CN114690218B - Method for observing GNSS reflected signals and capturing GNSS direct signals - Google Patents

Abstract

The invention relates to the technical and application fields of GNSS remote sensing, in particular to a method and a system for observing GNSS reflected signals and capturing GNSS direct signals, wherein the method comprises the following steps: setting initial parameters; mixing the intermediate frequency signal of the GNSS signal observed by a certain target to obtain a zero intermediate frequency signal; performing downsampling according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal; the method comprises the steps of controlling the readout of a pre-stored pseudo code of a target observation GNSS signal by a local pseudo code NCO, performing correlation operation on the read local pseudo code and a zero intermediate frequency signal after downsampling to finish pseudo code demodulation, and then performing short-time coherent integration to obtain a short-time coherent integration result; performing FFT operation and incoherent integration operation on the short-time coherent integration result; according to the setting type, delay-doppler plot DDM data is output when set as reflected signal observation, and acquisition results are output when set as direct signal acquisition.

Description

A method for both GNSS reflected signal observation and GNSS direct signal capture

Technical Field

The present invention relates to GNSS remote sensing technology and application fields, and in particular to a method for taking into account both GNSS reflected signal observation and GNSS direct signal capture.

Background technique

GNSS remote sensing technology is a new type of earth remote sensing technology based on the Global Navigation Satellite System (GNSS) that has gradually developed in recent years. It has rapidly gained widespread attention worldwide due to its all-weather, low-cost, high-precision, and global coverage, and many satellite missions based on or including GNSS remote sensing have been successfully implemented at home and abroad. At present, the application scope of GNSS remote sensing technology has covered global neutral atmosphere remote sensing detection, global ionosphere remote sensing detection, global sea surface height measurement, global sea surface wind speed measurement, sea ice measurement, seawater salinity measurement, soil moisture measurement, etc.

One of the cores of GNSS remote sensing technology is to observe GNSS direct signals, GNSS refraction signals and GNSS reflection signals, and obtain corresponding observation quantities, which are finally used to invert the physical characteristic parameters of the corresponding remote sensing detection targets. Among them, GNSS direct signal observation mainly includes capturing, tracking and synchronizing direct signals, and then accurately positioning remote sensing satellites and obtaining the ephemeris of GNSS satellite constellations.

Currently, the use of GNSS reflected signal observation to measure global sea surface wind speed is one of the hot topics in the field of GNSS remote sensing technology and applications. The GNSS reflected signal observation mainly includes local correlation of reflected signals, followed by coherent accumulation and incoherent accumulation to obtain the "Delay-Doppler Map (DDM)", i.e. DDM data, and finally the global sea surface wind speed is inverted based on the DDM data, remote sensing satellite positions and the ephemeris of the GNSS satellite constellation.

However, current GNSS remote sensing detectors usually use two independent system modules to observe GNSS reflected signals and capture GNSS direct signals respectively. This causes GNSS remote sensing detectors designed and developed based on hardware platforms to consume more hardware resources, thereby increasing the cost of GNSS remote sensing detectors. There is no doubt that reducing the hardware resources required for GNSS remote sensing detectors and thus reducing the cost of GNSS remote sensing detectors has important practical significance.

Summary of the invention

The purpose of the present invention is to overcome the defects of the prior art and to propose a method and system for both observing GNSS reflected signals and capturing GNSS direct signals.

In order to achieve the above object, the present invention proposes a method for taking into account both GNSS reflected signal observation and GNSS direct signal capture, the method comprising:

Set initial parameters;

Performing mixing processing on the intermediate frequency signal of a target observation GNSS signal to obtain a zero intermediate frequency signal; performing downsampling processing according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal;

The local pseudo code NCO controls the reading of the pre-stored pseudo code of the target observation GNSS signal, performs correlation operation on the read local pseudo code and the down-sampled zero intermediate frequency signal, completes pseudo code demodulation, and then performs short-time coherent integration to obtain a short-time coherent integration result;

Perform FFT operation and incoherent integration operation on the short-time coherent integration result;

Depending on the setting type, when it is set to reflective signal observation, the delayed Doppler map DDM data is output, and when it is set to direct signal capture, the capture result is output.

As an improvement of the above method, the setting of initial parameters specifically includes:

Configure the control word of the carrier NCO and its initial value;

Configure the control word, initial pseudo code phase τ and signal type of the local pseudo code NCO.

As an improvement of the above method, the control word and initial value of the configuration carrier NCO specifically include:

The control word f _{car_NCO} of the carrier NCO is configured according to the following formula:

Wherein, f _clk represents the system clock frequency and is equal to the sampling frequency f _s of a target observed GNSS signal, W ₁ represents the bit width occupied by f _{car_NCO} , and f _l represents the center frequency of the carrier signal generated by the local carrier NCO, and the carrier signal is realized by a lookup table;

The initial value Ψ of the carrier NCO is configured according to the following formula:

Here, m represents the coefficient of the part less than an integer, which is a real number greater than 1.

As an improvement of the above method, the control word, initial pseudo code phase τ and signal type of the local pseudo code NCO are configured; specifically, the following are included:

Configure the control word f _{code_NCO} of the local pseudo code NCO according to the following formula:

Wherein, W ₂ represents the bit width occupied by f _{code_NCO} , f _code is the frequency of the local pseudo code c _l [n], n represents the chip number, n∈[1, L], and L represents the number of chips contained in one pseudo code period;

The initial pseudo code phase τ is configured according to the following formula:

Wherein, n ₀ is a preset phase offset, which is a non-negative integer and n ₀ ∈[0, L-1];

The signal types are classified according to the GNSS signal modulation types, where the modulation types include BPSK modulation type, BOC (1, 1) modulation type and BOC (2, 1) modulation type.

As an improvement of the above method, the intermediate frequency signal of a target observation GNSS signal is mixed to obtain a zero intermediate frequency signal; and downsampling is performed according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal; specifically comprising:

The intermediate frequency signal r[o] of a target observation GNSS signal is combined with the carrier signal generated by the local carrier NCO Perform mixing to obtain the mixed signal r _m (f _l , o):

Wherein, o represents the sample number of the intermediate frequency signal, and _Ts represents the sample time interval;

The continuous summation downsampling method is adopted to reduce the data rate of the mixed signal r _m (f _l , o) to the preset zero intermediate frequency data rate f _data , and the zero intermediate frequency signal r _d (f _l , k) after the kth downsampling is obtained as follows:

Wherein, T _d represents the time interval of sample data after downsampling operation;

The preset zero intermediate frequency data rate f _data satisfies the following formula:

f _data = D f _code

Wherein, D is a positive integer and D satisfies the Nyquist sampling theorem and signal power requirements.

As an improvement of the above method, the local pseudo code NCO controls the reading of the pseudo code of the target observed GNSS signal stored in advance, performs correlation operation on the read local pseudo code and the down-sampled zero intermediate frequency signal, completes pseudo code demodulation, and then performs short-time coherent integration to obtain a short-time coherent integration result; specifically includes:

Configure the coherent accumulation length N according to the following formula:

N = ceil [(f _data ·T _coh ) / (N _FFT / 2)]

Where, T _coh represents the coherent integration time, N _FFT represents the number of FFT points, which is a positive integer power of 2, and ceil represents rounding up;

The local pseudo code NCO controls the reading of the pre-stored pseudo code of the target observed GNSS signal, performs correlation operation on the read local pseudo code c _l [k-τ] and the down-sampled zero intermediate frequency signal r _d (f _l , k), and then performs short-time coherent integration operation to obtain the pth short-time coherent integration result F (τ; f _l , p):

As an improvement of the above method, the FFT operation and the incoherent integration operation are performed on the short-time coherent integration result; specifically, the method includes:

The number of non-coherent integrations is configured as M, where M is a positive integer;

Perform FFT operation on the short-time coherent integration result to obtain the u-th spectrum line result G(τ, _fl , u, v) of the v-th FFT operation;

Then perform the incoherent integration operation to obtain the z-th M-th incoherent integration result S(τ, _fl , u, z):

As an improvement of the above method, the method according to the setting type, when it is set to reflective signal observation, outputs delayed Doppler map DDM data, and when it is set to direct signal capture, outputs the capture result; specifically includes:

If configured as reflected signal observation, all the values in the two-dimensional numerical matrix corresponding to the incoherent integration result S(τ, _fl , u, z) are output in sequence in the order of {S(τ _i , _fl , u=0, z), S(τ _i , _fl , u=1, z), ..., S(τ _i , _fl , u=N _FFT -1, z), S(τ _i+1 , _fl , u=0, z), ...}, thereby completing the output of the delay Doppler map DDM data, where i is a positive integer;

Otherwise, find the maximum value S _max in S(τ, _fl , u, z), and the pseudo code phase delay τ _max and Doppler spectrum line u _max corresponding to S _max ; then find the average value S _ave in S(τ, _fl , u, z), output S _max , S _ave , τ _max and u _max , thereby completing the output of the capture result.

A system for observing GNSS reflected signals and capturing GNSS direct signals, the system comprising: an initialization module, a mixing and downsampling processing module, a coherent integration module, an FFT and incoherent integration module and a judgment output module; wherein:

The initialization module is used to set initial parameters;

The mixing and downsampling processing module is used to perform mixing processing on the intermediate frequency signal of a target observation GNSS to obtain a zero intermediate frequency signal; and perform downsampling processing according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal;

The coherent integration module is used to control the reading of the pre-stored pseudo code of the target observation GNSS signal by the local pseudo code NCO, perform correlation operation on the read local pseudo code and the down-sampled zero intermediate frequency signal, complete pseudo code demodulation, and then perform short-time coherent integration to obtain a short-time coherent integration result;

The FFT and incoherent integration module is used to perform FFT calculation and incoherent integration calculation on the short-time coherent integration result;

The judgment output module is used to output delayed Doppler map DDM data according to the setting type when it is set to reflection signal observation, and output capture results when it is set to direct signal capture.

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

1. The method and system proposed in the present invention can be used for both GNSS reflected signal observation and GNSS direct signal capture;

2. The method and system proposed by the present invention will reduce the hardware resources required for the GNSS remote sensing detector, thereby reducing the cost of the GNSS remote sensing detector;

3. The method and system proposed in the present invention are conducive to pipeline design, thereby improving the system data throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of a method for taking into account both GNSS reflected signal observation and GNSS direct signal capture according to the present invention;

FIG. 2 is a block diagram of the system structure of the present invention that takes into account both GNSS reflected signal observation and GNSS direct signal capture.

Detailed ways

The method proposed in the present invention for taking into account both GNSS reflected signal observation and GNSS direct signal capture includes the following steps:

Set initial parameters;

Performing mixing processing on the intermediate frequency signal of a target observation GNSS signal to obtain a zero intermediate frequency signal; performing downsampling processing according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal;

The local pseudo code NCO controls the reading of the pre-stored pseudo code of the target observation GNSS signal, performs correlation operation on the read local pseudo code and the down-sampled zero intermediate frequency signal, completes pseudo code demodulation, and then performs short-time coherent integration to obtain a short-time coherent integration result;

Perform FFT operation and incoherent integration operation on the short-time coherent integration result;

Depending on the setting type, when it is set to reflective signal observation, the delayed Doppler map DDM data is output, and when it is set to direct signal capture, the capture result is output.

The technical solution of the present invention is described in detail below with reference to the accompanying drawings and embodiments.

Example 1

As shown in FIG. 1 , a method for taking into account both GNSS reflected signal observation and GNSS direct signal capture is proposed in Embodiment 1 of the present invention, and the specific implementation steps include:

Step S101) Write a pseudo-random noise code (hereinafter referred to as pseudo-code) c _l [n] of a target observed GNSS signal into the pseudo-code RAM for local pseudo-code correlation demodulation, where n represents the nth code chip, and n∈[1, L], where L represents the number of code chips contained in a pseudo-code period.

For example, for the GPS L1CA signal, L=1023; for the BDSB1I signal, L=2046.

Step S102) configure the carrier NCO (Numerically Controlled Oscillator, NCO) control word _{fcar_NCO} and its initial value Ψ

Step S102-1) configures the carrier NCO control word _{fcar_NCO} and calculates it by the following formula:

Wherein, f _clk represents the system clock frequency and is equal to the sampling frequency of the input signal, that is, f _s =f _clk ; W ₁ represents the bit width occupied by the carrier NCO control word f _{car_NCO} , and in this embodiment, W ₁ =28 (unit: bit); f _l represents the locally generated carrier signal—— The center frequency of the local carrier signal is realized by means of a lookup table.

because Therefore, the lookup table consists of two parts: a cosine lookup table and a sinine lookup table, each of which contains 16 integer values. In this embodiment:

The cos lookup table is {3, 3, 2, 0, 0, -2, -3, -3, -3, -3, -2, 0, 0, 2, 3, 3}.

The sin lookup table is {0, -2, -3, -3, -3, -3, -2, 0, 0, 2, 3, 3, 3, 3, 2, 0}.

Step S102-2) The carrier NCO initial value Ψ is calculated by the following formula:

Wherein m represents the coefficient of the part less than an integer, m∈R and m＞1.

Step S103) configures the pseudo code NCO control word f _{code_NCO} and the initial pseudo code phase τ and the signal type. Step S103-1) f _{code_NCO} is calculated by the following formula:

Wherein, W ₂ represents the bit width occupied by the pseudocode NCO control word f _{code_NCO} , and in this embodiment W ₂ =32 (unit: bit); f _code represents the pseudocode frequency of the GNSS signal written in step S101, and the pseudocode NCO generates a pulse signal with a frequency of f _code to enable reading of the pseudocode.

For example, for the GPS L1CA signal, f _code =1.023 MHz; for the BDSB1I signal, f _code =2.046 MHz.

Step S103-2) The initial pseudo code phase τ is calculated by the following formula:

Wherein, n ₀ is a preset phase offset, which is a non-negative integer and n ₀ ∈ [0, L-1], m ∈ R and m>1, and L represents the number of chips contained in one pseudo code period.

Step S103 - 3) The signal type (Sig_type) is mainly classified according to the GNSS signal modulation type, including BPSK modulation type, BOC (1, 1) modulation type, BOC (2, 1) modulation type, etc.

For example, for the BPSK modulation type, no subcarrier is modulated in the signal; for the BOC (1, 1) modulation type, the numerical form of the modulated subcarrier in the signal is {-1, 1}, and the code chip frequency f _BOC = 2f _code ; for the BOC (2, 1) modulation type, the numerical form of the modulated subcarrier in the signal is {-1, 1, -1, 1}, and the code chip frequency f _BOC = 4f _code .

A pulse signal with a frequency of f _BOC is generated by the pseudo code NCO, enabling subcarrier generation of a BOC modulation type signal.

Step S104) configures the zero intermediate frequency data rate f _data , where f _data is calculated by the following formula:

f _data = D f _code (5)

Wherein, D∈ is a positive integer and D satisfies the Nyquist sampling theorem (Nyquist Law) and signal power requirements. For example, for GPS L1CA signal, D＝2 or D＝4, etc.

A pulse signal with a frequency of f _data is generated by the pseudo-code NCO to enable downsampling.

Step S105) configures the coherent accumulation length N, where N is calculated by the following formula:

N = ceil[(f _data ·T _coh )/( _NFFT /2)] (6)

Wherein, T _coh represents the coherent integration time, N _FFT represents the number of FFT points and N _FFT =2 ^a (a∈N ⁺ ). Because the actual coherent integration length cannot exceed the edge of the pseudo code period to avoid signal coherent integration gain loss, the part less than N is padded with zeros. In this embodiment, N _FFT =64.

Step S106) configure the number of non-coherent integration times M, where M∈ is a positive integer.

Step S107) IF signal input and mixing operation. IF signal input means enabling the system to start running.

Step S107-1) The intermediate frequency signal is expressed as:

Wherein, o represents the sample number of the intermediate frequency signal, P represents the power of the intermediate frequency signal, d represents the data, c represents the pseudo code, f _IF represents the intermediate frequency, f _d represents the Doppler frequency, T _s represents the sample time interval and T _s =1/f _s , represents the initial phase, η represents additive white Gaussian noise,/> The local carrier signal generated by the local carrier NCO.

Step S107-2) As mentioned above, the local carrier signal generated by the local carrier NCO is The local carrier signal is mixed with the input signal to obtain the mixed signal r _m (f _l , o):

Step S108) Downsampling operation. The present invention adopts a continuous summation downsampling method to reduce the input signal data rate from _fs (unit sps) to _fdata . The downsampled signal _rd ( _fl , k) is expressed as:

Wherein, k (k∈N) represents the kth sample obtained after the kth downsampling operation, _Td represents the sample data time interval after the downsampling operation and _Td = 1/ _fdata , Δf = _fIF + _fd - _fl , and _ηd represents the noise component.

Step S109) performs correlation operation and short-time coherent integration.

Step S109-1) As described above, the local pseudo code NCO controls the reading of the local pseudo code. The read pseudo code is correlated with the down-sampled signal.

On the one hand, in order to better match the GNSS reflected signal observation and the GNSS direct signal observation and save hardware resources as much as possible, in this embodiment, the number of correlators is 61. On the other hand, in order to reduce the data rate of the correlator post-stage module and thus reduce the computational burden, the 61 parallel correlator channels start the correlation operation in sequence along the shift direction of the pseudo code shift register, that is, the 60th correlator channel - Chl#60 starts the correlation operation first, and the 0th correlator channel - Chl#0 starts the correlation operation last.

Step S109-2) performs short-time coherent integration operation to obtain F(τ, _fl , p):

Wherein, p represents the pth short-time coherent integration result, _TF represents the short-time coherent integration time and _TF = _Tcoh /( _NFFT /2), Δτ represents the phase difference between the local pseudo code and the input signal pseudo code, R(Δτ) represents the pseudo code autocorrelation function, and _ηF represents the noise component.

Step S109-3) Write the short-time coherent integration result into the coherent integration RAM, which contains 61×32 basic storage units, i.e., 61 rows, 32 basic storage units in each row, and each storage unit stores one short-time coherent integration result. The short-time coherent integration result generated by the 0th correlator channel, Chl#0, is stored in the 1st row; the short-time coherent integration result generated by the 1st correlator channel, Chl#1, is stored in the 2nd row, and so on.

Two coherent integration RAMs are used for ping-pong storage, and the chip is selected through the Wr_CS signal. When Wr_CS is logic ‘0’, the short-time coherent integration result is written to the coherent integration RAM chip #1; when Wr_CS is logic ‘1’, the short-time coherent integration result is written to the coherent integration RAM chip #2.

Step S110) performs FFT operation, the number of FFT points is N _FFT , and the number of short-time coherent integration results is N _FFT /2, so zero padding is performed.

Step S110-1) Before performing FFT operation, first read the short-time coherent integration result from the coherent integration RAM, and start reading from the 1st row until the 61st row of data is read, and then switch to another coherent integration RAM to continue reading in the above manner. In this process, the chip is selected by the Rd_CS signal. When Rd_CS is logic '0', RAMChip#2 is read; when Rd_CS is logic '1', RAMChip#1 is read.

Step S110-2) performs FFT operation, and the FFT operation result G (τ, _fl , u, v) is expressed as:

Wherein, v represents the vth FFT operation, u represents the uth spectrum line result obtained by the vth FFT operation (u∈N and u∈[0, _NFFT -1]), T _coh = _NFFT /2· _TF , From the above, it can be concluded that the frequency resolution is _fres = 1/(2T _coh ).

Step S111) performs incoherent integration operation to obtain an incoherent integration result S(τ, _fl , u, z):

Where z(z∈N) represents the result obtained after the z-th M-times incoherent integration. The result after a certain M-times incoherent integration can be simply expressed as S(τ,u). S(τ,u) is a one-dimensional numerical matrix.

Step S111-1) When the first incoherent integration operation among the zth M incoherent integration operations is performed, the signal Non_0 is logic ‘0’, and when the Oth (O∈ a positive integer and O∈[2, M])th incoherent integration operation is performed, the signal Non_0 is logic ‘1’.

Step S111-2) Each intermediate result obtained by the non-coherent integration operation is written into the non-coherent integration RAM. The non-coherent integration RAM contains 61×64 basic storage units, that is, 61 rows, each row has 64 basic storage units, and each storage unit stores one non-coherent integration result.

When the Oth incoherent integration operation is performed in step S111-3), the intermediate result obtained by the O-1th incoherent integration operation needs to be read out from the incoherent integration RAM.

When the system is configured for reflection signal observation, that is, Sys_type is logic ‘0’, go to step S113; Sys_type is logic ‘1’, otherwise go to step S112.

Step S112) Output the capture result. First, find the maximum value in S(τ, u), that is, S _max = max{S(τ, u)}, and the pseudo code phase delay τ _max and Doppler spectrum line u _max corresponding to S _max ; then find the average value in S(τ, u), that is, S _ave = mean{S(τ, u)}; finally output S _max , S _ave , τ _max , u _max , and these four quantities are the capture result.

Step S113) Outputting DDM data means outputting all the numerical values in the two-dimensional numerical matrix corresponding to S(τ,u) in the order of {S(τ _i ,f _l ,u＝0,z),S(τ _i ,f _l ,u＝1,z),...,S(τ _i ,f _l ,u＝N _FFT -1,z),S(τ _i+1 ,f _l,u ＝0,z),...}(i∈N ⁺ ).

Example 2

Embodiment 2 of the present invention proposes a system for both GNSS reflected signal observation and GNSS direct signal capture, which is implemented based on the method of embodiment 1. The system includes: an initialization module, a mixing and downsampling processing module, a coherent integration module, an FFT and incoherent integration module, and a judgment output module; wherein,

The initialization module is used to set initial parameters;

The mixing and downsampling processing module is used to perform mixing processing on the intermediate frequency signal of a target observation GNSS to obtain a zero intermediate frequency signal; and perform downsampling processing according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal;

The coherent integration module is used to control the reading of the pre-stored pseudo code of the target observation GNSS signal by the local pseudo code NCO, perform correlation operation on the read local pseudo code and the down-sampled zero intermediate frequency signal, complete pseudo code demodulation, and then perform short-time coherent integration to obtain a short-time coherent integration result;

The FFT and incoherent integration module is used to perform FFT calculation and incoherent integration calculation on the short-time coherent integration result;

The judgment output module is used to output delayed Doppler map DDM data according to the setting type when it is set to reflection signal observation, and output capture results when it is set to direct signal capture.

The specific system structure block diagram is shown in Figure 2.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the embodiments, it should be understood by those skilled in the art that any modification or equivalent replacement of the technical solutions of the present invention does not depart from the spirit and scope of the technical solutions of the present invention and should be included in the scope of the claims of the present invention.

Claims (6)

1. A method of integrating GNSS reflected signal observation and GNSS direct signal acquisition, the method comprising:

setting initial parameters;

mixing the intermediate frequency signal of the GNSS signal observed by a certain target to obtain a zero intermediate frequency signal; performing downsampling according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal;

The method comprises the steps of controlling the readout of a pre-stored pseudo code of a target observation GNSS signal by a local pseudo code NCO, performing correlation operation on the read local pseudo code and a zero intermediate frequency signal after downsampling to finish pseudo code demodulation, and then performing short-time coherent integration to obtain a short-time coherent integration result;

performing FFT operation and incoherent integration operation on the short-time coherent integration result;

outputting delay Doppler map DDM data when the set is reflected signal observation and outputting a capturing result when the set is direct signal capturing according to the set type;

the initial parameter setting specifically comprises the following steps:

configuring a control word of a carrier NCO and an initial value thereof;

configuring a control word of a local pseudo code NCO, an initial pseudo code phase tau and a signal type;

the control word and the initial value of the configuration carrier NCO specifically comprise:

the control word f _{car_NCO} of the carrier NCO is configured according to:

Wherein f _clk represents the system clock frequency and the sampling frequency f _s,W₁ equal to a certain target observation GNSS signal represents the occupied space of f _{car_NCO}, f _l represents the carrier signal center frequency generated by the local carrier NCO, and the carrier signal is realized by a lookup table;

the initial value ψ of the carrier NCO is configured according to:

Wherein m represents a coefficient of less than the entire circumference portion, and is a real number greater than 1;

the control word of the local pseudo code NCO, the initial pseudo code phase tau and the signal type are configured; the method specifically comprises the following steps:

The control word f _{code_NCO} of the local pseudocode NCO is configured according to:

Wherein W ₂ represents the occupied space of f _{code_NCO}, f _code is the frequency of the local pseudo code c _l [ n ], n represents the chip sequence number, n E [1, L ], L represents the number of chips contained in one pseudo code period;

the initial pseudocode phase τ is configured according to:

Wherein n ₀ is a preset phase offset, is a non-negative integer and n ₀ E [0, L-1];

The signal types are classified according to GNSS signal modulation types, including BPSK modulation type, BOC (1, 1) modulation type, and BOC (2, 1) modulation type.

2. The method for simultaneously observing the reflected signals and capturing the direct signals of the GNSS according to claim 1, wherein the intermediate frequency signal of the GNSS signal observed by a certain target is mixed to obtain a zero intermediate frequency signal; performing downsampling according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal; the method specifically comprises the following steps:

carrier signal generated by intermediate frequency signal r [ o ] of GNSS signal observed by certain target and local carrier NCO Mixing is performed to obtain a mixed signal r _m(f_l, o):

Where o represents intermediate frequency signal sample number, and T _s represents sample time interval;

The method comprises the steps of adopting a continuous summation downsampling mode to reduce the data rate of signals r _m(f_l, o) after mixing to a preset zero intermediate frequency data rate f _data, and obtaining zero intermediate frequency signals r _d(f_l, k) after kth downsampling as follows:

wherein T _d represents the sample data time interval after the downsampling operation;

the preset zero intermediate frequency data rate f _data satisfies the following formula:

f_data＝D·f_code

wherein D is a positive integer and D satisfies nyquist sampling theorem and signal power requirements.

3. The method for simultaneously observing the reflected signal and capturing the direct signal of the GNSS according to claim 2, wherein the local pseudo code NCO controls the pre-stored pseudo code of the target observed GNSS signal to be read out, the read-out local pseudo code and the zero intermediate frequency signal after downsampling are subjected to correlation operation to complete pseudo code demodulation, and then short-time coherent integration is carried out to obtain a short-time coherent integration result; the method specifically comprises the following steps:

the coherent accumulation length N is configured according to:

N＝ceil[(f_data·T_coh)/(N_FFT/2)]

Wherein T _coh represents the coherent integration time, N _FFT represents the FFT point number, which is a positive integer power of 2, ceil represents the rounding up;

The readout of the pre-stored pseudo code of the target observation GNSS signal is controlled by a local pseudo code NCO, the read local pseudo code c _l [ k-tau ] and the zero intermediate frequency signals r _d(f_l, k after downsampling are subjected to correlation operation, and then short-time coherent integration operation is performed, so that a p-th short-time coherent integration result F (tau, F _l, p) is obtained:

4. A method for both GNSS reflected signal observation and GNSS direct signal acquisition according to claim 3, wherein said performing FFT operations and incoherent integration operations on short-time coherent integration results; the method specifically comprises the following steps:

the number of incoherent integration is configured as M, and M is a positive integer;

performing FFT operation on the short-time coherent integration result to obtain a nth spectral line result G (tau, f _l, u, v) of the nth FFT operation;

And performing incoherent integration operation to obtain a z M-th incoherent integration result S (tau, f _l, u, z):

5. the method for simultaneously observing reflected signals and capturing direct signals of GNSS according to claim 4, wherein the delay Doppler map DDM data is output when the reflected signals are observed and the capturing result is output when the direct signals are captured according to the setting type; the method specifically comprises the following steps:

If the configuration is reflected signal observation, outputting all values in a two-dimensional value matrix corresponding to a non-coherent integration result S (tau, f _l, u, z) in sequence of {S(τ_i,f_l,u＝0,z),S(τ_i,f_l,u＝1,z),…,S(τ_i,f_l,u＝T_FFT-1,z),S(τ_i+1,f_l,u＝0,z),…}, so as to finish outputting delay Doppler map DDM data, wherein i is a positive integer;

Otherwise, find the maximum value S _max in S (τ, f _l, u, z), and the pseudo code phase delay τ _max and doppler line u _max corresponding to S _max; the average value S _ave in S (τ, f _l, u, z) is found again, and the outputs S _max、S_ave、τ_max and u _max are outputted, thereby completing the output of the captured result.

6. A system based on the method of claim 1 for both GNSS reflected signal observation and GNSS direct signal acquisition, the system comprising: the device comprises an initialization module, a mixing and downsampling processing module, a coherent integration module, an FFT and incoherent integration module and a judging output module; wherein,

The initialization module is used for setting initial parameters;

the mixing and downsampling processing module is used for carrying out mixing processing on an intermediate frequency signal of a certain target observation GNSS to obtain a zero intermediate frequency signal; performing downsampling according to a preset zero intermediate frequency data rate to obtain a downsampled zero intermediate frequency signal;

The coherent integration module is used for controlling the readout of the pre-stored pseudo code of the target observation GNSS signal by the local pseudo code NCO, carrying out correlation operation on the read local pseudo code and the zero intermediate frequency signal after downsampling to complete pseudo code demodulation, and then carrying out short-time coherent integration to obtain a short-time coherent integration result;

the FFT and incoherent integration module is used for carrying out FFT operation and incoherent integration operation on the short-time coherent integration result;

And the judging and outputting module is used for outputting delay Doppler image DDM data according to the setting type when the setting is set to be reflected signal observation and outputting a capturing result when the setting is set to be direct signal capturing.