Methods, apparatus, and computer programs for a communication network involving a user device with multiple antennas

Abstract

A user device with multiple antennas receives, from a network device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions and a second in

Description

Field Various example embodiments relate to apparatus, methods, and / or computer programs for a communication network involving a user device with multiple antennas. Background Power amplifiers (PAs) can be used by user devices in communication networks to amplify low-power radio frequency (RF) signals for uplink (UL) transmissions from the user device, for instance, to increase the operable range of the user device. However, as the output power (or in other words, gain, amplification, etc.) of a PA increases, distortion can be introduced in the uplink (UL) transmissions, particularly when the PA is operating above the PAs saturation point in a nonlinear, or compression, regime. This distortion can include in-band distortion which can be represented as an error vector magnitude (EVM), and can lead to increased bit error rates at a receiving network device. Techniques such as digital post-distortion (DPoD) can be utilized at the receiving network device to reduce the in-band distortion. Summary According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. For instance, in a first aspect, this specification describes a user device comprising: means for receiving, from a network device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device and a second indication indicating that digital post-distortion (DPoD) is enabled at the network device; means for determining an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna, wherein, based on receipt of the second indication, the output power is determined such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; and means for performing one or more uplink transmissions using the selected antenna and the determined output power of the PA. In a second aspect, this specification describes a network device comprising: means for sending, to a user device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device; means for sending, to the user device, a second indication indicating that digital postdistortion (DPoD) is enabled at the network device, wherein the second indication is usable by the user device to determine an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; and means for receiving, from the selected antenna of the user device, one or more uplink transmissions. In a third aspect, this specification describes a method comprising: receiving, from a network device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device and a second indication indicating that digital post-distortion (DPoD) is enabled at the network device; determining an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna, wherein, based on receipt of the second indication, the output power is determined such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; and performing one or more uplink transmissions using the selected antenna and the determined output power of the PA. In a fourth aspect, this specification describes a method comprising: sending, to a user device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device; sending, to the user device, a second indication indicating that digital post-distortion (DPoD) is enabled at the network device, wherein the second indication is usable by the user device to determine an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; and receiving, from the selected antenna of the user device, one or more uplink transmissions. In a fifth aspect, this specification describes a network device comprising: means for receiving, from a first antenna of a user device, one or more uplink transmissions; means for obtaining, from a data repository configured to store digital post-distortion (DPoD) parameters for antennas of the user device capable of being used for uplink transmissions, DPoD parameters for the first antenna; and means for performing, using the DPoD parameters for the first antenna, DPoD on the one or more uplink transmissions. In a sixth aspect, this specification describes a method comprising: receiving, from a first antenna of a user device, one or more uplink transmissions; obtaining, from a data repository configured to store digital post-distortion (DPoD) parameters for antennas of the user device capable of being used for uplink transmissions, DPoD parameters for the first antenna; and performing, using the DPoD parameters for the first antenna, DPoD on the one or more uplink transmissions. In an eighth aspect, this specification describes computer-readable instructions which, when executed by a computing apparatus, cause the computing apparatus to perform (at least) any method as described herein (including the methods of the third, fourth, and sixth aspects described above). In a ninth aspect, this specification describes a computer-readable medium (such as a non-transitory computer-readable medium comprising program instructions stored thereon for performing (at least) any method described herein (including the methods of the third, fourth, and sixth aspects described above). In a tenth aspect, this specification describes an apparatus comprising: at least one processor, and at least one memory storing instructions that, when executed by the at least one processor, causes the apparatus to perform (at least) any method as described herein (including the methods of the third, fourth, and sixth aspects described above). In a eleventh aspect, this specification describes a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform (at least) any method as described herein (including the methods of the third, fourth, and sixth aspects described above). Brief description of the drawings Example embodiments will now be described, by way on non-limiting examples, with reference to the following schematic drawings, in which: FIG. 1 depicts a block diagram of an example environment that demonstrates various aspects of the present disclosure, and in which some implementations disclosed herein can be implemented; FIG. 2 depicts procedures in accordance with various example embodiments; FIG. 3 depicts an example configuration for a plurality of reference signals using different antennas of a user device, in accordance with various example embodiments; FIGs. 4, 5 and 6 are flowcharts depicting methods performed in accordance with example embodiments; FIG. 7 is a schematic diagram depicting components of one or more of the example embodiments described previously; FIG. 8 depicts a tangible media for storing computer-readable code which, when run by a computer, may perform methods according to example embodiments herein. Detailed description The scope of protection sought for various implementations of the subject matter disclosed herein is set out by the independent claims. The features of the subject matter described herein, if any, described in the specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various implementations of the subject matter described herein. In the description and drawings, like reference numerals refer to like elements throughout. In the following, different exemplifying embodiments will be described using, as an example of a communication network, a fifth generation (5G) or new radio (NR) or 5G-Advanced communication network, without restricting the embodiments to such an architecture. It will be appreciated that the embodiments described herein may also be applied to other kinds of communication networks having suitable means by adjusting parameters and procedures appropriately, such as fourth generation (4G) or long term evolution (LTE) communication networks, or to other future communication network technologies such as sixth generation (6G) communication networks. Some examples of other options for suitable systems are the universal mobile telecommunications system (UMTS) radio access (UTRA), long term evolution (LTE, also known as E-UTRA), long term evolution advanced (LTE Advanced, LTE-A), wireless local area network (WLAN or Wi-Fi), worldwide interoperability for microwave access (WiMAX), Bluetooth®, personal communications services (PCS), ZigBee®, wideband code division multiple access (WCDMA), systems using ultra-wideband (UWB) technology, sensor networks, mobile ad-hoc networks (MANETs) and Internet Protocol multimedia subsystems (IMS) or any combination thereof. In addition, in the following, the term user device typically refers to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop and / or touch screen computer, tablet, game console, notebook, multimedia device, aerial / terrestrial / maritime vehicle, etc. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video dips to a network. A user device may also be a device having capability to operate in Internet of Things (loT) network which is a scenario in which objects are provided with the ability to transfer data over the loT network without requiring human-to-human or human-to-computer interaction. In some applications, a user device may comprise a small portable device with radio parts (such as a watch, earphones or eyeglasses) whereby some or all computation is carried out in the cloud. A user device may also be called a UE, a terminal device, a subscriber unit, a mobile station, a remote terminal, an access terminal, or a user terminal just to mention but a few names or apparatuses. In certain situations (e.g., to increase coverage), user devices in a communication network (e.g., a 6G, or 5G communication network) can increase output power of their power amplifiers (PAs), and in some cases, operate their PAs in a compression (or, in other words, non-linear) regime. However, this can lead to degradation in both EVM (or otherwise referred to as in-band distortion) and adjacent channel leakage ratio (ACLR) (or otherwise referred to as out-of-band emission). EVM is a measure of the difference between a reference waveform and the measured (received) waveform. This difference can be referred to as the error vector. In some cases, before determining the EVM, the measured waveform can be corrected by a sample timing offset and a radio frequency (RF) frequency offset, and a carrier leakage may be removed from the measured waveform. The measured waveform can also be further equalized using channel estimates, where the channel estimates can be subjected to a EVM equalizer spectrum flatness requirement (e.g., as defined in an appropriate standard). In some implementations (e.g., for discrete Fourier transform-spread-orthogonal frequency division multiplexing (DFT-S-OFDM) waveforms), the EVM result can be defined, after a front-end fast Fourier transform (FFT) and inverse discrete Fourier transform (IDFT), as the square root of the ratio of the mean error vector power to the mean reference power, expressed as a %. In some implementations, (e.g., for cyclic prefix OFDM (CP-OFDM) waveforms), the EVM result can be defined, after the front-end FFT, as the square root of the ratio of the mean error vector power to the mean reference power, expressed as a %. In some implementations, the basic EVM measurement interval in the time domain can be one preamble sequence for the physical random access channel (PRACH), and one slot for physical uplink control channel (PUCCH) and physical uplink shared channel (PUSCH) in the time domain. The EVM measurement interval can be reduced by any symbols that contain an allowable power transient in the measurement interval (e.g., as defined in the appropriate standard). EVM can generally be expected to increase when the user device enhances its modulation scheme. In addition, EVM can be expected to increase with a lower modulation scheme if the PA is operated in a saturation regime (e.g., to achieve higher power efficiency and lower supply current). Some communication networks can define one or more transmit signal quality requirements, such as EVM requirements (e.g., a maximum EVM). For instance, it can be defined that the root mean square (RMS) average of the basic EVM measurements (over 10 subframes for the average EVM case, and over 60 subframes for the reference signal EVM case) shall not exceed certain maximum EVM values. In some implementations, the maximum EVM can be based on the modulation scheme used (e.g., because the simpler the modulation scheme, the more robust demodulation of the received signal can be to noise and / or distortion). For instance, when the modulation scheme is Pi / 2-binary phase shift keying (BPSK), the maximum EVM for the average EVM level can be relatively relaxed (e.g., 30%). When the modulation scheme is quadrature phase shift keying (QPSK), the threshold value for the average EVM level can be relatively less relaxed (or in other words, stricter) (e.g., 17.5%). When the modulation scheme is 16 quadrature amplitude modulation (QAM), the threshold value for the average EVM level can be relatively less relaxed again (12.5%). When the modulation scheme is 64 QAM, the threshold value for the average EVM level can be relatively less relaxed again (e.g., 8%). When the modulation scheme is 256 QAM, the threshold value for the average EVM level can be relatively less relaxed again (3.5%). Although only maximum EVM requirements are discussed in detail herein, it will be appreciated that the implementations described herein are not limited to this, and that any suitable transmit signal quality requirement can be used. In some cases, in-band distortion (e.g., EVM) can be mitigated at the network side (e.g., at a network device such as a gNB) using techniques such as digital postdistortion (DPoD) (otherwise referred to as digital post linearization). In more detail, a user device can send a reference signal (such as a UL reference signal, a sounding reference signal (SRS), a demodulation reference signal (DMRS), etc) through Its own PA to a network device. The reference signal can then be used to estimate DPoD parameters (otherwise referred to as DPoD weights, coefficients, etc.) at the network device. The network device can then process any subsequently received (and in some cases, pre-processed) signals from the user device, using DPoD techniques with the determined DPoD parameters, to mitigate the EVM received at the network device. For instance, various DPoD techniques involve processing the received (and in some cases, pre-processed) signals using one or more of an ML model, a lookup table, a linear function, and a nonlinear function. The DPoD parameters described herein can therefore correspond to one or more corresponding ML model weights, lookup table values, linear function mappings, nonlinear function mappings, etc., as appropriate. It will be appreciated that implementations described herein can utilize any suitable implementation of DPoD. Such techniques can allow the nominal transmit signal quality requirements (such as a nominal maximum EVM) to be relaxed whilst DPoD is utilized by the network device, or in other words, the nominal transmit signal quality requirements can be violated or exceeded (e.g., temporarily, or at least whilst DPoD is active at the network device). This means that PAs can operate at a higher power and / or modulation order (e.g., and thus increase coverage and / or capacity), since it can generally be expected that increasing the PA output power and / or modulation order will increase the EVM. Since techniques such as DPoD do not require extra hardware at the user device, these techniques can allow even low-cost user devices to be capable of high coverage and high-capacity transmission. As an example, assuming that a user device is transmitting with 256-QAM and a received EVM at a network device is 9%, by utilizing techniques such as DPoD, the EVM can be improved down to 3% at the network device. The maximum EVM requirement from the perspective of the user device can therefore be correspondingly relaxed (e.g., increased). For Instance, assuming that the nominal maximum EVM for 256-QAM is 3.5%, the user device can instead comply with a relaxed maximum EVM of 8%, or even higher, based on the improvement from using DPoD at the network device. The maximum PA power can therefore also be correspondingly relaxed (e.g., increased). In some cases, DPoD techniques can be combined with other linearization methods such as Envelope Tracking (ET) and / or digital pre-distortion (DPD). Whilst DPoD is utilized to improve in-band distortion, ET and / or DPD can be used to optimize power efficiency of the PA and reduce out-of-band emission (e.g., ACLR), to avoid violating or interfering with neighbour channels (e.g., which might belong to another network). Relaxing the transmit signal quality requirement and / or increasing the maximum PA power output can be implemented, for instance, by relaxing (e.g., reducing) a maximum power reduction (MPR) for the user device (e.g., for a particular modulation order). The MPR defines a required reduction of the output transmission power of the user device such that transmissions by the user device comply with various transmit signal quality requirements (e.g., including EVM and / or ACLR). The MPR can be determined based on testing, and stored at the user device for subsequent use. However, although one or more transmit signal quality requirements can be relaxed when DPoD is active at the network device as described herein, some communication networks can also define one or more maximum transmission output powers which must still be complied with. The maximum transmission output power(s) may be defined with respect to one or more respective power classes (which may be associated with various use cases or device types). As an example, a user device with power class 3 may be restricted to a maximum transmission power of 23 dBm. By restricting the maximum transmission output power of the devices in the communication network, coverage and quality of service for each of the devices can be balanced against increasing interference within the communication network. As such, even when the nominal transmit signal quality requirements are relaxed as described, the output power of a PA of a given user device still cannot exceed a PA output power which would result In the maximum transmission output power for the user device being violated. In addition, some user devices can include multiple antennas. Each antenna can be associated with an uplink (TX) antenna port and / or a downlink (RX) antenna port. For instance, various user devices can include 1 TX antenna port and 2 RX antenna ports (with this configuration accordingly being referred to as 1T2R), 1 TX antenna port and 4 RX antenna ports (with this configuration accordingly being referred to as 1T4R), 2 TX antenna port and 4 RX antenna ports (with this configuration accordingly being referred to as 2T4R), and so on. This configuration can indicate the number of antennas of the user device and / or the capability of the user device to perform SRS switching. SRS switching describes the ability to route an uplink transmission between the antennas (or corresponding antenna ports) that are capable of uplink transmission. The configuration can be indicated, for instance, by a supportedSRS-TxPortSwitch value for the user device. Each RX antenna port (or more simply, antenna port), can be associated with an SRS port or an SRS resource. In some cases, at least one main or primary antenna can be designated for the user device. This may be the antenna associated with the smallest post PA insertion loss. In addition, the testing of the user device may be conducted using a designated antenna, such as the main antenna (e.g., such that the maximum PA power output and / or MPR Is determined based on testing using the main antenna). However, each antenna of a user device can be associated with a different post PA insertion loss. For instance, the complexity of routing the physical RF tracks on the PCB between various RF front-end components can cause differences in the added post PA insertion loss in the uplink direction. Without mitigating the increased post PA insertion loss, the effective power available for transmission is reduced. This can affect the reception and decoding at the network device, potentially leading to degraded channel estimation and system performance. Furthermore, the received power of a reference signal sent using an antenna with unmitigated post PA insertion losses will be reduced. This can make it more challenging for the network device to detect the reference signal reliably, potentially leading to missed detections or false detections. This, in turn, can, for instance, impact antenna (or SRS) switching decisions. As another example, the increased post PA Insertion loss can increase the susceptibility of the reference signal to interference. If the transmission output power for a reference signal is reduced due to the post PA insertion loss, it may be more vulnerable to interference from other signals or noise sources. Furthermore, the difference in the routing for each of the antennas may change the linearity (e.g., through mismatch) of the PA and cause differences in the output power and output frequency spectrum for each of the antennas, thereby causing differences in the in-band distortion (e.g., relative to the main antenna). As such, DPoD parameters determined for uplink transmissions from one antenna (e.g., the main antenna) may not be optimal (or even usable) for uplink transmissions from the other antennas. For instance, using only a single set of DPoD weights that only matches one of the many uplink antennas could work counter constructively when used for signals received from the other antennas. Implementations described herein can improve coverage and capacity of uplink transmissions from a user device by considering that the performance of the uplink transmission depends on the antenna at which the user device gets the uplink transmission assigned (e.g., as a result of the SRS switching). For instance, it is generally desired to keep the output transmission power on a selected uplink antenna as high as possible (e.g., at least as high as on a main antenna) for maximum coverage, etc. However, this will not always be possible due to additional post-PA insertion losses associated with the selected antenna (e.g., reducing the actual transmission power when using the selected antenna) and due to the limited power capability of the PA of the user device. The power capability of the PA may be limited, for instance, if the user device is already using an output power for the PA which is determined to be approaching MPR or maximum transmission output power limits based on testing data determined with respect to a single antenna (e.g., a main antenna). As such, implementations described herein enable a user device to increase the output power of a PA (e.g., beyond limits determined based on testing data determined with respect to a single antenna), in order to mitigate a post PA insertion loss associated with the selected antenna. When DPoD Is being used at the network device, the output power of the PA can be increased beyond a nominal maximum PA output power (e.g., associated with a nominal maximum EVM) up to a relaxed maximum PA output power (e.g., associated with a relaxed maximum EVM). In other words, as described herein, by utilizing DPoD at the network device, it is possible to increase the output power of the PA connected to the lossy track of the front-end (e.g., and therefore mitigate the post PA insertion losses associated with the selected antenna). In some implementations, the user device must report to the network device that it (or the selected antenna specifically) is compatible with DPoD for the network device to activate DPoD on the received signal to mitigate the additional imposed insertion loss. Implementations described herein can also enable a network device to determine antenna port specific DPoD parameters that serve the individual antenna elements of the user device. For instance, the antenna port specific DPoD parameters can be found during an SRS switching procedure. As such, the network device can assist in linearizing the uplink signal upon reception relative to each of the possible uplink antennas of the user device. In these and other manners, implementations described herein can enable increased output power (within the allowed limits) at each UE antenna element that supports uplink transmission (and thereby improve throughput, range, etc.). Implementations described herein can be particularly advantageous when operating at higher frequencies (e.g., at least one GHz, such as in frequency range 2 (FR.2) which spans 24.25 GHz to 52.6 GHz, a frequency range which spans 7.125 GHz to 24.25 GHz, etc.). This is because, at higher frequencies, beamforming techniques can be utilized and thus out-of-band distortion (e.g., ACLR.) can be mitigated, meaning that EVM can become the limiting factor for PA output power. Turning to FIG. 1, a block diagram of an example environment 100 that demonstrates various aspects of the present disclosure is depicted. As illustrated in FIG. 1, the example environment 100 includes a user device 110 and a network device 120. Although, example environment 100 is shown as including a single user device 110 and a single network device 120, it will be appreciated that in various implementations, any number of user devices and network devices may be used. Furthermore, although the user device 110 and the network device 120 are shown as including a number of sub-systems, it will be appreciated that in various implementations, some, all, or none of the sub-systems may be included, and that in various implementations, other sub-systems not described herein may be included. As illustrated in example environment 100, and with respect to the uplink direction of communication, the user device 110 can include a power amplifier 112, a switch 114 and antennas (or antenna elements) 1 to N including ANT 1 116A, ANT 2 116B, ANT 3 116C, ..., ANT N 116N. Although the user device 110 is illustrated as including four antennas, it will be appreciated that implementations described herein are not limited to this, and can be used with user devices with any number of antennas, such as two antennas, eight antennas, etc. The PA 112 can amplify a signal for transmission, via one or more of the antennas 116A to 116N. The output power and / or gain of the PA 112 can be determined based on various factors, such as the distance between the user device 110 and the network device 120. For instance, when operating with an open loop power control, the user device 110 can estimate, based on a received power of a reference signal transmitted with a known transmit power by the network device 120, a target UL transmit power (e.g., since it can be assumed that the UL path losses and downlink (DL) path losses will be correlated). The output power of the PA 112 can thus be determined based on the target UL transmit power. Additionally or alternatively, when operating with closed loop power control, the network device 120 can determine whether the received power of UL transmissions from the user device 110 should be increased or decreased. The network device 120 can feedback this information to the user device 110 accordingly (e.g., as a UL transmit power control command to increase or decrease the UL transmit power). The user device 110 can then adjust the target UL transmit power, based on the received feedback. The output power of the PA 112 can thus be adjusted accordingly, based on the adjusted target UL transmit power. As described herein, the output power of the PA 112 can also be determined based on one or more transmit signal quality requirements (e.g., a maximum EVM). More specifically, the output power of the PA 112 can be determined such that it complies with the one or more transmit signal quality requirements. In some cases, the one or more transmit signal quality requirements can be associated with a maximum PA 112 output power which the determined PA output power must comply with. In some implementations, the output power of the PA 112 can be determined based on whether or not DPoD is activated at the network device 120. For instance, when DPoD is activated at the network device 120, the one or more transmit signal quality requirements (e.g., and corresponding maximum PA output power) can be relaxed. As such, when DPoD is activated at the network device 120, the output power of the PA 112 can be determined based on one or more relaxed transmit signal quality requirements (e.g., and a corresponding relaxed maximum PA output power), rather than the one or more nominal transmit signal quality requirements (e.g., and a corresponding nominal maximum PA output power) used when DPoD is not activated at the network device 120. In other words, when DPoD is activated at the network device 120, the user device can exceed (or violate) the one or more nominal transmit signal quality requirements. In some implementations, the output power of the PA 112 can be determined based on a modulation scheme being used. For instance, a given modulation scheme may be associated with a particular set of one or more transmit signal quality requirements. In some implementations, the output power of the PA 112 can be determined based on a maximum transmission output power (which may be associated with a maximum PA output power e.g., based on testing). The output power of the PA 112 may be determined such that the maximum transmission output power is complied with (e.g., such that it is not violated or exceeded). The output power of the PA 112 can be determined such that the maximum transmission output power is not exceeded even when the transmit signal quality requirements are relaxed (e.g., when DPoD is active at the network device 120). In other words, the nominal maximum PA output power can be determined based on the lower of (i) a PA output power associated with the one or more nominal transmit signal quality requirements and (ii) a PA output power associated with a maximum transmission output power. The relaxed maximum PA output power can be determined based on the lower of (i) a PA output power associated with the one or more relaxed transmit signal quality requirements and (ii) the PA output power associated with the maximum transmission output power. The nominal maximum PA output power can, for instance, be implemented using a nominal MPR, and the relaxed maximum PA output power can, for instance, be implemented using a relaxed MPR (e.g., such that the relaxed MPR is relaxed or reduced relative to the nominal MPR). In some implementations, the output power of the PA 112 can be determined based on the antenna selected to transmit uplink transmissions (e.g., based on an SRS switching procedure). Switch 114 can be used to route the amplified signal from PA 112 to the selected antenna. As described herein, each of ANT 1 116A, ANT2 116B, ANT3 116C, and ANT N116N can be associated with a different post PA insertion loss (e.g., because of the different physical tracks between PA 112 and each respective antenna). In some cases, this can be significant. For instance, ANT N 116N may introduce post PA insertion losses of 5dB (or even more) relative to ANT 1 116A. As such, the output power of the PA 112 can be increased for uplink transmissions using the selected antenna to account for the post PA insertion losses introduced by ANT N 116N (assuming there is margin in the one or more transmit signal quality requirements and the maximum transmission output power). The insertion losses for the antennas of the user device 110 (as well as e.g., resulting transmission output power and / or resulting transmit signal quality metrics) can be characterised by testing the user device (or a similar user device). More specifically, as described herein, during production or manufacture, a user device (e.g., the user device 210 or a similar user device) can be characterized for performance based on its design. When the user device supports antenna switching, it may undergo characterization on every antenna. In this process, it may be found that each antenna of the user device has potential short comings in output power due to variations in the pathloss of the PCB and the associated hardware components in the signal path. In some cases, even though a "main" antenna may be compliant with requirements, some or all of the other antennas may have such short comings. There can be, for instance, several dB differences in loss, and in some cases, there may be differences due to tolerances in design. In other words, without the techniques described herein, a user device may be calibrated to use PA output powers that secure the correct transmission output power absolute levels and relative step sizes for the main antenna only. By utilizing the techniques described herein, a user device can be calibrated to use PA output power levels for the additional uplink allowed antennas. For instance, the user device can target a specific "relaxed" transmit signal quality requirement (e.g., EVM), which is worse (higher) than a nominal transmit signal quality requirement (e.g., as a result of the use of DPoD). These relaxed transmit signal quality requirement(s) can be translated to the relative power offsets for the PA that removes / minimizes the impact from the insertion loss. For example, assuming that the maximum transmission output power is 23 dBm, a nominal transmit signal quality requirement is 3% EVM, and a relaxed signal quality requirement is 8% EVM (for instance, based on DPoD being supported by the network device e.g., according to a standardized agreement), ANT 2 116B is associated with a 1.5 dB insertion loss, ANT 3 116C is associated with a 4dB insertion loss, ANT N 116N is associated with a 5dB insertion loss, and PA output power P dBm results in a transmission output power of 23dBm at ANT 1 116A, the following testing data can be found during testing of the user device (or a similar user device): Antenna PA output power (dBm) Resulting power at antenna (dBm) Resulting EVM (%) PA output power (dBm) Resulting power at ANT (dBm) Resulting EVM (%) ANT 1 (main antenna) P 23 3 P 23 3 ANT 2 (1.5dB insertion loss) P 21.5 3 P+1.5 23 6 ANT 3 (4dB insertion loss) P 19 3 P+2 21 8 ANT N (5dB insertion loss) P 18 3 P+2 20 8 Table 1 Example testing data Here, ANT 1 116A has been designated as the main antenna. As such, the user device 110 has been calibrated for PA output powers and transmission output powers with respect to ANT 1 116A. In addition, PA output powers for ANT 2 116B, ANT 3 116C, and ANT N 116N are calibrated for DPoD through EVM targets. This EVM target can be found at different increases in PA output power beyond the calibration of ANTI. As can be seen in table 1, when DPoD is not active at the network device 120, the maximum PA output power cannot be increased for any of the antennas since it is constrained by the nominal maximum transmit signal quality requirement of 3% EVM. As can be further seen in table 1, when DPoD is active at the network device, the maximum PA output power can be increased (or in other words, relaxed) by 1.5dB when ANT 2 116B is selected to transmit uplink transmissions. The insertion losses associated with ANT 2 116B can therefore be fully mitigated. Although there is further margin in the transmit signal quality requirement of 8% (since PA output power of P+1.5dB results in only 6% EVM), the maximum PA output power cannot be further increased because it would then violate the maximum transmission output power at ANT 2 116B. As can be further seen in table 1, when DPoD is active at the network device, the maximum PA output power can be increased by 2dB when ANT 3 116C is selected to transmit uplink transmissions. In some cases, therefore, the insertion losses of ANT 3 116C may not be fully mitigated. However, the maximum PA output power cannot be increased any further, even though there is margin in the maximum output transmission power, as this would result in the transmit signal quality requirement being potentially violated (e.g., because PA output power of P+2dB already results in 8% EVM when using ANT 3 116C). Similarly, as can be further seen in table 1, when DPoD is active at the network device, the maximum PA output power can be increased by 2dB when ANT N 116N is selected to transmit uplink transmissions. In some cases, therefore, the insertion losses of ANT N 116N may not be fully mitigated. However, the maximum PA output power cannot be increased any further even though there is margin in the maximum output transmission power as this would result in the transmit signal quality requirement being potentially violated (e.g., because PA output power of P+2dB already results in 8% EVM when using ANT N 116N). In some implementations, the user device 110 can store information indicative of at least some of this training data. For instance, the user device 110 can store information indicative of a maximum PA output power for each of the antennas, which may be determined based on training data. In some implementations, the user device 110 can additionally or alternatively store a maximum PA output power delta (or otherwise referred to as increase, increment, difference, etc.,) from a designated antenna (e.g., a main antenna). In some implementations, the user device 110 can store this information on a per modulation order basis, e.g., such that a maximum PA output power is stored for any given combination of selected antenna and modulation order. In some implementations, the user device 110 can additionally or alternatively be stored on a per frequency range basis, e.g., since different frequency ranges may be associated with different transmit signal quality requirements and / or different maximum transmission output powers and / or different Internal path losses. This information may be referred to as calibration data or calibration parameters. This information can be internal data to the user device 110 that works in the output power calculations only when the absolute or relative PA output power steps have been determined from the open / closed loop power control calculations. This information can, for instance, be stored on the user device 110 during manufacture, entered via user input, updated via subsequent calibration, updated via a software update distributed to the user device 110, etc. When determining the output power of the PA 112, the user device 110 can retrieve the relevant maximum PA output power for the selected antenna (e.g., as well as DPoD status, modulation order, etc.,). The output power of the PA 112 can then be determined such that it complies with the retrieved maximum PA output power. In some implementations, the modulation order can additionally or alternatively be selected using the calibration data (e.g., to maximise throughput). This is because a relaxed EVM can allow for an increase in the modulation order without resulting in an increase of output transmission power. As further illustrated in example environment 100, the network device 120 can include one or more antenna(s) or array(s), a UL signal processing sub-system 122, and a digital post-distortion (DPoD) sub-system 124. The network device 120 can, for instance, include any component, or part thereof, of a cellular network. For instance, the network device 120 can include a gNodeB (gNB), an eNodeB (eNB), a base station, etc. The network device 120 can receive, via the one or more antenna(s) or array(s), UL transmissions from the user device 110. The network device 120 can process the received UL transmissions using the UL signal processing sub-system. The UL signal processing sub-system 122 can include, for instance, an analogue to digital conversion sub-system which can convert the received analogue signals into digital information, which can be further processed. Other processes involved in the UL signal processing subsystem 122 can include, for instance, demodulation, correction using sample timing offset and a radio frequency (RF) frequency offset, and a carrier leakage removal, equalization (e.g., using channel estimates), FFTs, etc. The DPoD subsystem 124, when activated, can also process the received UL transmissions (e.g., after being processed by the UL signal processing sub-system 122). For instance, the DPoD sub-system 124 can perform DPoD to compensate for distortion (e.g., EVM) introduced by the PA 112. As described herein (particularly in relation to FIG. 2), the DPoD sub-system 124 can perform DPoD using DPoD parameters specific to the antenna of the user device 110 selected to transmit the UL transmissions. Turning to FIG.2, procedures which can be performed in accordance with various example embodiments are depicted. One or more of the procedures of FIG. 2 can be performed by a user device 210, which may be the same or similar to any of the user devices described herein (e.g., user device 110 of FIG. 1). Furthermore, one or more of the procedures of FIG. 2 can be performed by a network device 220 which can be the same or similar to any of the network devices described herein (e.g., network device 120 of FIG. 1). The procedures of FIG. 2 can, for instance, provide the necessary signalling to facilitate per antenna PA output power selection at the user device. The procedures of FIG. 2 can additionally or alternatively, for instance, provide the necessary signalling to facilitate per antenna DPoD parameter estimation and / or utilisation. At operation S2.0, the user device 210 and the network device 220 perform an initial connection procedure. For instance, the initial configuration procedure can include one or more stages of a typical initial connection procedure up to and including PDU session establishment. Furthermore, as part of the initial connection procedure, the user device 210 can transition from an open loop power control to a closed loop power control. Additionally or alternatively, the initial connection procedure can include the network device 220 requesting the user device 210 for a configuration information and / or capability information. The configuration information may include, for instance, how many antennas the user device 210 includes. The capability information may include, for instance, which antennas of the user device 210 are capable of being used for uplink transmissions and / or which antennas of the user device 210 are compatible with DPoD. Additionally or alternatively, the initial connection procedure can include the user device 210 reporting configuration and / or capability information to the network device 220 (e.g., responsive to a request from the network device 220, or otherwise). For instance, the user device 210 can report to the network device 220 srs-TxSwitch information. As another example, the user device 210 can report to the network device 220 information indicating that the user device 210 supports DPoD only on a main antenna, or on any uplink antenna (e.g., using a DPoD antenna parameter). Additionally or alternatively, the initial connection procedure can include the network device 220 reporting to the user device 210 that DPoD is available and / or activated at the network device 220. In some implementations, the user device 210 can send to the network device 220 an acknowledgement that DPoD is available and / or activated at the network device respectively. In some implementations, DPoD will only be activated at the network device 220 (and correspondingly indicated to the user device 210) when acknowledgement is received from the user device 210. At operation S2.1, the network device 220 configures a data repository to store DPoD parameters for the antennas of the user device 210. The data repository can be configured based on configuration information and / or capability information associated with the user device 210 (e.g., which may have been received from the user device 210 during the initial configuration procedure). For instance, responsive to receiving information indicating that the user device 210 includes four antennas (and optionally that these antennas are capable of being used for uplink transmission and / or are compatible with DPoD), the network device 220 can configure the data repository to store DPoD parameters for each of the four antennas of the user device 210. Initially, the DPoD parameters can be set to some default value (e.g., typical DPoD parameters, NULL, etc.,), or left empty, since they have not yet been determined. In addition, at operation S2.1, the network device 220 can configure reference signal configuration information. For instance, the reference signal configuration information can be configured based on configuration information and / or capability information associated with the user device 210 (e.g., which may have been received during the initial configuration procedure). In some implementations, the reference signal configuration information can include information for the user device 210 such as which antennas of the user device 210 to be used to transmit the reference signals, UL transmit power control information, carrier information, etc. In some implementations, the reference signal configuration information can additionally or alternatively include a code for the reference signals (e.g., Gold code, Zadoff-Chu sequence, or any other known sequence of modulated symbols, etc.), a mapping of the reference signal code to frequency resources, a repetition rate and / or periodicity of the reference signals, and / or a frequency pattern (or comb) of the reference signals. The reference signals may be sounding reference signals (SRSs). In some implementations, the reference signals can be SRSs dedicated to a specific usage, for instance, SRSs useable for antenna selection and / or DPoD parameter determination. The reference signal configuration Information can be configured to cause the user device 210, upon receipt of the reference signal configuration information, to transmit reference signals (e.g., from each antenna of the user device 210) to the network device 220 according to the reference signal configuration information. For instance, turning briefly to FIG. 3, an example configuration for a plurality of reference signals using different antennas of a user device is depicted. As illustrated in FIG. 3, based on user device information 310 (e.g., configuration information and / or capability information associated with the user device 210, which may have been received during the initial configuration procedure), reference signal configuration information can be configured to cause the user device 210 to transmit the reference signals 320 using the different antennas of the user device 210. Based on the reference signals then received at the network device 220, one or more determinations 330 can be made, including selecting an antenna of the user device 210 for subsequent uplink transmissions and / or determining DPoD parameters for the antennas of the user device 210, as described in more detail herein. As illustrated In FIG. 3, in some implementations, the user device 210 can be configured, based on the reference signal configuration information or otherwise, to transmit the reference signals 320 using different antennas at different slots in the time domain. The reference signals 320 can, for instance, be sounding reference signals (SRS). During each slot, the user device can therefore be configured with an SRS ON power requirement (e.g., for time period Tsrs). In addition, between transmission of each reference signal there may be a transient period e.g., taken in the blanked symbol (e.g., for time period Ttp, which may be, for instance, 10 ps). In some implementations, the sequence of antennas used to send the reference signals (or In other words, the SRS sequence) can be configured according to a specific, consistent sequence (e.g., by the user device 210, by the network device 220 via the reference signal configuration information, etc.,). The sequence may be determined, for instance, based on an identifier associated with the antennas (e.g., in ascending identifier order such that the sequence is always ANT 1, ANT 2, ANT 3... ANT N). In this way, the network device 220 is enabled to associate each received reference signal with a particular antenna having a consistent position in the sequence, since the network device may not necessarily have any other way to identify which antenna was used to send any particular uplink signal. As such, the network device 220 can maintain and optimise the DPoD parameters relative to the sequence. In addition, this can enable the network device 220 to use a different parameter set when there is a shift in antenna selection (rather than having to redetermine the DPoD parameters each time a new antenna is selected). Returning now to FIG. 2, at operation S2.2, the network device 220 sends the reference signal configuration information to the user device 210. Sending the reference signal configuration information to the user device 210 can cause the user device 210 to configure and send the reference signals according to the reference signal configuration information (e.g., as described in relation to FIG. 3). In some implementations (e.g., in a semi-persistent or aperiodic configuration), the network device 220 may send a request to the user device 210 to send the reference signals. At operation S2.3, the user device 210 configures and generates UL reference signals (e.g., according to the reference signal configuration information received from the network device 220). For instance, the user device 210 can map antenna activation to the reference signal transmissions. In some implementations, the user device 210 can determine at least some of the reference signal configuration information (e.g., based on measurements at the user device 210, values defined in a standard, etc.). At operation S2.4, the user device 210 transmits the reference signals to the network device 220. The user device 210 can transmit the reference signals using each of the antennas of the user device 210 (e.g., as shown in FIG. 3), or in other words, can sweep the reference signal transmissions. The network device 220 can receive the reference signals transmitted by the user device 210. At operation S2.5, the network device 220 evaluates the received reference signals. For instance, the network device 220 can measure (or in other words, characterize, determine, calculate, etc.,) one or more transmit signal quality metrics of the received reference signal. For instance, the transmit signal quality metrics can include a path loss, a received signal strength of each of the received reference signals, an EVM of the received reference signals, a signal to noise ratio of the received signals, etc. The transmit signal quality metrics across the received reference signals from each of the antennas of the user device 210 can vary for any number of reasons. These reasons can include, for instance, the orientation of the user device (e.g., and thereby changing the relative distances and directions between the antennas of the user device 210 and the network device 220), how the user is holding the user device 210 (e.g., when the user's thumb is blocking one of the antennas of the user device 210), etc. The network device 220 can select an antenna of the network device 220 to be used for subsequent UL transmissions by the user device 210. The antenna selection can be based on the evaluation of the received reference signals. For instance, the antenna selection can be based on the measured transmit signal quality metrics of the received reference signals. As an example, the antenna associated with the received reference signal with the best / highest transmit signal quality metric(s) (e.g., the highest received signal strength) may be selected for subsequent UL transmissions by the user device 210. In some cases, the antennas of the user device 210 can be ranked based on the transmit signal quality metric(s) associated with the respective received reference signal. The highest ranked antenna can then be selected for subsequent UL transmissions by the user device 210. In some implementations, the network device 210 can apply standard procedures for subsequent UL scheduling based on the received reference signals (e.g., SRS transmissions). Furthermore, at operation S2.5, the network device 220 can determine (or in other words, estimate, calculate, characterise, etc.,) DPoD parameters for the antennas of the user device 210 (or at least the antennas of the user device 210 used to send reference signals). The DPoD parameters can be determined based on the received reference signals from the user device 210, and in some cases, further optimized using any subsequent transmission of the user device 210. This can be performed in any suitable manner. The determined DPoD parameters for each antenna of the user device 210 can be stored in the data repository. In this way, the network device 210 can recognize that when the network device 220 changes the uplink transmission antenna of the user device 210, that the network device 220 needs to use a new set of DPoD parameters (or otherwise referred to as compensation weights) specific to the chosen uplink antenna at the user device 210, and can act accordingly. In addition, since, as described herein (particularly in relation to FIG. 3), the sequence of antennas used to send the reference signals can be consistent, the antennas can be associated with a specific position within the sequence, and the DPoD parameters can be associated with an antenna via the position within the sequence, since otherwise the network device 220 may have no way to associate the DPoD parameters to a specific antenna. In some implementations, the network device 220 may determine only DPoD parameters for the selected antenna to conserve storage space and / or other computational resources. At operation S2.6, the network device 220 schedules subsequent UL transmissions by the user device 210. This can be based on the reference signals received from the user device 210 (e.g., based on the evaluation(s) at operation S2.5). The network device 220 can transmit, to the user device 210, an indication of an antenna of the user device 210 selected for subsequent UL transmissions. For instance, the network device can send an identifier of the UL reference signal associated with the selected antenna, such as an SRS resource identifier (SRI). In some implementations, the network device 220 can include information of DPoD assistance for the scheduled UL. In other words, the network device 220 can Indicate, to the user device 210, that it is "safe" to exceed the nominal limitations the user device applies for UL output power control. For instance, the network device 220 can transmit, to the user device 210, an Indication that DPoD will be used for the subsequent UL transmissions. In some of those implementations, the network device 220 may refrain from performing DPoD for the subsequent UL transmissions unless acknowledgement is received, from the user device 210, that DPoD will be used. In additional or alternative implementations, the network device 220 can send the indication that DPoD will be used during the initial connection procedure, for instance, as described in relation to operation S2.0. In some implementations, the indication(s) can be carried in a new information element (IE), MAC control element (CE), or via radio resource control (R.R.C). In some Implementations, the network device 220 can send information indicative of the relaxed transmit signal quality requirements themselves (e.g., an indication of the relaxed EVM requirement, an indication of the increase In the EVM requirement, etc.). In this case, the user device 210 can be capable of determining a resulting transmit signal quality metric based on a given PA output power. For instance, the user device 210 can store calibration information indicative of a given EVM for various PA output powers (e.g., at 1 dB intervals). The user device 210 can then select a PA output power which would comply with the received relaxed transmit signal quality requirement. In this way, the network device 220 can set various levels of relaxed transmit signal quality requirements, and which can also be updated at the network device, without making any changes at the user device 210. However, this would require relatively large amounts of testing of the user device 210 to generate such granular calibration information. At operation S2.7, the user device 210 takes action based on the indication(s) received from the network device 220. More specifically, the user device 210 can schedule UL transmissions using the selected antenna (e.g., as indicated by the received indication(s)). The user device 210 can determine an output power for the PA to be used for the UL transmissions. This can be determined, for instance, as described herein (particularly in relation to FIG. 1 or FIG. 4). For instance, an output power for the PA can be determined such that the UL transmissions using the selected antenna comply with a relaxed transmit signal quality requirement as a result of DPoD being activated at the network device 220. In some implementations, the user device 210 can additionally or alternatively determine a modulation order to be used for the UL transmissions as a result of DPoD being activated at the network device 220. For instance, a modulation order for the subsequent UL transmissions can be determined such that the subsequent UL transmissions using the selected antenna and the determined modulation order comply with the relaxed transmit signal quality requirement. At operation S2.8, the user device 210 performs one or more UL transmissions. The user device 210 can transmit the UL transmissions using the selected antenna. The user device 210 can transmit the UL transmissions using the determined output power of the PA and / or the determined modulation order. At operation S2.9, the network device 220 performs DPoD on the received UL transmission(s) from the user device 210 (or in other words, applies DPoD, processes the UL transmission(s) using DPoD, etc.,). The DPoD can be performed using the DPoD parameters specific to the selected antenna. For instance, the DPoD parameters for the selected antenna can be retrieved from the data repository. More specifically, the network device 220 can apply the DPoD parameters that linearizes the UL transmission(s) using the selected antenna (e.g., which may be subject to higher saturation from the insertion loss towards the selected antenna). As an example, assume that ANT 3 of the user device 210 is configured (e.g., at an iteration of operation S2.1, S2.2 and / or S2.3) to transmit a reference signal at a third position in the sequence of reference signal transmissions (e.g., at an iteration of S2.4). Assume further that it is determined (e.g., at an Iteration of S2.5), that antenna of the user device 210 which sent the reference signal in the third position in the sequence (i.e., ANT 3), or in other words, the third reference signal, should be selected for subsequent UL transmissions (e.g., based on determining that the third reference signal was associated with the least pathloss). Assume further that DPoD parameters for the antenna of the user device 210 which sent the reference signal in the third position in the sequence (i.e., ANT 3) are determined (e.g., at an iteration of S2.5). Assume further that the user device 210 has been scheduled accordingly and transmits a UL transmission using ANT 3 (e.g., at an iteration of S2.6, S2.7 and / or S2.8) which is received by the network device 220. As such, the network device 220 can (e.g., at an iteration of S2.9) apply a DPoD parameter set that matches the 3rd reference signal (and thus ANT 3, assuming that the reference signal sequence was configured correctly). Furthermore, at operation S2.9, whilst remaining in this UL configuration (e.g., until it is determined that the antenna of the user device 210 be reselected), the network device can update the DPoD parameters for the selected antenna. This can be based on, for instance, further reference signals and / or the UL transmissions sent using the selected antenna. At operation S2.10, the network device 220 determines that the antenna of the user device 210 used for UL transmissions should be reselected. For instance, this can be in response to determining that an antenna reselection condition has occurred. This may be based on a predetermined time period expiring, determining that one or more transmit signal quality metrics of received UL transmissions sent using the currently selected antenna has degraded at least a threshold amount, determining that the user device 210 has disconnected and then reconnected to the network device 220, determining that the UL power should be changed (e.g., by the network device 220 in closed loop power control, or by the user device 210 in open loop power control), etc. This may occur, for instance, when the distance between the user device 210 and the network device 220 changes (e.g., since the greater the distance, the higher UL transmit power is required for successful transmission), when the orientation of the user device 210 changes, when a user of the user device changes their grip of the user device, etc. In some implementations, antenna reselection conditions can be based on standard SRS configuration triggers for antenna switching. In response to determining that the antenna used for UL transmissions should be reselected, the network device 220 can restart the antenna selection procedure. For instance, the network device 220 can determine further reference signal configuration information (e.g., similarly to as described in relation to S.2.1), or simply reuse previously determined reference signal configuration information. If the reference signal configuration is changed, the network device 220 can send the further reference signal configuration information to the user device 210 (e.g., similarly to as described in relation to S2.2). The user device 210 can then configure further reference signals (e.g., according to the further reference signal configuration information) (e.g., similarly to as described in relation to S2.3). The user device 210 can send the further reference signals (e.g., similarly to as described in relation to S2.4). The network device 220 can evaluate the received further reference signals (e.g., similarly to as described in relation to S2.5). For instance, the network device 220 can determine which of the further reference signals is associated with the least path loss. The network device 220 can select an antenna (e.g., associated with the reference signal with the least path loss) for further subsequent UL transmissions at the user device 210, and schedule the user device 210 accordingly (e.g., similarly to as described in relation to S2.6, S2.7 and / or S2.8). This may be the same or a different antenna as was previously selected. In some Implementations, the network device 220 can also determine DPoD parameters based on the further reference signals (e.g., similarly to as described in relation to S2.5). For instance, the newly determined DPoD parameters can overwrite (or in other words, replace, etc.,) the DPoD parameters previously stored in the data repository. This may be the case, for instance, when a particular sequence is not enforced for the reference signals, since in this case the network device 220 cannot associate the stored DPoD parameters with any particular antenna. For instance, following the example described above, when no particular sequence is enforced for the reference signals, even if the third reference signal is again determined to have the lowest path loss, any of the antennas of the user device 210 may have been used to send the third reference signal. As such, the network device 220 has no way to associate the DPoD parameters determined based on the third reference signal with the already stored DPoD parameters. In some implementations, the network device 220 can update the DPoD parameters for the antennas of the user device 210 (and e.g., stored in the data repository) based on the further reference signals. This may be the case when the reference signals are sent according to a known sequence, and thus can be associated with the already determined DPoD parameters. In some implementations, the network device 220 can refrain from determining or updating the DPoD parameters already determined and stored in the data repository. Instead, the network device 220 can use the DPoD parameters for the selected antenna (e.g., by retrieving them from the data repository). This may again be the case when the reference signals are sent according to a known sequence, and thus can be associated with the already determined DPoD parameters. The network device 220 can then perform DPoD on further UL transmissions sent using the newly selected antenna of the user device 210, using the replaced / updated / stored DPoD parameters for the newly selected antenna. In some implementations, the newly selected antenna may not be compatible with DPoD at the network device 220 (e.g., if it Is an antenna other than the main antenna which does not support DPoD). In this case, the user device 210 can report to the network device 220 that the newly selected antenna is not compatible with DPoD and / or that the network should not perform DPoD on UL transmissions sent using the newly selected antenna. This can be performed, for Instance, using a MAC CE message, or similar. Continuing with the previous example, assume that the reference signals are sent according to a specific sequence such that ANT 2 is used to send the second reference signal and ANT 3 is used to send the third reference signal. Further assume that an antenna reselection condition has occurred. As such, a new antenna switching sequence can be scheduled (e.g., a new SRS antenna switching sequence) (e.g., as described in relation to S2.10). In the event that a reference signal other than the third reference signal is the one showing least pathloss (e.g., the second reference signal), the network device 220 can abandon / store the DPoD parameters for the third reference signal and instead start to use new or updated DPoD parameters for ANT 3, or recall the relevant DPoD parameters from memory. In this way, the network device can avoid using the same DPoD parameters for each of the antennas, since, as described herein, doing so will not serve for user devices supporting multiple uplink antenna configurations. In other words, implementations described herein can enable the user device 210 and the network device 220 to align on DPoD assignment across the antennas of the user device 210. Turning to FIG. 4, a flowchart depicting a method 400 performed in accordance with an example embodiment is depicted. The method 400 may be performed by a user device, such as a user device as described in relation to any of the FIGs described herein. At operation S4.1, the method 400 Includes receiving, from a network device, a first indication Indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device and a second Indication indicating that digital post-distortion (DPoD) is enabled at the network device (e.g., as described in relation to S2.5 and S2.6 of FIG. 2). In some implementations, the method may further include an initial connection procedure (e.g., as described in relation to S2.0 of FIG. 2). For instance, the user device can report, to the network device, a number of antennas of the user device capable of being used for uplink transmissions. In some implementations, the user device may receive, from the network device, reference signal configuration Information (e.g., as described more fully in relation to S2.2 of FIG. 2). For instance, this may be received responsive to information sent to the network device during an initial connection procedure. The user device may then send, to the network device and based on the reference signal configuration information, reference signals using the antennas of the user device capable of being used for uplink transmissions. The reference signals may be usable (e.g., by the network device) for determining DPoD parameters for respective ones of the antennas and for the selection of the selected antenna for the subsequent uplink transmissions. In some implementations, the user device can report, to the network device, that the selected antenna of the user device supports the use of DPoD at the network device. For instance, this may be reported during an initial connection procedure. The second indication can then be received from the network device responsive to the selected antenna of the user device supporting the use of DPoD at the network device. At operation S4.2, the method 400 includes determining an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna, wherein, based on receipt of the second indication, the output power is determined such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication. In some implementations, the relaxed transmit signal quality requirement comprises a maximum error vector magnitude (EVM) for the subsequent uplink transmissions. In some Implementations, the user device can retrieve data indicative of a relaxed maximum PA output power associated with the selected antenna and the relaxed transmit signal quality requirement. For instance, this may be stored at the user device as configuration data. In this case, determining the output power of the PA for the subsequent uplink transmissions such that the subsequent uplink transmissions using the selected antenna comply with the relaxed transmit signal quality requirement can include determining the output power of the PA for the subsequent uplink transmissions such that the output power of the PA complies with the maximum PA output power associated with the selected antenna and the relaxed transmit signal quality requirement. In some implementations, the relaxed maximum PA output power associated with the selected antenna and the relaxed transmit signal quality requirement can be based, at least in part, on (i) an internal path loss associated with the selected antenna, (II) a transmit signal quality associated with an uplink transmission using the maximum PA output power and the selected antenna complying with the relaxed transmit signal quality requirement, and / or (iii) a transmit output power associated with an uplink transmission using the maximum PA output power and the selected antenna complying with a maximum transmit output power. For Instance, this can be determined based on testing. In some implementations, the data indicative of a relaxed maximum PA output power indicates a maximum PA output power increment relative to a maximum PA output power associated with another antenna of the user device and the relaxed transmit signal quality requirement. At operation S4.3, the method 400 includes performing one or more uplink transmissions using the selected antenna and the determined output power of the PA (e.g., as described in relation to S2.8 of FIG. 2). For instance, the user device can perform one or more first uplink transmissions using a first antenna of the user device (which may be the same or different to the selected antenna). The one or more first uplink transmissions are transmitted using a first output power of the PA, and the first output power of the PA complies with a first maximum PA output power associated with the first antenna and the nominal transmit signal quality requirement. As described herein, in many situations, the maximum PA output power (e.g., the maximum PA power associated with the selected antenna and the relaxed transmit signal quality requirement) can be greater than the first maximum PA output power (e.g., which is associated with the first antenna and the nominal transmit signal quality requirement). Turning to FIG. 5, a flowchart depicting a method 500 performed in accordance with an example embodiment is depicted. The method 500 may be performed by a network device, such as a network device as described in relation to any of the FIGs described herein. At operation S5.1, the method 500 includes sending, to a user device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device (e.g., as described in relation to S2.6 of FIG. 2). In some implementations, the network device can receive, from the user device, information indicative of a number of antennas of the user device capable of being used for uplink transmissions (e.g., during an initial connection procedure, as described in relation to S2.0 of FIG. 2). The network device can configure a data repository to store DPoD parameters for the antennas of the user device capable of being used for uplink transmissions (e.g., as described In relation to S2.1 of FIG. 2). In some implementations, the network device can determine reference signal configuration information based on the received information indicative of a number of antennas of the user device capable of being used for uplink transmissions (e.g., as described in relation to S2.1 of FIG. 2). The network device can send, to the user device, the reference signal configuration information to cause the user device to send, based on the reference signal configuration information, reference signals using the antennas of the user device capable of being used for uplink transmissions (e.g., as described in relation to S2.2). The network device can receive, from the user device, the reference signals (e.g., as described in relation to S2.4). The network device can determine, based on the received reference signals, DPoD parameters for respective ones of the antennas (e.g., as described in relation to S2.5). The network device can store the DPoD parameters for the respective ones of the antennas In the data repository. In some implementations, the reference signal configuration information can be determined such that it causes the user device to send the reference signals from respective ones of the antennas of the user device capable of being used for uplink transmissions according to a predetermined order of the respective ones of the antennas of the user device. In some implementations, the network device can select, based on the received reference signals, the selected antenna of the user device to be used for the subsequent uplink transmissions. At operation S5.2, the method 500 includes sending, to the user device, a second indication indicating that digital post-distortion (DPoD) is enabled at the network device, wherein the second indication is usable by the user device to determine an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication (e.g., as described In relation to S2.0 and / or S2.5 of FIG. 2). In some implementations, the network device can receive, from the user device, information indicating that the selected antenna of the user device supports the use of DPoD at the network device. The second indication can then be sent to the user device responsive to the selected antenna of the user device supporting the use of DPoD at the network device. At operation S5.3, the method 500 includes receiving, from the selected antenna of the user device, one or more uplink transmissions (e.g., as described in relation to S2.8 of Fig. 2). In some implementations, the network device can obtain, from the data repository, DPoD parameters for the selected antenna (e.g., as described in relation to S2.9 and / or S2.10). The network device can perform DPoD, using the DPoD parameters for the selected antenna, on the one or more uplink transmissions. In some implementations, the network device can, responsive to a condition for updating the antenna selection having occurred, send, to the user device, further reference signal configuration information (or resend / re-activate / rely on the previously determined reference signal configuration information if there are no changes). Sending the further reference signal configuration information (or resending / re-activating / relying on the previously determined reference signal configuration information, as the case may be) can cause the user device to send, based on the further reference signal configuration information (or the previously determined reference signal configuration information, as the case may be), further reference signals using the antennas of the user device capable of being used for uplink transmissions. The network device can receive, from the user device, the further reference signals. The network device can, based on the received further reference signals, (i) determine updated DPoD parameters for respective ones of the antennas, and (ii) select a second antenna of the user device to be used for further subsequent uplink transmissions by the user device. The network device can replace the DPoD parameters for the respective ones of the antennas with the updated DPoD parameters in the data repository. The network device can send, to the user device, a third indication indicating the second selected antenna of the user device to be used for further subsequent uplink transmissions by the user device. The network device can receive, from the second selected antenna of the user device, one or more further uplink transmissions. The network device can obtain, from the data repository, updated DPoD parameters for the second selected antenna. The network device can perform, using the updated DPoD parameters for the second selected antenna, DPoD on the one or more uplink transmissions (e.g., as described in relation to S2.10 of FIG. 2). In some implementations, the network device can, responsive to a condition for updating the antenna selection having occurred, send, to the user device, a third indication indicating a second selected antenna of the user device to be used for further subsequent uplink transmissions by the user device. The network device can receive, from the second selected antenna of the user device, one or more further uplink transmissions. The network device can obtain, from the data repository, DPoD parameters for the second selected antenna, wherein the DPoD parameters are obtained without having been updated. The network device can perform, using the DPoD parameters for the second selected antenna, DPoD on the one or more uplink transmissions (e.g., as described in relation to S2.10 of FIG. 2). In some implementations, the network device can, responsive to a condition for updating the antenna selection having occurred, send, to the user device, a fourth indication indicating a third selected antenna of the user device to be used for further subsequent uplink transmissions by the user device. The network device can, responsive to receiving, from the user device, information indicating that the third selected antenna does not support the use of DPoD at the network device, refrain from sending, to the user device, a fifth indication indicating that DPoD is enabled at the network device for subsequent uplink transmissions using the third selected antenna. Turning to FIG. 6, a flowchart depicting a method 600 performed in accordance with an example embodiment is depicted. The method 600 may be performed by a network device, such as a network device as described in relation to any of the FIGs described herein. At operation S6.1, the method 600 includes receiving, from a first antenna of a user device, one or more uplink transmissions (e.g., as described in relation to S2.8 and / or S2.10 of FIG. 2). At operation S6.2, the method 600 includes obtaining, from a data repository configured to store digital post-distortion (DPoD) parameters for antennas of the user device capable of being used for uplink transmissions, DPoD parameters for the first antenna (e.g., as described in relation to S2.9 and / or S2.10 of FIG. 2). In some implementations, the network device can configure the data repository to store DPoD parameters for antennas of the user device capable of being used for uplink transmissions responsive to receiving information indicative of the antennas of the user device capable of being used for uplink transmissions (e.g., as described in relation to S2.1 of FIG. 2). At operation S6.3, the method 600 includes performing, using the DPoD parameters for the first antenna, DPoD on the one or more uplink transmissions (e.g., as described in relation to S2.9 and / or S2.10 of FIG. 2). Turning to FIG. 7, components of one or more of the example embodiments described previously Is depicted, which hereafter are referred to generically as a processing system 700. The processing system 700 may, for example, be the apparatus referred to in the claims below. The processing system 700 may have a processor 702, a memory 704 closely coupled to the processor 702 and comprised of a RAM 714 and a ROM 712, and, optionally, a user input 710 and a display 718. The processing system 700 may comprise one or more network / apparatus interfaces 708 for connection to a network / apparatus, e.g., a modem which may be wired or wireless. The network / apparatus interface 708 may also operate as a connection to other apparatus such as device / apparatus which Is not network side apparatus. Thus, direct connection between devlces / apparatus without network participation is possible. The processor 702 is connected to each of the other components in order to control operation thereof. The memory 704 may comprise a non-volatile memory, such as a hard disk drive (HDD) or a solid-state drive (SSD). The ROM 712 of the memory 704 stores, amongst other things, an operating system 715 and may store software applications 716. The RAM 714 of the memory 704 is used by the processor 702 for the temporary storage of data. The operating system 715 may contain code which, when executed by the processor implements aspects of the algorithms and sequences described above. Note that in the case of small device / apparatus the memory can be most suitable for small size usage i.e., not always a hard disk drive (HDD) or a solid-state drive (SSD) Is used. The processor 702 may take any suitable form. For instance, it may be a microcontroller, a plurality of microcontrollers, a processor, or a plurality of processors. The processing system 700 may be a standalone computer, a server, a console, or a network thereof. The processing system 700 and needed structural parts may be all inside devlce / apparatus such as loT device / apparatus i.e., embedded to very small size. In some example embodiments, the processing system 700 may also be associated with external software applications. These may be applications stored on a remote server devlce / apparatus and may run partly or exclusively on the remote server device / apparatus. These applications may be termed cloud-hosted applications. The processing system 700 may be in communication with the remote server device / apparatus in order to utilize the software application stored there. FIG. 8 shows a tangible media, In the form of a removable memory unit 810, storing computer-readable code which when run by a computer may perform methods according to example embodiments described above. The removable memory unit 810 may be a memory stick, e.g., a USB memory stick, having internal memory 820 storing the computer-readable code. The internal memory 820 may be accessed by a computer system via a connector 830. Of course, other forms of tangible storage media may be used, as will be readily apparent to those of ordinary skilled in the art. Tangible media can be any devlce / apparatus capable of storing data / information which data / information can be exchanged between devices / apparatus / network. Embodiments of the present invention may be implemented In software, hardware, application logic or a combination of software, hardware and application logic. The software, application logic and / or hardware may reside on memory, or any computer media. In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "memory" or "computer-readable medium" may be any non-transitory media or means that can contain, store, communicate, propagate or transport the Instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. Reference to, where relevant, "computer-readable medium", "computer program product", "tangibly embodied computer program" etc., or a "processor" or "processing circuitry" etc. should be understood to encompass not only computers having differing architectures such as single / multl-processor architectures and sequencers / parallel architectures, but also specialised circuits such as field programmable gate arrays FPGA, application specify circuits ASIC, signal processing devices / apparatus and other devices / apparatus. References to computer program, instructions, code etc. should be understood to express software for a programmable processor firmware such as the programmable content of a hardware device / apparatus as instructions for a processor or configured or configuration settings for a fixed function device / apparatus, gate array, programmable logic device / apparatus, etc. If desired, the different functions discussed herein may be performed in a different order and / or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined. Similarly, it will also be appreciated that the flow diagrams and sequences described herein are examples only and that various operations depicted therein may be omitted, reordered and / or combined. It will be appreciated that the above-described example embodiments are purely illustrative and are not limiting on the scope of the invention. Other variations and modifications will be apparent to persons skilled in the art upon reading the present specification. Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or any generalization thereof and during the prosecution of the present application or of any application derived therefrom, new claims may be formulated to cover any such features and / or combination of such features. Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described example embodiments and / or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims. It is also noted herein that while the above describes various examples, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

Claims

1. A user device comprising:means for receiving, from a network device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device and a second indication indicating that digital post-distortion (DPoD) is enabled at the network device;means for determining an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna, wherein, based on receipt of the second indication, the output power is determined such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; andmeans for performing one or more uplink transmissions using the selected antenna and the determined output power of the PA.

2. The user device of claim 1, wherein the relaxed transmit signal quality requirement comprises a maximum error vector magnitude (EVM) for the subsequent uplink transmissions.

3. The user device of claim 1 or claim 2, further comprising:means for retrieving data indicative of a maximum PA output power associated with the selected antenna and the relaxed transmit signal quality requirement,wherein determining the output power of the PA for the subsequent uplink transmissions such that the subsequent uplink transmissions using the selected antenna comply with the relaxed transmit signal quality requirement comprises:determining the output power of the PA for the subsequent uplink transmissions such that the output power of the PA complies with the maximum PA output power associated with the selected antenna and the relaxed transmit signal quality requirement.

4. The user device of claim 3, further comprising:means for performing one or more first uplink transmissions using a first antenna of the user device, wherein the one or more first uplink transmissions are transmitted using a first output power of the PA, the first output power of the PA complying with a first maximum PA output power associated with the first antenna and the nominal transmit signal quality requirement,wherein the maximum PA output power is greater than the first maximum PA output power.

5. The user device of claim 3 or claim 4, wherein the maximum PA output power associated with the selected antenna and the relaxed transmit signal quality requirement is based, at least in part, on:an insertion loss associated with the selected antenna,a transmit signal quality associated with an uplink transmission using the maximum PA output power and the selected antenna complying with the relaxed transmit signal quality requirement, and / ora transmit output power associated with an uplink transmission using the maximum PA output power and the selected antenna complying with a maximum transmit output power.

6. The user device of any one of claims 3 to 5, wherein the data indicative of a maximum PA output power indicates a maximum PA output power increment relative to a maximum PA output power associated with another antenna of the user device and the relaxed transmit signal quality requirement.

7. The user device of any one of the preceding claims, further comprising:means for reporting, to the network device, a number of antennas of the user device capable of being used for uplink transmission;means for receiving, from the network device, reference signal configuration information;means for transmitting, to the network device and based on the reference signal configuration information, reference signals using the antennas of the user device capable of being used for uplink transmissions, wherein the reference signals are usable for determining DPoD parameters for respective ones of the antennas and for the selection of the selected antenna for the subsequent uplink transmissions.

8. The user device of any one of the preceding claims, further comprising:means for reporting, to the network device, that the selected antenna of the user device supports the use of DPoD at the network device, wherein the second indication is received from the network device responsive to the selected antenna of the user device supporting the use of DPoD at the network device.

9. A network device comprising:means for sending, to a user device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device;means for sending, to the user device, a second indication indicating that digital post-distortion (DPoD) is enabled at the network device, wherein the second indication is usable by the user device to determine an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; andmeans for receiving, from the selected antenna of the user device, one or more uplink transmissions.

10. The network device of claim 9, further comprising:means for receiving, from the user device, information indicative of a number of antennas of the user device capable of being used for uplink transmissions; andmeans for configuring a data repository to store DPoD parameters for the antennas of the user device capable of being used for uplink transmissions.

11. The network device of claim 10, further comprising:means for determining reference signal configuration information based on the received Information indicative of a number of antennas of the user device capable of being used for uplink transmissions;means for sending, to the user device, the reference signal configuration information to cause the user device to send, based on the reference signal configuration information, reference signals using the antennas of the user device capable of being used for uplink transmissions;means for receiving, from the user device, the reference signals;means for determining, based on the received reference signals, DPoD parameters for respective ones of the antennas; andmeans for storing the DPoD parameters for the respective ones of the antennas in the data repository.

12. The network device of claim 11, further comprising:means for selecting, based on the received reference signals, the selected antenna of the user device to be used for the subsequent uplink transmissions.

13. The network device of claim 11 or claim 12, further comprising:means for obtaining, from the data repository, DPoD parameters for the selected antenna; andmeans for performing, using the DPoD parameters for the selected antenna, DPoD on the one or more uplink transmissions.

14. The network device of any one of claims 11 to 13, further comprising:means for, responsive to a condition for updating the antenna selection having occurred,sending, to the user device, further reference signal configuration information to cause the user device to send, based on the further reference signal configuration information, further reference signals using the antennas of the user device capable of being used for uplink transmissions;means for receiving, from the user device, the further reference signals;means for, based on the received further reference signals, (i) determining updated DPoD parameters for respective ones of the antennas, and (ii) selecting a second antenna of the user device to be used for further subsequent uplink transmissions by the user device;means for replacing the DPoD parameters for the respective ones of the antennas with the updated DPoD parameters in the data repository;means for sending, to the user device, a third indication indicating the second selected antenna of the user device to be used for further subsequent uplink transmissions by the user device;means for receiving, from the second selected antenna of the user device, one or more further uplink transmissions;means for obtaining, from the data repository, updated DPoD parameters for the second selected antenna; andmeans for performing, using the updated DPoD parameters for the second selected antenna, DPoD on the one or more uplink transmissions.

15. The network device of any one of claims 11 to 13, further comprising:means for, responsive to a condition for updating the antenna selection having occurred, sending, to the user device, a third indication indicating a second selected antenna of the user device to be used for further subsequent uplink transmissions by the user device;means for receiving, from the second selected antenna of the user device, one or more further uplink transmissions;means for obtaining, from the data repository, DPoD parameters for the second selected antenna, wherein the DPoD parameters are obtained without having been updated; andmeans for performing, using the DPoD parameters for the second selected antenna, DPoD on the one or more uplink transmissions.

16. The network device of any one of claims 11 to 15, wherein the reference signal configuration information is determined to cause the user device to send the reference signals from respective ones of the antennas of the user device capable of being used for uplink transmissions according to a predetermined order of the respective ones of the antennas of the user device.

17. The network device of any one of claims 9 to 16, further comprising: means for receiving, from the user device, information indicating that the selected antenna of the user device supports the use of DPoD at the network device, wherein the second indication is sent to the user device responsive to the selected antenna of the user device supporting the use of DPoD at the network device.

18. The network device of any one of claims 9 to 17, further comprising: means for, responsive to a condition for updating the antenna selection having occurred, sending, to the user device, a fourth indication indicating a third selected antenna of the user device to be used for further subsequent uplink transmissions by the user device; andmeans for, responsive to receiving, from the user device, information indicating that the third selected antenna does not support the use of DPoD at the network device, refraining from sending, to the user device, a fifth indication indicating that DPoD is enabled at the network device for subsequent uplink transmissions using the third selected antenna.

19. A method comprising:receiving, from a network device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device and a second indication indicating that digital post-distortion (DPoD) is enabled at the network device;determining an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna, wherein, based on receipt of the second indication, the output power is determined such that the subsequent uplink transmissions using the selected antenna comply with a relaxedtransmit signal quality requirement, wherein the relaxed transmit signal quality requirement Is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; andmeans for performing one or more uplink transmissions using the selected antenna, wherein the one or more uplink transmissions are transmitted using the determined output power of the PA.

20. A method comprising:sending, to a user device, a first indication indicating a selected antenna of the user device to be used for subsequent uplink transmissions by the user device;sending, to the user device, a second indication indicating that digital postdistortion (DPoD) is enabled at the network device, wherein the second indication is usable by the user device to determine an output power of a power amplifier (PA) of the user device for the subsequent uplink transmissions using the selected antenna such that the subsequent uplink transmissions using the selected antenna comply with a relaxed transmit signal quality requirement, wherein the relaxed transmit signal quality requirement is relaxed relative to a nominal transmit signal quality requirement to be complied with absent the receipt of the second indication; and receiving, from the selected antenna of the user device, one or more uplink transmissions.42

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