Distributed multi-user (MU) wireless communication

Abstract

This disclosure relates to distributed multi-user (MU) wireless communications. This disclosure provides systems, methods, and apparatus, including computer programs encoded on computer storage media, for group formation and sounding for distributed multi-user multiple-input multiple-output (MU-MIMO). Some implementations include a method of wireless communication. The method includes transmitting, from a first access point of a plurality of access points, an announcement frame for performing a beamforming procedure for a distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from a basic service set of the first access point.

Description

[0001] This application is a divisional application of the patent application filed on January 17, 2018, with international application number PCT / US2018 / 013943, Chinese application number 201880011682.2, and entitled "Distributed Multi-User (MU) Wireless Communication".

[0002] Cross-references to related applications

[0003] This application claims priority to U.S. Application No. 15 / 872,294, filed January 16, 2018, which claims the benefit of U.S. Provisional Patent Application S / N. 62 / 459,290, filed February 15, 2017. The contents of both applications are incorporated herein by reference in their entirety. Technical Field

[0004] This disclosure generally relates to wireless communications, and more particularly to systems and methods for group formation and probe for distributed multi-user multiple-input multiple-output (MU-MIMO).

[0005] Related technical descriptions

[0006] To address the ever-increasing bandwidth requirements of wireless communication systems, various solutions are being developed to allow multiple user terminals to communicate with a single access point (AP) or multiple APs simultaneously while sharing channel resources, thus achieving high data throughput. Multiple-input multiple-output (MIMO) technology represents one such approach and is a popular technology that has recently emerged for next-generation communication systems.

[0007] MIMO systems employ multiple (N) T (N) transmitting antennas and multiple (N) R Data is transmitted via N receiving antennas. T One transmitting antenna and N R A MIMO channel consisting of N receiving antennas can be decomposed into N S These are also known as independent channels in space, where N S ≤min{N T N R}. This N S Each of the independent channels corresponds to one dimension. If the additional dimension generated by these multiple transmit and receive antennas is utilized, the MIMO system can provide improved performance (such as higher throughput and greater reliability).

[0008] In a wireless network with multiple access points (APs) and multiple user stations (STAs), concurrent transmissions can occur on multiple channels (in both uplink and downlink directions) leading to different STAs. Several challenges exist in such systems. For example, APs may use different standards to transmit signals, such as IEEE 802.11n / a / b / g or IEEE 802.11ac (Very High Throughput (VHT)) standards. Receiver STAs may be able to detect the transmission pattern of the signal based on information included in the preamble of the transmitted packets.

[0009] Downlink multi-user MIMO (MU-MIMO) systems based on Space Division Multiple Access (SDMA) transmission can simultaneously serve multiple spatially separated STAs by applying beamforming at the AP's antenna array. Complex transmission precoding weights can be calculated by the AP based on Channel State Information (CSI) received from each of the supported STAs.

[0010] In a distributed MU-MIMO system, multiple access points (APs) can simultaneously serve multiple spatially separated STAs by coordinating beamforming performed by their antennas. For example, multiple APs can coordinate transmissions to each STA.

[0011] Overview

[0012] The systems, methods, and apparatus disclosed herein each have several innovative aspects, and no single aspect is solely responsible for the desired properties disclosed herein.

[0013] An innovative aspect of the subject matter described in this disclosure can be implemented in a wireless communication method. The method includes: transmitting an announcement frame from a first access point among a plurality of access points for performing a beamforming procedure for distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from that of the first access point. The method further includes: transmitting packets for measuring a channel from the first access point. The method further includes: receiving feedback information from the user terminal by the first access point based on the packets for measuring the channel. The method further includes: transmitting the distributed transmission by the first access point using the beamforming procedure. The beamforming procedure is based on the feedback information.

[0014] Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point among a plurality of access points. The first access point includes a memory and a processor coupled to the memory. The processor is configured to transmit an announcement frame for performing beamforming procedures for distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from that of the first access point. The processor is further configured to transmit packets for measuring channels. The processor is further configured to receive feedback information from the user terminal based on the packets for measuring channels. The processor is further configured to use the beamforming procedure to transmit the distributed transmission. The beamforming procedure is based on the feedback information.

[0015] Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point among a plurality of access points. The first access point includes means for transmitting an announcement frame to perform a beamforming procedure for distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from that of the first access point. The first access point further includes means for transmitting packets for measuring the channel. The first access point further includes means for receiving feedback information from the user terminal based on the packets for measuring the channel. The first access point further includes means for transmitting the distributed transmission using the beamforming procedure, wherein the beamforming procedure is based on the feedback information.

[0016] Another inventive aspect of the subject matter described in this disclosure can be implemented in a non-transient computer-readable medium that, when executed by at least one processor, causes the at least one processor to perform a wireless communication method. The method includes: transmitting an announcement frame from a first access point among a plurality of access points for performing a beamforming procedure for distributed transmission. The distributed transmission includes transmissions from the plurality of access points. The announcement frame includes at least one identifier of a user terminal in a basic service set different from that of the first access point. The method further includes: transmitting packets for measuring a channel from the first access point. The method further includes: receiving feedback information from the user terminal by the first access point based on the packets for measuring the channel. The method further includes: transmitting the distributed transmission by the first access point using the beamforming procedure. The beamforming procedure is based on the feedback information.

[0017] In some implementations, the method or first access point may include: transmitting from the first access point a group formation trigger for forming a group comprising multiple access points to perform beamforming procedures for distributed transmission. The method or first access point may further include: receiving an intention to participate from at least one of the multiple access points based on the group formation trigger. The method or first access point may further include: forming the group based on receiving the intention to participate from at least one of the multiple access points.

[0018] In some implementations, swarm formation triggering includes an indication of the number of spatial streams available for transmission to other access points.

[0019] In some implementations, the method or the first access point may include: transmitting a request frame requesting the feedback information by the first access point, wherein the request frame includes at least one identifier of a user terminal in a basic service set different from the basic service set of the first access point.

[0020] In some implementations, the announcement frame includes multiple spatial flows allocated to the multiple access points.

[0021] In some implementations, each of the plurality of access points transmits a separate packet for measuring the channel based on the announcement frame during a first time interval, and the plurality of access points use one or more of frequency division multiplexing, code division multiplexing, P-matrix, or time division multiplexing to multiplex the transmission of these separate packets.

[0022] In some implementations, each of the multiple access points transmits separate packets for measuring the channel during different time intervals based on the announcement frame.

[0023] In some implementations, each of the multiple access points transmits a separate announcement frame based on the announcement frame transmitted by the first access point.

[0024] In some implementations, each of the multiple access points transmits a separate packet for measuring the channel during the first time interval based on the announcement frame.

[0025] In some implementations, the method or the first access point may include: transmitting a request frame requesting the feedback information by the first access point, wherein the request frame includes at least one identifier of a user terminal in a basic service set different from the basic service set of the first access point.

[0026] Another innovative aspect of the subject matter described in this disclosure can be implemented in a wireless communication method. The method includes: transmitting from a first access point a group formation trigger for forming a group comprising a plurality of access points to perform beamforming procedures for distributed transmission. The method further includes: receiving an intention to participate from at least one of the plurality of access points based on the group formation trigger. The method further includes: forming the group based on receiving the intention to participate from at least one of the plurality of access points.

[0027] Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point. The first access point includes a memory and a processor coupled to the memory. The processor is configured to transmit a group formation trigger for forming a group comprising multiple access points to execute beamforming procedures for distributed transmission. The processor is further configured to receive a participation intention from at least one of the multiple access points based on the group formation trigger. The processor is further configured to form the group based on receiving the participation intention from at least one of the multiple access points.

[0028] Another innovative aspect of the subject matter described in this disclosure can be implemented in a first access point. The first access point includes means for transmitting a group formation trigger for forming a group comprising multiple access points to execute beamforming procedures for distributed transmission. The first access point further includes means for receiving an intention to participate from at least one of the multiple access points based on the group formation trigger. The first access point further includes means for forming the group based on receiving the intention to participate from at least one of the multiple access points.

[0029] Another inventive aspect of the subject matter described in this disclosure can be implemented in a non-transient computer-readable medium that, when executed by at least one processor, causes the at least one processor to perform a wireless communication method. The method includes: transmitting from a first access point a group formation trigger for forming a group comprising a plurality of access points to perform beamforming procedures for distributed transmission. The method further includes: receiving, based on the group formation trigger, an intention to participate from at least one of the plurality of access points. The method further includes: forming the group based on receiving the intention to participate from at least one of the plurality of access points.

[0030] In some implementations, the method or the first access point may include: wherein the group formation trigger includes an indication of the number of spatial streams available for transmission to other access points.

[0031] Details of one or more implementations of the subject matter described in this disclosure are set forth in the accompanying drawings and the following description. Other features, aspects, and advantages will become apparent from this description, the drawings, and the claims. It should be noted that the relative dimensions of the following drawings may not be drawn to scale. Brief description of the attached diagram

[0032] Figure 1 An example wireless communication network was explained.

[0033] Figure 2 The block diagrams for example access points and user terminals are explained.

[0034] Figure 3 The block diagram of the example wireless device is explained.

[0035] Figure 4 An example of a distributed multi-user multiple-input multiple-output (MU-MIMO) system is explained.

[0036] Figure 5 The signal diagram for an example joint trial procedure for distributed MU-MIMO is explained.

[0037] Figure 6 The signal diagram for an example sequential probe procedure used in distributed MU-MIMO is explained.

[0038] Figure 7 The signal diagram for an example air group formation procedure used in distributed MU-MIMO is explained.

[0039] Figure 8 Example operations for performing a probe procedure for distributed MU-MIMO are explained.

[0040] Figure 9 Example operations for performing over-the-air group formation procedures for distributed MU-MIMO are explained.

[0041] Similar reference numerals and naming conventions in the various figures indicate similar elements. Detailed description

[0042] The following description is directed to certain implementations in order to illustrate the innovative aspects of this disclosure. However, those skilled in the art will readily recognize that the teachings herein can be applied in many different ways. The described implementations can be implemented in any device, system, or network capable of transmitting and receiving RF signals according to any of the IEEE 16.11 or IEEE 802.11 standards. Bluetooth standard, Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Global System for Mobile Communications (GSM), GSM / General Packet Radio Service (GPRS), Enhanced Data GSM Environment (EDGE), Terrestrial Trunking Radio (TETRA), Wideband CDMA (W-CDMA), Evolved Data Optimized (EV-DO), 1xEV-DO, EV-DO Revision A, EV-DO Revision B, High-Speed ​​Packet Access (HSPA), High-Speed ​​Downlink Packet Access (HSDPA), High-Speed ​​Uplink Packet Access (HSUPA), Evolved High-Speed ​​Packet Access (HSPA+), Long Term Evolution (LTE), AMPS, or other known signals used for communication in wireless networks, cellular networks, or Internet of Things (IoT) networks (such as systems utilizing 3G, 4G, or 5G or technologies further implemented therefrom).

[0043] The techniques described herein can be used in a variety of broadband wireless communication systems, including those based on single-carrier transmission. For example, aspects may be advantageous for systems employing ultra-wideband (UWB) signals, including millimeter-wave signals. However, this disclosure is not intended to be limited to such systems, as other coded signals can benefit from similar advantages.

[0044] Various technologies can be incorporated into (implemented in or performed by) various wired or wireless devices (such as nodes). In some implementations, nodes include wireless nodes. Such wireless nodes can provide connectivity to or to a network (such as a wide area network (WAN), such as the Internet or a cellular network) via wired or wireless communication links, for example. In some implementations, wireless nodes may include access points or user terminals.

[0045] Multiple access points (APs) can transmit to multiple receiving user terminals at a time using distributed multiple-user multiple-input multiple-output (MU-MIMO). For example, multiple APs can transmit data to a given user terminal at a time, meaning that data transmission to that user terminal is distributed among the multiple APs. Multiple APs can utilize beamforming to spatially direct signals to the user terminal. In some implementations, for multiple APs performing distributed MU-MIMO, the multiple APs coordinate the beamforming performed by each AP to reduce interference with data transmission to the user terminal. In some implementations, the multiple APs execute procedures for forming an AP group to transmit to the user terminal, as discussed herein. Furthermore, in some implementations, to coordinate beamforming among the multiple APs, the multiple APs perform a probe procedure to collect feedback information from the user terminal regarding the radio channel between the multiple APs and the user terminal, as discussed herein. The multiple APs can use this feedback information to perform beamforming.

[0046] Specific implementations of the subject matter described in this disclosure can be implemented to achieve one or more of the following potential advantages. For example, APs can form a group for transmitting to user terminals using air signaling, rather than communicating on the backhaul. This can reduce data congestion on the backhaul. Additionally, the probe procedure can allow multiple APs to collect feedback information from user terminals in a coordinated manner. Accordingly, the feedback information for the multiple APs can include the channel conditions of each of the multiple APs in a time-coordinated manner, which can improve the accuracy of beamforming based on this feedback information. Furthermore, the probe procedure can limit the amount of data wirelessly exchanged to perform the probe procedure, which can reduce the bandwidth usage of the wireless channel.

[0047] Figure 1 The multiple access multiple input multiple output (MIMO) system 100 with access points and user terminals is explained. For simplicity, Figure 1 Only one access point 110 is shown. An access point (AP) is generally a fixed station that communicates with user terminals and may be referred to as a base station or some other term. User terminals may be fixed or mobile and may be referred to as mobile stations, stations (STAs), clients, wireless devices, or some other term. User terminals may be wireless devices, such as cellular phones, personal digital assistants (PDAs), handheld devices, wireless modems, laptops, personal computers, etc.

[0048] Access point 110 can communicate with one or more user terminals 120 on both downlink and uplink at any given time. The downlink (i.e., the forward link) is the communication link from the access point to the user terminal, while the uplink (i.e., the reverse link) is the communication link from the user terminal to the access point. User terminals can also communicate peer-to-peer with other user terminals. System controller 130 is coupled to each access point and provides coordination and control over these access points.

[0049] The MIMO system 100 employs multiple transmit antennas and multiple receive antennas for downlink and uplink data transmission. Access point 110 is equipped with N... ap There are multiple antennas, and for downlink transmission, this represents multiple inputs (MI), while for uplink transmission, it represents multiple outputs (MO). The set N of selected user terminals 120... u Commonly, this represents multiple outputs for downlink transmissions and multiple inputs for uplink transmissions. In some implementations, if used for these N... u If the data symbol streams of a user terminal are not multiplexed in terms of code, frequency, or time by some means, then it is expected that N ap ≥N u≥1. If the data symbol stream can be multiplexed using different code channels under CDMA, or using disjoint sub-band sets under OFDM, then N u It can be greater than N ap Each selected user terminal transmits user-specific data to and receives user-specific data from the access point. Generally, each selected user terminal may be equipped with one or more antennas (i.e., N). ut ≥1). This N u Each selected user terminal may have the same or different number of antennas.

[0050] MIMO system 100 can be a time-division duplex (TDD) system or a frequency-division duplex (FDD) system. In a TDD system, the downlink and uplink share the same frequency band. In an FDD system, the downlink and uplink use different frequency bands. MIMO system 100 can also utilize a single carrier (such as a carrier frequency) or multiple carriers for transmission. Each user terminal can be equipped with a single antenna (e.g., to suppress costs) or multiple antennas (e.g., where additional costs can be supported). MIMO system 100 can represent a high-speed wireless local area network (WLAN) operating in the 60 GHz frequency band.

[0051] Figure 2 A block diagram of an access point / base station 110 and two user terminals / user equipment 120m and 120x in a MIMO system 100 is shown. Access point 110 is equipped with N... ap Each antenna is 224a to 224ap. The user terminal 120m is equipped with N... ut,m Each antenna is 252 mA to 252 mA, while the user terminal 120x is equipped with N ut,x Each antenna ranges from 252xa to 252xu. Access point 110 is a transmitting entity for the downlink and a receiving entity for the uplink. Each user terminal 120 is a transmitting entity for the uplink and a receiving entity for the downlink. As used herein, a "transmitting entity" is an independently operating device or apparatus capable of transmitting data via a frequency channel, and a "receiving entity" is an independently operating device or apparatus capable of receiving data via a frequency channel. In the following description, the subscript "dn" indicates the downlink, the subscript "up" indicates the uplink, and N... up One user terminal is selected for simultaneous transmission on the uplink, while N dn One user terminal was selected for simultaneous transmission on the downlink. In addition, N up It can be equal to or not equal to N dn And N up and N dnIt can include static values ​​or can be varied for each scheduling interval. Beamforming (such as beam steering) or some other spatial processing technique can be used at the access point and user terminal.

[0052] On the uplink, at each user terminal 120 selected for uplink transmission, the TX data processor 288 receives traffic data from the data source 286 and control data from the controller 280. The TX data processor 288 processes (such as encoding, interleaving, and modulation) the user terminal's traffic data {d} based on the coding and modulation scheme associated with the rate selected for that user terminal. up,m} and provide data symbol stream {s up,m}. TX space processor 290 pairs of data symbol streams {s up,m} Perform space processing and provide it to N ut,m N antennas ut,m Each transmitter unit (TMTR) 254 receives and processes (such as converting to analog, amplifying, filtering, and up-converting) the corresponding transmit symbol stream to generate an uplink signal. ut,m Each transmitter unit 254 provides N ut,m A number of uplink signals are used to transmit from N ut,m Transmission from antenna 252 to access point 110.

[0053] Number N up Each user terminal can be scheduled to transmit simultaneously on the uplink. Each of these user terminals performs spatial processing on its data symbol stream and transmits its transmitted symbol stream set to the access point on the uplink.

[0054] At access point 110, N ap Antennas 224a to 224ap transmit all N data from the uplink. up Each user terminal receives an uplink signal. Each antenna 224 provides the received signal to its respective receiver unit (RCVR) 222. Each receiver unit 222 performs processing complementary to the processing performed by the transmitter unit 254 and provides the received symbol stream. The RX space processor 240 receives the signal from N. ap N of the receiver units 222 ap Each received symbol stream performs receiver spatial processing and provides N. up Each recovered uplink data symbol stream. Receiver spatial processing is performed using Channel Correlation Matrix Inversion (CCMI), Minimum Mean Square Error (MMSE), Successive Interference Cancellation (SIC), or some other technique. up,m} refers to the data symbol streams {s} transmitted by their respective user terminals. up,mThe RX data processor 242 estimates the uplink data symbol stream {s} for each recovered uplink data symbol stream. up,m The recovered uplink data symbol stream is processed (such as demodulation, deinterleaving, and decoding) at a rate of}. up,m The decoded data is obtained. The decoded data from each user terminal may be provided to the data trap 244 for storage and / or to the controller 230 for further processing.

[0055] On the downlink, at access point 110, TX data processor 210 receives N data from data source 208 scheduled for downlink transmission. dn The data includes traffic data from individual user terminals, control data from controller 230, and possibly other data from scheduler 234. Various types of data can be transmitted on different transport channels. TX data processor 210 processes (such as encoding, interleaving, and modulation) the traffic data of each user terminal based on a rate selected for each terminal. TX data processor 210 is for N... dn Each user terminal provides N dn One downlink data symbol stream. TX space processor 220 to N dn Each downlink data symbol stream undergoes spatial processing and is used for N. ap Each antenna provides N ap Each transmitter unit (TMTR) 222 receives and processes its respective transmit symbol stream to generate downlink signals. ap Each transmitter unit 222 provides N ap A downlink signal is provided from N ap One antenna 224 transmits data to the user terminal.

[0056] At each user terminal 120, N ut,m Antenna 252 receives N from access point 110 ap Each downlink signal. Each receiver unit (RCVR) 254 processes the received signal from the associated antenna 252 and provides the received symbol stream. The RX space processor 260 pairs the signals from N... ut,m N receiver units 254 ut,m The received symbol stream is processed by the receiver spatial processing and the recovered downlink data symbol stream is provided to the user terminal 120. dn,m Receiver spatial processing can be performed according to CCMI, MMSE, or other known techniques. The RX data processor 270 processes (such as demodulation, deinterleaving, and decoding) the recovered downlink data symbol stream to obtain decoded data for the user terminal.

[0057] At each user terminal 120, N ut,mAntenna 252 receives N from access point 110 ap Each downlink signal. Each receiver unit (RCVR) 254 processes the received signal from the associated antenna 252 and provides the received symbol stream. The RX space processor 260 pairs the signals from N... ut,m N receiver units 254 ut,m The received symbol stream is processed by the receiver spatial processing and the recovered downlink data symbol stream is provided to the user terminal. dn,m Receiver spatial processing is performed according to CCMI, MMSE, or some other technique. The RX data processor 270 processes (such as demodulation, deinterleaving, and decoding) the recovered downlink data symbol stream to obtain the decoded data for the user terminal.

[0058] Figure 3 The various components that can be utilized in the wireless device 302 that may be employed within the MIMO system 100 are explained. The wireless device 302 is an example of a device that can be configured to implement the various methods described herein. The wireless device 302 may be an access point 110 or a user terminal 120.

[0059] Wireless device 302 may include processor 304 that controls the operation of wireless device 302. Processor 304 may also be referred to as a central processing unit (CPU). Memory 306, which may include both read-only memory (ROM) and random access memory (RAM), provides instructions and data to processor 304. A portion of memory 306 may also include non-volatile random access memory (NVRAM). Processor 304 typically performs logical and arithmetic operations based on program instructions stored in memory 306. Instructions in memory 306 can be executed to implement the methods or operations described herein (such as regarding...). Figure 8 Or those methods or operations described in 9).

[0060] The wireless device 302 may also include a housing 308, which may include a transmitter 310 and a receiver 312 to allow data transmission and reception between the wireless device 302 and a remote location. The transmitter 310 and receiver 312 may be combined into a transceiver 314. Multiple transmitting antennas 316 may be attached to the housing 308 and electrically coupled to the transceiver 314. The wireless device 302 may also include (not shown) multiple transmitters, multiple receivers, and multiple transceivers.

[0061] Wireless device 302 may also include a signal detector 318, which can be used to detect and quantize the signal level received by transceiver 314. Signal detector 318 can detect signals such as total energy, energy per symbol per subcarrier, power spectral density, and other signals. Wireless device 302 may also include a digital signal processor (DSP) 320 for processing signals.

[0062] The various components of the wireless device 302 can be coupled together by a bus system 322, which may include a power bus, a control signal bus, and a status signal bus in addition to a data bus.

[0063] Distributed MU-MIMO

[0064] Such as about Figure 1-3 As discussed, a single AP 110 can transmit to multiple receiving user terminals 120 at a time using multi-user MIMO (MU-MIMO). AP 110 includes multiple antennas 224. By using the multiple antennas 224, AP 110 can utilize beamforming to spatially focus the energy of the transmitted signal (e.g., as a spatial stream to user terminals 120). To perform beamforming, AP 110 can exchange frames with user terminals 120 to measure the channel between AP 110 and user terminals 120. For example, AP 110 can transmit null data packets (NDPs) including one or more long training fields (LTFs) used by user terminals 120 to measure the channel. User terminals 120 can generate channel feedback information (such as a feedback matrix) based on this channel measurement and send the feedback matrix to AP 110. Using the feedback matrix, AP 110 can derive a guiding matrix used by AP 110 to determine how to transmit signals on each antenna 224 of AP 110 to perform beamforming. For example, the guiding matrix can indicate the phase shift, power level, etc., used to transmit signals on each antenna 224. For example, AP 110 can be configured to perform beamforming techniques similar to those described in the 802.11ac standard.

[0065] In some implementations, multiple APs 110 can be configured to transmit to one or more receiving user terminals 120 each time using distributed MU-MIMO. Various types of MU-MIMO transmissions can exist, including coordinated beamforming (COBF) and joint processing transmission (JT).

[0066] Figure 4 The distributed MU-MIMO system 400 has been explained. As shown, system 400 includes AP 110a and AP 110b. In some implementations, AP 110a and 110b refer to... Figure 1AP 110 is described. AP 110a is shown as part of a first Basic Service Set (BSS) (i.e., BSS1), and AP 110b is shown as part of a second BSS (i.e., BSS2). AP 110a and AP 110b can be adjacent APs. Furthermore, a portion of the coverage area of ​​AP 110a may overlap with a portion of the coverage area of ​​BSS2, resulting in an overlapping BSS (OBSS) situation. Communication between AP 110a and user terminals in BSS1 can be referred to as BSS communication. Similarly, communication between AP 110b and user terminals in BSS2 can be referred to as BSS communication. Furthermore, communication between AP 110a and user terminals in BSS2 can be referred to as OBSS communication, and communication between AP 110b and user terminals in BSS1 can also be referred to as OBSS communication.

[0067] In COBF, signals (such as data) for a given user terminal can be transmitted by only a single AP. For example, user terminals 120a and 120b are shown as part of BSS1, so only AP 110a can transmit signals intended for user terminals 120a and 120b. Similarly, user terminals 120c and 120d are shown as part of BSS2, so only AP 110b can transmit signals intended for user terminals 120c and 120d. In some implementations, user terminals 120a to 120d refer to... Figure 1 User terminal 120 is described. However, as discussed, the coverage areas of AP 110a and AP 110b can overlap, so the signal transmitted by AP 110a can reach user terminals 120c and 120d in BSS2 as OBSS signals. Similarly, the signal transmitted by AP 110b can reach user terminals 120a and 120d in BSS1 as OBSS signals. In COBF, AP 110a and 110b can be configured to perform beamforming to form nulls in the direction of the user terminals in the OBSS, such that any signals received at the OBSS user terminals have low power. For example, AP 110a can be configured to perform beamforming to form nulls toward user terminals 120c and 120d, and AP 110b can be configured to form nulls toward user terminals 120a and 120b to limit interference at the user terminals. Accordingly, in COBF, the AP is configured to form spatial elements for OBSS user terminals and to beamform signals destined for user terminals within the BSS.

[0068] In JT, signals for a given user terminal can be transmitted by multiple APs. For example, one or more user terminals 120a to 120d can receive signals from both AP 110a and AP 110b. For multiple APs to transmit data to the user terminal, each AP may need a copy of the data to be transmitted to that user terminal. Accordingly, these APs may need to exchange data with each other (e.g., via backhaul) for transmission to the user terminal. For example, AP 110a may have data to be transmitted to user terminal 120a and may further transmit that data to AP 110b via backhaul. AP 110a and AP 110b may then beamform the signal including the data destined for user terminal 120a.

[0069] In some implementations, within a JT, the antennas of multiple APs transmitting to one or more user terminals can be considered as a large antenna array (such as a virtual antenna array) used for beamforming and signal transmission. Accordingly, similar beamforming techniques, as discussed and used for transmission from multiple antennas of a single AP to one or more user terminals, can be alternatively used for transmission from multiple antennas of multiple APs. For example, the same beamforming used for transmission from multiple antennas of AP 110a can be applied to transmission from multiple antennas of both AP 110a and AP 110b. Multiple antennas of multiple APs can be able to form signals on multiple spatial streams (e.g., limited by the number of antennas). Accordingly, each user terminal can receive signals on one or more of these spatial streams. In some implementations, a specific number of spatial streams can be allocated to each AP for transmission to each user terminal in the BSS of that AP. Each spatial stream can be identified by a spatial stream index.

[0070] In some implementations, various factors can affect distributed MU-MIMO. For example, one factor can be the accuracy of channel feedback. As discussed, to perform beamforming, each AP can exchange signals with each user terminal on a communication channel, and each user terminal can measure the channel based on the exchanged signals. Each user terminal can further send information about the channel measurements back to each AP as channel feedback information. Each AP can use this channel feedback information to perform beamforming. However, the channel conditions may change between when each AP receives the channel feedback information and when each AP transmits signals on the channel. This is known as channel aging. Furthermore, inaccuracies may exist due to the quantization of information included in the channel feedback information. This can affect both COBF and JT distributed MU-MIMO, leading to leakage and interference.

[0071] Another factor could be the phase shift between the APs. For example, each AP might transmit in a different phase due to timing synchronization differences. Furthermore, the phase difference might drift or change between when receiving channel feedback information and when each AP transmits to its respective user terminal (e.g., due to phase noise, timing drift, carrier frequency offset (CFO) drift, etc.). This change in phase difference may not significantly affect COBF because each AP performs beamforming independently. However, this change in phase difference can affect JT because all APs perform beamforming together.

[0072] Another factor could be timing offset. For example, the delay spread, filter delay, and arrival time spread of each AP using JT and COBF may need to be focused on the cyclic prefix (CP). Additionally, for JT, relative timing offset (i.e., the change in timing offset between when measuring channel feedback information and when transmitting signals) may also affect phase offset and may need to be further controlled.

[0073] Another factor could be the CFO. In COBF, the synchronization requirements for the CFO may be lower compared to JT.

[0074] Another factor could be gain mismatch, where different APs use different gain states when measuring the channel of a user terminal. This can have a greater impact on JT than on COBF. In some implementations of COBF, the maximum gain can be approximately 75% of the minimum number of transmit antennas for any given AP. In some implementations of JT, the maximum gain can be approximately 75% of the sum of the transmit antennas of all APs.

[0075] In some implementations of MU-MIMO where a single AP transmits to multiple user terminals, all transmit antennas of the AP are probed together to perform channel measurements for beamforming. This means that all transmit antennas transmit NDP during the same transmission time interval (e.g., TTI, frame, subframe, etc.). All antennas can be probed together because if NDP for each antenna were transmitted at different TTIs, they could be transmitted in different phases, and the receiver automatic gain control (RxAGC) at each user terminal receiving these NDPs (which may affect the gain applied to the received signal) could be different for different TTIs, potentially making it difficult to stitch measurements from different NDPs together. Furthermore, the relative timing (e.g., relative to the start of the TTI) between all transmit antennas used to transmit NDP at the same TTI is constant for all transmit antennas and remains the same for both transmitting NDP and later transmitting data to user terminals based on channel feedback information. Therefore, there is no change in relative timing between NDP transmission and data transmission, thus ensuring better beamforming.

[0076] In some implementations, all antennas for multiple APs can be probed together to transmit NDPs at the same TTI for joint probe-through (JT) in the joint probe-through procedure, thus avoiding the problems discussed. In some implementations, NDPs from different APs can be probed at the same TTI using one or more techniques such as Time Division Multiplexing (TDM), Code Division Multiplexing (CDM) (e.g., using a P-matrix), and Frequency Division Multiplexing (FDM)).

[0077] For COBF, the beamforming direction of an AP does not depend on the channel between the user terminal and other APs. Accordingly, only loose synchronization may be required between APs. Therefore, for COBF, in addition to the joint probe procedure, a sequential probe procedure can also be used, in which each AP probes one at a time in separate TTIs and transmits the NDP at a different TTI for each AP.

[0078] Figure 5 The signal diagram for an example joint probe procedure for distributed MU-MIMO is explained. As shown, three APs (i.e., AP 110a, AP 110b, and AP 110c) can coordinate to perform distributed MU-MIMO transmissions to two user terminals (i.e., user terminal 120a and user terminal 120c). In some implementations, APs 110a to 110c and user terminals 120a and 120c refer to... Figure 1 AP 110 and user terminal 120 are described. However, it should be noted that distributed MU-MIMO transmissions can be made from any number of APs to any number of one or more user terminals. In this signal diagram, time is shown as increasing along the x-axis. Initially, any of the APs (shown here as AP 110a) transmits an NDP announcement (NDPA) frame. The NDPA may be a control frame indicating that an NDP will be transmitted. In some implementations, the NDPA includes information identifying one or more user terminals 120 to which the upcoming NDP is directed, so that one or more user terminals receiving the NDPA know to listen for the NDP to perform channel measurements. Accordingly, in this example, the NDPA may include identifiers for user terminals 120a and 120c. Since the NDPA sent from AP 110a can identify user terminals 120 associated with other APs, the NDPA can identify user terminals in the BSS and OBSS of AP 110a.

[0079] In some implementations, NDPA may include allocation information for spatial flows of AP 110. For example, this allocation information may include a mapping or association of spatial flow indices to AP 110. The allocation of spatial flows for a particular AP 110 may indicate that the spatial flow will be used for transmissions in the BSS of that particular AP 110.

[0080] In some implementations, NDPA may include allocation information for the spatial stream of user terminal 120. For example, the allocation information may include a mapping or association between spatial stream indices and user terminal 120. The allocation of the spatial stream to user terminal 120 may indicate that the spatial stream will be used for transmission to user terminal 120.

[0081] In some implementations, NDPA may include the identifiers (such as BSS ID, MAC address, etc.) of AP 110 (AP 110a to 110c in this example) that will participate in the joint communication protocol.

[0082] After AP 110a transmits the NDPA, each of APs 110a to 110c simultaneously (e.g., during the same TTI) transmits the NDP. In some implementations, APs 110a to 110c synchronize the transmission of the NDP based on the NDPA. For example, each AP 110a to 110c can be configured to transmit the NDP after receiving the NDPA, following a fixed time interval (e.g., a Short Interframe Spacing (SIFS)). In some implementations, APs 110a to 110c synchronize the transmission of the NDP via backhaul. User terminals 120a and 120c can receive each NDP.

[0083] In some implementations, each NDP is multiplexed to avoid interference with each other. Specifically, each LTF from each NDP of multiple APs can be multiplexed. In some implementations, FDM is used across APs to multiplex each LTF. Furthermore, in some implementations, FDM is used to multiplex each spatial stream belonging to each AP. For example, if there are N+M+X spatial streams, N belonging to AP 110a, M to AP 110b, and X to AP 110c, then each N+M+X stream is transmitted on a different frequency modulus for each symbol of the LTF. Furthermore, the LTF is transmitted on N+M+X symbols. Therefore, each stream is transmitted on each frequency modulus. Thus, each stream of each AP can be estimated on each frequency modulus.

[0084] In some implementations, FDM and P matrices are used to multiplex NDP. In some implementations, the P matrix is ​​an orthogonal code, with one dimension being the spatial stream and the other dimension being the LTF symbols. Accordingly, in some implementations, the P matrix is ​​used to multiplex the spatial stream of individual AP 110, but different AP 110s transmit for each LTF symbol on non-overlapping frequency moduli. Furthermore, the LTF is transmitted on enough symbols to allow each AP to transmit on every frequency moduli.

[0085] In some implementations, only the P matrix is ​​used to reuse the NDP. Specifically, the P matrix can have a size that can accommodate all spatial flows of all AP 110.

[0086] In some implementations, only TDM is used to multiplex NDP, where each spatial stream is assigned to an LTF symbol and transmitted on all frequency moduli of that LTF symbol.

[0087] In some implementations, TDM and P matrices are used to multiplex NDP. Correspondingly, in some implementations, P matrices are used to multiplex the spatial stream of individual AP 110, but different AP 110s transmit on different LTF symbols (such as all frequency modulations of LTF symbols).

[0088] Furthermore, after APs 110a to 110c transmit the NDP, one of the APs (such as AP 110a) transmits a trigger request for feedback (such as channel feedback information) to each of the user terminals 120a and 120c to which the NDP was transmitted. For example, this trigger request may be transmitted after a fixed period of time (such as SIFS) following the transmission of the NDP. Therefore, the trigger request from AP 110a may include identifiers of user terminals 120a and 120c. Since the trigger request sent from AP 110a can identify user terminals 120 associated with other APs, it can identify user terminals in the BSS and OBSS of AP 110a.

[0089] User terminals 120a and 120c, identified in the trigger request, can send channel feedback information to AP 110a based on the trigger request. As shown, user terminal 120 can transmit channel feedback information in parallel (e.g., using uplink orthogonal frequency division multiple access (UL-OFDMA), UL MU-MIMO, etc.). However, in some implementations, user terminals can transmit feedback information serially (e.g., sequentially). In some implementations, instead of AP 110a sending a single trigger request for multiple user terminals, AP 110a can send multiple trigger requests (e.g., sequentially), sending one trigger request for each user terminal.

[0090] Furthermore, as discussed, the remaining APs 110b and 110c can transmit trigger requests and receive feedback from user terminals 120a and 120c. As shown, each AP 110 transmits trigger requests and receives feedback information separately. However, in some implementations, each AP 110 can transmit trigger requests and receive feedback information in parallel (e.g., using OFDMA, MIMO, etc.).

[0091] Based on the received channel feedback information, APs 110a-110c can perform beamforming (such as by deriving the guidance matrix) and transmit data to user terminals 120a and 120c. In some implementations, APs 110a-110c can transmit data after the probe phase in a specific TTI, or in some implementations, AP 110a can send a trigger frame to indicate the TTI and coordinate data transmission. As discussed, NDP from multiple APs 110 can be synchronized via backhaul or pre-corrected based on received NDPA. Accordingly, in some implementations, for distributed MU-MIMO data transmission to user terminals 120a and 120c, APs 110 can utilize the same frequency and time synchronization used for NDP to ensure correct beamforming. In some implementations, the transmit power backoff used by each AP can be kept constant between the NDP and data transmission of each AP to ensure correct beamforming (such as preventing phase rotation).

[0092] In some implementations, the NDP transmitted from each AP 110a to 110c can carry the same preamble for all APs 110a to 110c. This preamble can be used by legacy devices that do not support distributed MU-MIMO to back off transmission.

[0093] In some implementations, different APs 110 may have different local oscillators. Therefore, when each AP 110 transmits NDP, phase drift may exist between them. Accordingly, in order for each user terminal 120 to determine when to listen for NDP, they may need to track the phase drift of each AP 110. In some implementations, if FDM is used to multiplex transmissions from each AP, phase tracking of different APs can be performed by tracking pilots transmitted at different frequency modulations for each AP. In some implementations, if TDM is used to multiplex transmissions from each AP, symbol transmissions for different APs can be interleaved instead of sequentially transmitting symbols for a single AP for better phase tracking (e.g., phase drift may change at different times, so tracking drift for each AP over a longer period may be beneficial).

[0094] In some implementations, if a P-matrix is ​​used to multiplex transmissions from each AP, non-overlapping frequency modulations can be assigned to transmissions from different APs for phase tracking. Alternatively, multi-stream pilots can be used, where one stream per AP is transmitted on the pilot frequency modulation to track the phase of each AP, or where the number of streams transmitted by each AP on the pilot frequency modulation is equal to the number of streams given to that AP for transmitting LTF.

[0095] Figure 6 The signaling diagram for an example sequential probe procedure used in distributed MU-MIMO is explained. In some implementations, initially, any of the APs (shown here as AP 110a) as per... Figure 5 The NDPA is transmitted as described. AP 110a then transmits NDP individually to user terminals 120a and 120c. As discussed, AP 110a then transmits one or more trigger requests requesting feedback to user terminals 120a and 120c. User terminals 120a and 120c then transmit channel feedback information to AP 110a serially or in parallel. After user terminals 120a and 120c transmit channel feedback information to AP 110a, AP 110b transmits NDP individually to user terminals 120a and 120c, transmits one or more trigger requests requesting feedback, and receives channel feedback information. Accordingly, a single NDPA is transmitted to initiate a probe procedure for multiple APs, but NDPs are transmitted sequentially.

[0096] In some implementations, although not shown, for sequential probe procedures, instead of one AP 110 transmitting one NDPA for multiple NDPs transmitted by multiple AP 110s, each AP 110 can sequentially transmit NDPAs and perform probe procedures. Accordingly, each AP 110 transmits its own NDPA (such as...) before sequentially transmitting NDPs. Figure 6 (as shown in the image).

[0097] In both of these sequential probe procedures, the NDPA can still identify user terminals associated with other APs besides the transmitting AP, and thus the NDPA can identify user terminals in the transmitting AP's BSS and OBSS. Furthermore, trigger requests sent from the transmitting AP can still identify user terminals associated with other APs, and thus the trigger requests can identify user terminals in the transmitting AP's BSS and OBSS.

[0098] In some implementations, the transmit power backoff used by each AP can be kept constant between the NDP and data transmission at each AP to ensure proper beamforming (such as preventing phase rotation). Furthermore, in some implementations, for sequential probe protocols, the RxAGC at the user terminal can be kept constant between the probe times of one AP and the probe times of another to prevent gain shift. In some implementations, NDPA can (e.g., implicitly) instruct the user terminal to keep the RxAGC constant.

[0099] As discussed, in distributed MU-MIMO, multiple AP 110s can coordinate beamforming. To this end, in some implementations, an AP 110 group is formed to perform distributed MU-MIMO. In some implementations, the AP 110 group can be formed by exchanging information on the backhaul. In some implementations, the AP 110 group can be formed by exchanging information over the air. For example, one AP 110 can invite other AP 110s to join the distributed MU-MIMO transmission and exchange frames with other AP 110s to form a group.

[0100] Figure 7 The signal diagram for an example air group formation procedure used in distributed MU-MIMO is explained.

[0101] Initially, AP 110 (AP 110a in this example) transmits a group formation trigger. For example, if AP 110a is scheduled for DL ​​MU-MIMO transmission and not using all available space streams at AP 110a for transmission, AP 110a can transmit a group formation trigger so that other AP 110s can use the remaining space streams. The group formation trigger may include the number of streams that AP 110a has available for additional transmissions.

[0102] Neighboring APs of AP 110a (APs 110b and 110c in this example) can receive a group formation trigger and determine whether they will join AP 110a in a distributed MU-MIMO transmission. For example, any neighboring AP with data to transmit can determine whether to join a group with AP 110a. For neighboring APs 110b and 110c that determine they want to join the group, they each transmit their intention to participate to AP 110a. The intention to participate may include, for example, a list of user terminals 120 to which AP 110a wishes to transmit data in a distributed MU-MIMO transmission. Furthermore, the intention to participate may include, for example, the number of spatial streams expected for transmission per user terminal. In some implementations, AP 110a uses open-loop MU-MIMO (similar to uplink MU-MIMO) or UL-OFDMA to transmit the intention to participate in parallel.

[0103] AP 110a can receive the intention to participate, determine the group, and perform probe phases and distributed MU-MIMO transfers, such as using the techniques described herein. In some implementations, if AP 110a receives an intention to participate requesting more spatial flows than AP 110a has available spatial flows, AP 110a can choose which APs to include in the group and which flows to assign to which APs.

[0104] In some implementations, AP 110a may transmit a final group configuration before the probe phase and after AP 110a receives the intent to participate. The final group configuration may include a list of APs 110 included in the group. Additionally, in some implementations, the final group configuration indicates which spatial flows are assigned to which APs 110 (e.g., by mapping AP identifiers to flow indices). In some implementations, the final group configuration may include a list of user terminals 120 to which the AP 110 group will send distributed transmissions (e.g., identifiers of user terminals 120). Furthermore, in some implementations, the final group configuration indicates which spatial flows, or how many spatial flows, are assigned to which user terminals 120 (e.g., by mapping user terminal identifiers to flow indices). In some implementations, instead of AP 110a transmitting the final group configuration, this information is included in the NDPA, as discussed in the probe phase.

[0105] Figure 8 Example operation 800 for performing a probe procedure for distributed MU-MIMO according to some implementations of this disclosure is described. According to some implementations, operation 800 may be performed by an access point (such as access point 110).

[0106] In 802, a first access point among a plurality of access points transmits a notice frame (such as NDPA) to perform beamforming procedures for distributed transmissions (such as distributed MU-MIMO). In some implementations, the distributed transmissions include transmissions from the plurality of access points. In some implementations, the notice frame includes at least one identifier of a user terminal from a base service set different from that of the first access point.

[0107] At 804, the first access point transmits packets (such as NDP) for measuring the channel to one or more user terminals. At 806, the first access point receives feedback information from the user terminal (and one or more other user terminals) based on the packets for measuring the channel.

[0108] At 808, the first access point uses a beamforming procedure to transmit the distributed transmission (such as the distributed transmission transmitted by multiple access points). The beamforming procedure is based on the feedback information.

[0109] Figure 9 Example operation 900 for performing an air group formation procedure for distributed MU-MIMO, according to some implementations of this disclosure, is described. According to some implementations, operation 900 may be performed by an access point (such as access point 110).

[0110] At 902, the first access point transmits a group formation trigger for forming a group comprising multiple access points to perform beamforming procedures for distributed transmissions (such as distributed MU-MIMO). At 904, the first access point receives an intention to participate from at least one of the multiple access points based on the group formation trigger. At 906, the first access point forms the group based on receiving the intention to participate from the at least one of the multiple access points.

[0111] The various operations of the methods described above can be performed by any suitable device capable of performing the corresponding functions. This device may include various hardware and software components and modules, including but not limited to circuits, application-specific integrated circuits (ASICs), or processors. Generally, in the context of operations illustrated in the accompanying drawings, those operations can be performed by any suitable corresponding paired device plus functional components.

[0112] According to some implementations, such devices can be implemented by a processing system configured to perform the corresponding functions by implementing the various algorithms described above (such as in hardware or by executing software instructions).

[0113] For example, the means for determining and the means for scheduling may include Figure 2 The AP 110 or user terminal 120 described herein may include one or more processors (such as RX data processors 242 and 270, controllers 230 and 280, and TX data processors 210, 288). Additionally, the means for transmitting and the means for receiving may include one or more transmitters / receivers (such as one or more transceivers TX / RX 222 and 254) or one or more antennas (such as one or more antennas 224 and 252).

[0114] As used in this article, the phrase “at least one” referring to a list of items means any combination of those items, including a single member. As an example, “at least one of a, b, or c” is intended to cover: a, b, c, ab, ac, bc, and abc.

[0115] The various descriptive logics, logic blocks, modules, circuits, and algorithmic processes described in conjunction with the implementations disclosed herein can be implemented as electronic hardware, computer software, or a combination of both. This interchangeability between hardware and software has been generally described in its functional form and is explained in the various descriptive components, blocks, modules, circuits, and processes described above. Whether such functionality is implemented in hardware or software depends on the specific application and the design constraints imposed on the overall system.

[0116] Hardware and data processing means for implementing the various descriptive logics, logic blocks, modules, and circuits described in conjunction with the implementations disclosed herein may be implemented or executed using a general-purpose single-chip or multi-chip processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. A general-purpose processor may be a microprocessor, or any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors cooperating with a DSP core, or any other such configuration. In some implementations, specific processes and methods may be executed by a circuit system dedicated to a given function.

[0117] In one or more implementations, the described functionality may be implemented in hardware, digital electronic circuit systems, computer software, firmware (including the structures disclosed in this specification and their structural equivalents), or any combination thereof. Implementations of the subject matter described in this specification may also be implemented as one or more computer programs, i.e., one or more modules of computer program instructions encoded on a computer storage medium for execution by a data processing apparatus or for controlling the operation of a data processing apparatus.

[0118] If implemented in software, the functions can be stored or transmitted as one or more instructions or codes on or through a computer-readable medium. The processes of the methods or algorithms disclosed herein can be implemented in a processor-executable software module that can reside on a computer-readable medium. Computer-readable media include both computer storage media and communication media, including any medium that can be implemented to transfer a computer program from one location to another. Storage media can be any available medium accessible to a computer. By way of example and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other medium that can be used to store desired program code in the form of instructions or data structures and is accessible to a computer. Any connection can also be properly referred to as a computer-readable medium. As used herein, disk and disc include compact discs (CDs), laser discs, optical discs, digital multi-purpose discs (DVDs), floppy disks, and Blu-ray discs, where disks typically reproduce data magnetically and discs reproduce data optically using lasers. The above combinations should also be included within the scope of computer-readable media. In addition, the operation of a method or algorithm may reside as one of the codes and instructions, or any combination or set of codes and instructions, on a machine-readable medium and a computer-readable medium that may be incorporated into a computer program product.

[0119] Various modifications to the implementations described in this disclosure may be apparent to those skilled in the art, and the general principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Therefore, the claims are not intended to be limited to the implementations shown herein, but are to be granted the broadest scope consistent with this disclosure, the principles disclosed herein, and the novel features.

[0120] In addition, those skilled in the art will readily appreciate that the terms “upper” and “lower” are sometimes used for the convenience of describing the figures and indicate a relative position corresponding to the orientation of the figures on the correctly oriented page, and may not reflect the true orientation of any device as implemented.

[0121] Some features described in this specification in the context of separate implementations may also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation may also be implemented separately or in any suitable sub-combination in multiple implementations. Furthermore, although features may be described above as operating in certain combinations and even originally claimed in this way, one or more features from the claimed combination may be removed from that combination in some cases, and the claimed combination may be for sub-combinations or variations thereof.

[0122] Similarly, although the operations are depicted in a specific order in the accompanying drawings, this should not be construed as requiring such operations to be performed in the specific order shown or sequentially, or requiring the performance of all explained operations to achieve the desired result. Furthermore, the drawings may schematically depict one or more example processes in the form of flowcharts. However, other operations not depicted may be incorporated into the schematically explained example processes. For example, one or more additional operations may be performed before, after, simultaneously with, or between any explained operation. In some environments, multitasking and parallel processing may be advantageous. Moreover, the separation of the various system components in the implementations described above should not be construed as requiring such separation in all implementations, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations also fall within the scope of the appended claims. In some cases, the actions recited in the claims may be performed in a different order and still achieve the desired result.

Claims

1. A method for wireless communication at a first access point, comprising: Transmit a group formation trigger to multiple access points for forming a group that includes one or more of the multiple access points; Based on the group formation trigger, the intention to participate is received from at least a second access point among the plurality of access points; Based on the stated intention to participate, a group is formed including the first access point and at least the second access point, wherein forming the group includes transmitting a group configuration to at least the second access point; as well as Beamforming is used to transmit distributed transmissions, wherein the distributed transmissions include transmissions from the first access point and transmissions from at least the second access point.

2. The method of claim 1, further comprising: A spatial stream is allocated to at least the second access point in the group, and the at least the second access point in the group will transmit packets for measuring the channel on the spatial stream; as well as An announcement frame is transmitted to the user terminal and at least the second access point in the group to perform the beamforming procedure for the distributed transmission, wherein the announcement frame includes the spatial stream allocation.

3. The method of claim 2, further comprising: After the announcement frame is transmitted, packets for measuring the channel are transmitted to the user terminal during the transmission time interval (TTI), wherein the packets for measuring the channel are configured such that the user terminal transmits feedback information based on the packets for measuring the channel. as well as Feedback information is received from the user terminal based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

4. The method of claim 3, wherein the announcement frame is configured such that each access point in the group transmits the packet for measuring the channel during the TTI after receiving the announcement frame.

5. The method of claim 1, further comprising receiving an announcement frame transmitted from the second access point to the group.

6. The method of claim 5, further comprising: A packet for measuring a channel is transmitted to a user terminal after receiving the announcement frame, wherein the packet for measuring the channel is transmitted over the same transmission time interval (TTI) as another packet for measuring another channel transmitted by one or more corresponding access points in the group, wherein the packet for measuring the channel is configured such that the user terminal transmits feedback information based on the packet for measuring the channel. as well as Feedback information is received from the user terminal based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

7. A first access point in a plurality of access points, comprising: transceiver; Memory including instructions; as well as A processor configured to execute the instructions such that the first access point: The transceiver transmits a group formation trigger for forming a group that includes one or more of the plurality of access points. The transceiver receives the intention to participate from at least a second access point among the plurality of access points based on the group formation trigger; as well as Based on the stated intention to participate, a group is formed that includes the first access point and at least the second access point among the plurality of access points, wherein the instruction for the first access point to form the group includes an instruction for the first access point to transmit a group configuration to at least the second access point via the transceiver. as well as Distributed transmissions are transmitted via beamforming procedures using the transceiver, wherein the distributed transmissions include transmissions from the first access point and transmissions from at least the second access point among the plurality of access points.

8. The first access point as described in claim 7, wherein, The processor is further configured to execute the instructions such that the first access point: A spatial stream is allocated to at least the second access point in the group, and the at least the second access point in the group will transmit packets for measuring the channel on the spatial stream; as well as The announcement frame is transmitted via the transceiver to the user terminal and at least the second access point in the group for performing the beamforming procedure for the distributed transmission, wherein the announcement frame includes the spatial stream allocation.

9. The first access point as described in claim 8, wherein, The processor is further configured to execute the instructions such that the first access point: After the announcement frame is transmitted, packets for measuring the channel are transmitted to the user terminal via the transceiver during the transmission time interval (TTI), wherein the packets for measuring the channel are configured such that the user terminal transmits feedback information based on the packets for measuring the channel. as well as Feedback information is received from the user terminal via the transceiver based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

10. The first access point of claim 9, wherein the announcement frame is configured such that each access point in the group transmits the packet for measuring the channel during the TTI after receiving the announcement frame.

11. The first access point as described in claim 7, wherein, The processor is further configured to execute the instructions such that the first access point receives, via the transceiver, an announcement frame transmitted from the second access point to the group.

12. The first access point as claimed in claim 11, wherein, The processor is further configured to execute the instructions such that the first access point: The transceiver transmits a packet to the user terminal for measuring the channel after receiving the announcement frame, wherein the packet for measuring the channel is transmitted over the same transmission time interval (TTI) as another packet for measuring another channel transmitted by one or more corresponding access points in the group, wherein the packet for measuring the channel is configured such that the user terminal transmits feedback information based on the packet for measuring the channel. as well as Feedback information is received from the user terminal via the transceiver based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

13. A first access point in a plurality of access points, comprising: A means for transmitting a group formation trigger for forming a group including one or more of the plurality of access points; A means for receiving an intention to participate from at least a second access point among the plurality of access points based on the group formation trigger; A means for forming a group including the first access point and at least the second access point among the plurality of access points based on the intention to participate, wherein the means for forming the group includes means for transmitting a group configuration to at least the second access point. as well as A means for transmitting distributed transmissions using beamforming procedures, wherein the distributed transmissions include transmissions from a first access point and transmissions from at least a second access point among the plurality of access points.

14. The first access point as described in claim 13, further comprising: A means for allocating a spatial stream to at least a second access point in the group, wherein the at least a second access point in the group will transmit packets for measuring the channel on the spatial stream; as well as A means for transmitting a declaration frame to a user terminal and at least a second access point in the group for executing the beamforming procedure for the distributed transmission, wherein the declaration frame includes the spatial stream allocation.

15. The first access point as described in claim 14, further comprising: Means for transmitting packets for measuring the channel to the user terminal during a transmission time interval (TTI) after transmitting the announcement frame, wherein the packets for measuring the channel are configured such that the user terminal transmits feedback information based on the packets for measuring the channel; as well as A means for receiving feedback information from the user terminal based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

16. The first access point of claim 15, wherein the announcement frame is configured such that each access point in the group transmits the packet for measuring the channel during the TTI after receiving the announcement frame.

17. The first access point of claim 13, further comprising means for receiving an announcement frame transmitted from the second access point to the group.

18. The first access point as described in claim 17, further comprising: A means for transmitting to a user terminal a packet for measuring a channel after receiving the announcement frame, wherein the packet for measuring the channel is transmitted over the same transmission time interval (TTI) as another packet for measuring another channel transmitted by one or more corresponding access points in the group, wherein the packet for measuring the channel is configured such that the user terminal transmits feedback information based on the packet for measuring the channel. as well as A means for receiving feedback information from the user terminal based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

19. A non-transient computer-readable medium having instructions stored thereon, the instructions, when executed by a first access point of a plurality of access points, causing the first access point to perform operations including: Transmit a group formation trigger for forming a group that includes one or more of the plurality of access points; Based on the group formation trigger, the intention to participate is received from at least a second access point among the plurality of access points; Based on the stated intention to participate, a group is formed that includes the first access point and at least the second access point among the plurality of access points, wherein forming the group includes transmitting a group configuration to at least the second access point; as well as Beamforming is used to transmit distributed transmissions, wherein the distributed transmissions include transmissions from the first access point and transmissions from at least the second access point among the plurality of access points.

20. The non-transient computer-readable medium of claim 19, wherein, The operation further includes: Assigning a spatial stream to at least the second access point in the group, the at least the second access point in the group will transmit packets for measuring the channel on the spatial stream; and An announcement frame is transmitted to the user terminal and at least the second access point in the group to perform the beamforming procedure for the distributed transmission, wherein the announcement frame includes the spatial stream allocation.

21. The non-transient computer-readable medium of claim 20, wherein, The operation further includes: After transmitting the announcement frame, packets for measuring the channel are transmitted to the user terminal during the Transmission Time Interval (TTI), wherein the packets for measuring the channel are configured such that the user terminal transmits feedback information based on the packets for measuring the channel; and Feedback information is received from the user terminal based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

22. The non-transient computer-readable medium of claim 21, wherein the announcement frame is configured such that each access point in the group transmits the packet for measuring the channel during the TTI after receiving the announcement frame.

23. The non-transient computer-readable medium of claim 19, wherein the operation further comprises receiving a declaration frame transmitted from the second access point to the group.

24. The non-transient computer-readable medium of claim 23, wherein, The operation further includes: A packet for measuring a channel is transmitted to a user terminal after receiving the announcement frame, wherein the packet for measuring the channel is transmitted over the same transmission time interval (TTI) as another packet for measuring another channel transmitted by one or more corresponding access points in the group, wherein the packet for measuring the channel is configured such that the user terminal transmits feedback information based on the packet for measuring the channel; and Feedback information is received from the user terminal based on the packets used to measure the channel, wherein the beamforming procedure is based on the feedback information.

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