阅读说明：本技术 一种基于低轨星座监测gnss信号与播发gnss频段导航增强信号的导航增强系统 (Navigation enhancement system based on low-orbit constellation monitoring GNSS signal and broadcasting GNSS frequency band navigation enhancement signal ) 是由 边朗 蒙艳松 严涛 王瑛 张蓬 刘玉洁 雷文英 贾亦哲 于 2019-09-26 设计创作，主要内容包括：一种基于低轨星座监测GNSS信号与播发GNSS频段导航增强信号的导航增强系统,包括：低轨星座、运控系统、导航终端；运控系统,对导航信号进行监测接收,获取导航信号的监测数据,并将监测得到的监测数据回传至运控系统；运控系统,根据低轨星座回传的监测数据和运控系统监测的监测数据,生成四大GNSS系统的导航卫星和低轨星座各自的轨道、钟差、码偏差(DCB)和载波相位偏差(FCB)的改正参数,进行组帧,得到导航增强数据,上注给低轨卫星,将播发数据进行调制编码后形成导航增强信号,广播给导航终端；导航终端,进行高精度的定位、测速和授时解算,解决了同频收发问题,并实现低轨导航增强。(A navigation enhancement system based on low earth orbit constellation monitoring GNSS signals and broadcasting GNSS frequency band navigation enhancement signals comprises: a low orbit constellation, an operation control system and a navigation terminal; the operation control system monitors and receives the navigation signals, acquires monitoring data of the navigation signals and transmits the monitoring data obtained by monitoring back to the operation control system; the operation control system generates correction parameters of respective orbit, clock error, code Deviation (DCB) and carrier phase deviation (FCB) of a navigation satellite and a low-orbit constellation of four GNSS systems according to the monitoring data returned by the low-orbit constellation and the monitoring data monitored by the operation control system, frames the correction parameters to obtain navigation enhancement data, and the navigation enhancement data is injected to the low-orbit satellite, and forms a navigation enhancement signal after modulation and coding the broadcast data and broadcasts the navigation enhancement signal to a navigation terminal; the navigation terminal carries out high-precision positioning, speed measurement and time service calculation, solves the problem of same-frequency receiving and transmitting and realizes low-orbit navigation enhancement.)

1. A navigation enhancement system based on low earth orbit constellation monitoring GNSS signals and broadcasting GNSS frequency band navigation enhancement signals is characterized by comprising: a low orbit constellation, an operation control system and a navigation terminal;

the operation control system monitors civil navigation signals of four GNSS systems of a Beidou navigation system, a GPS, a GLONASS and a GALILEO, and acquires monitoring data of the navigation signals, and comprises the following steps: pseudo range, carrier phase, navigation message;

the low-orbit constellation configured navigation enhancement load monitors and receives civil navigation signals of four GNSS systems of a Beidou navigation system, a GPS, a GLONASS and GALILEO and/or military navigation signals of B1 and B3 frequency bands of the Beidou navigation system, and acquires monitoring data of each navigation signal, wherein the monitoring data comprises the following steps: pseudo range, carrier phase and navigation message, and monitoring data obtained by monitoring is transmitted back to the operation control system;

the operation control system generates correction parameters of respective orbits, clock errors, code offsets (DCB) and carrier phase deviations (FCB) of the navigation satellites and the low-orbit constellations of the four large GNSS systems according to the monitoring data returned by the low-orbit constellation and the monitoring data monitored by the operation control system, frames the correction parameters of the respective orbits, clock errors, code offsets (DCB) and carrier phase deviations (FCB) of the navigation satellites and the low-orbit constellation of the four large GNSS systems with the navigation messages of the low-orbit constellation to obtain navigation enhancement data, and the navigation enhancement data are injected to the low-orbit satellites, and the low-orbit satellites modulate and encode broadcast data to form navigation enhancement signals which are broadcast to the navigation terminal;

the navigation terminal receives civil navigation signals of four GNSS systems and navigation enhancement signals of low-earth-orbit satellite broadcasting at the same time; and according to the civil navigation signals of the four GNSS systems and the navigation enhancement signals of the low-earth orbit satellite broadcast, performing high-precision positioning, speed measurement and time service calculation on the navigation terminal.

2. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: the low-orbit constellation comprises a plurality of low-orbit satellites, and the low-orbit constellation is distributed according to the walker constellation configuration, so that the global coverage of the navigation satellites is ensured.

3. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: monitoring data of navigation signals, comprising: pseudo-range of navigation signal, carrier phase, navigation message.

4. The system of claim 3, wherein the system is configured to monitor GNSS signals and broadcast GNSS frequency band navigation augmentation signals based on a low earth orbit constellation, and further comprising: navigation messages, including: clock error, orbit, satellite health information.

5. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: the navigation message of the low-orbit constellation means: satellite number, clock error, orbit, satellite health information of the low earth orbit satellite.

6. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: each low-orbit satellite on the low-orbit constellation is provided with a navigation enhancement subsystem, so that civil navigation signals of four large GNSS systems can be monitored, and the navigation enhancement signals can be broadcasted.

7. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: the navigation enhancement subsystem comprises a GNSS antenna, an LNA, a navigation enhancement processor, a navigation enhancement transmitting component and a navigation enhancement transmitting antenna;

when the navigation enhancement subsystem is used for receiving signals, the navigation enhancement subsystem can receive civil navigation signals of four GNSS systems, the civil navigation signals are sent to the LNA for low-noise amplification, then sent to the navigation enhancement processor, resolved by the navigation enhancement processor in pseudo-range and carrier phase, demodulated in navigation messages, measured values of the pseudo-range and carrier phase and navigation messages are obtained, and sent to the satellite platform, and the satellite platform is sent to the operation control system through a satellite-ground link, so that monitoring and returning of the civil navigation signals of the four GNSS systems are realized;

when the navigation enhancement subsystem is used for sending signals, the navigation enhancement processor receives navigation enhancement data injected by the operation control system, modulates and codes the navigation enhancement data and then sends the navigation enhancement data to the navigation enhancement transmitting assembly, the navigation enhancement transmitting assembly sequentially amplifies and filters the navigation enhancement data to form a navigation enhancement signal and sends the navigation enhancement signal to the navigation enhancement transmitting antenna, and the navigation enhancement transmitting antenna broadcasts the navigation terminal.

8. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: a low earth orbit satellite comprising: satellite platform, satellite load; the satellite payload includes a navigation enhancement subsystem;

the satellite platform is provided with a satellite-ground link and can return GNSS signals received in orbit and processed by data to the ground;

the satellite load has the functions of receiving civil navigation signals of four GNSS systems, resolving pseudo range and carrier phase, demodulating navigation messages, receiving, processing and broadcasting navigation enhancement data and the like.

9. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: the ground operation and control system is located in China.

10. The system of claim 1, wherein the GNSS signals are monitored based on a low earth orbit constellation and the GNSS frequency band navigation augmentation signals are broadcast, and wherein: the operation control system comprises: domestic monitoring stations, data processing centers and gateway stations; the domestic monitoring station collects observation data issued by the low earth orbit satellite and sends the observation data to the data processing center, the data processing center processes the observation data to generate enhanced information, and the gateway station performs the upper note of the enhanced information.

Technical Field

The invention relates to a navigation enhancement system for monitoring GNSS signals and broadcasting GNSS frequency band navigation enhancement signals based on a low-earth-orbit constellation, namely a navigation enhancement system based on multiple navigation signals, and belongs to the technical field of satellite navigation enhancement.

Background

At present, the key period of the Beidou satellite navigation system is in transition from the region to the world, however, the Beidou navigation signal is limited by international rules and has low landing power, is easy to interfere and block, and has insufficient application capability in a complex environment; due to the restriction of the territorial territory of China and other political factors, the global uniform station building is difficult, so that the global continuous monitoring of military and civil signals is difficult to realize; the high-precision GNSS service requirement expands from the region to the world, and the rapid high-precision positioning, speed measurement and time service resolving are difficult to meet only by a satellite navigation system. Under the background, a plurality of organizations at home and abroad provide researches for developing a low-orbit navigation enhancement system based on a low-orbit communication constellation or a special constellation, and most of published patents and articles at present are focused on analysis of a current low-orbit constellation DOP, determination of high, medium and low ground combined precision orbit determination and clock error, analysis of fast convergence performance of dual-frequency signal-accelerated PPP (Point-to-Point-protocol) broadcast by the low-. The low-orbit navigation enhancement needs to be applied and the cost of the user terminal is reduced, and the broadcasted navigation enhancement signal needs to be in the current GNSS frequency band so as to reduce the cost of the user terminal, so that essentially a low-orbit navigation enhancement system which simultaneously monitors the GNSS signal and broadcasts the navigation signal with the same frequency as the GNSS signal is to be established.

Disclosure of Invention

The technical problem solved by the invention is as follows: the navigation enhancement system based on the low-orbit constellation monitoring GNSS signal and the broadcast GNSS frequency band navigation enhancement signal solves the problems of same-frequency receiving and transmitting interference and global low-orbit satellite navigation enhancement, and can be applied to the low-orbit navigation enhancement system in China in the future.

The technical scheme of the invention is as follows: a navigation enhancement system based on low earth orbit constellation monitoring GNSS signals and broadcasting GNSS frequency band navigation enhancement signals is characterized by comprising: a low orbit constellation, an operation control system and a navigation terminal;

the operation control system monitors civil navigation signals of four GNSS systems of a Beidou navigation system, a GPS, a GLONASS and a GALILEO, and acquires monitoring data of the navigation signals, and comprises the following steps: pseudo range, carrier phase, navigation message;

the low-orbit constellation configured navigation enhancement load monitors and receives civil navigation signals of four GNSS systems of a Beidou navigation system, a GPS, a GLONASS and GALILEO and/or military navigation signals of B1 and B3 frequency bands of the Beidou navigation system, and acquires monitoring data of each navigation signal, wherein the monitoring data comprises the following steps: pseudo range, carrier phase and navigation message, and monitoring data obtained by monitoring is transmitted back to the operation control system;

the operation control system generates correction parameters of respective orbits, clock errors, code offsets (DCB) and carrier phase deviations (FCB) of the navigation satellites and the low-orbit constellations of the four large GNSS systems according to the monitoring data returned by the low-orbit constellation and the monitoring data monitored by the operation control system, frames the correction parameters of the respective orbits, clock errors, code offsets (DCB) and carrier phase deviations (FCB) of the navigation satellites and the low-orbit constellation of the four large GNSS systems with the navigation messages of the low-orbit constellation to obtain navigation enhancement data, and the navigation enhancement data are injected to the low-orbit satellites, and the low-orbit satellites modulate and encode broadcast data to form navigation enhancement signals which are broadcast to the navigation terminal;

the navigation terminal receives civil navigation signals of four GNSS systems and navigation enhancement signals of low-earth-orbit satellite broadcasting at the same time; and according to the civil navigation signals of the four GNSS systems and the navigation enhancement signals of the low-earth orbit satellite broadcast, performing high-precision positioning, speed measurement and time service calculation on the navigation terminal.

Preferably, the low-orbit constellation comprises a plurality of low-orbit satellites, and the low-orbit constellations are distributed according to the walker constellation configuration, so that the global coverage of the navigation satellites is ensured; further the satellite orbit altitude is preferably 1150 km.

Preferably, the monitoring data of the navigation signal includes: pseudo-range of navigation signal, carrier phase, navigation message.

Preferably, the navigation message includes: clock error, orbit, satellite health information.

Preferably, the navigation message of the low-orbit constellation means: satellite number, clock error, orbit, satellite health information of the low earth orbit satellite.

Preferably, each low-orbit satellite on the low-orbit constellation is provided with a navigation enhancement subsystem, so that civil navigation signals of four large GNSS systems can be monitored, and the navigation enhancement signals can be broadcasted.

Preferably, the navigation enhancement subsystem comprises a GNSS antenna, an LNA, a navigation enhancement processor, a navigation enhancement transmitting component and a navigation enhancement transmitting antenna;

when the navigation enhancement subsystem is used for receiving signals, the navigation enhancer can receive civil navigation signals of four GNSS systems, the civil navigation signals are sent to the LNA for low-noise amplification, then sent to the navigation enhancement processor, resolved by the navigation enhancement processor in pseudo range and carrier phase, demodulated in navigation messages, obtained in pseudo range and carrier phase measurement values and navigation messages, and sent to a satellite platform (low orbit satellite including satellite platform and satellite load), and the satellite platform is sent to the operation control system through a satellite-ground link, so that monitoring and returning of the civil navigation signals of the four GNSS systems are realized;

when the navigation enhancement subsystem is used for sending signals, the navigation enhancement processor receives navigation enhancement data injected by the operation control system, modulates and codes the navigation enhancement data and then sends the navigation enhancement data to the navigation enhancement transmitting assembly, the navigation enhancement transmitting assembly sequentially amplifies and filters the navigation enhancement data to form a navigation enhancement signal and sends the navigation enhancement signal to the navigation enhancement transmitting antenna, and the navigation enhancement transmitting antenna broadcasts a navigation terminal;

preferably, the low earth orbit satellite comprises: satellite platform, satellite load; the satellite payload includes a navigation enhancement subsystem; the satellite platform is provided with a satellite-ground link and can return the GNSS signals received and processed in orbit to the ground; the satellite load has the functions of receiving civil navigation signals of four GNSS systems, resolving pseudo range and carrier phase, demodulating navigation messages, receiving, processing and broadcasting navigation enhancement data and the like;

preferably, the ground operation and control system is located in China.

Preferably, the operation control system includes: the system comprises a domestic monitoring station, a data processing center and a gateway station, wherein the domestic monitoring station collects observation data issued by low-orbit satellites and sends the observation data to the data processing center, the observation data are processed by the data processing center to generate enhanced information, and the gateway station carries out the upper note of the enhanced information.

Compared with the prior art, the invention has the advantages that:

(1) the invention utilizes the low-earth orbit satellite to receive and monitor the GNSS signal in the space section, reduces the arrangement of the ground monitoring station and simultaneously realizes the continuous monitoring of the navigation satellite.

(2) The invention realizes the same-frequency receiving and transmitting of the GNSS signals by designing the signal broadcasting mode, and saves the cost of the user terminal.

(3) The low-orbit navigation enhancement system designed by the invention can realize real-time high-precision positioning, speed measurement and time service calculation of the user side.

Drawings

FIG. 1 is a schematic diagram of the system of the present invention;

FIG. 2 is a functional block diagram of the low-rail navigation enhancement subsystem of the present invention;

FIG. 3 is a schematic diagram of the energy-constant time domain compressed quasi-continuous signal broadcasting of the present invention;

FIG. 4 is a schematic diagram of a low-orbit constellation design according to the present invention; wherein (a) represents a low orbit constellation diagram with a low orbit satellite number of 9; (b) a low orbit constellation diagram representing a low orbit satellite number of 54;

Detailed Description

The invention is described in further detail below with reference to the figures and specific embodiments.

The invention relates to a navigation enhancement system for monitoring GNSS signals and broadcasting GNSS frequency band navigation enhancement signals based on a low-orbit constellation, which comprises: a low orbit constellation, an operation control system and a navigation terminal; the operation control system monitors and receives the navigation signals, acquires monitoring data of the navigation signals and transmits the monitoring data obtained by monitoring back to the operation control system; the operation control system generates correction parameters of respective orbit, clock error, code Deviation (DCB) and carrier phase deviation (FCB) of a navigation satellite and a low-orbit constellation of four GNSS systems according to the monitoring data returned by the low-orbit constellation and the monitoring data monitored by the operation control system, frames the correction parameters to obtain navigation enhancement data, and the navigation enhancement data is injected to the low-orbit satellite, and forms a navigation enhancement signal after modulation and coding the broadcast data and broadcasts the navigation enhancement signal to a navigation terminal; the navigation terminal carries out high-precision positioning, speed measurement and time service calculation, solves the problem of same-frequency receiving and transmitting and realizes low-orbit navigation enhancement.

The Beidou navigation signal has low landing power, is easy to interfere and block and has insufficient application capability in a complex environment; due to the restriction of the territorial territory of China and other political factors, the global uniform station building is difficult, so that the global continuous monitoring of military and civil signals is difficult to realize; the high-precision service requirement of modern GNSS and the implementation of global strategy in China need the high-precision service to be expanded from region to global. In the face of such current situation, low-rail enhancement is an effective way to solve these problems. However, the low-orbit navigation enhancement is to be applied and reduce the cost of the user terminal, and the navigation enhancement signal broadcasted by the low-orbit navigation enhancement system is necessary to be within the current GNSS frequency band to reduce the cost of the user terminal, so that essentially a low-orbit navigation enhancement system for simultaneously monitoring the GNSS signal and broadcasting the same-frequency navigation signal with the GNSS is to be established. The invention provides a system and a method for monitoring a GNSS signal and broadcasting a GNSS frequency band navigation enhancement signal based on a low-orbit constellation, solves the problem of same-frequency receiving and transmitting, and can be applied to a low-orbit navigation enhancement system in China in the future.

The invention relates to a navigation enhancement system for monitoring GNSS signals and broadcasting GNSS frequency band navigation enhancement signals based on a low-orbit constellation, which comprises: a low orbit constellation, an operation control system and a navigation terminal; the operation control system monitors civil navigation signals of four GNSS systems of Beidou, GPS, GLONASS and GALILEO, and acquires monitoring data of the navigation signals, and comprises the following steps: pseudo range, carrier phase, navigation message; the low-orbit constellation configured navigation enhancement load monitors and receives civil navigation signals of four GNSS systems of Beidou, GPS, GLONASS and GALILEO and (or) military navigation signals of Beidou B1 and B3 frequency bands, and acquires monitoring data of the navigation signals, and the method comprises the following steps: pseudo range, carrier phase and navigation message, and monitoring data obtained by monitoring is transmitted back to the operation control system; the operation control system generates correction parameters of respective orbits, clock errors, code offsets (DCB) and carrier phase deviations (FCB) of the navigation satellites and the low-orbit constellations of the four large GNSS systems according to the monitoring data returned by the low-orbit constellation and the monitoring data monitored by the operation control system, frames the correction parameters of the respective orbits, clock errors, code offsets (DCB) and carrier phase deviations (FCB) of the navigation satellites and the low-orbit constellation of the four large GNSS systems with the navigation messages of the low-orbit constellation to obtain navigation enhancement data, and the navigation enhancement data are injected to the low-orbit satellites, and the low-orbit satellites modulate and encode broadcast data to form navigation enhancement signals which are broadcast to the navigation terminal; the navigation terminal receives civil navigation signals of four GNSS systems and navigation enhancement signals of low-earth-orbit satellite broadcasting at the same time; according to the civil navigation signals of the four GNSS systems and the navigation enhancement signals of the low-orbit satellite broadcast, high-precision positioning, speed measurement and time service calculation are carried out, the problem of same-frequency transceiving is solved, and the low-orbit navigation enhancement in China is realized.

In the invention, the preferred scheme of the low-orbit constellation satellite is as follows: the orbit height is 1150km, the global coverage of navigation satellites is guaranteed according to the walker constellation configuration distribution, and inter-satellite links are arranged among low-orbit satellites, so that data communication can be carried out. The navigation enhancement load configured by the low-orbit satellite mainly completes monitoring and receiving of civil signals of Beidou, GPS, GLONASS and GALILEO four systems and (or) military signals of Beidou B1 and B3, and returns observed value information such as pseudo range, carrier phase and the like obtained by monitoring to the ground, as shown in FIG. 1;

the low-orbit satellite in the space section realizes the establishment and maintenance of the time frequency reference of the low-orbit satellite at low cost, a tunable high-stability crystal oscillator is used as a frequency source on the satellite, a GNSS monitoring receiver is configured on the satellite, the high-stability crystal oscillator is taminated by utilizing GNSS signal observation data, the long-term stability of the crystal oscillator is taminated on the GNSS, the atomic clock performance is realized on the low-orbit satellite through the equivalence of the high-stability crystal oscillator and the GNSS tamination, and the high-precision time frequency reference is established.

The low-orbit navigation enhancement payload is mainly composed of a GNSS antenna and LNA, a navigation enhancement processor, a navigation enhancement transmitting component and a navigation enhancement transmitting antenna, as shown in fig. 2. The navigation enhancement processor completes functions of GNSS signal receiving processing and downlink navigation enhancement signal generation, and the navigation enhancement transmitting assembly mainly comprises a filter and a power amplifier and completes functions of filtering and amplifying. The navigation enhancement load broadcasts navigation enhancement signals and navigation enhancement information, the frequency band of the specific broadcast signals can be selected and matched in the GNSS frequency band, and if the military navigation enhancement signals are broadcast, the military navigation enhancement signals and Beidou B1 and B3 military signals are required to be in the same frequency band.

The frequency bands and signal components for receiving the Beidou, GPS, GLONASS and GALILEO four-system civil navigation signals can be shown in table 1, and the frequency bands and signal components can be used for receiving the four-system civil navigation signals, and can also be used for receiving partial civil navigation signals of partial systems:

TABLE 1 frequency band of four GNSS civil signals and its signal subscale

In the method, the navigation enhancement signal and the navigation enhancement information are broadcasted, wherein at least one signal is positioned in the GNSS frequency band, or two signals are positioned in the GNSS frequency band. The signal is an energy constant time domain compression quasi-continuous signal system, and meanwhile, a monitoring receiver configured by a low-earth orbit satellite monitors navigation signals transmitted by four GNSS navigation satellites in a time slot without transmitting navigation enhancement signals, as shown in FIG. 3;

the operation control system comprises a ground monitoring station system, a data processing center and a gateway station. The ground monitoring station system mainly monitors four GNSS navigation signals, acquires monitoring data such as pseudo-range and carrier phase measurement values of the navigation signals, simultaneously sends the monitoring data to the data processing center, the data processing center comprehensively processes GNSS monitoring data returned by the low earth orbit satellite and GNSS monitoring data transmitted by the ground monitoring station to generate correction parameters of orbit, clock error, code bias (DCB) and carrier phase bias (FCB) of the four GNSS navigation satellites and the low earth orbit satellite, then frames are formed and injected to the low earth orbit satellite through the gateway station, and the low earth orbit satellite is broadcasted to users, as shown in figure 1.

The navigation terminal comprises a receiving and processing module of a GNSS navigation signal and a low-orbit satellite enhanced signal, high-precision positioning, speed measurement and time service resolving are carried out by jointly receiving the GNSS navigation signal and a dual-frequency navigation enhanced signal and navigation enhanced information broadcasted by the low-orbit satellite, the low-orbit satellite has the characteristic of fast motion, and the fast convergence of PPP can be accelerated after the low-orbit satellite is added into the navigation resolving.

The operation control system generates correction parameters of respective orbit, clock error, code bias (DCB) and carrier phase bias (FCB) of the navigation satellite and the low-orbit constellation of the four GNSS systems according to the monitoring data returned by the low-orbit constellation and the monitoring data monitored by the operation control system, and the preferred scheme is as follows, but is not limited to the following methods:

(1) the track correction number preferably adopts the following calculation mode:

wherein δ x, δ y, δ z andthe components of the correction quantity of the position and the speed under the geocentric geostationary coordinate system under the three axes of x, y and z are shown, and t is the observation time of a user; t is t₀The reference time is corrected for the satellite orbit.

(2) The clock error correction adopts non-differential combination phase and pseudo range observed values of a deionization stratum, and an error equation is preferably as follows:

wherein: r is station number, s is satellite number, i is observation epoch, c is speed of light, dt_r(i) For receiver clock difference, dt^s(i) In order to be the clock error of the satellite,

in order to account for the tropospheric delay error,

combining real ambiguity for station-to-satellite ionosphere free,

for multipath, noise, etc. as modeling errors,

the non-ionosphere combined observed values of the corresponding satellite and the corresponding survey station,

which is a residual error, is determined,the geometric distance between the satellite position at the time of signal transmission to the receiver position at the time of signal reception.

(3) The preferred scheme for determining the code bias (DCB) is as follows:

wherein the content of the first and second substances,

for a signal frequency of f_a、f_bThe smoothed observed value at time k is,

VTEC_IPPis the total electron content of the ionosphere in the zenith direction at the puncture point, f_aRepresenting the frequency of the signal a, f_bRepresenting the frequency of signal b.

R is the radius of the earth, H_ionFor single layer model height, z is the station zenith distance, α ═ 0.9782.

(4) The carrier phase offset (FCB) determination preference is as follows:

for the continuous observation arc segment, the wide lane ambiguity is smoothed by:

wherein the content of the first and second substances,

real-wide lane ambiguity calculated for the MW combination,the integer part of the integer number of weeks of the original widelane ambiguity and the phase offset from the receiver and satellite side; f_iFk is the decimal part of wide lane combination phase deviation of the receiver end and the satellite end respectively, namely FCB of wide lane carrier phases of the receiver end and the satellite end,<>to smooth the operation sign. And (3) on the basis of the formula, inter-satellite difference is calculated, so that the influence of the FCB at the receiver end is eliminated, and then the single-difference FCB between the satellites is estimated by using an averaging method.

The navigation terminal receives civil navigation signals of four GNSS systems and navigation enhancement signals of low-earth-orbit satellite broadcasting at the same time; according to civil navigation signals of four GNSS systems and navigation enhancement signals of low-earth orbit satellite broadcasting, high-precision positioning, speed measurement and time service resolving of a navigation terminal are carried out, and the preferable scheme is as follows:

(1) the positioning and time service calculation principle formula is optimized

Wherein, G is a geometric matrix, (delta x, delta y, delta z) is the component of the coordinate variation of the receiver at two adjacent observation moments under an earth-centered earth-fixed coordinate system under the three axes of x, y and z, and delta t_uAnd b is a measured value residual vector, and a high-precision positioning and time service result can be obtained by carrying out multiple iterations.

(2) The principle of speed measurement is preferably

Wherein G is a geometric matrix, (v)_x,v_y,v_z) Is the component of the speed of the receiver under the three axes of x, y and z under the geocentric geostationary coordinate system, delta f_uIn order for the receiver to be frequency-floating,

for the rate of change measurement residual vector,

is noise.

The navigation enhancement signal adopts an energy constant time domain compression quasi-continuous signal system, is a pulse signal in a time domain, receives navigation signals of four GNSS systems in a time slot in which the navigation enhancement signal is not broadcast, and solves the problem of isolation of co-frequency transmitting and receiving signals by a time division multiplexing method, as shown in FIG. 3.

The original baseband spread spectrum modulation modulates the coded text with the pseudo code. The message d (t) belongs to {1, -1}, the symbol rate is Rs, and the symbol width is Ts 1/Rs; the pseudo code sequence generated by the signal pseudo code generator is { cl }, cl belongs to {1, -1}, l is 0,1,2, …, the code rate is Rc, and the chip width is Tc is 1/Rc.

Carrying out chip waveform shaping on the code sequence to obtain a pseudo code waveform:

c (T) in time domain by chip width T_cGrouping is carried out, N chips are divided into a group, N is any integer of 1,2 and … with the maximum number of chips, M chips are continuously gated in the N chips, the rest are not gated, M is any integer of 0,1,2 and … N, and the power of the back N-M chips is concentrated on the front M chips, so that the average power of the energy constant time domain compression quasi-continuous signal system signal is ensured to be unchanged compared with the average power of the continuous system signal.

The receiving processing work of the GNSS signals such as capturing, tracking, ranging and demodulation is completed in the time slot without sending the quasi-continuous signals, so that the problem of common-frequency isolation is solved by time sharing of receiving and sending.

The low-orbit satellite corrects parameters by broadcasting orbits, clock errors, code offsets (DCB) and carrier phase offsets (FCB) of four GNSS system navigation satellites and the low-orbit satellite on the ground to help a user realize real-time high-precision positioning, speed measurement and time service resolving, the broadcast signal solves the problem of isolation of the same-frequency receiving and transmitting signals by a time division multiplexing method, and the low-orbit satellite has low orbit height and high landing power and can realize the navigation signal enhancement of the user.

The number of low orbit satellites affects the effect of navigation enhancement, two scenes, namely 9 scenes and 54 scenes, of low orbit satellites are designed respectively for navigation enhancement convergence time simulation calculation, the constellation is planned according to the requirements, as shown in fig. 4(a) and (b), and the calculation results are shown in table 2.

For a survey station at a fixed position, the convergence time of the precision positioning (30cm) which is purely dependent on the Beidou satellite is very long, and after the low-orbit enhancement system designed by the invention is added, the positioning convergence time is obviously reduced, so that the goal of navigation enhancement is achieved, and the precision positioning can enter the practical application scene. And as the number of low orbit satellites increases, the fine positioning convergence time also decreases significantly.

TABLE 2 Low-orbit enhanced Beidou precision positioning convergence time (30cm) table

The invention designs a navigation enhancement system for monitoring GNSS signals and broadcasting GNSS frequency band navigation enhancement signals based on a low-orbit constellation, which broadcasts navigation enhancement information through a low-orbit satellite, so that a user terminal can obtain real-time high-precision positioning, speed measurement and time service without increasing excessive extra cost, stations are not required to be uniformly arranged on the system globally, the global navigation enhancement service can be realized only by means of domestic monitoring stations, and the cost of a ground segment is reduced. Compared with a Beidou single system, the precision positioning convergence time can be improved by 80% by 54 low-orbit satellites, and the navigation positioning performance of a user can be obviously improved on the basis of global coverage.

The system of the invention is realized mainly by a navigation constellation, a low orbit constellation, a ground operation control system and a user terminal. The navigation constellation comprises one or more than one system of Beidou, GPS, GALILEO and GLONASS; the low orbit constellation can be a low orbit communication constellation, a low orbit remote sensing constellation, a low orbit navigation enhancement special constellation or other low orbit constellations; the method comprises the steps that a low earth orbit satellite broadcasts a navigation enhancement signal of a GNSS frequency band, the signal is an energy constant time domain compression quasi-continuous signal system, and meanwhile a monitoring receiver configured by the low earth orbit satellite monitors navigation signals transmitted by four GNSS navigation satellites in a time slot in which the navigation enhancement signal is not transmitted; the ground monitoring station system and the monitoring receiver configured by the low earth orbit satellite form a GNSS monitoring network integrating the sky and the ground. In order to realize the low-orbit navigation enhancement function, the navigation mode of the navigation enhancement system for monitoring the GNSS signals and broadcasting the GNSS frequency band navigation enhancement signals based on the low-orbit constellation comprises the following steps:

step 1: a space-based monitoring station configured by a low-orbit satellite monitors the signals of the Beidou, the GPS, the GALILEO and the GLONASS, and returns the observed quantities such as pseudo range, carrier phase and the like to the ground;

step 2: the ground data processing center jointly receives observation data of a ground monitoring station and a space-based monitoring station, generates precision correction numbers such as a precision orbit, a precision clock error and the like, and frames the precision correction numbers to a low orbit satellite;

and step 3: the low-orbit satellite receives signals of a Beidou, a GPS system and the like to perform clock taming, and a locally configured high-stability crystal oscillator is taminated on the GNSS and is equivalent to the performance of a locally reproduced atomic clock;

and 4, step 4: the low earth orbit satellite transmits the navigation enhancement signal of the GNSS frequency band, the signal comprises the generated GNSS satellite navigation enhancement information, the broadcasted signal is the energy constant time domain compressed quasi-continuous signal, and the navigation signal monitoring and receiving are carried out in the time slot which does not transmit the navigation enhancement signal.

The system of the invention, the energy constant time domain compression quasi-continuous signal broadcasting, includes the following steps:

step 1: the navigation enhancement processor baseband generates continuous navigation enhancement signals;

step 2: generating a control enabling signal of a broadcasting time slot according to the requirement of time domain compression of the navigation enhancement signal;

and step 3: gating the continuous signals by using the control enabling signals of the broadcasting time slots, and meanwhile, concentrating the energy of the time slots in which the navigation enhancing signals are not broadcasted into the broadcasting time slots;

according to the method, the low-earth-orbit satellite is used for receiving and monitoring the GNSS signals in a space section, the arrangement of a ground monitoring station is reduced, meanwhile, the continuous monitoring of the navigation satellite is realized, the real-time high-precision positioning, speed measurement and time service resolving of a user side can be realized, the same-frequency receiving and sending of the GNSS signals are realized by designing a signal broadcasting mode, and the cost of the user terminal is saved.