Method, apparatus and computer program relating to DMRS transmission

Abstract

There is disclosed an apparatus comprising: means for receiving a downlink, DL, demodulation reference signal, DMRS; means for receiving a modulation order, M, to be used for an uplink, UL, DMRS; means for generating the UL DMRS; and means for transmitting the generated UL DMRS, using the modulation order M. There is also disclosed an apparatus comprising: means for selecting a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission; means for transmitting a downlink, DL, DMRS; means for transmitting the selected modulation order, M, in the DL; means for receiving a UL DMRS, modulated using the selected modulation order; and means for deriving digital post distortion, DPoD, coefficients using the received UL DMRS.

Description

[0001] METHOD, APPARATUS AND COMPUTER PROGRAM RELATING TO DMRS TRANSMISSION

[0002] TECHNICAL FIELD

[0003] Various example embodiments of this disclosure relate to a method, apparatus and computer program and in particular but not exclusively to DMRS transmission.

[0004] BACKGROUND

[0005] A communication system can be seen as a facility that enables communication sessions between two or more entities such as communication devices, base stations and / or other nodes by providing carriers between the various entities involved in the communications path.

[0006] The communication system and associated entities typically operate in accordance with a given standard or specification which sets out what the associated entities are permitted to do and how that should be achieved. Communication protocols and / or parameters that shall be used for the connection are also typically defined. Examples of standard include the so-called 5G (5thgeneration) standards provided by 3GPP.

[0007] SUMMARY

[0008] Some example 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.

[0009] In an aspect there is provided an apparatus comprising: means for receiving a downlink, DL, demodulation reference signal, DMRS; means for receiving a modulation order, M, to be used for an uplink, UL, DMRS; means for generating the UL DMRS; and means for transmitting the generated UL DMRS, using the modulation order M.

[0010] The apparatus may further comprise means for measuring the DL DMRS to obtain a DL channel estimate, H.

[0011] The UL DMRS modulation order M may correspond to a UL data transmission modulation order.

[0012] The apparatus may further comprise means for transmitting at least part of a UL data transmission after the UL DMRS with a modulation order M. A modulation order of the DL DMRS may be independent of the modulation order used by the UL DMRS.

[0013] The apparatus may further comprise: means for pre-compensating the UL DMRS, to remove the DL channel estimate, H.

[0014] The means for pre-compensating the UL DMRS may comprise means for removing the DL channel estimate, H. The apparatus may further comprise: means for deriving a precoding matrix, U, for removing the DL channel estimate, H; and means for applying the pre-coding matrix in generating the UL DMRS. The means for transmitting the generated UL DMRS may transmit the UL DMRS without the DL channel estimate, H.

[0015] The apparatus may further comprise: means for transmitting the DL channel estimate, H. The DL channel estimate, H, may be transmitted with the UL DMRS or in a separate signal message to the UL DMRS. The DL channel estimate, H, may be transmitted in an UL transmission, wherein said transmission may be encoded with a robust modulation coding scheme. The modulation coding scheme may be quadrature phase shift key, QPSK, or may be quadrature amplitude modulation, QAM.

[0016] The apparatus may comprise a user equipment.

[0017] A time between receiving the DL DMRS, and transmitting the UL DMRS, may be less than or equal to a coherence time of the channel.

[0018] The means for receiving may be configured to receive multiple DL DM reference signals, each having a different modulation order; the means for generating may be configured to generate a UL DM reference signal, using each different modulation order; and the means for transmitting may be configured to transmit the multiple UL DMRS using the respective different modulation orders.

[0019] In an aspect there is provided apparatus comprising: means for selecting a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission; means for transmitting a downlink, DL, DMRS; means for transmitting the selected modulation order, M, in the DL; means for receiving a UL DMRS, modulated using the selected modulation order; and means for deriving digital post distortion, DPoD, coefficients using the received UL DMRS.

[0020] The apparatus may further comprise: means for measuring the combination, C, of a DL channel estimate, H, and a power amplifier, PA, response, G, in the received UL DMRS; means for obtaining the DL channel estimate, H; and means for deriving the power amplifier, PA, response by removing the DL measured channel estimate, H, from the combination, C, in the received UL DMRS. The apparatus may further comprise means for decoding the channel response from the payload of the UL DMRS to obtain the DL channel estimate, H.

[0021] The apparatus may comprising a base station.

[0022] The means for transmitting may be configured to transmit multiple DL DMRSs, each having a different modulation order; the means for receiving may be configured to receive multiple UL DMRSs, each having a different modulation order; and the means for deriving may be configured to derive digital post distortion, DPoD, coefficients for each different modulation order, using the UL DMRSs, of each different modulation order.

[0023] The DL DMRS may be QPSK modulated. The UL DMRS may be QAM.

[0024] In an aspect there is provided a method comprising: receiving a downlink, DL, demodulation reference signal, DMRS; receiving a modulation order, M, to be used for an uplink, UL, DMRS; generating the UL DMRS; and transmitting the generated UL DMRS, using the modulation order M.

[0025] The method may further comprise measuring the DL DMRS to obtain a DL channel estimate, H.

[0026] The UL DMRS modulation order M may correspond to a UL data transmission modulation order.

[0027] The method may further comprise transmitting at least part of a UL data transmission after the UL DMRS with a modulation order M.

[0028] A modulation order of the DL DMRS may be independent of the modulation order used by the UL DMRS.

[0029] The method may further comprise: pre-compensating the UL DMRS, to remove the DL channel estimate, H.

[0030] The step of pre-compensating the UL DMRS may comprise removing the DL channel estimate, H. The method may further comprise: deriving a precoding matrix, U, for removing the DL channel estimate, H; and applying the pre-coding matrix in generating the UL DMRS. The step of transmitting the generated UL DMRS may transmit the UL DMRS without the DL channel estimate, H.

[0031] The method may further comprise: transmitting the DL channel estimate, H. The DL channel estimate, H, may be transmitted with the UL DMRS or in a separate signal message to the UL DMRS. The DL channel estimate, H, may be transmitted in an UL transmission, wherein said transmission may be encoded with a robust modulation coding scheme. The modulation coding scheme may be quadrature phase shift key, QPSK, or may be quadrature amplitude modulation, QAM.

[0032] A time between receiving the DL DMRS, and transmitting the UL DMRS, may be less than or equal to a coherence time of the channel.

[0033] The step of receiving may be configured to receive multiple DL DM reference signals, each having a different modulation order; the step of generating may be configured to generate a UL DM reference signal, using each different modulation order; and the step of transmitting may be configured to transmit the multiple UL DMRS using the respective different modulation orders.

[0034] An apparatus may comprise a means for implementing the method.

[0035] The method may be implemented in user equipment.

[0036] The apparatus may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform any of the methods discussed.

[0037] In an aspect there is provided a method comprising: selecting a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission; transmitting a downlink, DL, DMRS; transmitting the selected modulation order, M, in the DL; receiving a UL DMRS, modulated using the selected modulation order; and deriving digital post distortion, DPoD, coefficients using the received UL DMRS.

[0038] The method may further comprise: measuring the combination, C, of a DL channel estimate, H, and a power amplifier, PA, response, G, in the received UL DMRS; obtaining the DL channel estimate, H; and deriving the power amplifier, PA, response by removing the DL measured channel estimate, H, from the combination, C, in the received UL DMRS.

[0039] The method may further comprise decoding the channel response from the payload of the UL DMRS to obtain the received DL channel estimate, H.

[0040] The method may be implemented in a base station.

[0041] The step of transmitting may transmit multiple DL DMRSs, each having a different modulation order; the step of receiving may receive multiple UL DMRSs, each having a different modulation order; and the step of deriving may derive digital post distortion, DPoD, coefficients for each different modulation order, using the UL DMRSs, of each different modulation order.

[0042] The DL DMRS in the method may be QPSK modulated. The UL DMRS in the method may be QAM. An apparatus may comprise a means for implementing the method.

[0043] The method may be implemented in a base station.

[0044] The apparatus may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform any of the methods discussed.

[0045] According to an aspect, there is provided a computer readable medium comprising program instructions stored thereon for performing at least one of the above methods.

[0046] According to an aspect, there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least one of the above methods.

[0047] According to an aspect, there is provided a non-volatile tangible memory medium comprising program instructions stored thereon for performing at least one of the above methods.

[0048] Any of the above methods may be computer-implemented.

[0049] In the above, many different aspects have been described. It should be appreciated that further aspects may be provided by the combination of any two or more of the aspects described above.

[0050] Various other aspects are also described in the following detailed description and in the attached claims.

[0051] BRIEF DESCRIPTION OF THE FIGURES

[0052] Some example embodiments will now be described, by way of non-limiting and illustrative example only, with reference to the accompanying drawings in which:

[0053] Fig. 1 shows a representation of an example of a communication system;

[0054] Fig. 2 shows a representation of an example of apparatus for implementing one or more network functions of the communication system;

[0055] Fig. 3 shows a representation of an example of user equipment according to some example embodiments;

[0056] Fig. 4 shows a first example of DMRS transmission;

[0057] Fig. 5 shows a second example of DMRS transmission;

[0058] Fig. 6 shows a third example of DMRS transmission;

[0059] Fig. 7 shows a method in accordance with a first example embodiment of a method; and

[0060] Fig. 8 shows a method in accordance with a second example embodiment of a method. DETAILED DESCRIPTION

[0061] In the following, various example embodiments are explained for the example of a user equipment operating according to a 3GPP 5thgeneration (5G) communication protocol, but the example embodiments may also be applicable to user equipment operating according to other communication protocols and more generally beyond communication networks.

[0062] Fig. 1 shows a schematic representation of a 5G communication system (5GS). The 5GS may comprise a user equipment (UE), an access network such as a 5G radio access network (5G-RAN) or next generation radio access network (NG-RAN), a 5G core network (5GC), and one or more application functions. The 5GS connects the UE to a data network the access network and the 5GC (e.g., a UPF of the 5GC).

[0063] The 5G-RAN may comprise one or more radio access nodes, such as gNodeB (GNB). A gNB may be a stand-alone entity or may be provided by a distributed architecture. The distributed architecture comprises one or more gNodeB (GNB) distributed units (gNB- DU) connected to gNodeB centralized unit control plane and user plane entities (gNB-CU-CP and gNB-CU-UP). Additionally one or more radio units RU (not shown) may be provided as part of the distributed architecture. One CU may serve a plurality of DUs. A DU may serve a plurality RUs. A RU may comprise the physical layer, and a RF (radio frequency) front end. The DU may make scheduling decisions. Embodiments use the PDCP protocol, and may use the gNB-CU-UP.

[0064] The interface between the gNB-CU-CP entity and the gNB-CU-UP entity is referred to as El interface. The interface between the gNB-CU-CP entity and the gNB-DU(s) is referred to as Fl-C interface. The interface between the gNB-CU-UP entity and the gNB-DU(s) is referred to as Fl-U interface.

[0065] The 5GC may comprise the following network functions: Network Slice Selection Function (NSSF); Network Exposure Function; Network Repository Function (NRF); Policy Control Function (PCF); Unified Data Management (UDM); Application Function (AF); Authentication Server Function (AUSF); an Access and Mobility Management Function (AMF); and Session Management Function (SMF), and a user plane function (UPF). Fig. 1 also shows the various interfaces (Nl, N2 etc.) that may be implemented between the various elements of the system.

[0066] Fig. 2 illustrates an example of at least a part 200 of the base station. The part 200 may have at least one processor and at least one memory storing instructions of the base station that, when executed by at least one of the at least one processor cause operations or actions of the base station to be performed. The at least a part of the base station may be a base station or part of the base station such as a DU in an architecture where a base station function is provided by CU, DU and RU architecture. The scheduling may be controlled by the DU.

[0067] The base station may comprise at least one random access memory (RAM) 211a, at least one read only memory (ROM) 211b, at least one processor 212, 213 and an input / output interface 214. The at least one processor 212, 213 may be coupled to the RAM 211a and the ROM 211b. The at least one processor 212, 213 may be configured to execute an appropriate software code 215. The software code 215 may include software code that allows, enables, or otherwise facilitates the apparatus to perform one or more operations of the base station.

[0068] The software code 215 may be stored in the ROM 211b.

[0069] Fig. 3 illustrates an example of a communication device 300, such as the user equipment (UE) illustrated in Fig. 1 and mentioned in the description of example embodiments below. The communication device 300 may be provided by any device capable of sending and receiving radio signals. Non-limiting examples of a communication device 300 comprise a user equipment, a mobile station (MS) or mobile device such as a mobile phone or what is known as a ’smart phone’, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), a personal data assistant (PDA) or a tablet provided with wireless communication capabilities, a machine-type communications (MTC) device, an Internet of things (loT) type communication device or any combinations of these or the like. The communication device may be an XR (extended reality) device such as a headset or may be capable of supporting an XR application (e.g., capable of executing or running an XR application). The headset may be a VR headset. The communication device may be or part of a vehicle. The communication device 300 may comprise a transceiver for transmitting and / or receiving, for example, wireless signals carrying communications, for example radio signals. The communications may be one or more of voice, electronic mail (email), text messages, multimedia data, machine data and so on.

[0070] The communication device 300 may receive wireless signals (e.g., radio signals) over an air or radio interface 307 via appropriate apparatus for receiving and may transmit wireless signals via appropriate apparatus for transmitting radio signals. In Fig. 3 transceiver is designated schematically by block 306. The transceiver 306 may comprise, for example, a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device and may comprise one or more antenna elements. The antenna arrangement may be a multi-input multi output (MIMO) antenna. The communication device 300 may be provided with at least one processor 301, at least one memory ROM 302a, at least one RAM 302b and other possible components 303 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access networks (e.g., the 5G-RAN or NG-RAN illustrated in Fig. 1) and other communication devices. The at least one processor 301 is coupled to the RAM 302b and the ROM 302a. The at least one processor 301 may be configured to execute an appropriate software code 308. The software code 308 may for example allow to perform one or more operations of the communication device. The software code 308 may be stored in the ROM 302a.

[0071] The processor, the ROM, and the RAM, the transceiver and other circuitry of the communication device (e.g., a modem) can be provided on a circuit board, in chipsets, or in a system on chip. The circuit board, chipsets or system on chip is denoted by reference 304. The communication device 300 may optionally have a user interface such as key pad 305, touch sensitive screen or pad, combinations thereof or the like. Optionally one or more of a display, a speaker and a microphone may be provided depending on the type of communication device.

[0072] It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and / or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0073] In 5G, a Demodulation Reference Signal (DMRS) is utilized to estimate Digital Predistortion (DPoD) coefficients, which are essential for compensating non-linear distortion and channel effects in a received signal. This estimation is conducted by applying a least-squares (LS) method on the received DMRS-bearing Orthogonal Frequency Division Multiplexing (OFDM) symbol. This, however, results in different envelope characteristics of the DMRS symbol compared to the actual data-bearing symbols as highlighted by existing literature and research.

[0074] To overcome this issue, the DMRS signal may be boosted. This has drawbacks, in that a reference signal with high peak-to-average power ratio (PAPR) is not suitable for channel estimation, and it requires an off-line tuning of the boosting level 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 power amplifier (PA) characteristics. Another proposal to overcome this issue is to use two DMRS symbols.

[0075] In 5G, uplink (UL) DMRS signals are typically utilized by the gNB to estimate the DPoD coefficients. The DPoD coefficients are essential for compensating the non-linear distortion (caused by the PA) and channel effects (due to wireless propagation) in the received signal. This approach is however sub-optimal for at least the two following reasons.

[0076] Firstly, the DMRS are quadrate phase shift keying (QPSK) modulated, while data is usually sent with much higher order quadrature amplitude modulation (QAM). Since the nonlinear effect of the PA is the most severe in high order modulations, a QPSK DMRS reception cannot effectively capture how the PA response will distort the M-ary QAM modulated data, such as 256 QAM.

[0077] Secondly, the propagation channel and PA responses cannot be effectively de-coupled, thus the DPoD coefficients estimated using UL DMRS will inherently contain some of the propagation channel effects. This means that the DPoD coefficients need to be re-derived every time the propagation channel changes.

[0078] A protocol is proposed that overcomes these shortcomings.

[0079] In accordance with the proposed protocol, the gNB is enabled to: i. Decouple the PA response from the propagation channel response. This is achieved, as described below, by removing the contribution of the channel estimate, H, to the combined channel response that the gNB is estimating. ii. Derive the power amplifier (PA) response of the UE for the exact QAM modulation order (or modulation factor) the UE is configured to use in its own UL data transmission. This is achieved by the gNB selecting the modulation order for the UL DMRS transmission of the UE, which follows after the DL DMRS. The DL DMRS may be modulated to a different order than modulation order M.

[0080] With reference to FIG. 4 there is illustrated an example of the general principles in accordance with the proposed technique. Then with reference to FIGS. 5 and 6 two example embodiments utilising these principles are described.

[0081] The proposed technique protocol consists of a looped DMRS transmission. In FIG. 4 communication is shown between a base station 402 (such as a gNodeB, an example of a base station) and a UE 404 (a user equipment).

[0082] In a step S2, the base station 402 determines a modulation order, M, for use by the UE 404 in configuring a DMRS for the UL physical uplink channel (PUSCH) that carries data.

[0083] As denoted by signal Ml, the base station 402 transmits a DL QPSK DMRS signal to the UE 404. The signal Ml identifies the DL DMRS. The DL DMRS is a raw signal.

[0084] As denoted by message M2, the base station 402 transmits the modulation order M, to be used for the UL DMRS, to the UE 404. The modulation order of the signal Ml or the message M2 may be different to M. The modulation order M may e.g. be 256. QPSK is the modulation technique used in the downlink in 5G, but other modulation techniques may be utilised.

[0085] The signal Ml or the message M2 may have a fixed modulation, and may e.g. be a QPSK signal.

[0086] The DL DMRS signal may be transmitted over a data channel or a control channel. The DL DMRS signal Ml may, for example, be included in the channel state information reference signal (CSI-RS) or in the physical downlink shared channel (PDSCH).

[0087] The UE transfers the selected modulation order M for use in encoding at the UE. The UE may recover the modulation order M to be used in transmitting the UL DMRS from the message M3, and store it for use when needed.

[0088] In a step S6, the UE measures the DL QPSK DMRS, to obtain a channel estimate H. The channel estimate H may be removed at the UE 404 in accordance with a first example embodiment described with reference to FIG. 5, or may be transmitted to the base station 402 in accordance with a second example embodiment described with reference to FIG. 6. When transmitted to the base station 402 in the second embodiment, the channel estimate H is removed at the base station as will be described.

[0089] Techniques for determining a channel estimate H from the DMRS signal in message Ml are known, for example in 5G.

[0090] In the first example embodiment of FIG. 5, the UE may be configured to pre-code the UL M-ary QAM transmission to remove the channel estimate H, so that the propagation channel is effectively pre-compensated during the UL transmission, and the base station observes a signal distorted purely by the PA response alone.

[0091] In the second example embodiment of FIG. 6, the UL M-ary DMRS transmission may include the reporting of the DL channel estimate H.

[0092] In a step S8, the UL M-ary QAM DMRS is configured by the UE for transmission to the base station 403. This configures or applies the modulation order M to the UL DMRS. QAM is the modulation technique used in the downlink in 5G, but other modulation techniques may be utilised.

[0093] The UL DMRS is configured in accordance with either the first or second embodiment described below with reference to FIGS. 5 and 6.

[0094] A message M3 then transmits the UL DMRS from the UE 404 to the base station 402. The UL DMRS signal M3 is preferably a QAM message. The UL DMRS signal M3 is preferably an M-ary message. The UL DMRS is a raw signal, and does not have any payload. The UL DMRS may be sent as part of a message, with a data part and the DMRS having distinct allocation, being associated with separate resource sets.

[0095] As denoted by step S10, the base station is configured to estimate the PA response G, and derive the SPoD coefficients.

[0096] In the first embodiment of FIG. 5, as the channel estimate H has been removed from the UL DMRS signal M3, this may be done directly.

[0097] In the second embodiment with respect to FIG. 6, the channel estimate H is included in the UL DMRS signal M3 and is removed at the base station before the DPoD coefficients are derived. In this embodiment, the channel estimate H may be included in the UL DMRS signal M3, or may be transmitted from the UE to the base station in a separate message.

[0098] As denoted by message M4 (which may be a single message, or may represent a plurality of messages), the UE subsequently sends an UL data transmission to the base station, which is modulated according to modulation order M. The modulation order for the UL data transmission is thus preferably the same as the modulation order M for the UL DMRS signal.

[0099] The DPoD coefficients derived in step S10 may be used for processing the UL data transmissions in message M4. The UL data transmission may be sent before the DPoD coefficients are derived, but are used in processing the UL data transmissions.

[0100] In general, as represented by the example of FIG. 4, the proposed technique selects a modulation order for the UL DMRS which is the same as the modulation order for the UL data transmissions. The modulation order is preferably set by the base station, and applied in the UE.

[0101] In addition, the channel estimate H is removed from the signal from which the DPoD coefficients are derived. As discussed below, in a first embodiment described with reference to FIG. 5 the channel estimate H is removed before the UL DMRS is generated, i.e. removed at the UE, and in a second embodiment described with reference to FIG. 6 the channel estimate H is removed after the UL DMRS is received, i.e. removed at the base station.

[0102] The first embodiment based on the example of FIG. 4 is now described with reference to FIG. 5, which shows communication between the base station 402 and the UE 404. In this first embodiment, the M-ary DMRS signal in the uplink from the UE is pre-coded in the UE by removing the channel estimate H.

[0103] As denoted by step S20, the base station 402 selects a modulation order M for the UL data transmission and UL DMRS transmission by the UE in the PUSCH. The base station 402 then configures the UL DMRS transmission for DPoD calibration in later steps S34 and S36, as discussed below.

[0104] The base station 402 transmits a DL DMRS signal M5 to the UE 404. With this signal M5 the base station 402 configures the UE 404 for looped DMRS transmission.

[0105] The base station 402 transmits a message M6 including the modulation order M.

[0106] The DMRS signal M5 and the message M6 may be a QPSK message, and may use a modulation order which is preferably fixed, and which is preferably agnostic of the modulation order M to be used in the UL.

[0107] The DL QPSK DMRS signal M5 and the modulation order M are used by the UE 404 as follows.

[0108] The UE 404 identifies the selected modulation order M for the UL PUSCH, and transfers this for use by the UE in the UL transmission. This may simply be a step of recovering the modulation order from the message M6, and storing it for later use.

[0109] In a step S24, the UE 404 measures the DL QPSK DMRS.

[0110] In a step S26 the UE 404 estimates the channel H based on this measurement.

[0111] In a step S28 the UE 404 derives a pre-coding matrix U. The pre-coding matrix is obtained using H. In the first embodiment the channel estimate H is removed before the UL DMRS is transmitted. The pre-coding matrix U may - in an example - thus be derived as the inverse of the channel estimate H. Thus when the pre-coding matrix U is applied in encoding, the channel estimate H is cancelled and removed. Providing a pre-coding matric which is an inverse of the channel estimate is only one example for removing the effect of the channel from the UL DMRS.

[0112] In a step S30 the UE pre-codes the UL DMRS signal with the response H using the matrix U.

[0113] In a step S32, the UL DMRS signal is configured using the same modulation order M as the DL, it having been transferred in step S22. This configuration applies the modulation order M in the UL.

[0114] The configuration of steps S22 to S32 may be carried out by one or more new information elements (IES) or by the medium access layer (MAC) radio resource control (RRC).

[0115] As denoted by signal M7, the UL DMRS signal M7 is then transmitted from the UE 404 to the base station 402, with the modulation order M applied.

[0116] The UL DMRS signal M7 may be a QAM signal. THE UL DMRS signal is preferably an M-ary signal. The UL M-ary QAM DMRS is transmitted as configured by the UE. After receipt of the message M6, the base station 402 is configured to measure the UL DMRS and estimate the response of the PA, G, as denoted by step S34.

[0117] The technique for estimating the response G is known, for example from 5G. This technique may be to compare the DL DMRS and the UL DMRS in a channel estimator such as LMMSE (linear minimum mean square estimator), zero forcing (ZF), etc, to reconstruct the channel response.

[0118] As denoted by step S36, the response G of the PA is then used by the base station to derive DPoD coefficients.

[0119] The derivation of the DPoD coefficients from the response G is in accordance with known techniques, such as techniques known in 5G.

[0120] As denoted by message M8, the UE subsequently sends an UL data transmission to the base station, which is modulated according to modulation order M. This is consistent with the general operation according to FIG. 4.

[0121] In accordance with the first embodiment illustrated in FIG. 5, the UE 404 thus estimates the DL channel H, derives a precoding matrix U, and uses the pre-coding matrix U to pre-code or pre-distort the UL M-ary QAM DMRS so as to remove the channel estimate H in advance of the transmission of the DMRS in the UL over the air from the UE.

[0122] A second embodiment based on the example of FIG. 4 is described with reference to FIG. 6, which shows communication between the base station 402 and the UE 404. In this second embodiment, the M-ary DMRS signal in the uplink from the UE includes the channel estimate H.

[0123] As denoted by step S40, the base station 402 selects a modulation order M for the UL data transmission of the UE in the PUSCH. The base station 402 then uses the same modulation to configure the UL DMRS transmission for DPoD calibration in later steps S52 to S60, as discussed below.

[0124] The base station 402 transmits a DL DMRS signal M9 to the UE 404. With this message M9 the base station 402 configures the UE 404 for loop DMRS transmission.

[0125] The base station 402 transmits a message M10 including the modulation order M.

[0126] The DMRS signal M9 or the message M10 may be QPSK modulated, and may use a modulation order which is preferably fixed, and which is preferably agnostic of the modulation order M to be used in the UL.

[0127] The DL DMRS and the modulation order M are used by the UE 404 as follows.

[0128] The UE 404 identifies the modulation order M for the UL PUSCH in message M10, and transfers this for use by the UE in the UL transmission. Again, this may simply involve recovering the modulation order M from the DMRS signal, and storing it in the UE for later use.

[0129] In a step S44, the UE 404 measures the DL DMRS.

[0130] In a step S46 the UE 404 estimates the channel H based on this measurement.

[0131] In a step S48 the UE pre-codes the UL DMRS transmission with the response H.

[0132] In a step S50, the UL DMRS is configured using the modulation order M, it having been transferred in step S22. This configuration applies the modulation order M in the UL.

[0133] The configuration of steps S42 to S50 may be carried out by one or more new information elements (IES) or by the medium access layer (MAC) radio resource control (RRC).

[0134] As denoted by message Mi l, the UL DMRS signal is then transmitted from the UE 404 to the base station 402 with the modulation order M applied.

[0135] The UL DMRS signal Dl l may be a QAM signal. The UL DMRS signal is preferably an M-ary signal.

[0136] The UL M-ary QAM DMRS is transmitted as configured by the UE.

[0137] After receipt of the message Ml 1, the base station 402 is configured to measure the UL DMRS and estimate a combination (C) of the channel response H and the PA response G as denoted by step S52. As in this example embodiment the channel response H is not removed prior to encoding the UL DMRS, it is included in the UL DMRS together with the PA response.

[0138] The technique for estimating the responses H and G is known, for example form 5G. This technique may be to compare the DL DMRS and the UL DMRS in a channel estimator such as LMMSE (linear minimum mean square estimator), zero forcing (ZF), etc, to reconstruct the channel response.

[0139] As denoted by step S56, the channel estimate H is then decoded from the payload of the UL DMRS signal M10.

[0140] As denoted by step S58, the PA response G is then derived by subtracting the channel response H determined in step S56 from the combination C determined in step S52.

[0141] As denoted by step S60, the response G of the PA is then used by the base station to derive DPoD coefficients.

[0142] The derivation of the DPoD coefficients from the response G is in accordance with known techniques, such as techniques known in 5G.

[0143] As denoted by message M12, the UE subsequently sends an UL data transmission to the base station, which is modulated according to modulation order M. This is consistent with the general operation according to FIG. 4. In accordance with the second embodiment illustrated in FIG. 6, the UE 404 thus includes the estimate of channel H in the DL DMRS, and the channel estimate H is removed from the DL DMRS to determine the DPoD coefficients at the base station.

[0144] In the second example embodiment of Figure 6, the UE is requested to report the estimated response H in addition to transmitting the UL DMRS. Preferably the report should be contained in a UL data channel which has a robust MCS, e.g., QPSK, modulated with a high code rate. This ensures that any eventual errors in the channel equalization do not impact the retrieval of the channel estimate H.

[0145] In any of the described examples and embodiment, the time between the DL reception at the UE and the UL transmission from the UE should preferably be equal to or less than a coherence time of the propagation channel, to ensure that the precoding is not obsolete when the UL DMRS is transmitted.

[0146] Any of the described examples and embodiment may be modified to send multiple consecutive DL DMRS signals, each with a different modulation order. The techniques described above are then applied for each different modulation order, so the UL modulation order for UL DMRS, corresponds to the modulation order of the DL DMRS on which it is based.

[0147] For example:

[0148] 1. UL Ml-ary DMRS for symboll

[0149] 2. UL M2-ary DMRS for symbol2

[0150] 3.

[0151] The base station may then use each DMRS in isolation to derive a DPoD coefficient set for each modulation order Ml, M2, etc.

[0152] In the above examples reference is made to a base station. This is an example of a base station, and the proposed techniques apply to other bases stations.

[0153] In the above examples reference is made to a UE. The proposed techniques apply to any user equipment , or a device configured for communication with a base station.

[0154] In the above examples, the DL DMRS is referred to as QPSK encoded. Other encoding techniques may be used for the DL DMRS.

[0155] In the above examples, the UL DMRS is referred to as QAM encoded. Other encoding techniques may be used for the UL DMRS.

[0156] Reference is made to Figs. 7 and 8 which show methods of some example embodiments.

[0157] Each method may be performed by an apparatus. The apparatus may comprise suitable means, such as circuitry for providing the method. The method of Fig. 7 may be implemented at a UE. Alternatively or additionally, the apparatus may be such as discussed in relation to Fig. 3.

[0158] The method of Fig. 8 may be implemented at a base station, for example a gNB. Alternatively or additionally, the apparatus may be such as discussed in relation to Fig. 1 or Fig. 2.

[0159] Alternatively or additionally, the apparatus may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor cause the apparatus at least to provide the method below.

[0160] Alternatively or additionally, the apparatus may be such as discussed in relation to Fig. 1.

[0161] Each method may be provided by computer program code or computer executable instructions.

[0162] Referring to Fig. 7 :

[0163] The method may comprise as referenced Al, receiving a downlink, DE, demodulation reference signal, DMRS. The method may comprise as referenced A2, receiving a modulation order, M, to be used for an uplink, UE, DMRS. The method may comprise as referenced A3, generating an UL DMRS. The method may comprise as referenced A4, transmitting the generated UL DMRS, using the modulation order M.

[0164] Referring to Fig. 8:

[0165] The method may comprise as referenced B 1 , selecting a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission. The method may comprise as referenced B2, transmitting a downlink, DL, DMRS. The method may comprise as referenced B3, transmitting the selected modulation order, M, in the DL. The method may comprise as referenced B4, receiving a UL DMRS, modulated using the selected modulation order. The method may comprise as referenced B5, deriving digital post distortion, DPoD, coefficients using the received UL DMRS.

[0166] Although certain example embodiments were described above, by way of non-limiting and illustrative example, and with reference to certain example architectures for communication systems operated by mobile network operators, technologies and standards, further example embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. For example, some example embodiments have been described in relation to a 5G communication system (5GS). It should be appreciated that other example embodiments may be provided in any other suitable communication system(s) or in any suitable combination with a 5GS, but embodiments are not limited to communication systems.

[0167] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0168] As used herein, the expression “and / or” includes any and all combinations of the listed terms, including at least any one of the elements, or at least any two or more of the elements, or at least all of the elements.

[0169] 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”).

[0170] 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”.

[0171] In general, the various example embodiments of this disclosure may be implemented in hardware or special purpose circuitry, software, logic or any combination thereof. Some aspects of this disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of this disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting and illustrative examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0172] As used herein, the term “circuitry” may refer to one or more or all of the following:

[0173] (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and

[0174] (b) combinations of hardware circuits and software, such as (as applicable):

[0175] (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

[0176] (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.

[0177] This definition of circuitry applies to all uses of this term herein , including in any claims. As a further example, as used here, 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, an integrated circuit such as a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, and / or other computing or network device.

[0178] The various example embodiments of this disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and / or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computerexecutable components which, when the program is run, are configured to carry out the various example embodiments of this disclosure. The one or more computer-executable components may include software code or any portion(s ) thereof.

[0179] Further in this regard it should be noted that any blocks of the logic flow as in the Figs, may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on physical media such as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media ( for example DVD and the data variants thereof, CD). The physical media is a non-transitory media.

[0180] The 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., RAM vs. ROM).

[0181] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting and illustrative examples.

[0182] The various example embodiments of the disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0183] The foregoing description has provided, by way of non-limiting and illustrative examples, a full and informative description of the various example embodiments of this disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the drawings and the claims. Indeed, there are further example embodiments comprising a combination of one or more example embodiments with any of the other example embodiments described herein. The scope of protection sought for some of the various example embodiments of this disclosure is set out by the claims. The various example embodiments in addition to its respective aspects and features thereof described herein that do not fall under the scope of the claims (if any) are to be interpreted as examples useful for understanding the various example embodiments of this disclosure. It should be noted that different claims with differing claim scope may be pursued in related applications, such as divisional or continuation applications.

Claims

CLAIMS1. Apparatus comprising: means for receiving a downlink, DL, demodulation reference signal, DMRS,; means for receiving a modulation order, M, to be used for an uplink, UL, DMRS; means for generating the UL DMRS; and means for transmitting the generated UL DMRS, using the modulation order M.

2. The apparatus of claim 1, further comprising means for measuring the DL DMRS to obtain a DLchannel estimate, H.

3. The apparatus of claim 1 or claim 2, wherein the UL DMRS modulation order M corresponds to a UL data transmission modulation order.

4. The apparatus of any one of claims 1 to 3 further comprising means for transmitting at least part of a UL data transmission after the UL DMRS with the modulation order M.

5. The apparatus of any one of claims 1 to 4, wherein a modulation order of the DL DMRS is independent of the modulation order used by the UL DMRS.

6. The apparatus of any one of claims 2 to 5 further comprising: means for pre-compensating the UL DMRS, to remove the DL channel estimate, H.

7. The apparatus of claim 6, wherein the means for pre-compensating the uplink DMRS comprises means for removing the DL channel estimate, H.

8. The apparatus of claim 6 or claim 7 further comprising: means for deriving a precoding matrix, U, for removing the DL channel estimate, H; and means for applying the pre-coding matrix in generating the UL DMRS.

9. The apparatus of any one of claims 2 to 4 wherein the means for transmitting the generated UL DMRS transmits the UL DMRS without the DL channel estimate, H.

10. The apparatus of any one of claims 2 to 5 further comprising: means for transmitting the DL channel estimate, H.

11. The apparatus of claim 10 wherein the DL channel estimate, H, is transmitted with the UL DMRS or in a separate signal message to the UL DMRS.

12. The apparatus of claim 10 or claim 11 wherein the DL channel estimate, H, is transmitted in an UL transmission, wherein said transmission is encoded with a robust modulation coding scheme.

13. The apparatus of claim 12 wherein the modulation coding scheme is quadrature phase shift key, QPSK, or quadrature amplitude modulation, QAM.

14. The apparatus of any one of claims 1 to 13 comprising a user equipment.

15. The apparatus of any one of claims 1 to 13 wherein a time between receiving the DL DMRS, and transmitting the UL DMRS, is less than or equal to a coherence time of the channel.

16. The apparatus of any one of claims 1 to 14 wherein: the means for receiving is configured to receive multiple DL DM reference signals, each having a different modulation order; the means for generating is configured to generate a UL DM reference signal, using each different modulation order; and the means for transmitting is configured to transmit the multiple UL DM reference signals using the respective different modulation orders.

17. Apparatus comprising: means for selecting a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission; means for transmitting a downlink, DL, DMRS; means for transmitting the selected modulation order, M, in the DL; means for receiving a UL DMRS, modulated using the selected modulation order; and means for deriving digital post distortion, DPoD, coefficients using the received UL DMRS.

18. The apparatus of claim 17, further comprising: means for measuring the combination, C, of a DL channel estimate, H, and a power amplifier, PA, response, G, in the received UL DMRS; means for obtaining the DL channel estimate, H; and means for deriving the power amplifier, PA, response by removing the DL measured channel estimate, H, from the combination, C, in the received UL DMRS.

19. The apparatus of claim 18 further comprising means for decoding the channel response from the payload of the UL DMRS to obtain the DL channel estimate, H.

20. The apparatus of any one of claims 17 to 19 comprising a base station.

21. The apparatus of any one of claims 17 to 20 wherein: the means for transmitting is configured to transmit multiple DL DMRSs, each having a different modulation order; the means for receiving is configured to receive multiple UL DMRSs, each having a different modulation order; and the means for deriving is configured to derive digital post distortion, DPoD, coefficients for each different modulation order, using the UL DMRSs, of each different modulation order.

22. The apparatus of any preceding claim, wherein the DL DMRS is QPSK modulated.

23. The apparatus of any preceding claim wherein the UL DMRS is QAM.

24. A method comprising: receiving a downlink, DL, demodulation reference signal, DMRS; receiving a modulation order, M, to be used for an uplink, UL, DMRS; generating the UL DMRS; and transmitting the generated UL DMRS, using the modulation order M.

25. A method comprising: selecting a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission; transmitting a downlink, DL, DMRS;transmitting the selected modulation order, M, in the DL; receiving a UL DMRS, modulated using the selected modulation order; and deriving digital post distortion, DPoD, coefficients using the received UL DMRS.

26. 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 a downlink, DL, demodulation reference signal, DMRS; receive a modulation order, M, to be used for an uplink, UL, DMRS; generate the UL DMRS; and transmit the generated UL DMRS, using the modulation order M.

27. 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: select a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission; transmit a downlink, DL, DMRS; transmit the selected modulation order, M, in the DL; receive a UL DMRS, modulated using the selected modulation order; and derive digital post distortion, DPoD, coefficients using the received UL DMRS.

28. A computer program product comprising at least one non-transitory computer-readable storage medium having computer-executable program code instructions stored therein, the computer-executable program code instructions comprising program code instructions configured to: receive a downlink, DL, demodulation reference signal, DMRS; receive a modulation order, M, to be used for an uplink, UL, DMRS; generate the UL DMRS; and transmit the generated UL DMRS, using the modulation order M.

29. A computer program product comprising at least one non-transitory computer-readable storage medium having computer-executable program code instructions stored therein, thecomputer-executable program code instructions comprising program code instructions configured to: select a modulation order, M, for an uplink, UL, demodulation reference signal, DMRS, transmission; transmit a downlink, DL, DMRS; transmit the selected modulation order, M, in the DL; receive a UL DMRS, modulated using the selected modulation order; and derive digital post distortion, DPoD, coefficients using the received UL DMRS.

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