CN109307873A - An INS-aided dual Kalman filter satellite signal tracking loop - Google Patents

Abstract

The present invention discloses a kind of Dual Kalman filtering device satellite-signal track loop of INS auxiliary, including satellite signal receiving antenna, RF front-end module, Inertial Measurement Unit, inertial reference calculation module, satellite ephemeris storage module, carrier frequency & phase estimator module, carrier tracking module and code tracking module；Inertial Measurement Unit measures carrier acceleration and angular speed；Inertial reference calculation module completes positioning calculation and posture renewal according to acceleration and angular speed；Satellite ephemeris storage module stores satellite ephemeris；Carrier frequency & phase estimator module calculates the carrier frequency shift and code phase of subsequent time according to satellite ephemeris and positioning calculation；Satellite signal receiving antenna receives satellite-signal；RF front-end module handles satellite-signal to obtain digital medium-frequency signal；Carrier tracking module is corrected the carrier frequency shift locally saved using digital medium-frequency signal and carrier frequency shift；Code tracking module is corrected the code phase locally saved using digital medium-frequency signal and code phase.

Description

An INS-aided dual Kalman filter satellite signal tracking loop

technical field

The invention belongs to the technical field of satellite positioning and navigation, in particular to an INS-assisted dual Kalman filter satellite signal tracking loop.

Background technique

The global satellite navigation system can provide real-time position, speed and time information around the clock, and has become an indispensable source of navigation information for low-cost guided weapons. However, in the application of high dynamic carriers such as rockets and missiles, due to the large Doppler frequency shift and Doppler frequency shift variation in satellite signals, it is difficult for traditional signal tracking methods to maintain continuous and reliable locking. This leads to a decrease in the positioning capability of the satellite navigation receiver. In order to solve this problem, some scholars have proposed a tracking loop that uses a Kalman filter to estimate signal parameters. In this loop design, the frequency-locked loop and the code loop are replaced by a single Kalman filter. There is a lot of literature that demonstrates the clear advantages of this signal tracking loop over traditional loops.

Using only one filter to estimate the tracking signal means that carrier tracking error and code tracking error are tightly coupled together. However, the tracking accuracy required by the carrier tracking loop and the code tracking loop is different, and the carrier loop is more fragile. In practical applications, the error coupling effect of the code loop will transfer the tracking error of the code loop to the carrier tracking loop, and eventually lead to the degradation of the tracking performance of the carrier loop, or even a complete loss of lock.

In addition, the INS system can sensitively detect the dynamic stress in the three axes of the carrier and the angular velocity in the three axes, by introducing the Doppler information in the satellite and receiver line-of-sight (LOS) directions predicted by the INS into the tracking loop of the GNSS receiver , which can largely compensate for the influence of carrier dynamics on the signal tracking loop, thereby improving the satellite signal tracking capability of the receiver in a high dynamic signal attenuation environment. Therefore, INS is often used to assist in practical applications, and the purpose of improving the positioning performance of the navigation system is achieved by combining INS and GNSS.

SUMMARY OF THE INVENTION

In view of this, the present invention provides an INS-assisted dual Kalman filter satellite signal tracking loop, which can effectively improve the positioning and navigation capability of a satellite navigation receiver in a high dynamic environment, and is especially suitable for satellite-guided munitions in a high dynamic environment. Navigation required under.

The technical scheme that realizes the present invention is as follows:

An INS-assisted dual Kalman filter satellite signal tracking loop, comprising a satellite signal receiving antenna, a radio frequency front-end module, an inertial measurement unit, an inertial navigation calculation module, a satellite ephemeris storage module, a carrier frequency & code phase estimation module, a carrier wave Tracking module and code tracking module;

The inertial measurement unit measures the acceleration and angular velocity of the carrier in three directions;

The inertial navigation calculation module completes the positioning calculation and attitude update according to the acceleration and angular velocity of the carrier;

The satellite ephemeris storage module is used to store the satellite ephemeris;

The carrier frequency & code phase estimation module calculates the carrier frequency offset and the code phase of the next moment according to the satellite ephemeris and the result of the positioning solution;

The satellite signal receiving antenna receives satellite signals;

The radio frequency front-end module processes the satellite signal to obtain a digital intermediate frequency signal;

The carrier tracking module uses the digital intermediate frequency signal and the carrier frequency offset to correct the carrier frequency offset stored locally by the carrier tracking module;

The code tracking module uses the digital intermediate frequency signal and the code phase to correct the code phase stored locally by the code tracking module.

Further, the carrier tracking module includes a carrier loop Kalman filter, and the carrier loop Kalman filter performs Kalman filtering based on the following model:

in, is the state vector of the carrier loop Kalman filter at time k, is the carrier phase error at time K, is the carrier frequency of the received signal at time K, is the rate of change of the carrier frequency at time K, is the carrier ring state transition matrix at time k-1;

is the INS auxiliary carrier state feedback matrix at time k-1, is the INS-assisted carrier frequency status feedback at time k-1; is the measurement matrix at time k, is the INS-assisted carrier state measurement matrix at time k, is the mean value of the carrier phase detector output at time k, represent the process noise covariance matrix and the measurement noise covariance matrix of the carrier loop filter at time k, respectively.

Further, the code tracking module includes a code loop Kalman filter, and the code loop Kalman filter performs Kalman filtering based on the following model:

in, is the state vector of the code loop Kalman filter at time k, is the code phase error at time k, is the C/A code frequency at time k, is the rate of change of the C/A code frequency at time k, is the mean value of the code phase detector output at time k; is the code loop state transition matrix at time k-1;

T is the loop filter update time; is the INS auxiliary code state feedback matrix at time k-1, is the INS-assisted code phase error state feedback at time k-1; is the measurement matrix of the code tracking system at time k, is the INS auxiliary code state measurement matrix at time k, are the process noise covariance matrix and the measurement noise covariance matrix of the code loop Kalman filter at time k-1, respectively.

Beneficial effects:

The invention uses two independent Kalman filters to track the carrier and C/A code respectively, which not only retains the advantages of the traditional Kalman filter signal tracking method in high dynamic and complex electromagnetic environments, but also combines the The two tracking errors are decoupled to improve the accuracy of signal tracking. At the same time, the assistance of the INS system is introduced to further improve the performance of the entire system in a highly dynamic environment.

The invention focuses on the key issues in the positioning and navigation of low-cost and high-dynamic guidance weapons, and every improvement made is to improve the dynamic performance of the entire navigation system, so it is especially suitable for missile-borne satellite navigation receivers in high-dynamic environments. navigation needs. The outstanding advantages of the invention are summarized as follows:

1. The algorithm uses Kalman filter to replace the traditional signal tracking loop filter, which improves the signal tracking ability of the loop under high dynamic conditions.

2. As another improvement of the algorithm, the signal tracking loop adopts the structure of double Kalman filtering, which avoids the error coupling effect in the traditional Kalman filtering signal tracking loop and has better tracking signal accuracy.

3. The method retains the hardware architecture of the traditional inertial measurement unit and the traditional satellite navigation receiver, and achieves the purpose of improving the navigation performance through the update of the software algorithm, which is convenient for the transformation of the traditional navigation system.

4. This method introduces the state quantity of INS feedback to directly assist the tracking loop, realizes the tightest coupling between the inertial navigation and satellite navigation systems, and improves the tracking ability of satellite signals in a high dynamic environment, which is especially suitable for applications. for low-cost highly dynamic guided weapons.

Description of drawings

FIG. 1 is a structural diagram of the INS-assisted double Kalman filtering signal tracking loop of the present invention.

FIG. 2 is a schematic structural diagram of a carrier tracking module.

Figure 3 is a schematic structural diagram of a code tracking module.

Figure 4(a) is the schematic diagram of the satellite scene of the high dynamic test; (b) is the schematic diagram of the flight trajectory of the carrier; (c) is the schematic diagram of the flight acceleration parameters of the carrier; (d) is the reference Doppler frequency shift and estimated by this method Schematic diagram of the comparison of the carrier Doppler frequency shift of the A schematic diagram of the carrier phase error of the tracking signal output by the method of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

The invention provides a signal tracking method using double Kalman filtering for signal tracking and introducing INS auxiliary loop to compensate for dynamic influence. The method can effectively improve the positioning and navigation capability of the satellite navigation receiver in a high dynamic environment, and is especially suitable for the navigation needs of satellite-guided munitions in a high dynamic environment.

An INS-assisted dual Kalman filter satellite signal tracking loop, as shown in Figure 1, includes a satellite signal receiving antenna, a radio frequency front-end module, a signal acquisition module, an inertial measurement unit, an inertial navigation calculation module, and a satellite ephemeris storage module. , carrier frequency & code phase estimation module, carrier tracking module and code tracking module;

The inertial measurement unit measures the acceleration and angular velocity of the carrier in three directions;

The inertial navigation calculation module completes the positioning calculation and attitude update according to the acceleration and angular velocity of the carrier;

The satellite ephemeris storage module is used to store the satellite ephemeris;

The carrier frequency & code phase estimation module calculates the carrier frequency offset and the code phase of the next moment according to the satellite ephemeris and the result of the positioning solution;

The satellite signal received by the satellite signal receiving antenna is processed by the RF front-end module and the signal capture module to obtain a digital intermediate frequency signal;

The carrier tracking module uses the digital intermediate frequency signal and the carrier frequency offset to correct the carrier frequency offset stored locally by the carrier tracking module;

The code tracking module uses the digital intermediate frequency signal and the code phase to correct the code phase stored locally by the code tracking module.

Figure 2 is a schematic structural diagram of a carrier tracking module, wherein 61 is a signal multiplier, 62 is a carrier I/Q branch mapping, 63 is a coherent integrator, 64 is a carrier loop phase detector, 65 is a carrier loop Kalman filter, 66 is the INS feedback state quantity, and 67 is the carrier ring NCO. The carrier loop Kalman filter performs Kalman filtering based on the following model:

in, is the state vector of the carrier loop Kalman filter at time k, is the carrier phase error at time K, is the carrier frequency of the received signal at time K, is the rate of change of the carrier frequency at time K, is the carrier ring state transition matrix at time k-1;

is the INS auxiliary carrier state feedback matrix at time k-1, is the INS-assisted carrier frequency status feedback at time k-1; is the measurement matrix at time k, is the INS-assisted carrier state measurement matrix at time k, is the mean value of the carrier phase detector output at time k, represent the process noise covariance matrix and the measurement noise covariance matrix of the carrier loop filter at time k, respectively.

The derivation and proof of the carrier loop Kalman filter modeling method are as follows:

1) The state vector adopted by the carrier tracker is in is the carrier phase error, is the carrier frequency of the received signal, is the rate of change of the carrier frequency at time K, and the relationship between them is as follows:

in is the mean value of the carrier phase detector output from 0 to T, T is the loop filter update time, is INS-assisted carrier frequency status feedback.

2) The relationship between the elements in the state vector of the carrier Kalman filter is as follows:

3) Substitute (7) into (6), and replace all the variables with the subscript K-1 with the variables with the subscript K to obtain the measurement equation of the system:

4) Combining (7) and (8), the system modeling of the carrier Kalman filter shown in (4) can be obtained.

3 is a schematic structural diagram of a code tracking module, wherein 71 is a signal multiplier, 72 is a lead/immediate/lag code generator, 73 is a coherent integrator, 74 is a code loop phase detector, 75 is a code loop Kalman filter, 76 is the INS feedback state quantity, and 77 is the code loop NCO. The code loop Kalman filter performs Kalman filtering based on the following model:

in, is the state vector of the code loop Kalman filter at time k, is the code phase error at time k, is the C/A code frequency at time k, is the rate of change of the C/A code frequency at time k, is the mean value of the code phase detector output at time k; is the code loop state transition matrix at time k-1;

T is the loop filter update time; is the INS auxiliary code state feedback matrix at time k-1, is the INS-assisted code phase error state feedback at time k-1; is the measurement matrix of the code tracking system at time k, is the INS auxiliary code state measurement matrix at time k, are the process noise covariance matrix and the measurement noise covariance matrix of the code loop Kalman filter at time k-1, respectively.

The derivation and proof of the code loop Kalman filter modeling are as follows:

1) The state vector of the code loop Kalman filter is in is the code phase error, is the C/A code frequency, is the rate of change of the C/A code frequency. Similar to the carrier loop, the code phase discriminator output in the code loop has the following relationship with the state quantity:

in is the average value of the code loop phase detector output from 0 to T time, is the INS-assisted code-phase error status feedback.

2) The elements in the state vector of the code tracker have the following relationship with each other

3) Similarly, by substituting (10) into (9) and replacing all the quantities with the subscript K-1, the measurement equation (11) of the system can be obtained as follows:

4) Combining (10) and (11), the code loop Kalman filter system model shown in (5) can be obtained.

The concrete realization process of the dual Kalman filtering satellite signal tracking assisted by the INS of the present invention is as follows:

Step 1. Use the carrier dynamic information measured by the INS as the auxiliary information, and combine the satellite ephemeris to generate the INS auxiliary state feedback variable of the signal tracking loop:

Step 1.1: The inertial measurement unit (IMU) measures the acceleration and angular velocity of the carrier in three directions;

Step 1.2: The inertial navigation calculation module (INS system) completes the positioning calculation and attitude update according to the measurement data of the inertial measurement unit;

Step 1.3: The carrier frequency & code phase estimation module calculates the carrier frequency offset and code phase at the next moment in combination with the inertial navigation positioning result and satellite ephemeris;

Step 2: After frequency conversion and sampling, the signal received by the satellite signal receiving antenna generates a digital intermediate frequency signal, and completes the rapid capture of the signal, providing initial value conditions for signal tracking:

Step 2.1: After the satellite signal is mixed and sampled by the radio frequency front-end module 21, intermediate frequency data is formed. The signal acquisition module 22 only works when the receiver does not have a tracking signal, and its purpose is to achieve fast acquisition of satellite signals and roughly set the code and carrier NCO control quantities. After the signal capture is completed, the intermediate frequency signal enters the dual Kalman filtering satellite signal tracking loop composed of the carrier tracking module 23 and the code tracking module 24;

Step 3, applying the dual Kalman filtering satellite signal tracking loop of the present invention to continuously track the current visible satellite signal:

Step 3.1: The I/Q branch map of the local carrier is generated by the carrier I/Q branch map 62, and multiplied by the signal multiplier 61 with the input intermediate frequency digital signal. The coherent integrator 63 integrates the input signal to increase the energy of the signal;

Step 3.2: The integrated signal is sent to the carrier ring phase detector 64, and the traditional Costa ring is used for phase detection, and the phase detection result is sent to the carrier ring Kalman filter 65 as the observation quantity, and is sent as a part of the observation quantity at the same time. In the final combined navigation filtering;

Step 3.3: The Kalman filter is combined with the INS feedback state quantity 66 to filter, and the optimal estimation result of the carrier frequency is used to drive the carrier loop NCO 67, and finally generate a new local replica carrier;

Step 3.4: After steps 2.1 to 3.3, the carrier in the digital intermediate frequency signal has been fully stripped, and only two channels of I/Q signals modulated with pseudo-random codes are retained. These two signals are respectively multiplied with the lead/immediate/lag code generated by the signal multiplier 71, and the multiplied result is sent to the coherent integrator 73 for integration to increase the signal energy;

Step 3.5: The integrated signal is sent to the code ring phase detector 74, and the traditional non-coherent integral phase detection method is used for phase detection, and the phase detection result is sent to the code ring Kalman filter 75 as the observation quantity, and is simultaneously observed as a part The amount is sent to the final combined navigation filter;

Step 3.6: The Kalman filter is combined with the INS feedback state quantity 76 to filter, and the optimal estimation result of the carrier frequency is used to drive the code loop NCO77, and finally generate a new local copy C/A code;

Step 4. After carrier stripping and code stripping, the received signal only contains the navigation message information, which is sent to the back-end combined navigation filter together with the ranging information for positioning and calculation:

Step 4.1: If the signal tracking is accurate enough, the integrated signal in step 3.5 can demodulate the navigation message required by the receiver;

Step 4.2: Transmit the navigation message and ranging information to the combined navigation filter for positioning solution, and the signal tracking loop returns to step 1 to process the next epoch. It should be noted that after the receiver enters the signal tracking state, the fast signal acquisition phase in step 2.1 can be skipped, and only continuous tracking can be maintained.

Fig. 4 is the MATLAB simulation test result of using the method of the present invention to carry out signal tracking. Among them, (a) is the satellite scene of the high dynamic test; (b) is the flight trajectory of the carrier, including stages such as constant speed, climb, and turn; (c) is the flight acceleration parameter of the carrier, including the jerk of 5g/s, the jerk of 5g acceleration and -5g/s jerk; (d) is the reference Doppler shift and the carrier Doppler shift estimated using this method; (e) is the error between the estimated Doppler shift and the reference value (f) is the carrier phase error output by the traditional signal tracking method, it can be seen that the tracking loop has lost lock; (g) is the carrier phase error output by the tracking signal using the method of the present invention, obviously the carrier loop still remains locked.

To sum up, the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (3)

1. a double Kalman filter satellite signal tracking loop of INS assistance, is characterized in that, comprises satellite signal receiving antenna, radio frequency front-end module, inertial measurement unit, inertial navigation calculation module, satellite ephemeris storage module, carrier frequency and Code phase estimation module, carrier tracking module and code tracking module; The inertial measurement unit measures the acceleration and angular velocity of the carrier in three directions; The inertial navigation calculation module completes the positioning calculation and attitude update according to the acceleration and angular velocity of the carrier; The satellite ephemeris storage module is used to store the satellite ephemeris; The carrier frequency & code phase estimation module calculates the carrier frequency offset and the code phase of the next moment according to the satellite ephemeris and the result of the positioning solution; The satellite signal receiving antenna receives satellite signals; The radio frequency front-end module processes the satellite signal to obtain a digital intermediate frequency signal; The carrier tracking module uses the digital intermediate frequency signal and the carrier frequency offset to correct the carrier frequency offset stored locally by the carrier tracking module; The code tracking module uses the digital intermediate frequency signal and the code phase to correct the code phase stored locally by the code tracking module. 2. a kind of INS-assisted dual Kalman filter satellite signal tracking loop as claimed in claim 1, is characterized in that, carrier tracking module comprises carrier loop Kalman filter, and carrier loop Kalman filter carries out Kalman filter based on following model : in, is the state vector of the carrier loop Kalman filter at time k, is the carrier phase error at time K, is the carrier frequency of the received signal at time K, is the rate of change of the carrier frequency at time K, is the carrier ring state transition matrix at time k-1; is the INS auxiliary carrier state feedback matrix at time k-1, is the INS-assisted carrier frequency status feedback at time k-1; is the measurement matrix at time k, is the INS-assisted carrier state measurement matrix at time k, is the mean value of the carrier phase detector output at time k, represent the process noise covariance matrix and the measurement noise covariance matrix of the carrier loop filter at time k, respectively. 3. the dual Kalman filter satellite signal tracking loop of a kind of INS assistance as claimed in claim 1 and 2, is characterized in that, code tracking module comprises code loop Kalman filter, and code loop Kalman filter carries out Kalman filter based on following model. Mann filter: in, is the state vector of the code loop Kalman filter at time k, is the code phase error at time k, is the C/A code frequency at time k, is the rate of change of the C/A code frequency at time k, is the mean value of the code phase detector output at time k; is the code loop state transition matrix at time k-1; T is the loop filter update time; is the INS auxiliary code state feedback matrix at time k-1, is the INS-assisted code phase error state feedback at time k-1; is the measurement matrix of the code tracking system at time k, is the INS auxiliary code state measurement matrix at time k, are the process noise covariance matrix and the measurement noise covariance matrix of the code loop Kalman filter at time k-1, respectively.