Transient error vector magnitude estimation

Abstract

There is provided techniques for transient EVM estimation. A method is performed by a radio transceiver device. The radio transceiver device comprises a transmitter and a receiver. The method comprises the transmitter transmitting a reference signal in samples of a slot. Transmission of the reference signal is directly preceded by an 5 abrupt change in transmission power by a power amplifier in the transmitter. The method comprises the receiver receiving the reference signal. The method comprises obtaining a value of the EVM per sample in the slot by computing a residual error per sample in the slot. Computing the residual errors comprises comparing the reference signal as received by the receiver to the reference signal as transmitted from the 10 transmitter. The method comprises estimating existence of transient EVM in the transmitter by comparing the value of the EVM for at least some of the samples in the slot to a reference.

Description

[0001] TRANSIENT ERROR VECTOR MAGNITUDE ESTIMATION

[0002] TECHNICAL FIELD

[0003] Embodiments presented herein relate to a method, a radio transceiver device, a computer program, and a computer program product for transient Error Vector Magnitude estimation.

[0004] BACKGROUND

[0005] In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.

[0006] For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is the Error Vector Magnitude (EVM). In general terms, EVM is a measure of signal quality in telecommunications, especially in digital modulation. It quantifies the difference between the ideal transmitted signal and the actual received signal by calculating the magnitude of the error vector, which is the deviation between these two signals in the in-phase / quadrature (I / Q) plane. A lower EVM indicates a more accurate signal with less distortion or interference.

[0007] Transient EVM behavior is one example of EVM fluctuations which occur when a certain circuit in the radio equipment, or other types of radio transceiver devices, is in a transient mode. For example, the EVM can become higher when a power amplifier (PA) changes its output power. The cause can be insufficient power supply or GaN trapping phenomenon (if a GaN transistor is used in the PA).

[0008] The averaging of EVM gives stable measurements, however such criterion may hide EVM transients. This implies that radio equipment with EVM fluctuation can fulfill EVM requirements whilst in practice cause serious link quality issues. For example, even though an EVM transient has a short time duration (e.g. a few microseconds to some tens of microseconds), it can cause a degradation of the peak throughput.

[0009] EVM measurement is relatively straightforward in controlled laboratory settings, and certain EVM-like metrics can be obtained in the digital domain. However, for radio transceiver devices deployed in live networks, identifying transient EVM issues presents a challenge. These issues may manifest differently depending on the specific model, hardware revision, or manufacturing batch of the radio transceiver device. Detecting and diagnosing transient EVM in live networks can therefore be difficult without extensive testing, which is both resource-intensive and operationally disruptive.

[0010] Hence, there is still a need for improved identification of transient EVM issues, especially in live networks.

[0011] SUMMARY

[0012] An object of embodiments herein is to address the above issues and enable efficient identification of transient EVM issues in live networks.

[0013] According to a first aspect there is presented a method for transient EVM estimation. The method is performed by a radio transceiver device. The radio transceiver device comprises a transmitter and a receiver. The method comprises transmitting, from the transmitter, a reference signal in samples of a slot. Transmission of the reference signal is directly preceded by an abrupt change in transmission power by a power amplifier in the transmitter. The method comprises receiving, by the receiver, the reference signal. The method comprises obtaining a value of the EVM per sample in the slot by computing a residual error per sample in the slot. Computing the residual errors comprises comparing the reference signal as received by the receiver to the reference signal as transmitted from the transmitter. The method comprises estimating existence of transient EVM in the transmitter by comparing the value of the EVM for at least some of the samples in the slot to a reference.

[0014] According to a second aspect there is presented a radio transceiver device for transient EVM estimation. The radio transceiver device comprises processing circuitry, a transmitter and a receiver. The processing circuitry is configured to cause the radio transceiver device to transmit, from the transmitter, a reference signal in samples of a slot. Transmission of the reference signal is directly preceded by an abrupt change in transmission power by a power amplifier in the transmitter. The processing circuitry is configured to cause the radio transceiver device to receive, by the receiver, the reference signal. The processing circuitry is configured to cause the radio transceiver device to obtain a value of the EVM per sample in the slot by computing a residual error per sample in the slot. Computing the residual errors comprises comparing the reference signal as received by the receiver to the reference signal as transmitted from the transmitter. The processing circuitry is configured to cause the radio transceiver device to estimate existence of transient EVM in the transmitter by comparing the value of the EVM for at least some of the samples in the slot to a reference.

[0015] According to a third aspect there is presented a computer program for transient EVM estimation. The computer program comprises computer code which, when run on processing circuitry of a radio transceiver device comprising a transmitter and a receiver, causes the radio transceiver device to perform actions. One action comprises the radio transceiver device to transmit, from the transmitter, a reference signal in samples of a slot. Transmission of the reference signal is directly preceded by an abrupt change in transmission power by a power amplifier in the transmitter. One action comprises the radio transceiver device to receive, by the receiver, the reference signal. One action comprises the radio transceiver device to obtain a value of the EVM per sample in the slot by computing a residual error per sample in the slot. Computing the residual errors comprises comparing the reference signal as received by the receiver to the reference signal as transmitted from the transmitter. One action comprises the radio transceiver device to estimate existence of transient EVM in the transmitter by comparing the value of the EVM for at least some of the samples in the slot to a reference.

[0016] According to a fourth aspect there is presented a computer program product comprising a computer program according to the third aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium.

[0017] Advantageously, these aspects enable efficient identification of transient EVM issues in live networks.

[0018] Advantageously, the transient EVM can be detected at the cost of very little overhead signaling.

[0019] Advantageously, these aspects allow an antenna calibration signal to be used as reference signal, and hence do not require any special purpose signal to be designed or transmitted. Advantageously, these aspects require only a very small traffic overhead since EVM characteristics of a radio transceiver device change very slowly over time.

[0020] Advantageously, these aspects have applications also outside transient EVM detection, for example of assessing transmission signal quality in general.

[0021] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0022] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0023] BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0025] Fig. 1 is a schematic diagram illustrating a communication network according to embodiments;

[0026] Fig. 2 is a block diagram of a radio transceiver device according to embodiments;

[0027] Fig. 3 is a flowchart of methods according to embodiments;

[0028] Fig. 4 shows the PAPR and CM levels of all 198 ZC sequences of length 199 according to an embodiment;

[0029] Fig. 5 shows the PAPR and CM levels of all 408 ZC sequences of length 409 according to an embodiment;

[0030] Fig. 6 schematically illustrates transmission of a reference signal according to an embodiment; Fig. 7 shows simulation results according to an embodiment;

[0031] Fig. 8 is a schematic diagram showing structural units of a radio transceiver device according to an embodiment; and

[0032] Fig. 9 shows one example of a computer program product comprising computer readable storage medium according to an embodiment.

[0033] DETAILED DESCRIPTION

[0034] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional.

[0035] Fig. 1 is a schematic diagram illustrating a communication network too where embodiments presented herein can be applied. The communication network too comprises a network node no. The network node no could be any of a (radio) access network node, (radio) base station, base transceiver station, node B (NB), evolved node B (eNB), gNB, integrated access and backhaul node (IAB), access point, access node, transmission and reception point (TRP) or the like. The network node no represents the fixed infrastructure responsible for transmitting and receiving signals within the communication network too and serves as the access point for mobile devices 120. The mobile device 120 represents a user terminal, such as a portable wireless device, mobile station, mobile phone, handset, wireless local loop phone, user equipment (UE), smartphone, laptop computer, tablet computer, network- equipped vehicle, or other type of wireless device, capable of communicating with the network node 110 over a wireless communication link 130. The wireless communication link 130 represents the bidirectional communication path between the network node 110 and the mobile device 120 and facilitates data exchange, including transmission and reception of signals, over a wireless medium. As noted above, there is still a need for improved identification of transient EVM issues, especially in live networks.

[0036] The embodiments disclosed herein therefore relate to techniques for transient EVM estimation. In order to obtain such techniques, there is provided a radio transceiver device, a method performed by the radio transceiver device, a computer program product comprising code, for example in the form of a computer program, that when run on a radio transceiver device, causes the radio transceiver device to perform the method. The radio transceiver device could be implemented as part of the network node no.

[0037] Fig. 2 is a block diagram of a radio transceiver device 200 according to an embodiment. The block diagram illustrates components involved in signal transmission, reception, and EVM calculation. A signal generator 240 is configured to generates a reference signal for testing and analysis. This reference signal is sent to both the transmitter 210 and an EVM calculation block 250. Examples of such reference signals will be disclosed below. The transmitter 210 is configured to modulate and amplify signals to be transmitted from the radio transceiver device. For this purpose the transmitter 210 comprises different components, for example a power amplifier. The signals as processed by the transmitter 210 is provided to an antenna array 230 for wireless transmission. The antenna array 230 may comprise one or more antennas for transmission and reception of wireless signals. As illustrated by the external loopback path 240, the reference signal may be looped back to the radio transceiver device 200 over an air interface. However, as illustrated by the internal loopback path 250, the reference signal may alternatively be provided directly from the transmitter 210 to the receiver 220. A receiver 220 is configured to capture the received signal from the antenna array 230 (or from the transmitter 210 as received over the internal loopback path 250) and send it to the EVM calculation block 250 for analysis. In general terms, the EVM calculation block 250 is configured to compares the transmitted and received signals to calculate the EVM. The comparison assesses deviations introduced during transmission and reception. Further aspects of EVM estimation and detection will be disclosed next.

[0038] Fig. 3 is a flowchart illustrating embodiments of methods for transient EVM estimation. The methods are performed by the radio transceiver device 200. The radio transceiver device 200 comprises a transmitter 210 and a receiver 220. The methods are advantageously provided as computer programs.

[0039] S102: The transmitter 210 transmits a reference signal in samples of a slot. Transmission of the reference signal is directly preceded by an abrupt change in transmission power by a power amplifier in the transmitter 210.

[0040] In this respect, the sample in which the transmission of the reference signal starts may be at a symbol border, or even a slot border, of a downlink signal, or at some other place in the slot.

[0041] S104: The receiver 220 receives the reference signal.

[0042] S106: The radio transceiver device 200 obtains a value of the EVM per sample in the slot by computing a residual error per sample in the slot. Computing the residual errors comprises comparing the reference signal as received by the receiver 220 to the reference signal as transmitted from the transmitter 210.

[0043] Existence of transient EVM can then be estimated from a difference between the value of the EVM and some reference during a preconfigured time period, as in step S114.

[0044] S114: The radio transceiver device 200 estimates existence of transient EVM in the transmitter 210 by comparing the value of the EVM for at least some of the samples in the slot to a reference.

[0045] Embodiments relating to further details of transient EVM estimation as performed by the radio transceiver device 200 will now be disclosed with continued reference to Fig. 3-

[0046] As specified in step S114, the value of the EVM for at least some of the samples in the slot is compared to a reference. There could be different types of such references. In some aspects, the reference is an EVM value obtained for other samples in the slot or an EVM value obtained for samples in another slot. In particular, in some embodiments, the reference is a steady-state value of the EVM based on remaining samples in the slot or a steady-state value of the EVM obtained from samples in another slot. Further, in some embodiments, the value of the EVM per sample is obtained after compensation of the received reference signal in terms of amplitude, phase error, and timing error.

[0047] As specified in step S102, the reference signal is transmitted from the transmitter 210. In this respect, the transmitter 210 may have a digital front-end and an analog front-end. The reference signal may then be transmitted from either a digital frontend or an analog front-end of the transmitter 210. The reference signal is then looped back to the receiver 220, as illustrated in Fig. 2. Thus, the reference signal may be loped back to the receiver 220 either via a wired interface or an air interface.

[0048] There can be different types of reference signals. Aspects relating thereto will be disclosed next.

[0049] In general terms, since the purpose of the reference signal is to at least enable identification of transient EVM, the reference signal should neither be a low Peak to Average Power Ratio (PAPR) signal nor a Cubic Metric (CM) signal.

[0050] In some embodiments, the reference signal is an antenna calibration signal. In some embodiments, the reference signal is a high peak to average power ratio, or cubic metric, signal based on a Zadoff-Chu (ZC) sequence. The reference signal could thus comprise, or be based on, a ZC sequence having a root sequence index dependent PAPR. Opposite to ordinary consideration, it is preferred to select a root sequence with high PAPR, e.g., reaching a level that is close to a typical downlink orthogonal frequency-division multiplexing (OFDM) signal for the EVM transient evaluation.

[0051] One non-limiting example of howto construct a high PAPR / CM signal based on ZC sequence will be disclosed next.

[0052] In general terms, ZC sequences exhibit ideal correlation. In more detail, the autocorrelation of a ZC sequence with a cyclically shifted version of itself is zero, i.e., it is non-zero only at one instant which corresponds to the zero cyclic shift. The crosscorrelation between two different root sequences of same length is constant.

[0053] However, ZC sequence normally presents low PAPR / CM, which is not desired for EVM measurement purpose. Further, traditionally, the PAPR / CM level does not change much for different ZC sequence length s. That is, a longer ZC sequence gives similar PAPR / CM levels as a shorter one, even though the longer ZC sequence occupies a wider bandwidth.

[0054] A high PAPR / CM signal that maintains the aforementioned ZC properties can be constructed as follows.

[0055] For a given number of subcarriers L used by the reference signal, the first prime number LO below L / 2 is determined. For example, if L = 408, then LO can be set to 199.

[0056] The PAPR / CM of all LO length ZC sequences is calculated. In Fig. 4 is shown the PAPR and CM levels of all 198 ZC sequences of length 199. In Fig. 5 is shown the PAPR and CM levels of all 408 ZC sequences of length 409.

[0057] Some root sequences with high PAPR / CM can then be selected. These root sequences are referred to as component sequences. For example, ZC76and ZC123are good candidates as they show high PAPR / CM in Fig. 4 and in Fig. 5. Since PAPR / CM is a time domain characteristic, the original ZC sequence is first converted to the frequency domain and mapped to subcarriers, and then convert back to the time domain.

[0058] The two selected component sequences are concatenated in the frequency domain, similar to frequency-division multiplexing, to yield a frequency domain signal S:

[0059] S = [FFT(ZC76), zeros(LO), FFT(ZC123)]

[0060] Here, FFT(A) represents the fast Fourier transform of the sequence X and zeros(LO) represents an all -zero sequence of length LO. The value of kO can be fine-tuned for reaching a desired PAPR / CM. The time domain signal can then be obtained as: s = IFFT(S) or as s = IFFT ([zeros(kl), S, zeros(L2)])

[0061] Here, 7FFT(A) represents the inverse fast Fourier transform of the sequence Y and zeros(kl) and zeros(L2) represent all-zero sequence of lengths kl and k2, respectively. The zero-padding in the frequency domain before and after the sequence S implies interpolation or frequency shift, which has only very minor impact on the PAPR / CM property.

[0062] In the above description, the two component sequences (ZC76) and (ZC123) are used as examples. Here, if kO = 2, then the PAPR can reach q.ydB and the CM reaches 5.2dB which are about 3dB higher than traditional ZC sequences. Similarly, symmetric indexes [ZC’77,ZC122], [ZC78,ZC’121], .... [ZC99,ZC100] also yield an increase in PAPR / CM over traditional ZC sequences. The CM in dB has here been calculated as:

[0063] > 201oglO(RMS(abs(s0)3) - 1.52) CM“ L56 where s0= s / RMS(s), where abs(y) is the absolute value of y, and RMS(z) is the root mean square of z.

[0064] The PAPR / CM can be adjusted by applying different phase shifts to the sequences, by tuning the kO parameter, and by selecting different root sequence pairs. Such adjustments can be used to control the PAPR / CM level in a precise way.

[0065] Although two candidate component ZC sequences are used in the above example, a straightforward extension to using more than two candidate component ZC sequences is possible.

[0066] Further aspects of the transient EVM detection will be disclosed next.

[0067] In general terms, transient EVM is commonly triggered by an abrupt change in signal power e.g., immediately after an uplink-downlink switch or any other power interruption. It is possible that a certain physical resource block (PRB) allocation change may introduce transient EVM, whilst power switches normally yield worst transient EVM. The herein disclosed embodiments are based on inserting some power interruption (or power change), before the reference signal is transmitted. As in step S102, this is achieved by the transmission of the reference signal being directly preceded by an abrupt change in the transmission power. As will be disclosed next, there can be different ways to achieve this abrupt change in the transmission power. In some aspects, the last sample before the reference signal is not allocated for traffic, and therefore indicated as zero power (or at least that the last sample is to have its power reduced) towards the front-end of the transmitter so that an immediate power reduction can be performed, that in turn triggers the transient EVM. Hence, in some embodiments, for a sample immediately preceding the samples in which the reference signal is transmitted, the power amplifier is switched off or at least has its power reduced by a predetermined amount. The transient EVM is likely to be similar for different antenna branches and change very slowly in time. It may therefore be adequate to monitor some of the antenna branches at long time intervals.

[0068] Intermediate reference is here made to Fig. 6 which schematically illustrates transmission of a reference signal along a timeline 6oo according to an example. The time tstartis set such that transmission of the reference signal starts from sample n + 1 in symbol k. The reference signal has a duration tdurationequal to io samples. The sample n is not allocated for traffic, and therefore indicated as zero power in SLOT_INFO. The power amplifier in the transmitter will therefore power off (due to e.g. power interruption or power saving) and power up again at sample n + 1.

[0069] The transient EVM (if any) should occur in the first few, or tens, of microseconds in sample n + 1. By means of the transmitted reference signal in sample n + 1, it is possible for the radio transceiver device 200 to estimate amplitude (d), phase error (5), and timing error (At). The residual error e after compensation and / or equalization is considered as a contribution from EVM or other interferences and can be found as: e = abs (r — s) where

[0070] Here, r is the received time domain signal and s is the estimate of the signal component in r. The transient EVM can then be detected from the residual error e, as will be further disclosed below.

[0071] The calculations can be extended to also consider frequency dependent amplitudes and phase errors. In some aspects, two occasions of the reference signal are transmitted, where one occasion is preceded by a non-zero power sample. For example, in order to better detect the transient EVM, the traffic allocation in sample n can change. For example, random data or other type of non-zero samples (as indicated as non-zero power in SLOT_INFO) may be scheduled for some samples which cause no transient EVM effect. A comparison can then be made to the zero-power case to improve the confidence level for the detected EVM property. In particular, in some embodiments, the samples are first samples, the reference signal is a first reference signal, and the first reference signal is transmitted in a first slot, and the transmitter 210 is configured to perform (optional) steps S108, S110, S112.

[0072] S108: The transmitter 210 transmits a second reference signal in samples of a second slot. Transmission of the second reference signal is not directly preceded by an abrupt change in transmission power by the power amplifier in the transmitter 210.

[0073] S110: The receiver 220 receives the second reference signal.

[0074] S112: The radio transceiver device 200 obtains a value of the EVM per second sample in the second slot by computing a residual error per sample in the second slot. Computing the residual errors comprises comparing the second reference signal as transmitted from the transmitter 210 to the second reference signal as received by the receiver 220.

[0075] Existence of the transient EVM can then in step S114 be estimated by comparing the value of the EVM per sample in the first slot to the value of the EVM per sample in the second slot.

[0076] The transmission of the second reference signal can be preceded by transmission of random data or other type of non-zero samples.

[0077] In some aspects, the transient EVM may be significantly higher in the initial part of a slot. For example, according to the simulation results shown in Fig. 7, the transient EVM is 4% or higher for the first symbol. Therefore, in some aspects, averaging of the residual error at the slot start and other parts of a slot, or other slot, can be used to indicate the transient EVM level more reliably. Therefore, in some embodiments, the existence of transient EVM is estimated based on an average of residual errors. According to a first example, the average is over several samples from different slots with the same relative position to the changed power. According to a second example, The EVM measured for the first sample in the slot is compared to an average of the EVM for the remaining samples in the same slot. Different examples of how this can be achieved will be disclosed next.

[0078] Assume that also a second reference signal has been transmitted and received, as in steps Sio8, Sno, S112, and thus that existence of the transient EVM then in step S114 is estimated by comparing the value of the EVM per sample in the first slot to the value of the EVM per sample in the second slot. Then, the average can be defined by a difference, E, calculated as: where ey is the residual error of sample x in slot y. For example, can be the residual error of the I :th sample in the 2 i:th (i.e. ,even number) occasions which follows a non-zero power sample n.

[0079] Otherwise, i.e., when a second reference signal is not transmitted, and hence steps S108, S110, S112 are not performed, then the average can be defined by a difference, E, calculated as: is the residual error of sample x in slot y. For example, e^i+i can be the residual error of the I :th sample in the 2i + l:th (i.e., odd number) occasions which follows zero power sample n.

[0080] In both preceding equations, E indicates the difference between transient EVM and normal EVM during a preconfigured time period e.g. the first M samples. The parameter E contains information about how much stronger the transient EVM is compared to normal EVM. The value of E can be compared to a threshold to indicate if transient EVM is considered too high or not, in accordance with what has been disclosed above. The value of M can be selected in accordance with the expected time length of the transient period. For example, for the simulation results in Fig. 5, M = 1 may be a good choice since the transient effect is most obvious on the first sample.

[0081] Due to the fact that the transient effect may also cause an output power decrease, or fluctuation, the detected amplitude A may fluctuate over time. Therefore, the detection of the transient EVM can also be based on the amplitude, in a similar way as the above disclosed residual error calculation. In particular, the difference, E, may comprise a bias term, / ? ■ A.A, where p is a weighting factor, and where A is calculated as: where Ay is amplitude for sample x in slot y. In this way, a parameter E' , where

[0082] E' = E + p ■ Ad can be used to indicate existence of transient EVM.

[0083] There can be different ways for the radio transceiver device to act once the transient EVM has been detected. In some embodiments, the radio transceiver device 200 is configured to perform (optional) step S116.

[0084] S116: The radio transceiver device 200 initiates an action when the transient EVM exceeds a predetermined threshold level.

[0085] There can be different types of such actions. In some non-limiting examples, the action pertains to at least one of: reporting of transient EVM to a control unit, or network function (such as a control unit or a network function in an operations and maintenance system), of the radio transceiver device 200, performing calibration of the transmitter 210, record a waveform (and / or or other signal characteristics) of the received reference signal, etc.

[0086] Fig. 8 schematically illustrates, in terms of a number of structural units, the components of a radio transceiver device 800 according to an embodiment. Processing circuitry 810 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 910 (as in Fig. 9), e.g. in the form of a storage medium 830. The processing circuitry 810 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0087] Particularly, the processing circuitry 810 is configured to cause the radio transceiver device 800 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 830 may store the set of operations, and the processing circuitry 810 may be configured to retrieve the set of operations from the storage medium 830 to cause the radio transceiver device 800 to perform the set of operations. The set of operations may be provided as a set of executable instructions.

[0088] Thus the processing circuitry 810 is thereby arranged to execute methods as herein disclosed. The storage medium 830 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The radio transceiver device 800 may further comprise a communications (comm.) interface 820 at least configured for communications with other entities, functions, nodes, and devices. As such the communications interface 820 may comprise one or more transmitters and receivers, comprising analogue and digital components. Further, the radio transceiver device 800 comprises a transmitter 822 and a receiver 824 as disclosed above.

[0089] The processing circuitry 810 controls the general operation of the radio transceiver device 800 e.g. by sending data and control signals to the communications interface 820 and the storage medium 830, by receiving data and reports from the communications interface 820, and by retrieving data and instructions from the storage medium 830. Other components, as well as the related functionality, of the radio transceiver device 800 are omitted in order not to obscure the concepts presented herein.

[0090] The radio transceiver device 800 may be provided as a standalone device or as a part of at least one further device. For example, the radio transceiver device 800 may be provided in a node of a radio access network. Alternatively, functionality of the radio transceiver device 800 may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as a radio access network or a core network) or may be spread between at least two such network parts. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the cell than instructions that are not required to be performed in real time. Thus, a first portion of the instructions performed by the radio transceiver device 8oo may be executed in a first device, and a second portion of the of the instructions performed by the radio transceiver device 8oo may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the radio transceiver device 8oo may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a radio transceiver device 8oo residing in a cloud computational environment. Therefore, although a single processing circuitry 810 is illustrated in Fig. 8 the processing circuitry 810 may be distributed among a plurality of devices, or nodes. The same applies to the computer program 920 of Fig. 9.

[0091] Fig. 9 shows one example of a computer program product 910 comprising computer readable storage medium 930. On this computer readable storage medium 930, a computer program 920 can be stored, which computer program 920 can cause the processing circuitry 810 and thereto operatively coupled entities and devices, such as the communications interface 820 and the storage medium 830, to execute methods according to embodiments described herein. The computer program 920 and / or computer program product 910 may thus provide means for performing any steps as herein disclosed.

[0092] In the example of Fig. 9, the computer program product 910 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 910 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 920 is here schematically shown as a track on the depicted optical disk, the computer program 920 can be stored in any way which is suitable for the computer program product 910. The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

CLAIMS1. A method for transient error vector magnitude, EVM, estimation, wherein the method is performed by a radio transceiver device (200, 800), wherein the radio transceiver device (200, 800) comprises a transmitter (210, 822) and a receiver (220, 824), and wherein the method comprises: transmitting (S102), from the transmitter (210, 822), a reference signal in samples of a slot, wherein transmission of the reference signal is directly preceded by an abrupt change in transmission power by a power amplifier in the transmitter (210, 822); receiving (S104), by the receiver (220, 824), the reference signal; obtaining (S106) a value of the EVM per sample in the slot by computing a residual error per sample in the slot, wherein computing the residual errors comprises comparing the reference signal as received by the receiver (220, 824) to the reference signal as transmitted from the transmitter (210, 822); and estimating (S114) existence of transient EVM in the transmitter (210, 822) by comparing the value of the EVM for at least some of the samples in the slot to a reference.

2. The method according to claim 1, wherein the reference is a steady-state value of the EVM based on remaining samples in the slot or a steady-state value of the EVM obtained for samples in another slot.

3. The method according to claim 1, wherein the reference signal is transmitted from either a digital front-end or an analog front-end of the transmitter (210, 822).

4. The method according to claim 1, wherein the reference signal is an antenna calibration signal.

5. The method according to claim 1, wherein the reference signal is a high peak to average power ratio, or cubic metric, signal based on a Zadoff-Chu sequence.

6. The method according to claim 1, wherein, for a sample immediately preceding the samples in which the reference signal is transmitted, the power amplifier is switched off or at least has its power reduced by a predetermined amount.

7. The method according to claim 1, wherein the value of the EVM per sample is obtained after compensation of the received reference signal in terms of amplitude, phase error, and timing error.

8. The method according to claim 1, wherein the existence of transient EVM is estimated based on an average of residual errors.

9. The method according to claim 1, wherein the samples are first samples, wherein the reference signal is a first reference signal, wherein the first reference signal is transmitted in a first slot, and wherein the method further comprises: transmitting (S108), from the transmitter (210, 822), a second reference signal in samples of a second slot, wherein transmission of the second reference signal is not directly preceded by an abrupt change in transmission power by the power amplifier in the transmitter (210, 822); receiving (S110), by the receiver (220, 824), the second reference signal; obtaining (S112) a value of the EVM per second sample in the second slot by computing a residual error per sample in the second slot, wherein computing the residual errors comprises comparing the second reference signal as transmitted from the transmitter (210, 822) to the second reference signal as received by the receiver (220, 824); and wherein existence of the transient EVM is estimated by comparing the value of the EVM per sample in the first slot to the value of the EVM per sample in the second slot.

10. The method according to claim 9, wherein the transmission of the second reference signal is preceded by transmission of random data.

11. The method according to claim 8 in combination with claim 9 or 10, wherein the average is defined by a difference, E, calculated as:where e is the residual error of sample x in slot y.

12. The method according to claim 8, wherein the average is defined by a difference, E, calculated as:where e is the residual error of sample x in slot y.

13. The method according to claim 11 or 12, wherein the difference, E, comprises a bias term, / ? ■ Ad, where is a weighting factor, and where Ad is calculated as:where Ay is amplitude for sample x in slot y.

14. The method according to claim 1, wherein the method further comprises: initiating (S116) an action when the transient EVM exceeds a predetermined threshold level.

15. The method according to claim 1,4 wherein the action pertains to at least one of: reporting of transient EVM to a control unit, or network function, of the radio transceiver device (200, 800), performing calibration of the transmitter (210, 822), record a waveform of the received reference signal.

16. A radio transceiver device (200, 800) for transient error vector magnitude, EVM, estimation, the radio transceiver device (200, 800) comprising processing circuitry (810), a transmitter (210, 822) and a receiver (220, 824), the processing circuitry being configured to cause the radio transceiver device (200, 800) to:transmit, from the transmitter (210, 822), a reference signal in samples of a slot, wherein transmission of the reference signal is directly preceded by an abrupt change in transmission power by a power amplifier in the transmitter (210, 822); receive, by the receiver (220, 824), the reference signal; obtain a value of the EVM per sample in the slot by computing a residual error per sample in the slot, wherein computing the residual errors comprises comparing the reference signal as received by the receiver (220, 824) to the reference signal as transmitted from the transmitter (210, 822); and estimate existence of transient EVM in the transmitter (210, 822) by comparing the value of the EVM for at least some of the samples in the slot to a reference.

17. The radio transceiver device (200, 800) according to claim 16, further being configured to perform the method according to any of claims 2 to 15.

18. A computer program (920) for transient error vector magnitude, EVM, estimation, the computer program comprising computer code which, when run on processing circuitry (810) of a radio transceiver device (200, 800) comprising a transmitter (210, 822) and a receiver (220, 824), causes the radio transceiver device (200, 800) to: transmit (S102), from the transmitter (210, 822), a reference signal in samples of a slot, wherein transmission of the reference signal is directly preceded by an abrupt change in transmission power by a power amplifier in the transmitter (210, 822); receive (S104), by the receiver (220, 824), the reference signal; obtain (S106) a value of the EVM per sample in the slot by computing a residual error per sample in the slot, wherein computing the residual errors comprises comparing the reference signal as received by the receiver (220, 824) to the reference signal as transmitted from the transmitter (210, 822); and estimate (S114) existence of transient EVM in the transmitter (210, 822) by comparing the value of the EVM for at least some of the samples in the slot to a reference.19- A computer program product (910) comprising a computer program (920) according to claim 18, and a computer readable storage medium (330) on which the computer program is stored.

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