CN105141337A - Fake-locking identification method of spread spectrum communication receiver - Google Patents

Abstract

A method for identifying a false lock in a spread spectrum communication receiver, the steps of which are: S1: use the signal tracking channel loop that needs to be locked for detection and identification as the channel to be detected; S2: after the channel to be detected is locked, pass the discriminator to The detection channel is judged as a suspected false lock channel, or it is judged that the lock is correct, and the identification is ended; S3: Add an independent signal tracking channel loop as the identification channel; S4: Start the identification channel, and send the real-time signal capture results to the identification channel ;S5: After the identification channel is locked, start the tracking difference detection module, and compare the carrier frequency and code phase data output by the suspected channel and the identification channel in real time; S6: Judgment; S7: Repeat steps S4, S5, S6 multiple times . The invention has the advantages of easy realization, reliable detection and identification, wide application range and the like.

Description

A False Lock Identification Method for Spread Spectrum Communication Receiver

technical field

The invention mainly relates to the design field of spread-spectrum digital receivers such as spread-spectrum measurement and control transponders and non-coherent spread-spectrum receivers, in particular to a false-lock identification method for spread-spectrum digital receivers.

Background technique

The spread spectrum technology is widely used in the satellite measurement and control system. The space application of the spread spectrum technology can realize a communication system with high sensitivity and anti-interference performance on the one hand, and can complete functions such as high-precision measurement and orbit determination on the other hand. . As the number of satellites using spread spectrum technology increases, the spread spectrum signals between satellites will interfere with each other, and the power of spread spectrum signals varies from satellite to country, orbit, and application type. At the same time, taking into account some hostile and malicious interference signals, etc., under this complex electromagnetic background, the spread spectrum receiver is faced with a severe problem of reliability of spread spectrum signal detection.

In the signal acquisition stage of spread spectrum signal detection, if the current signal does not contain useful (correct) signals, but only some interference signals, or there are useful signals in the current signal, but the strength of the interference signal is much greater than the useful signal, the capture will There is a certain probability of false alarm, causing the receiver to lock on the interference signal, that is, "false lock". This situation is more likely to occur when the interfering signal is strong, regardless of the type of spreading code used for the signal. In order to reduce the probability of false alarms, it is generally necessary to increase the capture threshold, and the increase of the capture threshold will reduce the probability of false alarms and also reduce the capture probability, thereby affecting the sensitivity of the receiver, especially the signal capture sensitivity in the background of hostile interference. This effect is especially significant in high sensitivity receivers. The false lock of the receiver after the false alarm occurs, and the receiver cannot exit the lock, which will prevent the receiver from receiving and demodulating the normal signal, cause the receiver to fail, and even demodulate the malicious information carried in the interference signal, interfering with the receiver The normal work of the end host, the harm of the false lock of the receiver is significant. In order to determine whether the current receiver is correctly locked, the receiver needs to have some detection measures to identify the lock or false lock, that is, once the false lock occurs, the receiver can exit the lock.

At present, the existing false lock detection methods include multi-peak detection and cross-correlation detection in the acquisition stage, judgment on the working condition of the code ring by using the correlation characteristics of the spreading code in the tracking stage, quadrature demodulation IQ path energy ratio, demodulation signal-to-noise Ratio, information layer identification and other signal detection methods. Among them, the detection of the signal layer is mainly based on the autocorrelation and cross-correlation characteristics of the spreading code, and the false lock identification can be carried out more effectively by setting the threshold, but the threshold setting is related to the signal strength and noise level, which will affect the interference background. Signal capture sensitivity performance. The identification of the information layer is not applicable to some spread spectrum systems that use the spread spectrum code as the only link identification feature. At the same time, as the number of satellites using spread spectrum technology increases, the spread spectrum signals between satellites will interfere with each other. , the information layer characteristics of the same type of satellite spread spectrum signals are often similar, but cannot be effectively distinguished. It can be seen from the above that the development of various satellite measurement and control spread spectrum digital receivers inevitably encounters the problem of false locks. Existing false lock detection methods use the autocorrelation and cross-correlation characteristics of spreading codes. The cross-correlation of strong interference signals is likely to be close to or even exceed the autocorrelation of weak useful signals. The strength of the useful signal is related to the strength of the interference signal, which affects the anti-jamming performance and sensitivity of the receiver.

Contents of the invention

The technical problem to be solved by the present invention is that, aiming at the technical problems existing in the prior art, the present invention provides a method for identifying a false lock of a spread spectrum communication receiver that is easy to implement, reliable in detection and identification, and widely applicable.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A method for identifying a false lock of a spread spectrum communication receiver, the steps of which are:

S1: The signal tracking channel loop that needs to be identified by lock detection is used as the channel to be detected;

S2: After the channel to be detected is locked, the discriminator judges the channel to be detected as a suspected false locked channel, or judges that the channel is locked correctly, and ends the identification;

S3: Add an independent signal tracking channel loop as a discrimination channel;

S4: Start the identification channel, and send the real-time signal capture result to the identification channel;

S5: After the identification channel is locked, start the tracking difference detection module to read the carrier frequency and code phase data output by the suspected channel and the identification channel in real time for comparison;

S6: If the difference between the carrier frequency of the suspected channel and the carrier frequency of the identification channel exceeds the error range of the tracking phase-locked loop, or the difference between the code phase of the suspected false-locked channel and the code phase of the identification channel exceeds the error range of the tracking code loop , it is considered that the suspected channel is falsely locked; otherwise, the suspected channel is considered to be locked correctly;

S7: Repeat steps S4, S5, and S6 multiple times. If a certain number of detections indicate that the suspected channel is falsely locked, then confirm the suspected false channel lock, reset the suspected channel tracking loop, and the receiver recaptures the signal to end the identification process. ; Or, if a certain number of detections indicates that the suspected false lock channel is correctly locked, then confirm that the suspected false lock channel is correctly locked, and end the identification process.

As a further improvement of the present invention: the process of the step S2 is:

S201: The tracking channel of the receiver to be detected has passed the conventional lock detection, and is considered to be locked;

S202: Start the discriminator and use the conventional lock detection mechanism. For example, if the demodulation signal-to-noise ratio of the receiver is less than a threshold, the tracking channel to be detected that may be a false lock is judged as a suspected false lock channel; otherwise, the tracking channel to be detected is judged to be locked Correct, end the identification.

As a further improvement of the present invention: in the step S3, the receiver adds an independent signal tracking channel on the basis of the original signal tracking channel.

As a further improvement of the present invention: in the step S4, the specific process of identifying the channel from starting to locking is as follows:

S401: The channel to be detected is judged as a suspected false lock channel;

S402: Start the identification channel, and notify the receiver signal capture module that the current capture result will be sent to the identification channel;

S403: The signal capture module appropriately relaxes the signal detection threshold;

S404: The signal capture module uses the relaxed detection threshold to capture the signal;

S405: After the capture is successful, the detection threshold of the capture module returns to normal, and the capture result is sent to the identification channel;

S406: The identification channel starts to track the signal, if the carrier phase-locked loop converges and the spreading code loop converges, then the identification channel is locked; otherwise, go to step S404.

As a further improvement of the present invention: the step S6 includes a wave frequency and code phase comparison process, and the process is:

S601: Set the error range of the carrier phase-locked loop used by the receiver to be ±a Hz, and the error of the spread code code loop used by the receiver to be ±b code chips; the period of the spread code used by the receiver corresponding to the spread spectrum communication system is L, Then the code phases of the L spreading codes are respectively expressed as 0.1.2.3.4...L-1;

S602: Set the carrier frequency CA output by the carrier phase-locked loop of the suspected false-locked channel at the current moment, and identify the carrier frequency CB output by the carrier phase-locked loop of the channel;

S603: Assume that at the current moment, the phase value of the spread code code output by the suspected false locked channel code ring is PA(PA∈[0, L-1]), and the phase value of the spread code code output by the identification channel code ring is PB(PB ∈[0,L-1]);

S604: If |PA–PB|>2*b, and |PA–PB|<(L-1-2*b), it is considered to be a suspected false lock channel and false lock, and enter step S607; otherwise, enter step S605;

S605: Convert A to Hz, record as AHz, convert B to Hz, record as BHz;

S606: If |AHz–BHz|>2*a, it is considered that the suspected false lock channel is falsely locked, otherwise it is considered that the suspected false lock channel is locked correctly;

S607: End this comparison.

As a further improvement of the present invention: it also includes a process of identifying and accumulating judgments multiple times, and the specific steps of the process are:

S1001: Determine that the current receiver is locked to a suspected false lock channel, and start identification;

S1002: Reset the identification channel, obtain the real-time capture result, and complete the signal tracking by the identification channel;

S1003: This identification considers that the channel is suspected to be a fake lock, and the counter of the suspected fake lock channel is incremented by 1, and enters step S1005; otherwise, enters step S1004;

S1004: Add 1 to the suspected false lock channel lock correct counter, and enter step S1007;

S1005: If the counter of the suspected false lock is greater than or equal to M, then finally determine the suspected false lock channel false lock; otherwise, enter step S1002;

S1006: End the receiver lock identification, reset the suspected false lock channel, lose the lock of the receiver, and enter recapture;

S1007: If the suspected false lock channel is correctly locked and the counter is greater than or equal to N, it is finally determined that the suspected false lock channel is correctly locked, and the receiver locks the false lock identification process, and the receiver completes signal locking; otherwise, enter step S1002.

Compared with the prior art, the present invention has the advantages of:

A false lock identification method of a spread spectrum communication receiver of the present invention is easy to implement, reliable in detection and recognition, and has a wide range of applications, and has nothing to do with receiver sensitivity or receiver parameters; it utilizes the modulated carrier frequency of spread spectrum signals, spread The frequency code code phase is used for identification, and its detection effect has nothing to do with the statistical characteristics of the signal. The judgment is made by the difference between the demodulation output results in the case of correct locking and false locking, which has high reliability and engineering feasibility.

Description of drawings

Fig. 1 is a schematic flow chart of the present invention.

Fig. 2 is a schematic flow chart of the present invention in a specific application example for judging the locking of the channel to be detected.

Fig. 3 is a schematic flow chart of starting the identification channel in a specific application example of the present invention.

Fig. 4 is a schematic flow chart of carrier frequency and code phase comparison in a specific application example of the present invention.

Fig. 5 is a schematic flow chart of the present invention performing multiple identification and cumulative judgments in a specific application example.

Fig. 6 is a schematic diagram of an embodiment of applying the method of the present invention to identify fake locks.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1, a kind of spread spectrum communication receiver false lock identification method of the present invention, its steps are:

S1: The signal tracking channel loop that needs to be identified by lock detection is used as the channel to be detected;

S2: After the channel to be detected is locked, the discriminator is used to judge the channel to be detected as a suspected false locked channel (referred to as a suspected channel), or determine that the locked channel is correct, and end the identification;

S3: Add an independent signal tracking channel loop (a copy of the receiver signal tracking module) as a discrimination channel;

S4: Start the identification channel, and send the real-time signal capture result to the identification channel;

S5: After the identification channel is locked, start the tracking difference detection module to read the carrier frequency and code phase data output by the suspected channel and the identification channel in real time for comparison;

S6: If the difference between the carrier frequency of the suspected channel and the carrier frequency of the identification channel exceeds the error range of the tracking phase-locked loop, or the difference between the code phase of the suspected channel and the code phase of the identification channel exceeds the error range of the tracking code loop, then It is considered that the suspected channel is falsely locked; otherwise, the suspected channel is considered to be locked correctly;

S7: Repeat steps S4, S5, and S6 multiple times. If the M times of detection are considered to be a suspected channel false lock, then confirm the suspected channel false lock, reset the suspected channel tracking loop, and the receiver recaptures the signal to end the identification process; or , if the N times of detections indicate that the suspected channel is locked correctly, it is confirmed that the suspected channel is locked correctly, and the identification process ends.

As shown in Figure 2, in a specific application example, the specific flow of the locked channel to be detected in step S2 is as follows:

S201: The tracking channel of the receiver to be detected has passed the conventional locking detection (such as phase-locked loop convergence), and is considered to be locked;

S202: Start the discriminator, still use the conventional lock detection mechanism, such as the receiver demodulation SNR is less than a threshold (a rough threshold X can be set in advance), and the tracking channel to be detected that may be a false lock is judged as suspected If the channel is falsely locked; otherwise, it is judged that the tracking channel to be detected is locked correctly, and the authentication ends.

In a specific application example, in step S3, the receiver adds an independent signal tracking channel on the basis of the original signal tracking channel, which can be based on a copy of the receiver signal tracking module, or can be similar to the receiver signal tracking module A simplified version of the design, used as a special channel for fake lock identification.

As shown in Figure 3, in a specific application example, the specific process of identifying the channel from starting to locking in step S4 is as follows:

S401: The channel to be detected is judged as a suspected false lock channel;

S402: Start the identification channel, and notify the receiver signal capture module that the current capture result will be sent to the identification channel;

S403: The signal capture module appropriately relaxes the signal detection threshold (making signal detection easier to succeed);

S404: The signal capture module uses the relaxed detection threshold to capture the signal;

S405: After the capture is successful, the detection threshold of the capture module returns to normal, and the capture result is sent to the identification channel;

S406: The identification channel starts to track the signal, if the carrier phase-locked loop converges and the spreading code loop converges, then the identification channel is locked; otherwise, go to step S404.

In a specific application example, in the steps S5 and S6, the basis for identifying whether the suspected false lock channel is correctly locked is a comparison based on the signal real-time tracking results of the suspected channel and the identification channel, and the comparison object can be a tracking solution. The modulated carrier frequency and the code phase of the spreading code can also only be compared to track and demodulate the code phase of the spreading code.

As shown in Figure 4, in a specific application example, step S6 further includes a wave frequency and code phase comparison process, which is:

S601: Set the error range of the carrier phase-locked loop used by the receiver to be ±a Hz, and the spread spectrum code loop error used by the receiver to be ±b chips. The spread spectrum code period used by the receiver corresponding to the spread spectrum communication system is L, and the phases of the L spread spectrum code codes are respectively expressed as 0.1.2.3.4...L-1;

S602: Set the carrier frequency CA output by the suspected channel carrier phase-locked loop at the current moment, and identify the carrier frequency CB output by the channel carrier phase-locked loop;

S603: Assume that at the current moment, the phase value of the spread code code output by the suspected channel code ring is PA(PA∈[0, L-1]), and the phase value of the spread code code output by the identification channel code ring is PB(PB∈[ 0, L-1]);

S604: If |PA–PB|>2*b, and |PA–PB|<(L-1-2*b), it is considered to be suspected channel false lock, and enter step S607; otherwise, enter step S605;

S605: Convert A to Hz, record as AHz, convert B to Hz, record as BHz;

S606: If |AHz–BHz|>2*a, it is considered that the suspected channel is falsely locked, otherwise it is considered that the suspected channel is locked correctly;

S607: End this comparison.

As shown in Figure 5, as a preferred embodiment, this example further includes a flow of multiple identification and cumulative judgments, and the specific steps of the flow are:

S1001: Determine that the current receiver lock is a suspected false lock (suspected false lock channel), and start identification;

S1002: Reset the identification channel, obtain the real-time capture (recapture) result, and complete the signal tracking by the identification channel;

S1003: This identification considers that the channel is suspected of being a false lock, and the counter of the suspected channel of false lock is incremented by 1, and enters step S1005; otherwise, enters step S1004;

S1004: Add 1 to the suspected channel locked correct counter, and enter step S1007;

S1005: If the suspected false lock counter is greater than or equal to M, then finally determine the suspected channel false lock; otherwise, enter step S1002;

S1006: End the receiver lock identification, reset the suspected channel, lose the receiver lock, and enter recapture;

S1007: If the suspected channel lock correct counter is greater than or equal to N, then finally determine that the suspected channel lock is correct, end the false lock identification process of receiver locking, and the receiver completes signal locking; otherwise, go to step S1002.

As shown in Figure 6, for adopting the application example of the inventive method on a certain type of spaceborne multi-channel spread spectrum receiver:

(1), CAP is the receiver multi-channel capture module, LINK_CTRL is the receiver logic link control module, TRK_1, TRK_2, TRK_3 are three independent logic link tracking modules, FD_1, FD_2, FD_3 are the tracking corresponding fake lock identification module;

(2) Take TRK_1 and FD_1 as examples for illustration;

(3) When the receiver starts, the CAP sends the capture result of link 1 to TRK_1. After TRK_1 is locked, it sends the real-time output information combination {signal-to-noise ratio snr, carrier frequency carr_freq, code phase PA} of the tracking loop to the fake Lock identification module FD_1;

(4) The FD_1 lock decision unit compares snr with the signal-to-noise ratio threshold X (such as X=20dB), if snr>=20, then judges that TRK_1 is locked correctly, and the false lock detection process is completed. If snr<20, the multi-detection controller of FD_1 starts, and the false lock identification for TRK_1 starts;

(5) FD_1 acquires the capture result of link 1 sent by the CAP, including carrier frequency (carr_freq_init) and code phase (pn_init) information.

(6), considering the problem of tight receiver hardware resources under multi-channel, a simplified copy of the signal tracking module is used in this implementation example, that is, FD_1 only uses a code phase tracking synchronization loop (such as a DLL code loop), It is used to obtain the real-time code phase PB of the signal according to the capture result pn_init. The carrier frequency directly uses the value of carr_freq_init, and the error is the capture frequency accuracy (such as 200Hz).

(7) After the code ring of FD_1 is locked, start the tracking difference detector, and compare the carrier frequency and code phase values output by TRK_1 and FD_1 respectively.

(8) Example Design After the tracking loop is locked, the carrier frequency deviation is less than 10 Hz, the code phase deviation is less than 0.5 code phase, and the code phase period is L. Then if |carr_freq_init–carr_freq|>2*(200+10)Hz, or |PA–PB|>2*0.5 and |PA–PB|<(L-1-2*0.5), the false lock detection result of this time If it is "suspected false lock", the suspected false lock counter is incremented by 1. Otherwise, the correct lock counter is incremented by one.

(9) The multi-detection controller of FD_1 resets the code ring of FD_1, continues to obtain the capture result of link 1, and enters the next detection, and repeats.

(10) If the suspected false lock counter is greater than or equal to M (such as M=3), it will finally determine that TRK_1 is falsely locked, FD_1 outputs a false_en signal to LINK_CTRL, LINK_CTR sends an rst reset signal to reset TRK_1, and link 1 enters recapture.

(11) If the lock correct counter is greater than or equal to N (for example, N=3), the authentication process of TRK_1 is all over, and TKR_1 maintains the lock.

(12), from the application of this example, lengthening the spread spectrum code period L used by the spread spectrum system, improving the accuracy of tracking carrier ring and code ring or capturing the output frequency accuracy, etc., can all improve the identification probability of the false lock identification method of the present invention ; and increasing the value of M and N to expand the number of testing samples can improve the confidence of the testing results.

The above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions under the idea of the present invention belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (6)

1. A false lock identification method for a spread spectrum communication receiver, characterized in that the steps are: S1: The signal tracking channel loop that needs to be identified by lock detection is used as the channel to be detected; S2: After the channel to be detected is locked, the discriminator judges the channel to be detected as a suspected false locked channel, or judges that the channel is locked correctly, and ends the identification; S3: Add an independent signal tracking channel loop as a discrimination channel; S4: Start the identification channel, and send the real-time signal capture result to the identification channel; S5: After the identification channel is locked, start the tracking difference detection module to read the carrier frequency and code phase data output by the suspected channel and the identification channel in real time for comparison; S6: If the difference between the carrier frequency of the suspected channel and the carrier frequency of the identification channel exceeds the error range of the tracking phase-locked loop, or the difference between the code phase of the suspected false-locked channel and the code phase of the identification channel exceeds the error range of the tracking code loop , it is considered that the suspected channel is falsely locked; otherwise, the suspected channel is considered to be locked correctly; S7: Repeat steps S4, S5, and S6 multiple times. If a certain number of detections indicate that the suspected channel is falsely locked, then confirm the suspected false channel lock, reset the suspected channel tracking loop, and the receiver recaptures the signal to end the identification process. ; Or, if a certain number of detections indicates that the suspected false lock channel is correctly locked, then confirm that the suspected false lock channel is correctly locked, and end the identification process. 2. the false lock identification method of spread spectrum communication receiver according to claim 1, is characterized in that, the flow process of described step S2 is: S201: The tracking channel of the receiver to be detected has passed the conventional lock detection, and is considered to be locked; S202: Start the discriminator and use the conventional lock detection mechanism. For example, if the demodulation signal-to-noise ratio of the receiver is less than a threshold, the tracking channel to be detected that may be a false lock is judged as a suspected false lock channel; otherwise, the tracking channel to be detected is judged to be locked Correct, end the identification. 3. The false lock identification method of the spread spectrum communication receiver according to claim 1, characterized in that, in the step S3, the receiver adds an independent signal tracking channel on the basis of the original signal tracking channel. 4. the false lock identification method of spread spectrum communication receiver according to claim 1, is characterized in that, in the described step S4, the concrete flow process that discriminates channel and starts to locking is: S401: The channel to be detected is judged as a suspected false lock channel; S402: Start the identification channel, and notify the receiver signal capture module that the current capture result will be sent to the identification channel; S403: The signal capture module appropriately relaxes the signal detection threshold; S404: The signal capture module uses the relaxed detection threshold to capture the signal; S405: After the capture is successful, the detection threshold of the capture module returns to normal, and the capture result is sent to the identification channel; S406: The identification channel starts to track the signal, if the carrier phase-locked loop converges and the spreading code loop converges, then the identification channel is locked; otherwise, go to step S404. 5. the false lock identification method of spread spectrum communication receiver according to claim 1, is characterized in that, comprises wave frequency and code phase comparison flow process in described step S6, and flow process is: S601: Set the error range of the carrier phase-locked loop used by the receiver to be ±a Hz, and the error of the spread code code loop used by the receiver to be ±b code chips; the period of the spread code used by the receiver corresponding to the spread spectrum communication system is L, Then the code phases of the L spreading codes are respectively expressed as 0.1.2.3.4...L-1; S602: Set the carrier frequency CA output by the carrier phase-locked loop of the suspected false-locked channel at the current moment, and identify the carrier frequency CB output by the carrier phase-locked loop of the channel; S603: Assume that at the current moment, the phase value of the spread code code output by the suspected false locked channel code ring is PA(PA∈[0, L-1]), and the phase value of the spread code code output by the identification channel code ring is PB(PB ∈[0,L-1]); S604: If |PA–PB|>2*b, and |PA–PB|<(L-1-2*b), it is considered to be a suspected false lock channel and false lock, and enter step S607; otherwise, enter step S605; S605: Convert A to Hz, record as AHz, convert B to Hz, record as BHz; S606: If |AHz–BHz|>2*a, it is considered that the suspected false lock channel is falsely locked, otherwise it is considered that the suspected false lock channel is locked correctly; S607: End this comparison. 6. the false lock identification method of spread spectrum communication receiver according to claim 1, is characterized in that, also comprises the flow process of multiple discrimination cumulative judgment, the concrete steps of this flow process are: S1001: Determine that the current receiver is locked to a suspected false lock channel, and start identification; S1002: Reset the identification channel, obtain the real-time capture result, and complete the signal tracking by the identification channel; S1003: This identification considers that the channel is suspected to be a fake lock, and the counter of the suspected fake lock channel is incremented by 1, and enters step S1005; otherwise, enters step S1004; S1004: Add 1 to the suspected false lock channel lock correct counter, and enter step S1007; S1005: If the counter of the suspected false lock is greater than or equal to M, then finally determine the suspected false lock channel false lock; otherwise, enter step S1002; S1006: End the receiver lock identification, reset the suspected false lock channel, lose the lock of the receiver, and enter recapture; S1007: If the suspected false lock channel is correctly locked and the counter is greater than or equal to N, it is finally determined that the suspected false lock channel is correctly locked, and the receiver locks the false lock identification process, and the receiver completes signal locking; otherwise, enter step S1002.