JPH0644747B2 - Spread spectrum receiver - Google Patents

Description

The present invention relates to a receiver in a spread spectrum communication system.

(Prior Art) PSK (Phase Shift Ke) with pseudo noise code (PN code)
In order to receive the modulated and spread spectrum radio transmission wave and demodulate the information signal on the transmission side, it is obtained by generating a PN code in the receiving device and correlating with the received signal. Therefore, it is necessary to synchronize the phase of the bit and the period of the constituent code between the internally generated pseudo noise code (hereinafter referred to as PN code) and the PN code of the received signal.

FIG. 5 is one of the conventional examples and shows a block diagram of a spread spectrum receiver using a delay locked loop circuit. In the figure, the E signal (advanced phase signal), the L signal (delayed phase signal) and the P signal (synchronized signal) output from the PN code generator 35 are shifted by 1/2 bit each. There is. That is, FIG. 2 is a diagram showing the bit-by-bit correlation characteristics of the above signals in the synchronized state. As shown in the figure, the P signal (1), the E signal (2) and the L signal (3) are each 1 The correlation level is maximized by shifting by / 2 bits. The P signal is used for information demodulation, and the E signal and the L signal are used for phase synchronization of the PN code. In the method using the delay locked loop, the correlation signals of the E signal and the L signal are independently obtained, and then the E-L correlation signal (correlation characteristic as shown in FIG. 2 (4) in the synchronized state) is obtained to obtain the PN code phase. It is supplied to the numerical control oscillator for synchronization 36 and controls the PN code generator 35 to achieve phase synchronization. Therefore, this method is such that the spread spectrum signal received by the receiving antenna 1 is passed through the high frequency amplifier 2, the first frequency converter 3, and the first intermediate frequency amplifier 4, and then the three systems of the second frequency converter and the correlator 5, 6, 7,
Third frequency converters 11, 12, 13, phase detector 18, envelope detectors 19, 20, and A / D converters 25, 2
Requires 6,27. Therefore, there is a drawback that the configuration is rather complicated.

As another method, FIG. 6 shows a block diagram of a spread spectrum receiver using a conventional taud dither loop circuit, which is a PN code advance of the E signal and L signal and their correlation signals. By switching between the slow phase switching device 40 and the sample hold device 39 at a constant cycle, the second
From the frequency converters and correlators 5, 6 to the A / D converter 25,
The system up to 26 is composed of two systems. This is slightly simpler than the former method shown in FIG. 5, but the third method
As shown in the figure, when the phase synchronization is taken, the point A corresponding to the E signal and the point B corresponding to the L signal are switched to trace the phase synchronization, so that the S / N is compared with the method of FIG. However, there is a drawback that the actual measurement results in a decrease of almost 6 dB.

(Problems to be Solved by the Invention) As described above, both of the methods of FIGS. 5 and 6 are not economical because the configuration is complicated, and the latter is S / N.
There was a defect such as bad. Therefore, an economical method and a good S / N ratio have been demanded.

(Means for Solving the Problems) In view of such a point, the present invention provides a phase-locking PN code with a phase-advancing signal (E signal) and a phase-lagging signal (L signal) from a PN code generator. A subtracter for obtaining a difference signal is provided, and a means for obtaining a signal used for phase synchronization by correlating the difference signal and the PN code of the received signal is provided with a phase detector, and a phase detector for phase synchronization from the phase detector is provided. It is a spread spectrum receiver provided with means for controlling the phases of the plurality of PN codes generated by the PN code generator by a signal. The details will be described below with reference to the drawings.

(Embodiment) FIG. 1 is a block diagram of an embodiment of the present invention, in which 1 is a receiving antenna, 2 is a high frequency amplifier and bandpass filter for spread spectrum signals captured by the receiving antenna, 3 is a first frequency converter, Reference numeral 4 is a first intermediate frequency amplifier and band filter, 5 and 6 are second frequency converters and correlators, 8 and 9 are second intermediate frequency amplifiers and narrow band filters, and 11 and 12 are third.
Frequency converters, 14 and 15 are third intermediate frequency amplifiers, 1
Reference numeral 7 is a reference oscillator, 18 and 41 are phase detectors, 21 and 22 are low-pass filters, 24 is a D / A converter, and 25 and 2
6 is an A / D converter, 28 is a central processor, 29 is a frequency synthesizer, 30 and 31 are PN code modulators, 34 is a numerically controlled oscillator for carrier phase synchronization, 35 is a PN code generator, and 36 is a PN code generator. Numerically controlled oscillator for code phase synchronization, 3
Reference numeral 7 is a frequency divider, and 42 is a subtractor.

Next, the operation will be described in detail.

(Operation) The spread spectrum signal captured by the reception antenna 1 is amplified by the high frequency amplifier 2, and then the first local oscillator signal generated by the frequency synthesizer 29 from the output of the reference oscillator 17 is transmitted by the first frequency converter 3. Converted to the first intermediate frequency. This first
The intermediate frequency is amplified by the first intermediate frequency amplifier 4 and input to the second frequency converter and the correlators 5 and 6, respectively. Up to this point, the signal that has been spread spectrum passes through the bandpass filter.

Next, the second local oscillator signal generated by the frequency synthesizer 29 is P
The PN code produced by the N code generator 35 is modulated by the PN code converter 31 by the P signal for information demodulation,
It is input to the second frequency converter and the correlator 5. This second
The frequency converter / correlator 5 correlates two input signals and simultaneously performs frequency conversion. The PN of the received signal output from the first intermediate frequency amplifier and the bandpass filter 4 is obtained.
When the phase of the code matches the phase of the PN code of the signal output from the PN code modulator 31, the second intermediate frequency signal is output. The received signal that has become the second intermediate frequency signal is extracted and amplified by the second intermediate frequency amplifier and narrow band filter 8 only, is input to the third frequency converter 11, and then is input by the frequency synthesizer 29. It is mixed with the generated third local oscillation signal to become a third intermediate frequency signal. This signal, after being amplified by the third intermediate frequency amplifier 14, is input to the phase detector 18, is synchronously detected with the output of the numerically controlled oscillator 34 for carrier phase synchronization, and is passed through the low-pass filter 21.
The phase error and amplitude information obtained by the synchronous detection are converted into A / D converter 2
It is converted into digital information at 5 and input to the central processing unit 28. The central processing unit 28 controls the numerically controlled oscillator 34 for carrier wave phase synchronization according to the phase error to synchronize with the input signal. In this way, the carrier phase locked loop is constructed. Then, when synchronized with the input signal, the information modulated on the transmitting side is demodulated and input to the central processing unit 28 through the A / D converter 25. Further, using the amplitude information, the central processing unit 28 controls the gains of the second intermediate frequency amplifier and the narrow band filters 8 and 9 so as to keep the amplitude constant.

The subtractor 42 calculates the difference between the E signal, which is advanced by 1/2 bit phase from the P signal generated by the PN code generator 35, and the L signal, which is also delayed by 1/2 bit phase. . The output of the subtractor 42 becomes a ternary signal of 1, 0, -1. The second local oscillation signal is PSK-modulated in the PN code modulator 30 by the E-L signal. The carrier wave of the signal obtained here has a positive phase when the E-L signal is 1, a reverse phase (180 ° inversion) when the E-L signal is -1, and nothing when the signal is 0.
The correlation between this signal and the received signal output from the first intermediate frequency amplifier and the bandpass filter 4 is obtained by the second frequency converter and correlator 6. The carrier of the third intermediate frequency obtained after this correlation also has three values of positive phase, negative phase, and nothing. When the PN code is synchronized, the number of positive and negative phase signals is the same, when it is advanced, the number of positive phases is large, and when it is delayed, the number of negative phases is large. Therefore, the signal, which has been amplified by the third intermediate frequency amplifier 15 and then phase-detected by the phase detector 41 and averaged by the low-pass filter 22, is zero when the PN code is synchronized and when it is advanced. Is positive, and is negative when delayed. That is, in FIG.
An output signal corresponding to the phase error of the PN code having a characteristic similar to (4) is obtained. The central processing unit 28 controls the numerical control oscillator 36 for PN code phase synchronization according to the phase error of the PN code so as to synchronize with the received signal. That is, when the phase of the PN code deviates from the zero point of the characteristic diagram of (4) of FIG. 2, it is detected as an error signal by the phase detector 41 and input to the central processing unit 28 via the A / D converter 26. The central processing unit 28 controls the numerically controlled oscillator 36 so that the output of the phase detector 41 becomes zero, and controls the phase of the PN code. In this way, the PN code phase locked loop is constructed. In the above description, the subtractor 42
The PN code modulator 30 and the PN code modulator 30 can also be realized by a double balanced modulator as shown in FIG. 4, for example.

(Effect of the Invention) As described above, according to the present invention, the signal (E) in which the phase of the PN code is advanced and the signal (L) in which the phase is delayed are subtracted in advance by the subtractor, and the PN code is obtained by this difference signal. Since the signal modulated by the modulator and the received signal are correlated with each other, the phase detection is performed to obtain the signal for phase synchronization, and the phase of the PN code is controlled. The S
/ N can be realized with two systems without deterioration, and a simple and economical spread spectrum receiver can be obtained.
This is much simpler than the conventional method of FIG.

[Brief description 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 tau dither loop circuit, and FIG. 4 is an example of a PN code modulator. 5 and 6 are block diagrams of conventional circuit examples. 1 ... Receiving antenna, 2 ... High frequency amplifier and band 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 processing unit, 29 ... Frequency synthesizer, 3
0, 31 ... PN code modulator, 34, 36 ... Numerically controlled oscillator, 35 ... PN code oscillator, 37 ... Frequency divider, 42 ... Subtractor.

Claims (1)

[Claims] 1. A signal having a spectrum spread by a pseudo noise code (PN code) is received, and a PN code in the signal is correlated with a PN code for phase synchronization of PN codes generated internally. Means for obtaining a correlation signal used for phase synchronization, a PN code of the received signal and the internally generated P
In a spread spectrum receiver having means for demodulating an information signal on the transmitting side by correlating with a PN code for information demodulation of N codes, a phase advance of the PN code for phase synchronization from a PN code generator A subtractor for obtaining the difference signal between the signal (E signal) and the delay signal (L signal) and a signal used for phase synchronization by the phase detector by correlating the difference signal and the PN code of the received signal. A spread spectrum receiving apparatus comprising: a means for obtaining the phase and a means for controlling the phases of the plurality of PN codes generated by the PN code generator by a signal for phase synchronization from the phase detector.