KR100320428B1 - Compensation Method and system for Distortion of Digital TV transmitter - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital TV repeater, and more particularly, to a distortion compensation method and system for a digital TV repeater that is suitable for precompensating a broadcast signal distorted and outputted from a transmitter to relay a clear broadcast signal to a subscriber. The distortion compensation method of the digital TV repeater according to the present invention comprises the steps of extracting the output signal of the modulator provided in the transmitter as a reference signal, the output signal of the high output amplifier as a measurement signal, and the extracted reference signal and measurement Demodulating the signal into baseband signals, synchronizing between the baseband demodulated reference signal and the measurement signal, and calculating an error of the reference signal with respect to the measurement signal, and a distortion for correcting the calculated error. Generating a compensation coefficient and inputting the generated distortion compensation coefficient to the modulator to perform pre-compensation on the measurement signal, thereby eliminating expensive instruments such as a vector signal analyzer and a high performance computer without the need for a high performance computer. Distortion can be compensated for to reduce the complexity of the transmitter without increasing system complexity. There is an effect to improve the stability and performance.

Description

Distortion compensation method and system of digital TV repeater {Compensation Method and system for Distortion of Digital TV transmitter}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital TV repeater, and more particularly, to a distortion compensation method and system for a digital TV repeater that is suitable for precompensating a broadcast signal distorted and outputted from a transmitter to relay a clear broadcast signal to a subscriber.

In general, the digital TV repeater is provided to service a radio shadow area that the digital broadcast transmitter does not reach, and serves to enhance the overall viewing rights of the digital TV.

To this end, the receiving end of the digital TV repeater receives the weak broadcast signal transmitted from the digital TV transmitter, and then converts the frequency down to an intermediate frequency (IF) and transmits it to the transmitting end, and the transmitting end transmits the desired intermediate frequency transmitted from the receiving end. After modulation, the signal is amplified and transmitted by a signal having a predetermined power level so that a subscriber located in a radio wave shadow area can receive it.

Considering the transmitting end of the digital TV repeater, a broadcast signal amplified and output through a high power amplifier (HPA) after a modulation process has a high probability of nonlinear distortion.

Thus, as a method for compensating for nonlinear distortion of a broadcast signal output from a high output amplifier, a LUT (Look Up Table) type distortion compensation system and an adaptive error correction system have been proposed.

1 is a block diagram illustrating a nonlinear distortion compensation system using a conventional vector signal analyzer.

Referring to FIG. 1, a LUT type nonlinear distortion compensation system includes a transmitter of a digital TV repeater and a nonlinear compensation receiver configured to extract and precompensate nonlinear distortion of a signal output from the transmitter. Here, the transmitter has the same configuration as that of the conventional digital TV repeater, and thus the description thereof is omitted, and the nonlinear compensation receiver comprises a vector signal analyzer composed of a down converter 107 and a demodulator 108 and a computer 109.

The LUT-type nonlinear distortion compensation system configured as described above first extracts a signal output from the high power amplifier (HPA) 104 of the transmitter, and generates a reference signal through a slice technique based on the extracted signal.

Here, the reference signal is generated according to the process as follows.

First, the signal extracted from the high power amplifier 104 is input to the down converter 107, down-converted to an intermediate frequency of 44 MHz, and then converted into baseband digital signals of I and Q via the demodulator 108. At this time, since the digital signals of I and Q are distortion-containing signals, a reference signal is generated through the measurement signal extracted from the high output amplifier 104 using the computer 109.

Subsequently, the nonlinear compensation receiver generates an LUT coefficient based on the generated reference signal, and the generated LUT coefficient is input to the modulator 100 of the transmitter through RS-232C.

Then, the LUT unit 101 of the modulator 100 first precompensates the nonlinear distortion generated by the high output amplifier 104 using the input LUT coefficient to output a broadcast signal.

2 is a block diagram illustrating a conventional adaptive error correction system.

Referring to FIG. 2, the adaptive error correction system includes a linear equalizer 200, a nonlinear corrector (LUT) 201, an RF up / down converter 203, a high power amplifier 204, and a signal processor 202. .

The adaptive error correction system configured as described above feeds back and converts the broadcast signal output from the high power amplifier 204 into an intermediate frequency and baseband signal to correct an error of the broadcast signal in real time and compensate for nonlinear distortion.

In more detail, the adaptive error correction system further configures the signal processing unit 202 for compensating for distortion of the RF signal inside the modulator of the transmitting end, thereby continuously modifying the LUT coefficient of the nonlinear corrector 201 in the signal processing unit 202. To compensate for the distortion of the signal extracted by the RF up / down converter 203 in real time.

But. The conventional nonlinear distortion compensation method has the following problems.

First, the LUT method using the vector signal analyzer requires additional equipment such as a vector signal measurer and a high-performance computer, which increases system complexity and operating cost, and also takes considerable time to run the software used to generate the LUT coefficients. As a result, a large time delay occurs until the nonlinear distortion is compensated for.

Second, the LUT method using the vector signal analyzer generates a reference signal after down-converting the RF signal passing through the high power amplifier, so that an accurate reference signal cannot be generated, and thus an error occurs when compensating for nonlinear distortion.

Third, the adaptive error correction system can compensate for nonlinear distortion in real time, but the system is complicated and difficult to implement.

Accordingly, an object of the present invention has been made in view of the above-mentioned problems of the prior art, and the distortion of the digital TV repeater which can precompensate the nonlinear distortion included in the broadcast signal output through the high output amplifier without the addition of hardware. To provide a compensation method and system.

According to an aspect of the present invention for achieving the above object, a distortion compensation method of a digital TV repeater is provided in the transmitting end in a digital TV repeater consisting of a receiving end and a transmitting end for relaying a broadcast signal to a plurality of subscribers; Extracting the output signal of the modulator as a reference signal, extracting the output signal of the high power amplifier as a measurement signal, and demodulating the extracted reference signal and the measurement signal into baseband signals, respectively, Synchronizing between a demodulated reference signal and a measurement signal, calculating an error of the reference signal with respect to the measurement signal, and generating a distortion compensation coefficient for correcting the calculated error, and converting the generated distortion compensation coefficient into the modulator. And performing precompensation for the measurement signal.

According to another aspect of the present invention for achieving the above object, the distortion compensation system of the digital TV repeater is a digital TV repeater consisting of a receiving end and a transmitting end for relaying a broadcast signal to a plurality of subscribers, A first coupler for extracting a modulator output signal as a reference signal without distortion, a second coupler for extracting a high output amplifier output signal of the transmitter as a measurement signal including distortion, and a reference signal and a measurement signal extracted through the coupler An adaptive precompensation system configured to generate a distortion compensation coefficient for correcting the distortion included in the measurement signal by calculating an error, wherein the modulator is distorted and outputted through the high power amplifier using the generated distortion compensation coefficient. Precompensate the signal.

1 is a block diagram showing a LUT nonlinear distortion compensation system using a conventional vector signal analyzer.

2 is a block diagram illustrating a conventional adaptive error correction system.

Figure 3 is a block diagram showing a distortion compensation system of a digital TV repeater according to the present invention.

4 is a block diagram showing a modulator shown in FIG.

* Description of the symbols for the main parts of the drawings *

300: modulator 303: RF unit

302, 304: first coupler, second coupler 306: down converter

307 and 308: first demodulator and second demodulator 309: data acquisition and synchronization processing unit

310: signal processor 311: RS-232C interface

Hereinafter, a configuration and an operation according to an exemplary embodiment of the present invention will be described with reference to the accompanying drawings.

In the present invention, by pre-compensating a broadcast signal that is distorted and output from a high-power amplifier by modulating a reference signal without distortion and a measurement signal with distortion from the transmitting end of the digital TV repeater and generating a distortion compensation coefficient accordingly, the modulator can precompensate the broadcast signal. We propose a distortion compensation method and system for a digital TV repeater.

Here, the distortion compensation system according to the present invention can be applied to a modulator that does not have its own compensation signal processing processor therein, and in this case, by adding an intermediate frequency signal output from the modulator as a reference signal without distortion, addition of hardware It is possible to precompensate the distortion signal of a high-power amplifier without using it.

3 is a block diagram showing a distortion compensation system of a digital TV repeater according to the present invention, and FIG. 4 is a block diagram showing a modulator shown in FIG.

3 to 4, the distortion compensating system according to the present invention is composed of a transmitter of a digital TV repeater and an adaptive precompensation system for compensating for nonlinear distortion of a broadcast signal output from a high output amplifier of the transmitter.

Here, the transmitting end receives a broadcast signal of the intermediate frequency (IF) and a reference sampling frequency from a receiving end (not shown), and modulator 300 for 8T-VSB modulation and the intermediate frequency IF output from the modulator 300. A first coupler 302 for extracting a broadcast signal as a reference signal without distortion, an RF unit 303 for up-frequency converting an intermediate frequency (IF) broadcast signal output from the modulator 300 into an RF broadcast signal, and RF The antenna 305 includes a second coupler 304 for extracting a signal that is up-converted into an RF broadcast signal and outputted as a measurement signal including distortion.

In addition, the adaptive precompensation system includes a down converter 306 that down-converts a measurement signal extracted by the second coupler 304 into an intermediate frequency (IF) signal, and an intermediate frequency (IF) signal output from the down converter 306. Is a first demodulator 307 that demodulates into baseband I and Q signals, and a second demodulator 308 that demodulates an intermediate frequency (IF) signal extracted by the first coupler 302 into baseband I and Q signals. And a data acquisition and synchronization processor 309 for synchronizing data between baseband I / Q signals output from the first demodulator 307 and the second demodulator 308, and the measurement extracted by the second coupler 304. And a signal processor 310 for generating and updating LUT coefficients for compensating for nonlinear distortion included in the signal, and an RS-232C interface 311 for transmitting the updated LUT coefficients to the modulator 300 of the transmitter. .

On the other hand, the modulator 300 of the transmitting end is configured as follows.

A VSB processor 400 which receives an intermediate frequency broadcast signal in the form of an MPEG-II transport stream from a receiver and performs channel coding, and the broadcast signal output from the VSB processor 400. A linear filter 401 for correcting linear errors, a nonlinear precompensator 402 for correcting nonlinear errors, and an analog I signal through a digital / analog converter (not shown) after 8T VSB modulation of the intermediate frequency broadcast signal. And an IF modulator 403 for outputting as a Q signal.

The distortion compensation system configured as described above extracts the intermediate frequency (IF) broadcast signal output from the modulator 300 of the transmitting end through the first coupler 302 and uses it as a reference signal, and outputs it through the RF unit 303. The extracted RF broadcast signal is extracted through the second coupler 304 and is regarded as a measurement signal. Subsequently, the reference signal and the measurement signal extracted by the first coupler 302 and the second coupler 304 are demodulated into baseband I and Q signals, and then subjected to a complex operation to compensate for errors between the two signals. The generated LUT coefficient is transmitted to the LUT unit 301 of the modulator 300 to precompensate the amplitude and phase of the intermediate frequency (IF) broadcast signal in advance.

Hereinafter, the operation of the transmitter and the adaptive precompensation system according to the present invention will be described in detail.

First, the first coupler 302 extracts an intermediate frequency (If) broadcast signal that the modulator 300 modulates and outputs in the 8T-VSB scheme as a reference signal without distortion. In addition, the second coupler 304 extracts the RF broadcast signal that is up-converted and output from the RF unit 303 as a measurement signal whose spectrum is distorted due to nonlinearity of the high output amplifier.

Then, the down converter 306 of the adaptive precompensation system receives the RF measurement signal extracted through the second coupler 304 and downconverts the frequency to an intermediate frequency (IF) band of 44 MHz, and the first demodulator 307 The down converter 306 demodulates the measurement signal output in the intermediate frequency band of 44 MHz and outputs it as a digital I signal and a Q signal including distortion.

Meanwhile, the second demodulator 308 demodulates the reference signal of the intermediate frequency extracted through the first coupler 302 and outputs the undistorted digital I and Q signals.

At this time. The first demodulator 307 and the second demodulator 308 are synchronized with the modulator 300 by receiving a clock from the modulator 300 and applying it as a reference clock.

Subsequently, the measurement signal and the reference signal output as digital I and Q signals through the first demodulator 307 and the second demodulator 308 are input to the data acquisition and synchronization processing unit 309, and the data acquisition and synchronization processing unit 309. ) Stores the measured signal and the reference signal in a part of memory and calculates the delay values of the two signals to synchronize with each other.

In this case, the data acquisition and synchronization processor 309 may perform cross-correlation between the reference signal and the measurement signal in order to synchronize the measurement signal with the reference signal. That is, by performing cross-correlation operation, each point is captured based on the reference signal among the output values, and the measurement signal is shifted to a point of high correlation, and then the reference signal and the measurement signal are synchronized at the point of highest correlation. Will be obtained.

Then, this data acquisition process is repeated to distribute the data so that it is constant.

Subsequently, the signal processor 310 complexly receives the reference signal and the measurement signal synchronized with each other through the data acquisition and synchronization processor 309, calculates an error with respect to the amplitude and phase of the measurement signal, and calculates the error as the LUT coefficient. It is created in the form of real part and imaginary part.

In the process of generating the LUT coefficients, first, the magnitudes of the reference signal and the measurement signal are adjusted to the reference magnitude, and the inserted pilot may be removed according to a selection.

Here, the I signal and the Q signal have a complex shape and perform a complex operation to calculate an error of the reference signal with respect to the measurement signal as shown in Equation 1 below.

In consideration of Equation 1, α and β values, which are error components of the measurement signal, are obtained as in Equation 2 below. At this time, the default value of the LUT table is initialized to α = 1.0, β = 0.

Based on the α and β values obtained using Equation 2, a compensation value table (LUT) is generated according to the input signal power.

In other words, the V _{reference signal} , which is the input signal, is divided into small steps and large values according to the power, in steps (for example, 8192 steps). After adjusting the α and β values for the region and the adjacent region, a polylinomial fitting process is performed to form the LUT, which is a compensation value table, according to the result.

Then, when the preparation of the LUT coefficient is finished, the LUT scale process is performed to calculate the power of the reference signal and the signal to be compensated by the LUT coefficient and adjust the α and β values of the LUT coefficient at a constant ratio so that the overall output does not change. Therefore, the value stored in the LUT table is a scaled value of 14 bits represented by a value between -2 and 2 in the pipeline, and is divided and stored in the entire input power range in the 8192 LUT table.

After the polynomial fitting and LUT scale process, the LUT coefficient values of α and β are transmitted to the LUT unit 301 of the modulator 300 through the RS-232C interface 311, respectively. At this time, the LUT coefficient value is converted into a binary file of 2 bytes for downloading to the modulator 300 and then transmitted.

The LUT section 301 of the modulator 300 then complexly computes the α and β values of the LUT coefficients transmitted from the adaptive precompensation system, respectively, to the baseband I and Q signals passing through the Root Raised Cosine Filter (RRC) filter. By using the nonlinear precompensator 402, a distortion-compensated predistortion signal may be generated.

The predistortion compensation signal is converted to the intermediate frequency IF and then output to the modulator 300 to reduce the nonlinear distortion occurring in the high output amplifier.

As described above, the distortion compensation system of the digital TV repeater of the present invention can compensate for the nonlinear distortion of the transmitter without the need for an expensive instrument such as a vector signal analyzer and a high-performance computer, thereby increasing the stability and performance of the transmitter without increasing system complexity. There is an effect to improve.

In addition, the distortion compensation system of the present invention has no effect of additional hardware is configured to reduce the installation and operating costs.

Claims (5)

In a digital TV repeater consisting of a receiving end and a transmitting end for relaying a broadcast signal to a plurality of subscribers, Extracting an output signal of a modulator provided in the transmitter as a reference signal and extracting an output signal of a high output amplifier as a measurement signal; Demodulating the extracted reference and measured signals into baseband signals, respectively; Synchronizing the reference signal demodulated to the baseband with a measurement signal, calculating an error of the reference signal with respect to the measurement signal, and generating a distortion compensation coefficient for correcting the calculated error; And performing pre-compensation for the measurement signal by inputting the generated distortion compensation coefficient to the modulator. According to claim 1, in the demodulation step, The method for compensating distortion in a digital TV repeater, wherein a clock is received from the modulator and used as a reference clock when demodulating the reference signal and the measurement signal. The method of claim 1, wherein in the generating step, And the distortion compensation coefficients are calculated by complex operation of the reference signal and the measurement signal to generate phase and amplitude errors of the reference signal with respect to the measurement signal, respectively, by a real part and an imaginary part. In a digital TV repeater consisting of a receiving end and a transmitting end for relaying a broadcast signal to a plurality of subscribers, A first coupler extracting a modulator output signal of the transmitting end into a reference signal without distortion; A second coupler for extracting a high output amplifier output signal of the transmitting end into a measurement signal including distortion; An adaptive precompensation system configured to calculate a difference between the reference signal and the measurement signal extracted by the coupler and to generate a distortion compensation coefficient for correcting the distortion included in the measurement signal. And precompensating the broadcast signal that is distorted and outputted through the high output amplifier by using the distortion compensation system of the digital TV repeater. The method of claim 4, wherein the adaptive precompensation system, A down converter for frequency down converting the measurement signal extracted from the second coupler into an intermediate frequency (IF) band; A first demodulator for demodulating the reference signal extracted by the first coupler into baseband I and Q signals; A second demodulator for demodulating the measurement signal extracted by the second coupler into baseband I and Q signals; A data acquisition and synchronization processor for synchronizing synchronization between the I and Q signals output from the first and second demodulators, respectively; A signal processor which complexly computes each of the I and Q signals output from the data acquisition and synchronization processor, calculates an amplitude and a phase error of the reference signal with respect to the measurement signal, and generates a distortion compensation coefficient for correcting the calculated error; Wow, And a modulator interface unit for transmitting the generated distortion compensation coefficients to the modulator.