KR20000031138A - Pre-compensator of transmission system including linear distortion and nonlinear distortion and method for estimating delay between transmission signal and feedback signal and phase difference therebetween - Google Patents

Abstract

PURPOSE: A technique for compensating distortions in a transmitter for a broadcasting system and radio communication is provided to effectively compensate distortions in a transmission system where a linear and nonlinear distortion are mixed, and correctly estimate time delay between a transmission signal and feedback signal and phase difference therebetween by way of software. CONSTITUTION: A transmission signal input unit(100) compensates signal from a transmission system via a pre-equalizer(102). A pre-distortion unit(200) compensates a nonlinear distortion of the input signal of the transmission signal input unit(100). A transmission unit(300) converts the output signal of the pre-distortion unit(200) to an analog signal before filtering the analog signal, and then amplifies the filtered signal prior to sending it via an antenna(310). A signal processing unit(400) converts the signal from the transmission unit(300) to a signal for a distortion coefficient and equalization filter coefficient. A coefficient generator(500) controls the pre-distortion unit(200) and pre-equalizer(102) based on the distortion coefficient from the pre-distortion unit(200) and the equalization filter coefficient from the pre-equalizer(102).

Description

Predistorter and Delay and Phase Difference Estimation Method between Predistorter and Transmitted Signal and Feedback Signal in Mixed Linear and Nonlinear Distortion Systems

The present invention relates to a predistorter configuration of a transmission system in which linear and nonlinear distortions are mixed, and a method of estimating delay and phase difference between a transmission signal and a feedback signal.

The technical field of the present invention is a distortion compensation technique for coping with problems such as spectral distortion and inter-symbol interference caused by nonlinear distortion and linear distortion in broadcast and wireless communication transmitters.

As a typical countermeasure technique in the field of distortion compensation, non-linear distortion has a predistorter in front of the power amplifier, so that it is distorted and canceled as much as it is in the amplifier.

In addition, the linear distortion is pre-equipped to cancel as much as the linear distortion using the pre-equalizer, so that the distortion is not seen as a whole.

However, conventionally, the countermeasures have been taken when only linear distortion or nonlinear distortion exists seriously in the system.

In addition, in order to obtain a compensation coefficient by comparing the distorted signal through the transmission data and the transmitter, first, the delay and the phase difference between the transmission signal and the feedback signal should be eliminated.

This estimation is made of hardware in the past, the system has a complicated problem.

In order to solve the above problems, the present invention provides a method for compensating for distortion of a transmission system in which linear and nonlinear distortions are mixed, and accurately estimating delay and phase difference between a transmission signal and a feedback signal in software. The purpose.

Therefore, in the present invention, a countermeasure of a transmission system in which linear and nonlinear distortions are mixed is considered. When the two methods are simply applied, both the predistorter and the pre-equalizer are different because the characteristics of the distortion characteristics are very different when the two distortions are moderately large. Since the compensation coefficient cannot be estimated properly, a system for compensating for the distortion when these two causes exist at the same time is found.

In addition, in order to perform this precompensation, the compensation coefficient of the predistorter should be calculated by comparing the feedback signal of the distorted signal through the transmission data and the transmitter. For this purpose, timing synchronization and phase synchronization between the transmission data and the feedback signal should be performed.

Since the synchronization is made of hardware in the past, the system is complicated, and the compensation technology needs to be performed very accurately. Therefore, the present invention provides a method capable of accurately processing software.

In order to achieve the above object, the present invention, the transmission signal input unit 100 for pre-lightening the generated signal of the digital broadcast transmission system through a pre-equalizer for linear distortion compensation to match the broadcast and wireless communication processing, Pre-distortion unit 200 for non-linear distortion compensation of the input signal, Transmitter 300 for converting and filtering the output signal of the pre-distortion unit 200 to an analog signal and then amplifying the signal through an antenna And a signal selection processor 400 for switching and feedbacking the transmission signal to a program to obtain a distortion coefficient and an equalization filter coefficient, and the predistortion based on a delay and a phase difference between the feedback signal and the transmission signal. Signal distortion compensation coefficient for controlling the predistorter and the pre-equalizer by obtaining the distortion coefficient of the unit 200 and the equalization filter coefficient of the pre-equalizer. It is composed of a living part 500, characterized in that to compensate for the linear and non-linear distortion existing at the same time.

Also, in order to estimate the timing synchronization and the phase synchronization between the transmission signal and the feedback signal, the data is passed through the quadrature down converter 650 from the A / D converter 405 and then interpolated (interpolated) through the interpolator 640. The output of the I / Q channel 101 of the VSB modulation of the transmission data is interpolated 610, and the decimation 720, 820 is performed after finding the delay value through the delay value calculator 620 using the interpolated two data. ), And the phase difference calculator 630 obtains the phase difference of the data using the two interpolated data and transmits the phase difference of the data to the frequency downconverter 740.

Next, in order to obtain the distortion coefficient of the predistorter using the delay value obtained by receiving the transmission signal and the feedback signal in a system in which linear and nonlinear distortions are mixed, while the switch is connected to the directional coupler 307, A / D Receives data from the converter 405 and interpolates through the interpolator 810, receives the delay value from the delay calculator 620, performs the decimation 820, and performs orthogonal down converter 830 after decimation. The predistortion coefficient is calculated along with the output data of the VSB filter 104 and stored in the reference table 202.

In order to obtain the equalization filter coefficient of the pre-equalizer using the delay value and the phase difference obtained by receiving the transmission signal and the feedback signal in a transmission system having a mixture of linear and nonlinear distortion, the switch 401 is connected to the directional coupler 309. In the connected state, it receives data from the A / D converter 405 and interpolates through the interpolator 710, receives the delay value from the delay value calculator 620, performs the decimation 720, and then performs an acquiring filter ( Pass 730 to receive the phase difference value from the phase difference calculator 630 and pass it to the frequency downconverter 740 and then perform decimation 750 and linear equalizer with the data from the signal generator 101. Through 760, the pre-lighting coefficient generated at this time is stored in the pre-equalizer 102.

1 is a block diagram of a transmission system to which the present invention is applied;

2 is a block diagram illustrating a delay and phase difference estimation between a transmission signal and a feedback signal according to the present invention;

3A to 3B are flow charts for calculating filter coefficients and pre-distorter reference table (LUT) coefficients of a pre-equalizer according to the present invention.

* Explanation of symbols for main parts of the drawings

100: transmission signal input unit 101: signal generator

102: pre-equalizer 103: interpolator

104: VSB filter 200: predistortion

201: Complex Multiplier 202: Look-Up Table (LUT)

203: address generator 300: transmitter

301: Mixer 302: D / A Converter and Lowpass Filter

303: adder 304: mixer

305: bandpass filter 306: power amplifier

307,309 Directional Coupler 308 Bandpass Filter

310: antenna 311: oscillator

400: signal selection processing unit 401: switch

402: gain controller 403: mixer

404: low pass filter 405: A / D conversion unit

500: signal distortion compensation coefficient generator 501: digital signal processor

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a transmission system to which the present invention is applied and includes a transmission signal input unit 100 for pre-lighting a generated signal with a pre-equalizer for linear distortion, and inputting the signal according to broadcasting or wireless communication processing. A predistortion unit 200 for nonlinear distortion of the pre-distorted signal, a transmitter 300 for converting the predistortion unit output signal from a digital signal to an analog signal, filtering and amplifying the amplified signal and transmitting the amplified signal through an antenna; A signal selection processing unit 400 for programmatically switching and feedback a signal and converting the signal into a signal for obtaining a distortion coefficient and an equalization filter coefficient, and the predistortion unit based on a delay and a phase difference between the feedback signal and the transmission signal. Obtain a distortion coefficient and an equalization filter coefficient of the pre-equalizer to generate a signal distortion compensation coefficient for controlling the predistorter and the pre-equalizer It is composed of 500.

In addition, a more specific configuration of FIG. 1 will be described.

First, the transmission signal input unit 100 includes an information generation unit 101 for generating digital information, a pre-equalizer 102 for battery equalization for linear distortion compensation of the generated signal, and a VSB modulation for the pre-lighted signal. The interpolator 103 interpolates (interpolates) and the VSB filter 104 filters the interpolated signals.

Next, the predistortion unit 200 receives the reference signal 202 for storing the distortion coefficient obtained through the control of the signal distortion compensator 400 and the output signal of the transmission signal input unit 100 to receive the reference signal. An address generator 203 used to find a value of the table 202 and a complex multiplier 201 that receives an output signal from the transmission signal input unit 100 and performs a complex multiplication by referring to the value of the reference table 202. It consists of.

In addition, the transmitter 300, a mixer 301 for mixing the output signal and the carrier signal of the predistortion unit 200, respectively, and converts each mixed signal from a digital signal to an analog signal and then filter D / An adder and a frequency uplinker 303, 304 for adding an A converter and a lowpass filter 302, a signal passing through the lowpass filter 302, and then raising the frequency of the signal using an oscillation signal, It consists of two bandpass filters and power amplifiers 305, 306, and 308 that transmit power through an antenna by performing primary bandpass filtering and then amplifying the frequency upstream signal.

Next, the signal selection processing unit 400 includes a first directional coupler 307 for receiving and feeding back the power-amplified transmission signal to obtain a predistortion coefficient, and the second bandpass transmission for obtaining a pre-equalization filter coefficient. A second directional coupler 309 for receiving a signal and a feedback signal; and a second directional coupler 307 for obtaining a distortion coefficient of the predistortion portion; A programmable switch 401 connected to the combiner 309, a gain controller 402 for controlling the output of the switch 401 so that the magnitude of the transmission signal and the reception signal are at a similar level, and the same oscillation as in the transmission A / D converter 405 converts an analog signal into a digital signal through a frequency downlinker 403 using a signal.

In addition, the signal distortion compensation coefficient generator 500 is configured by using a digital signal processor (hereinafter referred to as a DSP) 501.

Referring to the operation by the above configuration is as follows.

First, the digital signal to be sent is generated in the information generator 101 such as a source encoder, a channel encoder, an interleaver, etc., and the interpolator 103 is pre-equipped in the pre-equalizer 102 to perform VSB modulation. Through interpolation (interpolation) through, and filtered through the filter 104, and passes through the complex multiplier 201 for predistortion.

The complex multiplier 201 outputs again through a mixer 301, a digital-to-analog (D / A) converter that converts digital to analog signals, and a low pass filter (hereinafter referred to as LPF) 302 again. It goes through the riser (303).

This signal is broadcast via an antenna 310 via a power amplifier 306 having a nonlinear distortion characteristic, through a bandpass transmission filter 308.

In order to obtain the distortion coefficients of the predistorters 201, 202, and 203, the transmission signal is fed back through the directional coupler 307 immediately after the power amplifier 306, and the equalization filter coefficient of the pre-equalizer 102 is obtained. The transmission signal is fed back through the directional coupler 309 immediately after the bandpass transmission filter 308.

A program controllable switch 401 connects the directional coupler 307 directly behind the power amplifier 306 to obtain the distortion coefficients of the predistorters 201, 202, and 203, and the pre-equalizer 102. In order to obtain the equalization filter coefficient of, the directional coupler 309 is connected directly after the bandpass transmission filter 308.

The output of the switch 401 is passed through the gain controller 402 so that the magnitude of the transmission signal and the reception signal in the digital signal processor 501 is at a similar level, and using the oscillator 311 as in the transmission, The digital signal processor 501 passes through an A / D converter 405 that converts an analog signal into a digital signal via the 403.

The digital signal processor 501 calculates the equalization filter coefficients of the pre-equalizer 102 and the distortion coefficients of the predistorters 201, 202, and 203.

In order to obtain the compensation coefficient as described above, the timing synchronization and the phase synchronization between the transmission signals 101 and 104 and the reception signal 405 should be made.

In order to match the timing synchronization and the phase synchronization between the transmission signals 101 and 104 and the reception signal 405, the following calculation procedure is performed.

The timing synchronization is obtained by using the data from the A / D converter 405 and the output data from the VSB filter 104. The data from the A / D converter 405 is converted into an orthogonal down converter 650. After coarse, the delay value is calculated through the delay calculator 620 using data interpolated (interpolated) through the interpolator 640 and data interpolated from the output 104 of the I / Q channel of VSB modulation of the transmission data. Use the following method to find it.

The data obtained by interpolating (interpolating) the output 104 of the I / Q channel of the VSB modulation is referred to as f1 and f2, respectively, and the A / D converted data 405 is passed through the quadrature down converter 650 and then interpolated. When the Q data are b1 and b2, respectively, the time delay m at which the average signal size difference e (m) between the transmission and reception signal strings is minimum is estimated as the propagation delay value as shown in Equation 1 below.

Where k is a discrete time delay index and m is a delay time index between the transmission signal and the feedback signal.

The method of using the correlation function between the transmission signal and the feedback signal is not a problem in the general digital communication system. However, in the present case where the interpolation between symbols is used to find the sophisticated propagation delay, the maximum value of the correlation function is stably found. It's a problem because it can't be counted and it will shake by multiple samples.

However, using the above method, the propagation delay value can be found very stably compared with the case of using the correlation function.

Once the propagation delay value is estimated, the phase difference should be obtained. In a channel with linear distortion, the phase difference cannot be obtained by a simple average value of phase comparison between many transmission signals and feedback signals.

In addition, in the broadcast transmission system as shown in FIG. 1, since the pre-equalizer is a one-dimensional equalizer, the equalization coefficient cannot be obtained if there is a phase difference between the transmission signal and the feedback signal.

That is, the output of the I / Q channel of VSB modulation of data and transmission data interpolated (interpolated) by the interpolator 640 after passing the data from the A / D converter 405 through the quadrature down converter 650 ( If the complex filter coefficient of the complex equalizer is obtained using the interpolated data, and the phase of the first term is obtained, this becomes the phase difference between the transmission signal and the feedback signal.

Using the propagation delay value and the phase difference obtained as described above, the distortion coefficient of the predistorter and the filter coefficient of the pre-equalizer are obtained as shown in FIG.

3A to 3B are flow charts illustrating the filter coefficients and the distortion coefficients of the predistorter according to the present invention. In the transmission system in which linear and nonlinear distortions are mixed, the predistorters 201, 202, and 203 of FIG. The distortion coefficient should be obtained first. The distortion coefficient is obtained by using the data from the A / D converter 405 and the output data of the VSB filter 104 with the switch 401 connected to the directional coupler 307. The flow is as follows.

After receiving data from the A / D converter 405, interpolating (interpolating) through the interpolator 810, receiving a delay value from the delay calculator 620, performing decimation 820, and then performing an orthogonal down converter ( A distortion coefficient is calculated and stored in the reference table 202 along with the output data of the VSB filter 104 via 830. The value of the reference table 202 is found and predistorted to compensate for nonlinear distortion.

Then, the data is received from the A / D converter 405 with the switch 401 connected, interpolated (interpolated) through the interpolator 710, and the decimation is received from the delay calculator 620. After the 720, the filter passes through the filter 730, receives the phase difference value from the phase difference calculator 630, passes the frequency down converter 740, and then decimates the signal from the signal generator 101. When linear equalization is performed in the linear equalizer 760 based on the data, the coefficient of the linear equalizer is the pre-equalization coefficient of the pre-equalizer 102.

As described above, the present invention can effectively compensate for distortion of a transmission system in which linear distortion and nonlinear distortion are mixed, not only when only linear distortion or nonlinear distortion is seriously present in the system.

In addition, accurate timing synchronization and phase synchronization are important in obtaining the coefficients of the predistorter, and by providing a method for estimating the propagation delay and phase difference that is accurate in software, it was necessary to pay a large price in hardware. Can greatly increase the complexity and economic efficiency of the.

Claims (9)

A transmission signal input unit which pre-lightens the generated signal of the digital broadcast transmission system through a pre-equalizer for linear distortion, and processes and inputs the signal for the broadcasting and wireless communication processing; A predistortion unit for nonlinear distortion of the input signal; A transmitter which converts the output signal of the predistortion unit into an analog signal, filters the signal, and then amplifies and transmits the signal through an antenna; A signal selection processor for converting and transmitting the transmission signal into a program and converting the signal into a signal for obtaining a distortion coefficient and an equalization filter coefficient; A signal distortion compensator for controlling the predistorter and the pre-equalizer by obtaining a distortion coefficient of the predistorter and an equalization filter coefficient of the pre-equalizer based on a delay and a phase difference between the feedback signal and the transmitted signal. And a predistorter of a transmission system in which linear and nonlinear distortions are mixed, wherein linear and nonlinear distortions are compensated for at the same time. The method of claim 1, wherein the transmission signal input unit An information generator for generating a digital signal; A pre-equalizer for pre-lightening the signal for linear distortion of the generated signal; An interpolator for interpolating the pre-lighted signal for VSB modulation; A predistorter of a transmission system in which linear and nonlinear distortions are mixed, comprising a VSB filter for filtering each waveform of an interpolated signal. According to claim 1, wherein the predistortion portion A reference table for storing a distortion coefficient obtained through control of the signal distortion compensation unit; An address generator that receives an output signal of the transmission signal input unit and finds a value of the reference table and predistorts the compensating nonlinear distortion; And a complex multiplier configured to receive an output signal from the transmission signal input unit and perform a complex multiplication by referring to a value of the reference table. The method of claim 1, wherein the transmitting unit A mixer for mixing the output signal and the carrier signal of the predistortion unit, respectively; A D / A converter and a low pass filter for converting each mixed signal from a digital signal into an analog signal and filtering the mixed signal; An adder and a frequency upr that adds signals passing through each of the lowpass filters and then raises the frequency of the signals by using an oscillation signal; In the transmission system in which the linear and nonlinear distortions are mixed, the band-pass filter and the power amplifier are characterized in that the frequency-upped signal is first amplified after the bandpass filtering and then amplified. Predistortion Compensator. The method of claim 1 or 4, wherein the signal selection processing unit A first directional coupler for receiving and feeding back the power-amplified transmission signal to obtain a distortion coefficient; A second directional coupler for receiving and feeding back the secondary bandpass filtered transmission signal to obtain an equalization filter coefficient; A programmable switch coupled to said first directional coupler to obtain a distortion coefficient of said predistortion portion and coupled to said second directional coupler to obtain an equalization filter coefficient of said pre-equalizer; A gain controller for controlling the output of the switch so that the signal magnitudes of the transmission signal and the reception signal are similar to each other; A predistorter of a transmission system in which linear distortion and nonlinear distortion are mixed, comprising an A / D converter for converting an analog signal passing through a frequency downlinker into a digital signal using the same oscillation signal as the transmission. The method of claim 5, wherein the signal distortion compensation unit A predistorter of a transmission system in which linear and nonlinear distortions are mixed, using a digital signal processor (DSP). In the timing synchronization and phase synchronization estimation method between a transmission signal and a feedback signal in order to obtain a compensation coefficient while a switch is connected to a directional coupler immediately after the power amplifier, A first step of interpolating data from the A / D converter by an orthogonal downward converter and interpolating the interpolator through an interpolator; Interpolating an output of an I / Q channel of VSB modulation of transmission data; A third step of finding a delay value through a delay value calculator using the interpolated two data and transmitting the delay value to a matched filter; And a fourth step of obtaining the phase difference of the data through a phase difference calculator and transmitting the data to the decimation using the interpolated data. Delay and phase difference estimation method. In the method of calculating the distortion coefficient of the predistorter using the delay value and the phase difference obtained by receiving the transmission signal and the feedback signal in a transmission system having a mixture of linear and nonlinear distortion, A first step of receiving data from an A / D converter and interpolating through an interpolator and receiving a delay value from a delay value calculator to perform decimation; And a second step of calculating the predistortion coefficient along with the output data of the VSB filter after performing the decimation and storing the predistortion coefficient as a reference table. In a method for obtaining an equalization filter coefficient of a pre-equalizer using a reference table obtained by using a delay value and a phase difference obtained by receiving a transmission signal and a feedback signal in a transmission system having a mixture of linear distortion and nonlinear distortion, A first step of interpolating data through an interpolator by receiving data from an A / D converter in a state in which a switch is connected; After interpolating the data from the A / D converter, receiving the delay value from the delay calculator, decimating, passing through the filter, and receiving the phase difference from the phase difference calculator Steps; And a third step of performing decimation after passing the phase difference value from the phase difference calculator to the down-converter, passing the linear equalizer together with the data from the signal generator, and storing it as the reference table. Calculation method of equalization filter coefficient of equalizer.