JPH05145586A - Burst modulation circuit for radio transmitter - Google Patents

Abstract

PURPOSE:To prevent the production of an undesired wave and to attain burst transmission with high quality by using a modulation signal whose signal level is zero for the non-transmission period of a burst wave so as to apply phase modulation to a carrier and switching the carrier thereby obtaining a transmission burst wave. CONSTITUTION:Prescribed waveform shaping processing is implemented to transmission data DT by a digital filter 10 in response to on/off of a switching control signal SS. A data string is analog-converted by a DAC 2 and a modulation signal MS' whose sampling frequency component is eliminated is obtained by an LPF 3 and inputted to a mixer 4. Thus, the signal level of the signal MS' is made zero for the OFF period of the signal SS. Furthermore, a modulated carrier signal MCS' is switched at an IF switch 7 by using the signal SS' extended by a pulse width expansion circuit 7 to obtain a transmission burst signal BS'. Thus, a discontinuous burst signal is avoided and the occurrence of an undesired wave is prevented to attain burst transmission with high quality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a burst modulation circuit for modulating a carrier wave by transmission data to obtain a modulated carrier in burst form in a radio transmitter used in a satellite communication system, for example.

[0002]

2. Description of the Related Art In a radio transmitter used in a satellite communication system adopting a time division multiple access (TDMA) system as an access system, it is necessary to generate and transmit a burst modulated carrier wave.

FIG. 4 is a circuit block diagram showing an example of the configuration of a burst modulation circuit which has been conventionally considered. In the figure, the transmission digital data DT output from a transmission data generation unit (not shown) is first subjected to roll-off shaping processing for removing extra frequency components outside the transmission band in the waveform shaping digital filter 1. Next, after being converted into an analog signal by a digital-analog converter (DAC) 2, a low pass filter (LPF) 3
Then, the sampling frequency of the transmission digital data DT is removed, whereby the modulated signal MS is obtained and the mixer 4
Entered in. In the mixer 4, the carrier signal CS generated from the carrier oscillator 5 and the modulation signal MS supplied from the LPF 3 are mutually multiplied, whereby the carrier signal M that is, for example, two-phase modulated by the modulation signal MS.
CS is output. Then, this modulated carrier signal MC
In the intermediate frequency switch (IFSW) 6, S is switched in synchronization with a switching control signal SS generated from a control unit (not shown), and its output is supplied to a transmission unit (not shown) as a transmission burst signal BS. Note that FIG.
FIG. 4 is a signal waveform diagram showing a signal waveform of each part of the burst modulation circuit.

[0004]

However, in such a conventional circuit, since the change point of the modulated carrier signal MCS output from the mixer 4 and the change point of the switching control signal SS do not coincide with each other, The waveform of the transmission burst signal BS output from the IF switch 6 becomes discontinuous at its leading edge portion and trailing edge portion as shown in FIG. Therefore, an unwanted spectrum wave is generated each time switching is performed, and this unwanted wave may cause adverse effects such as interference and interference in other radio frequency channels, which is not very preferable.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent transmission burst signals from becoming discontinuous due to switching, thereby preventing generation of unnecessary waves and achieving high quality. It is an object of the present invention to provide a burst modulation circuit of a wireless transmission device that can perform burst transmission.

[0006]

In order to achieve the above-mentioned object, the present invention provides a modulation signal generating means for synchronizing transmission digital data with a switching control signal for generating a burst wave and the contents of the switching control signal. By performing a predetermined waveform shaping process in consideration of, a modulated signal in which the signal level in the period corresponding to the non-transmission period of the burst wave is zero is generated, and the carrier wave is phase-modulated by this modulated signal, The modulated carrier wave thus obtained is switched by the switching means in accordance with the switching control signal to obtain a transmission burst wave.

The present invention is also characterized in that the switching means is provided with means for adjusting the pulse width of the switching control signal, and the modulated carrier wave is switched in synchronization with the switching control signal having the adjusted pulse width. ..

[0008]

As a result, according to the present invention, in the waveform shaping processing of the modulation signal generating means, the transmission digital data is subjected to the normal waveform shaping such as roll-off shaping and in accordance with the contents thereof in synchronization with the switching control signal. Waveform shaping is performed, whereby a modulated signal in which the signal level becomes zero in the period corresponding to the non-transmission period of the burst wave is obtained. Therefore, the output of the modulated carrier wave during the burst non-transmission period becomes almost no signal. Therefore, even if the timing of the change point of the modulated carrier does not coincide with the timing of the change point of the switching control signal, the leading edge portion of the transmission burst wave becomes no signal, which causes at least the leading edge portion of the transmission burst wave to fail. There will be no continuity. Therefore, generation of unnecessary waves in the leading edge portion of the transmission burst wave is prevented, and thereby interference and interference with other radio frequency channels are reduced.

Further, by switching the modulated carrier wave in synchronization with the switching control signal whose pulse width is adjusted, it is possible to eliminate the discontinuity of the trailing edge portion of the transmission burst wave. Therefore, generation of unnecessary waves at the trailing edge of the transmission burst wave is also prevented, and interference and interference with other radio frequency channels can be further reduced.

[0010]

EXAMPLE An example of the present invention will be described below.

FIG. 1 is a circuit block diagram showing a configuration of a burst modulation circuit according to an embodiment of the present invention. In addition,
In the figure, the same parts as those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

The switching control signal SS is input to the waveform shaping digital filter 10 together with the transmission digital data DT. The digital filter 10 is composed of, for example, a DSP (Digital signal processor), and responds to the contents of the transmission digital data DT in synchronization with the switching control signal SS, in addition to normal waveform shaping processing such as roll-off shaping. Perform a predetermined waveform shaping process.

For example, for each bit of the transmission digital data DT, when the switching control signal SS is "1" as shown in FIG.
"1" and "0" of T are "1" and "-", respectively.
1 "and the switching control signal SS is" 0 "
In the case of, each of "1" and "0" of the transmission digital data DT is interpreted as "0". Then, the change of the data string consisting of "1", "-1" and "0" is convolutively integrated, and the digital filtering process is executed according to a predetermined transfer function. Here, the transfer function is the modulation signal M output from the LPF 3 in the subsequent stage.
S'is set to a predetermined "positive voltage" and "negative voltage" when the data string is "1" and "-1", respectively, and is set to "0 V" when it is "0".

A pulse width expansion circuit 7 is inserted in the control signal supply path to the IF switch 6. The pulse width expansion circuit 7 extends the trailing edge side of the switching control signal SS by a predetermined amount, and supplies the switching control signal SS ′ extended during this period to the IF switch 6.

Due to this structure, it is assumed that FIG.
It is assumed that the transmission digital data DT shown in (1) is input and the switching control signal SS is input in synchronization with the transmission digital data DT. Then, in the digital filter 10, first, in addition to the normal waveform shaping process, the transmission digital data DT is subjected to a predetermined waveform shaping process according to the on / off state of the switching control signal SS in accordance with the correspondence relationship shown in FIG. The waveform-shaped data string is converted into an analog signal by the DAC 2 and then the sampling frequency component of the digital signal is removed by the LPF 3 to be a modulated signal MS 'and input to the mixer 4. That is, by the waveform shaping process of the digital filter 10, as shown in FIG. 3, the modulated signal MS 'having a signal level of "0 V" is generated in the "0" period of the switching control signal SS, that is, in the non-transmission period of the burst wave. can get.

Then, when the modulation signal MS 'is input,
In the mixer 4, the modulated signal MS 'and the carrier signal CS are mutually multiplied, whereby a modulated carrier signal MCS' as shown in FIG. 3 in which the carrier signal CS is two-phase phase-modulated by the modulated signal MS '. can get. The modulated carrier signal MCS 'is input to the IF switch 6 where it is switched according to the switching control signal SS'. At this time, the leading edge portion of the modulated carrier signal MCS 'is substantially in a non-signal state corresponding to the signal level "0V" of the modulated signal MS'. Therefore, the modulated carrier wave MC is affected by the processing delay of the digital filter 10, the DAC 2, the LPF 3, and the mixer 4, for example.
Even if the start timing of S ′ does not coincide with the rising timing of the switching control signal SS ′, it is possible to prevent the occurrence of a discontinuity at the leading edge of the transmission burst signal BS ′ after switching.

The switching control signal SS is
In the pulse width expansion circuit 7, the trailing edge of the pulse width expansion circuit 7 is set to be extended for a certain period T as shown in FIG. Therefore, I
In the F switch 7, it is possible to prevent a problem in which the trailing edge portion of the modulated carrier signal MCS 'is cut midway and a discontinuous portion is generated.

As described above, according to this embodiment, the digital filter 10 performs a predetermined waveform shaping process on the transmission digital data DT according to the on / off state of the switching control signal SS, thereby switching the modulation signal MS '. The signal level corresponding to the off period of the control signal SS is set to 0V, the trailing edge side of the switching control signal SS is further extended by the pulse width expansion circuit 7, and the carrier wave signal modulated by the switching control signal SS 'is set. Since the MCS 'is switched, it is possible to maintain excellent isolation in switching and obtain the transmission burst signal BS' having no discontinuity in the signal waveform at both the leading edge portion and the trailing edge portion. Therefore, generation of unnecessary spectrum waves due to waveform discontinuity is prevented, and high-quality burst transmission can be realized without causing interference.

In the present embodiment, the signal processing for setting the signal level of the modulation signal MS 'corresponding to the off period of the switching control signal SS to 0V is performed by the existing waveform shaping digital filter 10. Therefore, it is not necessary to provide a new signal processing circuit, and this has an advantage that the circuit can be realized with a simple circuit configuration without causing the circuit to become complicated and large.

The present invention is not limited to the above embodiment. For example, in the above-mentioned embodiment, the description has been given by taking the modulation circuit adopting the two-phase modulation method as an example, but it may be applied to the modulation circuit adopting the multi-phase modulation method such as four-phase modulation. In addition, the configurations of the modulation signal generating means and the switching means can be variously modified and implemented without departing from the scope of the present invention.

[0021]

As described above in detail, according to the present invention, in the modulation signal generating means, the transmission digital data is synchronized with the switching control signal for generating the burst wave and the contents of the switching control signal are added. A predetermined waveform shaping process to generate a modulated signal in which the signal level becomes zero in the period corresponding to the non-transmission period of the burst wave, and the modulated signal phase-modulates the carrier wave to obtain It is possible to prevent the transmission burst signal from becoming discontinuous due to the switching by switching the modulated carrier wave thus obtained by the switching means in accordance with the switching control signal so that the transmission burst signal is not discontinuous. A burst modulation circuit for a wireless transmitter that can prevent high-frequency waves and perform high-quality burst transmission. It can be provided.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of a burst modulation circuit according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining a part of processing contents of a waveform shaping digital filter in the burst modulation circuit shown in FIG.

FIG. 3 is a diagram showing a signal waveform of each part of the burst modulation circuit shown in FIG.

FIG. 4 is a circuit block diagram showing a configuration of a conventional burst modulation circuit.

5 is a diagram showing a signal waveform of each part of the burst modulation circuit shown in FIG.

[Explanation of symbols]

2 ... Digital-analog converter (DAC), 3 ... Low-pass filter (LPF), 4 ... Mixer, 5 ... Carrier oscillator, 6 ... IF switch (IFSW), 7 ... Pulse width expansion circuit, 10 ... Waveform shaping Digital filter for DT ...
Transmission digital data, BS '... Transmission burst signal, C
S ... Carrier signal, MS '... Modulated signal, MCS' ... Modulated carrier signal, SS ... Switching control signal, SS '... Switching control signal with extended period.

Claims (2)

[Claims] 1. A transmission burst wave is generated by shaping a waveform of transmission digital data to generate a modulation signal, phase-modulating a carrier wave by the modulation signal, and switching the modulated carrier wave in synchronization with a switching control signal. In a burst modulation circuit of a radio transmission device to be obtained, a predetermined waveform shaping process is performed on the transmission digital data in synchronization with the switching control signal and the contents of the switching control signal are added, and a non-transmission period of a burst wave , A modulation signal generating means for generating a modulation signal in which the signal level becomes zero in a period corresponding to, a modulation means for phase modulating a carrier wave by the modulation signal generated by the modulation signal generating means, and this modulation means. The modulated carrier wave obtained by the above is switched according to the switching control signal to transmit burst. A burst modulation circuit for a wireless transmission device, comprising: a switching means for outputting a wave. 2. The switching means has means for adjusting the pulse width of the switching control signal, and switches the modulated carrier wave in synchronization with the switching control signal having the adjusted pulse width. A burst modulation circuit of the wireless transmission device according to Item 1.