WO2014046582A1

WO2014046582A1 - Method and radio network node for controlling transmission of signals from the radio network node

Info

Publication number: WO2014046582A1
Application number: PCT/SE2012/051002
Authority: WO
Inventors: Alireza Nejatian; Youping Su
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2012-09-21
Filing date: 2012-09-21
Publication date: 2014-03-27
Anticipated expiration: 2015-03-21

Description

METHOD AND RADIO NETWORK NODE FOR CONTROLLING TRANSMISSION OF SIGNALS FROM THE RADIO NETWORK NODE

Technical field

[0001 ] The present disclosure relates generally to a method performed by a radio network node for controlling transmission of signals from the radio network node, and a radio network node configured to control, transmission of signals from the radio network node.

Background

[0002] A power amplifier of a transmitter in e.g. a base station is used to amplify a signal to be transmitted in a wireless network. Such a power amplifier needs to be highly linear over a wide dynamic range. Amplification may create in-band and out-of-band disturbances, such as intermodulation products. If amplification is not performed in the linear range of the power amplifier, the disturbances, especially the out-of-band disturbances may become high and may disturb other radio network nodes in the wireless network, such as other transmitters, receivers and UEs. A typical amplification characteristics between input power and output power of a power amplifier is shown in figure 1 . To use an amplifier as efficiently as possible, the amplifier should work at a high operating point, i.e. with a high input power and high output power. However, as could be seen in the amplification characteristics, the amplifier has non-linear characteristics at high input powers. There is a point of the amplification characteristics called the 1 dB gain

compression point. Above that point the amplifier does not react linearly anymore and the disturbances generated due to the non-linear characteristics will become too high. Therefore, the power amplifier usually should operate below the 1 dB gain compression point.

[0003] At the same time, operators of wireless mobile networks are constantly striving to lower total cost of ownership of the network by identifying cost-effective methods of expanding the mobile networks within predefined performance criteria. For this reason, non-constant envelope modulation schemes like Code Division Multiple Access (CDMA), Wideband CDMA and Orthogonal Frequency Division Multiplex (OFDM) techniques are used to achieve high spectral efficiency. Also, multi-carrier base stations have been employed to enable communication with mobile terminals over a plurality of carriers. A drawback with such modulation schemes and multi-carrier base stations are that they have a very high Peak to Average Ratio (PAR), which in some cases may exceed 10 dB.

[0004] Consequently, the power amplifier needs to be designed for peak power, such that peak power is amplified in the linear range of the amplifier. Therefore, the amplifier average output power, i.e. the average operating point, needs to be backed off from the 1 dB gain compression point (see figure 1 ). Although the amplifier is designed for peak power, it will mostly work around the average power level. If the signal has a high PAR, working in such a backed-off mode results in poor power efficiency of the power amplifier, and consequently poor efficiency of the transmitter.

[0005] Consequently, there is a trade-off between linearity of the power amplifier and efficiency of the transmitter. In other words, there is a need to achieve a high transmission efficiency at the same time as the disturbances are kept within acceptable limits, to eventually achieve a good network performance.

Summary

[0006] It is an object of the invention to address at least some of the problems and issues outlined above. More specifically, it is an object to improve

transmission efficiency of a radio network node while keeping disturbances within acceptable limits. It is possible to achieve these objects and others by using a method and a radio network node as defined in the attached independent claims.

[0007] According to one aspect, a method performed by a radio network node in a wireless communication network is provided, for controlling transmission of signals from the radio network node. The radio network node comprises a transmitter having a power amplifier. The method comprises: measuring, on a signal to be transmitted from the radio network node, a level of out-of band emissions, after the signal to be transmitted has been amplified by the power amplifier, detecting a difference, D, between the measured level of out-of-band emissions and a pre-defined out-of-band emission threshold, and adapting characteristics of the transmitter based on the detected difference D, such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

[0008] Out-of-band emissions are disturbances generated as distortions of the original signal, which disturbances are situated outside the transmission frequency bandwidth of the radio network node/transmitter, i.e. the frequency band at which the signal is transmitted. The out-of band emissions may be intermodulation distortions. The out-of-band emissions may for example be measured at the channels situated closest to, but outside the transmission frequency bandwidth, e.g. the 100 MHz closest to the transmission frequency bandwidth. A radio network node is a node in a wireless network configured to transmit radio signals over an air interface. The radio network node may be e.g. a radio base station or a user equipment, such as a mobile terminal. By characteristics of the transmitter is meant transmitter characteristics that influence throughput of the transmitter or quality of the signal to be transmitted, such as signal input power to a power amplifier in the transmitter, supply power of the power amplifier or signal clipping level in a crest factor reduction unit of the transmitter.

[0009] According to another aspect, a radio network node in a wireless communication network is provided. The radio network node is arranged to control transmission of signals from the radio network node. The radio network node further comprises a transmitter having a power amplifier. The radio network node comprises a measuring unit, configured to measure, on a signal to be transmitted from the radio network node, a level of out-of band emissions, after the signal to be transmitted has been amplified by the power amplifier; a detection unit configured to detect a difference, D, between the measured level of out-of-band emissions and a pre-defined out-of-band emission threshold, and a control unit configured to adapt characteristics of the transmitter based on the detected difference D, such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

[00010] According to a third aspect, a computer program product is provided, comprising computer readable code means, which when run in a radio network node causes the node to perform the method according to the first aspect.

[0001 1 ] Further possible features and benefits of this solution will become apparent from the detailed description below.

Brief description of drawings

[00012] The solution will now be described in more detail by means of exemplary embodiments and with reference to the accompanying drawings, in which:

[00013] Fig. 1 is a graph of a transfer characteristic of a typical power amplifier.

[00014] Fig 2 is a schematic block diagram of a typical radio node.

[00015] Fig. 3 is a graph illustrating in-band signals and out-of-band signals from a typical radio node.

[00016] Figs. 4-5 show flow charts of methods for controlling transmission of signals from a radio network node according to possible embodiments.

[00017] Fig. 6 is a graph illustrating amplitude over time for a signal to be transmitted, which signal is exposed to signal clipping.

[00018] Fig. 7 is a graph of a transfer characteristic of a power amplifier exposed to Crest Factor Reduction (CFR).

[00019] Fig. 8 is a flow chart of a method for controlling transmission of signals from a radio network node according to a possible embodiment.

[00020] Figs. 9-10 are schematic block diagrams illustrating radio network nodes according to possible embodiments. Detailed description

[00021 ] Briefly described, a solution is provided to improve transmission efficiency of a radio network node, such as a radio base station. The solution is based on the understanding that the radio network nodes, e.g. base stations, of today are designed to meet regulatory requirements for out-of-band emissions at worst case, such as highest working temperature and/or highest PAR, transmitter band edge operation and/or highest output power. Although, in most cases, the working conditions of the power amplifier are less demanding than those of such a worst case scenario. Consequently, a higher out-of-band emission than what is actually experienced may be tolerated when the power amplifier is not in the worst case scenario. By measuring the current out-of-band emission and comparing the current out-of band emission to a predefined threshold that may be set according to regulatory requirements, transmitter characteristics, such as transmitter signal quality or power efficiency of the power amplifier, may be improved without risking that the current out-of band emissions exceed the predefined threshold. In other words, by dynamically adapting transmitter characteristics based on current out-of band emissions, such that current out-of-band emissions do not exceed the predefined threshold, a transmitter may be used more efficiently without risking that the out-of band emissions exceed the predefined threshold, thereby avoiding the risk that regulatory requirements are violated.

[00022] According to an embodiment, a method in a radio network node is provided, comprising: measuring a level of current out-of-band emissions at the radio network node on a signal to be transmitted after the signal has been amplified by a power amplifier of the radio network node, comparing the measured level of out-of-band emissions with a pre-defined threshold, and adapting transmitter characteristics based on the result of the comparison, such that the current level of out-of band emissions does not exceed the predefined threshold.

[00023] Thereby, a more efficient use of the transmitter is achieved. For example, an increased throughput may be achieved, realized as an improved signal quality, or a more efficient usage of power in the power amplifier. By such a method, it may for example be possible to move the operating point of the power amplifier and the 1 dB compression point more closely towards each other without the current level of out-of band emissions exceeding the pre-defined out-of band emission threshold. As a result, an improved transmission efficiency is achieved, as compared to prior art methods.

[00024] In an embodiment, the transmitter characteristic that is adapted is the PA supply power. The PA supply power is the power that is supplied to the PA for operating the PA such that the PA can amplify an input power to a requested output power. PA supply power = (PA supply voltage) ^* (PA supply current). In this case, a PA supply power level, or value, is adapted based on the comparison between the measured level of out-of-band emission and the pre-defined threshold. When the PA supply power level is decreased and an unaltered input power level is used, the 1 dB compression point may be moved towards the operating point. Consequently, the out-of-band emissions will increase. If the comparison between the measured level of out-of-band emission and the predefined threshold shows that the measured level of out-of-band emission is lower than the predefined threshold, the PA supply power can be decreased to a level such that the current level of out-of-band emissions is increased but still does not exceed the predefined threshold. Thereby, the power efficiency of the PA is increased. The PA works with an unaltered input power level but uses a lower PA supply power. PA The PA supply power may be decreased by decreasing PA supply voltage or PA supply current. Consequently, transmission efficiency of the radio network node is improved.

[00025] The described method may be used together with other methods for improving power efficiency of a transmitter, such as PA linearization and crest factor reduction (CFR).

[00026] In CFR methods, the output signal is clipped such that peaks of the output signal are transmitted on a lower power level, i.e. peaks of the output signal are clipped. Thereby, less out-of-band emissions are generated and higher power efficiency of the transmitter is achieved. However, by clipping an output signal, the output signal itself is disturbed, which results in a higher Bit Error Rate (BER) and/or a higher Error Vector Magnitude (EVM). Consequently, there is a trade-off between clipping of the signal to achieve lower out-of-band emissions and no clipping of the signal in order not to distort the output signal.

[00027] In an embodiment, the transmitter characteristic that is adapted is the CFR clipping level. In this case the CFR clipping level is adapted based on the comparison between the measured level of out-of-band emissions and the predefined threshold. If the comparison shows that the CFR clipping level can be increased, the CFR clipping level is increased to a level such that the current level of out-of-band emissions does not exceed the predefined threshold. Thereby, an improved signal quality is achieved while the PA power level is maintained.

Consequently, an increased transmission efficiency is achieved. For example, a more complex modulation scheme or higher transmission rate may be selected which increases transmitter efficiency by increasing throughput. In other words, an increased transmission efficiency can be achieved without risking too much output signal disturbances, neither as in-band disturbances nor as out-of-band emissions. .

[00028] Figure 2 shows a network node comprising a transmitter, TX, 10 and an antenna 30. The transmitter comprises a PA 12. The transmitter may also comprise a CFR unit 22. An input signal is fed to the CFR unit 22, if there is a CFR unit, and, after passing the CFR unit 22, the input signal is fed to the PA 12. In the PA 12, the input signal is amplified to an output signal according to a power amplifier characteristic such as the one shown in figure 1 . The output signal is fed to the antenna 30 for further wireless transmission to another network node. The PA 12 also comprises an input for supply power, P_Dc, for driving the PA 12. The network node may comprise many other units, which are not shown in figure 2 in order to make the figure easier to understand. Such units may be digital to digital converters (DDC), digital to analog converters (DAC), analog to digital converters (ADC), modulation units, up-conversion units, demodulation units, down- conversion units etc. [00029] Such a network node, whether or not it has a CFR unit, may give rise to unwanted emissions such as out-of-band emissions and spurious emissions. Out- of-band emissions are disturbances generated as distortions of the original signal, which disturbances are situated outside the transmission frequency band of the radio network node/transmitter. The out-of-band emissions are generated from non-linearities of the transmitter, mainly from non-linearities when amplifying the signal in the PA 12, and from the modulation process. Figure 3 shows the output signal as a function of frequency and amplitude comprising out-of-band emissions and in-band signals. In the figure, frequency components of the out-of-band emissions and of the in-band signal are illustrated. However, in practice the output signal is a modulated signal within a pre-defined channel bandwidth and as such represented as a continuous curve with a varying amplitude, but in principle highest amplitude closest to the in-band signal and with a slowly decreasing amplitude the further away in frequency from the in-band signal.

[00030] There are mandatory requirements defined by the 3rd Generation

Partnership Project (3GPP) for out-of-band emissions. Also, there are type approval specifications, defined by e.g. Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI) that need to be met before parts of a wireless network, such as radio network nodes can be sold and put in drift to specific markets. The 3GPP requirements and type approval requirements and other similar requirements are hereinafter called regulatory requirements for out-of-band emissions. The radio network nodes, such as radio base stations, should be designed to meet all these regulatory requirements at worst case scenarios, such as highest possible temperature and highest possible PAR, operation at transmitter band edge and highest output power. However, most use cases are not as pessimistic as the worst case scenario. For example, when the temperature gets lower, the PA 1 dB compression point will be higher and so the level of out-of-band emission will be lower. As another example, for configurations generally having lower PAR values, such as a configuration having only 1 LTE carrier, there is a larger back-off from the PA 1 dB compression point, resulting in a lower out-of-band emission level, than for highest possible PAR. As yet another example, if the output power at the antenna is lower than the highest output power the level of out-of-band emission will be lower than for highest possible PAR. Also, there is a design margin reserved for components batch variation and aging. As shown above, in most cases the out-of-band emission is less than stipulated by the regulatory requirements.

[00031 ] The present invention is based on the understanding that this over- design is a waste of resources at the transmitter. It would be advantageous to achieve a higher transmission efficiency by e.g. having the PA work at an average operating point that lies closer to the 1 dB compression point at most times.

[00032] According to an embodiment described in figure 4, a higher transmission efficiency is achieved by a method performed by a radio network node in a wireless communication network, which method is used for controlling

transmission of signals from the radio network node. The radio network node comprises a transmitter 10 having a power amplifier 12 (see e.g. fig. 2). The method comprises: measuring 102, on a signal to be transmitted from the radio network node, a level of out-of band emissions after the signal to be transmitted has been amplified by the power amplifier 12; detecting 104 a difference, D, between the measured level of out-of-band emissions and a pre-defined out-of- band emission threshold, and adapting 106 characteristics of the transmitter based on the detected difference D, such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

[00033] This method may be further explained in light of the graph of figure 3. Here a typical level of out-of-band emissions could be seen at a certain moment. As illustrated, the out-of-band emission threshold is higher than the current level of out-of-band emissions, i e it is higher than the amplitude of any one of the frequency components contributing to the out-of-band emissions. More generally, this means that a measure of the level of out-of-band emissions is at or below the out-of-band emission threshold. The measure may be the level of the highest peak of any one of the out-of-band emission frequency components, or any other value reflecting the amount of out-of-band emissions, as long as the threshold is set in correspondence with the measure to control that the level of out-of-band emissions is kept within the limits of the regulatory requirements. By measuring the level of out-of-band emissions, and detecting the difference D between the measured level and the out-of-band emission threshold, the difference D may be used to adapt transmitter characteristics such that the level of out of-band emission rises to a higher level but to a level that still does not exceed the out-of- band emission threshold. The difference D between the measured level of out-of- band emissions and the out-of-band emission threshold is illustrated in figure 3. An example of adapting transmitter characteristics that will lead to more efficient usage of the transmitter, is to decrease the supply power to the PA. When decreasing supply power to the PA, the PA will of course use less energy and thereby be used more efficiently. At the same time, when supply power is decreased, it will be more difficult for the PA to linearly amplify the input signal, and the 1 dB compression point will be moved towards the working point of the PA (see figure 1 ), if the same input power is fed to the PA. Consequently, there will be a higher level of out-of-band emissions. But as long as the current level of out-of- band emissions is controlled and kept on a level that does not exceed the predefined out-of-band emission threshold, this increase is acceptable and does not risk that the regulatory requirements are violated. As a result, a similar output power level is achieved from a lower supply power. Consequently, the transmitter is more efficiently used.

[00034] According to an embodiment, the adapting 106 of the characteristics of the transmitter based on the detected difference D comprises:

when the measured level of out-of band emissions is below the pre-defined out-of band emission threshold, adapting the characteristics of the transmitter such that an increase in out-of band emissions up to or just below the pre-defined out-of- band emission threshold is achieved, and

when the measured level of out-of band emissions exceeds the pre-defined out-of band emission threshold, adapting the characteristics of the transmitter such that a decrease in out-of band emissions down to or just below the pre-defined out-of- band emission threshold is achieved. [00035] When the characteristics of the transmitter is adapted such that the out- of-band emissions are increased to a level up to or just below the out-of-band emission threshold, it might happen that later on the measuring step detects that the out-of-band emissions are above the threshold, or are about to become above the threshold. Therefore it is also necessary to adapt the characteristics of the transmitter such that a decrease in out-of-band emissions down to or just below the predefined out-of-band emission threshold is achieved.

[00036] According to an embodiment, the pre-defined out-of-band emission threshold is defined based on regulatory requirements on out-of band emissions. For example, the pre-defined out-of-band emission threshold may be set to a level similar to the regulatory requirements or to a level just below the regulatory requirements. A suitable level just below the regulatory requirements may be 1 -3 dB below the regulatory requirements.

[00037] According to another embodiment, the adapting 106 of characteristics of the transmitter based on the detected difference D comprises adapting a power level of the power amplifier 12 based on the detected difference D such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

[00038] As mentioned earlier, the PA is fed by a supply power. The supply power of the PA is defined as the power, i.e. supply voltage and supply current, that supplies the PA with energy for amplifying the signal to be transmitted, received as a low power level signal input to the PA, to an output signal which can be sent wirelessly to a receiver. According to an embodiment, the adapting 106 of characteristics of the transmitter based on the detected difference D comprises adapting 107 the supply power level based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold. This embodiment is also shown in figure 5.

[00039] Figure 5 shows a method performed by a radio network node in a wireless communication network, for controlling transmission of signals from the radio network node, the radio network node comprising a transmitter 10 having a power amplifier 12. The method comprises: measuring 102, on a signal to be transmitted from the radio network node, a level of out-of band emissions, after the signal to be transmitted has been amplified by the power amplifier 12; detecting 104 a difference, D, between the measured level of out-of-band emissions and a pre-defined out-of-band emission threshold, and adapting 107 a supply power level of the power amplifier based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold. The PA supply power level may be adapted by adapting the supply voltage level or by adapting the supply current level.

[00040] The power efficiency of radio network nodes such as radio base stations is becoming a major concern because of rising cost of energy and due to environmental impact consciousness. The PA is the largest consumer of power in a radio base station. The PA's ability to convert the DC power supply into signal power may be a measure of PA efficiency. This ability may be defined as the PA power added efficiency, PAE, and can be represented in the following equation:

P - P P - P

x

¹ P DC V DC 1 DC where P_out is the output power of the PA, P_in is the input power of the PA, P_Dc is the supply power of the PA, V_Dc is the supply voltage of the PA and l_Dc is the supply current of the PA. As could be read out from the equation above, PA PAE will increase if PA supply voltage and PA supply current can be reduced. By reducing PA supply power the 1 dB compression point will move down the slope of figure 1 , towards the average operating point of the PA. In some situations, it may however be necessary to increase the input power somewhat in order to achieve the same output power when the supply power is decreased.

[00041 ] Alternatively or additionally, the input power level, i.e. the level of the power fed into the power amplifier to be amplified, may be adapted. In one alternative embodiment, the adapting 106 of characteristics of the transmitter based on the detected difference D comprises adapting the input power level for the signal to be transmitted based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold. If the input power is increased, the output power will also increase and there will be an increased efficiency of the transmitter, since a small increase of input power normally results in a larger increase of output power. Also, it is much cheaper to increase input power (which is low) than to increase amplification. An increase of input power will lead to that the PA has its average operating point closer to the 1 dB compression point, which would result in higher out-of-band emissions. But, as mentioned, the out-of-band emissions are controlled such that they do not exceed the pre-defined out-of-band emission threshold. Further, in this embodiment a control of in-band distortions may be needed.

[00042] Figures 6 and 7 show the function of the CFR unit 22. As mentioned, CFR is a method to reduce the magnitude of peaks of an input signal and thereby achieve a lower PAR. By clipping the input signal, i.e. the original signal x(n) in figure 6, at a defined signal level clipping threshold, the highest peaks are avoided, such peaks which result in high out-of-band emissions since they are amplified in the non-linear area of the PA. Alternatively, the clipping threshold may be set at a defined amplitude whereby input signals having a higher amplitude than the defined amplitude are clipped at the defined amplitude clipping threshold.

Consequently, the more the PAR can be reduced, the higher the average output power can be. Figure 7 illustrates the movement of the average operating point to a new operating point which can be used when using CFR. As shown, the operating point has been moved closer to the 1 dB compression point by the same amount as the reduction of PAR, see PAR after CFR and PAR before CFR in figure 7. However, in the frequency domain, CFR transforms the energy in the peaks of the input signal to uncorrelated noise within and outside the transmission frequency bandwidth. This will degrade the signal quality. A signal to be

transmitted need to fulfill a certain signal quality. The signal quality may be measured by BER or EVM. EVM is a measure of the fidelity of a digital

communication system. The EVM is the root-mean-square (RMS) value of an error vector over time at instants of symbol clock transitions or chip clock transitions. Consequently, when using CFR to increase power efficiency of a PA there is a risk that the signal quality of the amplified signal within the transmission frequency bandwidth becomes too weak, i.e. that the EVM becomes too weak.

[00043] By having control of the out-of-band emissions and keeping the level of out-of-band emissions just a little lower than the regulatory requirements, the clipping threshold, e. g. the signal strength clipping threshold, of the CFR may in some situations be increased and the out-of-band emissions will still be below the pre-defined out-of-band emission threshold, so that the regulatory requirements are not violated. By increasing the clipping threshold, less noise will be emitted in the channel and the signal quality will consequently increase. That is, EVM and thereby also BER will increase and there will still be out-of-band emissions below the pre-defined out-of-band emission threshold, thereby avoiding violating the regulatory requirements. Improved BER will benefit transmission efficiency and consequently the network throughput may increase, for example in that higher modulation order can be used.

[00044] The above described aspects may be realized according to an

embodiment described in figure 8. In fig. 8 a method performed by a radio network node in a wireless communication network for controlling transmission of signals from the radio network node is described. The radio network node comprises a transmitter 10 having a power amplifier 12. The method comprises: clipping 101 the signal to be transmitted at a defined clipping threshold, wherein the clipping may e.g. be performed in a CFR unit 22 of the transmitter 10, measuring 102 on a signal to be transmitted from the radio network node, a level of out-of band emissions after the signal to be transmitted has been amplified by the power amplifier 12, detecting 104 a difference, D, between the measured level of out-of- band emissions and a pre-defined out-of-band emission threshold, and adapting 108 the defined clipping threshold based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold. Thereby, a better EVM and consequently a higher BER is achieved while the level of out-of-band emissions is still below the pre-defined out- of-band emission threshold so that the regulatory requirements are not violated. As a result a higher network throughput may be achieved with an acceptable out- of-band emission.

[00045] According to an embodiment, which may be used for all embodiments of the invention, the level of out-of-band emissions is continuously measured during use of the transmitter and the characteristics of the transmitter is continuously adapted to the detected difference between the measured level of out-of-band emissions and the predefined out-of-band emission threshold such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold. Thereby, a suitable and/or efficient transmitter characteristic is achieved and it is still continuously controlled that the level of out-of-band emissions does not exceed the predefined out-of-band emissions threshold during use of the transmitter.

[00046] Further, it may be possible to use a combination of the method described in figure 5 and the method described in figure 8. In other words, after detecting a difference D between the measured level of out-of-band emissions and a predefined out-of-band emission threshold, the supply power level and the clipping threshold may be adapted based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold. Consequently, there may be a compromise between the amount of adaptation of the supply power level and the amount of adaptation of the clipping threshold. A control unit in the radio network node may decide if the supply power level or the clipping threshold should be adapted, or if there should be a

compromise between the amount of adaptation of the supply power level and the amount of adaptation of the clipping threshold. Alternatively, it may be predefined by the operator which method to use.

[00047] Figure 9 describes a radio network node in a wireless communication network according to an embodiment. The radio network node is configured to control transmission of signals from the radio network node, the radio network node comprising a transmitter 10 having a PA 12. The radio network node comprises a measuring unit 202 configured to measure on a signal to be

transmitted from the radio network node a level of out-of band emissions, after the signal to be transmitted has been amplified by the PA, a detection unit 204 configured to detect a difference, D, between the measured level of out-of-band emissions and a pre-defined out-of-band emission threshold, and a control unit 206 configured to adapt characteristics of the transmitter based on the detected difference D, such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

[00048] In the embodiment described in relation to figure 9, a signal to be transmitted from the radio network node is received at an input 42 of the

transmitter 10. Thereafter, the signal is amplified by the PA 12 of the transmitter 10 and delivered as an output signal 44 for transmission wirelessly by the antenna 30. Further, the output signal 44, which is the signal to be transmitted from the radio network node after it has passed the PA, is also fed to the measuring unit 202, and further to the detection unit 204 and further to the control unit 206. The control unit 206 is configured to adapt characteristics of the transmitter 10, such as a clipping threshold of a CFR unit 22, e g as shown in figure 10, or a supply voltage or supply current of the PA 12, such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold. The input for supply voltage/ supply current to the PA 12 is illustrated by the input P_Dc in fig. 9.

[00049] Figure 10 illustrates another embodiment of a radio network node.

Except for the units already explained in relation to figure 9, figure 10 shows a CFR unit 22 configured to clip the signal to be transmitted at a defined clipping threshold, a digital to analog converter (DAC) 24 configured to convert a digital input signal into an analog signal, a modulation and up-conversion unit 26 configured to modulate the signal to be transmitted and to convert the signal from a low frequency to a radio frequency. A PA linearization unit (not shown) may also be arranged before the PA 12, for example between the CFR 22 and the DAC 24. Further, figure 10 also illustrates a demodulation and down-conversion unit 28 and an analog to digital converter (ADC) 30 arranged in the line that branches off from the output signal, towards the measuring unit 202. In this embodiment, the demodulation and down-conversion unit 28 and the ADC 30 are configured to convert the output signal to a format that is measurable for the measuring unit 202, which in this embodiment may be realized as a digital out-of-band emission meter.

[00050] According to an embodiment, the control unit 206 is configured to adapt characteristics of the transmitter based on the detected difference D by:

when the measured level of out-of band emissions is below the pre-defined out-of band emission threshold, adapt the characteristics of the transmitter 10 such that an increase in out-of band emissions up to or just below the pre-defined out-of- band emission threshold is achieved, and when the measured level of out-of band emissions exceeds the pre-defined out-of band emission threshold, adapt the characteristics of the transmitter 10 such that a decrease in out-of band emissions down to or just below the pre-defined out-of-band emission threshold is achieved.

[00051 ] According to an embodiment, the pre-defined out-of-band emission threshold is defined based on regulatory requirements on out-of band emissions. For example, the pre-defined out-of-band emission threshold may be set to a level similar to the regulatory requirements or to a level just below the regulatory requirements.

[00052] According to another embodiment, the radio network node comprises a CFR unit 22 configured to clip the signal to be transmitted at a defined clipping threshold. Further, the control unit 206 is configured to adapt characteristics of the transmitter 10 by adapting the clipping threshold of the CFR unit 22 based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold. This is illustrated in fig. 10 by the dotted arrow from the control unit 206 towards the CFR unit 22.

[00053] According to another embodiment, the control unit 206 is configured to adapt characteristics of the transmitter based on the detected difference D by adapting a power level of the power amplifier 12 based on the detected difference D such that the level of out-of-band emissions does not exceed the predefined out- of-band emission threshold.

[00054] According to another embodiment, the power amplifier 12 is configured to be fed by a supply power. Further, the control unit 206 is configured to adapt characteristics of the transmitter based on the detected difference D by adapting the supply power level based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold. The supply power level may be adapted by either adapting supply current or supply voltage. This is illustrated in fig. 10 by the dotted arrow from the control unit 206 towards the PA 12, at the P_Dc input.

[00055] According to another embodiment, the control unit 206 is configured to adapt characteristics of the transmitter based on the detected difference D by adapting the input power level for the signal to be transmitted based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold.

[00056] According to another embodiment, the radio network node is a radio base station or a user equipment.

[00057] The radio network node of figures 9 and 10 further comprises a memory 32. In the memory 32, according to an embodiment, a computer program can be stored, which when loaded into a processor and run on the radio network node is arranged for carrying out the method described in the embodiments of this disclosure. According to another embodiment, a computer program product is disclosed, comprising computer-readable code means which can be stored in the memory 32. When run on e.g. a processor of the control unit 206 in the radio network node, the computer-readable code means causes the node to perform the methods described in the embodiments of this disclosure.

[00058] While the solution has been described with reference to specific exemplary embodiments, the description is generally only intended to illustrate the inventive concept and should not be taken as limiting the scope of the solution. The solution is defined by the appended claims.

Claims

1 . A method performed by a radio network node in a wireless

communication network, for controlling transmission of signals from the radio network node, the radio network node comprising a transmitter (10) having a power amplifier (12), the method comprising:

measuring (102), on a signal to be transmitted from the radio network node, a level of out-of band emissions, after the signal to be transmitted has been amplified by the power amplifier (12);

detecting (104) a difference, D, between the measured level of out-of- band emissions and a pre-defined out-of-band emission threshold; and

adapting (106) characteristics of the transmitter based on the detected difference D, such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

2. Method according to claim 1 , wherein the adapting (106) of the characteristics of the transmitter based on the detected difference D comprises: when the measured level of out-of band emissions is below the pre-defined out-of band emission threshold, adapting the characteristics of the transmitter such that an increase in out-of band emissions up to or just below the pre-defined out-of- band emission threshold is achieved, and

when the measured level of out-of band emissions exceeds the pre-defined out-of band emission threshold, adapting the characteristics of the transmitter such that a decrease in out-of band emissions down to or just below the pre-defined out-of- band emission threshold is achieved.

3. Method according to claim 1 or 2, wherein the pre-defined out-of-band emission threshold is defined based on regulatory requirements on out-of band emissions, and wherein the pre-defined out-of-band emission threshold is set to a level similar to the regulatory requirements or to a level just below the regulatory requirements.

4. Method according to any of claims 1 -3, further comprising: clipping (101 ) the signal to be transmitted at a defined clipping threshold;

and wherein the adapting (106) of characteristics of the transmitter involves adapting (108) the clipping threshold based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold.

5. Method according to any of claims 1 -4, wherein the adapting (106) of characteristics of the transmitter based on the detected difference D comprises adapting a power level of the power amplifier (12) based on the detected difference D such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

6. Method according to any of claims 1 -5, wherein the power amplifier is fed by a supply power, and wherein the adapting (106) of characteristics of the transmitter based on the detected difference D comprises adapting (107) the supply power level based on the detected difference D such that the level of out- of-band emissions does not exceed the pre-defined out-of-band emission threshold.

7. Method according to claim 5, wherein the adapting (106) of

characteristics of the transmitter based on the detected difference D comprises adapting the input power level for the signal to be transmitted based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold.

8. Method according to any of the preceding claims, wherein the radio network node is a radio base station or a user equipment.

9. A radio network node in a wireless communication network, configured to control transmission of signals from the radio network node, the radio network node comprising a transmitter (10) having a power amplifier (12), the radio network node comprising: a measuring unit (202), configured to measure, on a signal to be transmitted from the radio network node, a level of out-of band emissions, after the signal to be transmitted has been amplified by the power amplifier;

a detection unit (204) configured to detect a difference, D, between the measured level of out-of-band emissions and a pre-defined out-of-band emission threshold; and

a control unit (206) configured to adapt characteristics of the transmitter based on the detected difference D, such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

10. Radio network node according to claim 9, wherein the control unit (206) is configured to adapt characteristics of the transmitter based on the detected difference D by:

when the measured level of out-of band emissions is below the pre-defined out-of band emission threshold, adapt the characteristics of the transmitter (10) such that an increase in out-of band emissions up to or just below the pre-defined out-of- band emission threshold is achieved, and

when the measured level of out-of band emissions exceeds the pre-defined out-of band emission threshold, adapt the characteristics of the transmitter (10) such that a decrease in out-of band emissions down to or just below the pre-defined out-of- band emission threshold is achieved.

1 1 . Radio network node according to claim 9 or 10, wherein the pre-defined out-of-band emission threshold is defined based on regulatory requirements on out-of band emissions, and wherein the pre-defined out-of-band emission threshold is set to a level similar to the regulatory requirements or to a level just below the regulatory requirements.

12. Radio network node according to any of claims 9-1 1 , further comprising:

a crest factor reduction unit (22) configured to clip the signal to be transmitted at a defined clipping threshold;

and wherein the control unit (206) is configured to adapt characteristics of the transmitter (10) by adapting the clipping threshold based on the detected difference D such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

13. Radio network node according to any of claims 9-12, wherein the control unit (206) is configured to adapt characteristics of the transmitter based on the detected difference D by adapting a power level of the power amplifier (12) based on the detected difference D such that the level of out-of-band emissions does not exceed the predefined out-of-band emission threshold.

14. Radio network node according to any of claims 9-13, wherein the power amplifier (12) is fed by a supply power, and wherein the control unit (206) is configured to adapt characteristics of the transmitter based on the detected difference D by adapting the supply power level based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold.

15. Radio network node according to claim 13, wherein the control unit (206) is configured to adapt characteristics of the transmitter based on the detected difference D by adapting the input power level for the signal to be transmitted based on the detected difference D such that the level of out-of-band emissions does not exceed the pre-defined out-of-band emission threshold.

16. Radio network node according to any of claims 9-15, wherein the radio network node is a radio base station or a user equipment.

17. A computer program product comprising computer readable code means, which when run in a radio network node causes the node to perform the method according to any of claims 1 -8.