Patent Description:
Signal processing is a part of wireless communication that requires hardware and software to function effectively and reliably. Effective use of hardware resources helps to save costs and may be at least partly achieved using software algorithms. <CIT> discloses a system for use with beam signals, the system including: a crest factor reduction module having inputs and corresponding outputs, wherein each of the inputs is for receiving a corresponding different beam signal of the beam signals and wherein each output corresponds to a different input of the plurality of inputs and is for outputting a different CFR-adjusted signal of the plurality of CFR-adjusted signals, each CFR-adjusted signal of the plurality of CFR-adjusted signals corresponding to a different beam signal of the plurality of beam signals; and a transmitter connected to the outputs of the CFR module, wherein the CFR module is configured to perform crest factor reduction on the beam signals to generate the plurality of CFR-adjusted signals, and wherein the crest factor reduction performed on the beam signals is based on the weighted sum of the magnitudes of multiple beam signals among the beam signals. <CIT> discloses methods and systems for crest factor reduction of multistandard carrier aggregated signals. In one embodiment, a method of providing crest factor reduction for a carrier aggregated signal is provided. In one embodiment, the method comprises estimating a peak of a carrier aggregated signal based on a summation of instantaneous amplitudes of baseband representations of a number of component carriers of the carrier aggregated signal. The number of component carriers of the carrier aggregated signal is greater than or equal to <NUM>. The method further comprises clipping the baseband representations of the component carriers if the estimated peak of the carrier aggregated signal is greater than a predefined clipping threshold.

Dependent claims define further embodiments included in the scope of protection. The exemplary 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.

In the following, the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which:.

As used in this application, the term 'circuitry' refers to all of the following: (a) hardwareonly circuit implementations, such as implementations in only analog and/or digital circuitry, and (b) combinations of circuits and software (and/or firmware), such as (as applicable): (i) a combination of processor(s) or (ii) portions of processor(s)/software including digital signal processor(s), software, and memory(ies) that work together to cause an apparatus to perform various functions, and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

The techniques and methods described herein may be implemented by various means. For example, these techniques may be implemented in hardware (one or more devices), firmware (one or more devices), software (one or more modules), or combinations thereof. For a hardware implementation, the apparatus(es) of embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), graphics processing units (GPUs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. For firmware or software, the implementation can be carried out through modules of at least one chipset (e.g. procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in a memory unit and executed by processors. The memory unit may be implemented within the processor or externally to the processor. In the latter case, it can be communicatively coupled to the processor via various means, as is known in the art. Additionally, the components of the systems described herein may be rearranged and/or complemented by additional components in order to facilitate the achievements of the various aspects, etc., described with regard thereto, and they are not limited to the precise configurations set forth in the given figures, as will be appreciated by one skilled in the art.

<FIG> illustrates an apparatus <NUM>, which comprises a radio frequency unit, RF unit <NUM>, which may be a logical unit in some exemplary embodiments. The RF unit <NUM> may be comprised in an apparatus that comprises an antenna <NUM>, a processor <NUM> and/or a memory <NUM>. Alternatively, the RF unit may be connected to one or more of the antenna <NUM>, the processor <NUM> and/or the memory <NUM>. The apparatus <NUM> may be an apparatus such as, or comprised in, a terminal device, or an access node for example.

The RF Unit <NUM> enables wireless connectivity to external networks. The RF Unit <NUM> is connected to, or comprises, the antenna <NUM>. The antenna <NUM> may comprise one or more antennas. The RF unit <NUM> may comprise an integrated circuit or a set of integrated circuits that provide the wireless communication capability for the apparatus <NUM>. The RF unit <NUM> is configured to transmit and receive radio frequency signals and, in some exemplary embodiments, to process the signals. It is to be noted that the RF unit <NUM> may comprise hardware and/or software for realizing communication connectivity according to one or more communication protocols. In some exemplary embodiments, the RF unit <NUM> is configured to modulate a radio wave to carry data and to transmit the radio wave. Additionally, or alternatively, the RF unit <NUM> may be configured to receive a modulated radio wave and to demodulate the received modulated radio wave. Further, additionally or alternatively, the RF unit <NUM> may comprise a microcontroller configured to handle data packetization and/or managing a communications protocol.

The processor <NUM> interprets computer program instructions and processes data. The processor <NUM> may comprise one or more programmable processors. The processor <NUM> may comprise programmable hardware with embedded firmware and may, alternatively or additionally, comprise one or more application specific integrated circuits, ASICs. The processor <NUM> is coupled to a memory <NUM>. The processor is configured to read and write data to and from the memory <NUM>. The memory <NUM> may comprise one or more memory units. The memory units may be volatile or non-volatile. It is to be noted that in some example embodiments there may be one or more units of non-volatile memory and one or more units of volatile memory or, alternatively, one or more units of non-volatile memory, or, alternatively, one or more units of volatile memory. Volatile memory may be for example RAM, DRAM or SDRAM. Non-volatile memory may be for example ROM, PROM, EEPROM, flash memory, optical storage or magnetic storage. In general, memories may be referred to as non-transitory computer readable media. The memory <NUM> stores computer readable instructions that are execute by the processor <NUM>. For example, non-volatile memory stores the computer readable instructions and the processor <NUM> executes the instructions using volatile memory for temporary storage of data and/or instructions. The computer readable instructions may have been pre-stored to the memory <NUM> or, alternatively or additionally, they may be received, by the apparatus, via electromagnetic carrier signal and/or may be copied from a physical entity such as computer program product. Execution of the computer readable instructions causes the apparatus <NUM> to perform functionality described above.

It is to be noted that the apparatus <NUM> may further comprise various component not illustrated in the <FIG>. The various components may be hardware component and/or software components.

When a signal is received, for example by an RF unit such as the RF unit <NUM>, filtering may be applied to extract the correct RF bandwidth. The signal may also be amplified which may enable better processing of the received signal. For signal processing purposes, a peak amplitude of a received signal may be determined. Peak amplitude may be understood as a maximum absolute value of the signal in view of a reference. The reference may be for example zero and as such the peak amplitude may be understood as the maximum value of difference compared to the zero.

A crest factor is a parameter that may be used to indicate how different peak values in a waveform of the signal are compared to the effective value of the waveform. The higher the crest factor, the greater the peaks of the waveform. The crest factor may be determined by dividing the peak amplitude of the waveform by the root mean square, RMS, value of the waveform. A peak-to-average power ratio, PAPR, may be understood as indicating the average power of the waveform. The PAPR may be determined by dividing the squared peak amplitude by the RMS value squared.

A peak-to-average ratio, PAR, on the other hand indicates the ratio of the peak power level to the time-averaged power level in an electrical circuit. The PAR may be determined for various signal parameter such as voltage, current, power, frequency and phase.

The smaller the crest factor, the more bits per second may typically be transmitted. Therefore, modulation techniques with small crest factors may be desirable and crest factor reduction, CFR, techniques are useful as they enable more bits per second to be transmitted using the same hardware resources. Examples of CFR techniques include peak windowing, noise shaping, pulse injection and peak cancellation. Minimum crest factor occurs in a waveform that has a constant envelope signal. An envelope signal may be understood as a curve outlining the extremes of a signal's waveform. A constant envelope signal therefore may be understood as an envelope signal for a sinusoidal waveform that is in equilibrium.

A signal may be limited once its amplitude exceeds a threshold. This limitation may be understood as clipping. Clipping may introduce noise to the clipped signal. Clipping effectively distorts the signal thereby limiting the amplitudes to a threshold value.

In data communication information is transferred using modulated sine waves that may be called carriers. To effectively transmit information, a single frequency sine wave may not be sufficient. Therefore, a plurality of sine waves that form a composite signal may be utilized. The bandwidth of such a composite signal may be understood as the difference between the highest and the lowest frequencies comprised in the composite signal.

Radio signals, which may be carriers or composite signals, may be characterized by their corresponding radio bandwidth. <FIG> illustrates this by indicating a radio bandwidth <NUM>, <NUM> and <NUM>. The radio bandwidth may be limited due to various factors such as cost, performance requirements and physical properties of an apparatus such as the apparatus <NUM>. However, in some exemplary embodiments a radio bandwidth may comprise two or more separate RF bands such as those illustrated in <FIG>, RF bands <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>, that have a gap in between them. In such exemplary embodiments, a question arises regarding how to handle each RF band. One solution is to allocate an RF unit, such as an RF unit <NUM>, for each band.

<FIG> illustrates a wideband configuration <NUM> in which the RF band <NUM> corresponds to the radio bandwidth <NUM>. Another configuration illustrated in <FIG> is the dual-band configuration <NUM> in which the RF bands <NUM> and <NUM> have a gap in between them and are comprised in the radio bandwidth <NUM>. Yet another configuration illustrated in <FIG> is the multi-band configuration <NUM> in which the RF bands <NUM>, <NUM> and <NUM> have a gap in between them and are comprised in the radio bandwidth <NUM>. It is to be noted that a dual-band configuration may also be understood as a multi-band configuration.

In an exemplary embodiment, an RF unit, such as the RF unit <NUM>, is used to process all RF bands in a dual- and multiband configurations. In the dual-band and multi-band configuration the signals may be placed within the assigned RF bands separated by the frequency gaps between them. Each RF band covers a certain frequency region, the width of which is defined as the RF bandwidth, RF BW. The RF BW may be understood as an RF band specific parameter that is different for each RF band.

When CFR is performed as part of signal processing, the processing effort needed increases as the radio bandwidth of the signal may increase. If the wideband CFR is used for the dual- or multi-band signal, the two or more separate RF bands are still interpreted as one wideband corresponding to the radio bandwidth. Consequently, the signal processing must operate at sampling rates that match with the radio bandwidth of the radio signal although only part of the radio bandwidth is occupied by the radio signal. Therefore, the aspect that only a part of the radio bandwidth is occupied by the radio signal may be utilized to reduce the signal processing effort required for CFR.

In a multi-band configuration, which includes a dual-band configuration, a preview signal is utilized to provide information regarding position and level of each peak comprised in a radio signal. The information may then be used by the CFR algorithm to limit the signal power, thus reducing the resulting PAR. In the CFR algorithm, each band is processed in a separate path, but the band specific clipping signal is generated using the information from all bands at the same time.

<FIG> illustrates the difference between wideband CFR <NUM>, dual-band CFR <NUM> and multi-band CFR <NUM>. The CFR in this exemplary embodiment is an iterative procedure which gradually reduces the peak to average power ratio (PAR) of the radio signal. The block diagrams <NUM>, <NUM> and <NUM> illustrate the various iteration rounds of CFR applied to the radio signals. In the wideband CFR <NUM> a radio signal S and clipped signals Z<NUM>,Z<NUM>,. , ZI for wideband are illustrated in the block diagram exemplifying the signal processing chain. In the dual-band CFR <NUM> radio signals SA and SB as well as clipped signals ZA,<NUM>, ZA,<NUM>,. , ZA,I, that are in an RF band A and clipped signals ZB,<NUM>, ZB,<NUM>,. , ZB,I that are in an RF band B are illustrated in the block diagram exemplifying the signal processing chain. A processing chain for multi-band CFR <NUM> is illustrated in <FIG> as well. The multi-band CFR <NUM> is a generalization of the dual-band mode. Radio signals SA, SB and up to SX as well as clipped signals ZA,<NUM>, ZA,<NUM>,. , ZA,I, that are in an RF band A, clipped signals ZB,<NUM>, ZB,<NUM>,. , ZB,I that are in an RF band B and up to clipped signals ZX,<NUM>, ZX,<NUM>,. , ZX,I that are in an RF band X are illustrated in the block diagram exemplifying the signal processing chain. It is to be noted that the number of CFR iteration rounds is not limited.

For the sake of simplifying discussion of exemplary embodiments, dual-band configurations are discussed from now on, but it is to be noted that the multi-band configuration is a generalization of the dual-band configuration and therefore the exemplary embodiments discussed are applicable to multi-band configurations as well.

In <FIG>, a block diagram of an exemplary embodiment of a single iteration of a CFR applied in a wideband configuration <NUM> is illustrated. A composite signal S is fed to the input of the CFR block <NUM> as well as to the preview block <NUM>. The preview block <NUM> performs oversampling to meet requirements regarding clipping accuracy. Then the composite signal S with increased time resolution is fed to the Peak Signal block <NUM> and is used to generate a peak signal P. The clipping gain block <NUM> then uses the peak signal P to generate clipping gain signal <MAT>. The clipping gain signal <MAT> is then used by the CFR wideband block <NUM> to provide the clipped signal Z.

In <FIG> a block diagram of an exemplary embodiment of a single iteration of a CFR applied in a dual-band configuration <NUM> is also illustrated. A composite signal SA for a first RF band, RF band A and a composite signal SB for a second RF band, RF band B are fed to the CFR blocks <NUM> for RF band A and B and to the preview blocks <NUM>. The preview blocks <NUM> oversample the composite signals to meet requirements regarding clipping accuracy. The composite signals SA and SB with increased time resolution are then used to generate either a peak signal P or an envelope signal E in a peak or envelope signal block <NUM>. The clipping gain block <NUM> then uses either the signal P or E in order to generate clipping gain signals <MAT> and <MAT>. Each clipping gain signal is used by its corresponding CFR block CFR <NUM> for RF band A or for RF band B, to provide clipped signals ZA and ZB. The CFR blocks <NUM> illustrated in the exemplary embodiments of <FIG> may be implemented as an additive or as a multiplicative clipper. It is to be noted that determining may also be understood as generating.

To generate a preview signal for the CFR algorithms a peak signal may be utilized as illustrated in the previous exemplary embodiments. The peak signal may be understood as an amplitude or power of peaks of the composite signal. The peak signal may be obtained using the following equation: P = |SA + SB|. If the peak signal is used in the wideband CFR configuration, then it may be obtained using the following calculation: P = |S|. In addition to the peak signal, also an envelope signal may be used to generate a preview signal for the CFR algorithms. The envelope signal may be generated as the sum of amplitude of the RF band specific composite signals. The envelope signal may be obtained using the following equation: E = |SA| + |SB|. <FIG> illustrates an exemplary representation of a peak signal <NUM> and an envelope signal <NUM> for a frequency gap between the bands of <NUM>.

It is to be noted that a peak signal may be utilized in wideband and dual-band CFR. In case a peak signal is utilized for a dual-band CFR, an alignment of frequency and phase information of both RF bands in the preview processing path and in the main processing path is needed. If an envelope signal is utilized for the dual-band CFR, the envelope signal in the preview path is immune to possible phase and frequency deviation in each RF band in the preview processing path and in the main processing path. <FIG> illustrates an exemplary comparison of the PAR performance between a peak-signal based CFR <NUM> and an envelope-signal based CFR <NUM> with perfect phase alignment between the main processing path and the preview processing path. Each RF band in this example comprises three adjacent LTE20 carriers and the RF BW of each RF band is <NUM>. As is illustrated, the peak level is approximately constant in case the dual band CFR utilizes the envelope signal or the peak signal. Therefore, no degradation occurs when a frequency gap Δf_c between the RF bands is decreasing in this example.

<FIG> illustrates an exemplary comparison of the PAR performance between a peak-signal based CFR <NUM> and an envelope-signal based CFR <NUM>, both of them being misaligned. Carrier configuration is the same as in the example of <FIG>. Phase misalignment is set to the maximum value π in this example. It is illustrated that the peak level is approximately constant in case of the dual-band CFR that utilizes the envelope signal. For the dual-band CFR that utilizes the peak signal, the peak level is strongly increasing when frequency gap Δf_c between bands is decreasing in this example.

The sampling rate in oversampling of the preview path for the peak-signal based dual-band CFR may be dependent on radio bandwidth, while the sampling rate in oversampling of the preview path for the envelope signal based dual-band CFR may be dependent on the maximum RF BW of all the RF bands. Therefore, a benefit of using the CFR algorithm that utilizes the envelope signal instead of peak signal in the preview path may be a significantly reduced need for sampling rates.

The power inside each RF band may be different and that may have an effect on an envelope signal based dual-band CFR. In such a situation the RF band with less power may suffer more due to unbalanced or unregulated clipping noise distribution. Therefore, it may get unintentionally more EVM compared to the RF band with higher power. EVM, error vector magnitude, may be understood as a measure used to quantify the performance of a digital radio transmitter or receiver. In some examples, EVM may be traded between the RF bands by applying weighing factors, weights. Yet incorporating band specific weights into the additive clipping pulses in the dual-band envelope CFR algorithm may be problematic in some examples. Usage of weights into the per-band specific CFR paths, in some examples, incorporates PAR degradation. For example, one may define band specific additive clipping pulses Cp,A and Cp,B and band specific clipping weights VA and VB. In this example, the additive dual-band CFR algorithm based on envelope signal generates the following clipped envelope signal: <MAT>.

If the clipping weights are VA=<NUM> and VB=<NUM> are the additional factors equal to zero and the multiplicative part for both RF bands is equal to one, thus one may obtain: <MAT>.

It may therefore be desirable to balance clipping noise between RF bands without increasing a PAR level of an output signal. By balancing clipping noise between the RF bands, the EVM level of carriers inside the RF bands may be affected. To achieve this, clipping pulses Cp,A and Cp,B for both RF bands separately may be provided with clipping noise balancing functionality. Consequently, signal such as ZA and ZB are hard clipped and produce an envelope signal EZ which is thereby also hard clipped. Additionally, in some examples, pulse shaping and protection against over-clipping may be utilized.

Some examples of calculations inside a single iteration of the CFR are discussed below. It is to be noted that the number of iterations is not limited in these examples. The number of iterations may depend on the target use cases for the processing chain. Also, the examples do not restrict how the clipping pulses are filtered to provide the best spectral properties, but instead, different methods may be utilized to handle this functionality depending on, for example, the requirements of the target implementation. For example, the filtering may be done using time domain finite impulse response, FIR, filter or frequency domain filter. The examples do not restrict how to suppress over-clipping that can occur during the filtering of the clipping pulses either. For example, the method to avoid over-clipping may be based on the windowing procedure or on pulse scaling procedure. The examples also do not restrict how the signals are processed inside of the bands. Both carrier and/or composite signals may be processed.

In an exemplary embodiment illustrated as a block diagram in <FIG>, separate composite signals from each RF band of a dual-band configuration, SA and SB, are obtained and used to generate band specific envelope signals |SA| and |SB|. The term generate is used here although alternatively term determining could be used as well. The composite signal SA and SB are fed to RF band specific CFR, blocks <NUM> and to preview processing, blocks <NUM>. From the preview processing the composite signals are then processed to determine the envelope signal in blocks <NUM> after which the RF band specific envelope signals are used, in block <NUM>, to determine a preview envelope signal, E, for a CFR algorithm: E = |SA| + |SB|. Next, the preview envelope signal is processed to obtain a common clipping gain signal Cg in block <NUM> after which in block <NUM> RF band specific weighing factors WA and WA are combined to the common clipping gain signal Cg to determine the band specific clipping gain constrain signal <MAT> and <MAT> that are then used for band-specific CFR in block <NUM>. It is to be noted that determining may be understood as obtaining and/or defining in some exemplary embodiments.

In this exemplary embodiment, the sampling rate of the preview envelope signal E is higher compared to either sample rate of the composite signal SA in RF band A and composite signal SB in RF band B. The sample rate may be chosen according to application specific requirements of a target architecture.

In this exemplary embodiment, a clipping threshold is described as Thr. Therefore, the common clipping gain signal may be defined as: <MAT>.

Then weighted clipping gain signals for RF band A and RF band B may be defined as: Cg,A = WACg and Cg,B=WBCg, where WA and WB are RF band specific weights for RF band A and RF band B. This is illustrated in <FIG>. The band specific weights in this exemplary embodiment fulfil the condition WA +WB =<NUM>. Both clipping gain signals Cg,A and Cg,B may be constrained <NUM>. The constraining may be done, for example, by using the following conditions:.

These restrictions are imposed by the initial constrains <NUM> ≤ |ZA| ≤ Thr and <NUM> ≤ |ZA| ≤ Thr. It is to be noted that the above constrains are examples that illustrates a simplified dual-band subcase of constrains for a multiband system. In another example, constrains for a multiband system (set of bands <IMG> = {A, B, C,. }) may follow the conditions indicated below:.

It is to be noted that in this example the subset <IMG> = {k ∈ <IMG> | Cg,k > |Sk|] comprises all bands k from the set <IMG> for which the condition Cg,k > |Sk| is true. The band specific weights in this example fulfill the condition <IMG>Wk = <NUM>. In a dual-band example a set of bands may be <IMG> = {A, B}. In such an example, if the limiting constrain (Step <NUM>) is applied to the subset of bands <IMG> = {B}, then the normalizing constrain (Step <NUM>) is applied to the subset of bands <IMG> = {A}. In another example, a multiband with five bands example, the set of bands may be <IMG> = {A, B, C, D, E}. In such an example, if the limiting constrain (Step <NUM>) is applied to the subset of bands <IMG> = {A, B, D}, then the normalizing constrain (Step <NUM>) is applied to the subset of bands <IMG> = {C, E}.

Combined signals SA and SB separately for RF band A and RF band B may be clipped using the equations: <MAT> <MAT>.

In this exemplary embodiment, the component exp(<NUM>i ∠SA) and exp(<NUM>i ∠SB) may also be extracted as <MAT> and <MAT> and an RF band specific pulse may be defined as <MAT> <MAT>.

<FIG> illustrates block diagram according to exemplary embodiments of the structure of the CFR RF band A <NUM> and the structure of the CFR RF band B <NUM>. In this exemplary embodiment, the combination of the clipped signals in the RF bands A and B is Z = ZA + ZB. The envelope EZ of the clipped combined signal Z may be determined as<MAT>.

The clipped envelope may be determined as <MAT>.

Therefore, two possible clipped envelopes may be obtained depending on the unclipped envelope E: <MAT>.

The above discussed exemplary embodiments may have a benefit of CFR not limiting the radio bandwidth in case of dual-band, or multi-band, use cases.

<FIG> and <FIG> illustrate exemplary performance results of dual-band envelope-signal based CFR, including pulse shaping and over-clipping protection compared with the wideband CFR with the same pulse shaping and over-clipping protection as a reference. In each band two LTE20 carriers are used. Band B has 6dB higher power compared to band A. Maximum RF BW is <NUM>, radio bandwidth is <NUM> and the frequency gap Δf_c is <NUM>. In the CFR algorithm used, the target PAR is set to 7dB. The clipping noise is deliberately adjusted between carriers. Carrier number <NUM>,<NUM> and <NUM> have the same clipping noise balancing ratio, whereas carrier number <NUM> has the opposite clipping noise balancing ratio. The EVM performance results are depicted in <FIG>. Dashed lines represent the high effort EVM reference of the carriers at the output of the wideband CFR algorithm. Solid lines represent the EVM of the carriers at the output of the dual-band CFR algorithm. Both algorithms provide comparable performance in meaning of the EVM and the PAR of the output signal.

Target EVM ratio for carrier <NUM>, <NUM> and <NUM> is the same (see blue, green and orange solid and dashed lines). Target EVM ratio for carrier number <NUM> is on the opposite value (see solid and dashed lines), as shown by the following equation:<MAT>.

Performance results for the PAR as a function of target EVM ratios are illustrated in <FIG>. Both algorithms provide comparable PAR results. The provided dual-band CFR using envelope signal does not have any performance degradation due to target EVM ratio balancing between carriers and bands.

The exemplary embodiments discussed above may further have benefits including good EVM balancing without PAR degradation, lower power consumption compared to the CFR in wideband mode, immunity for phase and frequency misalignment between bands in main and preview path, lower sampling rates in the preview path, reduced requirements for the filtering chain, lower amount of hardware resources in the DFE, lower power consumption of the DFE, possibility to use separate non-coherent DAC with lower sampling rates compared to wideband signal and possibility to use non-coherent carrier up-converters in the analogue domain to carrier frequency up-convert signals separately for band A and band B.

Embodiments described herein may be implemented in a communication system, such as in at least one of the following: Global System for Mobile Communications (GSM) or any other second generation cellular communication system, Universal Mobile Telecommunication System (UMTS, <NUM>) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, a system based on IEEE <NUM> specifications, a system based on IEEE <NUM> specifications, and/or a fifth generation (<NUM>) mobile or cellular communication system.

<FIG> shows terminal devices <NUM> and <NUM> configured to be in a wireless connection on one or more communication channels in a cell with an access node (such as (e/g)NodeB) <NUM> providing the cell. The access node <NUM> may also be referred to as a node. The physical link from a terminal device to a (e/g)NodeB is called uplink or reverse link and the physical link from the (e/g)NodeB to the terminal device is called downlink or forward link. It should be appreciated that (e/g)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage. It is to be noted that although only one cell is discussed in this exemplary embodiment, for the sake of simplicity of explanation, multiple cells may be provided by one access node in some exemplary embodiments.

A communication system typically comprises more than one (e/g)NodeB in which case the (e/g)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signalling purposes. The (e/g)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The NodeB may also be referred to as a base station, an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (e/g)NodeB includes or is coupled to transceivers. From the transceivers of the (e/g)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (e/g)NodeB is further connected to core network <NUM> (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of terminal devices (UEs) to external packet data networks, or mobile management entity (MME), etc..

The terminal device (also called UE, user equipment, user terminal, user device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a terminal device may be implemented with a corresponding apparatus, such as a relay node. Another example of such a relay node is a layer <NUM> relay. Such a relay node may contain a terminal device part and a Distributed Unit (DU) part. A CU (centralized unit) may coordinate the DU operation via F1AP -interface for example.

The terminal device typically refers to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), or an embedded SIM, eSIM, 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, and multimedia device. A terminal device may also be a device having capability to operate in Internet of Things (IoT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. The terminal device may also utilise cloud. In some applications, a terminal device may comprise a small portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. The terminal device (or in some embodiments a layer <NUM> relay node) is configured to perform one or more of user equipment functionalities.

<NUM> enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. <NUM> mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications such as (massive) machine-type communications (mMTC), including vehicular safety, different sensors and real-time control. <NUM> is expected to have multiple radio interfaces, namely below <NUM>, cmWave and mmWave, and also being integratable with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and <NUM> radio interface access comes from small cells by aggregation to the LTE. In other words, <NUM> is planned to support both inter-RAT operability (such as LTE-<NUM>) and inter-RI operability (inter-radio interface operability, such as below <NUM> - cmWave, below <NUM> - cmWave - mmWave). One of the concepts considered to be used in <NUM> networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

The communication system is also able to communicate with other networks, such as a public switched telephone network or the Internet <NUM>, or utilise services provided by them.

It should also be understood that the distribution of labour between core network operations and base station operations may differ from that of the LTE or even be nonexistent. Some other technology probably to be used are Big Data and all-IP, which may change the way networks are being constructed and managed.

It is to be noted that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (e/g)NodeBs, the terminal device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the (e/g)NodeBs may be a Home(e/g)nodeB.

Claim 1:
An apparatus (<NUM>) comprising means for
obtaining a first radio signal, which is a first composite signal and is comprised in a first set of radio frequency bands comprising a first plurality of radio frequency bands, and a second radio signal, which is a second composite signal and is comprised in a second set of radio frequency bands comprising a second plurality of radio frequency bands, wherein the first set of frequency bands is a first subset of a third set of frequency bands, and the second set of frequency bands is a second subset of the third set of frequency bands;
performing a first preview processing to the first radio signal and a second preview processing to the second radio signal;
determining a first envelope signal based on the preview processed first radio signal and a second envelope signal based on the preview processed second radio signal;
determining a preview envelope signal based on the first envelope signal and the second envelope signal;
determining a common clipping gain signal based on the preview envelope signal;
determining a first clipping gain signal, that is a first constrained clipping gain signal in accordance with a first constraint that is a limiting constraint applied to the first set of radio frequency bands, based on the common clipping gain signal and a first weighing factor;
determining a second clipping gain signal, that is a second constrained clipping gain signal in accordance with a second constraint that is a normalizing constraint applied to the second set of radio frequency bands, based on the common clipping gain signal and a second weighing factor;
performing a first crest factor reduction for the first radio signal utilizing the first clipping gain signal; and
performing a second crest factor reduction for the second radio signal utilizing the second clipping gain signal.