HK1242905A1 - Energy efficient transmitter power control - Google Patents

Description

Power control for energy efficient transmitter

Technical Field

The present disclosure relates to wireless communication systems, and more particularly to transmitter power control for point-to-point microwave radio links implementing Adaptive Coding and Modulation (ACM).

Background

A microwave radio link or radio link system is a communication system that transmits data between two fixed locations over point-to-point links. The microwave radio link transmitter and receiver are typically comprised in one unit, here denoted as a microwave transceiver.

Radio transmissions, such as microwave radio transmissions, typically interfere with adjacent communication systems. If the microwave radio transmission is strong enough, this interference can degrade the performance of the adjacent communication system, at least in the case of overlapping frequency spectra. Accordingly, it is desirable to reduce radio interference in wireless communication systems.

Power consumption is a significant contributor to the cost of the owner of a data transmission system (e.g., a microwave radio link). As networks become more dense, power consumption becomes even more important as the number of radio links continues to increase. Not only the operational expenditure (OPEX) of electrical energy but also the capital expenditure (CAPEX) associated with, for example, the size of the electrical distribution. Therefore, power consumption is a problem that adversely affects Total Cost of Ownership (TCO) in a communication system, and therefore, reduction of power consumption is required.

Disclosure of Invention

It is an object of the present disclosure to seek microwave transceivers, DSP circuits and methods that mitigate, alleviate or eliminate one or more of the above-identified deficiencies in the art and disadvantages singly or in any combination.

This object is achieved by a microwave transceiver comprising a data buffer, an adaptive coding and modulation ACM module, a power amplifier PA and an antenna. The ACM module is configured to receive buffered data from the data buffer and modulate the buffered data in a modulation format having spectral efficiency. The PA is configured to receive the modulated buffered data from the ACM module and to transmit the amplified modulated buffered data at an output power to a remote microwave transceiver via an antenna. The modulation format is selected from a plurality of modulation formats based on a feedback signal from a remote microwave transceiver. The microwave transceiver further comprises a control module configured to monitor a buffer status of the data buffer and to control an output power of the PA based on the monitored buffer status.

Thus, the overall cost of ownership of the microwave transceiver is reduced. In particular, a reduced power consumption of the microwave transceiver is obtained due to the control of the PA output power.

Furthermore, selecting a spectral efficiency that is appropriate for the current traffic conditions results in reduced signal processing of the microwave transceiver, thereby reducing the power consumption of the microwave transceiver.

Thereby, radio interference to neighboring communication systems is also reduced due to the control of the output power of the PA.

The reduction in power consumption achieved by the present technique may also affect Mean Time Before Failure (MTBF) in a positive way, since the components (in particular the PA) run colder for certain periods of time.

According to some aspects, the buffer status comprises a buffer fill level of the data buffer. The buffer fill level indicates when the buffer status is such as to allow for a reduction in the spectral efficiency of the transmission without risking buffer overflow.

Thus, according to these aspects, the control module is configured to decrease the output power of the PA when the buffer filling level is below a first predetermined threshold, and to increase the output power of the PA when the buffer filling level is above a second predetermined threshold.

According to some other aspects, the buffer status includes a priority level of data in the current data buffer. Then, the control module is configured to: the output power of the PA is increased when the priority level of the data in the current data buffer is above a priority threshold, and the output power of the PA is decreased when the priority level of the data in the current data buffer is below the priority threshold.

Thus, high priority data is not or less affected by an increase in transmission delay due to control of the output power of the PA and variations in spectral efficiency of data transmission by the microwave transceiver.

According to some other aspects, the buffer status comprises a predicted future buffer fill level, and when the control module is configured to: the output power of the PA is controlled based on the predicted future buffer fill level.

Thus, a faster response to changes in the buffer status is obtained, resulting in a reduced risk of e.g. buffer overflow and a reduced transmission delay.

The above object is also achieved by a digital signal processor, DSP, circuit comprising an input data port, a data buffer and an adaptive coding and modulation, ACM, module. The data buffer is configured to: data is received on an input data port and buffered data is output on an output data port to the ACM module. The ACM module is configured to: the buffered data is received and modulated in a modulation format having spectral efficiency, and the modulated buffered data is output on an output port of the DSP circuit. The modulation format is selected from a plurality of modulation formats based on a feedback signal received on an ACM feedback port of the DSP circuit. The DSP circuit further includes: a control module configured to monitor a buffer status of the data buffer and to output a power control signal on a power control port of the DSP circuit for controlling an output power of a power amplifier PA connectable to the DSP circuit based on the monitored buffer status.

Also disclosed herein are devices including the above-described DSP circuit, and methods in the DSP circuit for controlling the spectral efficiency of data transmission of the DSP circuit. The DSP circuit includes a data buffer and an adaptive coding and modulation, ACM, module. The ACM module is configured to modulate buffered data received from the data buffer in a modulation format having spectral efficiency. The method comprises the following steps: the buffer status of the data buffer is monitored and a power control signal for controlling the output power of a PA connectable to the DSP circuit is generated based on the monitored buffer status.

In addition to the above-described methods, there is provided herein a computer program comprising computer program code which, when executed in DSP circuitry, causes the DSP circuitry to perform a method according to the present teachings.

The DSP circuit, a device comprising the DSP circuit, a computer program and a method all show advantages corresponding to those already described for a microwave transceiver.

Drawings

Further objects, features and advantages of the present disclosure will appear from the following detailed description, wherein some aspects of the present disclosure will be described in more detail, with reference to the accompanying drawings, in which:

fig. 1 is a block diagram illustrating a radio link according to the present disclosure.

Fig. 2 is a block diagram illustrating a digital signal processing circuit according to the present disclosure.

Fig. 3 illustrates a diagram showing an example sequence of events in accordance with aspects of the present disclosure.

Fig. 4 is a flow chart illustrating a method according to the present disclosure.

Fig. 5 is a block diagram illustrating DSP circuitry according to the present disclosure.

Detailed Description

The present teachings relate to optimization of energy consumption in communication systems, and in particular, in microwave radio links implementing data transmission through Adaptive Coding and Modulation (ACM) or adaptive coding and modulation and baud rate (ACMB).

The main idea of the present disclosure relates to adjusting the output power of a Power Amplifier (PA) for data transmission based on the buffer status of a data buffer. The output power adjustment is done such that the PA output power is reduced when there is only a small amount of data or data with a lower priority level, and increased as the buffer fills or when the buffer contains high priority data.

This results in the ACM system automatically responding to the changed power level by adjusting the spectral efficiency of the data transmission to match the current power level, thereby avoiding transmission errors despite the reduced output power. Due to the control of the output power of the PA, the power consumption of the microwave transceiver is reduced, resulting in a reduction of the Total Cost of Ownership (TCO). Another advantage of the present technique is that there is no need to specifically control the spectral efficiency, as this is handled by existing ACM systems, which enables the proposed technique to be implemented efficiently.

Furthermore, with the proposed technique, the spectral efficiency is selected to be suitable for the current traffic conditions, resulting in a reduced processing requirement of the microwave transceiver, thereby further reducing the power consumption of the microwave transceiver.

A problem with almost any electronic device is component wear or component aging, which ultimately leads to device failure. A measure of component aging is its Mean Time Before Failure (MTBF). It is known that thermal assemblies operating under high load conditions typically age faster than components that are allowed to operate under less stress (i.e., operate in a cooler state). The reduction in power consumption achieved by the present technique therefore also affects the MTBF in a positive way, since the components (in particular the PA) run cooler.

Thereby, radio interference to neighboring communication systems is also reduced due to the control of the output power of the PA.

Another advantage resulting from the transmission with reduced spectral efficiency is the increased resilience of the microwave transceiver to external interference.

Aspects of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. The computer programs and methods disclosed herein may, however, be embodied in many different forms and should not be construed as limited to the embodiments and aspects set forth herein. Throughout the drawings, like reference numerals designate like elements.

The terminology used herein is for the purpose of describing particular aspects of the disclosure only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Fig. 1 shows a radio link according to the present disclosure. In particular, a microwave transceiver 100 is shown, comprising a data buffer 110, an Adaptive Coding and Modulation (ACM) module 120, a Power Amplifier (PA)130 and an antenna 140. The microwave transceiver 100 is configured to communicate with a remote microwave transceiver 180 over a point-to-point link 170. Thus, data input to the data input port 111 is transmitted over the radio link and output from the remote microwave transceiver 180 on the output data port 181. The microwave transceiver 100 constitutes one point of a point-to-point microwave radio link 170 and the remote microwave transceiver 180 constitutes another point of said point-to-point microwave radio link 170.

The microwave transceiver 100 shown in fig. 1 and discussed herein only shows a transmitter chain ending with a PA130 and an antenna 140. It should be understood, however, that a transceiver will typically also include a receiver chain for receiving data over point-to-point link 170. This is indicated by the double-headed arrow of the point-to-point link 170.

The microwave transceiver 100 implements ACM or, according to some aspects, adaptive coding, modulation, and baud rate (ACMB). ACM is a mechanism that adjusts the spectral efficiency (typically measured in bits/second/Hz) of data transmission according to current transmission conditions. Thus, as the attenuation and/or interference of a hop increases, the spectral efficiency of the transmission decreases and increases as the transmission conditions improve. Since a reduced spectral efficiency leads to an improved detection resilience, a low error rate can be maintained during reduced transmission conditions. The ACM is typically fed back over an ACM feedback channel 121 from the receiver that transmitted the data, which is used to determine the appropriate modulation and/or coding level, i.e., modulation format and channel code, which together determine the spectral efficiency of the data transmission. In addition to the change in spectral efficiency of the transmitted signal, ACMB further changes the baud rate of the transmitted signal, thereby changing the channel frequency bandwidth occupied by the transmitted signal.

Thus, the ACM module 120 is configured to receive buffered data from the data buffer 110 and modulate the buffered data in a modulation format having spectral efficiency. The PA130 is configured to receive the modulation buffered data from the ACM module 120 and transmit the amplified modulation buffered data at an output power to a remote microwave transceiver 180 via an antenna 140.

A modulation format is selected from a plurality of modulation formats based on a feedback signal from the remote microwave transceiver 180. Examples of modulation formats include quadrature amplitude modulation (M-QAM) of different orders, phase shift keying (M-PSK). Other examples include various modulation formats used with Orthogonal Frequency Division Multiplexing (OFDM).

The microwave transceiver 100 further comprises a control module 150 configured to monitor a buffer status of the data buffer 110 and to control the output power of the PA130 based on the monitored buffer status.

The sequence of events is initiated by monitoring the buffer status (e.g., buffer fill level, buffer read/write pointer, buffer fill rate, etc.) and controlling the PA output power based on the monitored status. This sequence of events will be discussed further below in connection with fig. 3, but it is assumed that e.g. the buffer fill level is to allow transmission at reduced spectral efficiency without risking buffer overflow. In this case, the PA output power of the transmitter is reduced. The receiver 180 then detects a corresponding degradation in received signal quality, which prompts the ACM feedback signal 121 from the receiver to request a modulation format and/or coding with reduced spectral efficiency to account for the degradation in received signal quality. Thus, the reduction in output power results in an automatic adjustment of the transmission rate by the ACM system to keep the data transmission at a low error rate but using the reduced output power.

Here, signal quality is to be interpreted broadly, including, for example, signal power, signal-to-noise ratio (SNR), signal-to-interference-and-noise ratio (SNIR), mean square detection error (MSE), etc., which may be used to determine ACM feedback signal 121.

Thus, according to some aspects, the control module 150 is configured to reduce the output power of the PA130 when the buffer filling level is below a first predetermined threshold.

According to other aspects, the control module 150 is configured to continuously adjust the output power as a function of a predetermined or configured buffer fill level. According to some other aspects, the control module 150 is configured to increase the output power of the PA130 when the buffer fill level is above a second predetermined threshold.

As described above, when controlling the PA output power, not only the buffer fill level, the buffer fill rate, or the properties of the currently buffered data are of interest. One such example is a priority level of buffered data, e.g., a priority level indicated in a data header of a data packet, such as an Internet Protocol (IP) packet. Thus, according to some aspects, the buffer status comprises a priority level of data in the current data buffer, and the control module 150 is configured to increase the output power of the PA130 when the priority level of data in the current data buffer meets a predetermined criterion, and to decrease the output power of the PA130 when the priority level of data in the current data buffer meets another predetermined criterion.

Examples of the predetermined criteria include priority levels, different packet types, packet sizes, or information indicating different data flows to be prioritized. One reason for controlling the output power based on priority level is that some data types may be sensitive to delay, in which case it is preferable to send the data at a high rate to minimize transmission delay, regardless of buffer status.

In some cases, future buffer states may be predicted based on past buffer states. One example is to infer the buffer filling level from time, in which case future buffer filling levels may be estimated. In other words, according to some aspects, the buffer status includes a predicted future buffer fill level, and the control module 150 is configured to control the output power of the PA130 based on the predicted future buffer fill level. Another example is to store the arrival time of high priority data from which a pattern of arrival times can be deduced, e.g. a high priority video stream may only occur during office hours. Another example is simply to mark the first arrival occurrence of high priority data, inferring that this single occurrence indicates the likelihood that higher priority data will arrive in the near future (in which case the transmission rate should remain high).

According to different aspects, the control of the PA output power may be activated in different ways, some of which will now be described. In accordance with some such aspects, the control module 150 is configured to control the output power of the PA130 over a continuous range of output powers between minimum and maximum output power levels.

According to some other aspects, the control module 150 is configured to select the output power of the PA130 from a plurality of discrete output powers.

Furthermore, it should be appreciated that due to bandwidth limitations in the Automatic Gain Control (AGC) at the receiver 180 side, the output power of the PA130 should preferably not be abruptly changed in too large a step size, since such large abrupt changes in output power may result in detection errors at the receiver side. Thus, according to some aspects, the output power of the PA is varied at a predetermined rate of change (W/sec) and/or according to a predetermined maximum step size (given in W/step size).

The output power of the PA130 may be set in a number of different ways, for example, according to certain aspects, the control module 150 is configured to select the output power of the PA130 from a look-up table (LUT) of power levels indexed by buffer states.

According to some aspects, the microwave transceiver 100 comprises a limiter module 160. The limiter module 160 is configured to limit control of the output power of the PA130 to output power above a minimum output power and/or to output power below a predetermined maximum output power. It will be appreciated that this type of limiter module may be integrated with an Automatic Transmit Power Control (ATPC) system, wherein the limiter module limits the output power to an acceptable range, wherein data transmission may occur at a given error rate performance.

According to some aspects, the ACM module 120 is further configured to select a channel code and/or a corresponding code rate from a plurality of channel codes and/or code rates, and to apply the channel code when modulating the buffered data, the spectral efficiency being determined by the selected modulation format and the selected channel code and/or code rate.

Fig. 2 is a block diagram illustrating a Digital Signal Processing (DSP) circuit according to the present disclosure, including an input data port 111', a data buffer 110, and an adaptive coding and modulation ACM module 120. The data buffer 110 is configured to receive data on an input data port 111' and output buffered data on an output data port 112 to the ACM module 120. The ACM module is configured to receive and modulate the buffered data in a modulation format having spectral efficiency, and to output the modulated buffered data on the DSP circuit 200 output port 122 ', wherein the modulation format is selected from a plurality of modulation formats based on a feedback signal 121 received on an ACM feedback port 121' of the DSP circuit 200. The DSP circuit 200 further includes: a control module 150 configured to monitor a buffer status of the data buffer 110 and to output a power control signal 151, 151b on a power control port 151 b' of the DSP circuit 200 for controlling the output power of a power amplifier PA connectable to the DSP circuit 200 based on the monitored buffer status.

According to some aspects, the DSP circuit 200 further comprises a limiter module 160. The limiter module 160 is configured to limit the power control signal 151, 151b to an output power corresponding to above a predetermined minimum output power of the PA and/or to an output power corresponding to below a predetermined maximum output power of the PA.

The DSP circuitry provides functionality corresponding to the discussion above in relation to the microwave transceiver. Indeed, according to one embodiment, the microwave transceiver 100 shown in fig. 1 includes a DSP circuit 200. For the sake of brevity, the DSP circuit 200 or other devices that include the DSP circuit 200 will not be discussed further herein, but rather refer to the discussion above regarding the microwave transceiver.

Fig. 3 shows a diagram illustrating an example sequence of events in accordance with the present disclosure to better understand the proposed technique. According to the illustrated scenario, the flow of the data buffer varies over time. First the buffer filling level rises, followed by a period of time when the buffer filling level is relatively stable, and ending with a drop in the buffer filling level. The buffer fill level is here measured as a percentage of the total buffer capacity. The output power of the PA, the spectral efficiency of the ACM, is shown temporally aligned with the pattern of the buffer fill level. The output power is measured as a percentage of the maximum total output power. ACM efficiency is measured here as a percentage of the maximum available spectral efficiency. Four events a-D are marked with dashed lines.

At event 'a', the monitored buffer fill level percentage rises above a first threshold T1. This results in an increase of the PA output power here according to a ramp function. The increase in output power results in improved reception conditions at the receiver, which in turn contributes to an increase in the spectral efficiency of the data transmission of the ACM system. At event 'B', the buffer filling level rises above the second threshold T2, which causes the PA output power to increase further, and subsequently the spectral efficiency of the data transmission to increase further. This spectral efficiency is maintained until an event 'C' occurs, wherein the buffer filling level is again below the second threshold T2, so that the output power decreases, resulting in a decrease of the spectral efficiency of the data transmission. At event 'D', the buffer filling level is below the first threshold T1, resulting in a further reduction in the spectral efficiency of the data transmission.

In terms of power consumption, lower power consumption can be expected before event 'a' and even after event 'D' compared to the period between events 'B' and 'C' using high output power.

Fig. 4 is a flow chart illustrating a method according to the present disclosure. In particular, a method in the DSP circuitry 200 for controlling the spectral efficiency of data transmission of the DSP circuitry is shown. The DSP circuit 200 corresponds to the DSP circuit shown in fig. 2 and discussed above, i.e. it comprises the data buffer 110 and the adaptive coding and modulation ACM module 120. The ACM module 120 is configured to modulate buffered data received from the data buffer 110 in a modulation format having spectral efficiency. The method comprises the following steps: the buffer status of the data buffer 110 is monitored S1 and a power control signal 151, 151b for controlling the output power of the PA130 connectable to the DSP circuit 200 is generated S3 based on the monitored buffer status.

According to some aspects, monitoring S1 includes monitoring S11 a buffer fill level of the data buffer 110.

According to some aspects, monitoring S1 includes predicting S12 a future buffer fill level of the data buffer 110.

According to some aspects, monitoring S1 includes monitoring S13 the priority level of the data currently in the data buffer 110.

According to some aspects, generating S3 further comprises: the power control signal for reducing the output power of the S31 PA130 is generated when the buffer filling level or the predicted future buffer filling level is below a first predetermined threshold.

According to some aspects, generating S3 further comprises: generating a power control signal for increasing the output power of the S32 PA130 when the buffer filling level or the predicted future buffer filling level is above a second predetermined threshold.

According to some aspects, generating S3 further comprises: a power control signal is generated S35 based on the predicted future buffer fill level.

According to aspects, generating S3 further includes: generating a power control signal for increasing the output power of the S33 PA130 when the priority level of the data in the current data buffer is above the priority threshold, and generating S3 further comprises: when the priority level of the data in the current data buffer is below the priority threshold, a power control signal for reducing the output power of the S34 PA130 is generated.

The above aspects of the disclosed method have been discussed in connection with corresponding functions and features of the DSP circuitry and the microwave transceiver and will therefore not be described in further detail here.

Fig. 5 is a block diagram illustrating a DSP circuit for controlling spectral efficiency of data transmission by the DSP circuit according to the present disclosure. The DSP circuit includes: a buffer monitoring module SX1 configured to monitor a buffer status of data buffer 110 of the DSP circuit; and a power control module SX3 configured to generate a power control signal for the DSP circuit that controls the output power of the PA130 connectable to the DSP circuit 200 based on the monitored buffer status.

In addition to the buffer monitoring and power control modules, according to some aspects, the DSP circuitry also includes other modules SX11-SX13 and SX31-SX 35. These modules are configured to perform functions corresponding to the method steps discussed above in connection with fig. 4.

Various example embodiments described herein are described in the general context of method steps or processes, which may be implemented in one aspect by a computer program product embodied in a computer-readable medium including computer-executable instructions, such as program code, executed by computers in network environments. The computer readable medium may include removable and non-removable storage devices including, but not limited to, read only memory ROM, random access memory RAM, compact disk CDs, digital versatile disks DVD, and the like. Generally, program modules may include routines, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes.

Claims (24)

1. A microwave transceiver (100) comprising a data buffer (110), an adaptive coding and modulation, ACM, module (120), a power amplifier, PA, (130) and an antenna (140), the ACM module (120) being configured to receive buffered data from the data buffer (110) and to modulate the buffered data in a modulation format having a spectral efficiency, the PA (130) being configured to: receiving modulated buffered data from the ACM module (120) and transmitting the amplified modulated buffered data at an output power via an antenna (140) to a remote microwave transceiver (180), wherein the modulation format is selected from a plurality of modulation formats based on a feedback signal from the remote microwave transceiver (180), the microwave transceiver (100) further comprising: a control module (150) configured to monitor a buffer status of the data buffer (110) and to control an output power of the PA (130) based on the monitored buffer status.

2. The microwave transceiver (100) of claim 1, wherein the buffer status comprises a buffer fill level.

3. The microwave transceiver (100) of claim 2, wherein the control module (150) is configured to: reducing the output power of the PA (130) when the buffer filling level is below a first predetermined threshold.

4. The microwave transceiver (100) of any one of claims 2 to 3, wherein the control module (150) is configured to: increasing the output power of the PA (130) when the buffer filling level is above a second predetermined threshold.

5. The microwave transceiver (100) of any of claims 1 to 4, wherein the buffer status comprises a priority level of data currently in the data buffer, and the control module (150) is configured to: the output power of the PA (130) is increased when the priority level of the data in the current data buffer is above a priority threshold, and the output power of the PA (130) is decreased when the priority level of the data in the current data buffer is below the priority threshold.

6. The microwave transceiver (100) of any of claims 1 to 5, wherein the buffer status comprises a predicted future buffer fill level, and the control module (150) is configured to: the output power of the PA (130) is controlled based on the predicted future buffer fill level.

7. The microwave transceiver (100) of any one of claims 1 to 6, wherein the control module (150) is configured to: controlling the output power of the PA (130) over a continuous range of output power between minimum and maximum output power levels.

8. The microwave transceiver (100) of any one of claims 1 to 6, wherein the control module (150) is configured to: an output power of the PA (130) is selected from a plurality of discrete output powers.

9. The microwave transceiver (100) of claim 8, wherein the control module (150) is configured to: the output power of the PA (130) is selected from a look-up table LUT of power levels indexed by buffer states.

10. The microwave transceiver (100) of any one of claims 1 to 9, further comprising a limiter module (160), the limiter module (160) being configured to: limiting control of the output power of the PA (130) to an output power above a minimum output power and/or an output power below a predetermined maximum output power.

11. The microwave transceiver (100) of any one of claims 1 to 10, wherein the ACM module (120) is further configured to: selecting a channel code and/or a corresponding code rate from a plurality of channel codes and/or code rates and applying the channel code when modulating the buffered data, the spectral efficiency being determined by the selected modulation format and the selected channel code and/or code rate.

12. The microwave transceiver (100) according to any one of claims 1 to 11, wherein the microwave transceiver (100) constitutes one point of a point-to-point microwave radio link (170) and the remote microwave transceiver (180) constitutes another point of the point-to-point microwave radio link (170).

13. A digital signal processor, DSP, circuit (200) comprising an input data port (111'), a data buffer (110), and an adaptive coding and modulation, ACM, module (120), the data buffer (110) being configured to: receiving data on an input data port (111') and outputting buffered data on an output data port (112) to the ACM module (120); the ACM module is configured to: receiving and modulating the buffered data in a modulation format having spectral efficiency, and outputting the modulated buffered data on an output port (122 ') of the DSP circuit (200), wherein the modulation format is selected from a plurality of modulation formats based on a feedback signal (121) received on an ACM feedback port (121') of the DSP circuit (200), the DSP circuit (200) further comprising: a control module (150) configured to: the buffer status of the data buffer (110) is monitored and a power control signal (151, 151b) for controlling the output power of a power amplifier PA connectable to the DSP circuit (200) is output on a power control port (151 b') of the DSP circuit (200) based on the monitored buffer status.

14. The DSP circuit (200) of claim 13, further comprising: a limiter module (160), the limiter module (160) configured to: limiting the power control signal (151, 151b) to an output power corresponding to above a predetermined minimum output power of the PA and/or to an output power corresponding to below a predetermined maximum output power of the PA.

15. An apparatus comprising the DSP circuit of any one of claims 13 to 14.

16. A method in a DSP circuit (200) for controlling spectral efficiency of data transmission of the DSP circuit, the DSP circuit (200) comprising a data buffer (110) and an adaptive coding and modulation, ACM, module (120), the ACM module (120) being configured to modulate buffered data received from the data buffer (110) in a modulation format having spectral efficiency, the method comprising:

-monitoring (S1) a buffer status of the data buffer (110); and

-generating (S3) a power control signal (151, 151b) for controlling the output power of a PA (130) connectable to the DSP circuit (200) based on the monitored buffer status.

17. The method of claim 16, wherein the monitoring (S1) includes monitoring (S11) a buffer fill level of the data buffer (110).

18. The method of any of claims 16 to 17, wherein the monitoring (S1) comprises: predicting (S12) a future buffer fill level of the data buffer (110).

19. The method of any of claims 16 to 18, wherein the monitoring (S1) comprises: monitoring (S13) a priority level of data currently in the data buffer (110).

20. The method according to claim 17 or 18, wherein the generating (S3) further comprises: generating a power control signal for reducing (S31) the output power of the PA (130) when the buffer filling level or the predicted future buffer filling level is below a first predetermined threshold.

21. The method according to claim 17 or 18, wherein the generating (S3) further comprises: generating a power control signal for increasing (S32) the output power of the PA (130) when the buffer filling level or the predicted future buffer filling level is above a second predetermined threshold.

22. The method of claim 18, wherein the generating (S3) further comprises: generating (S35) the power control signal based on the predicted future buffer fill level.

23. The method of claim 19, wherein the generating (S3) further comprises: generating (S33) a power control signal for increasing (S33) the output power of the PA (130) when the priority level of the data in the current data buffer is above a priority threshold, and generating (S34) a power control signal for decreasing (S34) the output power of the PA (130) when the priority level of the data in the current data buffer is below a priority threshold.

24. A computer program comprising computer program code which, when executed in a DSP circuit (200), causes the DSP circuit (200) to perform the method according to any one of claims 16 to 23.