JP2650553B2 - Spread spectrum demodulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carrier modulated spectrum diffusion reception of modulated waves, optimum spectrum demodulation operation
It relates to an improvement of the diffusion demodulation equipment.

[0002]

[Technical Background] In recent years, spread spectrum (Spre
ad Spectrum: “SS”) In communication, S
Communication between mobile units using a multiple access method based on the S technology has reached a practical range. The main reason is that it is necessary to use frequencies effectively because radio resources are finite, whereas SS signals have begun to prove to be able to contribute to an improvement in frequency utilization efficiency due to technological advances. In particular, vinegar
Since the spectrum spread modulated wave is spread over a wide frequency band and the power spectrum density of the modulated wave is very small, it has little effect on other conventional communication radio waves, etc., so it can be mixed in the existing communication frequency band There is also a big feature that it becomes. For these reasons, wireless communication by SS is also becoming familiar, and in the future, its future potential and development potential, such as application to inter-mobile communication mounted on vehicles and the like, are expected to be very high.

[0003]

2. Description of the Related Art In a spread spectrum demodulator , synchronization acquisition and synchronization holding on the receiving side are basically important, and various synchronization acquisition and holding methods have been proposed.
It has also been put to practical use. Among them, PSK (Phase Shift Keyin) which is primary modulation at the time of modulation
g) Synchronize the carrier for modulation and the clock signal for spread code used for SS modulation, which is the secondary modulation, with S
A synchronous SS modulation scheme for performing S modulation and a synchronous SS demodulation scheme for demodulating such a modulated wave are also adopted as schemes that can somewhat simplify the circuit configuration in reception demodulation.

[0004] Hereinafter, conventional specs will be described with reference to FIGS. 2 to 5.
A tor spread demodulation device will be described. Figure 2 shows a conventional spectrum
Spreading demodulation device, FIG. 3 is a specific circuit configuration of the signal processing unit serving as a major part of the DLL (delay locked loop) type synchronous holding circuit, FIG 4 is a synchronization hold characteristic in DLL synchronous holding circuit, Fig. 5 Indicates correlation characteristics indicating a sliding correlation type synchronization acquisition operation, respectively.

First, the configuration and operation of a conventional spread spectrum demodulator will be described with reference to FIG. A spread spectrum modulated wave transmitted from a transmitting side (not shown) is received by an antenna (not shown), and is received from an input terminal In2.
Through a bandpass filter (hereinafter referred to as BPF) 12, a multiplier 3 for both sliding correlation and despread demodulation,
L-type synchronous hold signal processing circuit (hereinafter, to serial signal processing <br/> circuits for D LL) supplied to 36. A spreading code generated by a spreading code generator ( hereinafter, referred to as PNG) 10 is always supplied to the multiplier 3, and a clock signal for this spreading code is a voltage controlled oscillator (hereinafter, referred to as VCO) 21. Before the synchronization is acquired, the VCO 21 sets the voltage slightly higher than when the synchronization is maintained. Therefore, the sliding correlation and the despread demodulation are performed in time series.

Next, the operation leading to synchronization acquisition (establishment) will be described. Spread spectrum modulated wave p (t) * d (t) c in which unnecessary frequency band components are attenuated or removed by BPF 12
osωt is used for demodulation from PNG 10 in multiplier 3.
Is despread by multiplication with the spread code p (t).
This spread code p (t) is generated by a spread code generator ( not shown ) on the receiving side.
Compared to the spreading code p (t) generated by the genital (PNG ) ,
Actually, it is p (t−τ) having a delay of time τ, which is expressed by adding a Λ (hat) to the letter p of p (t). Due to constraints, it is represented by “ρ (t)”. Therefore, the multiplied output from the multiplier 3 is p (t) * ρ (t) * d (t)
cosωt.

[0007] The multiplied output is branched into two systems and known.
Multipliers 4 and 5 for synchronous detection forming a Costas loop
, And a voltage-controlled oscillator (hereinafter, VC)
O) Regenerated carrier cos from 22 (ωt-φ)
And synchronous detection is performed by multiplication. Therefore, the multiplier 4 outputs (１ ／) p (t) * ρ (t) * d (t) * ｛co
A signal of sφ + cos (2ωt−φ)｝ is output, and a low-pass filter (hereinafter, referred to as an LPF) 15 at the next stage 15 outputs p (t).
The component of * ρ (t) * d (t) cos (2ωt−φ) / 2 is removed, and p (t) * ρ (t) * d (t) cos
becomes φ. If φ is a value close to 0, the output p (t) * ρ (t) * d (t) cos φ of the LPF 15 will be about １ ／ the level.

On the other hand, the multiplier 5, than V C O 22 π /
Siωt) t− obtained through the two-phase shift circuit 23
φ). Therefore, the multiplier 5
Is (− ／) p (t) * ρ (t) * d (t) *
{Sinφ + sin (2ωt−φ)}, low-pass filtering
(Hereinafter referred to as LPF) 16 to -p (t) * ρ
(T) * d (t) sin φ is output, but if φ is close to 0, the actual level will be close to 0.

The outputs of the LPF 15 and the LPF 16 are both supplied to a multiplier 6 where a multiplication between them is performed, and the output is (− ／) p ² (t) * ρ ² (t) * d
^An error signal of ² (t) sin2φ is obtained. The error signal obtained in this way is further converted into an error signal of -Ksin2φ by a loop filter 24 that determines a response time constant of the loop, and then supplied to the VCO 22 as a VCO control signal. In such a carrier recovery circuit 50 composed of a single phase-locked loop, P
SK demodulation can be performed simultaneously.

[0010] After <br/> was turned on with the spread spectrum demodulation apparatus, it is this carrier recovery circuit 50 to start working in the first, therefore, after the carrier recovery, obtained through the output terminal Out2 from LPF15 demodulation (Correlation ) output p
(T) * ρ (t) that is, the output based on the triangular output characteristic around the t ₀ point of Figure 5 is supplied to the synchronization judgment circuit 34 for performing a sliding correlation type SS synchronization, where-threshold level (Synchronous capture point SHL; see FIG. 5)
Is detected, the synchronous detection of the demodulation (correlation ) output is performed.

The synchronization detection information obtained by the synchronization determination circuit 34
It is supplied to the waveform shaping circuit 35 to the control signal (DC level)
Generates, after adding the correlation output from DLL signal processing circuit 36 where it is supplied to the adding circuit 41, VCO 21
To supply. According to the obtained addition output, VCO 21
Is controlled, the voltage-controlled oscillation output becomes a clock signal for generating a spread code at the time of maintaining proper synchronization. That is, the clock signal has the same frequency and phase (time) as the spread code generating clock signal on the modulator side.

It is necessary to maintain synchronization while following the synchronization acquisition operation. This synchronization maintaining operation is performed by the DLL circuit in the DLL signal processing circuit 36, the VCO 21, and the PN.
Performed at G10. Therefore, the synchronization maintaining operation will be described with reference to FIG. FIG. 3 is a specific circuit configuration example of the DLL signal processing circuit 36.
Are multipliers 7 and 8; bandpass filters (hereinafter referred to as BPFs)
13, 14; absolute value circuit (or envelope detection circuit)
38, 39; a subtraction circuit 42, a loop filter 40 and the like are used, and these are connected as shown in the figure.

[0013] The spread spectrum modulated wave from the BPF12 is supplied simultaneously to the multiplier 7 and the multiplier 8 through the terminal In3. On the other hand, the terminal In4 is supplied with a spreading code (i) of p (t-Δt) which is advanced by Δt (one chip) from the normal spreading code p (t) supplied to the multiplier 3, and is supplied from the PNG10. A spreading code (b) of p (t + Δt) which is Δt slower is supplied to PNG from In10. Here, Δt is the time for one bit of the spread code of the spread spectrum system, that is, one chip time. Accordingly, the output of the multiplier 7 is a PSK modulated wave which is a despread output at the time of normal operation, and is supplied to the absolute value circuit 38 via the BPF 13 having a narrow band pass characteristic capable of transmitting the PSK modulated wave. Similarly, the output of the multiplier 8 is supplied to the absolute value circuit 39 via the narrow band pass characteristic BPF 14.

Accordingly, the output of the absolute value circuit 38 is approximately p (t) * p (t-
Δt), and the absolute value circuit 39 similarly applies p (t) * p (t + Δ) to a component twice the carrier frequency.
t). These signals are supplied to a subtraction circuit 40, and the subtraction calculation power is further converted into a control signal by a loop filter 40 and supplied to a VCO 21 via an addition circuit 41. The control signal keeps synchronization. Error voltage of the DLL.

The control characteristic (synchronous holding characteristic) is a correlation characteristic of the inverse S-shaped characteristic as shown in FIG. In this figure, point (a) is a correlation output appearing at a point advanced by Δ time, and point (b) is a correlation output appearing at a point delayed by Δ time. Therefore, a point (c) between the points (a) and (b) is a synchronization holding point, and the voltage at the point (c) is an error voltage of the DLL. Note that the part (d) is a time region where no correlation is obtained. As described above, conventionally, despread demodulation on the receiving side is performed by synchronization acquisition, synchronization maintenance, and reproduction synchronization detection of a carrier for PSK modulation.

[0016]

By the way, the conventional spec
In the spread spectrum demodulator , it is clear that the basic performance such as noise immunity and interference immunity depends on the process gain of the spread spectrum system, and in the synchronous acquisition which has been used more often than before, it operates within the process gain. It does not operate when it exceeds the process gain.

Further, even if the level of the interference wave is lowered halfway, there is a problem that it takes a long time to acquire and hold the synchronization, and other than the spread spectrum demodulation using an expensive circuit element such as a matched filter. , Instantaneous rise of operation is impossible. Therefore, if a function of suppressing noise and interference waves can be obtained, noise (interference) resistance to synchronization is improved, reliability is improved, and it is easier to use. Since the noise ratio can be improved, such an interference wave suppressing function has been desired.

[0018]

The present invention has been made in view of the above-mentioned problems.
Spectrum expansion with interference waves
Receives a spread-spectrum modulated wave but despreads the spread-spectrum modulated wave.
After demodulation, obtain the demodulated output with the interference wave removed
Generate spread code in spread spectrum demodulator
A spread code generator, and the spread code is corrected by a correction filter.
Inverse for generating reciprocal spreading code after correcting frequency characteristics
A number circuit and the reciprocal circuit of the spread spectrum modulated wave.
The despread output signal is despread by the despreading spread code
And the interference wave is spread by the reciprocal spreading code.
A first multiplier to be used as diffusion noise and the first multiplier;
The despread output signal and the spread noise from
To form a Costas loop, and the Costas loop
The demodulated output signal from the voltage-controlled oscillator.
Second, a third multiplier, the co synchronous detection by Yariya
Provided in the stass loop, from the second and third multipliers.
From the spread noise band
First and second high-pass filters to be removed, and said Costas loop
And the despreading by the first and second high-pass filters.
The correction noise is applied to the diffusion noise from which the output signal has been removed.
Despreading by a spreading code through a filter
Generated spread noise is generated in the band from which
Generating fourth and fifth multipliers and the costas loop.
And the output from the fourth and fifth multipliers is
Spread by the reciprocal spreading code from the reciprocal circuit,
Diffusion noise with the band of the generated diffusion noise missing
6 to generate again, a seventh multiplier, the Costa through
And the output from the sixth and seventh multipliers.
To correct the missing band due to the generated diffusion noise
First, a second frequency characteristic correcting circuit, before returning to the diffusion noise
The first multiplier is provided in the Costas loop.
The despread output signal and the spread noise;
Subtract the diffusion noise from the second frequency characteristic correction circuit
First and second subtraction circuits for extracting only the despread output signal
And unnecessary unnecessary signals in the despread output signal from the first subtraction circuit.
A low-pass filter that removes the diffuse noise component and obtains a demodulated output
Spread spectrum demodulation device characterized by having
To offer .

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spread spectrum demodulation apparatus according to the present invention will be described below.
One embodiment of the device will be described with reference to FIGS. Figure 1
Block showing a spread spectrum demodulator according to the present invention
FIGS. 6 and 7 show a spread spectrum demodulator according to the present invention.
To suppress (eliminate) diffuse noise and generated diffuse noise
It is a spectrum figure for demonstrating work. Shown in FIG.
In the spread spectrum demodulator according to the present invention,
When demodulating these spread spectrum modulated waves by despreading,
Spread noise due to the interference wave included in the reception and this interference
The frequency of demodulated information in the process of removing diffusion noise due to waves
Eliminates newly generated diffusion noise corresponding to the band
Thus, the signal-to-noise ratio ( S / N ratio) of the demodulated information can be significantly improved . In addition, of explanation
For the sake of convenience, the same constituent members as those shown in the conventional example above are used.
The same reference numerals are used for the description, and
A description will be given by attaching new reference numerals to constituent members different from those described above.

In FIG. 1, reference numerals 25 to 28 denote multipliers for reproducing diffusion noise, reference numerals 19 and 20 denote correction filters and reciprocal circuits for reproducing diffusion noise, reference numerals 29 and 30 denote frequency characteristic correction circuits, and reference numerals 31 and 32 denote demodulation information. High-pass filter for removal (hereinafter
Below, it is described as HPF) , 43, 44 are subtraction circuits, 17, 1
Reference numeral 8 denotes a low-pass filter (hereinafter, referred to as an LPF) , and the same components as those of the conventional device shown in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The spectrum expansion received from the input terminal In1.
The scattered modulated wave is attenuated or eliminated by a BPF (low-pass filter) 12 to remove unnecessary components other than the main lobe band, and then a multiplier 3 for both sliding correlation and despread demodulation, and a DL
It is supplied to the L signal processing circuits 3 6. On the other hand, VCO (power
A clock signal is generated in the pressure control oscillator 21. The clock frequency is set to be slightly higher than that used for spread modulation on the transmission side, compared to the time when synchronization is maintained, until synchronization is acquired. I have. Then, the sliding correlation and the despread demodulation are performed in time series.

Based on such a clock signal, PNG (spreading)
A code generator 10 generates a spread code ρ (t) for demodulation . This spreading code ρ (t) is obtained by
Wave transmission system and input correction filter designed in consideration of the transmission characteristic of the filter (hereinafter, referred to as LPF) is corrected frequency characteristic by 19, inverse of the spreading code {[rho further by reversed several circuits 20 ( t)｝ ^{− 1} , the multiplier 3 and L
Output to PF17. Therefore, in the multiplier 3, the input spread spectrum modulated wave S (t) and the inverse spread code ｛ρ
(T) Sliding correlation with ^{−１ −1} is performed, and a state where the sign coincides instantaneously occurs as an output of the sliding correlation. S (t) * {ρ (t)} ⁻¹ and spec
Interference components, such as noise and interference waves, which are caused by the tor spread modulation wave are generated. At this time, the spreading code ρ (t) from PNG10 is converted to LP
After correcting the frequency characteristic in F19, the reciprocal is calculated by the reciprocal circuit 20.
Ρ (t)} ^{− 1} , and the inverse spread code
Spread spectrum modulated wave s by code {ρ (t)} ^-1
Since (t) is despread, S / N during despread is improved.
it can.

Assuming that this interfering component is I (t), this I
(T) is multiplied by a reciprocal spreading code {ρ (t)} ⁻¹ as a composite component (also referred to as diffusion noise) of diffusion noise I (t) * {ρ (t)} ⁻¹ of the multiplier 3 Occurs in the output signal. Such a complex component is branched into two systems to form a well-known
It is sent to multipliers 4 and 5 forming a sta-loop, where
After carrier recovery and synchronous detection by the multiplier 4 ,
The signal is supplied to the HPF 31 for removing demodulated information and the subtraction circuit 43 via the LPF 15 for transmitting the baseband converted SS signal. The HPF 31 removes a signal component corresponding to a frequency band of demodulated information obtained by demodulating the spread spectrum modulated wave ,
Output to the multiplier 25. The multiplier 25 performs multiplication with the output of the correction filter 19 and outputs the result to one input terminal of the multiplier 27.

The other input terminal of the multiplier 27 has an LPF
17 is supplied. Note that the LPF 17 is used to remove the high-frequency part and the side lobe of the main lobe of the frequency spectrum of the inverse spread code {ρ (t)} ⁻¹ . Therefore, only the middle and low frequency components of the main lobe of the reciprocal spreading code are supplied to the multiplier 27.
The frequency band component of the demodulated information lost by F31 is partially restored and output.

The partial restoration output is supplied to the frequency characteristic correction circuit 29, where the partial restoration in the necessary frequency band is corrected so as to be completely restored, and is output as a restored composite component. The restored composite component is added to the subtraction circuit 43
Where the subtraction is performed with the sliding correlation output from the LPF 15 , and the composite component is canceled (suppressed) by the canceling operation. That is, the CN whose diffusion noise is suppressed is reduced by the correlation output at the time of correlation (see FIG. 5) and the composite component (diffusion noise) generated at the time of the correlation operation (all times).
A good correlation output (signal-to-noise ratio) is obtained.

[0026] In the circuit leading to the subtraction circuit 4 4 than the other of the multiplier 5 in Costa loop, instead of the reproduction carrier cos (ωt-φ) of from VCO 22, this π
A carrier of sin (ωt−φ) whose phase is shifted by π / 2 in the / 2 phase shift circuit 23 is supplied.
Since the configuration and function of the circuit from the multiplier 4 to the subtraction circuit 43 are the same, detailed description of the operation is omitted.

The two correlation outputs from the subtraction circuits 43 and 44 whose C / N ratios have been greatly improved are both supplied to a multiplier 6 and multiplied to generate an error signal. Further, the response time constant of the loop is reduced. -Ksin2 in the loop filter 24 to be determined
After being converted into an error signal of φ, it is supplied to the VCO 22 as a VCO control signal. In such a carrier recovery circuit comprising a single phase locked loop, PSK demodulation can be performed simultaneously in synchronization with the input carrier.

On the other hand, the output of the subtraction circuit 43 is also supplied to the LPF 18, where unnecessary diffusion noise components are removed, and then output as a demodulated signal from an output terminal Out1, and a synchronization determination including an envelope detection circuit is performed. Circuit 34
(For synchronous acquisition). Here, the correlation output of the positive and negative polarities generated in the SS modulation signal is adjusted to one polarity to provide an appropriate integration time constant. That is, the obtained converted correlation output is supplied to the synchronization determination circuit 34, and the synchronization is detected by the preset threshold level SHL.

After the detection information at the time of the synchronization detection is converted into a control signal by the waveform shaping circuit 35, a VC
By supplying the clock to the O21, a clock having the same frequency as the clock at the time of the spread modulation is generated from the VCO 21,
Supply to PNG10. Since the time (clock frequency) of the spread code obtained in this way matches the time of the spread code used for spread modulation on the transmission side, synchronization is established. The synchronization detection information is supplied to the waveform shaping circuit 35 to generate a control signal. The control signal is added to the correlation output from the DLL signal processing circuit 36 by the addition circuit 41, and then supplied to the VCO 21 for synchronization acquisition and synchronization. doing.

As described above, since the VCO 21 is controlled by the output from the adder circuit 41, the voltage-controlled oscillation output is a clock signal for generating a spread code at the time of maintaining normal synchronization. That is, a clock signal having the same frequency and phase (time) as the clock signal for generating the spreading code on the modulator side is supplied to the PNG 10 for synchronization acquisition, synchronization holding, and despread demodulation.

Here, the spread spectrum decoding according to the present invention will be described.
Suppresses the diffuse noise and generated diffuse noise (excluding
The operation to be described later will be described in detail with reference to FIGS.

First, the spread spectrum sent from the transmitting side
In the frequency band of the modulated wave DS (f),
There is no interference wave I (f) from another station. Follow
Input terminal In1 when received by an antenna (not shown).
Spread-spectrum modulated wave DS mixed with interference wave I (f)
(F) has been input. Then, as shown in FIG.
Thus, the spread spectrum modulation input to the input terminal In1
The wave DS (f) and the interference wave I (f) are BPF (band-pass filtered).
Unit 12), and the spectrum spread by the BPF 12
Unwanted components other than the band of the modulated wave DS (f) are attenuated or eliminated.
After being removed, the spread spectrum modulated wave DS (f) and the interference
Wave I (f) is sent to multiplier 3.

Next, from a PNG (voltage controlled oscillator) 10
Is transmitted to an LPF (correction filter) 19
The frequency characteristics are further corrected, and the reciprocal
Ρ (t)} ⁻¹ and the multiplier 3 and
The signal is output to an LPF (low-pass filter) 17. And FIG.
As shown in (B), the multiplier 3 outputs the signal from the reciprocal circuit 20.
Spread spectrum by reciprocal spreading code {ρ (t)} ^-1
The modulated wave DS (f) is despread to obtain a despread output signal D
(F), while the interference wave I (f) is spread,
A spread output signal IS (f) that becomes a noise component is obtained and despread.
Multiplier for output signal D (f) and spread output signal IS (f)
It is sent in a state of branching to 4,5.

Next, the multipliers 4 and 5 are connected to the well-known Costa
And one multiplier 4 performs inverse expansion.
By the diffuse output signal D (f) and the diffuse output signal IS (f)
Carrier from VCO (voltage control circuit) 22 to the composite component
Is multiplied by the carry of the despread output signal D (f).
After reproduction and synchronous detection, an HPF (high-pass filter) 3
1 and the subtraction circuit 43. The other multiplier 5
Then, the despread output signal D (f) and the spread output signal IS
VCO (voltage control circuit) 22
Key shifted by π / 2 from the
Carrier and the despread output signal D (f)
After carrier recovery and synchronous detection, HPF (high-pass filtering)
) 32 and a subtraction circuit 44.

Next, as shown in FIG.
In the HPFs 31 and 32 in the loop, the despread output signal D
The frequency band components corresponding to (f) are removed respectively, and
The spread output signal IS (f) serving as a noise component is a despread output.
The state where the frequency band component corresponding to the signal D (f) is removed
Then, the remaining diffused noise signal IS '(f) becomes
These are sent to the multipliers 25 and 26 in the task loop, respectively.

Next, as shown in FIG.
In the multipliers 25 and 26 in the loop, the signal from the PNG 10 to the LP
The frequency characteristic is corrected through an F (correction filter) 19.
With the spread code ρ (t), the remaining spread noise signal iS
'(F) are respectively despread and converted into the original interference wave signal I (f).
Returned, the original interference wave signal I (f) is in the Costas loop
To the multipliers 27 and 28, respectively. Where Costas
In the multipliers 25 and 26 in the loop, the remaining spread noise signal
When the signal IS '(f) is despread, the despread output signal D
The part where the frequency band component corresponding to (f) is removed is diffused
And a diffusion noise signal n generated by the removed portion.
(F) newly occurs as shown by the dotted line.

Next, as shown in FIG.
Multipliers 27 and 28 in the loop receive signals from reciprocal circuit 20.
The inverse spread code {ρ (t)} ⁻¹ is an LPF (low-pass filtering).
Unit 17). In addition, LPF17
Is the frequency spectrum of the inverse spreading code {ρ (t)} ⁻¹
To remove the high frequency and side lobes of the main lobe
Used for Then, as shown in FIG.
In the multipliers 27 and 28 in the Costas loop, the LPF
The inverse of the spreading code {ρ ^{(t)} -1} passing through the 17
And the original interference wave signal I (f) from the multipliers 25 and 26 is
While being despread, the raw signals newly generated in the multipliers 25 and 26 are generated.
The diffusion noise signal n (f) is diffused, and the two are synthesized.
The synthesized signal iS ′ (f) is obtained.
(F) is a frequency characteristic correction circuit 29 in the Costas loop ,
30, respectively. Where the square in the Costas loop
The synthesized signal iS ′ (f) obtained by the arithmetic units 27 and 28 is
A portion of a frequency component corresponding to the generated diffusion noise signal n (f)
Is missing.

Therefore, as shown in FIG.
In the frequency characteristic correction circuits 29 and 30 in the sloop, multiplication is performed.
In the composite signal iS ′ (f) obtained by the devices 27 and 28
Repairs and corrects missing band corresponding to diffused noise signal n (f)
To obtain the corrected combined signal iS ″ (f),
The signal iS ″ (f) is subtracted from the subtraction circuit 43 in the Costas loop,
Send to 44.

Next, as shown in FIG.
In the subtraction circuits 43 and 44 in the loop,
The output from the LPFs 15 and 16 (FIG. 6B) and the cost
Output from the frequency characteristic correction circuits 29 and 30 in the task loop
6 (G)}, thereby obtaining demodulated information.
Although D (f) is obtained, the result of this subtraction
The size ps (f) is left.

Next, as shown in FIG.
The demodulated information D (f) from the subtraction circuit 43 in the loop and the residual
Diffusion noise ps (f) to LPF (low pass filter) 18
Where the residual diffusion noise ps (f) is removed and
Finally, demodulation information D (f) is obtained. Therefore, FIG.
And the interference wave I (f) mixed in the transmission system is almost completely removed.
And the process of removing the interference wave I (f)
Newly generated corresponding to the frequency band of demodulation information D (f)
At a glance that the generated diffusion noise
It is obvious. Also, the subtraction circuit 43 in the Costas loop
Output from the subtraction circuit 44 in the Costas loop.
Is multiplied by a multiplier 6 to obtain an error signal.
The signal is applied to the loop filter 24 which determines the response time constant of the loop.
After being converted into an error signal -Ksin2φ
It is supplied to the VCO 22 as a control signal. Furthermore,
The final demodulated information D (f) obtained by the LPF 18 is
And supplies the synchronization determination circuit 34 as described above.

By the way, the spread spectrum according to the present invention
In the demodulator, the spread noise suppression function must be
Not be affected by interference waves
In practice, it is better to acquire synchronization than to maintain synchronization.
Is susceptible to interference waves, etc., and S / N
There is no practical problem if it can be improved. Synchronization hold times
Loop filter 40 having a sufficiently large integration time constant
Because it is used, even if the interference wave level is quite strong,
This can be sufficiently absorbed.

[0042]

The spectrum according to the present invention described in detail above.
According to the spread demodulator, especially generated by the spread code generator
Frequency characteristics of the spread code
After that, a reciprocal spreading code is generated by a reciprocal circuit.
Spread spectrum modulated wave is despread by spreading code
Therefore, the S / N at the time of despreading can be improved. Also, the spect
The interfering wave mixed into the spread-spectrum modulated wave is expanded to the reciprocal spreading code.
When removing diffuse noise that occurs when
Spread noise generated by despread output signal of tor spread modulated wave
Appears in the diffuse noise in a missing state,
Compensate for the missing band due to the diffusion noise and complete the diffusion noise.
Because it has been completely removed, the spread spectrum modulated wave
Finally, a demodulated output with a good S / N can be obtained.

[Brief description of the drawings]

1 is a block diagram showing the spread spectrum demodulator according to the present invention.

FIG. 2 is a block diagram of a conventional spread spectrum demodulator.
There is .

FIG. 3 is a circuit configuration diagram of a signal processing unit serving as a main part of a DLL type synchronization holding circuit.

FIG. 4 is a diagram showing synchronization holding characteristics in a DLL type synchronization holding circuit;
It is .

5 is a correlation graph showing the sliding correlator synchronous catching operation.

[6] suppresses <br/> diffusion noise and generate diffusion noise caused by the spread spectrum demodulation apparatus according to the present invention (removal) operates
FIG. 4 is a spectrum diagram for explaining

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Spread spectrum demodulator 3 ... 1st multiplier (multiplier) 4, 5 ... 2nd, 3rd multiplier (multiplier) 25, 26 ... 4th, 5th multiplier (multiplier) 27, 28 ... Sixth and seventh multipliers (multipliers) 10 ... Spreading code generators (PNG) 12 to 14 ... Band-pass filters (BPF) 15 to 18 ... Low-pass filters (LPF) 19 ... Correction filters (LPF) 20 . Reciprocal circuits 21, 22 ... voltage controlled oscillator (VCO) 23 ... π / 2 phase shift circuits 24, 40 ... loop filters 29, 30 ... first and second frequency characteristic correction circuits (frequency characteristics
Sex correction circuit) 31, 32 first, second high frequency filter (HPF) 34 ... synchronization determination circuit 35 ... waveform shaping circuit 36 ... DLL synchronous holding signal processing circuit 38, 39 ... absolute value circuit (envelope detector circuit) 41 ... adder circuit 42 ... No. calculation circuits 43 and 44 ... first, second subtraction circuit (subtraction circuit) 50 ... carrier reproducing circuit

Claims (1)

(57) [Claims] 1. A spread spectrum modulated wave mixed with an interference wave.
Even after receiving, after despreading the spread spectrum modulated wave
Spectrum for obtaining demodulated output with the interference wave removed
In a spread demodulator, a spread code generator for generating a spread code, and a frequency characteristic of the spread code corrected by a correction filter.
A reciprocal circuit for generating the inverse of spreading codes after the inverse of the spread spectrum modulated wave from the inverse unit
Despread with digitized spreading code to get despread output signal
Also, the interference wave is spread by the reciprocal spreading code and expanded.
A first multiplier serving as scattered noise, and the despread output signal and the spread signal from the first multiplier
The noise is branched into two paths to form a Costas loop,
Voltage-controlled oscillator for despreading the output signal in a Costas loop
2nd and 3rd power for synchronous detection by demodulation carrier from
An arithmetic unit and the second and third multiplications provided in the Costas loop.
The despread output signal from the filter to the spread noise band?
A first and a second high-pass filter for removing the first and second high-pass filters, respectively, provided in the Costas loop;
The spread noise obtained by removing the despread output signal with a filter
Is inversely expanded by the spread code through the correction filter.
To the band from which the despread output signal has been removed.
A fourth and fifth multiplier for generating generated diffusion noise, and the fourth and fifth multipliers provided in the Costas loop.
Output from the reciprocal circuit to the reciprocal expansion.
Spreading by the spread code, the band of the generated spread noise is lost.
6th and 7th power to generate diffusion noise again in the dropped state
An arithmetic unit and the sixth and seventh multiplications provided in the Costas loop.
Zone due to the generated diffusion noise with respect to the output from the filter
1st and 2nd frequency characteristics to correct the frequency range and return to the original diffusion noise
A sex correction circuit , provided in the Costas loop, from the first multiplier.
The despread output signal and the spread noise of the
1, subtraction from diffusion noise from the second frequency characteristic correction circuit
First and second subtraction circuits for extracting only the despread output signal
Path and unwanted spreading in the despread output signal from the first subtraction circuit.
A low-pass filter that removes noise components and obtains a demodulated output.
A spread spectrum demodulator characterized by the above.