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 method for detecting distortion correction of the emulator. The emulator simulates distortion models of various transmitters through a linear distortion emulation module and a non-linear distortion emulation module, and detects the performance of system distortion correction. The emulator also comprises a down converter and an up converter processing a radio-frequency signal, so that both a radio-frequency band signal and a digital baseband signal can be processed. The method comprises correction performance testing method of a broadcast communication transmitter and distortion performance testing method of a broadcast communication system anti-transmitter. The method evaluates the correction performance of an exciter and the anti-transmission distortion performance of the communication system by simulating transmission distortion through a distortion emulator. With the device and the method, the performance of the transmitter and a receiver of the broadcast communication system can be evaluated under a laboratory environment. Compared with the traditional experiment method, the complexity degree of laboratory equipment is lowered and experimental costs are reduced.

Description

Distortion simulator of broadcast communication transmitter and distortion correction test method thereof

Technical Field

The invention belongs to the field of digital communication test, and relates to a distortion simulator of a broadcast communication transmitter and a distortion correction test method thereof, in particular to a simulation device for simulating transmission distortion, a method for testing the correction performance of the broadcast communication transmitter and a method for testing the anti-distortion interference performance of a broadcast communication system.

Background

With the development of digital communication technology, various new technologies are continuously generated, new digital communication systems are continuously generated, digitally modulated signals have wider bandwidth and larger dynamic range of output amplitude compared with analog modulated signals, and various modulation devices and means are provided, which puts higher requirements on the research and development and manufacture of equipment.

On one hand, the influence of linear distortion is caused, because communication transmission standards are different, devices and technologies adopted in modulation and frequency conversion processes are different, and because device processes and circuit manufacturing processes are not ideal, distortion to baseband signals can be introduced due to modulation, frequency conversion devices and circuits, and because the value of the distortion and input signals are mostly linearly changed, the distortion is called linear distortion. Through mathematical model description, there are various types of distortions of the modulation process, mainly three types: carrier leakage, gain imbalance, and component orthogonality deviation.

If the correct output modulation signal is not interfered to be

s₀(t)＝I·cos2πf_ct+Q·sin2πf_ct

Wherein I and Q are orthogonal baseband signals, respectively_cIs the carrier frequency.

(1) The component orthogonality deviation is caused by incomplete orthogonality of carrier phases multiplied by baseband signals during frequency conversion of an up-converter, and distortion of a constellation diagram shape is formed. The constellation diagram of the 16QAM modulation changes from a square envelope to a diamond envelope when the component orthogonality deviates.

Signal s disturbed by component orthogonality deviations₁(t) is:

wherein,

and

respectively two paths of phase angle deviation components.

(2) The gain imbalance is caused by the difference in gain of the two orthogonal baseband signals input to the up-converter. If the gains of two paths of orthogonal baseband signals are different, the shape of a constellation diagram is distorted. A constellation diagram such as 16QAM modulation will change from a square envelope to a rectangular envelope when the gain is unbalanced.

Signal s disturbed by gain imbalance₂(t) is:

s₂(t)＝α_I·I·cos2πf_ct+α_Q·Q·sin2πf_ct

wherein alpha is_IAnd alpha_Q(α_I≠α_Q) Respectively, the gains of the two baseband signals.

(3) The carrier leakage occurs because an analog baseband signal output from the baseband digital-to-analog conversion circuit is mixed with an additive direct-current component, the analog baseband signal added with the direct-current component is input to a frequency conversion circuit at the subsequent stage, and an unnecessary power is added to a carrier frequency point, so that a spectrogram is distorted.

Signal s disturbed by carrier leakage₃(t) is:

s₃(t)＝(I+Δ_I)cos2πf_ct+(Q+Δ_Q)sin2πf_ct

＝(I·cos2πf_ct+Q·sin2πf_ct)+(Δ_I·cos2πf_ct+Δ_Q·sin2πf_ct)

wherein, Delta_IAnd Δ_QRespectively two direct current offset components.

On the other hand, the power amplifier is influenced by nonlinear distortion, an output signal needs to be amplified after modulation and then transmitted, and at the radio frequency output end of a transmitter of a broadcast communication system, due to the saturation effect of devices, the power of the power amplifier cannot increase linearly after exceeding a linear amplification area, so that the power amplifier presents nonlinear amplification characteristics, and the distortion belongs to nonlinear distortion. The nonlinear distortion effect can directly affect the waveform of an output signal, and the nonlinear distortion caused by power amplification can cause the spread of the original input signal frequency spectrum and generate in-band distortion, thereby causing adverse effects on adjacent frequency signals and self signals.

The nonlinear distortion of the power amplifier is classified into memoryless nonlinearity and memoryless nonlinearity. The output value of the memoryless non-linear amplifier is only related to the instantaneous value of the current input. The output value of the non-linear 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 linear distortion, and several nonlinear distortion models are exemplified below.

(1) For the analysis of memoryless nonlinear amplifiers, the simplest model is to use a Taylor series. Let the input signal be s₀(t), an output signal s after a signal has passed through a memoryless non-linear amplifier₁(t) can be expressed as:

s₁(t)＝c₁·s₀(t)+c₂·s₀(t)²+c₃·s₀(t)³+…

the description of the memoryless power amplifier is not only a power series model, but also a Saleh model, a Rapp model, a limiting model and the like which are widely adopted.

(2) The model of the memory nonlinear amplifier is complex, and many description methods are proposed, most commonly a Volterra series model. To reduce the complexity of the Volterra series here, only the third order expression is used here:

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wherein N is₁，N₂，N₃Respectively representing the first, second and third order memory depths, h₁，h₂，h₃Respectively representing coefficients of each order. When a nonlinear system is represented by a Volterra series, corresponding coefficients of each order must be known, and the number of the coefficients rapidly increases along with the increase of the order.

In an actual system, linear and nonlinear distortions generally exist, in order to overcome the distortions, inverse transformation is required to be adopted aiming at the distortion effect of an amplifier, the functions are completed by linear and nonlinear correction functions in an exciter, and the adopted main methods comprise a feedforward method, a feedback method, a predistortion method and the like.

The effect of the correction algorithm is verified by firstly simulating in software, realizing the algorithm on hardware after the simulation proves that the algorithm is effective, manufacturing a correction device which is actually used as a part of an exciter, and performing an experiment on an actual transmitter power amplifier to verify the performance of the correction device. In each experiment, the performance of the calibration device in power amplifier matching with a certain transmitter can only be verified, if the calibration device is required to be verified to be matched with various transmitters of different types, calibration equipment needs to be installed on other transmitters, and the verification experiment method is inconvenient to realize because one transmitter cannot represent the characteristics of various transmitters of different types.

From another perspective, the communication transmission system needs to have a capability of resisting channel noise and fading, and in case of high-power transmission, because the system is also affected by distortion effect of the power amplifier, the communication transmission system needs to have a certain capability of resisting nonlinear distortion. In the process of developing a transmission system, how a communication transmission system works under linear and nonlinear distortion interference needs to be tested.

Therefore, there is a need for a test method and a simulator device for testing the calibration performance of a broadcast communication exciter and the transmission performance of a broadcast communication transmitting and receiving system against nonlinear distortion. The corrector in the existing exciter is used for counteracting the distortion effect in the power amplifier, but not for simulating the distortion effect in the power amplifier, and a similar simulator device is not mentioned in the prior document, so that the equipment for simulating linear and nonlinear distortion provided by the invention is necessary.

Disclosure of Invention

The invention provides a distortion simulator of a broadcast communication transmitter and a distortion correction test method thereof, in particular to a simulation device for simulating the distortion of the broadcast communication transmitter, a method for testing the correction performance of the broadcast communication transmitter and a method for testing the anti-distortion interference performance of a broadcast communication system.

The invention relates to a distortion simulator of a broadcast communication transmitter, which comprises:

a 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 the analog baseband signal to the analog-to-digital converter, and the carrier frequency point value of the down-conversion is sent to the down converter by the controller.

An 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; .

A first selection switch: and selecting a digital baseband signal F externally input into the simulator or a digital baseband signal G output by the analog-to-digital converter, outputting the selected signal to the linear distortion simulation module, and selecting and controlling by the controller.

A linear distortion simulation module: the linear distortion simulation module carries out linear distortion conversion on the input digital baseband signal, the controller sends a command and parameters to the linear distortion simulation module according to a linear distortion model set by a user, the linear distortion simulation module carries out linear distortion simulation on the signal output by the first selection switch according to the command and the parameters, and the distorted digital baseband signal is output to the nonlinear distortion simulation module.

A nonlinear distortion simulation module: the nonlinear distortion simulation module carries out nonlinear distortion conversion on an input digital baseband signal, the controller sends commands and parameters to the nonlinear distortion simulation module according to a nonlinear distortion model and model parameters set by a user, the nonlinear distortion simulation module carries out nonlinear distortion simulation on a linearly distorted signal according to the commands and the parameters, and outputs the nonlinear distortion signal to the power protection module.

A power protection module: the nonlinear distortion simulation module outputs the signal to the power protection module, if the amplitude of the signal output by the nonlinear distortion simulation module exceeds a certain value, the power protection module takes amplitude limiting measures to protect the safety of a rear-stage circuit and sends an overload signal to the controller, and the signal after amplitude limiting is output to the second selection switch; if the amplitude of the input signal 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.

A second selector switch: the digital baseband signal output by the power protection module is input into the second selection switch, is controlled by the controller, and is directly output (as an output signal K) or is sent to the digital-to-analog converter.

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

An up converter: and up-converting the analog baseband signal into a radio frequency signal as an output signal J of the simulator.

A controller: setting the central frequency of a down converter, setting the input signal selection of a first selection switch, setting a linear distortion model of a linear distortion simulation module, setting a nonlinear distortion model of a nonlinear distortion simulation module, setting the output signal selection of a second selection switch, setting the central frequency of an up converter, receiving an overload flag signal sent by a power protection module, sending state information to a user interface, and receiving operation information of the user interface.

A user interface: and receiving the state information of the controller and displaying the state information to a user, and sending operation information to the controller by the user through a user interface.

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

inputting a radio frequency signal E output by a tested system exciter to a down converter; the carrier frequency of the down converter is set by the controller, and the input signal E is converted into a baseband analog signal after down conversion; then the signal is converted into a digital baseband signal through an analog-to-digital converter, marked as a signal G and input to one end of a first selection switch; if the exciter has a digital baseband signal output, marking the digital baseband output signal as a signal F and inputting the signal F to the other end of the first selection switch; the first selection switch is controlled by the controller, and a selection signal G or a selection signal F is input into the linear distortion simulation module; the linear distortion simulation module stores a linear distortion mathematical model inside, the controller sends parameters of the linear distortion model to the linear distortion simulation module, the linear distortion simulation module adds a linear distortion effect in a digital baseband signal and outputs the converted digital baseband signal to the nonlinear distortion simulation module; the nonlinear distortion simulation module stores a nonlinear distortion mathematical model, the controller sends the type and parameters of the nonlinear distortion model to the nonlinear distortion simulation module, the nonlinear distortion simulation module adds a nonlinear distortion effect in a digital baseband signal, and the converted digital baseband signal is input to the power protection module; the power protection module carries out amplitude limiting processing when the amplitude of the input signal exceeds a threshold, and sends an overload mark to the controller, and if the amplitude of the input signal does not exceed the threshold, the overload mark is output to the second selection switch; the second selection switch is controlled by the controller, and outputs the input signal to the digital-to-analog converter as an input signal H of the digital-to-analog converter or as a digital baseband output signal K; the digital-to-analog converter converts the digital baseband signal H into an analog baseband signal, inputs the analog baseband signal into the up-converter, the carrier frequency value of the up-converter is sent by the controller, and the up-converter up-converts the analog baseband signal into a radio frequency signal which is then used as an output signal J.

The testing method of the invention comprises two aspects: on one hand, the method is a method for testing the correction performance of a broadcast communication transmitter; another aspect is a method for testing the transmitter distortion resistance of a broadcast communication system.

The invention relates to a method for testing the correction performance of a broadcast communication transmitter, which comprises the following steps:

a data generator generating a data signal modulated by the exciter;

an exciter generating a radio frequency broadcast transmission signal;

the transmitting distortion simulator is used for adding the influence of a distortion effect into a transmitting signal and outputting a distorted signal;

and the frequency spectrograph is used for measuring the frequency spectrum of the output signal of the transmission distortion simulator.

Step one, data A is sent to an exciter by a data source, the exciter outputs a signal E after modulation and frequency conversion to a transmission distortion simulator, the exciter does not correct the signal, the simulator does not perform distortion processing on the signal at the moment, the simulator outputs a normal signal J, and a frequency spectrum of the signal J output by the simulator is observed to be a correct frequency spectrum by a frequency spectrograph;

setting the transmitting distortion simulator as a linear and nonlinear distortion model specified by a user, observing the frequency spectrum of an output signal J of the simulator by using a frequency spectrograph, and generating distortion by the frequency spectrum;

step three, the transmitting distortion simulator maintains a distortion model, the exciter starts an internal correction function to correct an output signal E, the exciter outputs a signal E which is changed into a pre-distorted signal, the frequency spectrograph observes whether the frequency spectrum of a signal J output by the simulator is correct or not, and if the frequency spectrum of the signal J is correct, the exciter performs correct pre-correction on the distortion model; if the signal J 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.

The invention discloses a method for testing the distortion performance of a transmitter of a broadcast communication system, which comprises the following steps:

a data generator generating a data signal modulated by the exciter;

an exciter generating a radio frequency broadcast transmission signal;

the transmitting distortion simulator is used for adding the influence of a distortion effect into a transmitting signal and outputting a distorted signal;

and the receiver demodulates the output signal of the transmission distortion simulator and observes the receiving effect.

Step one, a data source sends data A to an exciter, the exciter outputs a digital baseband signal F or a signal E 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 E or the signal F at the moment, and the simulator outputs a normal baseband signal K or a radio frequency signal J;

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

step three, observing the output P 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 various 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 transmission performance of different systems.

The transmission distortion simulator and the distortion correction test method are used for simulating the transmission distortion of digital broadcast signals by adopting a hardware digital device simulation method under the condition that a high-power transmitter is not used for signal amplification and transmission, and testing the system. The linear distortion simulation module and the nonlinear distortion simulation module in the simulator are operation platforms formed by digital circuit devices, a mathematical algorithm model is applied in the distortion simulation process, and a distortion digital baseband signal after model calculation is output. The input port of the simulator can be a digital baseband signal or a radio frequency signal after up-conversion of the exciter, and the output port of the simulator can be a digital baseband signal or a radio frequency signal after up-conversion.

The test method of the invention can be applied to the test of the digital broadcast transmission system and can also be applied to the test of the digital communication system. The invention is used for the digital broadcasting system because the transmitting signal power of the transmitter of the broadcasting transmission system is larger, the problem of nonlinear distortion is most easily encountered, and the invention can simulate various nonlinear distortion conditions; the invention is used for simulating linear distortion in a digital communication system, and can simulate various linear distortion conditions by using the invention. In summary, the present invention provides a test evaluation method and a reconfigurable distortion simulation platform, which can be used under various digital transmission systems and standards, and the test result is provided for the researchers of the transmission system to refer to in the device development stage.

The distortion simulator of the broadcast communication transmitter and the distortion correction test method thereof have the advantages that:

(1) the testing of the correction performance of the exciter and the distortion resistance performance of the system is carried out under the condition that a high-power transmitter is not needed, and the complexity of the experiment is reduced.

(2) In the past, a specific power amplifier is adopted for experiments, only one input/output interface is provided, and the device provided by the invention is provided with two interfaces and can adapt to the connection of various transmitting and receiving devices.

(3) The invention uses one device to simulate the distortion effect of various power amplifiers, and the parameters are set by the user, thereby saving the experiment cost.

Drawings

FIG. 1 is a block diagram of the internal structure of a transmission distortion simulator according to the present invention;

FIG. 2 is a block diagram of a method for testing calibration performance of a broadcast communication transmitter according to the present invention;

FIG. 3 is a block diagram of the structure of the method for testing the distortion resistance of the transmitter in the broadcast communication system;

FIG. 4 is an algorithm diagram of a linear distortion simulation module within the transmit distortion simulator of the present invention;

FIG. 5 is an example of a 16QAM constellation of an input signal for a linear distortion simulation module of the present invention;

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

FIG. 7 is an example of a gain imbalance simulation output signal constellation for the linear distortion simulation module of the present invention;

FIG. 8 is an example of a carrier leakage simulation output signal constellation for the linear distortion simulation module of the present invention;

FIG. 9 is an example of a 16QAM spectrum plot of an input signal to the linear distortion simulation module of the present invention;

FIG. 10 is an example plot of a carrier leakage simulation output signal spectrum for a linear distortion simulation module of the present invention;

FIG. 11 is a schematic diagram of an algorithm of a nonlinear distortion simulation module in the transmission distortion simulator of the present invention;

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

FIG. 13 is a third schematic diagram of an algorithm of a nonlinear distortion simulation module in the transmission distortion simulator of the present invention;

FIG. 14 is an example input signal multi-carrier spectrum plot of a nonlinear distortion simulation module of the present invention;

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

In the figure:

1. data generator 2, exciter 21, digital baseband modulation module 22, predistortion corrector

23. Digital-to-analog converter 24, up converter 3, transmitting distortion simulator 31 and 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. Third multiplication unit 3408, fourth multiplication unit 3409, first addition unit

3400. Second adding unit

341. Gain imbalance simulation unit 3411, fifth multiplication unit 3412 and sixth multiplication unit

342. Carrier leakage simulation unit 3421, third addition unit 3422, fourth addition unit

35. Nonlinear distortion simulation module 3501, module taking unit 3502 and phase angle unit

3503. Clipping model unit

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

3511. Multiplication cell group 13512, multiplication cell group 23513, addition cell group 1

352 Volterra series simulation unit

3521. Delay cell group 13522, Volterra series operation unit

36. Power control module 37, second selection switch 38, digital-to-analog converter

39. Up-converter 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. Frequency spectrograph

Detailed Description

The invention is illustrated below with reference to the accompanying drawings: the transmission distortion simulator 3 for distortion correction test of the broadcast communication transmitter is, as shown in fig. 1, structurally comprises a down converter 31, an analog-to-digital converter 32, a 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 up converter 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, the radio frequency signal is down converted into an analog baseband signal, and the analog baseband signal is input to 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 selection switch 33; a baseband signal F is input into a digital baseband input port of the simulator 3 and input into the other end of the first selection switch 33, and the first selection switch 33 sends an instruction to control the selection signal F or the signal G to be input into the linear distortion simulation module 34 through the controller 310; the linear distortion simulation module 34 is controlled by the controller 310, selects an internally stored linear distortion model and sets parameter values of the model, performs linear distortion processing on an input digital baseband signal, and inputs the digital baseband signal subjected to the linear distortion processing into the nonlinear distortion simulation module 35; the nonlinear distortion simulation module 35 is controlled by the controller 310, selects an internally stored nonlinear distortion model and sets parameter values of the model, performs nonlinear distortion processing on the input digital baseband signal subjected to the linear distortion processing, and inputs the digital baseband signal subjected to the nonlinear distortion processing into the power control module 36; if the amplitude of the baseband signal exceeds the threshold of the power control module 36, performing amplitude limiting to make the amplitude of the output signal not higher than the threshold, and sending an overload flag to the controller 310, and if the amplitude of the output signal does not exceed the threshold, outputting the overload flag to one end 37 of the second selection switch; the second selection switch 37 is controlled by the controller 310 to select to output the input digital baseband signal to the digital-to-analog converter 38 as the signal H, or to directly output the input digital baseband signal as the signal K; the signal H is input to a digital-to-analog converter 38, converted into an analog baseband signal, and input to an up-converter 39; the carrier frequency of the up-converter 39 is set by the controller 310, and converts the input analog baseband signal into a radio frequency signal, which is used as the simulator radio frequency output signal J; all of the above parameters sent by the controller 310 to the other modules are set via the user interface 311, and the user interface 311 has functions of inputting commands and displaying the state of the simulator.

The simulation of the linear distortion simulation module 34 and the nonlinear distortion simulation module 35 of the internal component module of the simulator 3 is independent from the mathematical model, but the sequence can not be changed, because in the transmitter of the broadcasting system, the linear distortion is mostly introduced in the frequency conversion process, and the nonlinear distortion is mostly introduced in the power amplification process after the frequency conversion;

in addition, hardware devices inside the emulator 3 inevitably have certain distortion interference, when the input is a radio frequency signal E, the down converter 31 and the analog-to-digital converter 32 contain analog devices, a certain amount of noise and frequency distortion are introduced, when the output is a radio frequency signal J, the digital-to-analog converter 38 and the up converter 39 also contain analog devices, the working principle is similar to that of the rear stage of the exciter, noise, linear distortion in the frequency conversion process and nonlinear distortion in the amplification process also have influences, the emulator is used as test equipment, elements adopted by the modules are calibrated by the noise and the distortion, and the influences caused by the modules can be ignored compared with signal distortion caused by the linear distortion emulation module 34 and the nonlinear distortion emulation module 35;

in the device interference problem mentioned above, if the input signal is the digital baseband signal F and the output signal is the digital baseband signal K, the processing procedure of the emulator is completely digital quantity in the digital device, and there is no interference from the analog device.

As shown in fig. 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 types of linear distortion simulations: orthogonality deviation simulation, gain imbalance simulation and carrier leakage simulation.

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 multiplication unit 3407, a fourth multiplication unit 3408, a first addition unit 3409, and a second addition unit 3400. I to be input by the orthogonality deviation simulation unit 340₀And Q₀Multiplying the signal by the signal output by the function generator and then phase-shiftingThe result of the multiplication is added to output a signal I₁And Q₁And giving the gain imbalance simulation unit. The specific operation is as follows: the signal I to be input to the orthogonality deviation simulation unit 340₀With output of the first function generator 3401

The signals are multiplied by the first multiplication unit 3405, and the signal Q inputted to the orthogonality deviation simulation unit 340 is inputted₀With output of a fourth function generator 3404

The signals are multiplied by a fourth multiplication unit 3408, the output result of the first multiplication unit 3404 is taken as negative, and the result output by the fourth multiplication unit 3408 is added in a second addition unit 3400, outputting a signal Q₁(ii) a Will input signal I₀With output of a third function generator 3403

The signals are multiplied by a third multiplication unit 3407 to input a signal Q₀With output of function generator 23402

The signals are multiplied by a second multiplication unit 3406, the output result of the second multiplication unit 3406 and the output result of the third multiplication unit 3407 are added in a first addition unit 3409, and a signal I is output₁。

The gain imbalance simulation unit 341 includes a fifth multiplication unit 3411 and a sixth multiplication unit 3412. I of the gain imbalance simulation unit 341 is input₁And Q₁Multiplying the signals by coefficients respectively to output signals I₂And Q₂And the carrier leakage simulation unit is provided. The specific operation is as follows: the controller 310 sends the parameter a to the gain imbalance simulation unit 341 in the linear distortion simulation module 34_IAnd A_QThen, the signal I inputted to the gain imbalance simulation unit 341₁With the coefficient A in a fifth multiplying unit 3411_IMultiplying and outputting the result I₂(ii) a The signal Q of the input gain imbalance simulation unit 341₁In a sixth multiplying unit 3412 is multiplied by the coefficient to output a result Q₂。

The carrier leakage simulation unit 342 includes a third addition unit 3421 and a fourth addition unit 3422. I to be input to the carrier leakage simulation unit 342₂And Q₂Adding the signal to the coefficient to output a signal I₃And Q₃As the output of the linear distortion simulation module 34, the specific operations are: controller 310 sends parameter Δ to carrier leakage simulation unit 342 in linear distortion simulation module 34_IAnd Δ_QThen, the signal I inputted to the carrier leakage simulation unit 342₂In a third adding unit 3421 with the parameter Δ_IAdding and outputting the result I₃(ii) a Signal Q input to carrier leakage simulation unit 342₂In a fourth adding unit 3422 with the parameter Δ_QAdding and outputting the result Q₃；

The final output signal subjected to linear distortion simulation is as follows:

the linear distortion simulation module 34 processes the baseband signal in the digital domain, and according to nyquist sampling law, in order to ensure that the signal is not distorted after sampling, the sampling frequency should be greater than twice of the highest frequency contained in the baseband signal spectrum. Sampling rate R at which the linear distortion simulation module 34 operates₁Set by the controller 310. The parameters sent by the controller 310 to the linear distortion simulation module 34 include: homodromous phase deviation

Quadrature phase offset

Path I gain A_IQ path gain A_QDirect current deviation delta of path I_IQ path DC deviation delta_QAnd a sampling frequency R₁。

Let f be the center frequency of the carrier wave of the frequency converter in the exciter 2_cThe real and imaginary components of the baseband signal input to the frequency converter are I₀And Q₀Correct output signal s₀(t) is: s₀(t)＝I₀·cos2πf_ct+Q₀·sin2πf_ct。

(1) The orthogonality deviation is caused by the fact that the phase difference between the homodromous component and the quadrature component of the frequency-converted carrier wave in the frequency conversion process is not equal to 90 degrees. If the co-directional component of the carrier is out of phase

The phase deviation of the quadrature component is

Let the affected output signal be s₁(t)：

It can be found that the processing algorithm used for the orthogonality deviation simulation in the linear distortion simulator 34 is described as follows, and the converted digital baseband signal is set as I₁And Q₁：

(2) The gain imbalance is caused by the fact that after the digital-to-analog converter 23 converts the two paths of I/Q digital baseband signals into I/Q analog baseband signals, the gains of the two paths of I/Q analog baseband signals in the circuit are different. Let the gain of the path I be A_IThe gain of the Q path is A_QThe processing algorithm used for the gain imbalance simulation in the linear distortion simulator 34 is described as follows:

I₂＝I₁·A_I

Q₂＝Q₁·A_Q

wherein, I₁And Q₁For input signal, I₂And Q₂Is a converted digital baseband signal.

(3) The carrier leakage is caused by mixing a direct current component into a baseband analog signal in the frequency conversion process of the up converter 24, so that the mean value of the baseband signal is not equal to 0, and the energy of a carrier frequency point on a frequency spectrum is higher than that of other frequencies. Let the DC offset of the I path be Δ_IThe DC deviation of the Q path is delta_QThe processing algorithm used for carrier leakage simulation in the linear distortion simulator 34 is described as follows,

I₃＝I₂·(1+Δ_I)

Q₃＝Q₂·(1+Δ_Q)

wherein, I₂And Q₂For input signal, I₃And Q₃Is a converted digital baseband signal.

The nonlinear distortion simulation module processes the baseband signals in a digital domain, and according to the Nyquist sampling law, in order to ensure that the signals are not distorted after sampling, the sampling frequency is more than 2 times of the highest frequency contained in the frequency spectrum of the baseband signals. Sampling rate R at which the nonlinear distortion simulation module 35 operates₂Set by the controller 310.

Fig. 11 shows an example of the structure of the nonlinear distortion simulation module 35, which includes a modulus 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 implements three non-linear distortion models, clipping model unit 3503, Saleh model unit 3504, Rapp model unit 3505. The input signal enters a module taking unit 3501 to carry out module taking operation, and the output is a signal module value; the input signal enters a phase angle unit 3502 to perform phase angle taking operation, and the phase angle value is output; the signal mode values and signal phase angle values are used as input signals for slice model unit 3503, Saleh model unit 3504, Rapp model unit 3505.

(1) Saleh model

The Saleh model has a good approximation of the non-linear characteristics of a traveling wave tube power amplifier (TWTA). Let the input signal be s₀(t)＝r(t)cos[ω₀t+ψ(t)]Where r (t) is the input signal modulus, ω₀For carrier frequency, psi (t) for input signal phase, output signal s under Saleh model₁Comprises the following steps:

s₁＝A₁[r(t)]cos{ω₀t+ψ(t)+Φ₁[r(t)]}

wherein A is₁() And phi₁() Is a nonlinear function of amplitude and phase under the Saleh model, which are both functions of a modulus value r:

wherein alpha is_a、β_a、

Are 4 parameters of the Saleh model, set by the controller 310.

(2) Rapp model

The Rapp model has good nonlinear characteristics for a solid-state power amplifier (SSPA)An approximation of. Let the input signal be s₀(t)＝r(t)cos[ω₀t+ψ(t)]Where r (t) is the input signal modulus, ω₀For carrier frequency, psi (t) for input signal phase, output signal s under Rapp model₂Comprises the following steps:

s₂＝A₂[r(t)]cos[ω₀t+ψ(t)]

wherein A is₂() Is a nonlinear function of amplitude and phase under Rapp model, which is a function of modulus r:

$A_2\left(r\right)=v\frac{r}{{\{1+{\left[{\left(\frac{\mathrm{vr}}{A_0}\right)}^2\right]}^P\}}^{\frac{1}{2P}}}$

wherein A is₀For the output maximum, P and v are Rapp model parameters, A₀P and v are set by the controller 310.

(3) Clipping model

The clipping model is the simplest description of the effects of power amplifier saturation, when the input signal amplitude exceeds a certain value,the output signal amplitude does not increase any more. Let the input signal be

r (t) is the amplitude value,

for phase angle, limiting the model output signal s₃(t) is:

wherein A is₀To output the maximum value, it is set by the controller 310.

Fig. 12 shows another configuration example of the nonlinear distortion simulation module 35, which implements the power series nonlinear model processing unit 351 including the first multiplying unit group 3511, the second multiplying unit group 3512, and the adding unit group 3513.

The power series model is a model in which the nonlinear distortion is represented by a Taylor series. Let the input signal of the power series nonlinear model processing unit 351 be s₀(t), the signal gets N power series s through the first multiplication unit group 3511₀(t)，s₀(t)²，…，s₀(t)ⁱI is 1, 2, … N, and then multiplied by the parameters by the second multiplying unit group 3512 to obtain the power series c multiplied by the coefficients₁·s₀(t)，c₂·s₀(t)²，…，c_i·s₀(t)ⁱThen, the summation result c is obtained by the addition unit group 3513₁·s₀(t)+c₂·s₀(t)²+c₃·s₀(t)³+…+c_i·s₀(t)ⁱThus, the output signal s after the power series model processing₄(t) can be expressed as:

s₄(t)＝c₁·s₀(t)+c₂·s₀(t)²+c₃·s₀(t)³+…+c_i·s₀(t)ⁱ

wherein s is₀(t) and s₄(t) denotes the amplifier input signal and output signal, respectively, c_iIs a real coefficient, i is an integer, i is 1, 2, … N. Experiments have shown that for moderately non-linear systems, when i>At 3 time, c_iSmall enough to be ignored for simplicity. In the present example, a Taylor series of the highest power of 3 is implemented, the output signal s₄(t) the expression is:

s₄(t)＝c₁·s₀(t)+c₂·s₀(t)²+c₃·s₀(t)³

wherein, c₁、c₂And c₃Which are parameters of the power series model, are set by the controller 310.

For example: the input signal being a single-frequency signal s₀(t)＝Acos2πf_ct, can be obtained from the above formula:

<math> <mrow> <msub> <mi>s</mi> <mn>4</mn> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>c</mi> <mn>1</mn> </msub> <mo>&CenterDot;</mo> <mi>A</mi> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mi>c</mi> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>c</mi> <mn>2</mn> </msub> <mo>&CenterDot;</mo> <msup> <mrow> <mo>[</mo> <mi>A</mi> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mi>c</mi> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>]</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msub> <mi>c</mi> <mn>3</mn> </msub> <mo>&CenterDot;</mo> <msup> <mrow> <mo>[</mo> <mi>A</mi> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mi>c</mi> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>]</mo> </mrow> <mn>3</mn> </msup> </mrow></math>

<math> <mrow> <mo>=</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>c</mi> <mn>2</mn> </msub> <msup> <mi>A</mi> <mn>2</mn> </msup> <mo>+</mo> <mrow> <mo>(</mo> <msub> <mi>c</mi> <mn>1</mn> </msub> <mi>A</mi> <mo>+</mo> <mfrac> <mn>3</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mo>)</mo> </mrow> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mi>c</mi> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>c</mi> <mn>2</mn> </msub> <msup> <mi>A</mi> <mn>2</mn> </msup> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <mo>&CenterDot;</mo> <mn>2</mn> <msub> <mi>f</mi> <mi>c</mi> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mn>1</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <mo>&CenterDot;</mo> <mn>3</mn> <msub> <mi>f</mi> <mi>c</mi> </msub> <mi>t</mi> <mo>)</mo> </mrow> </mrow></math>

it can be seen that the output contains not only the fundamental frequency f_cComponent, including DC component and second harmonic 2f_cComponent and third harmonic 3f_cAnd (4) components.

If the input is a double single-frequency signal s with the same amplitude₀(t)＝A(cos2πf₁t+cos2πf₂t), one can obtain:

<math> <mrow> <msub> <mi>s</mi> <mn>4</mn> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>c</mi> <mn>1</mn> </msub> <mo>&CenterDot;</mo> <mi>A</mi> <mrow> <mo>(</mo> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>1</mn> </msub> <mi>t</mi> <mo>+</mo> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>2</mn> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <msub> <mi>c</mi> <mn>2</mn> </msub> <mo>&CenterDot;</mo> <msup> <mrow> <mo>[</mo> <mi>A</mi> <mrow> <mo>(</mo> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>1</mn> </msub> <mi>t</mi> <mo>+</mo> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>2</mn> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>]</mo> </mrow> <mn>2</mn> </msup> <mo>+</mo> <msub> <mi>c</mi> <mn>3</mn> </msub> <mo>&CenterDot;</mo> <msup> <mrow> <mo>[</mo> <mi>A</mi> <mrow> <mo>(</mo> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>1</mn> </msub> <mi>t</mi> <mo>+</mo> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>2</mn> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>]</mo> </mrow> <mn>3</mn> </msup> </mrow></math>

<math> <mrow> <mo>=</mo> <msub> <mi>c</mi> <mn>2</mn> </msub> <msup> <mi>A</mi> <mn>2</mn> </msup> <mo>+</mo> <msub> <mi>C</mi> <mn>2</mn> </msub> <msup> <mi>A</mi> <mn>2</mn> </msup> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mi>t</mi> <mo>+</mo> <mrow> <mo>(</mo> <msub> <mi>c</mi> <mn>1</mn> </msub> <mi>A</mi> <mo>+</mo> <mfrac> <mn>9</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mo>)</mo> </mrow> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>1</mn> </msub> <mi>t</mi> <mo>+</mo> <mrow> <mo>(</mo> <msub> <mi>c</mi> <mn>1</mn> </msub> <mi>A</mi> <mo>+</mo> <mfrac> <mn>9</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mo>)</mo> </mrow> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <msub> <mi>f</mi> <mn>2</mn> </msub> <mi>t</mi> </mrow></math>

<math> <mrow> <mo>+</mo> <mfrac> <mn>3</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>-</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mi>t</mi> <mo>+</mo> <mfrac> <mn>3</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>-</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> <mi>t</mi> <mo>+</mo> <msub> <mi>c</mi> <mn>2</mn> </msub> <msup> <mi>A</mi> <mn>2</mn> </msup> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mi>t</mi> </mrow></math>

<math> <mrow> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>c</mi> <mn>2</mn> </msub> <msup> <mi>A</mi> <mn>2</mn> </msup> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <mo>&CenterDot;</mo> <mn>2</mn> <msub> <mi>f</mi> <mn>1</mn> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mn>1</mn> <mn>2</mn> </mfrac> <msub> <mi>c</mi> <mn>2</mn> </msub> <msup> <mi>A</mi> <mn>2</mn> </msup> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <mo>&CenterDot;</mo> <mn>2</mn> <msub> <mi>f</mi> <mn>2</mn> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mn>3</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <mn>2</mn> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>+</mo> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mi>t</mi> </mrow></math>

<math> <mrow> <mo>+</mo> <mfrac> <mn>3</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mi>cos</mi> <mn>2</mn> <mi>&pi;</mi> <mrow> <mo>(</mo> <msub> <mi>f</mi> <mn>1</mn> </msub> <mo>+</mo> <mn>2</mn> <msub> <mi>f</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <mi>t</mi> <mo>+</mo> <mfrac> <mn>1</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <mo>&CenterDot;</mo> <mn>3</mn> <msub> <mi>f</mi> <mn>1</mn> </msub> <mi>t</mi> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <mn>1</mn> <mn>4</mn> </mfrac> <msub> <mi>c</mi> <mn>3</mn> </msub> <msup> <mi>A</mi> <mn>3</mn> </msup> <mi>cos</mi> <mrow> <mo>(</mo> <mn>2</mn> <mi>&pi;</mi> <mo>&CenterDot;</mo> <mn>3</mn> <msub> <mi>f</mi> <mn>2</mn> </msub> <mi>t</mi> <mo>)</mo> </mrow> </mrow></math>

it can be seen that for a double single frequency input signal s₀(t) output signal s₄(t) not only having the fundamental frequency f₁And f₂Component, DC parasitic component, second harmonic frequency 2f₁And 2f₂Component, third harmonic frequency 3f₁And 3f₂Component and also the second order intermodulation frequency f₁±f₂Component and third order intermodulation frequency 2f₁±f₂、f₁±2f₂And (4) components. In systems where the operating bandwidth is less than one octave, the sum of the direct currents f₁±f₂、2f₁、2f₂、3f₁、3f₂、2f₁±f₂、f₁±2f₂The spurious components will all fall outside the passband and may be filtered using a suitable filter, but the third order intermodulation frequency 2f₁-f₂、2f₂-f₁The components form interfering components to the system and are also a major source of power amplifier non-linearity.

Fig. 13 is a structural diagram of another structure of the nonlinear distortion simulation module 35, in which the Volterra series simulation unit 352 implements a signal processing structure of Volterra series simulation. The model comprises a delay unit group 3521 consisting of delay units and a Volterra series operation unit 3522.

The Volterra series is a memory system, the correlation time of a memory signal is one of the parameters of the model, the reciprocal of a time span T between correlated sampling points is used as the sampling frequency, the time span T is one of the parameters of the Volterra series model, and the time span T determines the number of sampling periods of the correlated signal. The following description will be given by taking a third order Volterra series as an example. The input signal first enters a delay cell group 3521, which is composed of first to Mth delay cells, M being the maximum order of the delay,obtaining delayed signals s of different stages₀[n]，s₀[n-1]，s₀[n-2]，…，s₀[n-(M-1)]Then enters a Volterra series operation unit 3522 to set the input signal as s₀[n]Output signal s₅[n]Comprises the following steps:

<math> <mrow> <msub> <mi>s</mi> <mn>5</mn> </msub> <mrow> <mo>[</mo> <mi>n</mi> <mo>]</mo> </mrow> <mo>=</mo> <munderover> <mi>&Sigma;</mi> <mrow> <msub> <mi>m</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>0</mn> </mrow> <msub> <mi>N</mi> <mn>1</mn> </msub> </munderover> <msub> <mi>h</mi> <mn>1</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>m</mi> <mn>1</mn> </msub> <mo>)</mo> </mrow> <msub> <mi>s</mi> <mn>0</mn> </msub> <mrow> <mo>[</mo> <mi>n</mi> <mo>-</mo> <msub> <mi>m</mi> <mn>1</mn> </msub> <mo>]</mo> </mrow> <mo>+</mo> <munderover> <mi>&Sigma;</mi> <mrow> <msub> <mi>m</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>0</mn> </mrow> <msub> <mi>N</mi> <mn>2</mn> </msub> </munderover> <munderover> <mi>&Sigma;</mi> <mrow> <msub> <mi>m</mi> <mn>1</mn> </msub> <mo>=</mo> <mn>0</mn> </mrow> <msub> <mi>N</mi> <mn>2</mn> </msub> </munderover> <msub> <mi>h</mi> <mn>2</mn> </msub> <mrow> <mo>(</mo> <msub> <mi>m</mi> <mn>1</mn> </msub> <mo>,</mo> <msub> <mi>m</mi> <mn>2</mn> </msub> <mo>)</mo> </mrow> <msub> <mi>s</mi> <mn>0</mn> </msub> <mrow> <mo>[</mo> <mi>n</mi> <mo>-</mo> <msub> <mi>m</mi> <mn>1</mn> </msub> <mo>]</mo> </mrow> <msub> <mi>s</mi> <mn>0</mn> </msub> <mrow> <mo>[</mo> <mi>n</mi> <mo>-</mo> <msub> <mi>m</mi> <mn>2</mn> </msub> <mo>]</mo> </mrow> </mrow></math>

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wherein N is₁、N₂、N₃Respectively representing the first, second and third order memory depths, h₁、h₂、h₃Respectively representing coefficients of each order. In this embodiment, the first order coefficient h is implemented₁Is provided with

Second order coefficient h₂Is provided with

Third order coefficient h₃Is provided withAnd (4) respectively. N is a radical of₁、N₂、N₃First set by the user through the controller 310 and then all h₁、h₂、h₃And (4) the coefficient.

The invention relates to a distortion correction test method of a broadcast communication transmitter, which comprises the following two aspects: on one hand, the method is a method for testing the correction performance of a broadcast communication transmitter; another aspect is a method for testing the transmitter distortion resistance of a broadcast communication system.

The calibration performance test method of the broadcast communication transmitter is shown in fig. 2, and the test equipment comprises: the device comprises a data generator 1, an exciter 2, a transmission distortion simulator 3 and a frequency spectrograph 5.

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

the exciter 2 comprises a digital baseband modulation module 21, a predistortion corrector 22, a digital-to-analog converter 23 and an up-converter 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 a digital television transmission standard, outputs a digital baseband signal B, the predistortion corrector 22 performs predistortion on the signal B, outputs a digital baseband signal C, the digital-to-analog converter 23 converts the signal C into an analog baseband signal D, and the up-converter 24 performs up-conversion on the signal D to generate a digital television broadcast radio frequency emission signal E;

the transmission distortion simulator 3 adds the influence of distortion effect to the digital television radio frequency transmission signal E and outputs a distorted signal J;

the frequency spectrograph 4 measures the frequency spectrum of the output signal J of the transmission distortion simulator 3.

The method for testing the correction performance of the broadcast communication transmitter comprises the following steps:

firstly, a data source 1 sends a digital television image code stream signal A to an exciter 2, the exciter 2 outputs a signal E obtained by modulating and frequency-converting the signal A to a transmission distortion simulator 3, a pre-distortion corrector 22 does not start a pre-correction function, the simulator 3 does not perform distortion processing on the signal at the moment, the simulator 3 outputs a normal signal J, and a frequency spectrum instrument 5 observes that the frequency spectrum of the signal J output by the simulator 3 is a correct frequency spectrum;

setting the transmitting distortion simulator 3 as a linear and nonlinear distortion model specified by a user, and observing the frequency spectrum of an output signal J of the simulator 3 by using a frequency spectrograph 5 to generate distortion;

step three, the transmission distortion simulator 3 keeps a distortion model, the predistortion corrector 22 starts a correction function, the exciter 2 outputs a signal E which becomes a signal after the predistortion, and the frequency spectrograph 5 observes whether the frequency spectrum of a signal J output by the simulator becomes correct: if the distortion model becomes correct, the exciter 2 makes correct pre-correction on the distortion model; if the signal J spectrum still contains distortion, the exciter 2 can not correct the distortion model;

step four, changing the linear and nonlinear distortion parameters and models set by the transmission distortion simulator 3, repeating the step three, and testing the correction performance of the exciter 2 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.

The method for testing the distortion performance of the transmitter in the broadcast communication system is shown in fig. 3, and comprises the following steps: data generator 1, exciter 2, transmission distortion simulator 3, receiver 4.

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

the exciter 2 comprises a digital baseband modulation module 21, a predistortion corrector 22, a digital-to-analog converter 23 and an up-converter 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 a digital television transmission standard, outputs a digital baseband signal B, the predistortion corrector 22 performs predistortion on the signal B, outputs a digital baseband signal C as an emulator input signal F, the digital-to-analog converter 23 converts the signal C into an analog baseband signal D, and the up-converter 24 performs up-conversion on the signal D and outputs a digital television broadcast radio frequency emission signal E;

the transmission distortion simulator 3 adds the influence of distortion effect to the digital baseband signal F or the transmission signal E and outputs a distorted radio frequency signal J or a distorted 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 into an analog baseband signal L, the analog-to-digital converter 42 converts the signal L into a digital baseband signal M, and the selection switch 343 selects the signal M or the signal K to enter the digital baseband demodulation module 44, and outputs the image signal P after demodulation processing.

In order to match the selection of two input ports and two output ports of the simulator in the invention, the exciter 2 is provided with a radio frequency output and a digital baseband output port at the same time, and the adopted emission correction scheme is corrected in a forward digital baseband predistortion mode; the receiver 4 has both a radio frequency input and a digital baseband input port.

The method for testing the distortion resistance of the transmitter of the broadcast communication system comprises the following steps:

firstly, a data source 1 sends a digital television image code stream signal A to an exciter 2, the exciter 2 outputs a baseband signal C after the signal A is modulated or a signal E after the signal A is modulated and frequency-converted to a transmission distortion simulator 3, a pre-distortion corrector 22 does not start a pre-correction function, the simulator 3 does not perform distortion processing on input signals F and E at the moment, and the simulator 3 outputs a normal baseband signal K or a radio frequency signal J;

step two, the transmitting distortion simulator 3 is set as a linear and nonlinear distortion model specified by a user;

step three, detecting an output signal P of the receiver 4 and evaluating the receiving effect of the receiver 4 at the moment;

step four, changing linear and nonlinear distortion parameters and models set by the transmission distortion simulator 3, repeating the step three, and testing the transmission performance of a system formed by the exciter 2 and the receiver 4 under various 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 transmission performance among different systems.

The following distortion simulation is performed by using a digital television terrestrial radio broadcasting transmission standard (DTMB) system as a specific embodiment:

the digital television terrestrial radio broadcasting system is a typical broadband system, and because the transmission power is large, and the digital modulation signal, especially the multi-carrier modulation signal, has the characteristics of large power output dynamic range and high peak-to-average power ratio (PAR), the digital modulation signal is easily affected by the nonlinear effect of the transmitter, and meanwhile, the circuit of the transmitter often generates linear distortion. In the research work of the digital television terrestrial radio broadcasting originating exciter, how to correct linear distortion and nonlinear distortion of the transmission process is very important research content.

The standard technical scheme of digital television ground wireless broadcasting mainly comprises a single carrier modulation mode and a multi-carrier modulation mode, wherein the two modes have the advantages respectively, and the degrees of the distortion influence of a transmitter are different. Compared with a single carrier working mode, the multi-carrier working mode has higher peak-to-average power ratio (PAPR) and is more easily influenced by nonlinear distortion, so that when the working process and the effect of a nonlinear distortion module are described, the multi-carrier working mode is adopted in the modulation mode; when the single carrier is affected by linear distortion, the distortion on the constellation diagram is obviously reflected, and the effect is easy to observe, so that when the working process and the effect of the linear distortion module are described, the modulation mode adopts a single carrier working mode.

In a specific embodiment 1 of the orthonormal deviation simulation unit 340 of the linear distortion simulation module 34 of the present invention, the structure is as shown in fig. 4, and the parameters of the first function generator 3401 and the third function generator 3403 are set

Setting parameters of the second and fourth function generators 3402, 3404

Baseband signal I₀And Q₀The signal is a single carrier 16QAM modulated signal, the constellation diagram of which is shown in figure 5, and the baseband signal I is added with orthogonality deviation₁And Q₁Constellation as shown in fig. 6, it can be seen that the shape of the constellation is no longer rectangular, and is significantly changed.

In a specific embodiment 2 of the gain imbalance simulation unit 341 of the linear distortion simulation module 34 according to the present invention, the structure is shown in fig. 4, and the working state of the orthogonality deviation simulation unit 340 is set as no distortion, i.e. I₁＝I₀And Q₁＝Q₀Setting the parameter a of the fifth multiplying unit 3411_IThe parameter a of the sixth multiplying unit 3412 is set to 2.0_Q1.2, baseband signal I₀And Q₀For single carrier 16QAM modulationThe constellation diagram of the signal is shown in fig. 5, and the constellation diagram of the baseband signal after the gain imbalance effect is added is shown in fig. 7, it can be seen that the amplitudes of the I path and the Q path in the shape of the constellation diagram become obviously 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 shown in fig. 4, and both the orthogonality deviation simulation unit and the gain imbalance unit are set to work without distortion, i.e. I₂＝I₁＝I₀And Q₂＝Q₁＝Q₀Setting a parameter Δ of the addition unit 3421_I＝I₂10%, setting the parameter Δ of the addition unit 3422_Q＝Q₂(-5%) base band signal I₀And Q₀For a signal modulated by a single carrier 16QAM, its constellation diagram is shown in fig. 5, its frequency spectrum is shown in fig. 9, the constellation diagram of the baseband signal after the carrier leakage influence is added is shown in fig. 8, and the frequency spectrum is shown in fig. 10, it can be seen that the relative position of the constellation diagram and the coordinate axis has shifted, and the frequency spectrum has an obvious bump displayed at the center frequency point.

One 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 signals entering the power amplifier is high, so that when the nonlinear effect simulation module 35 is verified, a multicarrier modulation signal is adopted, which is different from the linear effect simulation verified in the previous example. In the prior art, a method for observing the frequency spectrum spreading of a transmitted signal is generally adopted for evaluating the linearity of a power amplifier, the shoulder ratio of an original transmitted signal of a digital television is very high and is generally more than 40dB according to the original standard, the shoulder ratio is deteriorated under the influence of a nonlinear effect, the shoulder ratio is deteriorated from several deci to ten and several decibels according to the difference of the nonlinear degree, and then the shoulder ratio is corrected to 36dB according to the correction of the nonlinear correction function in an exciter 2, so that a high-power transmitter generally requires the output of the shoulder ratio to meet the requirement. Since the influence of the nonlinear model is similar in shape in the spectrum, taking an example of application of the Saleh model as an example, as shown in fig. 11, parameter α of Saleh model unit 3504 is set_a＝1、β_a＝0.05、

、

Fig. 14 shows the spectrum of the original multicarrier modulation signal input to nonlinear distortion simulation module 35, and fig. 15 shows the spectrum of the signal after the signal is simulated by Saleh model unit 3504, which shows that the output signal is degraded by more than 30dB from the shoulder level of the input signal.

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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