JPH04132429A - Interference wave eliminating circuit - Google Patents

Abstract

PURPOSE:To surely eliminate an interference wave mixed in a spread spectrum signal by extracting the interference wave by a discriminator as a low frequency component signal and using a high pass filter so as to eliminate the signal of the low frequency component. CONSTITUTION:The circuit is provided with a discriminator 1 outputting a signal corresponding to a frequency change in a reception signal and a high pass filter 2 blocking the low frequency component of the output signal of the discriminator 1 and passing the high frequency component. In this case, the discriminator 1 in a reception circuit receiving a spread spectrum signal and reproducing the original information outputs a reception signal such as a signal corresponding to a frequency change in the spread spectrum signal converted from a radio frequency signal into an intermediate frequency signal. The high pass filter 2 blocks the low frequency component of the output signal of the discriminator 1 and passes the high frequency component. Thus, disable synchronization due to the effect of the interference wave is not caused and the increase in a data error rate due to the mixture of the interference wave into the spread spectrum signal is avoided.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a method for transmitting and receiving information on the receiver side of spread spectrum communication.
For example, by extracting a signal converted from a radio frequency signal to an intermediate frequency signal using a discriminator as a signal frequency change, narrowband interference waves are converted to a low frequency signal, and the output of the discriminator is converted into a high-pass It is characterized in that it passes through a filter to cut low frequency components and remove interference waves mixed in the spread signal.

[Industrial application field]

The present invention relates to an interference wave removal circuit that removes narrowband interference waves mixed in received signals in spread spectrum communication.

[Prior Art] A spread spectrum communication system is a communication system that performs communication using signals spread over a much wider frequency band than the frequency band required for transmitting information. Due to the difference in the method of frequency spreading the signal, there is a direct spread method (Dir
ect 5equence: DS method) Frequency hopping method (Frequency Hop'rng:
FH method), etc.

In the DS system, a signal modulated by the information to be sent is
It is further modulated with a pseudo-noise code called a PN code and converted into a wideband spread signal.

(For example, BPSK modulation Binary Phase
5hiftKeying) When demodulating (despreading) the above spread signal on the receiving side, the received signal is multiplied by the same PN code as on the transmitting side,
In order to demodulate into a narrowband modulated signal, it is necessary to synchronize the phase of the PN code to be multiplied with the phase of the PN code of the received signal.

FIG. 8 is a configuration diagram of a boat-based spread spectrum communication system.

In the same figure, a primary modulation circuit 11 on the transmitting side is a circuit that modulates a carrier wave according to information to be transmitted, and a secondary modulation circuit 12 further modulates a -gradation tone signal with a PN code, and a spread spectrum signal is generated. This is a circuit that converts it into a signal. The RF/IF circuit 13 converts the spread signal into a radio frequency signal, amplifies it, and then transmits it from the antenna 14.

On the receiving side, the spread signal input from the antenna 15 is
After the signal is converted into an intermediate frequency signal and amplified by the F/IF circuit 16, the synchronization circuit 17 synchronizes the phase of the PN code on the receiving side with the signal. When synchronization is established, the synchronization circuit 17 outputs a despread narrowband modulation signal, and the demodulation circuit 18 reproduces the original information from the modulation signal.

Next, the configuration of the synchronization circuit 17 will be explained using FIG. 9.

The synchronous circuit 17 can be divided into two blocks based on the circuit functions. One is a synchronization acquisition circuit that roughly synchronizes from an asynchronous state until the phases of the PN codes almost match, and the other is a synchronization acquisition circuit that roughly synchronizes from an asynchronous state until the phases of the PN codes almost match.The other is a synchronization acquisition circuit that roughly synchronizes from an asynchronous state until the phases of the PN codes almost match.The other one is a synchronization acquisition circuit that roughly synchronizes from an asynchronous state until the phases of the PN codes almost match. This is a synchronization holding circuit that further reduces the

First, the synchronization acquisition circuit will be explained. RF/IF circuit 16
The intermediate frequency signal output from the multiplier 19a is input to one input terminal of the multiplier 19a, and the PN code generated by the PN code generation circuit 26 is given as the output signal P to the other input terminal of the multiplier 19a. The zero multiplier 19a multiplies these signals and outputs the result to the bandpass filter 20a.

The bandpass filter 20a is composed of a crystal filter or the like, and has a characteristic of passing signals within a specific band and blocking signals outside the band.

The signal that has passed through this band pass filter 20a is amplified by the next stage amplifier 21a, further passes through the next stage band pass filter 22a, and then passes through the detector 23a and the next stage demodulation circuit 18.
is output to.

The detector 23a is a detector that performs envelope detection of the signal from the bandpass filter 22a, and the detection output of this detector is integrated for a certain period in an integrator 24 and output to a comparator 25.

The comparator 25 is a circuit that determines whether or not the received signal is synchronized by comparing the output of the integrator 24 with a predetermined dark value, and when it is less than the dark value, it is determined that the synchronization is not achieved. , outputs to the PN code generation circuit 26 a control signal for shifting the PN code phase to positive or negative. Upon receiving this control signal, the PN code generation circuit 26 generates 1/2
The PN code whose phase is advanced by a chip or delayed by 1/2 chip is outputted to the multiplier 19a as an output signal P to synchronize with the PN code phase of the received spread signal.

On the other hand, when the output of the integrator 24 exceeds the dark value of the comparator 25, the phases of the PN codes on the transmitting side and the receiving side almost match, and the output is passed through the above-mentioned bandpass filters 20a, 22a and amplifier 21a. This is the case when the narrow band original signal (-level-adjusted signal) is reproduced, and at this time the comparator 25
The N code generation circuit 26 and the system described later? A control signal is output to the 1llt pressure generation circuit 27 to notify that synchronization has been acquired.

Next, the operation of the synchronization holding circuit in a state where synchronization has been acquired will be explained.

The multipliers 19b and 19c are circuits that multiply the intermediate frequency signal from the RF/IF circuit 16 by a PN code having a phase difference of ±172 chips with respect to the signal P multiplied by the received signal in the multiplier 19a. Yes, the multiplier 19b outputs the output signal P
PN code (signal E
) is multiplied by the intermediate frequency signal, and in the multiplier 19c, 1/
A PN code (signal L) with a two-chip phase delay is multiplied by the intermediate frequency signal.

The outputs of these multipliers 19b and 19c are transmitted through the bandpass filters 20a and 22a described above, and the multipliers 111iiH.
Bandpass filters 20b and 22 having the same configuration as 21a
20c, 22c and amplifiers 21b, 21c, the signals in a specific band are amplified, and the signals are envelope-detected by detectors 23b, 23c, and then sent to the control voltage generation circuit 27.
is output to.

Regulation? 11 voltage generation circuit 27 includes a detector 23b and a detector 2.
This is a circuit that generates a control voltage according to the output difference with 3c, and the generated control voltage? 1lii pressure is output to the loop filter 28. The loop filter 28 is constituted by a filter having a low-pass It transition characteristic, and removes a high frequency component from the control It pressure from the control voltage generation circuit 27 and outputs it to the VCXO 29 .

(2) CX029 is a circuit that generates a frequency signal according to the applied voltage, and the frequency from this VCXO29 controls the phase and frequency of the PN code generated by the PN code generating circuit 26.

In other words, in a synchronized state, when a signal P is multiplied by a signal E with a 172-chip phase lead, the detection output is a signal multiplied by a signal E with a 1/2-chip phase delay. The output voltage becomes equal to the output C, and the output voltage of the control voltage generation circuit 27 also becomes O, so that the PN code phase is maintained as it is and synchronization is maintained.

On the other hand, if the phase shifts for some reason, the detector 23b,
Alternatively, the output voltage of one of the detectors 23c increases, and the oscillation frequency of the VCOX 29 changes. This results in
The PN code generation circuit 26 outputs a PN code whose phase is more advanced or delayed than the current PN code, and synchronization is maintained.

(Problem to be solved by the invention) By the way, in the above-mentioned spread spectrum communication receiver,
In order to widen the receiving input dynamic range, RF
/IF16 A G C (Automatic Gain
Control) is applied to keep the output signal level constant. Therefore, if there is a narrowband interference wave that is larger than the spread signal to a certain extent (for example, 30 dB) within the spread signal band, AGC works on the narrowband interference wave to suppress the spread signal level, resulting in a synchronization failure. The problem was that it was possible.

Furthermore, even if synchronization is not impossible, the signal after despreading contains a narrowband interference wave component, which causes a problem in that the SZN ratio decreases and the data error rate deteriorates. Particularly when communicating using weak radio waves, the influence of narrowband interference waves on received signals is large, and it has been desired to eliminate narrowband interference waves.

The problem of the present invention is to remove narrowband interference waves from a received signal,
The objective is to achieve stable synchronization and further improve the data error rate.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention.

In a receiving circuit that receives a spread spectrum signal and reproduces the original information, a discriminator 1 includes:
A signal corresponding to a frequency change of a received signal, for example, a spread signal converted from a radio frequency signal to an intermediate frequency signal, is output.

The high-pass filter 2 blocks low frequency components of the output signal of the discriminator 1 and passes high frequency components.

[For production]

Now, the received signal mixed with interference waves is received by the receiving circuit,
Assume that the signal is converted into an intermediate frequency signal and input to the discriminator 1.

The discriminator 1 extracts a signal that corresponds to the frequency change of the input signal, but since the interference wave is a signal whose frequency changes much more slowly than the spread signal, it is output to the disc as a lower frequency component than the spread signal. Output from liminator 1.

The interference waves output as low frequency components from the discriminator 1 are blocked by the high pass filter, and only the spread signal extending to the high frequency components passes through the high pass filter 2.

As a result, a signal from which interference waves have been removed is obtained as the output signal of the high-pass filter 2, so this signal is again
By despreading after multiplying by C, it is possible to realize demodulation without losing synchronization and with fewer data errors.

Furthermore, in the present invention, since the discriminator 1 extracts a signal corresponding to the frequency change of the received signal, the signal input to the despreading circuit becomes a baseband signal. Therefore, the accuracy of the filter, local oscillator, etc. can be made coarser, and the device can be made smaller and lower in cost.

〔Example〕 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing a circuit configuration of a transmitter for spread spectrum communication according to an embodiment of the present invention, and FIG. 3 is a diagram showing a circuit configuration of a receiver.

In the transmitter of FIG. 2, the transmitted data is transmitted to the differential encoding circuit 3.
1, the exclusive OR circuit 32
In this step, an exclusive OR with the PN code output from the PN code generation circuit 33 is taken, and the signal is converted into a spread signal spread over a 1.2 MHz band as shown in FIG. 4(a), for example.

The FSK modulation circuit 34 modulates the intermediate frequency (for example, 10.7 MHz) according to the output signal of the exclusive OR circuit 32.
The frequency is switched around, for example, as shown in FIG. 4(b), and the signal is converted into a signal that spreads over a band of ±1.2 MHz with the center frequency at 10.7 MHz.

Then, in the RF/IF circuit 35, the intermediate frequency signal is converted into a radio frequency signal (for example, 290 MHz), amplified, and sent out from the transmitting antenna 36.

On the receiver side in FIG. 3, the RF/IF circuit converts the radio frequency signal input from the antenna 37 into an intermediate frequency signal and outputs it to a discriminator (frequency discriminator) 39. The discriminator 39 is, for example, as shown in FIG.
It has a linear frequency/output voltage characteristic as shown in , and performs FM demodulation by outputting a voltage corresponding to the frequency of the input signal.

Due to the action of this discriminator 39, as shown in FIG.
) is converted into a baseband signal d extending over a band from 0 to 1.2 MHz as shown in FIG. 4(d).

The high-pass filter 40 is a filter having band characteristics that blocks low frequency components and passes high frequency components, and removes the low frequency components from the output signal d of the discriminator 39, as shown in FIG. 4(e). Such a signal e is output to the despreading circuit 41 at the next stage.

The despreading circuit 41 multiplies the output signal of the high-pass filter 40 by a PN code to obtain a narrowband despread signal. This despread signal is demodulated into the original information in the demodulation circuit 42.

Next, the operation of the receiver configured as described above will be explained with reference to the spectrum of the output signal of each part of the circuit shown in FIG. 4, the characteristic diagram of the discriminator shown in FIG. 5, etc.

First, the operation when the received signal does not contain narrowband interference waves will be explained.

In this case, the frequency spectrum of the output signal C, which is converted from a radio frequency signal to an intermediate frequency signal in 3 days by the receiver's RF/IF circuit, has a waveform with no interference waves mixed in, as shown in Figure 4 (C). becomes. When this signal C is input to the discriminator 39, the frequency change of the signal C is extracted and converted into a baseband signal d spread over a 1.2 MHz band as shown in FIG. 4(d).

The output signal d of the discriminator 39 has the same bandwidth as the input signal a of the FSK modulation circuit 34 of the transmitter. However, due to band limitations by the transmitting side RF/IF circuit 35 and the receiving side RF/IF circuit 38, the signal d has a distorted waveform compared to the input signal a of the FSX modulation circuit 34.

Here, since the cutoff frequency of the high-pass filter 40 is set low (for example, 50 kHz), the output signal d of the discriminator 39 mostly passes through the high-pass filter 40.

As shown in FIG. 4(e), a signal e obtained by cutting off the low frequency components of the signal d is output to the next-stage despreading circuit 41. At this time, since the signal component cut by the high-pass filter 40 is much smaller than the bandwidth of the spread signal, the original spread signal is not affected by the low-frequency component being cut.

Next, a case where narrowband interference waves are mixed in the received signal will be explained.

In this case, the output signal C' of the RF/IF circuit 38 which converted the radio frequency signal into an intermediate frequency signal is as shown in FIG. 4(e').
The result is a signal mixed with narrowband interference waves as shown in the figure. When this signal C' is passed through the discriminator 39, the frequency of the narrowband interference wave changes more slowly than that of the spread signal, so the interference wave has a lower frequency as shown in Figure 4(d'). Output as component signals.

On the other hand, since the spread signal has a very rapid frequency change, it is output as a signal that extends to high frequency components, resulting in an overall frequency spectrum as shown in FIG. 4(d').

When this signal d' is passed through a high-pass filter 40, narrowband interference waves existing in the low frequency region are removed, and as shown in Fig. 4 (e'
), resulting in a signal e' as shown in FIG. By despreading and demodulating this signal e', the original information containing no interference waves can be reproduced.

Here, it will be explained with reference to FIG. 5 that the above-mentioned discriminator 39 and high-pass filter 40 can remove narrowband interference waves without depending on the frequency of the interference waves.

Now, suppose that two narrowband interference waves A and B with different frequencies are mixed in the intermediate frequency signal as shown in FIG. 5(a).

Since the discriminator 39 has input/output characteristics as shown in the figure (b), the output voltage of the discriminator 39 regarding the interference wave A is equal to the output voltage of the interference wave A as shown in the figure (C). This is a signal whose voltage level changes in response to frequency changes. Further, the output voltage of the discriminator 39 regarding the interference wave B is also the same as that of the interference wave B as shown in FIG.
This is a signal whose voltage level changes in response to changes in frequency.

Since the bands of the interference waves A and B are much narrower than the spread signal, the discriminator 39 for the interference waves A and B is
The output signal is a low frequency signal that differs only in voltage level.

This means that the discriminator 39 can extract interference waves with different frequencies as almost the same low frequency signal. Therefore, by cutting those low frequency signals with the high pass filter 40, it is possible to remove the interference waves regardless of their frequency.

Furthermore, according to the interference wave removal circuit of the present invention, the accuracy of the filter and oscillator of the despreading circuit 41 can be made coarse.

In the conventional synchronous circuit (despreading circuit) shown in Fig. 9, the RF/I
An intermediate frequency signal (for example, 10
．． 7 MHz), and uses a steep and narrow band filter (for example, a crystal filter) to improve the S/N ratio in the subsequent demodulation circuit. Therefore, when a signal deviating from the intermediate frequency by several KHz is input, there is a problem that the despread signal is cut by the filter, making it impossible to acquire synchronization. Therefore, it is necessary to increase the precision of the oscillation frequency of the carrier wave 1 local oscillator, and a high precision filter such as a crystal filter is required.

Furthermore, the oscillation frequency for synchronization needs to be highly accurate, which necessitates the use of large and expensive devices such as temperature-compensated crystal oscillators.

In contrast, in the present invention, since it is sufficient that the spread signal is included in the frequency range of the discriminator 39, it is not necessary to make the input signal of the discriminator 39 exactly match the intermediate frequency. Furthermore, since the despreading circuit 41 only has to despread a baseband signal that spreads over a 1.2 MHz band as shown in FIGS. 4(e) and (e'), a narrowband filter is used as a filter after despreading It is sufficient to use a low-pass filter of 100 MHz, which reduces the cost of the filter and oscillator.

Next, another embodiment of the present invention will be described with reference to FIGS. 6 and 7.

Figures 6 and 7 show the configurations of the transmitter and receiver when spread spectrum is performed using BPSK modulation.
BPSK modulation circuit 43 of the transmitter and integration circuit 44 of the receiver
The rest is the same as FIGS. 2 and 3.

The intermediate frequency signal output from the RF/IF circuit 38 is
Similar to the operation described above, the discriminator 39 extracts the frequency change of the signal as a voltage change, and the high-pass filter 40 cuts the low frequency component to remove interference waves mixed in the signal.

Here, the signal output from the discriminator 39 is a signal obtained by extracting the frequency change of the phase-modulated signal, so the integration circuit 44 integrates the frequency change to convert it into a phase component, and converts it into a phase component. The phase modulated signal is restored.

As described above, according to the above embodiment, by utilizing the fact that the bandwidth of the interference wave is much narrower than the bandwidth of the spread signal,
The narrowband interference waves mixed in the spread signal are extracted as low-frequency signals by the discriminator 39, and the low-frequency components are cut by the high-pass filter, thereby making it possible to reliably remove the interference waves.

Therefore, synchronization will not become impossible due to the influence of interference waves, and interference waves will not mix into the spread signal and increase the data error rate.

[Effects of the Invention] According to the present invention, by utilizing the fact that the bandwidth of interference waves is narrower than that of a spread signal, a discriminator extracts the interference waves as a low frequency component signal, and a high pass filter extracts the low frequency components. Since the component signal was removed,
Interference waves mixed in the spread signal can be reliably removed. In addition, since the received signal is converted to a signal in a lower frequency band by a discriminator, the configuration of the filter in the despreading circuit is simplified, and at the same time, there is no need to use a high-precision oscillator, etc., making the device more compact. can realize cost reduction.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the present invention, Part 2 is a block diagram of a transmitter according to an embodiment, Fig. 3 is a block diagram of a receiver according to an embodiment, and Fig. 4 is a diagram showing a transmitter and a receiver. Figure 5 is a diagram explaining the operation of the discriminator, Figures 6 and 7 are configuration diagrams of the transmitter and receiver of other embodiments, and Figure 8 is a waveform diagram of the signal spectrum of each part of the circuit. , a system configuration diagram of a spread spectrum communication system. FIG. 9 is a configuration diagram of a conventional synchronization circuit. 1.39...discriminator, 2.40...high pass filter. Figure 1 Patent applicant Toyota Industries Corporation Figure (a) 1hi+1))

Claims (1)

[Claims] 1) A receiving circuit that reproduces original information from a spread spectrum signal, comprising: a discriminator that outputs a signal corresponding to a frequency change of the received signal; and an output signal of the discriminator. An interference wave removal circuit characterized by comprising a high-pass filter that blocks low frequency components and passes high frequency components. 2) The interference wave removal circuit according to claim 1, wherein the spread signal is FSK modulated. 3) a discriminator that outputs a signal corresponding to a frequency change of a PSK-modulated spread signal; a high-pass filter that blocks low-frequency components of the output signal of the discriminator and passes high-frequency components; and the high-pass filter. 2. The interference wave removal circuit according to claim 1, further comprising an integrating circuit that integrates the output signal of.