CN102375146A - Method and system for simulating GPS (Global Positioning System) digital medium-frequency signal - Google Patents
Method and system for simulating GPS (Global Positioning System) digital medium-frequency signal Download PDFInfo
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Abstract
The invention provides a method and system for simulating a GPS (Global Positioning System) digital medium-frequency signal with a software method. The method comprises the following steps of: I, reading a configuration file written by a user according to a specified format, extracting system configuration parameter, and configuring simulative signal characteristics and input needed by system working; II, extracting RINEX (Receiver Independent Exchange Format) file header information and ephemeris data groups of all satellites within a defined time interval; III, coding ephemeris data extracted in the step II to form a binary navigation message code stream; and IV, modulating the carrier wave and spreading code of the message code stream obtained in the step III to synthesize medium-frequency digital signal data. The system comprises a signal generating module, an RINEX management module and an auxiliary module. In the invention, the GPS digital medium-frequency signal is simulated with a software method for serving as a test vector of a GPS prototype receiver system and a sub-module thereof, so that the problem of signal acquisition during testing is simplified, and the requirement of testing personnel on signal characteristic richness is met quickly.
Description
Technical field
The present invention relates to a kind of method and system of field of satellite navigation, specially a kind of use software approach simulates the method and system of GPS digital medium-frequency signals.
Background technology
The GPS of complete function needs three functional modules：First is Receiver Module, concrete function is to receive the radiofrequency signal that gps satellite is launched by antenna, radiofrequency signal is changed into the relatively low intermediate-freuqncy signal of frequency by mixing and filtering process again, gives baseband processing module to handle as data signal after eventually passing ADC samplings；Second is baseband processing module, is responsible for that the data signal that Receiver Module is exported is captured and tracked, obtains navigation message information and the propagation time information of each satellite；3rd is navigation calculation module, and the information for being responsible for exporting baseband processing module handles the PVT for obtaining receiver by certain mathematical operation（Position, speed, time）Information, realizes GPS location.
Therefore, GPS chip requires gps signal source as test and excitation during early stage design verification, and design verification personnel need to be grasped certain prior information of signal, can verify the correctness and robustness of receiver.The solution typically used has two kinds.One kind is to set up real reception environment, buy third-party Receiver Module and the test system of oneself is docked, receive and measure to obtain test statisticses result by field level signal, and need a reference receiver to run with putting same condition in the same time and place, obtain contrast test data；Another is to build independent radio frequency reception and sampling system, and the system is needed to connect storage device, and the signal gathered on the spot is stored with document form, test and excitation is used as.The limitation of both solutions is all that Environmental costs are higher, and experiment condition is very harsh.For the first scheme, on the one hand test environment can be only done system level testing in real time, module testing or System-Level Model test difficult to realize, on the other hand need to carry out out of doors, it is necessary to a large amount of extra costs of labor and the use such as extra auxiliary equipment of locomotive, compact power, instrument.For second scheme, need also exist for extra artificial and equipment, and the signal stored is no priori, extra Software tool is needed to analyze it, to grasp be used for after reliable information and test, and whether the excavation that the reliability of test result is again relied on to signal message is correct.
The content of the invention
The present invention is directed to the shortcoming and defect in above-mentioned technology, it is proposed that GPS digital intermediate frequency signals analogy method and system that a kind of software mode based on universal computer platform is realized.This method uses true almanac data, modulated by Software Coding and the real carrier wave of simulation with spreading code, and the time difference of the signal arrival receiver of different satellites is adjusted by backstepping computing, synthesize the visible satellite signal of preset time, place and signal to noise ratio, stored in binary file form, test and excitation can be used at any time.ADC output signal in the radio-frequency module for GPS navigation receiver of the system simulation.Software approach ensure that the convenience used and flexibility, and signal can generate and meet the demand of arbitrary signal characteristic at any time.
According to an aspect of the present invention, a kind of analogy method of GPS digital medium-frequency signals is proposed, is comprised the following steps：Step one, the configuration file that user writes according to regulation form is read, extraction system configuration parameter configures the signal characteristic and system work required input of simulation；Step 2, extracts RINEX File header informations and defines the almanac data group of whole satellites in the period；Step 3, the almanac data extracted in step 2 is encoded, and forms binary navigation message code stream；Step 4, modulates carrier wave and spreading code by the text code stream obtained in step 3, synthesizes digital intermediate frequency signal data.
According to another aspect of the present invention, a kind of simulation system of GPS digital medium-frequency signals is also provided, including：Signal generation module, RINEX management modules and supplementary module, wherein, the submodule that supplementary module is mainly included has navigation calculation module, time system management module, geographical coordinate modular converter, macroblock.
More specifically, the present invention is realized by following technical scheme：
Software GPS digital intermediate frequency signal analogy method of the present invention based on universal computer platform, comprises the following steps：
Step one, the configuration file that user writes according to regulation form is read, extraction system configuration parameter configures the signal characteristic and system work required input of simulation.The system configuration parameter includes：
The step reads the modules that configuration parameter listed above configures system from configuration file, sets the generation mode of the current method of operation of system and data.
The RINEX ephemeris File header information, comprising：RINEX version informations, observation station positional information, signal receive period information, ionospheric correction model parameter, UTC time information etc..It is wherein more important to have：Version information, determines the form of file；Ionospheric correction model parameter and UTC time information, these parameters are existed in the navigation message that satellite is broadcast, and are respectively used to correction ionosphere delay and are changed in GPST between UTC.Any kind information occupies some rows in file header, and with a descriptor（descriptor）Distinguish.The step caches the file header of RINEX files first, and then user can search for corresponding information in the buffer as desired by specific descriptor, be used in signal generation.
The effect of ephemeris is illustrated in step one, it is used for describing satellite-orbit information and satellite motion information.The ephemeris that gps satellite is broadcast using two hour as cycles renewals, it is ensured that the precision of these information.Satellite-signal can be received incessantly by making the observation station of RINEX files, a period（Such as one day）Many set ephemeris of the interior whole satellites that can be observed are stored in a RINEX navigation ephemeris file sequentially in time.
The step extracts whole almanac datas in the signal imitation period after RINEX file headers have been parsed, and is stored in composition almanac data group in a Dynamic Two-dimensional array.The type of the almanac data group is a self-defined structure body, and the structure stores a set of ephemeris of a satellite.Why being dynamic array, being because when there is theoretic ephemeris renewal in the time span of signal imitation, every satellite needs many set ephemeris.Every a line one gps satellite of correspondence of the two-dimensional array, totally 32 row, and a set of almanac data of each row correspondence, the different lines correspondence different periods, columns then by.
The step searches whole satellite ephemeris corresponding to the period according to signal initial time and the configuration information of time span in RINEX navigates ephemeris file, and calculating updates with the presence or absence of ephemeris, updates altogether several times.For example, needing the signal generated to be updated comprising an ephemeris when calculating, then every satellite need to extract two sets of ephemeris continuous in time, and be coincide with the configuration information of initial time and length.
It is described to be encoded the almanac data extracted in step 2, binary navigation message code stream is formed, is referred to：According to the signal initial time and time span simulated, and GPS official documents are to the regulation of message format, the ephemeris of each satellite is encoded, form binary navigation message code stream, parity bits are calculated simultaneously, and finally the code stream of every satellite is all stored in an independent file.Navigation message is binary format, with 30 seconds for a frame, the almanac data extracted in step 2 the information that i.e. one frame of correspondence is included.One frame includes 5 subframes, numbers from 1 to 5, and each subframe includes 300 bit datas, so the width per bit data is 20 ms.Every satellite is all from world concordant time（UTC）Morning on Sunday start broadcast navigation message, constantly circulated from 1 work song frame to 5 work song frames, and be updated with two hours for interval.The algorithm encoded to all satellite messages is identical, and its flow is as follows：
1. TOW when being calculated according to the information of signal initial time in week；
2. the business obtained with TOW divided by 6 is to 5 remainders,（Remainder+1）The as subframe numbers k of subframe where signal initial time (time of every satellite launch subframe is synchronous, the starting subframe for the navigation message code stream that the subframe numbers that the above is calculated can be generated as all satellites in theory)；
3. according to signal time span n（Unit is the second）Calculate the sub-frame number that every satellite needs to generate：N = n/6+1；
4. couple satellite p is, it is necessary to i-th generated（0
I ＜ N）The subframe numbers of individual subframe：
Itow, which is calculated, during according in the subframe corresponding week should choose the almanac data in which ephemeris group：
2 hours ephemeris renewable times in simulated signal time span are found, the period that itow occurs is judged, the almanac data group that choose is judged.The coding of i-th of subframe is carried out according to the corresponding sub-frame formats of sf work song frames and selected almanac data group Satellite p almanac data；The coding that the step completes all subframes is repeated, satellite p text code stream is obtained.
1. calculate GPS spread spectrum code sequences.Generating mode realizes that the sequence of generation is stored in a two-dimensional array CA_Code, and its row vector represents the CA code sequences of a gps satellite according to the definition of GPS officials interface document.The CA code cycles are 1ms, and the length comprising 1023 chips, therefore row vector is 1023, deposits CA code a cycle sequential values.
Calculate the number of samples Nsample of digital medium-frequency signal to be generated.Computational methods are 
.Wherein n is the time span of signal（Unit is the second）,
For sample rate（Unit is Hz）.
When i is less than Nsample, start calculating i-th（Initial value is 0）The value of individual sampled point.Into step 4.Otherwise step 6 is entered.
Judge whether i corresponds to the number of samples of whole millisecond.The algorithm calculates the propagation time of the signal of every satellite at whole millisecond（Signal is from satellite antenna to receiver antenna）And assume that the propagation time is constant in ensuing 1 millisecond, it is constant that the propagation time of the signal of receiver is reached in i.e. ensuing 1 millisecond, this hypothesis ensure that minimum error, and avoid the propagation time of each satellite-signal corresponding to each sampled point from calculating, on the premise of sample rate is more than 1,000,000, efficiency of algorithm is improved more than 1000 times.If i is the number of samples of whole millisecond, to each satellite（In the range of all 32 gps satellites）Carry out following steps 1）To 5）Calculating, otherwise skip to step 5：
1）Current time corresponding satellite almanac data group is found according to i, present satellites p ephemeris is therefrom extracted, the validity of ephemeris is checked, invalid, the satellite is set to invisible, and skips to the flow of next satellite repeat step 4；
2）Explanation according to GPS officials interface document calculates current time（It is corresponding with i）The signal of the satellite received is in the propagation time 
Satellite clock correction corrected value clk and clock drift corrected value clk_drift before second；Propagation time The value obtained when being calculated using last whole millisecond, i.e., temporarily think that the propagation time does not change in past 1ms, is defined as 0.07 second in initialization；
3）Calculate current time（It is corresponding with i）The x time of the signal of the satellite received, x time
For signal initial time（When in all）, ms is the millisecond number of current record（Unit is the second）；
4）Satellite PVT information, satellite and receiver distance and its rate of change information at the time of the signal that loop iteration calculating is currently calculated is launched.Specific method is：
I. the propagation time is recalculated：
Obtained satellite and receiver distance are calculated when range is last progress step 4, LIGHTSPEED is the light velocity；
Ii. signal x time tow is recalculated：
Iii. the method defined according to GPS officials interface document calculates PVT information of the satellite at the tow moment；
Iv. calculated under ECEF coordinate systems between tow moment satellite and receiver apart from range and range rate
；
V. return to the i-th step and repeat this process, iteration obtain for 4 times accurate range, 
With
。
）Calculate in the satellite elevation angle and azimuth at tow moment, if the elevation angle is more than 0, calculate Doppler frequency shift：
Wherein WAVELENGTHL1 is GPS L1 signal carrier wavelength.Negative sign herein is because it is considered that Receiver Module inverts frequency spectrum in down coversion, therefore doppler symbol occurs in that reversion；
Then the carrier phase step-length under current sample rate is calculated：
Wherein IF is IF-FRE.
Finally calculate the accurate propagation time：
Clk is the 2nd）Walk the satellite clock correction calculated.Calculating returns to the 1st after finishing）Step, into the x time and corresponding PVT information of the signal reached to next satellite at the current whole millisecond moment.
If the elevation angle is less than 0, this satellite is set to invisible, skips other computings of the step, same to return to the 1st）Step performs above step to next satellite.
To the value of the signal of change ith sample point of current visible every satellite.The observability of satellite determines in step 4, and in process step 4 next time（Reach next whole millisecond）Keep before constant.The algorithm steps of the step are as follows：
1）Calculate the current visible satellite q corresponding navigation message numerical value of ith sample point.Its false code is as follows：
Wherein, 
The initial time of subframe where representing signal initial time, then
Represent time gap of the current sampling point apart from the subframe starting point.Calculate
The reason for be the navigation message code stream that every obtained satellite is encoded in step 3 using the subframe as starting point, therefore find the corresponding text numerical value of current sampling point and also need with this as the starting point.If the subframe is
。
）Calculate the current visible satellite q corresponding spreading code of ith sample point and carrier wave numerical value.Its false code is as follows：
Because CA codes are using 1ms as the cycle, a cycle includes 1023 chips, and the algorithm is assumed
It is 0 to originate corresponding code phase, and the doppler effects of CA codes are ignored.Therefore codephase is the corresponding spreading code code phase of current sampling point.
For carrier phase, its step-length is calculated by the 4th step and obtained, and keeps constant in 1ms.The data data of synthesis is the sum of products of navigation message of each satellite at current sampling point, CA codes and carrier wave numerical value.
）White Gaussian noise is superimposed to data, its signal to noise ratio is in step one by user configuring.Data is stored in the binary file opened in advance.
All sampled points are calculated and finished, exit step four, while having obtained the file of GPS digital medium-frequency signals.
GPS digital medium-frequency signals simulation system of the present invention, including signal generation module, RINEX management modules and supplementary module, the submodule that wherein supplementary module is mainly included has navigation calculation module, time system management module, geographical coordinate modular converter, macroblock.
The signal generation module provides the interface of following functions, including：The extraction of system configuration information；RINEX management modules are called to extract the almanac data group of requirement, whole ephemeris of all gps satellites of almanac data group correspondence in two hours terms of validity, and the group number of the ephemeris group is determined by the initial time and time span of the signal simulated, occur the renewal of how many times ephemeris in the time span, then need to extract the almanac data group of respective numbers；Almanac data is encoded and check bit addition, obtain navigation message code stream；Carrier wave and spreading code are modulated to navigation message code stream；Gaussian noise is simulated；The total algorithm flow that combination function above part realizes signal imitation is provided.
The RINEX management modules provide the interface of following functions, including：Obtain the RINEX ephemeris files of user configuring；Resolution file name checks the information that file availability and extraction document name are included, including base station name abbreviation, signal acquisition time；Cache the file header data of RINEX ephemeris files；Extract the RINEX version informations in the file header of RINEX ephemeris files, base station position information, signal and receive period information, ionosphere corrections parameter, UTC time information etc.；One group of almanac data is extracted according to a time reference, the functional module is called repeatedly by the interface that almanac data group is extracted in aforementioned signal generation module, obtains the almanac data group of requirement.
The navigation calculation module provides the interface of following functions, including：Satellite clock correction and the calculating of clock drift；The calculating of satellite position, velocity information；Satellite, receiver distance, the calculating of range rate；The elevation angle of the satellite relative to receiver and azimuthal calculating.
The time system management module is responsible for the data conversion between different time system.
The geographical coordinate modular converter is responsible for the conversion of coordinate value between different geographical co-ordinate systems.
The macroblock is responsible for the grand management of completion system, including the managing of global constant, the management that self-defined mathematical operation is grand.
Brief description of the drawings
Fig. 1 is the input and output schematic diagram of GPS digital medium-frequency signals simulation system of the present invention；
Fig. 2 is software top level flow diagram of the invention；
Fig. 3 is the schematic diagram that present system inputs configuration file format；
Fig. 4 is the process schematic that RINEX File header informations of the present invention are extracted；
Fig. 5 is the process schematic that satellite almanac data group of the present invention is extracted；
Fig. 6 is the schematic diagram of the satellite message code stream generating process of the present invention；
Fig. 7 is the algorithm flow chart of the signal building-up process of the present invention；
Fig. 8 is software logic hierarchical chart of the invention.
Embodiment
Embodiments of the invention are elaborated below in conjunction with the accompanying drawings：The present embodiment is implemented lower premised on technical solution of the present invention, gives detailed embodiment and specific operating process, but protection scope of the present invention is not limited to following embodiments.
As shown in Figure 1, for the I/O mode of the system provided according to the present invention, the configuration text file that the input of the system is write for user by the demand and system of the signal to generation to the call format of configuration file, is output as storing the binary file of digital medium-frequency signal.
As shown in Fig. 2 being the software top level flow diagram of the system provided according to the present invention.The figure illustrates GPS digital medium-frequency signals analogy method provided by the present invention, including step in detail below：
Step one, the configuration file that user writes according to regulation form is read, extracts the parameters such as receiver location, RINEX ephemeris file path, signal time information.
The schematic diagram that the system inputs configuration file format is illustrated in figure 3, configurable parameter is divided into three classes, and uses tilde（
）Plus capitalization English letter mark, it is receiver coordinate information, RINEX ephemeris file path information and temporal information respectively.Distinguished between each unit information in per group information with space.Illustrate referring to following table：
The configuration file format of table 1 illustrates table
As shown in figure 4, the parameter of ionosphere delay calibration model is present in the third line and fourth line of file header in the present embodiment.After file header is buffered in an one-dimensional character string dimension, by end mark of newline, behavior unit scan for, corresponding with ionospheric correction model parameter descriptor is searched in each search unit（descriptor）, the search unit is extracted after finding and is put into an interim array, next search unit is then checked, so repeatedly until the end of file header buffering area.All interim arrays sequentially constitute new buffering area, finally extract corresponding data according to RINEX official's form from the buffering area.
As shown in figure 5, extracting satellite ephemeris according to the signal initial time of configuration, time span, the almanac data group number updated.The body part of RINEX files stores the ephemeris of every visible satellite on a time period, and the time segment length is the update cycle of gps satellite ephemeris --- and 2 hours.The RINEX files that the present embodiment is used store the ephemeris of one day, so its text is divided into 12 sections.And the initial time 1 point for the signal simulated 58 minutes, time span is 330 seconds, therefore occurs in that an ephemeris is updated, it is necessary to extract two groups of almanac data groups.The period searched for where signal initial time, by the period and a subsequent period, totally two groups of almanac data groups are extracted, and are put into a two-dimensional array.One group of almanac data of each row one period of correspondence of the two-dimensional array, row length is gps satellite sum；Correspond to same satellite per a line, whether the ephemeris that its data structure identifies this satellite comprising flag bit is effective within the correspondence period（In the presence of）.
As shown in fig. 6, TOW when the signal initial time configured in step one was converted in week, is in the present embodiment 93520s, because GPS subframe length is 6s, so being encoded since 93516s to navigation message by subframe.The subframe numbers of starting subframe are calculated first：
Then sequence of subframes hereafter is
；
While the subframe sum for needing generation is
I.e. every satellite is both needed to encode 56 continuous subframes since 2 work song frames.
For satellite p i-th of subframe 
, its subframe numbers that should be generated 
If sf is equal to 0, it is 5 to make it.
Calculate which ephemeris group should be chosen during according in its corresponding week.2 hours integral multiple times in the present embodiment in signal time span come across 93600s.Therefore, the time that i-th of subframe is present is calculated：
When it is less than 93600, then first group of ephemeris group Satellite p ephemeris is chosen, second group of ephemeris group Satellite p ephemeris is otherwise chosen.
Then ephemeris is carried out according to GPS message formats encoding the code stream for obtaining correspondence subframe.
After the completion of satellite p all subframes coding, a single file is stored in.The step of all satellites are carried out as above.
As shown in fig. 7, being the algorithm flow chart of the signal building-up process.
Calculate GPS spread spectrum code sequences.Generating mode realizes that the sequence of generation is stored in a two-dimensional array according to the definition of GPS officials interface document
In, its row vector represents the CA code sequences of a gps satellite.The CA code cycles are 1ms, and the length comprising 1023 chips, therefore row vector is 1023, deposits CA code a cycle sequential values.
Calculate number of samples
.Wherein 5.714285e6 is sample rate.
Sample value is calculated by sampled point.If temporary variable i=0.When i is less than Nsample, the value of ith sample point is calculated.Into step 4.Otherwise step 6 is entered.
Judge
Whether it is 0, wherein 5714 take the approximate number of 1ms sampling numbers.If whether i corresponds to the number of samples of whole millisecond, following 1 is carried out to whole gps satellites）To 5）The step of, otherwise skip the step：
1）Current time corresponding satellite almanac data group is found according to i, present satellites p ephemeris is therefrom extracted, the validity of ephemeris is checked, invalid, satellite p is set to invisible, and skips to the flow of next satellite repeat step 4；
2）The signal for the satellite that explanation calculating current time according to GPS officials interface document receives is in the propagation time 
Satellite clock correction corrected value clk and clock drift corrected value before second
；Propagation time
The value obtained when being calculated using last whole millisecond, i.e., temporarily think that the propagation time does not change in past 1ms, is defined as 0.07 second in initialization；
3）Calculate current time（It is corresponding with i）The x time of the signal of the satellite received
；
4）Satellite PVT information, satellite and receiver distance and its rate of change information at the time of the signal that loop iteration calculating is currently calculated is launched.Specific method is：
I. the propagation time is recalculated：
Obtained satellite and receiver distance are calculated when range is last progress step 4, LIGHTSPEED is the light velocity.
Recalculate signal x time tow：
Iii. the method defined according to GPS officials interface document calculates PVT information of the satellite at the tow moment；
Iv. calculated under ECEF coordinate systems between tow moment satellite and receiver apart from range and range rate
；
V. return to the i-th step and repeat this process, iteration obtain for 4 times accurate range, With
。
）Calculate in the satellite elevation angle and azimuth at tow moment, if the elevation angle is more than 0, calculate Doppler frequency shift：
Wherein WAVELENGTHL1 is GPS L1 signal carrier wavelength.Negative sign herein is because it is considered that Receiver Module inverts frequency spectrum in down coversion, therefore doppler symbol occurs in that reversion；
Then the carrier phase step-length under current sample rate is calculated：
Wherein IF is IF-FRE.
Finally calculate the accurate propagation time：
Clk is the 2nd）Walk the satellite clock correction calculated.Calculating returns to the 1st after finishing）Step, into the x time and corresponding PVT information of the signal reached to next satellite at the current whole millisecond moment.
If the elevation angle is less than 0, this satellite is set to invisible, skips other computings of the step, same to return to the 1st）Step performs above step to next satellite.
To the value of the signal of change ith sample point of current visible every satellite.The observability of satellite determines in step 4, and in process step 4 next time（Reach next whole millisecond）Keep before constant.The algorithm steps of the step are as follows：
1）Calculate the visible satellite q corresponding navigation message numerical value of ith sample point：
2）Calculate the satellite q corresponding spreading code of ith sample point and carrier wave numerical value.Its false code is as follows：
3）White Gaussian noise is superimposed to data, its signal to noise ratio is in step one by user configuring.Data is stored in the binary file opened in advance.
All sampled points are calculated and finished, exit step four, while having obtained the file of GPS digital medium-frequency signals.
As shown in figure 8, the software logic hierarchical chart of the GPS intermediate-freuqncy signal simulation systems provided for the present invention, software of the invention, which is realized, includes three logical levels：Signal generation module, RINEX management modules, supplementary module.
The signal generation module provides the interface of following functions, including：The extraction of system configuration information；RINEX management modules are called to extract the almanac data group of requirement, whole ephemeris of all gps satellites of almanac data group correspondence in two hours terms of validity, and the group number of the ephemeris group is determined by the initial time and time span of the signal simulated, occur the renewal of how many times ephemeris in the time span, then need to extract the almanac data group of respective numbers；Almanac data is encoded and check bit addition, obtain navigation message code stream；Carrier wave and spreading code are modulated to navigation message code stream；Gaussian noise is simulated；The total algorithm flow that combination function above part realizes signal imitation is provided.
The RINEX management modules provide the interface of following functions, including：Obtain the RINEX ephemeris files of user configuring；Resolution file name checks the information that file availability and extraction document name are included, including base station name abbreviation, signal acquisition time；Cache the file header data of RINEX ephemeris files；Extract the RINEX version informations in the file header of RINEX ephemeris files, base station position information, signal and receive period information, ionosphere corrections parameter, UTC time information etc.；One group of almanac data is extracted according to a time reference, the functional module is called repeatedly by the interface that almanac data group is extracted in aforementioned signal generation module, obtains the almanac data group of requirement.
The navigation calculation module provides the interface of following functions, including：Satellite clock correction and the calculating of clock drift；The calculating of satellite position, velocity information；Satellite, receiver distance, the calculating of range rate；The elevation angle of the satellite relative to receiver and azimuthal calculating.
The time system management module is responsible for the data conversion between different time system.
The geographical coordinate modular converter is responsible for the conversion of coordinate value between different geographical co-ordinate systems.
The macroblock is responsible for the grand management of completion system, including the managing of global constant, the management that self-defined mathematical operation is grand.
Claims (10)
1. a kind of analogy method of GPS digital medium-frequency signals, it is characterised in that comprise the following steps：
Step one, the configuration file that user writes according to regulation form is read, extraction system configuration parameter configures the signal characteristic and system work required input of simulation；
Step 2, extracts RINEX File header informations and defines the almanac data group of whole satellites in the period；
Step 3, the almanac data extracted in step 2 is encoded, and forms binary navigation message code stream；
Step 4, modulates carrier wave and spreading code by the text code stream obtained in step 3, synthesizes digital intermediate frequency signal data.
2. the analogy method of GPS digital medium-frequency signals according to claim 1, it is characterised in that the system configuration parameter includes：RINEX navigation ephemeris file path, receiver location information, the reception initial time for the signal simulated, time span and ephemeris use group number information；Wherein, ephemeris file path specifies RINEX navigation ephemeris file used in signal imitation, and the source of message coding is used as using the ephemeris in this document；Receiver location information specifies the receiving position of institute's analog signal；Receive temporal information and ephemeris fresh information that initial time, time span and ephemeris describe institute's analog signal using group number information；Step one includes sub-step：Extract the operational factor of full detail configuration system work required input and each module.
3. the analogy method of GPS digital medium-frequency signals according to claim 1, characterized in that, the RINEX File header informations receive period information, ionospheric correction model parameter, UTC time information etc. comprising RINEX version informations, observation station positional information, signal；Wherein, RINEX version informations determine the form of file；Ionospheric correction model parameter and UTC time information, these parameters are existed in the navigation message that satellite is broadcast, and are respectively used to correction ionosphere delay and are changed in GPST between UTC；Any kind information occupies some rows in file header, and is distinguished with a descriptor, and corresponding information can be searched for from the RINEX file headers of caching according to this descriptor and is extracted, is used in signal generation.
4. the analogy method of GPS digital medium-frequency signals according to claim 1, it is characterized in that, satellite ephemeris and occur the ephemeris updated in simulated time span that the almanac data group includes simulated signal initial time, stored according to two-dimensional array form, one group of almanac data of each row one period of correspondence of two-dimensional array, row length is gps satellite sum；Correspond to same satellite per a line, whether the ephemeris that its data structure identifies this satellite comprising flag bit is effective within the correspondence period.
5. the analogy method of GPS digital medium-frequency signals according to claim 1, it is characterised in that the almanac data coding, refers to：According to the signal initial time and time span simulated, and GPS official documents are to the regulation of message format, the ephemeris of each satellite is encoded, form binary navigation message code stream, parity bits are calculated simultaneously, and finally the code stream of every satellite is all stored in an independent file.
6. the analogy method of GPS digital medium-frequency signals according to claim 1, it is characterised in that described to modulate carrier wave and spreading code to navigation message, synthesizes digital intermediate frequency signal data, refers to：Complete the last analog synthesis function of signal, it includes calculating signal sample by sampled point, the signal calculated in each sample point received by this moment antenna is synthesized by the signal of which satellite, it is what kind of text numerical value, spread spectrum code phase and carrier phase, frequency respectively, and consider that antenna pair signal carries out the factor such as frequency folding, ADC quantization exponent number of appearance during frequency reducing, the influence of the behavior of accurate simulation receiving terminal to signal.
7. a kind of simulation system of GPS digital medium-frequency signals, it is characterised in that including：Signal generation module, RINEX management modules and supplementary module, wherein, the submodule that supplementary module is mainly included has navigation calculation module, time system management module, geographical coordinate modular converter, macroblock.
8. simulation system according to claim 7, it is characterised in that the signal generation module provides the interface of following functions, including：The extraction of system configuration information；RINEX management modules are called to extract the almanac data group of requirement, whole ephemeris of all gps satellites of almanac data group correspondence in two hours terms of validity, and the group number of the ephemeris group is determined by the initial time and time span of the signal simulated, occur the renewal of how many times ephemeris in the time span, then need to extract the almanac data group of respective numbers；Almanac data is encoded and check bit addition, obtain navigation message code stream；Carrier wave and spreading code are modulated to navigation message code stream；Gaussian noise is simulated；The total algorithm flow that combination function above part realizes signal imitation is provided.
9. simulation system according to claim 7, it is characterised in that the RINEX management modules provide the interface of following functions, including：Obtain the RINEX ephemeris files of user configuring；Resolution file name checks the information that file availability and extraction document name are included, including base station name abbreviation, signal acquisition time；Cache the file header data of RINEX ephemeris files；Extract the RINEX version informations in the file header of RINEX ephemeris files, base station position information, signal and receive period information, ionosphere corrections parameter, UTC time information etc.；One group of almanac data is extracted according to a time reference, the functional module is called repeatedly by the interface that almanac data group is extracted in aforementioned signal generation module, obtains the almanac data group of requirement.
10. simulation system according to claim 7, it is characterised in that the navigation calculation module provides the interface of following functions, including：Satellite clock correction and the calculating of clock drift；The calculating of satellite position, velocity information；Satellite, receiver distance, the calculating of range rate；The elevation angle of the satellite relative to receiver and azimuthal calculating；
The time system management module is responsible for the data conversion between different time system；
The geographical coordinate modular converter is responsible for the conversion of coordinate value between different geographical co-ordinate systems；
The macroblock is responsible for the grand management of completion system, including the managing of global constant, the management that self-defined mathematical operation is grand.
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