CN115877416A - High-availability high-orbit GNSS receiving system and method - Google Patents
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Abstract
A high-availability high-orbit GNSS receiving system and method utilize a dual-polarized antenna to simultaneously receive LHCP signals and RHCP signals of navigation satellites. Judging whether the signal-to-noise ratio of the two paths of signals is lower than a set threshold, when only one path of signal-to-noise ratio exceeds the set threshold, selecting the frequency error and the code phase error of the path to respectively push a frequency locking ring and a code ring, when the signal-to-noise ratio of the two paths of signals exceeds the set threshold, fusing the frequency error and the code phase error, respectively pushing the frequency locking ring and the code ring by utilizing the fused frequency error and the fused code phase error, obtaining a carrier frequency control word, sending the carrier frequency control word to a carrier NCO, and obtaining a code frequency control word, and sending the code frequency control word to the code NCO. The carrier NCO generates local carrier according to the carrier frequency control word and sends the local carrier to the two mixers at the same time, and the code NCO generates local regeneration spread spectrum code according to the code frequency control word and sends the local regeneration spread spectrum code to the two correlators at the same time. The invention improves the receiving performance of the high-orbit GNSS by improving the hardware design and improving two modes in cooperation with the receiving algorithm.
Description
Technical Field
The invention belongs to the field of satellite-borne GNSS navigation receivers, and relates to a high-sensitivity GNSS receiver tracking system and method for a high-orbit satellite.
Background
High orbit spacecrafts such as geostationary orbit, inclined geosynchronous orbit, large eccentric orbit satellites, lunar deep space detectors and the like have important application in the fields of satellite communication, early warning monitoring, meteorological detection and the like. Currently, high earth orbit satellites mainly rely on ground measurement and control to realize orbit determination. With the increasing variety and number of high orbit spacecrafts, the requirement of high orbit earth observation load on high precision orbit determination is gradually increased, and the resources of the traditional ground measurement and control system are increasingly tensed.
The Global Navigation Satellite System (GNSS) has the characteristics of all-time, all-weather and global coverage, is widely applied to low-orbit spacecrafts, and can effectively relieve ground measurement and control pressure and realize autonomous real-time navigation by using a GNSS navigation mode in high-orbit space.
Compared with the traditional GNSS navigation, the high-orbit GNSS receiver needs to receive GNSS side lobe leakage signals, the signal power of the high-orbit GNSS receiver is about 20dB less than that of a main lobe signal, the spatial continuity of signal power distribution is poor, and the received power is further reduced due to the fact that the GEO orbit user is farther away from a GNSS constellation. Meanwhile, referring to the directional diagram characteristic of a GPS signal transmitting antenna published by the Lockheed Martin company, the side lobes of the GNSS signal are distributed in different areas in space in a discrete manner.
In order to improve the navigation performance of the high earth orbit satellite GNSS, a traditional solution is to develop a high-sensitivity GNSS signal processing algorithm, and the main research focuses on improving the system availability by improving the sensitivity, and the main lobe leakage signal or the side lobe leakage signal is received by a traditional right-hand circularly polarized (RHCP) antenna so that the conventional right-hand circularly polarized (RHCP) antenna can process more GNSS leakage signals. By the method, the power distribution of the GNSS signals in a side lobe coverage area cannot be fully utilized, and satellite visibility is influenced.
Conventional high-orbit navigation receivers are: wang, single billow, king shield, high orbit spacecraft GNSS technological development, survey and mapping, 2020, 49 (9): 1158-1167.Doi 10.11947/j. Agcs.2020.20200170 introduces the situation of high-orbit GNSS receiver, and it is mentioned that "in terms of high-sensitivity signal tracking technology, the existing main technical means mainly tracks weak signal tracking capability by means of traditional Phase Locked Loop (PLL) and Frequency Locked Loop (FLL), and does not improve system performance by considering the polarization mode of receiving antenna.
The common dual-polarized receiver is mostly used for solving the influence of the ground reflection multipath signal on the main signal, such as: sgamma mmini, matteo & Caizzone, stefano & Iliopoulos, andrea & Hornbostel, achim & Meurer, michael. (2016.) Interference simulation Using double-Polarized Antenna in a Real environmental management.10.33012/2016.14798 describes a Dual-Polarized receiver for terrestrial Interference suppression. A Receiver for suppressing multipath interference by receiving a reflected Signal through a left-handed Antenna by using The principle that The polarization direction of The Signal changes after The Signal is reflected by The ground is introduced by a connecting Mandhar, ryosubek, shibasaki and Per-Ludvig Normal, GPS Signal Analysis using LHCP/RHCP Antenna and Software GPS Receiver, and The concept of receiving The reflected Signal through a left-handed Antenna without processing a right-handed Signal as an effective Navigation Signal to supplement a processing mode for Navigation positioning.
In the mode of simply using the right-handed antenna, due to polarization isolation of the antenna, the left-handed part of the GNSS side lobe signal cannot be received, and the spatial distribution of ideal signal energy cannot be fully realized.
Disclosure of Invention
The invention solves the technical problems that: the high-availability high-orbit GNSS receiving system and the method overcome the defects of the prior art, improve the receiving performance of the high-orbit GNSS by two modes of hardware design improvement and receiving algorithm improvement, improve the visibility of the satellite to the BDS signal under a high-orbit member by 20 percent, reduce the sensitivity requirement of a receiver by 2dB under the same visibility condition, and improve the availability of the GNSS receiver under the high-orbit member.
The technical solution of the invention is as follows: a high-availability high-orbit GNSS receiving system comprises a dual-polarized antenna, an LHCP signal receiving channel, an RHCP signal receiving channel, a signal-to-noise ratio estimation module, a data fusion selection module, a carrier NCO and a code NCO, wherein:
the dual-polarized antenna is used for simultaneously receiving LHCP signals and RHCP signals of the navigation satellite;
the LHCP signal receiving channel and the RHCP signal receiving channel have the same structure and respectively comprise a low noise amplifier, a down converter, an analog-to-digital converter, a mixer, a correlator and a discriminator which are connected in sequence;
a signal-to-noise ratio estimation module for simultaneously receiving the signals corr output by the two correlators L (k) And corr R (k) For corr, pair of corr L (k) And corr R (k) Performing signal-to-noise ratio estimation to obtain two noise estimation values
Sending the data to a data fusion selection module;
a data fusion selection module for simultaneously receiving the frequency error X input by the two discriminators L ,X R Code phase error X Lcode ,X Rcode And two noise estimation values input by the SNR estimation module
Judging whether the signal-to-noise ratio of the two paths of signals exceeds a set threshold, when only one path of signal-to-noise ratio of the two paths of signals exceeds the set threshold, selecting a path of frequency error and a path of code phase error which exceed the set threshold to respectively push a frequency locking loop and a code loop, obtaining a carrier frequency control word, sending the carrier frequency control word to a carrier NCO, and obtaining a code frequency control word, and sending the code frequency control word to the code NCO; when the signal-to-noise ratio of the two paths of signals exceeds a set threshold, the frequency error and the code phase error are fused, the frequency locking loop and the code loop are respectively pushed by the fused frequency error and the fused code phase error, and a carrier wave is obtainedThe frequency control word is sent to a carrier NCO, and the code frequency control word is obtained and sent to a code NCO;
the carrier NCO generates local carrier according to the carrier frequency control word and sends the local carrier to the two mixers at the same time, and the code NCO generates local regeneration spread spectrum code according to the code frequency control word and sends the local regeneration spread spectrum code to the two correlators at the same time.
Further, the fusion of the frequency error and the code phase error specifically includes:
blending frequency errors
Merging code phase errors
Further, the signals corr output by the two correlators L (k) And corr R (k) The method specifically comprises the following steps:
wherein a is i Representing the amplitude of the ith received signal, L and R corresponding to the LHCP signal and RHCP signal, respectively, T coh Representing the coherent integration time, f L(k) And n fL Representing the LHCP signal residual carrier and LHCP signal noise, f R(k) And n fR Respectively representing the residual carrier wave of the RHCP signal and the noise of the RHCP signal when the loop is stable
Further, the frequency error X of the two discriminator inputs L ,X R The method specifically comprises the following steps:
wherein e L And n L Respectively showing the left-hand frequency error and the left-hand frequency errorFrequency observation noise, e R And n R Respectively representing a right-hand frequency error and a right-hand frequency observation noise, an observation noise n L ，n R The power is obtained by the signal-to-noise ratio estimation module according to the real-time signal-to-noise ratio estimation.
A high-availability high-orbit GNSS receiving method comprises the following steps:
simultaneously receiving LHCP signals and RHCP signals of a navigation satellite by using a dual-polarized antenna; the LHCP signal receiving channel and the RHCP signal receiving channel have the same structure and respectively comprise a low noise amplifier, a down converter, an analog-to-digital converter, a mixer, a correlator and a discriminator which are connected in sequence;
receiving signals corr output by two correlators L (k) And corr R (k) Performing signal-to-noise ratio estimation to obtain two noise estimation values
Receiving frequency error X of two discriminator inputs L ,X R Error of code phase X Lcode ,X Rcode Two noise estimate values
Judging whether the signal-to-noise ratio of the two paths of signals exceeds a set threshold, when only one path of signal-to-noise ratio of the two paths of signals exceeds the set threshold, selecting a path of frequency error and a path of code phase error which exceed the set threshold to respectively push a frequency locking loop and a code loop, obtaining a carrier frequency control word, sending the carrier frequency control word to a carrier NCO, and obtaining a code frequency control word, and sending the code frequency control word to the code NCO; when the signal-to-noise ratios of the two paths of signals exceed a set threshold, fusing a frequency error and a code phase error, respectively pushing a frequency locking loop and a code loop by utilizing the fused frequency error and code phase error, obtaining a carrier frequency control word, sending the carrier frequency control word to a carrier NCO, and obtaining a code frequency control word, and sending the code frequency control word to the code NCO;
the carrier NCO generates local carrier according to the carrier frequency control word and sends the local carrier to the two mixers at the same time, and the code NCO generates local regeneration spread spectrum code according to the code frequency control word and sends the local regeneration spread spectrum code to the two correlators at the same time.
Compared with the prior art, the invention has the advantages that: the invention fully utilizes the capacity of GNSS leakage signals in a high-orbit service area, has left-handed and right-handed components and discontinuous distribution, fuses the power of left-handed and right-handed dual-channel signals through the fusion and receiving of the dual-polarized antenna, fully fuses the dual-channel signals, expands the visibility of the signals, improves the signal-to-noise ratio and the system continuity, improves the performance and the availability of a high-orbit GNSS receiver, improves the availability based on BDS signals by 20 percent, and can be widely applied to the high-orbit GNSS receiver.
Drawings
FIG. 1 is a schematic block diagram of the system of the present invention.
Detailed Description
As is well known, all GNSS system (GPS, galileo, glonass, BDS, etc.) transmit antennas are designed using array antennas, the gain pattern is optimized for users on the ground, users in the area covered by the main lobe and around the earth within 3000Km range are signal main lobes within ± 22 degrees of the antenna beam angle, the main lobe signal polarization mode is RHCP, and signals in the main lobe beam are stable and continuous, so conventional GNSS receivers all use RHCP receive antennas. Because the signal polarization mode is not optimized when the transmitting antenna is designed outside the main lobe beam (signal leakage), LHCP and RHCR components exist in the same side lobe irradiation area at the same time, and the energy distribution of each component signal is irregular.
The invention improves the structure of the traditional high-orbit GNSS receiver, adds a left-handed circular polarization (LHCP) port on the traditional right-handed circular polarization (RHCP) receiving antenna, and simultaneously sends LHCP signals and RHCP signals into a signal processing unit through an independent low-noise amplifier and receiving channel to finish the acquisition, tracking, pseudo-range measurement and navigation positioning of the signals.
The main idea of the invention is to receive LHCP signals and RHCP signals simultaneously through a single antenna, and to perform fusion processing on left-handed and right-handed signal characteristics at a signal processing end, thereby improving the continuity of the system.
Because the carrier phases of the left-handed signal and the right-handed signal are different, the switching can not be carried out under the PLL tracking condition, but the frequencies of the two paths of signals and the phase of the modulated spread spectrum code have better consistency, and in order to improve the continuity, the dual-polarized antenna matched with the self-fusion switching frequency locking ring and the code ring improves the system sensitivity.
As shown in fig. 1, the GNSS receiving system of the present invention is a schematic block diagram, and includes a dual-polarized antenna, a dual-path LNA (low noise amplifier L, low noise amplifier R), a dual-path channel portion (including channel L, channel R, analog-to-digital conversion L, and analog-to-digital conversion R), a dual-path mixer (mixing frequency L, mixing frequency R), a dual-path correlator (correlator L, correlator R), a dual-path discriminator, a signal-to-noise ratio estimation module, a data fusion selection module, a frequency-locked loop, a code loop, a carrier NCO, and a code NCO.
The dual-polarized antenna receives LHCP signals and RHCP signals at the same time (corresponding processing devices are distinguished by L and R subsequently), for the LHCP signals (left-handed signals and L paths), low-noise amplification is carried out on the LHCP signals sequentially through the low-noise amplification L, down-conversion operation is carried out on the channel L, and after analog-to-digital conversion is carried out on the AD _ L, digital intermediate-frequency signals s are obtained iL (k)＝a iL cos(2πf L k)c i (k) And when the signal reaches a mixer L, the RHCP signal (right-handed signal, R path) is subjected to low-noise amplification by a low-noise amplifier R in sequence, a channel R is subjected to down-conversion operation, and AD _ R is subjected to analog-to-digital conversion to obtain a digital intermediate frequency signal s iR (k)＝a iR cos(2πf R k)c i (k) To the mixer R. Wherein the parameter a i Representing the amplitude of the i-th received signal, f representing the intermediate frequency, c i A spreading code representing the ith received signal, k represents time, and L and R correspond to the LHCP signal and the RHCP signal, respectively.
In a mixer L, mixing L path signals with local carrier waves generated by a carrier NCO to obtain 0 intermediate frequency signals, sending the 0 intermediate frequency signals into a correlator L, and performing correlation processing on the correlator L path 0 intermediate frequency signals and local regenerated spread spectrum codes of the code NCO to obtain IQ correlation values corr L (k) Simultaneously sending the signals into an L-path discriminator and a signal-to-noise ratio estimation module, and obtaining L-path frequency error X of the dual-polarized antenna after the L-path discriminator carries out frequency discrimination on the input signals L And sending the data to a data fusion selection module. Similarly, in the mixer R, the R path signal and the local carrier generated by the carrier NCO are mixed to obtain 0 intermediate frequency signal, the 0 intermediate frequency signal is sent to the correlator R, after the correlation processing is carried out on the 0 intermediate frequency signal of the correlator R and the R path signal and the local regenerated spread spectrum code of the code NCO,obtaining IQ correlation value corr R (k) Simultaneously sending the signals into a discriminator of the R path and a signal-to-noise ratio estimation module, and obtaining L path frequency error X of the dual-polarized antenna after the discriminator of the R path discriminates the frequency of the input signals R And sending the data to a data fusion selection module.
Wherein
T coh Denotes the adenosine integration time, f L(k) And n fL Representing the left-hand residual carrier and the left-hand signal noise, f R(k) And n fR Representing the right-hand residual carrier and the right-hand signal noise, respectively.
When the loop is stable
In the SNR estimation module, two input signals corr are processed L (k) And corr R (k) Carrying out signal-to-noise ratio estimation to obtain a noise estimation value of the dual-polarized signal
Sending the signal to a data fusion selection module (the signal ratio obtained by amplitude estimation is positively correlated with the frequency estimation error).
In a data fusion selection module, the observed quantity is introduced into a loop according to the fusion judgment of the noise estimation value, the seamless switching is realized, and the result is superior to X L And X R Fused frequency error X of RL ；
The principle of the above formula is:
the measurement results of the left-right-handed two correlators are assumed to be Z respectively 0 ，Z 1 Corresponding to standard deviation of observed noise as σ 0 And σ 1 The fusion aims to obtain the optimal observed quantity (the signal-to-noise ratio is maximum) of Z by linear combination of two kinds of observation, and an estimated signal is set as
The linear combination of the left and right handed two sets of observations can be expressed as:
The variance is derived for k and equals 0:
can find out
The optimal fusion observation is obtained.
Therefore, it is not only easy to use
Meanwhile, in the data fusion selection module, the code phase error is obtained according to the correlation value output by the correlator, the dual-polarization code loop error fusion calculation is carried out,
wherein n is Lcode ，n Rcode Left-handed and right-handed dual polarized observation noise, and the proportional relation thereof with n L ，n R Identity, X Lcode 、e Lcode 、X Rcode 、e Rcode And respectively representing a left-hand code phase error, a left-hand code phase observation noise, a right-hand code phase error and a right-hand code phase observation noise.
Obtaining optimal code error estimated value X by adopting the same processing mode as carrier wave RLcode
In a locked frequency loop, using the obtained fusion frequency error X RL And obtaining a corresponding carrier NCO frequency control word through a loop filter and sending the control word to the carrier NCO.
In the code ring, the obtained code ring is used to fuse the error X RLcode And the corresponding code frequency control word is obtained by the loop filter and is sent to the code NCO.
The implementation modes of the code loop filter, the code NCO, the carrier loop filter and the carrier NCO are consistent with those of a traditional receiver.
And the tracking loop is closed by continuously updating the frequency control word, so that the loop is closed.
Considering the influence of the SNR estimation of the left-hand branch and the right-hand branch on the system stability in the fusion process, when the SNR estimation is low (
Adjustable according to different signal types threshold), the observed quantity of the path is not introduced into the data fusion algorithm, and the identification error of the signal-to-noise ratio branch path is directly usedPushing the loop.
Those skilled in the art will appreciate that those matters not described in detail in the present specification are well known in the art.
Claims (8)
1. A high-availability high-orbit GNSS reception system, characterized by: the system comprises a dual-polarized antenna, an LHCP signal receiving channel, an RHCP signal receiving channel, a signal-to-noise ratio estimation module, a data fusion selection module, a carrier NCO and a code NCO, wherein:
the dual-polarized antenna is used for simultaneously receiving LHCP signals and RHCP signals of the navigation satellite;
the LHCP signal receiving channel and the RHCP signal receiving channel have the same structure and respectively comprise a low noise amplifier, a down converter, an analog-to-digital converter, a mixer, a correlator and a discriminator which are connected in sequence;
a signal-to-noise ratio estimation module for simultaneously receiving the signals corr output by the two correlators L (k) And corr R (k) For corr L (k) And corr R (k) Performing signal-to-noise ratio estimation to obtain two noise estimation values
Sending the data into a data fusion selection module;
a data fusion selection module for receiving the frequency error X from the two discriminators L ,X R Error of code phase X Lcode ,X Rcode And two noise estimation values input by the SNR estimation module
Judging whether the signal-to-noise ratio of the two paths of signals exceeds a set threshold, when only one path of signal-to-noise ratio of the two paths of signals exceeds the set threshold, selecting a path of frequency error and a path of code phase error which exceed the set threshold to respectively push a frequency locking loop and a code loop, obtaining a carrier frequency control word, sending the carrier frequency control word to a carrier NCO, and obtaining a code frequency control word, and sending the code frequency control word to the code NCO; when the signal-to-noise ratios of the two paths of signals exceed a set threshold, the frequency error and the code phase error are fused, and the fused frequency error and the fused code phase error are utilized to respectivelyPushing the frequency locking ring and the code ring to obtain a carrier frequency control word and send the carrier frequency control word to a carrier NCO, and obtaining a code frequency control word and sending the code frequency control word to a code NCO;
the carrier NCO generates local carrier according to the carrier frequency control word and sends the local carrier to the two mixers at the same time, and the code NCO generates local regeneration spread spectrum code according to the code frequency control word and sends the local regeneration spread spectrum code to the two correlators at the same time.
2. The high availability high orbit GNSS receiver system of claim 1, wherein: the fusion of the frequency error and the code phase error specifically comprises the following steps:
blending frequency errors
Merging code phase errors
3. The high availability high orbit GNSS reception system of claim 2, wherein: the signals corr output by the two correlators L (k) And corr R (k) The method specifically comprises the following steps:
wherein a is i Representing the amplitude of the ith received signal, L and R corresponding to the LHCP signal and RHCP signal, respectively, T coh Representing the coherent integration time, f L(k) And n fL Representing the LHCP signal residual carrier and LHCP signal noise, f R(k) And n fR Respectively representing the residual carrier wave of the RHCP signal and the noise of the RHCP signal when the loop is stable
4. According toThe high availability high orbit GNSS receiver system of claim 2, wherein: frequency error X of said two discriminator inputs L ,X R The method specifically comprises the following steps:
wherein e L And n L Respectively representing the left-hand frequency error and the left-hand frequency observation noise, e R And n R Respectively representing a right-hand frequency error and a right-hand frequency observation noise, an observation noise n L ，n R The power is obtained by the signal-to-noise ratio estimation module according to the real-time signal-to-noise ratio estimation.
5. A high-availability high-orbit GNSS receiving method is characterized in that:
simultaneously receiving LHCP signals and RHCP signals of a navigation satellite by using a dual-polarized antenna; the LHCP signal receiving channel and the RHCP signal receiving channel have the same structure and respectively comprise a low noise amplifier, a down converter, an analog-to-digital converter, a mixer, a correlator and a discriminator which are connected in sequence;
receiving the corr signals output by two correlators L (k) And corr R (k) Performing signal-to-noise ratio estimation to obtain two noise estimation values
Receiving frequency error X of two discriminator inputs L ,X R Error of code phase X Lcode ,X Rcode Two noise estimate values
Judging whether the signal-to-noise ratio of two paths of signals exceeds a set threshold, when only one path of signal-to-noise ratio of two paths of signals exceeds the set threshold, selecting one path of frequency error and code phase error which exceed the set threshold to respectively push a frequency locking loop and a code loop, obtaining a carrier frequency control word, sending the carrier frequency control word to a carrier NCO, and obtaining a codeThe frequency control word is sent to a code NCO; when the signal-to-noise ratios of the two paths of signals exceed a set threshold, fusing a frequency error and a code phase error, respectively pushing a frequency locking loop and a code loop by utilizing the fused frequency error and code phase error, obtaining a carrier frequency control word, sending the carrier frequency control word to a carrier NCO, and obtaining a code frequency control word, and sending the code frequency control word to the code NCO;
the carrier NCO generates local carrier according to the carrier frequency control word and sends the local carrier to the two mixers at the same time, and the code NCO generates local regeneration spread spectrum code according to the code frequency control word and sends the local regeneration spread spectrum code to the two correlators at the same time.
6. The high availability high orbit GNSS receiving method of claim 5, wherein: the fusion of the frequency error and the code phase error specifically comprises the following steps:
blending frequency errors
Fused code phase error
7. The high availability high orbit GNSS reception method of claim 6, characterized in that: the signals corr output by the two correlators L (k) And corr R (k) The method specifically comprises the following steps:
wherein a is i Representing the amplitude of the ith received signal, L and R corresponding to the LHCP signal and RHCP signal, respectively, T coh Representing the coherent integration time, f L(k) And n fL Representing the LHCP signal residual carrier and LHCP signal noise, f R(k) And n fR Respectively representing the residual carrier wave of the RHCP signal and the noise of the RHCP signal when the loop is stable
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8. The method of claim 6, wherein the GNSS receiver comprises: frequency error X of the two discriminator inputs L ,X R The method specifically comprises the following steps:
wherein e L And n L Respectively representing the left-hand frequency error and the left-hand frequency observation noise, e R And n R Respectively representing a right-hand frequency error and an observation noise of the right-hand frequency, the observation noise n L ，n R The power is obtained by the signal-to-noise ratio estimation module according to the real-time signal-to-noise ratio estimation.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116381757A (en) * | 2023-06-05 | 2023-07-04 | 中国科学院空天信息创新研究院 | Iridium opportunistic signal Doppler frequency fine estimation method based on phase difference |
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