KR101203748B1 - Gap filler system and operation method thereof - Google Patents

Abstract

Disclosed is a gap filler system for reducing the maximum average power ratio and a method of operating the same.

According to the invention, a tuner; FPM that modulates the TDM demodulation signal provided by the tuner and reduces the maximum power average ratio (PAR) by clipping the signal level when the digital value of the modulated CDM signal exceeds the threshold. (FPGA: Field Programmable Gate Array); Holding look up table information corresponding to a threshold in an arbitrary memory, determining the level of a currently input CDM signal based on the look up table information, and instructing clipping control to FPI A control unit; And a D / A converter which converts the output signal of FPI to an analog signal and outputs the analog signal.

Accordingly, the present invention compares the currently received CDM signal with a predetermined threshold value, and performs a clipping of the digital signal above the reference value according to the comparison result to perform the maximum power average ratio for the gap filler CDM output signal ( It has the effect of reducing PAR: Peak Power Average Ratio.

Satellite DMB, DMB, Digital, System E, PAR, Maximum Power Average Ratio, Gap Filler

Description

GAP FILLER SYSTEM AND OPERATION METHOD THEREOF

1 is a configuration diagram for explaining a conventional gap filler.

FIG. 2 is a diagram for describing a CDM conversion process of FIG. 1.

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

4 is an arithmetic process diagram for explaining the main operation of FIG. 4.

<Explanation of symbols for main drawings>

401 Tuner 403 FPGA

405: D / A converter 407: phase locked loop (PLL)

411 control unit 413 CDM frame forming unit

415: CDM Modulator 417: CFR Block

419: Compensator

The present invention relates to a gap filler of satellite DMB system E. More particularly, the present invention relates to a satellite DMB capable of reducing a peak power average ratio (PAR) of a gap filler CDM output signal. The present invention relates to a gap filler system for reducing the maximum power average ratio in the system (E) and a method of operating the same.

In general, the digital satellite broadcasting service provides a broadcasting service using a broadcasting satellite or a communication satellite on a geostationary track. The advantage of this digital satellite broadcasting service is that it can provide broadcasting services to a wide range of areas without the need for a large-scale infrastructure including broadcasting facilities on the ground.

The radiocommunication sector of the International Telecommunication Union is intended for the use of car and portable receivers and fixed receivers in the 1400-2700 MHz frequency band allocated to the broadcast-satellite service band under the ITU-R BO.1130-4 standard. It proposes the standard of digital satellite broadcasting system. The ITU-R BO.1130-4 standard recommends five systems: digital systems A, B, DS, DH and E for satellite broadcasting, of which digital system E is a high-quality receiver for automotive, portable and stationary receivers. It provides voice and multimedia data and is optimized in the frequency band 2630-2655MHz. The digital system E uses a code division multiplexing (hereinafter referred to as CDM) method based on quaternary phase shift keying (QPSK) modulation.

The digital system E includes an Earth Station, a Broadcasting Satellite, and two types of Gap Fillers and Receivers. A signal is transmitted from the earth station to the broadcast satellite using a geostationary satellite service link (11 GHz or 14 GHz), which is converted into a CDM signal in the 2.6 GHz frequency band through the broadcast satellite and amplified to a desired level. Is sent.

As mentioned earlier, satellites can be used to provide broadcast services over a wide area without the need for large-scale infrastructure on the ground. However, under some conditions, such as building densities, areas where it is difficult to receive directly from satellites due to attenuation of the signal due to shadowing or blocking. In areas where satellite signals cannot be directly received, an auxiliary relay, or gap filler, is used to receive satellite signals. Such a gap filler is classified into a direct amplifying gap filler and a frequency conversion gap filler.

In general, a gap filler system receives a time division multiplex (TDM) type broadcast signal of 11 GHz from a broadcast satellite, converts it into a CDM signal in a 2.6 GHz frequency band, and transmits the broadcast signal. In order to play this role, the gap filler system is the same frequency as the frequency transmitted by satellite to remove the shadow area where the satellite broadcast signal is not received in the satellite broadcasting system that relays the broadcast signal transmitted by the earth station to the ground using the satellite. A system for wirelessly transmitting a broadcast signal is shown.

As shown in FIG. 1, the gap filler system performs a low noise block down converter (LNB), a tuner unit 203, and TDM demodulation, and modulates and outputs a TDM demodulation signal as a CDM signal. The signal processor 205 includes a low power amplifier (LPA) 207 and a band pass filter (BPFU).

The output signal converted by the LNB unit 201 is converted into a baseband signal by the tuner unit 203, and the signal converted into a baseband through the tuner unit 203 through TDM demodulation of the signal processing unit 205. After performing a series of Quadrature Phase Shift Keying (QPSK) demodulation and Viterbi decoding, FEC (Forward Error Correction), deinterleaving, RS decoding and descrambling to minimize errors, CDM modulates the TDM demodulated signal.

The CDM modulation modulates the output signal of the TDM demodulation into a 2.6 GHz (S band) CDM signal so that a user terminal can receive the signal, and then up-converts the modulated CDM signal through RF modulation. 207: LPA). The amplified signal passes through the band pass filter 209 to detect only a predetermined band, removes noise, and outputs a CDM signal. Therefore, the broadcast signal can be wirelessly transmitted at the same frequency as the frequency transmitted from the satellite even in the shaded area.

Meanwhile, as shown in FIG. 2, the conventional CDM modulation modulates the output signal according to the TDM demodulation into a 2.6 GHz (S band) CDM signal so that a user terminal can receive it, and outputs the digital signal according to the CDM modulation. A finite impulse response (FIR) filter unit 301 for filtering data, and a D / A converter unit 303 for converting I / Q signals output from the FIR filter unit 301 into respective analog signals. . Then, RF conversion for transmitting the output signal of each D / A converter section 303 to 2.6 GHz is performed. As shown, the phase-modulated I output signal of the FIR filter unit 301 with respect to cosωt, the phase-modulated Q output signal with respect to sinωt, and then synthesized with each other to be output.

However, since power amplification of the analog signal is performed during the CDM modulation, it has a maximum power average ratio (PAR) of about 11 dB. Therefore, high PAR characteristics increase the signal deterioration and cause a problem of not maintaining the stability of the system.

The present invention has been made to solve the above problems, and an object of the present invention is to reduce the maximum power average ratio (PAR) of the gap filler CDM output signal to minimize the deterioration of the characteristics of the output signal The present invention provides a gap filler system and a method of operating the same to reduce the maximum power average ratio.

Another object of the present invention is to reduce the maximum power average ratio that can be achieved by providing a CFR (Crest Factor Reduction) function in the CDM signal processing in order to reduce the maximum power average ratio (PAR) described above. In order to provide a gap filler system and its operation method.

It is still another object of the present invention to reduce the maximum power average ratio that can minimize signal degradation by implementing the above-described CFR device after the RRC (Root Raised Cosine) filter of the CDM modulator. The present invention provides a gap filler system and a method of operating the same.

In the gap filler system for reducing the maximum power average ratio according to the first aspect of the present invention for achieving the above object, the gap filler system in the satellite DMB system (E) for reducing the maximum power average ratio (PAR) Converts the output signal converted from the LNB to a baseband signal, and uses Quadrature Phase Shift Keying (QPSK) demodulation, Viterbi decoding, Forward Error Correction (FEC), and deinterleaving through TDM demodulation. a tuner for performing deinterleaving, RS decoding and descrambling; FPM that CDM modulates the TDM demodulation signal provided by the tuner, and when the digital value of the modulated CDM signal exceeds a threshold, clipping the corresponding signal level to reduce the maximum power average ratio (PAR). Field Programmable Gate Array (FPGA); Holds look up table information corresponding to the threshold in an arbitrary memory, determines a level of a currently input CDM signal based on the look up table information, and determines the FPI aero clipping control result. A control unit for commanding; And a D / A converter which converts the output signal of the F-PG to an analog signal and outputs the analog signal.

According to a preferred embodiment of the present invention, the FPGA (FPGA) is a CDM frame forming unit for forming a CDM frame to convert the demodulation data for the TDM signal to a CDM signal; A compensator for providing a correction function according to the data structure modification of the CDM frame forming unit; A CDM modulator for performing digitized modulation based on output data of the CDM frame forming unit; And CFR (CFR) for performing digital intermediate frequency (IF) modulation on the output data of the CDM modulator for each I channel and Q channel, and reducing the maximum power average ratio PAR of the output signal. Characterized in that the block portion.

In addition, the clipping signal is characterized in that the CI block performs a clipping control in conjunction with RRC (Root Raised Cosine) in order to prevent degradation of the CDM signal.

In addition, the RRC filter is characterized in that implemented in the front end of the RF block.

On the other hand, the operation method of the gap filler system for reducing the maximum power average ratio according to the second aspect of the present invention for achieving the above object, in the operating method of the gap filler system according to claim 1, a) currently received CDM Performing digital phase modulation on the I and Q channels via respective Finite Impulse Responses (FIRs) for filtering respective digital data for the I and Q channels of the signal; b) performing signal combining on the I channel and the Q channel according to the digital phase modulation; c) determining, by the controller, whether a magnitude of a digital signal for each channel is normal based on a predetermined threshold; d) As a result of the determination in step c), if the size of the currently received CDM signal does not exceed the reference value, digital intermediate frequency (IF) modulation of the current CDM modulated signal for each channel is performed and the D / A converter is used. Converting and outputting an analog signal; And e) when the magnitude of the currently received CDM signal exceeds a reference value, assuming that the output value of the CDM signal is a threshold value and outputting it to the D / A converter. It features.

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

3 is a view showing the main configuration of a gap filler equipped with a CFR device according to the present invention. As shown, the output signal converted from the LNB (not shown) is converted into a baseband signal, and a beater for minimizing Quadrature Phase Shift Keying (QPSK) demodulation and error through TDM demodulation of the baseband converted signal. Tuner 401 for serially performing non-decoding, forward error correction, deinterleaving, RS decoding, and descrambling, and TDM demodulation signal provided by the tuner 401 Field programmable gate array (FPGA) which reduces the maximum power average ratio (PAR) by CDM modulation and clipping the signal level when the digital value of the modulated CDM signal exceeds the threshold. 403) retaining look up table information corresponding to the threshold in an arbitrary memory, and determining a level of a currently input CDM signal based on the look up table information; Consists of a control unit (411), D / A converter 405 for converting the output signal output from the sebum F. A 403 into an analog signal for controlling the clipping command to unity and the sebum F. A 403.

On the other hand, a phase locked loop (PLL) for generating clocks of 10MHz and 65.536MHz to process the signal of the gap filler system from the 2.304MHz reference clock extracted during the TDM demodulation process.

In addition, the FpG 403 includes a CDM frame forming unit 413 for forming a CDM frame for converting and outputting demodulated data for the TDM signal into a CDM signal, and the CDM frame forming unit 413. A compensator 419 for providing a correction function according to the data structure modification, a CDM modulator 415 for performing digitized modulation based on the output data of the CDM frame forming unit 413, and the CDM modulator ( A CFR block 417 which performs digital intermediate frequency (IF) modulation on the output data of the 415 for each of the I and Q channels and reduces the maximum power average ratio (PAR) of the output signal thereto. )

Hereinafter, the operation of the present invention will be described in detail with reference to the accompanying drawings. First, Figure 4 is a calculation process for explaining the main operation of the CF block according to the present invention. In the lower part of the figure, arithmetic processing procedures are described for ease of explanation.

The gap filler according to the present invention is for relaying a broadcast signal transmitted by an earth station to the ground through a satellite, and an output signal converted through a satellite antenna and an LNB is received by the tuner 401. do. The tuner 401 converts the received satellite signal into a baseband signal. The baseband signal thus converted is demodulated into a TDM signal.

The demodulated TDM signal is supplied to the CDM frame forming unit 413, and the CDM frame forming unit 413 is processed into a formatted data form through the corrector 419. Thereafter, the CDM modulator 415 modulates the S-band for the TDM demodulated signal, that is, a CDM signal of 2.6 GHz. As shown in FIG. 5, CDM modulation performs digital phase modulation on each channel through each finite impulse response (FIR) that performs filtering on respective digital data for I and Q channels in step S501. do.

Thereafter, the control unit 411 enters step S503, and performs mutual synthesis on I (t _k ) cosωt as phase modulation for the I channel and Q (t _k ) sinωt as phase modulation for the Q channel. Do this. The control unit 411 provides S _i (t _k ) = I (t _k ) cos omega t + Q (t _k ) sin omega t as a result of the operation. The control unit 411 stores the operation result of the currently received CDM signal in an arbitrary register.

This is to set the characteristics of all digital signals for each channel converted into CDM signals to register values of the controller 411. The controller 411, at step S505, based on a pre-stored arbitrary threshold value. It is determined whether the magnitude of the digital signal for each channel is normal. The threshold value is the look-up table value described above, and the controller 411 extracts an unnecessary signal for S _i (t _k ), that is, an operation result for the currently received CDM signal.

As a result of determination, if the magnitude of the currently received CDM signal does not exceed the reference value, the controller 411 enters the step S507. The controller 411 performs digital intermediate frequency (IF) modulation on each current CDM modulated signal, and controls the CS block 417 to convert the CDM modulated signal into an analog signal through the D / A converter 405. The intermediate frequency IF represents a frequency of 2.6 GHz of the S band that the user terminal can receive.

On the other hand, when the controller 411 determines in step S505 that the size of the currently received CDM signal exceeds a reference value, that is, when the currently received CDM signal is larger than the signal size of the lookup table previously stored in the internal memory of the controller, the CDM The output value S ₀ (t _k ) of the signal is output as a threshold. This is an excessively large CDM signal is clipped to a predetermined value under the instruction of the controller 411, and is processed in the CF block 417.

The RF block 417 supplies the clipped signal to the D / A converter 405 in step S507, and the clipping signal is supplied to the reception frequency of the user terminal as it is converted into an analog signal.

Here, the clipping signal according to the present invention may promote degradation of the CDM signal, so that the RF block 417 may perform clipping control in conjunction with RRC (Root Raised Cosine). At this time, the RRC filter is preferably implemented at the front end of the CB block 417. For this reason, the RRC filter minimizes signal degradation characteristics due to clipping of the digital signal.

As described above, the gap filler system for reducing the maximum power average ratio and its operation method in the system of the satellite DMB according to the present invention is to compare the currently received CDM signal with a predetermined threshold value, the comparison result As a result, clipping of a digital signal above a reference value may be performed to reduce a peak power average ratio (PAR) for the gap filler CDM output signal.

In addition, the present invention may provide an effect of minimizing signal degradation for the clipped CDM signal by using the RRC filter when performing the clipping on the digital signal.

What has been described above is only an embodiment of the gap filler system for reducing the maximum power average ratio in the system of the satellite DMB according to the present invention and its operation method, and is not limited to the embodiment of the present invention in the claims As claimed, any person having ordinary skill in the art without departing from the gist of the present invention will have the technical spirit of the present invention to the extent that various modifications can be made.

Claims (7)

In the gap filler system in the satellite DMB system (E) to reduce the maximum power average ratio (PAR), By converting the output signal converted in the LNB (base not shown) to a baseband signal, Quadrature Phase Shift Keying (QPSK) demodulation, Viterbi decoding, Forward Error Correction (FEC), deinterleaving (TDM) a tuner for performing deinterleaving, RS decoding and descrambling; FPM that CDM modulates the TDM demodulation signal provided by the tuner, and when the digital value of the modulated CDM signal exceeds a threshold, clipping the corresponding signal level to reduce the maximum power average ratio (PAR). Field Programmable Gate Array (FPGA); Holds look up table information corresponding to the threshold in an arbitrary memory, determines a level of a currently input CDM signal based on the look up table information, and determines the FPI aero clipping control result. A control unit for commanding; And A D / A converter converting the output signal of the F-PGA into an analog signal and outputting the analog signal; The FPGA includes: a CDM frame forming unit for forming a CDM frame for converting and outputting demodulated data for the TDM signal into a CDM signal; A compensator for providing a correction function according to the data structure modification of the CDM frame forming unit; A CDM modulator for performing digitized modulation based on output data of the CDM frame forming unit; The output data of the CDM modulator is a CFR block that performs digital intermediate frequency (IF) modulation for each of I and Q channels and reduces the maximum power average ratio (PAR) of the output signal. Consisting of, gap filler system. delete The gap filler system according to claim 1, wherein the CF block performs clipping control in association with a root raised cosine (RRC) to prevent degradation of the CDM signal due to a clipped signal. 4. The gap filler system of claim 3, wherein the RRC filter is implemented at the front end of the RF block. In the method of operating the gap filler system according to claim 1, a) performing digital phase modulation on the I and Q channels via respective Finite Impulse Responses (FIRs) for filtering respective digital data for the I and Q channels of the currently received CDM signal; b) performing signal combining on the I channel and the Q channel according to the digital phase modulation; c) determining, by the controller, whether a magnitude of a digital signal for each channel is normal based on a predetermined threshold; d) As a result of the determination in step c), if the size of the currently received CDM signal does not exceed the reference value, digital intermediate frequency (IF) modulation of the current CDM modulated signal for each channel is performed and the D / A converter is used. Converting and outputting an analog signal; And e) when the magnitude of the currently received CDM signal exceeds a reference value, the step of assuming that the output value of the CDM signal as a threshold value and outputting it to the D / A converter. Operating method of a gap filler system. The method of claim 5, wherein the threshold is look-up table information set to an internal memory of the controller. The method of claim 5, further comprising a root raised cosine (RRC) filtering step to prevent degradation of the CDM signal as a step before the step e).

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