Method and apparatus for protecting multi-user (MU) transmissions

Abstract

Described herein are methods and apparatus for protecting multi-user (MU) transmissions. An apparatus includes a receiver, a transmitter, and a processor. The receiver and processor detect a trigger frame regarding an uplink (UL) multi-user (MU) transmission. The processor and transmitter generate and send a frame in response to the trigger frame, and transmit channel availability information regarding multiple channels in response to the trigger frame. The receiver and processor detect data in a resource unit (RU) in a downlink (DL) MU physical layer (PHY) protocol data unit (PPDU) on one of the multiple channels. The one of the multiple channels is based on the transmitted channel availability information.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 201780005564.6, entitled “Method and Apparatus for Protecting Multi-User (MU) Transmission”, filed on January 6, 2017, the contents of which are incorporated herein by reference.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 276,090, filed January 7, 2016, the contents of which are incorporated herein by reference. Summary of the invention

[0004] Described herein are methods and apparatus for protecting multi-user (MU) transmissions. An apparatus includes: a receiver, a transmitter, and a processor. The receiver and processor detect a trigger frame regarding an uplink (UL) multi-user (MU) transmission. The processor and transmitter generate and transmit a frame in response to the trigger frame, and transmit channel availability information regarding multiple channels in response to the trigger frame. The receiver and processor detect data in a resource unit (RU) in a downlink (DL) MU physical layer (PHY) protocol data unit (PPDU) on one of the multiple channels. The one of the multiple channels is based on the transmitted channel availability information. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] A more detailed understanding may be obtained from the following description given by way of example in conjunction with the accompanying drawings, in which:

[0006] Figure 1A is a system diagram of an example communication system in which one or more disclosed embodiments may be implemented;

[0007] Figure 1B Yes, you can Figure 1A A system diagram of an example wireless transmit / receive unit (WTRU) used within the communication system shown;

[0008] Figure 1C Yes, you can Figure 1A A system diagram of an example radio access network and an example core network used within the communication system shown;

[0009] Figure 2 is a diagram of an example of a multi-user (MU) request to send (RTS) with a simultaneous clear to send (CTS);

[0010] Figure 3 is a diagram of an example trigger frame for MU transmission;

[0011] Figure 4 is a diagram providing other examples of trigger frame formats;

[0012] Figure 5 is a diagram of an example of access point (AP) scheduling with overlapping basic service set (OBSS) interference avoidance;

[0013] Figure 6 is a flowchart of another example of AP scheduling with OBSS interference avoidance;

[0014] Fig. 7A and 7B is a diagram of an example method for using a trigger frame to trigger a frame relay retransmission in a downlink (DL) MU transmission;

[0015] Figure 8 is a signal diagram of an example multi-user request to send / clear to send (MU-RTS / CTS) supporting both high throughput (HT) and non-HT CTS frames for backward compatibility;

[0016] Fig. 9 is a diagram of an example of using MU-RTS and split CTS to protect MU transmission opportunities (TXOPs);

[0017] Fig.10 is a flow chart of an exemplary method for splitting CTX;

[0018] Fig.11 is a flow chart of another example of using a trigger frame by an AP to poll a split CTS of a user-specific sequence (USS);

[0019] Fig.12 is a diagram of an example of code division multiple access (CDMA) for a USS frame;

[0020] Fig.13 is a diagram of an example common information field of a trigger frame;

[0021] Fig.14 is a diagram of an example user information field of a trigger frame;

[0022] Fig.15 is a diagram of an exemplary user-specific sequence (USS) frame;

[0023] Fig.16 is a diagram of an example of MU-RTS and simultaneous CTS operation using energy measurement;

[0024] Fig.17 is a diagram of another example of MU-RTS and simultaneous CTS operation using energy measurement;

[0025] Fig.18is a diagram of an example of MU-RTS with simultaneous CTS using CTS triggering;

[0026] Fig.19 is a diagram of an example of semi-protection for DL ​​MU transmission;

[0027] Fig. 20 is an illustration of another semi-protection example for DL ​​MU transmission;

[0028] Fig.21 is a diagram of an example of semi-protection for uplink (UL) MU transmission;

[0029] Fig. 22 is a diagram of an example of semi-protection for cascaded MU transmission;

[0030] Fig.23 is a diagram of an example of dual protection for DL ​​MU transmission;

[0031] Fig.24 is a diagram of another dual protection example for DL ​​MU transmission;

[0032] Fig.25 is a diagram of an example of dual protection for UL MU transmission;

[0033] Fig.26 is a diagram of another dual protection example for UL MU transmission;

[0034] Fig. 27 is a diagram showing a situation where an OBSS network allocation vector (NAV) unnecessarily prohibits directional transmissions;

[0035] Fig.28 is a diagram showing a situation where the OBSS is unaware of the directional transmission of the neighboring BSS;

[0036] Fig.29A and 29B is a diagram of an example of using an OBSS Facilitation Information (OFI) to indicate to a station (STA) whether a directional transmission may be sent while setting OBSSNAV;

[0037] Fig.30 is a diagram of three pre-HE-STF preamble formats. DETAILED DESCRIPTION

[0038] Figure 1Ais a diagram of an exemplary communication system 100 in which one or more disclosed embodiments may be implemented. The communication system 100 may be a multiple access system that provides content such as voice, data, video, messaging, broadcast, etc. to multiple wireless users. The communication system 100 may allow multiple wireless users to access such content by sharing system resources including wireless bandwidth, and as an example, the communication system 100 may use one or more channel access methods such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single carrier FDMA (SC-FDMA), etc.

[0039] like Figure 1A As shown, the communication system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it should be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network components. Each WTRU 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. For example, the WTRUs 102a, 102b, 102c, 102d may be configured to transmit and / or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular phone, a personal digital assistant (PDA), a smart phone, a laptop, a netbook, a personal computer, a wireless sensor, a consumer electronic device, and the like.

[0040] The communication system 100 may also include a base station 114a and a base station 114b. Each base station 114a, 114b may be any type of device configured to facilitate access to one or more communication networks, such as the core network 106, the Internet 110, and / or other networks 112, by wirelessly interfacing with at least one WTRU 102a, 102b, 102c, 102d. The base stations 114a, 114b may be, by way of example, a base transceiver station (BTS), a Node B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. Although each base station 114a, 114b is depicted as a single component, it should be appreciated that the base stations 114a, 114b may include any number of interconnected base stations and / or network components.

[0041] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network components (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station 114a and / or the base station 114b may be configured to transmit and / or receive wireless signals within a specific geographic area called a cell (not shown). The cell may be further divided into cell sectors. For example, the cell associated with the base station 114a may be divided into three sectors. Thus, in one embodiment, the base station 114a may include three transceivers, that is, each transceiver corresponds to a sector of the cell. In another embodiment, the base station 114a may use multiple-input multiple-output (MIMO) technology, and thus multiple transceivers may be used for each sector in the cell.

[0042] The base stations 114a, 114b may communicate with one or more WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0043] More specifically, as described above, the communication system 100 may be a multiple access system and may use one or more channel access schemes such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, etc. As an example, the base station 114a in the RAN 104 and the WTRUs 102a, 102b, 102c may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may use Wideband CDMA (WCDMA) to establish the air interface 116. WCDMA may include communication protocols such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink Packet Access (HSDPA) and / or High Speed ​​Uplink Packet Access (HSUPA).

[0044] In another embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface 116 using Long Term Evolution (LTE) and / or LTE-Advanced (LTE-A).

[0045] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement radio access technologies such as IEEE 802.16 (Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1X, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile Communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like.

[0046] As an example, Figure 1A The base station 114b in the example may be a wireless router, a Home NodeB, a Home eNodeB, or an access point, and may use any appropriate RAT to facilitate wireless connectivity in a local area such as a business location, a residence, a vehicle, a campus, or the like. In one embodiment, the base station 114b and the WTRUs 102c, 102d may establish a wireless local area network (WLAN) by implementing a radio technology such as IEEE 802.11. In another embodiment, the base station 114b and the WTRUs 102c, 102d may establish a wireless personal area network (WPAN) by implementing a radio technology such as IEEE 802.15. In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may establish a picocell or a femtocell by using a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.). Figure 1A As shown, the base station 114b can be directly connected to the Internet 110. Thus, the base station 114b does not need to access the Internet 110 via the core network 106.

[0047] The RAN 104 may be in communication with a core network 106, which may be any type of network configured to provide voice, data, application and / or voice over Internet Protocol (VoIP) services to one or more WTRUs 102a, 102b, 102c, 102d. For example, the core network 106 may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and / or perform high-level security functions such as user authentication. Although Figure 1AAlthough not shown, it should be appreciated that the RAN 104 and / or the core network 106 may communicate directly or indirectly with other RANs, and that these RANs may use the same RAT or different RATs. For example, in addition to being connected to the RAN 104 using E-UTRA radio technology, the core network 106 may also communicate with another RAN (not shown) using GSM radio technology.

[0048] The core network 106 may also act as a gateway for the WTRUs 102a, 102b, 102c, 102d to access the PSTN 108, the Internet 110, and / or other networks 112. The PSTN 108 may include a circuit-switched telephone network that provides plain old telephone service (POTS). The Internet 110 may include a global system of interconnected computer network devices that use a common communication protocol, and the protocol may be the Transmission Control Protocol (TCP), the User Datagram Protocol (UDP), and the Internet Protocol (IP) in the TCP / IP Internet protocol suite. The networks 112 may include wired or wireless communication networks owned and / or operated by other service providers. For example, the networks 112 may include another core network connected to one or more RANs, which may use the same RAT as the RAN 104 or a different RAT.

[0049] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communication system 100 may include multi-mode capabilities, that is, the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links. Figure 1A The illustrated WTRU 102c may be configured to communicate with the base station 114a, which may employ a cellular-based radio technology, and with the base station 114b, which may employ an IEEE 802 radio technology.

[0050] Figure 1B is a system diagram of an example WTRU 102. Figure 1B As shown, the WTRU 102 may include a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a numeric keypad 126, a display / touchpad 128, a non-removable memory 130, a removable memory 132, a power source 134, a global positioning system (GPS) chipset 136, and other peripherals 138. It should be appreciated that the WTRU 102 may include any sub-combination of the foregoing components while remaining consistent with the embodiments.

[0051] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, any other type of integrated circuit (IC), a state machine, and the like. The processor 118 may perform signal coding, data processing, power control, input / output processing, and / or any other functionality that enables the WTRU 102 to operate in a wireless environment. The processor 118 may be coupled to the transceiver 120, which in turn may be coupled to the transmit / receive element 122. Although Figure 1B The processor 118 and the transceiver 120 are depicted as separate components, however it should be appreciated that the processor 118 and the transceiver 120 may also be integrated into one electronic component or chip.

[0052] The transmit / receive component 122 may be configured to transmit or receive signals to or from a base station (e.g., base station 114a) via the air interface 116. For example, in one embodiment, the transmit / receive component 122 may be an antenna configured to transmit and / or receive RF signals. As an example, in another embodiment, the transmit / receive component 122 may be an emitter / detector configured to transmit and / or receive IR, UV, or visible light signals. In yet another embodiment, the transmit / receive component 122 may be configured to transmit and receive RF and light signals. It should be appreciated that the transmit / receive component 122 may be configured to transmit and / or receive any combination of wireless signals.

[0053] In addition, although Figure 1B 102 as a single component, but the WTRU 102 may include any number of transmit / receive components 122. More specifically, the WTRU 102 may employ MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive components 122 (e.g., multiple antennas) for transmitting and receiving radio signals via the air interface 116.

[0054] The transceiver 120 may be configured to modulate signals to be transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As described above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers that allow the WTRU 102 to communicate via multiple RATs, such as UTRA and IEEE 802.11.

[0055] The processor 118 of the WTRU 102 may be coupled to a speaker / microphone 124, a numeric keypad 126, and / or a display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit), and may receive user input data from these components. The processor 118 may also output user data to the speaker / microphone 124, the numeric keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information from and store information in any suitable memory such as a non-removable memory 130 and / or a removable memory 132. The non-removable memory 130 may include a random access memory (RAM), a read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory 132 may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor 118 may access information from, and store data in, memory that is not physically located on the WTRU 102, such as, for example, on a server or a home computer (not shown).

[0056] The processor 118 may receive power from the power source 134, and may be configured to distribute and / or control power for use by other components in the WTRU 102. The power source 134 may be any suitable device for powering the WTRU 102. For example, the power source 134 may include one or more dry cell batteries (e.g., nickel-cadmium (Ni-Cd), nickel-zinc (Ni-Zn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0057] The processor 118 may also be coupled to the GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) related to the current location of the WTRU 102. In addition to or in lieu of the information from the GPS chipset 136, the WTRU 102 may receive location information from a base station (e.g., base stations 114a, 114b) via the air interface 116 and / or determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may acquire location information using any suitable positioning method while remaining consistent with an embodiment.

[0058] The processor 118 may also be coupled to other peripheral devices 138, which may include one or more software and / or hardware modules that provide additional features, functionality, and / or wired or wireless connectivity. For example, the peripheral devices 138 may include an accelerometer, an electronic compass, a satellite transceiver, a digital camera (for photos or videos), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands-free headset, modules, FM radio units, digital music players, media players, video game console modules, Internet browsers, and more.

[0059] Figure 1C 1 is a system diagram of the RAN 104 and an example core network 106. As noted above, the RAN 104 may employ an E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also be in communication with the core network 106.

[0060] The RAN 104 may include eNode-Bs 140a, 140b, 140c, however it will be appreciated that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. Each of the eNode-Bs 140a, 140b, 140c may include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 140a, 140b, 140c may implement MIMO technology. For example, the eNode-B 140a may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU 102a.

[0061] Each eNodeB 140a, 140b, 140c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, uplink and / or downlink user scheduling, etc. Figure 1C As shown, the eNode-Bs 140a, 140b, 140c may communicate with one another over an X2 interface.

[0062] Figure 1C The illustrated core network 106 may include a mobility management gateway (MME) 142, a serving gateway 144, and a packet data network (PDN) gateway 146. Although each of the foregoing components are described as being part of the core network 106, it should be appreciated that any of these components may be owned and / or operated by an entity other than the core network operator.

[0063] The MME 142 may be connected to each of the eNode-Bs 140a, 140b, 140c in the RAN 104 via an S1 interface and may serve as a control node. For example, the MME 142 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, performing bearer activation / deactivation processing, selecting a particular serving gateway during an initial attach of the WTRUs 102a, 102b, 102c, and the like. The MME 142 may also provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA.

[0064] The serving gateway 144 may be connected to each of the eNode-Bs 140a, 140b, 140c in the RAN 104 via an S1 interface. The serving gateway 144 may generally route and forward user data packets to / from the WTRUs 102a, 102b, 102c. The serving gateway 144 may also perform other functions such as anchoring the user plane during inter-eNode-B handovers, triggering paging processing when downlink data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, and the like.

[0065] The serving gateway 144 may also be connected to a PDN gateway 146, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0066] The core network 106 may facilitate communications with other networks. For example, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to circuit-switched networks such as the PSTN 108 to facilitate communications between the WTRUs 102a, 102b, 102c and traditional land-line communications devices. For example, the core network 106 may include or be in communication with an IP gateway, such as an IP Multimedia Subsystem (IMS) server, which may serve as an interface between the core network 106 and the PSTN 108. In addition, the core network 106 may provide the WTRUs 102a, 102b, 102c with access to the networks 112, which may include other wired or wireless networks that are owned and / or operated by other service providers.

[0067] The other networks 112 may further be connected to a wireless local area network (WLAN) 160 based on IEEE 802.11. The WLAN 160 may include an access router 165. The access router 165 may include a gateway function. And the access router 165 may communicate with multiple access points (APs) 170a, 170b. The communication between the access router 165 and the APs 170a, 170b may be carried out via wired Ethernet (IEEE 802.3 standard) or any type of wireless communication protocol. The AP 170a communicates with the WTRU 102d via an air interface.

[0068] The Institute of Electrical and Electronics Engineers (IEEE) 802.11 High Efficiency (HE) Wireless Local Area Network (WLAN) (HEW) is designed to enhance the user's quality of service experience, such as in high-density scenarios in the 2.4GHz and 5GHz bands. For example, potential applications of HEW may include data delivery for sporting events, high-density scenarios such as train stations or enterprise / retail environments, video delivery and wireless services for medical applications. To enhance the quality of service in these environments, HEW can utilize multi-user (MU) communications, which include uplink (UL) and downlink (DL) OFDMA and UL and DL MU multiple-input / multiple-output (MIMO).

[0069] IEEE 802.11 uses Carrier Sense Multiple Access with Collision Detection (CSMA / CA) to perform channel access. CSMA / CA uses a Network Allocation Vector (NAV) setting based on the duration information announced in the Request to Send (RTS) / Clear to Send (CTS) frames before actually exchanging data in order to maintain a prediction of the future traffic on the medium.

[0070] Since the AP will not hear transmissions from nodes in adjacent or overlapping basic service sets (OBSS), DL MU transmissions may cause hidden node problems, which in turn may cause interference to nodes in the AP's BSS, especially nodes on or near the edge of the AP's coverage area. By extending the RTS / CTS concept of CSMA / CA to MU DL transmissions, MU-RTS with simultaneous CTS can be used to solve the hidden node problem.

[0071] Figure 2 FIG. 2 is a diagram 200 showing an example of a MU-RTS with a simultaneous CTS (also referred to herein as MU RTS / CTS). Figure 2In the example shown, an access point (AP) transmits a MU-RTS 202, and the MU-RTS 202 may be received by a plurality of IEEE 802 stations (STAs) (STA1, 2, 3, and 4 in the example shown). In response to the MU-RTS 202, STA1, 2, 3, and 4 may simultaneously transmit a CTS 204. Based on the CTS received from the STAs, the AP may send DL MU data 206. Figure 2 Not shown, but the NAV may be set based on duration information contained in the MU RTS 202, such as an indication of the duration of the TXOP initiated by the MU RTS 202.

[0072] The HEW may synchronize and schedule upcoming simultaneous UL MU transmissions by using a trigger frame so that a concept similar to MU-RTS / CTS is used for UL MU transmissions. The MU-RTS frame and the trigger frame may be variations of each other. A UL MU physical layer convergence procedure (PLCP) protocol data unit (PPDU) (MU-MIMO or OFDMA) may be sent as an immediate response to a trigger frame sent by the AP, and the NAV may be set based on duration information contained in the trigger frame, such as an indication of the duration of the TXOP initiated by the trigger frame. The trigger frame may have a control frame format that carries information sufficient to identify the STA transmitting the UL MU PPDU and to allocate resources for the UL MU PPDU.

[0073] Figure 3 is a diagram 300 of an example trigger frame format for MU transmission. Figure 3 In the example shown, the trigger frame 300 includes a frame control (FC) field 302, a duration field 304, address fields 306, 308, a common information field 310, a plurality of per-user information fields 312 corresponding to the number of STAs expected to perform transmissions in the upcoming UL MU transmission, and a frame check sequence (FCS) 314. As an example, the common information contained in the common information field 310 may include information format, duration, and trigger purpose indication. As an example, the per-user information contained in the per-user information field 312 may include an association ID (AID), a resource unit (RU) allocation description, and power control information. Figure 4 4 is a diagram 400 providing other examples of trigger frame formats 402, 404, and 406, which may include optional additional or alternative information, such as type-specific common information and type-specific per-user information at different locations in the frame.

[0074] As described above, while the use of MU RTS / CTS and trigger frames helps solve the hidden node problem with respect to DL and UL MU transmissions, the NAVs set based on the duration information contained in the MU RTS / trigger frames may introduce new problems. Such problems (and others) are addressed here.

[0075] One of the new issues may involve interference from a pre-existing OBSS. For example, at the target wake time (TWT), the AP can use a trigger frame to schedule a power save poll (PS-POLL) transmission from a STA, and then send a DL frame accordingly. However, if the STA's clear channel assessment (CCA) status indicates that the OBSS NAV is busy, the STA will not send a PS-POLL in response to the trigger frame. Furthermore, the AP may not be able to know whether the unresponsive STA leaves the BSS or when it can trigger the PS-POLL again. This may not be effectively addressed by using a common CTS before the trigger frame, because the interference may have already begun before the CTS can be sent. However, if the AP knows the interference that the STA may encounter after sending the PS-POLL, it can intelligently schedule DL transmissions within the TWT on different time / frequency resources to avoid interference.

[0076] Figure 5 FIG. 5 is a diagram 500 of an example of AP scheduling with OBSS interference avoidance. Figure 5 In the example shown, the BSS includes AP 508 and serving STAs 510, 512, and 514, and the OBSS includes AP 502 and STA 504. STA 504 transmits OBSS UL frame 506 on channel A (eg, a 20 MHz channel), which may interfere with transmissions to / from STA 510.

[0077] In order to avoid interference from OBSS, Figure 5In the example shown, AP 508 sends a trigger frame 522A to STAs 510, 512, and 514, and replicates a trigger frame 522B in each 20 MHz channel (channel B in the example shown). In response to the trigger frames 522A and 522B, each of STAs 510, 512, and 514 selects a 20 MHz channel that can decode the trigger frame / replicated trigger frame, and transmits PS-POLL frames 524, 526, and 528 on the selected channel. For STA 510, in the example shown, the trigger frame cannot be decoded on channel A due to interference caused by the UL frame transmitted by OBSS STA 504. Accordingly, in the example shown, STA 510 transmits PS-POLL 524 on channel B, while STAs 512 and 514 transmit PS-POLL 526 and 528 on channel A.

[0078] If the resources assigned by the trigger frame 522A, 522B for PS-Poll transmission correspond to a channel that cannot be decoded by the STA, then, if random access is allowed on the selected 20 MHz channel, the STA can use a random access (RA) resource unit (RU) to send PS-POLL in the selected 20 MHz channel. Otherwise, the STA may not be able to reply to the trigger frame. In response to receiving the PS-POLL 524, 526, 528 from the STA 510, 512, 514, the AP can use the RU to send DL data frames 516, 518, and 520 to the corresponding STA 510, 512, and 514 in the channel used to receive the PS-POLL from the corresponding STA.

[0079] In an embodiment, in addition or in lieu thereof, a STA, such as STA 510, 512, 514, may use a PS-POLL frame carrying interference information to send interference information to an AP, such as AP 508. For example, a PS-POLL frame may include an idle channel and / or a busy channel index. The idle channel index may be used to indicate an idle 20 MHz channel, and the busy channel index may be used to indicate a 20 MHz channel occupied by an IEEE 802.11 or other signal. As another example, in addition or in lieu of the idle and / or busy channel indexes, the PS-POLL frame may also include information related to the interference level and / or the duration of interference. As an example, the interference level information may indicate the strength of the interference obtained as a measurement result such as a signal-to-noise ratio (SNR) or a received signal strength indicator (RSSI).

[0080] Figure 6 FIG. 6 is a flowchart 600 of another example of AP scheduling with OBSS interference avoidance. Figure 6In the example shown, a STA detects a trigger frame for UL MU transmission (602). In response to the trigger frame, the STA may generate a frame and transmit the frame (604). In an embodiment, the frame may be sent within an uplink (UL) MU PPDU, or may be sent via a simultaneous CTS using any other format. The STA may also send channel availability information about multiple channels in response to the trigger frame (604). In an embodiment, the channel availability information may be included in the generated frame. In a further embodiment, the trigger frame may be a request to send (RTS) frame, and the generated frame may be a split clear to send (CTS) frame. As will be described in more detail below, the split CTS frame may include a CTS frame followed by the channel availability information (e.g., the channel availability information may be sent after an interframe space after the CTS frame, or the channel availability information may be attached to the end of the CTS frame). As further described below, the split CTS frame may include identification information for the STA, such as a user specific sequence (USS), which may be transmitted together with the channel availability information. The split CTS will be described in detail below, and the split CTS described in this paragraph may include any or all features of the CTS described in other sections.

[0081] The multiple channels may be a combination of 20 MHz channels in wider channels (e.g., 40 MHz, 80 MHz, or 160 MHz) supported by the AP serving the STA. The STA may detect data in the RU of the DL MUPPDU on one of the multiple 20 MHz channels. The one of the multiple channels may be based on the transmitted channel availability information (606).

[0082] In another embodiment, for example, if the original transmission, such as a frame in a DL MU transmission to a STA, is not received due to OBSS interference, the AP may use the proximity of the STAs to each other to retransmit to the STA. This embodiment may use other STAs located near the STA that is experiencing OBSS interference to relay the DL transmission, where the nearby STAs do not experience the same interference as the STA.

[0083] Fig. 7A and 7B 700A, 700B are diagrams of example methods for using a trigger frame to trigger frame relay retransmission in a DL MU transmission. Fig. 7A In the example shown, when AP 702A sends a DL MU transmission 710 (e.g., an aggregated MAC PPDU (AMPDU)) directed to STAs 704A and 706A, STA 706A is experiencing OBSS interference. Fig. 7AIn the example shown, STA 704A does not experience OBSS interference and is able to receive transmission 710. Accordingly, STA 704A responds to the trigger with a UL frame 712, while STA 706A does not respond to the trigger frame.

[0084] exist Figure 7B In the example shown, by using the proximity of STA 704B to 706B, AP 702B may send a DLMU transmission to trigger a MU transmission 716, wherein the MU transmission 716 includes a triggered UL transmission from STA 708 and a DL retransmission from STA 704B to STA 706B of the transmission 710. In one embodiment, the trigger frame may specify a scrambler initialization process for the DLMU transmission 710 plus the STAID of STA 706B to identify the AMPDU to be retransmitted. The MU transmission 716 may include a packet extension (PE) 718 to allow the receiver sufficient time to decode the packet before responding.

[0085] All UL MU-PPDUs may be padded to the same length. Accordingly, the STA may use the padding bits before the forward error correction (FEC) in the UL-AMPDU to feedback the overheard DL-AMPDU before the UL transmission 712. The STA may also feedback information indicating that the STA 706B is nearby based on previous knowledge of the overheard UL transmission. By using this information, the AP 702 may schedule a trigger frame for DL ​​retransmission immediately after the UL transmission 712. Since the PPDU has a PE, the padding bits after the PE or FEC may be used to feedback the overheard DL-AMPDU before the UL transmission. Although the AP 702 may not have time to decode the information carried in the padding bits after the PE or FEC, the AP 702 may use this information to schedule DL retransmissions in a later trigger frame. In an embodiment, the PPDU following the trigger frame may be entirely in the DL, such as when both the AP 702 and the STA 704 retransmit the DL AMPDU in the same or different RUs to increase diversity.

[0086] Another new issue may involve backward compatibility. In particular, to support backward compatibility, the use of both high throughput (HT) and non-HT CTS frames must be supported. However, for MU RTS / CTS, the use of HT and non-HT CTS frames may result in waste of resource allocation. For example, multiple STAs may transmit non-HT CTS frames in the same time slot based on a 20 MHz channel, and the receiving AP may not be able to distinguish the STA that transmitted the CTS frame. As a result, the AP may blindly send a DLMU frame to the STA, and the STA may not be able to receive it.

[0087] Figure 8 FIG. 8 is a signal diagram 800 of an example MU-RTS / CTS that supports both HT and non-HT CTS frames for backward compatibility. Figure 8 In the example shown, AP 802 sends MU-RTS 812 to STAs 804, 806, 808, and 810, but only STAs 804 and 810 can receive it. Therefore, STAs 804 and 810 will simultaneously send CTS frames 814, 816 to AP 802. STAs 806 and 808 will not reply to MU-RTS 812. AP 802 can detect the reception of CTS 814, 816, but will not know the identity of the STA that transmitted the CTS 814, 816. Accordingly, AP 802 can use DL MU PPDU 818 (such as Figure 8 ) or independent transmission (not shown) to assign resources to all STAs 804, 806, 808, and 810. Since only STAs 804 and 810 can use the assigned resources ( Figure 8 820 and 826 in ) to send data, therefore, the resources assigned to STA806 and 808 ( Figure 8 822 and 824) will be wasted. Figure 8 In another scenario not shown, the AP 802 may start DL MU transmission for the STAs 804, 806, 808, and 810 directly after receiving the CTS, and the transmission for the STAs 806 and 808 will be wasted.

[0088] Another new issue may involve NAV extension for STAs that cannot understand HE frames. For example, if both HE and non-HE CTS are supported, the MU-RTS / CTS exchange can set the NAV at the beginning of the MU TXOP. However, if the AP and / or STA decide to extend the NAV at some point, the legacy STAs will not be able to successfully update the NAV setting because they cannot understand HE frames. Another new issue may involve the combined energy of the combined CTS potentially exceeding the automatic gain control (AGC) of the AP receiver.

[0089] Another new problem may involve the protection of directional transmission. As an example, for a wireless network, such as an IEEE802.11 network, the network may support directional transmission for MU and single-user (SU) PPDUs, including using the legacy preamble part for SU PPDUs. However, since directional and omnidirectional transmissions have different coverage, doing so may introduce additional hidden nodes.

[0090] In an embodiment, simultaneous non-HT CTS may be used, where the AP may poll an integer number M of STAs in a MU-RTS frame, and the AP may operate on a channel with an integer number N of 20 MHz subchannels. The AP may request or suggest that the M STAs respond using non-HT CTS frames on one or more 20 MHz subchannels using one of a number of different methods described below. The different methods described herein may be implemented individually or in combination.

[0091] In an exemplary method, the AP may request all STAs that successfully received the MU-RTS frame and are able to respond to transmit non-HT CTS frames. The AP may indicate a request for a complete response in the MU-RTS frame. The AP may operate on a channel bandwidth wider than 20 MHz, and non-HT CTS frames are transmitted on a 20 MHz channel. The AP may schedule non-HT CTS frame transmission using one or more of symmetric MU-RTS / CTS, asymmetric MU-RTS / CTS, and STA-driven MU-RTS / CTS.

[0092] When using symmetric MU-RTS / CTS, the AP can request the STA to respond with a CTS frame on a 20MHz channel basis and replicate the frame with or without phase rotation in all 20MHz subchannels. Therefore, CTS protection can cover the entire channel and can be symmetrical with MU-RTS. By using this method, if the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle in all subchannels, the STA addressed by the MU-RTS frame can transmit a CTS frame after an inter-frame interval (e.g., a short inter-frame interval (SIFS) period). The STA may need to perform a primary channel CCA, a secondary channel CCA, and / or a CCA on all 20MHz subchannels.

[0093] When using asymmetric MU-RTS / CTS, the AP may request the STA to respond using a CTS frame in one or more assigned 20MHz subchannels. The assigned one or more subchannels may or may not include the primary 20MHz subchannel. If more than one 20MHz channel is assigned to a STA, the STA may replicate the CTS frame based on the 20MHz channel. By using this method, if the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle in the assigned subchannel, the STA addressed by the MU-RTS frame may send a CTS frame after an inter-frame interval (e.g., a SIFS period). The STA may need to perform a primary channel CCA and / or a secondary channel CCA. The AP may include subchannel scheduling information in the MU-RTS frame.

[0094] In an example method for asymmetric MU-RTS / CTS, the AP may try to evenly distribute users into subchannels. For example, the AP may operate on N 20MHz subchannels, and MU-RTS may be sent to M STAs. The AP may schedule a number of users equal to round(M / N) to the first N-1 20MHz subchannels, and the last 20MHz subchannel may be used for M-round(M / N)*(N-1) users. Other functions such as rounding up, rounding down, or modulo may also be used.

[0095] In another example method for asymmetric MU-RTS / CTS, the AP can use the same resource allocation to perform CTS scheduling and data transmission after MU-RTS / CTS exchange. In this example, the STA needs to send a CTS frame on one or more 20MHz subchannels.

[0096] In the case of STA-driven MU-RTS / CTS, the AP may allow the STA to select one or more subchannels and reply with a CTS frame on the selected one or more subchannels. By using this method, if the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle in the selected one or more subchannels, the STA addressed by the MU-RTS frame may send a CTS frame on one or more subchannels after an inter-frame interval (e.g., a SIFS period). The STA may need to perform a primary channel CCA, a secondary channel CCA, and / or a CCA on all 20MHz subchannels.

[0097] In another exemplary method, the AP may request some intended STAs that successfully received the MU-RTS frame and can respond to transmit non-HT CTS frames. The AP may indicate in the MU-RTS frame that a partial response is requested, and may identify the STAs that are requested to respond using non-HT CTS frames. The AP may operate on a channel bandwidth wider than 20 MHz, and non-HT CTS frames may be transmitted on a 20 MHz channel. The AP may schedule non-HT CTS frame transmissions using one or more of the CTS scheduling methods described herein.

[0098] As briefly described above, the MU RTS frame may be a variation of a trigger frame, which may carry multiple fields, such as a trigger type field, a type-specific information field, and a user-specific type-specific information field, as an example. The trigger type field may be used to indicate that the trigger frame is a MU-RTS frame. A non-AP STA may respond to a trigger frame in accordance with its NAV setting and / or the trigger type of the trigger frame. A STA polled using a trigger frame with a trigger type of MU-RTS will not respond if the STA has a NAV setting from one or more non-AP STAs in the same BSS in one or more subchannels or one or more non-AP and / or AP STAs in an OBSS in one or more subchannels.

[0099] If the STA has a NAV pre-set by the AP that transmits the MU-RTS frame, the STA may ignore or update the previously set NAV and respond. As an example, this may occur if the AP's MAC address is set in the TA field and the STA's MAC address is set in the receiver address (RA) field of the MU-RTS / trigger frame, or the AP's MAC address is in the transmitter address (TA) field and the STAID is included in the common information and / or user-by-user information fields. As an example, this scenario may occur in a cascaded MU TXOP, where the AP may communicate with a group of STAs in one time slot. In the next time slot, the AP may decide to communicate with another group of STAs and poll the new group of STAs using the MU-RTS frame.

[0100] The type-specific information field of the MU-RTS and / or the type-specific information field of the user-by-user information field may carry subchannel assignment, resource allocation, or scheduling information. In an embodiment, the 20MHz subchannels acquired by the AP may be sorted according to a certain criterion. For example, the subchannels may be sorted by the channel start frequency. Thus, when using a bitmap or subchannel indexing method, both the AP and the STA may identify the subchannels. In an embodiment, a subchannel bitmap may be used for each STA, whereby N bits may be used to indicate N subchannels for each STA. In such an embodiment, if the kth bit is set, the STA may transmit a CTS frame on the kth 20MHz subchannel. In other embodiments, a user bitmap method may be used, whereby M bits may be used to indicate M users for each subchannel. In such an embodiment, for example, if the kth bit is set, STA k may transmit a CRS frame on a 20MHz subchannel (the STA may be sorted by a predetermined criterion). The STA ID that may be included in the user-by-user information field may not be included in the bitmap. In other embodiments, a subchannel indexing method may be used, where each STA may be assigned a set of 20MHz subchannels. In such an embodiment, the length of the subchannel index may be ceil(log2(N)) bits, and the index may be used to indicate the assigned subchannels. In other embodiments, a user indexing method may be used, where each subchannel may be assigned a set of STAs. In such an embodiment, the length of the STA index may be ceil(log2(M)) bits, and the index may be used to indicate the assigned STAs (which may be sorted using predefined criteria). The STA ID that may be included in the user-by-user information field may not be included in the user index.

[0101] A directional transmission starting from the legacy part may be signaled in the MU-RTS trigger frame. For example, one or more bits in the common information and / or user-specific information field may be used to indicate that the transmission after the MU-RTS / CTS frame exchange may be a directional transmission. In particular, the directional transmission may be performed on the entire PPDU including the legacy preamble, the HE preamble, and the data part. The directional transmission duration may be signaled in the MU-RTS trigger frame. The directional transmission duration may bidirectionally cover the period used for directional transmission.

[0102] In an embodiment, the directional single-user transmission may also be protected with MU-RTS / CTS exchange. The directional single-user transmission may also be protected with other types of protection mechanisms where there is a directional transmission and directional transmission duration field.

[0103] In an embodiment, a trigger frame with a trigger frame type MU-RTS may be transmitted in SU PPDU format over the entire band or in each 20 MHz channel (and repeated in the remaining 20 MHz channels). A trigger frame with a trigger type MU-RTS may also be transmitted in MU PPDU format using one or more RUs or by using one or more RUs in each 20 MHz channel (and repeated in the remaining 20 MHz channels with or without phase rotation). Such embodiments may be applied to other trigger frames with different trigger types.

[0104] To support backward compatibility for legacy STAs, the CTS frame may be transmitted in a non-HT PPDU format. The non-HT PPDU contains a legacy short training field (L-STF), a legacy long training field (L-LTF), a legacy OFDM signal (L-SIG) field, and a data field. CTS frames transmitted in a non-HT PPDU may use the same modulation and coding scheme (MCS) and scrambling seed, so that frames transmitted from multiple STAs may be the same. However, an AP receiving a non-HT CTS frame may not know the identity of the STA that transmitted the non-HT CTS frame, and may thus ineffectively send downlink transmissions to all STAs addressed in the MU RTS, regardless of whether the STA sent a CTS.

[0105] In an embodiment, a CTS frame may be transmitted as a split CTS. The split CTS frame may include a conventional CTS frame and a user-specific sequence (USS). The conventional CTS frame may be carried in a non-HT PPDU and may be detected by legacy STAs. The USS may be carried in a HT or other PPDU and may be detected by a HE or other STA. The AP may assign the USS using a MU-RTS frame, a beacon frame, an association frame, or a reassociation frame.

[0106] Fig. 9 FIG. 9 is a diagram of an example of using MU-RTS and split CTS to protect MU TXOP. Fig. 9 In the example shown, the AP 902 sends a MU-RTS frame 912, and the frame may indicate that a split CTS transmission is desired. The duration field of the MU-RTS frame may be set to cover the entire TXOP. If the MU-RTS frame 912 is transmitted in the middle of a MU-TXOP, the duration field may be used to redefine the MU TXOP duration.

[0107] For the STA addressed by the MU-RTS frame 912 ( Fig. 9For example, for STAs 904 and 906 in the MU-RTS frame, if the NAV on the STA receiving the MU-RTS frame 912 indicates that the medium is idle, the STA may transmit a split CTS frame in an interframe spacing (e.g., a SIFS period) after the MU RTS frame. STAs 904 and 906 may use non-HT PPDUs to send regular CTS frames 914, 916. The duration field may be set with the duration set by the MU-RTS frame and may be adjusted by subtracting the interframe spacing (e.g., SIFS time) and the number of microseconds required to transmit the CTS frame at the data rate determined by the MU-RTS frame. The length field indicated in the L-SIG of the CTS frame may indicate the length of the CTS frame (excluding USS). STAs 904, 906 may continue to transmit USS 918, 920 in an interframe spacing (e.g., SIFS, reduced interframe spacing (RIFS), or xIFS) period after the end of the CTS frame. Alternatively, the STA may attach the USS to the end of the CTS frame without an interframe spacing.

[0108] In an embodiment, the USS may include an LTF sequence scrambled with a P matrix. For example, if the MU-RTS frame addresses 8 or fewer users, an 8×8 P matrix may be used. In this example, the AP may assign a user index in the range [1,8] to each STA. This user index assignment may be indicated in the MU-RTS frame or other frames transmitted by the AP, such as a beacon frame, a trigger frame, or an association frame. The STA with user index k may use the kth row or column of the P matrix to scramble the LTF sequence. Other orthogonal matrices such as FFT matrices may also be used to generate the USS in the same manner.

[0109] In an embodiment, a USS frame may be used to carry a USS. The USS frame may be a specially designed PPDU, which may contain the USS only in the frequency domain or the time domain. Alternatively, a USS frame may carry an STF and a USS. As an example, the STF may be used for AGC and / or timing / frequency synchronization. The USS frame may be transmitted using the same subchannel used by the previous CTS transmission, or the USS frame may be allowed to be transmitted on other subchannels different from the subchannel used for the CTS transmission.

[0110] In the above embodiments, the term non-HT CTS is used to refer to a CTS frame transmitted using a non-HT PPDU. However, the embodiments herein are not limited thereto and may be applicable to any type of CTS frame. The split CTS capability may be used to indicate that the device is capable of performing split CTS transmission, and this capability may be transmitted by the AP and STA in the MU capability field, other capability fields, and / or information elements of the following: beacon frames, association or reassociation request / response frames, probe request / response frames, and other types of frames.

[0111] Fig.10 1000 is a flow chart of an exemplary method for splitting a CTS. Fig.10 In the example shown, the WTRU may detect a MU RTS frame (1010) and may transmit a CTS frame using a non-HT PPDU format in response to the MU RTS frame (1020). In response to the MU RTS frame, the WTRU may send additional control information after the CTS frame (1030). In response to the CTS frame, the WTRU may receive a DL transmission based on the additional control information sent after the CTS frame (1040).

[0112] Fig.11 FIG. 1100 is another example of a split CTS in which the AP uses a trigger frame to poll the USS. Fig.11 In the example shown, AP 1122 transmits a MU-RTS frame 1128, which may indicate an expected split CTS transmission in response to the MU-RTS frame 1128. The duration field of the MU-RTS frame 1128 may be set to cover the entire TXOP. If a MU-RTS frame (e.g., MU-RTS frame 1128) is transmitted in the middle of a TXOP, the duration field may be used to redefine the MUTXOP duration.

[0113] For STAs addressed in MU-RTS frame 1128 (e.g. Fig.11 For example, if the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle, the split CTS frame may be sent at an interframe spacing (e.g., SIFS duration) after the end of the MU-RTS frame 1128. Fig.11As shown, as an example, STAs 1124 and 1126 may transmit regular CTS frames 1130, 1132 using a non-HT PPDU. The duration of the regular CTS frame may be set using the duration set by the MU-RTS frame and may be adjusted by subtracting the SIFS time and the number of microseconds required to transmit the CTS frame at the data rate determined by the MU-RTS frame. The length subfield indicated in the L-SIG field of the CTS frame 1130, 1132 may indicate the length of the CTS frame (e.g., the length of the regular CTS frame 1130, 1132). Fig.11 In the example shown, AP 1122 has enhanced capabilities and may receive a trigger from one or more enhanced non-AP STAs ( Fig.11 STA 1124 and 1126) in requests USS.

[0114] After receiving the trigger frame 1134, the STA that can respond ( Fig.11 STAs 1124 and 1126 in the STA 1124 and 1126) can transmit user-specific packets or USS 1136, 1138. The USS or user-specific packets may include a USS modulated with a specific user sequence (e.g., a P matrix sequence) or one or more parts of a user-specific packet (e.g., a PLCP header). The xIFS duration may be a SIFS, RIFS, xIFS, or other frame interval period.

[0115] In an embodiment, the AP may acquire a channel with a wide bandwidth (which may include multiple subchannels). However, a non-AP STA may transmit on a narrower channel or one or more subchannels based on STA capabilities, carrier sensing, and / or virtual carrier sensing results. Information about the availability of the STA on one or more subchannels may be exchanged with a second trigger frame and subsequent USS frames. To achieve this, the AP needs to distinguish the packets transmitted by each STA.

[0116] The availability of a STA on one or more subchannels may be signaled implicitly by transmitting an extended service set user-specific sequence (USS) frame with a given sequence on one or more subchannels. Alternatively, a USS frame with a given sequence may be transmitted via one or more RUs on one or more subchannels. For example, an AP may want to communicate with a STA on channel 2. The AP may allocate RU x on channel 2 to the STA. In order to allow more STAs to signal channel availability implicitly at the same time, the AP may also allocate a sequence to the STA to be transmitted in RU x on channel 2. The STA may puncture the sequence in an unallocated RU, for example, by sending 0 instead of a modulation symbol according to the sequence. If the AP supports multi-stream transmission / reception, the sequence may be repeated and scrambled by a P matrix. The AP may indicate a stream index by indicating which row or column in the P matrix is ​​used to scramble the sequence.

[0117] Fig.12 FIG12 is a diagram 1200 of an example of code division multiple access (CDMA) for a USS frame. Fig.12 In the example shown, the AP may observe that channels 3 and 5 are busy, while channels 1, 2, 4, 6, 7, and 8 are available. The AP may also want to communicate with two STAs, STA 1 and 2. In the example shown, STA 1 is available on channels 1, 2, 3, 4, and 5, and STA 2 is available on channels 1, 4, 5, 6, 7, and 8.

[0118] exist Fig.12 In the example shown, the AP transmits a first trigger frame (1220) with a MU-RTS variant to STAs 1 and 2. Channel 1 may be a primary channel. In an embodiment, the AP may use a legacy (e.g., non-HT) PPDU to carry the MU-RTS frame, and may transmit the frame over channels 1 and 2. In other embodiments, the MU-RTS frame may be carried by an enhanced (e.g., HT) PPDU, and may thus be transmitted on all available channels (e.g., Fig.12 Channels 1, 2, 4, 6, 7 and 8 in the example shown).

[0119] STA 1 and 2 may reply to MU-RTS 1220 with a CTS frame (1222) based on their availability on channels 1 and 2, such as by using a legacy PPDU. If STA 2 is not available on channel 2, it may transmit its CTS frame on channel 1 only.

[0120] Upon receiving simultaneous CTS (1222), the AP may not be aware of the subchannel availability of STAs 1 and 2, and thus may transmit a second trigger frame (1224), for example, in an enhanced PPDU on channels 1, 2, 3, 6, 7, and 8, thereby performing a channel bandwidth information exchange. A user-specific sequence may be transmitted in the second trigger frame to the STA that is being triggered to reply using a USS frame (1226). In an embodiment, the second trigger frame may be used independently of the first trigger frame / CTS frame exchange (1220 / 1222).

[0121] In an embodiment, the common information field of the trigger frame may indicate a variant of the trigger and USS frame format expected in the reply to the second trigger frame. The user information field of the trigger frame may indicate the sequence index / ID assigned to the STA. If the AP operates on multiple channels, the AP may indicate one or more channels on which the STA availability will be checked. Alternatively, the AP may not indicate any channels, and the STA may prepare to transmit on all available channels.

[0122] A set of sequences with good correlation properties or orthogonality can be explicitly defined in the system, and the sequence set can be known to the STA. The sequences in the set can be sorted according to the sequence index / ID specified and known by the STA. For example, the good correlation property can be a zero correlation property, and the sequence can be a Golay sequence or a Zadoff-Chu sequence. If multiple channel bandwidths are supported, a sequence set for the minimum basic channel bandwidth can be specified, and a sequence index / ID can be defined. A sequence set for the minimum basic channel bandwidth can be specified, and a sequence index / ID can be defined. For example, for IEEE 802.11ax, the minimum basic channel bandwidth can be 20MHz. In order to transmit over a wider bandwidth, the sequence can be repeated in the time domain or frequency domain with or without phase rotation.

[0123] In other embodiments, one or more known sequences may be specified, such as a Long Training Field (LTF). Assume that the AP is capable of performing transmission / reception with up to N data streams, and each frequency channel may have M non-overlapping Resource Units (RUs). The AP may assign the nth stream and the mth RU to the STA for RSS transmission. Thus, in the user information field, a triple <AID, RU index / range, spatial stream index / range> may be used to assign the STA associated with the AID to perform transmission on one or more RUs using a specific spatial stream. The trigger and the expected variant of the USS frame format may be indicated in the common information field. For example, the trigger type may indicate that the expected response frame should only contain a preamble and should not include a MAC frame (e.g., Null Data Packet (NDP) type response). Alternatively, this information may also be indicated in the user information field.

[0124] In one example, the expected USS frame may be a frame that only contains a preamble and does not include a MAC frame. The sequence may be an enhanced LTF sequence in which unallocated RUs are punctured (e.g., only sending 0s without sending modulation symbols). In this example, the AP may want to check the availability of STA 1 and STA 2 on channels 1, 2, 4, 6, 7, and 8. In one example, the AP may only want to distinguish them in the frequency domain, and it may assign RUs 1-4 on channel x to STA1 and RUs 5-8 on channel x to STA 2. Channel x may include channels 1, 2, 4, 6, 7, and 8. For both STA1 and STA2, the spatial index may be 1 or the default value. Alternatively, the AP may only want to distinguish them in the spatial domain, and it may assign all RUs on channel x to STA 1 with a spatial index of 1, and all RUs on channel x to STA 2 with a spatial index of 2. The channel x may include channels 1, 2, 4, 6, 7, and 8.

[0125] If the AP expects responses from a large set of STAs, then the AP may distinguish them in both the frequency domain and the spatial domain. If there are STAs that cannot be uniquely assigned with frequency and spatial resources, then the AP may transmit more trigger frames after the trigger / USS frame exchange (1224 / 1226). In this example, the concatenation indication in the trigger frame may be set to indicate that more trigger frames are expected.

[0126] In a further embodiment, the sequence may be specified and known to the STA. Each STA may scramble the sequence using its ID. The ID may be assigned by the AP and / or signaled in the trigger frame. The ID may be an AID, the BSSID of the AP, another type of ID, or a combination of multiple IDs.

[0127] Non-AP STAs not addressed by the trigger frame can sense the channel. If the channel is idle, they can use the instructions in the second trigger frame and transmit USS frames based on the available channel.

[0128] In the above embodiment, the common information field of the trigger frame indicates the expected trigger and USS format variant, and the user information field of the trigger frame indicates the sequence index / ID assigned to the STA, and the STA can transmit the assigned sequence on all available channels. If the AP indicates certain channels for the STA, the STA can transmit the assigned sequence on all available channels indicated by the AP. In the above embodiment, one or more known sequences are specified, where if the corresponding channel is idle for the STA, the STA can use the assigned idle index to transmit the assigned sequence on the assigned RU. In an embodiment where the sequence is specified by the STA and the sequence is known to the STA, the STA can use its own ID to scramble the sequence and transmit the sequence on all available channels. If the AP indicates certain channels for the STA, the STA can transmit the scrambled sequence on all available channels indicated by the AP. When receiving the USS frame (1226), the AP can know the channel availability of the STA based on the fact that the AP has received a signal on the channel. In other words, the AP can check the reception of the USS frame on each channel. If the AP receives a valid signal on the assigned RU(s) and spatial stream(s), it may consider the corresponding STA to be available for the channel.

[0129] In a more specific example, assume that the AP can transmit on two channels, channel 1 and channel 2. In this example, channel 1 is the primary channel. The AP can check the availability of ten STAs, STA 1-10. The first trigger frame (e.g., MU-RTS) and the simultaneous CTS exchange may or may not be performed. Assume that each channel has 9 RUs and the AP is capable of transmitting / receiving at least two MU-MIMO data streams.

[0130] The AP may transmit a trigger frame requesting channel availability reports from STAs 1-10. The AP may use different combinations to assign RUs and spatial streams to STAs. For example, the AP may perform the following assignments: assign STA 1 to respond on RU 1-2 of channels 1 and 2 by using spatial stream 1; assign STA 2 to respond on RU 1-2 of channels 1 and 2 by using spatial stream 2; assign STA 3 to respond on RU 3-4 of channels 1 and 2 by using spatial stream 1; assign STA 4 to respond on RU 3-4 of channels 1 and 2 by using spatial stream 2; assign STA 5 to respond on RU 5-6 of channels 1 and 2 by using spatial stream 1; assign STA 6 to respond on RU 5-6 of channels 1 and 2 by using spatial stream 2; assign STA 7 to respond on RU 7-8 of channels 1 and 2 by using spatial stream 1; assign STA 8 to respond on RU 7-8 of channels 1 and 2 by using spatial stream 2; assign STA 9 to respond on RU 9 of channels 1 and 2 by using spatial stream 1; and assign STA 10 is assigned to respond on RU 10 on channels 1 and 2 by using spatial stream 2.

[0131] Fig.13 is a diagram 1300 of example common information fields regarding a trigger frame. Fig.13 The illustrated common information field includes multiple subfields, including a trigger type subfield 1302, a length subfield 1304, a HE-LTF symbol number subfield 1306, an STBC subfield 1310, an LDCP additional symbol subfield 1312, a packet extension subfield 1314, a spatial reuse subfield 1308, and a Doppler subfield 1316. A value may be used in the trigger type subfield 1302 to indicate whether the trigger frame is an NDP trigger or whether the trigger is for a bandwidth report, a channel availability report, or both. The length subfield 1304 may indicate the value of the L-SIG length field of the expected UL response frame. If this subfield is set to override the enhanced LTF field instead of the MAC data field, it may also implicitly indicate a request for an NDP response. The HE-LTF symbol number subfield 1306 may indicate the enhanced LTF symbols in the expected UL response frame. Fig.13 In the example shown, subfield 1306 is set to 2, and thus two spatial streams are expected. As an example, spatial reuse subfield 1308 may not be allowed for NDP responses.

[0132] For other subfields, such as the STBC subfield 1310, the LDCP additional symbol subfield 1312, the packet extension subfield 1314, and the Doppler subfield 1316, if the trigger type subfield 1302 or the length subfield 1304 indicates that the trigger frame is an NDP type trigger and / or a trigger for a bandwidth request, then these fields can be reinterpreted and thus can be used for other purposes. For example, these bits can be used to indicate that the AP will signal the RU / spatial index allocation for a channel with a basic / minimum bandwidth (as an example, 20MHz for IEEE 802.11ax), and the STA can be allowed to use the RU / spatial index allocation for all available channels with basic / minimum bandwidth. In one example, the AP can check the channel availability of STA 1 and STA 2 on all channels (e.g., channels 1 and 2). Once the bit is set, the AP may need to signal the RU / spatial index allocation for a basic channel, and the STA can use it for channels 1 and 2.

[0133] Fig.14 is a diagram 1400 of an example user information field for a trigger frame. Fig.14 The illustrated example user information field includes multiple subfields, including an AID subfield 1402, an RU allocation subfield 1404, a coding type subfield 1406, an MCS subfield 1408, a DCM subfield 1410, and an SS allocation subfield 1412. The AID subfield 1402 may indicate the STAAID. The RU allocation subfield 1404 may indicate the RU allocation as usual. Alternatively, if only the RU allocation on the basic / minimum channel (e.g., the 20 MHz channel in IEEE 802.11ax) is required (as announced using the common information field), then fewer bits may be used by modifying this subfield. If necessary, the coding type subfield 1406, the MCS subfield 1408, and the DCM subfield 1410 may be reinterpreted for other purposes. The SS allocation subfield 1412 may indicate the spatial streams allocated to the STA.

[0134] USS frames sent from one or more STAs to the AP may use an enhanced trigger-based PPDU, where the PPDU may carry a preamble but no MAC packet. For example, STA2 may be assigned to respond on RU 1-2 of channels 1 and 2 using spatial stream 2. STA2 may transmit a USS frame such as Fig.15 The USS frame shown.

[0135] Fig.15 FIG1500 is a diagram of an exemplary USS frame. Fig.15In the example shown, the USS frame is transmitted by STA2 on channel 1. The legacy portion of the preamble may be transmitted using the entire channel, and as an example, the portion includes the L-STF field 1502, the L-LTF field 1504, the L-SIG field 1506, the RL-SIG field 1508, and the enhanced SIG-A field 1510. The enhanced portion of the preamble may be transmitted on the assigned RU using the assigned spatial stream, and as an example, the portion includes the enhanced STF field 1512 and the enhanced LTF field 1514. The PPDU may be repeated on channel 2 without phase rotation.

[0136] In another exemplary embodiment of split CTS and USS, the AP may transmit a MU-RTS to a group of STAs with allocated resources for the STAs to transmit simultaneous CTSs. The MU-RTS may also contain NAV information, such as stored in a preamble or MAC header, to reserve the medium for the channel on which the MU-RTS is transmitted. Upon receipt of the MU-RTS, if the STA is not prohibited from transmitting a CTS, such as by NAV or carrier sensing, and if the STA is the intended recipient of the MU-RTS, then the STA may transmit a CTS on the allocated resources indicated in the MU-RTS.

[0137] If the AP does not receive a CTS frame in response to the MU-RTS, it may transmit a second trigger frame to poll the availability of the STA on a different channel or subchannel. In addition or alternatively, the AP may poll the availability of the STA on a different channel or subchannel by transmitting a trigger frame without first transmitting a MU-RTS frame. After receiving at least one CTS frame from at least one predetermined STA, the AP may transmit a second trigger frame, which may be a variant of the trigger frame.

[0138] If a second trigger frame or a variant of a trigger frame for polling is transmitted without first sending a MU-RTS, the second trigger frame or the variant of the trigger frame may include one or more of a STA ID related to a predetermined set of STAs, allocated resources, a user-specific sequence, or a user-specific sequence index of the STA. The STA ID may be an ID of the STA, such as a MAC address, a compressed MAC address, an AID of the STA, a group ID, or one or more specific AIDs for specific purposes such as random access in a per-user information field.

[0139] Regarding the allocated resources, the AP may specify the resources allocated to the STA so that the STA indicates its channel or subchannel availability by transmitting its USS frame, such as the channel, subchannel or RU on which the STA should indicate its availability. As an example, the availability may include channel conditions, spatial reuse opportunities or STA capabilities. In addition or alternatively, the AP may indicate the granularity of the RU and / or channel on which the STA should indicate its availability. For example, the AP may indicate that the STA may indicate the availability of 26 subcarrier RUs or 52 subcarrier RUs. As an example, the size of different RUs may be affected by the channels or subchannels indicated in the common information field or the user information field of the trigger frame. In one embodiment, the AP may indicate that STA1 should provide its availability on the 26-SC RU in channels 1 and / or 3. In another embodiment, the AP may indicate in the common information field that the STA set should provide its availability and the RU size for which it is targeted. In another embodiment, the bandwidth of the trigger frame may implicitly indicate the channel on which the STA should provide its availability. In another embodiment, as indicated by the MU-RTS, the allocated resources assigned to the STA for transmitting the CTS may indicate a channel for which the STA should provide its availability.

[0140] Regarding user-specific sequences or user-specific sequence indices, as an example, the AP may indicate in a user-specific field of a trigger frame a user-specific sequence or one or more indices of the user-specific sequence that will be used by the STA to indicate its availability to the AP. Such user-specific sequences may be orthogonal. For example, such user-specific sequences may be associated with a P matrix or a Zadoff-Chu sequence. The index of the USS may be associated with a pre-assigned sequence, such as one or more elements, rows, or columns of a predefined P matrix. As an example, the USS may be indicated by a spatial stream number, where the number may be associated with a specific P matrix. The specific P matrix used may be indicated in the trigger frame, or the matrix may be explicitly or implicitly indicated by the indicated channel, subchannel, and / or RU size. As an example, the AP may assign one or more USSs to a specific STA on one or more RUs.

[0141] The second trigger frame may include duration information in its preamble and / or MAC header to set the NAV on the receiving STA by implementing media reservation, but the STA that is the intended recipient of the trigger frame is not included. For example, the AP may send the second trigger frame to a group of STAs through one or more allocated channels for UL random access and a certain RU size.

[0142] When a STA receives a trigger frame for polling channel availability, it can respond by sending a USS to the AP. The USS may include a legacy header. The USS may be transmitted as part of a PPDU based on UL triggering. The USS may contain only a preamble and may be an empty data packet. The USS may be modulated by a user-specific sequence only on an available channel of the STA. The USS may also be modulated on all channels, subchannels and / or RUs of the indicated channels, and may be encoded to indicate available or preferred channels, subchannels and / or RUs. For UL random access, the STA may randomly select one or more user-specific sequences and one or more available RUs, channels and / or subchannels, and may transmit its USS using the selected USS on one or more RUs, channels and / or subchannels.

[0143] In an embodiment, only STAs that previously responded to the MU-RTS with a CTS may transmit the USS using a user-specific sequence or a sequence and resource allocation contained in a second trigger frame sent by the AP. In other embodiments, if the second trigger frame allows transmission on available and / or preferred resources, all STAs addressed by the MU-RTS and / or the second trigger frame may respond to the second trigger frame even if the STA failed to respond to the MU-RTS in advance by transmitting a CTS because the resources indicated in the MU-RTS were unavailable.

[0144] The USS may include a duration in its preamble and / or MAC header to implement medium reservation processing. The USS from a specific STA may include one or more fields, such as one or more LTF fields, which may be modulated by one or more user-specific sequences, such as elements, rows, and columns of a P matrix. In addition, each symbol, field, and / or subfield may be modulated and / or encoded with one or more data bits, such as by phase rotation or other methods. Such data may be used to indicate whether a STA is available on a particular RU or channel, and may also be used to indicate whether the availability of a STA is limited by spatial reuse and / or channel conditions or user capabilities. Such data may also be used to indicate whether a channel, subchannel, and / or RU is preferred or not preferred.

[0145] If the AP receives one or more USSs from a STA, the AP may transmit DL traffic in the form of DL MU packets to the one or more STAs on RUs for which availability or preference has been indicated by the STA in its USS. Fig.12In addition or alternatively, when the AP receives one or more USSs from the STA, it may transmit another trigger frame using resources (e.g., subchannels, RUs, channels, and / or spatial streams) allocated to the STA in accordance with the availability and / or preference of the STA indicated in its USS, so as to trigger UL data from the group of STAs.

[0146] To avoid the AGC at the AP receiver being unable to sustain the energy received from the simultaneous CTS, the AP can set a desired transmit power for each user. This transmit power can be explicitly signaled in the HE-SIG-B field of the MU-RTS preamble or in the MAC body of the MU-RTS frame. Alternatively, the AP can implicitly signal the transmit power to be used by each STA.

[0147] If power control is not used, each STA will typically transmit frames at the maximum power allowed. If power control is used, each STA can negotiate the expected transmit power with the AP in advance, thereby ensuring that the transmitted signal is received at the expected receive power. Alternatively, the AP can indicate the expected receive power level to all STAs in the HE-SIG field and / or the MAC body of the MU-RTS frame. In an embodiment, this power is referred to as the nominal power. In one embodiment, the STA can transmit simultaneous CTSs while reducing its transmit power by a numerical value, where the numerical value may depend on the number of users transmitting simultaneous CTSs. For example, in the case of two users, the STA can transmit with their maximum transmit power or the nominal transmit power reduced by 3dB or other functions of 2. In an embodiment, the STA may not reduce the power by a full 3dB, thereby ensuring that all hidden nodes can inadvertently hear the CTS frame.

[0148] In other embodiments, the AP may designate specific STAs as simultaneous CTS STAs. In such embodiments, the goal of simultaneous CTS may be to clear the medium rather than to identify whether the STA is ready to send data. The AP may identify specific STAs in different corners of the network and may designate their transmit power. If the AP needs to clear the channel, it may send MU-RTS to the STAs and request simultaneous CTS from these specific STAs.

[0149] In another embodiment that enables the AP to identify specific STAs that reply to the MU-RTS with a simultaneous CTS, the AP can estimate the number of STAs that reply to the MU-RTS based on the energy received during the simultaneous CTS. This embodiment can be combined with other embodiments, such as with the AP explicitly and / or implicitly sending transmit power level information to each STA to improve the expected energy. In such a combined embodiment, the AP can decide to always schedule users, schedule a new set of users, end MU transmission (MU TXOP truncation), or initiate frame exchange for further identifying STAs that can be used to send data based on the estimate. If the AP schedules a new set of users, then the new set of users can be a subset of the users previously addressed by the MU-RTS frame, and / or a set of users that were not addressed by a previous MU-RTS transmission.

[0150] Fig.16 FIG1600 is a diagram of an example of MU-RTS and simultaneous CTS operation with energy measurement. Fig.16 In the example shown, the AP 1102 sends a MU-RTS 1112 to multiple STAs 1104, 1106, 1108, and 1110. The AP can set the desired transmit power for each STA 1104, 1106, 1108, 1110 in the MU-RTS 1112. The desired transmit power can be signaled in the HE-SIG-B of the MU-RTS 1112 and / or in the MAC body of the MU-RTS frame. Alternatively, the AP 1102 can set the desired receive power level and the AP transmit power in the MU-RTS frame (e.g., in the HE-SIG-B field and / or the MAC body portion). The AP can also set simultaneous CTS power scaling for the STAs. In such an embodiment, each STA 1104, 1106, 1108, 1110 can reduce its maximum or nominal transmit power by the amount specified in the MU-RTS. The AP may also request the STA to change its transmit power and use its nominal or maximum transmit power during simultaneous CTS transmissions.

[0151] In an interframe interval (e.g., SIFS duration) after the MU-RTS 1112, the STAs 1104, 1106, 1108, and 1110 may send simultaneous CTS 1114a, 1114b, 1114c, 1114d (not shown) to the AP via the MU-CTS, and the AP 1102 may measure the received energy. If the received energy is greater than a threshold, the AP 1102 may assume that most of the STAs sent simultaneous CTSs. In an interframe interval (e.g., SIFS duration) after the AP receives the simultaneous CTSs, the AP 1102 may schedule user data by sending a regular trigger frame 1116. STAs 1104 , 1106 , 1108 , and 1110 may send their data 1118 a , 1118 b , 1118 c , 1118 d , respectively, on the scheduled resources, and in response, AP 1102 may send a block acknowledgement (ACK) 1120 to STAs 1104 , 1106 , 1108 , and 1110 .

[0152] Fig.17 FIG1700 is another example of MU-RTS and simultaneous CTS operation with energy measurement. Fig.17 In the example shown, AP 1202 sends MU-RTS 1212 to multiple STAs 1204, 1206, 1208, and 1210. Fig.16 Similar to the described embodiment, the AP 1202 may set the desired transmit power for each STA 1204, 1206, 1208, 1210 in the MU-RTS 1212. In an interframe interval (e.g., SIFS duration) after the MU-RTS 1212, the STAs 1204 and 1210 that are able to detect the MU-RTS 1212 may send simultaneous CTS 1214, 1216 to the AP 1202, and the AP 1202 may measure the received energy.

[0153] If the received energy is less than the threshold, then AP 1202 may assume that multiple users have failed to reply during simultaneous CTS periods and may take steps to resolve this failure. Fig.17 In the illustrated embodiment, the AP 1202 may cancel subsequent transmissions by sending a CF-END frame 1218 or similar frame at an interframe spacing (eg, SIFS duration) after the AP 1202 receives the simultaneous CTS.

[0154] Fig.18 FIG1800 is a diagram of an example of MU-RTS with simultaneous CTS using CTS triggering. Fig.18In the example shown, AP 1302 sends MU-RTS 1312 to multiple STAs 1304, 1306, 1308, and 1310. Fig.12 and 13 Similar to the described embodiment, the AP 1302 may set the desired transmit power for each STA 1304, 1306, 1308, 1310 in the MU-RTS 1312. In an interframe interval (e.g., SIFS duration) after the MU-RTS 1312, the STAs 1304 and 1310 that are able to detect the MU-RTS 1312 may send simultaneous CTS 1314, 1316 to the AP 1302, and the AP 1302 may measure the received energy.

[0155] If the received energy is less than the threshold, then AP 1302 may assume that multiple users have failed to reply during simultaneous CTS periods and may take steps to resolve this failure. Fig.18 In the illustrated embodiment, the AP 1302 may send a separable MU-RTS 1318 at an interframe interval (e.g., SIFS duration) after receiving a simultaneous CTS to enable it to identify a specific STA that is ready to send data. In the MU-RTS frame, the AP 1302 may indicate that a CTS frame is expected to be transmitted using a MU-PPDU. Subsequent CTS frames 1320, 1322 may use OFDMA-based CTS, UL_MU-MIMO-based CTS, and / or code-separable CTS. However, the CTS should be separable and identifiable. In an embodiment, if the STA is ready to send information with a packet size less than a threshold, the STA may send that information in place of the scheduled CTS.

[0156] In the interframe interval (e.g., SIFS duration) after the AP receives the CTS 1320, 1322, the AP may schedule data transmission by sending a regular trigger frame 1324. The AP 1302 may also reserve some resources for random access CTS. The AP may then schedule the user in a subsequent trigger frame.

[0157] When the AP transmits a trigger frame or a DL MU frame, one or more STAs may respond using a UL MU PPDU. If a STA that is supposed to transmit on certain subchannels, channels, or resource blocks is unable to transmit, other STAs may incorrectly assume that the medium is idle and may start using these channels, subchannels, or resources for their own transmissions. In another example, when the AP transmits a trigger frame for random access, some channels, subchannels, or resource blocks may be empty because no STA selects the channel, subchannel, or resource for UL transmission. In addition, when multiple STAs are unable to transmit through their channels, subchannels, or resource blocks, the total energy detected on the entire or partial channel may be below a detection threshold, such as an energy detection (ED), OBSS_ED, signal detection (SD), or OBSS_SD level. For a STA (e.g., an OBSS STA), the STA may start using a channel, subchannel, or part of a channel for transmission, thereby causing interruption and interference to the ongoing transmission. This situation may be particularly serious when using a cascade structure with alternating DL and UL SU and / or MU transmissions.

[0158] The AP may prevent other STAs, such as OBSS STAs, from using all or part of a channel, subchannel, or resource block for their transmission by transmitting packets or energy on an empty channel, subchannel, or resource block, thereby occupying an empty channel, subchannel, or resource block that is not used in UL transmission. To this end, after transmitting a trigger frame, a DL MU PPDU, a DL PPDU, or one or more packets or aggregate packets containing a trigger frame for requesting responses from multiple STAs, the AP may monitor all channels, subchannels, and resource blocks for which response frames are expected. These channels, subchannels, and resource blocks may be indicated in a resource allocation, such as in a previous trigger frame, DL MU PPDU, or DL ​​PPDU.

[0159] If the AP detects the start of a PPDU (e.g., reported by a PHY-RXStart.indication primitive from the PHY layer) within a certain period of time (e.g., after a SIFS period of time), then the AP may continue to receive these packets. If the AP does not detect the start of a PPDU on one or more channels, subchannels, or resource blocks within a certain period of time (e.g., after a SIFS period of time), then the AP may transmit packets or null data packets (NDPs) on the one or more channels, subchannels, or resource blocks after a period of time (e.g., a PIFS period of time), or may transmit energy on one or more subcarriers within these channels, subchannels, or resource blocks to keep them occupied. Such transmissions on unused channels, subchannels, or resource blocks may use a relatively narrow spectrum mask compared to the channels, subchannels, or resource blocks to prevent interference with the channels, subchannels, or resource blocks on which the AP is currently receiving frames. Such transmissions on these unused channels, subchannels, or resource blocks may also be implemented by using one or more TX / RX chains, where the TX / RX chains may have been previously used for reception or may not have been previously used for reception.

[0160] In order to support the reception of trigger-based UL PPDU, it is necessary to update the PHY-RXStart.indication primitive. In particular, the parameter RXVector used for PHY-RXStart.indication may need to be enhanced. When the detected frame format is MU PPDU or trigger-based UL PPDU, RXVector may include the number of users. The channels, subchannels, or resource blocks used by each user can be listed. This number of users and the channels, subchannels, or resource blocks used by each user can also be included in the TXVECTOR. In addition, unused channels, subchannels, or resource blocks can be identified in the RXVECTOR. Similarly, MCS, TXPower, and RXPower (e.g., receiver channel power indicator (RCPI)) can be specified in the TXVector and / or RXVector for each user, channel, subchannel, or resource block associated with the MU PPDU or trigger-based UL PPDU.

[0161] Another new issue may involve legacy device protection, which may be more important in densely deployed systems than hidden node protection. In an embodiment, MU semi-protection capability may be used to indicate that the device can perform semi-protection for MU transmissions, and the MU semi-protection capability may be set in the MU capability field, other capability fields, and / or other information elements that can be transmitted by the AP and STA in the following: beacon frames, association or reassociation request / response frames, probe request / response frames, and / or other types of frames. Alternatively, DL MU semi-protection, UL MU semi-protection, and tandem semi-protection capabilities may be indicated separately in the fields and frames described above.

[0162] Fig.19 is a diagram 1900 of an example of semi-protection for DL ​​MU transmission. Fig.19 In the example shown, the AP 1402 may start a DL MU TXOP using a CTS-to-self or CTS-to-AP frame 1408. The random access (RA) field in the frame 1408 may be set to the MAC address of the AP. The duration field may be set to the end of the DL MU TXOP. The AP 1402 may continue to transmit DL MU PPDUs 1410 to the STAs 1404 and 1406 for an inter-frame space (e.g., a SIFS period) after the end of the CTS-to-self or CTS-to-AP frame 1408.

[0163] Fig. 20 is a diagram 2000 of another semi-protection example for DL ​​MU transmission. Fig. 20 In the example shown, the AP 1502 may start a DL MU TXOP using a CTS-to-self or CTS-to-AP frame 1508. The RA field in the frame may be set to the AP's MAC address. The duration field may be set to the end of the DL MU TXOP. The AP may continue to transmit a trigger frame 1510 in the interframe space (e.g., SIFS period) after the end of the CTS-to-self or CTS-to-AP frame 1508. The trigger frame 1510 may indicate whether it is a trigger type MU-RTS or other type.

[0164] For the STAs (e.g., STAs 1506 and 1506) addressed by the trigger frame 1510, if the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle, the STA may transmit the newly defined MU CTS frames 1512, 1514 in the interframe space (e.g., SIFS period) after the end of the trigger frame 1510. In an alternative method, the STA may transmit a CTS frame, which may be carried in a MU PPDU. In response to receiving the MU CTS frames 1512, 1514, the AP 1502 may know which STAs are ready to receive DL MU packets, and the AP 1502 may use the MU frame 1516 to schedule available STAs for DL ​​transmission.

[0165] Fig.21 is a diagram 2100 of an example of semi-protection for UL MU transmission. Fig.21 In the example shown, the AP 1602 starts the UL MU TXOP using a CTS-to-self or CTS-to-AP frame 1608. The RA field in the frame may be set to the AP's MAC address. The Duration field may be set to the end of the UL MU TXOP. The AP may continue to transmit DL trigger frames 1610 in an interframe space (e.g., a SIFS period) after the end of the CTS-to-self or CTS-to-AP frame 1610.

[0166] The STAs 1604 and 1606 triggered by the trigger frame 1610 may update the NAV set by the previous CTS-to-self / CTS-to-AP frame 1608, and may transmit ULMU PPDU frames 1612, 1614 in an interframe interval (e.g., a SIFS period) after the end of the trigger frame transmission 1610. The AP 1602 may respond with an ACK or a multi-STA ACK 1616.

[0167] Fig. 22 FIG2200 is a diagram of an example of semi-protection for tandem MU transmissions. The AP 1702 may or may not use a CTS-to-self or CTS-to-AP frame (not shown) to start a tandem MU-TXOP. Fig. 22In the example shown, in the middle of the cascaded transmission, the AP 1702 may perform semi-protection using a CTS-to-self or CTS-to-AP frame 1704. The RA field in the frame may be set to the AP's MAC address. The duration field may be set to the end of the cascaded MU TXOP. The AP may use the CTS-to-self or CTS-to-AP frame 1704 to update, extend, and / or reduce the NAV setting for the current MU TXOP. The AP may continue to transmit a DLMU PPDU 1706 in an inter-frame interval (e.g., a SIFS period) after the end of the CTS-to-self or CTS-to-AP frame 1704. The DL MU PPDU 1706 may carry a trigger frame, a control frame, a management frame, and / or a data frame.

[0168] The MU dual protection capability may be used to indicate that the device can perform dual protection for MU transmission, and the capability may be set by the AP and STA in the MU capability field, other capability fields, and / or other information elements that may be transmitted in the following: beacon frames, reassociation or association request / response frames, probe request / response frames, and / or other types of frames. Alternatively, DL MU dual protection, UL MU dual protection, and tandem dual protection capabilities may also be indicated separately in the above fields and frames.

[0169] Fig.23 is a diagram 2300 of an example of dual protection for DL ​​MU transmission. Fig.23 In the example shown, the AP 1802 uses a MU-RTS / trigger frame 1808 to start a DL MU TXOP. In the MU-RTS / trigger frame 1808, the AP 1802 may indicate that a dual protection mechanism is being used. If the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle in some or all subchannels, the STAs 1804 and 1806 addressed by the MU-RTS frame 1808 may send CTS frames 1810, 1812 in an interframe space (e.g., a SIFS period) after the end of the MU-RTS / trigger frame 1808.

[0170] If the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle in some or all subchannels, the STAs 1804 and 1806 addressed by the MU-RTS frame 1808 may transmit MU-CTS frames 1814 and 1816 in the interframe interval (e.g., SIFS period) after the end of the CTS frames 1810 and 1812. The transmission of the MU-CTS frames 1814 and 1816 may be based on resource units (RUs) or on 20 MHz subchannels. The MU-CTS frames 1814 and 1816 may be frames modified from CTS frames. The MU-CTS frames 1814 and 1816 may carry a STA ID, a STA MAC address, and / or a STA signature that can be used by the AP to distinguish the transmitter of the MU-CTS frames 1814 and 1816. The MU-CTS frames 1814 and 1816 may also carry information that can be used by the AP 1802 for resource allocation or scheduling, subchannel and / or RU preference indication. The MU-CTS frames 1814 and 1816 may be transmitted in a frequency / time / space / power / code division multiplexing manner. The AP 1802 may continue to send the DL MU PPDU 1818 in an inter-frame interval (eg, SIFS period) after the MU-CTS frames 1814 and 1816 end.

[0171] Fig.24 FIG2400 is another example of dual protection for DLMU transmission. Fig.24 In the example shown, AP 1902 initiates DL MU TXOP using MU-RTS / trigger frame 1908. In MU-RTS / trigger frame 1908, AP 1902 may indicate that a dual protection mechanism is being used. Fig.23 Unlike the CTS frame sent in the interframe space after the MU-RTS frame, Fig.24 In the example shown, if the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle in some or all subchannels, then the STAs 1904 and 1906 addressed by the MU-RTS frame 1908 will instead transmit CTS-to-self frames 1910, 1912 in the inter-frame interval (e.g., SIFS period) after the end of the MU-RTS frame 1908.

[0172] Fig.25 is a diagram 2500 of an example of dual protection for UL MU transmission. Fig.25In the example shown, STA 2004 starts UL transmission using RTS frame 2008. However, AP 2002 may also decide to use a time slot for UL MU TXOP. If this is the case, AP 2002 addressed by RTS frame 2008 may transmit CTS frame 2010 to STA 2004. If both STA 2004 and AP 2002 have UL dual protection capability, AP 2002 may send MU-CTS / trigger frame 2012 in an interframe space (e.g., xIFS period) after the end of CTS transmission 2010. The xIFS may be equal to or less than a SIFS period, whereby STA 2004 cannot start normal data transmission within a SIFS period after receiving CTS frame 2010. In MU-CTS / trigger frame 2012, AP 2002 may indicate and schedule UL MU TXOP. If the NAV on the STA receiving the MU-RTS frame indicates that the medium is idle in some or all subchannels, the STA addressed by the MU-RTS frame may send a CTS frame in an interframe space (e.g., a SIFS period) after the MU-RTS frame. The STAs 2004 and 2006 addressed by the MU-CTS frame 2012 may send UL MU frames 2014, 2016 in an interframe space (e.g., a SIFS period) after the MU-CTS frame 2012. The AP 2002 may send an ACK frame and / or a multi-user BA 2018 after receiving the UL MU frames 2014, 2016.

[0173] For cascaded MU TXOPs, dual protection mechanisms for both DL and UL are applicable. Protection frame exchange may occur at the beginning and / or in the middle of a cascaded MU TXOP. The protection mechanism may be initiated by an AP or a non-AP STA. The protection mechanism in the middle of a cascaded MU TXOP may be used to update the NAV setting. The update may include extending / reducing / truncating the current TXOP.

[0174] Fig.26 FIG2600 is another example of dual protection for UL MU transmission. Fig.26 In the example shown, if the NAV on the AP 2102 receiving the RTS frame 2106 indicates that the medium is idle in some or all subchannels, then instead of sending a CTS frame in the SIFS period after the RTS frame, the AP 2102 may instead send a CTS-to-self frame 2108 in the interframe space (e.g., xIFS period) after the end of the RTS frame 2106. In such a scenario, the STA and the AP may indicate that they have UL dual protection capability. Therefore, the STA may expect a CTS or CTS-to-self frame after sending the RTS frame.

[0175] In an embodiment, the system may need to enact a protection mechanism (e.g., RTS / CTS protection, MU-RTS / CTS protection, or other types of protection) for any directional transmission starting from the legacy preamble. The Capability field may be set to indicate that the STA is capable of performing directional transmissions starting from the beginning of a packet, including both the legacy part and the HE part. Capability information may be included in the HE MU Capability field.

[0176] Another issue may involve the use of directional transmissions when setting up OBSS NAV. Fig. 27 FIG2700 is a diagram illustrating a situation where OBSSNAV does not necessarily prohibit directional transmissions. Fig. 27 In the example shown, STA 2202 can send an UL directional transmission 2208 to AP 2204. However, its TXOP is constrained by the OBSS NAV set by the OBSS trigger frame 2212 from OBSS AP 2209 and the response OBSS UL frame 2210 from OBSSS TA 2206. Fig.28 FIG28 is a diagram showing a situation where the OBSS does not see directional transmissions from neighboring BSSs. Fig.28 In the example shown, STA 2302 sends a directional transmission 2306 to AP 2304. OBSS AP 2308 does not see directional transmission 2306 and begins its own TXOP, which may cause the OBSS NAV to be set. Since the OBSS NAV is set, STA 2306 may subsequently refrain from sending other directional transmissions. The embodiments described herein may address these issues by enabling a STA (e.g., STA 2202 or 2302) to determine whether its UL directional transmission is likely to occur while the OBSS NAV is set. One way to perform this process may be to send an OBSS Facilitation Information (OFI), which the STA may detect and use while the OBSS NAV is set to determine whether it may send an UL directional transmission.

[0177] Fig.29A and 29B FIG. 2900A and FIG. 2900B are diagrams showing an example of using OFI to indicate to a STA whether a directional transmission can be sent while setting an OBSS NAV. Fig.29A and Fig.29BIn the example shown, STA 2401 sends a first directional UL frame 2403 to AP 2405. At the same time, OBSS AP 2402 starts a TXOP by sending an OBSS trigger frame 2412 for STAs 2406 and 2408. The trigger frame 2412 may include an OFI. The OFI may carry information such as the start time of the TXOP initiated by the trigger frame 2412 (e.g., a timestamp or time offset relative to a known reference), the CCA threshold of the AP 2402, and / or the average received power level during the CCA sensing period before the first trigger frame 2412. In an embodiment, the OFI may be carried in a DL control or management frame (e.g., a trigger frame or a multi-STA block ACK frame) transmitted by the AP 2402, and / or a UL control / management frame (e.g., an ACK frame) sent by a non-AP STA.

[0178] The OFI may also be signaled in a subsequent trigger frame or other DL frame from the OBSS AP 2402 so that the STA 2401 is aware of the impact of its previous directional transmission 2403 if it has previously performed a directional transmission 2403. Fig.29A In the illustrated example, for example, OBSS AP 2402 may send an OFI in an OBSS trigger frame 2410 for OBSS STA 2404, where STA 2401 may overhear the OBSS trigger frame 2410. Based on the determination that OBSS AP 2402 initiated a TXOP in the middle of a directional transmission 2403 from STA 2401, and that OBSS AP 2402 correctly received an OBSS UL / DL PPDU 2409 that overlapped with the directional transmission 2403 and the DL BA, STA 2401 may infer from the OFI that OBSS AP 2402 did not observe its previous directional transmission 2403 or DL ​​BA (not shown) as interference.

[0179] Based on this determination, if it is determined that the directional transmission 2403 does not interfere with the OBSS, then the STA 2401 can continue to decrement its backoff timer, and the OBSS NAV is set by the second OBSS trigger frame 2410 and based on possible alternative physical sensing mechanisms and / or virtual physical sensing mechanisms, and no NAV between BSSs is set. Even if the OBSS NAV is set, the STA 2401 can perform another directional transmission in the duration. For example, if Fig.29BAs shown, STA 2401 may send another directional transmission 2420, which may overlap with a UL frame transmission 2422 from OBSS AP 2402 to STA 2404, for example, when OBSS NAV is set. Depending on the OBSS TXOP duration, STA 2401 may or may not truncate a directional transmission 2420, such as UL frame transmission 2422, that may overlap with an OBSS transmission.

[0180] In the absence of OBSS NAV, STA 2401 may use the same directional antenna pattern to perform carrier sensing and reception. This carrier sensing process may ensure that the OBSS transmission does not cause interference when STA 2401 receives a DL ACK from OBSS AP 2402. To avoid collisions within the BSS and to prevent interference with OBSS AP 2402 during the OBSS UL duration, STA 2401 may send an RTS frame to the AP 2405 it is associated with in a directional transmission, and the AP 2405 may reply using an omni-directional transmission and with a CTS frame to reserve air time in the BSS.

[0181] Another new issue may involve the NAV set by the RTS frame being reset by a STA that overhears the RTS frame if it does not hear a response CTS frame or the start of a data frame. For example, if no PHY-RXSTART.indcation primitive is received from the PHY within a period of (2×aSIFSTime)+(CTS_Time)+aRxPHYStartDelay+(2×aSlotTime) starting with the PHY-RXTEND.indcation primitive corresponding to the detection of the RTS frame, then a STA that uses the information from the RTS frame as the latest basis for updating its NAV setting may be allowed to reset its NAV. This behavior is necessary for HE-STAs because the intended recipient of the (MU-)RTS frame may not respond due to interference, OBSS NAV busy, or other reasons.

[0182] The HE preamble may be designed so that the STA can obtain the TXOP duration (NAV) / color information without decoding the entire MU PPDU frame. However, if the STA only decodes the HE preamble, it is unclear how the STA knows that the TXOP duration set by the PPDU encounters a NAV reset. As an example, by providing different TXOP duration values ​​in the HE preamble and the MAC header, the embodiments described herein can solve this problem.

[0183] In an embodiment, the TXOP duration in the HE-SIG-A may be different / shorter than the duration / NAV in the MAC header of the frame where the NAV is reset. For example, the duration in the MAC header of the OBSS MU-RTS may be set to T in order to signal the NAV setting of the corresponding CTS frame. While the TXOP duration in the HE-SIG-A field of the MU-RTS frame may be set to the _t required for the duration to complete, such as SIFSTime plus the number of microseconds required to transmit the CTS frame at the data rate determined by the MU_RTS frame. Alternatively, the transmitter of the MU-RTS frame may always set the TXOP duration in the HE-SIG-A field to be the same as the duration in the MAC header, but if no response is received from the intended recipient, it may perform PIFS recovery or TXOP truncation processing (CE-End).

[0184] Fig.30 FIG3000 is a diagram showing the preamble format before three types of HE-STF. Fig.30 The three preamble formats 30 shown include SU format 2502, MU format 2504, and extended range SU format 2506. SU format 2502 and MU format 2504 may be mandatory, and SU format 2502 may be for trigger-based UL. Fig.30 In the example shown, the L-SIG length set to mod3 = 1 may indicate a SU format, and the L-SIG length set to mod3 = 2 may indicate a MU format or an extended range SU format. QBPSK on the HE-SIGA2 field may indicate an extended range SU format. Table 1 below provides the format of the HE-SIG-A field for the HE SUPPDU. Table 2 below provides the format of the HE-SIG-A field for the HE MU PPDU. Table 3 below provides the format of the HE-SIG-A field for the UL PPDU based on HE triggering.

[0185] Table 1

[0186]

[0187] Table 2

[0188]

[0189] Table 3

[0190]

[0191] However, there is some redundancy in the defined formats. For example, a triggered UL PPDU should use L-SIG length Mod3=1 (SU format). However, in Table 3, there is no DL / UL bit before this format field. This leaves some questions as to how a receiver can decide how to interpret the two different formats provided in Table 1 and Table 3. As another example, if a triggered UL PPDU is signaled using L-SIG length Mod3=1 (sent by a STA), then L-SIG length Mod3=2 can be used for a DL HE MU PPDU (sent by an AP). When a receiver receives a frame with L-SIG length Mod3=2 and detects HE-SIG-A2 BPSK, the receiver can determine that this is a DL HE MU PPDU. Therefore, DL / UL is redundant. Alternatively, if the triggered UL PPDU uses L-SIG length Mod3=2 (MU format / extended range SU), then when the receiver receives a packet with L-SIG length Mod3=1, the receiver can determine that the packet is a SU packet. Therefore, the Format bits in Tables 1 and 3 may not be required. The embodiments described herein can reduce or eliminate this redundancy.

[0192] Triggered UL PPDUs may be signaled with L-SIG length mod3=1. With this arrangement, the direction of the MU PPDU may be implicitly signaled, whereby for the DL direction, L-SIG length mod3=2 and BSPK modulation will be used for HE-SIG-A2 (the second symbol of HE-SIG-A), while for the UL direction (UL triggered PPDU), L-SIG length mod3=1 and the HE-SIG-A format bit will be included, where the bit indicates that it is not a SU format PPDU. Further, in Table 1, the format bit may be moved before the DL / UL tag in Table 1, and there is no need to add the DL / UL bit in Table 3. In Table 2, the UL / DL bit may be removed. Thus, the space used by the DL / UL bit may be used for other purposes, such as identification color, for DL / UL MU / trigger based PPDUs.

[0193] In an embodiment, the trigger-based UL PPDU may be notified with L-SIG length mod-2. With this arrangement, the direction of the MU PPDU may be explicitly notified through the DL / UL flag of the HE-SIG-A field in Table 2. For SU format PPDUs without range extension, the format bit may be removed and may be used for other purposes.

[0194] Although the features and elements are described above in specific combinations, it will be recognized by those skilled in the art that each feature can be used alone or in any combination with other features and elements. In addition, the methods described herein can be implemented in a computer program, software, or firmware that is introduced into a computer-readable medium for operation by a computer or processor. Examples of computer-readable media include electrical signals (transmitted via a wired or wireless connection) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, read-only memory (ROM), random access memory (RAM), registers, buffer memory, semiconductor storage devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks and digital versatile disks (DVDs). A processor associated with the software can be used to implement a radio frequency transceiver in a WTRU, UE, terminal, base station, RNC, or any computer host.

Claims

1. A station (STA), comprising: transceiver; as well as processor, wherein the transceiver and the processor are configured to detect a trigger frame for bandwidth reporting from an access point (AP), wherein the trigger frame comprises a plurality of user information fields, each of the user information fields comprising an association identifier (AID) subfield and a resource unit (RU) allocation, the AID subfield comprising an AID of an individual STA addressed by the trigger frame, the resource unit (RU) allocation being used for the STA identified by the AID subfield to send the bandwidth report in an uplink (UL) multi-user (MU) protocol data unit (PPDU); wherein the transceiver and the processor are further configured to send a bandwidth report in response to the trigger frame, wherein the bandwidth report indicates whether a specific 20 MHz subchannel of a wider channel supported by the AP is available at the STA, and Wherein the transceiver and the processor are further configured to detect data in a resource unit (RU) of a downlink (DL) MU physical layer (PHY) protocol data unit (PPDU) on one of the 20 MHz subchannels, wherein the one of the 20 MHz subchannels is based on the transmitted bandwidth report. 2 . The STA according to claim 1 , wherein the trigger frame comprises a common information field, and the common information field comprises a trigger type subfield, the trigger type subfield indicating that the trigger is for bandwidth reporting.

3. The STA of claim 1, wherein the transceiver and the processor are further configured to send the bandwidth report in response to the trigger frame based on the trigger frame including a user information field containing the AID of the STA.

4. The STA of claim 1, wherein the trigger frame further comprises an assignment of subchannels and spatial streams for each STA identified by an AID in the trigger frame.

5. A method implemented in a station (STA), the method comprising: detecting a trigger frame for bandwidth reporting from an access point (AP), wherein the trigger frame comprises a plurality of user information fields, each of the user information fields comprising an association identifier (AID) subfield and a resource unit (RU) allocation, the AID subfield comprising an AID of an individual STA addressed by the trigger frame, the resource unit (RU) allocation being used for the STA identified by the AID subfield to send the bandwidth report in an uplink (UL) multi-user (MU) protocol data unit (PPDU); In response to the trigger frame, sending a bandwidth report, wherein the bandwidth report indicates whether a specific 20 MHz subchannel of a wider channel supported by the AP is available at the STA; as well as Data in a resource unit (RU) of a downlink (DL) MU physical layer (PHY) protocol data unit (PPDU) is detected on one of the 20 MHz subchannels, wherein the one of the 20 MHz subchannels is based on the transmitted bandwidth report.

6. The method according to claim 5, wherein: The trigger frame includes a common information field, and the common information field includes a trigger type subfield, the trigger type subfield indicating that the trigger is for bandwidth reporting.

7. The method according to claim 5, wherein: The sending the bandwidth report further includes sending the bandwidth report in response to the trigger frame based on the trigger frame including a user information field containing the AID of the STA.

8. The method according to claim 5, wherein: The trigger frame further includes an assignment of subchannels and spatial streams for each STA identified by an AID in the trigger frame.

9. An access point (AP), comprising: transceiver; as well as processor, wherein the transceiver and the processor are configured to send a trigger frame for bandwidth reporting, wherein the trigger frame includes a plurality of user information fields, each of the user information fields includes an association identifier (AID) subfield and a resource unit (RU) allocation, the AID subfield including an AID of an individual STA addressed by the trigger frame, the resource unit (RU) allocation being used for the STA identified by the AID subfield to send the bandwidth report in an uplink (UL) multi-user (MU) protocol data unit (PPDU), wherein the transceiver and the processor are further configured to receive at least one bandwidth report in response to the trigger frame, wherein the bandwidth report indicates whether a particular 20 MHz subchannel of a wider channel supported by the AP is available at one or more STAs, and Wherein the transceiver and the processor are further configured to transmit data in a resource unit (RU) of a downlink (DL) MU physical layer (PHY) protocol data unit (PPDU) on one or more of the 20 MHz subchannels, wherein the one or more of the 20 MHz subchannels are based on the received at least one bandwidth report.

10. The AP according to claim 9, wherein: The trigger frame includes a common information field, and the common information field includes a trigger type subfield indicating that the trigger is for bandwidth reporting.

11. The AP according to claim 9, wherein: The transceiver and the processor are further configured to receive a UL MU PPDU including a plurality of bandwidth reports from a plurality of STAs, each of the STAs being triggered based on the trigger frame including a plurality of user information fields, each of the plurality of user information fields including the AID of one of the plurality of STAs.

12. The AP according to claim 9, wherein: Each of the received bandwidth reports is received in the UL MU PPDU in the RU allocated for each of the plurality of STAs in the trigger frame.

13. The AP of claim 9, wherein the trigger frame further comprises an assignment of subchannels and spatial streams for each STA identified by an AID in the trigger frame.

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