A three-star time difference positioning method based on reverse transmission

Abstract

The present invention relates to a three-satellite time difference positioning method based on reverse transparent transmission, comprising: a first and a second secondary satellite respectively receiving a radiation source signal; obtaining first and second reverse transparent forwarding signals based on the respectively received radiation source signals and self-positioning position information; and forwarding the signals to a primary satellite; the primary satellite generating a primary satellite concealed forwarding signal based on the radiation source signal, self-positioning position information, and the received first and second reverse transparent forwarding signals; and transmitting the signal to a ground receiving station; the ground receiving station performing interference cancellation and demodulation on the primary satellite concealed forwarding signal to obtain the radiation source signal and self-positioning position information received by the primary satellite, as well as the radiation source signal and self-positioning position information received by the first and second secondary satellites; obtaining time difference information between the primary satellite and the first secondary satellite, and between the primary satellite and the second secondary satellite; and constructing a time difference equation and jointly solving an earth surface constraint equation to obtain the radiation source positioning position. Thus, concealed transmission of the forwarding signal and precise positioning of the radiation source are achieved.

Description

Technical Field

[0001] The present invention relates to the field of radio positioning technology, and in particular to a three-star time difference positioning method based on reverse transmission. Background Art

[0002] Three-satellite time difference positioning technology is one method for achieving high-precision positioning of emitter sources. Generally, this positioning system requires complex intersatellite links and a high-precision time reference to achieve real-time positioning capabilities onboard the satellite. However, due to the limited processing power onboard the satellite, this method's efficiency in locating emitter signals decreases dramatically, making it unsuitable for large-scale emitter signal positioning.

[0003] If the positioning system includes low-orbit satellites, its transparent forwarding is affected by the geographical location of the ground receiving station, and large-scale real-time transparent forwarding cannot be achieved. The positioning area is greatly limited, and due to the Doppler frequency shift characteristics of low-orbit satellites, the signal-to-noise ratio loss of scrambled covert forwarding will be relatively large; if the positioning system uses all synchronous orbit satellites (usually referring to geosynchronous orbit satellites, which belong to the category of high-orbit satellites), real-time transparent forwarding can be achieved, and the signal-to-noise ratio loss of covert forwarding using scrambling is small, but the three satellites are all in synchronous orbit, and their positioning configuration is not ideal, resulting in positioning blind spots in low-latitude areas near the equator. Summary of the Invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a three-star time difference positioning method based on reverse transparent transmission, so as to solve the technical problems that the existing high-orbit three-star time difference positioning has positioning blind spots in low-latitude areas and low-orbit satellites cannot transparently forward in real time over a large range.

[0005] The present invention provides a three-star time difference positioning method based on reverse transmission, comprising the following steps:

[0006] Step S1: The first and second secondary satellites respectively receive radiation source signals, obtain first and second reverse transparent forwarding signals based on the respectively received radiation source signals and self-positioning position information, and forward them reversely to the primary satellite;

[0007] Step S2: The master satellite generates a master satellite covert forwarding signal based on the radiation source signal received by itself, the master satellite self-positioning position information, and the first and second reverse transparent forwarding signals received, and sends the signal to the ground receiving station;

[0008] Step S3: The ground receiving station performs interference cancellation and demodulation and decompression processing on the concealed forwarding signal of the primary satellite to obtain the radiation source signal and self-positioning position information of the primary satellite received by the primary satellite, as well as the radiation source signals and self-positioning position information of the first and second secondary satellites received by the first and second secondary satellites; based on the radiation source signals received by the primary satellite, the first and second secondary satellites, the time difference information between the primary satellite and the first secondary satellite, and the time difference information between the primary satellite and the first secondary satellite, and the main satellite and the second secondary satellite are obtained; based on the time difference information and the self-positioning position information of the primary satellite, the first and second secondary satellites, a time difference equation is constructed, and the time difference equation is jointly solved with an earth surface constraint equation to obtain the positioning position of the radiation source.

[0009] Furthermore, the master satellite generates a master satellite covert forwarding signal based on the radiation source signal received by itself, the master satellite self-positioning position information, and the first and second received reverse transparent forwarding signals, including:

[0010] The master satellite receives the ground radiation source signal, amplifies and filters it, and obtains the master satellite broadband receiving signal;

[0011] Up-converting the primary satellite broadband received signal to obtain an up-converted primary satellite broadband received signal;

[0012] The master satellite self-positioning information is modulated and digital-to-analog converted to obtain a master satellite modulation signal;

[0013] Up-converting the master satellite modulation signal to obtain an up-converted master satellite modulation signal;

[0014] Adjusting the relative amplitudes of the up-converted primary satellite bandwidth received signal and the up-converted primary satellite modulated signal, and combining them to obtain a primary satellite combined signal;

[0015] The primary satellite combines the primary satellite combined signal and the first and second reverse transparent forwarding signals to obtain a three-star combined signal;

[0016] The main satellite generates an interference signal, adjusts the amplitude of the interference signal, and combines it with the combined signal of the three satellites to obtain a total combined signal;

[0017] The amplitude of the total combined signal is adjusted and amplified to obtain a primary satellite concealed forwarding signal.

[0018] Furthermore, the step S1 includes:

[0019] The first and second secondary satellites respectively receive ground radiation source signals, and respectively amplify and filter them to obtain first and second secondary satellite broadband receiving signals;

[0020] Up-converting the first and second secondary satellite broadband received signals respectively to obtain first and second secondary satellite up-converted broadband received signals;

[0021] The self-positioning position information of the first and second secondary satellites is modulated and converted into first and second secondary satellite modulation signals after digital-to-analog conversion;

[0022] After the first and second secondary satellite modulation signals are up-converted, the first and second secondary satellite up-converted modulation signals are obtained respectively;

[0023] Adjusting the relative amplitudes of the broadband received signal after up-conversion by the first secondary satellite and the modulated signal after up-conversion, and then combining them, adjusting the amplitude of the combined signal and amplifying it to obtain a first reverse transparent forwarding signal;

[0024] The broadband received signal after up-conversion by the second secondary satellite and the modulated signal after up-conversion are adjusted in relative amplitude and then combined, and the amplitude of the combined signal is adjusted and amplified to obtain a second reverse transparent forwarding signal.

[0025] Furthermore, the master satellite covert forwarding signal is covertly forwarded to the ground receiving station through a forwarding link between the master satellite and the ground receiving station.

[0026] Furthermore, the ground receiving station uses a ground receiving and positioning system to perform interference cancellation and demodulation and translation processing on the hidden forwarding signal of the primary satellite to obtain the radiation source signals received by the primary satellite and the first and second secondary satellites, as well as the self-positioning position information of the primary satellite and the first and second secondary satellites.

[0027] Based on the self-positioning position information, the position vectors r1, r2, and r3 of the primary satellite, the first secondary satellite, and the second secondary satellite in the geocentric fixed coordinate system are obtained, and the position vector of the radiation source in the geocentric fixed coordinate system is set to r p

[0028] Based on r1, r2, r3, r p and the speed of light, and obtain the real time difference Δt between the radiation source signal reaching the primary star and the first secondary star 21 pt The expression of, and the real time difference Δt between the primary star and the second secondary star 31 pt Expressions of

[0029] The ground receiving and positioning system extracts the radiation source signals received by the primary satellite, the first secondary satellite, and the second secondary satellite as s1(n), s2(n), and s3(n), respectively, and calculates the time difference estimation value Δt between s1(n) and s2(n) 21 pa , the estimated time difference Δt between s1(n) and s3(n) 31 pa ;

[0030] Based on Δt21 pt , Δt 31 pt and Δt 21 pa , Δt 31 pa The relationship between them is converted to construct the time difference equation.

[0031] Furthermore, the time difference equation is solved jointly with the earth surface constraint equation, as shown in formulas (1)-(3):

[0032]

[0033] Among them, formulas (1)-(2) are time difference equations, and formula (3) is the earth surface constraint equation; x pe 、y pe 、z pe are the coordinates of the radiation source in the x-axis, y-axis, and z-axis directions of the Earth-centered fixed coordinate system, [x pe ,y pe ,z pe ] T =r p , a and e are the semi-major axis and oblateness of the Earth, respectively.

[0034] Furthermore, the interference signal bandwidth is consistent with the three-star combined signal bandwidth, and the interference signal amplitude is higher than the three-star combined signal amplitude;

[0035] The interference signal spectrum overlaps with the three-star combined signal spectrum, and the three-star combined signal is buried under the interference signal spectrum;

[0036] The interference signal is a spread spectrum signal with a known spread spectrum code.

[0037] Furthermore, the first and second reverse transparent forwarding signals are forwarded reversely to the primary satellite through the first and second inter-satellite links respectively.

[0038] Furthermore, the primary satellite, the first and second secondary satellites have the same ground reception working frequency band.

[0039] Furthermore, the primary satellite is a high-orbit satellite, and the first and second secondary satellites are low-orbit satellites.

[0040] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0041] 1. This invention uses a method whereby a low-orbit secondary satellite transparently forwards signals to the primary satellite, and a high-orbit primary satellite uniformly and covertly forwards signals to the ground. Simultaneously, an interference signal is added to the primary satellite's forwarded signal, and interference is canceled on the ground, achieving flexible and covert forwarding of signals received on the ground. The primary satellite uses a synchronous orbit satellite, and the secondary satellites use two low-orbit satellites. Three-way time difference positioning is performed on the ground, achieving high-precision positioning of all radiation source signals within the working frequency band, thereby significantly improving the positioning efficiency of large-scale radiation source signals.

[0042] 2. The present invention overcomes the positioning blind spot problem of the high-orbit three-satellite time difference positioning system in low-latitude areas. By combining high-orbit satellites and low-orbit satellites, the present invention can achieve real-time transparent forwarding over a large range, effectively expanding the positioning coverage range and reducing the positioning blind spots caused by geographical location restrictions.

[0043] 3. The radiation source positioning capability of the present invention is based on the positioning and processing capability of the ground receiving station and is not limited by the onboard processing capability. It can achieve high-precision positioning of all radiation source signals within the three-satellite common view area, greatly improving the positioning efficiency of the radiation source.

[0044] 4. The low-orbit satellite of the present invention transparently forwards signals to the high-orbit satellite in reverse. The high-orbit satellite uses scrambling technology for confidential transmission, thus realizing the covert forwarding of signals received on the ground. At the same time, it overcomes the limitation of transparent forwarding of low-orbit satellites being restricted by the location of ground receiving stations.

[0045] 5. The satellite self-positioning information of the present invention is modulated and transmitted to the ground receiving station simultaneously with the forwarding signal, which is decoupled from the ground operation and control system, making positioning more flexible.

[0046] 6. The three-star time difference positioning method of the present invention can expand the processing capacity of the ground receiving station according to specific needs, and can adapt to different application scenarios and positioning requirements.

[0047] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0049] Figure 1 This is a flow chart of a three-star time difference positioning method based on reverse transmission in an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of a framework for reverse transparent forwarding of received payloads by a secondary satellite in an embodiment of the present invention;

[0051] Figure 3 The relative frequency spectrum relationship between the modulated signal and the broadband received signal in the embodiment of the present invention;

[0052] Figure 4 This is a schematic diagram of a framework for concealed forwarding and receiving payloads from a primary satellite to the ground in an embodiment of the present invention;

[0053] Figure 5 The relative relationship between the primary and secondary satellite transparent forwarding spectrum and the interference signal spectrum in the embodiment of the present invention;

[0054] Figure 6 This is the radiation source signal positioning processing flow of the ground receiving and positioning system in an embodiment of the present invention;

[0055] Figure 7 The positional relationship between the primary satellite, the first secondary satellite, the second secondary satellite, and the ground radiation source in the geocentric fixed coordinate system in the embodiment of the present invention;

[0056] Figure 8 The positional relationship between the three-star nadir point and a typical radiation source in an embodiment of the present invention;

[0057] Figure 9 This is a CEP (Circular Error Probable) distribution diagram (unit: km) of the three-star time difference positioning based on reverse transmission in an embodiment of the present invention;

[0058] Figure 10 This is the CEP distribution map (unit: km) of the high-orbit three-star time difference positioning in an embodiment of the present invention. DETAILED DESCRIPTION

[0059] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, and are not used to limit the scope of the present invention.

[0060] In order to overcome the above-mentioned defects of the prior art and give full play to the advantages of the long baseline of the high-orbit and low-orbit combination and the covert forwarding advantages of the high-orbit satellite, the present invention proposes a three-star time difference positioning method based on reverse transparent forwarding, which reversely and transparently forwards the radiation source signal and satellite self-positioning information in the low-orbit satellite working frequency band to the synchronous orbit satellite (i.e., the high-orbit satellite, the main satellite), and after combining with the radiation source signal and satellite self-positioning information in the synchronous orbit satellite working frequency band, the synchronous orbit satellite uniformly scrambles and conceals the forwarding to the ground receiving station, and then performs interference cancellation and radiation source signal positioning processing on the ground, thereby realizing the three-star time difference positioning of all radiation source signals in the working frequency band. For example, it is suitable for the UHF (Ultra High Frequency, frequency range between 300MHz-3GHz) frequency band and application environments with complex signal environments.

[0061] The three-star time difference positioning method based on reverse transparent transmission proposed in the present invention can overcome the positioning blind spot problem of the high-orbit three-star time difference positioning system in low-latitude areas; it is based on transparent forwarding by high-orbit satellites (i.e., main satellites) and covert transmission by adding interference signals, thereby realizing confidential and covert forwarding of ground-received signals, and at the same time overcoming the limitation of transparent forwarding of low-orbit satellites being restricted by the position of ground receiving stations; the satellite self-positioning information is modulated to obtain a modulated signal, and the modulated signal is transmitted to the ground receiving station at the same time as the forwarding signal, which is decoupled from the ground operation and control system, and the positioning application is more flexible; by improving the computing power of the ground receiving and positioning system of the ground receiving station, high-precision positioning of all radiation source signals in the working frequency band can be achieved, greatly improving the positioning efficiency.

[0062] This invention has broad application prospects in multi-satellite high-precision positioning. The three-satellite time-of-day positioning method proposed in this invention can achieve high-precision positioning of stationary or slow-moving targets on the ground. However, if expanded to a four-satellite time-of-day positioning system, it can also achieve high-precision positioning of aerial targets and is also suitable for positioning high-speed dynamic targets. It can even be expanded to a multi-satellite time-of-day positioning system to obtain useful information at higher dimensions of the radiation source signal.

[0063] The present invention is applicable to the high-orbit and low-orbit joint time difference positioning in which a low-orbit satellite transparently transmits the radiation source signal within the working frequency band to a synchronous orbit satellite, thereby realizing high-precision positioning of the radiation source signal, overcoming the limitation of transparent forwarding of the low-orbit satellite being restricted by the location of the ground receiving station, and avoiding the technical problem of the high-orbit three-star time difference positioning system having a positioning blind spot in low-latitude areas.

[0064] In view of the fact that the current high-orbit three-star time difference positioning method has positioning blind spots in the low-latitude area of ​​10 degrees north and south latitude, and the limitation of low-orbit satellite transparent forwarding being restricted by the location of ground receiving stations, the present invention adopts a synchronous orbit satellite combined with two low-orbit satellites to transparently forward signals to the high-orbit satellite through the low-orbit satellite, rather than directly transparently forwarding them to the ground. This avoids the influence of the location of the ground receiving station on the transparent forwarding of the low-orbit satellite, realizes flexible and covert forwarding of the radiation source signal and high-precision positioning, and overcomes the technical problem of positioning blind spots in low-latitude areas of the high-orbit three-star time difference positioning system.

[0065] A specific embodiment of the present invention discloses a three-star time difference positioning method based on reverse transmission, such as Figure 1 As shown, the following steps are included:

[0066] Step S1: The first and second secondary satellites respectively receive radiation source signals, obtain first and second reverse transparent forwarding signals based on the respectively received radiation source signals and self-positioning position information, and forward them reversely to the primary satellite;

[0067] Step S2: The master satellite generates a master satellite covert forwarding signal based on the radiation source signal received by itself, the master satellite self-positioning position information, and the first and second reverse transparent forwarding signals received, and sends the signal to the ground receiving station;

[0068] Step S3: The ground receiving station performs interference cancellation and demodulation and decompression processing on the concealed forwarding signal of the primary satellite to obtain the radiation source signal and self-positioning position information of the primary satellite received by the primary satellite, as well as the radiation source signals and self-positioning position information of the first and second secondary satellites received by the first and second secondary satellites; based on the radiation source signals received by the primary satellite, the first and second secondary satellites, the time difference information between the primary satellite and the first secondary satellite, and the time difference information between the primary satellite and the first secondary satellite, and the main satellite and the second secondary satellite are obtained; based on the time difference information and the self-positioning position information of the primary satellite, the first and second secondary satellites, a time difference equation is constructed, and the time difference equation is jointly solved with an earth surface constraint equation to obtain the positioning position of the radiation source.

[0069] The primary satellite, the first secondary satellite and the second secondary satellite have the same ground receiving working frequency band.

[0070] For example, the working frequency band range of the three-star ground receiving working frequency band may be the UHF band; the three-star simultaneously receives the ground radiation source signal;

[0071] The primary satellite is a high-orbit satellite, and the first and second secondary satellites are low-orbit satellites.

[0072] The step S1 comprises:

[0073] The first and second secondary satellites respectively receive ground radiation source signals, and respectively amplify and filter them to obtain first and second secondary satellite broadband receiving signals;

[0074] Up-converting the first and second secondary satellite broadband received signals respectively to obtain first and second secondary satellite up-converted broadband received signals;

[0075] The self-positioning position information of the first and second secondary satellites is modulated and converted into first and second secondary satellite modulation signals after digital-to-analog conversion;

[0076] After the first and second secondary satellite modulation signals are up-converted, the first and second secondary satellite up-converted modulation signals are obtained respectively;

[0077] Adjusting the relative amplitudes of the broadband received signal after up-conversion by the first secondary satellite and the modulated signal after up-conversion, and then combining them, adjusting the amplitude of the combined signal and amplifying it to obtain a first reverse transparent forwarding signal;

[0078] Adjust the relative amplitudes of the broadband received signal after up-conversion by the second secondary satellite and the modulated signal after up-conversion, then combine them, adjust the amplitude of the combined signal and amplify it to obtain a second reverse transparent forwarding signal.

[0079] The first and second secondary satellites respectively combine the working frequency band containing the radiation source signal (i.e., broadband receiving signal) with the modulated self-positioning information of the first and second secondary satellites, and then transparently forward them to the primary satellite through the first inter-satellite link and the second inter-satellite link respectively. Then, together with the combined working frequency band containing the radiation source signal (i.e., broadband receiving signal of the primary satellite) and the modulated self-positioning information of the primary satellite, they are covertly forwarded to the ground receiving station. After sampling and processing by the ground receiving and positioning system of the ground receiving station, high-precision positioning of the radiation source target signal is achieved.

[0080] The first and second secondary stars have the same structure. Figure 2 As shown, the secondary satellite reverse transparent forwarding receiving payload framework. The receiving payload framework of the first and second secondary satellites both include: a receiving antenna, a radio frequency front end, a modulation and digital-to-analog conversion module, a first upconverter, a second upconverter, a first adjustable attenuator, a second adjustable attenuator, a third adjustable attenuator, a combiner, a power amplifier, and a reverse transparent forwarding antenna;

[0081] The first and second secondary satellites perform the same actions. The steps for the first and second secondary satellites to obtain the first and second reverse transparent forwarding signals are as follows:

[0082] (1) The first and second secondary satellites receive ground radiation source signals through receiving antennas, respectively, and input the signals into the RF front ends of the first and second secondary satellites, respectively. The ground radiation source signals are amplified and filtered by the RF front ends to obtain broadband receiving signals of the first and second secondary satellites containing the radiation source signals;

[0083] At the same time, the secondary satellite self-positioning information is input to the modulation and digital-to-analog conversion module for modulation, and digital-to-analog conversion is performed to obtain the first and second secondary satellite modulation signals. For example, the modulation method is QPSK, Quadrature Phase Shift Keying.

[0084] (2) The broadband receiving signals of the first and second secondary satellites are input to the first up-converters of the first and second secondary satellites, respectively, and the up-converted first and second broadband receiving signals are output;

[0085] At the same time, the modulation signals of the first and second secondary satellites are respectively input into the second up-converters of the first and second secondary satellites for up-conversion, thereby obtaining the up-converted modulation signals of the first and second secondary satellites respectively. The broadband receiving signal is converted from the original UHF band signal to the Ku / Ka band signal, but the spectrum characteristics remain unchanged and are the same.

[0086] (3) the first and second bandwidth received signals after up-conversion are input to the first adjustable attenuators of the first and second secondary satellites respectively;

[0087] The up-converted modulation signals of the first and second secondary satellites are respectively input into the second adjustable attenuators of the first and second secondary satellites;

[0088] By controlling the attenuation of the first and second adjustable attenuators (where the attenuation is a control value), the relative amplitudes of the broadband received signal and the modulated signal are adjusted, and the first and second secondary satellite broadband received signals with adjusted relative amplitudes, as well as the first and second secondary satellite modulated signals with adjusted relative amplitudes, are output; the relative amplitudes of the modulated signal and the broadband received signal are adjusted to ensure that the modulated signal has sufficient transmission power so that the ground can correctly obtain satellite self-positioning information;

[0089] (4) Combining the first secondary satellite broadband receiving signal with the adjusted relative amplitude and the first secondary satellite modulated signal to obtain the first secondary satellite combined signal, inputting the combined signal into the third adjustable attenuator of the first secondary satellite, adjusting the combined signal amplitude through the third adjustable attenuator of the first secondary satellite, and obtaining the first reverse transparent forwarding signal with adjusted amplitude; flexibly controlling the transmission power of the reverse transparent forwarding signal to ensure the primary satellite receiving signal-to-noise ratio;

[0090] The broadband received signal of the second secondary satellite with the adjusted relative amplitudes and the modulated signal of the second secondary satellite are combined to obtain a second secondary satellite combined signal, which is input into the third adjustable attenuator of the second secondary satellite. The amplitude of the combined signal is adjusted by the third adjustable attenuator of the second secondary satellite, and the signal after the adjusted amplitude is amplified by a power amplifier to obtain a second reverse transparent forwarding signal;

[0091] The first and second reverse transparent forwarding signals are forwarded reversely to the primary satellite via the first and second inter-satellite links respectively.

[0092] like Figure 3 As shown in Figure 1, the relative frequency spectrum relationship between the modulated signal and the broadband received signal, the horizontal axis f represents the signal frequency, and the vertical axis x(t) represents the signal amplitude;

[0093] The modulation signal is set at the edge of the reverse transparent forwarding frequency band, or in an area where there is no broadband receiving signal, to avoid the modulation signal from overlapping the radiation source signal in the broadband receiving signal, thereby reducing the interference that the modulation signal may cause to the radiation source signal (since the modulation rate required for satellite self-positioning information is very low, only a few kbps is needed, which means that the bandwidth required for the modulation signal is relatively small, so the modulation signal will occupy a few kHz of bandwidth in the forwarding frequency band, and the broadband receiving signal band contains narrowband radiation source signals. As long as the modulation signal and the radiation source signal do not overlap, they will not affect the radiation source signal in the broadband forwarding signal band). At the same time, the modulation signal needs to be higher than the broadband receiving signal noise floor to ensure that the signal-to-noise ratio requirements for demodulation are met.

[0094] For the modulation signal being higher than the noise floor of the broadband receiving signal, for example, for each receiving system, the power spectral density of its noise floor is known, assuming it is N0, and the bandwidth of the modulation signal is also known, assuming it is B. Therefore, assuming that the modulation signal is required to be 12dB higher than the noise floor, the modulation signal power is expressed as (N0+12)×B.

[0095] Regarding the signal-to-noise ratio requirements for demodulation, the demodulation signal-to-noise ratio threshold generally has a theoretical value, such as the QPSK bit error rate of 10 -4 When the signal-to-noise ratio is required to be 11.8dB, a margin of more than 3dB is generally required. If the bit error rate requirement is increased, the signal-to-noise ratio requirement must also be increased.

[0096] Step S2 includes steps S21-S22.

[0097] Step S21: The master satellite generates a master satellite covert forwarding signal based on the radiation source signal received by the master satellite, the master satellite self-positioning position information, and the first and second received reverse transparent forwarding signals, including:

[0098] The master satellite receives the ground radiation source signal, amplifies and filters it, and obtains the master satellite broadband receiving signal;

[0099] Up-converting the primary satellite broadband received signal to obtain an up-converted primary satellite broadband received signal;

[0100] The master satellite self-positioning information is modulated and digital-to-analog converted to obtain a master satellite modulation signal;

[0101] Up-converting the master satellite modulation signal to obtain an up-converted master satellite modulation signal;

[0102] Adjusting the relative amplitudes of the up-converted primary satellite bandwidth received signal and the up-converted primary satellite modulated signal, and combining them to obtain a primary satellite combined signal;

[0103] The primary satellite combines the primary satellite combined signal and the first and second reverse transparent forwarding signals to obtain a three-star combined signal;

[0104] The main satellite generates an interference signal, adjusts the amplitude of the interference signal, and combines it with the combined signal of the three satellites to obtain a total combined signal;

[0105] The amplitude of the total combined signal is adjusted and amplified to obtain a primary satellite concealed forwarding signal.

[0106] like Figure 4 Figure 2 shows a schematic diagram of the primary satellite's covert forwarding and receiving payload framework. The primary satellite's function of receiving signals from ground-based radiation sources is the same as that of the first and second secondary satellites.

[0107] like Figure 4 As shown, the hidden forwarding signal of the main satellite is obtained, and the specific implementation is as follows:

[0108] (1) Receive the ground radiation source signal through the main satellite receiving antenna, input it to the first RF front end of the main satellite, amplify and filter it, and obtain the main satellite broadband receiving signal;

[0109] The main satellite self-positioning information is input into the main satellite modulation and digital-to-analog conversion module for digital-to-analog conversion and modulation to obtain the main satellite modulation signal;

[0110] (2) The broadband receiving signal of the main satellite is input into the third up-converter of the main satellite for up-conversion to obtain the broadband receiving signal of the main satellite after up-conversion;

[0111] The main satellite modulation signal is input into the fourth up-converter of the main satellite for up-conversion to obtain the main satellite modulation signal after up-conversion;

[0112] (3) Inputting the up-converted broadband signal of the primary satellite into the fourth adjustable attenuator of the primary satellite, inputting the up-converted modulated signal of the primary satellite into the fifth adjustable attenuator of the primary satellite, adjusting the relative amplitudes of the up-converted broadband received signal and the up-converted modulated signal, and then combining them. The combined signal is input into the sixth adjustable attenuator of the primary satellite to adjust the amplitude, thereby obtaining the combined signal of the primary satellite;

[0113] (4) The primary satellite receives the first and second reverse transparent forwarding signals of the first and second secondary satellites through the reverse transparent signal receiving antennas of the first and second secondary satellites;

[0114] The first reverse transparent forwarding signal is input to the second RF front end for up-conversion and then input to the seventh adjustable attenuator for amplitude adjustment to obtain the first reverse transparent forwarding signal with adjusted amplitude;

[0115] The second reverse transparent forwarding signal is input to the third RF front end for up-conversion and then input to the eighth adjustable attenuator for amplitude adjustment to obtain the second reverse transparent forwarding signal with adjusted amplitude;

[0116] The first and second reverse transparent forwarding signals after amplitude adjustment are combined with the main satellite combined signal after up-conversion to obtain a three-star combined signal;

[0117] (5) The main satellite generates an interference signal through the interference signal generation module, which is input into the ninth adjustable attenuator of the main satellite to adjust the amplitude, and then combined with the three-star combined signal, and the spectrum overlaps to obtain a total combined signal, so that the interference signal covers the three-star combined signal to achieve a concealment effect; then it is input into the tenth adjustable attenuator of the main satellite to adjust the amplitude, control the transmission power of the transparent forwarding signal to the ground, ensure the ground receiving station to receive it reasonably, and avoid power leakage; it is amplified by the main satellite power amplifier to obtain the main satellite concealed forwarding signal.

[0118] The interference signal bandwidth is consistent with the three-star combined signal bandwidth, and the interference signal amplitude is higher than the three-star combined signal amplitude;

[0119] The interference signal spectrum overlaps with the three-star combined signal spectrum, and the three-star combined signal is buried under the interference signal spectrum;

[0120] The interference signal is a spread spectrum signal with a known spread spectrum code.

[0121] The main satellite transmits the main satellite's covert forwarding signal to the ground receiving and positioning system of the ground receiving station through the forwarding link.

[0122] Step S22: Covertly forward the master satellite forwarding signal to the ground receiving and positioning system of the ground receiving station through the forwarding link between the master satellite and the ground receiving station.

[0123] The relative relationship between the forwarding spectrum of the primary satellite, the first secondary satellite and the second secondary satellite and the spectrum of the interference signal, such as Figure 5 As shown in the figure, the center frequencies of the forwarding spectra of the primary satellite, the first secondary satellite, and the second secondary satellite are f1, f2, and f3, respectively. A protection gap is left between the forwarding spectra of the primary satellite, the first secondary satellite, and the second secondary satellite to prevent crosstalk between the signals. The interference signal spectrum overlaps with the forwarding spectrum of the combined primary satellite's covert forwarding signal, and the primary satellite's covert forwarding signal is just buried under the interference signal spectrum, achieving a covert forwarding effect to the ground.

[0124] Step S3 is divided into steps S31-S32.

[0125] Step S31: The ground receiving station demodulates the hidden forwarding signal of the primary satellite to obtain the self-positioning position information of the primary satellite and the self-positioning position information of the first and second secondary satellites.

[0126] The ground receiving station uses a ground receiving and positioning system to perform interference cancellation and restoration processing on the concealed forwarding signal of the primary satellite to obtain radiation source signals received by the primary satellite and the first and second secondary satellites;

[0127] Based on the self-positioning position information, the position vectors r1, r2, and r3 of the primary satellite, the first secondary satellite, and the second secondary satellite in the geocentric fixed coordinate system are obtained, and the position vector of the radiation source in the geocentric fixed coordinate system is set to r p

[0128] Based on r1, r2, r3, r p and the speed of light, and obtain the real time difference Δt between the radiation source signal reaching the primary star and the first secondary star 21 pt The expression of, and the real time difference Δt between the primary star and the second secondary star 31 pt Expressions of

[0129] The ground receiving and positioning system extracts the radiation source signals received by the primary satellite, the first secondary satellite, and the second secondary satellite as s1(n), s2(n), and s3(n), respectively, and calculates the time difference estimation value Δt between s1(n) and s2(n) 21 pa , the estimated time difference Δt between s1(n) and s3(n) 31 pa ;

[0130] Based on Δt 21 pt , Δt 31 pt and Δt 21 pa and Δt 31 pa The relationship between them is converted to construct the time difference equation.

[0131] The ground receiving and positioning system of the ground receiving station receives the hidden forwarding signal from the main satellite, such as Figure 6 shown.

[0132] The ground receiving and positioning system receives the hidden forwarding signal from the main satellite through the ground receiving antenna and performs digital processing. It also uses interference cancellation technology to cancel out the interference signal and restore the transparent forwarding signal after the three satellites are combined.

[0133] The main satellite hidden forwarding signal after the interference signal is offset is separated and processed to obtain: a main satellite combined signal, a first reverse transparent forwarding signal and a second reverse transparent forwarding signal.

[0134] Figure 6 The transparent forwarding signal of the central main satellite represents the main satellite combined signal; the transparent forwarding signal of the secondary satellite represents the first reverse transparent forwarding signal and the second reverse transparent forwarding signal.

[0135] The main satellite combined signal includes the main satellite broadband receiving signal carrying the radiation source signal and the main satellite modulation signal;

[0136] The first reverse transparent forwarding signal includes the first secondary satellite broadband receiving signal carrying the radiation source signal and the first secondary satellite modulated signal;

[0137] The second reverse transparent forwarding signal includes the second secondary satellite broadband receiving signal and the second secondary satellite modulated signal carrying the radiation source signal;

[0138] Decode and translate the modulation signal of the main satellite to obtain the self-positioning position information of the main satellite;

[0139] Decode and translate the modulation signal of the first secondary satellite to obtain the self-positioning position information of the first secondary satellite;

[0140] Decode and translate the modulation signal of the second secondary satellite to obtain the self-positioning position information of the second secondary satellite;

[0141] By processing the corresponding radiation source signals of the primary star, the first secondary star and the second secondary star, the time difference information is obtained;

[0142] Get the time difference information as follows:

[0143] like Figure 7 As shown, the primary star, the first secondary star, the second secondary star, and the radiation source (P) are in the geocentric fixed coordinate system (abbreviated as S e )’s positional relationship.

[0144] The position vectors of the primary star, the first secondary star, the second secondary star, and the radiation source in the geocentric fixed coordinate system are r1, r2, r3, r p , get the real time difference Δt between the radiation source signal reaching the primary star and the first secondary star21 pt , the real time difference Δt between the primary star and the second secondary star 31 pt , as shown in formulas (1)-(2):

[0145]

[0146] Where c is the speed of light.

[0147] The ground receiving and positioning system of the ground receiving station extracts the radiation source signals transparently forwarded by the primary satellite, the first secondary satellite, and the second secondary satellite as s1(n), s2(n), and s3(n), respectively, and processes the radiation source signals received by the primary and secondary satellites to obtain the time difference estimation value Δt between s1(n) and s2(n) 21 pa , the estimated time difference Δt between s1(n) and s3(n) 31 pa , then the real time difference Δt between the radiation source signal reaching the primary star and the first secondary star is 21 pt , the real time difference Δt between the primary star and the second secondary star 31 pt , as shown in formulas (3)-(4):

[0148]

[0149] Substituting formulas (3) and (4) into formulas (1) and (2), we can obtain formulas (5)-(6).

[0150] The time difference equation is solved jointly with the earth surface constraint equation, as shown in formulas (5)-(7):

[0151]

[0152]

[0153] Among them, formulas (5)-(6) are time difference equations, and formula (7) is the earth surface constraint equation; x pe 、y pe 、z pe are the coordinates of the radiation source in the x-axis, y-axis, and z-axis directions of the Earth-centered fixed coordinate system, [x pe ,y pe ,z pe ] T =r p , a and e are the semi-major axis and oblateness of the Earth, respectively.

[0154] If the radiation source is a ground target, the position of the ground radiation source is subject to the earth surface constraint.

[0155] Step S32: jointly solve the time difference equation and the earth surface constraint equation to obtain the positioning position of the radiation source.

[0156] By solving the simultaneous equations (5), (6), and (7), we can achieve high-precision positioning of the radiation source P. pe 、y pe 、z pe .

[0157] The following is a positioning accuracy analysis of a three-star time difference positioning method based on reverse transmission proposed in the present invention, so as to guide the application of this positioning method in engineering design and actual business scenarios.

[0158] Differentiating both sides of formulas (5)-(7) respectively, we get:

[0159] (u 1p -u 2p )·dr p -(u 1p -u 12 )·dr1+(u 2p -u 12 )·dr2=cd(Δt 21 pa )

[0160] (u 1p -u 3p )·dr p -(u 1p -u 13 )·dr1+(u 3p -u 13 )·dr3=cd(Δt 31 pa )

[0161] g p ·dr p =0

[0162] Formula (8)

[0163] Among them, g p It is related to the position of the ground radiation source and is expressed as shown in formula (9):

[0164]

[0165] u 1p 、u 2p 、u 3p 、u 12 、u 13 are all unit vectors, expressed as shown in formula (10):

[0166]

[0167] Among them, r ij =||r i -r j ||.

[0168] Converting formula (8) into matrix form, we get formula (11):

[0169]

[0170] make:

[0171] C=[(u 1p -u 2p ) (u 1p -u 3p ) g p ] T Formula (12)

[0172] dT=[d(Δt 21 pa ) d(Δt 31 pa ) 0] T Formula (13)

[0173] dU1=[(u 1p -u 12 ) T dr1(u 1p -u 13 ) T dr1 0] T Formula (14)

[0174] dU2=[(u 2p -u 12 ) T dr2 (u 3p -u 13 ) T dr3 0] T Formula (15)

[0175] And transform formula (11), then the radiation source position error dr p :

[0176] dr p =C -1 (cdT+dU1-dU2) Formula (16)

[0177] Then the radiation source position error dr p The covariance matrix of Expressed as formula (17):

[0178]

[0179] Assume that the satellite position error and time difference estimation error are Gaussian white noise and are uncorrelated with each other.

[0180] Right now:

[0181] E[dT]=[0 0 0] T Formula (18)

[0182]

[0183] E[dr i ]=[0 0 0] T (i=1,2,3) Formula (20)

[0184]

[0185] Among them, σ t21 , σ t31 are the time difference estimation errors between the first secondary star and the primary star, and between the second secondary star and the primary star, σ xei , σ yei , σ zei are the position errors of different satellites in the x-axis, y-axis, and z-axis directions, respectively, then:

[0186] E[dr p ]=C -1 (cE[dT]+E[dU1]-E[dU2])=[0 0 0] T Formula (23)

[0187] Then, formula (17) is simplified to:

[0188]

[0189] Therefore, the radiation source position error dr p Covariance matrix It consists of three terms, namely E[dTdT T ], E[dU1dU1 related to the satellite position error T ]、E[dU2dU2 T ], the specific expression is as follows:

[0190]

[0191] In summary, the covariance matrix P of the ground radiation source position error is obtained drpThe covariance matrix provides a complete description of the positioning error distribution, including the magnitude and direction of the error. From the covariance matrix, the standard deviation of the positioning error (i.e., the square root of the variance) can be calculated, and then the CEP (Circular Error Probable) distribution of the positioning accuracy can be estimated.

[0192] A smaller CEP value indicates a higher positioning accuracy, which means that the positioning positions of most ground emitters are close to the true position. Conversely, a larger CEP value indicates a lower positioning accuracy.

[0193] In order to make the technical effect of the present invention more obvious, a specific example will be given below to illustrate that a three-star time difference positioning system based on reverse transmission is established based on the method of the present invention, and then the CEP distribution of the positioning system is given.

[0194] Let two low-orbit satellites be secondary satellites and be in a sun-synchronous orbit at an altitude of 800 km. The distance between the two secondary satellites is 600 km (Sat1 and Sat2). The beam width of the ground receiving antenna is 120 degrees. One geosynchronous orbit satellite is the primary satellite (GEO1). The beam width of the ground receiving antenna is 5 degrees. The typical ground radiation source (ship) is in the common view area of ​​the three satellites. Their relative position relationship is as follows: Figure 8 shown.

[0195] Assume that the position error of the low-orbit satellite in each direction is 5m (1σ, σ is the mean square error), the position error of the high-orbit satellite in each direction is 200m (1σ), and the time difference estimation error of the radiation source signal is 600ns (1σ). Substitute the various errors into formula (24) to obtain the covariance matrix Covariance matrix Representing the error distribution, the CEP distribution of the positioning system can be obtained.

[0196] like Figure 9 As shown in the figure, it can be seen that the positioning accuracy near the low-orbit satellite sub-satellite point is better than 2km, achieving high-precision positioning of the radiation source, and there is no positioning blind spot in the low-latitude area. The typical high-orbit three-star time difference positioning system has a positioning blind spot in the low-latitude area, such as Figure 10 shown.

[0197] In summary, the three-star time difference positioning system based on reverse transmission according to the embodiment of the present invention has the following beneficial effects:

[0198] 1. This invention uses a method whereby a low-orbit secondary satellite transparently forwards signals to the primary satellite, and a high-orbit primary satellite uniformly and covertly forwards signals to the ground. Simultaneously, an interference signal is added to the primary satellite's forwarded signal, and interference is canceled on the ground, achieving flexible and covert forwarding of signals received on the ground. The primary satellite uses a synchronous orbit satellite, and the secondary satellites use two low-orbit satellites. Three-way time difference positioning is performed on the ground, achieving high-precision positioning of all radiation source signals within the working frequency band, thereby significantly improving the positioning efficiency of large-scale radiation source signals.

[0199] 2. The present invention overcomes the positioning blind spot problem of the high-orbit three-satellite time difference positioning system in low-latitude areas. By combining high-orbit satellites and low-orbit satellites, the present invention can achieve real-time transparent forwarding over a large range, effectively expanding the positioning coverage range and reducing the positioning blind spots caused by geographical location restrictions.

[0200] 3. The radiation source positioning capability of the present invention is based on the positioning and processing capability of the ground receiving station and is not limited by the onboard processing capability. It can achieve high-precision positioning of all radiation source signals within the three-satellite common view area, greatly improving the positioning efficiency of the radiation source.

[0201] 4. The low-orbit satellite of the present invention transparently forwards signals to the high-orbit satellite in reverse. The high-orbit satellite uses scrambling technology for confidential transmission, thus realizing the covert forwarding of signals received on the ground. At the same time, it overcomes the limitation of transparent forwarding of low-orbit satellites being restricted by the location of ground receiving stations.

[0202] 5. The satellite self-positioning information of the present invention is modulated and transmitted to the ground receiving station simultaneously with the forwarding signal, which is decoupled from the ground operation and control system, making positioning more flexible.

[0203] 6. The three-star time difference positioning method of the present invention can expand the processing capacity of the ground receiving station according to specific needs, and can adapt to different application scenarios and positioning requirements.

[0204] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A three-star time difference positioning method based on reverse transmission, characterized in that: The steps include: Step S1: The first and second secondary satellites respectively receive radiation source signals, obtain first and second reverse transparent forwarding signals based on the respectively received radiation source signals and self-positioning position information, and forward them reversely to the primary satellite; Step S2: The master satellite generates a master satellite covert forwarding signal based on the radiation source signal received by itself, the master satellite self-positioning position information, and the first and second reverse transparent forwarding signals received, and sends the signal to the ground receiving station; Step S3: The ground receiving station performs interference cancellation and demodulation on the concealed forwarding signal of the primary satellite to obtain the radiation source signal received by the primary satellite and the self-positioning position information of the primary satellite, as well as the radiation source signal received by the first and second secondary satellites and the self-positioning position information of the first and second secondary satellites; Based on the radiation source signals received by the primary satellite, the first secondary satellite and the second secondary satellite, time difference information between the primary satellite and the first secondary satellite and between the primary satellite and the second secondary satellite is obtained; Constructing a time difference equation based on the time difference information and the self-positioning position information of the primary satellite and the first and second secondary satellites, and jointly solving the time difference equation and the earth surface constraint equation to obtain the positioning position of the radiation source; The ground receiving station uses a ground receiving and positioning system to perform interference cancellation and demodulation on the concealed forwarding signal of the primary satellite to obtain the radiation source signals received by the primary satellite and the first and second secondary satellites, as well as the self-positioning position information of the primary satellite and the first and second secondary satellites; Based on the self-positioning position information, the position vectors r1, r2, and r3 of the primary satellite, the first secondary satellite, and the second secondary satellite in the geocentric fixed coordinate system are obtained, and the position vector of the radiation source in the geocentric fixed coordinate system is set to r p ; Based on r1, r2, r3, r p and the speed of light, and obtain the real time difference Δt between the radiation source signal reaching the primary star and the first secondary star 21 pt The expression of, and the real time difference Δt between the primary star and the second secondary star 31 pt Expressions of The ground receiving and positioning system extracts the radiation source signals received by the primary satellite, the first secondary satellite, and the second secondary satellite as s1(n), s2(n), and s3(n), respectively, and calculates the time difference estimation value Δt between s1(n) and s2(n) 21 pa , the estimated time difference Δt between s1(n) and s3(n) 31 pa ; Based on Δt 21 pt , Δt 31 pt and Δt 21 pa , Δt 31 pa The relationship between them is converted to construct the time difference equation; The time difference equation is solved jointly with the earth surface constraint equation, as shown in formulas (1)-(3): Among them, formulas (1)-(2) are time difference equations, and formula (3) is the earth surface constraint equation; x pe 、y pe 、z pe are the coordinates of the radiation source in the x-axis, y-axis, and z-axis directions of the Earth-centered fixed coordinate system, [x pe ,y pe ,z pe ] T =r p , a and e are the semi-major axis and oblateness of the Earth, respectively.

2. The method according to claim 1, characterized in that The primary satellite generates a primary satellite concealed forwarding signal based on the radiation source signal received by the primary satellite, the primary satellite self-positioning position information, and the first and second received reverse transparent forwarding signals, including: The master satellite receives the ground radiation source signal, amplifies and filters it, and obtains the master satellite broadband receiving signal; Up-converting the primary satellite broadband received signal to obtain an up-converted primary satellite broadband received signal; The master satellite self-positioning information is modulated and digital-to-analog converted to obtain a master satellite modulation signal; Up-converting the master satellite modulation signal to obtain an up-converted master satellite modulation signal; Adjusting the relative amplitudes of the up-converted primary satellite bandwidth received signal and the up-converted primary satellite modulated signal, and combining them to obtain a primary satellite combined signal; The primary satellite combines the primary satellite combined signal and the first and second reverse transparent forwarding signals to obtain a three-star combined signal; The main satellite generates an interference signal, adjusts the amplitude of the interference signal, and combines it with the combined signal of the three satellites to obtain a total combined signal; The amplitude of the total combined signal is adjusted and amplified to obtain a primary satellite concealed forwarding signal.

3. The method according to claim 1, characterized in that The step S1 comprises: The first and second secondary satellites respectively receive ground radiation source signals, and respectively amplify and filter them to obtain first and second secondary satellite broadband receiving signals; Up-converting the first and second secondary satellite broadband received signals respectively to obtain first and second secondary satellite up-converted broadband received signals; The self-positioning position information of the first and second secondary satellites is modulated and converted into first and second secondary satellite modulation signals after digital-to-analog conversion; After the first and second secondary satellite modulation signals are up-converted, the first and second secondary satellite up-converted modulation signals are obtained respectively; Adjusting the relative amplitudes of the broadband received signal after up-conversion by the first secondary satellite and the modulated signal after up-conversion, and then combining them, adjusting the amplitude of the combined signal and amplifying it to obtain a first reverse transparent forwarding signal; Adjust the relative amplitudes of the broadband received signal after up-conversion by the second secondary satellite and the modulated signal after up-conversion, then combine them, adjust the amplitude of the combined signal and amplify it to obtain a second reverse transparent forwarding signal.

4. The method according to claim 2, characterized in that The master satellite covert forwarding signal is covertly forwarded to the ground receiving station through a forwarding link between the master satellite and the ground receiving station.

5. The method according to claim 2, characterized in that: The interference signal bandwidth is consistent with the three-star combined signal bandwidth, and the interference signal amplitude is higher than the three-star combined signal amplitude; The interference signal spectrum overlaps with the three-star combined signal spectrum, and the three-star combined signal is buried under the interference signal spectrum; The interference signal is a spread spectrum signal with a known spread spectrum code.

6. The method according to claim 1, characterized in that The first and second reverse transparent forwarding signals are forwarded reversely to the primary satellite via the first and second intersatellite links respectively.

7. The method according to any one of claims 1 to 6, characterized in that: The primary satellite, the first secondary satellite and the second secondary satellite have the same ground receiving working frequency band.

8. The method according to any one of claims 1 to 6, characterized in that: The primary satellite is a high-orbit satellite, and the first and second secondary satellites are low-orbit satellites.

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