Communication apparatus and method

文档序号：1895303 发布日期：2021-11-26 浏览：12次中文

阅读说明：本技术 通信装置和方法 (Communication apparatus and method ) 是由达纳·乔基纳托马斯·翰特纳比尔·斯文·洛金费利克斯·费尔豪尔于 2020-04-20 设计创作，主要内容包括：一种第一通信装置：其使用多用户多输入多输出MU-MIMO通信同时向一组两个或更多个第二通信装置发送；通过以下方式与第二通信装置的组中的选择的第二通信装置执行波束成形训练；发送包括一个或多个训练单元的一个或多个发送分组,其中,在一个或多个训练单元上应用适于与选择的第二通信装置进行波束成形训练的模拟波束成形训练矩阵和/或数字波束成形训练矩阵,从选择的第二通信装置接收响应于发送的发送分组的反馈,反馈包括由选择的第二通信装置基于发送分组的接收而确定的波束成形信息,以及基于模拟波束成形训练矩阵和接收到的反馈确定更新的模拟波束成形矩阵和/或基于数字波束成形训练矩阵和/或接收到的反馈确定更新的数字波束成形矩阵,用于向包括所述选择的第二通信装置的一组两个或更多个第二通信装置同时发送数据。(A first communication device: transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication; performing beamforming training with a selected second communication device of the group of second communication devices by; transmitting one or more transmission packets including one or more training elements, wherein an analog beamforming training matrix and/or a digital beamforming training matrix adapted for beamforming training with a selected second communication device is applied on the one or more training elements, receiving feedback from the selected second communication device in response to the transmitted transmission packets, the feedback including beamforming information determined by the selected second communication device based on the reception of the transmission packets, and determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or determining an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback, for simultaneously transmitting data to a group of two or more second communication devices including the selected second communication device.)

1. A first communications apparatus comprising circuitry configured to:

transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming training with a selected second communication device of the group of second communication devices by:

-transmitting one or more transmission packets comprising one or more training elements on which analog and/or digital beamforming training matrices adapted for beamforming training with the selected second communication device are applied,

-receive feedback from the selected second communication device in response to the transmitted transmission packet, the feedback comprising beamforming information determined by the selected second communication device based on reception of the transmission packet, and

-determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback for simultaneous transmission of data to the set of two or more second communication devices comprising the selected second communication device.

2. The first communication device of claim 1,

wherein the circuitry is configured to transmit a packet to the two or more second communication devices, wherein a first portion of the transmit packet carries data for data communication with the two or more second communication devices and a second portion of the transmit packet carries the one or more training elements, wherein the first portion of the transmit packet is transmitted with an initial digital beamforming matrix and/or an initial analog beamforming matrix and the second portion of the transmit packet is transmitted with a digital beamforming training matrix and/or an analog beamforming training matrix.

3. The first communication device of claim 2,

wherein portions of the analog beamforming training matrix and the initial analog beamforming matrix corresponding to the selected second communication device are different.

4. The first communication device of claim 1,

wherein the circuitry is configured to include an indication of the selected second communications device and/or an indication that one or more digital beamforming training matrices and/or an analog beamforming matrix are applied to one or more training elements in the one or more transmit packets.

5. The first communication device of claim 1,

wherein the circuitry is configured to receive feedback from the selected second communication device, the feedback comprising information indicative of the training element resulting in the best value of a reception metric and/or digital beamforming feedback information, the information comprising one or more of:

-signal-to-noise ratio information for each stream,

-signal-to-noise ratio information for each training unit or group of training units,

-elements of a digital beamforming feedback matrix in uncompressed form,

-a set of angles corresponding to the digital beamforming matrix compressed by means of Givens rotation.

6. The first communication device of claim 1,

wherein the circuitry is configured to receive interference feedback from one or more non-selected second communication devices of the group other than the selected second communication device, the interference feedback indicating that the training unit causes interference to the one or more non-selected second communication devices and optionally indicating an interference level or measures allowing derivation of the interference level of the interference caused by the training unit.

7. The first communication device of claim 1,

wherein the circuitry is configured to compute the digital beamforming training matrix by:

-selecting one or more analog beam combinations;

-for each analog beam combination, calculating an interference matrix based on channel state information from previous beamforming training and calculating a digital beamforming training matrix by selecting a rotation matrix and/or calculating a null vector such that interference at the unselected second communication devices is minimized or null.

8. The first communication device of claim 2,

wherein the circuitry is configured to calculate the updated digital beamforming matrix by updating rows and/or columns corresponding to the selected second communication device in the initial digital beamforming matrix for data communication using a matrix obtained by multiplying a digital beamforming training matrix with an uncompressed second digital beamforming matrix obtained from beamforming information included in the received feedback.

9. The first communication device of claim 1,

wherein the circuitry is configured to transmit one or more transmit packets, each packet comprising a plurality of training elements, wherein the analog beamforming training matrix and/or the digital beamforming training matrix applied to each training element or each group of training elements varies from training element to training element or from group of training elements to group of training elements and is different from an initial analog beamforming matrix and/or an initial digital beamforming matrix used to transmit a data portion of the packet.

10. The first communication device of claim 1,

wherein the circuitry is configured to apply the same analog beamforming training matrix and/or digital beamforming training matrix on one or more training units as an initial analog beamforming matrix used to transmit the data portion of the transmission packet to train using the selected second communications device.

11. The first communication device of claim 1,

wherein the circuitry is configured to: receiving a transmission packet including one or more training units from the selected second communication apparatus and estimating a channel based on the received training units, and/or receiving channel state information indicating a corresponding stable and/or unstable channel from one or more second communication apparatuses of the group, and preemptively performing beamforming training using the second communication apparatus that transmitted the channel state information indicating instability with respect to the channel of the first communication apparatus using the received channel state information.

12. A second communications apparatus comprising circuitry configured to:

communicating with a first communication device configured to simultaneously transmit to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming training with the first communication device by:

-receiving one or more transmission packets comprising one or more training elements, wherein an analog beamforming training matrix and/or a digital beamforming training matrix adapted for beamforming training with the second communication device is applied on the training elements by the first communication device,

-determining beamforming information based on the received transmission packet, an

-transmitting feedback to the first communication device in response to the received transmission packet, the feedback comprising the determined beamforming information.

13. The second communication device of claim 12,

wherein the circuitry is configured to receive the one or more transmit packets including one or more training elements using a fixed receive analog beamforming matrix.

14. The second communication device of claim 12,

wherein the circuitry is configured to change a receive analog beamforming matrix during reception of each training element or group of training elements included in the one or more transmit packets.

15. The second communication device of claim 12,

wherein the circuitry is configured to transmit beamforming feedback information to the first communication device including one or more of:

-an indication of the training unit yielding the best reception metric,

-an indication of a channel quality or a received signal strength or a signal-to-noise ratio of the training unit yielding the best reception metric,

-elements of a digital beamforming feedback matrix calculated for the training unit received with the best metric, and

-a set of angles corresponding to a compression of the Givens rotation matrix of the digital beamforming matrix calculated for the training unit received with the best metric.

16. The second communication device of claim 12,

wherein the circuitry is configured to transmit one or more of:

-if the second communication device is not selected for performing beamforming training, providing interference feedback to the first communication device, the interference feedback indicating that the training unit causes interference to the second communication device and optionally indicating an interference level or measures allowing to derive the interference level of the interference caused by the training unit;

-a transmit packet comprising one or more training elements enabling the first communication device to estimate a channel; and

-channel state information to the first communication device indicating stable and/or unstable channels.

17. The second communication device of claim 12,

wherein the circuitry is configured to calculate the digital beamforming feedback matrix based on an analog beamforming matrix used by the first communication device to transmit the transmission packet and an analog beamforming matrix used by the second communication unit to receive the transmission packet at a strongest power.

18. A first method of communication, comprising:

transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming training with a selected second communication device of the group of second communication devices by:

-determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback for simultaneous transmission of data to a group of two or more second communication devices comprising the selected second communication device.

19. A second communication method, comprising:

performing beamforming training with the first communication device by:

-determining beamforming information based on the received transmission packet, an

-transmitting feedback to the first communication device in response to the received transmission packet, the feedback comprising the determined beamforming information.

20. A non-transitory computer-readable recording medium having stored therein a computer program product, which, when executed by a processor, causes the method according to claim 18 or 19 to be performed.

Technical Field

The present disclosure relates to communication devices and methods, in particular for performing multi-user multiple-input multiple-output (MU-MIMO) communications.

Background

To compensate for large path losses and reduce crosstalk between multiple antennas and/or between multiple sites (also referred to herein as communication devices), two types of beamforming are employed in millimeter wave communications (i.e., communications near and/or above 30 GHz). First, Analog Beamforming (ABF) is performed, which includes steering the beam, the characteristics of which are given by the settings of the phase shifters in the Phased Antenna Array (PAA). This ensures that each user has a sufficient link budget as a primary goal. Second, Digital Beamforming (DBF) is performed, which applies amplification and phase to all transmit streams on the RF chain connected to the antenna to limit interference among various user devices (also referred to simply as users) and/or various streams. Furthermore, digital beamforming allows to balance the transmit power and to increase the rate observed by the user (injection or bit loading, respectively). The combination of analog and digital beamforming is commonly referred to as hybrid beamforming.

Because the multiple antenna arrays provide spatial separation and/or different polarizations, multiple users can be served simultaneously, thereby improving spectral efficiency. Providing services to multiple users simultaneously through spatial or polarization separation is commonly referred to as multi-user (MU) multiple-input multiple-output (MIMO) transmission. A group of users served simultaneously in MU MIMO transmission is commonly referred to as a MU group.

However, there are several obstacles to implementing MU MIMO transmission. First, finding the appropriate analog beam for the users in the group is a time consuming search problem. Furthermore, digital beamforming introduces additional complexity due to the need for channel information at the transmitter side, which typically involves obtaining feedback from the peer communication device. It is well known that even for simple channel estimation, the determination and assembly of feedback reports results in significant computational complexity. Furthermore, if explicit digital beamforming is used in the OFDM (i.e., frequency selective) case, a large beamforming matrix of large subcarriers needs to be calculated and reported.

The "background" description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

Disclosure of Invention

It is an object to enable beamforming correction in an efficient manner by a communication device and method for use in MU MIMO communication, in particular without interrupting transmissions to stable communication devices of a group of MUs and without requiring a large number of feedback reports from the communication devices of the group of MUs. Another object is to provide a corresponding computer program and a non-transitory computer-readable recording medium for implementing the communication method.

According to an aspect, there is provided a first communication device comprising circuitry configured to:

transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming training with a selected second communication device of the group of second communication devices by:

transmitting one or more transmit packets comprising one or more training elements, wherein an analog beamforming training matrix and/or a digital beamforming training matrix adapted for beamforming training with the selected second communication device is applied on the one or more training elements,

receiving feedback from the selected second communication device in response to the transmitted transmission packet, the feedback including beamforming information determined by the selected second communication device based on the reception of the transmission packet, an

Determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or determining an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback for simultaneous transmission of data to the set of two or more second communication devices including the selected second communication device.

According to another aspect, there is provided a second communications apparatus comprising circuitry configured to:

performing beamforming training with a first communication device by:

receiving one or more transmit packets comprising one or more training elements, wherein an analog beamforming training matrix and/or a digital beamforming training matrix suitable for beamforming training with a second communication device is applied on the training elements by a first communication device,

determining beamforming information based on the received transmission packet, an

Transmitting feedback to the first communication device in response to the received transmission packet, the feedback including the determined beamforming information.

According to another aspect, there is provided a first communication method comprising:

transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming training with a selected second communication device of the group of second communication devices by

-transmitting one or more transmission packets comprising one or more training elements, wherein an analog beamforming training matrix and/or a digital beamforming training matrix adapted for beamforming training with the selected second communication device is applied on the one or more training elements,

-determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback for simultaneous transmission of data to a group of two or more second communication devices comprising the selected second communication device.

According to another aspect, there is provided a second communication method including:

performing beamforming training with a first communication device by:

-receiving one or more transmission packets comprising one or more training elements, wherein an analog beamforming training matrix and/or a digital beamforming training matrix adapted for beamforming training with a second communication device is applied on the training elements by the first communication device,

-determining beamforming information based on the received transmission packet, an

-transmitting feedback to the first communication device in response to the received transmission packet, the feedback comprising the determined beamforming information.

According to yet another aspect, there is provided: a computer program comprising program means for causing a computer to carry out the steps of the methods disclosed herein when said computer program is carried out on a computer; and a non-transitory computer-readable recording medium having stored therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed.

Embodiments are defined in the dependent claims. It shall be understood that the disclosed communication method, the disclosed computer program and the disclosed computer readable recording medium have similar and/or identical further embodiments as the claimed communication device, as defined in the dependent claims and/or as disclosed herein.

For millimeter-wave communications, the coherence time of the effective channel (effective after analog beamforming) depends on the beamwidth and pointing direction of the analog beam. Thus, users at less favorable angles relative to the boresight of the antenna may need to perform channel estimation and beam tracking more frequently.

If one or a small number of stations (STAs; also referred to as "second communication devices") in a MU group that an access point (AP; also referred to as "first communication device") may communicate simultaneously need to track at some time while other stations of the MU group have a stable channel, corrections may be made to the analog and/or digital beamforming matrices and still maintain MU communication. Known techniques currently only allow for tracking of single-user millimeter wave communications by appending non-precoded training elements to packets to allow for beam correction. For MU MIMO communications, algorithms and protocols for analog and digital beamforming training have been developed to date and are defined in existing standards. However, digital and analog beam tracking for MU MIMO communication has not been defined, and applying the algorithms developed for analog and digital beamforming training directly to multi-user beam tracking would result in large delays. One reason for this is that existing procedures require interruption of ongoing data communication to allow STAs in the MIMO group to perform analog beam searching again, collect channel information, perform digital beamforming matrix calculations and send feedback information to the AP.

One aspect of the present disclosure is to propose tracking techniques to allow performing hybrid beamforming corrections for one or a group of STAs within a MU MIMO group in an efficient way, i.e. with good (in a stable sense) channels within the MI group without interrupting the transmissions of the STAs. Accordingly, a communication apparatus and method for performing beamforming correction during millimeter wave MU downlink MIMO transmission are disclosed.

According to one aspect of the disclosure, it is an object to perform analog beam re-adjustment and/or digital beam forming re-calculation without interrupting transmissions to stable STAs within a group of STAs participating in MU transmissions and without changing the beam forming configuration of users having stable channels. This may be achieved by appending one or more training elements using hybrid beamforming matrix modulation (specifically designed to produce minimal interference to stable STAs) to the downlink transmission packet. Another advantage of the disclosed solution is that the size of the feedback report is reduced. Thus, the disclosed solution is particularly effective if one or a small number of STAs of the MU group need to track at the same time.

In the context of the present disclosure, analog beamforming corresponds to the act of physically directing one or more directional beams into a preferred direction, e.g. by analog phase shifters or by changing the phase characteristics of an antenna array. Furthermore, the complete array, rather than each individual element thereof, may be connected to an RF link. In addition to analog beamforming, finer digital beamforming may also be applied. In this way full MIMO capability can be obtained, where multiple streams can be transmitted simultaneously and spatial multiplexing can be achieved. Digital beamforming corresponds to a more general concept in which the amplitude and phase of each transmit beam can be controlled. After precoding (at the transmitter) and decoding (at the receiver), the beams can be separated again.

The above paragraphs are provided as a general introduction and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

Drawings

A more complete appreciation of the present disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

fig. 1 shows a schematic diagram of a communication system according to the present disclosure.

Fig. 2 shows a schematic configuration of a first and a second communication device according to an embodiment of the present disclosure.

Fig. 3 shows a schematic diagram of a communication system according to an embodiment of the present disclosure.

Fig. 4 shows a diagram illustrating the downlink and uplink phases of an embodiment of TX hybrid beam tracking according to the present disclosure.

Fig. 5 shows a flow chart illustrating operation at the AP in the TX hybrid beam tracking embodiment shown in fig. 4.

Fig. 6 shows a format of a transmit packet with an additional training unit (MU PPDU) used in the embodiment of TX hybrid beam tracking shown in fig. 4.

Fig. 7 shows a flow chart of operations at the receiving STA in the embodiment of TX hybrid beam tracking shown in fig. 4.

Fig. 8 shows a schematic diagram of an embodiment of an AP according to the present disclosure.

Fig. 9 shows a diagram illustrating a downlink phase and an uplink phase of an embodiment of RX hybrid beam tracking according to the present disclosure.

Fig. 10 shows a flow chart illustrating operation at the STA in the RX mixed beam tracking embodiment shown in fig. 9.

Fig. 11 shows a format of a transmit packet with an additional training unit (MU PPDU) used in the embodiment of RX mixed beam tracking shown in fig. 9.

Fig. 12 is a diagram showing an uplink phase in the case of using reciprocal calibration.

Fig. 13 shows a format of a transmission packet (PPDU) to which analog and digital beamforming are applied.

Detailed Description

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, fig. 1 shows a schematic diagram of a communication system according to an embodiment of the present disclosure. The communication system is configured with a first communication device 10 and a plurality of second communication devices 20. Each of the first and second communication devices 10 and 20 has a wireless communication function. Specifically, the first communication apparatus 10 has a multi-user communication function of transmitting a frame to one or more second communication apparatuses 20. Further, the first communication device 10 operates as an Access Point (AP) and the second communication device 20 operates as a Station (STA). For this reason, in the communication system, multi-user communication from the AP10 to a plurality of STAs 20 can be performed, that is, the first communication apparatus 10 can simultaneously communicate with a group of two or more second communication apparatuses 20 using MU-MIMO communication. Communication from AP10 to STA20 is referred to as the Downlink (DL) and communication from STA20 to AP10 is referred to as the Uplink (UL).

To enable MIMO communications, the AP10 may be equipped with multiple antennas and multiple RF links, allowing it to transmit multiple streams to multiple STAs 20 simultaneously. Each STA20 device may have multiple antennas and multiple RF links to receive multiple streams simultaneously from AP10 or transmit multiple streams simultaneously to AP 10.

For example, as shown in fig. 1, the communication system may be configured with an AP10 and a plurality of STAs 20a through 20 d. The AP10 and the STAs 20a to 20d are connected to each other via wireless communication and directly perform transmission and reception of frames with each other. For example, the AP10 is a communication apparatus compliant with IEEE 802.11 and transmits MU DL PPDU (multi-user downlink PHY protocol data unit) having each STA20a to 20d as a destination.

Fig. 2 shows a schematic diagram of a configuration of a communication device 30 according to an embodiment of the present disclosure. In general, each AP10 and STAs 20a to 20d may be configured as shown in fig. 2, and may include a data processing unit 31, a wireless communication unit 32, a control unit 33, and a storage unit 34.

As a part of the communication apparatus 30, the data processing unit 31 performs processing on data for transmission and reception. Specifically, the data processing unit 31 generates a frame based on data from a higher layer of the communication device 30, and supplies the generated frame to the wireless communication unit 32. For example, the data processing unit 31 generates a frame (in particular, a MAC frame) from data by performing processes such as fragmentation, aggregation, addition of a MAC header for Medium Access Control (MAC), addition of an error detection code, and the like. Further, the data processing unit 31 extracts data from the received frame and supplies the extracted data to a higher layer of the communication device 30. For example, the data processing unit 31 acquires data by analyzing the MAC header of a received frame, detecting and correcting a code error, and performing retransmission processing and the like.

The wireless communication unit 32 has a signal processing function, a wireless interface function, and the like as a part of the communication unit. Furthermore, a beam forming function is provided. The unit generates and transmits a PHY layer packet (or, particularly for WLAN standards, a PHY layer protocol data unit (PPDU)).

The signal processing function is a function of performing signal processing, for example, frame modulation. Specifically, the wireless communication unit 32 performs encoding, interleaving, and modulation on the frame supplied from the data processing unit 31 according to the encoding and modulation scheme set by the control unit 313, adds a preamble and a PHY header, and generates a PHY layer packet. Further, the wireless communication unit 32 recovers the frame by performing demodulation, decoding, and the like on the PHY layer packet obtained by the processing of the radio interface function, and supplies the obtained frame to the data processing unit 31 or the control unit 33.

The wireless interface function is a function of transmitting/receiving signals via one or more antennas. Specifically, the wireless communication unit 32 converts a signal related to a symbol stream obtained by the processing performed by the signal processing function into an analog signal, amplifies the signal, filters the signal, and up-converts the signal. Next, the wireless communication unit 32 transmits the processed signal via the antenna. Further, on the signal obtained via the antenna, the wireless communication unit 32 performs processing reverse to that at the time of signal transmission, for example, down-conversion of frequency or digital signal conversion.

The beamforming function performs analog beamforming and/or digital beamforming.

As a part of the communication unit, a control unit 33 (e.g., a base Station Management Entity (SME)) controls the entire operation of the communication apparatus 30. Specifically, the control unit 33 performs processing such as information exchange between functions, setting of communication parameters, or scheduling of frames (or packets) in the data processing unit 31.

The storage unit 34 stores information for processing performed by the data processing unit 31 or the control unit 33. Specifically, the storage unit 34 stores information stored in a transmission frame, information acquired from a reception frame, information on communication parameters, and the like.

In an alternative embodiment, the first and second communication devices (in particular each of the AP10 and STA 20) may be configured using circuitry that implements the elements and functions to be performed shown in fig. 2. The circuit may be implemented, for example, by a programmed processor. Generally, the functions of the first and second communication means and the units of the communication means 30 shown in fig. 2 may be implemented in software, hardware or a mixture of software and hardware.

Fig. 3 shows a schematic diagram of a communication system including an access point AP (including analog beamforming and digital beamforming circuits or blocks) and a plurality of stations STA 1-STAi (only the analog portion is shown), according to an embodiment of the present disclosure. Each antenna element of an AP or STA is connected to a phase shifter, and a plurality of antenna elements are physically combined in one Phased Antenna Array (PAA). When multiple PAAs are available, each PAA is further connected to a dedicated RF link. Each RF link controls the phase shifter settings of the PAA to which it is connected. The j-th phase setting parameter for the i-th PAA is represented in FIG. 3 asAnd all phase shifter settings at the transmitter side can be represented abstractly as a matrix F_RFAs shown in fig. 3. Transmitting streams through a digital beamforming matrix F_BBMapping to RF links is also depicted in fig. 3. At the receiver end, the phase shifter settings based on which the analog receive beams are controlled are abstractly grouped in a matrix W_iAnd further to RF chains, similar to on the transmit side.

Mathematically, Ns streams (where N_sIs the total number of streams for all STAs in the MU group) to N_RFDigital beamforming matrix F for a transmit chain_BBTake the following forms

And has a dimension N_RFxN_s. In a MU MIMO scenario, the first N _ s1 list represents the first of the first STAsWeighting coefficients to N _ s1 spatial streams. Analog beamforming matrix F_RFCan be expressed as N_TXxN_RFMatrix, which can be written as F_RF＝[F_RF1F_RF2…F_RF，Nrf]In which F is_RF，_iOf a size equal to the total number N of (sub) antenna elements_TXColumn i. Finally, hybrid beamforming can be represented as a matrix, represented by an analog beamforming matrix F_RFAnd a digital beamforming matrix F_BBAnd multiplying the two to obtain the product.

For the case depicted in fig. 3, if there is a connection to the RF link, F_RFEach column of the matrix is composed of N_PUnit norm element composition, which indicates the phase shifter setting for the nth PAA, otherwise it is zero. Therefore, the analog precoding takes the following form

F_RF，1

Wherein the content of the first and second substances,a jth phase shifter setting representing an ith PAA, and N_PIs the total number of phase shifters for the ith PAA. Here, it is assumed that each antenna array has the same number of phase shifters. However, this is only an example and the further presented method is not dependent thereon.

It should be noted that for simplicity, the present disclosure exemplifies a partially connected array, but the present disclosure is not limited to this particular case and may be generalized to a fully connected array, where the RF link may be connected to all sub-antenna elements.

At the receiver, each STA applies an analog receive combining matrix, further denoted W for STA i_i. The matrix represents a mapping between the receive RF chains and the receive antenna elements. Wi can be regarded as F_RFReceive the counterpart.

A solution will be proposed for the following cases: (i) when Transmit (TX) hybrid beamforming requires correctionTiming, i.e., requiring an analog beamforming matrix and a Digital Beamforming (DBF) matrix F corresponding to the STA_BBAdjusting the column (b); (ii) when a-Receive (RX) Analog Beamforming (ABF) requires modification, i.e. analog combining matrix W for STAi is required_i(ii) a change; and (iii) when analog beamforming is still stable but the channel variation exceeds some acceptable threshold, digital beamforming needs to be adjusted accordingly.

Several cases will be described, namely, where a STA requests analog beam re-adjustment (receive hybrid beam tracking) on its side, where an AP needs to re-adjust its analog beam to the STA (transmit hybrid beam tracking), and where either the STA or the AP requests only digital beam tracking. The type of tracking performed may be indicated by the AP in the header of the MU PPDU. Further, a method of determining the type of beam tracking required will be described. The case of analog-only beam tracking at the transmitting end or the receiving end can be considered as a special case of hybrid beamforming training.

Depending on the type of rescaling, one or more analog beamforming is used for transmission from the AP and testing at the STA (in the case of hybrid TX tracking), one or more analog beams are used for reception and testing at the STA (in the case of RX tracking), or new channel estimates are calculated at the selected STA (in the case of digital beam tracking). The one or more STAs that request or are requested to perform the beamforming update procedure are further referred to as STAs, prospective STAs or selected STAs. STAs that are part of the MU group but are not dedicated to performing beamforming updates are also referred to as unselected or untracked STAs.

For simultaneous transmission to multiple STAs, a MU Downlink (DL) PHY Protocol Data Unit (PPDU) may be transmitted as follows: the first part (consisting of legacy elements (legacy preamble and header)) that is modulated with the first column of the analog and digital beamforming matrices and transmitted sequentially over the associated RF link. The second part of the MU PPDU is transmitted using a hybrid beamforming matrix consisting of an analog beamforming matrix and a digital beamforming matrix F for all antennas_BBAnd (4) forming. The latter digital beamforming matrix is obtained after the previous acquisition (i.e., training) phaseAs a result, this stage has been performed after analog beam training or after joint analog-to-digital beamforming training. After the MU PPDU transmission, each STA continuously transmits an UL Single User (SU) PPDU (e.g., an acknowledgement according to a reception status of the MU PPDU) as a reply to an individual poll or trigger or a schedule included in the initial MU PPDU.

To allow for labor-efficient beam tracking, one disclosed solution involves appending a training unit (TRN) to the MU dl ppdu, which is transmitted with an analog beamforming matrix. Since this matrix may be particularly suitable for tracking of the selected STAs, it may be different from the analog beamforming matrix used in the transmission of the MU dl ppdu, depending on the type of re-adjustment required. This matrix is therefore also referred to as the analog beamforming training matrix. Furthermore, for the case where the analog beamforming interval is not sufficient, in addition to the analog beamforming matrix, a digital beamforming matrix (also referred to herein as a digital beamforming training matrix) may be applied for dimensionality reduction of tracking operations at the intended STAs, and most importantly for maintaining low or no interference to the remaining STAs of the MU group. Since the digital beamforming matrix applied on the training unit is dedicated to tracking, as described above, it may be different from the digital beamforming matrix used for transmitting the MU dl ppdu according to the type of re-adjustment required, and thus the matrix is further referred to as a digital beamforming training matrix. Since only one or a limited number of STAs can perform tracking simultaneously by this technique, the AP should include an indication of one or more STAs in the MU PPDU with the TRN, which should re-adjust their analog, digital or mixed beams based on additional training units or should compute and send feedback for the additional training units.

The effective channel impulse response (which is the channel between the transmitter and receiver for a particular beamforming setting) is estimated by the intended STA (referring to the STA that has requested beam tracking or has been requested by the AP to perform beam tracking; also referred to as the selected STA or the target STA) based on the TRN, which may further use the estimate to compute the singular value decomposition. Based on this, a second part of the digital beamforming matrix (also referred to as the digital beamforming feedback matrix) may be computed and fed back to the AP. Thus, after decomposing the effective channel matrix (i.e., the channel matrix estimated after applying the analog transmit and receive beams and the transmit digital beamforming training matrix), the final corrected hybrid beamforming matrix for the intended STA by the AP is a combination of the digital beamforming training matrix used by the AP during the TRN transmission and the beamforming matrix (digital beamforming feedback matrix) calculated by the STA.

In other words, at the end of the nth STA's tracking round, the new digital beamforming matrix for that STA is a function of a digital beamforming training matrix computed at the transmitter based on the channel of the stable STA and a second matrix computed at the STA based on the digital beamforming training matrix and one or more analog beamforming combinations and reported back to the AP. The rest of the digital beamforming remains unchanged.

Digital and analog beamforming of STAs not aimed at by the tracking wheel remains unchanged, i.e., F_RFColumn of matrix, from primary point to STA_jPhase shifters with j ≠ i and corresponding STAs_jColumn composition of the FBB matrix for flows j ≠ i. A method for efficiently calculating the digital beamforming of a training unit based on the type of retuning required is disclosed herein.

Finally, an alternative method for efficiently obtaining channel estimates at the AP is proposed, where the STA facilitates a reciprocity-based estimation at the AP during the acknowledgement phase.

In the context of the present disclosure, a digital beamforming training matrix is understood to be a digital beamforming matrix applied by the first communication device (AP) on each training element (corresponding to one MIMO analog beamforming configuration). As proposed and disclosed herein, one of the design criteria is to minimize or eliminate the interference experienced by a stable second communication device (STA) after applying the analog beamforming matrix. The digital beamforming training matrix depends on the analog beamforming matrix applied to a particular MIMO training element.

A digital beamforming feedback matrix is to be understood as a digital beamforming matrix computed by a STA with the aim of optimally receiving a stream intended for itself. Depending on the analog beamforming combination used by the transmitting and receiving ends (i.e., the AP and the STAs), the applied digital beamforming training matrix, and the estimated channel. Unlike the digital beamforming training matrix, it relies only on channel knowledge of the STAs that compute it, i.e., between the AP and the STAs, and does not rely on knowledge of channel information from/to other STAs in the group. Its dimensions may be lower than the digital beamforming training matrix.

An updated digital beamforming matrix (also referred to as a "complete" or "final" digital beamforming matrix) is understood to be a digital beamforming matrix that the AP will use to transmit data (PHY layer) packets after a successful beam tracking procedure, as disclosed. It is formed by a digital beamforming matrix for transmitting the data packet, wherein the sub-matrix corresponding to the selected STA is updated as follows. The sub-matrix corresponding to the selected STA is calculated as the product of a digital beamforming training matrix and a digital beamforming feedback matrix (reconstructed from the feedback sent by the selected STA).

Whenever the term beamforming is used in this disclosure, it denotes a physical effect of the beamforming matrix or the application of the beamforming matrix. Herein, the term "analog beamforming matrix" is used to denote a set of analog phase shifter settings (applied to steer the radiation beam in the desired direction), while the term "digital beamforming matrix" is used to denote a set of complex weights corresponding to the mapping between the symbol stream and the RF chain.

The first case, referred to as hybrid TX beam tracking, where STA movement or channel fluctuations require updating of the analog and digital beamforming configuration at the AP (at TX) will be described below.

In order to have a feasible solution in this case, the AP should obtain CSI information of the beam to be tested from all STAs before MU DL transmission. This information may be collected during beamforming training and sounding prior to beam tracking.

A first proposed tracking procedure is depicted in fig. 4, which shows a Downlink (DL) phase and an Uplink (UL) phase illustrating TX hybrid beam tracking according to the present disclosure. In fig. 4 and the following equations and description, it is assumed that STA_iIs the STA for which beam correction is requested or assumed, and STA_jThe remaining STAs in the group j ≠ i have stable channels. To facilitate exposure, it is assumed that the STAs are indexed such that the STAs are_iWith the largest index. As shown, the AP appends K TRN units (or a group of two or more TRN units) to the MU DL data packet, with the primary and STA being changed_i(i.e., from the ith STA during the beam training phase_iBeams of RF chains that have indicated good reception) are transmitted with one analog beamforming matrix (i.e., an analog beamforming training matrix), and F is transmitted with each TRN element or a group of two or more TRN elements_RFThe rest of the matrix will remain unchanged. Before transmission, each TRN unit is first shaped by a digital beamforming training matrix Q, which depends on the analog beamforming training matrix to be applied to that particular TRN unit, and the structure of which will be discussed below. The tracking-performing STA uses a fixed receive analog beam matrix W_iTo receive each training unit or TRN unit group and calculate the feedback. Each unselected STA of the MU group uses a fixed simulated receive beam matrix and evaluates an interference metric.

Before transmitting the tracking PPDU, the AP must decide to model and compute the corresponding digital beamforming training matrix to be used in the tracking process. The process required for this determination is illustrated in the flow chart shown in fig. 5. To perform beam tracking in this case, K transmit beamforming training matrices, denoted asThe index K is between 1 and K (step S10). Since the phase shifter settings corresponding to PAAs radiating to the tracked STAs are mostly modified during the actual transmission, the analog beamforming matrix of the kth analog beamforming matrix modifies the columns according to these analog beams(Primary steering STA)_i) While the remaining columns remain unchanged (i.e., with respect to the analog beamforming matrix used in transmitting the MU PPDU).

For each of the K tested analog beam combinations (step S11), a matrix is constructed containing analog beamforming channels for STAs for which the current beam tracking operation is not directed (step S12):

wherein H_jIs each antenna element of the AP to the STA_jEach antenna element of (1), andrepresenting application of a receive analog beamforming matrix W_iAnd transmit analog beamforming training matrix F_RFBack AP and STA_jOf the p-th PAA. For OFDM, the matrix in (3) is defined per subcarrier or per subcarrier group in the frequency domain with an average channel, while in the case of single carrier, an average channel or best tap is defined in the time domain.

In the next step (step S13), the matrix defined in equation (3) is decomposed by a matrix decomposition rule of a separate null space. Further, Ls vectors in the null space of the effective interference matrix in (3) are selected, wherein Ls is at least equal to the number of spatial streams of the ith STA. These vectors may be obtained by performing a matrix decomposition, for example by using Givens rotations. This is because the matrix in (3) can be equivalently written as

Where St represents the set of indices of the column corresponding to the null value, with r_i,jComplex valued sum q₁...q_NUnitary norm vector.

For each beam combination, only a small fraction of the columns of the matrix in equation (3) are modified (i.e., only the columns corresponding to the simulated beam combination tested during one training unit), while most of the matrix in (3) is virtually unchanged from the previous training or tracking round. Thus, a large number of Givens rotation matrices can be reused to obtain the necessary vectors in the null space of the composite channel matrix (3).

In one embodiment, it may not be necessary to perform a full decomposition as in (4), but only the required number of columns is appropriately selected to be zeroed out, e.g., corresponding to the angle most pointing to the STA that needs tracking.

Obtaining a null space q_lAfter one or more vectors in l ∈ Si, these are grouped in a matrixThe matrix is further used for precoding a k-th MIMO training field appended at the end of the MU PPDU. The final format of the MU PPDU with the additional TRNs is shown in fig. 6, which depicts Analog Beamforming (ABF) and Digital Beamforming (DBF) matrices for transmitting the PPDU during the beam tracking procedure described in fig. 4, i.e., emphasizing different analog and digital beamforming configurations for different portions of the MU PPDU.

Each digital beam forming matrixNumber of columns L_sMay be selected to be equal to the number of streams supported by the ith STA, or greater than but not exceeding the number of receive RF links at that STA. In many operations, it is expected that L will be selected_s＝N_sIt is sufficient. However, L_sThe larger the final digital precoder will be, the better, since more information from the null space is available and thus a matrix more suitable for the ith STA channel can be selected.

The operation at the STA receiving the tracking is illustrated in the flowchart shown in fig. 7. As shown in fig. 4, the receiving STA keeps its analog beam fixed during reception of each digital beamforming MIMOTRN cell (step S20) and estimates the effective channel on each training cell (or group of training cells), depending on the application at the transmitting end (analog and/or digital beamforming training matrices) and the receiving end W_iThe beamforming matrix of (step S21). In addition, it evaluates a measure of signal strength (RSSI or signal-to-noise ratio (SNR)) and determines the training element for which the value is optimal (step S22). For the training unit that has obtained the strongest value, the channel estimation performed in step S21 is used to perform Singular Value Decomposition (SVD) (step S23), based on which a digital beamforming feedback matrix (denoted as V and the corresponding diagonal matrix D containing the power or SNR level) is calculated.

The ith STA then feeds BAck the index of the TRN for which the best metric is obtained, e.g., the corresponding powers in matrices V and D are appended to the next bak frame or UL frame. The format of the feedback matrix may be uncompressed, i.e., per row and per column, or compressed (e.g., rotated by Givens), in which case angle and power are reported, or by similarity to certain beamforming codebook entries, in which case metrics are reported. The information received for the strongest training element will be fed back to the AP to allow the latter to determine an updated analog beamforming matrix. In particular, the analog beamforming matrix used for packet transmission will be updated so that the analog beamforming sub-matrix corresponding to the tracked STA will change based on the analog beamforming settings used in the training unit receiving at the strongest power.

For example, assume that the last two PAAs are directed to the STA_iOnly a matrixThe last two columns of (a) change on each training cell. The best analog phase shifters, i.e., those applied on the training elements that are best received by the selected STAs, are then captured in the last two columns of the analog beamforming matrix and may be represented asIn the updated analog beamforming matrix (to be used for subsequent MU packets), the last two columns are updated, while the remaining columns of F _ RF are the same as used in the data packet transmission, as shown in equation (6).

Finally, the digital beamforming matrix F used by the AP in the transmission of the next MU PPDU_BBWill be updated in the sense that if tracking is needed again, the column of streams corresponding to the ith STA will be new before the TXOP time or the next trainingMatrix of calculationsInstead, and will be used for the following null-space calculation. The updated beamforming matrix then has the following format:

F_BB＝[F_BB，1，F_BB，2，...，F_BB，i-1，Q⁽ⁱ⁾VD] (5)

the operation at the non-selected STAs, i.e., STAs that have not requested and are not instructed to perform tracking but are part of the MU group, is as follows. During each training unit, the units maintain an analog receive beam for receiving the data portion of the packet and evaluate a measure of received signal strength or interference. By selecting the initial digital beamforming in the null space of the beamforming channels of the STAs, the interference to these STAs should be null in the ideal case. However, interference may occur due to imperfections in the channel information or due to erroneous estimates or changes of the channel. Thus, the STAs should also have an opportunity to indicate whether the interference level experienced by any digital or analog beamforming training matrix used in the tracking process is greater than a given threshold. If the interference is greater than the threshold, the affected STAs should indicate the index of the mimo otrn that exceeds the threshold, and optionally the level of interference or interference plus noise received or the estimated SINR.

Based on this information, the AP may decide to retain the corrected hybrid beamforming matrix for the ith STA and update F accordingly_RFAnd F_BBThe matrix is used for the next PPDU transmission, or to request new tracking of the ith STA, or to perform some type of scheduling if the interference is too large (e.g., not serving the nth STA).

So far, we consider the Q matrix to have N_RFAnd L_sColumn, thus being smaller than F before_BBAnd (4) matrix. Alternatively, a similar tracking scheme for the data portion of the PPDU may be devised, whichDBF and F for transmitting TRN_BBHave the same dimensions. This can be achieved by reusing F corresponding to flows of users with stable links (user j ≠ i)_BBMatrix combining columns of matrixReplacing the column corresponding to the nth user. In the latter case, the operation of STAs for which the tracking wheel (j111) is not aimed may be slightly modified, for example, these may estimate interference only (by looking at the estimated sequence of the user to be tracked), or a function of signal-to-interference-plus-noise (SINR) or SINR.

Fig. 8 shows a schematic diagram of an embodiment of a first communication device 10 (i.e., AP) according to the present disclosure. As with a conventional AP, it includes an encoder 11, a stream parser 12, and a constellation mapper 13 for each station for processing data to be transmitted to different STAs. The processed data streams for the different STAs are then used by a common digital beamformer 14 using a digital beamforming matrix F_BBAnd carrying out precoding. Further, a TRN builder 15 is provided for building a training unit different from the conventional AP, and then pre-coded by a digital training beamformer 16 using a digital beamforming training matrix Q. The outputs of the digital beamformer 14 and the digital training beamformer 16 are then fed through the RF data stream obtained by N_RFThe PAAS18 output is processed on various RF chains before being processed by a DAC (digital to analog converter) and analog processing unit 17 (including steering using an analog beamformer).

For the case of analog TX beam tracking, the operation shown in fig. 4 is simplified as follows: k1.. K, on the AP side of each training unit or set of training units, only the analog beamforming training matrix is appliedWithout further precoding using the digital beamforming training matrix Q. Given some a priori knowledge (location, location variation, previous training information), the decision of the analog beamforming matrix (for use by the AP) may be similar to the hybrid TX case, e.g., minimizing the elements of the matrix in (3) and adding a machine that improves reception at the selected STAsWill be described. The selected STA maintains an analog receive beam for receiving the remainder of the data packet and evaluates a measure of signal strength. Since digital beamforming is not required, it is not necessary to perform full channel estimation, channel decomposition, and calculation of a digital beamforming feedback matrix (S23 in fig. 7). In this case, the feedback contains only the index of the TRN at which the evaluated reception metric gives the best result. Based on this, the AP updates the phase shifter setting according to the phase shifter setting used to transmit the specified TRN (as shown in equation 6).

A second scenario, referred to as hybrid RX beam tracking, where STA movement or channel change requires re-adjustment at the STA (in RX) will be described below. When analog receive beam tracking is performed on the STA side, the operation is similar to the first case described above, but with some simplification.

In this case, on the transmitter side, the operation is as shown in fig. 9. Similar to the hybrid TX beam tracking case, the AP attaches to the MU DL packet, K training units, and applies an analog beamforming training matrix on each unit. As a simplification to the former case, for hybrid RX beam tracking, it is sufficient for the AP to reuse the analog beamforming matrix (also as an analog beamforming training matrix) applied in the transmission of the MU-DL packet for the selected STAs applied to each of the K TRN units or groups of TRN units. Repetition of the analog beamforming training matrix is necessary to allow the receiver end to change its analog beamforming configuration and measure the channel. By finding the matrix in the null space of (3), the digital beamforming training matrix Q can be computed as in the hybrid TX beam tracking case⁽ⁱ⁾. However, in this case, it may not be necessary to recalculate the vectors from null space to form Q⁽ⁱ⁾Matrices, since digital beamforming matrices have been used to transmit MU DL packets, especially for STAs_iAnd is actually (3) a part of the null space. However, if some a priori knowledge is available, e.g., STA at AP_iThe direction of movement is available, which can be used to improve Q⁽ⁱ⁾The selection of the matrix (e.g., multiplication by the rotation matrix preserves the null-space property and may improve performance). This operation is depicted in FIG. 9, which shows the graphical rootDiagrams of downlink and uplink phases of an embodiment of RX hybrid beam tracking according to the present disclosure. Fig. 10 depicts a flow diagram of the operation at the STA in the RX mixed beam tracking embodiment shown in fig. 9.

At the receiver end of the selected STA, one receive beam is tested on each MIMOTRN unit (step S30) and a measure of signal strength (RSSI or signal-to-noise ratio (SNR)) is evaluated and channel estimation is performed (step S31). The received analog beam for which the strongest metric has been obtained will be further usedFor the effective channel depending on the analog beam (step S32) (i.e., the effective channel is determined by the analog beam)) The SVD decomposition is performed (step S33) to calculate a digital beamforming training matrix to be used for the selected STA:where U and V are unitary matrices corresponding to the second receive and transmit beamforming matrices, respectively, and D is a diagonal matrix whose main diagonal values contain the SNR values that would potentially be achieved. The STA then transforms the digital beamforming feedback matrix into a desired format, e.g., a set of angles resulting from repeated application of Givens rotation matrices or real and imaginary parts corresponding to uncompressed entries in these matrices. Finally, it feeds BAck the respective powers in the matrices V and D, e.g. appended to the next pack frame or some other UL frame.

For the case of analog RX beam tracking, the operation is similar to that depicted in fig. 9 and 10, with the following simplification. On the AP side, the AP applies the same analog beamforming matrix used in the transmission of the data portion of the packet on each of the k training elements, without applying the digital beamforming matrix Q. At the selected receiver, at each training element or group k of training elements, the STA changes the received analog beam and evaluates only a measure of the received signal strength, rather than a complete channel estimate, in step S31. Further, step S33 is not necessary, since no further digital beamforming matrix is applied. In this case, the operation may even work without feedback to the transmitter, or the feedback may be a simple acknowledgement. However, since MU transmissions are susceptible to interference, and can only be managed by the PA based on accurate channel knowledge of all STAs in the group, it is often a beneficial change to transmit updated channel information to the AP after receiving the beam.

The digital beamforming matrix that the AP will use in the transmission of the next DLPPDU will also be updated, in the sense that the column corresponding to the ith STA will be the newly calculated matrix Q⁽ⁱ⁾And V is replaced. This will also be used for the null-space calculation that should need to be tracked again during the TXOP time, i.e. before the next training. The remaining columns of the FBB matrix remain unchanged and then have the following format:

F_RF＝[F_RF，1，F_RF，2，...，F_RF，i] (8)

wherein

The dependence of the computed digital beamforming feedback matrix on the applied receive analog beamforming matrix is shown for which the best reception of the TRN unit is obtained.

Analog and digital beamforming used in PPDU transmission for tracking mode is shown in fig. 11, depicting analog bf (abf) and digital bf (dbf) matrices for transmitting PPDUs during the tracking procedure described in fig. 9.

By using a catalyst derived from H_iF_RFPerforms initial digital beamforming on the TRN with the channel dimension to be estimated from N_RX×N_RFReduction to N_RX×I_SAnd will be reversedFeed from N_RF×L_s×N_fIs reduced to (L)_s)×N_s×N_fWherein N is_fRepresenting the number of subcarriers or subcarrier groups.

Once the Q matrix is available, an alternative transmission scheme shown in fig. 6 and 11 is to introduce MIMOTRN elements that only simulate beamforming or the ABF and DBF settings used during reuse preamble transmission; on one or more training units, before a TRN dedicated to the tracking process, or before each TRN unit or group of TRN units used to track and test new ABF and DBF settings. This is to simplify the effective channel estimation by providing a clean reference for these.

A third case will be described below in which only digital beamforming tracking is required. If STA_iOnly digital BF tracking needs to be performed, only one MIMO TRN unit is sufficient, since the analog beamforming configuration is maintained at both the transmitting and the receiving end. In this case, the analog beamforming training matrix applied to the MIMO training element or group of training elements is the same as the matrix used to transmit the data portion of the MU DL packet, since in this case only re-estimating the channel may be necessary. At the receiving end, the selected STA keeps the same received analog beam as the MU DL packet, estimates the channel and sends back a digital beamforming feedback matrix to allow the AP to determine an updated digital beamforming matrix for the next MU DL packet transmission, as described in the hybrid TX beam tracking case.

If multiple STAs must perform tracking simultaneously, the initial digital beamforming matrix is extended to include null vectors for all of these STAs, e.g., if a STA must perform tracking simultaneously_iAnd STA_kIf tracking must be performed simultaneously, i and k are excluded for all matrices in matrix construction (3), and L is selected_sNull vector where Ls is greater than or equal to STA_iAnd STA_kThe total number of streams at (a) to construct a Q matrix. However, in this case, the AP may need to perform additional diagonalization to remove possible interference between 2 STAi and k. The Q matrix protects only STAs other than i and k from interference.

For OFDM operation, the matrix in (3) and the decomposition in (4) are preferably created and calculated separately for each frequency subcarrier or group of subcarriers. In this case, the training sequence is transmitted in the OFDM mode, and thus estimation of an effective channel matrix can be performed for each subcarrier.

It may be noted that when the STAs are spatially well separated, the columns within the matrix in (3) may naturally be very small or close to empty. In this special case, the qt vector can simply be chosen as the column of the unitary matrix, which equivalently reduces the non-precoded transmission of the TRN field.

For all three cases described above involving digital beamforming matrices, when only the Q matrix is used as the digital beamforming training matrix (i.e., the digital beamforming training matrix) of the training unit, a sudden change in the number of transmit streams occurs (from data packet to training unit). However, the MIMO TRN must be selected so that the intended STA and the remaining STAs in the group can estimate the channel and interference, respectively. A possible solution to this is to select TRN units to correspond to the same stream index previously used for the ith STA, or they may be predefined in the standard, e.g. using the first L_sA MIMO TRN sequence.

Another approach is to transmit the TRN with a digital beamforming training matrix with the same dimensions as used during the data portion of the DL PPDU. In this case, the Q matrix would replace F corresponding to the ith user_BBThe columns of the matrix, while all other columns remain unchanged. This allows for a smoother transition between the data portion and the training portion of the PPDU, but may allow for more processing at the receiver. In this case, the same MIMO TRN is used for the same stream and user without additional definition.

While the calibration procedure may be performed at a stage prior to actual MU DL transmission and tracking, to ensure that the downlink and uplink effective channels are similar or that differences between them can be compensated for, simplifications to CSI acquisition and hybrid beam tracking can be devised by using the effective channel information from the uplink.

For example, in case it is difficult to perform analog beam selection and sufficiently good channel estimation of the selected beam on the same PPDU, i.e. good enough to further allow digital beamforming calculations, one option of how to use the obtained effective reciprocity in the hybrid or analog beam tracking protocols proposed so far is as an alternative to acquiring channel information after hybrid TX beamforming tracking. To exploit the effective uplink downlink reciprocity, the ith STA will transmit during the next UL PPDU using the selected analog beamforming matrix (the one used to receive the training unit for tracking, or the one that results in the best reception by the training unit) and allow the AP to estimate the effective downlink channel and to complete the necessary digital beamforming matrix by itself. In addition, it may be used by STAs that receive interference during TRN transmission using a digital beamforming training matrix. By allowing the AP to estimate the effective downlink channel from the effective uplink channel, the Q matrix can be updated and the tracking retried using the next MU PPDU.

To obtain the latest channel information but avoid feedback overhead, the AP requests a particular STA to send an acknowledgement or UL PPDU in a manner that allows for such estimation.

Generally, it is not necessary for a STA to transmit multiple streams in the UL for acknowledgement only. Furthermore, the number of streams in the UL may be different from the number of streams used in the DL, and therefore, even if the STA transmits acknowledgements for multiple streams without digital beamforming, the channel estimation field in the UL PPDU will be less than the number needed to obtain the necessary channels.

Thus, to allow the AP to obtain the necessary DL channel estimates, the STA should transmit an UL PPDU containing an acknowledgement (whether in MIMO mode without precoding or using the same set of antennas and RF chains used to receive the data packet) or the STA may transmit in digital beamforming mode, but then append a number of MIMO TRN units equal to the number of received RF chains.

In contrast, for full channel estimation without reciprocity, the AP needs to append non-precoded MIMO TRNs corresponding to all RF chains used in the transmission and the STAs need to assemble relatively complex feedback reports, which the present disclosure avoids.

In FIG. 12, the description is depicted inGraph of uplink phase with reciprocal calibration. As shown, an UL frame such as an acknowledgement (Ack) or block acknowledgement (bak) frame is transmitted in the MIMO mode, and a TRN field corresponding to the number of antennas used by the STA RX is appended. In the previous DL PPDU, the BAck schedule contains the update time of the STA in order to consider the STA_iThe TRN of (1). If the interference level is 1, tracking will be performed again on i and k using the extended Q matrix.

In an embodiment, an indication of link stability may be used. In order to provide the AP with a priori information about the link, which may be less stable than other links, a possible solution is to define a metric at each STA based on, for example, beam width, angle of pointing to the AP, level of motion, and indicate this value before MU DL data transmission begins. This will depend on the implementation and will represent a trade-off between accuracy and complexity, since (i) the more accurate the CSI knowledge of the fth STA at the AP, the less interference the STA i is expected to experience, and (ii) the more accurate the CSI is at the AP, the more effort it takes to estimate and aggregate the feedback.

The value of this metric will be sent to the AP after beam training and may be updated, for example during a tracking request or after beam modification has been performed. For a particular STA, the metric will be associated with information on the pointing angle and beamwidth used at the AP to provide the latter with an indication of the expected stability of the channel. The AP may eventually use this final metric to preemptively append a training sequence to the STA, the value of which indicates a potentially more unstable link.

In another embodiment, a method may be applied as to how a STA can decide whether analog or hybrid beamforming is needed. It involves estimating the non-digital beamformed channels, e.g., in the case of WLAN 60GHz, based on a legacy estimation sequence sent before the PPDU, and comparing them with previous estimates obtained based on these fields of the previous PPDU. It also includes estimating digital beamformed channels based on the MIMO channel estimation sequences, such as in the case of a 60GHz WLAN.

Analog tracking may be triggered if the received power of a channel without digital beamforming changes significantly from a previous packet estimate. If the received power for non-digital beamforming does not change significantly but the MIMO estimate changes, or if the SNR is valid or the error rate increases, then digital tracking is requested.

Fig. 13 shows a format of a transmission packet (PPDU) to which analog and digital beamforming are applied.

By evaluating whether the difference between the a-function of the instantaneous effective channel information and the a-function of the statistically effective channel information is above a certain threshold, the type of tracking required can be inferred from the retransmission rate or SNR/SINR reduction or UL channel deviation, e.g. by calculating the distance function:

wherein d is_*(.,) represents a selected distance metric, e.g., Frobenius norm, riemann distance, where the parameters may represent instantaneous and statistically significant channel knowledge or a function of instantaneous and statistically significant channel knowledge, respectively. If the inequality is not true, the AP needs to track STAi.

Alternatively, if the STA is in an angle where the coherence time changes faster, the AP may preemptively request the STA to perform tracking. Alternatively, the AP may preemptively schedule tracking of various STAs during MU data transmission according to their mobility levels (e.g., as indicated by the STAs through some IMU-based data).

The signaling content for enabling the tracking operation as described above may include a tracking indication in the control portion of the header (e.g., header a) or data packet carrying common information for all STAs: all STAs should know that the TRN is appended and precoded because typically the appended TRN is not precoded. The dimension of the Q matrix for precoding the TRN may be indicated in one of the headers.

Further, the indication of digital tracking may be provided in a header (header B) carrying specific information for each STA or in a control portion of the data packet to inform a specific STA whether the tracking request is for itself or for some other STA. If it is designed for itself, it should send back feedback indicated by the AP (e.g., for the analog and/or digital training matrices corresponding to the best received training elements) in the format requested by the AP or all precoders used by the AP. If the tracking request is not for itself, it can still estimate the resulting interference level. If any of them provides an interference level greater than the allowed, it should be indicated to the AP at the next opportunity.

One possible way to indicate this information is to use a control tail, e.g., a BAck frame, appended to the next PPDU sent in the uplink, with the control tail containing information about a particular SNR. An indication (e.g., appended to an acknowledgement frame) should be reported to the AP whether STAs that are not tracking targets are receiving interference above a predefined threshold. To enable STAs to prepare feedback reports, the AP may schedule Ack responses from the tracking STAs at the end of an Ack round.

The present disclosure may provide one or more of the following advantages. It may allow analog beamforming re-adjustment and/or digital beamforming calculations to be made for certain STAs without changing the beamforming configuration of STAs with stable links. It may be desirable to reduce feedback overhead. Computational efficiency at the STA may increase due to the reduction of the estimation dimension, while computational efficiency at the AP may increase due to the reusability of the rotation matrix.

Accordingly, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting, of the scope of the disclosure and the other claims. The present disclosure, including any readily identifiable variations taught herein, defines, in part, the scope of the foregoing claim terms, such that no inventive subject matter is dedicated to the public.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

To the extent that embodiments of the present disclosure have been described as being implemented at least in part by software-controlled data processing apparatus, it will be understood that non-transitory computer-readable media (e.g., optical disks, magnetic disks, semiconductor memory, etc.) carrying such software are also considered to represent embodiments of the present disclosure. Further, such software may also be distributed in other forms, for example, via the internet or other wired or wireless telecommunication systems.

Elements of the disclosed apparatus, devices, and systems may be implemented by corresponding hardware and/or software elements, e.g., dedicated circuits. A circuit is an architectural collection of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, standard integrated circuits, application specific standard products, and field programmable gate arrays. Further, the circuitry includes a central processing unit, a graphics processing unit, and a microprocessor programmed or configured according to software code. The circuitry does not include pure software, although the circuitry includes the hardware described above to execute software.

The following is a list of further embodiments of the disclosed subject matter:

1. a first communication device includes a circuit configured to

Transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming training with a selected second communication device of the group of second communication devices by:

Determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or determining an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback for simultaneous transmission of data to a set of two or more second communication devices including the selected second communication device.

2. According to the first communication apparatus defined in embodiment 1,

wherein the circuitry is configured to transmit a packet to two or more second communication devices, wherein a first portion of the transmit packet carries data for data communication with the two or more second communication devices and a second portion of the transmit packet carries one or more training elements (for a selected second communication device), wherein the first portion of the transmit packet is transmitted with an initial digital beamforming matrix and/or an initial analog beamforming matrix and the second portion of the transmit packet is transmitted with a digital beamforming training matrix and/or an analog beamforming training matrix.

3. According to the first communication apparatus defined in embodiment 2,

wherein the portions of the analog beamforming training matrix and the initial analog beamforming matrix corresponding to the selected second communication device are different.

4. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to include an indication of the selected second communications device and/or an indication that one or more digital beamforming training matrices and/or analog beamforming matrices are applied to one or more training elements in one or more transmitted packets.

5. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to include an indication of the selected second communication device in one or more of the transmission packets, in particular in a header of the one or more transmission packets.

6. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to receive feedback from the selected second communication device including a digital beamforming feedback matrix and determine an updated digital beamforming matrix from the digital beamforming training matrix and the received digital beamforming feedback matrix.

7. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to receive feedback from the selected second communication device, the feedback comprising information indicative of the training unit resulting in the best value of the reception metric and/or digital beamforming feedback information, the information comprising one or more of:

the signal-to-noise ratio information for each stream,

signal-to-noise ratio information for each training unit or group of training units,

the elements of the digital beamforming feedback matrix in uncompressed form,

a set of angles corresponding to the compressed digital beamforming matrix rotated by Givens.

8. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to receive feedback including information indicative of the training unit that resulted in the best value of the receive metric.

9. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to receive interference feedback from one or more non-selected second communication devices of the group other than the selected second communication device, the interference feedback indicating that the training unit causes interference to the one or more non-selected second communication devices, and optionally indicating an interference level or measures allowing derivation of the interference caused by the training unit.

10. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to compute the digital beamforming training matrix by:

selecting one or more analog beam combinations;

for each analog beam combination, an interference matrix is calculated based on channel state information from previous beamforming training, and a digital beamforming training matrix is calculated by selecting a rotation matrix and/or calculating a null vector such that interference at the unselected second communication devices is minimized or null.

11. According to the first communication apparatus defined in embodiment 2,

wherein the circuitry is configured to calculate an updated digital beamforming matrix by updating rows and/or columns corresponding to the selected second communication device in an initial digital beamforming matrix for data communication using a matrix obtained by multiplying the digital beamforming training matrix with an uncompressed second digital beamforming matrix obtained from beamforming information included in the received feedback.

12. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to transmit one or more transmit packets, each packet comprising a plurality of training elements, wherein the analog beamforming training matrix and/or the digital beamforming training matrix applied to each training element or a set of training elements is changed from training element to training element or from set of training elements to set of training elements and is different from the initial analog beamforming matrix and/or the initial digital beamforming matrix used to transmit the data portion of the packet.

13. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to apply the same analog beamforming training matrix and/or digital beamforming training matrix on the one or more training elements as an initial analog beamforming matrix used to transmit the data portion of the transmission packet to train using the selected second communications device.

14. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to receive a transmit packet including one or more training units from the selected second communications device and to estimate a channel based on the received training units.

15. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to receive channel state information from one or more second communication devices of the group indicative of respective stable and/or unstable channels and to use the received channel state information to preemptively perform beamforming training using the second communication device that transmitted the channel state information indicative of instability with respect to the channel of the first communication device.

16. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to initiate beamforming training with the selected second communication device if:

-the second communication device requesting beamforming training, and/or

-the retransmission rate requested by the second communication device exceeds a threshold, and/or

-one or more channel estimates indicate channel instability, or

-the variation of the analog and/or digital beamforming channels exceeds a threshold, and/or

-the mobility of the second communication device exceeds a threshold or is greater than the mobility of the other second communication devices, and/or

The position of the second communication means has changed to a degree greater than the threshold or to a position which causes a change in the beam angle whose coherence time is faster than before or faster than the threshold.

17. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to include in one or more of the transmitted packets, in particular in a header of the one or more transmitted packets, an indication of the one or more training elements precoded by the digital beamforming training matrix and/or how the one or more training elements are precoded by the digital beamforming training matrix.

18. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to communicate with the two or more second communication devices using the updated analog beamforming matrix and/or the updated digital beamforming matrix.

19. According to the first communication device as defined in any one of the preceding embodiments,

wherein the digital beamforming training matrix is designed to minimize interference to one or more unselected second communications devices for one or more analog beam combinations corresponding to the analog beamforming training matrix.

20. According to the first communication device as defined in any one of the preceding embodiments,

wherein the analog beamforming training matrix is designed to maximize a probability of being received by the selected second communication device with a signal strength greater than a threshold.

21. According to the first communication device as defined in any one of the preceding embodiments,

wherein the analog beamforming training matrix is designed to maximize the probability of reception by setting phase shifters such that the generated analog beam covers sectors adjacent to the sector used for communication, or by steering the analog beam in a direction towards an alternative strong path of the selected second communication device, or by steering the analog beam by an angle determined based on position or motion information indicated by the selected second communication device at a previous transmission phase.

22. According to the first communication device as defined in any one of the preceding embodiments,

wherein the circuitry is configured to determine the updated analog beamforming matrix based on an indication of a best received training element included in the feedback received from the selected second communication device and/or based on an analog beamforming training matrix applied on training elements indicated in the feedback received from the selected communication device.

23. According to the first communication device as defined in any one of the preceding embodiments,

wherein the digital beamforming training matrix applied on the training unit has a lower dimensionality than the digital beamforming matrix applied during data packet transmission.

24. A second communications device comprising circuitry configured to:

performing beamforming training with a first communication device by:

determining beamforming information based on the received transmission packet, an

Transmitting feedback to the first communication device in response to the received transmission packet, the feedback including the determined beamforming information.

25. According to the second communication device defined in embodiment 24,

wherein the circuitry is configured to receive one or more transmit packets including one or more training elements using a fixed receive analog beamforming matrix.

26. The second communications apparatus defined in embodiment 24 or 25 wherein the circuitry is configured to change the receive analog beamforming matrix during reception of each training element or group of training elements included in the one or more transmit packets.

27. According to the second communication device as defined in any one of claims 19 to 26,

wherein the circuitry is configured to transmit beamforming feedback information to the first communication device, including one or more of:

-an indication of the training unit yielding the best reception metric,

-an indication of the channel quality or received signal strength or signal-to-noise ratio of the training unit yielding the best received metric,

-elements of a digital beamforming feedback matrix calculated for the training unit received with the best metric, and

-a set of angles corresponding to a compression of the Givens rotation matrix of the digital beamforming matrix calculated for the training unit received with the best metric.

28. According to the second communication device as defined in any one of claims 24 to 27,

wherein the circuitry is configured to provide interference feedback to the first communication device indicating that the training unit causes interference to the second communication device and optionally indicating an interference level or measures allowing derivation of an interference level of the interference caused by the training unit, if the second communication device is not selected for performing beamforming training.

29. The second communications apparatus defined in any one of claims 24 to 27, wherein the circuitry is configured to transmit a packet comprising one or more training units enabling the first communications apparatus to estimate or derive the channel information.

30. According to the second communication device as defined in any one of claims 24 to 27,

wherein the circuitry is configured to transmit channel state information indicative of a stable and/or unstable channel to the first communication device.

31. According to the second communication device as defined in any one of claims 24 to 29,

32. According to the second communication device as defined in any one of claims 24 to 31,

wherein the circuitry is configured to evaluate the best reception training unit and to send an indication of the best reception training unit back to the first communication device.

33. According to the second communication device defined in embodiment 32,

wherein the circuitry is configured to determine an updated analog receive beamforming matrix from the analog receive beamforming configuration used in reception of the best training unit.

34. According to the second communication device as defined in any one of 24 to 33,

wherein the circuitry is configured to transmit the packet using at least as many training units as there are receive RF links used in communication with the first communication device to enable the first communication device to derive valid channel information from the first communication device to the second communication device.

35. A first method of communication, comprising:

transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming training with a selected second communication device of the group of second communication devices by:

Determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or determining an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback for simultaneous transmission of data to a set of two or more second communication devices including the selected second communication device.

36. A second communication method, comprising:

performing beamforming training with a first communication device by:

determining beamforming information based on the received transmission packet, an

Transmitting feedback to the first communication device in response to the received transmission packet, the feedback including the determined beamforming information.

37. A non-transitory computer-readable recording medium having stored therein a computer program product, which, when executed by a processor, causes the steps according to embodiment 35 or 36 to be performed.

38. A computer program comprising program code means for causing a computer to carry out the steps of the method according to example 35 or 36 when said computer program is carried out on the computer.

39. A first communication device comprising circuitry configured to:

transmitting simultaneously to a group of two or more second communication devices using multi-user multiple-input multiple-output (MU-MIMO) communication;

performing beamforming correction training with at least one selected second communication device of the group of second communication devices (but not applicable to all second communication devices of the group) by:

transmitting one or more transmit packets comprising one or more training elements to the second communication device group, wherein an analog beamforming training matrix and/or a digital beamforming training matrix adapted for beamforming training with the selected second communication device is applied on the one or more training elements,

Determining an updated analog beamforming matrix based on the analog beamforming training matrix and the received feedback and/or determining an updated digital beamforming matrix based on the digital beamforming training matrix and/or the received feedback for simultaneous transmission of data to a set of two or more second communication devices including the selected second communication device.

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