A GNSS Navigation Receiver Satellite Expansion Support Method

Abstract

The present invention relates to a method for satellite expansion support of a GNSS navigation receiver, including: obtaining information of newly added satellites; calculating the current code phase estimation value and Doppler frequency estimation value of the newly added satellites according to the information of the newly added satellites; inputting the current code phase estimation value and Doppler frequency estimation value of the newly added satellites into a tracking engine, and adjusting the control parameters of the tracking engine according to the search ranges of the code phase and Doppler frequency to capture and track the signals of the newly added satellites; decoding the telegrams of the newly added satellites to obtain the broadcast ephemeris of the newly added satellites, and then performing positioning calculation on the newly added satellites in combination with the observation quantities obtained by the tracking engine. The present invention realizes the support for newly added satellites without re-designing and tape-out, greatly reducing the receiver cost.

Description

Technical Field

[0001] The present invention relates to the field of satellite technology, and particularly to a method for satellite extension support of a GNSS navigation receiver. Background Art

[0002] Since the end of 2012, after China's Beidou navigation and positioning system completed the launch and networking of 14 satellites, GNSS chip and receiver manufacturers have successively completed the support for the Beidou-2 satellite navigation system. The construction of the Beidou-3 navigation and positioning system started in 2009 and the last satellite was not launched until the end of June 2020. During this period, a large number of GNSS navigation receivers supporting Beidou-2 satellites have been widely used in all aspects of people's lives, such as navigation, positioning, time service, asset tracking, and emergency rescue. In addition, due to the long construction period of Beidou-3, many manufacturers have launched receivers supporting Beidou-3 satellites during the construction of the satellite system. However, with the continuous launch of the third-generation satellites, these mass-produced chips or receivers cannot support the newly launched satellites, resulting in the number of actually available Beidou satellites being far less than the number of visible Beidou satellites in the sky. The difference in the number of satellites will have a significant impact on the accuracy of navigation and positioning. Especially for complex environments, the number of satellites is one of the decisive factors determining positioning accuracy.

[0003] Figure 1 It is a schematic diagram of the framework of a GNSS receiver. Currently, the acquisition process of a GNSS receiver is to search for satellite signals through an acquisition engine to obtain the rough C / A code phase and carrier frequency of the signal, and then enter the tracking stage. The tracking engine gradually and finely estimates these two signal parameters through a tracking loop according to the rough C / A code phase and carrier frequency information, so as to obtain the measurement value of the GNSS signal and demodulate the satellite message. Since the pseudo-random code of the newly launched satellite is unpredictable and cannot be pre-solidified into the hardware in advance, it is impossible to achieve the acquisition of the newly added satellite through the acquisition engine. Therefore, for the newly launched satellite, the acquisition engine becomes unavailable, and thus the subsequent work of the GNSS receiver cannot be carried out.

[0004] The traditional method for supporting newly added satellites is to redesign a new chip to increase the support for newly added satellites. If the chip is redesigned and taped out only for supporting newly added satellites, the cost is high. It not only increases the chip cost, but also has a long time to market, which has a great impact on the promotion and sales of products. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for satellite extension support of a GNSS navigation receiver to achieve the support for newly added satellites without the need for re-design and tape-out.

[0006] The technical solution adopted by the present invention to solve its technical problems is: to provide a method for GNSS navigation receiver satellite expansion support, including the following steps:

[0007] (1) Obtain new satellite information;

[0008] (2) Calculate the current code phase estimation value and Doppler frequency estimation value of the new satellite according to the new satellite information;

[0009] (3) Input the current code phase estimation value and Doppler frequency estimation value of the new satellite into the tracking engine, and adjust the control parameters of the tracking engine according to the search range of the code phase and Doppler frequency to capture and track the new satellite signal;

[0010] (4) Decode the message of the new satellite to obtain the broadcast ephemeris of the new satellite, and then combine the observed values obtained by the tracking engine to perform positioning calculation using the new satellite.

[0011] In step (1), the new satellite information is obtained by means of message parsing. The method of message parsing is to obtain the almanac information of the new satellite broadcast by other existing satellites, and then estimate the position, speed and clock offset of the new satellite through the almanac information of the new satellite.

[0012] In step (1), the new satellite information is obtained by means of AGNSS assistance. The method of AGNSS assistance is to issue the broadcast ephemeris related to the new satellite by the AGNSS server, and then calculate the position, speed and clock offset of the new satellite at the emission time through the current receiver time.

[0013] In step (1), the new satellite information is obtained by means of historical information. The method of historical information is to obtain the broadcast ephemeris that has been positioned and parsed for the new satellite before and has not expired, and then estimate the position, speed and clock offset of the new satellite through the broadcast ephemeris.

[0014] In step (2), through T transmit_est =T transmit_Ref +ΔT travel_Ref -ΔT travel_est Calculate the current code phase estimation value of the new satellite. Among them, T transmit_est is the estimated signal emission time of the new satellite. There is a corresponding relationship between the signal emission time of the new satellite and the code phase of the new satellite. T transmit_Ref is the signal emission time of the reference satellite, and ΔT travel_Ref is the time required for the signal of the reference satellite to propagate from the reference satellite to the receiver. ΔT travel_estis the time required for the signal of the newly added satellite to propagate from the newly added satellite to the receiver.

[0015] In step (2), through Doppler estSat = Doppler RefSat + f satDoppler_RefSat - f satDoppler_estSat calculate the current Doppler frequency estimate of the newly added satellite, where Doppler estSat represents the Doppler frequency estimate of the newly added satellite, Doppler RefSat is the Doppler frequency of the reference satellite, f satDoppler_RefSat is the Doppler frequency shift caused by the relative motion of the reference satellite and the receiver, f satDoppler_estSat is the Doppler frequency shift caused by the relative motion of the newly added satellite and the receiver; the reference satellite is a satellite that has already been in a tracking state and whose observation quality exceeds the threshold.

[0016] In step (2), through T transmit = T Receiver - ΔT travel calculate the current code phase estimate of the newly added satellite, where T transmit is the estimated signal transmission time of the newly added satellite, and there is a corresponding relationship between the signal transmission time of the newly added satellite and the code phase of the newly added satellite, T Receiver is the current receiver time, and ΔT travel is the time required for the signal of the newly added satellite to propagate from the newly added satellite to the receiver.

[0017] In step (2), through Doppler = - f satDoppler_i + f clkDrift calculate the current Doppler frequency estimate of the newly added satellite, Doppler represents the Doppler frequency estimate of the newly added satellite, and f satDoppler_i is the Doppler frequency shift caused by the relative motion of the newly added satellite and the receiver, and f clkDrift is the frequency offset introduced by the receiver clock drift.

[0018] The search range of the code phase in step (3) is determined by the receiver time ambiguity, position ambiguity, and the error table of the code phase estimation based on the ephemeris obtained from prior information. The search range of the Doppler frequency is determined by the receiver clock drift ambiguity, position ambiguity, velocity ambiguity, and the error table of the Doppler frequency estimation based on the ephemeris obtained from prior information.

[0019] Beneficial effects

[0020] Due to the adoption of the above technical solution, compared with the prior art, the present invention has the following advantages and positive effects: The present invention parses the telegram, obtains the newly added satellite information through AGNSS assistance or historical information, calculates the current code phase and Doppler estimation value based on the obtained newly added satellite information, and uses them as the input information of the tracking engine to capture the satellite signal, thereby realizing the measurement of the newly added satellite. The entire process does not require re-design and tape-out, greatly reducing the receiver cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic framework diagram of a GNSS receiver in the prior art

[0022] Figure 2 is a flowchart of an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0024] An embodiment of the present invention relates to a method for satellite expansion support of a GNSS navigation receiver, as Figure 2 shown, including: obtaining newly added satellite information; calculating the current code phase estimation value and Doppler frequency estimation value of the newly added satellite according to the newly added satellite information; inputting the current code phase estimation value and Doppler frequency estimation value of the newly added satellite into a tracking engine, and adjusting the control parameters of the tracking engine according to the search range of the code phase and Doppler frequency to capture and track the newly added satellite signal; decoding the telegram of the newly added satellite to obtain the broadcast ephemeris of the newly added satellite, and then combining the observation data obtained by the tracking engine to perform positioning and calculation on the newly added satellite.

[0025] In this embodiment, the satellite is captured by the tracking engine instead of the acquisition engine, so there is no need for the chip to support the code generator of the newly added satellite, and the capture and tracking of the newly added satellite can be completed through software, which specifically includes the following steps:

[0026] First, in step 201, the GNSS receiver starts to start, and the GNSS receiver starts the acquisition engine to capture the satellite. After the rough acquisition is successful, the relevant information is transmitted to the tracking engine for fine acquisition and tracking. Through a series of processes of the code loop and carrier loop, the code phase, carrier Doppler, and data code modulated on the carrier of the satellite, that is, the navigation telegram, are finally obtained. Among them, the newly added satellite cannot be captured in this step due to the lack of its code generator in the acquisition engine.

[0027] Step 202: Obtain new satellite information. In this step, the acquisition of new satellite information can mainly be achieved through three ways. One is through message parsing, another is through AGNSS assistance, and the third is through historical information acquisition.

[0028] The first method is to obtain it through message parsing. Since the new satellite has not been captured and tracked at this time, its message cannot be obtained by demodulating the signal of this satellite. However, in addition to broadcasting its own broadcast ephemeris, each satellite also broadcasts the almanac information of other satellites. Like the broadcast ephemeris, the almanac also contains information for calculating the satellite's position, velocity, and clock offset. Therefore, the almanac information of the new satellite broadcast by other satellites can be obtained, and then the position, velocity, and clock offset of the new satellite can be estimated through the almanac information of the new satellite. The main disadvantage of the almanac is that its accuracy is lower than that of the broadcast ephemeris. When making an estimate, the impact of the almanac on acquisition needs to be considered additionally.

[0029] The second method is AGNSS assistance, which is to send the broadcast ephemeris related to the new satellite through the AGNSS server, and then calculate the position, velocity, and clock offset of the satellite at the time of launch through the current receiver time. The premise of AGNSS assistance is that the server can provide support for the new satellite. In actual situations, there may also be lags, so it cannot be completely relied on AGNSS assistance.

[0030] The third method through historical information means that the broadcast ephemeris of this satellite has been parsed and obtained during previous positioning and stored in media such as FLASH. During this GNSS positioning process, this ephemeris has not expired and can be applied to the satellite acquisition parameter estimation and positioning solution of this time, that is, obtain the broadcast ephemeris that has been positioned and parsed and has not expired for the new satellite before, and then estimate the position, velocity, and clock offset of the new satellite through the broadcast ephemeris.

[0031] Step 203: Calculate the current code phase estimate and Doppler frequency estimate according to the satellite information, and these information will be used as the input information of the tracking engine. The Doppler frequency estimate and code phase estimate of the new satellite need to be processed for different situations. If the new satellite information is obtained through message parsing, then generally the receiver is already in the positioning state at this time. The receiver position, time, and clock drift information are all accurately known at this time, and the code phase estimate can be calculated from the following formula:

[0032] T transmit =T Receiver -ΔT travel (1)

[0033] Where: T transmitFor the signal transmission time of the newly added satellite. The C / A code lengths and duration periods of different constellations vary. There is a clear corresponding relationship between the transmission time and the code phase, and the code phase can be directly determined through the transmission time. Taking GPS as an example, the signal length of one cycle of the C / A code is 1023 chips, and the duration is 1 millisecond. When the precise transmission time is obtained and the part below the millisecond is considered, the precise chip position can be calculated.

[0034] T Receiver is the current receiver time, which includes the receiver clock error. ΔT travel is the time required for the signal of the newly added satellite to propagate from the newly added satellite to the receiver. This time can be obtained by dividing the distance between the newly added satellite and the receiver by the speed of light. In addition, satellite clock error and other time delays introduced during signal propagation need to be considered, including ionospheric delay, tropospheric delay, etc.

[0035] And the Doppler frequency estimation at this time can be calculated by the following formula:

[0036] Doppler=-f satDoppler_i +f clkDrift (2)

[0037] Doppler is the carrier Doppler to be estimated, that is, the estimated value of the Doppler frequency of the newly added satellite, f satDoppler_i is the Doppler frequency shift caused by the relative motion between the newly added satellite and the receiver, f clkDrift is the frequency offset introduced by the receiver clock drift.

[0038] If the information of the newly added satellite is obtained through AGNSS assistance or historical ephemeris information, the receiver position and time at this time have not been accurately obtained, and the above method cannot be used for estimation. In this embodiment, an estimation method based on a reference satellite is adopted, that is, the estimation is performed according to the satellite parameters of the satellites in the tracking state with better observation quality. The reference satellite is usually selected as the satellite with the strongest signal strength. It can be inferred from formula (1) that:

[0039] T transmit_est =T transmit_Ref +ΔT travel_Ref -ΔT travel_est (3)

[0040] Where:

[0041] T transmit_est is the estimated signal transmission time of the newly added satellite;

[0042] T transmit_Ref is the transmission time of the reference satellite, which can be calculated through information such as the code phase and ephemeris given by the tracking engine.

[0043] ΔT travel_Ref ΔT is the time required for the signal of the reference satellite to propagate from the reference satellite to the receiver, which can be calculated based on information such as the broadcast ephemeris of the reference satellite and the approximate receiver position. However, there may be certain errors in the receiver position obtained through AGNSS assistance or historical positioning information, and this part of the error will be used as an input condition for the acquisition range and will be considered in subsequent steps.

[0044] ΔT travel_est ΔT is the time required for the signal of the new satellite to propagate from the new satellite to the receiver, which can be calculated based on information such as the broadcast ephemeris and the approximate receiver position.

[0045] The carrier Doppler estimation can also be deduced according to formula (2):

[0046] Doppler estSat =Doppler RefSat +f satDoppler_RefSat -f satDoppler_estSat (4)

[0047] Where:

[0048] Doppler estSat is the carrier Doppler of the satellite to be estimated, that is, the estimated value of the Doppler frequency of the new satellite;

[0049] Doppler RefSat is the carrier Doppler of the reference satellite, which can be obtained from the measured values acquired at the baseband;

[0050] f satDoppler_RefSat is the Doppler frequency shift caused by the relative motion between the reference satellite and the receiver;

[0051] f satDoppler_estSat is the Doppler frequency shift caused by the relative motion between the new satellite and the receiver;

[0052] It can be seen from formula (4) that the receiver clock drift that has not been accurately known yet is eliminated in the above operations. The clock drift is an important factor affecting the carrier Doppler, so the accuracy of the carrier Doppler estimation can be improved by the method of estimating through the reference satellite.

[0053] The biggest difference between the code phase and carrier Doppler estimated by the above two methods and the existing estimation methods lies in using the almanac to calculate satellite position, velocity and other information, and its accuracy is worse than that of broadcast ephemeris. Therefore, when considering the setting of the acquisition range, it is also necessary to increase the consideration of the almanac accuracy. The accuracy of the almanac in calculating satellite position and other information is related to the time difference between the update time of the almanac and the current time. In the actual solution, through a large number of verifications, the code phase errors caused by different elevation satellites in different almanac ages are calculated, and a table of chip estimation ranges caused by almanac coordinate errors is summarized (see Table 1), which is used as a prior information for a control parameter when the tracking engine captures in step 404.

[0054] Table 1: Example of the correspondence between almanac age and code phase estimation error

[0055] Type Age of Almanac Maximum Code Phase Error (chip) Type1 <3 days CodephaseErr01 Type2 ≥3 days and < 1 week CodephaseErr02 Type3 ≥1 week and < 3 weeks CodephaseErr03

[0056] Similarly, a similar method can be used to obtain a corresponding table of the error of the almanac in estimating the Doppler frequency.

[0057] According to information such as receiver time ambiguity, clock drift ambiguity, position ambiguity, velocity ambiguity, and ambiguity estimated through broadcast ephemeris or almanac, etc., the acquisition range of satellite signals can be set, including code search range and Doppler search range.

[0058] Step 204, input the code phase and carrier Doppler frequency estimated according to the above steps into the tracking engine, and adjust the control parameters of the tracking engine according to the search ranges of the code phase and frequency to capture the satellite signal. After successful capture, the measurement of the newly added satellite can be realized, and measurement values such as satellite code phase and Doppler frequency can be obtained, and the carrier wave can be stripped to obtain the navigation message.

[0059] Step 205, the message decoding module realizes frame synchronization and orbital element parsing of the navigation message of the newly added satellite. According to the time of the receiver, the coordinates, velocity, clock error and other information of the current satellite are calculated. The positioning and solution module takes the satellite as an observable and brings it into the least squares or Kalman solution equation according to the satellite measurement values and information such as coordinates, velocity, clock error, etc. obtained in the above steps, so as to finally achieve the purpose of the newly added satellite participating in the positioning and solution.

[0060] It is not difficult to find that the present invention obtains new satellite information through AGNSS assistance, message parsing or historical information, and calculates the current code phase and Doppler estimation values according to the obtained new satellite information, and uses them as input information of the tracking engine to capture satellite signals, so as to realize the measurement of newly added satellites. The whole process does not require re-design and tape-out, greatly reducing the receiver cost.

Claims

1. A method for satellite extended support of a GNSS navigation receiver, characterized in that, Including the following steps: (1) Obtain new satellite information; (2) Calculate the current code phase estimation value and Doppler frequency estimation value of the newly added satellite according to the newly added satellite information; wherein, through T transmit_est = T transmit_Ref + ΔT travel_Ref - ΔT travel_est Calculate the current code phase estimation value of the newly added satellite, T transmit_est is the estimated signal transmission time of the newly added satellite, and there is a corresponding relationship between the signal transmission time of the newly added satellite and the code phase of the newly added satellite, T transmit_Ref is the signal transmission time of the reference satellite, and ΔT travel_Ref is the time required for the signal of the reference satellite to propagate from the reference satellite to the receiver. ΔT travel_est is the time required for the signal of the newly added satellite to propagate from the newly added satellite to the receiver; (3) Input the current code phase estimation value and Doppler frequency estimation value of the new satellite into the tracking engine, and adjust the control parameters of the tracking engine according to the search ranges of the code phase and Doppler frequency to capture and track the new satellite signal; (4) Decode the message of the new satellite to obtain the broadcast ephemeris of the new satellite, and then combine with the observables obtained by the tracking engine to perform positioning calculation using the new satellite.

2. The GNSS navigation receiver satellite expansion support method according to claim 1, characterized in that In step (1), the new satellite information is obtained by means of message parsing. The way of message parsing is to obtain the almanac information of the new satellite broadcast by other existing satellites, and then estimate the position, velocity and clock bias of the new satellite through the almanac information of the new satellite.

3. The GNSS navigation receiver satellite expansion support method according to claim 1, wherein, In step (1), the new satellite information is obtained by means of AGNSS assistance. The way of AGNSS assistance is that the AGNSS server issues the broadcast ephemeris related to the new satellite, and then calculates the position, velocity and clock bias of the new satellite at the emission moment through the current receiver time.

4. The GNSS navigation receiver satellite expansion support method according to claim 1, wherein In step (1), the new satellite information is obtained by means of historical information. The way of historical information is to obtain the broadcast ephemeris that has been positioned and parsed for the new satellite before and has not expired, and then estimate the position, velocity and clock bias of the new satellite through the broadcast ephemeris.

5. The GNSS navigation receiver satellite expansion support method according to claim 2 or 3, characterized in that, In step (2), the current Doppler frequency estimate of the newly added satellite is calculated through Doppler estSat = Doppler RefSat + f satDoppler_RefSat - f satDoppler_estSat , where Doppler estSat represents the Doppler frequency estimate of the newly added satellite, Doppler RefSat is the Doppler frequency of the reference satellite, f satDoppler_RefSat is the Doppler frequency shift caused by the relative motion between the reference satellite and the receiver, and f satDoppler_estSat is the Doppler frequency shift caused by the relative motion between the newly added satellite and the receiver; the reference satellite is a satellite that has been in a tracking state and whose observation quality exceeds a threshold value.

6. The GNSS navigation receiver satellite expansion support method according to claim 2, wherein In step (2), the current Doppler frequency estimate of the newly added satellite is calculated by Doppler = -f satDoppler_i +f clkDrift where Doppler represents the Doppler frequency estimate of the newly added satellite, and f satDoppler_i is the Doppler frequency shift caused by the relative motion between the newly added satellite and the receiver, and f clkDrift is the frequency offset introduced by the receiver clock drift.

7. The GNSS navigation receiver satellite expansion support method according to claim 1, wherein The search range of the code phase in step (3) is determined by the receiver time ambiguity, position ambiguity, and error table of code phase estimation by the almanac based on prior information. The search range of the Doppler frequency is determined by the receiver clock drift ambiguity, position ambiguity, velocity ambiguity, and error table of Doppler frequency estimation by the almanac based on prior information.

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