Satellite-ground cooperative communication system and performance analysis method thereof

Abstract

The invention relates to a satellite-ground cooperative communication system and a performance analysis method thereof, the system comprises a source satellite and a cooperative relay satellite, the source satellite and the cooperative relay satellite share cooperative information through an inter-satellite link, and the source satellite and the cooperative relay satellite transmit information to a ground user together through a satellite-ground link; the cooperative process of the source satellite and the cooperative relay satellite comprises the following steps: in an initial stage, the source satellite and the cooperative relay satellite establish cooperative communication, and the source satellite transmits a first cooperative symbol x2 to the cooperative relay satellite; in the cooperative transmission stage, a source satellite sends a symbol x1 to a ground user and a cooperative relay satellite at the same time in a first time slot, and the cooperative relay satellite decodes and forwards a first cooperative symbol x2 to the ground user after receiving the symbol x1; and in a second time slot, the source satellite sends the symbol to the ground user and sends a second cooperation symbol x4 to the cooperation relay satellite, and the cooperation relay satellite sends the symbol to the ground user. According to the invention, the coverage probability and communication stability of satellite downlink transmission can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of satellite communication, in particular to a satellite-ground cooperative communication system and a performance analysis method thereof. BACKGROUND

[0002] With the rapid growth of global communication demand, low earth orbit (LEO) satellite communication has become an important direction to realize wireless seamless coverage and efficient communication. The wide coverage advantage of satellite communication plus the high bandwidth and low delay characteristics of ground network can provide ubiquitous communication services for users.

[0003] However, compared with the traditional ground network, the high mobility of satellites and the long transmission delay of satellite-ground link greatly affect satellite communication, which makes it difficult to obtain accurate channel state information (CSI) at the transmitting end. At the same time, satellites are in high altitude and lack scattering environment around them, resulting in a very small signal angle spread, and the transmitting signals of the same satellite form a highly correlated line-of-sight (LoS) channel. This highly spatially correlated LoS channel limits the diversity gain of multiple-input multiple-output (MIMO) systems.

[0004] In order to overcome the dependence on transmitting end CSI, space-time block code (STBC) has been widely used in ground communication networks. The most representative of STBC is Alamouti code, which has a full-rate orthogonal space-time block code suitable for two transmitting antennas and low decoding complexity. For the influence of satellite-ground strong correlation channel, an effective solution is to use cooperative communication, which generates multiple independent channels at the source end, so that sufficient diversity gain can be obtained. However, since the cooperative relay node is a ground base station, the cooperative signal and the source signal cannot arrive at the destination node at the same time, so asynchronous cooperative communication is needed, which increases the cooperative time slot. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a satellite-ground cooperative communication system and a performance analysis method thereof, which can improve the coverage probability and communication stability of satellite downlink transmission.

[0006] The technical solution adopted by the present application to solve the technical problem is: providing a satellite-ground cooperative communication system, including a source satellite and a cooperative relay satellite, the source satellite and the cooperative relay satellite share cooperative information through inter-satellite link, the source satellite and the cooperative relay satellite both transmit information to ground users through satellite-ground link; the cooperative process of the source satellite and the cooperative relay satellite includes:

[0007] Initial stage: the source satellite establishes cooperative communication with the cooperative relay satellite, and the source satellite transmits a first cooperative symbol x2 to the cooperative relay satellite;

[0008] Cooperative transmission phase: In the first time slot, the source satellite simultaneously transmits symbol x1 to both the ground user and the cooperative relay satellite; after receiving symbol x1, the cooperative relay satellite decodes and forwards the first cooperative symbol x2 received in the initial phase to the ground user; in the second time slot, the source satellite transmits symbol - to the ground user. And send a second cooperation symbol x4 to the cooperative relay satellite for the next cooperation cycle; the cooperative relay satellite will send the symbol Send to ground users;

[0009] Among them, symbols For the complex conjugate of symbol x1, the symbol - It is the inverse of the complex conjugate of the first cooperative symbol x2.

[0010] The technical solution adopted by this invention to solve its technical problem is: to provide a performance analysis method for the above-mentioned satellite-ground cooperative communication system, comprising the following steps:

[0011] The instantaneous signal-to-noise ratio of the inter-satellite FSO link is determined, and the pointing error angle and tracking error angle are modeled as Rayleigh distributions to obtain the probability density function and cumulative distribution function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link.

[0012] The instantaneous signal-to-noise ratio (SNR) of the satellite-to-ground Rf link is determined, and the probability density function and cumulative distribution function of the instantaneous SNR of the satellite-to-ground Rf link are obtained based on the fact that the fading of the satellite-to-ground RF channel follows the shadowed Ricean channel distribution.

[0013] The upper bounds of the outage probability and average bit error rate of the satellite-ground cooperative communication system are calculated based on the cumulative distribution function of the inter-satellite FSO link and the cumulative distribution function of the satellite-ground Rf link.

[0014] The instantaneous signal-to-noise ratio of the inter-satellite FSO link is expressed as: Where, γ FSO The instantaneous signal-to-noise ratio of the inter-satellite FSO link. θ represents the average signal-to-noise ratio of the inter-satellite FSO link. R L represents the tracking error angle. R (θ R θ represents the tracking error at the receiver. T L represents the pointing error angle. T (θ T ) represents the pointing error of the transmitter.

[0015] The probability density function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link is expressed as: The cumulative distribution function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link is expressed as: in, Let be the probability density function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link. Let γ be the cumulative distribution function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link. FSO The instantaneous signal-to-noise ratio of the inter-satellite FSO link. ψ and C represent the average signal-to-noise ratio of the inter-satellite FSO link. T and C R As an intermediate quantity, it is represented as: G T G represents the transmit antenna gain. R ε1 represents the receiving antenna gain, ε2 represents the lower bound of the tracking error at the receiving end, and ε3 represents the lower bound of the pointing error at the transmitting end.

[0016] The instantaneous signal-to-noise ratio of the satellite-to-ground Rf link is expressed as: Where, γ RF The instantaneous signal-to-noise ratio of the satellite-to-ground Rf link. g represents the average signal-to-noise ratio of the satellite-to-ground Rf link. RF For path loss, h RF This is due to channel fading.

[0017] The probability density function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link is expressed as: The cumulative distribution function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link is expressed as: in, Let be the probability density function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link. Let be the cumulative distribution function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link, where b0, m, and Ω are channel fading distribution parameters. g represents the average signal-to-noise ratio of the satellite-to-ground Rf link. RF For path loss, 1F1() represents the first-type merging hypergeometric function, k is the cumulative index variable, Γ() is the gamma function, and γ() represents the lower incomplete gamma function.

[0018] The interruption probability of the satellite-ground cooperative communication system is calculated as follows: P out =P CO (R)(1-P SR (R))+P SD (R)P SR (R), where P out Let P be the probability of an outage in a satellite-to-ground cooperative communication system. CO (R) is the probability of interruption of RF link cooperative transmission between the source satellite and the cooperating relay satellite at a rate of R, expressed as: P CO (R)=F γ+ (2 R -1), F γ+ (2 R -1) represents two random variables from the same family with a velocity of R and γ.+ The cumulative distribution value of P; SD (R) is the probability of transmission interruption between the source satellite and the ground user at a rate of R, expressed as: P represents the cumulative distribution value of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link at a rate of R. SR (R) represents the probability of inter-satellite FSO link interruption at a rate of R, expressed as: This represents the cumulative distribution of the instantaneous signal-to-noise ratio of the inter-satellite FSO link at a rate of R.

[0019] The upper bound of the average bit error rate is calculated as follows: ABEP = P out P(e|o)+P b Where ABEP is the upper bound of the average bit error rate, P out Let P(e|o) be the probability of an outage in the satellite-to-ground cooperative communication system, and let P(e|o) be the bit error rate when an outage occurs in the satellite-to-ground cooperative communication system. b The bit error rate of the satellite-ground cooperative communication system without interruption is denoted as: P b =P bFSO +(1-P bFSO )P bCO P bFSO P represents the bit error rate occurring in inter-satellite FSO links. bCO This represents the bit error rate of the joint transmission via the satellite-to-ground RF link.

[0020] The technical solution adopted by the present invention to solve its technical problem is: to provide an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-mentioned performance analysis method.

[0021] The technical solution adopted by the present invention to solve its technical problem is: to provide a computer-readable storage medium on which a computer program is stored, wherein the computer program, when executed by a processor, implements the steps of the above-mentioned performance analysis method.

[0022] Beneficial effects

[0023] Due to the adoption of the above technical solution, this invention has the following advantages and positive effects compared with the prior art: This invention establishes a satellite-to-ground communication system with a relay satellite and a distributed Alamouti protocol, which can improve the coverage probability and communication stability of satellite downlink transmission. Furthermore, it provides a performance analysis method for this satellite-to-ground communication system. By analyzing the system performance, it significantly overcomes the adverse effects of the strongly correlated LOS channel between satellite and ground on the system. Compared with a single-input single-output (SISO) system without cooperative communication and a two-transmit antenna (MISO) system, this system demonstrates its advantages in terms of bit error rate and outage probability. Attached Figure Description

[0024] Figure 1 This is a model diagram of the satellite-ground cooperative communication system according to the first embodiment of the present invention;

[0025] Figure 2 This is a flowchart of the performance analysis method for the satellite-ground cooperative communication system according to the second embodiment of the present invention. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0027] The first embodiment of the present invention relates to a satellite-ground cooperative communication system, such as... Figure 1 As shown, the system includes a source satellite and a cooperating relay satellite. The source satellite and the cooperating relay satellite share cooperative information via an inter-satellite link, and both transmit information to the ground user via a satellite-to-ground link. Both the source satellite and the cooperating relay satellite have the ability to simultaneously transmit and receive RF / FSO signals. The ground user is a Very Small Aperture Satellite Terminal (VSAT), which jointly decodes the information received from the two satellites.

[0028] In this embodiment, the cooperation process between the source satellite and the cooperative relay satellite includes an initial phase and a cooperative transmission phase.

[0029] In the initial phase, the source satellite establishes cooperative communication with the cooperative relay satellite. The source satellite transmits the first cooperative symbol x2 to the cooperative relay satellite. At this time, the signal received by the cooperative relay satellite is represented as:

[0030]

[0031] Among them, Y sr (0) represents the signal received by the relay satellite during the initial phase of cooperation, P FSO h represents the satellite's optical transmission power. sr Indicates the fading of the channel from the source satellite to the ground user, n sr (0) represents noise.

[0032] The cooperative transmission phase is divided into two time slots. In the first time slot, the source satellite simultaneously transmits symbol x1 to both the ground user and the cooperative relay satellite. After receiving symbol x1, the cooperative relay satellite decodes and forwards the first cooperative symbol x2 received in the initial phase to the ground user. At this time, the signals received by the ground user and the relay satellite are respectively represented as:

[0033]

[0034] Where Y1 is the signal received by the ground user in the first time slot, Y sr (1) For the signal received by the cooperative relay satellite in the first time slot, P RF Indicates the satellite's radio frequency transmission power, g sd h represents the path loss from the source satellite to the ground user. sd Indicates the fading of the channel from the source satellite to the ground user, g rd h represents the path loss from relay satellite to ground user. rd This represents the channel fading from relay satellite to ground user, n. RF (1) and n sr (1) is noise.

[0035] In the second time slot, the source satellite sends symbols to the ground user. And send a second cooperative symbol x4 to the cooperative relay satellite for the next cooperative cycle; the cooperative relay satellite will send the symbol... The signal is sent to the ground user. At this time, the signals received by the ground user and the relay satellite are respectively represented as:

[0036]

[0037] Where Y2 is the signal received by the ground user in the second time slot, Y sr (2) The signal received by the cooperative relay satellite in the second time slot, n RF (2) and n sr (2) is noise.

[0038] At this point, one cooperative transmission cycle ends, and the next cycle will cooperatively transmit (x3, x4) and begin directly from the cooperative transmission phase.

[0039] The decoding process for ground users is as follows:

[0040] The conjugate of the signal Y1 received by the ground user in the first time slot and the signal received by the ground user in the second time slot. In matrix form, that is:

[0041]

[0042] make exist Multiply by the left get:

[0043]

[0044] Thus, decoding can be performed twice using ML detection alone, i.e.:

[0045]

[0046] Where M represents the size of the signal constellation diagram.

[0047] It is easy to see that this implementation improves the order of the Alamouti code protocol, enabling it to be used in a distributed cooperative communication system with one node as the information center and the other as the relay node, thereby achieving distributed synchronous transmission.

[0048] The second embodiment of the present invention relates to a performance analysis method for a satellite-ground cooperative communication system according to the first embodiment, such as... Figure 2 As shown, it includes the following steps:

[0049] Step 1: Determine the instantaneous signal-to-noise ratio (SNR) of the inter-satellite FSO link, and model the pointing error angle and tracking error angle as Rayleigh distributions to obtain the probability density function and cumulative distribution function of the instantaneous SNR of the inter-satellite FSO link.

[0050] In this step, for inter-satellite FSO communication, the errors considered include the pointing error of the transmitter. Tracking error at the receiver Where, θ R θ represents the tracking error angle. T G represents the pointing error angle. T G represents the transmit antenna gain. R Indicating the receiving antenna gain, the instantaneous signal-to-noise ratio (SNR) of the inter-satellite FSO link can be expressed as:

[0051]

[0052] Where, γ FSO The instantaneous signal-to-noise ratio of the inter-satellite FSO link. This represents the average signal-to-noise ratio of the inter-satellite FSO link.

[0053] By modeling both the pointing error angle and the tracking error angle as Rayleigh distributions, the instantaneous signal-to-noise ratio γ of the inter-satellite FSO link can be derived. FSO The probability density function and cumulative distribution function are expressed as follows:

[0054]

[0055] in, Let be the probability density function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link. Let ψ and C be the cumulative distribution function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link. T and C R As an intermediate quantity, it is represented as: ε1 is the lower bound of the tracking error at the receiver, and ε2 is the lower bound of the pointing error at the transmitter.

[0056] Step 2: Determine the instantaneous signal-to-noise ratio (SNR) of the satellite-to-ground Rf link, and obtain the probability density function and cumulative distribution function of the instantaneous SNR of the satellite-to-ground Rf link based on the fact that the fading of the satellite-to-ground RF channel follows the shadowed Rice channel distribution.

[0057] In this step, for the satellite-to-ground Rf link, the instantaneous signal-to-noise ratio γ of the satellite-to-ground Rf link is... RF It can be represented as:

[0058]

[0059] in, g represents the average signal-to-noise ratio of the satellite-to-ground Rf link. RF For path loss, h RF This is due to channel fading.

[0060] The fading of the satellite-to-ground RF channel follows a shadowed-Rician channel distribution. Based on this, the instantaneous signal-to-noise ratio γ of the satellite-to-ground Rf link is derived. RF PDF and CDF are represented as follows:

[0061]

[0062] in, Let be the probability density function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link. Let be the cumulative distribution function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link, b0, m and Ω are channel fading distribution parameters, 1F1() represents the first type of merging hypergeometric function, k is the cumulative index variable, Γ() is the gamma function, and γ() represents the lower incomplete gamma function.

[0063] In this embodiment, the channel estimation error is modeled as the number of pilots N. p and pilot energy E p If the function is such that, due to the existence of channel estimation error, the relationship between the estimated value and the true value of channel fading is:

[0064]

[0065] Where, n k It is Gaussian white noise. and For the estimated channel fading, h FSO and h RF This represents actual channel fading.

[0066] After considering channel estimation errors, the derived PDFs for the SNR of the FSO link and the SNR of the RF link with errors are as follows:

[0067]

[0068] in, The equivalent average SNR includes channel estimation error; in For white noise n k variance For the MeijerG function.

[0069] Step 3: Calculate the upper bounds of the outage probability and average bit error rate of the satellite-ground cooperative communication system based on the cumulative distribution function of the inter-satellite FSO link and the cumulative distribution function of the satellite-ground Rf link.

[0070] In this step, given that the two satellites are at different angles relative to the ground user, the fading parameters of the communication channels between the source satellite and the cooperating satellite and the ground are different. To analyze the performance of the cooperative system, it is necessary to determine the PDF and CDF of the sum of two family-distributed random variables γ1 and γ2. Let γ + =γ1+γ2, then γ + The PDF and CDF are represented as follows:

[0071]

[0072] in, For beta function;

[0073]

[0074]

[0075] Among them, b 01 b 02 m1, m2, Ω1, and Ω2 are all channel fading distribution parameters. and Represents the average signal-to-noise ratio, where k1, k2, n1, and n2 are all cumulative index variables. (b) n Let b be an ascending factorial, representing the product of n consecutive increasing integers starting from b.

[0076] Regarding the outage probability of a cooperative communication system, its successful operation depends on the availability of the cooperative relay satellite. That is, if the relay satellite is interrupted, the cooperative communication system cannot complete the cooperation, and communication between the source satellite and the ground user can only proceed. Therefore, when the rate is R, the outage probability of the cooperative communication system can be expressed as:

[0077] P out =P CO (R)(1-P SR (R))+P SD (R)P SR (R);

[0078] Among them, P out Let P be the probability of an outage in a satellite-to-ground cooperative communication system. CO (R) is the probability of interruption of RF link cooperative transmission between the source satellite and the cooperating relay satellite at a rate of R, expressed as: P CO (R)=P(log(1+γ1+γ2)<R)=F γ+ (2 R -1), F γ+ (2 R -1) represents two random variables from the same family with a velocity of R and γ. + The cumulative distribution value of P; SD (R) is the probability of transmission interruption between the source satellite and the ground user at a rate of R, expressed as: P represents the cumulative distribution value of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link at a rate of R. SR (R) represents the probability of inter-satellite FSO link interruption at a rate of R, expressed as: This represents the cumulative distribution of the instantaneous signal-to-noise ratio of the inter-satellite FSO link at a rate of R.

[0079] The upper bound of the average bit error rate (BER) for a satellite-ground cooperative communication system refers to the probability of bit errors detected by the receiver. In the case of an infinite block length, the BER of a satellite-ground cooperative communication system depends entirely on channel attenuation, as the additive atypical noise and adjacent codewords are averaged out. However, when the block length is finite, both the error probability during an interruption and the error probability without an interruption increase. Neither the error probability during an interruption nor the error probability without an interruption can be ignored. Therefore, the upper bound of the average BER of a satellite-ground cooperative communication system is given by the following formula:

[0080] ABEP = P out P(e|o)+P b ≤P out +P b ;

[0081] Where ABEP is the upper bound of the average bit error rate, P out Let P(e|o) be the probability of an outage in the satellite-to-ground cooperative communication system, and let P(e|o) be the bit error rate when an outage occurs in the satellite-to-ground cooperative communication system. b The bit error rate (BER) of a satellite-ground cooperative communication system without interruption consists of two parts: the BER occurring in the inter-satellite FSO link, denoted as P. bFSO; and the bit error rate P of the joint transmission via satellite-to-ground RF link. bCO Therefore, the bit error rate of the satellite-ground cooperative communication system when no interruption occurs can be expressed as:

[0082] P b =P bFSO +(1-P bFSO )P bCO .

[0083] In this embodiment, the modulation scheme used in the satellite-ground cooperative communication system is binary phase shift keying (BPSK). Therefore, P bFSO It can be represented as:

[0084]

[0085] in, It represents γ FSO The moment generating function (MGF) is expressed as:

[0086]

[0087] Bit error rate P of joint transmission via satellite-to-ground RF link bCO The upper limit is derived through the well-known joint boundary:

[0088]

[0089] Wherein, P(X) i →X j ) is the pairwise error probability representation of sending X i Mistakenly identified as X j The probability of n. i,j Symbol X i and X j The Hamming distance. The pairwise error probability is calculated as:

[0090]

[0091] Where g1 and g2 represent path fading, and φ represents the integration parameter.

[0092] Substituting into the above equation, we get P bCO The expression:

[0093]

[0094] It is easy to see that this invention establishes a satellite-to-ground communication system with a relay satellite and a distributed Alamouti protocol, which can improve the coverage probability and communication stability of satellite downlink transmission. Furthermore, a performance analysis method for this satellite-to-ground communication system is provided. By analyzing the system performance, the adverse effects of the strongly correlated LOS channel between satellite and ground on the system are significantly overcome. By comparing with the SISO system and the MISO system using two transmit antennas, the advantages of the satellite-to-ground communication system of this invention in terms of bit error rate and outage probability are demonstrated.

[0095] The third embodiment of the present invention relates to an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the performance analysis method of the second embodiment described above.

[0096] The fourth embodiment of the present invention relates to a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the performance analysis method of the second embodiment.

[0097] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage and optical storage) containing computer-usable program code.

[0098] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0099] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction methods implemented in a process. Figure 1 One or more processes and / or boxesFigure 1 The function specified in one or more boxes.

[0100] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0101] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A satellite-ground cooperative communication system, characterized in that, It includes source satellites and cooperative relay satellites, which share cooperative information through inter-satellite links, and both source satellites and cooperative relay satellites jointly transmit information to ground users through satellite-to-ground links; The collaboration process between the source satellite and the cooperating relay satellite includes: Initial phase: The source satellite establishes cooperative communication with the cooperative relay satellite, and the source satellite transmits the first cooperative symbol x2 to the cooperative relay satellite; Cooperative transmission phase: In the first time slot, the source satellite simultaneously transmits symbol x1 to both the ground user and the cooperative relay satellite; after receiving symbol x1, the cooperative relay satellite decodes and forwards the first cooperative symbol x2 received in the initial phase to the ground user; in the second time slot, the source satellite transmits symbol x2 to the ground user. And send a second cooperation symbol x4 to the cooperative relay satellite for the next cooperation cycle; the cooperative relay satellite will send the symbol Send to ground users; Among them, symbols For the complex conjugate of symbol x1, symbol It is the inverse of the complex conjugate of the first cooperative symbol x2.

2. A performance analysis method for a satellite-ground cooperative communication system as described in claim 1, characterized in that, Includes the following steps: The instantaneous signal-to-noise ratio of the inter-satellite FSO link is determined, and the pointing error angle and tracking error angle are modeled as Rayleigh distributions to obtain the probability density function and cumulative distribution function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link. The instantaneous signal-to-noise ratio (SNR) of the satellite-to-ground Rf link is determined, and the probability density function and cumulative distribution function of the instantaneous SNR of the satellite-to-ground Rf link are obtained based on the fact that the fading of the satellite-to-ground RF channel follows the shadowed Ricean channel distribution. The upper bounds of the outage probability and average bit error rate of the satellite-ground cooperative communication system are calculated based on the cumulative distribution function of the inter-satellite FSO link and the cumulative distribution function of the satellite-ground Rf link.

3. The performance analysis method according to claim 2, characterized in that, The instantaneous signal-to-noise ratio of the inter-satellite FSO link is expressed as: Where, γ FSO The instantaneous signal-to-noise ratio of the inter-satellite FSO link. θ represents the average signal-to-noise ratio of the inter-satellite FSO link. R L represents the tracking error angle. R (θ R θ represents the tracking error at the receiver. T L represents the pointing error angle. T (θ T ) represents the pointing error of the transmitter.

4. The performance analysis method according to claim 2, characterized in that, The probability density function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link is expressed as: The cumulative distribution function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link is expressed as: in, Let be the probability density function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link. Let γ be the cumulative distribution function of the instantaneous signal-to-noise ratio of the inter-satellite FSO link. FSO The instantaneous signal-to-noise ratio of the inter-satellite FSO link. ψ and C represent the average signal-to-noise ratio of the inter-satellite FSO link. T and C R As an intermediate quantity, it is represented as: G T G represents the transmit antenna gain. R ε1 represents the receiving antenna gain, ε2 represents the lower bound of the tracking error at the receiving end, and ε3 represents the lower bound of the pointing error at the transmitting end.

5. The performance analysis method according to claim 2, characterized in that, The instantaneous signal-to-noise ratio of the satellite-to-ground Rf link is expressed as: Where, γ RF The instantaneous signal-to-noise ratio of the satellite-to-ground Rf link. g represents the average signal-to-noise ratio of the satellite-to-ground Rf link. RF For path loss, h RF This is due to channel fading.

6. The performance analysis method according to claim 2, characterized in that, The probability density function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link is expressed as: The cumulative distribution function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link is expressed as: in, Let be the probability density function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link. Let be the cumulative distribution function of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link, where b0, m, and Ω are channel fading distribution parameters. g represents the average signal-to-noise ratio of the satellite-to-ground Rf link. RF For path loss, 1F1() represents the first-type merging hypergeometric function, k is the cumulative index variable, Γ() is the gamma function, and γ() represents the lower incomplete gamma function.

7. The performance analysis method according to claim 2, characterized in that, The interruption probability of the satellite-ground cooperative communication system is calculated as follows: P out =P CO (R)(1-P SR (R))+P SD (R)P SR (R), where P out Let P be the probability of an outage in a satellite-to-ground cooperative communication system. CO (R) is the probability of interruption of RF link cooperative transmission between the source satellite and the cooperating relay satellite at a rate of R, expressed as: P CO (R)=F γ+ (2 R -1), F γ+ (2 R -1) represents two random variables from the same family with a velocity of R and γ. + The cumulative distribution value of P; SD (R) is the probability of transmission interruption between the source satellite and the ground user at a rate of R, expressed as: P represents the cumulative distribution value of the instantaneous signal-to-noise ratio of the satellite-to-ground Rf link at a rate of R. SR (R) represents the probability of inter-satellite FSO link interruption at a rate of R, expressed as: This represents the cumulative distribution of the instantaneous signal-to-noise ratio of the inter-satellite FSO link at a rate of R.

8. The performance analysis method according to claim 2, characterized in that, The upper bound of the average bit error rate is calculated as follows: ABEP = P out P(e|o)+P b Where ABEP is the upper bound of the average bit error rate, P out Let P(e|o) be the probability of an outage in the satellite-to-ground cooperative communication system, and let P(e|o) be the bit error rate when an outage occurs in the satellite-to-ground cooperative communication system. b The bit error rate of the satellite-ground cooperative communication system without interruption is denoted as: P b =P bFSO +(1-P bFSO )P bCO P bFSO P represents the bit error rate occurring in inter-satellite FSO links. bCO This represents the bit error rate of the joint transmission via the satellite-to-ground RF link.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the performance analysis method as described in any one of claims 2-8.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the performance analysis method as described in any one of claims 2-8.

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