A low-orbit satellite-based communication and remote sensing integrated method and device

Abstract

The application discloses a kind of communication remote sensing integration method and device based on low-orbit satellite.Low-orbit satellite sends a kind of periodic embedding communication remote sensing shared signal wireless frame to beam coverage area.After receiving wireless frame, ground user obtains channel state information by a kind of channel estimation method based on shared signal cross ambiguity function, then utilizes message passing method to detect the data information sent by low-orbit satellite.Meanwhile, low-orbit satellite receives and stores the ground echo signal of shared signal, and obtains SAR image by using synthetic aperture radar (SAR) imaging algorithm to echo signal processing.The application provides a kind of simple but effective communication and SAR remote sensing function integration method and device for low-orbit satellite system.

Description

Technical Field

[0001] This invention relates to the field of wireless communication, and more particularly to an integrated communication and remote sensing method and apparatus based on low-Earth orbit satellites. Background Technology

[0002] In recent years, with the rapid development of the economy and society, the demand for more real-time satellite remote sensing data has become increasingly prominent. Meanwhile, due to the advantages of low-Earth orbit (LEO) satellite systems, such as low transmission latency and low propagation loss, they have become a focus of research and development for future 6G communication systems. Against this backdrop, the integrated construction of communication and remote sensing based on LEO satellite systems has become an inevitable trend. To study integrated communication and remote sensing methods for LEO satellites, it is necessary to combine the characteristics of LEO communication and remote sensing satellites themselves to design a shared signal and wireless frame structure for integrated communication and remote sensing functions, thereby achieving the integrated realization of satellite communication and remote sensing capabilities.

[0003] However, existing integrated communication and sensing technologies primarily rely on ground-based radar technology and static communication links. Remote sensing satellites, however, typically carry imaging radars, such as SAR, which differ significantly from ground-based radars in their remote sensing principles. Furthermore, the satellite-to-ground links of low-Earth orbit (LEO) satellites suffer from high mobility and bi-selective channels due to multipath fading, making data transmission under these channel conditions difficult for existing satellite modulation techniques. Although ODDM modulation technology is generally considered suitable for the LEO satellite communication environment, there is currently no research on applying ODDM signals to SAR imaging, nor has a solution been proposed to integrate ODDM communication with SAR remote sensing. Summary of the Invention

[0004] The purpose of this invention is to achieve the integration of communication and SAR remote sensing functions in the aforementioned low-Earth orbit satellite environment, and to propose an integrated communication and remote sensing method and device based on low-Earth orbit satellites.

[0005] The specific technical solution adopted in this invention is as follows:

[0006] In a first aspect, the present invention provides an integrated communication and remote sensing method based on low-Earth orbit satellites, which includes the following steps:

[0007] S1. A low-orbit satellite sends a periodic wireless frame containing a shared communication and remote sensing signal to the beam coverage area to simultaneously realize satellite-to-ground communication and SAR remote sensing functions within the beam range.

[0008] S2. After receiving the radio frames containing periodically embedded communication and remote sensing shared signals transmitted by the low-Earth orbit satellite, the ground user terminal uses a channel estimation method based on cross-fuzzy functions to obtain the path parameters of one line-of-sight path and multiple non-line-of-sight paths of the low-Earth orbit satellite channel, and then constructs the channel matrix. Implement received symbol detection;

[0009] S3. The low-orbit satellite receives the echo signals of the shared signal within the beam coverage area, processes the shared signal echo data according to the beam type used by the low-orbit satellite to obtain SAR images, and then stores them.

[0010] Preferably, the wireless frame in S1 that periodically inserts the communication remote sensing shared signal consists of multiple time slots of the same length, wherein each time slot consists of multiple orthogonal time-delayed Doppler multiplexed (ODDM) signals, and the number of ODDM signals contained in different time slots is the same; all time slots in the wireless frame are divided into two categories: shared time slots and communication time slots, and the shared time slots are periodically embedded in the communication time slots; each shared time slot consists of two parts: a shared signal and broadcast data, wherein the shared signal is a signal modulated by ODDM using orthogonal Gold codes in matrix form, and also serves as a pilot sequence for channel estimation and a detection signal in SAR remote sensing; each communication time slot consists of communication data.

[0011] Preferably, the channel estimation method based on the cross-fuzzy function in S2 is as follows:

[0012] S21. After receiving the radio frame containing the periodic embedded communication remote sensing shared signal sent by the low-orbit satellite, the ground user terminal samples the shared signal in it to obtain the shared signal sampling sequence r.

[0013] S22. The ground user terminal calculates the normalized cross-ambiguity function value ρ(r,s)[l,k] corresponding to any l-th Doppler frequency shift point and k-th time delay difference point using the following formula, based on the shared signal sampling sequence r and the original shared signal s embedded in the radio frame:

[0014]

[0015] In the formula: M and N represent the number and length of the orthogonal Gold codes constituting the shared signal, respectively. MN This represents the remainder operation; the values ​​of l and k are 0 ≤ l ≤ L-1, -K ≤ k ≤ K, where L and K represent the maximum number of Doppler frequency shift points and the maximum number of time delay difference points of the multipath channel, respectively; r(n) is the nth sampling point of the shared signal sampling sequence r, s * The conjugate of the shared signal s;

[0016] S23. Extract the P+1 largest normalized cross-ambiguity function values ​​from (2K+1)×L normalized cross-ambiguity function values ​​as multipath channel parameters, where the p-th normalized cross-ambiguity function value ρ(r,s)[l,k] is denoted as the multipath channel parameter α. p The corresponding Doppler frequency shift point index l and time delay difference point k are denoted as l. p and kp p = 0, 1, ..., P, where p = 0 corresponds to the maximum value of the normalized cross-fuzzy function. From this, we obtain the path parameters <α> for the one line-of-sight path corresponding to p = 0 and the remaining P non-line-of-sight paths. p ,l p ,k p Then construct the channel parameter matrix. To store P+1 multipath channel parameters α p The k-th element in the channel parameter matrix θ p +K line l p The elements θ(k) of the column p +K,l p )=α p p = 0, 1, ..., P, and θ contains P+1 multipath channel parameters α p All other elements are 0;

[0017] S24. Calculate the effect of the m-th symbol on the ml-th transmitted symbol in the received ODDM signal using the following formula. Then construct the estimated channel matrix.

[0018]

[0019] In the formula: x = 0, 1, ..., M-1, y = 0, 1, ..., M-1,

[0020] To represent the diagonal matrix of phase rotation, C k In C, the superscript k represents the power, and C is an N×N dimensional matrix with N 1s and all the rest being 0s.

[0021] Preferably, if the low-Earth orbit satellite uses a fixed beam, corresponding to the strip mode of SAR imaging, then the range Doppler algorithm of SAR imaging is used to process the shared signal echo data to obtain the SAR image; if the low-Earth orbit satellite uses a staring beam, corresponding to the spotlight mode of SAR imaging, then the polar coordinate format algorithm of SAR imaging is used to process the shared signal echo data to obtain the SAR image.

[0022] Secondly, the present invention provides a communication and remote sensing integrated device based on low-Earth orbit satellite, which includes a low-Earth orbit satellite equipped with a phased array antenna and multiple ground user terminals. The low-Earth orbit satellite and the ground user terminals realize satellite-to-ground communication and SAR remote sensing functions in accordance with the communication and remote sensing integrated method based on low-Earth orbit satellite described in any of the first aspects above.

[0023] The beneficial effects of this invention are as follows: The shared signal construction method proposed in this invention generates ODDM signals through a set of orthogonal Gold codes, effectively realizing the integration of low-Earth orbit satellite communication signals and remote sensing signals. The integrated communication and remote sensing wireless frame construction method proposed in this invention periodically embeds shared time slots containing shared signals into the frame structure, which can adapt to the requirements of SAR remote sensing for periodic transmission of detection pulses. The channel estimation method based on cross-ambiguity functions proposed in this invention allows ground users to obtain the channel state information required for symbol detection at the receiver through shared signals, thus solving the channel estimation problem of low-Earth orbit satellite ODDM communication. Attached Figure Description

[0024] Figure 1 This is a block diagram of a communication and remote sensing integrated method and device based on low-Earth orbit satellites;

[0025] Figure 2 This is a wireless frame structure diagram for integrated communication and remote sensing based on low-Earth orbit satellites;

[0026] Figure 3 It compares the performance of the mean square error in estimating channel parameters under different signal-to-noise ratios and Gold code levels;

[0027] Figure 4 It is a comparison of range and azimuth slices of the SAR ambiguity function of the shared signal and the linear frequency modulated signal. Detailed Implementation

[0028] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. Technical features in the various embodiments of the present invention can be combined accordingly without mutual conflict.

[0029] like Figure 1 The diagram illustrates a block diagram of the aforementioned integrated communication and remote sensing device based on a low-Earth orbit (LEO) satellite, according to a preferred embodiment of the present invention. The device includes a LEO satellite equipped with a phased array antenna and multiple ground user terminals. Communication between the LEO satellite and the ground user terminals is achieved using an integrated communication and remote sensing method based on LEO satellite, enabling both satellite-to-ground communication and SAR remote sensing functions. Specifically, the ground user terminals receive data transmitted by the LEO satellite, such as... Figure 2The integrated communication and remote sensing wireless frame shown estimates the channel matrix through shared signals and detects received digital symbols using a message passing method. Low-Earth orbit satellites receive and store echo signals from within the beam coverage area of ​​the shared signals, and SAR images are obtained through echo signal processing using SAR imaging algorithms.

[0030] In an embodiment of the present invention, the specific steps of the above-mentioned integrated communication and remote sensing method based on low-Earth orbit satellites are as follows:

[0031] S1. A low-orbit satellite sends a periodic wireless frame containing a shared communication and remote sensing signal to the beam coverage area to simultaneously realize satellite-to-ground communication and SAR remote sensing functions within the beam range.

[0032] In an embodiment of the present invention, the wireless frame in step S1 above, which periodically inserts the communication remote sensing shared signal, consists of multiple time slots of the same length. Each time slot consists of multiple orthogonal time-delayed Doppler multiplexed (ODDM) signals, and the number of ODDM signals contained in different time slots is the same. All time slots in the wireless frame are divided into two categories: shared time slots and communication time slots, and the shared time slots are periodically embedded in the communication time slots. Each shared time slot consists of two parts: a shared signal and broadcast data. The shared signal is a signal modulated by ODDM using orthogonal Gold codes in matrix form, and also serves as a pilot sequence for channel estimation and a detection signal in SAR remote sensing. Each communication time slot consists of communication data.

[0033] like Figure 2 The diagram illustrates an exemplary implementation of the periodically inserted communication remote sensing shared signal wireless frame, containing 1024 frames. Each wireless frame has a length of L (10 ms in this example) and contains d time slots of equal length (10 in this example). Each time slot contains a series of ODDM signals, functionally divided into shared time slots and communication time slots. The shared time slots are periodically embedded in the wireless frame structure; in this example, one shared time slot is inserted every four communication time slots. Each shared time slot can be divided into shared signals and broadcast data. The shared signals are designed as ODDM signals generated by ODDM modulation using a set of orthogonal Gold codes (constructed as an M×N matrix). These signals can serve simultaneously as pilot sequences for channel estimation and novel detection signals in SAR remote sensing. The broadcast data also consists of a series of data sequences in ODDM signal form. Additionally, the communication time slots consist of a series of data sequences in ODDM signal form. Furthermore, in this example, a cyclic prefix is ​​added before each ODDM signal to avoid mutual interference between signals.

[0034] S2. After receiving the radio frames containing periodically embedded communication and remote sensing shared signals transmitted by the low-Earth orbit satellite, the ground user terminal uses a channel estimation method based on cross-fuzzy functions to obtain the path parameters of one line-of-sight path and multiple non-line-of-sight paths of the low-Earth orbit satellite channel, and then constructs the channel matrix. Implement received symbol detection.

[0035] In an embodiment of the present invention, the channel estimation method based on the cross-fuzzy function in step S2 above is specifically as follows:

[0036] S21. After receiving the radio frame containing the periodic embedded communication remote sensing shared signal sent by the low-orbit satellite, the ground user terminal samples the shared signal in it to obtain the shared signal sampling sequence r.

[0037] S22. The ground user terminal calculates the normalized cross-ambiguity function value ρ(r,s)[l,k] corresponding to any l-th Doppler frequency shift point and k-th time delay difference point using the following formula, based on the shared signal sampling sequence r and the original shared signal s embedded in the radio frame:

[0038]

[0039] In the formula: M and N represent the number and length of the orthogonal Gold codes constituting the shared signal, respectively. MN This represents the remainder operation; the values ​​of l and k are 0 ≤ l ≤ L-1, -K ≤ k ≤ K, where L and K represent the maximum number of Doppler frequency shift points and the maximum number of time delay difference points of the multipath channel, respectively; r(n) is the nth sampling point of the shared signal sampling sequence r, s * The conjugate of the shared signal s;

[0040] S23. Extract the P+1 largest normalized cross-ambiguity function values ​​from (2K+1)×L normalized cross-ambiguity function values ​​as multipath channel parameters, where the p-th normalized cross-ambiguity function value ρ(r,s)[l,k] is denoted as the multipath channel parameter α. p The corresponding Doppler frequency shift point index l and time delay difference point k are denoted as l. p and k p p = 0, 1, ..., P, where p = 0 corresponds to the maximum value of the normalized cross-fuzzy function. This yields the path parameters <α for one line-of-sight path (corresponding to p = 0) and the remaining P non-line-of-sight paths (corresponding to p > 0). p ,l p ,k p Then construct the channel parameter matrix. To store P+1 multipath channel parameters α p The k-th element in the channel parameter matrix θ p +K line l pThe elements θ(k) of the column p +K,l p )=α p p = 0, 1, ..., P, and θ contains P+1 multipath channel parameters α p All other elements are 0;

[0041] S24. Calculate the effect of the m-th symbol on the ml-th transmitted symbol in the received ODDM signal using the following formula. Then construct the estimated channel matrix.

[0042]

[0043] In the formula: x = 0, 1, ..., M-1, y = 0, 1, ..., M-1, It is an M×M submatrix The matrix formed by these elements has an element at any position (p, q) that is a submatrix. p=0,1,…,M-1, q=0,1,…,M-1.

[0044] To represent the diagonal matrix of phase rotation, C k In C, the superscript k is the power, and C is an N×N dimensional matrix with N 1s and all the rest being 0s (the last column in the first row is 1, the first column in the second row is 1, the second column in the third row is 1, and so on, and the (t-1)th column in any other t-th row is 1).

[0045] S3. The low-orbit satellite receives the echo signals of the shared signal within the beam coverage area, processes the shared signal echo data according to the beam type used by the low-orbit satellite to obtain SAR images, and then stores them.

[0046] In an embodiment of the present invention, the specific method for processing shared signal echo data to obtain SAR images according to the beam type used by the low-Earth orbit satellite is as follows: if the low-Earth orbit satellite uses a fixed beam, corresponding to the strip mode of SAR imaging, then the range Doppler algorithm of SAR imaging is used to process the shared signal echo data to obtain SAR images; if the low-Earth orbit satellite uses a staring beam, corresponding to the spotlight mode of SAR imaging, then the polar coordinate format algorithm of SAR imaging is used to process the shared signal echo data to obtain SAR images.

[0047] Computer simulations show that, Figure 3 As shown, the channel estimation method based on cross-fuzzy functions proposed in this invention exhibits a gradual decrease and stabilization of the mean square error (MSE) between the estimated channel parameters and the ideal channel parameters as the Gold code level and signal-to-noise ratio increase. Therefore, it can obtain the channel matrix more accurately for symbol detection. Furthermore, Figure 4This indicates that the shared signal and the linear frequency modulated signal maintain consistent azimuth imaging performance, while in the range slice, the shared signal exhibits faster sidelobe attenuation and a lower integrated sidelobe ratio. Therefore, the integrated communication and remote sensing method and apparatus based on low-Earth orbit satellites proposed in this invention can provide a method for integrating communication and SAR remote sensing functions for low-Earth orbit satellite systems.

[0048] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.

Claims

1. A method for integrating communication and remote sensing based on low-Earth orbit satellites, characterized in that... Includes the following steps: S1. A low-orbit satellite sends a periodic wireless frame containing a shared communication and remote sensing signal to the beam coverage area to simultaneously realize satellite-to-ground communication and SAR remote sensing functions within the beam range. S2. After receiving the radio frame of the periodic embedded communication remote sensing shared signal sent by the low-orbit satellite, the ground user terminal uses a channel estimation method based on cross-fuzzy function to obtain the path parameters of one line-of-sight path and multiple non-line-of-sight paths of the low-orbit satellite channel, and then constructs the channel matrix to realize the detection of received symbols. S3. The low-orbit satellite receives the echo signal of the shared signal within the beam coverage area, processes the shared signal echo data according to the beam type used by the low-orbit satellite to obtain SAR images, and then stores them. The channel estimation method based on the cross-fuzzy function in S2 is as follows: S21. After receiving the radio frame containing the periodic embedded communication remote sensing shared signal sent by the low-orbit satellite, the ground user terminal samples the shared signal in it to obtain the shared signal sampling sequence r. S22. The ground user terminal calculates the normalized cross-ambiguity function value ρ(r,s)[l,k] corresponding to any l-th Doppler frequency shift point and k-th time delay difference point using the following formula, based on the shared signal sampling sequence r and the original shared signal s embedded in the radio frame: In the formula: M and N represent the number and length of the orthogonal Gold codes constituting the shared signal, respectively. MN This represents the remainder operation; the values ​​of l and k are 0 ≤ l ≤ L-1, -K ≤ k ≤ K, where L and K represent the maximum number of Doppler frequency shift points and the maximum number of time delay difference points of the multipath channel, respectively; r(n) is the nth sampling point of the shared signal sampling sequence r, s * The conjugate of the shared signal s; S23. Extract the P+1 largest normalized cross-ambiguity function values ​​from (2K+1)×L normalized cross-ambiguity function values ​​as multipath channel parameters, where the p-th normalized cross-ambiguity function value ρ(r,s)[l,k] is denoted as the multipath channel parameter α. p The corresponding Doppler frequency shift point index l and time delay difference point k are denoted as l. p and k p p = 0, 1, ..., P, where p = 0 corresponds to the maximum value of the normalized cross-fuzzy function. From this, we obtain the path parameters <α> for the one line-of-sight path corresponding to p = 0 and the remaining P non-line-of-sight paths. p ,l p ,k p Then construct the channel parameter matrix. To store P+1 multipath channel parameters α p The k-th element in the channel parameter matrix θ p +K line l p The elements θ(k) of the column p +K,l p )=α p p = 0, 1, ..., P, and θ contains P+1 multipath channel parameters α p All other elements are 0; S24. Calculate the effect of the m-th symbol on the ml-th transmitted symbol in the received ODDM signal using the following formula. Then construct the estimated channel matrix. In the formula: x = 0, 1, ..., M-1, y = 0, 1, ..., M-1, It is an M×M submatrix The matrix formed by these elements has an element at any position (p, q) that is a submatrix. p=0,1,…,M-1, q=0,1,…,M-1; To represent the diagonal matrix of phase rotation, C k In C, the superscript k represents the power, and C is an N×N dimensional matrix with N 1s and all the rest being 0s.

2. The integrated communication and remote sensing method based on low-Earth orbit satellites according to claim 1, characterized in that, The radio frame in S1 that periodically inserts the shared remote sensing signal consists of multiple time slots of the same length, each time slot consisting of multiple orthogonal time-delayed Doppler multiplexed (ODDM) signals. The number of ODDM signals contained in different time slots is the same. All time slots in the radio frame are divided into two categories: shared time slots and communication time slots. The shared time slots are periodically embedded in the communication time slots. Each shared time slot consists of two parts: a shared signal and broadcast data. The shared signal is a signal modulated by ODDM using orthogonal Gold codes in matrix form. It also serves as a pilot sequence for channel estimation and a detection signal in SAR remote sensing. Each communication time slot consists of communication data.

3. The integrated communication and remote sensing method based on low-Earth orbit satellites according to claim 1, characterized in that, If the low-Earth orbit satellite uses a fixed beam, corresponding to the strip mode of SAR imaging, then the range Doppler algorithm of SAR imaging is used to process the shared signal echo data to obtain the SAR image; if the low-Earth orbit satellite uses a staring beam, corresponding to the spotlight mode of SAR imaging, then the polar coordinate format algorithm of SAR imaging is used to process the shared signal echo data to obtain the SAR image.

4. A communication and remote sensing integrated device based on low-Earth orbit satellites, characterized in that, The system includes a low-Earth orbit satellite equipped with a phased array antenna and multiple ground user terminals. The low-Earth orbit satellite and the ground user terminals communicate with each other using the integrated communication and remote sensing method based on the low-Earth orbit satellite as described in any one of claims 1 to 3 to achieve satellite-to-ground communication and SAR remote sensing functions.

Images