JPH03236643A - Spread spectrum communication equipment - Google Patents

Abstract

PURPOSE:To realize a spread spectrum communication equipment able to eliminate efficiently a disturbing wave and to male communication with high reliability by providing a disturbing wave elimination signal processing circuit comprising a BPF and a mixer having a square characteristic to a post stage of a receiver. CONSTITUTION:A mixer having a square characteristic is used as a means simply eliminating an excess component efficiently generated from disturbance or the like in addition to a desired correlation peak after inverse spread of a spread spectrum signal at a receiver side. After an output of a correlation device of a spread spectrum signal having a disturbing wave is amplified by an amplifier 1 in an IF stage of the receiver, the signal is divided into two, the one is given directly to a double balance mixer(DBM) 2 and the other is led to other input of the DBM 2 through an attenuator 3 for signal level adjustment. Then the disturbing wave is eliminated through the BPF 4 and a desired correlation output is extracted with excellent S/N. Thus the communication with high reliability is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement for eliminating interference waves in a spread spectrum communication device that transmits and receives various information using spread spectrum.

[Summary of the Invention] In a spread spectrum communication device using a correlator in the IF stage of a receiver, interference waves or interference waves and a desired spread spectrum signal are processed in a stage before or after the correlator to eliminate interference. It is configured to remove waves or interference waves and extract a desired spread spectrum signal.

[Prior Art] Various communication methods have been researched and developed up to now, and a spread spectrum communication method is known as one method with high reliability.

In this spread spectrum communication method, on the transmitting side, primary modulation signals such as narrowband data and voice of baseband information are hopped at high speed to a plurality of wideband frequencies (FH method, Frequency Hopping).

Alternatively, the spectrum can be spread over a wide band using a high-speed pseudo-noise code (PN code) (DS method, D 1rec
t S aquanca) or a combination of these (FH/DS method), and transmits the wideband signal by spreading the spectrum, and on the receiving side, the wideband signal is despread into the original narrowband primary modulation signal using a correlator, and the information signal is It is something to be regenerated. The spread spectrum communication method has recently attracted attention as a highly reliable communication method because it is resistant to external interference and noise, and has high confidentiality.

Now, the most important point of this spread spectrum communication system is the configuration of the correlator on the receiving side. Currently, in wireless spread spectrum communication, the surface acoustic wave (SAW, 5U) correlator is considered to be the simplest and most reliable.
This is a device that uses rface acoustic wave.

SAW correlators generally include a correlator type (tapped delay line type) and a convolver type. here,
The correlator type has a simple structure and is generally efficient, but it is also greatly affected by the temperature coefficient of the substrate. Furthermore, although the convolver type is less susceptible to temperature changes, it generally has low efficiency. However, while the correlator type cannot be fixed in response to the above-mentioned variable PN code, the convolver type can freely change the type of PN code. Therefore, if the efficiency is at a practical level, a convolver type correlator is much easier to use.

In addition, in the spread spectrum method, the DS method mixes a high-speed PN code with baseband information using a single mixer to widen the band, so it can be implemented very easily, but it may cause problems such as interference, separation from other channels, or near and far problems. has one weakness.

The signal directly spread by the PN code is subjected to correlation processing with a reference signal by a correlator at the reception side IF stage, and when the PN codes match between the transmitter and the receiver, a correlation peak is output from the correlator. However, when the ratio of the total power of the spectrum of interference etc. to the total power of the spread spectrum signal approaches or exceeds the process gain of the correlator, it is difficult to use only the DS method even though it is a spread spectrum communication.

A communication error occurs.

FIGS. 7 and 8 illustrate problems with the conventional method. These figures show a DS system using a SAW convolver as a correlator, and the system modulation method is determined so that the convolution peak is output when the baseband information is #137 and the convolution peak is not output when the information is "O". Here is an example.

As shown in Figure 7, when there is no interference etc., the information
", the convolution peak is correctly demodulated according to the information "O". However, as shown in Figure 8, the ratio of the total power of the spectrum of interference etc. to the total power of the spread spectrum signal, or If it approaches or becomes larger, it becomes impossible to determine whether the information is ``1'' or 0, and an error occurs.

Therefore, it is necessary to remove these interference waves and the like through some other signal processing to improve the interference resistance.

One method of improvement is to remove the interference spectrum shown in Figure 8(a) with a filter, but since the location of the spectrum due to interference cannot be known in advance, a real-time programmable filter is required. .

However, at the current technological level, this filter is
Not enough has been developed yet.

[Problems to be Solved by the Invention] As mentioned above, it is not possible to determine in advance at which frequency position in the spectrum of the desired spread spectrum communication interference, etc. will appear, so no matter what frequency position the interference wave appears, It is desired to improve S/N deterioration due to interference.

[Object of the invention] Therefore, the present invention has been made in consideration of these points,
The purpose is to eliminate interference waves using a simple method and ensure highly reliable communications without the need for complex programmable filters.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a spread spectrum communication device in which, after despreading a spread spectrum signal on the receiving side, extra components generated from interference etc. in addition to the desired correlation peak are detected. There is a means for efficiently and conveniently removing .

As this means, the first invention uses a mixer having a square characteristic, and the second invention uses F
The third invention uses a configuration in which the center of the spectrum of the spread spectrum signal, which is susceptible to interference, is removed by a filter. Although the configurations of the first to third aspects of the invention are effective when used alone, they are even more effective when combined.

[Operation] According to the configuration of the first invention described above, the correlation output on which the interference wave is superimposed is squared, and the bandpass filter (B, P, F,
), the interference wave component is removed. This is because the interference wave components are squared and concentrated in the vicinity of DC and around twice the frequency of the original interference wave component. This is because by removing the components using the band pass filters (B, P, F,), the interference wave components can be removed and the desired spread spectrum signal component can be detected with a good S/N ratio.

Next, according to the FM modulation method of the reference signal, which is the configuration of the second invention, six frequencies of the reference signal input to the correlator are modulated by FM.
By providing the modulating means, a time lag always occurs with the frequency component of the interference wave, and it is possible to prevent the interference wave component from being output to the output of the correlator during correlation processing.

Furthermore, according to the filter single type that is the configuration of the third invention,
In the spectrum of a spread spectrum signal, the power is concentrated near the center, making it especially vulnerable to interference waves. By removing incoming interference wave components, a correlation output with a good S/N ratio can be obtained.

[Example] Each example of the present invention will be described below with reference to one drawing.

FIG. 1 shows the main parts (D, B, M,
, signal processing unit).

In Figure 1, 1 is an amplifier, 2 is a double-balanced
Mixers (D, B, M,) 3 are attenuators.

After the correlator output of the spread spectrum signal accompanied by interference waves is amplified by amplifier 1 at the IF stage of the receiver,
One is directly divided into two, B, and M.

2, and the other is led to another input of D, B, M, 2 after passing through an attenuator 3 for signal level adjustment.

After that, when it passes through a band pass filter (B, P, F,) 4, the interference waves are removed and the desired correlation output has a good S/N
It is taken out according to the ratio.

An example of signal processing is shown in Figures 2 and 3.
As shown in the figure.

Figure 2 (a) shows the frequency spectrum of the output of the receiver's correlator. In addition to the broad spectrum that is the correlation output of the desired spread spectrum signal, a sharp peak due to the interference wave appears in the part (a). ing.

Also, the waveform with respect to the time axis at this time is shown in Fig. 2(b).
In this waveform, (b) is the desired correlation peak, and the interference wave is observed as a large undulating wave (c) on the baseline.

In this way, since the correlation peak overlaps with the interference wave, the S/N ratio is poor and an error occurs when demodulating the baseband information by detecting the correlation peak.

However, if you use the signal processing circuit shown in Figure 1, B, M configuration, and a bandpass filter with the characteristics as shown in Figure 3(a), the signal processing circuit shown in Figure 3(b) can be obtained. A time axis waveform of correlation peak (d) with a good S/N ratio and suppressed interference waves can be obtained. The S/N ratio was improved because of D.
, B, M, 2, the correlation output on which the interference wave is superimposed is 2
B, P.

This is because only the frequency component of the correlation peak could be selected by F,4.

The embodiment described above is an effective method when there is only one interfering wave. In the embodiment shown in FIG. 4, when there are two or more interference waves, two or more interference waves can be removed by configuring D, B, M, and B, P, F in multiple stages. This is what I did. In the same figure, 5, 9.13 is an amplifier,
6, 10.14 is a double balance mixer, 7, 11.1
5 is an attenuator, 8. 12, 16 are B, P, F. If there are two or more interference waves, the first stage is B, M, 6, a correlation that includes two or more interference waves. When the output of the detector is squared, the frequency component of the frequency difference between the interference waves (this is called Δf as a representative) appears in the frequency band of the correlation peak (this is called the correlation peak information band). In this embodiment, interference waves can be removed regardless of the value of the frequency component Δf of the frequency difference between interference waves.

For this purpose, as shown in FIG. 4, D, B, M.

and B, P, and F in a multi-stage configuration.

The passband of F (ft is the lower cutoff frequency of B, P, F, fH is the upper cutoff frequency of B, P, F, and the n value of fLo or fH is the final stage of.

i in f and (i) represents the number of stages) is selected so that it satisfies the following relational expression.

n≧2... (2) fL〉O... (3) i"1@2t...n...
(4) Set each passband so that B, P, and F of each stage satisfy equations (1) to (4). Also, an attenuator? , 11 and 15 adjust the level of the input signal to each stage, B, and M, so that D, B, and M exhibit a square characteristic with respect to the input.

First, in the first stage B, P, F, and 8, Δf≦fL on the low frequency side.
■...Those with a frequency difference between interference waves that satisfy (5) are removed.

Δf≧fL■ ...The difference in frequency between interference waves that satisfies (6) is determined by the combination of B, M, 10, 14 and B, P, F, l 2゜16 in the second and subsequent stages. be removed. If this is set as in equation (1), the components of the frequency difference between the interference waves will be 2'-"XΔf>fu@ ・+・(7 )
This is because the condition of equation (3) is D at each stage.

It is necessary to cut the noise of the DC component after passing through B and M.

The fH of B, P, and F at each stage may be any value as long as it passes the correlation peak information band, but the fH at the final stage B,
It is better to use a SAW convolver (input center Frequency: 215M)k, Bandwidth: 23MHz), the center frequency 43
A correlator output with a frequency of 0 MHz and a bandwidth of 46 MHz is output. The stage after this correlator output consists of n=3 stages, B, M,
and B.P.

F, fo (3) = 30M) h, f L (D = 8
A multi-stage signal processing circuit with MHz frequency was fabricated.

With this configuration, interference waves can be removed no matter what value the frequency component Δf of the frequency difference between the interference waves is. Also, at this time, what is the difference between when only the correlator is used and when the signal processing circuit of this embodiment is loaded after the correlator?

The ratio of the total power (U) of interference, etc. entering the spread spectrum communication band to the total power of the desired spread spectrum signal: Expressed as D/U, the interference resistance characteristic of this implementation circuit is The D/U ratio was relatively improved by about 15 dB or more.

The above numerical values are examples of glue, and in short, multi-stage glue, B,
It is sufficient that the signal processing circuit is composed of M, B, P, and F.Also, any mixer that exhibits square characteristics can be used without using D, B, and M. good. B, P, F,
If it also satisfies the conditions (1) to (4) above,
Any filter will do.

In the embodiment shown in FIG. 5 above, the reference signal of the correlator is FM
This is an example corresponding to the second invention having a configuration for modulation. In the figure, 17 is a convolver, 18 is a mixer, and 19 is an F
20 is a PN coco generator, and 21 is a clock signal generator. Although the received signal contains interference waves at the IF stage of the receiver, it is input as a transmitted signal to the SAW convolver 17 used as a correlator.

On the other hand, the clock signal from the clock signal generator 21 is
The PN code is applied to the N-coco generator 20, which generates a PN code that is temporally inverted from the PN code of the received signal. At this time, a carrier subjected to FM modulation is generated using the FM modulation oscillator 19, and the mixer 1
At step 8, the above-mentioned PN code and multiplication unit output a reference signal, and input this reference signal to the convolver 17.

At this time, in the case of the SAW convolver 17, it was effective to arbitrarily shift the shift width of the FM modulation to the reciprocal of the time for the SAW to propagate through the convolution electrode = τg.

To give an example of specific numerical values, the center frequency of the convolver is 215MHz, and the convolution gate delay time is 9μ.
In the case of sec, when the deviation width of the reference signal (from the center frequency to one side) is 50 &, the speed of the deviation is the modulated wave: 20 &, compared to when the reference signal is not FM modulated, The anti-jamming characteristics were improved by about 10 dB or more.

The above-mentioned value is just an example; in short, the essence of the second invention is that the center frequency of the reference signal is FM modulated to prevent it from colliding with the frequency component of the interfering wave. An effect was obtained if the deviation width was within τg.

Further, any FM modulation method may be used, and any method is effective as long as the deviation width can be set within l/τg and a modulated wave is added.

Next, the embodiment shown in FIG. 6 corresponds to the third invention, in which the center of the spectrum of the spread spectrum signal, which is particularly susceptible to interference, is removed by a fixed notch filter. In the same figure.

22 is a fixed notch filter, 23 is an amplifier, and 24 is S.
It is an AW convolver. D is a spread spectrum method.
The S method is a simple method, but it has the disadvantage that power is concentrated near the center of the spectrum of the spread spectrum signal, and when interference waves come to the center, it has poor interference resistance due to the characteristics of the convolver.

In this embodiment, only the vicinity of the center of the spectrum of the received signal of the IF stage, which has been simply spread spectrum, is extracted in advance by the notch filter 22, passed through the amplifier 23, and then inputted to the convolver 24 as the received signal. Doing so had the drawbacks mentioned above. We were able to improve the drawback that the spread spectrum signal was particularly vulnerable to interference waves that entered near the center of the frequency spectrum.

To give a specific example of the numerical values used in this example, a DS with a code rate of 14M and a PN code of 127 chips.
In the case of this method, if a convolver with a center frequency of 215 M and a convolution gate delay time of 9 μsec is used, the notch filter has a center frequency of 215 M and a convolver of 3 dB.
Zone approximately 1.5M cells.

A center attenuation of approximately 38 dB was used. The frequency spectrum of a spread spectrum signal is approximately 28MHz.

Even if about 1.5 MHz is subtracted by the notch filter, the correlation peak deteriorates only slightly.

We were able to effectively improve the weak area in the center caused by interference waves.

The above numerical example is just one example, and in short, inserting a notch filter to attenuate the center part of the frequency spectrum of a spread spectrum signal is an effective method for improving interference resistance. As such, any of LCR circuits, stripline type filters, digital filters, and SAW filters were effective.

Furthermore, although not shown in the drawings, the B, M, and configuration methods shown in the embodiments of FIG. 1 or FIG. 4, the method of FM modulating the reference signal of the correlator shown in FIG. By combining two of each of the single notch filter methods shown in FIG. 6, or by using all three methods, the anti-interference performance was significantly improved compared to the single method.

[Effects of the Invention] As explained above, according to the present invention, in a spread spectrum communication device, interference waves can be efficiently removed by applying a simple method to the receiver, and highly reliable communication can be achieved. becomes possible.

In particular, this interference removal effect is extremely effective in practical use when communication is performed using weak radio waves.

Furthermore, the interference wave removal method according to the present invention can be widely applied as an interference wave removal method not only in spread spectrum communication but also when a wide band information band receives a narrow band interference wave.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of an interference wave removal signal processing circuit having a one-stage, B, and M configuration according to the present invention. Figure 2 is a correlation output frequency spectrum diagram and time waveform diagram before applying the signal processing shown in Figure 1, and Figure 3 is a frequency spectrum of the correlation output after applying the signal processing shown in Figure 1. Figure and time waveform diagram, Figure 4 is a multi-stage according to the present invention,
FIG. 5 is a block diagram of an embodiment of an interference wave cancellation signal processing circuit having the configuration B, M, and FIG. 7 is a block diagram of an embodiment of an interference removal signal processing circuit using a one-type notch filter according to the present invention, FIG. 7 is a correlation output waveform diagram when there is no interference wave due to the conventional method, and FIG. FIG. 3 is a waveform diagram showing correlation output deterioration when

Claims (10)

[Claims] (1) In a spread spectrum communication device, a signal processing circuit for removing interference waves consisting of a mixer having a square characteristic and a bandpass filter, into which the output of the correlator is input, is placed after the correlator of the receiver constituting the device. A spread spectrum communication device characterized by being provided with. (2) The spectrum according to claim 1, wherein the signal processing circuit including the mixer and the bandpass filter is provided in multiple stages, so that interference waves entering the spread spectrum communication band can be efficiently removed. Diffusion communication device. (3) A spread spectrum communication device characterized in that interference waves are removed by providing means for FM modulating a reference signal applied to a correlator of a receiver constituting the device. . (4) A spread spectrum communication device is characterized in that a filter that removes the center part of the frequency spectrum of the received signal is provided at the front stage of the input side of the correlator of the receiver constituting the device to improve interference resistance. Spread spectrum communication equipment. (5) In a spread spectrum communication device, a signal processing for removing interference waves consisting of a mixer having a square characteristic and a bandpass filter to which the output of the correlator is input, in the subsequent stage of the correlator of the receiver constituting the device. A spread spectrum communication device comprising: a circuit; and means for FM modulating a reference signal applied to the correlator. (6) In a spread spectrum communication device, a signal processing for removing interference waves consisting of a mixer having a square characteristic and a bandpass filter to which the output of the correlator is input, at a stage subsequent to the correlator of the receiver constituting the device. 1. A spread spectrum communication device, comprising: a circuit; and a filter for removing a central part of a frequency spectrum of a received signal at a stage before the input side of the correlator. (7) In a spread spectrum communication device, a signal processing circuit for removing interference waves comprising a mixer having a square characteristic and a bandpass filter to which the output of the correlator is input, which is disposed downstream of the receiver constituting the device; Spread spectrum communication characterized by comprising means for FM modulating a reference signal applied to the correlator, and a filter for removing the center part of the frequency spectrum of the received signal at a stage before the input side of the correlator. Device. (8) In a spread spectrum communication device, a signal processing for removing interference waves consisting of a mixer having a square characteristic and a bandpass filter to which the output of the correlator is input, in a stage subsequent to the correlator of the receiver constituting the device. A spread spectrum communication device, characterized in that the circuit is provided in multiple stages and includes means for FM modulating a reference signal applied to the correlator. (9) In a spread spectrum communication device, a signal processing for removing interference waves consisting of a mixer having a square characteristic and a bandpass filter to which the output of the correlator is input, in a stage subsequent to the correlator of the receiver constituting the device. A spread spectrum communication device characterized in that the circuit is provided in multiple stages, and a filter for removing the center part of the frequency spectrum of the received signal is provided at a stage before the input side of the correlator. (10) In a spread spectrum communication device, the output of the correlator is inputted to the subsequent stage of the receiver that constitutes the device.
A signal processing circuit for removing interference waves consisting of a mixer having a multiplicative characteristic and a bandpass filter is provided in multiple stages, and means for FM modulating a reference signal applied to the correlator, and a stage before the input side of the correlator, A spread spectrum communication device comprising: a filter that removes the center part of the frequency spectrum of a received signal.