Transmitter and program

Abstract

To provide a transmission device and program capable of mitigating amplitude distortion of a reception signal caused on a transmission path and improving reception performance.SOLUTION: A transmission device, for transmitting a modulation wave signal with which a digital signal is modulated with predetermined modulation system through a predetermined transmission channel, includes: an IQ signal output part; a pseudo transmission channel including a pseudo transmitter having a characteristic approximated to a characteristic of a transmitter on the transmission path; signal compensation calculation means for calculating an error signal between the IQ signal passed through the pseudo transmission channel and the IQ signal with no distortion, and generating a distortion compensated IQ signal based on the error signal multiplied by a coefficient; and a characteristic analysis part for obtaining information on IQ signal constellation at the IQ signal output part, the characteristic and an operating point of the pseudo transmitter, and the coefficient in the signal compensation calculation means, and analyzing an IQ signal constellation at the transmission channel output, and for compensating the characteristic of the pseudo transmitter according to the amount of distortion.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a transmission apparatus and a program, and more particularly, to a digital signal transmission apparatus that performs distortion compensation of signal points via a transmission path, and a program for distortion compensation. Although the present invention is described taking satellite broadcasting as an example, it is applicable to distortion compensation of signal points via general transmission paths.

Background Art

[0002] Among digital broadcasts of various standards currently in operation, taking satellite broadcasting as an example, broadcast wave signals are multiplexed and transmitted so that a plurality of broadcasters can transmit independent TS (Transport Stream) using a transmitter (satellite transponder) provided on a broadcasting satellite. Standards already adopted for satellite digital broadcasting include ISDB (Integrated Services Digital Broadcasting)-S, ISDB-S3, DVB (Digital Video Broadcasting)-S2, DVB-S2X, and the like.

[0003] Figure 8 is a block diagram showing a configuration example of a satellite broadcasting system via a satellite transponder. The satellite broadcasting system shown in Figure 8 includes a transmission apparatus 1, a satellite transponder 2 provided on a broadcasting satellite (actual satellite), and a plurality of reception apparatuses 6 (reception apparatuses 6-1 to 6-N, where N is a natural number equal to or greater than 1). The transmission apparatus 1 is described as a general transmission apparatus conforming to the various standards for satellite digital broadcasting described above.

[0004] Transmitter 1 generates a modulated wave signal based on a predetermined modulation scheme specified by control information called a TMCC (Transmission and Multiplexing Configuration and Control) signal, and transmits a main signal multiplexed with video, audio, and data broadcasting to satellite transceiver 2. The predetermined modulation scheme includes, for example, BPSK including π / 2 shift BPSK (Binary Phase Shift Keying), QPSK including π / 4 shift QPSK (Quadrature Phase Shift Keying), 8PSK, 16APSK (Amplitude Phase Shift Keying), and 32APSK in the case of the ISDB-S3 system, a digital satellite broadcasting standard. The modulated wave signal generated by Transmitter 1 is converted to a predetermined frequency band and then uplinked to the broadcasting satellite (satellite transceiver 2).

[0005] The satellite transponder 2 of the broadcast satellite is a transmitter that transmits the modulated wave signal transmitted from the transmitting device 1. The satellite transponder 2 is equipped with an input multiplexer filter (hereinafter referred to as "IMUX filter") 3, which is an input filter placed before the amplifier 4, a traveling wave tube amplifier (hereinafter referred to as "TWTA") 4, and an output multiplexer filter (hereinafter referred to as "OMUX filter") 5, which is an output filter placed after the amplifier 4.

[0006] IMUX filter 3 is a band-pass filter corresponding to each channel frequency. IMUX filter 3 suppresses unwanted frequency components from the modulated wave signal (broadcast wave signal) received from transmitter 1, extracting only the band components for one channel. TWTA 4 amplifies the power of the broadcast wave signals for each channel extracted by IMUX filter 3. OMUX filter 5 is a band-pass filter corresponding to each channel frequency, suppressing out-of-band unwanted frequency components from the signal amplified by TWTA 4, extracting only the band components for one channel. Subsequently, the broadcast wave signals for all channels are combined by a subsequent combiner (not shown) following OMUX filter 5, and the broadcast wave signals are transmitted from the antenna (not shown) to each receiving device 6-1 to 6-N.

[0007] The receiving device 6 (6-1 to 6-N) receives the broadcast wave signal (downlink signal) via the satellite transponder 2, selects the broadcast wave signal of the desired channel, and demodulates it. By constantly monitoring control information such as the TMCC signal transmitted along with the multiplexed broadcast wave signal, the receiving device 6 can follow various transmission controls performed by the transmitting device 1 and switch the receiving method accordingly.

[0008] This section describes the characteristics and operation of satellite transponder 2. Figure 9 shows an example of the input / output characteristics (input / output power [AM / AM] characteristics, phase shift [AM / PM] characteristics) of TWTA4 in satellite transponder 2. Figure 10 shows an example of the response characteristics (frequency vs. amplitude, frequency vs. group delay characteristics) of IMUX filter 3 and OMUX filter 5.

[0009] In a satellite broadcasting system, the satellite transponder 2 is essential for the analog system, but due to the input / output power characteristics and phase shift characteristics of the TWTA4, a deviation from the desired IQ signal point may occur. In addition, in the IMUX filter 3 and OMUX filter 5, intersymbol interference occurs due to the effects of frequency amplitude and group delay characteristics, which may cause a spread from the IQ signal point at the desired symbol timing. These deviations and spreads of the IQ signal point then mutually affect each other within the transmission path, resulting in an increase in the required C / N ratio and a deterioration of transmission quality (see Non-Patent Literature 1). For this reason, when the modulated wave signal output from the transmitter 1 is multi-level amplitude phase modulation, power amplifiers such as the TWTA4 of the satellite transponder 2 generally take a back-off stance.

[0010] Here, we will explain the relationship between backoff and signal point placement in TWTA4. Ideally, TWTA4 should perform power amplification processing so that the relationship between the input level and the output level is proportional. However, the input / output characteristics of TWTA4 actually exhibit nonlinearity, where the gain decreases as the input level increases, and at the same time, the phase of the output signal relative to the input signal also rotates (Figure 9). Therefore, when the input level is gradually increased, the output level also increases up to a certain level, but beyond that input level, the output level decreases. The operating point just before this decrease in output level occurs is generally called the output saturation point. Furthermore, when the input level is reduced by X [dB] from this output saturation point and the device is operated, it is called "input backoff (IBO) X [dB]", and similarly, when the input level is reduced and the output level is lowered by Y [dB] and the device is operated, it is called "output backoff (OBO) Y [dB]".

[0011] However, while backoff is implemented, the output power decreases, resulting in a smaller receiving C / N margin in the receiving device (see Non-Patent Literature 1). Satellite broadcasting systems generally have small receiving antenna apertures of 45 cm, and even in clear weather, the receiving C / N margin is small, about 20 dB. Therefore, there is a trade-off relationship between the required C / N and output backoff, and operation that minimizes the sum of the required C / N and output backoff is advantageous in terms of circuit design.

[0012] Next, the configuration of a conventional transmitter 1 will be described. Figure 11 is a block diagram showing an example configuration of a generalized transmitter 1-1 that does not have a distortion compensation function for the transmission line and conforms to the ISDB-S3 method. Transmitter 1-1 includes an IQ signal output unit 10, an upsampling (U / S) unit 21, a root roll-off filter (hereinafter referred to as RRF) unit 22, and a digital-to-analog (D / A) conversion / quadrature modulation unit 23. The IQ signal output unit 10 includes a serial-to-parallel (S / P) conversion unit 101 and a mapping unit 102. Each component will be described below.

[0013] The S / P conversion unit 101 receives the digital signal to be transmitted (a serial sequence of information bits) as input. This digital signal is generally a digital signal to which error correction codes, etc., have been added to the original signal. The S / P conversion unit 101 converts this digital signal into a parallel sequence according to the number of bits of the mapping (for example, 5 bits for 32APSK) and outputs it to the mapping unit 102.

[0014] The mapping unit 102 maps the information bit sequence output from the S / P conversion unit 101 onto the IQ plane using a predetermined modulation scheme (π / 2 shift BPSK, QPSK, 8PSK, 16APSK, 32APSK, etc.) and outputs the generated IQ signal to the U / S unit 21. Therefore, the IQ signal output unit 10 converts the digital signal to be transmitted into an IQ signal and outputs it.

[0015] The upsampling (U / S) unit 21 performs upsampling of the IQ signal by a factor of N (where N is an integer of 2 or more) relative to the sample points (interpolating the gaps between sample points with non-sample points). N can be set arbitrarily, but in the following embodiment, the U / S unit 21 performs upsampling by a factor of 2.

[0016] The RRF section 22 is a waveform shaping section that performs waveform shaping on the IQ signal, which includes unsampled points that have been upsampled by 2x, by performing band-limiting filtering. Generally, a digital filter with root roll-off characteristics is used for band-limiting filtering. Root roll-off characteristics are based on the theoretical formula for roll-off characteristics (Nyquist theorem), and the root filter characteristics are set at the transmitting and receiving sides. ISDB-S3 uses a roll-off ratio of 0.03, and the same value is adopted in the embodiment of the present invention.

[0017] The D / A conversion and quadrature modulation unit 23 performs D / A conversion on the signal after waveform shaping by the RRF unit 22, quadrature modulates the D / A converted signal, and outputs it as an analog modulated wave signal.

[0018] Thus, the transmitting device 1-1 converts the digital signal into an IQ signal using a predetermined modulation scheme, further upsamples it by a factor of two, shapes the waveform with an RRF, and then outputs it as a modulated wave signal. The U / S section 21 and the RRF section 22 are circuit sections commonly used to improve the quality of the transmitted and received signals.

[0019] Figure 12 shows an example of the signal point arrangement of the mapping output signal by the IQ signal output unit 10 in Figure 11. Figure 12 is an example where the modulation scheme is 32APSK and the internal code coding rate is 3 / 4, and the radius ratio of the signal points in this case is specified in the ISDB-S3 method as r2 / r1=2.97 and r3 / r1=5.57, respectively. When expressed in decibels (dB), the average power r ave When normalized to 0 dB, r1 = -12.78 dB, r2 = -3.32 dB, and r3 = 2.14 dB.

[0020] Digital signal modulation schemes used in terrestrial broadcasting include QPSK, 16QAM, and 64QAM, and are multi-carrier transmissions framed more effectively than OFDM (Orthogonal Frequency Division Multiplexing). A key characteristic of terrestrial broadcasting is the effect of multipath fading due to the propagation path, but since amplifiers can operate in the linear domain compared to satellite broadcasting, linear transmission of modulated signals is possible.

[0021] In recent years, for next-generation terrestrial broadcasting, there is a layered division multiplexing (LDM) method that multiplexes multiple data carriers on a single channel. As an example of LDM, attempts have been made to multiplex the current ISDB-T data carrier (hereinafter referred to as the 2K layer) and the next-generation broadcasting data carrier (hereinafter referred to as the 4K layer) on a single channel (see Non-Patent Document 2). The transmitting side multiplexes the 4K layer with the 2K layer using low power, and transmits the two signals, the high layer (2K) and the low layer (4K), using the power difference. The receiving side first demodulates and decodes the high layer to obtain the 2K data signal, and then subtracts the signal obtained by re-encoding and re-modulating the decoded signal (the high layer (2K) signal) from the original received signal (a signal containing both the high layer (2K) and the low layer (4K)) to obtain the low layer (4K) signal. Here, the power ratio between the higher and lower levels is defined by IL (Injection Level), which represents the ratio of the average power of the higher level to the average power of the lower level.

[0022] This LDM technology can also be incorporated into satellite broadcasting. Figure 13 is a block diagram showing an example configuration of a generalized LDM transmitter 1-2 that does not have a distortion compensation function for the transmission line and conforms to the ISDB-S3 system. The transmitter 1-2 comprises an IQ signal output unit 11, a U / S unit 21, an RRF unit 22, and a D / A conversion / quadrature modulation unit 23. The IQ signal output unit 11 consists of a serial / parallel (S / P) conversion unit 111, a high-level mapping unit 112, an S / P conversion unit 113, a low-level mapping unit 114, an amplitude adjustment unit 115, and a combining unit 116. The following describes each component, but the description of the same component will be omitted or simplified.

[0023] The S / P conversion unit 111 receives a high-layer digital signal (for example, a serial sequence of 2K information bits). This digital signal is generally a digital signal in which an error correction code or the like is added to the original signal. The S / P conversion unit 111 converts this digital signal into a parallel sequence corresponding to the number of bits for mapping (for example, 2 bits in the case of QPSK), and outputs the parallel sequence to the high-layer mapping unit 112.

[0024] The high-layer mapping unit 112 maps the information bit sequence output from the S / P conversion unit 111 onto the IQ plane using a predetermined modulation scheme (for example, QPSK), and outputs the generated IQ signal to the combining unit 116.

[0025] The S / P conversion unit 113 receives a low-layer digital signal (for example, a serial sequence of 4K information bits). This digital signal is generally a digital signal in which an error correction code or the like is added to the original signal. The S / P conversion unit 113 converts this digital signal into a parallel sequence corresponding to the number of bits for mapping (for example, 3 bits in the case of 8PSK), and outputs the parallel sequence to the low-layer mapping unit 114.

[0026] The low-layer mapping unit 114 maps the information bit sequence output from the S / P conversion unit 113 onto the IQ plane using a predetermined modulation scheme (for example, 8PSK), and outputs the generated IQ signal to the amplitude adjustment unit 115. The modulation scheme for the high layer and the modulation scheme for the low layer may be different. Note that the high-layer mapping unit 112 and the low-layer mapping unit 114 synchronize their processing so that the timings of the IQ signals (symbols) match in the combining unit 116.

[0027] The amplitude adjustment unit 115 adjusts the signal amplitude of the low-layer IQ signal so as to set a desired level difference (IL) between the power of the high layer and the power of the low layer, and outputs the amplitude-adjusted IQ signal to the combining unit 116.

[0028] The combining unit 116 combines the high-layer IQ signal and the low-layer IQ signal, normalizes the power, and outputs the combined signal.

[0029] Accordingly, the IQ signal output unit 11 converts the high-layer and low-layer digital signals into IQ signals respectively, combines the high-layer and low-layer IQ signals with a desired power difference (IL), and outputs the combined signal to the U / S unit 21.

[0030] The processing of the output signal (combined IQ signal) from the IQ signal output unit 11 is the same as that of the aforementioned transmission apparatus 1-1. The U / S unit 21 performs upsampling by a factor of 2 on the sample points of the IQ signal, and the RRF unit 22 performs waveform shaping processing on the upsampled IQ signal using a band-limited filter with a root roll-off characteristic. The D / A conversion and quadrature modulation unit 23 performs D / A conversion on the signal after waveform shaping by the RRF unit 22, performs quadrature modulation on the D / A-converted signal, and outputs the result as an analog modulated wave signal.

[0031] In this way, the LDM transmission apparatus 1-2 is provided with an S / P conversion unit and a mapping unit respectively for the high layer and the low layer, synchronizes the symbol timings of both, combines the high-layer and low-layer signals with a desired level difference (IL) in power, further upsamples the combined signal by a factor of 2, shapes the waveform by RRF, and then outputs the result as a modulated wave signal.

[0032] Figure 14 shows an example of a signal constellation in which a power difference of IL=r UL / r LL =1.5 dB is applied to the output signals of high-layer (QPSK) mapping and low-layer (8PSK) mapping by the IQ signal output unit 11 of Figure 13, and the signals are combined. In the example of Figure 14, five amplitudes are generated. When the average power r ave is normalized to 0 dB, r1=-18.29 dB, r2=-5.16 dB, r3=0.024 dB, r4=2.31 dB, and r5=3.00 dB.

[0033] As mentioned above, in satellite broadcasting systems, the required C / N and output backoff are in a trade-off relationship. In the case of LDM transmission shown in Figures 13 and 14, the modulation error ratio (MER) of the received signal relative to the signal point arrangement in Figure 14 and the required C / N are in an equivalent relationship. For example, if the MER is improved, the required C / N of higher layers is also improved. Furthermore, if higher layers are received without errors, the improvement in MER directly leads to a reduction in the required C / N of lower layers (see Non-Patent Document 3). In other words, in the case of LDM transmission, there is a trade-off relationship between MER and output backoff.

[0034] Next, we compare Figure 12 and Figure 14 from the perspective of signal point arrangement. Both Figure 12 (single transmission) and Figure 14 (LDM transmission) have a 32-point arrangement, but the influence of the nonlinear input / output characteristics (AM / AM, AM / PM characteristics) of TWTA4 in Figure 9 is different. For example, the average power r corresponding to the dotted line in Figures 12 and 14 ave This corresponds to the operating point power of TWTA4. The signal point r3, which is the outermost circle in Figure 12, is input to TWTA4 with a power 2.14 dB higher than the operating point of TWTA4. Also, the signal point r5, which is the maximum amplitude in Figure 14, is input to TWTA4 with a power 3.00 dB higher than the operating point of TWTA4. Therefore, especially when the operating point is near the saturation power, it is more susceptible to the effects of nonlinear distortion compared to Figure 12.

[0035] Against this backdrop, research has been conducted on transmission devices to compensate for distortion occurring in the transmission path (satellite transponder) in satellite broadcasting systems (Patent Document 1).

[0036] A conventional distortion-compensated transmission device will be described. Figure 15 is a block diagram showing an example of the configuration of a conventional distortion-compensated transmission device, in which a function for compensating for distortion generated in satellite transponders is incorporated inside the transmission device. Transmission device 1-3 in Figure 15 applies the conventional distortion compensation function to LDM transmission device 1-2, and is realized by incorporating a distortion compensation unit 30 between the IQ signal output unit 11 and the upsampling unit 21 in Figure 13. The distortion compensation unit 30 is a pseudo-transmission path 310 ("Pseudo" and "simulated" are synonymous.)The system consists of a signal compensation calculation means 320. The pseudo-transmission path 310 is composed of an upsampling (U / S) unit 301, an RRF (waveform shaping) unit 302, a pseudo-transmitter 303, an RRF (waveform shaping) unit 307, and a downsampling (D / S) unit 308. The signal compensation calculation means 320 in this device is a vector calculation means and consists of a delay unit 321, a vector summation unit 322, an inverse characteristic coefficient unit 323, and a vector summation unit 324. The following describes each component. Note that the components included in Figure 13 will be omitted or simplified in their description.

[0037] The IQ signal output unit 11 outputs an IQ signal obtained by combining the high-level and low-level IQ signals with a desired power difference (IL). The IQ signal output from the IQ signal output unit 11 is input to the distortion compensation unit 30, and then to the upsampling unit 301 and the delay unit 321.

[0038] The upsampling unit 301 has the same characteristics as the upsampling unit 21 and performs upsampling of the input IQ signal by a factor of N (where N is an integer greater than or equal to 2) relative to the sample point. In this device, the upsampling unit 301 performs upsampling by a factor of 2.

[0039] The RRF section 302 has the same characteristics as the RRF section 22 and is a waveform shaping section that performs waveform shaping on the IQ signal, which includes upsampled non-sampled points, by performing a band-limiting filter process with root roll-off characteristics. The waveform-shaped signal is output to the pseudo-transmitter 303.

[0040] The pseudo-transmitter 303 is equipped with a pseudo-IMUX filter 304, a pseudo-TWTA 305, and a pseudo-OMUX filter 306, and has characteristics that approximate the phase and amplitude frequency characteristics and nonlinear characteristics of the actual satellite repeater 2 shown in Figure 8. Specifically, the pseudo-IMUX filter 304 and pseudo-OMUX filter 306 reflect the characteristics of the IMUX filter 3 and OMUX filter 5 shown in Figure 10. Furthermore, the characteristics of the pseudo-TWTA 305 reflect the input / output characteristics shown in Figure 16 (actual data characteristics of TWTA 4 in Figure 9), for example, setting the input power at the operating point to -3.3dB (input backoff: IBO=3.3dB). Note that IBO=3.3dB is the operating point set so that the output backoff (OBO) becomes OBO=2.2dB, which is close to actual operation. The characteristics of the actual satellite in Figure 8 also have similar operating point and characteristic settings. As a result, the pseudo-transmitter 303 outputs an IQ signal that simulates the signal point shift that may occur due to the satellite repeater 2, relative to the ideal IQ signal point after mapping the signal points of the digital signal to be transmitted.

[0041] The RRF section 307 has the same characteristics as the RRF section 302 and is a waveform shaping section that performs waveform shaping on the IQ signal that has passed through the pseudo-transmitter 303 using a band-limiting filter with root roll-off characteristics. By multiplying the characteristics of the RRF section 302 and the RRF section 307, a signal without inter-symbol interference is obtained.

[0042] The downsampling (D / S) unit 308 thins out IQ signal points (symbol points) that include non-sampled points at a predetermined ratio (1 / N) and returns them to the original sampled points. In this device, the thinning is 1 / 2. The U / S unit 301 and RRF unit 302 preceding the pseudo-transmitter 303 correspond to the transmitting device, the RRF unit 307 and D / S unit 308 following the pseudo-transmitter 303 correspond to the receiving device, and the upsampling unit 301 to the downsampling unit 308 constitute the assumed transmission path for the IQ signal.

[0043] The signal compensation calculation means 320 is a means for generating a distortion-compensated IQ signal by calculation from two signals: the distortion-free IQ signal (ideal IQ signal) input from the IQ signal output unit 11 and the IQ signal that has passed through the pseudo-transmission path 310 (containing transmission path distortion). The signal compensation calculation means 320 of this device is a vector calculation means that generates a distortion-compensated IQ signal using vector processing. The functions of each part of the vector calculation means are described below.

[0044] The delay unit 321 adjusts the timing to synchronize the two signals input to the vector summing unit 322. Specifically, the delay unit 321 applies the same delay amount D as the delay amount D generated by the pseudo-transmitter 303 and the waveform shaping unit 307 to the ideal IQ signal input from the IQ signal output unit 11, thereby synchronizing the two signals.

[0045] The vector summing unit 322 performs vector operations (subtraction) on two synchronized IQ signals. Specifically, it calculates the error vector caused by passing through the pseudo-transmission path 310 by subtracting the vector of the undistorted IQ signal (ideal IQ signal) from the vector of the IQ signal that has passed through the pseudo-transmission path 310 (which contains transmission path distortion).

[0046] The inverse characteristic coefficient section 323 multiplies the error vector resulting from passage through the pseudo-transmission line 310 by a coefficient K (weight). For example, in Non-Patent Literature 1, this coefficient K is set to 1.

[0047] The vector summing unit 324 generates a distortion-compensated IQ signal by performing a vector operation on the ideal IQ signal from the IQ signal output unit 11, subtracting an error vector multiplied by coefficient weights (adding the inverse vector).

[0048] The distortion-compensated IQ signal (distortion-compensated data IQ signal point vector) output from the distortion compensation unit 30 is processed in the same way as the LDM transmitter 1-2 and output as a modulated wave signal. Specifically, the U / S unit 21 performs upsampling of the IQ signal sample points by a factor of 2, and the RRF unit 22 performs waveform shaping processing on the upsampled IQ signal using a band-limiting filter with root roll-off characteristics. The D / A conversion / quadrature modulation unit 23 performs D / A conversion on the signal after waveform shaping by the RRF unit 22, quadrature modulates the D / A converted signal, and outputs it as an analog modulated wave signal.

[0049] This shows a comparison of satellite broadcast reception signals with and without conventional distortion compensation. Figure 17 is the received constellation when transmitted via satellite using LDM transmitter 1-2 (Figure 13) without distortion compensation. Figure 18 is the received constellation when transmitted via satellite using conventional LDM transmitter 1-3 (Figure 15) with distortion compensation.

[0050] Table 1 shows the calculation results (characteristic analysis results) of the signal characteristics based on the received signals shown in Figures 17 and 18. The signal characteristics were compared by determining the amplitude (centroid amplitude) and MER of the received signals. For the calculation, the amplitude of the received signal was determined by taking the centroid from a set of points that are considered to be the same signal point on the transmitting side, and also by taking the amplitude average of points that have the same amplitude on the transmitting side. For example, the centroid of the signal corresponding to the four signal points located at r5 in Figure 14 was determined for each, and the r5 value (centroid amplitude) at the receiving side was obtained by taking the amplitude average of these four centroid points.

[0051] [Table 1]

[0052] Regarding the effect of conventional distortion compensation, firstly, the MER is (a) 17.3 dB without distortion compensation, compared to (b) 21.7 dB with conventional distortion compensation, indicating an improvement in reception performance. The amplitude of r5, which is susceptible to nonlinear effects, has increased from 2.22 dB to 2.70 dB, approaching the original signal amplitude of 3.00 dB. However, the amplitude of r5 after compensation still has a residual amplitude distortion of 0.3 dB, which is higher than the residual distortion of the other amplitudes r1 to r4. [Prior art documents] [Patent Documents]

[0053] [Patent Document 1] Patent No. 6681672 specification [Non-patent literature]

[0054] [Non-Patent Document 1] M. KOJIMA, et al., “Comparative Study of Digital Pre-Distortion for 32APSK by Hardware Experiments and Numerical Calculations”, IEICE Technical Report SAT2019-53, pp.31-35, (2019-10) [Non-Patent Document 2] Akihiko Sato, et al., "Evaluation of Transmission Characteristics During Integrated Demodulation of a System for Multiplexing Next-Generation Broadcasts with LDM over ISDB-T," IEICE Winter Conference 14C-5, (2019) [Non-Patent Document 3] Minoru Okada, "Carrier Superposition Method in Satellite Communications - Towards the Realization of LDM," IEICE Technical Report BCT2017-47, pp. 33-36, (2017) [Overview of the Initiative] [Problems that the invention aims to solve]

[0055] Conventional distortion compensation (Patent Document 1) shows improvement in the required C / N ratio when passing through the transmission line. However, in cases where the signal point has high power, such as in LDM transmission, the signal point with the maximum amplitude is particularly affected by the nonlinear distortion of the transmission line, resulting in residual amplitude distortion at the received signal point after distortion compensation.

[0056] Therefore, in view of the above-mentioned problems, the object of the present invention is to provide a transmitting device and program that can reduce the amplitude distortion of the received signal occurring in the transmission line and improve the receiving performance compared to conventional distortion compensation means. [Means for solving the problem]

[0057] To solve the above problems, the transmitting device according to the present invention (1) A transmitting device that transmits a modulated wave signal obtained by modulating a digital signal with a predetermined modulation scheme via a predetermined transmission path, comprising an IQ signal output unit that generates an IQ signal obtained by modulating the digital signal with the predetermined modulation scheme, The IQ signal is input from the IQ signal output unit. Includes a pseudo-transmitter having characteristics similar to those of the transmitter on the transmission line. pseudo A pseudo-transmission path and the signal that passed through the aforementioned pseudo-transmission path The aforementioned A distortion compensation unit comprising: a signal compensation calculation means that calculates an error signal between the IQ signal and the corresponding undistorted IQ signal input from the IQ signal output unit, and generates a distortion-compensated IQ signal based on the coefficient-multiplied error signal and the undistorted IQ signal; and information of the IQ signal point arrangement in the IQ signal output unit, the characteristics and operating point of the pseudo-transmitter, and the coefficients in the signal compensation calculation means, The predetermined transmission line of Output Actual IQ signal point The acquired IQ signal point The transmitting device is characterized by comprising a characteristic analysis unit that analyzes and corrects the characteristics of the pseudo-transmitter according to the amount of distortion.

[0058] (2) The transmitting device described in (1) above is further equipped with the characteristic analysis unit, The predetermined transmission line of Output The aforementionedIt is preferable to analyze the IQ signal point and perform a process multiple times to correct the characteristics of the pseudo-transmitter according to the amount of distortion.

[0059] (3) The transmitting device described in (1) or (2) above is further described as pseudo The transmission line is the aforementioned pseudo The preceding stage of the transmitter includes an upsampling (U / S) unit that performs upsampling by N times (where N is an integer greater than or equal to 2) with respect to the IQ signal point, and a waveform shaping unit that performs waveform shaping with a root roll-off filter, pseudo Preferably, the transmitter is configured to include, downstream of the transmitter, a waveform shaping unit that performs waveform shaping with a root roll-off filter, and a downsampling (D / S) unit that reduces the number of IQ signal points to 1 / N. The transmitting device further preferably includes an upsampling (U / S) unit that performs upsampling by N times (where N is an integer of 2 or more) on the IQ signal points output from the distortion compensation unit, a waveform shaping unit that performs waveform shaping with a root roll-off filter, and a D / A conversion / quadrature modulation unit that performs D / A conversion on the waveform-shaped signal, quadrature modulates the D / A-converted signal, and outputs it as an analog modulated wave signal.

[0060] (4) Any of the transmitting devices described in (1) to (3) above further has the signal compensation calculation means that the vector of the IQ signal that has passed through the pseudo transmission path and the corresponding The aforementioned distortion-free The error vector, which is the difference from the IQ signal vector, is obtained, and the inverse vector of the error vector multiplied by the coefficient is obtained. The aforementioned distortion-free Preferably, the vector calculation means adds the vectors of the IQ signals to generate a distortion-compensated IQ signal.

[0061] (5) Any of the transmitting devices described in (1) to (3) above further includes the signal compensation calculation means which converts the amplitude and phase values ​​obtained by passing the IQ signal through the pseudo transmission path into amplitude and phase, and the corresponding Undistorted IQ signal The amplitude error value and phase error value, which are the difference between the ideal amplitude value and ideal phase value obtained by converting the IQ signal point into amplitude and phase, are calculated, and the sign inverted values ​​of the respective amplitude error value and phase error value multiplied by the coefficient are obtained. The aforementioned distortion-freePreferably, the amplitude-phase calculation means adds the ideal amplitude value and ideal phase value of the IQ signal point, converts the added amplitude value and phase value back into the IQ signal point, and generates a distortion-compensated IQ signal.

[0062] (6) It is preferable that any of the transmitting devices described in (1) to (5) above further includes BPSK, QPSK, 8PSK, 16APSK, or 32APSK as the predetermined modulation scheme, or includes two different modulation schemes, one high-level and one low-level.

[0063] To solve the above problems, the program according to the present invention (7) The computer is connected to the IQ signal output section of any of the transmitting devices described in (1) to (6) above. pseudo This is a program that functions as a transmission path, a signal compensation calculation means, and a characteristic analysis unit. [Effects of the Invention]

[0064] According to the transmitting device and program of the present invention, amplitude distortion of the received signal can be reduced and reception performance can be improved compared to conventional distortion compensation means. [Brief explanation of the drawing]

[0065] [Figure 1] This is a block diagram showing an example configuration of a transmitting device according to the first embodiment of the present invention. [Figure 2] This is an example of correcting the input / output characteristics of a pseudo-transmitter obtained from the results of the first characteristic analysis. [Figure 3] This is an example of a received constellation during satellite transmission, with distortion compensation performed by a distortion compensation unit that reflects the results of the first characteristic analysis. [Figure 4] This is an example of correcting the input / output characteristics of a pseudo-transmitter obtained from the results of the second characteristic analysis. [Figure 5] This is an example of a received constellation during satellite transmission, with distortion compensation performed by a distortion compensation unit that reflects the results of the second characteristic analysis. [Figure 6] This is a block diagram showing an example configuration of a transmitting device according to a second embodiment of the present invention. [Figure 7] This is a modified example of the strain compensation unit in the present invention. [Figure 8] This is a block diagram showing an example configuration of a satellite broadcasting system using satellite transponders. [Figure 9] This is an example of the input / output characteristics of TWTA in a satellite transponder. [Figure 10] This is an example of the response characteristics of IMUX filters and OMUX filters in a satellite transponder. [Figure 11] This block diagram shows an example configuration of a generalized transmitter without distortion compensation. [Figure 12] Figure 11 shows an example of the mapping output signal (signal point arrangement) from the IQ signal output unit. [Figure 13] This is a block diagram showing an example configuration of a generalized LDM transmitter without distortion compensation. [Figure 14] Figure 13 shows an example of the output signal (signal point arrangement) after combining the high-level and low-level signals by the IQ signal output unit. [Figure 15] This is a block diagram showing an example configuration of a conventional distortion-compensated transmission device. [Figure 16] This is an example of the input / output characteristics of TWTA in a conventional pseudo-transmitter. [Figure 17] This is an example of a received constellation when transmitting via satellite using an LDM transmitter without distortion compensation. [Figure 18] This is an example of a received constellation when transmitting via satellite using a conventional distortion-compensated LDM transmitter. [Modes for carrying out the invention]

[0066] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0067] (First Embodiment) Figure 1 is a block diagram showing an example configuration of a transmitting device according to the first embodiment of the present invention. Compared to the conventional LDM transmitting device 1-3 with distortion compensation function shown in Figure 15, the transmitting device 100 in Figure 1 has a configuration in which a characteristic analysis unit 40 is added.

[0068] The transmitting device 100 of the first embodiment is a transmitting device that can be adapted to a satellite broadcasting system via the satellite repeater 2 shown in Figure 8, and can transmit broadcast wave signals to an existing system. Therefore, the transmitting device of this embodiment can be made compliant with standards adopted in digital broadcasting, such as ISDB-S, ISDB-S3, DVB-S2, DVB-S2X, etc.

[0069] The first embodiment of the transmitting device 100 includes an IQ signal output unit 11, a distortion compensation unit 30, a characteristic analysis unit 40, an upsampling (U / S) unit 21, a root roll-off filter (RRF) unit 22, and a digital-to-analog (D / A) conversion / quadrature modulation unit 23. The distortion compensation unit 30 includes a pseudo-transmission path 310 and a signal compensation calculation means 320. The following describes each component, but components that have already been described will be omitted or simplified in their description.

[0070] The IQ signal output unit 11 is the same as the LDM type IQ signal output unit 11 shown in Figures 13 and 15, and consists of a serial / parallel (S / P) conversion unit 111, a high-level mapping unit 112, an S / P conversion unit 113, a low-level mapping unit 114, an amplitude adjustment unit 115, and a combining unit 116. As will be described later, the IQ signal output unit is not limited to the LDM type, and an IQ signal output unit of any modulation type can be used.

[0071] In this embodiment, the input high-level digital signal (serial sequence of information bits) is converted to a parallel sequence by the S / P conversion unit 111 and mapped onto the IQ plane by the high-level mapping unit 112 using a predetermined modulation scheme (e.g., QPSK). On the other hand, the low-level digital signal (serial sequence of information bits) is converted to a parallel sequence by the S / P conversion unit 113 and mapped onto the IQ plane by the low-level mapping unit 114 using a predetermined modulation scheme (e.g., 8PSK). The high-level mapping unit 112 and the low-level mapping unit 114 synchronize their processing. The amplitude adjustment unit 115 adjusts the signal amplitude of the low-level IQ signal to set a desired level difference (IL) between the high-level and low-level powers, and the synthesis unit 116 synthesizes the high-level IQ signal and the amplitude-adjusted low-level IQ signal, normalizes the power, and outputs the synthesized signal. The IQ signal thus generated is output to the distortion compensation unit 30.

[0072] The distortion compensation unit 30 consists of a pseudo-transmission path 310 and a signal compensation calculation means 320. The pseudo-transmission path 310 consists of an upsampling (U / S) unit 301, a waveform shaping (RRF) unit 302, a pseudo-transmitter 303, an RRF unit 307, and a downsampling (D / S) unit 308. In this embodiment, the signal compensation calculation means 320 is a vector calculation means and consists of a delay unit 321, a vector addition unit 322, an inverse characteristic coefficient unit 323, and a vector addition unit 324.

[0073] The upsampling unit 301 performs upsampling of the input IQ signal by a factor of N (in this embodiment, N=2) relative to the sample point. The RRF unit 302 performs waveform shaping by a band-limiting filter with root roll-off characteristics. The upsampling unit 301 and the RRF unit 302 are equivalent elements to the upsampling unit 21 and RRF unit 22 in the transmitting device, and are provided in the pseudo-transmission path 310. They can be appropriately configured to correspond to the output configuration of the transmitting device.

[0074] The pseudo-transmitter 303 is equipped with a pseudo-IMUX filter 304, a pseudo-TWTA 305, and a pseudo-OMUX filter 306, and has characteristics that approximate the phase and amplitude frequency characteristics and nonlinear characteristics of the actual satellite repeater 2 shown in Figure 8.

[0075] The pseudo-IMUX filter 304 and pseudo-OMUX filter 306 reflect the characteristics of the IMUX filter 3 and OMUX filter 5 shown in Figure 10.

[0076] In this embodiment, the characteristics of the pseudo-TWTA305 are based on the input / output characteristics shown in Figure 16 (actual data characteristics of TWTA4 in Figure 9), and the input / output power [AM / AM] characteristics are adjusted by commands from the characteristic analysis unit 40, which will be described later. In this embodiment, the input power at the operating point is set to -3.3dB for signal processing calculations.

[0077] A transmitting device equipped with a distortion compensation unit 30 can be implemented in an actual device, but as described later, the processing of the distortion compensation unit can be implemented as digital signal processing by a computer and program. In digital signal processing, the characteristics in Figures 10 and 16 are reflected as a table file. The pseudo-transmitter 303 outputs an IQ signal that simulates the shift in signal points that may occur due to transmitters on the transmission path (in this case, satellite repeater 2) relative to the ideal IQ signal point after mapping the signal points of the digital signal to be transmitted.

[0078] The RRF unit 307 performs waveform shaping on the IQ signal that has passed through the pseudo-transmitter 303 using a band-limiting filter with root roll-off characteristics. The downsampling unit 308 then thins out IQ signal points, including non-sampled points, by a predetermined ratio (1 / 2 in this embodiment) and returns them to the original sampled points. The RRF unit 307 and the downsampling unit 308 are equivalent elements to the RRF unit and downsampling unit in the receiving device, and the pseudo-transmission path 310 serves as a hypothetical transmission path for the IQ signal, taking into account the transmitting and receiving devices.

[0079] The signal compensation calculation means 320 is a means for generating a distortion-compensated IQ signal by calculation from two signals: an undistorted IQ signal (ideal IQ signal) input from the IQ signal output unit 11 and an IQ signal that has passed through the pseudo-transmission path 310 (containing transmission path distortion). In this embodiment, the signal compensation calculation means 320 is a vector calculation means.

[0080] The delay unit 321 adjusts the timing to synchronize the two signals input to the vector summing unit 322. Specifically, the delay unit 321 applies the same delay amount D as the delay amount D caused by passing through the pseudo-transmission path 310 to the undistorted IQ signal input from the IQ signal output unit 11, thereby synchronizing the two signals.

[0081] The vector summing unit 322 calculates the error vector caused by passing through the pseudo-transmission path 310 by performing vector operations (subtraction) on two synchronized IQ signals. The inverse characteristic coefficient section 323 multiplies the error vector resulting from passage through the pseudo-transmission line 310 by a coefficient K (weight). For example, in this embodiment, the coefficient K is set to 1, but the coefficient K can be adjusted as appropriate depending on the degree of compensation.

[0082] The vector summer 324 generates a distortion-compensated IQ signal (distortion-compensated data IQ signal point vector) by performing a vector operation on the distortion-free IQ signal (ideal IQ signal) from the IQ signal output unit 11, subtracting an error vector multiplied by coefficient weights (adding the inverse vector). Alternatively, the inverse characteristic coefficient unit 323 may multiply the coefficients by negative values ​​and then perform the addition in the vector summer 324.

[0083] Therefore, the signal compensation calculation means 320 obtains an error signal between the IQ signal that has passed through the pseudo-transmission path 310 and the corresponding undistorted IQ signal input from the IQ signal output unit 11, and generates a distortion-compensated IQ signal based on the coefficient-multiplied error signal and the undistorted IQ signal.

[0084] The distortion-compensated IQ signal output from the distortion compensation unit 30 is output as a modulated wave signal. Specifically, the U / S unit 21 performs upsampling of the IQ signal by a factor of 2 at the sample point, and the RRF unit 22 performs waveform shaping processing on the upsampled IQ signal using a band-limiting filter with root roll-off characteristics. The D / A conversion / quadrature modulation unit 23 performs D / A conversion on the signal after waveform shaping by the RRF unit 22, quadrature modulates the D / A converted signal, and outputs it as an analog modulated wave signal.

[0085] The characteristic analysis unit 40 acquires at least information on the IQ signal point arrangement in the IQ signal output unit 11, the characteristics and operating point of the pseudo-transmitter 303, and the coefficient K in the signal compensation calculation means 320, analyzes the IQ signal points in the transmission line output, and corrects the characteristics of the pseudo-transmitter 303 according to the amount of distortion.

[0086] The following describes the specific processing of the characteristic analysis unit 40 and its effects compared to a conventional distortion compensation transmission device (Figure 15), along with verification calculations assuming satellite transmission.

[0087] The characteristic analysis unit 40 first acquires information on the signal point arrangement of the output signal in the IQ signal output unit 11, the characteristics of the pseudo-transmitter 303 and the set operating point of the pseudo-TWTA 305, and coefficient information of the signal compensation calculation means 320. From this information, it is possible to estimate and analyze the IQ signal points after passing through the transmission path. Furthermore, the characteristic analysis unit 40 monitors the output unit of the OMUX filter 306 and acquires the OBO, thereby detecting the trade-off amount with MER and enabling higher-performance distortion compensation.

[0088] The first characteristic analysis uses the input / output power [AM / AM] characteristics of the pseudo-transmitter 303 (i.e., pseudo-TWTA 305) as the input / output characteristics shown in Figure 16 (actual data characteristics of TWTA4 of satellite repeater 2) to estimate and analyze the IQ signal point after passing through the transmission path. This result is the calculation result for (b) conventional distortion compensation obtained in Table 1. Table 2 also reproduces the characteristic analysis results for conventional distortion compensation as "(b) Centroid amplitude of received signal with conventional distortion compensation". The amplitude of the received signal (centroid amplitude) is obtained by taking the centroid from a set of points that are considered to be the same signal point on the transmitting side, based on the receiving constellation, and also by taking the amplitude average of points that have the same amplitude on the transmitting side. From the results of the first characteristic analysis, it can be seen that in the case of the LDM modulation method, the amplitude of r5, which is susceptible to nonlinear effects, is 2.70 dB, and there is a residual amplitude distortion of 0.3 dB compared to the original signal amplitude of 3.00 dB.

[0089] Figure 2 shows an example of correcting the input / output characteristics of the pseudo-transmitter 303 obtained from the first characteristic analysis results described above. When IBO is set to 3.3dB, the input power of the pseudo-TWTA 305 corresponding to the power of r5 corresponds to -0.3 (=-3.3 + 3.00)dB. In this embodiment, since the characteristics are reflected by spline interpolation in 1dB steps, the output power corresponding to an input power higher than -0.3dB of the input / output power [AM / AM] characteristic of the pseudo-transmitter 303 (pseudo-TWTA 305) is reduced by 0.3dB. At this time, the subsequent signal compensation calculation means 320 attempts to raise it by approximately 0.3dB, thus reducing the amplitude distortion at r5 of the received signal. The characteristic analysis unit 40 corrects the input / output characteristics of the pseudo-TWTA 305 of the pseudo-transmitter 303 so that the characteristics are as shown in Figure 2.

[0090] Figure 3 shows an example of a received constellation when distortion compensation is performed by the distortion compensation unit 30, which reflects the results of the first characteristic analysis of the present invention, and the signal is transmitted via satellite. Furthermore, Table 2 shows (c) the received signal characteristics (amplitude and MER) according to the present invention based on this received signal, compared with (b) the received signal characteristics with conventional distortion compensation.

[0091] [Table 2]

[0092] As a result of distortion compensation using the present invention (first characteristic analysis), (b) compared to the case of conventional distortion compensation, the MER decreased from 21.7 dB to 21.9 dB, indicating an improvement in reception performance. At this time, the OBO was 2.7 dB in both (b) and (c), so even considering the trade-off, it can be said that there is an improvement. In addition, the amplitude of r5 also decreased from 2.70 dB to 2.74 dB, approaching the amplitude of the original signal of 3.00 dB. Therefore, the present invention can reduce the amplitude distortion of the received signal generated in the transmission line and improve reception performance compared to conventional distortion compensation means.

[0093] However, the distortion compensation results based on the first characteristic analysis show a residual amplitude distortion of 0.26 dB. The above analysis of the received signal characteristics based on distortion compensation from the first characteristic analysis corresponds to the second characteristic analysis. In this invention, the characteristics can be further improved by utilizing the results of this characteristic analysis.

[0094] Figure 4 shows an example of the correction of the input / output characteristics of the pseudo-transmitter 303 obtained from the second characteristic analysis results described above. Similar to the first time, the output power corresponding to an input power higher than the power of r5 (-0.3dB) in the input / output power [AM / AM] characteristics of the pseudo-transmitter 303 (pseudo-TWTA 305) is further reduced by 0.26dB. The characteristic analysis unit 40 corrects the input / output characteristics of the pseudo-TWTA 305 of the pseudo-transmitter 303 so that the characteristics shown in Figure 4 are obtained.

[0095] Figure 5 shows an example of a received constellation when distortion compensation is performed by the distortion compensation unit 30, which reflects the results of the second characteristic analysis of the present invention, during satellite transmission. Furthermore, Table 3 shows a comparison of (d) the received signal characteristics (amplitude and MER) based on this received signal according to the present invention (second characteristic analysis), (c) the received signal characteristics according to the present invention (first characteristic analysis), and (b) the received signal characteristics with conventional distortion compensation.

[0096] [Table 3]

[0097] According to Table 3, the distortion compensation results based on the second characteristic analysis of the present invention show an improvement in reception performance compared to the distortion compensation based on the first characteristic analysis (c), with the MER increasing from 21.9 dB to 22.0 dB. Similarly, the OBO was 2.7 dB in both (c) and (d), indicating improvement even considering the trade-off. Furthermore, the amplitude of r5 also increased from 2.70 dB to 2.77 dB, which is even closer to the original signal amplitude of 3.00 dB.

[0098] Furthermore, based on the third characteristic analysis, it is possible to correct the input / output power [AM / AM] characteristics of the pseudo-transmitter 303 (pseudo-TWTA305) and improve the compensation effect.

[0099] Through repeated analyses as described above, MER improves, and so does reception performance. Although no change in OBO was observed in this embodiment, it is expected that OBO will gradually increase with the updating of the pseudo-TWTA characteristics as described above. Therefore, the optimal characteristics can be derived from the trade-off between MER and OBO.

[0100] In this embodiment, the same amount of correction as the amplitude distortion was reflected in the input / output characteristics, but this is only one example, and it goes without saying that another method of the present invention is to repeatedly update the values ​​using a bisection method or the like (in this embodiment, to change the correction amount of the output power for the first time from 0.30 dB to 0.15 dB).

[0101] (Second Embodiment) Although an LDM transmission device was given as an example of the configuration of the first embodiment of the present invention, the present invention is applicable to general transmission devices and is not dependent on transmission methods such as ISDB-S3.

[0102] Figure 6 is a block diagram showing an example configuration of a transmitting device according to a second embodiment of the present invention, and is an example of applying the distortion compensation of the present invention to a general transmitting device shown in Figure 11. The transmitting device 200 of this embodiment includes an IQ signal output unit 10, a distortion compensation unit 30, a characteristic analysis unit 40, an upsampling (U / S) unit 21, a root roll-off filter (RRF) unit 22, and a digital-to-analog (D / A) conversion / quadrature modulation unit 23. The distortion compensation unit 30 includes a pseudo-transmission line 310 and a signal compensation calculation means 320. In the following description, components that are the same as those already described will be omitted or simplified in their description.

[0103] The IQ signal output unit 10 has the same configuration as the IQ signal output unit 10 in Figure 11, and consists of a serial / parallel (S / P) conversion unit 101 and a mapping unit 102. The S / P conversion unit 101 converts the input digital signal into a parallel sequence according to the number of mapping bits (for example, 5 bits for 32APSK) and outputs it, and the mapping unit 102 maps the information bit sequence output from the S / P conversion unit 101 onto the IQ plane using a predetermined modulation scheme (π / 2 shift BPSK, QPSK, 8PSK, 16APSK, 32APSK, etc.) and outputs the generated IQ signal.

[0104] Furthermore, the functions of the upsampling (U / S) section 21, the root roll-off filter (RRF) section 22, and the digital-to-analog (D / A) conversion / quadrature modulation section 23 are the same as those already described.

[0105] The distortion compensation unit 30 has the same configuration as the distortion compensation unit 30 in Figure 1 and consists of a pseudo-transmission path 310 and a signal compensation calculation means 320. The pseudo-transmission path 310 consists of an upsampling (U / S) unit 301, a waveform shaping (RRF) unit 302, a pseudo-transmitter 303, an RRF unit 307, and a downsampling (D / S) unit 308. In this embodiment, the signal compensation calculation means 320 is a vector calculation means and consists of a delay unit 321, a vector addition unit 322, an inverse characteristic coefficient unit 323, and a vector addition unit 324. The functions and characteristics of each component are the same as those of the distortion compensation unit 30 of the transmitter 100 in Figure 1, so a description is omitted.

[0106] The pseudo-transmitter 303 is equipped with a pseudo-IMUX filter 304, a pseudo-TWTA 305, and a pseudo-OMUX filter 306. The pseudo-IMUX filter 304 and the pseudo-OMUX filter 306 reflect the characteristics of the IMUX filter 3 and OMUX filter 5 of the satellite repeater 2 shown in Figure 10. Furthermore, the characteristics of the pseudo-TWTA 305 are based on the characteristics of the TWTA 4 shown in Figure 16, and the input / output power [AM / AM] characteristics are adjusted by commands from the characteristic analysis unit 40.

[0107] The function of the characteristic analysis unit 40 is the same as that of the characteristic analysis unit 40 in Figure 1. It acquires at least information on the IQ signal point arrangement in the IQ signal output unit 10, the characteristics and operating point of the pseudo-transmitter 303, and the coefficient K in the signal compensation calculation means 320. It analyzes the IQ signal points at the transmission line output and corrects the characteristics of the pseudo-transmitter 303 according to the amount of distortion.

[0108] Specifically, as described in the first embodiment, the characteristic analysis unit 40 estimates and analyzes the IQ signal point after passing through the transmission line from the acquired information, and obtains the error (residual distortion) between the IQ signal point of the original signal and the IQ signal point of the receiving side as a characteristic analysis result, for example, based on the received constellation. Then, it corrects the characteristics of the pseudo-transmitter 303 (for example, the input / output power [AM / AM] characteristics of the pseudo-TWTA 305) according to the amount of distortion (see Figure 2). In this way, distortion compensation is improved based on the signal characteristic analysis results. As a result, the amplitude distortion of the received signal generated in the transmission line can be reduced and the MER of the received signal can be improved compared to conventional distortion compensation means.

[0109] As with the first embodiment, the characteristics of the pseudo-transmitter 303 may be corrected multiple times based on the signal characteristic analysis results to further reduce signal distortion and improve reception performance.

[0110] In this way, excellent distortion compensation is also provided for the IQ signal output from the general IQ signal output unit 10.

[0111] (Modified version of the distortion compensation section) Figure 7 shows a modified example of the distortion compensation unit in the present invention. In the distortion compensation unit 30 of the first embodiment (Figure 1) and the second embodiment (Figure 6), the signal compensation calculation means 320 was a vector calculation means, but in this modified example, the distortion compensation unit 31 uses an amplitude phase calculation means as the signal compensation calculation means 330.

[0112] The distortion compensation unit 31 comprises a pseudo-transmission path 310 and a signal compensation calculation means 330. The pseudo-transmission path 310 consists of an upsampling (U / S) unit 301, a waveform shaping (RRF) unit 302, a pseudo-transmitter 303, an RRF unit 307, and a downsampling (D / S) unit 308. The pseudo-transmitter 303 comprises a pseudo-IMUX filter 304, a pseudo-TWTA 305, and a pseudo-OMUX filter 306. The configuration of the pseudo-transmission path 310 is the same as that of the distortion compensation unit 30, so a description is omitted.

[0113] The signal compensation calculation means (amplitude phase calculation means) 330 comprises a delay unit 331, IQ / amplitude phase conversion units 332 and 333, amplitude phase addition units 334 and 336, inverse characteristic coefficient unit 335, and amplitude phase / IQ conversion unit 337. The signal compensation calculation means 330 is a means for generating a distortion-compensated IQ signal by calculation from two signals: an input distortion-free IQ signal (ideal IQ signal) and an IQ signal containing transmission line distortion that has passed through the pseudo-transmission line 310. Each component will be described below.

[0114] The delay unit 331 adjusts the timing to synchronize the two signals input to the amplitude-phase summing unit 334. Specifically, it applies the same delay amount D as the delay amount D generated by the pseudo-transmission path 310 to the IQ signal (ideal IQ signal) input to the distortion compensation unit 31, thereby synchronizing the two signals.

[0115] The IQ / amplitude-phase conversion unit 332 outputs values ​​(ideal amplitude value, ideal phase value) obtained by converting the ideal IQ signal input via the delay unit 331 into amplitude and phase. The IQ / amplitude-phase conversion unit 333 also outputs values ​​obtained by converting the IQ signal after it has passed through the pseudo-transmission path 310 into amplitude and phase.

[0116] The amplitude-phase summing unit 334 inverts the sign of one of the inputs and outputs amplitude and phase values ​​obtained by subtracting the amplitude and phase values ​​input from the IQ / amplitude-phase conversion unit 332 from the amplitude and phase values ​​input from the IQ / amplitude-phase conversion unit 333. The calculation process by the amplitude-phase summing unit 334 corresponds to determining the difference between the amplitude and phase values ​​of the IQ signal points of the digital signal that has passed through the pseudo-transmission path 310 and the ideal amplitude and ideal phase values ​​of the corresponding ideal IQ signal points as amplitude error values ​​and phase error values ​​for each signal point.

[0117] The inverse characteristic coefficient unit 335 multiplies the amplitude error value and phase error value generated from the amplitude-phase summing unit 334 by a coefficient K. This coefficient K is, for example, 1, and is appropriately selected depending on the degree of compensation.

[0118] The amplitude-phase summing unit 336 calculates corrected amplitude and corrected phase values ​​by adding the ideal amplitude and ideal phase values ​​of the ideal IQ signal point to the error values ​​obtained by sign-inverting the amplitude error value and phase error value obtained by multiplying the amplitude error value and phase error value obtained by coefficient multiplication from the inverse characteristic coefficient unit 335 (sign-inverted amplitude error value and sign-inverted phase error value). Alternatively, the coefficient in the inverse characteristic coefficient unit 335 may be multiplied by a negative value, and a simple addition may be performed in the amplitude-phase summing unit 336.

[0119] The amplitude-phase / IQ conversion unit 337 converts the corrected amplitude value and corrected phase value input from the amplitude-phase summing unit 336 into IQ signal points and outputs a distortion-compensated (corrected) IQ signal.

[0120] In this manner, the distortion compensation unit 31 generates and outputs an IQ signal that has been distortion-compensated by the amplitude-phase calculation means. Although not explicitly shown in Figure 7, when applied to the transmitting device of the present invention, the distortion compensation unit 31 outputs information such as the characteristics and operating point of the pseudo-transmitter 303 and the coefficients in the signal compensation calculation means 320 to the characteristic analysis unit 40. It also receives correction instructions for the characteristics of the pseudo-transmitter 303 from the characteristic analysis unit 40 and reflects the correction in the characteristics of the pseudo-transmitter 303.

[0121] Therefore, in the transmitting devices of the first and second embodiments, a strain compensation unit 31 can be used instead of a strain compensation unit 30.

[0122] In the above embodiment, the configuration and operation of the transmitting device have been described, but the present invention is not limited thereto and may be configured as a transmitting method for transmitting a distortion-compensated signal. That is, the present invention may be configured as a transmitting method that includes the steps of: obtaining an error signal between the IQ signal that has passed through a pseudo-transmission path and the distortion-free IQ signal according to the data flow in Figure 1; generating a distortion-compensated signal based on the coefficient-multiplied error signal and the distortion-free IQ signal; and obtaining at least information on the IQ signal point arrangement in the IQ signal output section, the characteristics and operating point of the pseudo-transmitter, and the coefficients in the signal compensation calculation means; analyzing the IQ signal points at the transmission path output; and correcting the characteristics of the pseudo-transmitter according to the amount of distortion.

[0123] Furthermore, a computer and a program can be suitably used to enable the transmission device described above. A program describing the processing content that enables the computer to function as the IQ signal output unit, pseudo-transmission path, signal compensation calculation means, characteristic analysis unit, etc., of the transmission device is stored in the computer's memory, and the central processing unit (CPU) of the computer reads and executes this program, thereby realizing distortion compensation for the transmission device of the present invention. This program can be recorded on a computer-readable recording medium.

[0124] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the embodiments described above, and various modifications or changes are possible without departing from the scope of the claims. For example, the functions, etc., included in each block, step, etc., described in the embodiments can be rearranged in a logically consistent manner, and multiple constituent blocks, steps, etc., can be combined into one or divided. [Explanation of symbols]

[0125] 1. Transmitter 2 Satellite repeaters 3 IMUX Filter 4. Traveling Wave Tube Amplifier (TWTA) 5 OMUX filters 6. Receiving device 10. IQ signal output section 101 Serial / Parallel (S / P) Conversion Unit 102 Mapping section 11. IQ signal output section 111 Serial / Parallel (S / P) Conversion Unit 112 High-level mapping section 113 S / P conversion section 114 Lower-level mapping section 115 Amplitude adjustment section 116 Synthesis section 21 Upsampling (U / S) section 22 Root Roll-Off Filter (RRF) Section 23 D / A Conversion / Quaternary Modulation Section 30, 31 Distortion compensation section 301 Upsampling (U / S) section 302 RRF (waveform shaping) section 303 Pseudo-transmitter 304 Pseudo IMUX filter 305 Pseudo TWTA 306 Pseudo-OMUX filter 307 RRF (waveform shaping) section 308 Downsampling (D / S) section 310 Pseudo-transmission path 320 Signal compensation calculation means (vector calculation means) 321 Delay section 322 Vector Addition Unit 323 Inverse characteristic coefficient section 324 Vector Addition Unit 330 Signal compensation calculation means (amplitude phase calculation means) 331 Delay section 332 IQ / Amplitude Phase Transformation Unit 333 IQ / Amplitude Phase Transformation Unit 334 Amplitude Phase Addition Section 335 Inverse characteristic coefficient section 336 Amplitude Phase Addition Section 337 Amplitude Phase / IQ Conversion Unit 40 Characteristic analysis section 100,200 Transmitters

Claims

1. A transmitting device that transmits a modulated wave signal obtained by modulating a digital signal with a predetermined modulation scheme via a predetermined transmission path, An IQ signal output unit that generates an IQ signal obtained by modulating the digital signal using the predetermined modulation scheme, A distortion compensation unit comprising: a pseudo-transmission path to which the IQ signal is input from the IQ signal output unit and which includes a pseudo-transmitter having characteristics approximating those of a transmitter on the transmission path; a signal compensation calculation means to obtain an error signal between the IQ signal that has passed through the pseudo-transmission path and the corresponding undistorted IQ signal input from the IQ signal output unit, and to generate a distortion-compensated IQ signal based on the coefficient-multiplied error signal and the undistorted IQ signal; A characteristic analysis unit that acquires at least information on the arrangement of IQ signal points in the IQ signal output unit, the characteristics and operating point of the pseudo-transmitter, and the coefficients in the signal compensation calculation means, acquires the actual IQ signal points at the output of the predetermined transmission path, analyzes the acquired IQ signal points, and corrects the characteristics of the pseudo-transmitter according to the amount of distortion, A transmitting device characterized by comprising the following features.

2. In the transmitting device according to claim 1, The transmission device is characterized in that the characteristic analysis unit analyzes the IQ signal point at the output of the predetermined transmission line and performs a process multiple times to correct the characteristics of the pseudo-transmitter according to the amount of distortion.

3. In the transmitting device according to claim 2, The pseudo-transmission path includes, in front of the pseudo-transmitter, an upsampling (U / S) unit that performs upsampling by N times (where N is an integer of 2 or more) with respect to the IQ signal points, and a waveform shaping unit that performs waveform shaping with a root roll-off filter; and in behind the pseudo-transmitter, the waveform shaping unit that performs waveform shaping with a root roll-off filter, and a downsampling (D / S) unit that reduces the IQ signal points to 1 / N. The transmitting device further comprises an upsampling (U / S) unit that performs N times (where N is an integer of 2 or more) upsampling on the IQ signal point output from the distortion compensation unit; a waveform shaping unit that performs waveform shaping with a root roll-off filter; and a D / A conversion / quadrature modulation unit that performs D / A conversion on the waveform-shaped signal, quadrature modulates the D / A-converted signal, and outputs it as an analog modulated wave signal.

4. In the transmitting device according to claim 3, The signal compensation calculation means is a vector calculation means that obtains an error vector which is the difference between the vector of the IQ signal that has passed through the pseudo-transmission path and the corresponding undistorted IQ signal vector, adds the undistorted IQ signal vector to the inverse vector of the error vector multiplied by a coefficient, and generates a distortion-compensated IQ signal.

5. In the transmitting device according to claim 3, The signal compensation calculation means is an amplitude-phase calculation means characterized by determining amplitude error values ​​and phase error values, which are the difference between the amplitude and phase values ​​obtained by converting the IQ signal that has passed through the pseudo-transmission path into amplitude and phase, and the ideal amplitude and ideal phase values ​​obtained by converting the IQ signal point of the corresponding undistorted IQ signal into amplitude and phase, adding the sign-inverted values ​​of the respective amplitude error values ​​and phase error values ​​multiplied by a coefficient to the ideal amplitude and ideal phase values ​​of the undistorted IQ signal point, and converting the added amplitude and phase values ​​into an IQ signal point to generate a distortion-compensated IQ signal.

6. In the transmitting device according to claim 1, The transmission device is characterized in that the predetermined modulation scheme includes BPSK, QPSK, 8PSK, 16APSK, or 32APSK, or includes two different modulation schemes, one high-level and one low-level.

7. A program that causes a computer to function as an IQ signal output unit, a pseudo transmission path, a signal compensation calculation means, and a characteristic analysis unit of the transmitting device described in any one of claims 1 to 6.

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