Method and apparatus for joint multi-AP transmission in WLAN

Abstract

To provide a method of multi-access point (multi-AP) communication performed by a wireless transmit / receive unit (WTRU).SOLUTION: A method comprises: receiving a first trigger frame comprising first information from a first access point (AP) of a plurality of APs; receiving a second trigger frame comprising the first information of the first trigger frame from a second AP; generating a synchronization frame comprising synchronization information based on the first trigger frame and the second trigger frame; transmitting the synchronization frame to the first AP and the second AP; and receiving a data transmission based on the synchronization information from each of the first AP and the second AP.SELECTED DRAWING: Figure 18

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 an interface to a distribution system (DS) or another type of wired / wireless network that carries traffic into and out of the BSS. Traffic to a STA originating from outside the BSS arrives through the AP and is delivered to the STA. Traffic originating from a STA to a destination outside the BSS is sent to the AP to be delivered to its respective destination. Traffic between STAs within a BSS can also be transmitted through the AP, with the source STA transmitting traffic to the AP, which delivers the traffic to the destination STA. Such traffic between STAs within a BSS is actually peer-to-peer traffic. Such peer-to-peer traffic can also be transmitted 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 AP and / or STAs that communicate directly with each other. This mode of communication is called 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 signals arrive at the STA with similar receive power, time, and frequency, allowing the STA to properly decode the signal. In addition, a channel access scheme that enables this operation needs to be defined.

[0004] overview A method for 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 data transmissions from each of the first AP and the second AP based on the synchronization information.

[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 access point (AP) of a plurality of 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. The receiver is further 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 explanation 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] 1B is a system diagram illustrating an example of a wireless transmit / receive unit (WTRU) that may be used within the communication system shown in FIG. 1A, according to one embodiment. [Figure 1C]

[0009] 1B is a system diagram illustrating an example radio access network (RAN) and an example 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 shown in FIG. 1A, according to one embodiment. [Figure 2]

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

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

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

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

[0015] 1 illustrates 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 below. [Figure 10]

[0019] 1 illustrates 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. [Figure 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 INVENTION

[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, broadcasts, 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 multicarrier (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, subscription-based 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 wearable items, 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 communications 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 communications 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 eNodeB (eNB), a Home Node B, a Home eNodeB, 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. While the base stations 114a, 114b are each shown 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 base station 114b may be configured to transmit and / or receive radio 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 for 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 per 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 station 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 communication 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 jointly implement LTE radio access and NR radio access, e.g., using the principle of dual connectivity (DC). Thus, the air interface utilized by the WTRUs 102a, 102b, 102c may be characterized by transmissions sent to and from multiple types of radio access technologies and / or 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 (e.g., Wireless Fidelity (WiFi)), IEEE 802.16 (e.g., 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] 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 local 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 establish a picocell or femtocell using a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, LTE-A Pro, NR, etc.). 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, billing 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 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 technology.

[0020]

[0046] The CN 106 may also serve 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 communication protocols, such as Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and / or Internet Protocol (IP) within the TCP / IP Internet protocol suite. The networks 112 may include wired and / or wireless communication networks owned and / or operated by other service providers. For example, the network 112 may include another CN connected to one or more RANs, which 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 that may use a cellular-based wireless technology and a base station 114b that may use an IEEE 802 wireless technology.

[0022]

[0048] 1B is a system diagram illustrating an example of a WTRU 102. As shown in FIG. 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 in association 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. While 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 IR, UV, or visible light signals, for example. 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 understood that the transmit / receive element 122 may be configured to transmit and / or receive any combination of wireless signals.

[0025]

[0051] 1B depicts 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. Additionally, the processor 118 may access information from and store data in any type of suitable memory, such as non-removable memory 130 and / or removable memory 132. The non-removable memory 130 may include random access memory (RAM), 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, etc. In other embodiments, the processor 118 may access information 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 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 instead 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 determine its location based on the timing of signals received from two or more nearby base stations. It will be appreciated that the WTRU 102 may obtain location information by any suitable location 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, etc. 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, a direction 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, a humidity sensor, etc.

[0031]

[0057] The WTRU 102 may include a full-duplex radio (e.g., in which transmission and reception of some or all of the signals associated with a particular subframe 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 processor-based signal processing (e.g., by a separate processor (not shown) or 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, and 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, and 160c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the eNode-Bs 160a, 160b, and 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 Figure 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 by 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 attach 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, and managing and storing the context of the WTRUs 102a, 102b, 102c.

[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 use a wired communication interface (e.g., temporarily or permanently) with a communication network.

[0041]

[0067] In a representative 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 to or interface with a distribution system (DS) or another type of wired / wireless network that carries traffic into and out of the BSS. Traffic to a STA originating from outside the BSS may arrive and be delivered to the STA through the AP. Traffic originating from a STA to a destination outside the BSS may be sent to the AP to be delivered to the respective destination. Traffic between STAs within the BSS may be sent through the AP; for example, a source STA may send traffic to the AP, which may deliver the traffic to the destination STA. Traffic between STAs within 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 a source STA and a destination STA using 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 within or using an IBSS (e.g., all of the STAs) can communicate directly with each other. IBSS mode communication may also be referred to herein as "ad hoc" mode communication.

[0043]

[0069] When using 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 configured width. The primary channel may be the 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 the 802.11 system. In CSMA / CA, STAs (e.g., all STAs), including the AP, may sense the primary channel. If a particular STA senses / detects and / or determines that the primary channel is in use, 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 can be formed by combining contiguous 20 MHz channels. A 160 MHz channel can be formed by combining eight contiguous 20 MHz channels or by combining two non-contiguous 80 MHz channels, which may be called an 80+80 configuration. In the 80+80 configuration, the channel-encoded data can be passed through a segment parser that can split the data into two streams. Inverse Fast Fourier Transform (IFFT) processing and time-domain processing can be performed separately for each stream. The streams can be mapped onto two 80 MHz channels, and the data can be transmitted by the transmitting STA. At the receiver of the receiving STA, the above 80+80 configuration operation can be reversed, and the combined data can 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 reduce channel operating bandwidths and carriers. 802.11af supports 5 MHz, 10 MHz, and 20 MHz bandwidths in the TV White Space (TVWS) spectrum, while 802.11ah supports 1 MHz, 2 MHz, 4 MHz, 8 MHz, and 16 MHz bandwidths using non-TVWS spectrum. According to representative embodiments, 802.11ah can support meter-type control / machine-type communication (MTC), such as MTC devices within macro coverage areas. MTC devices may have limited functionality, including support for (e.g., only) specific and / or limited bandwidths. MTC devices may include batteries with above-threshold battery life (e.g., to maintain very long battery life).

[0047]

[0073] WLAN systems that can support multiple channels and channel bandwidths, such as 802.11n, 802.11ac, 802.11af, and 802.11ah, can include a channel that can be designated as a primary channel. The primary channel can have a bandwidth equal to the maximum common operating bandwidth supported by all STAs in the BSS. The bandwidth of the primary channel can be set and / or limited by a STA among all STAs operating in the BSS that can support the smallest bandwidth operating mode. In the example of 802.11ah, for a STA (e.g., an MTC-type device) that supports (e.g., only supports) the 1 MHz mode, the primary channel can 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. Carrier sensing and / or network allocation vector (NAV) setting can depend on the state of the primary channel. For example, if the primary channel is in use by a STA (that only supports the 1 MHz mode of operation) transmitting to the AP, the entire available frequency band can be considered in use, even if a large portion 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, and 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, and 180c may each include one or more transceivers for communicating with the WTRUs 102a, 102b, and 102c over the air interface 116. In one embodiment, the gNBs 180a, 180b, and 180c may implement MIMO technology. For example, the gNBs 180a and 180b may transmit and / or receive signals to and from the gNBs 180a, 180b, and 180c using beamforming. 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, and 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 unlicensed spectrum, while the remaining component carriers may be on licensed spectrum. In one embodiment, the gNBs 180a, 180b, and 180c may implement coordinated multipoint (CoMP) technology. For example, the WTRU 102a may receive coordinated transmissions from the gNBs 180a and 180b (and / or 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 can 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 can utilize one or more of the gNBs 180a, 180b, 180c as mobility anchor points. In a standalone configuration, the WTRUs 102a, 102b, 102c can 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 substantially simultaneously. 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 can be associated with a particular cell (not shown) and can 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 can communicate with each other over the Xn interface.

[0054]

[0080] 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. While 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 with 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. For example, different network slices may be established for different use cases, such as services relying on Ultra-Reliable Low-Latency (URLLC) access, services relying on Enhanced Massive Mobile Broadband (eMBB) access, and services for MTC access. The AMFs 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 and 183b may be connected to the AMFs 182a and 182b in the CN 106 via an N11 interface. The SMFs 183a and 183b may also be connected to the UPFs 184a and 184b in the CN 106 via an N4 interface. The SMFs 183a and 183b may select and control the UPFs 184a and 184b and configure the routing of traffic through the UPFs 184a and 184b. The SMFs 183a and 183b may perform other functions such as managing and assigning IP addresses for UEs, managing PDU sessions, enforcing policy and controlling QoS, providing DL data notifications, 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, and the gNBs 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 communications 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 one 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 WTRU.

[0060]

[0086] The emulation device may be designed to perform one or more tests of other devices within a laboratory environment and / or 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 within 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 wireless communications.

[0061]

[0087] The one or more emulation devices may perform one or more functions, including all functions, without being implemented / deployed as part of a wired and / or wireless communication network. For example, the emulation devices may be utilized in test labs and / or test scenarios within undeployed (e.g., test) wired and / or wireless communication networks to perform tests of one or more components. The one or more emulation devices may be test equipment. Direct RF coupling and / or wireless communication via RF circuitry (which may include, for example, one or more antennas) may be used by the emulation devices 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 an interface to a distribution system (DS) or another type of wired / wireless network that carries traffic into and out of the BSS. Traffic to a STA originating from outside the BSS arrives through the AP and is delivered to the STA. Traffic originating from a STA to a destination outside the BSS is sent to the AP to be delivered to its destination. Traffic between STAs within a BSS can also be transmitted through the AP, with the source STA transmitting traffic to the AP, which delivers the traffic to the destination STA. Such traffic between STAs within a BSS can be referred to as peer-to-peer traffic. Such peer-to-peer traffic can also be transmitted 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 the infrastructure mode of operation defined in the Institute of Electrical and Electronics Engineers (IEEE) 802.11ac standard, an AP can 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 can 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 busy, the STA backs off. Therefore, only one STA within a given BSS can transmit at any given time.

[0064]

[0090] In some implementations, such as systems conforming to the IEEE 802.11n standard, high-throughput (HT) STAs can also use 40 MHz-wide channels for communication. This can be achieved 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, such as systems compliant with the IEEE 802.11ac standard, a very high throughput (VHT) STA may support channels of 20 MHz, 40 MHz, 80 MHz, and 160 MHz width. 40 MHz and 80 MHz channels can be formed by combining contiguous 20 MHz channels, as in 802.11n above. A 160 MHz channel can 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 can be passed through a segment parser that splits the data into two streams. IFFT and time-domain processing can be performed separately for each stream. The streams can be mapped onto two channels, and the data can be transmitted. At the receiver, this mechanism is reversed, and the combined data is sent to the MAC.

[0066]

[0092] Some implementations, such as systems compliant with the IEEE 802.11af and / or IEEE 802.11ah standards, support sub-1 GHz modes of operation. In such implementations, channel operating bandwidths and carriers may be reduced compared to those used in systems compliant with 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, while 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 functionality, such as limited bandwidth support, and may include requirements for very long battery life.

[0067]

[0093] WLAN systems supporting multiple channels and / or channel widths, such as those conforming to the IEEE 802.11n, 802.11ac, 802.11af, and / or 802.11ah standards, may include a channel designated as the 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 a STA among all STAs operating in the BSS that supports the smallest bandwidth operating mode. In the example of an IEEE 802.11ah system, if the BSS includes STAs (e.g., MTC-type devices) that support only 1 MHz mode, the primary channel may be 1 MHz wide, 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 conditions of the primary channel. In some such cases, if the primary channel is in use, for example by STAs that only support a 1 MHz mode of operation transmitting to the AP, the entire available frequency band is considered in use, even though a large portion of the available frequency band remains unused and available.

[0068]

[0094] In the United States, the available frequency band that can 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 across a wide range of use scenarios, including high-density scenarios in the 2.4 GHz, 5 GHz, and 6 GHz bands. New use cases that support high-density deployment of APs and STAs and 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 associate with a single AP and transmit to or from that AP with little or no coordination with transmissions in neighboring BSSs. STAs may follow overlapping BSS (OBSS) transmissions based on a CSMA protocol that is completely independent between BSSs. Some systems (e.g., 802.11ax-compliant systems) may use spatial reuse procedures to introduce some degree of coordination between OBSSs, allowing OBSS transmissions based on adjusted energy detection thresholds (e.g., using the OBSS Packet Detection (OBSS PD) procedure) or knowledge of the amount of interference that can be tolerated by the receiving OBSS STAs (e.g., using the Spatial Reuse Parameter (SRP) procedure).

[0071]

[0097] Some implementations include procedures that enable 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 compliant with 3GPP LTE Release 10, while 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 will use eNB for convenience)) can transmit to the same or multiple WTRUs within the same time and frequency resources using joint processing / transmission. This can have the effect of improving the overall throughput of the WTRUs under consideration. Dynamic cell selection can be treated as a special case of joint processing, where only one of a set of WTRUs is actively transmitting data at any one time. On the other hand, multiple eNBs can transmit to different WTRUs (each eNB serving its own WTRU) within the same time and frequency resources using coordinated beamforming / scheduling. This can have the effect of reducing the interference experienced by each WTRU. For example, using CoMP in an LTE system can achieve significant improvements in cell-average and / or cell-edge throughput. 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., through explicit feedback. Furthermore, 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). Furthermore, 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 WLANs 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 can be used by only one AP to transmit or receive data. Information can be beamformed on each RU or can include MU-MIMO. Complexity can be described as relatively low to medium. In some simple cooperative OFDMA schemes, the APs can divide the OFDMA RUs among APs in a cooperative manner, with each AP restricted to specific RUs. 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 access for STAs that may be affected. This approach can be called fractional frequency reuse (FFR).

[0076]

[0102] Figure 2 shows FFR in cooperative OFDMA. The central 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 to and from its desired STAs and can suppress interference with other STAs.

[0078]

[0104] FIG. 4 shows an example of CN / CB. As shown in FIG. 4, there is AP2 and STA1. Data transmission between AP1 and STA1 is desired data transmission 410. There is also AP2 and STA1. Data transmission between AP2 and STA2 is desired data transmission 420. However, in this scenario, AP1 may also transmit data to another STA or other STAs, thus resulting in interfering data transmission, i.e., interference 430. AP2 may also transmit data to another STA or other STAs, thus resulting in 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 cooperative single-user (SU) or multi-user (MU) transmission, multiple APs can cooperate to simultaneously transmit information to or from a single STA or multiple GSTAs. 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 within one RU. Cooperative SU transmission may include dynamic point selection, cooperative SU beamforming, or joint precoding, in order of complexity.

[0081]

[0107] Figure 5 illustrates single-user joint precoded multi-AP transmission or cooperative SU beamforming. As shown in Figure 5, in dynamic point selection, transmissions 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, transmissions may be simultaneous from multiple APs and beamformed or precoded to a desired STA on one or more RUs. As shown in Figure 5, both AP1 and AP2 may transmit to a STA, i.e., 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 to or from multiple STAs via one or more RUs. 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 where a trigger frame (TF) is transmitted 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 error can make DL sounding undesirable. Assuming channel reciprocity, some implementations can 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 the DL sounding procedure, in some implementations, a non-AP STA is the entity that measures the signal and / or estimates the channel. The non-AP STA in this case has perfect knowledge of the received signal phase difference between the Rx antennas at the non-AP STA. However, in UL sounding with multiple APs, the 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, we assume the following: (1) the Master AP performs its own channel estimation and the channel estimation of the Slave APs; (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 Inter-Frame Time (IFS) after transmitting Frame A; and (4) the Slave AP starts joint transmission one IFS after receiving Frame A.

[0087]

[0113] 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 at AP1 corresponds to its own clock.

[0088]

[0114] FIG. 8 shows an example of a phase offset for UL sounding. As shown in FIG. 8, a WTRU 810 transmits an UL sounding signal to AP1 and AP2. The sounding signal is 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 this information with its own channel estimate 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 issue, 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 and slave APs in addition to CFO / SFO correction. It may be desirable to provide a system and method that does not require clock synchronization between the master and slave APs 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 methods, systems, and apparatus for an AP to synchronize with a STA so that signals arrive at the STA with similar receive power, time, and frequency, for example, to enable proper decoding of the signals 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. For 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 signals 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, the 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 the APs have different transmit powers for the 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 calculations in UL sounding and / or channel estimation.

[0098]

[0126] 10 shows an example of trigger frame-based DL joint transmission based on the steps discussed above. As shown in FIG. 10, AP1 transmits a trigger frame (TF) to AP2, and AP1 and AP2 each transmit data to the WTRU 1010. 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 FIG. 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 itself 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 can combine the channel estimates as follows: H=[H AP1 e2πfΔt H AP2 ], or H=[H AP1 H AP2 e -2πfΔt ] where H AP1 and H AP2 corresponds to the estimated channel at AP1 and AP2. In this case, the master AP can perform precoding using H.

[0101]

[0131] Instead, in some implementations, the master AP: H=[H AP1 H AP2 ] As a composite channel, AP1 can compute the precoder. However, in this case, AP1 can delay its DL joint transmission (e.g., from transmitting TF until IFS+Δt, or from receiving TF until AP1 instructs the slave AP to advance its transmission, e.g., until IFS−Δt). 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] Figure 11 illustrates this UL sounding scenario. As shown in Figure 11, 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 UL sounding feedback to AP1 with a fixed delay D after the rx UL sounding signal.

[0104]

[0135] This example scenario can be applied when multiple non-AP STAs are simultaneously performing UL sounding by using one STA and one AP1 / AP2 antenna pair as a reference, thereby calculating Δt using that reference antenna pair. Different STAs may have different Δt, but the same Δt may be used for H, e.g., because the same entity (AP1 or AP2) was observing / estimating multiple STAs. AP1 and H AP2 The phase difference between the two can be automatically adjusted.

[0105]

[0136] In some implementations, if multiple non-AP STAs are performing 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 APs may need to synchronize with the STA so that the signals arrive at the STA with similar receive power. Synchronization in time and frequency may also be required in some implementations. Therefore, 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 exemplary 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 for simultaneous transmission to a STA. In some examples, AP1 may be considered the primary AP and AP2 may be considered the 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 a 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 within the multi-AP trigger frame. In some implementations, AP1, the primary AP, can configure a 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 STA's ID. The STA's role can indicate whether the STA is a transmitting or receiving STA. The STA's ID can be an association identifier (AID), a compressed AID, a BSS identifier (BSSID, compressed BSSID), a BSS color, an enhanced BSS color, etc.

[0109]

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

[0110]

[0141] The common information may include a type field, which may indicate a DL multi-AP transmission, or 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, a STA can transmit a reverse trigger frame 1220 to multiple APs. In the reverse trigger frame 1220, the STA can indicate complete or partial repetition information carried by the trigger frame 1210 transmitted by AP1. This field can be used, for example, when it is difficult for AP1 and AP2 to communicate directly with each other. This information can be provided opportunistically, or one of the APs can instruct the other AP. Alternatively, one of the APs can opportunistically instruct the other AP as needed. In the reverse trigger frame 1220, the STA can additionally or alternatively indicate synchronization-related information, such as power control information. In such partial 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. Note that if there is a power imbalance between AP1 and AP2, the STA may request that transmission from one of the STAs be turned off to result in single-AP transmission. Within 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. Note 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] 12, the STA may receive data transmissions (i.e., Data 1 and Data 2) from AP1 and AP2. Depending on the packet IDs in the trigger frame 1210, the STA may or may not combine the transmissions. The STA may transmit an acknowledgement frame to the AP.

[0114]

[0145] In the example of Figure 12, AP1 and AP2 may negotiate to transmit simultaneously to the STA. In some implementations, AP1 may be considered the primary AP and AP2 may be considered the secondary AP in the negotiation. In some implementations, AP1 and AP2 may 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 using, for example, UL OFDMA and / or UL MU-MIMO.

[0116]

[0147] 13, AP1 transmits a trigger frame 1310 to both STA1 and STA2. STA1 then transmits a reverse trigger frame 1320 to both AP1 and AP2. STA2 then 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] 14, AP1 transmits a trigger frame 1410 to both STA1 and STA2. STA1 then transmits a reverse trigger frame 1420 to both AP1 and AP2. STA2 then 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 15-18. The method for multi-AP communication according to the present application may be performed by a WTRU.

[0120]

[0151] Figure 15 illustrates an exemplary multi-AP communication procedure according to one embodiment of the present application. Figure 16 illustrates an exemplary multi-AP MU-MIMO communication procedure according to one embodiment of the present application. Figure 17 illustrates an exemplary multi-AP MU-MIMO communication procedure according to another embodiment of the present application. Figure 18 is a flowchart illustrating a method 1800 of multi-AP communication according to one embodiment of the present application.

[0121]

[0152] The method for 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 the AP and the 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 a scenario in which both multiple APs and multiple STAs are deployed with reference to Figures 16 and 17.

[0124]

[0155] A method 1800 according to an embodiment of the present application will be described in detail below with reference to Figures 15 and 18. The method 1800 is a multi-AP communication method that can be applied in a 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 listed 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 a 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 reference to the following embodiments.

[0126]

[0157] The following description explains the process in 1801 in more detail. Method 1800 may be applied to a scenario in which two APs are deployed, for example, AP1 and AP2 (shown in FIG. 15). Therefore, the apparatus for multi-AP transmission according to the embodiments of the present application may also be applied to a two-AP scenario, such as the scenario in FIG. 15.

[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 determine 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] 15 shows only two APs, this is for illustrative purposes only and is not intended to be exclusive or a limitation on the embodiments of the present application. For example, the method 1800 may also be applied to a scenario having three APs, i.e., a first AP, a second AP, and a third AP. Therefore, a device (e.g., a WTRU) for multi-AP communication according to an embodiment of the present application may also be applied to the above three-AP scenario.

[0129]

[0160] The number of APs in the embodiment of the present application may be four 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 upcoming data transmission between the AP and the STA, 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 STA.

[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 one embodiment of multi-AP downlink transmissions (i.e., data 1 and data 2) from AP1 and AP2 to a 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, trigger frame 1910 can be used to trigger a reverse trigger frame (e.g., reverse trigger frame 1920) transmitted by a STA. In the embodiment shown in Figure 20, 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 a 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 a 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. 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 the 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 the 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 the 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., the STA shown in FIG. 15). Generally speaking, it will be understood that a WTRU (e.g., the STA shown in FIG. 15) and an AP (e.g., AP1 shown in FIG. 15) may be referred to as an STA. For example, in a WLAN scenario, a router (e.g., an AP) may be referred to as a station, and a laptop (e.g., an 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., the STA shown in FIG. 15).

[0136]

[0167] The ID of the STA can be an AID, a compressed AID, a BSSID, a compressed BSSID, a BSS color, or an enhanced BSS color, etc.

[0137]

[0168] If the STA 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 fields corresponding to multiple APs and determine whether a single packet is being transmitted from multiple APs or multiple packets are being 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 to the transmitting side (i.e., AP1).

[0141]

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

[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, Figures 16 and 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, the 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 a next data transmission from AP1 to a STA, a time field to indicate a start time of the next data transmission from AP1 to a STA, and a frequency field to indicate a transmission frequency of the next data transmission from AP1 to a 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 herein may include any combination of the above exemplary information or any other information available for achieving the technical solution of the present 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, second information, and third information are completely different pieces of 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 upcoming 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 upcoming 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 can be used to pre-adjust the transmission power from multiple APs to STAs so that signals (e.g., data transmissions) from the AP can arrive at the STAs with similar received powers. The transmission start time information carried by the first trigger frame can be used to pre-adjust the transmission start times from multiple APs to STAs so that signals from the AP can arrive at the STAs with similar received times. The transmission frequency information carried by the first trigger frame can be used to pre-adjust the transmission frequencies from multiple APs to STAs so that signals from the AP can arrive at the STAs with similar received frequencies.

[0150]

[0181] It will be understood that the above three parameters for multi-AP transmission are provided by way of example only and are not intended to be exclusive or limiting 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 achieved by the first trigger frame 1510 alone. While the first trigger frame 1510 is the main part of the synchronization, the method 1800 and device (e.g., a WTRU) according to the present application still require the second trigger frame 1520 and synchronization frame 1530 (described below) to achieve synchronization. For example, as shown in FIG. 15, after receiving the first trigger frame 1510, the STA may transmit a synchronization frame 1530 to multiple APs, which may carry synchronization information necessary to synchronize subsequent data transmissions from each of the multiple APs. The following description describes the second trigger frame 1520 and 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 except 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). Because both the next data transmissions from AP1 and AP2 may be configured by the first trigger frame 1510, the next data transmissions from both AP1 and AP2 may be synchronized accordingly. The following description explains how the first trigger frame 1510 is used to configure the next data transmission from AP2 for the process in 1802.

[0153]

[0184] In embodiments 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 WLAN receiver, or any other type of receiver that can be used to receive signals transmitted in the WLAN scenarios shown in Figures 15 and 4.

[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 may be referred to as the first data transmission, and the next data transmission from AP2 to the STA may be referred to as the second data transmission. As shown in Figures 15 to 17, the first data transmission may be referred to as Data 1, and the second data transmission may be referred to as Data 2.

[0156]

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

[0157]

[0188] 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. Although these blocks are located at different locations in the vertical direction, it will be understood that these blocks are illustrated in this manner merely to indicate the source of each frame, and their projection in the horizontal direction may represent the time at which each frame is received at the STA.

[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, once 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. Therefore, the length of time for generating the second trigger frame can also be known. Therefore, 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-mentioned 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 in the first trigger frame 1510 may be transmit power information for the next data transmission from AP1 to the STA. AP2 determines that the transmit power indicated by the transmit power information is within its transmit power limit. Therefore, AP2 can directly write the transmit 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 provided by way of example only 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 have 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 in 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 in 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 differ from the second information in the first trigger frame 1510. For example, the first trigger frame 1510 may instruct AP2 to use a particular channel (e.g., channel 2) for the next data transmission to the STA (i.e., data 2). That is, the second information in the first trigger frame 1510 may be information on channel 2 to be 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 configuration information to both AP1 and the STA to indicate that channel 2 is unavailable. In that case, the configuration information (i.e., the unavailability of channel 2) differs from the second information in the first trigger frame 1510 (i.e., the selection of channel 2).

[0168]

[0199] In the above example, AP2 may know that channel 2 is unavailable for its data transmission, but that another channel (e.g., channel 3) is available. AP2 may 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 this case, the configuration information (i.e., the unavailability of channel 2 and the selection of channel 3) differs from the second information (i.e., the selection of channel 2) in the first trigger frame 1510. In other words, the configuration information may overwrite the second information in the first trigger frame 1510.

[0169]

[0200] For example, the first trigger frame 1510 may instruct AP2 to use a specific transmit 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 about the transmit power (e.g., Transmit Power 2) to be used by AP2 for the second data transmission. However, AP2 may find that the transmit power 2 exceeds its power limit. In that case, AP2 may transmit a second trigger frame along with configuration information to both AP1 and the STA to indicate that the transmit power 2 is unavailable and that AP2 will use its desired transmit power (e.g., Transmit Power 3) for the second data transmission. In that case, the configuration information (i.e., the unavailable transmit power 2 and the selection of the transmit power 3) differs from the second information (i.e., Transmit Power 2) of the first trigger frame 1510. 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 transmission power information and transmission start time information used by AP2 for the second data transmission. AP2 may then transmit a second trigger frame 1520 along with configuration information to both AP1 and the STA to indicate AP2's desired transmission frequency for the second data transmission. In this case, the configuration information (i.e., AP2's desired transmission frequency) is additional information not included in the first trigger frame. In the above example, the STA may transmit a synchronization frame 1530 (described further below) to both AP1 and AP2 along with AP2's desired transmission frequency, so that the APs can perform data transmission by using the desired transmission frequency. Thus, transmission frequency synchronization can be achieved. 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 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 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 may 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 may 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 frame indicates 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 predetermined rule. For example, AP1, the primary AP, may transmit the trigger frame first. The remaining APs may transmit in ascending / descending order based on the BSSID or MAC address of the AP. It will be understood that all APs in the group may know the BSSID or MAC address of the member APs.

[0178]

[0209] The following description explains 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 Figure 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. Therefore, these pieces of information may also be configured in different fields for the synchronization frame 1530 to carry. The above information may be referred to as 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 Figure 15, the processor is configured to generate the synchronization frame 1530 based on the first and second trigger frames 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 confirmation information.

[0184]

[0215] In formats (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, if it may be difficult for AP1 and AP2 to communicate directly with each other, the STA may transmit 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 transmit power of a first data transmission is output 1, and the second trigger frame 1520 indicates that the transmit power of a 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 referred to as 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 may share the same format as the second trigger frame 1520. In other words, the synchronization frame 1530 may 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-mentioned configuration information in the second trigger frame 1520.

[0188]

[0219] In formats (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, if it may be difficult for AP1 and AP2 to communicate directly with each other, the STA may transmit information originating from AP2 to AP1 to synchronize data transmission.

[0189]

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

[0190]

[0221] 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 a first data transmission may be frequency 1, and a second trigger frame 1520 received from AP2 may indicate that the transmission frequency of a second data transmission may be frequency 2. The STA may then generate a synchronization frame 1530 with specific transmission frequency information to indicate the desired transmission frequencies for both of the next data transmissions. AP1 and AP2 may then conduct their next data transmissions based on the desired transmission frequencies.

[0192]

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

[0193]

[0224] It will be understood that according to an embodiment of the present application, the synchronization process of upcoming data transmissions from multiple APs may not be completed by the synchronization frame 1530 alone, but 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 synchronization frame 1530 to both AP1 and AP2. In embodiments with more than two APs and one STA, at 1804, the STA may transmit a synchronization frame 1530 to at least AP1 and AP2. However, the embodiment shown in FIG. 15 is not intended to be exclusive or a limitation on the principles of the present application. For example, the STA may select that only AP1 or only AP2 can transmit data to the STA. AP downselection may depend on information carried in trigger frames transmitted from AP1 and AP2 or on the STA's 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 predetermined / predetermined threshold, the STA may exclude that AP from multi-AP transmissions.

[0195]

[0226] Based on the synchronization frame from the STA, AP1 may perform a first data transmission to the STA, and AP2 may perform a second data transmission to the STA. That is, in 1805, the STA may receive data transmissions from each of 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 may 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 present method of multiple AP transmission can be extended to multi-AP MU-MIMO, with each STA in the 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] 16, STA1 may receive a first trigger frame 1610 from AP1 and a second trigger frame 1620 from AP2. STA1 may then 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 the second trigger frame 1620 from AP2. STA2 may then 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 Figure 16, STA1 may first transmit a synchronization frame 1630, followed by STA2 transmitting a synchronization frame 1640. The first trigger frame 1610 may be similar to or the same as the first trigger frame 1510 shown in Figure 15. The second trigger frame 1620 may be similar to or the same as the second trigger frame 1520 shown in Figure 15. The synchronization frames 1630 and 1640 may be similar to or the same as the synchronization frame 1530 shown in Figure 15.

[0201]

[0232] As shown in Figure 16, after AP1 and AP2 receive sync frames 1630 and 1640, AP1 and AP2 can transmit data (i.e., data 1 and data 2 shown in Figure 16) to STA1 and STA2, respectively. Then, STA1 can transmit an ACK 1650 to AP1 and AP2, respectively. STA2 can transmit an 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] 17, STA1 may receive a first trigger frame 1710 from AP1 and may receive a second trigger frame 1720 from AP2. STA1 may then 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 may receive the first trigger frame 1710 from AP1 and may receive the second trigger frame 1720 from AP2. STA2 may then 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 Figure 17, STA1 and STA2 can simultaneously transmit their synchronization frames. A first trigger frame 1710 is similar to or the same as the first trigger frame 1510 shown in Figure 15. A second trigger frame 1720 is similar to or the same as the second trigger frame 1520 shown in Figure 15. A synchronization frame 1730 and a synchronization frame 1740 are similar to or the same as the synchronization frame 1530 shown in Figure 15.

[0205]

[0236] As shown in Figure 17, after AP1 and AP2 receive synchronization frames 1730 and 1740, AP1 and AP2 can transmit data (i.e., data 1 and data 2 shown in Figure 16) to STA1 and STA2, respectively. Then, STA1 can transmit an ACK 1750 to AP1 and AP2, respectively. STA2 can transmit an 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 embodiments with more than two APs, the STA may select one AP or multiple APs to send synchronizations to. Thus, only the AP receiving synchronizations 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 acknowledgement 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 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 correction. 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 simultaneously receive from a STA. As shown in FIG. 19, AP1 transmits a trigger frame 1910 to the STA. The trigger frame 1910 is similar to 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 the 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 can transmit to multiple APs simultaneously in the UL. If the APs cannot hear from each other or from the primary AP, they can 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 STA simultaneously. In some implementations, AP1 can be considered the primary AP and AP2 can be considered 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, or the STA can perform the sounding and acquire the channel between itself and the AP. In this case, the STA can acquire the UL channel from each AP by individually or jointly transmitting an NDPA and NDP to the AP and, for example, polling each AP, or by the AP sending an UL trigger to send its channel information in a predetermined manner, for example, in a DL multi-AP transmission.

[0212]

[0243] The channel access procedure for UL multi-AP transmissions 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 STAs. In some implementations, AP1 may acquire the channel and transmit a multi-AP trigger frame to trigger transmissions from the STAs. In the multi-AP trigger frame, AP1 may configure the next UL multi-AP transmission within the multi-AP trigger frame. In some implementations, AP1, being the primary AP, may configure the transmission from AP2 to the STAs. For example, the multi-AP trigger frame may indicate STA-specific information and / or common information. The STA-specific information (here, STA indicates an AP STA or a non-AP STA) may indicate the STA's role and / or the STA's ID. The STA's role may indicate whether the STA is a transmitting / AP or a receiving / STA. The STA's ID may be an association identifier (AID), a compressed AID, a BSS identifier (BSSID, compressed BSSID), a BSS color, an enhanced BSS color, etc.

[0213]

[0244] If the STA role indicates a transmitter / 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 / transmitter 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 allocated to the STA for transmitting a multi-AP packet to the AP. In an OFDMA transmission scenario, resources may be allocated in resource units (RUs). The spatial stream allocation may indicate the starting spatial stream index and the number of spatial streams to be used by 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, or 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 complete or partial information of the repetition carried by the multi-AP trigger frame transmitted by AP1. This field can be used, for example, when AP1 and AP2 have difficulty communicating directly with each other. In such cases, or if 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, AP2, or a combination of AP1 and AP2.

[0217]

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

[0218]

[0249] FIG. 20 shows an example of a channel access scheme that allows multiple APs to simultaneously receive data from a STA. As shown in FIG. 20, AP1 transmits a trigger frame 2010 to the STA. The trigger frame 2010 is similar to or the same as the first trigger frame 1510 shown in FIG. 15. AP2 then transmits a short trigger frame 2020, which may include availability information, to the STA. The STA then 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. The STA then transmits data 2060 to both AP1 and AP2 based on the information in the reverse trigger frame 2030. After receiving data 2060, 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 (e.g., in the case of dynamic point selection). The target AP can be addressed within 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 transmissions 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 Figure 20, AP1 and AP2 can negotiate to receive from the STA simultaneously. In some implementations, AP1 can be considered the primary AP and AP2 can be considered the secondary AP in the negotiation. In some examples, AP1 and AP2 can 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 negotiation may be via the STA.

[0222]

[0253] AP1 may transmit a multi-AP trigger frame to acquire the channel and trigger transmissions from STAs. The multi-AP trigger frame allows AP1 to configure the next UL multi-AP transmission within the multi-AP trigger frame. In some methods, AP1, the primary AP, may be able to configure transmissions from AP2 to STAs. For example, the multi-AP trigger frame may indicate STA-specific information and / or common information. The STA-specific information (here, STA indicates an AP STA or a non-AP STA) may indicate the STA's role and / or the STA's ID. The STA's role may indicate whether the STA is a transmitter / AP or a receiver / STA. The STA's ID 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 can indicate a transmitter / STA, the STA role can include a packet ID. The packet ID can be used to indicate that the packet is transmitted from the STA. In some examples, this field can be an AP / transmitter specific field. The STA can 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 can 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 allocated to the STA for transmitting a multi-AP packet to the AP. In an OFDMA transmission scenario, resources may be allocated in resource units (RUs). The spatial stream allocation may indicate the starting spatial stream index and the number of spatial streams to be used by 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 an 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, for example, 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 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 designated 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 multi-AP trigger frames from multiple APs, a STA can transmit reverse trigger frames to multiple APs. In the reverse trigger frame, the STA can indicate the complete or partial information of the repetition carried by the multi-AP trigger frame transmitted by AP1. This field can be used, for example, when AP1 and AP2 have difficulty communicating directly with each other. In such cases, or if 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, AP2, or a combination of AP1 and AP2.

[0228]

[0259] The STA can transmit data to AP1 and AP2. In some implementations, at the end of the transmission, the STA can concatenate another reverse trigger frame to trigger a simultaneous transmission of an acknowledgment from the AP. Within the reverse trigger frame, the STA can include synchronization information. The synchronization information can include power control information. The synchronization information can include time and / or frequency correction information. The power control information can indicate the transmission power of the reverse trigger frame and / or the expected RSSI of the multi-AP data transmission. The AP can use these two fields to determine its own transmission power. Within the time and / or frequency correction information, the STA can request one or more of the APs to make time or frequency corrections to the trigger frame. The AP can 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 occur in baseband, and in some implementations, the descaling or inversion of the output may occur in the analog domain while the inversion of the remaining part of the channel may occur 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 an 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 in which the master AP designs the precoder. Figures 22 and 24 show the JT procedure for an unbalanced output scenario in which 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] An 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 STA indicate that they are capable of analog and digital processing of power imbalance. Note that if they are not capable, 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 exemplary transmission phases, 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 processes of 2110 through 2140 represent an example of a JT procedure. In 2110, each STA associates with multiple APs and can identify the type of multi-AP transmission it is capable of. For example, both the APs (e.g., AP1 and AP2) and the 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 via master trigger 2151, NDP 2153, NDP 2154, master trigger 2152, FB 2155, and FB 2156. AP2 can then send relative power information, i.e., power level feedback 2157, to AP1. In 2130, AP1 can send precoder information to AP2 via 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 illustrates an example of a JT procedure using a master AP for an imbalanced power scenario in which each AP designs its own precoder (explicit feedback). As shown in FIG. 22, processes 2210 through 2230 represent an example of a JT procedure. In 2210, each STA associates with multiple APs and can 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 acquired by the master AP (e.g., AP1), and each AP can design its own precoder using 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 using a master AP for an imbalanced power scenario in which the master AP designs the precoder (implicit feedback). At 2310, each STA may 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) may indicate that they are capable of analog and digital processing for power imbalance. At 2320, powder and channel information may be acquired by the master AP (e.g., AP1), allowing AP1 to design a precoder via master trigger 2351, NDP 2353, NDP 2354, master trigger 2352, and power level feedback 2355. Then, at 2330, AP1 may send the precoder information to AP2 via master trigger 2356, effective power level precoder 2357, and master trigger 2358. Then, at 2340, both APs may transmit JT frames (ie, 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 using a master AP for an imbalanced power scenario in which each AP designs a precoder (implicit feedback). At 2410, each STA associates with multiple APs and can identify the type of multi-AP transmission it is capable of. For example, both the APs (e.g., AP1 and AP2) and the 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 using 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 to the AP, respectively.

[0244]

[0275] Although features and elements have been described above in particular combinations, those skilled in the art will understand that each feature and element can be used alone or in any combination with the 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 first trigger frame from a first access point (AP) of a plurality of APs, the first trigger frame including first information; 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; generating a synchronization frame based on the first trigger frame and the second trigger frame, the synchronization frame including synchronization information; transmitting the synchronization frame to at least the first AP and the second AP; receiving a data transmission from each of the first AP and the second AP based on the synchronization information; A method comprising:

2. The method of claim 1 , wherein the synchronization information includes transmission power information, transmission start time information, or transmission frequency information.

3. 2. The method of claim 1, wherein the second trigger frame further includes configuration information for a second data transmission, the configuration information being different from second information of the first trigger frame.

4. The method of claim 3 , wherein the synchronization frame further includes confirmation information corresponding to the configuration information.

5. The method of claim 1 , wherein the synchronization frame further includes third information of the first trigger frame.

6. The method of claim 1 , further comprising transmitting an ACK / NACK report to each of the first AP and the second AP.

7. The method of claim 1 , wherein the first trigger frame includes WTRU-related information.

8. The method of claim 7 , wherein the WTRU-related information includes a packet ID, a resource allocation, a spatial stream allocation, or MCS-related information.

9. 1. A wireless transmit / receive unit (WTRU) configured for multi-access point (multi-AP) communication, comprising: receiving a first trigger frame from a first access point (AP) of a plurality of APs, the first trigger frame including first information; and 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; a receiver configured to: a processor configured to generate a synchronization frame based on the first trigger frame and the second trigger frame, the synchronization frame including synchronization information; and a transmitter configured to transmit the synchronization frame to at least the first AP and the second AP; and the receiver is further configured to receive a data transmission from each of the first AP and the second AP based on the synchronization information.

10. The WTRU of claim 9 , wherein the synchronization information includes transmission power information, transmission start time information, or transmission frequency information.

11. The WTRU of claim 9 , wherein the second trigger frame further includes configuration information for a second data transmission, the configuration information being different from second information of the first trigger frame.

12. The WTRU of claim 11 , wherein the synchronization frame further includes confirmation information corresponding to the configuration information.

13. The WTRU of claim 9 , wherein the synchronization frame further includes third information of the first trigger frame.

14. The WTRU of claim 9 , wherein the transmitter is further configured to transmit an ACK / NACK report to each of the first AP and the second AP.

15. The WTRU of claim 9 , wherein the first trigger frame includes WTRU-related information.

16. The WTRU of claim 9 , wherein the WTRU-related information includes a packet ID, a resource allocation, a spatial stream allocation, or MCS-related information.

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