A High-Availability Geostationary GNSS Receiving System and Method

Abstract

A high-availability high-orbit GNSS receiving system and method use a dual-polarized antenna to simultaneously receive the LHCP signal and the RHCP signal of a navigation satellite. Determine whether the signal-to-noise ratios of the two signals are lower than a set threshold. When only one signal-to-noise ratio exceeds the set threshold, select the frequency error and code phase error of this path to drive the frequency-locked loop and code loop respectively. When the signal-to-noise ratios of both signals exceed the set threshold, fuse the frequency error and code phase error, and use the fused frequency error and code phase error to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO. The carrier NCO generates a local carrier according to the carrier frequency control word and sends it to two mixers at the same time, and the code NCO generates a local regenerated spreading code according to the code frequency control word and sends it to two correlators at the same time. The present invention improves the high-orbit GNSS receiving performance through two methods: hardware design improvement and receiving algorithm improvement.

Description

Technical Field

[0001] The present invention belongs to the field of spaceborne GNSS navigation receivers, and relates to a high-sensitivity GNSS receiver tracking system and method for geostationary satellites. Background Art

[0002] High-orbit spacecraft, such as geostationary orbit, inclined geosynchronous orbit, highly elliptical orbit satellites, and lunar deep space probes, etc., have important applications in the fields of satellite communication, early warning and surveillance, meteorological detection, etc. Currently, high-orbit satellites mainly rely on ground measurement and control to achieve orbit determination. With the increasing variety and quantity of high-orbit spacecraft, the demand for high-precision orbit determination by high-orbit earth observation payloads is gradually increasing, and the resources of traditional ground measurement and control systems are becoming increasingly tense.

[0003] The Global Navigation Satellite System (GNSS) has the characteristics of all-weather, all-day, and global coverage, and has been widely applied to low-orbit spacecraft. Using the GNSS navigation method in high-orbit space can effectively relieve the pressure of ground measurement and control and achieve autonomous real-time navigation.

[0004] Compared with traditional GNSS navigation, high-orbit GNSS receivers need to receive GNSS sidelobe leakage signals, whose signal power is about 20 dB smaller than that of the main lobe signal and the spatial continuity of the signal power distribution is poor. Since the distance from users in the GEO orbit to the GNSS constellation is farther, the received power is further reduced. At the same time, referring to the GPS signal transmitting antenna pattern characteristics released by Lockheed Martin Corporation, the sidelobes of GNSS signals are discretely distributed in different regions of space.

[0005] In order to improve the GNSS navigation performance of high-orbit satellites, the traditional solution is to develop high-sensitivity GNSS signal processing algorithms. The main research focuses on improving the system availability by improving the sensitivity, and making it possible to process more GNSS leakage signals by receiving the main lobe leakage signal or sidelobe leakage signal through a traditional right-hand circular polarization (RHCP) antenna. This fails to make full use of the power distribution of GNSS signals in the sidelobe coverage area and affects satellite visibility.

[0006] Traditional high-orbit navigation receivers such as: Wang Meng, Shan Tao, Wang Dun. Development of GNSS Technology for High-orbit Spacecraft. Acta Geodaetica et Cartographica Sinica, 2020, 49(9): 1158-1167. DOI: 10.11947 / j.AGCS.2020.20200170 introduced the situation of high-orbit GNSS receivers, and mentioned that "in terms of high-sensitivity signal tracking technology, the existing main technical means mainly rely on the weak signal tracking capabilities of traditional phase-locked loops (PLLs) and frequency-locked loops (FLLs), and do not consider improving the system performance from the perspective of the polarization mode of the receiving antenna.

[0007] Most ordinary dual-polarized receivers are used to solve the influence of ground-reflected multipath signals on the main signal. For example, Sgammini, Matteo & Caizzone, Stefano & Iliopoulos, Andreas & Hornbostel, Achim & Meurer, Michael. (2016). Interference Mitigation Using a Dual-Polarized Antenna in a Real Environment. 10.33012 / 2016.14798 introduced a dual-polarized receiver for ground interference suppression. Dinesh Manandhar, Ryosuke Shibasaki and Per-Ludvig Normark, GPS Signal Analysis using LHCP / RHCP Antenna and Software GPS Receiver, Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) introduced a receiver that suppresses multipath interference by receiving reflected signals with a left-handed antenna based on the principle that the polarization direction of the signal changes after being reflected by the ground, without treating the right-handed signal as a valid navigation signal and supplementing the processing method for navigation and positioning.

[0008] In the above-mentioned method of simply using a right-handed antenna, due to the polarization isolation of the antenna itself, the left-handed part of the GNSS sidelobe signal cannot be received, and the spatial distribution of the ideal signal energy cannot be fully utilized. Summary of the Invention

[0009] The technical problem solved by the present invention is: overcoming the deficiencies of the prior art, providing a high-availability high-orbit GNSS receiving system and method, improving the high-orbit GNSS receiving performance through two methods of hardware design improvement and receiving algorithm improvement, increasing the visibility of the BDS signal by 20% for a satellite under high-orbit conditions, and reducing the receiver sensitivity requirement by 2 dB under the same visibility conditions, thus improving the availability of the GNSS receiver under high-orbit conditions.

[0010] The technical solution of the present invention is: a high-availability high-orbit GNSS receiving system, including 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:

[0011] Dual-polarized antenna, used for simultaneously receiving LHCP signals and RHCP signals of navigation satellites;

[0012] The LHCP signal receiving channel and the RHCP signal receiving channel have the same structure, both including a low-noise amplifier, a down-converter, an analog-to-digital converter, a mixer, a correlator, and a discriminator connected in sequence;

[0013] Signal-to-noise ratio estimation module, simultaneously receiving the signals corr L (k) and corr R (k), estimating the signal-to-noise ratio of corr L (k) and corr R (k), obtaining two noise estimation values and sending them to the data fusion selection module;

[0014] Data fusion selection module, simultaneously receiving the frequency errors X L , X R , the code phase errors X Lcode , X Rcode , and the two noise estimation values input by the signal-to-noise ratio estimation module judging whether the signal-to-noise ratios of the two paths of signals exceed the set threshold. When only one of the two paths of signals has a signal-to-noise ratio exceeding the set threshold, select the frequency error and code phase error of the path exceeding the set threshold to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO; when the signal-to-noise ratios of both paths of signals exceed the set threshold, then fuse the frequency error and code phase error, and use the fused frequency error and code phase error to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO;

[0015] The carrier NCO generates a local carrier according to the carrier frequency control word and sends it to the two mixers simultaneously, and the code NCO generates a local regenerated spreading code according to the code frequency control word and sends it to the two correlators simultaneously.

[0016] Furthermore, the fusion of the frequency error and code phase error is specifically as follows:

[0017] Fused frequency error

[0018] Fused code phase error

[0019] Furthermore, the signals corr L (k) and corr R (k) output by the two correlators are specifically:

[0020]

[0021] where a i represents the amplitude of the i-th received signal, L and R correspond to the LHCP signal and the RHCP signal respectively, and T coh represents the coherent integration time, f L(k) and n fL represent the residual carrier of the LHCP signal and the noise of the LHCP signal, f R(k) and n fR represent the residual carrier of the RHCP signal and the noise of the RHCP signal respectively. When the loop is stable

[0022] Furthermore, the frequency errors X L , X R input to the two discriminators are specifically as follows:

[0023]

[0024] where e L and n L represent the left-handed frequency error and the left-handed frequency observation noise respectively, and e R and n R represent the right-handed frequency error and the right-handed frequency observation noise respectively. The observation noise n L , n R power is estimated by the signal-to-noise ratio estimation module according to the real-time signal-to-noise ratio.

[0025] A high-availability high-orbit GNSS receiving method includes:

[0026] Simultaneously receiving the LHCP signal and the RHCP signal of a navigation satellite by using a dual-polarization antenna; the LHCP signal receiving channel and the RHCP signal receiving channel have the same structure, and both include a low-noise amplifier, a down-converter, an analog-to-digital converter, a mixer, a correlator, and a discriminator connected in sequence;

[0027] Receiving the signals corr L (k) and corr R (k) output by the two correlators to perform signal-to-noise ratio estimation to obtain two noise estimation values

[0028] Receiving the frequency errors X L , X R , the code phase errors X Lcode , X Rcode , and the two noise estimation values Determine whether the signal-to-noise ratios of two signals exceed the set threshold. When only one of the two signals has a signal-to-noise ratio exceeding the set threshold, select the frequency error and code phase error of the signal that exceeds the set threshold to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO; when the signal-to-noise ratios of both signals exceed the set threshold, then fuse the frequency error and code phase error, and use the fused frequency error and code phase error to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO;

[0029] The carrier NCO generates a local carrier according to the carrier frequency control word and sends it to two mixers at the same time. The code NCO generates a local regenerated spreading code according to the code frequency control word and sends it to two correlators at the same time.

[0030] The advantages of the present invention compared with the prior art are as follows: The present invention makes full use of the fact that the GNSS leakage signal has left-handed and right-handed components and discontinuous distribution in the high-orbit service area. Through the fusion reception of a dual-polarized antenna, the signal powers of the left-handed and right-handed dual channels are fused, achieving full fusion of the dual signals, expanding the visibility of the signals, improving the signal-to-noise ratio and system continuity, improving the performance and availability of high-orbit GNSS receivers. Based on the BDS signal, the availability is increased by 20%, and it can be widely applied to high-orbit GNSS receivers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a block diagram of the composition principle of the system of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] As is well known, the transmitting antennas of all GNSS systems (GPS, Galileo, Glonass, BDS, etc.) adopt an array antenna design, and the gain pattern is optimized for ground users. The main lobe covers the area of the main lobe and users within 3000 Km around the earth. Within the antenna beam angle of ±22 degrees is the main lobe of the signal, and the polarization mode of the main lobe signal is RHCP. The signal within the main lobe beam is stable and continuous, so traditional GNSS receivers all adopt RHCP receiving antennas. Since the transmitting antenna design does not optimize the signal polarization mode outside the main lobe beam (leakage signal), there are both LHCP and RHCR components in the same sidelobe illumination area, and the energy distribution of each component signal is irregular.

[0033] The present invention improves the structure of the traditional high-orbit GNSS receiver, adds a left-handed circular polarization (LHCP) port to the traditional right-handed circular polarization (RHCP) receiving antenna, and sends the LHCP signal and RHCP signal to the signal processing unit through independent low-noise amplifiers and receiving channels at the same time to complete signal acquisition, tracking, pseudorange measurement and navigation positioning work.

[0034] The main idea of the present invention is to simultaneously receive LHCP signals and RHCP signals through a single antenna, and fuse and process the characteristics of the left- and right-handed signals at the signal processing end to improve the continuity of the system.

[0035] Since the carrier phases of the left-handed signal and the right-handed signal are different, it is impossible to perform switching under PLL tracking conditions. However, the frequencies of the two signals and the phases of the spreading codes of the modulation have good consistency. In order to improve the continuity, the present invention improves the system sensitivity through a dual-polarized antenna in cooperation with an autonomous fusion switching frequency-locked loop + code loop.

[0036] As Figure 1 shown, it is the composition principle block diagram of the GNSS receiving system of the present invention, which includes a dual-polarized antenna, a dual-channel LNA (LNA L, LNA R), a dual-channel part (including channel L, channel R, analog-to-digital conversion L, analog-to-digital conversion R), a dual-channel mixer (mixer L, mixer R), a dual-channel correlator (correlator L, correlator R), a dual-channel 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.

[0037] The dual-polarized antenna simultaneously receives LHCP signals and RHCP signals (the subsequent corresponding processing components are distinguished by L and R). For the LHCP signal (left-handed signal, L path), it is successively subjected to low-noise amplification by LNA L, down-conversion operation by channel L, and analog-to-digital conversion by AD_L to obtain the digital intermediate-frequency signal s iL (k) = a iL cos(2πf L k)c i (k) reaches mixer L. Similarly, for the RHCP signal (right-handed signal, R path), it is successively subjected to low-noise amplification by LNA R, down-conversion operation by channel R, and analog-to-digital conversion by AD_R to obtain the digital intermediate-frequency signal s iR (k) = a iR cos(2πf R k)c i (k) reaches mixer R. Among them, the parameter a i represents the amplitude of the i-th received signal, f represents the intermediate frequency, c i represents the spreading code of the i-th received signal, k represents the time, and L and R respectively correspond to the LHCP signal and the RHCP signal.

[0038] In mixer L, the L-path signal is mixed with the local carrier generated by the carrier NCO to obtain a 0-intermediate-frequency signal and sent to correlator L. In correlator L, the L-path 0-intermediate-frequency signal is correlated with the local regenerated spreading code of the code NCO to obtain the IQ correlation value corr L(k), and are simultaneously sent to the discriminators and signal-to-noise ratio estimation modules of L channels. After the discriminators of L channels perform frequency discrimination on the input signals, the frequency errors X of L channels of the dual-polarized antenna are obtained L , and are sent to the data fusion and selection module. Similarly, in mixer R, the R-channel signal is mixed with the local carrier generated by the carrier NCO to obtain a 0 IF signal, which is sent to correlator R. In correlator R, the 0 IF signal of R channels and the locally regenerated spreading code of code NCO are subjected to correlation processing to obtain the IQ correlation value corr R (k), and are simultaneously sent to the discriminators and signal-to-noise ratio estimation modules of R channels. After the discriminators of R channels perform frequency discrimination on the input signals, the frequency errors X of L channels of the dual-polarized antenna are obtained R , and are sent to the data fusion and selection module.

[0039] Where T coh represents the adenosine integration time, f L(k) and n fL represent the left-handed residual carrier and left-handed signal noise, f R(k) and n fR represent the right-handed residual carrier and right-handed signal noise respectively.

[0040] When the loop is stable

[0041] The parameters e L and n L represent the left-handed frequency error and left-handed frequency observation noise respectively, e R and n R represent the right-handed frequency error and right-handed frequency observation noise respectively. 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, and the calculation method is not limited. At the same time, the frequency discrimination method is also not limited.

[0042] In the signal-to-noise ratio estimation module, the signal-to-noise ratio of the two input signals corr L (k) and corr R (k) is estimated to obtain the noise estimation value of the dual-polarized signal and sent to the data fusion and selection module (the signal ratio obtained by amplitude estimation is positively correlated with the frequency estimation error).

[0043] In the data fusion and selection module, according to the noise estimation value, the observed quantity is introduced into the loop through fusion judgment to achieve seamless switching, and the fusion frequency error X better than X L and X R is obtained; RL ;

[0044]

[0045] The principle of the above formula is as follows:

[0046] Assume that the measurement results of the left - hand and right - hand correlators are Z0 and Z1 respectively, and the standard deviations of the corresponding observation noises are σ0 and σ1. The purpose of fusion is to obtain the optimal observation of Z (with the maximum signal - to - noise ratio) through the linear combination of the two observations. Let the estimated signal be

[0047] The linear combination of the left - hand and right - hand observations can be expressed as:

[0048]

[0049] The observation variance is (the two observations are independent)

[0050]

[0051] Take the derivative of the variance with respect to k and set it equal to 0:

[0052]

[0053] It can be obtained that when the optimal fusion observation is obtained.

[0054] So

[0055]

[0056] Meanwhile, in the data fusion selection module, the code - phase error is also obtained according to the correlation value output by the correlator, and the dual - polarization code - loop error fusion calculation is carried out,

[0057]

[0058] where n Lcode , n Rcode are the left - hand and right - hand dual - polarization observation noises, and their proportional relationship is the same as that of n L , n R , X Lcode , e Lcode , X Rcode , e Rcode represent the left - hand code - phase error, left - hand code - phase observation noise, right - hand code - phase error, and right - hand code - phase observation noise respectively.

[0059] The optimal code - error estimate value X RLcode

[0060]

[0061] In the frequency - locked loop, the fusion frequency error X RL, the corresponding carrier NCO frequency control word is obtained through a loop filter and sent to the carrier NCO.

[0062] In the code loop, the obtained code loop fusion error X is utilized RLcode , and the corresponding code frequency control word is obtained through a loop filter and sent to the code NCO.

[0063] The implementation manners of the code loop filter, the code NCO, the carrier loop filter and the carrier NCO are consistent with those of the traditional receiver.

[0064] By continuously updating the frequency control word, the tracking loop is closed to achieve the loop closed-loop.

[0065] During the fusion process, the influence of the signal-to-noise ratio estimation of the left-handed and right-handed branches on the system stability is considered. When the signal-to-noise ratio estimation is low ( adjustable according to the threshold of different signal types threshold), then the observation of this path is not introduced into the data fusion algorithm, and the discrimination error of the branch with a higher signal-to-noise ratio is directly used to drive the loop.

[0066] The content not described in detail in the specification of the present invention belongs to the well-known technology of those skilled in the art.

Claims

1. A high-availability high-orbit GNSS receiving system, characterized in that: It includes 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, where: The dual-polarized antenna is used to simultaneously receive the LHCP signal and the RHCP signal of a navigation satellite; The LHCP signal receiving channel and the RHCP signal receiving channel have the same structure, both including a low-noise amplifier, a down-converter, an analog-to-digital converter, a mixer, a correlator, and a discriminator connected in sequence; The signal-to-noise ratio estimation module simultaneously receives the signals corr L (k) and corr R (k), estimates the signal-to-noise ratio of corr L (k) and corr R (k), and obtains two noise estimation values which are sent to the data fusion selection module; Data fusion selection module, which simultaneously receives the frequency errors X input by two discriminators L ,X R , and the code phase error X Lcode ,X Rcode , as well as two noise estimates input by the signal-to-noise ratio estimation module Determine whether the signal-to-noise ratios of the two paths of signals exceed the set threshold. When only one of the two paths of signals has a signal-to-noise ratio exceeding the set threshold, select the frequency error and code phase error of the path exceeding the set threshold to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO; when the signal-to-noise ratios of both paths of signals exceed the set threshold, fuse the frequency error and code phase error, and use the fused frequency error and code phase error to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO; The carrier NCO generates a local carrier according to the carrier frequency control word and sends it to the two mixers simultaneously, and the code NCO generates a local regenerated spreading code according to the code frequency control word and sends it to the two correlators simultaneously.

2. The high-availability high-orbit GNSS receiving system according to claim 1, characterized in that: The fusion of the frequency error and the code phase error is specifically as follows: Fusion frequency error Fusion code phase error 3. The high-availability high-orbit GNSS receiving system according to claim 2, characterized in that: The signals corr L (k) and corr R (k) output by the two correlators are specifically as follows: where a i represents the amplitude of the i-th received signal, L and R correspond to the LHCP signal and the RHCP signal respectively, and T coh denotes the coherent integration time, f L(k) and n fL represent the residual carrier of the LHCP signal and the noise of the LHCP signal respectively, f R(k) and n fR represent the residual carrier of the RHCP signal and the noise of the RHCP signal respectively. When the loop is stable 4. A highly available high-orbit GNSS receiving system according to claim 2, characterized in that: The frequency error X of the two discriminator inputs L , X R , specifically: where e L and n L represent the left - hand rotation frequency error and the left - hand rotation frequency observation noise respectively, and e R and n R represent the right - hand rotation frequency error and the right - hand rotation frequency observation noise respectively. 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.

5. A high-availability high-orbit GNSS receiving method, characterized in that: Use a dual-polarized antenna to simultaneously receive the LHCP signal and the RHCP signal of a navigation satellite; the LHCP signal receiving channel and the RHCP signal receiving channel have the same structure, both including a low-noise amplifier, a down-converter, an analog-to-digital converter, a mixer, a correlator, and a discriminator connected in sequence; Receive the signals corr L (k) and corr R (k) to perform signal-to-noise ratio estimation and obtain two noise estimation values Receive the frequency error X of two discriminator inputs L , X R , the code phase error X Lcode , X Rcode , two noise estimates Determine whether the signal-to-noise ratios of the two paths of signals exceed the set threshold. When only one of the two paths of signals has a signal-to-noise ratio exceeding the set threshold, select the frequency error and code phase error of the path exceeding the set threshold to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO; when the signal-to-noise ratios of both paths of signals exceed the set threshold, then fuse the frequency error and code phase error, and use the fused frequency error and code phase error to drive the frequency-locked loop and code loop respectively, obtain the carrier frequency control word and send it to the carrier NCO, and obtain the code frequency control word and send it to the code NCO; The carrier NCO generates a local carrier according to the carrier frequency control word and sends it to the two mixers simultaneously, and the code NCO generates a local regenerated spreading code according to the code frequency control word and sends it to the two correlators simultaneously.

6. The high-availability high-orbit GNSS receiving method according to claim 5, characterized in that: The fusion of the frequency error and the code phase error is specifically as follows: Combined frequency error Fusion code phase error 7. A high-availability high-orbit GNSS receiving method according to claim 6, characterized in that: The signals corr L (k) and corr R (k) output by the two correlators are specifically as follows: where a i represents the amplitude of the i-th received signal, L and R correspond to the LHCP signal and the RHCP signal respectively, T coh represents the coherent integration time, f L(k) and n fL represent the LHCP signal residual carrier and the LHCP signal noise respectively, f R(k) and n fR represent the RHCP signal residual carrier and the RHCP signal noise respectively. When the loop is stable 8. A high-availability high-orbit GNSS receiving method according to claim 6, characterized in that: The frequency error X input to the two discriminators L , X R , specifically: where e L and n L represent the left - hand rotation frequency error and the left - hand rotation frequency observation noise respectively, and e R and n R represent the right - hand rotation frequency error and the right - hand rotation frequency observation noise respectively. 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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