JPH06338871A - Spread spectrum demodulator - Google Patents

Abstract

PURPOSE:To improve the S/N by dividing the interference component in the band from the interference component which is modulated by the frequency of the reciprocal of the cycle of a spreading code and canceling and demodulating the interference component by the subtraction processing. CONSTITUTION:A clock signal to be supplied to an input terminal In3 is supplied also to a frequency divider 22 having the divided frequency of 1/L, the reciprocal of a spreading code synchronization L, and obtains a frequency divider clock signal. By passing a BPF 23, a carrier signal is obtained. The carrier signal and the amplitude modulation wave being the output of a BPF 20 are added by an adder 21 to prevent the waveform collapse. The output of the circuit 21 is applied to an envelope detection circuit 24 and the AM detection is performed. By removing the high frequency component by an LPF 25 and cutting the dc component, the same signal as the interference wave component can be obtained. This signal is supplied to a subtraction circuit 26 to cancel the interference wave component included in the output of the LPF 18. Thus, the output suppressing the interference component can be obtained from an output terminal out and the information with the good S/N is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum system for inputting, receiving and demodulating a spread spectrum modulated wave obtained by directly spreading an angle modulated wave on the transmission (modulation device) side through a predetermined transmission medium. The present invention relates to a demodulation device, and more particularly, to a spread spectrum demodulation device capable of significantly suppressing and reducing an interference wave mixed during transmission in a demodulation operation.

[0002]

[Technical background] In the technical field of spread spectrum (SS) communication system, research on elimination or suppression of interference waves from other stations mixed during transmission is advanced day and night by major organizations including the applicant company, Various technological developments are being made. Among them, a method of suppressing a known SS modulated wave which becomes an interference, or when an unknown narrow band interference wave is added to the SS modulated wave which has been carrier modulated in advance and then SS modulated,
Adaptive filtering of narrowband interference (narrowband removal)
Well known how to do. Such technology is
This can contribute to improving the frequency utilization efficiency of the communication system.

[0003]

2. Description of the Related Art In the conventional interference wave suppression technique in SS communication, the circuit scale gradually increases, and it is not sufficient to compare the suppression effect with the circuit size. No development technology has been found for this purpose, and the current situation is that it depends on interference wave suppression corresponding to the process gain of the SS communication system.

In describing conventional SS demodulation,
A technique of SS-modulating an angle-modulated wave that has been angle-modulated in advance as primary modulation on the transmission (SS modulator) side and an interference wave generated in a demodulation output in demodulation of this SS-modulated wave will be described with reference to FIG.

FIG. 1 (A) is a block diagram of a modulator in a transmitter, 2 is an angle modulator, 3 is a spread modulator, 5 is a spread code generator, 6 is a BPF (bandpass filter), and 7 is a bandpass filter. Is a transmitting antenna. Further, FIG. 1B is a block diagram of a demodulation device in the receiving section. 11 is a receiving antenna, 12 and 16 are BPFs, 13 is a despreading demodulation circuit, 15 is a spreading code generation circuit, and 17 is an angle demodulation circuit. 1
Reference numeral 8 is an LPF (low pass filter). An ordinary SS communication device is equipped with both the modulator and the demodulator,
In that case, the antennas 7 and 11 and the spread code generation circuit 5
One of each of 15 and 15 is also used.

Next, the circuit operation will be described. First, Fig. 1
In the SS modulator of (A), the information S that uses a lower frequency than the modulation signal described later is input from the input terminal In1.
(t) is supplied to the angle modulation circuit 2, where it is angle-modulated by the modulation signal of the carrier angular frequency ω ₀ to generate the angle modulation signal fm (t) represented by the following equation.

[0007]

[Equation 1] ………………………… (1) As is clear from this equation, FM modulation and phase modulation are specifically performed as the angle modulation, and the angle modulation output fm (t) is obtained by the spread modulation circuit 3 Is supplied to.

On the other hand, a clock signal C (t) for generating a spread code is supplied to the spread code generating circuit 5 from the input terminal In2. Here, the spread code P (t) is generated to generate the spread modulation circuit 3
And the angle modulation output fm (t) is subjected to SS modulation by multiplication. Therefore, the SS modulation output or S
S wave SS (t) is

[0009]

[Equation 2] ……………………… (2), which is output from the transmitting antenna 7 via the BPF 6. The SS wave radiated in the air from the transmitting antenna 7 is a radio wave used between other stations until it is received by the SS communication device on the receiving side (this is assumed to be an interference wave fn (t)}, etc. Receives communication interference due to the mixture of

Next, referring to FIG. 1B, the receiving side (SS
The demodulation device) will be described. The SS wave received by the reception antenna 11 has unnecessary frequency components other than the main lobe of the SS wave removed by the BPF 12, and then the despreading demodulation circuit 1
3 is supplied. Here, the interference wave fn (t) can be expressed as the following equation, provided that it has an angular frequency ω _n0 close to the carrier angular frequency ω ₀ of the SS wave.

[0011]

[Equation 3] ………………………… (3) where ω _n0 −ω ₀ = ω _n {interference wave component shown in FIG. 3 (A) described later}, the interference wave fn (t) and the SS wave The composite wave of SS (t) can be transformed as follows by applying the above condition (condition that the frequency of the interference wave is close to the carrier angular frequency of the SS wave).

[0012]

[Equation 4] ……………………… (4) However, X = E ₂ / E _{1 and} the power E _{2 of the} interference wave compared to the power E _{1 of the} SS wave.
If is small, X ² << 1, so Eq. (4) can be approximated as follows.

[0013]

[Equation 5] (5) On the other hand, the clock signal C (t-τ) is supplied from the clock signal generator (not shown) to the spreading code generating circuit 15 via the input terminal In3, and here the spreading code P (T−τ) is generated and supplied to the despreading circuit 13, and the spreading code P (t−τ)
Is multiplied by the composite wave fn (t) + SS (t) to perform despread demodulation of SS wave or the like. The despread demodulation output Dss
(t) is

[0014]

[Equation 6] ……………………… (6). Here, τ represents a time delay with respect to the clock signal C (t) used on the side of the SS modulator, and Rp (τ) and Pn (t) in the equation (6) respectively represent an autocorrelation component and a diffusion component. . Both Rp (τ) and Pn (t) are expressed by very complicated mathematical formulas, but the correlation component Rp (τ) is Rp (τ) <1,
Since the spread component Pn (t) is band-limited by the BPF 16, the description of specific mathematical expressions is omitted here.

When the BPF 16 removes the amplitude fluctuation component and the angle demodulation circuit 17 detects the instantaneous frequency (detection of the despread demodulation output Dss (t) by differentiation), the output Dss' (t) is

[0016]

[Equation 7] …………………… (7). However, the amplitude component (absolute value of amplitude) and the autocorrelation component are set to 1. The actual angle demodulated output is shown with the carrier component removed. Therefore, the angle demodulation output Ds (t) is

[0017]

[Equation 8] …………………… (8). In addition, "'" in a formula is a differential symbol. This output Ds (t) is further filtered by the LPF 18 to remove frequency components higher than the frequency band of the information S (t), and output as the following demodulation output D (t) from the output terminal Out. .

[0018]

[Equation 9] …………………… (9) By the way, the spreading code components generated by the spreading code generation circuits 5 and 15 have a cycle (spreading code length) of the spreading code of L.
Then, the reciprocal frequency (repetition frequency) 1 / L
Is generally sufficiently higher than the frequency band of information S (t), so L
Although removed by the PF 18, the demodulation interference wave component having the same frequency band as the information S (t) remains without being removed.

[0019]

In the conventional SS demodulator described above, the interference wave existing in the frequency band of the demodulation information remains as a demodulation interference wave in the demodulation output signal as described above. If t) is an analog signal, the SN ratio deteriorates, and if it is a digital signal such as data, there is a drawback that a data error is likely to occur. These problems occur in principle, and as is well known, the extent of the problems is SS.
It corresponds to the process gain in communication. Therefore, the appearance of an SS demodulator capable of performing sufficient interference removal regardless of the degree of interference received in the carrier frequency band and the type of interference wave has been desired.

[0020]

A spread spectrum demodulating device of the present invention is a spread code generating circuit for inputting a clock signal to generate a spread code of period L, and a spread spectrum modulated wave is inversed by the obtained spread code. A despread demodulation circuit for spread demodulation, an angle demodulation circuit for demodulating an angle modulated wave obtained by despread demodulation to obtain an original information signal, and a BPF for extracting an interference wave component included in the angle demodulated output, A divider that divides the frequency of the clock signal into 1 / L, an adder circuit that adds the divided output and the output of the BPF, an envelope detection circuit that envelope-detects the added output, and an envelope curve. The above problem is solved by configuring the LPF that extracts a necessary frequency component from the detected output and a subtraction circuit that subtracts the low-pass filtered output and the angle demodulated output.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the SS demodulator of the present invention will be described with reference to FIG. FIG. 2 is a block system diagram of the SS demodulation device 1 of the present invention. In FIG.
Reference numerals 0 and 23 are BPFs (each pass characteristic is described later), 21 is an adder circuit, 22 is a frequency divider, 24 is an envelope (Env) detection circuit, 25 is an LPF, and 26 is a subtraction circuit. Other,
Receiving antenna 11, BPF 12, 16; despreading demodulation circuit 13, spreading code generation circuit 15, angle demodulation circuit 17, LP
Since F18 and the like have the same configuration as the conventional device shown in FIG. 1B, the same reference numerals are given and detailed description thereof is omitted.

The principle of operation of the SS demodulation device of the present invention having such a configuration will be described with reference to the signal waveform diagram of FIG. The output Ds (t) of the angle demodulation circuit 17 is (8)
In the equation, the output of the LPF 18 is the same as that shown in the equation (9), respectively, but in the equation (8), Pn (t) S (t) becomes small in level and may be omitted. Therefore, the angle demodulation output Ds (t) is

[0023]

[Equation 10] ………………………… (10) However, Am (t) = Pn ′ (t) −Pn (t) (ω _n0 −ω ₀ ). Spreading components Pn '(t) and Pn (t) pass through BPF 20 that transmits only a frequency band near 1 / L, which is the reciprocal of period L of the spreading code, and the first term on the right-hand side of equation (10) and Second
The low frequency component of the term is removed, and the diffuse interference component Am
A band-limited interference component of (t) is obtained, and the spread component Pn
The continuous frequency components in (t) are the components of the interference wave (ω _n0
The signal is amplitude-modulated by −ω ₀ ) {see FIG. 3 (A)}.

On the other hand, the clock signal C (t-τ) supplied from the input terminal In3 is 1 / which is the reciprocal of the spread code period L.
It is also supplied to the frequency divider 22 having a frequency division number of L to obtain a frequency-divided clock signal, and further the frequency-divided clock signal is transmitted to the BPF 23 that passes only the fundamental frequency component of the frequency-divided clock signal. A signal having the same frequency as the reciprocal, that is, a carrier signal is generated. The obtained carrier signal is referred to as B above.
The amplitude-modulated wave that is the output of the PF 20 (the signal that has been subjected to the amplitude modulation) is supplied to the adder circuit 21 and added (synthesized),
A signal with a waveform as shown in (B) is obtained. As a result, BP
Even if the amplitude of the interference wave is large and the degree of modulation is deep (overmodulation), the amplitude-modulated wave from F20 is prevented from being distorted as an amplitude-modulated wave.

The output of the adder circuit 21 (amplitude modulated wave to which the carrier signal is added) is supplied to the envelope detection circuit 24 and AM detection is performed to obtain an output signal having a waveform as shown in FIG. 3C. Next, the LPF 25 removes high frequency components, and the direct current component is cut by a capacitor or the like (not shown) to generate a signal having a waveform as shown in FIG. 3 (D). This signal is, of course, the same as the interference wave component (ω _n0 −ω ₀ ) shown in FIG. 3 (A). By supplying this to the subtraction circuit 26, the output D ( t) Cancel (cancel) the interference wave component included in {see Eq. (10)}. As a result, an output in which the interference wave component is sufficiently suppressed can be obtained from the output terminal Out. That is, the information S (t) with good S / N is output.

[0026]

As described above, according to the SS demodulator of the present invention, the interference wave component existing (dropped) in the demodulation information frequency band and the reciprocal (1 / L) of the period L of the spread code are calculated. The interference wave component modulated by the frequency is separated and detected, the interference wave component existing in the demodulation information frequency band is canceled by the subtraction process, and the demodulation information in which the interference is sufficiently suppressed is output.
As a result, the S / N ratio is good when the information signal is an analog signal, and the data error can be greatly reduced when the information signal is a digital signal such as data.

[Brief description of drawings]

FIG. 1 is an SS modulator in SS communication and a conventional SS.
The block diagram which shows a demodulator.

FIG. 2 is a block diagram of an SS demodulation device of the present invention.

FIG. 3 is a signal waveform diagram (timing chart) for explaining the operation of the device of the present invention.

[Explanation of symbols]

 1 ... SS demodulation device 2 ... angle modulation circuit 3 ... spreading modulation circuit 5,15 ... spreading code generation circuit 6,12,16,20,23 ... BPF (bandpass filter) 7,11 ... antenna 13 ... despreading demodulation circuit 17 ... Angle demodulation circuit 18, 25 ... LPF (low-pass filter) 21 ... Addition circuit 22 ... Frequency divider 24 ... Envelope detection circuit 26 ... Subtraction circuit

Claims (1)

[Claims] 1. A spread spectrum modulated wave output by angularly modulating an information signal on the side of a spread spectrum modulator and further spread-modulated with a spread code having a period L via a predetermined transmission line into which an interference wave can be mixed. In a spread spectrum demodulation device for inputting a clock signal and generating a spread code of a period L, a spread code demodulation circuit for inputting a clock signal and generating a spread code of the period L, and the spread spectrum modulated wave is inverted by the obtained spread code. Despread demodulation circuit for spread demodulation, angle demodulation circuit for demodulating an angle modulated wave obtained by despread demodulation to obtain the original information signal, and band for extracting an interference wave component included in the output of the angle demodulation circuit The frequency of the above clock signal is 1 / L
(L: spreading period), a frequency divider, an adder circuit for adding the output of the frequency divider and the output of the bandpass filter, and an envelope detection for performing envelope detection of the output of the adder circuit. A circuit, a low-pass filter that extracts a necessary frequency component from the output of the envelope detection circuit, and a subtraction circuit that subtracts the output of the low-pass filter and the output of the angle demodulation circuit. Spread spectrum demodulator.