Transmitter and Receiver of Hierarchical Transmission Method

Abstract

To provide a transmission device and a receiving device capable of correcting non-linear distortion caused by a broadcasting transmission path of satellite broadcasting while increasing resistance to rain attenuation and the like when hierarchically transmitting two systems of modulated signals with a single carrier.SOLUTION: A transmission device 1 according to the present invention includes a function (11,12,13) to synchronize each data of the upper layer and the lower layer transmitted by a power hierarchical transmission system (LDM), add a pilot signal for transmission channel distortion correction of LDM only to the upper layer, and form each modulation signal for the upper layer and the lower layer, and a function (14, 15) for generating a complex baseband signal by synthesizing each modulated signal through level adjustment and performing quadrature modulation. A receiving device 2 according to the present invention includes functional unit (22, 23, 24, 25) for detecting and correcting non-linear distortion caused by a satellite broadcasting transmission channel in the complex baseband signal obtained from the transmission device 1, and a functional unit (21, 26, 27, 28) for synchronizing and restoring each data in the upper and lower layers on the basis of LDM.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a transmission device and a reception device that hierarchically transmit two modulated signals using a single carrier.

Background Art

[0002] Modulation methods in 12 GHz band satellite digital broadcasting include BPSK including π / 2-shift BPSK, QPSK including π / 4-shift QPSK, 8PSK, 16APSK, etc., and are transmitted using a single carrier. This transmission method for 12 GHz band 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 (see, for example, Non-Patent Document 1). In this satellite broadcasting, hierarchical transmission combining a strong layer (a layer using a lower-order modulation method and a lower coding rate to enhance transmission tolerance) and a weak layer (a layer using a higher-order (multi-value) modulation method and a higher coding rate to enable high-capacity transmission) is possible. For example, QPSK·coding rate 1 / 2 is used for the strong layer, and 16APSK·coding rate 7 / 9 is used for the weak layer. The hierarchical transmission of 12 GHz band satellite broadcasting is a time-division hierarchical transmission method in which one frame is divided into a strong layer and a weak layer and transmitted in a time-division manner. Although the number of transmission bits per symbol is different between the strong layer and the weak layer, the symbol rate is constant. In recent years, 21 GHz band satellite broadcasting has also been studied.

[0003] In terrestrial digital broadcasting, a multi-carrier modulation method called OFDM is adopted, and its carrier modulation methods include QPSK, 16QAM, 64QAM, etc. This transmission method of terrestrial digital broadcasting is called ISDB-T (see, for example, Non-Patent Document 2). In recent years, in terrestrial broadcasting for the next generation, a power layer transmission (hereinafter referred to as "LDM") method in which another modulation signal is added powerfully to the modulation signal of the existing ISDB-T and multiplexed has been studied. This LDM method is a layer transmission method in which the data carrier of the next-generation broadcast (hereinafter referred to as the "4K layer") is OFDM-modulated and multiplexed with the data carrier of the existing ISDB-T (hereinafter referred to as the "2K layer"), and both 2K and 4K are broadcast on the same channel as before (see, for example, Non-Patent Document 3). In this method, the 4K layer is multiplexed with a small power with respect to the 2K layer, and transmission is performed with the power difference between the two power levels of the strong layer (upper layer: 2K) and the weak layer (lower layer: 4K). On the receiving side, first, the 2K data signal is obtained by demodulating and error-correcting decoding from the upper layer, and the decoded signal is error-correction encoded and remodulated again, and only the 2K signal, which is the transmission signal of the upper layer, is reproduced. The signal of only the lower layer (4K) is obtained by subtracting this reproduced 2K signal from the received signal (the composite signal including both the upper layer (2K) and the lower layer (4K)), and is demodulated and error-correction decoded to obtain the 4K data signal (see, for example, Non-Patent Document 4). In this LDM method, generally, the FFT clocks of OFDM for the upper layer and the lower layer are the same for simplification of demodulation.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] In satellite broadcast transmission, received power is attenuated due to rain attenuation, and the received C / N decreases. In time-division hierarchical transmission, the difference in the strength of hierarchical transmission can only be created by the difference in the strength of transmission due to the modulation method and the coding rate of the error correction code. The difference in the required C / N between the strong layer and the weak layer in hierarchical transmission is about 9.5 dB. For example, when the strong layer is QPSK·coding rate 1 / 2, the required C / N is about 1.2 dB, and when the weak layer is 16APSK·coding rate 7 / 9, the required C / N is about 10.8 dB. When received with a 45 cm parabolic antenna in Tokyo, the received C / N on a sunny day is about 20 dB, but the attenuation due to rain exceeds 10 dB and can be 20 dB or more. Also, in 21 GHz band satellite broadcast, the attenuation due to rain is extremely large. In order to further increase the difference in the required C / N between the strong layer and the weak layer, there was a limit with only the difference in the modulation method and the coding rate of the error correction code.

[0006] And in the case where the rainfall attenuation amount exceeds 20 dB in satellite broadcasting, since the received C / N becomes 0 dB or less, in the conventional time-division hierarchical transmission system, errors occurred even in the strong layer, and information could not be transmitted.

[0007] Therefore, even in the case where there is attenuation of the transmission signal due to rainfall attenuation of 20 dB or more, an LDM system transmitter and receiver capable of transmitting at least minimum information in the strong layer are desired.

[0008] Furthermore, in satellite broadcasting, as its broadcast transmission path, the distance between the satellite repeater and the receiver is extremely long (the artificial satellite is stationary at an altitude of 36,000 km), so it is desirable to transmit the satellite broadcast signal from the satellite repeater with as high power (maximum power) as possible. In the vicinity of the maximum output of this satellite broadcast signal, non-linear distortion occurs due to the input-output characteristics of the relay amplifier (traveling wave tube amplifier (TWTA)) in the satellite repeater. That is, as the input-output characteristics of the relay amplifier, the characteristics of the normalized output power with respect to the normalized input power (AM-AM characteristics), and the characteristics of the relative phase shift of the normalized output with respect to the normalized input power (AM-PM characteristics) do not become linear (straight line). However, generally, if it is used at an output several dB lower than the maximum output of the satellite broadcast signal, the input-output characteristics are almost linear, so the influence of non-linear distortion can be ignored in any transmission system including LDM.

[0009] However, depending on the input signal level of the relay amplifier, it is also assumed that the output reaches near the maximum output of 0 dB of the normalized output power. In this case, unless a device for compensating or correcting the non-linear distortion caused by the broadcast transmission path of satellite broadcasting is provided, any transmission system including LDM will be affected by non-linear distortion and the transmission performance will deteriorate.

[0010] For this reason, an object of the present invention is to provide a transmitter and a receiver that can correct non-linear distortion caused by the broadcast transmission path of satellite broadcasting while enhancing the resistance to rainfall attenuation and the like when hierarchically transmitting two modulation signals with a single carrier.

Means for Solving the Problem

[0011] The transmission device of the present invention defines modulation signals of two types of transmission path coding systems as the upper layer and the lower layer respectively, and adds the two types of modulation signals powerfully at different levels and transmits them via a satellite broadcast transmission path with a single carrier in a power layer transmission method. The transmission device includes: a symbol rate for transmitting the upper layer data is m, a symbol rate for transmitting the lower layer data 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 that generates a reference clock of 4 times M×N common to the upper layer and the lower layer, and a clock generation unit having a frequency divider that generates sampling clocks respectively divided for the upper layer and the lower layer based on the reference clock; inputting upper layer data transmitted at a symbol rate m, and configuring an upper layer modulation frame that can store a pilot signal predetermined for transmission path distortion correction of the power layer transmission method in front of the upper layer data, and for the upper layer modulation frame, based on the upper layer sampling clock based on the reference clock, generating a complex baseband signal for the upper layer based on a predetermined transmission path 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, and an upper layer transmission path coding unit that forms it as the modulation signal of the upper layer sampled by the reference clock; inputting lower layer data transmitted at a symbol rate n, and configuring a lower layer modulation frame having the same structure as the upper layer modulation frame without storing the pilot signal, and the lower layer modulation frame Re - For the frame, based on the upper layer sampling clock based on the reference clock, generating a complex baseband signal for the upper layer based on a predetermined transmission path 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, and forming it as the modulation signal of the upper layer sampled by the reference clock; inputting lower layer data transmitted at a symbol rate n, and without storing the pilot signal, configuring a lower layer modulation frame having the same structure as the upper layer modulation frame, and the lower layer modulation frame ReBased on the sampling clock for the lower layer with respect to the reference clock for the beam, a complex baseband signal for the lower layer is generated based on a predetermined transmission path coding method that specifies at least the error correction coding rate, modulation method, and roll-off rate of waveform shaping for the lower layer, and is formed as a modulation signal for the lower layer sampled by the reference clock. A transmission path coding unit for the lower layer, and after performing level adjustment on either one or both of the modulation signal for the upper layer and the modulation signal for the lower layer so that the average amplitude level of the modulation signal for the upper layer becomes a predetermined level difference with respect to the average amplitude level of the modulation signal for the lower layer, a power addition unit that generates a complex baseband signal synthesized by power addition of the modulation signal for the upper layer and the modulation signal for the lower layer, and an orthogonal modulation unit that uses the reference clock as a sampling clock to perform orthogonal modulation on the synthesized complex baseband signal to generate a modulated wave signal for transmission. It is characterized by comprising.

[0012] Further, in the transmission device of the present invention, the ratio of the symbol rate m for transmitting the upper layer data to the symbol rate n for transmitting the lower layer data is any one of m:n = 1:1, 1:2, 1:4, 2:3, 3:4. It is characterized by this.

[0013] Further, in the transmission device of the present invention, as the ratio of the symbol rate m for transmitting the upper layer data to the symbol rate n for transmitting the lower layer data, n is an integer multiple of m, and the reference clock generation unit is configured to generate a reference clock of 4 times N with M = 1. It is characterized by this.

[0014] The receiving apparatus of the present invention is a receiving apparatus that receives a modulated wave signal generated by the transmitting apparatus of the present invention via a broadcast transmission path of satellite broadcasting and restores the upper layer data and the lower layer data. The receiving apparatus includes: a receiving-side reference clock generation unit that generates a quadruple M×N reference clock common to the upper layer and the lower layer; and a receiving-side clock generation unit having a receiving-side frequency divider that generates sampling clocks respectively divided for the upper layer and the lower layer based on the reference clock. The receiving-side clock generation unit includes: a quadrature demodulation and analog / digital conversion unit that uses the reference clock as a sampling clock to quadrature demodulate a received signal in a predetermined frequency band in the received modulated wave signal and obtains a complex baseband signal in digital signal format; a non-linear distortion detection unit that detects an operating point on a non-linear distortion curve of input / output characteristics occurring in the broadcast transmission path of the satellite broadcasting for the complex baseband signal; a non-linear distortion correction unit that corrects distortion for the complex baseband signal based on the operating point; an upper layer demodulation and decoding unit that treats the complex baseband signal after the distortion correction as an upper layer complex baseband signal and inputs it, and performs demodulation and decoding processing with a symbol rate m based on a transmission path coding method corresponding to the upper layer on the transmitting apparatus side to restore the upper layer data; an upper layer retransmission path coding unit that inputs the upper layer data restored by the upper layer demodulation and decoding unit, regenerates an upper layer complex baseband signal based on a predetermined transmission path coding method in which at least an error correction coding rate, a modulation method, and a roll-off rate of waveform shaping are specified for the upper layer, and forms it as a replica signal of the upper layer complex baseband signal; a lower layer complex baseband signal forming unit that inputs the complex baseband signal after the distortion correction, performs waveform shaping with a roll-off rate for the lower layer to form a lower layer complex baseband signal, and adjusts the level of either one or both of the replica signal of the upper layer complex baseband signal formed by the upper layer retransmission path coding unit and the lower layer complex baseband signal so that the average amplitude level of the replica signal of the upper layer complex baseband signal becomes the predetermined level difference with respect to the average amplitude level of the lower layer complex baseband signal. After the level adjustment,A new complex baseband signal for the lower layer, which consists only of the complex baseband signal of the lower layer, is generated by performing power subtraction so as to subtract a replica signal of the complex baseband signal for the upper layer from the complex baseband signal for the lower layer, and demodulation and decoding processing with a symbol rate of n based on the transmission path coding method for the lower layer corresponding to the transmission device side is performed on the new complex baseband signal for the lower layer to restore the data of the lower layer, and a demodulation and decoding unit for the lower layer is provided.

[0015] Further, in the receiving apparatus of the present invention, the non-linear distortion detection unit holds input / output characteristics having non-linear distortion of the broadcast transmission path of the satellite broadcast, and on the input / output characteristics, the average power and peak power of the quadrature-demodulated complex baseband signal are detected, and means for inferring and detecting each operating point on the input / output characteristics in the broadcast transmission path of the satellite broadcast from these two points is provided.

[0016] Further, in the receiving apparatus of the present invention, a pilot signal predetermined for correcting transmission path distortion of the power layer transmission method is stored in the modulation frame for the upper layer in the transmission apparatus, and in the modulation frame for the lower layer that is hierarchically transmitted in synchronization with the modulation frame for the upper layer, the pilot signal is not stored and there is no signal during the signal period in which the pilot signal in the modulation frame for the upper layer is stored. The non-linear distortion detection unit holds input / output characteristics having non-linear distortion of the broadcast transmission path of the satellite broadcast, and on the input / output characteristics, at least three types of pilot signals having different amplitudes are detected from the pilot signal period of the quadrature-demodulated received signal, and means for inferring and detecting each operating point on the input / output characteristics in the broadcast transmission path of the satellite broadcast from the at least three types of signal levels is provided.

[0017] Also, in the receiving apparatus of the present invention, the non-linear distortion correction unit obtains, based on each operating point on the input / output characteristics in the broadcast transmission path of the satellite broadcast obtained from the non-linear distortion detection unit, a correction operating point on the linear characteristic corresponding to each operating point on the input / output characteristics using a linear characteristic assumed to have no non-linear distortion in the input / output characteristics, and when the complex baseband signal, which is the quadrature demodulated received signal, is located between each operating point on the input / output characteristics, distortion correction is performed by correcting the amplitude and phase of the complex baseband signal so as to have a linear characteristic based on each correction operating point.

[0018] Also, in the receiving apparatus of the present invention, the ratio between the symbol rate m for transmitting the upper layer data and the symbol rate n for transmitting the lower layer data is set to any one of m:n = 1:1, 1:2, 1:4, 2:3, 3:4 in accordance with the transmitting apparatus.

[0019] Also, in the receiving apparatus of the present invention, as the ratio between the symbol rate m for transmitting the upper layer data and the symbol rate n for transmitting the lower layer data, n is an integer multiple of m, and the reception-side reference clock generation unit is configured to generate a reference clock of 4 times N with M = 1.

Advantages of the Invention

[0020] According to the present invention, compared with the conventional time-division hierarchical transmission method, it is possible to make the difference in the transmission strength (the difference in required C / N) between the strong layer and the weak layer of the power-division hierarchical transmission (LDM) method larger. In particular, even in a situation where the receiving side is affected by the non-linear distortion of the satellite repeater, the distortion can be corrected, and even when an attenuation of 20 dB or more occurs due to rainfall, the reception operation of the transmission data of the strong layer can be stabilized, and it becomes possible to obtain information on the transmission data of both the strong layer and the weak layer in a more resistant manner.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Best Mode for Carrying Out the Invention

[0022] Hereinafter, with reference to the drawings, a transmission device 1 and a reception device 2 of a power division hierarchical transmission (LDM) system according to an embodiment of the present invention will be described. Also, as an embodiment of the present invention, an example will be described assuming that the data in the upper layer is a 2K data signal and the data in the lower layer is a 4K data signal.

[0023] (Transmission System) FIG. 1 is a block diagram showing a schematic configuration of a transmission system 100 including a transmission device 1 and a reception device 2 of a power division hierarchical transmission (LDM) system according to an embodiment of the present invention. The transmission system 100 of the embodiment shown in FIG. 1 can be made compliant with standards adopted in digital broadcasting, such as ISDB-S, ISDB-S3, etc., and includes a transmission device 1, a power amplifier 101, and a transmission antenna 102 at an earth station, a reception antenna 103, a satellite repeater 104, and a transmission antenna 105 at a satellite relay station, and a reception antenna 106 and a reception device 2 in a receiving facility.

[0024] The transmission device 1 inputs transmission data composed of TS packets (or IP packets) such as video, audio, and data broadcasts in a TS (or IP (Internet Protocol)) for each broadcaster as a main signal, generates a modulated wave signal, and outputs it to the power amplifier 101. The power amplifier 101 amplifies the modulated wave signal output from the transmission device 1 and transmits it as an uplink signal to the satellite relay station via the transmission antenna 102.

[0025] In the satellite relay station, the satellite repeater 104 receives an uplink signal via the receiving antenna 103, and includes a receiving filter 1041 that performs band extraction for each channel from the modulated wave signals constituting the uplink signal, a relay amplifier 1042 that amplifies the power of the band-extracted signal, a transmitting filter 1043 that generates a broadcast wave signal with out-of-band unwanted frequency components (spectrum regrowth) suppressed after the power amplification, and a synthesizer (not shown) following the transmitting filter 1043 generates a satellite broadcast signal by synthesizing the broadcast wave signals for all channels, and transmits it as a downlink signal to a ground receiving facility.

[0026] The receiving device 2 is configured as a device that receives and demodulates a downlink signal from a satellite relay station via a receiving antenna 106, performs a decoding process corresponding to the reverse process of each process in the transmitting device 1, and restores the transmission data transmitted by the transmitting device 1 as received data.

[0027] In such satellite broadcasting, as described above, since the distance between the satellite repeater 104 and the receiving device 2 is extremely long as the broadcast transmission path (the artificial satellite is stationary at an altitude of 36,000 km), it is desirable to transmit the satellite broadcast signal from the satellite repeater 104 with as high power (maximum power) as possible. In the vicinity of the maximum output of this satellite broadcast signal, non-linear distortion occurs due to the input-output characteristics of the relay amplifier 1042 in the satellite repeater 104. FIG. 2 illustrates the input-output characteristics (AM-AM characteristics, AM-PM characteristics) showing the non-linear distortion characteristics of the relay amplifier 1042 in the satellite repeater 104.

[0028] That is, as the input / output characteristics of the relay amplifier 1042, the AM-AM characteristic and the AM-PM characteristic do not become linear (straight lines). Depending on the input signal level of the relay amplifier 1042, it is also assumed that the output reaches near the maximum output of 0 dB of the normalized output power. In this case, unless a device for compensating or correcting the non-linear distortion caused by the broadcast transmission path of satellite broadcasting is provided, any transmission method including LDM will be affected by non-linear distortion and the transmission performance will deteriorate. In particular, in the transmission system 100 shown in FIG. 1, when the transmission device 1 and the reception device 2 are configured as a power division hierarchical transmission method (LDM), a transmission spectrum including an interference wave component caused by the non-linear distortion output from the satellite repeater 104 is formed.

[0029] More specifically, in the transmission device 1 and the reception device 2 of the power division hierarchical transmission (LDM) method according to an embodiment of the present invention, it is assumed that they are applied to a satellite digital broadcast system such as a 12 GHz band or 21 GHz band satellite broadcast. The outline of the transmission spectrum in the transmission device 1 is as shown in FIG. 3. FIG. 3 shows the outline of the transmission spectrum in the transmission device 1 of the power division hierarchical transmission (LDM) method according to the present invention. As shown in FIG. 3, the Nyquist frequency bandwidth of the lower layer is BWb (the symbol rate is n, and the roll-off rate is b), and the Nyquist frequency bandwidth of the upper layer is BWa (the symbol rate is m, and the roll-off rate is a). A new modulation signal is generated by adding the modulation signal of the upper layer (strong layer) to the modulation signal of the lower layer (weak layer) at a level α times the average amplitude level of the modulation signal of the lower layer (weak layer), and hierarchical transmission is performed toward the reception device 2. Here, m ≦ n (when m = n, they have the same bandwidth), and α ≧ 1. Also, as the modulation method for each layer, it may be different or the same between layers, such as BPSK, QPSK, 8PSK, 16QAM, 16APSK, 32APSK, etc. Also, as the error correction method for each layer, although not limited, in this example, concatenated codes of LDPC and BCH are assumed.

[0030] On the one hand, Fig. 4 shows a schematic of the transmission spectrum including the interference wave component caused by the non-linear distortion output from the satellite repeater 104 in the transmission system 100 according to the present invention. As shown in Fig. 4, when the satellite repeater 104 has input-output characteristics with non-linear distortion, mainly, the third-order distortion component of the upper layer with a high signal level becomes the interference wave component and occurs over a bandwidth three times the bandwidth BWa of the upper layer frequency band. However, since it is band-limited by the transmission filter 1043 of the satellite repeater 104, the actually radiated satellite broadcast signal has a bandwidth approximately the same as the channel bandwidth in the lower layer, but specific non-linear distortion is caused by the interference wave component.

[0031] Therefore, conventionally, there are forms of generating and transmitting a modulated wave signal that is compensated in advance on the transmitter side using the inverse characteristics of the non-linear distortion caused by the broadcast transmission path of satellite broadcasting, and techniques for correcting the non-linear distortion on the receiver side using a pilot signal transmitted from the transmitter. However, in the transmission system 100 shown in Fig. 1, when the transmitter 1 and the receiver 2 are configured as a power division hierarchical transmission system (LDM), it is necessary to provide a device for compensating or correcting the non-linear distortion peculiar to the LDM. That is, it is necessary to perform distortion correction on the complex baseband signal for the upper layer before demodulation of each layer of the upper layer and the lower layer.

[0032] Therefore, in the transmitter 1 and the receiver 2 according to the present embodiment, although the detailed configuration will be described later, generally, on the transmitter 1 side, a modulation frame including a pilot signal for the upper layer that enables the non-linear distortion of the satellite repeater 104 to be corrected on the receiver 2 side together with the transmission data is configured and a modulated wave signal is sent out. Then, on the receiver 2 side, using the orthogonally demodulated received signal (complex baseband signal for the upper layer) or the pilot signal, the correction characteristics for the orthogonally demodulated received signal (complex baseband signal for the upper layer) are obtained, and distortion correction is performed during LDM demodulation.

[0033] There are two embodiments for the distortion correction on the receiving device 2 side. The distortion correction in Embodiment 1 is a method of obtaining its correction characteristics by using the quadrature-demodulated received signal (complex baseband signal of LDM), and the distortion correction in Embodiment 2 is a method of obtaining the correction characteristics for the quadrature-demodulated received signal (complex baseband signal of LDM) by using the pilot signal obtained from the quadrature-demodulated received signal (complex baseband signal for the upper layer).

[0034] In the transmitting device 1 of the present embodiment, in particular, in order to enable distortion correction on the receiving device 2 side by the above Embodiment 2, the modulation frame for the upper layer of the power division hierarchical transmission system (LDM) includes a pilot signal for transmission path distortion correction of LDM.

[0035] Hereinafter, more specifically, the configurations and operations of the transmitting device 1 and the receiving device 2 of the present embodiment will be described.

[0036] (Transmitting device) FIG. 5 is a block diagram showing a schematic configuration of a transmitting device of a power division hierarchical transmission (LDM) system according to an embodiment of the present invention.

[0037] The transmitting device 1 shown in FIG. 5 has functional units for performing error correction coding, modulation mapping, and roll-off filtering on two systems of data, namely, data of the upper layer (strong layer) transmitted at symbol rate m and data of the lower layer (weak layer) transmitted at symbol rate n, respectively. The two systems of modulation signals (combinations of symbol rate, error correction coding rate, modulation method, and roll-off rate) are power-added and transmitted as a single-carrier power division hierarchical transmission (LDM) system. More specifically, the transmitting device 1 shown in FIG. 5 basically includes a clock generation unit 11, an upper layer transmission path coding unit 12, a lower layer transmission path coding unit 13, a power addition unit 14, and a quadrature modulation unit 15.

[0038] The clock generation unit 11 includes a reference clock generation unit 111 and a frequency divider 112.

[0039] The reference clock generation unit 111 is a functional unit that generates a reference clock with a frequency of 4 times M×N (where 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). And m≦n, M≦N.

[0040] The divider 112 is a functional unit that divides the reference clock generated by the reference clock generation unit 111 and generates the necessary sampling clocks for each part of the transmission device 1 shown in FIG. 5. In this example, it includes a division unit 112a and a division unit 112b.

[0041] The division unit 112a divides the reference clock generated by the reference clock generation unit 111 by 1 / (N×4) and generates a sampling clock with a frequency of M.

[0042] The division unit 112b divides the reference clock generated by the reference clock generation unit 111 by 1 / (M×4) and generates a sampling clock with a frequency of N.

[0043] In this way, in the transmission device 1 shown in FIG. 5, the clock generation unit 11 uses 4 times M×N as the common reference clock for the upper layer and the lower layer, and by dividing this reference clock, it generates sampling clocks with frequencies M and N. However, the clock generation unit 11 may also generate other sampling clocks (for example, sampling clocks of 2M, 2N), and can be appropriately used for upsampling associated with the roll-off filter units 123, 133 and the level adjustment unit 141 described later using each divided clock.

[0044] The upper layer transmission path encoding unit 12 includes a frame configuration unit 120, an error correction encoding unit 121, a modulation mapping unit 122, and a roll-off filter unit 123.

[0045] The frame forming unit 120 inputs data of an upper layer (for example, a strong layer of 2K) to be transmitted as encoded data with a symbol rate of m, and forms a modulation frame in which a pilot signal for LDM transmission path distortion correction is added to the data of the upper layer serving as the main signal within the LDM pilot signal period at the front stage of the data (which will be described later with reference to FIGS. 6 to 8), and outputs it to the error correction encoding unit 121.

[0046] The error correction encoding unit 121 inputs a modulation frame of an upper layer (for example, a strong layer of 2K) to be transmitted as encoded data with a symbol rate of m from the frame forming unit 120, and performs error correction encoding processing to form encoded data by adding error correction parity by a block code (for example, a concatenated code of LDPC and BCH) with a predetermined encoding rate (for example, an encoding rate of 1 / 2) for the upper layer to the modulation frame of the upper layer, and outputs it to the modulation mapping unit 122.

[0047] The modulation mapping unit 122 synchronizes with a sampling clock of a frequency M corresponding to the symbol rate m, maps the encoded data of the upper layer obtained from the error correction encoding unit 121 to a constellation of a predetermined digital modulation method (for example, QPSK), and performs mapping on the complex (IQ) plane to generate a complex baseband signal for the upper layer (a signal that is an orthogonal signal of the in-phase component I and the quadrature phase component Q and can be represented as a signal point series of signal points on the IQ plane), and outputs it to the roll-off filter unit 123.

[0048] The roll-off filter unit 123 is composed of a root roll-off filter which is a kind of band-limiting filter having a predetermined roll-off rate (let the roll-off rate of the upper layer be a). It performs waveform shaping by appropriately performing upsampling on the complex baseband signal for the upper layer obtained from the modulation mapping unit 122 to remove unnecessary high-frequency components, forms a complex baseband signal for the upper layer that is upsampled to match the sampling clock between the upper layer and the lower layer, and outputs it to the level adjustment unit 141.

[0049] The transmission path encoding unit 13 for the lower layer includes a frame configuration unit 130, an error correction encoding unit 131, a modulation mapping unit 132, and a roll-off filter unit 133.

[0050] The frame configuration unit 130 inputs data of the lower layer (for example, a weak layer of 4K) to be transmitted as encoded data with a symbol rate of n, and constructs a modulation frame having the same structure as the modulation frame in the frame configuration unit 120 described above. However, during the pilot signal period for LDM in the front stage of the data of the lower layer serving as the main signal, a modulation frame is constructed with no signal (that is, Null is inserted) without adding a pilot signal for transmission path distortion correction of LDM (to be described later with reference to FIG. 6), and outputs it to the error correction encoding unit 131.

[0051] The error correction encoding unit 131 inputs a modulation frame of the lower layer (for example, a weak layer of 4K) to be transmitted as encoded data with a symbol rate of n, and performs error correction encoding processing to form encoded data by adding error correction parity by a block code (for example, a concatenated code of LDPC and BCH) with a predetermined encoding rate (for example, an encoding rate of 7 / 9) for the lower layer to the modulation frame of the lower layer, and outputs it to the modulation mapping unit 132.

[0052] The modulation mapping unit 132 synchronizes with a sampling clock of frequency N corresponding to the symbol rate n, maps the encoded data of the lower layer obtained from the error correction encoding unit 131 to a constellation of a predetermined digital modulation method (for example, 16APSK), generates a complex baseband signal for the lower layer mapped on the complex (IQ) plane, and outputs it to the roll-off filter unit 133.

[0053] The roll-off filter section 133 is composed of a root roll-off filter, which is a type of band-limiting filter having a predetermined roll-off rate (let the roll-off rate of the lower layer be b). For the complex baseband signal for the lower layer obtained from the modulation mapping section 132, appropriate upsampling is performed to perform waveform shaping to remove unnecessary high-frequency components, and an upsampled complex baseband signal for the lower layer is formed so as to match the sampling clock between the upper layer and the lower layer, and is output to the addition section 142.

[0054] In addition, in the upsampling for matching the sampling clock between the upper layer and the lower layer in the roll-off filter section 123 and the roll-off filter section 133, here, an example is given in which a clock with the same frequency 4MN as the reference clock is used. Instead, by using a clock that is twice the least common multiple of M and N for upsampling, a configuration that handles frequencies as low as possible can also be achieved.

[0055] The power addition section 14 includes a level adjustment section 141 and an addition section 142.

[0056] The level adjustment section 141 performs level adjustment to make the average amplitude level of the complex baseband signal for the upper layer obtained from the roll-off filter section 123 α times that of the average amplitude level of the complex baseband signal for the lower layer (see FIG. 3 or FIG. 4), and outputs the level-adjusted complex baseband signal for the upper layer to the addition section 142.

[0057] The addition section 142 adds (synthesizes by adding power to the symbols sampled at the same timing) the level-adjusted complex baseband signal for the upper layer (QPSK·coding rate 1 / 2 in this example) obtained from the level adjustment section 141 and the complex baseband signal for the lower layer (16APSK·coding rate 7 / 9 in this example) obtained from the upsampling section 135 on the complex plane to obtain a modulated wave signal in a single frequency band, generates a complex baseband signal for hierarchical transmission with a single symbol rate, and outputs it to the quadrature modulation·D / A conversion section 151.

[0058] The quadrature modulation unit 15 includes a quadrature modulation / digital-to-analog (D / A) conversion unit 151 and a band-pass filter (BPF) unit 152.

[0059] Using a reference clock with a frequency of 4MN as a sampling clock, the quadrature modulation / D / A conversion unit 151 adds (quadrature-modulates) an I-axis signal and a Q-axis signal to the complex baseband signal of hierarchical transmission obtained from the adder 142 with a phase difference (time difference) of 90 degrees, and then performs digital-to-analog (D / A) conversion to generate a modulated wave signal in a single frequency band for hierarchical transmission, and outputs it to the BPF unit 152.

[0060] The BPF unit 152 performs band-pass filter processing for band-limiting the modulated wave signal obtained from the quadrature modulation / D / A conversion unit 151 to extract only signals near the reference clock with a frequency of 4MN, generates a modulated wave signal in the intermediate frequency (IF) band, sets it to a level corresponding to the transmitted power normalized in the state of the IF band signal, and transmits it. For the modulated wave signal in the IF band, in order to transmit it to the receiving device 2 via a transmission path including a satellite repeater such as a 12 GHz band or 21 GHz band satellite broadcast, it is transmitted with the total transmitted power of the upper layer and the lower layer set to a predetermined (normalized) transmitted power.

[0061] (Modulation frame) FIG. 6 is a diagram showing the insertion position of a pilot signal for transmission path distortion correction of LDM transmitted by a transmission apparatus 1 of a power division hierarchical transmission (LDM) system according to an embodiment of the present invention. As described above, the frame configuration unit 120 in the upper layer transmission path encoding unit 12 forms a modulated frame in which a pilot signal for transmission path distortion correction of LDM is added within the LDM pilot signal period in the front stage of the data for the upper layer data to be transmitted as encoded data with a symbol rate m. On the other hand, the frame configuration unit 130 in the lower layer transmission path encoding unit 13 forms a modulated frame having the same structure as the modulated frame in the frame configuration unit 120, but inserts Null (no signal) without adding a pilot signal for transmission path distortion correction of LDM to the lower layer data to be transmitted as encoded data with a symbol rate n. In this example, it is assumed that the modulated frame is formed with the "repetition period" shown in FIG. 6 (the "data" area shown in FIG. 6 includes the data area of the main signal and the parity area of the concatenated code). Note that the modulated frame according to the present embodiment can also be configured to have the same structure as a modulation slot compliant with, for example, ISDB-S3. In this case, a pilot signal for transmission path distortion correction of LDM is added to the frame header (176 bits) provided in the front stage of the data of the main signal.

[0062] In the transmission apparatus 1 of the present embodiment, a pilot signal for transmission path distortion correction of LDM is included in the upper layer modulated frame of the power division hierarchical transmission system (LDM) so that transmission path distortion correction can be performed particularly when using a pilot signal obtained from an orthogonally demodulated received signal (upper layer complex baseband signal) related to the distortion correction in Example 2.

[0063] FIG. 7 is an IQ plane diagram showing an example of a pilot signal for transmission path distortion correction of LDM transmitted by the transmission apparatus 1 of the present embodiment, and FIG. 8 is an IQ plane diagram showing another example thereof.

[0064] Figures 7 and 8 show three types of pilot signals that differ only in amplitude, namely, a reference pilot signal with an amplitude of "1", a pilot signal with an amplitude of "2" which is twice that, and a pilot signal with an amplitude of "0.5" which is half. The pilot signal for transmission path distortion correction of LDM as exemplified in Figures 7 or 8 is periodically inserted only into the modulation frames of the upper layer (strong layer). The signal point arrangement of the pilot signal for transmission path distortion correction of LDM is determined in advance by the transmitting device 1 regardless of the modulation method (BPSK, QPSK, 8PSK, 16QAM, 16APSK, 32APSK, etc.) used in the upper layer, and the receiving device 2 performs reception processing for distortion correction based on the amplitude and phase of the predetermined pilot signal. Incidentally, as described with reference to Figure 6, during the period when the pilot signal is inserted into the upper layer, the lower layer (weak layer) has no signal (no signal).

[0065] (Receiving Device) Figure 9 is a block diagram showing a schematic configuration of a receiving device 2 of a power division hierarchical transmission (LDM) system according to an embodiment of the present invention.

[0066] The receiving device 2 shown in Figure 9 receives the satellite broadcast signal via a receiving antenna 106 that receives a transmission signal at a satellite broadcast frequency and inputs a received signal converted to an intermediate frequency (IF) band. Then, the receiving device 2 extracts only the IF signal transmitted by the transmitting device 1 shown in Figure 5 from the received IF band received signal (IF signal), and is configured as a receiving device capable of separately receiving two systems of data, namely, data of the upper layer (strong layer) transmitted at a symbol rate of m and data of the lower layer (weak layer) transmitted at a symbol rate of n. More specifically, the receiving device 2 shown in Figure 9 basically includes a clock generation unit 21, a BPF unit 22, an orthogonal demodulation / analog-to-digital (A / D) conversion unit 23, a non-linear distortion detection unit 24, a non-linear distortion correction unit 25, an upper layer demodulation and decoding unit 26, an upper layer retransmission path encoding unit 27, and a lower layer demodulation and decoding unit 28.

[0067] The clock generation unit 21 includes a reference clock generation unit 211 and a frequency divider 212.

[0068] The reference clock generation unit 211 is a functional unit that generates a reference clock with a frequency of 4 times M×N (where 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 generation unit 111 on the transmission device 1 side shown in FIG. 5.

[0069] The divider 212 is a functional unit that divides the reference clock generated by the reference clock generation unit 211, similar to the divider 112 on the transmission device 1 side shown in FIG. 5, and generates the necessary sampling clocks for each part of the receiving device 2 shown in FIG. 9. In this example, it includes a dividing unit 212a and a dividing unit 212b.

[0070] The dividing unit 212a divides the reference clock generated by the reference clock generation unit 211 by 1 / (N×4) to generate a sampling clock with a frequency of M.

[0071] The dividing unit 212b divides the reference clock generated by the reference clock generation unit 211 by 1 / (M×4) to generate a sampling clock with a frequency of N.

[0072] In this way, in the receiving device 2 shown in FIG. 9, the clock generation unit 21 uses 4 times M×N as the common reference clock for the upper and lower layers, and generates sampling clocks with frequencies M and N by dividing this reference clock. Furthermore, the frequency of the reference clock is made the same between the transmission device 1 shown in FIG. 5 and the receiving device 2 shown in FIG. 9. However, the clock generation unit 21 may also generate other sampling clocks (for example, sampling clocks of 2M, 2N), and can be appropriately used for upsampling and downsampling associated with the roll-off filter units 251, 261, 271 and the level adjustment unit 272 described later using each divided clock.

[0073] The BPF unit 22 performs band-pass filter processing on the IF signal received via the reception antenna 106, extracts only the received signal in a desired frequency band from the IF signal transmitted by the transmission device 1 shown in FIG. 5, and outputs it to the quadrature demodulation / A / D conversion unit 23.

[0074] The quadrature demodulation / A / D conversion unit 23 uses a reference clock of 4 MN as a sampling clock, quadrature demodulates the received signal obtained from the BPF unit 22, divides it into I-axis data and Q-axis data, and then performs analog / digital (A / D) conversion processing to obtain a received signal of a complex baseband signal, which is output to the non-linear distortion detection unit 24 and the non-linear distortion correction unit 25.

[0075] The non-linear distortion detection unit 24 detects the operating points on the non-linear distortion curve of the input / output characteristics that occur in the satellite repeater 104 for the complex baseband signal obtained from the quadrature demodulation / A / D conversion unit 23, and outputs them to the non-linear distortion correction unit 25. More specifically, although details will be described later, the non-linear distortion detection unit 24 holds in advance the input / output characteristics having non-linear distortion of the satellite repeater 104 (in this example, the AM-AM characteristics and AM-PM characteristics in the relay amplifier 1042, but may also include the input / output characteristics of the reception filter 1041 and the transmission filter 1043). On its input / output characteristics, as the distortion correction of the first embodiment, the average power and peak power of the quadrature-demodulated received signal (complex baseband signal) are detected, and each operating point on the input / output characteristics in the satellite repeater 104 is inferred from these two points, or as the distortion correction of the second embodiment, at least three types of pilot signals with different amplitudes are detected from the pilot signal period of the quadrature-demodulated received signal, and each operating point on the input / output characteristics in the satellite repeater 104 is inferred and detected from these at least three types of signal levels, and then output to the non-linear distortion correction unit 25.

[0076] The non-linear distortion correction unit 25 performs distortion correction on the complex baseband signal obtained from the quadrature demodulation and A / D conversion unit 23 based on each operating point on the input / output characteristics in the satellite repeater 104 obtained from the non-linear distortion detection unit 24, and outputs the received signal after distortion correction to the upper layer demodulation and decoding unit 26 and the lower layer demodulation and decoding unit 28. More specifically, although details will be described later, the non-linear distortion correction unit 25, based on each operating point on the input / output characteristics in the satellite repeater 104 obtained from the non-linear distortion detection unit 24, uses the linear characteristics assumed to have no non-linear distortion in the input / output characteristics to obtain the correction operating points on the linear characteristics corresponding to each operating point on the input / output characteristics. When the quadrature-demodulated received signal (complex baseband signal) is located between each operating point on the input / output characteristics, the amplitude and phase of the quadrature-demodulated received signal (complex baseband signal) are corrected so as to have linear characteristics based on each correction operating point, thereby performing distortion correction on the quadrature-demodulated received signal obtained from the quadrature demodulation and A / D conversion unit 23, and outputting the received signal after distortion correction to the upper layer demodulation and decoding unit 26 and the lower layer demodulation and decoding unit 28.

[0077] The upper layer demodulation and decoding unit 26 is a functional unit that demodulates and decodes the upper layer complex baseband signal from the received signal after distortion correction, and includes a roll-off filter unit 261, a demodulation demapping unit 262, and an error correction decoding unit 263.

[0078] The roll-off filter unit 261 is composed of a root roll-off filter, which is a type of band-limiting filter having the same roll-off rate as that on the transmission device 1 side (the roll-off rate a of the upper layer). For the symbols of the received signal after distortion correction obtained from the non-linear distortion correction unit 25, appropriate downsampling is performed to perform waveform shaping to remove unnecessary high-frequency components, generate the upper layer complex baseband signal after waveform shaping, and output it to the demodulation demapping unit 262.

[0079] The demapping section 262 samples the complex baseband signal for the upper layer obtained from the roll-off filter section 261 at the symbol rate m using a sampling clock of frequency M, demaps it onto the complex plane of the digital modulation method (e.g., QPSK) corresponding to the transmitting device 1 side for the upper layer, obtains soft decision data (likelihood values) of the bits constituting each symbol by comparing with the constellation of the ideal signal points, and outputs it to the error correction decoding section 263.

[0080] The error correction decoding section 263 performs error correction decoding processing on the soft decision data for the upper layer obtained from the demapping section 262 for a block code (e.g., concatenated code of LDPC and BCH) with a coding rate (e.g., coding rate 1 / 2) predetermined for the upper layer, restores the data of the upper layer (strong layer), outputs it externally, and also outputs it to the error correction encoding section 271.

[0081] The retransmission path encoding section 27 for the upper layer is a functional section that re-encodes the data of the upper layer (strong layer) obtained from the error correction decoding section 263 by the same processing as the transmission path encoding processing in the transmission path encoding section 12 on the transmitting device 1 side to generate a replica of the complex baseband signal for the upper layer, and includes an error correction encoding section 271, a remodulation mapping section 272, a roll-off filter section 273, and a level adjustment section 274.

[0082] The error correction encoding section 271 inputs the data of the upper layer (strong layer) obtained from the error correction decoding section 263, performs error correction encoding processing to add error correction parity by a block code (e.g., concatenated code of LDPC and BCH) with a coding rate (e.g., coding rate 1 / 2) predetermined for the upper layer to the data of the upper layer as the main signal to form encoded data, and outputs it to the remodulation mapping section 272.

[0083] The remodulation mapping unit 272 synchronizes with a sampling clock of frequency M corresponding to the symbol rate m, and maps the upper-layer encoded data obtained from the error correction encoding unit 271 to a constellation of a predetermined digital modulation method (QPSK in this example), performs mapping on the complex (IQ) plane, generates a complex baseband signal for the upper layer, and outputs it to the roll-off filter unit 273.

[0084] The roll-off filter unit 273 is composed of a root roll-off filter which is a type of band-limiting filter having a roll-off rate (the roll-off rate a of the upper layer). For the complex baseband signal for the upper layer obtained from the remodulation mapping unit 272, it appropriately performs upsampling to perform waveform shaping to remove unnecessary high-frequency components, forms a replica signal of the complex baseband signal for the upper layer upsampled so as to match the sampling clock between the upper layer and the lower layer, and outputs it to the level adjustment unit 274.

[0085] The level adjustment unit 274, in cooperation with the level adjustment unit 282 described later, performs level adjustment to make the average amplitude level of the replica signal of the complex baseband signal for the upper layer obtained from the roll-off filter unit 273 α times that of the average amplitude level of the complex baseband signal for the lower layer (see FIG. 3 or FIG. 4), and outputs the replica signal of the complex baseband signal for the upper layer after the level adjustment to the subtraction unit 283.

[0086] On the other hand, the demodulation and decoding unit 28 for the lower layer is a functional unit that demodulates and decodes the received signal of the lower layer (weak layer), and includes a roll-off filter unit 281, a level adjustment unit 282, a subtraction unit 283, a demodulation demapping unit 284, and an error correction decoding unit 285.

[0087] The roll-off filter section 281 is composed of a root roll-off filter, which is a type of band-limiting filter having the same roll-off rate (the roll-off rate b of the lower layer) as that on the transmission device 1 side. For the symbols of the received signal after distortion correction obtained from the non-linear distortion correction section 25, appropriate downsampling is performed, waveform shaping is applied to remove unnecessary high-frequency components, and a complex baseband signal for the lower layer after waveform shaping is generated and output to the level adjustment section 282.

[0088] The level adjustment section 282, in cooperation with the above-described level adjustment section 274, performs level adjustment on the complex baseband signal for the lower layer obtained from the roll-off filter section 281 such that the average amplitude level of the complex baseband signal for the upper layer is α times that of the complex baseband signal for the lower layer (see FIG. 3 or FIG. 4), and outputs the complex baseband signal for the lower layer after the level adjustment to the subtraction section 283.

[0089] The subtraction section 283 subtracts (subtracts in terms of power for the symbols sampled at the same timing) the replica signal of the complex baseband signal for the upper layer after level adjustment obtained from the level adjustment section 274 from the complex baseband signal for the lower layer after level adjustment obtained from the level adjustment section 282 on the complex plane, generates a complex baseband signal for the lower layer composed of only the original lower layer (weak layer) complex baseband signal, and outputs it to the demodulation demapping section 284.

[0090] The demodulation demapping section 284 samples the complex baseband signal for the lower layer obtained from the subtraction section 283 at the symbol rate n using a sampling clock of frequency N, demaps it onto the complex plane of the digital modulation method (e.g., 16ASK) corresponding to the transmission device 1 side for the lower layer, compares it with the constellation of the ideal signal points, obtains soft decision data (likelihood values) of the bits constituting each symbol, and outputs them to the error correction decoding section 285.

[0091] The error correction decoding unit 285 performs error correction decoding processing on the soft decision data for the lower layer obtained from the demodulation demapping unit 284 with respect to a block code (for example, a concatenated code of LDPC and BCH) having a coding rate (for example, coding rate 7 / 9) determined in advance as the lower layer, restores the data of the lower layer (weak layer), and outputs it externally.

[0092] In the above-described embodiment, an example where the symbol rates of the upper layer and the lower layer are m:n has been described. However, as the simplest example, it is preferable that m:n = 1:1 or 1:2. When m:n = 1:1, that is, when the symbol rate of the upper layer is the same as the symbol rate of the lower layer, the basic configurations of the transmission device 1 and the reception device 2 may be set to 4MN = 4N, M = N. By setting m:n = 1:1, the advantage is that the operating clock is as low as 4N at maximum, and the clock generation unit 11 may also be a simple frequency division circuit of 1 / 2. Similarly, when m:n = 1:2, that is, when the symbol rate of the upper layer is half of the symbol rate of the lower layer, the basic configurations of the transmission device 1 and the reception device 2 may be set to 4MN = 4N, M = N / 2. By setting m:n = 1:2, the advantage is that the operating clock is as low as 4N at maximum, and the clock generation unit 11 may also be a simple frequency division circuit of 1 / 2. Here, since N is the symbol clock of the lower layer, when a multi-value (5-bit) modulation method such as 32APSK is used as the digital modulation method, the bit rate of the lower layer becomes 5N, and a clock larger than 4N is required.

[0093] However, as a preferred example, in addition to setting m:n = 1:1 or 1:2, it can also be set to m:n = 1:4, 3:4, 2:3, etc. In the case of these ratios, for example, compared to setting m:n = 3:5, the least common multiple of 2M and 2N becomes relatively small, and the frequency of the reference clock of 4MN becomes low, so the operation can be stabilized. Therefore, the ratio of m:n is set as a simple integer ratio, and in particular, it can be any one of m:n = 1:1, 1:2, 1:4, 2:3, 3:4, and preferably m:n = 1:1 or 1:2. And the reference clock generation unit 111 is configured to generate a reference clock of 4 times N with M = 1 when n is an integer multiple of m as the ratio of m:n (that is, in the above examples, the cases of 1:1, 1:2, 1:4). Thereby, the clock generation unit 11 can be configured with a simple frequency division circuit, and an operation with high stability can be realized.

[0094] Next, the distortion correction of Examples 1 and 2 in the non-linear distortion detection unit 24 and the non-linear distortion correction unit 25 in the receiving device 2 will be described more specifically.

[0095] (Distortion correction of Example 1) In the distortion correction of the first embodiment in the receiving apparatus 2, the non-linear distortion detection unit 24 holds in advance the input-output characteristics having non-linear distortion of the satellite repeater 104 (in this example, the AM-AM characteristics and AM-PM characteristics in the relay amplifier 1042 are targeted, but may include the input-output characteristics of the receiving filter 1041 and the transmitting filter 1043). On the input-output characteristics, the average power and peak power of the quadrature-demodulated received signal (complex baseband signal) are detected, and the most probable input value (normalized input power) corresponding to the average power and peak power is obtained from the output values (normalized output power and relative phase shift) of the input-output characteristics in the satellite repeater 104 so that the least squares error with respect to the input-output characteristics is minimized. The operating points of two points on the input-output characteristics are inferred and output to the non-linear distortion correction unit 25. The non-linear distortion correction unit 25 obtains two correction operating points on the linear characteristics corresponding to the two operating points on the input-output characteristics using the linear characteristics assumed to have no non-linear distortion in the input-output characteristics. When the quadrature-demodulated received signal (complex baseband signal) is located between the two operating points on the input-output characteristics, the amplitude and phase of the quadrature-demodulated received signal (complex baseband signal) are corrected so as to have linear characteristics based on each correction operating point, thereby performing distortion correction of the quadrature-demodulated received signal obtained from the quadrature demodulation / A / D conversion unit 23.

[0096] FIG. 10 is a diagram illustrating how the non-linear distortion detection unit 24 obtains the correction characteristics using the quadrature-demodulated received signal as the distortion correction in Example 1 in the receiving apparatus 2 according to an embodiment of the present invention. In FIG. 10, the solid line is a curve of the non-linear distortion characteristics of the relay amplifier 1042 measured in advance, and the dotted line is the linear characteristic when there is no non-linear distortion. As the distortion correction in Example 1 in the receiving apparatus 2 of the present embodiment, the non-linear distortion detection unit 24 detects the average power and the peak power of the quadrature-demodulated received signal, and from these two points, the input-output characteristics (AM-AM characteristics, AM-PM characteristics) of the relay amplifier 1042 that holds the respective values in advance. The curve of the non-linear distortion characteristics is fitted so that the minimum error is reduced, that is, the most probable input value (normalized input power) corresponding to the average power and the peak power is obtained from the output values (normalized output power and relative phase shift) of the input-output characteristics in the satellite repeater 104 so that the minimum mean square error with respect to the input-output characteristics is minimized, and thereby the operating points of the two points on the input-output characteristics are inferred. Note that it is preferable to select the average power around a few dB lower than 0 dB of the normalized power of the distorted line, and to select the peak power around 0 dB. And since the difference between the average power and the peak power when there is no non-linear distortion is known, the constraint condition is also used to determine the operating points of the two points where the minimum mean square error is the smallest as shown in FIG. 10 (the “●” and “▲” shown in the figure). The non-linear distortion correction unit 25 obtains correction values (the “〇” and “△” shown in the figure) on the linear characteristic with respect to the normalized input power corresponding to each of these operating points (the “●” and “▲” shown in the figure), and based on the operating points of the two points on the input-output characteristics (the “●” and “▲” shown in the figure), distortion correction can be performed to associate the level relationship between the amplitude, phase, and linear characteristic of the complex baseband signal. Note that since the level of the received signal is not limited to only the two operating points (the “●” and “▲” shown in the figure), the non-linear distortion correction unit 25 performs distortion correction according to the amplitude level of the complex baseband signal with these two points as the reference of the operating points.

[0097] (Distortion correction in Example 2) In the distortion correction of Example 2 in the receiving apparatus 2, the non-linear distortion detection unit 24 holds in advance the input-output characteristics having non-linear distortion of the satellite repeater 104 (in this example, the AM-AM characteristics and AM-PM characteristics in the relay amplifier 1042 are targeted, but may include the input-output characteristics of the receiving filter 1041 and the transmitting filter 1043). On the input-output characteristics, at least three types of pilot signals with different amplitudes are detected from the pilot signal period of the quadrature-demodulated received signal, and the most probable input values (normalized input power) corresponding to the at least three types of signal levels are obtained from the output values (normalized output power and relative phase shift) of the input-output characteristics of the satellite repeater 104 so that the least squares error with respect to the input-output characteristics is minimized. The operating points of at least three types of signal levels on the input-output characteristics are estimated and output to the non-linear distortion correction unit 25. The non-linear distortion correction unit 25 obtains the lowest three correction operating points on the linear characteristics corresponding to at least three types of signal levels on the input-output characteristics using the linear characteristics assumed to have no non-linear distortion in the input-output characteristics. When the quadrature-demodulated received signal (complex baseband signal) is located between the operating points of the lowest three points on the input-output characteristics, the amplitude and phase of the quadrature-demodulated received signal (complex baseband signal) are corrected so as to have linear characteristics based on each correction operating point, thereby performing distortion correction of the quadrature-demodulated received signal obtained from the quadrature demodulation / A / D conversion unit 23.

[0098] FIG. 11 is a diagram illustrating a state of obtaining correction characteristics for a quadrature-demodulated received signal (complex baseband signal for the upper layer) using a pilot signal obtained from the quadrature-demodulated received signal as distortion correction of Example 2 in the receiving apparatus 2 according to an embodiment of the present invention. In FIG. 11, the solid line is a curve of the non-linear distortion characteristics of the relay amplifier 1042 measured in advance, and the dotted line is the linear characteristics when there is no non-linear distortion. As the distortion correction of Example 2 in the receiving apparatus 2 of the present embodiment, the non-linear distortion detection unit 24 detects at least three types of pilot signals with different amplitudes from the pilot signal period of the quadrature-demodulated received signal, and infers each operating point on the input-output characteristics of the satellite repeater 104 from the at least three types of signal levels.

[0099] In FIG. 11, examples of a reference pilot signal with an amplitude of “1” corresponding to FIG. 7 or FIG. 8 described above, and three pilot signals with amplitudes of “0.5” and “2” are shown. That is, these pilot signals have a power difference of 3 dB. As described with reference to FIG. 6, the pilot signal is transmitted only in the upper layer, and at that time, the lower layer is a period without a signal. From these three points, fitting is performed so that the curve of the non-linear distortion characteristics on the input / output characteristics (AM-AM characteristics, AM-PM characteristics) of the relay amplifier 1042 that holds each value in advance and the minimum error are reduced. That is, from the output values (normalized output power and relative phase shift) of the input / output characteristics in the satellite repeater 104, the most probable input value (normalized input power) corresponding to at least three types of signal levels is obtained so that the minimum mean square error with respect to the input / output characteristics is minimized, and thereby the operating points of at least three types of signal levels on the input / output characteristics are inferred and obtained. Note that the reference pilot signal with an amplitude of “1” is at a level several dB lower than 0 dB of the normalized power of the distortion line, and it is preferable to select the other two types of pilots centered around +3 dB (near 0 dB of the normalized power) and -3 dB. In the illustrated example, since the pilot signal has three points with a 3 dB difference, while maintaining the interval, the point where the distortion characteristic curve and the minimum mean square error are minimized is searched, and the operating point with the minimum mean square error as shown in FIG. 11 is determined (the “●”, “▲” and “■” shown in the figure). The non-linear distortion correction unit 25 obtains correction values (the “〇”, “△” and “□” shown in the figure) on the linear characteristics with respect to the normalized input power corresponding to these operating points (the “●”, “▲” and “■” shown in the figure), and based on the three operating points (the “●”, “▲” and “■”) on the input / output characteristics, distortion correction can be performed to associate the level relationship between the amplitude, phase, and linear characteristics of the complex baseband signal. Note that the level of the received signal is not limited to only the three operating points (the “●”, “▲” and “■” shown in the figure), so the non-linear distortion correction unit 25 performs distortion correction according to the amplitude level of the complex baseband signal with these three points as the reference of the operating points.

[0100] The transmission device 1 and the reception device 2 according to the present invention use a power division hierarchical transmission (LDM) method, which not only enables the same symbol rate in the upper layer and the lower layer but also allows different symbol rates. As a result, it is possible to achieve a difference in required C / N between the upper layer and the lower layer of 10 dB or more, and even when a signal attenuation of 20 dB or more occurs, the operation can be stabilized by enabling the acquisition of the information of the transmission data of the strong layer, and it becomes possible to obtain the information of the transmission data of both the strong layer and the weak layer in a more resistant manner on the reception device 2 side.

[0101] In particular, in the transmission device 1, for the modulation signals of each layer that have two systems with different symbol rates (m≠n), that is, different bandwidths, and can be independently set in terms of error correction coding rate, digital modulation method, roll-off rate, and transmission level, regardless of the difference in symbol rate between each layer, they are combined based on a single reference clock aligned identically between each layer (the same also between the transmission device 1 side and the reception device 2 side), and can be transmitted by a single frequency band and a single layer transmission modulation wave signal with a single symbol rate.

[0102] Also, in the reception device 2, even when there is non-linear distortion by the satellite repeater 104, after correcting the non-linear distortion, the upper layer and the lower layer can be demodulated. When the reception device 2 demodulates and decodes the reception signals of the upper layer (strong layer) and the lower layer (weak layer), it first demodulates and decodes the upper layer (with a symbol rate (m≦n, including the same case, a low symbol rate), error correction coding rate, digital modulation method, roll-off rate, due to the difference in transmission level) that is more resistant to transmission degradation. Then, using the replica signal encoded by the retransmission path based on the highly reliable demodulation and decoding result of the upper layer, the replica signal is subtracted from the reception signal including the modulation signals of the upper layer and the lower layer and demodulated and decoded, so that highly reliable lower layer data can be obtained.

[0103] Therefore, according to the transmission device 1 and the reception device 2 of the power division hierarchical transmission (LDM) method of the present embodiment, compared with the conventional time division hierarchical transmission method in satellite broadcasting, when the power division hierarchical transmission (LDM) method is adopted, by making the symbol rates between the layers the same or having differences, it becomes possible to make the difference in the transmission strengths (the difference in required C / N) between the upper layer (strong layer) and the lower layer (weak layer) larger. Even when an attenuation of 20 dB or more occurs due to rainfall or the like, the operation can be stabilized by making it possible to obtain the information of the transmission data of the strong layer, and it becomes possible to receive the data of each layer in a more resistant manner on the reception device 2 side.

[0104] As described above, according to the transmission device 1 and the reception device 2 of the power division hierarchical transmission (LDM) method of the present embodiment, it is possible to efficiently correct the transmission path distortion peculiar to LDM that affects not only the upper layer but also the signal transmission of the lower layer, and improve the transmission performance of both the upper layer and the lower layer signals.

[0105] Although the above-described embodiment has been described as a representative example, it is obvious 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 each of the above-described embodiments, although the distortion correction of Example 1 and the distortion correction of Example 2 have been described separately as distortion corrections, the receiving device 2 can be configured to selectively or jointly perform both the distortion correction of Example 1 and the distortion correction of Example 2. Further, although the receiving device 2 holds in advance information on the input / output characteristics of the satellite repeater 104 (the input / output characteristics of the relay amplifier 1042 in the above-described embodiment), the information on the input / output characteristics of the satellite repeater 104 can be transmitted from the transmitting device 1 to the receiving device 2 each time or periodically using a transmission control signal and held by the receiving device 2. Further, in the above-described embodiment, an example in which the average amplitude level of the upper-layer modulation signal is set to α times the average amplitude level of the lower-layer modulation signal has been described. Instead, a configuration may be provided in which a level adjustment unit is provided that sets the average amplitude level of the lower-layer modulation signal to 1 / α times the average amplitude level of the upper-layer modulation signal. That is, any configuration may be used as long as it is provided with a level adjustment unit that performs level adjustment so that the average amplitude level of the upper-layer modulation signal has a predetermined level difference (average amplitude level difference of α times) with respect to the average amplitude level of the lower-layer modulation signal. Further, in the above-described example, an example in which the upper layer is a 2K data signal and the lower layer is a 4K data signal has been described. However, any configuration may be used as long as two systems of data, such as 2K and 8K, audio and video, etc., are defined as the upper layer and the lower layer, respectively. Further, according to the transmitting device 1 and the receiving device 2 according to the present invention, various modulation methods and error correction codes for the upper layer and the lower layer can be selectively set. Therefore, the present invention should not be construed as being limited by the above-described embodiments, but is limited only by the scope of the claims.

Industrial Applicability

[0106] According to the present invention, with respect to a transmission signal in a hierarchical transmission system that combines modulation signals of two types of transmission path coding methods and transmits them using a single carrier, it is possible to increase the resistance to attenuation while performing distortion correction, which is useful for applications of the hierarchical transmission system.

Explanation of Signs

[0107] 1 Transmitting device 2 Receiving device 11 Clock generation unit 12 Transmission path encoding unit for upper layer 13 Transmission path encoding unit for lower layer 14 Power addition unit 15 Quadrature modulation unit 21 Clock generation unit 22 Band-pass filter (BPF) unit 23 Quadrature demodulation and analog / digital (A / D) conversion unit 24 Nonlinear distortion detection unit 25 Nonlinear distortion correction unit 26 Demodulation and decoding unit for upper layer 27 Retransmission path encoding unit for upper layer 28 Demodulation and decoding unit for lower layer 100 Transmission system 101 Power amplifier 102 Transmitting antenna of earth station 103 Receiving antenna of satellite relay station 104 Satellite repeater 105 Transmitting antenna of satellite relay station 106 Receiving antenna of receiving equipment 111 Reference clock generation unit 112 Divider 112a, 112b Dividing section 120 Frame configuration unit for upper layer 121 Error correction encoding unit 122 Modulation mapping unit 123 Roll-off filter unit 130 Frame configuration unit for lower layer 131 Error correction encoding unit 132 Modulation mapping unit 133 Roll-off filter unit 141 Level adjustment unit 142 Addition unit 151 Quadrature modulation and digital / analog (D / A) conversion unit 152 Band-pass filter (BPF) unit 211 Reference Clock Generation Unit 212 Divider 212a, 212b Dividing Sections 261 Roll-off Filter Section 262 Demodulation Demapping Section 263 Error Correction Decoding Section 271 Error Correction Encoding Section 272 Remodulation Mapping Section 273 Roll-off Filter Section 274 Level Adjustment Section 281 Roll-off Filter Section 282 Level Adjustment Section 283 Subtraction Section 284 Demodulation Demapping Section 285 Error Correction Decoding Section 1041 Receiver Filter of Satellite Repeater 1042 Repeater Amplifier of Satellite Repeater 1043 Transmitter Filter of Satellite Repeater

Claims

Claim 1 A transmission apparatus for a power layer transmission method that defines modulation signals of two system transmission path encoding methods as an upper layer and a lower layer respectively, and adds the modulation signals of the two systems power-wise at different levels and transmits them via a satellite broadcast transmission path using a single carrier, wherein a symbol rate for transmitting the upper layer data is m, a symbol rate for transmitting the lower layer data 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 that generates a reference clock of 4 times M×N common to both the upper layer and the lower layer, and a clock generation unit having a frequency divider that generates sampling clocks respectively divided for the upper layer and the lower layer based on the reference clock, An upper layer transmission path encoding unit that inputs data for the upper layer transmitted at a symbol rate m, forms an upper layer modulation frame that can store a pilot signal predetermined for transmission path distortion correction of the power layer transmission method in front of the upper layer data, and based on the upper layer sampling clock based on the reference clock for the upper layer modulation frame, generates a complex baseband signal for the upper layer based on a predetermined transmission path encoding 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, and forms it as the modulation signal of the upper layer sampled by the reference clock, A lower layer transmission path encoding unit that inputs data for the lower layer transmitted at a symbol rate n, forms a lower layer modulation frame having the same structure as the upper layer modulation frame without storing the pilot signal, and based on the lower layer sampling clock based on the reference clock for the lower layer modulation frame, generates a complex baseband signal for the lower layer based on a predetermined transmission path encoding 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, and forms it as the modulation signal of the lower layer sampled by the reference clock, A power addition unit that generates a complex baseband signal synthesized by performing level adjustment on one or both of the upper layer modulation signal and the lower layer modulation signal so that the average amplitude level of the upper layer modulation signal has a predetermined level difference with respect to the average amplitude level of the lower layer modulation signal, and then adding the upper layer modulation signal and the lower layer modulation signal in power. An orthogonal modulation unit that uses the reference clock as a sampling clock to orthogonally modulate the synthesized complex baseband signal to generate a modulation wave signal for transmission. A transmission device characterized by comprising the above.

2. The transmission device according to claim 1, wherein the ratio of the symbol rate m for transmitting the upper layer data to the symbol rate n for transmitting the lower layer data is any one of m:n = 1:1, 1:2, 1:4, 2:3, 3:

4.

3. As the ratio of the symbol rate m for transmitting the upper layer data to the symbol rate n for transmitting the lower layer data, n is an integer multiple of m. The transmission device according to claim 1, wherein the reference clock generation unit is configured to generate a reference clock that is 4 times N with M = 1.

4. A receiving device that receives a modulation wave signal generated by the transmission device according to any one of claims 1 to 3 via a broadcast transmission path for satellite broadcasting and restores the upper layer data and the lower layer data. A receiving side reference clock generation unit that generates a reference clock that is 4 times M×N common to the upper layer and the lower layer, and a receiving side clock generation unit that has a receiving side frequency divider that generates sampling clocks respectively divided for the upper layer and the lower layer based on the reference clock. An orthogonal demodulation / analog-to-digital conversion unit that uses the reference clock as a sampling clock to orthogonally demodulate a received signal in a predetermined frequency band in the received modulation wave signal to obtain a complex baseband signal in digital signal form. A non-linear distortion detection unit that detects an operating point on a non-linear distortion curve of input / output characteristics occurring in the broadcast transmission path of the satellite broadcast for the complex baseband signal. A non-linear distortion correction unit that corrects distortion for the complex baseband signal based on the operating point. The complex baseband signal after the distortion correction is handled as the complex baseband signal for the upper layer and input, and demodulation and decoding processing of symbol rate m based on the transmission path coding method for the upper layer corresponding to the transmission device side is performed to restore the data of the upper layer. An upper layer demodulation and decoding unit; The data of the upper layer restored by the upper layer demodulation and decoding unit is input, and a complex baseband signal for the upper layer based on a predetermined transmission path coding method that designates at least an error correction coding rate, a modulation method, and a roll-off rate of waveform shaping for the upper layer is regenerated and formed as a replica signal of the complex baseband signal for the upper layer. An upper layer retransmission path coding unit; The complex baseband signal after the distortion correction is input, a complex baseband signal for the lower layer with waveform shaping of the roll-off rate for the lower layer is formed, and the average amplitude level of the replica signal of the complex baseband signal for the upper layer formed by the upper layer retransmission path coding unit is adjusted to the average amplitude level of the complex baseband signal for the lower layer. One or both of the replica signal of the complex baseband signal for the upper layer and the complex baseband signal for the lower layer are adjusted in level so that the predetermined level difference is obtained. After the level adjustment, power subtraction is performed so as to subtract the replica signal of the complex baseband signal for the upper layer from the complex baseband signal for the lower layer to generate a new complex baseband signal for the lower layer composed only of the complex baseband signal for the lower layer. Demodulation and decoding processing of symbol rate n based on the transmission path coding method for the lower layer corresponding to the transmission device side is performed on the new complex baseband signal for the lower layer to restore the data of the lower layer. A lower layer demodulation and decoding unit; A receiving device, characterized by comprising:

5. The non-linear distortion detection unit holds the input-output characteristics having non-linear distortion of the broadcast transmission path of the satellite broadcast, and on the input-output characteristics, detects the average power and peak power of the quadrature-demodulated complex baseband signal, and analogizes and detects each operating point on the input-output characteristics in the broadcast transmission path of the satellite broadcast from these two points. The receiving device according to claim 4, characterized by having means for

6. In the modulation frame for the upper layer in the transmission device, a pilot signal predetermined for correcting transmission path distortion of the power layer transmission method is stored, and in the modulation frame for the lower layer that is hierarchically transmitted in synchronization with the modulation frame for the upper layer, during the signal period for storing the pilot signal in the modulation frame for the upper layer, the pilot signal is not stored and is a no-signal state. The non-linear distortion detection unit holds input / output characteristics having non-linear distortion of the broadcast transmission path of the satellite broadcast, and on the input / output characteristics, detects at least three types of pilot signals with different amplitudes from the pilot signal period of the quadrature demodulated received signal, and has means for inferring and detecting each operating point on the input / output characteristics in the broadcast transmission path of the satellite broadcast from the at least three types of signal levels. The receiving device according to claim 4 or 5, characterized in that.

7. Based on each operating point on the input / output characteristics of the broadcast transmission path of the satellite broadcast obtained from the non-linear distortion detection unit, the non-linear distortion correction unit uses a linear characteristic assumed to have no non-linear distortion in the input / output characteristics, obtains a correction operating point on the linear characteristic corresponding to each operating point on the input / output characteristics, and when the complex baseband signal, which is the quadrature demodulated received signal, is located between each operating point on the input / output characteristics, performs distortion correction by correcting the amplitude and phase of the complex baseband signal so as to have a linear characteristic based on each correction operating point. The receiving device according to any one of claims 4 to 6, characterized in that.

8. 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 set to any one of m:n = 1:1, 1:2, 1:4, 2:3, 3:4 according to the transmission device. The receiving device according to any one of claims 4 to 7, characterized in that.

9. As 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, n is an integer multiple of m. The receiving side reference clock generation unit is configured to generate a reference clock of 4 times N with M = 1. The receiving device according to any one of claims 4 to 7, characterized in that.

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