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CN115866051B - An edge caching method based on content popularity - Google Patents

An edge caching method based on content popularity Download PDF

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CN115866051B
CN115866051B CN202211427004.9A CN202211427004A CN115866051B CN 115866051 B CN115866051 B CN 115866051B CN 202211427004 A CN202211427004 A CN 202211427004A CN 115866051 B CN115866051 B CN 115866051B
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popularity
prediction
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server cluster
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CN115866051A (en
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何利
陈炀环
程惠明
金婷
张富华
苏佳建
邓林海
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Shanxi Qianjin Network Technology Co ltd
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Shenzhen Hongyue Information Technology Co ltd
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Abstract

本发明请求保护一种基于内容流行度的边缘缓存方法,包括下列主要步骤:S1,根据服务器集群、设备和用户请求内容构建相关系统模型;S2,对不同长度的历史数据进行分类,采用对应的算法预测内容未来时刻的流行度;S3,根据S2得到的流行度以及内容的大小计算得到每个内容的总收益价值;S4,对于每个服务器集群,计算出在当前容量下效益最高的内容序列;S5,获知每个内容是否缓存在边缘服务器集群中的结果。本发明方法与现有的方法相比,具有以下主要优点:(1)对于不同长度的历史数据采用不同的算法进行预测,使得预测结果误差更小。(2)将内容缓存放置问题转化为一个效益价值最大化问题,能够将总收益较大的内容缓存在边缘服务器集群中。

The present invention seeks to protect an edge caching method based on content popularity, comprising the following main steps: S1, constructing a relevant system model based on server clusters, devices and user request content; S2, classifying historical data of different lengths and using corresponding algorithms to predict the popularity of content at future times; S3, calculating the total revenue value of each content based on the popularity obtained in S2 and the size of the content; S4, for each server cluster, calculating the content sequence with the highest benefit under the current capacity; S5, obtaining the result of whether each content is cached in the edge server cluster. Compared with existing methods, the method of the present invention has the following main advantages: (1) Different algorithms are used for prediction of historical data of different lengths, so that the error of the prediction result is smaller. (2) The content cache placement problem is transformed into a benefit value maximization problem, and content with larger total benefits can be cached in the edge server cluster.

Description

Edge caching method based on content popularity
Technical Field
The invention relates to the field of mobile edge computing, in particular to an edge content caching method based on content popularity.
Background
Today, the fifth generation of mobile communication is attracting attention worldwide and has been formally commercially used. The core technology of 5G mainly comprises millimeter waves, large-scale multiple input multiple output and the like. In future developments, increasing the communication mode selection of the user and further improving the network experience of the user are important targets for 5G evolution. The advent of 5G has meant that the demand for video streaming services will increase further, which will present a significant challenge to streaming service systems. The collaborative-edge cloud computing architecture combining cloud computing and edge computing can effectively reduce the burden of a streaming media service system. Streaming media content caching under the collaborative edge cloud computing architecture has important significance for improving user service quality. The buffering technology can reduce delay, promote transmission rate and save consumption of backhaul link, is one of important technologies for dealing with exponentially growing mobile data traffic, and will necessarily play a key role in future 5G systems.
In conventional networks, content requested by a mobile user is typically served by a remote Internet content server provided by a content provider. When a user retrieves the same popular content from a remote server, the remote server needs to repeatedly send the same file, which may present a large amount of repeated traffic, and network congestion problems may occur during peak network times. The storage service provided by the mobile edge computing server is utilized in the mobile edge caching network to cache popular content at a position closer to a user, so that repeated content transmission from the content server to an edge caching node can be reduced, the network congestion problem is effectively relieved, and the delay and transmission energy consumption of content retrieval are also effectively reduced. However, in the current edge computation caching method, the considered factors are generally quite limited. The caching method has close relation with factors such as popularity of the content to be cached, mobility of the user and the like. Therefore, research on the selection method of the cache content in the edge calculation is important to reduce the transmission delay and improve the experience of the terminal user. In addition, the global content popularity is different from the content which is interested by the terminal user served by each micro base station, so that the placement method of the cache content needs to be researched, and the most needed content of the cache users of each base station is realized under the limited cache space.
The service provider may deploy the streaming media content on an edge server. The edge server is responsible for responding to the content request of the user, reducing the transmission delay and ensuring the service quality of the user. Meanwhile, the streaming media server can dynamically use the powerful computing resources of the cloud server according to actual demands. Therefore, a corresponding caching method is designed according to the content request frequency of the terminal user, so that the cost of a service provider and the delay of acquiring the content by the user are reduced. But popularity in the content access process varies over time. Therefore, it is required to find a content caching method considering popularity of content so that an edge service provider can cache content at a low cost, and at the same time, improve hit rate of the content, and meet the requirement of users for low delay of acquiring the content.
Although the storage capacity of the edge server is far higher than that of the terminal equipment, the storage capacity of the edge server is limited, so that the content with great benefits of the edge server needs to be cached as much as possible, the popularity is considered firstly, a relevant model is built for the behavior characteristics of the user, and then future behaviors can be predicted according to specific historical data. Meanwhile, considering the influence of the size of the content, for example, larger content may cause other content to be unable to be cached and the acquisition time is longer. And meanwhile, the popularity gain and the time delay gain are set, the duty ratio of the two factors is considered, and the value total income of each content is finally obtained. In the subsequent cache placement scheme, the aim is to select the content with high value and total income for caching, which is a NP difficult problem, the problem is changed into a benefit maximization problem, and a batch of content with the highest value can be cached under the condition that the limiting condition is met, so that the time delay cost of the user for acquiring the content is reduced and the hit rate is improved finally.
The application publication number is CN113965937A, a content popularity prediction method based on clustering federation learning in a fog wireless access network is characterized by comprising the following steps of S1, constructing initial characteristics of each local user and each content by utilizing fog access points according to local user information and content information acquired by a neighborhood set of the local user and the content, S2, taking the initial characteristics of the local user and the content as input, taking the content request probability of the local user as a prediction target, establishing a prediction model based on a dual-channel neural network for each fog access point, setting a binary cross entropy loss as a loss function, optimizing model parameters, S3, utilizing the clustering federation learning method to perform distributed training on the prediction model of each fog access point, and adaptively clustering fog access points with similar area types, realizing the specialization of model parameters for each fog access point, S4, obtaining the activity degree of the local user by utilizing the historical request quantity, obtaining the local user according to the activity degree and the predicted request probability of the local user, then taking the content request probability of the local user as a prediction target, setting a motion preference function according to the motion request probability of the local user, and the motion request probability of the current request, S5, setting the popularity of each fog access point as a motion request, and the popularity request of the current target, and the motion request of the current target, respectively, and comparing the motion request of the current target with the motion target model, and the motion target is set to be the motion target, and the popularity of the current target is optimized, and the popularity target is set according to the motion target, and the motion target is 7, and the motion target is optimized, and obtaining the content popularity of each fog access point.
According to the method, the characteristics are built by collecting the user information and the content information, the popularity of the content is predicted by building a two-channel neural network model, the model parameters are optimized, the long time expenditure is caused by the fact that the neural network is used for prediction without considering data with shorter history length, and if some new content enters the network, only a small amount of history data is needed, and the quantity of input data of the neural network is not reached, so that the prediction accuracy is reduced. Meanwhile, the invention takes the content request probability of the mobile user as a prediction target, and establishes a preference model objective function for each mobile user, however, the influence of the behavior of a single user on the group is very little, the local group behavior is considered during prediction, and the popularity of the content in the current region can be represented by the selection of most people. In the invention, considering the two points, the behaviors of most users of a certain server cluster are selected, the popularity of the content is obtained after collection, the content with different lengths is classified, only the content with less historical data is predicted by using an improved exponential smoothing algorithm, a result with higher accuracy can be obtained in a shorter time, and the content popularity with enough historical data is predicted by using a dynamic optimization LSTM neural network, so that parameters are continuously optimized, and the deviation between the obtained result and a true value is smaller.
Disclosure of Invention
The invention aims to solve the problems of content popularity prediction and an edge server caching method in the existing edge calculation, provides a classification prediction algorithm, so that content popularity prediction errors are smaller, and simultaneously uses a related algorithm to enable an edge server to cache content with the largest income in a limited storage space, so that the cache hit rate of a user for obtaining the content is improved, and the time delay for obtaining the content is reduced. An edge caching method based on content popularity is provided. The technical scheme of the invention is as follows:
an edge caching method based on content popularity, which comprises the following steps:
S1, constructing an end-edge cloud system model according to server clusters, equipment and user request content, obtaining the request times of each content in different time periods, and regarding the request times of the content in unit time by an end user as the historical popularity of the content in the unit time period;
s2, classifying the historical data with different lengths, and predicting popularity at future time by using an improved exponential smoothing prediction algorithm and a dynamic optimization long-short-term memory algorithm after classification;
S3, regarding the popularity predicted in the step S2 as popularity gain, and calculating to obtain the value total income of each content as compared with the time delay obtained from the cloud as time delay spending gain if the content is cached in the edge server cluster because the time delay of the obtained content is related to the size of the content;
S4, for each server cluster, calculating a content sequence with highest benefit under the current capacity by adopting a cache placement algorithm, and caching the content corresponding to the content sequence in the server;
S5, knowing whether each content is cached in the result of the edge server cluster.
Further, in the step S1, a terminal edge cloud system model is constructed, and the method for obtaining the historical popularity concretely includes:
Most of the contents are stored in a cloud, the edge server clusters select part of the contents for storage, a terminal user initiates a request, three environments of the cloud, edges and terminals are divided, a cloud server is a device far away from a user terminal, some terminal devices are served in each edge server cluster, the terminal devices can initiate requests for some contents in different time periods, the edge server acquires the popularity of the contents in different time periods by collecting the historical data of the requested contents, and therefore a historical popularity set of all the contents in the edge server clusters is acquired and used for later popularity prediction.
Further, step S2 is described, where historical data with different lengths are classified, and an improved exponential smoothing prediction algorithm and a dynamic optimization long-short-term memory algorithm are used to predict popularity of popularity prediction at future time after classification, and specifically includes:
setting lp as the length of the content set, and setting a length limit LB;
(1) If lp < LB, dividing into new contents, and predicting by adopting an improved exponential smoothing prediction algorithm;
(2) If lp is larger than or equal to LB, the popularity is predicted by using a dynamic optimization long-short-term memory algorithm.
Further, in the step (1), an improved exponential smoothing prediction algorithm is adopted for prediction. In the traditional exponential smoothing prediction method, the weight factor alpha determines the magnitude of a predicted final value, when alpha is larger, popularity of the current time period is more influenced on a prediction result, otherwise when alpha is smaller, popularity of the content is more influenced more long, and the formula is shown as follows.
Representing content popularity at time t n predicted using an exponential smoothing prediction algorithm, whereThe content popularity of the last moment is represented, the subsequent operation needs to be carried out according to the popularity of the last moment, t n is represented by the current time period, t s is represented by the initial time period, alpha is a variable factor, the value range is [0,1] is fixed, and the influence degree of the popularity of the previous time period on the future time period is determined. Since the weighting factor α in the conventional method is static, so that the smooth prediction is difficult to conform to the variation of the time series itself, the present invention uses an exponential smooth prediction method in which the weighting factor is dynamically changed, the formula of which is as follows.
The content popularity at the time t n is predicted by using the improved exponential smoothing prediction algorithm, and compared with the traditional method, in the improved method, the value of the weight factor alpha is dynamically changed along with the change of t n, is not a fixed value any more, and is dynamically corrected along with time, so that the accuracy of the prediction is more similar to a true value.
Further, in the step (2), the predicting popularity using the dynamic optimization long-short term memory algorithm specifically includes:
For the content with longer historical data, namely the old content, the dynamic optimized LSTM is adopted for prediction, and the time window size, the dense layer number, the LSTM network layer number and the neuron number are used as optimizing objects. Setting m time window to-be-selected values, k dense layer number to-be-selected values, n LSTM layer number to-be-selected values and u neuron number to-be-selected values, and selecting an average percentage error MAPE of LSTM model verification data obtained after training times reach a limit to measure the merits of parameters, wherein the MAPE is defined as follows:
y' n is a value obtained by model prediction, y n is a true value of a sample, N is a sample number, M (M, k, N, u) is set to represent average percentage error obtained after LSTM model prediction of current parameter construction, a group of parameters with the best performance in the test set M (M, k, N, u) are selected through continuous iterative training, then a model used for old content prediction is determined, and meanwhile, the obtained optimal M time window values are the standard LB for dividing new content and old content.
Further, the step S3 is to consider the popularity predicted in the step S2 as popularity gain, and calculate the value total income of each content compared with the time delay obtained from the cloud as delay overhead gain if the content is cached in the edge server cluster because the time delay of obtaining the content has a relation with the size of the content; the specific formula is shown in the formula;
Gi=A*ΔLi+B*Pi
Where a and B are two variable factors a+b=1 for controlling the ratio of the two benefits to the total value benefit, Δl i represents the delay gain for obtaining the content, P i represents the popularity gain for the content, and G i represents the total value benefit for the content.
Further, in the step S4, the cache placement problem is converted into the benefit value maximization problem, the original problem makes a decision for each content, 0 represents non-selection, 1 represents selection, which is a 0-1 variable, and then the 0-1 plan problem is a constraint 0-1 plan problem, which is not only the NP difficult problem, but also the problem is converted into the benefit maximization problem by considering the content of the cache which can bring the maximum benefit to the server cluster, and the problem is converted into the following formula;
The content with the maximum total gain is selected from the collection and cached.
The invention has the advantages and beneficial effects as follows:
1. For popularity prediction related problems, existing related methods consider predicting a user's movement path to obtain potential predictability of user mobility, and thus potentially popular content. There are also block-based video popularity prediction methods, but most of these methods do not consider the impact of historical data of different lengths on the prediction results, and do not consider reducing the prediction error. In the invention, in consideration of the point in the prediction, the terminal edge cloud system is established, the characteristic that the content popularity is defined by the historical information of the collected content is classified according to the historical data with different lengths, and the popularity of the content at the future moment is predicted by using an improved algorithm respectively, so that the errors of the predicted result and the true value are effectively reduced.
2. For the historical data with different lengths, different methods are selected for prediction in the step S2, an improved exponential smoothing prediction algorithm is provided for the historical data with shorter lengths, the weight factors in the traditional exponential smoothing prediction are not changed after the determination, the weight factors which dynamically change along with time are provided, the weight factor values at different moments are different, the real scene is more met, and popularity obtained by predicting the short historical data is more similar to real popularity. For long history data, a model with the lowest average percentage error is obtained by setting a long-short-period memory model and inputting training data, so that a time window with the lowest average percentage error can be selected as input, the time window is also a demarcation point of the long history data, the history data with different lengths can be predicted by a more accurate method, and more ready selection can be made based on the subsequent server cluster.
3. Based on the above problems, a caching method based on content popularity is proposed, the popularity obtained through prediction is regarded as popularity benefits, and the acquisition time delay reduced after certain content is cached in an edge server cluster is regarded as time delay overhead gain. The content cache placement problem is translated into a benefit value maximization problem. And selecting the content which maximizes the total income of the server through an algorithm to cache, and fully using the storage resources of the server. And meanwhile, the hit rate of the content acquired by the user is improved, and the time delay expenditure of acquiring the content is reduced.
Drawings
FIG. 1 is a cloud-side system model constructed in accordance with a preferred embodiment of the present invention;
FIG. 2 is a flow chart of an edge caching method based on content popularity in the present invention;
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and specifically described below with reference to the drawings in the embodiments of the present invention. The described embodiments are only a few embodiments of the present invention.
The technical scheme for solving the technical problems is as follows:
the invention provides an edge caching method based on content popularity, which comprises the following steps:
s1, an end-edge cloud system model is built according to server clusters, equipment and user request content, and ES= {1,2,3, & gt, m } represents an edge server cluster set, CS= { c1, c2, c3, & gt, cn } represents a request content set, and TD= {1,2,3, & gt, q } represents a terminal equipment set as shown in FIG. 1. The number of requests of each content in different time periods is counted and taken as popularity.
S2, classifying historical data with different lengths according to a standard, dividing the historical data into new content and old content, and predicting the classified historical data by using a corresponding algorithm to obtain popularity of the content at a future moment;
s3, according to the popularity predicted in the S2, regarding the popularity as a popularity gain, caching certain content in an edge server cluster, regarding the reduced time delay obtained from the cloud as a time delay overhead gain, and obtaining the value total income of each content according to calculation;
S4, for each server cluster, calculating a content sequence with highest benefit under the current capacity by adopting a cache placement algorithm, obtaining a cache decision of a server on the content, and caching the corresponding content in the server;
s5, according to a final result, the server cluster selects to cache or not cache each content, and when the content cached in the server cluster is requested by a user, the content can be directly obtained from the edge server without sending a request to the cloud;
Further, in the step S1, a terminal edge cloud system model is constructed, and the method for obtaining the historical popularity concretely includes:
(1) According to the related information, three environments of a cloud end, edges and terminals are divided, a cloud end server is a device far away from a user terminal, some terminal devices are served in each edge server cluster, the terminal devices can initiate requests for certain contents in different time periods, and the edge servers collect historical data of the requested contents. Es= {1,2,3,..m } represents an edge server cluster set, cs= {1,2,3,..n } represents a set of requested contents, td= {1,2,3,..q } represents a set of terminal devices, let t j=Tj-Tj-1 represent a unit time period, let Indicating whether the device initiated a request for content c i e CS during time period t j, the popularity of content c i under server S during time period t j may be expressed as:
and obtaining popularity of the content in different time periods through the step, so that a historical popularity set of all the content under the edge server cluster is obtained and is used for predicting the popularity at the later time.
Further, in the step S2, classifying the historical data with different lengths according to the standard, and predicting by using the corresponding algorithm includes:
(1) By using The method comprises the steps of representing all historical data sets of content c epsilon CS in an edge server cluster s epsilon ES in a time period t 1~tn, setting lp as the length of the content set, setting a length limit LB, dividing the content into new content if lp is smaller than LB, predicting by adopting an improved exponential smoothing prediction algorithm IESP, and predicting popularity by adopting a dynamic optimization long-short-term memory algorithm DO-LSTM if lp is larger than LB.
(2) For new content prediction, an improved exponential smoothing prediction algorithm is used for prediction. In the traditional exponential smoothing prediction method, the weight factor alpha determines the magnitude of a predicted final value, when alpha is larger, popularity of the current time period is more influenced on a prediction result, otherwise when alpha is smaller, popularity of the content is more influenced more long, and the formula is shown as follows.
Representing content popularity at time t n predicted using an exponential smoothing prediction algorithm, whereThe content popularity of the last moment is represented, the subsequent operation needs to be carried out according to the popularity of the last moment, t n is represented by the current time period, t s is represented by the initial time period, alpha is a variable factor, the value range is [0,1] is fixed, and the influence degree of the popularity of the previous time period on the future time period is determined. Since the weighting factor α in the conventional method is static, so that the smooth prediction is difficult to conform to the variation of the time series itself, the present invention uses an exponential smooth prediction method in which the weighting factor is dynamically changed, the formula of which is as follows.
The content popularity at time t n is predicted by using the improved exponential smoothing prediction algorithm, and compared with the traditional method, in the improved method, the value of the weight factor alpha is dynamically changed along with the change of t n, and is not a fixed value any more, but is dynamically corrected along with time.
(3) For the content with longer historical data, namely the old content, the dynamic optimized LSTM is adopted for prediction, and the time window size, the dense layer number, the LSTM network layer number and the neuron number are used as optimizing objects. Setting m time window candidate values, k dense layer number candidate values, n LSTM layer number candidate values and u neuron number candidate values, and selecting an average percentage error (MAPE) of LSTM model verification data obtained after the training times reach the limit to measure the quality of the parameters. Wherein MAPE is defined as follows:
y' n is the model predicted value, y n is the true value of the sample, and N is the number of samples. Let M (M, k, n, u) represent the average percentage error obtained after prediction of the LSTM model constructed by the current parameters. Through continuous iterative training, a set of parameters that perform best in the test set M (M, k, n, u) can be selected, and then the model used for old content prediction is determined. Meanwhile, the obtained optimal m time window values are standard LB for dividing new and old contents.
Further, in the step S3, calculating the total gain of the content value includes the following steps:
(1) When the content C i requested by the terminal is already cached in the edge server, the edge server can directly meet the request and start transmitting the content, and the total delay overhead at this time is the delay of uploading the request L u,i plus the delay of downloading the content from the server L d,i, which can be expressed as:
Ledge,i=Lu,i+Ld,i
(2) If the edge server does not cache the content of the request, the request can only be forwarded to the cloud data center, and the delay overhead can be expressed as:
Lcloud,i=Lu,i+Letc+Lc,i
L etc is the latency overhead for the edge server to send the request to the cloud, and L c,i is the latency overhead required to return the content from the cloud to the terminal.
(3) If a content C i originally needs to be obtained from the cloud, the delay overhead is L cloud,i. When it is put into the edge server, the delay cost must be shortened, and the delay cost becomes L edge,i. Thus, the delay gain is defined as follows:
ΔLi=Lcloud,i-Ledge,i
(4) The value total income of the content is determined by combining the content popularity P i obtained by the prediction and the time delay gain, and the specific formula is as follows:
Gi=A*ΔLi+B*Pi
Where a and B are two variable factors a+b=1 for controlling the ratio of the two benefits to the total value benefit, Δl i represents the delay gain for obtaining the content, P i represents the popularity gain for the content, and G i represents the total value benefit for the content.
Further, in the step S4, according to the obtained total benefit of the content value, the cache placement problem is converted into the benefit value maximization problem, and the adopted cache placement algorithm comprises the following steps:
(1) The original problem will make a decision for each content, 0 representing no choice, 1 representing a choice, which is a 0-1 variable, which is then a constrained 0-1 programming problem, which is not the NP-hard problem. By considering the content that the cache can bring the greatest benefit to the server cluster, the problem is turned into a benefit maximization problem, and the problem is turned into the following formula.
G= { G1, G2..gn } is the calculated total value revenue set of the content, where S e is the edge server capacity size, ca i is a 0-1 variable, ca i =1 indicates that the content is selected for caching, and vice versa. s i is the size of the content:
(2) The cache placement algorithm adopted by the invention solves the problem of cache placement of the content in the server, and comprises the following steps:
1) A two-dimensional array Fj is defined. Fi j represents the maximum benefit obtained by selecting a plurality of contents from the first i contents and putting the contents into a server cluster with the residual space j.
2) The selected capacity size is gradually increased from 0, and if the current size j is smaller than the size S i of the content, the bit array F [ i ] [ j ] =f [ i-1] [ j ].
3) If S i is greater than or equal to j, then Fi [ j ] = max { Fi-1 [ j-S [ i ] ] +Gi, fi-1 [ j ] }, execute the decision of put and no put according to the gain of the ith content.
4) And finally obtaining a buffer decision set through reverse derivation.
And the edge server selects the content with the maximum total gain from the calculated set for caching. According to the edge caching method based on the content popularity, not only can the prediction result error be smaller, but also the content with larger total income can be cached in the edge server cluster, so that the hit rate of the content acquired by the user is improved, and the experimental cost of acquiring the content is reduced.
The system, apparatus, module or unit set forth in the above embodiments may be implemented in particular by a computer chip or entity, or by a product having a certain function. One typical implementation is a computer. In particular, the computer may be, for example, a personal computer, a laptop computer, a cellular telephone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.
Computer readable media, including both non-transitory and non-transitory, removable and non-removable media, may implement information storage by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of storage media for a computer include, but are not limited to, phase change memory (PRAM), static Random Access Memory (SRAM), dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), read Only Memory (ROM), electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium, which can be used to store information that can be accessed by a computing device. Computer-readable media, as defined herein, does not include transitory computer-readable media (transmission media), such as modulated data signals and carrier waves.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises an element.
The above examples should be understood as illustrative only and not limiting the scope of the invention. Various changes and modifications to the present invention may be made by one skilled in the art after reading the teachings herein, and such equivalent changes and modifications are intended to fall within the scope of the invention as defined in the appended claims.

Claims (4)

1.一种基于内容流行度的边缘缓存方法,其特征在于,包括以下步骤:1. An edge caching method based on content popularity, characterized in that it comprises the following steps: S1,根据服务器集群、设备和用户请求内容构建端边云系统模型,获得每个内容在不同时间段的请求次数,将单位时间内容被终端用户的请求次数视为该内容在该单位时间段历史流行度;S1, build an end-edge cloud system model based on server clusters, devices and user request content, obtain the number of requests for each content in different time periods, and regard the number of requests per unit time by terminal users as the historical popularity of the content in the unit time period; S2,对不同长度的历史数据进行分类,分类后使用改进的指数平滑预测算法和动态优化长短期记忆算法预测未来时刻的流行度;S2, classify historical data of different lengths, and use the improved exponential smoothing prediction algorithm and dynamic optimization long short-term memory algorithm to predict the popularity at future moments after classification; S3,将步骤S2中预测得到的流行度视为流行度增益,由于获取内容的时延与内容自身的大小有关系,假若内容缓存在边缘服务器集群中,相比于从云端获取所减少的时延视为时延开销增益,计算得到每个内容的价值总收益;S3, the popularity predicted in step S2 is regarded as popularity gain. Since the delay of obtaining content is related to the size of the content itself, if the content is cached in the edge server cluster, the reduced delay compared to obtaining it from the cloud is regarded as the delay cost gain, and the total value benefit of each content is calculated; S4,对于每个服务器集群,采用缓存放置算法计算出在当前容量下效益最高的内容序列,将这一批内容序列对应的内容缓存在服务器中;S4: For each server cluster, a cache placement algorithm is used to calculate the most efficient content sequence under the current capacity, and the content corresponding to this batch of content sequences is cached in the server; S5,获知每个内容是否缓存在边缘服务器集群中的结果;S5, obtaining the result of whether each content is cached in the edge server cluster; 所述步骤S2,对不同长度的历史数据进行分类,分类后使用改进的指数平滑预测算法和动态优化长短期记忆算法预测流行度预测未来时刻的流行度,具体包括:The step S2, classifying historical data of different lengths, and using an improved exponential smoothing prediction algorithm and a dynamically optimized long short-term memory algorithm to predict popularity after classification, specifically includes: 设定lp为内容集合的长度,设定长度界限LB;Set lp to the length of the content set and set the length limit LB; (1)若lp<LB则划分为新内容,采用改进的指数平滑预测算法预测;(1) If lp<LB, it is classified as new content and predicted using the improved exponential smoothing prediction algorithm; (2)若lp≥LB,则使用动态优化长短期记忆算法预测流行度;(2) If lp ≥ LB, the dynamic optimization long short-term memory algorithm is used to predict popularity; 所述步骤(1)中,采用了改进的指数平滑预测算法进行预测;传统的指数平滑预测方法中,权重因子α决定了预测最终数值的大小,α较大时,越接近当前时间段的流行度对预测结果的影响更大,反之当α取值较小时,越久远的内容流行度影响更大,其公式如下所示;In the step (1), an improved exponential smoothing prediction algorithm is used for prediction. In the traditional exponential smoothing prediction method, the weight factor α determines the size of the final predicted value. When α is larger, the popularity closer to the current time period has a greater impact on the prediction result. Conversely, when α is smaller, the popularity of older content has a greater impact. The formula is as follows: 表示使用指数平滑预测算法预测得到tn时刻的内容流行度,其中代表的是上一时刻的内容流行度,需要根据上一时刻的流行度进行后续操作,tn代表的是当前时间段,ts代表的是起始时间段,α是一个变量因子,固定不变,取值范围为[0,1],是为了确定前面时间段流行度对未来时间段的影响程度;由于传统方法中的权重因子α是静态的,使得平滑预测难以符合时间序列自身的变化,因此使用权重因子动态改变的指数平滑预测方法,其公式如下; Indicates the content popularity at time tn predicted using the exponential smoothing prediction algorithm, where represents the popularity of the content at the previous moment, and subsequent operations need to be performed based on the popularity at the previous moment. tn represents the current time period, ts represents the starting time period, and α is a variable factor that is fixed and has a value range of [0,1]. It is used to determine the influence of the popularity of the previous time period on the future time period. Since the weight factor α in the traditional method is static, it is difficult for smooth prediction to conform to the changes in the time series itself. Therefore, an exponential smoothing prediction method with dynamically changing weight factors is used. The formula is as follows; 表示使用改进的指数平滑预测算法预测得到tn时刻的内容流行度,相比于传统的方法,改进后的方法中,权重因子α的值将会随着tn的变化而动态改变,不再是一个固定的值,随时间而动态修正,使得预测的准确性更接近真实值; It indicates that the improved exponential smoothing prediction algorithm is used to predict the content popularity at time tn. Compared with the traditional method, in the improved method, the value of the weight factor α will change dynamically with the change of tn . It is no longer a fixed value and is dynamically modified over time, making the prediction accuracy closer to the true value; 所述步骤(2)中,使用动态优化长短期记忆算法预测流行度具体包括:In the step (2), using the dynamic optimization long short-term memory algorithm to predict popularity specifically includes: 对于历史数据较长的内容,即旧内容,采用动态优化的LSTM进行预测,将时间窗口大小,dense层数,LSTM网络层数和神经元个数作为寻优的对象;设置m个时间窗口待选值,k个dense层数待选值,n个lstm层数待选值和u个神经元数待选值,选择训练次数到达极限后得到的LSTM模型验证数据的平均百分比误差MAPE来衡量参数的优劣;其中MAPE的定义如下:For content with a long history of data, i.e. old content, dynamically optimized LSTM is used for prediction, and the time window size, dense layer number, LSTM network layer number and neuron number are used as optimization objects; m time window candidate values, k dense layer candidate values, n LSTM layer candidate values and u neuron candidate values are set, and the average percentage error MAPE of the LSTM model verification data obtained after the number of training times reaches the limit is selected to measure the quality of the parameters; the definition of MAPE is as follows: y′n是模型预测得到的值,yn是样本的真实值,N是样本数,设M(m,k,n,u)表示当前参数构建的LSTM模型预测后得到的平均百分比误差,通过不断的迭代训练,选出在测试集中M(m,k,n,u)表现效果最好的一组参数,然后确定旧内容预测所用的模型;同时,其中得到的最优m个时间窗口值就是划分新旧内容的标准LB。 y′n is the value predicted by the model, yn is the true value of the sample, N is the number of samples, and M(m,k,n,u) represents the average percentage error obtained after prediction by the LSTM model constructed with the current parameters. Through continuous iterative training, a set of parameters with the best performance in the test set M(m,k,n,u) is selected, and then the model used for old content prediction is determined; at the same time, the optimal m time window values obtained are the standard LB for dividing new and old content. 2.根据权利要求1所述的一种基于内容流行度的边缘缓存方法,其特征在于,所述步骤S1中构建端边云系统模型,获取历史流行度的方法具体包括:2. According to the edge caching method based on content popularity of claim 1, it is characterized in that the method of constructing the end-edge-cloud system model in step S1 and obtaining the historical popularity specifically includes: 大多数内容存储在云端,边缘服务器集群选取部分内容存储,终端用户发起请求,因此划分云端,边缘与终端三种环境,云端服务器是距离用户终端较远的设备,每个边缘服务器集群中都服务一些终端设备,终端设备会在不同时间段对某些内容发起请求,边缘服务器通过收集请求内容的历史数据,得到不同时间段的内容流行度,从而得到边缘服务器集群下所有内容的历史流行度集合,用于后面的流行度预测。Most content is stored in the cloud, and the edge server cluster selects some content for storage. The terminal user initiates the request, so the three environments are divided into cloud, edge and terminal. The cloud server is a device far away from the user terminal. Each edge server cluster serves some terminal devices. The terminal devices will initiate requests for certain content in different time periods. The edge server collects historical data of the requested content and obtains the content popularity in different time periods, thereby obtaining the historical popularity set of all content under the edge server cluster for subsequent popularity prediction. 3.根据权利要求1所述的一种基于内容流行度的边缘缓存方法,其特征在于,所述S3,将步骤S2中预测得到的流行度视为流行度增益,由于获取内容的时延与内容自身的大小有关系,假若内容缓存在边缘服务器集群中,相比于从云端获取所减少的时延视为时延开销增益,计算得到每个内容的价值总收益;具体公式如式所示;3. According to the edge caching method based on content popularity of claim 1, it is characterized in that, in step S3, the popularity predicted in step S2 is regarded as popularity gain. Since the delay of obtaining content is related to the size of the content itself, if the content is cached in the edge server cluster, the reduced delay compared to obtaining from the cloud is regarded as delay cost gain, and the total value benefit of each content is calculated; the specific formula is shown in the formula; Gi=A*ΔLi+B*Pi Gi =A* ΔLi +B* Pi 其中A和B是两个变量因子A+B=1,用于控制两种收益在总价值收益中的占比;ΔLi代表的是获取内容的时延增益,Pi代表的是内容的流行度增益,Gi代表的是内容的总价值收益。Among them, A and B are two variable factors A+B=1, which are used to control the proportion of the two types of benefits in the total value benefits; ΔL i represents the delay gain of obtaining content, P i represents the popularity gain of content, and G i represents the total value benefit of the content. 4.根据权利要求3所述的一种基于内容流行度的边缘缓存方法,其特征在于,所述步骤S4中,将缓存放置问题转化为了效益价值最大化问题,原问题会对每个内容做出决策,0代表不选择,1代表选择,这是一个0-1变量,则其是一个约束的0-1规划问题,即是NP难问题;通过考虑缓存能给服务器集群带来最大利益的内容,将问题转为利益最大化问题,问题转化为下式;4. According to the edge caching method based on content popularity of claim 3, it is characterized in that in the step S4, the cache placement problem is transformed into a benefit value maximization problem. The original problem will make a decision for each content, 0 represents no selection, 1 represents selection, which is a 0-1 variable, then it is a constrained 0-1 planning problem, that is, an NP-hard problem; by considering the content that the cache can bring the greatest benefit to the server cluster, the problem is transformed into a benefit maximization problem, and the problem is transformed into the following formula; 即从集合中选取使得总增益最大的内容进行缓存即可。That is, the content with the largest total gain is selected from the collection for caching.
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