Wireless communication device and related method

Abstract

The present application relates to frame formats for distributed MIMO. Disclosed herein are systems and methods for multiple-input multiple-output MIMO communications. In one aspect, during a first time period, a master access point transmits information to a slave access point for joint transmission by the master access point and the slave access point. In one aspect, the slave access point estimates synchronization information for the joint transmission based on the information for the joint transmission. In one aspect, during a second time period after the first time period, the master access point transmits part of a null data packet to a station device. In one aspect, during the second time period, the slave access point transmits the part of the null data packet to the station device based on the synchronization information for the joint transmission. In one aspect, the station device determines guidance information for the MIMO communication based on the null data packet.

Description

[0001] Information about divisional applications

[0002] This case is a divisional application. The parent case of the divisional application is an invention patent application with an application date of August 29, 2019, application number 201910808894.X, and invention name “Frame format for distributed MIMO”.

[0003] CROSS REFERENCE TO RELATED APPLICATIONS

[0004] This application claims priority to U.S. Provisional Patent Application No. 62 / 724,294 filed on August 29, 2018, U.S. Provisional Patent Application No. 62 / 805,821 filed on February 14, 2019, and U.S. Provisional Patent Application No. 62 / 828,874 filed on April 3, 2019, all of which are incorporated by reference in their entirety for all purposes. Technical Field

[0005] The present invention generally relates to systems and methods for providing joint transmissions by a distributed group of access points, including but not limited to frame formats for joint transmissions for sounding and steering. Background Art

[0006] Over the past few decades, the market for wireless communication devices has grown by several orders of magnitude, thanks to the use of portable devices and the increase in connectivity and data transfer between a wide variety of devices. Digital switching technology has facilitated the large-scale deployment of affordable, easy-to-use wireless communication networks. In addition, improvements in digital and radio frequency (RF) circuit manufacturing and advances in circuit integration and other aspects have made wireless devices smaller, cheaper and more reliable. Wireless communications can operate according to various standards, such as IEEE 802.11x, Bluetooth, Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA). As data throughput becomes higher and other changes develop, new standards are constantly being developed for adoption, such as the progression from IEEE 802.11n to IEEE802.11ac. Summary of the invention

[0007] Various embodiments of a method for multiple-input multiple-output (MIMO) communication are disclosed herein. In some embodiments, the method includes, during a first time period, transmitting, by a master access point, information to a slave access point for joint transmission by the master access point and the slave access point. In some embodiments, the method includes, by the slave access point, estimating synchronization information for joint transmission based on the information for the joint transmission. In some embodiments, the method includes, during a second time period following the first time period, transmitting, by the master access point, a portion of a null data packet to a station device. In some embodiments, the method includes, during the second time period, transmitting, by the slave access point, the portion of the null data packet to the station device based on the synchronization information for the joint transmission. In some embodiments, the method includes, by the station device, determining guidance information for MIMO communication based on the null data packet.

[0008] In some embodiments, estimating the synchronization information by the slave access point includes estimating, by the slave access point, a carrier frequency offset or a sampling frequency offset relative to the master access point. In some embodiments, the method includes transmitting, by the master access point, a slave trigger frame to the slave access point during a third time period prior to the first time period. In some embodiments, the method includes estimating, by the slave access point, additional synchronization information for a null data packet declaration based on the slave trigger frame. In some embodiments, the method includes transmitting, by the master access point, the null data packet declaration to the station device during a fourth time period between the third time period and the first time period. In some embodiments, the method includes transmitting, by the slave access point, the null data packet declaration to the station device during the fourth time period. In some embodiments, the method includes preparing, by the station device, for the null data packet in response to receiving the null data packet.

[0009] In some embodiments, transmitting, by the master access point, information for the joint transmission to the slave access point during the first time period includes transmitting, by the master access point, the information for the joint transmission to the slave access point in a preamble of the null data packet. In some embodiments, transmitting, by the master access point, information for the joint transmission to the slave access point during the first time period includes transmitting, by the master access point, the information for the joint transmission to the slave access point in a null data packet declaration. In some embodiments, the method further includes preparing, by the station device, for the null data packet in response to the station device receiving the null data packet declaration. In some embodiments, the method further includes transmitting, by the master access point, a training field to the station device during a third time period between the first time period and the second time period. In some embodiments, the method further includes transmitting, by the slave access point, the training field to the station device during the third time period. In some embodiments, the method includes adjusting, by the station device, a gain setting to receive the portion of the null data packet according to the training field.

[0010] Various embodiments of a first access point for multiple-input multiple-output (MIMO) communication are disclosed herein. In some embodiments, the first access point includes a transceiver and a sounding controller. In some embodiments, the sounding controller is configured to cause the transceiver to transmit information to a second access point for joint transmission by the first access point and the second access point during a first time period. In some embodiments, the information for the joint transmission allows the second access point to estimate synchronization information for the joint transmission. In some embodiments, the sounding controller is configured to cause the transceiver to transmit a portion of a null data packet to a station device based on the synchronization information for the joint transmission during a second time period after the first time period. In some embodiments, the second access point transmits the portion of the null data packet to the station device. In some embodiments, the joint transmission of the portion of the null data packet by the first access point and the second access point allows the station device to determine guidance information for the MIMO communication.

[0011] In some embodiments, the detection controller is configured to cause the transceiver to transmit the portion of the null data packet in a training field. In some embodiments, the detection controller is further configured to cause the transceiver to transmit a slave trigger frame to the second access point during a third time period prior to the first time period. In some embodiments, the slave trigger frame allows the second access point to estimate additional synchronization information for a null data packet declaration. In some embodiments, the detection controller is further configured to cause the transceiver to transmit the null data packet declaration to the station device during a fourth time period between the third time period and the first time period, and the second access point transmits the null data packet declaration to the station device according to the synchronization information during the fourth time period. In some embodiments, the null data packet declaration transmitted by the first access point and the second access point allows the station device to prepare for the null data packet. In some embodiments, the detection controller is further configured to cause the transceiver to transmit information for the joint transmission in a preamble of the null data packet.

[0012] In some embodiments, the sounding controller is further configured to cause the transceiver to transmit the information for the joint transmission in a null data packet declaration. In some embodiments, the null data packet declaration allows the station device to prepare for the null data packet. In some embodiments, the sounding controller is further configured to cause the transceiver to transmit a training field to the station device during a third time period between the first time period and the second time period, and the second access point transmits the training field to the station device during the third time period. In some embodiments, the training field transmitted by the first access point and the second access point allows the station device to adjust a gain setting to receive a portion of the null data packet. In some embodiments, the sounding controller is further configured to cause the transceiver to transmit a null data packet declaration to the station device during a third time period between the first time period and the second time period, and the second access point transmits the null data packet declaration to the station device according to the synchronization information during the third time period. In some embodiments, the null data packet declaration transmitted by the first access point and the second access point allows the station device to prepare for the null data packet. In some embodiments, the information for the joint transmission includes at least two or more groups of long training field (LTF) symbols separated by symbols. In some embodiments, the second time period immediately follows the first time period.

[0013] Various embodiments disclosed herein relate to an access point for multiple-input multiple-output (MIMO) communication. In some embodiments, the access point includes a transceiver and a sounding controller. In some embodiments, the sounding controller is configured to cause the transceiver to receive information from another access point during a first time period for the access point and the other access point to perform joint transmission. In some embodiments, the sounding controller is configured to estimate synchronization information for the joint transmission based on the information for the joint transmission. In some embodiments, the sounding controller is configured to cause the transceiver to transmit a portion of a null data packet to a station device during a second time period after the first time period based on the synchronization information, and the other access point transmits the portion of the null data packet to the station device during the second time period. In some embodiments, the portion of the null data packet transmitted by the access point and the other access point allows the station device to determine guidance information for the MIMO communication.

[0014] In some embodiments, the sounding controller is configured to cause the transceiver to transmit the portion of the null data packet in a training field. In some embodiments, the sounding controller is configured to estimate the synchronization information for the joint transmission by estimating a carrier frequency offset, a sampling frequency offset, a first reference value of a common phase offset, or a second reference value of a timing offset relative to the other access point.

[0015] In some embodiments, the detection controller is further configured to cause the transceiver to receive a slave trigger frame from the other access point during a third time period prior to the first time period. In some embodiments, the detection controller is further configured to estimate additional synchronization information for a null data packet declaration based on the slave trigger frame. In some embodiments, the detection controller is further configured to cause the transceiver to transmit the null data packet declaration to the station device during a fourth time period between the third time period and the first time period, and the other access point transmits the null data packet declaration to the station device based on the synchronization information during the fourth time period. In some embodiments, the null data packet declaration transmitted by the access point and the other access point allows the station device to prepare for the null data packet. In some embodiments, the detection controller is configured to cause the transceiver to receive information for the joint transmission in a preamble of the null data packet.

[0016] In some embodiments, the detection controller is configured to cause the transceiver to receive the information for the joint transmission in a null data packet declaration. In some embodiments, the null data packet declaration allows the station device to prepare for the null data packet. In some embodiments, the detection controller is configured to cause the transceiver to transmit a training field to the station device during a third time period between the first time period and the second time period, and the other access point transmits the training field to the station device during the third time period. In some embodiments, the training field transmitted by the access point and the other access point allows the station device to adjust a gain setting to receive the portion of the null data packet. In some embodiments, the detection controller is configured to deactivate the transceiver for a short interframe space during a third time period between the first time period and the second time period. In some embodiments, the detection controller is configured to cause the transceiver to transmit a null data packet declaration to the station device during a third time period between the first time period and the second time period, and the other access point transmits the null data packet declaration to the station device according to the synchronization information during the third time period. In some embodiments, the null data packet declaration transmitted by the access point and the other access point allows the station device to prepare for the null data packet. In some embodiments, the second time period immediately follows the first time period.

[0017] Various embodiments disclosed herein relate to a method for multiple-input multiple-output (MIMO) communication. In some embodiments, the method includes transmitting, by a master access point, information to a slave access point for joint transmission by the master access point and the slave access point during a first time period. In some embodiments, the method includes causing, by the master access point, the slave access point to estimate synchronization information for the joint transmission based on the information for the joint transmission. In some embodiments, the method includes transmitting, by the master access point, a portion of a guided frame to a station device during a second time period following the first time period. In some embodiments, the method includes transmitting, by the slave access point, the portion of the guided frame to the station device based on the synchronization information for the joint transmission during a second time period. In some embodiments, the method includes decoding, by the station device, the portion of the guided frame transmitted by the master access point and the slave access point to obtain content data in the portion of the guided frame.

[0018] In some embodiments, estimating the synchronization information by the slave access point includes estimating, by the slave access point, a carrier frequency offset or a sampling frequency offset relative to the master access point. In some embodiments, the information for the joint transmission is transmitted in a slave trigger frame during the first time period.

[0019] In some embodiments, the guided frame transmitted by the master access point includes a mid-amble. In some embodiments, the method includes bypassing transmission by the slave access point, while the master access point transmits the mid-amble of the guided frame. In some embodiments, the guided frame transmitted by the master access point includes a mid-amble. In some embodiments, the method further includes resynchronizing by the slave access point according to the mid-amble for another joint transmission of another portion of the guided frame by the master access point and the slave access point.

[0020] In some embodiments, the method includes bypassing transmission by the master access point for a short interframe space during a third time period between the first time period and the second time period. In some embodiments, the method includes transmitting, by the master access point, a training field to the station device during a third time period between the first time period and the second time period. In some embodiments, the method includes transmitting, by the slave access point, the training field to the station device during the third time period. In some embodiments, the method includes adjusting, by the station device, a gain setting according to the training field to receive the portion of the guided frame.

[0021] In some embodiments, the method includes transmitting, by the master access point, a null data packet to the slave access point during a third time period after the first time period and the second time period. In some embodiments, the method includes resynchronizing, by the slave access point, during the third time period for another joint transmission of another guided frame by the master access point and the slave access point. In some embodiments, the method includes transmitting, by the master access point, the other guided frame to the station device during a fourth time period after the third time period. In some embodiments, the method includes transmitting, by the slave access point, the other guided frame to the station device during the fourth time period. In some embodiments, the method includes decoding, by the station device, the other guided frame transmitted by the master access point and the slave access point to obtain additional content data in the other guided frame. In some embodiments, the method includes transmitting, by the station device, an acknowledgment frame to the master access point and the slave access point during a fifth time period between the second time period and the third time period. In some embodiments, the method includes scheduling, by the master access point and the slave access point, the other joint transmission of the other guided frame in response to the acknowledgment frame.

[0022] Various embodiments disclosed herein relate to a first access point for multiple-input multiple-output (MIMO) communication. In some embodiments, the first access point includes a transceiver and a steering controller. In some embodiments, the steering controller is configured to cause the transceiver to transmit information to a second access point during a first time period for the first access point and the second access point to perform a joint transmission. In some embodiments, the information for the joint transmission allows the second access point to estimate synchronization information for the joint transmission. In some embodiments, the steering controller is configured to cause the transceiver to transmit a portion of a guided frame to a station device based on synchronization information during a second time period after the first time period, and the second access point transmits the portion of the guided frame to the station device according to the synchronization information. In some embodiments, the joint transmission of the portion of the guided frame by the first access point and the second access point allows the station device to receive the portion of the guided frame and decode the portion of the guided frame to obtain content data in the portion of the guided frame. In some embodiments, the second time period is immediately after the first time period.

[0023] In some embodiments, the information for the joint transmission is transmitted in a slave trigger frame during the first time period. In some embodiments, the guided frame transmitted by the first access point includes a midamble. In some embodiments, the second access point is configured to bypass transmission while the first access point transmits the midamble of the guided frame. In some embodiments, the guided frame transmitted by the first access point includes a midamble. In some embodiments, the midamble allows the second access point to resynchronize for another joint transmission of another portion of the guided frame by the first access point and the second access point. In some embodiments, the midamble allows the second access point to transition from a transmit mode to a receive mode during the transmission of the midamble by the first access point and back to the transmit mode for the another joint transmission of the another portion of the guided frame by the first access point and the second access point.

[0024] In some embodiments, the steering controller is configured to cause the transceiver to bypass transmission for a short interframe space during a third time period between the first time period and the second time period. In some embodiments, the steering controller is configured to cause the transceiver to transmit a training field to the station device during the second time period, and the second access point to transmit the training field to the station device during the second time period. In some embodiments, the training fields transmitted by the first access point and the second access point allow the station device to adjust a gain setting to receive the portion of the guided frame.

[0025] In some embodiments, the steering controller is configured to cause the transceiver to transmit a null data packet to the second access point during a third time period after the first time period and the second time period. In some embodiments, the null data packet allows the second access point to resynchronize for another joint transmission of another guided frame by the first access point and the second access point. In some embodiments, the steering controller is configured to cause the transceiver to transmit the other guided frame to the station device during a fourth time period after the third time period, and the second access point transmits the other guided frame to the station device during the fourth time period after the resynchronization. In some embodiments, the other guided frame transmitted by the first access point and the second access point allows the station device to receive the other guided frame and decode the other guided frame to obtain additional content data in the other guided frame. In some embodiments, the steering controller is configured to cause the transceiver to receive an acknowledgment frame from the station device during a fifth time period between the second time period and the third time period. In some embodiments, the steering controller is configured to schedule the other joint transmission of the other guided frame in response to the acknowledgment frame. In some embodiments, the steering controller is configured to cause the transceiver to transmit a unique pilot sequence associated with the first access point to enable the station device to estimate additional synchronization information, and receive the additional synchronization information as feedback.

[0026] Various embodiments disclosed herein relate to an access point for multiple-input multiple-output (MIMO) communications. In some embodiments, the access point includes a transceiver and a steering controller. In some embodiments, the steering controller is configured to cause the transceiver to receive information from another access point during a first time period for the access point and the other access point to perform joint transmission. In some embodiments, the steering controller is configured to estimate synchronization information for the joint transmission based on the information for the joint transmission. In some embodiments, the steering controller is configured to cause the transceiver to transmit a portion of a guided frame to a station device according to the synchronization information during a second time period after the first time period, and the other access point transmits the portion of the guided frame to the station device during the second time period. In some embodiments, the portion of the guided frame transmitted by the access point and the other access point allows the station device to receive the portion of the guided frame and decode the portion of the guided frame to obtain content data in the portion of the guided frame.

[0027] In some embodiments, the guidance controller is configured to estimate the synchronization information for the joint transmission by estimating a first reference value of a carrier frequency offset, a sampling frequency offset, a common phase offset, or a second reference value of a timing offset relative to the other access point. In some embodiments, the guidance controller is configured to cause the transceiver to receive the information for the joint transmission from the other access point in a trigger frame during the first time period. In some embodiments, the second time period is immediately after the first time period. In some embodiments, the guidance controller is configured to determine the synchronization information based on a change in a phase offset or a timing offset between a sounding sequence and a guidance sequence. In some embodiments, the guided frame transmitted by the other access point includes a midamble. In some embodiments, the guidance controller is configured to cause the transceiver to bypass transmission while the other access point transmits the midamble of the guided frame. In some embodiments, the steering controller is configured to resynchronize another joint transmission of another portion of the guided frame by the access point and the other access point during the transmission of the midamble by the other access point, and transition from a transmit mode to a receive mode and back to the transmit mode for the another joint transmission of the other portion of the guided frame by the access point and the other access point. In some embodiments, the steering controller is configured to cause the transceiver to transmit a training field to the station device during the second time period, and the other access point to transmit the training field to the station device during the second time period. In some embodiments, the training field transmitted by the access point and the other access point allows the station device to adjust a gain setting to receive the portion of the guided frame. In some embodiments, the steering controller is configured to cause the transceiver to receive a null data packet from the other access point during a third time period after the first time period and the second time period. In some embodiments, the null data packet allows the access point to resynchronize another joint transmission of another guided frame by the access point and the other access point. In some embodiments, the bootstrap controller is configured to cause the transceiver to transmit the other guided frame to the station device after the resynchronization during a fourth time period after the third time period, and the other access point transmits the other guided frame to the station device during the fourth time period. In some embodiments, the other guided frame transmitted by the access point and the other access point allows the station device to receive the other guided frame and decode the other guided frame to obtain additional content data in the other guided frame. In some embodiments, the bootstrap controller is configured to cause the transceiver to receive an acknowledgment frame from the station device during a fifth time period between the second time period and the third time period.In some embodiments, the steering controller is configured to cause the transceiver to transmit a unique pilot sequence associated with the access point to enable the station device to estimate additional synchronization information, and receive the additional synchronization information as feedback.

[0028] In some embodiments, the directed frame transmitted by the other access point includes a midamble. In some embodiments, the steering controller is configured to cause the transceiver to bypass transmission while the other access point transmits the midamble of the directed frame. In some embodiments, the steering controller is configured to cause the transceiver to resynchronize according to the midamble for another joint transmission of another portion of the directed frame by the access point and the other access point.

[0029] In some embodiments, the steering controller is configured to cause the transceiver to bypass transmission for a short interframe space during a third time period between the first time period and the second time period. In some embodiments, the steering controller is configured to cause the transceiver to transmit a training field to the station device during a third time period between the first time period and the second time period, and the other access point transmits the training field to the station device during the third time period. In some embodiments, the training fields transmitted by the access point and the other access point allow the station device to adjust a gain setting to receive the portion of the guided frame.

[0030] In some embodiments, the directed controller is configured to schedule the another joint transmission of the another directed frame in response to the acknowledgement frame. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Various objects, aspects, features and advantages of the present invention will become more apparent and better understood by referring to the detailed description made in conjunction with the accompanying drawings, in which like reference characters identify corresponding elements from beginning to end. In the accompanying drawings, like reference numerals generally indicate identical, functionally similar and / or structurally similar elements.

[0032] Figure 1A is a block diagram depicting a network environment including one or more access points in communication with one or more devices or stations in accordance with some embodiments.

[0033] Figure 1B and 1C is a block diagram depicting a computing device that may be used in conjunction with the methods and systems described herein, according to some embodiments.

[0034] Figure 2A is a block diagram illustrating a system for performing channel estimation between a beamformer and a beamformed receive end according to some embodiments.

[0035] Figure 2B is a block diagram illustrating a system for performing channel estimation between at least one beamformer and at least one beamformed receiver in accordance with some embodiments.

[0036] Figure 3A is a block diagram illustrating an example network environment including a master access point and multiple station devices for joint transmission in accordance with some embodiments.

[0037] Figure 3B is a flow chart illustrating an example process for establishing an example multiple-input multiple-output (MIMO) communication in accordance with some embodiments.

[0038] Figure 4 An example timing diagram illustrating joint transmissions from a master access point and from an access point to a station device.

[0039] Figures 5 to 9 An example timing diagram illustrating a probing sequence in accordance with some embodiments.

[0040] Figures 10 to 13 An example timing diagram illustrating a boot sequence according to some embodiments.

[0041] The details of various embodiments of the method and system are set forth in the accompanying drawings and the description below. DETAILED DESCRIPTION

[0042] The entire contents of the following IEEE standard(s) (including any draft versions of such standard(s)) are incorporated herein by reference and are made a part of the present invention for all purposes: IEEE P802.11n TM ; and IEEE P802.11ac TM Although the present invention may refer to aspects of these standards, the present invention is in no way limited to these standards.

[0043] For the purpose of reading the description of the various embodiments below, the following description of the sections of the specification and their corresponding contents may be helpful:

[0044] - Section A describes a network environment and a computing environment that can be used to practice the embodiments described herein; and

[0045] - Section B describes an embodiment of a frame format for joint transmission of sounding and steering in MIMO communications.

[0046] A. Computing and Network Environment

[0047] Before discussing specific embodiments of the present solution, it may be helpful to describe aspects of the operating environment and associated system components (eg, hardware elements) in conjunction with the methods and systems described herein. Figure 1A, depicting an embodiment of a network environment. Briefly, the network environment includes a wireless communication system, which includes one or more access points (APs) 106, one or more wireless communication devices 102, and network hardware components 192. The wireless communication device 102 may, for example, include a laptop computer 102, a tablet computer 102, a personal computer 102, and / or a cellular telephone device 102. Reference Figure 1B and 1C The details of the embodiments of each wireless communication device 102 and / or AP 106 are described in more detail. In one embodiment, the network environment may be an ad hoc network environment, an infrastructure wireless network environment, a subnet environment, etc. The AP 106 may be operably coupled to the network hardware 192 via a local area network connection. The network hardware 192 (which may include routers, gateways, switches, bridges, modems, system controllers, devices, etc.) may provide a local area network connection for the communication system. Each of the APs 106 may have an associated antenna or antenna array to communicate with wireless communication devices in its area. The wireless communication device 102 may register with a specific AP 106 to receive services from the communication system (e.g., via SU-MIMO or MU-MIMO configuration). For direct connections (e.g., point-to-point communications), some wireless communication devices may communicate directly via allocated channels and communication protocols. Some wireless communication devices 102 may be mobile or relatively stationary relative to the AP 106.

[0048] In some embodiments, AP 106 includes a device or module (including a combination of hardware and software) that allows wireless communication devices 102 to connect to a wired network using wireless fidelity (WiFi) or other standards. AP 106 may sometimes be referred to as a wireless access point (WAP). AP 106 may be implemented (e.g., configured, designed and / or constructed) to operate in a wireless local area network (WLAN). In some embodiments, AP 106 may be connected to a router (e.g., via a wired network) as a standalone device. In other embodiments, AP 106 may be a component of a router. AP 106 may provide access to a network to multiple devices. For example, AP 106 may be connected to a wired Ethernet connection and use a radio frequency link to provide wireless connections for other devices 102 to utilize the wired connection. AP 106 may be implemented to support standards that use one or more radio frequencies to send and receive data. The standards and the frequencies they use may be defined by IEEE (e.g., IEEE 802.11 standards). AP 106 may be configured and / or used to support public Internet hotspots and / or on a network to extend the Wi-Fi signal range of the network.

[0049] In some embodiments, the access point 106 may be used for a wireless network (e.g., IEEE 802.11, Bluetooth, ZigBee, any other type of radio frequency based network protocol, and / or variations thereof) (e.g., in a home or within a building). Each of the wireless communication devices 102 may include a built-in radio and / or be coupled to a radio. Such wireless communication devices 102 and / or access points 106 may operate in accordance with various aspects of the present invention as presented herein to enhance performance, reduce cost and / or size, and / or enhance broadband applications. Each wireless communication device 102 may have the ability to act as a client node that seeks to access resources (e.g., data and connections to networked nodes (e.g., servers)) via one or more access points 106.

[0050] The network connection may include any type and / or form of network and may include any of the following: a point-to-point network, a broadcast network, a telecommunications network, a data communications network, and a computer network. The network topology may be a bus, star, or ring network topology. The network may be any such network topology known to those of ordinary skill in the art that is capable of supporting the operations described herein. In some embodiments, different types of data may be transmitted via different protocols. In other embodiments, the same type of data may be transmitted via different protocols.

[0051] The communication device(s) 102 and the access point(s) 106 may be deployed as and / or executed on any type and form of computing device, such as a computer, network device, or appliance capable of communicating over any type and form of network and performing the operations described herein. Figure 1B and 1C A block diagram of a computing device 100 is depicted that may be used to practice embodiments of a wireless communication device 102 or AP 106. Figure 1B and 1C As shown in FIG. 1 , each computing device 100 includes a central processing unit 121 and a main memory unit 122. Figure 1B As shown in FIG. 1 , computing device 100 may include storage device 128, installation device 116, network interface 118, I / O controller 123, display devices 124a to 124n, keyboard 126, and pointing device 127, such as a mouse. Storage device 128 may include an operating system and / or software. Figure 1C As shown in , each computing device 100 may also include additional optional elements that communicate with the central processing unit 121, such as a memory port 103, a bridge 170, one or more input / output devices 130a to 130n, and a cache memory 140.

[0052] The central processing unit 121 is any logic circuit that responds to and processes instructions fetched from the main memory unit 122. In many embodiments, the central processing unit 121 is provided by a microprocessor unit, such as: a microprocessor unit manufactured by Intel Corporation of Santa Clara, California; a microprocessor unit manufactured by International Business Machines Corporation of White Plains, New York; or a microprocessor unit manufactured by Advanced Micro Devices of Sunnyvale, California. The computing device 100 may be based on any of these processors or any other processor capable of operating as described herein.

[0053] The main memory unit 122 may be one or more memory chips capable of storing data and allowing direct access to any storage location by the microprocessor 121, such as any type or variant of static random access memory (SRAM), dynamic random access memory (DRAM), ferroelectric RAM (FRAM), NAND flash memory, NOR flash memory, and solid-state drive (SSD). The main memory 122 may be based on any of the memory chips described above, or any other available memory chip capable of operating as described herein. Figure 1B In the embodiment shown in , processor 121 communicates with main memory 122 via system bus 150 (described in more detail below). Figure 1C An embodiment of computing device 100 is depicted in which the processor communicates directly with main memory 122 via memory port 103. For example, in Figure 1C In the embodiment, the main memory 122 may be DRDRAM.

[0054] Figure 1C An embodiment is depicted in which the main processor 121 communicates directly with the cache memory 140 via an auxiliary bus (sometimes referred to as a back-end bus). In other embodiments, the main processor 121 communicates with the cache memory 140 using the system bus 150. The cache memory 140 typically has a faster response time than the main memory 122 and is provided by, for example, SRAM, BSRAM, or EDRAM. Figure 1C , the processor 121 communicates with various I / O devices 130 via a local system bus 150. Various buses may be used to connect the central processing unit 121 to any of the I / O devices 130, such as a VESA VL bus, an ISA bus, an EISA bus, a Micro Channel Architecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or a NuBus. For embodiments in which the I / O device is a video display 124, the processor 121 may communicate with the display 124 using an Advanced Graphics Port (AGP). Figure 1CAn embodiment of the computer 100 is depicted in which the main processor 121 can communicate directly with the I / O device 130b, such as via HYPERTRANSPORT, RAPIDIO, or INFINIBAND communication technology. Figure 1C Also depicted are embodiments in which local busses and direct communications are mixed: processor 121 communicates with I / O device 130a using a local interconnect bus while communicating directly with I / O device 130b.

[0055] The computing device 100 may have a variety of I / O devices 130a to 130n. Input devices include keyboards, mice, trackpads, trackballs, microphones, dials, touchpads, touch screens, and drawing tablets. Output devices include video displays, speakers, inkjet printers, laser printers, projectors, and dye sublimation printers. The I / O devices may be controlled by an I / O controller 123, such as Figure 1B 100. The I / O controller may control one or more I / O devices, such as a keyboard 126 and a pointing device 127, such as a mouse or light pen. In addition, the I / O devices may also provide storage and / or installation media 116 for the computing device 100. In yet other embodiments, the computing device 100 may provide a USB connection (not shown) to receive a handheld USB storage device, such as the USB flash memory drive series of devices manufactured by Twintech Industries, Inc. of Los Alamos, California.

[0056] Reference again Figure 1B , the computing device 100 may support any suitable installation device 116, such as a disk drive, a CD-ROM drive, a CD-R / RW drive, a DVD-ROM drive, a flash memory drive, a tape drive of various formats, a USB device, a hard drive, a network interface, or any other device suitable for installing software and programs. The computing device 100 may further include a storage device, such as one or more hard drives or a redundant array of independent disks, for storing an operating system and other related software and for storing application software programs (such as any program or software 120) that implement (e.g., are configured and / or designed for) the systems and methods described herein. Optionally, any of the installation devices 116 may also be used as a storage device. In addition, the operating system and software may be run from a bootable media.

[0057] In addition, computing device 100 may include a network interface 118 to interface to network 104 through various connections, including but not limited to standard telephone lines, LAN or WAN links (e.g., 802.11, T1, T3, 56kb, X.25, SNA, DECNET), broadband connections (e.g., ISDN, Frame Relay, ATM, Gigabit Ethernet, Ethernet over SONET), wireless connections, or some combination of any or all of the above. The connection may be established using various communication protocols (e.g., TCP / IP, IPX, SPX, NetBIOS, Ethernet, ARCNET, SONET, SDH, Fiber Distributed Data Interface (FDDI), RS232, IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE802.11g, IEEE 802.11n, IEEE 802.11ac, IEEE 802.11ad, CDMA, GSM, WiMax, and direct asynchronous connection). In one embodiment, computing device 100 communicates with other computing devices 100' via any type and / or form of gateway or tunneling protocol, such as Secure Sockets Layer (SSL) or Transport Layer Security (TLS). Network interface 118 may include a built-in network adapter, a network interface card, a PCMCIA network card, a card bus network adapter, a wireless network adapter, a USB network adapter, a modem, or any other device suitable for interfacing computing device 100 to any type of network capable of communicating and performing the operations described herein.

[0058] In some embodiments, the computing device 100 may include or be connected to one or more display devices 124a to 124n. Thus, any of the I / O devices 130a to 130n and / or the I / O controller 123 may include any type and / or form of suitable hardware, software, or combination of hardware and software to support, enable, or provide the computing device 100 with connection and use of (several) display devices 124a to 124n. For example, the computing device 100 may include any type and / or form of video adapter, video card, driver, and / or library to interface, communicate, connect, or otherwise use (several) display devices 124a to 124n. In one embodiment, the video adapter may include multiple connectors to interface to (several) display devices 124a to 124n. In other embodiments, the computing device 100 may include multiple video adapters, each of which is connected to (several) display devices 124a to 124n. In some embodiments, any portion of the operating system of the computing device 100 may be configured to use multiple displays 124a to 124n. In a further embodiment, the I / O device 130 may be a bridge between the system bus 150 and an external communication bus, such as a USB bus, an Apple desktop bus, an RS-232 serial connection, a SCSI bus, a FireWire bus, a FireWire 800 bus, an Ethernet bus, an AppleTalk bus, a Gigabit Ethernet bus, an asynchronous transfer mode bus, a Fibre Channel bus, a serial attached small computer system interface bus, a USB connection, or an HDMI bus.

[0059] Figure 1B and 1C A computing device 100 of the type shown in the figure may operate under the control of an operating system that controls the scheduling of tasks and access to system resources. The computing device 100 may run any operating system, such as any version of the MICROSOFT WINDOWS operating system, different versions of the Unix and Linux operating systems, any version of the MAC OS for Macintosh computers, any embedded operating system, any real-time operating system, any open source operating system, any proprietary operating system, any operating system for a mobile computing device, or any other operating system capable of running on a computing device and performing the operations described herein. Typical operating systems include, but are not limited to: Android produced by Google Inc.; WINDOWS 7 and 8 produced by Microsoft Corporation of Redmond, Washington; MAC OS produced by Apple Inc. of Cupertino, California; WebOS produced by BlackBerry (RIM), Inc.; OS / 2 produced by International Business Machines Corporation of Armonk, New York; and Linux, a free operating system released by Catera, Inc. of Salt Lake City, Utah, or any type and / or form of Unix operating system, etc.

[0060] The computer system 100 may be any workstation, phone, desktop computer, laptop or notebook computer, server, handheld computer, mobile phone or other portable telecommunication device, media playback device, gaming system, mobile computing device, or any other type and / or form of computing, telecommunication or media device capable of communication. In some embodiments, the computing device 100 may have a different processor, operating system and input device consistent with the device. For example, in one embodiment, the computing device 100 is a smart phone, mobile device, tablet computer or personal digital assistant. In addition, the computing device 100 may be any workstation, desktop computer, laptop or notebook computer, server, handheld computer, mobile phone, any other computer, or other form of computing or telecommunication device capable of communication and having sufficient processor power and memory capacity to perform the operations described herein.

[0061] Aspects of the operating environment and components described above will become apparent in the context of the systems and methods disclosed herein.

[0062] B. Frame Formats for Probing and Guidance in MIMO Communications

[0063]

[0013] Disclosed herein is directed to a system and method for providing joint transmission by a distributed access point group (or multiple distributed access points).In one aspect, disclosed herein is directed to frame formats for sounding and steering of joint transmissions.

[0064] Systems and methods for establishing a MIMO connection among two or more access points and at least station devices (sometimes referred to as stations or STAs) are described herein. In some embodiments, the access points include a master access point and two or more slave access points capable of transmitting data over a wireless medium. In some embodiments, the master access point configures or coordinates different slave access points for joint transmission. In one aspect, a station device may not be able to successfully receive and decode a transmission through a single master access point or a single slave access point. However, a station device may successfully receive and decode a joint transmission through two or more access points.

[0065] In some embodiments, the master access point configures different station devices to perform joint transmissions in two phases: sounding and steering. During sounding, channel estimation is performed to determine the signal strength, relative signal phase, and / or quality of transmissions from different access points received by the station device, and / or the configuration of the joint transmission is determined based on the determined signal strength, relative signal phase, or quality of transmissions from different access points. Examples of configurations for joint transmissions may include timing, power, gain, channel bandwidth, frequency, steering vectors for transmissions through one or more antennas, or any information indicating how to radiate energy in a particular direction, frequency correlation within a channel, signal-to-noise ratio (SNR), and / or appropriate data rate adjustments. During the steering phase, the access point and the station device may communicate through beamforming according to the configuration determined during sounding so that the station device can receive and decode the joint transmission from the access point.

[0066] Disclosed herein are frame formats for sounding and / or steering. In one aspect, the frame formats disclosed herein may enable a slave access point to estimate or determine synchronization information for joint transmission with a master access point. Examples of synchronization information may include a first reference value of a carrier frequency offset, a sampling frequency offset, a common phase offset, and / or a second reference value of a timing offset relative to the master access point. For example, the master access point transmits a preamble of a slave trigger frame or a null data packet that enables the slave access point to estimate or determine synchronization information. Based on the synchronization information, the master access point and the slave access point may transmit together simultaneously for sounding, steering, or both.

[0067] Methods and systems are described herein for performing channel estimation between a beamformer and a beamformee (e.g., at least one AP 106 and at least one device 102), such as in a multi-user multiple input multiple output (MU-MIMO) environment. For example, in a MU-MIMO configuration, an AP 106 (hereinafter sometimes generally referred to as an "access point" or "AP") may include an AP 106 that may communicate with each of a plurality of devices 102 (e.g., beamformee). The AP 106 may include a number of antennas and may support a number of spatial streams for transmission to the devices (sometimes referred to as stations (STAs) or users) 102. The AP 106 may utilize and use one or more sounding frames (e.g., null data packets (NDPs) or NDP announcement (NDPA) frames or other control frames) to request channel estimation feedback from the devices 102.

[0068] The dimensionality of an AP 106 (embodied as a beamformer) sometimes refers to the number of spatial streams supported by the AP 106 or the number of available transmit antennas. The dimensionality of a wireless communication device 102 (embodied as a beamformer receiver) sometimes refers to the number of spatial streams that the device 102 can support, for example, for channel estimation. In some aspects, the present methods and systems may allow a higher dimensional AP 106 or a group of coordinated APs 106 (both of which are sometimes generally referred to as a single "beamformer" hereinafter, where the group of coordinated APs 106 may be configured to operate as a single beamformer in some manners) to use the transmit antennas of the beamformer to steer and achieve full array gain even when paired with a lower dimensional device 102. The device 102 may be able to support fewer spatial streams than the number of spatial streams that the AP 106 can include in a sounding to perform multiple-input multiple-output (MIMO) channel estimation. The present solution may use a subset of the antennas of the beamformer to provide multiple soundings instead of using all of the antennas of the beamformer to provide a single sounding (which is not supported by the beamformer receiver). The coordinated sounding sequences from the antenna subsets may elicit different sets of MIMO channel estimation results from the low-dimensional beamforming receiving end, which may be combined to produce full channel estimation information. For example, in some embodiments, by defining the subsets as having overlapping antennas, the channel estimation feedback matrices for different subsets / soundings may be merged or combined to produce a channel estimate for the full channel of the AP 106.

[0069] In some embodiments, multiple beamformers (e.g., AP 106) may operate in a coordinated manner as a higher dimensional beamformer communicates with one or more beamformer receivers. Multiple sounding reports from the same device 102 to different APs 106 may be combined and / or shared between coordinating APs 106 to understand the MU-MIMO channel between each beamformer-beamformer receiver pair. In another embodiment, the coordinating AP 106 may be time and / or frequency synchronized (e.g., using frequency diversity or offset) to provide a sounding sequence that may appear to be a single sounding sequence from a higher dimensional beamformer.

[0070] In some embodiments, AP 106 (e.g., embodied as a beamformer) may receive responses to a plurality of sounding frames from device 102 (e.g., embodied as a beamformer receiver). The responses may include channel estimates for a plurality of transmit spatial stream subsets. AP 106 may generate full channel estimation information based on the received responses. The full channel estimation information may include channel estimation information corresponding to all transmit spatial streams that AP 106 may provide. AP 106 may direct a plurality of transmit antennas of AP 106 based on the full channel estimation information.

[0071] In yet another aspect, the present disclosure is directed to a method for performing channel estimation between a plurality of APs 106 embodied as beamformers and at least one device 102 embodied as a beamformed receiver. The method may include configuring a first AP 106 and a second AP 106 to communicate with the first device 102. The first AP 106 may support a first plurality of transmit spatial streams. The second AP 106 may support a second plurality of transmit spatial streams. The first AP 106 and the second AP 106 may determine, between the first AP 106 and the second AP 106, a plurality of transmit spatial stream subsets from the first plurality of transmit spatial streams and the second plurality of transmit spatial streams. The first AP 106 and the second AP 106 may coordinate transmission of a plurality of sounding frames to the first device 102 between the first beamformer 106 and the second beamformer 106 to perform channel estimation based at least on the determined plurality of transmit spatial stream subsets.

[0072] In some embodiments, the first AP 106 and the second AP 106 are configured to communicate with the first device 102. The first AP 106 and the second AP 106 may be operably coupled via a backbone connection. The first AP 106 and / or the second AP 106 may combine at least some responses to a plurality of sounding frames from the first device 102, the responses including channel estimates for a plurality of transmit spatial stream subsets. The first AP 106 and / or the second AP 106 may generate full channel estimation information between the first AP 106 and the second AP 106 based on the combination of at least some of the responses. The first AP 106 and the second AP 106 may be configured to communicate with a plurality of beamforming receivers 102. The first AP 106 and the second AP 106 may coordinate the transmission of a plurality of sounding frames to a plurality of devices 102 between the first AP 106 and the second AP 106. The first AP 106 and / or the second AP 106 may use frequency diversity to send a sounding frame from the first AP 106 and a sounding frame from the second AP 106 simultaneously.

[0073] refer to Figure 2A , depicting an embodiment of a system for establishing MIMO communications between at least one AP 106 and at least one device 102. Briefly, one embodiment of the system may include an AP 106 in communication with a device 102. The AP 106 may include a wireless transceiver 228, a sounding controller module (SCM) 222 (also referred to as "sounding controller 222"), a steering controller module 225 (also referred to as "steering controller 225"), an integration module 221 (also referred to as "integrated controller 221"), a storage module 223, and / or a configuration 224. The device 102 may include a wireless transceiver and a channel estimation module (CEM) 212 (also referred to as "channel estimation controller 212"). The AP 106 may include multiple antennas (e.g., phased array antennas).

[0074] In some embodiments, the system may support at least some aspects of a MU-MIMO transmit configuration 224 between an AP 106 embodied as a beamformer and a device 102 embodied as a beamformed receiver. For example, the AP 106 may have a higher dimensionality relative to the device 102. The device 102 may perform channel estimation for a number of spatial communication streams up to the dimensionality of the device 102. In one embodiment, the device 102 may provide channel estimation for more dimensions than the antennas it has. For example, the device 102 may have only one antenna, but may have the ability to estimate three antenna channels. By way of illustration, the AP 106 may have a higher dimensionality and / or capability than some devices 102 (e.g., legacy beamformed receivers) in a deployment. In one embodiment, the device 102 may, for example, be able to perform channel estimation for up to a preconfigured number of transmit spatial streams from the AP 106, the preconfigured number of transmit spatial streams being less than the number of transmit spatial streams that the AP 106 may provide.

[0075] AP 106 may be implemented (e.g., configured and / or constructed) to support (simultaneously or otherwise) a first number of transmit streams, channels, or connections, e.g., within a transmit or sounding frame. AP 106 may include a set of coordinated APs 106. Sounding frames may include MU-MIMO frames, SU-MIMO frames, and / or NDP frames. AP 106 may be implemented to include a first number of transmit chains and / or transmit antennas. Device 102 may be implemented to support (simultaneously or otherwise) a second number of spatial streams, channels, or connections (sometimes generally referred to hereinafter as "spatial streams" or "Nss"). The second number of spatial streams may be lower than the first number of streams.

[0076] In some embodiments, the beamforming receiving end capability field may store or indicate the total number or a predetermined number of spatial streams that the device 102 can support - "the number of compressed steering of beamformer antennas supported". This field may be defined or included in the management field. For example, this field may contain or indicate the Nss that the AP 106 can handle or support in the NDP frame. This field may set the range of transmit spatial dimensions for which the device 102 can perform channel estimation, generate appropriate beamforming reports, and / or create sounding feedback frames (sometimes commonly referred to as "responses") to the AP 106. In some embodiments, this capability is fixed once the device 102 or AP 106 is implemented and / or deployed in the field, and in some embodiments is not upgradeable (e.g., via a software patch).

[0077] In some embodiments, a preconfigured or upper limit Nss of a device 102 may limit the transmit beamforming performance of, for example, an AP 106 and / or the device 102. For example, when the channel estimation capability of the device fails to support the full range of the AP's transmit antennas, the AP 106 may not be able to use all of its transmit antennas for steering and may not achieve full array gain. In some embodiments, for multi-user transmit beamforming, the AP 106 may have to use the minimum sounding capability among the devices 102 with different sounding capabilities. The AP 106 may have to turn on antennas that are less than the full set of antennas corresponding to the minimum sounding capability. Existing transmit beamforming (TXBF) enabled devices with limited sounding capabilities may remain commercially available and / or deployable in the field for a period of time before these devices are eventually replaced by higher capability devices. In some aspects, the present methods and systems provide support for such devices 102.

[0078] In some embodiments, the AP 106 includes a transceiver 228 that allows the beamformer 106 to communicate with other devices (e.g., a beamformed receiver 102 or another beamformer 106) through one or more antennas. For example, the transceiver 228 includes a transmitter that encodes data (e.g., content data, control data, response data, announcements, etc.) at a baseband frequency, up-converts the encoded data to a radio frequency, and transmits the up-converted signal through one or more antennas. As another example, the transceiver 228 includes a receiver that down-converts a wireless signal at a radio frequency received through one or more antennas to a baseband frequency, and decodes the converted signal to obtain data (e.g., content data, control data, response data, announcements, etc.). In some embodiments, the AP 106 transmits and receives data at the same frequency, separate frequencies, or overlapping frequencies.

[0079] In some embodiments, the AP 106 includes an SCM 222. The SCM 222 may manage and / or control the transmission of multiple sounding frames (e.g., NDP sounding frames) to the low-capability device 102. The SCM 222 may include hardware or a combination of hardware and software. For example, the SCM 222 may include any application, program, library, script, task, service, process, or executable instructions of any type and form that executes on the hardware of the AP 106. In one embodiment, the SCM 222 includes an executable instruction set that executes on the core or processor of the AP 106. The SCM 222 may include circuits designed and / or constructed to perform any of the operations and functions described herein. In some embodiments, the SCM 222 is configured to control the transmission of sounding frames to the device 102 via one or more antennas of the AP 106. For example, the SCM 222 may be configured to allocate, select, or assign certain antennas to participate in one or more soundings within a sounding set. The SCM 222 may, for example, tune a subset of antennas (e.g., phased array antennas) of a beamformer to participate in a particular sounding. In some embodiments, the SCM 222 of the master AP determines, directs, or schedules a sounding sequence as disclosed herein. In some embodiments, the SCMs 222 of different APs coordinate with each other to determine or schedule a sounding sequence as disclosed herein.

[0080] In some embodiments, the SCM 222 includes firmware executed on the AP 106 hardware. The firmware may operate in a layer of the protocol stack of the AP 106 (e.g., in an upper layer). In certain embodiments, the SCM 222 operates in a MAC layer, such as a MAC layer residing between a lower layer of the MAC and a higher layer of the MAC. The AP 106 or the SCM 222 may, for example, divide, allocate, or otherwise assign multiple antennas into multiple antenna subsets based on the configuration 224. In some embodiments, antennas may be assigned to more than one subset. Each antenna subset may be selected according to the configuration 224, which may be consistent with one or more predefined rules, policies, requirements, and / or guidelines. For example, each antenna subset may include antennas that are physically adjacent to each other on the AP 106 and / or selected according to a certain order or sequence. In some embodiments, each antenna subset may include antennas separated from each other by at least one other antenna that is not in the subset, such as to include a certain degree of spatial freedom or separation. In some embodiments, the SCM 222 configures each subset to include at least one antenna common to at least one other subset.

[0081] The SCM 222 may manage or control the transmission of multiple sounding frames corresponding to the antenna subsets. Each sounding may cover a subset of the AP antennas. The SCM 222 or the AP 106 may instruct, cause, or allow coordinated transmission in the sounding frames in a specific order through different antennas. The SCM 222 or the AP 106 may cause the transceiver 228 to transmit sounding frames that are distributed or staggered over a period of time (e.g., at predetermined intervals). The SCM 222 or the AP 106 may provide the AP 106 with sufficient time to process each sounding frame and / or provide a response to each sounding frame before sending the next sounding frame. The SCM 222 may store information about the configured subsets and / or about the corresponding sounding sequences to the configuration 224 and / or the storage module 223.

[0082] Configuration 224 may include, maintain or store information about assigning or allocating antennas to subsets for sounding purposes and / or about sounding sequences corresponding to configured subsets. Configuration 224 may include information about connecting or coupling specific antennas to specific transmit chains. Configuration 224 may include scheduling or timing information for performing sounding. Configuration 224 may be stored in storage module 223. Storage module 223 may include one or more interconnected storage devices, such as those described above in conjunction with Figure 1B and 1C Any of the described embodiments of storage devices 128, 140, 122. In some embodiments, SCM 222 and / or integrated modules may generate, access and / or update configurations.

[0083] The configuration 224 may include a list, table, or other database structure, and may include, for example, at least one entry, record, or specification corresponding to, for example, each device 102. The configuration 224 may be specified and / or defined in a file or a batch of records stored or maintained in the storage module 223. The SCM 222 and / or the integration module 221 may access portions of the configuration to perform partial channel estimation through multiple soundings. For example, the integration module may use hashing to perform a lookup for an antenna or device in the configuration 224 to process channel estimation feedback.

[0084] In some embodiments, the device 102 includes a CEM 212. The CEM 212 may process the sounding frames received by the device 102. For example, the CEM 212 may perform channel estimation and / or provide channel estimation feedback. The channel estimation may include any form of channel measurement and / or calibration or channel response determination. For example, the channel estimation results may be used to provide feedback to the AP 106 regarding how energy is radiated in a particular direction, frequency correlation within a channel, signal-to-noise ratio (SNR), and / or appropriate data rate adjustment. The CEM 212 may include hardware or a combination of hardware and software. For example, the CEM 212 may include any application, program, library, script, task, service, process, or executable instructions of any type and form that executes on the hardware of the CEM 212. In one embodiment, the CEM 212 includes an executable instruction set that executes on a core or processor of the CEM 212.

[0085] The CEM 212 may include circuitry designed and / or constructed to perform any of the operations and functions described herein. In some embodiments, the CEM 212 is preconfigured to perform channel estimation in a specific environment (e.g., a SU-MIMO or MU-MIMO environment). In some embodiments, the CEM 212 includes firmware executed on hardware of the device 102. The firmware may operate in a layer of a protocol stack of the device 102 (e.g., in an upper layer). The CEM 212 may operate in a MAC layer, such as residing between a lower layer of the MAC and an upper layer of the MAC. The CEM 212 may provide channel estimation feedback to include in a response to a sounding frame from the AP 106. The CEM 212 may manage or direct the transmission of one or more responses to the AP 106.

[0086] In some embodiments, the AP 106 may include an integration module 221. The integration module 221 may manage, track, and / or process responses received from the device 102. The integration module 221 may store information (e.g., channel estimation information) from one or more responses in the storage module 223. The integration module 221 may, for example, sort and / or combine channel estimation information from the responses based at least in part on information stored in the configuration 224 (e.g., information about the configured subsets and / or the sounding sequences corresponding to the configured subsets). Based on the channel estimation information, the integration module 221 may determine steering information. In one aspect, the steering information indicates a configuration of the transceiver 228 of the AP 106 and / or other APs 106 for steering. For example, the steering information indicates timing, power, gain, channel bandwidth, frequency, steering vectors for transmitting through one or more antennas, or indicates how to radiate energy in a particular direction, frequency correlation within a channel, signal-to-noise ratio (SNR), and / or appropriate data rate adjustment for joint transmission with other access points.

[0087] The integrated module 221 may include hardware or a combination of hardware and software. For example, the integrated module 221 may include any application, program, library, script, task, service, process or any type and form of executable instructions executed on the hardware of AP106. In one embodiment, the integrated module 221 includes an executable instruction set executed on the core or processor of AP 106. The integrated module 221 may include a circuit designed and / or constructed to perform any of the operations and functions described herein. In some embodiments, the integrated module 221 includes firmware executed on the hardware of AP 106. The firmware may operate in a layer of the protocol stack of AP106 (e.g., in an upper layer). In certain embodiments, the integrated module 221 operates in the MAC layer, for example, residing between a lower layer of the MAC and a higher layer of the MAC. In some embodiments, the integrated module 221 is configured to combine, integrate, merge, normalize, adjust and / or aggregate information from the response to obtain full channel information. In some embodiments, the integrated module 221 is integrated with the detection controller 222 or implemented as part of the detection controller 222.

[0088] In some embodiments, the AP 106 includes a steering module 225. The steering module 225 may manage and / or control the transmission of guided frames to the low-capability device 102. The steering module 225 may include hardware or a combination of hardware and software. For example, the steering module 225 may include any application, program, library, script, task, service, process, or executable instructions of any type and form executed on the hardware of the AP 106. In one embodiment, the steering module 225 includes an executable instruction set executed on the core or processor of the AP 106. The steering module 225 may include a circuit designed and / or constructed to perform any of the operations and functions described herein. In some embodiments, the steering module 225 is configured to control the transmission of guided frames to the device 102 via one or more antennas of the AP 106. For example, the steering module 225 may be configured to allocate, select, or assign certain antennas to participate in one or more steerings. The steering module 225 may, for example, tune a subset of antennas (e.g., phased array antennas) of a beamformer to participate in a specific steering.

[0089] In some embodiments, the steering module 225 includes firmware executed on the AP 106 hardware. The firmware may operate in a layer of the protocol stack of the AP 106 (e.g., in an upper layer). In certain embodiments, the steering module 225 operates in the MAC layer, for example, residing between a lower layer of the MAC and an upper layer of the MAC. The AP 106 or the steering module 225 may divide, allocate, or otherwise assign multiple antennas into multiple antenna subsets, for example, based on the configuration 224 or the integration module 221. In some embodiments, antennas may be assigned to more than one subset. Each antenna subset may be selected according to the configuration 224 and / or by the integration module 221, which may be consistent with one or more predefined rules, policies, requirements, and / or guidelines. For example, each antenna subset may include antennas that are physically adjacent to each other on the AP 106 and / or selected according to a certain order or sequence. In some embodiments, each antenna subset may include antennas separated from each other by at least one other antenna that is not in the subset, for example, to include a certain degree of spatial freedom or separation. In some embodiments, the directing module 225 configures each subset to include at least one antenna that is common to at least one other subset.

[0090] The steering module 225 may manage or control the transmission of data (e.g., content data) corresponding to the antenna subset. The steering module 225 may cause the coordinated transmission or joint transmission of content data in the guided frame through different antennas or with another AP 106 in a specific order. The steering module 225 may transmit according to the steering information (e.g., steering vectors). The steering module 225 may cause the transceiver 228 to transmit guided frames distributed or staggered over a period of time (e.g., at predetermined intervals). The steering module 225 may provide sufficient time for another AP 106 or device 102 to process each guidance and / or provide a response to each guidance before sending the next guided frame.

[0091] In some embodiments, the present method may be implemented or applied without the knowledge of the low-capability device 102. For example, the device 102 may not even be aware or aware that multiple access points 106 are coordinating and transmitting sounding frames or directed frames simultaneously.

[0092] In some embodiments, a high-dimensional transmit structure (eg, a single AP 106) may be formed by combining and / or coordinating two or more low-dimensional beamformers 106. Figure 2B, depicting an embodiment of a system for performing detection and steering between at least one AP 106 and at least one device 102. In brief, the system may include at least two APs operably coupled together to effectively operate as a single AP 106 (hereinafter sometimes referred to as a "coordinated beamformer" or a single "beamformer"). The coordinated beamformer may communicate with one or more devices 102 embodied as beamforming receiving ends. The coordinated beamformer may include a transceiver 228, an SCM 222, an integration module 221, a steering module 225, a storage module 223, and / or a configuration 224, each of which may include the above in combination with Figure 2A Each of these modules may reside on at least one of the coordinating beamformers (APs 106), be distributed among different APs 106, or may reside at one or more networking locations.

[0093] In some embodiments, increasing or combining the number of antennas at the AP 106 may provide better or improved array gain and diversity. By way of illustration, for single-user transmit beamforming, the array gain may be represented by 10*log10(NTX / Nss) dB, and the corresponding diversity order may be represented as NTX*NRX, where NTX may represent the number of transmit antennas and NRX may represent the number of receive antennas. A large number of transmit antennas at the beamformer side may provide more spatial degrees of freedom, for example, thereby allowing improved link quality. In some embodiments, the total capacity of the system may increase linearly (e.g., in an asymptotic sense) with respect to the number of beamformer antennas. A larger number of transmit antennas may support or host more beamformed receivers (e.g., multi-user STAs), thereby achieving better spectral efficiency, for example, using multi-user guided frames. In certain embodiments, a larger number of transmit antennas may allow better multi-user precoding matrices for a given set of beamformed receivers (e.g., multi-user STAs). A significant portion of existing access points 106 may be implemented with a limited number of transmit antennas, for example, up to three antennas. According to certain aspects of the present invention, transmit antennas from several low-dimensional beamformers 106 may be combined or aggregated to achieve better performance.

[0094] In some embodiments, multiple low-dimensional APs 106 are connected to each other, for example, via an Ethernet backbone or other connection (e.g., a wireless connection such as Wi-Fi, cellular, Bluetooth, etc.). These APs 106 can be coordinated to generate multiple sounding sequences between the APs 106 and the devices 102 to determine the channel (e.g., MU-MIMO channel) between each beamformer-beamformer receiver pair. For example, a combination of at least Figure 2A and 2BThe described techniques share and / or process sounding feedback reports from different devices 102 between coordinating beamformers (e.g., APs 106). For example, multiple sounding feedback reports from the same device 102 to multiple APs 106 may be combined, for example, as if the AP 106 comprised a single higher dimensional AP 106 in communication with the device 102. Multi-user precoding may be performed, for example, using the combined MU-MIMO channel. When performing multi-user steering, the coordinating beamformer 106 may have to coordinate guided frame transmissions so that the formed guided frames appear to come from a larger dimensional AP 106 rather than several different lower dimensional APs 106. The coordinating APs 106 may be time synchronized. For example, the APs 106 may coordinate guided frame transmissions over a backbone Ethernet or other connection (e.g., a wireless connection such as Wi-Fi, cellular, Bluetooth, etc.).

[0095] In certain embodiments, the system may synchronize the coordinated APs 106 in time and / or frequency, for example, by adjusting frame timing and / or carrier frequency offset (CFO). The coordinated APs 106 may transmit sounding frames, guided frames, or a combination thereof in a coordinated manner as if the frames were sent from a single larger dimension AP 106. Precoding matrices and / or guided frames may be formed in a coordinated manner. When performing multi-user guidance, the coordinated APs 106 may have to coordinate guided frame transmissions so that the guided frames formed appear to come from a larger dimension AP 106 rather than from several different lower dimension APs 106. When performing frequency synchronization, the coordinated APs 106 may synchronize their carrier frequency offsets or CFOs. This may be performed by observing uplink transmissions from different devices 102, sharing the CFO among the APs 106. In some embodiments, the coordinated APs 106 may be time synchronized. For example, one of the APs 106 may start frame transmissions first (e.g., transmit L-STF and L-LTF signals first). The remaining coordinated APs 106 may join in the transmission starting with the VHT-STF signal, for example, by monitoring the presence and / or timing of L-STF and L-LTF signals over the air.

[0096] Figure 3A 3 is a block diagram illustrating an example network environment 300 according to some embodiments, the network environment 300 includes a master AP 310 and a plurality of slave APs 320A, 320B for joint transmission of station devices 330A to 330E. In some embodiments, each of the master AP 310 and the slave APs 320A, 320B or the combination of the master AP 310 and the slave APs 320A, 320B is implemented or operated as Figure 2A and 2B In some embodiments, the network environment 300 includes more, less, or different than Figure 3A The components shown in .

[0097] In some embodiments, the master AP 310 is able to communicate directly with the slave APs 320A, 320B and the station devices 330A, 330C over the wireless medium, but may not be able to communicate directly with the station devices 330B, 330D, 330E individually. For example, the station devices 330A, 330C may individually successfully receive and decode wireless transmissions made by the master AP 310, but the station devices 330B, 330D, 330E may not individually successfully receive and decode wireless transmissions made by the master AP 310. In some embodiments, the slave AP 320A is able to communicate directly with the master AP 310 and the station devices 330B, 330C, 330D. In some embodiments, the slave AP 320B is able to communicate directly with the master AP 310 and the station devices 330C, 330D, 330E.

[0098] In some embodiments, the master AP 310 may configure, cause, or instruct the slave access points 320A, 320B to perform a joint transmission. In one aspect, the station devices 330A to 330E may successfully receive and decode the joint transmission performed by the master AP 310 and the slave APs 320A, 320B. In some embodiments, the master AP 310 and the slave APs 320A, 320B communicate with each other in a specific frame format over a wireless medium to achieve the joint transmission. In one aspect, the frame format disclosed herein enables the slave APs 320A, 320B to estimate or determine synchronization information for joint transmission with the master AP 310. Examples of synchronization information include a carrier frequency offset (CFO), a sampling frequency offset (SFO), a phase offset (PO), a timing offset (TO), a first reference value of a common phase offset, and / or a second reference value of a timing offset relative to the master AP 310. For example, the master AP 310 transmits a preamble of a slave trigger frame or a null data packet to the slave APs 320A, 320B containing information that enables the slave APs 320A, 320B to estimate or determine synchronization information. In some embodiments, the synchronization information is determined based on the measurement differences obtained in the sounding sequence and the guidance sequence. In one method, the slave AP uses the channel estimates represented here by the vectors h_ndp (for the channel before NDP) and h_data (for the channel before joint data transmission) to calculate two parameters related to phase drift: timing error (or acquisition error) and common phase drift. In some embodiments, the timing error is exhibited as a linear phase drift across frequency, where the common phase drift is due to different RF clocks and phase noise between the master AP 310 and the slave AP 320. Assuming frequency modulation i,

[0099]

[0100] Where N i is the noise component of tone i, corresponds to the timing error, and θ corresponds to the common phase drift. If h_data(i) and h_ndp(i) are known, then the phase difference h_diff(i) between h_data and h_ndp(i) can be considered as:

[0101]

[0102] Where N i ' is the modified noise component of tone i. Note that the channel phase appears and a positive real number is obtained by multiplying the phasor. In one aspect, this means that the channel impact is manifested by the variation of amplitude with frequency. With a MIMO configuration, in some embodiments, this metric is summed across the receive antennas. In one aspect, to determine the timing error, the following equation may be used:

[0103]

[0104] in is the noise component of tone i. In some embodiments, since the channel phase is not present in the timing metric shown in equation (3), it is allowed to increase K because it is the only angle contributor. In one aspect, to determine the common phase drift, the following equation may be used:

[0105] angle(Σ i (h_diff(i)*h_diff(-i))) / 2 Equation (4)

[0106] The synchronization information may be determined based on the timing error obtained by equation (3) and the common phase shift obtained by equation (4). In addition, based on the synchronization information, the master AP 310 and the slave APs 320A, 320B may perform joint transmission.

[0107] Figure 3B 3 is a flow chart illustrating an example process 350 for establishing an example multiple-input multiple-output (MIMO) communication according to some embodiments. In some embodiments, process 350 is performed by master AP 310, or by master AP 310 and slave APs 320A, 320B. In other embodiments, process 350 is performed by other entities. In other embodiments, process 350 includes more, less, or different than Figure 3B The steps shown in .

[0108] In one approach, the master AP 310 and the slave access points 320A, 320B perform 360 sounding. For example, the sounding controller 222 of the master AP 310 may initiate sounding to obtain or collect channel estimation information. The sounding controller 222 of the master AP 310 may cause the transceiver 228 of the master AP 310 to transmit, to the slave APs 320A, 320B over the wireless medium, a frame or portion of a frame that allows the slave APs 320A, 320B to obtain synchronization information for joint transmission to perform sounding. For example and in some embodiments, the sounding controller 222 of the master AP 310 causes the transceiver 228 of the master AP 310 to transmit a preamble of a slave trigger frame or a null data packet that allows the sounding controller 222 of the slave APs 320A, 320B to determine or estimate a carrier frequency offset, a sampling frequency offset, a phase offset, a timing offset, a first reference value of a common phase offset, and / or a second reference value of a timing offset relative to the master AP 310. In one aspect, it may be difficult to confirm the absolute phase offset and timing offset of the slave AP relative to the master AP. In some embodiments, the slave APs 320A, 320B may estimate the change in phase / timing offset between the sounding and the steering according to the above equations (1) to (4) (via the previous trigger frame). The sounding controller 222 of the master AP 310 causes the transceiver 228 of the master AP 310 to transmit a portion of a frame (e.g., an NDP frame) to the station devices 330A to 330E to cause the station devices 330A to 330E to perform channel estimation. The sounding controller 222 of the slave APs 320A, 320B may cause the transceiver 228 of the slave APs 320A, 320B to transmit a portion of a frame to the station devices 330A to 330E according to the synchronization information, while the master AP 310 transmits a portion of a frame (e.g., an NDP frame). The joint transmission of the master AP 310 and the slave APs 320A, 320B allows the station devices 330A to 330E to successfully receive and decode portions of the frame. In one approach, the station devices 330A to 330E may measure or determine the signal strength and / or signal quality of the joint transmission used for sounding and generate channel estimation information indicative of the measured signal strength or signal quality. Figures 5 to 9 Provides a detailed description of example frame formats and detection operations.

[0109] In one approach, the master AP 310 generates 365 steering information in response to the channel estimation information. In some embodiments, the integration module 221 of the master AP 310 receives and integrates the channel estimation information from the different station devices 330A to 330B, and determines or generates steering information based on the integrated channel estimation information to perform steering. In one aspect, the steering information indicates the configuration of the transceiver 228 for steering for each AP. For example, the steering information indicates the timing, power, gain, channel bandwidth, frequency, steering vectors for transmission through one or more antennas, or indicates how to radiate energy in a specific direction, frequency correlation within a channel, signal-to-noise ratio (SNR), and / or appropriate data rate adjustments for joint transmission with other access points. The integration module 221 of the master AP 310 generates steering information based on the channel estimation information, which allows the access points 310, 320A, 320B to perform joint transmission. In one aspect, the master AP 310 generates the steering information and shares the steering information with the slave APs 320A, 320B. In some embodiments, each slave AP 320 generates the steering information itself, provided that the same channel information is available for all APs.

[0110] In one approach, the master AP 310 performs 370 bootstrapping according to the bootstrapping information. For example, the bootstrapping controller 225 of the master AP 310 may initiate bootstrapping. The bootstrapping controller 225 of the master AP 310 may cause the transceiver 228 of the master AP 310 to transmit a frame that allows the slave APs 320A, 320B to obtain synchronization information for joint transmission to the slave APs 320A, 320B to perform bootstrapping. For example, the bootstrapping controller 225 of the master AP 310 causes the transceiver 228 of the master AP 310 to transmit a preamble of a slave trigger frame or a bootstrapping frame that allows the bootstrapping controller 225 of the slave APs 320A, 320B to determine or estimate a carrier frequency offset, a sampling frequency offset, a phase offset, a timing offset, a first reference value of a common phase offset, and / or a second reference value of a timing offset relative to the master AP 310. In one aspect, it may be difficult to confirm the absolute phase offset and timing offset of the slave AP relative to the master AP. In some embodiments, the slave APs 320A, 320B may estimate the change in phase / timing offset between the sounding and the steering according to the above equations (1) to (4) (via the previous trigger frame). The steering controller 225 of the master AP 310 causes the transceiver 228 of the master AP 310 to transmit a portion of the guided frame to the station devices 330A to 330E. The portion of the guided frame may include content data (e.g., text, images, video, or any data). The steering controller 225 of the slave APs 320A, 320B may cause the transceiver 228 of the slave APs 320A, 320B to transmit a portion of the guided frame to the station devices 330A to 330E according to the synchronization information, while the master AP 310 transmits the portion of the guided frame. The joint transmission of the master AP 310 and the slave APs 320A, 320B allows the station devices 330A to 330E to successfully receive and decode the portion of the guided frame and extract the content data from the guided frame. Figures 10 to 13 Provides a detailed description of the example frame format and boot operations.

[0111] Figure 4 Example timing diagram illustrating joint transmission of a master AP and slave APs to a station device. In some embodiments, the detection controller 222 of the master AP causes or configures its transceiver 228 to communicate with the slave AP and the station device. In some embodiments, the detection controller 222 of the slave AP causes or configures its transceiver 228 to communicate with the master AP and the station device. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0112] In some embodiments, the detection controller 222 of the master AP causes or configures the transceiver 228 of the master AP to transmit 410 a slave trigger frame to the slave AP. In some embodiments, the slave trigger frame is a frame transmitted by the master AP for triggering some or all slave APs to jointly transmit subsequent frames. In one aspect, the slave trigger frame is similar to the trigger frame of the HE TB PPDU in 802.11ax. In one aspect, the slave trigger frame may be replaced by the preamble of the subsequent frame. In some embodiments, the slave trigger frame indicates which slave APs participate in the subsequent joint transmission, which may be dynamically changed from one joint TX to the next joint TX. In some embodiments, the slave trigger frame allows the slave AP to estimate its CFO / SFO, phase offset (PO), timing offset (TO), first reference value of PO and / or second reference value of TO relative to the master AP through the long training field (LTF) contained in the frame. In order to improve the accuracy of these estimates, the number of LTFs may be greater than the number sufficient for channel estimation. In some embodiments, these LTFs may be located non-continuously in the frame, such as in the midamble or in the postamble. In some embodiments, the slave trigger frame contains PHY / MAC level information for constructing and jointly transmitting subsequent frames, for example and may contain frame type / purpose, rate, receiver MAC address(es), payload, etc. In some embodiments, the slave trigger frame contains data for the slave AP to be used for future joint AP transmissions, either in a subsequent packet or in the same packet with a certain delay. In some embodiments, the detection controller 222 of the slave AP causes or configures its transceiver 228 to receive the slave trigger frame, and decodes the slave trigger frame to generate 415 synchronization information by estimating the reference value of CFO, SFO, PO, TO, PO, and / or TO relative to the master AP. In one aspect, the station device may not successfully listen to or decode 418 the slave trigger frame.

[0113] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 420 a joint frame to the station device, for example, after a short interframe space (SIFS) after the end of the slave trigger frame. During the short interframe space, the master AP and the slave AP may not transmit. In one aspect, the detection controller 222 of the slave AP causes its transceiver 228 to transmit 422 a joint frame to the station device, while the master AP transmits 420 the joint frame. The detection controller 222 of the slave AP may correct its reference value of CFO, SFO, PO, TO, PO and / or TO relative to the master AP and transmit jointly with the master AP. In one aspect, CSI-related steering vectors may not be applied, so that the joint transmission of the master AP and the slave AP cannot be beamformed. In some embodiments, the joint transmission may be broadcast / multicast or unicast in the absence of CSI. In one aspect, some or all APs transmit the same preamble and payload encoded at the same PHY rate in the joint frame. In some embodiments, the AP's sounding controller 222 modulates the signal for transmission with a set of different cyclic delays to avoid unintentional beamforming, for example, in 802.11n / ac / ax single-user transmissions.

[0114] In some embodiments, the station device receives the joint transmission of the master AP and the slave AP, and processes or decodes 428 the joint transmission. For example, the station device measures or determines the signal strength or signal quality of the joint transmission, and generates channel estimation information indicating the measured signal strength or signal quality. In some embodiments, the station device transmits or provides the channel estimation information to the master AP, the slave AP, or any AP.

[0115] Figure 5 An example timing diagram illustrating a sounding sequence according to some embodiments. In some embodiments, a master AP and a slave AP perform a joint transmission for sounding. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0116] In some embodiments, the detection controller 222 of the master AP configures or causes its transceiver to transmit 510 a slave trigger frame to the slave AP. In one aspect, the slave trigger frame reminds the slave AP to start the detection sequence. In one aspect, the slave trigger frame contains information to be transmitted jointly with the slave AP in a subsequent NDP declaration frame. In one aspect, the slave trigger frame indicates the content of the preamble code 2 and / or the number of LTFs in the NDP frame. The slave trigger frame can be decoded by some or all slave APs. In some embodiments, the detection controller 222 of the slave AP estimates 515 synchronization information for the NDP declaration frame. For example, the detection controller 222 of the slave AP measures or estimates the reference value of CFO, SFO, PO, TO, PO and / or TO relative to the master AP, and synchronizes with the master AP according to the reference value of CFO, SFO, PO, TO, PO and / or TO for subsequent NDP declaration frames. In some embodiments, the station device may or may not decode 518 the slave trigger frame.

[0117] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 520 an NDP declaration frame to the station device, for example, after a SIFS after the end of the slave trigger frame. During the short inter-frame interval, the master AP and the slave AP may not transmit. In some embodiments, the NDP declaration frame contains information about which station devices are expected to feedback channel information and the type of channel information. In one aspect, the detection controller 222 of the slave AP causes its transceiver 228 to transmit 522 an NDP declaration frame to the station device, and the master AP transmits 520 the NDP declaration frame. In one aspect, the slave AP synchronizes with the master AP according to the synchronization information used for the joint transmission of the NDP declaration frame. The station device may receive the joint transmission of the NDP declaration frame by the master AP and the slave AP, and prepare 528 for subsequent NDP frames, similar to the HE / VHT sounding sequence. In some embodiments, the station device checks whether the station device is on a list of devices that should receive subsequent NDP frames.

[0118] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit the NDP, for example, after a SIFS after the end of the NDP announcement frame. During the short interframe interval, the master AP and the slave AP may not transmit. In some embodiments, the NDP frame includes a preamble 1, a preamble 2, and an LTF. In one aspect, preamble 1 is transmitted 530 by the master AP rather than by the slave AP. In some embodiments, the slave AP receives preamble 1 and estimates 535 or updates synchronization information (e.g., a reference value of CFO, SFO, PO, TO, PO, and / or TO relative to the master AP) based on preamble 1. In one aspect, preamble 1 allows the slave AP enough time to switch from a receive mode to a transmit mode to jointly transmit the remainder of the NDP frame. In some embodiments, preamble 1 indicates the content of a portion of a subsequent frame (e.g., preamble 2) and / or the number of LTFs. In some embodiments, the station device may not listen / decode 538 preamble 1, or may choose to ignore preamble 1.

[0119] In some embodiments, the sounding controller 222 of the master AP causes its transceiver 228 to transmit 540 Preamble 2 after the end of Preamble 1. In some embodiments, the sounding controller 222 of the slave AP causes its transceiver 228 to transmit 542 Preamble 2 to the station device according to the synchronization information while the master AP transmits Preamble 2. In some embodiments, the joint transmission of Preamble 2 by the master and slave APs causes or allows the station device to receive, decode and / or process the LTF, such as a mixed mode preamble in the HE / VHT NDP.

[0120] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 550 LTF after the end of the preamble 2. In some embodiments, the detection controller 222 of the slave AP configures its transceiver 228 to transmit 552 LTF to the station device according to the synchronization information, and the master AP transmits 550 LTF. In some embodiments, the joint transmission of LTF by the master AP and the slave AP indicates, causes or allows the station device to measure the channel from the master AP and the slave AP. In one aspect, the total number of LTFs may exceed the maximum number of detection dimensions supported by any single AP. In some embodiments, the master AP and (several) slave APs independently modulate the LTFs using different orthogonal codes (e.g., different rows of the Hadamard matrix, similar to HE UL MUMIMO transmissions) to facilitate separation at the station device. In some embodiments, the station device detects the NDP frame and generates 548 channel estimation information for the downlink channel according to the LTF. In one method, the station device transmits the channel estimation information to the master AP and / or the slave AP. The integration module 221 of the master AP or the slave AP may integrate the channel estimation information from the station devices and calculate the steering vectors for joint MU-MIMO transmission.

[0121] Figure 6An example timing diagram illustrating another sounding sequence according to some embodiments. In some embodiments, the master AP and slave APs perform a joint transmission for sounding. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0122] In some embodiments, the detection controller 222 of the master AP configures or causes its transceiver to transmit 610 a slave trigger frame 1 to the slave AP. In one aspect, the slave trigger 1 reminds the slave AP to start a detection sequence. In one aspect, the slave trigger frame 1 contains information to be transmitted jointly with the slave AP in a subsequent NDP declaration frame. In one aspect, the slave trigger frame 1 indicates the content of the NDP frame and / or the number of LTFs in the NDP frame. The slave trigger frame 1 can be decoded by some or all slave APs. In some embodiments, the detection controller 222 of the slave AP estimates 615 synchronization information for the NDP declaration frame. For example, the detection controller 222 of the slave AP measures or estimates a reference value of CFO, SFO, PO, TO, PO and / or a reference value of TO relative to the master AP, and synchronizes with the master AP according to the reference value of CFO, SFO, PO, TO, PO and / or a reference value of TO for subsequent NDP declaration frames. In some embodiments, the station device may or may not decode 618 the slave trigger frame 1.

[0123] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 620 an NDP declaration frame to the station device, for example, after SIFS after the end of the slave trigger frame 1. During the short inter-frame interval, the master AP and the slave AP may not transmit. In some embodiments, the NDP declaration frame contains information about which station devices are expected to feedback channel information and the type of channel information. In one aspect, the detection controller 222 of the slave AP causes its transceiver 228 to transmit 622 an NDP declaration frame to the station device, and the master AP transmits 620 the NDP declaration frame. In one aspect, the slave AP synchronizes with the master AP according to the synchronization information used for the joint transmission of the NDP declaration frame. The station device may receive the joint transmission of the NDP declaration frame by the master AP and the slave AP, and prepare 628 for subsequent NDP frames, similar to the HE / VHT sounding sequence. In some embodiments, the station device checks whether the station device is on the list of devices that should receive subsequent NDP frames.

[0124] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 630 a slave trigger frame 2, for example, after a SIFS after the end of the NDP declaration frame. During the short interframe interval, the master AP and the slave AP may not transmit. In one aspect, the slave trigger frame 2 is transmitted 630 by the master AP rather than by the slave AP. In some embodiments, the detection controller 222 of the slave AP configures the transceiver 228 of the slave AP to receive the slave trigger frame 2, and estimates 635 or updates synchronization information (e.g., CFO, SFO, PO, TO, reference values ​​of PO and / or reference values ​​of TO relative to the master AP) based on the slave trigger frame 2. In one aspect, the slave trigger frame 2 allows the slave AP to have enough time to switch from a receive mode to a transmit mode to jointly transmit an NDP frame. In some embodiments, the slave trigger frame 2 indicates the content of the NDP frame and / or the number of LTFs in the NDP frame. In some embodiments, the station device may not listen / decode 638 the slave trigger frame 2, or may choose to ignore the slave trigger frame 2.

[0125] In some embodiments, the sounding controller 222 of the master AP causes its transceiver 228 to transmit 640 NDP, for example, after SIFS after the end of the slave trigger frame 2. During the short interframe interval, the master AP and the slave AP may not transmit. In some embodiments, the slave AP transmits 642 the NDP frame to the station device according to the synchronization information, and the master AP transmits 640 the NDP frame. In some embodiments, the joint transmission of the NDP frame by the master AP and the slave AP causes or allows the station device to receive, decode and / or process LTFs, such as mixed mode preambles in HE / VHT NDP. In some embodiments, the joint transmission of the NDP frame by the master AP and the slave AP indicates, causes or allows the station device to measure channels from the master AP and the slave AP. In one aspect, the total number of LTFs in the NDP frame may exceed the maximum number of sounding dimensions supported by any single AP. In some embodiments, the master AP and the slave AP independently modulate the LTFs in the NDP frame using different orthogonal codes (e.g., different rows of the Hadamard matrix, similar to HE UL MUMIMO transmissions) to facilitate separation at the station device. In some embodiments, the station device detects the NDP frame and generates 648 channel estimation information for the downlink channel according to the LTF in the NDP frame. In one method, the station device transmits the channel estimation information to the master AP and / or the slave AP. The integration module 221 of the master AP or the slave AP can integrate the channel estimation information from the station device and calculate the steering vector for joint MU-MIMO transmission.

[0126] Figure 7 An example timing diagram illustrating another sounding sequence according to some embodiments. In some embodiments, the master AP and slave APs perform a joint transmission for sounding. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0127] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 710 an NDP announcement frame to the slave AP and the station device. In some embodiments, the NDP announcement frame notifies or indicates the joint transmission of the NDP frame. The NDP announcement frame may contain information for the station device to use in processing the NDP and constructing the CSI feedback. In some embodiments, the NDP announcement frame is used as Figure 5 or Figure 6 The slave trigger frame in the NDP declaration frame. The NDP declaration frame may indicate the slave APs participating in the joint transmission of the NDP frame. The NDP declaration frame may allow the slave AP to estimate the reference values ​​of CFO, SFO, PO, TO, PO and / or TO relative to the master AP. In addition, the NDP declaration frame may contain information about how to construct the NDP frame (for example, the number of LTFs, etc.). In some embodiments, the detection controller 222 of the slave AP configures the transceiver 228 of the slave AP to receive the NDP declaration frame, and estimates 715 or updates the synchronization information (for example, the reference values ​​of CFO, SFO, PO, TO, PO and / or TO relative to the master AP) according to the NDP declaration frame. In some embodiments, the NDP declaration frame indicates the content of the NDP frame and / or the number of LTFs in the NDP frame. In some embodiments, the station device receives and decodes the NDP declaration frame of the master AP, and obtains 718 information to receive or process the NDP and construct CSI feedback.

[0128] In some embodiments, the sounding controller 222 of the master AP causes its transceiver 228 to transmit 720 the NDP, for example, after SIFS after the end of the NDP declaration frame. During the short interframe interval, the master AP and the slave AP may not transmit. In some embodiments, the sounding controller 222 of the slave AP configures or causes the transceiver 228 of the slave AP to transmit 722 the NDP frame to the station device according to the synchronization information, and the master AP transmits 720 the NDP frame. In some embodiments, the joint transmission of the NDP frame by the master AP and the slave AP causes or allows the station device to receive, decode and / or process the LTFs in the NDP frame. In some embodiments, the joint transmission of the NDP frame by the master AP and the slave AP indicates, causes or allows the station device to measure the channels from the master AP and the slave AP. In one aspect, the total number of LTFs in the NDP frame may exceed the maximum number of sounding dimensions supported by any single AP. In some embodiments, the master AP and (several) slave APs independently modulate the LTFs in the NDP frame using different orthogonal codes (e.g., different rows of the Hadamard matrix, such as in HE UL MUMIMO transmissions) to facilitate separation at the station device. In some embodiments, the station device detects the NDP frame and generates 728 channel estimation information for the downlink channel according to the LTF in the NDP frame. In one method, the station device transmits the channel estimation information to the master AP and / or the slave AP. The integration module 221 of the master AP or the slave AP can integrate the channel estimation information from the station device and calculate the steering vector for joint MU-MIMO transmission.

[0129] Figure 8 An example timing diagram illustrating another sounding sequence according to some embodiments. In some embodiments, the master AP and slave APs perform a joint transmission for sounding. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0130] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 810 a first portion of a frame (e.g., an NDP frame) to the slave APs and station devices. In some embodiments, the first portion of the frame includes a preamble and a payload. In some embodiments, the preamble of the first portion of the frame may indicate a special frame type to distinguish it from other types of detection sequences. In some embodiments, the first portion of the frame indicates the number of tail LTFs, and the positions of the tail STFs and LTFs. In some embodiments, the first portion of the frame identifies the participating stations and notifies detection parameters, expected CSI, etc. In some embodiments, the first portion of the frame identifies the participating slave APs and allows estimation of CFO, SFO, PO, TO, reference values ​​of PO and / or reference values ​​of TO relative to the master AP. In some embodiments, the first portion of the frame allows the slave AP to transition from a receive mode to a transmit mode. In some embodiments, the first portion of the frame is used as Figure 5 or Figure 6In some embodiments, the detection controller 222 of the slave AP configures the transceiver 228 of the slave AP to receive the first part of the frame, and estimates 815 or updates synchronization information (e.g., relative to CFO, SFO, PO, TO, reference value of PO and / or reference value of TO to the master AP) according to the first part of the frame. In some embodiments, the station device receives and decodes 818 the first part of the frame transmitted by the master AP, and obtains information for CSI feedback estimation.

[0131] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 820 a second portion of the frame after the first portion of the frame. In some embodiments, the second portion of the frame includes a short training field (STF). In some embodiments, the detection controller 222 of the slave AP configures or causes the transceiver 228 of the slave AP to transmit 822 the second portion of the frame to the station device according to the synchronization information while the master AP transmits the second portion of the frame. In some embodiments, the joint transmission of the second portion of the frame by the master AP and the slave AP causes or allows the station device to receive the second portion of the frame and perform 828 automatic gain control (AGC) or adjust gain settings.

[0132] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 830 the third part of the frame after the second part of the frame. In some embodiments, the third part of the frame includes a long training field (LTF). In some embodiments, the detection controller 222 of the slave AP configures or causes the transceiver 228 of the slave AP to transmit 832 the third part of the frame to the station device according to the synchronization information, while the master AP transmits 830 the third part of the frame. In some embodiments, the joint transmission of the third part of the frame by the master AP and the slave AP causes or allows the station device to receive, decode and / or process the LTFs in the third part of the frame. In some embodiments, the joint transmission of the third part of the frame by the master AP and the slave AP indicates, causes or allows the station device to measure the channels from the master AP and the slave AP. In one aspect, the total number of LTFs in the third part of the frame may exceed the maximum number of detection dimensions supported by any single AP. In some embodiments, the master AP and (several) slave APs independently modulate the LTFs in the third part of the frame using different orthogonal codes (e.g., different rows of the Hadamard matrix, similar to HE UL MUMIMO transmission) to facilitate separation at the station device. In some embodiments, the station device detects the third portion of the frame and generates 838 channel estimation information for the downlink channel based on the LTFs in the third portion of the frame. In one method, the station device transmits the channel estimation information to the master AP and / or the slave AP. The integration module 221 of the master AP or the slave AP may integrate the channel estimation information from the station device and calculate the steering vector for joint MU-MIMO transmission.

[0133] Fig. 9An example timing diagram illustrating another sounding sequence according to some embodiments. In some embodiments, the master AP and slave APs perform a joint transmission for sounding. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0134] In some embodiments, the detection controller 222 of the master AP configures or causes its transceiver to transmit 910 a slave trigger frame to the slave AP. In one aspect, the slave trigger frame reminds the slave AP to start the detection sequence. In one aspect, the slave trigger frame contains information to be transmitted jointly with the slave AP in a subsequent NDP announcement frame. In one aspect, the slave trigger frame indicates the content of the NDP frame and / or the number of LTFs in the NDP frame. The slave trigger frame can be decoded by some or all slave APs. In some embodiments, the detection controller 222 of the slave AP estimates 915 synchronization information for the NDP announcement frame (e.g., reference values ​​of CFO, SFO, PO, TO, PO, and / or reference values ​​of TO relative to the master AP). For example, the detection controller 222 of the slave AP measures or estimates reference values ​​of CFO, SFO, PO, TO, PO, and / or reference values ​​of TO relative to the master AP, and synchronizes with the master AP according to the reference values ​​of CFO, SFO, PO, TO, PO, and / or reference values ​​of TO for subsequent NDP announcement frames. In some embodiments, the station device may or may not decode 918 the slave trigger frame.

[0135] In some embodiments, the detection controller 222 of the master AP causes its transceiver 228 to transmit 920 an NDP declaration frame to the station device, such as after a SIFS after the end of the slave trigger frame. During the short interframe interval, the master AP and the slave AP may not transmit. In some embodiments, the NDP declaration frame contains information about which station devices are expected to feedback channel information and the type of channel information. In one aspect, the detection controller 222 of the slave AP causes its transceiver 228 to transmit 922 an NDP declaration frame to the station device, and the master AP transmits 920 the NDP declaration frame. In one aspect, the slave AP synchronizes with the master AP based on synchronization information for the joint transmission of the NDP declaration frame. The station device may receive the joint transmission of the NDP declaration frame by the master AP and the slave AP, and prepare 928 for subsequent NDP frames, similar to the HE / VHT sounding sequence. In some embodiments, the station device checks whether the station device is on a list of devices that should receive subsequent NDP frames.

[0136] In some embodiments, the sounding controller 222 of the master AP causes its transceiver 228 to transmit 930 the NDP, for example, after a SIFS after the end of the NDP declaration frame. During the short interframe interval, the master AP and the slave AP may not transmit. In some embodiments, the slave AP transmits 932 the NDP frame to the station device according to the synchronization information, and the master AP transmits 930 the NDP frame. In some embodiments, the joint transmission of the NDP frame by the master AP and the slave AP causes or allows the station device to receive, decode and / or process LTFs, such as mixed mode preambles in HE / VHT NDP. In some embodiments, the joint transmission of the NDP frame by the master AP and the slave AP indicates, causes or allows the station device to measure channels from the master AP and the slave AP. In one aspect, the total number of LTFs in the NDP frame may exceed the maximum number of sounding dimensions supported by any single AP. In some embodiments, the master AP and (several) slave APs independently modulate the LTFs in the NDP frame using different orthogonal codes (e.g., different rows of the Hadamard matrix, similar to HE UL MUMIMO transmissions) to facilitate separation at the station device. In some embodiments, the station device detects the NDP frame and generates 938 channel estimation information for the downlink channel according to the LTF in the NDP frame. In one method, the station device transmits the channel estimation information to the master AP and / or the slave AP. The integration module 221 of the master AP or the slave AP can integrate the channel estimation information from the station device and calculate the steering vector for joint MU-MIMO transmission.

[0137] Fig.10 An example timing diagram illustrating a bootstrap sequence according to some embodiments. In some embodiments, a master AP and a slave AP perform a joint transmission for bootstrapping. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0138] In some embodiments, the guidance controller 225 of the master AP configures or causes its transceiver to transmit 1010 a slave trigger frame to the slave AP. In one aspect, the slave trigger frame reminds the slave AP to start the guidance sequence. In one aspect, the slave trigger frame includes a preamble that allows the slave AP to determine or estimate synchronization information. In one aspect, the slave trigger frame includes a payload indicating how to construct a guided frame (e.g., the target station device for the guided frame, the PHY / MAC transmission parameters for each station device, which data frames are transmitted to each station device, etc.). In one method, the guidance controller 225 of the slave AP calculates a guidance vector for the joint transmission of the guided frame to the indicated station device. The slave trigger frame can be decoded by some or all slave APs. In some embodiments, the guidance controller 225 of the slave AP estimates 1015 the synchronization information for the guided frame. For example, the guidance controller 225 of the slave AP measures or estimates the CFO, SFO, PO, TO relative to the master AP, and synchronizes with the master AP according to CFO, SFO, PO, TO for subsequent guided frames. In some embodiments, the station device may or may not decode 1018 the slave trigger frame. In some embodiments, PO, TO, or a combination of PO and TO is not determined during the probe sequence, and in step 1015, the probe controller 225 from the AP may determine the change in PO and / or TO between the probe sequence and the guidance sequence as described above with respect to equations (1) to (4).

[0139] In some embodiments, the steering controller 225 of the master AP causes its transceiver 228 to transmit 1020 a preamble of a control frame to the station device, for example, after a SIFS after the end of the slave trigger frame. During the short interframe interval, the master AP and the slave AP may not transmit. In some embodiments, the steering controller 225 of the slave AP causes its transceiver 228 to transmit 1022 a preamble of a guided frame to the station device, and the master AP transmits the preamble 1020 to the station device. In some embodiments, the station device receives and processes 1028 the preamble. In one aspect, the station device prepares for subsequent data transmission. In some embodiments, the station device estimates or determines a field (e.g., a signal field) containing information used to decode the payload in a subsequent joint transmission of the master AP and the slave AP. In one aspect, the master AP and the slave AP jointly transmit a guided frame by applying the corresponding steering vector indicated in the steering information. In one aspect, the steering controller 225 of the slave AP compensates the CFO, SFO, TO, PO, reference value of PO and / or reference value of TO for the joint transmission of the preamble according to the synchronization information.

[0140] In some embodiments, the master AP's steering controller 225 causes its transceiver 228 to transmit 1030 content data via a guided frame to the station device, e.g., following a preamble. In some embodiments, the slave AP's steering controller 225 causes its transceiver 228 to transmit 1032 content data via a guided frame to the station device, while the master AP transmits 1030 the content data to the station device. In some embodiments, the station device receives and decodes 1038 the joint transmission of content data.

[0141] In some embodiments, the steering controller 225 of the master AP causes its transceiver to transmit 1040 a midamble of the guided frame, for example, after transmitting 1030 the content data. In some embodiments, the steering controller 225 of the slave AP estimates 1045 or adjusts synchronization information for the remainder of the guided frame. For example, the steering controller 225 of the slave AP measures or adjusts a reference value of CFO, SFO, PO, TO, a reference value of PO, and / or a reference value of TO relative to the master AP. In some embodiments, PO, TO, or a combination of PO and TO is not determined during the sounding sequence, and at step 1045, the sounding controller 225 of the slave AP may determine a change in PO and / or TO between the sounding sequence and the steering sequence as described above with respect to equations (1) to (4). In one aspect, the slave AP may not transmit, while the master AP transmits 1040 a midamble. In some embodiments, the station device may or may not decode 1048 a slave trigger frame. In some embodiments, the slave AP updates the synchronization information for the remainder of the frame by using the content of the midamble. In some embodiments, the midamble allows the slave AP sufficient time to switch from the transmit mode to the receive mode before updating the synchronization information and switch back to the transmit mode after updating the synchronization information.

[0142] In some embodiments, the master AP's steering controller 225 causes its transceiver 228 to transmit 1050 the content data via a guided frame to the station device, e.g., after a midamble. In some embodiments, the slave AP's steering controller 225 causes its transceiver 228 to transmit 1052 the content data via a guided frame to the station device, while the master AP transmits 1050 the content data to the station device. In some embodiments, the station device receives and decodes 1058 the joint transmission of the content data. In some embodiments, during transmission 1052, the slave AP uses updated synchronization information obtained from the midamble to jointly transmit with the master AP.

[0143] Fig.11 An example timing diagram illustrating a bootstrap sequence according to some embodiments. In some embodiments, a master AP and a slave AP perform a joint transmission for bootstrapping. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0144] In some embodiments, the guidance controller 225 of the master AP configures or causes its transceiver to transmit 1110 guidance information of a frame (e.g., a slave trigger frame) to the slave AP. In one aspect, the guidance information of the frame alerts the slave AP to start the guidance sequence. In one aspect, the guidance information of the frame includes a preamble and a payload. The preamble of the guidance information may indicate the frame type to distinguish it from other types of frames. In some embodiments, the guidance information of the frame provides information for the guidance controller 225 of the slave AP to decode portions of the frame to extract content data. In one aspect, the guidance information of the frame indicates the presence of any midambles in the frame. In one aspect, the guidance information of the frame is used as Fig.10 1115 , the slave trigger frame. In one approach, the steering controller 225 of the slave AP calculates a steering vector for the joint transmission of the frame to the indicated station device. The steering information of the frame may be decoded by some or all of the slave APs. In some embodiments, the steering controller 225 of the slave AP estimates 1115 synchronization information for the frame (e.g., a guided frame). For example, the steering controller 225 of the slave AP measures or estimates a reference value of CFO, SFO, PO, TO, a reference value of PO, and / or a reference value of TO relative to the master AP, and synchronizes with the master AP according to the reference value of CFO, SFO, PO, TO, a reference value of PO, and / or a reference value of TO for subsequent guided frames. In some embodiments, PO, TO, or a combination of PO and TO is not determined during the sounding sequence, and at step 1115, the sounding controller 225 of the slave AP may determine a change in PO and / or TO between the sounding sequence and the steering sequence as described above with respect to equations (1) to (4). In one aspect, the station device receives the joint transmission of the steering information of the frame and prepares 1118 to decode the remainder of the guided frame. In some embodiments, the station device estimates or determines a field (eg, a signal field) that includes information used to decode the payload in a subsequent joint transmission of the master and slave APs.

[0145] In some embodiments, the steering controller 225 of the master AP causes its transceiver 228 to transmit 1120 an STF of a frame (e.g., a guided frame) to the station device, e.g., after transmitting the steering information. In some embodiments, the steering controller 225 of the slave AP causes its transceiver 228 to transmit 1122 an STF of a frame to the station device, and the master AP transmits 1120 the STF to the station device. In some embodiments, the master AP and the slave AP jointly transmit the guided frame by applying the respective steering vectors indicated in the steering information. In some embodiments, the STFs transmitted by the master AP and the slave AP allow the station device to perform 1128 automatic gain control (AGC) or adjust gain settings.

[0146] In some embodiments, the steering controller 225 of the master AP causes its transceiver 228 to transmit 1130 an LTF of a frame (e.g., a guided frame) to the station device, e.g., after transmitting the STF. In some embodiments, the steering controller 225 of the slave AP causes its transceiver 228 to transmit 1132 an LTF of a frame to the station device, while the master AP transmits 1130 the LTF to the station device. In some embodiments, the master AP and the slave AP jointly transmit guided frames by applying respective steering vectors indicated in the steering information. In some embodiments, the LTFs transmitted by the master AP and the slave AP allow the station device to estimate 1138 channel information. Based on the channel estimate, the station device can decode the jointly transmitted data from the master AP and the slave AP.

[0147] In some embodiments, the master AP's steering controller 225 causes its transceiver 228 to transmit 1140 the content data via a guided frame to the station device, e.g., following a preamble. In some embodiments, the slave AP's steering controller 225 causes its transceiver 228 to transmit 1142 the content data via a guided frame to the station device, while the master AP transmits 1140 the content data to the station device. In some embodiments, the station device receives and decodes 1148 the joint transmission of the content data.

[0148] In some embodiments, the guidance controller 225 of the master AP causes its transceiver to transmit 1150 a midamble of the guided frame, for example, after transmitting 1140 the content data. In some embodiments, the guidance controller 225 of the slave AP estimates 1155 or adjusts synchronization information for the remaining portion of the guided frame. For example, the guidance controller 225 of the slave AP measures or adjusts a reference value of CFO, SFO, PO, TO, a reference value of PO, and / or a reference value of TO relative to the master AP. In some embodiments, PO, TO, or a combination of PO and TO is not determined during the sounding sequence, and at step 1155, the sounding controller 225 of the slave AP may determine or update a change in PO and / or TO between the sounding sequence and the guidance sequence as described above with respect to equations (1) to (4). In one aspect, the slave AP may not transmit, while the master AP transmits 1150 a midamble. In some embodiments, the station device may or may not decode the slave trigger frame. In some embodiments, the slave AP updates synchronization information of one or more subsequent frames by using the content of the midamble. In some embodiments, the midamble allows the slave AP sufficient time to switch from the transmit mode to the receive mode before updating the synchronization information and switch back to the transmit mode after updating the synchronization information.

[0149] In some embodiments, the master AP's steering controller 225 causes its transceiver 228 to transmit 1160 content data via a guided frame to the station device, e.g., after a midamble. In some embodiments, the slave AP's steering controller 225 causes its transceiver 228 to transmit 1162 content data via a guided frame to the station device, while the master AP transmits 1160 the content data to the station device. In some embodiments, the station device receives and decodes 1168 the joint transmission of the content data. In some embodiments, during transmission 1162, the slave AP uses updated synchronization information obtained from the midamble to jointly transmit with the master AP.

[0150] Fig.12 An example timing diagram illustrating a bootstrap sequence according to some embodiments. In some embodiments, a master AP and a slave AP perform a joint transmission for bootstrapping. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0151] In some embodiments, the steering controller 225 of the master AP configures or causes its transceiver to transmit 1210 a slave trigger frame to the slave AP. In one aspect, the slave trigger frame reminds the slave AP to start a steering sequence. In one aspect, the slave trigger frame indicates, causes or allows the slave AP to determine or estimate synchronization information. In one method, the steering controller 225 of the slave AP calculates a steering vector for joint transmission of a first guided frame to the indicated station device. The slave trigger frame can be decoded by some or all of the slave APs. In some embodiments, the steering controller 225 of the slave AP estimates 1215 the synchronization information for the first guided frame. For example, the steering controller 225 of the slave AP measures CFO, SFO, PO, TO, a reference value of PO and / or a reference value of TO relative to the master AP, and synchronizes with the master AP to jointly transmit the first guided frame. In some embodiments, PO, TO, or a combination of PO and TO is not determined during the sounding sequence, and at step 1215, the sounding controller 225 of the slave AP may determine the change in PO and / or TO between the sounding sequence and the steering sequence as described above with respect to equations (1) to (4). In some embodiments, the station device may or may not decode the slave trigger frame.

[0152] In some embodiments, the steering controller 225 of the master AP causes its transceiver 228 to transmit 1220 a first guided frame containing content data to the station device, e.g., after a SIFS (e.g., 16 μs) or less after the end of the slave trigger frame. In some embodiments, the master AP and the slave AP may not transmit during the IFS. In some embodiments, the steering controller 225 of the slave AP causes its transceiver 228 to transmit 1222 a first guided frame to the station device, and the master AP transmits 1220 the first guided frame to the station device. In some embodiments, the master AP and the slave AP jointly transmit the first guided frame by applying the respective steering vectors indicated in the steering information. In some embodiments, the station device receives and decodes 1228 the joint transmission of content data.

[0153] In some embodiments, the master AP's guided controller 225 configures or causes its transceiver to transmit 1230 a slave NDP frame to the slave AP, e.g., after an interframe space following the end of the first guided frame. In some embodiments, the IFS may be a SIFS (e.g., 16 μs) or less. In one aspect, the slave NDP frame includes a preamble and an additional LTF, but no content data. In one aspect, the slave NDP frame is used as Fig.10 or Fig.11 In one aspect, the slave trigger frame indicates, causes or allows the slave AP to determine or estimate synchronization information. In some embodiments, the guidance controller 225 of the slave AP estimates 1235 synchronization information for the second guided frame. For example, the guidance controller 225 of the slave AP measures or estimates CFO, SFO, PO, TO, reference values ​​of PO and / or reference values ​​of TO relative to the master AP, and synchronizes with the master AP according to the reference values ​​of CFO, SFO, PO, TO, reference values ​​of PO and / or reference values ​​of TO for the second guided frame. In some embodiments, PO, TO or a combination of PO and TO is not determined during the sounding sequence, and in step 1235, the sounding controller 225 of the slave AP may determine or update the change of PO and / or TO between the sounding sequence and the guidance sequence as described above with respect to equations (1) to (4). In some embodiments, the station device may or may not decode the slave trigger frame.

[0154] In some embodiments, the steering controller 225 of the master AP causes its transceiver 228 to transmit 1240 a second guided frame containing content data to the station device, for example, after the IFS after the end of the slave NDP frame. In some embodiments, the IFS may be a SIFS (e.g., 16 μs) or less. In some embodiments, the master AP and the slave AP may not transmit during the IFS. In some embodiments, the steering controller 225 of the slave AP causes its transceiver 228 to transmit 1242 a second guided frame to the station device, and the master AP transmits 1240 the second guided frame to the station device. In some embodiments, the slave AP transmits 1242 using the estimated or updated synchronization information obtained in step 1235. In some embodiments, the master AP and the slave AP jointly transmit the second guided frame by applying the corresponding steering vectors indicated in the steering information. In some embodiments, the station device receives and decodes 1248 the joint transmission of content data.

[0155] In one aspect, any phase drift (e.g., from CFO drift) may be prevented or corrected by transmitting a first guided frame and a second guided frame with an NDP frame in between. Fig.12 The larger time interval between guided frames shown in allows the slave AP to compare LTFs across multiple slave NDP frames and / or slave trigger frames to improve CFO estimates. In one aspect, the IFS among different frames may be variable or changed. In some embodiments, the time allocated to the first guided frame and the second guided frame may be different. For example, the time allocated to the first guided frame may be shorter than the time allocated to the second guided frame because the CFO estimate may be more accurate after being estimated based on the slave NDP.

[0156] Fig.13 An example timing diagram illustrating a bootstrap sequence according to some embodiments. In some embodiments, a master AP and a slave AP perform a joint transmission for bootstrapping. In other embodiments, a different number of master APs, slave APs, or station devices may be included for joint transmission.

[0157] In some embodiments, the steering controller 225 of the master AP configures or causes its transceiver to transmit 1310 a slave trigger frame to the slave AP. In one aspect, the slave trigger frame reminds the slave AP to start a steering sequence. In one aspect, the slave trigger frame indicates, causes or allows the slave AP to determine or estimate synchronization information. In one method, the steering controller 225 of the slave AP calculates a steering vector for the joint transmission of the first guided frame to the indicated station device. The slave trigger frame can be decoded by some or all of the slave APs. In some embodiments, the steering controller 225 of the slave AP estimates 1315 the synchronization information for the first guided frame. For example, the steering controller 225 of the slave AP measures CFO, SFO, PO, TO, a reference value of PO and / or a reference value of TO relative to the master AP, and synchronizes with the master AP for the first guided frame. In some embodiments, PO, TO, or a combination of PO and TO is not determined during the sounding sequence, and at step 1315, the sounding controller 225 of the slave AP may determine the change in PO and / or TO between the sounding sequence and the steering sequence as described above with respect to equations (1) to (4). In some embodiments, the station device may or may not decode the slave trigger frame.

[0158] In some embodiments, the steering controller 225 of the master AP causes its transceiver 228 to transmit 1320 a first guided frame containing content data to the station device, for example, after the IFS after the end of the slave trigger frame. In some embodiments, the master AP and the slave AP may not transmit during the IFS. In some embodiments, the steering controller 225 of the slave AP causes its transceiver 228 to transmit 1322 a first guided frame to the station device, and the master AP transmits 1320 the first guided frame to the station device. In some embodiments, the master AP and the slave AP jointly transmit the first guided frame by applying the corresponding steering vectors indicated in the steering information. In one aspect, the IFS among different frames may be variable or changed. In some embodiments, the time allocated to the first guided frame and the second guided frame may be different. In some embodiments, the station device receives and decodes 1328 the joint transmission of content data.

[0159] In some embodiments, the station device transmits 1333 an acknowledgment frame acknowledging successful reception of the first guided frame. In some embodiments, different station devices may transmit acknowledgment frames sequentially or jointly, for example, via UL-OFDMA or UL MU-MIMO. In some embodiments, the master AP's steering controller 225 and the slave AP's steering controller 225 receive 1334 and schedule 1335 a joint transmission of a second guided frame. For example, the master AP and the slave AP's steering controller 225 decide which data to jointly transmit in the second guided frame and the MCS / Nss for encoding based on the received ACK frame based on a previously negotiated policy (e.g., whether to retransmit unacknowledged frames at a different MCS, etc.).

[0160] In some embodiments, the master AP's bootstrap controller 225 configures or causes its transceiver to transmit 1340 a slave NDP frame to the slave AP, e.g., after the confirmed IFS. In some embodiments, the IFS preceding the NDP frame may be SIFS (e.g., 16 μs) or less. In one aspect, the slave NDP frame includes a preamble and possibly additional LTFs, but no content data. In one aspect, the slave NDP frame is used as Fig.10 or Fig.11 In one aspect, the slave trigger frame indicates, causes or allows the slave AP to determine or estimate synchronization information. In some embodiments, the guidance controller 225 of the slave AP estimates 1345 synchronization information for the second guided frame. For example, the guidance controller 225 of the slave AP measures or estimates CFO, SFO, PO, TO, reference values ​​of PO and / or reference values ​​of TO relative to the master AP, and synchronizes with the master AP according to the reference values ​​of CFO, SFO, PO, TO, reference values ​​of PO and / or reference values ​​of TO for the second guided frame. In some embodiments, PO, TO or a combination of PO and TO is not determined during the sounding sequence, and in step 1345, the sounding controller 225 of the slave AP may determine the change of PO and / or TO between the sounding sequence and the guidance sequence as described above with respect to equations (1) to (4). In some embodiments, the station device may or may not decode the slave trigger frame.

[0161] In some embodiments, the steering controller 225 of the master AP causes its transceiver 228 to transmit 1350 a second guided frame containing content data to the station device, for example, after the IFS after the end of the slave NDP frame. In some embodiments, the time allocated for the second guided frame is longer than the time allocated for the first guided frame. In some embodiments, the IFS may be a SIFS (e.g., 16 μs) or less. In some embodiments, the master AP and the slave AP may not transmit during the IFS. In some embodiments, the steering controller 225 of the slave AP causes its transceiver 228 to transmit 1352 a second guided frame to the station device, and the master AP transmits 1350 a second guided frame to the station device. In some embodiments, the master AP and the slave AP jointly transmit the second guided frame by applying the corresponding steering vectors indicated in the steering information. In some embodiments, the station device receives and decodes 1358 the joint transmission of content data.

[0162] In some embodiments, the slave AP performs synchronization with the master AP for joint transmission, such as for sounding, steering, or both. In one aspect, the slave AP is configured to maintain a reference phase / timing offset (PO_ref and TO_ref or H_ref) relative to the master AP as measured before joint sounding, and compares it with the phase / timing offset (PO_new and TO_new or H_new) observed before steering. Any difference between the two can be compensated during the joint steering transmission. However, there may be a potential time lag T1 between PO_ref, TO_ref, H_ref and the measurement of the actual joint sounding. Similarly, there may be a time lag T2 between PO_new, TO_new, H_new and the measurement of the actual joint steering. The two lags T1 and T2 may be different. During these lags, the phase offset and timing offset relative to the master AP may drift (for example, due to CFO / SFO) because the lags may not be equal. When compensating for phase / timing offsets, the slave AP may account for any drift that may have occurred between the measurement time of these offsets and the time of the joint TX (eg, by accurately compensating for CFO / SFO from the measurement time until the joint TX of the sounding or guided frame has completed).

[0163] In some embodiments, the slave AP may refine its CFO / SFO / PO / TO relative to the master AP in various ways. In one approach, the slave AP may refine the CFO / SFO / PO / TO based on an NDP frame transmitted by the master AP containing a variable number of LTFs (signaled in the preamble).

[0164] In another method, the slave AP may refine CFO / SFO / PO / TO based on the piggybacked training frame. For example, the master AP may designate any frame that it transmits for CFO / SFO / PO / TO refinement. The master AP may indicate in the preamble of the frame that the frame is for CFO / SFO / PO / TO refinement, for example, based on the BSS color. In one method, the master AP may embed additional LTFs that may not be continuous. For example, the master AP transmits two or more groups of LTF symbols separated by at least a symbol. In one example, the first group of LTF symbols is positioned in the preamble of the data packet, and the second group of LTF symbols is positioned at the end of the data packet, where the interval corresponds to at least the symbol between the first group of LTF symbols and the second group of LTF symbols. In one aspect, the payload of the frame for CFO / SFO / PO / TO refinement may be encoded, but the slave AP may still perform CFO / SFO / PO / TO correction or estimation based on the preamble of the frame transmitted by the master AP.

[0165] In another approach, the slave AP may refine CFO / SFO / PO / TO based on feedback from the station device. For example, the station device may provide the measured CFO / SFO / PO / TO (per AP) from the master AP and the slave AP as feedback, or provide the difference of the offset of the slave AP relative to the master AP as feedback. The station device may track this difference via a dedicated LTF or pilot in the joint guided frame (e.g., as a simple scheme, in 80MHz, 16 pilots may be divided among 4 APs, with each AP having 4 pilots). In some embodiments, the slave AP receives estimates from the STAs and applies the received estimates to resynchronize its CFO / SFO / PO / TO relative to the master AP. In one aspect, estimates from multiple STAs may help improve the quality of the estimates.

[0166] In some embodiments, the master AP may be heard by only some of the slave APs, while the remaining slave APs may be heard by the slave APs that hear the master AP. In this case, the scheme may be extended by repeating the slave trigger two or more times. For example, the first transmission may be sent by only the master AP and the slave APs. The slave APs that hear the master AP may join the master AP in the next transmission. For example, a slave AP with an RSSI above a threshold (e.g., -70 dBm) may join the master AP in subsequent slave triggered transmissions. The master AP and the slave APs that hear the master AP may jointly send a second transmission. The slave AP may perform CFO / SFO pre-correction as described above. Additional APs may hear the joint transmission of the master AP and the slave APs, and the additional APs may participate in the next joint transmission.

[0167] In some embodiments, an intermediate code may be utilized to allow correction or adjustment, for example, as described above with reference to Fig.10 and 11 Described synchronization. In some embodiments, instead of implementing a midamble, a slave AP may track a master AP during a joint transmission of all APs. A slave AP may track a master AP when the slave AP supports receiving on one channel while transmitting on another channel. In some embodiments, the transmit channel is used to communicate with a station device (e.g., joint AP transmission), while the receive channel is used by the slave AP to track the master AP and may be used to receive new data from the master AP to be jointly transmitted to the station device in a subsequent packet or during the current packet after a fixed or known amount of time greater than the highest decoding delay of all slave APs. In some embodiments, the same reference oscillator can be used for both channels, so tracking on the receive channel enables the slave AP to remove phase drift on the transmit channel. Small errors may still exist due to uncorrelated random phase noise between the two channels, but this error may be small enough that the midamble can be omitted or bypassed.

[0168] In some embodiments, a first access point (e.g., a master AP) includes a first transceiver, a second transceiver, and a steering controller. In some embodiments, the steering controller is configured to cause the first transceiver to communicate synchronization information for joint transmission of the first access point and the second access point with a second access point (e.g., a slave AP) over a first channel frequency (e.g., transmit to and / or receive from the second access point), and cause the second transceiver to transmit a portion of a guided frame to a station device over a second channel frequency, and the second access point transmits a portion of the guided frame to the station device over the second channel frequency according to the synchronization information for joint transmission. In some embodiments, the synchronization information includes a carrier frequency offset or a sampling frequency offset. In some embodiments, the second access point is configured to synchronize with the first access point for joint transmission according to the synchronization information. In some embodiments, the first transceiver and the second transceiver share or are coupled to the same reference clock.

[0169] In some embodiments, an access point (e.g., a slave AP) includes a first transceiver, a second transceiver, and a steering controller. In some embodiments, the steering controller is configured to cause the first transceiver to receive synchronization information for joint transmission of the access point and the other access point from another access point (e.g., a master AP) through a first channel frequency, and cause the second transceiver to transmit a portion of a guided frame to a station device through a second channel frequency according to the synchronization information for joint transmission, while the other access point transmits a portion of the guided frame to the station device through the second channel frequency. In some embodiments, the synchronization information includes a carrier frequency offset or a sampling frequency offset. In some embodiments, the first transceiver and the second transceiver share or are coupled to the same reference clock.

[0170] It should be noted that certain paragraphs of the present disclosure may refer to transmit spatial stream subsets, sounding frames, responses, and device reference terms, such as "first" and "second" for the purpose of identifying or distinguishing one from another. These terms are not intended to relate entities (e.g., first device and second device) only in time or according to a sequence, but in some cases, these entities may include such a relationship. These terms also do not limit the number of possible entities (e.g., beamformers and / or beamformed receivers) that can operate within a system or environment. It should be understood that the system described above may provide multiple of any of the components or each of the components, and these components may be provided on a stand-alone machine or, in some embodiments, on multiple machines in a distributed system. In addition, the systems and methods described above may be provided as one or more computer-readable programs or executable instructions embodied on or in one or more articles of manufacture (e.g., floppy disk, hard disk, CD-ROM, flash memory card, PROM, RAM, ROM, or tape). The program may be implemented in any programming language (e.g., LISP, PERL, C, C++, C#) or any byte code language (e.g., JAVA). A software program or executable instructions may be stored as object code on or in one or more articles of manufacture.

[0171] Although the foregoing written description of the methods and systems enables one of ordinary skill in the art to make and use embodiments thereof, one of ordinary skill in the art will understand and appreciate that there are variations, combinations, and equivalents of the specific embodiments, methods, and examples. Therefore, the methods and systems should not be limited to the embodiments, methods, and embodiments described above, but rather to all embodiments and methods within the scope and spirit of the invention.

Claims

1. A method for multiple-input multiple-output (MIMO) communication for a first access point and a second access point, the method comprising: During a first time period before a second time period, the first access point transmits a trigger frame to the second access point, and the second access point estimates synchronization information for a first null data packet declaration based on the trigger frame; transmitting, by the first access point, the first null data packet announcement to a device during a third time period between the second time period and the first time period; as well as During the second time period after the first time period, the first access point transmits a portion of a null data packet to the device, the second access point transmits the portion of the null data packet to the device according to the synchronization information used for joint transmission by the first access point and the second access point to the device, and the device determines guidance information for the MIMO communication according to the null data packet. 2 . The method according to claim 1 , wherein the second access point estimates the synchronization information by estimating a carrier frequency offset or a sampling frequency offset relative to the first access point.

3. The method according to claim 1, further comprising: During the third time period between the first time period and the second time period, the second access point transmits a second empty data packet declaration to the device according to the synchronization information, and the device prepares for the empty data packet according to the first empty data packet declaration and the second empty data packet declaration transmitted by the first access point and the second access point. 4 . The method of claim 1 , wherein the second access point transmits the portion of the null data packet during the second time period.

5. A first access point, comprising: Transceiver; and A circuit configured to: causing the transceiver to transmit information to a second access point during a first time period for joint transmission by the first access point and the second access point to a device, the second access point estimating synchronization information for the joint transmission based on the information for the joint transmission, and causing the transceiver to transmit a portion of a null data packet to the device during a second time period after the first time period, and the second access point to transmit the portion of the null data packet to the device according to the synchronization information, the device determining steering information for multiple-input multiple-output (MIMO) communication according to the null data packet to determine a steering vector for the joint transmission by the first access point and the second access point to the device, wherein the circuit is further configured to cause the transceiver to: transmitting a trigger frame to the second access point during a third time period prior to the first time period, the second access point estimating additional synchronization information for a null data packet declaration based on the trigger frame, and During a fourth time period between the third time period and the first time period, the null data packet declaration is transmitted to the device, and the second access point transmits the null data packet declaration to the device according to the additional synchronization information during the fourth time period, and the device prepares for the null data packet according to the null data packet declarations transmitted by the first access point and the second access point.

6. The first access point of claim 5, wherein the circuit is further configured to cause the transceiver to transmit the information for the joint transmission in a preamble of the null data packet.

7. The first access point of claim 5, wherein the circuit is further configured to cause the transceiver to transmit the information for the joint transmission in the null data packet announcement, the device preparing for the null data packet based on the null data packet announcement.

8. The first access point of claim 7 , wherein the circuit is further configured to cause the transceiver to transmit a training field to the device during a fifth time period between the first time period and the second time period, and the second access point to transmit the training field to the device during the fourth time period, the device adjusting a gain setting to receive the portion of the null data packet based on the training fields transmitted by the first access point and the second access point.

9. The first access point of claim 5, wherein the information for the joint transmission comprises two or more groups of long training field (LTF) symbols separated by at least one symbol.

10. The first access point of claim 5, wherein the second time period is after the first time period.

11. A first access point, comprising: Transceiver; and A circuit configured to: causing the transceiver to receive information from a second access point during a first time period for joint transmission of the first access point and the second access point to a device, estimating synchronization information for the joint transmission based on the information for the joint transmission, and causing the transceiver to transmit a portion of a null data packet to the device based on the synchronization information during a second time period after the first time period, and the second access point to transmit the portion of the null data packet to the device during the second time period, the device determining steering information for multiple-input multiple-output (MIMO) communication based on the portion of the null data packet to determine a steering vector for the joint transmission from the first access point and the second access point to the device; and causing the transceiver to transmit a trigger frame to the second access point during a third time period prior to the first time period, the second access point estimating additional synchronization information for a null data packet declaration based on the trigger frame, and The transceiver is caused to transmit the null data packet announcement to the device during a fourth time period between the third time period and the first time period.

12. The first access point of claim 11, wherein the circuit is configured to estimate the synchronization information for the joint transmission by estimating a first reference value of a carrier frequency offset, a sampling frequency offset, a common phase offset, or a second reference value of a timing offset relative to the second access point.

13. The first access point of claim 11, wherein the circuit is configured to cause the transceiver to receive the information for the joint transmission in a preamble of the null data packet.

14. The first access point of claim 11, wherein the circuit is configured to cause the transceiver to receive the information for the joint transmission in the null data packet announcement, the device preparing for the null data packet based on the null data packet announcement.

15. The first access point of claim 14, wherein the circuit is configured to cause the transceiver to transmit a training field to the device during a fifth time period between the first time period and the second time period, and the second access point to transmit the training field to the device during the third time period, the device adjusting a gain setting to receive the portion of the null data packet based on the training fields transmitted by the first access point and the second access point.

16. The first access point of claim 11, wherein the circuit is configured to cause the transceiver to: The null data packet declaration is transmitted to the device during the fourth time period between the third time period and the first time period while the second access point transmits the null data packet declaration to the device according to the additional synchronization information during the fourth time period, and the device prepares for the null data packet according to the null data packet declarations transmitted by the first access point and the second access point.

17. The first access point of claim 11, wherein the second time period is after the first time period.

18. A method for multiple-input multiple-output (MIMO) communication, the method comprising: transmitting a first null data packet announcement from the first access point to the device during a first time period prior to a second time period; During the second time period, the first access point transmits information to a second access point for joint transmission by the first access point and the second access point to the device, and the second access point estimates synchronization information for the joint transmission based on the information for the joint transmission; and During a third time period after the second time period and the first time period, the first access point transmits a portion of a null data packet to the device, the second access point transmits the portion of the null data packet to the device according to the synchronization information used for joint transmission by the first access point and the second access point to the device, and the device determines guidance information for the MIMO communication according to the null data packet.

19. The method of claim 18, wherein the first null data packet announcement and the information for the joint transmission are provided in the same transmission.

20. The method of claim 18, wherein the first null data packet announcement and the information for the joint transmission are provided in different transmissions.

21. The method of claim 19, further comprising: During the first time period, a second null data packet announcement is transmitted to the device by the second access point based on additional synchronization information, and the device prepares for the null data packet based on the first and second null data packet announcements transmitted by the first and second access points.

22. A first access point, comprising: Transceiver; and A circuit configured to: causing the transceiver to receive information from a second access point during the first time period for joint transmission by the first access point and the second access point to a device, estimating synchronization information for the joint transmission based on the information for the joint transmission, and causing the transceiver to transmit a portion of a null data packet to the device based on the synchronization information during a second time period after the first time period, and the second access point to transmit the portion of the null data packet to the device during the second time period, the device determining steering information for multiple-input multiple-output (MIMO) communication based on the portion of the null data packet to determine a steering vector for the joint transmission by the first access point and the second access point to the device, wherein the circuit is further configured to: causing the transceiver to receive a trigger frame from the second access point during a third time period prior to the first time period, and estimating additional synchronization information for null data packet declaration according to the trigger frame, and The transceiver is caused to transmit the null data packet declaration to the device according to the additional synchronization information during a fourth time period between the third time period and the first time period, and the two access points transmit the null data packet declaration to the device during the fourth time period, and the device prepares for the null data packet according to the null data packet declaration transmitted by the first access point and the second access point.

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