A deep space cooperative relay transmission method and system based on adaptive selection

Abstract

The present invention discloses a deep space collaborative relay transmission method and system based on adaptive selection, the method comprising the following steps: (1) establishing a deep space collaborative relay transmission model; (2) enabling a dual-hop free space optical relay link for signal transmission; (3) dual-hop free space optical relay link channel estimation; (4) transmission strategy selection; (5) obtaining key performance indicators based on the optimal transmission strategy. The present invention establishes a reliable deep space collaborative relay transmission link based on the channel estimation result, adopts adaptive collaborative technology to increase the signal-to-noise ratio of the signal received by the deep space detector, enhances the intelligence of the communication system, reduces the impact of complex deep space environment on deep space communication performance, improves the system communication quality and the transmission efficiency of the network, and has practical engineering application significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of deep space communications, and in particular relates to a deep space collaborative relay transmission method and system based on adaptive selection. Background Art

[0002] Deep space communication is an important way to transmit deep space information. With the changes in ultra-long-distance exploration missions, transmission opportunities and resources are limited. In addition, complex environments such as deep space solar wind plasma, cosmic space noise, solar flares, and periodic sunspot eruptions have become uncertain factors in deep space communication, bringing extremely adverse effects to deep space communication, seriously reducing deep space communication performance, and greatly restricting the depth and breadth of exploration. Nowadays, facing the complex characteristics of the deep space environment, establishing a reliable deep space communication system has become an important task that aerospace agencies need to carry out in the communication mission planning stage.

[0003] The traditional deep space RF direct transmission system is affected by the complex deep space environment, showing the characteristics of fragile links and extremely low signal-to-noise ratio, and is constrained by equipment manufacturing process bottlenecks and wireless performance limits. Optical communication has become a new technology growth point for deep space communication due to its advantages such as large bandwidth, high speed, high security and anti-electromagnetic interference, and has been applied in some deep space communication systems. However, solar wind turbulence and satellite orbit perturbations pose serious challenges to the stable operation of deep space optical communication systems, greatly reducing the reliability of communication links.

[0004] In recent years, deep space relay communications have adopted a variety of signal forwarding modes to assist satellites in sending signals to target detectors, which brings a large spatial diversity gain to deep space communication systems, enabling the system to achieve improved transmission efficiency under specific reliability conditions, and has become a consensus to improve the performance of deep space communication systems. However, the design complexity of deep space relay systems will inevitably bring additional overhead to system performance, thereby offsetting the diversity gain. Therefore, how to combine the advantages of RF direct transmission and optical communication to design a deep space relay transmission solution to improve the performance of deep space relay communications has become an important issue that needs to be solved in deep space communications. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a deep space cooperative relay transmission method and system based on adaptive selection, and the present invention includes a geosynchronous satellite, a deep space relay satellite, and a deep space probe. The transmission technology scheme of the present invention has two available communication links, namely 1) a double-hop free space optical (FSO) relay link: the geosynchronous satellite transmits the signal to the relay satellite based on optical communication technology, and the relay satellite then transmits the optical signal to the deep space probe after amplification and forwarding; 2) a radio frequency (RF) direct transmission link: the geosynchronous satellite transmits the radio frequency signal directly to the deep space probe in a broadcast mode. Based on engineering practice considerations, the present invention considers the large-scale attenuation and small-scale fading caused by the rapid fluctuations in the density of solar wind plasma on the radio frequency and optical signals. In addition, the technical scheme of the present invention further considers the influence of solar wind plasma absorption and satellite perturbation changes on the energy attenuation, aiming error and arrival angle fluctuations on the optical signal. The present invention uses channel estimation to provide a decision basis for the establishment of a system link, and uses adaptive cooperation technology to increase the signal-to-noise ratio of the signal received by the deep space probe, improve the system communication quality, and establish a reliable signal transmission mechanism.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A deep space cooperative relay transmission method based on adaptive selection adopts channel estimation to provide a decision basis for link establishment of a deep space communication system, adopts adaptive cooperative technology to increase the signal-to-noise ratio of signals received by deep space detectors, improves the communication quality of the system, and establishes a relatively reliable signal transmission mechanism; the specific steps are as follows:

[0008] (1) Establish a universal and feasible deep space cooperative relay transmission model, including geosynchronous satellites, deep space relay satellites, and deep space probes. The geosynchronous satellite is used as the source, the relay satellite is used as the relay node, and the deep space probe is used as the destination. There are two communication links that can be enabled in this transmission scheme, namely 1) a dual-hop free space optical (FSO) relay link: the geosynchronous satellite transmits the signal to the relay satellite based on optical communication technology, and the relay satellite transmits the optical signal to the deep space probe after signal processing; 2) a radio frequency (RF) direct transmission link: the geosynchronous satellite transmits the RF signal directly to the deep space probe in a broadcast mode. For the dual-hop FSO relay link, it is considered that the link nodes are equipped with FSO antennas, and the amplification and forwarding protocol is pre-set on the relay satellite. The geosynchronous satellite and the relay satellite have the necessary hardware and software conditions for FSO signal transmission; for the RF direct transmission link, it is considered that the link nodes are equipped with RF antennas. Due to the rapid fluctuations in the density of solar wind plasma, both RF and optical signals experience large-scale attenuation and small-scale fading. In addition, considering solar wind plasma absorption and satellite perturbation changes, the optical signal will further suffer from energy attenuation, pointing errors and arrival angle fluctuations.

[0009] (2) Enable the dual-hop free-space optical relay link for signal transmission; the dual-hop FSO relay link includes the geosynchronous satellite to relay satellite link and the relay satellite to deep space probe link. The geosynchronous satellite sends an MPSK-modulated optical signal to the relay satellite. The relay satellite processes the received optical signal based on the amplification and forwarding protocol and forwards it to the deep space probe. The deep space probe demodulates the received optical signal to obtain information. The preferred transmission scheme considers four influencing factors: solar wind plasma absorption, solar wind turbulence, pointing error, and arrival angle fluctuation. Solar wind plasma absorption and solar wind turbulence are used to characterize the absorption and scintillation effects suffered by optical signals when transmitted in solar wind plasma, and are characterized by the Beer-Lambert law and the Malaga distribution model, respectively. The transmission scheme uses zero aiming error and Rayleigh distribution models to characterize the effects of aiming error and arrival angle fluctuation caused by satellite perturbations and trajectory changes.

[0010] (3) Channel estimation of the two-hop free-space optical relay link: Perform channel estimation on the two-hop FSO relay link of the established deep space collaborative relay transmission scheme to obtain the channel state information (instantaneous signal-to-noise ratio) of the link, and feed back the channel state information of the two-hop FSO relay link to the geosynchronous satellite to provide a decision basis for the subsequent signal transmission of the geosynchronous satellite.

[0011] (4) Transmission strategy selection: Based on the channel estimation results, the best transmission strategy is selected for the system. When the instantaneous signal-to-noise ratio of the dual-hop FSO relay link is greater than or equal to the system preset switching signal-to-noise ratio, the geosynchronous satellite only enables the dual-hop FSO relay link for communication; when the instantaneous signal-to-noise ratio of the dual-hop FSO relay link is less than the system preset switching signal-to-noise ratio, the system continues to use the dual-hop FSO relay link while enabling the RF direct transmission link, that is, the geosynchronous satellite simultaneously sends optical signals and radio frequency signals with the same information. Preferably, for the RF direct transmission link, the transmission model uses the α-η-κ-μ distribution model to characterize the impact of solar wind turbulence on radio frequency signal flicker. In the deep space detector, the maximum ratio combining technology is used to combine the optical signal and radio frequency signal received simultaneously. The deep space detector performs phase adjustment and synchronous equalization on the received optical signal and radio frequency signal, and then amplifies the two signals separately, with the gain being its own attenuation coefficient, and then adds the two signals in the same term, and finally demodulates to obtain the baseband signal. The output instantaneous signal-to-noise ratio is the sum of the instantaneous signal-to-noise ratio of the FSO relay link and the instantaneous signal-to-noise ratio of the RF link.

[0012] (5) Based on the optimal transmission strategy, obtain the key performance indicators of the system.

[0013] The present invention also discloses a deep space cooperative relay transmission system based on adaptive selection, which is used to execute the above method, and includes the following modules:

[0014] Transmission model establishment module: establish a deep space collaborative relay transmission model, the transmission model has two enabled communication links, namely: 1) double-hop free space optical relay link: the geosynchronous satellite transmits the signal to the deep space relay satellite based on optical communication technology, and the deep space relay satellite transmits the optical signal to the deep space detector after signal processing; 2) RF direct transmission link: the geosynchronous satellite transmits the RF signal directly to the deep space detector in a broadcast mode;

[0015] Signal transmission module: Enables dual-hop free-space optical relay link for signal transmission;

[0016] Channel estimation module: double-hop free-space optical relay link channel estimation;

[0017] Transmission strategy selection module: When the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is greater than or equal to the preset switching signal-to-noise ratio, the geosynchronous satellite only uses the free-space optical relay link for communication; when the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is less than the preset switching signal-to-noise ratio, while using the dual-hop free-space optical relay link, the RF direct transmission link is further enabled, that is, the geosynchronous satellite simultaneously sends optical signals and RF signals with the same information;

[0018] Performance indicator acquisition module: obtains key performance indicators based on the optimal transmission strategy.

[0019] The present invention not only supports deep space collaborative relay uplink transmission, but can also be used for downlink transmission, and can be further extended to a deep space collaborative multi-relay transmission system.

[0020] The present invention provides a deep space collaborative relay transmission technical solution based on adaptive selection, including geosynchronous satellites, deep space relay satellites, and deep space probes. Its innovation is reflected in the relationship between the channel state (instantaneous signal-to-noise ratio) of the double-hop FSO relay link and the system preset signal-to-noise ratio as the decision basis, combined with the channel evaluation result, to decide whether to enable the RF direct transmission link, so that the deep space communication system is more intelligent, reducing the impact of the complex deep space environment on deep space communication, improving its transmission performance, and accelerating the proposed solution into practical application. In addition, the present invention comprehensively considers the impact of four factors, namely solar wind plasma absorption, solar wind turbulence, pointing error and arrival angle fluctuation, on the FSO relay link, and considers the impact of solar wind turbulence on radio frequency signal flicker, so that the transmission scheme design is more complete, and the key performance indicator calculation results are more accurate. Furthermore, the present invention can not only support deep space collaborative relay uplink transmission, but also be used for downlink transmission, and can be further extended to deep space collaborative multi-relay transmission system, with strong scalability. Collaborative relay communication has become one of the key technologies for the construction of deep space communication systems. With the continuous improvement of deep space collaborative relay communication related technologies, the present invention will have good promotion and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly explain the specific technical solutions of the present invention, the drawings required to be used in the embodiments or the description of the prior art will be briefly introduced below.

[0022] Figure 1 A flowchart of the operation steps of a deep space cooperative relay transmission method based on adaptive selection provided by the present invention;

[0023] Figure 2 A system architecture diagram of a deep space cooperative relay transmission method based on adaptive selection provided by the present invention;

[0024] Figure 3 It is a performance comparison diagram of a specific embodiment of the present invention and the prior art, that is, a schematic diagram of the interruption probability of a deep space cooperative relay transmission method based on adaptive selection, a direct transmission scheme, and a relay transmission scheme;

[0025] Figure 4 This is a block diagram of a deep space collaborative relay transmission system based on adaptive selection according to the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0027] The preferred embodiment of the present invention provides a deep space cooperative relay transmission method based on adaptive selection, giving different switching signal-to-noise ratios γ s The channel characteristics of the double-hop FSO relay link and the RF direct transmission link, as well as the end-to-end performance formula of the system, are used to minimize the system outage probability and bit error rate, maximize the channel capacity, and ultimately improve the deep space cooperative relay transmission performance based on adaptive selection, providing deep space communication with efficient communication under the set reliability constraints. This embodiment is applied to geosynchronous satellites, deep space relay satellites, and deep space probes, see Figure 1 , the specific steps include:

[0028] Step 1: Establish a universal and feasible deep space cooperative relay transmission model, which considers geosynchronous satellites, deep space relay satellites and deep space probes, such as Figure 2 shown.

[0029] The geosynchronous satellite is the source of the information, the deep space relay satellite is the relay node, and the deep space probe is the destination of the information. Figure 2As shown in the figure, there are two enabled communication links in this transmission model, namely: 1) dual-hop free space optical (FSO) relay link: the geosynchronous satellite transmits the signal to the deep space relay satellite based on optical communication technology, and the deep space relay satellite then transmits the optical signal to the deep space detector after amplification and forwarding; 2) radio frequency (RF) direct transmission link: the geosynchronous satellite transmits the RF signal directly to the deep space detector in a broadcast mode. For the dual-hop FSO relay link, the link nodes are equipped with FSO antennas, and the amplification and forwarding protocol is preset in the deep space relay satellite node. The geosynchronous satellite and the deep space relay satellite have the necessary hardware and software conditions to realize FSO signal transmission; for the RF direct transmission link, the link nodes are equipped with RF antennas.

[0030] Because deep space is filled with solar wind plasma, the radio frequency and optical signals are subject to large-scale attenuation and small-scale fading due to the rapid fluctuations in solar wind plasma density. In addition, considering the absorption of solar wind plasma and changes in satellite perturbations, the optical signal will further suffer from energy attenuation, aiming errors, and arrival angle fluctuations.

[0031] Step 2: Enable the dual-hop FSO relay link for signal transmission.

[0032] Signal transmission process of dual-hop FSO relay link: For dual-hop FSO relay link, it includes the link from geosynchronous satellite to deep space relay satellite and the link from deep space relay satellite to deep space detector. Geosynchronous satellite sends MPSK modulated optical signal to deep space relay satellite. Deep space relay satellite processes the received optical signal based on amplification and forwarding protocol and forwards it to deep space detector. Deep space detector demodulates the received optical signal to obtain information.

[0033] The transmission scheme of this embodiment simultaneously considers four influencing factors, namely, solar wind plasma absorption, solar wind turbulence, pointing error, and arrival angle fluctuation. Solar wind plasma absorption and solar wind turbulence are used to characterize the absorption and scintillation effects suffered by light when it is transmitted in solar wind plasma, and can be characterized by the Beer-Lambert law and the Malaga distribution model, respectively. The transmission scheme of this embodiment uses zero aiming error and Rayleigh distribution model to characterize the effects of aiming error and arrival angle fluctuation caused by satellite perturbations and trajectory changes.

[0034] The signals received by the i-th hop (i=1, 2) FSO relay link are expressed as:

[0035] y1=Rh1x1+n1,

[0036] y2=GRh2y1+n2,

[0037] Where R represents the responsivity of the photodetector, h irepresents the attenuation coefficient of the i-th hop FSO channel, and x1 is the average optical power value in the first hop FSO link, which is P t Optical signal, n i is the background noise of the i-th hop, and G represents the gain value applied by the relay end to the signal. The background noise is the main noise of the FSO link, with a mean of zero and a variance of Where e is the elementary charge, B e represents the bandwidth of the FSO signal (in Hz), P b Represents the background light power. b =N b B o Ω FOV A r , N b is the radiation spectrum of wavelength, B o is the receiver filter bandwidth. Ω FOV =2π(1-cos(θ FOV )) is the field of view at the receiver, A r Represents the receiver lens area (in cm 2 ), θ FOV Represents the field of view at the receiver (unit: mrad). Considering heterodyne detection and intensity modulation direct detection of optical signals, the instantaneous signal-to-noise ratio of the i-th hop FSO link is expressed as Wherein, τ=1 and τ=2 indicate that the system adopts heterodyne detection and intensity modulation direct detection respectively.

[0038] The attenuation coefficient of the i-th hop FSO link is written as represents the solar wind plasma absorption attenuation coefficient of the i-th hop link, represents the solar wind turbulence attenuation coefficient of the i-th hop link, represents the pointing error attenuation coefficient of the i-th hop link, represents the arrival angle fluctuation attenuation coefficient of the i-th hop link. Therefore, with respect to h i The probability density function (PDF) of can be expressed as in, is the Meijer-G function, A i and is a constant, φ i and They represent the large-scale and small-scale vortices in the light scattering process of the i-th hop link, ζ represents the power of the scattered part obtained by the off-axis vortex, χ is the power from the coherent contribution, and w zi represents the beam width of the i-th hop link, σ ri represents the standard deviation of the distance between the center of the beam at the receiver and the center of the detector in the i-th hop link, σ 0irepresents the standard deviation of the light incident angle at the receiver of the i-th link and the aperture normal deviation angle, r ai represents the receiver aperture radius of the i-th hop link. Using the integral formula, h i The cumulative probability distribution function (CDF) of can be expressed as

[0039] consider The CDF of the instantaneous signal-to-noise ratio of the i-th hop FSO link can be rewritten as:

[0040]

[0041] in, γ i Taking the derivative, we can further obtain the PDF of the instantaneous signal-to-noise ratio of the i-th FSO link:

[0042]

[0043] Considering the use of amplification and forwarding protocol at the deep space relay satellite, the instantaneous signal-to-noise ratio of the double-hop FSO relay link is expressed as Among them, γ1 represents the instantaneous signal-to-noise ratio of the first-hop FSO link, γ2 represents the instantaneous signal-to-noise ratio of the second-hop FSO link, and C is the relay gain constant. Through double integration and exchange integration, the CDF of the instantaneous signal-to-noise ratio of the double-hop FSO relay link is expressed as:

[0044]

[0045] Substitute about γ i The CDF and PDF formulas of , and using the definition of the Meijer-G function, It can be expressed as:

[0046]

[0047] Among them, C1 and C2 are the s-plane profile and v-plane profile respectively. By integration simplification, F2(γ FSO ) can be expressed as:

[0048]

[0049] in, is the extended generalized bivariate H function. F3(γ FSO ) can be expressed as

[0050]

[0051] Therefore, about γ FSO The CDF of can be written as

[0052]

[0053] in,

[0054] use Through γ FSO Derivative, about γ FSO The PDF of can be expressed as:

[0055]

[0056] Step 3: Dual-hop FSO relay link channel estimation. Perform channel estimation on the dual-hop FSO relay link of the established deep space collaborative relay transmission model to obtain the channel state information (instantaneous signal-to-noise ratio) of the link, and feed back the channel state information of the dual-hop FSO relay link to the geosynchronous satellite to provide a decision basis for subsequent signal transmission of the geosynchronous satellite. The channel state information here refers to the instantaneous signal-to-noise ratio of the FSO relay channel.

[0057] Step 4: Design a transmission strategy: Using the channel estimation results from step 3, select the best transmission strategy for the system.

[0058] Specific:

[0059] 4-1. When the instantaneous signal-to-noise ratio γ of the dual-hop FSO relay link is greater than or equal to the system preset switching signal-to-noise ratio γ s When , the geosynchronous satellite only enables the dual-hop FSO relay link in step 2 for communication;

[0060] 4-2. When the instantaneous signal-to-noise ratio γ of the dual-hop FSO relay link is less than the system preset switching signal-to-noise ratio γ s When the system uses the dual-hop FSO relay link for communication, it enables the RF direct link, that is, the geosynchronous satellite simultaneously sends optical signals and RF signals with the same information. For the RF direct link, the transmission model uses the α-η-κ-μ distribution model to characterize the impact of solar wind turbulence on RF signal flicker. The α-η-κ-μ distribution model includes the nonlinear degree of the propagation medium α, the power ratio η of the in-phase scattered wave and the orthogonal scattered wave of the multipath cluster, the ratio κ of the main component power to the scattered wave power, and the number of multipath clusters μ. The relationship between the instantaneous signal-to-noise ratio γ and the amplitude r of the RF signal at the receiver is expressed as follows: Represents the average signal-to-noise ratio of the RF signal. The CDF of the α-η-κ-μ distribution model is expressed as:

[0061]

[0062] Among them, m k is a parameter, Γ(·) is the Gamma function.

[0063] When the instantaneous signal-to-noise ratio γ of the dual-hop FSO relay link is less than the system preset switching signal-to-noise ratio γ s When the deep space detector uses the maximum ratio combining technology to combine the optical signal and the radio frequency signal received at the same time. The deep space detector adjusts the phase and synchronizes the received optical signal and radio frequency signal, and then amplifies the two signals with the gain of their own fading coefficients. After amplification, the two signals are added in the same terms, and finally demodulated to obtain the baseband signal. The instantaneous signal-to-noise ratio of the output is γ MRC Equal to the instantaneous signal-to-noise ratio γ of the FSO relay link FSO The instantaneous signal-to-noise ratio of the RF link is RF Therefore, the instantaneous signal-to-noise ratio γ of the system is expressed as γ = γ MRC =γ FSO +γ RF .

[0064] Step 5: According to the optimal transmission strategy in step 4, obtain the key performance indicators of the system.

[0065] According to the working principle of the system, the CDF of the instantaneous signal-to-noise ratio of the system can be written as

[0066]

[0067] in, Can be achieved through γ FSO The CDF of F1(γ) is obtained. Using Taylor expansion, the closed-form expression of F1(γ) is written as

[0068]

[0069] also, It can be expressed as After integral transformation, The closed-form expression can be rewritten as:

[0070]

[0071] Taking the derivative of the CDF about γ, we get the end-to-end PDF about γ:

[0072]

[0073] in, Can be achieved through γ FSO The PDF of F1(γ) is obtained by differentiating the variable γ of the closed-form expression, and f1(γ) is written as

[0074] f1(γ)=IH(N+1)γ H(N+1)-1 .

[0075] According to the definition of the extended generalized two-variable H function, Taking the derivation, we can get The closed form expression for is:

[0076]

[0077] in,

[0078]

[0079] According to the above CDF and PDF expressions of γ, we can further get the transmission system outage probability P out (γ th ), bit error rate P e and channel capacity They are:

[0080]

[0081]

[0082] F1(γ th )and It can be seen that FSO CDF, F1(·) and the relationship between γ MRC The closed-form expression of the CDF is obtained.

[0083] Consider the average optical power P of the FSO relay link t →∞, i.e. D i →0, we can further obtain the system outage probability and bit error rate under high signal-to-noise ratio:

[0084]

[0085] in,

[0086] And, b j ={Τ1,φ1,k1}, e j ={H+1,Δ(τ,1+Τ1)},f j ={Δ(τ,Τ1),Δ(τ,φ1),Δ(τ,k1)},

[0087] The above preferred embodiment of the present invention has been simulated. Figure 3 The instantaneous signal-to-noise ratio γ of the double-hop FSO relay link of the present invention is less than the system preset switching signal-to-noise ratio γ sThe system interruption probability comparison diagram of the first embodiment is shown in FIG. The simulation environment is: the system preset switching signal-to-noise ratio γ s is 10dB, α=1, η=5, κ=5, μ=1, ρ=0.596, b0=0.1079, Ω=1.3265, C=1, ξ=-45dB / km, σ0=10mrad, σ r =1m, r = 0.5m, θ FOV =50mrad, w z =1m. The solar wind turbulence environment is weak turbulence (φ, ζ) = (8, 4). Figure 3 The displayed results show that the system interruption probability of the deep space collaborative relay transmission method based on adaptive selection of the present invention is significantly lower than that of the system interruption probability of the transmission strategies such as the existing RF direct transmission link and the dual-hop FSO relay link, that is, the present invention has better performance advantages.

[0088] like Figure 4 As shown, this embodiment discloses a deep space cooperative relay transmission system based on adaptive selection, which is used to execute the above method, and includes the following modules:

[0089] Transmission model establishment module: establish a deep space collaborative relay transmission model, the transmission model has two enabled communication links, namely: 1) double-hop free space optical relay link: the geosynchronous satellite transmits the signal to the deep space relay satellite based on optical communication technology, and the deep space relay satellite transmits the optical signal to the deep space detector after signal processing; 2) RF direct transmission link: the geosynchronous satellite transmits the RF signal directly to the deep space detector in a broadcast mode;

[0090] Signal transmission module: Enables dual-hop free-space optical relay link for signal transmission;

[0091] Channel estimation module: double-hop free-space optical relay link channel estimation;

[0092] Transmission strategy selection module: When the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is greater than or equal to the preset switching signal-to-noise ratio, the geosynchronous satellite only uses the free-space optical relay link for communication; when the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is less than the preset switching signal-to-noise ratio, while using the dual-hop free-space optical relay link, the RF direct transmission link is further enabled, that is, the geosynchronous satellite simultaneously sends optical signals and RF signals with the same information;

[0093] Performance indicator acquisition module: obtains key performance indicators based on the optimal transmission strategy.

[0094] For other contents of this embodiment, please refer to the aforementioned method embodiment.

[0095] In summary, the present invention discloses a deep space collaborative relay transmission technology solution based on adaptive selection, which is applied to geosynchronous satellites, deep space relay satellites, and deep space probes. The present invention takes into account the large-scale attenuation and small-scale fading caused by the rapid fluctuations in solar wind plasma density on radio frequency and optical signals, and further considers the influence of solar wind plasma absorption and satellite perturbation changes on the energy attenuation, aiming error and arrival angle fluctuations on optical signals. The main operation steps are: (1) establishing a universal and feasible deep space collaborative relay transmission model; (2) enabling the double-hop FSO relay link for signal transmission; (3) double-hop FSO relay link channel estimation; (4) transmission strategy selection; (5) based on the optimal transmission strategy, obtaining system key performance indicators. The present invention establishes a reliable deep space collaborative relay transmission link based on the channel estimation results, adopts adaptive collaborative technology to increase the signal-to-noise ratio of the signal received by the deep space probe, enhances the intelligence of the communication system, reduces the impact of the complex deep space environment on the deep space communication performance, improves the system communication quality and the transmission efficiency of the network, and has practical engineering application significance.

[0096] The above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, according to the ideas provided by the present invention, there will be changes in the specific implementation methods, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A deep space cooperative relay transmission method based on adaptive selection, characterized in that: The steps include: (1) Establishing a deep space collaborative relay transmission model, the transmission model has two enabled communication links, namely: 1) a double-hop free-space optical relay link: the geosynchronous satellite transmits the signal to the deep space relay satellite based on the optical communication technology, and the deep space relay satellite then transmits the optical signal to the deep space detector after signal processing; 2) RF direct link: Geosynchronous satellites transmit RF signals directly to deep space probes in broadcast mode; (2) Enabling a dual-hop free-space optical relay link for signal transmission; (3) Channel estimation for two-hop free-space optical relay links; (4) Transmission strategy selection: When the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is greater than or equal to the preset switching signal-to-noise ratio, the geosynchronous satellite only uses the free-space optical relay link for communication; when the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is less than the preset switching signal-to-noise ratio, while using the dual-hop free-space optical relay link, the RF direct transmission link is further enabled, that is, the geosynchronous satellite simultaneously sends optical signals and RF signals with the same information; (5) Obtain key performance indicators based on the optimal transmission strategy.

2. A deep space cooperative relay transmission method based on adaptive selection as claimed in claim 1, characterized in that: In step (2), the Beer-Lambert law, Malaga distribution model, zero pointing error and Rayleigh distribution model are used to characterize the effects of solar wind plasma absorption, solar wind turbulence, pointing error and arrival angle fluctuation on the optical signal transmission caused by the outside world.

3. A deep space cooperative relay transmission method based on adaptive selection as claimed in claim 2, characterized in that: In step (2), the signals received by the i-th hop FSO relay link are respectively expressed as: y1=Rh1x1+n1, y2=GRh2y1+n2, Where i = 1, 2; R represents the response rate of the photodetector, h i represents the attenuation coefficient of the i-th hop FSO channel, and x1 is the average optical power value in the first hop FSO link, which is P t Optical signal, n i is the background noise of the i-th hop, G represents the gain value applied by the relay end to the signal; the background noise is the main noise of the FSO link, with a mean of zero and a variance of Where e is the elementary charge, B e represents the bandwidth of the FSO signal, P b Represents the background light power; P b =N b B o Ω FOV A r , N b is the radiation spectrum of wavelength, B o is the receiver filter bandwidth; Ω FOV =2π(1-cos(θ FOV )) is the field of view at the receiver, A r represents the receiver lens area, θ FOV represents the field of view at the receiver; considering the heterodyne detection and intensity modulation direct detection of the optical signal, the instantaneous signal-to-noise ratio of the i-th hop FSO link is expressed as Wherein, τ = 1 and τ = 2 indicate that the system adopts heterodyne detection and intensity modulation direct detection respectively; The attenuation coefficient of the i-th hop FSO link is written as represents the solar wind plasma absorption attenuation coefficient of the i-th hop link, represents the solar wind turbulence attenuation coefficient of the i-th hop link, represents the pointing error attenuation coefficient of the i-th hop link, represents the arrival angle fluctuation attenuation coefficient of the i-th hop link; therefore, with respect to h i The probability density function PDF is expressed as in, is the Meijer-G function, A i and is a constant, φ i and They represent the large-scale and small-scale vortices in the light scattering process of the i-th hop link, ζ represents the power of the scattered part obtained by the off-axis vortex, χ is the power from the coherent contribution, and w zi represents the beam width of the i-th hop link, σ ri represents the standard deviation of the distance between the center of the beam at the receiver and the center of the detector in the i-th hop link, σ 0i represents the standard deviation of the light incident angle at the receiver of the i-th link and the aperture normal deviation angle, r ai represents the receiver aperture radius of the i-th hop link; using the integral formula, h i The cumulative probability distribution function CDF is expressed as consider The CDF of the instantaneous signal-to-noise ratio of the i-th hop FSO link is rewritten as: in, γ i Taking the derivative, we can further obtain the PDF of the instantaneous signal-to-noise ratio of the i-th FSO link: Considering the use of amplification and forwarding protocol at the deep space relay satellite, the instantaneous signal-to-noise ratio of the double-hop FSO relay link is expressed as Among them, γ1 represents the instantaneous signal-to-noise ratio of the first-hop FSO link, γ2 represents the instantaneous signal-to-noise ratio of the second-hop FSO link, and C is the relay gain constant. Through double integration and exchange integration, the CDF of the instantaneous signal-to-noise ratio of the double-hop FSO relay link is expressed as: Substitute about γ i The CDF and PDF formulas of , and using the definition of the Meijer-G function, It is expressed as: Among them, C1 and C2 are the s-plane profile and v-plane profile respectively; by integration simplification, F2(γ FSO ) is expressed as: in, is the extended generalized bivariate H function; F3(γ FSO ) is expressed as: Therefore, about γ FSO The CDF of is written as: in, use Through γ FSO Derivative, about γ FSO The PDF of is represented as:

4. A deep space cooperative relay transmission method based on adaptive selection as claimed in claim 1, characterized in that: In step (4), when a dual-hop free-space optical relay link and a radio frequency direct transmission link are used, the deep space detector uses a maximum ratio combining technique to combine the optical signal and the radio frequency signal received simultaneously; the deep space detector performs phase adjustment and synchronous equalization on the received optical signal and radio frequency signal, and then amplifies the two signals respectively, with the gain being its own fading coefficient, and then adds the two signals in the same terms, and finally demodulates to obtain a baseband signal; the output instantaneous signal-to-noise ratio is equal to the sum of the instantaneous signal-to-noise ratio of the free-space optical relay link and the instantaneous signal-to-noise ratio of the radio frequency link.

5. A deep space cooperative relay transmission method based on adaptive selection as claimed in claim 4, characterized in that: In step (4), the α-η-κ-μ distribution model is used to characterize the effect of solar wind turbulence on the RF signal flicker of the RF direct transmission link.

6. A deep space cooperative relay transmission method based on adaptive selection as claimed in claim 5, characterized in that: In step (4), the α-η-κ-μ distribution model includes the nonlinear degree α of the propagation medium, the power ratio η of the in-phase scattered wave and the orthogonal scattered wave of the multipath cluster, the ratio κ of the main component power to the scattered wave power, and the number μ of the multipath clusters; the relationship between the instantaneous signal-to-noise ratio γ and the amplitude r of the RF signal at the receiving end is expressed as Represents the average signal-to-noise ratio of the RF signal; the CDF of the α-η-κ-μ distribution model is expressed as: Among them, m k is a parameter, Γ(·) is the Gamma function.

7. A deep space cooperative relay transmission system based on adaptive selection, used to execute the method according to any one of claims 1 to 6, characterized in that: Includes the following modules: Transmission model establishment module: establish a deep space collaborative relay transmission model, the transmission model has two enabled communication links, namely: 1) double-hop free-space optical relay link: the geosynchronous satellite transmits the signal to the deep space relay satellite based on optical communication technology, and the deep space relay satellite transmits the optical signal to the deep space detector after signal processing; 2) RF direct link: Geosynchronous satellites transmit RF signals directly to deep space probes in broadcast mode; Signal transmission module: Enables dual-hop free-space optical relay link for signal transmission; Channel estimation module: double-hop free-space optical relay link channel estimation; Transmission strategy selection module: When the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is greater than or equal to the preset switching signal-to-noise ratio, the geosynchronous satellite only uses the free-space optical relay link for communication; when the instantaneous signal-to-noise ratio of the dual-hop free-space optical relay link is less than the preset switching signal-to-noise ratio, while using the dual-hop free-space optical relay link, the RF direct transmission link is further enabled, that is, the geosynchronous satellite simultaneously sends optical signals and RF signals with the same information; Performance indicator acquisition module: obtains key performance indicators based on the optimal transmission strategy.

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