CN103475710A - Inter-vehicle cooperation downloading scheme based on feedback method - Google Patents

Abstract

The invention provides an inter-vehicle cooperation downloading scheme based on a feedback method to overcome the effects that in an existing vehicle data downloading method and technology, contradiction exists among the coverage area, the data downloading rate and the traffic expenses. According to the method, the data downloading time of a single vehicle can be obviously shortened. Meanwhile, due to the fact that data can be shared through V2V communication, time is shortened, no expenses are produced when V2V communication is used, and the expenses for data downloading are greatly lowered. The 3G communication method and the DSRC communication method are utilized at the same time, the 3G communication method is used as a control channel and responsible for uploading request information to a roadside access point so that data can be prepared well before the vehicle passes by the roadside access point, the DSRC communication method is used for downloading the data, and therefore the data can be downloaded at a high speed.

Description

Cooperation download scenarios between the vehicle based on feedback system

Technical field:

The invention belongs to field of traffic, be specifically related to data file downloading field in traffic.

Background technology

At present along with car networking (VANET) [HARTENSTEIN H, LABERTEAUX K P.Vanet vehicular application and inter-network technologies[M] .] and the development of Internet of Things and standard is constantly perfect, people are more and more interested for the business development of vehicle-mounted data information service, for example car entertainment and vehicle-mounted office [UZCATEGUI R, ACOSTA-MARUM, G.Wave:a tutorial[J] .IEEECommunication Magazine.2009:126-133.].Therefore, can predict, increasing automobile will be installed in-vehicle wireless communications device in the near future, and we will be to Intelligent life further.Intelligent transportation system has boundless application scenarios: to vehicle, push local more detailed transport information (advertisement as traffic safety is reminded, map upgrades, based on current location etc.), obtain specific data message (as near parking stall from the webserver, local hotel is introduced and scenic spot is introduced) [ZHU J, ROY S.Mac for dedicated short range communications in intelligent transport system[J] .IEEE Communications Magazine, 2003,41:60-67.], etc.

The current intelligent transportation system mainly 2G/3G network based on extensive use and the vehicle Dedicated Short Range Communications (DSRC) that is applied between vehicle is vehicle data information service [UZCATEGUI R, ACOSTA-MARUM, G.Wave:a tutorial[J] .IEEE Communication Magazine.2009:126-133.].Current a lot of vehicle-mounted service company carries out with existing Cellular Networks the communication module that data are connected and comes from network terminal download service information by carrying, because existing Cellular Networks is laid extensively and through commercial for a long time, the stability that its data are downloaded can guarantee the stable connection of communicating by letter with coverage, the continuity that data are downloaded.Constantly perfect along with the 802.11P agreement on the other hand, also have part company and research institution to attempt by DSRC(vehicle Dedicated Short Range Communications) reach the direct communication of car and car, car and roadside infrastructure (being used as data download use), due to the agreement that is the special vehicle development for high-speed mobile, so be in a ratio of 2G and the 3G Cellular Networks of mobile communication design, DSRC communication can reach very high data download rate, and in constantly improving.

Yet these two kinds of communication modes have its limitation: for the 2G/3G network, the not high and expensive mass file data of especially relatively downloading of its data transmission bauds, therefore also make the scope of relevant vehicle-mounted service application greatly reduce, can't realize with prior art as vehicle-mounted office and car entertainment etc. require large or application real time communication of data volume; And although DSRC communication has met that high data communication requires but the distribution density that is limited to the coverage of basis, roadside access point and access point be difficult to guarantee the communicating requirement [JIANG D, DELGROSSI L.IEEE802.11p:Toward an international standard for wireless access in vehicular environments[C] of continuous seamless //Vehicular Technology Conference.2008:2036-2040.].Even if increase the laying density of current basis, roadside access point, need on the one hand a large amount of fund inputs, before reaching certain density, also need the regular hour on the other hand, therefore this communication mode is also the communication support that does not reach requirement in a short time.

The mode that between the difficult vehicle that in networking in order to overcome to get on the bus, Data dissemination runs into, cooperation is downloaded has occurred: if the downloading data content can obtain in the part of a group vehicle, simultaneously other vehicles want to download this data content, use so V2V(Vehicle-to-Vehicle) to car, communication reaches P2P(Peer-to-Peer to car) can to shorten greatly download time simultaneously also very economical economically for the method for contents distribution.

It is a kind of agreement [KORKMAZG that carries out Data dissemination in all nodes of network that cooperation is downloaded, EKICI E, OZGUNER F, et al.Urban multi-hop broadcast protocol for inter-vehicle communication systems[C] //ACM Intl workshop on Vehicularad hoc networks.2004:76-85.] [XU B, OUKSEL A, WOLFSON O.Opportunistic resource exchange in inter-vehicle ad-hoc networks[C] //IEEE Mobile Data Management.2004, 4-12.].At present, the method has been subject to very large concern [GHANDEHARIZADE S in the learned society that researches and develops and improve the car networking and commercial undertaking, KAPADIA S, KRISHNAMACHARI.Pavan:a policy framework for content availability in vehicular ad-hoc networks[C] //the1st ACM international workshop on Vehicular ad hoc networks.2004:57-65.], become the study hotspot of industry.The general Data dissemination in the car networking mainly forms [JERBI M by two stages, MARLIER P.Experimental assessment of V2V and I2V communications[C] //IEEE International Conference on Mobile Ad hoc and Sensor Systems.2007:1-6.] [JERBI M, SENOUCI S.Characterizing multi-hop communication in vehicular networks[C] //IEEE Wireless Communications and Networking Conference.2008:3309-3313.]:

Vehicle-to-Infrastructure (V2I) vehicle is connected stage of communication with the roadside access point: in this stage, when vehicle enters in the coverage of roadside access point, vehicle is from access point AP(Access Point) obtain data

Vehicle-to-Vehicle(V2V) car and inter-vehicle communication stage: after vehicle leaves the coverage of roadside access point, mutual exchange message between vehicle.When this stage finishes, all nodes have all obtained identical data.

The cooperation that this programme is considered download be mainly a vehicle " bunch " in cooperation download rather than regardless of spaces of vehicles how far away several workshops can.Wherein vehicle " bunch " formation mechanism and maintenance mechanism and bunch in the workshop V2V mode reference [LITTLE T D C, AGARWAL A.An information propagation scheme for vanets[C] of communicating by letter //IEEE Conference on Intelligent Transportation Systems.2005:13-16.].It is main in this programme that what pay close attention to is that to adopt mode based on feedback be that vehicle was first uploaded accepted partial document AP and only broadcasted to vehicle receiving portion not accordingly before download file from roadside access point AP download data files to the V2I process.

Compare, the grouping selection mode based on random be simple repetition pass down at random part to vehicle from whole file, so vehicle to download the repetition rate of part very high.Suppose that the file grouping (size of file is weighed with how many grouping Packets) that vehicle receives after V2I can be in the fully shared exchange of V2V stage.For privacy and the security consideration of vehicle downloading contents, the roadside access point AP download file of once only communicating by letter with a car, other vehicle can not obtain this document information (being different from the broadcast distribution data).

We claim that one bunch through a download point, and in bunch, vehicle is downloaded corresponding document (V2I), in leaving after this download point bunch, between vehicle, by the V2V(car, with car, communicate by letter) fully shared downloading contents separately be one " circulation " (V2I+V2V).Therefore downloading a large file just needs just can complete through a plurality of circulations.Theory analysis and the emulation of back shows, the present invention suggests plans and can greatly shorten data in the car networking and download required time (being presented as that cycle-index greatly reduces).Main contributions of the present invention: the first, theory analysis has also verified that vehicle cooperation based on feedback system downloads the required time (take cycle-index as unit) and repeat to select at random the packet mode contrast, has greatly shortened the download time of file.The second, analytic explanation participates in respect to increasing the vehicle number that cooperation is downloaded, and the download capabilities (the grouping number of downloading during process AP) that preferentially increases single unit vehicle can more effectively shorten download time.The 3rd, the vehicle number that increases the cooperation download can shorten download time, but not The more the better, very little to the effect that reduces download time after vehicle number is increased to certain value, even can ignore.

The present invention is directed to the defect that existing vehicle data downloading mode and technology exist: the contradiction between coverage, downloading data rate and flow rate problem three, cooperation data download method between the vehicle based on feedback system has been proposed, can significantly shorten the single unit vehicle data download time, simultaneously by V2V(car and car) communicate by letter and share mutual data, not only shortened time V2V communication simultaneously and do not produced cost, also made the rate of downloading data greatly reduce.

Vehicle boarded 2G/3G communication module is downloaded major way as data, utilize existing ripe mobile phone Cellular Networks as communication network, reliable and stable and communication should not be interrupted, and charge method is pressed regular handset flow rate, expenses standard user by existing flow is easy to accept, easily universal.

Although this scheme will have the ripe communication technology now and use data download in the car networking, convenient stable, but the 2G/3G network technology is developed mainly for mobile phone, mobile speed is had to upper limit requirement, in the situation that the frequent change of topological structure and the speed of a motor vehicle are very high, data download rate does not reach the download rate of its publicity, and similar vehicle-mounted office, car entertainment etc. there are certain requirements (requirement of real time) to the data speed of download, the total amount of data of downloading again very large (entertainment applications) thus produce the too high problem of rate, in reality is used, all the diversification of forms to vehicular applications forms obstruction.

V2I (vehicle – to-infrastructure) vehicle and roadside access point are by the random fashion download communication, communication protocol is that DSRC is characterized in that data transmission rate is high (after vehicle and access point connection request related content, the random selection passed to vehicle under part), leave after the coverage of access point by V2V (vehicle-to-vehicle) car and car by the DSRC mutual sharing download content (the vehicle chance formula of travelling runs into a vehicle identical with its downloading contents mutually, by intercoming mutually, data content is shared alternately) of communicating by letter.

So because the random situation that exists downloading contents to repeat from the access point downloading data, this in the situation that with the access point very precious waste communication opportunity of chance that establishes a communications link be very unworthy.Secondly, vehicle will run into its limited opportunities of wanting another car of downloading data content, and prerequisite is that this vehicle can inquire whether the other side have the related data content, easily causes the communication inundation with all vehicles that it meets, stop up communication channel, make on the contrary data transmission rate descend.

Summary of the invention

Goal of the invention: the present invention is directed to the defect that existing vehicle data downloading mode and technology exist: the contradiction between coverage, downloading data rate and flow rate problem three, cooperation data download method between the vehicle based on feedback system has been proposed, can significantly shorten the single unit vehicle data download time, simultaneously by V2V(car and car) communicate by letter and share mutual data, not only shortened time V2V communication simultaneously and do not produced cost, also made the rate of downloading data greatly reduce.Utilize two kinds of communication mode 3G to communicate by letter with DSRC simultaneously, using 3G as control channel, be responsible for can making like this vehicle pass through the roadside access point before just by DSR to roadside access point upload request information, DSRC downloads use as data, can the high-speed downloads data.

Scheme of the invention

System model:

Due to the relatively discrete distribution of the distribution of roadside download point, cause the vehicle a very long time not in the coverage of download point, vehicle is always intermittent with being connected of download point, and interval is relatively very long, not yet in effect using.Consider that the file that single unit vehicle is downloaded does not separately separately have cooperation each other simultaneously, this programme has proposed the mode that cooperation is downloaded, take full advantage of vehicle not in interval time of roadside download point coverage, after leaving between the area of coverage of download point, the V2V(car undertaken between vehicle by DSRC (short-range communication protocol between vehicle) is communicated by letter with car) mutually share downloading contents separately, reach the purpose that doulbe-sides' victory is downloaded in cooperation.In order to realize that V2V communication shares downloading contents separately fully, we adopt the adjacent vehicle in a kind of geographical position form vehicle " bunch " mode.Vehicle " bunch " in vehicle can share downloading data each other fully.For random downloading mode, between vehicle and download point, do not link up, the content of download may be the data content part that vehicle has contained simultaneously, and this is undoubtedly the waste to bandwidth and downloading machine meeting.System model of the present invention adopts the downloading mode based on feedback not waste each downloading machine meeting.Concrete execution mode is to utilize the wide spreadability of 3G channel as control channel, want that the access point closed on uploads the existing data division of vehicle, like this when vehicle enters the roadside download point, access point can only pass down to vehicle the data division that vehicle does not also receive targetedly, avoid redundancy and repetition, utilized the wide spreadability of 3G and the advantage of the High Data Rate that the roadside access point is downloaded simultaneously.For realizing above purpose, this programme also needs to set up an AP(and downloads access point) server, preserve the positional information of all roadsides access point, like this after vehicle utilizes the 3G channel to upload receiving unit data and vehicle current location (by the GPS positioner is installed onboard), server can contrast current vehicle location and AP position, find out the position that the vehicle direct of travel is about to the next AP of arrival, now can notify this access point ready, the content server of wanting downloading contents with corresponding vehicle is connected, obtain in advance downloading contents, download access point when vehicle enters this AP() coverage after, pass down its not data of receiving unit to vehicle.

As shown in Figure 1, between a complete vehicle, cooperation download flow process means complete system model as follows:

The vehicle that travels on road stream by geographical position many adjacent cars can mutually form one by one " bunch ", claim each " bunch " accordingly " bunch head " vehicle be header, " bunch tail " vehicle is trailer.Consider such scene: in certain bunch, have k car (red vehicle in figure) to want to download the file that same size is M grouping simultaneously and (suppose that this M grouping is numbered respectively: P ₁, P ₂..., P _m).The fileinfo of this k car wish download is aggregated into " bunch head " vehicle, by this vehicle, information is uploaded to (for example, being reported by the mobile network), then is sent in the content server of storing this document [12] by the webserver.Suppose that the webserver of processing this document download request can obtain geographical location information and the direction of motion (vehicle is installed the GPS positioner) of this bunch, and this webserver is preserved the exact position of all roadsides access point, thereby can judge this " bunch " access point that be about to arrive, then from content server, the download file content is kept in the middle of this server, after bunch entering the coverage of this access point, with bunch in k car communicate by letter and download this document information.

Might as well suppose that any grouping number homogeneous phase of downloading in the V2I stage in k car is all m(m<M), m is less than the file total packet and counts M.Obviously, from M grouping How to choose to go out m grouping download most important to the performance of whole file download system to the system of selection of vehicle.This paper considers to use the selection mode based on feedback: at the V2I of each car in the stage, vehicle first is uploaded to roadside download point AP by the file grouping catalogue received, and access point AP in roadside just selects at random m and out downloads to vehicle from the unreceived grouping of this vehicle like this.

After a bunch tail vehicle also leaves the overlay area of roadside access point AP, all vehicles in bunch enter the V2V stage.In this stage, all vehicle sharing download contents in bunch.Therefore, after waiting V2V to complete, all k car all will contain identical content (all vehicle downloading contents sums).When vehicle enters next download point, this k in bunch repeats above-mentioned downloading process until download complete file.

Performance of the present invention and Simulation Evaluation:

For simplifying the analysis, suppose that each bunch of vehicle stream formation is relatively stable, can not cause because of the difference of speed between vehicle adding frequently and exiting certain bunch.Such hypothesis is that cooperation is feasible in short time interval relatively.In hypothetical network, in certain bunch, there is any k car wish to download the file of size for M grouping.As mentioned above, in each V2I stage, all from download, point out and download m grouping (m≤M) for any one in k car.In the ensuing V2V stage, this k car exchanges their just-downloaded this m groupings mutually, thus each car all to contain m of other vehicle grouping be that the packet count that each car contains is increased to km (may comprise and repeat identical grouping) by m.Suppose x in i circulation _irepresent different grouping number in this km grouping (remove repeated packets after remaining grouping number).Obvious x _ia stochastic variable value set for 0,1,2 ..., km}.Next we define S _ithe grouping number (each grouping is not identical, does not repeat) that while being i circulation end, each car contains.Therefore x when finishing, is arranged in each circulation _iindividual new grouping adds wherein, therefore to S _ifollowing recurrence formula is arranged

S _i=S _i-1+x _i (1)

When all vehicles all contain this M grouping, send downloading process and just stop.If the cycle-index of variable T when having downloaded.Have

Wherein

rounding operation in expression, download at most km different groupings so will complete the minimum needs of download because once circulate

inferior.

Next calculate the send mode utilized based on feedback, complete probability-distribution function and the desired value (download completes required cycle-index) of downloading required cycle-index T.

Formula 1: given S _i-1during=s, newly-increased different grouping number x in i circulation _ithe conditional probability distribution function as follows:

$\begin{array}{c}P(X_i=x|S_{i-1}=s)\\ =\left\{\begin{array}{cc}\frac{C_{M-s}^x{C}_x^m[{\left(C_x^m\right)}^{k-1}+{\mathrm{\&Sigma;}}_{i=1}^{x-m}{(-1)}^i{C}_{x-m}^i{\left(C_{x-i}^m\right)}^{k-1}]}{{\left(C_{M-s}^m\right)}^k}& m\&le;x\&le;\min (\mathrm{km},M-s)\\ 1& 1\&le;x<m\end{array}\right.\end{array}$

Proof: probability P (x _i=x|S _i-1=s) meaning shown is that vehicle has been accepted s number that wraps in newly-increased bag in the next one (V2I+V2V) process, each car all can be downloaded at random m different grouping from remaining (M-s) individual bag, therefore x at least equals m, and when residue bag number (M-s)<m, vehicle one has been accepted remaining bag surely.So have when x get [1,2 ..., min (m, M-s)] time, this conditional probability P(x _i=x|S _i-1=s)=1, wherein min (m, M-s) shows that vehicle can only be got at most this remaining bag or grouping if when remaining not the bag number of downloading and being less than the download capabilities m of vehicle.

Situation when x >=m is as follows:

Denominator means to get likely number of combinations of m the institute divided into groups from (M-s).Molecule is illustrated in the institute's number of combinations likely that has just increased x different grouping in the set that this k car form newly.

Obviously the fine understanding of expression formula of denominator.Here we only explain the developed by molecule formula.

expression is selected x from remaining M-s grouping.And $C_x^m[{\left(C_x^m\right)}^{k-1}+{\mathrm{\&Sigma;}}_{i=1}^{x-m}{(-1)}^i{C}_{x-m}^i{\left(C_{x-i}^m\right)}^{k-1}]$ Mean front from

in certain x of selecting be grouped in this k car have how many in the permutation and combination numbers.

Below stress formula $[{\left(C_x^m\right)}^{k-1}+{\mathrm{\&Sigma;}}_{i=1}^{x-m}{(-1)}^i{C}_{x-m}^i{\left(C_{x-i}^m\right)}^{k-1}],$ The meaning of its expression is that k each car of car all never receives in (M-s) individual grouping and select m grouping, added together remove afterwards the identical remaining different grouping of grouping of deduplication be just from in certain x grouping selecting.Suppose from

in the x that selects be grouped into set (P ₁, P ₂..., P _x).Above event is equivalent in k car one from (P ₁, P ₂..., P _x) in select m out, remaining (k-1) car also selects m out from this set, remove m outer remaining (x-m) in addition car of that car choosing but this (k-1) car selects respectively the summation of m must comprise in set, their union must be set itself.For example in k car has selected (P ₁, P ₂..., P _x) in (P ₁, P ₂..., P _m) this m grouping, must comprise (P in m grouping of (k-1) * that so remaining (k-1) car is selected _m+1, P _m+2..., P _x) this remaining (x-m) individual grouping, their union has formed set (P ₁, P ₂..., P _x) itself.This problem can be calculated according to the inclusion-exclusion principle in Combinational Mathematics.Suppose this remaining (x-m) individual be grouped into set p ' ₁, p ' ₂..., p ' _x-m.Set E represents event: (k-1) car selects respectively m grouping (x >=m) from x is divided into groups.Its element number comprised is designated as | and the number of the following all events of E|(is all used | .| means) have if event A ₁, A ₂..., A _x-mfor the subset of finite aggregate E, A _i=(x|xE, and make in E not contain grouping p ' _i,

so, event just mean to meet in character E to comprise p ' simultaneously ₁, p ' ₂..., p ' _x-mthe event of this (x-m) individual grouping (being us required).Subset A ₁, A ₂..., A _x-mthere is therefore order of symmetric property:

$R_1=\left|A_1\right|=\left|A_2\right|=\&CenterDot;\&CenterDot;\&CenterDot;=\left|A_{x-m}\right|={\left(C_{x-1}^m\right)}^{k-1}$

$R_2=\left|A_1{A}_2\right|=\left|A_1{A}_3\right|=\&CenterDot;\&CenterDot;\&CenterDot;=\left|A_{x-m-1}{A}_{x-m}\right|={\left(C_{x-2}^m\right)}^{k-1}$

…

$R_{x-m}=|A_1{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA0000379792080000021.png,HDA0000379792080000022.png"\; state="\{\{state\}\}">A</figure-callout>}}_2...A_{x-m}|={\left(C_m^m\right)}^{k-1}=1$

By inclusion-exclusion principle: establish F ₁, F ₂... F _nfor the subset of finite aggregate F,

$\begin{array}{c}|\stackrel{\&OverBar;}{F_1}\stackrel{\&OverBar;}{{\mathrm{<figure-callout\; id="2"\; label="F"\; filenames="HDA0000379792080000021.png,HDA0000379792080000022.png"\; state="\{\{state\}\}">F</figure-callout>}}_2}...\stackrel{\&OverBar;}{F_n|}=|F|-\underset{i=1}{\overset{n}{\mathrm{\&Sigma;}}}|F_i|+\underset{1\&le;i<j\&le;n}{\mathrm{\&Sigma;}}|F_i{F}_j|-\underset{1\&le;i<j<k\&le;m}{\mathrm{\&Sigma;}}|F_i{F}_j{F}_k|+\&CenterDot;\&CenterDot;\&CenterDot;\\ +{(-1)}^n(F_1{\mathrm{<figure-callout\; id="2"\; label="F"\; filenames="HDA0000379792080000021.png,HDA0000379792080000022.png"\; state="\{\{state\}\}">F</figure-callout>}}_2...F_n)\end{array}$

Therefore, can obtain the formula of deriving as follows:

$\begin{array}{c}|\stackrel{\&OverBar;}{A_1}\stackrel{\&OverBar;}{{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA0000379792080000021.png,HDA0000379792080000022.png"\; state="\{\{state\}\}">A</figure-callout>}}_2}...\stackrel{\&OverBar;}{A_{x-m}}|=\left|E\right|-\underset{i=1}{\overset{X-m}{\mathrm{\&Sigma;}}}\left|A_i\right|+\underset{1\&le;i<j\&le;(x-m)}{\mathrm{\&Sigma;}}\left|A_i{A}_j\right|-\underset{1\&le;i<j<k\&le;(x-m)}{\mathrm{\&Sigma;}}\left|A_i{A}_j{A}_k\right|+\&CenterDot;\&CenterDot;\&CenterDot;\\ +{(-1)}^{(x-m)}(A_1{\mathrm{<figure-callout\; id="2"\; label="A"\; filenames="HDA0000379792080000021.png,HDA0000379792080000022.png"\; state="\{\{state\}\}">A</figure-callout>}}_2...A_{x-m})\\ =\left|E\right|+{\mathrm{\&Sigma;}}_{i=1}^{x-m}{(-1)}^i{C}_{x-m}^i{R}_i\\ ={\left(C_x^m\right)}^{k-1}+{\mathrm{\&Sigma;}}_{i=1}^{x-m}{(-1)}^i{C}_{x-m}^i{\left(C_{x-i}^m\right)}^{k-1}\end{array}$

Formula 2: the derivation of probability-distribution function that completes the required cycle-index of the file of downloading whole M size is as follows:

$\begin{array}{c}P(T=t)=P(T=t|S_{t-1}=M-1)*P(S_{t-1}=M-1)+\&CenterDot;\&CenterDot;\&CenterDot;\\ +P(T=t|S_{t-1}=M-\mathrm{km})*P(S_{t-1}=M-\mathrm{km})\\ =P(X_t=1|S_{t-1}=M-1)*P(S_{t-1}=M-1)+\&CenterDot;\&CenterDot;\&CenterDot;\\ +p(X_t=\mathrm{km}|S_{t-1}=M-\mathrm{km})*P(S_{t-1}=M-\mathrm{km})\\ ={\mathrm{\&Sigma;}}_{i=m}^{\min (s,\mathrm{km})}P(X_t=i|S_{t-1}=M-i)*P(S_{t-1}=M-i)\end{array}$

The span of T numerical value be to download required minimal circulation number of times,

numerical value be to download required maximum cycle-index.

Wherein, P (S _t-1=s) can be calculated by following iterative formula

$P(S_{t-1}=s)=\left\{\begin{array}{cc}\underset{i=m}{\overset{\min (s,\mathrm{km})}{\mathrm{\&Sigma;}}}P(X_t=i|S_{t-1}=M-i)*P(S_{t-1}=M-i)& s\&GreaterEqual;m\\ 0& 0<s<m\end{array}\right.$

Initial formula is:

$\begin{array}{c}P(S_1=s)\\ =\left\{\begin{array}{cc}P(X_1=s|{\mathrm{<figure-callout\; id="0"\; label="S"\; filenames="HDA0000379792080000022.png"\; state="\{\{state\}\}">S</figure-callout>}}_0=0)=\frac{C_m^s{C}_s^m[{\left(C_s^m\right)}^{k-1}+{\mathrm{\&Sigma;}}_{i=1}^{s-m}{(-1)}^i{C}_{s-m}^i{\left(C_{s-i}^m\right)}^{k-1}}{{\left(C_M^m\right)}^k}& s\&GreaterEqual;\mathrm{<figure-callout\; id="0"\; label="m"\; filenames="HDA0000379792080000022.png"\; state="\{\{state\}\}">m</figure-callout>}\\ 0& 0<s<m\end{array}\right.\end{array}$

The Performance Evaluation result:

This part to the above mode based on feedback cooperate the theoretical analysis result downloaded carried out checking and and the result that draws of real process contrast, with matlab by the simulation result drafting pattern.

We have write mean value and probability distribution probability function thereof that vehicle that the C++ program calculated respectively theory analysis is downloaded the required cycle-index of specific large small documents; Use the C++ program out abstract to this cooperation downloading mode simultaneously, simulated the cycle-index of downloading in the real scene, below actual scene emulation in each figure be 300 the data obtaineds of operation, gained average and theory analysis value are compared to verify to our theoretical analysis result.Simultaneously and under the grouping selection mode based on random repetition between vehicle the cooperation method for down loading contrasted, result shows that the method for this programme has shortened the download time of file greatly.

Fig. 2 shows that fixed vehicle counts k=6, and when vehicle is downloaded grouping number m=3 through an AP, the variation of file size M is on completing the situation that affects of downloading required cycle-index.The curve that between the vehicle of selecting to divide into groups based on feedback system of the theory analysis of this programme and actual emulation, the cooperation method for down loading forms as seen from the figure is substantially identical, has proved the correctness of theory analysis.Give under equal conditions between the vehicle based on random selection packet mode the cooperation method for down loading with the change curve of file size simultaneously, can find out that between the vehicle based on feedback system, the download time that has greatly shortened file is downloaded in cooperation, and along with file increase effect is all the more obvious.

Fig. 3 explanation is at M=40, under the m=3 equal conditions, along with the increase of vehicle number completes file, downloads required expectation cycle-index and reduces gradually the time that completes download and reduce gradually.Also seeing and reach 30 when above when vehicle number clearly in figure, complete and download required time and descend and substantially stop, and therefore in order to shorten download time, increases vehicle number the upper limit is arranged, and the effect of its generation is just not obvious to surpass some.

Set M=40 in Fig. 4, during m*k=12 along with the increase of k, the required cycle-index that the completes download situation that gradually changes.M*k=12 shows that between V2V stage vehicle, shared total number packets is identical, and the situation in figure is known, now increases vehicle number k and can shorten download time.The enlightenment of therefore giving us is when consideration increases vehicle number and increases the vehicle download capabilities, in order to shorten the shared vehicle number of preferential increase of download time, can reach better effect.

Beneficial effect

1) the present invention is directed to the defect that existing vehicle data downloading mode and technology exist: the contradiction between coverage, downloading data rate and flow rate problem three, cooperation data download method between the vehicle based on feedback system has been proposed, can significantly shorten the single unit vehicle data download time, simultaneously by V2V(car and car) communicate by letter and share mutual data, not only shortened time V2V communication simultaneously and do not produced cost, also made the rate of downloading data greatly reduce.

2) than cooperation data between the vehicle of random fashion, download and 3G network, between the vehicle based on feedback, the advantage that combines the two is downloaded in cooperation, utilize the ubiquitous property of 3G network as control channel, the information of just the vehicle request being downloaded before entering the roadside access point is uploaded to network, after vehicle enters the access point coverage, utilize the High Data Rate of roadside access point AP transmission, the down-transmitting data content.

3) cooperative, the single vehicle of comparing 3G network is the downloading data content separately, and the method that the present invention proposes adopts between vehicle to cooperate with each other shares the content of downloading separately, and more shared the vehicle of cooperation inner capacities be just larger, and concerning single unit vehicle, income is larger.

The accompanying drawing explanation

Fig. 1: system model.

The impact of the variation of Fig. 2: M on the cycle-index that completes download.

Fig. 3: the impact of vehicle number on cycle-index.

The impact of vehicle number k on cycle-index when Fig. 4: m*k is definite value.

Embodiment

Due to the relatively discrete distribution of the distribution of roadside download point, cause the vehicle a very long time not in the coverage of download point, vehicle is always intermittent with being connected of download point, and interval is relatively very long, not yet in effect using.Consider that the file that single unit vehicle is downloaded does not separately separately have cooperation each other simultaneously, this programme has proposed the mode that cooperation is downloaded, take full advantage of vehicle not in interval time of roadside download point coverage, after leaving between the area of coverage of download point, the V2V(car undertaken between vehicle by DSRC (short-range communication protocol between vehicle) is communicated by letter with car) mutually share downloading contents separately, reach the purpose that doulbe-sides' victory is downloaded in cooperation.In order to realize that V2V communication shares downloading contents separately fully, we adopt the adjacent vehicle in a kind of geographical position form vehicle " bunch " mode.Vehicle " bunch " in vehicle can share downloading data each other fully.For random downloading mode, between vehicle and download point, do not link up, the content of download may be the data content part that vehicle has contained simultaneously, and this is undoubtedly the waste to bandwidth and downloading machine meeting.System model of the present invention adopts the downloading mode based on feedback not waste each downloading machine meeting.Concrete execution mode is to utilize the wide spreadability of 3G channel as control channel, upload the existing data division of vehicle to the access point closed on, like this when vehicle enters the roadside download point, access point can only pass down to vehicle the data division that vehicle does not also receive targetedly, avoid redundancy and repetition, utilized the wide spreadability of 3G and the advantage of the High Data Rate that the roadside access point is downloaded simultaneously.For realizing above purpose, this programme also needs to set up an AP(and downloads access point) server, preserve the positional information of all roadsides access point, like this after vehicle utilizes the 3G channel to upload receiving unit data and vehicle current location (by the GPS positioner is installed onboard), server can contrast current vehicle location and AP position, find out the position that the vehicle direct of travel is about to the next AP of arrival, now can notify this access point ready, the content server of wanting downloading contents with corresponding vehicle is connected, obtain in advance downloading contents, download access point when vehicle enters this AP() coverage after, pass down its not data of receiving unit to vehicle.

As shown in Figure 1, between a complete vehicle, cooperation download flow process means complete system model as follows:

The vehicle that travels on road stream by geographical position many adjacent cars can mutually form one by one " bunch ", claim each " bunch " accordingly " bunch head " vehicle be header, " bunch tail " vehicle is trailer.Consider such scene: in certain bunch, have k car (red vehicle in figure) to want to download the file that same size is M grouping simultaneously.The fileinfo of this k car wish download is aggregated into " bunch head " vehicle, by this vehicle, information is uploaded to (for example, being reported by the mobile network), then by the webserver, is sent in the content server of storage this document.Suppose that the webserver of processing this document download request can obtain geographical location information and the direction of motion (vehicle is installed the GPS positioner) of this bunch, and this webserver is preserved the exact position of all roadsides access point, thereby can judge this " bunch " access point that be about to arrive, then from content server, the download file content is kept in the middle of this server, after bunch entering the coverage of this access point, with bunch in k car communicate by letter and download this document information.

Might as well suppose that any grouping number homogeneous phase of downloading in the V2I stage in k car is all m(m<M), m is less than the file total packet and counts M.Obviously, from M grouping How to choose to go out m grouping download most important to the performance of whole file download system to the system of selection of vehicle.This programme consider to be used the selection mode based on feedback: at the V2I of each car in the stage, vehicle first is uploaded to roadside download point AP by the file grouping catalogue received, and access point AP in roadside just selects at random m and out downloads to vehicle from the unreceived grouping of this vehicle like this.

After a bunch tail vehicle also leaves the overlay area of roadside access point AP, all vehicles in bunch enter the V2V stage.In this stage, all vehicle sharing download contents in bunch.Therefore, after waiting V2V to complete, all k car all will contain identical content (all vehicle downloading contents sums).When vehicle enters next download point, this k in bunch repeats above-mentioned downloading process until download complete file.

Claims (1)

1. cooperation download scenarios between the vehicle based on feedback system, is characterized in that, the general data in the car networking are downloaded and mainly are comprised of two stages:

Vehicle-to-Infrastructure (V2I) vehicle is connected stage of communication with the roadside access point: in this stage, when vehicle enters in the coverage of roadside access point, vehicle is from access point AP(Access Point) obtain data;

Vehicle-to-Vehicle(V2V) car and inter-vehicle communication stage: after vehicle leaves the coverage of roadside access point, mutual exchange message between vehicle; When this stage finishes, all nodes have all obtained identical data;

Cooperation download be a vehicle " bunch " in cooperation download rather than regardless of spaces of vehicles how far away several workshops can; Wherein vehicle " bunch " formation mechanism and maintenance mechanism and bunch in the workshop V2V mode reference of communicating by letter; That to adopt mode based on feedback be that vehicle was first uploaded accepted partial document AP and only broadcasted to vehicle receiving portion not accordingly before download file from roadside access point AP download data files to the V2I process;

Compare, the grouping selection mode based on random be simple repetition pass down at random part to vehicle from whole file; Grouping selection mode based on feedback, need vehicle first to upload download section sectional lists before download, and download point just only passes down vehicle does not like this have the partial data received; Suppose that the file grouping (size of file is weighed with how many grouping Packets) that vehicle receives after V2I can be in the fully shared exchange of V2V stage; For privacy and the security consideration of vehicle downloading contents, the roadside access point AP download file of once only communicating by letter with a car, other vehicle can not obtain this document information (being different from the broadcast distribution data);

One bunch through a download point, and in bunch, vehicle is downloaded corresponding document (V2I), in leaving after this download point bunch, between vehicle, by the V2V(car, with car, communicates by letter) fully shared downloading contents separately be one " circulation " (V2I+V2V); Therefore downloading a large file just needs just can complete through a plurality of circulations.

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