CN118174769A - Double-layer satellite network transmission method and system combining geosynchronous orbit and low orbit - Google Patents
Double-layer satellite network transmission method and system combining geosynchronous orbit and low orbit Download PDFInfo
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Abstract
The invention discloses a method and a system for transmitting a double-layer satellite network combining a geosynchronous orbit and a low orbit, wherein the method 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 combines signals from the GEO satellite and the LEO satellite in a maximum ratio combination mode. The power distribution factor of the self-adaptive non-orthogonal multiple access technology provided by the invention is dynamically adjusted along with the channel state, satellite elevation angle and common-frequency interference variation, 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.
Description
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 contemplates two users having different channel conditions: users with good channel conditions (CU N) and users with poor channel conditions (CU F). Furthermore, all devices are equipped with a single antenna. The midpoint between two cellular subscribers is denoted as U 0,hL 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 U 0. Further, β ε [ β min,βmax ] is used to represent the average elevation angle of LEO satellites observed by cellular users. By taking GEO satellite-geocenter as a reference line, use/>Represents the polar angle of LEO satellite motion, i.e., the angle between the L 2 -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 the interfering signal of the j-th wireless access point, where/(No.)P a is the fixed transmit power of all wireless access points. n L and/>Representing additive white gaussian noise at LEO satellites and cellular subscribers respectively,The received signal-to-noise ratio (SNR) of LEO satellite and cellular user is/>, respectivelyWherein/>P L represents the transmission power of LEO satellite, P G represents the transmission power of GEO satellite,/>Is co-channel interference experienced by cellular users, where the signal-to-noise ratio/>, of the 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 represent antenna gains for GEO satellite and LEO satellite, respectively; the channel attenuation coefficient of the GEO-LEO link is denoted as |h GL|2; use/>Representing the path loss factor of the GEO-LEO link; wherein c is about 3× 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; t n denotes the noise temperature of the LEO satellite, B c denotes the carrier bandwidth; d GL denotes 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 as Wherein G G and G U represent antenna gains for GEO satellites and cellular users, respectively; /(I)Representing the path loss factor of a GEO satellite to cellular user link,/>Wherein 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-ground link, PDF and CDF are denoted as:
Wherein, The 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 a Nakagami parameter, which 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.
Preferably, in step S2, the distance of the GEO-LEO link is:
wherein the polar angle Satisfy/>And/>H L denotes LEO satellite altitude, h G denotes GEO satellite altitude, r E denotes earth radius; the angular velocity of the LEO satellite is considered constant throughout the visible window, noted ω; from the formula/>The method comprises the following steps: polar angle/>Is uniformly distributed within the satellite visibility duration t, which is marked astmin＜t＜tmax。
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, respectivelyAnd/>Representation (channel coefficient with better channel state is/>)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≥aN,aN+aF =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, and 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; /(I)Representing the path loss factor of LEO satellite and cellular subscriber link,/>Wherein/>Representing the distance of the LEO satellite from the cellular user; /(I)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, For normalizing parameters,/>The number Nm of wireless access points interfering with cellular users is a positive integer; (2N m -1) ++! ! Representing a double-order multiplication of (2N m -1); /(I)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 as follows: 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 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 is/>I 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. Furthermore, considering the LEO satellite moving, an elevation distribution model of the LEO satellite is proposed, which specifically includes: introducing the definition of the duration of the visible window of the satellite, deducing the cumulative distribution function expression of the elevation angle of the LEO satellite, and deriving the cumulative distribution function to obtain the probability density function expression of the elevation angle.
The distance of the GEO-LEO link is:
wherein the polar angle Satisfy/>And/>H 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 formula/>It can be seen that: polar angle/>Is uniformly distributed within the satellite visibility duration t, which is marked astmin＜t＜tmax。
Let U 0 be the midpoint of CU N and CU F, the distance between the LEO satellite and U 0 is calculated as:
Wherein the elevation angle beta satisfies beta min<β<βmax. 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 obtainedAnd/>Expressed as:
the invention provides a Cumulative Distribution Function (CDF) expression of LEO satellite elevation angles, which is as follows:
Wherein, 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, and t β represents the time when the elevation angle is beta; χ (t max) represents the LEO satellite to user angular distance 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 adopts/>Representing the path loss factor of the GEO-LEO link. Where c.apprxeq.3.times.10 10 8 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. /(I)Representing the path loss factor of a GEO satellite to cellular user link,/>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, The 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; /(I)Representing the path loss factor of LEO satellite and cellular subscriber link,/>Wherein/>Representing the distance of the LEO satellite from the cellular user; /(I)Is the channel attenuation coefficient of the LEO satellite-ground link, PDF and CDF are expressed as:
The same-frequency interference suffered by the user is approximately solved, and the method is specifically as follows: the envelope of each wireless access point-user CU m link is represented as a statistically independent rayleigh random variable, the sum distribution of which must be determined if the cumulative co-channel interference experienced by the user is calculated. 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, For normalizing parameters,/>The number of wireless access points Nm of interfering cellular users is a positive integer. (2N m -1) ++! ! Representing a double-order multiplication of (2N m -1). /(I)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, Representing the average channel gain. /(I)And/>Representing the average co-channel interference of CU N and CU F, respectively. The average channel fading coefficient is obtained by adopting the 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,
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,
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:
And a signal transmitting module: geosynchronous orbit GEO satellites transmit signals to low orbit LEO satellites and cellular users;
a signal receiving module: LEO satellites and cellular users receive signals transmitted by GEO satellites;
and the signal decoding and forwarding module is used for: the LEO satellite adopts a decoding forwarding relay protocol and an adaptive NOMA to send signals to the cellular user;
Signal receiving and combining module: 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 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 cellular subscribers, 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; signals are transmitted simultaneously to the LEO satellite and to two cellular users using frequency division multiple access techniques, wherein the signal transmitted to the LEO satellite is a combination of the two cellular user signals.
Step S102: LEO satellites and cellular subscribers receive signals transmitted by GEO satellites.
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.
Step S103: the LEO satellite uses a decode-and-forward (DF) relay protocol and an adaptive NOMA technique to transmit signals to two cellular subscribers, respectively.
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. After the LEO satellite successfully decodes the signals, converting the signals into signals which are transmitted to different cellular users based on the same frequency; the channel state and link distance of the LEO satellite to two cellular users, the elevation angle of the LEO satellite, and the channel state of wireless nodes around the cellular users that are interfering with them are obtained. Judging channel conditions of two users according to the information, and designing corresponding self-adaptive power distribution coefficients; the LEO satellites distribute power to signals to be transmitted to two subscribers and transmit signals to two cellular subscribers using 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 signals of LEO satellites, a user CU N with a better channel state adopts a serial interference elimination technology, part of signals which have higher power and are sent to a user CU F with a worse channel state in the aliasing signals are removed, and the rest signals are signals required by the user CU F; CU F does not need to employ serial interference cancellation and treats the less powerful part of the aliased signal that is sent to CU N as noise. 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:
And a signal transmitting module: geosynchronous orbit GEO satellites transmit signals to low orbit LEO satellites and cellular users;
a signal receiving module: LEO satellites and cellular users receive signals transmitted by GEO satellites;
and the signal decoding and forwarding module is used for: the LEO satellite adopts a decoding forwarding relay protocol and an adaptive NOMA to send signals to the cellular user;
Signal receiving and combining module: 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.
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 describes in detail a method and a system for transmitting a combined geosynchronous orbit/low orbit double-layer satellite network based on adaptive non-orthogonal multiple access, and the invention applies the preferred embodiments to explain the principle and implementation of the invention, and the above description of the embodiments is only used to help understand the method and core idea of the invention; meanwhile, as those skilled in the art will have variations in the specific embodiments and application scope in accordance with the ideas of the present invention, the present description should not be construed as limiting the present invention in view of the above.
Claims (10)
1. The method for transmitting the combined geosynchronous orbit and low orbit double-layer satellite network is characterized by comprising the following steps of:
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.
2. The method of claim 1, wherein in step S2, signals received by LEO satellites and cellular user U m are represented as Wherein H Gl and H GU represent 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 denotes the number of wireless access points interfering with the cellular user; s j represents an interference signal of the j-th wireless access point; p a is the fixed transmit power of all wireless access points; n L and/>Representing additive white gaussian noise at LEO satellite and cellular users, respectively,/> Representing a solution desire; the received signal-to-noise ratio of LEO satellite and cellular user is/>, respectivelyWherein,P L represents the transmission power of LEO satellite, P G represents the transmission power of GEO satellite,/> Is co-channel interference experienced by cellular users, where the signal-to-noise ratio/>, of the 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.
3. The method of combining geosynchronous orbit and low orbit two-layer satellite network transmission according to claim 2, wherein in step S2, the channel coefficient of GEO-LEO link is expressed asWherein G G and G L represent antenna gains for GEO satellite and LEO satellite, respectively; the channel attenuation coefficient of the GEO-LEO link is denoted as |h GL|2; by usingRepresenting the path loss factor of the GEO-LEO link; wherein c is about 3× 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; t n denotes the noise temperature of the LEO satellite, B c denotes the carrier bandwidth; d GL denotes 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 as Wherein G G and G U represent antenna gains for GEO satellites and cellular users, respectively; /(I)Representing the path loss factor of a GEO satellite to cellular user link,/>Wherein 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-ground link, PDF and CDF are denoted as:
Wherein, The 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 a Nakagami parameter, which 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.
4. The combined geosynchronous orbit and low orbit two-layer satellite network transmission method according to claim 3, wherein in step S2, the GEO-LEO link distance is:
wherein the polar angle Satisfy/>And/>H L denotes LEO satellite altitude, h G denotes GEO satellite altitude, r E denotes earth radius; the angular velocity of the LEO satellite is considered constant throughout the visible window, noted ω; from the formula/>The method comprises the following steps: polar angle/>Is uniformly distributed within the satellite visibility duration t, which is marked as
5. The combined geosynchronous orbit and low orbit two-layer satellite network transmission method according to claim 4, wherein in step S3, in view of the high-speed motion of the LEO satellite, the channel state between the user and the satellite is changed; channel coefficients for low-orbit satellite and cellular subscriber link, respectivelyAnd/>The representation, wherein, the channel coefficient with good channel state isChannel coefficient of poor channel state is/>Defining CU N and CU F to respectively represent users with better channel states and users with worse channel states; the power allocation coefficients of CU N and CU F are denoted as a N and a F, respectively, according to the definition of NOMA technology, where a F≥aN,aN+aF = 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, and s k represents the signal transmitted by the kth wireless access point to CU F; h j,bm denotes the channel coefficient of the jth wireless access point to CU N link, and h k,bm denotes 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.
6. The method of claim 5, wherein in step S3, the channel coefficients of the LEO satellite-terrestrial link are expressed asWherein G L represents the antenna gain of the GEO satellite; /(I)Representing the path loss factor of LEO satellite and cellular subscriber link,/>Wherein/>Representing the distance of the LEO satellite from the cellular user; /(I)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, For normalizing parameters,/>The number Nm of wireless access points interfering with cellular users is a positive integer; (2N m -1) ++! ! Representing a double-order multiplication of (2N m -1); /(I)Representing the SNR of the wireless access point in the system.
7. The method for combining geosynchronous orbit and low orbit two-layer satellite network transmission according to claim 6, wherein in step S3, let U 0 be the midpoint between CU N and CU F, and the distance between LEO satellite and U 0 is calculated by the formula:
Wherein the elevation angle beta satisfies beta min<β<βmax; beta min >0 is obtained according to the definition of elevation angle;
Let z represent the horizontal distance between two cellular users, and according to the cosine law, the distance between the LEO satellite and two cellular users is obtained And/>Expressed as:
8. The method of claim 7, wherein in step S3, the definition of the duration of the visible window of the satellite is introduced, and the cumulative distribution function CDF expression of the elevation angle of the LEO satellite is derived:
Wherein, 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, and t β represents the time when the elevation angle is beta; χ (t max) represents the LEO satellite to user angular distance at time t max;
The probability density function PDF expression for deriving the elevation angle beta by deriving F (beta) is:
Wherein,
9. The combined geosynchronous orbit and low orbit dual-layer satellite network transmission method according to claim 8, wherein in step S4, signal S N is decoded at CU N using a serial interference cancellation scheme, i.e. the S F signal can be completely rejected at CU N; the signal-to-interference-and-noise ratio of CU N is expressed as For the average signal-to-noise ratio of CU N, I N is the co-channel interference suffered by CU N; the signal s N received by CU F is regarded as interference, and therefore, the SINR of CU F is/> For the average signal-to-noise ratio of CU F, I F is the co-channel interference suffered by CU F; the received signals from GEO satellites and LEO satellites are combined in a maximal ratio combining manner, and the SNRs of CU N and CU F are respectively expressed as:
10. A dual-layer satellite network transmission system combining geosynchronous orbit and low orbit, based on the method of any one of claims 1-9, comprising the following modules:
And a signal transmitting module: geosynchronous orbit GEO satellites transmit signals to low orbit LEO satellites and cellular users;
a signal receiving module: LEO satellites and cellular users receive signals transmitted by GEO satellites;
and the signal decoding and forwarding module is used for: the LEO satellite adopts a decoding forwarding relay protocol and an adaptive NOMA to send signals to the cellular user;
Signal receiving and combining module: 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.
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