Communication device, control method, and program

Abstract

To reduce communication collisions between a communication device that acquires TXOP and shares it with other communication devices and the other communication devices in the surroundings.SOLUTION: The communication device acquires a Transmission Opportunity (TXOP) for transmitting a wireless frame. The communication device ensures a first TXOP period using a first wireless frame. The communication device allocates a second TXOP period of the first TXOP period to other communication devices using a Trigger frame. The communication device receives a predetermined control frame indicating that the second TXOP period is to be terminated during the second TXOP period. When the communication device receives the predetermined control frame during the second TXOP period, it controls transmission of a second wireless frame after a predetermined Inter Frame Space (IFS) time has elapsed from reception. The communication device controls the transmission of the second wireless frame on the basis of a predetermined condition.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a communication device that performs wireless communication, a control method for the communication device, and a program.

Background Art

[0002] In recent years, with the increase in the amount of data to be communicated, the development of communication technologies such as wireless LAN (Local Area Network) has been promoted. As the main communication standards for wireless LAN, the IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard series is known. The IEEE 802.11 standard series includes standards such as IEEE 802.11a / b / g / n / ac / ax. Currently, the standardization of the IEEE 802.11be standard, which is the successor standard to IEEE 802.11ax, is in progress.

[0003] In addition, as a channel access method of the IEEE802.11 standard, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) method is known. In the case of this CSMA / CA method, a communication device attempting to start communication must always check whether other surrounding communication devices are emitting radio waves before starting communication. After confirming that no other surrounding communication devices are emitting radio waves (the channel is in an idle state), communication is started. For example, when other surrounding communication devices are emitting radio waves (the channel is in a busy state), it waits for a certain period (IFS: Inter Frame Space), and after the said period, it checks again whether other surrounding communication devices are emitting radio waves. As a result of the check, if the channel is in an idle state, it waits for a certain random waiting time. And if the channel is still in an idle state after waiting for the random waiting time, it is considered to have acquired a Transmission Opportunity (TXOP), and communication is started. Also, a communication device that has acquired a transmission opportunity declares the time of the said transmission opportunity (TXOP period) in the first frame to be transmitted, thereby causing other surrounding communication devices to set a Network Allocation Vector (NAV) for the TXOP period. Other surrounding communication devices are controlled not to perform the above-mentioned channel access process regardless of whether the channel is in an idle state during the period when the NAV is set due to this NAV setting.

[0004] In addition, a Contension Free-End (CF-End) frame is known as a radio frame for releasing the set NAV. This is a radio frame used when a communication device securing a TXOP notifies other surrounding communication devices, thereby informing them of the end of the TXOP period. Therefore, a communication device that has received a CF-End frame releases the NAV set in its own device, thereby restarting the above-mentioned channel access process.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2021-103805 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] In addition, in the above-mentioned IEEE802.11be, a mechanism called TXOP sharing is being considered. This is a mechanism in which a part of the TXOP acquired by an AP (Access Point) is allocated to a STA (Station), and the TXOP secured by the AP is shared with the STA. Also, a mechanism in which a part of the TXOP acquired by the AP is allocated to the STA by the AP sending a Trigger frame to the STA is called Triggered TXOP sharing. By sharing the TXOP acquired by the AP with the STA designated by the AP in this way, only the AP and the designated STA can communicate during the period of this shared TXOP. That is, by prohibiting communication of non-designated STAs during this shared TXOP period, it is possible to avoid communication collisions and channel utilization by unnecessary transmission frames, and communication efficiency can be improved.

[0007] Also, in TXOP sharing, when the STA that shares the TXOP ends communication before the end of the period of the shared TXOP, it is being considered to notify the end of the use of the TXOP period by transmitting a CF-End frame. As a result, it becomes possible to return the remaining TXOP period to the AP, and the AP can start communication during the remaining TXOP period as needed.

[0008] However, in other surrounding communication devices that have received the CF-End frame, although the AP has secured the remaining TXOP period, it is assumed that the NAV set in the own device is released and communication is started. Therefore, if a communication device that has released the NAV starts communication after waiting for the same waiting time as the AP that has secured the TXOP period, there is a risk that the communication between the communication device and the AP that has secured the TXOP period will collide.

[0009] In view of the above problems, one object of the present invention is to reduce the collision of communication between a communication device that has acquired a TXOP and shared it with other communication devices and other surrounding communication devices.

Means for Solving the Problems

[0010] To achieve the above object, a communication device according to an aspect of the present invention includes an acquisition means for acquiring a Transmission Opportunity (TXOP) for transmitting a wireless frame, and a securing means for securing a first TXOP period using a first wireless frame. A sharing means for allocating a second TXOP period within the first TXOP period to other communication devices using a Trigger frame, a receiving means for receiving a predetermined control frame indicating the end of the second TXOP period in the second TXOP period, and when the predetermined control frame is received in the second TXOP period, control means for controlling to transmit a second wireless frame after a predetermined Inter Frame Space (IFS) time has elapsed from the reception, and the control means controls to transmit the second wireless frame based on a predetermined condition.

Effects of the Invention

[0011] According to one aspect of the present invention, it is possible to reduce the collision of communication between a communication device that has acquired a TXOP and shared it with other communication devices and other surrounding communication devices.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0014] (Network Configuration) FIG. 1 shows an example of the network configuration according to the present embodiment. The network of the present embodiment has networks (100, 110, 111 respectively) constructed by three access point (hereinafter referred to as AP) devices (AP101, AP102, AP103). A station (hereinafter referred to as STA) device (STA105) participates in network 100, and STA104 participates in network 110. Hereinafter, AP101 to 103 and STA104 to 105 are collectively referred to as communication devices.

[0015] Each communication device is configured to be capable of performing communication of wireless frames compliant with the IEEE 802.11bn standard, which is a successor standard to the IEEE 802.11be standard and aims for a maximum transmission speed exceeding 90 Gbps - 100 Gbps. Similarly, STA104 and STA105 are also configured to be capable of performing communication of wireless frames compliant with IEEE 802.11bn. Note that IEEE is an abbreviation for Institute of Electrical and Electronics Engineers. In this IEEE 802.11bn, support for high-reliability communication, low-latency communication, and AP cooperation are listed as the main features. The wireless frame communicated using the successor standard is also referred to as a UHR (Ultra High Reliability) PPDU. PPDU is an abbreviation for physical layer (PHY) protocol data unit.

[0016] Note that the name UHR is provided for convenience based on the goals to be achieved by the successor standard and the prominent features of the standard, and it may be replaced by another name when the standard formulation is completed. Similarly, the name IEEE 802.11bn may also be replaced by another name when the standard formulation is completed. On the other hand, it should be noted that this specification and the appended claims are essentially applicable to all successor standards that are successor standards to the 802.11be standard. Each communication device can communicate at frequencies in the 2.4 GHz band, 3.6 GHz band, 5 GHz band, 6 GHz band, and the 45 GHz band and 60 GHz band called millimeter waves. The frequency band used by each communication device is not limited to this, and for example, different frequency bands such as the Sub1GHz band may be used. Each communication device can communicate using bandwidths of 20 MHz, 40 MHz, 80 MHz, 160 MHz, 320 MHz, 540 MHz, 640 MHz, 1080 MHz, and 2160 MHz. The bandwidth used by each communication device is not limited to this, and for example, different bandwidths such as 240 MHz and 4 MHz may be used.

[0017] Note that, in FIG. 1, as an example, a wireless network composed of three APs and two STAs is shown. However, the number of these devices may be more or less than that shown, and any network configuration composed of at least two APs is acceptable.

[0018] APs 101 to 103 are APs that perform cooperative operations, and AP 101 is an AP that performs overall control for cooperation. In the present embodiment, an AP such as AP 101 that performs overall control is also referred to as a Coordinator AP. Further, APs 102 to 103 are APs that function as controlled devices controlled by the Coordinator AP. In the present embodiment, APs such as APs 102 to 103 that are controlled by the Coordinator AP are also referred to as Coordinated APs.

[0019] Also, APs 101 to 103 can perform cooperative operations. Specifically, AP 101 can allocate part or all of the transmission opportunity (TXOP: transmission opportunity) period (TXOP period) of wireless frames in the communication channel secured by itself to AP 102. AP 102 to which the TXOP period is allocated can transmit wireless frames to STAs participating in its own wireless network or surrounding APs during the period. Note that, in the present embodiment, the backhaul line for transmitting and receiving data and control signals between the APs for performing the cooperative operations of the above-described APs uses a communication path using a wireless medium.

[0020] AP101 to AP103 can perform MU (Multi User) communication that communicates with multiple STAs simultaneously using OFDMA technology. In MU communication using OFDMA technology, one channel is divided into multiple sub-channels called RUs (Resource Units). Then, by treating each of the divided RUs as a resource for communicating with different STAs (which may be a group of STAs composed of multiple STAs), it becomes possible for the AP and multiple STAs to communicate simultaneously on one channel. In this case, an MU (Multi User) PPDU in which data is modulated by OFDMA is transmitted from the AP to one or more STAs. When all devices comply with the IEEE802.11bn standard, it is assumed that a UHR MU PPDU, which is an MU PPDU compliant with the IEEE802.11bn standard, is transmitted to one or more STAs.

[0021] Also, each communication device may be an MLD (Multi-Link Device) capable of establishing a plurality of parallel links via a plurality of different frequency channels with other communication devices. Each communication device that is an MLD can perform multi-link communication with other communication devices by establishing the plurality of links in parallel with other communication devices.

[0022] Each communication device is assumed to be compliant with the IEEE802.11bn standard. In addition to this, it may also be compliant with legacy standards that are older than the IEEE802.11bn standard. Specifically, AP101 and STA102 may be compliant with at least one of the IEEE802.11a / b / g / n / ac / ax / be standards. Also, in addition to the IEEE802.11 series of standards, it may be compliant with other communication standards such as Bluetooth (registered trademark), NFC, BLE (registered trademark), UWB, ZigBee, MBOA, etc. Note that UWB is the abbreviation for Ultra Wide Band, and MBOA is the abbreviation for Multi Band OFDM Alliance. Also, NFC is the abbreviation for Near Field Communication, and BLE is the abbreviation for Bluetooth Low Energy. UWB includes wireless USB, wireless 1394, WiNET, etc. It may also be compliant with the communication standards of wired communication such as wired LAN. Specific examples of AP101 to 103 include, but are not limited to, wireless LAN routers and personal computers (PCs). Also, AP101 to AP103 may be information processing devices such as wireless chips that can execute wireless communication compliant with the IEEE802.11bn standard. Specific examples of STA104 and STA105 include, but are not limited to, cameras, tablets, smartphones, PCs, mobile phones, video cameras, headsets, etc. Also, STA104 and STA105 may be information processing devices such as wireless chips that can execute wireless communication compliant with the IEEE802.11bn standard.

[0023] In this embodiment, it is assumed that the BSSIDs corresponding to the respective wireless networks when AP101 to AP104 provide a wireless network are all different. Note that BSSID is an abbreviation for Basic Service Set Identifier and is an identifier for identifying an access point. On the other hand, it is assumed that the SSIDs indicated by AP101 to AP103 in each wireless network are all common. Note that SSID is an abbreviation for Service Set Identifier and is an identifier for identifying a wireless network.

[0024] (Hardware Configuration of Communication Device) FIG. 2 shows an example of the hardware configuration of each communication device (AP and STA). As an example of its hardware configuration, the communication device includes a storage unit 201, a control unit 202, a functional unit 203, an input unit 204, an output unit 205, a communication unit 206, and an antenna 207.

[0025] The storage unit 201 is composed of both a ROM and a RAM, or either one of them, and stores programs for performing various operations described later and various information such as communication parameters for wireless communication. RAM is an abbreviation for Random Access Memory, and ROM is an abbreviation for Read Only Memory. Note that as the storage unit 201, in addition to memories such as ROM and RAM, storage media such as non-volatile storage devices such as hard disks and SSDs (Solid State Drives) may be used.

[0026] The control unit 202 is composed of, for example, a processor such as a CPU or MPU, an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), etc. Here, CPU is the abbreviation of Central Processing Unit, and MPU is the abbreviation of Micro Processing Unit. The control unit 202 executes the program stored in the storage unit 201 and controls the entire device by operating the hardware circuit such as an ASIC. Note that the control unit 202 may control the entire device in cooperation with the program stored in the storage unit 201 and the OS (Operating System).

[0027] Further, the control unit 202 controls the functional unit 203 to execute predetermined processes such as imaging, printing, and projection. The functional unit 203 is hardware for the device to execute predetermined processes. For example, when the communication device is a camera such as a digital still camera or a smartphone having a camera, the functional unit 203 is an imaging unit, and performs imaging processing of surrounding images via a camera unit (not shown) included in the communication device. Also, for example, when the communication device is a printer, the functional unit 203 is a printing unit, and performs printing processing on a sheet such as paper based on print data obtained by wireless communication from the outside. Also, for example, when the communication device is a projector or smart glasses, the functional unit 203 is a projection unit, and performs projection processing of image data or video data obtained by wireless communication from the outside. In the case of smart glasses, the projection surface is the retina of the end user or the like. The data processed by the functional unit 203 may be data stored in the storage unit 201, or may be data communicated with other APs or STAs via the communication unit 206 described later. Furthermore, a communication device such as AP101 can also provide a network storage function such as NAS (Network Attached Storage). The said function is provided to other communication devices as a web service such as a network storage service. For example, a communication device such as an STA connects to the network storage services provided by APs 101 to 103 etc. using protocols such as SMB, FTP, and WebDAV. Then, a communication device such as an STA uploads a file to the said storage service or downloads a file in the said storage. The data communication for the said upload and download is also realized by communicating UHR PPDU between devices.

[0028] The input unit 204 receives various operations from the user. The output unit 205 performs various outputs to the user. Here, the output by the output unit 205 includes, for example, at least one of display on the screen, voice output by the speaker, and vibration output. Note that both the input unit 204 and the output unit 205 may be realized by one module such as a touch panel.

[0029] The communication unit 206 controls wireless communication compliant with the IEEE 802.11 standard series and IP communication. In this embodiment, the communication unit 206 can execute communication control for transmitting and receiving a UHR PPDU, which is a wireless frame of the UHR standard, and a PPDU corresponding to a previous standard in cooperation with the antenna 207. The antenna 207 is, for example, an antenna capable of transmitting and receiving signals in at least any one of the frequency bands of the sub-GHz band, 2.4 GHz band, 5 GHz band, 6 GHz band, and millimeter wave band. In this embodiment, it is assumed to have three antennas, but one antenna may be used, or a plurality of different antennas may be provided for each frequency band. Further, when there are a plurality of antennas, the communication unit 206 corresponding to each antenna may be provided.

[0030] In addition, when the communication device supports the above-described NFC standard, Bluetooth standard, wired communication standard, etc., the communication unit 206 may be configured to control wireless communication and wired communication compliant with these communication standards.

[0031] (Functional Configuration of Communication Device) Subsequently, FIG. 3 shows an example of a block diagram of the functional configuration of the communication device (AP and STA). In this embodiment, each functional block is stored as a program in the storage unit 201, and the function is implemented by executing the program by the control unit 202. The control unit 202 realizes each function by controlling each hardware and performing calculation and processing of information by executing the program. Note that part or all of the functional blocks included in this may be implemented in hardware. In this case, part or all of the functional blocks included are configured by, for example, an ACIC (Application Specific Integrated Circuit).

[0032] In this embodiment, the communication device includes a frame generation unit 301, a frame analysis unit 302, a wireless communication control unit 303, a TXOP sharing control unit 304, a Multi-AP control unit 305, a UI control unit 306, and a storage unit 307.

[0033] The frame generation unit 301 is a functional unit that performs the process of generating a wireless frame transmitted by the wireless communication control unit 303.

[0034] The frame analysis unit 302 is a functional unit that performs the analysis process of the wireless frame received by the wireless communication control unit 303.

[0035] The wireless communication control unit 303 notifies the frame generated by the frame generation unit 301 to surrounding terminals or transmits it unicast to the communication partner device. Alternatively, it sends the received wireless frame from the surroundings or the communication partner to the frame analysis unit 302.

[0036] The TXOP sharing control unit 304 controls to allocate the period during which it obtains the transmission opportunity (TXOP) it has secured to other APs. Alternatively, it instructs the frame generation unit 301 to generate the next wireless frame to be transmitted during the period it has secured. Also, it grasps the implementation status of TXOP sharing based on the result interpreted by the frame analysis unit 302.

[0037] The Multi-AP control unit 305 performs control for operating in cooperation with other APs. It grasps the APs participating in the current Multi-AP group from the content interpreted by the frame analysis unit 302 and instructs the frame generation unit 301 to generate the wireless frame to be transmitted for cooperation with other APs.

[0038] The UI control unit 306 is configured to include hardware related to a user interface (UI) such as a touch panel or buttons for receiving operations on the communication device by a user (not shown) and programs for controlling them. Note that the UI control unit 306 also has a function for presenting information such as display of an image or the like, or audio output to the user. Further, for example, the UI control unit 306 can display a setting screen related to the Multi-AP of the communication device 101 and receive a user operation on the display. In this case, the UI control unit 306 of the communication device 101 displays a setting screen for selecting some other APs that can form a Multi-AP in cooperation with the communication device 101. Then, the user may be allowed to select via the setting screen which other AP to cooperate with to form a Multi-AP.

[0039] The storage unit 307 is a storage device that can be configured by a ROM, a RAM, or the like that stores programs and data for the operation of the communication device 101.

[0040] (Acquisition of TXOP) Next, an example of a sequence diagram of a mechanism by which each communication device in the present embodiment acquires a TXOP will be described. FIG. 4 is a diagram showing an example of a mechanism by which the communication device 101 acquires a TXOP by the Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) method. Further, in the present embodiment, it is assumed that the communication device 101 and the communication device 105 perform channel access based on Enhanced Distributed Channel Access (EDCA). Note that EDCA is a mechanism for performing CSMA / CA in consideration of the priority of data by varying parameters for setting an Inter Frame Space (IFS) and a waiting time, etc., to be described later, according to the type of data (AC: Access Category). Note that IFS is an abbreviation for Inter Frame Space. Further, it is assumed that the parameters related to the EDCA (EDCA parameters) are periodically notified (for example, at intervals of 100 Time Units) by the AP using a Beacon frame.

[0041] 401 indicates that the communication channel of network 100 is busy (a state where other surrounding terminals are emitting radio waves). For example, it is assumed that communication device 103 is performing communication during the period indicated by 401. Also, checking whether the channel is in a busy state or an idle state like this is called carrier sense.

[0042] Next, when the channel changes from the busy state to the idle state, communication device 101 checks whether the channel is in the idle state during the AIFS period (402). AIFS is a type of IFS and is the abbreviation of Arbitration IFS. Note that the AIFS is determined based on the AIFSN of the EDCA parameter. In addition, if the channel changes to the busy state during the AIFS period in 402, after the channel changes to the idle state, it is checked again whether the channel is in the idle state during the AIFS period.

[0043] The communication device 101 that has confirmed that the channel is in the idle state during the AIFS period in 402 waits for the backoff period (403). The backoff period is managed by a backoff timer held by each communication device. Also, the backoff period for each data is also determined based on the EDCA parameter, and a random value is set from 0 to the value range of the Contension Window (CW) parameter. The decrement of the backoff timer when the waiting time of the AIFS in 402 ends is started. For example, if the channel becomes busy because another communication device starts communication during the backoff period waiting, the decrement of the backoff timer is interrupted. Then, when the channel becomes idle again, after passing the AIFS waiting time just now, the decrement of the backoff timer is resumed. That is, even if the channel becomes busy during the backoff period, the backoff timer is not reset, and the decrement resumes from the intermediate value.

[0044] When the backoff timer reaches 0, communication device 101 acquires a TXOP (Transmission Opportunity) and starts transmitting a wireless frame (404). In this embodiment, communication device 101 transmits a CTS-to-self frame as the wireless frame to be transmitted after backoff, but it is not limited to this. The wireless frame here may be a wireless frame including at least a MAC header. Note that CTS is the abbreviation of Clear to Send, and MAC is the abbreviation of Medium Access Contorol. The CTS-to-self frame is a CTS frame that communication device 101 transmits with communication device 101 as the destination. Also, the CTS frame is a frame for notifying other communication devices to refrain from communication during the TXOP period. Therefore, other communication devices that receive the CTS frame control themselves not to transmit during the period of the NAV by setting the NAV for themselves.

[0045] In the wireless frame that communication device 101 communicates in 403, it notifies the surrounding communication devices of the period of the TXOP secured by itself. Specifically, communication device 101 transmits a CTS-to-self frame in 404, and by storing the TXOP in the Duration field included in the frame, it notifies the surrounding other communication devices of the period of the TXOP acquired by communication device 101.

[0046] Communication device 105 that receives a wireless frame including a value other than 0 in the Duration field sets the NAV based on the value included in the Duration field (405). Communication device 105 assumes that the channel is in a busy state during the period of the NAV and does not perform the channel access process for transmitting a wireless frame.

[0047] After transmitting the CTS-to-self frame, communication device 101 performs data transmission with other communication devices within the TXOP acquired by itself (406).

[0048] Thus, in this embodiment, a communication device having a wireless frame to be transmitted waits for transmission during a predetermined IFS period and further waits for transmission during a backoff period after the channel becomes idle. In this way, the communication device with the shortest waiting time including the predetermined IFS period and the backoff period acquires a transmission opportunity (TXOP) and transmits the wireless frame.

[0049] (TXOP sharing) Next, an example of the mechanism of TXOP sharing in this embodiment will be described. In FIG. 5, the TXOP acquired by the communication device 101 is shared with the communication device 105 by allocating the TXOP acquired by the communication device 101 to the communication device 105. As a result, the communication device 105 can transmit a wireless frame during the allocated TXOP period.

[0050] First, the communication device 101 acquires a TXOP based on the above-described channel access and transmits a CTS-to-self frame (501). Information regarding the TXOP period (502) secured by the communication device 101 is stored in the Duration field of the frame. Therefore, the communication device 105 that has received the frame sets the NAV corresponding to the TXOP period in its own device.

[0051] Next, communication device 101 determines to allocate some or all of the TXOP acquired by itself to other communication devices, and transmits a Trigger frame (TF) (503). In this embodiment, communication device 101 determines to allocate a part of the TXOP acquired by itself to communication device 105, and transmits a TF including information regarding the allocation. For example, communication device 101 transmits a MU-RTS TXS Trigger frame as the Trigger frame. Communication device 101 stores information indicating the period of the TXOP to be allocated to communication device 105 in the MU-RTS TXS Trigger frame. Thereby, communication device 105 grasps the TXOP period (504) allocated from communication device 101. At this time, communication device 101 may store information indicating the period of the TXOP in the Allocation Duration subfield of the MU-RTS TXS Trigger frame. Further, communication device 101 stores "1" or "2" in the Triggerd TXOP Sharing Mode subfield. Storing "1" in the subfield means limiting the destination of data transmission in the TXOP to communication device 101. Also, storing "2" in the subfield means not limiting the destination of data transmission in the TXOP. Note that the MU-RTS TXS Trigger frame is an abbreviation of the Multi User-Request To Send TXOP Sharing Trigger frame.

[0052] Next, communication device 105 transmits a CTS frame as a response to TF 503 (505). Communication device 105 stores information indicating the TXOP period 504 allocated from communication device 101 in the Duration field included in the CTS frame, thereby setting the NAV for the communication devices around communication device 105.

[0053] After that, communication device 105 starts data communication with other communication devices (506 - 509). First, after transmitting CTS frame 505, communication device 105 transmits data after the SIFS period (506). After receiving the data 506, communication device 101 transmits a Block Ack frame as an acknowledgment response for the data 506 after the SIFS period (507). After receiving the Block Ack frame 507, since the assigned TXOP 504 remains and there is data to be transmitted, communication device 105 transmits data after the SIFS period (508). Communication device 104 transmits a Block Ack frame 509 in the same manner as communication device 101 transmits the Block Ack frame 507. Note that SIFS is the abbreviation of Short Inter Frame Space.

[0054] After the period of the TXOP assigned to communication device 105 has elapsed, communication device 101 performs carrier sense for a PIFS period that is longer than the SIFS period (510). In response to determining that the channel is in an idle state by the carrier sense, communication device 101 transmits data (511).

[0055] In the conventional TXOP sharing like this, it is also assumed that communication occurs between other communication devices different from the communication device to which the TXOP is assigned during the period of the assigned TXOP. In such a case, communication device 101 will resume data transmission after performing carrier sense for the PIFS period after the period of the assigned TXOP has elapsed. For example, it is also assumed that there is no data to be transmitted by communication device 105 and a predetermined remaining period occurs until the assigned TXOP period 504 elapses from the Block Ack frame 509. In such a case, communication devices around communication device 105 cannot communicate even though the channel is in an idle state.

[0056] Therefore, when such a remaining period occurs, it is considered that the communication device 105 notifies the surrounding communication devices that the allocated TXOP period 504 ends by transmitting a CF-End frame. However, at this time, the period of the TXOP acquired by the CTS frame 501 remains in the communication device 101. Also, the surrounding communication devices of the communication device 105 release the NAV by the CF-End frame. Therefore, depending on the standby time after receiving the CF-End frame by the surrounding communication devices that have released the NAV, there is a risk that the transmission of radio frames between the communication device 101 and the surrounding communication devices may collide. Therefore, the present invention proposes a control method after the communication device 101 that performs TXOP allocation receives a CF-End frame.

[0057] (TXOP sharing in this embodiment) Subsequently, FIG. 6 shows an example of the operation sequence of this embodiment in TXOP sharing. In this sequence, AP101 acquires a transmission opportunity (TXOP) and performs TXOP sharing in which a part or all of the acquired TXOP is allocated to AP102. Next, AP102 ends and returns the remaining TXOP to AP101 during the period of the allocated TXOP. Then, after receiving a radio frame indicating the end of the TXOP, AP101 adjusts the transmission standby time so that it can communicate before other communication devices and transmits a radio frame. In this embodiment, AP101 sets the SIFS time as the standby time. The SIFS is an IFS in which the shortest time is set among the IFSs. Therefore, AP101 can transmit a radio frame before other communication devices start transmitting a radio frame. As a result, other communication devices determine that the channel is busy due to the radio frame of AP101 and do not transmit a radio frame, so it is possible to reduce the collision of radio frames transmitted between AP101 and other communication devices.

[0058] First, AP101 secures the TXOP period 602 by transmitting a CTS-to-self frame 601. AP101 determines to allocate the TXOP period 603 within the TXOP period 602 to AP102. AP101 allocates the TXOP period 603 within the TXOP period 602 to AP102 using a MU-RTS TXS Trigger frame 604. That is, AP101 transmits a MU-RTS TXS Trigger frame 604 to AP102 and stores information indicating the TXOP period 603 in the Allocation Duration subfield. AP102 receives the MU-RTS TXS Trigger frame 604 and recognizes that the TXOP 603 has been allocated to itself. Note that AP101 may secure the TXOP period 602 and allocate the TXOP period 603 only using the MU-RTS TXS Trigger frame 604 without transmitting the CTS-to-self frame 601.

[0059] Next, AP102 transmits a CTS frame 605 as a response to the MU-RTS TXS Trigger frame 604. Note that AP102 stores information indicating the TXOP period 603 in the Duration field to set the NAV for a period equivalent to the TXOP period 603 in other surrounding communication devices. For example, STA104 receives the CTS frame 605 transmitted by AP102, recognizes that AP102 has secured the TXOP period 603, and sets the NAV606. Through the exchange up to the CTS frame 605 in this sequence, surrounding communication devices recognize the TXOP periods secured by AP101 and AP102 as NAV periods and control not to generate unnecessary radio waves during the NAV periods.

[0060] Subsequently, AP102 transmits data 607 to STA104 during TXOP period 603. Note that AP102 can prompt other STAs to transmit data by transmitting a Trigger frame instead of transmitting the data. Also, the transmission of the data may be sent to multiple communication devices. Note that AP102 may perform a directed (directional) transmission of data 607 to STA104. For example, AP102 controls the directivity of data 607 by beamforming. By controlling the directivity in this way, the communication speed and communication error rate can be improved, and the communication can be stabilized.

[0061] Next, STA104 transmits a Block Ack (BA) frame 608 to AP102 indicating that it has received data from AP102.

[0062] Upon receiving the BA frame, AP102 confirms that the communication with STA104 has ended during the TXOP period allocated to AP101, and transmits a CF-End frame 609 to AP101 indicating the end and return of the remaining period of TXOP period 603. By receiving the CF-End frame 609 during TXOP period 603, AP101 recognizes that AP102 has truncated the remaining period of TXOP period 603. Also, STA104, which has set the NAV regarding TXOP period 603, releases the NAV606 in response to receiving the CF-End frame 609. Then, when STA104 confirms that the channel is in an idle state, it resumes the channel access process. By releasing the NAV of the surrounding communication devices (STA104) in conjunction with the return of TXOP in this way, it is possible to prevent communication devices (STA104) outside the communication range of the communication device (AP101) that secures TXOP from remaining with an unintended NAV set.

[0063] Note that the CF-End frame is an abbreviation of the Contension Free-End frame. The CF-End frame is a type of control frame. In the MAC frame, the Type field indicates 01, and the Subtype field indicates 1110. The CF-End frame is a frame that can be transmitted by a communication device holding a TXOP. By transmitting the CF-End frame, the communication device can notify other communication devices of the end of the TXOP it holds. Also, a communication device that receives a CF-End frame can resume channel access processing by canceling the NAV set for itself. In this embodiment, by using the CF-End frame, AP102 notifies the end of the remaining period of the TXOP period 603. However, the frame used is not limited to this. For example, a frame that notifies the end of the remaining period of the TXOP period 603 may be any predetermined control frame. The predetermined control frame in this embodiment is a MAC frame, in which the Type field indicates 01 and the Subtype field indicates 1110. Also, the predetermined control frame can notify the end of the remaining period of the TXOP period. Further, the predetermined control frame can cancel the NAV of other surrounding communication devices. Here, the control frame to be transmitted does not have to be a CF-End frame. For example, it may be a field in which the Type field indicates 01 and the Subtype field indicates 1111. This frame may be defined as a frame for the Shared AP to return the TXOP shared with the SharingAP.

[0064] When AP101 receives the CF-End frame 609 transmitted by AP102, it waits until the SIFS time 610 elapses from the completion of the reception of the CF-End frame. When the SIFS time 610 elapses, it transmits a data frame 611 to STA105.

[0065] In this way, by starting to transmit a wireless frame after the SIFS period, which is shorter than the standby time of other communication devices, AP101 can transmit data before other communication devices newly acquire a TXOP. As a result, other communication devices determine that the channel is busy due to the data frame of 606, and thus determine that they have not yet obtained a transmission opportunity. Therefore, it becomes possible to avoid a collision between the transmission of the wireless frame of AP101 and the transmission of the wireless frame of other communication devices.

[0066] Subsequently, FIG. 7 shows an example of a flowchart showing the operation of AP101 when performing TXOP sharing. Note that this operation flow is processed when the control unit 202 reads and executes the computer program stored in the storage unit 201 according to a connection instruction or a communication instruction with a communication partner by AP101. Hereinafter, the operation of AP101 will be described, but AP102 and AP103 can also operate in the same manner. Note that at the start of this flowchart, AP101 to AP103 are assumed to have already formed a Multi-AP group for cooperative operation.

[0067] First, the control unit 202 of AP101 attempts to acquire a TXOP (Transmission Opportunity) by checking whether the channel is in an idle state during the waiting time for collision avoidance determined with randomness (S701). If it is confirmed that the channel is in an idle state during the waiting time for collision avoidance, it determines that it has acquired the transmission opportunity. When the control unit 202 determines that its own device has acquired the transmission opportunity, it proceeds to S702. On the other hand, if the operating channel is busy, or if another communication device acquires the transmission opportunity and starts data transmission during its own waiting time, causing the operating channel to become busy, it determines that the transmission opportunity has not been acquired. When the control unit 202 determines that the transmission opportunity has not been acquired, it waits until the channel becomes idle again and then attempts to acquire the transmission opportunity again. When AP101 acquires the transmission opportunity, it secures the acquired TXOP period 602 by transmitting a CTS-to-self frame 601. Also, other communication devices that receive the CTS-to-self frame shall set the NAV corresponding to the TXOP period.

[0068] Subsequently, the control unit 202 determines whether to allocate a part of the TXOP period acquired by AP101 to other APs (S703). In this step, AP101 makes this determination based on, for example, information acquired in advance. The information acquired in advance is, for example, information indicating that another AP has a large amount of data to communicate with the connected STA. In this case, in S703, AP101 determines to allocate a part of the TXOP to another AP. Also, the information acquired in advance is information indicating that low-latency information is regularly communicated between another AP and the STA connected to this AP. In this case, in S703, AP101 determines to allocate a part of the TXOP to another AP. When the control unit 202 determines to allocate a part of the period during which it has obtained the transmission opportunity to other APs, it proceeds to S704. When the control unit 202 determines not to allocate a part of the period during which other APs have obtained the transmission opportunity, it proceeds to S711.

[0069] In S704, the control unit 202 performs TXOP sharing to allocate to other APs a part of the period during which the own device has obtained a transmission opportunity by transmitting a MU-RTS TXS Trigger frame. In this embodiment, it is assumed that a MU-RTS TXS Trigger is transmitted from AP101 to AP102 to perform TXOP sharing for AP102. When transmitting the MU-RTS TXS Trigger frame, the communication unit 206 controls the antenna 207 to control the signal to be transmitted externally in an omnidirectional manner. When it is desired to keep the period secured by itself longer than the period allocated by the MU-RTS TXS Trigger frame, the communication unit 206 controls the antenna 207 to transmit a CTS-to-self frame. A period indicating that the own device has obtained a transmission opportunity is presented by the CTS-to-self frame, and a MU-RTS TXS Trigger frame is transmitted to allocate a part of the period to AP102. Regarding the frame transmission operation, the functional units 301 to 304 cooperate to perform the frame transmission. In this embodiment, it is assumed that AP101 that has secured the TXOP period 602 allocates the TXOP period 603 to AP102 using the MU-RTS TXS Trigger frame.

[0070] Subsequently, the wireless communication control unit 303 waits for reception of a CTS frame that is a response to the transmitted MU-RTS TXS Trigger frame (S705). The frame received (detected) by the wireless communication control unit 303 is analyzed by the frame analysis unit 302, and reception is confirmed by determining whether it is a CTS frame. If AP102 has received the MU-RTS TXS Trigger frame, after transmitting the MU-RTS TXS Trigger frame, AP102 transmits a CTS frame after the SIFS time has elapsed. If the CTS frame cannot be received within a certain period, the process returns to S702. If the CTS frame is received, the process proceeds to S706. Note that the TXOP period indicated by the CTS frame is equal to the period allocated to AP102 by the MU-RTS TXS Trigger frame transmitted by AP101.

[0071] When AP101 receives a CTS frame, it means that AP102 recognizes TXOP sharing and starts communication during the assigned TXOP period. Here, the control unit 202 checks in the CF-End frame received from AP102 whether the frame analysis unit 302 has returned the assigned period halfway (S706). If the CF-End frame is not received, the process proceeds to S707. If received, the process proceeds to S708. If the CF-End frame is not received, the control unit 202 simply checks whether the assigned period has elapsed (S707). S706 and S707 are repeated until the assigned period elapses. When the assigned period elapses, the process proceeds to S709. In S708, it also waits for a predetermined period after receiving the CF-End frame (S708). In this embodiment, the waiting period is set to wait until the SIFS time elapses. Note that the waiting time only needs to be shorter than the time until it is determined that all other communication devices have obtained a transmission opportunity after receiving the CF-End frame. For example, it may be the PIFS (PCF (Point Coordination Function) Inter Frame Space) time.

[0072] In S708, the control unit 202 uses the TXOP sharing control unit 304 to check whether the TXOP period secured by transmitting the CTS-To-self frame in S702 remains. If there is a remaining period, the process proceeds to S710. If there is no remaining period, this flow is terminated assuming that the TXOP period acquired by the own device has ended.

[0073] Note that in S704, a part of the TXOP period may be allocated to the STA connected to AP101. In this case, in S706, it is also necessary to wait for whether or not to receive a frame including the CAS Control subfield of the HT Control field and having a value of 0 in the RDG / More PPDU subfield of the field. As a result, the STA allocated with the TXOP can return the TXOP by using a frame having a value of 0 in the RDG / More PPDU subfield or a CF-End frame. For example, when the STA allocated with the TXOP wants to return the TXOP together with data transmission, a frame having a value of 0 in the RDG / More PPDU subfield can be used. On the other hand, when it wants to return the TXOP in conjunction with canceling the NAV of other surrounding communication devices, a CF-End frame can be used. In this way, the STA allocated with the TXOP can perform more efficient TXOP return processing by properly using the above two frames.

[0074] If there is a remaining period of the TXOP period acquired by itself, the control unit 202 determines again whether or not to allocate a part of the period to another AP or STA (S710). If reallocation is performed, the process returns to S704. If no allocation is made, the process proceeds to S711.

[0075] In S711 and S712, it is assumed that AP101 makes a determination such as whether to send a Trigger frame or a data frame based on predetermined conditions. The determination based on each condition is a determination for determining the operation that AP101 executes after the SIFS time has elapsed after receiving the CF-End frame in the present embodiment. The content of the determination based on each condition after the SIFS time has elapsed in the present embodiment is not limited to these. Also, the order in which the determination based on each condition is made is not limited to these. Further, the timing at which the determination based on each condition for determining the operation after the SIFS time has elapsed is not limited to these. For example, the determination based on each condition for determining the operation may be performed in parallel with the standby during the SIFS period (S708) as the above-described predetermined period. Also, the determination based on each condition for determining the operation may be made in advance by making a determination at the timing of receiving each data or at regular intervals. In this way, AP101 makes a determination based on each condition for determining the operation and determines which wireless frame to send.

[0076] In S711, the control unit 202 cooperates with the communication unit 206 and the communication control unit 303 to determine whether to promote data transmission to another communication device and perform data communication as the receiving side of the data (S711). Here, if it is determined to promote data transmission to another communication device, AP101 sends a Trgger frame (S712). In this case, for example, AP101 sends a Trigger frame to STA105 to prompt uplink data transmission to STA105. When sending the Trigger frame, the communication unit 206 controls the antenna 207 to control the signal to be transmitted externally in an omnidirectional manner. When prompting STA105 to send data, after receiving a data frame from STA105, a Block Ack (BA) frame for reception confirmation is sent to STA105. When the procedure for data reception is completed, the process proceeds to S716.

[0077] In S712, the control unit 202 cooperates with the communication unit 206 and the communication control unit 303 to determine whether to transmit data to other communication devices (S712). When transmitting a data frame, the communication unit 206 controls the antenna 207 to control the signal to be transmitted externally in an omnidirectional manner. Then, a BA frame for reception confirmation is received. When the data transmission procedure is completed, the process proceeds to S716.

[0078] In S715, the control unit 202 ends and releases the TXOP period secured in S702. S715 is an operation executed in response to the determination by AP101 that the remaining TXOP period is to be released. In the present embodiment, AP101 executes this process in response to the determination of No in S711 and S712, but it is not limited to this. For example, the determination of whether to release the TXOP period may be made prior to the determination in S711 and S712.

[0079] In the present embodiment, in S715, AP101 controls whether to transmit a CF-End frame or not to transmit any radio frame. In response to the determination in S715 that it is necessary to release the NAV of the surroundings, AP101 controls to transmit a CF-End frame. By transmitting a CF-End frame by AP101, it is possible to release the unintended NAV of the surrounding communication devices. Also, in response to the determination in S715 that it is not necessary to release the NAV of the surroundings, AP101 controls not to transmit any radio frame. Since there is no communication device that sets an unintended NAV in the surrounding communication devices, it is possible to release the TXOP period to other surrounding communication devices without transmitting unnecessary radio frames. Note that, in the present embodiment, an example in which AP101 transmits a CF-End frame in S715 has been described, but it is not limited to this. For example, a frame in which the value of the RDG / More PPDU subfield is 0 may be transmitted in the CAS Control subfield of the HT Control field.

[0080] In S716, the control unit 202 uses the TXOP sharing control unit 304 to check whether there is any remaining TXOP period secured by transmitting the CTS-to-self frame in S702. If there is a remaining period, it returns to S703. If there is no remaining period, the process ends.

[0081] (Other Embodiments) Furthermore, a recording medium storing the program code of software for realizing the above-described functions may be supplied to a system or apparatus, and a computer (CPU, MPU) of the system or apparatus may read and execute the program code stored in the recording medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the above-described apparatus.

[0082] As the storage medium for supplying the program code, for example, 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 ROM, a DVD, etc. can be used.

[0083] Also, by executing the program code read by the computer, not only are the above-described functions realized, but also based on the instructions of the program code, the OS running on the computer performs part or all of the actual processing to realize the above-described functions. The OS is an abbreviation for Operating System.

[0084] Furthermore, the program code read from the storage medium is written into the memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Then, based on the instructions of the program code, the CPU provided in the function expansion board or the function expansion unit performs part or all of the actual processing to realize the above-described functions.

[0085] The present invention can also be implemented by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. It can also be implemented by a circuit (for example, ASIC) that realizes one or more functions.

[0086] Also, the disclosure of the above-described embodiments includes the following configurations.

[0087] (Configuration 1) A communication device, acquisition means for acquiring a Transmission Opportunity (TXOP) for transmitting a wireless frame; securing means for securing a first TXOP period using a first wireless frame; sharing means for allocating a second TXOP period within the first TXOP period to another communication device using a Trigger frame; receiving means for receiving a predetermined control frame indicating the end of the second TXOP period during the second TXOP period; control means for controlling to transmit a second wireless frame after a predetermined Inter Frame Space (IFS) time has elapsed since the reception when the predetermined control frame is received during the second TXOP period, and the control means controls to transmit the second wireless frame based on a predetermined condition A communication device characterized by the above.

[0088] (Configuration 2) The predetermined control frame is a Contension Free-End (CF-End) frame The communication device according to Configuration 1, characterized by the above.

[0089] (Configuration 3) The predetermined IFS is a Short IFS The communication device according to Configuration 1 or Configuration 2, characterized by the above.

[0090] (Configuration 4) The specified IFS is Point Coordination Function IFS The communication device according to Configuration 1 or Configuration 2, characterized in that

[0091] (Configuration 5) The Trigger frame is a Multi User-Request To Send TXOP Sharing Trigger (MU-RTS TXS Trigger) frame The communication device according to any one of Configurations 1 to 4, characterized in that

[0092] (Configuration 6) The communication device and the other communication device are APs, and The communication device further has a construction means for constructing a wireless network The communication device according to any one of Configurations 1 to 5, characterized in that

[0093] (Configuration 7) The second wireless frame is the Trigger frame, and The control means controls to transmit the Trigger frame based on the determination that the third TXOP period among the first TXOP periods is allocated to another communication device different from the other communication device The communication device according to any one of Configurations 1 to 6, characterized in that

[0094] (Configuration 8) The second wireless frame is a data frame, and The control means controls to transmit the data frame based on the determination that data is to be transmitted to a communication device participating in the wireless network The communication device according to any one of Configurations 1 to 6, characterized in that

[0095] (Configuration 9) The second wireless frame is the Trigger frame, and the control means controls to transmit the Trigger frame based on a determination that the control means has determined to prompt a communication device participating in the wireless network to transmit a data frame The communication device according to any one of Configurations 1 to 6, characterized in that

[0096] (Configuration 10) The second wireless frame is the predetermined control frame, and the control means controls to transmit the predetermined control frame based on a determination that the control means has determined to end the first TXOP period The communication device according to any one of Configurations 1 to 6, characterized in that

[0097] (Configuration 11) When the control means determines to end the first TXOP period after receiving the predetermined control frame, the control means controls not to transmit the second wireless frame after a predetermined IFS time has elapsed from the reception of the predetermined control frame in the second TXOP period The communication device according to any one of Configurations 1 to 10, characterized in that

[0098] (Configuration 12) The first wireless frame used by the securing means and the Trigger frame used by the sharing means are the same frame The communication device according to any one of Configurations 1 to 11, characterized in that

Explanation of Signs

[0099] 201 Storage unit 202 Control unit 203 Functional unit 204 Input unit 205 Output unit 206 Communication unit

Claims

1. A communication device, comprising: an acquisition means for acquiring a Transmission Opportunity (TXOP) for transmitting a wireless frame; a securing means for securing a first TXOP period using a first wireless frame; a sharing means for allocating a second TXOP period within the first TXOP period to another communication device using a Trigger frame; a receiving means for receiving a predetermined control frame indicating the end of the second TXOP period during the second TXOP period; a control means for controlling to transmit a second wireless frame after a predetermined Inter Frame Space (IFS) time has elapsed since the reception when the predetermined control frame is received during the second TXOP period; and the control means controls to transmit the second wireless frame based on a predetermined condition A communication device characterized by the above.

2. The predetermined control frame is a Contention Free - End (CF - End) frame The communication device according to claim 1, characterized by the above.

3. The predetermined IFS is a Short IFS The communication device according to claim 1, characterized by the above.

4. The predetermined IFS is a Point Coordination Function IFS The communication device according to claim 1, characterized by the above.

5. The Trigger frame is a Multi User - Request To Send TXOP Sharing Trigger (MU - RTS TXS Trigger) frame The communication device according to claim 1, characterized by the above.

6. The communication device and the other communication device are APs, and the communication device further has a construction means for constructing a wireless network The communication device according to any one of claims 1 to 4, characterized by the above.

7. The second wireless frame is the Trigger frame, and the control means controls to transmit the Trigger frame based on a determination that a third TXOP period within the first TXOP period is allocated to another communication device different from the other communication device The communication device according to claim 6, characterized by the above.

8. The second wireless frame is a data frame, The control means controls to transmit the data frame based on determining that the data is to be transmitted to a communication device participating in the wireless network. The communication device according to claim 6, characterized in that.

9. The second wireless frame is the Trigger frame, The control means controls to transmit the Trigger frame based on determining that the communication device participating in the wireless network is prompted to transmit a data frame. The communication device according to claim 6, characterized in that.

10. The second wireless frame is the predetermined control frame, The control means controls to transmit the predetermined control frame based on determining that the first TXOP period ends. The communication device according to claim 6, characterized in that.

11. When the control means determines that the first TXOP period ends after receiving the predetermined control frame, the control means controls not to transmit the second wireless frame after a predetermined IFS time has elapsed from the reception of the predetermined control frame in the second TXOP period. The communication device according to claim 6, characterized in that.

12. The first wireless frame used by the securing means and the Trigger frame used by the sharing means are the same frame. The communication device according to claim 1, characterized in that.

13. A control method for a communication device, comprising: An acquisition step of acquiring a Transmission Opportunity (TXOP) for transmitting a wireless frame; A securing step of securing a first TXOP period using a first wireless frame; A sharing step of allocating a second TXOP period within the first TXOP period to another communication device using a Trigger frame; A receiving step of receiving a predetermined control frame indicating the end of the second TXOP period in the second TXOP period; A control step of controlling to transmit a second wireless frame after a predetermined Inter Frame Space (IFS) time has elapsed from the reception when the predetermined control frame is received in the second TXOP period, and In the control step, control is performed to transmit the second wireless frame based on predetermined conditions. A control method for a communication device, characterized in that.

14. A program for causing a computer to function as the control method of the communication device according to claim 13.

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