KR100478331B1 - Gap Filler in Satellite Broadcasting System - Google Patents

Abstract

A gap filler in which the transmission frequency stability is high to the transmission frequency stability level of the satellite by generating a system clock having a high frequency stability and converting the format of the signal from the satellite to retransmission. The gap filler of the present invention receives an RF broadcast signal from a stationary satellite, demodulates it, multiplexes it by a first multiplexing method, and transmits it. The gap filler includes an RF receiver, a signal processor, and an RF transmitter. The RF receiver receives the RF broadcast signal from the stationary satellite, the signal processor demodulates the RF broadcast signal, restores satellite broadcast data, and multiplexes by the first multiplexing technique, and the RF transmitter transmits the first multiplexed signal from the signal processor. Amplify and send. In the signal processing section, the demodulation section demodulates the RF broadcasting signal to restore the satellite broadcasting data and the frame synchronizing signal, and the buffering and synchronizing signal generating section uses the frame synchronizing signal while buffering the satellite broadcasting data. It generates a clock for modulation and outputs satellite broadcasting data in synchronization with the system clock. The modulator multiplexes satellite broadcast data by the first multiplexing technique in synchronization with a modulation clock.

Description

Gap Filler in Satellite Broadcasting System

The present invention relates to a satellite broadcasting system, and more particularly, to a gap filler for use in a radio shading area in a satellite broadcasting system.

Various communication systems are being developed in accordance with the advancement of communication demands and the development of communication technologies. One of them is a satellite broadcasting system using a satellite or a communication satellite on a geostationary orbit. In satellite broadcasting, a signal transmitted from a broadcasting station or a satellite base station is amplified / modulated by a transponder of a satellite, and then transmitted to the ground again, and the satellite receives the signal using a satellite antenna. According to such a satellite broadcasting system, there is an advantage that it is possible to provide a broadcast service for a wide range of service areas without having to maintain a large infrastructure on the ground.

Satellite DAB (Digital Digital Audio Broadcasting) system among satellite broadcasting systems is to provide digital voice broadcasting service for on-board, portable and fixed receivers. In ITU-R BO.1130-4 ", five standards of digital systems A, B, D _S , D _H and E have been proposed for satellite broadcasting services from 1400 to 2700 MHz.

The "digital system E" is for providing multimedia contents to a mobile terminal using a frequency band of 2630 to 2655 MHz, and a schematic configuration of the system according to this standard is shown in FIG. In the system of FIG. 1, a broadcasting station or a satellite base station transmits a multi-channel broadcast signal to a broadcast satellite in a 14 GHz Ku band by code division multiplexing (CDM), and the satellite transmits a frequency band of the broadcast signal in a 14 GHz band. It converts to 2.6 GHz band and amplifies it to the desired level and transmits it to terrestrial terminal or receiver. On the other hand, in order to alleviate signal attenuation problems due to shadowing or blocking due to buildings or other shields, an auxiliary relay, or gap filler, may be used in places where satellite waves cannot be directly received. The gap filler includes a direct amplified gap filler that simply amplifies and relays a broadcast signal from a satellite, and a frequency-converted gap filler that receives a 11 GHz broadcast signal from a satellite and converts the frequency band into a 2.6 GHz band. Can be.

In such a system, the signal coming directly from the satellite and the signal via the gap filler cannot be distinguished from the point of view of the terminal receiving the service so that any one of the two signals can be restored and reproduced. However, when the stability of the clock in the gap filler is low, the transmission frequency stability is lower than the satellite transmission frequency stability, and as a result, from the terminal's point of view, the synchronization between the signal coming directly from the satellite and the signal passing through the gap filler is greatly shifted. This makes it difficult to recover and reproduce the signal. Therefore, it can be said that the clock stability is very important in the gap filler for retransmitting the received signal, and a method of increasing such clock stability is required. In general, since the frequency stability of the demodulator used in the terminal receiving the final service is lower than that required by the gap filler, the demodulator chip for the broadcast receiving terminal is dedicated to using the gap demodulator chip used in the broadcast receiving terminal. Driving the retransmission circuit using this output clock can significantly degrade the reliability of the gap filler.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a gap filler for generating a system clock having high frequency stability and performing retransmission of the signal by using the same when demodulating and remodulating the signal from the satellite. Let it be the technical problem.

In order to achieve the above technical problem, the gap filler of the present invention receives an RF broadcast signal from a stationary satellite, demodulates it, and multiplexes and transmits the RF broadcast signal by a first multiplexing technique. A sending part is provided. The RF receiver receives the RF broadcast signal from the stationary satellite, the signal processor demodulates the RF broadcast signal, restores satellite broadcast data, and multiplexes by the first multiplexing technique, and the RF transmitter transmits the first multiplexed signal from the signal processor. Amplify and send. In the signal processing section, the demodulation section demodulates the RF broadcasting signal to restore the satellite broadcasting data and the frame synchronizing signal, and the buffering and synchronizing signal generating section uses the frame synchronizing signal while buffering the satellite broadcasting data. It generates a clock for modulation and outputs satellite broadcasting data in synchronization with the system clock. The modulator multiplexes satellite broadcast data by the first multiplexing technique in synchronization with a modulation clock. In the buffering and synchronization signal generator according to the preferred embodiment, the buffer buffers satellite broadcast data to adjust timing, and the serial / parallel converter converts the buffered satellite broadcast data into a parallel format by synchronizing the system clock to a parallel satellite. The synchronization signal detector detects a frame synchronization signal from the satellite broadcast data, and a phase locked loop generates the system clock and the modulation clock using the frame synchronization signal. In the phase-locked loop according to the preferred embodiment, the counter counts the modulation clock in units of one frame sync interval of the frame sync signal and outputs a difference between a count value and a predetermined reference value, and the digital / analog converter is used to output the counter output value. The low-pass filter outputs the filtered signal by low-pass filtering the output signal of the digital / analog converter. The oscillator oscillates a signal whose frequency varies according to the filtered signal level, and a clock generator generates the system clock and the modulation clock using an oscillator signal of the oscillator. Preferably, the counter and the digital / analog converter are connected via a photo coupler.

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

2 shows a preferred embodiment of the satellite broadcasting system according to the present invention. In a preferred embodiment, the satellite broadcasting system includes a terrestrial broadcasting station 10, a satellite base station 12, a control station 14, and a stationary satellite 16. Although only one broadcast station 10 is shown in FIG. 2, there may be several such terrestrial broadcast stations 10.

The satellite base station 12 receives program information created / edited by each broadcasting company from the broadcasting station 10, and uses an uplink transmission path of the Ku band (12.5-18 GHz) or the Ka band (26.5-40 GHz). Transmit to stationary satellite 16. The geostationary satellite 16 amplifies a Ku or Ku band (hereinafter, abbreviated to only 'Ku band') broadcast signal received from the satellite base station 12 and converts the signal into an S band. The stop satellite 16 then transmits the band-converted broadcast signal along with the Ku band signal toward the service area. Meanwhile, the satellite control station 14 monitors and controls the operating state of the stationary satellite 16.

In the satellite broadcasting service area, the receiver 40a at a point where the broadcast receiving antenna is at the line of sight point from the satellite satellite 16 or the multipath fading is not seriously receives a broadcast signal from the satellite satellite 16. It accepts it directly and plays the broadcast. However, at a point where signal attenuation due to shadowing or blocking due to buildings or other shields is serious, the gap filler 20 relays the broadcast signal.

In the present invention, the satellite base station 12 performs code division multiplexing (CDM) on broadcast data of a plurality of channels and transmits it in the Ku band. Meanwhile, the satellite base station 12 transmits through the Ku band or a separate band by time division multiplexing (TDM) the broadcast data separately from the CDM signal (described below based on the transmission through the Ku band). . The geostationary satellite 16 band-converts and transmits the CDM signal to the S band among the TDM and CDM signals from the satellite base station 12, so that the receiver 40a in the visible position can receive it and reproduce the broadcast. In addition, the stationary satellite 16 simply amplifies the Ku band TDM signal from the satellite base station 12 and retransmits it to the gap filler 20. On the other hand, the gap filler 20 receives the Ku band TDM signal from the stationary satellite, converts it into an S band CDM signal, and sends it out. Accordingly, the receiver 40b in the service area of the gap filler 20 demodulates a signal having a large intensity among the S band CDM signals received directly from the satellite and the S band CDM signals received via the gap filler 20. Will play.

3 is a block diagram of a gap filler 20 according to the present invention. The gap filler 20 includes an RF receiver 100, a baseband signal processor 110, and an RF transmitter 120. Although not shown in FIG. 3, the gap filler 20 controls the RF receiver 100, the baseband signal processor 110, and the RF transmitter 120, monitors an abnormality occurring during operation, and generates an abnormality. It may include a control unit for performing a function for notifying the outside when.

In the RF receiver 100, the antenna 102 receives satellite broadcast signals and provides them to the low noise amplifiers 104 (LNA). In one embodiment, the antenna 102 may be configured as a commercially available parabola antenna, but other antennas such as, but not limited to, a parabola antenna, an offset antenna, a caseegrain antenna, or a Gregory antenna may be used. The low noise amplifier 104 amplifies the signal received through the antenna 102 and converts the signal band into the IF band. The tuner 106 receives the IF signal from the low noise amplifier 104, separates the baseband I and Q signals, performs a frequency tuning function, and controls the gain of the low noise amplifier 104.

The baseband signal processor 110 includes a TDM receiver 112, a buffering and synchronization signal generator 114, and a CDM modulator 116. The baseband signal processor 110 demodulates the received TDM signal and adjusts the timing while demodulating the code division. do. The TDM receiver 112 demodulates, decodes, and outputs a TDM signal output from the tuner. The buffering and synchronizing signal generator 114 stores the demodulated broadcast data in a memory while generating a system clock and provides the broadcast data to the CDM modulator 116 according to the system clock. The CDM modulator 116 multiplexes broadcast data and synthesizes CDM signals of various channels and provides them to the RF transmitter 130.

The RF transmitter 120 includes a digital / analog converter 122, a high output amplifier 124, and a transmit antenna 126. The digital / analog converter 122 converts the synthesized CDM signal into an analog signal, and the high output amplifier 124 amplifies the signal and provides it to the transmission antenna 126 so that the amplified signal is transmitted by the transmission antenna 126. It is to be transmitted by radio waves.

4 shows the TDM receiver 112 shown in FIG. 3 in detail. The QPSK demodulator QPSK demodulates the QPSK modulated signal output from the tuner by absolute phase locked demodulation. The Viterbi decoder decodes the convolutional code output from the QPSK demodulator by a Viterbi decoding algorithm that searches for several data paths and then selects the path with the highest similarity. The sync byte detector detects the sync byte and the inverse sync byte to find the frame boundary for deinterleaving. The deinterleaver is a convolutional de-interleaver with I = 12, and deinterleaves the decoded data. The Reed-Solomon (RS) decoder calculates errors and errors in the deinterleaved data by the Reed-Solomon (204,188) coding scheme obtained by shortening from the Reed-Solomon (255,239) code. Correct the error by calculating the position and size of. The descrambler performs a function of restoring the original data by passing the irregular sequence once again from the data spread by the irregular sequence. The de-framer demultiplexes the descrambled data to restore the original broadcast data, and the serial / parallel converter converts the serial broadcast data into parallel data and outputs the parallel broadcast data.

FIG. 5 shows the CDM modulator 116 shown in FIG. 3 in detail. The CDM modulator 116 includes a band spreader 150 and a shaping filter 168. In the present embodiment, since the CDM modulator 116 uses a Walsh code of 64 chips in length, 64 CD channels can be multi-transmitted. Of the 64 channels, one channel is used as a pilot channel for transmitting control data, a unique word for frame synchronization, a frame counter for super frame synchronization, and all or some of the remaining 63 channels. It can be used for transmission of a load, that is, broadcast data. In the following description, it is assumed that only 31 channels are used for transmission of payload, that is, satellite broadcast data.

In each channel path of the spreader 150, data is encoded and spread by the Reed-Solomon (RS) encoders 152_0 to 152_31 to the QPSK modulators 164_0 to 164_31. The combiner 166 synthesizes the spread spectrum data. Specifically, referring to any one channel, for example, the first satellite broadcast data channel, the channel data is convolutional code and Reed-Solomon code by the RS encoder 152_1 and the convolutional encoder 156_1. It is encoded by a concatenated code consisting of. Here, the Reed-Solomon (204, 188) code used as the outer code of the chain code is obtained by shortening the Reed-Solomon (255, 239) code. Inner code uses convolutional code with constraint length K = 7. In payload data channel, r = 1/2 and 3/4 obtained by puncturing the code rate r = 1/2 The code rate r = 1/2 is used for the pilot channel.

The byte interleaver 154_1 serves to correct a concatenation error of several seconds and is implemented using a depth 12 convolutional interleaver. The bit interleaver 158_1 performs bit interleaving by dividing the convolutional coded bits into subdivisions and performing convolutional interleaving. The time delay degree due to this bit interleaving, that is, the ability to correct the aggregation error, is determined by the parameter m. When m = 5, a time delay of 3.257 seconds is generated. It becomes possible.

The Walsh code spreader 160_1 and the PN code spreader 162_1 spread the encoded and interleaved data by a unique Walsh code and a pseudorandom code. The QPSK modulator 164_1 performs QPSK modulation on the spread data. Although the above description has been focused on the first satellite broadcast data channel, similar signal processing is performed on other channels. The synthesizer 166 synthesizes the signals of the spread spectrum channels, where each modulated signal is distinguished by a unique Walsh code, and thus can be multiplexed and transmitted in the same frequency band. On the other hand, the shaping filter 168 is implemented using a root-raised cosine (RRC) filter.

FIG. 6 shows the buffering and synchronization signal generator 114 shown in FIG. 3 in detail. In a preferred embodiment, the buffering and synchronization signal generator 114 includes a memory controller 200, a RAM 202, a buffer 204, a serial / parallel converter 206, and a synchronization signal detector 208. ) And the phase locked loop 210. 3 illustrates a TDM receiver 112 and a CDM modulator 116 together for convenience of description.

The memory controller 200 receives broadcast data from the TDM receiver 112 and stores the broadcast data in the RAM 202. In this case, the TDM receiver 112 may provide a clock CLK necessary for the memory controller 200 to operate. The buffer 204 implemented using the first-in, first-out memory buffers data transferred from the RAM 202 to the serial / parallel converter 206 to adjust timing and prevent data loss during synchronization. The serial / parallel converter 206 converts the serial broadcast data read from the buffer 204 into a parallel format with a system clock of 39.216 Hz and provides the same to the CDM modulator 116.

The phase locked loop 210 (PLL) receives a frame sync signal of 39.216 Hz from the TDM receiver 112 through the sync signal detector 208, and based on the system clock and chip rate of 39.216 Hz with high frequency stability Generates a signal of 6x (1x = 16.384 MHz, 6x = 98.304 MHz) with a speed of 6 times. The system clock is provided to the serial / parallel converter 206 so that the serial / parallel converter 206 can stably supply broadcast data to the CDM modulator 116. Meanwhile, the 6x signal is provided to the CDM modulator 116 and used for signal spreading.

In the PLL 210, the voltage controlled crystal oscillator (VCXO) 212 outputs an oscillation signal of 3x (= 49.152 MHz), where the oscillation frequency of the VCXO varies according to the magnitude of the input voltage. In a preferred embodiment, the frequency stability of the VCXO 212 is preferably within the range of 1-3 ppm / year or less. The clock generator 214 receives the 3x signal generated from the VCXO 212, generates a 6x signal and a system clock of 39.216 Hz, supplies the 6x signal to the CDM modulator 116 and the counter 216, and supplies the system clock. The serial / parallel converter 206 is supplied.

The counter 216 receives the frame sync signal and the 6x signal from the TDM receiver 112 and counts the 6x signal for one frame sync interval (25.5 ms). That is, when the system clock and the 6x signal are exactly synchronized to the frame synchronization signal, the 6x signal is generated 2,506,752 times in one frame sync interval (25.5 ms), but the system clock and the 6x signal are not exactly synchronized to the frame sync signal. This count will have a different value. The counter 216 outputs the difference of count values to the digital / analog converter 220. In this case, the photo coupler 218 is connected to the counter 216 and the digital / analog converter 220 to separate the interference of the electrical signal. It is preferable to arrange in between.

The digital / analog converter 220 converts the count value into an analog signal based on the 2.5V reference voltage provided from the reference voltage generator 222. The reference voltage of the reference voltage generator 222 preferably has a precise level so as to be robust against temperature. In addition, in the preferred embodiment, the digital-to-analog converter 220 is a 16-bit converter with a voltage resolution of 38.15 V / bit per bit. The low pass filter 224 low pass filters the output of the digital / analog converter 220 to provide the filtered signal to the VCXO 212 so that the VCXO 212 changes the oscillation frequency corresponding to the filtered signal. do.

According to the buffering and synchronizing signal generator 114 as described above, the frequency stability of the clock output from the TDM receiver 112 is very low. Therefore, the system clock generated by the self-generated system clock is not used as the system clock. After synchronization, the data output from the TDM receiver 112 is stored in RAM and then read as a system clock. In addition, it is possible to generate an accurate system clock even without a PP2S (Pulse Per Even Second) signal as in the IS-95. In addition, while a conventional phase locked loop uses a charge pumping method, a small amount of leakage current may affect frequency stability, but according to the present invention, a D / A converter is used and a reference voltage is used. By maintaining the accuracy of the desired frequency stability can be obtained.

Those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features. Therefore, the above-described embodiments are to be understood as illustrative in all respects and not as restrictive. The scope of the present invention is shown by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention. do.

As described above, according to the present invention, when demodulating and remodulating a signal from a satellite, the received frame synchronizing signal is applied to a PLL to generate a system clock having high frequency stability and remodulate the signal using the same. The transmission frequency stability of the gap filler can be increased to the transmission frequency stability level of the satellite. Accordingly, the reliability of the gap filler is improved, and it is impossible to distinguish between a signal directly coming from a satellite and a signal via the gap filler from a terminal receiving a broadcast service, and one of the two signals can be easily restored and reproduced. It works.

1 is a diagram showing the schematic configuration of a satellite broadcasting system according to digital system E, which is one of the standard proposals recommended by the International Telecommunication Union Standard ITU-R BO.1130-4.

2 is a view showing a preferred embodiment of the satellite broadcasting system according to the present invention.

3 is a block diagram of a gap filler according to the present invention.

4 is a detailed block diagram of the TDM receiver shown in FIG. 3;

5 is a detailed block diagram of the CDM modulator shown in FIG. 3;

FIG. 6 is a detailed block diagram of the buffering and synchronization signal generator shown in FIG. 3; FIG.

Claims (6)

A gap filler which receives an RF broadcast signal from a stationary satellite, demodulates the RF broadcast signal, and multiplexes and transmits the same by using a first multiplexing technique. An RF receiver for receiving the RF broadcast signal from the stationary satellite; A signal processor for demodulating the RF broadcast signal to restore satellite broadcast data and multiplexing the satellite broadcast data by the first multiplexing technique; And An RF transmitter for amplifying and transmitting a first multiplexed signal from the signal processor; Equipped with The signal processor A demodulator for demodulating the RF broadcast signal to restore satellite broadcast data and a frame synchronization signal; A buffering and synchronization signal generator for generating a system clock and a modulation clock by a phase locked loop using the frame synchronization signal while buffering the satellite broadcast data, and outputting the satellite broadcast data in synchronization with the system clock; And A modulator for receiving the satellite broadcast data and the modulation clock and multiplexing the satellite broadcast data by the first multiplexing technique in synchronization with the modulation clock to output the first multiplexed signal; Gap filler having a. The method of claim 1, wherein the buffering and synchronization signal generator A buffer for buffering the satellite broadcast data to adjust timing; A serial / parallel converter for converting the buffered satellite broadcast data from the buffer into a parallel format in synchronization with the system clock to output parallel satellite broadcast data; A synchronization signal detector for detecting the frame synchronization signal from the satellite broadcast data; And The phase lock loop for generating the system clock and the modulation clock using the frame synchronization signal; Gap filler having a. The method of claim 2, wherein the phase locked loop A counter which receives the frame synchronization signal and the modulation clock, counts the modulation clock in units of one frame synchronization interval of the frame synchronization signal, and outputs a difference between a count value and a predetermined reference value; A digital / analog converter for converting the counter output value into an analog signal; A low pass filter configured to low pass filter the output signal of the digital / analog converter to output a filtered signal; An oscillator for oscillating a signal whose frequency varies according to the filtered signal level; And A clock generator which generates the system clock and the modulation clock by using the oscillator signal of the oscillator; Gap filler with. The gap filler according to claim 3, wherein the counter and the digital / analog converter are connected via a photo coupler. The RF broadcast signal according to any one of claims 1 to 4, wherein the RF broadcast signal from the static satellite is received and the RF broadcast signal is a signal multiplexed by a second multiplexing technique in a second frequency band. The signal processor demultiplexes and demodulates the second multiplexed signal to restore the satellite broadcast data, and multiplexes the satellite broadcast data by the first multiplexing technique. Wherein the first multiplexing technique and the second multiplexing technique are different techniques. 6. The gap filler of claim 5, wherein the first multiplexing technique is code division multiplexing using any one Walsh code and a long code selected from a predetermined number of Walsh code groups, and the second multiplexing technique is time division multiplexing. .