KR19990056979A - Method for demodulating channel modem for satellite communication system and device therefor - Google Patents

Abstract

The present invention provides a method and apparatus for demodulating a channel modem for a satellite communication system in a burst mode in which a demodulation operation is performed on data input in a burst mode, so as to compensate for and output an error of data caused by a satellite. A channel comprising a demodulation device for compensating for an error in demodulated data by encoding and quantizing a signal input from an intermediate frequency receiver in burst mode, demodulating the same, and estimating an error component of the demodulated data. In a satellite communication system having a modem, a data demodulation step of outputting original data generated from a transmitter by performing low pass filtering by performing quantization and decoding on data that has undergone the encoding step, and voice from the demodulated data. Detecting the SOF signal which is the start signal of data Emitter and the detection step, including the error component compensation step to estimate the error of the data input to the data detected by the voice data detection process on the basis of compensating for an error component is characterized in that configured.

Description

Method for demodulating channel modem for satellite communication system and device therefor

The present invention relates to a channel modem for a satellite communication system, and in particular, in performing a demodulation operation on data input in a burst mode, a satellite in a burst mode capable of compensating for and outputting an error of data caused by a satellite. A method for demodulating a channel modem for a communication system and an apparatus therefor.

With the recent rapid development of communication technology, wireless communication is being spread and activated to transmit and receive voice signals or data through airwave transmission network rather than the conventional wired network, so that subscribers located at remote sites can perform mutual communication through satellites. Satellite communication is becoming more and more common.

In the above-mentioned satellite communication, since communication is performed through satellites located thousands to tens of thousands of KHz from the ground, signal transmission and reception are usually performed through digital communication, and as the transmission / reception frequency, for example, 14.0 to 14.5 GHz for uplink. In the case of downlink, a high frequency of 12.25 to 12.75 GHz is used.

Currently, in some commercial satellite communication systems, pulse code modulation (PCM) data input through, for example, a public switched telephone network (PSTN) is used for binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK). Modulation is performed to generate a 512KHz modulated signal, which is then up-converted to generate a 70MHz intermediate frequency signal. The 70 MHz intermediate frequency signal is further frequency-converted to generate a transmission frequency of 14.0 to 14.5 GHz.

On the receiving side receiving the frequency signal transmitted as described above, the downlink signal of 12.25 to 12.75 GHz is frequency-converted to an intermediate frequency of 70 MHz, and then down-converted to a frequency signal of 384 KHz, and the demodulation unit converts the data into a frequency signal of 384 KHz. The demodulation operation is executed.

Meanwhile, in the satellite communication system, error components such as timing error and amplitude according to time delay generated through satellites are transmitted to the demodulator, and the demodulator performs an error estimation operation on input data. .

However, since the voice data input to the demodulator in burst mode does not always exist, the demodulation device configured to always perform an error estimation operation on the input data has a problem of performing an error estimation operation on unnecessary data. Will occur.

Therefore, a function for detecting the presence or absence of voice data and performing the error estimation function only on the information data is required.

Accordingly, the present invention has been made in view of the above-described circumstances. The present invention demodulates data applied to the demodulator in burst mode, detects a voice signal in burst mode, and detects a timing error and a predetermined error component of the detected voice signal. The purpose of the present invention is to realize a method and apparatus for demodulating a channel modem for a satellite communication system that can be estimated and compensated for.

1 is a block diagram showing an internal configuration of a demodulation device 20 according to the present invention.

*** Explanation of symbols for the main parts of the drawing ***

1: downconverter, 2: encoder,

3: quantizer, 4: demodulator,

5: low pass filter (LPF), 6: synthesizer,

7: matching filter, 8: decimator,

9: error estimator, 10: voice detector.

A method for demodulating a channel modem for a satellite communication system according to a first aspect of the present invention for realizing the above object is to encode, quantize, and demodulate a signal input from an intermediate frequency receiver in burst mode. In a satellite communication system having a channel modem configured to include a demodulator for compensating for errors in demodulated data by estimating error components, a low pass filtering is performed by quantizing and decoding data that has been encoded. A data demodulation step of outputting original data generated from a transmitting end, a voice data detection step of detecting an SOF signal as a start signal of voice data from the demodulated data, and an input based on the data detected in the voice data detection step Error component compensation for compensating error component by estimating error of data Characterized in that it comprises a step.

On the other hand, the demodulation device for a channel communication system for a satellite communication system according to the second aspect of the present invention for realizing the above object, in burst mode, the signal input from the intermediate frequency receiving device is coded, quantized and demodulated and demodulated A satellite communication system having a channel modem configured to include a demodulation device for compensating for errors in demodulated data by estimating an error component of data, the baseband filtering based on a reference frequency (0 Hz) of the demodulated data A low pass filter for performing a signal, a voice data detector for detecting a SOF signal as a start signal of voice data from the data passed through the low pass filter, and an error of data input based on a voice data detection signal applied from the voice data detector And an error estimator for estimating the component.

According to the present invention having the above-described configuration, in estimating an error component generated while passing through a satellite in burst mode, the voice data is detected from data input to the demodulator and an error estimation operation is performed based on the detected signal of the voice data. By doing so, it is possible to prevent power waste due to the error estimation operation for unnecessary data.

Next, an embodiment according to the present invention will be described with reference to the accompanying drawings.

1 is a block diagram showing an internal configuration of a demodulation device 50 of a channel modem for a satellite communication system according to the present invention.

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 device (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 to 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 a root selected by a modulator (not shown). By convoluting the same root-laid cosine function with the signal applied by the las- cosine function, the sampling instant value of the applied signal is detected.

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 10 to be applied to the filter 7 is a voice data detector for detecting voice data from data applied from the low pass filter 5, which is a SOF (Start) that means the start of voice data in an input data frame. Of Frame) signal is detected.

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, 70 ± 20 MHz received at the IF stage is down-converted to 384 KHz through the down converter 1, and the 384 KHz signal is applied to the encoder 2, where 512 KHz It is sampled according to the sampling clock.

Thereafter, the sampled signal is quantized by the quantizer 3, and the demodulator 4 performs a synchronous detection process, and baseband processes the signal detected by the demodulator 4 to perform a low pass filter ( 5), only the baseband processed signal can be extracted by this low pass filter (5).

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 compensated data is passed through the matching filter 7 to transmit the demodulated data to a decoder (not shown) of the voice / data processor (SDP).

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.

On the other hand, the error estimator 9 for estimating the timing error performs an error estimating operation based on the SOF detection signal of the voice data detection unit 10, and thus detects the voice data irregularly applied in the burst mode. By only performing the error estimation operation for the data, it is possible to prevent waste of power due to the error estimation operation for unnecessary data.

In addition, this invention is not limited to the said Example, It can variously deform and implement within the range which does not deviate from the technical summary of this invention.

As described above, according to the present invention, in estimating an error component generated while passing through a satellite in burst mode, voice data is detected from data input to the demodulator and an error estimation operation is performed based on the detected signal of the voice data. By doing so, it is possible to prevent power waste due to the error estimation operation for unnecessary data.

Claims (2)

In the burst mode, a channel modem configured to include a demodulation device for compensating for errors in the demodulated data by encoding and quantizing a signal input from the intermediate frequency reception device, demodulating the same, and estimating an error component of the demodulated data. In one satellite communication system, A data demodulation step of outputting original data generated from a transmitting end by performing quantization and decoding on the data that has undergone the encoding step and performing low pass filtering; A voice data detection step of detecting an SOF signal as a start signal of voice data from the demodulated data; And an error component compensating step for estimating an error component by estimating an error of data input based on the data detected in the voice data detection step. In the burst mode, a channel modem configured to include a demodulation device for compensating for errors in the demodulated data by encoding and quantizing a signal input from the intermediate frequency reception device, demodulating the same, and estimating an error component of the demodulated data. In one satellite communication system, A low pass filter for performing baseband filtering on the demodulated data at a reference frequency (0 Hz); A voice data detection unit for detecting an SOF signal as a start signal of voice data from the data passing through the low pass filter; And an error estimator for estimating an error component of data input based on the voice data detection signal applied from the voice data detection unit.