JPS61199347A - Spread spectrum receiver - Google Patents

Abstract

PURPOSE:To obtain a inexpensive device with high S/N by tracing synchronously a PBN code of reception signal with a correlation output signal between the reception signal of a reception antenna and a difference signal between a lead signal (signal E) and a delay signal (L signal) from a pseudo noise code (PN code) generator. CONSTITUTION:A subtractor 42 extracting a difference signal between the signals E and L from the PN code generator 35, a PN code modulator 30 and a correlation device 6 are provided to add a control output from a numerical control oscillator 3 for carrier phase synchronization to phase detectors 18 and 41 and a central processing unit 28 controls the gain of the 2nd intermediate frequency amplifier and narrow band pass filters 8, 9 so as to keep a prescribed amplitude. Then the subtractor 42 takes difference between the signals E and L, and the difference signal is correlated with a signal modulated by the PN code modulator 30. Thus, circuits after the correlation device 6 are realized by two systems. Further, the central processing unit 28 controls the gain of the 2nd intermediate frequency amplifier and the narrow band pass filters 8, 9 through a D/A converter 24 so as to keep a prescribed amplitude to improve the S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a receiving device in a spread spectrum communication system.

(Prior Art) FIG. 5 shows a block diagram of a conventional spread spectrum communication system using this type of delay-locked loop circuit.
5 to E signal (advanced phase signal), [signal (lag phase signal) and P
Each signal (synchronized signal) has a code phase of 1/2
Since the signals are shifted bit by bit, the P signal is used for information demodulation, and the E and L signals are used as the difference between the two signals and used as a signal for the PN code phase cycle. That is, as shown in Figure 2, if the phase relationship of the PN code is P signal (1), E signal (2>, L signal (3)), the difference (4) between the E and 1- signals is In order to achieve this, the spread spectrum signal received by the receiving antenna 1 must be transmitted through a high frequency amplification stage, a first frequency converter, and a first intermediate frequency amplification stage (2 to 4 ), a second frequency conversion stage of three systems,
After passing through the third frequency conversion stage, phase detection, A/D conversion stage (including envelope detector), the central processor (8~25.9~26
．． 10 to 27 and 2B), resulting in a rather complicated configuration.

As another method, FIG. 6 shows a block diagram of a spread spectrum communication system using a conventional tow dither loop circuit. A sample and hold device 39 is switched at a constant cycle to detect a phase error signal, and PN code phase synchronization is performed by the method shown in FIG. This method has a slightly simpler configuration than the former method shown in Figure 5, but
As shown in Figure 3, when establishing phase synchronization, the phase synchronization is tracked by switching between point A, which corresponds to the E signal, and point B, which corresponds to the L signal, so the S/N ratio is as shown in Figure 5. Compared to this, there was a drawback that the actual measurement was approximately 6 db lower.

(Problems to be Solved by the Invention) As mentioned above, both the methods shown in FIGS. 5 and 6 are uneconomical because of their complicated configuration, and the latter has a poor S/N ratio. There has been a demand for an economical method with a good S/N ratio.

(Means for Solving the Problems) In view of the above points, the present invention uses a difference signal between an advanced phase signal (E signal) and a delayed phase signal (L signal) from a PN code generator, and a reception antenna. This is a spread spectrum receiving apparatus characterized in that a PN code of a received signal is synchronously tracked by a correlation output signal with a received signal captured from the received signal. This will be explained in detail below with reference to the drawings.

(Embodiment) FIG. 1 shows a block diagram of an embodiment of the present invention, in which 1 is a receiving antenna, 2 is a high frequency amplifier and a bandpass filter for the spread spectrum signal captured by the receiving antenna, 3 is a first frequency converter, 4 is a first intermediate frequency amplifier; 5 and 6 are second frequency converters and correlators; 8 and 9 are second intermediate frequency amplifiers and narrowband filters; 11 and 12 are third frequency converters;
4 and 15 are third intermediate frequency amplifiers, 17 is a reference generator, 18 and 4''1 are phase detectors, 21 and 22 are low-pass filters, 24 is a D/A converter, 25 and 26 are A/ D converter, 28 is a central processor, 2 are frequency synthesizers, 30 and 31 are PN code modulators, 34 is a numerically controlled oscillator for carrier phase synchronization, 35 is a PN code generator, 36 is a PN
Numerical control generator 1 for code phase synchronization, 37 is a frequency divider,
42 is a subtracter 6 As is clear from FIG.
The central processor applies the control output from the numerically controlled oscillator for carrier phase synchronization to the phase detectors 18 and 41, and controls the second intermediate frequency amplifier and the narrowband filters 8 and 9 to maintain a constant amplitude. The object of the present invention can be achieved by configuring the gain to be controlled. Next, I will explain its operation.

(Function) The spread spectrum signal captured by the receiving antenna 1 is amplified by the high frequency amplifier 2, and then is amplified by the first frequency converter 3 using the first local oscillator signal generated by the frequency synthesizer 29 from the output of the reference oscillator 17. is converted to a first intermediate frequency. This first
The intermediate frequency is amplified by a first intermediate frequency amplifier 4 and input to a second intermediate frequency converter and correlators 5 and 6, respectively.

On the other hand, the second local oscillation signal generated by the frequency synthesizer 29 is P
The P signal of the PN code generated by the N code generator 35
It is modulated by the N code modulator 31 and input to the correlator 5. This correlator 5 correlates the signals and at the same time converts the frequency, and when the phases of the PN codes of both signals match, outputs it as a second intermediate frequency signal. The received signal, which has become the second intermediate signal, is extracted by the second intermediate frequency amplifier and narrow band filter 8, amplified, and inputted to the third intermediate frequency converter 11. The third intermediate frequency is mixed with the third local oscillator signal and becomes the third intermediate frequency. After being amplified by the third intermediate frequency amplifier] 4, it is input to the phase detector 18, where it is synchronously detected with the output of the numerically controlled oscillator 34 for carrier phase synchronization, and passed through the low-pass filter 21 to obtain phase error information and The amplitude information is converted into digital information by the A/D converter 25 and input to the central processor 28 . The central processor 28 controls the numerically controlled oscillator 34 for carrier phase synchronization according to the phase error, and synchronizes it with the input signal. In this way, a carrier phase locked loop is constructed. Therefore, when synchronized with the input signal, the -order modulated information is demodulated and the A, 'D modulation @
The signal is input to the central processor 2B through the device 25. Also, the central processor 28 uses amplitude information to maintain a constant amplitude.
controls the gains of the second intermediate frequency amplifier and narrow band filters 8 and 9 through the D/A converter 24. Further, the received signal input to the second frequency converter and correlator 6 is PN
1 from the PN code (P) generated by the code generator 35
/2-bit phase advanced PN code (E signal) and 1/
The difference between the 2-bit phase delayed PN code (N>) is determined by the difference between the signal taken by the subtracter 42 and the signal obtained by modulating the second local oscillation signal by the PN code modulator 30, and the second frequency converter and The correlation is taken by the correlator 6.The correlation characteristics at that time are as described in FIG.
controls the numerically controlled oscillator 36 for PN code phase synchronization in accordance with the phase error of the PN code, so as to synchronize it with the received signal. In this way, a PN code phase-locked loop is constructed.

In the above explanation, the subtracter 42 and the PN code modulator 3
0 can be easily realized, for example, by a double-balanced modulator as shown in FIG. It can be used as clock information for the device 28.

(Effects of the Invention) As explained above, the present invention calculates the difference between the phase-advanced signal (E) of the PN code and the phase-delayed signal (L) using a subtracter, and combines this difference signal with the PN code. Since it is designed to correlate with the modulated signal in the modulator, it can be realized with two simple and economical systems from the correlator to the A/D converter, so compared to the conventional method shown in Figure 5. , is much simplified. Further, the central processor controls the gains of the second intermediate frequency amplifier and the narrow band filter through the D/A converter so as to maintain a constant amplitude, thereby obtaining a good S/N ratio.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a correlation characteristic diagram of a delay locked loop, FIG. 3 is a correlation characteristic diagram of a tow dither loop circuit, and FIG. 4 is an example of a PN code modulator. FIGS. 5 and 6 are block diagrams of conventional circuit examples. 1... Receiving antenna, 2... High frequency amplifier and bandpass filter, 3... First frequency converter,
4...First intermediate frequency amplifier, 5.6...
- Second frequency converter and correlator, 8, 9... Second intermediate frequency amplifier and narrow band filter, 11, 12...
...Third frequency converter, 14.15...Third intermediate frequency amplifier, 17...Reference oscillator, 18
．． 41... Phase detector, 24... D/
A converter, 25.26...A/D converter, 28
... Central processor, 29 ... Frequency synthesizer, 30.31 ... PN code modulator, 34.
36...numerically controlled oscillator, 35...P
N code oscillator, 37... Frequency divider, 42...
...Subtractor.

Claims (1)

[Claims] In a receiving device that has a function of receiving a signal whose spectrum is spread with a pseudo noise code (PN code) and tracking it to the reception frequency, a function of demodulating information, and a function of synchronously tracking the PN code, the PN code It has means for synchronously tracking the PN code of the received signal using a difference signal (E-L) between an advanced phase signal (E signal) and a delayed phase signal (L signal) from the generator and a correlation output signal between the received signal and the received signal. A spread spectrum receiving device characterized by: