KR100284321B1 - Demodulation Device and Method of Channel Modem for Satellite Communication System - Google Patents

Abstract

The present invention relates to a device for demodulating a channel modem for a satellite communication system and a method for compensating for a timing error value of a signal transmitted from an IF stage. The present invention relates to encoding, quantizing, and demodulating an input signal. And a demodulator for estimating an error component of the demodulated data and compensating for the error of the demodulated data, and outputting the demodulated data, wherein the input signal has a predetermined filter coefficient value. A matching filter for filtering into a band, an error estimator for estimating a timing error component of data passing through the matching filter, and a voltage controlled oscillator for varying and outputting a frequency according to a voltage level corresponding to a timing error component applied from the error estimator And inputted based on a frequency value applied by the voltage controlled oscillator. Is configured to include an encoder for sampling the signal.

Description

Demodulation Device and Method of Channel Modem for Satellite Communication System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a satellite communication system, and in particular, for a satellite communication system configured to detect a sampling instant value by compensating a timing error value of a signal transmitted from an IF stage by controlling a voltage controlled oscillator based on an estimated timing error value. A demodulation device for a channel modem and a method thereof are provided.

Recently, with the rapid development of communication technology, satellite communication using satellites to transmit and receive voice signals or data through the airborne transmission network rather than the conventional wired network has been spread and activated.

1 is a block diagram schematically showing the configuration of a demodulation device for a channel modem for a conventional satellite communication system.

In the drawing, reference numeral 1 denotes a down converter that down-converts an intermediate frequency signal transmitted from an intermediate frequency stage (IF stage) to a band of 384 KHz based on a synchronization signal applied from an RX synchronizer (not shown). 2 denotes an encoder that samples the 384 KHz signal applied from the down converter 1 based on a sampling frequency of 512 KHZ, and 3 denotes a quantizer that quantizes the 128 KHz sampled signal applied from the encoder 2.

Reference numeral 4 denotes a demodulation unit for synchronously detecting the 128KHz signal transmitted from the quantizer 3 based on the oscillation frequency applied from the 128KHz oscillator and converting the signal band to 0Hz. A low pass filter (LPF) that performs baseband filtering around a reference frequency (0 Hz), and the signal passing through the low pass filter (5) outputs only the original signal before both sides are removed and modulated. .

Reference numeral 6 denotes a synthesizer, which synthesizes and outputs a signal applied from the low pass filter 5 and a signal applied through the error estimator 9 to be described later.

On the other hand, reference numeral 7 denotes a matched filter for filtering into a band having a predetermined filter coefficient value in order to detect a sampling instant value of the signal applied from the synthesizer 6, which is selected by a modulator (not shown). By convoluting the same lased cosine function to the signal applied by the zide cosine function, the sampling instant value of the applied signal is detected. Here, the lased cosine function is a function of setting a filter coefficient value close to an ideal Nyquist channel satisfying a condition for eliminating inter-symbol interference (ISI) in the matched filter.

Also, reference numeral 8 denotes a decimator which detects the data applied from the matching filter 7 at predetermined intervals, which has a predetermined size between the information data in a modulator (not shown) on the transmitting side. As a corresponding process of the receiving side in inserting the dummy data and performing the modulation process, if the size of the dummy data is one bit, the decimator 8 of the demodulator is defined as having a detection interval of '2'.

Further, reference numeral 9 detects an error component of data applied from the decimator 8, applies the detected signal to the synthesizer 6, and matches the timing error component data along the satellite. An error estimator applied to the filter 7.

Next, the operation of the device having the above configuration will be described.

First, QPSK modulates the signal sent from the transmitter and transmits the modulated signal to another terminal station through the IF terminal and the RF terminal through the satellite, and the transmitted signal is synchronized with the system through the RF terminal and the IF terminal of the receiver. A demodulator is used to demodulate the original signal sent by the transmitter, which compensates for the frequency error on the satellite that occurs while passing through the satellite, the time error that occurs during sampling, and the error portion of the transmitted signal size. You will go through the process.

Subsequently, referring to the detailed operation of the demodulator, first, ± 70KHz received at the IF stage is down-converted to 384KHz through the down converter 1, and this 384KHz signal is applied to the encoder 2, where 512KHz sampling is performed. It will be sampled according to the clock.

Thereafter, the sampled signal is quantized, the synchronous detection processing is performed, and the low pass filter 5 is used to baseband the detected signal. The low pass filter 5 Only baseband processed signals can be extracted.

In addition, an error component generated on the satellite is estimated by the signal component output from the low pass filter 5, and the estimated error component affects the data passed through the low pass filter 5 to compensate for the error component. The demodulated data is demodulated, and the demodulated data is transmitted to a decoder (not shown) by passing the matched filter 7 through the compensated data.

In addition, in the process of passing through the matching filter 7, the data sampled by the sampling clock of 512 KHz is slightly distorted by passing through the satellite, so that the timing error of the received data is estimated to accurately detect this sampling instant. The sampling value is detected by shifting the matching filter so as to correspond thereto. The filter coefficient value of the matching filter shifted according to the timing error is stored in the lookup table in advance, and the lookup table is addressed according to the applied timing error value. The filter coefficient value of the matched filter is specified.

However, the lookup table is stored in the EPROM by binary quantizing a frequency value between -512KHz and + 512KHz. When the sampling frequency needs to be increased or a more detailed sampling value needs to be detected, an EPROM having a larger capacity is required. Will be required.

Accordingly, the present invention was created in view of the above circumstances, and generates a voltage according to the estimated timing error value, and shifts the sampling frequency according to the generated voltage, thereby compensated for the timing error value. It is an object of the present invention to provide a demodulation device for a channel modem for a satellite communication system and a method thereof capable of detecting.

1 is a block diagram showing the configuration of a conventional demodulation device for a conventional channel modem.

2 is a block diagram showing the configuration of an apparatus according to the present invention.

3 is a block diagram showing the internal configuration of the error estimator 22 and the voltage controlled oscillator 23 of FIG.

* Explanation of symbols for main parts of the drawings

1: downconverter 2: encoder

3: quantizer 4: demodulator

5: low pass filter (LPF) 6: synthesizer

7,21: matching filter 8: decimator

9,22: Error estimator 10,23: Voltage controlled oscillator (VCO)

22a: Timing Error Detection Unit (TED) 22b: Loop Filter

23a: D / A converter 23b: voltage generation function storage unit

23c: voltage controlled oscillator

In order to achieve the above object, the apparatus for demodulating a channel modem for a satellite communication system according to the first aspect of the present invention is characterized by encoding and quantizing an input signal, demodulating it, and estimating an error component of the demodulated data. A satellite communication system having a channel modem configured to include a demodulator for compensating and outputting an error of data, the satellite communication system comprising: a matching filter for filtering an input signal into a band having a predetermined filter coefficient value; An error estimator for estimating a timing error component of data, a voltage controlled oscillator for changing a frequency according to a voltage level corresponding to a timing error component applied from the error estimator, and a frequency value applied by the voltage controlled oscillator Characterized in that it comprises an encoder for sampling the signal input to.

Meanwhile, the method for demodulating a channel modem for a satellite communication system according to a second aspect of the present invention for achieving the above object includes encoding and quantizing an input signal, demodulating it, and estimating an error component of the demodulated data. A satellite communication system having a channel modem comprising a demodulator for compensating and outputting an error of demodulated data, the satellite communication system comprising: an encoding step of sampling an input signal based on a frequency applied from a voltage controlled oscillator; A data demodulation step of outputting original data generated from a transmitting end by performing low pass filtering by quantizing and decoding the data that has passed through the data, and an error component compensation step of synthesizing the error components generated from the demodulated data and the error estimator. The data of which the error component is compensated for is a band having a predetermined filter coefficient value. A matching filtering step of filtering, an error estimation step of decimating the data subjected to the matching filtering, outputting only a signal having information, and estimating an error component from the output data, and the timing estimated in the error estimation step. And a sampling frequency generation step of generating a voltage value based on the error data and applying a corresponding frequency to the encoder.

That is, according to the present invention having the above-described configuration, the timing error is estimated and the voltage controlled oscillator is controlled analogously and the timing error is compensated accordingly to apply the sampling frequency to thereby obtain a more accurate sampling value in which the error component is compensated. In addition to being able to detect, the error estimation process of the demodulation is faster, and it is not necessary to implement a lookup table in which the filter coefficient value of the conventional matched filter is stored to compensate for timing errors.

Hereinafter, an apparatus and a method according to the present invention will be described with reference to the drawings.

2 is a block diagram showing the configuration of a demodulation device for a channel modem for a satellite communication system according to the present invention, in which parts carrying out the same functions as those shown in FIG. Is omitted.

In the drawing, reference numeral 21 denotes a signal having a predetermined filter coefficient value, which is obtained by combining a signal input through the low pass filter 5 and an error component applied from the error estimator 22 to be described later into a band having a prescribed filter coefficient value. 22 is an error estimator for estimating an error component of data passing through the matched filter 21, which estimates a timing error of a sampling instant value generated by going through a satellite, and will be described later. (VCO: Voltage Controlled Oscillator).

In addition, reference numeral 23 denotes a voltage controlled oscillator whose frequency changes according to an externally applied voltage, which generates a voltage corresponding to a timing error value applied from the error estimator 22 and based on the generated voltage level. As a result, the frequency is generated.

Next, the configuration of the error estimator 22 and the voltage controlled oscillator 23 in FIG. 2 will be described with reference to FIG.

In the drawing, the error estimator 22 includes a timing error detector (TED: 22a) for detecting a timing error (Timing Error) of current data caused by shifting a sampling instant value among error components generated by passing through a satellite, To the loop filter 22b which compares the current timing error value applied from the timing error detection unit 22a with the previously transmitted timing error value and transmits data on the difference to the voltage controlled oscillator 23 which will be described later. Consists of.

The voltage controlled oscillator 23 also includes a D / A converter 23a for converting a digital signal corresponding to an estimated value of a timing error applied from the error estimator 22 into an analog signal, and the D / A converter 23b. A voltage generation function storage unit 23b for storing a voltage generation function corresponding to the analog applied from the voltage and voltage control for generating a frequency corresponding to the voltage value based on the voltage value applied from the D / A converter 23a It is comprised by the oscillator 23c.

Next, the operation of the device having the above configuration will be described.

First, when a 70 MHz signal is input from the intermediate frequency IF stage, the frequency is down-converted to a signal of 384 KHz and transmitted to the encoder 2. In the encoder 2, the voltage is controlled from the voltage controlled oscillator 23. Sampling will be based on the frequency.

Thereafter, the data sampled through the encoder 2 is quantized, and only the data down to the baseband is extracted through the synchronous detection process and the low pass filter.

Subsequently, the extracted data is combined with the error component data applied from the error estimator 22 and subjected to matched filtering. Then, only the information data is detected and output through the decimator 8, and the error estimator 22 is output to the error estimator 22. The data is applied.

The error estimator 22 detects an error component based on the applied data. In particular, the error estimator 22 detects a timing error generated while passing through the satellite through the timing error detection unit 22a, and detects the error in the loop circuit 22b. The timing error value of the current data is compared with the timing error value of the previous data, and data corresponding to the difference is transmitted to the voltage controlled oscillator 23.

Subsequently, the data transmitted to the voltage control generator 23 is converted into an analog signal via the D / A converter 23a, and the voltage generation function storage 23b reads the voltage value corresponding to the converted analog value. This voltage value is applied to the voltage controlled oscillator 23c.

Thereafter, the voltage controlled oscillator 23c receiving the voltage value outputs a frequency corresponding to the voltage value, which is a sampling frequency at which a timing error value is compensated and output at a conventionally defined sampling frequency of 512 KHz, which is 512 KHz. There is a slight difference from, but this is compensated by the filtering which is processed at the time of synchronous detection in the demodulator 4.

That is, according to the present invention having the above configuration, the timing error value is estimated and the voltage controlled oscillator is controlled analogously, and the sampling error is applied by compensating the timing error accordingly, thereby providing a more accurate sampling value with error components compensated. It can be detected.

In addition, by detecting and processing the sampling value of which the error component is compensated for, the process of estimating the error of the demodulation is not only faster, but it is not necessary to implement the lookup table in which the filter coefficient value of the conventional matched filter is stored to compensate for the timing error. do.

In addition, this invention is not limited to the said Example, It can implement in a various deformation | transformation in the range which does not deviate from the technical summary of this invention.

As described above, according to the present invention, the timing error is estimated and the voltage-controlled oscillator is controlled analogously, and the sampling error is applied by compensating the timing error accordingly, whereby a more accurate sampling value in which an error component is compensated for can be detected. In addition, the error estimation process of the demodulation is faster, and it is not necessary to implement a lookup table in which the filter coefficient value of the conventional matched filter is stored to compensate for the timing error.

Claims (3)

A satellite communication system having a channel modem comprising a demodulator for encoding and quantizing an input signal, demodulating the same, and estimating an error component of the demodulated data to compensate for and output an error of the demodulated data. A matching filter for filtering an input signal into a band having a predetermined filter coefficient value, an error estimator for estimating a timing error component of data passing through the matched filter, a voltage level corresponding to a timing error component applied from the error estimator And a voltage controlled oscillator for varying the frequency and outputting the signal, and an encoder for sampling the input signal based on the frequency value applied by the voltage controlled oscillator. . The timing error detector of claim 1, wherein the error estimator detects a timing error of a current data generated by shifting a sampling instant value among error components generated by passing through a satellite, and from the timing error detector. And a loop filter which compares the current timing error value applied with the previously transmitted timing error value and transmits data on the difference to the voltage controlled oscillator, wherein the voltage controlled oscillator is a timing error applied from the error estimator. A D / A converter for converting a digital signal corresponding to an estimated value of the analog signal into an analog signal, a voltage generation function storage unit for storing a voltage generation function according to an analog value applied from the D / A converter, and the D / A converter Including a voltage controlled oscillator for generating a frequency corresponding to the voltage based on the applied voltage value Demodulator of the modem channel for a satellite communication system, characterized in that a generated. A satellite communication system having a channel modem configured to include a demodulator for encoding and quantizing an input signal, demodulating the same, and estimating an error component of the demodulated data to compensate for and output an error of the demodulated data. Sampling an input signal based on a frequency applied from a voltage controlled oscillator, performing quantization and decoding on the data passed through the encoding step, and performing low pass filtering to output original data generated from a transmitter. A data demodulation step, an error component compensation step of synthesizing the error components generated from the demodulated data and the error estimator, a matched filtering step of filtering the data compensated for the error components into a band having a prescribed filter coefficient value, and the matching Data is decimated after filtering Outputs only a signal, and an error estimating step of estimating an error component from the output data, and a sampling for generating a voltage value based on the timing error data estimated in the error estimating step and applying a corresponding frequency to the encoder. Method for demodulating a channel modem for a satellite communication system comprising a frequency generation step.

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