JPH05284142A - Diffused spectrum signal receiver - Google Patents

Abstract

PURPOSE:To provide a diffused spectrum signal receiver which can prevent an A/D converter from being saturated without lowering the S/N of received signals when receiving diffused spectrum signals superimposed external noise with the large amplitude of narrow band width. CONSTITUTION:One of bisected received signals is inputted to a phase synchronizing circuit 51, outputted while selecting the signal at the frequency of noise, and calculated the difference from the other received signal by a subtracter 54. This output is detected by a level detector 56 and the output of the subtracter 54 is adjusted at a minimum level by controlling a variable attenuator 55 so as to remove noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct spread spectrum spread communication type receiver, and more particularly to a spread spectrum communication type receiver which prevents the influence of external noise.

[0002]

2. Description of the Related Art FIG. 6 shows a principle block diagram of a direct spread spectrum spread system. Information from the information source 1 modulates a signal input from a local oscillator incorporated in the primary modulator 2. This modulation is FSK (Frequency Shift Keying)
And PSK (Phase Shift Keying) and other digital modulation. The output signal of the primary modulator 2 is modulated in the spread modulator 5 by the spread code generated in the spread code generator 4. A pseudo noise code (PN code) such as an M-sequence code is used as the spreading code generated by the spreading code generator 4. The PN code has a wide white spectrum and is characterized by a small power density per unit frequency.

The spread-modulated signal is frequency-converted in the frequency converter 6 by the local oscillation signal input from the local oscillator 7 into a high frequency signal, which is transmitted from the transmitting antenna 8.

In the receiver, the signal received by the receiving antenna 11 is demodulated in the demodulation circuit 12 by the local oscillation signal from the local oscillator 13 and converted into an intermediate frequency. The output signal from the demodulation circuit 12 is demodulated in the spread demodulator 14 by the spread code from the spread code generator 15. This spreading code is the same signal as the spreading code generated by the spreading code generator 4 in the transmitter, and the spreading code generator 15
Is generated at the same timing as the spreading code on the transmission side by the synchronization signal generated by the code synchronization circuit 16 and is subjected to spread demodulation to reduce the spread spectrum to the frequency spectrum of the primary modulation. This operation is called despreading.

The signal restored by this primary modulation signal is demodulated by the primary demodulator 17 to obtain an information signal. FIG. 7 shows a conventional circuit example based on the above principle. In this example, digital signal processing is performed based on the principle shown in the principle diagram of FIG. In the figure, the same reference numerals are used for the same parts as in FIG. In the figure, (a) is a block diagram of a transmitter, and (b) is a block diagram of a receiver. The pseudo noise signal output from the PN code generator 21 is spread-modulated by the spread modulator 5 to the output signal from the primary modulator 2. This signal is DA converter 2
In 2, the signal is converted into an analog signal, and the LPF 23 removes unnecessary high frequency signals.

The output signal of the LPF 23 is amplified by the amplifier 24, and then converted into a high frequency signal by the local oscillator frequency from the local oscillator 7 in the frequency converter 5, and the BPF is supplied.
Unwanted frequency components such as harmonics of the high frequency signal are removed at 25, amplified by the amplifier 26, and then transmitted from the transmission antenna 8.

In the receiver shown in (b), the signal received by the receiving antenna 11 is filtered by the LPF 30 to remove unnecessary frequency components, amplified by the amplifier 31, and then locally oscillated by the local oscillator 13 by the mixer 32. The signal is converted to an intermediate frequency and is input to the AGC amplifier 34 via the BPF 33.

The AGC amplifier 34 rectifies the input signal and determines the gain of the amplifier in accordance with the magnitude of the input signal, thereby limiting the magnitude of the output signal, and the AD converter 35.
To prevent saturation.

The signal digitized by the AD converter 35 is despread by the signal obtained by modulating the output signal of the carrier reproducing oscillator 37 at the multiplier 36 with the PN code of the output of the PN code generator 38 at the modulator 39. And is returned to the primary modulation signal. The primary demodulator 40 primary demodulates the signal returned to the primary modulation signal and outputs an information signal. AD
A demodulator 41 is configured by each circuit after the converter 35.

[0010]

Here, the AD converter is used on the receiving side. However, when external noise is added to the received radio wave in space, the AD converter 35 is provided in the preceding stage so as not to be saturated. The gain of the provided AGC amplifier 34 is lowered. However, in that case, the AD converter 3
The SN ratio is lowered due to the quantization noise of 5, etc.

As a countermeasure against this, there is a method of increasing the dynamic range of the AD converter 35, but this leads to an increase in cost. The present invention has been made in view of the above points, and an object thereof is a receiving device for receiving and detecting a spread spectrum signal, in the case where a large external noise having a narrow bandwidth is superimposed on the signal. It is an object of the present invention to realize a spread spectrum communication type receiver equipped with a device that prevents saturation of a detection device including an AD converter in a receiver without reducing the SN ratio.

[0012]

DISCLOSURE OF THE INVENTION The present invention for solving the above-mentioned problems is, in a spread spectrum signal receiving apparatus for receiving and demodulating a spread spectrum signal, a large amplitude of one of the two divided received signals. Of the phase-locked circuit configured to output the signal of the frequency of the signal component of VCO and the VCO, and the difference between the output of the phase-locked circuit to which the other signal of the halved received signal is input. A level detector that detects the level of the output signal of the subtractor and outputs a control signal corresponding to the detected level; and the resistance value changes according to the control signal of the output of the level detector And a variable attenuator for adjusting the output signal level of the phase locked loop input to the subtractor.

[0013]

One of the halved reception signals is input to the phase locked loop circuit to output a signal having a frequency matching the frequency of the maximum amplitude signal of the input signal, and the variable attenuator receives the attenuation corresponding to the amplitude. Input to the subtractor. The subtractor finds the difference between the two divided reception signals and the other. The signal level of the difference is detected by the level detector, and the variable attenuator is controlled so that the output level of the subtractor is minimized.

[0014]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of a receiver according to an embodiment of the present invention. In the figure, the same parts as those in FIG. 7 are designated by the same reference numerals. In the figure, 51 is a phase comparator 52 and VC
It is a PLL diagram constituted by an O (Voltage Controlled Oscillator) 53. The signal received by the receiving antenna 11 is divided into two, one of which is input as the comparison frequency of the phase locked loop 51 and the other of which is directly input to the subtractor 54.

Reference numeral 55 is a variable attenuator connected to the output end of the phase locked loop circuit 51 and the other input end of the subtractor 54, and a level detector 56 connected to the output end of the subtractor 54.
Controlled by the output of.

Next, the operation of the embodiment configured as described above will be described with reference to FIGS. 2, 3 and 4. In each figure, (a) shows a frequency spectrum and (b) shows a signal waveform.

The signal received by the receiving antenna 11 is the sum of a spectrum-spread signal and a signal emitted from an external noise source (in this case, external noise whose spectrum is concentrated in a narrow range). .. Two signals are added to this signal as shown in FIG.

The received signal is filtered by the LPF 30, amplified by the amplifier 31, and then halved. One is input to the phase locked loop 51 and the other is input to the subtractor 54. When the received signal input to the phase synchronization circuit 51 is input to the phase comparator 52 as a comparison signal, the phase comparator 52 constantly compares the phase difference between the input signal and the output signal of the VCO 53, and this phase difference The voltage of the phase comparator 52 generated by this acts as the control voltage of the VCO 53, and makes the frequency of the VCO exactly match the frequency of the input signal. Therefore, VCO5
The output frequency of 3 is the frequency of the signal component having the largest amplitude in the frequency domain. Therefore, the phase synchronization circuit 51
The output signal spectrum and the time axis waveform are only the noise waveform shown in FIG.

In the subtractor 54, the received signal and the phase synchronization circuit 5
Subtract the output of 1 and output. The spectrum and time-axis waveform of this signal are as shown in FIG. 4, and a noise-free signal is output. Therefore, finally, only the spread spectrum signal remains. Subtractor 54
The output of is input to the demodulator 41 and demodulated as described in FIG. 7, and the original information is output.

On the other hand, the output of the subtractor 54 is the level detector 5
6, the output level is detected, and the data controls the variable attenuator 55 to adjust its resistance value. The variable attenuator 55 is for making the output level of the VCO 53 equal to the level of external noise, and is controlled by the control signal of the level detector 56 so that the output level of the subtractor 54 is minimized.

Now, comparing the signal on which noise is superimposed ((b) in FIG. 2) with the time axis waveform after noise is subtracted ((b) in FIG. 4), the signal on which noise is superimposed is compared. 2 has a large amplitude level, which causes the AD converter 35 to be saturated.

Therefore, when it is attempted to keep a signal on which such noise is superimposed within the input range of the AD converter 35, it is necessary to lower the gain of the AGC amplifier 34, and the amplitude level of the signal lowers together with the noise level. As a result, the SN ratio of the required signal is reduced.

However, since the amplitude level of the signal after the noise shown in FIG. 4 has been subtracted is stable, the AGC amplifier 34 can sufficiently keep it within the input range of the AD converter 35.

As described above, according to this embodiment, when external noise is present, the external noise is detected and subtracted. Therefore, even when spread spectrum communication is performed in an environment with large external noise. A receiver having a good SN ratio can be obtained.

The present invention is not limited to the above embodiment. FIG. 5 is a block diagram of another embodiment of the present invention. In the figure, the same parts as those in FIGS. 1 and 6 are designated by the same reference numerals. In the figure, reference numeral 60 is an amplifier for amplifying the received signal converted into the intermediate frequency by the local oscillator 13 and the mixer 32.

Since this embodiment is obtained by adding a frequency conversion section consisting of the local oscillator 13 and the mixer 32 shown in FIG. 6 to the apparatus of the embodiment shown in FIG. However, the oscillation frequency of the carrier reproduction oscillator 37 in the demodulator 41 is different.

[0027]

As described in detail above, according to the present invention, in a receiving device for receiving and detecting a spectrum-spread signal, even when external noise having a narrow bandwidth and large amplitude is superimposed, the reception is performed. It is possible to prevent the saturation of the detection device including the AD converter without lowering the signal level, and the practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

2A and 2B are diagrams of a spread signal including noise, in which FIG. 2A is a frequency spectrum diagram, and FIG. 2B is a time axis waveform diagram.

FIG. 3 is a diagram of a noise signal, where (a) is a frequency spectrum diagram and (b) is a time axis waveform diagram.

FIG. 4 is a diagram of a spread signal from which noise has been subtracted.
Is a frequency spectrum diagram, and (b) is a time axis waveform diagram.

FIG. 5 is a block diagram of an apparatus according to another embodiment of the present invention.

FIG. 6 is a principle configuration diagram of a direct spread spectrum spread system transceiver.

FIG. 7 is a block diagram of a conventional spread spectrum transceiver.

[Explanation of symbols]

 51 Phase Synchronous Circuit 52 Phase Comparator 53 VCO 54 Subtractor 55 Variable Attenuator 56 Level Detector

Claims (1)

[Claims] 1. A spread spectrum signal receiving apparatus for receiving and demodulating a spread spectrum signal, wherein a phase comparator which outputs a signal having a frequency of a large amplitude signal component of one of the two divided received signals ( 52) and a VCO (53), and a subtractor for calculating the difference between the phase-locked loop circuit (51) and the output of the phase-locked loop circuit (51) to which the other signal of the received signal divided in two is input. (5
4) and a level detector (5) for detecting the level of the output signal of the subtractor (54) and outputting a control signal according to the detected level.
6) and a variable attenuator for adjusting the output signal level of the phase locked loop circuit (51) which is input to the subtractor (54) by changing the resistance value by the control signal of the output of the level detector (56) (55) A spread spectrum signal receiving device comprising: