CN108919314B - An adaptive GNSS carrier multi-loop tracking device and method - Google Patents

Abstract

The invention discloses an adaptive GNSS carrier multi-loop tracking device and method, comprising a Doppler estimator, an integrator, an output fuser and N adaptive sub-loop modules. controller, fuzzy logic bandwidth controller, loop filter, carrier NCO, multiplier, tracking fusion and integrator; carrier tracking technology based on multi-loop and fuzzy variable bandwidth can be used in high dynamic and weak signal environments. Maintaining stable carrier tracking provides an effective solution for the development of receivers with wider versatility, and has practical engineering significance.

Description

An adaptive GNSS carrier multi-loop tracking device and method

technical field

The invention belongs to the field of GNSS baseband signal processing, in particular to a GNSS carrier multi-loop tracking technology for adaptively adjusting parameters.

Background technique

The rapid development of intelligent transportation, aerospace, pedestrian, indoor navigation and other fields has expanded the application scope of the Global Navigation Satellite System (GNSS), and also put forward higher requirements for the global satellite navigation system. Due to the complex terrain of urban canyons, buildings, and forests and mountains, the power of satellite signals is seriously attenuated, and it is very easy to cause the GNSS receiver to lose lock and unable to locate the stage. Therefore, improving the tracking ability in the weak signal environment has become a key issue in the fields of navigation requirements such as geodetic surveying and urban traffic navigation. In addition, the application of GNSS in the aerospace field is also very common. Most aircraft are in a highly dynamic working state. The relative motion between the carrier receiver and the GNSS satellite will cause a large Doppler frequency shift and frequency shift rate of change. , and the traditional receiver cannot accurately track and estimate the Doppler frequency shift, which changes drastically, resulting in loss of carrier tracking and unable to provide effective navigation information. Therefore, improving the carrier tracking capability of the receiver in a highly dynamic environment has also become another requirement of the GNSS receiver. Faced with different needs, it is of great significance to study a receiver carrier tracking technology that can autonomously adapt to high dynamic and weak signal environments.

For the weak signal environment, incoherent integration, vector tracking, Kalman filter and various improved Kalman filter algorithms, FFT frequency locking and other methods are mainly used to enhance the adaptability of the loop in the weak signal environment. For a highly dynamic environment, the velocity information output by the inertial navigation system is usually used to assist the tracking loop, while the high-precision inertial devices are expensive, and filtering estimation and loop internal optimization methods are used to solve the tracking problem in a highly dynamic environment.

However, no matter it is high dynamic or weak signal, only by reducing the measurement error of the tracking loop can the stable tracking of the receiver be guaranteed. In the weak signal environment, the GNSS signal quality is low, and the thermal noise jitter error is the source of loop measurement error, which needs to be suppressed by extending the integration time and reducing the loop bandwidth. In the high dynamic environment, the dynamic stress error is the main error source, and the loop bandwidth is large. and short integration times are common solutions. However, traditional receivers use a fixed bandwidth, which is difficult to solve the tracking problem of high dynamics and weak signals. Therefore, it is an effective solution to design a multi-loop with adaptive adjustment of bandwidth, order and integration time.

SUMMARY OF THE INVENTION

At present, there are few related researches on GNSS carrier tracking suitable for high dynamic and weak signal environments, such as code loop tracking in multi-loop multi-purpose and anti-jamming technology, and carrier tracking in ionospheric scintillation. In view of the above problems and difficulties, the present invention proposes an adaptive GNSS carrier multi-loop tracking device and method. Based on multi-loop and fuzzy variable bandwidth carrier tracking technology, it can maintain stability in high dynamic and weak signal environments. Carrier tracking provides an effective solution for the development of receivers with wider versatility, and has practical engineering significance.

The invention discloses an adaptive GNSS carrier multi-loop tracking device, which comprises a Doppler estimator, an integrator, an output fuser and N adaptive sub-loop modules, each adaptive sub-loop module is equipped with a phase detector , fuzzy logic bandwidth controller, loop filter, carrier NCO, multiplier, tracking fuser and integrator; the output fuser has N inputs, and the tracking fuser has N+1 inputs; the carrier signal is used as the input signal Input to the first input end of the phase detector, the first output end of the phase detector is connected to the input end of the fuzzy logic bandwidth controller, the second output end of the phase detector is connected to the first input end of the loop filter, the fuzzy logic The output end of the bandwidth controller is connected to the second input end of the loop filter, the output end of the loop filter is connected to the input end of the carrier NCO, the output end of the carrier NCO is connected to the first input end of the multiplier, and the second end of the multiplier is connected. The input terminal inputs the captured Doppler frequency, and the multiplier outputs the Doppler frequency shift result; the second output terminal of the multiplier is connected to the first input terminal of the tracking fusion device, and the second input terminal of the tracking fusion device receives the Doppler estimation The other input ends of the tracking fuser receive the Doppler frequency shift results output by other adaptive sub-loop modules respectively, the first output end of the tracking fuser is connected to the first input end of the integrator, and the tracking fusion The second output end of the integrator outputs the Doppler estimated value, the second input end of the integrator receives the intermediate frequency, and the output end of the integrator is connected to the second input end of the phase detector; Doppler estimate output from the channel module.

Further, the adaptive sub-loop adopts a PLL tracking loop.

Further, the order and integration time of each adaptive sub-loop are not required to be consistent.

Further, the phase detector adopts a two-quadrant arc tangent function phase detector to obtain the phase estimation error of the carrier signal.

Further, the fuzzy logic bandwidth controller adopts a central solution fuzzy strategy to control the bandwidth of each adaptive loop filter.

否则，需要多普勒估计器提供

参考值进行判断：若

则认为子环路i正常工作，

否则，子环路i失锁，重新赋予子环路i正确的多普勒估计值，辅助子环路恢复重跟踪状态，

Further, the tracking fusion device is used to determine whether the loop is out of lock: in the tracking environment, there is a sub-loop j such that the Doppler frequency shift ω _{D,i of the sub-loop i} satisfies ω _D,i ≈ω _D,j , then Considering that sub-loop i is working properly, the Doppler estimate

Otherwise, the Doppler estimator is required to provide

Judging by reference value: if

Then the sub-ring i is considered to be working normally,

Otherwise, the sub-loop i loses the lock, and the correct Doppler estimation value is re-assigned to the sub-loop i, and the auxiliary sub-loop restores the re-tracking state.

用于比较环路是否失锁和为失锁环路提供可靠多普勒，辅助失锁环路重新跟踪。Further, the output fuser uses a fuzzy exponential trust function to quantify the trust of each adaptive sub-loop module Doppler shift, and establishes a trust matrix to determine the weight ratio of each loop Doppler shift to achieve fusion. The adaptive GNSS carrier multi-loop tracking device according to claim 1, wherein the Doppler estimator saves the final Doppler frequency shift estimated by the output fuser at each moment, and uses it as historical information as: Tracking fusion at the next moment provides reference Doppler values

It is used to compare whether the loop is out of lock and provide reliable Doppler for the out-of-lock loop to assist the re-tracking of the out-of-lock loop.

The invention also discloses an adaptive GNSS carrier multi-loop tracking method, which adopts the adaptive GNSS carrier multi-loop tracking device with the above characteristics, including:

In each adaptive sub-loop, the fuzzy logic bandwidth controller calculates and gives the control amount according to the phase estimation error, and adjusts the bandwidth of the loop filter according to the control amount; After filtering, the carrier NCO tracks and adjusts the filtered carrier signal, and then the adjusted carrier signal is input to the multiplier and multiplied by the captured Doppler frequency to obtain the Doppler frequency tracked by the adaptive sub-loop. If it is a reasonable value, the Doppler frequency shift result is the Doppler estimated value; The reference value output by the Le estimator is used as the Doppler estimated value; the Doppler estimated value is accumulated by the integrator and the input intermediate frequency, and then fed back to the phase detector to realize the closed-loop tracking of the adaptive sub-loop;

The Doppler estimates of each adaptive sub-loop are simultaneously input to the output fuser outside the loop for information fusion to obtain the final Doppler shift result at this moment; One channel is input to the external integrator to calculate the phase estimation value, and then together with the carrier signal, it is input to the phase detector of each adaptive sub-loop to obtain the phase estimation error; the other channel is input to the external Doppler estimator for saving, as A reference value for a moment.

The beneficial effects of the present invention

(1). The adaptive sub-loop can use PLL tracking loops with different orders and different integration times. According to the noise performance (size, severity, etc.) of the carrier tracking weak signal, different coherent integration time phase-locked loop tracking can be used. It can improve the accuracy of Doppler estimation by fusing the multi-loop carrier tracking results through the confidence function.

(2) The fuzzy logic algorithm adaptively controls and adjusts the PLL loop bandwidth to reduce the probability of the phase-locked loop losing lock in a high dynamic environment and improve the stability and accuracy of carrier tracking.

(3) Feedback fusion of the tracking results of each loop provides a reliable reference value for the sub-loop tracking, improves the ability of the sub-loop to lose lock and re-track, and improves the utilization rate and robustness of the loop.

(4) This carrier tracking scheme can provide stable and accurate carrier tracking results, ensure the accuracy of subsequent navigation data demodulation and positioning, and improve the reliability and stability of the GNSS receiver.

(5). This scheme is completed by software algorithm, which ensures the flexibility and low-cost advantage of the algorithm.

Description of drawings

FIG. 1 is a schematic structural diagram of an adaptive GNSS carrier multi-loop tracking device.

Detailed ways

1, an adaptive GNSS carrier multi-loop tracking device (referred to as the device) is disclosed in the embodiment, which mainly includes a Doppler estimator, an integrator, an output fuser and four parallel adaptive sub-loops Road module (referred to as sub-ring). Each sub-loop is equipped with a phase detector, a fuzzy logic bandwidth controller, a loop filter, a carrier NCO, a multiplier, a tracking fuser and an integrator. The input signals involved mainly include the carrier signal (ie the carrier signal output by the front end), the intermediate frequency (ie the center frequency of the sampler) and the acquisition Doppler frequency (ie the initial Doppler frequency provided to the tracking loop).

The adaptive sub-loop can use PLL tracking loops with different orders and different integration times. In the embodiment, the four adaptive sub-loop modules adopted by the device are specifically: sub-loop 1 adopts a second-order PLL loop with a coherent integration time of 1ms; sub-loop 2 adopts a second-order PLL loop with a coherent integration time of 5ms; Sub-loop 3 adopts a third-order PLL loop with a coherent integration time of 1ms; sub-loop 4 adopts a third-order PLL loop with a coherent integration time of 5ms.

In the multi-loop parallel adaptive GNSS carrier multi-loop tracking device: the carrier signal, the intermediate frequency and the captured initial Doppler frequency are input to each sub-loop, and each sub-loop outputs two signals, one is the Doppler frequency shift , and the other is the Doppler estimate of the fusion correction. Among them, the Doppler estimated value is input to the output fusion device, and the output signal of the output fusion device is divided into two channels, one channel outputs the phase estimated value through the integrator; the other channel is input to each sub-loop through the Doppler estimator Track Fusion.

The internal connection structure of each adaptive sub-loop module: the intermediate frequency signal is input to the phase detector as an input signal, and the output of the phase detector is divided into two channels, one input is also to the fuzzy logic bandwidth controller, and the other is input to the loop filter. . The output of the loop filter is input to the carrier NCO, and the output of the carrier NCO and the initial Doppler frequency acquired by capture are input to the multiplier. The output of the multiplier is divided into two channels, one outputs the initial Doppler frequency shift result, and the other Input to the tracking fusion device, the output of the tracking fusion device is divided into two channels, one input is input to the integrator inside the sub-loop together with the intermediate frequency, the output of the integrator is input to the phase detector, and the other is input to the external loop. Output fusion.

The working method of the adaptive GNSS carrier multi-loop tracking device is as follows:

(1) The carrier signal information is input to the phase detector of sub-loop 1 to obtain the phase estimation error of the carrier signal.

(2) The fuzzy logic bandwidth controller inside the sub-loop 1 calculates and gives the control amount according to the phase estimation error, and adjusts the bandwidth of the loop filter according to the control amount.

(3). The adjusted inner loop filter filters the phase estimation error of the carrier signal, the carrier NCO tracks and adjusts the filtered carrier signal, and then inputs the adjusted carrier signal to the multiplier and the captured The Doppler frequency is multiplied to obtain the Doppler frequency shift result tracked by sub-loop 1, that is, the Doppler frequency shift 1;

(4) Determine whether the Doppler frequency shift result of each sub-loop is a reasonable value by comparing the combination of the tracking and fusing device. If it is a reasonable value, the Doppler frequency shift of 1 is the Doppler estimated value of 1. The reference value of the Doppler estimator is taken as the Doppler estimator value 1. Specifically, the Doppler frequency shift results of each sub-loop and the reference value given by the Doppler estimator are tracked and fused, and the tracking and fusion device compares these Doppler shift results in pairs. 1 and other arbitrary loop results conform to the same distribution, it is considered that sub-loop 1 is not out of lock; otherwise, it is compared with the reference value of the Doppler estimator, if it conforms to the same distribution as the reference value, then sub-loop 1 is also judged to be out of lock. If the lock is lost, the Doppler frequency shift of the sub-loop is 1 as the final Doppler estimate (ie, the Doppler estimate is 1); otherwise, the sub-loop 1 is judged to be out of lock, and the reference given by the Doppler estimator value as the final Doppler estimate for sub-loop 1 (ie, Doppler estimate 1).

(5). The Doppler estimated value 1 is accumulated by the integrator and the input digital intermediate frequency, and fed back to the sub-loop phase detector to realize the closed-loop tracking of the sub-loop 1.

(6). At the same time, the carrier signal information is also input to other adaptive sub-loops 2-4, and the working process is the same as steps (1)-(5), to obtain the final Doppler estimated value of each loop tracking, and The closed-loop tracking of each sub-loop is realized.

(7) The estimated Doppler values of sub-loops 1 to 4 are simultaneously input to the output fuser outside the loop for information fusion, so as to obtain the final Doppler frequency shift result at this moment.

(8) The final Doppler frequency shift result at this moment is input to the external integrator all the way to calculate the phase estimation value, which is input to the phase detector together with the input signal to obtain the phase estimation error; the other channel is input to the external Doppler The estimator is stored as the historical information of the Doppler estimated value and used as the reference value at the next moment to judge whether the auxiliary sub-loop is out of lock, and provide the initial parameters of re-tracking.

In the above process, the relevant algorithms of each working module are as follows:

Phase detector: A two-quadrant arc tangent function phase detector is used to obtain the phase estimation error of the carrier signal:

为载波信号的相位实际误差，

为输入噪声(例如，热噪声、设备抖动)引起的相位干扰。Among them, φ _e (t) is the phase estimation error of the carrier signal, Q _p (t), I _p (t) are the quadrature and in-phase instantaneous correlation values, respectively,

is the actual phase error of the carrier signal,

Phase disturbance due to input noise (eg, thermal noise, device jitter).

Fuzzy logic bandwidth controller: used to control the bandwidth of each adaptive loop filter. Specifically, the central solution fuzzy strategy can be used:

Among them, u is the output control quantity, u _k is the control quantity of k fuzzy subsets, y _k is the membership value of u _k ;

Further, an exponential algorithm is used to control the loop bandwidth change, and the bandwidth of each adaptive sub-loop is calculated:

B _n (t)=B _n (t-1)·e ^u (3)

Among them, B _n (t) is the loop bandwidth at time t.

否则，需要多普勒估计器提供多普勒参考值

进行判断：Tracking Fusion: Used to determine whether the loop is out of lock. In the tracking environment, if there is a sub-loop j such that the Doppler frequency shift ω _{D,i of the sub-loop i} satisfies ω _D,i ≈ω _D,j , it is considered that the sub-loop i is working normally, and the estimated Doppler value is

Otherwise, the Doppler estimator is required to provide the Doppler reference value

To judge:

则认为子环路i正常工作，

否则，子环路i失锁，重新赋予子环路i正确的多普勒估计值，辅助子环路恢复重跟踪状态，

like

Then the sub-ring i is considered to be working normally,

Otherwise, the sub-loop i loses the lock, and the correct Doppler estimation value is re-assigned to the sub-loop i, and the auxiliary sub-loop restores the re-tracking state.

Output fuser: The fuzzy exponential trust function is used to quantify the trust of each sub-loop Doppler shift, and a trust matrix is established to determine the weight ratio of each loop Doppler shift to achieve fusion.

The trust degree function b _i,j represents the trust degree of the Doppler frequency shift ω _i of the sub-loop i and the Doppler frequency shift ω _j of the sub-loop j:

Among them, M (M>0) is a threshold, which can be obtained through multiple trials and tests according to the receiver used. When |ω _i -ω _j |>M, it is considered that sub-ring i and sub-ring j do not trust each other.

With n sub-loop output Doppler, the trust function can form a trust matrix B:

The weight of sub-loop i is defined as:

Among them, A=[a ₁ ,..., _an ] ^T , according to the eigenvector A corresponding to the largest eigenvalue λ of B:

λA=BA (7)

Normalize the weight coefficients:

The final Doppler shift estimated by the output fuser is:

用于比较环路是否失锁和为失锁环路提供可靠多普勒，辅助失锁环路重新跟踪。Doppler Estimator: Provides reference information for tracking fusion using the historical Doppler of the previous moment. Specifically, save the final Doppler frequency shift estimated by the output fusion device at each moment, and use it as historical information to provide a reference Doppler value for the tracking fusion at the next moment

It is used to compare whether the loop is out of lock and provide reliable Doppler for the out-of-lock loop to assist the re-tracking of the out-of-lock loop.

To sum up, the adaptive GNSS carrier multi-loop tracking device proposed by the present invention expands multiple multi-loop parallel carrier tracking loops with adaptive adjustment bandwidth on the basis of the traditional carrier tracking loop of the GNSS receiver. It ensures stable carrier tracking in high dynamic, conventional and weak signal environments, improves the tolerance of GNSS receivers to complex environments, has stronger versatility, and has important engineering significance.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. 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 (9)

1. A self-adaptive GNSS carrier multi-loop tracking device is characterized by comprising a Doppler estimator, an integrator, an output fusion device and N self-adaptive sub-loop modules, wherein each self-adaptive sub-loop module is provided with a phase discriminator, a fuzzy logic bandwidth controller, a loop filter, a carrier NCO, a multiplier, a tracking fusion device and an integrator; the output fusion device has N input ends, and the tracking fusion device has N +1 input ends; the carrier signal is input to a first input end of a phase discriminator as an input signal, a first output end of the phase discriminator is connected with an input end of a fuzzy logic bandwidth controller, a second output end of the phase discriminator is connected with a first input end of a loop filter, an output end of the fuzzy logic bandwidth controller is connected with a second input end of the loop filter, an output end of the loop filter is connected with an input end of a carrier NCO, an output end of the carrier NCO is connected with a first input end of a multiplier, a second input end of the multiplier inputs the captured Doppler frequency, and the multiplier outputs a Doppler frequency shift result; the second output end of the multiplier is connected with the first input end of the tracking fusion device, the second input end of the tracking fusion device receives the reference value output by the Doppler estimator, the other input ends of the tracking fusion device respectively receive Doppler frequency shift results output by other self-adaptive sub-loop modules, the first output end of the tracking fusion device is connected with the first input end of the integrator, the second output end of the tracking fusion device outputs a Doppler estimated value, the second input end of the integrator receives the intermediate frequency, and the output end of the integrator is connected with the second input end of the phase discriminator; the input end of the output fusion device respectively receives the Doppler estimated values output by the adaptive sub-loop modules.

2. The adaptive GNSS carrier multi-loop tracking apparatus of claim 1 wherein the adaptive sub-loop employs a PLL tracking loop.

3. The adaptive GNSS carrier multi-loop tracking apparatus of claim 1, wherein the order and integration time of the respective adaptation sub-loops do not require to be consistent.

4. The adaptive GNSS carrier multi-loop tracking apparatus of claim 1, wherein the phase detector employs a two-quadrant arctangent function phase detector for obtaining a phase estimation error of the carrier signal:

wherein phi is_e(t) is the phase estimation error of the carrier signal, Q_p(t)、I_p(t) are quadrature and in-phase instantaneous correlation values respectively,

is the actual error in the phase of the carrier signal,

phase interference caused by input noise.

5. The adaptive GNSS carrier multi-loop tracking apparatus of claim 1, wherein the fuzzy logic bandwidth controller controls the bandwidth of each adaptive loop filter using a central solution fuzzy strategy:

wherein u is an output control amount, u_kControl quantities for k fuzzy subsets, y_kIs u_kA membership value of; further, the bandwidth of each adaptive sub-loop is calculated by an exponential algorithm as follows:

B_n(t)＝B_n(t-1)·e^u (3)

wherein, B_nAnd (t) is the loop bandwidth at time t.

6. The adaptive GNSS carrier multi-loop tracking apparatus of claim 1, wherein the tracking fuser is configured to determine whether the loop is out-of-lock:

in a tracking environment, the existence of the sub-loop j causes the Doppler frequency shift of the sub-loop iω_D,iSatisfy omega_D,i≈ω_D,jThen the sub-loop i is considered to be working normally and the Doppler estimated valueOtherwise, Doppler estimator provision is required

And (4) judging the reference value:

if it is

The sub-loop i is considered to be operating normally,

otherwise, the sub-loop i loses lock, the sub-loop i is endowed with a correct Doppler estimated value again, the sub-loop is assisted to recover a re-tracking state,

7. the adaptive GNSS carrier multi-loop tracking apparatus of claim 1, wherein the output fusion device quantizes the confidence of the Doppler frequency shift of each adaptive sub-loop module by using a fuzzy index confidence function, establishes a confidence matrix to determine the weight ratio of the Doppler frequency shift of each loop, and realizes fusion, wherein the confidence function b_i,jRepresenting the Doppler shift ω of the sub-loop i_iDoppler shift omega of minor loop j_jDegree of trust of:

wherein M is a threshold value, M>0, when | ω_i-ω_j|>M, considering that the sub-loop i and the sub-loop j do not trust each other;

n sub-loop output Doppler is set, and a confidence function can form a confidence matrix B:

the weight of the sub-loop i is defined as:

wherein A ═ a₁,…,a_n]^TAnd according to the eigenvector A corresponding to the maximum eigenvalue lambda of B:

λA＝BA (7)

normalizing the weight coefficients:

the final doppler shift of the output fusion estimate is:

8. the adaptive GNSS carrier multi-loop tracking apparatus of claim 1, wherein the Doppler estimator stores the final Doppler shift estimated by the output fusion device at each time and uses it as historical information to provide a reference Doppler value for the tracking fusion at the next time

The method is used for comparing whether the loop is out-of-lock or not and providing reliable Doppler for the out-of-lock loop, and assists the out-of-lock loop in retracing.

9. An adaptive GNSS carrier multi-loop tracking method using the adaptive GNSS carrier multi-loop tracking apparatus according to any one of claims 1 to 8, comprising:

in each adaptive sub-loop, a fuzzy logic bandwidth controller calculates and provides a control quantity according to the phase estimation error, and adjusts the bandwidth of a loop filter according to the control quantity; the adjusted loop filter filters the phase estimation error of the carrier signal, the carrier NCO tracks and adjusts the filtered carrier signal, and then the adjusted carrier signal is input to a multiplier to be multiplied by the captured Doppler frequency, so that the Doppler frequency shift result of the adaptive sub-loop tracking is obtained; the tracking fusion device is used for comparing and judging whether the Doppler frequency shift result of each adaptive sub-loop is a reasonable value or not, if so, the Doppler frequency shift result is a Doppler estimated value, otherwise, a reference value output by an external Doppler estimator is used as the Doppler estimated value; accumulating Doppler estimated values with input intermediate frequency through an integrator, and feeding back to a phase discriminator to realize closed-loop tracking of the adaptive sub-loop;

doppler estimated values of the adaptive sub-loops are simultaneously input into an output fusion device outside the loop for information fusion, and a final Doppler frequency shift result at the current moment is obtained;

inputting one path of the final Doppler frequency shift result at the current moment into an external integrator, calculating a phase estimation value, and inputting the phase estimation value and a carrier signal into phase discriminators of adaptive sub-loops to obtain a phase estimation error; and the other path is input to an external Doppler estimator to be stored as a reference value of the next moment.

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