Secondary satellite load design method applied to ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning

Abstract

The invention relates to a secondary satellite load design method applied to ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning. The method comprises the following steps of: calculating analog ground noise total power PNAD of an input AD and a maximum gain value Gmax of a secondary satellite receiving load channel; calculating the signal-to-noise ratio SNRr of the auxiliary satellite receiving signal, and obtaining the power spectrum density Ssignal of the auxiliary satellite receiving signal at the AD inlet end; selecting an AD device according to the instantaneous working bandwidth and the AD quantization bits, calculating the quantization noise power spectrum density SSNR of the selected AD device, and further obtaining the quantization signal-to-noise ratio SNRd of the received signal after AD quantization; calculating a gain minimum value Gmin based on a set AD quantization signal-to-noise ratio threshold value and the SNRd; if Gmax is greater than or equal to Gmin, taking the selected AD device as an AD device of a secondary satellite receiving load channel link, and selecting an arbitrary value between Gmin and Gmax as a channel gain design value; otherwise, the AD device with the signal-to-noise ratio higher than the current signal-to-noise ratio is selected again until the condition that Gmax is larger than or equal to Gmin is met, and the selected AD device is obtained; the selected AD device, the channel gain design value, the receiving channel noise coefficient and the instantaneous working bandwidth are designed for a secondary satellite load top layer.

Description

Technical Field

[0001] The present invention relates to the field of radio positioning technology, and in particular to a secondary satellite payload design method applied to ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning. Background Art

[0002] With the development of radio positioning technology, multi-satellite time difference of arrival (TDOA) or time frequency difference of arrival (TDOA / FDOA) positioning system is one of the means to obtain high-precision positioning of the radiation source. In general, the receiving signal-to-noise ratio of multiple satellites of this positioning system for the target signal is equivalent, and there will be no asymmetric situation of high and low receiving signal-to-noise ratio of the main and secondary satellites, and there is no special requirement for the design of the target signal receiving payload of the positioning system.

[0003] However, for weak signal or high-orbit multi-satellite positioning systems, the gain of the main satellite receiving antenna is generally relatively high, which can realize target signal identification and demodulation. Considering the engineering cost, the gain of the secondary satellite receiving antenna is generally relatively small, which can only realize zero signal-to-noise ratio or negative signal-to-noise ratio reception of the target signal, and cooperate with the extraction of time-frequency difference, that is, asymmetric time-frequency difference positioning occurs. Especially for high-frequency target signals, such as X (frequency range of 8-12GHz), Ku (frequency range of 12-18GHz) and above, the main lobe and side lobe of these terminal antennas are relatively large. The main satellite is aligned with the main lobe of the target signal terminal antenna, which can achieve a higher positive signal-to-noise ratio. The general design considers about 15dB. At the same time, in order to obtain higher positioning accuracy, the distance between the main and secondary satellites cannot be too small. At this time, the main lobe of the secondary satellite receiving antenna may be aligned with the far side lobe of the terminal antenna, and the gain of the secondary satellite receiving antenna itself is relatively low. The two reasons The main factors (the main lobe of the secondary satellite's receiving antenna may be aligned with the far side lobe of the terminal antenna, and the secondary satellite's receiving antenna gain is relatively low) are coupled together, which will lead to a very low signal-to-noise ratio of the secondary satellite's reception, with a signal-to-noise ratio less than -30dB, or even an ultra-low negative signal-to-noise ratio less than -40dB. At this time, the difference in the receiving signal-to-noise ratio of the main and secondary satellites reaches more than 50dB of asymmetry. If the traditional receiving payload design idea is used to design the secondary satellite's receiving payload, it will no longer be able to effectively quantify the target signal characteristics, which will lead to the inability to effectively estimate the time-frequency difference between the main and secondary satellites, making the multi-satellite positioning system invalid. Summary of the invention

[0004] In view of the above analysis, an embodiment of the present invention aims to provide a secondary satellite payload design method for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning, so as to solve the technical problem of how to design the secondary satellite payload when the signal-to-noise ratio of the secondary satellite received signal is extremely low, so as to effectively quantize the target signal and achieve high-precision positioning of the target signal.

[0005] The present invention provides a secondary satellite payload design method for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning, comprising the following steps:

[0006] Step S1: Calculate the total analog noise floor power P of the input AD based on the instantaneous working bandwidth of the secondary satellite receiving payload and the noise coefficient of the receiving channel. NAD and the maximum value of the secondary satellite receiving payload channel gain G max ;

[0007] Step S2: Calculate the signal-to-noise ratio (SNR) of the secondary satellite receiving signal based on the EIRP, signal bandwidth, antenna pattern characteristics of the ground radiation source target, the secondary satellite receiving antenna gain, and the receiving channel noise coefficient. r , obtain the power spectrum density S of the secondary satellite receiving signal at the AD input end signal ;

[0008] Step S3: Select the AD device of the secondary satellite payload channel link according to the instantaneous working bandwidth and the number of AD quantization bits, obtain the sampling rate and the corresponding signal-to-noise ratio based on the selected AD device, and calculate the quantization noise power spectrum density S of the selected AD device. SNR , and then obtain the quantized signal-to-noise ratio SNR of the received signal after AD quantization d ; Based on the set AD quantization signal-to-noise ratio threshold, and SNR d The minimum gain value G of the secondary satellite receiving payload channel is calculated min ;

[0009] Step S4: If G max ≥G min , then the selected AD device is used as the AD device of the secondary satellite receiving payload channel link, and G min With G max Any value between G and G is used as the channel gain design value; otherwise, return to step S3 to reselect an AD device with a higher signal-to-noise ratio than the current AD device until G is satisfied. max ≥G min A selected AD device is obtained; the selected AD device, channel gain design value, receiving channel noise coefficient and instantaneous working bandwidth are used as the top-level design of the secondary satellite payload for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning.

[0010] Furthermore, the total analog noise floor power P of the input AD NAD , calculated as follows:

[0011] P NAD =G+N f +10×log10(MT 0 k) Formula (1)

[0012] Among them, G is the receiving channel gain, N f is the noise coefficient of the receiving channel, M is the instantaneous working bandwidth of the secondary satellite receiving payload, T 0 is the reference temperature and k is the Boltzmann constant.

[0013] Furthermore, the maximum value of the receiving channel gain of the secondary satellite payload is G max , calculated as follows:

[0014] To prevent AD saturation, let:

[0015] P NAD ≤-1dBFS-E Formula (2)

[0016] Combining formulas (1)-(2), we get:

[0017] G≤-1dBFS-EN f -10×log10(MT 0 k) Formula (3)

[0018] According to inequality (3), we can get the maximum value of G max for:

[0019] G max =-1dBFS-EN f -10×log10(MT 0 k) Formula (4)

[0020] Among them, -1dBFS is 1dB less than the full-scale level of the AD, and E is the design margin for protecting the AD from saturation.

[0021] Furthermore, according to the AD full-scale level, the design margin E for protecting the AD from unsaturation is designed as follows:

[0022] When only analog noise floor input is used, the AD quantization bit number is one less than the full-scale level, that is, the total power of analog noise floor is about 6dB less than the AD full-scale level, and the design margin E is about 5dB.

[0023] Furthermore, the signal-to-noise ratio (SNR) of the secondary satellite receiving signal is r , calculated as follows:

[0024] SNR r =EIRP-L d -N f-10×log 10 (BT 0 k) Formula (5)

[0025] Where EIRP is the equivalent isotropic radiated power of the ground terminal radiation source target, L d is the total loss of the uplink, including propagation loss and mismatch loss between the transmitting antenna and the receiving antenna.

[0026] Furthermore, the power spectrum density of the secondary satellite receiving signal at the AD input end is calculated as follows:

[0027] S signal =G+N f +10×log 10 (T 0 k)+SNR r Formula (6)

[0028] Among them, S signal is the power spectrum density of the secondary satellite receiving signal at the AD input end.

[0029] Furthermore, the quantization noise power spectral density S of the selected AD device is calculated. SNR ,as follows:

[0030] S SNR =-1dBFS-SNR AD -10×log10(f S / 2) Formula (7)

[0031] Among them, SNR AD 、f S are the signal-to-noise ratio and sampling rate of the AD device respectively.

[0032] Furthermore, the received signal is quantized by AD to obtain a quantized signal-to-noise ratio (SNR). d ,as follows:

[0033] SNR d =S signal -S SNR Formula (8)

[0034] According to formulas (5)-(8), calculate SNR d ,as follows:

[0035] SNR d =G+N f +10×log10(T 0 k)+SNR r -S SNR Formula (9).

[0036] Furthermore, the minimum gain G of the AD receiving channel min , calculated as follows:

[0037] SNR d ≥SNR th Formula (10)

[0038] According to formulas (9)-(10), we can get G min ,as follows:

[0039] G min =SNR th +S SNR -SNR r -N f -10×log10(T 0 k) Formula (11)

[0040] Among them, SNR th is the quantization signal-to-noise ratio threshold.

[0041] Furthermore, the channel link of the secondary satellite payload includes a secondary satellite receiving antenna, a radio frequency front end, a superheterodyne receiver, an AD device and a digital processor;

[0042] The target signal of the ground terminal radiation source enters the RF front end of the secondary satellite receiving payload channel through the secondary satellite receiving antenna, and is amplified and filtered to obtain an amplified and filtered analog signal;

[0043] The amplified and filtered analog signal is input into a superheterodyne receiver, and the amplified and filtered target signal is further amplified and frequency-converted, and then input into the AD device to convert the analog signal output by the superheterodyne receiver into a digital signal;

[0044] The digital signal finally enters a digital processor for digital processing to obtain a processed digital signal.

[0045] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0046] 1. The secondary satellite payload design method proposed in the present invention solves the problem of ultra-low negative signal-to-noise ratio asymmetric time-frequency difference extraction, supports multi-satellite asymmetric time-frequency difference positioning, and especially targets the ultra-low negative signal-to-noise ratio reception of the secondary satellite, avoids the problem of being unable to quantify due to too low signal-to-noise ratio, and improves the adaptability of multi-satellite asymmetric positioning;

[0047] 2. According to the implementation steps of the present invention, the selection of AD for the secondary satellite payload and the top-level design of the channel gain can be guided; the secondary satellite payload designed according to the present invention cooperates with the primary satellite, and under the condition of ultra-low negative signal-to-noise ratio reception of the secondary satellite, the asymmetric time-frequency difference extraction of the primary and secondary satellites can be realized, and the ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning problem can be realized, which makes up for the lack of multi-satellite time-frequency difference positioning capability of high-frequency band signals such as X and Ku; the invention has been applied in actual model engineering, and has realized the ultra-low negative signal-to-noise ratio asymmetric time-frequency difference high-precision positioning of multi-satellite joint;

[0048] 3. The present invention enhances the asymmetric adaptability of the system. When the difference in signal-to-noise ratio between the primary and secondary satellites reaches an asymmetry of more than 50 dB, the present invention provides a design method that enables the secondary satellite to effectively participate in the time-frequency difference positioning, thereby enhancing the system's adaptability to such asymmetric conditions.

[0049] 4. The present invention optimizes the selection and use of AD devices. By calculating the quantization noise power spectrum density of AD devices and setting the quantization signal-to-noise ratio threshold value, the present invention can accurately select and design AD devices and receiving channel gains suitable for ultra-low negative signal-to-noise ratio environments, thereby optimizing the digital processing and subsequent processing of signals;

[0050] 5. The present invention realizes the refined design of the secondary satellite receiving payload. The present invention not only takes into account the integrated design of the secondary satellite receiving antenna, RF front end, superheterodyne receiver, AD device and digital processor, but also pays special attention to the special needs of ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning, thereby realizing the refined design and optimization of the secondary satellite receiving payload.

[0051] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The drawings are only for the purpose of illustrating specific embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0053] Figure 1 This is a flow chart of a secondary satellite payload design method for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning in an embodiment of the present invention;

[0054] Figure 2 Schematic diagram of a typical scenario of ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning application in an embodiment of the present invention;

[0055] Figure 3This is a schematic diagram of a secondary satellite receiving payload channel link in an embodiment of the present invention;

[0056] Figure 4 Schematic diagram of AD working characteristics of a traditional receiving payload in an embodiment of the present invention;

[0057] Figure 5 Schematic diagram of the relative relationship between the analog noise floor, the AD noise floor, and the received signal spectrum under the ultra-low negative signal-to-noise ratio reception condition in an embodiment of the present invention;

[0058] Figure 6 This is a ground verification test block diagram of ultra-low negative signal-to-noise ratio time-frequency difference extraction in an embodiment of the present invention;

[0059] Figure 7 This is a spectrum diagram of signals received by the primary and secondary satellite payloads in an embodiment of the present invention;

[0060] Figure 8 Schematic diagram of the time-frequency difference correlation peak of the signals received by the primary and secondary satellites in an embodiment of the present invention. DETAILED DESCRIPTION

[0061] The preferred embodiments of the present invention are 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, but are not used to limit the scope of the present invention.

[0062] The present invention is suitable for multi-satellite asymmetric time-frequency difference positioning. For the ultra-low negative signal-to-noise ratio reception situation of the secondary satellite, the time-frequency difference can be accurately extracted, thereby achieving the purpose of accurately positioning the ground terminal radiation source by the ultra-low negative signal-to-noise ratio asymmetric multi-satellite time-frequency difference.

[0063] The secondary satellite payload design method proposed in the present invention is applied to an ultra-low negative signal-to-noise ratio asymmetric multi-satellite time-frequency difference positioning system. When the primary and secondary satellites receive signals with an ultra-low negative signal-to-noise ratio asymmetric, effective estimation of the time-frequency difference can still be achieved, thereby achieving high-precision positioning of the target signal. Compared with the traditional multi-satellite positioning system that can only adapt to target signals below the C band (frequency range of 4-8GHz), after applying the design method of the present invention, the positioning signal frequency band can be extended to the X and Ku bands, or even higher frequency bands, and the positioning capability will be greatly improved. The present invention has broad application prospects in multi-satellite high-precision positioning of high-frequency band target signals.

[0064] At present, the receiving payloads of the main and secondary satellites of the multi-satellite positioning system adopt the same design, and their ability to extract the time-frequency difference of asymmetric signal-to-noise ratio is relatively weak, resulting in the current multi-satellite high-precision time-frequency difference positioning of target signals below the C band, and the lack of positioning capability of high-frequency band target signals above X and Ku. In view of this situation, it is necessary to specially design the receiving payload of the secondary satellite of the multi-satellite positioning system so that it can still effectively quantize the received signal under the condition of ultra-low negative signal-to-noise ratio of the received signal, obtain effective estimation of the time-frequency difference under the asymmetric condition of ultra-low negative signal-to-noise ratio, and thus realize high-precision positioning of the radiation source target signal.

[0065] The present invention proposes a secondary satellite payload design method for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning. The typical application scenarios of this method are as follows: Figure 2 shown.

[0066] Satellite i is the master satellite, and its high-gain receiving antenna is aligned with the main lobe of the antenna of the ground terminal radiation source. The master satellite is located in the main radiation direction of the ground terminal radiation source. Due to the high gain of the master satellite receiving antenna, it can receive the target signal with a high signal-to-noise ratio, and can achieve a positive signal-to-noise ratio reception of the target signal of the ground terminal radiation source;

[0067] Satellite j is a secondary satellite, and its low-gain receiving antenna is aimed at the antenna sidelobe direction of the ground terminal radiation source. The received signal comes from the antenna sidelobe direction of the ground terminal radiation source. The secondary satellite is located in the secondary radiation direction of the ground terminal radiation source. At the same time, considering the engineering implementation cost, due to the low gain of the secondary satellite receiving antenna, the signal-to-noise ratio of the received target signal is extremely low, resulting in an asymmetric signal-to-noise ratio between the main and secondary satellites, resulting in an ultra-low negative signal-to-noise ratio.

[0068] The difference in signal-to-noise ratio between the primary and secondary satellites is called signal-to-noise ratio asymmetry. Under ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning conditions, the secondary satellite may not be able to effectively participate in time-frequency difference positioning because the signal received by the secondary satellite is too weak to extract useful information from it.

[0069] When the signal-to-noise ratio of the signal received by the secondary satellite is extremely low, even lower than -30dB or -40dB, this situation is called ultra-low negative signal-to-noise ratio. Under this condition, the traditional secondary satellite receiving payload design may not work effectively because the signal is submerged by the noise and is difficult to quantify and process effectively.

[0070] In order to achieve effective signal processing under ultra-low negative signal-to-noise ratio conditions, the secondary satellite payload needs to be specially designed to improve the signal reception and processing capabilities, including selecting appropriate receiving channel gain and selecting AD devices with lower noise characteristics.

[0071] In a multi-satellite positioning system, the coordinated work of the primary and secondary satellites is crucial to achieve high-precision positioning. That is, when the signal-to-noise ratio of the signal received by the secondary satellite is extremely low, the secondary satellite payload design is required to ensure the effective extraction of the time-frequency difference.

[0072] In order to obtain multi-satellite time-frequency difference estimation, the secondary satellite receiving payload must be able to effectively quantify the target signal, that is, the power spectrum density of the target signal from the ground terminal radiation source reaching the secondary satellite AD must be greater than the noise floor power spectrum density of the secondary satellite AD itself, and it needs to be at least 10dB. Only when the received ground terminal radiation source target signal power is higher than the secondary satellite AD noise floor power, can the AD effectively quantize and characterize the target signal.

[0073] The power spectral density difference between the target signal of the ground terminal radiation source and the background noise of the secondary satellite AD needs to be at least 10dB. This 10dB margin ensures that the target signal can be clearly quantized in the AD, reduces quantization errors, and improves the reliability of signal processing.

[0074] If the power spectral density of the target signal is lower than the AD noise floor, or the signal-to-noise ratio is less than 10dB, the target signal will be submerged by the noise or be equivalent to the noise, resulting in the inability to accurately extract the time-frequency difference, which in turn affects the target positioning accuracy.

[0075] like Figure 3 As shown, the secondary satellite receiving payload channel link is as follows:

[0076] The channel link of the secondary satellite payload includes a secondary satellite receiving antenna, a radio frequency front end, a superheterodyne receiver, an AD device and a digital processor;

[0077] The target signal of the ground terminal radiation source enters the RF front end of the secondary satellite receiving payload channel through the secondary satellite receiving antenna, and is amplified and filtered to obtain an amplified and filtered analog signal;

[0078] The amplified and filtered analog signal is input into a superheterodyne receiver, and the amplified and filtered target signal is further amplified and frequency-converted, and then input into the AD device to convert the analog signal output by the superheterodyne receiver into a digital signal;

[0079] The digital signal finally enters a digital processor for digital processing to obtain a processed digital signal.

[0080] (1) The secondary satellite receiving antenna receives the target signal from the ground terminal radiation source, and the target signal enters the secondary satellite receiving payload channel; the secondary satellite receiving antenna has a small gain and may receive signals in the far sidelobe direction of the ground terminal radiation source, so the target signal is weak;

[0081] (2) The target signal is input into the RF front end, amplified and filtered, and an amplified and filtered analog signal is obtained;

[0082] Amplification: The received target signal is first amplified at the RF front end to increase the target signal strength.

[0083] Filtering: The amplified target signal passes through a filter to remove noise and interference, ensuring that only the desired signal components are retained.

[0084] (3) The amplified and filtered analog signal is input into a superheterodyne receiver, which further amplifies and frequency-converts the amplified and filtered target signal to ensure that the signal strength is sufficient to be processed by subsequent AD devices;

[0085] (5) AD device: converts the analog signal output by the superheterodyne receiver into a digital signal;

[0086] (6) The digital signal finally enters a digital processor for digital processing; for example, such as digital down-conversion, signal extraction, signal filtering, etc.; and the processed digital signal is obtained.

[0087] According to traditional design ideas, it is necessary to focus on the trade-off between the minimum received signal and the two-tone dynamic range of the receiving channel, that is, taking the signal bandwidth of the minimum received signal as the processing resolution, design the gain of the secondary satellite receiving channel so that no spurious signals appear in the secondary satellite receiving payload channel, and at the same time maximize the two-tone dynamic range.

[0088] The AD working characteristics of the traditional receiving payload are as follows: Figure 4 As shown, the horizontal axis is the sampling frequency f s / 2, the number of times the AD collects analog signals per second, in hertz; the ordinate is the level, in dBm (decibel milliwatt), where SFDR (Spurious-Free Dynamic Range) is the spurious-free dynamic range of the AD, which indicates the ratio of the input signal level to the maximum spurious level when the analog sweep input at the AD input is -1dBFS (1dB less than the full-scale level). The two level ranges of the input signal level and the maximum spurious level are the analog signal range of the normal input AD, that is, the normal working area of ​​the AD. In order to meet the minimum receiving signal processing capability, the analog noise floor power reaching the AD input end (the processing resolution is the signal bandwidth of the minimum receiving signal) needs to be greater than the spurious level of the AD. At this time, for signals with a positive signal-to-noise ratio, the AD spurious level will not affect signal demodulation and other processing.

[0089] A specific embodiment of the present invention, as Figure 1 As shown, a secondary satellite payload design method for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning is disclosed, comprising the following steps:

[0090] Step S1: Calculate the total analog noise floor power P of the input AD based on the instantaneous working bandwidth of the secondary satellite receiving payload and the noise coefficient of the receiving channel. NAD and the maximum value of the secondary satellite receiving payload channel gain G max ;

[0091] Step S2: Calculate the signal-to-noise ratio (SNR) of the secondary satellite receiving signal based on the EIRP, signal bandwidth, antenna pattern characteristics of the ground radiation source target, the secondary satellite receiving antenna gain, and the receiving channel noise coefficient. r , obtain the power spectrum density S of the secondary satellite receiving signal at the AD input end signal ;

[0092] Step S3: Select the AD device of the secondary satellite payload channel link according to the instantaneous working bandwidth and the number of AD quantization bits, obtain the sampling rate and the corresponding signal-to-noise ratio based on the selected AD device, and calculate the quantization noise power spectrum density S of the selected AD device. SNR , and then obtain the quantized signal-to-noise ratio SNR of the received signal after AD quantization d ; Based on the set AD quantization signal-to-noise ratio threshold, and SNR d The minimum gain value G of the secondary satellite receiving payload channel is calculated min ;

[0093] Step S4: If G max ≥G min , then the selected AD device is used as the AD device of the secondary satellite receiving payload channel link, and G min With G max Any value between G and G is used as the channel gain design value; otherwise, return to step S3 to reselect an AD device with a higher signal-to-noise ratio than the current AD device until G is satisfied. max ≥G min A selected AD device is obtained; the selected AD device, channel gain design value, receiving channel noise coefficient and instantaneous working bandwidth are used as the top-level design of the secondary satellite payload for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning.

[0094] The ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning is:

[0095] The high-gain receiving antenna of the main satellite receives the target signal of the ground terminal radiation source with a positive signal-to-noise ratio;

[0096] The signal-to-noise ratio of the target signal received by the ground terminal radiation source by the low-gain receiving antenna of the secondary satellite is extremely low, resulting in the asymmetry of the signal-to-noise ratio between the primary and secondary satellites;

[0097] Under the ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning conditions, the traditional secondary satellite payload cannot effectively participate in the time-frequency difference positioning of the target signal of the ground terminal radiation source.

[0098] Step S1, specifically.

[0099] Let the noise coefficient of the secondary satellite receiving channel be N f (is the design value of the actual payload of the secondary satellite, which can be measured), the channel gain is G, and the minimum receiving signal bandwidth is B. Then the power S of the simulated background noise power reaching the entrance of the AD device under the bandwidth B is NAD , as shown in formula (1):

[0100] S NAD =G+N f +10×log10(BT 0 k) Formula (1)

[0101] Among them, T 0 is the reference temperature (usually 290°C, a common value), and k is the Boltzmann constant.

[0102] According to the traditional receiving load design concept, as long as S NAD ≥AD spurious level, and consider a certain design margin D. The design margin D is the value at which the AD spurious level is less than the analog noise floor level, so as not to affect the signal-to-noise ratio of the received signal.

[0103] The minimum receiving signal bandwidth B of the secondary satellite receiving channel takes into account the ground terminal radiation source positioning task requirements. In order to meet the ground radiation source positioning accuracy requirements, the secondary satellite receiving system must be able to process the minimum value of the signal bandwidth range.

[0104] Let the AD spurious level be S SFDR , then we only need to satisfy the conditions shown in formula (2):

[0105] S NAD ≥S SFDR +D Formula (2)

[0106] Where D is the design margin required to meet minimum signal processing requirements.

[0107] Substituting formula (1) into formula (2), we get formula (3):

[0108] G≥S SFDR +DN f -10×log10(BT 0 k) Formula (3)

[0109] According to the receiving channel noise coefficient N f , AD spurious level S SFDR , minimum receiving signal bandwidth B, design margin D, and design channel gain G of the secondary satellite receiving payload.

[0110] For the secondary satellite receiving payload in the ultra-low negative signal-to-noise ratio reception situation, if this design method is followed, since the received signal has been buried 40 to 50 dB below the analog noise floor, the signal is already below the AD noise floor, that is, the received signal cannot be effectively quantized and characterized by AD, resulting in the primary and secondary satellites being unable to perform time-frequency difference correlation extraction on the received signal.

[0111] In order to maximize the number of effective bits of the received signal quantized by AD, the power spectral density of the received signal input to AD needs to be as large as possible, that is, the channel gain G needs to be increased. However, G cannot be too large and cannot exceed the full-scale range of AD. Otherwise, AD saturation and received signal distortion will occur, making it impossible to extract the time-frequency difference.

[0112] For ultra-low negative signal-to-noise ratio reception, the relative relationship between the channel analog noise floor, AD noise floor, and received signal spectrum is as follows: Figure 5 As shown in Figure 1, the received signal spectrum is already below the simulated noise floor, and the relative power level difference is the received signal-to-noise ratio (SNR) of the received signal. r Since the spurious level basically does not affect the time-frequency difference extraction, it is only necessary to ensure that the received signal spectrum is higher than the AD noise floor. The relative power level difference is the quantized signal-to-noise ratio (SNR) of the received signal quantized by AD. d .

[0113] In order to make SNR d As large as possible, the channel gain G needs to be increased. At this time, for the broadband receiving load, its analog background noise power dominates the receiving channel power, that is, the total analog background noise power P of the input AD NAD .

[0114] The total power P of the analog noise floor of the input AD NAD , as shown in formula (4):

[0115] P NAD =G+N f +10×log10(MT 0 k) Formula (4)

[0116] Among them, G is the receiving channel gain, N f is the noise coefficient of the receiving channel, M is the instantaneous working bandwidth of the secondary satellite receiving payload, T 0 is the reference temperature and k is the Boltzmann constant.

[0117] According to the AD full-scale level, the design margin E to protect the AD from saturation is designed as follows:

[0118] When only analog noise floor input is used, the AD quantization bit number is one less than the full-scale level, that is, the total power of analog noise floor is about 6dB less than the AD full-scale level, and the design margin E is about 5dB.

[0119] The maximum value of the receiving channel gain G of the secondary satellite payload max , calculated as follows:

[0120] To prevent AD saturation, let:

[0121] P NAD ≤-1dBFS-E Formula (5)

[0122] Combining formulas (4)-(5), we get inequality (6):

[0123] G≤-1dBFS-EN f -10×log10(MT 0 k) Formula (6)

[0124] According to inequality (6), we can get the maximum value of G max As shown in formula (7):

[0125] G max =-1dBFS-EN f -10×log10(MT 0 k) Formula (7)

[0126] Among them, -1dBFS is 1dB less than the full-scale level of the AD, and E is the design margin for protecting the AD from saturation.

[0127] In order to prevent AD from saturation and stabilize in a reasonable working state, P NAD Need to meet P NAD ≤-1dBFS-E relationship.

[0128] E is the preset value, which can generally be considered to be around 5dB.

[0129] E and D are not the same concept. D is the design margin of the minimum signal being higher than the spurious level. In this patent, since the traditional load design concept is no longer used, D will no longer be used. E is the design margin of the entire channel analog noise floor being less than the -1dBFS input of the AD.

[0130] The function of step S1 is to calculate the total analog noise floor power and the maximum channel gain of the input AD of the secondary satellite receiving payload to ensure effective quantization of the received signal and avoid AD saturation.

[0131] Step S2, specifically.

[0132] According to the EIRP value, signal bandwidth, antenna pattern characteristics of the ground radiation source target, the gain of the secondary satellite receiving antenna, and the noise coefficient of the receiving channel, the signal-to-noise ratio (SNR) of the secondary satellite receiving signal is determined through the receiving link budget. r .

[0133] The signal-to-noise ratio (SNR) of the secondary satellite receiving signal r , calculated as follows:

[0134] SNR r =EIRP-L d -N f -10×log 10 (BT 0 k) Formula (8)

[0135] Where EIRP is the equivalent isotropic radiated power of the ground terminal radiation source target, L d is the total loss of the uplink, including propagation loss and mismatch loss between the transmitting antenna and the receiving antenna. The power spectral density of the simulated background noise at the AD input is G+N f +10×log10(T 0 k), since the received signal-to-noise ratio is SNR r , then calculate the power spectrum density S of the secondary satellite receiving signal at the AD input end signal , calculated as shown in formula (9):

[0136] S signal =G+N f +10×log 10 (T 0 k)+SNR r Formula (9)

[0137] The function of step S2 is to calculate the signal-to-noise ratio of the secondary satellite receiving signal and determine the power spectrum density at the AD input end by comprehensively considering the EIRP value, signal bandwidth, antenna pattern characteristics, secondary satellite receiving antenna gain and receiving channel noise coefficient of the ground radiation source target.

[0138] Step S3, specifically.

[0139] According to the system's instantaneous working bandwidth, AD quantization bit number and other requirements, select the AD device of the secondary satellite receiving payload channel link. Based on the selected AD device, consult the manual to obtain the signal-to-noise ratio corresponding to the required working sampling rate, and calculate the quantization noise power spectral density S of the selected AD device. SNR .

[0140] The quantization noise power spectral density S of the selected AD device is calculated. SNR , as shown in formula (10):

[0141] S SNR =-1dBFS-SNR AD -10×log10(f S / 2) Formula (10)

[0142] Among them, SNR AD 、f S are the signal-to-noise ratio and sampling rate of the AD device respectively.

[0143] AD device characteristics, different sampling frequencies f S Corresponding to different signal-to-noise ratios SNR AD .

[0144] The quantized signal-to-noise ratio SNR of the received signal after AD quantization d , as shown in formula (11):

[0145] SNR d =S signal -S SNR Formula (11)

[0146] According to formulas (8)-(11), calculate SNR d , as shown in formula (12):

[0147] SNR d =G+N f +10×log10(T 0 k)+SNR r -S SNR Formula (12)

[0148] SNR d Must be greater than or equal to the AD quantization signal-to-noise ratio threshold SNR th (about 10dB can be considered) to effectively quantize the received signal, SNR th is the preset design value;

[0149] By SNR d Must be greater than or equal to the AD quantization signal-to-noise ratio threshold SNR th , we get formula (13):

[0150] SNR d ≥SNR th Formula (13)

[0151] This gives formula (14):

[0152] G+N f +10×log10(T 0 k)+SNR r -S SNR ≥SNR th Formula (14)

[0153] Based on formula (14), we get formula (15):

[0154] G ≥ SNR th -Nf -10×log10(T 0 k)-SNR r +S SNR Formula (15)

[0155] Based on formulas (14)-(15), the minimum gain G of the AD receiving channel is min , calculated as shown in formula (16):

[0156] G min =SNR th +S SNR -SNR r -N f -10×log10(T 0 k) Formula (16)

[0157] Among them, SNR th is the quantization signal-to-noise ratio threshold.

[0158] The function of step S3 is to select a suitable AD device and calculate the quantization noise power spectrum density based on its signal-to-noise ratio and sampling rate to ensure that the quantization signal-to-noise ratio meets the threshold value requirement, thereby effectively quantizing the received signal.

[0159] Step S4, specifically.

[0160] The value range of the secondary satellite receiving channel gain G is shown in formula (17):

[0161] G∈[G min G max ] Formula (17)

[0162] In general, in order to obtain ultra-low negative signal-to-noise ratio receiving capability, the channel gain G is set as high as possible. It should be noted that in the actual receiving load design, if the received signal noise ratio is very low and the AD quantization noise is relatively large (S SNR The larger the AD quantization noise, the greater the G min >G max In this case, it is necessary to replace the AD chip and re-design and calculate.

[0163] If G max ≥G min , the selected AD device is used as the AD device of the secondary satellite receiving payload channel link; G max as the AD channel gain design value; otherwise, return to step S2 to reselect an AD device with a higher signal-to-noise ratio than the current AD device until G is satisfied. max ≥G min Get the selected AD device.

[0164] Based on the aforementioned selected AD devices, channel gain design values, receiving channel noise coefficient and instantaneous working bandwidth, the top-level design of the secondary satellite payload for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning is proposed.

[0165] The function of step S4 is to determine the gain design value of the secondary satellite receiving channel and verify whether the selected AD device meets the quantitative signal-to-noise ratio requirement. If not, a more suitable AD device is reselected until a suitable AD device is found to ensure effective signal reception and processing under ultra-low negative signal-to-noise ratio conditions.

[0166] In practical applications, for the ultra-low negative signal-to-noise ratio asymmetric time-frequency difference multi-satellite positioning application, the design steps of the secondary satellite receiving payload are as follows:

[0167] (1) Based on the AD full-scale level (generally adjustable to about 0 dBm), the design margin E, the instantaneous working bandwidth M of the secondary satellite receiving payload, and the receiving channel noise coefficient N f According to formula (7), we can get G max ;

[0168] (2) According to the EIRP (Effective Isotropic Radiated Power) value of the ground radiation source target, signal bandwidth, antenna pattern characteristics, as well as the secondary satellite receiving antenna gain and receiving channel noise coefficient, the signal-to-noise ratio (SNR) of the secondary satellite receiving signal is determined through the receiving link budget. r ;

[0169] (3) Select AD devices according to system requirements (system instantaneous working bandwidth requirements, AD quantization bit requirements), and check the device manual to calculate its quantization noise power spectrum density S SNR ;

[0170] (4) Setting the quantization signal-to-noise ratio threshold SNR th , and according to SNR r , S SNR 、N f And formula (16) to get G min ;

[0171] (5) If G max ≥G min , you can directly select G min With G max Any value between 0 and 1 is used as the channel gain design value. Otherwise, return to step 3 and reselect the signal-to-noise ratio SNR. AD Higher AD devices until G max ≥G min , and select the appropriate channel gain value;

[0172] (6) Satisfy G max ≥G min AD device, channel gain G, receiving channel noise coefficient N f After the instantaneous working bandwidth M is determined, the top-level design framework of the secondary satellite payload for ultra-low negative signal-to-noise ratio reception is basically determined, which can be used to guide actual engineering research and development.

[0173] So far, the secondary satellite payload status has been determined, and an ultra-low negative signal-to-noise ratio of SNR can be achieved. r In the actual ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning application, the primary satellite performs signal detection and search, and the secondary satellite blindly samples within the instantaneous working bandwidth. After the primary satellite finds the signal, it cooperates with the secondary satellite to perform time-frequency difference correlation extraction, and then obtains high-precision positioning of the target signal. The specific process will not be described in detail in this invention.

[0174] In order to make the technical effect of the present invention more obvious, a specific example is given below. First, the secondary satellite payload is designed, and then the secondary satellite payload is developed with the design value. Finally, the on-orbit signal receiving situation of the main and secondary satellite payloads is simulated on the ground to verify the ultra-low negative signal-to-noise ratio asymmetric time-frequency difference extraction capability.

[0175] Consider the scenario of high-precision positioning of ground radiation sources by multiple satellites in high orbit. Figure 2 As shown in the figure, it is assumed that the signal-to-noise ratio of the ground radiation source signal received by the primary satellite is 15dB. Let the radiation source terminal work in the X-band, the antenna size is 2.0m, the EIRP is 59dBW, the signal bandwidth is 1MHz, and the secondary satellite receives the incoming signal in the direction of 15 degrees away from the beam center. At this time, the primary-secondary ratio of the ground terminal antenna will reach 45dB. Considering the 10dBi secondary satellite receiving antenna gain, 4dB secondary satellite receiving channel noise coefficient, and 40711km receiving distance, the secondary satellite receiving signal-to-noise ratio is about -45dB, that is, the secondary satellite has an ultra-low negative signal-to-noise ratio reception situation. The specific link calculation and related parameters are shown in Table 1.

[0176] Table 1: Calculation table of the secondary satellite receiving signal link

[0177]

[0178]

[0179] Select a certain type of AD device and check the device manual. When the AD sampling rate is 1600Msps, its signal-to-noise ratio SNR AD The quantization noise power spectral density S is 56.6dB, that is, when the input is -1dBFS (assuming the full-scale level is 0dBm), the noise power in the 800MHz bandwidth is -57.6dBm. SNR It is -176.6dBW / Hz. Considering the quantization signal-to-noise ratio threshold SNR this 10dB, then according to formula (16) we can calculate G min for:

[0180] G min =10-176.6+44.72-4-10×log10(290×1.38e-23)

[0181] =78.12dB

[0182] For G max Calculation, considering that the -1dBFS level of AD is -31dBW (full-scale level is 0dBm), the design margin E is 5dB, and the instantaneous working bandwidth M of the receiving load is 60MHz, then according to formula (7), G can be obtained max for:

[0183] G max =-31-5-4-10×log10(60e6×290×1.38e-23)

[0184] =86dB

[0185] From the above calculation, it can be seen that satisfying G max ≥G min , so the receiving load channel gain can be [G min G max ], the channel gain is 85dB, and the AD device is used to develop the secondary satellite receiving payload. Finally, the primary satellite receiving payload and the secondary satellite receiving payload are verified on the ground for ultra-low negative signal-to-noise ratio time-frequency difference extraction. The test block diagram is as follows Figure 6 shown.

[0186] By setting the signal source output code rate to 1Msps QPSK (Quadrature Phase Shift Keying) modulation signal, and setting the signal source output signal level and attenuator attenuation value, the signal-to-noise ratio of the primary and secondary satellite receiving payloads can be 15dB and -45dB respectively. The signal spectrum received by the primary and secondary satellite payloads is as follows: Figure 7 As shown in the figure, the signal spectrum envelope can be clearly seen on the primary satellite, while only a relatively flat simulated noise floor can be seen on the secondary satellite. At this time, the signal is already below the noise floor. The signals received by the primary and secondary satellites are processed by time-frequency difference correlation, and the accumulation time is set to 1s. The correlation peak is quite obvious, as shown in the figure below. Figure 8 As shown, the time difference extraction error is 102.73ns.

[0187] According to the above conditions, the CR limit (Critical Range, fault tolerance limit of time-frequency difference extraction) of time-frequency difference extraction can be obtained as 70.4ns, and the actual extraction error satisfies about 1 to 3 of the CR limit, indicating that the secondary satellite payload design method proposed in the present invention can realize the time-frequency difference extraction under ultra-low negative signal-to-noise ratio asymmetric conditions and can ensure the extraction accuracy.

[0188] In order to adapt to the ultra-low negative signal-to-noise ratio requirements, AD selection and channel gain design are required, and matching designs with instantaneous working bandwidth, receiving channel noise coefficient, etc. are required. Only through continuous iterative optimization can the on-orbit working requirements of the secondary satellite payload be met.

[0189] In summary, the secondary satellite payload design method for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning according to an embodiment of the present invention has the following beneficial effects:

[0190] 1. The secondary satellite payload design method proposed in the present invention solves the problem of ultra-low negative signal-to-noise ratio asymmetric time-frequency difference extraction, supports multi-satellite asymmetric time-frequency difference positioning, and especially targets the ultra-low negative signal-to-noise ratio reception of the secondary satellite, avoids the problem of being unable to quantify due to too low signal-to-noise ratio, and improves the adaptability of multi-satellite asymmetric positioning;

[0191] 2. According to the implementation steps of the present invention, the selection of AD for the secondary satellite payload and the top-level design of the channel gain can be guided; the secondary satellite payload designed according to the present invention cooperates with the primary satellite, and under the condition of ultra-low negative signal-to-noise ratio reception of the secondary satellite, the asymmetric time-frequency difference extraction of the primary and secondary satellites can be realized, and the ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning problem can be realized, which makes up for the lack of multi-satellite time-frequency difference positioning capability of high-frequency band signals such as X and Ku; the invention has been applied in actual model engineering, and has realized the ultra-low negative signal-to-noise ratio asymmetric time-frequency difference high-precision positioning of multi-satellite joint;

[0192] 3. The present invention enhances the asymmetric adaptability of the system. When the difference in signal-to-noise ratio between the primary and secondary satellites reaches an asymmetry of more than 50 dB, the present invention provides a design method that enables the secondary satellite to effectively participate in the time-frequency difference positioning, thereby enhancing the system's adaptability to such asymmetric conditions.

[0193] 4. The present invention optimizes the selection and use of AD devices. By calculating the quantization noise power spectrum density of AD devices and setting the quantization signal-to-noise ratio threshold value, the present invention can accurately select and design AD devices and receiving channel gains suitable for ultra-low negative signal-to-noise ratio environments, thereby optimizing the digital processing and subsequent processing of signals;

[0194] 5. The present invention realizes the refined design of the secondary satellite receiving payload. The present invention not only takes into account the integrated design of the secondary satellite receiving antenna, RF front end, superheterodyne receiver, AD device and digital processor, but also pays special attention to the special needs of ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning, thereby realizing the refined design and optimization of the secondary satellite receiving payload.

[0195] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for designing a secondary satellite payload for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning, characterized in that: The steps include: Step S1: Calculate the total analog noise floor power P of the input AD based on the instantaneous working bandwidth of the secondary satellite receiving payload and the noise coefficient of the receiving channel. NAD and the maximum value of the secondary satellite receiving payload channel gain G max ; Step S2: Calculate the signal-to-noise ratio (SNR) of the secondary satellite receiving signal based on the EIRP, signal bandwidth, antenna pattern characteristics of the ground radiation source target, the secondary satellite receiving antenna gain, and the receiving channel noise coefficient. r , obtain the power spectrum density S of the secondary satellite receiving signal at the AD input end signal ; Step S3: Select the AD device of the secondary satellite payload channel link according to the instantaneous working bandwidth and the number of AD quantization bits, obtain the sampling rate and the corresponding signal-to-noise ratio based on the selected AD device, and calculate the quantization noise power spectrum density S of the selected AD device. SNR , and then obtain the quantized signal-to-noise ratio SNR of the received signal after AD quantization d ; Based on the set AD quantization signal-to-noise ratio threshold, and SNR d The minimum gain value G of the secondary satellite receiving payload channel is calculated min ; Step S4: If G max ≥G min , then the selected AD device is used as the AD device of the secondary satellite receiving payload channel link, and G min With G max Any value between G and G is used as the channel gain design value; otherwise, return to step S3 to reselect an AD device with a higher signal-to-noise ratio than the current AD device until G is satisfied. max ≥G min A selected AD device is obtained; the selected AD device, channel gain design value, receiving channel noise coefficient and instantaneous working bandwidth are used as the top-level design of the secondary satellite payload for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning.

2. The method according to claim 1, characterized in that: The analog noise floor total power P of the input AD NAD , calculated as follows: P NAD =G+N f +10×log10(MT0k) formula (1) Among them, G is the receiving channel gain, N f is the receiving channel noise coefficient, M is the instantaneous working bandwidth of the secondary satellite receiving payload, T0 is the reference temperature, and k is the Boltzmann constant.

3. The method according to claim 2, characterized in that: The maximum value of the receiving channel gain G of the secondary satellite payload max , calculated as follows: To prevent AD saturation, let: P NAD ≤-1dBFS-E Formula (2) Combining formulas (1)-(2), we get: G ≤ -1dBFS-EN f -10×log10(MT0k) Formula (3) According to inequality (3), we can get the maximum value of G max for: G max = -1dBFS-EN f -10×log10(MT0k) Formula (4) Among them, -1dBFS is 1dB less than the full-scale level of the AD, and E is the design margin for protecting the AD from saturation.

4. The method according to claim 3, characterized in that: According to the AD full-scale level, the design margin E to protect the AD from saturation is designed as follows: When only analog noise floor input is used, the AD quantization bit number is one less than the full-scale level, that is, the total power of analog noise floor is about 6dB less than the AD full-scale level, and the design margin E is about 5dB.

5. The method according to claim 1, characterized in that: The signal-to-noise ratio (SNR) of the secondary satellite receiving signal r , calculated as follows: SNR r = EIRP - L d - N f - 10 × log 10 (BT0k) Equation (5) Where EIRP is the equivalent isotropic radiated power of the ground terminal radiation source target, L d is the total loss of the uplink, including propagation loss and mismatch loss between the transmitting antenna and the receiving antenna.

6. The method according to claim 5, characterized in that: The power spectrum density of the secondary satellite receiving signal at the AD input end is calculated as follows: S signal =G+N f +10×log 10 (T0k)+SNR r Formula (6) Among them, S signal is the power spectrum density of the secondary satellite receiving signal at the AD input end.

7. The method according to claim 6, characterized in that: The quantization noise power spectral density S of the selected AD device is calculated. SNR ,as follows: S SNR = -1dBFS-SNR AD -10×log10(f S / 2) Official(7) Among them, SNR AD 、f S are the signal-to-noise ratio and sampling rate of the AD device respectively.

8. The method according to claim 7, characterized in that: The quantized signal-to-noise ratio SNR of the received signal after AD quantization d ,as follows: SNR d =S signal -S SNR Formula (8) According to formulas (5)-(8), calculate SNR d ,as follows: SNR d =G+N f +10×log10(T0k)+SNR r -S SNR Formula (9).

9. The method according to claim 8, characterized in that: The minimum gain of the AD receiving channel is G min , calculated as follows: SNR d ≥SNR th Official(10) According to formulas (9)-(10), we can get G min ,as follows: G min =SNR th +S SNR -SNR r -N f -10×log10(T0k) Formula (11) Among them, SNR th is the quantization signal-to-noise ratio threshold.

10. The method according to any one of claims 1 to 9, characterized in that: The channel link of the secondary satellite payload includes a secondary satellite receiving antenna, a radio frequency front end, a superheterodyne receiver, an AD device and a digital processor; The target signal of the ground terminal radiation source enters the RF front end of the secondary satellite receiving payload channel through the secondary satellite receiving antenna, and is amplified and filtered to obtain an amplified and filtered analog signal; The amplified and filtered analog signal is input into a superheterodyne receiver, and the amplified and filtered target signal is further amplified and frequency-converted, and then input into the AD device to convert the analog signal output by the superheterodyne receiver into a digital signal; The digital signal finally enters a digital processor for digital processing to obtain a processed digital signal.

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