CN107643527B - GPS (global positioning system) common-view signal simulation generation method and GPS common-view signal simulator - Google Patents

GPS (global positioning system) common-view signal simulation generation method and GPS common-view signal simulator Download PDF

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CN107643527B
CN107643527B CN201710806122.3A CN201710806122A CN107643527B CN 107643527 B CN107643527 B CN 107643527B CN 201710806122 A CN201710806122 A CN 201710806122A CN 107643527 B CN107643527 B CN 107643527B
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CN107643527A (en
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纪元法
刘迎
符强
孙希延
欧阳缮
林绍灏
付文涛
郭小娟
李有明
蔚保国
甘兴利
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Guilin University of Electronic Technology
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Abstract

The invention is suitable for the field of navigation and provides a GPS (global positioning system) common-view signal simulation generation method and a GPS common-view signal simulator. The method comprises the following steps: receiving ephemeris parameters and parameter information set by a user; calculating the positions of all satellites according to the ephemeris parameters and the simulation time; respectively calculating the elevation angles of the two observation stations relative to any satellite, and respectively determining all the satellites visible to the two observation stations; determining satellites which are visible at the same time for two observation stations, and taking the satellites which are visible at the same time for the two observation stations as common-view satellites of the two observation stations; generating a corresponding GPS common-view signal navigation message for each common-view satellite; and sequentially carrying out spread spectrum modulation and carrier modulation on the GPS common-view satellite navigation message of each common-view satellite to generate a GPS common-view satellite intermediate frequency signal. The invention realizes the simulation of the GPS common-view signal, and has simple method and good expandability.

Description

GPS (global positioning system) common-view signal simulation generation method and GPS common-view signal simulator
Technical Field
The invention belongs to the field of navigation, and particularly relates to a GPS (global positioning system) common-view signal simulation generation method and a GPS common-view signal simulator.
Background
Since GPS has a high-precision time system and time service function, it has been regarded as important to compare time with GPS since the GPS system was built. There are four main methods for accurate time comparison using GPS: one-way method, satellite two-way comparison method, two-station common view method and short-base VLBI technology. The one-way method is the simplest method, and can meet the timing precision requirement of most users, so the method is developed and applied firstly. However, the one-way method can only achieve the precision of about 20ns, and cannot meet the requirement of time comparison between modern high-precision laboratories. On the basis, a common view method is proposed. The common-view method can eliminate or weaken common errors between two stations, thereby greatly improving the precision of time comparison. Currently, the GPS co-vision method is the most widely used comparison means in many time systems including international atomic time.
The GPS co-view method is based on the simultaneous (to the nearest second) tracking of the same satellite by the GPS receivers of two observers at different locations. The basic principle is as follows: according to a global GPS common view table provided by BIPM, two common view observation stations select common view tracking time and a tracking satellite and perform tracking observation in the selected time, so that the time difference between a local clock and a GPS satellite clock is measured, the clock difference between the local clock and the GPS system time is obtained after a series of corrections, then the two stations exchange data, and the data is the tracking result of the two stations to the same satellite at the same time, so that the difference between the two stations can obtain the high-precision relative clock difference between the two stations, and the time comparison between the two stations is realized.
The research on the GPS common-view time comparison requires observing the same satellite at two different places, the observation condition is easily interfered by the outside (such as weather), and then the observation is carried out at two different observation stations, so that the research on the common-view time comparison is inconvenient.
Disclosure of Invention
The invention aims to provide a GPS (global positioning system) common-view signal simulation generation method, a computer readable storage medium and a GPS common-view signal simulator, aiming at solving the problems that the GPS common-view time comparison is easily interfered by the outside world and the common-view time comparison is inconvenient to study due to observation at two different observation stations in the prior art.
In a first aspect, the present invention provides a method for analog generation of a GPS common view signal, where the method includes:
receiving ephemeris parameters and parameter information set by a user, wherein the parameter information set by the user at least comprises the positions of two observation stations, an elevation threshold of the two observation stations and simulation time;
calculating the positions of all satellites according to the ephemeris parameters and the simulation time;
respectively calculating the elevation angles of the two observation stations relative to any satellite according to the positions of the two observation stations and the positions of all satellites, and respectively determining all satellites visible to the two observation stations according to the elevation angles of the two observation stations relative to any satellite and the elevation angle thresholds of the two observation stations;
determining satellites which are visible at the two observation stations at the same time according to all visible satellites of the two observation stations, and taking the satellites which are visible at the two observation stations at the same time as common-view satellites of the two observation stations;
generating a corresponding GPS common-view signal navigation message for each common-view satellite;
and sequentially carrying out spread spectrum modulation and carrier modulation on the GPS common-view signal navigation message of each common-view satellite to generate a GPS common-view intermediate frequency signal.
In a second aspect, the present invention provides a computer-readable storage medium, which stores a computer program, which when executed by a processor, implements the steps of the GPS co-view signal simulation generation method as described above.
In a third aspect, the present invention provides a GPS common view signal simulator, including:
one or more processors;
a memory; and
one or more computer programs, wherein the one or more computer programs are stored in the memory and configured to be executed by the one or more processors, which when executed perform the steps of the method of analog generation of GPS co-view signals as described above.
In the invention, after ephemeris parameters and parameter information set by a user are received, the positions of all satellites are calculated, all satellites visible to two observation stations are determined, the satellites visible to the two observation stations at the same time are used as common-view satellites of the two observation stations, a corresponding GPS common-view signal navigation message is generated for each common-view satellite, and the GPS common-view signal navigation message of each common-view satellite is subjected to spread spectrum modulation and carrier modulation in sequence to generate a GPS common-view intermediate frequency signal. Therefore, the method realizes the simulation of the GPS common-view signal, and has simple method and good expandability. The simulated GPS common-view signal provides a simulation signal source and a corresponding analysis tool for research of an experimental system, test of customer premise equipment and performance evaluation.
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Fig. 1 is a flowchart of a GPS co-view signal simulation generation method according to an embodiment of the present invention.
FIG. 2 is a schematic elevation view of an observation station relative to a satellite.
Fig. 3 is a diagram of a GPS navigation message format.
Fig. 4 is a flowchart of S106.
FIG. 5 is a logic diagram of a C/A code generator.
Fig. 6 is a specific structural block diagram of a GPS co-view signal simulator according to a third embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In order to explain the technical means of the present invention, the following description will be given by way of specific examples.
The first embodiment is as follows:
referring to fig. 1, a method for generating a GPS common view signal in a simulation mode according to an embodiment of the present invention includes the following steps: it should be noted that, if the result is substantially the same, the method for generating the GPS co-view signal in an analog manner according to the present invention is not limited to the flow sequence shown in fig. 1.
S101, ephemeris parameters and parameter information set by a user are received, wherein the parameter information set by the user at least comprises the positions of the two observation stations, the elevation angle thresholds of the two observation stations and simulation time.
In the first embodiment of the present invention, the observation station is actually a satellite navigation receiver.
The positions of the two observation stations may specifically be the positions of the two observation stations in the geodetic coordinate system, for example the coordinates of the first and second observation stations are (30, 50, 50) and (30.18, 50, 50), respectively. The parameter information set by the user may further include an intermediate frequency and a sampling frequency.
The ephemeris receiving parameters are specifically: ephemeris parameters are acquired by reading in a RINEX (Receiver dependent Exchange Format) file. The specific implementation process is as follows:
initializing relevant variables according to the characteristics of the ephemeris data for accessing ephemeris parameters;
opening a RINEX file to acquire the starting position of ephemeris data;
and acquiring the number of data lines through the cycle statements, calculating the number of satellites, and storing the data into the structure array according to the serial numbers of the satellites.
And S102, calculating the positions of all the satellites according to the ephemeris parameters and the simulation time.
In the first embodiment of the present invention, S102 may specifically include the following steps:
obtaining the transmission time tr from the time t of the current moment, wherein the tr is t-0.075 seconds, and the simulation time is a certain moment in the simulation time period and is essentially the time t of the current moment of the user;
calculating the planned time t of the transmission time at the current moment relative to the ephemeris at the momentk，tk＝tr-toeWherein, toeIs the ephemeris reference time;
the semimajor axis a of the satellite is calculated from the square root of the semimajor axis in the satellite ephemeris,
Figure GDA0002458138780000041
calculating the average angular velocity n of the satellite according to the Kepler's third law0，
Figure GDA0002458138780000042
Wherein Kepler's third law is
Figure GDA0002458138780000043
Wherein T represents the operating period of the satellite, GM and μ both represent gravitational constants of the earth, and the average angular velocity of the satellite
Figure GDA0002458138780000044
Calculating the corrected average angular velocity n, n being n0+ Δ n, where Δ n is a correction value broadcast in ephemeris;
according to the mean-near point angle M of the reference time broadcast in the ephemeris0And calculating the mean approximate point angle M from the corrected mean angular velocity nk，Mk＝M0+ntk；
According to a relation formula M of a flat near point angle and a partial near point angle given in a Kepler equationk＝Ek-esinEkBy iteratively solving for the angle of approach EkWherein e is the elliptical orbital eccentricity;
calculating the true near point angle v of the signal emission momentk，
Figure GDA0002458138780000051
Calculating the lifting point angular distance phi of signal transmitting time according to the calculated true near point angle and the near point angular distance broadcast in ephemerisk，Φk＝vk+ ω, where ω is the orbital perigee angular separation;
according to the lift-off point angular distance phikAnd calculating a perturbation correction term of signal transmitting time according to the amplitude of the harmonic correction number broadcasted in the ephemeris:
uk＝cussin2Φk+cuccos2Φk；
rk＝crssin2Φk+crccos2Φk；
ik＝cissin2Φk+ciccos2Φk(ii) a Wherein u iskIs latitude argument correction term rkIs a radial correction term, ikIs a track inclination correction term, cusIs the rising point angular distance sine harmonic correction amplitude, crsIs a radial sinusoidal harmonic correction amplitude, cisIs track inclination sine harmonic correction amplitude, cucIs the rising-crossing angle distance cosine harmonic correction amplitude, crcIs the radial cosine harmonic correction amplitude, cicIs track inclination cosine harmonic correction amplitude;
calculating corrected true paraxial angle ukRadial direction rkAnd track inclination angle ik：
uk＝Φk+uk；
rk＝A(1-ecosEk)+rk；
ik＝i0+ik+(IDOT)tk(ii) a Wherein i0Is toeThe track inclination angle;
calculating the position (x) of the satellite in the orbital plane at the moment of signal transmissionk′，yk′)：
Figure GDA0002458138780000052
Calculating the rising point right ascension omega of the signal emission momentk，
Figure GDA0002458138780000053
Wherein the content of the first and second substances,
Figure GDA0002458138780000054
is the angular velocity constant of the earth's rotation,
Figure GDA0002458138780000055
is the rate of change of the right ascension of the orbit at the intersection point with respect to time, omega0Is the right ascension of the orbit intersection point when the week time is equal to 0;
calculating the coordinates (x) of the satellite in the geocentric coordinate systemk，yk，zk)：
Figure GDA0002458138780000061
S103, respectively calculating the elevation angles of the two observation stations relative to any satellite according to the positions of the two observation stations and the positions of all satellites, and respectively determining all the satellites visible to the two observation stations according to the elevation angles of the two observation stations relative to any satellite and the elevation angle thresholds of the two observation stations.
In the first embodiment of the present invention, a schematic diagram of calculating the elevation angles of two observation stations with respect to any satellite is shown in fig. 2. The specific steps for determining that the satellite is visible to the observation station are:
and comparing the elevation angle of the observation station relative to the satellite with the elevation angle threshold of the observation station, and determining that the satellite is visible to the observation station if the elevation angle of the observation station relative to the satellite is greater than the elevation angle threshold of the observation station. For example the elevation threshold of the observation station may be 5 degrees.
And S104, determining satellites which are visible at the two observation stations at the same time according to all visible satellites of the two observation stations, and taking the satellites which are visible at the two observation stations at the same time as common-view satellites of the two observation stations.
In the first embodiment of the present invention, S104 may specifically include the following steps:
sequentially traversing the satellites visible to one observation station one by the satellites visible to the other observation station;
the same satellite that is visible to one of the observatory stations as the satellite that is visible to the other observer station is taken as the common-view satellite for both observatory stations. The number of co-view satellites may be one or more.
In the first embodiment of the present invention, S103 and S104 may be executed once when the step of the GPS co-view signal simulation generation method is started, and may be executed again every predetermined time, for example, once every half hour.
And S105, generating a corresponding GPS common-view signal navigation message for each common-view satellite.
In the first embodiment of the present invention, S105 specifically is: and for each co-view satellite, writing a corresponding GPS co-view signal navigation message according to the ICD file of the GPS.
Fig. 3 is a diagram of a GPS navigation message format.
The GPS navigation message is sent in 5 subframes of 300 bits. Each subframe itself consists of 10 words of 30 bits. The last 6 bits of each word in the GPS navigation message are used for parity checking to provide the user equipment with the ability to detect bit errors during demodulation, using a (32, 26) hamming code. The 5 subframes are sequentially transmitted from subframe 1. Subframe 4 and subframe 5 each contain 25 pages, so in the first cycle of 5 subframes, page 1 of subframe 4 and subframe 5 is broadcast, in the next cycle of 5 subframes, page 2 of subframe 4 and subframe 5 is broadcast, and so on.
The navigation message coding algorithm is subdivided into the following modules according to the specific structure of the navigation message:
1. checking an algorithm;
TLM word encoding algorithm;
HOW word encoding algorithm;
4. basic text coding algorithm (overall coding algorithm of subframes 1, 2, 3);
5. and (4) a complete text coding algorithm.
The TLM word encoding algorithm and the HOW word encoding algorithm are simpler, and only the Z count and the subframe number need to be dynamically provided because the content is relatively fixed. For the basic telegraph text coding, according to parameters provided by an interface control document of the GPS, the ephemeris parameters read from the broadcast ephemeris file are divided by different coefficients respectively, extracted according to bits and stored in an array.
And S106, sequentially carrying out spread spectrum modulation and carrier modulation on the GPS common-view signal navigation message of each common-view satellite to generate a GPS common-view intermediate frequency signal.
According to the theory of satellite navigation, the final generated GPS common view intermediate frequency signal is as follows:
Figure GDA0002458138780000071
wherein i denotes a different satelliteStar, PcRepresenting the average power, x, of the C/A code signal(i)(t) C/A code level value, D, generated by satellite i(i)(t) represents a GPS common-view signal navigation message corresponding to the common-view satellite i, f represents a carrier frequency, and theta represents an initial phase of the carrier.
As can be seen from the above formula, in the process of generating the intermediate frequency signal, the GPS co-vision signal navigation message described in S105 is firstly subjected to spread spectrum modulation, i.e. X(i)(t)D(i)(t), followed by carrier modulation with a locally generated cosine signal cos (2 π ft + θ).
In the process of spread spectrum modulation, firstly generating a corresponding C/A code table for each common-view satellite, then calculating a code NCO frequency control word, finally accumulating overflow values of the code NCO frequency control word, searching the C/A code table to generate a C/A code corresponding to the common-view satellite, carrying out XOR addition operation with a GPS common-view signal navigation message, and using a symbol to carry out XOR addition operation
Figure GDA0002458138780000081
And the spread spectrum modulation is completed, and the combined code of the GPS common-view signal navigation message and the C/A code is obtained.
In the process of carrier modulation, local carriers with corresponding frequencies and phases are generated according to the control of carrier NCO frequency control words, and then BPSK modulation is carried out on the generated local carriers through a combined code of GPS (global positioning system) co-view signal navigation messages and C/A (code/analog) codes obtained through spread spectrum modulation, so that intermediate frequency signals are obtained.
Referring to fig. 4, in the first embodiment of the present invention, S106 specifically includes the following steps:
and S1061, generating a corresponding C/A code table for each co-view satellite.
The GPS navigation system adopts a Code Division Multiple Access (CDMA) mode to distinguish satellites, C/A code sequences used by each satellite are different, in order to ensure that each satellite does not interfere with each other, Gold (Gold) codes with good autocorrelation and cross-correlation performance are selected as C/A codes for GPS signals, the period of one complete C/A code is 1023 chips, the chip rate is 1.023Mcps, and the duration of one C/A code period is 1ms (1023/1.023 Mcps).
As shown in fig. 5, a pseudorandom sequence of 1023 bits in maximum length is generated by two ten-stage shift registers G1 and G2 (initially set to 1) under the clock control of 1.023 MHz. G1 and G2 can be expressed as polynomials:
Figure GDA0002458138780000082
in the formula xiThe output value of the ith stage of the shift register is added modulo two and then fed back to the first stage as input. The G1 shift register selects the 3 rd and 10 th stages as feedback taps, and the G2 shift register selects the 2 nd, 3 rd, 6 th, 8 th, 9 th and 10 th stages as feedback taps. The G1 shift register outputs the 10 th stage register data at the rate of 1.023Mcps, the G2 shift register selects the modulo two sum value of two registers as output, and finally the G1 direct output sequence and the G2 delayed output sequence are modulo two summed to obtain the C/A code sequence at the rate of 1.023 Mcps.
Known from the Gold code property: the pseudo-random sequence is the same as the pseudo-random sequence only if the polynomial expressions are the same, and the pseudo-random sequence is the same as the pseudo-random sequence only if the phase changes, regardless of the fact that the data is output in the last stage or after modulo two and any two stages are output as output. The GPS satellite obtains 1025 different tap selection combinations through the difference of two tap selections of the G2 shift register, and 32 sequences with good autocorrelation and poor cross correlation are preferably selected from the tap selection combinations to be used as C/A code sequences of 32 satellites. Thus the C/a code sequence for each satellite is only related to the tap selection of the G2 shift register. The relationship is shown in Table 1:
TABLE 1 GPS PRN (Pseudo-Random Noise) number vs. G2 tap
Figure GDA0002458138780000091
And S1062, calculating code NCO frequency control words and carrier NCO frequency control words of each co-view satellite.
As can be seen from the foregoing, the key to generate the GPS common view intermediate frequency signal is to calculate a code NCO frequency control word and a carrier NCO frequency control word to generate a corresponding C/a code and a local carrier, thereby completing spread spectrum modulation and carrier modulation.
The calculating of the code NCO frequency control word of each co-view satellite may specifically include the following steps:
calculating the geometric distance between the common-view satellite and the observation station according to the position of the common-view satellite and the position of the observation station, and correcting by using clock error to obtain a pseudo-range value rho;
the code phase of the code NCO frequency control word for each co-view satellite is calculated,
Figure GDA0002458138780000092
the code phase comprises an integer code phase and a decimal code phase, and the decimal part of the integer code phase is taken
Figure GDA0002458138780000093
And according to
Figure GDA0002458138780000094
Calculating an initial value CodeNcoAc1 of the code NCO accumulator, wherein N is the bit width of a phase accumulator in a code NCO frequency control word; in the first embodiment of the present invention, the word length of the carrier and code phase accumulator is set to 36 bits;
calculating code NCO frequency control word Kbias_codeAs shown in the following formula:
Figure GDA0002458138780000101
wherein, IFcodeRepresenting the code intermediate frequency, fclkIs the system clock frequency;
on the basis of calculating the code NCO frequency control word, adding the correction quantity of the code NCO frequency control word to obtain the code NCO frequency control word at the current moment, wherein the formula is as follows:
Kcode＝Kbias_code+Kdelta_code
wherein, Kdelta_codeThe correction quantity is a code NCO frequency control word correction quantity and is calculated according to the following formula:
Δρ＝ρt-ρ0；
Figure GDA0002458138780000102
where ρ is0Indicating the value of the pseudorange, p, at the previous time instanttA value of a pseudo-range representing a current time, Δ ρ being a rate of change of the pseudo-range, λcodeRepresents the wavelength of the C/A code;
updating the code NCO accumulator initial value CodeNcoAc1 to obtain the code NCO accumulated value CodeNcoAc2, CodeNcoAc2 ═ CodeNcoAc1+ Kcode。
The calculating the carrier NCO frequency control word of each co-view satellite may specifically include the following steps:
calculating carrier phase
Figure GDA0002458138780000103
Figure GDA0002458138780000104
Wherein, the lambda is the wavelength of the carrier wave,
Figure GDA0002458138780000105
the unit of (1) is radian, rho is a pseudo range value, the carrier phase comprises the whole-cycle number of the carrier and the small-cycle number of the carrier, and then 2 pi is subjected to complementation to obtain the small-cycle part of the carrier less than 2 pi
Figure GDA0002458138780000106
And according to
Figure GDA0002458138780000107
An initial value of the carrier NCO accumulator, CarNcoAc1, is calculated, where N is the bit width of the phase accumulator in the carrier NCO. In the first embodiment of the present invention, the word length of the carrier and code phase accumulator is set to 36 bits;
assuming that there is no relative motion between the satellite and the satellite navigation receiver, i.e. no doppler effect, the carrier NCO frequency control word KbiasThe calculation formula of (2) is as follows:
Figure GDA0002458138780000108
wherein, the IF is the carrier center frequency f of the set GPS common vision intermediate frequency signalclkIs the system clock frequency, N isThe bit width of the phase accumulator in the carrier NCO can be seen from the above formula, the carrier center frequency and the system clock frequency are fixed values set in the software, so the carrier NCO frequency control word obtained thereby is also a fixed value, so the actual carrier NCO frequency control word is the sum of the carrier NCO frequency control word and the correction quantity of the carrier NCO frequency control word, as shown in the following formula: kcarr＝Kbias+Kdelta，KdeltaIs the carrier NCO frequency control word correction, which is calculated according to the following formula: Δ ρ ═ ρt-ρ0，
Figure GDA0002458138780000111
Where ρ is0Indicating the value of the pseudorange, p, at the previous time instanttThe pseudo range value at the current moment is represented, delta rho is the pseudo range change rate, and lambda represents the wavelength of a carrier wave;
updating the initial value of the carrier NCO accumulator CarNcoAc1 to obtain the carrier NCO accumulated value CarNcoAc2, CarNcoAc2 ═ CarNcoAc1+ Kcarr；
The local carrier phase theta at the current time instant is calculated,
Figure GDA0002458138780000112
and S1063, sequentially performing spread spectrum modulation and carrier modulation on the GPS common-view signal navigation message of each common-view satellite to generate a GPS common-view intermediate frequency signal.
S1063 specifically includes the following steps:
when the code NCO accumulated value CodeNcoAc2 is more than or equal to 2NThen, the accumulated overflow value CodeNcoAc3 of the code NCO frequency control word is obtained, CodeNcoAc3 ═ CodeNcoAc2-2N；
Accumulating the accumulated overflow value CodeNcoAc3 of the code NCO frequency control word and searching a C/A code table to obtain a corresponding C/A code chip value;
carrying out XOR addition operation on the C/A code and a corresponding GPS common-view signal navigation message to finish spread spectrum modulation;
the cosine of the local carrier phase theta is multiplied by the amplitude to generate a local carrier in a simulation mode;
and the combined code obtained after the GPS common-view signal navigation message modulates the C/A code carries out BPSK modulation on the local carrier, and generates a GPS common-view intermediate frequency signal corresponding to each common-view satellite.
In the first embodiment of the present invention, the GPS common view signal simulation generation method may be implemented based on a Matlab platform.
Example two:
the second embodiment of the present invention further provides a computer-readable storage medium, where a computer program is stored, and when the computer program is executed by a processor, the steps of the method for generating a GPS co-view signal simulation according to the first embodiment of the present invention are implemented.
Example three:
fig. 6 shows a specific structural block diagram of a GPS co-view signal simulator provided in the third embodiment of the present invention, in which a GPS co-view signal simulator 100 includes:
one or more processors 101;
a memory 102; and
one or more computer programs, wherein the one or more computer programs are stored in the memory 102 and configured to be executed by the one or more processors 101, and when the computer programs are executed by the processors 101, the steps of the GPS co-view signal simulation generation method provided in the embodiment of the present invention are implemented.
In the embodiment of the invention, after ephemeris parameters and parameter information set by a user are received, the positions of all satellites are calculated, all satellites visible to two observation stations are determined, the satellites visible to the two observation stations at the same time are used as common-view satellites of the two observation stations, a corresponding GPS common-view signal navigation message is generated for each common-view satellite, and the GPS common-view signal navigation messages of each common-view satellite are subjected to spread spectrum modulation and carrier modulation in sequence to generate GPS common-view intermediate frequency signals. Therefore, the method realizes the simulation of the GPS common-view signal, and has simple method and good expandability. The simulated GPS common-view signal provides a simulation signal source and a corresponding analysis tool for research of an experimental system, test of customer premise equipment and performance evaluation.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (7)

1. A GPS common-view signal simulation generation method is characterized by comprising the following steps:
receiving ephemeris parameters and parameter information set by a user, wherein the parameter information set by the user at least comprises the positions of two observation stations, an elevation threshold of the two observation stations and simulation time;
calculating the positions of all satellites according to the ephemeris parameters and the simulation time;
respectively calculating the elevation angles of the two observation stations relative to any satellite according to the positions of the two observation stations and the positions of all satellites, and respectively determining all satellites visible to the two observation stations according to the elevation angles of the two observation stations relative to any satellite and the elevation angle thresholds of the two observation stations;
determining satellites which are visible at the two observation stations at the same time according to all visible satellites of the two observation stations, and taking the satellites which are visible at the two observation stations at the same time as common-view satellites of the two observation stations;
generating a corresponding GPS common-view signal navigation message for each common-view satellite;
sequentially carrying out spread spectrum modulation and carrier modulation on the GPS common-view signal navigation message of each common-view satellite to generate a GPS common-view intermediate frequency signal;
the step of sequentially performing spread spectrum modulation and carrier modulation on the GPS common-view signal navigation message of each common-view satellite to generate a GPS common-view intermediate frequency signal specifically comprises the following steps:
generating a corresponding C/A code table aiming at each co-view satellite;
calculating code NCO frequency control words and carrier NCO frequency control words of each co-view satellite;
sequentially carrying out spread spectrum modulation and carrier modulation on the GPS common-view signal navigation message of each common-view satellite to generate a GPS common-view intermediate frequency signal;
the specific calculation of the code NCO frequency control word of each co-view satellite comprises the following steps:
calculating the geometric distance between the common-view satellite and the observation station according to the position of the common-view satellite and the position of the observation station, and correcting by using clock error to obtain a pseudo-range value rho;
the code phase of the code NCO frequency control word for each co-view satellite is calculated,
Figure FDA0002731862330000011
the code phase comprises an integer code phase and a decimal code phase, and the decimal part of the integer code phase is taken
Figure FDA0002731862330000012
And according to
Figure FDA0002731862330000021
Calculating an initial value CodeNcoAc1 of the code NCO accumulator, wherein N is the bit width of a phase accumulator in a code NCO frequency control word;
calculating code NCO frequency control word Kbias_codeAs shown in the following formula:
Figure FDA0002731862330000022
wherein, IFcodeRepresenting the code intermediate frequency, fclkIs the system clock frequency;
on the basis of calculating the code NCO frequency control word, adding the correction quantity of the code NCO frequency control word to obtain the code NCO frequency control word K at the current momentcodeAs shown in the following formula: kcode＝Kbias_code+Kdelta_codeWherein, K isdelta_codeThe correction quantity is a code NCO frequency control word correction quantity and is calculated according to the following formula:
Δρ＝ρt-ρ0；
Figure FDA0002731862330000023
where ρ is0Indicating the value of the pseudorange, p, at the previous time instanttA value of a pseudo-range representing a current time, Δ ρ being a rate of change of the pseudo-range, λcodeRepresents the wavelength of the C/A code;
updating the code NCO accumulator initial value CodeNcoAc1 to obtain the code NCO accumulated value CodeNcoAc2, CodeNcoAc2 ═ CodeNcoAc1+ Kcode；
The specific calculation of the carrier NCO frequency control word of each co-view satellite comprises the following steps:
calculating carrier phase
Figure FDA0002731862330000024
Figure FDA0002731862330000025
Wherein, the lambda is the wavelength of the carrier wave,
Figure FDA0002731862330000026
the unit of (1) is radian, rho is a pseudo range value, the carrier phase comprises the whole-cycle number of the carrier and the small-cycle number of the carrier, and then 2 pi is subjected to complementation to obtain the small-cycle part of the carrier less than 2 pi
Figure FDA0002731862330000027
And according to
Figure FDA0002731862330000028
Calculating an initial value CarNcoAc1 of a carrier NCO accumulator, wherein N is the bit width of a phase accumulator in the carrier NCO;
assuming that there is no relative motion between the satellite and the satellite navigation receiver, i.e. no doppler effect, the carrier NCO frequency control word KbiasThe calculation formula of (2) is as follows:
Figure FDA0002731862330000029
wherein, the IF is the carrier center frequency f of the set GPS common vision intermediate frequency signalclkThe system clock frequency is adopted, and N is the bit width of a phase accumulator in a carrier NCO;
the actual carrier NCO frequency control word is the sum of the carrier NCO frequency control word and the correction quantity of the carrier NCO frequency control word, and is shown as the following formula: kcarr＝Kbias+Kdelta，KdeltaIs carrier NCO frequencyA control word correction amount calculated according to: Δ ρ ═ ρt-ρ0，
Figure FDA0002731862330000031
Where ρ is0Indicating the value of the pseudorange, p, at the previous time instanttThe pseudo range value at the current moment is represented, delta rho is the pseudo range change rate, and lambda represents the wavelength of a carrier wave;
updating the initial value of the carrier NCO accumulator CarNcoAc1 to obtain the carrier NCO accumulated value CarNcoAc2, CarNcoAc2 ═ CarNcoAc1+ Kcarr；
The local carrier phase theta at the current time instant is calculated,
Figure FDA0002731862330000032
the method for generating the GPS common-view intermediate frequency signal by sequentially performing spread spectrum modulation and carrier modulation on the GPS common-view signal navigation message of each common-view satellite specifically comprises the following steps:
when the code NCO accumulated value CodeNcoAc2 is more than or equal to 2NThen, the accumulated overflow value CodeNcoAc3 of the code NCO frequency control word is obtained, CodeNcoAc3 ═ CodeNcoAc2-2N；
Accumulating the accumulated overflow value CodeNcoAc3 of the code NCO frequency control word and searching a C/A code table to obtain a corresponding C/A code chip value;
carrying out XOR addition operation on the C/A code and a corresponding GPS common-view signal navigation message to finish spread spectrum modulation;
the cosine of the local carrier phase theta is multiplied by the amplitude to generate a local carrier in a simulation mode;
and the combined code obtained after the GPS common-view signal navigation message modulates the C/A code carries out BPSK modulation on the local carrier, and generates a GPS common-view intermediate frequency signal corresponding to each common-view satellite.
2. The method of claim 1, wherein the calculating the positions of all satellites based on the ephemeris parameters and the simulation times specifically comprises:
obtaining the transmitting time tr from the time t of the current moment, wherein the tr is t-0.075 seconds;
calculating the current time of dayThe time tr of flight relative to the planned time t of the ephemeris at that momentk，tk＝tr-toeWherein, toeIs the ephemeris reference time;
the semimajor axis a of the satellite is calculated from the square root of the semimajor axis in the satellite ephemeris,
Figure FDA0002731862330000033
calculating the average angular velocity n of the satellite according to the Kepler's third law0，
Figure FDA0002731862330000041
Wherein Kepler's third law is
Figure FDA0002731862330000042
Wherein T represents the operating period of the satellite, GM and μ both represent gravitational constants of the earth, and the average angular velocity of the satellite
Figure FDA0002731862330000043
Calculating the corrected average angular velocity n, n being n0+ Δ n, where Δ n is a correction value broadcast in ephemeris;
according to the mean-near point angle M of the reference time broadcast in the ephemeris0And calculating the mean approximate point angle M from the corrected mean angular velocity nk，Mk＝M0+ntk；
According to a relation formula M of a flat near point angle and a partial near point angle given in a Kepler equationk＝Ek-esinEkBy iteratively solving for the angle of approach EkWherein e is the elliptical orbital eccentricity;
calculating the true near point angle v of the signal emission momentk，
Figure FDA0002731862330000044
Geodesic angular distance meter broadcast by true geodesic angle and ephemerisCalculating the angular distance phi of the rising point at the time of signal transmissionk，Φk＝vk+ ω, where ω is the orbital perigee angular separation;
according to the lift-off point angular distance phikAnd calculating a perturbation correction term of signal transmitting time according to the amplitude of the harmonic correction number broadcasted in the ephemeris:
uk＝cus sin2Φk+cuccos2Φk；
rk＝crs sin2Φk+crc cos2Φk；
ik＝cis sin2Φk+ciccos2Φk(ii) a Wherein u iskIs latitude argument correction term rkIs a radial correction term, ikIs a track inclination correction term, cusIs the rising point angular distance sine harmonic correction amplitude, crsIs a radial sinusoidal harmonic correction amplitude, cisIs track inclination sine harmonic correction amplitude, cucIs the rising-crossing angle distance cosine harmonic correction amplitude, crcIs the radial cosine harmonic correction amplitude, cicIs track inclination cosine harmonic correction amplitude;
calculating corrected true paraxial angle ukRadial direction rkAnd track inclination angle ik：
uk＝Φk+uk；
rk＝A(1-ecosEk)+rk；
ik＝i0+ik+(IDOT)tk(ii) a Wherein i0Is toeThe track inclination angle;
calculating the position (x) of the satellite in the orbital plane at the moment of signal transmissionk′，yk′)：
Figure FDA0002731862330000051
Calculating the rising point right ascension omega of the signal emission momentk，
Figure FDA0002731862330000052
Wherein the content of the first and second substances,
Figure FDA0002731862330000053
is the angular velocity constant of the earth's rotation,
Figure FDA0002731862330000054
is the rate of change of the right ascension of the orbit at the intersection point with respect to time, omega0Is the right ascension of the orbit intersection point when the week time is equal to 0;
calculating the coordinates (x) of the satellite in the geocentric coordinate systemk，yk，zk)：
Figure FDA0002731862330000055
3. The method of claim 1, wherein determining that the satellite is visible to the observation station is specifically:
and comparing the elevation angle of the observation station relative to the satellite with the elevation angle threshold of the observation station, and determining that the satellite is visible to the observation station if the elevation angle of the observation station relative to the satellite is greater than the elevation angle threshold of the observation station.
4. The method of claim 1, wherein determining the satellites that are simultaneously visible to both observers from all of the satellites that are visible to each of the two observers comprises, as the common-view satellites for both observers:
sequentially traversing the satellites visible to one observation station one by the satellites visible to the other observation station;
the same satellite that is visible to one of the observatory stations as the satellite that is visible to the other observer station is taken as the common-view satellite for both observatory stations.
5. The method of claim 1, wherein the generating a respective GPS co-view signal navigation message for each co-view satellite is specifically:
and for each co-view satellite, writing a corresponding GPS co-view signal navigation message according to the ICD file of the GPS.
6. A computer-readable storage medium, in which a computer program is stored, which, when being executed by a processor, carries out the steps of the method for analog generation of a GPS co-view signal according to any one of claims 1 to 5.
7. A GPS co-view signal simulator, comprising:
one or more processors;
a memory; and
one or more computer programs, wherein the one or more computer programs are stored in the memory and configured to be executed by the one or more processors, characterized in that the processors, when executing the computer programs, implement the steps of the GPS co-view signal simulation generation method according to any one of claims 1 to 5.
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