JP2000324015A - Spread spectrum modulation / demodulation method, apparatus therefor, and spread code generator - Google Patents

Abstract

(57) [Problem] To accurately detect an autocorrelation peak while preventing the influence of ringing occurring in a PN code. SOLUTION: A PN code generator 10 which does not have two or more detected autocorrelation peaks up to a predetermined delay amount of a delay circuit 17 set according to a chip rate and a propagation distance between transmission and reception. , And by performing spread spectrum modulation in the double balanced modulator 13 using this spreading code and despreading in the correlator 18, the peaks of the second and third autocorrelation due to ringing are detected by the detection unit 19. Prevent it from appearing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum modulation / demodulation method for transmitting a transmission signal after performing phase modulation with a spread code and obtaining a received signal based on the signal, a device and a spread code generator.

[0002]

2. Related Background Art Conventionally, in this type of spread spectrum modulation / demodulation apparatus, a pseudo noise signal (hereinafter, referred to as a "PN code") is output from a PN code generator 10 on a transmission side as shown in FIG. , The PN code of the oscillator 12
Is modulated by the double balanced modulator 13 and up-converted by the high-frequency circuit 14, and then the transmission antenna 1
Send from 5.

On the receiving side, the transmission signal is reflected by the target, received by the reception antenna 16 as a reception signal, down-converted by the high-frequency circuit 14, and then delayed by the delay circuit 17 The autocorrelation was detected by the correlator 18 based on the code. The autocorrelation detected in this manner has a peak a and a flat side lobe b as shown in the ideal autocorrelation characteristic in FIG. 8, and a radar apparatus is generally realized by using the above spread spectrum modem. Then, the detection unit 1
In step 9, the peak a of the autocorrelation was measured to detect the target.

Codes having such autocorrelation include, for example, M-sequence codes. The autocorrelation of the M sequence has only one peak when the delay is “0”, and the interval between the peaks is one code length. When a radar device is realized using the M-sequence PN code, as shown in the figure, it is slightly higher than the side lobe level (for example, about 3 dB higher).
The threshold Th was set, and the peak of the correlation was detected.

[0005]

However, in the above device, the PN code of the M sequence actually generated from the PN code generator is used.
Symbols indicate output signals (eg, 0 V,
The signal of + 5V level is converted to a predetermined voltage (for example, + aV, -b) by using a level conversion circuit (not shown) in the generator.
V), and outputs it to the double balanced modulator.
The output PN code often has ringing c as shown in FIG. 9 depending on the characteristics of the level conversion circuit.
Using this PN code with ringing, spread spectrum modulation is performed by a double balanced modulator, and the autocorrelation is detected by a correlator for one target under the same conditions as in FIG. As shown in FIG. 10, there are a main peak a and some multiple peaks d. When the secondary peak d exceeds the threshold Th, the detection unit detects a plurality of peaks for one target, and regards a signal exceeding this threshold as a correlation peak, and There is a problem in that identification causes a false alarm.

In order to avoid this, it is possible to raise the threshold value. However, in this case, the spreading gain of the PN code is reduced, and there is a possibility that the target that should be detected cannot be detected. As a result, there is a problem in that the target discrimination ability is degraded, the radar dynamic range is narrowed, and the inherent characteristics of the M-sequence cannot be used.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a spread spectrum modulation / demodulation method capable of accurately detecting an autocorrelation peak while preventing the influence of ringing generated in a PN code, a device therefor, and a spread code generator. The purpose is to provide.

[0008]

In order to achieve the above object, according to the present invention, a transmission signal is subjected to spread spectrum modulation using a spread code and transmitted, and the received radio wave is despread by a spread code to obtain a correlation. In the spread spectrum modulation / demodulation method for obtaining a received signal by detecting, between the main peak of the detected autocorrelation and a predetermined delay amount, the spreading code in which there is no multiple peak of the autocorrelation is set, and the spread code is used. A spread spectrum modulation / demodulation method for performing spread spectrum modulation and despreading of a signal is provided.

Further, according to the present invention, a transmission signal is subjected to spread spectrum modulation using a spreading code and transmitted.
In a spread spectrum modulation / demodulation device that performs despreading on a fetched radio wave by a spreading code and detects a correlation to obtain a received signal, a secondary peak of the autocorrelation is detected from a main peak of the detected autocorrelation to a predetermined delay amount. And a spread spectrum modulation / demodulation device including a spread code generator for generating the spread code in which there is no.

Further, according to the present invention, a spread code generator for generating spread codes for performing spread spectrum modulation or detecting autocorrelation of a captured signal has a predetermined delay from a main peak of detected autocorrelation. Up to the amount, comprising a generating means for generating the spreading code in which the secondary peak of the autocorrelation does not exist, the generating means has a tap setting unit for setting a tap for generating the spreading code , A spreading code generator for generating the spreading code by a combination of logical combinations based on the set taps.

That is, a spreading code (PN) having no autocorrelation secondary peaks up to the predetermined delay amount set in accordance with a chip rate and a required transmission / reception propagation distance.
) Is generated from a spread code generator and subjected to spread spectrum modulation and despreading using the spread code, thereby preventing the appearance of second and third autocorrelation secondary peaks due to ringing.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spread spectrum modulation / demodulation device using a spread spectrum modulation / demodulation method according to the present invention, and a PN.
One embodiment of the code generator will be described with reference to FIGS. In the following drawings, the same components as those in FIG. 7 are denoted by the same reference numerals for convenience of explanation.

FIG. 1 is a block diagram showing the configuration of a first embodiment of a spread spectrum modulation / demodulation device and a PN code generator according to the present invention. In the first embodiment shown in FIG. 1, a PN code constituting a spreading code of the present invention composed of a predetermined code string in which ringing does not occur is generated by a PN code generator 20 constituting a spreading code generator of the present invention. Yes, the storage device 21 of the PN code generator constituting the capturing means of the present invention
For example, time-base data of, for example, an M-sequence PN code is stored, and the data sequence is read out to a high-speed digital / analog converter (hereinafter, referred to as a “D / A converter”) 22 that constitutes the conversion means of the present invention. Then, the PN code data without ringing is reproduced as an analog waveform and modulated by the double balanced modulator 13, and the PN code data is delayed by the delay circuit 17. Detected.

As described above, in the present embodiment, the PN code held as digital data is converted into analog data in which ringing does not occur, and the autocorrelation is detected. Therefore, the detected autocorrelation is as shown in FIG. That is, one peak is detected for one target, and the peak of the autocorrelation can be accurately detected, so that the identification accuracy for the target can be improved.

By the way, in a radar device mounted on a vehicle, it is necessary to be able to identify a plurality of targets in a certain area, and for that purpose, for example, it is sometimes desired to increase the distance resolution of each target. In this case, a high-speed PN code having a chip rate of, for example, 40 MHz is required as the PN code used for spread spectrum modulation. With the increase in the speed of the PN code, the PN code generator of the first embodiment also requires a D / A converter that performs conversion processing at a high speed (for example, about 10 times the chip rate). However, such a high-speed D / A converter has a high cost, and is not suitable for use in a radar device mounted on a vehicle whose production cost can be reduced.

In general, an M-sequence generator (PN code generator) having shift registers of the same number of stages generates M
It is known that different types of M-sequences can be generated by combining a plurality of stages of logical combinations, although the code lengths of the sequences are the same. For example, considering a case where an M-sequence generator is configured using an eight-stage shift register, a code length of 2
An M sequence of 55 chips is generated. In this case, a combination of logical combinations by a plurality of stages of shift registers is, for example, a code generated using taps [8, 4, 3, 2] and a code generated using taps [8, 6, 5, 1]. And
The types are different. That is, the generated code is a code having different patterns of “1” and “0” forming the code sequence depending on the set tap.

Therefore, the inventor has determined the autocorrelation of a plurality of codes obtained in this manner. as a result,
Similarly, in a code having ringing, FIG.
As shown in FIG. 3, it has been found that the delay amounts at which the multiple peaks d, e, and f due to the ringing appear differ. FIG. 2 shows the case of a code generated using taps [8, 4, 3, 2], and FIG. 3 shows the case of a code generated using taps [8, 6, 5, 1]. .

In the above-mentioned radar apparatus of the spread spectrum system of the 76 GHz band, it is sufficient to detect the auto-correlation in the delay amount of 31 chips, for example, in order to measure the distance 100 m ahead, and to input the signal to the correlator. Receiver P
For the N code, the distance can be measured by sequentially changing the delay amount with a delay circuit from a delay amount of zero with respect to the transmission side PN code to a delay amount of 31 chips.

Therefore, in the present invention, by setting an appropriate M-sequence, a PN code capable of avoiding the influence of a plurality of peaks due to ringing is generated, and a characteristic as an ideal M-sequence is derived. . That is, as shown in the configuration of the second embodiment of the PN code generator in FIG. 4, the M-sequence includes a plurality of n-stage shift registers D1 to Dn constituting the generating means according to the present invention, and the states of the plurality of stages. Generated by the logic circuits E1 to Em constituting the above-mentioned generating means for feeding back the logical connection of the shift register to the input of the shift register, and the tap setting unit 23 according to the present invention for setting taps for determining a combination of logical connections by the shift register. Is done. As described above, the radar device mounted on the vehicle sequentially changes the delay amount up to 31 chips, so that the tap setting unit 23 includes, for example, the tap [8, 6, 5, 5].
1], and generates and outputs an appropriate PN code from the shift register.

The overall configuration of the radar device according to the present invention is as follows.
7 is the same as that of FIG. 7, and the PN code generator having the configuration of the present embodiment is used as the PN code generator 10 in the figure, so that the reception side transmits the reception signal based on the transmission signal from the transmission side to the high-frequency circuit 14. , The autocorrelation is detected by the correlator 18 based on the PN code sequentially delayed by the delay amount from the delay circuit 17 to the delay amount of 0 to 31 chips. As shown in FIG. 8, the detected auto-correlation has one main peak a and one flat side lobe b for one target. The target can be detected by measuring a.

As described above, in the present embodiment, when the correlation is detected, an appropriate M which eliminates a plurality of peaks caused by ringing is removed.
Since a series of PN codes is generated, the influence of ringing occurring in the PN codes can be prevented, and one autocorrelation peak can be detected for one target, whereby the target can be accurately identified, and the target identification accuracy can be improved. Can be improved.

In this embodiment, an example of a radar device mounted on a vehicle has been described. However, the present invention is not limited to this, and can be used for a radar device for identifying a moving body such as a ship. . In this case, there is no need to use a high-speed PN code as used in a vehicle, so that, for example, the chip rate of the PN code can be set to about 20 MHz, and the delay amount depends on this and the measurement distance. Can be set to, for example, about 16 chips. Therefore, the taps set by the tap setting unit are, for example, the taps [8,
4, 3, 2].

Further, the spread spectrum modulation / demodulation method of the present invention can be used, for example, in a spread spectrum communication apparatus. In this case, for example, as shown in FIG. 5, the transmission PN code generator 31 and the reception PN code generator 32
It comprises a spreading code generator according to the invention. The spread spectrum communication apparatus 1 includes a data modulation / demodulation circuit 30 using a frequency division method and a high frequency circuit 40.
In the data modulation / demodulation circuit 30, transmission and reception taps are set in advance with the communication partner, and the transmission PN code generator 31 and the reception PN code generator 32 use the set taps to influence ringing. Is generated. In this spread spectrum communication device,
It is important to maintain synchronization with the communication partner, and the synchronization maintaining unit 34 performs the synchronization maintenance by controlling the amount of delay of the PN code based on the peak of the autocorrelation detected by the detection unit 35.

That is, the intermediate frequency signal, which is a transmission signal, is modulated in the double balanced modulator 33 of the data modulation / demodulation circuit 30 by an appropriate PN code from the transmission PN code generator 31, and further, in the mixer 41 of the high frequency circuit 40. Is up-converted by the frequency signal from the oscillator 42 in the transmission antenna 4 via the band-pass filter 43.
4 to the communication spread spectrum communication apparatus 2 of the communication partner shown in the two-way one-way communication system of FIG.

Spread spectrum communication device 2 of communication partner
Also has a configuration similar to that of the spread spectrum communication apparatus 1. The signal from the communication apparatus 1 is received by the reception antenna 45, and down-converted by the frequency signal from the oscillator 42 in the mixer 46 of the high frequency circuit 40. later,
The autocorrelation is detected by the correlator 36 of the data modulation / demodulation circuit 30, and based on the peak of the autocorrelation detected by the detection unit 35, the synchronization holding unit 34 outputs the PN code output from the reception PN code generator to the correlator 36. By controlling the amount of delay, the demodulation unit 37 demodulates and outputs the received signal (the above-described intermediate frequency signal) when the peak of the autocorrelation is detected.

In the present embodiment, the transmission P
N code generators and the receiving PN code generators of the communication device 2
Alternatively, the reception PN code generator of the communication device 1 and the transmission PN code generator of the communication device 2 can perform correlation detection using the same code sequence. Regarding the PN code generator, the same code sequence or different code sequences may be used.

As described above, in this embodiment, an appropriate M-sequence PN code from which generation of a plurality of peaks due to ringing is removed is generated as a transmission PN code and a reception PN code, and when a correlation is detected, the correlation is detected by the PN code. So
By preventing the effect of ringing occurring in the PN code, one autocorrelation peak can be detected for one user, thereby enabling accurate communication and improving the reliability of spread spectrum communication.

The present invention is not limited to these embodiments, and various modifications can be made without departing from the gist of the present invention. For example, when a PN code generator is configured using an eight-stage shift register, taps [8, 4, 3, 3,
2], [8, 6, 5, 3], [8, 6, 5, 2],
[8, 5, 3, 1], [8, 6, 5, 1], [8, 7,
[6,1], [8,7,6,5,2,1], [8,6
[4, 3, 2, 1], and the spread spectrum modulation of the present invention makes it possible to set an appropriate tap from these taps according to the conditions to be used, the application, and the like. Become.

[0029]

As described above, according to the present invention, in the spread spectrum modulation / demodulation method, the spread spectrum in which no secondary peak of the autocorrelation exists between the main peak of the detected autocorrelation and the predetermined delay amount. Since the code is set and the signal is subjected to spread spectrum modulation and despreading by the spread code, the influence of ringing generated in the PN code can be prevented, and the main peak of the autocorrelation can be accurately detected.

According to the present invention, in the spread spectrum modulation / demodulation device, a spread code for generating the spreading code having no multiple peak of the autocorrelation exists between a main peak of the detected autocorrelation and a predetermined delay amount. Since a code generator is provided, it is possible to accurately detect the main peak of the autocorrelation while preventing the influence of ringing occurring in the PN code. When the above device is used for a communication device, the reliability of spread spectrum communication can be improved.

Further, according to the present invention, in the spread code generator, a generating means for generating the spread code in which the secondary peak of the autocorrelation does not exist from the detected main peak of the autocorrelation to a predetermined delay amount. Therefore, by using the present invention in a spread spectrum modulation / demodulation device, it is possible to prevent the influence of ringing occurring in the PN code and accurately detect the peak of the autocorrelation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of a spread spectrum modulation / demodulation device and a PN code generator using a spread spectrum modulation / demodulation method according to the present invention.

FIG. 2 is a characteristic diagram illustrating an example of an autocorrelation characteristic.

FIG. 3 is a characteristic diagram showing another example of the autocorrelation characteristic.

FIG. 4 is a block diagram illustrating a configuration of a PN code generator according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of an example of a spread spectrum communication apparatus using a spread spectrum modulation / demodulation method according to the present invention.

FIG. 6 is a diagram illustrating a communication system using the spread spectrum communication apparatus illustrated in FIG. 5;

FIG. 7 is a block diagram illustrating a configuration of an example of a spread spectrum modulation / demodulation device.

FIG. 8 is a characteristic diagram showing ideal autocorrelation characteristics.

FIG. 9 is a waveform chart showing an example of a waveform of a PN code.

FIG. 10 is a characteristic diagram showing an autocorrelation characteristic when the PN code shown in FIG. 9 is used.

[Explanation of symbols]

 1, 2 spread spectrum communication apparatus 10, 20, 31, 32 PN code generator 13, 33 double balanced modulator 14, 40 high-frequency circuit 17 delay circuit 18, 36 correlator 19, 35 detector 21 storage 22 D / A converter 23 Tap setting unit 30 Data modulation / demodulation circuit 34 Synchronization holding unit 37 Demodulation unit 41, 46 Mixer 42 Oscillator 43 Bandpass filter 44, 45 Antenna

Claims (8)

[Claims] 1. A spread-spectrum modulation / demodulation method for transmitting a transmission signal by applying spread-spectrum modulation using a spreading code, performing despreading on a fetched radio wave with a spreading code, and detecting a correlation to obtain a received signal. Between the main peak of the autocorrelation and a predetermined delay amount, setting the spreading code in which there is no secondary peak of the autocorrelation, and performing at least spread spectrum modulation or despreading of the signal by the spreading code. Spread spectrum modulation and demodulation method. 2. The spread spectrum modulation / demodulation method according to claim 1, wherein the predetermined delay amount of the spread code is set according to a chip rate and a required transmission distance between transmission and reception. 3. The spread spectrum modulation / demodulation method is used in either a radar device for detecting a target or a communication device for communicating with a communication partner, and when used in the radar device, a spread code for performing the spread spectrum modulation and the spread code. The spreading code performing despreading is set to the same code, and when used in the communication device, the spreading code performing the spread spectrum modulation and the spreading code performing the despreading are set to the same or different codes. 3. The spread spectrum modulation / demodulation method according to claim 1, wherein: 4. A spread spectrum modulation / demodulation apparatus for transmitting a transmission signal by applying spread spectrum modulation using a spread code and performing despreading on a fetched radio wave by a spread code to detect a correlation and obtain a received signal. Digital data of the spreading code consisting of a sequence,
A spread-spectrum modulation / demodulation device comprising a spread code generator for converting into analog data free of ringing and outputting the converted data. 5. A spread spectrum modulation / demodulation apparatus for transmitting a transmission signal by performing spread spectrum modulation using a spread code and performing despreading on a fetched radio wave by a spread code to detect a correlation and obtain a received signal. A spread-spectrum modulator / demodulator comprising: a spread-code generator for generating the spread code having no auto-correlation secondary peak between a main peak of the auto-correlation and a predetermined delay amount. 6. A fetching means for fetching digital data of a predetermined spread code string, and a conversion means for converting the fetched spread code string into analog data free from ringing and outputting the analog data. And a spreading code generator. 7. A spread code generator for performing spread spectrum modulation or for generating a spread code for detecting an autocorrelation of a fetched signal, wherein a spread code is generated from a main peak of the detected autocorrelation to a predetermined delay amount. A spread code generator for generating the spread code having no multiple peak of the autocorrelation. 8. The generating means has a tap setting unit for setting taps for generating the spreading code in which the secondary peak of the autocorrelation does not exist, and a combination of logical combinations based on the set taps. The spread code generator according to claim 7, wherein the spread code is generated by: