Method for detecting loss-of-lock of a GNSS signal tracking loop based on frequency compensation

1. A method for detecting loss-of-lock of a GNSS signal tracking loop based on frequency compensation, characterized by comprising the steps of:

(1) performing multi-channel frequency compensation on I-channel and Q-channel signals after down-conversion and pseudo-code stripping;

(2) performing coherent integration and non-coherent integration for a fixed time, and finding out a maximum value after the non-coherent integration as a signal value;

(3) performing parabolic interpolation frequency identification to solve for a frequency corresponding to the signal value; and

(4) with an average value of non-coherent integration results with frequency differences relative to the frequency corresponding to the signal value of +/−50 Hz and +/−100 Hz as a noise value, and a ratio of the signal value to the noise value as a detection volume, performing loop loss-of-lock detection.

2. The method for detecting the loss-of-lock of the GNSS signal tracking loop based on the frequency compensation of claim 1 , the step (1) further comprising:

(1.1) subjecting an input intermediate frequency signal to carrier wave mixing and multiplication to achieve down-conversion, wherein the input intermediate frequency signal is multiplied with a sine signal to form an I-channel signal and a cosine signal to form a Q-channel signal;

(1.2) multiplying mixed signals of I-channel and Q-channel by a C/A code respectively to strip a pseudo code; and

(1.3) filtering out high frequency noise in the I-channel and Q-channel signals by an integration clearer.

3. The method for detecting the loss-of-lock of the GNSS signal tracking loop based on the frequency compensation of claim 1 , characterized in that, in the step (1), a multi-channel frequency compensation strategy is such that a small compensation interval is adopted at a small frequency compensation value and a large compensation interval is adopted at a large frequency compensation value.

4. The method for detecting the loss-of-lock of the GNSS signal tracking loop based on the frequency compensation of claim 1 , characterized in that, in the step (4), the loop loss-of-lock detection specifically comprises the steps of:

(4.1) when the ratio of the signal value to the noise value is greater than a ratio threshold value, considering that the loop does not loss lose lock, tracking normally, updating a carrier phase and a code phase, and clearing a number of loss-of-lock failures;

when the ratio of the signal value to the noise value is less than the ratio threshold value:

(4.2) storing the ratio of the signal value to the noise value in a cache and increasing the number of loss-of-lock failures by 1;

(4.3) calculating a carrier-to-noise ratio and judging whether the carrier-to-noise ratio is less than a minimum carrier-to-noise ratio, if so, judging that the loop losses lock, stopping updating the carrier phase and the code phase, and entering a recapture process; if not, proceeding to step (4.4);

(4.4) judging whether the number of loss-of-lock failures is less than 2, if so, judging that the loop is stable, and updating the carrier phase and the code phase normally; if not, proceeding to step (4.5); and

(4.5) determining whether an average value of the ratio of the signal value to the noise value and the carrier-to-noise ratio is less than the ratio threshold value, if so, considering that the loop losses lock, and entering recapture; if not, considering the loop stable.

5. The method for detecting the loss-of-lock of the GNSS signal tracking loop based on the frequency compensation of claim 1 , characterized in that, in the step (3), a parabolic interpolation method is specifically as follows:

taking a discrete point value of a nearest point as a frequency estimation value, and given coordinates of L(x 1 ,y 1 ), M(x 2 ,y 2 ) and R(x 3 ,y 3 ) points, horizontal and vertical coordinates of a maximum point E(x 0 ,y 0 ) are as follows:

x

0

=

(

y

3

-

y

1

)

⁢

d

2

⁢

(

2

⁢

y

2

-

y

1

-

y

3

)

+

x

2

y

0

=

(

y

3

-

y

1

)

2

8

⁢

(

2

⁢

y

2

-

y

1

-

y

3

)

+

y

2

where, M point is a point corresponding to the maximum value of non-coherent integration results, and L and R points are the nearest points on the left and right sides of the M point.