CN105527635A - Method and device for capturing weak signals - Google Patents

Abstract

The invention provides a method for capturing weak signals. According to the method, the Doppler frequency offset and the transmission time of a captured strong signal satellite are acquired; the Doppler frequency offset of a non-captured weak signal satellite can be determined according to the Doppler frequency offset of the captured strong signal satellite; a spreading code period and a spreading code phase of the non-captured weak signal satellite can be determined according to the transmission time of the captured strong signal satellite. The invention further provides a device for capturing the weak signals.

Description

Method and device for capturing weak signal

Technical Field

The invention relates to a Beidou satellite navigation assisting technology, in particular to a method and a device for capturing weak signals.

Background

Currently, with the demands of people on indoor weak signal environments and the time for first positioning, an Assisted global navigation satellite system (a-GNSS) has been developed. The a-GNSS provides the navigation receiver with the assistance information required by means of a wireless communication network to support the navigation receiver positioning capability or enhance the acquisition capability of the navigation receiver in weak signal conditions.

The conventional navigation receiver needs to acquire 4 or more satellite signals for realizing the positioning function, and different satellite signals have different pseudo random codes of starting time and different Doppler frequency shifts. Therefore, in order to search for a certain satellite signal, the navigation receiver usually needs to perform two-dimensional search, and search for each pseudo random code with different starting time at each possible doppler frequency shift, and the assisted navigation receiver can estimate the doppler frequency shift caused by satellite motion by using the assisted time, ephemeris/almanac and navigation receiver position so as to shorten the acquisition frequency search space. However, without a given local clock frequency offset, the doppler shift caused by the local clock frequency offset cannot be estimated, and a smaller local clock frequency offset may generate a doppler shift of up to kilohertz (Hz), which may increase the acquisition search space and affect the time to first fix.

The 3GPP ts36.171 defines a minimum set of assistance information for a-GNSS technology, including time assistance information, almanac/ephemeris assistance information, user location assistance information, etc., and the wireless communication network may provide two different time assistance modes, defined according to the 3GPP standard: fine time assist (accuracy of ± 10 μ s) and coarse time assist (accuracy of ± 2 s).

In a precise time-aided positioning mode, the conventional receiver can estimate the Doppler frequency offset and the code phase of a satellite through time, almanac/ephemeris and user position information acquired from a wireless communication network, so that a two-dimensional search space of satellite acquisition frequency and code phase is reduced. For a Global Positioning System (GPS) and a beidou system, the length of a ranging code is 1ms, and the time precision of fine time assistance is less than 1ms, so that the edge of a navigation message bit can be estimated, the coherent integration time of capturing is further increased, the sensitivity of capturing is improved, and high-sensitivity positioning in a weak signal environment is realized.

However, in the coarse-time aided positioning mode, since the time accuracy is greater than the length of one ranging code, the code phase and the navigation message bit edge cannot be predicted, and therefore, under the same aiding information, the sensitivity of acquisition is smaller than that of the fine-time aided acquisition. Moreover, due to weather, shading and other reasons of the actual environment, the power of many satellite signals is weak, and often only one or two slightly stronger satellite signals can be captured, so that positioning cannot be completed.

In summary, how to realize fast acquisition of weak signals in a coarse-time aided positioning mode of a receiver becomes an urgent problem to be solved in the aided positioning technology.

Disclosure of Invention

In view of this, embodiments of the present invention are intended to provide a method and an apparatus for acquiring a weak signal, which enable a receiver to achieve fast acquisition of the weak signal in a coarse-time aided positioning manner.

In order to achieve the above purpose, the technical solution of the embodiment of the present invention is realized as follows:

the embodiment of the invention provides a method for capturing a weak signal, which comprises the following steps:

acquiring Doppler frequency offset and transmission time of the captured strong signal satellite;

determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite;

and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite.

In the foregoing solution, the determining the doppler frequency offset of the uncaptured weak signal satellite according to the acquired doppler frequency offset of the captured strong signal satellite includes:

determining the Doppler frequency offset estimation value of the current visible satellite by using ephemeris information, coarse time auxiliary time and the reference position coordinate of the receiver of the satellite; the current satellites in view include the acquired strong signal satellites and the uncaptured weak signal satellites;

and determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite and the determined Doppler frequency offset estimation value of the current visible satellite.

In the foregoing solution, the determining a spreading code period and a spreading code phase of an uncaptured weak signal satellite according to the acquired transmission time of a captured strong signal satellite includes:

correcting the reference time of the receiver by using the acquired transmission time of the strong signal satellite to obtain the corrected reference time of the receiver;

and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the corrected receiver reference time, the ephemeris information of the satellite and the receiver reference position coordinate.

In the above solution, the determining the doppler frequency offset estimation value of the current visible satellite by using ephemeris information, coarse time assistance time, and a receiver reference position coordinate of the satellite includes:

determining the position coordinates of the current visible satellite according to the ephemeris information, the coarse time assistance time and the receiver reference position coordinates of the satellite, and further determining the time t corresponding to the coarse time assistance time of the current visible satellite_kThe speed of (d); then according to the determined current visible satellite at t_kAnd determining the Doppler frequency offset estimation value of the current visible satellite signal by the speed at the moment.

In the above scheme, the value range of the number N1 of the captured strong signal satellites is 1-3 of N1.

The embodiment of the invention also provides a device for capturing the weak signal, which comprises: the device comprises a strong signal acquisition module, a Doppler correction module and a spread spectrum code estimation module; wherein,

the strong signal acquisition module is used for acquiring the Doppler frequency offset and the transmission time of the acquired strong signal satellite;

the Doppler correction module is used for determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite;

and the spread spectrum code estimation module is used for determining the spread spectrum code period and the spread spectrum code phase of the uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite.

In the above solution, the doppler correction module includes a doppler estimation module and a doppler determination module; wherein,

the Doppler estimation module is used for determining a Doppler frequency offset estimation value of the current visible satellite by using ephemeris information, coarse time assistance time and a receiver reference position coordinate of the satellite; the current satellites in view include the acquired strong signal satellites and the uncaptured weak signal satellites;

and the Doppler determining module is used for determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite and the determined Doppler frequency offset estimation value of the current visible satellite.

In the above scheme, the spread spectrum code estimation module is configured to correct the receiver reference time by using the acquired transmission time of the strong signal satellite, and obtain a corrected receiver reference time; and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the corrected receiver reference time, the ephemeris information of the satellite and the receiver reference position coordinate.

In the above solution, the doppler estimation module is configured to determine the position coordinates of the current visible satellite according to ephemeris information of the satellite, coarse time assistance time, and reference position coordinates of the receiver, and further determine the position coordinates of the current visible satelliteDetermining the corresponding moment t of the current visible satellite in the coarse auxiliary time_kThe speed of (d); then according to the determined current visible satellite at t_kAnd determining the Doppler frequency offset estimation value of the current visible satellite signal by the speed at the moment.

In the above scheme, the value range of the number N1 of the strong signal satellites captured by the strong signal capturing module is 1 or more and N1 or more and 3 or less.

The method and the device for capturing the weak signal, provided by the embodiment of the invention, are used for acquiring the Doppler frequency offset and the transmission time of the captured strong signal satellite; determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite; and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite. Therefore, on the basis of accurately determining the Doppler frequency offset, the spread spectrum code period and the spread spectrum code phase of the uncaptured weak signal satellite, the two-dimensional search space of the satellite capture frequency and the code phase can be reduced, and the receiver can be ensured to realize the rapid capture of the weak signal in a coarse auxiliary positioning mode.

Drawings

Fig. 1 is a schematic flow chart illustrating an implementation of a method for capturing a weak signal according to an embodiment of the present invention;

fig. 2 is a schematic flowchart of a specific implementation of a method for capturing a weak signal according to an embodiment of the present invention;

FIG. 3 is a diagram illustrating transmission times of strong signal satellites that have been acquired according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a structure of a device for capturing a weak signal according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram illustrating a doppler correction module in an apparatus for capturing a weak signal according to an embodiment of the present invention.

Detailed Description

In the embodiment of the invention, the Doppler frequency offset and the transmission time of the captured strong signal satellite are obtained; determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite; and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite.

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

Fig. 1 is a schematic flow chart of an implementation of a method for capturing a weak signal according to an embodiment of the present invention, and as shown in fig. 1, the method for capturing a weak signal according to an embodiment of the present invention includes:

step S10: acquiring Doppler frequency offset and transmission time of the captured strong signal satellite;

here, the number N1 of strong signal satellites that have been acquired by the receiver ranges from 1. ltoreq. N1. ltoreq.3 because the receiver is in the coarse-time aided positioning mode.

Step S11: determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite;

specifically, step S11 includes the following steps a and B; wherein,

step A: determining the Doppler frequency offset estimation value of the current visible satellite by using ephemeris information, coarse time auxiliary time and the reference position coordinate of the receiver of the satellite; the current satellites in view include the acquired strong signal satellites and the uncaptured weak signal satellites; the value range of the total number N of the current visible satellites is that N is more than or equal to 2 and less than or equal to 34, and N is N1+ N2; where N2 is the number of weak signal satellites not acquired.

In particular, the coarse time assistance time, and the receiver reference position are determined based on ephemeris information of the satellitesDetermining the position coordinates of the current visible satellite according to the coordinates, and further determining the corresponding moment t of the current visible satellite in the coarse auxiliary time_kThe speed of (d); then according to the determined current visible satellite at t_kAnd determining the Doppler frequency offset estimation value of the current visible satellite signal by the speed at the moment.

And B: and determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite and the determined Doppler frequency offset estimation value of the current visible satellite.

Step S12: and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite.

Specifically, firstly, correcting the reference time of the receiver by using the acquired transmission time of the strong signal satellite to obtain the corrected reference time of the receiver; and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the corrected receiver reference time, the ephemeris information of the satellite and the receiver reference position coordinate.

Here, the spreading code period refers to an integer number of spreading codes within one navigation message bit period. For a Beidou geostationary orbit (GEO) satellite, the bit period of a navigation message is 2ms, so that the value of the spread spectrum code period is less than or equal to 2 ms; for a non-geostationary orbit (NGEO) satellite, the period of the spreading code takes a value of 20ms or less since the navigation message bit period is 20 ms. In addition, one spreading code of the Beidou satellite comprises 2046 chips, so that the value of the phase of the spreading code is less than or equal to 2046.

Therefore, the Doppler frequency offset of the uncaptured weak signal satellite determined by the embodiment of the invention can reduce the Doppler search range, and meanwhile, the edge of the Beidou GEO satellite signal navigation message and the Neuman-Hoffman (NH) code phase of the NGEO satellite can be quickly calculated by utilizing the spectrum spreading code period and the spectrum spreading code phase of the uncaptured weak signal satellite determined by the embodiment of the invention, so that the coherent integration time of capturing is further increased, and the quick capturing of the weak signal is realized.

Fig. 2 is a schematic flowchart of a specific implementation of the method for capturing a weak signal according to the embodiment of the present invention, and as shown in fig. 2, the method for capturing a weak signal according to the embodiment of the present invention includes:

step S20: acquiring Doppler frequency offset and transmission time of the captured strong signal satellite;

step S21: determining the Doppler frequency offset estimation value of the current visible satellite by using ephemeris information, coarse time auxiliary time and the reference position coordinate of the receiver of the satellite; the current satellites in view include the acquired strong signal satellites and the uncaptured weak signal satellites;

specifically, the step S21 includes:

step 1, determining the position coordinates of the current visible satellite according to the ephemeris information, the coarse time assistance time and the receiver reference position coordinates of the satellite, and further determining the time t corresponding to the coarse time assistance time of the current visible satellite_kSpeed of

Specifically, since the position coordinates and the velocity calculation methods of the Beidou GEO satellite and the NGEO satellite are different, the calculation methods are required to be respectively calculated, and the specific calculation method is as follows:

1) in a GC2000 coordinate system, for an NGEO satellite, t corresponding to the coarse auxiliary time is determined according to ephemeris information of the satellite_kTime of day, position coordinates (X) of the currently visible satellites_k,Y_k,Z_k) The calculation formula of (a) is as follows:

${\mathrm{\Ω}}_k={\mathrm{\Ω}}_0+(\stackrel{.}{\mathrm{\Ω}}-{\stackrel{.}{\mathrm{\Ω}}}_e)*t_k-{\stackrel{.}{\mathrm{\Ω}}}_e*t_{\mathrm{oe}};$

$\left\{\begin{array}{c}{X}_k=x_k\cos {\mathrm{\Ω}}_k-y_k\cos i_k\sin {\mathrm{\Ω}}_k\\ Y_k=x_k\sin {\mathrm{\Ω}}_k-y_k\cos i_k\cos {\mathrm{\Ω}}_k\\ Z_k=y_k\sin i_k\end{array}\right.;$

wherein omega_kIs the perpendicular ascension (Earth fixed system) of epoch₀Is the rising point right ascension calculated according to the reference time,is the rate of change of the right ascension at the ascending crossing point,the rotation rate of the earth in the CGCS2000 coordinate system is 7.2921150 × 10e-5rad/s, t_kFor the time difference from the observation epoch to the reference epoch, t_oeFor ephemeris reference time, x_k、y_kAs coordinates of the satellite in the orbital plane, i_kIs the corrected track inclination angle.

Further, NGEO satellites are at t_kVelocity of time of dayThe calculation formula of (a) is as follows:

$\left\{\begin{array}{c}{V}_x=-Y_k{{\mathrm{\Ω}}_k}^{\′}-(y_k^{\′}\cos i_k-y_k\sin i_k*{i_k}^{\′})\sin {\mathrm{\Ω}}_k\\ +x_k^{\′}\cos {\mathrm{\Ω}}_k\\ V_y=X_k{{\mathrm{\Ω}}_k}^{\′}+(y_k^{\′}\cos i_k-y_k\sin i_k*{i_k}^{\′})\cos {\mathrm{\Ω}}_k\\ +x_k^{\′}\sin {\mathrm{\Ω}}_k\\ V_z=y_k^{\′}\sin i_k+y_k{i}_k^{\′}\cos i_k\end{array}\right.;$

wherein, x'_k、y'_kAre respectively x_k、y_kFor t_kDerivative of (Q)_k'、i_k' are each omega_k、i_kFor t_kThe derivative of (c).

2) In the GC2000 coordinate system, for GEO satellites, t corresponding to the coarse auxiliary time is determined according to ephemeris information of the satellites_kTime of day, position coordinates (X) of the currently visible satellites_k,Y_k,Z_k) The calculation formula of (a) is as follows:

${\mathrm{\Ω}}_k={\mathrm{\Ω}}_0+\stackrel{.}{\mathrm{\Ω}}*t_k-{\stackrel{.}{\mathrm{\Ω}}}_e*t_{\mathrm{oe}};$

$\left\{\begin{array}{c}{X}_{\mathrm{GK}}=x_k\cos {\mathrm{\Ω}}_k-y_k\cos i_k\sin {\mathrm{\Ω}}_k\\ Y_{\mathrm{GK}}=x_k\sin {\mathrm{\Ω}}_k-y_k\cos i_k\sin {\mathrm{\Ω}}_k\\ Z_{\mathrm{GK}}=y_k\sin i_k\end{array}\right.;$

$\left\{\begin{array}{c}{X}_k=\cos \left(\mathrm{\φ}\right)\·X_{\mathrm{GK}}+k_1\·\sin \left(\mathrm{\φ}\right)\·Y_{\mathrm{GK}}+k_2\·\sin \left(\mathrm{\φ}\right)\·Z_{\mathrm{GK}}\\ Y_k=-\sin \left(\mathrm{\φ}\right)\·X_{\mathrm{GK}}+k_1\·\cos \left(\mathrm{\φ}\right)\·Y_{\mathrm{GK}}+k_2\·\cos \left(\mathrm{\φ}\right)\·Z_{\mathrm{GK}}\\ Z_k=-k_2\·Y_{\mathrm{GK}}+k_1\·Z_{\mathrm{GK}}\end{array}\right.;$

wherein k is₁＝cos(-5°)，k₂＝sin(-5°)，Ω_kIs the perpendicular ascension (Earth fixed system) of epoch₀Is the rising point right ascension calculated according to the reference time,is the rate of change of the right ascension at the ascending crossing point,the rotation rate of the earth in the CGCS2000 coordinate system is 7.2921150 × 10e-5rad/s, t_kFor the time difference from the observation epoch to the reference epoch, t_oeFor ephemeris reference time, x_k、y_kAs coordinates of the satellite in the orbital plane, i_kIs the corrected track inclination angle.

Further, the GEO satellite is at t_kVelocity of time of dayThe calculation formula of (a) is as follows:

$\left\{\begin{array}{c}{V}_x={\stackrel{.}{\mathrm{\Ω}}}_e\·Y_k+\cos \left(\mathrm{\φ}\right)\·{\stackrel{.}{X}}_{\mathrm{GK}}+\sin \left(\mathrm{\φ}\right).[k_1\·{\stackrel{.}{Y}}_{\mathrm{GK}}+k_2\·{\stackrel{.}{Z}}_{\mathrm{GK}}]\\ V_y=-{\stackrel{.}{\mathrm{\Ω}}}_e\·X_k-\sin \left(\mathrm{\φ}\right)\·{\stackrel{.}{X}}_{\mathrm{GK}}+\cos \left(\mathrm{\φ}\right)\·[k_1\·{\stackrel{.}{Y}}_{\mathrm{GK}}+k_2\·{\stackrel{.}{Z}}_{\mathrm{GK}}]\\ V_z=-k_2\·{\stackrel{.}{Y}}_{\mathrm{GK}}{+k}_1\·{\stackrel{.}{Z}}_{\mathrm{GK}}\end{array}\right.;$

wherein,is composed ofFor t_kThe derivative of (c).

Step 2, determining the current visible satellite at t according to the step 1_kVelocity of time of dayDetermining the Doppler frequency offset estimation value f of the current visible satellite signal_d。

In particular, said f_dThe calculation formula of (a) is as follows:

$f_d=f\frac{{\stackrel{.}{v}}^{\left(s\right)}\·e^{\left(s\right)}}{c};$

$e^{\left(s\right)}=\frac{\left(X_k^{\left(s\right)}{Y}_k^{\left(s\right)}{Z}_k^{\left(s\right)}\right)-\left(X_{\mathrm{rec}}{Y}_{\mathrm{rec}}{Z}_{\mathrm{rec}}\right)}{\left|\right|\left(X_k^{\left(s\right)}{Y}_k^{\left(s\right)}{Z}_k^{\left(s\right)}\right)-\left(X_{\mathrm{rec}}{Y}_{\mathrm{rec}}{Z}_{\mathrm{rec}}\right)\left|\right|};$

wherein, the carrier frequency f of the current visible satellite signal is 1561.098MHz,the relative speed in the direction of the connection line between the s-th current visible satellite and the receiver, and c is the speed of light. e.g. of the type^(s)At t for the currently visible satellite signal_kUnit observation vector from receiver to current visible satellite at time, (X)_rec,Y_rec,Z_rec) Is t_kThe coordinates of the position of the receiver at the moment,is t_kAnd the position coordinates of the current visible satellite at the time s in the CGCS2000 coordinate system.

Step S22: and determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite and the determined Doppler frequency offset estimation value of the current visible satellite.

Specifically, the estimated doppler frequency shift values of all the currently visible satellites estimated and determined through the step S21 are ${\stackrel{.}{F}}_d=\left[\begin{array}{cccc}{f}_{d1}& f_{d2}& ......& f_{\mathrm{dN}}\end{array}\right],$ 2≤N≤34，Can be split into two vectorsAndwherein,for doppler frequency offset estimates for acquired strong signal satellites,the Doppler frequency offset estimation value of the weak signal satellite which is not acquired is 1 ≦ N1 ≦ 3, and N ≦ N1+ N2. And the Doppler frequency of the acquired strong signal acquired by the receiver is shifted to $\stackrel{.}{F_{\mathrm{ds}\_\mathrm{acq}}}=\left[\begin{array}{ccc}{f}_{\mathrm{ds}\_\mathrm{acq}1}& ......& f_{\mathrm{ds}\_\mathrm{acqN}1}\end{array}\right].$

Therefore, the Doppler shift due to the clock bias of the receiver is estimated asWhereinEach component of (a) is an estimate of the doppler bias caused by the clock bias of each of the strong signal satellites acquired.

It should be noted that, for one receiver, it can be considered that the receiver clock bias fluctuation is small, and therefore, when the number of acquired strong signal satellites N1 satisfies 2 ≦ N1 ≦ 3, the vector is passedIs averaged to obtain Δ F_dAnd will be Δ F_dAs a receiver frequency offset correction for the uncaptured weak signal satellites. Of course, in the case where the number N1 of strong signal satellites acquired is 1, it is obvious that,with only one component Δ F_dTherefore, Δ F can be directly converted into_dAs a receiver frequency offset correction for the uncaptured weak signal satellites.

Further, using Δ F_dCorrecting the Doppler frequency offset estimation value of the uncaptured weak signal satellite to obtain the Doppler frequency offset of the uncaptured weak signal satellite as

Step S23: correcting the reference time of the receiver by using the acquired transmission time of the strong signal satellite to obtain the corrected reference time of the receiver;

specifically, fig. 3 is a schematic diagram of the transmission time of the acquired strong signal satellite, and as shown in fig. 3, the transmission time of the kth strong signal satellite is TOT^k＝SOW^k+ΔT^kWherein representing the k strong signal satellite finding the SOW^kThe number of the following navigation bits is,represents the number of spreading code cycles of the k-th strong signal satellite, namely the whole millisecond number after the transmission of the last navigation message bit by the k-th strong signal satellite,representing the code phase of the kth strong signal satellite. Thus, the transmission time of the kth strong signal satellitek＝1～N1。

Further, the calculation formula of the position coordinates of the satellite signals is used for TOT^kObtaining the coordinates of k strong satellite signals at any momentk is 1 to N1, and the propagation time of the kth strong signal satelliteIs calculated by ${\mathrm{TOF}}_s^k=\sqrt{{(X_s^k-X_{\mathrm{rec}})}^2+{(Y_s^k-Y_{\mathrm{rec}})}^2+{(Z_s^k-Z_{\mathrm{rec}})}^2}/c$ And calculating the propagation time of the kth strong signal satellite.

Thus, the receiver reference time of the kth strong signal satellite can be obtainedIs composed of

When the number of acquired strong signal satellites N1 is 2. ltoreq.N 1. ltoreq.3, the corrected receiver reference time TOR is obtained by averaging the receiver reference times of the N1 strong signal satellites_corrIs composed of $\underset{k=1}{\overset{N1}{\mathrm{\Σ}}}{\mathrm{TOR}}_{\mathrm{corr}}^k/N1.$

Thus, the accuracy of the local reception time can be effectively improved by the step S23 in the embodiment of the present invention.

Step S24: and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the corrected receiver reference time, the ephemeris information of the satellite and the receiver reference position coordinate.

Specifically, step S24 includes:

step a, determining the position at TOR according to the calculation formula of the position coordinates of the satellite signals_corrSatellite coordinates of weak signals not captured at time kthAccording to the formula ${\mathrm{TOF}}_w^k=\sqrt{{(X_w^k-X_{\mathrm{rec}})}^2+{(Y_w^k-Y_{\mathrm{rec}})}^2+{(Z_w^k-Z_{\mathrm{rec}})}^2}/c$ Calculating the propagation time of the kth uncaptured weak signal satelliteFurther utilizeObtaining the transmission time of the kth uncaptured weak signal satellite

Step b, according to the obtained transmission time of the kth uncaptured weak signal satelliteDetermining a spreading code period for a kth unacquired weak signal satelliteAnd spreading code phase

Here, for the big Dipper GEO satellite,for a satellite that is an NGEO satellite, $N_w^k=\mathrm{floor}(\mathrm{mod}({\mathrm{TOT}}_w^k,20\mathrm{ms})*1000).$

in addition, the spread spectrum code phase of the kth unacquired weak signal satelliteIs composed of $\mathrm{mod}({\mathrm{TOT}}_w^k,20\mathrm{ms})*2046000.$

Therefore, the doppler frequency offset of the uncaptured weak signal satellite determined in the step S22 in the embodiment of the present invention can reduce the doppler search range, and meanwhile, the edge of the Beidou GEO satellite signal navigation message and the NH code phase of the NGEO satellite can be quickly calculated by using the spread code period and the spread code phase of the uncaptured weak signal satellite determined in the step S24 in the embodiment of the present invention, so as to further increase the coherent integration time of capturing, thereby realizing the quick capturing of the weak signal.

Fig. 4 is a schematic structural diagram of a device for capturing a weak signal according to an embodiment of the present invention, and as shown in fig. 4, the device for capturing a weak signal according to an embodiment of the present invention includes: a strong signal acquisition module 10, a doppler correction module 20, and a spreading code estimation module 30; wherein,

the strong signal acquisition module 10 is configured to acquire a doppler frequency offset and a transmission time of an acquired strong signal satellite;

here, since the receiver is in the coarse-time aided positioning mode, the range of the number N1 of strong signal satellites that can be acquired by the receiver is 1 ≦ N1 ≦ 3.

The doppler correction module 20 is configured to determine the doppler frequency offset of an uncaptured weak signal satellite according to the acquired doppler frequency offset of the captured strong signal satellite;

specifically, as shown in fig. 5, the doppler correction module 20 includes a doppler estimation module 21 and a doppler determination module 22; wherein,

the doppler estimation module 21 is configured to determine a doppler frequency offset estimation value of a current visible satellite by using ephemeris information of the satellite, coarse time assistance time, and a receiver reference position coordinate; the current satellites in view include the acquired strong signal satellites and the uncaptured weak signal satellites;

specifically, the doppler estimation module 21 determines the position coordinates of the current visible satellite according to the ephemeris information, the coarse time assistance time, and the receiver reference position coordinates of the satellite, and further determines the time t corresponding to the coarse time assistance time of the current visible satellite_kThe speed of (d); then according to the determined current visible satellite at t_kAnd determining the Doppler frequency offset estimation value of the current visible satellite signal by the speed at the moment.

The doppler determination module 22 is configured to determine the doppler frequency offset of the uncaptured weak signal satellite according to the acquired doppler frequency offset of the captured strong signal satellite and the determined doppler frequency offset estimation value of the current visible satellite.

The spreading code estimation module 30 is configured to determine a spreading code period and a spreading code phase of an uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite.

Specifically, the spreading code estimation module 30 first corrects the receiver reference time by using the acquired transmission time of the strong signal satellite, to obtain a corrected receiver reference time; and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the corrected receiver reference time, the ephemeris information of the satellite and the receiver reference position coordinate.

In practical applications, the strong signal capturing module 10, the doppler correction module 20, the spreading code estimation module 30, the doppler estimation module 21, and the doppler determination module 22 may be implemented by a Central Processing Unit (CPU), a microprocessor unit (MPU), a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA), or the like in the apparatus for capturing a weak signal according to the embodiment of the present invention; in addition, the strong signal acquisition module 10, the doppler correction module 20 and its sub-modules, the doppler estimation module 21 and the doppler determination module 22, and the spreading code estimation module 30, may also be implemented by a strong signal acquisition tracker, a doppler corrector, and a spreading code estimator, respectively.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention.

Claims (10)

1. A method of capturing weak signals, the method comprising:

acquiring Doppler frequency offset and transmission time of the captured strong signal satellite;

determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite;

and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite.

2. The method of claim 1, wherein determining the Doppler shift of the uncaptured weak signal satellite from the acquired Doppler shift of the acquired strong signal satellite comprises:

determining the Doppler frequency offset estimation value of the current visible satellite by using ephemeris information, coarse time auxiliary time and the reference position coordinate of the receiver of the satellite; the current satellites in view include the acquired strong signal satellites and the uncaptured weak signal satellites;

and determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite and the determined Doppler frequency offset estimation value of the current visible satellite.

3. The method of claim 1, wherein determining the spreading code period and the spreading code phase of the non-acquired weak signal satellite based on the acquired transmission time of the acquired strong signal satellite comprises:

correcting the reference time of the receiver by using the acquired transmission time of the strong signal satellite to obtain the corrected reference time of the receiver;

and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the corrected receiver reference time, the ephemeris information of the satellite and the receiver reference position coordinate.

4. The method of claim 2, wherein determining the doppler frequency offset estimate for the currently visible satellite using the ephemeris information, the coarse time assistance time, and the receiver reference position coordinates for the satellite comprises:

determining the position coordinates of the current visible satellite according to the ephemeris information, the coarse time assistance time and the receiver reference position coordinates of the satellite, and further determining the time t corresponding to the coarse time assistance time of the current visible satellite_kThe speed of (d); then according to the determined current visible satellite at t_kVelocity determination of time of dayAnd the Doppler frequency offset estimation value of the current visible satellite signal.

5. The method of claim 1, wherein the number N1 of the acquired strong signal satellites ranges from 1. ltoreq. N1. ltoreq.3.

6. An apparatus for capturing weak signals, the apparatus comprising: the device comprises a strong signal acquisition module, a Doppler correction module and a spread spectrum code estimation module; wherein,

the strong signal acquisition module is used for acquiring the Doppler frequency offset and the transmission time of the acquired strong signal satellite;

the Doppler correction module is used for determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite;

and the spread spectrum code estimation module is used for determining the spread spectrum code period and the spread spectrum code phase of the uncaptured weak signal satellite according to the acquired transmission time of the captured strong signal satellite.

7. The apparatus of claim 6, wherein the Doppler correction module comprises a Doppler estimation module and a Doppler determination module; wherein,

the Doppler estimation module is used for determining a Doppler frequency offset estimation value of the current visible satellite by using ephemeris information, coarse time assistance time and a receiver reference position coordinate of the satellite; the current satellites in view include the acquired strong signal satellites and the uncaptured weak signal satellites;

and the Doppler determining module is used for determining the Doppler frequency offset of the uncaptured weak signal satellite according to the acquired Doppler frequency offset of the captured strong signal satellite and the determined Doppler frequency offset estimation value of the current visible satellite.

8. The apparatus of claim 6, wherein the spreading code estimation module is configured to use the acquired transmission time of the strong signal satellite to correct a receiver reference time to obtain a corrected receiver reference time; and determining the spreading code period and the spreading code phase of the uncaptured weak signal satellite according to the corrected receiver reference time, the ephemeris information of the satellite and the receiver reference position coordinate.

9. The apparatus of claim 7, wherein the Doppler estimation module is configured to determine the position coordinates of the current visible satellite according to the ephemeris information, the coarse time aiding time, and the receiver reference position coordinates of the satellite, and further determine the time t corresponding to the coarse time aiding time of the current visible satellite_kThe speed of (d); then according to the determined current visible satellite at t_kAnd determining the Doppler frequency offset estimation value of the current visible satellite signal by the speed at the moment.

10. The apparatus of claim 6, wherein the number N1 of strong signal satellites acquired by the strong signal acquisition module has a value in a range of 1 ≦ N1 ≦ 3.