WO2025052640A1 - Modulator and modulation method - Google Patents

Abstract

This modulator comprises: a carrier signal generation unit that outputs a carrier signal; and a plurality of modulation units which are cascade-connected downstream from the carrier signal generation unit and into which transmission signals of mutually different frequencies are input. Each of the modulation units comprises a distribution unit, a multiplication unit, a multiplexing unit, and a phase adjustment unit. The distribution unit outputs a first signal and a second signal obtained by bifurcating one carrier signal output by the carrier signal generation unit located upstream or one signal output by another modulation unit located upstream. The multiplication unit multiplies the first signal by the transmission signal inputted into the corresponding modulation unit. The multiplexing unit multiplexes the first signal which the multiplication unit multiplied by the transmission signal with the second signal which was output by the distribution unit, and outputs the resulting multiplexed signal. The phase adjustment unit rotates the phase of the first signal output from the distribution unit to the multiplication unit or the phase of the second signal output from the distribution unit to the multiplexing unit.

Description

Modulator and modulation method

The present invention relates to a modulator and a modulation method.

　Armstrong type modulators have been proposed and put into practical use (see, for example, Non-Patent Document 1). This is a simple configuration that displaces the phase or frequency of a carrier wave. In other words, Armstrong type modulators perform phase modulation or frequency modulation. Figure 9 is a diagram showing an example of the configuration of a modulator 99 of the prior art. Modulator 99 is an example of an Armstrong type modulator configured as a frequency modulator, and an integrator is placed at the input section of the transmission signal.

The distribution unit divides the carrier signal output by the carrier signal generation unit into two. One of the divided carrier signals is input to the phase adjustment unit. The phase adjustment unit performs a 90-degree phase rotation on the input carrier signal and then outputs it to the multiplication unit. Here, the phase adjustment unit may be configured to be placed between the distribution unit and the multiplication unit as shown in FIG. 9, or may be placed between the distribution unit and the multiplexing unit at the other distribution unit output. When the phase adjustment unit is placed between the distribution unit and the multiplexing unit, the phase rotation degree in the phase adjustment unit is minus 90 degrees. The integration unit integrates the transmission signal and outputs the integrated transmission signal to the multiplication unit. The multiplication unit multiplies the phase-rotated carrier signal by the integrated transmission signal and outputs the multiplied signal to the multiplexing unit. The multiplexing unit outputs a signal obtained by multiplexing the signal output from the multiplication unit with the other carrier signal distributed by the distribution unit.

Ryozo Nagahama, "On Phase Modulation Methods for VHF-FM", Hitachi Hyoron, Special Issue on Electron Tubes and Applications of Electron Tubes, Special Issue No. 3, 1953, pp. 71-81

In conventional modulators, the output signal from the carrier signal generator is split into two, one of which is phase-rotated by 90 degrees using a phase shifter (phase adjustment section), and then this signal is multiplied by the transmission signal in a multiplier (multiplication section). The signal multiplied by the multiplier is then added to the other output signal of the split, thereby obtaining a pseudo carrier signal and first sidewave signal. With this type of configuration, it is not possible to obtain second or subsequent sidewave components in a systematic way.

Ideal frequency modulation and phase modulation signals have second and subsequent sidewave components. In other words, the absence of a sidewave means that the distortion characteristics of the signal have deteriorated. Furthermore, when multiple transmission signals are involved, interference between the multiple signals increases the number of distortion components that are generated. This distortion poses the problem of further deteriorating signal quality.

In view of the above circumstances, the present invention aims to provide a modulator and a modulation method that can achieve low distortion modulation.

The modulator of one embodiment of the present invention comprises a carrier signal generating unit that outputs a carrier signal, and a plurality of modulation units that are connected in cascade to the rear of the carrier signal generating unit and to which transmission signals of different frequencies are input, and each of the plurality of modulation units comprises a distribution unit that outputs a first signal and a second signal obtained by branching the carrier signal output by the carrier signal generating unit in the previous stage or the signal output by another modulation unit in the previous stage into two, a multiplication unit that multiplies the first signal by the transmission signal input to the modulation unit, a combining unit that combines the first signal multiplied by the transmission signal by the multiplication unit and the second signal output by the distribution unit and outputs the combined signal, and a phase adjustment unit that rotates the phase of the first signal output from the distribution unit to the multiplication unit or the second signal output from the distribution unit to the combining unit.

The modulation method of one aspect of the present invention includes a signal output step in which a carrier signal generating unit outputs a carrier signal, and a modulation step in which a plurality of modulation units connected in cascade to the rear of the carrier signal generating unit receive transmission signals of different frequencies, and modulate the carrier signal output by the carrier signal generating unit in the previous stage or the signal output by another modulation unit in the previous stage using the input transmission signal, and the modulation step performed by each of the modulation units includes a distribution step in which the carrier signal output by the carrier signal generating unit in the previous stage or the signal output by another modulator in the previous stage is split into two to obtain a first signal and a second signal, a multiplication step in which the first signal is multiplied by the transmission signal, a combining step in which the first signal multiplied by the transmission signal is combined with the second signal and the combined signal is output, and a process of rotating the phase of the first signal before the multiplication step, or a phase adjustment step in which the phase of the second signal is rotated before the combining step.

The present invention makes it possible to perform modulation with low distortion.

FIG. 2 is a configuration diagram of a modulator according to the first embodiment. FIG. 11 is a configuration diagram of a modulator according to a second embodiment. FIG. 11 is a configuration diagram of a modulator according to a third embodiment. FIG. 13 is a configuration diagram of a modulator according to a fourth embodiment. FIG. 1 is a diagram showing the FM spectrum of a signal FM modulated with two waves. FIG. 2 illustrates a frequency spectrum of an output signal from a prior art modulator. 4 is a frequency spectrum of an output signal from the modulator according to the first embodiment. 1A and 1B are diagrams illustrating simulation results of a modulator according to the prior art and a modulator according to the first embodiment. FIG. 1 is a block diagram of a modulator according to the prior art.

Below, an embodiment of the present invention will be described in detail with reference to the drawings. This embodiment provides a modulator and modulation method that performs phase modulation or frequency modulation with lower distortion than conventional ones. The modulator of this embodiment has a configuration in which multiple Armstrong type modulation sections are connected in cascade. The transmission signal is branched off for each of these Armstrong type modulation sections and input to the multiplication section of each Armstrong type modulation section, or to the multiplication section via an integration section. Each of the multiple Armstrong type modulation sections performs multiple modulation using the branched transmission signal, making it possible to obtain an output frequency spectrum that is closer to an ideal frequency spectrum than conventional methods. Therefore, the output from the modulator of this embodiment has low distortion. By using the modulator of this embodiment, it is possible to improve the quality of the transmission signal. Each embodiment will be described below.

[First embodiment]
The modulator of the first embodiment has Armstrong modulators connected in cascade, and transmission signals of different frequencies are input to each Armstrong modulator. Each Armstrong modulator has an integrator that integrates the transmission signal. This allows the modulator to function as a frequency modulator.

FIG. 1 is a configuration diagram of a modulator 1 according to a first embodiment of the present invention. The modulator 1 has a carrier signal generating section 2 and n (n is an integer of 2 or more) Armstrong-type modulation sections 3. A conventional Armstrong-type modulator can be used as the Armstrong-type modulation sections 3. The n Armstrong-type modulation sections 3 are cascaded after the carrier signal generating section 2. The i-th (i is an integer of 1 to n) Armstrong-type modulation section 3 is referred to as Armstrong-type modulation section 3-i. A transmission signal Pi is input to the Armstrong-type modulation section 3-i. The transmission signals P1 to Pn each have a different wavelength.

The Armstrong type modulation unit 3 has a distribution unit 31, a phase adjustment unit 32, an integration unit 33, a multiplication unit 34, and a multiplexing unit 35. The distribution unit 31, phase adjustment unit 32, integration unit 33, multiplication unit 34, and multiplexing unit 35 of the Armstrong type modulation unit 3-i are respectively referred to as the distribution unit 31-i, the phase adjustment unit 32-i, the integration unit 33-i, the multiplication unit 34-i, and the multiplexing unit 35-i.

The carrier signal generating unit 2 outputs a carrier signal. The distributor 31-i inputs the carrier signal output by the carrier signal generating unit 2 in the previous stage, or the signal output by the multiplexing unit 35-(i-1) of the Armstrong type modulation unit 3-(i-1) in the previous stage. The distributor 31-i distributes the input signal into two. The distributor 31-i outputs one of the distributed signals (first signal) to the phase adjustment unit 32-i, and outputs the other distributed signal (second signal) to the multiplexing unit 35-i.

The phase adjustment unit 32-i rotates the signal input from the distribution unit 31-i by 90 degrees and outputs it to the multiplication unit 34-i. The integration unit 33-i integrates the transmission signal Pi and outputs the signal Si obtained by the integration to the multiplication unit 34-i. The multiplication unit 34-i multiplies the signal received from the phase adjustment unit 32-i by the signal Si received from the integration unit 33-i and outputs the signal obtained by the multiplication to the multiplexing unit 35-i. The multiplexing unit 35-i multiplexes the signal input from the multiplication unit 34-i and the signal input from the distribution unit 31-i and outputs the signal obtained by the multiplication to the next stage. When i is n-1 or less, the next stage is the Armstrong type modulation unit 3-(i+1). When i=n, the next stage is the device subsequent to the modulator 1.

With the above configuration, the modulator 1 operates as follows. The carrier signal generating unit 2 of the modulator 1 outputs a carrier signal. The Armstrong type modulation unit 3-i, where i=1, operates as follows. That is, the distribution unit 31-1 of the Armstrong type modulation unit 3-1 inputs the carrier signal output by the carrier signal generating unit 2 and branches the input signal into two. The distribution unit 31-1 outputs one signal to the phase adjustment unit 32-1 and outputs the other signal to the multiplexing unit 35-1. The phase adjustment unit 32-1 performs a 90-degree phase rotation on the signal input from the distribution unit 31-1. The integrating unit 33-1 outputs a signal S1 obtained by integrating the transmission signal P1. The multiplier unit 34-1 multiplies the signal received from the phase adjustment unit 32-1 by the signal S1 received from the integrating unit 33-1. The multiplexer 35-1 outputs a signal obtained by multiplexing the signal multiplied by the multiplier 34-1 and the signal distributed by the distributor 31-1.

Next, the Armstrong type modulation unit 3-i where i=2 performs the same processing as above. That is, the distribution unit 31-2 splits the signal output by the multiplexing unit 35-1 of the Armstrong type modulation unit 3-1 into two, outputs one signal to the phase adjustment unit 32-2, and outputs the other signal to the multiplexing unit 35-2. The phase adjustment unit 32-2 performs a 90-degree phase rotation on the signal input from the distribution unit 31-2. The integration unit 33-2 outputs a signal S2 obtained by integrating the transmission signal P2. The multiplication unit 34-2 multiplies the signal received from the phase adjustment unit 32-2 by the signal S2 received from the integration unit 33-2. The multiplexing unit 35-2 outputs a signal obtained by multiplexing the signal multiplied by the multiplication unit 34-2 and the signal distributed by the distribution unit 31-2.

Modulator 1 performs the same processing of Armstrong type modulation unit 3-i as described above while incrementing n by 1 until the value of i reaches n. Modulator 1 then outputs the signal output by multiplexer 35-n of Armstrong type modulation unit 3-n to a device downstream of modulator 1 via a transmission line, etc.

Second Embodiment
The modulator of the second embodiment is configured by further comprising a demultiplexing section for separating signals input to the integrating section of each Armstrong type modulation section according to frequency in addition to the modulator of the first embodiment. The second embodiment will be described focusing on the differences from the first embodiment described above.

FIG. 2 is a configuration diagram of a modulator 11 in a second embodiment of the present invention. In the figure, the same parts as those of the modulator 1 according to the first embodiment shown in FIG. 1 are given the same reference numerals, and their description will be omitted. The modulator 11 shown in FIG. 2 differs from the modulator 1 shown in FIG. 1 in that the modulator 11 further includes a demultiplexing unit 4. The demultiplexing unit 4 receives a transmission signal P and demultiplexes the received transmission signal P into transmission signals P1 to Pn according to wavelength. The demultiplexing unit 4 outputs the transmission signal Pi to the integrating unit 33-i of the Armstrong type modulation unit 3-i. The carrier signal generating unit 2 and the Armstrong type modulation units 3-1 to 3-n operate in the same manner as in the first embodiment.

[Third embodiment]
The modulator of the third embodiment has a configuration in which the integrating section is removed from the modulator of the first embodiment. As a result, the modulator of the third embodiment functions as a phase modulator. The third embodiment will be described focusing on the differences from the above-mentioned embodiments.

FIG. 3 is a configuration diagram of a modulator 12 in a third embodiment of the present invention. In the figure, the same parts as those of the modulator 1 according to the first embodiment shown in FIG. 1 are given the same reference numerals, and their description will be omitted. The modulator 12 shown in FIG. 3 differs from the modulator 1 shown in FIG. 1 in that it has an Armstrong-type modulation section 3a instead of the Armstrong-type modulation section 3. The Armstrong-type modulation section 3a differs from the Armstrong-type modulation section 3 shown in FIG. 1 in that it does not have an integrator section 33.

The n Armstrong type modulation units 3a are connected in cascade to the rear stage of the carrier signal generating unit 2. The i-th (i is an integer between 1 and n) Armstrong type modulation unit 3a is referred to as Armstrong type modulation unit 3a-i. The distribution unit 31, phase adjustment unit 32, multiplication unit 34, and multiplexing unit 35 of the Armstrong type modulation unit 3a-i are referred to as distribution unit 31-i, phase adjustment unit 32-i, multiplication unit 34-i, and multiplexing unit 35-i, respectively.

The carrier signal generating unit 2, the distributor 31-i, the phase adjustment unit 32-i, and the multiplexing unit 35-i of each Armstrong type modulation unit 3a-i operate in the same manner as in the first embodiment. The multiplier unit 34-i multiplies the signal received from the phase adjustment unit 32-i by the transmission signal Pi, and outputs the signal obtained by the multiplication to the multiplexing unit 35-i.

[Fourth embodiment]
The modulator of the fourth embodiment is configured by further comprising a demultiplexing section for separating signals input to the multiplication section of each Armstrong type modulation section according to frequency in addition to the modulator of the third embodiment. The fourth embodiment will be described focusing on the differences from the above-mentioned embodiments.

FIG. 4 is a configuration diagram of a modulator 13 in the fourth embodiment of the present invention. In the figure, the same parts as those in the modulator 11 according to the second embodiment shown in FIG. 2 and the modulator 12 according to the third embodiment shown in FIG. 3 are given the same reference numerals, and their description will be omitted. The modulator 13 shown in FIG. 4 differs from the modulator 12 in the third embodiment shown in FIG. 3 in that the modulator 13 further includes a demultiplexing unit 4. The demultiplexing unit 4 receives a transmission signal P and demultiplexes the received transmission signal P into transmission signals P1 to Pn according to wavelength. The demultiplexing unit 4 outputs the transmission signal Pi to the multiplier unit 34-i of the Armstrong type modulation unit 3a-i. The carrier signal generating unit 2 and the Armstrong type modulation units 3a-1 to 3a-n operate in the same manner as in the third embodiment.

Next, we will explain why the modulators 1, 11, 12, and 13 of the embodiments have lower distortion than conventional modulators.

The reason why the modulator of this embodiment has lower distortion than the conventional method is that when comparing the frequency spectrum of the output signal from the modulator, the present embodiment is closer to the ideal frequency spectrum than the conventional method. This is further explained below.

For simplicity, consider the case of frequency modulation where the number of transmission signals is two and the number of cascaded Armstrong modulators is two. The frequencies of the two transmission signals are _f1 and _f2 , respectively, and the frequency of the carrier signal output from the carrier signal generating unit 2 is _fc . Here, the FM wave SFM(t) obtained by FM-modulating the carrier signal of frequency _fc with two signals of frequencies _f1 and _f2 is expressed by the following formula (1).

Here, m ₁ and m ₂ are FM modulation indices. For simplicity, the initial phase of each signal is normalized to zero and the signal amplitude is normalized to 1, but this does not affect the essence.

Furthermore, equation (1) can be expanded in Bessel functions, as described on page 18 of Reference 1. This can be expressed as the following equation (2).

(Reference 1) Sugawara Teizan, "FM Radio Engineering (New Edition)", Nikkan Kogyo Shimbun, July 1964

In formula (2), _JN is an Nth-order Bessel function. Formula (2) means that each sidewave obtained by FM-modulating a carrier signal of frequency _fc with a transmission signal of frequency _f1 is further FM-modulated with a transmission signal of frequency _f2 . The signal of formula (2) is shown in FIG. 5 as a frequency spectrum. FIG. 5 is a diagram showing the FM spectrum of a signal FM-modulated with two waves. For simplicity, FIG. 5 shows a case where _m1 and _m2 are sufficiently smaller than 1, and the components after _J2 can be ignored. That is, since the FM modulation index after the second sidewave is << 1, FIG. 5 shows up to the first sidewave. If the components after _J2 are also included in the spectrum, it becomes an ideal frequency spectrum.

Next, consider the frequency spectrum of the signal S _armstrg (t) at the output of the conventional modulator 99 shown in Fig. 9. The conventional modulator 99 splits a carrier signal of frequency f _c into two, shifts the phase of one of the carrier signals by π/2, and then multiplies it by a transmission signal of frequency f ₁ and a transmission signal of frequency f ₂ using a multiplier (multiplication unit). The modulator 99 combines the multiplied signal with the other branched carrier signal. Therefore, this combined signal can be written as the following equation (3).

Here, the carrier signal amplitude is normalized to 1. Furthermore, _k1 and _k2 are parameters related to the modulation depth of the two transmission signals, and are determined by the carrier signal amplitude and transmission signal amplitude input to the multiplier. Figure 6 is a diagram showing the frequency spectrum of the output signal from the modulator 99 shown in equation (3). That is, Figure 6 shows the frequency spectrum of the output signal from the Armstrong type modulator according to the conventional technology when the number of transmission signals is 2.

Next, consider the frequency spectrum of the signal S _armstrg2 (t) output from the modulator 1 in the first embodiment shown in Fig. 1. In this embodiment, two Armstrong type FM modulation circuits are connected in cascade, and each modulation circuit Armstrong-type modulates the transmission signals of frequencies _f1 and _f2 . Therefore, the output spectrum is expressed by the following equation (4).

FIG. 7 is a diagram showing the frequency spectrum of the formula (4). That is, FIG. 7 shows the frequency spectrum of the output signal from the modulator 1 when the number of transmission signals is 2. When comparing the output frequency spectrum of the modulator 99 of the conventional technology shown in FIG. 6 with the output frequency spectrum of the modulator 1 of the present embodiment shown in FIG. 7, the output from the modulator ₁ of the present embodiment has components of _{f c ±} f ₁ ±f 2, which are four side waves generated by the modulation of f ₂ with respect to the side waves of frequencies f c ±f ₁ , and is therefore close to the ideal FM signal spectrum shown in FIG. 5. Since deviation from the ideal spectrum appears as distortion after FM demodulation, it can be said that the modulator 1 of the present embodiment is a method with lower distortion. This also holds true when the Armstrong type modulation method is phase modulation.

FIG. 8 shows the results of a MATLAB® simulation of a modulator 99 according to the prior art and the modulator 1 of the first embodiment shown in FIG. 1. The simulation conditions are as follows: the FM carrier signal frequency is 3 GHz, the transmission signal P1 is 106 MHz, the transmission signal P2 is 497 MHz, and the delay detection method is used for the FM demodulation method.

Using a conventional modulator 99 shown in Figure 9, a 3 GHz FM carrier signal was Armstrong-type modulated (FM modulated) by transmission signals P1 and P2, and then FM demodulated using a delay detection method. Figure 8 (a) shows an example of the frequency spectrum of the signal after this FM demodulation.

On the other hand, using the modulator 1 in Figure 1, a 3 GHz FM carrier signal was Armstrong-type modulated (FM modulation) using transmission signals P1 and P2, and then FM demodulated using a differential detection method. Figure 8 (b) shows an example of the frequency spectrum of the signal after this FM demodulation. From Figures 8 (a) and 8 (b), it can be seen that the output signal of the modulator 1 of this embodiment has less distortion than the output signal of a conventional modulator.

In the above embodiment, the phase adjustment unit 32 of the Armstrong type modulation unit 3, 3a is provided between the distribution unit 31 and the multiplication unit 34, but it may be provided between the distribution unit 31 and the multiplexing unit 35. When the phase adjustment unit 32 is provided between the distribution unit 31 and the multiplexing unit 35, the phase adjustment unit 32 rotates the phase of the signal input from the distribution unit 31 by minus 90 degrees and outputs it to the multiplexing unit 35, and the multiplexing unit 35 outputs the signal obtained by multiplexing the signal input from the multiplication unit 34 and the signal input from the phase adjustment unit 32 to the next stage.

According to the above-described embodiment, the modulator performs phase modulation or frequency modulation on a carrier signal using a plurality of transmission signals of different frequencies. The modulator includes a carrier signal generating unit and a plurality of modulation units. The plurality of modulation units are connected in cascade to the rear stage of the carrier signal generating unit, and each of the modulation units receives a transmission signal of a different frequency. Each modulation unit includes a distribution unit, a multiplication unit, a combining unit, and a phase adjustment unit. The distribution unit outputs a first signal and a second signal obtained by branching the carrier signal output by the carrier signal generating unit in the previous stage or the signal output by another modulation unit in the previous stage into two. The multiplication unit multiplies the first signal by the transmission signal input to the modulation unit. The combining unit combines the first signal multiplied by the transmission signal by the multiplication unit and the second signal output by the distribution unit, and outputs the combined signal to the next stage. The phase adjustment unit rotates the phase of the first signal output from the distribution unit to the multiplication unit by 90 degrees, or rotates the phase of the second signal output from the distribution unit to the combining unit by minus 90 degrees. The modulation section corresponds to, for example, the Armstrong type modulation section 3a in the embodiment.

The modulation unit may further include an integrator unit that integrates the transmission signal input to the modulation unit. The multiplier unit multiplies the first signal by the transmission signal integrated by the integrator unit. In this case, the modulation unit corresponds to, for example, the Armstrong type modulation unit 3 of the embodiment.

The modulator may further include a branching unit. The branching unit receives a transmission signal, branches the input transmission signal according to frequency, and outputs the branched transmission signals to different modulation units.

　Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and includes designs that do not deviate from the gist of the present invention.

1, 11, 12, 13, 99 Modulator 2 Carrier signal generating section 3-1 to 3-n, 3a-1 to 3a-n Armstrong type modulation section 31-1 to 31-n Distribution section 32-1 to 32-n Phase adjustment section 33-1 to 33-n Integration section 34-1 to 34-n Multiplication section 35-1 to 35-n Multiplexing section 4 Demultiplexing section

Claims (4)

a carrier signal generating unit that outputs a carrier signal;
a plurality of modulation units connected in cascade to a rear stage of the carrier signal generating unit and receiving transmission signals of different frequencies,
Each of the multiple modulation units is
a distributor that outputs a first signal and a second signal obtained by splitting the carrier signal output from the carrier signal generating unit in the previous stage or a signal output from another modulation unit in the previous stage into two signals;
a multiplication unit that multiplies the first signal by the transmission signal input to the modulation unit;
a multiplexing unit that multiplexes the first signal obtained by multiplying the transmission signal by the multiplier unit and the second signal output by the distributor unit, and outputs the multiplexed signal;
a phase adjustment unit that rotates a phase of the first signal output from the distribution unit to the multiplication unit or the second signal output from the distribution unit to the multiplexing unit.
Modulator. The modulation unit is
further comprising an integrating unit that integrates the transmission signal input to the modulating unit;
The multiplication unit multiplies the first signal by the transmission signal integrated by the integration unit.
The modulator of claim 1 . the modulator further includes a demultiplexing unit that receives a transmission signal, demultiplexes the received transmission signal based on a frequency, and outputs the demultiplexed transmission signals to different modulators.
3. A modulator according to claim 1 or 2. a signal output step in which a carrier signal generating unit outputs a carrier signal;
a modulation step in which a plurality of modulation units connected in cascade to a rear stage of the carrier signal generating unit receive transmission signals of different frequencies, and modulate the carrier signal output by the carrier signal generating unit in the previous stage or a signal output by another modulation unit in the previous stage using the received transmission signals;
The modulation step performed by each of the modulation units is
a distribution step of splitting the carrier signal output from the carrier signal generating unit in the previous stage or the signal output from another modulator in the previous stage into two to obtain a first signal and a second signal;
a multiplying step of multiplying the first signal by the transmission signal;
a multiplexing step of multiplexing the first signal and the second signal multiplied by the transmission signal and outputting the multiplexed signal;
a process of rotating the phase of the first signal before the multiplication step, or a phase adjustment step of rotating the phase of the second signal before the combining step.
Modulation method.

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