CN113970765A - Tracking loop and method for multimode satellite navigation receiver - Google Patents
Tracking loop and method for multimode satellite navigation receiver Download PDFInfo
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- CN113970765A CN113970765A CN202111255577.3A CN202111255577A CN113970765A CN 113970765 A CN113970765 A CN 113970765A CN 202111255577 A CN202111255577 A CN 202111255577A CN 113970765 A CN113970765 A CN 113970765A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/29—Acquisition or tracking or demodulation of signals transmitted by the system carrier including Doppler, related
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/30—Acquisition or tracking or demodulation of signals transmitted by the system code related
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/33—Multimode operation in different systems which transmit time stamped messages, e.g. GPS/GLONASS
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Abstract
The invention relates to a tracking loop of a multimode satellite navigation receiver, which comprises the following components: the down converter is used for converting the received satellite signals into intermediate frequency signals through down conversion, and the intermediate frequency signals serve as input signals of the tracking loop module; the tracking loop module is used for tracking the signal to finally obtain a navigation message for resolving the subsequent three-dimensional position, speed and time; the tracking loop module comprises 12 GPS tracking loops and 12 BD tracking loops, wherein each tracking loop comprises a carrier tracking loop for tracking a signal carrier so as to realize carrier stripping and a code tracking loop for tracking a spread spectrum code so as to realize code stripping. The invention has weak signal tracking capability, and can ensure that the tracking loop still keeps accurate tracking of signals under the condition of weak signals; the invention has lower power consumption, designs the interval accumulation and low-frequency working mode, and reduces the power consumption of the tracking loop on the basis of ensuring the positioning performance.
Description
Technical Field
The invention relates to the technical field of satellite navigation, in particular to a tracking loop and a tracking method of a multimode satellite navigation receiver.
Background
The global satellite navigation system mainly comprises a GPS, BD, Galileo and Glonass system, and is a space-based radio navigation positioning system which can provide all-weather three-dimensional coordinate, speed and time information for users at any place on the earth surface or in a near-earth space. Because of its remarkable superiority, it is widely used by various industries, and at present, the utilization rate is higher than that of the GPS and BD systems.
Along with the completion of BD navigation satellite networking in China, a receiver which can compatibly receive GPS and BD multimode navigation satellite signals occupies an important position in the market. The multimode satellite navigation receiver consists of a radio frequency, a baseband and a software algorithm, wherein the radio frequency is used for receiving a high-frequency satellite signal and carrying out frequency reduction processing on the high-frequency satellite signal to obtain an intermediate-frequency signal; the base band further reduces the frequency of the intermediate frequency signal to be converted into a base band signal, so that navigation messages, time and other information are obtained, and the information is processed by navigation software, so that three-dimensional coordinate, speed and time information is obtained. Therefore, the important part determining the performance of the receiver is the baseband, and the key technology of the baseband design is the design of the tracking loop.
Currently, the existing multimode satellite navigation receivers and their loop technologies can be roughly classified into three categories: firstly, the receiving methods of different systems are simply combined together, and a universal tracking loop is constructed by adopting a simple method in a superposition way, so that the used resource amount is increased, and meanwhile, the power consumption and the cost are also improved; secondly, in order to reduce resource waste and limit by the number of loops, a method of tracking loop multiplexing is adopted, time slot multiplexing loop resources are customized for each type of satellite, and when more satellites are tracked, the tracking performance is reduced due to too short time slots, even signals are unlocked; and thirdly, the software receiver realizes the function of the tracking loop by software, so that the software receiver has great flexibility, but the operation in the tracking stage is intensive, the data volume is large, the time consumption is high, and the requirement on a CPU is high.
Disclosure of Invention
The invention aims to provide a tracking loop of a multimode satellite navigation receiver, which has low power consumption and can ensure that the tracking loop still keeps accurate tracking of signals under the condition of weak signals.
In order to achieve the purpose, the invention adopts the following technical scheme: a multimode satellite navigation receiver tracking loop comprising:
the down converter is used for converting the received satellite signals into intermediate frequency signals through down conversion, and the intermediate frequency signals serve as input signals of the tracking loop module;
the tracking loop module is used for tracking the signal to finally obtain a navigation message for resolving the subsequent three-dimensional position, speed and time; the tracking loop module comprises 12 GPS tracking loops and 12 BD tracking loops, wherein each tracking loop comprises a carrier tracking loop for tracking a signal carrier so as to realize carrier stripping and a code tracking loop for tracking a spread spectrum code so as to realize code stripping.
The carrier tracking loop includes:
the carrier generator is used for generating copied carriers, generating three paths of carriers under the control of a frequency offset constant w, wherein the three paths of carriers are respectively a leading carrier se, a real-time carrier sp and a lagging carrier sl, and the frequency difference of the three paths of carriers is wHZ;
the first mixer module multiplies the intermediate frequency signal by a leading carrier se, a real-time carrier sp and a lagging carrier sl respectively, and strips the carrier, wherein the signal obtained by a branch mixed with the real-time carrier sp is a baseband signal;
the first correlator module is used for carrying out correlation operation on the three paths of signals;
a first non-coherent module for performing non-coherent integration on the result of the correlation operation;
the selector module is used for controlling data to flow into the carrier discriminator through the configuration parameters;
and the carrier discriminator is used for discriminating the phase difference and the frequency difference of the signals, the output result of the carrier discriminator is the phase difference and the frequency difference between the intermediate frequency carrier signals copied by the receiver and the received intermediate frequency carrier signals, the phase and the frequency of the carrier generator are regulated through feedback, the intermediate frequency carrier time copied by the carrier generator of the receiver is consistent with the received intermediate frequency carrier, and the Doppler information in the current signals is obtained at the same time, so that the stripping of the intermediate frequency carrier is realized.
The code tracking loop includes:
the first frequency mixer multiplies the intermediate frequency signal by a real-time carrier sp in a carrier tracking loop and strips the carrier;
a spread code generator for generating a copied spread code cp and generating a leading code ce and a lagging code cl based on the generated code cp;
the second correlator module is used for carrying out correlation operation;
the second non-coherent device module is used for performing non-coherent integration on the correlation operation result;
the code discriminator is used for phase discrimination to obtain the phase difference between the replica code and the received code, and the phase of the spread spectrum code generator is adjusted through the feedback of the low-pass filter, so that the replica spread spectrum code of the receiver is consistent with the received spread spectrum code, the peeling of the spread spectrum code is realized, and the signal-to-noise ratio of the signal is improved;
the code tracking loop in the GPS tracking loop is a GPS code tracking loop; the 12 BD tracking loops comprise 4 BD-GEO tracking loops and 8 BD-MEO tracking loops, wherein a code tracking loop in the BD-GEO tracking loops is a BD-GEO code tracking loop, and a code tracking loop in the BD-MEO tracking loops is a BD-MEO code tracking loop.
The first mixer module comprises a first mixer, a second mixer and a third mixer, and the structures of the first mixer, the second mixer and the third mixer are the same; the first correlator module comprises a first correlator, a second correlator and a third correlator, and the structures of the first correlator, the second correlator and the third correlator are the same; the first non-coherent module comprises a first non-coherent device, a second non-coherent device and a third non-coherent device; the three paths of carriers of the leading carrier se, the instant carrier sp and the lagging carrier sl are respectively and correspondingly input into a first mixer, a second mixer and a third mixer to be mixed with an intermediate frequency signal one by one, 3 branch signals are formed and respectively and correspondingly sent into a first correlator, a second correlator and a third correlator to be accumulated one by one, the number of accumulated data is controlled by correlation time, a correlation result is output after every 1 correlation time, the accumulated result is truncated to obtain a final correlation result, and the three paths of correlation results are respectively and correspondingly input into a first incoherent device, a second incoherent device and a third incoherent device;
the input of the first non-coherent device is the output of the first correlator, and the output result of the first correlator comprises an in-phase component I and a quadrature component Q; the first non-coherent device calculates the modulus of the correlation result and then accumulates, and the accumulation times are controlled by the non-correlation time parameter; after the accumulation reaches the set value of the incoherent times, the accumulated result is subjected to bit cutting to obtain an incoherent result Se, and the incoherent result Se is sent to a carrier discriminator for amplitude frequency discrimination;
the input of the second non-coherent device is the output of the second coherent device, and the output result of the second coherent device comprises an in-phase component I and a quadrature component Q; the second non-coherent device calculates the modulus of the correlation result and then accumulates, and the accumulation times are controlled by the non-correlation time parameter; after the accumulation reaches the set value of the incoherent times, the accumulated result is subjected to bit cutting processing to obtain an incoherent result S1, and the incoherent result S1 is sent to a carrier discriminator for amplitude frequency discrimination;
the carrier discriminator comprises a first sub-discriminator and a second sub-discriminator, and the second sub-discriminator is an amplitude discriminator;
the output of the third correlator has 4 branch cases:
(4a) when the parameter sets the number of times of non-coherence to 0, the coherent result S1Directly sending the signals into a first sub discriminator to carry out phase discrimination;
(4b) when the parameter sets that the number of incoherent times is not 0, the modulus of the correlation result is calculated, the control parameter of a third selector is 0, the data passes through the third selector to be subjected to incoherent accumulation, the output of the third incoherent device is Sp, and the Sp is sent to an amplitude frequency discriminator to be used for amplitude frequency discrimination;
(4c) when the parameter sets that the number of times of non-coherence is not 0, the correlation results are multiplied in a conjugate mode, the control parameter of a third selector is 1, data pass through the third selector to be subjected to non-coherent accumulation, the output of the third non-coherent selector is Sp, and the data are sent to a first sub-discriminator to be subjected to frequency discrimination;
(4d) when the parameter sets the number of incoherent times as 0, the correlation results are multiplied in a conjugate mode, the output of the third incoherent device is Sp, and the Sp is sent to the first sub discriminator to carry out frequency discrimination.
The second correlator module comprises a fourth correlator and a fifth correlator which have the same structure; the second incoherent module comprises a fourth incoherent device and a fifth incoherent device which are identical in structure; the spread spectrum code generator generates a combined code of a BD ranging code and an NH code copied by the receiver, and the combined code is taken as an instant code cp, and an advance code ce advanced by half a chip and a lag code cl lagging by half a chip are regenerated by taking the instant code cp as a reference; the time code cp is sent into a carrier tracking loop to assist carrier tracking, and the advance code ce and the lag code cl respectively enter a fourth correlator and a fifth correlator;
the correlation results output by the fourth correlator and the fifth correlator are subjected to modulus in the fourth noncoherent device and the fifth noncoherent device, and the modulus data has 2 branches:
(5a) aiming at the fourth incoherent device, when the parameter sets the incoherent times to be 0, the selector of the fourth incoherent device is 1, and the modulus result Ce is output from the fourth incoherent device and sent to the code phase discriminator;
(5b) for the fourth incoherent device, when the parameter sets that the incoherent times are not 0, the modulus result is sent to an accumulator for incoherent calculation, meanwhile, data is sent to a queue FIFO, if the size of the FIFO exceeds a preset value, namely the incoherent times, the number of the queue head is detected, the number is subtracted by an accumulation register, and the situation that the accumulation times are 1 time more than the set incoherent times is avoided; after the accumulation reaches the set value of incoherent times, the accumulated result is subjected to truncation processing, so that an incoherent result Ce is obtained and is sent to a code phase discriminator to be used for phase discrimination;
the principle of the fourth non-coherent device is the same as that of the fifth non-coherent device;
the code phase difference output by the code phase discriminator is fed back to the spread spectrum code generator through the low pass filter, and the phase of the spread spectrum code generator is adjusted, so that the copied code is dynamically consistent with the received code;
and the output results of the fourth incoherent device and the fifth incoherent device are used as the input of the code phase discriminator, division calculation is carried out in the code phase discriminator, phase discrimination is carried out, and the obtained output is the phase difference between the code copied by the spread spectrum code generator and the received code.
Another object of the present invention is to provide a tracking method for a tracking loop of a multimode satellite navigation receiver, the method comprising the following sequential steps:
(1) the method comprises the steps that received satellite signals are converted into intermediate frequency signals through down-conversion, the intermediate frequency signals serve as input signals of a tracking loop module, and parameters of the tracking loop are configured through an interface;
(2) respectively sending the intermediate frequency signals to 12 GPS tracking loops and 12 BD tracking loops, and in the tracking loops, mixing the intermediate frequency signals to obtain baseband signals;
(3) enabling the intermediate frequency signal obtained in the step (1) to pass through a carrier tracking loop to obtain phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal, and adjusting the phase and frequency of a carrier generator through feedback to enable the intermediate frequency carrier copied by the receiver to be consistent with the received intermediate frequency carrier at the moment, so that Doppler information in the current signal is obtained, and stripping of the intermediate frequency carrier is realized; the tracking loop is adapted to signals with different intensities, the baseband signal processing mode comprises a full accumulation mode and a half accumulation mode, and the identification mode of the carrier identifier comprises a frequency identification mode, a phase identification mode and an amplitude frequency identification mode; when the signal is strong, a full accumulation mode is adopted for the correlation operation of the baseband signal, and a phase frequency discrimination or phase discrimination mode is adopted for the carrier discriminator; when the signal is weak, carrying out long-time correlation operation on the baseband signal, and when the correlation time reaches 20ms, adopting a semi-accumulation mode and adopting an amplitude frequency discrimination mode by a carrier discriminator;
(4) the baseband signals obtained in the step (2) pass through a code tracking loop to obtain the phase difference between the spread spectrum code copied by the receiver and the received spread spectrum code, and the phase of the spread spectrum code generator is adjusted through a feedback mechanism to ensure that the time of copying the spread spectrum code of the receiver is consistent with the received spread spectrum code, thereby realizing the stripping of the spread spectrum code;
(5) after the step (3) is finished, the carrier is stripped, after the step (4) is finished, the spread spectrum code is stripped, and the signal only contains navigation messages; carrying out bit synchronization on the navigation message, and searching a bit edge of the navigation message;
(6) and carrying out frame synchronization, searching for a frame header of navigation message data, and realizing the analysis of the navigation message for the subsequent resolution of the three-dimensional position, speed and time.
The half accumulation mode is that data accumulation only lasts for half of the set correlation time in the correlation operation of the baseband data, and the correlation operation is carried out in the first half interval of the correlation time.
The amplitude frequency discrimination mode is that a leading carrier Se, a real-time carrier Sp and a lagging carrier Sl are respectively mixed with an intermediate frequency signal, correlation calculation and incoherent integration are carried out to obtain three paths of outputs Sl, Sp and Se, the three paths of outputs are simultaneously sent to an amplitude frequency discriminator, and the output result of the amplitude frequency discriminator is a frequency difference we:
according to the technical scheme, the beneficial effects of the invention are as follows: first, the present invention has weak signal tracking capability: aiming at signals with different intensities, the invention designs a full-accumulation and semi-accumulation baseband data processing mode and a carrier identification mode of phase identification, frequency identification and amplitude frequency identification, so that a tracking loop can still keep accurate tracking on the signals under the condition of weak signals; second, the invention has lower power consumption: aiming at the problem of power consumption, the invention designs an interval accumulation and low-frequency working mode, and reduces the power consumption of the tracking loop on the basis of ensuring the positioning performance.
Drawings
FIG. 1 is a schematic down conversion diagram;
FIG. 2 is a schematic diagram of the overall structure of the tracking loop of the present invention;
FIG. 3 is a schematic diagram of a tracking loop;
FIG. 4 is a schematic diagram of the third non-coherent device of FIG. 3;
FIG. 5 is a schematic diagram of the amplitude discriminator of FIG. 3;
FIG. 6 is a schematic diagram of a full accumulation, half accumulation;
FIG. 7 is a schematic diagram of amplitude frequency discrimination;
FIG. 8 is a graph of amplitude phase discrimination effect;
FIG. 9 is a power mode switching diagram;
FIG. 10 is a schematic view of a normal mode and an interval accumulation mode;
FIG. 11 is a schematic illustration of an interval accumulation mode positioning error;
FIG. 12 is a schematic diagram of a normal mode and a low frequency mode;
FIG. 13 is a diagram illustrating low frequency mode positioning errors.
Detailed Description
As shown in fig. 2, a multimode satellite navigation receiver tracking loop comprises:
the down converter is used for converting the received satellite signals into intermediate frequency signals through down conversion, and the intermediate frequency signals serve as input signals of the tracking loop module;
the tracking loop module is used for tracking the signal to finally obtain a navigation message for resolving the subsequent three-dimensional position, speed and time; the tracking loop module comprises 12 GPS tracking loops and 12 BD tracking loops, wherein each tracking loop comprises a carrier tracking loop for tracking a signal carrier so as to realize carrier stripping and a code tracking loop for tracking a spread spectrum code so as to realize code stripping.
As shown in fig. 1, a received satellite signal is down-converted into an initial intermediate frequency signal, and meanwhile, data saturation is prevented according to the register width limitation, valid data information is retained, and the initial intermediate frequency signal is truncated to obtain an intermediate frequency signal. The intermediate frequency signal is limited in a range from-7 FFF to 7FFF through bit cutting, and the loop working frequency 240f0 and f0 are 1.023 MHz.
As shown in fig. 3, the carrier tracking loop includes:
the carrier generator is used for generating copied carriers, generating three paths of carriers under the control of a frequency offset constant w, wherein the three paths of carriers are respectively a leading carrier se, a real-time carrier sp and a lagging carrier sl, and the frequency difference of the three paths of carriers is wHZ;
the first mixer module multiplies the intermediate frequency signal by a leading carrier se, a real-time carrier sp and a lagging carrier sl respectively, and strips the carrier, wherein the signal obtained by a branch mixed with the real-time carrier sp is a baseband signal;
the first correlator module is used for carrying out correlation operation on the three paths of signals;
a first non-coherent module for performing non-coherent integration on the result of the correlation operation;
the selector module is used for controlling data to flow into the carrier discriminator through the configuration parameters;
and the carrier discriminator is used for discriminating the phase difference and the frequency difference of the signals, the output result of the carrier discriminator is the phase difference and the frequency difference between the intermediate frequency carrier signals copied by the receiver and the received intermediate frequency carrier signals, the phase and the frequency of the carrier generator are regulated through feedback, the intermediate frequency carrier time copied by the carrier generator of the receiver is consistent with the received intermediate frequency carrier, and the Doppler information in the current signals is obtained at the same time, so that the stripping of the intermediate frequency carrier is realized.
As shown in fig. 3, the code tracking loop includes:
the first frequency mixer multiplies the intermediate frequency signal by a real-time carrier sp in a carrier tracking loop and strips the carrier;
a spread code generator for generating a copied spread code cp and generating a leading code ce and a lagging code cl based on the generated code cp;
the second correlator module is used for carrying out correlation operation;
the second non-coherent device module is used for performing non-coherent integration on the correlation operation result;
the code discriminator is used for phase discrimination to obtain the phase difference between the replica code and the received code, and the phase of the spread spectrum code generator is adjusted through the feedback of the low-pass filter, so that the replica spread spectrum code of the receiver is consistent with the received spread spectrum code, the peeling of the spread spectrum code is realized, and the signal-to-noise ratio of the signal is improved;
the code tracking loop in the GPS tracking loop is a GPS code tracking loop; the 12 BD tracking loops comprise 4 BD-GEO tracking loops and 8 BD-MEO tracking loops, wherein a code tracking loop in the BD-GEO tracking loops is a BD-GEO code tracking loop, and a code tracking loop in the BD-MEO tracking loops is a BD-MEO code tracking loop.
The serial number of the GPS code tracking loop is 1-12, the serial number of the BD-GEO tracking loop is 12-16, and the serial number of the BD-MEO tracking loop is 17-24. The GPS code tracking loop, the BD-GEO tracking loop and the BD-MEO tracking loop have the same structure except that the principle of the spread spectrum code generator is different, the frequency of the numerical control oscillator is different and the other structures are consistent.
The first mixer module comprises a first mixer, a second mixer and a third mixer, and the structures of the first mixer, the second mixer and the third mixer are the same; the first correlator module comprises a first correlator, a second correlator and a third correlator, and the structures of the first correlator, the second correlator and the third correlator are the same; the first incoherent module comprises a first incoherent device, a second incoherent device and a third incoherent device, and the first incoherent device and the second incoherent device have the same structure; the three paths of carriers of the leading carrier se, the instant carrier sp and the lagging carrier sl are respectively and correspondingly input into a first mixer, a second mixer and a third mixer to be mixed with an intermediate frequency signal one by one, 3 branch signals are formed and respectively and correspondingly sent into a first correlator, a second correlator and a third correlator to be accumulated one by one, the number of accumulated data is controlled by correlation time, a correlation result is output after every 1 correlation time, the accumulated result is truncated to obtain a final correlation result, and the three paths of correlation results are respectively and correspondingly input into a first incoherent device, a second incoherent device and a third incoherent device;
the input of the first non-coherent device is the output of the first correlator, and the output result of the first correlator comprises an in-phase component I and a quadrature component Q; the first non-coherent device calculates the modulus of the correlation result and then accumulates, and the accumulation times are controlled by the non-correlation time parameter; after the accumulation reaches the set value of the incoherent times, the accumulated result is subjected to bit cutting to obtain an incoherent result Se, and the incoherent result Se is sent to a carrier discriminator for amplitude frequency discrimination;
the input of the second non-coherent device is the output of the second coherent device, and the output result of the second coherent device comprises an in-phase component I and a quadrature component Q; the second non-coherent device calculates the modulus of the correlation result and then accumulates, and the accumulation times are controlled by the non-correlation time parameter; after the accumulation reaches the set value of the incoherent times, the accumulated result is subjected to bit cutting processing to obtain an incoherent result S1, and the incoherent result S1 is sent to a carrier discriminator for amplitude frequency discrimination;
as shown in fig. 4, the correlator output includes an in-phase component I and a quadrature component Q in the form of an imaginary number I + Qj. The input of the third non-coherent device is the output of the third coherent device. The input signal has 3 branches:
(1) when the parameter sets the number of incoherent times to be not 0, the modulus of the correlation result is calculated
The selector control parameter is set to 0, and data passes through the selector and passes through the time delay unit D2The data is delayed for one correlation calculation period and then sent to an accumulator for noncoherent calculation to obtain a noncoherent result. While data is also fed into the queue FIFO. The incoherent result is passed through a delay unit D3If the size of FIFO exceeds the preset value (incoherent times), the incoherent result is sent back to the accumulator, the FIFO finds out the number of the queue head, and the accumulation register subtracts the number to avoid that the accumulated times are 1 more than the set incoherent times. And after the incoherent result is subjected to bit truncation, the incoherent result is output as Sp.
(2) When the parameter sets the number of incoherent times to be not 0, the correlation results are multiplied in a conjugate manner. The coherent result is I + Qj, after conjugation is
After conjugate calculation, the signal passes through a delay unit D4The delay time of the delay unit is a correlation calculation period, and the conjugation result of the current time
Multiplying by I + Qj at the next moment, setting the control parameter of the selector to be 1, and enabling the conjugate multiplication result to pass through the selector and D2And then carrying out incoherent accumulation, and outputting a result Sp.
(3) When the number of times of noncoherence is set to 0 by the parameter, the correlation results are multiplied by conjugate, and the output is S2.
As shown in fig. 5, the input signal is input through the input terminals a and b of the amplitude discriminator, and a/b is calculated by division in the discriminator, and the division result is output from the discriminator.
The carrier discriminator comprises a first sub-discriminator and a second sub-discriminator, and the second sub-discriminator is an amplitude discriminator;
the output of the third correlator has 4 branch cases:
(4a) when the parameter sets the number of times of non-coherence to 0, the coherent result S1Directly sending the signals into a first sub discriminator to carry out phase discrimination;
(4b) when the parameter sets that the number of incoherent times is not 0, the modulus of the correlation result is calculated, the control parameter of a third selector is 0, the data passes through the third selector to be subjected to incoherent accumulation, the output of the third incoherent device is Sp, and the Sp is sent to an amplitude frequency discriminator to be used for amplitude frequency discrimination;
(4c) when the parameter sets that the number of times of non-coherence is not 0, the correlation results are multiplied in a conjugate mode, the control parameter of a third selector is 1, data pass through the third selector to be subjected to non-coherent accumulation, the output of the third non-coherent selector is Sp, and the data are sent to a first sub-discriminator to be subjected to frequency discrimination;
(4d) when the parameter sets the number of incoherent times as 0, the correlation results are multiplied in a conjugate mode, the output of the third incoherent device is Sp, and the Sp is sent to the first sub discriminator to carry out frequency discrimination.
The second correlator module comprises a fourth correlator and a fifth correlator which have the same structure; the second incoherent module comprises a fourth incoherent device and a fifth incoherent device which are identical in structure; the spread spectrum code generator generates a combined code of a BD ranging code and an NH code copied by the receiver, and the combined code is taken as an instant code cp, and an advance code ce advanced by half a chip and a lag code cl lagging by half a chip are regenerated by taking the instant code cp as a reference; the time code cp is sent into a carrier tracking loop to assist carrier tracking, and the advance code ce and the lag code cl respectively enter a fourth correlator and a fifth correlator;
the correlation results output by the fourth correlator and the fifth correlator are subjected to modulus in the fourth noncoherent device and the fifth noncoherent device, and the modulus data has 2 branches:
(5a) aiming at the fourth incoherent device, when the parameter sets the incoherent times to be 0, the selector of the fourth incoherent device is 1, and the modulus result Ce is output from the fourth incoherent device and sent to the code phase discriminator;
(5b) for the fourth incoherent device, when the parameter sets that the incoherent times are not 0, the modulus result is sent to an accumulator for incoherent calculation, meanwhile, data is sent to a queue FIFO, if the size of the FIFO exceeds a preset value, namely the incoherent times, the number of the queue head is detected, the number is subtracted by an accumulation register, and the situation that the accumulation times are 1 time more than the set incoherent times is avoided; after the accumulation reaches the set value of incoherent times, the accumulated result is subjected to truncation processing, so that an incoherent result Ce is obtained and is sent to a code phase discriminator to be used for phase discrimination;
the principle of the fourth non-coherent device is the same as that of the fifth non-coherent device;
the code phase difference output by the code phase discriminator is fed back to the spread spectrum code generator through the low pass filter, and the phase of the spread spectrum code generator is adjusted, so that the copied code is dynamically consistent with the received code;
and the output results of the fourth incoherent device and the fifth incoherent device are used as the input of the code phase discriminator, division calculation is carried out in the code phase discriminator, phase discrimination is carried out, and the obtained output is the phase difference between the code copied by the spread spectrum code generator and the received code.
Another object of the present invention is to provide a tracking method for a tracking loop of a multimode satellite navigation receiver, the method comprising the following sequential steps:
(1) the method comprises the steps that received satellite signals are converted into intermediate frequency signals through down-conversion, the intermediate frequency signals serve as input signals of a tracking loop module, and parameters of the tracking loop are configured through an interface; the tracking loop parameter configuration comprises the following steps: truncation, correlation time, number of incoherences, low pass filter coefficients, queue length, initial carrier frequency, initial code frequency, frequency offset, selector parameters, full accumulation mode enable, half accumulation mode enable, amplitude mode enable, discriminator enable, loop enable, power consumption mode, reset, etc.;
(2) respectively sending the intermediate frequency signals to 12 GPS tracking loops and 12 BD tracking loops, and in the tracking loops, mixing the intermediate frequency signals to obtain baseband signals;
(3) enabling the intermediate frequency signal obtained in the step (1) to pass through a carrier tracking loop to obtain phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal, and adjusting the phase and frequency of a carrier generator through feedback to enable the intermediate frequency carrier copied by the receiver to be consistent with the received intermediate frequency carrier at the moment, so that Doppler information in the current signal is obtained, and stripping of the intermediate frequency carrier is realized; the tracking loop is adapted to signals with different intensities, the baseband signal processing mode comprises a full accumulation mode and a half accumulation mode, and the identification mode of the carrier identifier comprises a frequency identification mode, a phase identification mode and an amplitude frequency identification mode; when the signal is strong, a full accumulation mode is adopted for the correlation operation of the baseband signal, and a phase frequency discrimination or phase discrimination mode is adopted for the carrier discriminator; when the signal is weak, long-time correlation operation is carried out on the baseband signal, when the correlation time reaches 20ms, a semi-accumulation mode is adopted, the problem that the correlation result is offset due to navigation message data jumping can be effectively avoided, and an amplitude frequency discrimination mode is adopted by a carrier discriminator;
(4) the baseband signals obtained in the step (2) pass through a code tracking loop to obtain the phase difference between the spread spectrum code copied by the receiver and the received spread spectrum code, and the phase of the spread spectrum code generator is adjusted through a feedback mechanism to ensure that the time of copying the spread spectrum code of the receiver is consistent with the received spread spectrum code, thereby realizing the stripping of the spread spectrum code;
(5) after the step (3) is finished, the carrier is stripped, after the step (4) is finished, the spread spectrum code is stripped, and the signal only contains navigation messages; carrying out bit synchronization on the navigation message, and searching a bit edge of the navigation message; the successful bit synchronization can further assist the tracking of the code loop and the carrier loop.
(6) And carrying out frame synchronization, searching for a frame header of navigation message data, and realizing the analysis of the navigation message for the subsequent resolution of the three-dimensional position, speed and time.
The tracking loop module adopts a low-power consumption design and comprises three working modes of normal, interval accumulation and low frequency. And under the condition that the satellite signal does not enter the stable tracking condition or the power supply is sufficient, the power supply is carried out in a normal mode, and all modules of the tracking loop continuously work under full load. After entering the stable tracking state, an interval accumulation mode or a low frequency mode can be adopted.
The half accumulation mode is that data accumulation only lasts for half of the set correlation time in the correlation operation of the baseband data, and the correlation operation is carried out in the first half interval of the correlation time.
The amplitude frequency discrimination mode is that a leading carrier Se, a real-time carrier Sp and a lagging carrier Sl are respectively mixed with an intermediate frequency signal, correlation calculation and incoherent integration are carried out to obtain three paths of outputs Sl, Sp and Se, the three paths of outputs are simultaneously sent to an amplitude frequency discriminator, and the output result of the amplitude frequency discriminator is a frequency difference we:
the present invention will be further described with reference to fig. 1 to 11.
As shown in fig. 6, the start position of the correlation of the baseband signal is random compared to the actual data bits. The correlation time and accumulation mode will be unambiguous when the tracking loop is configured with parameters. The correlation time is usually set to 1ms, 2ms, 4ms, 5ms, 10ms, 20ms, and the accumulation mode is a full accumulation mode or a half accumulation mode. The full accumulation mode is a correlation time set for data accumulation in correlation operation of baseband data. When the signal is strong, the correlation operation is usually performed on the baseband data in a full accumulation mode, and all effective information is reserved. The half accumulation mode is a mode in which data accumulation continues for only half of a set correlation time in correlation calculation of baseband data, and correlation calculation is usually performed in the first half of the correlation time. The semi-accumulation mode is mainly applied to the weak signal condition, the relevant time needs to be correspondingly increased when the signal is weak, when the relevant time reaches 20ms, the relevant accumulated data offset condition caused by the inversion of the navigation data bit can occur, so that the long-time correlation can not play a role in improving the signal to noise ratio, the relevant data offset problem can not occur only when the relevant operation starting moment is aligned with the actual navigation data bit edge, and the data offset problems of different degrees of the relevant operations started at other moments occur. When the correlation time is 20ms, the semi-cumulative correlation time is 10ms, the probability of data cancellation in the actual correlation operation is greatly reduced, and the problem of data cancellation can be effectively avoided.
The carrier discrimination modes include frequency discrimination, phase discrimination, and amplitude discrimination modes. The principle of frequency and phase discrimination is the same as that introduced in the Schott & ltGPS principle and receiver design & gt. The phase discrimination method fails when the signal strength is too low, so the amplitude discrimination method is used when the signal is weak, see fig. 7. The amplitude frequency discrimination method comprises the steps of respectively carrying out frequency mixing, correlation calculation and incoherent integration on a leading carrier Se, a real-time carrier Sp and a lagging carrier Sl with an intermediate frequency signal to obtain three paths of outputs Sl, Sp and Se, simultaneously sending the three paths of outputs to an amplitude frequency discriminator, and outputting a frequency difference we by the frequency discriminator:
the amplitude discriminator has the calculation formula as follows:
the amplitude discrimination effect is shown in fig. 8. Under the conditions of no shielding and clear weather of the signals, the carrier-to-noise ratio of the signals received by the receiver is 40 dB-35 dB. The carrier-to-noise ratio is 37dB at the beginning of the signal, and when the signal is strong, the amplitude frequency discrimination method can make the tracking loop stably track the GPS satellite signal, the Doppler shows slow and uniform change, which is the continuous and stable change of Doppler caused by the stable movement of the satellite; along with the reduction of the signal intensity, the carrier-to-noise ratio is gradually reduced from 37dB, and the Doppler still presents slow and uniform change, which shows that the tracking loop can still stably track the satellite signal along with the reduction of the signal intensity; when the signal continues to drop and the carrier-to-noise ratio is less than 15dBHz, Doppler begins to fluctuate in a large range, and as the carrier-to-noise ratio is further reduced, the tracking loop is unlocked, and Doppler information of the current signal cannot be obtained. Therefore, the amplitude frequency discrimination mode can stably track the satellite signals with the signal intensity of more than 15 dBHz.
Referring to fig. 9, power consumption mode. The tracking loop adopts a low-power consumption design and comprises a normal mode, an interval accumulation mode and a low-frequency mode. And when the satellite signal is not stably tracked or the power supply is sufficient, the power supply is carried out in a normal mode, and all modules of the tracking loop work at full load. After entering the stable tracking state, an interval accumulation mode or a low frequency mode can be adopted. The normal mode can be switched with the low-frequency mode and the interval accumulation mode.
Referring to fig. 10, the indirect accumulation mode is illustrated. After the tracking loop enters a steady state, the tracking loop may switch to an indirect accumulation mode. Normal mode means that the loop is in steady state and the correlator and the non-coherent device are working continuously. The working time of the indirect accumulation mode correlator and the incoherent device is discontinuous, and because the loop enters a stable tracking state, all parameters cannot be suddenly changed, the data accumulation is only carried out in the first half of the loop updating period, the accumulation result is sent to the phase discriminator in advance, the loop correlator and the incoherent device are powered off in the remaining time, and the low power consumption is achieved until the next loop just starts the updating period.
Referring to fig. 11, the positioning error in the interval accumulation mode. The loop update cycle is set to 1ms, 1000 pieces of data are accumulated, the continuous interval (XX) indicates the number of integration data experienced during the continuous power-off time, the integration data does not actually participate in the correlation operation, and the interval (XX) indicates the number of data accumulated during the power supply time interval, and the integration data participates in the correlation operation. With the reduction of the data accumulated at intervals, the error change is not large, so the interval accumulation mode does not affect the positioning accuracy, the five-pointed star in fig. 11 represents the geometric accuracy factor GDOP of the current satellite, the positioning error is positively correlated with the GDOP, and the error fluctuation is not caused by the interval accumulation time change.
See fig. 12, low frequency mode diagram. After the tracking loop enters a steady state, the tracking loop may switch to a low frequency mode. The normal mode means that the loop is in a steady state, and the driving clock clr of the loop keeps a high frequency. The frequency of the low-frequency mode loop driving clock is reduced, and because the loop enters a stable tracking state, each parameter cannot be suddenly changed, the driving clock only keeps high frequency in the first half part of a loop updating period to meet phase/frequency identification of a tracking loop, and the frequency of the driving clock is halved in the rest time until the next loop just starts to update the period, and the low-power consumption purpose is achieved.
Referring to fig. 13, the positioning error in the low frequency mode. The loop update period is set to 1ms, 1000 pieces of accumulated data are obtained, and 12(XX) represents the high frequency clock 12f0The number of integration data experienced at the time of driving, 6(XX) represents the low frequency clock 6f0The number of data accumulated during driving. It can be found from the positioning error curve in fig. 13 that as the driving time of the low-frequency clock increases, the error change is not large, so the positioning accuracy is not affected by the low-frequency mode, the five-pointed star in fig. 13 represents the geometric accuracy factor GDOP of the current satellite, the positioning error is positively correlated with the GDOP, and the error fluctuation is not caused by the driving clock change.
In summary, the present invention has weak signal tracking capability: aiming at signals with different intensities, the invention designs a full-accumulation and semi-accumulation baseband data processing mode and a carrier identification mode of phase identification, frequency identification and amplitude frequency identification, so that a tracking loop can still keep accurate tracking on the signals under the condition of weak signals; the invention has lower power consumption: aiming at the problem of power consumption, the invention designs an interval accumulation and low-frequency working mode, and reduces the power consumption of the tracking loop on the basis of ensuring the positioning performance.
Claims (8)
1. A multimode satellite navigation receiver tracking loop, characterized by: the method comprises the following steps:
the down converter is used for converting the received satellite signals into intermediate frequency signals through down conversion, and the intermediate frequency signals serve as input signals of the tracking loop module;
the tracking loop module is used for tracking the signal to finally obtain a navigation message for resolving the subsequent three-dimensional position, speed and time; the tracking loop module comprises 12 GPS tracking loops and 12 BD tracking loops, wherein each tracking loop comprises a carrier tracking loop for tracking a signal carrier so as to realize carrier stripping and a code tracking loop for tracking a spread spectrum code so as to realize code stripping.
2. The multimode satellite navigation receiver tracking loop of claim 1, wherein: the carrier tracking loop includes:
the carrier generator is used for generating copied carriers, generating three paths of carriers under the control of a frequency offset constant w, wherein the three paths of carriers are respectively a leading carrier se, a real-time carrier sp and a lagging carrier sl, and the frequency difference of the three paths of carriers is wHZ;
the first mixer module multiplies the intermediate frequency signal by a leading carrier se, a real-time carrier sp and a lagging carrier sl respectively, and strips the carrier, wherein the signal obtained by a branch mixed with the real-time carrier sp is a baseband signal;
the first correlator module is used for carrying out correlation operation on the three paths of signals;
a first non-coherent module for performing non-coherent integration on the result of the correlation operation;
the selector module is used for controlling data to flow into the carrier discriminator through the configuration parameters;
and the carrier discriminator is used for discriminating the phase difference and the frequency difference of the signals, the output result of the carrier discriminator is the phase difference and the frequency difference between the intermediate frequency carrier signals copied by the receiver and the received intermediate frequency carrier signals, the phase and the frequency of the carrier generator are regulated through feedback, the intermediate frequency carrier time copied by the carrier generator of the receiver is consistent with the received intermediate frequency carrier, and the Doppler information in the current signals is obtained at the same time, so that the stripping of the intermediate frequency carrier is realized.
3. The multimode satellite navigation receiver tracking loop of claim 1, wherein: the code tracking loop includes:
the first frequency mixer multiplies the intermediate frequency signal by a real-time carrier sp in a carrier tracking loop and strips the carrier;
a spread code generator for generating a copied spread code cp and generating a leading code ce and a lagging code cl based on the generated code cp;
the second correlator module is used for carrying out correlation operation;
the second non-coherent device module is used for performing non-coherent integration on the correlation operation result;
the code discriminator is used for phase discrimination to obtain the phase difference between the replica code and the received code, and the phase of the spread spectrum code generator is adjusted through the feedback of the low-pass filter, so that the replica spread spectrum code of the receiver is consistent with the received spread spectrum code, the peeling of the spread spectrum code is realized, and the signal-to-noise ratio of the signal is improved;
the code tracking loop in the GPS tracking loop is a GPS code tracking loop; the 12 BD tracking loops comprise 4 BD-GEO tracking loops and 8 BD-MEO tracking loops, wherein a code tracking loop in the BD-GEO tracking loops is a BD-GEO code tracking loop, and a code tracking loop in the BD-MEO tracking loops is a BD-MEO code tracking loop.
4. The multimode satellite navigation receiver tracking loop of claim 2, wherein: the first mixer module comprises a first mixer, a second mixer and a third mixer, and the structures of the first mixer, the second mixer and the third mixer are the same; the first correlator module comprises a first correlator, a second correlator and a third correlator, and the structures of the first correlator, the second correlator and the third correlator are the same; the first non-coherent module comprises a first non-coherent device, a second non-coherent device and a third non-coherent device; the three paths of carriers of the leading carrier se, the instant carrier sp and the lagging carrier sl are respectively and correspondingly input into a first mixer, a second mixer and a third mixer to be mixed with an intermediate frequency signal one by one, 3 branch signals are formed and respectively and correspondingly sent into a first correlator, a second correlator and a third correlator to be accumulated one by one, the number of accumulated data is controlled by correlation time, a correlation result is output after every 1 correlation time, the accumulated result is truncated to obtain a final correlation result, and the three paths of correlation results are respectively and correspondingly input into a first incoherent device, a second incoherent device and a third incoherent device;
the input of the first non-coherent device is the output of the first correlator, and the output result of the first correlator comprises an in-phase component I and a quadrature component Q; the first non-coherent device calculates the modulus of the correlation result and then accumulates, and the accumulation times are controlled by the non-correlation time parameter; after the accumulation reaches the set value of the incoherent times, the accumulated result is subjected to bit cutting to obtain an incoherent result Se, and the incoherent result Se is sent to a carrier discriminator for amplitude frequency discrimination;
the input of the second non-coherent device is the output of the second coherent device, and the output result of the second coherent device comprises an in-phase component I and a quadrature component Q; the second non-coherent device calculates the modulus of the correlation result and then accumulates, and the accumulation times are controlled by the non-correlation time parameter; after the accumulation reaches the set value of the incoherent times, the accumulated result is subjected to bit cutting processing to obtain an incoherent result S1, and the incoherent result S1 is sent to a carrier discriminator for amplitude frequency discrimination;
the carrier discriminator comprises a first sub-discriminator and a second sub-discriminator, and the second sub-discriminator is an amplitude discriminator;
the output of the third correlator has 4 branch cases:
(4a) when the parameter sets the number of times of non-coherence to 0, the coherent result S1Directly sending the signals into a first sub discriminator to carry out phase discrimination;
(4b) when the parameter sets that the number of incoherent times is not 0, the modulus of the correlation result is calculated, the control parameter of a third selector is 0, the data passes through the third selector to be subjected to incoherent accumulation, the output of the third incoherent device is Sp, and the Sp is sent to an amplitude frequency discriminator to be used for amplitude frequency discrimination;
(4c) when the parameter sets that the number of times of non-coherence is not 0, the correlation results are multiplied in a conjugate mode, the control parameter of a third selector is 1, data pass through the third selector to be subjected to non-coherent accumulation, the output of the third non-coherent selector is Sp, and the data are sent to a first sub-discriminator to be subjected to frequency discrimination;
(4d) when the parameter sets the number of incoherent times as 0, the correlation results are multiplied in a conjugate mode, the output of the third incoherent device is Sp, and the Sp is sent to the first sub discriminator to carry out frequency discrimination.
5. The multimode satellite navigation receiver tracking loop of claim 3, wherein: the second correlator module comprises a fourth correlator and a fifth correlator which have the same structure; the second incoherent module comprises a fourth incoherent device and a fifth incoherent device which are identical in structure; the spread spectrum code generator generates a combined code of a BD ranging code and an NH code copied by the receiver, and the combined code is taken as an instant code cp, and an advance code ce advanced by half a chip and a lag code cl lagging by half a chip are regenerated by taking the instant code cp as a reference; the time code cp is sent into a carrier tracking loop to assist carrier tracking, and the advance code ce and the lag code cl respectively enter a fourth correlator and a fifth correlator;
the correlation results output by the fourth correlator and the fifth correlator are subjected to modulus in the fourth noncoherent device and the fifth noncoherent device, and the modulus data has 2 branches:
(5a) aiming at the fourth incoherent device, when the parameter sets the incoherent times to be 0, the selector of the fourth incoherent device is 1, and the modulus result Ce is output from the fourth incoherent device and sent to the code phase discriminator;
(5b) for the fourth incoherent device, when the parameter sets that the incoherent times are not 0, the modulus result is sent to an accumulator for incoherent calculation, meanwhile, data is sent to a queue FIFO, if the size of the FIFO exceeds a preset value, namely the incoherent times, the number of the queue head is detected, the number is subtracted by an accumulation register, and the situation that the accumulation times are 1 time more than the set incoherent times is avoided; after the accumulation reaches the set value of incoherent times, the accumulated result is subjected to truncation processing, so that an incoherent result Ce is obtained and is sent to a code phase discriminator to be used for phase discrimination;
the principle of the fourth non-coherent device is the same as that of the fifth non-coherent device;
the code phase difference output by the code phase discriminator is fed back to the spread spectrum code generator through the low pass filter, and the phase of the spread spectrum code generator is adjusted, so that the copied code is dynamically consistent with the received code;
and the output results of the fourth incoherent device and the fifth incoherent device are used as the input of the code phase discriminator, division calculation is carried out in the code phase discriminator, phase discrimination is carried out, and the obtained output is the phase difference between the code copied by the spread spectrum code generator and the received code.
6. The tracking method of the tracking loop of the multimode satellite navigation receiver according to any one of claims 1 to 5, characterized in that: the method comprises the following steps in sequence:
(1) the method comprises the steps that received satellite signals are converted into intermediate frequency signals through down-conversion, the intermediate frequency signals serve as input signals of a tracking loop module, and parameters of the tracking loop are configured through an interface;
(2) respectively sending the intermediate frequency signals to 12 GPS tracking loops and 12 BD tracking loops, and in the tracking loops, mixing the intermediate frequency signals to obtain baseband signals;
(3) enabling the intermediate frequency signal obtained in the step (1) to pass through a carrier tracking loop to obtain phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal, and adjusting the phase and frequency of a carrier generator through feedback to enable the intermediate frequency carrier copied by the receiver to be consistent with the received intermediate frequency carrier at the moment, so that Doppler information in the current signal is obtained, and stripping of the intermediate frequency carrier is realized; the tracking loop is adapted to signals with different intensities, the baseband signal processing mode comprises a full accumulation mode and a half accumulation mode, and the identification mode of the carrier identifier comprises a frequency identification mode, a phase identification mode and an amplitude frequency identification mode; when the signal is strong, a full accumulation mode is adopted for the correlation operation of the baseband signal, and a phase frequency discrimination or phase discrimination mode is adopted for the carrier discriminator; when the signal is weak, carrying out long-time correlation operation on the baseband signal, and when the correlation time reaches 20ms, adopting a semi-accumulation mode and adopting an amplitude frequency discrimination mode by a carrier discriminator;
(4) the baseband signals obtained in the step (2) pass through a code tracking loop to obtain the phase difference between the spread spectrum code copied by the receiver and the received spread spectrum code, and the phase of the spread spectrum code generator is adjusted through a feedback mechanism to ensure that the time of copying the spread spectrum code of the receiver is consistent with the received spread spectrum code, thereby realizing the stripping of the spread spectrum code;
(5) after the step (3) is finished, the carrier is stripped, after the step (4) is finished, the spread spectrum code is stripped, and the signal only contains navigation messages; carrying out bit synchronization on the navigation message, and searching a bit edge of the navigation message;
(6) and carrying out frame synchronization, searching for a frame header of navigation message data, and realizing the analysis of the navigation message for the subsequent resolution of the three-dimensional position, speed and time.
7. The tracking method according to claim 6, characterized in that: the half accumulation mode is that data accumulation only lasts for half of the set correlation time in the correlation operation of the baseband data, and the correlation operation is carried out in the first half interval of the correlation time.
8. The tracking method according to claim 6, characterized in that: the amplitude frequency discrimination mode is that a leading carrier Se, a real-time carrier Sp and a lagging carrier Sl are respectively mixed with an intermediate frequency signal, correlation calculation and incoherent integration are carried out to obtain three paths of outputs Sl, Sp and Se, the three paths of outputs are simultaneously sent to an amplitude frequency discriminator, and the output result of the amplitude frequency discriminator is a frequency difference we:
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| CN114609652B (en) * | 2022-03-11 | 2024-06-07 | 北京航空航天大学 | Multi-frequency open-loop receiver tracking method and system under extreme ionosphere abnormality |
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