of performing carrier sensing and acquiring a transmission opportunity (TXOP) and transmitting a control frame to the other access point device, wherein the control frame is used to share the acquired TXOP with the other access point device, and the length of the TXOP that can be acquired varies depending on whether or not cooperation with other access point devices is performed.

[0012] According to the present invention, when access points cooperate with each other, the time resources acquired are limited, thereby improving throughput and frequency utilization efficiency while minimizing the impact on existing communication devices.

[0013] FIG. 1 is a diagram illustrating an example of a MAC layer frame configuration in a wireless LAN system. FIG. 2 is a diagram illustrating an example of a PPDU configuration in a wireless LAN system. FIG. 3 is a diagram illustrating an example of a sounding procedure in a wireless LAN system. FIG. 4 is a diagram illustrating an example of a configuration of a communication system according to an embodiment of the present invention. FIG. 5 is a block diagram illustrating an example of a configuration of a station device according to an embodiment of the present invention. FIG. 6 is a block diagram illustrating an example of a configuration of an access point device according to an embodiment of the present invention. FIG. 7 is a diagram illustrating an example of a C-TDMA procedure according to an embodiment of the present invention. FIG. 8 is a table illustrating an example of a relationship between an access category and a TXOP limit according to an embodiment of the present invention. FIG. 9 is a table illustrating an example of a relationship between the presence or absence of inter-AP cooperation and the TXOP limit according to an embodiment of the present invention. FIG. 10 is a table illustrating an example of a relationship between the number of cooperated APs and the TXOP limit according to an embodiment of the present invention. FIG. 11 is a table illustrating an example of a relationship between an access category and the maximum number of cooperated APs according to an embodiment of the present invention. FIG. 12 is a table illustrating an example of a relationship between the presence or absence of inter-AP cooperation and a CW size according to an embodiment of the present invention. FIG. 13 is a diagram illustrating an example of a C-RTWT procedure according to an embodiment of the present invention. FIG. 14 is a diagram illustrating an example of a relationship between the presence or absence of inter-AP cooperation and the R-TWT SP limit according to an embodiment of the present invention.

[0014] The wireless communication system in this embodiment includes an access point device (also referred to as an AP or base station device) and multiple station devices (also referred to as STAs or terminal devices). The communication system and network configured with the access point device and the station devices are referred to as a basic service set (BSS, management range). The station device according to this embodiment can have the functions of an access point device. Similarly, the access point device according to this embodiment can have the functions of a station device. Therefore, hereinafter, when simply referring to a communication device or a wireless communication device, the communication device or wireless communication device can refer to both the access point device and the station device.

[0015] The access point device and station devices within the BSS communicate based on CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance). This embodiment focuses on infrastructure mode, in which an access point device communicates with multiple station devices. However, the method of this embodiment can also be implemented in ad hoc mode, in which station devices communicate directly with each other. In ad hoc mode, a single station device acts as an access point device to form a BSS. A BSS in ad hoc mode is also referred to as an IBSS (Independent Basic Service Set). Hereinafter, a station device forming an IBSS in ad hoc mode can also be considered an access point device. The method of this embodiment can also be implemented in Wi-Fi Direct (registered trademark), in which station devices communicate directly with each other. In Wi-Fi Direct, one station device acts as an access point device to form a group. This station device is called a group owner and can also be considered an access point device.

[0016] In the IEEE 802.11 system, each device can transmit multiple types of frames (communication frames) with a common frame format, which are defined in the physical (PHY) layer, medium access control (MAC) layer, and logical link control (LLC) layer.

[0017] A PHY layer frame is called a physical protocol data unit (PPDU, PHY layer frame). A PPDU is composed of a physical layer header (PHY header) containing information for signal processing in the physical layer, and a physical service data unit (PSDU, PHY service data unit), which is a data unit processed in the physical layer. A PSDU can be composed of an aggregated MPDU (A-MPDU), which aggregates multiple MAC protocol data units (MPDU, MAC layer frames), which serve as retransmission units in wireless sections.

[0018] The PHY header includes reference signals such as a short training field (STF) used for signal detection and synchronization, and a long training field (LTF) used to acquire channel information for data demodulation, as well as control signals such as a signal (SIG) containing control information for data demodulation. Furthermore, STF is classified into Legacy-STF (L-STF), High Throughput-STF (HT-STF), Very High Throughput-STF (VHT-STF), High Efficiency-STF (HE-STF), Extremely High Throughput-STF (EHT-STF), etc. depending on the corresponding standard, and LTF and SIG are similarly classified into L-LTF, HT-LTF, VHT-LTF, HE-LTF, L-SIG, HT-SIG, VHT-SIG, HE-SIG, and EHT-SIG. VHT-SIG is further classified into VHT-SIG-A1, VHT-SIG-A2, and VHT-SIG-B. Similarly, HE-SIG is classified into HE-SIG-A1 to HE-SIG-A4 and HE-SIG-B. In addition, a Universal SIGNAL (U-SIG) field containing additional control information may be included, assuming technology updates within the same standard.

[0019] Furthermore, the PHY header can include information for identifying the BSS that is the sender of the frame (hereinafter also referred to as BSS identification information). The information for identifying the BSS can be, for example, the SSID (Service Set IDentifier) ​​of the BSS or the MAC address of the access point device of the BSS. The information for identifying the BSS can also be a value unique to the BSS (for example, a BSS Color) other than the SSID or MAC address. Information indicating the BSS Color can be included in the HE-SIG-A or U-SIG.

[0020] The PPDU is modulated according to the corresponding standard, for example, in the case of the IEEE 802.11n standard, it is modulated into an Orthogonal Frequency Division Multiplexing (OFDM) signal.

[0021] An MPDU consists of a MAC header containing information for signal processing at the MAC layer, a MAC Service Data Unit (MSDU) or frame body, which is a data unit processed at the MAC layer, and a Frame Check Sequence (FCS), which checks whether the frame is error-free (see Figure 1). Multiple MSDUs can also be aggregated as an Aggregated MSDU (A-MSDU).

[0022] Frame types in the MAC layer are broadly classified into three types: management frames that manage the connection status between devices, control frames that manage the communication status between devices, and data frames that contain actual transmission data. Each type is further classified into multiple subframe types. Control frames include acknowledgement (Ack or ACK) frames, block acknowledgement (BA or BlockAck) frames, request to send (RTS) frames, and clear to send (CTS) frames. BlockAck can acknowledge (notify completion of reception) multiple MPDUs. Management frames include beacon frames, probe request frames, probe response frames, authentication frames, association request frames, and association response frames. Data frames include data frames and polling (CF-poll) frames. Each device can recognize the frame type and subframe type of a received frame by reading the contents of the frame control field included in the MAC header.

[0023] A beacon frame includes a field indicating the period (beacon interval) at which the beacon is transmitted and the SSID. An access point device can periodically broadcast a beacon frame within a BSS, and a station device can recognize surrounding access point devices by receiving the beacon frame. The act of a station device recognizing an access point device based on a beacon frame broadcast by an access point device is called passive scanning. On the other hand, the act of a station device searching for an access point device by broadcasting a probe request frame within a BSS is called active scanning. An access point device can transmit a probe response frame in response to the probe request frame, and the content of the probe response frame is the same as the content of the beacon frame.

[0024] After recognizing an access point device, a station device performs a connection process with the access point device. The connection process is classified into an authentication procedure and an association procedure. The station device transmits an authentication request frame to the access point device with which it wishes to connect. Upon receiving the authentication request frame, the access point device transmits an authentication response frame to the station device, the authentication response frame including a status code indicating whether the station device has been authenticated. The station device can determine whether its authentication request has been approved by the access point device by reading the status code included in the authentication response frame. The access point device and station device can exchange authentication request frames and authentication response frames (both of which are collectively referred to as authentication frames) multiple times.

[0025] Following the authentication procedure, the station device transmits a connection request frame to the access point device to perform a connection procedure. Upon receiving the connection request frame, the access point device determines whether to permit the connection of the station device and transmits a connection response frame to notify the determination. The connection response frame contains a status code indicating whether the connection process is successful, as well as an association identifier (AID) for identifying the station device. The access point device can manage multiple station devices by setting different AIDs for each station device to which it has issued connection permission.

[0026] After the connection process is completed, the access point device and the station device perform actual data transmission. In the IEEE 802.11 system, the Distributed Coordination Function (DCF), the Point Coordination Function (PCF), and their extended Hybrid Coordination Function (HCF) are defined as media access methods. Specific implementation methods of the HCF include Enhanced Distributed Channel Access (EDCA) and HCF Controlled Channel Access (HCCA).

[0027] First, an example of the operation when an access point device transmits a signal to a station device based on DCF will be described. In DCF, the access point device and the station device perform carrier sense (CS) to check the usage status of the wireless channel around the device before communication. For example, if an access point device or a station device that is about to transmit a frame receives a signal with a received power higher than a predetermined clear channel assessment level (CCA level) on the wireless channel during the carrier sense period performed prior to transmission, the access point device or the station device postpones the transmission of the frame on the wireless channel. Hereinafter, a state in which a signal with a received power equal to or higher than the CCA level is detected on the wireless channel is referred to as a busy state, and a state in which a signal with a received power equal to or higher than the CCA level is not detected is referred to as an idle state. In this way, CS performed by each device based on the power level of the signal actually received is referred to as physical carrier sense (physical CS). The CCA level is also referred to as the carrier sense level (CS level) or the CCA threshold (CCAT). When the access point device and station device detect a signal with a reception power equal to or higher than the CCA level, they begin to demodulate at least the PHY layer signal.

[0028] An access point device performs carrier sensing during an interframe space (IFS) period set according to the type of frame to be transmitted, and determines whether the wireless channel is busy or idle. The period during which the access point device performs carrier sensing varies depending on the frame type and subframe type of the frame to be transmitted. The IEEE 802.11 system defines multiple IFS periods with different periods, including a short interframe space (SIFS) used for frames assigned the highest priority, a polling interframe space (PIFS: PCF IFS) used for frames with relatively high priority, and a distributed arbitration interframe space (DIFS: DCF IFS) used for frames with low priority. When transmitting data frames using DCF, the access point device uses the DIFS.

[0029] After waiting for the DIFS period, the access point device further waits for a random backoff time to prevent frame collisions. In the IEEE 802.11 system, a random backoff time based on a contention window (CW) is used. CSMA / CA assumes that a frame transmitted by a transmitting station is received by a receiving station without interference from other transmitting stations. Therefore, if multiple transmitting stations transmit frames at the same time, the frames may collide with each other, potentially preventing the receiving station from receiving the frames correctly. Therefore, frame collisions are avoided by each transmitting station waiting for a randomly set time before starting transmission. When the access point device determines that the wireless channel is idle through carrier sense, it starts counting down a backoff counter set based on the CW. Only when the backoff counter reaches 0 can it acquire the right to transmit and transmit a frame to the station device. If the access point device determines that the wireless channel is busy through carrier sense during the backoff counter countdown, it stops counting down the backoff counter. Then, when the wireless channel becomes idle again, the access point device waits for the same period as the previous IFS, and then resumes counting down the remaining part of the previous backoff counter.

[0030] The receiving station, a station device, receives the frame, reads the PHY header of the frame, and demodulates the received frame. The station device can then determine whether the frame is addressed to itself by reading the MAC header of the demodulated signal. The station device can also determine the destination of the frame based on information contained in the PHY header (e.g., a group identification number (GID: Group ID) contained in VHT-SIG-A).

[0031] If a station device determines that a received frame is addressed to itself and demodulates the frame without error, it must transmit an Ack frame to the access point device, which is the transmitting station, indicating that the frame was received correctly. The Ack frame is one of the highest-priority frames that is transmitted after waiting only an SIFS period (without a random backoff time). The access point device terminates a series of communications upon receiving the Ack frame from the station device. If the station device fails to receive a frame correctly, it will not transmit an Ack frame. Therefore, if the access point device does not receive an Ack frame from the receiving station (station device) within a certain period (SIFS + Ack frame length) after transmitting the frame, it will determine that the communication has failed and terminate the communication. Thus, the end of a single communication (also called a burst) in an IEEE 802.11 system is always determined by whether or not an Ack frame is received, except in special cases such as when a beacon frame or other notification signal is transmitted or when fragmentation is used to divide the transmitted data.

[0032] When a station device determines that a received frame is not addressed to the station device, the station device sets a network allocation vector (NAV) based on the length of the frame included in the PHY header or the like. The station device does not attempt transmission during the period set in the NAV. In other words, the station device performs the same operation as when it determines that the wireless channel is busy by physical CS during the period set in the NAV. Therefore, communication control using NAV is also called virtual carrier sense (virtual CS). In addition to being set based on information included in the PHY header, the NAV is also set by RTS frames and CTS frames introduced to solve the hidden terminal problem.

[0033] Next, an example of the operation when an access point device transmits a signal to a station device based on PCF will be described. Unlike DCF, in which each device performs carrier sensing and autonomously acquires the transmission right, in PCF, a control station called a Point Coordinator (PC) controls the transmission right of each device within the BSS. Generally, an access point device becomes the PC and acquires the transmission right of the station device within the BSS.

[0034] The communication period by PCF includes a contention-free period (CFP) and a contention period (CP). During the CP, communication is performed based on the DCF described above, and the PC controls the transmission right during the CFP. The access point device, which is the PC, broadcasts a beacon frame including information such as the CFP duration (CFP Max duration) within the BSS prior to PCF communication. Note that the beacon frame broadcast at the start of PCF transmission uses PIFS and is transmitted without waiting for the CW. A station device that receives the beacon frame sets the CFP Max duration included in the beacon frame in its NAV. Thereafter, until the period set in the NAV elapses or a signal announcing the end of the CFP (e.g., a data frame including CF-end) is received within the BSS, the station device can acquire the transmission right only when it receives a signal signaling acquisition of the transmission right for the device from the PC (e.g., a data frame including CF-poll). During the CFP period, no packet collisions occur within the same BSS, so each station device does not take the random backoff time used in DCF.

[0035] The wireless communication device has either a function for transmitting a PPDU or a function for receiving a PPDU, or both. Fig. 2 is a diagram showing an example of the configuration of a PPDU transmitted by a wireless communication device. A PPDU conforming to the IEEE 802.11a / g standard is configured to include an L-STF, an L-LTF, an L-SIG, and a Data frame (MAC frame, payload, data section, data, information bits, etc.). A PPDU conforming to the IEEE 802.11n standard is configured to include an L-STF, an L-LTF, an L-SIG, an HT-SIG, an HT-STF, an HT-LTF, and a Data frame. A PPDU conforming to the IEEE 802.11ac standard is configured to include some or all of the following: L-STF, L-LTF, L-SIG, VHT-SIG-A, VHT-STF, VHT-LTF, VHT-SIG-B, and a Data frame. A PPDU conforming to the IEEE 802.11ax standard is configured to include some or all of the following: L-STF, L-LTF, L-SIG, RL-SIG, which is a time-repeated L-SIG, HE-SIG-A, HE-STF, HE-LTF, HE-SIG-B, and a Data frame. The PPDU being considered for the IEEE 802.11be standardization is a structure that includes some or all of the L-STF, L-LTF, L-SIG, RL-SIG, U-SIG, EHT-SIG, EHT-STF, HET-LTF, and Data frames.

[0036] The L-STF, L-LTF, and L-SIG enclosed by dotted lines in Figure 2 are structures commonly used in the IEEE 802.11 standard (hereinafter, L-STF, L-LTF, and L-SIG are also collectively referred to as the L-header). For example, a wireless communication device compatible with the IEEE 802.11a / g standard can properly receive an L-header in a PPDU compatible with the IEEE 802.11n / ac / ax / be standard. A wireless communication device compatible with the IEEE 802.11a / g standard can receive a PPDU compatible with the IEEE 802.11n / ac / ax / be standard as a PPDU compatible with the IEEE 802.11a / g standard.

[0037] However, wireless communication devices that comply with the IEEE 802.11a / g standards cannot demodulate PPDUs that comply with the IEEE 802.11n / ac / ax / be standards that follow the L-header, and therefore cannot demodulate information related to the transmitter address (TA), receiver address (RA), duration / ID field, etc.

[0038] IEEE 802.11 specifies a method of inserting Duration information into L-SIG as a method for a wireless communication device conforming to the IEEE 802.11a / g standard to appropriately set NAV (or perform reception operation for a predetermined period of time). Information on the transmission rate in the L-SIG (RATE field, L-RATE field, L-RATE, L_DATARATE, L_DATARATE field) and information on the transmission period (LENGTH field, L-LENGTH field, L-LENGTH) are used by a wireless communication device conforming to the IEEE 802.11a / g standard to appropriately set NAV.

[0039] The wireless communication device can transmit the L-SIG multiple times (L-SIG Repetition). In this case, the receiving wireless communication device can improve the demodulation accuracy of the L-SIG by receiving the L-SIG transmitted multiple times using maximal ratio combining (MRC), for example. Furthermore, when the wireless communication device has correctly received the L-SIG using MRC, it can interpret the PPDU including the L-SIG as a PPDU that complies with the IEEE 802.11ax or IEEE 802.11be standard.

[0040] Even during a PPDU reception operation, the wireless communication device can perform a reception operation of a part of a PPDU other than the PPDU (for example, a preamble, L-STF, L-LTF, PHY header, etc., as defined by IEEE 802.11) (also referred to as a dual reception operation). When the wireless communication device detects a part of a PPDU other than the PPDU during a PPDU reception operation, the wireless communication device can update some or all of the information related to the destination address, source address, PPDU, or Data period.

[0041] Ack and BA can also be called responses (response frames). Also, probe responses, authentication responses, and connection responses can also be called responses.

[0042] Fig. 3 is a diagram showing an example of a sounding procedure for the purpose of channel estimation of a wireless communication path in IEEE 802.11ax. In the example shown in Fig. 3, an access point device (AP) first transmits a Null Data PPDU (NDP) Announcement frame 3001 that specifies information indicating a station device (STA) that will be the target of the upcoming sounding (the receiver of the sounding frame) and the type of feedback information. The access point device then transmits an NDP frame 3002 including a training field for channel estimation SIFS after the NDP Announcement frame. The station device performs channel estimation based on the received NDP frame 3002, and transmits a frame, such as a Compressed Beamforming / CQI frame 3003, that feeds back the channel estimation result to the access point device SIFS after the NDP frame 3002. [1. First Embodiment]

[0043] FIG. 4 is a diagram showing an example of a wireless communication system according to this embodiment. Wireless communication system 4003-1 includes wireless communication device 4001-1 and wireless communication devices 4002-1 to 4002-3. Wireless communication device 4001-1 is also referred to as access point device 4001-1, and wireless communication devices 4002-1 to 4002-3 are also referred to as station devices 4002-1 to 3. Wireless communication devices 4002-1 to 4002-3 (station devices 4002-1 to 4002-3) are also referred to as wireless communication device 4002A (station device 4002A) as devices connected to wireless communication device 4001-1. Wireless communication device 4001-1 and wireless communication device 4002A are wirelessly connected and are capable of transmitting and receiving PPDUs to and from each other. The wireless communication system according to this embodiment may also include wireless communication system 4003-2 in addition to wireless communication system 4003-1. Wireless communication system 4003-2 includes wireless communication device 4001-2 and wireless communication devices 4002-4 to 4002-6. Wireless communication device 4001-2 is also referred to as access point device 4001-2, and wireless communication devices 4002-4 to 4002-6 are also referred to as station devices 4002-4 to 4002-6. Wireless communication devices 4002-4 to 4002-6 (station devices 4002-4 to 4002-6) are also referred to as wireless communication device 4002B (station device 4002B) as devices connected to wireless communication device 4001-2. Furthermore, when wireless communication device 4001-1 and wireless communication device 4001-2 (access point devices 4001-1, 4001-6) are described without specifying each other, they are also referred to as wireless communication device 4001 (access point device 4001), and when wireless communication devices 4002-1 to 4002-6 (station devices 4002-1 to 4002-6) are described without specifying each other, they are also referred to as wireless communication device 4002 (station device 4002). Wireless communication system 4003-1 and wireless communication system 4003-2 form different BSSs, but this does not necessarily mean that the ESSs (Extended Service Sets) representing service sets forming LANs (Local Area Networks) are different.In other words, wireless communication devices belonging to the same ESS can be regarded as belonging to the same network from a higher layer. Furthermore, BSSs are connected via a DS (Distribution System) to form an ESS. Note that each of the wireless communication systems 4003-1 and 4003-2 can also include multiple wireless communication devices.

[0044] 5 is a diagram showing an example of the configuration of station device 4002. Station device 4002 includes a wireless control unit (wireless control step) 5001, a timer unit (timer step) 5002, a wireless communication unit (wireless communication step) 5003, and an antenna unit 5004. Furthermore, wireless communication unit 5003 includes a physical layer frame generation unit (physical layer frame generation step) 5003a, a wireless transmission unit (wireless transmission step) 5003b, a wireless reception unit (wireless reception step) 5003c, a received power measurement unit (received power measurement step) 5003d, a channel estimation unit (channel estimation step) 5003e, and a signal demodulation unit (signal demodulation step) 5003f.

[0045] The wireless control unit 5001 performs information processing on layers higher than the physical layer, such as the MAC layer and LLC layer, for information handled within the wireless communication device itself (such as information related to frames to be transmitted and MIB (Management Information Base)) and frames received from other wireless communication devices, and also controls the wireless communication unit 5003.

[0046] The timer unit 5002 includes one or more timers and manages the timers related to the sounding process. Details of the timer unit 5002 will be described later. Note that, in the example of Fig. 5, the timer unit 5002 is described as being included in the wireless control unit 5001, but is not limited to this configuration. The timer unit 5002 may be provided outside the wireless control unit 5001 and configured to operate under control from the wireless control unit 5001.

[0047] The physical layer frame generation unit 5003a has a function of generating a physical layer frame (PPDU). The physical layer frame generation unit 5003a performs error correction coding, modulation, beamforming processing (precoding processing), etc. on the MAC layer frame sent from the wireless control unit 5001. The beamforming processing may be realized by multiplying the modulated signal by a beamforming matrix (beamforming filter) notified by the wireless control unit 5001. The physical layer frame generation unit 5003a outputs the generated physical layer frame to the wireless transmission unit 5003b.

[0048] The wireless transmitting unit 5003b converts the physical layer frame input from the physical frame generating unit 5003a into a radio frequency (RF) band signal to generate a wireless signal. The processing performed by the wireless transmitting unit 5003b includes digital-to-analog conversion, filtering, frequency conversion from baseband frequency to wireless frequency, etc. The wireless transmitting unit 5003b transmits the generated wireless signal via the antenna unit 5004.

[0049] The wireless receiving unit 5003c has a function of converting a wireless signal received via the antenna unit 5004 into a baseband signal and generating a physical layer signal (for example, a physical layer frame). The processing performed by the wireless receiving unit 5003c includes frequency conversion processing from a wireless frequency to a baseband frequency, filtering, analog-to-digital conversion, etc. The physical layer signal, which is the received signal converted into a digital signal by the wireless receiving unit 5003c, is input to a received power measuring unit 5003d, a channel estimating unit 5003e, and a signal demodulating unit 5003f.

[0050] The received power measurement unit 5003d measures the received power of the received signal input from the wireless receiving unit 5003c. The received power measurement unit 5003d can measure the received power of the radio wave received on the frequency channel to be measured, the received power of the LTF of the received physical layer frame, etc. The received power measurement unit 5003d can notify the wireless control unit 5001 of the measurement result of the received power.

[0051] The channel estimation unit 5003e estimates the channel state through which the physical layer frame has propagated, based on the received signal of the LTF (L-LTF, HT-LTF, VHT-LTF, HE-LTF, etc.) included in the physical layer frame received by the wireless receiving unit 5003c. The channel estimation unit 5003e can notify the signal demodulation unit 5003f and the wireless control unit 5001 of the channel estimation result.

[0052] The signal demodulation unit 5003f performs channel equalization, demodulation, error correction decoding, etc. on the physical layer frame received by the wireless receiving unit 5003c, and acquires information such as the PHY header and MAC layer frame. The channel equalization process can use the channel estimation results of the channel estimator 5003e, etc. The signal demodulation unit 5003f outputs the acquired PHY header and MAC layer frame to the wireless control unit 5001.

[0053] The wireless control unit 5001 can perform physical carrier sensing and virtual carrier sensing based on the received power measurement results in the received power measuring unit 5003 d and information acquired in the signal demodulation unit 5003 f, and can determine the state of the wireless channel (including determining whether it is in an idle state or a busy state). The wireless control unit 5001 can notify the wireless communication unit 5003 of this wireless channel state determination information.

[0054] When there is control information, data, etc. to be transmitted, the wireless control unit 5001 can start a backoff procedure using the wireless channel state determination information. The wireless control unit 5001 generates a backoff counter based on the CW and has a countdown function for the backoff counter. For example, the wireless control unit 5001 can count down the backoff counter when the wireless channel state determination information indicates an idle state, and can stop the countdown of the backoff counter when the wireless channel state determination information indicates a busy state. Furthermore, the wireless control unit 5001 makes a transmission decision using either the wireless channel state determination information or the backoff counter value, or both. For example, the wireless control unit 5001 can notify the wireless communication unit 5003 of transmission decision information when the wireless channel state determination information indicates an idle state and the backoff counter value is 0. Furthermore, the wireless control unit 5001 can notify the wireless communication unit 5003 of transmission decision information when the wireless resource state determination information indicates an idle state.

[0055] FIG. 6 shows an example of the configuration of an access point device 4001. The access point device 4001 includes a wireless control unit (wireless control step) 6001, a wireless communication unit (wireless communication step) 5003, and an antenna unit 5004. Furthermore, the wireless communication unit 5003 includes a physical layer frame generation unit (physical layer frame generation step) 5003a, a wireless transmission unit (wireless transmission step) 5003b, a wireless reception unit (wireless reception step) 5003c, a received power measurement unit (received power measurement step) 5003d, a channel estimation unit (channel estimation step) 5003e, and a signal demodulation unit (signal demodulation step) 5003f. The access point device 4001 of FIG. 6 is basically configured similarly to the station device 4002 of FIG. 5. Therefore, the following description will focus on the differences between the two, and will omit a description of similar parts. Furthermore, parts corresponding to those in the station device of FIG. 5 will be described using the same reference numerals.

[0056] The wireless control unit 6001 processes information handled within the wireless communication device (such as information related to frames to be transmitted and MIB (Management Information Base)) and frames received from other wireless communication devices at layers higher than the physical layer, such as the MAC layer and LLC layer, and also controls the wireless communication unit 5003.

[0057] The physical layer frame generation unit 5003a has a function of generating a physical layer frame (PPDU). The physical layer frame generation unit 5003a performs error correction coding, modulation, beamforming processing (precoding processing), etc. on the MAC layer frame sent from the wireless control unit 6001. The beamforming processing may be realized by multiplying the modulated signal by a beamforming matrix (beamforming filter) notified by the wireless control unit 6001. The physical layer frame generation unit 5003a outputs the generated physical layer frame to the wireless transmission unit 5003b.

[0058] The received power measurement unit 5003d measures the received power of the received signal input from the wireless receiving unit 5003c. The received power measurement unit 5003d can measure the received power of the radio wave received on the frequency channel to be measured, the received power of the LTF (L-LTF, HT-LTF, VHT-LTF, HE-LTF, etc.) of the received physical layer frame, etc. The received power measurement unit 5003d can notify the wireless control unit 6001 of the measurement result of the received power.

[0059] The channel estimation unit 5003e estimates the channel state through which the physical layer frame has propagated, based on the LTF received signal included in the physical layer frame received by the wireless receiving unit 5003c. The channel estimation unit 5003e can notify the signal demodulation unit 5003f and the wireless control unit 6001 of the channel estimation result.

[0060] The signal demodulation unit 5003f performs channel equalization, demodulation, error correction decoding, etc. on the physical layer frame received by the wireless receiving unit 5003c, and acquires information such as the PHY header and MAC layer frame. The channel equalization process can use the channel estimation results of the channel estimator 5003e, etc. The signal demodulation unit 5003f outputs the acquired PHY header and MAC layer frame to the wireless control unit 6001.

[0061] When there is control information, data, a beacon, or the like to be transmitted, the wireless control unit 6001 can start a backoff procedure using the wireless channel state determination information. The wireless control unit 6001 generates a backoff counter based on the CW and has a countdown function for the backoff counter. For example, the wireless control unit 6001 can count down the backoff counter when the wireless channel state determination information indicates an idle state, and can stop the backoff counter countdown when the wireless channel state determination information indicates a busy state. Furthermore, the wireless control unit 6001 makes a transmission decision using either the wireless channel state determination information or the backoff counter value, or both. For example, the wireless control unit 6001 can notify the wireless communication unit 5003 of transmission decision information when the wireless channel state determination information indicates an idle state and the backoff counter value is 0. Furthermore, the wireless control unit 6001 can notify the wireless communication unit 5003 of transmission decision information when the wireless resource state determination information indicates an idle state.

[0062] To improve throughput and reliability, multiple access point devices can communicate in cooperation (cooperative). For example, there are several cooperation (cooperative) methods between access points, such as Coordinated Time Division Multiple Access (C-TDMA) and Coordinated Restricted Target Wake Time (C-RTWT), which coordinate and use time resources between access points.

[0063] Figure 7 shows an example of the C-TDMA cooperation process. Assume that AP1 and STA1 communicate via BSS1, and AP2 and STA2 communicate via BSS2. AP1 acquires a TXOP as a result of carrier sensing. AP1 and STA1 first exchange frames, but can share some or all of the remaining TXOP with AP2. To share a TXOP, a TXOP sharing (TXS) trigger frame (TF) is used. A trigger frame is a control frame that can be used to allocate resources for PPDU transmission. An AP / STA that receives a trigger frame sends a TB PPDU (trigger-based PPDU) in response. The TXS TF is used to share a TXOP with other APs / STAs. The TXS TF contains information indicating the destination with which the TXOP will be shared, the duration of the allocated TXOP, and whether the TXOP will be returned. If the destination is a STA, the STA that receives the TXS TF sends a non-TB PPDU in response. The Non-TB PPDU can be sent to the AP that sent the TXF TF or to another STA. If the destination is an AP, the AP that receives the TXS TF can exchange frames with the connected STA. In the example of FIG. 7, AP1 sends a TXF TF to AP2, and AP1's TXOP can be shared with AP2. AP2 can then exchange frames with STA2. After the TXOP period allocated by AP1 expires, if the information included in the TXS TF indicating whether to return the TXOP indicates that it should be returned, AP2 sends a TXOP return to AP1 indicating that it will return the TXOP. Note that in the example of FIG. 7, C-TDMA is performed between two access point devices, AP1 and AP2, but the present invention is not limited to this. C-TDMA can also be performed between three or more access point devices.

[0064] As described above, C-TDMA allows multiple APs to share TXOPs for communication. Therefore, since APs can cooperate to acquire TXOPs, the AP that acquires TXOPs first among multiple APs and the other APs will use C-TDMA. APs using C-TDMA are more likely to acquire TXOPs and can communicate more efficiently than existing (also called legacy) APs / STAs that do not cooperate to acquire TXOPs. However, the fact that C-TDMA prioritizes TXOP acquisition is considered unfair to existing APs / STAs. Therefore, fairness with existing APs / STAs must be considered. From the perspective of fairness, for example, the TXOP limit can be considered. The TXOP limit is the maximum TXOP duration that can be acquired in one carrier sense. The TXOP acquisition priority and the TXOP limit are related. Figure 8 shows an example of the TXOP limit. The example in Figure 8 shows the relationship between the TXOP acquisition priority and the available TXOP duration for each access category (AC). AC indicates QoS and has four options: background (AC_BK), best effort (AC_BE), video (AC_VI), and voice (AC_VO). CWmin is the minimum contention window size, and CWmax is the maximum contention window size. Also, aCWmin and aCWmax are set values; for example, aCWmin is 15 and aCWmax is 1023. Also, AIFSN (arbitration interframe space number) is used to calculate AIFS (arbitrary inter frame space). AIFS is the frame interval, and the smaller the AIFS, the higher the priority.

[0065] Figure 9 shows an example of the TXOP limit that can be acquired in the case of C-TDMA (AP cooperation). In C-TDMA, cooperation between APs makes it easier to acquire a TXOP, so the TXOP limit is set smaller with AP cooperation than without AP cooperation. Figure 10 shows an example of setting the TXOP limit based on the number of cooperating APs. As the number of cooperating APs increases, the TXOP limit is set shorter. When the number of cooperating APs is 1 (without AP cooperation), the TXOP limit is set to aTXOP, and as the number of cooperating APs increases, the TXOP limit is set shorter. Note that aTXOP is, for example, 4.096 msec. Furthermore, the TXOP limit may be set small depending on the access category. Further shortening the TXOP limit through AP cooperation may result in a decrease in communication efficiency. Therefore, the maximum number of cooperative APs that can cooperate with AP cooperation can be set for each access category. Figure 11 shows an example of access categories and the maximum number of cooperative APs. In the example of Figure 11, AC_BK and AC_BE are not permitted to acquire a TXOP using AP cooperation, and the maximum number of cooperative APs is set to 1. In addition, because AC_VO has a higher priority than AC_VI, the maximum number of APs that AC_VO cooperates with is set smaller than that of AC_VI. In addition, TXOP acquisition using inter-AP cooperation is not performed when the maximum number of APs that AC_VO cooperates with is exceeded.

[0066] It is also possible to set the contention window size depending on whether or not inter-AP cooperation is present. Figure 12 shows an example of setting CWmin and CWmax depending on whether or not inter-AP cooperation is present. This can be set for each access category, with (a) being an example for AC_VO and (b) being an example for AC_VI. In both (a) and (b) of Figure 12, the contention window size is set larger when inter-AP cooperation is present than when there is no inter-AP cooperation.

[0067] The number of cooperating APs may be the number of candidate APs to cooperate with or the number of APs that share a TXOP. For example, APs that may cooperate can be registered as members, and the number of registered members can be used as the number of candidate APs to cooperate with. The number of candidate APs to cooperate with may also be determined as a result of negotiation with neighboring APs. The number of APs that become able to cooperate as a result of negotiation with neighboring APs becomes the number of candidate APs to cooperate with. In this case, each candidate AP performs carrier sensing. The number of APs that share a TXOP is the number of APs that share a TXOP within a TXOP acquired by an AP. Note that the number of APs that share a TXOP may be unknown when the TXOP is acquired. In this case, the number of cooperating APs that can share a TXOP with an AP is limited to the number of cooperating APs determined by the length of the acquired TXOP. For example, in the example of Figure 10, if a TXOP is acquired with aTXOP / 2, the number of APs that can share the TXOP is limited to two.

[0068] Information regarding the number of APs that can share a TXOP and information regarding the TXOP limit when sharing a TXOP may be included in beacons or capability information and exchanged between access point devices. Information regarding the number of APs that can share a TXOP and information regarding the TXOP limit when sharing a TXOP may be shared between access point devices by defining information elements including information regarding the number of APs that can share a TXOP and information regarding the TXOP limit when sharing a TXOP and transmitting the information elements in beacon frames or various control frames. An access category (AC) to be used when sharing a TXOP between access point devices and some or all of the corresponding CWmin, CWmax, AIFSN, and TXOP limit may be newly defined and used to control the number of APs sharing a TXOP. Information regarding the access category to be used when sharing a TXOP between access point devices and information regarding the TXOP limit to be used when sharing a TXOP between access point devices may be shared between access point devices by transmitting the information elements in beacons as an EDCA parameter set to be used when sharing a TXOP between access point devices.

[0069] When an AP (also called a shared AP) receives a TXS TF in C-TDMA and shares a TXOP, it initializes the backoff counter to a random backoff number without using the remaining backoff counters before performing carrier sensing after completing frame exchange. The backoff counter to be initialized is the access category of the traffic communicated with the shared TXOP or all access categories.

[0070] Figure 13 shows an example of the C-RTWT coordination process. In C-RTWT, APs coordinate the R-TWT service period (SP). R-TWT is an extension of TWT, providing medium access protection and resource reservation for transmitting low-latency traffic. TWT is a function for reducing collisions between station devices and the time spent in an awake state. The period during which a station device is awake to transmit or receive data for TWT is called the TWT service period (SP). The start timing and duration (or wake period) of the TWT SP are transmitted by the access point via a management frame. The start timing and duration of the R-TWT SP are also transmitted via a management frame, similar to the TWT SP. The R-TWT SP is a period negotiated using the R-TWT setup. During the R-TWT SP, if the station device is an R-TWT member, it can transmit low-latency traffic with priority. In R-TWT setup (R-TWT membership setup), a station device can request (Request TWT) addition to the R-TWT member list from the access point device to which it is connected. If the Request TWT is accepted by the access point device (Accept TWT), the station device can become an R-TWT member. If the Request TWT is not accepted by the access point device (Reject TWT), the station device cannot become an R-TWT member. To protect the R-TWT SP, an access point device or station device that supports R-TWT completes a TXOP before the R-TWT SP. The access point device can set a quiet interval to overlap with the R-TWT SP. This quiet interval is set to prohibit access from non-R-TWT members. This protects the R-TWT SP from access by access point devices or station devices that do not support R-TWT.

[0071] When configuring the C-RTWT, each of multiple access point devices may exchange capability information with each other and may configure the R-TWT using information such as the beacon interval (or target beacon transmission time (TBTT)) included in this capability information. Beacon-related parameters used between cooperating access point devices may be common parameters, or beacon-related parameters such as TBTT set in one of the cooperating access point devices may be used by the other access point device. To exchange beacon-related parameters, an information element related to a beacon separate from the capability information may be prepared, and the beacon parameters to be configured between cooperating access point devices may be included in this information element. This parameter may indicate various information related to the beacon, such as the value of a Timing Synchronization Function (TFS) timer used by the cooperating access point devices, information related to the TFS timer such as the TFS timer offset value, the beacon interval, the beacon offset, the C-RWTW SP, or the C-RTWT offset value. The beacon offset is the offset of the beacon timing between access point devices, e.g., the difference in TBTT between each AP. The C-RTWT offset value is the offset value of the C-RTWT SP set between access point devices, e.g., the difference from the start timing of the R-TWT SP of the reference access point.

[0072] In the example of FIG. 13 , to protect the R-TWT SP from interference from neighboring cells (or overlapping BSSs (OBSSs)), APs cooperate to prevent the R-TWT SP (also referred to as the first R-TWT SP) set by a first access point device (AP1) from overlapping with the R-TWT SP (also referred to as the second R-TWT SP) set by a second access point device (AP2). When setting this R-TWT, the first access point device may refer to information contained in the beacon of the second access point device received by the first access point device or the beacon of the first access point device received by the second access point device. Alternatively, the R-TWT SP may be set by referring to previously exchanged capability information or parameters contained in information elements, such as information elements related to the beacon. Furthermore, the first R-TWT SP can be protected by AP2 and a station device (STA2) connected to AP2 terminating a TXOP before the first R-TWT SP. Furthermore, AP1 and a station device (STA1) connected to AP1 can protect the second R-TWT SP by terminating the TXOP before the second R-TWT SP. AP1 can set a quiet interval to overlap with the first R-TWT SP, and AP2 can set a quiet interval to overlap with the second R-TWT SP. While the example in FIG. 13 shows two access point devices cooperating with each other, the present invention is not limited to this example and also includes cases where three or more access point devices cooperate with each other. Similarly, when three or more access point devices cooperate with each other, the R-TWT SPs set by each access point device are configured so as not to overlap with each other.

[0073] As described above, in C-RTWT, the R-TWT SP is set so that it does not overlap between access point devices. Therefore, when there are many cooperating access point devices or when the R-TWT SP length per access point device is long, the communication time of existing (traditional, legacy) access point devices or station devices is significantly limited, resulting in fairness issues. Therefore, it is necessary to set the R-TWT SP with fairness in mind. FIG. 14 shows an example of limiting the R-TWT SP length depending on whether or not APs are cooperating. Note that the R-TWT SP length limit is also referred to as the R-TWT SP limit. In the example of FIG. 14, the R-TWT SP limit can be set to 4.096 ms without AP cooperation and 2.080 ms with AP cooperation. Compared to when APs are not cooperating, the R-TWT SP limit is set shorter when APs are cooperating. FIG. 15 also shows an example of setting the R-TWT SP limit depending on the number of cooperating APs. When the number of cooperating APs is 1 (no inter-AP cooperation), the R-TWT SP limit is set to aRTWTSP, and as the number of cooperating APs increases, the R-TWT SP limit is set to a shorter value. For example, aRTWTSP can be set to 4.096 ms. Information indicating the R-TWT SP limit used by C-RTWT may be included in the beacon, or may be included in the capability information and shared between access point devices.

[0074] Note that the number of APs that can cooperate may be limited by the beacon interval, since the R-TWT SP limit may become shorter depending on the beacon interval. The beacon interval is the time interval between two consecutive target beacon transmission times (TBTT). For example, if the beacon interval is longer than a certain threshold, the number of cooperated APs may be set to four, and if the beacon interval is shorter than a certain threshold, the number of cooperated APs may be set to two. In addition, the number of cooperated APs may be determined for each time range of the beacon interval.

[0075] The number of associated APs can be determined by the number of access points that set R-TWT SPs without overlapping, or the number of access points that set R-TWT SPs within a beacon interval. The number of candidate APs to associate with can also be determined as the number of associated APs. The number of associated APs can be determined as the number of access points that become capable of association as a result of C-RTWT negotiation. Access points that become capable of association may become members of the C-RTWT.

[0076] The communication device according to the present invention can communicate in a frequency band (frequency spectrum) that does not require permission to use from a country or region, which is called an unlicensed band, but the usable frequency band is not limited to this. The communication device according to the present invention can also be effective in, for example, a frequency band called a white band that is not actually used for purposes such as preventing interference between frequencies even though permission to use it for a specific service is granted by a country or region (for example, a frequency band allocated for television broadcasting but unused in some regions), or in a shared spectrum (shared frequency band) that is expected to be shared by multiple operators.

[0077] The program running on the wireless communication device according to the present invention is a program that controls the CPU and other components (programs that cause a computer to function) to implement the functions of the above-described embodiments of the present invention. Information handled by these devices is temporarily stored in RAM during processing, and then stored in various ROMs or HDDs. The information is then read, modified, and written by the CPU as needed. The recording medium for storing the program may be a semiconductor medium (e.g., a ROM, a non-volatile memory card, etc.), an optical recording medium (e.g., a DVD, an MO, an MD, a CD, a BD, etc.), a magnetic recording medium (e.g., a magnetic tape, a flexible disk, etc.), or the like. Furthermore, not only are the functions of the above-described embodiments implemented by executing the loaded program, but the functions of the present invention may also be implemented by processing in cooperation with an operating system or other application programs, etc., based on instructions from the program.

[0078] Furthermore, when distributing the program on the market, the program can be stored and distributed on a portable recording medium, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server computer is also included in the present invention. Furthermore, part or all of the communication device in the above-described embodiments may be realized as an LSI, which is typically an integrated circuit. Each functional block of the communication device may be individually formed into a chip, or part or all of the functional blocks may be integrated into a chip. When each functional block is formed into an integrated circuit, an integrated circuit control unit that controls them is added.

[0079] Furthermore, the method of integration is not limited to LSI, but may be realized by a dedicated circuit or a general-purpose processor. Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology, it may also be possible to use an integrated circuit based on that technology.

[0080] It should be noted that the present invention is not limited to the above-described embodiments. The wireless communication device of the present invention is not limited to application to mobile station devices, but can of course be applied to stationary or non-mobile electronic devices installed indoors or outdoors, such as AV equipment, kitchen equipment, cleaning / washing equipment, air conditioning equipment, office equipment, vending machines, and other household appliances.

[0081] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included in the scope of the claims.

[0082] The present invention is suitable for use in an access point device and a communication method.

[0083] 10-1 to 10-4 Station devices 11-1 to 11-3 Station devices 20-1, 20-2, user groups 30-1, 30-2, sub-user groups 3001 NDP Announcement frame 3002 NDP frame 3003 Compressed Beamforming / CQI frame 4001-1, 4001-2 Wireless communication devices (access point devices) 4002-1 to 4002-6 Wireless communication devices (station devices) 4003-1, 4003-2 Wireless communication system 5001 Wireless control unit 5002 Timer unit 5003 Wireless communication unit 5003a Physical layer frame generation unit 5003b Wireless transmission unit 5003c Wireless reception unit 5003d Received power measurement unit 5003e Channel estimation unit 5003f Signal demodulation unit 5004 Antenna unit 6001 Wireless control unit

Claims

1. An access point device that communicates with a station device in cooperation with other access points, comprising: a control unit that performs carrier sensing and acquires a transmission opportunity (TXOP); and a transmission unit that transmits a control frame to the other access point device, wherein the control frame is used to share the acquired TXOP with the other access point device, and the length of the TXOP that can be acquired changes depending on whether or not the access point device cooperates with other access point devices.

2. The access point device according to claim 1, wherein the length of a TXOP that can be acquired is limited according to the number of associated access point devices.

3. The access point device according to claim 2, wherein the number of cooperating access point devices is the number of members registered through negotiation between the access point devices.

4. The access point device according to claim 1, wherein the number of access point devices that can cooperate is limited for each access category.

5. The access point device according to claim 1, wherein the number of access points that can share the acquired TXOP is determined by the length of the acquired TXOP.

6. A communication method in an access point device that communicates with a station device in cooperation with another access point device, comprising the steps of: performing carrier sensing and acquiring a transmission opportunity (TXOP); and transmitting a control frame to the other access point device, wherein the control frame is used to share the acquired TXOP with the other access point device, and the length of the TXOP that can be acquired varies depending on whether or not cooperation with another access point device is performed.

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