WO2025076727A1

WO2025076727A1 - Determining correction coefficients for a wireless communication signal

Info

Publication number: WO2025076727A1
Application number: PCT/CN2023/124002
Authority: WO
Inventors: Atanu Guchhait; Ang FENG; Christian Braun; Hao Zhang
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-10-11
Filing date: 2023-10-11
Publication date: 2025-04-17
Anticipated expiration: 2026-04-11

Abstract

In an example, a method in a first network node of determining correction coefficients for a wireless communication signal is provided. The method comprises receiving, from a second network node on a first channel, a reference signal, and receiving information identifying properties of a second channel from the first network node to the second network node. The method also comprises determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.

Description

DETERMINING CORRECTION COEFFICIENTS FOR A WIRELESS COMMUNICATION SIGNAL

Technical Field

Example embodiments of this disclosure relate to determining correction coefficients for a wireless communication signal, such as for example an uplink signal from a User Equipment (UE) to a Radio Access Network (RAN) node.

Background

Large multiple-input multiple-output (MIMO) or full-dimension MIMO technology in 4G and 5G radio access networks (RAN) is used to enhance spectral efficiency, cell coverage, and to improve performance in noise and interference limited scenarios. A large number of transmit and receive antennas in the base station and User Equipment (UE) helps in exploiting signal-to-interference-and-noise ratio (SINR) and/or spatial dimensions of the wireless channel to create a favourable information propagation condition. MIMO and its successor Massive-MIMO are key technologies for 5G and upcoming 6G standards. In high frequency wireless networks utilizing millimeter-wave and above spectrum, the expected number of antennas in a base station or UE may be more than hundreds.

To achieve required performance gains, the impact of transmitter hardware impairments in the transmitted and received signal should be considered in the design of MIMO transceivers for superior end-to-end performance. For instance, non-linear distortions introduced by a power amplifier (PA) in a transmitter may introduce gain and phase errors in the carrier bandwidth that may significantly deteriorate the error vector magnitude (EVM) , or may induce spectrum regrowth outside the carrier that may deteriorate the adjacent channel leakage ratio (ACLR) conditions making it unfit for operations in the field. IQ imbalances present in a transmitter employing homodyne architecture introduces distortion at the image frequency and will degrade the EVM metric as well.

Digital predistortion (DPD) and IQ correction (IQC) are widely used techniques in the uplink (UL) by MIMO capable UEs to compensate for PA nonlinearity and IQ imbalances present in the signal transmission paths, respectively. Figure 1 illustrates an example of a transmitter 100 implementing DPD and IQC for a typical MIMO transmitter system implemented in a UE. The transmitter 100 includes two transmitter chains, each of which includes a DPD block 102, IQC block 104, digital-to-analog converter (DAC) 106, power amplifier (PA) 108 and antenna 110. The signal output from each PA 108 is provided to a TOR (Transmitter Observation Receiver) path 116. That is, the signal output from each PA 108 is tapped at 112 and the tapped signal is provided to switches or combiner block 114. The output from block 114 is provided to TOR path 116 which provides an input to adaptation block 118. The adaptation block 118 provides coefficients for the DPD blocks 102 and IQC blocks 104 which are copied to the appropriate blocks in block 120.

To support higher order modulation schemes, for example in the uplink (UL) , such as for example 256 QAM and 1K QAM, high signal quality (very low EVM) is necessary. High efficiency in the PA also needs high performance algorithms and associated hardware and software to improve signal quality. However, the cost of DPD and IQC in hardware and software is high to for a MIMO capable UE, due to high requirements on signal pureness and integrity.

In existing solutions, only a memoryless nonlinear model is considered for power amplifier modelling. This is because it is difficult to separate the memory effects occurring in both power amplifier and channel multipath fading if the memory nonlinear model is used. However, as signal bandwidth increases, the memory effects of a power amplifier become important, therefore such an assumption is not accurate. On the other hand, it is common to model a simple wireless channel where non-line-of-sight (NLOS) paths are excluded. In this case, the wireless channel is assumed to be memoryless, and therefore memory nonlinear model can be used for power amplifier modelling. However, this assumption is also inaccurate.

Summary

Examples of this disclosure may have certain advantages. For example, a RAN node may compute UL correction parameters and share them with a UE (pre-correction by the UE) or uses them locally (post-correction by the RAN node) . Pre-correction may result in significant reduction of UE hardware/software cost by allowing removing the feedback TOR path in the UE, or relaxing requirements on feedback TOR path. Post-correction can enable further UE hardware/software complexity reductions without performance compromise. Disclosed embodiments may also be applicable to legacy UEs. A UE may be able to use higher modulation schemes (e.g., 256QAM or 1024QAM) , resulting for example in improved signal quality (EVM reduction) and hence improving system spectral efficiency, capacity and/or coverage.

One aspect of the present disclosure provides a method in a first network node of determining correction coefficients for a wireless communication signal. The method comprises receiving, from a second network node on a first channel, a reference signal, and receiving information identifying properties of a second channel from the first network node to the second network node. The method also comprises determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.

Another aspect of the present disclosure provides apparatus in a first network node for determining correction coefficients for a wireless communication signal. The apparatus comprises a processor and a memory. The memory contains instructions executable by the processor such that the apparatus is operable to receive, from a second network node on a first channel, a reference signal, receive information identifying properties of a second channel from the first network node to the second network node, and determine, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.

A further aspect of the present disclosure provides apparatus in a first network node for determining correction coefficients for a wireless communication signal. The apparatus is configured to receive, from a second network node on a first channel, a reference signal, receive information identifying properties of a first channel from the first network node to the second network node, and determine, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.

Brief Description of the Drawings

For a better understanding of examples of the present disclosure, and to show more clearly how the examples may be carried into effect, reference will now be made, by way of example only, to the following drawings in which:

Figure 1 illustrates an example of a transmitter implementing DPD and IQC for a typical MIMO transmitter system implemented in a UE;

Figure 2 is a flow chart of an example of a method in a first network node of determining correction coefficients for a wireless communication signal;

Figure 3 illustrates an example of UE assisted UL channel estimation;

Figure 4 illustrates an example of UL channel prediction from DL explicit CSI feedback;

Figure 5 illustrates an example of computation of correction coefficients for a signal on the first or second channel;

Figure 6 illustrates an example of communications in a network when determining pre-correction coefficients for a wireless communication signal;

Figure 7 illustrates an example of communications in a network when determining post-correction coefficients for a wireless communication signal; and

Figure 8 is a schematic of an example of an apparatus in a first network node for determining correction coefficients for a wireless communication signal.

Detailed Description

The following sets forth specific details, such as particular embodiments or examples for purposes of explanation and not limitation. It will be appreciated by one skilled in the art that other examples may be employed apart from these specific details. In some instances, detailed descriptions of well-known methods, nodes, interfaces, circuits, and devices are omitted so as not obscure the description with unnecessary detail. Those skilled in the art will appreciate that the functions described may be implemented in one or more nodes using hardware circuitry (e.g. analog and/or discrete logic gates interconnected to perform a specialized function, Application Specific Integrated Circuits (ASICs) , Programmable Logic Arrays (PLAs) , etc. ) and/or using software programs and data in conjunction with one or more digital microprocessors or general purpose computers. Nodes that communicate using the air interface also have suitable radio communications circuitry. Moreover, where appropriate the technology can additionally be considered to be embodied entirely within any form of computer-readable memory, such as solid-state memory, magnetic disk, or optical disk containing an appropriate set of computer instructions that would cause a processor to carry out the techniques described herein.

Hardware implementation may include or encompass, without limitation, digital signal processor (DSP) hardware, a reduced instruction set processor, hardware (e.g. digital or analogue) circuitry including but not limited to application specific integrated circuit (s) (ASIC) and/or field programmable gate array (s) (FPGA (s) ) , and (where appropriate) state machines capable of performing such functions.

Embodiments of this disclosure provide systems and methods to help a wireless communication device to improve transmit signal quality by correcting for distortions to a signal on a wireless communication channel caused by apparatus of the wireless communication device, such as for example PA nonlinearity. For example, systems and methods disclosed herein may improve UL transmit signal quality by applying correction with assistance from a RAN node to correct for UE apparatus distortions, either pre-correction at the UE and/or post-correction at the RAN node.

In some examples, it is assumed that one of two network nodes involved in wireless communication (e.g. the UE and the RAN node) has already estimated its own distortions introduced by the hardware (also referred to in some examples as RF impairments) and applied corrections for its transmissions.

Examples of this disclosure are described in the context of improve UL transmit signal quality by applying correction with assistance from a RAN node to correct for UE apparatus distortions, either pre-correction at the UE and/or post-correction at the RAN node. However, these are illustrative examples, and the disclosed examples may also be applied to other scenarios, such as for example improving DL transmit signal quality by applying correction to correct for RAN node apparatus distortions, either pre-correction at the RAN node and/or post-correction at the UE node, or other scenarios or network nodes.

Further, examples of this disclosure may be assumed to have full bandwidth (BW) and port allocation to a network node for simplicity. We have also assumed that the network node has only one transmit or receive antenna port. In case of partial BW and port allocation with multiple transmit and receive antenna ports, extension of the proposed example embodiments is straightforward where the network node can have the same or fewer than the maximum supported BW and port allocation.

In some examples, using UL reference signal (RS) transmissions from a UE, a RAN node such as a base station estimates the UL channel, which consists of an over-the-air (OTA) channel and hardware distortions at the UE. The RAN node then predicts the UL OTA channel and equalizes its impacts from the estimated UL channel. For example, the RAN node may use data driven or model driven functions to predict the UL OTA channel from DL full channel (explicit) CSI feedback from the UE (see for example RP-213560, “Study on artificial intelligence (AI) /machine learning (ML) for NR air interface, ” 3GPP TSG RAN Meeting #94e, December 2021, and 3GPP TR 38.843, “Study on Artificial Intelligence (AI) /Machine Learning (ML) for NR Air Interface” ) .

For CSI feedback sharing to the RAN node, the UE may for example apply transmit power restrictions to avoid the impact of UE hardware impairments on the CSI transmission. In this process, the RAN node may also for example assume that the downlink channel is already corrected for impairments, such as for example those caused by the RAN node hardware.

Further, the RAN node estimates correction coefficients (correcting for the UE’s hardware/apparatus distortions) from the equalized UL channel estimates, and either shares these with the UE by the second channel for application to subsequent UL transmissions or uses them locally for post-correction of UL signals.

In another example, the UE can also estimate correction coefficients for the downlink (DL) channel, for example by utilizing DL channel estimates and DL channel information-based DL channel predictions. DL channel information can be shared by the RAN node to the UE for example. In such cases, the uplink (UL) channel is assumed to be corrected beforehand, and the RAN node may in some examples apply a transmit power restriction while sharing UL channel CSI to the UE node in order to avoid the impact of hardware impairments on the CSI transmission. The UE can for example either share the correction coefficients with the RAN node over the UL channel for application to subsequent DL transmissions, or use them locally for post-correction of DL signals.

Figure 2 is a flow chart of an example of a method 200 in a first network node of determining correction coefficients for a wireless communication signal, such as for example an UL signal, DL signal or other signal. The first network node may be for example a RAN node such as a base station, a UE, or another network node. The method 200 comprises, in step 202, receiving, from a second network node on a first channel, a reference signal. The reference signal may be for example a sounding reference signal (SRS) , Channel State Information Reference Signal (CSI-RS) and/or demodulation reference signal (DMRS) , and/or any other type of reference signal.

Step 204 of the method 200 comprises receiving information identifying properties of a second channel from the first network node to the second network node (e.g. received from, the second network node) . This may be for example channel response or estimated channel response of the second channel, or Channel State Information (CSI) for the second channel. This could be determined by the second node in some examples from another reference signal that was transmitted by the first network node and received by the second network node.

Step 206 of the method 200 comprises determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel. The correction coefficients may thus in some examples correct or compensate for distortions to a signal on the first channel or the second channel caused by apparatus of the first network node or the second network node, such as for example power amplifier nonlinearities, including in examples where there is no observation path in the first network node and/or the second network node.

In some examples, the method 200 may comprise determining, from the measurements of the reference signal, properties of the first channel, such as for example a channel response or estimated channel response of the first channel. In such examples, the determining the correction coefficients in step 206 may comprise determining, from the information and the properties of the first channel, the correction coefficients for a signal on the first channel or the second channel.

Some examples of the method 200 may comprise determining, from the information identifying properties of the second channel, an estimate of properties of the first channel, such as for example a channel response or an estimate of a channel response of the first channel. In such examples, determining the correction coefficients in step 206 may comprise determining, from the estimate of properties of the second channel and the measurements of the reference signal, the correction coefficients for a signal on the first channel or the second channel. The method 200 may also in some examples comprise equalizing, using the estimate of properties of the first channel, a channel response or an estimation of a channel response of the first channel determined from measurements of the reference signal, to obtain an equalized channel response. Thus, for example, determining the correction coefficients in step 206 may comprise determining the correction coefficients from the equalized channel response.

In some examples, determining the estimate of properties of the first channel may comprise using, the properties of the second channel. This may be the case for example where UL/DL channel reciprocity is assumed, such as in time division duplex (TDD) systems, although this may also be applicable in frequency division duplex (FDD) systems in some examples.

In some examples, determining the correction coefficients in step 206 comprises determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel. In such examples, the method 200 may comprise applying the correction coefficients to a signal received from the second network node on the first channel. Thus, in this way, the first network node may apply post-correction for distortions caused by apparatus or hardware of the second network node, such as for example power amplifier nonlinearities, on the received signal. Additionally or alternatively, the method 200 may in some examples comprise sending the correction coefficients to the second network node, so that the second network node may apply pre-correction to the signal.

In some examples, determining the correction coefficients in step 206 comprises determining, from the information and measurements of the reference signal, correction coefficients for a signal on the second channel. In such examples, the method 200 may comprise comprising applying the correction coefficients to a signal to be transmitted to the second network node to obtain a corrected signal, and transmitting the corrected signal to the second network node on the second channel. Thus, in this way, the transmitted signal is pre-corrected for distortions caused by apparatus or hardware of the first network node, such as for example power amplifier nonlinearities. Additionally or alternatively, the method 200 may in some examples comprise sending the correction coefficients to the second network node, such that the second network node may perform post-correction of a signal transmitted from the first network node to the second network node on the second channel.

The first network node may in some examples be a Radio Access Network (RAN) node and the second network node comprises a User Equipment (UE) . Thus, for example, the second channel comprises a downlink channel and the first channel comprises an uplink channel. Alternatively, in some examples, the first network node comprises a User Equipment (UE) and the second network node comprises a Radio Access Network (RAN) node. Thus, for example, the second channel comprises an uplink channel and the first channel comprises a downlink channel.

A particular example implementation of the method 200 is now described. Assume that a RAN node selects a kth UE UE_k for UL calibration from a set of total K active UEs. It is also assumed that UE_k has full bandwidth (BW) and one DL/UL antenna port. In some examples, all active UEs under the RAN node may have non-overlapping BW-antenna ports, or time multiplexed overlapping BW-antenna port allocations. For each of these cases, the UE can be scheduled for different ports and UL/DL RS transmission/reception respectively for the UE’s port specific hardware distortion estimation and correction purpose. Multiple UEs may in some examples be scheduled separately for hardware distortion estimation and correction. UEs are also assumed to be capable of processing explicit DL CSI and sharing the CSI with the RAN node.

In a first step, a User Equipment UE_k transmits a UL reference signal (e.g. the reference signal referred to in step 202 above) on an UL channel (e.g. the first channel referred to above) , and a RAN node receives the reference signal and applies literature available channel estimation algorithms to estimate the UL channel (e.g. the the properties of the first channel, such as channel response or estimated channel response of the first channel, referred to above) , which has UL OTA channel distortions and distortions due to UE hardware/apparatus. When needed, the RAN node may apply data driven mechanisms for the UL channel estimation.

For example, UE_k may be selected by the RAN node from the set of active UEs, {UE_i} , i=1, …, K under the RAN node. Each UE may be equipped with M antennas. When UE_k is scheduled for UL transmissions, it sends UL reference signals (example SRS, DMRS as supported by 3GPP New Radio (NR) standard) . No transmission power restriction is applied in this example to ensure that the UE’s hardware/apparatus distortions are present in the UL signal. The RAN node receives the UL RS using all N of its antenna ports. Upon receiving these RS transmissions in the UL from its N receive antenna ports, the RAN node estimates set of full-band OTA channelswhich has dimension of UE uplink transmitter port number (here assumed one, M=1) and is generated as weighted combination of all UL channel estimationsn=1, …, N. This process is shown in Figure 3, which illustrates an example of UE assisted UL channel estimation for single UE equipped with 2 antennas. As shown in Figure 3, UE 302 transmits M reference signals 304 over channel 306 (e.g. the first channel referred to above) to N antennas and radio branches 308 of network node 310 (e.g. first network node referred to above) . Radio branches 308 pass signals to UL channel estimation block 312 to compute

Next in the example implementation, the UE provides full channel (explicit) CSI feedback to the RAN node based on DL RS transmissions on a DL channel (e.g. the second channel referred to above) , assuming that the DL path is free from distortions due to the RAN node’s hardware/apparatus. For example, the DL RS may be pre-corrected for these distortions. The RAN node now predicts the UL OTA channel responsefrom the full channel DL CSI feedback. This channel prediction does not include the UE’s hardware or apparatus distortions. For example, the RAN node may assume that the UL and DL channel responses are the same due to channel reciprocity, particularly for TDD systems. For other systems, such as for example FDD systems, data driven methods can in some examples predict the UL channel from the received DL CSI feedback operating on different frequency, see for example Yang et al, “Deep Learning-Based Downlink Channel Prediction for FDD Massive MIMO System” , IEEE Communications Letters, vol. 23, no. 11, pp. 1994-1998, Nov. 2019, doi: 10.1109/LCOMM. 2019.2934851.

In some examples, for the UE_k, the RAN node schedules DL RS transmissions for a full-set of downlink antenna ports occupying full-bandwidth and informs the UE through the DL control channel. At this stage, it can be assumed in this example that DL hardware/apparatus distortions (e.g. at the first network node or RAN node) are estimated/known and compensated beforehand at the RAN node, and does not impact DL RS transmissions. At the UE_k, the received DL RS signalfrom DL antenna transmit ports n=1…N with DL OTA channelcan be expressed as follows:

whereis the effective DL channel seen by the UE_k for the DL transmit antenna port n. For a multiport UE, a similar expression can be derived for other receive ports.

The UE_k estimates the effective DL channeland prepares explicit DL CSI n=1…. N for feedback to the RAN node over subsequent UL OTA transmissions. In some examples, the explicit DL CSI is transmitted to the RAN node with a transmit power restriction to avoid the impact of hardware impairments (i.e. distortions to the CSI transmission caused by apparatus of the UE) on the CSI transmission. After receiving DL explicit CSIn=1…. N, the RAN node processes this set of CSI through a model or data driven function to generate per-port UL channel prediction. The predicted UL channelis per UL transmitter port (here assumed one) from n=1, …, N available DL CSIs. An example of this process is shown in Figure 4, which illustrates an example of UL channel prediction from DL explicit CSI feedback. The channel prediction can be represented as follows for a one-port UE_k:

As illustrated in Figure 4, RAN node 310 transmits DL reference signals 402 to UE 302 (e.g. on the second channel referred to above) , which transmits DL explicit CSI feedback 406 to the RAN node 310 (e.g. on the first channel referred to above, such as UL channel) . In the RAN node 310 an UL channel prediction block 408 estimates or predicts UL channel properties (e.g. estimated response) from the CSI feedback.

In some examples, a P_pred {·} prediction function performs UL instantaneous OTA channel response prediction from explicit CSI feedback from the UE_k. When UE is not capable of full-BW and full-DL antenna port operations, the RAN node can for example schedule partial band DL RS from the set of antenna ports available and gather explicit CSI within a predefined scheduling interval to maintain OTA channel delay-Doppler and spatial coherency.

Next in the example implementation, using the predicted UL OTA channelthe RAN node equalizes the estimated UL channelwherein the estimate of UE’s UL distortion due to hardware/apparatus is retained asThe RAN node subsequently computes a correction coefficient setfrom the estimated UL distortions channelThis could be pre or post signal correction coefficients depending on the solution architecture.

For pre-correction, the correction coefficient setis sent back to the UE_k over the air interface, for example as extended DL control information. The UE applies those correction coefficients for correction to subsequent UL transmissions.

For post-correction, the correction coefficient setcan be used by the RAN node to compensate for UE apparatus/hardware distortions present in the UL signal.

For example, the RAN node can use the UL channel predictionto equalize the OTA channel impacts from the estimated UL channelThis process is shown as OTA channel equalization process in Figure 5, which illustrates an example of computation of correction coefficients for a signal on the first or second channel, e.g. for power amplifier nonlinearity distortion correction. In Figure 5, an OTA channel equalization block 502 receivesandand produces an estimate of the hardware distortion on the first or second channel, which can be represented asIn subsequent processing steps, in some examples, the RAN node can apply data driven methods (e.g. Machine Learning) or other traditional model driven algorithms F (·) to compute correction coefficients for mitigating the UE’s UL hardware distortion. This process can be represented as the following example for UEs having one UL transmission port:

Alternatively, in some examples, multiple estimates of the UE’s UL hardware distortions based on UL channel predictions can be obtained, e.g. one per receive antenna port, and coherently combine them to get one estimation which can be represented as follows:

In the case of a multi-port UE, the RAN node can in some examples decide to use different combinations of receiver RAN node ports to generate separate correction coefficients sets for different UE ports.

In some examples, the first network node (e.g. RAN node) can exploit the presence of multiple antenna ports for better performance. For example, combining gain or beamforming gain can be obtained when estimating the UL hardware distortions fromandper port because, for example, the RAN node uses multiple antennas to receive the UE signals while every RAN node antenna can be used to estimate UL hardware distortion.

In some examples, the correction coefficients can be improved iteratively using the method 200 and/or the example implementation above. That is, for example, further RS transmissions on the first channel (e.g. UL channel) may be pre-or post-corrected and used to further improve the correction coefficients. For example, the method 200 or example implementation may be performed iteratively by a first network node-second network node pair (e.g. RAN node-UE pair) when the number of antenna ports and operating BW supported by the UE for UL transmission and DL reception is less than the number of antenna ports in the RAN node. In such cases, the RAN node may for example adapt 3GPP NR standard supported DL/UL RS transmission/reception scheduling mechanisms to cover all DL/UL ports for RS transmissions/reception to/from the UE covering full BW/ports supported by the UE.

The method 200 or example implementation may also be repeated over time to correct for hardware degradation or characteristics change over time.

Figure 6 illustrates an example of communications in a wireless communication network when determining pre-correction coefficients for a wireless communication signal. In Figure 6, UE 602 sends UL RS transmissions (port limited) 604 to UL processing block of RAN node 606. UL processing block performs UL channel estimation at 608 and forwards UL channel estimates 610 to UL RF impairment processing block 612 (e.g. in the RAN node 606) , which implements determining correction coefficients for an UL signal on an UL channel. DL processing block of RAN node 606 sends DL RS transmissions (port limited) 612 to UE 602, which computes full channel CSI at 614. UE 602 then sends CSI transmissions 616 to UL RF impairment processing block 613. At 618, UL RF impairment processing block 613 predicts the UL channel from the CSI transmissions 616, performs UL channel equalization, and computes UL RF impairments pre-correction coefficients (i.e. UE UL hardware distortion correction coefficients) for all antenna ports. The correction coefficients 620 are sent to UE 602. At 622, UE applies the pre-correction coefficients to UL data transmission 624 and then transmits the UL data transmission.

Figure 7 illustrates an example of communications in a wireless communication network when determining post-correction coefficients for a wireless communication signal. In Figure 7, UE 702 sends UL RS transmissions (port limited) 704 to UL processing block of RAN node 706. UL processing block performs UL channel estimation at 708 and forwards UL channel estimates 710 to UL RF impairment processing block 713 (e.g. in the RAN node 707) , which implements determining correction coefficients for an UL signal on an UL channel. DL processing block of RAN node 706 sends DL RS transmissions (port limited) 712 to UE 702, which computes full channel CSI at 714. UE 702 then sends CSI transmissions 716 to UL RF impairment processing block 713. At 718, UL RF impairment processing block 713 predicts the UL channel from the CSI transmissions 716, performs UL channel equalization, and computes UL RF impairments pre-correction coefficients (i.e. UE UL hardware distortion correction coefficients) for all antenna ports. The correction coefficients 720 are provided to UL processing block of RAN node 706. The UE performs UL data transmission 722, and at 724 the UL processing block of RAN node 706 performs UL channel equalization and post-correction of the UL data transmission 722.

Figure 8 is a schematic of an example of an apparatus 800 in a first network node for determining correction coefficients for a wireless communication signal. The apparatus 800 comprises processing circuitry 802 (e.g. one or more processors) and a memory 804 in communication with the processing circuitry 802. The memory 804 contains instructions, such as computer program code 410, executable by the processing circuitry 802. The apparatus 800 also comprises an interface 806 in communication with the processing circuitry 802. Although the interface 806, processing circuitry 802 and memory 804 are shown connected in series, these may alternatively be interconnected in any other way, for example via a bus.

In one embodiment, the memory 804 contains instructions executable by the processing circuitry 802 such that the apparatus 800 is operable/configured to receive, from a second network node on a first channel, a reference signal; receive information identifying properties of a second channel from the first network node to the second network node; and determine, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel. In some examples, the apparatus 800 is operable/configured to carry out the method 200 described above with reference to Figure 2.

It should be noted that the above-mentioned examples illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative examples without departing from the scope of the appended statements. The word “comprising” does not exclude the presence of elements or steps other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the statements below. Where the terms, “first” , “second” etc. are used they are to be understood merely as labels for the convenient identification of a particular feature. In particular, they are not to be interpreted as describing the first or the second feature of a plurality of such features (i.e., the first or second of such features to occur in time or space) unless explicitly stated otherwise. Steps in the methods disclosed herein may be carried out in any order unless expressly otherwise stated. Any reference signs in the statements shall not be construed so as to limit their scope.

Claims

A method in a first network node of determining correction coefficients for a wireless communication signal, the method comprising:

receiving, from a second network node on a first channel, a reference signal;

receiving information identifying properties of a second channel from the first network node to the second network node; and

determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.
The method of claim 1, comprising determining, from the measurements of the reference signal, properties of the first channel.
The method of claim 2, wherein determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel comprises determining, from the information and the properties of the first channel, correction coefficients for a signal on the first channel or the second channel.
The method of claim 2 or 3, wherein the properties of the first channel comprise a channel response or estimated channel response of the first channel.
The method of any of claims 1 to 4, wherein the information identifying properties of the second channel comprises Channel State Information (CSI) of the second channel.
The method of any of claims 1 to 5, comprising determining, from the information identifying properties of the second channel, an estimate of properties of the first channel.
The method of claim 6, wherein determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel comprises determining, from the estimate of properties of the second channel and the measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.
The method of claim 6 or 7, wherein the estimate of properties of the first channel comprises a channel response or an estimate of a channel response of the first channel.
The method of any of claims 6 to 8, comprising equalizing, using the estimate of properties of the first channel, a channel response or an estimation of a channel response of the first channel determined from measurements of the reference signal, to obtain an equalized channel response,

wherein determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel comprises determining the correction coefficients from the equalized channel response.
The method of any of claims 6 to 9, wherein determining, from the information identifying properties of the second channel, an estimate of properties of the first channel comprises using, as the estimate of the properties of the first channel, the properties of the second channel.
The method of any of claims 1 to 10, wherein determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel comprises determining, from the information and measurements of the reference signal, correction coefficients for a signal on the second channel.
The method of claim 11, comprising applying the correction coefficients to a signal to be transmitted to the second network node to obtain a corrected signal, and transmitting the corrected signal to the second network node on the second channel.
The method of claim 11 or 12, comprising sending the correction coefficients to the second network node.
The method of any of claims 1 to 13, wherein determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel comprises determining, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel.
The method of claim 14, comprising applying the correction coefficients to a signal received from the second network node on the first channel.
The method of claim 14 or 15, comprising sending the correction coefficients to the second network node.
The method of any of claims 1 to 16, wherein the correction coefficients correct or compensate for distortions to a signal on the first channel or the second channel caused by apparatus of the first network node or the second network node.
The method of any of claims 1 to 17, wherein the first network node comprises a Radio Access Network (RAN) node and the second network node comprises a User Equipment (UE) .
The method of claim 18, wherein the second channel comprises a downlink channel and the first channel comprises an uplink channel.
The method of any of claims 1 to 17, wherein the first network node comprises a User Equipment (UE) and the second network node comprises a Radio Access Network (RAN) node.
The method of claim 20, wherein the second channel comprises an uplink channel and the first channel comprises a downlink channel.
The method of any of claims 1 to 21, wherein the reference signal comprises a sounding reference signal (SRS) , Channel State Information Reference Signal (CSI-RS) and/or demodulation reference signal (DMRS) .
The method of any of claims 1 to 22, wherein the information identifying properties of the second channel is received from the second network node.
A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out a method according to any of claims 1 to 23.
A carrier containing a computer program according to claim 24, wherein the carrier comprises one of an electronic signal, optical signal, radio signal or computer readable storage medium.
A computer program product comprising non transitory computer readable media having stored thereon a computer program according to claim 24.
Apparatus in a first network node for determining correction coefficients for a wireless communication signal, the apparatus comprising a processor and a memory, the memory containing instructions executable by the processor such that the apparatus is operable to:

receive, from a second network node on a first channel, a reference signal;

receive information identifying properties of a second channel from the first network node to the second network node; and

determine, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.
The apparatus of claim 27, wherein the memory contains instructions executable by the processor such that the apparatus is operable to perform the method of any of claims 2 to 23.
Apparatus in a first network node for determining correction coefficients for a wireless communication signal, the apparatus configured to:

receive, from a second network node on a first channel, a reference signal;

receive information identifying properties of a first channel from the first network node to the second network node; and

determine, from the information and measurements of the reference signal, correction coefficients for a signal on the first channel or the second channel.
The apparatus of claim 29, wherein the apparatus is configured to perform the method of any of claims 2 to 23.