JPH0783291B2 - Correlator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is used in a spread spectrum communication device used for radio control control of a crane or the like, on-premise communication or confidential communication, for example, and spreads information data by a spread code. The present invention relates to a correlator that decodes a spread DS signal.

[Prior Art] Spread spectrum communication has been used in the past for confidential communication, remote control,
It has been studied in various fields such as local area networks, and has been put to practical use in some areas.

By the way, in spread spectrum communication, in order to decode the received signal, it is necessary to synchronize the transmitting side and the receiving side.
Normally, correlation decoding is performed for decoding this kind of spread signal, and as one method there is a method using a delay lock loop (DLL).

However, in the case of this DLL method, there is a problem in terms of synchronization supplement time and stable operation, and in recent years, decoding by the matched filter (adaptive filter) method has been drawing attention.

There are methods of using surface acoustic waves (SAW), methods of using digital circuits, etc. for the matched filter, and they have the advantage of being capable of high-speed synchronization and stable operation. The correlation calculation is expressed by the following formula.

Where d _k is the input signal, P _{(k + n)} is each bit of the spreading code,
N is the code length of the spread code.

Therefore, the above equation can be realized by performing the product-sum calculation the number of times equal to the code length of the spread code.

FIG. 4 shows a block configuration of a matched filter in which the above equation is realized by a digital circuit.

In the figure, 11 is a shift register, 12 is a multiplier, and 13 is an adder. The input signal Vi received from the transmitting side is a DS signal obtained by spreading the baseband signal with a spreading code, and is sequentially input to the shift register 11. The data d _{0 to} d _N-1 stored in the shift register 11 are respectively multiplied by the same spreading code as the transmitting side spreading code. That is, each bit P _{0 to} P _{N-1 of} the spread code is multiplied by the multiplier 12. afterwards,
Addition is performed by the adder 13 to obtain the correlation signal Vo corresponding to the baseband signal.

[Problems to be Solved by the Invention] By the way, in the case of synchronizing signals when demodulating data by decoding, as shown in FIG. 2 (b), a main lobe that appears as a peak value at predetermined time intervals, Of the correlation signal Vo represented by the side lobes appearing on both sides of this main lobe, the main lobe showing the peak value exceeding the threshold level set in advance is determined by the sampling signal for each predetermined time (for example, 1/2 chip). To be detected.

However, the main lobe appearing as the correlation signal Vo drops in level due to this effect when external noise is superimposed on the transmission signal and the detected waveform is disrupted (see FIG. 3 (a)) (see FIG. 3 (b). )), If this level is below the threshold level, there is a problem that the peak detection of the main lobe becomes impossible and accurate data demodulation cannot be performed, resulting in lack of reliability.

Further, as described above, even if external noise is not superimposed on the transmission signal, variations in the amplitude and frequency of the modulated transmission signal cause variations in the detected output waveform, and the correlation signal Vo decreases in level as a whole. The margin with the level was reduced and it became difficult to detect the peak of the main lobe, so that the data could not be demodulated accurately.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to vary the threshold level to an optimum value according to the level of the peak value of the correlation signal to obtain the correlation signal required for data demodulation. An object of the present invention is to provide a highly reliable correlator capable of detecting peaks and accurately demodulating transmitted data.

[Means for Solving the Problem] In order to achieve the above object, a correlator according to the present invention is a correlator for decoding a DS signal obtained by spreading information data transmitted from a transmitting side with a spreading code, The lower limit of the threshold level is set to a value at which the side lobe of is not detected, and when the level of the correlation signal obtained by the correlation between the DS signal and the same spreading code as the transmitting side exceeds the threshold level, the status signal is A threshold detection circuit for outputting and detecting a peak value of the main lobe appearing in the correlation signal within a preset detection time and outputting a peak detection signal, and a correlation signal exceeding the threshold level within the detection time is detected. A peak detection circuit that outputs a peak detection signal indicating a peak value within the detection time when no input is made. And a threshold level determination circuit that compares the level of the peak detection signal with the threshold level, determines an optimal threshold level for detecting the peak value, and variably controls the threshold level. .

[Operation] The correlation signal is obtained by the correlation between the DS signal obtained by spreading the information data transmitted from the transmitting side with the spreading code and the same spreading code as the transmitting side. In the threshold detection circuit, the lower limit value of the threshold level is preset to a value at which the side rope of the correlation signal is not detected, and the state signal is output when the level of the correlation signal exceeds the threshold level. The peak detection circuit detects the peak value of the main lobe appearing in the correlation signal within a preset detection time and outputs a peak detection signal. At that time, the peak detection circuit outputs the peak detection signal within the detection time even if the correlation signal exceeding the threshold level is not input within the detection time. Then, the threshold level determination circuit compares the level of the peak detection signal with the threshold level, determines the threshold level optimum for detecting the peak value, and variably controls the threshold level.

[Embodiment] FIG. 1 is a block diagram showing an embodiment of a correlator according to the present invention.

In the correlator according to this embodiment, the information data from the transmitting side is
The DS signal spread by the PN code is decoded, and the shift register 1, the multiplier 2, the first adder 3, the threshold detection circuit 4, the output device 5, the peak detection circuit 6, and the second adder 7, A decoder 8 and a threshold level determination circuit 9 are provided.

The shift register 1 is a signal received and detected from the transmission side, and sequentially stores and stores the DS signal Vi, which is a baseband signal spread by a spreading code, and stores the data d ₀ sequentially stored with the shift operation. It outputs ~ d _N-1 to the multiplier 2.

The multiplier 2 is the data sequentially input from the shift register 1.
d ₀ ~d _N-1 the same spread code as the spread code on the transmission side to P ₀ ~P _N-1
Is multiplied by. That is, each data d _{0 to} d _N-1 is multiplied with each bit P _{0 to} P _N-1 of the spread code, and the result is sequentially output to the first adder 3.

The first adder 3 receives each data d ₀ · P _{0 to} d _N−1 from the multiplier 2.
The P _N-1 is sequentially added and the correlation signal Vo corresponding to the baseband signal is output to the threshold detection circuit 4, the output device 5, and the peak detection circuit 6.

The threshold detection circuit 4 outputs "1" as the status signal when the level of the input correlation signal Vo exceeds the threshold level Ls (-Ls), and this signal is output from the output device 5 as the output trigger S1. Is output to.

The output device 5 is an output trigger from the threshold detection circuit 4.
The correlation signal Vo is output to the second adder 7 by S1.

The peak detection circuit 6 detects the peak value (main lobe) of the correlation signal Vo output from the first adder 3, and outputs this peak detection signal S2 to the threshold level determination circuit 9. Further, the peak detection circuit 6 has a threshold level Ls (-L within a predetermined detection time set in advance).
When the correlation signal Vo exceeding s) is not input, the peak detection signal within the detection time is output to the second adder 7.

The second adder 7 adds the signal Vo from the output device 5 and the signal S2 from the peak detection circuit 6, and outputs the added signal S3 thus added to the decoder 8.

Here, the correlation signal Vo has a positive peak V + when the spreading code is synchronized and a negative peak V- when the spreading code is negative. Here, the period of the baseband signal and the period of the spreading code are generated. Are set to the same, and the positive peak V
+ Corresponds to the trailing edge of the baseband signal, and synchronization is achieved at this point, whereby decoding is performed in the decoder 8 and data is demodulated.

The threshold level determination circuit 9 detects the level of the peak detection signal S2 from the peak detection circuit 6 and the threshold level.
Ls (-Ls) is compared to determine the optimum threshold level for detecting the next peak value.
A threshold level control signal S4 for variably controlling the threshold level according to the level of the detected peak detection signal S2 is output to the threshold detection circuit 4.

When determining the threshold level Ls (-Ls), the lower limit level thereof is determined in advance so that the side lobe Vs of the correlation signal Vo does not exceed the threshold level Ls (-Ls). .

Further, as shown in FIG. 3 (a), the threshold level determination circuit 9 cannot obtain a sufficient detection output due to the modulation state on the transmission side, and even if the level of the correlation signal Vo is low overall, the peak value The threshold level is averaged based on the detected peak value so that detection can be performed, and the threshold level control signal S5 corresponding to the averaged threshold level is output to the threshold detection circuit 4.

Next, the operation of the correlator configured as above will be described.

When the transmission signal from the transmission side is detected, the DS signal Vi based on this detection signal is sequentially shifted while shifting to the shift register 1
It is captured and stored in. The data d _{0 to} d _N-1 stored in the shift register 1 are sequentially multiplied by the multiplier 2 with the same spreading codes P _{0 to} P _N-1 on the transmission side, and then sequentially added to the first adder 3 And the correlation signal Vo corresponding to the baseband signal is output from the first adder 3.

The correlation signal Vo output from the first adder 3 is output to the threshold detection circuit 4 and the peak detection circuit 6, and in the threshold detection circuit 4, the level of the input correlation signal Vo exceeds the threshold level Ls (-Ls). If
The state signal “1” is output to the output device 5 as the output trigger S1. When the output trigger S1 is output to the output device 5, the correlation signal Vo is input to the second adder 7 via the output device 5.

The second adder 7 performs addition operation each time the correlation signal Vo is input from the output unit 5 in response to the input of the output trigger S1 from the threshold detection circuit 4, and outputs the addition signal to the decoder 8.
The decoder 8 decodes the signals sequentially input from the second adder 7 to demodulate the data.

On the other hand, the peak detection circuit 6 detects the peak value of the input correlation signal Vo and outputs the peak detection signal S2 to the threshold level determination circuit 9. Further, the peak detection circuit 6 outputs the peak detection signal S2 within the detection time to the second adder 7 when the correlation signal Vo exceeding the threshold level Ls (-Ls) is not input within the detection time.

Next, when the threshold level determination circuit 9 determines that the level of the peak detection signal S2 from the peak detection circuit 6 is lower than the threshold level Ls (-Ls), the threshold level control that matches the level of the peak detection signal S2. The signal S4 is output to the threshold detection circuit 4.

Then, when the threshold level control signal S4 is input from the threshold level determination circuit 9, the threshold detection circuit 4 has the threshold level Ls (-Ls) at the optimum level with respect to the peak value detected by the peak detection circuit 6. Is variably controlled.

By the above operation, the threshold level Ls (-Ls) is variably set, and when the correlation signal Vo detected by the threshold detection circuit 4 does not exceed the threshold level Ls (-Ls) after that, the peak detection at that time is further performed. signal
Threshold level Ls ′ (−L
s') is variably set.

Then, when the level of the peak detection signal S2 exceeds the threshold level Ls '(-Ls'), it is variably set to the threshold level Ls (-Ls) set at the initial stage.

Furthermore, if the detected output waveform fluctuates due to fluctuations in the amplitude and frequency of the modulated transmission signal, and the correlation signal Vo decreases in level overall, the threshold level is detected based on the peak detection signal S2 detected at that time. Ls (-L
s) is averaged and variably set to a threshold level that matches the level of the correlation signal Vo at that time.

Therefore, in the above-described embodiment, the subsequent correlation signal Vo according to the level of the peak value of the detected peak detection signal S2.
Since the threshold level Ls (-Ls) at the time of detection is variably controlled to the optimum value, external noise is superimposed and the detected waveform is disrupted, and this effect lowers the level of the correlation signal Vo and lowers the threshold level Ls ( Even if it is lower than −Ls), the peak of the correlation signal (main lobe) Vo can be detected, accurate data demodulation can be performed, and reliability can be improved.

Further, even if the detected output waveform fluctuates due to fluctuations in the amplitude and frequency of the modulated transmission signal and the correlation signal Vo is entirely leveled down, the threshold level Ls (corresponding to the peak value of the correlation signal Vo at that time -Ls), the peak of the correlation signal Vo required for data demodulation can be detected.

By the way, the correlator according to the present invention is not limited to the above-described configuration as long as it can variably control the threshold level Ls (-Ls) at the time of detecting the correlation signal Vo according to the peak value of the correlation signal Vo.

[Effects of the Invention] As described above, according to the correlator of the present invention, since the lower limit value of the threshold level is set to a value at which the side lobe of the correlation signal is not detected, the external noise and the correlation signal are clarified. Can be distinguished. Even if the level of the correlation signal does not exceed the threshold level, the peak detection signal that shows the peak value within the detection time is output, so even if there is a sudden change in the input level, the transmitted data can be accurately demodulated. The reliability can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a correlator according to the present invention, FIGS. 2 (a) and 2 (b) are waveform diagrams showing a detection output and a correlation signal in a stable state, and FIG. 3 (a), (B) is a waveform diagram showing a detection output and a correlation signal in an unstable state,
FIG. 4 is a diagram showing an example of a conventional correlator. 4 ... Threshold detection circuit, 5 ... Output device, 6 ...
Peak detection circuit, 9 ... Threshold level judgment circuit, Vo ... Correlation signal, Ls, Ls '(-Ls, -Ls') ... Threshold level.

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Claims (1)

[Claims] 1. A correlator that decodes a DS signal obtained by spreading information data transmitted from a transmitting side with a spreading code, wherein a lower limit value of a threshold level is set in advance to a value at which a side lobe of the correlation signal is not detected, A threshold detection circuit that outputs a status signal when the level of the correlation signal obtained by the correlation between the DS signal and the same spreading code as the transmission side exceeds the threshold level, and the peak value of the main lobe appearing in the correlation signal. A peak detection signal is output that detects and outputs a peak detection signal within a preset detection time, and when a correlation signal exceeding the threshold level is not input within the detection time, a peak detection signal indicating a peak value within the detection time. Comparing the level of the peak detection signal with the threshold level. And a threshold level determination circuit that variably controls the threshold level by determining a threshold level optimal for detecting the peak value.