DSSS Parallel Code Phase Capture Judgment Method Based on Noise Threshold

Abstract

The present invention proposes a DSSS parallel code phase capture judgment method based on a noise threshold. First, perform parallel code phase capture on the received signal to obtain the received signal code phase correlation value results of points; remove the top points in terms of amplitude ranking in the correlation value results to obtain the overall correlation value set regarding noise; calculate the mean value of the noise correlation values in the overall correlation value set of noise; extract the correlation values higher than the mean value in the overall correlation value set and count the number of their points to obtain the correlation value set in the high-noise area; count the mean value of the correlation value set in the high-noise area to obtain the average correlation value of high noise; use the average correlation value of high noise to determine the capture threshold; when the highest peak value of the parallel code phase correlation value results is stably higher than the capture threshold, it indicates successful capture. The present invention can effectively judge the correct signal from the interference signals with inconsistent noise and spreading codes, thereby improving the effectiveness and reliability of DSSS receiver capture.

Description

Technical Field

[0001] The present invention relates to the technical field of direct sequence spread spectrum communication, and particularly to a parallel code phase capture and judgment method for a direct sequence spread spectrum (DSSS) communication receiver, and more particularly to a direct sequence spread spectrum parallel code phase capture and judgment method based on a noise threshold. Background Art

[0002] A direct sequence spread spectrum communication system expands the spectrum through spread spectrum modulation, which can effectively improve the anti-interference ability of the communication system, and thus has been widely applied.

[0003] In a direct sequence spread spectrum communication system, a transmitting device spreads and modulates a digital signal through a spreading code, and then modulates the signal to a required frequency band through carrier modulation; a receiving device receives and demodulates the signal through a receiving circuit and capture and tracking technologies. In the capture part, a parallel code phase capture method is usually adopted and the capture judgment is carried out by means of the correlation value of the received signal to determine whether the required signal exists currently and complete the capture process. An incorrect judgment will cause time loss to the receiver and seriously affect signal reception. In actual DSSS communication, the receiver will copy multiple received channels with different spreading codes. Each transmitting device uses a spreading code to modulate and transmit a signal, which corresponds to a received channel of the receiver. When the transmitting device does not match the current channel, the spreading code of the transmitting end is inconsistent with the spreading code copied by the received channel. Since the spreading codes are not completely orthogonal to each other, there will be a relatively small correlation peak in the correlation result of the capture calculation. At this time, if the capture threshold is set too low, false capture is likely to occur, which will cause the receiver to incorrectly switch from capture to tracking, and the tracking process and phase adjustment are relatively slow. If the correct signal of this channel arrives during the tracking process, it will not be received by the receiver, resulting in data loss. However, too large a capture threshold will cause misjudgment of the capture of the correct signal and missed capture when the signal-to-noise ratio is small. The existing capture judgment methods mainly consider the judgment when the signal is noise or a correct signal. When false capture occurs in the received channel, the current communication is abandoned and retransmitted at the next moment, but the judgment requirement for interference signals with inconsistent spreading codes cannot be met, affecting the success rate and timeliness of communication. Therefore, a new capture judgment method that can effectively cope with interference signals with different spreading codes is urgently needed to be proposed. Summary of the Invention

[0004] To overcome the deficiencies of the prior art and achieve accurate judgment of correct signals and interference signals with different spreading codes, the present invention provides a DSSS parallel code phase capture and judgment method based on a noise threshold. Through this method, effective judgment of correct signals, noise, and interference signals with inconsistent spreading codes can be completed, thereby improving the effectiveness and reliability of DSSS receiver capture.

[0005] The steps of the technical solution adopted by the present invention to solve its technical problems are as follows:

[0006] Step 1: In DSSS communication, both the receiver and the transmitting device agree to use a spreading code of a certain length for spreading modulation; during reception, parallel code phase capture is performed on the received signal to obtain the received signal code phase correlation value results at points;

[0007] Step 2: Remove the top points in terms of amplitude ranking from the correlation value results to obtain the overall correlation value set about noise, where is the th overall correlation value in the set , and

[0008] is the number of points occupied by the peak value of the main peak in the received signal code phase correlation value; Step 3: Calculate the mean value of the noise correlation values of the overall correlation value set

[0009]

[0010] Step 4: Extract the correlation values in the overall correlation value set that are higher than the mean value and count the number of their points to form the correlation value set of the high-noise region, where is the th correlation value in the set ;

[0011] Step 5: Statistically calculate the mean value of the correlation value set of the high-noise region to obtain the average correlation value of the high noise:

[0012]

[0013] Step 6: Determine the capture threshold using the average correlation value of the high noise :

[0014]

[0015] Among them is the false alarm rate, which represents the probability that when the receiver receives a correct DSSS signal but fails to capture the signal. The false alarm rate needs to be set before making the capture judgment value size;

[0016] Step 7: Perform parallel code phase capture on the received signal. If the peak value in the obtained parallel code phase correlation value result is steadily higher than the capture threshold

[0017] Furthermore, in step 1, according to different correlator spacings, generally required .

[0018] Furthermore, in step 2 , among which represents rounding up.

[0019] Furthermore, in step 7, perform parallel code phase capture on the received signal, and adopt the Tong search method to repeat the search multiple times within the set time, and observe the peak value in the obtained parallel code phase correlation value result is whether it is steadily higher than the capture threshold

[0020] If so, mark the capture as successful.

[0021] An electronic device, including a processor and a memory, where the memory is used to store one or more programs; when the one or more programs are executed by the processor, the above method is implemented.

[0022] A readable storage medium stores a computer program, and when the computer program is executed by a processor, the above method is implemented.

[0023] Beneficial effects:

[0024] The beneficial effects of the present invention are as follows: The magnitude of the high-noise correlation value, which has a greater impact on the judgment in the capture threshold calculation, is introduced into the capture calculation. Combining the noise distribution and the false alarm rate, the capture threshold calculation and judgment are completed. By removing the influence of the low-noise region in the noise on the threshold calculation, the calculated capture threshold is higher than the main peak correlation value of the interference signal (i.e., the signal with inconsistent spreading codes) that is not much different from the noise peak, thereby effectively coping with the signal interference when the spreading codes are inconsistent, greatly improving the effectiveness and stability of the DSSS receiver capture, and realizing the parallel code phase capture judgment of the DSSS receiver. Description of the Drawings

[0025] Figure 1 is a flowchart for calculating the capture threshold value based on the noise threshold of the present invention. The correlation value of the received signal is calculated by parallel code phase capture (implemented by inverse Fourier transform). Subsequently, through peak-removing filtering, a set of overall correlation values of the noise is obtained. Subsequently, the mean value of the noise correlation value is calculated through integral-mean calculation. The set of correlation values in the high-noise region is obtained through a comparator. The average correlation value of the high noise is calculated through integral-mean calculation. Then, it is multiplied by the false alarm rate parameter to obtain the capture threshold value for the current parallel code phase capture.

[0026] Figure 2 is a schematic diagram of the noise region of the present invention. In the figure, the abscissa is the phase deviation PH, the ordinate is the correlation value of the signal, the curve in the figure is the correlation value of the signal obtained by parallel code phase capture, the lower region part is the low-noise region part, and the upper region part is the high-noise region part.

[0027] Figure 3 is a schematic diagram of the capture effect when the received signal is pure noise. The curve in the figure is the correlation value of the received signal, and the dashed line is the capture threshold value calculated by this method.

[0028] Figure 4 is a schematic diagram of the capture effect when the received signal is a received signal with inconsistent spreading codes. The curve in the figure is the correlation value of the received signal, and the dashed line is the capture threshold value calculated by this method. It can be seen that there is a relatively small correlation peak. If the capture threshold is set inappropriately, mis-capture will occur.

[0029] Figure 5 is a schematic diagram of the capture effect when the received signal is a correct signal. The curve in the figure is the correlation value of the received signal, and the dashed line is the capture threshold value calculated by this method. Detailed Embodiment

[0030] The present invention will be further described below in conjunction with the drawings and embodiments.

[0031] The parallel code phase capture discrimination method based on the noise threshold proposed by the present invention combines the statistical advantages of noise distribution and the advantages of high-noise region discrimination, solves the problem of mis-capture when the spreading codes are inconsistent, reduces the resource overhead of the receiver, and improves its stability. The specific steps are as follows:

[0032] Step 1: In DSSS communication, both the receiver and the transmitting device agree to use Perform spread spectrum modulation with the spread spectrum code; during reception, the receiver performs parallel code phase acquisition, and obtains the point inverse Fourier transform to obtain the point received signal code phase correlation value result ;

[0033] Step 2: Remove the top points in terms of amplitude in the correlation value result to obtain the overall correlation value set about noise, where is the number of points occupied by the peak value of the main peak in the received signal code phase correlation value obtained through parallel code phase acquisition. Take , where the symbol is rounding up;

[0034] Step 3: Calculate the mean value of the noise correlation values in the overall correlation value set :

[0035] (1)

[0036] Step 4: Extract the correlation values in the overall correlation value set that are higher than the mean value and count the number of their points to form the correlation value set of the high-noise region, is the th correlation value in the set , ;

[0037] Step 5: As Figure 2 shown, count the mean value of the correlation value set of the high-noise region to obtain the average correlation value of the high noise:

[0038] (2)

[0039] Step 6: Determine the acquisition threshold using the average correlation value of the high noise; the acquisition threshold of the DSSS receiver is the standard for completing acquisition judgment.

[0040] When the probability that the receiver receives a correct DSSS signal but fails to acquire the signal is called the false alarm rate , in this embodiment, before performing acquisition judgment, the false alarm rate value is first set to 0.0001. And the acquisition threshold The distribution is Rayleigh distribution when no correct DSSS signal is received. Therefore, the false alarm rate is expressed as:

[0041] (3)

[0042] Where represents the exponential operation with the natural constant as the base. Then, according to formula (3), we get:

[0043] (4)

[0044] The difference between the peak value of the main peak of the correlation value and the remaining noise peak values is the core of the capture judgment. When using the average noise correlation value for calculation in the traditional method, the noise correlation values in the low-noise regions that are not concerned in the noise will participate in the calculation of the average noise correlation value, thus interfering with the calculation of the capture threshold, resulting in a relatively low final capture threshold, and then causing the relatively low main peak of the correlation value when the spreading codes are inconsistent to exceed the capture threshold, leading to false capture. Therefore, this method uses the average correlation value of high noise to replace the overall correlation value to remove the interference of the low-noise regions on the calculation of the capture threshold, so as to realize the judgment of the interference signal with inconsistent spreading codes. Therefore, the present invention determines the capture threshold using the average correlation value of high noise :

[0045] (5)

[0046] Step 7: Adopt the Tong search method to repeat the search multiple times within the set time, and observe the peak value in the obtained parallel code phase correlation value result whether it is stably higher than the capture threshold . If so, mark the capture as successful

[0047] Performance analysis:

[0048] In the simulation analysis, the parallel code phase capture process uses a spreading code with a length of 255 and performs operations with 32768 Fourier transform points. As Figures 3 to 5 shown Figure 3 is the capture judgment situation under noise. At this time, there is no obvious main peak in the correlation value result. The capture threshold value of the method proposed by the present invention is higher than the overall correlation result, and the capture judgment is correct Figure 4 is the capture judgment situation of the interference signal with inconsistent spreading codes. At this time, the peak value of the correlation result does not exceed the capture threshold value of the method proposed by the present invention, and the capture judgment is correct without false capture Figure 5This is the capture judgment situation under the correct signal. At this time, there is an obvious main peak in the correlation value, and the peak value exceeds the capture threshold of the method proposed by the present invention, so the capture is successful. It can be seen that the method proposed by the present invention can meet the capture requirements in different situations, especially has good anti-interference ability for interference signals with inconsistent spreading codes, and can realize the stable capture of the receiver.

[0049] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations of the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and purposes of the present invention.

Claims

1. A DSSS parallel code phase capture and judgment method based on a noise threshold, characterized in that: Including the following steps: Step 1: In DSSS communication, both the receiver and the transmitting device agree to use the spreading code of length for spread spectrum modulation; during reception, perform parallel code phase acquisition on the received signal to obtain the correlation value result of the received signal code phase at points; Step 2: Remove the relevant value results The points with the top amplitudes are obtained to form the overall set of relevant values regarding noise , is the -th overall relevant value in the set , , is the number of points occupied by the peak value of the main peak in the relevant value of the received signal code phase; Step 3: Calculate the set of overall correlation values of the noise The mean value of the noise correlation values : Step 4: Extract the set of overall relevant values with values higher than the mean from the relevant values and count the number of points to form the set of relevant values for the high-noise region , which is the th relevant value in the set ; Step 5: Statistically analyze the relevant value set of the high-noise area to obtain the average correlation value of the high noise : Step 6: Determine the acquisition threshold using the average correlation value of high noise : wherein is the false alarm rate; Step 7: Perform parallel code phase acquisition on the received signal. If the peak value in the result of the parallel code phase correlation value is stably higher than the acquisition threshold , it indicates successful acquisition.

2. The method for judging the phase capture of DSSS parallel codes based on a noise threshold according to claim 1, wherein: In Step 1, it is required that .

3. The method for judging the phase capture of DSSS parallel codes based on a noise threshold according to claim 1, characterized in that: In step 2, , where represents rounding up.

4. A method for judging the phase capture of DSSS parallel codes based on a noise threshold according to claim 1, characterized in that: In step 7, perform parallel code phase acquisition on the received signal, and adopt the Tong search method to repeat the search multiple times within the set time, and observe the peak value in the obtained parallel code phase correlation value result whether it is stably higher than the acquisition threshold , if so, mark the acquisition as successful.

5. An electronic device, comprising a processor and a memory, the memory being configured to store one or more programs; characterized in that: When the one or more programs are executed by the processor, implement any of the methods recited in claims 1 to 4.

6. A readable storage medium storing a computer program, characterized in that: When a computer program is executed by a processor, implement any of the methods recited in claims 1 to 4.

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