A secondary satellite payload design method for ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning

Abstract

A design method for secondary satellite payloads used in ultra-low negative signal-to-noise ratio asymmetric time-frequency difference positioning, calculating the total simulated noise floor power P of the input AD NAD and the maximum value of the secondary satellite receiving payload channel gain G max ; Calculate the signal-to-noise ratio (SNR) of the secondary satellite's received signal r , obtain the power spectrum density S of the secondary satellite receiving signal at the AD input signal ; Select AD devices according to the instantaneous working bandwidth and AD quantization bit number, and calculate the quantization noise power spectral 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 Calculate the minimum gain G min 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, reselect an AD device with a higher signal-to-noise ratio than the current one until G is satisfied. max ≥G min The selected AD device is obtained; the selected AD device, channel gain design value, receiving channel noise figure and instantaneous working bandwidth are the top-level design of the secondary satellite payload.

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 Difference of Arrival / Frequency Difference of Arrival (TDOA / FDOA) positioning systems have become a means of achieving high-precision positioning of radiating sources. Generally, the signal-to-noise ratio (SNR) of target signals received by multiple satellites in such a positioning system is comparable, eliminating the asymmetry of high and low SNRs between the primary and secondary satellites. Consequently, there are no special requirements for the design of the target signal receiving payload in the positioning system.

[0003] However, for weak signals 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. However, 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 time-frequency difference extraction, that is, asymmetric time-frequency difference positioning occurs. Especially for high-frequency target signals, such as X (8-12GHz frequency range), Ku (12-18GHz frequency range) and above frequency bands, the main lobe and side lobe of these terminal antennas are relatively large. If the main satellite is aligned with the main lobe of the target signal terminal antenna, a higher positive signal-to-noise ratio can be achieved, which is generally designed to be around 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 secondary satellite receiving antenna gain itself is relatively low. The two reasons 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 (SNR) of the secondary satellite's reception, with a SNR less than -30dB or even an ultra-low negative SNR less than -40dB. At this time, the difference in SNR between the primary and secondary satellites reaches asymmetry of more than 50dB. If the traditional receiving payload design approach 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 primary 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 a secondary satellite payload when the signal-to-noise ratio of the secondary satellite received signal is extremely low, so that it can 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’s received signal based on the EIRP, signal bandwidth, antenna pattern characteristics of the ground radiation source target, as well as the secondary satellite’s receiving antenna gain and receiving channel noise coefficient. r , obtain the power spectrum density S of the secondary satellite receiving signal at the AD input 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 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 and 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 figure and instantaneous operating 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 power P of the analog noise floor of the input AD NAD , calculated as follows:

[0011] P NAD =G+N f +10×log10(MT0k) formula (1)

[0012] Among them, G is the receiving channel gain, N f is the receiving channel noise coefficient, M is the instantaneous operating bandwidth of the secondary satellite receiving payload, T0 is the reference temperature, and k is the Boltzmann constant.

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

[0014] To prevent AD saturation, let:

[0015] P NAD ≤-1dBFS-E Formula (2)

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

[0017] G≤-1dBFS-EN f -10×log10(MT0k) Formula (3)

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

[0019] G max =-1dBFS-EN f -10×log10(MT0k) Formula (4)

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

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

[0022] When only analog noise floor is input, the AD quantization bit number is one less than the full-scale level, that is, the total power of the analog noise floor is about 6dB smaller 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 (BT0k) Formula (5)

[0025] Among them, 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 pattern.

[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 (T0k)+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 quantized signal-to-noise ratio (SNR) of the received signal after AD quantization is 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(T0k)+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 thFormula (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(T0k) 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, is amplified and filtered, and obtains 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 this invention solves the problem of extracting asymmetric time-frequency differences with ultra-low negative signal-to-noise ratios, supports multi-satellite asymmetric time-frequency difference positioning, and is particularly targeted at the ultra-low negative signal-to-noise ratio reception of secondary satellites. This avoids the problem of being unable to quantify due to too low a signal-to-noise ratio, and improves the adaptability of multi-satellite asymmetric positioning.

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

[0048] 3. The present invention enhances the system's adaptability to asymmetric conditions. When the difference in signal-to-noise ratio between the primary and secondary satellites reaches 50 dB or more, the present invention provides a design method that enables the secondary satellite to effectively participate in time-frequency difference positioning, thus 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 spectral density of AD devices and setting the quantization signal-to-noise ratio threshold, 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, realizing the refined design and optimization of the secondary satellite receiving payload.

[0051] 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

[0052] 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.

[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 according to 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 3 Schematic diagram of the 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, AD noise floor, and received signal spectrum under ultra-low negative signal-to-noise ratio reception conditions in an embodiment of the present invention;

[0058] Figure 6 This is a ground verification test block diagram for 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 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.

[0062] The present invention is applicable to multi-satellite asymmetric time-frequency difference positioning. In view of the ultra-low negative signal-to-noise ratio reception 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 using 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. Even when the primary and secondary satellites receive signals with an ultra-low negative signal-to-noise ratio asymmetry, effective estimation of the time-frequency difference can still be achieved, thereby achieving high-precision positioning of the target signal. Compared with traditional multi-satellite positioning systems 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 expanded to the X and Ku bands, and 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 target signals.

[0064] Currently, the primary and secondary satellite receiving payloads of a multi-satellite positioning system use the same design, but their ability to extract time-frequency differences (TFDs) under asymmetric signal-to-noise ratios (SNRs) is relatively weak. This results in only high-precision multi-satellite TFD positioning of target signals below the C band, while lacking the ability to locate target signals in high-frequency bands above X and Ku. To address this issue, the secondary satellite receiving payload of a multi-satellite positioning system needs to be specially designed to effectively quantize the received signal even under ultra-low negative SNRs. This allows for effective TFD estimation under asymmetric conditions, thereby achieving high-precision positioning of the radiating target signal.

[0065] This paper proposes a method for designing a secondary satellite payload 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 primary satellite, and its high-gain receiving antenna is aligned with the main lobe of the antenna of the ground terminal radiation source. The primary satellite is located in the main radiation direction of the ground terminal radiation source. Due to the high gain of the primary 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 aligned with 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 primary and secondary satellites, and an ultra-low negative signal-to-noise ratio.

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

[0069] When the signal-to-noise ratio (SNR) of the signal received by the secondary satellite is extremely low, even below -30dB or -40dB, this condition is called an ultra-low negative SNR. Under such conditions, traditional secondary satellite receiving payload designs may not work effectively because the signal is overwhelmed by the noise, making it difficult to quantize and process effectively.

[0070] To achieve effective signal processing under ultra-low negative signal-to-noise ratio conditions, the secondary satellite payload requires special design to improve signal reception and processing capabilities. This includes selecting appropriate receiving channel gain and AD devices with lower noise characteristics.

[0071] In a multi-satellite positioning system, the coordinated operation of the primary and secondary satellites is crucial for achieving high-precision positioning. Specifically, when the signal-to-noise ratio (SNR) of the signal received by the secondary satellite is extremely low, the secondary satellite payload must be designed to ensure effective extraction of the time-frequency difference (TFD).

[0072] To obtain multi-satellite TFD estimates, the secondary satellite's receiving payload must be able to effectively quantize the target signal. This means the power spectral density of the target signal from the ground terminal's radiator arriving at the secondary satellite's AD must be at least 10dB greater than the secondary satellite's AD's noise floor. Only when the received ground terminal's radiator's target signal power is higher than the secondary satellite's AD's noise floor can the AD effectively quantize and characterize the target signal.

[0073] The power spectral density difference between the target signal from the ground terminal radiation source and the secondary satellite AD noise floor must 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 target signal power spectral density 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, thereby affecting 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, is amplified and filtered, and obtains 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 is passed 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 the 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 the 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, the signal bandwidth of the minimum received signal is used as the processing resolution, and the gain of the secondary satellite receiving channel is designed so that no spurious signals appear in the secondary satellite receiving payload channel, while the two-tone dynamic range is maximized.

[0088] The AD working characteristics of traditional receiving payload are as follows: Figure 4 As shown, the horizontal axis is the sampling frequency f s / 2 is the number of times the AD acquires analog signals per second, measured in hertz; the vertical axis is the level, measured in dBm (decibel milliwatts). SFDR (Spurious-Free Dynamic Range) is the AD's spurious-free dynamic range, representing the ratio of the input signal level to the maximum spurious level when the AD input is subjected to an analog sweep input of -1dBFS (1dB below full-scale). This range represents the analog signal range normally input to the AD, and is also the AD's normal operating range. To meet the minimum receive signal processing capability, the analog noise floor power reaching the AD input (with a processing resolution equal to the minimum receive signal bandwidth) must be greater than the AD's spurious level. For signals with a positive signal-to-noise ratio, the AD's 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’s received signal based on the EIRP, signal bandwidth, antenna pattern characteristics of the ground radiation source target, as well as the secondary satellite’s receiving antenna gain and receiving channel noise coefficient. r , obtain the power spectrum density S of the secondary satellite receiving signal at the AD input 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 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 and 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 figure and instantaneous operating 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 an asymmetric 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 (The design value of the actual payload of the secondary satellite is measurable), the channel gain is G, the minimum receiving signal bandwidth is B, then the power S of the simulated background noise power reaching the AD device entrance under the bandwidth B is NAD , as shown in formula (1):

[0100] S NAD =G+N f +10×log10(BT0k) formula (1)

[0101] Where T0 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. 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 mission 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 it only needs to meet 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(BT0k) 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, the received signal is already buried 40 to 50 dB below the analog noise floor. At this time, the signal is already below the AD noise floor, that is, the received signal cannot be effectively quantized and characterized by the 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 the 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 the AD. Otherwise, the AD will be saturated, the received signal will be distorted, and time-frequency difference extraction will be impossible.

[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, 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. rSince 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 the 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 noise floor power dominates the receiving channel power, that is, the total analog noise floor 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(MT0k) formula (4)

[0116] Among them, G is the receiving channel gain, N f is the receiving channel noise coefficient, M is the instantaneous operating bandwidth of the secondary satellite receiving payload, T0 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 is input, the AD quantization bit number is one less than the full-scale level, that is, the total power of the analog noise floor is about 6dB smaller 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(MT0k) Formula (6)

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

[0125] G max =-1dBFS-EN f-10×log10(MT0k) Formula (7)

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

[0127] In order to prevent AD from saturation and keep it in a stable and 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 for the minimum signal to be higher than the spurious level. In this patent, D will no longer be used because the traditional load design concept is no longer used. E is the design margin for the entire channel analog noise floor to be 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 the 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, 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 .

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

[0134] SNR r =EIRP-L d -N f -10×log 10 (BT0k) Formula (8)

[0135] Among them, 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 spectrum density of the simulated background noise at the AD input is G+N f +10×log10(T0k), because the signal-to-noise ratio of the received signal 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] Ssignal =G+N f +10×log 10 (T0k)+SNR r Formula (9)

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

[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 accordingly. 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(T0k)+SNR r -SSNR 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(T0k)+SNR r -S SNR ≥SNR th Formula (14)

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

[0154] G ≥ SNR th -N f -10×log10(T0k)-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(T0k) 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 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 reception capability, the channel gain G is set as high as possible. It should be noted that in the actual receiving payload design, if the received signal-to-noise ratio is very low and the AD quantization noise is relatively large (S SNR The larger the AD quantization noise is, 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 , then 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 and 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 figure and instantaneous operating 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 purpose 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 quantized 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 ultra-low negative signal-to-noise ratio asymmetric time-frequency difference multi-satellite positioning applications, 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 0dBm), 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) Based on 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 1 and 2 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 devices, 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 and 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 (SNR) can be achieved. r In actual ultra-low negative signal-to-noise ratio (NSR) asymmetric time-frequency difference (TFD) positioning applications, the primary satellite performs signal detection and search, while the secondary satellite blindly samples within the instantaneous operating bandwidth. After the primary satellite detects a signal, it collaborates with the secondary satellite to perform TFD correlation extraction, thereby achieving 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 effects of the present invention more obvious, a specific example will be given below. First, the secondary satellite payload is designed, then the secondary satellite payload is developed based on the design value, and finally the on-orbit signal reception situation of the primary 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, such as Figure 2 As shown in Figure 1, assuming the primary satellite receives a 15dB signal-to-noise ratio (SNR) for ground-based radiation sources. Assuming the radiation source terminal operates in the X-band, has a 2.0m antenna size, an EIRP of 59dBW, and a signal bandwidth of 1MHz, and the secondary satellite receives incoming signals 15 degrees away from the beam center, the primary-to-secondary antenna ratio at the ground terminal will reach 45dB. Considering a 10dBi secondary satellite receiving antenna gain, a 4dB secondary satellite receiving channel noise figure, and a receiving distance of 40,711km, the secondary satellite's SNR is approximately -45dB, indicating an extremely low negative SNR reception situation. The specific link calculation and related parameters are shown in Table 1.

[0176] Table 1: Secondary satellite receiving signal link calculation table

[0177]

[0178]

[0179] Select a certain AD device and check the device manual. When the AD sampling rate is 1600Msps, its signal-to-noise ratio (SNR) is AD The noise power within the 800MHz bandwidth is -57.6dBm when the input is -1dBFS (assuming the full-scale level is 0dBm), which is the quantization noise power spectral density S SNR Considering the quantization signal-to-noise ratio threshold SNR th is 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) we can get G 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 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) modulated 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 achieved to 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 time-frequency difference correlation processing is performed on the signals received by the primary and secondary satellites, and the accumulation time is set to 1s. The correlation peak is relatively obvious, as shown in the figure. Figure 8 As shown, the time difference extraction error is 102.73ns.

[0187] According to the above conditions, the critical range (CR) for time-frequency difference extraction is 70.4 ns. The actual extraction error is approximately 1 to 3 times the CR limit. This shows that the secondary satellite payload design method proposed in this invention can achieve time-frequency difference extraction under ultra-low negative signal-to-noise ratio asymmetric conditions while ensuring extraction accuracy.

[0188] In order to meet the ultra-low negative signal-to-noise ratio requirements, AD selection and channel gain design are required, and matching design with instantaneous working bandwidth, receiving channel noise coefficient, etc. 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 this invention solves the problem of extracting asymmetric time-frequency differences with ultra-low negative signal-to-noise ratios, supports multi-satellite asymmetric time-frequency difference positioning, and is particularly targeted at the ultra-low negative signal-to-noise ratio reception of secondary satellites. This avoids the problem of being unable to quantify due to too low a signal-to-noise ratio, and improves the adaptability of multi-satellite asymmetric positioning.

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

[0192] 3. The present invention enhances the system's adaptability to asymmetric conditions. When the difference in signal-to-noise ratio between the primary and secondary satellites reaches 50 dB or more, the present invention provides a design method that enables the secondary satellite to effectively participate in time-frequency difference positioning, thus 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 spectral density of AD devices and setting the quantization signal-to-noise ratio threshold, 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, realizing the refined design and optimization of the secondary satellite receiving payload.

[0195] 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 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’s received signal based on the EIRP, signal bandwidth, antenna pattern characteristics of the ground radiation source target, as well as the secondary satellite’s receiving antenna gain and receiving channel noise coefficient. r , obtain the power spectrum density S of the secondary satellite receiving signal at the AD input 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 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 and 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 figure and instantaneous operating 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 total power P of the analog noise floor 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 operating 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) and (2), we get: G≤-1dBFS-EN f -10×log10(MT0k) Formula (3) According to inequality (3), the maximum value of G is 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 designed to protect 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 is input, the AD quantization bit number is one less than the full-scale level, that is, the total power of the analog noise floor is about 6dB smaller 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's received signal r , calculated as follows: SNR r = EIRP - L d - N f - 10 × log 10 (BT0k) Equation (5) Among them, 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 pattern.

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 AD receiving channel minimum gain 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, is amplified and filtered, and obtains 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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