Patent Description:
In the state of the art, over-the-air (OTA) measurements of a device under test are known wherein a pre-equalization matrix is determined. Then, the pre-equalization matrix is applied in order to pre-equalize a radio channel established between a radio communication tester and the device under test. Accordingly, the signal outputted by the radio communication tester is adapted by means of the pre-equalization matrix such that the signal received by the device under test is already equalized. In fact, the pre-equalization matrix and a channel matrix, also called transfer matrix, compensate each other, wherein the channel matrix describes the influences that occur in the radio channel established between the device under test and the radio communication tester.

Accordingly, the channel matrix for the respective radio channel has to be determined and mathematically inverted, thereby obtaining the pre-equalization matrix that can be used for equalizing the radio channel. Then, quasi-conducted test conditions for the device under test are obtained, as the influence of the radio channel are equalized by applying the pre-equalization matrix. Since quasi-conducted test conditions are achieved, OTA conformance testing of the device under test can be performed. In <CIT>, <CIT> or the article "<NPL>), a system and a method for inverting the channel matrix are described.

However, the concept known in the state of the art is very time-consuming, as the channel matrix has to be determined and inverted, which might require mathematically complex processes.

Accordingly, there is a need for a simple and fast approach to establish quasi-conducted test conditions for the device under test such that OTA conformance testing of the device under test can be performed.

The invention provides a method for determining a pre-equalization matrix to be used for testing, the method comprising the steps of:.

Accordingly, quasi-conducted test conditions for the device under test are achieved such that over-the-air (OTA) conformance testing can be performed, wherein additive white Gaussian noise (AWGN) is considered, particularly respective influences associated with non-intrinsic noise. The additive white Gaussian noise (AWGN) simulates the effect of many random processes that occur in nature. For instance, the AWGN encompasses many different natural noise sources, such as thermal vibrations of atoms in conductors, also called thermal noise, shot noise or any other natural noise sources. In fact, the AWGN relates to a basic noise model used in information theory, wherein it is assumed that the summation of many random processes has a Gaussian distribution. Thus, the AWGN is Gaussian because the noise has a normal distribution in time domain. Further, the AWGN is white because the power of the noise is distributed uniformly across the frequency. Moreover, the AWGN is additive since the respective noise is added to any intrinsic noise of the test setup. For instance, the AWGN may be calculated and generated accordingly, wherein the AWGN is (artificially) introduced into a test chamber, for instance an anechoic chamber. Alternatively, the AWGN is calculated and (only) mathematically considered when determining the pre-equalization matrix.

Since the device under test forwards the RSRP-B measurement values to the radio communication tester, particularly the channel emulator, a respective feedback of the device under test is provided that is taken into consideration by the radio communication tester when calculating the pre-equalization matrix. Hence, the influence of the additive white Gaussian noise (AWGN) is considered appropriately, as the influence of the AWGN has an impact on the RSRP-B measurement values that are fed back to the radio communication tester.

Generally, the reference signal received power per branch (RSRP-B) is a measurement of the received power level per branch of the device under test, namely per receiving branch. The reference signal received power (RSRP) is a Received Signal Strength Indicator (RSSI) type of measurement.

In fact, the reference signal received power per branch (RSRP-B) corresponds to the linear average over the power contributions of the resource elements. The reference signal received power per branch (RSRP-B) is also called reference signal receiving power per branch (RSRP-B).

The device under test may have at least two (reception) antennas that are associated with the at least two branches of the device under test. The at least two (reception) antennas establish the MIMO connection with the radio communication tester, particularly at least two transmission antennas of the radio communication tester.

In general, the power dynamic range can be maximized, as the (remaining) branches of the device under test are balanced by means of the pre-calibration matrix. As cross-talk between the channels can be compensated by means of the pre-calibration matrix, the isolation between reception antennas of the device under test is maximized, yielding improved testing conditions.

Accordingly, cross-talk of the channels can be minimized and isolation between the branches or rather antennas of the device under test can be improved when applying the pre-equalization matrix during the testing of a device under test.

Since the radio communication tester comprises the base station emulator and the channel emulator, the respective channels are emulated channels that may simulate real radio communication channels established between the device under test and a real base station.

The base station emulator may be configured to emulate different kinds of base stations. Further, the channel emulator may be configured to emulate different kinds of channels. Hence, the same radio communication setup may be emulated for different conditions, for instance an ideal channel, a real channel and/or a disturbed channel.

The radio communication tester, particularly the channel emulator, is configured to selectively activate a certain number of channels during the testing/calibration in order to determine the pre-equalization matrix. Thus, only one channel may be activated at once or rather two channels simultaneously. In fact, the respective number of channels activated simultaneously may vary, as it depends on the step performed for determining the pre-equalization matrix.

Particularly, at least two different steps are performed when determining the pre-equalization matrix, wherein the at least two different steps are associated with different numbers of channels activated, for instance a single channel in a first step and two or more channels in a second step.

The device under test may be a <NUM> user equipment, for instance a tablet or a phone such as a smartphone. Further, the base station emulator may be a <NUM> base station emulator that is configured to establish a <NUM> connection with the device under test.

In general, the channel matrix is estimated based on the feedback provided by the device under test, namely the quantized power per branch. Based on the feedback from the device under test, the pre-equalization matrix is determined, particularly approximated, thereby minimizing cross-talk between the channels and maximizing power dynamic range across the respective OTA channel.

Further, the NxM MIMO connection means that N and M are equal or greater than <NUM> in order to establish the MIMO connection. Particularly, the NxM MIMO connection is a 2x2 connection such that two transmission antennas of the radio communication tester and two reception antennas of the device under test are involved. In fact, the 2x2 connection ensures that the respective pre-calibration matrix can be determined easily.

Hence, the pre-equalization matrix is based on two matrices that have different purposes, namely compensation and balancing, thereby ensuring that the pre-equalization matrix determined compensates the cross-talk between the at least two channels and balances the branches of the device under test simultaneously when applied during the testing of the device under test. Thus, the device under test receives equal power at its reception antennas.

During the optimization phase, the initialized values are optimized in order to determine optimal values for the compensation matrix such that the compensation matrix is determined in an improved manner.

During the adjustment phase, the balancing matrix is optimized with regard to its purpose, namely providing an equal power distribution at the branches of the device under test. In other words, the device under test receives equal power at its reception antennas.

An aspect provides that it is verified if the pre-equalization matrix calculated solves the optimization problem min∥A · G - I∥<NUM>, wherein A relates to a transfer matrix, G relates to the pre-equalization matrix and I relates to the identity matrix. The verification may be done continuously, particularly once the pre-equalization matrix is available even though the respective pre-equalization matrix available does not correspond to the optimized one. As mentioned above, the pre-equalization matrix is determined or rather estimated based on the reference signal received power per branch (RSRP-B) measurement values while considering AWGN such that the pre-equalization matrix determined/estimated usually does not correspond to the inverted channel matrix. Therefore, it is verified if the estimated/determined pre-equalization matrix approximates the inverted channel matrix, thereby reducing the result of the condition ∥A · G - I∥<NUM> to be solved by the optimization problem mentioned above.

As the AWGN is taken into consideration when calculating the pre-equalization matrix, the pre-equalization matrix does not correspond to the inverse of the transfer matrix.

Particularly, the transfer matrix describes the NxM MIMO connection between the radio communication tester and the device under test. The transfer matrix may describe the (ideal) channel established between the radio communication tester and the device under test.

For instance, an initialization phase takes place during which the respective parameters of the compensation matrix and the balancing matrix are initialized. During the initialization phase, the compensation parameters of the compensation matrix as well as the balancing parameters of the balancing matrix are initialized by initialized values. For instance, the compensation parameters and the balancing parameters equal <NUM> in the initialization phase.

Further, an initial calibration of the compensation matrix may be performed, thereby initially calibrating amplitude values of the compensation parameters. The initial calibration may be part of the initialization phase, wherein the respective amplitude values of the compensation parameters are determined initially while starting from the initialized values, for instance <NUM>. Hence, initially calibrated values of the amplitude values are obtained after the initial calibration that may differ from the initialized values.

Particularly, the amplitude values of the compensation parameters are determined during the initial calibration by taking the reference signal received power per branch measurement values into account. The respective measurement values fed back from the device under test are considered by the radio communication tester, particularly the channel emulator. The respective measurement values received are processed accordingly, thereby determining the amplitude values of the compensation parameters in order to obtain the initially calibrated amplitude values that may differ from the initialized values, namely the starting values.

Another aspect provides that, during the initial calibration, only one channel is activated at once and the reference signal received power per branch measurement values are collected by each branch. Thus, the respective amplitude values of the compensation parameters can be determined by <MAT>, wherein RSRPij is the RSRP-B from branch Rj while only activating the respective channel Ti. This is done for each channel Ti such that all compensation parameters can be determined successively.

Particularly, optimal phase values and/or optimal amplitude values for the compensation parameters are determined during the optimization phase. A suitable search interval for the phase values of the compensation parameters is determined that is used in order to find the optimal phase values for the compensation parameters. Once the optimal phase values are determined, the amplitude values may be optimized subsequently.

Hence, the optimization phase may comprise a two-step approach, as the phase values and the amplitude values of the compensation parameters are optimized subsequently, thereby optimizing the compensation parameters entirely. The optimization of the amplitude values ensure that they are optimized with respect to the values obtained during the initialization phase, particularly during the initial calibration.

For instance, the optimal phase values are determined by pairwise activating two channels while deactivating all other channels. The optimal phase values provide the highest mutual (pairwise) isolation between the reception antennas of the device under test. The isolation corresponds to a destructive interference.

The pairwise activation of the channels, namely the activation of transmitter pairs, is repeated for each possible transmitter pair successively. By doing so, the entire compensation matrix is optimized accordingly.

When optimizing the amplitude values afterwards, the mutual (pairwise) isolation between the branches of the device under test is improved further.

As mentioned above, the radio communication tester, particularly the channel emulator, is configured to selectively activate different numbers of channels during the testing/calibration in order to determine the pre-equalization matrix. During the initialization phase (first step) only a single channel is activated at once, whereas during the optimization phase (second step) two channels are activated at once. Hence, two different numbers of channels are activated during the calibration in order to determine the pre-equalization matrix.

Generally, a modified standard search algorithm can be applied for determining the optimal phase values and/or the optimal amplitude values.

Particularly, the optimization phase takes place after the initialization phase and/or the initial calibration. The respective compensation parameters of the compensation matrix are set to initial values during the initialization phase, which correspond to starting points. During the initial calibration, initially calibrated amplitude values are determined. In the subsequent optimization phase, the compensation parameters are optimized.

Once the optimization phase has been completed, the compensation matrix obtained can be inversed, thereby obtaining the inverse of the compensation matrix. The inversion of the compensation matrix may be done by means of numerical methods (depending on the rank of the compensation matrix).

Generally, the inverted compensation matrix and the balancing matrix are multiplied with each other in order to arrive at the pre-equalization matrix.

For instance, the adjustment phase takes place after the optimization phase. The balancing parameters are adjusted subsequently. Hence, cross-talk is minimized by optimizing the compensation matrix. Afterwards, the balancing matrix is varied by adjusting the balancing parameters in order to ensure that the branches of the device under test each receive an equal power.

Generally, the optimized pre-equalization matrix corresponds to the one obtained after the steps mentioned above are performed, namely the optimization phase and the adjustment phase. As mentioned above, the optimized pre-equalization matrix does not necessarily correspond to the inverse of the channel matrix or rather transfer matrix, as it is derived from the RSRP-B measurement values.

Furthermore, an intermediate pre-equalization matrix may be determined after the initialization phase and/or the optimization phase, wherein the intermediate pre-equalization matrix may be used for the optimization problem mentioned above.

Accordingly, a solution may be obtained in a very fast manner, resulting in a significant speed advantage compared to the techniques known in the state of the art provided that the intermediate pre-equalization matrix already solves the optimization problem given above. Even if the intermediate pre-equalization matrix does not solve the optimization problem given above, the method is significantly faster, as it is not necessary to determine the inversed channel matrix or rather transfer matrix.

Generally, the reference signal received power per branch measurement values forwarded by the device under test are processed by the radio communication tester, particularly the channel emulator, in order to determine/estimate the pre-equalization matrix, for instance the compensation matrix based on which the pre-equalization matrix is computed.

Moreover, the invention provides a test setup for testing a device under test. The test setup comprises a radio communication tester as well as a device under test. The test setup is configured to perform the method described above. The characteristics and advantages mentioned above also apply to the test setup in a similar manner. Hence, reference is made to the explanations given above.

The test setup may also comprise an anechoic chamber that encompasses the device under test during the testing and the determination of the pre-equalization matrix. In other words, the device under test is located in the anechoic chamber when it receives the signals emitted by the radio communication tester. The device under test measures the RSRP-B, thereby obtaining RSRP-B measurement values that are fed back to the radio communication tester, particularly the channel emulator. The radio communication tester, particularly the channel emulator, takes the respective measurement values into account in order to determine the pre-equalization matrix as described above.

In fact, the reference signal received power per branch measurement values and the presence of additive white Gaussian noise are taken into account when calculating the pre-equalization matrix.

The device under test receives a signal r that is associated with a signal s provided by the radio communication tester. Both signals are associated with each other by r = A · G · s + n, wherein A relates to the (ideal) transfer matrix, G relates to the pre-equalization matrix, and n relates to the additive white Gaussian noise. The (optimal/optimized) pre-equalization matrix determined as described above equalizes the (ideal) transfer matrix A and the additive white Gaussian noise (AWGN) n.

Generally, the pre-equalization matrix determined may be applied during the testing of the device under test by means of the test setup. Accordingly, OTA conformance testing of the device under test can be performed since quasi-conducted test conditions are achieved.

In <FIG>, a test setup <NUM> is shown that comprises a radio communication tester <NUM> and a device under test ("DUT") <NUM> that communicate with each other via a radio communication connection <NUM> established.

The radio communication tester <NUM> has a base station emulator <NUM> and a channel emulator <NUM>. The base station emulator <NUM> and the channel emulator <NUM> are commonly housed in the housing of the radio communication tester <NUM>.

Furthermore, the test setup <NUM> comprises an anechoic chamber <NUM>. The device under test <NUM> is located within the anechoic chamber <NUM>.

Besides the radio communication connection <NUM>, a feedback connection <NUM> is also established between the device under test <NUM> and the radio communication tester <NUM>, particularly the channel emulator <NUM>.

The device under test <NUM> is configured to perform measurements in order to obtain reference signal received power per branch (RSRP-B) measurement values.

Via the feedback connection <NUM>, the device under test <NUM> is enabled to forward these RSRP-B measurement values gathered to the radio communication tester <NUM>, particularly the channel emulator <NUM>.

Accordingly, the radio communication tester <NUM>, particularly the channel emulator <NUM>, is enabled to consider the RSRP-B measurement values, which are received from the device under test <NUM> via the feedback connection <NUM>.

In the shown embodiment, the radio communication tester <NUM> has four transmission antennas <NUM>, whereas the device under test <NUM> has two reception antennas <NUM>. The reception antennas <NUM> are associated with respective branches <NUM> of the device under test <NUM>.

Generally, the radio communication tester <NUM> and the device under test <NUM> establish a NxM multiple-input multiple-output (MIMO) connection <NUM> with each other. For instance, the MIMO connection <NUM> corresponds to a 2x2 connection.

In <FIG>, two active (intended) channels <NUM> are illustrated.

The test setup <NUM> shown in <FIG> is generally configured to perform the method illustrated in <FIG> and <FIG>, wherein <FIG> shows detailed steps of the method shown in <FIG>.

In a first step S1, the test setup <NUM> as illustrated in <FIG> is provided, namely the radio communication tester <NUM> and the device under test <NUM>. Particularly, the device under test <NUM> is located within the anechoic chamber <NUM>.

In a second step S2, the MIMO connection <NUM>, for instance the 2x2 connection, is established between the radio communication tester <NUM> and the device under test <NUM>.

In a third step S3, a signal is provided by the radio communication tester <NUM> that represents a certain base station and channel conditions, wherein these characteristics are defined by the base station emulator <NUM> and the channel emulator <NUM>.

In a fourth step S4, the signal is transmitted into the anechoic chamber <NUM> and received by the device under test <NUM> that processes the signal accordingly.

Additive white Gaussian noise (AWGN) may be calculated and introduced into the anechoic chamber <NUM> such that the device under test <NUM> additionally receives a signal associated with the AWGN as schematically illustrated in <FIG>. Alternatively, the AWGN is mathematically considered at a later stage as will be described later.

In a fifth step S5, the device under test <NUM> performs measurements on the signal received in order to obtain reference signal received power per branch (RSRP-B) measurement values.

In a sixth step S6, the RSRP-B measurement values are forwarded via the feedback line <NUM> to the radio communication tester <NUM> that processes the information obtained from the device under test <NUM>.

In a seventh step S7, a pre-equalization matrix G is determined. In other words, the pre-equalization matrix G is computed by the radio communication tester <NUM>, particularly the channel emulator <NUM>.

When determining/computing the pre-equalization matrix G, the AWGN may be considered in a mathematical manner provided that the AWGN was not introduced into the anechoic chamber <NUM> previously.

The respective steps to be performed in order to determine/compute the pre-equalization matrix G are illustrated in <FIG> in more detail to which reference is made hereinafter.

In general, the pre-equalization matrix G is computed based on two different matrices, namely a compensation matrix B and a balancing matrix C, wherein the compensation matrix B is inverted such that G = B-<NUM> · C.

The compensation matrix B comprises compensation parameters ωij such that the compensation matrix B can be defined by <MAT>.

The balancing matrix C comprises balancing parameters ci such that the balancing matric can be defined by <MAT>.

Generally, the compensation matrix B compensates cross-talk between the at least two channels <NUM>, whereas the balancing matrix C balances the branches <NUM> such that the device under test <NUM> receives equal power at its reception antennas <NUM>.

Accordingly, the pre-equalization matrix G, obtained by multiplying the above-mentioned matrices B, C, compensates cross-talk between the at least two channels <NUM> and balances the branches <NUM> such that the device under test <NUM> receives equal power at its reception antennas <NUM>.

In a first sub-step of determining/estimating the pre-equalization matrix G, an initialization phase takes place as shown in <FIG>. In the first step, a parameters initialization is done, for instance by setting the compensation parameters ωij and the balancing parameters ci to be equal <NUM>. Generally, each other initialization value can be used, for instance <NUM>, <NUM> or <NUM> and so on. For instance, the pre-defined values may be used that are stored on a memory of the radio communication tester <NUM>.

During the first step, an initial calibration is performed in order to determine the amplitude values of the compensation parameters (|ωij|). In other words, the amplitude values of the compensation parameters are initially calibrated.

This is done by activating only one channel at once, wherein the reference signal received power per branch <NUM> measurement values are collected by each branch <NUM>. Accordingly, the initially calibrated amplitude values of the compensation parameters can be determined by <MAT>, wherein RSRPij is the RSRP-B from branch Rj while only activating the respective channel Ti. This done for each channel Ti such that the initially calibrated amplitude values for all compensation parameters can be determined in a successive manner.

Accordingly, the amplitude values of the compensation parameters are determined during the initial calibration by taking the RSRP-B measurement values into account that are fed back from the device under test <NUM> to the radio communication tester <NUM>.

Afterwards, the first step, namely the initialization phase comprising the initial calibration, is completed.

In a second sub-step of determining/estimating the pre-equalization matrix G, an optimization phase takes place during which the compensation parameters of the compensation matrix are optimized, as optimal compensation parameters are determined, particularly by determining optimal phase values and/or optimal amplitude values for the compensation parameters.

As shown in <FIG>, the optimal phase values ϕ(ωij) are determined within a suitable search interval. The optimal phase values are determined by pairwise activating two channels <NUM> while deactivating all other channels. This is typically done by activating two transmitter antennas <NUM> while deactivating the other transmitter antennas <NUM>, thereby activating one transmitter pair.

Then, a search algorithm is applied in order to determine the optimal phase values ϕ(ωij) that provides the highest mutual isolation for the respective transmitter pair of transmitter antennas <NUM>.

The signals emitted by the respective transmitter antennas <NUM> of the active transmitter pair may be received by a single reception antenna <NUM> of the device under test <NUM> at once. Then, the different reception antennas <NUM> are subsequently exposed to the respective transmitter pair. Alternatively, the reception antennas <NUM> receive the signals emitted by the respective transmitter pair simultaneously, as they relate to distinguishable branches <NUM>.

In any case, the procedure indicated above is repeated for all possible transmitter pairs such that the optimal phase values for all compensation parameters can be determined.

Afterwards, an amplitude adjustment may take place in order to increase the isolation of the branches <NUM>, thereby optimizing the amplitude values of the compensation parameters (|ωij|) such that the compensation parameters are optimized in their entirety.

Hence, an optimized compensation matrix B is obtained at the end of the second step, as the compensation matrix B comprises the optimized compensation parameters ωij.

Accordingly, the radio communication tester <NUM>, particularly the channel emulator <NUM>, is configured to selectively activate different numbers of channels <NUM> when determining the pre-equalization matrix G, namely the compensation matrix B as a part thereof.

In a third sub-step, the (optimized) compensation matrix B is inversed in order to obtain the matrix to be multiplied with the balancing matrix. The inversed compensation matrix B is labeled with D.

In a fourth sub-step, the balancing parameters ci are adjusted, thereby ensuring that the device under test <NUM> receives equal power at its reception antennas <NUM>. Accordingly, the respective balancing parameters ci are adapted with respect to their starting values set during the initialization phase mentioned above.

In a fifth sub-step, the (optimal/optimized) pre-equalization matrix G is defined by multiplying the inverse of the compensation matrix B, namely matrix D, with the balancing matrix C.

As mentioned above, the (optimal/optimized) pre-equalization matrix G compensates cross-talk between the at least two channels <NUM> and balances the branches <NUM> such that the device under test <NUM> receives equal power at its reception antennas <NUM>.

Accordingly, it is not necessary to determine and inverse the channel matrix/transfer matrix in order to pre-equalize the channel(s) <NUM>, as the pre-equalization matrix can be determined/computed/estimated based on the steps indicated above, wherein the AWGN as well as feedback from the device under test <NUM> via the reference signal received power per branch (RSRP-B) measurement values.

During the steps indicated above, the pre-equalization matrix G can be determined/estimated/computed based on the respective matrices available such that an intermediate pre-equalization matrix G is obtained that differs from the optimal/optimized pre-equalization matrix G. However, the intermediate pre-equalization matrix G is obtained earlier.

Further, it can be verified if the (intermediate) pre-equalization matrix G calculated already solves the optimization problem min∥A · G - I∥<NUM>, wherein I relates to the identity matrix and A relates to the transfer matrix that describes the NxM MIMO connection <NUM> between the radio communication tester <NUM> and the device under test <NUM>.

In <FIG>, the detailed steps of <FIG> are illustrated for a preferred embodiment associated with a 2x2 MIMO connection established.

Accordingly, in the first sub-step, namely the initialization phase, the balancing parameters c<NUM> and c<NUM> are set to be <NUM>, whereas the phase values for the compensation parameters are set to be zero ϕ(ω<NUM>) = ϕ(ω<NUM>) = <NUM>.

Then, the initial calibration takes place in order to initially calibrate the amplitude values for the compensation parameters (|ω<NUM>|, |ω<NUM>|).

In the second sub-step, the optimized values for the phase and amplitude of the respective compensation parameters are determined, particularly in a subsequent manner.

Accordingly, the search interval is determined first that is used for identifying the optimal ϕ(ω<NUM>). Once the optimal phase value has been determined for the respective compensation parameter, the amplitude value |ω<NUM>| is adjusted accordingly.

Then, the same steps are done for the second compensation parameter such that the optimal phase value ϕ(ω<NUM>) as well as the optimal amplitude value |ω<NUM>| for the second compensation parameter are determined.

Thus, the compensation matrix is obtained.

Afterwards, in the third sub-step, the balancing parameters c<NUM> and c<NUM> are adjusted as discussed above.

Then, the optimal/optimized pre-equalization matrix can be determined based on the optimized compensation matrix B and the balanced/adjusted balancing matrix C.

In any case, a fast method, namely a high-speed method, is provided for estimating the pre-equalization matrix for the NxM OTA channel matrix, namely the transfer matrix, wherein this is done based on quantized feedback from the device under test <NUM> and presence of AWGN, as the RSRP-B measurement values fed back to the radio communication tester <NUM> are taken into consideration.

Generally, the respective emulator <NUM>, <NUM> may relate to an emulating module. Hence, the radio communication tester <NUM> may be established by a module.

Therein and in the following, the term "module" is understood to describe suitable hardware, suitable software, or a combination of hardware and software that is configured to have a certain functionality.

The hardware may, inter alia, comprise a CPU, a GPU, an FPGA, an ASIC, or other types of electronic circuitry.

Certain embodiments disclosed herein, particularly the respective module(s), utilize circuitry (e.g., one or more circuits) in order to implement standards, protocols, methodologies or technologies disclosed herein, operably couple two or more components, generate information, process information, analyze information, generate signals, encode/decode signals, convert signals, transmit and/or receive signals, control other devices, etc. Circuitry of any type can be used.

Claim 1:
A method for determining a pre-equalization matrix to be used for testing, the method comprising the steps of:
- Providing a radio communication tester (<NUM>) having a base station emulator (<NUM>) and a channel emulator (<NUM>),
- Providing a device under test (<NUM>) having at least two branches (<NUM>),
- Establishing a NxM multiple-input multiple-output, MIMO, connection (<NUM>) between the radio communication tester (<NUM>) and the device under test (<NUM>), the NxM MIMO connection (<NUM>) comprising at least two channels (<NUM>),
- Forwarding reference signal received power per branch (<NUM>) measurement values continuously from the device under test (<NUM>) to the radio communication tester (<NUM>), and
- Determining a pre-equalization matrix by means of the radio communication tester (<NUM>), wherein the reference signal received power per branch (<NUM>) measurement values and presence of additive white Gaussian noise, AWGN, are taken into account when calculating the pre-equalization matrix, and wherein the pre-equalization matrix compensates cross-talk between the at least two channels (<NUM>) and balances the branches (<NUM>) such that the device under test (<NUM>) receives equal power at its reception antennas (<NUM>),
wherein the pre-equalization matrix is obtained by multiplying the inverse of a compensation matrix having compensation parameters and a balancing matrix having balancing parameters,
wherein the compensation matrix is determined during an optimization phase, thereby optimizing the compensation parameters of the compensation matrix, and
wherein the balancing matrix is determined during an adjustment phase, thereby adjusting the balancing parameters.