CN112702443B - Multi-satellite multi-level cache allocation method and device for satellite-ground cooperative communication system - Google Patents
Multi-satellite multi-level cache allocation method and device for satellite-ground cooperative communication system Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L67/00—Network arrangements or protocols for supporting network services or applications
- H04L67/50—Network services
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- H04L67/568—Storing data temporarily at an intermediate stage, e.g. caching
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L67/00—Network arrangements or protocols for supporting network services or applications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L67/00—Network arrangements or protocols for supporting network services or applications
- H04L67/50—Network services
- H04L67/56—Provisioning of proxy services
- H04L67/568—Storing data temporarily at an intermediate stage, e.g. caching
- H04L67/5681—Pre-fetching or pre-delivering data based on network characteristics
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- H—ELECTRICITY
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- H04W—WIRELESS COMMUNICATION NETWORKS
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Abstract
The invention provides a multi-satellite multi-level cache allocation method and a multi-satellite multi-level cache allocation device for a satellite-ground cooperative communication system, which comprises the steps of collecting content popularity information, cache size information and transmission delay information required by the satellite-ground cooperative communication system for completing cache allocation; determining a system cache allocation problem based on a content service mode of multi-star multi-level cache; solving the cache allocation problem to obtain an optimal cache allocation strategy; and performing content caching on the multi-satellite multi-level edge server in the system based on the optimal caching distribution strategy so as to optimize the performance of the satellite-ground cooperative communication system. The method makes full use of a multi-satellite multi-level cache architecture in the satellite-ground cooperative communication system, provides edge content service for users through cooperation among multi-level edge servers and cooperation among a plurality of satellite edge servers, can effectively reduce the problem that delay indexes cannot be reached due to long delay of satellite-ground links in the satellite-ground cooperative communication system, and ensures transmission of delay sensitive services of the users.
Description
Technical Field
The invention relates to the technical field of resource allocation in wireless communication, in particular to a multi-satellite multi-level cache allocation method and a multi-satellite multi-level cache allocation device for a satellite-ground cooperative communication system.
Background
The development of satellite internet is rapid, the 6G wireless network is also proposed in the next generation mobile communication 6G white paper, the seamless connection among the ground, the satellite and the airborne network is realized, and the satellite-ground cooperative communication system is an important development direction of the next generation mobile communication. However, the user needs to go through the satellite-ground link to access the internet through the satellite, which causes a very large network delay. Taking a low-orbit satellite with a height of 1000km orbit as an example, the satellite-ground link delay reaches 13ms, while the satellite-ground link delay of an orbit satellite in a 20000km orbit reaches 270ms, which is far from reaching the delay indexes of 1ms for 5G communication and 0.1ms for 6G communication.
The rapid development of global smart phones has promoted the development of mobile terminals and "edge processing", and edge processing systems have come to the fore. By introducing the edge server, various processing works are completed on a local edge layer without uploading to the cloud, so that the processing efficiency is greatly improved, the user delay is reduced, and the network response speed is improved. Multimedia content now takes an increasing weight in communications, and unlike private data, multimedia content generally has a higher repeatability. Therefore, partial content is cached at the edge of the network, and when a user needs the corresponding content, the content is taken out from the edge server to provide service, and the content does not need to be taken back from the cloud, so that the system delay is effectively reduced. Since the caching of the edge server is limited, an optimal caching strategy needs to be determined according to the user interest, and the service delay when the user requests the content is minimized.
Possible cache positions in the satellite-ground cooperative communication system comprise a base station, a satellite and a ground station, and multi-satellite cooperative cache can be performed between the satellite and the satellite. Currently existing cache allocation methods generally consider a simplified satellite communication model, such as only content caching at the satellite or only content caching at the terrestrial base station. The existing method is lack of complete analysis on an overall system, and does not fully utilize a multi-satellite multi-level cache architecture in a satellite-ground cooperative communication system. In order to fully excavate the performance of the satellite-ground cooperative communication system and guarantee the delay sensitive service quality of a user, an innovative cache allocation method needs to be provided by utilizing a multi-satellite multi-level cache architecture in the satellite-ground cooperative communication system.
Disclosure of Invention
The invention aims to provide a multi-satellite multi-level cache allocation method and a multi-satellite multi-level cache allocation device for a satellite-ground cooperative communication system.
In order to achieve the purpose, the invention provides the following technical scheme:
the application discloses a multi-satellite multi-level cache allocation method for a satellite-ground cooperative communication system, which comprises the following steps:
(1) collecting content popularity information, cache size information and transmission delay information required by the satellite-ground cooperative communication system to finish cache allocation; the satellite-ground cooperative communication system comprises a space section and a ground section; the space section consists of a plurality of satellites, and the ground section consists of a user, a base station, a ground station and a cloud server;
(2) determining a system cache allocation problem based on a content service mode of multi-star multi-level cache;
(3) solving the cache allocation problem to obtain an optimal cache allocation strategy;
(3.1) setting the cached content of the ground station as a content set with the highest popularity;
(3.2) calculating to obtain a common cache content set of the base stations according to the content popularity distribution and the transmission delay information, wherein all the base stations cache all the content in the content set;
(3.3) calculating to obtain a satellite common cache content set according to the content popularity distribution and the transmission delay information, wherein all the satellites cache all the content in the content set;
(3.4) initializing and setting the cache contents of all base stations, initializing and setting the cache contents of all satellites, and calculating the average content service delay of the system under the initialization cache strategy;
(3.5) keeping a common cache content set unchanged for each base station satellite, and solving the cache allocation problem to obtain an optimal cache allocation strategy of the base station and the satellite;
(3.6) using the optimal cache allocation strategy as the optimal cache allocation strategy of the satellite-ground cooperative communication system;
(4) and performing content caching on the multi-satellite multi-level edge server in the system based on the optimal caching distribution strategy so as to optimize the performance of the satellite-ground cooperative communication system.
Preferably, an inter-satellite link for content transmission of adjacent satellites is arranged between the satellites in the step (1), each satellite is covered with a plurality of base stations and ground stations, and the satellites are connected with the base stations, the adjacent satellites and the ground stations in the coverage range of the satellite; each base station is covered with a plurality of users, the base stations are connected with the users in the coverage range of the base stations, the ground station is connected with the satellite and the cloud server, and the satellite, the base stations and the ground station are provided with edge servers capable of caching content for content service.
Preferably, the content popularity information is collected in the step (1) by performing estimation calculation based on the requested historical data of all the content stored in the cloud server, so as to obtain the probability that all the content stored in the cloud server is requested by the user; the cache size information comprises the cache size of a base station edge server, the cache size of a satellite edge server and the cache size of a ground station edge server; the mode of collecting the transmission delay information is to estimate and calculate the delay information based on the transmission delay information of the historical transmission process and the ergodic capacity of the transmission channel, and calculate the average transmission delay information of the contents retrieved from different edge servers; the transmission delay information includes: the method includes the steps that a user retrieves transmission delay information of content from a base station, the base station retrieves transmission delay information of the content from a satellite, the satellite retrieves transmission delay information of the content from an adjacent satellite, the satellite retrieves transmission delay information of the content from a ground station, and the ground station retrieves transmission delay information of the content from a cloud server.
Preferably, the step (2) includes the following sub-steps:
(2.1) calculating cache hit rates of different storage positions when a user requests content services in the coverage area of each satellite; the cache hit rate comprises a base station cache hit rate, a current satellite cache hit rate, an adjacent satellite cache hit rate, a ground station cache hit rate and a cloud server cache hit rate;
(2.2) calculating the satellite average content service delay based on the cache hit rate and the transmission delay information;
(2.3) weighting the average content service delay to obtain weighted average content service delay of each satellite;
and (2.4) summing the weighted average content service delays of all the satellites, and minimizing the sum of the weighted average content service delays under the constraint condition of the cache size to obtain the cache allocation problem.
Preferably, the substep (3.5) comprises in particular the following iterative procedure:
(3.5.1) calculating the caching profit of the content in the non-common caching content set cached by the base station in the coverage area for each satellite; (3.5.2) for each satellite, updating the cache of the base station in the coverage range into a common cache content set and cache contents with maximum profit in a non-common cache content set;
(3.5.3) for each satellite, calculating a cache gain for the satellite to cache content in the non-common cache content set;
(3.5.4) for each satellite, updating the cache of the satellite to a common cache content set and cache revenue maximization content in a non-common cache content set;
(3.5.5) calculating the average content service delay of the system after the cache strategy is updated;
(3.5.6) judging whether the average content service delay after updating the cache strategy is the same as the average content service delay before updating;
(3.5.7) if the two are the same, ending the iteration;
(3.5.8) if the difference is not the same, repeating the iteration process until the iteration is finished.
The invention has the beneficial effects that: compared with the prior art, the multi-satellite multi-level cache allocation method of the satellite-ground cooperative communication system firstly collects content popularity information, cache size information and transmission delay information required by the satellite-ground cooperative communication system to finish cache allocation; then, determining a system cache allocation problem based on a content service mode of multi-satellite multi-level cache, and solving the cache allocation problem to obtain an optimal cache allocation strategy; finally, content caching is carried out on the multi-satellite multi-level edge server in the system based on the optimal caching distribution strategy so as to optimize the performance of the satellite-ground cooperative communication system; the method can make full use of a multi-satellite multi-level cache architecture in the satellite-ground cooperative communication system, provide edge content service for users through cooperation among multi-level edge servers and cooperation among a plurality of satellite edge servers, effectively reduce content service delay in the satellite-ground cooperative communication system, relieve the problem that delay indexes cannot be reached due to long delay of satellite-ground links in the satellite-ground cooperative communication system, and ensure transmission of delay sensitive services of the users.
The features and advantages of the present invention will be described in detail by embodiments in conjunction with the accompanying drawings.
Drawings
Fig. 1 is a flowchart of a multi-satellite multi-level cache allocation method of a satellite-ground cooperative communication system according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a satellite-ground cooperative communication system according to an embodiment of the present invention;
fig. 3 is a flowchart of collecting content popularity information, cache size information, and transmission delay information required by the satellite-ground cooperative communication system to complete cache allocation according to the embodiment of the present invention;
FIG. 4 is a flow chart of a system cache allocation problem determination based on a content service approach of multi-star multi-level caching according to an embodiment of the present invention;
fig. 5 is a flowchart for solving a cache allocation problem to obtain an optimal cache allocation policy according to the embodiment of the present invention;
fig. 6 is a flowchart of solving a cache allocation problem to obtain an optimal cache allocation strategy for a base station and a satellite, where a common cache content set is maintained for each base station satellite;
fig. 7 is a schematic diagram illustrating comparison of performance of a multi-satellite multi-level cache allocation method of a satellite-ground cooperative communication system according to an embodiment of the present invention;
fig. 8 is a block diagram of a multi-satellite multi-level buffer allocation apparatus of a satellite-ground cooperative communication system according to an embodiment of the present invention.
In the figure: 11-an information collection module; 12-a cache allocation problem determination module; 13-an optimal cache solving module; 14-cache allocation module.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood, however, that the description herein of specific embodiments is only illustrative of the invention and is not intended to limit the scope of the invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.
To facilitate understanding of the embodiment, first, a multi-satellite multi-level buffer allocation method of a satellite-ground cooperative communication system disclosed in the embodiment of the present invention is described in detail.
The first embodiment is as follows:
a multi-satellite multi-level cache allocation method for a satellite-ground cooperative communication system, referring to fig. 1, the method comprising:
s101, collecting content popularity information, cache size information and transmission delay information which are required by a satellite-ground cooperative communication system to finish cache distribution;
in the embodiment of the invention, the execution subject of the method is a resource management center. Specifically, if the resource management center is disposed on a satellite, the satellite is an execution subject of the method, and if the resource management center is disposed on a ground station, the ground station is an execution subject of the method.
Specifically, in the embodiment of the present invention, the satellite-ground cooperative communication system provides a content transmission service for a ground user, and the ground user is located outside the coverage of the conventional ground cellular network and can only obtain content from the cloud server through a satellite. Therefore, partial content is cached in the edge server of the satellite-ground cooperative communication system, the content is taken out from the edge server to provide service when a user needs the corresponding content, the content does not need to be taken back from the cloud, and therefore the system delay is effectively reduced.
The following will describe in detail the process of collecting content popularity information, cache size information, and transmission delay information required by the satellite-ground cooperative communication system to complete cache allocation, which is not described herein again.
S102, determining a system cache allocation problem based on a content service mode of multi-satellite multi-level cache, wherein the content service mode of the multi-satellite multi-level cache indicates that content caching is performed through base station, satellite, ground station cooperation and multi-satellite cooperation to provide content service for users, the cache allocation problem indicates that under the condition that cache size constraint is met, average content service delay of all users is minimized, and the cache allocation problem comprises content popularity information, cache size information and transmission delay information;
after the content popularity information, the cache size information and the transmission delay information of the satellite-ground cooperative communication system are obtained, the system cache allocation problem is determined based on a content service mode of multi-satellite multi-level cache, the content service mode of the multi-satellite multi-level cache indicates that content caching is carried out through cooperation of a base station, a satellite and a ground station and cooperation among multiple satellites, content service is provided for users, the cache allocation problem comprises the content popularity information, the cache size information and the transmission delay information, and the cache allocation problem indicates that the average content service delay of all users is minimized under the condition that the cache size constraint is met. The process is described in detail below and will not be described herein.
S103, solving the cache allocation problem to obtain an optimal cache allocation strategy;
and after the cache allocation problem is obtained, solving the cache allocation problem to obtain an optimal cache allocation strategy. The process is described in detail below and will not be described herein.
And S104, performing content caching on the multi-satellite multi-level edge server in the system based on the optimal caching distribution strategy so as to optimize the performance of the satellite-ground cooperative communication system.
The existing cache allocation method usually considers a simplified satellite communication model, for example, only content caching is considered on a satellite, or only content caching is considered on a ground base station, complete analysis on an entire system is lacked, a multi-satellite multi-level cache architecture in a satellite-ground cooperative communication system is not fully utilized, and system performance is poor. Compared with the existing cache allocation method based on a simplified satellite communication model, in the multi-satellite multi-level cache allocation method of the satellite-ground cooperative communication system, content popularity information, cache size information and transmission delay information required by the satellite-ground cooperative communication system for completing cache allocation are collected firstly; then, determining a system cache allocation problem based on a content service mode of multi-satellite multi-level cache, and solving the cache allocation problem to obtain an optimal cache allocation strategy; and finally, performing content caching on the multi-satellite multi-level edge server in the system based on the optimal caching distribution strategy so as to optimize the performance of the satellite-ground cooperative communication system. The method can make full use of a multi-satellite multi-level cache architecture in the satellite-ground cooperative communication system, provide edge content service for users through cooperation among multi-level edge servers and cooperation among a plurality of satellite edge servers, effectively reduce content service delay in the satellite-ground cooperative communication system, relieve the problem that delay indexes cannot be reached due to long delay of satellite-ground links in the satellite-ground cooperative communication system, and ensure transmission of delay sensitive services of the users.
The foregoing briefly introduces a multi-satellite multi-level buffer allocation method of a satellite-ground cooperative communication system, and the following describes the specific contents involved in the method in detail.
In an alternative embodiment, referring to fig. 2, a satellite-to-ground cooperative communication system comprises:
the satellite-ground cooperative communication system comprises a space section and a ground section;
the space section consists of a plurality of satellites, an inter-satellite link exists among the satellites, content transmission can be carried out between the satellites and adjacent satellites through the inter-satellite link, the adjacent satellites refer to the satellites with the inter-satellite link existing among the current satellites, the current satellite refers to any current concerned satellite and is used for distinguishing the current concerned satellite from the adjacent satellites,
indicating the current satellite
Is/are as follows
Skipping over a set of adjacent satellites,
jump adjacent satellite finger pass
Secondary inter-satellite link transmissions to reach adjacent satellites;
the satellite is connected with a base station, an adjacent satellite and a ground station in the coverage range of the satellite, an edge server exists in the satellite and can cache contents for content service, the satellite provides content transmission service for the base station in the coverage range of the satellite, and for the uncached contents, corresponding contents can be obtained from the adjacent satellite through an inter-satellite link and can also be obtained from the ground station;
the ground section consists of a user, a base station, a ground station and a cloud server;
the user is only connected with the subordinate base station, the subordinate base station means that the user is positioned in the coverage range of the base station, and the user obtains the content transmission service through the base station;
the base station is connected with users in the coverage range of the base station and subordinate satellites, the subordinate satellites mean that the base station is positioned in the coverage range of the satellites, an edge server exists in the base station and can cache contents for content service, the base station provides content transmission service for the users in the coverage range of the base station, and for the contents which are not stored in the base station, corresponding contents can be obtained from the subordinate satellites;
the ground station is connected with the satellite and the cloud server, the edge server exists in the ground station and can cache contents for content service, the ground station provides content transmission service for the satellite, and corresponding contents can be obtained from the cloud server for the contents which are not stored in the ground station;
the cloud server stores all contents and provides content service for the ground station;
for any satellite
Any user in the coverage area, user requesting any content
The service process of the time is as follows:
if the content is
The content transmission service is cached in a subordinate base station of the user, and the subordinate base station directly provides the content transmission service for the user;
if the content is
Not cached in the user's slave base station, cached in the satellite
Middle and satellite
Firstly, transmitting the content to a subordinate base station, and then providing content transmission service for a user by the subordinate base station;
if the content is
Slave base station and satellite not cached in user
In the satellite, buffer memory
Of adjacent satellites of (1), a satellite
First, the content is obtained from the adjacent satellite, and then the satellite
Transmitting the content to the subordinate base station, and then providing a content transmission service for the user by the subordinate base station;
if the content is
Subordinate base station, satellite not cached in user
Satellite, satellite
In the adjacent satellite, cached in the ground station, the satellite
First, the content is obtained from the ground station, and then the satellite
Transmitting the content to the subordinate base station, and then providing a content transmission service for the user by the subordinate base station;
if the content is
Subordinate base station, satellite not cached in user
Satellite, satellite
The adjacent satellite and the ground station are cached in the cloud server, the ground station firstly obtains the content from the cloud server, and then the satellite
Obtain the content from a ground station, followed by a satellite
And transmitting the content to the subordinate base station, and finally providing a content transmission service for the user by the subordinate base station.
Optionally, referring to fig. 3, collecting content popularity information, cache size information, and transmission delay information required by the satellite-ground cooperative communication system to complete cache allocation includes:
s201, estimating and calculating based on historical data of requested content to obtain popularity distribution information of the content;
the content set is all the content stored in the cloud server and is represented as
Wherein in front of
Content of a kindIs the most popular front
Species content of
The seed content is the set of all the remaining content. Popularity distribution information refers to the probability that content is requested by a user, expressed as
The popularity distribution of different contents is sorted in descending order
And the sum of all content popularity distributions is 1, denoted as
。
S202, collecting cache size information of each edge server in the satellite-ground cooperative communication system;
the collected cache size information includes: base station edge server cache size
Satellite edge server cache size
Ground station edge server cache size
Considering that the buffer memory of the ground station is sufficient, the buffer memory size of the ground station is satisfied
。
S203, performing delay information estimation calculation based on the delay information of the historical transmission process and the ergodic capacity of the transmission channel, and calculating the average transmission delay information of contents retrieved from different edge servers;
collectingThe transmission delay information includes: transmission delay information for user retrieving content from base station
Base station retrieving transmission delay information of content from satellite
Satellite retrieving transmission delay information of content from neighboring satellites
Satellite retrieving content transmission delay information from ground station
The ground station retrieves the transmission delay information of the content from the cloud server
。
Optionally, referring to fig. 4, the determining a system cache allocation problem based on a content service method of multi-star multi-level cache includes:
s301, calculating cache hit rates of different storage positions when a user requests content service in a coverage area of each satellite, wherein the cache hit rates refer to the probability that the content requested by the user is cached in the corresponding position;
for satellite
The served user, when requesting arbitrary content:
base station cache hit probability of
Wherein, in the step (A),
as a satellite
Base station buffering in coverageA collection of stored content is stored in a memory,
the allocation factor is buffered for the base station,
representing content
Cached in the satellite
And in the base station within the coverage area, otherwise, the buffer memory is not carried out.
Base station cache miss, satellite
The cache hit probability is
Wherein
As a satellite
The collection of the content that is cached,
a factor is allocated to the satellite cache in order to,
representing content
Cached in the satellite, otherwise uncached.
Base station cache miss, satellite
Cache miss, satellite
Is/are as follows
Hop neighbor satellite cache hit probability of
，
Wherein
As a satellite
Is/are as follows
Skipping over the collection of cached content from neighboring satellites,
representing content
Cached in the satellite
And jumping into the adjacent satellite, otherwise, not caching.
The ground station has relatively large cache before caching
Seed content, base station cache miss, satellite
Cache miss, satellite
The cache miss of the adjacent satellite and the cache hit probability of the ground station are
Wherein
The maximum number of inter-satellite hops.
Base station cache miss, satellite
Cache miss, satellite
The cache of the adjacent satellite is not hit, the cache of the ground station is not hit, and the cache hit probability of the cloud server is
。
S302, for each satellite, calculating the average content service delay of the satellite based on the cache hit rate and the transmission delay information, wherein the average content service delay of the satellite refers to the average content service delay when a user requests content service in the coverage range of the satellite;
Satellite
the average content service delay is:
s303, carrying out weighting processing on the average content service delay to obtain weighted average content service delay of each satellite;
Satellite
weighted average content service latency of
。
S304, summing the weighted average content service delays of all satellites, and minimizing the sum of the weighted average content service delays under the constraint condition of cache size to obtain the problem of cache allocation, wherein the constraint condition of cache size means that the content stored in the base station and the satellite edge server cannot exceed the cache size;
the cache allocation problem is obtained as follows:
wherein
A set of factors is allocated for the caches of all base stations and satellites.
Optionally, referring to fig. 5, solving the cache allocation problem to obtain the optimal cache allocation policy includes:
s401, setting the cached content of the ground station as a content set with the highest popularity;
the ground station caches the popularity rank top
A content, expressed as
。
S402, calculating to obtain a common cache content set of the base stations according to content popularity distribution and transmission delay information, wherein all the base stations cache all the content in the content set;
all base stations commonly buffer the content as
Wherein
The calculation formula is as follows:
s403, calculating to obtain a satellite common cache content set according to content popularity distribution and transmission delay information, wherein all the satellites cache all the content in the content set;
all satellites commonly cache content as
Wherein the content of the first and second substances,
and
the calculation formula is as follows:
s404, initializing and setting the cache contents of all base stations and satellites as the most popular contents;
the buffer contents of all base stations are initially set to
Initially setting the cache contents of all satellites as
And calculating the average content service delay of the system under the initialization caching strategy.
S405, keeping a common cache content set unchanged for each base station satellite, solving a cache allocation problem, and obtaining an optimal cache allocation strategy of the base station and the satellite;
in solving the cache allocation problem, each base station will maintain a set of cache contents
Invariably, each satellite will maintain a set of cached content
And (4) solving to obtain an optimal cache allocation strategy and minimizing the weighted average content service delay without changing. This process is described in detail below.
And S406, taking the obtained optimal cache allocation strategy as an optimal cache allocation strategy of the satellite-ground cooperative communication system.
Optionally, referring to fig. 6, the step of keeping the common cache content set unchanged for each base station satellite, and solving the cache allocation problem to obtain the optimal cache allocation policy of the base station and the satellite includes:
the following iterative process is performed:
s501, for each satellite, calculating cache benefits of the base station caching contents in the non-common cache content set in the coverage range;
for each satellite
For content collections
Each of which is
Calculating cache revenue
Caching of revenue
As a satellite
Base station buffer content in coverage area
And uncached content
Compared to the amount of reduction in the average content service delay of the system. Order to
Representing satellites
Uncached content for base stations within coverage
The average content service delay of the system over time,
representing satellites
Base station buffer content in coverage area
The system average content service delay of time can be obtained
。
if the content is
Cached in the satellite
In, the cache benefits are
；
If the content is
Recently cached as satellite
Is/are as follows
Jump adjacent satellite, cache gain as
Wherein, the latest cache refers to a cache location where the content is cached and the delay for retrieving the content is the lowest;
if it is
Not cached in the satellite
And its neighboring satellites, the cache gain is
；
S502, for each satellite, updating the cache of the base station in the coverage range into a common cache content set and cache income maximum content in a non-common cache content set;
for each satellite
A satellite
Updating the buffer of the base station in the coverage area to
Wherein
Is composed of
And the content with the maximum income is cached until the upper limit of the cache size of the base station is reached.
By using
Representation collection
Due to the buffer size of the base station
The size of the cache for the remaining cacheable content is
To thereby aggregate
Is composed of
Maximum benefit of medium cache
And (4) the content.
S503, for each satellite, calculating the caching benefit of the content in the satellite caching non-common caching content set;
for each satellite
For content collections
Each of which is
Calculating cache revenue
Wherein, calculating
The formula used is as follows:
caching revenue
As a satellite
Caching content
And uncached content
Compared to the amount of reduction in the average content service delay of the system. Order to
Representing satellites
Uncached content
The average content service delay of the system over time,
representing satellites
Caching content
The system average content service delay of time can be obtained
。
if it is
Cached in the satellite
In the base station within the coverage area,
；
if it is
Recently cached as a satellite
Is/are as follows
Jumping to the adjacent satellite or satellites,
；
if it is
Not cached in the satellite
Base station and satellite in coverage area
Of the adjacent satellites of the satellite system (c),
。
for satellite
Arbitrary
Jumping adjacent satellite
Suppose a satellite
Not caching any content, accumulating and calculating
。
To satellite
Each of which is
Jumping adjacent satellite
，
The calculation method of (2) is as follows:
if it is
Cached in the satellite
Or a satellite
In the base station within the coverage area,
；
if it is
Recently cached as a satellite
Is/are as follows
Jumping to the adjacent satellite or satellites,
；
if it is
Recently cached as a satellite
Is/are as follows
Jumping to the adjacent satellite or satellites,
；
if it is
Not cached in the satellite
Base station and satellite in coverage area
Of the adjacent satellites of the satellite system (c),
。
s504, for each satellite, updating the cache of the satellite into a common cache content set and cache contents with maximum profit in a non-common cache content set;
for each satellite
Update its cache to
Wherein
Is composed of
And the middle cache has the maximum income content until reaching the upper limit of the satellite cache size.
By using
Representation collection
Due to the buffer size of the satellite
The size of the cache for the remaining cacheable content is
To thereby aggregate
Is composed of
Maximum benefit of medium cache
And (4) the content.
S505, calculating the average content service delay of the system after updating the cache strategy;
calculating the system average content service delay after updating the cache strategy
Wherein
The calculation process can be referred to the previous method embodiment, and is not described herein again.
S506, judging whether the average content service delay after the cache strategy is updated is the same as the average content service delay before the cache strategy is updated;
s507, if the two are the same, the iteration is ended;
and S508, if the difference is not the same, the iteration process is repeatedly executed until the iteration is finished.
The invention provides a multi-satellite multi-level cache allocation method and a multi-satellite multi-level cache allocation device for a satellite-ground cooperative communication system. The method comprises the steps of calculating to obtain common cache contents of all base stations based on a base station fixed cache strategy, calculating to obtain common cache contents of all satellites based on a satellite fixed cache strategy, calculating cache benefits of contents except the common cache contents to obtain the cache contents of each base station and each satellite outside the common cache, and finally solving to obtain a system cache strategy with the minimum average content service delay.
FIG. 2 shows a schematic diagram of a satellite-ground cooperative communication system, in which the total content is set to 500-5000-
100, satellite cache
200, number of satellites 100, delay for user to retrieve content from base station
20 ms delay for the base station to retrieve content from the satellite
Delay of a satellite to retrieve content from a neighboring satellite for 100 ms
Delay of the satellite to retrieve content from the ground station of 40 ms
90 ms delay for the ground station to retrieve content from the cloud server
Is 200 ms. The content popularity distribution adopts zipf distribution with a factor of 0.7, and the calculation mode is
. Referring to fig. 7 (comparing the performance of the proposed multi-star multi-level cache allocation method with the most popular cache allocation method and the random cache allocation method), it can be seen that the proposed cache allocation method can effectively reduce the content service delay in the satellite-ground collaborative communication system, and can reduce the average content service delay by 20% compared with the most popular cache allocation method.
Example two:
a multi-satellite multi-level buffer allocation apparatus for a satellite-ground cooperative communication system, referring to fig. 8, the apparatus comprising:
the information collection module 11 is configured to collect content popularity information, cache size information, and transmission delay information required by the satellite-ground cooperative communication system to complete cache allocation;
the cache allocation problem determining module 12 is configured to determine a system cache allocation problem based on a content service mode of a multi-satellite multi-level cache, where the content service mode of the multi-satellite multi-level cache indicates that content is cached through cooperation of a base station, a satellite, a ground station and cooperation among multiple satellites to provide content services for users, the cache allocation problem indicates that average content service delay of all users is minimized under the condition that cache size constraints are met, and the cache allocation problem includes content popularity information, cache size information and transmission delay information;
the optimal cache solving module 13 is configured to solve the cache allocation problem to obtain an optimal cache allocation strategy;
and the cache allocation module 14 is configured to perform content caching on the multi-star multi-level edge servers in the system based on the optimal cache allocation policy, so as to optimize performance of the satellite-ground cooperative communication system.
In the multi-satellite multi-level cache allocation device of the satellite-ground cooperative communication system, content popularity information, cache size information and transmission delay information required by the satellite-ground cooperative communication system for completing cache allocation are collected firstly; then, determining a system cache allocation problem based on a content service mode of multi-satellite multi-level cache, and solving the cache allocation problem to obtain an optimal cache allocation strategy; and finally, performing content caching on the multi-satellite multi-level edge server in the system based on the optimal caching distribution strategy so as to optimize the performance of the satellite-ground cooperative communication system. The device can make full use of a multi-satellite multi-level cache architecture in the satellite-ground cooperative communication system, provides edge content service for users through cooperation among multi-level edge servers and cooperation among a plurality of satellite edge servers, can effectively reduce content service delay in the satellite-ground cooperative communication system, relieves the problem that delay indexes cannot be reached due to long delay of satellite-ground links in the satellite-ground cooperative communication system, and ensures transmission of delay sensitive services of the users.
Optionally, the information collecting module includes:
the content popularity collecting unit is used for carrying out estimation calculation based on historical data of content requested to obtain popularity distribution information of the content, wherein the content refers to all content stored by the cloud server;
the system cache information collecting unit is configured to collect cache size information of each edge server in the satellite-ground cooperative communication system, where the cache size information includes: caching size information of a base station edge server, caching size information of a satellite edge server and caching size information of a ground station edge server;
a system transmission delay information collection unit, configured to perform delay information estimation calculation based on delay information of a historical transmission process and an ergodic capacity of a transmission channel, and calculate average transmission delay information of contents retrieved from different edge servers, where the transmission delay information includes: the method includes the steps that a user retrieves transmission delay information of content from a base station, the base station retrieves transmission delay information of the content from a satellite, the satellite retrieves transmission delay information of the content from an adjacent satellite, the satellite retrieves transmission delay information of the content from a ground station, and the ground station retrieves transmission delay information of the content from a cloud server.
Optionally, the cache allocation problem determining module includes:
the system comprises a cache hit rate calculation unit, a cache hit rate calculation unit and a content service processing unit, wherein the cache hit rate calculation unit is used for calculating the cache hit rates of different storage positions when a user requests content service in the coverage area of each satellite, and the cache hit rates refer to the probability that the content requested by the user is cached in the corresponding positions;
the satellite average content service delay calculating unit is used for calculating the satellite average content service delay for each satellite based on the cache hit rate and the transmission delay information, wherein the satellite average content service delay refers to the average content service delay when a user requests content service in the satellite coverage range;
the weighting processing unit is used for weighting the average content service delay to obtain the weighted average content service delay of each satellite;
and the minimization unit is used for summing the weighted average content service delays of all the satellites and minimizing the sum of the weighted average content service delays under the constraint condition of the cache size to obtain the problem of cache allocation, wherein the constraint condition of the cache size means that the content stored by the base station and the satellite edge server cannot exceed the cache size.
Optionally, the optimal cache solving module includes:
the ground station fixed cache computing unit is used for setting the cache content of the ground station as a content set with the highest popularity;
the base station fixed cache calculating unit is used for calculating a common cache content set of the base stations according to the content popularity distribution and the transmission delay information, and all the base stations cache all the content in the content set;
the satellite fixed cache computing unit is used for computing a satellite common cache content set according to content popularity distribution and transmission delay information, and all the satellites cache all the content in the content set;
the cache initialization unit is used for initializing and setting cache contents of all base stations and satellites as most popular contents;
the solving unit is used for keeping a common cache content set unchanged for each base station satellite, solving a cache allocation problem and obtaining an optimal cache allocation strategy of the base station and the satellite;
and the setting unit is used for taking the obtained optimal cache allocation strategy as the optimal cache allocation strategy of the satellite-ground cooperative communication system.
Optionally, the solving unit includes:
the following iterative process is performed:
for each satellite, calculating the caching benefit of the content in the non-common caching content set cached by the base station in the coverage range;
for each satellite, updating the cache of the base station in the coverage range into a common cache content set and cache contents with maximum profit in a non-common cache content set;
for each satellite, calculating the caching income of the satellite for caching the contents in the non-common caching content set;
for each satellite, updating the cache of the satellite into a common cache content set and cache contents with maximum profit in a non-common cache content set;
calculating the average service delay of the system content after updating the cache strategy;
judging whether the average content service delay after updating the cache strategy is the same as the average content service delay before updating;
if the two are the same, the iteration is ended;
if the difference is not the same, the iteration process is repeatedly executed until the iteration is finished.
For details in the second embodiment, reference may be made to the details in the first embodiment, which are not described herein again.
The computer program product of the method and the apparatus for allocating multi-satellite multi-level caches in a satellite-ground cooperative communication system according to the embodiments of the present invention includes a computer readable storage medium storing a program code, where instructions included in the program code may be used to execute the method described in the foregoing method embodiments, and specific implementation may refer to the method embodiments, which are not described herein again.
It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the system and the apparatus described above may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.
The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A multi-satellite multi-level cache allocation method for a satellite-ground cooperative communication system is characterized by comprising the following steps:
(1) collecting content popularity information, cache size information and transmission delay information required by the satellite-ground cooperative communication system to finish cache allocation; the satellite-ground cooperative communication system comprises a space section and a ground section; the space section consists of a plurality of satellites, and the ground section consists of a user, a base station, a ground station and a cloud server;
(2) determining a system cache allocation problem based on a content service mode of multi-star multi-level cache;
(3) solving the cache allocation problem to obtain an optimal cache allocation strategy;
(3.1) setting the cached content of the ground station as a content set with the highest popularity;
(3.2) calculating to obtain a common cache content set of the base stations according to the content popularity distribution and the transmission delay information, wherein all the base stations cache all the content in the content set;
(3.3) calculating to obtain a satellite common cache content set according to the content popularity distribution and the transmission delay information, wherein all the satellites cache all the content in the content set;
(3.4) initializing and setting the cache contents of all base stations, initializing and setting the cache contents of all satellites, and calculating the average content service delay of the system under the initialization cache strategy;
(3.5) keeping a common cache content set unchanged for each base station satellite, and solving the cache allocation problem to obtain an optimal cache allocation strategy of the base station and the satellite;
(3.6) using the optimal cache allocation strategy as the optimal cache allocation strategy of the satellite-ground cooperative communication system;
(4) and performing content caching on the multi-satellite multi-level edge server in the system based on the optimal caching distribution strategy so as to optimize the performance of the satellite-ground cooperative communication system.
2. The multi-satellite multi-level buffer allocation method for the satellite-ground cooperative communication system according to claim 1, wherein in the step (1), inter-satellite links for content transmission of adjacent satellites are provided between the satellites, each satellite is covered with a plurality of base stations and ground stations, and the satellite is connected with the base stations, the adjacent satellites and the ground stations within the coverage range of the satellite; each base station is covered with a plurality of users, the base stations are connected with the users in the coverage range of the base stations, the ground station is connected with the satellite and the cloud server, and the satellite, the base stations and the ground station are provided with edge servers capable of caching content for content service.
3. The multi-satellite multi-level cache allocation method for the satellite-ground cooperative communication system according to claim 2, wherein the content popularity information is collected in the step (1) by performing estimation calculation based on history data of all content requests stored in the cloud server, so as to obtain a probability that all content stored in the cloud server is requested by a user; the cache size information comprises the cache size of a base station edge server, the cache size of a satellite edge server and the cache size of a ground station edge server; the mode of collecting the transmission delay information is to estimate and calculate the delay information based on the transmission delay information of the historical transmission process and the ergodic capacity of the transmission channel, and calculate the average transmission delay information of the contents retrieved from different edge servers; the transmission delay information includes: the method includes the steps that a user retrieves transmission delay information of content from a base station, the base station retrieves transmission delay information of the content from a satellite, the satellite retrieves transmission delay information of the content from an adjacent satellite, the satellite retrieves transmission delay information of the content from a ground station, and the ground station retrieves transmission delay information of the content from a cloud server.
4. A multi-satellite multi-level buffer allocation method for a satellite-to-ground cooperative communication system according to claim 3, wherein the step (2) comprises the following sub-steps:
(2.1) calculating cache hit rates of different storage positions when a user requests content services in the coverage area of each satellite; the cache hit rate comprises a base station cache hit rate, a current satellite cache hit rate, an adjacent satellite cache hit rate, a ground station cache hit rate and a cloud server cache hit rate;
(2.2) calculating the satellite average content service delay based on the cache hit rate and the transmission delay information;
(2.3) weighting the average content service delay to obtain weighted average content service delay of each satellite;
and (2.4) summing the weighted average content service delays of all the satellites, and minimizing the sum of the weighted average content service delays under the constraint condition of the cache size to obtain the cache allocation problem.
5. The multi-satellite multi-level buffer allocation method for the satellite-to-ground cooperative communication system according to claim 1, wherein the sub-step (3.5) specifically comprises the following iterative process:
(3.5.1) calculating the caching profit of the content in the non-common caching content set cached by the base station in the coverage area for each satellite;
(3.5.2) for each satellite, updating the cache of the base station in the coverage range into a common cache content set and cache contents with maximum profit in a non-common cache content set;
(3.5.3) for each satellite, calculating a cache gain for the satellite to cache content in the non-common cache content set;
(3.5.4) for each satellite, updating the cache of the satellite to a common cache content set and cache revenue maximization content in a non-common cache content set;
(3.5.5) calculating the average content service delay of the system after the cache strategy is updated;
(3.5.6) judging whether the average content service delay after updating the cache strategy is the same as the average content service delay before updating;
(3.5.7) if the two are the same, ending the iteration;
(3.5.8) if the difference is not the same, repeating the iteration process until the iteration is finished.
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