Arrow-borne multi-antenna GNSS receiver loop tracking method for drop point control

Abstract

The invention relates to a drop point control-oriented rocket-borne multi-antenna GNSS receiver loop tracking method, and belongs to the technical field of satellite navigation. For a rocket-borne N-antenna GNSS receiver, N loops are configured for each GNSS satellite, and the loops are divided into the following three classes: 1) a main loop: autonomously completing loop phase discrimination, filtering and integration, resolving observed quantity and extracting navigation messages from the loop; 2) a semi-open loop: carrier PLL and FLL form an autonomous closed loop, and a pseudo code DLL is updated by the main loop; and the tracked GNSS signal is integrated according to the parameters of the main ring. And the receiver determines the loop type according to the C / N0 value and the phase-locked PLD value of each path of signal, and completes stable tracking and continuous positioning of the GNSS signal in a rocket reentry section high-dynamic high-rotation environment.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite navigation and relates to a loop tracking method of an arrow-borne multi-antenna GNSS receiver for landing point control. Background Art

[0002] Focusing on the development direction of rocket reusability, the overall parameter identification design of the new profiles and new modes of the first-stage reentry phase of the new generation of near-Earth manned rockets, such as the thermal environment, is quite different from the traditional design, and further in-depth research is needed in combination with satellite navigation PVT data. When the first stage of the rocket enters the reentry phase, not only is the radial dynamics of the projectile large, but it is also accompanied by high-speed rolling. Generally, the axial angular velocity of the projectile is not less than 400° / s, and the lateral angular velocity is not less than 260° / s. Because during the rolling process, the missile-borne antenna frequently switches between the sky-to-ground state, resulting in discontinuous navigation signals. Traditional satellite navigation terminals will experience signal loss of lock and will not be able to position normally. Summary of the invention

[0003] In view of this, an object of the present invention is to provide a loop tracking method of an arrow-borne multi-antenna GNSS receiver for landing point control.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] To solve this problem, we first consider the GPSL1 C / A signal with 1) a main code period of 1ms, 2) a code length of 1023, and 3) a main code modulation method of BPSK. If converted into spatial length, the half-chip length of the signal is about 150m, which is significantly smaller than the circumference of a general rocket or missile body. If it is assumed that the GNSS antennas are all installed on the same cross-section of the carrier, then for the received signal at the same time, consider 1) the expression of the integrated energy envelope of the BPSK signal:

[0006]

[0007] Where I and Q represent the integrated energy values ​​of the in-phase and quadrature branches, A is the signal power, τ is the code phase difference between the local signal and the actual signal, and T is the chip length; and 2) the expression of carrier Doppler:

[0008]

[0009] where f ca is the carrier Doppler in the satellite-user radial direction, v st represents the satellite velocity, v user is the user velocity, cosθ is the star-user direction cosine, c is the speed of light constant, f nominal is the nominal carrier frequency.

[0010] Assuming that the circumference of the carrier is 10m, the straight-line distance d between any two antennas on the same cross section is less than 10m. Substituting this distance into equation (1) and further converting it into signal-to-noise ratio, it can be obtained that the SN0 difference Δ between any two loops is no more than 0.3dB, which is negligible in terms of the correct loop update for strong signals. At the same time, it can be found from equation (2) that the contribution of d to Doppler is only reflected in the direction cosine cosθ, and for the satellite-user distance of 20,000km to 30,000km, the influence of d on cosθ is negligible.

[0011] In summary, among the GNSS observations provided by multiple antennas, if the code phase of one of the signals is known to be β and the code Doppler is f cd , the carrier Doppler is f ca , the following approximation can be made:

[0012]

[0013]

[0014]

[0015] It can be seen from the above equation that if the pseudo code phase, pseudo code Doppler and carrier Doppler of a certain antenna receiving signal can be correctly obtained at any time, then the pseudo code phase, pseudo code Doppler and carrier Doppler of any antenna receiving signal are known and equal to the corresponding parameters of the antenna receiving signal.

[0016] After making the above approximation, a loop tracking method for an N-antenna GNSS receiver on a rocket is designed: N loops are configured for each GNSS satellite, and the loops are divided into the following three categories, namely 1) Main loop: autonomously complete loop phase discrimination, filtering and integration, and solve the observation quantity and navigation message from this loop 2) Semi-open loop: carrier PLL and FLL form an autonomous closed loop, and the pseudo code DLL is updated by the main loop 3) Open loop: All loop updates are completed by the main loop, and the tracked GNSS signal is integrated according to the parameters of the main loop. The receiver determines the loop type based on the C / N0 value and phase-locked PLD value of each signal, and completes stable tracking and continuous positioning of GNSS signals in high dynamic and high rotation environments.

[0017] The beneficial effects of the present invention are:

[0018] (1) By adopting the classification management of main loop, semi-open loop and open loop, it is possible to track GNSS signals more continuously and accurately, especially in high-dynamic and high-rotation environments. This helps the rocket body maintain its position during the reentry phase, thereby providing continuous and reliable navigation data and making the calculation of the landing point more accurate.

[0019] (2) By reasonably allocating and managing RF front-end resources and opening up an appropriate amount of tracking channels in hardware, the present invention effectively utilizes limited hardware resources and improves system efficiency.

[0020] (3) The method of the present invention is applicable to different GNSS systems and signal types and has good versatility and adaptability.

[0021] (4) By autonomously completing loop phase detection, filtering, and integration operations, the system reduces dependence on external systems and improves overall system reliability.

[0022] (5) The method of the present invention can quickly process the captured signals and timely update the configuration of the tracking channel, thereby improving the speed and real-time performance of data processing.

[0023] (6) Through continuous observation and analysis of the phase-lock indication factor, the present invention can effectively distinguish between noise signals and real signals, thereby reducing the probability of false positive phase lock.

[0024] (7) The method of the present invention simplifies the traditional complex operation process, making the operation more intuitive and easy to manage.

[0025] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0027] Figure 1 It is the principle diagram of the present invention;

[0028] Figure 2 Loop update strategies corresponding to the carrier main loop, semi-open loop, and open loop;

[0029] Figure 3 It is the loop update strategy corresponding to the pseudo code main loop, semi-open loop and open loop. DETAILED DESCRIPTION

[0030] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0031] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0032] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0033] See also Figure 1 to Figure 3 , is a navigation multi-antenna diversity method for landing point control, the method comprising the following steps:

[0034] S1: The receiver is equipped with N RF front ends, i.e. the number of antennas, and processes the GNSS RF signals from the N antennas independently. The GNSS intermediate frequency signals after amplification and down-conversion are quantized by the ADC into N digital intermediate frequencies and transmitted to the baseband processing circuit;

[0035] S2: Perform preprocessing operations such as DC component removal, low-pass filtering, re-quantization, and downsampling on the digital intermediate frequency. The preprocessed signal is transmitted to the capture circuit and tracking circuit for capture and tracking;

[0036] S3: As a compromise between capture efficiency and hardware circuit resource overhead, the intermediate frequency signals before entering the capture circuit are combined in pairs. A is the intermediate frequency signal from channel A, IF B is the intermediate frequency signal from channel B, then the combined signal is (IFA +IF B ) / 2. The antennas corresponding to the two signals to be combined should be distributed diagonally relative to the cross section of the rocket body as much as possible.

[0037] S4: A certain number of tracking channels are opened in the hardware according to the number of frequencies and satellites to be processed. In the tracking channel corresponding to each satellite, 1 pseudo code NCO, 1 pseudo code generator, N correlators and N carrier NCOs are configured. Among them, N carrier NCOs and N correlators, together with corresponding filters and phase detectors, form a total of N tracking loops, corresponding to the number of antennas.

[0038] S5: The loops are divided into the following three categories, namely 1) Main loop: autonomously complete loop phase discrimination, filtering and integration, and the observed quantity and navigation message are extracted from this loop. In view of the uniqueness of the pseudo code NCO, there can only be one main loop at any time; 2) Semi-open loop: carrier PLL and FLL form an autonomous closed loop, and the pseudo code DLL is updated by the main loop parameters; 3) Open loop: all autonomous loop updates are closed, and all loop parameters are shared with the main loop. It generates local signals based on the parameters of the main loop and correlates with the intermediate frequency signal of the corresponding antenna.

[0039] S6: After any star is captured successfully, the tracking channel is configured according to the captured carrier Doppler and pseudo code phase. Specifically, the captured Doppler is Then for N carriers NCO, all are configured with frequency control words Configure the frequency control word for the pseudo code NCO in, is the nominal frequency of the pseudo code, δ is the ratio of carrier frequency to pseudo code frequency, M is the NCO bit width, and f is the operating frequency of the tracking circuit.

[0040] S7: As a supplement to S6: At this time, the tracking loop corresponding to any one of the signals A and B is selected as the main loop. The main loop updates the carrier loop and the code loop; the remaining (N-1) loops are semi-open loops or open loops, and the pseudo-code DLL phase detection is not performed. The pseudo-code NCO frequency control word is shared with the main loop. At the same time, according to the condition (*), it is determined whether to upgrade the semi-open loop to the main loop (and at the same time downgrade the original main loop to a semi-open loop), and according to the condition (**), it is determined whether to upgrade the open loop to a semi-open loop.

[0041] S7: The tracking channel performs coherent integration, and the integration time is the pseudo code period T of the signal. At the end of each pseudo code period, the tracking channel generates 2N in-phase, orthogonal and centered (prompt) integration values, recorded as S I,k,1 ,S I,k,2 …S I,k,N ,S Q,k,1 ,S Q,k,2 …S Q,k,N . Where S I,k,iis the I-way integral value of the ith loop at time element k, S Q,k,i is the Q-path integral value of the ith loop at time k. If the time of the loop pre-integration is MT, the loop is updated every MT time.

[0042] S8: Considering the high radial dynamics of the arrow-borne receiver, a second-order frequency-locked loop is used to assist a third-order phase-locked loop for signal tracking. At this time, the frequency-locked loop is configured with an integrator (except the NCO), which is denoted as Ω α , the phase-locked loop is equipped with two integrators (except NCO), denoted as Θ α ,Θ β .

[0043] S9: In one data cycle, a total of M = T Data / T times the coherent integration length is the bit code period. Take the following broadband signal energy Narrowband signal energy In J data cycles, multiple continuous observations are made on WBP and NBP, and we get:

[0044]

[0045] Substituting Z into the following formula, we can get the loop C / N0 value:

[0046]

[0047] Where Z is the mean of the narrowband-broadband energy ratio, and E is the mathematical expectation.

[0048] S10: N C / N0 calculators are configured in the tracking engine. Each C / N0 value is calculated for each loop according to step S9 in each data cycle, and is recorded as C / N01, C / N02, ..., C / N0 N .

[0049] S11 (condition (*)): According to the above probability, for the data modulation signal setting: if the SN0 criterion is met and the phase is locked for 3 consecutive times, then this antenna is selected as the main antenna. For the pilot signal setting: if the SN0 criterion is met and the phase is locked for 6 consecutive times, then this antenna is selected as the main antenna.

[0050] S12: The phase-locked indicator factor PLD expression is: Specific calculation method: Let the message bit period be T data , the coherent integration time is T, then first The integral value is smoothed.

[0051]

[0052]

[0053] Where 1≤k≤l is the number of coherent integration accumulations within a single cycle l,

[0054] S13: For the BD D2 signal with a data period of 2ms, the phase-locked indication factor calculation period is l*T data , the step S12 k ,Q k is the I and Q path integration value in the kth data cycle.

[0055] S14: Continuously observe the phase-locked indicator factor |Q / I| of each loop. If the currently tracked signal is received by a shielded antenna, the energy of the I and Q paths is approximately Gaussian noise, and the quotient |Q / I| is regarded as a Cauchy distribution, and its probability density distribution function is:

[0056]

[0057] The corresponding CDF is:

[0058]

[0059] For BPSK GNSS signals with data modulation, a phase difference of less than 30° is considered locked, and the phase lock factor under this threshold is ±0.577. The probability that the noise signal phase locker falsely reports phase lock is 2F(-0.577). For BPSK GNSS pilot signals without data modulation, a phase difference of less than 60° is considered locked, and the phase lock factor under this threshold is ±X. The probability that the noise signal phase locker falsely reports phase lock is 2F(-X).

[0060] S15 (condition (**)): According to the above probabilities, for the data modulation signal setting: if the SN0 criterion is met and the phase is locked for 3 consecutive times, then this antenna is selected as the main antenna. For the pilot signal setting: if the SN0 criterion is met and the phase is locked for 6 consecutive times, then this antenna is selected as the main antenna.

[0061] S16: After condition (*) is met, the autonomous carrier phase detection function of loop γ is turned on, and the integral value involved in the carrier loop filter in the main loop α is passed to loop γ.

[0062]

[0063]

[0064]

[0065] Ω 2y =Ω 2α

[0066] in is the accumulated value of the integrator except NCO in the second-order FLL loop, Ω 2y It is the accumulated value of the two-stage integrator except NCO in the third-order PLL.

[0067] S17: After condition (**) is met, loop γ is upgraded to the main loop. Specifically, the pseudo code phase detection function of loop γ is turned on, and the pseudo code phase detection function of loop α is turned off, and the pseudo code NCO frequency control word updated by loop γ is distributed to all other loops. The observation quantity extraction function and the telegram demodulation function of loop α are turned off, and the corresponding functions of loop γ are turned on.

[0068] S18: After the above main loop-semi-open loop-open loop selection strategy is implemented, at the start of the solution, the main loop is observed and extracted, where the extraction formula of the pseudo-range observation p is:

[0069] p=(t local -t sv )*c

[0070] where t local The local time of the extraction moment, t sv is the satellite launch time, and c is the speed of light. Specifically, t sv Calculated by the following formula

[0071] t sv =SOW+N bit *0.002+N C *0.001+0.4887φ C *10 -6

[0072] Where SOW is the seconds per week in the message, N bit is the current bit count, N C is the current pseudo code chip count, φ C is the current pseudo code phase.

[0073] Doppler Observations The extraction formula is:

[0074]

[0075] in is the carrier NCO frequency control word, f is the NCO operating frequency, and bias is a fixed frequency offset.

[0076] Figure 2It reflects the loop update strategies corresponding to the carrier main loop, semi-open loop, and open loop. It can be seen that for the open loop, the phase difference required for its loop update comes from the main loop, and its own phase detection function is in a closed state. For the semi-open loop or main loop, the loop update is performed autonomously, but only the carrier phase of the main loop is used for observation extraction. At the same time, for the three loops, correlation integration is required.

[0077] Figure 3 It reflects the loop update strategy corresponding to the pseudo-code main loop, semi-open loop and open loop. Except that the phase detector is different from the carrier loop, the pseudo-code phase difference of the semi-open loop and open loop of the pseudo-code loop all comes from the main loop.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. Loop tracking method of rocket-borne multi-antenna GNSS receiver for landing point control, Features: The method comprises the following steps: Configure multiple RF front ends to independently process GNSS RF signals from multiple antennas; Pre-process the digital intermediate frequency and transmit it to the capture circuit and the tracking circuit; According to the number of frequencies and satellites to be processed, a corresponding number of tracking channels are opened in the hardware; The loops are divided into three categories: main loop, semi-open loop and open loop, and corresponding configuration and operation are performed; After successful acquisition, the tracking channel is configured according to the captured carrier Doppler and pseudo code phase; Select any corresponding tracking loop as the main loop, and other loops as semi-open loops or open loops; Perform coherent integration and update the loop according to the integration result; Signal tracking is performed by using a second-order frequency-locked loop to assist a third-order phase-locked loop; Calculate the broadband signal energy and narrowband signal energy, and calculate the C / N0 value; The main antenna is selected based on the results of continuous observation of the phase-locked indicator factor; Open or close the loop's autonomous carrier phase detection function and pseudo code phase detection function; Extract observations, including pseudorange observations and Doppler observations.

2. The method for loop tracking of an arrow-borne multi-antenna GNSS receiver for landing point control according to claim 1, Features: The pre-processing steps include DC component removal, low-pass filtering, re-quantization and down-sampling.

3. The method for loop tracking of an arrow-borne multi-antenna GNSS receiver for landing point control according to claim 1, Features: The configuration of the tracking channel includes configuring a pseudo code NCO, a pseudo code generator, a correlator and a carrier NCO in the tracking channel corresponding to each star.

4. The method for loop tracking of an arrow-borne multi-antenna GNSS receiver for landing point control according to claim 1, Features: The main loop autonomously completes loop phase discrimination, filtering and integration, and the observed quantities and navigation messages are extracted from this loop.

5. The method for loop tracking of an arrow-borne multi-antenna GNSS receiver for landing point control according to claim 1, Features: In the semi-open loop, the carrier PLL and FLL form an autonomous closed loop, and the pseudo code DLL is updated by the main loop.

6. The method for loop tracking of an arrow-borne multi-antenna GNSS receiver for landing point control according to claim 1, Features: In the open loop, all autonomous loop updates are in a closed state, and all loop updates are completed by the main loop, and the tracked GNSS signal is integrated according to the parameters of the main loop; the receiver determines the loop type based on the C / N0 value and the phase-locked PLD value of each signal, and completes stable tracking and continuous positioning of the GNSS signal in a high-dynamic and high-rotation environment.

Images