JPH06141020A - Method and device for demodulating spread spectrum signal - Google Patents

Abstract

PURPOSE:To surely demodulate reception data even when it is hard to detect a correlation peak by an impulse noise, etc., by normalizing the integral of the square or the absolute value of the correlation value in a time window in which the correlation peak can exists, and demodulating the reception data from comparison between them. CONSTITUTION:A transmission request signal RS is inputted to a timing generator 3, and a switch 6 is turned on by the output of the generator. The circuit 3 inputs a clock signal to PN sequence generators 1, 2, and outputs PN1 and PN0 sequence signals to a switch 5. Communication data SD is inputted to a synchronizing circuit 4, and the signals PN1 and PN0 are selected by switching the switch 5 corresponding to the output clock signal of the circuit 4, and outputs them to a transmission line 10 via the switch 6, an amplifier 7, a filter 8, and a transformer 9. Correlation is detected from the signals PN1, PN0 by correlators 24, 26, and those output signals and the output signal of a timing generator 38 are inputted to and integrated by integrators 33-36, and they are normalized by dividers 39, 40, and output difference is taken by a comparator 41, and the reception data RD can be decoded by processing circuits 41, 42. The circuit 42 outputs a carrier detection signal CD.

Description

Detailed Description of the Invention

[0001]

This invention relates to spread spectrum,
In particular, it relates to a demodulation method in a direct spread system and an apparatus therefor.

[0002]

2. Description of the Related Art As one method of spread spectrum communication, two PN series signals having the same cycle length and small cross-correlation are assigned to bit values "1" and "0" of data to be transmitted, and spread spectrum signals are assigned. Correlation values of the two PN series signals are provided by generating means and carrying the spread spectrum signal to the transmission line, and at the reception side, obtaining the correlation value of the reception signal using the PN series signal used on the transmission side as a reference signal. A method of demodulating received data by finding the magnitude of the peak of is proposed, and in Japan, it is attempted to adopt this method for a modem. (G.
S.Glisic, IEEE Military Communication Conference Re
cord., Boston, MA, Oct, 20-23, 1985 / NEC technical report, vo
l. 42, No. 9, 1966, P.98-106)

FIG. 3 shows the state of a demodulated signal using a conventional spread spectrum communication system. From the absolute values Cor1 and Cor2 of the outputs of two correlators using a PN series signal as a reference signal, P _ow : correlator 0 Maximum absolute value of output W part P _1w : Maximum absolute value of correlator 1 output W part S _0e : Sum of absolute value E of correlator 0 output E part S _1e : Absolute correlator 1 output The sum of the E parts of the values is calculated. If P _1w × S _oe −P _OW × S _ie is negative, the received data is “O”, and if it is positive, the received data is
Data is determined to be "1". In the figure, T is the 1-bit length of the transmission data. That is, in the conventional spread spectrum communication, the received data is demodulated using the peak value of the correlation values obtained at the outputs of the two correlating means using the PN series signal as the reference signal and the added value of the correlation values within the predetermined time window. ing.

However, in the above-described spread spectrum communication system, the received data cannot be demodulated without detecting the peak value, and the transmission line characteristics such as when the spread spectrum signal passes through the actual transmission line such as a distribution line. Due to the impulsive noise in the transmission line, the remarkable correlation peak as shown in FIG.
The current situation is that you can't get it. Therefore, there is a problem that it is difficult to transmit data over a long distance using a distribution line or the like.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional method and apparatus for demodulating a spread spectrum signal. In the case of performing spread spectrum communication using a distribution line, etc. It is an object of the present invention to provide a spread spectrum communication method capable of reliably demodulating received data even when it is difficult to detect a correlation peak due to impulsive noise or the like.

[0006]

SUMMARY OF THE INVENTION To achieve this object, a spread spectrum communication method according to the present invention takes the following means. That is,
Even if the peak in the correlation is not detected, the original correlation peak
Using the fact that it exists in the vicinity of the sync point, the absolute value of the correlation value or the squared integrated value of the correlation value in the vicinity of the sync point is obtained, and A means for normalizing the integrated value of the absolute value or the squared value is provided after the output of the respective correlating means, and the normalized values are compared to demodulate the received data. It is characterized in that it is not affected by impulse noise in the transmission line because it does not have a wide range as in the conventional case and the correlation peak value is not detected, and that it enables long-distance data transmission.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on the embodiments shown in the drawings. In the following description, an example in which the cycle length of the PN series signal is 31 bits and the data rate of the transmission data SD is 300 b / s will be described.

FIG. 1 is a block diagram showing an embodiment in which the received data decoding method of the present invention is used for spread spectrum communication. In order to send out the PN series PN ₀ when the bit value of the transmission data to be transmitted is “0” and the signal PN ₁ when the bit value is “1” to the transmission line, the modulator 5
0 is provided with two PN sequence generators 1, 2.
The synchronization circuit 4 is applied a clock signal of 300H _Z output from the transmission data SD and the timing generator 3, the one based on the bit value of the transmission data SD PN
The generator output is applied to the circuit or a control signal for controlling the operation of the switch 5 is output.

A transmission request signal RS is sent to the timing generator 3.
There is applied, and outputs a control signal for controlling the opening and closing of the switch 6 on the basis of a transmission request signal RS, and supplies the clock signal of 9.3KH _Z to PN sequence generator 1.
In the switch 5, the contact a is the connected to the output terminal of the PN ₁ sequence generator 1, also contact b is connected to the output terminal of the PN _o sequence generator 2. Since the contact c of the switch 5 and the contact d of the switch 6 are connected, the switches 5, 6
When is turned on, the output of either of the PN generators 1 and 2 is applied to the transmission line 10 via the switches 5 and 6, the transmission amplifier 7, the filter 8 and the transformer 9. Reference numeral 60 denotes a demodulator, which includes a transformer 20, an amplifier 21, a filter 22, and an A / D converter 23 connected in series to the transmission line 10, and one output end of the A / D converter 23 has a correlation. Connected to the devices 24 and 26. Further, the same PN sequence generators 25 and 27 used in the transmitting section as reference signals are connected to the correlators 24 and 26, respectively.

The output terminals of the correlators 24 and 26 are square circuits 2
8 and 29, and the output terminals of the squaring circuits 28 and 29 are connected to the adder 32 and the integrators 33 to 36. The first divider 39 is connected to the output terminals of the integrators 33 and 34,
The second divider 40 is connected to the output terminals of the integrators 35 and 36, and the comparator 41 is connected to the output terminals of the dividers 39 and 40. A timing extractor 37 is connected to the output end of the adder 32, and a timing generator 38 is connected to the output end of the timing extractor 37. On the other hand, the other output end of the A / D converter 23 is connected to the clock oscillator 30, and one output end of the clock oscillator 30 is connected to the correlators 24 and 26. Also,
The other output end of the clock oscillator is connected to the control circuit 31, and the output end of the control circuit 31 is connected to the processing circuit 42. Output terminals of the timing generator 38 and the comparator 41 are connected to the processing circuit 42, and the reception data RD and the carrier detection CD are outputted to the output terminal of the processing circuit 42.

The spread spectrum device configured as described above operates as follows. The transmission request signal RS generated by a terminal or the like connected to the transmission unit is supplied to the timing generator 3,
The timing generation circuit 3 turns on the switch 6. Further, the timing generation circuit 3 to which the transmission request signal RS is input
Supplies a 9.3 kHz clock signal to the PN series generators 1 and 2, and the PN series generators 1 and 2 are 1 / 9,300 (s
1-bit PN series PN ₁ and PN _O are generated for each ec). Prior to the data transmission, the switch 5 is connected to the contact a and the PN series PN ₁ is sent to the transmission line 10 for the required time.
Since the PN sequence length used in this embodiment is 31 bits, 31 / 9,300 = 1/300 for transmitting one cycle.
(Sec) is required. For example, if 30 cycles are transmitted, the required time is 100 ms. The purpose of transmitting the PN sequence PN ₁ for 30 cycles is to receive a received signal at the demodulator,
That is, for judging the carrier detection is to detect the timing component of the 300H _Z. Therefore, the transmission data S is transmitted a predetermined time after the transmission request signal RS is generated.
It becomes possible to transmit D.

Transmit data SD (data rate 30 here)
0 b / s) is supplied to the synchronizing circuit 4, and the synchronizing circuit 4 outputs a signal to the switch 5 every 1/300 (sec) in synchronization with the clock signal (300 Hz) of the timing generator 3. At this time, the output of the synchronization circuit 4 of the switch 5 is "
If it is "1", the contact is switched to "a", and if the output of the synchronizing circuit 4 is "0", the contact is switched to "b".
Based on the 9.3 kHz signal supplied from the timing generator 3, the sequence signal generators 1 and 2 have a period of 1 cycle (31 bits) of PN sequence signal for 1 bit of transmission data.
It is transmitted at a clock of / 9,300 (sec). Therefore, when the transmission data SD is “1”, the PN ₁ generator ₁ generates the PN series signal and the contact of the switch 5 is connected to the side a, so that the PN ₁ series spectrum signal is transmitted to the transmission amplifier 7 and the filter. It is applied to the transmission line 10 via 8 and the transformer 9. Similarly, when the transmission data SD is “0”, the PN ₂ generator ₂ generates the PN series signal and the contact of the switch 5 is connected to the b side, so that the PN ₀ series spectrum signal is transmitted to the transmission line 10. Is applied.

The signal sent to the transmission line 10 is passed through the transformer 20 and the amplifier 21 of the demodulation device 60 and the filter 22.
Is input to the A / D converter 23 after removing unnecessary noise by the filter 22. Meinro filter 22 is spread signal - to retrieve Bed extracts the 9300H _Z following components, by combining the high-pass filter cutoff frequency 100H _Z to remove the power-frequency noise components in the low frequency band as needed bandwidth Use as a pass filter. Further, a comb filter (COMB FILTER) that removes high frequency components of the commercial frequency may be inserted if necessary. The received signal applied to the A / D converter 23 is quantized into each sample with a sampling frequency of, for example, three times 9300 Hz, that is, 27,900 Hz, and each sample is converted into a 16-bit digital signal. A /
Although the signal processing after the D converter 23 is all digital arithmetic processing, in order to facilitate the explanation, the digital value in each processing is converted into an analog waveform and explained below.

The output of the A / D converter 23 is the two correlators 2
4 and 26, and the correlators 24 and 26 detect the correlation value of the received signal with the outputs of the PN ₁ generator 25 and the PN ₀ generator 27 as reference signals. Since the outputs of the correlators 24 and 26 have positive and negative values, they are applied to the squaring circuits 28 and 29 to detect the absolute value of the received correlation signal. in this case,
The squaring circuit may be replaced with an absolute value circuit. Square circuit 2
When the 8th and 29th outputs are shown as analog waveforms, they have the shapes shown in FIGS. 2 (a) and 2 (b). If these signals are input to the adder 32 of the next stage, FIG. A signal as shown in c) can be obtained. Applying the adder 32 outputs to the timing extractor 37, when added to the timing wave extracting filter 300H _Z provided to the timing extractor 37 (not shown), 300 Hz as shown in FIG. 2 (d) Timing wave is obtained, and the cycle T = 1/300 (se shown in FIG. 2E is obtained by this timing wave.
c) clock pulses t ₁ , t ₂ , t _3, ..., t _n
.. is generated and supplied to the timing generator 38 of the next stage. In the timing generator 38, a pulse (time window) of ± T _m / 2 centered on t _n as shown in FIG. 2 (f) and a ± T _m / 2 centered on t _n as shown in FIG. 2 (g). A pulse (time window) of T _M / 2 is generated, and the pulse shown in (f) is supplied to the digital integrators 33 and 35, while the pulse shown in (g) is supplied to the digital integrators 34 and 36. To do.

The outputs of the squaring circuits 28 and 29 and the output of the timing generator 38 are applied to integrators 33 to 36,
Each of the integrators 33 to 36 digitally integrates the output signals of the squaring circuits 28 and 29 within the pulse section input from the timing generator 38. That is, in the integrator 33, the digital signal in the section T _m of the output of the squaring circuit 28 is
The integrator 34 integrates the digital signal in the section T _M of the output of the squaring circuit 28. Similarly, the integrator 35 converts the digital signal of the section T _m of the output of the squaring circuit 29 into the integrator 3
In 6, the digital signals in the section T _M of the outputs of the squaring circuit 29 are respectively integrated.

Here, the time T _m is set in advance as a section in which the correlation peak can exist, and is 3 to 5 of the PN sequence.
A fixed time of 3 to 5 / 9,300 (sec) may be set for the code, and the time Tm is a time of 10 to 15 chips wider than the section where the correlation peak can exist, that is,
A fixed time of 10 to 15/9300 (sec) may be set. When the quality of the transmission line is poor, the correlation value of the received signal becomes unclear due to the influence of noise and the phase characteristics of the transmission line, and when the correlation is obtained as shown in FIGS. 2 (a) and 2 (b). However, in practice, the correlation peak is hidden by noise or the like and becomes unclear. Therefore, the first time window t _{n1 in} which the peak exists is set as shown in _Formula 1.

[Equation 1] That is, the correlation peak is not directly detected but is replaced by the integrated value of the signal obtained by squaring the correlator output in the predetermined time interval, and the existence of the correlation peak is estimated.

Further, as shown in the equation 2, the second time window t _n2
By setting T _M << T without widening, the power within the time width in the vicinity of the presence of the correlation peak is detected, so that it is unlikely to be affected by transmission line noise, particularly impulsive noise.

[Equation 2] The output of each digital integrator 33, 34, 35, 36 is the second
As shown in FIGS. (H), (j), (i), and (k), the outputs of the squaring circuits 28 and 29 are ψ ₁ ² (t) and ψ, respectively.
_{If 0} ² (t) is given, the outputs of the integrators 33, 34, 35 and 36 can be expressed by Equations 3, 4, 5, and 6.

[Equation 3]

[Equation 4]

[Equation 5]

[Equation 6]

Therefore, the output value of the divider 39 is expressed by equation 7, and its output waveform is as shown in FIG.

[Equation 7] Further, the output value of the divider 40 is represented by the equation 8, and its output waveform is as shown in FIG. 2 (m).

[Equation 8] Further, the outputs of the dividers 39 and 40 are input to the comparator 41,
If the output difference is taken, the output as shown in FIG. 2 (n) is applied from the comparator 41 to the processing circuit 42. Therefore,
If this difference is positive at t = t _n + (T / 2), the received data RD
Is "1", and if negative, the reception data RD is "0" and the processing circuit 4
2 makes a decision, and as shown in FIG. 2 (p), the received data RD
To decrypt. Further, the processing circuit 42 uses the timing extractor 39.
When the timing wave of a predetermined level is detected for a predetermined time, it is determined that the carrier is received, and the carrier detection signal CD is output.

Although the clock oscillator 30 and the output of the timing extractor 37 are not synchronized in the above description,
Synchronizing has the advantage of facilitating the calculation of each unit in terms of timing. Further, the control circuit 31 includes a demodulation device 60.
It is provided to perform total control of the inside. That is, the process at the time of starting the power supply circuit, the process at the time of abnormality, etc. are performed,
Since it is not directly related to the gist of the present invention, details of its operation will be omitted. In the method of the present invention, since the correlators 24 and 26 need a means for correlating the received signal with the reference PN sequences PN ₁ and PN ₀ , the received data is the time of the period length of the PN sequence, that is, the time T. It will be output at least with a delay. Further, it is obvious to those skilled in the art that, in the integration of the equations 3, 4, 5 and 6, the time window is determined by using the timing pulse before T = t _n by T.

[0020]

In the receiving section of the spread spectrum communication apparatus, the peak of the correlator output is not directly detected, and the square or absolute value of the correlation value within the time window where the correlation peak may exist. In order to detect the integrated value and normalize by the square of the correlation value or the integrated value of the absolute value in a section slightly wider than the time window in which the correlation peak may exist, demodulate the spread spectrum signal using both integrated values. , The communication signal is not only affected by the attenuation of the received signal due to transmission loss but also is not affected by the transmission line noise, and communication is possible even in the transmission line where the existence of the correlation peak is not clear. It has a remarkable effect on the spread communication.

[0021]

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining an example of the present invention.

FIG. 3 is a configuration diagram for explaining a conventional spread spectrum communication method.

[Explanation of symbols]

 1, 2, 25 and 27 PN sequence generator 24 and 26 Correlator 22 Adder 33, 34, 35 and 36 Digital integrator 8 and 22 Filter 50 Modulator 60 Demodulator

Claims (2)

[Claims] 1. Transmission data "1", "1" having a transmission rate of 1 / T
In spread spectrum communication for transmitting one of two PN sequences having the same cycle length and a small cross-correlation value corresponding to 0 ", a correlating means for obtaining a correlation value using the received signal and each PN sequence signal as a reference signal is provided. The synchronous timing signal of the period T is extracted from the signal obtained by adding the absolute value or the squared value of the correlating means, and the time window t _n − (T _m / 2) is based on the synchronous timing signal t _n. <T <t _n + (T _m / 2) and the values X _m and Y _m obtained by integrating the absolute value or the squared value of the output of each correlating means and the time window t _n − (T _M / 2 ) <T <t _n + (T _M / 2) to obtain the values X _M and Y _M obtained by integrating the absolute value or the squared value of each correlating means to obtain X _m / X _M −Y _m / Y received data "1" by performing the negative determination of the values of _M, characterized in that demodulating the "0" spectrin Demodulating method of spreading signals. 2. Transmission data "1" and "1" at a transmission rate of 1 / T
In a spread spectrum communication device that sends out one of two PN sequences having the same cycle length and a small cross-correlation value corresponding to "0", two correlation values are obtained using a received signal and each PN sequence signal as a reference signal. A correlator, a sync timing extractor for extracting a sync timing signal having a cycle T from a signal obtained by adding the absolute value or the squared value of the correlator output, and a first correlator based on the sync timing signal t _n Time window t
₁ t _n − (T _m / 2) <t ₁ <t _n + (T _m / 2) and the second time window t ₂ t _n − (T _M / 2) <t ₂ <t _n + (T _M / 2), which is controlled by the timing generator for generating the first and second pulses and the output of the timing generator, and integrates the absolute value or square value of the correlator output when the first pulse is input. An integrator that detects the obtained values X _m and Y _m , and a value that is controlled by the timing generator output and that is obtained by integrating the absolute value or the squared value of the correlator output when the second pulse is input. and X _M and the integrator for detecting a Y _M, the integrator output _{X m, X M, Y m} , X m / X with Y _{M M} -Y _m / Y _M
A spread spectrum communication device comprising a calculation processing circuit for performing the above, and receiving data "1" and "0" are demodulated by determining whether the output of the calculation processing circuit is positive or negative.