Patent Description:
Wireless communication devices equipped with multiple antennas have to be calibrated and tested with respect to overall performance and conformance.

A well-known method for device testing is the so-called conducted test (CT) where the device' antennas are disconnected from the device under test (DUT) and a device tester is directly connected to the DUT. In such a conducted test, no wireless transmission is performed between the DUT and the device tester. This test setup in its simple manner does not consider the DUT' antenna radiation patterns during the device testing. A major drawback of the conducted test is that any kind of beamforming/beam-processing algorithms implemented in the DUT cannot be evaluated, as all signals "virtually" impinge at the same direction. Moreover, no direction- or frequency-dependent signal amplification or attenuation may be noticeable as the DUT' antennas are not present in this test.

An extension of the conducted test is the so called two-stage method (TSM) [<NUM>], see <FIG> and <FIG>. In detail, <FIG> show schematic views of antenna measurement principles for small devices and for large devices, respectively. <FIG> shows a schematic view of a calibration/test setup <NUM> for the TSM. In this setup, the DUT' <NUM> antenna radiation patterns are measured at a first stage (<FIG>) in an antenna measurement chamber where the DUT' antennas are rotated <NUM> such that a desired azimuth and elevation angle range is covered. When the size of the DUT <NUM> is too large to be rotated in all desired angular directions, it can be put onto a turntable to cover the azimuth angles by rotating the DUT <NUM>; the elevation angles are covered by movement of the transmitter antenna or by switching the active antenna on an antenna arc, cf. At the second stage of the TSM, a conducted test between the device tester (e.g. eNodeB) and the DUT <NUM> is performed (see <FIG>). In contrast to the simple CT setup described above, the DUT' antenna radiation patterns and the MIMO propagation channel are contained in the digital baseband signals.

In the TSM channel emulators emulate a time-variant MIMO propagation channel between the device tester/control site (CS) <NUM>, and the DUT <NUM>. When the communication link between the CS and DUT is successfully established, different performance metrics of the communication link are measured and analyzed, such as data throughput, received signal strength, etc. A major disadvantage of the conducted testing, however, is that self-interference effects caused by antenna coupling of the DUT antennas cannot be considered during the test. Furthermore, typical in-band interferences caused either by signals radiated from other devices in the close vicinity of the DUT, or from non-conformant radio devices cannot be evaluated during the test.

The radiated two-stage method (RTS) [<NUM>-<NUM>], cf. , <FIG> performs the TSM over-the air (OTA) in an anechoic chamber. Both self- and in-band-interference effects can be evaluated by this approach. Similar to the TSM, the DUT antenna radiation patterns are measured before device testing. For the RTS approach, the CS <NUM> radiates or receives phase coherent signals via O CS antenna ports <NUM>/ NOTA antennas <NUM>, while the DUT <NUM> which is equipped with M antenna ports <NUM>, receives or radiates the signals. In a first step, the chamber's <NUM> propagation channel characteristic is measured and stored in a channel matrix <MAT>. During this calibration measurement, the DUT antennas (DUT' antenna ports) <NUM> are disconnected from the DUT <NUM>. Based on the measured channel matrix HC, a precoder matrix is computed and applied to the transmit signals at the CS to realize orthogonal channels and to remove the influence of the chamber's propagation characteristic between the O CS- antenna ports <NUM>/N OTA antennas <NUM> and the M DUT antenna ports <NUM>. There exists a variety of approaches for signal precoding. As an example, the precoder matrix can be calculated by the Moore-Penrose pseudo-inverse of the channel transfer matrix HC. Furthermore, a realistic MIMO propagation channel matrix HT that contains the measured DUT antenna radiation pattern(s) can be incorporated in the transmit signal at the CS. Device testing is then performed by establishing a communication link between the CS and DUT and evaluating the performance.

The extension of the RTS-method is the so-called Wireless Cable approach (WLC), cf. <FIG>, [<NUM>] that can be applied in non-anechoic environments.

WLC description: The received signal at the DUT <NUM> (downlink case) is given as <MAT> where y(q) is the frequency-dependent received signal vector at the DUT <NUM> antenna ports <NUM> at frequency-bin q (q=<NUM>,. ,Q), x(q) is the frequency-dependent radiated signal at the CS <NUM>, and P(q) is the frequency-dependent precoding matrix. To measure the channel matrices HC(f) between the antenna ports <NUM> of the DUT <NUM> and the CS ports <NUM>, reference signals are transmitted and the precoding matrices P(q), q = <NUM>,. , Q are set to identity matrices. Then, by pseudo-inversion of the channel matrix HC and multiplication with a desired propagation channel matrix HT, the precoder matrix can be calculated as <MAT>.

Note that for simplicity, the frequency dependent notation has been omitted.

For the RTS (narrow band) and the WLC (wide band) method the following calibration procedure for the channel matrix HC is applied. To measure the influence of the N OTA antennas <NUM> at the CS-side <NUM>, the DUT antennas <NUM> and the propagation channel of the chamber <NUM>, the DUT <NUM> backend has to be separated from the DUT-antennas <NUM>. At the DUT-antenna ports <NUM>, the calibration measurement system has to be connected via cables to measure the chamber's <NUM> propagation channel characteristics including the OTA antenna <NUM> and DUT antennas <NUM> characteristics.

For small-sized DUTs, wave field synthesis (WFS) or the MIMO Multiprobe method [<NUM>,<NUM>] can be applied for device testing as well. Hereby, a set of plane waves, defined by the targeted propagation channel characteristic are emulated. This is done by an arrangement of several OTA emulation antennas. The number of emulation antennas and the operation frequency dictates the maximum dimension of a DUT in which plane waves can be emulated. The drawback of the WFS method is the high number of needed emulation antennas. As an example, <NUM> emulation antennas at an operating frequency of <NUM> in a 2D antenna arrangement allow for a maximum electrical DUT size of approximately <NUM>. Additionally, all signal paths that feed the emulation antennas have to be phase coherent for WFS. Compared to the other mentioned methods, WFS is the most expensive one in terms of hardware requirements especially if the DUT is large. Furthermore, this method cannot be applied in non-anechoic environments. This method is mentioned here for completion and because it does not require a DUT calibration as the previously mentioned methods.

<FIG> gives an overview of the existing test methods by showing the advances of each approach. The methods marked with a rectangle operate in non-anechoic environments; wile methods marked with a triangle can be used only in anechoic environments. As shown in <FIG>, the above described TSM (see <FIG>), RTS method (see <FIG>) and WLC method (see <FIG>) are only suitable for DUTs that allow disconnecting the DUT' antennas from the antenna ports. Although the WFS method can be used for highly integrated devices, it is very expensive and complex one in terms of hardware requirements.

To summarize, device interfaces of highly integrated communication devices are neither available nor accessible. As a consequence, non-destructive testing or calibration of the device' components (e.g., antennas, beamforming networks and down/up-converters, etc.) become impossible or very difficult.

<CIT> discloses a method for determining a beamforming vector or a beamforming channel matrix in a communication system including a transmitting station and a receiving station, and a communication system are described. The transmitting and receiving stations include respective antenna groups and respective codebooks include a plurality of predefined beamforming vectors for the antenna group.

Therefore, it is the object of the present invention to provide an efficient method for non-destructively testing/calibrating highly integrated communication devices.

This object is solved by the independent claims.

Advantageous implementations are addressed in the dependent claims.

Further embodiments provide a method for wirelessly calibrating/testing a receive module of a multi-antenna receiver of a device under test (for example, the method may be used for calibrating/testing components of the multi-antenna receiver downstream (in receive direction) RF ports of the multi-antenna receiver). The method comprises the step of wirelessly transmitting a first signaling information between the device under test and a device tester, the first signaling information indicating a calibration request, wherein the first signaling information is transmitted by the device under test or the device tester. Further, the method comprises the step of estimating, in response to the first signaling information, channel transfer function matrices between RF ports of the multi-antenna receiver of the device under test and antenna ports of the device tester using reference signals wirelessly transmitted from the device tester to the device under test, and transmitting the estimated channel transfer function matrices or an information derived therefrom from the device under test to the device tester. Further, the method comprises the step of wirelessly transmitting a second signaling information between the device under test and the device tester, the second signaling information indicating a precoded transmission request, wherein the second signaling information is transmitted by the device under test or the device tester. Further, the method comprises the step of wirelessly transmitting, in response to the second signaling information, reference signals from the device tester to the device under test using precoder matrices selected or determined based on the estimated channel transfer function matrices or the information derived therefrom, to obtain interference free channels between the device tester and the device under test allowing the reference signals to be received independently at each of the RF ports of the multi-antenna receiver of the device under test.

Embodiments of the present invention are described herein making reference to the appended drawings.

Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals.

In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagrams form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.

Before embodiments of methods for calibrating/testing RF components (e.g., antennas, antenna ports, RF ports, beamforming networks, Tx modules (Tx = transmitter) or Rx modules (Rx = receiver)) of a wireless communication device, referred herein as to device under test (DUT) <NUM>, are described in further detail, the device itself is described making reference to <FIG>, <FIG> and the calibration/test setup is described making reference to <FIG>.

<FIG> shows a schematic block diagram of a multi-antenna transceiver (transmitter and/or receiver) of a device under test <NUM>. The multi-antenna transceiver of the device under test <NUM> comprises an antenna array <NUM>, a beamforming network <NUM> and at least one RF module <NUM>. The beamforming network <NUM> comprises M array ports (or antenna ports) <NUM> and P RF ports <NUM>, wherein M can be a natural number greater than or equal to two, M ≥ <NUM>, and wherein P can be a natural number greater than or equal to two, P ≥ <NUM>. The antenna array <NUM>, or more precisely, the M antennas of the antenna array <NUM> can be connected to the M array ports <NUM> of the beamforming network <NUM>, wherein the at least one RF module <NUM> can be connected to the P RF ports <NUM> of the beamforming network <NUM>. Further, the multi-antenna transceiver (transmitter and/or receiver) of the device under test <NUM> may comprise at least one transceiver module (e.g., at least one transmitter module and/or at least one receiver module), configured to perform a digital signal processing. The at least one transceiver module can be connected to the at least one RF module <NUM>. Further, the Further, the multi-antenna transceiver (transmitter and/or receiver) of the device under test <NUM> may comprise analog-to-digital converters and/or digital-to-analog converters connected between the at least one RF module <NUM> and the at least one (digital) transceiver module.

In embodiments, the beamforming network <NUM> can be an analog beamforming network.

Further, in embodiments, the multi-antenna transceiver can be configured to perform a digital beamforming e.g., using the at least one transceiver module. In other words, the multi-antenna transceiver can comprise a hybrid beamforming network having an analog portion and a digital portion. Thereby, the analog portion of the hybrid beamforming network can be implemented in the beamforming network <NUM>, wherein the digital portion of the beamforming network can be implemented in the at least one transceiver module.

Further, in embodiments, the multi-antenna transceiver also can comprise only a digital beamforming network implemented in the at least one transceiver module. In that case, the M antenna ports <NUM> may be connected directly to the P RF ports <NUM>, such that each antenna port is connected to exactly one RF port, i.e. M=P.

In the below description of embodiments, it is exemplarily assumed that the multi-antenna transceiver comprises a hybrid beamforming network. However, the present invention is not limited to such embodiments. Rather, the below description is also applicable to analog and/or digital beamforming networks.

In embodiments, the relative amplitude and phase values across the antenna elements of the array <NUM> define the beams of the antenna array <NUM>. These relative phase and amplitude values are generated by the beamforming network (e.g., analog beamforming network <NUM> and/or digital beamforming network implemented in the at least one RF module <NUM>) that may comprise, for example, a plurality of phase shifters, controllable attenuators\PAs in Tx (PA = power amplifier) \LNAs in Rx (LNA = low noise amplifier), delay lines, etc., that are connected to the antenna elements of the array <NUM>. The beamforming network <NUM> can comprise M array ports (or antenna ports) <NUM> and P RF ports <NUM> that are connected to the M antenna elements <NUM> and the P transmit/receive (RF) modules <NUM> of the DUT <NUM>, respectively (see <FIG>).

In embodiments, a switch block can be included in the beamforming network <NUM> for calibration purposes, as shown by way of example in <FIG>. In detail, <FIG> shows a schematic block diagram of a beamforming network <NUM> comprising a separate switch block <NUM> configured to selectively activate or deactivate each antenna port of the M antenna ports <NUM> of the beamforming network, wherein <FIG> shows a schematic block diagram of a beamforming network <NUM> having integrated switches configured to selectively activate or deactivate each antenna port of the M antenna ports <NUM> of the beamforming network. In other words, <FIG> show examples of beamforming networks including a switch block for calibration purpose with a control signal. The switches in the switch block <NUM> can be controllable by a control signal and can disconnect selectively the antenna ports <NUM> from the BFN <NUM> (see <FIG>). Alternatively, the switch block can be directly a part of the beamforming network <NUM> (see <FIG>). The switches can be responsible to connect selectively a single array port m to a single RF port p during the calibration process.

Alternatively, instead of a switch block, LNAs (in receive mode of the DUT <NUM>) or PAs (in transmit mode of the DUT <NUM>) at the selected antenna elements can directly be switched off to increase the isolation between different antenna elements (switched off could mean, for example, a <NUM> dB higher isolation but depends upon the LNAs or PAs). In such a case, each LNA or PA at an antenna element or a plurality of LNAs or PAs (e.g. included in the beamforming network <NUM>) can jointly be gated by a control signal to "on" (i.e., activated) or to "off" (i.e., non-activated or deactivated). In the case that an LNA/PA is gated to "on" the signal from the related antenna/BFN array port can be amplified and passed to the BFN array port\antenna.

The above three configurations allow to remove or at least to reduce undesired coupling of array ports <NUM> or antenna elements during the calibration process.

<FIG> shows a schematic block diagram of a calibration/testing setup for calibrating/testing components of the multi-antenna transceiver of the device under test <NUM>. As shown in <FIG>, the device under test <NUM> can be placed or positioned in an echoic chamber <NUM>, wherein a device tester (or control site) <NUM> can be used for performing the calibration/testing of the components of the device under test <NUM>.

As already mentioned with respect to <FIG>, the multi-antenna transceiver of the device under test <NUM> can comprise an antenna array <NUM>, an analog beamforming network <NUM> and at least one RF module (not shown in <FIG>). The analog beamforming network <NUM> comprises M array ports (or antenna ports) <NUM> and P RF ports <NUM>. The antenna array <NUM>, or more precisely, the M antennas of the antenna array <NUM> can be connected to the M array ports <NUM> of the beamforming network <NUM>. The switch matrix <NUM>, which can also be implemented directly in the beamforming network (see Fig. 6b) or be realized by controlling, for example, the LNAs or PAs accordingly, is also indicated in <FIG>.

The control side <NUM> can comprise N antennas <NUM> connected to N antenna ports <NUM> of a precoder <NUM> of the control side <NUM>.

Subsequently, methods for calibrating/testing components (e.g., antennas, antenna ports, RF ports, beamforming networks, Tx modules (Tx = transmitter) or Rx modules (Rx = receiver)) of the multi-antenna transceiver (or transmitter or receiver) of the device under test <NUM> are described making reference to the calibrating/testing setup shown in <FIG>.

<FIG> shows a flowchart of a method <NUM> for wirelessly calibrating a beamforming network of a multi-antenna receiver of a device under test <NUM>, according to an embodiment. For example, the method <NUM> may be used for calibrating/testing components (i.e., the beamforming network <NUM>) of the multi-antenna receiver downstream (in receive direction) antenna ports <NUM> of the multi-antenna receiver.

The method <NUM> comprises the step of wirelessly transmitting a first signaling information between the device under test <NUM> and a device tester <NUM>, the first signaling information indicating a calibration request, wherein the first signaling information is transmitted by the device under test <NUM> or the device tester <NUM>.

For example, the calibration request can be initiated by the device under test <NUM> itself. In this case, the device under test <NUM> may transmit the first signaling information with the calibration request to the device tester <NUM>. Alternatively, the calibration request can be initiated by the device tester <NUM>. In this case, the device tester <NUM> may transmit the first signaling information with the calibration request to the device under test <NUM> which receives the first signaling information. The device under test <NUM> may switch into a calibration mode (different from a normal operation mode) upon transmitting or receiving the first signaling information.

For example, the first signaling information can be a BFN_CALIBRATION_REQUEST message.

Further, the method <NUM> comprises a step <NUM> of estimating, in response to the first signaling information, channel transfer function matrices between active antenna ports <NUM> of the multi-antenna receiver of the device under test <NUM> and antenna ports <NUM> of the device tester <NUM> using reference signals wirelessly transmitted from the device tester <NUM> to the device under test <NUM>, and transmitting the estimated channel transfer function matrices or an information derived therefrom from the device under test <NUM> to the device tester <NUM>.

For example, the estimated channel transfer function matrices or the information derived therefrom can be transmitted to the device tester <NUM> using a BFN_CALIBRATION_RESPONSE message.

In embodiments, the step <NUM> can comprise connecting each active antenna port <NUM> of the beamforming network <NUM> to exactly one RF port <NUM> of beamforming network for estimating the channel transfer function matrices.

In embodiments, the step <NUM> can comprise activating a first group of antenna ports of the beamforming network <NUM> of the device under test <NUM>, to obtain the active antenna ports, while deactivating the other antenna ports of the beamforming network <NUM>. Thus, channel transfer function matrices describing the channels between the first group of active antenna ports and the antenna ports <NUM> of the device tester <NUM> are obtained.

Optionally, the step <NUM> can comprise activating a second group of antenna ports <NUM> of the beamforming network <NUM> of the device under test <NUM>, while deactivating the other antenna ports of the beamforming network <NUM>, and estimating channel transfer function matrices between the second group of antenna ports of the device under test and antenna ports of the device tester using reference signals wirelessly transmitted from the device tester <NUM> to the device under test <NUM>, to obtain channel transfer function matrices describing channels between the second group of active antenna ports and the antenna ports <NUM> of the device tester <NUM>. These channel transfer function matrices can also be transmitted (e.g., together with the previously estimated channel transfer function matrices) to the device tester <NUM>.

Further, the method <NUM> comprises the step <NUM> of wirelessly transmitting a second signaling information between the device under test <NUM> and the device tester <NUM>, the second signaling information indicating a precoded transmission request, wherein the second signaling information is transmitted by the device under test <NUM> or the device tester <NUM>.

For example, the second signaling information can be a OTA_PRECODING_REQUEST message.

Further, the second signaling information may also indicate the active antenna ports of the multi-antenna receiver of the device under test, such as the first group of active antenna ports and the second group of active antenna ports.

Further, the method <NUM> comprises a step <NUM> of wirelessly transmitting, in response to the second signaling information, precoded reference signals from the device tester <NUM> to the device under test <NUM> using precoder matrices selected or determined based on the estimated channel transfer function matrices or the information derived therefrom, to obtain interference free channels (or orthogonal channels) between the device tester <NUM> and the device under test <NUM> allowing the reference signals to be received independently at each of the active antenna ports <NUM> of the multi-antenna receiver of the device under test <NUM>.

For example, after selecting or determining the precoder matrices and prior to transmitting the reference signals to the device under test <NUM>, the device tester <NUM> may transmit a OTA_PRECODING_RESPONSE message indicating the following transmission of reference signals.

In embodiments, the step <NUM> can comprise activating the first group of antenna ports of the beamforming network <NUM> of the device under test <NUM>, to obtain the active antenna ports, while deactivating the other antenna ports of the beamforming network <NUM>. Thereby, precoded reference signals can be transmitted from the device tester <NUM> to the device under test <NUM> using precoder matrices corresponding to the first group of active antenna ports <NUM>, such that interference free channels (or orthogonal channels) are obtained allowing the reference signals to be received independently at each port of the first group of active antenna ports <NUM>.

Optionally, the step <NUM> can comprise activating the second group of antenna ports of the beamforming network <NUM> of the device under test <NUM>, while deactivating the other antenna ports of the beamforming network <NUM>. Thereby, precoded reference signals can be transmitted from the device tester <NUM> to the device under test <NUM> using precoder matrices corresponding to the second group of active antenna ports <NUM>, such that interference free channels (or orthogonal channels) are obtained allowing the reference signals to be received independently at each port of the second group of active antenna ports <NUM>.

In embodiments, the step <NUM> can comprise characterizing the frequency response of the beamforming network using the received reference signals and using specific beamforming network operating parameters (e.g., specific values for phase-shifters and/or attenuators). For example, amplitude and/or phase measurements can be performed on the RF ports over the specified channel bandwidth, to characterize the frequency response of the beamforming network. After characterizing the frequency response of the beamforming network, the device under test <NUM> may optionally transmit a third signaling information (e.g., a BFN_CALIBRATION_RESPONSE message) to the device tester <NUM>.

Subsequently, the different steps of the DUT BFN receive mode calibration are described in further detail.

In embodiments, the control site (CS) <NUM> may trigger the DUT <NUM> to calibrate its BFN <NUM> by sending the BFN_CALIBRATION_REQUEST (first signaling information) message to the DUT <NUM>. When the DUT <NUM> is in the E-UTRA connected state and receives such a command, it enters the calibration mode and moves to step <NUM>. Note that the DUT <NUM> may also initiate the BFN <NUM> calibration by itself (without the indication from the CS (BFN_CALIBRATION_REQUEST message)).

In embodiments, in step <NUM>, the DUT <NUM> may select L (L≤P) active array ports <NUM> and switch off the remaining array ports <NUM> of its BFN <NUM>. The DUT <NUM> may set specific phases (e.g., <NUM>°) and gains (e.g., <NUM> dB) to the phase-shifters and attenuators\LNAs of the BFN <NUM>, respectively. It is assumed that each activated array port m is connected exactly to one RF port p. Hereby, it may be possible to activate a maximum of P antenna ports at the same time. In this case, we have that L=P. Note that this depends on the possible implementation of the switching block and BFN <NUM> realization at the DUT <NUM>. The algorithm for selecting the L active array ports <NUM> and the specific settings for the phase shifters and attenuators are left up to the DUT <NUM> implementation (e.g. maximum gain, no attenuation, phase <NUM>°).

For the selected m-th active DUT <NUM> array port <NUM>, the DUT <NUM> may estimate the channel transfer matrix <MAT> (for the selected frequency-bins q = <NUM>,. Q) between the O CS antenna ports (<NUM> ≥ L) and the active m-th DUT array port using reference signals (such as the CSI-RS (BS-UE link) or SRS (UE-BS link)) sent by the CS <NUM> over the N OTA illumination antennas <NUM>.

If the maximum number of different reference signals or CS ports <NUM> is smaller than N a sequential switching regime may be applied for the measurement of the N channels in Ĥm(q). The channel transfer matrix Ĥm(q) is composed of the anechoic\non-anechoic environment's <NUM> propagation characteristic <MAT> including the DUT antenna <NUM>, OTA antenna <NUM> responses and the frequency-dependent DUT's <NUM> BFN <NUM> characteristic <MAT>, <MAT>.

The above procedure (Step <NUM>) can be repeated for all groups of DUT array ports <NUM> that need to be calibrated. After the channel measurements/estimation, the DUT <NUM> may have full knowledge of all channels between the O CS antenna ports <NUM> and the M DUT array ports <NUM>. The channel transfer matrices between the O CS antenna ports <NUM> and M DUT array ports <NUM> are given by <MAT> where Fcal(q),q = <NUM>,. ,Q are diagonal matrices containing the DUT's BFN <NUM> coefficients for the chosen setting with fm(q), m=<NUM>,.

When the above procedure is finished, the DUT <NUM> may generates a report (BFN_CALIBRATION_RESPONSE message) containing information about the measured MIMO channel matrices in (<NUM>), and sends them via an uplink session to the CS <NUM>.

In embodiments, in step <NUM>, the DUT <NUM> may requests a signal-precoded transmission (OTA_PRECODING_REQUEST message (second signaling information)) by the CS <NUM> such that the DUT may perform calibration of its BFN <NUM>. As the number of DUT <NUM> array ports <NUM> may be larger than the number of CS antenna ports <NUM>, the DUT <NUM> may inform the CS <NUM> about the actual DUT <NUM> array ports <NUM> (OTA_PRECODING_REQUEST message) to be involved in the current DUT BFN calibration step. Note that the number of these DUT array ports <NUM> may have to be smaller or equal than the number of CS antenna ports <NUM>. When the CS <NUM> receives such a request, it may calculate a set of precoder matrices P(q), q = <NUM>,. , Q based on the channel transfer matrices Ĥ(q), q = <NUM>,. , Q for the involved DUT array ports <NUM>. There exist a variety of approaches for signal precoding. As an example, the precoder matrices can be calculated by the Moore-Penrose pseudo-inverse of the channel transfer matrices [<NUM>,<NUM>], <MAT> where c(q) is a scalar to meet a specific power constraint.

The precoder matrices can be applied at the CS <NUM> to the reference sequences sent over O CS antenna ports <NUM>/ N OTA antennas <NUM>. The aim of the signal precoding at the CS <NUM> is to create an interference-free downlink channel allowing the reference signals sent by the CS <NUM> to be received independently at each DUT array port <NUM>. After applying the precoder matrices to the reference signals, the CS <NUM> may inform the DUT <NUM> by sending an OTA_PRECODING_RESPONSE message indicating that the DUT <NUM> may start the calibration of its BFN <NUM>.

In embodiments, in step <NUM>, the calibration of the BFN <NUM> for the selected DUT <NUM> array ports <NUM> occurs in the second stage. The DUT <NUM> may select the involved array ports <NUM> in the calibration, switches off remaining array ports and sets specific values to the phase-shifters and attenuators of its BFN <NUM> with respect to a specific calibration procedure. Note that the involved DUT array ports <NUM> are advantageously identical to the selected DUT array ports <NUM> from Step <NUM>.

For each setting, the DUT <NUM> may perform amplitude and phase measurements on the RF ports <NUM> over the specified channel bandwidth to characterize the frequency response of the BFN <NUM>. Note that the detailed steps of the calibration procedure (settings of specific phase and gain values) are left up on the DUT <NUM> implementation. The measurement period that is used to determine the frequency response of the BFN <NUM> depends also on the DUT <NUM> implementation.

When DUT <NUM> has finished the measurements, it may send a BFN_CALIBRATION_RESPONSE message to the CS <NUM> containing information about the current calibration step. Moreover, it may send a request to the CS <NUM> to change the precoder matrices such that calibration of remaining DUT array ports <NUM> can be performed. (see Step <NUM>).

In embodiments, the CS <NUM> may inform the DUT on the selected active array ports and the settings for the phase shifters and attenuators during Step <NUM>.

In embodiments, the CS <NUM> may send a request to the DUT <NUM> to re-estimate the channel transfer matrices for selected antenna ports with a different setting for the phase shifters and attenuators of the DUT BFN <NUM> in Step <NUM>. In this way saturation effects of the LNAs may be reduced and an improved isolation between the different transmission streams may be achieved when applying the channel inverse in (<NUM>).

In embodiments, the selection of the optimal DUT <NUM> orientation can be included in the above procedure as well. The CS <NUM> can request to change the DUT <NUM> orientation (if possible and sends a control command to the DUT positioner) to improve the isolation between transmit streams and to avoid nulls in the antenna patterns.

In embodiments, the CS <NUM> may request the DUT <NUM> to selectively switch off antenna ports <NUM> and to set specific gain and phase values to the attenuators and phase-shifters of the BFN <NUM>, respectively, during Step <NUM>.

<FIG> shows a flowchart of a method <NUM> for a DUT BFN receive mode calibration. In a first step <NUM>, the first signaling information (e.g., BFN_CALIBRATION_REQUEST message) can be transmitted from the DUT <NUM> to the CS <NUM>, or from the CS <NUM> to the DUT <NUM>. In a second step <NUM>, N orthogonal sequences can be sent over N OTA illumination antennas <NUM> from the CS <NUM> to the DUT <NUM>. In a third step <NUM>, the DUT <NUM> may select L active antenna ports <NUM>, configure its BFN <NUM> and estimate the channel matrices. In a fourth step <NUM>, the DUT <NUM> may transmit the BFN_CALIBRATION_RESPONSE message with the estimated channels between O CS antenna ports <NUM> and M DUT array ports <NUM> to the CS <NUM>. In a fifth step <NUM>, the DUT <NUM> may transmit the second signaling information (e.g., OTA_PRECODING_REQUEST message) indicating the selected L DUT array ports <NUM> for calibration with L<=<NUM> to the CS <NUM>. In a sixth step <NUM>, the CS <NUM> may calculate precoder matrices and apply same to orthogonal sequences. In a seventh step <NUM>, the CS <NUM> may transmit the OTA_PRECODING_RESPONSE message and the precoded orthogonal sequences to the DUT <NUM>. In an eight step <NUM>, the DUT <NUM> may select the same active antenna ports as indicated in the second signaling information (e.g., OTA_PRECODING_REQUEST message) and switch off the remaining antenna ports and calibrate its BFN <NUM>. In a ninth step <NUM>, the BFN <NUM> may calculate the frequency response of its BFN <NUM>. In a tenth step <NUM>, the DUT <NUM> may transmit the BFN_CALIBRATION_RESPONSE message to the CS <NUM>. In an eleventh step <NUM>, the DUT <NUM> may determine whether its BFN <NUM> is calibrated for all M array ports <NUM>. If the BFN <NUM> is calibrated for all M array ports <NUM>, then calibration/testing is finished, else steps five to eleven are repeated.

<FIG> shows a flowchart of a method <NUM> for wirelessly calibrating/testing a beamforming network of a multi-antenna transmitter of a device under test <NUM>, according to an embodiment. For example, the method <NUM> may be used for calibrating/testing components (i.e., the beamforming network <NUM>) of the multi-antenna transmitter upstream (in transmit direction) antenna ports <NUM> of the multi-antenna transmitter.

The method <NUM> comprises a step <NUM> of wirelessly transmitting a first signaling information between the device under test <NUM> and a device tester <NUM>, the first signaling information indicating a calibration request, wherein the first signaling information is transmitted by the device under test <NUM> or the device tester <NUM>.

In embodiments, the step <NUM> can comprise wirelessly transmitting a second signaling information (e.g., BFN_CALIBRATION_RESPONSE message) between the device under test <NUM> and a device tester <NUM>, wherein the BFN_CALIBRATION_RESPONSE message transmitted by the device under test <NUM> or the device tester <NUM>. The BFN_CALIBRATION_RESPONSE message can indicate parameters to be used in the following steps, such as a required measurement accuracy, a configuration of the beamforming network, a number of antenna ports of the device under test <NUM> and/or a number of antenna ports <NUM> of the device tester.

Further, the method <NUM> comprises a step <NUM> of estimating, in response to the first signaling information, channel transfer function matrices between active antenna ports <NUM> of the multi-antenna transmitter of the device under test and antenna ports <NUM> of the device tester using reference signals wirelessly transmitted from the device under test <NUM> to the device tester <NUM>.

For example, the reference signals can be transmitted together with a BFN_CALIBRATION_START message indicating a start of the calibration from the device under test <NUM> to the device tester <NUM>.

Optionally, the step <NUM> can comprise activating a second group of antenna ports <NUM> of the beamforming network <NUM> of the device under test <NUM>, while deactivating the other antenna ports of the beamforming network <NUM>, and estimating channel transfer function matrices between the second group of antenna ports of the device under test <NUM> and antenna ports <NUM> of the device tester using reference signals wirelessly transmitted from the device under test <NUM> to the device tester <NUM>, to obtain channel transfer function matrices describing channels between the second group of active antenna ports <NUM> and the antenna ports <NUM> of the device tester <NUM>.

In embodiments, the step <NUM> can comprise wirelessly transmitting a third signaling information from the device tester <NUM> to the device under test <NUM>, the third signaling information indicating that the estimation of the channel transfer function matrices is finished.

For example, the third signaling information can be a BFN_CALIBRATION_FINISHED message.

Further, the method <NUM> comprises the step <NUM> of selecting or estimating equalizer matrices using the estimated channel transfer function matrices or the information derived therefrom.

In embodiments, the step <NUM> can comprise wirelessly transmitting a fourth signaling information from the device under test <NUM> to the device tester <NUM>, the fourth signaling information indicating a calibration data request, wherein the equalizer matrices or the information derived therefrom is transmitted from the device tester <NUM> to the device under test <NUM> in response to the fourth signaling information.

For example, the fourth signaling information can be a BFN_CALIBRATION_DATA_REQUEST message. Further, the equalizer matrices or the information derived therefrom can be transmitted from the device tester <NUM> to the device under test <NUM> using a BFN_CALIBRATION_DATA_RESPONSE message.

Subsequently, the different steps of the DUT BFN transmit mode calibration are described in further detail.

In embodiments, the CS <NUM> may send a BFN <NUM> calibration request message (BFN_CALIBRATION_REQUEST message (first signaling information)) to the DUT <NUM>. The message may contain information about the CS antenna port <NUM> configuration. Alternatively, the BFN calibration may be triggered directly by the DUT <NUM> by sending the BFN_CALIBRATION_REQUEST message to the CS <NUM>. Either the DUT <NUM> or the CS <NUM> initiate the DUT calibration, the following calibration information may be signaled (using the BFN_CALIBRATION_REQUEST message and/or a BFN_CALIBRATION_RESPONSE message) between the CS <NUM> and DUT <NUM>. For example, the calibration information may include a required measurement accuracy that has to be fulfilled per measurement by the CS <NUM>. Further, the calibration information may include a BFN configuration (number of links between P and M, number of possible settings per link e.g. number of attenuator steps, phase shifter steps, PA gain steps). Further, the calibration information may include a number of antenna ports <NUM>,<NUM> at DUT <NUM> and CS <NUM>. Further, the calibration information may include a channel bandwidth (note that it is typically the intention to measure the BFN frequency response using fully allocated channels (measurement of CSI-RS or SRS across the entire channel bandwidth)).

In embodiments, the DUT <NUM>/CS <NUM> may receive the BFN_CALIBRATION_RESPONSE message, wherein th DUT <NUM> and CS <NUM> can perform the following steps.

In embodiments, e.g., in a first step, the DUT <NUM> may select for each measurement u (u=<NUM>,. ,U) a number L of active array ports <NUM> and switches off the remaining array ports <NUM>. Each activated array port is now connected exactly to one RF port <NUM>. The DUT <NUM> may configure the BFN <NUM> with specific phase and gain values. The selection of array ports and BFN settings (phase and gain values) is left up to the DUT <NUM> implementation.

In embodiments, e.g., in a second step, after the configuration of the BFN <NUM>, the DUT <NUM> may send reference sequences on the activated DUT array ports <NUM> and send a BFN_CALIBRATION_START message (containing the labeling of activated DUT array ports for the specific measurement) to the CS <NUM>.

In embodiments, e.g., in a third step, the CS <NUM> may perform measurements on the received sequences sent from the DUT <NUM> and estimate the wideband channel matrix between the L activated DUT array ports <NUM> and the O CS antenna ports <NUM>/N OTA antennas <NUM>. The channel transfer matrix <MAT>, q = <NUM>,. Q of the m-th active DUT array port is composed of the anechoic or non-anechoic chamber's propagation characteristic <MAT> and the frequency-dependent DUT's and OTA antenna responses and BFN <NUM> characteristic for the chosen setting <MAT> at the q-th frequency-bin, <MAT>.

In embodiments, e.g., in a fourth step, after the channel estimation phase, the CS <NUM> may send a BFN_CALIBRATION_FINISHED message to the DUT <NUM> signaling that the measurement for the selected setup of DUT <NUM> antenna ports <NUM> and BFN <NUM> setting is finished.

In embodiments, e.g., in a fifth step, when the DUT receives the BFN_CALIBRATION_FINISHED message, it optionally selects another set of active DUT array ports and BFN settings.

In embodiments, e.g., in a sixth step, steps <NUM> to <NUM> can be repeated for all DUT array ports <NUM> and BFN <NUM> settings.

In embodiments, e.g., in a seventh step, after all measurements have been completed, the DUT <NUM> may send a BFN_CALIBRATION_DATA_REQUEST message to the CS <NUM>, indicating that the CS <NUM> shall provide the collected calibration date to the DUT <NUM>.

In embodiments, e.g., in an eight step, when the BFN_CALIBRATION_DATA_REQUEST message, it calculates a set of equalizer matrices W(q), q = <NUM>,. , Q and applies them to the estimated channels. The equalizer matrices W(q), q = <NUM>,. , Q are based on the estimated channel matrices <MAT>; between the O CS antenna ports <NUM> and K DUT array ports <NUM> (K<=O) for a specific BFN <NUM> configuration s (s=<NUM>,. ,S) of RF paths, phase and gain values. Here, <MAT> is a diagonal matrix containing the frequency response of the BFN <NUM> for the specific BFN configuration s. The equalizer matrices can be calculated based on MMSE, ZF or another objective function. Note that, the equalizer needs to be calculated for a specific BFN configuration ś,ś ∈ (<NUM>,. , S) of RF paths, phase and gain values. This configuration can be selected by the CS <NUM> itself, or optionally may be signaled by the DUT <NUM> to the CS <NUM>. The BFN calibration matrix containing the frequency response of the BFN <NUM> for the s-th setup is then given by <MAT>.

In embodiments, e.g., in a ninth step, the diagonal matrices <MAT> can be calculated for all setups and DUT antenna ports <NUM> involved in the calibration and send in a report (BFN_CALIBRATION_DATA_RESPONSE message) to the DUT <NUM>.

<FIG> shows a flowchart of a method <NUM> for for a DUT BFN transmit mode calibration. In a first step <NUM>, the first signaling information (e.g., BFN_CALIBRATION_REQUEST message) can be transmitted from the DUT <NUM> to the CS <NUM>, or from the CS <NUM> to the DUT <NUM>. Further, in the first step <NUM>, the second signaling information (e.g., BFN_CALIBRATION_RESPONSE message) can be transmitted from the DUT <NUM> to the CS <NUM>, or from the CS <NUM> to the DUT <NUM>. In a second step <NUM>, the DUT <NUM> can select active antenna ports <NUM>, switch off remaining antenna ports and configure its BFN <NUM>. In a third step <NUM>, the DUT can transmit a BFN_CALIBRATION_START message to the CS <NUM> and transmit the reference sequences (e.g., CSI-RS, SRS). In a fourth step <NUM>, the CS <NUM> can estimate channel matrices between active DUT antenna ports <NUM> and O CS antenna ports <NUM> (measurement #<NUM>). In a fifth step <NUM>, the CS <NUM> can transmit the third signaling information (BFN_CALIBRATION_FINISHED message) to the DUT <NUM>. In an optional sixth step <NUM>, the DUT <NUM> can select different active antenna ports <NUM>, switch off remaining antenna ports and configure its BFN <NUM>. In an optional seventh step <NUM>, the DUT <NUM> can transmit a BFN_CALIBRATION_START message to the CS <NUM> and transmit the reference sequences (e.g., CSI-RS, SRS). In an optional eight step <NUM>, the CS <NUM> can estimate channel matrices between the active DUT antenna ports <NUM> and O CS antenna ports <NUM> (measurement #U). In an optional ninth step <NUM>, the CS <NUM> can transmit the third signaling information (BFN_CALIBRATION_FINISHED message) to the DUT <NUM>. In a tenth step <NUM>, the DUT <NUM> can transmit the fourth signaling information (BFN_CALIBRATION_DATA_REQUEST message) to the CS <NUM>. In an eleventh step <NUM>, the CS <NUM> can calculate the frequency response of the DUT BFN <NUM>. In a twelfth step <NUM>, the CS <NUM> can transmit the fifth signaling information (BFN_CALIBRATION_DATA_RESPONSE message) with the DUT BFN response to the DUT <NUM>.

<FIG> shows a flowchart of a method <NUM> for wirelessly calibrating/testing a receive module of a multi-antenna receiver of a device under test <NUM>, according to an embodiment. For example, the method <NUM> may be used for calibrating/testing components (i.e., the receive module <NUM>) of the multi-antenna receiver downstream (in receive direction) RF ports <NUM> of the multi-antenna receiver.

The method <NUM> comprises a step <NUM> of wirelessly transmitting a first signaling information between the device under test and a device tester, the first signaling information indicating a calibration request, wherein the first signaling information is transmitted by the device under test or the device tester.

For example, the first signaling information can be a DUT_RX_CHANNEL_MEASURMENT_REQUEST message.

Further, the method <NUM> comprises a step <NUM> of estimating, in response to the first signaling information, channel transfer function matrices between RF ports <NUM> of the multi-antenna receiver of the device under test <NUM> and antenna ports <NUM> of the device tester <NUM> using reference signals wirelessly transmitted from the device tester <NUM> to the device under test <NUM>, and transmitting the estimated channel transfer function matrices or an information derived therefrom from the device under test <NUM> to the device tester <NUM>.

For example, the estimated channel transfer function matrices or the information derived therefrom can be transmitted to the device tester <NUM> using a DUT_RX_CHANNEL_MEASURMENT_RESPONSE message.

In embodiments, the step <NUM> can comprise activating a group of antenna ports of the beamforming network <NUM> of the device under test <NUM>, to obtain the active antenna ports, while deactivating the other antenna ports of the beamforming network <NUM>. Further, the step <NUM> can comprise connecting the active antenna ports <NUM> to the RF ports <NUM>.

In embodiments, the step <NUM> can further comprise setting specific beamforming network operating parameters, such as values for the phase shifters and attenuators of the beamforming network.

Further, the method <NUM> comprises a step <NUM> of wirelessly transmitting a second signaling information between the device under test <NUM> and the device tester <NUM>, the second signaling information indicating a precoded transmission request, wherein the second signaling information is transmitted by the device under test <NUM> or the device tester <NUM>.

For example, the second signaling information can be RECEIVER_SENSITIVITY_MEASUREMENT message.

Further, the method <NUM> comprises a step <NUM> of wirelessly transmitting, in response to the second signaling information, reference signals from the device tester to the device under test using precoder matrices selected or determined based on the estimated channel transfer function matrices or the information derived therefrom, to obtain interference free channels between the device tester and the device under test allowing the reference signals to be received independently at each of the RF ports of the multi-antenna receiver of the device under test.

In embodiments, the step <NUM> can comprise measuring metrics specifying the performance of the device under test <NUM>.

Subsequently, the different steps of the DUT Rx module calibration/testing are described in further detail.

In embodiments, e.g., in a first step, the DUT <NUM>/CS <NUM> may send a receiver testing request (DUT_RX_CHANNEL_MEASUREMENT_REQUEST message) to the CS <NUM>/DUT <NUM>.

In embodiments, e.g., in a second step, the DUT <NUM> can configure its BFN <NUM>, select a number of active DUT array ports <NUM> and set values for the phase shifters and attenuators of its BFN <NUM> (it is not required that each array port (m) is now connected to a single RF port (p)).

In embodiments, e.g., in a third step, the DUT <NUM> can perform measurements on the received reference sequences (e.g. CSI_RS or SRS sequences) sent by the CS <NUM> to estimate the channel matrices D(q) between the O CS antenna ports <NUM> and the P RF ports <NUM> of the DUT <NUM>. The estimated channel matrices are given by D̂(q) = B(q)H(q), q = <NUM>,. , Q, where <MAT> is the frequency response of the BFN <NUM> at the q-th frequency bin with P being the number of activated RF ports (P≤M) <NUM>.

In embodiments, e.g., in a fourth step, the DUT <NUM> can generate a report (DUT_RX_CHANNEL_MEASUREMENT_RESPONSE message) containing information about the measured multi-antenna channel matrices in D̂(q), q = <NUM>,. , Q and sends them via an uplink session to the CS.

In embodiments, e.g., in a fifth step, the CS <NUM> can calculate a set of precoder matrices P(q), q = <NUM>,. , Q based on the received channel transfer matrices D̂(q), q = <NUM>,. , Q from the DUT <NUM>. The precoder matrices can be applied to the transmitted signals at the CS <NUM> with the aim to create an equivalent ideally interference-free rank-P downlink channel allowing the (precoded) transmitted signals from the CS <NUM> to be received independently at each DUT RF port <NUM>.

In embodiments, e.g., in a sixth step, after performing the signal precoding at the CS <NUM>, the CS <NUM>/DUT <NUM> may request the measurement of certain performance metrics by the DUT <NUM>. The DUT <NUM> has to set the BFN <NUM> as in the second step and the remaining components of the DUT <NUM> can be running as in standard operation mode. Several metrics specifying the performance of the DUT <NUM> can be measured, such as throughput, CQI, BLER, etc. Furthermore, the CS <NUM> can change the transmit power, modulation scheme or any other parameter to measure the impact on the performance of the DUT <NUM>. For example, the DUT <NUM> measures the P RSSIs (received signal strength indicators) and send them back to the CS <NUM>. The CS <NUM> may reduce step-wise the transmit power after receiving P measured RSSIs from the DUT <NUM> corresponding to a certain transmit power (RECEIVER_SENSITIVITY_MEASUREMENT).

<FIG> shows a flowchart of a method <NUM> for wirelessly calibrating/testing a transmit module of a multi-antenna transmitter of a device under test <NUM>, according to an embodiment. For example, the method <NUM> may be used for calibrating/testing components (i.e., the transmit module <NUM>) of the multi-antenna transmitter upstream (in transmit direction) RF ports <NUM> of the multi-antenna receiver.

For example, the first signaling information can be a DUT_TX_CHANNEL_MEASUREMENT_REQUEST message.

Further, the method <NUM> comprises a step <NUM> of estimating, in response to the first signaling information, channel transfer function matrices between RF ports <NUM> of the multi-antenna transmitter of the device under test <NUM> and antenna ports <NUM> of the device tester <NUM> using reference signals wirelessly transmitted from the device under test <NUM> to the device tester <NUM>.

For example, the estimated channel transfer function matrices or the information derived therefrom can be transmitted to the device tester <NUM> using a second signaling information (DUT_RX_CHANNEL_MEASURMENT_RESPONSE message).

Further, the method <NUM> comprises a step <NUM> of selecting or estimating equalizer matrices using the estimated channel transfer function matrices or the information derived therefrom.

In embodiments, the method <NUM> can further comprise measuring metrics specifying the transmit performance of the device under test (e.g., throughput, CQI, BLER) using the selected or estimated equalizer matrices.

Subsequently, the different steps of the DUT Tx module calibration/testing are described in further detail.

In embodiments, e.g., in a first step, the DUT <NUM>/CS <NUM> may send a transmitter testing request (DUT_TX_CHANNEL_MEASUREMENT_REQUEST message) to the CS/DUT.

In embodiments, e.g., in a second step, the DUT <NUM> can configure its BFN <NUM> and select the active DUT array ports (it is not required that an array port (m) is exactly connected to only one RF port (p)).

In embodiments, e.g., in a third step, the DUT <NUM> can send reference sequences on its P RF ports <NUM>.

In embodiments, e.g., in fourth step, the CS <NUM> can performs measurements on the received sequences sent from the DUT <NUM> and estimates the wideband channel matrix U(q) between the P RF ports <NUM> and the O CS antenna ports <NUM>/N OTA antenna ports. The estimated channel matrices are given by Û(q) = B(q)H(q), q = <NUM>,. , Q, where <MAT> is the frequency response of the BFN <NUM> at the q-th frequency bin with P being the number of activated RF ports (P≤M) <NUM>.

In embodiments, e.g., in a fifth step, after the channel estimation phase, the CS <NUM> can send a DUT_RX_CHANNEL_MEASUREMENT_RESPONSE message to the DUT <NUM> signaling that the measurements are finished.

In embodiments, e.g., in a sixth step, the CS <NUM> can calculate a set of equalizer matrices W(q), q = <NUM>,. , Q based on the estimated channels Û(q) and applies them to the received signals.

In embodiments, e.g., in a seventh step, the DUT <NUM>/CS <NUM> may then request the measurement of certain performance metrics by the CS <NUM>. The DUT <NUM> has to set the BFN <NUM> as in step <NUM> and the remaining components of the DUT <NUM> can run as in standard operation mode. Several metrics specifying the performance of the DUT <NUM> can be measured at the CS <NUM>, such as throughput, CQI, BLER, etc. Furthermore, the CS <NUM> may request to change the Tx power of the DUT <NUM>, modulation scheme or any other parameter to measure the impact on the performance of the DUT <NUM>.

<FIG> shows a flowchart of a method <NUM> for wirelessly calibrating/testing antennas <NUM> of a multi-antenna transceiver of a device under test <NUM>, according to an embodiment. For example, the method <NUM> may be used for calibrating/testing components (i.e., the antennas) of the multi-antenna transceiver downstream (in transmit direction) or upstream (in receive direction) the antenna ports of the multi-antenna receiver.

Further, the method <NUM> comprises a step of wirelessly transmitting reference signals between the device under test <NUM> and the device tester <NUM> using one (e.g., exactly one) active antenna port <NUM> of the multi-antenna transceiver or using one RF port <NUM> of the multi-antenna transceiver and a fixed beamforming network, wherein the reference signals are transmitted by the device under test <NUM> or the device tester <NUM>.

Further, the method <NUM> comprises a step <NUM> of measuring at least one out of amplitude and phase of a antenna pattern for a first relative orientation between antennas of the device tester and antennas of the device under test. For example, the step <NUM> can comprise measuring the amplitude and phase of the full polarimetric antenna pattern for a first orientation.

Further, the method <NUM> comprises a step <NUM> of changing the relative orientation between antennas <NUM> of the device under test <NUM> and antennas <NUM> of the device tester <NUM> to a second relative orientation.

Further, the method <NUM> comprises a step <NUM> of iteratively repeating the steps of wirelessly transmitting reference signals, measuring at least one out of amplitude and phase of the antenna pattern (e.g., the amplitude and phase of the full polarimetric antenna pattern) and changing the relative orientation until a predetermined termination criterion is reached.

In embodiments, the method <NUM> can further comprise wirelessly transmitting a second signaling information from the device under test <NUM> to the device tester <NUM>, the second signaling information indicating a number of antenna ports <NUM> or RF ports <NUM> to be measured.

In embodiments, the method <NUM> can further comprise wirelessly transmitting a third signaling information from the device tester <NUM> to the device under test <NUM>, the third signaling information indicating a measured antenna pattern.

Subsequently, the different steps of the DUT Rx/Tx antenna calibration in an anechoic chamber are described in further detail.

In embodiments, similar to the DUT BFN receive mode calibration and DUT BFN transmit mode calibration, the BFN is fixed to one active antenna port <NUM> or one active RF port <NUM> with a fixed BFN (e.g. Buttler matrix).

In embodiments, e.g., in a first step, an antenna port calibration request (resolution in angle or number of steps l) can be initiated by the DUT <NUM> or CS <NUM>.

In embodiments, e.g., in a second step, the DUT <NUM> can feed back a number of M or P ports to be measured.

In embodiments, e.g., in a third step, the CS <NUM>/DUT <NUM> can start sending wideband reference sequences (e.g. CSI-RS, SRS).

In embodiments, e.g., in fourth step, the DUT <NUM> can send back the measured response of i-th step.

In embodiments, e.g., in fifth step, the third and fourth steps can be repeated after a positioner is set from CS <NUM> to a new angle and polarization.

In embodiments, e.g., in a sixth step, the CS <NUM> can feedback the complete antenna pattern as pattern or EADF.

<FIG> shows a flowchart of a method <NUM> for wirelessly calibrating/testing the digital portion of a device under test <NUM>, according to an embodiment.

For example, the first signaling information can be a DUT_CALIBRATION_REQUEST message.

Further, the method <NUM> comprises a step <NUM> of estimating, in response to the first signaling information, channel transfer function matrices between active antenna ports\RF ports <NUM>\<NUM> of the multi-antenna transceiver of the device under test <NUM> and antenna ports <NUM> of the device tester using reference signals wirelessly transmitted from the device tester to the device under test.

In embodiments, the step <NUM> can comprise activating a group of antenna ports of the beamforming network <NUM> of the device under test <NUM> to obtain active antenna ports\RF ports, while deactivating the other antenna ports <NUM> of the beamforming network <NUM>.

In embodiments, the step <NUM> can comprise setting specific beamforming network operating parameters to the analog portion of the hybrid beamforming network. The specific beamforming network operating parameters can be, for example, values for the phase shifters and attenuators of the beamforming network.

In embodiments, the step <NUM> can comprise wirelessly transmitting the estimated channel transfer function matrices or an information derived therefrom form the device under test <NUM> to the device tester <NUM>. The estimated channel transfer function matrices or the information derived therefrom can be transmitted from the device under test <NUM> to the device tester <NUM> using a DUT_CALIBRATION_RESPONSE message.

Further, the method <NUM> comprises a step <NUM> of wirelessly transmitting a second signaling information between the device under test and the device tester, the second signaling information indicating a precoded transmission request, wherein the second signaling information is transmitted by the device under test or the device tester.

Further, the method <NUM> comprises a step <NUM> of wirelessly transmitting, in response to the second signaling information, reference signals from the device tester to the device under test using precoder matrices selected or determined based on the estimated channel transfer function matrices or the information derived therefrom, to obtain interference free channels between the device tester and the device under test allowing the reference signals to be received independently at each RF port of the multi-antenna receiver of the device under test.

In embodiments, the method can comprise setting the analog portion of the hybrid beamforming network to specific beamforming network operating parameters and maintaining the operating parameters of the analog beamforming network <NUM> fixed during calibrating/testing of the digital portion of a multi antenna transceiver.

Thereby, the method can comprise wirelessly transmitting a third signaling information from the device under test to the device tester, the third signaling information indicating the specific analog beamforming network operating parameters.

In embodiments, the method can comprise that the DUT freely can change beamforming network operating parameters of the digital portion of the hybrid beamforming network during calibrating/testing of the digital portion of a multiantenna transceiver.

Thereby, the method can comprise wirelessly transmitting a fourth signaling information from the device under test to the device tester, the fourth signaling information indicating the current and/or operational beamforming network operating parameters of the analog portion of the beamforming network <NUM>.

In embodiments, the method can comprise measuring performance metrics specifying the performance of the digital portion of a multi-antenna tranceiver or of the RF module. Thereby, the transmit parameters of signals wirelessly transmitted from the device tester to the device under test can be varied, in order to measure the performance metrics specifying the performance of the digital portion of a multiantenna receiver or of the RF module.

Subsequently, the different steps of the DUT BFN test (digital part) in non-anechoic chamber are described in further detail.

In embodiments, e.g., in a first step, the DUT <NUM>/CS <NUM> sends a receiver testing request (DUT_CALIBRATION_REQUEST message) to the CS <NUM>/DUT <NUM>. The request may also include a predefined setting for the DUT BFN.

In embodiments, e.g., in a second step, the DUT <NUM> can configure its BFN <NUM> and select a number of active DUT array ports <NUM> and sets values for the phase shifters and attenuators of its BFN <NUM> to a predefined set (which may be signaled from the CS <NUM>).

In embodiments, e.g., in a third step, the DUT <NUM> can perform measurements on the received reference signals (e.g. CSI_RS or SRS sequences) to estimate the channel matrices D(q) between the O CS antenna ports <NUM>/ N OTA antennas <NUM> and the P RF ports <NUM> of the DUT <NUM>.

In embodiments, e.g., in a fourth step, the DUT <NUM> can generate a report (DUT_CALIBRATION_RESPONSE message) containing information about the measured MIMO channel matrices in D̂(q), q = <NUM>,. , Q and sends them via an uplink session or other data exchange interface to the CS <NUM>.

In embodiments, e.g., in a fifth step, the CS <NUM> can calculate a set of precoder matrices P(q), q = <NUM>,. , Q based on the estimated channel transfer matrices D̂(q),q = <NUM>,. , Q from the DUT <NUM>. The precoder matrices can be applied to the transmitted signals at the CS <NUM> with the aim to create an equivalent ideally interference-free rank-P downlink\uplink channel allowing the (precoded) transmitted signals from the CS to be received independently at each RF port <NUM>. The CS <NUM>/DUT <NUM> send/initialize the measurement (DUT_PERFTEST_REQUEST) of certain performance metrics e.g. Throughput. The CS <NUM> can apply the precoder PT(q) = c(q)P(q)HT(q, t), q = <NUM>,. , Q to the transmitted\received signals, where HT denotes the time-variant full-polarimetric description of the multipath propagation channel [e.g. any channel model used in 3GPP] including the antenna patterns of O antennas at the CS side as well as the P resulting or predefined antenna/port patterns at the DUT side. In this operation mode, the DUT <NUM> may send back at time t also the decision on the chosen BFN <NUM> setting to the CS <NUM>, while keeping actually the analog part of the BFN <NUM> as in step <NUM>. In this way, the P resulting antenna patterns could be calculated or taken from a database at the CS side to embed them in the propagation channel (matrix HT). In this way HT can be adaptively changed based on the decision of the DUT <NUM> w. the BFN <NUM>. Over the testing time the CS <NUM> can now vary for example transmit parameters such as power, modulation, channel characteristics and so on. If the settings of the analog BFN of the DUT can not be fixed during the operational mode the feedback analog BFN settings from the DUT <NUM> may also be applied at the CS <NUM> to modify P(q).

In other words, the DUT BFN test (digital part) in the non-anechoic chamber allows testing the (entire) receiver in a real environment. The real environment can be generated using a realistic propagation channel (e.g. 3GPP Channel model, etc.). Thereby, the channel can consider the beams formed using the BFN <NUM>. This can be included calculatively using a feedback information from the DUT <NUM> indicating the settings it would (normally) apply to the BFN <NUM>. However, the DUT <NUM> must maintain the BFN <NUM> (analog portion of the hybrid beamforming network) fixed, in order to maintain the wireless cable connection to the P RF ports <NUM>. The digital beamforming actually takes place in the DUT <NUM> after (downstream) the RF ports <NUM>.

In other words, the DUT BFN test (digital part) in the non-anechoic chamber allows testing the DUT under operational conditions, e.g., w. throughput in a real channel. For that purpose, the BFN <NUM> (analog beamforming network) is set to fixed settings even if the DUT <NUM> (or a software running on the DUT and controlling the DUT) normally would perform changes on the settings of the BFN <NUM>, for example, due to a channel projection onto the P RF Ports. However, these changes\the settings of the analog BFN that would be applied can be feedback to the CS, which may include the resulting beams in the channel.

Although, above the DUT BFN test (digital part) in a non-anechoic chamber\static propagation environment was described for the receive case, the same applies for the transmit case, as will be briefly described in the following.

<FIG> shows a flowchart of a method <NUM> for wirelessly calibrating/testing a digital transmitter module of a multi-antenna transmitter of a device under test. The method <NUM> comprises a step <NUM> of wirelessly transmitting a first signaling information between the device under test and a device tester, the first signaling information indicating a calibration request, wherein the first signaling information is transmitted by the device under test or the device tester. The method <NUM> further comprises a step <NUM> of estimating, in response to the first signaling information, channel transfer function matrices between active antenna ports or RF ports of the multi-antenna transmitter of the device under test and antenna ports of the device tester using reference signals wirelessly transmitted from the device under test to the device tester. The method <NUM> further comprises a step <NUM> of selecting or estimating equalizer matrices using the estimated channel transfer function matrices or the information derived therefrom.

Thereby, an analog beamforming network of the multi-antenna transmitter is set to specific beamforming network parameters and maintained fixed at the set specific beamforming network parameters, during calibrating/testing the digital transmitter module of the multi-antenna receiver, even if the propagation channel between the device under test and the device tester changes to emulate multipath propagation channel. In that case, a third signaling information can be wirelessly transmitting from the device under test to the device tester, the third signaling information indicating specific beamforming network operating parameters the device under test would apply in a normal operation mode to the analog beamforming network responsive to the emulated multipath propagation channel in order to adapt the analog beamforming network in the normal operation mode to the multipath propagation channel.

Wireless communication devices equipped with multiple antennas have to be calibrated and tested with respect to overall performance and conformance. These devices are typically highly integrated such that device interfaces are neither available nor accessible. Embodiments described herein provide a non-destructive testing and calibration approach for integrated DUTs equipped with analog, digital and hybrid beamforming networks in arbitrary laboratory environments. Feedback schemes for the new testing and calibration approach are also provided.

Various elements and features of the present invention may be implemented in hardware using analog and/or digital circuits, in software, through the execution of instructions by one or more general purpose or special-purpose processors, or as a combination of hardware and software. For example, embodiments of the present invention may be implemented in the environment of a computer system or another processing system. <FIG> illustrates an example of a computer system <NUM>. The units or modules as well as the steps of the methods performed by these units may execute on one or more computer systems <NUM>. The computer system <NUM> includes one or more processors <NUM>, like a special purpose or a general purpose digital signal processor. The processor <NUM> is connected to a communication infrastructure <NUM>, like a bus or a network. The computer system <NUM> includes a main memory <NUM>, e.g., a random access memory (RAM), and a secondary memory <NUM>, e.g., a hard disk drive and/or a removable storage drive. The secondary memory <NUM> may allow computer programs or other instructions to be loaded into the computer system <NUM>. The computer system <NUM> may further include a communications interface <NUM> to allow software and data to be transferred between computer system <NUM> and external devices. The communication may be in the form electronic, electromagnetic, optical, or other signals capable of being handled by a communications interface. The communication may use a wire or a cable, fiber optics, a phone line, a cellular phone link, an RF link and other communications channels <NUM>.

The computer program, when executed, enable the computer system <NUM> to implement the present invention. In particular, the computer program, when executed, enable processor <NUM> to implement the processes of the present invention, such as any of the methods described herein.

Claim 1:
A method (<NUM>) for wirelessly calibrating/testing a digital receiver module of a multi-antenna receiver of a device under test (<NUM>), the method comprising:
wirelessly transmitting (<NUM>) a first signaling information between the device under test (<NUM>) and a device tester (<NUM>), the first signaling information indicating a calibration request, wherein the first signaling information is transmitted by the device under test (<NUM>) or the device tester (<NUM>);
estimating (<NUM>), in response to the first signaling information, channel transfer function matrices between active antenna ports (<NUM>) or RF ports (<NUM>) of the multi-antenna receiver of the device under test (<NUM>) and antenna ports (<NUM>) of the device tester (<NUM>) using reference signals wirelessly transmitted from the device tester (<NUM>) to the device under test (<NUM>);
wirelessly transmitting (<NUM>) a second signaling information between the device under test (<NUM>) and the device tester (<NUM>), the second signaling information indicating a precoded transmission request, wherein the second signaling information is transmitted by the device under test (<NUM>) or the device tester (<NUM>); and
wirelessly transmitting (<NUM>), in response to the second signaling information, reference signals from the device tester (<NUM>) to the device under test (<NUM>) using precoder matrices selected or determined based on the estimated channel transfer function matrices or an information derived therefrom, to obtain interference free channels between the device tester (<NUM>) and the device under test (<NUM>) allowing the reference signals to be received independently at each active antenna port (<NUM>) or RF port (<NUM>) of the multi-antenna receiver of the device under test (<NUM>).