CN104849732B - A kind of binary offset carrier radio frequency navigation signal trace method - Google Patents

Abstract

An unambiguous tracking method of binary offset carrier. Aiming at the multi-peak problem of BOC signal, a unique tracking idea and method are designed. Provides efficient tracking for BOC(m,n). First, the subcarrier signal is replaced by the carrier signal to generate a BPSK signal, and the signal is captured by the BPSK method to eliminate the multi-peak of the signal. After the signal is captured, the BPSK method is used to track the signal; at the same time, according to the change of the code phase accumulator of the digital frequency synthesizer that generates the spreading code, the subcarrier signal is generated in real time, and the subcarrier signal is multiplied by the spreading code to generate a new spreading code. After the carrier/code loop tracking is stable, change the local oscillator frequency parameters of the carrier digital frequency synthesizer to generate a new carrier, and at the same time switch the spreading code to a new spreading code, and switch the carrier to a new carrier. Tracking to achieve higher tracking accuracy. This solution has a simple structure, less resource occupation, strong versatility, and effectively reduces the power consumption of the FPGA.

Description

A Binary Offset Carrier Radio Frequency Navigation Signal Tracking Method

technical field

The invention relates to a navigation signal tracking method, in particular to a binary offset carrier radio frequency navigation signal tracking method, which belongs to the field of satellite navigation signal reception.

Background technique

With the development of GPS, Galileo, GLONASS and Beidou navigation, a new signal modulation method, namely BOC (Binary Carrier Modulation), has emerged. The new BOC signal has a fission spectrum, and changing the corresponding parameters can change the position of the navigation signal spectrum around the center frequency point; the BOC signal has the characteristics of multiple peaks and narrow correlation peaks, and narrow correlation peaks improve the tracking accuracy and anti-interference ability of the signal, while The multi-peak characteristic poses certain challenges to the correct acquisition and tracking of signals.

At present, domestic and foreign scholars have proposed many improvement methods for the multi-peak characteristics of the BOC signal. The double-sideband capture algorithm proposed by Fishman regards the BOC signal as the sum of BPSK(m) of the two sidebands, and performs BPSK processing after filtering by the front-end filter. Its disadvantages include:

a) Increasing the front-end filter increases the complexity of the system;

b) The inconsistency of the two filters will also cause errors;

c) The processing method of BPSK also has a certain influence on the tracking accuracy of the signal.

The acquisition and tracking method of BPSK_LIKE proposed by Martin is to multiply the BOC(n,m) signal with two carriers with frequencies FC-FS and FC+FS and correlate it with the local pseudocode. The implementation process is very simple, and its autocorrelation function Very similar to BPSK. BPSK_LIKE can solve the multi-peak problem very well. The disadvantage is that the tracking accuracy is much worse than that of BOC narrow correlation peaks. For BOC(1,1), its tracking accuracy is half of the normal BOC narrow correlation peak tracking accuracy.

Olivier Julien proposed the ASPeCT correlation method in his doctoral dissertation. This method uses the subtraction of the autocorrelation function of the BOC modulated signal and the cross-correlation function of the pseudocode and the BOC modulated signal to eliminate the edge of the autocorrelation function of the BOC modulated signal. The disadvantage of this method is only applicable to modulated signals with the same subcarrier and pseudo-code rate.

Yang Zaixiu and Geng Shengqun of Beijing University of Aeronautics and Astronautics published a BOC tracking patent method using a three-loop tracking method, using three loops to track the pseudo code, sub-carrier and carrier respectively, and the sub-carrier is used as a code ring for tracking. This method solves the multi-peak problem very well, but the disadvantage of this method is that the structure is relatively complex, and there is one more subcarrier tracking loop, which consumes a lot of resources.

The subcarrier elimination method is proposed in some domestic literatures. Use the method of estimating the carrier to estimate the subcarrier, thereby eliminating the correlation, and generating an in-phase component and a quadrature component for the subcarrier (shifting the subcarrier period), which is equivalent to decomposing the signal again in the "subcarrier space" . The specific method is: first generate an in-phase component and a quadrature component according to the carrier; then further decompose each component, that is, generate a set of in-phase/orthogonal components for the sub-carriers respectively; correlate these four signals with the received signal Add the squares after integration. The resulting autocorrelation function has a good unimodality. The main disadvantage of this method is that the structure is relatively complex and requires a large number of correlators.

Contents of the invention

The technical problem solved by the present invention is: to overcome the deficiencies of the prior art, and provide a binary offset carrier radio frequency navigation signal tracking method, which combines the characteristics of BPSK tracking and BOC tracking, and can quickly and accurately complete binary offset carrier radio frequency The tracking of navigation signals has high tracking accuracy and small resource occupation, which meets the requirements of binary offset carrier radio frequency navigation signal tracking to the greatest extent.

The technical solution of the present invention is: a kind of binary offset carrier radio frequency navigation signal tracking method, the steps are as follows:

(1) The FPGA receives the binary offset carrier RF navigation signal BOC(n,m), down-converts the RF navigation signal BOC(n,m) to an intermediate frequency signal, and then samples it through an analog-to-digital converter to obtain a digital signal with an intermediate frequency of f ₀ Navigation signal BOC _IF (n,m);

(2) FPGA generates local BPSK spreading code Code _{bpsk_local} by code digital frequency synthesizer, and the code rate of described local BPSK spreading code is fc=m* _1.023MHz ; The frequency control word of BPSK spreading code Among them, N is the bit width of the phase accumulator in the code digital frequency synthesizer, and f _clk is the working master clock frequency of the FPGA, which will reduce to fraction form with no least common divisor Afterwards, the phase accumulator bit width of the digital frequency synthesizer is expanded to N', and the N' is equal to N+m'-1;

(3) generate local subcarrier Code _{deputy_carr_local} according to the phase accumulator that local BPSK spreading code changes in step (2), described local subcarrier code rate is f _c '=n*1.023MHz;

(4) Adjust the local BPSK spreading code and the local subcarrier so that the flipping moment when the local spreading code jumps from 0 to 1 is aligned with the flipping moment when the local subcarrier jumps from 0 to 1;

(5) Generate the local intermediate frequency carrier Carr _{bpsk_local} by the carrier digital frequency synthesizer, and utilize the local intermediate frequency carrier and the local BPSK spreading code in step (2) to generate the BPSK signal whose center frequency is (f ₀ +n*1.023) MHz , the center frequency of the local intermediate frequency carrier is f _IF =(f ₀ +n*1.023) MHz; the carrier frequency control word of the local carrier digital frequency synthesizer is Wherein M is the bit width of the phase accumulator in the carrier digital frequency synthesizer;

(6) Use the BPSK signal whose frequency is (f ₀ +n*1.023) MHz obtained in step (5) to replace the intermediate frequency navigation signal BOC _IF (n,m) whose center frequency is f ₀ obtained in step (1). Navigation signal capture, obtain the rough code phase and carrier frequency deviation of the radio frequency navigation signal, and obtain the BPSK signal with the center frequency of (f ₀ +df _carr +n*1.023) MHz, where df _carr is the captured carrier Doppler frequency;

(7) Utilize the carrier frequency that obtains in step (6) and code phase to generate center frequency to be local tracking intermediate frequency carrier and local tracking BPSK spreading code Code' _{deputy_carr_local} , the central frequency of described local tracking intermediate frequency carrier is (f ₀ + df _carr +n*1.023) MHz; the code rate of the local tracking BPSK spreading code is in The floor(x) indicates that the integer part of x is rounded down;

(8) generate local subcarrier Code ' _{deputy_carr_local} according to the phase accumulator of local BPSK spreading code digital frequency synthesizer in step (7), described local subcarrier code rate is

(9) utilize the local tracking intermediate frequency carrier generated in the step (7) and the local tracking BPSK spreading code to carry out the tracking of the radio frequency navigation signal; Described tracking adopts two-ring tracking, is respectively carrier tracking loop and code tracking loop;

(10) Carrier phase detection loop and the second-order filter of code phase detection loop are locked and judged respectively, whether the tracking of judgment step (9) is stable, specifically:

Subtract the current output value Acc_carr(n) of the accumulator of the second-order filter of the carrier phase detection loop from the last accumulator output value Acc_carr(n-1) to obtain the difference Accdt_carr, if the difference Accdt_carr is less than the preset value for K1 consecutive times threshold C1, the carrier loop tracking is stable, and the carrier loop lock flag is output; otherwise, the carrier loop tracking is unstable, and the carrier loop continues to track; the current output value of the accumulator Acc_code(n) of the code second-order filter is compared with The difference Accdt_code is obtained by subtracting the last accumulator output value Acc_code(n-1). If the difference Accdt_code is smaller than the preset threshold C2 for K2 consecutive times, the code loop tracking is stable, and the code loop lock flag is output; otherwise, the code loop is locked. The loop tracking is unstable, and the code loop continues to track;

If the carrier loop and the code loop are all locked, then output the loop lock sign and enter step (11);

(11) the local subcarrier Code ' _{deputy_carr} _local that step (8) obtains and the local tracking BPSK spreading code Code ' _{deputy_carr} _local that step (7) produces in the multiplication, produce a new local tracking spreading code signal Code_boc= Code' _bpsk _local*Code' _{deputy_carr} _local; the code rate of the local spreading code signal is

(12) generate local tracking intermediate frequency carrier Carr" _{boc_local} by carrier digital frequency synthesizer, the center frequency of described local intermediate frequency carrier is f _IF =(f ₀ +df _carr ) MHz;

(13) Utilize the local tracking intermediate frequency carrier Carr " _{boc_local} and the local tracking spread spectrum code Code_boc that step (11) produces in step (12) to generate to carry out the tracking of radio frequency navigation signal; tracking loop and code tracking loop;

(14) whether the carrier tracking loop and the code tracking loop in the judgment step (13) are locked, if the carrier tracking loop and the code tracking loop are all locked, then carry out subsequent information processing, if the lock is lost, then return to step (2 ), if one or both of the carrier tracking loop and the code tracking loop is unlocked, then return to step (13) to continue tracking.

The local subcarrier generating method in the step (3) and the step (8) is specifically:

parameter After simplification, the fraction without common divisor is The unexpanded phase accumulator of the code digital frequency synthesizer is N, and the bit width of the extended phase accumulator is N', and N' is equal to N+m'-1, so that

The sin type BOC signal subcarrier generation method is:

The ceil(x) means rounding up, if i is 0, then Code _{deputy_carr} _local is equal to 1, if i is 1, then Code _{deputy_carr} _local is equal to 0;

The cos type BOC signal subcarrier generation method is:

The ceil(x) indicates rounding up, if i is 0 or 3, then Code _{deputy_carr_local} is equal to 1, and if i is 1 or 2, then Code _{deputy_carr_local} is equal to 0.

The range of K1 is: 15-1000, the range of C1 is: 30-500; the range of K2 is: 15-1000, and the range of C2 is 3-300.

The beneficial effect of the present invention compared with existing method is:

(1) The present invention has adopted BPSK tracking method earlier, can lock the tracking process on the narrow correlation peak of radio frequency navigation signal and carry out, can effectively eliminate the multi-peak that BOC signal produces, effectively improved the reliability of tracking, reduced The complexity of subsequent BOC tracking;

(2) The present invention adopts the tracking method of two stages, and the first stage of tracking has eliminated the multi-peak that BOC signal produces, and the second stage has guaranteed the precision of tracking, and the tracking precision is high;

(3) The generation of each local subcarrier in the present invention does not need to increase the local subcarrier generation module additionally, produces according to code digital frequency synthesizer completely, and Doppler change releases according to code digital frequency synthesizer change, and resource occupation is few, is conducive to Implemented in FPGA;

(4) The present invention is suitable for tracking BOC(n, m) signals under different parameter conditions, is not affected by multi-peaks, and has strong versatility.

Description of drawings

Fig. 1 is a flowchart of the present invention;

Fig. 2 is a system structure block diagram of the present invention.

detailed description

Fig. 2 shows the system block diagram of the present invention, and as can be seen from Fig. 2, system among the present invention comprises following module:

The carrier generation module, which generates the required carrier signal according to the parameters, and performs signal acquisition and tracking.

Code generation module: This module generates the required spread spectrum code signal according to the parameters, and performs signal capture and tracking

Signal capture module: use the BPSK capture method to capture the signal, and obtain the rough code phase/carrier phase of the signal.

The integral reset module is used to track the signal, generate the immediate, leading and lagging related branch related values of the I and Q channels, and send them to the carrier/code loop module for phase detection, filtering, and frequency control word calculation;

Carrier loop module: Carrier phase detection, filtering, and carrier frequency control word calculation for the input I and Q correlation values.

Code loop module: perform pseudo-code phase detection, filtering, and code frequency control word calculation on the input lead, instant, and lag related values.

Carrier/code loop lock detection: judge the locked state of the carrier loop and code loop, feed back the judgment result to the carrier generation module and code generation module, perform carrier/pseudo code switching, and perform fine tracking.

As shown in Figure 1, it is a flow chart of the present invention, as can be seen from Figure 1, a kind of binary offset carrier radio frequency navigation signal tracking method provided by the present invention, the steps are as follows:

(1) The FPGA receives the binary offset carrier RF navigation signal BOC(n,m), down-converts the RF navigation signal BOC(n,m) to an intermediate frequency signal, and then samples it through an analog-to-digital converter to obtain a digital signal with an intermediate frequency of f ₀ Navigation signal BOC _IF (n,m);

(2) FPGA generates local BPSK spreading code Code _{bpsk_local} by code digital frequency synthesizer, and the code rate of described local BPSK spreading code is fc=m* _1.023MHz ; The frequency control word of BPSK spreading code Among them, N is the bit width of the phase accumulator in the code digital frequency synthesizer, and f _clk is the working master clock frequency of the FPGA, which will reduce to fraction form with no least common divisor Afterwards, the bit width of the phase accumulator of the digital frequency synthesizer is extended to N', where N' is equal to N+m'-1 bit width. For example BOC(15,10), will Simplified to a fractional form without the least common divisor is 2/3, so the bit width of the phase accumulator in the actual digital frequency synthesizer is N+2-1, that is, N' is equal to N+1 bits.

(3) generate local subcarrier Code _{deputy_carr_local} according to the phase accumulator that local BPSK spreading code changes in step (2), described local subcarrier code rate is f _c '=n*1.023MHz;

parameter After simplification, the fraction without common divisor is The unexpanded phase accumulator of the code digital frequency synthesizer is N, and the bit width of the extended phase accumulator is N', and N' is equal to N+m'-1, so that

The sin type BOC signal subcarrier generation method is:

The ceil(x) means rounding up, if i is 0, then Code _{deputy_carr} _local is equal to 1, if i is 1, then Code _{deputy_carr} _local is equal to 0;

The cos type BOC signal subcarrier generation method is:

The ceil(x) indicates rounding up, if i is 0 or 3, then Code _{deputy_carr_local} is equal to 1, and if i is 1 or 2, then Code _{deputy_carr_local} is equal to 0.

(4) Adjust the local BPSK spreading code and the local subcarrier so that the flipping moment when the local spreading code jumps from 0 to 1 is aligned with the flipping moment when the local subcarrier jumps from 0 to 1;

(5) Generate the local intermediate frequency carrier Carr _{bpsk_local} by the carrier digital frequency synthesizer, and utilize the local intermediate frequency carrier and the local BPSK spreading code in step (2) to generate the BPSK signal whose center frequency is (f ₀ +n*1.023) MHz , the center frequency of the local intermediate frequency carrier is f _IF =(f ₀ +n*1.023) MHz; the carrier frequency control word of the local carrier digital frequency synthesizer is Wherein M is the bit width of the phase accumulator in the carrier digital frequency synthesizer;

(6) Utilize the BPSK signal whose new frequency is (f ₀ +n*1.023) MHz obtained in step (5) to replace the intermediate frequency navigation signal BOC _IF (n,m) whose center frequency is f ₀ obtained in step (1) Carry out navigation signal capture, the capture method can choose time-domain sliding correlation method, matched filter algorithm, time-domain based fast search algorithm and frequency fast capture algorithm with large resource occupation according to its own design strategy. When the capture condition of the selected algorithm is greater than the capture When thresholding, the rough code phase and carrier frequency deviation of the RF navigation signal are obtained, and a BPSK signal with a center frequency of (f ₀ +df _carr +n*1.023) MHz is obtained, where df _carr is the captured carrier Doppler frequency ;

(7) Utilize the carrier frequency that obtains in step (6) and code phase to generate center frequency to be local tracking intermediate frequency carrier and local tracking BPSK spreading code Code' _{deputy_carr_local} , the central frequency of described local tracking intermediate frequency carrier is (f ₀ + df _carr +n*1.023) MHz; the code rate of the local tracking BPSK spreading code is in The floor(x) indicates that the integer part of x is rounded down;

(8) generate local subcarrier Code ' _{deputy_carr_local} according to the phase accumulator of local BPSK spreading code digital frequency synthesizer in step (7), described local subcarrier code rate is

parameter After simplification, the fraction without common divisor is The unexpanded phase accumulator of the code digital frequency synthesizer is N, and the bit width of the extended phase accumulator is N', and N' is equal to N+m'-1, so that

The sin type BOC signal subcarrier generation method is:

The ceil(x) means rounding up, if i is 0, then Code _{deputy_carr} _local is equal to 1, if i is 1, then Code _{deputy_carr} _local is equal to 0;

The cos type BOC signal subcarrier generation method is:

The ceil(x) indicates rounding up, if i is 0 or 3, then Code _{deputy_carr_local} is equal to 1, and if i is 1 or 2, then Code _{deputy_carr_local} is equal to 0.

(9) utilize the local tracking intermediate frequency carrier generated in the step (7) and the local tracking BPSK spreading code to carry out the tracking of the radio frequency navigation signal; Described tracking adopts two-ring tracking, is respectively carrier tracking loop and code tracking loop;

(10) Carrier phase detection loop and the second-order filter of code phase detection loop are locked and judged respectively, whether the tracking of judgment step (9) is stable, specifically:

Subtract the current output value Acc_carr(n) of the accumulator of the second-order filter of the carrier phase detection loop from the last accumulator output value Acc_carr(n-1) to obtain the difference Accdt_carr, if the difference Accdt_carr is less than the preset value for K1 consecutive times Threshold C1, the carrier loop tracking is stable, and the carrier loop lock flag is output; otherwise, the carrier loop tracking is unstable, and the carrier loop continues to track; the range of K1 is: 15 to 1000, and the range of C1 is: 30 to 500 ;

Subtract the current output value Acc_code(n) of the accumulator of the second-order filter of the code from the previous accumulator output value Acc_code(n-1) to obtain the difference Accdt_code, if the difference Accdt_code is less than the preset threshold C2 for K2 consecutive times, Then the code loop tracking is stable, and the code loop lock flag is output; otherwise, the code loop tracking is unstable, and the code loop continues to track; the range of K2 is: 15-1000, and the range of C2 is: 3-300;

If the carrier loop and the code loop are all locked, then output the loop lock sign and enter step (11);

(11) the local subcarrier Code ' _{deputy_carr} _local that step (8) obtains and the local tracking BPSK spreading code Code ' _{deputy_carr} _local that step (7) produces in the multiplication, produce a new local tracking spreading code signal Code_boc= Code' _bpsk _local*Code' _{deputy_carr} _local; the code rate of the local spreading code signal is

(12) generate local tracking intermediate frequency carrier Carr" _{boc_local} by carrier digital frequency synthesizer, the center frequency of described local intermediate frequency carrier is f _IF =(f ₀ +df _carr ) MHz;

(13) Utilize the local tracking intermediate frequency carrier Carr " _{boc_local} and the local tracking spread spectrum code Code_boc that step (11) produces in step (12) to generate to carry out the tracking of radio frequency navigation signal; tracking loop and code tracking loop;

(14) whether the carrier tracking loop and the code tracking loop in the judgment step (13) are locked, if the carrier tracking loop and the code tracking loop are all locked, then carry out subsequent information processing, if the lock is lost, then return to step (2 ), if one or both of the carrier tracking loop and the code tracking loop is unlocked, then return to step (13) to continue tracking.

Example

Now take Galileo's B1 frequency point signal BOC(1,1) as an example to illustrate the implementation process of the patent. The frequency of Galileo's B1 frequency point is 1575.42MHz, assuming that the center frequency after down-conversion is 30MHz, and the working clock of the FPGA system is 100MHz. Specific steps are as follows:

(1) The digital navigation signal BOC _30MHz (n,m) with an intermediate frequency of 30MHz is obtained after down-conversion and the adoption of an analog-to-digital converter;

(2) generate local BPSK spreading code Code _{bpsk_local} by code digital frequency synthesizer, the code rate of described local BPSK spreading code is f _c =1.023MHz, it is 32bit to establish digital frequency synthesizer phase accumulator bit width, so Said BOC(1,1) There is no least common divisor, that is, 1/1, the bit width of the phase accumulator of the actual digital frequency synthesizer is 32+1-1, which is equal to 32bit; the operating clock of the FPGA system is 100MHz, and the frequency control word of the BPSK spreading code After rounding down, the frequency control word in FPGA is 43937515;

(3) generate local subcarrier Code _{deputy_carr_local} according to the phase accumulator that local BPSK spreading code changes in the step (2), described local subcarrier code rate is f _c '=1.023MHz;

The generation process is as follows: the instantaneous phase of the code digital frequency synthesizer phase accumulator is NCO, the bit width is N', that is, 32bit, the parameters After simplification, the fraction without common divisor is make The ceil(x) represents rounding up. If i is an even number and 0≤i<n*m-1, then Code _{deputy_carr} _local is equal to 1, if i is an odd number and 0<i≤n*m-1, then Code _{deputy_carr} _local is equal to 0;

(4) Adjust the local BPSK spreading code and the local subcarrier in the FPGA, so that the flipping moment when the local spreading code jumps from 0 to 1 is aligned with the flipping moment when the local subcarrier jumps from 0 to 1;

(5) Generate the local intermediate frequency carrier Carr _{bpsk_local} by the carrier digital frequency synthesizer, and utilize the local intermediate frequency carrier and the local BPSK spreading code in step (2) to generate the BPSK signal whose center frequency is 31.023MHz; assuming the carrier digital frequency synthesizer Phase accumulator M is 32bit, and the carrier frequency control word of described local carrier digital frequency synthesizer is In order to implement in FPGA, take its integer part as the frequency control word in FPGA, that is, 1332427704;

(6) Utilizing the new frequency that obtains in step (5) is that the BPSK signal of 31.023MHz replaces the intermediate frequency navigation signal BOC _30MHz (1,1) that the center frequency that down conversion obtains in step (1) is 30MHz to carry out navigation signal capture, capture The method adopts the time-domain sliding correlation method, that is, slides the carrier frequency and code phase in the time domain, and outputs the signal energy corresponding to the carrier frequency and code phase of a code period of 10 ms. When the signal energy is greater than the capture threshold of 100,000, the rough Code phase and carrier frequency deviation, assuming that the carrier frequency deviation is 100Hz, a BPSK signal with a center frequency of (f _c +df _carr +n*1.023)MHz is obtained, which is 31.123MHz;

(7) utilize carrier frequency and code phase generation center frequency that obtains in step (6) to be local tracking intermediate frequency carrier and local tracking BPSK spreading code Code ' _{bpsk_local} , the central frequency of described local tracking intermediate frequency carrier is 31.123MHz; The code rate of the local tracking BPSK spreading code is Among them, 154 is calculated as follows The floor(x) indicates that the integer part of x is rounded down. Keep the rough code phase captured in (6), and only change the frequency control word of the code digital frequency synthesizer caused by the code rate change, that is, the code frequency control word is changed from the original 43937515.43808 to 43937543.43808.

(8) generate local subcarrier Code ' _{deputy_carr_local} according to the phase accumulator that local BPSK spreading code changes in step (7);

The generation process is: code digital frequency synthesizer phase accumulator instant phase is NCO, bit width is N', namely 32bit, parameter After simplification, the fraction without common divisor is make The ceil(x) represents rounding up. If i is an even number and 0≤i<n*m-1, then Code _{deputy_carr} _local is equal to 1, if i is an odd number and 0<i≤n*m-1, then Code _{deputy_carr} _local is equal to 0;

(9) utilize the local tracking intermediate frequency carrier generated in the step (7) and the local tracking BPSK spreading code to carry out the tracking of the radio frequency navigation signal; Described tracking adopts two-ring tracking, is respectively carrier tracking loop and code tracking loop;

(10) Carrier phase detection loop and the second-order filter of code phase detection loop are locked and judged respectively, whether the tracking of judgment step (9) is stable, specifically:

Subtract the current output value Acc_carr(n) of the accumulator of the second-order filter of the carrier phase detection loop from the last accumulator output value Acc_carr(n-1) to obtain the difference Accdt_carr, if the difference Accdt_carr is less than the preset value for 25 consecutive times If the threshold is 100, the carrier loop tracking is stable, and the carrier loop is locked; otherwise, the carrier loop tracking is unstable, and the carrier loop continues to track;

Subtract the current output value Acc_code(n) of the accumulator of the second-order filter of the code from the previous accumulator output value Acc_code(n-1) to obtain the difference Accdt_code, if the difference Accdt_code is less than the preset threshold 50 for 25 consecutive times, Then the code loop tracking is stable, and the code loop is locked; otherwise, the code loop tracking is unstable, and the code loop continues to track;

If the carrier loop and the code loop are all locked, then output the loop lock sign and enter step (11);

(11) the local subcarrier Code ' _{deputy_carr} _local that step (8) obtains and the local tracking BPSK spreading code Code ' _bpsk _local that produces in the step (7) are multiplied, produce a new local tracking spreading code signal Code_boc= Code' _bpsk _local*Code' _{deputy_carr} _local; the code rate of the local spreading code signal is 2.04600129MHz;

(12) Generate a local tracking intermediate frequency carrier Carr" _{boc_local} by a carrier digital frequency synthesizer, and the center frequency of the local intermediate frequency carrier is f _IF = (f ₀ +df _carr ) MHz = (300+0.1) MHz = 30.1 MHz

(13) the local tracking spreading code Code_boc of 2.04600129MHz to carry out the tracking of the radio frequency navigation signal utilizing the intermediate frequency carrier Carr " _{boc_local} of the local tracking 30.1MHz that generates in the step (12) and the code rate that the step (11) produces; Tracking adopts two-loop tracking, respectively carrier tracking loop and code tracking loop;

(14) Whether the carrier tracking loop and the code tracking loop in the judgment step (13) are locked, the judging method is the same as the step (10), if the carrier tracking loop and the code tracking loop are all locked, then carry out subsequent information processing, If the lock is lost, then return to step (2), if one of the carrier tracking loop and the code tracking loop is unlocked or both are unlocked, then return to step (13) to continue tracking.

The present invention can track on the narrow correlation peak of the BOC signal, and the tracking precision is high; it can effectively eliminate the multi-peak problem of the BOC signal, and the resource occupation is small, and it solves the problem of consuming more resources in order to eliminate the multi-peak or lowering the precision. cost, suitable for signal capture, tracking, and data demodulation in FPGA; strong versatility, suitable for BOC(n, m) signal capture, tracking, and data demodulation; in the future, GPS, GLONESS, GALIEO, and BEIDU will For the compatibility and interoperability of large systems, the BOC signal is modulated at the B1 frequency point, which requires the capture, tracking, and data demodulation of the BOC signal. The invention can be applied to the reception of BOC signals in future navigation signal receivers.

The content that is not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims (2)

1. a kind of binary offset carrier radio frequency navigation signal trace method, it is characterised in that step is as follows：

(1) FPGA receives binary offset carrier radio frequency navigation signal BOC (n, m), will become under radio frequency navigation signal BOC (n, m) Frequency obtains intermediate frequency for f to after intermediate-freuqncy signal, then through analog-digital converter sampling₀Digital navigation signal BOC_IF(n,m)；

(2) FPGA generates local BPSK spread spectrum codes Cs ode by code digital frequency synthesizer_bpsk_ local, the local BPSK expands The bit rate of frequency code is f_c=m*1.023MHz；The frequency control word of BPSK spreading codesWherein yardage word The instant phase value of frequency synthesizer phase accumulator is that the bit wide of phase accumulator in NCO, code digital frequency synthesizer is N, f_clkFor FPGA work master clock frequency；

(3) local subcarrier Code is generated according to the phase accumulator that local BPSK spreading codes change in step (2)_{deputy_carr}_ Local, the local subcarrier bit rate is f_c'=n*1.023MHz；

(4) local BPSK spreading codes and local subcarrier are adjusted so that local spreading code by 0 jump to 1 upset moment with Local subcarrier is alignd by the 0 upset moment for jumping to 1；

(5) local IF carrier Carr is generated by carrier wave digital frequency synthesizer_bpsk_ local, the local IF carrier Carr_bpsk_ local IF carrier speed is (f₀+ n*1.023) MHz is f using frequency₀IF carrier and step (2) in Local BPSK spread spectrum codes Cs ode_bpskLocal subcarrier Code in _ local and step (3)_{deputy_carr}_ local is multiplied, Generation centre frequency is (f₀+ n*1.023) MHz, spread-spectrum code rate is f_c=m*1.023MHz bpsk signal, it is described it is local in Frequency centre carrier frequency is f_IF=(f₀+n*1.023)MHz；The carrier frequency control word of local carrier digital frequency synthesizer isWherein M is the bit wide of phase accumulator in carrier wave digital frequency synthesizer；

(6) it is (f using the centre carrier frequency obtained in step (5)₀+ n*1.023) MHz bpsk signal in step (1) The centre carrier frequency arrived is f₀Digital intermediate frequency navigation signal BOC_IF(n, m) carries out navigation signal capture, obtains radio frequency navigation The rough code phase and carrier frequency frequency deviation of signal, and centre frequency is obtained for (f₀+df_carr+ n*1.023) MHz BPSK letter Number, wherein df_carrTo capture obtained carrier Doppler frequency；

(7) it is local trace IF carrier using the carrier frequency and rough code phase generation centre frequency that are obtained in step (6) With local trace BPSK spread spectrum codes C ode '_{deputy_bpsk}_ local, the centre frequency of the local trace IF carrier is (f₀+ df_carr+n*1.023)MHz；The spreading code bit rate of the local trace BPSK isWhereinThe floor (x) represents that x integer parts are rounded downwards；

(8) local subcarrier is generated according to the phase accumulator of local BPSK spreading code digital frequency synthesizers in step (7) Code′_{deputy_carr}_ local, the local subcarrier bit rate is

(9) radio frequency navigation letter is carried out using the local trace IF carrier and local trace BPSK spreading codes of generation in step (7) Number tracking；The tracking is using the tracking of two rings, respectively carrier tracking loop and code tracking loop；

(10) locking judgement, the tracking of judgment step (9) are carried out to the second order filter of carrier wave phase demodulation ring and code phase demodulation ring respectively Whether stablize, be specially：

By the current output valve Acc_carr (n) of accumulator of carrier wave phase demodulation ring second order filter and last accumulator output values Acc_carr (n-1), which subtracts each other, obtains difference Accdt_carr, if continuous K1 times of difference Accdt_carr is less than default thresholding C1, Then carrier loop tracking is stable, outgoing carrier loop-locking mark；Otherwise, carrier loop tracking is unstable, and carrier loop continues It is tracked；By the current output valve Acc_code (n) of the accumulator of code second order filter and last accumulator output values Acc_ Code (n-1), which subtracts each other, obtains difference Accdt_code, if continuous K2 times of difference Accdt_code is less than default thresholding C2, code Loop tracks are stable, output code loop-locking mark；Otherwise, code loop tracks are unstable, and code loop proceeds tracking；

If carrier loop and code loop are locked, loop lock flag is exported, into step (11)；

(11) the local subcarrier Code ' for obtaining step (8)_{deputy_carr}_ local expands with the local trace BPSK produced in step (7) Frequency code Code '_{deputy_bpsk}_ local is multiplied, and produces a new local trace spread-spectrum code signals Code_boc=Code '_bpsk_ local*Code′_{deputy_carr}_local；The bit rate of the local spread-spectrum code signals is

(12) local trace IF carrier Carr " is generated by carrier wave digital frequency synthesizer_boc_ local, the local intermediate frequency The centre frequency of carrier wave is f_IF=(f₀+df_carr)MHz；

(13) the local trace IF carrier Carr " of generation in step (12) is utilized_bocIt is local that _ local and step (11) are produced Track the tracking that spread spectrum codes C ode_boc carries out radio frequency navigation signal；The tracking is using the tracking of two rings, respectively carrier track Loop and code tracking loop；

(14) whether the carrier tracking loop and code tracking loop in judgment step (13) lock, if carrier tracking loop and code with Track loop is locked, then carries out follow-up processing, if losing lock, return to step (2), if carrier tracking loop and code tracking loop Lu Youyi unlocked or unlocked, then return to step (13), proceeds tracking.

2. a kind of binary offset carrier radio frequency navigation signal trace method according to claim 1, it is characterised in that：Institute The scope for stating K1 is：15~1000, C1 scope is：30~500；K2 scope is：15~1000, C2 scope be 3~ 300。