CN102590837B - Method for calibrating phase errors of global positioning system (GPS) signal source - Google Patents

Method for calibrating phase errors of global positioning system (GPS) signal source Download PDF

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CN102590837B
CN102590837B CN201110394219.0A CN201110394219A CN102590837B CN 102590837 B CN102590837 B CN 102590837B CN 201110394219 A CN201110394219 A CN 201110394219A CN 102590837 B CN102590837 B CN 102590837B
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phase
frequency control
control word
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CN102590837A (en
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林静然
李玉柏
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University of Electronic Science and Technology of China
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Abstract

The invention relates to the technical field of simulative generation of GPS signal source, in particular to a method for calibrating phase errors of a GPS signal source. The technical scheme of the method includes calculating a frequency control word of a floating point format by utilizing an input Doppler frequency parameter; subjecting the frequency control word to a fix-point process and calculating an overall error produced within a calibrating time internal; controlling phase accumulation by using the frequency control word after the fix-point process; if the calibrating time is reached, adding the overall error into the accumulation result, storing and outputting the final result, and storing and outputting the accumulation result directly otherwise; and if a parameter updated time interval is reached, recalculating the frequency control word of the floating point format according to the Doppler frequency at the moment and repeating the above steps, and proceeding phase accumulation otherwise. According to the technical scheme of the method for calibrating the phase errors of the GPS signal source, the high accuracy of floating point accomplishment and simplicity and low cost of fixed point accomplishment are balanced and combined, and the finite word-length effect in the fixed point accomplishment process can be calibrated simultaneously.

Description

A kind of method for the phase error of proofreading and correct the gps signal source
Technical field
The present invention relates to the technical field that simulation produces the gps signal source, be specifically related to a kind of method for the phase error of proofreading and correct the gps signal source.
Background technology
The gps signal source can provide repeatably simulating signal for every research, emulation and the test in satellite navigation field, contributes to the propelling of research work.Simultaneously, in the environment that is not easy to erect a television antenna, as the area of remote mountain areas and awful weather, the gps signal source also can guarantee the normal operation of navigation terminal, greatly reduces the construction cost and the maintenance cost that erect a television antenna.
In the simulation of gps signal source produces the process of gps signal, need to calculate the frequency control word of intermediate frequency carrier, the frequency control word of C/A code and the frequency control word of navigation message, and then with these three frequency control words, go control phase cumulative respectively, obtain respectively the phase place of intermediate frequency carrier, C/A code and navigation message.
Calculate the said frequencies control word and carry out phase-accumulated method and mainly comprise the steps:
Step 1: utilize the frequency control word of Doppler frequency calculation of parameter intermediate frequency carrier, the frequency control word of C/A code and the frequency control word of navigation message;
Step 2: according to sampling interval, the frequency control word that utilizes step 1 to obtain carries out phase-accumulated, obtains the phase place of intermediate frequency carrier, C/A code and navigation message.
Wherein, utilize the formula of the frequency control word FCW_Carrier_Float of Doppler frequency calculation of parameter intermediate frequency carrier to be:
FCW _ Carrier _ Float = f I + f d f s
F imean IF-FRE, f dmean Doppler frequency, f smean the signal sampling frequency.
Utilize the formula of the frequency control word FCW_Code_Float of Doppler frequency calculation of parameter C/A code to be:
FCW _ Code _ Float = f C + f d × ( f C / f T ) f s
F cfor the code check of C/A code, f tfor the gps signal carrier frequency.
The formula that utilizes the Doppler frequency calculation of parameter to calculate the frequency control word FCW_Data_Float of navigation message is:
FCW _ Data _ Float = f D + f d × ( f D / f T ) f s
F dmean the navigation message code check.
Step 2 is being carried out with frequency control word when phase-accumulated, if Doppler frequency used calculates for the first time for this satellite, should start from the initial phase of gps signal to add up, otherwise just continue cumulative on the cumulative phase-accumulated value basis obtained in last time.
As can be seen here, for the phase place of the intermediate frequency carrier, C/A code and the navigation message that calculate the gps signal source, the initial phase of Doppler frequency and this gps satellite signal is its basic input parameter, and these two parameters are generally that other modules by the gps signal source generate and export to the phase calculation module.
During the specific implementation above-mentioned steps, both can adopt the digital platform of fixed point on a digital platform, also can adopt the digital platform of floating-point.We the analysis found that, no matter adopt merely which kind of platform to realize, all there is following difficult point: if adopt the fixed point platform to realize, mean while with a time-limited binary string, meaning intermediate frequency carrier frequency control word, C/A code frequency control word and navigation message frequency control word, this just exists and means error, between the value that its fixed point mode means and ideal value, has deviation that is:.There is gap between the gps signal that this makes simulation produce and real signal.And, along with the increase of time, this gap may become greatly gradually, causes performance further to worsen.If mean and deal with data, can greatly reduce the error that finite word length effect causes, but this will increase the difficulty of realization, the cost of hardware platform and the power consumption of whole system on the floating-point platform.
From domestic and international disclosed document, we do not find the technical scheme that can effectively solve above-mentioned two aspect technical matterss simultaneously.
Summary of the invention
A kind of method for the phase error of proofreading and correct the gps signal source that the present invention proposes is characterized in that in turn including the following steps:
Step 1: the word length of setting digital platform is L w, intermediate frequency carrier, C/A code and the navigation message signals phase error of largest tolerable separately are Max_Phase_Err, parameter interval T update time u, the time interval T that finite word length effect is proofreaied and correct e, the sampling time interval T of signal s;
Step 2: utilize the Doppler frequency parameter of current time, calculate the frequency control word of floating-point format;
Step 3: it is L that the frequency control word of the floating-point format that step 2 is obtained converts word length to wthe frequency control word of fixed point format, record the error that single conversion produces, and calculate the time interval T proofreaied and correct at finite word length effect ethe summation of the error of interior generation, then preserve this sum of the deviations with fixed point format;
Step 4: the frequency control word of the fixed point format obtained by step 3, with the sampling time interval T of signal sfor the time beat, the phase place of signal is added up, then judge whether the time of cumulative process reaches the time interval T that finite word length effect is proofreaied and correct eif, reached this interval, first by this phase-accumulated value, add the sum of the deviations that step 3 obtains, obtain the phase error correction value, by this phase error correction value pair
Figure BSA00000627448800031
preserve after delivery and export, then entering step 5, if do not reach, directly that phase-accumulated value is right
Figure BSA00000627448800032
preserve and export this result after delivery, then enter step 5;
Step 5: judge whether to reach parameter interval T update time uif, reach, return to step 2; If do not reach, return to step 4.
Parameter interval T update time ube greater than or equal to the time interval T that finite word length effect is proofreaied and correct e.
Parameter interval T update time uthe time interval T that finite word length effect is proofreaied and correct eintegral multiple.
Described frequency control word is in intermediate frequency carrier frequency control word, C/A code frequency control word and navigation message frequency control word.
The time interval T that finite word length effect is proofreaied and correct eadopt following method to determine:
1) for each described frequency control word, calculate its needed minimum cumulative frequency Min_N=Max_Phase_Err/Max_ Δ FCW according to the described maximum phase error Max_Phase_Err that can tolerate respectively, wherein, the absolute value that Max_ Δ FCW is the maximum error that may cause while in described step 3, the frequency control word of floating-point format being converted to the frequency control word of fixed point format, for adopting the round up conversion method of mode of decimal place, Max_ Δ FCW=0.5, for adopting the conversion method of directly removing decimal place, Max_ Δ FCW=1;
2) for each described frequency control word, calculate respectively T e=T s* Min_N, wherein T ssampling time interval for described signal;
3) get 2) three T obtaining of step ein minimum value, be the time interval T that finite word length effect is proofreaied and correct e.
It is L that described step 3 converts the frequency control word of floating-point format to word length wthe step of fixed point format comprise:
4) frequency control word of described floating-point format is multiplied by
Figure BSA00000627448800041
5) by 1) value that obtains of step carry out round numbers computing that decimal place rounds up or by 1) value that obtains of step directly removes the rounding operation of decimal place.
The described time interval T proofreaied and correct at finite word length effect of step 3 eerror * T that the summation of the error of interior generation=described single conversion produces e/ T s.
It is that following formula is carried out in circulation: the frequency control word of phase-accumulated value=phase-accumulated value+fixed point format that described step 3 obtains that the phase place of described step 4 pair signal is carried out cumulative method, if be to calculate for the first time its Doppler frequency parameter for working as this gps satellite of front simulation, the prima facies place value that initial value of phase-accumulated value is signal, otherwise the initial value of phase-accumulated value is the phase-accumulated value preserved in described step 4.
Technical scheme of the present invention has been carried out good compromise on floating-point realization and fixed-point implementation, combine the accuracy of floating-point realization and the simplicity of fixed-point implementation, considered that floating-point format turns the error of introducing due to finite word length effect in the fixed point format process simultaneously, and it has been proofreaied and correct.Before the step 3 of the technical program, the calculated rate of parameter is lower (to be equaled parameter and upgrades interval T u), use floating-point to realize, to calculate more accurately the value of flat rate control word according to the Doppler frequency of current time satellite-signal; After step 3, calculated rate is higher (is mainly by sampling interval T scarry out phase-accumulated calculating), use fixed-point implementation, more the generation satellite-signal of Simple fast.Simultaneously, also calculate the accumulation of phase error that finite word length effect causes, and upgraded interval T in the parameter of fixed-point implementation part eproofread and correct at place, has guaranteed the accuracy of fixed-point implementation.
The accompanying drawing explanation
The overview flow chart of a kind of method for the phase error of proofreading and correct the gps signal source that accompanying drawing 1 is that the present invention proposes.
Embodiment
Below illustrate the embodiment of technical solution of the present invention.
Step 1: initialization specifically comprises: setup parameter comprises gps signal carrier frequency f t=1575.42MHz, C/A code check f c=1.023MHz, navigation message code check f d=50Hz, sample frequency f s=16.384MHz, sampling interval T s=1/16.384us, intermediate frequency f i=5.12MHz, the word length L of digital platform w=32bit,, the maximum phase error tolerance value that three frequency control word errors cause is equal 8192, adopts the method rounded up to realize fixed point, i.e. Max_ Δ FCW=0.5, the finite word length effect obtained is thus proofreaied and correct interval T e=1ms, proofread and correct the number of data points N in interval e=T e/ T s=16384, in addition, setting parameter upgrades interval T u=2ms, N u=T u/ T e=2.
Step 2: the frequency control word that calculates floating-point format according to the Doppler frequency of current time
(a) calculate the frequency control word FCW_Carrier_Float of intermediate frequency carrier,
FCW _ Carrier _ Float = 5.12 MHz + f d 16.384 MHz
(b) calculate the frequency control word FCW_Code_Float of C/A code,
FCW _ Code _ Float = 1.023 MHz + f d × ( 1.023 / 1575.42 ) 16.384 MHz
(c) calculate the frequency control word FCW_Data_Float of navigation message,
FCW _ Data _ Float = 50 Hz + f d × ( 50 Hz / 1575.42 MHz ) 16.384 MHz
F wherein dfor Doppler frequency.
Step 3: frequency control word is carried out to the fixed point processing, and record the error that finite word length effect causes, specifically comprise the steps:
Step 3-1: the IF-FRE control word FCW_Carrier_Float to floating-point format is multiplied by after carry out, to the rounding up of decimal place, obtaining the IF-FRE control word FCW_Carrier of fixed point format,
FCW_Carrier＝round{FCW_Carrier_Float×2 32}
Calculating is proofreaied and correct interval T at finite word length effect ein, the intermediate frequency carrier accumulation of phase error delta Phase_Carrier caused by finite word length effect, still mean by fixed point format,
ΔPhase_Carrier＝round{(FCW_Carrier_Float×2 32-FCW_Carrier)×16384}
Step 3-2: the C/A code frequency control word FCW_Code_Float to floating-point format is multiplied by
Figure BSA00000627448800065
after carry out, to the rounding up of decimal place, obtaining the C/A code frequency control word FCW_Code of fixed point format,
FCW_Code＝round{FCW_Code_Float×2 32}
Calculate finite word length effect and proofread and correct interval T ein, the C/A code phase cumulative errors Δ Phase_Code caused by finite word length effect, still mean by fixed point format,
ΔPhase_Code＝round{(FCW_Code_Float×2 32-FCW_Code)×16384}
Step 3-3: the navigation message frequency control word FCW_Data_Float to floating-point format is multiplied by
Figure BSA00000627448800066
after carry out, to the rounding up of decimal place, obtaining the navigation message frequency control word FCW_Data of fixed point format,
FCW_Data＝round{FCW_Data_Float×2 32}
Calculate finite word length effect and proofread and correct interval T ein, the navigation message accumulation of phase error delta Phase_Data caused by finite word length effect, still mean by fixed point format,
ΔPhase_Data＝round{(FCW_Data_Float×2 32-FCW_Data)×16384}
Round{} computing in above-mentioned formula, the round up operation of expression to decimal place, except adopting the mode that decimal place is rounded up to complete floating-point format to the conversion of fixed point format, can also directly decimal place be given up, the way that only retains integer-bit converts the frequency control word of fixed point format to, if adopt this method, and Max_ Δ FCW=1, other parameters relevant to Max_ Δ FCW, also should make corresponding change.
Step 4: utilize the frequency control word of fixed point format to carry out phase-accumulated, specifically comprise the steps:
Step 4-1: utilize the frequency control word of intermediate frequency carrier to carry out phase-accumulated,
Phase_Carrier＝Phase_Carrier+FCW_Carrier
Step 4-2: utilize the frequency control word of C/A code to carry out phase-accumulated,
Phase_Code＝Phase_Code+FCW_Code
Step 4-3: utilize the frequency control word of navigation message to carry out phase-accumulated,
Phase_Data＝Phase_Data+FCW_Data
Before the beginning that phase place added up with frequency control word, whether the Doppler frequency that needs judgement to adopt calculates for the first time for this satellite, if so, and the first phase that initial value of the phase place in top three cumulative formula is this satellite-signal; If not, the initial value of the phase place in top three cumulative formula is the last cumulative phase-accumulated value preserved later.
Step 5: if arrive finite word length effect, proofread and correct interval T e, utilize the cumulative errors amount to be proofreaied and correct finite word length effect, and will proofread and correct later accumulation result and preserve, specifically comprise the steps:
Step 5-1: proofread and correct the intermediate frequency carrier phase place,
Phase_Carrier＝Phase_Carrier+ΔPhase_Carrier
Step 5-2: proofread and correct the C/A code phase,
Phase_Code＝Phase_Code+ΔPhase_Code
Step 5-3: proofread and correct the navigation message phase place,
Phase_Data＝Phase_Data+ΔPhase_Data
Do not proofread and correct interval T if reach finite word length effect e, directly accumulation result is preserved.
Step 6: three phase-accumulated values that step 5 is preserved are by 2 32carry out delivery output, specifically comprise the steps:
Step 6-1: the intermediate frequency carrier phase is carried out to delivery,
Phase_Carrier＝mod{Phase_Carrier，2 32}
Step 6-2: the C/A code phase is carried out to delivery,
Phase_Code＝mod{Phase_Code，2 32}
Step 6-3: the navigation message phase place is carried out to delivery,
Phase_Data＝mod{Phase_Data，2 32}
In the fixed-point implementation process, delivery is exactly simply to get low level, to 2 32delivery is exactly to take out simply low 32 of phase-accumulated value to get final product.
Step 7: judge whether to have reached parameter and upgrade interval T uif, reach, return to step 2, otherwise return to step 4.
The step 2 of this specific embodiment adopts floating system to realize, step 3,4,5,6 adopts the fixed point mode to realize, from top step, describes and can find out, has only reached parameter and has upgraded interval T uthe time, just can require the floating-point platform to recalculate each frequency control word, and parameter is upgraded interval T uvalue generally all than finite word length effect, proofread and correct interval T egrow, this has just well taken into account precision and system cost, makes the floating-point operation amount of expensive and high power consumption fewer, and a large amount of computings is placed on the fixed point platform and realizes.Therefore, the technical program is when specific implementation, and suggestion realizes that by floating-point part and fixed-point implementation partly separate, be placed on different platforms, as adopted the pattern of " DSP+FPGA ", DSP is responsible for the calculating that floating-point is relevant, FPGA is responsible for phase-accumulated and tables look-up, and jointly completes the task of simulating GPS signal.

Claims (6)

1. the method for the phase error of proofreading and correct the gps signal source is characterized in that in turn including the following steps:
Step 1: the word length of setting digital platform is L w, intermediate frequency carrier, C/A code and the navigation message signals phase error of largest tolerable separately are Max_Phase_Err, parameter interval T update time u, the time interval T that finite word length effect is proofreaied and correct e, the sampling time interval T of signal s;
Step 2: utilize the Doppler frequency parameter of current time, calculate the frequency control word of floating-point format;
Step 3: it is L that the frequency control word of the floating-point format that step 2 is obtained converts word length to wthe frequency control word of fixed point format, record the error that single conversion produces, and calculate the time interval T proofreaied and correct at finite word length effect ethe summation of the error of interior generation, then preserve this sum of the deviations with fixed point format;
Step 4: the frequency control word of the fixed point format obtained by step 3, with the sampling time interval T of signal sfor the time beat, the phase place of signal is added up, then judge whether the time of cumulative process reaches the time interval T that finite word length effect is proofreaied and correct eif, reached this interval, first by this phase-accumulated value, add the sum of the deviations that step 3 obtains, obtain the phase error correction value, by this phase error correction value pair
Figure FSB0000114467210000011
preserve after delivery and export, then entering step 5, if do not reach, directly that phase-accumulated value is right
Figure FSB0000114467210000012
preserve and export this result after delivery, then enter step 5;
Step 5: judge whether to reach parameter interval T update time uif, reach, return to step 2; If do not reach, return to step 4;
Wherein, described frequency control word is in intermediate frequency carrier frequency control word, C/A code frequency control word and navigation message frequency control word; The time interval Te that finite word length effect is proofreaied and correct adopts following method to determine:
1) for each described frequency control word, calculate its needed minimum cumulative frequency Min_N=Max_Phase_Err/Max_ Δ FCW according to the described maximum phase error Max_Phase_Err that can tolerate respectively, wherein, the absolute value that Max_ Δ FCW is the maximum error that may cause while in described step 3, the frequency control word of floating-point format being converted to the frequency control word of fixed point format, for adopting the round up conversion method of mode of decimal place, Max_ Δ FCW=0.5, for adopting the conversion method of directly removing decimal place, Max_ Δ FCW=1;
2) for each described frequency control word, calculate respectively Te=Ts * Min_N, the sampling time interval that wherein Ts is described signal;
3) get 2) minimum value in three Te obtaining of step, be the time interval Te that finite word length effect is proofreaied and correct.
2. a kind of method for the phase error of proofreading and correct the gps signal source according to claim 1, is characterized in that: parameter interval T update time ube greater than or equal to the time interval T that finite word length effect is proofreaied and correct e.
3. a kind of method for the phase error of proofreading and correct the gps signal source according to claim 1, is characterized in that: parameter interval T update time uthe time interval T that finite word length effect is proofreaied and correct eintegral multiple.
4. a kind of method for the phase error of proofreading and correct the gps signal source according to claim 1, it is characterized in that: it is L that described step 3 converts the frequency control word of floating-point format to word length wthe step of fixed point format comprise:
1) frequency control word of described floating-point format is multiplied by
Figure FSB0000114467210000021
;
2) by 1) value that obtains of step carry out round numbers computing that decimal place rounds up or by 1) value that obtains of step directly removes the rounding operation of decimal place.
5. a kind of method for the phase error of proofreading and correct the gps signal source according to claim 1, is characterized in that: relate to the rapid 3 described time interval T that proofread and correct at finite word length effect eerror * T that the summation of the error of interior generation=described single conversion produces e/ T s.
6. a kind of method for the phase error of proofreading and correct the gps signal source according to claim 1, it is characterized in that: it is that following formula is carried out in circulation: the frequency control word of phase-accumulated value=phase-accumulated value+fixed point format that described step 3 obtains that the phase place of described step 4 pair signal is carried out cumulative method, if be to calculate for the first time its Doppler frequency parameter for working as this gps satellite of front simulation, the prima facies place value that initial value of phase-accumulated value is signal, otherwise the initial value of phase-accumulated value is the phase-accumulated value preserved in described step 4.
CN201110394219.0A 2011-11-22 2011-11-22 Method for calibrating phase errors of global positioning system (GPS) signal source Expired - Fee Related CN102590837B (en)

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