JPH0575573A - Spectrum sprezad communication equipment - Google Patents

Abstract

PURPOSE:To provide an equipment which receives a signal without degrading S/N even in the case of a large quantity of noise by subjecting the reception signal to FFT frequency analysis to extract the noise and subjecting the signal, which is obtained by eliminating the noise from the reception signal to inverse spread processing. CONSTITUTION:A signal is converted by an A/D conversion circuit 7 after being received through an antenna 5 by a reception circuit 6. The reception signal is divided into two with respect to time and is sampled by a fast Fourier transform (FFT) processing circuit 8, and each sampling signal has the noise detected and eliminated by FFT frequency analysis technique, and sampling signals where the noise is eliminated are synthesized. The signal adjusted to a signal which is not affected by the noise is processed by an inverse spread circuit 9 and passes a demodulating circuit 10 to obtain prescribed reception data. Since the reception signal which does not include the noise is inversely spread by the inverse spread circuit 9 in this constitution, data transmitted from a transmission side (a) is accurately extracted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum communication device, and more particularly to an FFT (Fast Fourier).
(Transform) The present invention relates to a device capable of removing noise by frequency analysis.

[0002]

2. Description of the Related Art Spread spectrum communication devices (hereinafter referred to as SS
A communication device) is a pseudo-noise code (hereinafter, a pseudo-noise code) having a spectrum width that is sufficiently wider than the data signal.
A PN code) is used for spreading and transmission, and on the other hand, the receiving side is subjected to despreading with the PN code to selectively receive only data signals. Since this SS communication device can extract only a target signal when it is spread and demodulated with a specific PN code, it can have excellent confidentiality and noise resistance.

[0003]

However, in the above-mentioned conventional SS communication apparatus, when the amount of noise (noise) is small, it is spread in the demodulation wide band by the despreading processing on the receiving side. Although it does not have an adverse effect, if the amount of noise becomes large to some extent, there arises a disadvantage that the S / N ratio decreases when the noise is spread within the demodulation band.

In order to avoid such an inconvenience, noise may be removed by using a notch filter, but when the frequency of the noise is unknown, the notch filter cannot be adopted. Further, even when the number of noise line spectra is large, it is impossible to remove the noise with the notch filter.

Therefore, the present invention has been made to solve such a problem, and an object thereof is to provide an SS communication device capable of receiving without reducing the S / N ratio even if the amount of noise is large. To provide.

[0006]

In order to achieve the above object, the present invention spreads data to be transmitted on the transmitting side and sends it out, and despreads the received signal on the receiving side to receive it. In an SS communication device adapted to selectively receive data, noise extraction means for FFT frequency-analyzing the received signal to extract noise, and noise removal means for removing the noise extracted by the noise extraction means from the received signal. And despreading processing means for performing despreading processing on the signal removed by the noise removing means.

[0007]

In the above structure, the noise extracting means extracts the noise by FFT analysis of the received signal. Then, the noise removing means removes the noise extracted from the received signal. Therefore, the despreading processing means performs despreading processing on the received signal that does not contain noise.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an apparatus according to an embodiment, in which a
Indicates the transmitting side and b indicates the receiving side.

The transmitting side a is the same as the transmitting side of a well-known SS communication device, and the transmission circuit a generates transmission data into a modulation data signal (see (a) in FIG. 1) and sends it to the spreading circuit 2. To do. Then, in the spreading circuit 2, after spreading processing using a predetermined PN code, it is sent to the transmitting circuit 3 and is output from here to the receiving side b via the antenna 4. The line spectrum shown in (b) of FIG. 1 shows a state in the middle of being transmitted from the transmitting side a to the receiving side b, and the smooth mountain-shaped a is a state in which the transmission data is spread by the PN code. And the dotted line B indicates the position and level of the transmission data for this spread state. The solid line C indicates the position and level of noise mixed in during transmission.

As in the well-known SS communication device, the receiving side b receives the signal by the receiving circuit 6 via the antenna 5 and then the analog-digital (A / D) conversion circuit which is a characteristic component of the present invention. 7 and the FFT processing circuit 8.

As the A / D conversion circuit 7, a known A / D conversion circuit can be adopted. The FFT processing circuit 8 will be described later in detail with reference to FIG.

The signal processed by the FFT processing circuit 8 is adjusted to a signal which is not affected by noise (see (c) in FIG. 1), and the signal is similar to that of a known SS communication device.
The same data signal as the modulated data signal on the transmitting side a is processed by the despreading circuit 9 that performs the despreading process with the PN code used at the time of the spreading processing on the transmitting side a, as shown in FIG. Selectively received. Then, this data signal passes through the demodulation circuit 10 and becomes predetermined reception data.

FIG. 2 shows a concrete example of the FFT processing circuit 8. A sampling circuit 11 for sampling the output of the A / D conversion circuit 7 by alternately dividing it into two parts in time, and an FFT of the sampled signal. It is composed of noise removal circuits 12a and 12b that remove noise by frequency analysis, and a synthesis circuit 13 that synthesizes the outputs of the noise removal circuits 12a and 12b into a temporally continuous signal.

The sampling circuit 11 has a pair of ANs each of which inputs the output of the A / D conversion circuit 7 to one input terminal.
D circuit 11a, 11b, AND circuit 11
The timing signal generating circuit 1 is provided at the other input terminals of a and 11b.
The signals are alternately input from 1c. That is, the timing signal generation circuit 11c generates a pulse signal having a time length A that is sufficiently longer than the transmission data bit length, and outputs the generated signal to one AND circuit 11a.
And the other is input via the inverting circuit 11a.

Since the noise removing circuits 12a and 12b have the same structure, the noise removing circuit 12a corresponding to the AND circuit 11a will be described as an example.
In 2a, the output of the AND circuit 11a is divided into two systems, and in one system, an FFT circuit 20, a noise detection circuit 21, a noise waveform creation circuit 22, and an inverting circuit 23 are provided in series. In addition, a memory 24 and an A / D conversion circuit 25 are provided in series in the other system. The outputs of these two systems are added by the adder circuit 2.
6 is input.

The synthesizing circuit 13 includes the noise removing circuits 12
It has a pair of AND circuits 13a and 13b for respectively inputting the outputs of a and 12b to one input terminal, and the timing signal from the timing generating circuit 11c is applied to the other input terminal of these AND circuits 13a and 13b. ，
11b is configured to be input while maintaining the opposite relationship. The output of both AND circuits 13a and 13b is O.
It is input to the R circuit 13c, and its OR circuit 13c
The output of is input to the despreading circuit 9.

The waveform diagrams (e) to (m) in FIG.
It is provided for the sake of convenience in order to facilitate the description of the processing operation of the processing circuit 8. Each waveform diagram shows the waveform at the position indicated by an arrow. In addition, in these waveform diagrams,
The protruding part is regarded as noise.

Next, referring to these waveform diagrams, the FFT
The operation of the processing circuit 8 will be described. First, the A / D conversion circuit 7
It is assumed that the signal shown in the waveform diagram is output from the.

The signal shown in the waveform diagram (e) is supplied to the noise removing circuits 12a and 12b by the sampling circuit 11.
Is divided into two and input in time. That is, the signal is 1 / one of one pulse of the timing pulse generation circuit 11c.
It is divided into two (A and bar A) and input to the respective noise removal circuits 12a and 12b (waveform diagram (f),
(See (g)).

Since the noise removing circuits 12a and 12b have the same configuration and the same processing operation, the noise removing circuit 12a will be mainly described below.

The signal sampled by the sun ring circuit 11 is input to the FFT circuit 20 and the memory 2
4 (see (f) of FIG. 2).

The FFT circuit 20 analyzes the frequency within a predetermined required band according to the well-known FFT frequency analysis method. That is, for the frequency within the predetermined required band, level and phase data are obtained for each frequency component. Then, the levels of all the obtained bands are added, and the added value is divided by the total number of components to obtain the average level value.

Internal memory (not shown) of the FFT circuit 20
Since the spectrum of the received signal wave is stored in advance, the spectrum corresponding to the average level value is extracted.

Next, in the noise detection circuit 21, if there is a level difference of a predetermined level or more, for example, 6 dB or more, between the extracted spectrum and each component value, it is determined as noise. Then, the noise waveform generation circuit 22 performs inverse Fourier transform on the component value of the frequency determined as noise to generate a noise wave (see (h) of FIG. 2). After that, an inversion signal of noise is obtained through the inversion circuit 23 (see (i) in FIG. 2B). The obtained inversion signal of noise is input to the addition circuit 26.

On the other hand, the signal temporarily stored in the memory 24 is input to the adder circuit 26 via the D / A converter circuit 25, where it is added to the above-mentioned noise inversion signal.

If this addition state is shown by (i) to (k) in FIG. 2, the sampled signal (j) and the inversion value (i) of the extracted noise signal are added, and no noise is included. A sampling signal (k) is obtained. Such noise removal is similarly performed in the other noise removal circuit 12b. That is, also in the noise removal circuit 12b, the noise-removed sampling signal (l) is obtained from the sampled signal (g) containing noise by the FFT frequency analysis method.

Each noise removal circuit 12 from which noise has been removed
The sampling signals from a and 12b are the AND circuits 1
3a and 13b, respectively, and output to the OR circuit 13c at the sampling timing. Therefore, the reception signal (see (m) of FIG. 2) containing no noise is output from the OR circuit 13c and input to the despreading circuit 9. Therefore, the despreading circuit can despread the received signal containing no noise, and can accurately extract the data transmitted from the transmission side a.

As described above, in the apparatus of this embodiment,
The received signal is temporally divided into two and sampled, and the respective sampled signals are respectively removed by the noise removing circuits 12a and 12b.
Then, the noise is detected and removed by the FFT frequency analysis method.
Further, since the noise-removed sampling signals are combined to perform the despreading process, the despreading circuit 9
The data from the transmitting side a can be accurately extracted.

[0029]

The apparatus of the present invention comprises a noise extraction means for extracting noise by FFT frequency analysis of a received signal, a noise removal means for removing the noise extracted by the noise extraction means from the received signal, and the noise removal thereof. Since it has a despreading processing means for performing despreading processing on the signal removed by the means, it is possible to perform despreading processing on the received signal that does not contain noise, and it is possible to accurately extract the data from the transmitting side.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of an FFT processing circuit.

[Explanation of symbols]

2 spreading circuit 8 FFT processing circuit (noise extraction means, noise removal means) 9 despreading circuit (despreading processing means) a transmission side b reception side

Claims (1)

[Claims] 1. A spread spectrum communication device in which data to be transmitted is spread and transmitted at a transmitting side, and despread processing is performed on a received signal at a receiving side to selectively receive data to be received. Noise extraction means for extracting noise by FFT frequency analysis of the signal, noise removal means for removing noise extracted by the noise extraction means from the received signal, and inverse spread processing for despreading the signal removed by the noise removal means. A spread spectrum communication device comprising: spread processing means;