Digital post-correction of a signal in a receiver device

Abstract

There is provided techniques for digital post-correction of a signal in a receiver device. The receiver device is adapted to compensate for impairments of a transmitter device. A method is performed by the receiver device. The method comprises receiving, in a receiver interface, the signal from the transmitter device over a wireless channel and passing the signal upstream in the receiver device. The method comprises applying digital post-correction to the signal using a set of coefficients in a digital post-correction block placed upstream the receiver interface. The method comprises filtering the signal after the digital post-correction having been applied to the signal in a filter block placed upstream the digital post-correction block. The method comprises updating, in an update block placed upstream the filter block, the set of coefficients based on the signal after the filtering having been applied to the signal.

Description

[0001] DIGITAL POST-CORRECTION OF A SIGNAL IN A RECEIVER DEVICE

[0002] TECHNICAL FIELD

[0003] Embodiments presented herein relate to a method, a receiver device, a computer program, and a computer program product for digital post-correction of a signal in the receiver device.

[0004] BACKGROUND

[0005] In communications networks, there maybe 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, the spectrum efficiency of the communications network can be increased by increasing the modulation order. For a communication device (such as a (radio) access network node or a user equipment) to reach a better transmit signal quality and to be able to transmit signals with a high modulation order, the communication device needs to either back of its transmission power or to improve the transmitted signal quality with digital predistortion, or similar. This might degrade the network coverage and / or driving the power consumption in the communication device. For a battery-operated communication device, this will also reduce the battery time. In summary, this puts tougher requirements on the communication devices.

[0007] One way to mitigate the need for these tougher requirements is to perform digital post-correction at the receiver. In this way, the tougher requirements at the transmitter can be relaxed. Digital post distortion techniques in this area have been published in the article “On Digital Post-Distortion Techniques”, by Ziv Alina and Ofer Amrani, as published in the IEEE transactions on signal processing, Vol. 64, No. 3, February, 2016 and in the article “Cellular Digital Post-Distortion: Signal Processing Methods and RF Measurements”, by Huseyin Babaroglu, Lauri Anttila, Guixian Xu, Matias Turunen, Markus Allen, and Mikko Valkama, as published in the proceedings of the 2023 IEEE Wireless and Microwave Technology Conference (WAMICON).

[0008] In general terms, digital post-correction (DPC) moves the correction of non-linear distortion of the transmitted signal as caused by non-linear components (such as power amplifiers, etc.) from the transmitter to the receiver. In Fig. 1 is schematically illustrated a communication system io comprising a first communication device (or transceiver; Tx / Rx) 20 communicating with a second communication device (or transceiver; Tx / Rx) 40 over a wireless channel 30. Assume without loss of generality that a signal is sent from the transmitter of the first communication device 20 and received by the receiver in the second communication device 40.

[0009] Operations performed at the receiver are illustrated in Fig. 2. Fig. 2 is a block diagram of a receiver 200 according to an example. In principle, at the receiver, the signal received from the transmitter is filtered, equalized, down-sampled, up- sampled, post-corrected, filtered, and down-sampled again.

[0010] Adaptation, or updating, of the coefficients of the digital post-correction is made in the up-sampled domain. In this case the adaption linearizes the up-sampled domain, as shown in the AM / AM plot in Fig. 3. As can be seen, with this adaptation the linearity is good in the up-sampled domain, but the error vector magnitude (EVM) is degraded when the signal is filtered and down-sampled. The EVM result with this type of adaptation is shown for the full constellation diagram in Fig. 4 and for the individual constellation points in Fig. 5 with and without compensation. Fig. 4 shows an in-phase (I) and quadrature (Q) diagram of the constellation points with and without compensation, and Fig. 5 shows the constellation error of the individual constellation points with and without compensation.

[0011] Hence, there is still a need for an improved receiver device.

[0012] SUMMARY

[0013] An object of embodiments herein is to provide a receiver device where the performance of the post-correction is improved compared to the prior art.

[0014] The method proposed in the aforementioned article “On Digital Post-Distortion Techniques” suffers from problems with adjacent channel interference. The method proposed in the aforementioned article “Cellular Digital Post-Distortion: Signal Processing Methods and RF Measurements” has a remaining bias after the compensation.

[0015] A particular object is therefore to address these issues in the aforementioned articles. According to a first aspect there is presented a receiver device for digital postcorrection of a signal. The receiver device is adapted to compensate for impairments of a transmitter device. The receiver device comprises a receiver interface configured to receive the signal from the transmitter device over a wireless channel and to pass the signal upstream in the receiver device. The receiver device comprises a digital post-correction block placed upstream the receiver interface and configured to apply digital post-correction to the signal using a set of coefficients. The receiver device comprises a filter block placed upstream the digital post-correction block and configured to filter the signal after the digital post-correction having been applied to the signal. The receiver device comprises an update block placed upstream the filter block and configured to update the set of coefficients based on the signal after the filtering having been applied to the signal.

[0016] According to a second aspect there is presented a method for digital post-correction of a signal in a receiver device. The receiver device is adapted to compensate for impairments of a transmitter device. The method is performed by the receiver device. The method comprises receiving, in a receiver interface, the signal from the transmitter device over a wireless channel and passing the signal upstream in the receiver device. The method comprises applying digital post-correction to the signal using a set of coefficients in a digital post-correction block placed upstream the receiver interface. The method comprises filtering the signal after the digital postcorrection having been applied to the signal in a filter block placed upstream the digital post-correction block. The method comprises updating, in an update block placed upstream the filter block, the set of coefficients based on the signal after the filtering having been applied to the signal.

[0017] According to a third aspect there is presented a receiver device for digital postcorrection of a signal in the receiver device. The receiver device is adapted to compensate for impairments of a transmitter device. The receiver device comprises processing circuitry. The processing circuitry is configured to cause the receiver device to receive, in a receiver interface, the signal from the transmitter device over a wireless channel and passing the signal upstream in the receiver device. The processing circuitry is configured to cause the receiver device to apply digital postcorrection to the signal using a set of coefficients in a digital post-correction block placed upstream the receiver interface. The processing circuitry is configured to cause the receiver device to filter the signal after the digital post-correction having been applied to the signal in a filter block placed upstream the digital post-correction block. The processing circuitry is configured to cause the receiver device to update, in an update block placed upstream the filter block, the set of coefficients based on the signal after the filtering having been applied to the signal.

[0018] According to a fourth aspect there is presented a computer program for digital postcorrection of a signal in a receiver device. The receiver device is adapted to compensate for impairments of a transmitter device The computer program comprises computer code which, when run on processing circuitry of the receiver device, causes the receiver device to perform actions. One action comprises the receiver device to receive, in a receiver interface, the signal from the transmitter device over a wireless channel and passing the signal upstream in the receiver device. One action comprises the receiver device to apply digital post-correction to the signal using a set of coefficients in a digital post-correction block placed upstream the receiver interface. One action comprises the receiver device to filter the signal after the digital post-correction having been applied to the signal in a filter block placed upstream the digital post-correction block. One action comprises the receiver device to update, in an update block placed upstream the filter block, the set of coefficients based on the signal after the filtering having been applied to the signal.

[0019] According to a fifth aspect there is presented a computer program product comprising a computer program according to the fourth 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.

[0020] According to a sixth aspect there is presented a radio device comprising a receiver device according to the first or third aspect.

[0021] Advantageously, the performance of the post-correction is improved compared to the prior art.

[0022] Advantageously, these aspects enable improved adaptation of the digital correction compared to state of the art. Advantageously, these aspects provide less bias than in the aforementioned article entitled “Cellular Digital Post-Distortion: Signal Processing Methods and RF Measurements”.

[0023] Advantageously, these aspects are more robust to adjacent channel interference than in the aforementioned article entitled “On Digital Post-Distortion Techniques”.

[0024] Advantageously, according to these aspects, the EVM after down-sampling can be improved.

[0025] 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.

[0026] 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.

[0027] BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0029] Fig. 1 is a schematic diagram illustrating a communication system according to embodiments;

[0030] Fig. 2 is a block diagram of a receiver device according to an example;

[0031] Figs. 3, 4, and 5 show simulation results according to examples;

[0032] Fig. 6 is a block diagram of a receiver device according to an embodiment;

[0033] Figs. 7 and 8 show simulation results according to an embodiment;

[0034] Fig. 9 is a block diagram of a receiver device according to an embodiment; Figs, io, n, 12,13, and 14 show simulation results according to an embodiment;

[0035] Fig. 15 is a flowchart of methods according to embodiments;

[0036] Fig. 16 is a schematic diagram showing structural units of a receiver device according to an embodiment; and

[0037] Fig. 17 shows one example of a computer program product comprising computer readable storage medium according to an embodiment.

[0038] DETAILED DESCRIPTION

[0039] 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.

[0040] As noted above there is still a need for an improved receiver device.

[0041] The embodiments disclosed herein therefore relate to techniques for digital postcorrection of a signal in a receiver device. In order to obtain such techniques, there is provided a receiver device, a method performed by the receiver device, and a computer program product comprising code, for example in the form of a computer program, that when run on a receiver device, causes the receiver device to perform the method.

[0042] In the disclosed receiver device, the updating of the coefficients in the digital postcorrection block is made after (channel) estimation and filtering. In this way, the coefficients can be transferred to before the channel filter for reduced computational complexity after the updating. This is possible since the digital post-correction is linear in its parameters. Embodiments of a receiver device 6oo, 900 for digital post-correction of a signal will be disclosed next with parallel references to Fig. 6 and Fig. 9 showing block diagrams of receiver devices 600, 900 according to embodiments. The receiver device 600, 900 is adapted to compensate for impairments of a transmitter device, which transmits the signal via the wireless channel 30.

[0043] The receiver device 600, 900 comprises a receiver interface 605, 905. The receiver interface 605, 905 is configured to receive the signal from the transmitter device over the wireless channel 30. Further, the receiver interface 605, 905 is configured to pass the signal upstream in the receiver device 600, 900.

[0044] There could be different types of signals that are transmitted by the transmitter device. In general terms, the type of signal will depend on which type of signals the transmitter device is capable of transmitting and which type of signals the receiver device 600, 900 is capable of receiving, and the protocols according to which the transmitter device and the receiver device 600, 900 are communicating with each other. According to some embodiments, the signal is an orthogonal frequency division multiplexing (OFDM) signal.

[0045] The receiver device 600, 900 further comprises a digital post-correction block 640, 940. The digital post-correction block 640, 940 is placed upstream the receiver interface 605, 905. The digital post-correction block 640, 940 is configured to apply digital post-correction to the signal using a set of coefficients.

[0046] The receiver device 600, 900 further comprises a filter block 650, 950. The filter block 650, 950 is placed upstream the digital post-correction block 640, 940. The filter block 650, 950 is configured to filter the signal after the digital post-correction having been applied to the signal.

[0047] The receiver device 600, 900 further comprises an update block 644, 944. The update block 644, 944 is placed upstream the filter block 650, 950. The update block 644, 944 is configured to update the set of coefficients. The set of coefficients is updated based on the signal after the filtering having been applied to the signal. That is, the set of coefficients is updated based on the signal as filtered by the filter block 650, 950. In general terms, only the in-carrier distortion is used for the correction. Hence, according to some embodiments, the update block 644, 944 is configured to only use in-carrier distortion of the signal when updating the set of coefficients. To only use the in-carrier distortion after the filtering for updating the set of coefficients gives a better and more robust adaptation compared to the prior art where the updating of the set of coefficients is performed before the down-sampling or without filtering.

[0048] Further aspects, embodiments, and examples of the receiver device 600, 900 will be disclosed next with continued parallel reference being made to Figs. 6 and 9.

[0049] Aspects of how the signal can be processed in the receiver 600, 900 before the signal reaches the digital post-correction block 640, 940 will be disclosed next.

[0050] As already disclosed, the signal is received and passed upstream in the receiver device 600, 900 by a receiver interface 605, 905. The receiver interface 605, 905 might comprise one or more antennas for receiving the signal from the transmitter over the air or be operatively connected to the one or more antennas. Analog to digital conversion (ADC) can then be applied by an ADC block 610 placed upstream the receiver interface 605, 905 to convert the received signal to digital form.

[0051] Filtering, implemented by root-raised-cosine filters 615, 915 can then be performed to receive a single carrier signal that has previously been transmitted using a corresponding root-raised-cosine filter, with the same characteristics, at the transmitter device in order to avoid, or at least reduce, inter symbol interference. In further detail, root-raised-cosine filtering can be performed to contain the carrier in a limited bandwidth and at the same time transmit the signal with a low peak to average power ratio. When the signal has been filtered with the root-raised-cosine filter at the receiver, the impulse response should become a root-raised cosine signal which ideally has no inter symbol interference.

[0052] According to the embodiments of the block diagrams of the receiver 600, 900 in Fig. 6 and Fig. 9, the receiver device 600, 900 further comprises an equalizer block 620, 920. The equalizer block 620, 920 is placed upstream the receiver interface 605, 905. Further, the equalizer block 620, 920 is placed downstream the digital postcorrection block 640, 940. The equalizer block 620, 920 is configured to apply equalization to the signal before the digital post-correction having been applied to the signal. In general terms, the equalizer block 620, 920 will process the signal according to the inverse of the channel. Further, in some examples, the signal is composed of at least two layers. The equalizer block 620, 920 can then be configured to separate the signal into the at least two layers. For example, the equalizer block 620, 920 might be configured to separate the signal into the at least two layers using interference rejection combining (IRC) when applying equalization. The digital postcorrection block 640, 940 is then configured to separately apply the digital postcorrection to each of the at least two layers.

[0053] Down-converters 625, 925 are used to down-sample and retain the transmitted signal at the sample points, and up-converters 630, 930 are then used to up-sample the signal and filter the signal with an additional root-raised-cosine filter 635, 935 to recreate the signal in-between the sample points inside the carrier.

[0054] Further aspects of the digital post-correction block 640, 940 will be disclosed next.

[0055] In general terms, the updating of the set of coefficients is based on symbols, or resources, with known values. Therefore, according to some embodiments, the signal represents a sequence of symbols, and the set of coefficients is updated based on symbols which in the sequence of symbols comprise values known to the receiver device 600, 900. The values of these symbols generally depend on what type of signals they represent. In some non-limiting examples, the signals are reference signals, such as demodulation reference signals (DM-RS), or other types of reference signals, where the nominal values of the reference signals thus are known to the receiver device 600, 900. The receiver device 600, 900 can then compare to the actual received values of the signals to these nominal values and update the set of coefficients to minimize an error between the actual received values and the nominal values of the signal. In particular, in some embodiments, the set of coefficients is updated based on minimizing an error between the symbols comprising values known to the receiver device 600, 900 and a sequence of reference symbols known to the receiver device 600, 900 and corresponding to the symbols comprising values known to the receiver device 600, 900. In general terms, the error between two values is computed according to some distance criterion. In this respect, in some nonlimiting examples the distance criterion is the squared error (and thus it is the squared error that is minimized), but also other distance criteria can be used. The digital post-correction as illustrated in the block diagrams of the receiver 6oo, 900 in Fig. 6 and Fig. 9 is based on using memory polynomials. Hence, according to some embodiments, the digital post-correction is based on memory polynomials, and the set of coefficients represents coefficients of the memory polynomials. The memory polynomials might, for example, be of order four or order five. However, any nonlinear function that can be adapted with linear parameters can be used. This means that lookup tables that are commonly used for digital pre-distortion also can also be used. Hence, in some embodiments, the digital post-correction is based on look-up tables, and the set of coefficients represents coefficients of entries in the lookup tables.

[0056] As illustrated in the block diagrams of the receiver 600, 900 in Fig. 6 and Fig. 9, performing the digital post-correction involves scaling the signal with a set of multipliers 643, 943. That is, according to some embodiments, the digital postcorrection block 640, 940 comprises a set of multipliers 643, 943. The set of multipliers 643, 943 is configured to scale the signal according to the set of coefficients.

[0057] Depending on the configuration of the digital post-correction block 640, 940, there could be different ways to implement the scaling of the signal with the set of multipliers 643, 943. For example, as in the block diagrams of the receiver 600, 900 in Fig. 6 and Fig. 9, the digital post-correction block 640, 940 further comprises at least one root-raised-cosine filter 642, 942. The at least one root-raised-cosine filter 642, 942 is configured to filter the signal. In the block diagrams of the receiver 600, 900 in Fig. 6 and Fig. 9 there are as many root-raised-cosine filters 642, 942 as there are multipliers 643, 943. This is the case where the root-raised-cosine filters 642, 942 are placed downstream the set of multipliers 643, 943. However, in other embodiments the at least one root-raised-cosine filter 642, 942 is placed upstream the set of multipliers 643, 943. In this case, only one single root-raised-cosine filter 642, 942 is needed. Therefore, in some embodiments, the digital post-correction block 640, 940 comprises only one single root-raised-cosine filter 642, 942. However, also other types of pulse-shaping techniques other than using a root-raised cosine filter can be used for this purpose, such as a sine-shaped filter or a Gaussian filter. According to some embodiments, the digital post-correction block 640 further comprises at least one up-conversion block. This is the case for the receiver 600 in Fig. 6. As illustrated in Fig. 6, the at least one up-conversion block is placed downstream a reference signal source (denoted “DMRS”) in the digital postcorrection block 640. The at least one up-conversion block is configured to up- convert reference signals from baseband before the set of coefficients having been updated. Hence, in this case, the set of coefficients are updated after digital postcorrection but before down-conversion.

[0058] Intermediate reference is here made to the simulation results shown in Fig. 7 and Fig. 8, as representing the implementation of the receiver 600 in Fig. 6. Here, the simulation results show that the SNR can be improved 4.6dB by adaptation of the parameters after the filtering compared to the prior art (the results of which are shown in Fig 4 and Fig. 5) with the same order of memory polynomial.

[0059] According to some embodiments, the digital post-correction block 940 further comprises at least one down-conversion block 945. This is the case for the receiver 900 in Fig. 9. As illustrated in Fig. 9, the at least one down-conversion block 945 is placed upstream the at least one root-raised-cosine filter 942 in the digital postcorrection block 940. The at least one down-conversion block 945 is configured to down-convert the signal to baseband after the filtering having been applied by the at least one root-raised-cosine filter 942 to the signal and before the set of coefficients having been updated. Hence, in this case, the set of coefficients are updated after digital post-correction and after down-conversion.

[0060] Intermediate reference is here made to the simulation results shown in Fig. 10 and Fig. 11, as representing the implementation of the receiver 900 in Fig. 9. Here, the simulation results show that the proposed receiver can be further improved by only adapting to the sample points for a single carrier RRC filtered signal (or a DFT spread OFDM signal). In this case the improvement in the simulation is 7.6 dB compared to the prior art (the results of which are shown in Fig 4 and Fig. 5). The sample points of the DMRS symbols are spread to the frequency domain. This is equivalent of performing an IDFT and then comparing the signals in the time domain. This true since the DFT is a linear transform. Further simulation results will be disclosed next with reference to Fig. 12, Fig. 13, and Fig. 14. In Figs. 12 and 13 the AM / AM signal is plotted. The dark curve is the uncompensated signal before and after the compensation and the light gray is the signal corrected by the digital post-correction block 640, 940. When the coefficients have been estimated they can be moved to before the channel filter since the channel filtering is a linear operation, representing a time-domain convolution. The post corrected signal now becomes overcompensated directly after the digital postcorrection block 640, 940 and the spectrum widened, as shown by the top curve in Fig. 14. When the signal is filtered again, the overcompensation seen in the AM / AM plots in Fig. 12 is removed. This is since the overcompensation in amplitude is outside the carrier bandwidth. The plot in Fig. 13 has discrete points on the x-axis related to the constellation point of the received symbol.

[0061] Fig. 15 is a flowchart illustrating embodiments of methods for digital post-correction of a signal in a receiver device 600, 900. The receiver device 600, 900 is adapted to compensate for impairments of a transmitter device. The methods are performed by the receiver device 600, 900. The methods are advantageously provided as computer programs 1720. In general terms, the same embodiments, aspects, and examples as disclosed above with reference to the receiver device 600, 900 applies here as well.

[0062] S102: The receiver device 600, 900 receives, in a receiver interface 605, 905, the signal from the transmitter device over a wireless channel 30 and passes the signal upstream in the receiver device 600, 900.

[0063] S106: The receiver device 600, 900 applies digital post-correction to the signal using a set of coefficients. The digital post-correction is applied in a digital post-correction block 640, 940 placed upstream the receiver interface 605, 905.

[0064] S108: The receiver device 600, 900 filters the signal after the digital post-correction having been applied to the signal. The filtering is performed in a filter block 650, 950 placed upstream the digital post-correction block 640, 940.

[0065] S114: The receiver device 600, 900 updates the set of coefficients based on the signal after the filtering having been applied to the signal. The updating is performed in an update block 644, 944 placed upstream the filter block 650, 950. Embodiments relating to further details of digital post-correction of a signal in a receiver device 6oo, 900 as performed by the receiver device 600, 900 will now be disclosed with continued reference to Fig. 15.

[0066] S104: The receiver device 600, 900 applies equalization to the signal before the digital post-correction having been applied to the signal. The equalization is applied in an equalizer block 620, 920 placed upstream the receiver interface 605, 905 and downstream the digital post-correction block 640, 940.

[0067] Steps S110 and S112 are alternatives to each other.

[0068] S110: The receiver device 600, 900 down-converts the signal to baseband after the filtering having been applied to the signal. The down-converting is performed in at least one down-conversion block 945 in the digital post-correction block 640, 940. The at least one down-conversion block 945 is in the digital post-correction block 640, 940 placed upstream the at least one root-raised-cosine filter 642, 942. The down-converting is performed before updating the set of coefficients.

[0069] S112: The receiver device 600, 900 up-converts a reference signal. The up-converting is performed in an up-conversion block in the digital post-correction block 640, 940. The up-conversion block is in the digital post-correction block 640, 940 placed downstream a reference signal source. The up-converting is performed before updating the set of coefficients.

[0070] Hence, either the received signal is down-converted, as in step S110, or the reference signal to which the received signal is compared is up-converted, as in step S112. That is, for the latter alternative, the sequence of reference symbols that the received signal is compared to is generated by the reference signal source.

[0071] The receiver device 600, 900 could be provided in a radio device 20, 40. The radio device 20, 40 might be a piece of network equipment, an access node, or a user equipment. Non-limiting examples of such radio devices 20, 40 are (radio) access network nodes, (radio) base stations, base transceiver stations, node Bs (NBs), evolved node Bs (eNBs), gNBs, transmission and reception points (TRPs), integrated access and backhaul (IAB) notes, portable wireless devices, mobile stations, mobile phones, handsets, wireless local loop phones, smartphones, laptop computers, tablet computers, network-equipped vehicles, etc.

[0072] Fig. 16 schematically illustrates, in terms of a number of structural units, the components of a receiver device 1600 according to an embodiment. Processing circuitry 16 io 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 1710 (as in Fig. 17), e.g. in the form of a storage medium 1630. The processing circuitry 1610 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0073] Particularly, the processing circuitry 1610 is configured to cause the receiver device 1600 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 1630 may store the set of operations, and the processing circuitry 1610 maybe configured to retrieve the set of operations from the storage medium 1630 to cause the receiver device 1600 to perform the set of operations. The set of operations maybe provided as a set of executable instructions.

[0074] Thus the processing circuitry 1610 is thereby arranged to execute methods as herein disclosed. The storage medium 1630 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 receiver device 1600 may further comprise a communications (comm.) interface 1620 at least configured for communications with other entities, functions, nodes, and devices. As such the communications interface 1620 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 1610 controls the general operation of the receiver device 1600 e.g. by sending data and control signals to the communications interface 1620 and the storage medium 1630, by receiving data and reports from the communications interface 1620, and by retrieving data and instructions from the storage medium 1630. Other components, as well as the related functionality, of the receiver device 1600 are omitted in order not to obscure the concepts presented herein.

[0075] The receiver device 1600 maybe provided as a standalone device or as a part of at least one further device. For example, the receiver device 1600 maybe provided in a radio device 20, 40. This radio device 20, 40 might be provided in a node of a radio access network or in a node of a core network. Alternatively, functionality of the receiver device 1600 maybe 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 the radio access network or the 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 maybe 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 receiver device 1600 maybe executed in a first device, and a second portion of the of the instructions performed by the receiver device 1600 maybe 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 receiver device 1600 may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a receiver device 1600 residing in a cloud computational environment. Therefore, although a single processing circuitry 1610 is illustrated in Fig. 16 the processing circuitry 1610 maybe distributed among a plurality of devices, or nodes. The same applies to the computer program 1720 of Fig. 17.

[0076] Fig. 17 shows one example of a computer program product 1710 comprising computer readable storage medium 1730. On this computer readable storage medium 1730, a computer program 1720 can be stored, which computer program 1720 can cause the processing circuitry 1610 and thereto operatively coupled entities and devices, such as the communications interface 1620 and the storage medium 1630, to execute methods according to embodiments described herein. The computer program 1720 and / or computer program product 1710 may thus provide means for performing any steps as herein disclosed.

[0077] In the example of Fig. 17, the computer program product 1710 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 1710 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 1720 is here schematically shown as a track on the depicted optical disk, the computer program 1720 can be stored in any way which is suitable for the computer program product 1710. 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 receiver device (6oo, 900) for digital post-correction of a signal, wherein the receiver device (600, 900) is adapted to compensate for impairments of a transmitter device, wherein the receiver device (600, 900) comprises: a receiver interface (605, 905) configured to receive the signal from the transmitter device over a wireless channel (30) and to pass the signal upstream in the receiver device (600, 900); a digital post-correction block (640, 940) placed upstream the receiver interface (605, 905) and configured to apply digital post-correction to the signal using a set of coefficients; a filter block (650, 950) placed upstream the digital post-correction block (640, 940) and configured to filter the signal after the digital post-correction having been applied to the signal; and an update block (644, 944) placed upstream the filter block (650, 950) and configured to update the set of coefficients based on the signal after the filtering having been applied to the signal.

2. The receiver device (600, 900) according to claim 1, wherein the digital postcorrection block (640, 940) comprises a set of multipliers (643, 943) configured to scale the signal according to the set of coefficients.

3. The receiver device (600, 900) according to claim 2, wherein the digital postcorrection block (640, 940) further comprises at least one root-raised-cosine filter (642, 942) placed downstream the set of multipliers (643, 943) and configured to filter the signal.

4. The receiver device (600, 900) according to claim 3, wherein the digital postcorrection block (640, 940) comprises only one single root-raised-cosine filter (642, 942).

5. The receiver device (600, 900) according to any preceding claim, wherein the update block (644, 944) is configured to only use in-carrier distortion of the signal when updating the set of coefficients.

6. The receiver device (6oo, 900) according to any preceding claim, wherein the receiver device (600, 900) further comprises: an equalizer block (620, 920) placed upstream the receiver interface (605, 905) and downstream the digital post-correction block (640, 940) and configured to apply equalization to the signal before the digital post-correction having been applied to the signal.

7. The receiver device (600, 900) according to claim 6, wherein the signal is composed of at least two layers, wherein the equalizer block (620, 920) is configured to separate the signal into the at least two layers using interference rejection combining when applying equalization, and wherein the digital post-correction block (640, 940) is configured to separately apply the digital post-correction to each of the at least two layers.

8. The receiver device (600, 900) according to claim 3, wherein the digital postcorrection block (940) further comprises: at least one down-conversion block (945) placed upstream the at least one root- raised-cosine filter (642, 942) and configured to down-convert the signal to baseband after the filtering having been applied by the at least one root-raised-cosine filter (642, 942) to the signal and before the set of coefficients having been updated.

9. The receiver device (600, 900) according to claim 3, wherein the update block (644, 944) further comprises: at least one up-conversion block placed downstream a reference signal source and configured to up-convert reference signals from baseband before the set of coefficients having been updated.

10. The receiver device (600, 900) according to any preceding claim, wherein the signal represents a sequence of symbols, and wherein the set of coefficients is updated based on symbols which in the sequence of symbols comprise values known to the receiver device (600, 900).

11. The receiver device (600, 900) according to claim 10, wherein the set of coefficients is updated based on minimizing an error between the symbolscomprising values known to the receiver device (6oo, 900) and a sequence of reference symbols known to the receiver device (600, 900) and corresponding to the symbols comprising values known to the receiver device (600, 900).

12. The receiver device (600, 900) according to a combination of claim 9 with claim 10 and / or claim 11, wherein the sequence of reference symbols is generated by the reference signal source.

13. The receiver device (600, 900) according to any preceding claim, wherein the digital post-correction is based on memory polynomials, and wherein the set of coefficients represents coefficients of the memory polynomials.

14. The receiver device (600, 900) according to any of claims 1 to 12, wherein the digital post-correction is based on look-up tables, and wherein the set of coefficients represents coefficients of entries in the look-up tables.

15. The receiver device (600, 900) according to any preceding claim, wherein the signal is an orthogonal frequency division multiplexing, OFDM, signal.

16. A radio device (20, 40) comprising a receiver device (600, 900) according to any preceding claim.

17. The radio device (20, 40) according to claim 16, wherein the radio device (20, 40) is a piece of network equipment, an access node, or a user equipment.

18. A method for digital post-correction of a signal in a receiver device (600, 900), wherein the receiver device (600, 900) is adapted to compensate for impairments of a transmitter device, wherein the method is performed by the receiver device (600, 900), and wherein the method comprises: receiving (S102), in a receiver interface (605, 905), the signal from the transmitter device over a wireless channel (30) and passing the signal upstream in the receiver device (600, 900); applying (S106) digital post-correction to the signal using a set of coefficients in a digital post-correction block (640, 940) placed upstream the receiver interface (605, 905);filtering (Sio8) the signal after the digital post-correction having been applied to the signal in a filter block (650, 950) placed upstream the digital post-correction block (640, 940); and updating (S114), in an update block (644, 944) placed upstream the filter block (650, 950), the set of coefficients based on the signal after the filtering having been applied to the signal.

19. The method according to claim 18, wherein the digital post-correction block (640, 940) comprises a set of multipliers (643, 943), and wherein applying (S106) the digital post-correction to the signal comprises scaling the signal according to the set of coefficients.

20. The method according to claim 19, wherein the digital post-correction block (640, 940) further comprises at least one root-raised-cosine filter (642, 942), and wherein applying (S106) the digital post-correction to the signal comprises filtering the signal using the at least one root-raised-cosine filter (642, 942).

21. The method according to claim 20, wherein the digital post-correction block (640, 940) comprises only one single root-raised-cosine filter (642, 942).

22. The method according to any of claims 18 to 21, wherein the update block (644, 944) is configured to only use in-carrier distortion of the signal when updating the set of coefficients.

23. The method according to any of claims 18 to 22, wherein the method further comprises: applying equalization (S104), in an equalizer block (620, 920) placed upstream the receiver interface (605, 905) and downstream the digital post-correction block (640, 940), to the signal before the digital post-correction having been applied to the signal.

24. The method according to claim 23, wherein the signal is composed of at least two layers, wherein applying the equalization to the signal comprises separating the signal into the at least two layers using interference rejection combining whenapplying equalization, and the digital post-correction is, in the digital post-correction block (640, 940), separately applied each of the at least two layers.

25. The method according to claim 20, wherein the method further comprises: down-converting (S110) the signal, in at least one down-conversion block (945) placed upstream the at least one root-raised-cosine filter (642, 942), to baseband after the filtering the signal with the at least one root-raised-cosine filter (642, 942) and before updating the set of coefficients.

26. The method according to claim 20, wherein the method further comprises: up-converting (S112) a reference signal, in an up-conversion block placed downstream a reference signal source, before updating the set of coefficients.

27. The method according to any of claims 18 to 26, wherein the signal represents a sequence of symbols, and wherein the set of coefficients is updated based on symbols which in the sequence of symbols comprise values known to the receiver device (600, 900).

28. The method according to claim 27, wherein the set of coefficients is updated based on minimizing an error between the symbols comprising values known to the receiver device (600, 900) and a sequence of reference symbols known to the receiver device (600, 900) and corresponding to the symbols comprising values known to the receiver device (600, 900).

29. The method according to a combination of claim 26 with claim 27 and / or claim 28, wherein the sequence of reference symbols is generated by the reference signal source.

30. The method according to any of claims 18 to 29, wherein the digital postcorrection is based on memory polynomials, and wherein the set of coefficients represents coefficients of the memory polynomials.

31. The method according to any of claims 18 to 29, wherein the digital postcorrection is based on look-up tables, and wherein the set of coefficients represents coefficients of entries in the look-up tables.

32. The method according to any of claims 18 to 31, wherein the signal is an orthogonal frequency division multiplexing, OFDM, signal.

33. A receiver device (1600) for digital post-correction of a signal in the receiver device (1600), wherein the receiver device (1600) is adapted to compensate for impairments of a transmitter device, wherein the receiver device (1600) comprises processing circuitry (1610), and wherein the processing circuitry is configured to cause the receiver device (1600) to: receive, in a receiver interface (605, 905), the signal from the transmitter device ogover a wireless channel (30) and passing the signal upstream in the receiver device (1600); apply digital post-correction to the signal using a set of coefficients in a digital post-correction block (640, 940) placed upstream the receiver interface (605, 905); filter the signal after the digital post-correction having been applied to the signal in a filter block (650, 950) placed upstream the digital post-correction block (640, 940); and update, in an update block (644, 944) placed upstream the filter block (650, 950), the set of coefficients based on the signal after the filtering having been applied to the signal.

34. The receiver device (1600) according to claim 33, further being configured to perform the method according to any of claims 18 to 32.

35. A computer program (1720) for digital post-correction of a signal in a receiver device (1600), wherein the receiver device (1600) is adapted to compensate for impairments of a transmitter device, the computer program comprising computer code which, when run on processing circuitry (1610) of the receiver device (1600), causes the receiver device (1600) to: receive (S102), in a receiver interface (605, 905), the signal from the transmitter device over a wireless channel (30) and passing the signal upstream in the receiver device (1600);apply (S106) digital post-correction to the signal using a set of coefficients in a digital post-correction block (640, 940) placed upstream the receiver interface (605, 905); filter (S108) the signal after the digital post-correction having been applied to the signal in a filter block (650, 950) placed upstream the digital post-correction block (640, 940); and update (S114), in an update block (644, 944) placed upstream the filter block (650, 950), the set of coefficients based on the signal after the filtering having been applied to the signal.

36. A computer program product (1710) comprising a computer program (1720) according to claim 35, and a computer readable storage medium (1730) on which the computer program is stored.

Images