CN103281742A - Vehicular Ad hoc network routing method based on autonomously acquired road information - Google Patents

Abstract

The invention discloses a vehicular Ad hoc network routing method based on autonomously acquired road information. The method is characterized in that when a packet forwarding direction and a vehicle driving direction are different, on the basis of the valid time of links and the distance from a predicted position of a vehicle to a target intersection, forwarding priority values of nodes are calculated, and therefore the valid time of packet transmission lines is long, and the stability of the links is improved during a routing process, and moreover, a node forwarding packet near a destination node is selected by combining the directions, and therefore the transmission time of the packet and the condition that the packet is transmitted repeatedly on the same road segment are reduced, and the time delay of packet transmission is greatly reduced. According to the method disclosed by the invention, road density information can be acquired more accurately, and moreover, routing nodes which are more efficient are selected by utilizing real-time road information more effectively. As a piecewise autonomous road density estimation method and a packet forwarding scheme of integrating a direction parameter and a position parameter are adopted by the method, the goal that the vehicle autonomously acquires the real-time road density information is achieved.

Description

Based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information

Technical field

The present invention relates to network route technology field, particularly a kind of based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information.

Background technology

At present, the vehicle communication network is a research topic that receives much concern, the concern of the development of cordless communication network, the demand of safe driving and automaker and public transport management mechanism impels intelligent transportation (ITS, Intelligent Transportation System) and vehicle-mounted self-organizing network (Vehicular Ad Hoc Networks, the VANET) formation of concept.Because the VANET network topology change is frequent, the urban environment lower node moves and is subjected to road layout restriction and marginal obstruction that stopping of wireless signal made that its Routing Protocol design is more complicated than mobile ad-hoc network, therefore, how in conjunction with the characteristics of VANET under the urban environment design stable, Routing Protocol is an emphasis of present VANET research efficiently.

Because node motion is fast among the VANET, network topology change is frequent, vehicle node frequently passes in and out and vehicle node a large amount of gatherings may take place, autgmentability is required characteristics such as height because of emergency, greatly reduce the performance based on the Routing Protocol of topology, and the line of reasoning partly of position-based information is fit to vehicle-mounted self-organizing network by scheme more because not needing to safeguard overall routing iinformation.In addition, the motion track of urban environment VANET network node is subjected to the restriction of road layout, track of vehicle has certain rules, add the popular gradually of GPS navigation system and electronic chart, vehicle node can conveniently obtain information such as vehicle location and speed, can predict the effective time of link between the position of vehicle node and vehicle node by these information, thereby can assist vehicle planning routed path, improve efficient and the reliability of transmitted in packets, this also impels location-based geographical route more extensively to be suitable for.

At present, the research direction of location-based geographical routing plan is mainly:

1) carries out routing optimality in conjunction with the road real-time road condition information.The Information Selection node density height such as node location, speed, direction and road node density that utilize mobile unit to obtain, the path that link stability is high.

2) move according to vehicle and be subjected to road limits, the foreseeable characteristics of motion track adopt the higher link of method foundation stability of moving projection to carry out transmitted in packets, can improve the reliability of transmitted in packets like this, reduce the number of times that rebulids route and reduced the time and the bandwidth cost that therefore bring.

RBVT-R(reactive mode of Road-based using Vehicular Traffic Routing) be by the collection of roadside transducer and by network infrastructure distribution density information, suppose before grouping is transmitted, to select all big highway section to transmit grouping than the traffic density in other adjacent highway sections, improve the connectivity in selected path like this, reduced the probability that the local maximum event of route takes place.This scheme adopts improved geographical routing mechanism to transmit grouping between adjacent node, when node is sent out in each next redirect of searching, seeks the nearest node in the next crossing of distance, and this is different from traditional searching node nearest apart from destination node.

This method gathers and issues roading density information by the roadside transducer, need to drop into a large amount of roadside infrastructure like this, realizes the cost height, and actual realization faces a lot of difficulties.In addition, the improved geographical routing mechanism that adopts when this method is transmitted grouping is that a kind of covert greediness is transmitted, though it is relatively big that the highway section of selecting in the discovery procedure of crossing all is traffic density, reduced the probability that the local maximum event of route takes place like this, but this greedy the forwarding do not consider that vehicle heading and grouping are to the relation between the direction of destination node forwarding, can cause being grouped in the transmission repeatedly on the same road segment like this, increase the transmitted in packets time-delay.

LOUVRE(Landmark Overlays for Urban Vehicular Routing Enviroments) be that a kind of formula terrestrial reference of answering earlier covers routing solution, crossroad on the road is made as terrestrial reference, vehicular traffic current density between two terrestrial references of distributed estimation, node can be approximately the traffic density of its present place road by the quantity that records the vehicle in the jumping scope that it meets on this road exactly, by periodic beacon message roading density information is broadcasted away then.

The roading density estimating and measuring method that adopts, be vehicle with the gross vehicle that runs on its place road and the roading density calculated with the total length of road, this is an assembly average, it does not consider randomness and the inhomogeneities that vehicle distributes in urban road, there is very big error between the roading density of the roading density of feasible estimation and reality, thereby reduced the stability of routed path.And, but because vehicle will be broadcasted away the traffic density message of its place road of own estimation, obtain the density message of other roads simultaneously, need periodic broadcast beacon messages, this is under the situation that number of nodes increases, a large amount of beacon messages can cause network congestion, can clash when utilizing channel based on competition mechanism, and then produce bigger transmission delay.In addition, if on the sparse road of node, the multi-hop breakpoint occurs, make roading density information propagate and do not go out, just make the estimation of roading density produce error, may cause the mistake of Route Selection, reduce the efficient of transmitted in packets.And the present invention can solve top problem well.

Summary of the invention

The object of the invention is based on the routing plan based on the geographical position of road real time information, proposes a kind of based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information, to improve efficient and the reliability of transmitted in packets in the vehicle-mounted self-organizing network of urban environment.This method adopts the grouping of the autonomous roading density evaluation method of a kind of formula piecemeal and comprehensive direction and two parameters of predicted position to transmit scheme, thereby realize that vehicle independently obtains the real-time density information of road, reduce the realization cost, thereby but improved the level of enforcement of scheme.

The technical solution adopted for the present invention to solve the technical problems is: the present invention proposes a kind of based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information, this method is when different grouping routing direction and vehicle heading, based on the far and near degree between link effective time and vehicle predicted position and purpose crossing, the forwarding priority valve of computing node, thereby the effective time of transmitted in packets link is long in the realization route, improve the stability of link, and the near node of bonding position chosen distance destination node is transmitted grouping, reduce the transmission packets number of times and repeated the transmission situation in same highway section, thereby reduced the time-delay of transmitted in packets greatly.The method for routing that the present invention proposes can obtain roading density information more accurately, and the more efficient use real-time road condition information is selected routing node more efficiently, thereby the payment rate of transmitted in packets and end-to-end transmission average delay have all obtained tangible improvement.

Method flow:

The present invention proposes a kind of based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information, and it comprises as follows:

One, the autonomous evaluation method of formula roading density piecemeal

In urban environment, because the restriction of road layout, the asynchronism(-nization) at the region difference of road (city center and suburb) and place whether (working peak period) makes that the distribution of vehicle is very inhomogeneous on the road, and traffic density is very big to the stability influence in the path of route foundation, and then can influence success rate and the efficient of transmitted in packets, it is very important therefore will to obtain in real time accurate roading density.

Utilize vehicle neighbor node quantity among the present invention, consider the distance between sending node and the forward node simultaneously, highway section density in two internodal links and the node one jumping scope is estimated, like this along with the foundation of routed path, density to road is estimated piecemeal, can obtain the traffic density of vehicle place road so more accurately for long road, more close to the practical significance of roading density.

Sending node is estimated the road vehicle density in sending node and highway section, via node to be selected place according to the quantity of the neighbor node of the distance of it and each via node to be selected and sending node and via node, and the concrete computing formula of the road vehicle density of the link of node and composition is as follows:

${\mathrm{\ρ}}_{\mathrm{ij}}=\frac{N_{\mathrm{ij}}}{d_{\mathrm{ij}}+2R}---\left(1\right)$

N in the formula _Ij=N _i∪ N _jBe two node n _iAnd n _jThe sum of neighbor node, this value is not the simple addition of the neighbor node number of two nodes, because there is common neighbor node in their neighbor nodes each other, N between them _IjCommon neighbor node is only added once, as shown in Figure 1; d _IjBe node n _iAnd n _jBetween distance, R is the wireless transmission radius; 2R is comprehensive propagation because of wireless signal, so its neighbor node distribution also is omnibearing.

Two, path discovery inundation mechanism is improved

Can't obtain in the routing plan of real time position of destination node at vehicle, the discovery procedure of route realizes by improved inundation mechanism: when a node receives a new route requests grouping RREQ(Rout-Request), it can directly not broadcasted this grouping again but a period of time is carried in this grouping, distance between length during this period of time and present node and the sending node is inversely proportional to, the calculating of stand-by period such as formula (2); In case the stand-by period finishes, if present node does not listen to this RREQ grouping by other are transmitted again apart from the farther node nearer apart from destination node just of sending node on the same highway section, it just can broadcast this RREQ grouping again, otherwise present node is just abandoned this RREQ grouping, and this process proceeds to the RREQ grouping repeatedly and arrives destination node; Such broadcast mechanism makes the preferential broadcast request of the node nearest apart from destination node divide into groups.

$\mathrm{WT}\left(d\right)=-\frac{\mathrm{MaxWT}}{\mathrm{Range}}\·\hat{d}+\mathrm{MaxWT}---\left(2\right)$

D is the distance between RREQ receiving node and the sending node, and MaxWT is maximum latency, and Range is radio transmission range.

But this inundation mechanism has only been considered the distance of next-hop node apart from destination node, and still a kind of greedy forwarding strategy is not in essence considered the traffic density in highway section, selected node place therefore to have the frequent local maximum problem that takes place.At this problem, the present invention proposes a kind of improvement project in conjunction with roading density and improve whole routing plan.

Obtain chain direction density between sending node and the node to be selected according to formula (1), by GPS and neighbor list information obtain between sending node and the node to be selected apart from d _Ij, traffic density is more big on the road, and is more short apart from the stand-by period of the node to be selected of sending node (more near apart from destination node) more far away.The wait function calculation formula that can obtain two parameters according to many Standard Map function is as the formula (3):

$\mathrm{WT}(d_{\mathrm{ij}},{\mathrm{\ρ}}_{\mathrm{ij}})=K{d}_{\mathrm{ij}}^{{\mathrm{\α}}_1}{\mathrm{\ρ}}_{\mathrm{ij}}^{{\mathrm{\α}}_2}+{\mathrm{WT}}_{\max }---\left(3\right)$

In the formula,

d _MaxBe the ultimate range between sending node and the node to be selected, value is the wireless transmission radius R; ρ _MaxIt is the maximum of sending node and internodal road vehicle density to be selected.WT _MaxIt is maximum latency; α ₁, α ₂Be respectively d _IjAnd ρ _IjWeighted factor, the weighted value of parameter can influence parameter to the influence degree of selection course.For α ₂, because the urban environment traffic density changes greatly, in the sparse place of vehicle, in order to set up stable path, should mainly consider the traffic density value, will make the variation of traffic density big to the influence degree of waiting for function, α among the present invention ₁, α ₂Value less than 1, therefore this moment α ₂Can be suitable reduce so just can increase functional value along with density changes and the trend of variation; And in the intensive place of vehicle, having abundant node to transmit grouping, can suitably increase α this moment ₂Value reducing the influence degree of traffic density, therefore order

Like this can be along with the increase α of density ₂Value is corresponding to be increased, according to the adaptive adjustment of actual vehicle density α ₂Value.

Three, transmit scheme based on the grouping of direction and prediction

In the route finding process, we have taken into full account the traffic density on the highway section when selecting the crossing sequence, what choose all is the higher highway section of traffic density, no longer considers this scalar of traffic density when selecting next-hop node in the geographical repeating process of grouping and only considers following factor: the relation of the direction that effective duration of link, the vehicle direction of travelling at the later position of certain hour and vehicle and grouping are transmitted.

(1) effective duration of link

Effective duration of link has influence on the stability of the link of transmitting packet, and be in order to be chosen in the closer forward node in distance objective crossing behind the certain hour to the prediction of vehicle location, can reduce the situation that repeats to transmit on the same highway section that is grouped in like this, can simplify routing procedure, reduce the time delay of transmitted in packets.

And between the vehicle there be relative direction relation: travel in the same way (the speed of a motor vehicle size according to the front and back vehicle of wherein travelling in the same way also be divided into catch up with and surpass and fall behind two kinds of situations respectively shown in Fig. 2,3), travel in opposite directions as Fig. 4, trailing moverment such as Fig. 5 predict effective duration of link between the vehicle by following formula (4) (5) (6) (7) these situations respectively.

1, in the same way

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R+d_{\mathrm{AB}}}{V_A-V_B}---\left(4\right)$

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R-d_{\mathrm{AB}}}{V_B-V_A}---\left(5\right)$

2, travel in opposite directions

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R+d_{\mathrm{AB}}}{V_A+V_B}---\left(6\right)$

3, trailing moverment

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R-d_{\mathrm{AB}}}{V_A+V_B}---\left(7\right)$

Above-mentioned formula can be seen, link between Yun Hang the vehicle node is the longest effective time in the same way, therefore in routing procedure, should at first consider to select more stable path like this selecting next redirect to send out node in the vehicle in the same way, improve the performance of Routing Protocol.

(2) relation of vehicle heading and grouping routing direction

The travel direction of vehicle and the routing direction of grouping different can have influence on effective duration of link and node to the target crossing apart from these two parameters to selecting the influence degree of next-hop node, therefore when selecting next-hop node, to adopt different choice criteria according to different directions.

Relation between the travel direction of vehicle and the routing direction of grouping is divided into: in the same way, and oppositely.In Fig. 6 (a), the direction at the crossing that the next one that the routing direction of grouping points to for forward node A will arrive, shown in dotted arrow among the figure, the travel direction of vehicle is for realizing shown in the arrow among the figure.As can be seen from the figure vehicle B is identical with the grouping routing direction, and vehicle C is opposite with the grouping routing direction, and the next-hop node choice criteria under the both of these case is as follows:

1, in the same way

Calculate effective duration of link according to link computing formula effective time in the same way, and calculate the distance that node to be selected arrives next crossing, select weights in conjunction with these two calculation of parameter nodes then, because Yun Hang the internodal link duration is long in the same way, so when calculate selecting weights, want emphasis consider node to be selected arrive next crossing apart from this parameter, preferentially choose the nearest node in target crossing thereby be implemented under the more stable situation of assurance link.

2, reverse

Inversion condition generally occurs in the last node repeating process does not have equidirectional node to transmit, just selected the node that travels in opposite directions, such as among Fig. 6 (a) if do not have B node or B node not in transmission range, grouping is carried node A and can be selected the C node to jump as next.Than only transmitting to node in the same way, just take to carry the reparation strategy of buffer memory when not having node in the same way, adopt among the present invention reverse node as via node continue transmission grouping forward than vehicle carry packet awaits in the same way vehicle to transmit the time-delay of generation little.

The node that carries grouping in the time of oppositely is the wide crossing, shown in Fig. 6 (b), in order to reduce the transmitted in packets time-delay that such situation produces, the node that carries the grouping backward going will be transmitted to the node identical with the routing direction that divides into groups to grouping as possible, just move closer to the next node of transmitting the crossing, and these nodes and the movement direction of nodes that carries grouping are opposite, in this case, compare that situation is much smaller in the same way effective duration of the link between the node.Therefore in order to guarantee the stability of transmitted in packets link, carry in these and grouping and select the relative node than length of link duration in the opposite node of movement direction of nodes, take the distance between they and next crossing simultaneously into consideration.

(3) transmitting priority valve calculates

Suppose that source node is S, forward node to be selected is A.

Calculate lifetime according to different situations by different computing formula of effective duration of link _SACalculate in the following way the position of Δ t time posterior nodal point:

The position of supposing node A is (x _A, y _A), its speed is (v _Ax, v _Ay), the position behind the Δ t is (x _A', y _A').

$\left\{\begin{array}{c}{x_A}^{\′}=x_A+v_{\mathrm{Ax}}\·\mathrm{\Δt}\\ {y_A}^{\′}=y_A+v_{\mathrm{Ay}}\·\mathrm{\Δt}\end{array}\right.---\left(8\right)$

Obtain the next crossing I that will arrive by map _iThe position

Node A behind Δ t with crossing I _iBetween distance

For:

$D_{A^{\′}{I}_i}=\sqrt{{(x_{A^{\′}}-x_{I_i})}^2+{(y_{A^{\′}}-y_{I_i})}^2}---\left(9\right)$

The direction calculating priority valve S of ordering according to A _A:

$S_A=\mathrm{\α}\×\frac{{\mathrm{lifetime}}_{\mathrm{SA}}}{\mathrm{MaxLifetime}}+\mathrm{\β}\×(1-D_p)---\left(10\right)$

MaxLifetime is the higher limit of link time setting in the literary composition, is used for retraining under the situation that vehicle travels in the same way and speed is very close infinitely-great situation of link time;

Represented node A distance objective crossing I to be selected _iFar and near degree, D _pMore little represent A behind elapsed time Δ t apart from crossing I _iMore near; α, β are effective duration of link and to the weighted value of crossing distance, alpha+beta=1, their value size has represented the influence degree of parameter to result of calculation, and according to the difference that concerns between the movement direction of nodes of introducing previously and the grouping routing direction, the value of α, β is also different.

Beneficial effect of the present invention:

1, the invention enables vehicle when route data, can obtain more accurately roading density value, in conjunction with the improved inundation mechanism of node density, can be according to the size of the different adaptive change traffic density of the road vehicle density weighted factor in waiting for function, select the intensive road of node to transmit grouping in the route discovery procedure thereby be implemented in, improve the successful transfer probability of grouping.

2, the present invention proposes a node and transmit the priority valve computing formula, make in the grouping repeating process, according to different grouping routing direction and vehicle heading, based on the far and near degree between link effective time and vehicle predicted position and purpose crossing, the forwarding priority valve of computing node, thereby select best forward node, the reliability that improves transmitted in packets has reduced according to positional information and has been grouped in the number of times that the probability that repeats to transmit in same highway section and path failure are rebuild, thereby has reduced packet transfer delay.

Description of drawings

Fig. 1 is node n of the present invention _iAnd n _jBetween distance, node distributes and the transmission range schematic diagram.

Fig. 2 is the relative position relation figure that vehicle A of the present invention catches up with and surpasses vehicle B.

Fig. 3 is that vehicle B of the present invention is gradually away from the relative position relation figure of vehicle A.

Fig. 4 is the relative position relation figure that AB of the present invention travels in opposite directions.

Fig. 5 is the relative position relation figure of AB trailing moverment of the present invention.

Fig. 6 is vehicle heading of the present invention and the identical and opposite situation map of grouping routing direction.

Fig. 7 is VanetMoBiSim simulating scenes figure of the present invention.

Fig. 8 is the grouping payment rate schematic diagram of different node of the present invention when counting.

Grouping payment rate schematic diagram when Fig. 9 is different CBR of the present invention.

Grouping payment rate schematic diagram when Figure 10 is different vehicle speed of the present invention.

Figure 11 is the end-to-end average delay schematic diagram of different node of the present invention when counting.

End-to-end average delay schematic diagram when Figure 12 is different CBR of the present invention.

End-to-end average delay schematic diagram when Figure 13 is different vehicle speed of the present invention.

Embodiment

Below by in conjunction with Figure of description, further specify technical scheme of the present invention.

We utilize simulating scenes shown in Figure 7 to carry out simulating, verifying, with improvement method for routing of the present invention with carry out the performance simulation contrast aspect two of the end-to-end mean transit delays of grouping payment rate and grouping.Next respectively in different vehicle node quantity, carry out emulation under different grouping transmission rate and the running velocity situation, can exert an influence because the randomness of node distribution randomness and motion can exert an influence to simulation result to simulation result with randomness motion because node is that distribute, so the present invention reduces randomness by the results averaged of emulation repeatedly influence so the present invention of simulation result is reduced randomness to the influence of simulation result by the results averaged with 5 emulation.

Before emulation begins, use VanetMobisim earlier ^[6]Generate the trail file of the scene of different node densities, then these trail files are imported to and carry out emulation acquisition data among the NS, adopt different node densities to be because vehicle skewness and have randomness under the urban environment, by the analysis of multiple density emulated data, can embody the quality of protocol capabilities more comprehensively.

The track of mobile node adopts the intelligent driving person model (IDM-IM, Intelligent Driver Model with Intersection Management) that has the crossing management among the VanetMobiSim.Simulating scenes adopts the simulating area of 2000m * 2000m, general according near the main roads layout the Xin Jie Kou, Nanjing, 32 sections highway sections are arranged, road junction all is provided with traffic lights, and all roads all are two-way 4 tracks, randomness for vehicle node distribution on the emulation road, VanetMoBiSim produces node at random at crossing, a plurality of road, and the maximum speed that the actual state of set basis road is travelled the road general vehicle is limited in the 15-55km/h scope, and simulation parameter sees Table 1 in detail.

Parameter	Parameter value
		Simulating area	2000m×2000m
The vehicle node number	100～300
		Radio transmission range	250m
Simulation time	500s
		Car speed	15-55km/h
CBR source number	15
		CBR	1～5packets/s
Mac-layer protocol	IEEE802.11DCF
		Number of track-lines	Two-way 2 tracks
Mobility model	IDM-IM
		The intersection number	17

Data packet size

512bytes

Table 1 simulation parameter

Fig. 8 is to be 1.5packets/s in the grouping transmission rate, and car speed is 45km/h, and different number of nodes are to the influence of grouping payment rate.Fig. 9 is to be 220 at the node number, and the speed of a motor vehicle is 45km/h, the variation tendency of the grouping payment rate of two agreements under the different grouping transmission rate situation.Figure 10 is to be 220 at the node number, and the grouping transmission rate is 1.5packets/s, the variation tendency of the grouping payment rate of two agreements under the different vehicle speed condition.

As can be seen from the figure, the grouping payment rate of two schemes all increases and increases along with the quantity of vehicle node, because they combine the Real-time Road information of vehicles, road vehicle density increases, the connectivity of node improves on the road, thereby has improved the success rate that grouping is transmitted.And along with the increase of CBR, the grouping payment rate of each agreement descends to some extent, and this is to cause blocking up of transmission path to make packet loss rise to some extent because wait to transmit increasing of grouping.In addition, if certain path failure will cause more packet transmission failure.Along with the raising of the speed of a motor vehicle, grouping payment rate reduces by increasing to become fast gradually, and this is because when the speed of a motor vehicle is very slow, traffic density is very big, this moment, a large amount of transmitted in packets caused the node processing burden to increase, and efficient reduces, and appearance transmission is simultaneously blocked up and collision phenomenon causes dividing into groups, and the payment rate reduces; Along with the increase jam situation of the speed of a motor vehicle is eased, but when the speed of a motor vehicle becomes bigger, vehicle location changes fast, causes the stability of link to reduce, and the node sparse connectivity that worsens link that becomes makes the decline of grouping payment rate.

Because IRBVT-R has adopted prediction that the path effectively holds time and the strategy of intermediate node route real-time update, the degree of stability of the feasible route of setting up is higher, the probability of path failure reduces, path change is littler to the influence of transmitted in packets, thereby has realized better grouping payment rate with respect to RBVT-R.

The grouping transmission rate is 1.5packets/s, different vehicle number of nodes when the speed of a motor vehicle is 45km/h, the node number is 220, different CBR when the speed of a motor vehicle is 45km/h, the grouping transmission rate is that 1.5packets/s, node number are that the influence of terminal delay time is arrived respectively as Figure 11 in 220 different speed of a motor vehicle opposite ends, shown in 12,13.

As seen from Figure 11, along with the increase of node number, the transmitted in packets time-delay reduces gradually, when this is sparse because of node, the node connectivity is poor on the road, can cause can not find the node that grouping is sent out in next redirect, make that grouping is temporarily carried, will produce bigger time delay like this, along with increasing of node number, the road connectivity improves, and makes that waiting to transmit grouping obtains in time transmitting reliably, and time delay reduces accordingly.Figure 12 then be presented at CBR smaller the time time-delay of transmitted in packets be to be tending towards metastable, the increase time-delay along with CBR then significantly increases, this is because when the number of packet of transmission was smaller, node can carry out processing forward to it fast, transmission fast in the network that nothing is blocked up; The phenomenon with network congestion will occur waiting in line after the limit that exceeds the transmission of node processing and network, thereby cause efficiency of transmission to descend, packet transfer delay increases.Can see among Figure 13, end-to-end delay was very little and very stable when the speed of a motor vehicle was very slow, along with the increase of speed presents ascendant trend gradually, this is because traffic density is big and stable when speed is very slow, at this moment set up the path than faster and also the path very stable, the time delay of transmitted in packets is naturally just low like this.And this moment, than RBVT-R, IRBVT-R adopts improves mechanism has increased amount of calculation on the contrary and causes packet transfer delay slightly to increase.When the speed of a motor vehicle is very big, because reducing, the stability of the sparse and link of node make the path of transmitted in packets frequent variations occur, cause the route frequent updating or even rediscover, so just caused the increase of delaying time.

IRBVT-R adopts based on upgrade in time the mechanism of route of the inundation mechanism of roading density and intermediate node, and the path connectivity height, the good stability that make foundation have reduced the number of times that rebulids the path; And choose predicted position and transmit grouping near the intermediate node at purpose crossing more, accelerated the transmission packets process, reduced the situation that same highway section repeats to transmit, these measures have reduced packet transfer delay.

Claims (3)

1. one kind based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information, it is characterized in that, comprising:

The sending node of this method is estimated the road vehicle density in sending node and highway section, via node to be selected place according to the quantity of the neighbor node of the distance of it and each via node to be selected and sending node and via node, and the concrete computing formula of the road vehicle density of the link of node and composition is as follows:

${\mathrm{\ρ}}_{\mathrm{ij}}=\frac{N_{\mathrm{ij}}}{d_{\mathrm{ij}}+2R}---\left(1\right)$

N in the formula _Ij=N _i∪ N _jBe two node n _iAnd n _jThe sum of neighbor node, this value is not the simple addition of the neighbor node number of two nodes, because there is common neighbor node in their neighbor nodes each other, N between them _IjCommon neighbor node is only added once d _IjBe node n _iAnd n _jBetween distance, R is the wireless transmission radius; 2R is comprehensive propagation because of wireless signal, so its neighbor node distribution also is omnibearing.

2. a kind ofly it is characterized in that based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information according to claim 1 is described, comprising:

Can't obtain in the routing plan of real time position of destination node at vehicle, the discovery procedure of route realizes by improved inundation mechanism: when a node receives a new route requests grouping RREQ(Rout-Request), it can directly not broadcasted this grouping again but a period of time is carried in this grouping, distance between length during this period of time and present node and the sending node is inversely proportional to, the calculating of stand-by period such as formula (2); In case the stand-by period finishes, if present node does not listen to this RREQ grouping by other are transmitted again apart from the farther node nearer apart from destination node just of sending node on the same highway section, it just can broadcast this RREQ grouping again, otherwise present node is just abandoned this RREQ grouping, and this process proceeds to the RREQ grouping repeatedly and arrives destination node; Such broadcast mechanism makes the preferential broadcast request of the node nearest apart from destination node divide into groups;

$\mathrm{WT}\left(d\right)=-\frac{\mathrm{MaxWT}}{\mathrm{Range}}\·\hat{d}+\mathrm{MaxWT}---\left(2\right)$

D is the distance between RREQ receiving node and the sending node, and MaxWT is maximum latency, and Range is radio transmission range;

A kind of improvement project in conjunction with roading density is improved whole routing plan:

Obtain chain direction density between sending node and the node to be selected according to formula (1), by GPS and neighbor list information obtain between sending node and the node to be selected apart from d _Ij, traffic density is more big on the road, and is more short apart from the stand-by period of the node to be selected of sending node (more near apart from destination node) more far away; The wait function calculation formula that can obtain two parameters according to many Standard Map function is as the formula (3):

$\mathrm{WT}(d_{\mathrm{ij}},{\mathrm{\ρ}}_{\mathrm{ij}})=K{d}_{\mathrm{ij}}^{{\mathrm{\α}}_1}{\mathrm{\ρ}}_{\mathrm{ij}}^{{\mathrm{\α}}_2}+{\mathrm{WT}}_{\max }---\left(3\right)$

In the formula,

d _MaxBe the ultimate range between sending node and the node to be selected, value is the wireless transmission radius R; ρ _MaxIt is the maximum of sending node and internodal road vehicle density to be selected; WT _MaxIt is maximum latency; α ₁, α ₂Be respectively d _IjAnd ρ _IjWeighted factor, the weighted value of parameter can influence parameter to the influence degree of selection course; For α ₂, because the urban environment traffic density changes greatly, in the sparse place of vehicle, in order to set up stable path, should mainly consider the traffic density value, will make the variation of traffic density big to the influence degree of waiting for function, α among the present invention ₁, α ₂Value less than 1, therefore this moment α ₂Can be suitable reduce so just can increase functional value along with density changes and the trend of variation; And in the intensive place of vehicle, having abundant node to transmit grouping, can suitably increase α this moment ₂Value reducing the influence degree of traffic density, therefore order

Like this can be along with the increase α of density ₂Value is corresponding to be increased, according to the adaptive adjustment of actual vehicle density α ₂Value.

3. according to claim 1 a kind ofly it is characterized in that based on independently obtaining the vehicle-mounted method for self-organizing network routing of road information, comprising:

(1) effective duration of link;

Effective duration of link has influence on the stability of the link of transmitting packet, and be in order to be chosen in the closer forward node in distance objective crossing behind the certain hour to the prediction of vehicle location, can reduce the situation that repeats to transmit on the same highway section that is grouped in like this, can simplify routing procedure, reduce the time delay of transmitted in packets;

And between the vehicle there be relative direction relation: travel in the same way, travel in opposite directions, trailing moverment, respectively these situations are predicted effective duration of link between the vehicle by following formula (4) (5) (6) (7);

1, travels in the same way

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R+d_{\mathrm{AB}}}{V_A-V_B}---\left(4\right)$

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R-d_{\mathrm{AB}}}{V_B-V_A}---\left(5\right)$

2, travel in opposite directions

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R+d_{\mathrm{AB}}}{V_A+V_B}---\left(6\right)$

3, trailing moverment

${\mathrm{lifetime}}_{\mathrm{AB}}=\frac{R-d_{\mathrm{AB}}}{V_A+V_B}---\left(7\right)$

Above-mentioned formula can see that the link between Yun Hang the vehicle node is the longest effective time in the same way, is therefore selecting next redirect to send out node in the vehicle in the same way in routing procedure;

(2) relation of vehicle heading and grouping routing direction;

The travel direction of vehicle and the routing direction of grouping different can have influence on effective duration of link and node to the target crossing apart from these two parameters to selecting the influence degree of next-hop node, therefore when selecting next-hop node, to adopt different choice criteria according to different directions;

Relation between the travel direction of vehicle and the routing direction of grouping is divided into: in the same way, oppositely, the next-hop node choice criteria under the both of these case is as follows:

1, in the same way

Calculate effective duration of link according to link computing formula effective time in the same way, and calculate the distance that node to be selected arrives next crossing, select weights in conjunction with these two calculation of parameter nodes then;

2, reverse

Inversion condition generally occurs in the last node repeating process does not have equidirectional node to transmit, just selected the node that travels in opposite directions, adopt reverse node as via node continue transmission grouping forward than vehicle carry packet awaits in the same way vehicle to transmit the time-delay of generation little;

(3) transmitting priority valve calculates

Suppose that source node is S, forward node to be selected is A;

Calculate lifetime according to different situations by different computing formula of effective duration of link _SA, calculate in the following way the position of Δ t time posterior nodal point:

The position of supposing node A is (x _A, y _A), its speed is (v _Ax, v _Ay), the position behind the Δ t is (x _A', y _A');

$\left\{\begin{array}{c}{x_A}^{\′}=x_A+v_{\mathrm{Ax}}\·\mathrm{\Δt}\\ {y_A}^{\′}=y_A+v_{\mathrm{Ay}}\·\mathrm{\Δt}\end{array}\right.---\left(8\right)$

Obtain the next crossing I that will arrive by map _iThe position

Node A behind Δ t with crossing I _iBetween distance For:

$D_{A^{\′}{I}_i}=\sqrt{{(x_{A^{\′}}-x_{I_i})}^2+{(y_{A^{\′}}-y_{I_i})}^2}---\left(9\right)$

The direction calculating priority valve S of ordering according to A _A:

$S_A=\mathrm{\α}\×\frac{{\mathrm{lifetime}}_{\mathrm{SA}}}{\mathrm{MaxLifetime}}+\mathrm{\β}\×(1-D_p)---\left(10\right)$

MaxLifetime is the higher limit of link time setting in the literary composition, is used for retraining under the situation that vehicle travels in the same way and speed is very close infinitely-great situation of link time;

Represented node A distance objective crossing I to be selected _iFar and near degree, D _pMore little represent A behind elapsed time Δ t apart from crossing I _iMore near; α, β are effective duration of link and to the weighted value of crossing distance, alpha+beta=1, their value size has represented the influence degree of parameter to result of calculation, and according to the difference that concerns between the above-mentioned direction of motion and the grouping routing direction, the value of α, β is also different.

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