A satellite baseband signal tracking method

Abstract

The application discloses a satellite baseband signal tracking method, and steps of the method comprise the following steps: step S1, establishing a joint state space equation suitable for high dynamic carrier tracking and code tracking; step S2, establishing an observation equation, taking the output δt k of a discriminator and the output δφ k of a phase discriminator as observation quantities; step S3, based on the state equation and the observation equation, adopting a Kalman filter to perform optimal estimation on a state; step S4, using optimal estimation values of carrier phase and Doppler frequency shift, introducing inertial auxiliary information to calculate line-of-sight acceleration, and calculating a carrier NCO control quantity; and step S5, calculating a code NCO control quantity. The application has the advantages of simple principle, wide application range, high tracking precision and the like.

Description

Technical Field

[0001] The present invention mainly relates to the field of navigation, guidance and control technology, and in particular to a satellite baseband signal tracking method. Background Art

[0002] The Global Navigation Satellite System (GNSS) mainly includes the United States' GPS (Global Positioning System), Russia's GLONASS (GLObal NAvigation Satellites System), Europe's Galileo and my country's Beidou Navigation System. It has global, all-weather, continuous, real-time precision three-dimensional navigation and positioning capabilities, and its error does not diverge over time, but it is susceptible to obstruction and interference.

[0003] The Inertial Navigation System (INS) is a fully autonomous navigation system that offers advantages such as independence from external information, excellent concealment, strong radiation resistance, and all-weather operation. It also provides multiple navigation parameters such as position, velocity, and attitude in real time. However, INS components, such as gyroscopes and accelerometers, can cause positioning errors to accumulate over time. Due to the complementary nature of INS and GNSS navigation, combining them in appropriate ways can improve the system's overall navigation accuracy and performance.

[0004] In high- and ultra-high-dynamic applications, standalone GNSS receivers struggle to function properly. The primary issue is that the receiver's carrier loop is insufficiently dynamic to track the Doppler variations of highly dynamic satellite carrier signals, potentially leading to lock loss for even already tracked signals. Tracking dynamics require the widest possible bandwidth to accommodate the large velocities, accelerations, and jerks generated by the carrier. However, excessive bandwidth inevitably introduces increased noise, reducing the output signal-to-noise ratio (SNR), and thus the navigation system's tracking sensitivity.

[0005] Using inertial information to assist GNSS receiver tracking can improve the dynamic performance of the tracking loop while ensuring tracking accuracy meets navigation data decoding requirements. This is an effective way to address the receiver's need for high and ultra-high dynamics. Current inertial information-assisted GNSS baseband signal processing methods primarily use second- or third-order PLLs to track the carrier signal. However, this approach suffers from poor tracking robustness when inertial errors are large, making it difficult to meet the increasingly urgent high-dynamic and high-precision requirements of aerospace and aviation. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: in response to the technical problems existing in the prior art, the present invention provides a satellite baseband signal tracking method with simple principle, wide application range and high tracking accuracy.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A satellite baseband signal tracking method, comprising the steps of:

[0009] Step S1: Establishing a joint state space equation suitable for high dynamic carrier tracking and code tracking;

[0010] Step S2: Establish the observation equation and transform the output δt of the discriminator k , the output of the phase detector δφ k As an observable quantity;

[0011] Step S3: Based on the state equation and observation equation, the Kalman filter is used to perform optimal state estimation;

[0012] Step S4: Use the optimal estimated values ​​of carrier phase and Doppler frequency shift, introduce inertial auxiliary information to calculate the line of sight acceleration, and calculate the carrier NCO control amount

[0013] Step S5: Calculate the code NCO control amount.

[0014] As a further improvement of the method of the present invention: in step S1, the code phase Code phase rate Carrier Phase Doppler shift Doppler shift rate Doppler shift acceleration As a state variable, the output of the carrier phase detector The output of the code discriminator As an observation.

[0015] As a further improvement of the method of the present invention: the state vector of the joint state space equation of carrier tracking and code tracking is:

[0016]

[0017] in, is the code phase at the kth moment, is the code phase rate at the kth moment, is the carrier phase at the kth moment, is the Doppler shift at the kth moment, is the Doppler shift rate at the kth moment, is the Doppler shift acceleration at the kth moment.

[0018] As a further improvement of the method of the present invention, the joint state space equation of the carrier tracking and code tracking is expressed as:

[0019]

[0020] Among them, f co is the code frequency without Doppler, which is 10.23MHz for BeiDou B3; f ca is the carrier frequency without Doppler. For BeiDou B3, it is 1268.52 MHz. τ is the loop update time. For B3 frequency, the data bit period is 2 ms. A loop update time of 1 ms is usually used. co,k is the code-related noise term, W ca,k is the carrier noise term; the system noise is expressed in the form of white noise:

[0021] E(w k )=0

[0022]

[0023] Among them, Q k represents the system noise variance matrix.

[0024] As a further improvement of the method of the present invention: in step S2, the code phase and carrier phase are combined as observation quantities, and the observation matrix is:

[0025]

[0026] The output of the discriminator δt k , the output of the phase detector δφ k As an observation, that is:

[0027]

[0028] Among them, Q p ,I p They are the quadrature phase and in-phase outputs of the baseband correlator, Q E ,I E are the quadrature phase and in-phase outputs of the baseband correlator advance path, Q L ,I L are the quadrature-phase and in-phase outputs of the baseband correlator lag path, respectively; the observation noise is expressed in the form of white noise:

[0029] E(v k )=0

[0030]

[0031] Among them, the observation noise covariance matrix Rk Determined by the carrier phase tracking noise caused by the noise source.

[0032] As a further improvement of the method of the present invention: in step S3, the recursive process is as follows:

[0033]

[0034] Use Kalman filter to align code phase Code phase rate Carrier Phase Doppler shift Doppler shift rate Doppler shift acceleration Make the best estimate.

[0035] As a further improvement of the method of the present invention: in step S4, the carrier-satellite line-of-sight acceleration is calculated based on the inertial information, and the Doppler change formula is obtained as follows:

[0036]

[0037] in, is the Doppler frequency shift change calculated from the inertial information at the kth moment, f ca is the carrier frequency of the transmitted signal, c is the speed of light, is the carrier acceleration vector at the kth moment, is the satellite acceleration vector at the kth moment, is the carrier-satellite sight vector, expressed as in, is the carrier position vector at the kth moment, is the satellite position vector at the kth moment.

[0038] As a further improvement of the method of the present invention: the carrier phase and Doppler frequency shift estimated by carrier tracking and the Doppler frequency shift calculated by inertial auxiliary information are The calculation formula of the carrier NCO control amount is:

[0039]

[0040] Among them, f IF is the intermediate frequency of the GNSS baseband signal, τ is the loop update time, is the carrier phase prediction value at the kth moment, is the carrier phase prediction value at the k+1th moment, and the superscripts - and + represent the before and after update respectively.

[0041] As a further improvement of the method of the present invention: in step S5, according to the optimal estimated value, the calculation formula of the code NCO control amount is:

[0042]

[0043] Compared with the prior art, the advantages of the present invention are:

[0044] 1. The satellite baseband signal tracking method of the present invention is aimed at the application background of guidance in harsh environments such as high dynamics and anti-interference. It provides a satellite baseband signal tracking method that uses inertial acceleration information to assist integrated navigation, guidance and control systems. It has the advantages of simple principle, wide application range and high tracking accuracy.

[0045] 2. The satellite baseband signal tracking method of the present invention addresses challenging application scenarios such as high dynamic range and high interference resistance by establishing a joint state-space equation for code and carrier tracking. Using the outputs of the code discriminator and the carrier phase detector as observations, a Kalman filter is employed to estimate the satellite signal's code phase, carrier phase, and Doppler shift. Compared to traditional second-, third-, or fourth-order PLLs, this method offers greater robustness and tracking accuracy due to the adaptive adjustment of the Kalman filter's equivalent loop bandwidth.

[0046] 3. The satellite baseband signal tracking method of the present invention uses inertial information to assist the carrier tracking loop. This approach, aided by acceleration, offsets the impact of carrier dynamics. The remaining dynamic performance tracking is robust, thereby improving the dynamic performance of carrier tracking. While traditional velocity-assisted methods place higher precision demands on the inertial navigation system, the acceleration-assisted approach reduces these requirements.

[0047] 4. The satellite baseband signal tracking method of the present invention effectively solves the dynamic and anti-interference problems of high-dynamic carrier receivers. The carrier and code tracking loop using this method has the advantages of high dynamics, strong anti-interference ability, good robustness and small tracking error, which makes GNSS receivers have better application prospects in high-dynamic applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic flow diagram of the method of the present invention. DETAILED DESCRIPTION

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] The invention discloses a satellite baseband signal tracking method, which utilizes inertial acceleration information to assist an integrated navigation, guidance, and control system. First, a state-space equation suitable for high-dynamic carrier tracking and code tracking is established, wherein code phase, code phase rate, carrier phase, Doppler shift, Doppler shift rate, and Doppler shift acceleration are used as state variables, and outputs of a phase detector and a code discriminator are used as observation quantities. Then, Kalman estimation is used to estimate the code phase, carrier phase, and Doppler shift for calculating a carrier NCO control variable and a code NCO control variable. Third, in order to offset the influence of carrier dynamic performance, inertial auxiliary information is introduced to calculate line-of-sight acceleration as an input quantity of the state-space equation to offset the influence of carrier dynamic performance.

[0051] like Figure 1 As shown, a satellite baseband signal tracking method of the present invention comprises the following detailed steps:

[0052] Step S1: Establishing a joint state space equation suitable for high dynamic carrier tracking and code tracking;

[0053] Step S2: Establish the observation equation and transform the output δt of the discriminator k , the output of the phase detector δφ k As an observable quantity;

[0054] Step S3: Based on the state equation and observation equation, the Kalman filter can be used to optimally estimate the state;

[0055] Step S4: Use the optimal estimated values ​​of carrier phase and Doppler frequency shift, introduce inertial auxiliary information to calculate the line of sight acceleration, and calculate the carrier NCO control amount

[0056] Step S5: Calculation of code NCO control amount.

[0057] In a specific application example, in step S1, the code phase Code phase rate Carrier Phase Doppler shift Doppler shift rate Doppler shift acceleration As a state variable, the output of the carrier phase detector The output of the code discriminator As an observation.

[0058] The state vector of the joint state space equation for carrier tracking and code tracking is:

[0059]

[0060] in, is the code phase at the kth moment, is the code phase rate at the kth moment, is the carrier phase at the kth moment, is the Doppler shift at the kth moment, is the Doppler shift rate at the kth moment, is the Doppler shift acceleration at the kth moment.

[0061] The joint state space equation of carrier tracking and code tracking can be expressed as:

[0062]

[0063] Among them, f co is the code frequency without Doppler, which is 10.23MHz for BeiDou B3; f ca is the carrier frequency without Doppler. For BeiDou B3, it is 1268.52 MHz. τ is the loop update time. For B3 frequency, the data bit period is 2 ms. A loop update time of 1 ms is usually used. co,k is the code-related noise term, W ca,k is the carrier noise term. The system noise is expressed as white noise:

[0064] E(w k )=0

[0065]

[0066] Among them, Q k represents the system noise variance matrix.

[0067] In a specific application example, in step S2, the code phase and carrier phase are combined as observation quantities, and the observation matrix is:

[0068]

[0069] The output of the discriminator δt k , the output of the phase detector δφ k As an observation, that is:

[0070]

[0071] Among them, Q p ,I p They are the quadrature phase and in-phase outputs of the baseband correlator, Q E ,I E are the quadrature phase and in-phase outputs of the baseband correlator advance path, Q L ,I L They are the quadrature-phase and in-phase outputs of the baseband correlator lag path, respectively.

[0072] The observation noise is expressed in the form of white noise:

[0073] E(v k )=0

[0074]

[0075] Among them, the observation noise covariance matrix R k Determined by carrier phase tracking noise caused by thermal noise, vibration noise, ionospheric scintillation, oscillators and other noise sources.

[0076] In a specific application example, in step S3, the recursive process is as follows:

[0077]

[0078] Use Kalman filter to align code phase Code phase rate Carrier Phase Doppler shift Doppler shift rate Doppler shift acceleration Make the best estimate.

[0079] In a specific application example, in step S4, the optimal estimated values ​​of carrier phase and Doppler frequency shift are used, and inertial auxiliary information is introduced to calculate the line of sight acceleration, and the carrier NCO control amount is calculated.

[0080] The Doppler change formula is obtained by calculating the carrier-satellite line-of-sight acceleration based on the inertial information:

[0081]

[0082] in, is the Doppler frequency shift change calculated from the inertial information at the kth moment, f ca is the carrier frequency of the transmitted signal, c is the speed of light, is the carrier acceleration vector at the kth moment, is the satellite acceleration vector at the kth moment, is the carrier-satellite sight vector, expressed as in, is the carrier position vector at the kth moment, is the satellite position vector at the kth moment.

[0083] The source of auxiliary information is not limited to inertial information, and other speed sensor output information can also be used for assistance.

[0084] Carrier phase and Doppler shift estimated by carrier tracking and Doppler shift calculated by inertial aided information The calculation formula of the carrier NCO control amount is:

[0085]

[0086] Among them, f IF is the intermediate frequency of the GNSS baseband signal (excluding the Doppler frequency), τ is the loop update time, is the carrier phase prediction value at the kth moment, is the carrier phase prediction value at the k+1th moment, and the superscripts - and + represent the before and after update respectively.

[0087] In a specific application example, in step S5, according to the optimal estimated value, the calculation formula of the code NCO control amount is:

[0088]

[0089] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A satellite baseband signal tracking method, characterized in that the steps include: Step S1: Establishing a joint state space equation suitable for high dynamic carrier tracking and code tracking; The joint state space equation of carrier tracking and code tracking is expressed as: in, is the code frequency without Doppler, which is 10.23 MHz for BeiDou B3; is the carrier frequency without Doppler, for BeiDou B3, it is 1268.52MHz, is the loop update time. For the B3 frequency, the data bit period is 2ms, and the loop update time is 1ms. is the code-dependent noise term, is the carrier noise term; the system noise is expressed in the form of white noise: in, represents the system noise variance matrix; Step S2: Establish the observation equation and transform the output of the discriminator , the output of the phase detector As an observable quantity; Step S3: Based on the state equation and observation equation, the Kalman filter is used to perform optimal state estimation; Step S4: Use the optimal estimated values ​​of carrier phase and Doppler frequency shift, introduce inertial auxiliary information to calculate the line of sight acceleration, and calculate the carrier NCO control amount ; Step S5: Calculate the code NCO control amount.

2. The satellite baseband signal tracking method according to claim 1, wherein: In step S1, the code phase , code phase rate , carrier phase , Doppler shift , Doppler shift rate , Doppler shift acceleration As a state variable, the output of the carrier phase detector The output of the code discriminator As an observation.

3. The satellite baseband signal tracking method according to claim 2, wherein: The state vector of the joint state space equation of carrier tracking and code tracking is: in, For the The code phase at time For the The code phase rate at time , For the The carrier phase at time , For the The Doppler shift at time For the The Doppler shift rate at time , For the The Doppler shift acceleration at time .

4. The satellite baseband signal tracking method according to any one of claims 1 to 3, wherein: In step S2, the code phase and carrier phase are combined as observation quantities, and the observation matrix is: Output of the Discriminator , the output of the phase detector As an observation, that is: in, They are the quadrature-phase and in-phase outputs of the baseband correlator, are the quadrature-phase and in-phase outputs of the baseband correlator advance path, are the quadrature-phase and in-phase outputs of the baseband correlator lag path, respectively; the observation noise is expressed in the form of white noise: Among them, the observation noise covariance matrix Determined by the carrier phase tracking noise caused by the noise source.

5. The satellite baseband signal tracking method according to any one of claims 1 to 3, characterized in that: In step S3, the recursive process is as follows: Use Kalman filter to align code phase , code phase rate , carrier phase , Doppler shift , Doppler shift rate , Doppler shift acceleration Make the best estimate.

6. The satellite baseband signal tracking method according to any one of claims 1 to 3, wherein: In step S4, the carrier-satellite line-of-sight acceleration is calculated based on the inertial information, and the Doppler change formula is obtained as follows: in, For the The Doppler frequency shift change calculated from the inertial information at the moment, is the carrier frequency of the transmitted signal, is the speed of light, For the The carrier acceleration vector at the moment, For the Satellite acceleration vector at time t, is the carrier-satellite sight vector, expressed as ,in, For the The moment carrier position vector, For the Satellite position vector at this moment.

7. The satellite baseband signal tracking method according to claim 6, wherein: Carrier phase and Doppler shift estimated by carrier tracking and Doppler shift calculated by inertial aided information , the calculation formula of the carrier NCO control amount is: in, is the intermediate frequency of the GNSS baseband signal, is the loop update time, For the The carrier phase prediction value at time , For the The carrier phase prediction value at time , superscript and Respectively indicate before and after the update.

8. The satellite baseband signal tracking method according to any one of claims 1 to 3, wherein: In step S5, according to the optimal estimated value, the calculation formula of the code NCO control amount is: 。

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