WO2021174463A1

WO2021174463A1 - Digital predistortion device and transmitter

Info

Publication number: WO2021174463A1
Application number: PCT/CN2020/077839
Authority: WO
Inventors: 程文昊; 吴宏星; 廖连贵
Original assignee: 海能达通信股份有限公司
Priority date: 2020-03-04
Filing date: 2020-03-04
Publication date: 2021-09-10

Abstract

Disclosed in the present application are a digital predistortion device and a transmitter. The digital predistortion device comprises a digital down conversion circuit, a signal strength acquisition circuit and a digital predistorter. The digital down conversion circuit is used to receive a first feedback signal and convert the first feedback signal into a second feedback signal, the frequency of the first feedback signal being greater than that of the second feedback signal. The signal strength acquisition circuit is used to acquire the power of the second feedback signal, the second feedback signal comprising at least two effective signals and an intermodulation component between the effective signals. The digital predistorter is used for carrying out predistortion according to the power of the second feedback signal so as to reduce the power of a nonlinear product in an output signal and output a first intermediate frequency signal, the nonlinear product being the intermodulation component between the effective signals. By means of the described means, the present application can keep the power of the nonlinear product at a low level for a long time, effectively suppress interference and improve anti-interference performance.

Description

Digital predistortion device and transmitter

Technical field

This application relates to the field of communication technology, and in particular to a digital predistortion device and transmitter.

Background technique

The transmitter of the communication system will produce obvious non-linear products due to the non-linearity of the hardware, such as three-order intermodulation (IM3, Three-order Intermodulation), and the spectrum resources are limited and used for the main signal, resulting in non-linearity outside the specified range The product will affect the legal use of spectrum resources by other users, resulting in the transmitter being unable to be used in a commercial environment.

In practical applications, in order to eliminate nonlinear products to a certain extent, so that they do not affect the use of users in other frequency bands, predistortion technology is often used. Currently, DPD (Digtal Pre-Distortion) is mainly used. DPD is a method of correcting transmitter nonlinear distortion. Technology, using feedback data and forward data to calculate and iterate coefficients, and correct the downlink nonlinearity through a matrix. However, when the nonlinear index is close to the limit value, the correction effect of DPD may jump a few dB near the limit value, which may cause non-linearity. Linear indicators have certain fluctuations.

The inventor of this application has discovered in long-term research and development that the prior art can use Fast Fourier Transformation (FFT) to collect feedback data or use downlink special data for transmitter nonlinearity evaluation; current analysis of terrestrial cluster radio ( The main method of non-linear products of TETRA, Trans European Trunked Radio transmitters is to use a spectrum analyzer or collect a small amount of data and perform FFT analysis. However, the use of a spectrum analyzer requires an environment and cannot be used in the field. The use of FFT analysis is due to the amount of data collected. Limitation results in larger analysis errors. Current transmitters usually use a central processing unit (CPU, Central Processing Unit) and a Field Programmable Gate Array (FPGA, Field Programmable Gate Array) architecture to perform FFT operations in the CPU, data collection in the FPGA, and collected data When the amount is large, the transmission and calculation delay will increase, and the data calculation delay of one frame can reach the level of 100 milliseconds.

Summary of the invention

The main problem to be solved by this application is to provide a digital predistortion device and transmitter, which can keep the power of nonlinear products at a low level for a long time, effectively suppress interference, and improve anti-interference performance.

In order to solve the above technical problems, the technical solution adopted in this application is to provide a digital predistortion device. The digital predistortion device includes a digital down-conversion circuit, a signal strength acquisition circuit, and a digital pre-distorter. The digital down-conversion circuit is used for receiving The first feedback signal and convert the first feedback signal into a second feedback signal, wherein the frequency of the first feedback signal is greater than the frequency of the second feedback signal; the signal strength acquisition circuit is connected to the digital down-conversion circuit for acquiring the second The power of the feedback signal, where the second feedback signal includes at least two effective signals and intermodulation components between the effective signals; Distortion processing to reduce the power of non-linear products in the output signal and output the first intermediate frequency signal; among them, the non-linear products are intermodulation components between effective signals.

In order to solve the above technical problems, another technical solution adopted by this application is to provide a transmitter, which includes a digital predistortion device, a transmitting circuit and a feedback circuit, and the digital predistortion device is used for predistorting input signals, And send the processed signal to the transmitting circuit. The transmitting circuit is used to receive and process the signal output by the digital predistortion device, and output the signal to the feedback circuit. The feedback circuit is used to process and output the signal output by the transmitting circuit. The result is a digital predistortion device, where the digital predistortion device is the above-mentioned digital predistortion device.

Through the above solution, the beneficial effects of the present application are: the digital predistortion device includes a digital down-conversion circuit, a signal strength acquisition circuit, and a digital predistorter. The digital down-conversion circuit is used to convert the first feedback signal of the intermediate frequency into a low-rate The second feedback signal; the signal strength acquisition circuit is used to acquire the power of the nonlinear product in the second feedback signal at a low rate; the digital predistorter is used to perform predistortion processing based on the power of the nonlinear product to reduce the output signal. The power of the linear product can use the power of the nonlinear product to make the decision of the digital predistorter, reduce the number of iterations of the digital predistorter, so as to keep the power of the nonlinear product at a low level for a long time, effectively suppress interference, and improve immunity. Intrusive.

Description of the drawings

In order to explain the technical solutions in the embodiments of the present invention more clearly, the following will briefly introduce the drawings needed in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. in:

FIG. 1 is a schematic structural diagram of an embodiment of a digital predistortion device provided by the present application;

2 is a schematic structural diagram of another embodiment of a digital predistortion device provided by the present application;

Fig. 3 is a schematic structural diagram of an embodiment of a transmitter provided by the present application.

Detailed ways

The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of this application.

Referring to FIG. 1, FIG. 1 is a schematic structural diagram of an embodiment of a digital predistortion device provided by the present application. The digital predistortion device includes: a digital down-conversion circuit 11, a signal strength acquisition circuit 12, and a digital predistorter 13.

The digital down-conversion circuit 11 is used to receive a first feedback signal and convert the first feedback signal into a second feedback signal; wherein the frequency of the first feedback signal is greater than the frequency of the second feedback signal.

The first feedback signal may be an intermediate frequency digital signal collected by an analog-to-digital converter (not shown in the figure). After receiving the first feedback signal, the digital down-conversion circuit 11 performs down-conversion processing on the first feedback feedback signal, A second feedback signal with a low rate is obtained, and the first feedback signal may include a variety of signals.

The signal strength acquisition circuit 12 is connected to the digital down-conversion circuit 11, and is used to acquire the power of the second feedback signal; wherein the second feedback signal includes at least two effective signals and the intermodulation component between the effective signals, and the effective signal is available To synthesize a new signal with other non-interfering signals, the intermodulation products generated by the interaction of at least two effective signals through nonlinear devices (not shown in the figure) may cause interference to the effective signal, making the spectrum of the effective signal and mutual The frequency spectrum of the tonal component is aliased.

The signal strength acquisition circuit 12 is used to receive the low-frequency second feedback signal output by the digital down-conversion circuit 11, and calculate the power of the second feedback signal to obtain the two effective signals in the second feedback signal and the mutual relationship between the effective signals. The modulation component, thereby calculating the power difference between the two effective signals in the second feedback signal and their intermodulation components.

The digital predistorter 13 is connected to the signal strength acquisition circuit 12, and is used to perform predistortion processing according to the power of the second feedback signal to reduce the power of the nonlinear product in the output signal and output the first intermediate frequency signal; The linear product is the intermodulation component between the effective signals.

The digital predistorter 13 receives the power value of the signal contained in the second feedback signal output by the signal strength acquisition circuit 12, and uses the power value for the digital predistorter 13 to make iterative decisions to speed up the iterative rate of the digital predistorter 13, This shortens the processing time of the digital predistorter 13 so as to maintain a stable state for a long time; for example, the existing digital predistortion device needs to iterate 20 times to reach a stable state, and this embodiment introduces nonlinear products in the decision parameters The power of this speed increases the speed of iteration. When 15 iterations are possible, the digital predistortion device can reach a stable state, extending the stable state time.

This embodiment provides a digital predistortion device. The digital predistortion device includes a digital down-conversion circuit 11, a signal strength acquisition circuit 12, and a digital pre-distorter 13. The digital down-conversion circuit 11 is used to convert a first feedback signal of an intermediate frequency Converted into a low-rate second feedback signal; the signal strength acquisition circuit 12 is used to acquire the power of the nonlinear product in the low-rate second feedback signal; the digital predistorter 13 is used to perform predistortion based on the power of the nonlinear product Processing to reduce the power of the nonlinear product in the output signal, the power of the nonlinear product can be used for the digital predistorter 13 decision, reduce the number of iterations of the digital predistorter 13, so as to maintain the power of the nonlinear product at a long time A lower level can effectively suppress interference and improve anti-interference.

Referring to FIG. 2, FIG. 2 is a schematic structural diagram of another embodiment of a digital predistortion device provided by the present application. The digital predistortion device includes: a digital down-conversion circuit 11, a signal strength acquisition circuit 12, and a digital predistorter 13.

Further, the digital down-conversion circuit 11 includes: a first oscillator 111, a first mixer 112, and a first filter 113; the first oscillator 111 is used to generate a digital oscillating signal, which may be a numerically controlled oscillator (NCO, Numerical Control Oscillator), NCO can generate orthogonal sine and cosine samples.

The first mixer 112 is connected to the first oscillator 111, and is used for mixing the first feedback signal and the digital oscillation signal to obtain the second feedback signal; the first mixer 112 is a digital mixer, The first feedback signal and the signal output by the NCO can be multiplied to obtain a low-rate second feedback signal.

The first filter 113 is connected to the first mixer 112 and is used to filter the second feedback signal; the first filter 113 can filter the signal output by the first mixer 112 to obtain a relatively clean low rate Digital signal.

The signal strength acquisition circuit 12 is connected to the digital down-conversion circuit 11, and is used to acquire the power of the second feedback signal; wherein the second feedback signal includes at least two effective signals and an intermodulation component between the effective signals.

The digital predistorter 13 is connected to the signal strength acquisition circuit 12, and is used to perform predistortion processing according to the power of the second feedback signal to reduce the power of the nonlinear product in the output signal and output the first intermediate frequency signal; The linear product is the intermodulation component between the effective signals, and the non-linear product includes the third-order intermodulation component or the fifth-order intermodulation component between the effective signals.

The digital predistortion device can be applied to the transmitter. Some components in the transmitter are respectively connected with the digital predistorter 13 and the first mixer 112 to form a closed loop structure, so that the digital predistorter 13 continues to iterate until the output The signal meets the requirements, reducing the nonlinear distortion of the transmitter.

Further, in order to shorten the iteration time of the digital predistorter 13, the digital predistorter 13 stores the effective signal frequency, the effective signal power, the power of the nonlinear product, and the mapping of the power difference between the effective signal and the nonlinear product. surface. The method of acquiring data in the mapping table is that the digital predistorter 13 detects the power of the nonlinear product in the output signal, and the amount of change in the power difference between the effective signal and the nonlinear product in the output signal is preset When it is within the range, stop the iteration, and use the minimum value of the power of the nonlinear product in the iteration process as the power of the nonlinear product in the mapping table.

In a specific embodiment, under different carrier frequency intervals and different carrier powers, the signal strength acquisition circuit 12 measures the power of the nonlinear product and the effective signal, thereby obtaining the power difference between the nonlinear product and the effective signal. The corresponding mapping table is established and can be stored in the digital predistorter 13. For example, the carrier frequency is 100MHz, the carrier spacing is 200KHz, the two carrier frequencies are 100MH+200KHz and 100MH-200KHz, and the carrier power is 20W. After multiple iterations of the digital predistorter 13, the power of the third-order intermodulation component The values are stabilized at about -70dBc and -76dBc respectively. This data is stored in the digital predistorter 13, so that when the signal is transmitted with the same carrier frequency and power, this data can be directly used to make iterative decisions to reduce the number of iterations. .

The digital predistorter 13 is also used to determine the preset first threshold and the preset second threshold according to the power difference between the effective signal and the non-linear product in the mapping table to determine whether to iterate. When the output signal is detected When the power difference between the effective signal and the nonlinear product is less than the preset first threshold, stop iteration; when the power difference between the effective signal and the nonlinear product in the output signal is greater than the preset second threshold, continue iterating , Until the power difference between the effective signal and the nonlinear product is less than the preset first threshold; wherein the preset first threshold and the preset second threshold are respectively positively correlated with the power of the nonlinear product in the mapping table, and the preset first threshold A threshold is less than the preset second threshold.

In a specific embodiment, the effective signal includes a first intermediate frequency signal and a second intermediate frequency signal. The first intermediate frequency signal is a signal generated after the first carrier signal is modulated by a digital baseband signal, and the second intermediate frequency signal is a second carrier signal that is modulated by a digital baseband signal. The signal generated after digital baseband signal modulation.

For example, for a dual-carrier base station, the frequency of the carrier signal is f1 and f2, and the nonlinear product is the third-order intermodulation component. The third-order intermodulation component includes 2f1-f2 and 2f2-f1. When the power of the third-order intermodulation component, record the minimum value of the larger power of the two third-order intermodulation components, that is, if the power of the third-order intermodulation component 2f1-f2 is greater than the power of the third-order intermodulation component 2f2-f1, Record the power of the third-order intermodulation components 2f1-f2, assuming that the amplitude difference between the third-order intermodulation components 2f1-f2 and the effective signals f1 and f2 is -20dB at the beginning, and their power difference is stable after 10 iterations At about -70dB, take -70dB as the power difference A between the effective signal and the nonlinear product in the mapping table, so that the preset first threshold AB and the preset second threshold AC can be determined according to the power difference A. The power values B and C can be set as required. Assuming that the first threshold AB is -75dB and the second threshold AC is -72dB, during transmission, since -70dB is greater than -75dB, continue iterating 5 times and record these five times The minimum value of the power difference, such as -73.5dB.

Understandably, the data in the mapping table in this embodiment can also be the Adjacent Channel Power Ratio (ACPR, Adjacent Channel Power Ratio), and the third-order intermodulation component, fifth-order intermodulation component, and ACPR can be combined as one Comprehensive indicators for the digital predistorter 13 to make decisions.

In this embodiment, under the architecture of CPU and PFGA, accurate nonlinear product power can be obtained with a smaller delay for the digital predistorter 13 to make decisions, and the power difference between the effective signal and the nonlinear product can be resolved by pre-establishing a mapping table. After reaching the index value, the problem of fluctuation occurs. Using the slow-changing characteristics of the hardware, it is less iterative to maintain a good correction effect for a long time, and it can also save the cost of the instrument and facilitate automatic control.

Referring to FIG. 3, FIG. 3 is a schematic structural diagram of an embodiment of a transmitter provided by the present application. The transmitter includes a digital predistortion device 10, a transmitting circuit 20 and a feedback circuit 30.

The digital predistortion device 10 is used to perform predistortion processing on the input signal and send the processed signal to the transmitting circuit 20. The transmitting circuit 20 is used to receive the signal output by the digital predistortion device 10 and process it, and output the signal to feedback The circuit 30 and the feedback circuit 30 are used for processing the signal output by the transmitting circuit 20 and outputting the processing result to the digital predistortion device 10. The specific structure of the digital predistortion device 10 is the same as that in the above-mentioned embodiment and will not be omitted here. Go into details.

Further, the transmitting circuit 20 includes: a digital-to-analog converter 21, a second oscillator 22, a second mixer 23, a second filter 24, a power amplifier 25, a coupler 26, and an antenna 27.

The digital-to-analog converter 21 is connected to the digital predistortion device 10, and is used to convert the first intermediate frequency signal output by the digital predistortion device 10 into a second intermediate frequency signal; in a specific embodiment, the digital-to-analog converter 21 and the digital The output terminal of the predistorter 13 is connected to convert the digital signal output by the digital predistorter 13 into an analog signal.

The second oscillator 22 is used to generate a local oscillation signal. The second oscillator 22 may be a voltage-controlled oscillator, and the local oscillation signal is an analog signal.

The second mixer 23 is respectively connected to the digital-to-analog converter 21 and the second oscillator 22, and is used to mix the second intermediate frequency signal and the local oscillation signal to obtain the first radio frequency signal; the second mixer 23 It is an analog mixer, which up-converts the signal output by the second oscillator 22 and the signal output by the digital-to-analog converter 21 to obtain a higher frequency signal.

The second filter 24 is connected to the output end of the second mixer 23, and is used to filter the signal output by the second mixer 23 to obtain the first radio frequency signal; the second filter 24 is an analog filter, Interference signals may be included in the signal generated after mixing, and the second filter 24 can be used to filter out, so as to obtain a clean first radio frequency signal.

The power amplifier 25 is connected to the second filter 24, and is used to amplify the first radio frequency signal to obtain the second radio frequency signal; the power amplifier 25 can amplify the power of the signal output by the second mixer 23 to be suitable for transmission .

The coupler 26 is connected to the power amplifier 25, and is used to couple the signal output by the power amplifier 25 to output the second radio frequency signal and the third feedback signal; the output of the coupler 26 has two channels, one is for the second transmission signal It is sent to the antenna 27, and the other way is to use part of the second transmission signal as a feedback signal and send it to the feedback circuit 30.

The antenna 27 is connected to the coupler 26 and is used to receive the second radio frequency signal output by the coupler 26.

The feedback circuit 30 includes an analog-to-digital converter 31. The analog-to-digital converter 31 is respectively connected to the coupler 26 and the digital predistortion device 10, and is used to convert the third feedback signal into the first feedback signal and input it to the digital predistortion device 10. In a specific embodiment, the analog-to-digital converter 31 is respectively connected to the first mixer 112 and the digital predistorter 13, which can collect part of the RF signal fed back as a digital signal and provide it to the first mixer. The processor 112 and the digital predistorter 13 perform processing.

In other embodiments, the coupler 26 may also be connected to the antenna 27 through a duplexer 28, and the duplexer 28 may isolate the transmission signal from the reception signal to ensure that the reception and transmission can work normally without interfering with each other.

During the scanning time, the digital predistortion device 10 is used to detect the amplitude of nonlinear products. The scanning time is determined by the physical layer signal mode and can be adjusted according to actual needs; since the number of channels can be multiple, it can also be based on channel information, etc. Control information to determine which communication non-linear product amplitude to record; it can also determine whether to enable the predistortion function according to the enable signal, for example, when the enable signal is 1, the predistortion function is turned on, and when the enable signal is 0, it is not used Predistortion function.

In a specific embodiment, each channel is dual-carrier transmission, the index of the power difference between the third-order intermodulation component and the effective signal is -70dBc, the carrier frequency interval is 200KHz, and the first threshold and the second threshold are set. The threshold value is -75dBc and -72dBc, the frequency sweep mode is ±200KHz alternately, and the sweep time is a time slot 14.167ms. The digital predistorter 13 iterates until it reaches a stable state, and always checks whether the power of the nonlinear product meets the requirements. If the power of the current non-linear product increases, the iteration will be resumed until a steady state is reached, so that the power of the non-linear product meets the requirements.

The frequency is swept through the feedback circuit 30 of the transmitter, and the frequency of the sweep is flexibly controlled in combination with the transmission frame format, and the reliable nonlinear product amplitude and low delay are reported to the digital predistorter 13 for iterative decision-making; for the transmission in the communication system It can keep the amplitude of nonlinear products at a low level for a long time. Compared with the frequency sweeping scheme of traditional receivers, it can save instrument use, reduce material and labor costs, and facilitate automatic remote monitoring.

The above are only examples of this application, and do not limit the scope of this application. Any equivalent structure or equivalent process transformation made using the content of the description and drawings of this application, or directly or indirectly applied to other related technical fields, The same reasoning is included in the scope of patent protection of this application.

Claims

A digital predistortion device, which includes:

A digital down-conversion circuit for receiving a first feedback signal and converting the first feedback signal into a second feedback signal, wherein the frequency of the first feedback signal is greater than the frequency of the second feedback signal;

A signal strength acquisition circuit, connected to the digital down-conversion circuit, for acquiring the power of the second feedback signal, wherein the second feedback signal includes at least two effective signals and intermodulation between the effective signals Weight

A digital predistorter, connected to the signal strength acquisition circuit, and configured to perform predistortion processing according to the power of the second feedback signal to reduce the power of the nonlinear product in the output signal, and output a first intermediate frequency signal;

Wherein, the non-linear product is the intermodulation component between the effective signals.
The digital predistortion device according to claim 1, wherein the digital down-conversion circuit comprises:

The first oscillator is used to generate a digital oscillation signal;

A first mixer, connected to the first oscillator, and configured to perform mixing processing on the first feedback signal and the digital oscillation signal to obtain the second feedback signal;

The first filter is connected to the first mixer and used to filter the second feedback signal.
The digital predistortion device according to claim 1, wherein:

The digital predistorter stores a mapping table of the frequency of the effective signal, the power of the effective signal, the power of the nonlinear product, and the power difference between the effective signal and the nonlinear product.
The digital predistortion device according to claim 3, wherein:

The digital predistorter is used to detect the power of the nonlinear product in the output signal, and the amount of change in the power difference between the effective signal and the nonlinear product in the output signal is in the predistortion When the range is set, stop iteration, and use the minimum value of the power of the nonlinear product in the iteration process as the power of the nonlinear product in the mapping table.
The digital predistortion device according to claim 4, wherein:

The digital predistorter is further configured to determine a preset first threshold and a preset second threshold according to the power difference between the effective signal and the nonlinear product in the mapping table to determine whether to perform iteration, When it is detected that the power difference between the effective signal and the non-linear product in its output signal is less than the preset first threshold, the iteration is stopped; in the output signal, the effective signal and the non-linear product When the power difference between the products is greater than the preset second threshold, iterating continues until the power difference between the effective signal and the nonlinear product is less than the preset first threshold, wherein the The preset first threshold and the preset second threshold are respectively positively correlated with the power of the nonlinear product in the mapping table, and the preset first threshold is smaller than the preset second threshold.
The digital predistortion device according to claim 1, wherein:

The non-linear products include third-order intermodulation products or fifth-order intermodulation products between the effective signals.
The digital predistortion device according to claim 1, wherein:

The effective signal includes a first intermediate frequency signal and a second intermediate frequency signal. The first intermediate frequency signal is a signal generated after a first carrier signal is modulated by a digital baseband signal, and the second intermediate frequency signal is a second carrier signal that is modulated by the The signal generated after digital baseband signal modulation.
A transmitter, which includes a digital predistortion device, a transmitting circuit, and a feedback circuit. The digital predistortion device is used for predistorting an input signal and sending the processed signal to the transmitting circuit. The transmitting circuit is used to receive and process the signal output by the digital predistortion device, and output the signal to the feedback circuit. The feedback circuit is used to process the signal output by the transmitting circuit and output the processing result to all The digital predistortion device, wherein the digital predistortion device is used as the digital predistortion device according to any one of claims 1-7.
The transmitter according to claim 8, wherein the transmitting circuit comprises:

A digital-to-analog converter connected to the digital predistortion device and used to convert the first intermediate frequency signal output by the digital predistortion device into a second intermediate frequency signal;

The second oscillator is used to generate a local oscillation signal;

A second mixer, respectively connected to the digital-to-analog converter and the second oscillator, for mixing the second intermediate frequency signal and the local oscillation signal;

A second filter, connected to the output end of the second mixer, and used for filtering the signal output by the second mixer to obtain the first radio frequency signal;

A power amplifier, connected to the second filter, for amplifying the first radio frequency signal to obtain a second radio frequency signal;

A coupler, connected to the power amplifier, and used to couple the signal output by the power amplifier to output the second radio frequency signal and the third feedback signal;

The antenna is connected to the coupler and is used to receive the second radio frequency signal output by the coupler.
The transmitter according to claim 9, wherein:

The feedback circuit includes an analog-to-digital converter, which is connected to the coupler and the digital predistortion device, respectively, for converting the third feedback signal into the first feedback signal, and Input to the digital predistortion device.