Downlink broadcast unicast joint transmission method based on spectrum sharing and rate splitting for star-ground fusion network

Abstract

The application provides a downlink broadcast unicast joint transmission method based on spectrum sharing and rate splitting for a satellite-ground fusion network. The satellite-ground fusion network provides global seamless information services, and the terminal users of the services are diverse, the service types are rich, and the information services are often in a mixed form of broadcast and unicast. Therefore, the application combines data types (such as broadcast and unicast data) to design a NOBU joint transmission scheme for downlink multi-satellite joint services. Because the designed NOBU joint transmission scheme is based on a one-layer successive interference cancellation algorithm, the system complexity linearly increases with the increase of the number of terminals, and the detection algorithm complexity is obviously lower than that of other non-orthogonal access technologies. Therefore, the algorithm of the application has low complexity and can improve the spectrum efficiency and communication QoS of the system.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of radio, in particular to a downlink broadcast unicast joint transmission method based on spectrum sharing and rate splitting for a satellite-ground integrated network. BACKGROUND

[0002] The satellite-ground integrated network has become an important development direction of future wireless communication systems by organically integrating the advantages of satellite networks and ground networks. In the satellite-ground integrated network, users need information services anytime and anywhere, and these information services are usually a mixture of broadcast and unicast communication data. Compared with ground networks, satellite communication systems have a larger coverage area and can provide seamless global information services, and can better realize joint broadcast and unicast services than ground networks. On the other hand, the rate-splitting multiple access (RSMA) technology divides user data into public data and private data, and then overlaps the transmission of the two parts in the power domain, which is very suitable for joint broadcast and unicast transmission modes, and has higher spectrum efficiency than orthogonal multiple access. Based on this fact, it would be very meaningful to introduce the RSMA technology into satellite communication systems and design a non-orthogonal broadcast and unicast (NOBU) joint transmission scheme. On the other hand, the ground network and the satellite network in the satellite-ground integrated network share the same spectrum resources, and the communication of the ground network inevitably affects satellite communication. The development of spectrum sharing technology provides an important guarantee for the coordinated use of spectrum resources by satellite networks and ground networks. Therefore, it would be very meaningful to explore a downlink broadcast unicast joint transmission scheme based on spectrum sharing and rate splitting technology for the downlink of a satellite-ground integrated network. SUMMARY

[0003] The purpose of the present application is to solve the problems in the prior art, and a downlink broadcast unicast joint transmission method based on spectrum sharing and rate splitting for a satellite-ground integrated network is proposed. The satellite-ground integrated network provides global seamless information services, and the terminal users of its services must be diverse, with rich business types and information services often in the form of a mixture of broadcast and unicast. Therefore, the present application designs a NOBU joint transmission scheme for downlink multi-satellite joint service in combination with data types (such as broadcast and unicast data).

[0004] The present application is realized by the following technical scheme, and the present application proposes a downlink broadcast unicast joint transmission method based on spectrum sharing and rate splitting for a satellite-ground integrated network, which comprises the following steps:

[0005] Step one: the satellite control center first analyzes the current time slot access terminal quantity and request service type, in this process, the satellite terminal cooperates to capture the spectrum use of the ground terminal in the surrounding environment, real-time detects the spectrum hole;

[0006] Step two: the satellite terminal cooperates to capture the state information of the ground terminal in the surrounding environment, reports the perception result to the unified fusion center, in the distributed cooperative spectrum sensing mode, the satellite terminal exchanges the perception result and decides the spectrum resource allocation as the fusion center;

[0007] Step three: the fusion center analyzes all terminal channels according to the available spectrum resource perceived by the satellite terminal, allocates the most suitable channel for access according to the terminal service demand and communication service quality;

[0008] Step four: in the satellite-ground fusion network, the satellite control center and the ground base station cooperate, so that the satellite terminal and the ground terminal can share the same spectrum resource;

[0009] Step five: it is judged whether the satellite terminal can continue to use the spectrum resource, assuming that the satellite terminal only temporarily uses the spectrum resource of the ground terminal, if the ground terminal wants to restore communication in the data transmission process of the satellite terminal, the satellite terminal shifts to another idle spectrum resource;

[0010] Step six: the satellite control center and the ground station jointly select the spectrum sharing mode of multiple access;

[0011] Step seven: the satellite control center designs the access mode according to the available spectrum resource of the current time slot, the terminal quantity and the service demand type of the request access, that is, the user quantity and the broadcast data size superimposed on a time-frequency resource block; the public data and the private data of the user are designed on a time-frequency resource block; the public data and the private data are transmitted through different power layers, each power layer adopts different channel coding, modulation and interleaving set; the public data is transmitted in power layer 1, and the private data is transmitted in power layer 2; the user will first demodulate the public data, and use SIC to eliminate the broadcast data before executing the demodulation of its own private data;

[0012] Step eight: N satellites provide services for K single-antenna users on the same time-frequency resource, in each time-frequency resource, user k, needs broadcast message W0 and private unicast message W k ; on the satellite, the broadcast message W0 and the K unicast data W1, W2,..., W K are encoded into data stream vector Where E (ss H ) = I; user k, The unicast message W k of the user is divided into a sub-public message Wk,c and one sub-private message W k,p ; sub-private message W 1,p of the unicast message 2,p ,…,W K,p are independently encoded into private streams s K , while the sub-common message W 1,c of the unicast message 2,c ,…,W K,c are jointly encoded into a super-common stream s0 together with the broadcast message W0, the super-common stream s0 including the entire broadcast message and part of the unicast message;

[0013] Step nine: the satellite control center linearly precodes the total data stream s = [s0, s1,..., s K ] with a precoding matrix P = [p0, p1,..., p K ],

[0014]

[0015] The optimal system performance is obtained by optimizing the linear precoding matrix P;

[0016] Step ten: the received signal at user k can be expressed as,

[0017]

[0018] where, is the channel gain between the N satellites and user k; the received noise n k is complex Gaussian white noise; the decoding order follows the rule that the data stream for more users has a higher decoding priority; before decoding each user's private stream, the common stream s0 is decoded first and eliminated from the received signal using SIC; the signal SINR of decoding s0 at user k can be expressed as:

[0019]

[0020] Step eleven: after decoding s0 and eliminating it from the received signal y k , user k decodes his own private data s k by treating the private data of other users as noise; the SINR of decoding s k at user k can be expressed as:

[0021]

[0022] Then, the corresponding achievable rate of decoding s0 and s k at user k is R k,0 = log2(1 + γk,0 ) and R k = log2(l + γ k ); the actual information transmission rate R0of s0should not exceed R k,0 , k e K, i.e., R0= min{R 1,0 ,..., R K,0}; R0is the common arrival rate of the broadcast message W0and the sub-common messages W 1,c ,..., W K,c , which can be expressed as C0+∑ k∈K C k,0 = R0, where C0is the part corresponding to the broadcast data W0in R0, and C k,0 is the part corresponding to the sub-common messages W k,c split from the user k's unicast data in R0; in the NOBU transmission model, the transmission rate of each user data contains C k,0 via the transmission in the super-common stream s0and R k encoded and transmitted in the private stream s k ; then, the achievable rate of the user k's unicast data W k is:

[0023] R k,tot = C k,0 + R k

[0024] Step twelve: establish a weighted sum rate model of the system to optimize the system performance, which can be modeled as,

[0025]

[0026]

[0027]

[0028]

[0029]

[0030] tr(PP H ) ≤ P t

[0031] where c = [C0, C1,..., C K ] represents the common rate vector, which should be optimized under the constraints of ensuring the quality of service QoS of broadcast and unicast communication; constraints and ensure the QoS of broadcast and unicast communication, constraint ensures that all users can successfully decode the common data, and constraint tr(PPH )≤P t Ensuring that the transmit power does not exceed the maximum transmit power on a time-frequency resource, constraint C k,0 ≥0 ensures that the common data portion split by user k cannot be negative.

[0032] Further, the spectrum sharing mode includes superimposed spectrum access, bottom spectrum access and hybrid access.

[0033] Further, the common data contains broadcast and unicast type data, and the private data only contains unicast data.

[0034] The beneficial effects of the present application are:

[0035] (1) For the scenario of satellite-ground integrated network, a resource sharing model and a service demand model are established, in which the ground terminal is regarded as the primary user, the satellite terminal is regarded as the secondary user (sensing terminal), and the data type is divided into broadcast data and unicast data.

[0036] (2) Based on multi-satellite joint service, combined with spectrum sharing and RSMA technology, considering the diversity of terminal service types, a unicast-multicast joint transmission scheme based on rate splitting is proposed, which meets the diversity of terminal service demand, improves the spectrum resource utilization and communication QoS.

[0037] (3) Because the designed NOBU joint transmission scheme is based on one-layer successive interference cancellation algorithm, the system complexity increases linearly with the increase of the number of terminals, and the detection algorithm complexity is obviously lower than other non-orthogonal access technologies. Therefore, the algorithm of the present application has low complexity in improving the spectrum efficiency and communication QoS of the system. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 It is a schematic diagram of the satellite-ground integrated network system architecture.

[0039] Figure 2 It is a schematic diagram of the spectrum sharing mode.

[0040] Figure 3 It is a schematic diagram of non-orthogonal power multiplexing based on RSMA.

[0041] Figure 4 It is a schematic diagram of non-orthogonal broadcast and unicast joint transmission model based on RSMA.

[0042] Figure 5 It is a graph showing the relationship between the weighted sum rate and the number of satellites on average per time-frequency resource block. DETAILED DESCRIPTION

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] Space-Ground Integrated Network System Figure 1 As shown, N satellites and ground base stations jointly serve all ground terminals, such as satellite phones, ships, and cars. Simultaneously, in the space-ground converged network, the satellite network and the ground network use the same spectrum resources. In this invention, considering that ground communication is more convenient and lower in cost than satellite communication, ground terminals (terminals communicating with base stations) are designated as primary users, and satellite terminals (terminals communicating with satellites) are designated as sensing users.

[0045] This invention proposes a downlink broadcast-unicast joint transmission method for satellite-ground converged networks based on spectrum sharing and rate splitting. The method includes the following steps:

[0046] Step 1: The satellite control center first analyzes the number of terminals accessing the current time slot and the type of requested services. During this process, the satellite terminals collaboratively capture the spectrum usage of ground terminals in the surrounding environment and detect spectrum holes in real time.

[0047] Step 2: The satellite terminal collaboratively captures the status information of the ground terminal in the surrounding environment and reports its perception results to the unified fusion center. In the distributed collaborative spectrum perception mode, the satellite terminal acts as the fusion center to exchange perception results and determine the allocation of spectrum resources.

[0048] Step 3: The fusion center analyzes all terminal channels based on the available spectrum resources sensed by the satellite terminals, and allocates the most suitable access channel according to the terminal's service requirements and communication service quality.

[0049] Step 4: In a space-ground converged network, the satellite control center and ground base stations collaborate to enable satellite terminals and ground terminals to share the same spectrum resources. Common spectrum sharing methods include overlay spectrum access, underlying spectrum access, and hybrid access, such as... Figure 2 As shown, PT represents the ground terminal and ST represents the satellite terminal;

[0050] Step 5: Determine whether the satellite terminal can continue to use the spectrum resources. Assume that the satellite terminal is only temporarily using the spectrum resources of the ground terminal. If the ground terminal wants to resume communication during the data transmission of the satellite terminal, the satellite terminal will switch to another available spectrum resource.

[0051] Step Six: The satellite control center and the ground station jointly select the spectrum sharing mode for multiple access;

[0052] Step Seven: The satellite control center designs the access mode based on the available spectrum resources in the current time slot, the number of terminals requesting access, and the type of service requirements; that is, the number of users and the size of broadcast data superimposed on a time-frequency resource block; for example... Figure 3 As shown, a user's public and private data are designed on a time-frequency resource block; the public data includes both broadcast and unicast data, while the private data only contains unicast data. The basic concept of NOBU transmission is that public and private data are transmitted through different power layers, each employing different channel coding, modulation, and interleaving sets. Because public data is needed by all users, all users need to demodulate it; while private data is only needed by the user and can only be demodulated by the user themselves. Typically, data needed by more users is demodulated first, so public data is transmitted in power layer 1, and private data is transmitted in power layer 2. Users will first demodulate the public data and use SIC to remove broadcast data before performing their own private data demodulation.

[0053] Step 8: Taking a time-frequency resource as an example, let's analyze the NOBU transmission scheme. N satellites provide services to K single-antenna users on the same time-frequency resource. This scheme can be easily extended to the time-frequency resources of the entire system. In each time-frequency source, there are k users. Requires broadcast message W0 and dedicated unicast message W k On the satellite, broadcast message W0 and K unicast data points W1, W2, ..., W K Encoded into data stream vector Where E(ss) H ) = I; User k, unicast message W k Divided into a sub-public message W k,c and a sub-private message W k,p ; Private sub-message W of a unicast message 1,p W 2,p ,…,W K,p Encoded independently into private streams s1,…,s K And the sub-public message W of the unicast message 1,c W 2,c ,…,W K,c The broadcast message W0 is jointly encoded into a super common stream s0, which includes the entire broadcast message and a portion of the unicast message, such as... Figure 4 As shown;

[0054] Step Nine: The satellite control center uses a precoding matrix P = [p0, p1, ..., p...] KThe total data stream s = [s0, s1,..., sK] is linearly precoded, K

[0055]

[0056] The optimal system performance is obtained by optimizing the linear precoding matrix P;

[0057] Step ten: The received signal at user k can be expressed as,

[0058]

[0059] where, is the channel gain between N satellites and user k; the received noise n k is complex Gaussian white noise; the decoding order follows the rule that the data stream for more users has higher decoding priority; before decoding each user's private stream, the common stream s0 is decoded first and eliminated from the received signal using SIC; the SINR of decoding s0 at user k can be expressed as:

[0060]

[0061] Step eleven: After user k decodes s0 and eliminates it from the received signal y k , his private data s k is decoded by treating other users' private data as noise; the SINR of decoding s k at user k can be expressed as:

[0062]

[0063] Then, the corresponding achievable rates of decoding s0 and s k at user k are R k,0 = log2(1 + γ k,0 ) and R k = log2(1 + γ k ), respectively; to ensure that all users can successfully decode the common data stream, the actual information transmission rate R0 of s0 should not exceed R k,0 ,k∈K, i.e., R0 = min{R 1,0 ,...R K,0}; R0 is the arrival rate common to the broadcast message W0 and the sub-common messages W 1,c ,..., W K,c , which can be expressed as C0 + ∑ k∈K C k,0 = R0, where C0 is the part corresponding to the broadcast data W0 in R0, and C k,0 ​It corresponds to the sub-public message W split from the unicast data of user k in R0. k,c The portion; in the NOBU transmission model, the transmission rate of each user's data includes C transmitted via the super public stream s0. k,0 and in private streams k R encoded in the transmission k Then, user k's unicast data W k The achievable speed is:

[0064] R k,tot =C k,0 +R k

[0065] Step 12: Establish a weighted sum rate model for the system to optimize system performance. The weighted sum rate maximization problem can be modeled as follows:

[0066]

[0067]

[0068]

[0069]

[0070]

[0071] tr(ΡΡ H )≤P t

[0072] Where c = [C0, C1, ..., C K The ] represents the common rate vector, which should be optimized under the constraint of guaranteeing the Quality of Service (QoS) for both broadcast and unicast communications; constraint and Ensure QoS of broadcast and unicast communications, and constrain... Ensure all users can successfully decode public data, constraining tr(PP) H )≤P t Ensure that the transmit power does not exceed the maximum transmit power on a given time-frequency resource, constraining C. k,0 ≥0 ensures that the common data portion partitioned by user k cannot be negative. By using an alternating optimization algorithm, a very good suboptimal solution to the above problem can be obtained.

[0073] Example

[0074] In a space-ground converged network, a NOBU-transmitted downlink multi-satellite joint service system, such as... Figure 1As shown in the figure, N satellites and ground base stations jointly serve all ground terminals, such as satellite phones, ships, cars, etc. At the same time, in the satellite-ground fusion network, the satellite network and the ground network use the same spectrum resource. In the present application, considering that ground communication is more convenient and less costly than satellite communication, the ground terminal (the terminal communicating with the base station) is specified as the main user, and the satellite terminal (the terminal communicating with the satellite) is specified as the sensing user. Assuming that the satellite orbit height is set to 100 km, the gain of the satellite transceiver antenna is 30 dB, and each satellite provides 1 W per km on a time-frequency resource block. The satellite orbit height is 1000 km, the carrier frequency is 2.4 GHz, the total bandwidth is 5 MHz, the bandwidth of each time-frequency resource is 100 kHz, and the number of users is K = 2. In order to study the maximum achievable rate of unicast message under the condition of guaranteeing the QoS of broadcast data transmission, the rate constraint of unicast message is set to 0, At the same time, for the satellite channel, the present application takes three different shadow Rician fading as an example: Frequent Heavy Shadow (FHS) (b0=0.063, m=0.739, Ω=8.97×10 -4 ), Average Shadowing (AS) (b0=0.126, m=10.1, Ω=0.835), and Infrequent Light Shadowing (ILS) (b0=0.158, m=19.4, Ω=1.29). The number of carriers occupied by the ground terminal in the current time slot is uniformly distributed in [10, 30].

[0075] The method for realizing data transmission comprises the following steps:

[0076] Step one: the satellite control center first analyzes the number of terminals accessing the current time slot and the type of requested service, and in this process, the satellite terminal cooperates to capture the spectrum usage of the ground terminal in the surrounding environment and detects the spectrum hole in real time;

[0077] Step two: the satellite terminal cooperates to capture the state information of the ground terminal in the surrounding environment and reports the sensing result to the unified fusion center. In the distributed cooperative spectrum sensing mode, the satellite terminal exchanges the sensing result as the fusion center and decides the spectrum resource allocation;

[0078] Step three: the fusion center analyzes all terminal channels according to the available spectrum resource sensed by the satellite terminal, and allocates the most suitable channel for access according to the business demand and communication service quality of the terminal;

[0079] Step 4: In a space-ground converged network, the satellite control center and ground base stations collaborate to enable satellite terminals and ground terminals to share the same spectrum resources. Common spectrum sharing methods include overlay spectrum access, underlying spectrum access, and hybrid access, such as... Figure 2 As shown, PT represents the ground terminal and ST represents the satellite terminal;

[0080] Step 5: Determine whether the satellite terminal can continue to use the spectrum resources. Assume that the satellite terminal is only temporarily using the spectrum resources of the ground terminal. If the ground terminal wants to resume communication during the data transmission of the satellite terminal, the satellite terminal will switch to another available spectrum resource.

[0081] Step Six: The satellite control center and the ground station jointly select the spectrum sharing mode for multiple access;

[0082] Step Seven: The satellite control center designs the access mode based on the available spectrum resources in the current time slot, the number of terminals requesting access, and the type of service requirements; that is, the number of users and the size of broadcast data superimposed on a time-frequency resource block; for example... Figure 3 As shown, a user's public and private data are designed on a time-frequency resource block; the public data includes both broadcast and unicast data, while the private data only contains unicast data. The basic concept of NOBU transmission is that public and private data are transmitted through different power layers, each employing different channel coding, modulation, and interleaving sets. Because public data is needed by all users, all users need to demodulate it; while private data is only needed by the user and can only be demodulated by the user themselves. Typically, data needed by more users is demodulated first, so public data is transmitted in power layer 1, and private data is transmitted in power layer 2. Users will first demodulate the public data and use SIC to remove broadcast data before performing their own private data demodulation.

[0083] Step 8: Taking a time-frequency resource as an example, let's analyze the NOBU transmission scheme. N satellites provide services to K single-antenna users on the same time-frequency resource. This scheme can be easily extended to the time-frequency resources of the entire system. In each time-frequency source, there are k users. Requires broadcast message W0 and dedicated unicast message W k On the satellite, a broadcast message W0 and K unicast data points W1, W2, ..., W are transmitted. K Encoded into data stream vector Where E(ss) H ) = I; User k, unicast message W k Divided into a sub-public message W k,c and a sub-private message W k,p ; Private sub-message W of a unicast message 1,pW 2,p ,…,W K,p are independently encoded into private streams s K 1,...,s 1,c while the sub-common messages W 2,c 1,...,W K,c are jointly encoded with the broadcast message W0 into a super-common stream s0, which includes the entire broadcast message and part of the unicast messages, as shown in Figure 4 ;

[0084] Step nine: the satellite control center linearly precodes the total data stream s = [s0, s1,..., s K ] with a precoding matrix P = [p0, p1,..., p K ],

[0085]

[0086] The optimal system performance is obtained by optimizing the linear precoding matrix P;

[0087] Step ten: the received signal at user k can be expressed as,

[0088]

[0089] where, is the channel gain between the N satellites and user k; the received noise n k is complex Gaussian white noise; the decoding order follows the rule that the data stream for more users has a higher decoding priority; before decoding each user's private stream, the common stream s0 is decoded first and eliminated from the received signal using SIC; the signal SINR of decoding s0 at user k can be expressed as:

[0090]

[0091] Step eleven: after decoding s0 and eliminating it from the received signal y k , user k decodes his own private data s k by treating the private data of other users as noise; the SINR of decoding s k at user k can be expressed as:

[0092]

[0093] Then, the corresponding achievable rates of decoding s0 and s k at user k are R k,0 = log2(l + γ k,0 ) and R k = log2(l + γk To ensure that all users can successfully decode the public data stream, the actual information transmission rate R0 of s0 should not exceed R. k,0 ,k∈K, that is, R0=min{R 1,0 ,...R K,0}; R0 is the broadcast message W0 and the sub-public message W 1,c ,…,W K,c The common arrival rate can be expressed as C0 + ∑ k∈K C k,0 =R0, where C0 corresponds to the portion of broadcast data W0 in R0, and C k,0 It corresponds to the sub-public message W split from the unicast data of user k in R0. k,c The portion; in the NOBU transmission model, the transmission rate of each user's data includes C transmitted via the super public stream s0. k,0 and in private streams k R encoded in the transmission k Then, user k's unicast data W k The achievable speed is:

[0094] R k,tot =C k,0 +R k

[0095] Step 12: Establish a weighted sum rate model for the system to optimize system performance. The weighted sum rate maximization problem can be modeled as follows:

[0096]

[0097]

[0098]

[0099]

[0100]

[0101] tr(ΡΡ H )≤P t

[0102] Where c = [C0, C1, ..., C K The ] represents the common rate vector, which should be optimized under the constraint of guaranteeing the Quality of Service (QoS) for both broadcast and unicast communications; constraint and Ensure QoS of broadcast and unicast communications, and constrain... Ensure all users can successfully decode public data, constraining tr(PP) H )≤Pt To ensure that the transmit power does not exceed the maximum transmit power on a time-frequency resource, constraint C k,0 ≥ 0 ensures that the common data portion split by user k cannot be negative, using an alternating optimization algorithm, a good suboptimal solution to the above problem can be obtained.

[0103] Figure 5 The relationship between the weighted sum rate and the number of satellites is simulated. The common data contains two parts, broadcast data and unicast data. In order to ensure that all users can successfully demodulate the common data, the minimum threshold R0 th of the broadcast data transmission rate cannot be too large. In Figure 5 , R0 th is set to 1 bps / Hz, and each satellite provides 0.5 W of transmission power for a time-frequency resource block. From Figure 5 , it can be found that the NOBU joint transmission scheme based on spectrum sharing for satellite-ground integration is significantly better than the Orthogonal Multiple Access (OMA) transmission scheme with the same parameters. At the same time, it can also be found that the weighted sum rate is larger when the shadowing degree is smaller.

Claims

1. A method for downlink broadcast-unicast joint transmission based on spectrum sharing and rate splitting in a satellite-terrestrial converged network, characterized in that: The method comprises the following steps: Step one: the satellite control center first analyzes the number of terminals accessing the current time slot and the type of requested services, in the process, the satellite terminal cooperatively captures the spectrum usage of the ground terminals in the surrounding environment, and detects the spectrum holes in real time; Step two: the satellite terminal cooperatively captures the state information of the ground terminals in the surrounding environment, and reports the sensing results to the unified fusion center, in the distributed cooperative spectrum sensing mode, the satellite terminal exchanges the sensing results and decides the spectrum resource allocation as the fusion center; Step three: the fusion center analyzes all terminal channels according to the available spectrum resources sensed by the satellite terminal, and allocates the most suitable channel for access according to the service demand and communication quality of service of the terminal; Step four: in the satellite-ground fusion network, the satellite control center and the ground base station cooperate to enable the satellite terminal and the ground terminal to share the same spectrum resource; Step five: it is judged whether the satellite terminal can continue to use the spectrum resource, assuming that the satellite terminal only temporarily uses the spectrum resource of the ground terminal, if the ground terminal wants to restore communication in the data transmission process of the satellite terminal, the satellite terminal shifts to another idle spectrum resource; Step six: the satellite control center and the ground station jointly select the spectrum sharing mode of multiple access; Step seven: the satellite control center designs the access mode according to the available spectrum resource in the current time slot, the number of terminals requesting access and the type of service demand, that is, the number of users superimposed on a time-frequency resource block and the size of broadcast data; the public data and private data of the user are designed on a time-frequency resource block; the public data and private data are transmitted through different power layers, each power layer uses different channel coding, modulation and interleaving set; the public data is transmitted in power layer 1, and the private data is transmitted in power layer 2; the user will first demodulate the public data, and use SIC to eliminate the broadcast data before performing its own dedicated data demodulation; Step 8: N satellites provide services to K single-antenna users on the same time and frequency resources. In each time and frequency source, user k... Requires broadcast message W0 and dedicated unicast message W k On the satellite, a broadcast message W0 and K unicast data points W1, W2, ..., W are transmitted. K Encoded into data stream vector Where E(ss) H ) = I; User k, unicast message W k Divided into a sub-public message W k,c and a sub-private message W k,p ; Private sub-message W of a unicast message 1,p W 2,p ,…,W K,p Encoded independently into private streams s1,…,s K And the sub-public message W of the unicast message 1,c W 2,c ,…,W K,c The broadcast message W0 is jointly encoded into a super common stream s0, which includes the entire broadcast message and a portion of the unicast message. Step Nine: The satellite control center uses a precoding matrix P = [p0, p1, ..., p...] K For the total data stream s = [s0, s1, ..., s...] K Perform linear precoding. By optimizing the linear precoding matrix P, the optimal system performance is obtained; Step ten: the received signal at user k can be expressed as, wherein, is the channel gain between N satellites and user k; received noise n k is complex Gaussian white noise; the decoding order follows the rule that the data stream for more users has a higher decoding priority; before decoding the private stream of each user, the common stream s0 is decoded first and eliminated from the received signal using SIC; the signal SINR at user k to decode s0 can be expressed as: Step 11: User k decodes s0 and extracts it from the received signal y. k After elimination, the private data of other users is decoded by treating other users' private data as noise. k Decode s at user k k SINR can be expressed as: Then, decode s0 and s at user k. k The corresponding achievable rate is R k,0 =log2(1+γ) k,0 ) and R k =log2(1+γ) k The actual information transmission rate R0 of s0 should not exceed R. k,0 ,k∈K, that is, R0=min{R 1,0 ,…R K,0 }; R0 is the broadcast message W0 and the sub-public message W 1,c ,…,W K,c The common arrival rate can be expressed as C0 + ∑ k∈K C k,0 =R0, where C0 corresponds to the portion of broadcast data W0 in R0, and C k,0 It corresponds to the sub-public message W split from the unicast data of user k in R0. k,c The portion; in the NOBU transmission model, the transmission rate of each user's data includes C transmitted via the super public stream s0. k,0 and in private streams k R encoded in the transmission k Then, user k's unicast data W k The achievable speed is: R k,tot = C k,0 + R k Step twelve: a weighted sum rate model of the system is established to optimize the system performance, the weighted sum rate maximization problem can be modeled as, tr(PP H )≤P t where c = [Co, Ci,..., C K ] denotes the common rate vector, which should be optimized under the constraints of guaranteeing the quality of service (QoS) of broadcast and unicast communications; constraints and guarantee the QoS of broadcast and unicast communications, constraints guarantee that all users can successfully decode the common data, constraint tr(PP H ) < P t guarantee that the transmit power does not exceed the maximum transmit power on a time-frequency resource, constraint C k,0 ≥ 0 ensures that the common data portion partitioned by user k cannot be negative.

2. The method of claim 1, wherein, The spectrum sharing mode includes superimposed spectrum access, bottom spectrum access and hybrid access.

3. The method of claim 1, wherein, The public data includes broadcast and unicast type data, and the private data only includes unicast data.

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