JPH04124926A - Correlator - Google Patents

Abstract

PURPOSE:To correctly demodulate transmitted data by detecting the peak of a correlation signal required for demodulating the data by varying a threshold level into an optimum value according to the level of the peak value of the correlation signal. CONSTITUTION:When a threshold level control signal is inputted to threshold detection circuit 4 from a threshold level decision circuit 9, its threshold level Ls (-Ls) is varied and controlled so as to be an optimum level for the peak value detected by a peak detection circuit 6. In case that dispersion arises in detected output waveform because of the variation of the amplitude or the frequency of a modulated transmission signal, and the level of the correlation signal Vo is lowered as a whole, the threshold level Ls (-Ls) is averaged on the basis of a peak detection signal S2 detected at that time, and it is varied and set into the threshold level to meet the level of the correlation signal Vo at that time. Accordingly, the data can correctly be demodualted, and reliability can be improved.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is used in a spread spectrum communication device used for, for example, radio control of cranes, etc., internal communications, secret communication, etc. This relates to a correlator that decodes a DS signal spread by .

[Prior art] Spread spectrum communication has traditionally been used for confidential communication, remote control,
It has been studied in various fields such as local area networks, and has been put into practical use in some cases.

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, this type of spread signal is decoded by correlation decoding, one of which is a method using a delay locked loop (DLL).

However, in the case of this DLL method, there are problems in terms of synchronization acquisition time and stable operation, and in recent years, decoding using a matted filter (adaptive filter) method has become mainstream.

There are two types of matted filters, such as those that use surface acoustic waves (SAW) and those that use digital circuits.They have the advantages of high-speed synchronization and stable operation. The correlation calculation used is expressed by the following formula.

Y(nl = Σ d m'P Ik+n where d5
is the input signal, Po. . , is each bit of the spreading code, and N is the code length of the spreading code.

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

FIG. 4 shows a block configuration of a matched filter that implements the above-mentioned equation using a digital circuit.

In the figure, 11 is a shift register, 12 is a multiplier, 1
3 is an adder. The input signal Vi received from the transmitting side is a DS signal obtained by spreading a baseband signal using a spreading code, and is sequentially input to the shift register 11. The data d0 to dN-1 stored in the shift register 11 are
Each is multiplied by the same spreading code as the transmitting side spreading code.

That is, each bit P0 to P N-1 of the spreading code is multiplied by the multiplier 12. Thereafter, the signals are added by an adder 13 to obtain a correlation signal Vo corresponding to a baseband signal.

[Problems to be Solved by the Invention] By the way, when synchronizing signals when demodulating data by decoding, as shown in FIG. 2(b), a main lobe that appears as a peak value at every predetermined time, Among the correlation signals expressed by the side lobes appearing on both sides of the main lobe, the main lobe whose peak value exceeds a preset threshold level is a signal sampled at predetermined time intervals (for example, 1/2 chip). detected by.

However, when the detected waveform becomes distorted due to external noise in the transmitted signal, the level of the main lobe that appears as a correlation signal ○ decreases due to this effect (see Figure 3 (a)). b) e) If this level is below the threshold level, it becomes impossible to detect the peak of the main lobe, and there is a problem in that accurate data demodulation cannot be performed, resulting in a lack of reliability.

In addition, as mentioned above, even if no external noise is superimposed on the transmitted signal, variations in the amplitude and frequency of the modulated transmitted signal will cause variations in the detected output waveform, and if the overall level of the correlation signal 0 decreases, The margin with the threshold level became small, making it difficult to detect the peak of the main lobe, making it impossible to demodulate the data accurately.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to vary the threshold level to an optimal value according to the level of the peak value of the correlation signal, thereby improving the correlation signal necessary for data demodulation. The object of the present invention is to provide a highly reliable correlator that can perform peak detection and accurately demodulate transmitted data.

[Means for Solving the Problem] In order to achieve the above object, the correlator according to the present invention uses a DS that spreads information data transmitted from the transmitting side with a spreading code.
The correlator for decoding a signal includes means for variably controlling a threshold level when detecting the correlation signal in accordance with a peak value of the correlation signal obtained by correlating the DS signal with the same spreading code as that on the transmitting side. It is characterized by

[Operation] When a DS signal in which information data is spread with a spreading code is transmitted from the transmitting side, the correlation signal is adjusted according to the peak value of the correlation signal obtained by the correlation between this DS signal and the same spreading code as the transmitting side. The threshold level at the time of detection is variably controlled.

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

The correlator according to this embodiment decodes a DS signal in which information data from the transmitting side is spread with a PN code, and includes a shift register 1, a multiplier 2, a first adder 3, a threshold detection circuit 4, an output 5, peak detection circuit 6, second adder 7, decoder 8, threshold level determination circuit 9
It is configured with.

Shift register 1 receives and detects a signal from the transmitting side, which is a DS signal Vi which is a baseband signal spread by a spreading code.
are taken in and stored while being shifted sequentially, and the data d0 to dN-1 sequentially stored along with the shift operation are output to the multiplier 2.

The multiplier 2 converts the data d, -d, .

-P is multiplied by N-1. That is, each data d.

-dN-+ is multiplied by each Bi, Soto, Po-P, . . . of the spreading code, and the results are sequentially output to the adder 3.

The first adder 3 receives each data do'' from the multiplier 2.
A correlation signal VO corresponding to a baseband signal is outputted to a threshold detection circuit 4, an output device 5, and a peak detection circuit 6 by sequentially adding P o to d N-I' P M-1.

The threshold detection circuit 4 outputs "1" as a state signal when the level of the input correlation signal ■0 exceeds the threshold level Ls (-Ls), and this signal is sent to the output as an output trigger Sl. 5 is output.

The output device 5 outputs the correlation signal 0 to the second adder 7 in response to the output trigger S1 from the threshold detection circuit 4.

The peak detection circuit 6 detects the peak value (main lobe) of the correlation signal ■○ output from the first adder 3, and outputs this peak detection signal S2 to the threshold level determination circuit 9. In addition, this peak detection circuit 6 detects the threshold level L within a predetermined detection time set in advance.
When the correlation signal VO exceeding s(-Ls) 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 0 from the output device 5 and the signal S2 from the peak detection circuit 6, and outputs the added signal S3 to the decoder 8.

Here, in the correlation signal Vo, a positive peak V+ occurs when the spreading code is synchronized, and a negative peak ■- occurs when there is an anti-correlation.Here, the period of the baseband signal and the period of the spreading code are are set to be the same, and the positive peak + corresponds to the trailing edge of the baseband signal, synchronization is achieved at this point, and decoding is performed in the decoder 8 and the data is demodulated. It has become.

The threshold level determination circuit 9 compares the level of the peak detection signal S2 from the peak detection circuit 6 with the threshold level Ls (-Ls), and determines the optimal threshold level for detecting the next peak value. A threshold level control signal S4 is outputted to the threshold detection circuit 4 for variable control of the threshold level according to the level of the peak detection signal S2.

Note that when determining the threshold level Ls (-Ls), the lower limit level is determined in advance so that the sidelobe Vs of the correlation signal 0 does not exceed the threshold level Ls (-Ls). There is.

In addition, in this threshold level determination circuit 9, as shown in FIG. 3(a), a sufficient detection output cannot be obtained due to the modulation state on the transmitting side, and even if the level of the correlation signal 0 is low overall, the peak value The threshold level is averaged based on the detected peak value, and a threshold level control signal S5 corresponding to the averaged threshold level is output to the threshold detection circuit 4 so that the threshold level can be detected.

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

When the transmitted signal from the transmitting side is detected, the <DS signal Vi is sequentially shifted based on the detected signal and taken into the shift register 1 and stored. Each data d0 to ds-+ stored in this shift register 1 is sequentially multiplied by a spreading code P0 to P8-1, which is the same as that on the transmitting side, by a multiplier 2, and then sequentially added by an adder 3. A correlation signal Vo corresponding to the baseband signal is output from this 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 so, the state signal "1" is outputted to the output device 5 as the output trigger Sl. Then, an output trigger s is sent to the output device 5.
When 1 is output, the correlation signal ``0'' is input to the second adder 7 via the output device 5.

In the second adder 7, in response to the input of the output trigger S1 from the threshold detection circuit 4, the correlation signal ■○
Each time the adder 7 is input, an addition operation is performed and the result is output to the decoder 8, and 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 a peak detection signal S2 to the threshold level determination circuit 9. Moreover, this peak detection circuit 6 detects the threshold level Ls(-
When the correlation signal Vo exceeding Ls) is not input,
The peak detection signal S2 within the detection time is output to the second adder 7.

Next, when the threshold level determination circuit 4 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 determination circuit 4 performs threshold level control that matches the level of the peak detection signal S2. A signal S4 is output to the threshold detection circuit 4.

The threshold detection circuit 4 receives a threshold level control signal S4 from the threshold level determination circuit 9.
is input, the threshold level Ls (-Ls)
is variably controlled so that it is at an optimal level with respect to the peak value detected by the peak detection circuit 6.

Through the above operation, the threshold level Ls (-L
s) is set variably, and then the correlation signal Vo detected by the threshold detection circuit 4 reaches the threshold level L.
If the threshold level does not exceed s (-Ls), the threshold level Ls (-Ls') is variably set to match the peak value of the peak detection signal S2 at that time.

When the level of the peak detection signal S2 exceeds the threshold level Ls'(-Ls'), it is variably set to the initially set threshold level Ls (-Ls).

Furthermore, if the detected output waveform varies due to fluctuations in the amplitude and frequency of the modulated transmission signal, and the level of the correlation signal 0 decreases overall, the threshold is set based on the peak detection signal S2 detected at that time. Level Ls
(-Ls) is averaged and variably set to a threshold level that matches the level of the correlation signal 0 at that time.

Therefore, in the embodiment described above, the threshold level Ls (-L
s) is variably controlled to the optimum value, external noise is superimposed and the detected waveform is distorted, and this influence causes the correlation signal V
The level of O drops to the threshold level Ls(-L
s), it is possible to detect the peak of the correlation signal (main lobe) ①0, and accurate data demodulation can be performed to improve reliability.

Furthermore, even if the detected output waveform varies due to fluctuations in the amplitude and frequency of the modulated transmission signal and the overall level of the correlation signal Vo decreases, the threshold level Ls( -Ls)
Since the correlation signal V required for data demodulation is variably controlled,
○ peak detection can be performed.

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) when detecting the correlation signal (2) 0 according to the peak value of the correlation signal Vo.

[Effects of the Invention] As explained above, according to the correlator of the present invention, the threshold level is varied to an optimum value according to the level of the peak value of the correlation signal, and peak detection of the correlation signal necessary for data demodulation is performed. The transmitted data can be accurately demodulated and reliability can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block configuration diagram showing an embodiment of the correlator according to the present invention, FIGS. 2(a) and (b) are waveform diagrams showing the detection output and correlation signal in a stable state, and FIG. 3(a), (b) is a waveform diagram showing the detection output and 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 determination circuit, VO...Correlation signal, Ls, Ls(-Ls,
-Ls')...Threshold level. Patent Applicant: Futaba Electronics Co., Ltd. Agent/Patent Attorney: Norimitsu Nishimura Figure 4: ■1

Claims (1)

[Claims] In a correlator that decodes a DS signal obtained by spreading information data transmitted from a transmitting side with a spreading code, the correlation is determined according to the peak value of the correlation signal obtained by correlating the DS signal with the same spreading code as that of the transmitting side. A correlator characterized by comprising means for variably controlling a threshold level when detecting a signal.