Method and System for Transmitting in a Dual-Layer Satellite Network Combining Geostationary Orbit and Low Orbit

Abstract

The present invention discloses a method and system for transmitting in a combined geosynchronous orbit and low-orbit double-layer satellite network. The method includes the following steps: S1, a geosynchronous orbit (GEO) satellite transmits signals to low-earth orbit (LEO) satellites and cellular users; S2, the LEO satellites and cellular users receive the signals transmitted by the GEO satellite; S3, the LEO satellites use the decode-and-forward relay protocol and adaptive non-orthogonal multiple access (NOMA) to send signals to the cellular users; S4, the cellular users receive the signals relayed by the LEO satellites and combine the signals from the GEO satellite and the LEO satellite using the maximum ratio combining method. The power allocation factor of the adaptive non-orthogonal multiple access technology proposed by the present invention is dynamically adjusted according to the channel state, satellite elevation angle, and co-channel interference, and can achieve differential power allocation for different users' dynamic channels, improving the spectrum utilization rate and power allocation fairness.

Description

Technical Field

[0001] The present invention belongs to the field of satellite wireless communication, and particularly relates to a joint geostationary orbit / low Earth orbit dual-layer satellite network transmission method and system based on adaptive non-orthogonal multiple access. Background Art

[0002] Multilayer satellite networks (MLSNs) can integrate satellites in different orbits, including geostationary Earth orbit (GEO) and low Earth orbit (LEO) satellites, to achieve complementary functions and information interaction, improve the reliability and throughput of communication systems, and thus realize global high-speed communication coverage. They are an important supplement and research hotspot for 5G and 6G mobile communications. In addition, the high-speed movement nature of LEO satellites makes them suitable for disaster areas to provide mobility support, and the network resilience of MLSNs can also ensure the continuity of communication during disasters.

[0003] Regarding the research on communication technologies between MLSNs and terrestrial users, currently, the orthogonal multiple access (OMA) scheme is mainly adopted, where various orthogonal communication resource blocks are allocated to each user in the system. However, the spectrum utilization rate of OMA is low and it is difficult to meet the surging traffic demands of 5G and 6G networks. The non-orthogonal multiple access (NOMA) technology differentiates users through different power allocations, allowing multiple users to simultaneously use the same time-frequency resources, which can improve communication capacity, throughput, and fairness, and can effectively address the limited spectrum resources in MLSNs communication. Therefore, NOMA is considered to have great application value and broad application prospects in future MLSNs communication.

[0004] However, most current studies on NOMA in the field of communication adopt the method of fixed power allocation factor. This method simplifies the system design and analysis to a certain extent, but there are also some potential limitations and defects. In the actual communication environment, the channel state between the user and the transmitter may change. Fixed power allocation cannot optimally adapt to the needs of different users, resulting in a reduction in the overall communication capacity and efficiency of the communication system, thus affecting the communication performance. In addition, in the current research on NOMA in satellite communication, most studies mainly consider geostationary orbit satellites and have not considered the impact of satellite mobility on communication performance. However, in MLSNs, the high-speed movement of LEO satellites will cause the rapid change of the satellite-ground distance, thus triggering fluctuations in path loss. Therefore, the 5G and 6G research integrating satellite communication needs to more comprehensively consider the impact of satellite mobility on the application of NOMA in satellite communication to ensure that the system design and performance evaluation are more accurate and reliable. Summary of the Invention

[0005] In view of the above situation of the prior art, the present invention proposes a joint geostationary orbit / low earth orbit double-layer satellite network transmission method and system based on adaptive non-orthogonal multiple access, which is applied to GEO satellites, LEO satellites, cellular users and wireless access points. The present invention belongs to the field of satellite wireless communication. In the present invention, the GEO satellite directly transmits a signal s to the LEO satellite and the cellular user G , where represents solving the expectation. The LEO satellite adopts a decode-and-forward (DF) relay protocol and uses its decoding and re-encoding capabilities to improve communication reliability. Subsequently, the LEO satellite uses adaptive NOMA technology to send a signal s to the cellular user G . In addition, the cellular user uses the maximum ratio combining scheme to decode the signals from the LEO satellite and the GEO satellite. The power allocation factor of the adaptive NOMA technology is determined by the channel fading, path loss, co-channel interference in the communication link and the elevation angle change during the movement of the LEO satellite.

[0006] The present invention adopts the following technical solutions:

[0007] The joint geostationary orbit / low earth orbit double-layer satellite network transmission method based on adaptive non-orthogonal multiple access of the present invention, the network consists of a GEO satellite, an LEO satellite, cellular users and multiple wireless access points. The present invention considers two users with different channel conditions: a user with good channel state (CU N ) and a user with poor channel state (CU F ). In addition, all devices are equipped with a single antenna. The midpoint between the two cellular users is denoted as U0, h L and h Grespectively represent the heights of LEO satellites and GEO satellites from the ground, and r E is the radius of the earth, and d GL is the distance of the GEO-LEO link, represents the distance between LEO and U0. Furthermore, β ∈ [β min , β max is used to represent the average elevation angle of the LEO satellite observed by the cellular user. Taking the GEO satellite-earth center as the reference line, is used to represent the polar angle of the LEO satellite's movement, that is, the angle between the L2-O line and the S-O line. Among them, In addition, it is assumed that the wireless access point in the ground cellular network shares the licensed spectrum with the cellular user, and the wireless access point will generate co-channel interference to the cellular user. Co-channel interference will cause the received signal to be interfered, thereby reducing the signal quality. The specific technical solution of the present invention is as follows:

[0008] A transmission method for a combined geosynchronous orbit and low-orbit double-layer satellite network, comprising the following steps:

[0009] S1, the geosynchronous orbit GEO satellite transmits signals to the low-orbit LEO satellite and the cellular user;

[0010] S2, the LEO satellite and the cellular user receive the signals transmitted by the GEO satellite;

[0011] S3, the LEO satellite uses the decode-and-forward relay protocol and adaptive NOMA to send signals to the cellular user;

[0012] S4, the cellular user receives the signals relayed by the LEO satellite and combines the signals received from the GEO satellite and the LEO satellite using the maximum ratio combining method.

[0013] Preferably, in step S1, the GEO satellite directly transmits the signal s m to the LEO satellite and the cellular user (U G ), m ∈ {N, F} (set a threshold, those greater than or equal to the threshold are represented by U N indicating users with better channel conditions; those less than the threshold are represented by U F indicating users with better channel conditions).

[0014] Preferably, in step S2, the signals received by the LEO satellite and the cellular user U m can be respectively expressed as Among them, H Gl and H GU respectively represent the channel coefficients of the GEO-LEO link and the GEO-cellular user link. P G is the transmission power of the GEO satellite. N mIndicates the number of wireless access points interfering with cellular users. s j Indicates the interference signal of the j-th wireless access point, where P a is the fixed transmit power of all wireless access points. n L and represent the additive white Gaussian noise at the LEO satellite and the cellular user respectively. The received signal-to-noise ratios (SNRs) of the LEO satellite and the cellular user are respectively where P L represents the transmission power of the LEO satellite, P G represents the transmission power of the GEO satellite. is the co-channel interference experienced by the cellular user, where the signal-to-noise ratio of the wireless access point P a represents the transmission power of the wireless access point, h j,bm represents the channel coefficient of the j-th wireless access point to the U m link.

[0015] Preferably, in step S2, the channel coefficient of the GEO-LEO link is expressed as where G G and G L represent the antenna gains of the GEO satellite and the LEO satellite respectively; the channel attenuation coefficient of the GEO-LEO link is expressed as |h GL | 2 ; use to represent the path loss factor of the GEO-LEO link; where c≈3×10 8 m / s represents the speed of light, f c represents the carrier frequency; k B =1.38×10 -23 J / K is the Boltzmann constant; T n represents the noise temperature of the LEO satellite, B c represents the carrier bandwidth; d GL represents the distance between the GEO satellite and the LEO satellite.

[0016] |h GL | 2 The PDFs and CDFs of are respectively expressed as:

[0017]

[0018]

[0019] where K represents the Rice factor;

[0020] Considering the path loss and rapid channel fading of the GEO satellite-ground link, the channel coefficient of this link is expressed as where G G and G U represent the antenna gains of the GEO satellite and the cellular user respectively; represents the path loss factor of the GEO satellite-cellular user link, where d GU represents the distance between the GEO satellite and the cellular user; |h GU | 2 is the channel attenuation coefficient of the satellite-ground link, and the PDF and CDF are expressed as:

[0021]

[0022]

[0023] where the average power of the LOS component in the satellite-ground link is denoted by Ω s and the average power of the multipath component is denoted by 2n s ; m s represents the Nakagami parameter, indicating the degree of shadowing affecting the channel; 1F1(·;·;·) and γ(·,·) are the confluent hypergeometric function and the lower incomplete gamma function respectively.

[0024] Preferably, in step S2, the distance of the GEO-LEO link is:

[0025]

[0026] where the polar angle satisfies and h L represents the LEO satellite altitude, h G represents the GEO satellite altitude, r E represents the radius of the earth; the angular velocity of the LEO satellite is considered constant throughout the visible window, denoted as ω; from the formula it is obtained that: the polar angle is uniformly distributed within the satellite visibility duration t, denoted as t min <t<t max .

[0027] Preferably, in step S3, considering the high-speed movement of the LEO satellite, the channel state between the user and the satellite will change. The channel coefficients of the low-earth orbit satellite and the cellular user link are denoted by and respectively (the channel coefficient with better channel state is The channel coefficient of the channel with poor channel state is ). Define CU N and CU F to represent the user with good channel state and the user with poor channel state respectively (the channel state can be distinguished by setting a threshold. For example, if it is greater than or equal to the threshold, the channel state is good; if it is less than the threshold, the channel state is poor). According to the definition of NOMA technology, in the present invention, the power allocation coefficients of CU N and CU F are respectively represented as a N and a F , where a F ≥a N , and a N +a F =1. Therefore, let m∈{N,F}, and the received signals of CU N and CU F are comprehensively expressed as:

[0028]

[0029] where s F represents the signal transmitted by LEO to CU F , s N represents the signal transmitted by LEO to CU N , s j represents the signal transmitted by the jth radio access point to CU N , s k represents the signal transmitted by the kth radio access point to CU F ; h j,bm represents the channel coefficient of the link from the jth radio access point to CU N , h k,bm represents the channel coefficient of the link from the kth radio access point to CU F . The number of radio access points interfering with CU N is N N , and the number of radio access points interfering with CU F is N F .

[0030] Preferably, in step S3, considering the path loss and fast channel fading of the LEO satellite - terrestrial link, the channel coefficient of this link is expressed as where G L represents the antenna gain of the GEO satellite; represents the path loss factor of the link between the LEO satellite and the cellular user, where represents the distance between the LEO satellite and the cellular user; is the channel attenuation coefficient of the LEO satellite-ground link, and the PDF and CDF are respectively expressed as:

[0031]

[0032]

[0033] Using the small parameter approximation method, the closed-form expression of the PDF of the co-channel interference received by the user is derived as:

[0034]

[0035] where is the normalization parameter, the number of wireless access points Nm interfering with the cellular user is a positive integer; (2N m -1)!! represents the double factorial of (2N m -1); represents the SNR of the wireless access point in this system.

[0036] Preferably, in step S4, the present invention uses a perfect successive interference cancellation (SIC) scheme to decode the signal s N at CU N , that is, the s F signal can be completely eliminated at CU N . The signal-to-interference-plus-noise ratio (SINR) of CU N is expressed as I N represents the co-channel interference received by CU N . The adaptive NOMA power allocation technology is as follows: To ensure the fairness of power allocation, that is, to balance the channel capacities of the two cellular users, the present invention designs a dynamically changing power allocation scheme. The power allocation factor is dynamically adjusted according to the channel state, satellite elevation angle, and co-channel interference to achieve differential power allocation for different user dynamic channels. According to the NOMA principle, the signal s F received by CU N can be directly regarded as interference. Therefore, the SINR of CU F is I F represents the co-channel interference received by CU F . The signals received from the GEO satellite and the LEO satellite are combined using the maximum ratio combining method, and the SNR of CU N and CU F can be expressed as:

[0037]

[0038]

[0039] In order to obtain the propagation loss of each link, the present invention proposes a distance distribution model for each link. In addition, considering the moving LEO satellites, an elevation angle distribution model of LEO satellites is proposed, which specifically includes: introducing the definition of the satellite visibility window duration, deriving the expression of the cumulative distribution function of the LEO satellite elevation angle, and deriving the expression of the cumulative distribution function of the LEO satellite elevation angle, and taking the derivative of the cumulative distribution function to obtain the expression of the probability density function of the elevation angle.

[0040] The distance of the GEO-LEO link is:

[0041]

[0042] where the polar angle satisfies and h L represents the height of the LEO satellite, h G represents the height of the GEO satellite, and r E represents the radius of the earth. The angular velocity of the LEO satellite can be regarded as constant throughout the visibility window, denoted as ω. From the formula it can be known that: the polar angle is uniformly distributed within the satellite visibility duration t, denoted as t min < t < t max .

[0043] Let U0 be the midpoint of CU N and CU F . The calculation formula for the distance between the LEO satellite and U0 is:

[0044]

[0045] where the elevation angle β satisfies β min < β < β max . According to the definition of the elevation angle, it can be obtained that β min > 0.

[0046] Let z represent the horizontal distance between two cellular users. According to the cosine theorem, the distances and between the LEO satellite and the two cellular users can be respectively expressed as:

[0047]

[0048] The present invention gives the expression of the cumulative distribution function (CDF) of the LEO satellite elevation angle as:

[0049]

[0050] Among them, t max represents the moment when the ground cellular user observes the maximum elevation angle of the LEO satellite, and t min represents the initial moment when the ground user observes the LEO satellite, and t β represents the moment when the elevation angle is β; χ(t max ) represents the angular distance from the LEO satellite to the user at the moment of t max .

[0051] Taking the derivative of F(β) gives the expression of the probability density function (PDF) of the elevation angle β as:

[0052]

[0053] For different types of links, different channel models need to be adopted to characterize. Specifically, for the inter-satellite link without shadow occlusion, the Rice model is selected by the present invention for fitting. There is shadow occlusion in the satellite-ground link, and the present invention uses the shadow Rice model to characterize. Since there are a large number of buildings on the ground and it can be regarded as having no direct path, the wireless access point-CU m link adopts the Rayleigh model.

[0054] Long-distance satellite communication will cause serious path loss in the inter-satellite link. In addition, the inter-satellite link is easily affected by frequency-selective fading caused by multipath (usually called fast fading). Therefore, the channel coefficient of the GEO-LEO link is expressed as where G G and G L respectively represent the antenna gains of the GEO satellite and the LEO satellite. The channel attenuation coefficient of the GEO-LEO link is expressed as |h GL | 2 . The present invention uses to represent the path loss factor of the GEO-LEO link. Among them, c≈3×10 8 m / s represents the speed of light, and f c represents the carrier frequency. k B = 1.38×10 - 23 J / K is the Boltzmann constant. In addition, T n represents the noise temperature of the LEO satellite, and B c represents the carrier bandwidth.

[0055] The PDF and CDF distributions of the Rice distribution are expressed as:

[0056]

[0057]

[0058] Among them, K represents the Rice factor.

[0059] Considering the path loss and fast channel fading of the GEO satellite-ground link, the channel coefficient of this link is expressed as where G G and G U represent the antenna gains of the GEO satellite and the cellular user, respectively. represents the path loss factor of the GEO satellite-cellular user link, where d GU represents the distance between the GEO satellite and the cellular user. |h GU | 2 is the channel attenuation coefficient of the satellite-ground link, and the PDF and CDF are expressed as:

[0060]

[0061]

[0062] Among them, the average power of the LOS component in the satellite-ground link is represented by Ω s and the average power of the multipath component is represented by 2n s m s represents the Nakagami parameter, indicating the degree of shadowing affecting the channel. 1F1(·;·;·) and γ(·,·) are the confluent hypergeometric function and the lower incomplete gamma function, respectively.

[0063] In addition, the LEO satellite-ground link also suffers from path loss and fast channel fading, and the channel coefficient of this link is expressed as where G L represents the antenna gain of the GEO satellite; represents the path loss factor of the LEO satellite-cellular user link, where represents the distance between the LEO satellite and the cellular user; is the channel attenuation coefficient of the LEO satellite-ground link, and the PDF and CDF are expressed as:

[0064]

[0065]

[0066] The co-channel interference received by the user is approximately solved as follows: Each wireless access point-user CU mThe envelope of the link is represented as statistically independent Rayleigh random variables. To calculate the cumulative co-channel interference suffered by the user, it is necessary to determine the sum distribution of these Rayleigh random variables. The small-parameter approximation method simplifies complex mathematical expressions by ignoring high-order terms. Using the small-parameter approximation method, the closed-form expression of the PDF of the co-channel interference suffered by the user is derived as follows:

[0067]

[0068] where is the normalization parameter, the number of wireless access points Nm interfering with the cellular user is a positive integer. (2N m - 1)!! represents the double factorial of (2N m - 1). represents the SNR of the wireless access points in the system.

[0069] The present invention gives the channel capacity of a joint geostationary orbit / low-earth orbit two-layer satellite network based on adaptive non-orthogonal multiple access. To ensure the fairness of power allocation, that is, to balance the channel capacities of two cellular users, the present invention designs a dynamically changing power allocation scheme. The power allocation factor is dynamically adjusted according to factors such as the channel state, satellite elevation angle, co-channel interference, etc., to achieve differential power allocation for different users' dynamic channels.

[0070] Channel capacity refers to the maximum transmission rate that can be achieved for error-free communication over a channel and is an index for evaluating channel efficiency and information transmission ability. The channel capacities of CU N and CU F are respectively written as:

[0071]

[0072]

[0073] where represents the average channel gain. and respectively represent the average co-channel interference of CU N and CU F . The average channel fading coefficient is obtained in the form of an expectation Similarly, by solving the expectation value, the average co-channel interference can be calculated as:

[0074]

[0075] The channel capacities of CU N and CU F are rewritten as:

[0076]

[0077]

[0078] Among them,

[0079] To ensure the fairness of power allocation, that is, to balance the channel capacity of CU N and CU F The power allocation coefficients are derived and denoted as a N and a F , expressed as:

[0080]

[0081] Among them,

[0082] It can be seen from the above formula that the power allocation coefficient is affected by the co-channel interference, path loss, channel fading, and antenna gain of the transmitter and receiver.

[0083] The present invention also discloses a joint geosynchronous orbit and low-orbit double-layer satellite network transmission system. Based on the above method, it includes the following modules:

[0084] Signal transmission module: The geosynchronous orbit GEO satellite transmits signals to the low-orbit LEO satellite and cellular users;

[0085] Signal reception module: The LEO satellite and cellular users receive the signals transmitted by the GEO satellite;

[0086] Signal decoding and forwarding module: The LEO satellite uses the decode-and-forward relay protocol and adaptive NOMA to send signals to cellular users;

[0087] Signal reception and combination module: Cellular users receive the signals forwarded by the LEO satellite and combine the signals received from the GEO satellite and the LEO satellite using the maximum ratio combination method.

[0088] In summary, based on the adaptive cooperative NOMA technology, the present invention establishes a joint geosynchronous orbit / low-orbit double-layer satellite network transmission method and system based on adaptive non-orthogonal multiple access. Considering that the high-speed movement of the LEO satellite will cause the rapid change of the satellite-ground distance, thus triggering the fluctuation of path loss, the present invention proposes an elevation angle distribution model of the LEO satellite and gives the PDF and CDF of the satellite elevation angle. The power allocation factor of the adaptive non-orthogonal multiple access technology proposed in this patent is dynamically adjusted according to the channel state, satellite elevation angle, and co-channel interference, which can achieve differential power allocation for different user dynamic channels, improve the spectrum utilization rate and power allocation fairness. Description of the Drawings

[0089] To more clearly explain the specific technical method of the present invention, the following will briefly introduce the drawings required in the description of the embodiments or the prior art.

[0090] Figure 1 It is a communication process flowchart of a transmission method for a joint geostationary orbit / low-earth orbit double-layer satellite network based on adaptive non-orthogonal multiple access in a preferred embodiment of the present invention;

[0091] Figure 2 It is a structural diagram of a communication system involved in a transmission method for a joint geostationary orbit / low-earth orbit double-layer satellite network based on adaptive non-orthogonal multiple access provided by the present invention;

[0092] Figure 3 It is a block diagram of a transmission system for a joint geostationary orbit / low-earth orbit double-layer satellite network based on adaptive non-orthogonal multiple access in a preferred embodiment of the present invention. Specific embodiments

[0093] In order to enable those skilled in the art to better understand the method of the present invention, the present invention will be further described in detail below with reference to the drawings and preferred embodiments.

[0094] The present invention provides a transmission method and system for a joint geostationary orbit / low-earth orbit double-layer satellite network based on adaptive non-orthogonal multiple access, which relates to an adaptive NOMA technology, and its power allocation factor is determined by the antenna gains of the transmitter and receiver, channel fading, co-channel interference, and path loss. In addition, the present invention relates to a method for analyzing the elevation angle distribution of LEO satellites, and gives closed-form expressions for the PDF and CDF of the elevation angle of LEO satellites. Using the adaptive NOMA technology can improve the outage performance of the double-layer GEO / LEO satellite communication system and achieve fair channel capacity.

[0095] The transmission method for a joint geostationary orbit / low-earth orbit double-layer satellite network based on adaptive non-orthogonal multiple access in this embodiment is applied to cellular users, LEO satellite relay nodes, and GEO satellite nodes. See Figure 1 , and specifically includes the following steps:

[0096] Step S101: The GEO satellite sends RF signals to the LEO satellite and the cellular user respectively.

[0097] In this embodiment, the GEO satellite can provide wireless coverage and realize wireless signal transmission with wireless terminals. The orbital altitude range of the LEO satellite is 500 to 1500 kilometers, and the orbital altitude range of the GEO satellite is 35786 kilometers. The orbital altitude of the satellite is not limited in this embodiment. The GEO satellite generates transmission signals based on three different frequencies; the frequency division multiple access technology is used to simultaneously transmit the signals to the LEO satellite and two cellular users. Among them, the signal sent to the LEO satellite is a combination of the signals of the two cellular users.

[0098] Step S102: The LEO satellite and the cellular users receive the signals transmitted by the GEO satellite.

[0099] In this embodiment, the LEO satellite and the cellular users simultaneously receive the signals from the GEO satellite. If the LEO satellite fails to successfully decode the signals or moves to a range that cannot be covered by the GEO satellite, the transmission will stop. The cellular users can finally only receive the signals from the GEO satellite.

[0100] Step S103: The LEO satellite uses the decode-and-forward (DF) relay protocol and the adaptive NOMA technology to separately send the signals to the two cellular users.

[0101] In this embodiment, when the LEO satellite sends signals based on the adaptive NOMA technology, the signals received from the GEO satellite should be converted into two signals sent to different cellular users based on the same frequency. After the LEO satellite successfully decodes the signals, it converts the signals into signals sent to different cellular users based on the same frequency; obtains the channel states, link distances from the LEO satellite to the two cellular users, the elevation angle of the LEO satellite, and the channel states of the wireless nodes that interfere with the cellular users around. And judge the channel conditions of the two users according to the above information, and design the corresponding adaptive power allocation coefficients; the LEO satellite performs power allocation on the signals to be sent to the two users, and uses the adaptive NOMA technology to transmit the signals to the two cellular users. The user with better channel conditions (CU N ) is allocated a lower proportion of the transmission power, and the user with poorer channel conditions (CU F ) is allocated a higher proportion of the transmission power. The satellite superimposes these signals to generate a superimposed signal, so that the superimposed signal can be transmitted in the same channel, improving the transmission throughput and communication fairness of the system.

[0102] It should be particularly noted that the link distances and channel states between the LEO satellite and the two cellular users are changing. And the power allocation factor of the adaptive NOMA technology proposed by the present invention will change with the change of the channel state, and can adapt to the dynamically changing channel state.

[0103] Step S104: The cellular user receives the signal relayed by the LEO satellite and combines the received signals from the GEO satellite and the LEO satellite using the maximum ratio combining method.

[0104] In this embodiment, the cellular user receives the signal relayed by the LEO satellite. If the LEO satellite fails to decode successfully, the signal cannot be received.

[0105] For the signal of the LEO satellite, the user CU with better channel state N employs the successive interference cancellation technique. First, it eliminates the part of the signal with larger power in the overlapping signal that is sent to the user CU with worse channel state F and the remaining signal is the signal it needs; the CU F does not need to use successive interference cancellation and treats the part of the signal with smaller power in the overlapping signal that is sent to the CU N as noise for processing. Finally, both users respectively adopt the maximum ratio combining technique to integrate the signals from different signal sources and obtain their respective required signals.

[0106] As Figure 3 shown, this embodiment discloses a combined geosynchronous orbit and low orbit double - layer satellite network transmission system. Based on the above - mentioned method embodiment, it includes the following modules:

[0107] Signal transmission module: The geosynchronous orbit GEO satellite transmits signals to the low - orbit LEO satellite and the cellular user;

[0108] Signal reception module: The LEO satellite and the cellular user receive the signals transmitted by the GEO satellite;

[0109] Signal decoding and forwarding module: The LEO satellite uses the decode - and - forward relay protocol and adaptive NOMA to send signals to the cellular user;

[0110] Signal reception and combination module: The cellular user receives the signal relayed by the LEO satellite and combines the received signals from the GEO satellite and the LEO satellite using the maximum ratio combining method.

[0111] Other content of this embodiment can refer to the above - mentioned method embodiment.

[0112] In summary, the present invention discloses a joint geostationary orbit / low-earth orbit dual-layer satellite network transmission method and system based on adaptive non-orthogonal multiple access, which is applied to geostationary orbit satellites, low-earth orbit satellites, cellular users, and wireless access points, and belongs to the field of satellite wireless communication. In the present invention, the geostationary orbit satellite directly sends signals to the low-earth orbit satellite and two cellular users. The low-earth orbit satellite obtains the channel states of the two users, the link distances, and the channel states of the wireless nodes that interfere with the users around them, and designs corresponding adaptive power allocation coefficients according to the above information, and uses the adaptive non-orthogonal multiple access technology to transmit signals to the two users. The users receive signals from the low-earth orbit satellite and the geostationary orbit satellite, and use the serial interference cancellation technology and the maximum ratio combining technology to decode and integrate the signals. Among them, the channel fading of the inter-satellite link is described by the Rice model, and the channel fading of the satellite-to-ground link is described by the shadow Rice model. The Rayleigh model is used to describe the channel fading of the cellular user-wireless access point link. In addition, the present invention introduces the concept of the satellite visibility window duration and gives the distribution of the elevation angle of the low-earth orbit satellite. The present invention is applicable to the dual-layer geostationary orbit low-earth orbit satellite communication network. The power allocation factor of the proposed adaptive non-orthogonal multiple access technology is dynamically adjusted according to the channel state, satellite elevation angle, and co-channel interference, which can achieve differential power allocation for different users' dynamic channels, improve the spectrum utilization rate and power allocation fairness.

[0113] The above has introduced in detail a joint geostationary orbit / low-earth orbit dual-layer satellite network transmission method and system provided by the present invention. The present invention uses preferred embodiments to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A combined geosynchronous orbit and low-orbit double-layer satellite network transmission method, characterized in that: The steps include: S1, geosynchronous orbit GEO satellite transmits signals to low-orbit LEO satellites and cellular users; S2, LEO satellites and cellular users receive signals transmitted by GEO satellites; S3, LEO satellites use decode-and-forward relay protocols and adaptive NOMA to send signals to cellular users; S4, the cellular user receives the signal forwarded by the LEO satellite and combines the received signals from the GEO satellite and the LEO satellite using a maximum ratio combining method; In step S3, due to the high-speed movement of LEO satellites, the channel state between users and satellites will change; the channel coefficients of LEO satellite and cellular user links are respectively and Indicates that, where the channel coefficient with good channel status is The channel coefficient of the poor channel state is Defining CU N and CU F Represent users with better channel status and users with worse channel status respectively; according to the definition of NOMA technology, CU N and CU F The power allocation coefficients are expressed as a N and a F , where a F ≥a N , a N +a F =1; therefore, let m∈{N,F}, CU N and CU F The received signal is comprehensively expressed as: Among them, P L represents the transmission power of the LEO satellite, P a is the fixed transmit power of all wireless access points, s F Indicates LEO to CU F The transmitted signal, s N Indicates LEO to CU N The transmitted signal, s j Indicates that the jth wireless access point sends N The transmitted signal, s k Indicates that the kth wireless access point sends F the signal transmitted; represents the additive white Gaussian noise at the cellular user; Indicates the jth wireless access point to CU N The channel coefficient of the link, Indicates the kth wireless access point to CU F Channel coefficient of the link; interference CU N The number of wireless access points is N N , interference CU F The number of wireless access points is N F ; In step S3, considering the path loss and rapid channel fading of the LEO satellite-ground link, the channel coefficient of the link is expressed as Among them, G L represents the antenna gain of the GEO satellite; represents the path loss factor between the LEO satellite and the cellular user link, Where c is the speed of light, f c Indicates the carrier frequency; k B is the Boltzmann constant; T n represents the noise temperature of the LEO satellite, B c Indicates the carrier bandwidth; Indicates the distance between the LEO satellite and the cellular user; is the channel attenuation coefficient of the LEO satellite-ground link, and the probability density function PDF and cumulative distribution function CDF are expressed as: in, Ω s represents the average power of the LOS component in the satellite-to-ground link, 2ns represents the average power of the multipath component; ms represents the degree of shadowing affecting the channel; 1F1(·; ·; ·) and γ(·, ·) are the converged hypergeometric function and the lower incomplete gamma function, respectively; The PDF closed-form expression of the co-channel interference suffered by the user is derived by using the small parameter approximation method: in, is the normalization parameter, The number of wireless access points Nm that interfere with cellular users is a positive integer; (2N m -1)! ! means (2N m -1) double factorial; Indicates the SNR of the wireless access point; In step S3, let U0 be CU N and CU F The distance between the LEO satellite and U0 is calculated as: Among them, h L represents the LEO satellite altitude, r E is the radius of the Earth, β represents the average elevation angle of the LEO satellite observed by the cellular user, and β satisfies β min <β<β max ; According to the definition of elevation angle, β min >0; Let z represent the horizontal distance between two cellular users. According to the law of cosines, the distance between the LEO satellite and the two cellular users is obtained as and Respectively expressed as: In step S3, the definition of satellite visible window duration is introduced to derive the cumulative distribution function CDF expression of LEO satellite elevation angle: in, t max It represents the time when the ground cellular user observes the maximum elevation angle of the LEO satellite, t min represents the initial time when the ground user observes the LEO satellite, t β represents the moment when the elevation angle is β; χ(t max ) indicates that at t max The angular distance from the LEO satellite to the user at the moment; The probability density function PDF expression of the elevation angle β obtained by differentiating F(β) is: in, In step S4, in CU N The decoded signal s is decoded using a serial interference cancellation scheme N , that is, s F Signal in CU N can be completely eliminated; CU N The signal-to-interference-noise ratio is expressed as For CU N The average signal-to-noise ratio, I N For CU N The same-channel interference received; CU F The received signal N is considered as interference, therefore, CU F The SINR is For CU F The average signal-to-noise ratio, I F For CU F The signals received from the GEO satellite and the LEO satellite are combined by the maximum ratio combination method to obtain CU N and CU F The SNRs are expressed as: in, in, is the average co-channel interference, G L represents the antenna gain of the LEO satellite, G U represents the antenna gain of the cellular user, Represents the average channel gain.

2. The combined geosynchronous orbit and low-orbit double-layer satellite network transmission method according to claim 1, characterized in that: In step S2, the LEO satellite and the cellular user U m The received signals are expressed as Among them, H Gl and H GU represent the channel coefficients of GEO-LEO link and GEO-cellular user link respectively; P G is the transmission power of the GEO satellite; N m Indicates the number of wireless access points that interfere with cellular users; s j represents the interference signal of the jth wireless access point; n L represents the additive white Gaussian noise at the LEO satellite, represents the expected solution; the received signal-to-noise ratios of LEO satellite and cellular users are in, P G represents the transmission power of the GEO satellite, is the co-channel interference experienced by cellular users, where the signal-to-noise ratio of the wireless access point is P a represents the transmission power of the wireless access point, h j,bm Indicates the jth wireless access point to U m The channel coefficient of the link.

3. The combined geosynchronous orbit and low-orbit double-layer satellite network transmission method according to claim 2, characterized in that: In step S2, the channel coefficient of the GEO-LEO link is expressed as Among them, G G represents the antenna gain of the GEO satellite; the channel attenuation coefficient of the GEO-LEO link is represented by h GL 2 ;use represents the path loss factor of the GEO-LEO link; where d GL Indicates the distance between GEO satellite and LEO satellite; |h GL 2 The PDF and CDF of are expressed as: Where K represents the Rice factor; Taking into account the path loss and rapid channel fading of the GEO satellite-ground link, the channel coefficient of the link is expressed as represents the path loss factor between the GEO satellite and the cellular user link, Among them, d GU Indicates the distance between the GEO satellite and the cellular user; |h GU 2 is the channel attenuation coefficient of the satellite-to-ground link, and the PDF and CDF are expressed as:

4. The combined geosynchronous orbit and low-orbit double-layer satellite network transmission method according to claim 3 is characterized in that: In step S2, the distance of the GEO-LEO link is: Among them, the polar angle satisfy and h G represents the GEO satellite altitude, r E represents the radius of the earth; the angular velocity of the LEO satellite is considered constant in the entire visible window and is recorded as ω; from the formula Get: polar angle It is uniformly distributed within the satellite visibility duration t, denoted as t min <t<t max .

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