JP2523410B2 - Spread spectrum demodulator - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum modulation / demodulation device, and more particularly to various interference waves and noises contained in a spread spectrum signal obtained through an arbitrary transmission means or recording / reproducing medium. The present invention relates to a spread spectrum demodulation device suitable for use in a package system, a broadcast system, etc., which can be greatly suppressed by a demodulation side with a relatively simple configuration.

[0002]

2. Description of the Related Art In various fields dealing with information, how to increase the amount of information within fixed limits is an eternal theme. It is not an exaggeration to say that recent technological advances and directions are represented by highly efficient coding and modulation / demodulation techniques. For example, multi-level QAM (Quadrature Amplification) in the communication field
As seen in the application of itude modulation to quadrature amplitude modulation 振幅 in mobile communications, it can be said that research and development of techniques for increasing the transmission speed within a predetermined frequency band are common.
However, for multilevel QAM, 16QAM to 256
Although progress has been made in QAM and multi-valued, considering this vector, the next becomes 2 ¹⁶ (= 65536) QAM, which is unrealistic. For example, to realize a capacity 1.5 times that of 256 QAM, 4096 QAM is required. From such a thing,
In the future, research on the integration of modulation / demodulation technology and coding technology will become more and more desired, and research and development to increase the amount of information based on new ideas that are not bound by conventional thinking are expected.

Spread spectrum (Spread Spectr) is one of the integration of modulation / demodulation technology and coding technology that can meet such expectations.
um: hereinafter also referred to as “SS”) modulation and demodulation method.
The SS modulation / demodulation method is such that the modulation side spread-modulates an information signal or the like with a wideband noise-like spreading code to spread over a very wide frequency band, and the demodulation side is equivalent to the spreading code used on the modulation side. This is a method of despreading with a spreading code.
The SS communication method for performing communication using such a modulation / demodulation method has a very high degree of confidentiality, is resistant to external interference, noise, and intentional interference, can coexist with a conventional system, and can transmit with weak power. Since there are many features such as multiplexing in the same frequency band by changing the noise code,
Nowadays, it is being applied not only in the field of communication equipment but also in other fields, and its application to consumer equipment is also beginning.

[0004]

2. Description of the Related Art The basic idea of the SS modulation and demodulation method including the SS communication method is that information is output during demodulation when there is interference between the modulation section (transmission side) and the demodulation section (reception side). A canceling interference wave component is generated from the interference wave (interference wave) component, and by the calculation processing of the demodulation output and the generated interference wave component,
This is based on the idea of obtaining only an information signal, and spread spectrum modulation and demodulation are used for the modulator and demodulator, respectively.

Such SS communication system (SS modulation / demodulation system)
FIG. 3 shows a basic configuration of an SS communication (SS modulation / demodulation) device capable of implementing the above. In the figure, 2 and 3 are multipliers, 6 is ROF
(Roll-off filter), 8 and 9 are spread code generation circuits (PNG), 10 is a modulator (SS modulator), and 11 is L.
PF (low-pass filter), 17 is a subtractor, 20 is a demodulator (S
S demodulator), 21 is an HPF (high-pass filter), and 25 is a noise generation circuit. PNG8 and 9 are input terminals In _{2 and} In respectively
_A spread code P (t) (usually a pseudo noise code) is generated based on mutually equivalent clock signals C (t) from ₄ , and both are synchronized. ROF6 is usually cosin ro
It has the ll off characteristic and is configured to limit the band while preventing the intersymbol interference problem. Although the adder 19 does not exist in the actual SS communication device, it is drawn for convenience of explanation of the interference wave removing operation.

In the SS modulation / demodulation apparatus having the above-mentioned configuration, the information signal d (t) such as data given from the input terminal In ₁ of the modulation section 10 is removed by the ROF 6 after unnecessary frequency components are removed, and then is sent to the multiplier 2. Supplied. On the other hand, in the PNG8, the spread code P is generated based on the clock signal C (t) from the input terminal In _2.
(t) is generated and is supplied to the multiplier 2 to supply the information signal d
Spreading modulation is performed by multiplying (t), and the modulated signal D _ss {= d (t) * P (t)} is output from, for example, an antenna (not shown) via the output terminal Out1. Here, assuming that the interference wave mixed during passing through the transmission medium is I (t), the input signal to the demodulation unit 20 is represented by d (t) * P (t) + I (t).

In the PNG9 on the demodulation section 20 side, the input terminal In
_Based on the clock signal from _4, a spreading code P (t) equivalent to the PNG8 is generated and supplied to the despreading multiplier 3. Despreading output from the multiplier 3 is therefore, {d (t) * P (t) + I (t)} P (t) = d (t) * P 2 (t) + I (t) * P ( t) ………… (1). By the way, since P (t) is a code that takes only a value of 1 or -1, P ² (t) = 1. Therefore, the despread output is d (t) + I (t) * P (t). That is, demodulation information d
The diffused interference wave I (t) * P (t) in which the interference wave is diffused is output to (t) as being mixed. If such an output signal is passed through an LPF (low pass filter) 11 having appropriate characteristics,
The demodulation output d (t) + n (t) {n (t): noise component} is obtained {a typical conventional configuration}.

On the other hand, when the HPF 21 (high-pass filter) having the same cutoff frequency as the LPF 11 (first order) is passed, the HPF 21
21 output is I (t) * P (t) -n (t). This HPF
The output is supplied to the noise generation circuit 25 at the next stage, where -n
By making the (t) component extremely small, I
(t) * P (t) remains. The canceling generated diffused interference wave I (t) * P (t) thus obtained is subtracted from the despreading output d (t) + I (t) * P (t) in the subtractor 17. The diffuse interference wave component is canceled by the calculation, and almost only the information d (t) is output (a more improved conventional configuration).

[0009]

As described above, the principle is quite clear, but since it is based on the subtraction method, it is an important point how much the accuracy of the generated interference wave can be improved. Since the shapes, the phases, and the amplitudes can be completely matched to cancel each other, it is difficult to suppress 10 dB if they are compared and observed with an oscilloscope or the like and appear to be substantially equal. In addition, since it covers a very wide frequency band, wideband circuit technology is also required. Furthermore, since sharing the same frequency inevitably prevents mutual interference, if the signal power from other stations becomes very large, S
Even in the S communication method, the performance deteriorates due to the interference wave.

Therefore, if the SS signal power of the local station is increased, the quality of the signal is improved, but there is a problem that interference with other signals cannot be ignored. Furthermore, the conventional method is effective only for known SS interference waves,
Random noise and unknown SS interference waves can hardly be dealt with, and when trying to deal with a plurality of known SS interference waves, a plurality of despread demodulators, a plurality of narrowband filters having different pass bands, a plurality of spreaders. A modulator loop and an adder are required, which has a drawback that the structure is considerably complicated and the cost is increased.

[0011]

A spread spectrum demodulator according to the present invention includes an input filter for removing a high frequency interference signal component in a main code band or more of a spread code from an input signal,
A spreading code generating circuit for generating a spreading code equivalent to the spreading code on the modulator side, a correction filter having a transfer function substantially equal to that of an input filter, and a spreading code signal transmitted from the spreading code generating circuit to the correction filter. A reciprocal circuit for taking the reciprocal of the corrected spread code, the first multiplier for despreading by multiplying the output signal of the reciprocal circuit by the output signal of the input filter, and the output signal of the multiplier. A low-cut filter for removing the demodulation information signal component,
A second multiplier that multiplies the output of the low-cut filter by the spread code to be corrected, a high-cut filter that removes high-frequency components from the output of the multiplier, and the output of the high-cut filter by the output of the reciprocal circuit. A third multiplier that performs the correction, an equalizer circuit that corrects the spectrum of the spread interference signal obtained by the multiplier to be substantially equal to the spectrum of the spread interference signal in the output of the first multiplier, and the output of the equalizer circuit. And a first multiplier output, and a subtracter for subtracting the output of the first multiplier and a low-pass filter for removing high-frequency components above the demodulation information signal in the subtractor output. However, the demodulation loss has been greatly reduced.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The spread spectrum demodulation device of the present invention (hereinafter referred to as "S
(Also referred to as “S demodulator”) will be described with reference to the drawings. FIG. 1 is a block diagram of an SS demodulation device 1 of the present invention. In this figure, the same components as those of (the demodulation unit 20 of) the conventional device shown in FIG. To do. In the figure, 3 to 5 are multipliers, 1
2 and 13 are input filters and correction filters of the transfer function H _L (s), 14 is an inverse circuit, 15 is LCF (low cut filter, high-pass filter), 16 is HCF (high-cut filter, low-pass filter) , 18 are equalizer circuits. The characteristics of the equalizer circuit 18 may be equivalent to those disclosed in Japanese Patent Application No. 2-253689, which is a prior application of the present applicant.

Next, the function and operation of the SS demodulator 1 will be described with reference to the signal waveform diagram (frequency spectrum) of FIG. In addition to the SS modulation signal d (t) * P (t), interference signals I1 (t), I2 (t), noise, etc. are included in the signal coming into the input terminal In ₃ of the SS demodulator 1. It is generally mixed. I1 (t) and I2 (t) are, as shown in FIG. 2 (A),
The interference signal having a low frequency and the interference signal having a high frequency are represented respectively. Such input signal d (t) * P (t) + I1 (t) + I2 (t)
First, unnecessary frequency components having a frequency of 1 / T or more (frequency components other than the main lobe of the spread signal) are removed by the first-stage filter 12. As a result, the interference signal I2 (t) is completely removed, but the high frequency component of the SS modulation signal d (t) * P (t) is also reduced, so that it is supplied to the multiplier 3 for despreading. The resulting signal is d (t) {P (t) -P '(t)} + I1 (t) {see FIG. 2 (B)}.

On the other hand, the clock signal C from the input terminal In ₄
The spread code P (t) generated by the PNG 9 based on (t) is supplied to the correction filter 13. Since the correction filter 13 has substantially the same transfer function as the filter 12, its output (corrected spread code) is P (t) -P '(t). The corrected spread code is supplied to the reciprocal circuit 14 and the multiplier 4. The reciprocal circuit 14 outputs a reciprocal signal of 1 / {P (t) -P '(t)} and supplies it to the multipliers 3 and 5. To be done. Therefore, from the despreading multiplier 3, the spread interference signal component I1 (t) / {P (t) -P '(t)} is mixed and output in addition to the demodulated data d (t). {Refer to FIG. 2 (C)}. In the despread output, the demodulated data d (t) is removed by the LCF 15 in the next stage, {the removal component is α (t)} I1 (t) / {P (t) -P '(t)}. -Α
(t) and {see FIG. 2 (D)}, and the multiplier 4 multiplies the corrected spread code to obtain I1 (t) -α (t) {P (t) -P '.
(t)} and is supplied to the HCF 16 in the next stage.

That is, the multiplier 4 causes the interference signal component I1 (t)
However, it is not a complete restoration to be exact, and the level is slightly reduced by the amount removed by the LCF 15, so I _{1 ′} is written in FIG. 2 (E). Further, for the same reason, i ₁ P is also written in FIG. 2D, but for convenience of description, the description will be given here as “I 1 (t)”. HC
As can be seen from FIG. 2 (F), F16 is a filter that cuts off the high frequency component of the main lobe of the SS frequency band, which allows the interference signal component I1 (t) to be transmitted as it is and is a spread component α. (t) {P (t) -P '(t)} is band-limited {the removal component is β (t)}. This allows
The output of the HCF 16 is I1 (t) + α (t) {P (t) -P '(t)}-
.beta. (t), which is supplied to the multiplier 5 where it is multiplied by the reciprocal output from the reciprocal circuit 14, and the output is I1 (t) / {P (t) -P '(t )}-Α (t) + β (t)
A signal of / {P (t) -P '(t)} is obtained and supplied to the equalizer circuit 18 in the next stage.

The equalizer circuit 18 includes unnecessary components -α (t) (spreading interference signal components in the data frequency band) and β (t) / {P (t) -P in the output signal of the multiplier 5. '
(t)} {Spreading interference signal component that is in antiphase with α (t)}
Is reduced to 0 or a low level without causing any trouble. Therefore, the frequency spectrum of FIG. 2 (G) has the low-frequency component corrected by the equalizer circuit 18 as shown in FIG. 2 (H). That is, the signal processing from the LCF 15 to the equalizer circuit 18 generates the suppressing spread interference signal I1 (t) / {P (t) -P '(t)} + γ (t), which is By supplying the despreading output d (t) + I1 (t) / {P (t) -P '(t)} to the subtractor 17 of the stage, the diffuse interference component is canceled, d (t) −γ
(t) is obtained. Of these, the residual component γ (t) is the LP of the next stage.
Almost all of the demodulation information data d (t) is almost removed at F11 and is output from the output terminal Out2.

[0017]

As described above, according to the spread spectrum demodulation device of the present invention, even if a filter (input filter) having a cutoff frequency in the SS signal frequency band is used, the influence of the interference signal can be obtained without any problem. This can be avoided, and the spread interference signal, spread noise, etc. in the despread output can be efficiently suppressed or removed. The interference signal includes other SS modulation signals that are not synchronized with the SS modulation signal used in the device of the present invention, and the same reduction effect can be obtained. Therefore,
Widely applicable for demodulation of SS communication device,
For example, it has an excellent feature that it can contribute to the spread and development of in-vehicle wireless telephones and cordless telephones.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a spread spectrum demodulation device of the present invention.

FIG. 2 is a signal spectrum diagram for explaining the operation of the SS demodulation device of the present invention.

FIG. 3 is a block diagram showing a basic configuration of a conventional SS modulation / demodulation device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 SS (spread spectrum) demodulator 2-5 Multiplier 8,9 Spreading code generation circuit (PNG) 11 LPF (low-pass filter) 12 Input filter 13 Correction filter 14 Reciprocal circuit 15 LCF (low-cut filter) 16 HCF ( High cut filter) 17 Subtractor 18 Equalizer circuit.

Claims (1)

(57) [Claims] 1. A spread spectrum signal obtained by spreading and modulating an information signal with a spread code in a spread spectrum modulator and various interference signals mixed in a transmission system are input, and despreading is performed by multiplication. In a spread spectrum demodulation device for demodulating an information signal, an input filter for removing a high-band interference signal component in the input signal above a main lobe band of the spread code and a spread code equivalent to the spread code on the modulator side are generated. A spreading code generating circuit, a correction filter having a transfer function substantially equal to that of the input filter, and a reciprocal number of the spread code to be corrected obtained by transmitting the spreading code signal from the spreading code generating circuit to the correction filter. A reciprocal circuit, a first multiplier for performing despreading by multiplying an output signal of the input filter by an output of the reciprocal circuit, and a multiplier of the multiplier. A low-cut filter that removes a demodulation information signal component of the output signal, a second multiplier that multiplies the output of the low-cut filter by the corrected spread code, and a high-frequency component of the output of the second multiplier. , A third multiplier for multiplying the output of the high cut filter by the output of the reciprocal circuit, and the spectrum of the spread interference signal obtained by the third multiplier for the first multiplier. An equalizer circuit that corrects the spread interference signal so that it has a spectrum substantially equal to that of the spread interference signal, a subtractor that subtracts the output of the equalizer circuit from the output of the first multiplier, and the demodulation information of the subtractor output. A low-pass filter that removes high-frequency components above the signal, and is configured to output a demodulated information signal from which the various interference signal components are substantially completely removed. Spread spectrum demodulation apparatus.