Apparatus, method and computer program

Abstract

The invention addresses the need for a digital post distortion (DpoD) technique that remains effective regardless of how large the data modulation order is. The solution is in providing a first low or

Description

TECHNICAL FIELD

[0001] Various embodiments of this disclosure relate generally to methods, apparatus and computer programs, and in particular - but not exclusively, to DMRS-based digital post distortion for Higher Order Modulation Schemes in 6G communication systems. BACKGROUND

[0002] A communication system can be seen as a facility that enables communication sessions between two or more communication devices, or provides communication devices access to a network, a mobile or wireless communication network is one example of a communication network, a communication device may be provided with a service by an application server.

[0003] A mobile or wireless communication network may operate in accordance with standard(s), such as those provided by 3GPP (Third Generation Partnership Project) or ETSI (European Telecommunications Standards Institute). Examples of mobile or wireless communication network that operate in accordance with 3GPP standards are generally referred to as 4G (4th Generation) networks, 5G (5th Generation) network, 5G-Advanced networks and 6G networks. SUMMARY

[0004] Some embodiments of this disclosure will be described with respect to certain aspects. These aspects are not intended to indicate key or essential features of the various example embodiments of this disclosure, nor are they intended to be used to limit the scope of thereof. Other features, aspects, and elements will be readily apparent to a person skilled in the art in view of this disclosure. For example, it should be appreciated that further aspects may be provided by the combination of any two or more of the various aspects described herein.

[0005] In a first aspect there is provided an apparatus comprising means for multiplexing a signal comprising data symbols, first reference symbols and second reference symbols, modulating the data symbols using a first modulation scheme, modulating the first reference symbols using a second modulation scheme, modulating the second reference symbols using the first modulation scheme, wherein the first modulation scheme is different from the second modulation scheme; and causing the signal comprising the modulated data symbols, modulated first reference symbols and modulated second reference symbols to be transmitted at a first power.

[0006] The first reference symbols may comprise demodulation reference signals.

[0007] The second reference symbols may comprise demodulation reference signals.

[0008] A symbol location and size of a sequence of the first reference symbols and a symbol location and size of a sequence of the second reference symbols may be the same or different.

[0009] The first modulation scheme may be of a higher order than the second modulation scheme.

[0010] At least one modulated signal point in at least one symbol of the second reference symbols may be different from any of the modulated points in the first reference symbols.

[0011] The data symbols may be physical uplink shared channel data symbols.

[0012] The apparatus may comprise means for receiving, from a network, a first transmission block configuration for the signal and requesting, based on a change of transmission parameters at the apparatus, a second transmission block configuration from the network.

[0013] The change in transmission parameters may comprise a change in temperature at the user equipment, a change of the power amplifier at the user equipment or a change of the front-end path at the user equipment.

[0014] The first modulation scheme may be determined from a first modulation and coding scheme, MCS, and the second modulation scheme may be determined from a second MCS.

[0015] The apparatus may comprise a user equipment or be comprised in the user equipment.

[0016] In a second aspect there is provided an apparatus comprising means for receiving a signal comprising data symbols, first reference symbols and second reference symbols, wherein the data symbols and the second reference symbols are modulated using a first modulation scheme and the first reference symbols are modulated using a second modulation scheme, wherein the first modulation scheme is different from the second modulation scheme, performing channel estimation using the first reference symbols and determining digital post distortion parameters based on the second reference symbols.

[0017] The first reference symbols may comprise demodulation reference signals.

[0018] The second reference symbols may comprise demodulation reference signals.

[0019] A symbol location and size of a sequence of the first reference symbols and a symbol location and size of a sequence of the second reference symbols may be the same or different.

[0020] The first modulation scheme may be of a higher order than the second modulation scheme.

[0021] At least one modulated signal point in at least one symbol of the second reference symbols may be different from any of the modulated points in the first reference symbols.

[0022] The apparatus may comprise means for providing, to the user equipment, a first transmission block configuration for determining digital post distortion parameters and providing, based on at least one of a request from the user equipment or a determination at the apparatus, to provide a second transmission block configuration to the user equipment.

[0023] The determination at the apparatus may comprise at least one of the following: the apparatus determining to change the user equipment transmission power, a number of time slots elapsing or determining to change the first modulation scheme or the second modulation scheme.

[0024] The request from the user equipment may be based on a change of transmission parameters at the user equipment.

[0025] The change in transmission parameters may comprise a change in temperature at the user equipment, a change of the power amplifier at the user equipment, a change of the front-end path at the user equipment, receiving an indication to change a modulation scheme or receiving an indication to transition between different frequency bands or physical resource blocks.

[0026] The apparatus may comprise means for determining to handover the user equipment to a target node and providing the digital post distortion parameters to the target node.

[0027] In a third aspect there is provided a method comprising multiplexing a signal comprising data symbols, first reference symbols and second reference symbols, modulating the data symbols using a first modulation scheme, modulating the first reference symbols using a second modulation scheme, modulating the second reference symbols using the first modulation scheme, wherein the first modulation scheme is different from the second modulation scheme and causing the signal comprising the modulated data symbols, modulated first reference symbols and modulated second reference symbols to be transmitted at a first power.

[0028] The first reference symbols may comprise demodulation reference signals.

[0029] The second reference symbols may comprise demodulation reference signals.

[0030] A symbol location and size of a sequence of the first reference symbols and a symbol location and size of a sequence of the second reference symbols may be the same or different.

[0031] The first modulation scheme may be of a higher order than the second mod ulation scheme.

[0032] At least one modulated signal point in at least one symbol of the second reference symbols may be different from any of the modulated points in the first reference symbols.

[0033] The data symbols may be physical uplink shared channel data symbols.

[0034] The method may comprise receiving, from a network, a first transmission block configuration for the signal and requesting, based on a change of transmission parameters at the apparatus, a second transmission block configuration from the network.

[0035] The change in transmission parameters may comprise a change in temperature at the user equipment, a change of the power amplifier at the user equipment or a change of the front-end path at the user equipment.

[0036] The first modulation scheme may be determined from a first modulation and coding scheme, MCS, and the second modulation scheme may be determined from a second MCS.

[0037] The method may be performed at an apparatus. The apparatus may comprise a user equipment or be comprised in the user equipment.

[0038] In a fourth aspect there is provided a method comprising receiving a signal comprising data symbols, first reference symbols and second reference symbols, wherein the data symbols and the second reference symbols are modulated using a first modulation scheme and the first reference symbols are modulated using a second modulation scheme, wherein the first modulation scheme is different from the second modulation scheme, performing channel estimation using the first reference symbols and determining digital post distortion parameters based on the second reference symbols.

[0039] The first reference symbols may comprise demodulation reference signals.

[0040] The second reference symbols may comprise demodulation reference signals.

[0041] A symbol location and size of a sequence of the first reference symbols and a symbol location and size of a sequence of the second reference symbols may be the same or different.

[0042] The first modulation scheme may be of a higher order than the second modulation scheme.

[0043] At least one modulated signal point in at least one symbol of the second reference symbols may be different from any of the modulated points in the first reference symbols.

[0044] The method may comprise providing, to the user equipment, a first transmission block configuration for determining digital post distortion parameters and providing, based on at least one of a request from the user equipment or a determination at the apparatus, to provide a second transmission block configuration to the user equipment.

[0045] The determination at the apparatus may comprise at least one of the following: the apparatus determining to change the user equipment transmission power, a number of time slots elapsing or determining to change the first modulation scheme or the second modulation scheme.

[0046] The request from the user equipment may be based on a change of transmission parameters at the user equipment.

[0047] The change in transmission parameters may comprise a change in temperature at the user equipment, a change of the power amplifier at the user equipment, a change of the front-end path at the user equipment, receiving an indication to change a modulation scheme or receiving an indication to transition between different frequency bands or physical resource blocks.

[0048] The method may comprise determining to handover the user equipment to a target node and providing the digital post distortion parameters to the target node.

[0049] In a fifth aspect there is provided an apparatus comprising at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to perform a method according to the third aspect.

[0050] In a sixth aspect there is provided an apparatus comprising at least one processor, and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to perform a method according to the fourth aspect.

[0051] In a seventh aspect there is provided a non-transitory computer readable medium comprising instructions wherein the instructions when executed by at least one processor of an apparatus cause the apparatus to perform the method according to the third aspect.

[0052] In an eighth aspect there is provided a non-transitory computer readable medium comprising instructions wherein the instructions when executed by at least one processor of an apparatus cause the apparatus to perform the method according to the fourth aspect.

[0053] Some embodiments of the invention are defined in the dependent claims.

[0054] In the above, many different aspects have been described. As previously noted, it should be appreciated that further aspects may be provided by the combination of any two or more of the aspects described above (or otherwise in this disclosure).

[0055] Various other aspects are also described in the following detailed description and in the claims. BRIEF DESCRIPTION OF THE FIGURES

[0056] Some embodiments will be described, by way of non-limiting and illustrative example only, with reference to the figures, in which:

[0057] Fig. 1 shows an example of a communication network to which examples disclosed herein may be applied;

[0058] Fig. 2 shows a block diagram of a digital post distortion scheme at a receiver;

[0059] Fig. 3 shows a flowchart of a method according to an example embodiment;

[0060] Fig. 4 shows a flowchart of a method according to an example embodiment;

[0061] Fig. 5 shows an example of symbol location and size of a signal;

[0062] Fig. 6 shows an example of symbol location and size of a signal;

[0063] Fig. 7 shows an example of a system model of a transmitter and receiver for a DPoD architecture;

[0064] Fig. 8 shows a flowchart of a method according to an example embodiment;

[0065] Fig. 9 shows a flowchart of a method according to an example embodiment;

[0066] Fig. 10 shows a flowchart of a method according to an example embodiment;

[0067] Fig. 11 shows a signalling flow according to an example embodiment;

[0068] Fig. 12 shows an example of an apparatus. DETAILED DESCRIPTION

[0069] The following embodiments are provided by way of non-limiting and illustrative example. Although the specification may refer to “an”, “one”, or “some” embodi-ment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Further, when a particular feature, structure, or characteristic is described in connection of an embodiment, it intended such feature, structure, or characteristic may be applied in connection with other embodiments (whether or not explicitly described).

[0070] It shall be understood that although the terms “first,” “second” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0071] For the purposes of this disclosure, the phrases “at least one of A or B”, “at least one of A and B”, and “A and / or B” means (A), (B), or (A and B). For the purposes of this disclosure, the phrase “A, B, and / or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0072] As used herein, the term “or” refers to a non-exclusive “or” unless otherwise indicated (e.g., use of “or else” or “or in the alternative”).

[0073] As used herein, unless stated explicitly, performing a respective feature, step, or functionality “in response to A” does not indicate that the respective feature, step, or functionality is performed immediately after “A” occurs as one or more intervening features, steps, or functionalities may be performed (at least in part) between an occurrence of the respective feature, step, or function and “A”. Analogously, performing a respective feature, step, or functionality “based on A” does not indicate that the respective feature, step, or functionality is performed solely based on “A” as the respective feature, step, or functionality may be further based on one or more other features, steps, or functionalities in addition to “A”.

[0074] Embodiments described herein may be implemented in a communication network, such as any of the following radio access technologies (RATs): Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE), 5G (also called NR), or any future RAT such as 6G. Moreover, communication within the communication network may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0075] As used herein, the term “network device” or “network node” refers to a node in a communication network via which user equipment may access the network and / or which is configured to control radio communication and managing radio resources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node, a non-terrestrial network (NTN) or nonground network device, such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, or an aircraft network device.

[0076] Moreover, in connection of split radio access network (RAN), the network device may refer to a centralised unit (CU) of a base station and / or a distributed unit (DU) of a base station. An interface between CU and DU may be referred to as an F1 interface in NR. In the split RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit, CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more Dus, acting at least as transmit / receive (Tx / Rx) nodes. In some embodiments, the Dus may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0077] The term “terminal device” refers to any end device that may be configured to perform wireless communication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, USB dongles, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0078] A term “resource”, as used herein, may refer to radio resources in time domain, in frequency domain, in space domain, and / or in code domain. Some examples of resources may include, e.g., a physical resource block (PRB), a radio frame, a subframe, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term “transmission” and / or “reception” may refer to wirelessly transmitting and / or receiving via a wireless propagation channel on radio resources.

[0079] Fig. 1 illustrates an example of a communication network to which examples disclosed herein may be applied. The communication network or a cellular communication network may comprise a network node 110 configured to provide one or more cells, such as cell 100, and a network node 112 configured to provide one or more other cells, such as cell 102. Each cell may, for example, be a macro cell, a micro cell, femto, or a pico cell. The cell may define a coverage area or a service area of the corresponding access node.

[0080] The network node (110, 112) may be configured to provide a user equipment (UE) 120 (one or more Ues) with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node (110, 112) to the UE 120 and uplink (UL) communication from the UE 120 to the network node (110, 112). Examples of uplink channels may comprise physical uplink control channel (PLICCH) for transmitting control information and physical uplink shared channel (PUSCH) for transmitting data towards the network. Examples of downlink channels may comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the user equipment.

[0081] There may be a plurality of Ues (120, 122) in the system. Each of the plurality of Ues may be served by the same or by different network nodes (110, 112). UE may be configured with dual connectivity (DC), wherein the UE, for example UE 120, may be connected to multiple network nodes (110, 112). The Ues (120, 122) may communicate with each other, in case device-to-device (D2D) communication interface islOqualizerhed between them via a so-called sidelink (SL). Such D2D communications may be referred to as machine-to-machine, peer-to-peer (P2P) communications, or ve-hicle-to-vehicle (V2V), for example.

[0082] In the case of multiple network nodes in the communication network, the network nodes may be connected to each other via an interface. LTE specifications, for example, refer to such an interface as an X2 interface. An interface between an LTE node and a 5G node, or between two 5G nodes may be called an Xn interface.

[0083] The network nodes 110 and 112 may be further connected via another interface to a core network 116 of the communication network. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise a plurality of entities (e.g. a mobility management entity (MME) and a gateway node). The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signalling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices. The 5G specifications specify the core network as a 5G core (5GC). The 5GC may, for example, comprise an access and mobility management function (AMF) and a user plane function / gateway (UPF) and other functions. The AMF may handle termination of non-access stratum (NAS) signalling, NAS ciphering &integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may, for example, support packet routing and forwarding, packet inspection and quality of service (QoS) handling.

[0084] Out of band emissions are unwanted emissions immediately outside the assigned channel bandwidth. Out of band emissions may result from the modulation process and non-linearity in the transmitter but exclude spurious emissions. An out of band emission limit is specified in terms of a spectrum emission mask and an adjacent channel leakage power ratio (ACLR).

[0085] To improve measurement accuracy, sensitivity and efficiency, the resolution bandwidth may be smaller than the measurement bandwidth. When the resolution bandwidth is smaller than the measurement bandwidth, the result should be integrated over the measurement bandwidth in order to obtain the equivalent noise bandwidth of the measurement bandwidth.

[0086] NR Adjacent Channel Leakage power Ratio (NRaclr) is the ratio of the filtered mean power centred on the assigned NR channel frequency to the filtered mean power centred on an adjacent NR channel frequency at nominal channel spacing.

[0087] The assigned NR channel power and adjacent NR channel power are measured with rectangular filters with measurement bandwidths as specified and illustrated in Table 1. Channel bandwidth (MHz) 5,10,15,20,25,30,35,40,45,50 60,70,80,90,100 REF_SCS (kHz) 15 30 NRACLR measurement bandwidth (MHz) MBW=REF_SCS*(12‘Nrb+1) / 1000 NOTE : “Nrb” in the formula is the maximum transmission bandwidth configuration as defined in Table 5.3.2-1. Table 1

[0088] If the measured adjacent channel power is greater than -50 dBm then the NRaclr shall be higher than the value specified and illustrated in Table 2. Power class 1 Power class 1.5 Power class 2 Power class 3 NRACLR 37 dB 31 dB 31 dB 30 dB NOTE 1 : Void Table 2

[0089] The Error Vector Magnitude (EVM) is a measure of the difference between the reference waveform and the measured waveform. This difference is called the error vector. Before calculating the EVM the measured waveform is corrected by the sample timing offset and RF frequency offset. Then the carrier leakage shall be removed from the measured waveform before calculating the EVM.

[0090] The measured waveform is further 11qualizer using the channel estimates subjected to the EVM Hqualizer spectrum flatness requirement specified. For DFT-s-OFDM waveforms, the EVM result is defined after the front-end FFT and IDFT as the square root of the ratio of the mean error vector power to the mean reference power expressed as a %. For CP-OFDM waveforms, the EVM result is defined after the frontend FFT as the square root of the ratio of the mean error vector power to the mean reference power expressed as a %.

[0091] The basic EVM measurement interval in the time domain is one preamble sequence for the PRACH and one slot for PUCCH and PUSCH in the time domain. The EVM measurement interval is reduced by any symbols that contains an allowable power transient in the measurement interval.

[0092] The RMS average of the basic EVM measurements over 10 subframes for the average EVM case, and over 60 subframes for the reference signal EVM case, for the different modulation schemes shall not exceed the values specified as illustrated in Table 3 for the parameters defined in Table 4. For EVM evaluation purposes, all 13 PRACH preamble formats and all 5 PUCCH formats are considered to have the same EVM requirement as QPSK modulated. Parameter Unit Average EVM Level Pi / 2-BPSK % 30 QPSK % 17.5 16 QAM % 12.5 64 QAM % 8 256 QAM % 3.5 Table 3 Parameter Unit Level UE Output Power dBm > Table 6.3.1-1 UE Output Power for 256 QAM dBm > Table 6.3.1-1 + 10dB Operating conditions Normal conditions Table 4

[0093] Digital Post Distortion (DpoD) is used for compensating nonlinear distortion and channel effects in a received signal. A Demodulation Reference Signal (DMRS) may be utilized to estimate DpoD coefficients. This estimation is conducted by applying a least-squares (LS) method on the received DMRS-bearing Orthogonal Frequency Division Multiplexing (OFDM) symbol. The mathematical representation of the memory polynomial model (MPM) of the transmitted signal is given by: PTX DTX y(n) = ^^cp^x(n-d)\x(n-d)^-1 (1) p=l d=o p odd where (cpd) are the complex nonlinear coefficients modelling the UE power amplifier and x(n) is the input data signal to the power amplifier and “d” represents the memory effect of the power amplifier.

[0094] Fig. 2 shows a block diagram of a DpoD scheme at a receiver. It is assumed that the DMRS-bearing OFDM symbol carries only the DMRS sequence with no data being frequency-multiplexed. This may result in different envelope characteristics of the DMRS symbol compared to the actual data-bearing.

[0095] It has been proposed to boost the DMRS signal (e.g., transmit the DMRS signal at a higher power). However, a reference signal with high PAPR is not suitable for channel estimation. Further, off-line tuning of the boosting level may be required to find an optimum level that matches both channel estimation and parameter estimation. This offline approach may not be suitable for practical cases with variations in actual channels and variations in PA characteristics.

[0096] If we assume that the propagation channel has been perfectly estimated and equalized out, then the up-sampled IFFT transferred signal (q(n) in Fig. 7), may represent y(n). The input now should be estimated based on the output of the equation (1). This done by switching the inputs and outputs. Where cp, d denotes the MPM model coefficients used in the gNB: x(n) = / ■ p=i u odd (2)

[0097] If we could in gNB find the model parameters, cpd then we can find xA(n). For finding i we use the known transmit DMRS replica, xref, and the received up sampled DMRS signal, qref, in gNB. We define input-output relation again as a MPM model: xre prx Dtx d Wn _ lp-1 P=1 d=0 (3) Cp a can be found by LS algorithm.

[0098] To find the coefficients, the estimation problem is cast into a vector-matrix form for computational efficiency. Now letting cpd be the vector of complex nonlinear coefficients to be estimated, and (Y) the matrix whose columns are samples of the nonlinear basis functions with: Ypd(n) = 9ref(«-^)lQref(n-rf)lP 1 Thus, the vectorized form of the DpoD output is expressed as: (4) xref = Yc Given this, the LS estimation of cp j is obtained by: Cp d = (YHY)'-1YHXref (5) Equation (5) minimizes the error between the actual received DMRS-bearing OFDM samples and the estimated model, allowing for the precise determination of DpoD coefficients to mitigate nonlinear distortion effects and enhance receiver performance.

[0099] As shown by Equation (5), LS algorithm minimizes the error between the actual received DMRS-bearing OFDM samples and the estimated model, allowing for the precise determination of DpoD coefficients to mitigate nonlinear distortion effects and enhance receiver performance.

[0100] However, the assumption is that the propagation channel has been perfectly estimated and equalized out.

[0101] In FR1, gains by DpoD are expected for higher modulations. Specifically, DpoD is suitable for FR1 in the case of a high modulation scheme, e.g. >256 QAM where the EVM is the gating factor. The challenge with existing DpoD using DMRS is that the different DMRS sequences have different peak-to-average power ratios (PAPR) compared to the data signals, which is unsuitable for cases with high-order modulation schemes. The core challenge is ensuring the DpoD model’s applicability across various modulation schemes when utilizing DMRS-based reference signals for DpoD.

[0102] There is a question of how to use DMRS with lower order modulation schemes (e.g. Zadoff-Chu (ZC) sequences or QPSK / tt / 2-BPSK based Computer Generated Sequences, CGS) to get an accurate DpoD model for compensating nonlinearities on modulations of orders larger or equal to 256 QAM in 6G / In other words, there should be a compensation for the DpoD model being obtained / derived using data of much lower modulation order than the data on which the model is used.

[0103] The objective is to design a DpoD model that accurately predicts DpoD coefficients for any high-order modulation scheme based on reference symbols.

[0104] The following addresses the need for a DpoD technique that remains effective regardless of how large the modulation order is. Traditional DpoD solutions, which rely on DMRS for estimating DpoD coefficients, face performance degradation because the DMRS signal typically has a low modulation order (i.e. QPSK), low PAPR, whereas the data signal may have higher order modulation, high PAPR.

[0105] The easiest approach may be to change the DMRS signal to be as high as the data signal e.g. 256 QAM modulated. However, the channel estimation (which uses DM RS) accuracy may decrease.

[0106] Fig. 3 shows a flowchart of a method according to an example embodiment. The method may be performed at an apparatus. The apparatus may comprise a user equipment or be comprised in the user equipment.

[0107] At 301, the method comprises multiplexing a signal comprising data symbols, first reference symbols and second reference symbols;

[0108] At 302, the method comprises modulating the data symbols using a first modulation scheme;

[0109] At 303, the method comprises modulating the first reference symbols using a second modulation scheme.

[0110] At 304, the method comprises modulating the second reference symbols using the first modulation scheme, wherein the first modulation scheme is different from the second modulation scheme; and

[0111] At 305, the method comprises causing the signal comprising the modulated data symbols, modulated first reference symbols and modulated second reference symbols to be transmitted at a first power.

[0112] Fig. 4 shows a flowchart of a method according to an example embodiment.

[0113] At 401, the method comprises receiving a signal comprising data symbols, first reference symbols and second reference symbols, wherein the data symbols and the second reference symbols are modulated using a first modulation scheme and the first reference symbols are modulated using a second modulation scheme, wherein the first modulation scheme is different from the second modulation scheme.

[0114] At 402, the method comprises performing channel estimation using the first reference symbols.

[0115] At 403, the method comprises determining digital post distortion parameters based on the second reference symbols.

[0116] The first modulation scheme may be of a higher order than the second modulation scheme. The first modulation scheme may be determined from a first modulation and coding scheme, MCS, and the second modulation scheme may be determined from a second MCS. For example, the first modulation scheme may be Zadoff-Chu (ZC) sequences or QPSK / tt / 2-BPSK based Computer Generated Sequences (CGS). The second modulation scheme may be 256 QAM or >256 QAM. At least one modulated signal point in at least one symbol of the second reference symbols is different from any of the modulated points in the first reference symbols.

[0117] The first reference symbols and second reference symbols may comprise any known sequence suitable for channel estimation or DpoD parameter estimation, respectively. The first reference symbols may comprise DMRS symbols. The second reference symbols may comprise DMRS symbols. The data symbols may be PUSCH data symbols.

[0118] In an example embodiment, two DMRS symbols are used where the first DMRS symbol (denoted as DMRS_1 symbol) is for channel equalization (as in 5G) and a second part (denoted as DMRS_2 symbol) is modulated as 256 QAM (or as the actual MCS used for the PUSCH data). In gNB, during DpoD activation two DMRS replicas are received where the first part (“DMRS Replica”) is used to ensure that channel estimation remains accurate and the second part (“DMRS_Replica_2”) is used to ensure an accurate DpoD model.

[0119] Both parts of the DMRS should be used to perform both tasks A and B since these cannot be effectively decoupled. QPSK is used first since the dominant distortion is that introduced by the propagation channel, and 256QAM is used second where the dominant distortion is that introduced by the propagation channel + PA response. Having approximated the channel from the QPSK pilots, we can approximate the PA response.

[0120] DMRS_2 is the same as the user data with the exception that the data sequence is known by the receiver. gNB decides the symbol location and size of the known sequence. A symbol location and size of a sequence of the first reference symbols and a symbol location and size of a sequence of the second reference symbols may be the same or different. Fig. 5 shows an example where the symbol location and size of DMRS_2 is the same as that of DMRS_1 and Fig. 6 shows a case where the symbol location and size of DMRS_2 is different from that of DMRS_1. In both cases, the DMRS are known REs with the same MCS and PAPR as PUSCH.

[0121] Fig. 7 shows a block diagram of a system model for the proposed method according to an example. At the UE side, PUSCH symbols, DMRS_1 symbols and DM RS-2 symbols are multiplexed and modulated and transmitted from a UE antenna. At the NW side, by using the existing DMRS symbol, denoted by DMRS-1, which has a low modulation order, successful channel equalisation can be achieved. For DpoD estimation, “DMRS_2 replica” uses the same modulation scheme as, and has a PAPR close to, the actual data-bearing symbol. The actual “duplicate” of the data signal’s MCS may be used for the “DMRS_2 replica” reference signal.

[0122] The reference signal for digital post-distortion (i.e. the second reference symbols) doesn’t need to be sent in each slot. How often the second reference symbols needs to be transmitted, e.g., every slot or each frame, is a choice taken by gNB dependent on how accurately DpoD works since it is dependent on the actual PA and channel characteristics.

[0123] Using a method as described with reference to Figs. 3 and 4 means that existing 3GPP-specified DM RS signal do not need to be boosted. This may avoid the impact signal boosting may have on other applications where the DM RS reference signal is used. The amplitude level of the DM RS signal does not need to be tuned offline offline to find an optimum level for both channel estimation and digital pre-distortion, avoiding impractical offline data tuning.

[0124] Fig. 8 shows a flowchart of a method according to an example embodiment. The method may be performed at an apparatus. The apparatus may comprise a UE or be comprised in the UE.

[0125] At 801, the method comprises receiving, from a network, a first transmission block configuration for determining digital post distortion parameters; and

[0126] At 802, the method comprises requesting, based on a change of transmission parameters at the apparatus, a second transmission block configuration from the network.

[0127] The method may comprise receiving the second transmission block configuration from the network.

[0128] Fig. 9 shows a flowchart of a method according to an example embodiment. The method may be performed at an apparatus. The apparatus may comprise a network node, such as a BS (e.g., gNB) or NF or be comprised in the network node.

[0129] At 901, the method comprises providing, to a user equipment, a first transmission block configuration for determining digital post distortion parameters.

[0130] At 902, the method comprises providing, based on at least one of a request from the user equipment or a determination at the apparatus, to provide a second transmission block configuration to the user equipment.

[0131] The request from the user equipment may be based on a change of transmission parameters at the user equipment.

[0132] The first transmission block configuration may comprise a configuration of first data symbols, first reference symbols and second reference symbols, wherein the first data symbols and second reference symbols are modulated using a first modulation scheme and the first reference symbols are modulated using a second modulation scheme, wherein the first modulation scheme is different from the second modulation scheme for causing a signal to be transmitted as described with reference to Figs. 3 and 4. The second transmission block may comprise a configuration of second data symbols, third reference symbols and fourth reference symbols, wherein the second data symbols and fourth reference symbols are modulated using a third modulation scheme and the third reference symbols are modulated using a fourth modulation scheme, wherein the third modulation scheme is different from the fourth modulation scheme for causing a signal to be transmitted as described with reference to Figs. 3 and 4. The first modulation scheme may be different from the third modulation scheme or the second modulation scheme may be different from the fourth modulation scheme.

[0133] The change in transmission parameters may comprise a change in temperature at the user equipment, a change of the power amplifier at the user equipment or a change of the front-end path at the user equipment. The change in transmission parameters may comprise at least one of receiving an indication to change a modulation scheme or receiving an indication to transition between different frequency bands or physical resource blocks. The method may comprise receiving the indication to change the modulation scheme in a downlink control information message or receiving the indication to transition between different frequency bands or physical resource blocks in a radio resource control message.

[0134] The determination at the apparatus may comprise at least one of the following: the apparatus determining to change the user equipment transmission power, a number of time slots elapsing or determining to change the first modulation scheme or the second modulation scheme. Changes in the MCS, as defined by standards may trigger the need for new DPOD parameters and a second transmission block configuration. Transitions between different frequency bands or PRBs to comply with spectrum usage may also trigger the need for new DPOD parameters and a second transmission block configuration. This may include moving to a different band to avoid interference. (SEP related)

[0135] In an example embodiment, if the PA parameters at the UE change, the UE may inform the gNB to request for another PUSCH block configuration because the transmitter behavior has changed and the gNB configures the UE to send “DMRS_2 replica” again to measure the transmitter parameters at the gNB (e.g., provides a second transmission block configuration). It can be for example in the cases where the UE device is getting heated, and PA’s power will consequently change. Since only the UE knows its actual temperature, it is aware of the effect of temperature on the transmission power. It could also be the case where UE choose another Power amplifier or front-end path PA for its transmission.

[0136] A method as described with reference to Fig. 4 may comprise determining to handover the user equipment to a target node and providing the digital post distortion parameters to the target node.

[0137] Fig. 10 shows a flowchart of a method according to an example embodiment. The method may be performed at an apparatus. The apparatus may comprise a network node such as a BS (e.g., gNB) or NF or be comprised in the network node.

[0138] At 1001 the method comprises receiving a signal comprising data symbols, first reference symbols and second reference symbols, wherein the data symbols and the second reference symbols are modulated using a first modulation and coding scheme, modulation scheme and the first reference symbols are modulated using a second modulation scheme, wherein the first modulation scheme is different from the second modulation scheme.

[0139] At 1002, the method comprises performing channel estimation using the first reference symbols.

[0140] At 1003, the method comprises determining digital post distortion parameters based on the second reference symbols.

[0141] At 1004, the method comprises determining to handover the user equipment to a target node.

[0142] At 1005, the method comprises providing the digital post distortion parameters to the target node.

[0143] During handover, if the UE is disconnected from one gNB and moves to another gNB, the latest estimated DPoD coefficients may be transferred from the source gNB to the destination gNB and this may be communicated via the destination gNB to the UE.

[0144] The method may comprise receiving an indication from the user equipment of a change of transmission parameters at the user equipment and providing an indication to the target node of the change of transmission parameters.

[0145] If gNB is targeting new M-ary PUSCH for UL or if gNB decides to change UL power then gNB estimates the new set of coefficients. However, this estimation is not free of charge and gNB needs to run the DPoD algorithm each time. If gNB makes a “log file” of the already estimated coefficients for a previous M-ary or previous UL power for this specific UE, then gNB does not need to re-estimate the coefficient for those actual cases again and can only reuse the coefficients in the “log file”. This log file can be handovered by the source gNB to the destination gNB. The whole procedure of the handover of the “log file” is in principle independent of how the PA coefficients were estimated.

[0146] Fig. 11 shows a proposed signaling diagram. The gNB selects a first configuration of the modulation order M for the UL data transmission of the UE. The UE will then use the same modulation scheme to configure the UL DM RS transmission for DPoD implementation.

[0147] At step 1, the gNB configures a block of PUSCH, DMRS (e.g., first reference symbols with a modulation scheme other that that of PUSCH) and “M-ary” QAM DMRS (e.g., second reference signals with the same modulation scheme as PUSCH). This configuration is a first transmission block configuration.

[0148] At step 2, the UE transmits PUSCH with the configured DMRS symbols.

[0149] Following step 2, the gNB activates DPoD. The gNB may repeat “Step 1” and reconfigured the PUSCH symbols in, e.g., the following cases, if gNB is targeting new M-ary PUSCH for UL or if gNB decide to change UL power or after a number of time slots (if gNB desires for any reason).

[0150] If UE’s transmission parameters get changed by e.g. temperature, switching of the PA or front-end path, etc., then the UE requests gNB for reconfiguration of PUSCH symbols. The gNB repeats step 1 and provides a second transmission block configuration.

[0151] At the final step, if the gNB determines to handover to another target or destination gNB, the gNB transfers the UE transmitter’s coefficients (e.g., DPoD coefficients) to the destination gNB.

[0152] Fig. 12 shows, by way of example, a block diagram of an apparatus 10. The apparatus 10 comprises, for example, at least one processor 12 and at least one memory 14 storing instructions 15 that, when executed by the at least one processor, cause the apparatus 10 at least to perform the method or methods (or portion(s) thereof) as disclosed herein, and any of the embodiments (or respective portion(s) thereof). In an example, the at least one memory and the instructions (e.g. a computer program code, software), are configured, with the at least one processor, to cause the apparatus 10 to perform the method or methods (or portion(s) thereof) as disclosed herein, and any of the embodiments (or respective portion(s) thereof).

[0153] A processor 12 may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with embodiments described herein.

[0154] As used herein, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a user equipment, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessors), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term herein, including in any claims. As a further example, as used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0155] The memory 14 may be implemented using any suitable data storage technology. The memory may comprise a database for storing data. The memory 14 may, for example, be at least in part external to apparatus 10 but accessible to apparatus 10.

[0156] The instructions 15 may be comprised in a computer readable medium or a non-transitory computer readable medium. A term non-transitory, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. random access memory, RAM, vs. read only memory, ROM).

[0157] For example, the apparatus 10 is a terminal device, such as a UE. As another example, the apparatus is comprised in such a terminal device, e.g. as a chipset configured to control the terminal device. The apparatus 10 may be caused or configured or comprise means to perform at least the method of Figs. 3 or 8 and / or any one or more of the embodiments described herein.

[0158] As another example, the apparatus 10 is a network entity. In another embodiment, the apparatus is comprised in such a network entity, e.g. as a chipset configured to control the network entity. The apparatus 10 may be caused or configured or comprise means to perform at least the method of Figs. 4, 9 or 10 and / or any one or more of the embodiments described herein.

[0159] The apparatus may comprise one or more entities of any of protocol layers, such as a MAC entity, an RRC entity, an RLC entity, a PDCP entity or a PHY entity. In some embodiments, the entity is configured to perform at least the method of Figs. 4, 9 or 10, and / or any one or more of the embodiments described.

[0160] The apparatus 10 comprises a radio interface 16. The radio interface 16 may provide the apparatus 10 with communication capabilities. The radio interface 16 may comprise a receiver configured to receive information in accordance with at least one cellular or non-cellular standard. The radio interface 16 may comprise a transmitter configured to transmit information in accordance with at least one cellular or non-cellular standard. The receiver may comprise more than one receiver. The transmitter may comprise more than one transmitter. The radio interface 16 may comprise a transceiver configured to receive and transmit information in accordance with at least one cellular or non-cellular standard. The transceiver may comprise more than one transceiver.

[0161] The apparatus 10 may comprise a user interface 18 comprising, for example, at least one of a keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 18 may be used to control the apparatus by the user. The user interface 18 may be external to the apparatus 10. For example, the apparatus 10 may be connected to another device, such as a computer, either via wireless or wired connection, and the apparatus 10 is controlled by the user via the computer.

[0162] In an embodiment, at least some of the processes described herein may be carried out by an apparatus comprising means for carrying out at least some of the described processes. Means for performing method steps as disclosed herein may include software and / or hardware components of the apparatus 10. For example, the at least one processor 12, the memory 14, and the computer program code form means for carrying out the method or methods (or portion(s) thereof) as disclosed herein, and any of the embodiments (or respective portion(s) thereof). As used herein the term “means” is to be construed in singular form, i.e. referring to a single element, or in plural form, i.e. referring to a combination of single elements. Therefore, terminology “means for [performing A, B, C]”, is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C. Further, terminology “means for performing A, means for performing B, means for performing C” is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

[0163] Even though this disclosure has been described above with reference to non-limiting and illustrative examples according to the accompanying figures, it is clear that the scope of this disclosure is not restricted thereto - but can be modified in many 5 different ways. As technology advances, it will become apparent to a person skilled in art as to how the disclosure can be further implemented and / or modified in various ways. Further, it is clear to a person skilled in the art that the embodiments described herein may, but are not required to, be combined in various ways with other embodiments described herein. 10

Claims

1. An apparatus comprising means for:multiplexing a signal comprising data symbols, first reference symbols and second reference symbols;modulating the data symbols using a first modulation scheme;modulating the first reference symbols using a second modulation scheme;modulating the second reference symbols using the first modulation scheme, wherein the first modulation scheme is different from the second modulation scheme; andcausing the signal comprising the modulated data symbols, modulated first reference symbols and modulated second reference symbols to be transmitted at a first power.

2. The apparatus according to claim 1, wherein the first reference symbols comprise demodulation reference signals.

3. The apparatus according to claim 2, wherein the second reference symbols comprise demodulation reference signals.

4. The apparatus according to any of claims 1 to 3, wherein a symbol location and size of a sequence of the first reference symbols and a symbol location and size of a sequence of the second reference symbols is the same or different.

5. The apparatus according to any of claims 1 to 4, wherein the first modulation scheme is of a higher order than the second modulation scheme.

6. The apparatus according to any of claims 1 to 5, wherein at least one modulated signal point in at least one symbol of the second reference symbols is different from any of the modulated points in the first reference symbols.

7. The apparatus according to any of claims 1 to 6, wherein the data symbols are physical uplink shared channel data symbols.

8. The apparatus according to any of claims 1 to 7, comprising means for:receiving, from a network, a first transmission block configuration for the signal; andrequesting, based on a change of transmission parameters at the apparatus, a second transmission block configuration from the network.

9. The apparatus according to claim 8, wherein the change in transmission parameters comprises a change in temperature at the user equipment, a change of the power amplifier at the user equipment or a change of the front-end path at the user equipment10. The apparatus according to any of claims 1 to 9, wherein the first modulation scheme is determined from a first modulation and coding scheme, MCS, and the second modulation scheme is determined from a second MCS.

11. The apparatus according to any of claims 1 to 10, wherein the apparatus comprises a user equipment or is comprised in the user equipment.

12. An apparatus comprising means for:receiving a signal comprising data symbols, first reference symbols and second reference symbols, wherein the data symbols and the second reference symbols are modulated using a first modulation scheme and the first reference symbols are modulated using a second modulation scheme, wherein the first modulation scheme is different from the second modulation scheme;performing channel estimation using the first reference symbols; anddetermining digital post distortion parameters based on the second reference symbols.

13. The apparatus according to claim 12, wherein the first reference symbols comprise demodulation reference signals.

14. The apparatus according to claim 13, wherein the second reference symbols comprise demodulation reference signals.

15. The apparatus according to any of claims 12 to 14, wherein a symbol location and size of a sequence of the first reference symbols and a symbol location and size of a sequence of the second reference symbols is the same or different.

16. The apparatus according to any of claims 12 to 15, wherein the first modulation scheme is of a higher order than the second modulation scheme.

17. The apparatus according to any of claims 12 to 16, wherein at least one modulated signal point in at least one symbol of the second reference symbols is different from any of the modulated points in the first reference symbols.

18. The apparatus according to any of claims 12 to 17, comprising means for: providing, to the user equipment, a first transmission block configuration for determining digital post distortion parameters; andproviding, based on at least one of a request from the user equipment or a determination at the apparatus, to provide a second transmission block configuration to the user equipment.

19. The apparatus according to claim 18, wherein the determination at the apparatus comprises at least one of the following: the apparatus determining to change the user equipment transmission power, a number of time slots elapsing or determining to change the first modulation scheme or the second modulation scheme.

20. The apparatus according to claim 18 or claim 19, wherein the request from the user equipment is based on a change of transmission parameters at the user equipment.

21. The apparatus according to claim 20, wherein the change in transmission parameters comprises a change in temperature at the user equipment, a change of the power amplifier at the user equipment, a change of the front-end path at the user equipment, receiving an indication to change a modulation scheme or receiving an indication to transition between different frequency bands or physical resource blocks.

22. The apparatus according to any of claims 12 to 21, comprising means for: determining to handover the user equipment to a target node; and providing the digital post distortion parameters to the target node.

23. A method, comprising:multiplexing a signal comprising data symbols, first reference symbols and second reference symbols;modulating the data symbols using a first modulation scheme;modulating the first reference symbols using a second modulation scheme;modulating the second reference symbols using the first modulation scheme, wherein the first modulation scheme is different from the second modulation scheme; andcausing the signal comprising the modulated data symbols, modulated first reference symbols and modulated second reference symbols to be transmitted at a first power.

24. A method, comprising:receiving a signal comprising data symbols, first reference symbols and second reference symbols, wherein the data symbols and the second reference symbols are modulated using a first modulation scheme and the first reference symbols are modulated using a second modulation scheme, wherein the first modulation scheme is different from the second modulation scheme;performing channel estimation using the first reference symbols; and determining digital post distortion parameters based on the second reference symbols.

25. A computer program product comprising program instructions which, when the program is executed by an apparatus, cause the apparatus to perform: multiplexing a signal comprising data symbols, first reference symbols and second reference symbols;modulating the data symbols using a first modulation scheme;modulating the first reference symbols using a second modulation scheme;modulating the second reference symbols using the first modulation scheme, wherein the first modulation scheme is different from the second modulation scheme; andcausing the signal comprising the modulated data symbols, modulated firstreference symbols and modulated second reference symbols to be transmitted at a first power.

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