Method and apparatus for joint multi-AP transmission in a WLAN

Abstract

To provide a method and a wireless transmit / receive unit that cause an access point (AP) to synchronize with a station (STA) to enable the STA to appropriately decode a signal in multi-access point (multi-AP) communication.SOLUTION: A method includes the steps of: receiving, by a wireless transmit / receive unit (WTRU), from a first AP of a plurality of APs, a trigger frame including an identifier of the first AP and an identifier of a second AP of the plurality of APs; generating an inverse trigger frame including the identifier of the first AP, identifier of the second AP, and synchronization information; transmitting the inverse trigger frame to at least the first AP and the second AP; and receiving data transmission from the first AP and the second AP based on the synchronization information.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 757,611, filed November 8, 2018, and U.S. Provisional Patent Application No. 62 / 815,113, filed March 7, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] background

[0002] A WLAN in infrastructure basic service set (BSS) mode has an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP typically has access or interface to a distribution system (DS) or another type of wired / wireless network that carries traffic in and out of the BSS. Traffic to the STA originating from outside the BSS arrives through the AP and is delivered to the STA. Traffic originating from the STA to a destination outside the BSS is sent to the AP to be delivered to the respective destination. Traffic between STAs in the BSS can also be sent through the AP, where the source STA sends traffic to the AP, which delivers the traffic to the destination STA. Such traffic between STAs in the BSS is actually peer-to-peer traffic. Such peer-to-peer traffic can also be sent directly between the source and destination STAs using direct link setup (DLS) using 802.11e DLS or 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode has no APs and / or STAs that communicate directly with each other. This mode of communication is referred to as an "ad-hoc" mode of communication. Summary of the Invention

[0003]

[0003] Downlink cooperative single-user (SU) beamforming or joint precoding requires a method for an AP to synchronize to a STA so that the signal arrives at the STA with similar receive power, time and frequency to enable proper decoding of the signal by the STA. In addition, a channel access scheme that enables this operation needs to be defined.

[0004] overview

[0004] A method of multi-access point (multi-AP) communication performed by a wireless transmit / receive unit (WTRU) includes receiving a first trigger frame from a first AP of a plurality of access points (APs), the first trigger frame including first information. The WTRU receives a second trigger frame from a second AP of the plurality of APs at a predetermined time period after receiving the first trigger frame. The second trigger frame also includes the first information of the first trigger frame. The WTRU generates a synchronization frame based on the first trigger frame and the second trigger frame. The synchronization frame includes the synchronization information. The WTRU transmits the synchronization frame to at least the first AP and the second AP. Finally, the WTRU receives a data transmission from each of the first AP and the second AP based on the synchronization information.

[0005]

[0005] A wireless transmit / receive unit (WTRU) configured for multi-access point (multi-AP) communication includes a receiver configured to receive a first trigger frame from a first AP of a plurality of access points (APs). The first trigger frame includes first information. The receiver is also configured to receive a second trigger frame from a second AP of the plurality of APs at a predetermined time period after receiving the first trigger frame. The second trigger frame also includes the first information of the first trigger frame. The WTRU further includes a processor configured to generate a synchronization frame based on the first trigger frame and the second trigger frame. The synchronization frame includes synchronization information. The WTRU further includes a transmitter configured to transmit the synchronization frame to at least the first AP and the second AP. Furthermore, the receiver is configured to receive a data transmission from each of the first AP and the second AP based on the synchronization information.

[0006] BRIEF DESCRIPTION OF THE DRAWINGS A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings, in which like reference numerals indicate similar elements and in which: [Brief description of the drawings]

[0007] [Figure 1A] FIG. 1 is a system diagram illustrating an example of a communication system in which one or more disclosed embodiments may be implemented. [Figure 1B]

[0008] 1A is a system diagram illustrating an example of a wireless transmit / receive unit (WTRU) that may be used within the communications system illustrated in FIG. 1A, according to one embodiment. [Figure 1C]

[0009] 1A is a system diagram illustrating an example of a radio access network (RAN) and an example of a core network (CN) that may be used within the communication system illustrated in FIG. 1A, according to one embodiment. [Figure 1D]

[0010] 1B is a system diagram illustrating a further example of a RAN and a further example of a CN that may be used within the communication system illustrated in FIG. 1A, according to one embodiment. [Diagram 2]

[0011] We present fractional frequency reuse (FFR) in cooperative orthogonal frequency division multiple access (OFDMA). [Diagram 3]

[0012] The associated OFDMA resource allocation for the example of FIG. [Figure 4]

[0013] 1 shows an example of cooperative nulling / beamforming. [Diagram 5]

[0014] 1 shows single-user joint pre-coded multi-AP transmission. [Figure 6]

[0015] 1 shows multi-user joint pre-coded multi-AP transmission. [Figure 7]

[0016] 1 illustrates an example of trigger-based multi-AP sounding. [Figure 8]

[0017] 1 shows an example of a phase offset for uplink (UL) sounding. [Figure 9]

[0018] An example of cooperative MU beamforming is shown. [Figure 10]

[0019] 1 shows an example of a trigger frame-based downlink (DL) joint transmission. [Figure 11]

[0020] 1 illustrates an exemplary channel access procedure. [Figure 12]

[0021] 1 illustrates an exemplary channel access procedure. [Figure 13]

[0022] 1 illustrates an exemplary channel access procedure. [Figure 14]

[0023] 1 illustrates an exemplary channel access procedure. [Figure 15]

[0024] 1 illustrates an exemplary channel access procedure. [Figure 16]

[0025] 1 illustrates an exemplary channel access procedure. [Figure 17]

[0026] 1 illustrates an exemplary channel access procedure. [Figure 18]

[0027] 1 illustrates an exemplary channel access procedure. [Figure 19]

[0028] 1 illustrates an exemplary channel access procedure. [Figure 20]

[0029] 1 illustrates an exemplary channel access procedure. [Figure 21]

[0030] 1 shows an example of a procedure and frame exchange for an example of JT MU-MIMO. [Figure 22]

[0031] 1 shows an example of a procedure and frame exchange for an example of JT MU-MIMO. [Diagram 23]

[0032] 1 shows an example of a procedure and frame exchange for an example of JT MU-MIMO. [Figure 24]

[0033] 1 shows an example of a procedure and frame exchange for an example of JT MU-MIMO. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Detailed Description

[0034] 1A illustrates an example of a communication system 100 in which one or more disclosed embodiments can 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 enable multiple wireless users to access such content by sharing system resources, including wireless bandwidth. For 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), Zero-Tailed Unique Word Discrete Fourier Transform Spread OFDM (ZT-UW-DFT-S-OFDM), Unique Word OFDM (UW-OFDM), Resource Block Filtered OFDM, Filter Bank Multi-Carrier (FBMC), etc.

[0009]

[0035] 1A, communications system 100 may include wireless transmit / receive units (WTRUs) 102a, 102b, 102c, 102d, a radio access network (RAN) 104, a core network (CN) 106, a public switched telephone network (PSTN) 108, the Internet 110, and other networks 112, although it will be understood that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and / or network elements. Each of WTRUs 102a, 102b, 102c, 102d may be any type of device configured to operate and / or communicate in a wireless environment. By way of example, the WTRUs 102a, 102b, 102c, 102d, any of which may be referred to as a station (STA), may be configured to transmit and / or receive wireless signals and may include user equipment (UE), mobile stations, fixed or mobile subscriber units, per-subscription units, pagers, mobile phones, personal digital assistants (PDAs), smartphones, laptops, netbooks, personal computers, wireless sensors, hotspot or Mi-Fi devices, Internet of Things (IoT) devices, watches or other wearables, head mounted displays (HMDs), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in connection with industrial and / or automated process chains), consumer electronic devices, devices operating on commercial and / or industrial wireless networks, etc. Any of the WTRUs 102a, 102b, 102c, and 102d may be referred to interchangeably as a UE.

[0010]

[0036] The communication system 100 may also include a base station 114a and / or a base station 114b. Each of the base stations 114a, 114b may be any type of device configured to wirelessly interface with at least one of the WTRUs 102a, 102b, 102c, 102d to facilitate access to one or more communication networks, such as the CN 106, the Internet 110, and / or other networks 112. By way of example, the base stations 114a, 114b may be a base transceiver station (BTS), a NodeB, an eNode B (eNB), a Home Node B, a Home eNode B, a next generation NodeB such as a gNodeB (gNB), a new radio (NR) NodeB, a site controller, an access point (AP), a wireless router, etc. Although the base stations 114a, 114b are each illustrated as a single element, it will be understood that the base stations 114a, 114b may include any number of interconnected base stations and / or network elements.

[0011]

[0037] The base station 114a may be part of the RAN 104, which may also include other base stations and / or network elements (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 on one or more carrier frequencies, which may be referred to as cells (not shown). These frequencies may be in licensed spectrum, unlicensed spectrum, or a combination of licensed and unlicensed spectrum. A cell may provide wireless service coverage to a particular geographic area, which may be relatively fixed or may change over time. A 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, one for each sector of the cell. In one embodiment, the base station 114a may use multiple input / output (MIMO) technology and may utilize multiple transceivers for each sector of the cell. For example, beamforming can be used to transmit and / or receive signals in desired spatial directions.

[0012]

[0038] The base stations 114a, 114b may communicate with one or more of the WTRUs 102a, 102b, 102c, 102d over an air interface 116, which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, centimeter wave, micrometer wave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface 116 may be established using any suitable radio access technology (RAT).

[0013]

[0039] More specifically, as noted above, the communications 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. For example, the base stations 114a and the WTRUs 102a, 102b, 102c in the RAN 104 may implement a radio technology, such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface 116 using Wideband CDMA (WCDMA). WCDMA may include communications protocols, such as High Speed ​​Packet Access (HSPA) and / or Evolved HSPA (HSPA+). HSPA may include High Speed ​​Downlink (DL) Packet Access (HSDPA) and / or High Speed ​​Uplink (UL) Packet Access (HSUPA).

[0014]

[0040] In one 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) and / or LTE-Advanced Pro (LTE-A Pro).

[0015]

[0041] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement a radio technology such as NR radio access, which may establish the air interface 116 using NR.

[0016]

[0042] In one embodiment, the base station 114a and the WTRUs 102a, 102b, 102c may implement multiple radio access technologies. For example, the base station 114a and the WTRUs 102a, 102b, 102c may implement LTE radio access and NR radio access together, for example, using a dual connectivity (DC) principle. Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by multiple types of radio access technologies and / or transmissions sent to and from multiple types of base stations (e.g., eNBs and gNBs).

[0017]

[0043] In other embodiments, the base station 114a and the WTRUs 102a, 102b, 102c may implement a wireless technology such as IEEE 802.11 (i.e., Wireless Fidelity (WiFi), IEEE 802.16 (i.e., 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), or the like.

[0018]

[0044] The base station 114b of FIG. 1A may be, for example, a wireless router, a Home Node B, a Home eNode B, or an access point, and may utilize any suitable RAT to facilitate wireless connectivity within a localized area, such as a business, a home, a vehicle, a campus, an industrial facility, an air corridor (e.g., for use by drones), a road, etc. In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology, such as IEEE 802.11, to establish a wireless local area network (WLAN). In one embodiment, the base station 114b and the WTRUs 102c, 102d may implement a radio technology, such as IEEE 802.15, to establish a wireless personal area network (WPAN). In yet another embodiment, the base station 114b and the WTRUs 102c, 102d may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.) to establish a picocell or femtocell. 1A, the base station 114b may have a direct connection to the Internet 110. Thus, the base station 114b may not need to access the Internet 110 through the CN 106.

[0019]

[0045] The RAN 104 may communicate with the CN 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 of the WTRUs 102a, 102b, 102c, 102d. The data may have various Quality of Service (QoS) requirements, such as different throughput requirements, delay requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, etc. The CN 106 may provide call control, charging services, mobile location-based services, prepaid calling, Internet connectivity, video distribution, etc., and / or perform high level security functions, such as user authentication. Although not shown in FIG. 1A, it will be understood that the RAN 104 and / or the CN 106 may communicate directly or indirectly with other RANs that use the same RAT as the RAN 104 or a different RAT. For example, in addition to being connected to the RAN 104, which may utilize NR radio technology, the CN 106 may also communicate with another RAN (not shown) that uses GSM, UMTS, CDMA2000, WiMAX, E-UTRA or WiFi radio technologies.

[0020]

[0046] The CN 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 providing Plain Old Telephone Service (POTS). The Internet 110 may include a worldwide system of interconnected computer networks and devices that use common communications protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and / or Internet Protocol (IP) in the TCP / IP Internet protocol suite. The networks 112 may include wired and / or wireless communications networks owned and / or operated by other service providers. For example, the networks 112 may include another CN connected to one or more RANs that may use the same RAT as the RAN 104 or a different RAT.

[0021]

[0047] Some or all of the WTRUs 102a, 102b, 102c, 102d in the communications system 100 may include multi-mode capabilities (e.g., the WTRUs 102a, 102b, 102c, 102d may include multiple transceivers for communicating with different wireless networks over different wireless links). For example, the WTRU 102c shown in FIG. 1A may be configured to communicate with a base station 114a, which may use a cellular-based wireless technology, and a base station 114b, which may use an IEEE 802 wireless technology.

[0022]

[0048] Figure 1B is a system diagram illustrating an example of a WTRU 102. As shown in Figure 1B, the WTRU 102 may include, among other things, a processor 118, a transceiver 120, a transmit / receive element 122, a speaker / microphone 124, a keypad 126, a display / touchpad 128, non-removable memory 130, removable memory 132, a power source 134, a Global Positioning System (GPS) chipset 136, and / or other peripherals 138. It will be understood that the WTRU 102 may include any subcombination of the above elements while remaining consistent with an embodiment.

[0023]

[0049] The processor 118 may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), multiple 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), any other type of integrated circuit (IC), a state machine, etc. The processor 118 may perform signal coding, data processing, output 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 may be coupled to the transmit / receive element 122. Although FIG. 1B depicts the processor 118 and the transceiver 120 as separate components, it will be understood that the processor 118 and the transceiver 120 may be integrated within an electronic package or chip.

[0024]

[0050] The transmit / receive element 122 may be configured to transmit or receive signals to or from a base station (e.g., base station 114a) over the air interface 116. For example, in one embodiment, the transmit / receive element 122 may be an antenna configured to transmit and / or receive RF signals. In one embodiment, the transmit / receive element 122 may be an emitter / detector configured to transmit and / or receive, for example, IR, UV, or visible light signals. In yet another embodiment, the transmit / receive element 122 may be configured to transmit and / or receive both RF and light signals. It will be appreciated that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0025]

[0051] 1B illustrates the transmit / receive element 122 as a single element, the WTRU 102 may include any number of transmit / receive elements 122. More specifically, the WTRU 102 may use MIMO technology. Thus, in one embodiment, the WTRU 102 may include two or more transmit / receive elements 122 (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface 116.

[0026]

[0052] The transceiver 120 may be configured to modulate signals transmitted by the transmit / receive element 122 and to demodulate signals received by the transmit / receive element 122. As mentioned above, the WTRU 102 may have multi-mode capabilities. Thus, the transceiver 120 may include multiple transceivers to enable the WTRU 102 to communicate over multiple RATs, such as NR and IEEE 802.11.

[0027]

[0053] The processor 118 of the WTRU 102 may be coupled to and may receive user input data from the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128 (e.g., a liquid crystal display (LCD) display unit or an organic light emitting diode (OLED) display unit). The processor 118 may also output user data to the speaker / microphone 124, the keypad 126, and / or the display / touchpad 128. In addition, the processor 118 may access information in and store data in any type of 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, or the like. In other embodiments, the processor 118 may access information in, and store data in, memory that is not physically located on the WTRU 102, such as on a server or on a home computer (not shown).

[0028]

[0054] The processor 118 may obtain power from the power source 134 and may be configured to distribute and / or control the power to other components within 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 batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel-metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, etc.

[0029]

[0055] The processor 118 may also be coupled to a GPS chipset 136, which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU 102. In addition to or in lieu of information from the GPS chipset 136, the WTRU 102 may receive location information over the air interface 116 from a base station (e.g., base stations 114a, 114b) and / or may locate 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 obtain location information by way of any suitable position determination method while remaining consistent with an embodiment.

[0030]

[0056] The processor 118 may further be coupled to other peripherals 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 peripherals 138 may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photos and / or videos), a universal serial bus (USB) port, a vibration device, a television receiver, a hands-free headset, a Bluetooth module, a frequency modulation (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, a virtual reality and / or augmented reality (VR / AR) device, an activity tracker, and the like. The peripherals 138 may include one or more sensors. The sensors may be one or more of a gyroscope, an accelerometer, a Hall effect sensor, a magnetometer, an orientation sensor, a proximity sensor, a temperature sensor, a time sensor, a geolocation sensor, an altimeter, a light sensor, a touch sensor, a magnetometer, a barometer, a gesture sensor, a biometric sensor, and a humidity sensor, and the like.

[0031]

[0057] The WTRU 102 may include a full-duplex radio where transmission and reception of some or all of the signals associated with a particular subframe (e.g., for both the UL (e.g., for transmission) and DL (e.g., for reception) may be parallel and / or simultaneous. The full-duplex radio may include an interference management unit to reduce and / or substantially eliminate self-interference by hardware (e.g., chokes) or signal processing by a processor (e.g., by a separate processor (not shown) or by processor 118). In one embodiment, the WTRU 102 may include a half-duplex radio for transmission and reception of some or all of the signals (e.g., associated with a particular subframe for either the UL (e.g., for transmission) or DL ​​(e.g., for reception).

[0032]

[0058] 1C is a system diagram illustrating the RAN 104 and the CN 106 according to one embodiment. As mentioned above, the RAN 104 may use E-UTRA radio technology to communicate with the WTRUs 102a, 102b, 102c over the air interface 116. The RAN 104 may also communicate with the CN 106.

[0033]

[0059] The RAN 104 may include eNode-Bs 160a, 160b, 160c, although it will be understood that the RAN 104 may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs 160a, 160b, 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, 160c may implement MIMO technology. Thus, for example, the eNode-B 160a may transmit and / or receive wireless signals to and from the WTRU 102a using multiple antennas.

[0034]

[0060] Each of the eNode-Bs 160a, 160b, 160c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, etc. As shown in FIG 1C, the eNode-Bs 160a, 160b, 160c may communicate with each other over an X2 interface.

[0035]

[0061] 1C may include a Mobility Management Entity (MME) 162, a Serving Gateway (SGW) 164, and a Packet Data Network (PDN) Gateway (PGW) 166. Although the above elements are shown as part of the CN 106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0036]

[0062] The MME 162 may be connected to each of the eNode-Bs 162a, 162b, 162c in the RAN 104 over an S1 interface and may act as a control node. For example, the MME 162 may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, activating / deactivating bearers, selecting a particular serving gateway during initial attachment of the WTRUs 102a, 102b, 102c, etc. The MME 162 may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that employ other radio technologies, such as GSM and / or WCDMA.

[0037]

[0063] The SGW 164 may be connected to each of the eNode Bs 160a, 160b, 160c in the RAN 104 by an S1 interface. The SGW 164 may generally route and forward user data packets to and from the WTRUs 102a, 102b, 102c. The SGW 164 may perform other functions such as anchoring the user plane during handovers between eNode Bs, triggering paging when DL data is available for the WTRUs 102a, 102b, 102c, managing and storing the context of the WTRUs 102a, 102b, 102c, etc.

[0038]

[0064] The SGW 164 may be connected to a PGW 166, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks, such as the Internet 110, to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices.

[0039]

[0065] The CN 106 may facilitate communications with other networks. For example, the CN 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 CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers.

[0040]

[0066] Although FIGS. 1A-1D depict the WTRU as a wireless terminal, it is contemplated that in certain representative embodiments such a terminal may employ a wired communications interface (eg, temporarily or permanently) with a communications network.

[0041]

[0067] In an exemplary embodiment, the other network 112 may be a WLAN.

[0042]

[0068] A WLAN in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP may have access or interface to a distribution system (DS) or another type of wired / wireless network that carries traffic in and out of the BSS. Traffic to the STA originating from outside the BSS may arrive and be delivered to the STA via the AP. Traffic originating from the STA to a destination outside the BSS may be sent to the AP to be delivered to the respective destination. Traffic between STAs in the BSS may be sent via the AP, e.g., a source STA may send traffic to the AP, which may deliver the traffic to the destination STA. Traffic between STAs in the BSS may be considered and / or referred to as peer-to-peer traffic. Peer-to-peer traffic may be sent (e.g., directly) between the source and destination STAs using a direct link setup (DLS). In certain representative embodiments, the DLS may use 802.11e DLS or 802.11z tunneled DLS (TDLS). A WLAN using an Independent BSS (IBSS) mode may not have an AP, and STAs (e.g., all of the STAs) in or using an IBSS may communicate directly with each other. IBSS mode communication may also be referred to herein as an "ad-hoc" mode of communication.

[0043]

[0069] When using an 802.11ac infrastructure mode of operation or a similar mode of operation, an AP may transmit beacons on a fixed channel, such as a primary channel. The primary channel may be a fixed width (e.g., a 20 MHz wide band) or a dynamically set width. The primary channel may be an operating channel of the BSS and may be used by STAs to establish a connection with the AP. In certain representative embodiments, for example, Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA) may be implemented within an 802.11 system. In CSMA / CA, STAs (e.g., all STAs), including the AP, may sense the primary channel. If the primary channel is sensed / detected and / or determined to be in use by a particular STA, the particular STA may back off. Within a given BSS, one STA (e.g., only one station) may transmit at any given time.

[0044]

[0070] For example, by combining a primary 20 MHz channel with adjacent or non-adjacent 20 MHz channels to form a 40 MHz wide channel, a high throughput (HT) STA may use the 40 MHz wide channel for communication.

[0045]

[0071] A Very High Throughput (VHT) STA may support channels of 20 MHz, 40 MHz, 80 MHz, and / or 160 MHz width. A 40 MHz and / or 80 MHz channel may be formed by combining contiguous 20 MHz channels. A 160 MHz channel may be formed by combining eight contiguous 20 MHz channels, or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. In the 80+80 configuration, the channel-encoded data may be passed through a segment parser that may split the data into two streams. Inverse Fast Fourier Transform (IFFT) processing and time domain processing may be performed separately for each stream. The streams may be mapped onto two 80 MHz channels, and the data may be transmitted by the transmitting STA. At the receiver of the receiving STA, the above 80+80 configuration operation may be reversed, and the composite data may be sent to the Medium Access Control (MAC).

[0046]

[0072] Sub-1 GHz modes of operation are supported by 802.11af and 802.11ah. Compared to those used in 802.11n and 802.11ac, 802.11af and 802.11ah have reduced channel operating bandwidths and carriers. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to a representative embodiment, 802.11ah can support meter type control / machine type communication (MTC), such as MTC devices in macro coverage areas. MTC devices may have limited functionality, including specific features, such as support for (e.g., only) specific and / or limited bandwidths. MTC devices may include batteries with battery life above a threshold (e.g., to maintain very long battery life).

[0047]

[0073] WLAN systems that may support multiple channels and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, may include a channel that may be designated as a primary channel. The primary channel may have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel may be set and / or limited by a STA among all STAs operating in the BSS that may support the smallest bandwidth operating mode. In the example of 802.11ah, for STAs (e.g., MTC-type devices) that support (e.g., only) 1 MHz mode, the primary channel may be 1 MHz wide, even if the AP and other STAs in the BSS support 2 MHz, 4 MHz, 8 MHz, 16 MHz, and / or other channel bandwidth operating modes. The setting of the carrier sense and / or network allocation vector (NAV) may depend on the state of the primary channel. For example, if the primary channel is in use by STAs (that only support 1 MHz operating modes) transmitting to the AP, the entire available frequency band may be considered in use, even if most of the available frequency band remains unused.

[0048]

[0074] In the United States, the available frequency band that can be used by 802.11ah is 902MHz to 928MHz. In South Korea, the available frequency band is 917.5MHz to 923.5MHz. In Japan, the available frequency band is 916.5MHz to 927.5MHz. Depending on the country code, the total available bandwidth for 802.11ah is 6MHz to 26MHz.

[0049]

[0075] 1D is a system diagram illustrating the RAN 104 and the CN 106 according to one embodiment. As mentioned above, the RAN 104 can communicate with the WTRUs 102a, 102b, 102c over the air interface 116 using NR radio technology. The RAN 104 can also communicate with the CN 106.

[0050]

[0076] The RAN 104 may include gNBs 180a, 180b, 180c, although it will be understood that the RAN 104 may include any number of gNBs while remaining consistent with an embodiment. The gNBs 180a, 180b, 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, 180c may implement MIMO technology. For example, the gNBs 180a, 180b may utilize beamforming to transmit and / or receive signals to and from the gNBs 180a, 180b, 180c. Thus, for example, the gNB 180a may transmit and / or receive wireless signals to and from the WTRU 102a using multiple antennas. In one embodiment, the gNBs 180a, 180b, 180c may implement carrier aggregation technology. For example, the gNB 180a may transmit multiple component carriers (not shown) to the WTRU 102a. A subset of these component carriers may be on an unlicensed spectrum, while the remaining component carriers may be on a licensed spectrum. In one embodiment, the gNBs 180a, 180b, 180c may implement coordinated multipoint (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from gNBs 180a and 180b (and / or gNB 180c).

[0051]

[0077] The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using scalable numerology-related transmissions. For example, the OFDM symbol spacing and / or OFDM subcarrier spacing may be different for different transmissions, different cells, and / or different portions of the wireless transmission spectrum. The WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using subframes or transmission time intervals (TTIs) of different or scalable lengths (e.g., including different numbers of OFDM symbols and / or lasting for variable lengths of absolute time).

[0052]

[0078] The gNBs 180a, 180b, 180c may be configured to communicate with the WTRUs 102a, 102b, 102c in a standalone configuration and / or a non-standalone configuration. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c without accessing any other RANs (e.g., eNode-Bs 160a, 160b, 160c, etc.). In a standalone configuration, the WTRUs 102a, 102b, 102c may utilize one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c may communicate with the gNBs 180a, 180b, 180c using signals in unlicensed bands. In a non-standalone configuration, the WTRUs 102a, 102b, 102c may communicate with / connect to a gNB 180a, 180b, 180c while also communicating with / connecting to another RAN, such as an eNode-B 160a, 160b, 160c. For example, the WTRUs 102a, 102b, 102c may implement the DC principle to communicate with one or more gNBs 180a, 180b, 180c and one or more eNode-Bs 160a, 160b, 160c at approximately the same time. In a non-standalone configuration, the eNode-Bs 160a, 160b, 160c may act as mobility anchors for the WTRUs 102a, 102b, 102c, and the gNBs 180a, 180b, 180c may provide additional coverage and / or throughput for serving the WTRUs 102a, 102b, 102c.

[0053]

[0079] Each of the gNBs 180a, 180b, 180c may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the UL and / or DL, support for network slicing, DC, interworking between NR and E-UTRA, routing of user plane data to user plane (UPF) 184a, 184b, routing of control plane information to access and mobility management functions (AMF) 182a, 182b, etc. As shown in FIG. 1D, the gNBs 180a, 180b, 180c may communicate with each other over an Xn interface.

[0054]

[0080] The CN 106 shown in Figure 1D may include at least one AMF 182a, 182b, at least one UPF 184a, 184b, at least one Session Management Function (SMF) 183a, 183b, and possibly a Data Network (DN) 185a, 185b. Although the above elements are shown as part of the CN 106, it will be understood that any of these elements may be owned and / or operated by an entity other than the CN operator.

[0055]

[0081] The AMF 182a, 182b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 by an N2 interface and may act as a control node. For example, the AMF 182a, 182b may be responsible for authenticating users of the WTRUs 102a, 102b, 102c, supporting network slicing (e.g., handling various protocol data unit (PDU) sessions having different requirements), selecting a particular SMF 183a, 183b, managing registration areas, terminating non-access stratum (NAS) signaling, mobility management, etc. Network slicing may be used by the AMF 182a, 182b to customize the CN support of the WTRUs 102a, 102b, 102c based on the type of service being utilized. Different network slices may be established for different use cases, for example, services relying on Ultra-Reliable Low Latency (URLLC) access, services relying on Enhanced Massive Mobile Broadband (eMBB) access, and services for MTC access, etc. The AMF 182a, 182b may provide a control plane function for switching between the RAN 104 and other RANs (not shown) that use other radio technologies, such as LTE, LTE-A, LTE-A Pro, and / or non-3GPP access technologies, such as WiFi.

[0056]

[0082] The SMFs 183a, 183b may be connected to the AMFs 182a, 182b in the CN 106 by an N11 interface. The SMFs 183a, 183b may also be connected to the UPFs 184a, 184b in the CN 106 by an N4 interface. The SMFs 183a, 183b may select and control the UPFs 184a, 184b and configure the routing of traffic through the UPFs 184a, 184b. The SMFs 183a, 183b may perform other functions such as managing and assigning IP addresses for UEs, managing PDU sessions, controlling policy enforcement and QoS, providing DL data notification, etc. The type of PDU session may be IP-based, non-IP-based, Ethernet-based, etc.

[0057]

[0083] The UPFs 184a, 184b may be connected to one or more of the gNBs 180a, 180b, 180c in the RAN 104 by an N3 interface, which may provide the WTRUs 102a, 102b, 102c with access to packet-switched networks such as the Internet 110 to facilitate communications between the WTRUs 102a, 102b, 102c and IP-enabled devices. The UPFs 184, 184b may perform other functions such as routing and forwarding packets, enforcing user plane policies, supporting multi-homed PDU sessions, handling user plane QoS, buffering DL packets, providing mobility anchoring, etc.

[0058]

[0084] The CN 106 may facilitate communication with other networks. For example, the CN 106 may include or communicate with an IP gateway (e.g., an IP Multimedia Subsystem (IMS) server) that serves as an interface between the CN 106 and the PSTN 108. In addition, the CN 106 may provide the WTRUs 102a, 102b, 102c with access to other networks 112, which may include other wired and / or wireless networks owned and / or operated by other service providers. In an embodiment, the WTRUs 102a, 102b, 102c may be connected to the local DNs 185a, 185b via the UPFs 184a, 184b via an N3 interface to the UPFs 184a, 184b and an N6 interface between the UPFs 184a, 184b and the DNs 185a, 185b.

[0059]

[0085] 1A-1D and the corresponding descriptions thereof, one or more or all of the functions described herein with respect to one or more of the WTRUs 102a-d, base stations 114a-b, eNode-Bs 160a-c, MME 162, SGW 164, PGW 166, gNBs 180a-c, AMFs 182a-b, UPFs 184a-b, SMFs 183a-b, DNs 185a-b, and / or any other devices described herein may be performed by one or more emulation devices (not shown). An emulation device may be one or more devices configured to emulate one or more or all of the functions described herein. For example, the emulation device may be used to test other devices and / or to simulate the functionality of a network and / or a WTRU.

[0060]

[0086] The emulation device may be designed to perform one or more tests of other devices in a laboratory environment and / or in an operator network environment. For example, one or more emulation devices may perform one or more or all functions while fully or partially implemented and / or deployed as part of a wired and / or wireless communication network to test other devices in the communication network. One or more emulation devices may perform one or more or all functions while temporarily implemented / deployed as part of a wired and / or wireless communication network. The emulation device may be directly coupled to another device for testing and / or may perform testing using over-the-air communication.

[0061]

[0087] The emulation device(s) may perform one or more functions, including but not limited to, without being implemented / introduced as part of a wired and / or wireless communication network. For example, the emulation device(s) may be utilized in a test lab and / or in a test scenario within an unintroduced (e.g., test) wired and / or wireless communication network to perform testing of one or more components. The emulation device(s) may be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (which may include, e.g., one or more antennas) may be used by the emulation device to transmit and / or receive data.

[0062]

[0088] A wireless local area network (WLAN) in infrastructure basic service set (BSS) mode may have an access point (AP) for the BSS and one or more stations (STAs) associated with the AP. The AP typically has access or interface to a distribution system (DS) or another type of wired / wireless network that carries traffic in and out of the BSS. Traffic to the STA originating from outside the BSS arrives through the AP and is delivered to the STA. Traffic originating from the STA to a destination outside the BSS is sent to the AP to be delivered to the respective destination. Traffic between STAs in the BSS may also be sent through the AP, where the source STA sends traffic to the AP, which delivers it to the destination STA. Such traffic between STAs in the BSS may be referred to as peer-to-peer traffic. Such peer-to-peer traffic may also be sent directly between the source and destination STAs using direct link setup (DLS) using 802.11e DLS or 802.11z tunneled DLS (TDLS). A WLAN in Independent BSS (IBSS) mode does not have an AP and STAs communicate directly with each other. This mode of communication can be called an "ad-hoc" mode of communication.

[0063]

[0089] In some implementations, such as systems using infrastructure mode operation as defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.11ac standard, an AP may transmit beacons on a fixed channel, typically the primary channel. This channel may be 20 MHz wide and is the operating channel of the BSS. This channel may be used by STAs to establish a connection with the AP. Channel access in 802.11 systems is implemented using Carrier Sense Multiple Access with Collision Avoidance (CSMA / CA). In this mode of operation, all STAs, including the AP, can sense the primary channel. If the channel is detected as being in use, the STAs back off. Thus, only one STA within a given BSS may transmit at any given time.

[0064]

[0090] In some implementations, such as systems conforming to the IEEE 802.11n standard, high-throughput (HT) STAs may also use the 40 MHz wide channel for communication, which may be accomplished by combining a primary 20 MHz channel with adjacent 20 MHz channels to form a 40 MHz wide contiguous channel.

[0065]

[0091] In some implementations, e.g., systems conforming to the IEEE 802.11ac standard, Very High Throughput (VHT) STAs may support channels of 20 MHz, 40 MHz, 80 MHz, and 160 MHz width. The 40 MHz and 80 MHz channels may be formed by combining contiguous 20 MHz channels similar to 802.11n above. The 160 MHz channel may be formed by combining eight contiguous 20 MHz channels, or by combining two non-contiguous 80 MHz channels, which may be referred to as an 80+80 configuration. In the 80+80 configuration, the data after channel encoding may be passed through a segment parser that splits the data into two streams. IFFT and time domain processing may be performed separately for each stream. The streams may be mapped onto two channels, and the data may be transmitted. At the receiver, this mechanism is reversed, and the composite data is sent to the MAC.

[0066]

[0092] In some implementations, such as systems conforming to the IEEE 802.11af and / or IEEE 802.11ah standards, sub-1 GHz modes of operation are supported. In such implementations, channel operating bandwidths and carriers may be reduced compared to those used in systems conforming to the IEEE 802.11n and / or IEEE 802.11ac standards. For example, 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, and 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. A possible use case for 802.11ah is support for meter-type control or machine-type communication (MTC) devices in macro coverage areas. MTC devices may have limited capabilities, such as limited bandwidth support, and may include requirements for very long battery life.

[0067]

[0093] A WLAN system that supports multiple channels and / or channel widths, such as those that comply with the IEEE 802.11n, 802.11ac, 802.11af, and / or 802.11ah standards, may include a channel designated as a primary channel. The primary channel may, but need not, have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. Thus, in such cases, the bandwidth of the primary channel may be limited by the STAs of all STAs operating in the BSS that support the smallest bandwidth operating mode. In the example of an IEEE 802.11ah system, the primary channel may be 1 MHz wide if the BSS includes STAs (e.g., MTC-type devices) that support only 1 MHz mode, even if the AP and other STAs in the BSS may support 2 MHz, 4 MHz, 8 MHz, 16 MHz, or other channel bandwidth operating modes. Carrier sensing and NAV setting may depend on the condition of the primary channel. In some such cases, when the primary channel is in use, e.g., by STAs that only support a 1 MHz mode of operation transmitting to the AP, a large portion of the available frequency band remains unused and the entire available frequency band is considered to be in use, even though it may be available.

[0068]

[0094] In the United States, the available frequency band that may be used by 802.11ah compliant systems is 902MHz to 928MHz. In South Korea, the available frequency band is 917.5MHz to 923.5MHz, and in Japan, the available frequency band is 916.5MHz to 927.5MHz. Depending on the country code, the total available bandwidth for 802.11ah is 6MHz to 26MHz.

[0069]

[0095] Recently, the IEEE 802.11 Highly Efficient WLAN (HEW) Study Group (SG) was formed to consider the scope and objectives of possible future modifications to improve the quality of service experienced by all wireless users over a wide range of use scenarios, including high density scenarios in the 2.4 GHz, 5 GHz and 6 GHz bands. Emerging use cases that support high density deployment of APs and STAs, as well as associated Radio Resource Management (RRM) techniques, are being considered by the HEW SG.

[0070]

[0096] In a typical 802.11 network (i.e., a network conforming to one or more IEEE 802.11 standards), a STA may be associated with a single AP and transmit to or from that AP with little or no coordination with transmissions in neighboring BSSs. The STA may follow overlapping BSS (OBSS) transmissions based on a CSMA protocol that is completely independent between BSSs. In some systems (e.g., 802.11ax compliant systems), a spatial re-use procedure may be used to introduce some degree of coordination between OBSSs to allow OBSS transmissions based on adjusted energy detection thresholds (e.g., using an OBSS Packet Detection (OBSS PD) procedure) or knowledge of the amount of interference that can be tolerated by the receiving OBSS STA (e.g., using a spatial reuse parameter (SRP) procedure).

[0071]

[0097] Some implementations include procedures that allow for further coordination between OBSSs by allowing transmissions to or from multiple APs to a single or multiple STAs. In some implementations, this is similar to Coordinated Multipoint (CoMP) transmissions in systems that comply with 3GPP LTE Release 10, but in some implementations such procedures operate in unlicensed bands and / or are specific to one or more IEEE 802.11 protocols.

[0072]

[0098] In a system supporting coordinated multipoint (CoMP) transmission, multiple eNBs (or other types of base stations (we use eNB for convenience)) can transmit to the same or multiple WTRUs in the same time and frequency resources using joint processing / transmission. This can have the effect of improving the overall throughput of the considered WTRUs. Dynamic cell selection can be treated as a special case of joint processing where only one of a set of WTRUs actively transmits data at any one time. On the other hand, multiple eNBs can transmit to different WTRUs in the same time and frequency resources using coordinated beamforming / scheduling (each eNB serving its own WTRU). This can have the effect of reducing the interference experienced by each WTRU. For example, using CoMP in an LTE system, significant improvements in cell-average and / or cell-edge throughput can be achieved. In some implementations, multiple transmit antennas can be considered available for each base station. Using spatial domain signal processing at each base station, simultaneous interference suppression (for other WTRUs) and signal quality optimization (for the desired WTRU) can be performed.

[0073]

[0099] In some implementations, some degree of channel state information is assumed to be available at the base station, e.g., by explicit feedback. Additionally, in some implementations, some degree of timing / frequency synchronization is assumed, e.g., to avoid more complex signal processing to deal with inter-carrier interference (or inter-symbol interference). Additionally, in some implementations, the level of cooperation between eNBs may affect the particular CoMP schemes that may be possible.

[0074]

[0100] Multi-AP transmission schemes in a WLAN can be referred to using several classifications, including cooperative OFDMA, cooperative nulling / beamforming, and cooperative SU / MU transmission.

[0075]

[0101] In cooperative OFDMA, each group of RUs may be used by only one AP to transmit or receive data. Information may be beamformed on each RU or may include MU-MIMO. The complexity may be expressed as relatively low to medium. In some simple cooperative OFDMA schemes, the APs may divide the OFDMA RUs among the APs in a cooperative manner, with each AP restricted to a specific RU. In some more sophisticated cooperative OFDMA schemes, the AP allows STAs that are not affected by interference or that do not affect others to use the full bandwidth while limiting the access of STAs that may be affected. This approach may be called fractional frequency reuse (FFR).

[0076]

[0102] Figure 2 shows FFR in cooperative OFDMA. The center group can use all channels, while the edge groups can use different channels.

[0077]

[0103] Figure 3 shows the associated OFDMA resource allocation for the example of Figure 2. In this example, group 1 can use both subband 1 and subband 2. Group 2 can use subband 1, and group 3 can use subband 2. In cooperative nulling / beamforming (CN / CB), each AP can apply precoding to transmit information between its desired STAs and can suppress interference between other STAs.

[0078]

[0104] FIG. 4 shows an example of CN / CB. As shown in FIG. 4, there is AP2 and STA1. The data transmission between AP1 and STA1 is the desired data transmission 410. There is also AP2 and STA1. The data transmission between AP2 and STA2 is the desired data transmission 420. However, in this scenario, AP1 may also transmit data to another STA or other STAs, so there may be an interfering data transmission, i.e., interference 430. AP2 may also transmit data to another STA or other STAs, so there may be an interfering data transmission, i.e., interference 440. In some such cases, data for each STA is only needed at its associated AP, but channel information from the other STA may be needed at both APs.

[0079]

[0105] In a cooperative single-user (SU) or multi-user (MU) transmission, multiple APs can cooperate to transmit information to and from a single STA or multiple GSTAs simultaneously. In some such cases, both channel information and data for the STAs are required at both APs. Such transmissions may be cooperative SU transmissions.

[0080]

[0106] In cooperative SU transmission, multiple APs transmit to a STA in one RU. Cooperative SU transmission may include dynamic point selection, cooperative SU beamforming, or joint precoding, in order of complexity.

[0081]

[0107] Figure 5 shows single-user joint precoded multi-AP transmission or cooperative SU beamforming. As shown in Figure 5, in dynamic point selection, a transmission may be dynamically selected from one of a set of APs. In some such implementations, the selection may incorporate HARQ. In cooperative SU beamforming or joint precoding, a transmission may be simultaneous from multiple APs and may be beamformed or precoded to a desired STA on one or multiple RUs. As shown in Figure 5, both AP1 and AP2 may transmit to a STA, namely STA1.

[0082]

[0108] Figure 6 shows multi-user joint pre-coded multi-AP transmission or cooperative MU beamforming. In cooperative MU beamforming, multiple APs transmit or receive data on one or multiple RUs to and from multiple STAs. As shown in Figure 6, there are two APs (i.e., AP1 and AP2) and two STAs (i.e., STA1 and STA2). AP1 can transmit data to STA1, and AP2 can transmit data to STA2. On the other hand, AP1 can also transmit data to STAs other than STA1, and AP2 can also transmit data to STAs other than STA2. In addition, there may be a wireless backhaul in which a trigger frame (TF) is sent from AP1 to AP2.

[0083]

[0109] Various techniques discussed herein relate to joint multi-AP transmission. Various multi-AP schemes, including cooperative beamforming and joint processing, can be considered for EHT applications.

[0084]

[0110] Some implementations address synchronization between multiple APs for phase calculation in UL sounding / channel estimation. For DL ​​MIMO channel estimation with a larger number of antennas, the amount of feedback and quantization errors may make DL sounding undesirable. Assuming channel reciprocity, some implementations may use UL sounding to replace DL sounding for single-stage DL MIMO transmission. In some implementations, no feedback is required from non-AP STAs for UL sounding to a single AP. In some implementations, only partial channel (channel observed at the slave AP) feedback is required for UL sounding to multiple APs.

[0085]

[0111] In DL sounding procedure, in some implementations, non-AP STAs are the entities that measure signals and / or estimate channels. Non-AP STAs in this case have perfect knowledge of received signal phase difference between Rx antennas at non-AP STAs. However, in UL sounding with multiple APs, APs do not have a common reference clock. When combining estimated channels from multiple APs, the phase difference between channels measured by different APs is unknown in some implementations.

[0086]

[0112] In the following example illustrating the problem of multi-AP UL sounding, it is assumed that (1) the Master AP performs its own channel estimation and that of the Slave AP, (2) the Master AP performs precoder calculations and informs the precoders corresponding to the Slave AP antennas using a frame (called Frame A) such as a Trigger Frame (TF), (3) the Master AP starts joint transmission one Interframe Space Time (IFS) after transmitting Frame A, and (4) the Slave AP starts joint transmission one IFS after receiving Frame A.

[0087]

[0113] FIG. 7 shows an example of trigger-based multi-AP sounding. In FIG. 7, the master AP (i.e., AP1) transmits data to the WTRU 710. AP1 can initiate UL sounding by sending a null data packet (NDP) announcement (NDP-A) for UL sounding and a trigger frame (TF). After receiving the TF, the slave AP (i.e., AP2 or a non-AP STA) adjusts its oscillator so that the carrier frequency offset (CFO) and / or sampling frequency offset (SFO) are corrected for AP1. Although the oscillator frequency is adjusted, in this example AP2 still does not know which clock in AP1 corresponds to its own clock.

[0088]

[0114] FIG. 8 shows an example of UL sounding phase offset. As shown in FIG. 8, WTRU 810 transmits UL sounding signals to AP1 and AP2. The sounding signals are then received at AP2. AP2 can estimate the amplitude and phase of the channel between its antenna and the transmitting non-AP STA. Assuming a wireless backhaul where TF is transmitted from AP1 to AP2, the channel observed at AP2 can be reported back to AP1. However, in some implementations, AP1 cannot combine that information with its own channel estimation because AP1 may be performing channel estimation at slightly different times, which may result in a phase offset between the estimated channels of AP1 and AP2.

[0089]

[0115] In some implementations, to avoid this phase offset problem, AP1 would need information about when AP2 performed channel estimation relative to AP1's clock. In some implementations, this would require clock synchronization between the master AP and the slave AP in addition to CFO / SFO correction. It may be desirable to provide a system and method in which clock synchronization between the master / slave APs is not required for channel estimation and joint DL transmission.

[0090]

[0116] Some implementations address downlink cooperative SU beamforming or joint precoding. In downlink cooperative SU beamforming or joint precoding, it may be desirable to provide a method, system, and apparatus for an AP to synchronize with a STA so that the signal arrives at the STA with similar receive power, time, and frequency, for example, to enable proper decoding of the signal by the STA. Furthermore, it may be desirable to define a corresponding channel access scheme.

[0091]

[0117] Some implementations address uplink cooperative SU beamforming or joint precoding. In some implementations, transmission from a single STA to a single AP is supported. In uplink cooperative SU beamforming or joint precoding or dynamic AP selection, it may be desirable to provide a channel access method for a STA to transmit a signal to one or more APs.

[0092]

[0118] Some implementations address cooperative MU beamforming, in which several example scenarios can arise.

[0093]

[0119] In the first example, APs may have very different attenuation / configurations. For example, APs may have different transmit powers and / or error vector magnitudes (EVMs). In such cases, it may be desirable to balance the transmit powers, for example, to allow for reversal of the effective channel for MU transmissions. If APs have different transmit powers for STAs, the resulting effective channel may not be reversible (e.g., the effective channel may have a high condition number).

[0094]

[0120] Figure 9 shows an example of cooperative MU beamforming. In this example, the received signals {y1, y2} at each STA are expressed as follows:

number

[0095]

[0122] If the APs have different transmit powers to the STAs, the effective channel is:

number

number

[0096]

[0124] If there is a large power imbalance at the AP (eg, v>>w), the resulting channel may have a high condition number and inverting the channel may be problematic.

[0097]

[0125] Some implementations provide UL sounding and channel estimation from multiple APs without clock synchronization, which may address issues related to synchronization between multiple APs for phase calculation in UL sounding and / or channel estimation.

[0098]

[0126] Figure 10 shows an example of trigger frame-based DL joint transmission based on the steps discussed above. As shown in Figure 10, AP1 transmits a trigger frame (TF) to AP2, and AP1 and AP2 transmit data to the WTRU 1010, respectively. In this example, the DL signal from AP1 arrives at the non-AP STA (x+y)-z before the DL signal from AP2, where x, y, and z correspond to the propagation delays of each of the signals in Figure 10.

[0099]

[0127] In some implementations, the master AP does not need to know x, y, and z individually to combine the channels estimated by it and the slave AP; rather, in such implementations, the master AP only needs to know the value of Δt=(x+y)-z.

[0100]

[0128] For example, in some implementations, the AP may combine the channel estimates as follows: H=[H AP1 e 2πfΔt H AP2 ], or H=[H AP1 H AP2 e -2πfΔt ] Here, H AP1 and H AP2 corresponds to the estimated channel at AP1 and AP2. In this case, the master AP can use H to perform precoding.

[0101]

[0131] Instead, in some implementations, the master AP: H=[H AP1 H AP2 ] As a composite channel, AP1 may use IFS+Δt to compute the precoder. However, in this case, AP1 may delay its DL joint transmission (e.g., until IFS+Δt after transmitting TF, or until IFS-Δt after receiving TF, where AP1 instructs the slave AP to advance its transmission). Such delay adjustment may depend on the frequency of the subcarriers.

[0102]

[0133] In some implementations, Δt can be obtained by the master AP based on the time difference between when the master AP receives the start / end of frame B (e.g., sounding feedback or other frame from the slave AP) and when the master AP receives the start and / or end of the UL sounding signal from the non-AP STA minus a fixed delay D, where D is the known delay between when the slave AP receives the start of the UL signal and when the slave AP starts transmitting frame B. For example, when using the end of the frame to calculate the difference, some adjustment can also be made for the difference in frame length between frame B and the sounding signal.

[0103]

[0134] This UL sounding scenario is illustrated in Figure 11. As shown in Figure 11, the WTRU 1110 can transmit a UL sounding signal to each of AP1 and AP2. AP1 can observe Δt=z-(x+y) by calculating the time between the rx UL sounding and the rx UL sounding feedback minus a fixed delay D. AP2 transmits the UL sounding feedback to AP1 with a fixed delay D after the rx UL sounding signal.

[0104]

[0135] In the case where multiple non-AP STAs perform UL sounding simultaneously, this example scenario can be applied by using one STA and one AP1 / AP2 antenna pair as a reference, and then calculating Δt using that reference antenna pair. Different STAs may have different Δt, but the same Δt may be obtained because, for example, the same entity (AP1 or AP2) observed / estimated multiple STAs. AP1 and H AP2 The phase difference between the two can be automatically adjusted.

[0105]

[0136] In some implementations, when multiple non-AP STAs perform UL sounding simultaneously, the above procedure can be performed independently for each non-AP STA.

[0106]

[0137] Some implementations provide channel access with synchronization for DL ​​cooperative SU and MU beamforming. Such examples can address issues related to DL cooperative SU beamforming or joint precoding discussed above. In an example scenario where both AP1 and AP2 transmit simultaneously to a STA, the AP may need to synchronize with the STA so that the signal arrives at the STA with similar receive power. Synchronization in time and frequency may also be required in some implementations. Thus, in some implementations, various techniques discussed with respect to FIG. 12 can be used to synchronize transmissions from multiple APs.

[0107]

[0138] 12 illustrates an example channel access procedure that may enable multiple APs to transmit simultaneously to a STA. In the example of FIG. 12, AP1 and AP2 may negotiate to transmit simultaneously to a STA. In some examples, AP1 may be considered as a primary AP and AP2 may be considered as a secondary AP in the negotiation. In some implementations, AP1 and AP2 may perform multi-AP joint transmission sounding in advance or immediately to obtain channel state information.

[0108]

[0139] As shown in FIG. 12, AP1 can acquire the channel and transmit a multi-AP trigger frame (i.e., trigger frame 1210) to trigger a transmission to the STA. AP1 can configure the next multi-AP transmission in the multi-AP trigger frame. In some implementations, AP1, the primary AP, can configure the transmission from AP2 to the STA. The multi-AP trigger frame can indicate, for example, STA-specific information and / or common information. The STA-specific information (here, STA indicates an AP STA or a non-AP STA) can indicate the role of the STA and / or the ID of the STA. The role of the STA can indicate whether the STA is a transmitting / STA or a receiving / STA. The ID of the STA can be an association identifier (AID), a compressed AID, a BSS identifier (BSSID, compressed BSSID), a BSS color, or an enhanced BSS color, etc.

[0109]

[0140] If the STA role indicates a transmit side / STA, the STA role may include a packet ID, a resource allocation, a spatial stream allocation, or MCS-related information. The packet ID may be used to indicate the packet transmitted from the STA. In some implementations, this field may be an AP / transmit side specific field. The STA may detect packet IDs corresponding to multiple APs and determine whether a single packet is transmitted from multiple APs or multiple packets are transmitted from multiple APs. In the first case, the STA may combine transmissions from multiple APs to decode a single packet. The resource allocation may be used to indicate the resources assigned to the AP for transmitting the multi-AP packet. In an OFDMA transmission scenario, resources may be assigned in resource units (RUs). The spatial stream allocation may be used to indicate the starting spatial stream index and the number of spatial streams used for the transmit side. The MCS-related information may include the MCS, the coding scheme, whether DCM modulation is utilized, etc.

[0110]

[0141] The common information may include a type field, which may indicate a DL multi-AP transmission, which may indicate a trigger frame transmitted from an AP.

[0111]

[0142] In the case of multi-AP MU-MIMO, the multi-AP trigger frame may include a list of all STAs to which it is transmitting (see, for example, FIGS. 15 and 16).

[0112]

[0143] As shown in FIG. 12, after receiving the multi-AP trigger frame, the STA can transmit a reverse trigger frame 1220 to multiple APs. In the reverse trigger frame 1220, the STA can indicate the complete or partial information of the repetition carried by the trigger frame 1210 transmitted by AP1. This field can be used, for example, when AP1 and AP2 have difficulty in communicating directly with each other. This information can be provided expediently, or one of the APs can instruct the other AP. Alternatively, one of the APs can expediently instruct the other AP as needed. In the reverse trigger frame 1220, the STA can additionally or instead indicate synchronization-related information, such as power control information. In such some power information, the STA can indicate the transmission power of the reverse trigger frame 1220 and / or the expected received signal strength indicator (RSSI) for the multi-AP data transmission. The AP can use these two fields to determine its own transmission power. It should be noted that if the power between AP1 and AP2 is unbalanced, the STA may request to turn off the transmission from one of the STAs to result in a single AP transmission. In the reverse trigger frame 1220, the STA may additionally or alternatively indicate synchronization related information such as time and / or frequency correction information, where the STA may request one or more of the APs to perform time and / or frequency corrections on the trigger frame. It should be noted that the reverse trigger frame scheme can be extended to multi-AP MU-MIMO, with each STA in the MU-MIMO set transmitting an independent trigger either sequentially (e.g., see FIG. 14) or simultaneously (e.g., see FIG. 13).

[0113]

[0144] As shown in Figure 12, the STA may receive data transmissions (i.e., Data 1 and Data 2) from AP1 and AP2. Depending on the packet ID in the trigger frame 1210, the STA may or may not combine the transmissions. The STA may transmit an acknowledgment frame to the AP.

[0114]

[0145] In the example of Figure 12, AP1 and AP2 can negotiate to transmit simultaneously to the STA. In some implementations, AP1 can be considered as the primary AP and AP2 can be considered as the secondary AP in the negotiation. In some implementations, AP1 and AP2 can perform multi-AP joint transmission sounding in advance to obtain the necessary channel state information.

[0115]

[0146] FIG. 13 illustrates an example of a channel access scheme that may facilitate multiple APs transmitting simultaneously to STAs, where the STAs transmit independent trigger frames simultaneously, e.g., using UL OFDMA and / or UL MU-MIMO.

[0116]

[0147] As shown in Figure 13, AP1 transmits a trigger frame 1310 to both STA1 and STA2. Then, STA1 transmits a reverse trigger frame 1320 to both AP1 and AP2. STA2 transmits a reverse trigger frame 1330 to both AP1 and AP2. Both the reverse trigger frame 1320 and the reverse trigger frame 1330 are transmitted simultaneously. Then, after receiving data from AP1 and AP2, STA1 can transmit an ACK 1340 to both AP1 and AP2, and STA2 can transmit an ACK 1350 to both AP1 and AP2.

[0117]

[0148] FIG. 14 illustrates an example of a channel access scheme that may facilitate multiple APs transmitting simultaneously to STAs, where the STAs transmit independent trigger frames sequentially, e.g., using UL OFDMA and / or UL MU-MIMO.

[0118]

[0149] As shown in Fig. 14, AP1 transmits a trigger frame 1410 to both STA1 and STA2. Then, STA1 transmits a reverse trigger frame 1420 to both AP1 and AP2. STA2 transmits a reverse trigger frame 1430 to both AP1 and AP2. Both the reverse trigger frame 1420 and the reverse trigger frame 1430 are transmitted sequentially. Then, after receiving data from AP1 and AP2, STA1 can transmit an ACK 1440 to both AP1 and AP2, and STA2 can transmit an ACK 1450 to both AP1 and AP2.

[0119]

[0150] The method for multi-AP communication according to the present application is described below with reference to Figures 15 to 18. The method for multi-AP communication according to the present application may be performed by a WTRU.

[0120]

[0151] FIG 15 illustrates an exemplary multi-AP communication procedure according to an embodiment of the present application. FIG 16 illustrates an exemplary multi-AP MU-MIMO communication procedure according to an embodiment of the present application. FIG 17 illustrates an exemplary multi-AP MU-MIMO communication procedure according to another embodiment of the present application. FIG 18 illustrates a flow chart showing a method 1800 of multi-AP communication according to an embodiment of the present application.

[0121]

[0152] The method of multi-AP communication according to the embodiment of the present application can be applied to multi-AP communication between multiple APs and one STA. In other words, the method can be applied to a scenario in which multiple APs are deployed. Therefore, the device for multi-AP communication (e.g., WTRU) according to the embodiment of the present application can also be applied to a scenario in which multiple APs are deployed to transmit data between an AP and a STA.

[0122]

[0153] The method for multi-AP communication according to the embodiment of the present application can also be applied to a scenario involving multiple APs and multiple STAs. In other words, the method can be applied to a scenario in which multiple APs and multiple STAs are deployed. Therefore, the device for multi-AP communication (e.g., WTRU) according to the embodiment of the present application can also be applied to a scenario in which multiple APs and multiple STAs are deployed to transmit data between the APs and the STAs.

[0123]

[0154] The following embodiments will first describe a scenario in which multiple APs and one STA are deployed with reference to Figures 15 and 18, and then describe a scenario in which both multiple APs and multiple STAs are deployed with reference to Figures 16 and 17.

[0124]

[0155] The method 1800 according to an embodiment of the present application is described in detail below with reference to Figures 15 and 18. The method 1800 is a method of multi-AP communication that can be applied in WLAN. It will be understood that the method 1800 can also be applied to other wireless transmission fields, such as WIFI and VPMN. The above technical fields of application of the method 1800 are described only as examples and are not intended to be exclusive or limiting to the present application.

[0125]

[0156] The method 1800 includes, in step 1801, receiving a first trigger frame from a first AP of the plurality of APs, the first trigger frame including first information, in 1802, receiving a second trigger frame from a second AP of the plurality of APs at a predetermined time period after receiving the first trigger frame, the second trigger frame also including the first information of the first trigger frame, in 1803, generating a synchronization frame based on the first trigger frame and the second trigger frame, the synchronization frame including the synchronization information, in 1804, transmitting the synchronization frame to at least the first AP and the second AP, and in 1805, receiving a data transmission from each of the first AP and the second AP based on the synchronization information. The above process will be described in detail with respect to the following embodiments.

[0126]

[0157] The following description will explain the process in 1801 in more detail. The method 1800 can be applied to a scenario where two APs are deployed, for example AP1 and AP2 (shown in FIG. 15). Therefore, the device for multi-AP transmission according to the embodiment of the present application can also be applied to a two AP scenario, such as the scenario in FIG.

[0127]

[0158] In a scenario involving two APs, one may be a master AP or primary AP, and the other may be a slave AP or secondary AP. As shown in FIG. 15, AP1 and AP2 may negotiate and decide that AP1 is the master AP and AP2 is the slave AP. AP1 and AP2 may perform multi-AP joint transmission sounding in advance to obtain any necessary channel state information. For the sake of clarity and limited description of this application, unless otherwise specified, the terms "AP1", "master AP" and "primary AP" are used interchangeably in this application, and the terms "AP2", "slave AP" and "secondary AP" are used interchangeably.

[0128]

[0159] In the example shown in FIG. 15, only two APs are shown, but this is only for illustrative purposes and is not intended to be exclusive or a limitation on the embodiments of the present application. For example, the method 1800 can also be applied to a scenario having three APs, namely a first AP, a second AP, and a third AP. Therefore, the device for multi-AP communication (e.g., WTRU) according to the embodiments of the present application can also be applied to the above three AP scenario.

[0129]

[0160] The number of APs in the embodiment of the present application may be 4 or more. The embodiment of the present application does not specifically limit the number of APs. It will be understood that the number of APs may vary based on many variables, such as the demand for subsequent data transmission between APs and STAs, the wireless transmission technology used, and the number of STAs.

[0130]

[0161] As shown in FIG. 15, in one embodiment, AP1 may acquire the channel and transmit a first trigger frame 1510 (ie, a multi-AP trigger frame) to the STAs.

[0131]

[0162] The first trigger frame 1510 transmitted by AP1 can be used to trigger transmissions from other APs and / or STAs. Figure 15 illustrates an embodiment of multi-AP downlink transmissions (i.e., data 1 and data 2) from AP1 and AP2 to the STA. Thus, in a multi-AP downlink transmission scenario, the first trigger frame 1510 can be used to configure a data transmission (i.e., data 1) from AP1 to the STA. Furthermore, the first trigger frame 1510 can also be used to configure a data transmission (i.e., data 2) from AP2 to the STA. To synchronize both data transmissions, the first trigger frame 1510 can be used to trigger a second trigger frame (e.g., second trigger frame 1520) transmitted by AP2 and a synchronization frame (e.g., synchronization frame 1530) transmitted by the STA.

[0132]

[0163] It should be noted that, as shown in Figures 19 and 20, the trigger frame transmitted by AP1 can also be used to configure uplink transmission. For example, in the embodiment shown in Figure 19, the trigger frame 1910 can be used to trigger a reverse trigger frame (e.g., reverse trigger frame 1920) transmitted by the STA. In the embodiment shown in Figure 20, the trigger frame 2010 can be used to trigger a second trigger frame (e.g., short trigger frame 2020) transmitted by AP2 and a reverse trigger frame (e.g., reverse trigger frame 1920) transmitted by the STA. The embodiments shown in Figures 19 and 20 will be described in detail later.

[0133]

[0164] The first trigger frame 1510 may also be used to indicate to the STA how many spatial streams and what modulation and coding scheme (MCS) to use when transmitting on a specified RU. Because the first trigger frame 1510 is transmitted by the master AP (i.e., AP1), the term "first trigger frame" may also be referred to as "master trigger frame" unless otherwise specified.

[0134]

[0165] The first trigger frame 1510 may include one or any combination of the following information as its first information: RU allocation information, STA-specific information, and common information, etc. It will be understood that the above information carried by the first trigger frame 1510 may be configured in different fields. For example, the RU allocation information may be configured in a RU allocation information field, the STA-specific information may be configured in one or more STA information fields, and the common information may be configured in a common information field. When some specific information carried by the first trigger frame 1510 is described in the following description, it means the information configured in a specific field.

[0135]

[0166] The STA-specific information may include the role of the STA or the ID of the STA. The ID of the STA may indicate whether the STA is a transmitter (e.g., AP1 shown in FIG. 15) or a receiver (e.g., STA shown in FIG. 15). Generally speaking, it will be understood that the WTRU (e.g., STA shown in FIG. 15) and the AP (e.g., AP1 shown in FIG. 15) may be referred to as STAs. For example, in a WLAN scenario, the router (e.g., AP) may be referred to as a station, and the laptop (e.g., STA) may also be referred to as a station. The ID of the STA in this application may indicate whether the station is an AP STA (e.g., AP1 shown in FIG. 15) or a non-AP STA (e.g., STA shown in FIG. 15).

[0136]

[0167] The ID of the STA may be an AID, a compressed AID, a BSSID, a compressed BSSID, a BSS color, or an enhanced BSS color, and so on.

[0137]

[0168] If the STA's ID indicates a transmitting side (e.g., AP1), the first trigger frame 1510 may further include one or any combination of the following fields: a packet ID field, a resource allocation field, a spatial stream allocation field, and an MCS related information field.

[0138]

[0169] The packet ID field may be used to indicate the packet being transmitted to the STA. In some implementations, the packet ID field may be a transmit side / AP specific field. The STA may detect multiple packet IDs carried by the packet ID field corresponding to multiple APs and determine whether a single packet is transmitted from multiple APs or multiple packets are transmitted from multiple APs. In some embodiments, the STA may combine transmissions from multiple APs to decode a single packet.

[0139]

[0170] The resource allocation field may be used to indicate resources allocated to AP1 for transmitting the multi-AP packet. In an OFDMA transmission scenario, resources may be allocated in resource units (RUs).

[0140]

[0171] The spatial stream assignment field may be used to indicate the starting spatial stream index and the number of spatial streams to be used on the transmitting side (i.e., AP1).

[0141]

[0172] The MCS related information field may include information to indicate the MCS, the coding scheme, and whether DCM modulation is used, etc.

[0142]

[0173] The common information may include a type field. The type field may indicate DL multi-AP transmission. The type field may also indicate a trigger frame transmitted from an AP. In the case of multi-AP MU-MIMO communication, the multi-AP trigger frame may include a list of all STAs to which it is to transmit (see, for example, FIG. 16 and FIG. 17).

[0143]

[0174] The first trigger frame 1510 may further include at least one of the following information as its first information: transmission power information, transmission start time information, transmission frequency information, etc. Therefore, those information may also be configured in different fields for the first trigger frame to carry.

[0144]

[0175] For example, the first trigger frame 1510 may include an output field to indicate a transmission output of the next data transmission from AP1 to the STA. The first trigger frame 1510 may also include a time field to indicate a start time of the next data transmission from AP1 to the STA. The first trigger frame may also include a frequency field to indicate a transmission frequency of the next data transmission from AP1 to the STA.

[0145]

[0176] In another example, the first trigger frame 1510 may further include transmission start time information for transmitting the synchronization frame 1530 from the STA. In other words, the first trigger frame 1510 may indicate a start time for transmitting the synchronization frame 1530 shown in FIG. 15 from the STA. The start time information may also be configured in a specific field of the first trigger frame to be carried by the first trigger frame.

[0146]

[0177] Although the above description illustrates some exemplary embodiments of the first information in the first trigger frame 1510, these embodiments are not intended to be exclusive or a limitation on the first information. The first information described in this application may include any combination of the above exemplary information or any other information available to obtain the technical solution of this application.

[0147]

[0178] Furthermore, the first information of the first trigger frame is a relative term compared to the terms "second information of the first trigger frame" and "third information of the first trigger frame". In this application, the use of these terms does not mean that the first information, the second information and the third information are completely different information. In some embodiments, they may share the same information among each other. Their relationship will be described in detail below.

[0148]

[0179] The information carried by the first trigger frame may be used to synchronize data transmission between multiple APs (e.g., AP1 and AP2 shown in FIG. 15) and a STA. It will be understood that the term "synchronization" in this application means synchronizing one or more parameters of the next data transmission, such as synchronization of transmission power, synchronization of transmission start time, and synchronization of transmission frequency. In other words, the parameters synchronized for the next data transmission may include transmission power, transmission start time, and transmission frequency.

[0149]

[0180] For example, the transmission power information carried by the first trigger frame may be used to pre-correct the transmission power from multiple APs to STAs so that a signal (e.g., data transmission) from the AP may arrive at the STA with a similar reception power. The transmission start time information carried by the first trigger frame may be used to pre-correct the transmission start time from multiple APs to STAs so that a signal from the AP may arrive at the STA with a similar reception time. The transmission frequency information carried by the first trigger frame may be used to pre-correct the transmission frequency from multiple APs to STAs so that a signal from the AP may arrive at the STA with a similar reception frequency.

[0150]

[0181] It will be understood that the above three parameters for multi-AP transmission are shown by way of example only and are not intended to be exclusive or a limitation to the present application. For example, the first trigger frame 1510 may be used to synchronize any combination of those three parameters for the next data transmission.

[0151]

[0182] It will be understood that the synchronization described herein may not be obtained by the first trigger frame 1510 alone. Although the first trigger frame 1510 is the main part of the synchronization, the method 1800 and the device (e.g., WTRU) according to the present application still require the second trigger frame 1520 and the synchronization frame 1530 (described below) to obtain synchronization. For example, as shown in FIG. 15, after receiving the first trigger frame 1510, the STA can transmit the synchronization frame 1530 to multiple APs, which may carry synchronization information required to synchronize the next data transmission from each of the multiple APs. The following description describes the second trigger frame 1520 and the synchronization frame 1530 in more detail.

[0152]

[0183] In one embodiment, the first trigger frame 1510 may also be transmitted to other APs, such as AP2 shown in FIG. 15, i.e., the first trigger frame 1510 from AP1 can be overheard by all STAs shown in FIG. 15 other than AP1. Thus, the first trigger frame 1510 may be used to configure one or more parameters of the next data transmission from AP2 to the STA (i.e., data2 shown in FIG. 15). Since both the next data transmissions from AP1 and AP2, respectively, may be configured by the first trigger frame 1510, the next data transmissions from both AP1 and AP2 may be appropriately synchronized. The following description will explain how the first trigger frame 1510 is used to configure the next data transmission from AP2 for the process in 1802.

[0153]

[0184] In an embodiment with more than two APs, AP1 can send a first trigger frame to all other APs, and all subsequent data transmissions from those APs can be synchronized accordingly based on similar principles as shown above.

[0154]

[0185] To receive the first trigger frame from AP1, the STA may be configured to include a receiver, which may be a USB receiver, a wireless LAN receiver, or any other type of receiver that may be used to receive signals transmitted in the WLAN scenarios shown in Figs.

[0155]

[0186] For the sake of clarity and limited description of the embodiments of the present application, unless otherwise specified, the next data transmission from AP1 to the STA can be referred to as the first data transmission, and the next data transmission from AP2 to the STA can be referred to as the second data transmission. As shown in Figures 15 to 17, the first data transmission can be referred to as Data 1, and the second data transmission can be referred to as Data 2.

[0156]

[0187] The following description will explain the process in 1802 in more detail. As described above, AP1 can also send the first trigger frame 1510 to AP2. After receiving the first trigger frame 1510, AP2 can generate the second trigger frame 1520 and transmit it to the STA. Because it may take some time to transmit the first trigger frame 1510 from AP1 to AP2, and it may also take some time for AP2 to generate the second trigger frame 1520, there may be a period between transmitting the first trigger frame 1510 and transmitting the second trigger frame 1520 (i.e., SIFS shown in FIG. 15). Therefore, on the STA side, there may be a period SIFS between receiving the first trigger frame 1510 and receiving the second trigger frame 1520. That is, the STA can receive the first trigger frame 1510 first, and receive the second trigger frame 1520 after the period SIFS.

[0157]

[0188] As shown in Fig. 15, three blocks representing a first trigger frame 1510, a second trigger frame 1520, and a synchronization frame 1530, respectively, are located on three different horizontal lines, each representing AP1, AP2, and one of the STAs, respectively. Although these blocks are located at different locations in the vertical direction, it will be understood that these blocks are illustrated in this manner only to indicate the source of each frame, and their projection in the horizontal direction may represent the time of reception of each frame at the STA side.

[0158]

[0189] The period may be predetermined by some existing parameters. For example, the period may be predetermined based on the distance between AP1 and AP2 and the length of time for AP2 to generate the second trigger frame. In other words, as long as the distance between AP1 and AP2 is already known and the length of time for AP2 to generate the second trigger frame is already known, the period can be known.

[0159]

[0190] In an embodiment, when AP1 and AP2 are constructed, the distance between them is fixed and therefore known. Furthermore, the hardware that constitutes the APs can also be fixed after their construction. Thus, the length of time to generate the second trigger frame can also be known. Thus, the period can be predetermined after the construction of the APs.

[0160]

[0191] The period SIFS may be predetermined by AP1 and / or AP2. For example, the period may be predetermined by AP1. In that case, the first trigger frame 1510 may further include a period field for carrying period information. The period information may indicate when AP2 should send the second trigger frame 1520 after receiving the first trigger frame 1510. Then, after AP2 receives the first trigger frame 1510, AP2 generates and sends the second trigger frame 1520 based on the period information. In that case, it will be understood that the period SIFS indicated by the period information should be longer than the sum of the length of time for transmitting the first trigger frame 1510 from AP1 to AP2 and the length of time for AP2 to generate the second trigger frame 1520.

[0161]

[0192] In one embodiment, the period (i.e., SIFS as shown in FIG. 15) may be predetermined by any interframe interval time, such as short IFS (SIFS), point coordination function (PCF) IFS (PIFS), distributed coordination function (DCF) IFS (DIFS), etc.

[0162]

[0193] The second trigger frame may include the above first information of the first trigger frame 1510.

[0163]

[0194] The first information of the first trigger frame 1510 may be information that can be shared with the second trigger frame 1520. For example, the first information of the first trigger frame is the above common information indicating DL multi-AP transmission. Therefore, AP2 can directly duplicate that information in the second trigger frame 1520.

[0164]

[0195] In one embodiment, the first information of the first trigger frame 1510 may be transmission power information for the next data transmission from AP1 to the STA. AP2 determines that the transmission power indicated by the transmission power information is within its transmission power limit. Therefore, AP2 can directly write the transmission power information into the second trigger frame 1520.

[0165]

[0196] It will be understood that the above-described embodiments of the second trigger frame 1520 are merely examples and are not intended to be exhaustive or limiting to the present application.

[0166]

[0197] In an embodiment, the second trigger frame 1520 can be generated to be in any one of the following formats: in format (1), the second trigger frame 1520 is the same as the first trigger frame 1510, i.e., the second trigger frame 1520 includes all of the information of the first trigger frame 1510; in format (2), the second trigger frame 1520 is a subset of the first trigger frame 1510, i.e., the second trigger frame 1520 includes only a portion of the information of the first trigger frame 1510 (e.g., the first information described above for the first trigger frame 1510); and in format (3), the second trigger frame 1520 includes both a portion of the information of the first trigger frame 1510 (e.g., the first information described above for the first trigger frame 1510) and configuration information for the next data transmission from AP2 (i.e., data 2).

[0167]

[0198] In one embodiment, the configuration information in the second trigger frame 1520 may be different from the second information of the first trigger frame 1510. For example, the first trigger frame 1510 may instruct AP2 to use a specific channel (e.g., channel 2) for the next data transmission (i.e., data 2) to the STA. That is, the second information of the first trigger frame 1510 may be the information of channel 2 used by AP2 for the second data transmission. However, AP2 may find that channel 2 is unavailable for its transmission. In that case, AP2 may transmit the second trigger frame 1520 with the configuration information to both AP1 and the STA to indicate that channel 2 is unavailable. In that case, the configuration information (i.e., the unavailable channel 2) is different from the second information of the first trigger frame 1510 (i.e., the selection of channel 2).

[0168]

[0199] In the above example, AP2 knows that it cannot use channel 2 for data transmission, but can use another channel (e.g., channel 3). AP2 can transmit a second trigger frame with configuration information to both AP1 and the STA to indicate that channel 2 is unavailable and that AP2 will use channel 3 for the next data transmission from AP2 to the STA. In that case, the configuration information (i.e., the unavailability of channel 2 and the selection of channel 3) is different from the second information (i.e., the selection of channel 2) of the first trigger frame 1510. In other words, the configuration information can overwrite the second information of the first trigger frame 1510.

[0169]

[0200] For example, the first trigger frame 1510 may instruct AP2 to use a particular transmission power for the next data transmission (i.e., data 2) to the STA. That is, the second information of the first trigger frame 1510 may be information of the transmission power (e.g., transmission power 2) used by AP2 for the second data transmission. However, AP2 may know that the transmission power 2 exceeds the power limit of AP2. In that case, AP2 may transmit the second trigger frame with configuration information to both AP1 and the STA to indicate that the transmission power 2 is unavailable and that AP2 will use its desired transmission power (e.g., transmission power 3) for the second data transmission. In that case, the configuration information (i.e., the transmission power 2 is unavailable and the selection of the transmission power 3) is different from the second information of the first trigger frame 1510 (i.e., transmission power 2). In other words, the configuration information may overwrite the second information of the first trigger frame 1510.

[0170]

[0201] It will be understood that the above channels and transmission powers are listed by way of example only and are not intended to be exhaustive or a limitation on the configuration information in the second trigger frame 1520. The configuration information may include other information as may be necessary to configure the second data transmission.

[0171]

[0202] In one embodiment, the configuration information in the second trigger frame 1520 may be additional information not included in the first trigger frame 1510.

[0172]

[0203] For example, the first trigger frame 1510 may include transmission power information and transmission start time information, but not transmission frequency information. That is, the second information of the first trigger frame 1510 may be the transmission power information and transmission start time information used by AP2 for the second data transmission. Then, AP2 may send the second trigger frame 1520 with configuration information to both AP1 and the STA to indicate the desired transmission frequency of AP2 for the second data transmission. In that case, the configuration information (i.e., the desired transmission frequency of AP2) is additional information that is not included in the first trigger frame. In the above example, the STA may send a synchronization frame 1530 (further described below) with the desired transmission frequency of AP2 to both AP1 and AP2, so that the AP can perform data transmission by using the desired transmission frequency. Thus, synchronization of the transmission frequency can be obtained. The synchronization process is further described below with respect to the synchronization frame 1530 from the STA.

[0173]

[0204] It will be understood that the above transmission frequencies are listed merely as examples for the configuration information and are not intended to be exclusive or a limitation on the configuration information in the second trigger frame 1520. The configuration information may include other information not included in the first trigger frame 1510, as may be necessary to synchronize subsequent data transmissions.

[0174]

[0205] In an embodiment, the second trigger frame 1520 may be an NDP frame that may carry the identification information of AP2. The NDP frame may indicate that AP2 is ready for the next multi-AP transmission. The second trigger frame 1520 may also include a start time field that indicates a transmission start time for transmitting the synchronization frame 1530.

[0175]

[0206] As explained above, both the WTRU and the AP can be referred to as an STA. Thus, in an embodiment with more than two APs, the second trigger frame 1520 may also be transmitted to all other APs, i.e., the second trigger frame 1520 from AP2 can be overheard by all STAs other than AP2, including both AP STAs and non-AP STAs. In an embodiment with multiple AP STAs and multiple non-AP STAs as shown in FIG. 16, the second trigger frame may also be transmitted to all STAs.

[0176]

[0207] In one embodiment, multiple APs can transmit trigger frames sequentially, and the transmission order of the trigger frames can be negotiated among the multiple APs using management / control frames. For example, assume that the management / control frames indicate that AP1 can transmit a trigger frame (e.g., the first trigger frame 1510) first, and AP2 can transmit a trigger frame (e.g., the second trigger frame 1520) second.

[0177]

[0208] In one embodiment, the transmission order of the trigger frame may be predetermined by a certain rule. For example, AP1, the primary AP, may transmit the trigger frame first. The rest of the multiple APs may transmit in ascending / descending order based on the BSSID or MAC address of the AP. It may be understood that all APs in the group may know the BSSID or MAC address of the member APs.

[0178]

[0209] The following description will explain the process in 1803 in more detail. After receiving both the first trigger frame 1510 and the second trigger frame 1520, the STA shown in FIG. 15 can generate a synchronization frame 1530 based on the first trigger frame and the second trigger frame. The synchronization frame 1530 includes synchronization information for configuring data transmission from each of AP1 and AP2 to the STA.

[0179]

[0210] Similar to the first trigger frame 1510, the synchronization frame 1530 may include one or any combination of the following information: RU allocation information, STA-specific information, and common information, etc. The above information carried by the synchronization frame 1530 may be configured in different fields.

[0180]

[0211] The synchronization frame 1530 may further include transmission power information, transmission start time information, transmission frequency information, etc., and therefore, these information may also be configured in different fields for the synchronization frame 1530 to carry. The above information may be called synchronization information, and may be used to configure the next data transmission from each of AP1 and AP2 to the STA.

[0181]

[0212] It will be understood that the above information contained within the synchronization frame 1530 is provided by way of example only and is not intended to be exhaustive or a limitation on the information that may be contained within the synchronization frame 1530.

[0182]

[0213] To generate the synchronization frame 1530, a device (e.g., a WTRU) according to the present application includes a processor. As shown in FIG. 15, the processor is configured to generate the synchronization frame 1530 based on a first trigger frame and a second trigger frame received from AP1 and AP2, respectively.

[0183]

[0214] In an embodiment, the synchronization frame 1530 can share the same format as the first trigger frame 1510. In other words, the synchronization frame 1530 can be generated to be in any one of the following formats: in format (1), the synchronization frame 1530 is the same as the first trigger frame 1510, i.e., the synchronization frame 1530 includes all of the information of the first trigger frame 1510, in format (2), the synchronization frame 1530 is a subset of the first trigger frame 1510, i.e., the synchronization frame 1530 includes only a portion of the information of the first trigger frame 1510, and in format (3), the synchronization frame 1530 includes both a portion of the information of the first trigger frame and the acknowledgement information.

[0184]

[0215] In the forms (1) and (2), the synchronization frame 1530 may include the complete or partial information carried by the first trigger frame 1510 transmitted by AP1. This complete or partial information may be useful. For example, when AP1 and AP2 may have difficulty in communicating directly with each other, the STA may transmit the information originating from AP1 to AP2 to synchronize data transmission.

[0185]

[0216] In format (3), the confirmation information can be used to confirm information carried by the first trigger frame 1510 and / or the second trigger frame 1520. The confirmation information can also be used to confirm any configuration modifications by AP2. The confirmed configuration can be based on the first trigger frame 1510 or the second trigger frame 1520, or a combination of the first trigger frame 1510 and the second trigger frame 1520.

[0186]

[0217] For example, if the first trigger frame 1510 indicates that the transmission output of the first data transmission is output 1, and the second trigger frame 1520 indicates that the transmission output of the second data transmission is also output 1, the confirmation information can be used to confirm to both AP1 and AP2 that they can use output 1 for their next data transmission. On the other hand, if the first trigger frame 1510 includes an information group including spatial stream allocation and MCS related information, the information group can be called the third information of the first trigger frame 1510 and can be included in the synchronization frame 1530.

[0187]

[0218] In an embodiment, the synchronization frame 1530 can share the same format as that of the second trigger frame 1520. In other words, the synchronization frame 1530 can be generated to be in any one of the following formats: in format (1), the synchronization frame 1530 is the same as the second trigger frame 1520, i.e., the synchronization frame 1530 includes all of the information of the second trigger frame 1520; in format (2), the synchronization frame 1530 is a subset of the second trigger frame 1520, i.e., the synchronization frame 1530 includes only a portion of the information of the second trigger frame 1520; and in format (3), the synchronization frame 1530 includes both a portion of the information of the second trigger frame 1520 and confirmation information corresponding to the above configuration information in the second trigger frame 1520.

[0188]

[0219] In the forms (1) and (2), the synchronization frame 1530 may include the complete or partial information carried by the second trigger frame 1520 transmitted by AP2. This complete or partial information may be useful. For example, when AP1 and AP2 may have difficulty in communicating directly with each other, the STA may transmit the information originating from AP2 to AP1 to synchronize data transmission.

[0189]

[0220] In format (3), the confirmation information may be used to confirm any configuration modifications by AP2. The confirmed configuration may be based on the first trigger frame 1510 or the second trigger frame 1520, or a combination of the first trigger frame 1510 and the second trigger frame 1520.

[0190]

[0221] As shown in Figure 15, the synchronization information can be used to synchronize one or more parameters of a first data transmission from AP1 with one or more parameters of a second data transmission from AP2. In one embodiment, the synchronization information includes transmission power information, transmission start time information and transmission frequency information.

[0191]

[0222] For example, the synchronization information may include transmission frequency information. In that case, a first trigger frame 1510 received from AP1 may indicate that the transmission frequency of the first data transmission may be frequency 1, and a second trigger frame 1520 received from AP2 may indicate that the transmission frequency of the second data transmission may be frequency 2. The STA may then generate a synchronization frame 1530 with the specific transmission frequency information to indicate the desired transmission frequency for both of the next data transmissions. AP1 and AP2 may perform the next data transmission based on the desired transmission frequency.

[0192]

[0223] In an embodiment where there are more than two APs and one STA, a synchronization frame from the STA may be configured to synchronize a parameter (or parameters) of the next data transmission from each of the multiple APs.

[0193]

[0224] It should be understood that according to an embodiment of the present application, the synchronization process of the next data transmission from multiple APs may not be completed by the synchronization frame 1530 alone, and requires frame interaction between the STA and the AP. Based on the above description, the synchronization process can be realized by the first trigger frame 1510, the second trigger frame 1520 and the synchronization trigger frame 1530.

[0194]

[0225] At 1804, the STA may transmit a sync frame 1530 to both AP1 and AP2. In an embodiment with more than two APs and one STA, at 1804, the STA may transmit a sync frame 1530 to at least AP1 and AP2. However, the embodiment shown in FIG. 15 is not intended to be exclusive or a limitation to the principles of the present application. For example, the STA may select that only AP1 or only AP2 may transmit data to the STA. AP downselection may depend on information carried in trigger frames transmitted from AP1 and AP2 or STA measurements based on transmissions from AP1 and AP2. For example, if the received SNR (i.e., signal-to-noise ratio) or RSSI from an AP is below a predefined / predetermined threshold, the STA may exclude that AP from multi-AP transmission.

[0195]

[0226] Based on the synchronization frame from the STA, AP1 can perform a first data transmission to the STA, and AP2 can perform a second data transmission to the STA. That is, in 1805, the STA can receive data transmissions from AP1 and AP2 based on the synchronization information. It should be noted that the first data transmission and the second data transmission from AP1 and AP2 can be simultaneous using the same frequency resource (e.g., multi-AP MU-MIMO or multi-AP nulling or cooperative SU / MU or cooperative nulling / beamforming) or using different frequency resources (e.g., multi-AP OFDMA, cooperative OFDMA transmission).

[0196]

[0227] In one embodiment, after receiving the first data transmission and the second data transmission, the STA may transmit an ACK / NACK report (ie, ACK 1540 shown in FIG. 15) to AP1 and AP2, respectively.

[0197]

[0228] It should be noted that the multi-AP transmission method of the present application can be extended to multi-AP MU-MIMO, with each STA in a MU-MIMO set transmitting an independent trigger either sequentially (e.g., as shown in FIG. 16) or simultaneously (e.g., as shown in FIG. 17).

[0198]

[0229] FIG. 16 illustrates an exemplary multi-AP MU-MIMO communication procedure according to an embodiment of the present application.

[0199]

[0230] As shown in FIG. 16, STA1 may receive a first trigger frame 1610 from AP1 and a second trigger frame 1620 from AP2. Then, STA1 may generate a synchronization frame 1630 based on the first trigger frame 1610 and the second trigger frame 1620, and transmit the synchronization frame 1630 to both AP1 and AP2. STA2 may receive the first trigger frame 1610 from AP1 and may receive the second trigger frame 1620 from AP2. Then, STA2 may generate a synchronization frame 1640 based on the first trigger frame 1610 and the second trigger frame 1620, and transmit the synchronization frame 1640 to both AP1 and AP2.

[0200]

[0231] As shown in Fig. 16, STA1 may first transmit a synchronization frame 1630, and then STA2 may transmit a synchronization frame 1640. The first trigger frame 1610 is similar to or the same as the first trigger frame 1510 shown in Fig. 15. The second trigger frame 1620 is similar to or the same as the second trigger frame 1520 shown in Fig. 15. The synchronization frames 1630 and 1640 are similar to or the same as the synchronization frame 1530 shown in Fig. 15.

[0201]

[0232] As shown in Fig. 16, after AP1 and AP2 receive SYNC frame 1630 and SYNC frame 1640, AP1 and AP2 can transmit data (i.e., data 1 and data 2 shown in Fig. 16) to STA1 and STA2, respectively. Then, STA1 can transmit ACK 1650 to AP1 and AP2, respectively. STA2 can transmit ACK 1660 to AP1 and AP2, respectively.

[0202]

[0233] FIG. 17 illustrates an exemplary multi-AP MU-MIMO communication procedure according to another embodiment of the present application.

[0203]

[0234] As shown in FIG. 17, STA1 can receive a first trigger frame 1710 from AP1 and can receive a second trigger frame 1720 from AP2. Then, STA1 can generate a synchronization frame 1730 based on the first trigger frame 1710 and the second trigger frame 1720, and transmit the synchronization frame 1730 to both AP1 and AP2. STA2 can receive the first trigger frame 1710 from AP1 and can receive the second trigger frame 1720 from AP2. Then, STA2 can generate a synchronization frame 1740 based on the first trigger frame 1710 and the second trigger frame 1720, and transmit the synchronization frame 1740 to both AP1 and AP2.

[0204]

[0235] As shown in Fig. 17, STA1 and STA2 can transmit their own synchronization frames at the same time. The first trigger frame 1710 is similar to or the same as the first trigger frame 1510 shown in Fig. 15. The second trigger frame 1720 is similar to or the same as the second trigger frame 1520 shown in Fig. 15. The synchronization frames 1730 and 1740 are similar to or the same as the synchronization frame 1530 shown in Fig. 15.

[0205]

[0236] As shown in Fig. 17, after AP1 and AP2 receive SYNC frame 1730 and SYNC frame 1740, AP1 and AP2 can transmit data (i.e., data 1 and data 2 shown in Fig. 16) to STA1 and STA2, respectively. Then, STA1 can transmit ACK 1750 to AP1 and AP2, respectively. STA2 can transmit ACK 1760 to AP1 and AP2, respectively.

[0206]

[0237] It should be noted that the STA may receive data transmissions from AP1 and AP2. In an embodiment with more than two APs, the STA may select one AP or multiple APs to send a sync. Thus, only the APs receiving the sync may make the next data transmission. Depending on the packet ID in the multi-AP trigger frame, the STA may or may not combine transmissions. The STA may transmit an acknowledgment frame to the AP.

[0207]

[0238] The related STA procedure is shown in Figure 18, where the STA receives a master trigger. The master trigger identifies the parameters of the multi-AP transmission and the number of APs and the expected additional DL triggers. The STA receives trigger information for N-1 additional triggers. The STA estimates parameters for each AP, e.g., Rx power, timing offset and / or frequency offset. The STA selects parameters for the multi-AP transmission. The STA calculates parameters for the multi-AP transmission, e.g., Tx power, time and / or frequency offset corrections. The STA sends a reverse trigger to the AP with the proposed multi-AP transmission parameters. The STA receives the multi-AP transmission data. The STA sends an ACK to the AP.

[0208]

[0239] Some implementations provide channel access for uplink cooperative SU beamforming or UP dynamic point selection.

[0209]

[0240] FIG. 19 illustrates an example of a channel access scheme that allows multiple APs to receive from a STA simultaneously. As shown in FIG. 19, AP1 transmits a trigger frame 1910 to the STA. The trigger frame 1910 is similar or the same as the first trigger frame 1510 shown in FIG. 15. The STA then transmits a reverse trigger frame 1920 to both AP1 and AP2 based on the trigger frame 1910. The STA then transmits data 2 to both AP1 and AP2. After receiving data 2, AP1 can transmit an ACK 1930 to the STA, and AP2 can transmit an ACK 1940 to the STA. In this example, data can be addressed to both APs or to a specific AP (e.g., in case of dynamic point selection). The target AP can be addressed in the reverse trigger 1920. This example can address issues related to UL cooperative SU beamforming or joint precoding.

[0210]

[0241] In this example, a STA may transmit to multiple APs simultaneously in the UL. If the APs cannot hear from each other or from the primary AP, they may implement a channel access procedure to inform all desired APs that a multi-AP UL transmission can be expected.

[0211]

[0242] In this example, AP1 and AP2 can negotiate to receive from the STAs simultaneously. In some implementations, AP1 can be considered as the primary AP and AP2 can be considered as the secondary AP in the negotiation. In some implementations, AP1 and AP2 can do multi-AP joint transmission sounding in advance to obtain the necessary channel state information, or allow the STAs to do the sounding and obtain the channel between themselves and the APs. In this case, the STAs can send NDPA and NDP to the APs individually or jointly and obtain the UL channel from each AP, e.g., by polling each AP, or by the APs sending a UL trigger to send their channel information in a predetermined manner, e.g., in a DL multi-AP transmission.

[0212]

[0243] The channel access procedure for UL multi-AP transmission may be triggered by one or more of the APs. In some methods, AP1 and AP2 may not be able to hear from each other and negotiation may be via the STA. In some implementations, AP1 may acquire the channel and transmit a multi-AP trigger frame to trigger transmission from the STA. In the multi-AP trigger frame, AP1 may configure the next UL multi-AP transmission in the multi-AP trigger frame. In some implementations, AP1, the primary AP, may configure the transmission from AP2 to the STA. For example, the multi-AP trigger frame may indicate STA-specific information and / or common information. The STA-specific information (here STA indicates AP STA or non-AP STA) may indicate the role of the STA and / or the ID of the STA. The role of the STA may indicate whether the STA is a transmitting / AP or a receiving / STA. The ID of the STA may be an association identifier (AID), a compressed AID, a BSS identifier (BSSID, compressed BSSID), a BSS color or an enhanced BSS color, etc.

[0213]

[0244] If the STA role indicates a transmit / STA, the STA role may include a packet ID. The packet ID may indicate that the packet is transmitted from the STA. In some examples, this field may be an AP / transmit specific field. The STA may detect packet IDs corresponding to multiple APs and determine whether a single packet is transmitted from multiple APs or multiple packets are transmitted from multiple APs. In the first case, the STA may combine transmissions from multiple APs to decode a single packet.

[0214]

[0245] If the STA role indicates receiver / AP, the STA role may include resource allocation, spatial stream allocation, and / or MCS-related information. The resource allocation may indicate resources assigned to the STA for transmitting a multi-AP packet to the AP. In an OFDMA transmission scenario, resources may be assigned in resource units (RUs). The spatial stream allocation may indicate the starting spatial stream index and the number of spatial streams to be used for the receiver. The MCS-related information may include the MCS, coding scheme, whether DCM modulation is used, etc.

[0215]

[0246] The common information may include a type field, which may indicate a UL multi-AP transmission, which may indicate a trigger frame transmitted from an AP.

[0216]

[0247] After receiving the multi-AP trigger frame from AP1, the STA can transmit a reverse trigger frame to multiple APs. In the reverse trigger frame, the STA can indicate the repetitive complete or partial information carried by the multi-AP trigger frame transmitted by AP1. This field can be used, for example, when AP1 and AP2 have difficulty in communicating directly with each other. In such a case or when AP2 modifies something in its trigger frame, the reverse trigger frame can confirm the configuration to be used in the next multi-AP transmission. The confirmed configuration can be from AP1 or AP2 or a combination of AP1 and AP2.

[0217]

[0248] The STA may transmit data to AP1 and AP2. In some implementations, at the end of the transmission, the STA may concatenate another reverse trigger frame to trigger a simultaneous transmission of an acknowledgment from the AP. In the reverse trigger frame, the STA may include synchronization information such as power control information. The power control information may indicate the transmission power of the reverse trigger frame and / or the expected RSSI of the multi-AP data transmission. The AP may use those two fields to determine its own transmission power. The STA may request one or more of the APs to make time and / or frequency corrections to the trigger frame. The AP may transmit an acknowledgment frame to the STA.

[0218]

[0249] FIG. 20 shows an example of a channel access scheme that allows multiple APs to receive from a STA simultaneously. As shown in FIG. 20, AP1 transmits a trigger frame 2010 to the STA. The trigger frame 2010 is similar or the same as the first trigger frame 1510 shown in FIG. 15. Then, AP2 transmits a short trigger frame 2020 to the STA, which may include availability information. Then, the STA generates a reverse trigger frame 2030 based on the trigger frame 2010 and the short trigger frame 2020, and transmits the reverse trigger frame 2030 to both AP1 and AP2. Then, the STA transmits data 2060 based on the information in the reverse trigger frame 2030 to both AP1 and AP2. After receiving data 2, AP1 can transmit an ACK 2040 to the STA, and AP2 can transmit an ACK 2050 to the STA.

[0219]

[0250] The data 2060 can be addressed to both APs or to a specific AP (eg, in the case of dynamic point selection). The target AP can be addressed in the reverse trigger.

[0220]

[0251] In some examples, APs may be able to receive from each other. A channel access scheme may be used to exchange multi-AP UL transmission information while protecting the transmission from interference caused by others. Figure 20 shows another example of a channel access procedure that may allow a STA to transmit to multiple APs simultaneously in some implementations.

[0221]

[0252] In the example of FIG. 20, AP1 and AP2 may negotiate to receive from the STA simultaneously. In some implementations, AP1 may be considered as the primary AP and AP2 may be considered as the secondary AP in the negotiation. In some examples, AP1 and AP2 may perform multi-AP joint transmission sounding in advance to obtain the necessary channel state information. In some implementations, AP1 and AP2 may not be able to receive from each other and the negotiation may be via the STA.

[0222]

[0253] AP1 may transmit a multi-AP trigger frame to acquire the channel and trigger transmission from the STA. In the multi-AP trigger frame, AP1 may configure the next UL multi-AP transmission in the multi-AP trigger frame. In a manner, it may be possible for AP1, the primary AP, to configure the transmission from AP2 to the STA. For example, the multi-AP trigger frame may indicate STA-specific information and / or common information. The STA-specific information (here STA indicates AP STA or non-AP STA) may indicate the role of the STA and / or the ID of the STA. The role of the STA may indicate whether the STA is a transmitting / AP or a receiving / STA. The ID of the STA may be an association identifier (AID), compressed AID, BSS identifier (BSSID, compressed BSSID), BSS color or enhanced BSS color, MAC address, compressed MAC address, etc.

[0223]

[0254] If the STA role may indicate a transmit / STA, the STA role may include a packet ID. The packet ID may be used to indicate that the packet is transmitted from the STA. In some examples, this field may be an AP / transmit specific field. The STA may detect packet IDs corresponding to multiple APs and determine whether a single packet is transmitted from multiple APs or multiple packets are transmitted from multiple APs. In the first case, the STA may combine transmissions from multiple APs to decode a single packet.

[0224]

[0255] If the STA role indicates receiver / AP, the STA role may include resource allocation, spatial stream allocation, and / or MCS-related information. The resource allocation may indicate resources assigned to the STA for transmitting a multi-AP packet to the AP. In an OFDMA transmission scenario, resources may be assigned in resource units (RUs). The spatial stream allocation may indicate the starting spatial stream index and the number of spatial streams to be used for the receiver. The MCS-related information may include the MCS, coding scheme, whether DCM modulation is used, etc.

[0225]

[0256] The common information may include a type field. The type may indicate a UL multi-AP transmission. The type may indicate a trigger frame transmitted from an AP. The common information may include time and / or frequency correction information, such as a STA may request one or more of the APs to perform time and / or frequency corrections on the trigger frame.

[0226]

[0257] After receiving the multi-AP trigger frame, AP2 can transmit a multi-AP trigger frame that may be the same as that transmitted by AP1. Alternatively, AP2 can transmit a short multi-AP trigger frame that may carry a subset of the information transmitted by AP1. In some implementations, the short multi-AP trigger frame may be an NDP frame that may carry the identification information of AP2. The transmission from AP2 may indicate that AP2 is ready for the next multi-AP transmission. In some implementations, the multi-AP trigger frame or the short multi-AP trigger frame may overwrite some of the information transmitted by AP1. For example, AP2 may be specified to use channel 2 to receive from STAs, but channel 2 may be unavailable to AP2, and AP2 may indicate a list of unavailable or available channels to AP1 and the STAs.

[0227]

[0258] After receiving the multi-AP trigger frame from multiple APs, the STA can transmit a reverse trigger frame to multiple APs. In the reverse trigger frame, the STA can indicate the repetitive complete or partial information carried by the multi-AP trigger frame transmitted by AP1. This field can be used, for example, when AP1 and AP2 have difficulty in communicating directly with each other. In such a case or when AP2 modifies something in its trigger frame, the reverse trigger frame can confirm the configuration to be used in the next multi-AP transmission. The confirmed configuration can be from AP1 or AP2 or a combination of AP1 and AP2.

[0228]

[0259] The STA may transmit data to AP1 and AP2. In some implementations, at the end of the transmission, the STA may concatenate another reverse trigger frame to trigger a simultaneous transmission of an acknowledgment from the AP. In the reverse trigger frame, the STA may include synchronization information. The synchronization information may include power control information. The synchronization information may include time and / or frequency correction information. The power control information may indicate the transmission power of the reverse trigger frame and / or the expected RSSI of the multi-AP data transmission. The AP may use those two fields to determine its own transmission power. In the time and / or frequency correction information, the STA may request one or more of the APs to make a time or frequency correction to the trigger frame. The AP may transmit an acknowledgment frame to the STA.

[0229]

[0260] Some implementations provide transmit power and multi-user joint transmission. Such examples can address issues related to cooperative MU beamforming where APs have different attenuation and / or configurations (e.g., different transmit power and / or EVM).

[0230]

[0261] In some implementations, to solve the problem of inverting a JT MU-MIMO channel with a high transformation number, the output components and the effective channel can be inverted separately. In some implementations, eliminating the effect of the output can make the resulting matrix more invertible (e.g., have a lower condition number).

[0231]

[0262] In some implementations, the inversion of the two components may be performed in baseband, in some implementations, the descaling or inversion of the output may be performed in the analog domain while the inversion of the remaining part of the channel may be performed in baseband (e.g., combined analog and digital baseband JT MU-MIMO).

[0232]

[0263] In some implementations of combined analog and digital baseband JT MU-MIMO, the AP can send its Tx power value to the controller, and the controller can send the analog precoding power scale value to the AP, after which the AP can perform power scaling and start the JP precoding procedure.

[0233]

[0264] In some implementations of combined analog and digital baseband JT MU-MIMO, the master AP may request that the slave AP report its transmit power. The master AP can then send the analog power scale value to the slave AP. Figures 21 and 22 show example procedures and frame exchanges for an example JT MU-MIMO procedure with explicit feedback. Figures 23 and 24 show example procedures and frame exchanges for an example JT MU-MIMO procedure with implicit feedback. Figures 21 and 23 show the JT procedure for an unbalanced output scenario where the master AP designs the precoder. Figures 22 and 24 show the JT procedure for an unbalanced output scenario where each AP designs the precoder.

[0234]

[0265] In some implementations, the AP and STAs cooperate to set the AP's transmit power and the AP's precoder, and the precoder is designed in the master AP. In some implementations of combined analog and digital baseband JT MU-MIMO, the AP can request that the effective JP channel H be transmitted from the STA. The master AP or controller can then normalize the condition number of the effective channel and send separate analog scaling and digital precoding parameters for JP transmission to the AP.

[0235]

[0266] One example of such a procedure can be described as having a setup phase, a channel / power acquisition phase, a precoder information phase, and a transmission phase. These are exemplary and the procedure can be implemented with any suitable order or combination of phases.

[0236]

[0267] During an exemplary setup phase, each STA associates with multiple APs and identifies the type of multi-AP transmission it is capable of (e.g., joint transmission in this case). Both the AP and the STA indicate that they are capable of analog and digital processing of power imbalance. Note that if they do not have that capability, the AP / STA may decide to drop out of the multi-AP scheme and transmit / receive from a single AP / STA.

[0237]

[0268] During an exemplary channel / power acquisition phase, the AP and STAs undergo a sounding procedure to identify the effective MIMO channel. This can be explicit or implicit. During channel acquisition, additional APs can send relative power information (e.g., power level feedback) to the master AP.

[0238]

[0269] During an exemplary precoder information phase, the master AP can transmit analog and digital precoder information to the secondary / slave AP. The analog precoder can be a full matrix precoder. The analog precoder can be or include a power adjustment precoder that normalizes the power of both APs for power balancing.

[0239]

[0270] During the exemplary transmission phase, the AP transmits JT frames to the STAs using analog and digital precoders. Examples of these phases are shown in Figures 21, 22, 23, and 24 for explicit and implicit feedback, with Figure 21 showing an example of a JT procedure with a master AP for an unbalanced power scenario where the master AP designs the precoder (explicit feedback).

[0240]

[0271] As shown in FIG. 21, the process of 2110-2140 represents an example of a JT procedure. In 2110, each STA can associate with multiple APs and identify the type of multi-AP transmission it is capable of. For example, both APs (e.g., AP1 and AP2) and STAs (e.g., STA1 and STA2) indicate that they are capable of analog and digital processing for power imbalance. In 2120, powder and channel information can be acquired by a master AP (e.g., AP1), and AP1 can design a precoder by master trigger 2151, NDP 2153, NDP 2154, master trigger 2152, FB 2155, and FB 2156. Then, AP2 can send relative power information, i.e., power level feedback 2157, to AP1. In 2130, AP1 can send precoder information to AP2 by master trigger 2158, effective power level precoder 2159, and master trigger 2160. Then, at 2140, both APs may transmit JT frames (ie, JT MU-MIMO 2161 and JT MU-MIMO 2162) to the STA, and the STA may report ACK 2163 and ACK 2164, respectively, to the AP.

[0241]

[0272] FIG. 22 shows an example of a JT procedure with a master AP for an imbalanced power scenario where each AP designs a precoder (explicit feedback). As shown in FIG. 22, the process of 2210-2230 represents an example of a JT procedure. In 2210, each STA can associate with multiple APs and identify the type of multi-AP transmission it is capable of. For example, both the AP (e.g., AP1 and AP2) and the STA (e.g., STA1 and STA2) indicate that they are capable of analog and digital processing for power imbalance. In 2220, powder and channel information can be obtained by the master AP (e.g., AP1), and each AP can design its own precoder by the master trigger 2241, NDP 2242, NDP 2243, trigger 2244, FB 2245, FB 2246, power level feedback 2247, trigger 2248, FB 2249, FB 2250, and power level feedback 2251. Then, at 2130, AP1 may send a master trigger 2252 and a JT MU-MIMO 2253 to the STA. AP2 may send a JT MU-MIMO 2254 to the STA. The STA may report an ACK 2255 and an ACK 2256 to the AP, respectively.

[0242]

[0273] FIG. 23 shows an example of a JT procedure with a master AP for an imbalanced power scenario where the master AP designs a precoder (implicit feedback). At 2310, each STA can associate with multiple APs and identify the type of multi-AP transmission it is capable of. For example, both APs (e.g., AP1 and AP2) and STAs (e.g., STA1 and STA2) indicate that they are capable of analog and digital processing for power imbalance. At 2320, powder and channel information can be obtained by the master AP (e.g., AP1), and AP1 can design a precoder by master trigger 2351, NDP 2353, NDP 2354, master trigger 2352, and power level feedback 2355. Then, at 2330, AP1 can send precoder information to AP2 by master trigger 2356, effective power level precoder 2357, and master trigger 2358. Then, at 2340, both APs may transmit JT frames (i.e., JT MU-MIMO 2359 and JT MU-MIMO 2360) to the STA, and the STA may report ACK 2361 and ACK 2262, respectively, to the AP.

[0243]

[0274] FIG. 24 shows an example of a JT procedure with a master AP for an imbalanced power scenario where each AP designs a precoder (implicit feedback). At 2410, each STA can associate with multiple APs and identify the type of multi-AP transmission it is capable of. For example, both APs (e.g., AP1 and AP2) and STAs (e.g., STA1 and STA2) indicate that they are capable of analog and digital processing for power imbalance. At 2420, powder and channel information can be obtained by the master AP (e.g., AP1), and each AP can design its own precoder by master trigger 2441, trigger 2442, NDP 2443, NDP 2444, power level feedback 2245, trigger 2246, and power level feedback 2247. Then, at 2430, AP1 can send master trigger 2448 and JT MU-MIMO 2449 to the STAs. AP2 can send JT MU-MIMO 2450 to the STAs. The STA can report ACK2451 and ACK2452, respectively, to the AP.

[0244]

[0275] Although features and elements are described above in certain combinations, one skilled in the art will appreciate that each feature and element can be used alone or in any combination with other features and elements. In addition, the methods described herein can be implemented by a computer program, software, or firmware embodied in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) 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, cache memory, semiconductor memory 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 in association with software can be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.

Claims

1. 1. A method of multi-access point (multi-AP) communication performed by a wireless transmit / receive unit (WTRU), comprising: receiving a trigger frame from a first access point (AP) of a plurality of APs, the trigger frame including an identifier of the first AP and an identifier of a second AP of the plurality of APs; generating a reverse trigger frame including the identifier of the first AP, the identifier of the second AP, and synchronization information; transmitting the reverse trigger frame to at least the first AP and the second AP; receiving respective data transmissions from the first AP and the second AP based on the synchronization information; A method comprising:

2. The method of claim 1 , further comprising transmitting respective acknowledgement frames to the first AP and the second AP.

3. The method of claim 1 , wherein the synchronization information includes output control information.

4. The method of claim 3 , wherein the power control information includes one or more of a transmission power of the reverse trigger frame and an expected received signal strength indicator (RSSI) for the respective data transmission.

5. The method of claim 1 , wherein the trigger frame further comprises a list of one or more WTRUs to transmit to, the list of one or more WTRUs including the WTRU.

6. The method of claim 1 , wherein the identifier of the first AP comprises a first association identifier (AID) and the identifier of the second AP comprises a second AID.

7. The method of claim 1 , wherein the respective data transmissions from the first AP and the second AP are received simultaneously.

8. 1. A wireless transmit / receive unit (WTRU) configured for multi-access point (multi-AP) communication, comprising: A transceiver; 1. A processor comprising: receiving, via the transceiver, a trigger frame from a first AP of a plurality of access points (APs), the trigger frame including an identifier of the first AP and an identifier of a second AP of the plurality of APs; generating a reverse trigger frame including the identifier of the first AP, the identifier of the second AP, and synchronization information; transmitting the reverse trigger frame to at least the first AP and the second AP via the transceiver; a processor configured to receive, via the transceiver, respective data transmissions from the first AP and the second AP based on the synchronization information; A wireless transmit / receive unit (WTRU).

9. The WTRU of claim 8 , wherein the processor is further configured to transmit, via the transceiver, respective acknowledgement frames to the first AP and the second AP.

10. The WTRU of claim 8 , wherein the synchronization information includes power control information.

11. The WTRU of claim 10 , wherein the power control information comprises one or more of a transmission power of the reverse trigger frame and an expected received signal strength indicator (RSSI) for the respective data transmission.

12. The WTRU of claim 8 , wherein the trigger frame further comprises a list of one or more WTRUs to transmit to, the list of one or more WTRUs including the WTRU.

13. The WTRU of claim 8 , wherein the identifier of the first AP comprises a first association identifier (AID) and the identifier of the second AP comprises a second AID.

14. The WTRU of claim 8 , wherein the processor is configured to simultaneously receive the respective data transmissions from the first AP and the second AP.

15. 1. A method implemented in a plurality of access points (APs), comprising: transmitting a trigger frame to a first WTRU and a second WTRU of a plurality of WTRUs, the trigger frame including an identifier of a first AP and an identifier of a second AP of the plurality of APs; receiving respective reverse trigger frames from the first WTRU and the second WTRU, the respective reverse trigger frames including respective synchronization information; transmitting data to the first WTRU and the second WTRU based on the synchronization information; A method comprising:

16. The method of claim 15 , wherein the respective reverse trigger frames are received simultaneously from the first WTRU and the second WTRU.

17. The method of claim 15 , wherein the respective reverse trigger frames are received from the first WTRU and the second WTRU at different times.

18. An AP among a plurality of access points (APs), A transceiver; 1. A processor comprising: transmitting, via the transceiver, a trigger frame to a first WTRU and a second WTRU of a plurality of WTRUs, the trigger frame including an identifier of a first AP and an identifier of a second AP of the plurality of APs; receiving, via the transceiver, respective reverse trigger frames from the first WTRU and the second WTRU, the respective reverse trigger frames including respective synchronization information; a processor configured to transmit data to the first WTRU and the second WTRU via the transceiver based on the synchronization information; An access point (AP).

19. The AP of claim 18 , wherein the processor is configured to simultaneously receive the respective reverse trigger frames from the first WTRU and the second WTRU.

20. 20. The AP of claim 18, wherein the processor is configured to receive the respective reverse trigger frames from the first WTRU and the second WTRU at different times.

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