JP2023024198A - Digital signal transmission device - Google Patents

Abstract

To provide a digital signal transmission device capable of improving required C/N on the receiving side while reducing spectrum regrowth on a broadcast transmission line by compensating for distortion in a broadcast transmission line in a satellite broadcasting transmission system.SOLUTION: A transmission device 1 according to the present invention includes a data signal generator 11 that converts transmission data into an IQ data signal, a first distortion compensation unit 16 that pre-compensates an error in the IQ signal point caused by a satellite repeater 2 on a broadcast transmission path for the IQ data signal, a waveform shaping unit 13 that performs waveform shaping on the signal of the IQ data by the processing of the first distortion compensation unit 16, a second distortion compensation unit 17 that pre-compensates the error of the IQ signal point caused by a high power amplifier 1a of the earth station on the broadcast transmission path for the IQ data signal after the waveform shaping, and a transmission signal generation unit 14 that generates a modulated wave signal for the IQ data signal that has undergone distortion compensation by the processing of the second distortion compensation unit 17, and transmits the modulated wave signal to the high power amplifier 1a.SELECTED DRAWING: Figure 2

Description

The present invention relates to a digital signal transmission apparatus that compensates for distortion in a broadcast transmission line in a satellite broadcast transmission system.

Among the transmitters related to digital broadcasting of various standards currently in operation, the transmitters for digital signals for satellite broadcasting use satellite transponders installed on broadcasting satellites, and multiple broadcasters are independent TS Broadcast wave signals are multiplexed so as to be able to transmit (Transport Stream), and the standard of this satellite digital broadcasting includes ISDB-S, ISDB-S3, DVB-S2, DVB -S2X, etc.

Broadcasting transmission path components in a satellite broadcasting transmission system conforming to these standards will be explained in general terms. ), and a satellite repeater that receives an uplink signal as a satellite transmission path, amplifies the power, repeats the signal, and generates and radiates a downlink signal to each receiver on the ground.

Referring to FIG. 5, a schematic configuration of a conventional transmission device 10 generalized for satellite broadcasting conforming to the ISDB-S3 system will be described as a representative. FIG. 5 is a block diagram showing a schematic configuration of a conventional transmission apparatus 10 for satellite broadcasting which does not have a distortion compensation function.

A conventional transmission device 10 includes a data signal generation section 11 , an upsampling section 12 , a waveform shaping section 13 , and a transmission signal generation section 14 .

The data signal generation unit 11 receives as a main signal transmission data that constitutes a digital signal with TS packets such as video, audio, and data broadcasting in the TS of each broadcaster, and performs error correction on the information bit series of the main signal. A coded bit sequence signal is generated by performing predetermined preprocessing including coding processing, and mapping is performed using a mapping table based on a predetermined modulation method to generate an IQ data signal (in-phase component I and quadrature phase component Q). It is a functional unit that converts data into a digital data signal that is represented by a signal point sequence and can be represented as signal points on the IQ plane), and includes a transmission preprocessing unit 111 and a mapping unit 112 .

The transmission preprocessing unit 111 receives transmission data constituting the digital signal as a main signal, allocates the main signal to modulation slots in units of blocks constituting a predetermined transmission frame, and generates the synchronization signal and the main signal allocated in units of blocks. Predetermined preprocessing including error correction coding processing is performed on the information bit sequence including the signal to generate a modulated slot signal of the coded bit sequence and output to mapping section 112 .

Mapping section 112 performs mapping on the modulation slot signal obtained from transmission preprocessing section 111 using a mapping table based on a predetermined modulation scheme, converts the signal into an IQ data signal, and outputs the signal to upsampling section 12 . Although not shown, modulation slots for TMCC (Transmission and Multiplexing Configuration and Control) signals are also generated in addition to modulation slots for main signals. The modulation scheme for the main signal is designated by control information indicated in the TMCC signal, and includes π/2 shift BPSK, QPSK, 8PSK, 16APSK, and 32APSK. Also, the modulation scheme for the TMCC signal is π/2 shift BPSK. Then, the signal of the modulation slot for the main signal of each modulation scheme and the signal of the modulation slot for the TMCC signal are transmitted by time-division multiplexing.

The upsampling unit 12 upsamples the sample points of the IQ data signal obtained from the mapping unit 112 by a factor of 2 or more, and outputs the result to the waveform shaping unit 13 .

The waveform shaping section 13 applies a predetermined band-limiting filter process to the IQ data signal including non-sampled points obtained from the upsampling section 12, thereby performing waveform shaping to remove unnecessary high frequency components. , to generate a signal of the IQ data after waveform shaping, and output it to the transmission signal generator 14 . A digital filter having a root roll-off characteristic is generally used as the band-limiting filter. ISDB-S3 uses a root roll-off filter with a roll-over rate of 0.03.

The transmission signal generation unit 14 is a functional unit that generates a modulated wave signal according to the predetermined modulation method for the IQ data signal after waveform shaping by the waveform shaping unit 13, and includes a quadrature modulation unit 141, DA (digital/analog) A conversion unit 142 and a frequency conversion unit 143 are provided.

The quadrature modulation unit 141 generates a baseband IQ signal based on quadrature modulation processing according to the predetermined modulation method for the waveform-shaped IQ data signal obtained from the waveform shaping unit 13 , and outputs the baseband IQ signal to the DA conversion unit 142 . .

The DA conversion section 142 performs digital/analog conversion processing on the baseband IQ signal obtained from the quadrature modulation section 141 to generate a modulated wave signal, and outputs the modulated wave signal to the frequency conversion section 143 .

The frequency converter 143 frequency-converts the modulated wave signal obtained from the DA converter 142 into a modulated wave signal in the radio frequency band of the uplink signal, and transmits the modulated wave signal to the high power amplifier (HPA) of the earth station. For example, the radio frequency of the uplink signal in the ISDB-S3 satellite broadcasting transmission system is the 17 GHz band.

Then, the high power amplifier (HPA) of the earth station generates an uplink signal by power-amplifying the modulated wave signal obtained from the transmission signal generator 14, and uplinks the signal to the satellite transponder of the broadcasting satellite. The satellite transponder receives the uplink signal, power-amplifies it, relays it, and generates and radiates a downlink signal directed to each receiver on the ground. Then, each receiving device receives and demodulates the downlink signal, performs decoding processing corresponding to the reverse processing of each processing in the transmitting device 10 , and restores the transmission data transmitted by the transmitting device 10 .

The satellite transponder of an actual broadcasting satellite (actual satellite) includes an input multiplexer filter (hereinafter referred to as an "IMUX filter"), which is an input filter placed in front of a traveling wave tube amplifier, a traveling wave tube amplifier (hereinafter referred to as TWTA), an output multiplexer filter (hereinafter referred to as an OMUX filter) which is an output filter placed after the traveling wave tube amplifier, and the like. Then, the satellite transponder performs band extraction for each channel from the received uplink signal by the IMUX filter, performs power amplification for each channel by the TWTA, and uses the OMUX filter to extract out-of-band unnecessary frequency components (spectrum regrowth ) is suppressed, broadcast wave signals for all channels are combined by a combiner subsequent to the OMUX filter, and downlink signals (broadcast wave signals) are transmitted to a plurality of receivers on the ground.

Here, FIG. 6 shows, as input/output characteristics of a high power amplifier (HPA) of an earth station, characteristics of normalized output power (AM/AM characteristics) with respect to normalized input power normalized so as to be within a predetermined power. ), and phase shift characteristics (AM/PM characteristics) of the normalized output with respect to the normalized input power.

In addition, FIG. 7 shows, as input/output characteristics of a traveling wave tube amplifier (TWTA) in a satellite transponder of an actual satellite, characteristics of normalized output power with respect to normalized input power normalized to be within a predetermined power ( AM/AM characteristics), and phase shift characteristics of the normalized output with respect to the normalized input power (AM/PM characteristics).

Also, FIG. 8 shows frequency vs. amplitude showing the amplitude with respect to the normalized frequency normalized to be within a predetermined band as the frequency response generated by the input/output characteristics of the IMUX filter and the OMUX filter in the satellite transponder of the actual satellite. 1 shows an example of a frequency vs. group delay characteristic showing the characteristic and the group delay for that normalized frequency.

While the high power amplifier (HPA) of the earth station and the satellite transponder of the actual satellite are indispensable for the transmission system of satellite broadcasting, as can be understood from FIGS. amplitude) and its phase shift, the modulated wave signal of the transmitter 10 deviates from the desired IQ signal point. Inter-symbol interference occurs due to the influence of characteristics, etc., and a spread occurs from the desired IQ signal point.

It is known that the shift and spread of these IQ signal points affect each other on the broadcast transmission line, resulting in an increase in the required C/N ratio on the receiving device side and deterioration in transmission quality (for example, non-uniformity). See Patent Document 1).

Furthermore, in the case of multilevel amplitude phase keying modulation schemes such as 16APSK and 32APSK, power amplifiers such as the high power amplifier (HPA) of the earth station and the power amplifier such as the TWTA in the satellite transponder of the actual satellite generally operate with back-off. I'm trying Moreover, in the nonlinear amplification of the high power amplifier (HPA) of the earth station, apart from the problem of the above-mentioned increase in the required C/N caused by the nonlinear characteristics, the spectrum regrowth is reduced because the output filter is not provided. There is also the problem of growth.

The backoff in the TWTA in the high power amplifier (HPA) of the earth station and the satellite transponder of the real satellite will now be described in detail below. High power amplifiers (HPAs) and TWTAs are originally desired to perform power amplification processing so that the relationship between the input level and the output level is proportional. However, this input/output characteristic actually exhibits a nonlinear characteristic in which the gain decreases as the input level increases, and at the same time the phase of the output signal with respect to the input signal also rotates. Therefore, when the input level is gradually increased, the output level also increases up to a certain level, but when the input level exceeds the certain level, the output level decreases. An operating point immediately before such a drop in output level is generally called an output saturation point. In addition, the case where the input level is lowered by X [dB] from this output saturation point is called "input back-off X [dB]". The case of operating in this state is called "output backoff Y [dB]".

It is also known that if such a back-off operation is attempted, the output power will decrease, and as a result the reception C/N margin in the receiving apparatus will become smaller (see Non-Patent Document 1). On the receiver side in the transmission system of satellite broadcasting, the opening diameter of the receiving antenna is generally as small as 45 cm, and the reception C/N margin is as small as about 20 dB even in fine weather. Therefore, there is a trade-off between the required C/N and the output backoff, and it is advantageous in terms of circuit design to minimize the sum of the required C/N and the output backoff (Non-Patent Document 1). reference).

Therefore, the receiving device constantly monitors the control information of the TMCC signal multiplexed with the main signal transmitted as the broadcast wave signal, so that even if various transmission controls are performed on the transmitting device side, the receiving device can follow it. It is possible to switch the receiving method (switching of the modulation method, the coding rate of the error correction code, etc.).

By the way, as a conventional transmission device, a transmission device having a distortion compensation function for transmission path distortion generated in a satellite repeater is also disclosed (see, for example, Patent Document 1). FIG. 9 is a block diagram showing a generalized schematic configuration of a transmission apparatus 10A for satellite broadcasting with a distortion compensating function for a conventional satellite repeater so that it can be understood in comparison with that shown in FIG. be. 9, the same reference numerals are assigned to the same components as those of the transmitting apparatus 10 shown in FIG.

Compared to the transmission device 10 shown in FIG. 5, the transmission device 10A shown in FIG. , which includes the functions of the upsampling section 12), and the other components are configured in the same way.

The distortion compensating unit 15 performs waveform shaping on the IQ data signal obtained from the mapping unit 112 once after up-sampling in the same manner as the up-sampling unit 12, and simulates a satellite transponder of a real satellite. Using the input/output characteristics of the satellite transponder, a signal is generated in which the transmission path distortion caused by the satellite transponder is simulated. Subsequently, the distortion compensator 15 applies waveform shaping to the signal in which the transmission path distortion caused by the satellite repeater is artificially generated, and down-samples the signal so as to correspond to the original IQ data signal. A first vector operation is performed to subtract the corresponding original IQ data signal points from the signal points to obtain an error vector. Then, the distortion compensator 15 uses, as a correction vector, an inverse vector of the error vector viewed from an ideal transmission signal point (hereinafter referred to as an "ideal signal point") from the signal point of the original IQ data. A signal of distortion-compensated IQ data is generated by performing a second vector operation for subtracting the error vector multiplied by a predetermined coefficient weight, and the function of the distortion-compensated IQ data signal is the same as that of the upsampling unit 12. , and output to the waveform shaping section 13 .

Therefore, the transmission apparatus 10A shown in FIG. 9 causes the distortion compensator 15 in the preceding stage of the waveform shaping section 13 to generate the transmission path distortion in the real satellite in advance using the input/output characteristics of the pseudo satellite repeater, and the vector after that. It has a function of generating a distortion-compensated IQ data signal by correcting the signal points of the original IQ data by calculation. As a result, in the downlink signal (broadcast wave signal) radiated from the satellite transponder of the actual satellite, the deviation and spread of the IQ signal points caused by the satellite transponder of the actual satellite are canceled, so the receiver side is ideal. It is possible to converge on the signal point and improve the required C/N on the receiver side.

Japanese Patent No. 6681672

Kojima, Koizumi, Suzuki, Suji, "Comparative Study of Digital Pre-Distortion for 32APSK by Hardware Experiments and Numerical Calculations", IEICE Technical Report, IEICE Technical Report SAT2019-53, Electronics Information and Communication Society, October 10, 2019 Koizumi, Kojima, Suzuki, Saito, Tanaka, Nishida, "Transmission experiment of 32APSK signal using broadcasting satellite", ITE Technical Report Vol.39, No.47 BCT2015-80, General Incorporated Association The Institute of Image Information and Television Engineers, December 3, 2015

A digital signal transmission device that incorporates conventional DPD (Digital Pre-Distortion) technology as disclosed in Patent Document 1 and Non-Patent Document 1 regarding a satellite broadcasting transmission system is only a satellite transmission line (satellite repeater). was targeted for distortion compensation, and the high power amplifier (HPA) of the earth station was not targeted for distortion compensation. The reason for this is thought to be that the earth station's high power amplifier (HPA) generally allows more backoff than the satellite transponder. For example, according to Non-Patent Document 2, the output backoff of the satellite transponder is set at 2.2 dB, whereas the high power amplifier (HPA) of the earth station has a large backoff amount of 5 to 7 dB.

However, in the case of a multi-level modulation scheme such as 32APSK, reception performance deteriorates even with the above operating point setting for the high power amplifier (HPA) of the earth station (see Non-Patent Document 2). Furthermore, in a transmission device incorporating DPD technology as disclosed in Patent Document 1 and Non-Patent Document 1, since it is assumed that the high power amplifier (HPA) of the earth station is ideal linear amplification, the satellite When non-linear distortion occurs in the high power amplifier (HPA) of the earth station, which is the preceding stage of the repeater, not only the deterioration due to the high power amplifier (HPA) of the earth station but also the effect of the DPD for the satellite repeater deteriorates. expected to

Therefore, in order to solve the problem of nonlinear distortion in the high power amplifier (HPA) of the earth station by applying the technology of Patent Document 1, the pseudo transmission path in the technology of Patent Document 1 is replaced with the high power amplifier (HPA) of the earth station. ) can be considered. That is, the pseudo transmission path (pseudo-satellite repeater) of the distortion compensator in the transmission device is changed from the configuration of the IMUX filter-TWTA-OMUX filter to the high-power amplifier (HPA) of the earth station-IMUX filter-TWTA-OMUX filter. This is a method for expanding the range of the pseudo transmission path to a configuration that As a result, the nonlinear distortion of the high power amplifier (HPA) of the earth station is also reduced, so that the required C/N ratio is reduced and an improvement in reception performance can be expected.

However, since the DPD technology based on the method of extending the range of this pseudo transmission path is signal processing before the waveform shaping related to the modulated wave signal, even if the distortion of the signal within the Nyquist band can be compensated, the signal outside the Nyquist band It is not possible to mitigate the spectrum regrowth of the high power amplifier (HPA) of the earth station that becomes the source. Rather, if the distortion compensation before the waveform shaping is performed dynamically by the method of expanding the range of such a pseudo transmission path, the instantaneous power of the modulated wave signal is further increased, and the modulated wave signal is transmitted to the earth station. There is even concern that non-linear amplification via a power amplifier (HPA) will result, resulting in increased spectral regrowth. In addition, the Radio Law stipulates that wireless transmission (uplink signal and downlink signal) in the transmission system of satellite broadcasting should be suppressed to an occupied bandwidth of 34.5 MHz or less per channel (see Non-Patent Document 2). If spectrum regrowth increases, there is concern that this condition will no longer be met.

Therefore, in view of the above problems, an object of the present invention is to perform distortion compensation on a broadcast transmission line in a satellite broadcasting transmission system, reduce spectrum regrowth on the broadcast transmission line, and reduce the required C/C on the receiving side. It is an object of the present invention to provide a digital signal transmitter capable of improving N.

A transmitting device of the present invention is a transmitting device for transmitting a digital signal to a receiving device via a broadcasting transmission line including a large power amplifier and a satellite repeater of an earth station in a transmission system of satellite broadcasting, wherein the digital signal is is input as a main signal, the information bit series of the main signal is subjected to predetermined preprocessing including error correction coding processing to generate a coded bit series signal, and is applied to a predetermined modulation method. a data signal generation unit that performs mapping using a mapping table based on the data signal and converts it into an IQ data signal represented by a signal point series of in-phase components and quadrature phase components; a first distortion compensating unit for generating a signal of IQ data distortion-compensated by a first distortion compensating process for correcting an error of an IQ signal point in advance; a waveform shaping section that performs waveform shaping by applying a predetermined band-limiting filter process and generates a signal of the IQ data after the waveform shaping that has undergone the first distortion compensation process; and a waveform that has undergone the first distortion compensation process. A second distortion compensator for generating a distortion-compensated IQ data signal by performing a second distortion compensating process for pre-correcting an error in the IQ signal points caused by the high-power amplifier of the earth station for the shaped IQ data signal. a compensator, and a transmission signal generator that generates a modulated wave signal according to the predetermined modulation method for the IQ data signal distortion-compensated by the second distortion compensation processing, and transmits the modulated wave signal to the large power amplifier of the earth station. It is characterized by having

Further, in the transmitting apparatus of the present invention, the first distortion compensator performs waveform shaping after once up-sampling the IQ data signal obtained from the data signal generator as the first distortion compensation process. Then, using a table file approximating the input/output characteristics of the satellite repeater, a signal is generated in which the transmission line distortion caused by the satellite repeater is simulated, and the waveform is shaped to form the original IQ data signal. From the IQ signal points obtained by downsampling so as to correspond to , a first vector operation is performed to subtract the corresponding original IQ data signal points to obtain an error vector, and the error vector is viewed from the ideal signal point In order to use the inverse vector as a correction vector, a second vector operation is performed to subtract the error vector obtained by multiplying the signal point of the original IQ data by a predetermined coefficient weight, and the satellite relay is subjected to upsampling processing. It is characterized by having means for generating a distortion-compensated IQ data signal by correcting in advance an error in the IQ signal points caused by the device.

Further, in the transmitting apparatus of the present invention, the second distortion compensating section, as the second distortion compensating process, converts the waveform-shaped IQ data signal that has undergone the first distortion compensating process to the signal of the earth station. A signal of IQ data that is distortion-compensated by correcting in advance the error of the IQ signal points caused by the large power amplifier of the earth station using a table file showing the values that are the inverse components of the input/output characteristics of the large power amplifier. It is characterized by having means for generating

According to the transmitting apparatus of the present invention, the conventional DPD ( The second distortion compensator can reduce the spectral regrowth outside the Nyquist band in the uplink signal, which could not be solved by the configuration having only the first distortion compensator. Furthermore, according to the transmitting apparatus according to the present invention, the distortion compensation for the satellite transponder 2 can be executed without any adverse effect by the first distortion compensator as in the conventional art, so that the required C/N as the reception characteristic is also improved. It is possible to reduce the spectrum regrowth of the uplink signal and improve the reception performance. Further, according to the transmitting apparatus of the present invention, the process of simulating the characteristics of the broadcast transmission path in the first distortion compensator and the second distortion compensator can be sequentially updated by rewriting the table file. High versatility can be provided for various transmission methods and broadcast transmission lines without depending on the signal format of the transmission method.

1 is a block diagram showing a schematic configuration of a transmission system for satellite broadcasting according to an embodiment provided with a transmission device according to an embodiment of the present invention; FIG. 1 is a block diagram showing a schematic configuration of a transmitter of one embodiment according to the present invention; FIG. FIG. 3 is a block diagram showing a schematic configuration of a first distortion compensator in the transmitter of one embodiment according to the present invention; FIG. 10 is a diagram showing the inverse characteristics of the high power amplifier (HPA) of the earth station used for the processing of the second distortion compensator in the transmitter of one embodiment according to the present invention; FIG. 2 is a block diagram showing a schematic configuration of a transmission apparatus for satellite broadcasting (without distortion compensation function) in the prior art; FIG. 2 is a diagram showing an example of input/output characteristics (AM/AM characteristics, AM/PM characteristics) of a high power amplifier (HPA) of an earth station; FIG. 3 is a diagram showing an example of input/output characteristics (AM/AM characteristics, AM/PM characteristics) of a traveling wave tube amplifier (TWTA) in a satellite transponder of an actual satellite; FIG. 3 is a diagram showing an example of frequency responses (frequency vs. amplitude, frequency vs. group delay characteristics) caused by input/output characteristics of IMUX filters and OMUX filters in a satellite transponder of a real satellite; 1 is a block diagram showing a schematic configuration of a transmission device (with a distortion compensation function) for satellite broadcasting in the prior art; FIG.

A transmitter 1 according to an embodiment of the present invention will be described below with reference to the drawings.

[Transmission system]
First, FIG. 1 is a block diagram showing a schematic configuration of a transmission system for satellite broadcasting according to an embodiment having a transmission device 1 according to an embodiment of the present invention. The transmission system of one embodiment shown in FIG. A transmitting device 1 in a station, a high power amplifier (HPA) 1a in an earth station, a satellite repeater 2, and a plurality of receiving devices 3-1, 3-2, . is an integer and is collectively referred to as "receiving device 3").

The transmission device 1 of the present embodiment, which will be described in detail with reference to FIG. 2, receives as a main signal transmission data composed of TS packets such as video, audio, and data broadcasting in the TS of each broadcaster. generates a modulated wave signal that compensates for transmission path distortion caused by both the high power amplifier (HPA) 1a of the earth station and the satellite transponder 2 of the actual satellite, and transmits it to the high power amplifier (HPA) 1a of the earth station. It can be incorporated as a transmission system 1 by replacing the existing conventional transmission device 10 shown in FIG.

The satellite transponder 2 mounted on the broadcasting satellite includes an IMUX filter 21, a TWTA 22, and an OMUX filter 23. As described above, the IMUX filter 21 receives a modulated wave signal transmitted as an uplink signal by the transmission device 1 on the ground. is received, band extraction is performed for each channel from the modulated wave signal, power is amplified by the TWTA 22, the OMUX filter 23 suppresses out-of-band unnecessary frequency components (spectrum regrowth), and the OMUX filter 23 follows. Broadcast wave signals for all channels are combined by a combiner (not shown), and a downlink signal (broadcast wave signal) is transmitted to a plurality of receivers 3 on the ground.

The receiving device 3 receives and demodulates the downlink signal from the satellite transponder 2, performs decoding processing corresponding to the reverse processing of each processing in the transmitting device 1, and restores the transmission data transmitted by the transmitting device 1. It is configured as a device and has the same configuration as a conventional ISDB-S3 system-compliant receiving device, and further description thereof will be omitted.

Here, the high power amplifier (HPA) 1a of the earth station and the satellite transponder 2 of the actual satellite have input/output characteristics illustrated in FIGS. ) and its phase shift, the modulation wave signal of the transmitter 1 deviates from the desired IQ signal point. and the frequency response caused by the input/output characteristics of the OMUX filter 23, and the IMUX filter and the OMUX filter are assumed to cause inter-symbol interference due to the influence of frequency amplitude, group delay characteristics, etc., and spread from the desired IQ signal point. It's becoming

Therefore, the transmitting apparatus 1 according to the present invention is configured to generate a modulated wave signal that compensates for the transmission path distortion caused by both the high power amplifier (HPA) 1a of the earth station and the satellite transponder 2 of the actual satellite. and will be described in more detail below.

[Transmitter]
FIG. 2 is a block diagram showing a schematic configuration of a transmitter 1 of an embodiment according to the present invention, generalized so as to be understood in comparison with that shown in FIG. 2, the same reference numerals are assigned to the same components as those of the transmitting apparatus 10 shown in FIG.

Here, in comparison with the transmitting apparatus 10 shown in FIG. 5, the transmitting apparatus 1 according to one embodiment of the present invention shown in FIG. A first distortion compensating unit 16 (which includes the function of the upsampling unit 12 shown in FIG. 5) instead of the upsampling unit 12, and a waveform shaping unit 13 and a transmission signal generating unit 14 in that a second distortion compensator 17 is provided between them, and the other components are configured in the same way. The first distortion compensator 16 shown in FIG. 2 functions in the same manner as the distortion compensator 15 shown in FIG. 9, but a more specific configuration will be described later with reference to FIG.

Referring to FIG. 2, the transmission apparatus 10 of this embodiment includes a data signal generator 11, a first distortion compensator 16, a waveform shaping section 13, a second distortion compensator 17, and a transmission signal generator. a portion 14;

The data signal generation unit 11 receives, as a main signal, transmission data that constitutes a digital signal with TS packets such as video, audio, and data broadcasting in the TS of each broadcaster, and information of the main signal is input as in the conventional technology. A coded bit sequence signal is generated by performing predetermined preprocessing including error correction coding processing on the bit sequence, mapping is performed using a mapping table based on a predetermined modulation method, and an IQ data signal (in-phase component I and a signal point sequence of quadrature phase component Q and can be expressed as signal points on the IQ plane).

The transmission preprocessing unit 111 receives transmission data constituting the digital signal as a main signal, allocates the main signal to modulation slots in units of blocks constituting a predetermined transmission frame, and generates the synchronization signal and the main signal allocated in units of blocks. Predetermined preprocessing including error correction coding processing is performed on the information bit sequence including the signal to generate a modulated slot signal of the coded bit sequence and output to mapping section 112 .

Mapping section 112 performs mapping on the modulation slot signal obtained from transmission preprocessing section 111 using a mapping table based on a predetermined modulation scheme, converts the signal into an IQ data signal, and outputs the signal to upsampling section 12 . Although not shown, a modulated slot for the TMCC signal is also generated in addition to the modulated slot for the main signal. The modulation scheme for the main signal is designated by control information indicated in the TMCC signal, and includes π/2 shift BPSK, QPSK, 8PSK, 16APSK, and 32APSK. Also, the modulation scheme for the TMCC signal is π/2 shift BPSK. Then, the signal of the modulation slot for the main signal of each modulation scheme and the signal of the modulation slot for the TMCC signal are transmitted by time-division multiplexing.

The first distortion compensator 16, which will be described later in detail with reference to FIG. 3, is constructed in the same manner as the distortion compensator 15 in the prior art shown in FIG. That is, the first distortion compensator 16 once up-samples the IQ data signal obtained from the mapping unit 112 to shape the waveform, and creates a table file approximating the input/output characteristics of the satellite transponder 2 of the actual satellite. is used to generate a signal that simulates the transmission path distortion caused by the satellite repeater 2, and the IQ signal points obtained by performing waveform shaping and downsampling so as to correspond to the original IQ data signal , the error vector is obtained by subtracting the corresponding signal points of the original IQ data from the original IQ performing a second vector operation for subtracting the error vector multiplied by a predetermined coefficient weight from the signal point of the data, generating a signal of IQ data subjected to distortion compensation by a first distortion compensation process of upsampling, and compensating for the distortion; The resulting IQ data signal is up-sampled and output to the waveform shaping section 13 .

Therefore, the transmission device 1 of the present embodiment includes the first distortion compensator 16 before the waveform shaping unit 13 to correct in advance the IQ signal point error caused by the satellite transponder 2 of the actual satellite. It has a function of generating a signal of IQ data distortion-compensated by the first distortion compensation processing. As a result, in the downlink signal (broadcast wave signal) radiated from the satellite repeater 2 of the actual satellite, the shift and spread of the IQ signal points caused by the satellite repeater 2 of the actual satellite are cancelled. On the other hand, it is possible to converge to the ideal signal point, and the required C/N on the receiving device 3 side can be improved.

The waveform shaping unit 13 performs predetermined band-limiting filter processing on the IQ data signal (including upsampled non-sample points) after the first distortion compensation processing obtained from the first distortion compensation unit 16. By doing so, waveform shaping is performed to remove unnecessary high frequency components, and a signal of IQ data after waveform shaping that has undergone the first distortion compensation processing is generated and output to the transmission signal generating section 14 . A digital filter having root roll-off characteristics is generally used as the band-limiting filter. In this embodiment, a root roll-all filter with a roll-all rate of 0.03 adopted in ISDB-S3 is used.

The second distortion compensator 17 applies the waveform-shaped IQ data signal that has undergone the first distortion compensation processing obtained from the waveform shaper 13 to the input of the earth station high power amplifier (HPA) 1a shown in FIG. Using a table file showing the values of the inverse components of the output characteristics (AM/AM characteristics and AM/PM characteristics), the errors in the IQ signal points caused by the high power amplifier (HPA) 1a of the earth station are corrected in advance. A distortion-compensated IQ data signal is generated by the second distortion compensation process and output to the transmission signal generator 14 .

Therefore, the transmission apparatus 1 of the present embodiment includes the second distortion compensator 17 after the waveform shaping section 13, thereby correcting the IQ signal point error due to the high power amplifier (HPA) 1a of the earth station in advance. It has a function of generating a distortion-compensated IQ data signal by a second distortion compensating process for correcting to . This not only cancels the shift and spread of the IQ signal points caused by the high power amplifier (HPA) 1a of the earth station, but also makes it possible to reduce the spectrum regrowth outside the Nyquist band in the uplink signal. .

The transmission signal generation unit 14 generates a modulated wave signal according to the predetermined modulation method for the signal of the IQ data distortion-compensated by the second distortion compensation processing obtained from the second distortion compensation unit 17, and the high power of the earth station. It is a functional unit that transmits to the amplifier (HPA) 1 a, and includes a quadrature modulation unit 141 , a DA (digital/analog) conversion unit 142 and a frequency conversion unit 143 .

The quadrature modulator 141 modulates the transmission path distortion caused by both the satellite transponder 2 of the real satellite and the high power amplifier (HPA) 1a of the earth station obtained from the second distortion compensator 17 before and after the waveform shaping unit 13, respectively. A baseband IQ signal based on quadrature modulation processing according to the predetermined modulation scheme is generated for the IQ data signal after compensation by , and output to the DA conversion unit 142 .

The DA conversion section 142 performs digital/analog conversion processing on the baseband IQ signal obtained from the quadrature modulation section 141 to generate a modulated wave signal, and outputs the modulated wave signal to the frequency conversion section 143 .

The frequency converter 143 frequency-converts the modulated wave signal obtained from the DA converter 142 into a modulated wave signal in the radio frequency band of the uplink signal, and transmits the modulated wave signal to the high power amplifier (HPA) of the earth station. For example, the radio frequency of the uplink signal in the ISDB-S3 satellite broadcasting transmission system is the 17 GHz band.

(First distortion compensator)
FIG. 3 is a block diagram showing a schematic configuration of the first distortion compensator 16 in the transmitter 1 of one embodiment according to the present invention. An upsampling section 167 corresponding to the upsampling section 12 shown in FIG.

The first distortion compensator 16 compensates for the transmission path distortion caused by the input/output characteristics of the TWTA in the satellite repeater 2 shown in FIG. 7 and the frequency response characteristics of the IMUX filter and the OMUX filter in the satellite repeater 2 shown in FIG. It is configured as a functional unit that performs a first distortion compensation process that corrects distortion in advance. The first distortion compensator 16 may be either before or after the waveform shaping unit 13 in terms of compensating for the transmission path distortion caused by the satellite transponder 2 of the actual satellite. For the following reason, it is necessary to provide it before the waveform shaping section 13 for operational reasons. The reason for this is that the distortion compensation target of the first distortion compensator 16 is the nonlinearity of the satellite repeater 2, and the uplink signal transmitted by the transmitter 1 is corrected so as to have the opposite characteristics of the nonlinearity. This is because a spectrum regrowth occurs at the output stage due to the state, and the uplink signal is generated in a state in which unnecessary wave components remain outside the band. By providing it in the preceding stage of the waveform shaping section 13, it is possible to uplink the signal while suppressing the unnecessary wave component outside the band sufficiently.

Hereinafter, the configuration of the first distortion compensator 16 will be described more specifically with reference to FIG. The first distortion compensation section 16 includes an upsampling section 161 , a waveform shaping section 162 , a pseudo satellite repeater 163 , a waveform shaping section 164 , a downsampling section 165 , an IQ distortion compensation calculation section 166 and an upsampling section 167 .

Upsampling section 161 upsamples the sample points of the IQ data signal obtained from mapping section 112 by a factor of two or more, and outputs the result to waveform shaping section 162 .

The waveform shaping section 162 is a digital filter having a root roll-over filter characteristic with a roll-over rate of 0.03, and it filters the upsampled IQ data signal including non-sampled points obtained from the upsampling section 161 into a predetermined band. Waveform shaping is performed to remove unnecessary high-frequency components by performing limiting filtering, and a signal of IQ data after waveform shaping is generated and output to the pseudo satellite repeater 163 .

The pseudo-satellite repeater 163 is a functional unit that performs signal processing using table files that respectively approximate the input/output characteristics of the IMUX filter 21, TWTA 22, and OMUX filter 23 in the satellite repeater 2 of the real satellite shown in FIG. It has a corresponding IMUX filter 1631 , TWTA 1632 and OMUX filter 1633 . That is, the pseudo-satellite repeater 163 uses a table file that approximates the input/output characteristics of the satellite repeater 2 of the actual satellite for the signal of the IQ data after waveform shaping obtained from the waveform shaping unit 162, 2, and outputs the signal to the waveform shaping section 164 . The input/output characteristics of the pseudo satellite transponder 163 are composed of a table file used for digital signal processing. As a result, the pseudo-satellite repeater 163 generates a signal point that simulates in advance the deviation of the signal point that can occur by the satellite repeater 2 with respect to the ideal signal point of the IQ data after the mapping of the signal point of the digital signal to be transmitted. Generate a signal of the IQ data possessed.

The waveform shaping section 164 is a digital filter having root roll-over filter characteristics with a roll-over rate of 0.03, like the waveform shaping section 162 . In particular, the waveform shaping section 164 is used to remove unnecessary waves on the receiving side, and since the modulated signal passes through the waveform shaping section 162 and the waveform shaping section 164, the roll-off characteristic is maintained when viewed in the entire transmission path. It has the role of theoretically setting the symbol interference at the sample point to zero.

The down-sampling unit 165 applies non-sampling points by the up-sampling unit 161 to the IQ data signal in which the transmission path distortion caused by the satellite transponder 2 after waveform shaping obtained from the waveform shaping unit 164 is artificially generated. are thinned out to perform down-sampling processing so as to correspond to the sample points of the signal of the original IQ data, and output to the IQ distortion compensation calculation unit 166 . For example, when the upsampling unit 161 performs double upsampling, the downsampling unit 165 thins out to 1/2. That is, considering the transmission system 1, an up-sampling unit 161, a waveform shaping unit 162, a pseudo satellite repeater 163, a waveform shaping unit 164, and a down-sampling unit 165 are assumed between the uplink signal and the downlink signal. It becomes a pseudo transmission line corresponding to the transmission line.

The IQ distortion compensation calculation unit 166 calculates the corresponding original IQ signal points from the IQ signal points of the IQ data obtained from the downsampling unit 165, in which the transmission path distortion caused by the satellite transponder 2 after downsampling is artificially generated. In order to obtain an error vector by performing a first vector operation for subtracting data signal points, and to use an inverse vector of the error vector viewed from the ideal signal point as a correction vector, a predetermined A functional unit for generating a signal of IQ data subjected to distortion compensation by a first distortion compensation process for performing a second vector operation for subtracting the error vector multiplied by the coefficient weight and performing upsampling. It has a vector calculation section 1662 , an inverse characteristic coefficient section 1663 and a second vector calculation section 1664 .

The delay unit 1661 combines the down-sampled IQ data signal obtained from the down-sampling unit 165 in which the transmission path distortion caused by the satellite transponder 2 is simulated and the original signal obtained from the data signal generation unit 11 . This is a functional unit that adjusts the timing in order to synchronize the signals of the two systems of the IQ data signals. That is, the delay unit 1661 generates the data signal with a delay amount D corresponding to the time required for processing up to the up-sampling unit 161, the waveform shaping unit 162, the pseudo satellite repeater 163, the waveform shaping unit 164, and the down-sampling unit 165. The signal of the original IQ data obtained from the unit 11 is input and delayed, and is output to the first vector calculation unit 1662 and the second vector calculation unit 1664 so as to synchronize the signals of the two systems. .

The first vector calculation unit 1662 calculates the corresponding original IQ signal points from the IQ signal points of the IQ data obtained from the downsampling unit 165, in which the transmission path distortion caused by the satellite transponder 2 after downsampling is artificially generated. An error vector is generated by performing the first vector operation for subtracting the signal points of the IQ data, and is output to the inverse characteristic coefficient section 1663 .

Inverse characteristic coefficient section 1663 multiplies the error vector obtained from first vector calculation section 1662 by a predetermined coefficient weight, and outputs the result to second vector calculation section 1664 . For example, the coefficient weight may be set to 1 and the inverse characteristic coefficient unit 1663 may be omitted. The weight is multiplied so that it can be fine-tuned.

Second vector calculation section 1664 uses the inverse vector of the error vector obtained by multiplying the predetermined coefficient weight obtained from inverse characteristic coefficient section 1663 from the ideal signal point as a correction vector. An error vector multiplied by the predetermined coefficient weight is subtracted from the corresponding original IQ data signal point after adjustment, thereby generating a distortion-compensated IQ data signal and outputting it to upsampling section 167 .

The upsampling unit 167 upsamples the sample points of the distortion-compensated IQ data signal obtained from the second vector calculation unit 1664 by a factor of two or more, and outputs the result to the waveform shaping unit 13 .

In this manner, the transmission apparatus 1 of the present embodiment includes the first distortion compensator 16 before the waveform shaping section 13, so that errors in the IQ signal points caused by the satellite transponder 2 of the actual satellite are corrected in advance. It has a function of generating a signal of IQ data that is distortion-compensated by a first distortion compensation process that corrects for distortion. As a result, in the downlink signal (broadcast wave signal) radiated from the satellite repeater 2 of the actual satellite, the shift and spread of the IQ signal points caused by the satellite repeater 2 of the actual satellite are cancelled. On the other hand, it is possible to converge to the ideal signal point, and the required C/N on the receiving device 3 side can be improved.

(Second distortion compensator)
As described above, the second distortion compensation section 17 applies the first distortion compensation processing obtained from the waveform shaping section 13 to the waveform-shaped IQ data signal, which is processed by the earth station high-power amplifier (see FIG. 6). Using a table file showing values that are inverse components of the input/output characteristics (AM/AM characteristics and AM/PM characteristics) of the HPA) 1a, the IQ signal point error caused by the high power amplifier (HPA) 1a of the earth station A signal of IQ data whose distortion is compensated by the second distortion compensation process for correcting in advance is generated and output to the transmission signal generation unit 14 .

The second distortion compensator 17 according to the present embodiment is configured to have a table file as shown in FIG. The AM/AM characteristics and AM/PM characteristics for the second distortion compensation processing in the second distortion compensator 17 shown in FIG. AM/AM characteristic and AM/PM characteristic) corrected to a value that is the inverse component. In FIG. 4, the AM/AM characteristic for the second distortion compensation process is obtained by inverting the gain of the AM/AM characteristic of the high power amplifier (HPA) 1a. Also, in FIG. 4, the AM/PM characteristic for the second distortion compensation processing is obtained by inverting the value of the AM/PM characteristic of the high power amplifier (HPA) 1a. As a result of the second distortion compensation processing in the second distortion compensator 17, the linearity of the input/output characteristics of the earth station high power amplifier (HPA) 1a including the second distortion compensator 17 is improved. And since the IQ data signal including non-sample points passes through the input/output characteristics, the uplink signal can be transmitted with reduced spectrum regrowth at the output stage of the high power amplifier (HPA) 1a of the earth station. becomes. Although out-of-band spectrum regrowth occurs in the output signal of the transmitter 1 due to the second distortion compensator 17, since the transmitter 1 and the high power amplifier (HPA) 1a are wired, this is not a problem. not. As a result, it is preferable that the spectral regrowth at the output stage of the high power amplifier (HPA) 1a is reduced more than without compensation.

It should be noted that the second distortion compensator 17 may be placed either before or after the waveform shaping section 13 only in terms of compensating for signal distortion within the band caused by the high power amplifier (HPA) 1a of the earth station. Although it may be provided, it must be provided after the waveform shaping section 13 in order to reduce the out-of-band spectrum regrowth of the high power amplifier (HPA) 1a. Furthermore, since the post-waveform shaping section 13 has a block configuration closer to the target transmission line (high power amplifier (HPA) 1a), distortion compensation with higher accuracy than the pre-stage can be expected. Furthermore, if the high power amplifier (HPA) 1a becomes an equivalent linear transmission path by the second distortion compensator 17, the compensation accuracy of the first distortion compensator 16, which targets the satellite repeater 2, is also improved. .

Therefore, the transmission apparatus 1 of the present embodiment includes the second distortion compensator 17 after the waveform shaping section 13, thereby correcting the IQ signal point error due to the high power amplifier (HPA) 1a of the earth station in advance. It has a function of generating a distortion-compensated IQ data signal by a second distortion compensating process for correcting to . This not only cancels the shift and spread of the IQ signal points caused by the high power amplifier (HPA) 1a of the earth station, but also makes it possible to reduce the spectrum regrowth outside the Nyquist band in the uplink signal. .

(Summary)
Here, the functions and effects of the present invention with respect to the conventional technology will be described in general.
As shown in FIG. 9, in a conventional transmitting apparatus 10A having a configuration in which distortion compensating means (distortion compensating section 15) is provided only before the waveform shaping section 13, waveform shaping is performed after distortion compensation by the distortion compensating section 15. However, the distortion compensator 15 alone could not reduce the spectrum regrowth outside the Nyquist band in the uplink signal. Since the satellite transponder 2 has the OMUX filter 23, it is not necessary to reduce the spectrum regrowth component of the TWTA 22 as DPD. Conversely, in a transmission device (not shown) having a configuration including only the second distortion compensator 17, since the out-of-band uplink signal is affected, distortion compensation for the satellite transponder 2 is positively performed as a pre-processing. Therefore, further efforts are needed to reduce the required C/N at the receiver side while reducing the out-of-band spectral regrowth of the uplink signal.

Therefore, as in the transmitting apparatus 1 of the present embodiment, by providing individual distortion compensating means (first distortion compensating section 16 and second distortion compensating section 17) before and after the waveform shaping section 13, The spectrum regrowth outside the Nyquist band in the uplink signal, which could not be solved by the conventional DPD (corresponding to the configuration having only the first distortion compensator 16), can be reduced by the second distortion compensator 17. becomes. Furthermore, according to the transmitting apparatus 1 of the present embodiment, the distortion compensation for the satellite transponder 2 can be performed by the first distortion compensator 16 as in the prior art without any adverse effects, so the required C/N as reception characteristics is also improved. As a result, it is possible to reduce the spectrum regrowth of the uplink signal and improve the reception performance. Further, according to the transmission device 1 of the present embodiment, in the process of simulating the characteristics of the broadcast transmission path in the first distortion compensator 16 and the second distortion compensator 17, it is possible to sequentially update by rewriting the table file. It is possible to provide high versatility to various transmission systems and broadcasting transmission lines without depending on the signal formats of various transmission systems.

Although the above-described embodiment has been described as a representative example, it will be apparent to those skilled in the art that many modifications and substitutions may be made within the spirit and scope of the invention. For example, in the above-described examples, typical input/output characteristics were illustrated and explained in FIGS. However, the input/output characteristics of the high power amplifier (HPA) 1a of the earth station and the satellite transponder 2 of the actual satellite that are actually used may be applied. Further, the first distortion compensator 16 and the second distortion compensator 17 in the embodiment of the present invention use, for example, a distortion compensating method utilizing the input/output characteristics of the transmission path. is not limited to this, the first distortion compensator 16 is a compensation method intended for the satellite transponder 2 (or a transmission line equivalent thereto), and the second distortion compensator 17 is a large power amplifier (HPA) 1a (or a corresponding transmission line) may be compensated. Accordingly, the present invention should not be construed as limited by the above-described embodiments, but only by the appended claims.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to reduce the spectrum regrowth of an uplink signal in satellite broadcasting and to improve the receiving performance, so that it is useful for satellite broadcasting transmission systems.

1 Transmission device according to the present invention 1a High power amplifier (HPA) of earth station
2 satellite repeaters 3, 3-1, 3-2, 3-n receivers 10, 10A prior art transmitters 11 data signal generator 12 up-sampling unit 13 waveform shaping unit 14 transmission signal generator 15 distortion compensator 16 First distortion compensator 17 Second distortion compensator 21 Input multiplexer (IMUX) filter 22 Traveling wave tube amplifier (TWTA)
23 output multiplexer (OMUX) filter 111 transmission preprocessing unit 112 mapping unit 141 quadrature modulation unit 142 digital/analog (DA) conversion unit 143 frequency conversion unit 161 upsampling unit 162 waveform shaping unit 163 pseudo satellite repeater 164 waveform shaping unit 165 Down-sampling unit 166 IQ distortion compensation calculation unit 167 Up-sampling unit 1631 Functional unit for processing approximate input/output characteristics of IMUX filter 1632 Functional unit for processing approximate input/output characteristics of TWTA 1633 Function for processing approximate input/output characteristics of OMUX filter Section 1661 Delay Section 1662 First Vector Calculation Section 1663 Inverse Characteristic Coefficient Section 1664 Second Vector Calculation Section

Claims (3)

A transmitting device for transmitting a digital signal to a receiving device via a broadcasting transmission line including a large power amplifier of an earth station and a satellite repeater in a satellite broadcasting transmission system,
Transmission data constituting the digital signal is input as a main signal, and predetermined preprocessing including error correction coding processing is performed on the information bit sequence of the main signal to generate a coded bit sequence signal, and a predetermined a data signal generation unit that performs mapping using a mapping table based on a modulation scheme and converts the signal into an IQ data signal represented by a signal point sequence of in-phase and quadrature phase components;
a first distortion compensator for generating a distortion-compensated IQ data signal by a first distortion compensating process for pre-compensating an error in an IQ signal point caused by the satellite transponder for the IQ data signal;
Waveform shaping is performed by applying a predetermined band-limiting filter process to the IQ data signal after the first distortion compensation process, and a waveform-shaped IQ data signal that has undergone the first distortion compensation process is generated. a waveform shaping section;
IQ data distortion-compensated by a second distortion compensation process for pre-correcting an error in the IQ signal point caused by the high-power amplifier of the earth station for the signal of the IQ data after waveform shaping that has undergone the first distortion compensation process a second distortion compensator that generates a data signal;
a transmission signal generation unit that generates a modulated wave signal according to the predetermined modulation method for the IQ data signal distortion-compensated by the second distortion compensation processing, and transmits the modulated wave signal to the large power amplifier of the earth station;
A transmitting device comprising: As the first distortion compensation processing, the first distortion compensating unit upsamples and waveform-shapes the IQ data signal obtained from the data signal generating unit once, and inputs and outputs the signals to and from the satellite transponder. Using a table file whose characteristics are approximated, a signal is generated in which transmission path distortion caused by the satellite transponder is artificially generated, waveform shaping is performed, and the signal is down-sampled so as to correspond to the original IQ data signal. To obtain an error vector by performing a first vector operation of subtracting a corresponding original IQ data signal point from an obtained IQ signal point, and to use an inverse vector of the error vector viewed from the ideal signal point as a correction vector. , performs a second vector operation for subtracting the error vector multiplied by a predetermined coefficient weight from the signal point of the original IQ data, performs upsampling processing, and performs an error of the IQ signal point caused by the satellite repeater. 2. A transmitter as claimed in claim 1, characterized in that it comprises means for generating a signal of distortion-compensated IQ data by pre-correcting . As the second distortion compensation process, the second distortion compensator performs the waveform-shaping IQ data signal that has undergone the first distortion compensation process, and performs the inverse input/output characteristics of the high-power amplifier of the earth station. It is characterized by having means for generating a distortion-compensated IQ data signal by correcting in advance an error in the IQ signal points caused by the high-power amplifier of the earth station using a table file showing component values. 3. The transmission device according to claim 1 or 2, wherein

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