WO2022135692A1

WO2022135692A1 - Wireless multi-antenna transceiver with automatic boresight calibration

Info

Publication number: WO2022135692A1
Application number: PCT/EP2020/087607
Authority: WO
Inventors: Alexander KOBZANTSEV; Doron Ezri; Avi WEITZMAN
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2020-12-22
Filing date: 2020-12-22
Publication date: 2022-06-30
Also published as: EP4196812A1

Abstract

A wireless multi-antenna transceiver (110) for communication with a plurality of further wireless transceivers, including a plurality of neighboring wireless multi-antenna transceivers (120a-d), is disclosed. The transceiver (110) comprises a communication interface (113) comprising a plurality of antennas (113a,b) configured to receive channel state information from each of the plurality of neighboring wireless multi-antenna transceivers (120a-d). Moreover, the transceiver (110) comprises a processing circuitry (111) configured to obtain position information about a respective position of the plurality of neighboring wireless multi- antenna transceivers (120a-d). The processing circuitry (111) is further configured to determine a boresight orientation, in particular a boresight angle of the plurality of antennas (113a,b) used for a future data exchange based on the channel state information and the position information.

Description

Wireless multi-antenna transceiver with automatic boresight calibration

TECHNICAL FIELD

The present disclosure relates to for wireless communications. More specifically, the present disclosure relates to a wireless multi-antenna transceiver with automatic boresight calibration as well as a method for automatically calibrating the boresight of a wireless multi-antenna transceiver.

BACKGROUND

Accurate measurements of an Angle of Arrival (AOA) based on phase differences between elements of the antenna array of a wireless communication device, such as a multi-antenna WiFi access point, require an accurate calibration of the orientation of the boresight of the antenna array. This accurate calibration is usually performed during the mounting of the multi-antenna WiFi access point on a wall or a ceiling of a room. In order to save costs and time as well as in order to be able to easily recalibrate an already mounted multi-antenna WiFi access point, it would be desirable to have a multi-antenna communication device, in particular WiFi access point that can be automatically calibrated.

SUMMARY

It is an objective of the present disclosure to provide a wireless multi-antenna transceiver, in particular a WiFi multi-antenna access point with automatic boresight calibration as well as a corresponding method of automatic boresight calibration for a wireless multi-antenna transceiver.

The foregoing and other objectives are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.

According to a first aspect a wireless multi-antenna transceiver is provided configured to communicate with a plurality of further wireless transceivers, including a plurality of neighboring wireless multi-antenna transceivers. In an implementation form, the wireless multi-antenna transceiver and/or one or more of the plurality of neighboring wireless multiantenna transceivers may comprise one or more wireless access points or base stations as well as one or more wireless user terminals. In an implementation form, the wireless multiantenna transceiver is configured to operate in accordance with the IEEE 802.11 WLAN standard or a standard evolved therefrom.

The wireless multi-antenna transceiver comprises a communication interface comprising a plurality of antennas, i.e. an antenna array, wherein the communication interface is configured to receive channel state information from each of the plurality of neighboring wireless multi-antenna transceivers, i.e. information about the state of the communication channel between the wireless multi-antenna transceiver and the respective neighboring wireless multi-antenna transceivers.

The wireless multi-antenna transceiver further comprises a processing circuitry configured to obtain position information about a respective position of the plurality of neighboring wireless multi-antenna transceivers. The processing circuitry is further configured to determine a boresight orientation, in particular a boresight angle, of the plurality of antennas based on the channel state information and the position information. Thus, advantageously, a wireless multi-antenna transceiver with an automatic boresight calibration is provided.

In a further possible implementation form of the first aspect, the wireless multi-antenna transceiver further comprises a memory configured to store the position information about the respective position of the plurality neighboring wireless multi-antenna transceivers, wherein the processing circuitry is configured to obtain the position information from the memory.

In a further possible implementation form of the first aspect, the communication interface is configured to receive the position information about the respective position of the plurality of neighboring wireless multi-antenna transceivers from the plurality of neighboring wireless multi-antenna receivers, wherein the processing circuitry is configured to obtain the position information from the communication interface.

In a further possible implementation form of the first aspect, the processing circuitry is configured, based on the channel state information and the position information, to determine separately for each of the plurality of neighboring wireless multi-antenna transceivers a respective boresight orientation estimate and to determine the boresight orientation, in particular the boresight angle, of the plurality of antennas as an average of the plurality of boresight orientation estimates. In a further possible implementation form of the first aspect, the processing circuitry is configured to determine separately for each of the plurality of neighboring wireless multiantenna transceivers a respective boresight orientation estimate 9^ on the basis of the following equation:

wherein denotes an expected LOS direction and 0_LOS^ an estimated LOS direction.

In a further possible implementation form of the first aspect, the processing circuitry is configured to determine the estimated LOS direction 0_LOS^ for the I^th neighboring wireless multi-antenna transceiver on the basis of the following equations:

wherein a(0) denotes a steering vector of the plurality of antennas,

= y- i i' denotes the input covariance matrix and X_t denotes a matrix comprising the channel state information from the I^th neighboring wireless multi-antenna transceiver.

In a further possible implementation form of the first aspect, the processing circuitry is configured to determine the boresight orientation §_BS on the basis of the following equations:

wherein:

9_bs denotes a boresight orientation angle,

«t(e) denotes a steering vector relatively to the I^th neighboring wireless multi-antenna transceiver, which defines the phase response of the plurality of antennas, i.e. the antenna array to a wave arriving from the specific direction 9,

9t denotes an expected LOS direction from the plurality of antennas of the wireless multiantenna transceiver towards the I^th neighboring wireless multi-antenna transceiver, and 0_BS denotes a boresight direction estimate.

In a further possible implementation form of the first aspect, the processing circuitry is further configured to determine a respective phase of the plurality of antennas based on the channel state information and the position information.

According to a second aspect a method for determining a boresight orientation, in particular a boresight angle, of a plurality of antennas, i.e. an antenna array of a wireless multi-antenna receiver is provided. The method comprises the steps of: receiving channel state information from each of a plurality of neighboring wireless multiantenna transceivers; obtaining position information about a respective position of the plurality of neighboring wireless multi-antenna transceivers; and determining a boresight orientation, in particular a boresight angle, of the plurality of antennas based on the channel state information and the position information.

In a further possible implementation form of the second aspect, the method further comprises obtaining the position information from a memory of the wireless multi-antenna receiver.

In a further possible implementation form of the second aspect, the method further comprises receiving the position information about the respective position of the plurality of neighboring wireless multi-antenna transceivers from the plurality of neighboring wireless multi-antenna receivers.

In a further possible implementation form of the second aspect, the method comprises determining, based on the channel state information and the position information, separately for each of the plurality of neighboring wireless multi-antenna transceivers a respective boresight orientation estimate and determining the boresight orientation, in particular the boresight angle, of the plurality of antennas as an average of the plurality of boresight orientation estimates.

In a further possible implementation form of the second aspect, the method comprises determining separately for each of the plurality of neighboring wireless multi-antenna transceivers a respective boresight orientation estimate 0® on the basis of the following equation:

In a further possible implementation form of the second aspect, the method comprises determining the estimated LOS direction 0_LOS^ for the I^th neighboring wireless multiantenna transceiver on the basis of the following equations:

wherein a(0) denotes a steering vector of the plurality of antennas,

In a further possible implementation form of the second aspect, the method comprises determining the boresight orientation e_BS on the basis of the following equations:

0_BS = arg max L(0_bs), and

#BS

wherein:

0_bs denotes a boresight orientation angle,

«t(e) denotes a steering vector relatively to the I^th neighboring wireless multi-antenna transceiver, which defines the phase response of the antenna array to a wave arriving from the specific direction 0, t denotes an expected LOS direction from the plurality of antennas of the wireless multiantenna transceiver towards the I^th neighboring wireless multi-antenna transceiver, and

0_BS denotes a boresight direction estimate.

In a further possible implementation form of the second aspect, the method further comprises determining a respective phase of the plurality of antennas based on the channel state information and the position information. In a further possible implementation form of the second aspect, the method further comprises operating the wireless multi-antenna transceiver in accordance with the IEEE 802.11 WLAN standard or a standard evolved therefrom.

According to a third aspect a computer program product comprising a non-transitory computer-readable storage medium for storing program code is provided, which causes a computer or a processor to perform the method according to the second aspect, when the program code is executed by the computer or the processor.

Thus, implementation forms and embodiments disclosed herein provide an automatic, simple and low-cost antenna array boresight orientation calibration procedure, based on existing wireless infrastructure. Moreover, implementation forms and embodiments disclosed herein may operate with phase matched RF chains, but also in the case where the RF chains are not phase aligned.

Details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, embodiments of the present disclosure are described in more detail with reference to the attached figures and drawings, in which:

Fig. 1 is a schematic diagram of a wireless communication system, including a wireless multi-antenna transceiver according to an embodiment;

Fig. 2 is a diagram illustrating the spatial position and orientation of a wireless multiantenna transceiver according to an embodiment relative to a plurality of neighboring multi-antenna wireless transceivers;

Fig. 3 is a schematic diagram illustrating the definition of the boresight direction of a wireless multi-antenna transceiver according to an embodiment relative to a reference direction;

Fig. 4 is a schematic diagram illustrating an estimation module implemented by the processing circuitry of a wireless multi-antenna transceiver according to an embodiment for automatic boresight calibration; Fig. 5 is a schematic diagram illustrating two antennas of an antenna array of a wireless multi-antenna transceiver according to an embodiment, and the geometry of an incident far-field waveform;

Fig. 6 illustrates an operation implemented by a wireless multi-antenna transceiver according to an embodiment for generating a smoothed CSI for automatic boresight calibration;

Fig. 7 is a schematic diagram illustrating an estimation module implemented by the processing circuitry of a wireless multi-antenna transceiver according to a further embodiment for automatic boresight calibration;

Fig. 8 is a diagram illustrating the automatic boresight calibration of a wireless multiantenna transceiver according to an embodiment with four neighboring multiantenna wireless transceivers;

Fig. 9 shows graphs illustrating exemplary spectrum functions determined by a wireless multi-antenna transceiver according to an embodiment for automatic boresight calibration;

Fig. 10 illustrates an exemplary two-dimensional spectrum function used by a wireless multi-antenna transceiver according to an embodiment for automatic boresight calibration; and

Fig. 11 is a flow diagram illustrating a method of automatic boresight calibration of a wireless multi-antenna transceiver according to an embodiment.

In the following, identical reference signs refer to identical or at least functionally equivalent features.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the present disclosure or specific aspects in which embodiments of the present disclosure may be used. It is understood that embodiments of the present disclosure may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims.

For instance, it is to be understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps), even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units), even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Figure 1 is a schematic diagram of a wireless communication system 100, including a wireless multi-antenna transceiver 110 according to an embodiment. As illustrated in figure 1 , the wireless multi-antenna transceiver 110 is configured to communicate with a plurality of further wireless transceivers, including a plurality of neighboring wireless multi-antenna transceivers 120a-d as well as one or more wireless user terminals 130, such as a smart phone 130 and a laptop computer 130. In the embodiment shown in figure 1 , the wireless multi-antenna transceiver 110 and the neighboring wireless multi-antenna transceivers 120a- d are wireless access points (also known as base stations) configured to operate in accordance with the IEEE 802.11 WLAN standard or a standard evolved therefrom.

As illustrated schematically in figure 1, the wireless multi-antenna transceiver 110 comprises a plurality of, i.e. an array of antennas 113a, b, which may be part of a communication interface 113 of the wireless multi-antenna transceiver 110. By way of example, in the embodiment shown in figure 1 the wireless multi-antenna transceiver 110 comprises two antennas 113a, 113b. As will be appreciated, however, in other embodiments the wireless multi-antenna transceiver 110 may comprise an array of antennas 113a,b with more than two antennas, for instance, an array of antennas with 4 or 8 antennas. Each antenna 113a,b of the array may be arranged at a respective physical position, i.e. location of the array (which is usually fixed) and may have one or more antenna properties, such as a directionally dependent radiation pattern. By means of the array of antennas 113a, b the wireless multiantenna transceiver 110 may be configured to communicate with the plurality of further wireless transceivers, such as the plurality of neighboring wireless multi-antenna transceivers 120a-d and/or the one or more wireless user terminals 130, using a precoding or beamforming communication scheme, as defined, for instance, by a standard, in particular the IEEE 802.11 WLAN standard or a standard evolved therefrom.

As will be described in more detail below, the communication interface 113, including the array of antennas 113a,b is configured to receive channel state information from each of the plurality of neighboring wireless multi-antenna transceivers 120a-d, i.e. information about the state of the communication channel between the wireless multi-antenna transceiver 110 and the respective neighboring wireless multi-antenna transceivers 120a-d. In an embodiment, the channel state information may comprise information about a respective channel transfer function. In an embodiment, the respective neighboring wireless multi-antenna transceivers 120a-d may determine the channel state information based on a pilot signal transmitted by the wireless multi-antenna transceiver 110.

As schematically illustrated in figure 1 , the wireless multi-antenna transceiver 110 further comprises a processing circuitry or a processor 111 configured to obtain position information about a respective position of the plurality of neighboring wireless multi-antenna transceivers 120a-d. The processor 111 may be implemented in hardware and/or software, which when executed causes the wireless multi-antenna transceiver 110 to perform the functions and methods described herein. The hardware may comprise digital circuitry, or both analog and digital circuitry. Digital circuitry may comprise components such as application-specific integrated circuits (ASICs), field-programmable arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors.

The processing circuitry 111 of the wireless multi-antenna transceiver 110 is further configured to determine a boresight orientation, in particular a boresight angle, of the plurality of antennas 113a,b based on the channel state information and the position information. In an embodiment, the wireless multi-antenna transceiver 110 may further comprise a memory 115 configured to store the position information about the respective position of the plurality neighboring wireless multi-antenna transceivers 120a-d, wherein the processing circuitry 111 is configured to obtain the position information from the memory 115. In a further embodiment, the communication interface 113 may be configured to receive the position information about the respective position of the plurality of neighboring wireless multiantenna transceivers 120a-d from the plurality of neighboring wireless multi-antenna receivers 120a-d, wherein the processing circuitry 111 is configured to obtain the position information from the communication interface 113.

Thus, as will be appreciated, in an embodiment of the wireless multi-antenna transceiver 110, the boresight orientation of its antenna array 113a,b may be determined, i.e. calibrated using the transmission of Wi-Fi signals by the plurality of neighboring wireless multi-antenna transceivers 120a-d, which may be other network access points of an overlapping basic service set (OBSS). In the following more details about the determination of the boresight orientation of the antenna array 113a,b will be described, as implemented by further embodiments of the wireless multi-antenna transceiver 110.

As already described above, the wireless multi-antenna transceiver 110 comprises a plurality of antennas 113a, b, i.e. N antennas 113a, b. For boresight calibration, the wireless multiantenna transceiver 110 may use the channel state information obtained by the frame exchange mechanism with the P neighboring wireless access points 120a-d. The LOS azimuth angles from each neighboring wireless access points 120a-d to the wireless multiantenna transceiver 110 are known, e.g. the set of LOS azimuth angles {0;} ₌₁ illustrated in figure 2 for the case of 4 neighboring wireless access points 120a-d. As will be appreciated, this is valid under the assumption that the wireless multi-antenna transceiver 110 as well as the neighboring wireless access points 120a-d are located at the same height, which is usually the case, when these components are mounted on the ceiling of a room. However, in other embodiments, the wireless multi-antenna transceiver 110 as well as the neighboring wireless access points 120a-d may be located at different heights, i.e. different elevation angles.

As illustrated in figure 3, the boresight direction, i.e. orientation is defined by the angle between the array orientation 110a and a predefined reference direction (which in figure 3 corresponds to the y-axis of a coordinate system). In the following further embodiments of the wireless multi-antenna transceiver 110 will be described, wherein the processing circuitry 111 implements a boresight estimation algorithm for two main cases, namely (a) for the case that the phases of the antennas 113a, b of the wireless multi-antenna transceiver 110 are aligned (i.e. calibrated) and (b) for the case that the phases of the antennas 113a, b of the wireless multi-antenna transceiver 110 are not aligned yet.

For an embodiment of the wireless multi-antenna transceiver 110, where the phases of the antennas 113a,b of the wireless multi-antenna transceiver 110 are aligned (i.e. calibrated), an estimation module 111a implemented by the processing circuitry 111 of the wireless multiantenna transceiver 110 obtains as input the channel state information (CSI) matrices for frames obtained from the neighboring wireless access points 120a-d and determines the boresight direction, as illustrated in figure 4. For doing so, the estimation module 111a implemented by the processing circuitry 111 may make use of the steering vector defined by the antenna array 113a, b. As will be appreciated, the steering vector a(e) e C^M is the generally complex vector which reflects the phase differences obtained at the antenna array 113a, b, depending on the angle of arrival (AoA) of the impinging RF wave, i.e.:

wherein the vectors dj e (3 x 1) denote the 3D Cartesian coordinates of I^th antenna 113a,b of the wireless multi-antenna transceiver 110 and

denotes unit vector in the direction of the arriving RF wave, where az and el are the azimuth and elevation angels of the arriving RF signal. For example, for an embodiment with 2 antennas 113a, b (as illustrated in figure 1) separated by a distance d and an azimuth angle 0 (assuming the known elevation to be equal to 90°), the steering vector is given as (as illustrated in figure 5):

In an embodiment, the wireless multi-antenna transceiver 110 may use, in particular for a small multipath scenario (if, for instance, beamforming is applied), a separate or combined Capon approach (also known as MVDR - Minimum Variance Distortionless Response) for boresight estimation, as will be described in more detail in the following.

For the separate approach the processing circuitry 111 of the wireless multi-antenna transceiver 110 according to an embodiment is configured to estimate the LOS (line of sight) AOA for the I^th neighboring wireless access point 120a-d by performing a maximization of the following spectrum function, over the azimuth domain

SLOS = ^ar 9 max L® (0) where L®(0) = and where R_xm = —XiX^ denotes the input covariance matrix,

while X[ = CSI e c^{NantXNsubcarrlers} is the CSI matrix (i.e. the channel state information) obtained for the I^th neighboring wireless access point 120a-d. In this embodiment, the boresight direction is estimated as the difference between the measured LOS and the expected LOS direction:

wherein 0® denotes the known angle from the wireless multi-antenna transceiver 110 to the I^th neighboring wireless access point 120a-d. In an embodiment, the final boresight estimate may be obtained by averaging over all neighboring wireless access point 120a-d, i.e.: s > ¹ yJV fl® t>bs - -Lt=i _bs ■

A combined approach for the case of aligned antennas 113a,b is implemented by a further embodiment of the wireless multi-antenna transceiver 110. For this approach, the processing circuitry 111 of the wireless multi-antenna transceiver 110 may be configured to all CSI information directly and calculate the boresight direction by minimization of the global function:

and

9BS = arg max L(6_bs), &BS wherein 6_bs denotes the boresight orientation angle, a;(0) denotes the steering vector relatively to the I^th neighboring wireless multi-antenna access point 120a-d, which defines the phase response of the plurality of antennas 113a, b, i.e. the antenna array to a wave arriving from the specific direction 6, 9 denotes an expected LOS direction from the plurality of antennas 113a,b of the wireless multi-antenna transceiver 110 towards the I^th neighboring wireless multi-antenna access point 120a-d, and §_BS denotes the boresight direction estimate.

In a further embodiment, suited in particular for indoor scenarios that may exhibit a large number of multipaths, the processing circuitry 111 of the wireless multi-antenna transceiver 110 may be configured to implement more sophisticated AOA algorithms (for example, SpotFi algorithm) which provide a higher accuracy of the AOA measurements. In an embodiment, the processing circuitry 111 of the wireless multi-antenna transceiver 110 may be configured to generate a smoothed CSI matrix by applying a perturbation operator to the input CSI vector, as illustrated in figure 6. Moreover, a two-dimensional MUSIC algorithm (in AOA and Time domain) may be applied using a modified steering vector of the following form:

where:

The final estimation of the boresight direction is now done by maximization over the spectrum provided by the MUSIC algorithm, while using a modified covariance matrix and steering vector, i.e.:

wherein E_n denotes the null subspace of the modified covariance matrix R_x.

As will be described in more detail below, for an embodiment where the plurality of antennas 113a,b of the wireless multi-antenna transceiver 110 are arranged in the form of a uniform circular array (UCA), the processing circuitry 111 may be configured to use a modified version of the SpotFi algorithm (herein denoted as SpotFi-Butler algorithm). The uniform circular array (UCA) may be transformed into a virtual uniform linear array (ULA) by applying a so-called Butler Transformation to the UCA, i.e.:

X = JFX where X is the original CSI matrix, X is the transformed CSI matrix of the virtual array and where the weight matrix J and the spatial DFT matrix F are given as follows:

In this embodiment, the processing circuitry 111 of the wireless multi-antenna transceiver 110 may be configured to apply the MUSIC algorithm to the modified matrix X, while the steering vector is defined as follows: a(9) = [<, >^he

As already described above, in further embodiments of the wireless multi-antenna transceiver 110 the processing circuitry 111 may implement a boresight estimation algorithm for the case that the phases of the antennas 113a,b of the wireless multi-antenna transceiver 110 are not aligned yet. In other words, in further embodiments, the processing circuitry 111 of the wireless multi-antenna transceiver 110 is configured to calibrate both the boresight direction as well as the phases of the antennas 113a,b of its antenna array, as illustrated in figure 7.

For handling these more complex scenarios the "search algorithms" described above may be extended to additional dimensions (namely the unknown phases between the array antennas 113a, b), in order to simultaneously estimate the phases and the boresight direction of the antenna array 113a, b of the wireless multi-antenna transceiver 110. In an embodiment, the processing circuitry 111 of the wireless multi-antenna transceiver 110 may be configured to implement an estimation algorithm based on the following equations:

wherein

and i, 2 - ^are the unknown phases of the antennas 113a,b. In an embodiment, the processing circuitry 111 of the wireless multi-antenna transceiver 110 may be configured to perform an exhaustive grid search over a M-dimensional grid (1 dimension for 9_BS and (M-1) dimensions

Figure 8 shows a further embodiment of the wireless multi-antenna transceiver 110 with calibrated antenna phases. In the exemplary scenario shown in figure 8 the wireless multiantenna transceiver 110 comprise a ULA array with 4 antennas and 4 neighboring wireless access points 120a-d for boresight calibration. In this embodiment, each neighboring wireless access point 120a-d may activate a beamforming technique to steer the beam towards the wireless multi-antenna transceiver 110 (for decreasing the number of multipaths) so that consequently mostly LOS components are observed by the wireless multi-antenna transceiver 110 for each frame. Applying the AOA algorithm (Capon or Maximum Likelihood) described above produces the spectrum functions shown in figure 9. As will be appreciated, the respective differences between the known LOS direction and the estimated global peaks provides the estimation of boresight direction for the different neighboring wireless access point 120a-d. As already described above, an averaging over all neighboring wireless access point 120a-d may further improve the accuracy.

In case no beamforming is applied by the neighboring wireless access point 120a-d, the number of multipaths may increase. As already described above, in such a case, the processing circuitry 111 of the wireless multi-antenna transceiver 110 may be configured to implement more sophisticated AOA algorithms, such as the SpotFi algorithm which allows estimation of most received paths (LOS + multipath), and LOS path identification. In the following example, the processing circuitry 111 of the wireless multi-antenna transceiver 110 is configured to apply the SpotFi algorithm to a ULA-4 antenna array 113a, b, and identify the LOS direction to each one of the neighboring wireless access point 120a-d. By way of example, the simulated channel is the TGn D-LOS channel, which is the typical channel for an indoor scenario. The results of the SpotFi algorithm are illustrated in figure 10. In Fig.10 the two dimensional Spectrum function is presented, built using a smoothed CSI matrix, and defined over the AOA and the Time Delay domain. Each local peak corresponds to one of a plurality of arriving paths (with corresponding AOA and time delay). After the identification of all paths, the LOS is identified as the path with the shortest time delay.

After the LOS direction is identified for each neighboring wireless access point 120a-d, the boresight direction may be estimated in the same manner as for the embodiments described above, i.e. by subtracting from the known LOS and averaging over all neighboring wireless access point 120a-d. For typical indoor scenarios (TGn channels: “D”, “E”, LOS & NLOS) embodiments of the wireless multi-antenna transceiver 110 may achieve the performances listed in the following table for 3 exemplary approaches, namely Separated Capon, Combined Capon and SpotFi, when 4 neighboring wireless access point 120a-d are used for calibration.

As will be appreciated from the table above, the SpotFi approach provides the best accuracy amongst others.

Similarly to the previous embodiment, the Combined and Separate Capon approaches may be applied together with the modified SpotFi-Buttler algorithm for the case of 4 neighboring wireless access point 120a-d, while using Uniform Circular Array of 7 antennas 113a, b with half a wavelength separation. The performance for this example is illustrated in the following table for different channel models:

As in the previous embodiment, the modified SpotFi-Buttler approach provides the best performance amongst other methods.

In a further exemplary embodiment, the simultaneous phase and boresight calibration is performed and its results are compared with the combined Capon approach described above (for the case of already phase calibrated antennas 113a,b). For this case, more neighboring wireless access point 120a-d than in the previous examples are beneficial (because more unknown parameters have to be estimated). The performance for this example is presented in following table:

Figure 11 is a flow diagram illustrating a method 1100 for automatic boresight calibration, i.e. for determining a boresight orientation of the plurality of antennas 113a,b of the wireless multi-antenna receiver 110 according to an embodiment. The method 1100 comprises the steps of: receiving 1101 channel state information from each of the plurality of neighboring wireless multi-antenna transceivers 120a-d; obtaining 1103 position information about a respective position of the plurality of neighboring wireless multi-antenna transceivers 120a-d; and determining 1105 the boresight orientation of the plurality of antennas 113a,b based on the channel state information and the position information.

Further features of the method 1100 result directly from the structure and/or functionality of the wireless transmitter 110 as well as its different embodiments described above.

The person skilled in the art will understand that the "blocks" ("units") of the various figures (method and apparatus) represent or describe functionalities of embodiments of the present disclosure (rather than necessarily individual "units" in hardware or software) and thus describe equally functions or features of apparatus embodiments as well as method embodiments (unit = step).

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described embodiment of an apparatus is merely exemplary. For example, the unit division is merely logical function division and may be another division in an actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments. In addition, functional units in the embodiments of the invention may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit.

Claims

1. A wireless multi-antenna transceiver (110) for communication with a plurality of further wireless transceivers, including a plurality of neighboring wireless multi-antenna transceivers (120a-d), wherein the wireless multi-antenna transceiver (110) comprises: a communication interface (113) comprising a plurality of antennas (113a,b), wherein the communication interface (113) is configured to receive channel state information from each of the plurality of neighboring wireless multi-antenna transceivers (120a-d); and a processing circuitry (111) configured to obtain position information about a respective position of the plurality of neighboring wireless multi-antenna transceivers (120a-d); wherein the processing circuitry (111) is further configured to determine a boresight orientation of the plurality of antennas (113a,b) based on the channel state information and the position information.

2. The wireless multi-antenna transceiver (110) of claim 1, further comprising a memory (115) configured to store the position information about the respective position of the plurality neighboring wireless multi-antenna transceivers (120a-d), wherein the processing circuitry

(111) is configured to obtain the position information from the memory (115).

3. The wireless multi-antenna transceiver (110) of claim 1 or 2, wherein the communication interface (113) is configured to receive the position information about the respective position of the plurality of neighboring wireless multi-antenna transceivers (120a- d) from the plurality of neighboring wireless multi-antenna receivers (120a-d) and wherein the processing circuitry (111) is configured to obtain the position information from the communication interface (113).

4. The wireless multi-antenna transceiver (110) of any one of the preceding claims, wherein the processing circuitry (111) is configured, based on the channel state information and the position information, to determine separately for each of the plurality of neighboring wireless multi-antenna transceivers (120a-d) a respective boresight orientation estimate and to determine the boresight orientation of the plurality of antennas (113a,b) as an average of the plurality of boresight orientation estimates.

5. The wireless multi-antenna transceiver (110) of claim 4, wherein the processing circuitry (111) is configured to determine separately for each of the plurality of neighboring wireless multi-antenna transceivers (120a-d) a respective boresight orientation estimate 9^ on the basis of the following equation:

6. The wireless multi-antenna transceiver (110) of claim 5, wherein the processing circuitry (111) is configured to determine the estimated LOS direction 0_LOS^ for the I^th neighboring wireless multi-antenna transceiver (120a-d) on the basis of the following equations:

wherein a(0) denotes a steering vector of the plurality of antennas (113a, b), R_x^ = y- i i' denotes the input covariance matrix and X_t denotes a matrix comprising the channel state information from the I^th neighboring wireless multi-antenna transceiver (120a-d).

7. The wireless multi-antenna transceiver (110) of any one of claims 1 to 3, wherein the processing circuitry (111) is configured to determine the boresight orientation §_BS on the basis of the following equations:

wherein:

9_bs denotes a boresight orientation angle,

«t(e) denotes a steering vector relatively to the I^th neighboring wireless multi-antenna transceiver (120a-d), 0t denotes an expected LOS direction from the wireless multi-antenna transceiver (110) towards the I^th neighboring wireless multi-antenna transceiver (120a-d), and §_BS denotes a boresight direction estimate.

8. The wireless multi-antenna transceiver (110) of any one of the preceding claims, wherein the processing circuitry (111) is further configured to determine a respective phase of the plurality of antennas (113a,b) based on the channel state information and the position information.

9. The wireless multi-antenna transceiver (110) of any one of the preceding claims, wherein the wireless multi-antenna transceiver (110) and/or the plurality of neighboring wireless multi-antenna transceivers (120a-d) comprise one or more access points or base stations (110, 120a-d).

10. The wireless multi-antenna transceiver (110) of any one of the preceding claims, wherein the wireless multi-antenna transceiver (110) is configured to operate in accordance with the IEEE 802.11 WLAN standard or a standard evolved therefrom.

11. A method (1100) for determining a boresight orientation of a plurality of antennas (113a,b) of a wireless multi-antenna receiver (110), wherein the method (1100) comprises: receiving (1101) channel state information from each of a plurality of neighboring wireless multi-antenna transceivers (120a-d); obtaining (1103) position information about a respective position of the plurality of neighboring wireless multi-antenna transceivers (120a-d); and determining (1105) a boresight orientation of the plurality of antennas (113a,b) based on the channel state information and the position information.

12. The method (1100) of claim 11 , wherein the method (1100) further comprises obtaining the position information from a memory (115) of the wireless multi-antenna receiver (110).

13. The method (1100) of claim 11 or 12, wherein the method (1100) further comprises receiving the position information about the respective position of the plurality of neighboring wireless multi-antenna transceivers (120a-d) from the plurality of neighboring wireless multiantenna receivers (120a-d).

14. The method (1100) of any one of claims 11 to 13, wherein the method (1100) comprises determining, based on the channel state information and the position information, separately for each of the plurality of neighboring wireless multi-antenna transceivers (120a- d) a respective boresight orientation estimate and determining the boresight orientation of the plurality of antennas (113a,b) as an average of the plurality of boresight orientation estimates.

15. The method (1100) of claim 14, wherein the method (1100) comprises determining separately for each of the plurality of neighboring wireless multi-antenna transceivers (120a- d) a respective boresight orientation estimate 9^ on the basis of the following equation:

16. The method (1100) of claim 15, wherein the method (1100) comprises determining the estimated LOS direction 0_LOS^ for the I^th neighboring wireless multi-antenna transceiver (120a-d) on the basis of the following equations:

17. The method (1100) of any one of claims 11 to 13, wherein the method (1100) comprises determining the boresight orientation §_BS on the basis of the following equations:

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wherein:

6_bs denotes a boresight orientation angle,

«t(e) denotes a steering vector relatively to the I^th neighboring wireless multi-antenna transceiver (120a-d),

6t denotes an expected LOS direction from the wireless multi-antenna transceiver (110) towards the I^th neighboring wireless multi-antenna transceiver (120a-d), and §_BS denotes a boresight direction estimate.

18. The method (1100) of any one of claims 11 to 17, wherein the method (1100) further comprises determining a respective phase of the plurality of antennas (113a,b) based on the channel state information and the position information.

19. The method (1100) of any one of claims 11 to 18, wherein the wireless multi-antenna transceiver (110) and/or the plurality of neighboring wireless multi-antenna transceivers (120a-d) comprise one or more access points or base stations (110, 120a-d).

20. The method (1100) of any one of claims 11 to 19, wherein the method (1100) further comprises operating the wireless multi-antenna transceiver (110) in accordance with the IEEE 802.11 WLAN standard or a standard evolved therefrom.

21. A computer program product comprising a non-transitory computer-readable storage medium for storing program code which causes a computer or a processor to perform the method (1100) of any one of claims 11 to 20 when the program code is executed by the computer or the processor.

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