User Equipment Power Amplifier Operation

Abstract

The invention relates to an apparatus, method, and computer program product for user equipment power amplifier operation. The apparatus comprises at least one processor and at least one memory storing

Description

TECHNOLOGICAL FIELD Various example embodiments relate to user equipment power amplifier operation. In particular, example embodiments relate to an apparatus, method, and computer program product for user equipment power amplifier operation. BACKGROUND User Equipment (UE) operating in a communication network is typically configured to operate to meet various targets. Some of those targets relate to operation of a Power Amplifier (PA) in a transmission chain. Power Amplifier based targets may include, for example: compliance with output power requirements; reaching a target linearity performance, for example, using Digital Predistortion (DPD) techniques; and improving PA efficiency, for example, using Envelope Tracking (ET) and / or average power tracking (APT) methods. The methods applied by a UE to PA targets largely do not consider other metrics, which may be of relevance to overall efficient UE and / or communication network operation. It would be desirable if user equipment power amplifier operation could be performed according to a more holistic approach. BRIEF SUMMARY The scope of protection sought for various example embodiments of the invention is set out in the independent claims. The example embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention. According to various, but not necessarily all, example embodiments there is provided an apparatus, comprising at least one processor; and at least one memory storing instructions that when executed by the at least one processor cause the apparatus at least to perform: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. According to some embodiments, the predetermined network condition comprises: grant of a radio configuration identified as subject to cause cross-band self-interference to the user equipment. According to some embodiments, the predetermined network condition comprises: grant of an inter- radio access technology radio configuration identified as subject to cause unwanted emission in another radio communication system. According to some embodiments, the predetermined network condition comprises: grant of a multi-SIM radio configuration identified as subject to cause cross-band selfinterference to the user equipment. According to some embodiments, the predetermined network condition comprises: relaxation of a maximum power output transmission requirement at the user equipment. According to some embodiments, the predetermined network condition comprises: provision of a protected band in a radio frequency network within which the user equipment is operating. According to some embodiments, obtaining the indication of one or more trigger condition comprises: obtaining an indication of a transmission power level at which sensitivity in one or more receive band of user equipment operating under the predetermined network condition is impacted by cross-band self-interference. According to some embodiments, the indication of one or more trigger condition comprises: a maximum sensitivity degradation MSD value associated with a receive band of user equipment operating under the predetermined network condition. According to some embodiments, the apparatus is further caused to perform: transforming an obtained maximum sensitivity degradation MSD value associated with a receive band of user equipment operating under the predetermined network condition to a threshold output power in a transmit band of the user equipment. According to some embodiments, the indication of one or more trigger condition comprises: a threshold user equipment battery power level. According to some embodiments, the one or more trigger condition comprises: initiation of transmission in a transmission band of the user equipment at a power beyond a maximum power output transmission requirement. According to some embodiments, the one or more trigger condition comprises: transforming an obtained unwanted emission value associated with a protected radio system to a threshold output power in a transmit band of the user equipment. According to some embodiments, the one or more method of control of the power amplifier comprises: control of the power amplifier voltage supply. According to some embodiments, the one or more method of control of the power amplifier comprises: average power tracking control of the power amplifier voltage supply. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting a margin of the average power tracking control. According to some embodiments, adjusting the margin comprises: increasing the average power tracking control margin. According to some embodiments, the one or more method of control of the power amplifier comprises: envelope tracking control of the power amplifier voltage supply. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the envelope tracking margin. According to some embodiments, adjusting the envelope tracking margin comprises: increasing the margin. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the envelope tracking timing compared to an input signal. According to some embodiments, the one or more method of control of a power amplifier comprises: digital predistortion of a signal fed to the power amplifier for transmission. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: evaluating whether the user equipment is operating at maximum output power, and if not, adjusting the one or more method of control of the power amplifier to improve output linearity of the user equipment transmission spectrum. According to some embodiments, the apparatus is caused to perform: obtaining an indication of a region of radio spectrum in which transmission leakage is to be mitigated; and wherein configuring one or more method of control of the power amplifier of the user equipment to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the profile of the emission spectrum to reduce transmission spectrum amplitude in the indicated region. According to some embodiments, the region of radio spectrum in which transmission leakage is to be mitigated comprises: a receive band in which interference is expected, or a protected band. According to some embodiments, changing the profile of the emission spectrum associated with the power amplifier comprises: inducing an asymmetry in the emission spectrum. According to some arrangements, the apparatus comprises user equipment. According to various, but not necessarily all, example embodiments there is provided an apparatus comprising: means for obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; means for determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, means for configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. The means may perform the optional features set out in relation to the apparatus mentioned above. The processor, memory, and example algorithms, encoded as instructions, program, or code, may be the means for providing or causing the performance of the operation. According to various, but not necessarily all, example embodiments there is provided an apparatus comprising: circuitry configured to obtain an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; circuitry configured to determine whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, and evaluate whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, circuitry configured to adapt one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. The circuitry may be configured perform the optional features set out in relation to the apparatus mentioned above. According to various, but not necessarily all, example embodiments there is provided a method, comprising: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. According to some embodiments, the predetermined network condition comprises: grant of a radio configuration identified as subject to cause cross-band self-interference to the user equipment. According to some embodiments, the predetermined network condition comprises: grant of an inter- radio access technology radio configuration identified as subject to cause unwanted emission in another radio communication system. According to some embodiments, the predetermined network condition comprises: grant of a multi-SIM radio configuration identified as subject to cause cross-band selfinterference to the user equipment. According to some embodiments, the predetermined network condition comprises: relaxation of a maximum power output transmission requirement at the user equipment. According to some embodiments, the predetermined network condition comprises: provision of a protected band in a radio frequency network within which the user equipment is operating. According to some embodiments, obtaining the indication of one or more trigger condition comprises: obtaining an indication of a transmission power level at which sensitivity in one or more receive band of user equipment operating under the predetermined network condition is impacted by cross-band self-interference. According to some embodiments, the indication of one or more trigger condition comprises: a maximum sensitivity degradation MSD value associated with a receive band of user equipment operating under the predetermined network condition. According to some embodiments, the method comprises: transforming an obtained maximum sensitivity degradation MSD value associated with a receive band of user equipment operating under the predetermined network condition to a threshold output power in a transmit band of the user equipment. According to some embodiments, the indication of one or more trigger condition comprises: a threshold user equipment battery power level. According to some embodiments, the one or more trigger condition comprises: initiation of transmission in a transmission band of the user equipment at a power beyond a maximum power output transmission requirement. According to some embodiments, the one or more trigger condition comprises: transforming an obtained unwanted emission value associated with a protected radio system to a threshold output power in a transmit band of the user equipment. According to some embodiments, the one or more method of control of the power amplifier comprises: control of the power amplifier voltage supply. According to some embodiments, the one or more method of control of the power amplifier comprises: average power tracking control of the power amplifier voltage supply. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting a margin of the average power tracking control. According to some embodiments, adjusting the margin comprises: increasing the average power tracking control margin. According to some embodiments, the one or more method of control of the power amplifier comprises: envelope tracking control of the power amplifier voltage supply. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the envelope tracking margin. According to some embodiments, adjusting the envelope tracking margin comprises: increasing the margin. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the envelope tracking timing compared to an input signal. According to some embodiments, the one or more method of control of a power amplifier comprises: digital predistortion of a signal fed to the power amplifier for transmission. According to some embodiments, configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: evaluating whether the user equipment is operating at maximum output power, and if not, adjusting the one or more method of control of the power amplifier to improve output linearity of the user equipment transmission spectrum. According to some embodiments, the method comprises: obtaining an indication of a region of radio spectrum in which transmission leakage is to be mitigated; and wherein configuring one or more method of control of the power amplifier of the user equipment to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the profile of the emission spectrum to reduce transmission spectrum amplitude in the indicated region. According to some embodiments, the region of radio spectrum in which transmission leakage is to be mitigated comprises: a receive band in which interference is expected, or a protected band. According to some embodiments, changing the profile of the emission spectrum associated with the power amplifier comprises: inducing an asymmetry in the emission spectrum. According to some arrangements, the method is performed by user equipment. According to various, but not necessarily all, example embodiments there is provided a computer program product operable, when executed on a computer, to perform the method of: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. According to various, but not necessarily all, example embodiments there is provided a computer program comprising instructions which, when executed by an apparatus, cause the apparatus to perform at least the following: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. According to various, but not necessarily all, example embodiments there is provided a computer program comprising instructions [or a computer readable medium comprising instructions] stored thereon for performing at least the following: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. According to various, but not necessarily all, example embodiments there is provided a non-transitory computer readable medium comprising program instructions stored thereon for performing at least the following: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. The instructions may be for performing the optional features set out in relation to the method mentioned above. Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. BRIEF DESCRIPTION Some example embodiments will now be described with reference to the accompanying drawings in which: FIG. 1 illustrates an example user equipment (UE) architecture; FIG. 2 illustrates schematically a band combination of an uplink Frequency Division Duplexed (FDD) regime and a Time Division Duplexed (TDD) band FIG. 3 shows schematically an example relationship table held in a UE memory and a method of mapping the content of the relationship table onto a transmission aggressor band and a reception victim band; FIG. 4 illustrates schematically a principal system diagram, in which the two main controls for Power Amplifier efficiency improvements are shown; FIG. 5 illustrates in more detail a ‘No Envelope Tracking (No ET)’ and a “with envelope tracking ET’ Power Amplifier supply configuration; FIG. 6 illustrates schematically in more detail a mechanism by which Envelope Tracking can serve as a method to provide Power Amplifier efficiency; FIG. 7A and FIG. 7B illustrate graphically a transmission output spectrum from a UE; FIG. 8 illustrates schematically a method implementable by a UE to address crossband self-interference; FIGS. 9A to 9D illustrate graphically various approaches according to which a UE may operate to adjust its transmission spectrum; FIG. 10 shows schematically how misalignment of envelope tracking at a Power Amplifier can cause reshaping of the transmission spectrum; FIG. 11 illustrates schematically an example apparatus according to an arrangement; and FIG. 12 illustrates schematically an example method according to an arrangement. DETAILED DESCRIPTION Before discussing the example embodiments in any more detail, first a general overview of scenarios in which described approaches may be applied will be provided. If user equipment (UE) is operating in a network such that more than one transceiver is active at different spectrum allocations, for example, as may typically occur in carrier aggregation or dual connectivity scenarios, UE radio hardware is potentially subject to cause self-interference. Self-interference occurs if a UE transmitter has spectrum content, harmonic response, or harmonic products, that create interference inside an active receive band of the same UE. Coupling of a transmitted signal to the receiver happens via various mechanisms, including through a PCB internally to the transceiver and via antenna(s). Accordingly, the impact and extent of UE self-interference may be dependent upon UE design. An example UE architecture is shown schematically in FIG. 1. What determines the occurrence of self-interference is the exact frequency location of the simultaneous transmission and reception activities at the UE. As shown schematically in FIG. 1, coupling may occur between front-end modules where there are spectrum products that overlap, or in which there is likely to be harmonic response. There are different types of self-interference. One type of self-interference is cross band interference. Cross band interference is an expression of self-interference when 11 the output spectrum of an Uplink (UL) component carrier falls inside a Downlink (DL) component carrier bandwidth. This can be considered as adjacent channel leakage of the transmitter into its own receive band. The leakage may, for example, depend on the extent of non-linear behavior of a power amplifier in the transmitting transceiver chain. FIG. 2 illustrates schematically a band combination of an uplink Frequency Division Duplexed (FDD) regime and a Time Division Duplexed (TDD) band. The general transmission / reception regimes of the bands are shown at the top of FIG. 2. Those regimes are illustrated along with spectrum lines which indicate how uplink signals, ULi and UL2, are such that they develop an interfering product inside the receiver bands of the other band. In other words, the FDD uplink transmission causes interference in the TDD downlink (receive) band 2; and similarly, the TDD uplink transmission in band 2 causes interference in the FDD downlink of band 1. As is shown schematically in FIG. 2, while an FDD duplex filter operates to isolate the downlink from the uplink in one band of operation (as indicated with the dotted line of the Dplx filter below DL1), such a duplex filter may only provide limited or minimal isolation and attenuation of UL2. In TDD band 2, even less filtering of UL from band 1 can be seen at DL2. This issue of cross band interference is not isolated to carrier aggregation or dual connectivity but can occur as an issue, for example, in relation to co-existence of Wi-Fi and Cellular operation or in similar Inter-radio access technology (inter- RAT) combinations, where it is called an in-device co-existence issue. Approaches described may provide a method which can have use in the various modes of UE operation described above. Approaches may provide a mechanism which can improve UE performance in the event that the UE is operating under cross band interference conditions. There is a relationship between UE output power and Maximum Sensitivity Degradation (MSD). A UE has both an aggressor and victim role in the UE selfinterference case which occurs for some band combinations. In particular, an uplink (TX) signal which causes interference in the receive band is called an aggressor. The receive band of the UE where a product of the transmission (TX) aggressor ends up is called the RX victim band. FIG. 3 shows an example relationship table held in a UE memory (for example, tables of Carrier Aggregation, transmission output power and resulting maximum sensitivity degradation experienced in a receive band) and a method of mapping the content of the relationship table onto the TX aggressor and RX victim band. A Maximum Sensitivity Degradation (MSD) value is the level of relaxation a UE requires to be compliant with normal reference sensitivity (Refsens) requirements. Such relaxation may be required in a cross-band interference scenario because the TX aggressor(s) cause an interference level increase in the reception band. That interference level typically matches the MSD value. Accordingly, if a UE output power is relaxed by 1 dB from a maximum output power level, the level of the TX aggressor reduces the resulting self-interference experienced in the RX band by 1dB or more. This means that in a case where the the MSD value is xdB, a reduction of UE output power by xdB or a factor less than 1, would result in minimal appreciable selfinterference. The relation between transmission power and MSD at a UE lies in the order of the product (harmonic or IMD) that creates the interference. The relationship is shown schematically at the right of FIG. 3 as the UE output power SI (selfinterference) which is equal to, or matches, the UE MSD value divided by the order of the MSD type. A consequence of such a relationship is that any time the MSD value is known, the self-interference free output power range of a UE is known. Similarly, an output power range in which the UE will suffer from self-interference (as indicated with a “{“ marking in FIG. 3) is also known. By way of example, Refsens for FR1 NR operation is specified in TS 38.101-1 Clause 7, and the MSD for crossband issues is specifically addressed in Clause 7.3A.6. The standards set out that there are large UE relaxations granted for specific CA combinations. Those CA combinations could significantly benefit from improvements, for example, by implementing methods and approaches which can reduce the MSD needed by a UE. Power Amplification, Linearity, and Efficiency Methods FIG. 4 illustrates schematically a principal system diagram, in which the two main controls for Power Amplifier efficiency improvements are shown. The two controls comprise: (i) control of V supply (Vsup) which controls the voltage (including bias) of a 13 power amplifier; and (ii) a feedback loop for measuring PA output characteristic(s) at the transceiver. The measured characteristics may, for example, include: output power detected and compensated for by calibration; and a linearity measurement (Adjacent Channel Leakage Ratio (ACLR) level for determining digital predistortion (DPD)). FIG. 5 illustrates in more detail a ‘No Envelope Tracking (No ET)’ and a “with envelope tracking ET’ Power Amplifier supply configuration. A ’No ET’ configuration may also be using Average Power Tracking (APT) for step-wise adjustments of bias or supply voltages. The left-hand side of FIG. 5 illustrates Average Power Tracking (APT) in more detail. For APT, a PA supply voltage is fixed throughout an UL transmission at a given average transmission power. Average Power Tracking control typically operates such that rather than being set to a maximum possible supply voltage, the PA supply voltage can be adjusted over average transmission power levels to preserve a fixed supply headroom compared to peaks of UL modulation at any selected average TX power. Such a Power Amplifier control mechanism can be implemented and can maximize or improve efficiency across a TX power range whilst keeping spectral regrowth within specification limits. Envelope Tracking (ET) is shown in more detail on the right hand side of FIG. 5. In an ET approach, the PA supply voltage is not fixed, as in the APT approach, and instead is dynamic and follows an envelope of UL signal modulation. Such dynamic supply voltage can serve to keep the PA supply headroom low, not only at the modulation peaks, but for the entire waveform. Such tracking keeps the supply headroom down at a minimum threshold across the UL waveform thereby increasing the efficiency of the PA compared to an APT approach. For optimum ET operation, in terms of efficiency gain and spectral purity, it will be appreciated that time alignment between the power supply envelope waveform and the envelope of the transmitted RF signal at the PA must be accurate. FIG. 6 illustrates schematically in more detail the mechanism by which Envelope Tracking can serve as a method to provide Power Amplifier efficiency. FIG. 6 shows in more detail that by applying a Vsup which tracks the signal envelope, the efficiency of the PA increases because there is less wasted current resulting in a longer UE battery life. An ET PA is often designed with target to have an optimum efficiency Vsup / RF power mapping approximating a constant gain. Such an implementation of ET not only provides efficiency improvement but also effectively “linearizes” the PA approximating a fixed gain block. Any residual Amplitude Modulation AM / AM and Power Modulation AM / PM distortion can be compensated by pre-distorting an input signal to the PA using Digital Predistortion (DPD). In summary, a UE operating in a network is typically operating to meet various targets including: compliance with output power requirements; reaching a target linearity performance, for example, using DPD techniques; and improving PA efficiency, for example, using Envelope Tracking. Approaches described in more detail below recognize that UEs may, in some circumstances, suffer from reduced receiver sensitivity in the presence of selfinterference in the form of cross-band interference. Cross-band interference is linked to the UE’s own PA output power and associated linearity performance. The methods applied by a UE to control linearity and thereby PA output response / spectrum described above do not consider other metrics, for example, cross-band interference, which may be of relevance to overall efficient UE operation. Approaches described recognize that there can be a link between PA control methods and aspects of UE performance other than those directly linked to transmission. For example, PA control methods may be linked with receiver performance, such that a UE can adapt PA operation and make an improvement in UE receiver sensitivity as may happen in the case that the UE is experiencing cross-band self-interference in an Rx Victim band, or if the UE is experiencing receiver sensitivity degradation as a result of inter-RAT interference. An increase in receiver sensitivity may be achieved, for example, by altering the configurations controlling the ET and DPD of the PA. Alternately, an increase in receiver sensitivity can be achieved if using APT in a mode of maximum bias. A UE operating in accordance with described approaches may be configured at least to perform: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. Approaches recognize that some undesirable consequences may result from a particular shape or profile of an emission spectrum associated with operation of a user equipment. Typical operation of a UE power amplifier supports creation of an emission profile which is largely symmetrical, centred upon a frequency band of interest, and with a consistent drop off in adjacent frequency bands, irrespective of peak transmission amplitude in the frequency band of interest. Approaches recognize that adjusting the shape or profile of the emission spectrum is possible via power amplifier control mechanisms, and that such reshaping can serve to mitigate interference in frequency bands of interest. By way of example, the symmetry of the emission spectrum can be changed in dependence upon control of the power amplifier. Similarly, the shape of a decay or drop-off outside a transmission frequency band can change in dependence upon control of a power amplifier. It will be appreciated that changing the profile of an emission spectrum associated with a power amplifier can be used to change interference caused by transmissions associated with that power amplifier. A UE may be configured to determine a radio configuration of multiple simultaneous operations at different frequencies in close vicinity which is subject to self-interference from cross-band interference. Once the radio configuration is determined, the UE may be configured to evaluate or assess the output power level of a Tx aggressor(s) at which receiver sensitivity degradation is expected to occur. If the UE reaches that output power level, the UE may be configured to trigger monitoring of Rx performance. If the UE assesses that transmission is at, or above, the determined output power level at which self-interference may occur and the UE may be configured to monitor for a degradation in receiver performance. If receiver performance degradation is detected the UE may be configured to adjust PA operation, for example by taking steps to improve the PA output linearity, assuming the 16 UE is not yet operating at the maximum output power. In some implementations, the UE may alternatively, or additionally use ET timing to shift the ALCR, which also works at maximum output power. According to some approaches, the UE may operate to improve the output linearity of the Power Amplifier by using an increased ET margin or by switching to a high margin fixed supply voltage (APT mode) while running digital predistortion (DPD). Effectively the UE may be configured to perform a trade-off: favoring an improvement in receiver sensitivity by reducing spectrum interference from the transmitting PA, but at a cost of higher transmitter current consumption. Such an approach can be associated with various advantages: As described above, a UE operating in accordance with such approaches is capable of implementing a method for improving sensitivity in a cross-band interference scenario. Approaches link UE battery drain at the PA with receiver performance. Accordingly, approaches take a more holistic position in relation to overall efficient operation of a UE. If a battery is not depleted, then such an approach can support improved DL throughput and / or successful reception of critical DL data. Approaches allow a UE to operate to trade-off uplink spectrum emission to receiver sensitivity degradation relaxation. Approaches can be applied to carrier aggregation, dual connectivity, Multi-SIM operation and inter-RAT configurations. In some implementations, approaches may be triggered at differing levels of output power. Approaches generally may also provide mechanisms to improve UE performance in relation to power boosting and / or maximum power reduction targets. Having described a general scenario in which approaches may be applied, together with details of general features of the approach, a series of detailed possible implementations will now be described further: As described above, typically UEs are designed such that the transmitter which includes a power amplifier (PA) has as little margin as the UE vendor deems necessary to comply to the requirements of a chosen output spectrum at maximum transmission power level. If more output power is required, beyond maximum output power, the UE will no longer be able to comply with the spectrum requirements. PAs are designed to offer the best efficiency at the maximum output power level. Without the sophisticated methods of ET and DPD, described in brief above, the PA drops in efficiency and linearity if operated at backed off power levels. FIG. 7A and FIG. 7B illustrate graphically transmissions at several output power levels that form several spectrums from a UE. FIG. 7A shows schematically the form of the transmission spectrum in the case that the UE operates its PA using the approaches described above, where the spectrum shape remains even if output power changes. FIG. 7B shows schematically the form of the transmissions at several output power levels that form several spectrums in the case that the UE operates its PA using a different approach which trades some of the UE transmission power consumption for a differing transmission spectrum shape. Here the shape of the spectrum is not kept and it is seen that as the output power decreases, so does the spectral density outside the flat region representing the signal bandwidth. In FIG. 7A an exemplary UE spectrum is shown, representative for a UE operating its PA under APT / ET and DPD. The multiple overlapping plots shown in FIG. 7A illustrate how each 1dB reduction in PA output power in the desired transmission band has a one-to-one relation with the Adjacent Channel Leakage Ratio (ACLR). The adjacent channels are indicated by the dashed lines. Such approaches optimize the Power Amplifier efficiency but do not offer improved / changed ACLR at a given output power level. It will be appreciated that it is the channel leakage which generates cross-band self-interference. FIG. 7B shows the output spectrum of a UE operating with no standard methods to improve PA efficiency or linearity. One example would be a PA being operated at same fixed high supply voltage for all output power levels. It can be seen in the boxes shown schematically in FIG. 7B that the ACLR / spectrum decreases in amplitude as the maximum power amplitude changes at a ratio that is higher than the one-to-one shown in FIG. 7A. In other words, FIG. 7B shows an operational concept that was abandoned in UE design upon introduction of APT / ET and DPD features, but it also shows how a UE may perform if the APT / ET and DPD schemes are controlled differently during UE operation. Approaches now described in more detail introduce a UE method which operates, if selected conditions are met, to adapt the standard use of APT / ET, for example, by disabling APT / ET. Such a UE method may be appropriate, for example, in order to increase UE receiver sensitivity when receiver sensitivity has been detected to be impacted by cross-band self-interference. In one implementation, adaptation by the UE is triggered by a recognition that the UE may be subject to cross-band self-interference. According to such an implementation, the UE may be configured to determine that it has been granted a radio configuration that is subject to cause cross-band interference. Once determined, the UE may be configured to monitor for one or more trigger characteristic of operation which indicates the UE is likely to experience cross-band interference. On occurrence of such trigger characteristic(s) the UE may take steps to disable the APT / ET method usually applied at the PA. FIG. 8 illustrates schematically a method implementable by a UE to address crossband self-interference. FIG. 8 shows, at the left-hand side, some components of a UE. At the right-hand side, FIG. 8 illustrates schematically application of a trigger condition resulting in a change of operation to the PA control methods applied at the UE. The centre of FIG. 8 comprises a graphical representation of the transmission spectrum produced by the UE on application of a method in accordance with approaches described. In an arrangement in accordance with FIG. 8, a UE determines, for example by receiving an indication from a network, or by assessing that transmission and reception conditions meet a predetermined criteria, that the UE is operating such that cross band self-interference may occur. Once that determination has been made, the UE may be operable to apply a trigger or threshold at which adoption of standard PA operation occurs. In one implementation, a trigger level can be determined from a maximum sensitivity degradation value MSD known to the UE in relation to a reception band identified as being a likely candidate to experience cross-band interference. The MSD value for the reception band may be found in UE memory, calculated by the UE or signaled from network. The MSD value will have a relation one-to-one in UE designs for cross-band relation, meaning that the UE can only expect a sensitivity due to cross-band interference, which is at a higher level than “normal” reference sensitivity. This is represented schematically in the Rx victim band shown at the right hand side of FIG. 8Error! Reference source not found.. In one implementation, the UE may be configured to transform the receiver sensitivity degradation to a related output power in the transmission band, which then serves to identify an output power threshold at which a UE could expect RX sensitivity degradation in the reception band. The trigger output power level is indicated with a dashed line in the central transmission spectrum plot of FIG. 8. Once the UE is requesting use of output power levels beyond the determined trigger level in the output band of interest, the UE may be configured to monitor receiver performance in the band likely to experience cross-band interference. If the UE determines that receiver performance is being impacted by transmissions made by the UE, the UE may apply a method according to which the UE sets the voltage supply Vsup of the power amplifier in dependence on the current UL power level applied by the UE. On determining that the receiver band is likely to be starting to experience cross-band interference, the UE may switch to a fixed PA supply voltage and thereafter take a stepped approach towards Vsupmax (as shown in upper left corner of FIG. 8). In other words, the UE may be configured, on evaluation that a trigger condition has been met, to disable APT / ET methods usually applied to control the PA. Disabling APT / ET methods makes the UE consume more current, but also creates the positive impact on the transmission spectrum as shown previously in FIG. 7B. If the output power requests increase, the UE will gradually return to what might be considered “normal” performance that might be expected in a cross-band interference configuration, indicated by the arrow pointing upwards in the Rx Victim band. Nonetheless, by applying the method above to disable APT / ET when receiver degradation was first identified, the UE has gained increased receiver performance until the point of the UE maximum output power request. It will be apparent that various minor adaptations can be made to the general approach described: In one example, a table that relates UE radio configuration to an MSD value may be enhanced to encompass similar relationship which occur in Inter-RAT combinations resulting in a UE suffering from cross band interference. Such a table may comprise an MSD value which is indicative of how much sensitivity degradation aggressor and victim RATs suffer at maximum output power. Accordingly, a UE may be operable to determine when to implement a trade-off in sensitivity degradation to consumed current in an analogous manner to that described in relation to bands in a single RAT above. Similarly, in one example, a table that relates UE radio configuration to an MSD value may include Multi-SIM combinations that suffer from cross band interference and contain an MSD value indicative of how much sensitivity degradation identified aggressor and victim Multi-SIM bands suffer at maximum output power. Accordingly, a UE may be configured to determine when to apply the trade-off in sensitivity degradation in an analogous manner to that described in relation to bands in a single RAT above. In some implementations, a UE may be configured to monitor battery level and only use the method when there is battery level above a selected threshold. Accordingly, allowing the UE to trade efficiency and receiver improvements at the expense of additional current drain in the uplink may be contingent upon there being enough battery power available to support such an approach. Whilst described so far in relation to a mechanism to address UE self-interference, it will be appreciated that an ability to adapt a UE transmission spectrum via power amplifier control techniques may have applicability in other scenarios. By way of example, some such scenarios are described further below. According to some approaches, a UE may be operable to use the reconfigurability of PA control techniques such as envelope tracking to serve different purposes. For example, a UE may be operating under conditions in which no self-interference is likely to occur and is configured to apply standard APT / ET PA control methods. In one example of alternative use of approaches described above, the UE may be configured to utilize alternative PA control techniques if it transitions to operation in a maximum power reduction (A-MPR) impacted state. Such an A-MPR state occurs when a UE is allowed by the network to operate in a manner in which it may no longer need to comply with the usual regulatory requirements of spectrum such as ACLR, but instead can operate under new relaxed requirements in relation to spectrum emission and ACLR. FIGS. 9A TO 9D illustrate graphically various approaches according to which a UE may operate to adjust its transmission spectrum. FIG. 9A illustrates how adjacent channel leakage ratio (ACLR) and the general shape of UE spectrum emission is typically handled when regulatory requirements set out that the UE must lower the maximum output power (A-MPR) until the spectrum complies with protected band demands. A protected band is typically a spectrum range in which, for example, a different radio system operates. The UE must protect this spectrum range from its uplink emission to avoid generating interference into the different radio system. This can be done by the UE by reducing its uplink power spectral density. A network may allow a UE such maximum power relaxation, also allowing the UE to have higher ACLR. Such a relaxation typically means that the UE will reduce the Vsup margin of its envelope tracker in the high-power region. The standards suggest, in RP-240828, that relaxations of MPR may be tolerated inside network-owned spectrum in adjacent channels in order to boost the UE performance. FIG. 9B shows schematically transmission spectrum adjustment in accordance with approaches described above. As shown schematically, if UE has margin on supply, it can use that margin to increase linearity and lower the spectrum emission in adjacent, and further out, bands. This could be applied in the case of a power class 3 requirement in relation to a protected band where a UE has a power class 2 PA which, if operating under power class 3 requirements, can then improve its emission. FIG. 9C shows schematically how ACLR balancing by adjusting the UE transmission spectrum in accordance with the approaches described above can offer an operational advantage. FIG. 9D shows schematically how the power may be boosted in-band, and increased ACLR may be accepted in order to boost UE performance. Adjustment of a UE transmission spectrum in accordance with the approaches described above can offer an operational advantage. In some arrangements, rather than adjust PA operation as described above, the UE may be configured to assess whether to use the network offered MPR relaxations or to adjust the PA operation, based on the radio configuration and / or relative priorities of uplink or downlink communication for the UE. Some arrangements recognize that for optimum ET operation, in terms of efficiency gain and spectral purity, time alignment between a supply envelope waveform and an envelope of a transmitted RF signal must be accurate and use that requirement to deliberately adjust the form of the resulting UE transmission spectrum. While the main reasons for implementing ET in a UE are related to efficiency / linearity improvements and / or increased TX power capability, the ET can be used to deterministically reshape the transmission spectrum. If low emissions in a specific frequency offset from the active UL transmission sub-band is especially critical, offsetting the timings of the ET can be used to deterministically shape the UL transmission spectrum. In particular, a timing misalignment between the RF and envelope paths will cause asymmetric upper and lower side PA I M3 products. FIG. 10 shows schematically how misalignment of envelope tracking at a Power Amplifier can cause reshaping of the transmission spectrum. FIG. 10 shows the effect for a 20 MHz 4 frequency allocations WCDMA signal for matched time alignment and for positive and negative time misalignment settings (adjustable delay in RF path). It can be seen in FIG. 10 that the PA spectral regrowth decreases at a low side and increases at a high side for negative mismatch offsets and vice-versa for positive mismatch offsets. It can also be seen that the asymmetric spectrum tilt behavior is monotonic and increases for increased (+ / -) mismatched offsets. From the measurement results in FIG. 10, it appears that a timing misalignment of +-5ns gives a +-5MHz ACLR spectrum tilt of about ~4.5dB and a ~2.5dB improvement one side over the time aligned case. Such reshaping can support implementations in which a UE can choose or select to adjust the timing of an ET signal, rather than, for example, pushing a Vsup, and a resulting PA power, to maximum. Instead, a UE can utilize the timing relationship between the Vsup envelope and the RF signal envelope, to balance ACLR requirements. Delaying the Vsup envelope increases the ACLR at one side of the spectrum, while advancing the Vsup envelope shifts the ACLR degradation to the other side of the spectrum. Such an approach can be used to replace, for example, the action of putting the Vsup at maximum upon reaching a trigger level and then detecting the receiver degradation, and instead focuses UE operation on placing ACLR where it does less impact in relation to expected cross-band interference. In contrast to a fixed Vsup at maximum power such an approach can also apply to UL transmission at maximum power since it does not rely on backed off power supply headroom. The UE can also, in some implementations, use adjustment of ET timing to resolve matters in relation to relaxed MPR, rather than to deal with self-interference. Accordingly, the UE may, according to some implementations, focus the relaxation on the spectrum holding of network owned channels and away from the spectrum setting the MPR requirements. According to some example approaches, a UE may be configured with its own maximum sensitivity degradation MSD target or limit and may be equipped with a capability to assess or estimate its own MSD impact. According to such an approach, a UE may utilize adjustment to PA control methods to enhance MSD reduction from self-interference caused by ACLR. Such an approach may result in a higher UE energy usage, but the UE is likely not to need to reduce its uplink transmit power as much to achieve an appropriate MSD reduction. Summary of features of some possible Implementations FIG. 11 illustrates schematically an example apparatus according to an arrangement. FIG. 11 illustrates schematically an apparatus 900, for example, a UE, comprising: 910: circuitry configured to obtain an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; 920: circuitry configured to determine whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, and evaluate whether the one or more trigger condition is met by the user equipment;, 930: circuitry configured to adapt one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier in response to an evaluation that the trigger condition is met by the user equipment. FIG. 12 illustrates schematically an example method according to an arrangement. According to the example shown in FIG. 12 a method performed by user equipment such as user equipment 900 in FIG. 11, the method 1000 in accordance with an arrangement comprising steps of: 1010: obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition; determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, 1020: evaluating whether the one or more trigger condition is met by the user equipment; and in response to evaluating that the trigger condition is met by the user equipment, 1030: configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier. A person of skill in the art would readily recognize that steps of various abovedescribed methods can be performed by programmed computers. Herein, some embodiments are also intended to cover program storage devices, e.g., digital data storage media, which are machine or computer readable and encode machineexecutable or computer-executable programs of instructions, wherein said instructions perform some or all of the steps of said above-described methods. The program storage devices may be, e.g., digital memories, magnetic storage media such as a magnetic disks and magnetic tapes, hard drives, or optically readable digital data storage media. The embodiments are also intended to cover computers programmed to perform said steps of the above-described methods. The tern non-transitory as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. RAM vs ROM). As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. The ordering of method steps set out above may not be critical or fixed and the exact ordering of the steps may be varied as appropriate. Although example embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not. Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of 5 features hereinbefore referred to and / or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. An apparatus, comprisingat least one processor; andat least one memory storing instructions that when executed by the at least one processor cause the apparatus at least to perform:obtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition;determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; andin response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier.

2. An apparatus according to claim 1, wherein the predetermined network condition comprises: grant of a radio configuration identified as subject to cause crossband self-interference to the user equipment.

3. An apparatus according to claim 1 or claim 2, wherein the predetermined network condition comprises: grant of an inter-radio access technology radio configuration identified as subject to cause unwanted emission in another radio communication system.

4. An apparatus according to any preceding claim, wherein the predetermined network condition comprises: grant of a multi-SIM radio configuration identified as subject to cause cross-band self-interference to the user equipment.

5. An apparatus according to any preceding claim, wherein the predetermined network condition comprises: relaxation of a maximum power output transmission requirement at the user equipment.

6. An apparatus according to any preceding claim, wherein the predetermined network condition comprises: provision of a protected band in a radio frequency network within which the user equipment is operating.

7. An apparatus according to any preceding claim, wherein obtaining the indication of one or more trigger condition comprises: obtaining an indication of a transmission power level at which sensitivity in one or more receive band of user equipment operating under the predetermined network condition is impacted by crossband self-interference.

8. An apparatus according to any preceding claim, wherein the indication of one or more trigger condition comprises: a maximum sensitivity degradation MSD value associated with a receive band of user equipment operating under the predetermined network condition.

9. An apparatus according to any preceding claim, wherein the apparatus is further caused to perform:transforming an obtained maximum sensitivity degradation MSD value associated with a receive band of user equipment operating under the predetermined network condition to a threshold output power in a transmit band of the user equipment.

10. An apparatus according to any preceding claim, wherein the indication of one or more trigger condition comprises: a threshold user equipment battery power level.

11. An apparatus according to any preceding claim, wherein the one or more trigger condition comprises: initiation of transmission in a transmission band of the user equipment at a power beyond a maximum power output transmission requirement.

12. An apparatus according to any preceding claim, wherein the one or more trigger condition comprises: transforming an obtained unwanted emission value associated with a protected radio system to a threshold output power in a transmit band of the user equipment.

13. An apparatus according to any preceding claim, wherein the one or more method of control of the power amplifier comprises: control of the power amplifier voltage supply.

14. An apparatus according to claim 13, wherein the one or more method of control of the power amplifier comprises: average power tracking control of the power amplifier voltage supply.

15. An apparatus according to claim 14, wherein configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting a margin of the average power tracking control.

16. An apparatus according to any one of claims 13 to 15, wherein the one or more method of control of the power amplifier comprises: envelope tracking control of the power amplifier voltage supply.

17. An apparatus according to claim 16, wherein configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the envelope tracking margin.

18. An apparatus according to any preceding claim, wherein configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the envelope tracking timing compared to an input signal.

19. An apparatus according to any preceding claim, wherein the one or more method of control of a power amplifier comprises: digital predistortion of a signal fed to the power amplifier for transmission.

20. An apparatus according to any preceding claim, wherein configuring the one or more method of control of the power amplifier to change the profile of an emission spectrum associated with the power amplifier comprises: evaluating whether the user equipment is operating at maximum output power, and if not, adjusting the one or more method of control of the power amplifier to improve output linearity of the user equipment transmission spectrum.

21. An apparatus according to any preceding claim, wherein the apparatus is caused to perform:obtaining an indication of a region of radio spectrum in which transmission leakage is to be mitigated; andwherein configuring one or more method of control of the power amplifier of the user equipment to change the profile of an emission spectrum associated with the power amplifier comprises: adjusting the profile of the emission spectrum to reduce transmission spectrum amplitude in the indicated region.

22. An apparatus according to claim 21, wherein the region of radio spectrum in which transmission leakage is to be mitigated comprises: a receive band in which interference is expected, or a protected band.

23. An apparatus according to any preceding claim, wherein changing the profile of the emission spectrum associated with the power amplifier comprises: inducing an asymmetry in the emission spectrum.

24. A method, comprisingobtaining an indication of one or more trigger condition associated with user equipment operating under a predetermined network condition;determining whether the user equipment is operating under the predetermined network condition and, based on determining that the user equipment is subject to the predetermined network condition, evaluating whether the one or more trigger condition is met by the user equipment; andin response to evaluating that the trigger condition is met by the user equipment, configuring one or more method of control of a power amplifier of the user equipment to change a profile of an emission spectrum associated with the power amplifier.

25. A computer program product operable, when executed on a computer, to perform the method of claim 24.

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