JPS6347179B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a burst signal generation method that suppresses the generation of unnecessary waves when creating a burst signal by switching a modulated wave whose band is limited in the baseband.

In the time-division communication system, in order to send out signals during the allocated time slot of the station itself, phase-modulated or amplitude-modulated signals are transmitted in bursts. SCPC (Single
The Channel par Carrier method is also similar in this respect. Therefore, in these systems, a switch is installed after the modulator, and by switching the modulation wave on and off using a square wave signal, a burst signal is created and transmitted during the allocated time of the own station. I have to.

FIG. 1 shows the basic configuration when switching a modulated wave using a rectangular wave signal. In the figure, 1 is a low-pass filter that limits the band of a PN (pseudorandom code) signal, which is an input baseband signal. 2 is a modulator which phase-modulates or amplitude-modulates a carrier wave using a baseband signal band-limited by a low-pass filter 1;
Generates a modulated wave. A switch 3 switches the modulated wave signal of the modulator 2 in response to a rectangular wave signal input, and generates a burst-like RF (radio frequency) signal.

When switching the modulated wave using such a switch, unnecessary waves are instantaneously generated due to an impulse response based on the discontinuation of the modulated wave at the leading and trailing edges of the burst signal.
Since this unnecessary wave is based on an impulse response, its spectrum spreads widely and interferes with other communications.

FIG. 2 shows the waveform of the output signal in the configuration of FIG. 1. In the figure, a indicates a burst signal, which is switched in response to a rectangular wave signal input. b shows an impulse response based on switching of the modulated wave, which is shown to occur corresponding to the leading edge and trailing edge of the burst signal, respectively.

Further, FIG. 3 shows the frequency spectrum of each signal in FIG. 2. In the figure, a indicates the spectrum of the burst signal, which is shown to attenuate upward and downward in the form S() = (sinx/x) ^2, respectively, on the frequency axis with the carrier wave position indicated by O as the center. There is. On the other hand, Figure b shows an unnecessary wave based on an impulse response, and it is shown that it has a spectrum spread that is centered on the carrier wave at the position O and attenuated with tails drawn upward and downward on the frequency axis. Such spectrum broadening becomes wider as the pulse width of the impulse response becomes narrower.

Such spectrum expansion interferes with other communications. Therefore, conventionally, as shown in Figure 1, a low-pass filter is inserted at the baseband signal stage to limit the band in advance, thereby preventing the spectrum expansion of the burst signal shown in Figure 3a. However, with this method, the third
It is not possible to prevent the spectrum broadening based on the impulse response shown in Figure b. For this reason, a bandpass filter was inserted after the switch that creates the burst signal to remove unnecessary waves.

FIG. 4 shows the configuration of a conventional burst signal generation circuit. In this figure, the same parts as in FIG. 1 are designated by the same numbers, and 4 is a bandpass filter. Further, FIG. 5 shows signal waveforms of various parts in the burst signal generation circuit of FIG. 4. In the figure, a indicates the rectangular wave signal input of the switch 3, and b indicates the RF signal output of the modulator 3.

In FIG. 4, the PN signal input is band limited by a low pass filter 1 and then modulated by a modulator 2 to produce the output signal shown in FIG. 5b. The switch 3 switches the fifth
Switching is performed at the leading and trailing edges of the output signal in Figure b. As shown in FIG. 5b, the band-limited signal exhibits a characteristic in which the amplitude of its leading and trailing edges smoothly increases or decreases. Therefore, if switching is performed in this part using a rectangular wave signal, it is possible to prevent spectrum broadening caused by switching of the burst signal shown in Fig. 3a, and ideally, unnecessary broadening caused by impulse response can be prevented. There shouldn't be any waves, but in reality, based on carrier wave leakage in the modulator, etc.
This produces an impulse response as shown in Figure b. The bandpass filter 4 removes unnecessary waves outside the band from the output signal of the switch 3 to generate an RF signal output.

However, even if a bandpass filter for burst signals is provided in this way, it is extremely difficult to create a bandpass filter with a narrow bandwidth that can effectively remove unnecessary waves when the frequency of the RF signal is high. Not only that, but it is impossible to remove unnecessary waves within the band of the bandpass filter.

The present invention aims to eliminate such drawbacks of the prior art, and its purpose is to provide a method that can effectively remove unnecessary waves based on switching by utilizing the amplitude characteristics of a modulated wave signal. Our goal is to provide the following.

The burst signal generation method of the present invention utilizes the fact that a signal undergoing phase modulation or amplitude modulation is accompanied by a 100% amplitude change, and adds specific bits before and after the burst signal to perform switching. This is designed to prevent the instantaneous generation of unnecessary waves based on

Hereinafter, the principle and embodiments of the present invention will be explained in detail.

6 and 7 illustrate waveforms and unnecessary waves when the sign of the input data signal is reversed bit by bit at the leading and trailing edges of the burst signal. In FIG. 6, a indicates a rectangular wave signal for switching, and b indicates an input data signal. (c) shows a modulated wave envelope when such a data signal is applied to the circuit shown in FIG. 1 to perform phase modulation or amplitude modulation. By making the input data change sign in response to the rising edge or falling edge of the rectangular wave signal, the data signal b is changed from the rising edge or falling edge of the burst signal, and from the rising edge or falling edge of the burst signal.
100% at points separated by bit length time 1S
This causes an amplitude change. In this case, at each amplitude change point, the amplitude is limited by the low-pass filter, so that the amplitude changes smoothly. Furthermore, Fig. 7 shows unnecessary waves based on the impulse response when such a modulated wave is switched by a switch, and shows the unnecessary waves that are located at a frequency S above and below the carrier wave position indicated by O on the frequency axis. It has been shown that a spectrum that spreads out around the center has been shown to occur. In this way, as the unnecessary waves are distributed over a certain frequency range, their level is lowered and the degree of interference is reduced. A burst signal generation method based on such a principle has already been proposed. However, in the method shown in Fig. 6, the unwanted waves are generated centered at a point that is away from the frequency ±S, and as a result, the spectrum of the unwanted waves is expressed as ±x with the carrier wave position O as the center, as shown in Fig. 7. This causes unnecessary waves to be generated outside the permissible band, causing interference with other communications.

On the other hand, it is conceivable to cause a 100% amplitude change to occur at time 2S from the leading or trailing edge of the burst signal. FIG. 8 and FIG. 9 explain the waveform and unnecessary waves in this case. In FIG. 8, a indicates a rectangular wave signal for switching, and b indicates an input data signal.
Further, (c) shows a modulated wave envelope when the data signal shown in b is applied to the circuit of FIG. 1 to perform phase modulation or amplitude modulation. As shown in Figure 8b, a data signal in which two consecutive bits of different polarity follow the first bit undergoes phase inversion or 100% amplitude change in coincidence with the rising or falling edge of the rectangular wave signal. As a result, as shown in FIG. 8c, a 100% amplitude change occurs between the rise or fall of the burst signal and at a point 2S apart from the rise or fall. FIG. 9 shows the unnecessary waves based on the impulse response in the output of the switch in this case, with points spaced apart by frequency S/2 in the upper and lower directions on the frequency axis centering on the position of the carrier wave indicated by O. This produces a spectrum that is tailed and broadened. The level of unnecessary waves in this case is the same as in the case of Fig. 7, but the spectrum width of the unnecessary waves is ±y centered on the carrier wave, which is significantly reduced compared to the case of Fig. 7. As a result, interference with other communications is significantly reduced.

FIG. 10 shows the configuration of an embodiment of the burst signal generation method of the present invention. In the same figure, the same parts as in FIG. 1 are indicated by the same numbers, 5 is a burst signal controller, 6 is a code generator,
7 is a synthesizer.

In FIG. 10, a burst signal controller 5 controls a code generator 6 using an input rectangular wave. The code generator 6 thereby generates a code of "011" or "100" in response to the rising edge of the rectangular wave, and a code of "110" or "001" in response to the falling edge of the rectangular wave. do. The code generated by the code generator 6 is applied to a combiner 7 and is combined with input data. The output of the synthesizer 7 is applied to a low-pass filter 1 to limit the band, and then applied to a modulator 2 to generate a phase modulated wave or an amplitude modulated wave. The modulated wave output is applied to a switch 3, and the switch 3 performs switching based on a switching signal from a burst signal controller 5. The switching signal from the burst signal controller 5 is 2 times higher than the rising edge of the data signal input.
The signal rises after a bit length time of 2S and falls after a 2 bit length time of 2S after the falling edge of the data signal input, thereby performing switching of the modulated wave as shown in FIG. is possible,
Spreading of the spectrum of unnecessary waves based on the impulse response is prevented. Therefore, in this case, there is no need for a bandpass filter after the switch 3, and the burst signal can be extracted immediately. In this case, it goes without saying that the portion between the specific codes at the leading and trailing edges of the burst signal inserted by the code generator 6 is the required data to be transmitted.

FIG. 11 shows another embodiment of the burst signal generation method of the present invention, which is particularly suitable for the phase modulation method. In the figure, 8 is a code generator;
is a differential logic circuit. Generally, phase modulation is often performed using a differential logic circuit, and in this case, the generation of the additional bits as described above can be performed more easily.

In FIG. 11, the code generator 8 generates the code "10" according to the rising edge of the rectangular wave, and the code "01" according to the falling edge of the rectangular wave, under the control of the burst signal controller 5. occurs. The code generated by the code generator 8 is combined with the input data applied to the combiner 7. A differential logic circuit always produces an output that is inverted with respect to the previous bit when a "1" is input, and produces the same output when a "0" is input. Therefore, the output of the differential logic circuit 9 becomes "011" or "011" at the rise of the rectangular wave, as in the case of FIG. 10, regardless of the sign of the bit immediately before the code of the code generator 8 is input. It produces a code of "100" and a code of "110" or "001" at the falling edge of the square wave. Therefore, this signal is applied to the band-limited modulator 2 as in the case of Fig. 0 to generate a phase modulated wave, and this is applied to the switch 3 for switching as in the case of Fig. 10. Therefore, switching of the modulated wave as shown in FIG. 8 can be performed. In this case, the switching signal given from the burst signal controller 5 to the switch 3 rises 2S after the rising edge of the data input, and falls 1S after the falling edge of the data input. It is fine as long as it is something.

Although the above embodiment has been explained in the case of two-phase phase modulation, in the case of 4-phase, 8-phase, or more polyphase, 2-bit strings, 3-bit strings, etc. are grouped together, and the above-mentioned method can be applied. By performing processing, it can be realized with a similar configuration.

As explained above, according to the burst signal generation method of the present invention, switching is performed when the sign of the modulation input is inverted at the leading edge of the burst signal, and thereafter the same sign continues for two or more bits, and the switching is performed at the leading edge of the burst signal. In this method, the modulation input is controlled so that the same sign continues for two or more bits, and then switching is performed and the sign is inverted.Then, the modulation input is phase-modulated or amplitude-modulated, and the modulated wave is switched. This is extremely effective because it can reduce the spectrum spread of unnecessary waves in the signal.

If a roll-off filter that performs a 50% roll-off is used as low-pass filter 1,
Since the spectrum becomes zero at the point of ±3/2S, it is very effective when 2 bits are added.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration when switching a modulated wave using a rectangular wave signal.
2 is a diagram showing the output signals in the configuration of FIG. 1, FIG. 3 is a diagram showing the frequency spectrum of each signal in FIG. 2, and FIG. 4 is a block diagram showing the configuration of a conventional burst signal generation circuit. Fig. 5 is a diagram showing the signal waveforms of various parts in the burst signal generation circuit of Fig. 4, and Figs. 6 and 7 show that the input data signal has 100% amplitude after 1 bit time at the leading and trailing edges of the burst signal. Figures 8 and 9 show the waveform and unnecessary waves when a change occurs, respectively, where a 100% amplitude change occurs at a point 2 bits away from the leading edge or trailing edge of the burst signal. FIGS. 10 and 11 are block diagrams showing the configuration of an embodiment of the burst signal generation system of the present invention, respectively. 1...Low pass filter, 2...Modulator, 3...
...Switcher, 4...Band pass filter, 6...Code generator, 7...Synthesizer, 8...Code generator, 9
...Differential logic circuit.

Claims (1)

[Claims] 1. In a burst signal generation method in which a phase-modulated wave or an amplitude-modulated wave signal is burst-formed and transmitted during the allocated time of the own station, the sign of the data at the modulation input is inverted corresponding to the leading edge of the burst signal, and then at least 2 bits or more are generated. The burst signal continues to have the same sign state, and after the same sign state continues for at least 2 bits, the burst signal is inverted in response to the trailing edge of the burst signal. A burst signal generation method is characterized in that a modulated wave obtained by modulation or amplitude modulation is converted into a burst by switching in accordance with the leading edge and trailing edge of the burst signal.