CN117537827A

CN117537827A - Method for assisting GNSS receiver signal acquisition of lunar probe

Info

Publication number: CN117537827A
Application number: CN202311466242.5A
Authority: CN
Inventors: 樊敏; 李赞; 赵华; 陈少伍
Original assignee: 63921 Troops of PLA
Current assignee: 63921 Troops of PLA
Priority date: 2023-11-07
Filing date: 2023-11-07
Publication date: 2024-02-09

Abstract

The invention relates to a method for assisting the acquisition of signals of a GNSS receiver of a lunar probe, which comprises the steps of receiving navigation messages and ephemeris information of the lunar probe through a GNSS receiver of a ground measurement and control station, generating auxiliary information, sending the auxiliary information to the lunar probe, dividing a received signal into two paths through a low noise amplifier after the lunar probe receives the auxiliary information, enabling one path to reach a receiver of a measurement and control transponder through a down converter, demodulating the measurement and control information for normal measurement and control, enabling the other path to reach a special GNSS navigation receiver of the lunar probe after the down converter, demodulating the special GNSS navigation receiver to obtain the auxiliary information, identifying the content and jump position of the message in the received signal by utilizing the auxiliary information, so as to erase navigation message data, calculating Doppler and Doppler change rate of visible GNSS satellites by utilizing the auxiliary information, dynamically compensating the received signal of the lunar probe, and finally completing signal acquisition based on a parallel code phase search algorithm of fast Fourier transform. The invention can effectively improve the sensitivity of the GNSS receiver.

Description

Method for assisting GNSS receiver signal acquisition of lunar probe

Technical Field

The invention relates to the technical field of moon and deep space measurement and control, in particular to a method for assisting in capturing signals of a GNSS receiver of a moon detector.

Background

With the continuous promotion of lunar exploration projects in China, more and more detectors are applied to the environments of earth-moon round trip, lunar orbit, lunar relay, lunar base, lunar surface landing inspection and the like, and the real-time and accurate acquisition of navigation information such as position, speed and time for the detectors is one of important tasks of a measurement and control system. Currently, the measurement and navigation technology for moon detector mainly comprises two modes of foundation measurement orbit and space-based autonomous navigation. The space-based autonomous navigation mainly utilizes star sensors, sun sensors, inertial navigation equipment and the like on a satellite to realize real-time autonomous positioning navigation, the accuracy reaches kilometer level, and the high-accuracy navigation requirement of future moon detection tasks is difficult to meet. The foundation measurement rail system formed by the global distributed deep space measurement and control station ranging and speed measurement and Very Long Baseline Interferometry (VLBI) system is limited by the earth-moon position relationship, the global station arrangement is needed to improve the measurement and control arc section, and the construction and maintenance cost is high. And the lunar probe is autonomously navigated based on the GNSS technology, so that the burden of a ground measurement and control station can be greatly reduced, and real-time and autonomous navigation service can be provided for the probe.

However, the main lobe beam of the GNSS navigation satellite antenna mainly covers an area of 3000km or less from the ground. The GNSS receiver of the lunar probe can only receive the navigation signals transmitted by the navigation satellites on the other side of the earth, and at this time, most of the main lobe beam signals of the transmitting antenna are blocked by the earth, and side lobe signals with power which is more than 15dB lower than that of the main lobe signals need to be utilized. Moreover, the distance between the GNSS receiver of the lunar probe and the navigation satellite reaches 40 ten thousand kilometers, and the free space path loss of the signal reaches more than 20dB. This requires the GNSS receiver to have the capability of high sensitivity signal reception, typically requiring up to-190 dBW. This presents new challenges for GNSS receiver design.

According to the task planning of unmanned and manned moon detection, planetary detection engineering and the like in the future in China, the six, seven and eight moon detection tasks of the goddess, the two, three and four planetary detection tasks and the manned moon detection task are fully developed in the following 5-10 years. As a result, the number of future on-orbit moon and deep space detectors will increase dramatically, and the period of future tasks will be longer, typically up to months to years, even decades. The existing measurement and control equipment of the deep space network of the foundation is only used for simultaneously carrying out tracking measurement on dozens of detectors, so that the demand of multi-target real-time navigation cannot be met even when measurement and control resources are short. For this reason, the detector will be loaded with a high-sensitivity GNSS navigation receiver to achieve autonomous navigation, but since the earth-moon space distance is far, the GNSS signals received by the detector are weakened, the number of visible satellites is smaller, and the measurement geometry is worse, which will greatly affect the GNSS navigation performance. Therefore, it is necessary to design a signal capturing method for a GNSS receiver of an assisted lunar probe, so as to improve the receiving sensitivity of the navigation signal, shorten the first starting time of the receiver, and improve the usability of the GNSS navigation technology in the navigation of the lunar probe.

Disclosure of Invention

In view of the problems that the GNSS signals received by the lunar probe are weak and the sensitivity requirement of the receiver is extremely high, the invention provides a method for assisting the GNSS receiver signal acquisition of the lunar probe, which can improve the navigation signal receiving sensitivity, shorten the first starting time of the receiver and has wide practical engineering application prospect.

To achieve the above object of the present invention, a method for assisting GNSS receiver signal acquisition of a lunar probe according to an embodiment of the present invention includes:

s1, loading a GNSS receiver on a ground measurement and control station, and receiving navigation messages and lunar probe ephemeris information issued by a flight control center through the GNSS receiver;

s2, the ground measurement and control station generates auxiliary information according to the receiving information of the S1 and sends the auxiliary information to the lunar probe through a measurement and control uplink;

s3, the lunar probe receives the auxiliary information through a measurement and control antenna, and the received signal is divided into two paths after passing through a low noise amplifier, wherein one path of the auxiliary information passes through a down converter and then reaches a receiver of a measurement and control transponder to demodulate the measurement and control information for normal measurement and control, and the other path of the auxiliary information passes through the down converter and then reaches a special GNSS navigation receiver loaded by the lunar probe to demodulate the auxiliary information to obtain the auxiliary information;

s4, the moon detector utilizes the auxiliary information to identify the text content and the jump position in the received signal, so that the navigation text data is erased;

s5, calculating Doppler and Doppler change rate of visible GNSS satellites of the lunar probe by using the auxiliary information, and dynamically compensating the received signals of the lunar probe;

s6, completing signal capturing by using a parallel code phase searching algorithm based on fast Fourier transform.

Preferably, in the step S1, the lunar probe ephemeris information includes time information, position and velocity component information in a CGCS2000 coordinate system.

Preferably, in the step S2, when the auxiliary information is sent to the lunar probe through the measurement and control uplink, the auxiliary information is sent in a time-sharing manner in combination with a time slot requirement of the ground measurement and control station.

Preferably, in the step S4, navigation message information and receiver local time information are obtained from the auxiliary information, so as to obtain a millisecond-level signal reaching time estimated value and original navigation message bit stream information, thereby identifying message content and jump position in the received signal, and being used for navigation message erasure.

The method of the embodiment of the invention utilizes the ground measurement and control station to send the auxiliary information such as ephemeris information of the GNSS satellite to the lunar probe, thereby realizing the erasure of navigation message data and the dynamic compensation of the received signal, effectively improving the receiving sensitivity and shortening the first starting time of the receiver. The invention can effectively improve the sensitivity of the GNSS receiver and realize the GNSS navigation of the lunar probe.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic diagram illustrating auxiliary information injection according to an embodiment of the present invention.

Detailed Description

The description of the embodiments of this specification should be taken in conjunction with the accompanying drawings, which are a complete description of the embodiments. In the drawings, the shape or thickness of the embodiments may be enlarged and indicated simply or conveniently. Furthermore, portions of the structures in the drawings will be described in terms of separate descriptions, and it should be noted that elements not shown or described in the drawings are in a form known to those of ordinary skill in the art.

Any references to directions and orientations in the description of the embodiments herein are for convenience only and should not be construed as limiting the scope of the invention in any way. The following description of the preferred embodiments will refer to combinations of features, which may be present alone or in combination, and the invention is not particularly limited to the preferred embodiments. The scope of the invention is defined by the claims.

As shown in fig. 1, a method for assisting GNSS receiver signal acquisition of a lunar probe according to an embodiment of the present invention includes:

s1, loading a GNSS receiver on a ground measurement and control station, and receiving navigation messages and lunar probe ephemeris information issued by a flight control center through the GNSS receiver.

The ground measurement and control station is provided with the GNSS receiver, can be compatible with systems such as Beidou, GPS and GLONASS, and the like, and receives navigation messages. Meanwhile, the ground measurement and control station receives ephemeris information of the lunar probe issued by the flight control center, and mainly comprises time information, position and speed component information under a CGCS2000 coordinate system and the like.

And S2, the ground measurement and control station generates auxiliary information according to the receiving information of the S1 and sends the auxiliary information to the lunar probe through a measurement and control uplink.

And (3) synthesizing the GNSS navigation message received in the step (S1) and the ephemeris information of the lunar probe to generate auxiliary information. Considering that the valid period of the GNSS satellite ephemeris is 2 hours, the GNSS satellite ephemeris can be transmitted in a time-sharing way in combination with the time slot requirement of the ground measurement and control station.

S3, the lunar probe receives the auxiliary information through the measurement and control antenna, the received signal is divided into two paths after passing through the low noise amplifier, one path of the received signal passes through the down converter and then reaches a receiver of the measurement and control transponder to demodulate the measurement and control information for normal measurement and control, and the other path of the received signal passes through the down converter and then reaches a special GNSS navigation receiver loaded by the lunar probe to demodulate the received signal to obtain the auxiliary information.

And S4, the moon detector utilizes the auxiliary information to identify the text content and the jump position in the received signal, so that the navigation text data is erased.

From the auxiliary information obtained by demodulation, navigation message information, receiver local time information and the like can be directly obtained, and millisecond-level signal reaching time estimated value and original navigation message bit stream information are obtained, so that message content and jump positions in a received signal are identified, the navigation message is erased to prolong the coherent integration time, and the capturing sensitivity of Beidou navigation signals is effectively improved.

And S5, calculating Doppler and Doppler change rate of the visible GNSS satellite of the lunar probe by using the auxiliary information, and dynamically compensating the received signal of the lunar probe.

After the navigation message erasure is completed, the coherent integration time length is increased, but the search steps are reduced, and the search times are increased. Therefore, the Doppler and Doppler change rate of the visible GNSS satellites are calculated by using GNSS ephemeris, lunar probe ephemeris information and the like in the auxiliary information, and the received signals are dynamically compensated, so that the signal searching range is reduced, and the acquisition time is shortened.

The method of the embodiment of the invention can increase the coherent integration time length by using the auxiliary information, effectively improve the receiving sensitivity, realize the quick acquisition of the GNSS weak signals, shorten the first starting time of the receiver, and further improve the navigation positioning performance of the GNSS receiver of the lunar probe, and is used for navigation and orbit determination of the lunar probe.

The method of the invention is described in further detail below in connection with specific examples:

s1, a ground measurement and control station loads a GNSS receiver to receive navigation messages and receives ephemeris information of a lunar probe issued by a flight control center.

And installing 1 GNSS receiver compatible with systems such as Beidou, GPS and GLONASS on the existing ground measurement and control stations such as the karst, the Canon, the Argentina and the Qingdao and the Nami Biya, and receiving GNSS navigation messages. Taking a navigation message of a Beidou satellite navigation system as an example, according to a Beidou satellite navigation system space signal interface control file public service signal (version 2.1), the navigation message broadcast by a Beidou satellite can be divided into two types of D1 and D2 according to the speed and the structure, and the specific type is shown in a table 1.

D1 navigation messages are broadcast by Medium Earth Orbit (MEO)/inclined geosynchronous orbit (IGSO) satellites, and the content contains basic navigation information (the basic navigation information of the satellite, all satellite almanac information and other system time synchronization information).

D2 navigation messages are broadcast by geostationary orbit (GEO) satellite signals at a rate of 500bps, and the content contains basic navigation information and enhanced service information (differential and integrity information of the beidou system and grid point ionosphere information). The navigation message played by the Beidou satellite comprises detailed position time information (ephemeris) of the satellite, rough information (almanac) of other satellites, synchronization (D2 navigation message) of other systems and the like.

The length of each frame of the D1 navigation message and the D2 navigation message is 1500 bits, the D1 navigation message rate is 50bps, and the D2 navigation message rate is 500bps. Therefore, the D1 navigation message is broadcasted for 30s in each frame of message, the satellite ephemeris and clock error parameters are contained in the subframes 1 to 3, and 30s are needed for complete reception once; the D2 navigation message is distributed and arranged in 10 pages of the subframe 1 in a message broadcasting period of 3s per frame, and the complete receiving time is also required to be 30s.

Meanwhile, the ground communication networks of the measurement and control stations receive ephemeris information of the lunar probe issued by the flight control center in real time, and the ephemeris information mainly comprises time information, position and speed component information under a CGCS2000 coordinate system and the like, and the position and speed component information is shown in a table 2. And the transmission is carried out at intervals of 1s, and the length is 320 bits. The information is also transmitted to the ground measurement and control station for guiding the measurement and control equipment in real time by the flight control center in an actual task, so that the workload of the flight control center and the ground communication network is not increased additionally.

Table 2 ephemeris information content for lunar probe

Sequence number	Parameter name	Quantization unit	Description of the invention
				1	Time of data correspondence	0.1ms	Absolute time of the frame data time
2	X-direction position component	0.1m
				3	Y-direction position component	0.1m
4	Z-direction position component	0.1m
				5	Velocity component in the X-direction	0.01m/s
6	Velocity component in Y direction	0.01m/s
				7	Component of Z-direction velocity	0.01m/s

S2, the ground measurement and control station generates auxiliary information by integrating information such as GNSS clock error, broadcast ephemeris, lunar probe position and speed and the like, and transmits the auxiliary information to the lunar probe by using a measurement and control uplink.

And according to the information content of the S1, the received GNSS navigation message and the received lunar probe ephemeris information are comprehensively generated to generate auxiliary information, and the auxiliary information is specifically shown in a table 3. And according to the time slot requirement of the ground measurement and control station, transmitting through the measurement and control uplink in a time-sharing manner.

Table 3 auxiliary information and usage policy

S3, the measurement and control antenna of the detector receives the measurement and control uplink signal, the signal is divided into two paths after passing through the low noise amplifier, the 1 path of signal passes through the down converter and then reaches the receiver of the measurement and control transponder, and the receiver demodulates the measurement and control information to develop normal measurement and control; and the other 1 path of auxiliary information passes through the down converter and then reaches a special GNSS navigation receiver loaded by the detector, and the receiver demodulates auxiliary information sent by the ground measurement and control station.

And S4, identifying the text content and the jump position in the received signal by using auxiliary information such as navigation text and the like, and realizing data erasure of the navigation text.

Navigation message information, receiver local time information and the like are obtained from the auxiliary information, and millisecond-level signal reaching moment estimated value and original navigation message bit stream information are obtained, so that message content and jump positions in a received signal are identified, the navigation message is erased, the coherent integration time is prolonged to 200ms, and the Beidou navigation signal capturing sensitivity is effectively improved by about 20dB.

S5, calculating Doppler, doppler change rate and the like of the visible GNSS satellite by using the GNSS ephemeris, the moon detector position, the moon detector speed and other auxiliary information, and dynamically compensating the received signal

Since the coherent integration time length can be prolonged after the navigation message is erased, but the search steps are reduced and the search times are increased, the Doppler and Doppler change rate of the visible GNSS satellites need to be calculated by using GNSS ephemeris in the auxiliary information, lunar probe ephemeris information and the like, and the received signals are dynamically compensated, so that the signal search range is reduced to the order of 100Hz, and the acquisition time is shortened.

Signal acquisition is completed by using a parallel code phase search algorithm based on fast fourier transform, acquisition parameters are set as shown in table 4, and after multiple incoherent integration, a sufficient detection signal-to-noise ratio can be obtained.

Table 4 high sensitivity acquisition parameters based on side information

Simulations were performed using the capture parameters in table 4, which shows that: based on the auxiliary information, the GNSS receiver can quickly acquire signals and receive messages, navigation positioning can be started after signal demodulation is completed, and the initial starting time is reduced to be within 1 minute. Compared with the case without auxiliary information, the receiver cold start time is about 10 minutes considering signal acquisition, navigation message reception and demodulation time.

In conclusion, the method and the device can effectively improve the capturing sensitivity of the GNSS navigation receiver of the lunar probe, realize the rapid capturing of the GNSS weak signals in the earth-moon space, shorten the first starting time of the receiver and effectively improve the GNSS navigation positioning performance of the lunar probe.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.

Claims

1. A method of aiding in the acquisition of a lunar probe GNSS receiver signal, the method comprising:

2. The method of claim 1, wherein in S1, the lunar probe ephemeris information comprises time information, position and velocity component information in CGCS2000 coordinate system.

3. The method of claim 1, wherein in S2, the assistance information is sent to the lunar probe via the measurement and control uplink in conjunction with a time slot requirement of a ground measurement and control station.

4. The method according to claim 1, wherein in S4, navigation message information and receiver local time information are obtained from the auxiliary information, so as to obtain a millisecond-level signal reaching time estimated value and original navigation message bit stream information, thereby identifying the message content and jump position in the received signal for navigation message erasure.