JP2002152071A - Software receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a software receiver which can appropriately limit a band in accordance with signal band width and which is difficult to be affected by the interference wave of an adjacent frequency. SOLUTION: The receiver is provided with a frequency converter converting a high frequency signal into an intermediate signal and limiting the band in accordance with signal band width. The frequency converter is provided with frequency converters 5 and 13, local oscillators 4 and 14 and a multiband pass filter 16 having a plurality of pass bands. In the frequency converter, the frequency of the local oscillator is controlled so that the intermediate frequency signal obtained by mixing a local oscillation signal which the local oscillator outputs and a high frequency signal by a frequency mixer is supplied to the multiband pass filter and the intermediate frequency signal passes through one of the pass bands of the multiband pass filter in accordance with the signal band width of a radio wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a software receiver for receiving and demodulating radio signals in a plurality of radio wave formats having different modulation formats and signal bandwidths.

[0002]

2. Description of the Related Art Heretofore, a multi-function receiver, which is capable of coping with radio signals of various radio wave forms having different frequency bands, modulation methods, and bandwidths with one receiver, a so-called multi-mode receiver, has been studied. ,Proposed. 2. Description of the Related Art In recent years, software receivers have been proposed as a promising means for realizing a multi-mode receiver, and have attracted attention. In this technique, a received radio signal is once subjected to A / D conversion in a frequency band as high as possible, and a digital processing means such as a DSP is used to collectively perform processing such as filtering and demodulation. In this way, if only the content of the program (software) incorporated in the digital processing means such as a DSP is changed, it is possible to cope with various types of radio waves without changing the hardware configuration. It is well known that various types of means are being researched and developed as effective means for achieving functions, multifunctions and miniaturization.

FIG. 3 is a block diagram showing an embodiment of a conventional software receiver. The conventional software receiver shown in FIG. 3 includes an antenna 1 that receives a radio wave and outputs a high-frequency signal, an RF filter 2 that selects only a predetermined band of a high-frequency signal supplied from the antenna 1,
An RFAMP 2 for amplifying a high-frequency signal selected by the RF filter 2 and outputting a high-frequency amplified signal; a local oscillator 4 for outputting a local oscillation signal of a predetermined frequency;
A frequency mixer 5 that mixes the high-frequency amplified signal supplied by 3 and the local oscillation signal supplied by the local oscillator 4 to generate an intermediate frequency signal; and selects and outputs an intermediate frequency signal from the output of the frequency mixer 5. An IF filter 6 for removing unnecessary signal components other than the above, an AGCAMP 7 for amplifying the intermediate frequency signal and maintaining its output voltage at a constant value and outputting it as an intermediate frequency amplified signal, and an AGC control voltage from the intermediate frequency amplified signal. An AGC controller 8 that generates and controls the gain of the AGCAMP 7, an A / D converter 9 that converts an intermediate amplified signal supplied by the AGCAMP 7 into a digital signal, and a digital signal supplied by the A / D converter 9 A digital processing means 10 for processing and outputting a demodulated signal (digital signal); and a demodulated signal (analog signal) which converts the demodulated signal into an analog signal. D / A converter 11 for outputting a signal)
And

The operation of the conventional software receiver shown in the figure will be described below. First, the antenna 1 receives a radio wave and supplies a high-frequency signal to the RF filter 2. R
The F filter 2 selects only a predetermined frequency band and supplies a high frequency signal to the RFAMP 3. Here, the high-frequency signal passing through the RF filter 2 is R as shown in FIG.
A high-frequency signal that passes through a part of the entire pass band (fR1 to fR2) of the F filter 2 and has a predetermined signal bandwidth (ΔfR) and is simultaneously provided in all the pass bands of the RF filter 2 for n channels Can be multiplexed. Here, description will be made on the assumption that a high-frequency signal occupies a frequency range corresponding to channel 1 in FIG.

The high-frequency signal that has passed through the RF filter 2 is amplified by the RFAMP 3 and then supplied to the frequency mixer 5 as a high-frequency amplified signal. The frequency mixer 5 mixes the high frequency amplified signal and the local oscillation signal supplied from the local oscillator 4 to generate an intermediate frequency signal. When this is selected by the IF filter 6 and unnecessary frequency components generated by the frequency mixer 5 are removed, an intermediate frequency signal passing through a predetermined band is obtained as shown in FIG. Here, the pass band of the IF filter 6 has a pass band ΔfIF equal to or wider than the signal bandwidth of the high-frequency signal, that is, ΔfR which is the band of the channel 1.

Next, AGCAMP 7 amplifies the intermediate frequency signal and outputs an intermediate frequency amplified signal.
/ D converter 9 respectively. The AGC control unit 8 detects the intermediate frequency amplified signal, generates an AGC control voltage, and supplies it to the AGCAMP 7. Therefore, AGCA
AGCAMP so that the output voltage of MP7 becomes almost constant.
The gain of 7 is feedback controlled. On the other hand, the A / D converter 9 samples the intermediate frequency amplified signal whose output voltage is constant, converts it into a digital signal, and supplies the digital signal to the digital processing means 10. The digital processing means 10 filters the digital signal in a predetermined band in accordance with the signal bandwidth of the wireless signal, and performs a predetermined demodulation process in accordance with the modulation format of the wireless signal. As a result, the digital processing means 10 outputs a predetermined demodulated signal (digital signal), and the D / A converter 11 converts the demodulated signal into an analog signal and outputs it. Thus, an analog signal or a digital signal can be demodulated according to the modulation format.
Here, by changing the program (software) incorporated in the digital processing means 10, filtering and demodulation can be performed in accordance with the signal bandwidth and modulation format of the wireless signal.

[0007]

However, the above-mentioned conventional software receiver has the following problems. That is, the conventional software receiver is A / D
The intermediate amplified signal input to the converter 9 is band-limited by the IF filter 6. This is desirably narrowed to the minimum necessary for effectively removing out-of-band or near-band interference waves and signals of adjacent channels (channels 2 to n). However, the modulation format and the modulation signal of the received radio signal are various, and the signal bandwidth takes various values in accordance with the modulation format and the modulation signal. Therefore, the pass band of the IF filter 6 must be widened to the necessary maximum according to the radio signal having the maximum signal bandwidth. For this reason, it is usual that the digital processing means 10 performs appropriate band limitation according to the signal bandwidth of the wireless signal so that the demodulated signal secures a required SN ratio.

However, this method has a drawback that when an interference wave having an excessive signal strength is received, the intermediate frequency amplified signal input to the A / D converter 9 is easily suppressed by the interference wave. That is, when an excessive interference wave and a desired radio signal (hereinafter referred to as a desired wave) are close in frequency,
Since the IF filter 6 extends the pass band to the required maximum, it may not be possible to sufficiently remove the interfering wave. Therefore, a phenomenon occurs in which the desired signal is suppressed by amplifying the excessive interference wave that has passed through the IF filter 6 by the AGCAMP 7.

For example, if the interference wave passing through the IF filter 6 is higher than the desired wave by 10 dB, the AGCAMP 7 should perform an operation of amplifying up to a predetermined output voltage in accordance with the signal strength of the desired wave. Since the output voltage is controlled according to the high interference wave, the desired wave is suppressed by 10 dB from the normal output voltage. Therefore, if the A / D converter 9 performs the A / D conversion in a state including the interfering wave, the digital signal supplied to the digital processing means 10 includes the interfering wave component, and the component of the desired wave is also 10 dB.
The signal must be processed in the suppressed state. Although the interfering wave component can be filtered and removed by the digital processing means 10, the suppression of the amplitude value of the desired wave component affects the demodulated signal and degrades the S / N ratio.

In order to prevent this, even if the desired wave component is suppressed to some extent, the A / D converter 9 can process it, so that the dynamic range is wide, that is, A is high in resolution.
Although there is a method using an A / D converter, the resolution of the A / D converter is limited, so that it is not sufficient. FIG.
As shown in (1), the intermediate frequency signal output from the IF filter 6 is further amplified by an IFAMP 12 by making the entire configuration of the receiver a double superheterodyne system, and this is amplified by a frequency mixer 13 to a second local oscillation signal of a second local oscillator To obtain a second intermediate frequency signal. A method of preparing a plurality of bandpass filters 15, 16 and 17 having different passband widths and selecting and switching with the changeover switches 18a to 18f is also conceivable, but hardware becomes complicated such that a large number of changeover switches are required. Not preferred. SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-described drawbacks of the conventional software receiver which is weak to the interference wave in the vicinity of the frequency, and has an excellent selectivity that is strong against the interference wave without complicating the hardware configuration. It is intended to provide a software receiver.

[0011]

In order to solve the above-mentioned object, a software receiver according to the present invention is a software receiver for receiving and demodulating radio waves having different modulation formats and signal bandwidths. A software receiver comprising a frequency converter that converts a high-frequency signal of a predetermined frequency into an intermediate frequency signal and limits the band according to the signal bandwidth of the high-frequency signal, wherein the frequency converter is a frequency mixing device. A local oscillator and a multi-bandpass filter having a plurality of passbands, and an intermediate frequency signal generated by mixing the local oscillation signal and the high-frequency signal output from the local oscillator with the frequency mixer. The intermediate frequency signal is supplied to a multi-bandpass filter according to a signal bandwidth of the radio wave. Those having a frequency converter configured to control the frequency of the local oscillator so as to pass through one of the predetermined pass band.

According to a second aspect of the present invention, there is provided a software receiver according to the first aspect, wherein the multi-pass-band filter comprises a plurality of band-pass filters having different center frequencies and different pass-band widths connected in parallel. is there.
The invention according to claim 3 of the software receiver according to the present invention is directed to a software receiver for receiving and demodulating radio waves having different modulation formats and signal bandwidths. Frequency wave number converter and A
A / D converter and digital processing means for amplifying the radio wave received by the antenna by the high frequency amplifier and supplying the amplified radio wave to the frequency converter, and converting the intermediate frequency signal output from the frequency converter to an A / D converter A predetermined demodulated signal is output by converting the digital signal into a digital signal by a converter and processing the digital signal by digital processing means according to the modulation format and the signal bandwidth of the radio wave.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on embodiments shown in the drawings. FIG. 1 is a block diagram showing an embodiment of a software receiver according to the present invention. The software receiver according to the present invention shown in FIG. 1 is an antenna 1 that receives a radio wave and outputs a high-frequency signal.
An RF filter 2 for selecting only a predetermined band of a high-frequency signal supplied by the antenna 1, and an R filter for amplifying the high-frequency signal selected by the RF filter 2 and outputting a high-frequency amplified signal
FAMP 3, a local oscillator 4 that outputs a local oscillation signal of a predetermined frequency, and a frequency mixer 5 that mixes a high-frequency amplification signal supplied by the RFAMP 3 and a local oscillation signal supplied by the local oscillator 4 to generate an intermediate frequency signal. An IF filter 6 for selecting an intermediate frequency signal output from the frequency mixer 5 and removing other unnecessary signal components;
IFAMP 12 for amplifying the intermediate frequency signal selected by the IF filter 6 and outputting an intermediate frequency amplified signal, and a second local oscillator 14 for outputting a second local oscillation signal of a predetermined frequency
And a local oscillation control unit 15 for controlling the oscillation frequency of the local oscillator 14 to a different frequency according to the signal bandwidth of the radio signal.
And an intermediate frequency amplification signal supplied by the IFAMP 12 and a second local oscillation signal supplied by the second local oscillator 14 are mixed to generate a second intermediate frequency signal, and the frequency is adjusted to the frequency of the second local oscillator. A frequency mixer 13 that converts the frequency to a different frequency, a multi-bandpass filter 16 having a plurality of passbands corresponding to the frequency of the second intermediate frequency signal,
AG amplifies the selected second intermediate frequency signal, maintains its output voltage at a constant value, and outputs it as a second intermediate frequency amplified signal
CAMP7 and A for controlling the gain of AGCAMP7 by generating an AGC control voltage from the second intermediate frequency amplified signal.
A GC controller 8 which samples the second intermediate amplified signal supplied by the AGCAMP 7 and converts it into a digital signal
A / D converter 9, digital processing means 10 for processing a digital signal supplied by the A / D converter 9 and outputting a demodulated signal (digital signal), and a D / D converter for converting the demodulated signal into an analog signal and outputting the same. A converter 11 is provided.

The operation of the embodiment shown in FIG. 1 will be described below in detail. First, the radio wave received by the antenna 1 is band-limited by the RF filter 2 and then RFA.
The signal is amplified by the MP 3 and supplied to the frequency mixer 5. This is converted into an intermediate frequency signal by the frequency mixer 5 and supplied to the frequency mixer 13 as an intermediate frequency amplified signal after band limitation and amplification. The frequency mixer 13 outputs the second intermediate frequency amplified signal and the second
The second local oscillation signal supplied from the local oscillator is mixed with the second
Generate an intermediate frequency signal. Here, the second local oscillator 14
The frequency is controlled by a local oscillation control signal supplied from the local oscillation control unit 15. Local control unit 15
Controls the oscillation frequency of the second local oscillator 14 according to the signal bandwidth of the radio signal.

For example, it is assumed here that the signal bandwidth of a radio signal changes to three types of bands, a wide band, a medium band, and a narrow band, according to various modulation formats. At this time, frequency control is performed so that the oscillation frequencies of the second local oscillators 14 are different depending on the signal bandwidth of the radio signal. In this way, the frequency of the second intermediate frequency signal generated by the frequency mixer 13 is converted to a different frequency according to the signal bandwidth of the radio signal. Here, it is assumed that the frequencies of the second intermediate frequency signals are f1, f2, and f3, respectively, corresponding to the wide band, the middle band, and the narrow band.

This is selected by the multi-bandpass filter 16, and any of the frequencies f1, f2 and f3 can be passed as the second intermediate frequency signal according to the signal bandwidth. Here, the multi-bandpass filter is shown in FIG.
As shown in (a), the center frequencies are f1, f2 and f3.
, And each of the three passbands can be selected from three kinds of passbands of a wide band (Δf1), a middle band (Δf2), and a narrow band (Δf3) according to the signal bandwidth of the radio signal. It has become.

Next, the second intermediate frequency signal that has passed through the multi-bandpass filter 16 is supplied to the AGCAMP 7, and is controlled by the AGC control unit 8 so that the output voltage becomes constant, and the second intermediate frequency amplified signal / D converter 9. The A / D converter 9 performs A / D conversion on this, outputs a digital signal, and supplies it to the digital processing means 10. The digital processing means 10 processes the signal, generates a demodulated signal, and supplies the signal to the D / A converter 11. The D / A converter 11 can convert this into an analog signal as needed and output it. Here, in the digital processing means 10, predetermined filtering is performed as in the conventional example.
This is to make the filtering more effective in combination with the filtering by the multi-bandpass filter 16.

Accordingly, the frequency of the second intermediate frequency signal is changed to f1, f2 or f3 in accordance with the signal bandwidth of the radio signal, and the frequency is changed by a multi-bandpass filter having a plurality of passbands. Bandwidth can be appropriately limited according to That is, it is possible to prevent a desired wave from being suppressed by an interfering wave that is adjacent in frequency by appropriately band-limiting according to the signal bandwidth of the wireless signal.

In the above-described software receiver according to the present invention, the multi-bandpass filter itself has a plurality of bands. However, the present invention is not limited to this. For example, FIG. 3), a structure in which three types of bandpass filters having different center frequencies and different passbands are connected in parallel may be used. This makes the hardware configuration somewhat complicated. However, as in the embodiment shown in FIG. 1, the same effect can be obtained without changing the switch for switching the three filters. Further, the number of pass bands included in the multi-pass band filter is not limited to the three types shown in the embodiment, and the number may be further increased according to a use scene.

Conventionally, in the method of switching filters in the configuration of FIG. 4, the center frequency of each filter had to be designed at exactly the same frequency. However, the example of FIG. 2 adjusts the center frequency of each filter to its pass band. It has the advantage that the degree of design freedom can be obtained because it can be set freely.

[0021]

As described above, the present invention solves the drawback that a conventional software receiver can easily suppress a desired signal by an interfering signal of a nearby frequency, and converts a radio signal into a predetermined intermediate frequency signal. While converting to an intermediate frequency signal of a different frequency according to the signal bandwidth, the frequency of the intermediate frequency signal is controlled to pass through any one pass band of a multi-pass band filter having a plurality of pass bands. Therefore, the present invention is very effective in providing a software receiver which is capable of performing appropriate band limitation according to a signal bandwidth and is not easily affected by an interference wave of a nearby frequency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a software receiver according to the present invention.

FIG. 2 is a diagram showing a configuration example and selection characteristics of a multi-bandpass filter.

FIG. 3 is a block diagram showing a first embodiment of a conventional software receiver.

FIG. 4 is a block diagram showing a second embodiment of a conventional software receiver.

FIG. 5 is a block diagram showing selection characteristics of an RF filter and an IF filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Antenna 2 ... RF filter 3 ... RFAMP 4 ... Local oscillator 5, 13 ... Frequency mixer 6 ... IF filter 7 ... AGCAMP 8 ... AGC control part 9 ... A / D converter 10 ... Digital processing means 11 ... D / A converter 12 ... IFAMP 14 ... Second local oscillator 15 ... Local oscillator control unit 16 ... Multi Bandpass filter

Claims (3)

[Claims] 1. A software receiver for receiving and demodulating radio waves having different modulation formats and signal bandwidths, wherein a high-frequency signal of a predetermined frequency is converted into an intermediate frequency signal and a bandwidth is changed according to the signal bandwidth of the high-frequency signal. A software receiver having a frequency converter for limiting, wherein the frequency converter comprises a frequency mixer, a local oscillator, and a multi-bandpass filter having a plurality of passbands, and a local oscillation signal output from the local oscillator. An intermediate frequency signal generated by mixing the high frequency signal with the frequency mixer is supplied to the multi-bandpass filter, and the intermediate frequency signal is supplied to the multiband-pass filter according to the signal bandwidth of the radio wave. A frequency converter configured to control the frequency of the local oscillator to pass through one of a predetermined passband of the filter. A software receiver, comprising: 2. The software receiver according to claim 1, wherein the multi-bandpass filter is configured by connecting a plurality of bandpass filters having different center frequencies and different passbands in parallel. 3. A software receiver for receiving and demodulating radio waves having different modulation formats and signal bandwidths, wherein the antenna, the high-frequency amplifier, the frequency wave number converter and the A / D converter according to claim 1 or 2 are provided. A digital processing means for amplifying the radio wave received by the antenna by the high frequency amplifier and supplying the amplified radio wave to the frequency converter, and converting the intermediate frequency signal output from the frequency converter into a digital signal by an A / D converter And a digital demodulation signal output by subjecting the digital signal to digital processing means according to a modulation format and a signal bandwidth of the radio wave.