CN101431378A - Distortion simulator of broadcast communication transmitter and its distortion correction test method - Google Patents

Abstract

The invention relates to a distortion emulator of a broadcast communication transmitter and a distortion correction test method thereof. The emulator of the invention simulates various transmitter distortion models through a linear distortion simulation module and a nonlinear distortion simulation module to test the system distortion correction performance. It also includes a down-converter and an up-converter for processing radio frequency signals, which can process both radio frequency band signals and digital baseband signals. The method of the invention includes a broadcast communication transmitter calibration performance test method and a broadcast communication system anti-distortion performance test method. This method simulates the transmission distortion by a distortion simulator, evaluates the correction performance of the exciter, and evaluates the anti-transmission distortion performance of the communication system. The device and method of the invention can evaluate the performance of the transmitter and receiver of the broadcast communication system in a laboratory environment. Compared with the traditional experimental method, the complexity of the experimental equipment is simplified and the experimental cost is reduced.

Description

Distortion emulator of broadcast communication transmitter and its distortion correction test method

technical field

The invention belongs to the field of digital communication testing, and relates to a distortion emulator of a broadcast communication transmitter and a distortion correction test method thereof. Specifically, the invention relates to a simulation device for simulating transmission distortion and a method and method for performing correction performance tests on a broadcast communication transmitter A method for testing the anti-distortion interference performance of a broadcast communication system.

Background technique

With the development of digital communication technology, various new technologies are constantly emerging, and new digital communication systems are constantly emerging. Compared with analog modulated signals, digitally modulated signals have wider bandwidth, and the output amplitude has a larger dynamic range. There are also various modulation devices and means, which put forward higher requirements for the development and manufacture of equipment.

On the one hand, it is the influence of linear distortion. Due to the different communication transmission standards, the devices and technologies used in the modulation and frequency conversion process are also different. Because the technology of the device and the manufacturing process of the circuit are not ideal, due to the reason of the modulation, frequency conversion device and circuit It will introduce distortion to the baseband signal. Since the value of the distortion changes linearly with the input signal, it is called linear distortion. Described by a mathematical model, there are many types of distortion in the modulation process, mainly three types: carrier leakage, gain imbalance and component orthogonality deviation.

Let the undisturbed correct output modulation signal be

s ₀ (t)＝I·cos2πf _c t+Q·sin2πf _c t

Among them, I and Q are the baseband signal of quadrature respectively, f _c is the carrier frequency.

(1) The component orthogonality deviation is caused by the incomplete orthogonality of the carrier phase multiplied by the baseband signal during the frequency conversion process of the up-converter, which will form a distortion of the shape of the constellation diagram. For example, the constellation diagram of 16QAM modulation will change from a square envelope to a diamond envelope when the component orthogonality deviates.

The signal s ₁ (t) disturbed by component orthogonality deviation is:

和

分别为两路相角偏差分量。in,

and

are the two phase angle deviation components respectively.

(2) Gain imbalance is caused by the difference in gain of the two quadrature baseband signals input to the up-converter. If the two orthogonal baseband signals have different gains, the shape of the constellation diagram will be distorted. For example, the constellation diagram of 16QAM modulation will change from a square envelope to a rectangular envelope when the gain is unbalanced.

The signal s ₂ (t) disturbed by the gain imbalance is:

s ₂ (t)＝α _I ·I·cos2πf _c t+α _Q ·Q·sin2πf _c t

Wherein, α _I and α _Q (α _I ≠ α _Q ) are the gains of the two baseband signals, respectively.

(3) The reason for carrier leakage is that in the baseband digital-to-analog conversion circuit, the output analog baseband signal is mixed with an additive DC component, and the analog baseband signal with the DC component is input to the frequency conversion circuit of the subsequent stage, and the carrier frequency point is added. The undesired power causes the distortion of the spectrogram.

The signal s ₃ (t) interfered by carrier leakage is:

s ₃ (t)＝(I+Δ _I )cos2πf _c t+(Q+Δ _Q )sin2πf _c t

＝(I·cos2πf _c t+Q·sin2πf _c t)+( _ΔI ·cos2πf _c t+ _ΔQ ·sin2πf _c t)

Among them, _ΔI and _ΔQ are two DC offset components respectively.

On the other hand, it is the influence of nonlinear distortion. After modulation, the output signal needs to be amplified and then transmitted. At the radio frequency output end of the transmitter of the broadcast communication system, the power of the power amplifier cannot increase linearly after exceeding the linear amplification area due to the saturation effect of the device. However, it presents nonlinear amplification characteristics, and this type of distortion belongs to nonlinear distortion. The nonlinear distortion effect will directly affect the waveform of the output signal. The nonlinear distortion caused by the power amplifier will cause the spectrum expansion of the original input signal, and will cause in-band distortion, which will adversely affect the adjacent frequency signal and its own signal.

The nonlinear distortion of the power amplifier is divided into two types: non-memory nonlinearity and memory nonlinearity. The output value of the memoryless nonlinear amplifier is only related to the instantaneous value of the current input. The output value of the nonlinear amplifier with memory is not only related to the instantaneous value of the current input, but also related to the signal value of the previous input. The nonlinear distortion model is much more complex than the linear distortion model. Here are some examples of nonlinear distortion models.

(1) For the analysis of memoryless nonlinear amplifiers, the simplest model is to use Taylor series. Suppose the input signal is s ₀ (t), the output signal s ₁ (t) after a signal passes through the memoryless nonlinear amplifier can be expressed as:

s ₁ (t)=c ₁ ·s ₀ (t)+c ₂ ·s ₀ (t) ² +c ₃ ·s ₀ (t) ³ +...

In addition to the power series model, the description of the memoryless power amplifier is also widely used, such as the Saleh model, the Rapp model and the limiting model.

(2) The model of the non-linear amplifier with memory is relatively complicated, and many description methods have been proposed, the most common one is the Volterra series model. In order to reduce the complexity of the Volterra series, only the third-order expression is used here:

$\mathrm{<span\; class="notranslate">\; the\; y</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span>$

$<span\; class="notranslate">\; +</span>\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="N"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">N</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>$

$<span\; class="notranslate">\; +</span>\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="N"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">N</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="m"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="N"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">N</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="m"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="m"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ]</span>$

Among them, N ₁ , N ₂ , and N ₃ represent the memory depths of the first-order formula, the second-order formula, and the third-order formula, respectively, and h ₁ , h ₂ , and h ₃ represent the coefficients of each order. When using Volterra series to represent nonlinear systems, the corresponding coefficients of each order must be known. As the order increases, the number of coefficients increases rapidly.

In practical systems, linear and non-linear distortions are ubiquitous. In order to overcome this distortion, it is necessary to reverse the distortion effect of the amplifier. This part of the function is completed by the linear and non-linear correction functions in the exciter. The main method used is There are feedforward method, feedback method, predistortion method and so on.

To verify the effect of the correction algorithm, it is first necessary to perform simulation in the software. After the simulation proves that the algorithm is effective, the algorithm is implemented on the hardware, and the actual correction device is produced, which is used as a part of the exciter and used in the actual transmitter power amplifier. Experiments were carried out to verify the performance of the calibration device. Each experiment can only verify the performance of the calibration device with a certain transmitter power amplifier. If you want to verify how the calibration device cooperates with various types of transmitters, you need to install the calibration equipment on other transmitters. Because one transmitter cannot represent the characteristics of various different types of transmitters, it is inconvenient to implement this kind of verification experiment.

From another perspective, the communication transmission system first needs to have the ability to resist channel noise and fading. In the case of high-power transmission, because the system will also be affected by the distortion effect of the power amplifier, the communication transmission system also needs to have a certain resistance. Capability of non-linear distortion. In the development process of the transmission system, it is necessary to test the performance of the communication transmission system under the interference of linear and nonlinear distortion.

Therefore, there is a need for a testing method and an emulator device for testing the correction performance of a broadcast communication exciter and testing the transmission performance of a broadcast communication transmitting and receiving system against nonlinear distortion. The corrector in the existing exciter is to offset the distortion effect in the power amplifier, rather than to simulate the distortion effect in the power amplifier. There is no similar emulator device mentioned in the existing literature, so the simulation proposed by the present invention Linear and non-linear distortion equipment is necessary.

Contents of the invention

The invention proposes a distortion emulator of a broadcast communication transmitter and a distortion correction test method thereof. Specifically, the invention relates to a simulation device for simulating the distortion of a broadcast communication transmitter, a method for testing the correction performance of a broadcast communication transmitter, and a method for testing the correction performance of a broadcast communication transmitter. The method for testing the anti-distortion interference performance of the system, the transmission distortion simulation device can simulate the distortion effects of various high-power transmitters under the condition of not using high-power transmitters.

A kind of distortion emulator of broadcast communication transmitter of the present invention comprises:

Down-converter: When the input signal E is a radio frequency signal, the down-converter down-converts the input signal E into an analog baseband signal and outputs it to the analog-to-digital converter, and the down-converted carrier frequency value is sent to the down-converter by the controller.

Analog-to-digital converter: convert the analog baseband signal input by the down-converter into a digital baseband signal, and output it to the first selection switch;

The first selection switch: select the digital baseband signal F of the external input simulator or the digital baseband signal G output by the analog-to-digital converter, and output the selected signal to the linear distortion simulation module, and the selection is controlled by the controller.

Linear distortion simulation module: The linear distortion simulation module performs linear distortion transformation on the input digital baseband signal, the controller sends commands and parameters to the linear distortion simulation module according to the linear distortion model set by the user, and the linear distortion simulation module follows the commands and parameters performing linear distortion simulation on the signal output by the first selection switch, and outputting the distorted digital baseband signal to the nonlinear distortion simulation module.

Nonlinear distortion simulation module: The nonlinear distortion simulation module performs nonlinear distortion transformation on the input digital baseband signal, and the controller sends commands and parameters to the nonlinear distortion simulation module according to the nonlinear distortion model and model parameters set by the user. The nonlinear distortion simulation module performs nonlinear distortion simulation on the linearly distorted signal according to commands and parameters, and outputs the nonlinear distortion signal to the power protection module.

Power protection module: The nonlinear distortion simulation module outputs signals to the power protection module. If the output signal amplitude of the nonlinear distortion simulation module exceeds a certain value, the power protection module takes amplitude limiting measures to protect the safety of the subsequent stage circuit, and sends a " Overload" signal, the limited signal is output to the second selection switch; if the input signal amplitude is below the threshold, the output signal of the power protection module is the same as the input signal, and the signal is output to the second selection switch.

Second selection switch: the digital baseband signal output by the power protection module is input to the second selection switch, and is controlled by the controller to directly output the digital baseband signal (as output signal K), or send it to a digital-to-analog converter.

Digital-to-analog converter: convert the digital baseband signal output by the second selection switch into an analog baseband signal, and output it to the up-converter.

Up-converter: Up-convert the analog baseband signal into a radio frequency signal, which is used as the output signal J of the emulator.

Controller: set the center frequency of the down-converter, set the input signal selection of the first selection switch, set the linear distortion model of the linear distortion simulation module, set the nonlinear distortion model of the nonlinear distortion simulation module, and set the output of the second selection switch Signal selection, setting the center frequency of the up-converter, receiving the overload flag signal sent by the power protection module, sending status information to the user interface, and receiving operation information of the user interface.

User interface: Receive the status information of the controller and display it to the user, and the user sends operation information to the controller through the user interface.

The working process of the distortion simulator of the broadcast communication transmitter is as follows:

The RF signal E output by the exciter of the system under test is input to the down-converter; the carrier frequency of the down-converter is set by the controller, and the input signal E is down-converted to a baseband analog signal; and then converted to a digital baseband by an analog-to-digital converter The signal, marked as signal G, is input to one end of the first selection switch; if the exciter has a digital baseband signal output, the digital baseband output signal is marked as signal F, and is input to the other end of the first selection switch; the first selection switch is controlled by Controller control, select signal G or signal F to input the linear distortion simulation module; the linear distortion simulation module internally stores the linear distortion mathematical model, the controller sends the parameters of the linear distortion model to the linear distortion simulation module, and the linear distortion simulation module adds to the digital baseband signal Linear distortion effect, output the converted digital baseband signal to the nonlinear distortion simulation module; the nonlinear distortion simulation module internally stores the nonlinear distortion mathematical model, and the controller sends the type and parameters of the nonlinear distortion model to the nonlinear distortion simulation module, The nonlinear distortion simulation module adds nonlinear distortion effects to the digital baseband signal, and the converted digital baseband signal is input to the power protection module; the power protection module performs amplitude limiting processing when the input signal amplitude exceeds the threshold, and sends an overload flag to the controller. If it does not exceed the threshold, it is output to the second selection switch; the second selection switch is controlled by the controller, and the input signal is output to the digital-to-analog converter as its input signal H, or output as a digital baseband output signal K; digital-to-analog conversion The device converts the digital baseband signal H into an analog baseband signal, which is input to the upconverter, and the carrier frequency value of the upconverter is sent by the controller.

The test method of the invention includes two aspects: one is a test method for the correction performance of a broadcast communication transmitter; the other is a test method for the anti-distortion performance of a broadcast communication system transmitter.

In the present invention, the calibration performance test method of a broadcast communication transmitter comprises:

a data generator that generates a data signal modulated by the exciter;

An exciter for generating radio frequency broadcast transmission signals;

Transmit distortion simulator, add the influence of distortion effect to the transmitted signal, and output the distorted signal;

Spectrum Analyzer, which measures the spectrum of the output signal of the transmit distortion simulator.

Step 1: The data source sends data A to the exciter, and the exciter outputs the modulated and frequency-converted signal E to the transmission distortion simulator. The exciter does not correct the signal, and the emulator does not distort the signal at this time, and the emulator outputs It is a normal signal J, and the spectrum analyzer observes that the signal J spectrum output by the emulator is the correct spectrum;

Step 2, the launch distortion emulator is set to the linear and nonlinear distortion models specified by the user, and the spectrum of the emulator output signal J is observed with a spectrum analyzer, and the spectrum is distorted;

Step 3: The emission distortion simulator maintains the distortion model, the exciter starts the internal correction function, corrects the output signal E, the output of the exciter becomes the pre-distorted signal E, and the spectrum analyzer observes whether the spectrum of the signal J output by the emulator changes to Correct, if it becomes correct, it means that the exciter has made correct pre-correction to the distortion model; if the signal J spectrum still contains distortion after the exciter is corrected, it means that the exciter cannot correct the distortion model;

Step 4, change the linear and nonlinear distortion parameters and models set by the emission distortion simulator, repeat step 3, and test the correction performance of the exciter under different distortion models;

Step five, repeat the process of step two, step three and step four for other exciters, and compare the advantages and disadvantages of the calibration performance among different exciters.

In the present invention, the anti-transmitter distortion performance test method of the broadcast communication system, the equipment composition includes:

a data generator that generates a data signal modulated by the exciter;

An exciter for generating radio frequency broadcast transmission signals;

Transmit distortion simulator, add the influence of distortion effect to the transmitted signal, and output the distorted signal;

The receiver demodulates the output signal of the transmitter distortion simulator to observe the reception effect.

Step 1: The data source sends data A to the exciter, and the exciter outputs the digital baseband signal F or the signal E after modulation and frequency conversion to the transmission distortion simulator. The exciter does not start the signal pre-correction function, and the simulator does not correct the signal E at this time or F for distortion processing, the output of the emulator is a normal baseband signal K or RF signal J;

Step 2, the transmit distortion simulator is set to the linear and nonlinear distortion models specified by the user;

Step 3, observe the output P of the receiver and evaluate the receiving effect of the receiver at this time;

Step 4, change the linear and nonlinear distortion parameters and models set by the transmit distortion simulator, repeat step 3, and test the transmission performance of the system composed of exciter and receiver under various distortion models;

Step five, repeat the process of step two, step three and step four for other exciter and receiver systems, and compare the difference in transmission performance of different systems.

The transmission distortion emulator and distortion correction test method described above are to simulate the transmission distortion of digital broadcast signals by using hardware digital device simulation without using a high-power transmitter to amplify and transmit the signal, and to test the system test. The linear distortion simulation module and the nonlinear distortion simulation module in the emulator are computing platforms composed of digital circuit devices. The mathematical algorithm model is applied in the distortion simulation process, and the distorted digital baseband signal after model calculation is output. The input port of the emulator can be a digital baseband signal or an up-converted radio frequency signal of the exciter, and the output port of the emulator can be a digital baseband signal or an up-converted radio frequency signal.

The test method of the invention can be applied to the test of the digital broadcasting transmission system, and can also be applied to the test of the digital communication system. It is used in the digital broadcasting system because the transmission signal power of the broadcast transmission system transmitter is relatively large, and it is most likely to encounter nonlinear distortion problems. Using the present invention can simulate a variety of nonlinear distortion situations; it is used in digital communication systems to simulate linear distortion. Various linear distortion situations can be simulated by using the invention. In a word, the present invention provides a test and evaluation method and a reconfigurable distortion simulation platform, which can be used under various digital transmission systems and standards, and the test results can be used as a reference for the researchers of the transmitting system in the equipment development stage.

The advantages of the distortion emulator of the broadcast communication transmitter of the present invention and its distortion correction testing method are:

(1) Test the correction performance of the exciter and the anti-distortion performance of the system without a high-power transmitter, which reduces the complexity of the experiment.

(2) In the past, a specific power amplifier was used for experiments, which only had one input and output interface. The device of the present invention has two interfaces, which can be adapted to connect various transmitting and receiving devices.

(3) The present invention uses one device to simulate the distortion effects of various power amplifiers, and the parameters are set by the user, which saves the experiment cost.

Description of drawings

Fig. 1 is a transmission distortion emulator internal structure block diagram among the present invention;

Fig. 2 is a structural block diagram of a method for testing the correction performance of a broadcast communication transmitter in the present invention;

Fig. 3 is a structural block diagram of the method for testing the anti-transmitter distortion performance of the broadcast communication system in the present invention;

Fig. 4 is the algorithm schematic diagram of the internal linear distortion emulation module of transmitting distortion emulator among the present invention;

Fig. 5 is the example of the input signal 16QAM constellation diagram of the linear distortion emulation module of the present invention;

Fig. 6 is the example of the constellation diagram of the orthogonality deviation simulation output signal of the linear distortion simulation module of the present invention;

Fig. 7 is the gain unbalance simulation output signal constellation example of the linear distortion simulation module of the present invention;

Fig. 8 is an example of the carrier leakage simulation output signal constellation diagram of the linear distortion simulation module of the present invention;

Fig. 9 is the example of the input signal 16QAM spectrogram of linear distortion emulation module of the present invention;

Fig. 10 is an example of the frequency spectrum diagram of the carrier leakage simulation output signal of the linear distortion simulation module of the present invention;

Fig. 11 is one of the algorithm schematic diagrams of the internal nonlinear distortion simulation module of the transmission distortion simulator in the present invention;

Fig. 12 is the second schematic diagram of the algorithm of the nonlinear distortion simulation module inside the transmission distortion simulator in the present invention;

Fig. 13 is the third schematic diagram of the algorithm of the nonlinear distortion simulation module inside the transmission distortion simulator in the present invention;

Fig. 14 is the example of the multi-carrier frequency spectrum diagram of the input signal of the nonlinear distortion simulation module of the present invention;

Fig. 15 is an example of a multi-carrier spectrum diagram of the output signal of the nonlinear distortion simulation module of the present invention.

In the picture:

1. Data generator 2. Exciter 21. Digital baseband modulation module 22. Predistortion corrector

23. Digital-to-analog converter 24. Up-converter 3. Transmit distortion simulator 31. Down-converter

32. Analog-to-digital converter 33. First selection switch 34. Linear distortion simulation module

340 Orthogonality Deviation Simulation Unit

3401. First function generator 3402. Second function generator 3403. Third function generator

3404. Fourth function generator 3405. First multiplication unit 3406. Second multiplication unit

3407. The third multiplication unit 3408. The fourth multiplication unit 3409. The first addition unit

3400. The second addition unit

341. Gain imbalance simulation unit 3411. Fifth multiplication unit 3412. Sixth multiplication unit

342. Carrier Leakage Simulation Unit 3421. The Third Addition Unit 3422. The Fourth Addition Unit

35. Nonlinear distortion simulation module 3501. Modulo unit 3502. Phase angle unit

3503. Clipping model unit

3504. Saleh model unit 3505. Rapp model unit 351. Power series model processing unit

3511. Multiplication unit group 1 3512. Multiplication unit group 2 3513. Addition unit group 1

352. Volterra series simulation unit

3521. Delay unit group 1 3522. Volterra series operation unit

36. Power control module 37. Second selector switch 38. Digital-to-analog converter

39. Upconverter 310. Controller 311. User Interface

4. Receiver 41. Down-converter 42. Analog-to-digital converter 43. Third selection switch

44. Digital baseband demodulation module

5. Spectrum Analyzer

Detailed ways

Below in conjunction with accompanying drawing, the present invention is illustrated: the transmission distortion emulator 3 that is used for broadcast communication transmitter distortion correction test, as shown in Figure 1, structure comprises down-converter 31, analog-to-digital converter 32, first selection switch 33 , a linear distortion simulation module 34 , a nonlinear distortion simulation module 35 , a power protection module 36 , a second selection switch 37 , a digital-to-analog converter 38 , an upconverter 39 , a controller 310 , and a user interface 311 .

The radio frequency input signal E is input to the down converter 31, the carrier frequency of the down converter 31 is set by the controller 310, the down converter 31 completes the down conversion process, and the radio frequency signal is down converted into an analog baseband signal, which is input into the analog-to-digital converter 32; The analog-to-digital converter 32 converts the analog baseband signal into a digital baseband signal G, and the signal G is input to one end of the first selector switch 33; the digital baseband input port of the emulator 3 inputs the baseband signal F into the other end of the first selector switch 33, and the second end of the first selector switch 33 is input by the signal G. A selection switch 33 is sent by the controller 310 to control the selection signal F or signal G to input the linear distortion simulation module 34; the linear distortion simulation module 34 is controlled by the controller 310, selects the linear distortion model stored in the interior and sets the parameter value of the model, Carry out linear distortion processing to the input digital baseband signal, the digital baseband signal input nonlinear distortion simulation module 35 through the digital baseband signal of linear distortion processing; The parameter value of model carries out nonlinear distortion processing to the digital baseband signal of input through linear distortion processing, and the digital baseband signal input power control module 36 through nonlinear distortion processing; If baseband signal amplitude exceeds the threshold of power control module 36, then Limit the amplitude so that the output signal amplitude is not higher than the threshold, and send the overload sign to the controller 310. If there is no signal exceeding the threshold, it will be output to one end 37 of the second selector switch; the second selector switch 37 is controlled by the controller 310 , choose to output the input digital baseband signal to the digital-to-analog converter 38 as the signal H, or directly output the input digital baseband signal as the signal K; the signal H is input to the digital-to-analog converter 38 to become an analog baseband signal, input Up-converter 39; the carrier frequency of up-converter 39 is set by the controller 310, and the input analog baseband signal is frequency-converted into a radio frequency signal, which is used as the emulator radio frequency output signal J; all the above-mentioned parameters sent to other modules by the controller 310 are passed The user interface 311 is set, and the user interface 311 has functions of inputting commands and displaying the state of the emulator.

The simulations carried out by the linear distortion simulation module 34 and the nonlinear distortion simulation module 35 of the internal components of the emulator 3 are mutually independent from the mathematical model, but the sequence cannot be changed, because in the transmitter of the broadcasting system, most linear distortions Introduced in the process of frequency conversion, most of the nonlinear distortion is introduced in the power amplification process after frequency conversion;

In addition, the hardware devices inside the emulator 3 inevitably have certain distortion interference. When the input is the radio frequency signal E, the down converter 31 and the analog-to-digital converter 32 contain analog devices, which will introduce a certain amount of noise and frequency distortion. When the output is a radio frequency signal J, the digital-to-analog converter 38 and the up-converter 39 also contain analog devices, and their working principle is similar to that of the exciter rear stage, and there are also influences of noise, linear distortion in the frequency conversion process, and nonlinear distortion in the amplification process , the emulator is used as a test device, the components used in the above-mentioned modules have been calibrated for noise and distortion, and the influence caused by the above-mentioned modules can be ignored compared with the signal distortion caused by the linear distortion simulation module 34 and the nonlinear distortion simulation module 35;

For the device interference problem mentioned above, if the input signal is a digital baseband signal F and the output signal is a digital baseband signal K, the processing process of the emulator is completely digital in the digital device, and there will be no interference from the analog device.

As shown in Figure 4, the linear distortion simulation module 34 includes an orthogonality deviation simulation unit 340, a gain imbalance simulation unit 341, and a carrier leakage simulation unit 342, and completes three kinds of linear distortion simulations: orthogonality deviation simulation, gain imbalance Balance simulation, carrier leakage simulation.

信号通过第一乘法单元3405相乘，将输入正交性偏差仿真单元340的信号Q₀与第四函数发生器3404输出的

信号通过第四乘法单元3408相乘，第一乘法单元3404输出结果取负和第四乘法单元3408输出的结果在第二加法单元3400中相加，输出信号Q₁；将输入信号I₀与第三函数发生器3403输出的

信号通过第三乘法单元3407相乘，将输入信号Q₀与函数发生器23402输出的

信号通过第二乘法单元3406相乘，第二乘法单元3406输出结果和第三乘法单元3407输出的结果在第一加法单元3409中相加，输出信号I₁。The orthogonality deviation simulation unit 340 includes a first function generator 3401, a second function generator 3402, a third function generator 3403, a fourth function generator 3404, a first multiplication unit 3405, a second multiplication unit 3406, a third A multiplication unit 3407 , a fourth multiplication unit 3408 , a first addition unit 3409 , and a second addition unit 3400 . The orthogonality deviation simulation unit 340 multiplies the input I ₀ and Q ₀ signals by the output signal of the function generator, adds the multiplied results, and outputs signals I ₁ and Q ₁ to the gain imbalance simulation unit. The specific operation is: input the signal I ₀ of the orthogonality deviation simulation unit 340 and the output of the first function generator 3401

The signal is multiplied by the first multiplication unit 3405, and the signal Q ₀ input to the orthogonality deviation simulation unit 340 is output by the fourth function generator 3404.

The signal is multiplied by the fourth multiplication unit 3408, the output result of the first multiplication unit 3404 is negative and the result output by the fourth multiplication unit 3408 is added in the second addition unit 3400, and the output signal Q ₁ ; the input signal I ₀ and the first Three function generator 3403 output

The signal is multiplied by the third multiplication unit 3407, and the input signal Q ₀ is output by the function generator 23402

The signals are multiplied by the second multiplication unit 3406, and the output result of the second multiplication unit 3406 and the output result of the third multiplication unit 3407 are added in the first addition unit 3409 to output a signal I ₁ .

The gain imbalance simulation unit 341 includes a fifth multiplication unit 3411 and a sixth multiplication unit 3412 . The _I1 and _Q1 signals input to the gain imbalance simulation unit 341 are multiplied by coefficients respectively, and the output signals _I2 and _Q2 are given to the carrier leakage simulation unit. The specific operation is: the controller 310 sends parameters A _I and A _Q to the gain imbalance simulation unit 341 in the linear distortion simulation module 34, and then, the signal _I1 input to the gain imbalance simulation unit 341 is combined with the fifth multiplication unit 3411 The coefficient A _I is multiplied, and the result I ₂ is output; the signal Q ₁ input to the gain imbalance simulation unit 341 is multiplied by the coefficient in the sixth multiplication unit 3412 , and the result Q ₂ is output.

The carrier leakage simulation unit 342 includes a third adding unit 3421 and a fourth adding unit 3422 . The I ₂ and Q ₂ signals of the input carrier leakage simulation unit 342 are added to the coefficients, and the output signals I ₃ and Q ₃ are used as the output of the linear distortion simulation module 34. The carrier leakage simulation unit 342 sends parameters Δ _I and Δ _Q , then, the signal I ₂ input to the carrier leakage simulation unit 342 is added to the parameter Δ _I in the third addition unit 3421, and the output result I ₃ ; the input carrier leakage simulation unit 342 The signal Q ₂ of is added to the parameter Δ _Q in the fourth addition unit 3422, and the output result Q ₃ ;

The final output signal after linear distortion simulation is:

正交相位偏差

I路增益A_I、Q路增益A_Q、I路直流偏差Δ_I、Q路直流偏差Δ_Q和采样频率R₁。The linear distortion simulation module 34 processes the baseband signal in the digital domain. According to the Nyquist sampling law, in order to ensure that the signal is not distorted after sampling, the sampling frequency should be twice the highest frequency contained in the baseband signal spectrum. The sampling rate R ₁ of the linear distortion simulation module 34 is set by the controller 310 . The parameters sent by the controller 310 to the linear distortion simulation module 34 include: phase deviation in the same direction

quadrature phase deviation

I channel gain A _I , Q channel gain A _Q , I channel DC deviation Δ _I , Q channel DC deviation Δ _Q and sampling frequency R ₁ .

Let the center frequency of the inverter carrier in the exciter 2 be f _c , the real and imaginary components of the baseband signal input to the inverter are I ₀ and Q ₀ , and the correct output signal s ₀ (t) is: s ₀ (t) =I ₀ ·cos2πf _c t+Q ₀ ·sin2πf _c t.

正交分量的相位偏差为

设受影响后的输出信号为s₁(t)：(1) Orthogonality deviation is caused by the phase difference between the same direction component and the orthogonal component of the frequency conversion carrier during the frequency conversion process is not equal to 90°. If the phase deviation of the same direction component of the carrier is

The phase deviation of the quadrature component is

Let the affected output signal be s ₁ (t):

It can be concluded that the processing algorithm adopted in the linear distortion emulator 34 for the simulation of the orthogonality deviation is described in the following formula, and the transformed digital baseband signals are set as I ₁ and Q ₁ :

(2) The unbalanced gain is caused by the difference in gain of the I/Q two-way analog baseband signal in the circuit after the digital-to-analog converter 23 converts the I/Q two-way digital baseband signal into an I/Q analog baseband signal. Suppose the gain of the I path is A _I , the gain of the Q path is A _Q , and the processing algorithm adopted in the gain unbalance simulation in the linear distortion emulator 34 is described as follows:

I ₂ =I ₁ ·A _I

Q ₂ ＝Q ₁ ·A _Q

Among them, I ₁ and Q ₁ are input signals, and I ₂ and Q ₂ are converted digital baseband signals.

(3) Carrier leakage is caused by the baseband analog signal mixed with DC components during the 24 frequency conversion process of the up-converter, so that the mean value of the baseband signal is not equal to 0, which shows that the energy of the carrier frequency point on the spectrum is higher than other frequencies. Assuming that the DC deviation of the I path is _ΔI , and the DC deviation of the Q path is _ΔQ , the processing algorithm adopted by the carrier leakage simulation in the linear distortion simulator 34 is described in the following formula,

I ₃ =I ₂ ·(1+Δ _I )

Q ₃ ＝Q ₂ ·(1+Δ _Q )

Among them, I ₂ and Q ₂ are input signals, and I ₃ and Q ₃ are converted digital baseband signals.

The nonlinear distortion simulation module processes the baseband signal in the digital domain. According to the Nyquist sampling law, in order to ensure that the signal is not distorted after sampling, the sampling frequency should be greater than twice the highest frequency contained in the baseband signal spectrum. The sampling rate R ₂ of the nonlinear distortion simulation module 35 is set by the controller 310 .

FIG. 11 shows a structural example of the nonlinear distortion simulation module 35 , which includes a modulo unit 3501 , a phase angle unit 3502 , a clipping model unit 3503 , a Saleh model unit 3504 , and a Rapp model unit 3505 . This example realizes three kinds of nonlinear distortion models, which are clipping model unit 3503 , Saleh model unit 3504 , and Rapp model unit 3505 . The input signal enters the modulus unit 3501 for modulo calculation, and the output is the signal modulus value; the input signal enters the phase angle unit 3502 for phase angle calculation, and the output is the signal phase angle value; the signal modulus value and the signal phase angle value are used as the limiter model Input signal of unit 3503, Saleh model unit 3504, Rapp model unit 3505.

(1) Saleh model

The Saleh model has a good approximation to the nonlinear characteristics of the traveling wave tube power amplifier (TWTA). Let the input signal be s ₀ (t)=r(t)cos[ω ₀ t+ψ(t)], where r(t) is the modulus value of the input signal, ω ₀ is the carrier frequency, and ψ(t) is the input signal Phase, the output signal s ₁ under the Saleh model is:

s ₁ ＝A ₁ [r(t)]cos{ω ₀ t+ψ(t)+Φ ₁ [r(t)]}

Among them, A ₁ () and Φ ₁ () are the nonlinear action functions of amplitude and phase under the Saleh model, and they are both functions of the modulus r:

是Saleh模型的4个参数，由控制器310设定。Where α _a , β _a ,

are the four parameters of the Saleh model, which are set by the controller 310 .

(2) Rapp model

The Rapp model provides a good approximation to the nonlinear behavior of solid-state power amplifiers (SSPA). Let the input signal be s ₀ (t)=r(t)cos[ω ₀ t+ψ(t)], where r(t) is the modulus value of the input signal, ω ₀ is the carrier frequency, and ψ(t) is the input signal Phase, the output signal s ₂ under the Rapp model is:

s ₂ ＝A ₂ [r(t)]cos[ω ₀ t+ψ(t)]

Among them, A ₂ () is the nonlinear action function of amplitude and phase under the Rapp model, which is a function of the modulus r:

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; r</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; v</span>}\frac{\mathrm{<span\; class="notranslate">\; r</span>}}{{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; vr</span>}}{{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; \}</span>}^{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; P</span>}}}}$

Wherein, A ₀ is the maximum output value, P and v are Rapp model parameters, and A ₀ , P and v are set by the controller 310 .

(3) Clipping model

r(t)为幅值，

为相角，限幅模型输出信号s₃(t)为：The clipping model is the simplest description of the saturation effect of a power amplifier. When the input signal amplitude exceeds a certain value, the output signal amplitude no longer increases. Let the input signal be

r(t) is the amplitude,

is the phase angle, the output signal s ₃ (t) of the clipping model is:

Where A ₀ is the maximum output value, which is set by the controller 310 .

Fig. 12 shows another kind of structural example of described nonlinear distortion simulation module 35, what this example realizes is power series nonlinear model processing unit 351, comprises the first multiplication unit group 3511, the second multiplication unit group 3512 and Addition unit group 3513.

The power series model is a model in which nonlinear distortion is represented by Taylor series. Let the input signal of the power series nonlinear model processing unit 351 be s ₀ (t), and the signal passes through the first multiplication unit group 3511 to obtain N-level power series s ₀ (t), s ₀ (t) ² , ..., s ₀ (t) ⁱ , i=1, 2, ... N, then multiply the parameters by the second multiplication unit group 3512 to obtain the power series c ₁ ·s ₀ (t), c ₂ · s ₀ (t) ² ,..., c _i ·s ₀ (t) ⁱ , and then get the summation result c ₁ ·s ₀ (t)+c ₂ ·s ₀ (t) ² +c ₃ through the addition unit group 3513 ·s ₀ (t) ³ +…+c _i ·s ₀ (t) ⁱ , thus, the output signal s ₄ (t) after power series model processing can be expressed as:

s ₄ (t)＝c ₁ ·s ₀ (t)+c ₂ ·s ₀ (t) ² +c ₃ ·s ₀ (t) ³ +...+c _i ·s ₀ (t) ⁱ

Where s ₀ (t) and s ₄ (t) represent the input signal and output signal of the amplifier respectively, c _i is a real coefficient, i is an integer, i=1, 2, . . . N. Experiments show that for moderately nonlinear systems, when i>3, c _i is small enough to be ignored for simplicity. In this example, the Taylor series with the highest power of 3 is realized, and the expression of the output signal s ₄ (t) is:

s ₄ (t)=c ₁ ·s ₀ (t)+c ₂ ·s ₀ (t) ² +c ₃ ·s ₀ (t) ³

Wherein, c ₁ , c ₂ and c ₃ are parameters of the power series model, which are set by the controller 310 .

For example: the input signal is a single-frequency signal s ₀ (t) = Acos2πf _c t, according to the above formula can be obtained:

${\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="c"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">c</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="c"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">c</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="c"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">c</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}$

$<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="A"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="A"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="A"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

It can be seen that the output not only includes the fundamental frequency f _c component, but also includes the direct current component, the second harmonic 2f _c component and the third harmonic 3f _c component.

If the input is a dual single-frequency signal with equal amplitude s ₀ (t)=A(cos2πf ₁ t+cos2πf ₂ t), we can get:

${\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="c"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">c</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="c"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">c</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="c"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">c</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>}^{\mathrm{<span\; class="notranslate">\; 3</span>}}$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="A"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 9</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}$

$<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="A"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="A"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="A"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="f"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">f</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}$

$<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="A"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="A"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="A"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="f"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">f</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}$

$<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="A"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">cos</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="f"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">f</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="A"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="A"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">A</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 3</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; 3</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>$

It can be seen that for the dual-single frequency input signal s ₀ (t), the output signal s ₄ (t) not only has fundamental frequency f ₁ and f ₂ components, DC spurious components, second harmonic frequency 2f ₁ and 2f ₂ components , the third harmonic frequency 3f ₁ and 3f ₂ components, but also includes the second intermodulation frequency f ₁ ± f ₂ components and the third intermodulation frequency 2f ₁ ± f ₂ , f ₁ ± 2f ₂ components. When the operating bandwidth is less than one octave, the DC and f ₁ ±f ₂ , 2f ₁ , 2f ₂ , 3f ₁ , 3f ₂ , 2f ₁ ±f ₂ , f ₁ ±2f ₂ and other spurious components will fall on the channel outside the band, and can be filtered with appropriate filters, but the third intermodulation frequency 2f ₁ -f ₂ and 2f ₂ -f ₁ components form interference components to the system and are also the main source of power amplifier nonlinearity.

FIG. 13 shows another structural example of the nonlinear distortion simulation module 35. In this example, the Volterra series simulation unit 352 realizes the signal processing structure diagram of the Volterra series simulation. The model includes a delay unit group 3521 composed of delay units and a Volterra series operation unit 3522 .

Since the Volterra series is a memory system, the correlation time of the memory signal is one of the parameters of the model. The reciprocal of the time span T between relevant sampling points is used as the sampling frequency. The time span T is one of the parameters of the Volterra series model. Time The span T determines how many sampling periods the relevant signals are separated. The following takes the third-order Volterra series as an example to illustrate. The input signal first enters the delay unit group 3521, the delay unit group is composed of the first delay unit to the Mth delay unit, M is the maximum order of the delayer, and the delay signals of all levels are obtained s ₀ [n], s ₀ [n- 1], s ₀ [n-2], ..., s ₀ [n-(M-1)], then enter the Volterra series operation unit 3522, set the input signal as s ₀ [n], output signal s ₅ [n ]for:

${\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; +</span>\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="N"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">N</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>$

$<span\; class="notranslate">\; +</span>\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="N"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">N</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="m"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="N"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">N</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}\underset{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="m"\; filenames="A200810227593E00221.png,A200810227593E00222.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="m"\; filenames="A200810227593E00241.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="m"\; filenames="A200810227593E00222.png,A200810227593E00223.png"\; state="\{\{state\}\}">m</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; ]</span>$

个，二阶系数h₂有

个，三阶系数h₃有个。N₁、N₂、N₃首先由用户通过控制器310设定，然后设定所有的h₁、h₂、h₃系数。Among them, N ₁ , N ₂ , and N ₃ represent the memory depths of the first-order formula, the second-order formula, and the third-order formula, respectively, and h ₁ , h ₂ , and h ₃ represent the coefficients of each order, respectively. In this embodiment, the first-order coefficient h ₁ is realized

, the second-order coefficient h ₂ has

, the third-order coefficient h ₃ has indivual. N ₁ , N ₂ , N ₃ are firstly set by the user through the controller 310, and then all h ₁ , h ₂ , h ₃ coefficients are set.

The distortion correction test method of the broadcast communication transmitter of the present invention includes two aspects: one is the correction performance test method of the broadcast communication transmitter; the other is the broadcast communication system anti-distortion performance test method of the transmitter.

The test method for calibration performance of a broadcast communication transmitter is composed of test equipment as shown in FIG.

The data generator 1 generates a digital TV image stream signal A;

The exciter 2 includes a digital baseband modulation module 21, a predistortion corrector 22, a digital-to-analog converter 23, and an upconverter 24;

The digital baseband modulation module 21 performs encoding, interleaving, constellation mapping, framing, filtering and modulation processes on the code stream signal A according to the digital television transmission standard, and outputs the digital baseband signal B, and the predistortion corrector 22 precorrects the signal B , output a digital baseband signal C, the digital-to-analog converter 23 changes the signal C into an analog baseband signal D, and the upconverter 24 upconverts the signal D to generate a digital TV broadcast radio frequency transmission signal E;

The transmission distortion emulator 3 adds the influence of the distortion effect in the digital TV radio frequency transmission signal E, and outputs the signal J after the distortion;

The spectrum analyzer 4 measures the spectrum of the output signal J of the emission distortion simulator 3 .

The method for testing the calibration performance of a broadcast communication transmitter has the following steps:

Step 1, the digital TV image stream signal A is sent from the data source 1 to the exciter 2, and the exciter 2 outputs the signal E after modulation and frequency conversion of the signal A to the transmission distortion simulator 3, and the pre-distortion corrector 22 does not enable the pre-correction function , the emulator 3 does not distort the signal at this time, the output of the emulator 3 is a normal signal J, and the spectrum analyzer 5 observes that the signal J spectrum output by the emulator 3 is a correct spectrum;

Step 2, the launch distortion emulator 3 is set to the linear and nonlinear distortion models specified by the user, and the spectrum of the output signal J of the emulator 3 is observed with the spectrum analyzer 5, and the spectrum is distorted;

Step 3, the transmission distortion simulator 3 maintains the distortion model, the predistortion corrector 22 starts the correction function, the output signal E of the exciter 2 becomes the signal after precorrection, and the spectrum analyzer 5 observes whether the spectrum of the signal J output by the simulator becomes correct : If it becomes correct, it means that the exciter 2 has made correct pre-correction to the distortion model; if the signal J spectrum still contains distortion, it means that the exciter 2 cannot correct the distortion model;

Step 4, change the linear and nonlinear distortion parameters and models set by the launch distortion simulator 3, repeat step 3, and test the correction performance of the exciter 2 under different distortion models;

Step five, repeat the process of step two, step three and step four for other exciters, and compare the advantages and disadvantages of the calibration performance among different exciters.

The test method for anti-transmitter distortion performance of a broadcast communication system is composed of equipment as shown in FIG.

The data generator 1 generates a digital TV image stream signal A;

The exciter 2 includes a digital baseband modulation module 21, a predistortion corrector 22, a digital-to-analog converter 23, and an upconverter 24;

The digital baseband modulation module 21 performs encoding, interleaving, constellation mapping, framing, filtering and modulation processes on the code stream signal A according to the digital television transmission standard, and outputs the digital baseband signal B, and the predistortion corrector 22 precorrects the signal B , the digital baseband signal C is output as the emulator input signal F, the digital-to-analog converter 23 changes the signal C into an analog baseband signal D, the upconverter 24 performs upconversion on the signal D, and outputs the digital TV broadcast radio frequency transmission signal E;

The transmission distortion simulator 3 adds the influence of the distortion effect in the digital baseband signal F or the transmission signal E, and outputs the distorted radio frequency signal J or digital baseband signal K;

The receiver 4 includes a down converter 41 , an analog-to-digital converter 42 , a selection switch 343 , and a digital baseband demodulation module 44 .

The down-converter 41 down-converts the input signal J to an analog baseband signal L, the analog-to-digital converter 42 converts the signal L into a digital baseband signal M, and the selector switch 343 selects signal M or signal K to enter the digital baseband demodulation Module 44 outputs the image signal P after demodulation processing.

In order to cooperate with the selection of two kinds of input ports and two kinds of output ports of the simulator in the present invention, the anti-transmitter distortion performance test method of the broadcast communication system, the exciter 2 has a radio frequency output and a digital baseband output port simultaneously, and the emission correction scheme adopted is Forward digital baseband pre-distortion correction; the receiver 4 has both radio frequency input and digital baseband input ports.

The anti-transmitter distortion performance testing method of the broadcast communication system has the following steps:

Step 1, the digital TV image stream signal A is sent from the data source 1 to the exciter 2, and the exciter 2 outputs the baseband signal C after signal A modulation or the signal E after modulation and frequency conversion to the transmission distortion emulator 3, and the predistortion correction The device 22 does not open the pre-correction function, and the emulator 3 does not distort the input signals F and E at this time, and the emulator 3 outputs a normal baseband signal K or a radio frequency signal J;

Step 2, the transmit distortion simulator 3 is set to the linear and nonlinear distortion models specified by the user;

Step 3, detecting the output signal P of the receiver 4 and evaluating the receiving effect of the receiver 4 at this time;

Step 4, change the linear and nonlinear distortion parameters and models set by the transmission distortion simulator 3, repeat step 3, and test the transmission performance of the system composed of the exciter 2 and the receiver 4 under various distortion models;

Step five, repeat the process of step two, step three and step four for other exciter and receiver systems, and compare the differences in transmission performance between different systems.

Carry out distortion emulation with digital television terrestrial wireless broadcast transmission standard (DTMB) system below as specific embodiment:

As a typical broadband system, the digital TV terrestrial wireless broadcasting system is easily affected by the transmitter because of its large transmission power, and the digital modulation signal, especially the multi-carrier modulation signal, has a large dynamic range of power output and a high peak-to-average power ratio (PAR). Influenced by nonlinear effects, the circuit of the transmitter itself often produces linear distortion. How to correct the linear distortion and nonlinear distortion in the transmission process is a very important research content in the research work of the exciter for the digital TV terrestrial wireless broadcasting.

There are two types of standard technical solutions for digital TV terrestrial wireless broadcasting: single-carrier modulation and multi-carrier modulation. Both methods have their own advantages and are affected by transmitter distortion to different degrees. Since the peak-to-average power ratio (PAPR) of the multi-carrier working mode is higher than that of the single-carrier working mode, it is more susceptible to the influence of nonlinear distortion, so when describing the working process and effect of the nonlinear distortion module, the modulation mode uses multi-carrier Working mode: When a single carrier is affected by linear distortion, the distortion reflection on the constellation diagram is obvious, and the effect is easy to observe. Therefore, when describing the working process and effect of the linear distortion module, the modulation mode adopts the single carrier working mode.

设置第二函数发生器3402和第四函数发生器3404的参数

基带信号I₀和Q₀为单载波16QAM调制的信号，其星座图如图5所示，加入正交性偏差后的基带信号I₁和Q₁星座图如图6所示，可以看到星座图的形状不再是矩形，发生了明显改变。In a specific embodiment 1 of the orthogonality deviation simulation unit 340 of the linear distortion simulation module 34 of the present invention, the structure is as shown in Figure 4, and the parameters of the first function generator 3401 and the third function generator 3403 are set

Setting the parameters of the second function generator 3402 and the fourth function generator 3404

The baseband signals I ₀ and Q ₀ are single-carrier 16QAM modulated signals, and their constellation diagram is shown in Figure 5. The constellation diagram of the baseband signals I ₁ and Q ₁ after adding the orthogonality deviation is shown in Figure 6, and the constellation diagram can be seen The shape of the graph is no longer a rectangle, which has changed significantly.

In a specific embodiment 2 of the gain imbalance emulation unit 341 of the linear distortion emulation module 34 of the present invention, the structure is as shown in Figure 4, and the working state of the orthogonality deviation emulation unit 340 is set as not adding distortion, i.e. _I = I ₀ and Q ₁ =Q ₀ , the parameter A _I of the fifth multiplication unit 3411 is set=2.0, the parameter A _Q of the sixth multiplication unit 3412 is set=1.2, the baseband signal I ₀ and Q ₀ are signals modulated by single carrier 16QAM, Its constellation diagram is shown in Figure 5, and the baseband signal constellation diagram after adding the influence of gain imbalance is shown in Figure 7. It can be seen that the shape of the constellation diagram and the amplitude of the I-way and Q-way become significantly different.

In a specific embodiment 3 of the carrier leakage simulation unit 342 of the linear distortion simulation module 34 of the present invention, the structure is as shown in FIG. That is, I ₂ =I ₁ =I ₀ and Q ₂ =Q ₁ =Q ₀ , the parameter Δ _I of the addition unit 3421 is set=I ₂ ·10%, the parameter Δ _Q of the addition unit 3422 is set=Q ₂ ·(-5% ), baseband signals I ₀ and Q ₀ are signals modulated by single-carrier 16QAM, its constellation diagram is shown in Figure 5, its frequency spectrum is shown in Figure 9, and the baseband signal constellation diagram after adding the influence of carrier leakage is shown in Figure 8, The frequency spectrum is shown in Figure 10. It can be seen that the relative position of the constellation diagram and the coordinate axis has shifted, and the frequency spectrum shows an obvious bulge at the center frequency point.

、

，图14为输入非线性失真仿真模块35的原始多载波调制信号频谱，图15为该信号经过Saleh模型单元3504仿真之后的信号频谱，可以看出输出信号比输入信号肩电平恶化超过30dB。An embodiment of the nonlinear distortion simulation module 35 of the present invention: the nonlinear effect is more likely to occur when the peak-to-average ratio of the signal entering the power amplifier is high, so when verifying the nonlinear effect simulation module 35 in the present invention, a multi-carrier modulation signal is used , which is different from the previous example verifying the linear effect simulation. The prior art generally adopts the method of observing the spectrum expansion of the transmitted signal to evaluate the linearity of the power amplifier. The band-to-shoulder ratio of the original digital TV transmit signal is very high. According to the original regulations of the standard, it is generally above 40dB. Deterioration occurs, depending on the degree of nonlinearity, the deterioration ranges from a few decibels to more than ten decibels, and then after the correction of the nonlinear correction function in the exciter 2, the high-power transmitter generally requires the output shoulder to be corrected to 36dB, which is considered to meet the requirements . Since the influence of the nonlinear model has a similar performance shape on the frequency spectrum, the application example of the Saleh model is taken as an example here, as shown in Figure 11, the parameters of the Saleh model unit 3504 are set to α _a =1, β _a =0.05,

,

, FIG. 14 is the original multi-carrier modulation signal spectrum input to the nonlinear distortion simulation module 35, and FIG. 15 is the signal spectrum of the signal after the Saleh model unit 3504 simulation. It can be seen that the output signal is worse than the input signal shoulder level by more than 30dB.

Claims (8)

1. The distortion simulator of the broadcast communication transmitter is characterized by comprising a down converter, an analog-to-digital converter, a first selection switch, a linear distortion simulation module, a nonlinear distortion simulation module, a power protection module, a second selection switch, a digital-to-analog converter, an up converter, a controller and a user interface;

the down converter: down-converting a radio frequency input signal of the simulator, and outputting an analog baseband signal to an analog-to-digital converter;

the analog-to-digital converter: converting an analog baseband signal input by the down converter into a digital baseband signal and outputting the digital baseband signal to the first selection switch;

the first selection switch: selecting an output signal of the analog-to-digital converter or a digital input signal of the simulator, and outputting the selected signal to the linear distortion simulation module;

the linear distortion simulation module: according to the linear distortion model parameters set by a user, performing linear distortion simulation on the signal output by the first selection switch, and outputting the linear distortion signal to the nonlinear distortion simulation module;

the nonlinear distortion simulation module: according to a nonlinear distortion model and model parameters set by a user, carrying out nonlinear distortion simulation on a linearly distorted signal, and outputting the nonlinear distorted signal to a power protection module;

the power protection module: detecting the power of the nonlinear distortion signal, carrying out amplitude limiting processing and sending an overload mark to the controller if the power of the nonlinear distortion signal is greater than a certain threshold, and not carrying out processing if the power of the nonlinear distortion signal is not greater than the threshold, and outputting a signal to a second selection switch;

the second selection switch: selecting to directly output the output signal of the power protection module to the simulator or output the signal to the digital-to-analog converter;

the digital-to-analog converter: converting the digital baseband signal output by the second selection switch into an analog baseband signal and outputting the analog baseband signal to an up-converter;

the up-converter: up-converting the analog baseband signal into a radio frequency signal as an output signal of the simulator;

the controller: sending control information to a down converter, a first selector switch, a linear distortion simulation module, a nonlinear distortion simulation module, a second selector switch and an up converter, receiving overload flag information of a power protection module, sending state information to a user interface, receiving setting information of the user interface, and determining distortion processing models of the linear distortion simulation module and the nonlinear distortion simulation module according to the setting information of the user interface;

the user interface is: and receiving and displaying the state information of the controller to a user, and sending setting information to the controller.

2. The transmission distortion simulator of a broadcast communication transmitter of claim 1, wherein the linear distortion simulation module comprises an orthogonality deviation simulation unit, a gain imbalance simulation unit, a carrier leakage simulation unit;

an orthogonality deviation simulation unit: to be inputted I₀And Q₀Multiplying the signal by the signal output by the function generator, adding the multiplied results to output a signal I₁And Q₁Giving a gain imbalance simulation unit;

gain imbalance simulation unit: to be inputted I₁And Q₁Multiplying the signals by coefficients respectively to output signals I₂And Q₂A carrier leakage simulation unit is provided;

a carrier leakage simulation unit: to be inputted I₂And Q₂Adding the signal to the coefficient to output a signal I₃And Q₃As the output of the linear distortion simulation module.

3. The transmission distortion simulator of a broadcast communication transmitter of claim 1, wherein the nonlinear distortion simulation module comprises a modulus taking unit, a phase angle unit, a delay unit, a multiplication unit, and an addition unit, and the processing of the nonlinear distortion process is completed by the combination of the above units, and the model of the nonlinear distortion process conforms to the control information sent by the controller;

a module taking unit: to input of I₃And Q₃Performing modulus operation on the signal, wherein a modulus result is used as an input signal of a delay unit, a multiplication unit and an addition unit;

phase angle unit: to input of I₃And Q₃Carrying out phase angle operation on the signals, wherein the phase angle result is used as an input signal of a delay unit, a multiplication unit and an addition unit;

a delay unit: delaying the input signal by one or more clocks, and taking the delayed signal as the input signal of the multiplication unit and the addition unit;

a multiplication unit: multiplying the input signal by a set simulation coefficient, wherein the result of the multiplication is used as the input signal of the addition unit;

an addition unit: and performing addition operation on the input multi-path signals, and outputting a result signal after the addition.

4. The transmission distortion emulator of claim 1, wherein the distortion model of the nonlinear distortion module is set by a controller, and the distortion characteristic parameters of the linear and nonlinear distortion emulation modules are set by the controller.

5. A method for testing the calibration performance of a broadcast communication transmitter comprises the following steps:

step one, data are sent to an exciter by a data source, the exciter outputs signals after modulation and frequency conversion to a transmission distortion simulator, the exciter does not correct the signals, the simulator does not perform distortion processing on the signals at the moment, the simulator outputs normal signals, and a frequency spectrum instrument observes that the frequency spectrum of the signals output by the simulator is correct;

setting linear and nonlinear distortion parameters and models specified by a user by the transmission distortion simulator, observing a frequency spectrum output by the simulator by using a frequency spectrograph, and generating distortion by the frequency spectrum;

step three, the launching distortion simulator maintains a distortion model, the exciter starts an internal correction function to correct signals, the exciter outputs signals after being converted into pre-distortion, the frequency spectrograph observes whether the frequency spectrum of the signals output by the simulator becomes a correct frequency spectrum, and if the frequency spectrum becomes the correct frequency spectrum, the exciter corrects the distortion model correctly; if the frequency spectrum still contains distortion after the correction of the exciter, the exciter can not correct the distortion model;

changing linear and nonlinear distortion parameters and models set by the transmission distortion simulator, repeating the step three, and testing the correction performance of the exciter under different distortion models;

and step five, repeating the processes of the step two, the step three and the step four for other exciters, and comparing the advantages and the disadvantages of the correction performance among different exciters.

6. The broadcast communication transmitter distortion correction test method of claim 5, wherein the center frequencies of the radio frequency signal input to the emulator and the radio frequency signal output from the emulator are the same.

7. A method for testing distortion performance of a transmitter in a broadcast communication system comprises the following steps:

step one, a data source sends data to an exciter, the exciter outputs a baseband signal or a signal after modulation and frequency conversion to a transmission distortion simulator, the exciter does not start a signal pre-correction function, the simulator does not perform distortion processing on the signal at the moment, and the simulator outputs a normal baseband signal or a normal radio frequency signal;

setting a linear and nonlinear distortion model specified by a user by the transmission distortion simulator;

step three, observing the output of the receiver and evaluating the receiving effect of the receiver at the moment;

step four, changing linear and nonlinear distortion parameters and models set by the transmission distortion simulator, repeating the step three, and testing the transmission performance of a system formed by the exciter and the receiver under different distortion models;

and step five, repeating the processes of the step two, the step three and the step four for the system formed by other exciters and receivers, and comparing the difference of the receiving and demodulating performances of different systems.

8. The method as claimed in claim 7, wherein the center frequencies of the rf signal inputted to the emulator and the rf signal outputted from the emulator are the same.

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