JP3588560B2 - Receiver - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a receiving device for receiving a wideband signal, such as a pulse compression radar and a spread spectrum signal receiving device.
[0002]
[Prior art]
In recent years, the development of digital signal processing technology has been remarkable. From such a background, there has been provided a receiving apparatus that performs a receiving process after digitizing an analog received signal. By digitizing the received signal, various advantages such as improved noise resistance can be obtained.
[0003]
By the way, in recent years, the frequency band occupied by the signal to be received has been broadened by a pulse compression technique, a frequency spreading technique, or the like. However, at present, the processing capability of an analog / digital converter (hereinafter, referred to as an A / D converter) cannot keep up with the band of a target signal, and it is difficult to perform faithful reception and reproduction. Therefore, there has been proposed a receiving apparatus that divides a wideband signal into a plurality of narrowband signals, converts each of the signals into digital signals, and then performs a receiving process so that the wideband signal can be faithfully received.
[0004]
FIG. 5 schematically shows the configuration of this type of receiving apparatus. In the following description, it is assumed that a signal having a bandwidth of 240 MHz from 100 MHz to 340 MHz is received.
The wideband signal received by the antenna ANT is divided by the band division filters 41 to 412 into 12 narrowband signals. Each of the band division filters 41 to 412 has a pass band of 20 MHz, and divides and covers a signal band. That is, a band of 100 to 120 MHz is assigned to the filter 41, and a band of 120 to 140 MHz is assigned to the filter 42.
[0005]
The RF narrow band signals transmitted from the band division filters 41 to 412 are dropped to IF signals via converters 51 to 512, low pass filters (LPF) 61 to 612, and converters 71 to 712, respectively. These IF signals are respectively supplied to the A / D converter 2 via the anti-aliasing filter 8 and are converted into digital signals. Each A / D converter 2 has a sampling frequency Fs of 80 MHz.
[0006]
The anti-alias filter 8 is a low-pass filter having a steep characteristic, and cuts a frequency equal to or higher than the Nyquist frequency fN in each A / D converter 2 to prevent generation of noise (alias) in the converted signal. The Nyquist frequency fN is defined as 1/2 of the sampling frequency fs in the A / D converter, and therefore, the Nyquist frequency fN of the A / D converter 2 is 40 MHz. Here, the processing band of each A / D converter 2 is set to 20 MHz in order to give a margin to the characteristics of each filter.
[0007]
The digital reception signal obtained by each A / D converter 2 is provided to a signal processing unit 3 in the next stage, and is subjected to various kinds of reception signal processing. Then, the output signals from the signal processing units 3 of the respective systems are combined via an upconverter and a combiner (not shown) to restore the original band. As described above, by dividing the received signal into narrowband signals and then performing signal processing on each of them, it is possible to give a margin particularly to the processing capacity of each A / D converter 8, and as a result, high fidelity is achieved. It becomes possible to perform reception processing.
[0008]
[Problems to be solved by the invention]
However, the conventional receiving apparatus having the above configuration has a problem in that the number of components increases as much as the band is divided, resulting in an increase in weight and an increase in cost.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a receiving apparatus capable of receiving a wideband signal with a simple configuration.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention divides an incoming signal into a plurality of systems of signals, drops the frequency of each of these signals by a frequency converter, and further divides these signals into narrowband signals, thereby dividing these narrowband signals. To an analog / digital converter to convert the digital signal into a digital signal, and perform a receiving demodulation process on the arriving signal based on the digital signal obtained thereby.
An alias is generated in at least one output of the analog / digital converter.
[0010]
The present invention also provides an analog / digital signal provided for each narrowband signal after a plurality of narrowband signals are generated by dividing the band of an incoming signal, and the frequency of each narrowband signal is dropped by a frequency converter. A converter that converts each narrowband signal into a digital signal by a converter and performs reception demodulation processing on the incoming signal based on the digital signal obtained thereby,
At least one of the frequency converters is provided with two or more narrow band signals, and these narrow band signals are dropped by the same frequency. Among them, an analog / digital converter provided with a narrow band signal on the higher frequency side is provided. An alias is generated in the output.
[0011]
More specifically, the band of the arriving signal is divided into n, and the band dividing means for transmitting n systems of narrow band signals, and the occupied band of the narrow band signal transmitted from the band dividing means on the frequency axis. A band shifting means for shifting, and each of the n systems of narrow-band signals transmitted from the band shifting means are converted into digital signals, and n signals having a Nyquist frequency equal to or greater than the bandwidth of the given narrow-band signal are provided. Analog / digital converting means, and receiving means for performing reception demodulation processing on the incoming signal based on the digital signal transmitted from the analog / digital converting means,
In the band moving means,
A frequency converter for dropping the frequency of a given signal; and a frequency converter connected to the input side of each of the plurality of analog / digital converters to reduce the bandwidth of the given signal to the Nyquist frequency of the connected analog / digital converter. And n band filters for limiting,
M (m ≧ 2) or more narrow band signals among the n narrow band signals transmitted from the band dividing means are combined and supplied to at least one of the frequency converters to provide each narrow band signal. Drop the frequency of the band signal, apply the output of the frequency converter to m of the n band filters, and separate the passbands of the m band filters from the combined narrow band signals. It is characterized in that it has been set as much as possible.
[0012]
In this way, at least one analog / digital converter is provided with a narrow band signal equal to or higher than the Nyquist frequency, causing a so-called undersampling state, causing an alias at the output, and receiving the alias. Processing for demodulation is performed. In other words, by providing at least one narrow-band signal that does not fall below the Nyquist frequency, it is possible to drop a plurality of narrow-band signals including the narrow-band signal with one frequency converter.
[0013]
As a result, the number of frequency converters smaller than the number of band divisions is sufficient, and the configuration can be simplified.
[0014]
Further, in the present invention, at least the lowest Nyquist frequency of the analog / digital converters is provided between the mutual bands of the m narrow-band signals to be combined and between the mutual pass bands of the m band filters. Wherein an analog / digital converter having a frequency difference of not less than the Nyquist frequency is provided.
[0015]
This makes it possible to prevent alias inversion.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 schematically shows a configuration of a receiving apparatus according to the present invention. This receiving apparatus is applicable to a receiving section of a pulse compression radar, a receiving apparatus of a CDMA (Code Division Multiple Access) signal, and the like.
[0017]
For comparison, a signal having a bandwidth of 240 MHz from 100 MHz to 340 MHz is also received here. In FIG. 1, the same parts as those in FIG. 5 are denoted by the same reference numerals, and only different parts will be described here.
[0018]
This receiving apparatus includes 12 A / D converters 2 (2-1, 2-2, 2-3) and a signal processing unit 3 connected thereto, as in FIG. For convenience of description, A / D converters are denoted by reference numerals 2-1 to 2-2 and 2-3.
[0019]
That is, the wideband signal received by the antenna ANT is first provided to the filter units F1 to F4. Each of the filter units F1 to F4 is provided with a pass band of 100 to 280 MHz, 120 to 300 MHz, 140 to 320 MHz, and 160 to 340 MHz as shown in FIG. These pass bands are located at different locations on the frequency axis, respectively, and cover 100 MHz to 340 MHz as a whole.
[0020]
From each of the filter units F1 to F4, a band-limited signal located in the band shown in FIG. 2 is transmitted. These signals are applied to converters C1 to C4, respectively, and are frequency-dropped. Drop frequencies in the converters C1 to C4 are -90, -110, -130, and -150 [MHz], respectively. As a result, a signal in a band of 10 to 190 [MHz] is transmitted from each of the converters C1 to C4.
[0021]
These signals are provided to bandpass filters 11, 12, and 13. Pass bands of 10 to 30, 90 to 100, and 170 to 190 [MHz] are set in the bandpass filters 11, 12, and 13, respectively. Thus, the signals in the bands of 10 to 30, 90 to 100, and 170 to 190 are given to the A / D converters 2-1, 2-2, and 2-3, respectively.
[0022]
Here, each of the A / D converters 2-1, 2-2, and 2-3 has the same specifications as those of the related art, in which the sampling frequency fs = 80 MHz, the Nyquist frequency fN = 40 MHz, and the processing band is 20 MHz. .
[0023]
Now, since the A / D converter 2-1 is provided with a signal in the 10 to 30 MHz band that matches the specifications, there is no characteristic point in its output. On the other hand, the A / D converters 2-2 and 2-3 are provided with a signal located in a band higher than the Nyquist frequency fN, and therefore have the following characteristic operations.
[0024]
With reference to FIG. 3, the relationship between the signal band provided to A / D converters 2-1, 2-2, and 2-3 and the output thereof will be described. Note that the following discussion can be similarly applied to a general sampling system.
[0025]
In FIG. 3, (1), (2), and (4) indicate the pass bands of the bandpass filters 11, 12, and 13, respectively, and the hatched portions are the A / D converters 2-1 to 2-2, and 2-3. Shows the signal bands respectively given to. The width of the hatched portion corresponds to a processing band of 20 MHz for each of the A / D converters 2-1, 2-2 and 2-3.
[0026]
In general, in a sampling system, if a frequency component fa equal to or higher than the Nyquist frequency fN is included in the input, fa appears at a different frequency in the sampled data. This is called an alias, and appears in a form folded back to the Nyquist frequency fN. For example, when a signal in the band shown by (1) 'in FIG. 3 is given to the A / D converters 2-1, 2-2, and 2-3, output data corresponding to the input (1) is given. Get. Similarly, when signals in the bands indicated by (2) to (5) are given to the A / D converters 2-1 to 2-3, output data corresponding to the input (1) is obtained. However, it should be noted that the signals of the bands (1) ', (3), and (5) have inverted bands at the output.
[0027]
In a conventional sampling system, a signal in a band equal to or higher than the Nyquist frequency fN is not applied to an output after A / D conversion in order to avoid noise due to interference between an original signal and an alias. On the other hand, in the present embodiment, an alias is positively used and a signal located in a high frequency band is supplied to the A / D converter, thereby obtaining an output in a form where the band is reduced.
[0028]
In the above embodiment, signals in the bands of (2) and (4) are input to the A / D converters 2-2 and 2-3, respectively. Therefore, sampling data without inversion is obtained from the output. Of course, by giving appropriate values to the characteristics of the filter units F1 to F4, the converters C1 to C4, and the bandpass filters 11 to 13, the Nyquist frequency fN ( Since signals having a bandwidth smaller than 40 MHz) (each having a bandwidth of 20 MHz) are provided one by one, no interference occurs in the output.
[0029]
Then, based on the outputs of the A / D converters 2-1 to 2-3, signal processing is performed by the signal processing unit 3 so that reception and demodulation of a wideband signal in the range of 100 to 340 MHz can be performed without any trouble. It is.
[0030]
As described above, in the present embodiment, when a signal in a band of 100 to 340 MHz is received, for example, four signals having a band of 100 to 280 MHz, 120 to 300 MHz, 140 to 320 MHz, and 160 to 340 MHz are used. Divided into These signals are guided to the frequency converters C1 to C4 having frequency drop amounts of -90, -110, -130, and -150 in order from the low frequency side. The signals dropped by this are given to band filters 11, 12, and 13 of 20 ± 10, 100 ± 10, and 180 ± 10 MHz, respectively, to further divide the band, and A / D converters 2-1 and 2-2, respectively. , 2-3.
[0031]
With this configuration, it is possible to perform frequency conversion in a plurality of bands by using one converter, so that the number of converters can be reduced and the configuration can be simplified.
[0032]
More generally, the idea of the present invention will be described with reference to FIG. When a signal in the band equal to or higher than the Nyquist frequency fN is given to the A / D converter as shown by a dotted line in FIG. 4A, an alias in the form folded back by fN is output to the output as shown at the left end in the figure. Occurs. The alias of the signal in the hatched portion is not inverted.
[0033]
Conventionally, as shown in FIG. 4B, the band of an incoming signal is divided into narrowband signals having a width of fN or less (four in this figure), and all narrowband signals are dropped to fN or less. This requires a number of converters corresponding to each narrowband signal, and the configuration is complicated. In addition, since a larger drop amount is required especially for a high-frequency signal, the converter needs to have a multi-stage configuration, which may cause a systematic error.
[0034]
On the other hand, in the above-described embodiment, the reception signal processing for the alias is performed, so that the band-limited signal including the narrow-band signal can be frequency-dropped using the converter having the same drop amount. The number of converters may be less than the number of narrowband signals. Further, since it is not necessary to drop the signal on the high frequency side to fN or less, there is no need to provide a converter in a multi-stage configuration, so that systematic errors can be reduced.
[0035]
Note that the present invention is not limited to the above embodiment. For example, in the above embodiment, the output of the A / D converters 2-1 to 2-3 is configured not to invert the original signal, but this is not directly related to the idea of the present invention. That is, when the inversion of the outputs of the A / D converters 2-1 to 2-3 is allowed, the inversion may be compensated for in the signal processing unit 3 at the subsequent stage. Also, there may be systems that allow processing in the form of the inverted output without any need for compensation.
[0036]
Further, if the outputs of the A / D converters 2-1 to 2-3 are allowed to be inverted, it is possible to further simplify the configuration. That is, for example, if the band of the arriving signal is divided into 100 to 220 MHz and 220 to 340 MHz in FIG. 1 and dropped to −90 MHz and −210 MHz, the number of converters is two. Also, only two bandpass filters need be provided immediately after the antenna ANT. This makes it possible to further simplify the configuration.
[0037]
The setting of the pass bands of the filter units F1 to F4 is not limited to the above. For example, in the above embodiment, the filter unit F1 has 100 to 120 MHz, 180 to 200 MHz, 260 to 280 MHz, the filter unit F2 has 120 to 140 MHz, 200 to 220 MHz, 280 to 300 MHz, and the filter unit F3 has 140 to 160 MHz, 220 to 240 MHz, A pass band of 300 to 320 MHz and 160 to 180 MHz, 240 to 260 MHz, and 320 to 340 MHz may be set in the filter unit F4. This can be realized by providing three bandpass filters each having a pass band of 20 MHz in each of the filter units F1 to F4, and connecting these three bandpass filters in parallel. Even in this case, the same effect as described above can be obtained, and depending on how to set the characteristics of the filter units F1 to F4, the bandpass filters 11, 12, and 13 can be omitted, and further configuration can be achieved. It can be simplified.
In addition, various modifications can be made without departing from the spirit of the present invention.
[0038]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to provide a receiving apparatus capable of receiving a wideband signal with a simplified configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a receiving device according to the present invention.
FIG. 2 is a diagram showing setting of a pass band of filter units F1 to F4 in the configuration of FIG. 1;
FIG. 3 is a diagram for explaining the relationship between signal bands provided to A / D converters 2-1 2-2 and 2-3 and their outputs.
FIG. 4 is a diagram for explaining the concept of the present invention in a more general form.
FIG. 5 is a block diagram showing a configuration of a conventional receiving apparatus.
[Explanation of symbols]
ANT antennas 41-412 band division filters 51-512, 71-712 converters 61-612 low-pass filter (LPF)
8 anti-alias filter 2 (2-1, 2-2, 2-3) analog / digital converter (A / D)
3. Signal processing units F1 to F4 Filter units C1 to C4 Converters 11, 12, 13 ... Bandpass filters

Claims (4)

The incoming signal is divided into a plurality of signals, and the frequencies of these signals are dropped by frequency converters. Then, the signals are further divided into narrow-band signals, and these narrow-band signals are supplied to an analog / digital converter and converted into digital signals. A receiving device that converts the signal into a signal and performs reception demodulation processing on the incoming signal based on the digital signal obtained thereby,
A receiving device, wherein an alias is generated in at least one output of the analog / digital converter. A plurality of narrow-band signals are generated by dividing the band of the incoming signal, and the frequency of each narrow-band signal is dropped by a frequency converter. Then, each narrow-band signal is dropped by an analog / digital converter provided for each narrow-band signal. A receiving device that converts a band signal into a digital signal, and performs reception demodulation processing on the incoming signal based on the digital signal obtained thereby,
At least one of the frequency converters is provided with two or more narrow band signals, and these narrow band signals are dropped by the same frequency. Among them, an analog / digital converter provided with a narrow band signal on the higher frequency side is provided. A receiving device wherein an alias is generated in an output. Band dividing means for dividing a band of an incoming signal into n and transmitting n systems of narrow band signals;
Band moving means for moving the occupied band of the narrow band signal transmitted from the band dividing means on the frequency axis,
The n-band narrow-band signals transmitted from the band moving means are respectively converted into digital signals, and n analog / digital converting means having a Nyquist frequency equal to or more than the width of the band of the given narrow-band signal; ,
Receiving means for performing reception demodulation processing on the incoming signal based on the digital signal sent from the analog / digital conversion means,
The band moving means,
A frequency converter that drops the frequency of a given signal;
N bandpass filters connected to the input sides of the plurality of analog / digital converters, respectively, for limiting a band width of a given signal to a Nyquist frequency of a connected analog / digital converter or less.
Among the n narrow-band signals sent from the band dividing means, m (m ≧ 2) or more narrow-band signals are combined , input to one frequency converter, and the frequency of each narrow-band signal is changed. Dropping, applying the output of the frequency converter to m of the n band filters, and setting the pass bands of the m band filters to separate the combined narrowband signals. A receiving device characterized by the above-mentioned. An analog / digital converter having at least the lowest Nyquist frequency among the analog / digital converters between the mutual bands of the m narrow-band signals to be combined and between the mutual pass bands of the m band filters. 4. The receiving device according to claim 3, wherein the converter has a frequency difference equal to or greater than the Nyquist frequency.

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