JP2874457B2 - Demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a PSK (Phase)
The present invention relates to a demodulation device used in a shift keying (Shift Keying) modulation satellite communication, and more particularly to a demodulation device having an improved code error rate due to adjacent interference waves.

[0002]

2. Description of the Related Art FIG. 4 shows the configuration of a conventional demodulator of this type.

In FIG. 4, a received signal S 1 passes through an automatic gain amplifier 1, is divided into two by a distributor 2, and is input to mixers 3 and 4, respectively. Then, in the mixers 3 and 4, quasi-synchronous detection is performed at the same intermediate frequency (IF) as the reception signal S1 from the local oscillator 5. However, the input signal to the mixer 4 from the local oscillator 5 is shifted by 90 ° by the 90 ° phase shifter 6 with respect to the input signal to the mixer 3.

The output signals of the mixers 3 and 4 are sent to analog-to-digital converters 9 and 10 via low-pass filters 7 and 8 for removing interference wave noise of the baseband signal after quasi-synchronous detection. The digital signal is inputted, becomes an arbitrary bit digital signal, and is supplied to the next digital demodulator 13. In the digital demodulator 13, waveform shaping and synchronous detection are performed by digital signal processing. In this way, the demodulated PCM and QCH signals and the clock are sent to the next-stage error corrector 15.
The received demodulated data S2 and the received clock S3 are output after being corrected as necessary.

A digital signal for the sampling clock of the analog-to-digital converters 9 and 10 is sent from the digital demodulator 13 to the digital-to-analog converter 11.
A sampling clock for the analog-digital converters 9 and 10 is generated by a voltage-controlled oscillator 12 at the next stage.

Further, the digital demodulator 13 outputs
A digital signal is supplied to the analog converter 14, and the output signal of the digital-analog converter 14 controls the gain of the automatic gain amplifier 1.

[0007]

The conventional demodulation apparatus has the above-described configuration and functions well under limited conditions. If a wave is present and the level of the interference wave is high, the low-pass filters 7 and 8 cannot sufficiently suppress the interference wave, resulting in a problem that the code error rate increases.

It is an object of the present invention to provide a demodulator capable of improving the degradation of the bit error rate due to adjacent interference waves.

[0009]

In order to achieve the above object, the present invention provides a demodulator having a quasi-synchronous detection demodulation circuit, an error corrector, an automatic gain amplifier, and the like. A band-pass filter such as a band-pass low-pass filter for removing interference noise; and a band-pass filter for monitoring an adjacent interference level at an input end of the band-pass filter. , A detector, an analog-to-digital converter, and the like. Further, the bandwidth of the variable-bandwidth filter is adjusted, for example, via a digital-to-analog converter according to the level of the adjacent interference wave monitored by this means. It has control means for controlling.

[0010]

In the demodulator of the present invention, the means such as the band-pass filter, the detector, and the analog-to-digital converter are used to remove the interference wave noise from the baseband signal after the quasi-synchronous detection. The adjacent interference wave level inputted to the band variable filter such as the filter is monitored, and the control means controls the band through a digital-analog converter according to the adjacent interference wave level monitored by this means. The bandwidth of the tunable filter is controlled so that adjacent interference waves are sufficiently suppressed by the tunable filter.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a demodulation apparatus according to the present invention. The same reference numerals as those in FIG. 4 refer to the same parts, and reference numerals 101 and 102 denote band-variable low-pass filters.
03 and 104 are bandpass filters, 105 and 106 are detectors, 107 and 108 are analog-digital converters, 10
9 is a controller, 110 is a digital-analog converter, S4
Is a synchronization signal.

The difference between the demodulator of the present embodiment and the conventional demodulator shown in FIG. 4 is that the variable band low-pass filters 101 and 101 are replaced with the low-pass filters 7 and 8 of FIG. 102
And a band-pass filter 103, 104, a detector 105, 106 for detecting the output, and an analog-digital converter for converting the output to a digital signal. And the analog-digital converters 107, 108.
A controller 109 for controlling the bandwidth of the band-variable low-pass filters 101 and 102 via a digital-analog converter 110 according to the level of the adjacent interference wave output from 108
It is in the point with.

FIG. 2 shows a variable band low-pass filter 101,
The input end of 102, that is, the relationship between the desired wave and the adjacent interference wave in the baseband and the band characteristic example of the low-pass filter,
The vertical axis indicates the level, and the horizontal axis indicates the frequency. This figure 2
As shown in, when there is an interference wave of a higher level than the desired wave at a distance Δf from the center of the desired wave,
4 instead of the band-variable low-pass filters 101 and 102
When the low-pass filters 7 and 8 having fixed band characteristics as shown by broken lines in FIG. 2, for example, are used as in the conventional demodulator, the power of the adjacent interference wave is reduced to some extent. However, if the level of adjacent interference becomes very high,
The low-pass filters 7 and 8 having fixed band characteristics are not sufficiently reduced and supplied to the inputs of the analog-digital converters 9 and 10 to saturate the analog-digital converters 9 and 10. . Therefore, the bit error rate of the demodulated data deteriorates.

FIG. 3 shows the relationship between the bandwidth of the low-pass filter and the degradation of the bit error rate. In FIG. 3, the dashed line indicates the relationship between the bandwidth of the low-pass filter and the bit error rate due to the adjacent interference wave. As the bandwidth of the low-pass filter decreases, the adjacent interference decreases. This indicates that the influence of the waves is reduced. On the other hand, the solid line in FIG. 3 shows the relationship between the bandwidth of the low-pass filter and the bit error rate due to the waveform distortion of the desired signal. When the bandwidth of the low-pass filter is reduced,
This indicates that the waveform of the desired wave is distorted and the bit error rate of the desired wave signal itself is degraded.

Therefore, in this embodiment, as shown in FIG. 1, adjacent interference waves are extracted by band-pass filters 103 and 104, detected by detectors 105 and 106,
By passing the signals through the digital converters 107 and 108, the level of the adjacent interference wave is converted into a digital signal,
09 to monitor the level of the adjacent interference wave, and in accordance with the level of the adjacent interference wave, the digital-analog converter 110
, The bandwidths of the band-variable low-pass filters 101 and 102 are set to optimal values that minimize the overall code error rate.

The optimum value is the bandwidth when the degree of deterioration obtained by adding the degree of deterioration indicated by the solid line and the degree of deterioration indicated by the broken line is minimized. The controller 109 stores the optimum value of the bandwidth for each of several levels of the adjacent interference wave, and adjusts the bandwidth so that the bandwidth of the optimum value corresponding to the detected level of the adjacent interference wave is obtained. The low-pass filters 101 and 102 are controlled.

However, the setting of this bandwidth depends on the error correction unit 1
5 must be performed in a synchronized state, the controller 109 constantly monitors the synchronization signal S4. In this synchronized state, the control of the automatic gain amplifier 1 is also performed normally, so that the detection signals from the detectors 105 and 106 have correct values.

[0019]

As described above, the demodulator according to the present invention uses a band-variable filter such as a band-variable low-pass filter for removing interference wave noise of a baseband signal after quasi-coherent detection. However, since the level of the adjacent interference wave is constantly monitored and the bandwidth of the band variable filter is controlled in accordance with the level, the adjacent interference wave is sufficiently suppressed. This has the effect of preventing the bit error rate from deteriorating.

[Brief description of the drawings]

FIG. 1 is a block diagram of a demodulation device according to one embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a desired wave and an adjacent interference wave in a baseband band and an example of band characteristics of a low-pass filter.

FIG. 3 is a diagram illustrating a relationship between a bandwidth of a low-pass filter and deterioration of a bit error rate.

FIG. 4 is a block diagram of a conventional demodulation device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Automatic gain amplifier 2 ... Distributor 3,4 ... Mixer 5 ... Local oscillator 6 ... 90 degree phase shifter 7,8 ... Low-pass filter 9,10 ... Analog-digital converter 11 ... Digital-analog Converter 12: Voltage-controlled oscillator 13: Digital demodulator 14: Digital-analog converter 15: Error corrector 101, 102 ... Variable band low-pass filter 103, 104 ... Band-pass filter 105, 106 ... Detection Units 107 and 108 Analog-digital converter 109 Controller 110 Digital-analog converter S1 Received signal S2 Received demodulated data S3 Received clock S4 Synchronous signal

Claims (1)

(57) [Claims] 1. A means for providing a band variable filter for removing interference noise of a baseband signal after quasi-coherent detection, and for monitoring an adjacent interference level at an input terminal of the band variable filter; Control means for controlling the bandwidth of said variable-bandwidth filter in accordance with the level of adjacent interference waves monitored by said means.