CN118174769B - Combined geosynchronous orbit and low-orbit double-layer satellite network transmission method and system - Google Patents

Abstract

Translated fromChinese

本发明公开了一种联合地球同步轨道与低轨道双层卫星网络传输方法及系统，方法包括如下步骤：S1，地球同步轨道GEO卫星向低轨道LEO卫星和蜂窝用户发射信号；S2，LEO卫星和蜂窝用户接收GEO卫星发射的信号；S3，LEO卫星采用解码转发中继协议和自适应NOMA向蜂窝用户发送信号；S4，蜂窝用户接收LEO卫星转发的信号，采用最大比组合方式组合来自GEO卫星与LEO卫星的信号。本发明提出的自适应非正交多址接入技术的功率分配因子随信道状态、卫星仰角、同频干扰变化动态调节，能够实现对不同用户动态信道的差异化功率分配，提高了频谱利用率和功率分配公平性。

The present invention discloses a combined geosynchronous orbit and low-orbit double-layer satellite network transmission method and system, the method comprising the following steps: S1, geosynchronous orbit GEO satellite transmits signals to low-orbit LEO satellite and cellular users; S2, LEO satellite and cellular users receive signals transmitted by GEO satellite; S3, LEO satellite uses decode-forward relay protocol and adaptive NOMA to send signals to cellular users; S4, cellular users receive signals forwarded by LEO satellite, and use maximum ratio combination to combine signals from GEO satellite and LEO satellite. The power allocation factor of the adaptive non-orthogonal multiple access technology proposed by the present invention is dynamically adjusted with the channel state, satellite elevation angle, and co-channel interference, which can realize differentiated power allocation for dynamic channels of different users, and improve spectrum utilization and power allocation fairness.

Description

Double-layer satellite network transmission method and system combining geosynchronous orbit and low orbit

Technical Field

The invention belongs to the field of satellite wireless communication, and particularly relates to a combined geosynchronous orbit/low orbit double-layer satellite network transmission method and system based on self-adaptive non-orthogonal multiple access.

Background

The multi-layer satellite network (multilayer satellite networks, MLSNs) can complement functions and exchange information by integrating satellites with different orbits, including geosynchronous orbit (geostationary Earth orbit, GEO) and Low Earth Orbit (LEO) satellites, and improves the reliability and throughput of a communication system, so that the global high-speed communication coverage is realized, and is an important supplement and research hotspot for 5G and 6G mobile communication. Furthermore, the high-speed kinematic nature of LEO satellites makes them suitable for disaster areas, providing mobility support, and the network resilience of MLSNs also ensures that the persistence of communications is maintained during a disaster.

For the research on the communication technology of MLSNs and terrestrial users, an orthogonal multiple access (orthogonal multiple access, OMA) scheme is currently mainly adopted, and various orthogonal communication resource blocks are allocated to each user in the system. However, OMA has low spectrum utilization, and is difficult to meet the increasing traffic demands of 5G and 6G networks. The non-orthogonal multiple access (non-orthogonal multiple access, NOMA) technology realizes the distinction among users through different power allocations, allows multiple users to use the same time-frequency resource at the same time, can improve the communication capacity, throughput and fairness, and can effectively cope with the limitation of spectrum resources in MLSNs communication. Therefore, NOMA is considered to have great application value and wide application prospect in the future MLSNs communication.

However, most of the current NOMA research in the communication field adopts a fixed power division factor method, which simplifies the system design and analysis to some extent, but at the same time has some potential limitations and drawbacks. In an actual communication environment, the channel state between the user and the transmitting end may change, and the fixed power allocation cannot optimally adapt to the requirements of different users, so that the overall communication capacity and efficiency of the communication system are reduced, and the communication performance is affected. Furthermore, most of current studies on NOMA in satellite communication mainly consider stationary orbit satellite research, and the influence of satellite mobility on communication performance has not been considered. However, in MLSNs, the high-speed motion of the LEO satellites can cause rapid changes in satellite-to-ground distances, thereby inducing fluctuations in path loss. Therefore, the 5G and 6G studies fusing satellite communications need to more fully consider the impact of satellite mobility on the application of NOMA in satellite communications to ensure more accurate and reliable system design and performance assessment.

Disclosure of Invention

Aiming at the current situation of the prior art, the invention provides a combined geosynchronous orbit/low orbit double-layer satellite network transmission method and system based on self-adaptive non-orthogonal multiple access, which are applied to GEO satellites, LEO satellites, cellular users and wireless access points. The invention belongs to the field of satellite wireless communication, in the invention, a GEO satellite directly transmits a signal s_G to an LEO satellite and a cellular user, wherein,Representing the solution desire. LEO satellites employ decode-and-forward (DF) relay protocols, which exploit their decoding and re-encoding capabilities to improve communication reliability. The LEO satellite then transmits a signal s_G to the cellular user using an adaptive NOMA technique. In addition, the cellular user utilizes a maximum ratio combining scheme to decode signals from LEO satellites and GEO satellites. The power allocation factor of the adaptive NOMA technique is determined by channel fading, path loss, co-channel interference, and elevation changes during LEO satellite motion in the communication link.

The invention adopts the following technical scheme:

The invention relates to a combined earth synchronous orbit/low orbit double-layer satellite network transmission method based on self-adaptive non-orthogonal multiple access, wherein the network consists of a GEO satellite, a LEO satellite, a cellular user and a plurality of wireless access points. The present invention considers two users with different channel conditions, a user with good channel conditions (CU_N) and a user with poor channel conditions (CU_F). Furthermore, all devices are equipped with a single antenna. The midpoint between two cellular subscribers is denoted as U₀,h_L and h_G, respectively, the elevation of the LEO satellite and GEO satellite from the ground, r_E is the earth radius, d_GL is the distance of the GEO-LEO link,Representing the distance between LEO and U₀. Further, β ε [ β_min,β_max ] is used to represent the average elevation angle of LEO satellites observed by cellular users. By using GEO satellite-earth center as reference lineRepresents the polar angle of LEO satellite motion, i.e., the angle between the L₂ -O line and the S-O line, where,Further, assuming that a wireless access point in a terrestrial cellular network shares licensed spectrum with cellular users, the wireless access point may generate co-channel interference to the cellular users. Co-channel interference can cause the received signal to be disturbed, thereby degrading signal quality. The specific technical scheme of the invention is as follows:

the method for transmitting the combined geosynchronous orbit and low orbit double-layer satellite network comprises the following steps:

s1, a geosynchronous orbit GEO satellite transmits signals to a low orbit LEO satellite and a cellular user;

s2, the LEO satellite and the cellular user receive signals transmitted by the GEO satellite;

s3, the LEO satellite adopts a decoding forwarding relay protocol and an adaptive NOMA to send signals to the cellular user;

And S4, the cellular user receives signals forwarded by the LEO satellite, and the received signals from the GEO satellite and the LEO satellite are combined in a maximum ratio combination mode.

Preferably, in step S1, the GEO satellite transmits signals S_G, m e { N, F } directly to LEO satellites and cellular subscribers (U_m) (a set threshold, denoted by U_N, greater than or equal to the threshold, indicating a subscriber with a better channel state, and a smaller threshold, denoted by U_F, indicating a subscriber with a better channel state).

Preferably, in step S2, the signals received by the LEO satellite and the cellular user U_m may be expressed asWhere H_Gl and H_GU represent channel coefficients for the GEO-LEO link and the GEO-cellular user link, respectively. P_G is the transmit power of the GEO satellite. N_m represents the number of wireless access points interfering with the cellular user. s_j denotes an interfering signal of the j-th wireless access point, wherein,P_a is the fixed transmit power of all wireless access points. n_LRepresenting additive white gaussian noise at LEO satellites and cellular subscribers respectively,The LEO satellite and cellular user have received signal-to-noise ratios (SNR) ofWherein, theP_L denotes the transmission power of the LEO satellite, P_G denotes the transmission power of the GEO satellite,Is co-channel interference experienced by cellular users, wherein the signal-to-noise ratio of a wireless access pointP_a represents the transmission power of the wireless access point, h_j,bm represents the channel coefficient of the jth wireless access point to U_m link.

Preferably, in step S2, the channel coefficients of the GEO-LEO link are expressed asWherein G_G and G_L respectively represent antenna gains of GEO satellite and LEO satellite, channel attenuation coefficient of GEO-LEO link is represented as |h_GL|², andRepresenting the path loss factor of a GEO-LEO link, wherein c is approximately 3 multiplied by 10⁸ m/s, representing the speed of light, f_c representing the carrier frequency, K_B＝1.38×10^-23 J/K being the Bozmann constant, T_n representing the noise temperature of the LEO satellite, B_c representing the carrier bandwidth, d_GL representing the distance of the GEO satellite from the LEO satellite;

PDF and CDF of i h_GL|² are denoted as:

Wherein K represents a rice factor;

Considering the path loss and channel fast fading of a GEO satellite-terrestrial link, the channel coefficients of that link are expressed asWherein G_G and G_U represent antenna gains for GEO satellites and cellular users, respectively; representing the path loss factor of GEO satellites and cellular user links,Where d_GU represents the distance of the GEO satellite from the cellular user, |h_GU|² is the channel attenuation coefficient of the satellite-to-earth link, PDF and CDF are expressed as:

wherein, theThe average power of the LOS component in the satellite-to-ground link is denoted by Ω_s, the average power of the multipath component is denoted by 2n_s, m_s represents the Nakagami parameter, and represents the degree of shadowing affecting the channel,₁F₁ (; ·; ·) and γ (·), are the converging super-geometric function and the lower incomplete gamma function, respectively.

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

Wherein the polar angleSatisfy the following requirementsAndH_L denotes LEO satellite altitude, h_G denotes GEO satellite altitude, r_E denotes earth radius, LEO satellite angular velocity is considered constant over the entire visible window, noted ω, by the formulaObtaining polar angleIs uniformly distributed within the satellite visibility duration t, which is marked ast_min＜t＜t_max。

Preferably, in step S3, the channel state between the user and the satellite is changed in view of the high-speed motion of the LEO satellite. Channel coefficients for low-orbit satellite and cellular subscriber link, respectivelyAndRepresentation (channel coefficient with better channel state isThe channel coefficient with poor channel state is). CU_N and CU_F are defined to represent a user with a better channel state and a user with a worse channel state, respectively (by setting a threshold, for example, the channel state is better and the channel state is worse than or equal to the threshold, and the channel state is worse than the threshold). The present invention represents the power allocation coefficients of CU_N and CU_F as a_N and a_F, respectively, according to the definition of NOMA technology, where a_F≥a_N,a_N+a_F =1. Thus, let m ε { N, F }, the received signals of CU_N and CU_F are comprehensively represented as:

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 wireless access point to CU_N, s_k represents the signal transmitted by the kth wireless access point to CU_F, h_j,bm represents the channel coefficient of the jth wireless access point to CU_N link, and h_k,bm represents the channel coefficient of the kth wireless access point to CU_F link. The number of wireless access points of interference CU_N is N_N and the number of wireless access points of interference CU_F is N_F.

Preferably, in step S3, the path loss and channel fast fading of the LEO satellite-terrestrial link are taken into account, the channel coefficients of the link being expressed asWherein G_L represents the antenna gain of the GEO satellite; representing the path loss factor of the LEO satellite and cellular user link,Wherein, theRepresenting the distance of the LEO satellite from the cellular user; Is the channel attenuation coefficient of the LEO satellite-ground link, PDF and CDF are expressed as:

The PDF closed expression of the same-frequency interference suffered by the user is obtained by deduction through a small-parameter approximation method:

wherein, theIn order to normalize the parameters,The number of wireless access points Nm of interfering cellular subscribers is a positive integer, (2N_m -1) | represents a double-order multiplication of (2N_m -1); representing the SNR of the wireless access point in the system.

Preferably, in step S4, the present invention decodes the signal S_N using a complete serial interference cancellation (Successive Interference Cancellation, SIC) scheme at CU_N, i.e., the S_F signal can be completely eliminated at CU_N. The signal-to-interference-plus-noise ratio (SINR) of CU_N is expressed asI_N denotes co-channel interference to which CU_N is subjected. The adaptive NOMA power distribution technology is characterized in that a dynamic power distribution scheme is designed for ensuring fairness of power distribution, namely, balancing channel capacity of two cellular users. The power distribution factor is dynamically adjusted along with the channel state, satellite elevation angle and same-frequency interference variation, so that the differential power distribution of different user dynamic channels is realized. According to the NOMA principle, the signal s_N received by CU_F can be directly regarded as interference, so that the SINR of CU_F isI_F denotes co-channel interference to which CU_F is subjected. Combining the received signals from GEO satellites and LEO satellites using a maximal ratio combining approach, the SNR of CU_N and CU_F can be expressed as:

In order to obtain the propagation loss of each link, the invention provides a distance distribution model of each link. In addition, considering the moving LEO satellite, an elevation distribution model of the LEO satellite is provided, and the model specifically comprises the steps of introducing the definition of the duration of a satellite visible window, deducing a cumulative distribution function expression of the elevation of the LEO satellite, and deriving a probability density function expression of the elevation by the cumulative distribution function.

The distance of the GEO-LEO link is:

Wherein the polar angleSatisfy the following requirementsAndH_L denotes LEO satellite altitude, h_G denotes GEO satellite altitude, r_E denotes earth radius. The angular velocity of the LEO satellite can be considered constant throughout the visible window, denoted ω. From the formulaIt can be seen that the polar angleIs uniformly distributed within the satellite visibility duration t, which is marked ast_min＜t＜t_max。

Let U₀ be the midpoint of CU_N and CU_F, the distance between the LEO satellite and U₀ is calculated as:

Wherein the elevation angle beta satisfies beta_min<β<β_max. Beta_min >0 can be obtained according to the definition of elevation angle.

Let z represent the horizontal distance between two cellular users, according to the cosine law, the distance between the LEO satellite and the two cellular users can be obtainedAndExpressed as:

The invention provides a Cumulative Distribution Function (CDF) expression of LEO satellite elevation angles, which is as follows:

wherein, theT_max denotes the time when the terrestrial cellular user observes the maximum elevation angle of the LEO satellite, t_min denotes the initial time when the terrestrial user observes the LEO satellite, t_β denotes the time when the elevation angle is β, and χ (t_max) denotes the angular distance of the LEO satellite to the user at time t_max.

The Probability Density Function (PDF) for deriving F (β) to get the elevation β is expressed as:

For different types of links, different channel models need to be used for characterization. Specifically, for an inter-satellite link without shadow occlusion, the present invention selects the rice model to fit. The invention adopts a shadow rice model to describe the star-to-ground link with shadow shielding. Since there are a large number of buildings on the ground, which can be considered as no direct path, the wireless access point-CU_m link adopts a rayleigh model.

Long-range satellite communications can result in significant path loss of the inter-satellite link. In addition, the inter-satellite links are susceptible to frequency selective fading (commonly referred to as fast fading) caused by multipath. Thus, the channel coefficients of the GEO-LEO link are expressed asWherein G_G and G_L represent antenna gains for GEO satellites and LEO satellites, respectively. The channel attenuation coefficient of the GEO-LEO link is denoted as |h_GL|². The invention adoptsRepresenting the path loss factor of the GEO-LEO link. Where c.apprxeq.3.times.10 10⁸ m/s denotes the speed of light and f_c denotes the carrier frequency. K_B＝1.38×10^-23 J/K is the Boltzmann constant. In addition, T_n denotes the noise temperature of the LEO satellite, and B_c denotes the carrier bandwidth.

The PDF and CDF distributions of the rice distribution are expressed as:

Wherein K represents the rice factor.

Considering the path loss and channel fast fading of a GEO satellite-terrestrial link, the channel coefficients of that link are expressed asWhere G_G and G_U represent antenna gains for GEO satellites and cellular users, respectively.Representing the path loss factor of GEO satellites and cellular user links,Where d_GU represents the GEO satellite distance from the cellular user. |h_GU|² is the channel attenuation coefficient of the satellite-to-ground link, PDF and CDF are expressed as:

wherein, theThe average power of the LOS component in the satellite-to-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 and indicates the degree of shadowing affecting the channel.₁F₁ (. Cndot.; cndot. -) and γ (. Cndot.; cndot.) are the converging super-geometric function and the incomplete gamma function, respectively.

In addition, LEO satellite-terrestrial links also suffer from path loss and channel fast fading, the channel coefficients of the link being expressed asWherein G_L represents the antenna gain of the GEO satellite; representing the path loss factor of the LEO satellite and cellular user link,Wherein, theRepresenting the distance of the LEO satellite from the cellular user; is the channel attenuation coefficient of the LEO satellite-ground link, PDF and CDF are expressed as:

The co-channel interference suffered by the user is approximately solved, specifically, the envelope of each wireless access point-user CU_m link is expressed as a statistically independent rayleigh random variable, and if the cumulative co-channel interference suffered by the user is calculated, the sum and distribution of these rayleigh random variables must be determined. The small parameter approximation method simplifies complex mathematical expression by neglecting higher-order terms, and the PDF closed expression of the same-frequency interference suffered by the user is derived by using the small parameter approximation method, wherein the PDF closed expression comprises the following steps:

wherein, theIn order to normalize the parameters,The number of wireless access points Nm of interfering cellular users is a positive integer. (2N_m -1) | represents a double-order multiplication of (2N_m -1).Representing the SNR of the wireless access point in the system.

The invention provides a channel capacity of a combined geosynchronous orbit/low orbit double-layer satellite network based on self-adaptive non-orthogonal multiple access. In order to ensure fairness of power allocation, i.e. to equalize channel capacity of two cellular users, the present invention designs a dynamically varying power allocation scheme. The power distribution factor can be dynamically regulated along with factors such as channel state, satellite elevation angle, same-frequency interference and the like, and differential power distribution of dynamic channels of different users is realized.

Channel capacity, which is the maximum transmission rate that can be achieved for error-free communication over a channel, is an indicator of the estimated channel efficiency and information transmission capacity. The channel capacities of CU_N and CU_F are written as:

wherein, theRepresenting the average channel gain.AndRepresenting the average co-channel interference of CU_N and CU_F, respectively. Average channel fading coefficient is obtained by adopting expected formAlso, by solving the expected value, the average co-channel interference can be calculated as:

The channel capacities of CU_N and CU_F are rewritten as:

wherein, the

To ensure fairness of power allocation, i.e., to equalize the channel capacities of CUs_N and CU_F, power allocation coefficients are derived, denoted as a_N and a_F, respectively, expressed as:

wherein, the

From the above equation, the power distribution coefficient is affected by co-channel interference, path loss, channel fading, and antenna gain of the transmitter and the receiver.

The invention also discloses a double-layer satellite network transmission system combining the geosynchronous orbit and the low orbit, which is based on the method and comprises the following modules:

The signal transmitting module is used for transmitting signals to the low-orbit LEO satellite and the cellular user by the geosynchronous orbit GEO satellite;

The signal receiving module is used for receiving signals transmitted by the GEO satellite by the LEO satellite and the cellular user;

the LEO satellite adopts a decoding forwarding relay protocol and an adaptive NOMA to send signals to the cellular user;

And the signal receiving and combining module is used for receiving signals forwarded by the LEO satellites by the cellular users and combining the received signals from the GEO satellites and the LEO satellites in a maximum ratio combining mode.

In summary, the invention establishes a combined geosynchronous orbit/low orbit double-layer satellite network transmission method and system based on self-adaptive non-orthogonal multiple access based on self-adaptive cooperative NOMA technology. Considering that the rapid change of satellite-ground distance can be caused by the high-speed movement of the LEO satellite, so that the fluctuation of path loss is caused, the invention provides an elevation distribution model of the LEO satellite, and PDF and CDF of satellite elevation are given. The power distribution factor of the self-adaptive non-orthogonal multiple access technology provided by the patent is dynamically adjusted along with the change of channel state, satellite elevation angle and same-frequency interference, so that the differential power distribution of dynamic channels of different users can be realized, and the spectrum utilization rate and the power distribution fairness are improved.

Drawings

In order to more clearly explain the specific technical method of the present invention, the drawings that are required to be used in the description of the embodiments or the prior art will be briefly described below.

FIG. 1 is a flow chart of a communication process of a combined geosynchronous orbit/low orbit double-layer satellite network transmission method based on adaptive non-orthogonal multiple access according to a preferred embodiment of the present invention;

Fig. 2 is a block diagram of a communication system involved in a combined geosynchronous orbit/low orbit double-layer satellite network transmission method based on adaptive non-orthogonal multiple access provided by the invention;

fig. 3 is a block diagram of a combined geosynchronous orbit/low orbit dual-layer satellite network transmission system based on adaptive non-orthogonal multiple access according to a preferred embodiment of the present invention.

Detailed Description

In order to better understand the method of the present invention by those skilled in the art, the present invention will be described in further detail with reference to the accompanying drawings and preferred embodiments.

The invention provides a combined geosynchronous orbit/low orbit double-layer satellite network transmission method and system based on self-adaptive non-orthogonal multiple access, and relates to a self-adaptive NOMA technology, wherein a power distribution factor is determined by antenna gain, channel fading, co-channel interference and path loss of a transmitting end and a receiving end. In addition, the invention relates to an elevation distribution analysis method of the LEO satellite, which gives PDF and CDF closed expressions of the elevation of the LEO satellite. The self-adaptive NOMA technology can improve the interruption performance of the double-layer GEO/LEO satellite communication system and can realize fair channel capacity.

The method for transmitting the combined geosynchronous orbit/low orbit double-layer satellite network based on the self-adaptive non-orthogonal multiple access is applied to a cellular user, an LEO satellite relay node and a GEO satellite node, and specifically comprises the following steps of:

Step S101, the GEO satellite transmits radio frequency signals to the LEO satellite and the cellular user respectively.

In this embodiment, the GEO satellite can provide wireless coverage to enable wireless signal transmission with a wireless terminal. The LEO satellite orbit height range is 500 to 1500 km and the GEO satellite orbit height range is 35786 km. The present embodiment does not limit the orbital height of the satellite. The GEO satellite generates transmission signals based on three different frequencies, and the signals are transmitted to the LEO satellite and two cellular users simultaneously by adopting a frequency division multiple access technology, wherein the signals transmitted to the LEO satellite are the combination of the signals of the two cellular users.

Step S102, the LEO satellite and the cellular user receive signals transmitted by the GEO satellite.

In this embodiment, the LEO satellite and the cellular user receive signals from the GEO satellite at the same time, and if the LEO satellite cannot successfully decode the signals or moves to a range that the GEO satellite cannot cover, the transmission is stopped. The cellular subscriber can eventually only receive signals from GEO satellites.

In step S103, the LEO satellite adopts a decode-and-forward (DF) relay protocol and an adaptive NOMA technology to respectively send signals to two cellular users.

In this embodiment, when the LEO satellite transmits signals based on the adaptive NOMA technology, the signals received from the GEO satellite should be converted into two signals based on the same frequency and transmitted to different cellular subscribers. And acquiring the channel states and link distances from the LEO satellite to two cellular users, the elevation angle of the LEO satellite and the channel states of wireless nodes around the cellular users, which generate interference to the LEO satellite. And the LEO satellite distributes power to the signals to be sent to the two users, and the signals are transmitted to the two cellular users by adopting the self-adaptive NOMA technology. Users with better channel conditions (CU_N) are allocated a lower proportion of transmit power and users with worse channel conditions (CU_F) are allocated a higher proportion of transmit power. The satellite superimposes the signals to generate an aliasing signal, so that the aliasing signal can be transmitted in the same channel, and the transmission throughput and the communication fairness of the system are improved.

It should be noted in particular that the link distance and channel state of LEO satellites from two cellular subscribers varies. The power distribution factor of the self-adaptive NOMA technology provided by the invention changes along with the change of the channel state, and can adapt to the dynamically changed channel state.

Step S104, the cellular user receives the signals forwarded by the LEO satellites and combines the received signals from the GEO satellites and the LEO satellites in a maximum ratio combining mode.

In this embodiment, the cellular subscriber receives a signal forwarded from the LEO satellite, which cannot be received if the LEO satellite fails to decode successfully.

Aiming at the LEO satellite signals, the CU_N with better channel state adopts a serial interference elimination technology, firstly eliminates part of signals with higher power in the aliasing signals and sent to the CU_F with worse channel state, and the rest signals are the signals required by the CU_F without adopting serial interference elimination, and treats part of signals with lower power in the aliasing signals and sent to the CU_N as noise for processing. And finally, integrating signals from different signal sources by two users by adopting a maximum ratio combining technology to obtain the respective required signals.

As shown in fig. 3, this embodiment discloses a dual-layer satellite network transmission system combining geosynchronous orbit and low orbit, which comprises the following modules based on the above method embodiment:

The signal transmitting module is used for transmitting signals to the low-orbit LEO satellite and the cellular user by the geosynchronous orbit GEO satellite;

The signal receiving module is used for receiving signals transmitted by the GEO satellite by the LEO satellite and the cellular user;

the LEO satellite adopts a decoding forwarding relay protocol and an adaptive NOMA to send signals to the cellular user;

And the signal receiving and combining module is used for receiving signals forwarded by the LEO satellites by the cellular users and combining the received signals from the GEO satellites and the LEO satellites in a maximum ratio combining mode.

For other content in this embodiment, reference may be made to the above-described method embodiments.

In summary, the invention discloses a combined geosynchronous orbit/low orbit double-layer satellite network transmission method and system based on self-adaptive non-orthogonal multiple access, which are applied to geosynchronous orbit satellites, low orbit satellites, cellular users and wireless access points, and belong to the field of satellite wireless communication. In the present invention, geosynchronous orbit satellites send signals directly to low orbit satellites and to two cellular subscribers. The low orbit satellite obtains the channel state of two users, the link distance and the channel state of wireless nodes which generate interference to the users around the users, designs corresponding self-adaptive power distribution coefficients according to the information, and adopts the self-adaptive non-orthogonal multiple access technology to transmit signals to the two users. The user receives signals from the low orbit satellite and the geosynchronous orbit satellite, and the signals are decoded and integrated by adopting a serial interference cancellation technology and a maximum ratio combining technology. The channel fading of the inter-satellite link is described by a rice model, and the channel fading of the satellite-ground link is described by a shadow rice model. The rayleigh model is used to describe the channel fading of the cellular user-wireless access point link. Furthermore, the present invention introduces the concept of satellite visibility window duration, giving a distribution of low orbit satellite elevation angles. The invention is suitable for a double-layer geosynchronous orbit low-orbit satellite communication network, the power distribution factor of the self-adaptive non-orthogonal multiple access technology is dynamically regulated along with the change of channel state, satellite elevation angle and co-channel interference, the differential power distribution of dynamic channels of different users can be realized, and the frequency spectrum utilization rate and the power distribution fairness are improved.

The above detailed description of the method and system for transmitting a combined geosynchronous orbit/low orbit double-layer satellite network based on adaptive non-orthogonal multiple access provided by the present invention applies the preferred embodiments to illustrate the principle and implementation of the present invention, the above description of the embodiments is only used to help understand the method and core idea of the present invention, and meanwhile, to those skilled in the art, according to the idea of the present invention, there are variations in the specific implementation and application scope, so the present disclosure should not be construed as limiting the present invention.

Claims (4)

Translated fromChinese

1.联合地球同步轨道与低轨道双层卫星网络传输方法，其特征在于，包括如下步骤：1. A combined geosynchronous orbit and low-orbit dual-layer satellite network transmission method, characterized in that it comprises the following steps:S1，地球同步轨道GEO卫星向低轨道LEO卫星和蜂窝用户发射信号；S1, geosynchronous orbit GEO satellite transmits signals to low-orbit LEO satellites and cellular users;S2，LEO卫星和蜂窝用户接收GEO卫星发射的信号；S2, LEO satellites and cellular users receive signals transmitted by GEO satellites;S3，LEO卫星采用解码转发中继协议和自适应NOMA向蜂窝用户发送信号；S3, LEO satellites use decode-and-forward relay protocols and adaptive NOMA to send signals to cellular users;S4，蜂窝用户接收LEO卫星转发的信号，采用最大比组合方式将接收到的来自GEO卫星与LEO卫星的信号组合；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;步骤S3中，鉴于LEO卫星的高速运动，用户与卫星之间的信道状态会发生变化；低轨卫星和蜂窝用户链路的信道系数分别用和表示，其中，信道状态好的信道系数为信道状态差的信道系数为定义CU_N和CU_F分别表示信道状态较好的用户和信道状态较差的用户；根据NOMA技术的定义，将CU_N和CU_F的功率分配系数分别表示为a_N和a_F，其中，a_F≥a_N，a_N+a_F＝1；因此，令m∈{N,F}，CU_N和CU_F的接收信号综合表示为：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 Define CU_N and CU_F to represent users with better channel status and users with worse channel status, respectively. According to the definition of NOMA technology, the power allocation coefficients of CU_N and CU_F are expressed as a_N and a_F , respectively, where a_F ≥_{a N} , a_N + a_F ＝1. Therefore, let m∈{N,F}, the received signals of CU_N and CU_F are comprehensively expressed as:其中，P_L表示LEO卫星的传输功率，P_a是所有无线接入点的固定发射功率，s_F表示LEO向CU_F发射的信号，s_N表示LEO向CU_N发射的信号，s_j表示第j个无线接入点向CU_N发射的信号，s_k表示第k个无线接入点向CU_F发射的信号；表示蜂窝用户处的加性高斯白噪声；表示第j个无线接入点到CU_N链路的信道系数，表示第k个无线接入点到CU_F链路的信道系数；干扰CU_N的无线接入点数量为N_N，干扰CU_F的无线接入点数量为N_F；Wherein,_PL represents the transmission power of the LEO satellite,_Pa is the fixed transmission power of all wireless access points,_sF represents the signal transmitted by LEO to CU_F ,_sN represents the signal transmitted by LEO to CU_N ,_sj represents the signal transmitted by the jth wireless access point to CU_N , and_sk represents the signal transmitted by the kth wireless access point to CU_F ; represents the additive white Gaussian noise at the cellular user; represents the channel coefficient of the jth wireless access point to_CUN link, represents the channel coefficient of the link from the kth wireless access point to CU_F ; the number of wireless access points interfering with CU_N is N_N , and the number of wireless access points interfering with CU_F is N_F ;步骤S3中，考虑到LEO卫星-地面链路的路径损耗和信道快速衰落，该链路的信道系数表示为其中，G_L表示GEO卫星的天线增益；表示LEO卫星与蜂窝用户链路的路径损耗因子，其中，c表示光速，f_c表示载波频率；k_B是波兹曼常数；T_n表示LEO卫星的噪声温度，B_c表示载波带宽；表示LEO卫星与蜂窝用户的距离；是LEO卫星-地面链路的信道衰减系数，概率密度函数PDF和累积分布函数CDF分别表示为：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 Where, 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 represents the speed of light, f_c represents the carrier frequency, k_B is the Boltzmann constant, T_n represents the noise temperature of the LEO satellite, and B_c represents 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:其中，Ω_s表示星地链路中LOS分量的平均功率，2ns表示多径分量的平均功率；ms表示影响信道的阴影程度；₁F₁(·；·；·)和γ(·,·)分别是汇合超几何函数和下不完全伽马函数；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;₁ F₁ (·; ·; ·) and γ(·, ·) are the converged hypergeometric function and the lower incomplete gamma function, respectively;利用小参数近似法推导得到用户受到的同频干扰的PDF闭式表达式为：The PDF closed-form expression of the co-channel interference suffered by the user is derived by using the small parameter approximation method:其中，为归一化参数，干扰蜂窝用户的无线接入点数量Nm为正整数；(2N_m-1)！！表示(2N_m-1)的双阶乘；表示无线接入点的SNR；in, is the normalization parameter, The number of wireless access points Nm interfering with cellular users is a positive integer; (_2Nm -1)! ! represents the double factorial of (_2Nm -1); Indicates the SNR of the wireless access point;步骤S3中，令U₀为CU_N和CU_F的中点，LEO卫星和U₀之间的距离计算公式为：In step S3, let U₀ be the midpoint between CU_N and CU_F , and the distance calculation formula between the LEO satellite and U₀ is:其中，h_L表示LEO卫星高度，r_E为地球半径，β表示蜂窝用户观测到的LEO卫星的平均仰角，β满足β_min<β<β_max；根据仰角的定义得β_min>0；Wherein, h_L represents the altitude of LEO satellite, r_E is the radius of the earth, β represents the average elevation angle of LEO satellite observed by cellular users, and β satisfies β_min <β<β_max ; according to the definition of elevation angle, β_min >0;令z表示两个蜂窝用户之间的水平距离，根据余弦定理，得到LEO卫星与两个蜂窝用户之间的距离和分别表示为：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:步骤S3中，引入卫星可见窗口持续时间的定义，推到出LEO卫星仰角的累积分布函数CDF表达式：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:其中，t_max表示地面蜂窝用户观测到LEO卫星最大仰角的时刻，t_min表示地面用户观测到LEO卫星的初始时刻，t_β表示仰角为β的时刻；χ(t_max)表示在t_max时刻的LEO卫星到用户的角距离；in, t_max 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 time when the elevation angle is β; χ(t_max ) represents the angular distance from the LEO satellite to the user at the time t_max ;对F(β)求导得到仰角β的概率密度函数PDF表达式为：The probability density function PDF expression of the elevation angle β obtained by differentiating F(β) is:其中，in,步骤S4中，在CU_N处使用串行干扰消除方案解码信号s_N，即，s_F信号在CU_N处能够被完全剔除；CU_N的信干噪比表示为为CU_N的平均信噪比，I_N为CU_N受到的同频干扰；CU_F接收到的信号s_N视为干扰，因此，CU_F的SINR为为CU_F的平均信噪比，I_F为CU_F受到的同频干扰；采用最大比组合方式将接收到的来自GEO卫星与LEO卫星的信号组合，得到CU_N和CU_F的SNR分别表示为：In step S4, the serial interference cancellation scheme is used to decode the signal s_N at_CUN , that is, the s_F signal can be completely eliminated at_CUN ; the signal to noise ratio of_CUN is expressed as is the average signal-to-noise ratio of_CUN , I_N is the co-channel interference suffered by_CUN ; the signal s_N received by CU_F is regarded as interference, so the SINR of CU_F is is the average signal-to-noise ratio of CU_F , and_IF is the co-channel interference suffered by CU_F. The signals received from the GEO satellite and the LEO satellite are combined by the maximum ratio combination method, and the SNRs of CU_N and CU_F are expressed as follows:其中，in,其中，是平均同频干扰，G_L表示LEO卫星的天线增益，G_U表示蜂窝用户的天线增益，表示平均信道增益。in, is the average co-channel interference,_GL represents the antenna gain of the LEO satellite,_GU represents the antenna gain of the cellular user, Represents the average channel gain.2.根据权利要求1所述的联合地球同步轨道与低轨道双层卫星网络传输方法，其特征在于，步骤S2中，LEO卫星和蜂窝用户U_m接收到的信号分别表示为其中，H_Gl和H_GU分别表示GEO-LEO链路和GEO-蜂窝用户链路的信道系数；P_G是GEO卫星的发射功率；N_m表示干扰蜂窝用户的无线接入点数量；s_j表示第j个无线接入点的干扰信号；n_L表示LEO卫星处的加性高斯白噪声，表示求解期望；LEO卫星和蜂窝用户的接收信噪比分别为其中，P_G表示GEO卫星的传输功率，是蜂窝用户所经历的同频干扰，其中，无线接入点的信噪比P_a表示无线接入点的传输功率，h_j,bm表示第j个无线接入点到U_m链路的信道系数。2. The combined geosynchronous orbit and low-orbit dual-layer satellite network transmission method according to claim 1 is characterized in that in step S2, the signals received by the LEO satellite and the cellular user U_m are respectively expressed as Where H_Gl and H_GU represent the channel coefficients of the GEO-LEO link and the GEO-cellular user link respectively; P_G is the transmit power of the GEO satellite; N_m represents the number of wireless access points interfering with the cellular user; 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_Pa represents the transmission power of the wireless access point, and hj_,bm represents the channel coefficient of the link from the jth wireless access point to_Um .3.根据权利要求2所述的联合地球同步轨道与低轨道双层卫星网络传输方法，其特征在于，步骤S2中，GEO-LEO链路的信道系数表示为其中，G_G表示GEO卫星的天线增益；GEO-LEO链路的信道衰减系数表示为h_GL²；用表示GEO-LEO链路的路径损耗因子；其中，d_GL表示GEO卫星与LEO卫星的距离；3. The combined geosynchronous orbit and low-orbit dual-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 Where G_G represents the antenna gain of the GEO satellite; the channel attenuation coefficient of the GEO-LEO link is represented by h_GL² ; represents the path loss factor of the GEO-LEO link; where d_GL represents the distance between the GEO satellite and the LEO satellite;|h_GL²的PDF和CDF分别表示为：The PDF and CDF of |h_GL² are expressed as:其中，K表示莱斯因子；Where K represents the Rice factor;考虑到GEO卫星-地面链路的路径损耗和信道快速衰落，该链路的信道系数表示为表示GEO卫星与蜂窝用户链路的路径损耗因子，其中，d_GU表示GEO卫星与蜂窝用户的距离；|h_GU²是星地链路的信道衰减系数，PDF和CDF分别表示为：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, Where d_GU represents the distance between the GEO satellite and the cellular user; |h_GU² is the channel attenuation coefficient of the satellite-to-ground link. The PDF and CDF are expressed as:4.根据权利要求3所述的联合地球同步轨道与低轨道双层卫星网络传输方法，其特征在于，步骤S2中，GEO-LEO链路的距离为：4. The combined geosynchronous orbit and low-orbit dual-layer satellite network transmission method according to claim 3, characterized in that in step S2, the distance of the GEO-LEO link is:其中，极角满足和h_G表示GEO卫星高度，r_E表示地球半径；LEO卫星的角速度在整个可见窗口内视为不变，记为ω；由公式得到：极角在卫星可见度持续时间t内呈均匀分布，记为t_min＜t＜t_max。Among them, the polar angle satisfy and_hG represents the GEO satellite altitude,_rE represents the radius of the Earth; the angular velocity of the LEO satellite is considered constant in the entire visible window and is denoted as ω; from the formula Get: polar angle It is uniformly distributed within the satellite visibility duration t, denoted as_tmin ＜t＜_tmax .