Communication device, control method, and program therefor

Abstract

To perform efficient communication using a plurality of spatial streams.SOLUTION: A communication device that communicates according to IEEE 802.11 series standards aggregates spatial streams that can be used on a plurality of links by a communication partner device into a first link of the plurality of links, and performs predetermined communication with the partner device, identifies a communication status on a second link different from the first link among the plurality of links while the predetermined communication is being performed on the first link, and transmits a predetermined notification to the partner device, based on identifying the communication status in which the partner device can transmit a signal on the second link when the predetermined communication is completed on the first link.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a technology for improving the efficiency of wireless communication. [Background technology]

[0002] The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard is known as a communication standard for wireless local area networks (wireless LANs). The IEEE 802.11 standard is a series of standards that includes the IEEE 802.11a / b / g / n / ac / ax standards. The IEEE 802.11ax standard, the latest standard in the IEEE 802.11 series, enables the use of orthogonal frequency division multiple access (OFDMA) and achieves a peak throughput of up to 9.6 gigabits per second (see Patent Document 1).

[0003] Currently, the IEEE 802.11be standard is being developed as a new standard in the IEEE 802.11 series of standards to further improve throughput and communication latency. The IEEE 802.11be standard considers multilink communication, in which one access point (AP) establishes multiple wireless links with one station (STA) for communication. In multilink communication, for example, an AP establishes a connection with a STA using multiple frequency channels in the 2.4 GHz, 5 GHz, or 6 GHz frequency band, and communicates in parallel on each frequency channel. Furthermore, the IEEE 802.11be standard considers the introduction of Enhanced Multi-Link Multi-Radio (EMLMR), as described in Non-Patent Document 1. EMLMR enables efficient communication by temporarily concentrating the spatial streams available on each link on a specific link among multiple links established in multilink communication, thereby increasing the number of spatial streams on that link. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-050133 [Non-patent literature]

[0005] [Non-Patent Document 1] IEEE802.11-21 / 0774r05, Resolution for CIDs related to EMLMR(CC34)-Part2, [online], May 2021,<https: / / mentor.ieee.org / 802.11 / documents> Summary of the Invention [Problem to be solved by the invention]

[0006] When EMLMR is used to temporarily increase the number of spatial streams on a specific link, the number of spatial streams on other links will be decreased while the operation is in progress. For example, if the number of received spatial streams is changed, some links may temporarily have no spatial streams in use, and the communication device may be unable to receive signals on the frequency channel corresponding to that link. As a result, the communication device may be unable to receive control frames transmitted by other communication devices, reducing the effectiveness of EMLMR in improving communication efficiency.

[0007] The present invention provides a technique that enables efficient communication using multiple spatial streams. [Means for solving the problem]

[0008] A communication device according to one embodiment of the present invention is a communication device that communicates in accordance with the IEEE 802.11 series standard, and includes: a communication means that performs a predetermined communication by aggregating spatial streams that can be used by a communication partner device on a first link among the plurality of links; an identification means that identifies a communication status on a second link among the plurality of links that is different from the first link while the predetermined communication is being performed on the first link; and a notification means that sends a predetermined notification to the communication partner device based on the identification of the communication status in which the communication partner device can transmit a signal on the second link when the predetermined communication on the first link is terminated. [Effects of the Invention]

[0009] According to the present invention, it is possible to perform efficient communication using a plurality of spatial streams. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates an example of a network configuration. [Figure 2] FIG. 2 illustrates an example of a hardware configuration of a communication device. [Figure 3] FIG. 2 illustrates an example of a functional configuration of a communication device. [Figure 4] FIG. 1 is a diagram outlining multi-link communication. [Figure 5] FIG. 10 is a diagram illustrating an example of information elements transmitted and received. [Figure 6] FIG. 10 is a diagram illustrating an example of a communication flow. [Figure 7] FIG. 10 is a diagram illustrating an example of the flow of processing executed by AP MLD. [Figure 8] FIG. 10 is a diagram illustrating an example of the flow of processing executed by Non-AP MLD. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0012] (Network configuration) FIG. 1 shows an example of the configuration of a network 101 according to this embodiment. This network 101 is configured to include a plurality of communication devices. Each of the plurality of communication devices is capable of communication over a wireless local area network (LAN) conforming to the IEEE (Institute of Electrical and Electronics Engineers) 802.11 series standard. All of the communication devices according to this embodiment are compatible with the IEEE 802.11be (EHT (Extremely / Extreme High Throughput)) standard and can perform wireless communication according to this standard. Note that each communication device may also be capable of operating according to other IEEE 802.11 standards (for example, at least one of the IEEE 802.11a / b / g / n / ac / ax standards).

[0013] Each communication device is configured to be able to perform communications according to the IEEE 802.11 series standards in the 2.4 GHz, 5 GHz, and 6 GHz frequency bands. The frequency bands available to each communication device are not limited to these bands, and other frequency bands, such as the 60 GHz band, may also be used. Each communication device can communicate using frequency bandwidths of 20 MHz, 40 MHz, 80 MHz, 160 MHz, and 320 MHz. This is merely an example, and other frequency bandwidths, such as 240 MHz and 4 MHz, may also be available. If a new usable frequency bandwidth is defined in the IEEE 802.11 series standards, the communication device may be configured to use that frequency bandwidth. The IEEE 802.11 series standards define "frequency channels," and communication devices compliant with the standards can perform wireless communications using those frequency channels. The IEEE 802.11 series standards define multiple frequency channels in each frequency band, such as the 2.4 GHz, 5 GHz, and 6 GHz bands. In addition, the IEEE802.11 series of standards defines the bandwidth of each frequency channel as 20 MHz, except for the 60 GHz band. However, by bonding adjacent frequency channels, it is possible to use a bandwidth of 40 MHz or more in a single frequency channel. In the 60 GHz band, the bandwidth of the frequency channel is defined as 2.16 GHz.

[0014] The multiple communication devices according to this embodiment are configured to be capable of performing multilink communication in which one access point (AP) establishes multiple wireless links with one station (STA). A communication device capable of performing such multilink communication is called an MLD (Multi-Link Device). In particular, an MLD that functions as an access point (AP) and operates to build a network is called an AP MLD, and an MLD that functions as a station (STA) and operates to participate in the built network is called a Non-AP MLD. In this embodiment, it is assumed that the AP MLD 102 builds a network 101 and establishes links 104 and 105 with the Non-AP MLD 103 to perform multilink communication. Note that in this embodiment, when there is no need to particularly distinguish between the communication devices, the AP MLD 102 and the Non-AP MLD 103 are collectively referred to as communication devices.

[0015] The multiple wireless links established in multi-link communication may use frequency channels in different frequency bands. For example, the AP MLD 102 and the non-AP MLD 103 may establish link 104 using a first frequency channel in the 2.4 GHz band and link 105 using a second frequency channel in the 5 GHz band, and communicate via both links. In this case, the AP MLD 102 maintains link 104 and link 105 in parallel. Establishing multiple links between the AP MLD 102 and the non-AP MLD 103 using multiple frequency channels can improve the throughput of communications between these communication devices. Note that, although the above example shows the establishment of two links, three or more links may be established in parallel. For example, in addition to link 104 in the 2.4 GHz band and link 105 in the 5 GHz band, an additional link (not shown) in the 6 GHz band may be established between the AP MLD 102 and the non-AP MLD 103.

[0016] The AP MLD 102 and the non-AP MLD 103 may establish multiple links for multilink communication using different frequency bands as described above, or may establish the links using different frequency channels in the same frequency band. The multiple frequency channels used in the multiple links established between the AP MLD 102 and the non-AP MLD 103 may be selected from channels spaced at least 20 MHz apart. In one example, the link 104 and the link 105 may be established between the AP MLD 102 and the non-AP MLD 103 using channels 1 and 11 in the 2.4 GHz band. Alternatively, two or more of the multiple links may be established using different frequency channels in the same frequency band, and the remaining links may be established using a different frequency band. For example, two links may be established between the AP MLD 102 and the non-AP MLD 103 using channels 1 and 11 in the 2.4 GHz band, and another link may be established using channel 36 in the 5 GHz band. By establishing multiple links of different frequency bands between the AP MLD 102 and the Non-AP MLD 103, even if the communication rate of one frequency band drops due to a high load or the like, a constant communication rate can be ensured by communication in another frequency band, thereby suppressing a decrease in the throughput of communication between these communication devices.

[0017] Furthermore, the AP MLD 102 and the non-AP MLD 103 may be capable of performing communication using, for example, MIMO (Multiple-Input Multiple-Output). In this case, the AP MLD 102 and the non-AP MLD 103 have multiple antennas, and the transmitting communication device transmits different signals in parallel from each antenna using the same frequency channel. The receiving communication device receives all signals arriving from multiple streams in parallel using multiple antennas, and separates and decodes the signals of each stream. This makes it possible to communicate a large amount of data in a short period of time. When performing multi-link communication, the AP MLD 102 and the non-AP MLD 103 may perform MIMO communication on some links.

[0018] In addition to the IEEE802.11 series standards, the AP MLD 102 and the Non-AP MLD 103 may also comply with other communication standards such as Bluetooth (registered trademark), NFC, UWB, ZigBee (registered trademark), and MBOA. NFC stands for Near Field Communication, UWB stands for Ultra Wide Band, and MBOA stands for Multi Band OFDM Alliance. UWB also includes wireless USB, wireless 1394, WiNET, and the like. Each communication device may also comply with a communication standard for wired communication such as a wired LAN.

[0019] The AP MLD 102 may be, for example, a wireless LAN router or a personal computer (PC), but is not limited to these. The non-AP MLD 103 may be, for example, a camera, a tablet, a smartphone, a PC, a mobile phone, a video camera, a headset, but is not limited to these. The AP MLD 102 and the non-AP MLD 103 may be information processing devices such as wireless chips that can perform wireless communication in accordance with the IEEE802.11be standard.

[0020] Although the wireless network of Figure 1 has one AP MLD and one non-AP MLD, the number and arrangement of AP MLDs and non-AP MLDs are not limited to this. For example, the wireless network of Figure 1 may have more AP MLDs or non-AP MLDs. In this case, the frequency bands of each established link, the number of links, and the frequency bandwidth are not particularly limited.

[0021] The communication device according to this embodiment is configured to be able to perform communication using Enhanced Multi-Link Multi-Radio (EMLMR). In EMLMR, for some of the multiple links established in multi-link communication, the spatial streams available on each link are temporarily concentrated on a specific link, thereby increasing the number of spatial streams on that link and enabling efficient communication.

[0022] When EMLMR is used, it is possible that concentrating spatial streams on a specific link results in no usable spatial streams being available for other links. In this case, the communication device may be unable to receive any signals transmitted on the frequency channel of the link where the usable spatial stream is not available. As a result, during communication using EMLMR, the communication device may be unable to observe, for example, a Request To Send (RTS) frame or a Clear To Send (CTS) frame transmitted by another communication device on that frequency channel. Furthermore, because the communication device is unable to receive the RTS or CTS, it may be unable to properly set a transmission prohibition period (Network Allocation Vector, NAV). Therefore, the communication device may cause interference with the communication of other communication devices after the EMLMR communication is terminated.

[0023] Even when a STA connected to an AP is operating in power-save mode and transmits a packet immediately after returning from the Doze state, the STA cannot receive RTS or CTS signals in the power-saving state (Doze state). Therefore, the STA may not set its NAV and may initiate signal transmission if it fails to detect radio waves during power detection on a frequency channel. In this case, the signal transmitted by the STA may collide with signals from other STAs that are not observed by the STA. In consideration of this situation, the IEEE 802.11 series standards define a period called "NAVSyncDelay" and require that a STA returning from the Doze state wait for this period before beginning transmission. This prevents the STA from transmitting signals during the period when its NAV may be set by RTS or CTS, thereby preventing collisions between transmitted signals and signals from other STAs. Such NAVSyncDelay can also be applied to communication devices using the EMLMR described above. However, applying NAVSyncDelay may result in reduced throughput and reduced frequency utilization efficiency.

[0024] In this embodiment, after completing data transmission and reception on a link used in EMLMR communication, the AP MLD 102 notifies the non-AP MLD 103 of whether or not a frequency channel corresponding to a link not used in EMLMR communication is available. Note that EMLMR communication refers to communication performed by aggregating spatial streams for some links among multiple links configured as targets of EMLMR. Note that, hereinafter, multiple links configured as targets of EMLMR may be referred to as EMLMR links. Also, a link used in EMLMR communication refers to an EMLMR link on which communication using aggregated spatial streams was performed. On the other hand, a link not used in EMLMR communication refers to an EMLMR link on which communication was not performed because the spatial stream was used for another link. If the AP MLD 102 notifies that a frequency channel not used in EMLMR communication is available, the non-AP MLD 103 can attempt communication on that frequency channel without waiting the NAVSyncDelay period. Furthermore, if the AP MLD 102 notifies that a frequency channel that has not been used in EMLMR communication is unavailable, the non-AP MLD 103 may wait, for example, the NAVSyncDelay period on that frequency channel. This allows the non-AP MLD 103 to communicate without interfering with the communication of other communication devices and without having to wait unnecessarily for the NAVSyncDelay period depending on the situation.

[0025] (Configuration of communication device) An example of the hardware configuration of a communication device (AP MLD 102 and Non-AP MLD 103) according to this embodiment will be described with reference to Fig. 2. The communication device includes, as its hardware configuration, a storage unit 201, a control unit 202, a function unit 293, an input unit 204, an output unit 205, a communication unit 206, and an antenna 207, for example.

[0026] The storage unit 201 is configured to include one or more memories such as ROM and RAM, and stores various information such as computer programs for performing various operations described below and communication parameters for wireless communication. ROM stands for Read Only Memory, and RAM stands for Random Access Memory. The storage unit 201 may include storage media such as a flexible disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a non-volatile memory card, a DVD, etc., in addition to or instead of memories such as ROM and RAM. The storage unit 201 may also include multiple memories.

[0027] The control unit 202 is configured with one or more processors, such as a CPU or an MPU, and controls the entire communication device by executing a computer program stored in the storage unit 201, for example. The CPU stands for Central Processing Unit, and the MPU stands for Micro Processing Unit. The control unit 202 may be configured to perform processes for generating data and signals to be transmitted in communication with other communication devices, in addition to the overall control of the communication device. The control unit 202 may be configured to perform processes such as the overall control of the communication device in cooperation with a computer program stored in the storage unit 201 and an OS (Operating System). The control unit 202 may also include multiple processors, such as a multi-core processor, and may perform processes such as the overall control of the communication device using the multiple processors. The control unit 202 may also be configured with an ASIC (Application Specific Integrated Circuit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like.

[0028] Furthermore, the control unit 202 controls the functional unit 203 to perform predetermined processing such as capturing images, printing, and projection. The functional unit 203 is, for example, hardware that enables the communication device to perform predetermined processing. For example, if the communication device is a camera, the functional unit 203 is an imaging unit that performs imaging processing. For example, if the communication device is a printer, the functional unit 203 is a printing unit that performs printing processing. For example, if the communication device is a projector, the functional unit 203 is a projection unit that performs projection processing. The data processed by the functional unit 203 may be data stored in the storage unit 201, or may be data communicated with another communication device via the communication unit 206, which will be described later.

[0029] The input unit 204 receives various operations from the user. The output unit 205 outputs various types of information to the user. Here, the output by the output unit 205 includes, for example, at least one of a display on a screen, an audio output by a speaker, a vibration output, and the like. Note that both the input unit 204 and the output unit 205 may be implemented by a single module, such as a touch panel. Furthermore, the input unit 204 and the output unit 205 may each be built into a communication device, or may be configured as an external device connected to the communication device.

[0030] The communication unit 206 controls wireless communication compliant with the IEEE 802.11 series standards and IP communication. In this embodiment, the communication unit 206 is configured to control wireless communication compliant with the IEEE 802.11be standard, in particular. Note that the communication unit 206 may control wireless communication compliant with other IEEE 802.11 series standards in addition to the IEEE 802.11be standard, or wired communication such as a wired LAN. The communication unit 206 controls the antenna 207 to transmit and receive signals for wireless communication generated by, for example, the control unit 202. The communication device may have multiple communication units 206. If the communication device has multiple communication units 206, one link may be established by one communication unit 206 when establishing multiple links in multi-link communication. Note that the communication device may establish one link for each of some communication units 206, and establish multiple links for other communication units 206. Furthermore, when multiple links are established using one communication unit 206, the communication unit 206 may execute communication via the multiple links by, for example, switching the operating frequency channel in a time-division manner. If the communication device supports standards such as the NFC standard and Bluetooth (registered trademark) in addition to the IEEE 802.11be standard, it may control wireless communication in accordance with these communication standards. If the communication device is capable of executing wireless communication in accordance with multiple communication standards, it may have separate communication units and antennas compatible with each communication standard. The communication device communicates data such as image data, document data, and video data with other communication devices via the communication unit 206. The antenna 207 may be provided separately from the communication unit 206, or may be configured as a single module together with the communication unit 206.

[0031] Antenna 207 is an antenna that enables communication in various frequency bands, such as the sub-GHz band, the 2.4 GHz band, the 5 GHz band, the 6 GHz band, and the 60 GHz band. The communication device may have a single antenna, such as a multi-band antenna, as antenna 207, or may have multiple antennas corresponding to, for example, multiple frequency bands. When the communication device has multiple antennas, it may have one communication unit 206 for the multiple antennas, or multiple communication units 206 corresponding to the multiple antennas, respectively. Antenna 207 may be a single antenna or an antenna array. That is, antenna 207 may have multiple antenna elements and be configured to be able to perform communication using, for example, MIMO (Multi-Input and Multi-Output).

[0032] Next, an example of the functional configuration of the communication device of this embodiment will be described with reference to Fig. 3. The communication device (AP MLD 102 and Non-AP MLD 103) is configured to include, for example, a wireless LAN control unit 301, a frame processing unit 302, an EMLMR control unit 303, a UI control unit 304, and a storage control unit 305. Note that these are just examples, and some or all of these functional units may be replaced with other configurations, multiple functional units may be integrated to form one functional unit, or one functional unit may be divided into multiple functional units. Also, multiple identical functional units may be provided. For example, multiple wireless LAN control units 301 may exist.

[0033] The wireless LAN control unit 301 controls the antenna 207 and a communication circuit (e.g., the communication unit 206) to transmit and receive wireless signals to and from other wireless LAN communication devices. The frame processing unit 302 processes wireless frames transmitted and received by the wireless LAN control unit 301. The frame processing unit 302 generates wireless frames including control information and content data in accordance with the IEEE 802.11 series standards and transfers them to the wireless LAN control unit 301. The wireless LAN control unit 301 then performs predetermined wireless processing, such as frequency conversion, on the generated wireless frames and transmits them to other communication devices. The wireless LAN control unit 301 also receives wireless frames transmitted by other communication devices via the antenna, performs predetermined wireless processing on the wireless frames, and transfers them to the frame processing unit 302. The frame processing unit 302 then analyzes the contents of the received wireless frames to acquire the control information and content data. The control information generated by the frame processing unit 302 and the control information acquired by the frame processing unit 302 based on wireless frames from other communication devices may be restricted by settings stored in the storage unit 201. This control information may also be changed by user settings from the UI control unit 304 .

[0034] The EMLMR management unit 303 performs management control to determine which of multiple links established with other communication devices will be EMLMR links. Management control includes the establishment of EMLMR links and the deletion of EMLMR links. An EMLMR link is established by identifying an EMLMR link when or after the establishment of a multi-link. Furthermore, when a link identified as an EMLMR link is removed from that identification, the EMLMR link is deleted.

[0035] The UI control unit 304 controls hardware related to the user interface, such as a touch panel and buttons for accepting operations by a user (not shown) of the communication device. The UI control unit 304 also controls the display of images and the like, or the presentation of information such as audio output to the user. The storage control unit 305 controls the storage unit 201 to store programs and data for operating the communication device, and the like, and controls the reading of these programs and data from the storage unit 201.

[0036] (Overview of multi-link communication) Next, multi-link communication will be outlined using FIG. 4. The AP MLD 102 and the non-AP MLD 103 each have a plurality of (physical or logical) APs and STAs associated with a plurality of links. In FIG. 4, for example, the AP MLD 102 includes a first AP 401 to a third AP 403, and the non-AP MLD 103 includes a first STA 404 to a third STA 406. The first AP 401 and the first STA 404 establish a first link 407 using a first frequency channel. Similarly, the second AP 402 and the second STA 405 establish a second link 408 using a second frequency channel, and the third AP 403 and the third STA 406 establish a third link 409 using a third frequency channel. The first to third frequency channels are, for example, any of the frequency channels in the sub-GHz band, 2.4 GHz band, 3.6 GHz band, 4.9 and 5 GHz bands, 6 GHz band, and 60 GHz band. Hereinafter, the first link 407, the second link 408, and the third link 409 will be referred to as link 1, link 2, and link 3, respectively.

[0037] The number of spatial streams is assigned to each of Link 1 to Link 3 according to the per-link spatial stream capability. The per-link spatial stream capability indicates, for example, the number of spatial streams available for each link. For example, a link with a spatial stream capability of "2" can have two spatial streams configured for that link. The communication device performs spatial division within the spatial stream capability range and can transmit multiple data streams in parallel at the same timing and in the same frequency band to avoid spatial interference. In one example, if there are six antennas and three links are established, each link can be configured as a link using two antennas. In this case, the spatial stream capability of each link is "2." Here, if two of Link 1 to Link 3 are identified as EMLMR links, the spatial stream capability of one of the links that performs EMLMR operation is "4." Furthermore, if all of Link 1 to Link 3 are identified as EMLMR links, the spatial stream capability of one link performing communication by EMLMR operation will be "6." On the other hand, if EMLMR operation is performed on another link, the spatial stream capability of the other EMLMR link will be "0." For example, if Link 1 and Link 2 are configured as EMLMR links, when EMLMR operation is performed on Link 1, the spatial stream capability of Link 1 will be "4," and the spatial stream capability of Link 2 will be "0." By using EMLMR, the spatial stream capability of a specific link can be temporarily increased, enabling high-speed, high-capacity communication on that link.

[0038] Note that "EMLMR operation" here refers to communication using the EMLMR mechanism. In other words, EMLMR operation is performed on a link among EMLMR links that communicates by increasing spatial stream capability. On the other hand, among EMLMR links, for a link in which another EMLMR link is in EMLMR operation, the spatial stream capability is used by the other link according to the EMLMR mechanism. In other words, this link can also be said to operate in accordance with EMLMR, but this operation is not called EMLMR operation.

[0039] The number of spatial streams may be determined by an EHT Capabilities element or an EHT Operation element included in a frame in which Non-AP MLD declares to AP MLD that it supports EHT. For example, the number of spatial streams may be determined based on the value of the Supported EHT-MCS And NSS Set field included in the EHT Capabilities element or the EHT Operation element. Alternatively, the number of spatial streams may be determined based on the value of the Basic EHT-MCS And NSS Set field included in these information elements.

[0040] Here, the information elements used for setting EMLMR will be described. FIG. 5(A) shows a Basic variant Multi-Link element in an Association Request frame. This Basic variant Multi-Link element may be included, for example, in an Association Request frame when establishing a Multi-Link. However, this information is not limited to this, and may also be included in, for example, a Probe request frame, a Probe response frame, an Association response frame, or a Beacon frame. In FIG. 5(A), the values ​​of the Element ID and Element ID Extension fields indicate that this information element is a Basic variant Multi-Link element. The Length field indicates the length of this information element. The Multi-Link Control field stores control information related to the multi-link. This field will not be described in detail here. After the Multi-Link Control field, a Common Info field is placed, which stores information common to one or more STAs. This Common Info field includes an EMLMR Capabilities subfield, as shown in FIG. 5(B). This is followed by a Link Info field, which stores a profile for each STA (Per-STA Profile). This field will also not be described in detail here.

[0041] In the EMLMR Capabilities subfield in Figure 5(B), setting the EMLMR Support field to "0" indicates that the sender of this information does not support EMLMR. On the other hand, setting this field to "1" indicates that the sender of this information supports EMLMR. By sending / receiving or exchanging frames containing the EMLMR Support subfield set to the value "1", each link constituting a multilink can be configured as an EMLMR link.

[0042] Note that an EMLMR link may be established only on some of the links constituting a multilink by transmitting / receiving or exchanging the information on only some of the links. Alternatively, an EMLMR link may be established on multiple links, including other links, by transmitting / receiving or exchanging a frame including an EMLMR Support subfield set to a value of "1" on one link. In this case, an EMLMR link may be established on all of the links constituting a multilink, or on only some of the links. When specifying the link on which an EMLMR link is to be established, information for identifying the link on which the EMLMR link is to be established may be included in a frame including an EMLMR Support subfield set to a value of "1." This specifies the link on which the EMLMR link should be established. The information for identifying the link may be the link identifier, the BSSID (Basic Service Set Identifier) ​​corresponding to the link, the TID (Traffic Identifier), etc.

[0043] In the EMLMR Capabilities subfield in Figure 5(B), the EMLMR Supported MCS And NSS Set subfield stores the maximum number of spatial streams when transmitting and receiving PPDUs during EMLMR operation. When a specific link among EMLMR links operates as an EMLMR, the number of spatial streams assigned to EMLMR links other than that link is reduced, and the specific EMLMR link can transmit and receive PPDUs with an increased number of spatial streams.

[0044] In the above description, an instruction to establish an EMLMR link is given when a multi-link is established. However, the establishment of an EMLMR link may be specified by an Action frame transmitted after the multi-link is established. For this purpose, for example, a frame called an EML (Enhanced Multi-Link) Operating Mode Notification frame may be used. For example, the AP MLD transmits a frame including an EMLMR Support subfield with a value of "1," and the non-AP MLD receives this frame. Then, the non-AP MLD transmits an EML Operating Mode Notification frame including an EMLMR Mode subfield with a value of "1," and the AP MLD receives this frame. As a result, the link used when transmitting and receiving these frames may be configured as an EMLMR link. At this time, some or all of the other links constituting the multi-link that do not transmit or receive these frames may also be configured as EMLMR links. When some links are configured as EMLMR links, information for identifying the links specified as EMLMR links may be included in the EML Operating Mode Notification frame. As in the above case, the information for identifying the link may be a link identifier, a BSSID, a TID, or the like.

[0045] Although the example described here is one in which non-AP MLD takes the initiative in establishing an EMLMR link, AP MLD may also instruct the establishment of an EMLMR link. The EML Operating Mode Notification frame is an Action frame transmitted by non-AP MLD to operate in EMLMR mode. Non-AP MLD does not establish an EMLMR link when multi-link communication is established, but will transmit this EML Operating Mode Notification frame when establishing an EMLMR link thereafter. The EML Operating Mode Notification frame is also transmitted when an EMLMR link is set up and then deleted from the EMLMR link, and then the link is made to operate in EMLMR mode again.

[0046] (Communication flow) Next, an example of the flow of communication (frame exchange sequence) executed in this embodiment will be described with reference to FIG. 6. Here, an example of the flow of communication when data is transmitted from the AP MLD 102 to the non-AP MLD 103 will be described. It is assumed that the AP MLD 102 sets link 1 and link 2 in FIG. 4 as EMLMR links. For simplicity of explanation, it is assumed that the spatial stream capability of each link when EMLMR operation is not performed is "1," and the spatial stream capability of the link when EMLMR operation is performed is "2." It is noted that in FIG. 6, the AP functions used by the AP MLD 102 on the frequency channels of link 1 and link 2 are indicated as "AP1" and "AP2," respectively. Furthermore, the STA functions used by the non-AP MLD 103 on the frequency channels of link 1 and link 2 are indicated as "STA1" and "STA2," respectively.

[0047] In FIG. 6, time progresses from left to right, and radio frames transmitted and received over each link are shown along the time axis. Regarding AP functions, only the communication status of the transmitting side (TX) is shown. Regarding STA functions, the communication status of the transmitting side (TX) is shown at the top of the time axis, and the communication status of the receiving side (RX) is shown at the bottom. As an example, the AP MLD 102 always has at least one receiving function active on each link, even during EMLMR operation, and its spatial stream capability is always equal to or greater than that of the non-AP MLD 103. For example, the spatial stream capability of the AP MLD 102 is assumed to be "2" for both Link 1 and Link 2. In this case, the AP MLD 102 does not need to change its spatial stream capability even when the non-AP MLD 103 is operating in EMLMR mode.

[0048] Note that the "SS" in the radio frame shown on the transmitting side refers to the spatial stream used when transmitting a signal. For example, a radio frame shown as "2SS" is transmitted using two spatial streams. Also, the "SS" shown on the receiving side indicates the number of spatial streams that can be received. For example, a section shown as "2SS" on the receiving side indicates that two spatial streams can be received. Note that the period when 2SS is available is indicated by a wider vertical block. Also, the section shown by the dashed line on the receiving side indicates a state in which the number of available spatial streams is zero due to EMLMR operation being performed on another link, and reception is not possible. Note that the period shown as "RX SW" on the receiving side is the period required for the receiving function to change its settings and restart in order to move between links, i.e., the switching period.

[0049] In the following description, it is assumed that the AP MLD 102 transmits a data frame in EMLMR mode with spatial stream "2" to the non-AP MLD 103 on link 1. In this case, the AP MLD 102 first transmits an RTS (Request To Send) frame containing information necessary for EMLMR operation (F601). The non-AP MLD 103 can recognize that EMLMR operation is being started by this RTS frame. Then, upon receiving the RTS frame, if the non-AP MLD 103 is capable of EMLMR operation, it transmits a CTS (Clear To Send) frame to the AP MLD 102 in response to the RTS frame (F602). The non-AP MLD 103 notifies the AP MLD 102 by this CTS frame that it is capable of receiving a data frame with spatial stream "2" in EMLMR operation. The non-AP MLD 103 can also notify other surrounding communication devices using the same frequency channel of its NAV. Furthermore, the Non-AP MLD 103 moves the receiving function on link 2 to link 1, and sets the number of spatial streams for reception on link 1 to 2 and the number of spatial streams for reception on link 2 to 0 (F603). After the CTS frame transmission on link 1 is completed and the SIFS period has elapsed, the Non-AP MLD 103 starts transmission with the number of spatial streams set to "2", so the Non-AP MLD 103 operates to complete the transfer of the receiving function by then.

[0050] After receiving the CTS frame, the AP MLD 102 starts transmitting a data frame with the spatial stream set to "2" after a SIFS period has elapsed (F604). While Fig. 6 shows an example in which a data frame is transmitted immediately after the CTS frame, a procedure may be added in which the non-AP MLD 103 or the AP MLD 102 transmits a sounding packet before transmitting the data frame.

[0051] When the non-AP MLD 103 completes reception of the data frame with two spatial streams (F605), it transmits a Block Ack for the received data frame after the SIFS period has elapsed (F606). In addition, the non-AP MLD 103 returns the reception function that was concentrated on link 1 to link 2 (F607). This returns the non-AP MLD 103 to the state it was in before the EMLMR operation was started.

[0052] Before the non-AP MLD 103 resumes reception on link 2, it cannot recognize that another STA or AP has set a NAV on link 2. Therefore, in one example, after the non-AP MLD 103 resumes reception on link 2, it waits for transmission during the NAVSyncDelay period and monitors the usage status of the frequency channel. If the non-AP MLD 103 detects that a new NAV is set by another communication device before the end of this period, it stops waiting for transmission and can perform normal operation according to the newly set NAV. On the other hand, if a new NAV is not set, the non-AP MLD 103 performs normal operation after the NAVSyncDelay period expires. This reduces the probability that a signal transmitted by the non-AP MLD 103 on link 2 will collide with a transmission signal transmitted by another communication device. On the other hand, if the frequency channel is not congested, it is expected that such a collision will not occur even if the non-AP MLD 103 does not wait for the NAVSyncDelay period. That is, if transmission is delayed for the NAVSyncDelay period, the communication throughput cannot be improved by the time it is delayed.

[0053] However, the non-AP MLD 103 cannot independently determine whether a NAV has been set by another communication device immediately after resuming reception operations on link 2. On the other hand, the AP MLD 102 is constantly performing reception operations on link 2, even while communication is being performed using EMLMR. Therefore, the AP MLD 102 can determine whether a NAV has been set. Therefore, in this embodiment, the AP MLD 102 can notify the non-AP MLD 103 according to the NAV setting status on link 2. Furthermore, the AP MLD 102 can set and notify a new NAV according to the NAV setting status on link 2. In this way, the AP MLD 102 can cause the non-AP MLD 103 to wait, for example, for a period of time according to the NAV setting status. In other words, if a NAV has not been set on link 2, the AP MLD 102 notifies the non-AP MLD 103 so that it can transmit a signal on link 2 before waiting for the NAVSyncDelay period. In one example, the AP MLD 102 may transmit a CTS frame addressed to the non-AP MLD 103 so that the non-AP MLD 103 can transmit a signal on link 2. This CTS frame allows the AP MLD 102 to set a NAV on link 2, allowing the non-AP MLD 103 to transmit data on link 2 without waiting the NAVSyncDelay period. In other words, by addressing the CTS frame to the non-AP MLD 103, the non-AP MLD 103 can transmit data after sending and receiving the CTS frame.

[0054] This CTS frame is transmitted after the timing when it is assumed that the non-AP MLD 103 has resumed reception on link 2, and before the NAVSyncDelay period has elapsed since the reception operation was resumed. After the NAVSyncDelay period has elapsed, the non-AP MLD 103 can perform normal transmission operations on link 2, so no special action is required from the AP MLD 102. Furthermore, if another communication device notifies a new NAV, the AP MLD 102 no longer needs to transmit this CTS frame.

[0055] Furthermore, the AP MLD 102 may, for example, notify the non-AP MLD 103 of information indicating whether or not a NAV has been set. For example, if a NAV has not been set, the non-AP MLD 103 may not wait for the NAVSyncDelay period, and if a NAV has been set, may wait for the NAVSyncDelay period. Furthermore, if a NAV has been set, information specifying the period of that NAV may be notified to the non-AP MLD 103, and the non-AP MLD 103 may wait for that period.

[0056] In one example, during EMLMR operation, the non-AP MLD 103 may notify the AP MLD 102 of buffer status information for link 2 via link 1. Then, when the non-AP MLD 103 has data to transmit via link 2, the AP MLD 102 may transmit a CTS frame to cause the non-AP MLD 103 to transmit the data. Furthermore, after communication during EMLMR operation is completed, the AP MLD 102 may transmit a CTS frame if link 1 is being used by another communication device and transmission / reception via link 1 is not possible. Furthermore, for example, if the data frame is a TCP packet, the AP MLD 102 can predict that the non-AP MLD 103 will transmit a TCP Ack response. Therefore, the AP MLD 102 can appropriately set the NAV period set in the CTS frame to match the TCP Ack.

[0057] Note that, when the non-AP MLD 103 does not have data to transmit on link 2, the AP MLD 102 can notify the non-AP MLD 103 only of whether or not a NAV has been set. Furthermore, when the AP MLD 102 itself transmits data on the frequency channel of link 2, it can also transmit the data while the non-AP MLD 103 is waiting for the NAVSyncDelay period. This allows the non-AP MLD 103 to obtain a transmission opportunity earlier than if it waited for the NAVSyncDelay period when a NAV has not been set on link 2 and the non-AP MLD 103 should transmit data on link 2.

[0058] (AP MLD102 processing) 7 shows an example of the flow of processing executed by the AP MLD 102. This processing can be realized, for example, by the control unit 202 of the AP MLD 102 executing a program stored in the storage unit 201. Note that at least a part of the processing shown below may be executed by dedicated hardware provided in the AP MLD 102.

[0059] In this process, first, the AP MLD 102 executes a setting process to apply EMLMR to two or more links between the AP MLD 102 and the non-AP MLD 103, thereby establishing EMLMR links (S701). Note that some of the multiple links established between the AP MLD 102 and the non-AP MLD 103 may be selected as two or more EMLMR links to which the above-mentioned EMLMR is applied, or all of the multiple links may be selected as EMLMR links. Here, it is assumed that two links, link 1 and link 2, are set as EMLMR links, as described in FIG. 6.

[0060] As described above, the AP MLD 102 starts communication with the non-AP MLD 103 using a series of EMLMR operations starting with the RTS frame, and continues communication using the EMLMR operations until the communication is completed (S702, S703). While the EMLMR operation is being performed, all of the reception functions of the non-AP MLD 103 are used for the EMLMR operation on link 1. Therefore, even if another communication device notifies the non-AP MLD 103 of a NAV on link 2, the non-AP MLD 103 cannot receive it. Therefore, during the EMLMR operation, the AP MLD 102 monitors to determine the NAV setting status on link 2. After the EMLMR operation is completed, the AP MLD 102 determines whether to transmit a CTS frame to the non-AP MLD 103, for example, depending on the NAV setting status on link 2 and whether or not there is a frame for the AP MLD 102 to transmit.

[0061] For example, if NAV is set in link 2 while the non-AP MLD 103 is performing EMLMR operation in link 1 (YES in S704), the AP MLD 102 does nothing. As a result, the non-AP MLD 103 waits for the NAVSyncDelay period before transmitting a frame. Note that if the set NAV period expires before the NAVSyncDelay period expires, the AP MLD 102 may send a predetermined notification to the non-AP MLD 103 to cancel the standby state. Also, if the AP MLD 102 has a frame to transmit on link 2 (YES in S705), the AP MLD 102 transmits the frame from its own device and does nothing to the non-AP MLD 103. As a result, the non-AP MLD 103 waits for the NAVSyncDelay period before transmitting a frame. If the AP MLD 102 completes frame transmission before the NAVSyncDelay period expires, the AP MLD 102 may transmit a predetermined notification to the Non-AP MLD 103 to release the standby state.

[0062] On the other hand, if the NAV is not set in link 2 and the AP MLD 102 does not have a frame to transmit on link 2 (NO in S704 and S705), the AP MLD 102 transmits a CTS frame addressed to the non-AP MLD 103 (S706). Note that the AP MLD 102 transmits the CTS frame at a timing after the non-AP MLD 103 has completed the EMLMR operation on link 1 and resumed the receiving operation on link 2. This prevents the non-AP MLD 103 from transmitting a CTS frame at a timing before the non-AP MLD 103 has started the receiving operation on link 2, and makes it possible to reliably detect the CTS frame by the non-AP MLD 103.

[0063] The AP MLD 102 may determine whether the non-AP MLD 103 can receive data on link 2 during EMLMR communication, and may execute the processes of S704 to S706 only if such reception is not possible. In other words, the non-AP MLD 103 may perform the notification of S706 only if it is not possible to recognize that the NAV is being set by another nearby communication device.

[0064] 8 shows an example of the flow of processing executed by the non-AP MLD 103. This processing can be realized, for example, by the control unit 202 of the non-AP MLD 103 executing a program stored in the storage unit 201. Note that at least part of the processing shown below may be executed by dedicated hardware provided in the non-AP MLD 103.

[0065] S801 to S803 correspond to S701 to S703. That is, the non-AP MLD 103 executes a setting process to apply EMLMR to two or more links between the non-AP MLD 103 and the AP MLD 102, thereby establishing an EMLMR link (S801). Here, as described in FIG. 6, it is assumed that two links, link 1 and link 2, are set as EMLMR links. As described above, the non-AP MLD 103 starts communication with the AP MLD 102 using a series of EMLMR operations, starting with the reception of an RTS frame on link 1, and continues communication using the EMLMR operation until the communication is completed (S802, S803). After completing communication on link 1 using the EMLMR operation, the non-AP MLD 103 resumes reception operation on link 2 (S804).

[0066] Thereafter, if the non-AP MLD 103 receives a CTS frame on link 2 (YES in S805), it transmits a signal or sets a NAV in accordance with the CTS frame (S806). For example, if the non-AP MLD 103 receives a CTS frame addressed to its own device and there is a frame to transmit, it transmits the frame after completing reception of the CTS frame. On the other hand, even if the non-AP MLD 103 receives a CTS frame addressed to its own device, if there is no frame to transmit, it may terminate processing without performing a transmission operation. Furthermore, if the non-AP MLD 103 receives a CTS frame not addressed to its own device from any communication device (AP MLD 102 or another communication device), it may set a NAV in accordance with the CTS frame. In this case, even if the non-AP MLD 103 holds a frame to transmit on link 2, it waits without transmitting the frame until the NAV period expires. On the other hand, if the Non-AP MLD 103 does not receive a CTS frame on link 2 (NO in S805), it waits for the NAVSyncDelay period before transmitting (S807). This allows the Non-AP MLD 103 to wait for a certain period of time before transmitting a wireless frame if it does not receive a CTS frame addressed to itself from the AP MLD 102, for example.

[0067] Note that, other than the CTS frame, any procedure may be used that allows the non-AP MLD 103 to confirm that another communication device has not set a NAV when the non-AP MLD 103 resumes receiving operations on link 2. For example, the AP MLD 102 may notify the non-AP MLD 103 that a NAV has not been set on link 2 by transmitting a null data packet, which is a zero-length data frame, instead of a CTS frame. Furthermore, when a CTS frame is used, the non-AP MLD 103 may not be granted a transmission right. Alternatively, the length of the NAV period may be minimized, and a CTS frame addressed to the non-AP MLD 103 may be transmitted. In other words, the non-AP MLD 103 may be provided with a short transmission opportunity, such as that used to transmit a TCP Ack. Furthermore, when such a short NAV is set, it is possible to prevent the frequency channel from being unnecessarily occupied when there is no data to transmit in the non-AP MLD 103. Note that an RTS frame may be used instead of a CTS frame. Also, the NAV status of link 2, which has resumed receiving operations, may be notified using link 1, which has been communicating via EMLMR.

[0068] In the above example, the AP MLD 102 notifies the non-AP MLD 103, but this is not limiting. For example, if the non-AP MLD 103 can receive a signal transmitted from another surrounding communication device on link 2 while EMLMR is in operation on link 1, the non-AP MLD 103 may execute the processing of the AP MLD 102 described above. Furthermore, both the AP MLD 102 and the non-AP MLD 103 may notify each other of information regarding the NAV set by another surrounding communication device. That is, a communication device that can receive signals from another communication device on a link not used in EMLMR communication at least during that communication may execute processing similar to the AP MLD 102 described above. That is, this communication device notifies the other communication device of the communication status of a link not used in EMLMR communication. In this way, if a partner device in EMLMR communication is unable to perform reception on that link during EMLMR operation, the partner device can be notified of the communication status of that link and can set a NAV as necessary.

[0069] The above-described processing can also be applied to multi-link communications other than EMLMR communications, which aggregate and transmit available spatial streams from some links to other links. That is, the above-described processing can be applied when there is a communication device that cannot receive signals on other links by aggregating and using available spatial streams (or antennas) on multiple links into one link.

[0070] As described above, according to this embodiment, when a communication device resumes reception operation on an EMLMR link that was not used in EMLMR operation, data transmission can be started in a shorter time than waiting for the NAVSyncDelay period. In the above example, an example has been described in which notification from the AP MLD 102 to the non-AP MLD 103 is controlled according to information about the NAV setting status on link 2. However, this is not limiting. For example, a communication status including conditions for signal transmission, such as a limit on transmission power on link 2 or a limit on the number of transmission streams, may be identified, and information about the identified communication status may be notified. For example, during EMLMR communication with the non-AP MLD 103 on link 1, the AP MLD 102 identifies the communication status by monitoring whether a limit is imposed on signal transmission on link 2. Then, if the communication status continues after the EMLMR communication ends, the AP MLD 102 may notify the non-AP MLD 103 of information indicating the communication status (i.e., the conditions under which signal transmission is permitted). This information may be notified, for example, using link 1 during EMLMR communication, or may be notified using link 1 or link 2 after EMLMR communication. In one example, information regarding the conditions under which signal transmission is permitted may be notified only when the NAV is not set. That is, when the NAV is set, the device may wait for the NAVSyncDelay period without notifying anything, or may transmit a CTS frame for setting the NAV at least until the NAV expires. On the other hand, when the NAV is not set and signal transmission is possible but is subject to restrictions, the device may notify the restrictions. Note that if it is known that the remote device cannot comply with the restrictions, no notification may be sent. This avoids unnecessary waiting for signal transmission when signal transmission is possible, thereby improving communication efficiency.

[0071] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0072] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0073] 102: AP MLD, 103: Non-AP MLD, 201: storage unit, 202: control unit, 206: communication unit, 301: wireless LAN control unit, 303: EMLMR control unit

Claims

1. A communication device that communicates in accordance with the IEEE 802.11 series standard, a communication means for aggregating spatial streams available to a communication partner device over a plurality of links into a first link among the plurality of links, and performing predetermined communication with the communication partner device; a specifying means for specifying a communication status of a second link different from the first link among the plurality of links while the predetermined communication is being performed on the first link; a notification means for transmitting a predetermined notification to the other device based on the fact that the communication status in which the other device can transmit a signal has been identified in the second link when the predetermined communication in the first link has been completed; A communication device comprising:

2. the specifying means specifies, as the communication status, whether or not signal transmission is prohibited in the second link; the notification means transmits the predetermined notification to the counterpart device when the predetermined communication is completed on the first link and signal transmission on the second link is not prohibited.

2. The communication device according to claim 1.

3. The communication device according to claim 2, characterized in that, when signal transmission is prohibited on the second link when the specified communication is terminated on the first link, and when a first period during which signal transmission is prohibited does not exceed a second period during which the other device will not transmit a signal if the specified notification is not made, the notification means sends a notification to the other device to prohibit signal transmission until the first period expires.

4. 4. The communication device according to claim 3, wherein the notification for prohibiting signal transmission until the first period expires is a CTS (Clear To Send) frame not addressed to the other device.

5. 5. The communication device according to claim 2, wherein the predetermined notification is a CTS (Clear To Send) frame addressed to the other device.

6. The communication device according to claim 5 , wherein the predetermined notification is a CTS frame addressed to the other device, and a shortest transmission prohibition period is set in the CTS frame.

7. 3. The communication device according to claim 2, wherein the predetermined notification is a null data packet.

8. the specifying means specifies, as the communication status, a condition under which signal transmission is permitted through the second link; the notification means, when a condition exists under which signal transmission is permitted on the second link, transmits the condition to the counterpart device as the predetermined notification; 2. The communication device according to claim 1.

9. The specifying means further specifies, as the communication status, whether or not signal transmission is prohibited in the second link; the notification means, when the predetermined communication is terminated on the first link, if signal transmission on the second link is not prohibited and there is a condition that allows signal transmission on the second link, transmits the condition to the other device as the predetermined notification; 9. The communication device according to claim 8.

10. 10. The communication device according to claim 1, wherein the notification means transmits the predetermined communication through the first link.

11. 10. The communication device according to claim 1, wherein the notification means transmits the specified communication on the second link at a timing when the other device can receive a signal on the second link after completing the specified communication on the first link.

12. The method further includes determining whether the other device can receive a signal through the second link while the predetermined communication is being performed, A communication device described in any one of claims 1 to 11, characterized in that when the other device is unable to receive a signal on the second link while the specified communication is being performed, the notification means sends a specified notification to the other device based on the fact that the communication situation in which the other device can transmit a signal on the second link is identified when the specified communication is terminated on the first link.

13. 13. The communication device according to claim 1, wherein the predetermined communication is communication using EMLMR (Enhanced Multi-Link Multi-Radio).

14. A communication device that operates as an MLD (Multi-link Device) defined in the IEEE 802.11 series standard, A communication device having a communication means for setting a transmission prohibition period for another link that does not operate with EMLMR (Enhanced multi-link multi-radio) when a frame exchange sequence is started with EMLMR (Enhanced multi-link multi-radio) operation on a first link among a plurality of links established with a partner device.

15. A control method executed by a communication device that communicates in accordance with the IEEE 802.11 series standard, comprising: aggregating spatial streams that can be used by a communication partner device on a first link among the plurality of links, and performing predetermined communication with the communication partner device; Identifying a communication status of a second link different from the first link among the plurality of links while the predetermined communication is being performed on the first link; transmitting a predetermined notification to the other device based on the fact that the communication situation in which the other device can transmit a signal has been identified in the second link when the predetermined communication in the first link has been completed; A control method comprising:

16. A program for causing a computer to function as the communication device according to any one of claims 1 to 14.

Images