CN115086427A - Edge cache content placement method for satellite-ground integrated cooperative shared network - Google Patents

Edge cache content placement method for satellite-ground integrated cooperative shared network Download PDF

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CN115086427A
CN115086427A CN202210634973.5A CN202210634973A CN115086427A CN 115086427 A CN115086427 A CN 115086427A CN 202210634973 A CN202210634973 A CN 202210634973A CN 115086427 A CN115086427 A CN 115086427A
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顾术实
陈紫菡
左苗苗
余子超
张钦宇
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Shenzhen Graduate School Harbin Institute of Technology
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Abstract

The invention provides a method for placing edge cache content of a satellite-ground integrated cooperative sharing network, which comprises the following steps: step 1: firstly, the cache matrix of the auxiliary satellite is set to be 0, and when the sum of the SBS n and the number of the cache coding packets of the main satellite is less than or equal toKWhen the method is used, the ground sharing link is started, and then the content file placement matrix m of the SBSs is obtained by maximizing the total transmission flow i,n Then, a main satellite cache placement matrix is obtained by minimizing overall transmission energy consumption; step 2: after the cache placement matrixes of the SBSs and the main satellite are obtained, the integrated cooperation of the SBSs and the main satellite to the multi-satellite and ground is expandedShared network, introducing shared variablesɑ i Sharing variablesɑ i When the value is 0, the method indicates that only the ground shared link is started, at the moment, the cache placement matrix in the auxiliary satellite is cleared, and the shared variable is resetɑ i When the value is 1, the inter-satellite shared link is only started, and at the moment, the cache placement matrix in the SBSs is cleared. The invention has the beneficial effects that: the invention realizes the energy efficiency maximization of the satellite-ground integrated cooperative sharing network.

Description

Edge cache content placement method for satellite-ground integrated cooperative shared network
Technical Field
The invention relates to the technical field of satellites, in particular to a method for placing edge cache contents facing a satellite-ground integrated cooperative shared network.
Background
The explosive growth of mobile data traffic, 6G vision, further expands the range and depth of network coverage, which is a challenge for traditional terrestrial cellular networks. The satellite-ground integrated network has wide coverage and seamless access capability, can obviously improve the performance of the ground cellular network, and is a necessary trend of future technology development.
According to the characteristics of data traffic, that is, the main part of increased Mobile communication traffic is repeated downloading of some popular content items from a remote server, the popular content items can be cached in an intermediate server using Mobile Edge Caching and delivery technology (MEC), so that the content is closer to the user, less delivery delay is generated, the user experience quality is remarkably improved, and the transmission resource consumption of backhaul and core network is saved.
Terrestrial backhaul is a multi-hop unicast network, and therefore, the buffered content must travel multiple links and must be transmitted individually to each base station. While satellite systems can provide broadband backhaul links and operate in a multi/broadcast mode covering a wide area. Therefore, the cache and the satellite communication technology are combined together, typical application scenes such as hot video push and popular content distribution in a wide area or a global area can be handled, the load pressure of a ground core network can be further relieved, and the seamless connection and broadband communication capacity of cross-domain real-time information sharing is improved.
However, the satellite-ground integrated network has limited cache and energy resources and complex infrastructure, which severely increases the burden of the backhaul link and reduces the energy efficiency. The encoding caching is an emerging technology for improving the caching efficiency, each file can be divided into a plurality of sections by using the encoding technology in the caching process, and different sections of the file can be cached strategically at the edge node. The rateless coding has lower coding redundancy compared with the traditional coding scheme, and the rateless coding means that the coded data blocks can be continuously generated like a fountain, so that the data does not have a specific rate after being coded.
With the gradual implementation of the plan of Low Earth Orbit (LEO) satellite constellations such as Oneweb, Starlink and the like, a Low Earth Orbit satellite with Low delay and high bandwidth will be used as an access satellite of a future 6G air-space-ground integrated network to communicate with a ground base station. In designing and implementing a high-performance Radio Access Network (RAN), a low-earth orbit satellite constellation is considered in more and more researches, however, most researches concern the transmission delay and the transmission cost of a multi-satellite-to-satellite integrated Network, and a complete file is transmitted without involving a code caching technology, or only the code caching technology is applied to a single satellite-to-ground integrated Network.
Disclosure of Invention
The invention provides a method for placing edge cache content of a satellite-ground integrated cooperative sharing network, which comprises the following steps:
step 1: firstly, setting a cache matrix of an auxiliary satellite to be 0, starting a ground shared link when the sum of the number of the SBS n and the number of the cache coding packets of the main satellite is less than K, and then obtaining a content file placement matrix m of SBSs (satellite broadcast systems) by maximizing the total transmission flow i,n And then obtaining a main satellite cache placement matrix by minimizing the total transmission energy consumption, and obtaining the number of the code packets cached in the main satellite
Figure BDA0003681718310000021
To reach K-m i,n Time, file f i The ground sharing link is disabled, and the content file placement matrix m of the SBSs is adjusted i,n The overall transmission energy efficiency is optimized.
Step 2: to obtainAfter the SBSs and the main satellite cache placement matrix, expanding to a multi-satellite-ground integrated cooperative sharing network, and introducing a sharing variable a i Sharing a variable a i When the value is 0, the method only starts the ground shared link, the cache placement matrix in the auxiliary satellite is cleared, when the value of the shared variable ai is 1, the method only starts the inter-satellite shared link, and when the value of the cache placement matrix in the SBSs is cleared, the genetic algorithm is adopted to solve the cache placement matrix of the whole SBSs and LEO satellites.
As a further improvement of the present invention, in the step 1, the method further comprises:
step S1: and (5) initializing.
Step S2: placing the coding packets in the SBS; when the cache size constraint is satisfied
Figure BDA0003681718310000022
Then, for each SBS, according to the file set
Figure BDA0003681718310000023
In the order of (1), placing the files f in sequence i If m is i,n +1 < K and satisfying the power size constraint, then m i,n ＝m i,n +1, wherein,
Figure BDA0003681718310000024
representing a set of files, M T Representing the number of most storable code packets in each SBS, m i,n Representing files f cached in SBS n i I represents the file sequence number in the file set.
Step S3: and (4) placing the code packet in the row main satellite, and adjusting the placing condition of the code packet in the SBS.
Step S4: updating
Figure BDA0003681718310000025
Step S5: repeating steps S1-S4 until the variation of η is less than σ and stopping iteration.
As a further improvement of the present invention, in step S1, the initializing specifically includes:
step S10: m is to be i,n ,
Figure BDA0003681718310000026
Setting 0 at the same time; wherein m is i,n Representing files f cached in SBS n i The number of coded packets of (a) is,
Figure BDA0003681718310000027
indicating the number of code packets buffered in the primary satellite.
Step S11: ranking the popularity of the files of each cell from high to low to obtain a file set
Figure BDA0003681718310000031
Step S12: according to
Figure BDA0003681718310000032
The popularity of the files in the whole area is ranked from high to low by the value of (D) to obtain a file set
Figure BDA0003681718310000033
Wherein U is i,n Representing request files f in SBS n i The average number of users of the mobile terminal,
Figure BDA0003681718310000034
represents a set of cells, U i Indicating a requested file f in the whole area i The average number of users.
Step S13: setting an initial value eta of the total energy efficiency eta 0 。
As a further improvement of the present invention, in step S3, the method specifically includes:
according to file set
Figure BDA0003681718310000035
In the order of (1), placing files f in the main satellite in sequence i When the cache size constraint is satisfied
Figure BDA0003681718310000036
In which M is S Representing the maximum number of code packets capable of being cached in the satellite, the following operations are carried out: firstly, calculating the file f in the SBSs i The minimum buffer number of the coding packets is reduced by 1, and the file f i' The minimum buffer number of the coding packets is increased by 1, and the generated energy consumption is changed
Figure BDA0003681718310000037
If it is not
Figure BDA0003681718310000038
And satisfy
Figure BDA0003681718310000039
And a power magnitude constraint, then
Figure BDA00036817183100000310
Up to
Figure BDA00036817183100000311
Computing
Figure BDA00036817183100000312
If delta 2 ＞ηδ 1 And is and
Figure BDA00036817183100000313
satisfy the power size constraint, then
Figure BDA00036817183100000314
m i,n ＝m i,n -1，m i',n ＝m i',n +1。
As a further improvement of the present invention, in the steps S2 and S3, the formula of the power size constraint is as follows:
Figure BDA00036817183100000315
as a further improvement of the present invention, in step 2, solving the cache placement matrix by using a genetic algorithm specifically includes:
step 20: and G, 0 in the initialized parent population.
Step 21: and calculating the fitness, namely the total energy efficiency of the system.
Step 22: randomly selecting individuals with higher fitness in the parent population, and comparing the transmission files f in the selected individuals i Energy efficiency of, selecting a higher shared variable a i Value taking, then under the power constraint and the cache size constraint, regulating the number of encoding packets in the SBSs and the satellite according to the file popularity, and generating new individuals through variation;
step 23: calculating the fitness of the new individuals, combining the fitness with the parent population, sorting the new individuals from large to small according to the fitness, and reserving the n Pop individuals before ranking, namely the next generation population, wherein G is G + 1.
Step 24: and judging whether G is greater than the set genetic times GEN, if so, outputting the individual with the first fitness ranking, and otherwise, repeating the steps 22-24.
As a further improvement of the present invention, in step 20, initializing a parent population specifically includes:
according to cache placement vector m solved under single satellite scene i,n And
Figure BDA0003681718310000041
generating a first set of shared variables a i I.e. when buffering the file f in SBS n i When the total number of the coded packets is more than K, the variable a is shared i Taking the value of 0, otherwise taking the value of 1, and remaining nPop-1 shared variables a i And randomly generating, and then placing the rest required encoding packets by the SBSs and the auxiliary satellites according to the popularity of the file from low to high under the constraints of the cache size and the power, so as to generate a parent population with the nPop individuals.
As a further improvement of the present invention, in the steps 20 and 22, the formula of the power constraint is as follows:
Figure BDA0003681718310000042
the formula of the cache size constraint is as follows:
Figure BDA0003681718310000043
the invention has the beneficial effects that: 1. according to the satellite-ground cooperation sharing transmission strategy, the ground base station and the cache file on the satellite are placed in a combined mode, and the energy efficiency maximization of the satellite-ground integrated cooperation sharing network is achieved; 2. compared with a single satellite-ground integrated cooperative shared network, the space-based network adopts a satellite constellation to increase an inter-satellite shared link, and can effectively improve the transmission energy efficiency of the system.
Drawings
FIG. 1 is a schematic diagram of a satellite-ground integrated collaboration sharing network model proposed by the present invention;
FIG. 2 is a schematic diagram illustrating a comparison of two transmission strategies and two caching methods under different popularity parameters;
FIG. 3 is a schematic diagram showing the comparison of two transmission strategies and two buffering modes for different numbers of satellites according to the present invention;
FIG. 4 is a schematic diagram showing the comparison of two transmission strategies and two caching modes under different inter-satellite distances according to the present invention;
FIG. 5 is a schematic diagram comparing two transmission strategies and two buffering schemes under different SBS numbers according to the present invention;
FIG. 6 is a content placement flow diagram of the present invention.
Detailed Description
In order to fully utilize the advantages of a satellite network, the encoding caching technology is combined with a multi-satellite-ground integrated network, and due to the fact that satellite resources are limited, caching resource sharing of a satellite and a ground network and satellite-ground integrated cooperative transmission of hot spot data are considered, namely the satellite-ground integrated cooperative sharing network is built, and the caching content of a ground base station and the caching content of the satellite are designed in a combined mode, so that the accurate pushing of popular content is guaranteed, and the user service data flow and the overall transmission energy efficiency of different areas are improved. The satellite-ground integrated cooperative sharing network relates to double-layer multi-cache nodes, and the design of file caching and transmission strategies is particularly important and complex.
According to the invention, through research on the rateless coding, the coding mode is that data fault tolerance is realized by adding redundancy, the MDS characteristics need to be met (namely any k coding data blocks can recover original data), and a large number of nonlinear data blocks can be generated through rateless coding, so that the possibility is provided for cross-level multi-node caching and data transmission in the multi-satellite-ground integrated network.
The invention adopts a no-rate coding mode, LT (Luby transform) coding, can obtain infinite different coding packets, and can recover the original file by receiving K coding packets. The encoded packets generated by each file are stored in a distributed manner in Small Base Stations (SBSs) on the ground and in LEO satellites.
In the satellite-ground integrated cooperative sharing network, only one main satellite can communicate with ground equipment, two sharing links exist, one is the ground sharing link, the cached coding packet is transmitted to the main satellite through a ground base station, and then the satellite broadcasts the coding packet to users; and the other is an inter-satellite shared link, and the cached code packets are transmitted to the primary satellite through the secondary satellite (i.e. the satellite except the primary satellite). The SBSs and the LEO satellite cooperate to provide services for the ground users, and the rest required coding packets are transmitted through a shared link and then broadcast to the ground users through the main satellite.
The invention discloses a method for placing edge cache contents of a satellite-ground integrated cooperative shared network, which only has a ground shared link and adopts an iterative algorithm to solve. First, a content file placement matrix m of SBSs is obtained by maximizing the total transmission flow i,n And secondly, obtaining a cache placement matrix of the main satellite by minimizing the total transmission energy consumption when the number of the code packets cached in the main satellite
Figure BDA0003681718310000051
To reach K-m i,n Time, file f i The ground sharing link is disabled, and the content file placement matrix m of the SBSs is adjusted i,n The overall transmission energy efficiency is optimized.
And after the cache placement matrixes of the SBSs and the main satellite are obtained, expanding the cache placement matrixes to a multi-satellite-ground integrated cooperative sharing network, and solving the cache placement matrixes of all the SBSs and the LEO satellite by adopting a genetic algorithm. Sharing variable a i When the value is 0, the ground shared link is started, the cache placement matrix in the auxiliary satellite is cleared, and the shared variable a i And when the value is 1, the inter-satellite shared link is started, and the cache placement matrix in the SBSs is cleared. First, initializing the parent population, and obtaining m in the previous step i,n And
Figure BDA0003681718310000061
on the basis of (a), randomly generating a shared variable a i Under the constraints of cache and power, the SBSs and the auxiliary satellites place the rest of required coding packets from low to high according to the popularity of the file; then calculating the fitness, namely the total energy efficiency of the system, randomly selecting two individuals with higher fitness in the parent population, and comparing the transmission files f in the two individuals i Energy efficiency of, selecting a higher shared variable a i Taking values, generating new individuals through variation, combining the new individuals with the parent population and sequencing the new individuals to generate the next generation population; and repeating the genetic operation for a limited number of times and outputting an optimal cache placement matrix.
As shown in FIG. 1, the satellite-ground integrated cooperative sharing network model has cells of
Figure BDA0003681718310000062
The cells covered by each SBSs are not overlapped, and the associated user set is
Figure BDA0003681718310000063
A plurality of LEO satellites at the same orbital altitude jointly serve a ground area, only one LEO satellite is communicated with ground equipment and called as a main satellite, the rest of LEO satellites are auxiliary satellites, communication can be performed only between adjacent satellites, and the LEO satellites are collected into a set
Figure BDA0003681718310000064
The file set is
Figure BDA0003681718310000065
Prevalence of files in SBS n i,n In a Zipf distribution (a discrete probability distribution satisfying the Zipf law, i.e., the frequency of an item is inversely proportional to its rank in the frequency table; Zipf distribution Chinese called Ziff distribution, the Law of experimentation published in 1949 by the linguist George Kingsley Zipf of Harvard university, it can be stated that in a corpus of natural language, the frequency of a word occurrence is inversely proportional to its rank in the frequency table.):
Figure BDA0003681718310000066
Figure BDA0003681718310000067
assuming that all files have the same size s, LT encoding is performed on the files to obtain infinite different encoding packets, and the original files can be recovered by receiving K encoding packets. File f i Divided into k source packets each of size
Figure BDA0003681718310000068
D (d is more than or equal to 1 and less than or equal to K) source data packets are randomly and independently selected to carry out bit XOR, an infinite number of different encoding packets can be obtained, and the source file can be recovered at a certain probability by downloading K (1+ epsilon) encoding packets. And storing the LT code packets generated by each file in the SBSs and the LEO satellite in a distributed mode. m is i,n Representing files f cached in SBS n i The number of the encoded packets of (a) is,
Figure BDA0003681718310000069
representing files f cached in LEO satellite l i The number of encoded packets.
And the SBSs and the LEO satellite cooperatively transmit to provide services for ground users, and when the number of the coding packets is insufficient, the shared link is started to transmit the residual coding packets to the main satellite. In order to maximize the overall transmission energy efficiency of the network, the transmission strategies and the cache matrixes of the SBSs and the LEO satellite need to be designed carefully.
The secondary satellite's cache matrix is first set to 0, i.e., only the terrestrial shared links are considered. And when the sum of the SBS n and the number of the main satellite cache coding packets is less than K, starting the ground shared link. The transmission flow rates of the SBSs and the LEO satellite are respectively B T And B S The requests of all users should be satisfied as much as possible.
The transmission energy consumption of the SBSs is P T Mainly divided into two parts, power consumed for transmission to the user and power consumed for sharing to the satellite, and LEO transmission energy consumption is P S 。
The total network flow and the total energy consumption are respectively as follows:
B total ＝B T +B S
P total ＝P T +P S
we create an energy efficiency optimization problem:
Problem 1
Figure BDA0003681718310000071
Figure BDA0003681718310000072
Figure BDA0003681718310000073
Figure BDA0003681718310000074
Figure BDA0003681718310000075
Figure BDA0003681718310000076
Figure BDA0003681718310000077
(2) the buffer size constraint of the SBSs and the LEO satellite is shown in (3), (4) the transmission power constraint is shown in (5) the files f are guaranteed to be buffered by both the SBSs and the LEO satellite i And (6) indicates that the number of code packets shared to the satellite is non-negative.
The transmission file f in SBS n can be easily deduced i And the whole network transmission file f i The energy consumed is respectively
Figure BDA0003681718310000078
The optimization problem is a fractional polynomial which we convert to a linear polynomial
Figure BDA0003681718310000079
The specific algorithm comprises the following steps:
step S1: and (5) initializing. Will also m i,n ,
Figure BDA00036817183100000710
Setting 0 at the same time; ranking the popularity of the files of each cell from high to low to obtain a file set
Figure BDA00036817183100000711
According to
Figure BDA00036817183100000712
The popularity of the files in the whole area is ranked from high to low by the value of (D) to obtain a file set
Figure BDA0003681718310000081
Setting an initial value eta of the total energy efficiency eta 0 。
Step S2: the code packet placement in SBS is performed. When the cache size constraint is satisfied
Figure BDA0003681718310000082
Then, for each SBS, according to the file set
Figure BDA0003681718310000083
In the order of (1), placing the files f in sequence i If m is i,n +1 < K and satisfying the power size constraint (4), then m i,n ＝m i,n +1。
Step S3: and (4) placing the code packet in the row main satellite, and adjusting the placing condition of the code packet in the SBS. According to file set
Figure BDA0003681718310000084
In the order in (1), placing files f in the main satellite in sequence i When the cache size constraint is satisfied
Figure BDA0003681718310000085
Then, the following operations are performed: firstly, calculating the file f in the SBSs i The minimum buffer number of the coding packets is reduced by 1, and the file f i' The minimum buffer number of the coding packets is increased by 1, and the generated energy consumption is changed
Figure BDA0003681718310000086
If it is not
Figure BDA0003681718310000087
And satisfy
Figure BDA0003681718310000088
And a power size constraint (4), then
Figure BDA0003681718310000089
Up to
Figure BDA00036817183100000810
Computing
Figure BDA00036817183100000811
If delta 2 ＞ηδ 1 And is and
Figure BDA00036817183100000812
satisfy the power size constraint (4), then
Figure BDA00036817183100000813
m i,n ＝m i,n -1，m i',n ＝m i',n +1。
Step S4: updating
Figure BDA00036817183100000814
Step S5: repeating steps S1-S4 until the variation of η is less than σ and stopping iteration.
Through simulation analysis, the invention obtains different user densities theta 0 Under different buffer sizes M/sI (M represents the number of files in the buffer, and I represents the total number of files) and different file popularity parameters alpha, the comparison of different transmission modes and different buffer modes on transmission efficiency respectively comprises the steps of enabling a ground sharing link and optimized content placement (TS-OPP), enabling the ground sharing link and the hottest inner content placement (TS-MPP), not enabling the ground sharing link and optimized content placement (NS-OPP), and not enabling the ground sharing link and the hottest inner content placement (NS-MPP).
FIG. 2 shows the comparison of two transmission strategies and two buffering modes under different popularity parameters (10% buffering size and 100users/km user density) 2 )。
Therefore, the performance of the system in the aspect of transmission energy efficiency can be effectively improved by the provided transmission strategy and the cache mode under different cache sizes, different user densities and different file popularity parameters of the cache nodes.
The analysis shows that the cache content placement of the single satellite-ground integrated cooperative sharing network is expanded to a multi-satellite scene, namely, an inter-satellite sharing link is added, at the moment, a sharing vector ai is introduced, when the value is 0, the ground sharing link is only started, at the moment, the cache placement matrix in the auxiliary satellite is cleared, and the sharing variable a is shared i When the value is 1, the inter-satellite shared link is only started, and at the moment, the cache placement matrix in the SBSs is cleared. Re-transmission flow and transmission energy consumption of SBSs and LEO satellitesAnd analyzing, wherein a transmission flow formula in the network is the same as that in a single satellite scene, and the SBSs transmission energy consumption is as follows:
Figure BDA0003681718310000091
wherein,
Figure BDA0003681718310000092
represents the SBS n downlink transmission power;
Figure BDA0003681718310000093
represents the transmission power of the terrestrial shared link,
Figure BDA0003681718310000094
indicating the number of code packets, Pr (U), transmitted over the terrestrial shared link to the primary satellite i,n ≧ 1) means that at least one user in SBS n requests a file f i The probability of (c).
The transmission energy consumption of the main satellite is as follows:
Figure BDA0003681718310000095
wherein,
Figure BDA0003681718310000096
indicates the power of the LEO downlink transmission,
Figure BDA0003681718310000097
representing files f cached in SBSs i Is the minimum number of coded packets, Pr (U) i ≧ 1) means that there is at least one user request file f in all cells i The probability of (c).
The auxiliary satellite transmission energy consumption is as follows:
Figure BDA0003681718310000098
wherein l is represented byHop count of the primary satellite and satisfies
Figure BDA0003681718310000099
Figure BDA00036817183100000910
Indicating completion of transmission in time slot t
Figure BDA00036817183100000911
Inter-satellite link transmission power, W, consumed by individual coded packets S Is the channel bandwidth of the satellite, | σ |, C S | 2 Which is indicative of the power of the noise,
Figure BDA00036817183100000912
representing inter-satellite link fading coefficients, taking into account only free space losses, where H ISL Representing the distance between adjacent satellites, and λ is the wavelength of the carrier.
Total transmission flow: b is total ＝B T +B S
Total transmission energy consumption: p total ＝P T +P S +P ISL
The final optimization problem is thus:
Figure BDA0003681718310000101
s.t.(1)(2)(6)
Figure BDA0003681718310000102
Figure BDA0003681718310000103
Figure BDA0003681718310000104
a i ∈{0,1} (10)
(7) the method comprises the following steps of (1) representing buffer size constraint, (8) representing transmission power constraint, (9) representing that at least one encoding packet is buffered in both a satellite and an SBSs, and (10) representing that the value of a shared variable is 0 and 1.
Because the cache variable of double-layer multi-node is involved, a genetic algorithm is adopted to solve a cache placement matrix, and the specific algorithm steps are as follows:
step 20: and G, 0, initializing the parent population. According to cache placement vector m solved under single satellite scene i,n And
Figure BDA0003681718310000105
generating a first group a i I.e. when buffering the file f in SBS n i When the total number of coded packets is greater than K, a i Taking the value of 0, otherwise taking the value of 1, and remaining nPop-1 shared variables a i And (4) randomly generating. And then under the buffer size constraint (7) and the power constraint (8), the SBSs and the auxiliary satellites place the rest of the required code packets from low to high according to the file popularity to generate a parent population with nPop individuals.
Step 21: and calculating the fitness, namely the total energy efficiency of the system.
Step 22: randomly selecting two individuals with larger fitness in the parent population, and comparing the transmission files f in the two individuals i Energy efficiency of, selecting a higher shared variable a i And (3) taking values, and then regulating the number of encoding packets in the SBSs and the satellite according to the file popularity under the power constraint (8) and the cache size constraint (7), so as to generate new individuals through mutation.
Step 23: calculating the fitness of the new individual, combining the fitness with the parent population, then sorting the new individual and the parent population from big to small according to the fitness, and reserving n pop individuals before ranking, namely the next generation population, wherein G is G + 1.
Step 24: and judging whether G is greater than the set genetic times GEN, if so, outputting the individual with the first fitness ranking, and otherwise, repeating the steps 22-24.
Through simulation analysis, the invention obtains different satellite parameters, and under different SBSs (satellite service standards) quantity, the comparison of the non-start of the inter-satellite shared link and the comparison of the different transmission modes and the different cache modes on the transmission energy efficiency are respectively to start the two shared links and the optimized content placement (TSS-OPP), start the two shared links and the hottest internal storage placement (TSS-MPP), only the inter-satellite shared link and the optimized content placement (SS-OPP), and only the inter-satellite shared link and the hottest internal storage placement (SS-MPP). As shown in fig. 3-5, the comparison between the two transmission strategies and the two buffering modes under different satellite numbers in fig. 3 (the size of the satellite buffer is 20%, the inter-satellite distance is 100km, and the number of SBSs is 5); fig. 4 is a comparison of two transmission strategies and two caching methods at different inter-satellite distances (the number of satellites is 5, the size of the satellite cache is 20%, and the number of SBSs is 5), and fig. 5 is a comparison of two transmission strategies and two caching methods at different SBSs (the number of satellites is 5, the size of the satellite cache is 20%, and the inter-satellite distance is 100 km).
Therefore, for different satellite parameters and different SBSs (satellite service classes), inter-satellite and ground shared links are started, and the performance of the system in the aspect of transmission energy efficiency can be effectively improved by using the provided cooperative caching mode based on the genetic algorithm.
The invention researches a transmission strategy and an edge cache content placement method of a satellite-ground integrated network, considers limited cache resources and energy resources, and the layering heterogeneity of a system, combines a coding cache technology, provides a satellite-ground cooperation sharing transmission strategy, and places a ground base station and a cache file on a satellite in a combined manner, so as to realize the energy efficiency maximization of the satellite-ground integrated cooperation sharing network:
1. firstly, a single satellite-ground integrated network is considered, the concept of a ground shared link is provided, a transmission flow and transmission energy consumption expression required by a system according to user requirements within a certain time are deduced by combining a non-rate coding cache, a system energy efficiency expression is obtained and optimized, and the effectiveness of the provided cooperation sharing transmission strategy and cache mode in the aspect of improving the transmission energy efficiency of the system is verified.
2. The method comprises the steps of expanding a multi-satellite on the basis of a single-satellite scene, adding an inter-satellite shared link, further deducing a new transmission energy efficiency expression, applying a genetic algorithm, selecting a shared link and a cache file in a strategic manner, and verifying that compared with a single-satellite-ground integrated cooperative shared network, a space-based network adopts a satellite constellation to add an inter-satellite shared link, so that the transmission energy efficiency of the system can be effectively improved.
The invention has the beneficial effects that: 1. according to the satellite-ground cooperation sharing transmission strategy, the ground base station and the cache file on the satellite are placed in a combined mode, and the energy efficiency maximization of the satellite-ground integrated cooperation sharing network is achieved; 2. compared with a single satellite-ground integrated cooperative shared network, the space-based network adopts a satellite constellation to increase an inter-satellite shared link, and can effectively improve the transmission energy efficiency of the system.
The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims (8)

1. A method for placing edge cache content facing to a satellite-ground integrated cooperative shared network is characterized by comprising the following steps:
step 1: firstly, setting a cache matrix of an auxiliary satellite to be 0, starting a ground shared link when the sum of the number of the SBSn and the cache coding packets of the main satellite is less than K, and then obtaining a content file placement matrix m of the SBSs by maximizing the total transmission flow i,n And then obtaining a main satellite cache placement matrix by minimizing the total transmission energy consumption, and obtaining the number of the code packets cached in the main satellite
Figure FDA0003681718300000011
To reach K-m i,n Time, file f i The ground sharing link is disabled, and the content file placement matrix m of the SBSs is adjusted i,n The overall transmission energy efficiency is optimized;
step 2: after the cache placement matrixes of the SBSs and the main satellite are obtained, the integrated cooperation of the SBSs and the main satellite to the multi-satellite and ground is expandedShared network, introducing shared variable a i Sharing a variable a i When the value is 0, the method indicates that only the ground shared link is started, at the moment, the cache placement matrix in the auxiliary satellite is cleared, and the shared variable a i When the value is 1, the inter-satellite shared link is only started, at the moment, the cache placement matrix in the SBSs is cleared, and then the genetic algorithm is adopted to solve the cache placement matrix of the whole SBSs and LEO satellites.
2. The edge cache content placement method according to claim 1, further comprising, in step 1:
step S1: initializing;
step S2: placing the coding packets in the SBS; when the cache size constraint is satisfied
Figure FDA0003681718300000012
Then, for each SBS, according to the file set
Figure FDA0003681718300000013
In the order of (1), placing the files f in sequence i If m is i,n K is more than 1 and satisfies the power size constraint, then m i,n ＝m i,n +1, wherein,
Figure FDA0003681718300000014
representing a set of files, M T Representing the maximum number of storable code packets, m, in each SBS i,n Representing files f cached in SBSn i I represents the file sequence number in the file set;
step S3: placing the code packet in the row main satellite, and adjusting the placing condition of the code packet in the SBS;
step S4: updating
Figure FDA0003681718300000015
Step S5: repeating steps S1-S4 until the variation of η is less than σ and stopping iteration.
3. The method for placing edge cache content according to claim 2, wherein in the step S1, the initializing specifically includes:
step S10: m is to be i,n ,
Figure FDA0003681718300000021
Setting 0 at the same time; wherein m is i,n Representing files f cached in SBSn i The number of coded packets of (a) is,
Figure FDA0003681718300000022
indicating the number of code packets buffered in the primary satellite;
step S11: ranking the popularity of the files of each cell from high to low to obtain a file set
Figure FDA0003681718300000023
Step S12: according to
Figure FDA0003681718300000024
The popularity of the files in the whole area is ranked from high to low by the value of (D) to obtain a file set
Figure FDA0003681718300000025
Wherein U is i,n Indicating a request for file f in SBSn i Average number of users, U i Indicating a requested file f in the whole area i The average number of users of the mobile terminal,
Figure FDA0003681718300000026
representing a set of cells;
step S13: setting an initial value eta of the total energy efficiency eta 0 。
4. The method for placing edge cache content according to claim 2, wherein in the step S3, the method specifically includes:
according to file set
Figure FDA0003681718300000027
In the order in (1), placing files f in the main satellite in sequence i When the cache size constraint is satisfied
Figure FDA0003681718300000028
In which M is S Representing the maximum number of code packets capable of being cached in the satellite, the following operations are carried out: firstly, calculating the file f in the SBSs i The minimum buffer number of the coding package is reduced by 1, and the file f i' The minimum buffer number of the coding packets is increased by 1, and the generated energy consumption is changed
Figure FDA0003681718300000029
If it is not
Figure FDA00036817183000000210
And satisfy
Figure FDA00036817183000000211
And a power magnitude constraint, then
Figure FDA00036817183000000212
Up to
Figure FDA00036817183000000213
Computing
Figure FDA00036817183000000214
If delta 2 ＞ηδ 1 And is and
Figure FDA00036817183000000215
satisfy the power size constraint, then
Figure FDA00036817183000000216
m i,n ＝m i,n -1，m i',n ＝m i',n +1。
5. The edge cache content placement method according to claim 4, wherein in the steps S2, S3, the formula of the power size constraint is as follows:
Figure FDA00036817183000000217
6. the method for placing edge cache contents according to claim 1, wherein in the step 2, solving the cache placement matrix by using a genetic algorithm specifically comprises:
step 20: initializing a parent population G which is 0;
step 21: calculating the fitness, namely the total energy efficiency of the system;
step 22: randomly selecting individuals with higher fitness in the parent population, and comparing the transmission files f in the selected individuals i Energy efficiency of, selecting a higher shared variable a i Value taking, then under the power constraint and the cache size constraint, regulating the number of encoding packets in the SBSs and the satellite according to the file popularity, and generating new individuals through variation;
step 23: calculating the fitness of the new individual, combining the fitness with the parent population, sorting the fitness from large to small, and reserving n pop individuals before ranking, namely the next generation population, wherein G is G + 1;
step 24: and judging whether G is greater than the set genetic times GEN, if so, outputting the individual with the first fitness ranking, and otherwise, repeating the steps 22-24.
7. The method for placing edge cache content according to claim 6, wherein in the step 20, initializing a parent population specifically comprises:
according to cache placement vector m solved under single satellite scene i,n And
Figure FDA0003681718300000031
generating a first set of shared variables a i I.e. when caching the file f in the SBSn i Is greater than the total number of coded packetsK, share variable a i Taking the value of 0, otherwise taking the value of 1, and remaining nPop-1 shared variables a i And randomly generating, and then placing the rest required encoding packets by the SBSs and the auxiliary satellites according to the popularity of the file from low to high under the constraints of the cache size and the power, so as to generate a parent population with the nPop individuals.
8. The edge cache content placement method according to claim 7, wherein in said steps 20, 22,
the formula for the power constraint is as follows:
Figure FDA0003681718300000032
the formula of the cache size constraint is as follows:
Figure FDA0003681718300000033
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