CN103052093A - Link stability assessment method in VANET (Vehicular Ad-Hoc Network) - Google Patents

Abstract

The invention relates to a link stability evaluation method in VANET, which decomposes the velocity vector between two vehicles into a direction V _x parallel to the road and a direction V _y perpendicular to the road, and according to the current distance d between the two vehicles and the vehicle node The maximum wireless transmission distance R and the current speed V _x estimate the duration Δt of the link between the two vehicles, and then calculate the reliability of the estimated duration. It can be used to select the next hop transmission node of the data packet according to the stability of the expected link, improve the robustness of the link, improve the throughput of the entire path and reduce the transmission delay of the data packet.

Description

A Method for Evaluating Link Stability in VANET

technical field

The invention relates to the technical field of wireless network communication, in particular to a link stability evaluation method under the VANET environment.

Background technique

In VANET (VehicularAd-hocNETwork, vehicle self-organizing network), the nodes move fast, the network topology changes quickly, and the link is easy to break. Therefore, we hope to find a method that can calculate the connection time of the link and the reliability of the connection time. method. This method can be applied to route selection to improve the performance of the whole path.

Routing selection is a key factor in wireless network communication, which determines the throughput rate and transmission delay of the network, and directly affects the overall performance of the network. This is covered in almost all technical literature and research papers on routing protocols for wireless networks. Related literature: LEE J W, CHUN C L, SHIH PT, "A hybrid traffic geographic routing with cooperative traffic information collection scheme in VANET", 201113th International Conference on Advanced Communication Technology (ICACT), Feb2011, pp.1496-150 Harten Hstein andLaberteanx K P． "A tutorial survey on vehicular Ad hoc networks[J]". IEEE Communications Magazine, vol.46, no.6, pp.164-171, 2008.

With the increasingly prominent traffic problems, the transformation of traffic management concepts, the improvement of traffic policies, and the application of many technologies such as the use of intelligent transportation to improve traffic conditions, intelligent transportation technology has become one of the hot research areas in the forefront of science and technology. As an important part of the intelligent transportation system, in recent years, the vehicular ad hoc network (VANET) has been widely concerned by scholars all over the world. specific applications in. Through vehicle-to-vehicle (V2V), vehicle-to-roadside infrastructure (V2I) direct communication or multi-hop communication, a self-organizing, dynamic, and distributed control network is constructed.

Relevant literature: Chen Lijia, Jiang Hao, Wu Jing, etc. "Research on Transmission Control of Vehicle Ad Hoc Networks", Journal of Software, 2007, 18(6): 1477-1490. Wantanee Viriyasitavat, Fan Bai, Ozan K.Tonguz, "Dynamics of Network Connectivity in Urban Vehicular Networks”, IEEE Journal on Selected Areas in Communications, vol.29, no.3, Mar.2011. Yuchen Wu, Yanmin Zhu, Bo Li, “An Infrastructure-Assisted Routing in Vehicular Networks”, 2012 IEFO IN EE Proceedings , Mar2012, pp.1485-1493. Nianbo Liu, Ming Liu, Guihai Chen, Jiannong Cao, "The Sharing at Roadside: Vehicular Content Distribution Using Parked Vehicles", 2012 Proceeding IEEE INFCOM, Mar.2012, pp.2641-2645.

At present, domestic and foreign scholars have done a lot of research on routing selection in VANET, and proposed many solutions to solve this problem, such as active routing protocol (optimized link state routing, OLSR), geographic location routing protocol (geography source routing, GSR). ), and other routing protocols HTGR (hybrid traffic geographic routing), GPSR (greedy perimeter stateless routing), LAR (1ocaton-aided routing), RTRP (road and traffic-aware routing protocol1). However, relatively little research has been done on VANET topological connectivity, a prerequisite for vehicular networks to provide reliable services.

Related literature: B.Karp and H.Kung, "GPSR: Greedy perimeter stateless routing for wireless networks", Proc.6th Annu.Int.MobiCom, Aug.2000, pp.2315-2319.M.Jerbi, S.M.Senouci, T. Rasheed, Y. Ghamri-Doudane, "Towards Efficient Geographic Routing in Urban Vehicular Networks", IEEE Transaction onvehicular Technology, vol.58, no.9, pp.5048-5059, Nov.2009. Xiaojun Feng, Jin Zhang, and Qian Zhang , "Trajectory-Assisted Delay-Bounded Routing with Moving Receivers in Vehicular Ad-hoc Networks", Proceedings of the Nineteenth International Workshop on Quality of Service, ACM, Jun.2011, pp.1-3. Ruobing Jiang, Yanmin Zhu, "Coverage-aware Geocast Routing in Urban Vehicular Networks",2012IEEE26th InternationalParallel and Distributed Processing Symposium Workshops&PhD Forum(IPDPSW),May2012,pp.2522-2525.

Contents of the invention

In view of the above problems, the present invention proposes a method for evaluating link stability in a VANET environment.

A method for evaluating link stability in a VANET provided by the invention comprises the following steps:

1. Decompose the vehicle node speed into the direction parallel to the road and the direction perpendicular to the road;

2. Suppose the functional relationship between vehicle nodes and time t is,

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; ix</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; iy</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\end{array}\right.$

Among them, v _ix is the amount of vehicle speed decomposed in the horizontal direction to the road, v _iy is the amount of vehicle speed decomposed in the vertical direction to the road, θ _i is the angle between the vehicle speed and the horizontal direction of the road; x _i (0) represents the vehicle The position of the vehicle in the horizontal direction of the road at time _{t 0} , y _i (0) represents the position of the vehicle in the vertical direction of the road at time t ₀ ; x _i (t) represents the position of the vehicle in the horizontal direction of the road at time t, y _i (t ) represents the position of the vehicle in the vertical direction of the road at time t;

3. Carry out the calculation of the link duration, including calculating the link duration T=(R-d)/v according to the relative velocity v between the two vehicle nodes and the relative displacement d, where R is the maximum wireless transmission distance of the vehicle node;

4. The definition s(L _i ,t ₀ ,Δt) indicates the probability that L _i is still valid at time t ₀ +Δt under the condition that link L _i exists at time t ₀ , and the stability of path P S(P, t ₀ ,Δt) represents the probability that the transmission path P established at time t ₀ is still connected at time t ₀ +Δt;

5. Define the probability density function and cumulative function of the interval between two vehicles in the vehicle ad hoc network as f _g (x)=λe ^-λx and F _g (x)=1-e ^-λx , where λ=σ/Ev , σ is the arrival rate of vehicles passing through a certain section on the street, and Ev is the average speed of all vehicles;

6. The probability P that there are n vehicle nodes in the road section of length L obeys the Poisson distribution, the expression is as follows,

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; !</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}}$

Wherein, X is the number of vehicle nodes, and P(X=n) refers to the probability that the number of vehicle nodes is n;

7. The relationship between the probability P and the distance d of at least one vehicle node in the transmission range of a vehicle node is as follows,

P=1-P(X=0)

=1-e ^-λd

d₀是两车之间t₀时刻的距离。8. Obtain the stability of the link L _i formed by two vehicle nodes as s(L _i ,t ₀ ,Δt)=P ₀ , where

d ₀ is the distance between the two vehicles at time t ₀ .

The vehicle-mounted network uses vehicles on the road as transmission nodes to transmit data packets and select the next hop node to realize self-organization and self-management. Due to the fast movement of vehicle nodes, and the movement is affected by road constraints, the formed link is easy to break, which greatly affects the transmission of data packets in the vehicle network. Link stability is an important factor to measure the robustness and reliability of routing. The invention proposes a calculation method of the link stability based on the idea of probability under the VANET environment. It can be used to select the next hop transmission node of the data packet according to the stability of the expected link, improve the robustness of the link, improve the throughput of the entire path and reduce the transmission delay of the data packet.

Description of drawings

Fig. 1 is the schematic diagram of vehicle movement of the embodiment of the present invention;

Fig. 2 is a schematic diagram of data transfer according to an embodiment of the present invention.

Detailed ways

The technical scheme of the present invention can adopt computer software process to realize automatic operation during concrete implementation. The technical solution of the present invention will be described in detail below in conjunction with the drawings and embodiments.

Embodiments provide a link stability evaluation method in VANET comprising the following steps:

1. Decompose the vehicle node speed into the horizontal direction of the road and the vertical direction of the road as shown in Figure 1. In Figure 1, d is the distance between two vehicles, v _i is the speed of the vehicle, θ represents the angle between the relative speed of the two vehicles and the horizontal direction of the road, v _ix is the amount of vehicle speed decomposed in the horizontal direction of the road, v _iy is the amount of vehicle speed decomposed in the direction perpendicular to the road.

2. Let the functional relationship between vehicle nodes and time t be:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; ix</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; iy</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\end{array}\right.$

v _ix is the amount of vehicle speed decomposed in the horizontal direction to the road, v _iy is the amount of vehicle speed decomposed in the vertical direction to the road, θ _i is the angle between the vehicle speed and the horizontal direction of the road. x _i (0) represents the position of the vehicle in the horizontal direction of the road at time t ₀ , and y _i (0) represents the position of the vehicle in the vertical direction of the road at time t ₀ . x _i (t) represents the position of the vehicle in the horizontal direction of the road at time t, and y _i (t) represents the position of the vehicle in the vertical direction of the road at time t.

3. Calculate the link duration. It includes calculating the link duration T=(R-d)/v according to the relative velocity v and relative displacement d between the two vehicle nodes, where R is the maximum wireless transmission distance of the vehicle nodes.

4. _Define the stability of link L _i s(L _i ,t ₀ ,Δt) to indicate the probability that L _i is still valid at time t ₀ +Δt under the condition that link L i exists at time t ₀ . The stability S(P,t ₀ ,Δt) of the path P represents the probability that the transmission path P established at the time t ₀ is still connected at the time t ₀ +Δt.

5. Define the probability density function and cumulative function of the interval between any two vehicles in the vehicle ad hoc network as f _g (x)=λe ^-λx and F _g (x)=1-e ^-λx , where λ=σ/ Ev,σ is the arrival rate of vehicles passing through a certain section on the street, that is, how many vehicles pass through this section per minute. Ev is the total average speed of all vehicles. x is the distance between the two cars.

6. The probability P that there are n vehicle nodes in a section of length L obeys the Poisson distribution, the expression is as follows:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; !</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}}$

Among them, X is the number of vehicle nodes, and P(X=n) refers to the probability that the number of vehicle nodes is n.

7. The relationship between the probability P and the distance that there is at least one vehicle node within the transmission range of a vehicle node is as follows:

P=1-P(X=0)

=1-e ^-λd

d is the distance between two vehicle nodes, that is, the distance and relative displacement between two vehicles.

d₀是两车之间t₀时刻的距离。8. Obtain the stability of the link formed by two vehicle nodes as s(L _i ,t ₀ ,Δt)=P ₀ , where

d ₀ is the distance between the two vehicles at time t ₀ .

The present invention mainly obtains the following two-step results:

(1) Prediction of path duration.

(2) Calculation of link stability.

In step (1), the embodiment decomposes the velocity vector between two vehicles into a direction V _x parallel to the road and a direction V _y perpendicular to the road. In this way, according to the current distance d between the two vehicles, the maximum wireless transmission distance R of the vehicle node and the current speed V _x , we can estimate the duration Δt of the link between the two vehicles. Step (2) Calculate the reliability of the duration estimated in step (1).

The implementation processes of (1) and (2) in the embodiments are described in detail below:

(1) Prediction of path duration

Assuming that the distance between two vehicle nodes is d, the strength of the signal is only related to the transmission distance of the signal. Therefore, at a certain moment, the link remains connected only if the distance d between two nodes is smaller than the maximum wireless transmission distance R between nodes. Assuming that at a certain moment, nodes i and j can communicate directly, and the position of node i is known to be (xi _, y _i ), the velocity v _i forms an angle θ _i with the direction of the line connecting the two vehicles,

Then the displacement calculation formula of vehicle node i is:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; ix</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; iy</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\end{array}\right.$

In the same way, the position (x _j , y _j ) and velocity v _j of vehicle node j can be defined, and the relative displacement d of the two vehicles can be calculated, then the time for the two nodes to maintain the link is T=(Rd)/v, where v is the relative velocity between the two nodes. Extending the two-point model to the entire path yields the connectivity time of the path.

(2) Calculation of link stability

For the stability of link L _i , define s(L _i ,t ₀ ,Δt) to represent the probability that L _i is still valid at t ₀ +Δt under the condition that link L _i exists at time t ₀ . The stability S(P,t ₀ ,Δt) of the path P represents the probability that the transmission path P established at the time t ₀ is still connected at the time t ₀ +Δt.

When the vehicles are freely driving on the road, the separation distance between vehicles obeys the exponential distribution. Therefore, the distance d between the two vehicles can be expressed as follows:

f(d)=λe ^-λd

Among them, λ is the density of traffic flow.

It is assumed that R is the maximum wireless transmission range of the vehicle node. Then the probability FR,λ) of the connection between two vehicles can be calculated by the following formula:

$\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; 0</span>}}{\overset{\mathrm{<span\; class="notranslate">\; R</span>}}{<span\; class="notranslate">\; \&Integral;</span>}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; dd</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;R</span>}}$

Assuming that there are m vehicles in a one-way street with length L, there are m-1 workshop segments between these m vehicles, then if the link composed of these m vehicles is connected, then the The distance between every two vehicles should be smaller than the maximum transmission range R between the two vehicles. The probability expression of the connection of the link is as follows, where m can be approximated by rounding L/R.

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&Pi;</span>}}}\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;R</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; m</span>}}$

In the vehicle-mounted ad hoc network, the embodiment defines the probability density function and cumulative function of the interval between two vehicles as f _g (x)=λe ^-λx and F _g (x)=1-e ^-λx , where λ=σ /Ev,σ is the arrival rate of vehicles passing through a certain section on the street, that is, how many vehicles pass through this section per minute. Ev is the average speed of the vehicle. The probability P of n nodes in the road section (0, L] obeys the Poisson distribution. The expression is as follows:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; !</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}}$

In Fig. 2, dist(n ₁ , n ₂ ) is the distance between two vehicle nodes n ₁ and n ₂ , and R is the maximum wireless transmission range of the vehicle nodes. The solid circle in Fig. 2 is a circle whose center is the point phop and R is the radius. The node n ₁ is the node closest to the destination node and the node farthest from the phop within the transmission range of the node phop.

Assuming that n ₁ and n ₂ cannot communicate directly, if n ₁ and n ₂ can be connected, there must be at least one relay node n _x between n ₁ and n ₂ . According to the Poisson distribution, the probability P that there is at least one node between n ₁ and n ₂ is:

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span>}$

Where n _x is a node between n ₁ and n ₂ , then the probability P ₀ of connectivity between n ₁ and n _x has the following relationship with the distance d(n ₁ ,n _x ):

$\mathrm{<span\; class="notranslate">\; d</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ></span>\frac{\mathrm{<span\; class="notranslate">\; ln</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>}{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}$

v是车辆相对速度。所以，链路在t₀+Δt时刻仍然有效的概率也为P₀，即链路L_i的稳定度s(L_i,t₀,Δt)＝P₀。link connection time

v is the relative velocity of the vehicle. Therefore, the probability that the link is still valid at time t ₀ +Δt is also P ₀ , that is, the stability of link L _i s(L _i ,t ₀ ,Δt)=P ₀ .

The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which the present invention belongs can make various modifications or supplements to the described specific embodiments or adopt similar methods to replace them, but they will not deviate from the spirit of the present invention or go beyond the definition of the appended claims range.

Claims (1)

1. a method for evaluating link stability in VANET, is characterized in that, comprises the following steps: 1. Decompose the vehicle node speed into the direction parallel to the road and the direction perpendicular to the road; 2. Suppose the functional relationship between vehicle nodes and time t is, $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; ix</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; cos</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\\ {\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; v</span>}}_{\mathrm{<span\; class="notranslate">\; iy</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\mathrm{<span\; class="notranslate">\; t</span>}\end{array}\right.$ Among them, v _ix is the amount of vehicle speed decomposed in the horizontal direction to the road, v _iy is the amount of vehicle speed decomposed in the vertical direction to the road, θ _i is the angle between the vehicle speed and the horizontal direction of the road; x _i (0) represents the vehicle The position of the vehicle in the horizontal direction of the road at time _{t 0} , y _i (0) represents the position of the vehicle in the vertical direction of the road at time t ₀ ; x _i (t) represents the position of the vehicle in the horizontal direction of the road at time t, y _i (t ) represents the position of the vehicle in the vertical direction of the road at time t; 3. Carry out the calculation of the link duration, including calculating the link duration T=(R-d)/v according to the relative velocity v between the two vehicle nodes and the relative displacement d, where R is the maximum wireless transmission distance of the vehicle node; 4. The definition s(L _i ,t ₀ ,Δt) indicates the probability that L _i is still valid at time t ₀ +Δt under the condition that link L _i exists at time t ₀ , and the stability of path P S(P, t ₀ ,Δt) represents the probability that the transmission path P established at time t ₀ is still connected at time t ₀ +Δt; 5. Define the probability density function and cumulative function of the interval between two vehicles in the vehicle ad hoc network as f _g (x)=λe ^-λx and F _g (x)=1-e ^-λx , where λ=σ/Ev , σ is the arrival rate of vehicles passing through a certain section on the street, and Ev is the average speed of all vehicles; 6. The probability P that there are n vehicle nodes in the road section of length L obeys the Poisson distribution, the expression is as follows, $\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; x</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; no</span>}}}{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; !</span>}{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&lambda;L</span>}}$ Wherein, X is the number of vehicle nodes, and P(X=n) refers to the probability that the number of vehicle nodes is n; 7. The relationship between the probability P and the distance d of at least one vehicle node in the transmission range of a vehicle node is as follows, P=1-P(X=0) =1-e ^-λd 8. Obtain the stability of the link L _i formed by two vehicle nodes as s(L _i ,t ₀ ,Δt)=P ₀ , where

d ₀ is the distance between the two vehicles at time t ₀ .

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