KR20010011974A - Distortion Signal Compensation Method in Digital TV - Google Patents

Abstract

PURPOSE: A method for compensating a distortion signal in a digital TV translator is provided to use a VSB(Vestigial Side Band) receiver and a software controlling technology as substitutes for a vector signal interpreter, so as to prevent a signal error caused by a manual operation. CONSTITUTION: Distortion signals passing through a directional coupler(250) are converted into 44Mhz intermediate frequency(IF) signals from 470 to 806Mhz RF(Radio Frequency) signals, by an analog to digital(A/D) down converter(261) of a VSB(Vestigial Side Band) receiver. The 44Mhz IF signals are separated by an in-phase(I)-quadrature(Q) channel separator(262), respectively, and moved to a baseband, then separated into an I channel and a Q channel by an A/D converter(264). Two analog to digital converter synchronous signals are supplied, by a synchronous signal detector(265) composed of a digital TV VSB transmission receiving chip. A control signal of the I-Q channel separator(262) and a control signal of a down converter(261) are controlled by an RF controller(263). The control signals are transmitted to a computer controller(270) through a 104-bus from the VSB receiver. A signal of a VSB demodulator(271) enters as an input value of a software using a linear/non-linear characteristic compensating algorithm(272). If a demodulated signal is inputted, the software analyzes a characteristic of the inputted demodulated signal. When a characteristic relating to a linear signal is compensated, coefficient values of I/Q data of a digital filter of the VSB demodulator(271) are calculated. Compensated values are fed back through an RS-232C serial cable to a VSB modulator(210), to be transmitted. When a characteristic relating to a non-linear signal is compensated, an alpha and a beta value of the digital filter are calculated. Compensated values are fed back to the VSB modulator(210), to be transmitted.

Description

Distortion Signal Compensation Method in Digital TV Repeater

The present invention relates to a method for compensating a nonlinear distortion signal suitable for eliminating nonlinearity due to shock, aging, and temperature change of a nonlinear device such as a high power amplifier (HPA) having a nonlinear characteristic of a digital TV translator. will be.

In general, various linearization techniques and algorithms have been proposed to improve the nonlinearity of RF high power amplifiers (hereinafter abbreviated as HPA) that satisfy the standards related to digital communication systems.

Representative linearization methods include a method using a feed forward, a predistortion, and a vector signal analyzer. Such various linearization methods will be described as follows.

First, a linearization method using a predistortion method.

This method generally uses the predistortor located in front of the main amplifier to have the opposite characteristics when the gain and phase characteristics of the main amplifier input signal are distorted in a specific direction. It is possible to obtain an output with improved non-linearity by keeping the characteristics of the same as the input signal.

Next is the feed forward method.

In this method, when the original signal is amplified among the signals input to the main amplifier and the resulting intermodulation distortion signal components are output, the intermodulation distortion is performed using a delay line and an error amplifier. (Inter Modulation Distortion) This is a method of adjusting the phase of signal components to 180 ° so that only signals without distortion and similar to the original input signal are output.

Next, a method using a vector signal analyzer will be described with reference to the drawings.

1 is a block diagram illustrating a linearization method of a distorted signal of a high output amplifier using a conventional vector signal analyzer.

Referring to FIG. 1, the distorted signal passing through the directional coupler 250 is converted into a 44 MHz band by the down converter 161 inside the vector signal analysis instrument 160 and then converted into a digital signal to convert the digital signal into a digital signal. Input to analog-to-digital converter 162.

At this time, the intermediate frequency (IF) digital signal of 44 MHz is continuously separated into I and Q channels.

The signal separated by the I-Q signal from the IQ channel separation stage 165 is output by the residual sideband demodulator 166 to produce the final I and Q signals.

This signal is controlled by the control unit 163 and enters the input value of Zenith's software using the linear / nonlinear characteristic compensator algorithm 170 of the Windows 95 system via the GP-IB interface 164. Zenith software calculates the values of the I and Q data coefficients of the internal digital filter of the residual sideband modulator 110 and transmits them through RS-232C for linear characteristic compensation, and the residual sideband modulator (for nonlinear characteristic compensation). The α and β values of the internal digital filter are calculated and transmitted via RS-232C.

This series of steps can be performed in turn on linear and nonlinear compensators by manually manipulating the software on the PC at the desired time.

However, the prior art has to use a very expensive vector signal analyzer to compensate for the nonlinear characteristics of the high power amplifier. For this reason, it is inconvenient to carry a very heavy and expensive vector signal analyzer in a place such as an unmanned repeater, and even when a linear / nonlinear characteristic compensation is to be performed, a user must manually operate a complex vector signal analyzer.

In addition, it is very inconvenient to use the GP-IB protocol which is used for the interface between the vector signal analyzer and the PC to perform linear / nonlinear characteristic compensation.

An object of the present invention has been made in view of the above-mentioned disadvantages of the prior art, the impact, aging, changes in temperature of nonlinear devices such as large power amplifier (HPA) having the nonlinear characteristics of a digital TV translator (Translator) To provide a distortion signal compensation method in a digital TV repeater to be suitable for removing the non-linearity according to.

According to an aspect of the present invention for achieving the above object, after amplifying and outputting the input signal from the modulator, and converts the signal into an intermediate frequency signal by a down converter, and converts the converted signal into an IQ channel separator A digital TV repeater for processing a signal converted from an analog-to-digital converter, each separated by a; demodulating the signal by transmitting the signal converted from the analog-to-digital converter to a computer control unit; Calculating a compensation value of the distorted signal by inputting the demodulated signal to a program; And precompensating the calculated compensation value with the modulator.

Preferably, the calculating of the compensation value may include calculating coefficient values of I and Q data of the digital filter inside the residual sideband demodulator when compensating characteristics of the linear signal input according to a user's selection. In the case of compensating characteristics of the input of the nonlinear signal, α and β values of the internal digital filter of the SVB demodulator 271 are calculated to automatically compensate the distorted signal sequentially.

The demodulating may be performed by an application program implemented by software of the computer control unit by receiving a signal converted by the analog-digital converter.

1 is a block diagram illustrating a linearization method of a distorted signal of a high output amplifier using a conventional vector signal analyzer.

2 is a block diagram illustrating a linearization method of a distorted signal using a residual sideband receiver and a characteristic compensation algorithm according to the present invention;

Explanation of symbols on the main parts of the drawings

210: residual sideband modulator 220: up-converter

230: intermediate frequency amplifier (IPA) 240: high power amplifier (HPA)

250: directional coupler 260: RF control unit

261: downconverter 262: I-Q channel separator

263: RF controller 264: analog to digital converter

265: synchronization signal detector 270: computer control unit

271: residual sideband demodulator 272: linear / nonlinear characteristic compensator algorithm

Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

2 is a block diagram illustrating a linearization method of a distorted signal using a residual sideband receiver and a characteristic compensation algorithm according to the present invention.

Referring to FIG. 2, the RF & controller 260 and the computer controller 270 are components for implementing the method for linearizing a distorted signal.

First, the RF & controller 260 has a residual side band modulator (VSB) for amplifying and outputting a digital TV signal transmitted through a receiving antenna of a repeater, which is referred to as RF. There are an up converter 220, an intermediate frequency amplifier (IPA) 230, and a high power amplifier (HPA) 240 for converting to a band.

There is also a directional coupler 250 for returning to the input signal of a typical residual sideband (VSB) receiver.

The residual sideband (VSB) receiver has a down converter 261 for downconverting the largely returned residual sideband (VSB) signal and an IQ channel separator 262 for separating the I and Q channels. An analog-to-digital converter (A / D converter) 264 is present. The control of each part takes place in the RF controller 263 and consists of these elements.

In addition, the computer control unit 270 extracts a compensation value from the residual sideband demodulator 271 made by software to extract the actual residual sideband signal from the digital IQ signal input through the 104 bus. It consists of a linear / nonlinear feature compensator algorithm 272. Here, modulation and demodulation using the residual sideband (VSB) is used for SSB (single side band) modulation in information signals such as television images, facsimile, and high-speed data signals in which the power spectrum is spread to a low frequency region. Due to the fact that the filter requires fine cut-off characteristics, it is often difficult to realize it technically, so that the sideband is smoothed by trade-off between double sind band (DSB) modulation and SSB modulation with half the transmission band compared to DSB modulation. This can be said to achieve an efficient blocking of the distortion signal by leaving a part of the sideband removed by using a blocking filter.

An operation of the present invention having such a configuration will be described with reference to the drawings.

As shown in FIG. 2, the distorted signal passing through the directional coupler 250 is converted into an RF signal of 470 to 806 Mhz by an A / D converter 261 inside a general residual sideband receiver (VSB Receiver). Is converted to 44Mhz IF signal.

The 44 MHz signal thus converted is separated by the I-Q channel separator 262 and transferred to the baseband, and then separated by the analog-digital converter 264 into the I and Q channels, respectively.

In addition, the two analog-to-digital converter synchronization signals are supplied using a synchronization signal detector 265 including a digital TV residual sideband transmission receiver chip, and a control signal of the IQ channel separator 262 and a downward direction. The control signal of the down converter 261 is controlled by the RF controller 263.

Accordingly, such a control signal is transmitted from the residual sideband receiver to the computer controller 270 via the bus 104.

That is, the residual sideband demodulator (VSB Demodulator) processed in the conventional vector signal analyzer is software-processed in the computer controller 270.

The signal of the software-implemented residual sideband demodulator 271 enters an input value of software using a linear / nonlinear characteristic compensation algorithm Algorithm 272.

Therefore, when the demodulated signal is input, the software analyzes the characteristics of the input signal.

In case of compensating characteristics of the linear signal input, the RS-232C serial cable is calculated by calculating the coefficient values of the I and Q data of the internal digital filter of the VSB deodulator 271. The compensated value is fed back to the remaining sideband modulator (VSB Modulation) 210 and transmitted.

In addition, when compensating for the characteristics of the input of the nonlinear signal, the residual sideband is obtained by calculating the α and β values of the internal digital filter in the VSB demodulation 271 and calculating the values compensated through the RS-232C serial cable. It feeds back to the band modulator (VSB Modulation) (210).

This series of operations can be performed automatically by the linear and nonlinear compensators in turn at the point in time desired by the user.

According to the present invention mentioned above has the following effects.

First, the conventional linear / non-linear signal receiver and software control technique can be used to replace the vector signal analyzer, which is an expensive measurement equipment used to compensate for the distorted signal output by the nonlinear characteristics of the conventional high power amplifier. It does not need to carry equipment because it replaces the role of nonlinear characteristic compensator, and it is very convenient to operate protocol for mutual interface by implementing residual sideband demodulator in software to perform linear / nonlinear characteristic compensation. It has an effect.

Second, since the linear / nonlinear compensator can be automatically operated, there is an effect of preventing the occurrence of error in the signal value and the hassle caused by manual operation by the conventional manual operation.

Third, cost-effective vector analysis instruments and Pentium computer-class equipment requiring high throughput can be modularized into one unit, thereby reducing the required cost.

Claims (3)

After amplifying and outputting the input signal from the modulator, the signal is converted into an intermediate frequency signal by a downconverter, and each of the converted signals is separated by an IQ channel separator to process a signal converted from an analog-to-digital converter. On digital tv repeaters, Transmitting the signal converted from the analog-to-digital converter to a computer controller to demodulate the signal in the residual sideband; Calculating a compensation value of the distorted signal by inputting the demodulated signal to a program; And precompensating the calculated compensation value with the modulator. The method of claim 1, wherein the calculating of the compensation value comprises calculating coefficient values of I and Q data of the internal digital filter of the residual sideband demodulator when compensating characteristics of the linear signal input according to a user's selection. In the case of compensating the characteristics of the input of the nonlinear signal, compensation of the distorted signal is sequentially performed by calculating α and β values of an internal digital filter of the VSB demodulation 271. Distortion signal compensation method in a digital TV repeater, characterized in that. The method of claim 1, wherein the demodulating step comprises receiving the signal converted by the analog-to-digital converter and performing the same by an application program implemented by software of the computer controller. .