Transmission system and program

Abstract

To realize a distortion compensating function while reducing a hardware scale.SOLUTION: A transmission device 100 comprises a mapping unit 102 that generates an IQ signal in which a digital signal is modulated by a prescribed modulation technique, a QRRF unit 106 that carries out first waveform reshaping on the IQ signal by a fourth root roll-off filter, and a D / A conversion unit 105 that D / A converts the IQ signal after first waveform reshaping and outputs as a modulated wave signal to a signal processing device 200. The signal processing device 200 comprises an A / D conversion unit 201 that A / D converts the modulated wave signal outputted from the transmission device 100, a pseudo-transmitter 202 that adds a signal component that compensates a transmission line distortion by a prescribed transmitter, a QRRF unit 203 that carries out second waveform reshaping on the signal having passed through the pseudo-transmitter 202 by the fourth root roll-off filter, and a D / A conversion unit 204 that D / A converts the signal after second waveform reshaping and outputs to the prescribed transmitter.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a transmission system and a program.

Background Art

[0002] Among various standards of digital broadcasts currently in operation, taking satellite broadcast as an example, using a transmitter (satellite repeater) provided in a broadcast satellite, multiple broadcasters can transmit independent TS (Transport Stream)s, and thus broadcast wave signals are multiplexed. Standards already adopted in satellite digital broadcasts include ISDB-S, ISDB-S3, DVB-S2, DVB-S2X, and the like.

[0003] FIG. 4 is a diagram showing a configuration example of a conventional satellite broadcast system 1A. The satellite broadcast system 1A shown in FIG. 4 includes a transmission device 2, a satellite repeater 3, and a plurality of reception devices 4 (reception devices 4-1 to 4-N (N is a natural number of 1 or more)). Note that the transmission device 2 will be described as a general transmission device conforming to various standards of the above-described satellite digital broadcast.

[0004] The transmission device 2 generates a modulated wave signal based on a predetermined modulation method specified by control information such as a TMCC (Transmission and Multiplexing Configuration Control) signal, and transmits a main signal obtained by multiplexing video, audio, data signals, etc. to the satellite repeater 3. As the modulation method, for example, in the case of the ISDB-S3 method which is a satellite broadcast digital standard, there are BPSK including π / 2 shift BPSK (Binary Phase Shift Keying), QPSK including π / 4 shift QPSK (Quadrature Phase Shift Keying), 8PSK, 16APSK (Amplitude Phase Shift Keying), and 32APSK. The modulated wave signal generated by the transmission device 2 is converted to a predetermined frequency band and then uplinked toward the actual satellite (satellite repeater 3).

[0005] The satellite transponder 3 is a transmitter that transmits the modulated wave signal transmitted from the transmitting device 2. The satellite transponder 3 comprises a traveling wave tube amplifier (hereinafter referred to as "TWTA") 32, an input multiplexer filter (hereinafter referred to as "IMUX filter") 31 which is an input filter placed before the TWTA 32, and an output multiplexer filter (hereinafter referred to as "OMUX filter") 33 which is an output filter placed after the TWTA 32.

[0006] The IMUX filter 31 is a band-pass filter corresponding to each channel frequency. The IMUX 31 suppresses unwanted frequency components from the modulated wave signal (broadcast wave signal) received from the transmitter 2, and extracts only the band component for one channel. The TWTA 32 amplifies the power of the broadcast wave signal for one channel extracted by the IMUX 31. The OMUX filter 33 is a band-pass filter corresponding to each channel frequency. The OMUX filter 33 suppresses unwanted frequency components from the signal amplified by the TWTA 32, and extracts only the band component for one channel. After the suppression of unwanted frequency components by the OMUX filter 33, the broadcast wave signals for all channels are combined by a subsequent combiner (not shown) following the OMUX filter 33 and transmitted from the antenna (not shown) to the receivers 4-1 to 4-N. An example of the input / output characteristics (AM / AM characteristics and AM / PM characteristics) of the TWTA 32 is shown in Figure 5. Furthermore, an example of the response characteristics (frequency vs. amplitude characteristics and frequency vs. group delay characteristics) of the IMUX filter 31 and OMUX filter 33 is shown in Figure 6.

[0007] The receiving devices 4-1 to 4-N constantly monitor control information such as TMCC signals transmitted along with the multiplexed broadcast wave signals, enabling them to switch reception methods and other settings in response to various transmission controls performed by the transmitting device 2.

[0008] In the TWTA32, the input / output power and phase shift characteristics may cause a deviation from the desired IQ signal point. In addition, in the IMUX filter 31 and OMUX filter 33, the frequency amplitude and group delay characteristics may cause intersymbol interference, resulting in a spread from the desired signal point. Within the transmission line, the deviation and spread of the IQ signal point mutually affect each other, resulting in an increase in the required C / N and a deterioration of transmission quality (see, for example, Non-Patent Document 1). Furthermore, when using a multi-level amplitude phase modulation scheme such as 16APSK or 32APSK as the modulation scheme, power amplifiers such as the TWTA32 of the satellite transponder 3 are generally backed off (operated with a reduced input level and reduced output level).

[0009] Here, we will explain backoff in the TWTA32. It is desirable for the TWTA32 to perform power amplification processing so that the relationship between the input level and the output level is proportional. However, the input / output characteristics of the TWTA32 actually exhibit nonlinearity, where the gain decreases as the input level increases, and the phase of the output signal rotates relative to the input signal. Therefore, when the input level is gradually increased, the output level also increases up to a certain level, but beyond that input level, the output level decreases. The operating point just before such a decrease in output level occurs is generally called the output saturation point. When the input level is reduced by X [dB] from the output saturation point and the device is operated, it is called "input backoff X [dB]", and when the input level is reduced and the output level is lowered by Y [dB] and the device is operated, it is called "output backoff Y [dB]".

[0010] By taking a backoff, the output voltage decreases, and as a result, the receiving C / N margin in the receiving device 4 becomes smaller (see Non-Patent Literature 1). The receiving side of satellite broadcasting systems generally has a small receiving antenna aperture diameter of 45 cm, and even in clear weather, the receiving C / N margin is small, about 20 dB. Therefore, there is a trade-off relationship between the required C / N and the output backoff, and it is advantageous in circuit design to operate in a way that minimizes the sum of the required C / N and the output backoff.

[0011] The receiving device 4 constantly monitors control information such as TMCC signals transmitted along with the multiplexed broadcast wave signals, enabling it to switch reception methods and other settings in response to various transmission controls performed by the transmitting device 2.

[0012] Patent Document 1 describes a transmitting device equipped with a distortion compensation function that compensates for distortion generated in a satellite transponder. In the transmitting device described in Patent Document 1, the transmission path distortion generated in the satellite transponder 3 is pre-generated in the digital signal processing stage by adding the characteristics of a pseudo-transmission path that simulates the satellite transponder 3. Subsequently, the signal point is corrected by vector calculation so that it becomes the inverse vector of the distortion vector as seen from the ideal signal point (hereinafter referred to as the "ideal signal point"). In this way, the shift and spread of the IQ signal point in the actual transmission path are canceled out, so that the signal point on the receiving side can be converged to the ideal signal point.

[0013] Furthermore, Patent Document 2 describes a configuration in which a signal processing device with a distortion compensation function (external distortion compensation device) is installed after a general-purpose transmitter that does not have a distortion compensation function, with the aim of improving the versatility of distortion compensation. In the configuration described in Patent Document 2, the modulated wave signal generated by the transmitter is input to the external distortion compensation device. The external distortion compensation device performs A / D conversion on the input modulated wave signal, adds the inverse characteristics of transmission line distortion to the digital signal after A / D conversion, removes out-of-band unwanted wave components due to compensation using a band-limiting filter, and then performs D / A conversion. In this way, the external distortion compensation device described in Patent Document 2 can reduce the degradation of the required C / N due to the transmission line. Non-Patent Document 2 demonstrates the effectiveness of the configuration shown in Patent Document 2. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Patent No. 6681672 [Patent Document 2] Japanese Patent Publication No. 2021-164098 [Non-patent literature]

[0015] [Non-Patent Document 1] IEICE Technical Report SAT2019-53 [Non-Patent Document 2] IEICE Technical Report SAT2021-52 [Overview of the Initiative] [Problems that the invention aims to solve]

[0016] In the satellite broadcasting system described above, the transmitting equipment is required to implement distortion compensation while reducing the hardware size.

[0017] The object of the present invention is to solve the above-mentioned problems and to provide a transmission system and program that can implement distortion compensation while reducing the hardware size. [Means for solving the problem]

[0018] To solve the above problems, a transmission system according to the present invention includes a transmission device that generates a modulated wave signal in which a digital signal is modulated by a predetermined modulation method, and a signal processing device that adds a signal component for compensating for transmission line distortion caused by a predetermined transmission line through which the modulated wave signal is transmitted to the modulated wave signal. The transmission device includes a mapping unit that generates an IQ signal obtained by modulating the digital signal by the predetermined modulation method, a first waveform shaping unit that performs first waveform shaping on the IQ signal using a fourth root root roll-off filter, and a D / A conversion unit that performs D / A conversion on the IQ signal after the first waveform shaping and outputs the result to the signal processing device as the modulated wave signal. The signal processing device includes an A / D conversion unit that performs A / D conversion on the modulated wave signal output from the transmission device, a pseudo transmitter that has an inverse characteristic of a characteristic of a predetermined transmitter on the transmission line and adds a signal component for compensating for transmission line distortion caused by the predetermined transmitter when the signal after A / D conversion by the A / D conversion unit passes through, a second waveform shaping unit that performs second waveform shaping on the signal that has passed through the pseudo transmitter using a fourth root root roll-off filter, and a D / A conversion unit that performs D / A conversion on the signal after the second waveform shaping and outputs the result to the predetermined transmitter.

[0019] Also, to solve the above problems, a program according to the present invention causes a computer to operate as the above-described transmission device.

[0020] Also, to solve the above problems, a program according to the present invention causes a computer to operate as the above-described signal processing device.

Advantages of the Invention

[0021] According to the transmission system and program of the present invention, it is possible to realize a distortion compensation function while reducing the hardware scale.

Brief Description of the Drawings

[0022] [Figure 1] It is a diagram showing a configuration example of a satellite broadcast system including a transmission system according to an embodiment of the present invention. [Figure 2]Figure 1 shows an example configuration of a transmitting device and signal processing device. [Figure 3] Figures 2 and 9 show the spectral characteristics of the output signals of the signal processing devices shown. [Figure 4] This is a diagram showing an example of a satellite broadcasting system configuration. [Figure 5] This diagram shows an example of the characteristics of TWTA. [Figure 6] This figure shows an example of the characteristics of IMUX filters and OMUX filters. [Figure 7] This figure shows an example of the configuration of a conventional transmitter that does not have a distortion compensation function. [Figure 8] This figure shows an example of the configuration of a conventional transmitting device equipped with a distortion compensation function. [Figure 9] This diagram shows an example configuration of a conventional signal processing device (external distortion compensation device). [Figure 10] Figure 9 shows an example of the characteristics of a pseudo-transmitter. [Modes for carrying out the invention]

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0024] First, for comparison, we will describe the configuration of a conventional transmitter 10 without a distortion compensation function, the configuration of a conventional transmitter 300 with a distortion compensation function as disclosed in Patent Document 1, and the configuration of a conventional signal processing device (external distortion compensation device) 400 as disclosed in Patent Document 2, referring to Figures 7 to 9. First, we will describe the configuration of a conventional transmitter 10 without a distortion compensation function.

[0025] Figure 7 shows an example configuration of the transmitting device 10. The transmitting device 10 is, for example, a general transmitting device compliant with the ISDB-S3 system.

[0026] As shown in Figure 7, the transmitting device 10 comprises an S / P conversion unit 101, a mapping unit 102, a U / S unit 103, a root roll-off filter unit (hereinafter referred to as the "RRF unit") 104, and a D / A conversion / quadrature modulation unit 105.

[0027] The S / P conversion unit 101 receives the digital signal to be transmitted (a serial sequence of information bits) as input. The S / P conversion unit 101 converts the input digital signal bit by bit into a parallel bit sequence corresponding to the number of bits used for mapping by the mapping unit 102 (for example, 5 bits if the modulation scheme is 32APSK), and outputs it to the mapping unit 102.

[0028] The mapping unit 102 maps the parallel bit sequence output from the S / P conversion unit 101 onto the IQ plane using a predetermined modulation scheme (π / 2 shift BPSK, QPSK, 8PSK, 16APSK, 32APSK, etc.) to produce an IQ signal (IQ data ) is generated and output to the U / S unit 103.

[0029] The U / S unit 103 performs upsampling of the sample points of the IQ signal output from the mapping unit 102 by more than 2x (interpolating the gaps between sample points with non-sample points). In the following, the U / S unit 103 will be assumed to perform upsampling by 2x.

[0030] The RRF section 104 performs waveform shaping by band-limiting filtering on the IQ signal, which includes non-sampled points and has been upsampled by a factor of 2 by the U / S section 103. Generally, a digital filter with root roll-off characteristics is used for band-limiting filtering. The root roll-off characteristics are based on the theoretical formula for roll-off characteristics (Nyquist theorem), resulting in a root root (√R(f)) at the transmitting side and a root root (√R(f)) at the receiving side. Since these are multiplied together in the transmission path, reception without intersymbol interference is possible at the receiving side, satisfying the Nyquist theorem (R(f)) shown in equation (1) below.

[0031]

number

[0032] In equation (1), f is the frequency, T is the symbol period, and α is the roll-off rate (for example, 0.03 in this embodiment).

[0033] The D / A conversion and quadrature modulation unit 105 performs D / A conversion on the signal after waveform shaping by the RRF unit 104, and quadrature modulates the D / A converted signal to generate a modulated wave signal.

[0034] Next, the configuration of a conventional transmitter 300 equipped with a distortion compensation function will be described. Figure 8 shows an example of the configuration of a conventional transmitter 300 equipped with a distortion compensation function.

[0035] As shown in Figure 8, the conventional transmitter 300 equipped with a distortion compensation function comprises an S / P conversion unit 301, a mapping unit 302, U / S units 303, 312, RRF units 304, 306, 313, a pseudo-transmitter 305, a D / S unit 307, a delay unit 308, a vector summing unit 309, 311, an inverse characteristic coefficient unit 310, and a D / A conversion / quadrature modulation unit 314. The delay unit 308, the vector summing units 309, 311, and the inverse characteristic coefficient unit 310 constitute a vector calculation unit 315.

[0036] The S / P conversion unit 301 receives the digital signal to be transmitted (a serial sequence of information bits) as input. The S / P conversion unit 301 converts the input digital signal bit by bit into a parallel bit sequence corresponding to the number of bits used for mapping by the mapping unit 302 (for example, 5 bits if the modulation scheme is 32APSK), and outputs it to the mapping unit 302.

[0037] The mapping unit 302 maps the parallel bit sequence output from the S / P conversion unit 301 onto the IQ plane using a predetermined modulation scheme (π / 2 shift BPSK, QPSK, 8PSK, 16APSK, 32APSK, etc.) to produce an IQ signal (IQ data ) is generated and output to the U / S unit 303 and the delay unit 308.

[0038] The U / S unit 303 performs upsampling of the sample points of the IQ signal output from the mapping unit 302 by more than 2 times, and outputs the upsampled IQ signal to the RRF unit 304.

[0039] The RRF unit 304 processes the IQ signal after upsampling by the U / S unit 303 using a bandwidth-limiting filter, similar to the RRF unit 104 described with reference to Figure 7, and outputs the bandwidth-limiting filter-processed IQ signal to the pseudo-transmitter 305.

[0040] The pseudo-transmitter 305 generates a signal that simulates the signal that would occur if the IQ signal output from the RRF unit 304 passed through the satellite repeater (transmitter) 3, and outputs it to the RRF unit 306. The pseudo-transmitter 305 includes a pseudo-IMUX filter 31a, a pseudo-TWTA 32a, and a pseudo-OMUX filter 33a. The pseudo-IMUX filter 31a has a characteristic value that approximates the characteristics of the IMUX filter 31 shown in Figure 6, and extracts only the bandwidth component of one channel from the signal output from the RRF unit 304. The pseudo-TWTA 32a has a characteristic value that approximates the characteristics of the TWTA 32 shown in Figure 5, and amplifies the power of the bandwidth component signal of one channel extracted by the pseudo-IMUX filter 31a. The pseudo-OMUX filter 33a has characteristic values ​​that approximate the characteristics of the OMUX filter 33 shown in Figure 6, and suppresses unwanted frequency components from the signal amplified by the TWTA 32a, extracting and outputting only the bandwidth component for one channel. As a result, the pseudo-transmitter 305 can output an IQ signal that has a signal point that simulates the signal point shift that may occur due to the satellite repeater 3 relative to the ideal signal point after mapping the signal points of the digital signal to be transmitted.

[0041] The RRF unit 306 processes the IQ signal output from the pseudo-transmitter 305 using a bandwidth-limiting filter to shape the waveform, and outputs the bandwidth-limiting filter-processed IQ signal to the D / S unit 307.

[0042] The D / S unit 307 removes IQ signal points, including non-sampled points, from the IQ signal output from the RRF unit 306 (performing downsampling) to return to the original signal before upsampling by the U / S unit 303. For example, if the U / S unit 303 has performed a 2x upsampling, the D / S unit 307 removes half the signal points output from the RRF unit 306. The D / S unit 307 outputs the downsampled IQ signal to the vector summer unit 309.

[0043] The delay unit 308 delays the IQ signal output from the mapping unit 302 and outputs it to the vector adders 309 and 311 in order to synchronize the two sets of signals input to the vector adders 309 and 311. In other words, the delay unit 308 delays the IQ signal output from the mapping unit 302 by the same amount of delay as the delay caused by the pseudo-transmitter 305 and RRF unit 306, and outputs it to the vector adders 309 and 311.

[0044] The vector summer 309 adds the signal point vector of the IQ (IQ signal after passing through the pseudo-transmitter 305) output from the D / S unit 307 and the signal point vector of the IQ signal output from the delay unit 308, and outputs the result to the inverse characteristic coefficient unit 310. Here, the vector summer 309 inverts the sign of the input on the delay unit 308 side. Therefore, the vector summer 309 outputs an error vector to the inverse characteristic coefficient unit 310 obtained by subtracting the signal point vector of the IQ signal output from the delay unit 308 from the signal point vector of the IQ signal output from the D / S unit 307. As described above, the IQ signal output from the D / S unit 307 is a signal that contains distortion caused by the mapping signal passing through the pseudo-transmitter 305. Also, the IQ signal output from the delay unit 308 is a signal that is synchronized with the IQ signal output from the D / S unit 307. Therefore, the vector summing unit 309 outputs the distortion component generated by passing through the pseudo-transmitter 305 as an error vector to the inverse characteristic coefficient unit 310.

[0045] The inverse characteristic coefficient unit 310 multiplies the error vector output from the vector summing unit 309 by a predetermined coefficient (for example, 1) and outputs it to the vector summing unit 311.

[0046] The vector summer 311 adds the signal point vector of the IQ signal output from the delay unit 308 to an error vector multiplied by a predetermined coefficient by the inverse characteristic coefficient unit 310. Here, the vector summer 311 inverts the sign of the input on the inverse characteristic coefficient unit 310 side. Therefore, the vector summer 311 outputs a signal to the U / S unit 312 obtained by subtracting the error vector multiplied by a predetermined coefficient from the signal point vector of the IQ signal output from the delay unit 308. As described above, the IQ signal output from the delay unit 308 is a signal synchronized with the IQ signal output from the D / S unit 307. The error vector is a distortion component caused by the mapping signal passing through the pseudo-transmitter 305. Therefore, the vector summer 311 outputs a signal as a distortion compensation signal that corrects the distortion caused by passing through the pseudo-transmitter 305 (by adding the inverse characteristics of the pseudo-transmitter 305) to the mapping signal.

[0047] The U / S unit 312 performs upsampling of the sample points of the IQ signal output from the vector summing unit 311 by more than 2 times, and outputs the upsampled IQ signal to the RRF unit 313.

[0048] The RRF unit 313 performs waveform shaping on the IQ signal after upsampling by the U / S unit 312 using a band-limiting filter, and outputs the signal after the band-limiting filter processing to the D / A conversion / quadrature modulation unit 314.

[0049] The D / A conversion and quadrature modulation unit 314 performs D / A conversion on the signal output from the RRF unit 313, quadrature modulates the D / A converted signal, and outputs it as a modulated wave signal.

[0050] In the conventional transmitter 300 equipped with a distortion compensation function, as explained with reference to Figure 8, it is necessary to add the U / S unit 303, pseudo-transmitter 305, RRF unit 306, D / S unit 307, and vector calculation unit 315 compared to the conventional transmitter 10 which does not have a distortion compensation function, which leads to an increase in hardware size.

[0051] Next, the configuration of a conventional signal processing device (external distortion compensation device) 400 will be described. Figure 9 shows an example of the configuration of a conventional signal processing device 400.

[0052] As shown in Figure 9, the conventional signal processing device 400 includes an A / D conversion unit 201, a pseudo-transmitter 202, a bandwidth limiting filter 401, and a D / A conversion unit 204.

[0053] The A / D converter 201 receives a modulated wave signal generated by a conventional transmitter 10 that does not have a distortion compensation function. The transmitter 10 and the signal processing device 400 are connected, for example, by an IF signal cable. The A / D converter 201 receives the modulated wave signal from the transmitter 10 via the IF signal cable. The A / D converter 201 performs A / D conversion on the input modulated wave signal and outputs the IQ signal after A / D conversion to the pseudo-transmitter 202.

[0054] The pseudo-transmitter 202 has characteristics that are the inverse of those of a predetermined transmitter (satellite repeater 3) on the transmission path. For example, as shown in Figure 10, the pseudo-transmitter 202 has characteristics that are the inverse of the input / output characteristics (AM / AM characteristics and AM / PM characteristics) of the TWTA32 shown in Figure 5. That is, the input / output characteristics of the pseudo-transmitter 202 shown in Figure 10 are characteristics corrected to values ​​that are the inverse components of the AM / AM characteristics and AM / PM characteristics (Figure 5) of the TWTA32. Specifically, the AM / AM characteristics of the pseudo-transmitter 202 are characteristics in which the gain of the AM / AM characteristics of the TWTA32 is inverted. Also, the AM / PM characteristics of the pseudo-transmitter 202 are characteristics in which the sign of the AM / PM characteristics of the TWTA32 is inverted.

[0055] Referring again to Figure 9, the pseudo-transmitter 202 passes the A / D-converted IQ signal output from the A / D conversion unit 201 through to the band-limiting filter 401. By passing through the pseudo-transmitter 202, the inverse characteristics of the transmitter on the transmission path are added to the IQ signal. By adding the inverse characteristics of the transmitter on the transmission path to the IQ signal, the transmission path distortion caused by the predetermined transmitter on the transmission path is compensated for. In this way, the pseudo-transmitter 202 has the inverse characteristics of the characteristics of the predetermined transmitter on the transmission path (for example, the TWTA32 of the satellite repeater 3), and by passing the signal after A / D conversion by the A / D conversion unit 201 through it, it adds a signal component that compensates for the transmission path distortion caused by the predetermined transmitter.

[0056] The band-limiting filter 401 suppresses out-of-band unwanted signals generated by the nonlinear characteristics (Figure 10) of the pseudo-transmitter 202 from the IQ signal output from the pseudo-transmitter 202. Here, the transmitting device 10 performs waveform shaping using a digital filter with root roll-off characteristics. Therefore, if suppression is not performed in the bandwidth of ((1+α) / 2T)≦|f|, it may affect the quality of the digital signal and, as a result, cause a deterioration of the required C / N ratio. For example, in Non-Patent Literature 2, a band-limiting filter is designed with a passband of 35 MHz for the Nyquist bandwidth of ISDB-S3 (33.7561 MHz).

[0057] The band-limiting filter 401 outputs the IQ signal, after suppression of out-of-band unwanted signals, to the D / A converter 204.

[0058] The D / A converter 204 performs D / A conversion on the IQ signal output from the band-limiting filter 401 and transmits it as a modulated wave signal to the satellite transponder 3 (uplink).

[0059] Next, the configuration of the satellite broadcasting system 1, including the transmission system 5 according to one embodiment of this disclosure, will be described.

[0060] Figure 1 shows an example configuration of a satellite broadcasting system 1 including a transmission system 5 according to this embodiment. In Figure 1, components similar to those in Figure 4 are denoted by the same reference numerals, and their descriptions are omitted.

[0061] The transmission system 5 according to this embodiment generates a modulated wave signal obtained by modulating the digital signal to be transmitted using a predetermined modulation scheme, and transmits it to the satellite transponder 3. As shown in Figure 1, the transmission system 5 comprises a transmission device 100 and a signal processing device 200.

[0062] The transmitting device 100 generates a modulated wave signal in which the digital signal to be transmitted is modulated using a predetermined modulation scheme, and outputs it to the signal processing device 200.

[0063] The signal processing device 200 adds a signal component to the modulated wave signal to compensate for transmission path distortion in a predetermined transmission path (in the example of Figure 1, the satellite transponder 3) through which the modulated wave signal is transmitted, and transmits it to the satellite transponder 3. The signal processing device 200 is, for example, a device that can be attached externally to the transmitting device 100, and can perform distortion compensation on the modulated wave signal generated by the transmitting device 100 regardless of the transmission method in the transmitting device 100.

[0064] Next, the configuration of the transmitting device 100 and the signal processing device 200 will be described. Figure 2 is a diagram showing an example of the configuration of the transmitting device 100 and the signal processing device 200. In Figure 2, components similar to those in Figure 9 are denoted by the same reference numerals and their descriptions are omitted. First, the configuration of the transmitting device 100 will be described.

[0065] As shown in Figure 2, the transmitting device 100 according to this embodiment includes an S / P conversion unit 101, a mapping unit 102, a U / S unit 103, a QRRF unit 106, and a D / A conversion / quadrature modulation unit 105. The transmitting device 100 according to this embodiment differs from the conventional transmitting device 10 shown in Figure 9 in that the RRF unit 104 has been replaced with a QRRF unit 106.

[0066] The QRRF unit 106, acting as the first waveform shaping unit, performs waveform shaping on the IQ signal generated by the mapping unit 102 (the IQ signal after upsampling by the U / S unit 103) by band-limiting filtering. Here, the QRRF unit 106 performs waveform shaping (first waveform shaping) using a fourth root root roll-off filter. Therefore, the transfer function of the QRRF unit 106 is ( 4 The result is √R(f). Since R(f) is a positive real number less than or equal to 1, the signal after waveform shaping by the QRRF unit 106 retains higher frequency-amplitude components than the signal after waveform shaping by the RRF. The output from the QRRF unit 106 is assumed to have normalized power. The QRRF unit 106 outputs the waveform-shaped IQ signal (first waveform-shaped IQ signal) to the D / A conversion / quadrature modulation unit 105. The waveform-shaped IQ signal (first waveform-shaped IQ signal) output to the D / A conversion / quadrature modulation unit 105 is D / A converted, the D / A converted signal is quadrature-modulated, and output as a modulated wave signal to the signal processing device 200.

[0067] Next, the configuration of the signal processing device 200 according to this embodiment will be described.

[0068] As shown in Figure 2, the signal processing device 200 according to this embodiment comprises an A / D conversion unit 201, a pseudo-transmitter 202, a QRRF unit 203, and a D / A conversion unit 204. The signal processing device 200 according to this embodiment differs from the conventional signal processing device 400 shown in Figure 9 in that the band-limiting filter 401 has been replaced with a QRRF unit 203.

[0069] The QRRF unit 203, acting as a second waveform shaping unit, performs waveform shaping on the signal that has passed through the pseudo-transmitter 202 by bandwidth-limiting filtering. Here, the QRRF unit 203 performs waveform shaping (second waveform shaping) using a fourth-root root roll-off filter. Therefore, the transfer function of the QRRF unit 203 is ( 4 The result is √R(f). Since R(f) is a positive real number less than or equal to 1, the signal after waveform shaping by the QRRF unit 203 retains higher frequency-to-amplitude components than the signal after waveform shaping by the RRF unit.

[0070] Band-limiting filtering by QRRF units 106 and 203 results in a modulated wave signal output from the transmission system 5 (signal processing device 200) having a spectrum with root roll-off characteristics (√R(f)). Therefore, the receiving side can transmit a modulated wave signal such that the Nyquist theorem in equation (1) is satisfied. In other words, the transmission system 5 according to this embodiment can perform distortion compensation in the same way as a conventional transmission device 300 equipped with a distortion compensation function.

[0071] Furthermore, in this embodiment, since the signal that has passed through the pseudo-transmitter 202 is subjected to a bandwidth-limiting filter by the QRRF unit 203, the output signal of the signal processing device 200 has a reduced possibility of remaining out-of-band unwanted signals compared to the output signal of the signal processing device 400 shown in Figure 9.

[0072] Furthermore, the configuration of the transmitting device 100 according to this embodiment only requires changing the RRF section 104 in the conventional transmitting device 10, which does not have a distortion compensation function, to a QRRF section 106. Also, according to the transmitting device 100 according to this embodiment, unlike the conventional transmitting device 300 which has a distortion compensation function, there is no need to add the U / S section 303, pseudo-transmitter 305, RRF section 306, D / S section 307, and vector calculation section 315 to the conventional transmitting device 10, and thus it does not lead to an increase in hardware size. Furthermore, the configuration of the signal processing device 200 according to this embodiment only requires changing the band-limiting filter 401 in the conventional signal processing device 400 to a QRRF section 203.Therefore, according to the transmitting system 5 according to this embodiment, which consists of the transmitting device 100 and the signal processing device 200, it is possible to realize a distortion compensation function while reducing the hardware size.

[0073] The IQ signal input to the pseudo-transmitter 202 is preferably the IQ signal after bandwidth limiting filtering by the bandwidth limiting filter 401, as shown in Figure 9. However, the IQ signal after bandwidth limiting filtering by the QRRF unit 203 can also be handled approximately. Below, we verify that the reception performance is not affected even when bandwidth limiting filtering is performed by the QRRF units 106 and 203, in conjunction with the spectral characteristics of the output signals of the signal processing device 200 according to this embodiment and the conventional signal processing device 400.

[0074] The transmission parameters of the modulated wave signal conformed to ISDB-S3, with a modulation scheme of 32APSK and a coding rate of 3 / 4. Furthermore, the operating point of the TWTA32 shown in Figure 1 was set to an input backoff (IBO) of 3.46 dB. The operating point of the pseudo-transmitter 202 shown in Figure 2 was also set to the same value.

[0075] As shown in Figure 7, when satellite transmission was performed using a conventional transmitter 10 without distortion compensation, the output backoff (OBO) of the satellite repeater 3 was 2.2 dB, and the required C / N after reception was 14.3 dB. From a circuit design perspective, it is advantageous to operate in a way that minimizes the sum of the required C / N and OBO (required C / N + OBO). Therefore, when the conventional transmitter 100 was evaluated using required C / N + OBO, it was 16.5 dB.

[0076] In contrast, when satellite transmission was performed using the transmission system consisting of the transmitter 10 and signal processing device 400 shown in Figure 9, the OBO was 2.6 dB, the required C / N was 13.2 dB, and the required C / N + OBO was 15.8 dB. Therefore, the transmission system shown in Figure 9 showed an improvement of 0.7 dB compared to the conventional transmitter 10 shown in Figure 7, which does not have a distortion compensation function.

[0077] Furthermore, when satellite transmission was performed using the transmission system 5 according to this embodiment, the OBO was 2.6 dB, the required C / N was 13.2 dB, and the required C / N + OBO was 15.8 dB. Therefore, the transmission system 5 according to this embodiment achieved performance equivalent to that of the transmission system shown in Figure 9.

[0078] Figure 3 shows the spectral characteristics of the output signals of the signal processing device 400 shown in Figure 9 and the signal processing device 200 according to this embodiment. In Figure 3, a filter with a passband of 35 MHz described in Non-Patent Literature 2 was used as the band-limiting filter 401 of the signal processing device 400.

[0079] As shown in Figure 3, while the output signal of the conventional signal processing device 400 includes out-of-band unwanted signals, it was confirmed that these out-of-band unwanted signals are removed from the output signal of the signal processing device 200 according to this embodiment.

[0080] Although not specifically mentioned in the embodiments, a program may be provided that causes the computer to operate as a transmitting device 100 or a signal processing device 200. The program may also be recorded on a computer-readable medium. Using a computer-readable medium allows for installation on the computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may include, for example, a CD-ROM or DVD-ROM.

[0081] Alternatively, a chip may be provided that is mounted on the transmitting device 100 or the signal processing device 200, comprising a memory for storing programs for executing each process performed by the transmitting device 100 or the signal processing device 200, and a processor for executing the programs stored in the memory.

[0082] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the embodiments described above, and various modifications and changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple component blocks shown in the configuration diagram of the embodiments into one, or to divide one component block. [Explanation of Symbols]

[0083] 1.1A Satellite Broadcasting System 2,10,100,300 Transmitter 200,400 signal processing equipment 3 Satellite repeaters 4. Receiving device 5. Transmission System 31 IMUX Filter 31a Pseudo IMUX filter 32 TWTA 32a Pseudo TWTA 33 OMUX filters 33a Pseudo-OMUX filter 101,301 S / P conversion section 102,302 Mapping section 103,303,312 U / S section 106 QRRF section (first waveform shaping section) 304, 306, 313 RRF section 202,305 Pseudo-transmitter 307 D / S section 308 Delay section 309,311 Vector Addition Section 310 Inverse characteristic coefficient section 314 D / A Conversion / Quaternary Modulation Section 201 A / D Conversion Unit 203 QRRF section (second waveform shaping section) 204 D / A Conversion Section 401 Bandwidth Limiting Filter

Claims

1. The system comprises a transmitting device that generates a modulated wave signal in which a digital signal is modulated using a predetermined modulation scheme, and a signal processing device that adds a signal component to the modulated wave signal to compensate for transmission path distortion in a predetermined transmission path through which the modulated wave signal is transmitted. The transmitting device is A mapping unit that generates an IQ signal by modulating the digital signal with the predetermined modulation scheme, A first waveform shaping unit performs a first waveform shaping on the IQ signal using a fourth root root roll-off filter, The system includes a D / A conversion unit that performs D / A conversion on the first waveform-shaped IQ signal and outputs it to the signal processing device as the modulated wave signal, The signal processing device is An A / D conversion unit that performs A / D conversion on the modulated wave signal output from the transmitting device, A pseudo-transmitter having the inverse characteristics of the characteristics of a predetermined transmitter on the transmission path, and which adds a signal component that compensates for the transmission path distortion caused by the predetermined transmitter by passing the signal after A / D conversion by the A / D conversion unit through it, A second waveform shaping unit performs a second waveform shaping on the signal that has passed through the pseudo-transmitter using a fourth-root root roll-off filter, A transmission system comprising: a D / A conversion unit that performs D / A conversion on the second waveform-shaped signal and outputs it to the predetermined transmitter.

2. A program that causes a computer to operate as the transmitting device described in claim 1.

3. A program that causes a computer to operate as the signal processing device described in claim 1.

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