Multi-mode satellite navigation receiver tracking loop and method

Abstract

The present invention relates to a multi-mode satellite navigation receiver tracking loop, comprising: a down-converter for down-converting received satellite signals into intermediate frequency signals as input signals of a tracking loop module; a tracking loop module for tracking signals and finally obtaining navigation messages for subsequent three-dimensional position, speed and time calculations; the tracking loop module comprises 12 GPS tracking loops and 12 BD tracking loops, each of which comprises a carrier tracking loop for tracking signal carriers to achieve carrier stripping, and a code tracking loop for tracking spread spectrum codes to achieve code stripping. The present invention has weak signal tracking capability, and can enable the tracking loop to still accurately track the signal under weak signal conditions; the present invention has low power consumption, and is designed with interval accumulation and low-frequency working modes, which reduces the power consumption of the tracking loop while ensuring positioning performance.

Description

Technical Field

[0001] The present invention relates to the field of satellite navigation technology, and in particular to a multi-mode satellite navigation receiver tracking loop and method. Background Art

[0002] The global satellite navigation system mainly includes GPS, BD, Galileo and Glonass systems. The global satellite navigation system is an air-based radio navigation and positioning system that can provide users with all-weather three-dimensional coordinates, speed and time information at any location on the earth's surface or near-earth space. Due to its significant advantages, it is widely used in all walks of life, and the GPS and BD systems are currently the most widely used.

[0003] With the completion of my country's BD navigation satellite network, receivers that can be compatible with receiving GPS and BD multi-mode navigation satellite signals occupy an important position in the market. Multi-mode satellite navigation receivers are composed of radio frequency, baseband and software algorithms. Among them, radio frequency is used to receive high-frequency satellite signals and down-convert them to intermediate frequency signals; baseband further down-converts intermediate frequency signals to baseband signals, thereby obtaining navigation messages, time and other information. This information is processed by navigation software to obtain three-dimensional coordinates, speed and time information. Therefore, the important link that determines the performance of the receiver is the baseband, and the key technology of baseband design is the design of the tracking loop.

[0004] At present, the existing multi-mode satellite navigation receivers and their loop technologies can be roughly divided into three categories: first, simply merging the receiving methods of different systems together, and using a simple method to superimpose and construct a universal tracking loop, which results in an increase in the amount of resources used, and also increases power consumption and cost; second, in order to reduce resource waste and be limited by the number of loops, a tracking loop multiplexing method is adopted to customize time slot multiplexing loop resources for each type of satellite. When tracking more satellites, the tracking performance will be reduced or even the signal will be lost due to the short time slot; third, software receivers, which implement the functions of the tracking loop with software, have great flexibility, but the tracking stage is computationally intensive, large in data volume, time-consuming, and has high requirements on the CPU. Summary of the invention

[0005] The primary purpose of the present invention is to provide a multi-mode satellite navigation receiver tracking loop which has low power consumption and can enable the tracking loop to still accurately track the signal under weak signal conditions.

[0006] To achieve the above object, the present invention adopts the following technical solution: a multi-mode satellite navigation receiver tracking loop, comprising:

[0007] A down converter, used to down-convert the received satellite signal into an intermediate frequency signal as an input signal of the tracking loop module;

[0008] The tracking loop module is used to track the signal and finally obtain the navigation message for the subsequent three-dimensional position, speed and time solution; the tracking loop module includes 12 GPS tracking loops and 12 BD tracking loops, each tracking loop includes a carrier tracking loop for tracking the signal carrier to achieve carrier stripping, and a code tracking loop for tracking the spread spectrum code to achieve code stripping.

[0009] The carrier tracking loop comprises:

[0010] The carrier generator is used to generate a replicated carrier. Under the control of the frequency offset constant w, three carriers are generated, namely, the leading carrier se, the instantaneous carrier sp and the lagging carrier sl. The frequencies of the three carriers differ by wHZ in sequence.

[0011] The first mixer module multiplies the intermediate frequency signal with the leading carrier se, the instant carrier sp and the lagging carrier sl respectively, and strips off the carrier, wherein the signal obtained by the branch mixed with the instant carrier sp is the baseband signal;

[0012] A first correlator module, used for performing correlation operation on three signals;

[0013] A first incoherent device module, used for performing incoherent integration on the result of the correlation operation;

[0014] A selector module for controlling the flow of data into the carrier discriminator through configuration parameters;

[0015] The carrier discriminator is used to identify the phase difference and frequency difference of the signal. The output result of the carrier discriminator is the phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal. The phase and frequency of the carrier generator are adjusted by feedback so that the intermediate frequency carrier copied by the carrier generator of the receiver is consistent with the received intermediate frequency carrier, and the Doppler information in the current signal is obtained, thereby realizing the stripping of the intermediate frequency carrier.

[0016] The code tracking loop comprises:

[0017] The first mixer multiplies the intermediate frequency signal with the instantaneous carrier sp in the carrier tracking loop to strip off the carrier;

[0018] A spreading code generator, used to generate a replicated spreading code cp, and use this as a reference to generate an advance code ce and a lag code cl;

[0019] A second correlator module, used for performing correlation operation;

[0020] A second incoherent device module, used for performing incoherent integration on the correlation operation result;

[0021] The code discriminator is used for phase discrimination to obtain the phase difference between the replica code and the received code, and adjusts the phase of the spread spectrum code generator through feedback from the low-pass filter, so that the replica spread spectrum code of the receiver is consistent with the received spread spectrum code, thereby realizing the stripping of the spread spectrum code and improving the signal-to-noise ratio of the signal;

[0022] The code tracking loop in the GPS tracking loop is a GPS code tracking loop; the 12 BD tracking loops include 4 BD-GEO tracking loops and 8 BD-MEO tracking loops, the code tracking ring in the BD-GEO tracking loop is a BD-GEO code tracking ring, and the code tracking ring in the BD-MEO tracking loop is a BD-MEO code tracking ring.

[0023] The first mixer module includes a first mixer, a second mixer and a third mixer, and the three have the same structure; the first correlator module includes a first correlator, a second correlator and a third correlator, and the three have the same structure; the first incoherent device module includes a first incoherent device, a second incoherent device and a third incoherent device; the three carriers of the advance carrier se, the instant carrier sp and the lag carrier sl are respectively input into the first mixer, the second mixer and the third mixer in a one-to-one correspondence to mix with the intermediate frequency signal to form three branch signals which are respectively sent into the first correlator, the second correlator and the third correlator in a one-to-one correspondence to be accumulated, the number of accumulated data is controlled by the correlation time, and a correlation result is output after each correlation time, and the accumulated result is truncated to obtain the final correlation result, and the three correlation results are respectively input into the first incoherent device, the second incoherent device and the third incoherent device in a one-to-one correspondence;

[0024] The input of the first non-coherent device is the output of the first correlator, and the output result of the first correlator includes an in-phase component I and an orthogonal component Q; the first non-coherent device modulo-calculates the correlation result, and then accumulates it, and the number of accumulations is controlled by the non-correlation number parameter; after the accumulation reaches the non-coherence number setting value, the accumulation result is truncated to obtain the non-coherence result Se, which is sent to the carrier discriminator for amplitude frequency discrimination;

[0025] The input of the second non-coherent device is the output of the second correlator, and the output result of the second correlator includes an in-phase component I and an orthogonal component Q; the second non-coherent device modulo-calculates the correlation result, and then accumulates it, and the number of accumulations is controlled by the non-correlation number parameter; after the accumulation reaches the non-coherence number setting value, the accumulation result is truncated to obtain the non-coherence result S1, which is sent to the carrier discriminator for amplitude frequency discrimination;

[0026] The carrier discriminator includes a first sub-discriminator and a second sub-discriminator, wherein the second sub-discriminator is an amplitude discriminator;

[0027] The output of the third correlator has 4 branches:

[0028] (4a) When the parameter sets the number of incoherent times to 0, the coherent result S1 is directly sent to the first sub-discriminator for phase discrimination;

[0029] (4b) When the parameter setting of the incoherent number is not 0, the correlation result is modulo, the control parameter of the third selector is 0, the data passes through the third selector, and is incoherently accumulated. The output of the third incoherent selector is Sp, which is sent to the amplitude discriminator for amplitude discrimination;

[0030] (4c) When the parameter setting of the incoherent number is not 0, the correlation results are conjugate multiplied, the control parameter of the third selector is 1, the data passes through the third selector, and is incoherently accumulated. The output of the third incoherent selector is Sp, which is sent to the first sub-discriminator for frequency discrimination;

[0031] (4d) When the parameter sets the number of incoherent times to 0, the correlation results are conjugate multiplied, and the output of the third incoherent device is Sp, which is sent to the first sub-discriminator for frequency discrimination.

[0032] The second correlator module includes a fourth correlator and a fifth correlator, and the two have the same structure; the second incoherent device module includes a fourth incoherent device and a fifth incoherent device, and the two have the same structure; the spread spectrum code generator generates a combination code of the BD ranging code and the NH code copied by the receiver, and uses the combination code as the instant code cp, and uses the instant code cp as a reference to regenerate an advance code ce of half a chip ahead and a lag code cl of half a chip behind; the instant code cp is sent to the carrier tracking loop to assist in carrier tracking, and the advance code ce and the lag code cl enter the fourth correlator and the fifth correlator respectively;

[0033] The correlation results output by the fourth correlator and the fifth correlator are modulo-calculated in the fourth incoherent device and the fifth incoherent device, and the modulo-calculated data has two branches:

[0034] (5a) For the fourth incoherent device, when the parameter sets the incoherence times to 0, the selector of the fourth incoherent device is 1, and the modulo result Ce is output from the fourth incoherent device and sent to the code phase detector;

[0035] (5b) For the fourth incoherent device, when the parameter setting incoherent times is not 0, the modulo result is sent to the accumulator for incoherent calculation, and the data is sent to the input queue FIFO. If the size of the FIFO exceeds the preset value, i.e., the incoherent times, the number of the head of the queue is detected, and the accumulator register is subtracted from the number to avoid the accumulation times being more than the set incoherent times by one; after the accumulation reaches the set value of the incoherent times, the accumulation result is truncated to obtain the incoherent result Ce, which is sent to the code phase detector for phase detection;

[0036] The fourth incoherent device and the fifth incoherent device have the same principle;

[0037] The code phase difference output by the code phase detector is fed back to the spread spectrum code generator through a low-pass filter to adjust the phase of the spread spectrum code generator so that the copied code is dynamically consistent with the received code;

[0038] The output results of the fourth incoherent device and the fifth incoherent device are used as inputs of the code phase detector, and the code phase detector performs division calculation and phase detection. The output obtained is the phase difference between the code copied by the spread spectrum code generator and the received code.

[0039] Another object of the present invention is to provide a tracking method for a multi-mode satellite navigation receiver tracking loop, the method comprising the following steps in order:

[0040] (1) The received satellite signal is down-converted into an intermediate frequency signal as the input signal of the tracking loop module, and the tracking loop parameters are configured through the interface;

[0041] (2) The intermediate frequency signal is sent to 12 GPS tracking loops and 12 BD tracking loops respectively. In the tracking loops, the intermediate frequency signal is mixed to obtain the baseband signal;

[0042] (3) The intermediate frequency signal obtained in step (1) is passed through a carrier tracking loop to obtain the phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal, and the phase and frequency of the carrier generator are adjusted by feedback so that the intermediate frequency carrier copied by the receiver is consistent with the received intermediate frequency carrier, thereby obtaining the Doppler information in the current signal and realizing the stripping of the intermediate frequency carrier; the tracking loop is adapted to signals of different strengths, and the baseband signal processing modes include full accumulation mode and semi-accumulation mode, and the identification modes of the carrier discriminator include frequency discrimination, phase discrimination, and amplitude discrimination mode; when the signal is strong, the full accumulation mode is used for the baseband signal correlation operation, and the carrier discriminator adopts the frequency discrimination or phase discrimination mode; when the signal is weak, the baseband signal is subjected to a long-term correlation operation, and when the correlation time reaches 20ms, the semi-accumulation mode is used, and the carrier discriminator adopts the amplitude discrimination mode;

[0043] (4) The baseband signal obtained in step (2) is passed through a code tracking loop to obtain a phase difference between the spread spectrum code copied by the receiver and the received spread spectrum code. The phase of the spread spectrum code generator is adjusted through a feedback mechanism so that the receiver's copied spread spectrum code is consistent with the received spread spectrum code, thereby achieving spread spectrum code stripping;

[0044] (5) After step (3) is completed, the carrier is stripped, and after step (4) is completed, the spread spectrum code is stripped, and the signal contains only the navigation message; the navigation message is bit synchronized and the bit edge of the navigation message is found;

[0045] (6) Perform frame synchronization, find the frame header of the navigation text data, and implement the parsing of the navigation message for subsequent calculation of the three-dimensional position, speed, and time.

[0046] The semi-accumulation mode means that in the correlation operation of the baseband data, data accumulation only lasts for half of the set correlation time, and the correlation operation is performed in the first half of the correlation time.

[0047] The amplitude demodulation mode refers to using the leading carrier se, the immediate carrier sp, and the lagging carrier sl to mix with the intermediate frequency signal, perform correlation calculation, and non-coherent integration to obtain three outputs Sl, Sp, and Se, and send the three outputs to the amplitude demodulator at the same time. The output result of the amplitude demodulator is the frequency difference we:

[0048]

[0049] It can be seen from the above technical scheme that the beneficial effects of the present invention are: first, the present invention has the ability to track weak signals: the present invention designs full-accumulation and semi-accumulation baseband data processing modes for signals of different strengths, and carrier identification modes of phase detection, frequency detection, and amplitude detection, which can enable the tracking loop to maintain accurate tracking of the signal under weak signal conditions; second, the present invention has lower power consumption: in view of the power consumption problem, the present invention designs interval accumulation and low-frequency working modes, which reduces the power consumption of the tracking loop while ensuring positioning performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is a schematic diagram of down conversion;

[0051] Figure 2 It is a schematic diagram of the overall structure of the tracking loop of the present invention;

[0052] Figure 3 This is a schematic diagram of the tracking loop;

[0053] Figure 4 for Figure 3 Schematic diagram of the structure of the third incoherent device;

[0054] Figure 5 for Figure 3 Schematic diagram of the structure of the medium amplitude frequency discriminator;

[0055] Figure 6 It is the schematic diagram of full accumulation and semi-accumulation;

[0056] Figure 7 This is the principle diagram of amplitude frequency discrimination;

[0057] Figure 8 This is the amplitude phase discrimination effect diagram;

[0058] Fig. 9 It is the power consumption mode switching diagram;

[0059] Fig.10 Schematic diagram of normal mode and interval accumulation mode;

[0060] Fig.11 This is a schematic diagram of positioning error in interval accumulation mode;

[0061] Fig.12 Schematic diagram of normal mode and low frequency mode;

[0062] Fig.13 Schematic diagram of low-frequency mode positioning error. DETAILED DESCRIPTION

[0063] like Figure 2 As shown, a multi-mode satellite navigation receiver tracking loop comprises:

[0064] A down converter, used to down-convert the received satellite signal into an intermediate frequency signal as an input signal of the tracking loop module;

[0065] The tracking loop module is used to track the signal and finally obtain the navigation message for the subsequent three-dimensional position, speed and time solution; the tracking loop module includes 12 GPS tracking loops and 12 BD tracking loops, each tracking loop includes a carrier tracking loop for tracking the signal carrier to achieve carrier stripping, and a code tracking loop for tracking the spread spectrum code to achieve code stripping.

[0066] like Figure 1 As shown, the received satellite signal is down-converted into the initial intermediate frequency signal, and at the same time, according to the register width limit, data saturation is prevented and valid data information is retained, and the initial intermediate frequency signal is truncated to obtain the intermediate frequency signal. In the present invention, the intermediate frequency signal is limited to the range of -7FFF to 7FFF by truncation, and the loop operating frequency is 240f0, f0=1.023MHz.

[0067] like Figure 3 As shown, the carrier tracking loop includes:

[0068] The carrier generator is used to generate a replicated carrier. Under the control of the frequency offset constant w, three carriers are generated, namely, the leading carrier se, the instantaneous carrier sp and the lagging carrier sl. The frequencies of the three carriers differ by wHZ in sequence.

[0069] The first mixer module multiplies the intermediate frequency signal with the leading carrier se, the instant carrier sp and the lagging carrier sl respectively, and strips off the carrier, wherein the signal obtained by the branch mixed with the instant carrier sp is the baseband signal;

[0070] A first correlator module, used for performing correlation operation on three signals;

[0071] A first incoherent device module, used for performing incoherent integration on the result of the correlation operation;

[0072] A selector module for controlling the flow of data into the carrier discriminator through configuration parameters;

[0073] The carrier discriminator is used to identify the phase difference and frequency difference of the signal. The output result of the carrier discriminator is the phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal. The phase and frequency of the carrier generator are adjusted by feedback so that the intermediate frequency carrier copied by the carrier generator of the receiver is consistent with the received intermediate frequency carrier, and the Doppler information in the current signal is obtained, thereby realizing the stripping of the intermediate frequency carrier.

[0074] like Figure 3 As shown, the code tracking loop includes:

[0075] The first mixer multiplies the intermediate frequency signal with the instantaneous carrier sp in the carrier tracking loop to strip off the carrier;

[0076] A spreading code generator, used to generate a replicated spreading code cp, and use this as a reference to generate an advance code ce and a lag code cl;

[0077] A second correlator module, used for performing correlation operation;

[0078] A second incoherent device module, used for performing incoherent integration on the correlation operation result;

[0079] The code discriminator is used for phase discrimination to obtain the phase difference between the replica code and the received code, and adjusts the phase of the spread spectrum code generator through feedback from the low-pass filter, so that the replica spread spectrum code of the receiver is consistent with the received spread spectrum code, thereby realizing the stripping of the spread spectrum code and improving the signal-to-noise ratio of the signal;

[0080] The code tracking loop in the GPS tracking loop is a GPS code tracking loop; the 12 BD tracking loops include 4 BD-GEO tracking loops and 8 BD-MEO tracking loops, the code tracking ring in the BD-GEO tracking loop is a BD-GEO code tracking ring, and the code tracking ring in the BD-MEO tracking loop is a BD-MEO code tracking ring.

[0081] The GPS code tracking loops are numbered from 1 to 12, the BD-GEO tracking loops are numbered from 12 to 16, and the BD-MEO tracking loops are numbered from 17 to 24. The GPS code tracking loops, BD-GEO tracking loops, and BD-MEO tracking loops have the same structure except for the different spread spectrum code generator principles and digital control oscillator frequencies.

[0082] The first mixer module includes a first mixer, a second mixer and a third mixer, and the three have the same structure; the first correlator module includes a first correlator, a second correlator and a third correlator, and the three have the same structure; the first incoherent device module includes 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 carriers of the advanced carrier se, the instant carrier sp and the delayed carrier sl are respectively input into the first mixer, the second mixer and the third mixer in a one-to-one correspondence to mix with the intermediate frequency signal to form three branch signals, which are respectively sent into the first correlator, the second correlator and the third correlator in a one-to-one correspondence to accumulate, and the number of accumulated data is controlled by the correlation time. After each correlation time, a correlation result is output, and the accumulated result is truncated to obtain the final correlation result, and the three correlation results are respectively input into the first incoherent device, the second incoherent device and the third incoherent device in a one-to-one correspondence;

[0083] The input of the first non-coherent device is the output of the first correlator, and the output result of the first correlator includes an in-phase component I and an orthogonal component Q; the first non-coherent device modulo-calculates the correlation result, and then accumulates it, and the number of accumulations is controlled by the non-correlation number parameter; after the accumulation reaches the non-coherence number setting value, the accumulation result is truncated to obtain the non-coherence result Se, which is sent to the carrier discriminator for amplitude frequency discrimination;

[0084] The input of the second non-coherent device is the output of the second correlator, and the output result of the second correlator includes an in-phase component I and an orthogonal component Q; the second non-coherent device modulo-calculates the correlation result, and then accumulates it, and the number of accumulations is controlled by the non-correlation number parameter; after the accumulation reaches the non-coherence number setting value, the accumulation result is truncated to obtain the non-coherence result S1, which is sent to the carrier discriminator for amplitude frequency discrimination;

[0085] like Figure 4 As shown, the correlator output includes an in-phase component I and an orthogonal component Q, which are in the form of imaginary numbers I+Qj. The input of the third incoherent device is the output of the third correlator. The input signal has three branches:

[0086] (1) When the parameter setting of the number of incoherent times is not 0, the correlation result is modulo The selector control parameter is set to 0, and the data passes through the selector and the time delay unit D2, delaying the time of a relevant calculation cycle. The data is then sent to the accumulator for non-coherent calculation to obtain non-coherent results. At the same time, the data is also sent to the queue FIFO. The non-coherent result passes through the delay unit D3. If the size of the FIFO exceeds the preset value (the number of non-coherent times), the non-coherent result is sent back to the accumulator, and the FIFO then detects the number at the head of the queue, and the accumulation register subtracts this number to avoid the accumulation number being more than 1 time more than the set non-coherent number. After the non-coherent result is truncated, the output is Sp.

[0087] (2) When the parameter setting of the incoherent number is not 0, the correlation results are conjugate multiplied. The coherent result is I+Qj, and the conjugate result is After the conjugate calculation, it passes through the delay unit D4. The delay time of the delay unit is one related calculation cycle. The conjugate result at the current moment is Multiply it with I+Qj at the next moment, set the selector control parameter to 1, and the conjugate multiplication result passes through the selector and D2 for incoherent accumulation, and the output result is Sp.

[0088] (3) When the parameter sets the number of incoherent times to 0, the correlation results are conjugate multiplied and the output is S2.

[0089] like Figure 5 As shown, the input signal is input through the input terminals a and b of the amplitude discriminator, and the division calculation a÷b is performed inside the discriminator, and the division result is the output of the discriminator.

[0090] The carrier discriminator includes a first sub-discriminator and a second sub-discriminator, wherein the second sub-discriminator is an amplitude discriminator;

[0091] The output of the third correlator has 4 branches:

[0092] (4a) When the parameter sets the number of incoherent times to 0, the coherent result S1 is directly sent to the first sub-discriminator for phase discrimination;

[0093] (4b) When the parameter setting of the incoherent number is not 0, the correlation result is modulo, the control parameter of the third selector is 0, the data passes through the third selector, and is incoherently accumulated. The output of the third incoherent selector is Sp, which is sent to the amplitude discriminator for amplitude discrimination;

[0094] (4c) When the parameter setting of the incoherent number is not 0, the correlation results are conjugate multiplied, the control parameter of the third selector is 1, the data passes through the third selector, and is incoherently accumulated. The output of the third incoherent selector is Sp, which is sent to the first sub-discriminator for frequency discrimination;

[0095] (4d) When the parameter sets the number of incoherent times to 0, the correlation results are conjugate multiplied, and the output of the third incoherent device is Sp, which is sent to the first sub-discriminator for frequency discrimination.

[0096] The second correlator module includes a fourth correlator and a fifth correlator, and the two have the same structure; the second incoherent device module includes a fourth incoherent device and a fifth incoherent device, and the two have the same structure; the spread spectrum code generator generates a combination code of the BD ranging code and the NH code copied by the receiver, and uses the combination code as the instant code cp, and uses the instant code cp as a reference to regenerate an advance code ce of half a chip ahead and a lag code cl of half a chip behind; the instant code cp is sent to the carrier tracking loop to assist in carrier tracking, and the advance code ce and the lag code cl enter the fourth correlator and the fifth correlator respectively;

[0097] The correlation results output by the fourth correlator and the fifth correlator are modulo-calculated in the fourth incoherent device and the fifth incoherent device, and the modulo-calculated data has two branches:

[0098] (5a) For the fourth incoherent device, when the parameter sets the incoherence times to 0, the selector of the fourth incoherent device is 1, and the modulo result Ce is output from the fourth incoherent device and sent to the code phase detector;

[0099] (5b) For the fourth incoherent device, when the parameter setting incoherent times is not 0, the modulo result is sent to the accumulator for incoherent calculation, and the data is sent to the input queue FIFO. If the size of the FIFO exceeds the preset value, i.e., the incoherent times, the number of the head of the queue is detected, and the accumulator register is subtracted from the number to avoid the accumulation times being more than the set incoherent times by one; after the accumulation reaches the set value of the incoherent times, the accumulation result is truncated to obtain the incoherent result Ce, which is sent to the code phase detector for phase detection;

[0100] The fourth incoherent device and the fifth incoherent device have the same principle;

[0101] The code phase difference output by the code phase detector is fed back to the spread spectrum code generator through a low-pass filter to adjust the phase of the spread spectrum code generator so that the copied code is dynamically consistent with the received code;

[0102] The output results of the fourth incoherent device and the fifth incoherent device are used as inputs of the code phase detector, and the code phase detector performs division calculation and phase detection. The output obtained is the phase difference between the code copied by the spread spectrum code generator and the received code.

[0103] Another object of the present invention is to provide a tracking method for a multi-mode satellite navigation receiver tracking loop, the method comprising the following steps in order:

[0104] (1) The received satellite signal is down-converted into an intermediate frequency signal as the input signal of the tracking loop module, and the tracking loop parameters are configured through the interface; the tracking loop parameter configuration includes: truncation, correlation time, incoherence number, low-pass filter coefficient, queue length, initial carrier frequency, initial code frequency, frequency offset, selector parameter, full accumulation mode enable, half accumulation mode enable, amplitude mode enable, discriminator enable, loop enable, power consumption mode, reset, etc.;

[0105] (2) The intermediate frequency signal is sent to 12 GPS tracking loops and 12 BD tracking loops respectively. In the tracking loops, the intermediate frequency signal is mixed to obtain the baseband signal;

[0106] (3) The intermediate frequency signal obtained in step (1) is passed through a carrier tracking loop to obtain the phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal. The phase and frequency of the carrier generator are adjusted by feedback so that the intermediate frequency carrier copied by the receiver is consistent with the received intermediate frequency carrier at the same time, thereby obtaining the Doppler information in the current signal and realizing the stripping of the intermediate frequency carrier. The tracking loop is adapted to signals of different strengths. The baseband signal processing modes include full accumulation mode and semi-accumulation mode. The identification modes of the carrier discriminator include frequency discrimination, phase discrimination, and amplitude discrimination mode. When the signal is strong, the full accumulation mode is used for the baseband signal correlation operation, and the carrier discriminator adopts the frequency discrimination or phase discrimination mode. When the signal is weak, the baseband signal is subjected to a long-term correlation operation. When the correlation time reaches 20ms, the semi-accumulation mode is used to effectively avoid the problem of the correlation result being offset due to the jump of the navigation message data. The carrier discriminator adopts the amplitude discrimination mode.

[0107] (4) The baseband signal obtained in step (2) is passed through a code tracking loop to obtain a phase difference between the spread spectrum code copied by the receiver and the received spread spectrum code. The phase of the spread spectrum code generator is adjusted through a feedback mechanism so that the receiver's copied spread spectrum code is consistent with the received spread spectrum code, thereby achieving spread spectrum code stripping;

[0108] (5) After step (3) is completed, the carrier is stripped off, and after step (4) is completed, the spread spectrum code is stripped off, and the signal contains only the navigation message; the navigation message is bit synchronized and the bit edge of the navigation message is found; if the bit synchronization is successful, it can further assist the tracking of the code loop and the carrier loop.

[0109] (6) Perform frame synchronization, find the frame header of the navigation text data, and implement the parsing of the navigation message for subsequent calculation of the three-dimensional position, speed, and time.

[0110] The tracking loop module adopts a low-power design, including three working modes: normal, interval accumulation, and low frequency. When the satellite signal has not yet entered the stable tracking state, or when the power supply is sufficient, the normal mode is used for power supply, and all modules of the tracking loop work continuously at full load. After entering the stable tracking state, the interval accumulation mode or low frequency mode can be used.

[0111] The semi-accumulation mode means that in the correlation operation of the baseband data, data accumulation only lasts for half of the set correlation time, and the correlation operation is performed in the first half of the correlation time.

[0112] The amplitude demodulation mode refers to using the leading carrier se, the immediate carrier sp, and the lagging carrier sl to mix with the intermediate frequency signal, perform correlation calculation, and non-coherent integration to obtain three outputs Sl, Sp, and Se, and send the three outputs to the amplitude demodulator at the same time. The output result of the amplitude demodulator is the frequency difference we:

[0113]

[0114] The following combination Figures 1 to 11 The present invention is further described.

[0115] like Figure 6 As shown in the figure, compared with the actual data bit, the starting position of the baseband signal correlation is random. When configuring the parameters of the tracking loop, the correlation time and accumulation mode will be specified. The correlation time is usually set to 1ms, 2ms, 4ms, 5ms, 10ms, and 20ms, and the accumulation mode is full accumulation mode and half accumulation mode. Full accumulation mode means that the data accumulation in the correlation operation of the baseband data lasts for the set correlation time. When the signal is strong, the full accumulation mode is usually used to perform correlation operation on the baseband data to retain all valid information. Half accumulation mode means that the data accumulation in the correlation operation of the baseband data only lasts for half of the set correlation time, and the correlation operation is usually performed in the first half of the correlation time. The half accumulation mode is mainly used under weak signal conditions. When the signal is weak, the correlation time needs to be increased accordingly. When the correlation time reaches 20ms, the correlation accumulation data will be offset due to the flipping of the navigation data bit, which will make the long-term correlation unable to improve the signal-to-noise ratio. Only when the starting time of the correlation operation is aligned with the edge of the actual navigation data bit will there be no correlation data offset problem. The correlation operation started at other times will have different degrees of data offset problems. When the correlation time is 20ms, the semi-accumulated correlation time is 10ms. The probability of data offset occurring in the actual correlation operation is greatly reduced, and the data offset problem can be effectively avoided.

[0116] The carrier identification modes include frequency detection, phase detection, and amplitude detection. The principles of frequency detection and phase detection are exactly the same as those introduced in Xie Gang's GPS Principles and Receiver Design. The phase detection method fails when the signal strength is too low, so the amplitude detection method is used when the signal is weak. Figure 7 The amplitude demodulation method uses the leading carrier se, the immediate carrier sp, and the lagging carrier sl to mix with the intermediate frequency signal, perform correlation calculations, and perform incoherent integration to obtain three outputs Sl, Sp, and Se. The three outputs are simultaneously sent to the amplitude demodulator, and the demodulator outputs the frequency difference we:

[0117] The calculation formula of the amplitude frequency detector is:

[0118] Amplitude frequency discrimination effect Figure 8 . When the signal is unobstructed and the weather is clear, the carrier-to-noise ratio of the signal received by the receiver is between 40dB and 35dB. The carrier-to-noise ratio is 37dB at the beginning of the signal. When the signal is strong, the amplitude demodulation method can enable the tracking loop to stably track the GPS satellite signal, and the Doppler changes slowly and evenly. This is due to the continuous and stable change of the Doppler caused by the stable movement of the satellite; as the signal strength decreases, the carrier-to-noise ratio gradually decreases from 37dB, and the Doppler still changes slowly and evenly, indicating that the tracking loop can still stably track the satellite signal as the signal strength decreases; when the signal continues to decrease and the carrier-to-noise ratio is less than 15dBHz, the Doppler begins to fluctuate significantly. As the carrier-to-noise ratio further decreases, the tracking loop loses lock and the Doppler information of the current signal cannot be obtained. Therefore, the amplitude demodulation mode can stably track satellite signals with signal strength greater than 15dBHz.

[0119] See also Fig. 9 , power consumption mode. The tracking loop adopts a low-power design, including normal mode, interval accumulation mode, and low-frequency mode. When the satellite signal has not yet entered a stable tracking state, or the power supply is sufficient, the normal mode is used for power supply, and all modules of the tracking loop work at full load. After entering the stable tracking state, the interval accumulation mode or low-frequency mode can be used. The normal mode can be switched with the low-frequency mode and the interval accumulation mode.

[0120] See also Fig.10 , Schematic diagram of indirect accumulation mode. After the tracking loop enters a stable state, the tracking loop can switch to the indirect accumulation mode. Normal mode means that the correlator and the incoherent device continue to work when the loop is in a stable state. In the indirect accumulation mode, the correlator and the incoherent device work discontinuously. Since the loop has entered a stable tracking state, the parameters will not mutate. Therefore, data accumulation is only performed in the first half of the loop update cycle. The accumulation results are sent to the phase detector in advance. The correlator and the incoherent device of the loop are powered off for the remaining time until the next loop update cycle begins. This cycle repeats over and over again to achieve the purpose of low power consumption.

[0121] See also Fig.11 , positioning error in interval accumulation mode. The loop update cycle is set to 1ms, and 1000 data are accumulated. Continuous (XX) indicates the number of integrated data experienced during the continuous power-off time, which does not actually participate in the relevant calculations. Interval (XX) indicates the number of interval accumulated data during power supply, which participates in the relevant calculations. As the interval accumulated data decreases, the error changes little, so the interval accumulation mode will not affect the positioning accuracy. Fig.11 The five-pointed star in the middle represents the geometric precision factor GDOP of the current satellite. The positioning error is positively correlated with the GDOP, and the error fluctuation is not caused by changes in the interval accumulation time.

[0122] See also Fig.12 , low-frequency mode schematic. After the tracking loop enters a stable state, the tracking loop can switch to low-frequency mode. Normal mode means that the loop is in a stable state and the loop's driving clock clr clock maintains a high frequency. In low-frequency mode, the loop driving clock frequency is reduced. Since the loop has entered a stable tracking state, various parameters will not change suddenly. Therefore, the driving clock only maintains a high frequency in the first half of the loop update cycle to meet the phase / frequency identification of the tracking loop. The driving clock frequency is halved for the rest of the time until the next loop just starts to update the cycle, and it repeats over and over again to achieve the purpose of low power consumption.

[0123] See also Fig.13 , positioning error in low-frequency mode. The loop update cycle is set to 1ms, and the accumulated data is 1000. 12(XX) represents the number of integrated data experienced when the high-frequency clock is driven by 12f0, and 6(XX) represents the number of accumulated data when the low-frequency clock is driven by 6f0. Fig.13 From the positioning error curve, we can find that as the low-frequency clock driving time increases, the error changes little, so the low-frequency mode will not affect the positioning accuracy. Fig.13 The five-pointed star in the middle represents the geometric precision factor GDOP of the current satellite. The positioning error is positively correlated with the GDOP, and the error fluctuation is not caused by changes in the driving clock.

[0124] In summary, the present invention has the capability of weak signal tracking: for signals of different strengths, the present invention designs full-accumulation and semi-accumulation baseband data processing modes, and carrier identification modes of phase detection, frequency detection, and amplitude detection, which can enable the tracking loop to still accurately track the signal under weak signal conditions; the present invention has lower power consumption: in view of the power consumption problem, the present invention designs interval accumulation and low-frequency working modes, which reduces the power consumption of the tracking loop while ensuring positioning performance.

Claims

1. A multi-mode satellite navigation receiver tracking loop, characterized in that: include: A down converter, used to down-convert the received satellite signal into an intermediate frequency signal as an input signal of the tracking loop module; The tracking loop module is used to track the signal and finally obtain the navigation message for the subsequent three-dimensional position, speed and time calculation; The tracking loop module includes 12 GPS tracking loops and 12 BD tracking loops, each of which includes a carrier tracking loop for tracking the signal carrier to achieve carrier stripping, and a code tracking loop for tracking the spread spectrum code to achieve code stripping; The carrier tracking loop comprises: The carrier generator is used to generate a replicated carrier. Under the control of the frequency offset constant w, three carriers are generated, namely, the leading carrier se, the instantaneous carrier sp and the lagging carrier sl. The frequencies of the three carriers differ by wHZ in sequence. The first mixer module multiplies the intermediate frequency signal with the leading carrier se, the instant carrier sp and the lagging carrier sl respectively, and strips off the carrier, wherein the signal obtained by the branch mixed with the instant carrier sp is the baseband signal; A first correlator module, used for performing correlation operation on three signals; A first incoherent device module, used for performing incoherent integration on the result of the correlation operation; A selector module for controlling the flow of data into the carrier discriminator through configuration parameters; The carrier discriminator is used to discriminate the phase difference and frequency difference of the signal. The output result of the carrier discriminator is the phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal. The phase and frequency of the carrier generator are adjusted by feedback so that the intermediate frequency carrier copied by the carrier generator of the receiver is consistent with the received intermediate frequency carrier, and the Doppler information in the current signal is obtained, so as to realize the stripping of the intermediate frequency carrier. The code tracking loop comprises: The first mixer multiplies the intermediate frequency signal with the instantaneous carrier sp in the carrier tracking loop to strip off the carrier; A spreading code generator, used to generate a replicated spreading code cp, and use this as a reference to generate an advance code ce and a lag code cl; A second correlator module, used for performing correlation operation; A second incoherent device module, used for performing incoherent 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 adjusts the phase of the spread spectrum code generator through feedback from the low-pass filter, so that the replica spread spectrum code of the receiver is consistent with the received spread spectrum code, thereby realizing the stripping of the spread spectrum code and improving the signal-to-noise ratio of the signal; The code tracking loop in the GPS tracking loop is a GPS code tracking loop; the 12 BD tracking loops include 4 BD-GEO tracking loops and 8 BD-MEO tracking loops, the code tracking ring in the BD-GEO tracking loop is a BD-GEO code tracking ring, and the code tracking ring in the BD-MEO tracking loop is a BD-MEO code tracking ring.

2. The multi-mode satellite navigation receiver tracking loop according to claim 1, characterized in that: The first mixer module includes a first mixer, a second mixer and a third mixer, and the three have the same structure; the first correlator module includes a first correlator, a second correlator and a third correlator, and the three have the same structure; the first incoherent device module includes a first incoherent device, a second incoherent device and a third incoherent device; the three carriers of the advanced carrier se, the instant carrier sp and the delayed carrier sl are respectively input into the first mixer, the second mixer and the third mixer in a one-to-one correspondence to mix with the intermediate frequency signal to form three branch signals which are respectively sent into the first correlator, the second correlator and the third correlator in a one-to-one correspondence to be accumulated, the number of accumulated data is controlled by the correlation time, and a correlation result is output after each correlation time, and the accumulated result is truncated to obtain the final correlation result, and the three correlation results are respectively input into the first incoherent device, the second incoherent device and the third incoherent device in a one-to-one correspondence; The input of the first non-coherent device is the output of the first correlator, and the output result of the first correlator includes an in-phase component I and an orthogonal component Q; the first non-coherent device modulo-calculates the correlation result, and then accumulates it, and the number of accumulations is controlled by the non-correlation number parameter; after the accumulation reaches the non-coherence number setting value, the accumulation result is truncated to obtain the non-coherence result Se, which is sent to the carrier discriminator for amplitude frequency discrimination; The input of the second non-coherent device is the output of the second correlator, and the output result of the second correlator includes an in-phase component I and an orthogonal component Q; the second non-coherent device modulo-calculates the correlation result, and then accumulates it, and the number of accumulations is controlled by the non-correlation number parameter; after the accumulation reaches the non-coherence number setting value, the accumulation result is truncated to obtain the non-coherence result S1, which is sent to the carrier discriminator for amplitude frequency discrimination; The carrier discriminator includes a first sub-discriminator and a second sub-discriminator, wherein the second sub-discriminator is an amplitude discriminator; The output of the third correlator has 4 branches: (4a) When the parameter sets the number of incoherent times to 0, the coherent result S1 is directly sent to the first sub-discriminator for phase discrimination; (4b) When the parameter setting of the incoherent number is not 0, the correlation result is modulo, the control parameter of the third selector is 0, the data passes through the third selector, and is incoherently accumulated. The output of the third incoherent selector is Sp, which is sent to the amplitude discriminator for amplitude discrimination; (4c) When the parameter setting of the incoherent number is not 0, the correlation results are conjugate multiplied, the control parameter of the third selector is 1, the data passes through the third selector, and is incoherently accumulated. The output of the third incoherent selector is Sp, which is sent to the first sub-discriminator for frequency discrimination; (4d) When the parameter sets the number of incoherent times to 0, the correlation results are conjugate multiplied, and the output of the third incoherent filter is Sp, which is sent to the first sub-discriminator for frequency discrimination.

3. The multi-mode satellite navigation receiver tracking loop according to claim 1, characterized in that: The second correlator module includes a fourth correlator and a fifth correlator, and the two have the same structure; the second incoherent device module includes a fourth incoherent device and a fifth incoherent device, and the two have the same structure; the spread spectrum code generator generates a combination code of the BD ranging code and the NH code copied by the receiver, and uses the combination code as the instant code cp, and uses the instant code cp as a reference to regenerate an advance code ce of half a chip ahead and a lag code cl of half a chip behind; the instant code cp is sent to the carrier tracking loop to assist in carrier tracking, and the advance code ce and the lag code cl enter the fourth correlator and the fifth correlator respectively; The correlation results output by the fourth correlator and the fifth correlator are modulo-calculated in the fourth incoherent device and the fifth incoherent device, and the modulo-calculated data has two branches: (5a) For the fourth incoherent device, when the parameter sets the incoherence number to 0, the selector of the fourth incoherent device is 1, and the modulo result Ce is output from the fourth incoherent device and sent to the code phase detector; (5b) For the fourth incoherent device, when the parameter setting incoherent times is not 0, the modulo result is sent to the accumulator for incoherent calculation, and the data is sent to the input queue FIFO. If the size of the FIFO exceeds the preset value, i.e., the incoherent times, the number of the head of the queue is detected, and the accumulator register is subtracted from the number to avoid the accumulation times being more than the set incoherent times by one; after the accumulation reaches the set value of the incoherent times, the accumulation result is truncated to obtain the incoherent result Ce, which is sent to the code phase detector for phase detection; The fourth incoherent device and the fifth incoherent device have the same principle; The code phase difference output by the code phase detector is fed back to the spread spectrum code generator through a low-pass filter to adjust the phase of the spread spectrum code generator so that the copied code is dynamically consistent with the received code; The output results of the fourth incoherent device and the fifth incoherent device are used as inputs of the code phase detector, and the code phase detector performs division calculation and phase detection. The output obtained is the phase difference between the code copied by the spread spectrum code generator and the received code.

4. The tracking method of a multi-mode satellite navigation receiver tracking loop according to any one of claims 1 to 3, characterized in that: The method comprises the following steps in order: (1) Down-convert the received satellite signal into an intermediate frequency signal as the input signal of the tracking loop module, and configure the tracking loop parameters through the interface; (2) The intermediate frequency signal is sent to 12 GPS tracking loops and 12 BD tracking loops respectively. In the tracking loops, the intermediate frequency signal is mixed to obtain the baseband signal; (3) The intermediate frequency signal obtained in step (1) is passed through a carrier tracking loop to obtain the phase difference and frequency difference between the intermediate frequency carrier signal copied by the receiver and the received intermediate frequency carrier signal. The phase and frequency of the carrier generator are adjusted by feedback so that the intermediate frequency carrier copied by the receiver is consistent with the received intermediate frequency carrier, thereby obtaining the Doppler information in the current signal and realizing the stripping of the intermediate frequency carrier. In order to adapt to signals of different strengths, the tracking loop has a full accumulation mode and a semi-accumulation mode for baseband signal processing, and the identification modes of the carrier discriminator include frequency discrimination, phase discrimination, and amplitude discrimination mode. When the signal is strong, the full accumulation mode is used for the baseband signal correlation operation, and the carrier discriminator adopts the frequency discrimination or phase discrimination mode. When the signal is weak, a long-term correlation operation is performed on the baseband signal. When the correlation time reaches 20ms, the semi-accumulation mode is used, and the carrier discriminator adopts the amplitude discrimination mode. (4) The baseband signal obtained in step (2) is passed 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. The phase of the spread spectrum code generator is adjusted through a feedback mechanism so that the receiver's copied spread spectrum code is consistent with the received spread spectrum code, thereby achieving spread spectrum code stripping; (5) After step (3) is completed, the carrier is stripped, and after step (4) is completed, the spread spectrum code is stripped, and the signal contains only the navigation message; the navigation message is bit synchronized and the bit edge of the navigation message is found; (6) Perform frame synchronization, find the frame header of the navigation data, and parse the navigation message for subsequent calculation of the three-dimensional position, velocity, and time.

5. The tracking method according to claim 4, characterized in that: The semi-accumulation mode means that in the correlation operation of the baseband data, data accumulation only lasts for half of the set correlation time, and the correlation operation is performed in the first half of the correlation time.

6. The tracking method according to claim 4, characterized in that: The amplitude demodulation mode refers to using the leading carrier se, the immediate carrier sp, and the lagging carrier sl to mix with the intermediate frequency signal, perform correlation calculation, and non-coherent integration to obtain three outputs Sl, Sp, and Se, and send the three outputs to the amplitude demodulator at the same time. The output result of the amplitude demodulator is the frequency difference we: 。

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