JP7579207B2 - Transmitting Device - Google Patents

Description

The present invention relates to a digital broadcast transmission system that performs hierarchical transmission by multiplexing two types of data carriers on one channel, and in particular to a transmission device that defines two types of data carriers as a high hierarchical layer and a low hierarchical layer, respectively, and generates and transmits a modulated wave signal that combines the two types of data carriers at the same frequency band and the same symbol rate.

Digital broadcasting can be broadly divided into satellite broadcasting and terrestrial broadcasting, each of which transmits signals via transmission paths with their own unique characteristics.

First, the modulation methods for digital signals in satellite broadcasting include BPSK including π/2 shift BPSK, QPSK including π/4 shift QPSK, 8PSK, 16APSK, or 32APSK, and the carrier method used for signal transmission between the transmitting device and the receiving device is a single carrier method. Also, a satellite repeater is interposed on the transmission path between the transmitting device and the receiving device in satellite broadcasting. The satellite repeater is mainly composed of an input multiplexer filter (hereinafter referred to as an "IMUX filter"), which is an input filter, a traveling wave tube amplifier (hereinafter referred to as a "TWTA"), and an output multiplexer filter (hereinafter referred to as an "OMUX filter"), which is an output filter.

The IMUX filter is a bandpass filter that corresponds to each channel in satellite broadcasting. It receives modulated wave signals transmitted uplink by terrestrial transmitting equipment, extracts bands for each channel from the modulated wave signals, and outputs them to the TWTA for each channel.

The TWTA performs gain control (power amplification) on the band components of each channel extracted by the IMUX filter, and outputs them to the OMUX filter.

The OMUX filter is a bandpass filter corresponding to each channel, and suppresses unnecessary frequency components in the band components of each channel power-amplified by the TWTA. A modulated signal that combines all the channels is generated by a combiner (not shown) provided after the OMUX filter, and is output as a broadcast signal via downlink to a terrestrial receiving device.

However, in TWTAs, deviations occur from the desired IQ signal points (ideal IQ signal points) due to the influence of input/output amplitudes and phase shift characteristics. In addition, in IMUX and OMUX filters, inter-symbol interference occurs due to the influence of frequency amplitudes and group delay characteristics, causing a spread from the desired IQ signal points. For this reason, it is known that on transmission paths that include satellite repeaters, the deviations and spreads of these IQ signal points affect each other, causing nonlinear distortion in the transmission path characteristics, resulting in an increase in the required C/N ratio and a deterioration in transmission quality (see, for example, Non-Patent Document 1).

On the other hand, modulation methods for digital signals in terrestrial broadcasting include QPSK, 16QAM, or 64QAM, and the carrier method used for signal transmission between the transmitting device and the receiving device is framed multi-carrier transmission based on OFDM. Also, a major feature of terrestrial broadcasting is the effect of multipath fading in the transmission path, but amplifiers in the rear stage of the transmitting device and in the terrestrial relay equipment can be operated in a linear region, making linear transmission of modulated wave signals possible, unlike satellite broadcasting.

In recent years, for next-generation terrestrial broadcasting, a layered transmission (hereinafter referred to as "LDM") method in which two types of data carriers are multiplexed on one channel is being considered. Specifically, as an example of LDM, multiplexing the current ISDB-T data carrier (hereinafter referred to as "2K layer") and the next-generation broadcast data carrier (hereinafter referred to as "4K layer") on one channel is being considered (see, for example, Non-Patent Document 2). Here, the LDM disclosed in Non-Patent Document 2 has the following mechanism. On the transmitting side, the 4K layer is multiplexed with smaller power (i.e., amplitude) than the 2K layer, and the power difference (i.e., amplitude difference) between the high layer (2K) and the low layer (4K) is used for transmission. Then, on the receiving side, the 2K data signal is first obtained by demodulating and decoding the high layer. Next, on the receiving side, a high-level (2K) signal is generated by re-encoding and re-modulating the decoded 2K data signal, and the low-level (4K) signal is obtained by subtracting the re-encoded and re-modulated high-level (2K) signal from the data signal that contains both the high-level (2K) and low-level (4K) signals using vector operations.

It is therefore possible to improve the efficiency of signal transmission by incorporating the above-mentioned LDM technology in satellite broadcasting (see, for example, Non-Patent Document 3). However, as shown in Non-Patent Document 3, there is an issue that non-linear distortion of the transmission path through which the satellite repeater is interposed (particularly the non-linear characteristics of the TWTA) has a large impact on the signal components of particularly low hierarchical layers.

Kojima, Koizumi, Suzuki, and Sujikai, "Comparative Study of Digital Pre-Distortion for 32APSK by Hardware Experiments and Numerical Calculations", IEICE Technical Report SAT2019-53, Institute of Electronics, Information and Communication Engineers, October 10, 2019 Sato, K. Kanbara, Okuno, and T. Tsuchida, "Evaluation of transmission characteristics during integrated demodulation of ISDB-T and next-generation broadcasting using LDM," ITE Winter Annual Convention 2019, 14C-5, Institute of Image Information and Television Engineers, December 12, 2019 Okada, "Carrier Overlay Method in Satellite Communications - Toward the Realization of LDM -", ITE Technical Report Vol. 41, No. 11, BCT2017-47, Institute of Image Information and Television Engineers, March 10, 2017

As mentioned above, it is possible to incorporate LDM technology into satellite broadcasting.

Now, with reference to Figures 4 and 5, we will explain the generalized schematic configuration of a transmitter 1P and a receiver 3P using the LDM method based on conventional technology.

(Prior Art Transmitter)
First, FIG. 4 is a block diagram showing a generalized schematic configuration of a conventional LDM type transmitting device 1P.

The transmitting device 1P shown in FIG. 4 is configured as a device that defines two types of data carriers as a high hierarchy and a low hierarchy, respectively, and generates and transmits a modulated wave signal that combines the two types of data carriers at the same frequency band and the same symbol rate, and includes a high hierarchy encoding/modulation unit 11, a low hierarchy encoding/modulation unit 12, a low hierarchy amplitude adjustment unit 13, a combining unit 14, a synchronization control unit 15, a root roll-off filter unit 16, and a D/A conversion/orthogonal modulation unit 17.

The high-layer coding and modulation unit 11 inputs high-layer data to be transmitted as a data carrier of a high layer (2K in this example), performs coding processing on the high-layer data as a main signal to form coded data by adding error correction parity using a block code (LDPC and BCH concatenated code in this example) with a coding rate (1/2 in this example) predetermined for the high layer, and then performs mapping on the IQ plane based on a modulation method (QPSK in this example) predetermined for the high layer to generate a high-layer IQ signal (a signal of a signal point series that is an orthogonal signal of an in-phase component I and a quadrature-phase component Q and can be expressed as a signal point on the IQ plane), which is output to the multiplexing unit 14. The coding processing for the high-layer data may include energy dispersion processing and interleaving processing.

The low-layer coding and modulation unit 12 inputs low-layer data to be transmitted as a data carrier for a low layer (4K in this example), performs coding processing on the low-layer data as the main signal to form coded data by adding error correction parity using a block code (LDPC and BCH concatenated code in this example) with a coding rate (3/4 in this example) predetermined for the low layer, and then performs mapping on the IQ plane based on a modulation method (QPSK in this example) predetermined for the low layer to generate a low-layer IQ signal, which is output to the low-layer amplitude adjustment unit 13. The coding processing for the low-layer data may include energy diffusion processing and interleaving processing.

The low-layer amplitude adjustment unit 13 changes the average amplitude level of the low-layer IQ signal generated by the low-layer encoding/modulation unit 12 to an amplitude that is uniformly smaller than the average amplitude level of the high-layer IQ signal by a predetermined amount (in this example, the power difference is 7.0 dB), thereby generating a low-layer IQ signal with reduced power, and outputs it to the multiplexing unit 14.

The multiplexing unit 14 multiplexes (adds power) the high-layer IQ signal and the low-powered low-layer IQ signal in a multiplexing format at the same frequency band and the same symbol rate to generate a new IQ signal as a hierarchical multiplexed IQ signal, and outputs it to the root roll-off filter unit 16.

The synchronization control unit 15 is a functional unit that performs synchronization control of the high layer coding/modulation unit 11, the low layer coding/modulation unit 12, the low layer amplitude adjustment unit 13, and the multiplexing unit 14 so that the two types of data carriers, defined as the high layer and the low layer, are multiplexed at the same frequency band and the same symbol rate. In particular, when controlling the synchronization of the low layer amplitude adjustment unit 13, the synchronization control unit 15 controls the low layer IQ signal to be changed to an amplitude that is uniformly smaller than the amplitude of the high layer IQ signal by a predetermined amount so that the required C/N of the low layer IQ signal and the high layer IQ signal is satisfied and the low layer IQ signal can be identified by the difference due to vector calculation of the high layer IQ signal relative to the hierarchically multiplexed IQ signal.

The root roll-off filter unit 16 is a type of band-limiting filter that performs upsampling and waveform shaping to remove unnecessary high-frequency components on the hierarchical multiplexed IQ signal generated by the multiplexing unit 14 to generate a waveform-shaped hierarchical multiplexed IQ signal, which is then output to the D/A conversion and quadrature modulation unit 17.

The D/A conversion and quadrature modulation unit 17 performs digital/analog (D/A) conversion processing on the hierarchical multiplexed IQ signal after waveform shaping, generates a modulated wave signal based on quadrature modulation processing using a modulation method (QPSK in this example) predetermined for the high hierarchy, and transmits it to the receiving device 3P via a specified transmission path.

(Prior Art Receiving Device)
Next, FIG. 5 is a block diagram showing a generalized schematic configuration of a receiving device 3P of the LDM system based on the prior art.

The receiving device 3P shown in FIG. 5 is configured as a device that receives the modulated wave signal generated by the transmitting device 1P via a specified transmission path and demodulates and decodes the two types of data carriers, and includes an orthogonal demodulation and A/D conversion unit 31, a root roll-off filter unit 32, a high layer demodulation and decoding unit 33, a high layer re-encoding and re-modulation unit 34, a vector calculation unit 35, and a low layer demodulation and decoding unit 36.

The orthogonal demodulation and A/D conversion unit 31 receives the modulated wave signal generated by the transmitting device 1P via a specified transmission path, performs orthogonal demodulation processing using the modulation method (QPSK in this example), and then performs analog/digital (A/D) conversion processing to restore the above-mentioned hierarchical multiplexed IQ signal, and outputs it to the root roll-off filter unit 32.

The root roll-off filter unit 32 is a type of band-limiting filter, and generates a hierarchical multiplexed IQ signal after waveform shaping and downsampling to remove unnecessary high-frequency components from the hierarchical multiplexed IQ signal restored by the orthogonal demodulation and A/D conversion unit 31, leaving only symbol points, and outputs the signal to the high layer demodulation and decoding unit 33 and vector calculation unit 35.

The high layer demodulation and decoding unit 33 performs demodulation processing on the hierarchical multiplexed IQ signal after waveform shaping based on the predetermined modulation method (QPSK in this example), and then performs inverse processing corresponding to the encoding processing for the high layer in the transmitting device 1P, that is, performs decoding processing on a block code (concatenated codes of LDPC and BCH in this example) with a coding rate predetermined for the high layer (1/2 in this example), restores the high layer data and outputs it to the outside, and also outputs it to the high layer re-encoding and re-modulation unit 34. In other words, the high layer demodulation and decoding unit 33 can perform demodulation and decoding processing by regarding the reception of the hierarchical multiplexed IQ signal after waveform shaping as the reception of a high layer IQ signal under the likelihood judgment and error correction processing, thereby restoring the high layer data.

The high layer re-encoding and re-modulation unit 34 performs the same processing as the high layer encoding and modulation unit 11 in the transmission device 1P on the high layer data obtained from the high layer demodulation and decoding unit 33, that is, performs encoding processing on the high layer data as the main signal to form encoded data by adding error correction parity using a block code (in this example, concatenated codes of LDPC and BCH) with a coding rate (1/2 in this example) predetermined for the high layer, and then performs mapping on the IQ plane based on a predetermined modulation method (QPSK in this example) to regenerate an IQ signal for the high layer, and outputs it to the vector calculation unit 35.

The vector calculation unit 35 subtracts (subtracts power from) the high layer IQ signal regenerated by the high layer re-encoding and re-modulation unit 34 from the hierarchical multiplexed IQ signal output from the root roll-off filter unit 32 by vector calculation to restore the low layer IQ signal, and outputs it to the low layer demodulation and decoding unit 36.

The low-layer demodulation and decoding unit 36 performs demodulation processing on the low-layer IQ signal obtained from the vector calculation unit 35 based on a modulation method predetermined for the low layer (QPSK in this example), and then performs inverse processing corresponding to the encoding processing for the low layer in the transmitting device 1P, i.e., performs decoding processing on a block code (concatenated codes of LDPC and BCH in this example) with a coding rate predetermined for the low layer (3/4 in this example), restores the high-layer data, and outputs it externally.

The LDM transmission system based on the conventional technology shown in Figures 4 and 5 can also be applied to satellite broadcasting. However, in order to apply this LDM technology to a transmitting device in satellite broadcasting, some measure is required to reduce the effects of nonlinear distortion in the transmission path through the satellite repeater.

In other words, the transmitting device 1P shown in Figure 4 transmits a hierarchical multiplexed IQ signal at a signal point where a high-layer IQ signal and a low-layer IQ signal are directly added together. If this transmitting device 1P is also applied to satellite broadcasting, the transmission will be subject to the effects of nonlinear distortion caused by the transmission path including the satellite repeater, resulting in an increase in the required C/N ratio and a deterioration in transmission quality.

The object of the present invention is to provide a transmitting device that defines two types of data carriers as high and low hierarchical layers, respectively, and generates and transmits a combined modulated wave signal that is controlled to reduce nonlinear distortion of the transmission path characteristics for the two types of data carriers in the same frequency band and at the same symbol rate.

The transmission device of the present invention defines two types of data carriers as a high hierarchy and a low hierarchy, respectively, and generates and transmits a combined modulated wave signal by controlling the two types of data carriers to reduce nonlinear distortion of the transmission path characteristics at the same frequency band and the same symbol rate. The transmission device inputs high hierarchy data to be transmitted as the high hierarchy data carrier, performs an encoding process to form encoded data by adding error correction parity using a block code with a coding rate predetermined for the high hierarchy to the high hierarchy data, and then generates encoded data on an IQ plane based on a modulation method predetermined for the high hierarchy. a low-layer coding and modulation unit which receives low-layer data to be transmitted as a data carrier for the low layer, performs coding processing on the low-layer data by adding error correction parity using a block code having a coding rate predetermined for the low layer to the low-layer data to form coded data, and then performs mapping on an IQ plane based on a modulation method predetermined for the low layer to generate a low-layer IQ signal; and a low layer amplitude varying unit that performs a correction process to adjust the width to generate an amplitude-corrected second low layer IQ signal; an amplitude adjustment unit that adjusts the amplitude by changing the average amplitude level of the second low layer IQ signal to an amplitude that is uniformly smaller than the average amplitude level of the high layer IQ signal by a predetermined amount, or by changing the average amplitude level of the high layer IQ signal to an amplitude that is uniformly larger than the average amplitude level of the second low layer IQ signal by a predetermined amount; and multiplexing the amplitude-adjusted high layer IQ signal and the second low layer IQ signal in a form of combining them at the same frequency band and the same symbol rate, It is characterized by comprising a multiplexing unit that generates a new IQ signal as a hierarchical multiplexed IQ signal, a synchronization control unit that performs synchronization control of the high layer encoding/modulation unit, the low layer encoding/modulation unit, the low layer amplitude variable unit, the amplitude adjustment unit, and the multiplexing unit, a root roll-off filter unit that performs waveform shaping on the hierarchical multiplexed IQ signal to generate a second hierarchical multiplexed IQ signal, and a D/A conversion/quadrature modulation unit that performs digital/analog conversion processing on the second hierarchical multiplexed IQ signal, and generates and transmits a modulated wave signal based on quadrature modulation processing using a modulation method predetermined for the high layer.

In the transmission device of the present invention, the synchronization control unit is characterized in that, when synchronously controlling the correction process by the low layer amplitude variable unit, it has a function of performing synchronous control to perform a correction process for each signal point of the low layer IQ signal once generated by the low layer encoding/modulation unit, so that when the amplitude of the hierarchically multiplexed IQ signal becomes greater than a predetermined amount based on the amplitude of each signal point of the corresponding high layer IQ signal on the time axis, the correction process is performed to reduce the amplitude to within the predetermined amount.

In the transmitting device of the present invention, the synchronization control unit has a function of performing synchronization control to change the amplitude to be smaller within a range that satisfies the required C/N ratio required for receiving each of the low and high hierarchy data carriers on the receiving side and makes the low hierarchy IQ signal identifiable based on the difference between the received second hierarchical multiplexed IQ signal and the high hierarchy IQ signal due to vector calculation.

In addition, in the transmitting device of the present invention, the D/A conversion and quadrature modulation unit is configured to transmit the modulated wave signal toward a satellite repeater located on the transmission path of the satellite broadcasting.

According to the present invention, it is possible to reduce the effects of nonlinear distortion on the transmission path, and in particular to improve the transmission performance of low-layer IQ signals, compared to conventional LDM transmission devices. Furthermore, according to the present invention, it is possible to ensure a transmission capacity similar to that of conventional LDM transmission systems. In other words, it is possible to reduce the effects of nonlinear distortion on the transmission path, and in particular to improve the transmission performance of low-layer IQ signals, without reducing the transmission capacity of conventional LDM transmission systems.

1 is a block diagram illustrating a schematic configuration of a transmission system including a transmitting device and a receiving device according to an embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of a transmitting device according to an embodiment of the present invention; 1A and 1B are diagrams illustrating IQ signal point arrangements before and after correction in a transmitting device according to an embodiment of the present invention. FIG. 1 is a block diagram showing a generalized schematic configuration of an LDM type transmitting device based on the conventional technology. FIG. 1 is a block diagram showing a generalized schematic configuration of an LDM receiving device based on the prior art.

Below, we will explain a transmitter 1 according to one embodiment of the present invention with reference to the drawings.

[Transmission System]
Fig. 1 is a block diagram illustrating a schematic configuration of a transmission system including a transmitting device 1 and a receiving device 3 according to an embodiment of the present invention. The transmission system according to the embodiment shown in Fig. 1 is an example in which the LDM method is applied to satellite broadcasting, and is configured with a transmitting device 1 in a terrestrial broadcasting station, a satellite repeater 2, and multiple receiving devices 3-1, 3-2, ..., 3-n (hereinafter, n is an integer of 1 or more, and will be collectively referred to as "receiving devices 3").

The transmitter 1, which will be described in detail with reference to FIG. 2, defines two types of data carriers as a high hierarchy and a low hierarchy, respectively, and generates and transmits a combined modulated wave signal that is controlled to reduce nonlinear distortion of the transmission path characteristics for the two types of data carriers in the same frequency band and at the same symbol rate.

The satellite repeater 2 mounted on the broadcasting satellite is equipped with an IMUX filter 21, a TWTA 22, and an OMUX filter 23. As described above, the IMUX filter 21 receives the modulated wave signal transmitted by the terrestrial transmitting device 1 in the uplink, and performs band extraction for each channel from the modulated wave signal. After power amplification by the TWTA 22, the OMUX filter 23 suppresses unnecessary frequency components and generates a modulated wave signal by combining all the channels as a broadcast wave signal, which is then output as a downlink to the terrestrial receiving device.

The receiving device 3 is configured as a device that receives the modulated wave signal generated by the transmitting device 1 via a transmission path including the satellite repeater 2 and demodulates and decodes the two types of data carriers. It has a configuration similar to that of the LDM receiving device 3P based on the conventional technology shown in Figure 5, and further explanation is omitted.

[Transmitting device]
Fig. 2 is a block diagram illustrating a schematic configuration of a transmitting device 1 according to an embodiment of the present invention. In the transmitting device 1 shown in Fig. 2, components similar to those of the transmitting device 1P of the prior art shown in Fig. 4 are given the same reference numerals.

The transmitting device 1 shown in FIG. 2 includes a high-layer encoding/modulation unit 11, a low-layer encoding/modulation unit 12, a low-layer amplitude adjustment unit 13, a multiplexing unit 14, a synchronization control unit 15, a root roll-off filter unit 16, a D/A conversion/quadrature modulation unit 17, and a low-layer amplitude variable unit 18, and is configured similarly to the transmitting device 1P of the prior art shown in FIG. 4, except that it is further configured to include a low-layer amplitude variable unit 18, and that the synchronization control unit 15 is configured to also perform synchronization control of the low-layer amplitude variable unit 18. Each component of the transmitting device 1 will be described in more detail below.

The high-layer coding and modulation unit 11 inputs high-layer data to be transmitted as a data carrier of a high layer (2K in this example), performs coding processing on the high-layer data as the main signal to form coded data by adding error correction parity using a block code (concatenated codes of LDPC and BCH in this example) with a coding rate (1/2 in this example) predetermined for the high layer, and then performs mapping on the IQ plane based on a predetermined modulation method (QPSK in this example) to generate an IQ signal for the high layer, which is output to the multiplexing unit 14. The coding processing for the high-layer data may include energy diffusion processing and interleaving processing.

The low-layer coding and modulation unit 12 inputs low-layer data to be transmitted as a data carrier for a low layer (4K in this example), performs coding processing on the low-layer data as the main signal to form coded data by adding error correction parity using a block code (LDPC and BCH concatenated code in this example) with a coding rate (3/4 in this example) predetermined for the low layer, and then performs mapping on the IQ plane based on the same modulation method (QPSK in this example) as the high layer to generate a low-layer IQ signal, which is output to the low-layer amplitude variable unit 18. The coding processing for the low-layer data may include energy diffusion processing and interleaving processing.

The low layer amplitude variable unit 18 performs a correction process on each signal point of the low layer IQ signal generated by the low layer encoding/modulation unit 12, dynamically adjusting the amplitude by a predetermined amount based on the amplitude of the corresponding signal point of the high layer IQ signal on the time axis, to generate an amplitude-corrected low layer IQ signal, and output it to the low layer amplitude adjustment unit 13.

The low hierarchical amplitude adjustment unit 13 changes the average amplitude level of the low hierarchical IQ signal, which has been amplitude-corrected by the low hierarchical amplitude change unit 18, to an amplitude that is uniformly smaller than the average amplitude level of the high hierarchical IQ signal by a predetermined amount (in this example, the power difference is 7.0 dB), thereby generating a low-powered IQ signal and outputting it to the multiplexing unit 14.

The multiplexing unit 14 multiplexes (adds power) the high-layer IQ signal and the low-powered low-layer IQ signal in a multiplexing format at the same frequency band and the same symbol rate to generate a new normalized IQ signal as a hierarchical multiplexed IQ signal, and outputs it to the root roll-off filter unit 16.

The synchronization control unit 15 is a functional unit that performs synchronization control of the high layer coding/modulation unit 11, the low layer coding/modulation unit 12, the low layer amplitude variable unit 18, the low layer amplitude adjustment unit 13, and the multiplexing unit 14 so that the two types of data carriers, defined as the high layer and the low layer, are multiplexed at the same frequency band and the same symbol rate.

In particular, the synchronization control unit 15 according to the present invention has a function of performing synchronization control for each signal point of the low layer IQ signal once generated by the low layer encoding/modulation unit 12 when the correction process by the low layer amplitude variable unit 18 is synchronously controlled so that when the amplitude of the hierarchical multiplexed IQ signal becomes greater than a predetermined amount based on the amplitude of each signal point of the corresponding high layer IQ signal on the time axis, a correction process is performed to reduce the amplitude to within the predetermined amount.

The synchronization control unit 15 according to the present invention also has a function of performing synchronization control of the correction process by the low hierarchical amplitude variable unit 18 to change the amplitude to a smaller value within a range that satisfies the required C/N ratios required for receiving each data carrier of the low and high hierarchical layers on the receiving side and makes the low hierarchical IQ signal identifiable based on the difference between the received hierarchical multiplexed IQ signal and the high hierarchical IQ signal due to vector calculation.

The root roll-off filter unit 16 is a type of band-limiting filter that performs upsampling and waveform shaping to remove unnecessary high-frequency components on the hierarchical multiplexed IQ signal generated by the multiplexing unit 14 to generate a waveform-shaped hierarchical multiplexed IQ signal, which is then output to the D/A conversion and quadrature modulation unit 17.

The D/A conversion and quadrature modulation unit 17 performs digital/analog (D/A) conversion processing on the hierarchical multiplexed IQ signal (i.e., the standardized IQ signal) after waveform shaping, generates a modulated wave signal based on quadrature modulation processing using a modulation method (QPSK in this example) predetermined for the high hierarchy, and transmits it to the receiving device 3 via a transmission path including the satellite repeater 2.

In this way, in the transmitter 1 shown in FIG. 2, as transmission parameters in one embodiment, QPSK (coding rate 1/2) is used for coding and modulation for high hierarchy, and QPSK (coding rate 3/4) is used for coding and modulation for low hierarchy, and the power difference between the high hierarchy IQ signal and the low hierarchy IQ signal is 7.0 dB. Here, in this example, the symbol rate and center frequency used are the same, and the symbol points of the high hierarchy IQ signal and the low hierarchy IQ signal are synchronized. In accordance with the satellite broadcast transmission method ISDB-S3, the required C/N for QPSK (coding rate 1/2) is 1.2 dB, and the required C/N for QPSK (coding rate 3/4) is 4.0 dB, so considering the power difference of 7.0 dB, the high hierarchy IQ signal can be received with a receiving C/N margin of 5.8 dB under ideal transmission path conditions.

Using the transmission parameters of this embodiment, the operation of generating a hierarchical multiplexed IQ signal in the transmitting device 1 will be explained with reference to Figure 3.

First, because the high layer IQ signal is QPSK, there is one point in each of the first to fourth quadrants, for a total of four points (the "circles" shown in Figure 3). When the amplitude of the high layer IQ signal is normalized to 1, the points in the first to fourth quadrants are expressed as (real part of the IQ signal, imaginary part of the IQ signal) as (0.7071, 0.7071), (-0.7071, 0.7071), (-0.7071, -0.7071), and (0.7071, -0.7071).

Next, the IQ signal for the low layer has four QPSK points, just like the high layer, but the normalized amplitude of the low layer is 7.0 dB lower than the normalized amplitude of the high layer, 10^(-7/10) ≒ 0.1995, and the corresponding four points of the IQ signal for the low layer (QPSK) are (0.1411, 0.1411), (-0.1411, 0.1411), (-0.1411, -0.1411), and (0.1411, -0.1411).

If we add a high-level IQ signal and a low-level IQ signal with a power difference of 7.0 dB, the IQ signal point arrangement (shown as "◆" in Figure 3) will be a lattice of 16 points: (0.8482, 0.8482), (0.5660, 0.8482), (0.5660, 0.5660), (0.8482, 0.5660), (-0.5660, 0.8482), (-0.8482, 0.8482), (-0.8482, 0.8482), (-0.848 Possible values are (-0.2, 0.5660), (-0.5660, 0.5660), (-0.5660, -0.5660), (-0.8482, -0.5660), (-0.8482, -0.8482), (-0.5660, -0.8482), (0.8482, -0.5660), (0.5660, -0.5660), (0.5660, -0.8482), and (0.8482, -0.8482).

In other words, in the conventional transmitting device 1P, the signal is modulated and transmitted using a grid-like IQ signal point arrangement (shown as "◆" in Figure 3) similar to the QAM modulation method. However, in the case of this IQ signal point arrangement (shown as "◆" in Figure 3), in satellite broadcasting, the four points (0.8482, 0.8482), (-0.8482, 0.8482), (-0.8482, -0.8482), (0.8482, -0.8482) that are the maximum amplitudes in the IQ signal point arrangement (shown as "◆" in Figure 3) are particularly susceptible to the nonlinear distortion of the TWTA 22 (amplitude suppressed and phase rotated), which ultimately leads to degradation of reception performance. This is why the modulation method used in satellite broadcasting such as ISDB-S3 is not QAM, but PSK or APSK if it is 4 bits or more.

In normal 4-bit modulation, it is sufficient to change the arrangement of IQ signal points to APSK, but in the case of LDM, since it is a combination of adding a high layer IQ signal and a low layer IQ signal, it is necessary to dynamically change the amplitude of the hierarchical multiplexed IQ signal depending on how it is combined.

Therefore, in one embodiment of the transmitting device 1 according to the present invention, a low layer amplitude variable unit 18 that is synchronously controlled by a synchronization control unit 15 is provided, and a correction process is performed on each signal point of the low layer IQ signal once generated, dynamically adjusting the amplitude by a predetermined amount based on the amplitude of the corresponding signal point of the high layer IQ signal on the time axis. A low layer amplitude adjustment unit 13 generates a low layer IQ signal by reducing the power of the amplitude-corrected low layer IQ signal, and a multiplexing unit 14 multiplexes the high layer IQ signal and the reduced power low layer IQ signal in a form that multiplexes them at the same frequency band and the same symbol rate to generate a hierarchically multiplexed IQ signal.

To explain this using the first quadrant in Figure 3 as an example, the high-level IQ signal (the circle in Figure 3) is located at (0.7071, 0.7071) in the first quadrant, but of the four grid points (0.8482, 0.8482), (0.5660, 0.8482), (0.5660, 0.5660), (0.8482, 0.5660) after adding the high-level IQ signal and the low-level IQ signal (the diamond in Figure 3), the right The top coordinate point (0.8482, 0.8482) is the maximum normalized amplitude of 1.200, and if the coordinate point to the upper right (0.8482, 0.8482) is set to (+|0.8482-C1|, +|0.8482-C1|) (C1 is a positive constant) (the upper right of the two points "◇" in the first quadrant shown in Figure 3), it becomes possible to lower the amplitude from 1.200, making it possible to reduce the effects of nonlinear distortion. TWTA22 is linear below a certain amplitude, and here it is assumed to be linear below a normalized amplitude of 1.

In addition, after adding the high-level IQ signal and the low-level IQ signal (shown as "◆" in Figure 3), of the four grid points (0.8482, 0.8482), (0.5660, 0.8482), (0.5660, 0.5660), (0.8482, 0.5660), the bottom left coordinate point (0.5660, 0.5660) has the smallest normalized amplitude of 0.8005, and this bottom left coordinate point (0.5660, 0.5 If we set the power of the hierarchical multiplexed IQ signal from the low layer IQ signal to 0.1995 (=1-0.8005), the power difference between the high layer IQ signal and the low layer IQ signal can be maintained at 7.0 dB. If we set the power of the hierarchical multiplexed IQ signal from the low layer IQ signal to 0.1995 (=1-0.8005), the power difference between the high layer IQ signal and the low layer IQ signal can be maintained at 7.0 dB.

In this way, when the synchronization control unit 15 according to the present invention synchronously controls the correction process by the low layer amplitude variable unit 18, it synchronously controls each signal point of the low layer IQ signal once generated by the low layer encoding/modulation unit 12 to change the amplitude to within a predetermined amount when the hierarchical multiplexed IQ signal has an amplitude greater than a predetermined amount based on the amplitude of each signal point of the corresponding high layer IQ signal on the time axis, and further, in accordance with the synchronous control of the correction process by the low layer amplitude variable unit 18, it synchronously controls to change the amplitude to be smaller within a range that satisfies the required C/N ratio required for receiving each data carrier of the low layer and high layer on the receiving side and makes the low layer IQ signal identifiable by the difference due to vector calculation of the high layer IQ signal with respect to the received hierarchical multiplexed IQ signal.

The same processing is performed for the second to fourth quadrants shown in Figure 3, and the signal points of the hierarchical multiplexed IQ signal after correction (i.e., the signal points corrected for the added high-hierarchical IQ signal and low-hierarchical IQ signal) are indicated by "◇".

The optimal values of C1 and C2 depend on the characteristics of the satellite repeater 2 (IMUX filter 21, TWTA 22, and OMUX filter 23) and the operating point of TWTA 22, but they can be determined in advance by calculating the correction amount offline, or a mechanism (not shown) capable of calculating the correction amount can be provided within the transmitting device 1 to sequentially or periodically derive and update the values.

As described above, the transmitter 1 of this embodiment can reduce the effects of nonlinear distortion on the transmission path without reducing the transmission capacity, and can improve the transmission performance of the IQ signals for low hierarchical layers in particular, compared to the transmitter 1P of the conventional LDM system.

Although the above-mentioned embodiment has been described as a representative example, it is clear to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present invention. For example, in the above-mentioned example, the high layer is 2K and the low layer is 4K, but it is sufficient to define two types of data carriers as high and low layers, such as 4K for the high layer and 8K for the low layer (however, the prerequisite is that the high layer has higher reception resistance than the low layer). Furthermore, according to the transmitting device 1 of the present invention, since physical IQ signal processing is used to generate the modulated wave signal, various modulation methods and error correction block code methods for the high and low layers can be selected and set. Therefore, according to the transmitting device 1 of the present invention, high versatility is ensured regardless of the selected coding/modulation method (transmission line coding method), and the influence of nonlinear distortion can be reduced more than in the conventional LDM method while ensuring the same transmission capacity as the conventional LDM method. Furthermore, in the above-mentioned embodiment example, an example was described in which the transmitting device 1 of the present invention is applied to a satellite broadcasting transmission system, but since it is also possible to assume that an amplifier having a nonlinear characteristic will be interposed on the transmission line in terrestrial broadcasting in the future, it may also be applied to a terrestrial broadcasting transmission system.
In the above example, as a typical example that is easy to understand, the modulation method predefined for the high layer and the modulation method predefined for the low layer are the same (QPSK in the above example), but it goes without saying that the components according to the present invention may be applied as different modulation methods for the high layer and the low layer. For example, the high layer may be QPSK, and the low layer may be 8PSK. Furthermore, even if the modulation method is the same between the high layer and the low layer, the coding rate may be different. That is, it is sufficient that the form in which the modulation wave signal is generated and transmitted by multiplexing two types of data carriers at the same frequency band and the same symbol rate by utilizing the fact that the reception performance is different as a result of the hierarchical multiplexing IQ signal.
Furthermore, in the above example, an example was described in which the low layer amplitude adjustment unit 13 performs amplitude adjustment to uniformly reduce the average amplitude level of the low layer IQ signal relative to the average amplitude level of the high layer IQ signal, but instead of providing such a low layer amplitude adjustment unit 13, a high layer amplitude adjustment unit (not shown) may be provided that performs amplitude adjustment to uniformly increase the average amplitude level of the high layer IQ signal relative to the average amplitude level of the low layer IQ signal. That is, it is sufficient to provide an "amplitude adjustment unit" (not shown) that performs amplitude adjustment so that the average amplitude level of the high layer IQ signal has a uniform predetermined level difference from the average amplitude level of the low layer IQ signal.
Accordingly, the present invention should not be construed as limited by the above-described embodiments, but is limited only by the scope of the appended claims.

The present invention can reduce the effects of nonlinear distortion on the transmission path without reducing transmission capacity, and can improve the transmission performance of low-level IQ signals in particular, making it useful for LDM transmission systems.

1. Transmitting device (the present invention)
1P Transmitter (conventional technology)
2 Satellite repeater 3, 3P, 3-1, 3-2, ..., 3-n Receiving device 11 High-level hierarchy coding and modulation section 12 Low-level hierarchy coding and modulation section 13 Low-level hierarchy amplitude adjustment section 14 Multiplexing section 15 Synchronization control section 16 Root roll-off filter section 17 D/A conversion and quadrature modulation section 18 Low-level hierarchy amplitude variable section 21 IMUX filter 22 TWTA
23 OMUX filter 31 Orthogonal demodulation and A/D conversion unit 32 Root roll-off filter unit 33 High layer demodulation and decoding unit 34 High layer re-encoding and re-modulation unit 35 Vector calculation unit 36 Low layer demodulation and decoding unit

Claims (4)

A transmitting device that defines two types of data carriers as a high hierarchy and a low hierarchy, respectively, and generates and transmits a modulated wave signal that is combined by controlling the two types of data carriers to reduce nonlinear distortion of transmission path characteristics at the same frequency band and the same symbol rate,
a high layer coding and modulation unit that inputs high layer data to be transmitted as a data carrier for the high layer, performs coding processing on the high layer data by adding error correction parity using a block code having a coding rate predetermined for the high layer to form coded data, and then performs mapping on an IQ plane based on a modulation method predetermined for the high layer to generate an IQ signal for the high layer;
a low layer coding and modulation unit that inputs low layer data to be transmitted as the low layer data carrier, performs coding processing on the low layer data by adding error correction parity using a block code with a coding rate predetermined for the low layer to form coded data, and then performs mapping on an IQ plane based on a modulation method predetermined for the low layer to generate an IQ signal for the low layer;
a low layer amplitude varying unit that performs a correction process for dynamically adjusting the amplitude of each signal point of the low layer IQ signal by a predetermined amount based on the amplitude of a corresponding signal point of the high layer IQ signal on a time axis, thereby generating an amplitude-corrected second low layer IQ signal;
an amplitude adjustment unit that adjusts the amplitude by changing an average amplitude level of the second low layer IQ signal to an amplitude that is uniformly smaller than the average amplitude level of the high layer IQ signal by a predetermined amount, or by changing an average amplitude level of the high layer IQ signal to an amplitude that is uniformly larger than the average amplitude level of the second low layer IQ signal by a predetermined amount;
a multiplexing unit that multiplexes the amplitude-adjusted high layer IQ signal and the second low layer IQ signal in a multiplexing format at the same frequency band and the same symbol rate to generate a new IQ signal as a layer multiplexed IQ signal;
a synchronization control unit that performs synchronization control of the high layer coding/modulation unit, the low layer coding/modulation unit, the low layer amplitude varying unit, the amplitude adjustment unit, and the multiplexing unit;
a root roll-off filter unit that performs waveform shaping on the hierarchical multiplexed IQ signal to generate a second hierarchical multiplexed IQ signal;
a D/A conversion and quadrature modulation unit that performs digital/analog conversion processing on the second hierarchical multiplexed IQ signal, and generates and transmits a modulated wave signal based on quadrature modulation processing using a modulation method predetermined for the high layer;
A transmitting device comprising: The transmission device according to claim 1, characterized in that, when synchronously controlling the correction process by the low layer amplitude variable unit, the synchronization control unit has a function of performing synchronous control to perform a correction process for changing each signal point of the low layer IQ signal once generated by the low layer encoding and modulation unit so that when the amplitude of the hierarchically multiplexed IQ signal becomes greater than a predetermined amount based on the amplitude of each signal point of the corresponding high layer IQ signal on the time axis, the amplitude is reduced to within the predetermined amount. The transmitter according to claim 1 or 2, characterized in that the synchronization control unit has a function of performing synchronization control to perform correction processing to reduce the amplitude within a range that satisfies the required C/N ratio required for receiving each of the low and high hierarchical data carriers on the receiving side and makes the low hierarchical IQ signal identifiable based on the difference between the received second hierarchical multiplexed IQ signal and the high hierarchical IQ signal due to vector calculation. The transmitting device according to any one of claims 1 to 3, characterized in that the D/A conversion and quadrature modulation unit is configured to transmit the modulated wave signal to a satellite repeater located on a transmission path of a satellite broadcast.