JP7652614B2 - Transmitter and receiver for hierarchical transmission method - Google Patents

Description

The present invention relates to a transmitting device and a receiving device that transmit two systems of modulated signals hierarchically using a single carrier.

The modulation methods for 12 GHz satellite digital broadcasting include BPSK, including π/2 shift BPSK, QPSK, including π/4 shift QPSK, 8PSK, 16APSK, etc., and are transmitted by a single carrier. This transmission method for 12 GHz satellite broadcasting is called ISDB-S3. The strength of the transmission method is determined by the modulation method and the coding rate of the error correction code (for example, see Non-Patent Document 1). In this satellite broadcasting, hierarchical transmission is possible that combines a strong hierarchy (a hierarchy that uses a low-order modulation method and a low coding rate to strengthen transmission resistance) and a weak hierarchy (a hierarchy that uses a high-order (multiple-value) modulation method and a high coding rate to enable large-capacity transmission). For example, QPSK with a coding rate of 1/2 is used for the strong hierarchy, and 16APSK with a coding rate of 7/9 is used for the weak hierarchy. The hierarchical transmission of 12 GHz satellite broadcasting is a time-division hierarchical transmission method in which one frame is divided into a strong hierarchy and a weak hierarchy and transmitted in a time-division manner. The number of transmission bits per symbol differs between the strong and weak layers, but the symbol rate is constant. In recent years, 21 GHz band satellite broadcasting has also been considered.

In addition, terrestrial digital broadcasting employs a multi-carrier modulation method called OFDM, and the carrier modulation method is QPSK, 16QAM, or 64QAM. This terrestrial digital broadcasting transmission method is called ISDB-T (see, for example, Non-Patent Document 2). In recent years, for next-generation terrestrial broadcasting, a power hierarchical transmission (hereinafter referred to as "LDM") method has been considered, in which an existing ISDB-T modulated signal is power-wise added to another modulated signal for multiplexing. This LDM method is a hierarchical transmission method in which the data carrier for next-generation broadcasting (hereinafter referred to as the 4K layer) is OFDM-modulated and multiplexed onto the existing ISDB-T data carrier (hereinafter referred to as the 2K layer), and both 2K and 4K are broadcast on the same single channel as before (see, for example, Non-Patent Document 3). In this method, the 4K layer is multiplexed with less power than the 2K layer, and transmitted with two power differences: a strong layer (upper layer: 2K) and a weak layer (lower layer: 4K). On the receiving side, the upper layer is first demodulated and error-correction-decoded to obtain a 2K data signal, and the decoded signal is then error-correction-encoded and remodulated to reproduce only the 2K signal that is the upper layer transmission signal, and this reproduced 2K signal is subtracted from the received signal (a composite signal that includes both the upper layer (2K) and the lower layer (4K)) to obtain only the lower layer (4K) signal, which is then demodulated and error-correction-decoded to obtain a 4K data signal (see, for example, Non-Patent Document 4). In this LDM method, the FFT clocks of the upper and lower layers of OFDM are generally the same to simplify demodulation.

"Transmission method for advanced wideband digital satellite broadcasting (ISDB-S3) Standard ARIB STD-B44 Version 2.1", [online], revised March 25, 2016, ARIB, [searched March 30, 2021], Internet <URL: https://www.arib.or.jp/kikaku/kikaku_hoso/std-b44.html> "Standard for transmission method of terrestrial digital television broadcasting ARIB STD-B31 version 2.2", [online], revised March 18, 2014, ARIB, [searched March 30, 2021], Internet <URL: https://www.arib.or.jp/kikaku/kikaku_hoso/std-b31.html> Sato, Kambara, Okano, Tsuchida, "Transmission Characteristics Evaluation of ISDB-T and Next Generation Broadcasting Multiplexing with LDM during Integrated Demodulation," 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

In satellite broadcasting transmission, rain attenuation attenuates the received power, lowering the received C/N ratio. In the time-division hierarchical transmission method, the symbol rate of each layer is constant, and the strength of the hierarchical transmission (resistance to signal degradation) can only be differentiated by the difference in transmission strength due to the modulation method and the coding rate of the error correction code. For example, the required C/N for the strong layer is about 1.2 dB when QPSK and coding rate 1/2, and the required C/N for the weak layer is about 10.8 dB when 16APSK and coding rate 7/9, so the difference in the required C/N between the strong layer and the weak layer in hierarchical transmission is about 9.5 dB. When receiving with a 45 cm parabolic antenna in Tokyo, the received C/N on a clear day is about 20 dB, but attenuation due to rain exceeds 10 dB, and may reach 20 dB or more. In addition, it is expected that attenuation due to rain will be extremely large in 21 GHz band satellite broadcasting. Therefore, in order to further increase the difference in the required C/N between the strong and weak hierarchical layers, there was a limit to the difference in the modulation method and the coding rate of the error correction code alone.

When the amount of rain attenuation in satellite broadcasting exceeds 20 dB, the reception C/N ratio falls to 0 dB or less, so with the conventional time-division hierarchical transmission method, errors occur even in the strong hierarchical layer, making it impossible to transmit information.

Therefore, what is needed is a transmitter and receiver that use a hierarchical transmission method that can transmit a minimum amount of information in a strong hierarchy even when there is attenuation of the transmission signal due to rain attenuation or other factors of 20 dB or more.

The object of the present invention is to provide a transmitting device and a receiving device that have improved resistance to signal attenuation when hierarchically transmitting two systems of modulated signals.

The transmission device of the present invention is a power hierarchical transmission method transmission device that defines modulated signals of two systems of line coding as upper and lower layers, respectively, and adds the modulated signals of the two systems at different levels in terms of power to transmit them on a single carrier, and includes a reference clock generation unit that generates a reference clock of M×N, which is common to the upper layer and the lower layer, and a clock generation unit having a frequency divider that generates a sampling clock divided for the upper layer and the lower layer, respectively, based on the symbol rate m, and generates a complex baseband signal for the upper layer based on a predetermined line coding method that specifies at least an error correction coding rate, a modulation method, and a roll-off rate of waveform shaping for the upper layer, based on the sampling clock for the upper layer based on the reference clock, and transmits the complex baseband signal for the upper layer based on the predetermined line coding method that specifies at least an error correction coding rate, a modulation method, and a roll-off rate of waveform shaping for the upper layer ... The system is characterized by comprising: an upper layer transmission line coding unit that forms the modulated signal for the upper layer to be sampled with the reference clock; a lower layer transmission line coding unit that inputs data for the lower layer to be transmitted at a symbol rate n, generates a complex baseband signal for the lower layer based on a predetermined transmission line coding method that specifies at least an error correction coding rate, a modulation method, and a roll-off rate of waveform shaping for the lower layer based on a sampling clock for the lower layer based on the reference clock, and forms the modulated signal for the lower layer to be sampled with the reference clock; a power addition unit that adjusts the levels of either or both of the modulated signal for the upper layer and the modulated signal for the lower layer so that the average amplitude level of the modulated signal for the upper layer has a predetermined level difference from the average amplitude level of the modulated signal for the lower layer, and then generates a complex baseband signal that is synthesized by power-adding the modulated signal for the upper layer and the modulated signal for the lower layer; and an orthogonal modulation unit that uses the reference clock as a sampling clock to orthogonally modulate the synthesized complex baseband signal to generate a modulated wave signal for transmission.

In the transmitting device of the present invention, a ratio of a symbol rate m for transmitting the data of the upper layer to a symbol rate n for transmitting the data of the lower layer is set to m:n=1:2;
The reference clock generating section is characterized in that it is configured to generate N reference clocks, which is four times the normal clock.

The receiving device of the present invention is a receiving device that receives a modulated wave signal generated by the transmitting device of the present invention and restores the data of the upper layer and the data of the lower layer, and includes a receiving side reference clock generating unit that generates a common reference clock of four times M x N for the upper layer and the lower layer, and a receiving side clock generating unit having a receiving side divider that generates a sampling clock divided for the upper layer and the lower layer using the reference clock as a reference, and a receiving side clock generating unit that generates a sampling clock divided for the upper layer and the lower layer using the reference clock as a sampling clock, and a complex baseband signal generated by orthogonally demodulating the received signal using the reference clock as a sampling clock, the complex baseband signal generated by treating the synthesized complex baseband signal as a complex baseband signal for the upper layer and generating a complex baseband signal for the upper layer using the reference clock as a reference an upper layer demodulation/decoding unit that performs demodulation/decoding processing at a symbol rate m based on a channel coding scheme for an upper layer corresponding to the transmitting device side based on a sampling clock to restore the data of the upper layer; an upper layer re-channel coding unit that inputs the data of the upper layer restored by the upper layer demodulation/decoding unit, regenerates an upper layer complex baseband signal based on a predetermined channel coding scheme that specifies at least an error correction coding rate, a modulation scheme, and a roll-off rate of waveform shaping for the upper layer based on a sampling clock for the upper layer based on the reference clock, and forms it as a replica signal of the upper layer complex baseband signal sampled with the reference clock; a lower layer demodulation/decoding unit having means for treating the combined complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a lower layer complex baseband signal and forming a lower layer complex baseband signal by performing waveform shaping with at least the roll-off rate for the lower layer based on a lower layer sampling clock referenced to the reference clock; and a lower layer demodulation/decoding unit for decoding the replica signal of the upper layer complex baseband signal and the lower layer complex baseband signal such that an average amplitude level of the replica signal of the upper layer complex baseband signal formed by the upper layer re-transmission line coding unit is equal to the predetermined level difference from an average amplitude level of the lower layer complex baseband signal formed by the lower layer demodulation/decoding unit. and a level adjustment unit that adjusts the level of one or both of the complex baseband signals for the lower layer and the complex baseband signal for the upper layer. The demodulation/decoding unit for the lower layer generates a new complex baseband signal for the lower layer consisting of complex baseband signals for only the lower layer by subtracting power from the complex baseband signal for the lower layer after the level adjustment by the level adjustment unit, and performs demodulation/decoding processing of the new complex baseband signal for the lower layer at a symbol rate n based on a transmission line coding method for the lower layer corresponding to the transmitting device side based on a sampling clock for the lower layer based on the reference clock, thereby restoring the data for the lower layer.

The receiving device of the present invention is characterized in that the ratio of the symbol rate m for transmitting the data of the upper layer to the symbol rate n for transmitting the data of the lower layer is m:n = 1:2, and the receiving side reference clock generating unit is configured to generate a reference clock of N, which is four times the normal rate.

The transmission device of the present invention is a power hierarchical transmission method transmission device that defines two systems of modulation signals of a transmission line coding method as upper and lower hierarchical layers, respectively, and adds the two systems of modulation signals at different levels of power to transmit them on a single carrier, and includes a reference clock generation unit that generates a reference clock of M×N, where m is the symbol rate for transmitting data of the upper layer, n is the symbol rate for transmitting data of the lower layer, M is the symbol clock frequency corresponding to the symbol rate m, and N is the symbol clock frequency corresponding to the symbol rate n, and a frequency division unit that divides the reference clock to generate sampling clocks of frequencies M, 2M, N, and 2N. a clock generating unit having a frequency divider for dividing the data into a plurality of data bits, the clock generating unit inputting data for an upper layer to be transmitted at a symbol rate m, performing an error correction encoding process for forming encoded data by adding an error correction parity using a block code having a coding rate predetermined for the upper layer, generating an upper layer complex baseband signal based on a modulation method predetermined for the upper layer in synchronization with a sampling clock of a frequency M, up-sampling the upper layer complex baseband signal using a sampling clock of a frequency 2M, performing waveform shaping with a roll-off rate for the upper layer, and then up-sampling a new upper layer complex baseband signal using the reference clock as a sampling clock to a transmission line coding unit for an upper layer that forms the modulated signal for the upper layer and a transmission line coding unit for a lower layer that is transmitted at a symbol rate n, and performs an error correction coding process for forming coded data by adding an error correction parity using a block code having a coding rate predetermined for the lower layer, and then generates a complex baseband signal for the lower layer based on a modulation method predetermined for the lower layer in synchronization with a sampling clock of frequency N, upsamples the complex baseband signal for the lower layer using a sampling clock of frequency 2N, and then performs waveform shaping with a roll-off rate for the lower layer before upsampling using the reference clock as a sampling clock to generate a new lower layer The system is characterized by comprising a lower layer transmission line coding unit that forms a complex baseband signal for the lower layer as a modulated signal for the lower layer, a power addition unit that adjusts the levels of either or both of the modulated signal for the upper layer and the modulated signal for the lower layer so that the average amplitude level of the modulated signal for the upper layer has a predetermined level difference from the average amplitude level of the modulated signal for the lower layer, and then generates a combined complex baseband signal by power-adding the modulated signal for the upper layer and the modulated signal for the lower layer, and an orthogonal modulation unit that uses the reference clock as a sampling clock to orthogonally modulate the combined complex baseband signal to generate a modulated wave signal for transmission by a single carrier.

The receiving device of the present invention is a receiving device that receives the modulated wave signal generated by the transmitting device of the present invention via a satellite broadcast transmission path and restores the data of the upper layer and the data of the lower layer, and includes a receiving side reference clock generating unit that generates a reference clock of four times M x N, and a receiving side clock generating unit having a receiving side divider that divides the reference clock as a reference and generates sampling clocks of frequencies M, 2M, N, and 2N, and the combined complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock is treated as a complex baseband signal for the upper layer and downsampled using a sampling clock of frequency 2M, and then waveform shaping is performed with a roll-off rate for the upper layer, and then sampling is performed at a symbol rate m using a sampling clock of frequency M to obtain the composite complex baseband signal. an upper layer demodulation/decoding unit that demaps data onto a complex plane based on a modulation scheme predetermined for the upper layer to obtain soft decision data of bits constituting each symbol, performs error correction decoding processing on a block code having a coding rate predetermined for the upper layer to restore the data of the upper layer, and receives the data of the upper layer restored by the upper layer demodulation/decoding unit, performs error correction coding processing for the upper layer, and then regenerates an upper layer complex baseband signal based on the modulation scheme for the upper layer in synchronization with a sampling clock of frequency M, upsamples a replica signal of the upper layer complex baseband signal using a sampling clock of frequency 2M, performs waveform shaping with a roll-off rate for the upper layer, and then upsamples using the reference clock as a sampling clock to generate a new replica of the upper layer complex baseband signal a lower layer demodulation/decoding unit having means for treating the synthesized complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock as a lower layer complex baseband signal, downsampling the synthesized complex baseband signal using a sampling clock of a frequency 2N, performing waveform shaping with a roll-off rate for the lower layer, and then upsampling the synthesized complex baseband signal using the reference clock as a sampling clock to form a lower layer complex baseband signal; and a replica signal for the upper layer complex baseband signal formed by the upper layer re-transmission path coding unit so that the average amplitude level of the replica signal for the upper layer complex baseband signal formed by the upper layer re-transmission path coding unit is equal to the predetermined level difference from the average amplitude level of the lower layer complex baseband signal formed by the lower layer demodulation/decoding unit. and a level adjustment unit that adjusts the level of either or both of the upper layer complex baseband signal and the lower layer complex baseband signal, and the lower layer demodulation/decoding unit generates a new lower layer complex baseband signal consisting of complex baseband signals of only the lower layer by performing power subtraction so as to subtract a replica signal of the upper layer complex baseband signal from the lower layer complex baseband signal after the level adjustment by the level adjustment unit, samples the new lower layer complex baseband signal at a symbol rate n using a sampling clock of frequency N, demaps the new lower layer complex baseband signal on a complex plane based on a modulation method predetermined for the lower layer to obtain soft decision data of bits constituting each symbol, and performs error correction decoding processing on a block code having a coding rate predetermined for the lower layer to restore the data of the lower layer.

The transmission device of the present invention is a power hierarchical transmission method transmission device that defines two systems of modulation signals of a transmission line coding method as upper and lower hierarchical layers, respectively, and adds the two systems of modulation signals at different levels in terms of power to transmit them on a single carrier, and includes a reference clock generation unit that generates a reference clock of N, which is four times the symbol rate when the symbol rate for transmitting data of the upper layer is n/2, the symbol rate for transmitting data of the lower layer is n, and the symbol clock frequency corresponding to the symbol rate n is N, and a clock generation unit having a frequency divider that divides the reference clock based on the frequency to generate sampling clocks of frequencies 2N, N, and N/2; The data for the upper layer to be transmitted at a rate of n/2 is input, an error correction encoding process is performed to form encoded data by adding an error correction parity using a block code having a coding rate predetermined for the upper layer, and then an upper layer complex baseband signal is generated based on a modulation method predetermined for the upper layer in synchronization with a sampling clock having a frequency of N/2, the upper layer complex baseband signal is upsampled using a sampling clock having a frequency of N, and then waveform shaping is performed with a roll-off rate for the upper layer, and the new upper layer complex baseband signal that has been upsampled using the reference clock as a sampling clock is treated as the modulated signal for the upper layer. and a transmission line coding unit for an upper layer which receives data for a lower layer to be transmitted at a symbol rate n, performs error correction coding processing for forming coded data by adding error correction parity using a block code having a coding rate predetermined for the lower layer, generates a complex baseband signal for a lower layer based on a modulation method predetermined for the lower layer in synchronization with a sampling clock of frequency N, upsamples the complex baseband signal for the lower layer using a sampling clock of frequency 2N, performs waveform shaping with a roll-off rate for the lower layer, and then upsamples the complex baseband signal using the reference clock as a sampling clock to generate a new complex baseband signal for the lower layer. The system is characterized by comprising a lower layer transmission line coding unit that forms a complex baseband signal as the lower layer modulated signal, a power addition unit that adjusts the levels of either or both of the upper layer modulated signal and the lower layer modulated signal so that the average amplitude level of the upper layer modulated signal has a predetermined level difference from the average amplitude level of the lower layer modulated signal, and then generates a combined complex baseband signal by power adding the upper layer modulated signal and the lower layer modulated signal, and a quadrature modulation unit that uses the reference clock as a sampling clock to quadrature modulate the combined complex baseband signal and generate a modulated wave signal for transmission.

The receiving device of the present invention is a receiving device that receives the modulated wave signal generated by the transmitting device of the present invention via a satellite broadcast transmission path and restores the upper layer data and the lower layer data, and includes a receiving side reference clock generating unit that generates a reference clock of N, which is four times the normal frequency, and a receiving side clock generating unit having a receiving side divider that divides the reference clock to generate sampling clocks of frequencies 2N, N, and N/2, and treats the synthesized complex baseband signal obtained by orthogonally demodulating the received signal using the sampling clock of frequency 2N as a complex baseband signal for the upper layer and downsamples it using a sampling clock of frequency N, and then performs waveform shaping with a roll-off rate for the upper layer and samples it at a symbol rate n/2 using a sampling clock of frequency N/2. an upper layer demodulation/decoding unit that receives the upper layer data restored by the upper layer demodulation/decoding unit, performs error correction coding for the upper layer, regenerates an upper layer complex baseband signal based on the upper layer modulation method in synchronization with a sampling clock of frequency N/2, upsamples a replica signal of the upper layer complex baseband signal using a sampling clock of frequency N, and then performs waveform shaping with a roll-off rate for the upper layer before upsampling using a sampling clock of frequency 2N to generate a new upper layer complex baseband signal; a lower layer demodulation/decoding unit having means for treating the synthesized complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock as a lower layer complex baseband signal, downsampling the synthesized complex baseband signal using a sampling clock of a frequency 2N, and forming a lower layer complex baseband signal by performing waveform shaping with a roll-off rate for the lower layer; and a lower layer demodulation/decoding unit for decoding the replica signal of the upper layer complex baseband signal and the lower layer complex baseband signal so that an average amplitude level of the replica signal of the upper layer complex baseband signal formed by the upper layer retransmission path coding unit is equal to the predetermined level difference from an average amplitude level of the lower layer complex baseband signal formed by the lower layer demodulation/decoding unit. and a level adjustment unit that adjusts the level of one or both of the baseband signals, and the lower layer demodulation/decoding unit generates a new lower layer complex baseband signal consisting of complex baseband signals of only the lower layer by performing power subtraction so as to subtract a replica signal of the upper layer complex baseband signal from the lower layer complex baseband signal after the level adjustment by the level adjustment unit, samples the new lower layer complex baseband signal at a symbol rate n using a sampling clock of frequency N, and demaps it onto a complex plane based on a modulation method predetermined for the lower layer to obtain soft decision data of bits that constitute each symbol, and performs error correction decoding processing on a block code having a coding rate predetermined for the lower layer to restore the data of the lower layer.

In comparison with the conventional time-division hierarchical transmission method used in satellite broadcasting, the present invention uses a power-division hierarchical transmission (LDM) method and is configured to enable differences in symbol rates between the layers. This makes it possible to increase the difference in data transmission strength (difference in required C/N) between the upper layer (strong layer) and the lower layer (weak layer). This makes it possible to obtain information on the transmission data of the strong layer even when attenuation of 20 dB or more occurs due to rainfall, etc., stabilizing operation and making it possible for the receiving side to obtain information on the transmission data of both the strong layer and the weak layer in a more resistant manner.

1 is a block diagram showing a schematic configuration of a transmission device of a power division hierarchical transmission (LDM) system according to a first embodiment of the present invention; 1 is a block diagram showing a schematic configuration of a receiving device of a power division hierarchical transmission (LDM) system according to a first embodiment of the present invention; FIG. 11 is a block diagram showing a schematic configuration of a transmission device of a power division hierarchical transmission (LDM) system according to a second embodiment of the present invention. FIG. 11 is a block diagram showing a schematic configuration of a receiving device of a power division hierarchical transmission (LDM) system according to a second embodiment of the present invention. 1 is a diagram showing an outline of a transmission spectrum in a transmitting device of a power division hierarchical transmission (LDM) method according to the present invention;

Below, a transmitter 1 and a receiver 2 of a power division hierarchical transmission (LDM) method according to each embodiment of the present invention will be described with reference to the drawings. In addition, as each embodiment of the present invention, an example will be described in which the data in the upper layer is a 2K data signal and the data in the lower layer is a 4K data signal.

In the power division hierarchical transmission (LDM) type transmitter 1 and receiver 2 of each embodiment of the present invention, it is assumed that the transmitter 1 and receiver 2 are applied to a satellite digital broadcasting system such as 12 GHz band or 21 GHz band satellite broadcasting, and an outline of the transmission spectrum in the transmitter 1 is shown in Figure 5. As shown in Figure 5, the Nyquist frequency bandwidth of the lower layer is BWb (symbol rate is n, roll-off rate is b), the Nyquist frequency bandwidth of the upper layer is BWa (symbol rate is m, roll-off rate is a), and a new modulated signal is generated by adding the modulated signal of the upper layer (strong layer) to the modulated signal of the lower layer (weak layer) at a level α times the average amplitude level of the modulated signal of the lower layer (weak layer), and the new modulated signal is transmitted hierarchically to the receiver 2. Here, m ≦ n, α ≧ 1. In addition, the modulation method of each layer may be BPSK, QPSK, 8PSK, 16QAM, 16APSK, 32APSK, etc., and may be different or the same between layers. In addition, the error correction method for each layer is assumed to be, although not limited to, a concatenated LDPC and BCH code in this example.

Example 1
(Transmitting device)
FIG. 1 is a block diagram showing a schematic configuration of a transmitter 1 for a power division hierarchical transmission (LDM) system according to a first embodiment of the present invention.

The transmitting device 1 shown in FIG. 1 has a functional unit that performs error correction coding, modulation mapping, and roll-off filtering on two types of data: data on an upper layer (strong layer) transmitted at a symbol rate m, and data on a lower layer (weak layer) transmitted at a symbol rate n, and is configured as a single-carrier power division hierarchical transmission (LDM) type transmitting device that adds the power of the two types of modulated signals (a combination of symbol rate, error correction coding rate, modulation method, and roll-off rate) and transmits them. More specifically, the transmitting device 1 shown in FIG. 1 basically includes a clock generating unit 11, an upper layer transmission line coding unit 12, a lower layer transmission line coding unit 13, a power adding unit 14, and an orthogonal modulation unit 15.

The clock generating unit 11 includes a reference clock generating unit 111 and a frequency divider 112.

The reference clock generating unit 111 is a functional unit that generates a reference clock with a frequency that is four times higher, M x N (M is the symbol clock frequency of the upper layer and corresponds to the symbol rate m. N is the symbol clock frequency of the lower layer and corresponds to the symbol rate n). Here, m ≤ n and M ≤ N.

The frequency divider 112 is a functional unit that divides the reference clock generated by the reference clock generating unit 111 and generates the necessary sampling clocks for each unit of the transmitting device 1 shown in FIG. 1, and includes a 1/(N×4) frequency divider 112a, a 1/(M×4) frequency divider 112b, a 1/(N×2) frequency divider 112c, and a 1/(M×2) frequency divider 112d.

The 1/(N×4) divider 112a divides the reference clock generated by the reference clock generating unit 111 by 1/(N×4) to generate a sampling clock with a frequency of M.

The 1/(M×4) divider 112b divides the reference clock generated by the reference clock generating unit 111 by 1/(M×4) to generate a sampling clock with a frequency of N.

The 1/(N×2) divider 112c divides the reference clock generated by the reference clock generating unit 111 by 1/(N×2) to generate a sampling clock with a frequency of 2M.

The 1/(M×2) divider 112d divides the reference clock generated by the reference clock generating unit 111 by 1/(M×2) to generate a sampling clock with a frequency of 2N.

In this way, in the transmitting device 1 shown in Figure 1, the clock generating unit 11 uses four times the frequency, M x N, as a common reference clock for the upper and lower hierarchical layers, and generates sampling clocks with frequencies M, N, 2M, and 2N by dividing this reference clock.

The upper layer transmission line coding unit 12 includes an error correction coding unit 121, a modulation mapping unit 122, an upsampling unit 123, a roll-off filter unit 124, and an upsampling unit 125.

The error correction coding unit 121 inputs data of an upper layer (e.g., a strong layer of 2K) to be transmitted as coded data with a symbol rate m, performs error correction coding processing on the data of the upper layer as the main signal, and forms coded data by adding error correction parity using a block code (e.g., concatenated codes of LDPC and BCH) with a coding rate (e.g., coding rate 1/2) predetermined for the upper layer, and outputs the data to the modulation mapping unit 122.

The modulation mapping unit 122 synchronizes with a sampling clock of frequency M corresponding to the symbol rate m, maps the coded data of the upper layer obtained from the error correction coding unit 121 to a constellation of a predetermined digital modulation method (e.g., QPSK), generates a complex baseband signal for the upper layer (a quadrature signal of an in-phase component I and a quadrature-phase component Q, which is a signal of a signal point sequence that can be expressed as a signal point on the IQ plane) mapped onto the complex (IQ) plane, and outputs it to the upsampling unit 123.

The upsampling unit 123 uses a sampling clock with a frequency of 2M to form an upper layer complex baseband signal by upsampling the symbols of the upper layer complex baseband signal mapped by the modulation mapping unit 122 by a factor of 2, and outputs the signal to the roll-off filter unit 124.

The roll-off filter unit 124 is composed of a root roll-off filter, a type of band-limiting filter, that has a predetermined roll-off rate (the roll-off rate of the upper layer is a), and performs waveform shaping on the upper layer complex baseband signal obtained from the upsampling unit 123 to remove unnecessary high-frequency components, generates a waveform-shaped upper layer complex baseband signal, and outputs it to the upsampling unit 125.

The upsampling unit 125 uses a reference clock with a frequency of 4MN as a sampling clock to form a complex baseband signal for an upper layer by upsampling the symbols of the complex baseband signal for an upper layer after waveform shaping obtained from the roll-off filter unit 124 so as to match the sampling clock between the upper layer and lower layer, and outputs the signal to the level adjustment unit 141. Note that instead of using a clock with a frequency of 4MN, the upsampling unit 125 uses a clock with a frequency of twice the least common multiple of M and N for upsampling, which allows it to handle the lowest possible frequencies and enables stable operation and easy implementation, but here we show a case where the clock is the same as the reference clock.

The lower layer transmission path coding unit 13 includes an error correction coding unit 131, a modulation mapping unit 132, an upsampling unit 133, a roll-off filter unit 134, and an upsampling unit 135.

The error correction coding unit 131 inputs data of a lower layer (e.g., a weak layer of 4K) to be transmitted as coded data with a symbol rate of n, performs error correction coding processing on the data of the lower layer as the main signal, and forms coded data by adding error correction parity using a block code (e.g., concatenated codes of LDPC and BCH) with a coding rate (e.g., coding rate 7/9) predetermined for the lower layer, and outputs the data to the modulation mapping unit 132.

The modulation mapping unit 132 synchronizes with a sampling clock of frequency N corresponding to symbol rate n, maps the coded data of the lower layer obtained from the error correction coding unit 131 to a constellation of a predetermined digital modulation method (e.g., 16APSK), generates a complex baseband signal for the lower layer mapped onto the complex (IQ) plane, and outputs it to the upsampling unit 133.

The upsampling unit 133 uses a sampling clock with a frequency of 2N to form a lower layer complex baseband signal by upsampling the symbols of the lower layer complex baseband signal mapped by the modulation mapping unit 132 by a factor of 2, and outputs the signal to the roll-off filter unit 134.

The roll-off filter unit 134 is composed of a root roll-off filter, a type of band-limiting filter, that has a predetermined roll-off rate (the roll-off rate of the lower layer is designated b), and performs waveform shaping on the complex baseband signal for the lower layer obtained from the upsampling unit 133 to remove unnecessary high-frequency components, thereby generating a waveform-shaped complex baseband signal for the lower layer, which is output to the upsampling unit 135.

The upsampling unit 135 uses a reference clock with a frequency of 4MN as a sampling clock to upsample the symbols of the waveform-shaped lower-layer complex baseband signal obtained from the roll-off filter unit 134 so as to match the sampling clock between the upper and lower layers to form a lower-layer complex baseband signal, and outputs the signal to the adding unit 142. Note that instead of using a clock with a frequency of 4MN, the upsampling unit 135 uses a clock with a frequency of twice the least common multiple of M and N for upsampling, which allows it to handle the lowest possible frequencies and enables stable operation and easy implementation, but here we show a case where the clock is the same as the reference clock.

The power addition unit 14 includes a level adjustment unit 141 and an addition unit 142.

The level adjustment unit 141 performs level adjustment on the upper layer complex baseband signal obtained from the upsampling unit 125 to make its average amplitude level α times the average amplitude level of the lower layer complex baseband signal (see FIG. 5), and outputs the level-adjusted upper layer complex baseband signal to the addition unit 142.

The adder 142 adds (combines by power-wise adding the symbols sampled at the same timing) the level-adjusted complex baseband signal for the upper layer obtained from the level adjustment unit 141 (QPSK, coding rate 1/2 in this example) and the complex baseband signal for the lower layer obtained from the upsampling unit 135 (16APSK, coding rate 7/9 in this example) on the complex plane to generate a complex baseband signal for hierarchical transmission with a single symbol rate to obtain a modulated wave signal of a single frequency band, and outputs the resulting signal to the quadrature modulation and D/A conversion unit 151.

The quadrature modulation unit 15 includes a quadrature modulation/digital/analog (D/A) conversion unit 151 and a bandpass filter (BPF) unit 152.

The quadrature modulation and D/A conversion unit 151 uses a reference clock with a frequency of 4MN as a sampling clock to add (quadrature modulate) the I-axis signal and the Q-axis signal with a phase difference (time difference) of 90 degrees to the complex baseband signal of hierarchical transmission obtained from the addition unit 142, and then performs digital/analog (D/A) conversion to generate a modulated wave signal of a single frequency band that has been hierarchically transmitted, and outputs it to the BPF unit 152.

The BPF unit 152 performs bandpass filtering to limit the band of the modulated wave signal obtained from the quadrature modulation and D/A conversion unit 151 in order to extract only signals near the reference clock of frequency 4MN, generates an intermediate frequency (IF) band modulated wave signal, and transmits it at a level corresponding to the transmission power standardized in the IF band signal state. The IF band modulated wave signal is transmitted at a predetermined (standardized) transmission power, with the total transmission power of the upper and lower layers, in order to transmit it to the receiving device 3 via a transmission path including a satellite repeater such as a 12 GHz band or 21 GHz band satellite broadcast.

(Receiving device)
FIG. 2 is a block diagram showing a schematic configuration of a receiver 2 for a power division hierarchical transmission (LDM) system according to a first embodiment of the present invention.

The receiving device 2 shown in FIG. 2 receives a transmission signal of a satellite broadcast frequency via a receiving antenna (not shown) that receives the transmission signal and inputs a reception signal converted to an intermediate frequency (IF) band. The receiving device 2 extracts only the IF signal transmitted by the transmitting device 1 shown in FIG. 1 from the received IF band reception signal (IF signal), and is configured as a receiving device that can separately receive two types of data: data of an upper layer (strong layer) transmitted at a symbol rate m, and data of a lower layer (weak layer) transmitted at a symbol rate n. More specifically, the receiving device 2 shown in FIG. 2 basically includes a BPF unit 21, a clock generating unit 22, a demodulation and decoding unit for an upper layer 23, a retransmission path coding unit for an upper layer 24, and a demodulation and decoding unit for a lower layer 25.

The BPF unit 21 performs bandpass filtering on the IF signal received via the receiving antenna (not shown) to extract only the IF signal transmitted by the transmitting device 1 shown in FIG. 1, and outputs it to the orthogonal demodulation and analog-to-digital (A/D) conversion unit 231 in the upper layer demodulation and decoding unit 23 and the orthogonal demodulation and analog-to-digital (A/D) conversion unit 251 in the lower layer demodulation and decoding unit 25.

The clock generating unit 22 includes a reference clock generating unit 221 and a frequency divider 222.

The reference clock generating unit 221 is a functional unit that generates a reference clock with a frequency that is four times higher, M x N (M is the symbol clock frequency of the upper layer and corresponds to the symbol rate m, and N is the symbol clock frequency of the lower layer and corresponds to the symbol rate n), similar to the reference clock generating unit 111 on the transmitting device 1 side shown in FIG. 1.

The frequency divider 222 is a functional unit that divides the reference clock generated by the reference clock generating unit 221 and generates the necessary sampling clocks for each unit of the receiving device 2 shown in FIG. 2, and includes a 1/(N×2) frequency divider 222a, a 1/(M×2) frequency divider 222b, a 1/2 frequency divider 222c, and a 1/2 frequency divider 222d.

The 1/(N×2) divider 222a divides the reference clock generated by the reference clock generating unit 221 by 1/(N×2) to generate a sampling clock with a frequency of 2M.

The 1/(M×2) divider 222b divides the reference clock generated by the reference clock generating unit 221 by 1/(M×2) to generate a sampling clock with a frequency of 2N.

The 1/2 divider 222c divides the clock generated by the 1/(N x 2) divider 222a by 1/2 to generate a sampling clock with a frequency of M.

The 1/2 divider 222d divides the clock generated by the 1/(M×2) divider 222b by 1/2 to generate a sampling clock with frequency N.

In this way, in the receiving device 2 shown in FIG. 2, the clock generating unit 22 uses four times M×N as a common reference clock for the upper and lower hierarchical layers, and generates sampling clocks of frequencies M, N, 2M, and 2N by dividing this reference clock. Furthermore, the frequency of the reference clock is made the same between the transmitting device 1 shown in FIG. 1 and the receiving device 2 shown in FIG. 2. The frequency division configuration of the frequency divider 222 shown in FIG. 2 may be the same as the frequency division configuration of the frequency divider 112 shown in FIG. 1, and conversely, the frequency division configuration of the frequency divider 112 shown in FIG. 1 may be the same as the frequency division configuration of the frequency divider 222 shown in FIG. 2.

The upper layer demodulation/decoding unit 23 is a functional unit that demodulates and decodes the received signal of the upper layer (strong layer), and includes an orthogonal demodulation/analog/digital (A/D) conversion unit 231, a downsampling unit 232, a roll-off filter unit 233, a demodulation/demapping unit 234, and an error correction/decoding unit 235.

The quadrature demodulation and A/D conversion unit 231 uses a reference clock with a frequency of 4MN as a sampling clock to quadrature demodulate the IF signal obtained from the BPF unit 21, divides it into I-axis data and Q-axis data, and then performs analog/digital (A/D) conversion processing to obtain a complex baseband signal, which it then treats as a complex baseband signal for the upper layer and outputs to the downsampling unit 232.

The downsampling unit 232 uses a sampling clock with a frequency of 2M to downsample the symbols of the upper layer complex baseband signal obtained from the orthogonal demodulation and A/D conversion unit 231 to 2M samples to form an upper layer complex baseband signal, and outputs it to the roll-off filter unit 233.

The roll-off filter unit 233 is composed of a root roll-off filter, a type of band-limiting filter, that has the same roll-off rate (upper layer roll-off rate a) as the transmitting device 1 side, and performs waveform shaping to remove unnecessary high-frequency components from the upper layer complex baseband signal obtained from the downsampling unit 232 to generate a waveform-shaped upper layer complex baseband signal, which is output to the demodulation and demapping unit 234.

The demodulation demapping unit 234 uses a sampling clock of frequency M to sample the complex baseband signal for the upper layer obtained from the roll-off filter unit 233 at a symbol rate m, demaps it onto a complex plane of a digital modulation method (e.g., QPSK) corresponding to the transmitting device 1 side for the upper layer, compares it with a constellation of ideal signal points to obtain soft decision data (likelihood values) of the bits that make up each symbol, and outputs it to the error correction decoding unit 235.

The error correction decoding unit 235 performs error correction decoding processing on the soft decision data for the upper layer obtained from the demodulation demapping unit 234, for a block code (e.g., concatenated codes of LDPC and BCH) with a coding rate (e.g., coding rate 1/2) that is predetermined for the upper layer, to restore the data of the upper layer (strong layer), and outputs it to the outside as well as to the error correction coding unit 241.

The upper layer re-transmission path coding unit 24 is a functional unit that re-transmission path codes the data of the upper layer (strong layer) obtained from the error correction decoding unit 235 by the same process as the upper layer transmission path coding unit 12 on the transmitting device 1 side, and generates a replica of the complex baseband signal for the upper layer, and includes an error correction coding unit 241, a re-modulation mapping unit 242, an up-sampling unit 243, a roll-off filter unit 244, an up-sampling unit 245, and a level adjustment unit 246.

The error correction coding unit 241 inputs the data of the upper layer (strong layer) obtained from the error correction decoding unit 235, performs error correction coding processing on the data of the upper layer as the main signal, and forms coded data by adding error correction parity using a block code (e.g., concatenated codes of LDPC and BCH) with a coding rate (e.g., coding rate 1/2) predetermined for the upper layer, and outputs the coded data to the remodulation mapping unit 242.

The remodulation mapping unit 242 synchronizes with a sampling clock of frequency M corresponding to the symbol rate m, maps the coded data of the upper layer obtained from the error correction coding unit 241 to a constellation of a predetermined digital modulation method (QPSK in this example), generates a complex baseband signal for the upper layer mapped on the complex (IQ) plane, and outputs it to the upsampling unit 243.

The upsampling unit 243 uses a sampling clock with a frequency of 2M to form a complex baseband signal for the upper layer by upsampling the symbols of the complex baseband signal for the upper layer mapped by the remodulation mapping unit 242 by a factor of two, and outputs the signal to the roll-off filter unit 244.

The roll-off filter unit 244 is composed of a root roll-off filter, a type of band-limiting filter, that has a roll-off rate (upper layer roll-off rate a), and performs waveform shaping on the upper layer complex baseband signal obtained from the upsampling unit 243 to remove unnecessary high-frequency components, generates a waveform-shaped upper layer complex baseband signal, and outputs it to the upsampling unit 245.

The upsampling unit 245 uses a reference clock of frequency 4MN as a sampling clock to form a replica signal of the complex baseband signal for the upper layer by upsampling the symbols of the complex baseband signal for the upper layer after waveform shaping obtained from the roll-off filter unit 244 so as to align the sampling clock between the upper layer and the lower layer, and outputs the replica signal to the level adjustment unit 246.

The level adjustment unit 246 performs level adjustment on the replica signal of the complex baseband signal for the upper layer obtained from the upsampling unit 245 to make its average amplitude level α times that of the complex baseband signal for the lower layer (see FIG. 5), and outputs the replica signal of the complex baseband signal for the upper layer after the level adjustment to the addition unit 255.

On the other hand, the lower layer demodulation/decoding unit 25 is a functional unit that demodulates and decodes the received signal of the lower layer (weak layer), and includes an orthogonal demodulation/A/D conversion unit 251, a downsampling unit 252, a roll-off filter unit 253, an upsampling unit 254, a subtraction unit 255, a demodulation/demapping unit 256, and an error correction/decoding unit 257.

The orthogonal demodulation and A/D conversion unit 251 uses a reference clock of frequency 4MN as a sampling clock to orthogonally demodulate the IF signal obtained from the BPF unit 21, divides it into I-axis data and Q-axis data, and then performs analog/digital (A/D) conversion processing to obtain a digital complex baseband signal, which is treated as a complex baseband signal for a lower layer and output to the downsampling unit 252. In the case of the first embodiment, since the orthogonal demodulation and A/D conversion unit 251 operates in the same manner as the orthogonal demodulation and A/D conversion unit 231, the orthogonal demodulation and A/D conversion unit 251 may be omitted, and the digital complex baseband signal obtained from the orthogonal demodulation and A/D conversion unit 231 may be treated as a complex baseband signal for a lower layer and output to the downsampling unit 252.

The downsampling unit 252 uses a sampling clock with a frequency of 2N to downsample the symbols of the complex baseband signal obtained from the orthogonal demodulation and A/D conversion unit 251 to 2N samples to form a complex baseband signal for a lower layer, and outputs the signal to the roll-off filter unit 253.

The roll-off filter unit 253 is composed of a root roll-off filter, a type of band-limiting filter, that has the same roll-off rate (lower layer roll-off rate b) as the transmitting device 1 side, and performs waveform shaping on the lower layer complex baseband signal obtained from the downsampling unit 252 to remove unnecessary high-frequency components, generates a waveform-shaped lower layer complex baseband signal, and outputs it to the upsampling unit 254.

In order to adjust the sampling to subtract the replica signal of the level-adjusted complex baseband signal for the upper layer obtained from the level adjustment unit 246, the upsampling unit 254 uses a reference clock of frequency 4MN as a sampling clock to form a complex baseband signal for the lower layer that is upsampled so as to adjust the sampling clock between the upper layer and the lower layer for the symbols of the waveform-shaped complex baseband signal for the lower layer obtained from the roll-off filter unit 253, and outputs the signal to the subtraction unit 255.

The subtraction unit 255 subtracts on the complex plane (subtracts in terms of power for symbols sampled at the same timing) the replica signal of the level-adjusted upper layer complex baseband signal obtained from the level adjustment unit 246 from the lower layer complex baseband signal obtained from the upsampling unit 254, generates a lower layer complex baseband signal consisting of the original lower layer (weak layer) complex baseband signal only, and outputs it to the demodulation and demapping unit 256.

The demodulation demapping unit 256 uses a sampling clock of frequency N to sample the complex baseband signal for the lower layer obtained from the subtraction unit 255 at a symbol rate n, demaps it onto a complex plane of a digital modulation method (e.g., 16ASK) corresponding to the transmitting device 1 side for the lower layer, compares it with a constellation of ideal signal points to obtain soft decision data (likelihood values) of the bits that make up each symbol, and outputs it to the error correction decoding unit 235.

The error correction decoding unit 257 performs error correction decoding processing on the soft decision data for the lower layer obtained from the demodulation demapping unit 256, using a block code (e.g., concatenated codes of LDPC and BCH) with a coding rate (e.g., coding rate 7/9) that is predetermined for the lower layer, to restore the data for the lower layer (weak layer) and output it externally.

The configuration of the transmission system including the transmitter 1 and receiver 2 of the power division hierarchical transmission (LDM) method of the first embodiment as described above allows the transmitter 1 to transmit a single hierarchical transmission modulated wave signal with a single symbol rate and a single frequency band that is multiplexed based on a single reference clock that is the same between each layer (same between the transmitter 1 side and the receiver 2 side) regardless of the difference in symbol rate of each layer, for the modulated signals of each layer, which are two systems with different symbol rates (m ≠ n), i.e., different bandwidths, and in which the error correction coding rate, digital modulation method, roll-off rate, and transmission level can all be set independently.

In addition, when the receiver 2 demodulates and decodes the received signals of the upper layer (strong layer) and the lower layer (weak layer), it first demodulates and decodes the upper layer (due to differences in symbol rate (m≦n, including the same symbol rate), error correction coding rate, digital modulation method, roll-off rate, and transmission level) which has high resistance to transmission degradation, and then uses a replica signal that has been re-path coded based on the highly reliable demodulation and decoding results of the upper layer to subtract the replica signal from the received signal including the modulated signals of the upper and lower layers, and demodulates and decodes it, thereby obtaining highly reliable data of the lower layer.

Therefore, according to the transmitter 1 and receiver 2 of the power division hierarchical transmission (LDM) system of the first embodiment, compared to the conventional time division hierarchical transmission system in satellite broadcasting, the power division hierarchical transmission (LDM) system makes it possible to increase the difference in transmission strength (difference in required C/N) between the upper layer (strong layer) and the lower layer (weak layer) by making a difference in the symbol rate between the layers, and it becomes possible to obtain information on the transmission data of the strong layer even when attenuation of 20 dB or more occurs due to rainfall, etc., thereby stabilizing operation and enabling the receiver 2 to receive data of each layer in a more resistant manner.

Example 2
Fig. 3 is a block diagram showing a schematic configuration of a transmitter 1 of a power division hierarchical transmission (LDM) system according to a second embodiment of the present invention. Fig. 4 is a block diagram showing a schematic configuration of a receiver 2 of a power division hierarchical transmission (LDM) system according to a second embodiment of the present invention. In Fig. 3, the same components as those shown in Fig. 1 are given the same reference numbers, and in Fig. 4, the same components as those shown in Fig. 2 are given the same reference numbers.

In the above-mentioned embodiment 1 shown in Figs. 1 and 2, an example of a transmitter 1 and a receiver 2 is described in which an arbitrary modulation method is used for the upper layer and the lower layer, and the symbol rate of the upper layer and the lower layer is an arbitrary m:n. In the above-mentioned embodiment 1, if m:n = 1:2, it is possible to configure the transmitter 1 and the receiver 2 so that the symbol rate of the upper layer is half that of the symbol rate of the lower layer by configuring them to generate a reference clock with M:N = 1:2 for M and N.

On the other hand, in the second embodiment shown in Figures 3 and 4, when m:n = 1:2, the circuits that operate on the clock, including the clock generation unit, are the simplest and operate on the lowest possible reference clock. As an example, a transmitter 1 and a receiver 2 are shown in which the symbol rate of the upper layer is half that of the lower layer. Note that, in the example shown in Figures 3 and 4, the explanation will be given assuming that the modulation method of the lower layer is 16APSK, and that the modulation method of the upper layer is QPSK, which is a lower order than the lower layer (and therefore has higher resistance to signal degradation).

(Transmitting device)
As can be understood by comparing the configuration of the transmitting device 1 of the second embodiment shown in Fig. 3 with the configuration of the first embodiment shown in Fig. 1, the basic components are the same, but the configuration of the clock generating unit 11 is different. Therefore, in the second embodiment shown in Fig. 3, only the clock generating unit 11 will be mainly described.

The clock generating unit 11 shown in FIG. 3 includes a reference clock generating unit 111 and a frequency divider 112, similar to the clock generating unit 11 shown in FIG. 1, but in the example shown in FIG. 3, the reference clock generated by the reference clock generating unit 111 and the configuration of the frequency divider 112 are different.

The reference clock generating unit 111 shown in FIG. 3 is a functional unit that generates a reference clock with a frequency of 4 times N (N/2 is the symbol clock frequency of the upper layer and corresponds to the symbol rate m=n/2. Also, N is the symbol clock frequency of the lower layer and corresponds to the symbol rate n).

The frequency divider 112 shown in FIG. 3 is a functional unit that divides the frequency of the reference clock generated by the reference clock generating unit 111 and generates the sampling clock required for each unit of the transmitting device 1 shown in FIG. 3, and includes 1/2 frequency dividers 112e, 112f, and 112g.

The 1/2 divider 112e divides the reference clock generated by the reference clock generating unit 111 shown in FIG. 3 by 1/2 to generate a sampling clock with a frequency of 2N.

The 1/2 divider 112f divides the sampling clock generated by the 1/2 divider 112e by 1/2 to generate a sampling clock with frequency N.

The 1/2 divider 112g divides the sampling clock generated by the 1/2 divider 112f by 1/2 to generate a sampling clock with a frequency of N/2.

In this way, in the transmitting device 1 shown in Figure 3, the clock generating unit 11 uses four times N as a common reference clock for the upper and lower hierarchical layers, and by dividing this reference clock, generates sampling clocks with frequencies of 2N, N, and N/2, which are supplied to each functional unit as shown in Figure 3.

(Receiving device)
The receiving device 2 of the second embodiment shown in Fig. 4 receives a transmission signal of a satellite broadcast frequency via a receiving antenna (not shown) and inputs a reception signal converted to an intermediate frequency (IF) band. The receiving device 2 of the second embodiment shown in Fig. 4 extracts only the IF signal transmitted by the transmitting device 1 shown in Fig. 3 from the received IF band reception signal (IF signal), and is configured as a receiving device capable of separately receiving two systems of data, that is, data of an upper layer (strong layer) transmitted at a symbol rate of n/2 and data of a lower layer (weak layer) transmitted at a symbol rate of n.

As can be seen by comparing the receiving device 2 of Example 2 shown in FIG. 4 with the configuration of Example 1 shown in FIG. 2, the basic components are the same except that the upsampling unit 254 shown in FIG. 2 is not required, but the configuration of the clock generating unit 22 is different. For this reason, with regard to Example 2 shown in FIG. 4, only the clock generating unit 22 will be mainly described. However, in the case of Example 2, since the sampling clocks of the orthogonal demodulation and A/D conversion unit 251 and the orthogonal demodulation and A/D conversion unit 231 are different, the configuration does not omit the installation of the orthogonal demodulation and A/D conversion unit 251.

The clock generating unit 22 shown in FIG. 4 includes a reference clock generating unit 221 and a frequency divider 222, similar to the clock generating unit 22 shown in FIG. 2, but in the example shown in FIG. 4, the reference clock generated by the reference clock generating unit 221 and the frequency divider 222 have different configurations. Note that the clock generating unit 22 shown in FIG. 4 is configured in the same manner in terms of function as the clock generating unit 11 on the transmitting device 11 side shown in FIG. 3.

The reference clock generating unit 221 shown in FIG. 4 is a functional unit that generates a reference clock with a frequency of N, which is four times the frequency.

The frequency divider 222 shown in FIG. 4 is a functional unit that divides the reference clock generated by the reference clock generating unit 221 and generates the necessary sampling clocks for each unit of the receiving device 2 shown in FIG. 4, and includes 1/2 frequency dividers 222e, 222f, and 222g.

The 1/2 divider 222e divides the reference clock generated by the reference clock generating unit 221 shown in FIG. 4 by 1/2 to generate a sampling clock with a frequency of 2N.

The 1/2 divider 222f divides the sampling clock generated by the 1/2 divider 222e by 1/2 to generate a sampling clock with frequency N.

The 1/2 divider 222g divides the sampling clock generated by the 1/2 divider 222f by 1/2 to generate a sampling clock with a frequency of N/2.

In this way, in the receiving device 2 shown in Figure 4, the clock generation unit 22 uses four times N as a common reference clock for the upper and lower hierarchical levels, and by dividing this reference clock, generates sampling clocks with frequencies of 2N, N, and N/2, which are supplied to each functional unit as shown in Figure 4.

The advantages of the transmitter 1 and receiver 2 of the second embodiment include all the advantages of the first embodiment, but since the reference clock frequency is set to N, which is four times the symbol clock frequency N corresponding to the symbol rate n of the lower hierarchy, the operating frequency of the reference clock can be set to the lowest value, and furthermore, the configuration of the dividers 112 and 222 can be a simple configuration using only a 1/2 divider, which is advantageous for stabilizing operation and reducing costs.

In the second embodiment, the modulation method for the lower layer is assumed to be 16APSK, and the modulation method for the upper layer is assumed to be QPSK, which is of a lower order than the lower layer (and therefore more resistant to signal degradation), and N is the symbol clock frequency for the lower layer and the reference clock frequency is 4N. However, if a 5-bit multi-level modulation method such as 32APSK is used as the modulation method for the lower layer, the bit rate of the IF signal transmitted and received between the transmitting device 1 and the receiving device 2 will be 5N, so the reference clock frequency must also be 5N (the specific configurations of the transmitting device 1 and the transmitting device 2 will be the same as those in the first embodiment).

In addition, in the second embodiment, an example of m:n = 1:2 is shown as a preferred example, but as can be understood from the first embodiment, m:n = 1:4, 3:4, 2:3, etc. can also be used. In these ratios, the least common multiple of 2M and 2N is relatively smaller than, for example, m:n = 3:5, and the frequency of the 4MN reference clock is lower, making it possible to stabilize operation.

The transmitter 1 and receiver 2 of the present invention use a power division hierarchical transmission (LDM) method and have different symbol rates for the upper and lower hierarchical layers, thereby realizing a difference in the required C/N between the upper and lower hierarchical layers of 10 dB or more. Even if signal attenuation of 20 dB or more occurs, it is possible to obtain information on the transmission data of the strong hierarchical layer, stabilizing operation, and enabling the receiver 2 to obtain information on the transmission data of both the strong and weak hierarchical layers in a more resistant manner.

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 embodiments, the level adjustment units 141 and 246 have been described as examples in which the average amplitude level of the modulated signal of the upper layer is α times the average amplitude level of the modulated signal of the lower layer, but instead, a level adjustment unit that adjusts the average amplitude level of the modulated signal of the lower layer to 1/α times the average amplitude level of the modulated signal of the upper layer may be provided. That is, it is sufficient to provide a level adjustment unit that performs level adjustment so that the average amplitude level of the modulated signal of the upper layer has a predetermined level difference (α times the average amplitude level difference) with respect to the average amplitude level of the modulated signal of the lower layer. In the above-mentioned example, the upper layer is a 2K data signal and the lower layer is a 4K data signal, but other 2K and 8K, audio and video, etc. may be adopted as long as the two systems of data are defined as the upper layer and the lower layer, respectively. In addition, according to the transmitting device 1 and the receiving device 2 of the present invention, various modulation methods and error correction codes for the upper layer and the lower layer can be selected and set. Therefore, the present invention should not be construed as being limited by the above-described examples, but is limited only by the scope of the claims.

The present invention can improve the resistance to attenuation of transmission signals in a hierarchical transmission method that combines modulated signals from two line coding methods and transmits them on a single carrier, making it useful for use in a transmission system that transmits hierarchically.

REFERENCE SIGNS LIST 1 Transmitter 2 Receiving device 11 Clock generator 12 Upper layer transmission path coding unit 13 Lower layer transmission path coding unit 14 Power adder 15 Orthogonal modulation unit 21 Bandpass filter (BPF) unit 22 Clock generator 23 Upper layer demodulation and decoding unit 24 Upper layer re-transmission path coding unit 25 Lower layer demodulation and decoding unit 111 Reference clock generator 112 Divider 112a 1/(N×4) divider 112b 1/(M×4) divider 112c 1/(N×2) divider 112d 1/(M×2) divider 112e, 112f, 112g 1/2 divider 121 Error correction coding unit 122 Modulation mapping unit 123 Upsampling unit 124 Roll-off filter unit 125 Upsampling unit 131 Error correction coding unit 132 Modulation mapping unit 133 Upsampling unit 134 Roll-off filter unit 135 Upsampling unit 141 Level adjustment unit 142 Adding unit 151 Quadrature modulation/digital/analog (D/A) conversion unit 152 Bandpass filter (BPF) unit 221 Reference clock generating unit 222 Frequency divider 222a 1/(N×2) frequency divider,
222b 1/(M×2) divider 222c, 222d, 222e, 222f, 222g 1/2 divider 231 Orthogonal demodulation and analog/digital (A/D) conversion unit 232 Downsampling unit 233 Roll-off filter unit 234 Demodulation demapping unit 235 Error correction decoding unit 241 Error correction coding unit 242 Remodulation mapping unit 243 Upsampling unit 244 Roll-off filter unit 245 Upsampling unit 246 Level adjustment unit 251 Orthogonal demodulation and analog/digital (A/D) conversion unit 252 Downsampling unit 253 Roll-off filter unit 254 Upsampling unit 255 Subtraction unit 256 Demodulation demapping unit 257 Error correction decoding unit

Claims (8)

A transmitter of a power hierarchical transmission method, which defines two systems of modulated signals of a line coding method as upper and lower hierarchical layers, adds the modulated signals of the two systems at different power levels, and transmits the signals by a single carrier,
a symbol rate for transmitting data on the upper layer is m, a symbol rate for transmitting data on the lower layer is n, a symbol clock frequency corresponding to the symbol rate m is M, and a symbol clock frequency corresponding to the symbol rate n is N; a reference clock generation unit generates a reference clock of M×N, which is four times the frequency, and which is common to both the upper layer and the lower layer; and a clock generation unit having a frequency divider for generating sampling clocks which are frequency-divided based on the reference clock for the upper layer and the lower layer, respectively;
an upper layer line coding unit that receives data for an upper layer to be transmitted at a symbol rate m, generates a complex baseband signal for the upper layer based on a predetermined line coding scheme that specifies at least an error correction coding rate, a modulation scheme, and a roll-off rate of waveform shaping for the upper layer, based on a sampling clock for the upper layer that is based on the reference clock, and forms the complex baseband signal for the upper layer as a modulated signal for the upper layer that is sampled with the reference clock;
a lower layer channel coding unit that receives data for a lower layer to be transmitted at a symbol rate n, generates a lower layer complex baseband signal based on a predetermined channel coding scheme that specifies at least an error correction coding rate, a modulation scheme, and a roll-off rate of waveform shaping for the lower layer, based on a sampling clock for the lower layer referenced to the reference clock, and forms the lower layer modulated signal to be sampled with the reference clock;
a power adder that adjusts the level of one or both of the modulated signals of the upper layer and the modulated signals of the lower layer so that an average amplitude level of the modulated signal of the upper layer has a predetermined level difference with respect to an average amplitude level of the modulated signal of the lower layer, and then generates a combined complex baseband signal by power adding the modulated signals of the upper layer and the lower layer;
a quadrature modulation unit that uses the reference clock as a sampling clock to quadrature-modulate the combined complex baseband signal to generate a modulated wave signal for transmission;
A transmitting device comprising: A ratio of a symbol rate m for transmitting data of the upper layer to a symbol rate n for transmitting data of the lower layer is m:n=1:2,
2. The transmitting device according to claim 1, wherein the reference clock generating section is configured to generate N reference clocks, which is four times the normal clock. A receiving device that receives a modulated wave signal generated by the transmitting device according to claim 1 and restores the upper layer data and the lower layer data,
a receiving-side clock generating unit that generates a common reference clock having a frequency of M×N, which is four times the frequency of the reference clock, for the upper layer and the lower layer; and a receiving-side clock generating unit that has a receiving-side frequency divider that generates sampling clocks for the upper layer and the lower layer by dividing the frequency of the reference clock.
an upper layer demodulation/decoding unit that treats the combined complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock as an upper layer complex baseband signal and performs demodulation/decoding processing at a symbol rate m based on an upper layer line coding scheme corresponding to the transmitting device side, based on an upper layer sampling clock based on the reference clock, to restore data of the upper layer;
an upper layer re-path coding unit that receives the upper layer data restored by the upper layer demodulation/decoding unit, regenerates an upper layer complex baseband signal based on a predetermined path coding scheme that specifies at least an error correction coding rate, a modulation scheme, and a roll-off rate of waveform shaping for the upper layer, based on a sampling clock for the upper layer referenced to the reference clock, and forms the upper layer complex baseband signal as a replica signal of the upper layer complex baseband signal sampled with the reference clock;
a lower layer demodulation/decoding unit having means for treating the combined complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock as a lower layer complex baseband signal, and forming a lower layer complex baseband signal by performing waveform shaping with at least a roll-off rate for the lower layer based on a lower layer sampling clock based on the reference clock;
a level adjustment unit that adjusts the levels of one or both of the replica signal of the upper layer complex baseband signal and the lower layer complex baseband signal so that an average amplitude level of the replica signal of the upper layer complex baseband signal formed by the upper layer re-transmission path coding unit becomes equal to the predetermined level difference with respect to an average amplitude level of the lower layer complex baseband signal formed by the lower layer demodulation and decoding unit,
the lower layer demodulation/decoding unit generates a new lower layer complex baseband signal consisting of complex baseband signals of only the lower layer by performing power subtraction so as to subtract a replica signal of the upper layer complex baseband signal from the lower layer complex baseband signal after level adjustment by the level adjustment unit, and performs demodulation/decoding processing on the new lower layer complex baseband signal at a symbol rate n based on a lower layer line coding scheme corresponding to the transmitting device, based on a lower layer sampling clock referenced to the reference clock, to restore data of the lower layer. A ratio of a symbol rate m for transmitting data of the upper layer to a symbol rate n for transmitting data of the lower layer is m:n=1:2,
4. The receiving device according to claim 3, wherein said receiving side reference clock generating section is configured to generate N reference clocks which are four times the normal clocks. A transmitter of a power hierarchical transmission method, which defines two systems of modulated signals of a line coding method as upper and lower hierarchical layers, adds the modulated signals of the two systems at different power levels, and transmits the signals by a single carrier,
a symbol rate for transmitting data on the upper layer is m, a symbol rate for transmitting data on the lower layer is n, a symbol clock frequency corresponding to the symbol rate m is M, and a symbol clock frequency corresponding to the symbol rate n is N, the symbol rate comprises a reference clock generating unit that generates a reference clock of M×N, which is four times the symbol rate m, and a clock generating unit having a frequency divider that divides the reference clock to generate sampling clocks of frequencies M, 2M, N, and 2N;
an upper layer transmission path coding unit that inputs upper layer data to be transmitted at a symbol rate m, performs error correction coding processing to form coded data by adding error correction parity using a block code having a coding rate predetermined for the upper layer, generates an upper layer complex baseband signal based on a modulation method predetermined for the upper layer in synchronization with a sampling clock of frequency M, upsamples the upper layer complex baseband signal using a sampling clock of frequency 2M, performs waveform shaping with a roll-off rate for the upper layer, and then upsamples the new upper layer complex baseband signal using the reference clock as a sampling clock to form the upper layer modulated signal;
a lower layer transmission path coding unit that receives lower layer data to be transmitted at a symbol rate n, performs error correction coding processing to form coded data by adding error correction parity using a block code having a coding rate predetermined for the lower layer, generates a lower layer complex baseband signal based on a modulation method predetermined for the lower layer in synchronization with a sampling clock of frequency N, upsamples the lower layer complex baseband signal using a sampling clock of frequency 2N, performs waveform shaping with a roll-off rate for the lower layer, and then upsamples the new lower layer complex baseband signal using the reference clock as a sampling clock to form the lower layer modulated signal;
a power adder that adjusts the level of one or both of the modulated signals of the upper layer and the modulated signals of the lower layer so that an average amplitude level of the modulated signal of the upper layer has a predetermined level difference with respect to an average amplitude level of the modulated signal of the lower layer, and then generates a combined complex baseband signal by power adding the modulated signals of the upper layer and the lower layer;
a quadrature modulation unit that uses the reference clock as a sampling clock to quadrature-modulate the combined complex baseband signal to generate a modulated wave signal to be transmitted by a single carrier;
A transmitting device comprising: A receiving device that receives a modulated wave signal generated by the transmitting device according to claim 5 via a satellite broadcast transmission path and restores the upper layer data and the lower layer data,
a receiving-side reference clock generating unit that generates a reference clock of four times frequency M×N, and a receiving-side clock generating unit having a receiving-side frequency divider that divides the reference clock to generate sampling clocks of frequencies M, 2M, N, and 2N;
an upper layer demodulation/decoding unit that treats the synthesized complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock as an upper layer complex baseband signal, down-samples the synthesized complex baseband signal using a sampling clock of a frequency 2M, performs waveform shaping with a roll-off rate for the upper layer, samples the synthesized complex baseband signal using a sampling clock of a frequency M at a symbol rate m, and demaps the synthesized complex baseband signal onto a complex plane based on a modulation method predetermined for the upper layer to obtain soft decision data of bits constituting each symbol, and performs error correction decoding processing on a block code having a coding rate predetermined for the upper layer to restore the data of the upper layer;
an upper layer re-transmission path coding unit that receives the upper layer data restored by the upper layer demodulation and decoding unit, performs error correction coding processing for the upper layer, regenerates an upper layer complex baseband signal based on the upper layer modulation scheme in synchronization with a sampling clock of frequency M, upsamples a replica signal of the upper layer complex baseband signal using a sampling clock of frequency 2M, performs waveform shaping with a roll-off rate for the upper layer, and then forms a new replica signal of the upper layer complex baseband signal that is upsampled using the reference clock as a sampling clock;
a lower layer demodulation/decoding unit having means for treating the synthesized complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock as a lower layer complex baseband signal, downsampling the synthesized complex baseband signal using a sampling clock having a frequency of 2N, performing waveform shaping with a roll-off rate for the lower layer, and then upsampling the synthesized complex baseband signal using the reference clock as a sampling clock;
a level adjustment unit that adjusts the levels of one or both of the replica signal of the upper layer complex baseband signal and the lower layer complex baseband signal so that an average amplitude level of the replica signal of the upper layer complex baseband signal formed by the upper layer re-transmission path coding unit becomes equal to the predetermined level difference with respect to an average amplitude level of the lower layer complex baseband signal formed by the lower layer demodulation and decoding unit,
the lower layer demodulation/decoding unit comprises means for generating a new lower layer complex baseband signal consisting of complex baseband signals of only the lower layer by performing power subtraction so as to subtract a replica signal of the upper layer complex baseband signal from the lower layer complex baseband signal after level adjustment by the level adjustment unit, sampling the new lower layer complex baseband signal at a symbol rate n using a sampling clock of frequency N and demapping the new lower layer complex baseband signal onto a complex plane based on a modulation scheme predetermined for the lower layer to obtain soft decision data of bits constituting each symbol, and performing error correction decoding processing on a block code having a coding rate predetermined for the lower layer to restore the lower layer data. A transmitter of a power hierarchical transmission method, which defines two systems of modulated signals of a line coding method as upper and lower hierarchical layers, adds the modulated signals of the two systems at different power levels, and transmits the signals by a single carrier,
a symbol rate for transmitting the data of the upper layer is n/2, a symbol rate for transmitting the data of the lower layer is n, and a symbol clock frequency corresponding to the symbol rate n is N, the symbol rate being n. A clock generating unit has a reference clock generating unit that generates a reference clock of N, which is four times the symbol rate, and a frequency divider that divides the reference clock to generate sampling clocks of frequencies 2N, N, and N/2;
an upper layer transmission path coding unit that inputs upper layer data to be transmitted at a symbol rate of n/2, performs error correction coding processing to form coded data by adding error correction parity using a block code having a coding rate predetermined for the upper layer, generates an upper layer complex baseband signal based on a modulation method predetermined for the upper layer in synchronization with a sampling clock of frequency N/2, upsamples the upper layer complex baseband signal using a sampling clock of frequency N, performs waveform shaping with a roll-off rate for the upper layer, and then upsamples the new upper layer complex baseband signal using the reference clock as a sampling clock to form a modulated signal for the upper layer;
a lower layer transmission path coding unit that receives lower layer data to be transmitted at a symbol rate n, performs error correction coding processing to form coded data by adding error correction parity using a block code having a coding rate predetermined for the lower layer, generates a lower layer complex baseband signal based on a modulation method predetermined for the lower layer in synchronization with a sampling clock of frequency N, upsamples the lower layer complex baseband signal using a sampling clock of frequency 2N, performs waveform shaping with a roll-off rate for the lower layer, and then upsamples the new lower layer complex baseband signal using the reference clock as a sampling clock to form the lower layer modulated signal;
a power adder that adjusts the level of one or both of the modulated signals of the upper layer and the modulated signals of the lower layer so that an average amplitude level of the modulated signal of the upper layer has a predetermined level difference with respect to an average amplitude level of the modulated signal of the lower layer, and then generates a combined complex baseband signal by power adding the modulated signals of the upper layer and the lower layer;
a quadrature modulation unit that uses the reference clock as a sampling clock to quadrature-modulate the combined complex baseband signal to generate a modulated wave signal for transmission;
A transmitting device comprising: A receiving device that receives a modulated wave signal generated by the transmitting device according to claim 7 via a satellite broadcast transmission path and restores the upper layer data and the lower layer data,
a receiving-side clock generating unit that generates a reference clock of N, which is four times the frequency of the reference clock; and a receiving-side frequency divider that divides the reference clock to generate sampling clocks of frequencies 2N, N, and N/2;
an upper layer demodulation/decoding unit that treats the synthesized complex baseband signal obtained by orthogonally demodulating the received signal using a sampling clock of frequency 2N as an upper layer complex baseband signal, down-samples the signal using a sampling clock of frequency N, performs waveform shaping with a roll-off rate for the upper layer, samples the signal using a sampling clock of frequency N/2 at a symbol rate n/2, and demaps the signal onto a complex plane based on a modulation method predetermined for the upper layer to obtain soft decision data of bits constituting each symbol, and performs error correction decoding processing on a block code having a coding rate predetermined for the upper layer to restore the data of the upper layer;
an upper layer re-transmission path coding unit that receives the upper layer data restored by the upper layer demodulation and decoding unit, performs error correction coding processing for the upper layer, regenerates an upper layer complex baseband signal based on the upper layer modulation scheme in synchronization with a sampling clock of frequency N/2, upsamples a replica signal of the upper layer complex baseband signal using a sampling clock of frequency N, performs waveform shaping with a roll-off rate for the upper layer, and then upsamples using a sampling clock of frequency 2N to form a new replica signal of the upper layer complex baseband signal;
a lower layer demodulation/decoding unit having means for treating the synthesized complex baseband signal obtained by orthogonally demodulating the received signal using the reference clock as a sampling clock, downsampling the synthesized complex baseband signal as a lower layer complex baseband signal, using a sampling clock having a frequency of 2N, and then forming a lower layer complex baseband signal by performing waveform shaping with a roll-off rate for the lower layer;
a level adjustment unit that adjusts the levels of one or both of the replica signal of the upper layer complex baseband signal and the lower layer complex baseband signal so that an average amplitude level of the replica signal of the upper layer complex baseband signal formed by the upper layer re-transmission path coding unit becomes equal to the predetermined level difference with respect to an average amplitude level of the lower layer complex baseband signal formed by the lower layer demodulation and decoding unit,
the lower layer demodulation/decoding unit comprises means for generating a new lower layer complex baseband signal consisting of complex baseband signals of only the lower layer by performing power subtraction so as to subtract a replica signal of the upper layer complex baseband signal from the lower layer complex baseband signal after level adjustment by the level adjustment unit, sampling the new lower layer complex baseband signal at a symbol rate n using a sampling clock of frequency N and demapping the new lower layer complex baseband signal onto a complex plane based on a modulation scheme predetermined for the lower layer to obtain soft decision data of bits constituting each symbol, and performing error correction decoding processing on a block code having a coding rate predetermined for the lower layer to restore the lower layer data.