Crest factor reduction
阅读说明:本技术 波峰因子降低 (Crest factor reduction ) 是由 D·弗明 A·梅格雷特斯基 庄舜杰 Z·马哈茂德 李琰 H·H·金姆 G·斯通 于 2018-06-08 设计创作,主要内容包括:公开了波峰因子降低(CFR)实现,包括如下方法,该方法包括:获得表示包括一个或多个无线电传输频带的通信系统的特性的通信系统数据;以及至少部分地基于输入的通信系统数据来优化CFR系统中所使用的用于确定一个或多个脉冲的相应脉冲形状的多个可更新参数以及其它特定算法执行参数。优化多个可更新参数包括基于多个性能参数的迭代评价来迭代更新多个可更新参数。该方法还包括提供优化后的多个可更新参数,以将波峰因子降低系统配置用于使用应用于通过所述通信系统通信的一个或多个信号的脉冲相减方法来处理信号以供无线电传输。(Crest Factor Reduction (CFR) implementations are disclosed, including a method comprising: obtaining communication system data representing characteristics of a communication system comprising one or more radio transmission bands; and optimizing a plurality of updatable parameters used in the CFR system for determining respective pulse shapes of the one or more pulses and other specific algorithm execution parameters based at least in part on the input communication system data. Optimizing the plurality of updatable parameters includes iteratively updating the plurality of updatable parameters based on an iterative evaluation of the plurality of performance parameters. The method also includes providing an optimized plurality of updatable parameters to configure the crest factor reduction system for processing signals for radio transmission using a pulse subtraction method applied to one or more signals communicated over the communication system.)
1. A method, comprising:
receiving communication system data indicative of characteristics of a communication system comprising one or more radio transmission bands;
optimizing a plurality of updatable parameters used in a crest factor reduction system for determining respective pulse shapes of one or more pulses based at least in part on the received communication system data, wherein optimizing the plurality of updatable parameters comprises iteratively updating a plurality of updatable parameters based on an iterative evaluation of the plurality of performance parameters; and
providing an optimized plurality of updatable parameters for determining respective pulse shapes of the one or more pulses to configure a crest factor reduction system for processing signals for radio transmission using a pulse subtraction method applied to one or more signals communicated over the communication system.
2. The method of claim 1, wherein optimizing the plurality of updatable parameters comprises:
optimizing one or more of: a pulse shape factor to control a level of signal smoothing, a band extension ratio, a band relative weight factor to control a distribution of compensation scaling factors between the one or more radio transmission bands, a hard clipping factor, or a quantization window size value representing a minimum time interval between eliminated peaks.
3. The method of claim 1, wherein receiving the communication system data comprises:
receiving one or more of: an adjacent power value ratio, i.e., ACPR, an up-sampled value, a sampling rate, carrier configuration data, a pulse shape factor value, a band extension ratio, at least one pulse band weight, a hard clipping factor, a pulse length value, a number of peak trackers, a number of crest factor reduction stages, or a quantization window size value representing a minimum time interval between eliminated peaks.
4. The method of claim 1, wherein iteratively updating the plurality of updatable parameters based on an iterative evaluation of a plurality of performance parameters comprises:
defining at least one objective function representing the quality of the respective pulse shape of the one or more pulses;
determining one or more starting point pulse shapes for the one or more pulses based on the received communication system data and starting point values for the plurality of updatable parameters; and
iteratively updating the plurality of updatable parameters based on an iterative calculation of the at least one objective function to provide at least one intermittent output value obtained by applying the crest factor reduction system to a sample input signal using one or more pulse shapes of the intermittence, wherein the one or more pulse shapes of the intermittence are determined based on the received communication system data and the intermittently updated values of the plurality of updatable parameters.
5. The method of claim 4, wherein defining at least one objective function comprises:
an objective function comprising a linear combination of error vector magnitude, EVM, and adjacent channel power ratio, ACPR, is defined according to:
EVM+γ(ACPR-ACPRtarget)×ACPR,
wherein at t>In the case of 0, γ is determined according to the equation γ (t) ═ k1Barrier weight function γ (t) calculated by x t, or at t<In the case of 0, γ is determined according to the equation γ (t) ═ k2X t calculated barrier weight function γ (t), where k1And k2Is a tunable coefficient, and ACPRtargetRepresenting a predetermined target ACPR value.
6. The method of claim 1, further comprising:
configuring the crest factor reduction system with an optimization value; and
processing a received signal for transmission using the crest factor reduction system.
7. The method of claim 6, wherein processing the received signal comprises:
the received signal is pulse-subtracted using the respective one or more pulse shapes determined based at least in part on the optimized plurality of updatable parameters.
8. The method of claim 7, wherein pulse subtracting the received signal comprises:
identifying peaks in an aggregate time domain signal combined by one or more time domain representations of received signals in the one or more radio transmission bands; and
using the determined respective pulse shapes of the one or more pulses, performing individual pulse subtraction processing on respective one or more time-domain representations of respective received signals at a time instance of the received signals determined based at least in part on the identified locations of peaks in the aggregated time-domain signal.
9. The method of claim 8, wherein performing individual pulse subtraction processing comprises:
the respective one or more pulse shapes are weighted based on characteristics of the received signal in the one or more frequency bands.
10. The method of claim 9, wherein the characteristic of the received signal comprises at least a relative signal power of the received signal.
11. A system, comprising:
an interface for receiving communication system data representing characteristics of a communication system comprising one or more radio transmission bands;
an optimization engine configured to optimize a plurality of updatable parameters used in a crest factor reduction system for determining respective pulse shapes of one or more pulses based at least in part on the received communication system data, wherein optimizing the plurality of updatable parameters comprises iteratively updating a plurality of updatable parameters based on an iterative evaluation of the plurality of performance parameters; and
a communication module to provide an optimized plurality of updatable parameters for determining respective pulse shapes of the one or more pulses to configure a crest factor reduction system for processing signals for radio transmission using a pulse subtraction method applied to one or more signals communicated over the communication system.
12. The system of claim 11, wherein the optimizer for optimizing the plurality of updatable parameters is configured to:
optimizing one or more of: a pulse shape factor to control a level of signal smoothing, a band extension ratio, a band relative weight factor to control a distribution of compensation scaling factors between the one or more radio transmission bands, a hard clipping factor, or a quantization window size value representing a minimum time interval between eliminated peaks.
13. The system of claim 11, wherein the optimizer for iteratively updating the plurality of updatable parameters based on an iterative evaluation of a plurality of performance parameters is configured to:
defining at least one objective function representing the quality of the respective pulse shape of the one or more pulses;
determining one or more starting point pulse shapes for the one or more pulses based on the received communication system data and starting point values for the plurality of updatable parameters; and
iteratively updating the plurality of updatable parameters based on an iterative calculation of the at least one objective function to provide at least one intermittent output value obtained by applying the crest factor reduction system to a sample input signal using one or more pulse shapes of the intermittence, wherein the one or more pulse shapes of the intermittence are determined based on the received communication system data and the intermittently updated values of the plurality of updatable parameters.
14. The system of claim 13, wherein the optimizer for defining at least one objective function is configured to:
an objective function comprising a linear combination of error vector magnitude, EVM, and adjacent channel power ratio, ACPR, is defined according to:
EVM+γ(ACPR-ACPRtarget)×ACPR,
wherein at t>In the case of 0, γ is determined according to the equation γ (t) ═ k1Barrier weight function γ (t) calculated by x t, or at t<In the case of 0, γ is determined according to the equation γ (t) ═ k2X t calculated barrier weight function γ (t), where k1And k2Is a tunable coefficient, and ACPRtargetRepresenting a predetermined target ACPR value.
15. The system of claim 11, further configured to:
configuring the crest factor reduction system with an optimization value; and
processing a received signal for transmission using the crest factor reduction system.
16. A method for signal processing in a crest factor reduction system, the method comprising:
identifying peaks in an aggregate time domain signal combined by one or more time domain representations of received signals in one or more radio transmission bands; and
performing individual pulse subtraction processing on respective one or more time domain representations of respective received signals at a time instant of the received signals determined based at least in part on the positions of the identified peaks in the aggregated time domain signal using respective pulse shapes of one or more pulses determined based on optimization of a plurality of updatable parameters, wherein the optimization of the plurality of updatable parameters is based on earlier performance of iterative updating of a plurality of performance parameters according to iterative evaluation of the plurality of performance parameters using predetermined communication system data representing characteristics of a communication system comprising the one or more radio transmission bands at least in part.
17. The method of claim 16, wherein performing individual pulse subtraction processing comprises:
weighting the respective one or more pulse shapes based on characteristics of the received signal in the one or more radio transmission bands.
18. The method of claim 17, wherein the characteristic of the received signal comprises at least a relative signal power of the received signal.
19. The method of claim 16, wherein the optimization of the plurality of updatable parameters comprises optimization of one or more of: a pulse shape factor to control a level of signal smoothing, a band extension ratio, a band relative weight factor to control a distribution of compensation scaling factors between the one or more radio transmission bands, a hard clipping factor, or a quantization window size value representing a minimum time interval between eliminated peaks.
20. The method of claim 16, wherein the communication system data comprises one or more of: an adjacent power value ratio, i.e., ACPR, an up-sampled value, a sampling rate, carrier configuration data, a pulse shape factor value, a band extension ratio, at least one pulse band weight, a hard clipping factor, a pulse length value, a number of peak trackers, a number of crest factor reduction stages, or a quantization window size value representing a minimum time interval between eliminated peaks.
21. The method of claim 16, wherein the iterative updating of the plurality of updatable parameters in accordance with the iterative evaluation of the plurality of performance parameters is performed using at least one objective function representing a quality of a respective pulse shape of the one or more pulses and the iterative updating of the plurality of updatable parameters in accordance with the iterative calculation of the at least one objective function to provide at least one intermittent output value obtained by applying the crest factor reduction system to a sample input signal using intermittent one or more pulse shapes determined based on the communication system data and the intermittent updated values of the plurality of updatable parameters.
22. The method of claim 21, wherein the at least one objective function comprises a linear combination of EVM and ACPR, in accordance with:
EVM+γ(ACPR-ACPRtarget)×ACPR,
wherein at t>In the case of 0, γ is determined according to the equation γ (t) ═ k1Barrier weight function γ (t) calculated by x t, or at t<In the case of 0, γ is determined according to the equation γ (t) ═ k2X t calculated barrier weight function γ (t), where k1And k2Is a tunable coefficient, and ACPRtargetRepresenting a predetermined target ACPR value.
23. A crest factor reduction system, comprising:
peak identification circuitry to identify peaks in an aggregate time domain signal combined by one or more time domain representations of received signals in one or more radio transmission frequency bands; and
a pulse subtraction circuit for performing individual pulse subtraction processing of respective one or more time domain representations of respective received signals at a time instant of the received signals determined based at least in part on the positions of the identified peaks in the aggregated time domain signal using respective pulse shapes of one or more pulses determined based on optimization of a plurality of updatable parameters, wherein the optimization of the plurality of updatable parameters is based on earlier performance of iterative updating of a plurality of performance parameters according to iterative evaluation of the plurality of performance parameters using, at least in part, predetermined communication system data representing characteristics of a communication system comprising the one or more radio transmission frequency bands.
24. The system of claim 23, wherein the pulse subtraction circuit for performing the individual pulse subtraction process is configured to:
weighting the respective one or more pulse shapes based on characteristics of the received signal in the one or more radio transmission bands.
25. The system of claim 24, wherein the characteristics of the received signal comprise at least a relative signal power of the received signal.
26. The system of claim 23, wherein optimization of the plurality of updatable parameters comprises optimization of one or more of: a pulse shape factor to control a level of signal smoothing, a band extension ratio, a band relative weight factor to control a distribution of compensation scaling factors between the one or more radio transmission bands, a hard clipping factor, or a quantization window size value representing a minimum time interval between eliminated peaks.
27. A crest factor reduction system configured to perform all the steps of the method of any one of claims 1 to 10 or any one of claims 16 to 22.
28. A design structure encoded on a non-transitory machine-readable medium, the design structure comprising elements for generating a machine-executable representation of the calibration system of any one of claims 11 to 15, the crest factor reduction system of any one of claims 23 to 26, or the crest factor reduction system of claim 27 when processed in a computer-aided design system.
29. A non-transitory computer readable medium programmed with a set of computer instructions executable on a processor, the set of computer instructions, when executed, causing operations comprising the steps of the method of any of claims 1 to 10 or any of claims 16 to 22.
Background
The invention relates to crest factor reduction.
In many communication systems, the peak amplitude of the desired signal is limited relative to an average value (e.g., relative to a mean Root Mean Square (RMS) or mean absolute amplitude). For example, the amplifying components of a radio frequency power amplifier may have absolute limits on their output amplitude, or exhibit severe distortion beyond a certain output amplitude, and therefore, in order to avoid introducing distortion (e.g., "clipping") due to such limits, it is desirable to pre-process the signal so that the input signal does not cause distortion of the output. It is also desirable to pre-process the signal in such a way as to avoid introducing various forms of distortion into the signal and within a prescribed computational budget.
Disclosure of Invention
In a general aspect, a method of Crest Factor Reduction (CFR) processing utilizes subtraction of scaled pulses (or other application of pulses) from an input signal or from a baseband signal of multiple frequency bands. The pulses are pre-designed according to the specific requirements to be met by the CFR method in the context of the communication band and the coding method. The available computation and storage capacity of the system for implementing the CFR method may also be taken into account when designing the pulse shape. The pre-design process uses quantitative evaluation and optimization of various pulse shapes to produce pulse shapes for the CFR signal processing at runtime.
One or more of these approaches address the technical problem of limiting peak amplitude while minimizing or reducing distortion, e.g., quantified in terms of the amount of resulting Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR). By reducing the EVM, the effective communication data rate within the frequency band may be increased relative to prior approaches. By reducing ACPR, interference in adjacent channels is reduced, which may cause the communication data rate in these channels to increase due to the reduced interference.
In some variations, there is provided a method comprising: accepting communication system data representing characteristics of a communication system including one or more radio transmission bands; and optimizing a plurality of updatable parameters used in the crest factor reduction system for determining respective pulse shapes of one or more pulses based at least in part on the received communication system data. Optimizing the plurality of updatable parameters includes iteratively updating the plurality of updatable parameters based on an iterative evaluation of the plurality of performance parameters. The method also includes providing an optimized plurality of updatable parameters for determining respective pulse shapes of the one or more pulses to configure the crest factor reduction system for processing signals for radio transmission using a pulse subtraction method applied to one or more signals communicated over the communication system.
Embodiments of the method may include at least some of the features described in this disclosure, including one or more of the following features.
Optimizing the plurality of updatable parameters may include optimizing, for example, one or more of: a pulse shape factor to control the level of signal smoothing, a band extension ratio, a band relative weight factor to control the distribution of a compensation scaling factor between one or more radio transmission bands, a hard clipping factor, and/or a quantization window size value representing the minimum time interval between eliminated peaks.
Receiving communication system data may include receiving, for example, one or more of: an adjacent power value ratio (ACPR), an up-sampled value, a sampling rate, carrier configuration data, a pulse shape factor value, a band extension ratio, at least one pulse band weight, a hard clipping factor, a pulse length value, a number of peak trackers, a number of crest factor reduction stages, or a quantization window size value representing a minimum time interval between eliminated peaks.
Iteratively updating the plurality of updatable parameters based on the iterative evaluation of the plurality of performance parameters may include: defining at least one objective function representing the quality of the respective pulse shape of the one or more pulses; determining one or more starting point pulse shapes for the one or more pulses based on the received communication system data and starting point values for the plurality of updatable parameters; and iteratively updating the plurality of updatable parameters based on an iterative calculation of at least one objective function to provide at least one intermittent output value obtained by applying the crest factor reduction system to the sample input signal using intermittent one or more pulse shapes, wherein the intermittent one or more pulse shapes are determined based on the received communication system data and the intermittent updated values of the plurality of updatable parameters.
Defining at least one objective function may include defining at least one objective function according to EVM + gamma (ACPR-ACPR)target) xACPR defines an objective function comprising a linear combination of Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR), where at t>In the case of 0, γ is determined according to the equation γ (t) ═ k1Barrier weight function γ (t) calculated by x t, or at t<In the case of 0, γ is determined according to the equation γ (t) ═ k2X t calculated barrier weight function γ (t), where k1And k2Is a tunable coefficient, and ACPRtargetRepresenting a predetermined target ACPR value.
The method may further comprise: configuring a crest factor reduction system with the optimized value; and processing the received signal for transmission using a crest factor reduction system.
Processing the received signal may include: the received signal is pulse-subtracted using the respective one or more pulse shapes determined based at least in part on the optimized plurality of updatable parameters.
The pulse subtraction processing of the received signal may include: identifying peaks in an aggregate time domain signal combined by one or more time domain representations of received signals in one or more radio transmission bands; and using the determined respective pulse shapes of the one or more pulses, performing individual pulse subtraction processing on the respective one or more time-domain representations of the respective received signals at a time instant of the received signals determined based at least in part on the identified positions of the peaks in the aggregated time-domain signal.
Performing the individual pulse subtraction process may include: the respective one or more pulse shapes are weighted based on characteristics of the received signal in the one or more frequency bands.
The characteristic of the received signal may comprise at least a relative signal power of the received signal.
In some variations, there is provided a system comprising: an interface for receiving communication system data representing characteristics of a communication system comprising one or more radio transmission bands; and an optimization engine configured to optimize a plurality of updatable parameters used in the crest factor reduction system for determining respective pulse shapes of the one or more pulses based at least in part on the received communication system data. Optimizing the plurality of updatable parameters includes iteratively updating the plurality of updatable parameters based on an iterative evaluation of the plurality of performance parameters. The system further comprises: a communication module to provide an optimized plurality of updatable parameters for determining respective pulse shapes of one or more pulses to configure a crest factor reduction system for processing signals for radio transmission using a pulse subtraction method applied to one or more signals communicated over a communication system.
Embodiments of the system may include at least some of the features described in the present disclosure, including at least some of the features described above with respect to the method, and one or more of the following features.
The optimizer for optimizing the plurality of updatable parameters may be configured to: optimizing, for example, one or more of: a pulse shape factor to control the level of signal smoothing, a band extension ratio, a band relative weight factor to control the distribution of a compensation scaling factor between one or more radio transmission bands, a hard clipping factor, and/or a quantization window size value representing the minimum time interval between eliminated peaks.
The optimizer for iteratively updating the plurality of updatable parameters based on the iterative evaluation of the plurality of performance parameters may be configured to: defining at least one objective function representing the quality of the respective pulse shape of the one or more pulses; determining one or more starting point pulse shapes for the one or more pulses based on the received communication system data and starting point values for the plurality of updatable parameters; and iteratively updating the plurality of updatable parameters based on an iterative calculation of at least one objective function to provide at least one intermittent output value obtained by applying the crest factor reduction system to the sample input signal using intermittent one or more pulse shapes, wherein the intermittent one or more pulse shapes are determined based on the received communication system data and the intermittent updated values of the plurality of updatable parameters.
The optimizer for defining at least one objective function may be configured to: according to EVM + gamma (ACPR-ACPR)target) xACPR defines an objective function comprising a linear combination of Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR), where at t>In the case of 0, γ is determined according to the equation γ (t) ═ k1Barrier weight function γ (t) calculated by x t, or at t<In the case of 0, γ is determined according to the equation γ (t) ═ k2X t calculated barrier weight function γ (t), where k1And k2Is a tunable coefficient, and ACPRtargetRepresenting a predetermined target ACPR value.
The system may also configure the crest factor reduction system with the optimization values and process the received signal for transmission using the crest factor reduction system.
In some variations, a method for signal processing in a crest factor reduction system is provided. The method comprises the following steps: identifying peaks in an aggregate time domain signal combined by one or more time domain representations of received signals in one or more radio transmission bands; and performing individual pulse subtraction processing on the respective one or more time-domain representations of the respective received signals at instants of the received signals determined based at least in part on the positions of the identified peaks in the aggregated time-domain signal using respective pulse shapes of the one or more pulses determined based on optimization of the plurality of updatable parameters. The optimization of the plurality of updatable parameters is based on an earlier performance of an iterative update of the plurality of updatable parameters according to an iterative evaluation of the plurality of performance parameters at least partly using predetermined communication system data representing characteristics of the communication system including the one or more radio transmission bands.
Embodiments of the method may include at least some of the features described in the present disclosure, including at least some of the features described above with respect to the first method and system and one or more of the following features.
Performing the individual pulse subtraction process may include: the respective one or more pulse shapes are weighted based on characteristics of the received signal in one or more radio transmission bands.
The characteristic of the received signal may comprise at least a relative signal power of the received signal.
The optimization of the plurality of updatable parameters may include, for example, optimization of one or more of: a pulse shape factor to control the level of signal smoothing, a band extension ratio, a band relative weight factor to control the distribution of a compensation scaling factor between one or more radio transmission bands, a hard clipping factor, and/or a quantization window size value representing the minimum time interval between eliminated peaks.
The communication system data may include, for example, one or more of the following: an Adjacent Channel Power Ratio (ACPR), an up-sampling value, a sampling rate, a carrier configuration setting, a pulse shape factor, a band extension ratio, at least one pulse band weight, a hard clipping factor, a pulse length, a number of peak trackers, a number of crest factor reduction stages, and/or a quantization window size representing a minimum time interval between eliminated peaks.
Iterative updating of the plurality of updatable parameters based on the iterative evaluation of the plurality of performance parameters may be performed using at least one objective function representing a quality of a respective pulse shape of the one or more pulses and iterative updating of the plurality of updatable parameters based on iterative calculation of the at least one objective function to provide at least one intermittent output value obtained by applying a crest factor reduction system to the sample input signal using intermittent one or more pulse shapes, wherein the intermittent one or more pulse shapes are determined based on the communication system data and the intermittent updated values of the plurality of updatable parameters.
According to EVM + gamma (ACPR-ACPR)target) X ACPR, the at least one objective function may comprise a linear combination of Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR), where at t>In the case of 0, γ is determined according to the equation γ (t) ═ k1Barrier weight function γ (t) calculated by x t, or at t<In the case of 0, γ is determined according to the equation γ (t) ═ k2X t calculated barrier weight function γ (t), where k1And k2Is a tunable coefficient, and ACPRtargetRepresenting a predetermined target ACPR value.
In some variations, there is provided a crest factor reduction system comprising: a peak identification circuit for identifying peaks in an aggregate time domain signal combined by one or more time domain representations of a received signal in one or more radio transmission frequency bands; and a pulse subtraction circuit for performing individual pulse subtraction processing on respective one or more time domain representations of respective received signals at instants of the received signals determined based at least in part on the positions of the identified peaks in the aggregated time domain signal using respective pulse shapes of the one or more pulses determined based on optimization of the plurality of updatable parameters. The optimization of the plurality of updatable parameters is based on an earlier performance of an iterative update of the plurality of updatable parameters according to an iterative evaluation of the plurality of performance parameters at least partly using predetermined communication system data representing characteristics of the communication system including the one or more radio transmission bands.
Embodiments of the crest factor reduction system may include at least some of the features described in the present disclosure, including at least some of the features described above with respect to the first and second methods and the first system, and one or more of the following features.
The pulse subtraction circuit for performing individual pulse subtraction may be configured to: the respective one or more pulse shapes are weighted based on characteristics of the received signal in one or more radio transmission bands.
The characteristic of the received signal may comprise at least a relative signal power of the received signal.
The optimization of the plurality of updatable parameters may include, for example, optimization of one or more of: a pulse shape factor to control the level of signal smoothing, a band extension ratio, a band relative weight factor to control the distribution of a compensation scaling factor between one or more radio transmission bands, a hard clipping factor, and/or a quantization window size value representing the minimum time interval between eliminated peaks.
In some variations, a crest factor reduction system configured to perform one or more of the method steps provided above is provided.
In some variations, a design structure encoded on a non-transitory machine-readable medium is provided, where the design structure includes elements that, when processed in a computer-aided design system, generate machine-executable representations of one or more of the system modules described above.
In some variations, an integrated circuit definition dataset is provided, wherein the dataset, when processed in an integrated circuit manufacturing system, configures the integrated circuit manufacturing system to manufacture one or more of the system modules described above.
In some variations, a non-transitory computer-readable medium encoded with a set of computer instructions executable on a processor is provided, wherein the computer instructions, when executed, cause operations comprising the various method steps described above.
Embodiments of the crest factor reduction system, the design structure, the integrated circuit definition dataset, and the computer-readable medium may include at least some of the features described in this disclosure, including at least some of the features described above with respect to the first and second methods and the first and second systems.
Other features and advantages of the invention will be apparent from the following description, and from the claims.
Drawings
These and other aspects will now be described in detail with reference to the following drawings.
Fig. 1 is a diagram of an example communication system having multiple devices, each of which (or some of which) may be configured to implement a crest factor reduction system.
Fig. 2 is a flow chart of a process to determine/develop a crest factor reduction system.
Fig. 3 is a screen shot of an example interface that a user may use to provide communication system data.
Fig. 4 is a schematic diagram of an example implementation of a circuit to apply a predetermined pulse to a split band signal.
FIG. 5 is a schematic diagram of an example apparatus that may be used in the implementation of any of the apparatuses of FIG. 1.
FIG. 6 is a flow diagram of an example process to facilitate implementation of CFR processing.
Fig. 7 is a flow chart of an example process to perform CFR processing.
Like reference symbols in the various drawings indicate like elements.
Detailed Description
Methods, systems, apparatus, media, and other implementations are disclosed herein for determining an optimal or near-optimal ("optimal," but not necessarily "optimal") pulse shape to apply to signals in one or more radio transmission bands to achieve optimal or near-optimal Crest Factor Reduction (CFR). In this type of preprocessing, the "crest factor" can be defined as the ratio of the peak value to the average RMS value of the signal waveform. In the present disclosure, the following terms will be used. The "peak-to-average power ratio" (PAPR), which is a quantity, is defined as the square of the peak amplitude (given the peak power) divided by the square of the RMS value (given the average power), so the PAPR is equal to the square of the Crest Factor (CF). However, when expressed in logarithmic scale (decibel or dB), the PAPR value is the same as the CF value. Various measures of distortion may characterize the effectiveness of the pre-processing. For example, the Error Vector Magnitude (EVM) can be defined as the square root of the mean error power divided by the reference power (e.g., the maximum power of the coding constellation), expressed in decibels or as a percentage. Another measure of distortion is related to the spread of signal energy outside the desired signal band, e.g., measured as the "adjacent channel power ratio" (ACPR) and defined as the ratio between the total power in the adjacent channel (e.g., intermodulation signals) and the power of the desired channel.
Various methods may be used for CFR. One method involves upsampling and then clipping the signal, followed by filtering the clipped signal to reduce distortion (mainly in the form of ACPR). This process may be repeated multiple times, since the filtering itself may introduce new amplitude peaks. In some such methods, the level at which the signal is clipped may be stepped down to gradually meet a target maximum amplitude relative to the RMS value. In another approach, the up-sampled signal is clipped and the amount by which the signal exceeds the clipped signal is filtered by a predefined filter or multiplied by a predefined time domain window centered on the time position of the peak amplitude (i.e., appropriately band limited) and subtracted from the signal. Again, in such methods, the process may be repeated in multiple stages, as filtering or windowing may introduce new peak amplitudes that exceed the limit.
Yet another method identifies the location of peak amplitudes above a threshold in the input signal and subtracts a scaled version of the predefined pulse shape. This pulse shape may be designed such that it does not add significant energy outside the allowed signal band. This process may need to be repeated multiple times since the subtracted pulses may not remove the peak amplitude near, but not at, the point where the pulses are added.
In some systems, the input signal may represent a combination of signals in two or more frequency-limited frequency bands separated in frequency from an intervening frequency band. Some of the methods described herein attempt to process baseband signals representing respective limited frequency bands with the goal of limiting the amplitude of the combined signal.
Accordingly, in some embodiments, there is provided a method comprising: accepting communication system data representing characteristics of a communication system including one or more radio transmission bands; and optimizing a plurality of updatable parameters used in the crest factor reduction system for determining respective pulse shapes of the one or more pulses based at least in part on the received communication system data, wherein optimizing the plurality of updatable parameters comprises iteratively updating the plurality of updatable parameters based on an iterative evaluation of the plurality of performance parameters. By "optimizing" a value is meant determining a value to produce an improved or optimal goal, e.g., optimizing a value of a shape parameter to produce improved or optimal performance via performance parameter quantization. The method also includes providing an optimized plurality of updatable parameters for determining respective pulse shapes of the one or more pulses to configure the peak reduction system for processing signals for radio transmission using a pulse subtraction method applied to one or more signals communicated over the communication system.
The method may further include configuring a peak reduction system (which may be implemented at a network node, such as a base station or access point, or at a personal device) with the optimization values, and processing the received signal for transmission using the crest factor reduction system. The crest factor reduction system may be at the device where the CFR system design is made, or at some other device. Processing the received signal may include: the received signal is pulse-subtracted using the respective one or more pulse shapes determined based at least in part on the optimized plurality of updatable parameters. Pulse subtracting the received signal may include: identifying peaks in an aggregate time domain signal (or in some embodiments a spatial domain signal) combined by one or more time domain representations of received signals in one or more radio transmission bands; and performing a subtraction of the individual pulses of the respective one or more time-domain representations of the respective received signals at a time instant of the received signals determined based at least in part on the identified peak locations in the aggregated time-domain signal.
In some embodiments, devices (such as personal device 110, server 172, and/or network nodes such as access points 150 a-n and base stations 160 a-n depicted in the
As mentioned, CFR system implementations include two main stages: 1) a CFR development/design stage in which a single-band or multi-band configuration is subjected to crest factor reduction system design processing based on predetermined or specified communication system data (e.g., data representing attributes of a communication system such as the
Thus, referring to fig. 2, a flow diagram is provided that illustrates a
ACPR target or maximum level;
the sampling rate and upsampling factor of the input signal (or signal in a multiband configuration);
the carrier configuration, including the width and location of the communication band, and the coding method used within the band.
Thus, the interface implemented by
the pulse length;
the number of peak trackers;
the number of CFR stages;
a hard clipping factor, e.g., representing the amount of crest factor reduction for each stage in a series of stages;
the peak quantization window size, which determines the minimum time interval of the eliminated peaks (i.e., only the largest peak in the quantization window size can be explicitly eliminated).
For each of the above CFR design parameters, the user may select from 3 to 5 options, or may select any value within a predetermined range. Alternatively, the user may select any practical value for the pulse aspect described above as appropriate without limitation. As also shown in fig. 2, at the
the number of iterations of the shape optimization;
the number of starting shapes for optimization, where local iterations are performed to iteratively refine the shape;
an objective to be optimized, for example, by setting free parameters in an objective function that weights the EVM and ACPR (or some other parameter or property); and
tolerance variables and tolerance values, such as algorithm convergence settings, which are used to determine when the desired result is achieved, stop the algorithm after a certain number of steps, and control parameter comparisons.
The pulse shape is characterized by a set of quantities that are used to determine the pulse shape in the time (or spatial) domain. These quantities listed at the
"pulse shape factor", which may be a number between 0 and 1, is used to form a "smooth" discrete-time function that models the shape of the band-pass filter spectrum for the frequency band in which the pulse will be used. The higher the number, the closer the middle part of the function is to 1 (but the higher the number, the overall "quality" of its approximation to the ideal bandpass shape will generally be affected).
"band extension ratio", which is the number p between-1/2 and 1/2, which determines the basic spectral band extension [ -w; w → [ - (1+ ρ) w; factor (1+ ρ) of (1+ ρ) w ]. Finally, all these pulses are aggregated according to the carrier configuration. In some embodiments, all channels use the same p to reduce the dimensionality of the optimization problem, however, each channel may use a different p.
"band relative weight factor", which may be a number f between 1/2 and 3/2, for a multi-band configuration to determine how to assign a compensation scaling factor between the two (or more) bands. Generally, it can be represented by (k-1) numbers, where k is the number of channels/bands in a multi-band scenario (for a single-band CFR, the factor is not generally needed, nor is it derived).
In some embodiments, some parameters or variables may be optimized by the optimization process of FIG. 2, or may be pre-specified or pre-determined at one of the input stages (e.g., stages 210, 230, or 240) of
The
Various objective functions may be used to quantify the quality of the pulse shape. Generally, for a particular pulse shape, the EVM and ACPR implemented are determined by processing the input samples with a configured CFR system (or in some embodiments, with a software simulation of the CFR system). In some cases, a linear combination of EVM and ACPR may be used as the objective function. The nonlinear combination can be expressed as:
EVM+γ(ACPR-ACPRtarget)×ACPR,
wherein at t>In the case of 0, γ (t) is k1X t, and at t<When 0, γ (t) is k2X t. Such an objective function may enable the optimization process to reduce the ACPR mainly until it reaches the target ACPRtargetUntil then, the EVM is focused on. In the multi-band case, the same pulse shape may be used for each band (e.g., time scaled and weighted appropriately based on the relative power in each band to which the pulse is applied). In alternative embodiments, different pulse shapes may be used in different frequency bands. Thus, in some embodiments, the optimization stage (optimization engine) may be configured to determine one or more start point pulse shapes for the one or more pulses based on the received communication system data and the start point values of the plurality of updatable parameters. With the starting points of the plurality of updatable parameter sets, the
An example of an optimization problem to be solved using an objective function such as the one specified above is as follows. Consider the case of optimization of the following variables:
(1)x1pulse shape factor
(2)x2Band extension ratio
(3)x3Frequency bandRelative weight factor of
(4)x4Hard clipping factor
(5)x5Which is the size of the quantization window,
wherein in this example x ∈ R5={x1,x2,x3,x4,x5In which x1∈[0.1;0.9],x2∈[0.75;1.25],x3∈[0.7;1.3],x4∈[1.00;1.05]And x is5∈[0.0;1.0]. By optimizing these variables (e.g., within a specified range), the following objective function is minimized: minimize(x,PAPR(x)≈PAPRtarget){EVM(x)+γ(ACPR(x)–ACPRtarget)×ACPR(x)},
Wherein γ (t) is according to the formula>When 0, γ (t) is k1t, and when t is less than or equal to 0, k is2t (a piecewise linear function), and where k1And k2Is an adjustable factor. E.g. k1Can be selected to be relatively large (e.g., k)110), and k) is2May be smaller (e.g., k)20.01). This choice of coefficients indicates that it is more important to achieve the target ACPR during optimization than to maintain a low EVM. However, if the target ACPR is exceeded, it becomes more important to reduce EVM. In some embodiments, the minimization of the objective function may be based on differentiating the objective function terms/contributions and using the objective function derivatives to identify minima (corresponding to the values that will minimize the objective function), or otherwise identifying optimal values for the objective function. This minimization can be achieved based on techniques/processes such as conjugate gradients, simplex methods, simulated annealing, genetic algorithms, and the like.
The updatable parameters that achieve minimization of the selected objective function are considered optimal (or near optimal). These updatable parameters define the pulse shape that is subtracted from the time domain (or spatial domain) signal representation of the single or multi-band signal at the time (or location) of the signal based on identifying the location of the signal peak (within some defined window) that exceeds a particular amplitude threshold. In some implementations, similar optimization processes may be applied where different CFR methods are to be used.
Fig. 3 is a screen shot of an
The determined parameters resulting from the optimization process or the pulse representations corresponding thereto are provided to the device to be CFR processed. For example, these parameters may be communicated to remote devices that use processor-based devices and/or dedicated hardware to implement the CFR process using optimized updatable parameters determined from the optimization process. In some embodiments, the optimization parameters may be updated periodically to better match changing system conditions. Optionally, in some embodiments (e.g., where a generally non-modifiable CFR process is to be implemented using, for example, ASIC hardware or some other hardware intended for a more permanent, unchanging purpose), a circuit implementation based on optimization parameters may be installed on the target device.
As mentioned, in a pulse subtraction based approach, the peak amplitude within a certain time window is identified, and if the identified peak is above a certain predetermined peak amplitude threshold, a cancellation pulse (in this case a pulse determined according to the optimization process of, for example, fig. 2) is applied (e.g., subtracted from the signal). In some implementations, the pulse subtraction CFR method includes identifying amplitude peaks in an approximately aggregated time (or spatial) domain signal from different frequency bands. Aggregated signals from different frequency bands may be down-sampled approximations (resulting in reduced samples to be processed or analyzed, and thus reduced use of resources) used to identify peaks (higher sampled copies of the signal may be subsequently processed). Amplitude peak identification may be performed for different segments (i.e., the signal may be analyzed to identify the amplitude of individual segments), where in some embodiments only one peak is identified from each segment (even if there are multiple peaks that exceed a predetermined peak amplitude threshold).
The determined pulses are respectively applied to the respective frequency bands (processing of the single frequency band signal may occur at its normal sampling rate, or at an up-sampled or down-sampled copy of the signal) based on the identified peak locations in the approximated aggregate signal (e.g., peak locations in a non-frequency domain representation of the signal). For example, respective band pass filters may be applied to obtain respective band signals corresponding to respective frequency bands. In embodiments where different pulses are determined for different frequency bands, these different pulses are applied to (e.g., subtracted from) the respective frequency bands at times (or locations) that are based on the times (or locations) of peaks identified in the aggregate signal approximation. The specific time or position in each frequency band is not necessarily the same time as the identified peak, but may be applied according to some formula based on the time of the identified peak position. Thus, in some embodiments, an apparatus implementing a pulse subtraction method for CFR processing may be configured to identify peaks in an aggregate time domain (or spatial domain) signal combined by one or more time domain representations of received signals in one or more radio transmission frequency bands, and to perform individual pulse subtraction processing on the respective one or more time domain representations of the respective received signals at time instants of the received signals determined based at least in part on locations of the identified peaks in the aggregate time domain (or spatial domain) signal using respective pulse shapes of the determined one or more pulses.
In some implementations, the pulse shapes determined during the optimization process (e.g., a process similar to process 200 of fig. 2) may be scaled (weighted) according to one or more different criteria. In particular, due to the identification of peaks for the aggregate signal, a single frequency band with more energy or power will contribute a larger portion of the energy or power of the aggregate signal than other frequency bands. Therefore, the weight assigned to the pulse shape subtracted from the higher energy band should be more than the weight assigned to the pulse to be subtracted from the frequency band with the weaker signal. Thus, in these embodiments, the means configured to perform individual pulse subtraction may be configured to weight the respective one or more pulse shapes based on characteristics of the received signal in one or more frequency bands. The characteristic of the received signal may comprise at least a relative signal power of the received signal.
Fig. 4 is a schematic diagram of an example implementation of a
The
After CFR processing based on subtraction of individual pulses is performed on each frequency band signal, the resulting signals may be combined using a summing
The CFR system may be implemented in circuitry that contains a data store (configurable and/or read-only) of selected pulse shapes (or quantities that allow for computation of pulse shapes at runtime). The circuitry may also include dedicated logic (e.g., an arithmetic unit) and/or a processor or controller for implementing the CFR method.
As shown, the
A controller/
The
As shown in fig. 1-5, the implementations described above are applicable to a variety of technologies including RF technologies (including WWAN technologies such as cellular technologies and WLAN technologies), satellite communication technologies, cable modem technologies, cable network technologies, optical communication technologies, and all other RF and non-RF communication technologies. Implementations described herein include all techniques and embodiments involving the use of multi-band digital predistortion in a variety of different communication systems.
In some implementations, a computer-accessible non-transitory storage medium includes a database (also referred to as a "design structure" or "integrated circuit definition dataset") that represents a system that includes some or all of the components for the CFR implementation described herein. In general, a computer-accessible storage medium may include any non-transitory storage medium that is accessible by a computer during use to provide instructions and/or data to the computer. For example, the computer-accessible storage medium may include storage media such as magnetic or optical disks and semiconductor memories. In general, a database representing a system may be a database or other data structure readable by a program and used, directly or indirectly, in the manufacture of hardware comprising the system. For example, the database may be a behavioral level description or a Register Transfer Level (RTL) description of hardware functions in a high level design language (HDL) such as Verilog or VHDL. The description may be read by a synthesis tool that may synthesize the description to produce a netlist that includes a list of gates from a synthesis library. The netlist comprises a set of gates that also represent the functionality of the hardware comprising the system. The netlist can then be placed and routed to produce a data set describing the geometry to be applied to the mask. The mask may then be used in various semiconductor fabrication steps to produce one or more semiconductor circuits corresponding to the system. In other examples, the database itself may be a netlist (with or without a synthesis library) or a data set.
Referring now to fig. 6, a flow diagram of an
With continued reference to fig. 6, the
In some embodiments, iteratively updating the plurality of updatable parameters based on the iterative evaluation of the plurality of performance parameters may include: defining at least one objective function representing the quality of the respective pulse shape of the one or more pulses; determining one or more starting point pulse shapes for the one or more pulses based on the received communication system data and starting point values for the plurality of updatable parameters; to be provided withAnd iteratively updating the plurality of updatable parameters based on an iterative calculation of at least one objective function to provide at least one intermittent output value obtained by applying the crest factor reduction system to the sample input signal using intermittent one or more pulse shapes, wherein the intermittent one or more pulse shapes are determined based on the received communication system data and the intermittent updated values of the plurality of updatable parameters. Defining at least one objective function may include defining at least one objective function according to EVM + gamma (ACPR-ACPR)target) xACPR defines an objective function comprising a linear combination of Error Vector Magnitude (EVM) and Adjacent Channel Power Ratio (ACPR), where at t>In the case of 0, γ is determined according to the equation γ (t) ═ k1Barrier weight function γ (t) calculated by x t, or at t<In the case of 0, γ is determined according to the equation γ (t) ═ k2X t calculated barrier weight function γ (t), where k1And k2Is a tunable coefficient, and ACPRtargetRepresenting a predetermined target ACPR value.
Where optimized updatable parameters are determined,
Referring next to fig. 7, a flow diagram of an
In some implementations, during an optimization process (to determine an optimal or near optimal pulse shape), iterative updating of a plurality of updatable parameters according to the iterative evaluation of the plurality of performance parameters can be performed using at least one objective function representing a quality of a respective pulse shape of one or more pulses and iterative updating of the plurality of updatable parameters according to iterative computation of the at least one objective function to provide at least one intermittent output value obtained by applying a crest factor reduction system to a sample input signal using intermittent one or more pulse shapes determined based on communication system data and the intermittent updated values of the plurality of parameters, according to the iterative evaluation of the plurality of performance parameters. The objective function used may be similar to any of the objective functions discussed herein.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly or conventionally understood. As used herein, the articles "a" and "an" refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element. When referring to measurable values such as amounts and durations, the use of "about" and/or "approximately" herein encompasses variations of 20% or 10%, 5% or 0.1% from the stated values, as such variations are appropriate in the context of the systems, devices, circuits, methods and other implementations described herein. As used herein, "substantially" when referring to measurable values such as quantities, durations, and physical properties (such as frequency, etc.) also encompasses variations of 20% or 10%, 5%, or 0.1% from the specified values, as such variations are appropriate in the context of the systems, devices, circuits, methods, and other implementations described herein.
As used herein (including in the claims), the term "or" as used in a list of items headed by "at least one of …" or "one or more of …" denotes a disjunctive list such that, for example, a list of "at least one of A, B or C" means a or B or C or AB or AC or BC or ABC (i.e., a and B and C), or a combination having more than one feature (e.g., AA, AAB, ABBC, etc.). Furthermore, as used herein, unless otherwise stated, a statement that a function or operation is "based on" an item or condition means that the function or operation is based on the stated item or condition, and may be based on one or more items and/or conditions in addition to the stated item or condition.
Although specific embodiments have been disclosed herein in detail, this has been done by way of example for purposes of illustration only and is not intended to limit the scope of the invention, which is defined by the scope of the appended claims. Features of the disclosed embodiments can be combined, rearranged, etc. within the scope of the invention to produce further embodiments. Certain other aspects, advantages, and modifications are considered to be within the scope of the claims provided below. The claims presented represent at least some of the embodiments and features disclosed herein. Other non-claimed embodiments and features are also contemplated.
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