Transmissions of reference signal sequences

Abstract

According to an example aspect of the present disclosure, there is provided a method, comprising receiving, from a wireless network node, a resource allocation for an uplink data transmission, determining a first reference signal sequence, determining a second reference signal sequence based at least partly on the first reference signal sequence and transmitting, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission.

Description

[0001] TRANSMISSIONS OF REFERENCE SIGNAL SEQUENCES

[0002] FIELD

[0003] Various example embodiments relate in general to cellular communication networks and more specifically, to transmissions of reference signal sequences in such networks.

[0004] BACKGROUND

[0005] Reference signals may be exploited at least in various cellular communication networks, such as, in cellular communication networks operating according to 5G radio access technology. 5G radio access technology may also be referred to as New Radio, NR, access technology. 3rd Generation Partnership Project, 3GPP, develops standards for 5G / NR and for future radio access technologies. 6G radio access technology is under plan in 3GPP. Nevertheless, there is a need to enhance transmission of reference signal sequences at least for future radio access technologies.

[0006] SUMMARY

[0007] According to some aspects, there is provided the subject-matter of the independent claims. Some example embodiments are defined in the dependent claims.

[0008] The scope of protection sought for various example embodiments of the disclosure is set out by the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various example embodiments of the disclosure.

[0009] According to an aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to receive, from a wireless network node, a resource allocation for an uplink data transmission, determine a first reference signal sequence, determine a second reference signal sequence based at least partly on the first reference signal sequence and transmit, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission. The apparatus may be a user equipment or a control device configured to control the functioning thereof, when installed therein. Example embodiments of the aspect may comprise at least one feature from the following bulleted list or any combination of the following features:

[0010] • wherein the first and second reference signal sequences compose a combined reference signal sequence, wherein the combined reference signal sequence is for at least one of demodulation or distortion compensation;

[0011] • wherein the apparatus is caused to perform at least one of the following, interleaving the first reference signal sequence and the second reference signal sequence in one orthogonal frequency division multiplexing, OFDM, symbol, transmitting the first reference signal sequence and the second reference signal sequence in one OFDM symbol or transmitting the first reference signal sequence and the second reference signal sequence in one or more same resource blocks, RBs;

[0012] • wherein the at least one processing core and the at least one memory further cause the apparatus at least to determine a third reference signal sequence for demodulation and transmit the third reference signal sequence consecutive to the first reference signal sequence in another orthogonal frequency-division multiplexing, OFDM, symbol;

[0013] • wherein at least one of a total transmission power of the first reference signal sequence and the second reference signal sequence is substantially the same as a transmission power of the uplink data transmission, or a maximum total transmission power of the first reference signal sequence and the second reference signal sequence is higher than a maximum transmission power of a third reference signal sequence;

[0014] • wherein the at least one processing core and the at least one memory further cause the apparatus at least to determine the second reference signal sequence based on one of the following, conjugate of the first reference signal sequence, negative-conjugate of the first reference signal sequence, repetition of the first reference signal sequence, negative of the first reference signal sequence or zero power sequence when the first reference signal sequence is a boosted Gold sequence;

[0015] • wherein the at least one processing core and the at least one memory further cause the apparatus at least to determine at least one condition for transmission of at least one of the first reference signal sequence or the second reference signal sequence and trigger the transmission of the at least one of the first reference signal sequence or the second reference signal sequence when the at least one condition is met;

[0016] • wherein the at least one condition for transmission of the at least one of the first reference signal sequence or the second reference signal sequence comprises at least one of: radio resource control, RRC, configuration received from the wireless network node, a downlink control message trigger received from the wireless network node, a predefined modulation order, a predefined modulation coding scheme, a predefined waveform type, a predefined time slot number, or a length of a scheduled uplink data transmission;

[0017] • wherein the first reference signal sequence comprises a demodulation reference signal wherein the first reference signal sequence is generated based on a Zadoff-Chu sequence or a Gold sequence;

[0018] • wherein at least one of the first reference signal or the second reference signal sequence forms a distortion compensation reference signal, wherein the second reference signal sequence is generated based on the first reference signal sequence;

[0019] • wherein the uplink data transmission comprises a high order modulation transmission, wherein the modulation order of the high order modulation transmission is higher than a modulation order threshold;

[0020] • wherein an output signal envelope of the first reference signal sequence and the second reference signal sequence is substantially the same as an output signal envelope of the uplink data transmission, or an output signal envelope variation of the first reference signal sequence and the second reference signal sequence is higher than an output signal envelope variation of a third reference signal sequence.

[0021] According to an aspect of the present disclosure, there is provided an apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to receive, from a user equipment, a first reference signal sequence, receive, from the user equipment a second reference signal sequence, wherein the second reference signal sequence is determined based at least partly on the received first reference signal sequence and perform at least one of demodulation or distortion mitigation based on the received first reference signal sequence and the received second reference signal sequence. The apparatus may be a wireless network node or a control device configured to control the functioning thereof, when installed therein. Example embodiments of the aspect may comprise at least one feature from the following bulleted list or any combination of the following features:

[0022] • wherein the apparatus is caused to transmit, to the user equipment, at least one of a configuration on distortion mitigation compensation mode, or at least one condition for transmission of at least one of the first reference signal sequence or the second reference signal sequence;

[0023] • wherein the apparatus is caused to perform at least one of the following receiving the first reference signal sequence and the second reference signal sequence in one orthogonal frequency division multiplexing, OFDM, symbol or receiving the first reference signal sequence and the second reference signal sequence in one or more same resource blocks, RBs;

[0024] • wherein the apparatus is further caused to receive a third reference signal sequence for demodulation, wherein the third reference signal sequence is received consecutive to the first reference signal sequence in another OFDM symbol.

[0025] According to an aspect, there is provided a first method comprising, receiving, from a wireless network node, a resource allocation for an uplink data transmission, determining a first reference signal sequence, determining a second reference signal sequence based at least partly on the first reference signal sequence and transmitting, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission. The first method may be performed by a user equipment or a control device configured to control the functioning thereof, when installed therein.

[0026] According to an aspect, there is provided a second method comprising, receiving, from a user equipment, a first reference signal sequence, receiving, from the user equipment a second reference signal sequence, wherein the second reference signal sequence is determined based at least partly on the received first reference signal sequence and performing at least one of demodulation or distortion mitigation based on the received first reference signal sequence and the received second reference signal sequence. The second method may be performed by a wireless network node or a control device configured to control the functioning thereof, when installed therein.

[0027] According to an aspect of the present disclosure, there is provided an apparatus comprising means for receiving, from a wireless network node, a resource allocation for an uplink data transmission, means for determining a first reference signal sequence, means for determining a second reference signal sequence based at least partly on the first reference signal sequence and means for transmitting, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission. The apparatus of the aspect may be a user equipment or a control device configured to control the functioning thereof, when installed therein.

[0028] According to an aspect of the present disclosure, there is provided an apparatus comprising means for receiving, from a user equipment, a first reference signal sequence, means for receiving, from the user equipment a second reference signal sequence, wherein the second reference signal sequence is determined based at least partly on the received first reference signal sequence and means for performing at least one of demodulation or distortion mitigation based on the received first reference signal sequence and the received second reference signal sequence. The apparatus of the aspect may be a wireless network node or a control device configured to control the functioning thereof, when installed therein.

[0029] According to an aspect of the present disclosure, there is provided a computer program comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out receiving, from a wireless network node, a resource allocation for an uplink data transmission, determining a first reference signal sequence, determining a second reference signal sequence based at least partly on the first reference signal sequence and transmitting, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission.

[0030] According to an aspect of the present disclosure, there is provided a computer program comprising instructions which, when the program is executed by an apparatus, cause the apparatus to carry out receiving, from a user equipment, a first reference signal sequence, receiving, from the user equipment a second reference signal sequence, wherein the second reference signal sequence is determined based at least partly on the received first reference signal sequence and performing at least one of demodulation or distortion mitigation based on the received first reference signal sequence and the received second reference signal sequence.

[0031] According to an aspect of the present disclosure, there is provided a non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform receiving, from a wireless network node, a resource allocation for an uplink data transmission, determining a first reference signal sequence, determining a second reference signal sequence based at least partly on the first reference signal sequence and transmitting, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission.

[0032] According to an aspect of the present disclosure, there is provided a non-transitory computer readable medium having stored thereon a set of computer readable instructions that, when executed by at least one processor, cause an apparatus to at least perform receiving, from a user equipment, a first reference signal sequence, receiving, from the user equipment a second reference signal sequence, wherein the second reference signal sequence is determined based at least partly on the received first reference signal sequence and performing at least one of demodulation or distortion mitigation based on the received first reference signal sequence and the received second reference signal sequence.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 illustrates an example of a network scenario in accordance with at least some example embodiments;

[0035] FIG. 2a illustrates a first example of a configuration in accordance with at least some example embodiments;

[0036] FIG. 2b illustrates a second example of a configuration in accordance with at least some example embodiments; FIG. 2c illustrates a third example of a configuration in accordance with at least some example embodiments;

[0037] FIG. 2d illustrates a fourth example of a configuration in accordance with at least some example embodiments;

[0038] FIG. 3 illustrates an example apparatus capable of supporting at least some example embodiments;

[0039] FIG. 4 illustrates a flow graph of a first method in accordance with at least some example embodiments; and

[0040] FIG. 5 illustrates a flow graph of a second method in accordance with at least some example embodiments;

[0041] EXAMPLE EMBODIMENTS

[0042] Embodiments of the present disclosure provide enhancements for transmissions of reference signal sequences in cellular communication networks. In case of uplink transmissions, a User Equipment, UE, may transmit at least one Reference Signal, RS, sequence to a wireless network node so that the wireless network node can compensate the distortion of an uplink data transmission associated with the at least one RS sequence. More specifically, the UE may determine a first RS sequence and further a second RS sequence based at least partly on the first RS sequence. The UE may then transmit the first RS sequence and the second RS sequence to the wireless network node, so that the wireless network node may perform demodulation and / or distortion mitigation, such as Digital Post-Distortion, DPoD, mitigation of a nonlinear distortion, based on the first RS sequence and the second RS sequence.

[0043] FIG. 1 illustrates an example of a network scenario in accordance with at least some example embodiments. According to the example scenario of FIG. 1, there may be a beam -based wireless communication system, which comprises UE 110, wireless network node 120 and core network element 130. UE 110 may be connected to wireless network node 120 via air interface using beams 115, either simultaneously or one at a time.

[0044] UE 110 may comprise, for example, a smartphone, a cellular phone, a Machine-to-Machine, M2M, node, Machine-Type Communications, MTC, node, an Internet of Things, loT, node, a car telemetry unit, a laptop computer, a tablet computer or, indeed, any kind of suitable wireless terminal. In the example system of FIG. 1, UE 110 may communicate wirelessly with wireless network node 120 via at least one beam 115. Wireless network node 120 may be considered as a serving node for UE 110 and one cell of wireless network node 120 may be a serving cell for UE 110.

[0045] Air interface between UE 110 and wireless network node 120 may be configured in accordance with a Radio Access Technology, RAT, which both UE 110 and wireless network node 120 are configured to support. Examples of cellular RATs include Long Term Evolution, LTE, New Radio, NR, which may also be known as fifth generation, 5G, radio access technology, 6G radio access technology, and MulteFire.

[0046] For example in the context of LTE, wireless network node 120 may be referred to as eNB while wireless network node 120 may be referred to as gNB in the context of NR. In some example embodiments, wireless network node 120 may be referred to as a Transmission and Reception Point, TRP, or control multiple TRPs that may be co-located or non-co-1 ocated. In any case, example embodiments of the present disclosure are not restricted to any particular wireless technology. Instead, example embodiments may be exploited in any beam-based wireless communication system, wherein reference signal sequences are transmitted.

[0047] Wireless network node 120 may be connected, directly or via at least one intermediate node, with core network 130 via interface 125. Core network 130 may be, in turn, coupled via interface 135 with another network (not shown in FIG. 1), via which connectivity to further networks may be obtained, for example via a worldwide interconnection network. Wireless network node 120 may be connected, directly or via at least one intermediate node, with core network 130 or with another core network.

[0048] In some example embodiments, the network scenario may comprise a relay node instead of, or in addition to, UE 110 and / or wireless network node 120. Relaying may be used for example when operating on millimeter-wave frequencies. One example of the relay node may be an Integrated Access and Backhaul, IAB, node. The IAB node may be referred to as a self-backhauling relay as well. Another example of a relay may be an out-band relay. In general, the relay node may comprise two parts:

[0049] 1) Distributed Unit, DU, part which may facilitate functionalities of wireless network node 120, such as a gNB. Thus, in some example embodiments, the DU part of a relay may be referred to as wireless network node 120 and the DU may perform tasks of wireless network node 120; 2) Mobile Termination, MT, part which may facilitate functionalities of UE 110, i.e., a backhaul link which may be the communication link between a parent node (DU), such as a DU part of wireless network node 120, and the relay, such as an IAB node. In some example embodiments, the MT part may be referred to as UE 110 and perform tasks of UE 110.

[0050] In various cellular communication networks, such as networks operating according to 5G / NR standard specifications, different modulation methods, like Quadrature Phase-Shift Keying, QPSK, 16 Quadrature Amplitude Modulation, 16 QAM, 64QAM, 256QAM and 1024QAM may be used in at least in downlink. Moreover, uplink coverage for different modulations and / or spectral efficiencies is one important issue and different enablers to improve uplink coverage have been introduced and studied in 3rd Generation Partnership Project, 3GPP. As an example, at least two waveforms may be supported in uplink, like Orthogonal Frequency-Division Multiplexing, OFDM, and Discrete Fourier Transform- spread-OFDM, DFT-s-OFDM. DFT-s-OFDM may have significantly lower Peak-to- Average Power Ratio, PAPR, and thus may be used to achieve better coverage. Further, in 5G uplink it is possible to configure pi / 2 Binary Phase-Shift Keying, BPSK, and use Frequency Domain Spectrum Shaping, FDSS, to achieve very low PAPR. FDSS may be used also with QPSK, to increase coverage for QPSK modulation. In some example embodiments of the present disclosure, OFDM symbol may cover DFT-s-OFDM symbol, i.e., single carrier Frequency Division Multiple Access, FDMA, based on frequency domain processing.

[0051] A least for 6G, it would be desirable to improve the energy efficiency and coverage of the radio access solutions. DFT-s-OFDM may be used with higher modulation orders, but FDSS might not be applicable for improving coverage and / or energy efficiency for those. The use of DFT-s-OFDM with higher modulation orders may lead to large Maximum Power Reduction, MPR, values (power backoff). Especially with higher frequencies more backoff may be needed e.g., due to non-linearities caused by power amplifiers, and hence, it would be desirable to enable lower power backoffs by enabling methods to handle those nonlinearities.

[0052] Embodiments of the present disclosure therefore enable improving uplink cell coverage and energy efficiency with higher modulation orders, by facilitating larger transmitter Error Vector Magnitude, EVM, values with high modulation orders while improving the signal quality at the receiver using Digital Post-Distortion, DPoD. DPoD may be used for improved energy efficiency as well.

[0053] Embodiments of the present disclosure may be exploited, e.g., for EVM enhancement of received signals in a network using DFT-s-OFDM in uplink, through DPoD. Embodiments of the present disclosure provide uplink reference signal structures, allowing accurate estimation of the transmitter nonlinearity and the corresponding DPoD parameters at the receiver, such as wireless network node 120.

[0054] More specifically, at least one issue is related to differences in the PAPRs between an uplink Demodulation Reference Signal, DMRS, and Physical Uplink Shared Channel, PUSCH. The DMRS may comprise a sequence without amplitude modulation (e.g., Zad-off Chu sequences may be used in 5G NR) and PUSCH may comprise symbols modulated with QAM. So even if substantially the same power would be applied for DMRS and PUSCH, there would be different distortion between the DMRS and PUSCH signals at the receiver, such as wireless network node 120.

[0055] Even if boosting of DMRS would be applied, wherein the power of DMRS is adjusted compared to the power of PUSCH, the PAPR of DMRS may be largely different compared to the PAPR of PUSCH. In such a case, the DMRS and PUSCH symbols would be distorted differently in the power amplifier of the transmitter, such as UE 110. Thus, the distortion profile in the PUSCH symbols and the corresponding parametric models and processing systems to correct for the distortion could not be accurately estimated using a low-PAPR DMRS in uplink.

[0056] Embodiments of the present disclosure therefore provide enhanced Reference Signal, RS, sequence structures, such as DMRS structures, that allow for improved accuracy in the transmitter nonlinearity model estimation, and thus high-accuracy DPoD processing at the receiver. The provided RS sequence structures possess PAPR behavior close to that of the PUSCH symbols, further providing basis for high-accuracy PUSCH nonlinearity estimation at the receiver.

[0057] In some example embodiments, the DPoD compensation RS structure may be such that UE 110 may be configured for a specific DPoD compensation mode. The DPoD compensation mode may comprise a dedicated RS supporting DPoD compensation. The DPoD compensation mode may be configured by wireless network node 120 to UE 110 via Radio Resource Control, RRC, or UE 110 may determine that the DPoD compensation mode is to be used based on a standard specification, such as a 3GPP standard specification. The DPoD compensation mode may be applied for certain pre-defined modulation methods (e.g., 64QAM and higher), but not for other modulation methods. The DPoD compensation mode may be applied for certain waveforms (e.g., DFT-s-OFDM), but not for other waveforms.

[0058] In some example embodiments, the DPoD compensation mode may be applied for certain uplink transmissions and / or certain DMRS of the slot (e.g., the first DMRS only), but not for others. For example, when a transmitter configuration of UE 110 is unchanged between consecutive slots, it may be enough to have RS for DPoD estimation only at the first slot (of multiple slots), but not in other slots. For example, DPoD estimation may be performed only in the first slot, and used for DPoD compensation also in other slots not including RS for DPoD, if the non-linear distortion is varying slowly. Downlink control information may be used by wireless network node 120 to indicate if the DPoD RS is to be included in the current slot by UE 110, or not.

[0059] When applying the DPoD compensation mode, an RS may be, e.g., a single-symbol or a double-symbol configuration. In the single-symbol configuration, there may be one RS for joint demodulation (e.g., for channel estimation and coherent detection) and for distortion compensation. The RS (combined RS) may be formed by a first RS sequence and a second RS sequence. In a first example embodiment, a first RS sequence may be generated based on a Gold sequence and the first RS sequence may be boosted with higher transmission power while a second RS sequence may be empty. That is, the second RS sequence may be determined based on the first RS sequence, as a zero power sequence when the first RS sequence is a boosted Gold sequence. In a second example embodiment, the first RS sequence may be generated based on a Gold sequence and the second RS sequence may be generated based on the first RS sequence, as a non-empty sequence. That is, the first RS sequence may be a Gold sequence and the second RS sequence may be a conjugate, negativeconjugate, repetition or a negative of the first RS sequence. In a third example embodiment, the first RS sequence may be generated based on a Zad-off Chu sequence and the second RS sequence may be generated based on the first RS sequence being a Zad-off Chu sequence, e.g., a modified Zad-off Chu sequence, for example, being a conjugate, negative-conjugate, repetition or a negative of the first RS sequence. In the double-symbol configuration, along with the combined RS for distortion compensation, a third RS may be used for demodulation, i.e., for channel estimation. For example, in case the combined RS which is formed by the first RS sequence and the second RS sequence is too distorted for coherent detection, the third RS may be used for demodulation. The third RS may be a DMRS having lower peak-to-average power ratio than the data symbols of combined RS. The third RS sequence may be transmitted consecutive to the first RS sequence in another OFDM symbol, but not necessarily in a consecutive resource element in frequency domain. Such third RS may be e.g., configured by wireless network node 120, e.g., by RRC or Downlink Control Information, DCI. It is noted that even though DPoD is used as an example in various example embodiments, embodiments of the present disclosure may be applied similarly for any kind of distortion mitigation at the receiver, such as wireless network node 120.

[0060] The first RS sequence may be a DMRS signal, to be used to construct the distortion compensation RS at UE 110. The first RS sequence may be generated by UE 110 based on a Zadoff-Chu sequence or a Gold sequence. The second RS sequence may be based at least partly on the first RS sequence. The first RS sequence and the second RS sequence may comprise a distortion compensation reference signal and be generated by UE 110.

[0061] In some example embodiments, if there is only one OFDM symbol, the first RS sequence may be a boosted Gold sequence and the second RS sequence may be empty, i.e., a zero power sequence, for example when the first RS sequence is a Gold sequence. Alternatively, the first RS sequence may be a Gold sequence and the second RS sequence may be a conjugate, negative-conjugate, repetition or negative of the first RS sequence. Alternatively, the first RS sequence may be a Zadoff-Chu sequence and the second RS sequence may be a conjugate, negative-conjugate, repetition or negative of the first RS sequence.

[0062] In some example embodiments, if there are two OFDM symbols, (i.e., a third RS sequence included), then the DPoD RS (combined RS from the first and second RS) may be according to one of the above, and the third RS sequence may be used for channel estimation (and / or demodulation), and may be e.g., Zadoff-Chu sequence having lower PAPR. The third RS sequence may be, e.g., the same as the first RS sequence if the first RS sequence is a Zadoff- Chu sequence.

[0063] In some example embodiments, UE 110 may determine at least one condition for transmission of at least one of the first RS sequence or the second RS sequence. UE 110 may trigger the transmission of the at least one of the first RS sequence or the second RS sequence when the at least one condition is met. That is, the first RS sequence and / or the second RS sequence may be applied when at least one predefined triggering condition for the DPoD RS is met.

[0064] The at least one condition for transmission of the at least one of the first RS sequence or the second RS sequence may comprise at least one of: an RRC configuration received from wireless network node 120, a downlink control message trigger received from wireless network node 120, a modulation order threshold, a predefined waveform type, a predefined time slot number, or a length of a scheduled uplink data transmission. The downlink control message trigger may comprise for example DCI or an uplink grant.

[0065] In some example embodiments, time domain resources of the first RS sequence may be associated with time domain resources of the second sequence. The combined RS of the first RS sequence and the second RS sequence may be for DPoD compensation and occupy (DFT-s-)-OFDM symbols right after, or before, the third RS sequence, e.g., an DMRS signal to be used for demodulation. That is, the third RS and the combined RS may be consecutive in time. Thus, channel variation for the estimation may remain static over the estimation of the third RS and the combined RS.

[0066] In some example embodiments, frequency domain resources of the first RS sequence may be associated with frequency domain resources of the second sequence. The combined RS of the first RS sequence and the second RS sequence may be for DPoD compensation, and the second RS sequence may occupy subcarriers consecutive in frequency as the first RS sequence, but in same OFDM symbol. For example, the second RS sequence may occupy the same Physical Resource Blocks, PRBs, as the first RS sequence. That is, UE 110 may transmit the first RS sequence and the second RS sequence in the same one or more resource blocks, RBs, such as PRBs.

[0067] In some example embodiments, a configuration of the combined RS sequence for DPoD compensation may be determined by UE 110 such that a length of the first RS sequence is M / 2 and the first RS sequence is mapped to every second subcarrier of the resource allocation, where AT may be a size of a resource allocation in terms of number of subcarriers. UE 110 may determine that a length of the second RS sequence is M / 2 and the second RS sequence is mapped to every second subcarrier consecutive to the first RS sequence. The first and second RS sequences may thus be interleaved in frequency. UE 110 may determine the second RS sequence based at least partly on the first RS sequence based on one of the following:

[0068] • UE 110 may determine that the second RS sequence is a conjugate of the first sequence;

[0069] • UE 110 may determine that the second RS sequence is a negative-Conjugate of the first RS sequence;

[0070] • UE 110 may determine that the second RS sequence is a repetition of the first RS sequence;

[0071] • UE 110 may determine that the second RS sequence is a negative of the first RS sequence; or

[0072] • zero power sequence when the first reference signal sequence is a Gold sequence.

[0073] The combined RS may be boosted by UE 110 to match the power of an uplink data transmission, such as a PUSCH transmission. A boosting level may be predetermined by the specification, be a capability of UE 110 and / or configured by wireless network node 120.

[0074] In case of one RS, the first RS sequence and the second RS sequence may form one combined RS for joint demodulation and distortion compensation. The combined RS sequence may be boosted by UE 110 to match the power of the uplink data transmission, such as a PUSCH transmission. A boosting level may be predetermined by the specification, be a capability of UE 110 and / or configured by wireless network node 120. The combined RS may be constructed, by determining by UE 110 the second RS sequence based at least partly on the first RS sequence, to form the combined RS.

[0075] UE 110 may receive from wireless network node 120 a resource allocation for an uplink data transmission, such as a PUSCH, from wireless network node 120 and determine a resource allocation for the first and second RS sequences based on the resource allocation for the uplink data transmission. UE 110 may then transmit, to wireless network node 120, the first and second RS sequences associated with the uplink data transmission. A total transmission power of the first and second RS sequences may be substantially the same as a transmission power of the uplink transmission. Alternatively, or in addition, a maximum total transmission power of the first RS sequence and the second RS sequence may be higher than a maximum transmission power of a third RS sequence. The uplink data transmission may be a high modulation transmission, e.g., at least 64QAM. The uplink data transmission may be a high modulation transmission compared to a modulation order threshold, such as 64QAM, 256QAM, etc. That is, the uplink data transmission may comprise a high order modulation transmission, wherein the modulation order of the high order modulation transmission may be higher than the modulation threshold.

[0076] In some example embodiments, the applied RS configuration may depend on a length of a scheduled transmission. For example, the combined RS for DPoD compensation may be included only in every nth subframe or slot, where ri>l, because power amplifier properties may be changing slower than the channel.

[0077] In some example embodiments, there may be a need for separating distortion compensation and channel estimation. In such case, a third RS sequence may be used in another OFDM symbol. Such third RS may be using e.g., a DMRS sequence having lower peak-to-average power ratio than the RS used for distortion compensation, and the symbols used for data transmissions, such that the third RS may not experience any significant distortion. The transmission power of the first and second RS sequences may be higher than a transmission power of the third RS sequence. Alternatively or additionally, at least the maximum transmission power or peak transmission power, or peak-to-average power ratio, or envelope variation of the first and the second RS sequences may be larger than that of the third RS sequence. The third RS sequence may be for demodulation, comprising other related usage, such as channel sounding, timing measurements, and Modulation and Coding Scheme, MCS.

[0078] The third RS sequence may be a Zadoff-Chu sequence and Zadoff-Chu sequences may be used, e.g., in DMRS generation process in the case of DFT-s-OFDM uplink transmission. If a double-symbol DMRS is configured, the third RS sequence may be a DMRS in another OFDM symbol, e.g., mapped to every second or fourth subcarrier as in current 5G / NR, such that the third RS sequence has a low PAPR. Thus, the third RS sequence may be used for channel estimation, but not for distortion estimation, while the combined RS sequence may be used for DPoD.

[0079] The third RS and the combined RS (default DMRS and enhanced DMRS) may be transmitted in two OFDM symbols. The third RS sequence, i.e., default DMRS, in one OFDM symbol may be used in the channel estimation and equalization process first, and then the combined RS, i.e. enhanced DMRS, in another OFDM symbol may be used in nonlinear model parameter estimation of DPoD process. The default DMRS would be thus less affected by the transmitter nonlinearities of UE 110 due to its low PAPR characteristics, thereby enabling estimation of the channel between UE 110 and wireless network node 120 with high accuracy. The channel information obtained from the default DMRS may be used, e.g., to equalize the PUSCH and the enhanced DMRS, which carries the nonlinearity information of the transmitter, such as UE 110. Then, the enhanced DMRS, which is free from channel linear distortion may be used in the nonlinear model parameter estimation of a DPoD process of the receiver, such as wireless network node 120.

[0080] For illustration purpose, a DMRS, for example the first RS sequence, may be denoted with Akfor k=0,2,4, Nact and empty subcarriers on the DMRS carrying an OFDM symbol with Bk for k=l,3,5, Nact-i, where Nact may be the number of active subcarriers. The configuration of the enhanced DMRS structure, i.e., the second RS sequence, may be one of the following:

[0081] • Repeat, where Bk+ 1 =Ak for k=0, 2,4, • • • ,Nact-2,'

[0082] • Negative, where Bk+i=-Ak for k=0,2,4, ...,Nact-2,'

[0083] • Conjugate, where Bk+i=(Ak) * for k=0,2,4, ...,Nact-2,'

[0084] • Negative-Conjugate, where Bk+i=(Ak)* for k=0,2,4, ... ,Nact-2,' or

[0085] • Zero-power, where Bk+i=0 for k=0,2,4, ...,Nact-2.

[0086] FIG. 2a illustrates a first example of a configuration in accordance with at least some example embodiments. In the first example illustrated in FIG. 2a, an example of a resource grid of “Repeat” configuration is illustrated. User data is denoted by 202, empty subcarriers are denoted by 204, enhanced subcarriers are denoted by 206 and DMRS is denoted by 208. The first RS sequence is denoted by 210, the second RS sequence is denoted by 220 and the third RS sequence is denoted by 230.

[0087] In the “Repeat” configuration illustrated in FIG. 2a, second RS sequence 220 carries same symbols as first RS sequence 210. That is, enhanced subcarriers 206 carry the same symbols as DMRS subcarriers 208. OFDM symbol 2 illustrates a third RS (i.e., default DMRS configuration), wherein DMRS 208 may be transmitted in the same OFDM symbol as empty subcarriers 204. Transmission of DMRS 208 may be interleaved with empty subcarriers 204 in frequency. OFDM symbol 3 illustrates an enhanced DMRS configuration, wherein DMRS 208 may be transmitted in the same OFDM symbol as enhanced subcarriers 206. Transmission of enhanced subcarriers 206 may be interleaved with DMRS 208 in frequency. DMRS 208 of OFDM symbol 3 may be referred to as first RS sequence 210. Enhanced subcarriers 206 may be referred to as second RS sequence 220. DMRS 208 of OFDM symbol 2 may be referred to as third RS sequence 230.

[0088] As illustrated in FIG. 2a, first RS sequence 210 may be interleaved in frequency with second RS sequence 220 and first RS sequence 210 may be transmitted by UE 110 in the same, one OFDM symbol as second RS sequence 220. Third RS sequence 230 may be right next to first RS sequence 210, i.e., first RS sequence 210 and third RS sequence 230 may be in consecutive OFDM symbols. UE 110 may determine third RS sequence 230 for demodulation and transmit third RS sequence 230 consecutive to first RS sequence in another OFDM symbol.

[0089] In some example embodiments, first RS sequence 210 and second RS sequence 220 may compose a combined RS sequence, wherein the combined RS sequence is for demodulation and / or distortion compensation. For example, if only one OFDM symbol is used for reference signals, the combined RS may be used for both demodulation and distortion compensation. If two OFDM symbols are used for different type of reference signals (for example, third RS 230 and the combined RS), the combined RS may be used for only distortion compensation, while third RS 230 may be used for demodulation.

[0090] FIG. 2b illustrates a second example of a configuration in accordance with at least some example embodiments. In the second example illustrated FIG. 2b, an example of a resource grid of “Negative” configuration is illustrated. In the “Negative” configuration illustrated in FIG. 2b, enhanced subcarriers 206 carry the negative symbol compared to DMRS 208.

[0091] FIG. 2c illustrates a third example of a configuration in accordance with at least some example embodiments. In the third example illustrated FIG. 2c, an example of a resource grid of “Conjugate” configuration is illustrated. In the “Conjugate” configuration illustrated in FIG. 2c, enhanced subcarriers 206 carry the conjugate symbol compared to DMRS 208.

[0092] FIG. 2d illustrates a fourth example of a configuration in accordance with at least some example embodiments. In the fourth example illustrated FIG. 2d, an example of a resource grid of “Negative-conjugate” configuration is illustrated. In the “Negative-conjugate” configuration illustrated in FIG. 2d, enhanced subcarriers 206 carry the negative conjugate symbol compared to DMRS 208.

[0093] In particular, the configurations associated with conjugates in FIGs. 2c and 2d (the conjugate and negative conjugate configurations, respectively) may be exploited to provide optimum performance.

[0094] Wireless network node 120 may receive the first RS sequence and the second RS sequence from UE 110 and perform at least one of demodulation or DPoD mitigation based on the first and second RS sequences. In an example embodiment, wireless network node 120 may receive the first RS sequence and the second RS sequence in one OFDM symbol. In another example embodiment, wireless network node 120 may receive the first RS sequence and the second RS sequence in one or more same RBs. In a further example embodiment, wireless network node 120 may receive a third RS sequence consecutive to the first RS sequence in another OFDM symbol, and wireless network node 120 may use the third RS for demodulation. In a further example embodiment, wireless network node 120 may transmit to UE 110 at least one of a configuration on distortion mitigation compensation mode, or at least one condition for transmission of at least one of the first reference signal sequence or the second reference signal sequence.

[0095] FIG. 3 illustrates an example apparatus capable of supporting at least some example embodiments. Illustrated is device 300, which may comprise, for example, UE 110 or wireless network node 120, or a control device configured to control the functioning thereof, possibly when installed therein. Comprised in device 300 is processor 310, which may comprise, for example, a single- or multi-core processor wherein a single-core processor comprises one processing core and a multi-core processor comprises more than one processing core. Processor 310 may comprise, in general, a control device. Processor 310 may comprise more than one processor. Processor 310 may be a control device. Processor 310 may comprise at least one application-specific integrated circuit, ASIC. Processor 310 may comprise at least one field-programmable gate array, FPGA. Processor 310 may be means for performing method steps in device 300. Processor 310 may be configured, at least in part by computer instructions, to perform actions.

[0096] A processor may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein. As used in this application, 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 mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0097] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, 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.

[0098] Device 300 may comprise memory 320. Memory 320 may comprise random-access memory and / or permanent memory. Memory 320 may comprise at least one RAM chip. Memory 320 may comprise solid-state, magnetic, optical and / or holographic memory, for example. Memory 320 may be at least in part accessible to processor 310. Memory 320 may be at least in part comprised in processor 310. Memory 320 may be means for storing information. Memory 320 may comprise computer instructions that processor 310 is configured to execute. When computer instructions configured to cause processor 310 to perform certain actions are stored in memory 320, and device 300 overall is configured to run under the direction of processor 310 using computer instructions from memory 320, processor 310 and / or its at least one processing core may be considered to be configured to perform said certain actions. Memory 320 may be at least in part comprised in processor 310. Memory 320 may be at least in part external to device 300 but accessible to device 300.

[0099] Device 300 may comprise a transmitter 330. Device 300 may comprise a receiver 340. Transmitter 330 and receiver 340 may be configured to transmit and receive, respectively, information in accordance with at least one cellular or non-cellular standard. Transmitter 330 may comprise more than one transmitter. Receiver 340 may comprise more than one receiver. Transmitter 330 and / or receiver 340 may be configured to operate in accordance with Global System for Mobile communication, GSM, Wideband Code Division Multiple Access, WCDMA, Long Term Evolution, LTE, and / or 5G / NR standards, for example.

[0100] Device 300 may comprise a Near-Field Communication, NFC, transceiver 350. NFC transceiver 350 may support at least one NFC technology, such as Bluetooth, Wibree or similar technologies.

[0101] Device 300 may comprise User Interface, UI, 360. UI 360 may comprise at least one of a display, a keyboard, a touchscreen, a vibrator arranged to signal to a user by causing device 300 to vibrate, a speaker and a microphone. A user may be able to operate device 300 via UI 360, for example to accept incoming telephone calls, to originate telephone calls or video calls, to browse the Internet, to manage digital files stored in memory 320 or on a cloud accessible via transmitter 330 and receiver 340, or via NFC transceiver 350, and / or to play games.

[0102] Device 300 may comprise or be arranged to accept a user identity module 370. User identity module 370 may comprise, for example, a Subscriber Identity Module, SIM, card installable in device 300. A user identity module 370 may comprise information identifying a subscription of a user of device 300. A user identity module 370 may comprise cryptographic information usable to verify the identity of a user of device 300 and / or to facilitate encryption of communicated information and billing of the user of device 300 for communication effected via device 300.

[0103] Processor 310 may be furnished with a transmitter arranged to output information from processor 310, via electrical leads internal to device 300, to other devices comprised in device 300. Such a transmitter may comprise a serial bus transmitter arranged to, for example, output information via at least one electrical lead to memory 320 for storage therein. Alternatively to a serial bus, the transmitter may comprise a parallel bus transmitter. Likewise processor 310 may comprise a receiver arranged to receive information in processor 310, via electrical leads internal to device 300, from other devices comprised in device 300. Such a receiver may comprise a serial bus receiver arranged to, for example, receive information via at least one electrical lead from receiver 340 for processing in processor 310. Alternatively to a serial bus, the receiver may comprise a parallel bus receiver. Device 300 may comprise further devices not illustrated in FIG. 3. For example, where device 300 comprises a smartphone, it may comprise at least one digital camera. Some devices 300 may comprise a back-facing camera and a front-facing camera, wherein the back-facing camera may be intended for digital photography and the front-facing camera for video telephony. Device 300 may comprise a fingerprint sensor arranged to authenticate, at least in part, a user of device 300. In some example embodiments, device 300 lacks at least one device described above. For example, some devices 300 may lack a NFC transceiver 350 and / or user identity module 370.

[0104] Processor 310, memory 320, transmitter 330, receiver 340, NFC transceiver 350, UI 360 and / or user identity module 370 may be interconnected by electrical leads internal to device 300 in a multitude of different ways. For example, each of the aforementioned devices may be separately connected to a master bus internal to device 300, to allow for the devices to exchange information. However, as the skilled person will appreciate, this is only one example and depending on the example embodiment various ways of interconnecting at least two of the aforementioned devices may be selected without departing from the scope of the example embodiments.

[0105] FIG. 4 is a flow graph of a first method in accordance with at least some example embodiments. The phases of the illustrated first method may be performed by UE 110 or by a control device configured to control the functioning thereof, when installed therein.

[0106] The first method may comprise, at step 410, receiving, from a wireless network node, a resource allocation for an uplink data transmission. The first method may also comprise, at step 420, determining a first reference signal sequence. In addition, the first method may comprise, at step 430, determining a second reference signal sequence based at least partly on the first reference signal sequence. Finally, the second method may comprise, at step 440, transmitting, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission.

[0107] FIG. 5 is a flow graph of a second method in accordance with at least some example embodiments. The phases of the illustrated first method may be performed by wireless network node or by a control device configured to control the functioning thereof, when installed therein. The second method may comprise, at step 510, receiving, from a user equipment, a first reference signal sequence. The second method may also comprise, at step 520, receiving, from the user equipment a second reference signal sequence, wherein the second reference signal sequence is determined based at least partly on the received first reference signal sequence. Finally, the second method may comprise, at step 530, performing at least one of demodulation or distortion mitigation based on the received first reference signal sequence and the received second reference signal sequence.

[0108] It is to be understood that the example embodiments disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular example embodiments only and is not intended to be limiting.

[0109] Reference throughout this specification to one example embodiment or an example embodiment means that a particular feature, structure, or characteristic described in connection with the example embodiment is included in at least one example embodiment. Thus, appearances of the phrases “in one example embodiment” or “in an example embodiment” in various places throughout this specification are not necessarily all referring to the same example embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0110] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various example embodiments and examples may be referred to herein along with alternatives for the various components thereof. It is understood that such example embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations.

[0111] In an example embodiment, an apparatus, such as, for example, UE 110 or wireless network node 120, may comprise means for carrying out the example embodiments described above and any combination thereof. In an example embodiment, a computer program may be configured to cause a method in accordance with the example embodiments described above and any combination thereof. In an example embodiment, a computer program product, embodied on a non-transitory computer readable medium, may be configured to control a processor to perform a process comprising the example embodiments described above and any combination thereof.

[0112] In an example embodiment, an apparatus, such as, for example, UE 110 or wireless network node 120, may comprise at least one processor, and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform the example embodiments described above and any combination thereof.

[0113] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more example embodiments. In the preceding description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of example embodiments of the disclosure. One skilled in the relevant art will recognize, however, that the disclosure can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the disclosure.

[0114] While the forgoing examples are illustrative of the principles of the example embodiments in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the disclosure. Accordingly, it is not intended that the disclosure be limited, except as by the claims set forth below.

[0115] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality. INDUSTRIAL APPLICABILITY

[0116] At least some example embodiments find industrial application in cellular communication networks, for example in 3GPP networks, wherein reference signals are exploited.

[0117] ACRONYMS LIST

[0118] 3GPP 3rd Generation Partnership Project

[0119] BM Beam Management

[0120] BPSK Binary Phase-Shift Keying

[0121] BS Base Station

[0122] DCI Downlink Control Information

[0123] DFT-s-OFDM Discrete Fourier Transform-spread-OFDM

[0124] DMRS Demodulation Reference Signal

[0125] DPoD Digital Post-Distortion

[0126] DU Distributed Unit

[0127] EVM Error Vector Magnitude

[0128] FDMA Frequency Division Multiple Access

[0129] FDSS Frequency Domain Spectrum Shaping

[0130] GSM Global System for Mobile communication

[0131] IAB Integrated Access and Backhaul loT Internet of Things

[0132] LTE Long-Term Evolution

[0133] M2M Machine-to-Machine

[0134] MCS Modulation and Coding Scheme

[0135] MIMO Multiple-Input Multiple-Output

[0136] MPR Maximum Power Reduction

[0137] MT Mobile Terminal

[0138] MTC Machine-Type Communications

[0139] NFC Near-Field Communication

[0140] NR New Radio

[0141] OFDM Orthogonal Frequency-Division Multiplexing

[0142] PAPR Peak-to-Average Power Ratio

[0143] PUSCH Physical Uplink Shared Channel QAM Quadrature Phase-Shift Keying

[0144] QPSK Quadrature Amplitude Modulation

[0145] RAN Radio Access Network

[0146] RB Resource Block RRC Radio Resource Control

[0147] RS Reference Signal

[0148] TRP Transmission and Reception Point

[0149] UE User Equipment

[0150] UI User Interface UL UL

[0151] WCDMA Wideband Code Division Multiple Access

[0152] WiMAX Worldwide Interoperability for Microwave Access

[0153] WLAN Wireless Local Area Network

[0154] REFERENCE SIGNS LIST

Claims

CLAIMS:

1. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:- receive, from a wireless network node, a resource allocation for an uplink data transmission;- determine a first reference signal sequence;- determine a second reference signal sequence based at least partly on the first reference signal sequence; and- transmit, to the wireless network node, the determined first reference signal sequence and the determined second reference signal sequence, wherein the first reference signal sequence and the second reference signal sequence are associated with the uplink data transmission.

2. The apparatus according to claim 1, wherein the first and second reference signal sequences compose a combined reference signal sequence, wherein the combined reference signal sequence is for at least one of demodulation or distortion compensation.

3. The apparatus according to claim 1 or claim 2, wherein the apparatus is caused to perform at least one of the following:- interleaving the first reference signal sequence and the second reference signal sequence in one orthogonal frequency division multiplexing, OFDM, symbol;- transmitting the first reference signal sequence and the second reference signal sequence in one OFDM symbol; or- transmitting the first reference signal sequence and the second reference signal sequence in one or more same resource blocks, RBs.

4. The apparatus according to claim 3, wherein the at least one processing core and the at least one memory further cause the apparatus at least to:- determine a third reference signal sequence for demodulation; and- transmit the third reference signal sequence consecutive to the first reference signal sequence in another orthogonal frequency-division multiplexing, OFDM, symbol.

5. The apparatus according to any of the preceding claims, wherein at least one of:- a total transmission power of the first reference signal sequence and the second reference signal sequence is substantially the same as a transmission power of the uplink data transmission, or- a maximum total transmission power of the first reference signal sequence and the second reference signal sequence is higher than a maximum transmission power of a third reference signal sequence.

6. The apparatus according to any of the preceding claims, wherein the at least one processing core and the at least one memory further cause the apparatus at least to:- determine the second reference signal sequence based on one of the following: o conjugate of the first reference signal sequence; o negative-conjugate of the first reference signal sequence; o repetition of the first reference signal sequence; o negative of the first reference signal sequence; or o zero power sequence when the first reference signal sequence is a boosted Gold sequence.

7. The apparatus according to any of the preceding claims, wherein the at least one processing core and the at least one memory further cause the apparatus at least to:- determine at least one condition for transmission of at least one of the first reference signal sequence or the second reference signal sequence; and- trigger the transmission of the at least one of the first reference signal sequence or the second reference signal sequence when the at least one condition is met.

8. The apparatus according to claim 7, wherein the at least one condition for transmission of the at least one of the first reference signal sequence or the second reference signal sequence comprises at least one of: radio resource control, RRC, configuration received from the wireless network node, a downlink control message trigger received from the wireless network node, a predefined modulation order, a predefined modulation coding scheme, a predefined waveform type, a predefined time slot number, or a length of a scheduled uplink data transmission.

9. The apparatus according to any of the preceding claims, wherein the first reference signal sequence comprises a demodulation reference signal wherein the first reference signal sequence is generated based on a Zadoff-Chu sequence or a Gold sequence.

10. The apparatus according to any of the preceding claims, wherein at least one of the first reference signal or the second reference signal sequence forms a distortion compensation reference signal, wherein the second reference signal sequence is generated based on the first reference signal sequence.

11. The apparatus according to any of the preceding claims, wherein the uplink data transmission comprises a high order modulation transmission, wherein the modulation order of the high order modulation transmission is higher than a modulation order threshold.

12. An apparatus comprising at least one processing core and at least one memory storing instructions that, when executed by the at least one processing core, cause the apparatus at least to:- receive, from a user equipment, a first reference signal sequence;- receive, from the user equipment a second reference signal sequence, wherein the second reference signal sequence is determined based at least partly on the received first reference signal sequence; and- perform at least one of demodulation or distortion mitigation based on the received first reference signal sequence and the received second reference signal sequence.

13. The apparatus according to claim 12, wherein the apparatus is caused to- transmit, to the user equipment, at least one of: o a configuration on distortion mitigation compensation mode, or o at least one condition for transmission of at least one of the first reference signal sequence or the second reference signal sequence.

14. The apparatus according to claim 12 or claim 13, wherein the apparatus is caused to perform at least one of the following:- receiving the first reference signal sequence and the second reference signal sequence in one orthogonal frequency division multiplexing, OFDM, symbol; or- receiving the first reference signal sequence and the second reference signal sequence in one or more same resource blocks, RBs.

15. The apparatus according to claim 14, wherein the apparatus is further caused to: - receive a third reference signal sequence for demodulation, wherein the third reference signal sequence is received consecutive to the first reference signal sequence in another OFDM symbol.

Images