Carrier frequency tracking method in hybrid frequency discrimination mode

Abstract

The invention relates to a hybrid frequency discrimination mode carrier frequency tracking method, which comprises the following steps of: S1, based on bit synchronization information of a received telegraph text, receiving an IQ coherent integral value synchronously corresponding to front and back half bits of each telegraph text bit; s2, calculating a conjugate product value of front and back adjacent IQ coherent integral values, and generating an IQ differential value sequence; s3, according to the IQ differential sequence, performing coherent frequency discrimination on the IQ differential values in bits, performing incoherent frequency discrimination on the IQ differential values between adjacent bits, and generating a coherent frequency discrimination and incoherent frequency discrimination alternating frequency tracking error sequence; and S4, filtering the frequency tracking error sequence to form a carrier frequency tracking loop. According to the method, the coherent frequency discrimination method and the incoherent frequency discrimination method are combined, the signal carrier frequency tracking sensitivity can be improved, and the signal carrier frequency tracking threshold can be reduced.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to a hybrid frequency discrimination carrier frequency tracking method. Background Technology

[0002] With the increase in deep space exploration and other missions, the demand for GNSS navigation and positioning services has expanded to geostationary orbit (GEO) and even further into space. Against this backdrop, the high-orbit space environment presents new technical requirements and challenges for GNSS technology. Specifically, the main lobe signal received by GNSS satellites in high-orbit space originates from the opposite side of the Earth and travels a long distance, while the sidelobe signals that high-orbit satellites can receive radiate with very weak power, resulting in extremely weak GNSS signal power received by high-orbit satellites. This necessitates GNSS receivers with higher sensitivity in tracking navigation signals to ensure the navigation and positioning service capabilities of GNSS in high-orbit space.

[0003] In existing technologies, incoherent frequency discrimination can eliminate the effect of message bit polarity reversal, but it introduces squared loss, leading to insufficient tracking sensitivity. Furthermore, the pull range of incoherent frequency discrimination is limited to 180° (two quadrants), a narrow range that makes it difficult for the tracking loop to withstand significant dynamic stress. In contrast, coherent frequency discrimination avoids the multiplication of the I and Q branches, eliminating squared loss and significantly reducing the threshold of the carrier frequency tracking loop. Its pull range is also wider, at 360° (four quadrants), allowing the tracking loop to withstand greater dynamic stress. However, coherent frequency discrimination cannot eliminate the effect of message bit polarity reversal; it can only utilize the phase detection results calculated from adjacent coherent integral values ​​within a bit. This results in the phase detection results calculated from adjacent coherent integral values ​​between bits not being utilized, leading to undersampling problems, increasing loop frequency tracking error, and ultimately affecting frequency tracking performance.

[0004] Therefore, how to combine the high tracking sensitivity of coherent frequency discrimination with the frequency discrimination continuity of non-coherent frequency discrimination has become an urgent problem to be solved. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention aims to provide a hybrid frequency discrimination carrier frequency tracking method that improves signal carrier tracking sensitivity and reduces the carrier frequency tracking threshold, thereby increasing the effective range of received signals in high-orbit and deep space exploration.

[0006] To achieve the above-mentioned objectives, this invention provides a hybrid frequency discrimination carrier frequency tracking method, comprising the following steps:

[0007] Step S1: Based on the bit synchronization information of the received message, receive the IQ coherence integral value corresponding to the synchronization of the first and second half bits of each message bit.

[0008] Step S2: Calculate the conjugate product of adjacent IQ coherent integral values ​​in sequence to generate the IQ difference value sequence;

[0009] Step S3: Based on the IQ difference sequence, perform coherent frequency discrimination on the IQ difference values ​​within a bit and incoherent frequency discrimination on the IQ difference values ​​between adjacent bits to generate a frequency tracking error sequence that alternates between coherent and incoherent frequency discrimination.

[0010] Step S4: Filter the frequency tracking error sequence to form a carrier frequency tracking loop.

[0011] According to one technical solution of the present invention, in step S1, the receiving IQ coherent integral value corresponding to the synchronization of the first and second halves of each message bit has a coherent integration time T that is half the bit time of the received message, and its integration clearing time is synchronized with the message bit start time.

[0012] According to one technical solution of the present invention, step S2 specifically includes:

[0013] Step S21: Calculate the dot product of adjacent IQ coherent integral values:

[0014] ;

[0015] Step S22: Calculate the cross product of adjacent adjacent IQ coherence integral values:

[0016] ;

[0017] in, and For the k-th IQ coherent integral value, and This is the (k-1)th IQ coherent integral value;

[0018] Step S23: Based on the calculation results of the dot product and cross product, form the IQ difference value sequence { , }

[0019] According to one technical solution of the present invention, step S3 includes:

[0020] Step S31: Determine the IQ difference value attribute: If the coherent integration time of the adjacent IQ related integral values ​​required to calculate the IQ difference value is within the same bit time, then the IQ difference value is an intra-bit IQ difference value; if the coherent integration time of the adjacent IQ related integral values ​​required to calculate the IQ difference value belongs to different bit times, then the IQ difference value is an inter-bit IQ difference value.

[0021] Step S32: Perform coherent frequency discrimination on the intra-bit IQ differential value to obtain the coherent frequency discrimination frequency tracking error. ;

[0022] Step S33: Perform incoherent frequency discrimination on the inter-bit IQ difference value to obtain the incoherent frequency tracking error. ;

[0023] Step S34: Track frequency error of coherent frequency discrimination. Frequency tracking error of incoherent frequency discrimination The frequency tracking error sequence is formed by alternating outputs;

[0024] Where p represents the index of the coherent frequency discrimination value calculated from the intra-bit IQ difference value of the p-th bit, and i represents the index of the incoherent frequency discrimination value calculated from the inter-bit IQ difference value of the i-th bit.

[0025] According to one technical solution of the present invention, in step S32, coherent frequency discrimination is performed on the intra-bit IQ differential value, which is implemented by any of the following methods:

[0026] Method 1 ;

[0027] Method 2 ;

[0028] Where ATAN2 represents the four-quadrant arctangent operation, A represents the signal amplitude estimate, and T represents the coherent integration time.

[0029] According to one technical solution of the present invention, in step S33, noncoherent frequency discrimination is performed on the inter-bit IQ difference value, which is implemented by any of the following methods:

[0030] Method 1 ;

[0031] Method 2 ;

[0032] Method 3 ;

[0033] Method 4 ;

[0034] Where ATAN represents the arctangent operation in the second quadrant, sign represents the operation of determining the sign of the variable, A represents the signal amplitude estimate, and T represents the coherent integration time.

[0035] According to one technical solution of the present invention, step S4 includes:

[0036] Step S41: Filter the frequency tracking error sequence;

[0037] Step S42: Input the filtered signal into the voltage-controlled oscillator to generate a local carrier wave;

[0038] Step S43: Mix the local carrier with the input signal to achieve closed-loop tracking.

[0039] This invention proposes a hybrid frequency discrimination carrier frequency tracking method. It employs a signal carrier frequency tracking algorithm that combines coherent frequency discrimination within the same message bit with incoherent frequency discrimination across message bits. This fully utilizes coherent frequency discrimination to improve the tracking sensitivity of weak signals, while maintaining the continuity of frequency discrimination through incoherent frequency discrimination. Compared with conventional carrier frequency tracking methods, this invention can improve the signal carrier frequency tracking sensitivity and effectively reduce the carrier frequency tracking threshold, thus effectively solving the GNSS navigation signal carrier tracking problem in ultra-low signal-to-noise ratio environments in high-orbit space, and improving the effective range of received signals in high-orbit and deep-space exploration. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0041] Figure 1 This schematic diagram illustrates a carrier frequency tracking method with a hybrid frequency discrimination method according to the present invention.

[0042] Figure 2 This diagram illustrates the process of a hybrid frequency discrimination carrier frequency tracking method according to an embodiment of the present invention.

[0043] Figure 3 A schematic diagram illustrating the steps of carrier frequency tracking using embodiments of the present invention;

[0044] Figure 4 This is a comparison chart of the standard deviation of frequency tracking errors for conventional non-coherent frequency discrimination, intra-bit coherent frequency discrimination, and hybrid frequency discrimination methods. Detailed Implementation

[0045] The description of the embodiments in this specification should be taken in conjunction with the accompanying drawings, which should form part of the complete specification. In the drawings, the shape or thickness of the embodiments may be exaggerated and may be indicated in a simplified or convenient manner. Furthermore, parts of the various structures in the drawings will be described separately; it is worth noting that elements not shown in the figures or not described in words are in a form known to those skilled in the art.

[0046] The descriptions of the embodiments herein, including any references to directions and orientations, are for ease of description only and should not be construed as limiting the scope of the invention. The following description of preferred embodiments involves combinations of features, which may exist independently or in combination; the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.

[0047] like Figure 1 As shown in the figure, a hybrid frequency discrimination carrier frequency tracking method provided by an embodiment of the present invention includes the following steps:

[0048] Step S1: Based on the bit synchronization information of the received message, receive the IQ coherence integral value corresponding to the synchronization of the first and second half bits of each message bit.

[0049] Step S2: Calculate the conjugate product of adjacent IQ coherent integral values ​​in sequence to generate the IQ difference value sequence;

[0050] Step S3: Based on the IQ difference sequence, perform coherent frequency discrimination on the IQ difference value within a bit and incoherent frequency discrimination on the IQ difference value between adjacent bits to generate a frequency tracking error sequence that alternates between coherent and incoherent frequency discrimination.

[0051] Step S4: Filter the frequency tracking error sequence to form a carrier frequency tracking loop.

[0052] To address the issues of insufficient sensitivity in incoherent tracking and undersampling in coherent tracking in existing methods, this invention innovatively proposes a carrier frequency tracking method based on a hybrid frequency discrimination approach. This method combines coherent frequency discrimination within the same message bit with incoherent frequency discrimination across message bits, effectively improving the effective range of received signals in high-orbit and deep-space exploration.

[0053] In this embodiment of the invention, preferably, step S2 specifically includes:

[0054] Step S21: Calculate the dot product of adjacent IQ coherent integral values:

[0055] ;

[0056] Step S22: Calculate the cross product of adjacent adjacent IQ coherence integral values:

[0057] ;

[0058] in, and For the k-th IQ coherent integral value, and This is the (k-1)th IQ coherent integral value;

[0059] Step S23: Based on the calculation results of the dot product and cross product, form the IQ difference value sequence { , }

[0060] In a preferred embodiment of the present invention, step S3 includes:

[0061] Step S31: Determine the IQ difference value attribute: If the coherent integration time of the adjacent IQ related integral values ​​required to calculate the IQ difference value is within the same bit time, then the IQ difference value is the intra-bit IQ difference value; if the coherent integration time of the adjacent IQ related integral values ​​required to calculate the IQ difference value belongs to different bit times, then the IQ difference value is the inter-bit IQ difference value.

[0062] Step S32: Perform coherent frequency discrimination on the intra-bit IQ differential value to obtain the coherent frequency discrimination frequency tracking error. ;

[0063] Coherent frequency discrimination of the intra-bit IQ difference value can be achieved through any of the following methods:

[0064] Method 1 ;

[0065] Method 2 ;

[0066] Where ATAN2 represents the four-quadrant arctangent operation, A represents the signal amplitude estimate, and T represents the coherent integration time.

[0067] Step S33: Perform incoherent frequency discrimination on the inter-bit IQ difference value to obtain the incoherent frequency tracking error. ;

[0068] Incoherent frequency discrimination of the inter-bit IQ difference can be achieved through any of the following methods:

[0069] Method 1 ;

[0070] Method 2 ;

[0071] Method 3 ;

[0072] Method 4 ;

[0073] Where ATAN represents the arctangent operation in the second quadrant, sign represents the operation of determining the sign of the variable, A represents the signal amplitude estimate, and T represents the coherent integration time.

[0074] Step S34: Track frequency error of coherent frequency discrimination. Frequency tracking error of incoherent frequency discrimination Alternating outputs form a frequency tracking error sequence;

[0075] Where p represents the index of the coherent frequency discrimination value calculated from the intra-bit IQ difference value of the p-th bit, and i represents the index of the incoherent frequency discrimination value calculated from the inter-bit IQ difference value of the i-th bit.

[0076] In a preferred embodiment of the present invention, step S4 includes:

[0077] Step S41: Filter the frequency tracking error sequence;

[0078] Step S42: Input the filtered signal into the voltage-controlled oscillator to generate a local carrier wave;

[0079] Step S43: Mix the local carrier with the input signal to achieve closed-loop tracking.

[0080] like Figure 2 The diagram illustrates a process of a hybrid frequency discrimination carrier frequency tracking method in one embodiment of the present invention. The signal is received via a receiving antenna. After RF front-end processing and carrier stripping, coherent integration is performed to obtain the IQ coherent integral value. Then, the IQ coherent integral value is obtained by conjugate multiplication. Coherent and incoherent frequency discrimination are performed on the IQ differential value. Sampling is conducted at intervals T. For the intra-bit IQ differential value, a coherent frequency discrimination frequency tracking error is output; for the inter-bit IQ differential value, an incoherent frequency discrimination frequency tracking error is output, forming an alternating sequence of frequency tracking errors using coherent and incoherent frequency discrimination. In the diagram, the coherent integration time T is half the bit time of the received signal message, cross is the cross product of adjacent IQ coherent integral values, and dot is the dot product of adjacent IQ coherent integral values. Compared with conventional carrier frequency tracking methods, the present invention can improve the signal carrier frequency tracking sensitivity and is suitable for GNSS navigation signal carrier tracking in ultra-low signal-to-noise ratio environments in high-orbit space.

[0081] like Figure 3 As shown, the method of the present invention will be described below with reference to a specific embodiment, including the following steps:

[0082] Step S51: The navigation terminal captures the BDS B1I signal and downconverts the signal into a baseband signal;

[0083] Step S52: The navigation terminal mixes the baseband signal with the local carrier.

[0084] Step S53: After bit synchronization, the navigation terminal performs coherent integration on the IQ baseband signals corresponding to the synchronization of the first and second half bits of each message bit.

[0085] Step S54: The navigation terminal calculates the conjugate product of adjacent IQ coherent integral values ​​to generate an IQ difference value sequence;

[0086] Step S55: The navigation terminal determines whether the coherent integration time of the IQ-related integral value of the IQ difference is within the same bit time.

[0087] Step S56: If the coherent integration time of the IQ correlation integral value of the IQ difference is within the same bit time, then coherent frequency discrimination is performed; if the coherent integration time of the IQ correlation integral value of the IQ difference is not within the same bit time, then incoherent frequency discrimination is performed. A frequency tracking error sequence alternating between coherent and incoherent frequency discrimination is generated.

[0088] Step S57: The navigation terminal filters the frequency tracking error sequence, adjusts the local carrier frequency according to the filtering result, and inputs the local carrier into step S53 to form a carrier frequency tracking loop.

[0089] Figure 4 This is a comparison chart of the standard deviation of frequency tracking errors for conventional noncoherent frequency discrimination, intra-bit coherent frequency discrimination, and hybrid frequency discrimination methods. The chart shows that conventional noncoherent frequency discrimination loses lock at a carrier-to-noise ratio (CNR) of 24.5 dB, and when the CNR is less than 26 dB, the hybrid frequency discrimination method proposed in this invention has the smallest standard deviation of frequency tracking error.

[0090] Furthermore, it should be noted that the present invention can be provided as a method, apparatus, or computer program product. Therefore, embodiments of the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, embodiments of the present invention can take the form of a computer program product implemented on one or more computer-usable storage media containing computer-usable program code.

[0091] Embodiments of the present invention are described with reference to flowchart illustrations and / or block diagrams of methods, terminal devices (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, embedded processor, or other programmable data processing terminal device to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing terminal device, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0092] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing terminal device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The functions specified in one or more boxes. These computer program instructions may also be loaded onto a computer or other programmable data processing terminal equipment to cause a series of operational steps to be performed on the computer or other programmable terminal equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable terminal equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0093] It should also be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or terminal device that includes that element.

[0094] Finally, it should be noted that the above are preferred embodiments of the present invention. It should be pointed out that although preferred embodiments of the present invention have been described, those skilled in the art, once they understand the basic inventive concept of the present invention, can make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present invention.

Claims

1. A carrier frequency tracking method with hybrid frequency discrimination, characterized in that, Includes the following steps: Step S1: Based on the bit synchronization information of the received message, receive the IQ coherence integral value corresponding to the synchronization of the first and second half bits of each message bit. Step S2: Calculate the conjugate product of adjacent IQ coherent integral values ​​in sequence to generate the IQ difference value sequence; Step S3: Based on the IQ difference sequence, perform coherent frequency discrimination on the IQ difference values ​​within a bit and incoherent frequency discrimination on the IQ difference values ​​between adjacent bits to generate a frequency tracking error sequence that alternates between coherent and incoherent frequency discrimination. Step S4: Filter the frequency tracking error sequence to form a carrier frequency tracking loop.

2. The hybrid frequency discrimination carrier frequency tracking method according to claim 1, characterized in that, In step S1, the receiving IQ coherent integral value corresponding to the synchronization of the first and second halves of each message bit has a coherent integration time T that is half the bit time of the received message, and its integration clearing time is synchronized with the message bit start time.

3. The hybrid frequency discrimination carrier frequency tracking method according to claim 1, characterized in that, Step S2 specifically includes: Step S21: Calculate the dot product of adjacent IQ coherent integral values: ； Step S22: Calculate the cross product of adjacent IQ coherent integral values: ； in, and For the k-th IQ coherent integral value, and This is the (k-1)th IQ coherent integral value; Step S23: Based on the calculation results of the dot product and cross product, form the IQ difference value sequence { , } 4. The hybrid frequency discrimination carrier frequency tracking method according to claim 3, characterized in that, Step S3 includes: Step S31: Determine the IQ difference value attribute: If the coherent integration time of the adjacent IQ related integral values ​​required to calculate the IQ difference value is within the same bit time, then the IQ difference value is an intra-bit IQ difference value; if the coherent integration time of the adjacent IQ related integral values ​​required to calculate the IQ difference value belongs to different bit times, then the IQ difference value is an inter-bit IQ difference value. Step S32: Perform coherent frequency discrimination on the intra-bit IQ differential value to obtain the coherent frequency discrimination frequency tracking error. ; Step S33: Perform incoherent frequency discrimination on the IQ difference values ​​between adjacent bits to obtain the incoherent frequency discrimination frequency tracking error. ; Step S34: Calculate the frequency tracking error of the coherent frequency discriminator. Frequency tracking error of incoherent frequency discrimination The frequency tracking error sequence is formed by alternating outputs; Where p represents the index of the coherent frequency discrimination value calculated from the IQ difference value within the p-th bit, and i represents the index of the incoherent frequency discrimination value calculated from the IQ difference value between the i-th adjacent bits.

5. The hybrid frequency discrimination carrier frequency tracking method according to claim 4, characterized in that, In step S32, coherent frequency discrimination is performed on the intra-bit IQ differential value, which is achieved by any of the following methods: Method 1 ; Method 2 ; Where ATAN2 represents the four-quadrant arctangent operation, A represents the signal amplitude estimate, and T represents the coherent integration time.

6. The hybrid frequency discrimination carrier frequency tracking method according to claim 4, characterized in that, In step S33, noncoherent frequency discrimination is performed on the inter-bit IQ difference values, which is implemented by any of the following methods: Method 1 ; Method 2 ; Method 3 ; Method 4 ; Where ATAN represents the arctangent operation in the second quadrant, sign represents the operation of determining the sign of the variable, A represents the signal amplitude estimate, and T represents the coherent integration time.

7. The hybrid frequency discrimination carrier frequency tracking method according to claim 1, characterized in that, Step S4 includes: Step S41: Filter the frequency tracking error sequence; Step S42: Input the filtered signal into the voltage-controlled oscillator to generate a local carrier wave; Step S43: Mix the local carrier with the input signal to achieve closed-loop tracking.

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