JPH0799466A - Synchronization detection circuit - Google Patents

Abstract

PURPOSE:To detect a synchronization point even when a narrow band interference wave is received by applying series of specific processing to a reception signal. CONSTITUTION:The detection circuit is provided with a correlation difference absolute value arithmetic means calculating an absolute value of the difference between a correlation value calculated this time and a correlation value calculated at a preceding sampling time every time a reception signal from a transmitter is sampled, an adder means adding the absolute value of the calculated correlation difference by a number twice the sampling number to one chip of a pseudo noise code, and a synchronization point detection means comparing the sums for each added sampling and detecting a synchronization point based on the maximum value. The correlation value at a point other than the synchronization point is a constant value through the series of processing when a fluctuation level is constant and to be a smaller value in comparison with the correlation value at the synchronization point. Even when the correlation value is fluctuated by the effect of a narrow band interference wave, the fluctuation component is absorbed to detect the synchronization point and noise-proof against a narrow band interference wave is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a synchronization detection circuit in spread spectrum communication, and more particularly to a technique for improving noise resistance so that a synchronization point can be detected even when a narrow band interference wave is input.

[0002]

2. Description of the Related Art Conventionally, a spread spectrum communication system has been known as a communication system excellent in noise resistance. The spread spectrum communication method is a specific code called a pseudo noise (PN) code having a spectrum width sufficiently wider than that of a data signal, and an information signal modulated by data is modulated and transmitted, and the PN code is received at the receiving side. This is a method of selectively receiving only the signal modulated by.

According to this method, on the transmitting side, data is transmitted by performing spectrum spreading by the PN code, and on the receiving side, since the original data is reproduced, the received signal has the same phase as the transmitting side. It is multiplied by the same PN code as the transmitter. Therefore, in order to accurately match the phase with the PN code component of the received signal, the reception device is provided with a synchronization detection circuit that detects a synchronization point from the PN code component of the received signal and outputs the synchronization signal.

Next, the processing in the conventional sync detecting circuit for detecting the sync point will be described. Note that FIG. 8 shows an example of a method of allocating a PN code to data by the PSK method in spread spectrum communication. In FIG. 8, in the transmitter, for example, for one bit of data (A), a PN code “1 1 1 0 with one cycle of 7 chips as shown in (B) is used.
"100" is assigned. And data (A) and PN
By multiplying the code (B), (C) in which the data is modulated by the PN code is generated, the carrier wave is modulated based on (C), and is transmitted from the transmission device. In the receiving device,
This signal is received and input to the synchronization detection circuit of the receiving device. In the synchronization detection circuit, the PN code component is extracted from the input reception signal, sampled a predetermined number of times for A / D conversion, and then input to the correlator. The correlation value calculation coefficient corresponding to the PN code of the transmitting device is stored in advance in the correlator, and the correlation value of the input PN code component is obtained based on the correlation value calculation coefficient.

FIG. 9 is a diagram when the number of times of sampling is once per chip. FIG. 9A shows the PN code component of the received signal and sampling data when sampling is performed for each chip (however, PN Sign high level "H"
Is "1", and the low level "L" is "-1"),
(B) shows the coefficient for correlation value calculation previously stored in the receiving device. Although the PN code component of the received signal is a rectangular wave (ideal state) in FIG. 9A, it does not actually become a rectangular wave due to the influence of the characteristics of the transmission line, band limitation by filters, etc. .

To obtain the correlation value, the sum of products of the sampling data and the coefficient of the correlator is obtained for one period T of the PN code component. As shown in (C), the result of multiply-add is
In one cycle from t ₁ and t ₃ , both become “−1”, and t ₂
In one cycle from, it becomes "7". This result is a correlation value, which is graphed as shown in (D).
The point of the correlation value 7 in (D) is the synchronization point, and 1
It exists every cycle T.

When the number of samplings is set to 2 times per chip as shown in FIG. 10 (A), the coefficient of the correlator is "1 1 1 1 1 1 -1 -1 1" as shown in (B). 1 -1-
"1-1-1" is stored in advance, and similarly, if the product sum of one period T of the PN code component of the transmitter and the coefficient (B) is calculated, the correlation value is shown in (C). Thus, every 7 chips becomes "14", and the point of the correlation value "14" is detected as the synchronization point.

As described above, when the number of samplings for each chip increases, the correlation value at the synchronization point increases, and conversely, the correlation value at the points other than the synchronization point decreases. Therefore, when the number of samplings becomes very large, as shown in FIG. 11, a continuous correlation value waveform is obtained, and the correlation value at the synchronization point becomes a very large value with respect to the lowest level.

In the past, as shown in FIG. 11, the threshold value V
The _th provided, a method for determining a synchronization point on the basis of the periodicity of the correlation value equal to or greater than a threshold value V _th or the maximum value of the correlation values, the synchronization point by using the method of the point and the synchronization point Is being detected. By obtaining the product of the same PN code synchronized with the PN code on the transmission side and the received signal, the carrier wave that is not modulated by the PN code can be taken out and the original transmission data of the transmission device can be reproduced. Can be done.

[0010]

By the way, in the conventional synchronization detection circuit, the correlation value is shown in FIG.
If the waveform is as shown in (1), the synchronization point can be detected, but if a narrow band interference wave that is similar to a sine wave of a radio or the like is input, the synchronization point may not be detected. FIG. 13 is a diagram showing a waveform of a correlation value when such a narrow band interference wave is input, and the correlation value is affected by the narrow band interference wave, and increases / decreases and fluctuates accordingly. Further, as the input level of the narrowband interference wave increases, the influence on the correlation value also increases, and as shown in FIG. 14, the correlation values other than the synchronization point may exceed the correlation value at the synchronization point.

In such a state, the conventional method of monitoring the maximum value of the correlation value to obtain the synchronization point and the method of setting the threshold value and determining the synchronization point from the periodicity of the correlation value exceeding the threshold value are true. There is a problem that the maximum correlation point cannot be obtained. The present invention has been made in view of such conventional problems, and provides a synchronization detection circuit capable of detecting a synchronization point even when a narrow band interference wave is input and having excellent noise resistance. The purpose is to do.

[0012]

Therefore, the present invention is based on FIG.
As shown in FIG. 1, a signal which is spread spectrum and transmitted from the transmitter is received, and the received signal is set to 1 of the pseudo noise code.
The chip is sampled a predetermined number of times, and a correlation value is calculated from the sampled value and a correlation value calculation coefficient which is predetermined based on the number of times of sampling the one chip of the pseudo noise code. In the synchronization detection circuit that detects the synchronization point by monitoring the correlation value of the cycle, every time the reception signal from the transmission device is sampled, the difference between the correlation value calculated this time and the correlation value calculated at the time of the previous sampling is calculated. The correlation value difference absolute value calculating means for calculating the absolute value, and the absolute value of the correlation value difference calculated by the correlation value difference absolute value calculating means are double the sampling number for one chip of the pseudo noise code including the current value. The addition means for adding the numbers up to the previous one is compared with the addition value for each sampling added by the addition means, and the synchronization point is detected based on the maximum value. And check out means, it was to prepare for the.

[0013]

According to the above construction, the absolute value of the difference between the correlation values for each sampling is calculated by the correlation value difference absolute value calculating means. The absolute value of the difference between the correlation values is added by the adding means up to twice the number of sampling times per chip of the pseudo noise code, including the current value. The sync point is detected by the sync point detecting means based on the maximum value of the added values.

By this series of processing, the correlation values other than the synchronization point become substantially constant values if the fluctuation level is constant,
The value is smaller than the correlation value at the synchronization point. Further, for example, even when the correlation value fluctuates due to the influence of the narrow band interference wave, the fluctuation is absorbed and the synchronization point can be detected.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 2 shows a circuit configuration of the synchronization detection circuit and the despreading circuit of this embodiment. The synchronization detection circuit 1 is a circuit provided on the receiving device side in a communication device adopting a spread spectrum communication system. In the spread spectrum communication system, if the PN code prepared on the receiving side is different from the PN code on the transmitting side, or if the phases are out of phase, the original data cannot be reproduced. It is a circuit provided for calculating the correlation value of the PN code component of the transmitter, outputting the PN code in which the phases are matched, and reproducing the original data.

The synchronization detection circuit 1 receives a received signal and multiplies it by a carrier wave fc, a multiplier 2, a low-pass filter 3 which extracts a PN code component of a transmitter, and an extracted P.
A / D converter 4 that samples the N code component at a predetermined sampling frequency and performs A / D conversion, and a correlation value using the coefficient for correlation value calculation prepared in advance for the A / D converted PN code component. And a CPU 6 for inputting the output signal of the correlator 5 and processing it and outputting a signal for matching the phase of the PN code, are sequentially connected.

Reference numeral 7 is a PN code oscillator (hereinafter referred to as PNG) which oscillates and outputs a PN code based on a signal output from the CPU 6, and a multiplier 8 receives the PN code output from the PNG 7 and the reception. By calculating the product with the signal, the data not modulated by the PN code is extracted from the received signal. Next, the operation will be described. In addition, the case where the number of sampling times is two samplings for one chip is taken as an example.

The received signal from the transmitter is the synchronization detection circuit 1
Entered in. It is assumed that the transmission data of the transmission device is assigned the PN code shown in FIG. 8, for example.
This received signal is input to the multiplier 2, multiplied by the carrier wave fc in the multiplier 2, and its output is a low pass filter (LP
F) 3 is filtered to extract the PN code component of the received signal.

This PN code component is input to the A / D converter 4, sampled at a sampling rate of 2 times per chip, and input to the correlator 5. Next, the correlation value processing procedure of this embodiment will be described based on the flowchart of FIG. Step (indicated as "S" in the figure,
In the same way 1), the correlator 5 calculates the correlation value (N) of the PN code component from the coefficient prepared in advance.

As described above, the correlation value (N) is, for example, the result of multiply-add operation of the PN code assigned to each bit of the transmission data and the coefficient prepared in advance by the correlator 5, and every time sampling is performed. Is calculated. The rectangular PN code on the transmitting side as shown by the dotted line in FIG. 4 is actually input to the correlator 5 when it is input to the correlator 5 due to the characteristics of the transmission path and the band limitation performed by the low pass filter 3 or the like. Has a waveform as shown by the solid line. Therefore, FIG.
In FIG. 5 (A) in which one chip of FIG. 5 is enlarged, when sampling is performed at the sampling position indicated by an arrow, the sampling value indicated by a circle is shown on the rectangular wave indicated by the dotted line, and the correlation value is shown in the left diagram of FIG. Actually, what is shown is the sampling value shown by the triangle mark on the waveform of the PN code component shown by the solid line as shown in FIG. 5A, and the correlation value is, for example, the right diagram of FIG. 5B. As described above, the maximum value is decreased by ΔN.

The sampling in the A / D converter 4 and the frequency of the PN code of the transmitter are not synchronized. Furthermore, since it is difficult to make the frequencies of the transmitter and the receiver match exactly, even if the A / D converter 4 samples the PN code component at the position of the arrow in FIG. In the cycle of, the sampling point may be the position of the arrow in FIG. Therefore, also in this case, if it is a rectangular wave, the sampling value shown by the circle in FIG. 5C is obtained, and the correlation value is as shown in the left diagram of FIG. 5D. The sampling value of is the sampling value indicated by the triangle mark on the waveform indicated by the solid line, and the correlation value is as shown in the right diagram of FIG. That is, A
Since the sampling in the / D converter 4 and the frequency of the PN code of the transmitter are not synchronized, the correlation values are accompanied by the deviation of the sampling points, and the correlation values are shown by the dotted lines in the right diagrams of FIGS. 5B and 5D, respectively. It changes on the waveform of the correlation value shown by.

FIG. 6 is a diagram showing the correlation value in such a case, which will be described below with reference to FIG. In FIG. 6, T _{1 to} T ₆ are sampling points, and the correlation value N ₁
˜N ₆ are the correlation values calculated at the sampling points T ₁ ˜T ₆ , respectively. The correlation values N _{1 to} N ₆ are input to the CPU 6, and the CPU ₆ performs the synchronization point detection process.

In step 2, the current correlation value is subtracted from the previous correlation value, and the absolute value of the difference is calculated. For example, in FIG. 6, | N ₂ −N ₁ |, ..., | N at points T _{2 to} T ₆
The value of ₆ −N ₅ | is calculated. This step corresponds to the correlation value difference absolute value calculation means.

In step 3, the value calculated in step 2 is added up to twice the number of times of sampling for one chip of the PN code, including the current value, and the additional value is calculated. That is, in FIG. 6, the number of samplings is k (k = 2 in this embodiment), the absolute value of the difference between the correlation values at the sampling points T _i is | N _i −N _i−1 | = M _i , and the added value is Q _i
Then, Q _i = (M _i ) + (M _i−1 ) +. ． ． + (M _{i- (2K-1)} ).

This step corresponds to the adding means. In step 4, the maximum correlation value in one cycle of the sync signal is detected based on the added value calculated in step 3, and is compared with a preset threshold value. For example, in FIG. 6, the added value Q
₅ or Q ₆ is the maximum value among the added values Q _{1 to} Q ₆ ,
Its value, _{respectively, Q 5 = | N 2 -N} 1 | + | N 3 -N 2 | + | N 4 -N 3
_{| + | N 5 -N 4 |} Q 6 = | N 3 -N 2 | + | N 4 -N 3 | + | N 5 -N 4
| + | N ₆ −N ₅ |.

The point to be noted here is that when the section is divided into sections A to D as shown in FIG. 6, in the case of 1 chip 2 sampling, there is one sampling point in each section A to D. , Correlation values N ₂ , N ₃ , N at each sampling point
₄ and N ₅ are to move on the straight lines a and b due to the phase shift between the PN code frequency on the transmitter side and the sampling time. Therefore, when comparing the value of the sum Q ₅ and Q _6, the absolute value _{| N 3 -N 2 |, |} N 4 -N 3 |, | N 5
-N ₄ | is added together, and the added value Q ₅
And the magnitude relationship between Q ₆ and absolute value | N ₂ ─N ₁ | and | N ₆
--N ₅ |, the synchronization point can be detected by performing such processing.

In the example of FIG. 6, | N ₂ −N ₁ | <| N ₆ −
Since N ₅ |, the added value Q ₆ becomes the maximum value, and if the added value Q ₆ exceeds the preset threshold value Q _th , the correlation value N _{4 at the} point T ₄ is detected as the synchronization point. This step corresponds to the synchronization point detecting means. Next, the waveform of the correlation value when narrowband interference waves are mixed will be described.

As shown in FIG. 13, the correlation value level N ₀ changes when it is influenced by the narrow band interference wave, and when the influence of the narrow band interference wave is further increased, as shown in FIG. is the synchronization point should be greater than the correlation value level N ₀ and may be lower than the correlation value level N _0. FIG. 7 shows some examples of correlation value waveforms that can occur at each synchronization point in the case of FIG. Even in the case of such a waveform, by performing such a series of processing,
The processed values other than the synchronization points are smaller than the processed values of the synchronization points.

Further, even if the correlation value fluctuates due to the narrow band interference wave, this fluctuation part is almost absorbed by this series of processing, the influence part of the narrow band interference wave becomes less of a problem, and a few cycles more. By monitoring the correlation value, the synchronization point can be detected with certainty. A signal for determining the phase is output from the CPU 6 to the PNG 7 according to the detected synchronization point. The PNG 7 generates a PN code based on this signal, and the multiplier 8 obtains the product of the received signal and the PN code, thereby extracting the signal that is not modulated by the PN code, that is, the received signal is inverted. The original data on the transmitting device side can be reproduced by being spread.

With this configuration, the absolute value of the difference between a certain correlation value and the previous correlation value is calculated, and the PN including the current value is also included.
For example, even if narrow-band interference waves are mixed, the addition value is calculated up to twice the number of sampling times for one chip of the code, and the maximum value of this value is calculated and compared with a predetermined threshold value. The point can be reliably detected, and the noise resistance against narrow band interference waves is improved.

In this embodiment, the maximum value in one cycle of the sync signal is detected and compared with a predetermined threshold value, and if the value is greater than or equal to the threshold value, the detected maximum value is taken as the synchronization point. After the processing, the correlation value may be first compared with a predetermined threshold value, the maximum value among the correlation values that are equal to or greater than the threshold value may be detected, and this maximum value may be detected as the synchronization point.

[0032]

As described above, according to the present invention, the absolute value of the difference between a certain correlation value and the previous correlation value is calculated, and this correlation value difference absolute value is also included in the present value. Even if narrow-band interference waves are mixed, the number of samples up to twice the sampling number is added to one chip, and the maximum value is used as the synchronization point to detect the narrow-band interference waves. Since the fluctuation due to the influence can be absorbed, the synchronization point can be detected reliably, and the noise resistance against the narrow band interference wave is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration of the present invention.

FIG. 2 is a block circuit diagram of an embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of the CPU of FIG.

FIG. 4 is an explanatory diagram of waveforms of a PN code component whose band is limited.

5 is an enlarged waveform diagram of FIG.

FIG. 6 is an explanatory diagram when the sync point in FIG. 3 is detected.

FIG. 7 is an explanatory diagram showing an example of a waveform of a correlation value near a synchronization point when a narrow band interference wave is input.

FIG. 8 is an explanatory diagram of a PN code.

9 is an explanatory diagram for calculating a correlation value for the PN code in FIG. 8.

FIG. 10 is an explanatory diagram of the same as above.

FIG. 11 is an explanatory diagram of the same as above.

FIG. 12 is an explanatory diagram of a correlation value waveform when there is no influence of a narrow band interference wave.

FIG. 13 is an explanatory diagram of a correlation value waveform when there is an influence of a narrow band interference wave.

FIG. 14 is an explanatory diagram of the same as above.

[Explanation of symbols]

 1 Synchronization Detection Circuit 2 Multiplier 3 Low Pass Filter (LPF) 4 A / D Converter 5 Correlator 6 CPU

Claims (1)

[Claims] 1. A signal which is spread spectrum and transmitted from a transmitter is received, and the received signal is sampled at a predetermined sampling number for one chip of a pseudo noise code,
A correlation value is calculated from the sampling value and a coefficient for calculating a correlation value that is predetermined based on the number of times of sampling for one chip of the pseudo noise code, and the correlation value for one cycle of the pseudo noise code is monitored to determine the synchronization point. In the synchronization detection circuit for detecting, every time the reception signal from the transmitter is sampled,
Correlation value difference absolute value calculation means for calculating the absolute value of the difference between the correlation value calculated this time and the correlation value calculated at the previous sampling, and the absolute value of the correlation value difference calculated by the correlation value difference absolute value calculation means The value including the current value is added by a number up to twice the sampling number for one chip of the pseudo-noise code, and the added value for each sampling added by the adding means is compared, and based on the maximum value. And a sync point detecting means for detecting a sync point.