Correction scheme for correcting transmitter distortion

Abstract

A method includes providing (3010) to a receiver radio node (102) or obtaining (3010) from the correcting transmission errors of the data units. The correction scheme (750) includes the transmitter radio node (101) providing, to the receiver radio node (102), a component (313) of at least one signal (312) of the multiple signals affected by a transmitter distortion.

Description

[0001] D E S C R I P T I O N

[0002] CORRECTION SCHEME FOR CORRECTING TRANSMITTER DISTORTION TECHNICAL FIELD

[0003] Various examples of the disclosure generally relate to a correction scheme for correcting transmitter distortion such as clipping. Various examples of the disclosure specifically pertain to providing, to a receiver radio node, a component of a previously transmitted signal, which component is affected by the distortion.

[0004] BACKGROUND

[0005] The peak-to-average power ratio (PAPR) of a transmitted signal encoding one or more data units is typically limited the transmission power of a transmitter (TX) radio node: The power amplifier (PA) of an analog frontend (AFE) of the TX radio node clips the signal if the peak power level exceeds the saturation level of the PA. Such clipping of the signal is an example of a transmitter distortion, i.e. , a distortion of the transmitted signal stemming from processes at the TX radio node. A transmitter distortion is different than a channel distortion, i.e., a distortion of the signal resulting from the radio channel.

[0006] The clipping on the signal I waveform causes distortion of the received power and leads to a reduced signal-to-interference and noise (SI NR) at the RX radio node. This can cause a decoding error when decoding the signal to recover the one or more data units. In short, the transmission of the one or more data units fails (failed transmission).

[0007] To avoid this issue, it is possible to lower the TX power employed at the TX radio node. This, however, reduces the signal coverage. This may not always be an option, e.g., if the radio channel introduces significant loss.

[0008] To correct the failed transmission, the RX radio node can provide a negative acknowledgement (NACK) to the TX radio node. This triggers a hybrid automatic repeat request (HARQ) retransmission of the one or more data units encoded by the corrupted signal. The HARQ retransmission is typically implemented using a lower modulation and coding scheme (MCS). The MCS defines how many useful bits can be transmitted per resource element. Alternatively or additionally, another error correction can be applied, e.g., increasing the number of recovery bits, etc. Another redundancy version of the one or more data units may be subject to the HARQ retransmission. All this reduces the data throughput.

[0009] SUMMARY

[0010] Accordingly, a need exists for advanced techniques to correct corrupted signals. A need exists for advanced correction schemes for correcting transmitter distortions.

[0011] This need is met by the features of the independent claims. The features of the dependent claims define embodiments.

[0012] Hereinafter, techniques associated with a correction scheme to enable correction of failed transmissions due transmitter distortions are disclosed. The disclosed techniques enable large TX powers leading to clipping of a signal. Such clipping can be corrected using the correction scheme. Also, other types of distortions can be corrected.

[0013] A method of operating a TX radio node is disclosed. The TX radio node transmits, to an RX radio node, multiple signals. The multiple signals encode data units. The method includes providing to the RX radio node or obtaining from the RX radio node an indication of a configuration of a correction scheme. The correction scheme is for correcting transmission errors of data units. The correction scheme includes the transmitter radio node providing, to the receiver radio node, a component of at least one signal of the multiple signals. The at least one signal is affected by a transmitter distortion.

[0014] A TX radio node is disclosed. The TX radio node includes at least one processor configured to execute such method as disclosed above.

[0015] A method of operating an RX radio node is disclosed. The RX radio node receives, from a TX radio node, multiple signals encoding data units. The method includes providing to the TX radio node or obtaining from the TX radio node an indication of a configuration of a correction scheme. The correction scheme is for correcting transmission errors of the data units. The correction scheme includes the RX radio node obtaining, from the TX radio node, a component of at least one signal of the multiple signals that is affected by a transmitter distortion.

[0016] An RX radio node is disclosed. The RX radio node includes at least one processor configured to execute such method as disclosed above.

[0017] A method for use in a transmitter radio node is disclosed. The method includes obtaining one or more data units. The method also includes forming a signal encoding the one or more data units. The method also includes transmitting a distorted version of the signal to a receiver node. The method also includes obtaining, from the receiver radio node, a negative acknowledgement of the one or more data units. The method also includes, upon obtaining the negative acknowledgement of the one or more data units, providing, to the receiver radio node, an indication of a distortion component of the distorted version of the signal. The distortion component may include a clipped-off component of the distorted version of the signal. The indication may comprise be a compressed representation of the distortion component.

[0018] A method for use in a receiver radio node is disclosed. The method includes receiving, from a transmitter radio node, a distorted version of a signal, the signal encoding one or more data units. The method also includes attempting to decode the one or more data units based on the distorted version of the signal. The method further includes, upon said decoding failing, providing, to the transmitter radio node, a negative acknowledgement of the one or more data units. The method further includes obtaining, from the transmitter radio node, an indication of a distortion component of the distorted version of the signal. The method further includes attempting to decode the one or more data units based on the distorted version of the signal in combination with the distortion component.

[0019] It is to be understood that the features mentioned above and those yet to be explained below may be used not only in the respective combinations indicated, but also in other combinations or in isolation without departing from the scope of the invention.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 schematically illustrates a communication system including a transmitter radio node and a receiver radio node according to various examples.

[0022] FIG. 2 schematically illustrates a communication protocol stack including multiple layers according to various examples.

[0023] FIG. 3 schematically illustrates a signal according to various examples. FIG. 4 schematically illustrates a clipped-off version of the signal of FIG. 3 according to various examples.

[0024] FIG. 5 schematically illustrates the clipping component of the clipped-of version of the signal of FIG. 3.

[0025] FIG. 6 schematically illustrates an Automatic Repeat Request (ARQ) retransmission of a data unit using a different redundancy version of that data unit.

[0026] FIG. 7 schematically illustrates a correction scheme including the transmitter radio node providing, to the receiver radio node, a component of a signal that is affected by a transmitter distortion according to various examples.

[0027] FIG. 8 schematically illustrates data throughput according to various examples.

[0028] FIG. 9 schematically illustrates data throughput according to various examples.

[0029] FIG. 10 is a flowchart of a method for use in a transmitter node according to various examples.

[0030] FIG. 11 is a flowchart of a method for use in a receiver node according to various examples.

[0031] DETAILED DESCRIPTION

[0032] Some examples of the present disclosure generally provide for a plurality of circuits or other electrical devices. All references to the circuits and other electrical devices and the functionality provided by each are not intended to be limited to encompassing only what is illustrated and described herein. While particular labels may be assigned to the various circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits and the other electrical devices. Such circuits and other electrical devices may be combined with each other and / or separated in any manner based on the particular type of electrical implementation that is desired. It is recognized that any circuit or other electrical device disclosed herein may include any number of microcontrollers, a graphics processor unit (GPU), integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read only memory (ROM), electrically programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), or other suitable variants thereof), and software which co-act with one another to perform operation(s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute a program code that is embodied in a non-transitory computer readable medium programmed to perform any number of the functions as disclosed.

[0033] In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. It is to be understood that the following description of embodiments is not to be taken in a limiting sense. The scope of the invention is not intended to be limited by the embodiments described hereinafter or by the drawings, which are taken to be illustrative only.

[0034] The drawings are to be regarded as being schematic representations and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose become apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components, or other physical or functional units shown in the drawings or described herein may also be implemented by an indirect connection or coupling. A coupling between components may also be established over a wireless connection. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

[0035] Hereinafter, aspects with respect to a wireless communication system are disclosed. The wireless communication system includes a TX radio node transmitting signals that encode data units. The wireless communication system also includes an RX radio node receiving the signals. An example communication system is illustrated in FIG. 1.

[0036] FIG. 1 schematically illustrates a communication system 100. The communication system may be an Orthogonal Frequency Division Multiplex (OFDM) communication system.

[0037] The communication system 100 includes a TX radio node 101, e.g., a wireless communication device (UE) connected to a cellular network or a base station (BS) of the cellular network. The TX radio node 101 includes a compute circuitry that includes a processor 1011 and a memory 1015. The TX the radio node 101 also includes a communication interface 1012. The communication interface 1012 is configured to implement a communication protocol stack including multiple layers. The multiple layers may be classified in accordance with the Open System Interface (OSI) model. The communication interface 1012 is configured to transmit using OFDM. The communication interface 1012 includes a digital front end (DFE) as well as an AFE. To implement an OFDM transmission, an inverse Fast Fourier Transform (IFFT) operation may be executed at the DFE. The AFE includes a PA configured to amplify an analog signal encoding data. The output of the PA is coupled to an antenna array 1013 including multiple antennas 1014. It is not required in all scenarios that multiple antennas / an antenna array are provided.

[0038] The communication system 100 also includes a RX radio node 102. The RX radio node 102 includes a compute circuitry that includes a processor 1021 and a memory 1025. The RX radio node 102 also includes a communication interface 1022. The communication interface 1022 is configured to implement a communication protocol stack corresponding to the communication protocol stack implemented by the communication interface 1012 implemented by the TX radio node 101. The communication interface 1022 includes an AFE as well as DFE. To implement OFDM, the DFE is configured to execute a Fast Fourier Transform (FFT) operation. The communication interface 1022 is coupled to a single antenna 1024; but it would be equally possible that multiple antennas are provided in an antenna array.

[0039] FIG. 2 schematically illustrates a communication protocol stack 250 including multiple layers 251 , 252, 253, 254, 255.

[0040] The communication protocol stack 250 includes a Layer 1 251, the so-called physical layer. The physical layer accesses the radio channel 290. The physical layer generates time samples of a signal that is transmitted via the radio channel 290. The physical layer processing is at least partly implemented by a DFE and AFE. The signal is determined to encode one or more data units carrying higher-layer data, e.g., Layer 2 or Layer 3 data. A modulation scheme is used to determine the signal. This signal is then converted to the analog domain using an analog-to-digital converter. The analog signal is then amplified using a power amplifier and fed to one or more antennas. All this happens at the AFE. The communication protocol stack 250 also includes Layer 2 functionality provided by the Medium Access (MAC) layer 252 and the Radio Link Control (RLC) layer 253. The RLC layer 253 provides for one or more of the following functionalities: error correction, segmentation and reordering of data units , scheduling, etc.. The MAC layer 252 provides for one or more of the following functionalities: control of access to the physical transmission medium, framed the limiting and recognition; etc.

[0041] Next, Layer 3 is implemented by the Packet Data Convergence Protocol (PDCP) layer

[0042] 254 which provides one or more of the following functionalities: transfer of application data and control data; header compression such as robust header compression (RoHC); Access Stratum (AS) level encryption. Layer 3 is also implemented by the Radio Resource Control (RRC) layer

[0043] 255 which provides for control signaling functionality between the TX radio node 101 and the RX radio node 112.

[0044] Hereinafter, aspects of a correction scheme to correct transmission errors resulting in a failed transmission of one or more data units are disclosed. Specifically a correction scheme is disclosed to correct decoding errors at an RX node attempting to decode one or more data units encoded by a received signal. More specifically, the correction scheme corrects transmitter distortions of the signal, i.e., distortions occurring at theAFE of the TX radio node 101. Thus, the distortion scheme may be referred to as distortion correction scheme (DCS). The DCS is an alternative to the conventional HARQ retransmission protocol, as will be shown in detail below.

[0045] While, as a general rule, various types of distortion can be corrected using the DCS, hereinafter, for sake of simplicity, reference is being made to clipping-type distortions. Here, a signal is clipped at the TX radio node. In particular, the signal is clipped at the AFE of the TX radio node. This may be due to the PA of the AFE saturating.

[0046] FIG. 3 illustrates a signal 311. For example, the signal 311 may be present at the DFE of the communication interface 1012. The signal 311 is defined by time-domain samples 321 , 322. The signal 311 does not include distortions. The signal 311 encodes one or more data units, for instance one or more MAC packet data units (PDUs) or transport blocks.

[0047] For instance, the signal 311 in FIG. 3 may have the following time-domain samples:

[0048] TAB. 1 : Table of time position of time-domain samples 321 , 322 as well as associated amplitude values for the signal illustrated in FIG. 3.

[0049] FIG. 4 illustrates concepts with respect to TX distortion. FIG. 4 illustrates an example signal 312 at the AFE of the communication interface 1012. The signal 312 is obtained from the signal 311 , after digital-to-analog conversion and after amplification at an PA of the AFE. The signal 312 is a clipped version of the signal 312. Thus, the signal 312 may be labeled clipped signal (CS) 312. The peaks of the CS 312 are clipped / cropped. Respective clipping thresholds 399 are shown. The clipping thresholds 399 result from hardware limitations of the PA of the AFE. Thus, information carried by the time samples 322 (dotted lines in FIG. 3) is lost and not conveyed by the CS 312 to the RX radio node 102. The CS 312 still encodes the one or more data units. However, the risk of decoding of the one or more data units failing is increased due to the clipping-type transmitter distortion.

[0050] Note that FIG. 4 only illustrates a simple example of a TX distortion and manifold of the TX distortions are conceivable. FIG. 4 aims at explaining the concept of TX distortion rather than providing a comprehensive overview of all possible TX distortions that may be encountered.

[0051] The signal 312 in FIG. 4 would be described by the following time-domain samples (assuming a clipping threshold 399 of 0,9 and -0,9, respectively; note that the time domain samples are not shown in FIG. 4):

[0052] TAB. 2: Table of time position of time-domain samples as well as associated amplitude values for the signal 312 illustrated in FIG. 4. The values marked with * are clipped.

[0053] FIG. 5 illustrates a component 313 of the CS 312 that is clipped-off at the AFE of the communication interface 1012. This will be referred to as clipped-off component (CO) 313. The CO 313 is accordingly resembling that part of the CS 312 that is affected by the clipping.

[0054] Then, the CC 313 as illustrated in FIG .5 would be:

[0055]

[0056] TAB. 3: Table of time position of time-domain samples as well as associated amplitude values for the CC 313 illustrated in FIG. 5. The CC 313 is a signal that needs to be specifically determined or calculated; it is not inherently present when transmitting the signal 312.

[0057] Assuming the original signal 311 is Si, and its CS 312 and the CC 313 is e . Then:

[0058] Equation 1 Thus, a sum of the CC 313 and the CS 312 yields the signal 311.

[0059] The TX radio node 101 may in some scenarios select a TX power that is so high that the CS 312 Si is transmitted. This is due to the saturation of the PA. In this case, if the distortion is too severe, a decoding failure 680 will show at the RX radio node 102. A decoding failure (or more generally a transmission failure) may be detected at Layer 2, e.g., at the MAC layer 252 (cf. FIG. 2). A decoding failure may be detected based on check-bits (CRC).

[0060] When a HARQ retransmission scheme is employed according to reference techniques, one or more data units encoded by the signal 311 for which the transmission failed are retransmitted using another MCS: cf. FIG. 6 where responsive to a negative acknowledgement 601 another signal S2is transmitted, using a HARQ retransmission scheme 640.

[0061] According to disclosed examples, different than in such a HARQ retransmission scheme 740, the TX node 101 - when participating in the DCS 750 - provides, to the RX radio node 102, the CC 313 This may be triggered by obtaining a NACK 601 for the one or more data units. This is shown in FIG. 7. The RX radio node 102 can then - based on a combined consideration of the CC 313 e! and the CS 312 - decode the one or more data units. The variant of FIG. 7 - employing the DCS 750 - requires significantly fewer resources and power consumption at the TX radio node 101 if compared to the reference scenario of FIG. 6 employing the HARQ retransmission scheme 740. This is detailed next.

[0062] An analysis of the gains of providing the clipped component 313 is provided below. Assume an input x to the PA, and let the output be g(x). One may decompose said function into two parts, one ideal amplification and one nonlinear distortion. This can be expressed as g(x) = Af(x), where f (x) represents the non-linearity.

[0063] Under assumption that the number of subcarriers in an OFDM-based communication system (cf. FIG. 1) is large, the time-domain signal at the input of the nonlinear part of the PA at the TX radio node may be described, in the complex baseband, as a zero-mean complex Gaussian signal with variance P and whose samples are uncorrelated; this signal is denoted by the vector s. The nonlinear part of the PA transforms this signal by the memoryless map f (•), into the signal sc= f(s). In numerical examples to follow, the simple model is used:

[0064] Equation 2

[0065] This corresponds to the case illustrated in FIG. 3, FIG. 4, and FIG. 5.

[0066] As a general rule, an arbitrary f (x) may be used, as long it is known to the TX and RX radio nodes.

[0067] First, the data rate achievable in a reference implementation according to FIG. 6 using a HARQ retransmission scheme 740 is discussed. By standard Bussgang decomposition theory, one max express scas sc= Bos + n, where Bois known as the Bussgang gain and where n, which has power NB, is noise uncorrelated with the signal s. In a legacy system, the received signal (in a line-of-sight scenario) may be described as r = sc+ vv = BQS + n + w

[0068] Equation 3 where w is thermal noise added with power Noat the RX radio node. As the power of s has been assumed to be P, we have that the capacity per sample equals

[0069] Equation 4

[0070] In the case of a decoding failure, the TX radio node transmits all data units encoded by the initial signal in a further signal. This implies that the combined signal (original signal and further signal) is limited to a power gain of a factor 2. Thus, after one re-transmission, the data rate is:

[0071] Equation 5 Second, the data rate achievable using the DCS 750 as illustrated in FIG. 7 is discussed. Here, instead of a re-transmission of all failed data units, the CC 313 of the CS 312 is transmitted: e = s - sc. Assume that b bits per sample is used to represent the signal e. With that, the RX radio node observes a signal e = e + z

[0072] Equation 6 where z is noise with a power Nzthat depends on b. It is now possible combine the signal scwith e and apply Bussgang decomposition. This yields r = sc+ e + iv = B±s + n + w

[0073] Equation 7 where B is the Bussgang gain related to the nonlinear map between s and sc+ e and where n is the noise thereof (with power Ninv). The capacity becomes

[0074] Equation 8

[0075] The advantage of transmitting the CC 313 is apparent by comparing the rates Cinv, CHARQ, and Coand noting that Cinvis far superior in many cases of practical interest.

[0076] But before turning to that, the number of bits b required to represent e as e is discussed. For each sample in s, there is a probability p that the signal will be distorted. The TX radio node may indicate, to the RX radio node, which samples have undergone such distortion (these are the samples 322 in FIG. 3, but not the samples 321). I.e., a compressed representation of the CC 313 is determined and provided to the RX radio node:

[0077] TAB. 4: Compressed representation of the CC 313 illustrated in FIG. 5. In TAB. 4, the clipping thresholds 399 of + / - 0,9 are taken as baseline for the amplitude values (which is optional). The compressed representation includes a first list of those samples of the CS 312 that are affected by the transmitter distortion (first column) and a second list of respective amplitude values (second column). The CC 313 requires significantly fewer bits to be represented if compared to the CS 312, due to time domain sparsity of the clipped samples.

[0078] To do this, / i(p) bits / sample are required, where / i(p) is the binary entropy function. For all indicated samples, the values in e can be represented with b bits per sample (i.e. , br / 2 per real / imaginary dimension). A quantizer optimized so that all bit quantizer outputs are equiprobable. Thus, a compressed representation of the clipped component exploiting timedomain sparsity of the CC 313 (cf. TAB. 4) requires b = h(p) + pb-

[0079] Equation 9 bits / sample on average.

[0080] In the expression for the capacity Cinv- see Equation 8 - it has been implicitly assumed that these b bits / sample of the data unit(s) can be provided to the RX radio node without corruption or risk of failure, e.g., due to channel distortions. Thus, a secondary transmission with capacity Cois required. To avoid loss, Co> b. This is now exemplified for ? = Pc= 1. This implies that the saturation point of the PA is precisely that of the mean intended transmit power and implies that no power backoff is needed in the PA. FIG. 8 illustrates the resulting rate Co(where all Bussgang related quantities have been numerically established) as well as the rates h(p) + pb±for different b . It can be seen that the channel may only support the required feedback for b and that P / No> 11 dB is required. For b , all rates are plotted in FIG. 9. As the proposed method can only be used at the regime P / N_0>11 dB, the data rate in said regime is shown only. It is clearly seen that the DCS 750 substantially outperforms the HARQ retransmission scheme 740 .

[0081] FIG. 10 is a flowchart of a method according to various examples. The method of FIG. 10 may be executed by a TX radio node of a communication system. For example, the TX radio node may be a UE that is connected to a cellular network. The TX node may be a BS of the cellular network. The method of FIG. 10 may be executed by a compute circuitry of the TX node. The method of FIG. 10 may be executed by at least one processor upon loading program code from a memory and upon executing the program code. For instance, the method of FIG. 10 may be executed by the processor 1011 of the TX radio node 101 upon loading and executing program code that is stored in the memory 1015.

[0082] FIG. 10 illustrates aspects for executing a correction scheme for correcting transmission errors when transmitting data units from the TX radio node to an RX radio node. Specifically, transmitter- distortions can be corrected. FIG. 10 illustrates aspects of an DCS 750. The DCS 750 includes providing, by the TX radio node and to the RX radio node, a component of the signal that is affected by the distortion.

[0083] At box 3005, an indication of the RX radio node supporting the DCS 750 is obtained. Box 3005 may include capability signaling. For example, the RX radio node may indicate whether it is able to decode one or more data units based on, both, an CS 312 as well as the respective CC 313.

[0084] At box 3010, a configuration of the DCS 750 is determined, e.g., under the condition that both the RX radio node as well the TX radio node support the DCS 750. Box 3010 may include providing, to the RX radio node, a configuration of the DCS. Alternatively or additionally, box 3010 may include obtaining, from the RX radio node, the configuration of the DCS. The configuration may be negotiated. Unidirectional or bidirectional control signaling can be employed. For instance, a Layer 3 control message may be communicated, the control message being indicative of the configuration. For instance, an RRC control message may be communicated. For instance, a pointer may be provided, the pointer being indicative of one selected configuration of multiple candidate configurations that are preconfigured in accordance with the communication protocol.

[0085] It is not required in all scenarios that the configuration is communicated. In some scenarios, the configuration may be fixedly predefined. As such, box 3010 is optional.

[0086] The configuration the DCS 750 may be indicative of a compression scheme used for determining a compressed representation of the CC 313. Based on the compression scheme, the compressed representation of the CC can be determined (cf. TAB. 4).

[0087] The configuration of the DCS may - alternatively or additionally - be indicative of one or more criteria that trigger an activation of the DCS. Such criteria that trigger the activation of the DCS may, in particular, include a power headroom level determined for the RX radio node. Such one or more criteria are checked at box 3035, i.e. , upon detecting a transmission error. Thus, these one or more criteria may be labeled ad-hoc criteria for activating the DCS, because they are checked upon detecting the transmission error. It is not required to use ad-hoc activation of the DCS; the DCS may also be statically activated.

[0088] It is possible to enable or disable the DCS at box 3010. The configuration at box 3010 may enable the DCS. This means that based on the configuration the TX radio node as well as the RX radio node are then allowed to participate in the DCS (e.g., if activated using ad-hoc activation). For instance, if the RX radio node is not able to participate in the DCS 750, the DCS 750 may be disabled and, e.g., HARQ retransmission scheme 740 is used instead.

[0089] At box 3020, it is determined whether the DCS is generally enabled or disabled. For instance, the configuration of box 3010 may be indicative of the DCS being enabled. If this is not the case, the method commences using techniques out of scope of the subject disclosure, typically employing a HARQ retransmission scheme 740 to correct transmission errors. Otherwise, the method commences at box 3025.

[0090] At box 3025, the TX radio node transmits one or more CSs (such as the CS 312) that encode one or more data units to the RX radio node.

[0091] Box 3025 includes determining a redundancy version of the one or more data units, including error protection codes, at Layer 2 (cf. FIG. 2: e.g., at the MAC layer 252). This yields a bit sequence to be transmitted, handed over to Layer 1. Box 3025 also includes determining a signal using a modulation scheme and based on the bit sequence, e.g., at the Physical Layer 251. For an OFDM-based communication system, the signal includes multiple parts for multiple subcarriers. Then, an analog representation of the signal is determined and amplified. This leads to distortion, specifically clipping parts of the signal.

[0092] The signal is fed to one or more antennas. The RX radio node then receives the signal, being further modified by the radio channel. The RX radio node demodulates the signal and then attempts to decode the one or more data units.

[0093] At box 3030, it is determined whether the transmission of the one or more data units succeeded. In other words, it is determined whether a transmission error is present for the one or more data units that are encoded by the one or more signals transmitted at box 3025. A transmission error may be detected.

[0094] Box 3030 defines an iteration 3037: For each iteration 3031 of box 3025, there may be multiple iterations 3037 of determining, at box 3030, whether the transmission succeeded for the presently handled one or more data units.

[0095] For instance, box 3030 can include obtaining, at the TX radio node from the RX radio node, a negative acknowledgment for the one or more data units. For instance, a Layer 2 control message being indicated for such negative acknowledgment may be obtained. Typically, a MAC control message may be obtained. Alternatively or additionally, box 3030 can include not obtaining - e.g., within a certain timeout duration - a positive acknowledgment for the one or more data units from the RX radio node. The positive acknowledgment may be conveyed by an MAC control message or more generally a Layer 2 control message.

[0096] As will be appreciated, the presence or absence of a transmission error may be determined with respect to the encoded one or more data units rather than with respect to the transmitted one or more signals.

[0097] If the transmission succeeded, box 3025 may be re-executed in a further iteration 3031. I.e., it is possible to transmit further one or more signals encoding further one or more data units. However, if the transmission is not succeeded, the method commences at box 3035.

[0098] At box 3035, it is determined whether the DCS 750 is to be used, i.e., it is determined whether the DCS 750 is activated. Box 3035 is an optional box: in some examples, it would be possible that once configured, the DCS 750 is always activated upon detecting a transmission failure.

[0099] In other examples, it would be possible to determine whether one or more criteria are met. These one or more criteria to check at box 3035 could be configured at box 3010 or may be pre-configured. Example criteria may include a power headroom level at the TX radio node; the TX radio node can inform the RX radio node whether a power headroom is available. Other criteria include the iteration number of the iteration 3037. For instance, a first iteration may employ a HARQ retransmission while a second iteration may employ the DCS.

[0100] Yet another criteria may include an explicit request obtained from the RX radio node. For instance, a NACK of the one or more data units may be obtained from the RX radio node. This negative acknowledgment may be indicative of a request for providing the CC, i.e., may be indicative of a request to participate in the DCS 750.

[0101] If it is judged at box 3035 that the DCS scheme is not to be used, the method commences at box 3036. At box 3036, a retransmission of the one or more data units for which transmission failed is executed using a HARQ retransmission scheme 740. This is implemented using HARQ retransmission. A different MCS may be used. A different redundancy version of the one or more data units may be determined. An entirely new Layer 1 signal may be determined. As will be appreciated, box 3036 implements a retransmission on the level of the one or more data units. All bits of the one or more data units are re-transmitted. The RX radio node can decode the one or more data units based on that new signal alone, i.e., does not require the earlier transmitted CS. This is different for the DCS 750 where a part I component (the CC) of the initially transmitted CS is transmitted without a need to implement Layer 2 processing of the one or more data units. Rather, samples of the signal may be processed, e.g. at Layer 2, as will be shown in detail in connection with box 3040. The RX radio node needs, both, the CS as well as the CC to be able to decode the one or more data units.

[0102] If it is judged at box 3035 that the DCS 750 is to be used, then, at box 3040, the TX radio node participates in the DCS 750 to correct the transmission error. The TX radio node participates in the DCS based on the configuration determined at box 3010.

[0103] Such participating in the DCS may include - box 3050- providing the CC of the one or more signals transmitted at box 3025 to the RX radio node. It would be possible that a compressed representation of the CC is provided to the RX radio node. Details have been discussed in connection with TAB. 4.

[0104] Such participating in the DCS may include - box 3045 - determining the CC. The CC may be determined based on a feedback signal from the AFE of the TX radio node. The feedback signal may be indicative of the clipping threshold 399. The clipping threshold 399 may also be known.

[0105] Once the CC or specifically its compressed representation has been determined at box 3035, it is possible to inject respective data representing the CC into the data stream that is transmitted at Layer 2. Thus, the compressed representation of the CC 313 can be provided in a Layer 2 packet. It would also be possible implement all this at Layer 1. The time-frequency resources in which the CC or specifically its compressed representation is transmitted can be indicated by the Layer 1 , e.g., using a scheduling message; cf. box 3055.

[0106] A practical implementation of FIG. 10 is provided next: the TX radio node 101 is a UE connected to a cellular network. The RX radio node 102 is a BS of the cellular network. For instance, the UE and the BS can operate in accordance with the Third Generation Partnership Project (3GPP) New Radio (NR) 5G transmission protocol. The UE may operate at the cell edge (corresponding to strong losses on the radio channel). The BS may be aware of the UE being enabled to transmit the CC employing the DCS 750 (instead of a HARQ retransmission 740 as shown in FIG. 6), based on a respective configuration provided by the UE to the BS (box 3010). The ad-hoc decision to employ the DCS 750 instead of the HARQ retransmission 740 (cf. box 3035) can be based on a power headroom report, e.g., a negative power headroom. When the BS fails to decode the uplink signal (cf. CS 312) from the UE, the BS provides a negative acknowledgement that is indicative of a request to provide the clipped component 313 of the signal 312.

[0107] FIG. 11 is a flowchart of a method according to various examples. The method of FIG. 11 may be executed by an RX node of a communication system. For example, the RX node may be a UE that is connected to a cellular network. The RX node may be a base station of the cellular network. The method of FIG. 11 may be executed by a compute circuitry of the RX node. The method of FIG. 11 may be executed by at least one processor upon loading program code from a memory and upon executing the program code. For instance, the method of FIG. 11 may be executed by the processor 1021 of the RX radio node 102 upon loading and executing program code that is stored in the memory 1025.

[0108] FIG. 11 illustrates aspects for executing a correction scheme for correcting transmission errors when transmitting data units from a TX radio node to the RX radio node. Specifically, transmitter distortions can be corrected. FIG. 11 illustrates aspects of a DCS 750. The DCS 750 includes obtaining, at the RX radio node and from the TX radio node, a component of the signal that is affected by the distortion.

[0109] FIG. 11 is interrelated to the method of FIG. 10. I.e., the methods of FIG. 10 and FIG. 11 can be jointly executed at the TX radio node and the RX radio node, respectively.

[0110] At box 3105, an indication of the RX radio node supporting the DCS 750 is provided.

[0111] Box 3105 corresponds to box 3005.

[0112] At box 3110, a configuration of the DCS 750 is determined, e.g., under the condition that both the RX radio node as well as the TX radio node support the DCS 750. Box 3110 may include obtaining, from the TX radio node, a configuration of the DCS. Alternatively or additionally, box 3110 may include providing, to the TX radio node, the configuration of the DCS. The configuration may be negotiated. Box 3110 corresponds to box 3010.

[0113] At box 3120, it is determined whether the DCS is generally enabled or disabled. Box 3120 corresponds to box 3020.

[0114] At box 3125, the RX radio node receives those one or more CSs transmitted by the TX radio node. This includes physical layer processes. A waveform is received. The RX radio node demodulates the signal and then attempts to decode the one or more data units. Box 3125 corresponds to box 3025.

[0115] At box 3130, it is determined whether the transmission of the one or more data units succeeded. In other words, it is determined whether a transmission error is present for the one or more data units that are encoded by the one or more signals transmitted at box 3125. A transmission error may be detected. This may be based on check sums checked at the RX radio node. Layer 2 processing can be executed. Box 3130 corresponds to box 3030.

[0116] Box 3130 defines an iteration 3137: For each iteration 3131 of box 3125, there may be multiple iterations 3137 of determining, at box 3130, whether the transmission succeeded for the presently handled one or more data units.

[0117] For instance, box 3130 can include providing, to the TX radio node from the RX radio node, a negative acknowledgment for the one or more data units. For instance, a Layer 2 control message being indicated for such negative acknowledgment may be obtained. Typically, a MAC control message may be provided.

[0118] If the transmission succeeded, box 3125 may be re-executed in a further iteration 3131. I.e., it is possible to transmit further one or more signals encoding further one or more data units. However, if the transmission is not succeeded, the method commences at box 3135.

[0119] At box 3135, it is determined whether the DCS 750 is to be used, i.e., it is determined whether the DCS 750 is activated. Box 3135 is an optional box: in some examples, it would be possible that once configured, the DCS 750 is always activated upon detecting a transmission failure. Box 3135 corresponds to box 3035.

[0120] If it is judged at box 3135 that the DCS scheme is not to be used, the method commences at box 3136. At box 3136, a retransmission of the one or more data units for which transmission failed is executed using a HARQ retransmission scheme 740. Box 3136 corresponds to box 3036.

[0121] If it is judged at box 3135 that the DCS 750 is to be used, then, at box 3140 (corresponding to box 3040), the RX radio node participates in the DCS 750 to correct the transmission error. The RX radio node participates in the DCS based on the configuration determined at box 3110.

[0122] Such participating in the DCS may include - box 3150- obtaining the CC of the one or more signals transmitted at box 3125 from the TX radio node. It would be possible that a compressed representation of the CC is provided by the TX radio node. Details have been discussed in connection with TAB. 4.

[0123] The time-frequency resources in which the CC or specifically its compressed representation is transmitted can be indicated by the Layer 1, e.g., using a scheduling message; cf. box 3155.

[0124] Box 3140 also includes undistorting any distorted CSs based on the CCs, box 3160. This can be based on a combination I summation of the respective samples, e.g., at Layer 1.

[0125] Summarizing, at least the following EXAMPLES have been disclosed.

[0126] EXAMPLES

[0127] EXAMPLE 1. A method of operating a transmitter radio node (101) that transmits, to a receiver radio node (102), multiple signals encoding data units, wherein the method comprises:

[0128] - providing (3010) to the receiver radio node (102) or obtaining (3010) from the receiver radio node (102) an indication of a configuration of a correction scheme (750) for correcting transmission errors of the data units, the correction scheme (750) comprising the transmitter radio node (101) providing, to the receiver radio node (102), a component (313) of at least one signal (312) of the multiple signals affected by a transmitter distortion.

[0129] EXAMPLE 2. The method of EXAMPLE 1 , further comprising:

[0130] - upon detecting (3030) a transmission error of at least one data unit, participating (3040), in accordance with the configuration, in the correction scheme (750) to correct the transmission error.

[0131] EXAMPLE S. The method of EXAMPLE 2, wherein said participating (3040) in the correction scheme (750) comprises providing (3050), to the receiver radio node (102), a compressed representation of the component (313) of the at least one of the signals (312).

[0132] EXAMPLE 4. The method of EXAMPLE 3, wherein the compressed representation exploits a time-domain sparsity of the component (313) of the at least one of the signals (312).

[0133] EXAMPLE 5. The method of any one of EXAMPLE 3 or 4, wherein the compressed representation comprises a list of those samples of the at least one signal (312) that are affected by the transmitter distortion, wherein the compressed representation comprises a further list of amplitude values for each of the sample included in the list.

[0134] EXAMPLE 6. The method of any one of EXAMPLES 3 to 5, wherein the configuration is indicative of a compression scheme used for determining the compressed representation.

[0135] EXAMPLE 7. The method of any one of the preceding EXAMPLES, further comprising:

[0136] - obtaining (3030), from the receiver radio node 102, a negative acknowledgement (601) for the at least one data unit, the negative acknowledgement (601) being indicative of a request for providing the component (313) of the at least one signal (312) affected by the transmitter distortion.

[0137] EXAMPLE 8. The method of any one of the preceding EXAMPLES, wherein the configuration is indicative of the correction scheme (750) being enabled.

[0138] EXAMPLE 9. The method of any one of the preceding EXAMPLES, wherein the configuration is indicative of one or more criteria causing an activation of the correction scheme.

[0139] EXAMPLE 10. The method of EXAMPLE 9, wherein the one or more criteria that cause the activation of the correction scheme comprise a power headroom level.

[0140] Although the invention has been shown and described with respect to certain preferred embodiments, equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such equivalents and modifications and is limited only by the scope of the appended claims.

Claims

C L A I M S1. A method of operating a transmitter radio node (101) that transmits, to a receiver radio node (102), multiple signals encoding data units, wherein the method comprises:- providing (3010) to the receiver radio node (102) or obtaining (3010) from the receiver radio node (102) an indication of a configuration of a correction scheme (750) for correcting transmission errors of the data units, the correction scheme (750) comprising the transmitter radio node (101) providing, to the receiver radio node (102), a component (313) of at least one signal (312) of the multiple signals affected by a transmitter distortion.

2. The method of claim 1 , further comprising:- upon detecting (3030) a transmission error of at least one data unit, participating (3040), in accordance with the configuration, in the correction scheme (750) to correct the transmission error.

3. The method of claim 2, wherein said participating (3040) in the correction scheme (750) comprises providing (3050), to the receiver radio node (102), a compressed representation of the component (313) of the at least one of the signals (312).

4. The method of claim 3, wherein the compressed representation exploits a time-domain sparsity of the component (313) of the at least one of the signals (312).

5. The method of any one of claim 3 or 4, wherein the compressed representation comprises a list of those samples of the at least one signal (312) that are affected by the transmitter distortion, wherein the compressed representation comprises a further list of amplitude values for each of the sample included in the list.

6. The method of any one of claims 3 to 5, wherein the configuration is indicative of a compression scheme used for determining the compressed representation.

7. The method of any one of the preceding claims, further comprising:- obtaining (3030), from the receiver radio node 102, a negative acknowledgement (601) for the at least one data unit, the negative acknowledgement (601) being indicative of a request for providing the component (313) of the at least one signal (312) affected by the transmitter distortion.

8. The method of any one of the preceding claims, wherein the configuration is indicative of the correction scheme (750) being enabled.

9. The method of any one of the preceding claims, wherein the configuration is indicative of one or more criteria causing an activation of the correction scheme.

10. The method of claim 9,wherein the one or more criteria that cause the activation of the correction scheme comprise a power headroom level.

11. The method of claim 9 or 10, further comprising:- upon detecting a transmission error of at least one data unit, determining (3035) whether the one or more criteria are met, and- upon determining that the one or more criteria are being met, participating (3040), in accordance with the configuration, in the correction scheme (750) to correct the transmission error.

12. The method of claim 11 , further comprising:- upon determining that the one or more criteria are not being met, providing (3036) a re-transmission of the at least one data unit to the receiver radio node (102).

13. The method of any one of the preceding claims, further comprising:- indicating (3055), to the receiver radio node (102), time-frequency resources that carry the component (313) of the at least one signal (312) affected by the transmitter distortion.

14. The method of any one of the preceding claims, further comprising:- obtaining (3005), from the receiver radio node (102), an indication of the receiver radio node (102) supporting the correction scheme (750).

15. The method of claim 14, wherein the indication of the configuration of the correction scheme is provided upon obtaining the indication of the receiver radio node supporting the correction scheme (750).

16. The method of any one of the preceding claims, wherein the transmitter distortion comprises clipping of the at least one signal at the transmitter radio node.

17. The method of any one of the preceding claims, wherein the transmitter distortion comprises distortion of the at least one signal at an analog frontend of the transmitter radio node.

18. The method of any one of the preceding claims, further comprising:- obtaining a feedback signal from an analog frontend of the transmitter radio node (101) and determining the component (313) based on the feedback signal.

19. A method of operating a receiver radio node that receives, from a transmitter radio node, multiple signals encoding data units, wherein the method comprises:- providing (3010) to the transmitter radio node or obtaining (3010) from the transmitter radio node (102) an indication of a configuration of a correction scheme (750) for correcting transmission errors of the data units, the correction scheme (750) comprising the receiver radio node (102) obtaining, from the transmitter radio node, a component (313) of at least one signal (312) of the multiple signals affected by a transmitter distortion.

20. A transmitter radio node (101) comprising a compute circuitry configured to execute the method of any one of claims 1 to 18.

21. A receiver radio node (101) comprising a compute circuitry configured to execute the method of claim 19.

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