JPH057196A - Spread spectrum modulation/demodulation system - Google Patents

Abstract

PURPOSE:To demodulate a BPSK modulation signal with a single correlation device. CONSTITUTION:A clock generator 1 at a sender side is used to drive a PN code generator 2, its output signal is divided into two, the one is multiplied with an information signal to form a series 1 and the other is multiplied with a clock signal to form a series 2 and the series 1,2 are subject to weighting by gain adjustment circuits 5,6 and the result is added by an adder 7. The correlation of signals from a PN code generator 11 is calculated by a correlation device 8 and the result is given to a low pass filter 9 and used for a control voltage of a voltage controlled oscillator 10 to control a drive clock of the PN code generator 11. On the other hand, the output of the correlation device 8 is given to a discrimination device 12, signals before and after the low pass filter 9 are compared and an information signal is reproduced.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spread spectrum modulation / demodulation system. For example, it is applied to spread spectrum communication and wireless communication.

[0002]

2. Description of the Related Art As a publicly known document describing the prior art of the present invention, for example, "quadrature two-phase / frequency spread / modulation signal demodulation characteristics using a front end correlator" is used.
(Research Technique Vol.3 No.1, SSTA91-2, Keizo Suzuki, Shinya Okuyama). The method described in this document proposes a method in which another pseudo-noise code (PN) code with little correlation is prepared for synchronization and demodulation in a transmitter, and both codes are power-combined into a transmission signal. ing. That is, a method has been proposed in which different PN codes are used for synchronization holding and information transmission, and the combined signal is transmitted. In this system, another PN code and a correlator corresponding to the PN code are required on the receiving side, so that there is a drawback that the circuit becomes complicated.

The previously proposed Japanese Patent Application No. 2-1569.
The "pseudo noise code synchronization circuit" of No. 21 uses a PN code on the transmission side, uses the same PN code further Manchester-coded on the reception side, and constructs a synchronization circuit by utilizing the cross-correlation between the two. There is an example. This has the excellent feature that the number of correlators in the receiver can be reduced to one and the circuit becomes very simple. However, in this method, BPSK, which is often used for information modulation, is a normal direct spread method.
(Binary Phase Shift Keying) was not possible.

5A and 5B are block diagrams showing a conventional example of a modulator / demodulator which modulates a drive clock of a PN code with an information signal. FIG. 5A is a modulator, and FIG. It is a vessel.
In the figure, 41 is a voltage controlled oscillator, 42 is a PN code generator (transmission side), 43 is a correlator, 44 is a low pass filter (LPF), 45 is a voltage controlled oscillator, and 46 is a PN code generator (reception side). ) And 47 are EX-OR (exclusive OR).

In the modulator shown in FIG. 3A, the voltage controlled oscillator 4
The frequency of 1 is modulated by the information signal, and the PN code generator 42 is driven by using this as a clock signal to transmit the modulated PN code. In the demodulator of FIG. 6B, the same P
The output of the N code generator 46 and its driving clock signal are exclusively ORed to perform Manchester encoding, the correlation between this and the received signal is obtained by the correlator 43, and the output thereof is passed through the low pass filter 44 to obtain the voltage. Control the controlled oscillator 45,
Along with synchronizing the PN code, the low-pass filter 44
The output of can be taken out as a demodulation signal. The correlator 43 has a function of multiplying two input signals and integrating for a certain period of time,
As a realization means, a combination of a multiplier such as DBM and low pass, a SAW convolver, a DSP or the like can be considered.

[0006]

[Object] The present invention has been made in view of the above-mentioned circumstances, and a part of the same PN code sequence is used for information transmission, and the rest is used for synchronization holding. BPSK (Binary P
hase shift keying) to be used, and it can be applied to spread signals in the carrier frequency band, and to provide a spread spectrum modulation / demodulation method for removing the shift of the synchronization point. It was made for the purpose.

[0007]

In order to achieve the above object, the present invention provides (1)
On the transmission side, a pseudo noise (PN) code generator is driven by a clock generator, the output signal of the pseudo noise code generator is divided into two, one is multiplied by an information signal to form a series 1, and the other is a clock signal. Is multiplied by a multiplier to form a series 2, and the series 1 and the series 2 are weighted by a gain adjusting circuit and added by an adder to form a transmission signal. On the receiving side, the same pseudo noise as on the transmitting side is generated. Low-pass filter (LPF) that calculates the correlation between the output signal from the generator and the signal from the transmitter with a correlator and passes only the DC signal through the correlation output.
The control voltage of the voltage controlled oscillator is controlled through the control clock of the pseudo-noise code generator, while the correlation output is passed through the decision device or the signals before and after the low pass filter (LPF) are compared to obtain the information. Playing the signal,
Furthermore, (2) In (1), on the transmitting side, the pseudo-noise code generator is driven by a signal obtained by dividing the clock signal by n by a frequency divider, and the original clock signal, pseudo-noise code output, and information are output. A series obtained by multiplying three signals is called a series 1, while a series obtained by multiplying the original clock signal by π / 2 phase shift by a phase shifter and a pseudo noise code output is called a series 1, and the series 1 is The sequence 2 is weighted and added by an adder to form a transmission signal. On the reception side, the output of the voltage controlled oscillator is divided by n to drive the same pseudo noise code generator as on the transmission side, and the pseudo noise code generator is generated. Low-pass filter (LPF) that calculates the correlation of the signal from the transmitter and the sequence obtained by multiplying the output of the noise code generator and the output of the pseudo-noise code generator by the correlator, and passes the correlation output only the DC signal. Through the control voltage of the voltage controlled oscillator , Reproducing the information signal by controlling the drive clock of the pseudo-noise code generator while passing the correlation output through the determiner or by comparing the signals before and after the low pass filter (LPF). (3) In the above (1) or (2), the information signal is coded so that the average number of data of 1 and 0 of the information signal is equal, and (4) The above (1), ( In 2) or 3), a control switch is provided for stopping the output of the pseudo noise code sequence (sequence 1) for transmitting the information signal when there is no transmission information. Hereinafter, description will be given based on examples of the present invention.

First, in the conventional modulation / demodulation system shown in FIG. 5, the delay shown in FIG. 3 (b), which is a cross-correlation characteristic between the PN code of FIG. 2 (a) and the Manchesterized PN code of FIG. Since the discrimination characteristic is used for the synchronization control, when the BP code which is often used in the normal direct spread method is applied to the PN code, the characteristic of FIG. Can not be used as. Therefore, in the present invention, the codes of the transmitting side and the receiving side are exchanged in FIG.
By adding the same code as that of the modulated transmission side to form a transmission signal, it is possible to demodulate the BPSK modulation signal with a single correlator.

FIG. 1 is a block diagram for explaining an embodiment of a spread spectrum modulation / demodulation system according to the present invention.
Is a clock generator, 2 is a PN code generator (transmission side),
3, 4 are multipliers, 5 and 6 are gain adjustment circuits, 7 is an adder,
8 is a correlator, 9 is a low pass filter (LPF), 10 is a voltage controlled oscillator, 11 is a PN code generator (reception side), 1
2 is a judging device. First, the operation of the modulator shown in FIG. 1A will be described. 2 divides the output of the clock generator 1 such as a crystal oscillator into two, while driving the PN code generator 2.
The PN code sequence of (a) is generated. This sequence and the clock signal are multiplied by the multiplier 4 to obtain the Manchester-ized PN code sequence of FIG. In the case of a digital circuit, the multiplier 4 can be replaced by an exclusive OR circuit. On the other hand, the PN code is BPSK-modulated by an information signal by another multiplier 3, and the modulated signal and the Manchesterized PN code are gain-adjusted by gain adjustment circuits 5 and 6 and input to an adder 7, and the adder is added. The addition output of 7 is used as a transmission signal. Gain adjustment is PN
It is better to increase the Manchester code output so that synchronization cannot be lost due to code autocorrelation. FIG. 2C shows the pattern of the transmission signal when the amplitude ratio between the two is 2. Note that the gain adjustment circuit is not limited to the amplifier and may be an attenuator such as a resistor.

Before describing the demodulator, FIG.
The cross-correlation characteristics between the signal sequences of (a) to (c) and the PN code are shown in FIGS. 3 (a) to (c), respectively. FIG. 3 (c) shows (a),
The characteristic is such that the characteristic of (b) is linearly superimposed.
When the information signal is 0, the characteristic of FIG. 7C changes from the solid line state to the broken line state. Furthermore, considering the cross-correlation characteristics after passing the correlator output through a low-pass filter that blocks frequency components above the information signal band, FIG.
Since the fluctuation component of (a) is removed, only the synchronization control signal component of FIG. 3 (b) remains. Therefore, the low pass filter can maintain the synchronization point at the point where the delay time is zero. At this time, the output of the correlator fluctuates between positive and negative depending on the information signal, so that by extracting this, the BPSK modulated wave can be demodulated.

FIG. 1B is a block diagram of the demodulator. The same PN code generator 11 as that on the transmitting side is prepared, and the cross-correlation between the output and the received signal is obtained by the correlator 8. The output of the correlator 8 is passed through a low-pass filter 9 that blocks frequency components above the band of the information signal, and the output is used as a control signal to control the output clock frequency of the voltage-controlled oscillator 10 to synchronize the PN code. Since the information signal appears at the output of the correlator 8 in front of the low-pass filter 9, the information signal can be demodulated by passing it through the decision unit 12 such as a comparator having hysteresis. Although not shown, it is also possible to demodulate the information signal by comparing the signals before and after the low pass filter 9.

FIGS. 4A and 4B are diagrams showing another embodiment (claim 2) of the spread spectrum modulation / demodulation system according to the present invention. FIG. 4A is a modulator, and FIG. It is a vessel. In the figure, 21 is a clock generator, 22 is a π / 2 phase shifter, and 23
Is a frequency divider, 24 is a PN code generator (transmission side), 25, 2
6, 27 are multipliers, 28 and 29 are gain adjustment circuits, 30 is a control switch, 31 is an adder, 32 is a correlator, 33 is a low pass filter (LPF), 34 is a voltage controlled oscillator, 3
5 is a frequency divider, 36 is a PN code generator (reception side), 37 is a multiplier, and 38 is a determiner.

In the modulator of FIG. 4 (a), a frequency divider 23 is newly provided, and a PN code generator 24 is driven by a signal obtained by dividing the clock output, and the output, the original clock signal and the information signal. The three products of the above are set as the series 1, and the product of the PN code output and the clock output that is π / 2 phase-shifted by the phase shifter 22 is set as the series 2 and are combined to form a transmission signal as in the case of FIG. There is a control switch 30 in front of the adder 31,
This is for stopping the transmission of the spread signal for information transmission by the control signal when there is no information signal. This is for claim 4 and may be omitted. This can prevent the synchronization point from shifting.

The phase shift of the clock signal by π / 2 is equivalent to Manchester encoding the clock signal itself, and the cross-correlation between this sequence 2 and the sequence obtained by multiplying the PN code by the clock signal is shown in FIG. In this case, it can be used as a sync control signal. Since the spread signal can be placed on the carrier wave by multiplying it by the clock signal, this system can be applied to wireless communication. On the receiving side, the output of the voltage controlled oscillator 34 is divided into two, one is input to the frequency divider 35 to drive the PN code generator 36, and the output thereof and the output of the other voltage controlled oscillator 34 are multiplied by the multiplier 37. It is the same as the case of FIG. 1 except that the multiplication and the input signal to the correlator 32 are used.

The third aspect is a measure when the information signal itself has a DC component. If the information signal is in the state of 1 for a long time, the correlation characteristic of the control signal after passing through the low pass filter 33 becomes as shown in FIG. 3C, and a shift occurs in the synchronization point. Therefore, the information signal itself is encoded by Manchesterization or the like to balance the positive and negative of the data and remove the DC component to stabilize the synchronization point.

[0016]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: Since the spreading code for synchronization control and the spreading code for information transmission having a smaller output are added to form a transmission signal, the direct spreading method is used for the information transmission code. The BPSK modulation often used for Since the same PN code generator is used to generate two spread codes, the circuit configuration is easy. In the demodulator, the correlation output of the received signal and the output of the PN code generator on the receiving side has both the roles of synchronization and information demodulation, so that the number of correlators is one and the circuit configuration is simple. (2) Effect corresponding to claim 2: In addition to the effect described in claim 1, the spread code is multiplied by a carrier of an integer multiple of the code clock at the transmitting side and the receiving side. Since the new one is used as the spread communication, the signal band is provided in the carrier band, so that the invention of claim 1 can be applied to the wireless communication. (3) Effect corresponding to claim 3: The information signal itself is encoded such as Manchesterization to balance the positive and negative of the data and removes the direct current component, so that even if there is a direct current component of the information signal, It is possible to prevent the shift of the synchronization point. (4) Effect corresponding to claim 4: Since the transmission of the spread signal for information transmission is stopped by the control signal when there is no information signal, it is possible to prevent deviation of the synchronization point. At this time, the transmission output is reduced and the power consumption can be suppressed to some extent.

[Brief description of drawings]

FIG. 1 is a configuration diagram for explaining an embodiment of a spread spectrum modulation / demodulation system according to the present invention.

FIG. 2 is a diagram showing each signal sequence and a PN code.

FIG. 3 is a diagram showing a cross-correlation characteristic between each signal sequence and a PN code.

FIG. 4 is a diagram showing another embodiment of the spread spectrum modulation / demodulation system according to the present invention.

FIG. 5 is a diagram showing a conventional example of a modulator / demodulator that modulates a drive clock of a PN code with an information signal.

[Explanation of symbols]

1 ... Clock generator, 2 ... PN code generator (transmission side),
3, 4 ... Multiplier, 5, 6 ... Gain adjusting circuit, 7 ... Adder,
8 ... Correlator, 9 ... Low-pass filter (LPF), 10 ...
Voltage controlled oscillator, 11 ... PN code generator (reception side), 1
2 ... Judge.

Claims (4)

[Claims] 1. On the transmitting side, a pseudo noise code generator is driven by a clock generator, an output signal of the pseudo noise code generator is divided into two, and one is multiplied by an information signal to form a series 1.
Multiply the clock signal to the other by a multiplier to form series 2,
The series 1 and the series 2 are weighted by a gain adjusting circuit and added by an adder to form a transmission signal. On the receiving side, the same output signal from the pseudo noise generator as on the transmitting side and the transmitter are used. The correlation of the signal is calculated by a correlator, and the correlation output is determined as the control voltage of the voltage controlled oscillator through a low-pass filter that passes only the DC signal, and the drive clock of the pseudo noise code generator is controlled, while the correlation output is determined. A spread spectrum modulation / demodulation system characterized by reproducing an information signal by passing it through a filter or comparing the signals before and after a low pass filter. 2. The transmitting side drives a pseudo noise code generator with a signal obtained by dividing the clock signal by n by a frequency divider,
The series obtained by multiplying the original clock signal, the pseudo noise code output and the information signal by three is set as the series 1, while the original clock signal phase-shifted by π / 2 is multiplied by the pseudo noise code output. The sequence is set to the sequence 2, and the sequence 1 and the sequence 2 are weighted and added by an adder to form a transmission signal. The reception side divides the voltage controlled oscillator output by n to obtain the same signal as the transmission side. A pseudo noise code generator is driven, a correlation between a sequence obtained by multiplying the output of the pseudo noise code generator and the output of the pseudo noise code generator and a signal from the transmitter is calculated by a correlator, and the correlation output is a DC signal. The control voltage of the voltage controlled oscillator is controlled through a low-pass filter that passes only, and the drive clock of the pseudo-noise code generator is controlled, while the correlation output is passed through the determiner or the signals before and after the low-pass filter are compared. By Spread spectrum modulation and demodulation system of claim 1, wherein reproducing the broadcast signal. 3. The spread spectrum modulation / demodulation system according to claim 1, wherein the information signal is coded so that the average number of data of 1 and 0 of the information signal becomes equal. 4. The spread spectrum modulation / demodulation system according to claim 1, further comprising a control switch for stopping the output of the pseudo noise code sequence for transmitting the information signal when there is no transmission information.