JP3344004B2 - Digital modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital modulation device applied to constant envelope modulation represented by MSK modulation.

[0002]

2. Description of the Related Art As digital modulation, there is PSK modulation (phase shift modulation) that changes the phase of a carrier wave with respect to a digital signal. Such PSK modulation is used as a transmission power amplifier because the envelope of an output signal is not constant. A linear amplifier is used.

However, it is known that a linear amplifier used in such a linear modulation system has a power utilization ratio of about 5 to 10%, and its use efficiency as an amplifier is extremely poor.

On the other hand, in contrast to the linear modulation method represented by the PSK modulation, a constant envelope modulation method represented by the MSK modulation is known. In such MSK modulation, the envelope of the output signal is changed. Since it is constant, there is an advantage that even if a non-linear power amplifier having a power utilization factor of 70% is used as the transmission power amplifier, the spectrum of the output signal does not spread due to the non-linear amplification.

FIG. 6 shows a schematic configuration of such an MSK modulation system. In this case, the input data is input to the baseband waveform generator 1. The output signal of the baseband waveform generator 1 is composed of two systems, an I component and a Q component.
Input to modulators 2 and 3. In this case, in the constant envelope modulation, one of the I component and the Q component of the baseband waveform generator 1 is represented by a waveform shown in FIG.

The outputs from the 90-degree signal distributor 4 are given to the modulators 2 and 3. The 90-degree signal distributor 4 is supplied with a local signal serving as a carrier signal from a local oscillator 5, and outputs I and Q signals.
The two orthogonal local signals corresponding to the respective baseband signal components are supplied to the modulators 2 and 3.

[0007] The outputs from the modulators 2 and 3 are combined by a signal combiner 6 to form a modulated signal, which is sent to a transmission unit 7 where the signal is frequency-converted and power-amplified and output as a carrier signal. Become. The spectrum of the carrier here has a first side lobe whose level is lower by about 23 dB than the main lobe, as shown in a spectrum waveform of FIG.

[0008]

However, when such an MSK modulation method is used, the signal spectrum is as follows.
As shown in FIG. In this case, the signal of the main lobe 11 includes second side lobes 113 and 114 indicated by dotted lines in addition to the first side lobes 111 and 112, and these second side lobes 113 and 114 are adjacent to each other. The signal also spreads to the position of the first side lobe 121 and the main lobe 12. This means that, also in the main lobe 12, in addition to the first side lobes 121 and 122, there are second side lobes 123 and 124 indicated by dotted lines in FIG. It also extends to the position of one side lobe 112 and main lobe 11. Here, the first side lobes 111 and 11
Reference numerals 2, 121 and 122 correspond to the spectrum waveform in FIG.

In such an output signal spectrum, it is necessary to keep the ratio between the second side lobe 114 and the adjacent main lobe spectrum 12 sufficiently large in order to limit the range in which the signal fluctuates. . If this ratio cannot be made sufficiently large, it is necessary to greatly separate the places where the systems using adjacent frequencies use.

For these reasons, when the side lobes of the spectrum are large, such as those using the MSK modulation method, it is difficult to arrange the main lobes in close contact, and the frequency cannot be used effectively. was there.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances, and has a digital modulator capable of reducing frequencies of side lobes of a spectrum of an output signal to arrange frequencies at a high density and realizing effective use of frequencies. The purpose is to provide.

[0012]

According to the present invention, there is provided a baseband signal generating means for generating a baseband signal from input data, and a signal which is band-limited from the baseband signal generated by the baseband signal generating means. Band-limited signal output means, a signal delay means for outputting a signal obtained by delaying a baseband signal generated by the baseband signal generation means, a signal band-limited by the band-limited signal output means, and the signal delay means An error signal output means for outputting an error signal of the signal delayed by the step (a), a first carrier signal is generated by using a baseband signal output from the baseband signal generation means as a first modulation signal, and the error signal output is generated. A modulating means for generating a second carrier signal using the error signal output from the means as a second modulated signal; Is constituted by a combining means for combining the first and second carrier signals are generated by means.

According to the present invention, there is provided a baseband signal generating means for generating a baseband signal from input data, an error signal for canceling a side lobe and an error signal corresponding to the input data being read out. A signal generating means for generating a first carrier signal using the baseband signal output from the baseband signal generating means as a first modulation signal, and a second modulation method for generating an error signal output from the error signal generating means; The second signal
And a synthesizing means for synthesizing the first and second carrier signals generated by the modulating means.

[0014]

As a result, according to the present invention, a baseband signal is generated from input data, a band-limited signal is output from the baseband signal, and the band-limited signal and the baseband signal are delayed. An error signal of the signal is generated, a first carrier signal is generated using the baseband signal as a first modulation signal, and a second carrier signal is generated using the error signal as a second modulation signal. And the second carrier signal, so that
The side lobe of the output spectrum can be canceled, and the carrier frequency arrangement can be made dense.

According to the present invention, a baseband signal is generated from input data, while an error signal for canceling a side lobe is stored in advance and read out in accordance with the input data. A first carrier signal is generated using the baseband signal as a first modulation signal, a second carrier signal is generated using the error signal as a second modulation signal, and the first and second carrier signals are generated. Are combined, the side lobes of the output spectrum can be canceled in the same manner as described above, the carrier frequency arrangement can be made denser, and the configuration of the apparatus can be simplified.

[0016]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an MSK modulation system to which the present invention is applied. In this case, 21 is a baseband signal generator, 22 and 23 are signal delayers, 24 and 25 are modulators, 26 is a synthesizer, 27 is a first transmission unit, 28 and 29 are baseband band-limited LPFs, 30, 31 is a subtractor, 3
2, 33 are modulators, 34 is a synthesizer, 35 is a second transmission unit,
36 is a carrier signal combiner, 37 is a local oscillator, 38 is a signal distributor, and 39 and 40 are distributors.

In the configuration shown in the figure, when the input data is supplied to the baseband signal generator 21, the baseband signal generator 21 generates two types of output signals of an I component and a Q component. The signals of the I component and the Q component are respectively divided into two, and the first signal is a signal delay unit 2
2, 23. Then, the signal delay unit 22,
After being delayed at 23, the signal is again divided into two, and a part of the signal is supplied to modulators 24 and 25.

In this case, these modulators 24 and 25 include:
The local oscillator 37 generates a local oscillator signal which is divided by a signal distributor 38 into two local signals having phases different from each other by 90 degrees, and further distributed by dividers 39 and 40 into two signals having the same phase. .

The outputs from the modulators 24 and 25 are provided to a combiner 26, combined and provided as a modulated signal of a local oscillation frequency to a first transmission unit 27, and further converted to a carrier frequency. The signal is converted, amplified to a required level, and sent to the carrier signal combiner 36.

On the other hand, the second signal from the baseband signal generator 21 is supplied to baseband band-limited LPFs 28 and 29.
Given to. Baseband band limiting LPFs 28 and 29
Outputs a signal in which the band of the baseband signal is limited.

Then, this signal is sent to subtractors 30 and 31 and is subtracted from the first signal from the baseband signal generator 21 delayed by the signal delay units 22 and 23. The outputs subtracted by the subtracters 30 and 31 are provided to modulators 32 and 33. Also in this case, the modulators 32, 3
3, the signal is divided into two local signals generated by the local oscillator 37 and having a phase difference of 90 degrees from each other by the signal distributor 38.
Further, the local oscillator signals distributed to two signals of the same phase by the distributors 39 and 40 are provided.

The outputs from the modulators 32 and 33 are supplied to a combiner 34, where they are combined and sent to a second transmitter 35 as a modulated signal having a local oscillation frequency, and further converted to a carrier frequency. And amplified to the required level.

The output from the second transmitting section 35 is sent to a carrier signal combiner 36 and combined with the output of the first transmitting section 27. Thereby, the carrier signal combiner 36
, The side lobe signal of the MSK modulated signal spectrum output from the first transmission unit 27 is canceled by the signal of the opposite-phase side lobe amplified by the second transmission unit 35. An output signal in which only the lobe is left can be obtained.

FIG. 2 shows a baseband modulation waveform of each section obtained by the above-described operation, and FIG. 3 shows a spectrum waveform corresponding to each baseband modulation waveform. First, the waveform of the baseband signal output from the above-described baseband signal generator 21 is shown in FIG. 2A for both I and Q component signals, and the difference is that the I and Q component signals are That is, there is a time difference of 1/2 symbol from each other.
This signal waveform is the same as the signal waveform input to the modulation circuits 24 and 25, and the difference is that the signal delay unit 2
Only the time difference delayed by 2, 23. On the other hand, the waveforms of the output signals from the baseband band-limited LPFs 28 and 29 are as shown in FIG. 2B, and the waveforms of the output signals of the subtracters 30 and 31 are as shown in FIG. 2C.

The spectrum on one side of the modulated wave modulated by the baseband signal waveform shown in FIG. 2A is represented by the spectrum waveform shown in FIG. 3A. In the spectrum, the level of the second side lobe is only 23 dB lower than the level of the first side lobe.

On the other hand, baseband band limiting LP
FIG. 2 in which the baseband band is limited by F28 and F29
The spectrum of the signal modulated by the signal waveform shown in (b) is represented by the spectrum waveform shown in FIG. Further, the spectrum of the signal modulated by the signal waveform shown in FIG. 2C subtracted by the subtracters 30 and 31 is shown in FIG.
It is represented by the spectrum waveform shown in FIG.

By comparing the spectrum waveforms of FIG. 3A and FIG. 3C, it can be seen that the side lobe spectrum is the same, whereby the spectrum waveform shown in FIG. By subtracting the spectrum waveform shown in (c), the spectrum waveform shown in FIG.

This is achieved by subtracting the output signal waveforms of the subtracters 30 and 31 shown in FIG. 2C from the baseband signal waveform of the baseband signal generator 21 shown in FIG. As shown in FIG. 3B, the waveform shown in FIG. 3B is obtained, and as shown in FIG. 3B, an output signal of only the main lobe in which the side lobe level is greatly reduced by nearly 60 dB can be obtained.

As a result, even if the main lobes 41 and 42 are arranged close to each other as shown in FIG. 4, the ratio with the first side lobes 421 and 411 can be close to 60 dB. Can be ensured to be large enough to limit the frequency, thereby allowing the frequencies to be arranged at a high density, thereby improving the frequency utilization efficiency.

Accordingly, since the side lobes of the spectrum of the MSK modulation system can be greatly reduced in this manner, the carrier frequency intervals of the communication system using multiple frequencies can be formed more densely than the conventional intervals. And the frequency can be effectively used.

In the above-described embodiment, the second transmitting unit 34
Is about 3% of the power handled by the first transmission unit 27, so that even if a class A linear amplifier with low power use efficiency is used for the second transmission unit 34, the first transmission unit 2
Since a saturated non-linear amplifier having an excellent power utilization factor can be used for the device 7, a decrease in efficiency of the entire device can be reduced.

FIG. 5 shows another embodiment of the present invention. In this case, in the embodiment described with reference to FIG. 1, in order to generate an error signal for canceling unnecessary side lobes, the signal delay units 22 and 23 and the baseband band limiting LP are used.
Although the circuit configuration of F28 and F29 and the subtracters 30 and 31 is used, in the configuration shown in FIG. 5, an error signal for canceling unnecessary side lobes is calculated in advance, and R is stored.
An error signal generation circuit 51 having a memory such as an OM or a RAM is provided, and an error signal is read out simultaneously with a main signal according to input data. Others are shown in Fig. 1.
And the same parts are denoted by the same reference numerals.

In this case, the same effects as in the above-described embodiment can be expected, and in addition, the circuit configuration can be simplified. In addition, the present invention is not limited to the above embodiment, and can be appropriately modified and implemented without changing the gist.

[0034]

According to the present invention, by applying to a constant envelope modulation method represented by MSK modulation, the output spectrum of the MSK modulation can be minimized without impairing the effect of minimizing the loss of power use efficiency. The side lobes can be greatly reduced, and the carrier frequency intervals of a communication system using multiple frequencies can be formed densely as compared with the conventional intervals, so that the frequency can be used effectively.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a baseband modulation waveform of each unit for explaining one embodiment.

FIG. 3 is a diagram showing a spectrum waveform corresponding to each baseband modulation waveform for explaining one embodiment.

FIG. 4 is a view showing a spectrum waveform for explaining an embodiment.

FIG. 5 is a diagram showing a schematic configuration of another embodiment of the present invention.

FIG. 6 is a diagram showing a schematic configuration of a conventional MSK modulation method.

FIG. 7 is a view showing a spectrum waveform for explaining a conventional technique.

[Explanation of symbols]

21: baseband signal generator, 22, 23: signal delay unit, 24, 25: modulator, 26: synthesizer, 27: transmission unit, 28, 29: baseband band-limited LPF, 30,
31: subtractor, 32, 33: modulator, 34: synthesizer, 3
5: transmission unit, 36: carrier signal synthesizer, 37: local oscillator, 38: signal distributor, 39, 40: distributor, 51: error signal generation circuit.

Claims (2)

(57) [Claims] 1. A baseband signal generating means for generating a baseband signal from input data; a band-limited signal output means for outputting a signal band-limited from the baseband signal generated by the baseband signal generating means; A signal delay unit that outputs a signal obtained by delaying a baseband signal generated by the baseband signal generation unit; an error signal of a signal band-limited by the band-limited signal output unit and a signal delayed by the signal delay unit And an error signal output unit for generating a first carrier signal using the baseband signal output from the baseband signal generation unit as a first modulation signal, and an error signal output from the error signal output unit. Modulating means for generating a second carrier signal as a second modulated signal; Preliminary digital modulation apparatus characterized by a second carrier signal; and a combining means for combining. 2. A baseband signal generating means for generating a baseband signal from input data, and an error signal generating means for storing an error signal for canceling a side lobe in advance and reading out an error signal corresponding to the input data. Generating a first carrier signal using the baseband signal output from the baseband signal generating means as a first modulation signal and generating a second modulation signal using the error signal output from the error signal generating means as a second modulation signal; A digital modulator comprising: a modulator for generating a carrier signal; and a synthesizer for synthesizing the first and second carrier signals generated by the modulator.