JPH04192829A - Demodulating equipment for spread spectrum signal - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the frequency utilization efficiency by correcting an oscillation frequency of a local oscillator to a prescribed frequency, based on a center frequency of a band pass filter which outputs a signal exceeding a prescribed value. CONSTITUTION:At the time of demodulating a spread spectrum signal, a signal of a prescribed frequency is extracted from a reverse diffusion signal or a signal obtained by converting the reverse-spread signal to a necessary frequency by plural band pass filters 21, 25 and 28, F1-F101 whose center frequencies are different from each other, and also, whose passing band width is equal to each other. Subsequently, synchronization of the PN sequence between transmission and reception which detects a fact that the maximum value of an output signal level of each band pass filter exceeds a prescribed value is taken, and also, based on the center frequency of the band pass filter which outputs the signal exceeding this prescribed value, an oscillation frequency of a local oscillator 17 provided on a demodulating equipment W is corrected to a prescribed frequency. in such a way, original information data can be obtained without avoiding the frequency utilization efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a demodulator for a spread spectrum signal, and in particular to a demodulator for a spread spectrum signal, in which a change in the carrier frequency of a received signal occurs due to the Doubler effect or frequency fluctuation of a transmitting oscillator. The present invention relates to a spread spectrum signal demodulation device that can compensate for this and obtain information data to be accurately demodulated even when the local oscillation frequency on the receiving side fluctuates.

(Prior art) The spread spectrum overconfidence method spreads the information signal to be transmitted over a relatively wide frequency band and transmits it, so the transmission power per unit frequency is small and there is almost no interference with other communications. It also has many features such as being less susceptible to external noise and having excellent confidentiality.

The method shown in FIG. 4 is a common method for performing spread spectrum communication via a wireless communication channel.

That is, in this communication method, on the transmitting side T, the oscillator l uses the frequency t.
At the same time as generating a carrier wave of After the information data D is spectrum-spread by multiplicative modulation, it is sent to the receiving side R via a wireless communication channel.

On the other hand, on the receiving side R, the local oscillator 4 generates a local signal of frequency fL, and the PN sequence generator 5 generates the same PN sequence as that used at the transmitting side T, which is sent from the transmitting side T. After converting the spread spectrum signal into an intermediate frequency signal of frequency f@-ft (hereinafter referred to as intermediate frequency r+) by frequency-mixing the spread spectrum signal and the local signal in the mixer 6, the data demodulator 7 and a delay loop circuit (hereinafter referred to as DLL) 8, respectively. The data demodulation unit 7 despreads the intermediate frequency signal using the PN sequence using the multiplier 9, and uses the despread signal to obtain a center frequency of f with a bandwidth based on the transmission speed of the information data D. After extracting the signal component of − with the bandpass filter IO, the extracted signal is envelope-detected with the wave detector 11, and the original information data D is demodulated by removing the carrier component of the frequency f1. Also, the receiving side R has a level detector 12.
The absolute value of the information data is determined using The PN sequence generated by the PN sequence generator 5 is shifted by 1 bit until the PN sequence exceeds 1, and the PN sequences used on the transmitting side T and the receiving side R are synchronized with each other. Further, after synchronizing the PN sequence of the transmitter T and the PN sequence of the receiver R using this method, the receiver R uses the DDL 8 to maintain this synchronization state, e.g. by the PN sequence generator 5. Adjust the shift clock frequency of the PN series generated by the PN sequence.

However, in the above-described demodulation method, when the transmitting side, the receiving side, or both move at high speed, the frequency of the received signal changes due to the Doppler effect, and the frequency of the signal obtained by despreading the received signal with a PN sequence is in the band. There was a problem in that the original information data could not be demodulated as a result of being out of the pass band of the pass filter. Similar problems also occur when the frequency of the carrier wave generated on the transmitting side or the local signal generated on the receiving side fluctuates, especially when the transmission speed of information data is slow and the frequency of the carrier wave varies. This was noticeable when the amount was extremely high. Furthermore, as a way to solve this problem, it is conceivable to widen the passband of the bandpass filter by taking into account the frequency fluctuation of the carrier wave due to the Dobbler effect, etc., but this is not practical because the S/N deteriorates accordingly. .

Conventionally, as a method for solving this problem, as shown in FIG. 5, the transmitting side T transmits a continuous wave CW separate from a carrier wave for transmitting information data.

On the other hand, on the receiving side R, a Doffbra detector 13 is provided to measure the reception frequency of this continuous wave CW, and the frequency of the local signal generated by the local oscillator 4 is corrected based on the difference between the observed frequency and the specified frequency. The frequency of the signal despread using the PN sequence is always set to the center frequency f+ of the bandpass filter.

However, the above-mentioned spread spectrum signal communication method requires a transmitter and receiver for measuring the influence of the Doffbra effect in addition to the transmitter and receiver for communicating information data, making the equipment extremely complicated and expensive. In addition to this, there was also the drawback that frequency utilization efficiency deteriorated.

(Object of the Invention) The present invention has been made in order to solve the problems of the spread spectrum communication system when accompanied by the above-mentioned Dobbler effect or fluctuations in the carrier frequency on the transmitting side, It is an object of the present invention to provide a demodulating device for a spread spectrum signal, which can obtain original information data without causing interference and without detracting from frequency utilization efficiency.

(Summary of the Invention) In order to achieve the above object, the present invention takes the following measures.

That is, in a device that despreads a received signal using the same PN sequence as described above on the transmitting side and demodulates a spread spectrum signal superimposed on a carrier wave, a frequency conversion means is provided, and a plurality of devices having different center frequencies and the same passband width are provided. A signal of a predetermined frequency is extracted from the despread signal or a signal obtained by converting this signal to a desired frequency using a band pass filter, and it is detected that the maximum value of the output signal level of each of the band pass filters exceeds a predetermined value. to synchronize the PN series between transmitter and receiver, and correct the oscillation frequency of the local oscillator provided in the frequency conversion means to a predetermined frequency based on the center frequency of the bandpass filter that outputs the signal exceeding the predetermined value. Configure it to do so.

(Example) Hereinafter, the present invention will be described in detail based on the illustrated example.

FIG. 1 is a block diagram showing a demodulating device for a spread spectrum signal according to an embodiment of the present invention.

Here, in order to facilitate understanding of the operation, the transmission side will be included in the explanation.

On the same plane, T is the transmitting side, and the frequency is 1°575[
It comprises an oscillator 1 that generates a carrier wave of GHzl, a PN sequence generator with a Hibtorate of 1.023 [a PN sequence generator that generates a IO stage Gold code of MHzl], and a multiplier i
12 using bib tray) 50 [b I t/s
After modulating the carrier wave with the information data D to be transmitted and spreading the spectrum of the data D by multiply modulating the modulated signal with the Gold code using the multiplier 3, the non-wA communication channel is spread. The configuration is such that the signal is sent to the demodulator w via the demodulator w.

On the other hand, W is a demodulator according to the present invention, which has a frequency of 1.
VCXOI 5 for generating a 10th-cal signal of 512 [GHzl], a PN sequence generator 16 for generating a Gold code identical to the transmitted mT, and a frequency 62. 545 [
Local oscillation W that generates the 20th-cal signal of MHz
117, a signal extracted from a spread spectrum signal with a carrier frequency of 1,575 GHz sent from the transmitting side T via a low noise amplifier 18 and an image removal filter +9, and the 10th-cal signal. After frequency mixing with the mixer 20, the center frequency becomes 63 [Ml(Z
], the spread spectrum signal is converted into an intermediate frequency signal with a frequency of 63[M)+2] using a bandpass filter 21 with a passband width of IO[MH2], and the intermediate frequency signal is passed through an amplifier 22. The data is supplied to the input terminals of the data demodulation section 23 and the DLL 8 via the data demodulator 23 and the DLL 8, respectively. Data demodulation section 23
uses a multiplier 24 to despread the first intermediate frequency signal with the Gold code, and passes the despread signal to a bandpass filter 25 with a center frequency of 63 [M)IZI and a passband width of 2 [MH2]. After frequency-mixing the signal generated through the amplifier 26 and the 20th-cal signal in a mixer 27, a bandpass filter 28 with a center frequency of 455 [KHz] and a passband width of IOQ [Hz] is used. The despread signal is converted into a second intermediate frequency signal having a frequency of 455 KHz, and the second intermediate frequency signal is connected to an amplifier 29 and a detector 30 so as to demodulate the original information data. . The DLL 8 maintains the synchronization state between the Gold code of the transmitting side T and the Gold code of the PN sequence generator 8, as in the conventional one described above.
The connection is made so as to adjust the shift clock frequency of the Gold code generated by the sequence generator 8. Also, demodulator WW
supplies the output signal of the mixer 27 to the synchronization acquisition section 31, and sends the control signal from the synchronization acquisition section 31 to the input terminal of the VCXOI 5 via the correction circuit 32.
The detection signals from the PN sequence generator 6 are connected to be supplied to the input terminals of the PN sequence generator 6 via the timing generating circuit 33, respectively. The synchronization acquisition unit 31 has a passband width of 100[H4F and a center frequency of 450,450, 1. 450. 2,
..., 459.9.46o [KHzl] band pass filters F + to F +m+ are provided, and the output signal of the mixer 27 is passed through the band pass filters F1 to F
The control signal and the detection signal are outputted by supplying them to the determination unit 34 via the respective signals 1111 and 1111.

The demodulator tW configured as described above operates as follows.

That is, in the demodulator WIW, the synchronization acquisition unit 3I converts the frequency from the second intermediate frequency signal to 450.450.1°, 450.2, .
..., 459.9.460 [KHz] signal is extracted, and the determination unit 34 detects whether or not the signal level exceeds a predetermined value for each frequency, and the detection signal is continued until the level exceeds the predetermined value. The gold code output and generated by the PN sequence generator 16 is 1 for each bit period of the information data.
The bits/digits are set to synchronize the Gold codes of the transmitter T and the demodulator w with each other. Further, the determination unit 34 determines the bandpass filter that outputs a signal exceeding the predetermined value, and supplies the value of the center frequency of that filter to the correction circuit 32 as a control signal, and the second The frequency of the intermediate frequency signal is always 455 [KHzl]
Adjust the oscillation frequency of vcX015 so that

Therefore, according to this demodulator W, the reception frequency of the spread spectrum signal changes due to the influence of the Dobppler effect, and the frequency of the second intermediate frequency signal is changed to the frequency of the second intermediate frequency signal by the bandpass filter 28.
Even if it is out of the passband, the deviation of the receiving frequency is ±5.
[If KHzl, band pass filters F1 to F
Since the maximum value of the despread signal converted to the second intermediate frequency can be detected from either output end of the Ie+, the Gold codes on the transmitting side and the receiving side can always be synchronized with each other, and the bandpass The frequency of the despread signal converted to the second intermediate frequency without widening the passband of the filter 28 is always the center frequency 455 of the bandpass filter 28.
Since the oscillation frequency of the VCX015 is controlled to be [KHz], the original information data can be demodulated without deteriorating the S/N.

FIG. 2 shows a modified embodiment of the present invention, in which the passband width is 100 [Hz] and the center frequency is 450.450.1
．． 450. 2,...,459,9.460 [K
Hzl bandpass filter F to FN@1, frequency 62. Local oscillator 35 that generates the 30th-cal signal of 545 [MH2], effective value generation circuits R, to R1
111, mixers 36 and 37, and a phase shifter 38 are provided in the synchronization acquisition section 31 shown in FIG. The output signal of the amplifier 26 is set to a frequency of 455 [KH2
] is inputted in parallel to the bandpass filters F1 to FI@I, and the output signal of the amplifier 26 and the phase shifter 38 are used to convert the 30th intermediate frequency signal into the third intermediate frequency signal. A mixer 37 mixes the frequency of the signal with the signal whose phase is delayed by π/2 [rad] and converts the third intermediate frequency signal into a signal whose phase is delayed by π/2 [rad]. Input in parallel to F11@1. Further, using the effective value generation circuit R1, the output signals of the bandpass filters F and Fl+ are respectively squared and added together, and then the square root is determined and supplied to the determination section 34, and the effective value is generated in the same manner. Circuit R2 to RI
2 output signals of a predetermined bandpass filter for each I+
The control signal and the detection signal are output by multiplying the signals and adding them to each other, and then calculating the square root and supplying the square root to the determination unit 34.

According to this demodulator w, after obtaining the real term component and the imaginary term component of the output signal of the amplifier 26, that is, the signal obtained by despreading the first intermediate frequency signal, the frequency of each component is set to 45.
0.450.1.450°2,..., 459.9.4
A signal of 60 [KHz] is extracted, the effective value of the signal is determined for each frequency, and the determination unit 34 detects whether or not the effective value exceeds a predetermined value. The determination unit 34 outputs a detection signal up to the predetermined value, and the determination unit 34 supplies the correction circuit 32 with the value of the center frequency of the bandpass filter that supplies the signal to the effective value generation circuit that outputs the signal exceeding the predetermined value as a control signal, The frequency of the second intermediate frequency signal is always equal to the center frequency 455 [K
Since the oscillation frequency of the VCXOI 5 is controlled so that, for example, in the embodiment shown in FIG.
By being different from π [rad] to 1, it is originally noindo!
It is possible to keep the level of the signal input to the determination unit 34 constant without reducing the level of the signal to be output from the chair filter Fl to zero, that is, regardless of the phase difference between the 30th-cal signal and the despread signal. This allows the determination result of the determination unit 34 to be accurate.

In the above embodiment, the passband width is 100 [H
zl and the center frequency is 450.450.1°4502,・
..., a bandpass filter of 459.9.460 [KHz] or a set of such bandpass filters is provided in the synchronization acquisition section, but the passband width, center frequency, and synchronization of each/indopass filter are The number of bandpass filters provided in the capture section does not need to be limited to this. That is, the center frequency of the signal supplied to the synchronization acquisition section is f, [Hzl], and the maximum frequency deviation of the signal caused by the influence of the Doffbra effect, etc. is 1. i [Hzl], and when the bit rate of the information data to be transmitted is rr [bps], the passband width of each bandpass filter provided in the synchronization acquisition section is B [Hzl
can be calculated from 2B≧2fr[Hzl, and if the stepping frequency rs [H2] is calculated from the formula Off, ≦B, then the center frequency of the pantone square can be calculated as h rx
fa+fw-f4+ fs, f, -1d+2fa
, fx fd+3fa,..., fw+fa-2
fs, fx+fn-fa, rx+ra[Hzl
If so, the synchronization acquisition section can always output the detection signal and the control signal even if the center frequency of the signal supplied to the synchronization acquisition section changes due to the influence of the Doffbra effect or the like.

Furthermore, in the above embodiment, after converting the received signal to the first intermediate frequency signal, it is despread using the same Gold code as that on the transmitting side, and the signal further converted to the second intermediate frequency signal is input to the synchronization acquisition section. In order to at least supply a detection signal for synchronizing the Gold code between transmission and reception to the PN sequence generator via the timing generation circuit, and to correct the oscillation frequency of the oscillator used when converting into the first intermediate frequency signal. However, the present invention is not limited to this. For example, as shown in FIG. 3, a signal obtained by despreading the received signal is input to the synchronization acquisition section 31, and the detected signal is supplied to the PN sequence generator 16 via the timing generation circuit 33, and the mixer 20 is used. and a mixer 39 when converting the despread signal to a base Indian signal.
The band pass filter 28 and DLL 8
Alternatively, after converting the despread signal into a baseband signal using a mixer 41 and a local oscillator 42, a predetermined number n of bandpass filters F1 to F may be corrected. . may be input in parallel. That is, the present invention provides a signal despread by providing a predetermined number of frequency conversion means before or after the despreading means, or both, or the output of any one of the frequency conversion means provided after the despreading means. The signal is input to the synchronization acquisition section, the detection signal is supplied to the PN sequence generator via the timing generation circuit, and one of the oscillation frequencies of the oscillator used in the frequency conversion means provided after the despreading means is input. It is obvious that the present invention need not be limited to the above embodiments as long as a control signal for correction is output.

Furthermore, it is obvious that the synchronization acquisition section of the present invention may be realized by a digital circuit such as a digital signal processor (DSP).

(Effects of the Invention) As described above, the present invention, when demodulating a spread spectrum signal, uses a plurality of bandpass filters having different center frequencies and the same passband width to demodulate the despread signal,
Alternatively, a signal of a predetermined frequency is extracted from a signal obtained by converting a despread signal to a desired frequency, and the maximum value of the output signal level of each of the bandpass filters is detected to exceed a predetermined value, and the PN sequence between transmitting and receiving is detected. In addition to synchronizing, the oscillation frequency of the local oscillator provided in the frequency conversion means is corrected to a predetermined frequency based on the center frequency of the bandpass filter that outputs the signal exceeding the predetermined value, thereby eliminating the Doppler effect, etc. Even if the receiving frequency changes due to the influence of It is effective in providing the following.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIGS. 2 and 3 are diagrams showing modified embodiments of the present invention, and FIGS. 4 and 5 are diagrams explaining a conventional spread spectrum communication method. It is. W... Demodulator, 21.25.28 and Fl to F
+@I...bandpass filter, 15...vcx
o, 16...PN sequence generator, +7...local oscillator, 18.22.26 and 29...amplifier, 19...
Image removal filters, 20 and 27...mixers,
23...Data demodulation unit, 8...DLL, 24...
Multiplier, 3o/detector, 31... synchronization acquisition section, 32 river correction circuit, 33... timing generation circuit, 34... determination section. Patent applicant: Toyo Tsushinki Co., Ltd.

Claims (2)

[Claims] (1) In a device that despreads a received signal using the same PN sequence as that on the transmitting side and demodulates a spread spectrum signal superimposed on a carrier wave, a predetermined number of frequencies are used before or after the despreading means, or in both. A conversion means is provided, and a predetermined signal is generated from the signal despread by a plurality of bandpass filters having different center frequencies and the same passband width, or a signal generated by a frequency conversion means provided after the despreading means. The frequency signal is extracted, and the maximum value of the output signal level of any one of the bandpass filters is detected to exceed a predetermined value, and the PN sequence between transmitting and receiving is synchronized, and the signal exceeding the predetermined value is detected. A demodulating device for a spread spectrum signal, characterized in that the oscillation frequency of a local oscillator provided in the frequency conversion means is corrected to a predetermined frequency based on the center frequency of a bandpass filter that outputs the signal. (2) In a device that despreads a received signal using the same PN sequence as that on the transmitting side and demodulates the spread spectrum signal superimposed on a carrier wave, a predetermined number of frequencies are used before or after the despreading means, or in both. A conversion means is provided, and the despread signal or the signal generated by the frequency conversion means provided after the despreading means is branched into two, and each of the signals is divided into two parts whose phases are different from each other by π/2 [rad]. 1 signal and a second signal, two sets of a plurality of band pass filters having mutually different center frequencies and equal pass band widths are provided, and each of the band pass filters of one set generates a signal from the first signal. extracting a signal of a predetermined frequency, extracting a signal of a predetermined frequency from the second signal using each of the other set of bandpass filters, and squaring the output signals of the bandpass filters having the same center frequency. After adding each other, an effective value is generated by means of calculating the square root, and by detecting that the maximum value of the effective value exceeds a predetermined value, synchronization of the PN sequence between transmitting and receiving is performed, and the effective value exceeding the predetermined value is detected. A demodulating device for a spread spectrum signal, characterized in that the oscillation frequency of a local oscillator provided in the frequency conversion means is corrected to a predetermined frequency based on the center frequency of a bandpass filter that supplies the signal to the means for generating the signal.