CN111385734B - Internet of vehicles content caching decision optimization method - Google Patents

Internet of vehicles content caching decision optimization method Download PDF

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CN111385734B
CN111385734B CN202010102872.4A CN202010102872A CN111385734B CN 111385734 B CN111385734 B CN 111385734B CN 202010102872 A CN202010102872 A CN 202010102872A CN 111385734 B CN111385734 B CN 111385734B
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content
vehicle
caching
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vehicles
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CN111385734A (en
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黄晓舸
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崔艺凡
陈前斌
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Chongqing University of Post and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/02—Services making use of location information
    • H04W4/021—Services related to particular areas, e.g. point of interest [POI] services, venue services or geofences
    • 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
    • H04L67/01—Protocols
    • H04L67/12—Protocols specially adapted for proprietary or special-purpose networking environments, e.g. medical networks, sensor networks, networks in vehicles or remote metering networks
    • 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
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/02—Arrangements for optimising operational condition
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/02—Services making use of location information
    • H04W4/025—Services making use of location information using location based information parameters
    • H04W4/027—Services making use of location information using location based information parameters using movement velocity, acceleration information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/30—Services specially adapted for particular environments, situations or purposes
    • H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
    • H04W4/44—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P] for communication between vehicles and infrastructures, e.g. vehicle-to-cloud [V2C] or vehicle-to-home [V2H]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/30—Services specially adapted for particular environments, situations or purposes
    • H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
    • H04W4/46—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P] for vehicle-to-vehicle communication [V2V]

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Abstract

The invention relates to a content caching decision optimization method for Internet of vehicles, and belongs to the technical field of mobile communication. In the model, the internet of vehicles is provided with a plurality of content cache nodes, and the content requested by the vehicles can be stored in the content cache nodes. If the adjacent vehicle or the road side unit has cached the current vehicle request content, the current vehicle will acquire the content service from the caching node through the V2V link or the V2I link. The mobile edge computing server is deployed at the RSU side, and can provide storage and computing power for storing and processing the content. Because the vehicle is moving at a fast speed, the content requesting vehicle may not be able to fully acquire the desired content within the current RSU coverage area, and therefore they need to continue to acquire the remaining portion of the content within the next RSU coverage area. The present invention is directed to reducing the total delay in obtaining desired content by a content requesting vehicle. The method can solve the association problem of the vehicles and consider the content pre-caching, so that the optimal content caching decision is obtained.

Description

Internet of vehicles content caching decision optimization method
Technical Field
The invention belongs to the technical field of mobile communication, and relates to a content caching decision optimization method for Internet of vehicles.
Background
As one of application scenarios in the 5G network, the development of the internet of vehicles is significantly influenced by information and communication technologies, and these technologies promote a great deal of innovation in various fields, including communication and caching. Such as vehicles interconnecting various infrastructures, devices, users, etc., and various services, content and application providers interconnecting through a mobile wireless network, providing information and entertainment content for drivers and vehicles, typical applications of vehicular networks include early safety warning, managing and playing audio content, utilizing navigational driving, providing entertainment, such as movies, games, social networks, etc., and more complex applications, such as cooperative driving functions like lane merge assistance and queuing, and autonomous driving functions like unmanned driving. With the continuous commercialization of 5G networks, many services will be combined with these new applications, such as high resolution pictures, ultra-clear video, area maps, etc., and these rich service contents increase the traffic load of mobile networks, while the high access speed and low delay required to request these contents, especially video services, according to the technical report of CISCO, video traffic is estimated to occupy 82% of the annual internet traffic by the end of 2021. In view of the timeliness and reusability of content in the network, popular content is stored in content caching nodes, such as vehicles with storage and Road Side Units (RSUs), which deliver the desired content service to the vehicle requesting the content via a V2V link or a V2I link. A Mobile Edge Computing (MEC) server may provide a certain storage capability, and deploy it on the RSU side, and the MEC server may store functions on the radio access network side, which is convenient for storage and transmission of contents. The vehicle is directly connected to the nearest network edge supporting cloud services, so that the service quality of an application program requiring intensive calculation and low delay can be effectively improved, the data transmission delay is greatly reduced, and the experience of a vehicle user is improved.
Although the MEC server provides storage capacity, the available storage space is limited, and in order to optimize the experience of the vehicle user, reasonable caching of the content in the MEC server is required, so that the user experience can be improved. On the other hand, the vehicle is fast in running speed on the road, and the vehicle may be switched when the vehicle cannot acquire the complete content, so that the vehicle needs to establish a link with the remote server for many times due to switching, and the time delay of content acquisition is increased.
Disclosure of Invention
In view of this, the present invention provides a method for optimizing content caching decision in the internet of vehicles. The method solves the vehicle association problem and optimizes the cache decision to achieve the aim of minimizing time delay.
In order to achieve the purpose, the invention provides the following technical scheme:
a content caching decision optimization method for Internet of vehicles comprises the following steps:
s1: blocking the content to determine a cached content size;
s2: determining vehicle association, the size of the content which can be cached, and the acquisition delay of the content under the condition of uncached and cached content;
s3: optimizing content caching decisions without regard to pre-caching;
s4: on the basis of step S3, determining the content type and size to be pre-cached;
s5: and optimizing the caching decision by combining the caching content and the pre-caching content according to the optimization target.
Optionally, in step S1, the content is transmitted via the V2V link or the V2I link, and at the same time, the requesting vehicle can only select one transmission mode; let the vehicle request C contents, C ∈ {1, 2., C }, and the content C size is defined as ScAnd is divided into LcIndividual pieces of content, the set of which is represented as phic＝{1,2,...,Lc}; if the vehicle cannot completely acquire a certain content block within the coverage range of the current RSU, the content block is acquired again within the range of the next RSU, and all the content blocks can be completely acquired in no more than two RSUs; when the vehicle n requests content not cached by the MEC server of RSUm, the number of content blocks it can retrieve over the V2I link is
Figure BDA0002387455540000021
A size of
Figure BDA0002387455540000022
Content chunk set representationIs composed of
Figure BDA0002387455540000023
Optionally, in the step S1, in order to reduce cache redundancy, it is not necessary to cache all L of the content ccIndividual content blocks, only need to cache the L obtained in RSumc,mA block of content;
Figure BDA0002387455540000024
n represents the number of requesting vehicles; l isc,mEach content block having a size of
Figure BDA0002387455540000025
Content chunk collection
Figure BDA0002387455540000026
The optimization goal of the caching decision is to minimize vehicle acquisition
Figure BDA0002387455540000027
A time delay of a block of content; when the requesting vehicle cannot obtain the full content from the caching vehicle during the active connection of the V2V link, the requesting vehicle cannot be associated with the caching vehicle.
Optionally, in the step S2,
Figure BDA0002387455540000028
when the vehicle is not cached, obtaining the association result of the vehicle according to the association strategy of the vehicle, obtaining the RSUm coverage range based on the association result, and calculating the request vehicle to obtain
Figure BDA0002387455540000029
Time delay of individual content blocks
Figure BDA00023874555400000217
When the vehicle is cached, obtaining the association result of the vehicle according to the association strategy of the vehicle, obtaining the RSUm coverage range based on the association result, and calculating the request vehicle to obtain
Figure BDA00023874555400000212
Time delay of individual content blocks
Figure BDA00023874555400000213
Optionally, in the step S3, the optimization goal is to minimize the acquisition without considering the pre-cache
Figure BDA00023874555400000214
Time delay of a content block due to
Figure BDA00023874555400000215
Independent of caching policy
Figure BDA00023874555400000216
And the optimization target is equivalent to the maximized time delay difference, the problem is modeled and optimized, and a dynamic programming method is used for solving to obtain the cache strategy.
Optionally, in step S4, there are vehicles in the model that cannot acquire all content blocks in the coverage area of the current RSU, so RSUm needs to predict content requesting vehicles entering the coverage area of RSUm in the next Δ t period, that is, switching vehicles, the number of which is I, and the content blocks requested by them; and dividing different types of switching vehicles to obtain all content blocks needing to be pre-cached.
Optionally, in the step S4, for three types of switching vehicles, the content block caching scheme is as follows:
switching vehicle i needs
Figure BDA0002387455540000031
The content blocks are all cached, the pre-caching decision is not needed, and only the content block acquisition time delay needs to be recalculated
Figure BDA00023874555400000314
And
Figure BDA00023874555400000315
handoverRequired by vehicle i
Figure BDA0002387455540000032
The number of the content blocks which are partially cached and not cached is
Figure BDA0002387455540000033
A size of
Figure BDA0002387455540000034
The collection of content blocks is represented as
Figure BDA0002387455540000035
These content blocks need to be pre-cached; the number of the cached content blocks is
Figure BDA0002387455540000036
A size of
Figure BDA0002387455540000037
Computation acquisition
Figure BDA0002387455540000038
Time delay of each content block and update
Figure BDA00023874555400000318
And
Figure BDA00023874555400000317
if necessary
Figure BDA0002387455540000039
The number of all the content blocks is not cached, and the number of the content blocks needing to be subjected to the pre-caching decision is
Figure BDA00023874555400000310
Optionally, in the step S4, for the content c, the number of content blocks for which the pre-caching decision needs to be made is
Figure BDA00023874555400000311
A size of
Figure BDA00023874555400000312
The content blocks are collected as
Figure BDA00023874555400000313
Optionally, in step S5, the caching decision is performed again on the cached content block and the pre-cached content block; and the optimization target is equivalent to the maximization of time delay difference, modeling optimization problems are solved, and a final cache strategy is obtained by using a dynamic programming method.
The invention has the beneficial effects that: the invention aims to reduce the time delay of content acquisition and improve the data acquisition rate of a user. According to the method, the storage function of the vehicle and the storage function of the MEC server are utilized, the transmission pressure of the V2I link and the cache pressure of the MEC server are reduced in a cooperative cache mode that the content is transmitted through the V2V link, meanwhile, the content of the vehicle is switched, the partial content is pre-cached, and the content acquisition delay of a network is reduced.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the means of the instrumentalities and combinations particularly pointed out hereinafter.
Drawings
For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a V2V-assisted vehicle content request network model;
FIG. 2 is a vehicle association strategy flow diagram;
FIG. 3 is a pre-cache content classification;
FIG. 4 is a simulation deployment diagram of RSU at the intersection of city road and Guangzhong-West road in a quiet and quiet area of a certain city;
FIG. 5 is a content request popularity profile;
FIG. 6 is a diagram of simulation verification of the inventive arrangements.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.
Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.
FIG. 1 is a model diagram of a vehicle content request. The network consists of RSUs deployed on roads, content Request Vehicles (RVs) and Cache Vehicles (CVs), the RSUs and the mobile edge metersA computing (MEC) server is connected by wire, and the MEC server provides a storage content service. RSU ═ { RSU ═ RSU1,...,RSUMAnd is the RSU set, wherein RSUm represents the mth RSU. RV ═ { RV1,...,RVNIs RSUmSet of requested vehicles under coverage, CV ═ CV1,...,CVKAnd the vehicles are cached. The requesting vehicle may communicate with the RSU via the V2I link to obtain cached content or remote content, or with other caching vehicles via the V2V link to obtain cached content, and at the same time, the requesting vehicle may select only one link. To avoid interference between the V2I link and the V2V link, assuming that the V2I and the V2V link use different bandwidth resources, each of the V2I link and the V2V link uses an orthogonal channel with a bandwidth of W.
(1) Mobile model and cache model
Let the moving speed of vehicle be v ∈ [ v ]min,vmax]And d is the communication range of V2V, the maximum connection time of the V2V link between the two vehicles is delta t for the vehicles running in the same directionn,kWhich satisfies: | Δ dn,k+v1Δtn,k-v2Δtn,k|＝d，v1Indicating the speed, v, of the vehicle ahead2Indicating rear vehicle speed, Δ dn,kIndicating the distance between the two vehicles when connected. Similarly, the maximum connection time of the V2I link is delta tn,mWhich satisfies: Δ dn0+vnΔtn,m2r, wherein Δ dn0Is RVnPosition when establishing a connection with RSUm, vnRepresents RVnThe RSU has a radius of coverage of r.
Define C as the number of contents, the collection of contents as
Figure BDA0002387455540000051
Rank the c-th content for popularity
Figure BDA0002387455540000052
Content c has a size ScAnd can be divided into LcIndividual blocks of content, the set of blocks of content in c being denoted phic＝{1,2,...,Lc}. If the vehicle can not finish the process in the current RSU coverage areaWhen a certain content block is acquired completely, the content block is acquired again at the next RSU, and all the content blocks can be acquired completely through at most two RSUs. The probability that content c is requested at time t can thus be found to be:
Figure BDA0002387455540000053
wherein η represents the shape parameter of the Zipf distribution, and when the value of η is larger, the greater the content requested by most RVs is concentrated on the least popular content. Define F as the maximum buffer space deployed at the RSU side MEC server.
Due to the fast moving speed of the vehicle, when the vehicle is requested to acquire content through the V2I link, the complete content, that is, all content blocks, may not be acquired within the coverage of the current RSU. If the vehicle cannot completely acquire a certain content block in the coverage range of the current RSU, the content block is acquired again in the range of the next RSU, and all the content blocks can be completely acquired in no more than two RSUs. When the vehicle n requests the content not cached by the MEC server of the RSUm, the number of content pieces that the vehicle n can obtain through the V2I mode before leaving the coverage of the RSUm is equal to
Figure BDA0002387455540000054
A size of
Figure BDA0002387455540000055
Content chunk collection
Figure BDA0002387455540000056
When the requested content has been cached by the MEC server of RSUm, the number of pieces of content that the vehicle n can obtain by the V2I mode before the coverage of RSUm is the number
Figure BDA0002387455540000057
A size of
Figure BDA0002387455540000058
The collection of content blocks is represented as
Figure BDA0002387455540000059
To reduce cache redundancy, it is not necessary to cache all L's of content ccIndividual content blocks, only need to cache the available L in RSumc,mA piece of content.
Figure BDA00023874555400000510
N represents the number of requesting vehicles. L isc,mEach content block having a size of
Figure BDA00023874555400000511
Content chunk collection
Figure BDA00023874555400000512
The optimization goal of the caching decision is to minimize all requesting vehicle acquisitions
Figure BDA0002387455540000061
Time delay of (2).
(2) Communication model
Model delay of V2V
When the requesting vehicle cannot obtain the full content from the caching vehicle during the active connection of the V2V link, the requesting vehicle cannot be associated with the caching vehicle.
Figure BDA0002387455540000062
Set of content chunks from CVk over a V2V link, defined as RVn
Figure BDA0002387455540000063
Time delay of (2):
Figure BDA0002387455540000064
wherein x isn,kDenotes the RVn-CVk correlation factor, if xn,k1, representing RVn is associated with CVk through a V2V link; on the contrary, xn,k＝0。αk,cIndicating CVk a buffer variable for content c, if alphak,c1 means CVk cached c; otherwise, α k,c0. The inventionSuppose alphak,cIs given a constant, i.e., the content has been previously cached in CVk.
RVn obtains time delay T of content through CVkn,kThe following equation is satisfied:
Figure BDA0002387455540000065
Rn,k(t) represents a data transmission rate between RVn and CVk, which satisfies the following equation:
Figure BDA0002387455540000066
wherein the content of the first and second substances,
Figure BDA0002387455540000067
is a transmission power of CVk, gn,k(t) is the channel gain between RVn and CVk, σ2Is the noise power.
(V2I) mode delay
Figure BDA0002387455540000068
Acquisition of a set of content blocks over a V2I link, defined as RVn
Figure BDA0002387455540000069
Time delay of (c), namely:
Figure BDA00023874555400000610
xn,mis a correlation factor between RVn and RSUm, if xn,m1, denoting RVn is associated with RSUm through a V2I link; on the contrary, xn,m＝0。βcE {0,1} represents the MEC cache variable, if βc1 means MEC server cached βc(ii) a Conversely, betac＝0。
Figure BDA00023874555400000611
Represents RSUm through cloud acquisition
Figure BDA00023874555400000612
Time delay of (2). T isn,mRepresenting the transmission delay corresponding to the RVn obtaining content from RSUm over the V2I link, which satisfies the following equation:
Figure BDA00023874555400000613
Rn,m(t) represents the data transmission rate RVn to RSUm, which satisfies the following equation:
Figure BDA0002387455540000071
wherein the content of the first and second substances,
Figure BDA0002387455540000072
is the transmit power of RSUm, gn,m(t) is the channel gain, σ, from RVn to RSUm2Is the noise power.
(3) Initial optimization problem modeling
The invention provides a content caching decision optimization method in the Internet of vehicles, under the condition of not considering pre-caching, the optimization problem modeling is as follows:
Figure BDA0002387455540000073
s.t.C1:
Figure BDA0002387455540000074
C2:
Figure BDA0002387455540000075
C3:
Figure BDA0002387455540000076
C4:
Figure BDA0002387455540000077
C5:βc∈{0，1}
C6:
Figure BDA0002387455540000078
the problem has three optimization variables, two vehicle association variables and one content block cache variable, and the optimization problem can be divided into two sub-problems, a vehicle association problem and a cache decision problem. The vehicle association problem may be solved using a vehicle association strategy, shown in FIG. 2, from which vehicle association variables may be derived. Is firstly provided with
Figure BDA0002387455540000079
When the content blocks are not cached, obtaining the correlation result of the vehicles according to the correlation algorithm of the vehicles, obtaining the RSUm coverage range based on the correlation result, and requesting the vehicles to obtain the content blocks
Figure BDA00023874555400000710
Total time delay T of1 c(ii) a Secondly, set up
Figure BDA00023874555400000711
When the content is cached, obtaining the correlation result of the vehicle according to the correlation algorithm of the vehicle, obtaining the RSUm coverage range based on the correlation result, and requesting the vehicle to obtain the same content block
Figure BDA00023874555400000712
Total time delay of
Figure BDA00023874555400000713
Based on this, without considering the pre-cache, the optimization problem is modeled as:
Figure BDA00023874555400000714
s.t.C5:βc∈{0,1}
C6:
Figure BDA00023874555400000715
due to T1 cIndependently of the caching policy,
Figure BDA00023874555400000716
in relation to caching strategies, the optimization goal can thus be equated to maximizing the delay spread
Figure BDA00023874555400000717
Figure BDA0002387455540000081
s.t.C5:βc∈{0,1}
C6:
Figure BDA0002387455540000082
(4) Content caching and pre-caching decisions
There may be requesting vehicles in the network that fail to acquire all content blocks at the current RSU, and the RSUm will predict the number of vehicles I that will switch within the next Δ t period, as well as the content blocks they request. The number of content blocks required for switching the vehicle i into the coverage range of the RSUm is
Figure BDA0002387455540000083
A size of
Figure BDA0002387455540000084
The collection of content blocks is represented as
Figure BDA0002387455540000085
Fig. 3 is a schematic diagram of content block classification, and switching vehicles are classified into three categories:
based on step S3, the switching vehicle is classified into three categories:
1. need to make
Figure BDA0002387455540000086
The individual content blocks are completely cached;
2. need to make
Figure BDA0002387455540000087
The content blocks are partially cached;
3. need to make
Figure BDA0002387455540000088
Individual blocks of content are not cached.
For three types of switching vehicles, the content block division scheme needing cache decision is as follows:
1. need to make
Figure BDA0002387455540000089
The content is completely cached, the content block required by the vehicle switching is the same as the content block of the cache decision of the optimization problem (2), the pre-cache decision is not required, and only the time delay T needs to be updated1 cAnd T2 c。
Figure BDA00023874555400000810
Get when uncached
Figure BDA00023874555400000811
Plus the delay T before update1 cIs equal to the updated time delay T1 c，
Figure BDA00023874555400000812
Cache-time fetch
Figure BDA00023874555400000813
Plus the delay before update
Figure BDA00023874555400000814
Equal to the updated time delay
Figure BDA00023874555400000815
2. Need to make
Figure BDA00023874555400000816
The content blocks are partially cached, and the number of the content blocks required by the switching vehicle is different from the number of the content blocks of the caching decision of the optimization problem (2)
Figure BDA00023874555400000817
A size of
Figure BDA00023874555400000818
The collection of content blocks is represented as
Figure BDA00023874555400000819
The number of the required content blocks is the same as that of the cache decision of (2)
Figure BDA00023874555400000820
A size of
Figure BDA00023874555400000821
The content blocks required by switching the vehicles are
Figure BDA00023874555400000822
The content blocks are the same as the content blocks of the cache decision in the step (2), and the time delay T needs to be updated1 cAnd
Figure BDA00023874555400000823
Figure BDA00023874555400000824
get when uncached
Figure BDA00023874555400000825
Plus the delay T before update1 cEqual to the updated time delay
Figure BDA00023874555400000826
Figure BDA00023874555400000827
Cache-time fetch
Figure BDA00023874555400000828
Plus the delay before update
Figure BDA00023874555400000829
Equal to the updated time delay
Figure BDA00023874555400000830
3. Need to make
Figure BDA0002387455540000091
The number of all the content blocks is not cached, and the number of the content blocks needing to be subjected to the pre-caching decision is
Figure BDA0002387455540000092
It follows that for content c, the number of content blocks for which a pre-caching decision needs to be made is
Figure BDA0002387455540000093
A size of
Figure BDA0002387455540000094
The content blocks are collected as
Figure BDA0002387455540000095
Further, in step S5, the caching decision is re-performed on the cached content block and the pre-cached content block.
Figure BDA0002387455540000096
Is gammac∈{0,1}，
Figure BDA0002387455540000097
When not cached, the acquisition delay is T3 c，
Figure BDA0002387455540000098
When cached, the acquisition delay is T4 cThen the optimization problem can be expressed as:
Figure BDA0002387455540000099
s.t.C3:βc,γc∈{0,1}
C4:
Figure BDA00023874555400000910
the optimization problem can utilize dynamic programming to obtain an optimal caching decision. Through the steps, the optimal content caching and pre-caching decision can be obtained by combining the content blocks required by the request vehicles and the content blocks required by the switching vehicles.
Through the steps, the optimal content block caching and pre-caching decision is obtained by combining the content blocks required by the request vehicles and the content blocks required by the switching vehicles.
FIG. 4 is a schematic diagram of the RSU deployment at the intersection of the city road and the Guangzhong-Xi road in the quiet area of Shanghai city. Table 1 is the coordinates of the RSU in fig. 4.
TABLE 1 coordinates of RSUs
RSU Coordinates of the object
RSU1 (121.433181,31.283876)
RSU2 (121.43575,31.281218)
RSU3 (121.438656,31.283278)
RSU4 (121.444239,31.288169)
RSU5 (121.438638,31.278772)
RSU6 (121.441648,31.281102)
RSU7 (121.44516,31.28288)
RSU8 (121.448628,31.284663)
RSU9 (121.444334,31.278421)
Table 2 contents Heat ranking TOP10
Figure BDA00023874555400000911
Figure BDA0002387455540000101
The vehicle request content heat degree is based on the cat eye whole network heat degree list. Table 2 lists the cat eye popularity values for top10 content of the popularity ranking, and FIG. 5 is the requested content popularity. FIG. 6 is a graph of simulated verification of the popularity of the content of FIG. 5 for the scenario of the present invention, according to the scenario of FIG. 4, wherein the number of requesting vehicles obeys the tidal effect and the observed time is 5:00 to 23: 00.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.

Claims (9)

1. A content caching decision optimization method for the Internet of vehicles is characterized by comprising the following steps: the method comprises the following steps:
s1: blocking the content to determine a cached content size;
s2: determining vehicle association, the size of the content which can be cached, and the acquisition delay of the content under the condition of uncached and cached content;
s3: optimizing content caching decisions without regard to pre-caching;
the optimization problem is modeled as:
Figure FDA0003116738390000011
s.t.C5:βc∈{0,1}
Figure FDA0003116738390000012
Figure FDA0003116738390000013
indicating a request for vehicle acquisition
Figure FDA0003116738390000014
A time delay of a block of content;
Figure FDA0003116738390000015
indicating a request for vehicle acquisition
Figure FDA0003116738390000016
A time delay of a block of content; c represents the number of the contents requested by the vehicles, and C belongs to {1, 2.., C }; n represents the number of requesting vehicles; n represents a vehicle;
Figure FDA0003116738390000017
represents the number of content blocks available via the V2I link; l isc，mEach content block having a size of
Figure FDA0003116738390000018
Due to T1 cIndependently of the caching policy,
Figure FDA0003116738390000019
related to the caching strategy, the optimization objective is equivalent to maximizing the delay inequality
Figure FDA00031167383900000110
Figure FDA00031167383900000111
s.t.C5:βc∈{0,1}
Figure FDA00031167383900000112
S4: on the basis of step S3, determining the content type and size to be pre-cached;
s5: optimizing a caching decision according to an optimization target by combining the caching content and the pre-caching content;
Figure FDA00031167383900000113
is gammac∈{0,1}，
Figure FDA00031167383900000114
When not cached, the acquisition delay is
Figure FDA00031167383900000115
Figure FDA00031167383900000116
When cached, the acquisition delay is
Figure FDA00031167383900000117
The optimization problem is represented as:
Figure FDA00031167383900000118
s.t.C3:βc,γc∈{0,1}
Figure FDA00031167383900000119
2. the optimization method for content caching decision of the internet of vehicles according to claim 1, wherein: in the step S1, the content is transmitted via the V2V link or the V2I link, and at the same time, the requesting vehicle can select only one transmission mode; let the vehicle request C contents, C ∈ {1, 2., C }, and the content C size is defined as ScAnd is divided into LcIndividual pieces of content, the set of which is represented as phic＝{1,2,...,Lc}; if the vehicle cannot completely acquire a certain content block within the coverage range of the current RSU, the content block is acquired again within the range of the next RSU, and all the content blocks can be completely acquired in no more than two RSUs; when the vehicle n requests content not cached by the MEC server of RSUm, the number of content blocks it can retrieve over the V2I link is
Figure FDA0003116738390000021
A size of
Figure FDA0003116738390000022
The collection of content blocks is represented as
Figure FDA0003116738390000023
3. The optimization method for content caching decision of the internet of vehicles according to claim 2, wherein: in the step S1, in order to reduce the cache redundancy, it is not necessary to cache all the L of the content ccIndividual content blocks, only need to cache the L obtained in RSumc,mA block of content;
Figure FDA0003116738390000024
n represents the number of requesting vehicles; l isc,mEach content block having a size of
Figure FDA0003116738390000025
Content chunk collection
Figure FDA0003116738390000026
The optimization goal of the caching decision is to minimize vehicle acquisition
Figure FDA0003116738390000027
A time delay of a block of content; when the requesting vehicle cannot obtain the full content from the caching vehicle during the active connection of the V2V link, the requesting vehicle cannot be associated with the caching vehicle.
4. The optimization method for content caching decision of the internet of vehicles according to claim 1, wherein: in the step S2, in the above step,
Figure FDA0003116738390000028
when the vehicle is not cached, obtaining the association result of the vehicle according to the association strategy of the vehicle, obtaining the RSUm coverage range based on the association result, and calculating the request vehicle to obtain
Figure FDA0003116738390000029
Time delay of individual content blocks
Figure FDA00031167383900000210
Figure FDA00031167383900000211
When the vehicle is cached, obtaining the association result of the vehicle according to the association strategy of the vehicle, obtaining the RSUm coverage range based on the association result, and calculating the request vehicle to obtain
Figure FDA00031167383900000212
Time delay of individual content blocks
Figure FDA00031167383900000213
Wherein the content block is set
Figure FDA00031167383900000214
5. The optimization method for content caching decision of the internet of vehicles according to claim 1, wherein: in the step S3, the optimization goal is to minimize the acquisition without considering the pre-cache
Figure FDA00031167383900000215
Time delay of a content block due to
Figure FDA00031167383900000216
Independent of caching policy
Figure FDA00031167383900000217
And the optimization target is equivalent to the maximized time delay difference, the problem is modeled and optimized, and a dynamic programming method is used for solving to obtain the cache strategy.
6. The optimization method for content caching decision of the internet of vehicles according to claim 1, wherein: in step S4, there are vehicles in the model that cannot acquire all content blocks in the coverage area of the current RSU, and RSUm needs to predict the content requesting vehicles entering the coverage area of the RSU, i.e. switching vehicles, whose number is I, and the content blocks they request during the next Δ t period; and dividing different types of switching vehicles to obtain all content blocks needing to be pre-cached.
7. The optimization method for content caching decisions of the internet of vehicles according to claim 6, wherein: in the step S4, the content block caching scheme is as follows for three types of switching vehicles:
switching vehicle i needs
Figure FDA00031167383900000218
The content blocks are all cached, the pre-caching decision is not needed, and only the content block acquisition time delay needs to be recalculated
Figure FDA0003116738390000031
And
Figure FDA0003116738390000032
switching vehicle i needs
Figure FDA0003116738390000033
The number of the content blocks which are partially cached and not cached is
Figure FDA0003116738390000034
A size of
Figure FDA0003116738390000035
The collection of content blocks is represented as
Figure FDA0003116738390000036
These contentsThe block needs to make a pre-caching decision; the number of the cached content blocks is
Figure FDA0003116738390000037
A size of
Figure FDA0003116738390000038
Computation acquisition
Figure FDA0003116738390000039
Time delay of each content block and update
Figure FDA00031167383900000310
And
Figure FDA00031167383900000311
content c is defined as S in sizecAnd is divided into LcA block of content;
if necessary
Figure FDA00031167383900000312
The number of all the content blocks is not cached, and the number of the content blocks needing to be subjected to the pre-caching decision is
Figure FDA00031167383900000313
8. The optimization method for content caching decision of the internet of vehicles according to claim 7, wherein: in step S4, for the content c, the number of content blocks needed to make the pre-caching decision is
Figure FDA00031167383900000314
A size of
Figure FDA00031167383900000315
The content blocks are collected as
Figure FDA00031167383900000316
9. The optimization method for content caching decision of the internet of vehicles according to claim 1, wherein: in step S5, re-performing the caching decision on the cached content block and the pre-cached content block; and the optimization target is equivalent to the maximization of time delay difference, modeling optimization problems are solved, and a final cache strategy is obtained by using a dynamic programming method.
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