WO2025199867A1

WO2025199867A1 - Communication device and method therein for facilitating antenna calibration

Info

Publication number: WO2025199867A1
Application number: PCT/CN2024/084412
Authority: WO
Inventors: Hao Zhang; Ang FENG; Christian Braun; Yipeng ZHANG; Kang Lin; Yaling XING; Jinlai HE
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2024-03-28
Filing date: 2024-03-28
Publication date: 2025-10-02
Anticipated expiration: 2026-09-28

Abstract

The present application discloses a method (300) for facilitating Antenna Calibration, AC. The method (300) includes: transmitting (310) a plurality of sets of transmission signals via a plurality of transmitting branches, each set of transmission signals being generated from an AC signal based on one of a plurality of sets of transmitting phase shift values; receiving (320) a plurality of sets of reception signals corresponding to the transmission signals at a plurality of receiving branches; phase-shifting (330) each set of reception signals based on one of a plurality of sets of receiving phase shift values, thereby obtaining a plurality of decoded AC signals; and calculating (340) a channel response between the plurality of transmitting branches and the plurality of receiving branches based on the AC signal, the plurality of decoded AC signals, the plurality of sets of transmitting phase shift values, and the plurality of sets of receiving phase shift values.

Description

COMMUNICATION DEVICE AND METHOD THEREIN FOR FACILITATING ANTENNA CALIBRATION

TECHNICAL FIELD

The present disclosure relates to communication technology, and more particularly, to a communication device and a method therein for facilitating Antenna Calibration (AC) .

BACKGROUND

In the 4^th Generation (4G) and 5th Generation (5G) Radio Access Networks (RANs) , the massive Multiple Input Multiple Output (MIMO) or full-dimension MIMO technology is used to enhanced cell coverage, increase throughput, improve spectrum usage, etc. A large number of antennas is the key to support this technology. In high frequency wireless networks utilizing millimeter-wave spectrum, the number of antennas will be hundreds or more.

Massive MIMO or beamforming technology creates narrow beams to focus radiated energy towards a User Equipment (UE) . In a multi-user MIMO environment, multiple beams are transmitted towards UEs in order to increase the throughput. To enable beamforming, multiple antennas as well as their connected Radio Frequency (RF) components should be aligned coherently. Normally, it is difficult to achieve this by radio hardware alone. For this reason, Antenna Calibration (AC) is commonly deployed.

Mutual Coupling AC (MCAC) is an AC solution developed for mid-band and high-band Advanced Antenna System (AAS) . It doesn't need the hardware coupler network and can therefore reduce the size and cost of the AAS. MCAC requires an efficient scheme to identify coupled signals to/from different subarrays. This scheme is implemented in some products as a digital coding /decoding scheme based on multiplicative digital coding to create mutually orthogonal signals to/from multiple branches. In some existing MCAC solutions, there is only one coding instance per transmitting digital or Base Band (BB) port and one decoding instance per receiving digital or BB port.

Fig. 1 shows a hybrid beamforming architecture of an AAS for port expansion in RF branches. As shown, each BB port is connected to a Digital Frond End (DFE) and is then expanded to a number of RF branches (4 in the figure) , with a phase shifter (e.g., analog or time domain phase shifter) to control the phase of each RF branch. A beam angle can be controlled by the phase shifters. Each RF branch further includes a Power Amplifier (PA) for signal transmission and a Low Noise Amplifier (LNA) for signal reception, as well as a filter. In this architecture, a high beamforming gain can be supported without increase of the number of BB ports, and thus the cost of the AAS could be lower. This architecture is even more useful in higher bands like 10GHz to 100GHz to mitigate the path loss due to high frequency.

SUMMARY

However, there is a problem for MCAC with the architecture shown in Fig. 1. Fig. 2 shows an example of MCAC. As shown, a signal from each transmitting (TX) branch (TX_j1, TX_j2, TX_j3, TX_j4) is transmitted over the air and received by multiple receiving (RX) branches (RX_i1, RX_i2, RX_i3, RX_i4) . However, those RX branches are combined into one BB port, and thus the MCAC only has the observation of combined RX branches but not every individual RF branch. It is not possible to calibrate each RF branch in this case.

One straightforward solution is to add a switch in each RF branch. That means, all PAs can be muted or turned off except the one intended for TX calibration, or all LNAs can be muted or turned off except the one intended for RX calibration. However, the switching time for turning on/off PAs/LNAs is relatively long. It will introduce an unacceptable interruption of traffic as the traffic must be stopped when transmitting the MCAC signal. Another drawback is that the added switches increase the cost of the product. Typically, all PAs or all LNAs can share the same power supply to save cost and size. If they are switched on/off independently, then multiple power supplies may be needed to support such functionality.

It is an object of the present disclosure to provide a communication device and a method therein for facilitating AC, capable of solving or at least mitigating the above problem.

According to a first aspect of the present disclosure, a method for facilitating AC is provided. The method includes: transmitting a plurality of sets of transmission signals via a plurality of transmitting branches, each set of transmission signals being generated from an AC signal based on one of a plurality of sets of transmitting phase shift values. The method further includes: receiving a plurality of sets of reception signals corresponding to the transmission signals at a plurality of receiving branches. The method further includes: phase-shifting each set of reception signals based on one of a plurality of sets of receiving phase shift values, thereby obtaining a plurality of decoded AC signals. The method further includes: calculating a channel response between the plurality of transmitting branches and the plurality of receiving branches based on the AC signal, the plurality of decoded AC signals, the plurality of sets of transmitting phase shift values, and the plurality of sets of receiving phase shift values. The plurality of sets of transmitting phase shift values are orthogonal to each other and the plurality of sets of receiving phase shift values are orthogonal to each other.

In an embodiment, the operation of transmitting may include transmitting N*M sets of transmission signals via N transmitting branches. The N*M sets of transmission signals are dividable into M groups each including N sets. Each of the N sets in each of the M groups includes N transmission signals that are generated from an AC signal based on one of N sets of transmitting phase shift values, respectively. Each set of transmitting phase shift values includes N transmitting phase shift values, where N and M are each an integer greater than 1. The N sets of transmitting phase shift values are orthogonal to each other.

In an embodiment, the operation of receiving may include receiving N*M sets of reception signals corresponding to the transmission signals at M receiving branches, the N*M sets of reception signals being dividable into N groups each including M sets, each set of reception signals including M reception signals. The operation of phase-shifting may include phase-shifting, for each of the N groups, the M reception signals in each of the M sets based on one of M sets of receiving phase shift values, respectively, to obtain a decoded AC signal, thereby obtaining N*M decoded AC signals from the N*M sets of reception signals, each set of receiving phase shift values including M receiving phase shift values. The M sets of receiving phase shift values are orthogonal to each other. The operation of calculating may include calculating a channel response between the N transmitting branches and the M receiving branches based on the AC signal, the N*M decoded AC signals, the N sets of transmitting phase shift values, and the M sets of receiving phase shift values.

In an embodiment, the M sets of reception signals in each of the N groups may correspond to transmission signals generated based on one of N sets of transmitting phase shift values.

In an embodiment, the channel response may correspond to a combined transfer function of the N transmitting branches, an air interface between N transmitting antennas corresponding to the N transmitting branches respectively and M receiving antennas corresponding to the M receiving branches respectively, and the M receiving branches.

In an embodiment, a product of a first matrix formed based on the N sets of transmitting phase shift values and a Hermitian transposition of the first matrix may be a symmetric matrix, and/or a product of a second matrix formed based on the M sets of receiving phase shift values and a Hermitian transposition of the second matrix may be a symmetric matrix.

In an embodiment, the N transmitting branches may correspond to a first BB port and the M receiving branches may correspond to a second BB port.

In an embodiment, the method may further include, simultaneously with transmitting the transmission signals via the transmitting branches corresponding to the first BB port, transmitting transmission signals generated from the AC signal via transmitting branches corresponding to a third BB port.

In an embodiment, Mutual Coupling (MC) isolation or physical spacing between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the third BB port may be greater than a threshold, and/or a difference between a first MC loss and a second MC loss may be greater than a threshold, the first MC loss being an MC loss between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the second BB port, the second MC loss being an MC loss between the transmitting branches corresponding to the third BB port and the transmitting branches corresponding to the second BB port.

According to a second aspect of the present disclosure, a communication device is provided. The communication device may include an antenna array, a processor, and a memory. The memory contains instructions executable by the processor whereby the communication device is operative to perform the method according to the above first aspect.

According to a third aspect of the present disclosure, a computer-readable storage medium is provided. The computer-readable storage medium has computer-readable instructions stored thereon. The computer-readable instructions, when executed by a processor of a communication device, configure the communication device to perform the method according to the above first aspect.

According to a fourth aspect of the present disclosure, a computer program product is provided. The computer program product includes computer-readable instructions which, when executed by a processor of a communication device, configure the communication device to perform the method according to the above first aspect.

With certain embodiments of the present disclosure, orthogonal phase coding is introduced at both transmitting branches and receiving branches, thereby enabling MCAC in the hybrid beamforming architecture. An increased Signal to Interference plus Noise Ratio (SINR) can be achieved by transmitting and receiving MCAC signals in all transmitting and receiving branches, so as to get better MCAC performance, which in turn leads to improved performance of hybrid beamforming. A significant reduction in impact on traffic can be achieved due to the non-muting solution and sequence separations. No hardware change is required, thereby reducing the cost of the product. Compared with the scheme of switching on/off PAs/LNAs, the cost and size of the product can be reduced. In addition, within the same calibration time, targeting at the same SINR, PAs can work with certain power back-off, which also decreases the impact of nonlinearity.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages will be more apparent from the following description of embodiments with reference to the figures, in which:

Fig. 1 is a schematic diagram showing a hybrid beamforming architecture;

Fig. 2 is a schematic diagram showing an example of MCAC;

Fig. 3 is a flowchart illustrating a method for facilitating AC according to an embodiment of the present disclosure;

Fig. 4 is a schematic diagram showing an example of MCAC according to an embodiment of the present disclosure;

Fig. 5 is a schematic diagram showing a simulation result of phase coding according to an embodiment of the present disclosure;

Fig. 6 is a schematic diagram showing a simulation result comparison between phase responses without and with optimized phase shifter matrix;

Fig. 7 is a schematic diagram showing a comparison between a legacy MCAC solution and a new MCAC solution according to an embodiment of the present disclosure;

Fig. 8 is a schematic diagram showing a comparison of numbers of AC symbols required between a legacy MCAC solution and a new MCAC solution according to an embodiment of the present disclosure;

Fig. 9 is a schematic diagram showing an example of MCAC pattern according to an embodiment of the present disclosure;

Fig. 10 is a block diagram of an apparatus for facilitating AC according to an embodiment of the present disclosure; and

Fig. 11 is a block diagram of a communication device according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

References in the specification to "one embodiment, " "an embodiment, " "an example embodiment, " and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms "first" and "second" etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms "a" , "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" , "comprising" , "has" , "having" , "includes" and/or "including" , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

Fig. 3 is a flowchart illustrating a method 300 according to an embodiment of the present disclosure. The method 300 can be performed by a communication device, e.g., a base station or a (next) generation Node B (gNB) .

At block 310, a plurality of sets of transmission signals are transmitted via a plurality of transmitting branches. Each set of transmission signals is generated from an AC signal based on one of a plurality of sets of transmitting phase shift values.

At block 320, a plurality of sets of reception signals corresponding to the transmission signals are received at a plurality of receiving branches.

At block 330, each set of reception signals is phase-shifted based on one of a plurality of sets of receiving phase shift values, thereby obtaining a plurality of decoded AC signals.

At block 340, a channel response between the plurality of transmitting branches and the plurality of receiving branches is calculated based on the AC signal, the plurality of decoded AC signals, the plurality of sets of transmitting phase shift values, and the plurality of sets of receiving phase shift values.

Here, the plurality of sets of transmitting phase shift values are orthogonal to each other and the plurality of sets of receiving phase shift values are orthogonal to each other.

Without loss of generality, in the following example, the transmission signals may be transmitted via N transmitting branches corresponding to a first BB port and the reception signal may be received at M receiving branches corresponding to a second BB port, where N and M are each an integer greater than 1. N and M may or may not be equal to each other.

In this case, in the block 310, N*M sets of transmission signals are via N transmitting branches. The N*M sets of transmission signals are dividable into M groups each including N sets, and each of the N sets in each of the M groups including N transmission signals that are generated from the AC signal based on one of N sets of transmitting phase shift values, respectively. Each set of transmitting phase shift values includes N transmitting phase shift values. The N sets of transmitting phase shift values are orthogonal to each other.

Let x denote the AC signal, which may be e.g., a Zadoff-Chu sequence, denote a vector representing one of N sets of transmitting phase shift values, and T denote a vector representing transfer functions of N transmitting branches (e.g., combined transfer functions of PAs, filters, antennas, etc., in the respective transmitting branches) . Then, one set of transmission signals is transmitted via N transmitting branches at a time, denoted as:

For each n = 1, ..., N, the set of transmission signals is transmitted for M times (i.e., M groups) , to form the N*M sets of transmission signals.

In the block 320, N*M sets of reception signals corresponding to the transmission signals are received at M receiving branches. The N*M sets of reception signals are dividable into N groups each including M sets. Each set of reception signals includes M reception signals.

In the block 330, for each of the N groups, the M reception signals in each of the M sets are phase-shifted based on one of M sets of receiving phase shift values, respectively, to obtain a decoded AC signal, thereby obtaining N*M decoded AC signals from the N*M sets of reception signals. Each set of receiving phase shift values includes M receiving phase shift values. The M sets of receiving phase shift values are orthogonal to each other.

Here, the decoded AC signal may be represented as

where S denotes a mutual coupling channel matrix of an air interface between N transmitting antennas corresponding to the N transmitting branches respectively and M receiving antennas corresponding to the M receiving branches respectively, R is a vector representing transfer functions of M receiving branches (e.g., combined transfer functions of antennas, filters, LNAs, etc., in the respective receiving branches) , andis a vector representing one of M sets of receiving phase shift values.

Here, the M sets of reception signals in each of the N groups correspond to transmission signals generated based on one of N sets of transmitting phase shift values. In other words, for each possible value pair of (n, m) , a decoded AC signal y_m, n is obtained, resulting in N*M decoded AC signals in total.

In the block 340, a channel response between the N transmitting branches and the M receiving branches is calculated based on the AC signal, the N*M decoded AC signals, the N sets of transmitting phase shift values, and the M sets of receiving phase shift values.

Here, the channel response may correspond to a combined transfer function of the N transmitting branches, an air interface between N transmitting antennas corresponding to the N transmitting branches respectively and M receiving antennas corresponding to the M receiving branches respectively, and the M receiving branches. In the above example, the channel response corresponds to T2R= R *S *T. The object of MCAC measurement is to figure out the channel response T2R. Once the channel response T2R is calculated, the AC can be performed with any known or future developed calibration scheme.

Fig. 4 shows an example of MCAC according to an embodiment of the present disclosure. In this example, it is assumed that BB port 1 is connected to N=4 transmitting branches and BB port 2 is connected to M=4 receiving branches. In each transmitting branch, an AC signal, x, is fed into a transmitting phase shifter subjected to an equivalent transfer function of the transmitting branch (t₁～t₄) , and then transmitted via a transmitting antenna. In each receiving branch, a reception signal, corresponding to a transmission signal after transmission over the air interface, is received at a receiving antenna, subjected to an equivalent transfer function of the receiving branch (r₁～r₄) , and phase-shifted by a receiving phase shifter

In this example, the decoded AC signal can be represented as:

where

T = [t₁ t₂ t₃ t₄] (5)

R = [r₁ r₂ r₃ r₄] ^T (7)

Accordingly, the channel response to be calculated is now:

Here, a matrix P_t formed byis written as:

A matrix P_r formed byis written as:

Each of P_t and P_r has a rank of 4. That is, for different values of n, the vectors are orthogonal to each other, and for different values of m, the vectorsare orthogonal to each other.

According to Equation (3) , N*M=16 decoded AC signals can be obtained and written as:

The channel response can be calculated as:

In an example, the entries of the matrices P_t and P_r may be generated randomly. From matrix analysis it is likely that the matrices so generated will have full ranks. For illustration purpose, one example of P_t and P_r is given below, in units of degrees, with the ranks of the matrices being 4:

Fig. 5 shows a simulation result of phase coding of the above example of Equations (14) and (15) . As shown, the line is the actual phase response of T2R and dots are decoded phase response. In Fig. 5, T2R1x denotes an element in the 1st row and the x-th column of the T2R matrix. It can be seen from the result that the channel response is calculated accurately according to the embodiments of the present disclosure.

In practice there might be some errors in phase shifter setting, which is known as Phase Shifter (PS) Quantization Error. From an AAS radio product for spectrum above 6GHz, the maximum quantization error may be 2.8 degrees, which would degrade the decoding performance.

If an orthogonal matrix can be generated and the leakage between codes can be mitigated, it will be more resilient to quantization errors. In order to achieve better decoding performance, optimized matrices of P_t and P_r is given below, in units of degrees:

There might be other settings for optimized matrices but the rule is thatis a symmetric matrix, and/oris a symmetric matrix:

Here is an example of PS quantization error impact. The error is random distributed in the phase shifters in different time with a maximum value +/-2.8deg:

Fig. 6 shows a simulation result comparison between phase responses without and with optimized PS matrix. As shown, the line is the actual phase response of T2R and dots are decoded phase response. In Fig. 6, T2R3x denotes an element in the 3rd row and the x-th column of the T2R matrix. The phase error without the optimized PS matrices (e.g., using the matrices in Equations (14) and (15) ) could be up to 50 degrees while it is only 3 degrees with the optimized PS matrices (e.g., using the matrices in Equations (16) and (17) ) .

In other words, in the above method 300, a product of a first matrix formed based on the N sets of transmitting phase shift values and a Hermitian transposition of the first matrix may be a symmetric matrix, and/or a product of a second matrix formed based on the M sets of receiving phase shift values and a Hermitian transposition of the second matrix may be a symmetric matrix.

The above embodiments of the present disclosure allow AC for one subarray with expanded branches. For the entire antenna array, spatial separation can be introduced to achieve shorter calibration time.

For example, in the above method 300, simultaneously with transmitting the transmission signals via the transmitting branches corresponding to the first BB port, transmission signals generated from the AC signal can be transmitted via transmitting branches corresponding to a third BB port. Here, MC isolation or physical spacing between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the third BB port may be greater than a threshold. Alternatively or additionally, a difference between a first MC loss and a second MC loss may be greater than a threshold, the first MC loss being an MC loss between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the second BB port, the second MC loss being an MC loss between the transmitting branches corresponding to the third BB port and the transmitting branches corresponding to the second BB port.

Fig. 7 shows a comparison between a legacy MCAC solution (left) and the new MCAC solution according to the embodiments of the present disclosure (right) . As shown, four blocks in one column represent four branches, or referred to as one subarray, corresponding to one BB port. In either solution, eight subarrays are configured to transmit transmission signals at the same time, while other subarrays are configured to receive the signals. For the legacy MCAC solution, 8 orthogonal AC sequences are needed, with AC sequences highlighted in boxes and numbered as 1～8. For the new MCAC solution, only 4 orthogonal AC sequences are needed, with AC sequences highlighted in boxes and numbered as 1～4. It can be seen that according to the new MCAC solution, each orthogonal AC sequence 1～4 is used for generating transmission signals at two subarrays with sufficient MC isolation or physical spacing. The idea here is to utilize the MC loss to separate two identical AC sequences at the receiving subarrays.

Fig. 8 shows a comparison of numbers of AC symbols required between a legacy MCAC solution and the new MCAC solution according to the embodiments of the present disclosure. The legacy MCAC solution needs at least 8 Orthogonal Frequency Division Multiplexing (OFDM) symbols to secure the orthogonality, while only 40FDM symbols are needed for the new MCAC solution.

Fig. 9 shows an example of MCAC pattern according to an embodiment of the present disclosure. As shown, the same type of filling pattern represents subarrays transmitting the same AC sequence. In this example, a receiving subarray RX8 receives a same AC sequence from transmitting subarrays TX9 and TX19. The coupling loss is -20dB from TX9 to RX8 and -80dB from TX19 to RX8, and thus there will be very Iow interference from TX19. Therefore, for RX8, the impact from TX 19 can be ignored.

On the other hand, a receiving subarray RX10 receives a same AC sequence from transmitting subarrays TX13 and TX23. The coupling loss are -60dB from TX13 to RX10 and -70dB from TX23 to RX10. The 10dB difference may result in interference from each other. However, the mutual coupling path between RX10 and TX13 can be dropped due to the high coupling loss and there is no impact on overall calibration performance of the entire AAS, i.e., RX10 may receive signals from e.g., TX9.

Correspondingly to the method 300 as described above, an apparatus for facilitating AC is provided. Fig. 10 is a block diagram of an apparatus 1000 according to an embodiment of the present disclosure. The apparatus 1000 can be implemented in a communication device, e.g., a base station or a gNB.

As shown in Fig. 10, the apparatus 1000 includes a transmitting unit 1010 configured to transmit a plurality of sets of transmission signals via a plurality of transmitting branches, each set of transmission signals being generated from an AC signal based on one of a plurality of sets of transmitting phase shift values. The apparatus 1000 further includes a receiving unit 1020 configured to receive a plurality of sets of reception signals corresponding to the transmission signals at a plurality of receiving branches. The apparatus 1000 further includes a phase-shifting unit 1030 configured to phase-shift each set of reception signals based on one of a plurality of sets of receiving phase shift values, thereby obtaining a plurality of decoded AC signals. The apparatus 1000 further includes a calculating unit 1040 configured to calculate a channel response between the plurality of transmitting branches and the plurality of receiving branches based on the AC signal, the plurality of decoded AC signals, the plurality of sets of transmitting phase shift values, and the plurality of sets of receiving phase shift values. The plurality of sets of transmitting phase shift values are orthogonal to each other and the plurality of sets of receiving phase shift values are orthogonal to each other.

In an embodiment, the transmitting unit 1010 may be configured to transmit N*M sets of transmission signals via N transmitting branches. The N*M sets of transmission signals are dividable into M groups each including N sets. Each of the N sets in each of the M groups includes N transmission signals that are generated from an AC signal based on one of N sets of transmitting phase shift values, respectively. Each set of transmitting phase shift values includes N transmitting phase shift values, where N and M are each an integer greater than 1.The N sets of transmitting phase shift values are orthogonal to each other.

In an embodiment, the receiving unit 1020 may be configured to receive N*M sets of reception signals corresponding to the transmission signals at M receiving branches, the N*M sets of reception signals being dividable into N groups each including M sets, each set of reception signals including M reception signals. The phase-shifting unit 1030 may be configured to phase-shift, for each of the N groups, the M reception signals in each of the M sets based on one of M sets of receiving phase shift values, respectively, to obtain a decoded AC signal, thereby obtaining N*M decoded AC signals from the N*M sets of reception signals, each set of receiving phase shift values including M receiving phase shift values. The M sets of receiving phase shift values are orthogonal to each other. The calculating unit 1040 may be configured to calculate a channel response between the N transmitting branches and the M receiving branches based on the AC signal, the N*M decoded AC signals, the N sets of transmitting phase shift values, and the M sets of receiving phase shift values.

In an embodiment, the transmitting unit 1010 may be further configured to, simultaneously with transmitting the transmission signals via the transmitting branches corresponding to the first BB port, transmit transmission signals generated from the AC signal via transmitting branches corresponding to a third BB port.

In an embodiment, MC isolation or physical spacing between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the third BB port may be greater than a threshold, and/or a difference between a first MC loss and a second MC loss may be greater than a threshold, the first MC loss being an MC loss between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the second BB port, the second MC loss being an MC loss between the transmitting branches corresponding to the third BB port and the transmitting branches corresponding to the second BB port.

The units 1010～1040 can be implemented as a pure hardware solution or as a combination of software and hardware, e.g., by one or more of: a processor or a micro-processor and adequate software and memory for storing of the software, a Programmable Logic Device (PLD) or other electronic component (s) or processing circuitry configured to perform the actions described above, and illustrated, e.g., in Fig. 3.

Fig. 11 is a block diagram of a communication device 1100 according to an embodiment of the present disclosure.

The communication device 1100 includes an antenna array 1110, a processor 1120 and a memory 1130.

The memory 1130 may contain instructions executable by the processor 1120 whereby the communication device 1100 is operative to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 3. Particularly, the memory 1130 may contain instructions executable by the processor 1120 whereby the communication device 1100 is operative to transmit a plurality of sets of transmission signals via a plurality of transmitting branches, each set of transmission signals being generated from an AC signal based on one of a plurality of sets of transmitting phase shift values. The memory 1130 may further contain instructions executable by the processor 1120 whereby the communication device 1100 is operative to: receive a plurality of sets of reception signals corresponding to the transmission signals at a plurality of receiving branches. The memory 1130 may further contain instructions executable by the processor 1120 whereby the communication device 1100 is operative to: phase-shift each set of reception signals based on one of a plurality of sets of receiving phase shift values, thereby obtaining a plurality of decoded AC signals. The memory 1130 may further contain instructions executable by the processor 1120 whereby the communication device 1100 is operative to: calculate a channel response between the plurality of transmitting branches and the plurality of receiving branches based on the AC signal, the plurality of decoded AC signals, the plurality of sets of transmitting phase shift values, and the plurality of sets of receiving phase shift values. The plurality of sets of transmitting phase shift values are orthogonal to each other and the plurality of sets of receiving phase shift values are orthogonal to each other.

In an embodiment, the memory 1130 may further contain instructions executable by the processor 1120 whereby the communication device 1100 is operative to, simultaneously with transmitting the transmission signals via the transmitting branches corresponding to the first BB port, transmit transmission signals generated from the AC signal via transmitting branches corresponding to a third BB port.

The present disclosure also provides at least one computer program product in the form of a non-volatile or volatile memory, e.g., a non-transitory computer readable storage medium, an Electrically Erasable Programmable Read-Only Memory (EEPROM) , a flash memory and a hard drive. The computer program product includes a computer program. The computer program includes: code/computer readable instructions, which when executed by the processor 1120 causes the communication device 1100 to perform the actions, e.g., of the procedure described earlier in conjunction with Fig. 3.

The computer program product may be configured as a computer program code structured in computer program modules. The computer program modules could essentially perform the actions of the flow illustrated in Fig. 3.

The processor may be a single CPU (Central Processing Unit) , but could also comprise two or more processing units. For example, the processor may include general purpose microprocessors; instruction set processors and/or related chips sets and/or special purpose microprocessors such as Application Specific Integrated Circuits (ASlCs) . The processor may also comprise board memory for caching purposes. The computer program may be carried in a computer program product connected to the processor. The computer program product may comprise a non-transitory computer readable storage medium on which the computer program is stored. For example, the computer program product may be a flash memory, a Random Access Memory (RAM) , a Read-Only Memory (ROM) , or an EEPROM, and the computer program modules described above could in alternative embodiments be distributed on different computer program products in the form of memories.

The disclosure has been described above with reference to embodiments thereof. It should be understood that various modifications, alternations and additions can be made by those skilled in the art without departing from the spirits and scope of the disclosure. Therefore, the scope of the disclosure is not limited to the above particular embodiments but only defined by the claims as attached.

Claims

A method (300) for facilitating Antenna Calibration, AC, comprising:

transmitting (310) a plurality of sets of transmission signals via a plurality of transmitting branches, each set of transmission signals being generated from an AC signal based on one of a plurality of sets of transmitting phase shift values;

receiving (320) a plurality of sets of reception signals corresponding to the transmission signals at a plurality of receiving branches;

phase-shifting (330) each set of reception signals based on one of a plurality of sets of receiving phase shift values, thereby obtaining a plurality of decoded AC signals; and

calculating (340) a channel response between the plurality of transmitting branches and the plurality of receiving branches based on the AC signal, the plurality of decoded AC signals, the plurality of sets of transmitting phase shift values, and the plurality of sets of receiving phase shift values,

wherein the plurality of sets of transmitting phase shift values are orthogonal to each other and the plurality of sets of receiving phase shift values are orthogonal to each other.
The method (300) of claim 1, wherein said transmitting (310) comprises:

transmitting N＊M sets of transmission signals via N transmitting branches, the N＊M sets of transmission signals being dividable into M groups each including N sets, each of the N sets in each of the M groups including N transmission signals that are generated from the AC signal based on one of N sets of transmitting phase shift values, respectively, each set of transmitting phase shift values including N transmitting phase shift values, where N and M are each an integer greater than 1,

wherein the N sets of transmitting phase shift values are orthogonal to each other.
The method (300) of claim 2, wherein

said receiving (320) comprises:

receiving N＊M sets of reception signals corresponding to the transmission signals at M receiving branches, the N＊M sets of reception signals being dividable into N groups each including M sets, each set of reception signals including M reception signals,

said phase-shifting (330) comprises:

phase-shifting, for each of the N groups, the M reception signals in each of the M sets based on one of M sets of receiving phase shift values, respectively, to obtain a decoded AC signal, thereby obtaining N＊M decoded AC signals from the N＊M sets of reception signals, each set of receiving phase shift values including M receiving phase shift values, wherein the M sets of receiving phase shift values are orthogonal to each other, and said calculating (340) comprises:

calculating a channel response between the N transmitting branches and the M receiving branches based on the AC signal, the N＊M decoded AC signals, the N sets of transmitting phase shift values, and the M sets of receiving phase shift values.
The method (300) of claim 3, wherein the M sets of reception signals in each of the N groups correspond to transmission signals generated based on one of N sets of transmitting phase shift values.
The method (300) of claim 3 or 4, wherein the channel response corresponds to a combined transfer function of the N transmitting branches, an air interface between N transmitting antennas corresponding to the N transmitting branches respectively and M receiving antennas corresponding to the M receiving branches respectively, and the M receiving branches.
The method (300) of any of claims 3-5, wherein a product of a first matrix formed based on the N sets of transmitting phase shift values and a Hermitian transposition of the first matrix is a symmetric matrix, and/or a product of a second matrix formed based on the M sets of receiving phase shift values and a Hermitian transposition of the second matrix is a symmetric matrix.
The method (300) of any of claims 3-6, wherein the N transmitting branches correspond to a first Base Band, BB, port and the M receiving branches correspond to a second BB port.
The method (300) of claim 7, further comprising, simultaneously with transmitting the transmission signals via the transmitting branches corresponding to the first BB port:

transmitting transmission signals generated from the AC signal via transmitting branches corresponding to a third BB port.
The method (300) of claim 8, wherein

Mutual Coupling, MC, isolation or physical spacing between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the third BB port is greater than a threshold, and/or

a difference between a first MC loss and a second MC loss is greater than a threshold, the first MC loss being an MC loss between the transmitting branches corresponding to the first BB port and the transmitting branches corresponding to the second BB port, the second MC loss being an MC loss between the transmitting branches corresponding to the third BB port and the transmitting branches corresponding to the second BB port.
A communication device (1100) , comprising an antenna array (1110) , a processor (1120) , and a memory (1130) , the memory (1130) comprising instructions executable by the processor (1120) whereby the communication device (1100) is operative to perform the method according to any of claims 1-9.
A computer-readable storage medium having computer-readable instructions stored thereon, the computer-readable instructions, when executed by a processor of a communication device, configure the communication device to perform the method according to any of claims 1-9.
A computer program product, comprising computer-readable instructions which, when executed by a processor of a communication device, configure the communication device to perform the method according to any of claims 1-9.