CN105792278A - VANET channel congestion joint control method for safety index - Google Patents

Abstract

The invention discloses a VANET channel congestion joint control method for a safety index, and the method comprises the following steps: S1, building a double-Beacon transmission model; S2, building a traffic safety model, and calculating a close range and a guard range; S3, determining transmission power according to an electromagnetic determinacy propagation model; S4, calculating a transmission rate according to a Markov model of a VANET control channel; S5, determining a final transmission parameter according to a conversion algorithm. The method combines a microscopic vehicle moving model with a communication model. The microscopic vehicle moving model is used for the research of the driving behavior of a single vehicle and the mutual impact between vehicles. From the aspect of the vehicle safety, the moving model and the communication model are combined together, thereby reducing the channel load to the maximum degree under the condition of guaranteeing the vehicle safety and achieving the purpose of channel congestion control.

Description

A kind of VANET channel congestion combination control method towards safety index

Technical field

The present invention relates to car connected network communication and field of traffic.Especially towards the VANET channel congestion combination control method of safety index.

Background technology

World Health Organization (WHO) (WorldHealthOrganization, WHO) point out in the end of the year 2014, the traffic safety accident in the whole world in 2014, have resulted in nearly 1,300,000 people dead, nearly 50,000,000 people are injured, and simultaneously road safety accident becomes China and causes casualties the first place of reason.In recent years, automobile wireless self-organizing network (VehicularAd-hocNETwork, VANET) became the focus of car networking arenas research, and most important of which is exactly the application relevant to vehicle safety.VANET can give the ability of communication between vehicle so that vehicle can find in time and evade potential threat.

In 1999, the wireless frequency spectrum (5.850-5.925GHz frequency band) of the 75MHz that FCC's distribution is special is to DSRC (DedicatedShortRangeCommunication, DSRC), this is also referred to as IEEE802.11p/WAVE standard.Regulation according to FCC, these frequency ranges are divided into seven channels, the bandwidth of each channel occupancy 10MHz, control channel including one and stay a service channel.The function wherein controlling channel is the periodic safety message (PSM) for broadcasting van, comprises such as the information such as position, speed, and accident security message (EDSM), as brought to a halt, provides communication infrastructure for security cooperation between vehicle.In VANET, the communication between vehicle and vehicle is based on DSRC standard development.

For now, VANET distance is put on the schedule of business and government and implements on a large scale to have got long long way to go, one of its maximum challenge faced is how to solve the channel congestion problem under high concentration environment, and this will cause communication delay, follow the trail of precise decreasing or even security incident.Wherein causing that the topmost reason of traffic congestion is periodically broadcast safe message (PSM), this will take substantial amounts of bandwidth when high vehicle density.

In recent years, many researchs all begin to focus on the congestion problems in VANET, wherein the solution of main flow is to improve the performance of network by controlling to optimize the scope (range) of the speed (rate) or broadcast that generate message, also have and reach this purpose by optimizing other parameters, such as competition window, but limited efficiency.The existing research controlled about channel congestion is substantially all and concentrates on the communications field, and and do not take into account the particularity of traffic environment, such as high speed, topology polytropy and demand for security etc..Chinese car networking conference in 2015 proposes the viewpoint of " design of car networking related protocol should return essence, returns to application and comes up with safety ".

Summary of the invention

It is an object of the invention to provide a kind of can effective link road congestion problem ensure the VANET channel congestion combination control method towards safety index of vehicle safety.

This invention address that the technical scheme that prior art problem adopts: a kind of VANET channel congestion combination control method towards safety index, comprise the following steps:

S1, the double; two Beacon transmission pattern of foundation: setting up double; two Beacon transmission pattern according to wagon flow demand for security characteristic, the Beacon message that vehicle sends includes tracking Beacon information and finds Beacon information, every T_adaptTime flows through topology according to microcosmic traffic at that time and calculates the transmit power and speed [P that obtain following the trail of Beacon information and discovery Beacon information at that time_{crct_t}, P_{crct_a}, R_{crct_t}, R_{crct_a}], wherein, P_{crct_t}For following the trail of the transmit power of Beacon information, P_{crct_a}For finding the transmit power of Beacon information；R_{crct_t}For following the trail of the speed of Beacon information, R_{crct_a}For finding the speed of Beacon information；The parameter adjusting double; two Beacon transmission pattern makes it meet safety requirements model；

S2, set up traffic safety model, calculate tight confines and fence coverage: utilize the Beacon message constructing adjacent vehicle state table received from surrounding vehicles, and utilization state table calculates the parameter relevant to safety range: traffic safety model is made up of relation between vehicle and demand for security model two parts, the tight confines RNG of traffic safety model_nearWith fence coverage RNG_warnComputational methods as follows, wherein A for send vehicle:

RNG_near(A)=max{DST_close(A),DST_rough(A)}(1)

RNG_warn(A)=s^*(υ_a,Δυ_a)(2)

Wherein the computational methods of continuous item are as follows:

DST_close(A)=max{PICK (FN (A), A, N₀),PICK(BN(A),A,N₀)}(3)

${\mathrm{DST}}_{rough}\left(A\right)=N_0\·(\frac{36}{161}\·|{\stackrel{r}{V}}_A|+1)\·{\mathrm{Len}}_A---\left(4\right)$

$s^{*}({\mathrm{\υ}}_a,{\mathrm{\Δ\υ}}_a)=s_{0,a}+s_{1,a}\·\sqrt{\frac{{\mathrm{\υ}}_a}{{\mathrm{\υ}}_{0,a}}}+T_a\·{\mathrm{\υ}}_a+\frac{{\mathrm{\υ}}_a{\mathrm{\Δ\υ}}_a}{2\sqrt{a_a{b}_a}}---\left(5\right)$

${\mathrm{\υ}}_a={\mathrm{\υ}}_{\max },{\mathrm{\Δ\υ}}_a={\mathrm{\υ}}_a-\left|{\stackrel{\→}{V}}_A\right|---\left(6\right)$

Wherein N₀For the constant that is closely related, general value is 3；Len_ARepresent the length of A car；Represent the speed of A car；T_aRepresent the response time；a_aRepresent the forward acceleration that vehicle is maximum；b_aRepresent maximum backward acceleration；υ_maxRepresent the maximal rate that current road segment allows；Function PICK (S, A, N) represents and according to the distance of A, the vehicle in set S is ranked up, and exports the distance of the car little with A distance N, if number of vehicles is less than N, output-1 in set S；FN (A) be all directions identical and be positioned at A front side neighboring trace vehicle composition set；BN (A) be all directions identical and be positioned at A front side neighboring trace vehicle composition set；

Transmit power determined by S3, foundation electromagnetic wave definitiveness propagation model；The described transmit power following the trail of Beacon information and discovery Beacon information is tried to achieve according to electromagnetic wave definitiveness propagation model:

P_track=PL_LOS(RNG_near)+P_min(7)

P_aware=PL_LOS(RNG_warn)+P_min(8)

Wherein P_minIt is the lowest power that can recognise that, PL_LOSIt is the energy loss in electromagnetic wave propagation process, has following relation with transmitting node and receiving node spacing:

${\mathrm{PL}}_{los}\left(d\&lsqb;m\&rsqb;\right)=\left\{\begin{array}{c}22.7{\log }_{10}\left(d\&lsqb;m\&rsqb;\right)+41+20{\log }_{10}\left(f\&lsqb;GHz\&rsqb;/5\right)\\ \begin{array}{cc}if& d<R_{bp}\end{array}\\ 40{\log }_{10}\left(d\&lsqb;m\&rsqb;\right)+41-17.3{\log }_{10}\left(R_{bp}\right)+20{\log }_{10}\left(f\&lsqb;GHz\&rsqb;/5\right)\\ \begin{array}{cc}if& d\&GreaterEqual;R_{bp}\end{array}\end{array}\right.---\left(9\right)$

$R_{bp}=4\frac{(h_A-1)(h_B-1)}{\mathrm{\&lambda;}}---\left(10\right)$

Wherein, d is the air line distance between sender and recipient, h_AAnd h_BBeing send the antenna height with recipient respectively, λ is electromagnetic wavelength, and f is electromagnetic frequency；Formula (9) and (10) are substituted into respectively in formula (7) and (8), then can obtain respectively and follow the trail of Beacon and find the transmit power of Beacon, wherein tight confines RNG_nearWith fence coverage RNG_warnObtained by step S2.

S4, foundation VANET control the Markov model of channel and calculate transmission rate；Described VANET controls the Markov model of channel and meets following state transition equation:

$\mathrm{\&tau;}\left(p\right)=\frac{2{(1-p)}^2}{2-3p+{\mathrm{pW}}_s}---\left(11\right)$

${\mathrm{\&tau;}}^{*}\left(p\right)=1-{(1-p)}^{\frac{1}{N}}---\left(12\right)$

Wherein, τ (p) represents the probability successfully obtaining channel resource, the probability that namely single is successfully transmitted, W_sRepresenting the size of competition window, N is the interstitial content that communication range covers present node, is similar to the interstitial content in present node communication range, tight confines RNG_nearWith fence coverage RNG_warnInterior number of vehicles substitutes in equation (11) and (12), and the single obtained is successfully transmitted probability and corresponds to p respectively_trackAnd p_aware。

S5, foundation conversion algorithm determine final transmission parameter；The coordination system of the double; two Beacon sending mode of foundation, the power of the message transmission that before coordination, step obtains and speed, obtain final transmission parameter:

$R_{equal}=R_{aware}\frac{p_{aware}}{p_{track}}---\left(19\right)$

The primary condition of conversion is to find that the range of transmission of Beacon can cover the range of transmission following the trail of Beacon, i.e. P_trackLess than P_aware, to consider the conversion border issue that different wagon flow environment brings simultaneously, propose to send parameter conversion algorithm accordingly and be corrected sending parameter, to obtain final transmission parameter [P_{crct_t}, P_{crct_a}, R_{crct_t}, R_{crct_a}]。

Safety requirements model in step S1 is:

A. for being in tight confines RNG_nearInterior vehicle, at τ_trackThe probability of the Beacon message being at least successfully received a vehicle transmission in the time reaches p_{t_desire}

B. for being in fence coverage RNG_warnOutside vehicle, at entry time τ_awareInside at least it is successfully received a fence coverage RNG_warnWithin the probability of Beacon message that sends of vehicle reach p_{a_desire}。

Between described vehicle, relation includes correlation between the accumulation rate and speed, neighboring trace relation, forward direction relation, backward relation, same forwards neighboring trace vehicle relation, in the same direction front vehicle relation and same rearward neighboring trace vehicle relation.

Described correlation between the accumulation rate and speed is: symbol A ≡ B represents vehicle B and vehicle A in the same direction, when A and B meetsTime, it is in the same direction, whereinIt is the speed of A,It is the speed of B；

Neighboring trace relation is: it is adjacent with track, vehicle A place or in identical track that symbol A ≌ B represents track, vehicle B place, when A and B meets | L_B-L_A| during < 2, the two is neighboring trace relation, wherein L_AIt is ID, the L in track, A car place_BIt is the ID in track, B car place；

Forward direction relation is: symbol B ← A represents the B front at A, when A and B meetsTime, vehicle B and A is forward direction relation, whereinIt is the displacement of A,It it is the displacement of B；

Backward relation is: symbol B → A represents the B rear at A, when A and B meetsTime, vehicle B and A is backward relation；

With forwards neighboring trace vehicle relation it is: identical and the neighboring trace vehicle composition that is positioned at A front side the relation of set FN (A) and A in all directions is:

Front vehicle relation in the same direction: identical and the neighboring trace vehicle composition that is positioned at A front side the relation of set B (A) and A in all directions is:

With rearward neighboring trace vehicle relation it is: identical and the neighboring trace vehicle composition that is positioned at A front side the relation of set BN (A) and A in all directions is:

Step S4 specifically includes step:

S41, initialization: according to adjacent vehicle state table Tab, calculate current time t_cIn table, all vehicles are gathered with the distance of Current vehicle AWhereinIt is at t_riThe displacement of the vehicle i that moment A obtains from Beacon message and speed,It it is the displacement of A car；

S42, set of computations D_ATwo subset V_nearAnd V_warn, wherein V_nearMiddle vehicle distances D_Ai(i ∈ Tab) is less than RNG_near, V_warnMiddle vehicle distances D_Ai(i ∈ Tab) is less than RNG_warn, set sizes is designated as N respectively_nearAnd N_warn；

S43, by N_nearAnd N_warnSubstitute in state transition equation (11) and (12), obtain now sending and follow the trail of Beacon and find that Beacon successfully obtains the probability respectively p sending window_trackAnd p_aware；

The successful acquisition of S44, foundation safety index and two kinds of Beacon sends the probability of window, calculates the transmission rate R of two kinds of Beacon message_trackAnd R_aware。

Described safety requirements model meets the following conditions:

$p_{t\_desire}\&le;1-{(1-p_{track})}^{i_{track}}---\left(13\right)$

$p_{a\_desire}\&le;1-{(1-p_{aware})}^{N_{aware}\&CenterDot;t_{aware}}---\left(14\right)$

Wherein, N_awareFor being positioned at vehicle A rear and being in RNG_warnNumber of vehicles in scope, t_trackRepresent that vehicle is at τ_trackThe number of times of Beacon message, t is sent in time_awareFor at τ_awareThe number of times finding Beacon is sent in time:

$R_{track}=\frac{i_{track}}{{\mathrm{\&tau;}}_{track}}---\left(15\right)$

$R_{aware}=\frac{t_{aware}}{{\mathrm{\&tau;}}_{aware}}---\left(16\right).$

Described step S44) specifically include step:

S441, according to formula (13) and formula (15), obtain following the trail of the lower limit of the transmission rate of Beacon:

$R_{track}\&GreaterEqual;\frac{1}{{\mathrm{\&tau;}}_{track}}\&CenterDot;\frac{ln(1-p_{t\_desire})}{ln(1-p_{track})}---\left(17\right)$

By safety index p_{t_desire}And τ_trackAnd follow the trail of the Probability p of Beacon acquisition transmission window_trackBring formula (17) into and obtain rate limit as the transmission rate following the trail of Beacon；

S442、VB_warnRepresent and be positioned at vehicle A rear and be in RNG_warnThe set of the vehicle composition in scope,Filter out set VB_warn；

S443, according to formula (14) and formula (16), obtain finding the lower limit of the transmission rate of Beacon:

$R_{aware}\&GreaterEqual;\frac{1}{{\mathrm{\&tau;}}_{aware}\&CenterDot;N_{aware}}\&CenterDot;\frac{ln(1-p_{a\_desire})}{ln(1-p_{aware})}---\left(18\right)$

Wherein N_aware=VB_warn|, by safety index p_{a_desire}And τ_awareAnd find that Beacon obtains the Probability p sending window_awareBring formula (18) into and obtain rate limit as the transmission rate finding Beacon.

Described T_adaptIt it is 5 seconds.

The beneficial effects of the present invention is: microcosmic vehicle mobility model is combined by the present invention with traffic model.Microcosmic vehicle research of mobility models is influencing each other between single unit vehicle driving behavior and vehicle and vehicle.Can combine to lower channel loading to greatest extent under the premise ensureing vehicle safety by mobility model and traffic model from the angle of vehicle safety, reach the purpose that channel congestion controls.

Accompanying drawing explanation

Fig. 1 is the overview flow chart of the present invention.

Fig. 2 is the schematic diagram of the double; two Beacon sending mode of the present invention.

Detailed description of the invention

Below in conjunction with the drawings and the specific embodiments, the present invention will be described:

A kind of VANET channel congestion combination control method towards safety index, as it is shown in figure 1, include step:

1) set up double; two Beacon transmission pattern according to wagon flow demand for security characteristic, and set associated safety index:

As in figure 2 it is shown, the Beacon message that vehicle sends is divided into tracking Beacon and finds Beacon two kinds, every T_adaptTime needs to calculate corresponding transmit power and speed [P according to microscopic traffic flow topology at that time_{crct_t}, P_{crct_a}, R_{crct_t}, R_{crct_a}], T_adaptGeneral value 5 seconds.In order to ensure the safety of vehicle, the parameter of double; two Beacon transmission patterns must is fulfilled for demand for security model, and wherein A is that Beacon sends vehicle:

A. for being in RNG_nearVehicle in scope, at τ_trackThe probability of the Beacon message being at least successfully received an A transmission in the time reaches p_{t_desire}

B. for being in RNG_warnExtraneous vehicle, at entry time τ_awareInside at least it is successfully received a RNG_warnThe probability of the Beacon message that the vehicle in scope sends reaches p_{a_desire}

2) set up traffic safety model, utilize the message constructing adjacent vehicle state table received from surrounding vehicles, and utilization state table calculates the parameter relevant to safety range:

Traffic safety model is made up of relation between vehicle and demand for security model two parts, and the purpose setting up traffic safety model is to obtain two parameters closely-related with safety, tight confines RNG by microcosmic traffic topology_nearWith fence coverage RNG_warn。

Correlation between the accumulation rate and speed:

Symbol A ≡ B represents vehicle B and vehicle A in the same direction, when A and B meetsTime, it is believed that it is in the same direction.WhereinIt is the speed of A,Being the speed of B, it is straight for implying hypothesis road here.

Neighboring trace relation:

It is adjacent with track, vehicle A place or in identical track that symbol A ≌ B represents track, vehicle B place, when A and B meets | L_B-L_A| during < 2, it is believed that set up, wherein L_AIt is ID, the L in track, A car place_BIt is the ID in track, B car place.

Forward direction relation:

Symbol B ← A represents the B front at A, when A and B meetsTime, it is believed that set up, whereinIt is the displacement of A,It it is the displacement of B

Backward relation:

Symbol B → A represents the B rear at A, when A and B meetsTime, it is believed that set up.

With forwards neighboring trace vehicle relation:

All directions are identical and are positioned at the relation of set FN (A) and A of neighboring trace vehicle composition of A front side for having

Front vehicle relation in the same direction:

All directions are identical and are positioned at the relation of set B (A) and A of neighboring trace vehicle composition of A front side for having

With rearward neighboring trace vehicle relation:

All directions are identical and are positioned at the relation of set BN (A) and A of neighboring trace vehicle composition of A front side for having

Screening function is defined as:

Function PICK (S, A, N) represents and according to the distance of A, the vehicle in set S is ranked up, and exports the distance of the car little with A distance N, if number of vehicles is less than N, output-1 in set S.

Counting function is defined as:

Function COUNT (S, A, D) represents all numbers being not more than D with vehicle A distance in set S, it is assumed that set N (A) represents that all vehicle A distances are not more than the set of the vehicle composition of D, then have

$\&ForAll;n\&Element;N\left(A\right):|{\stackrel{\&RightArrow;}{S}}_n-{\stackrel{\&RightArrow;}{S}}_A|\&le;D$

COUNT (S, A, D)=| N (A) |

Close distance:

At close distance DST_closeVehicle in scope is all closely related with the safety of this car, and the value of close distance is relevant with current wagon flow micro environment.From the angle of microcosmic mobile behavior, for speed on for, it is necessary to it is considered that the state of fore-aft vehicle；For lane-change behavior, it is necessary to go forward rear vehicle in before and after considering and target track；For passing behavior, generally to consider the state of vehicle in front and back two cars and adjacent lane.Therefore, it is recognized herein that, the N that the safety of vehicle is nearest with front and back neighboring trace₀(general value is 3) car has close relation, it is possible to derive the calculation of the close distance of vehicle A:

DST_close(A)=max{PICK (FN (A), A, N₀),PICK(BN(A),A,N₀)}(1)

Desired intimate distance:

Desired intimate distance DST_roughThe close distance by estimating according to pipeline following-speed model, it is considered to factor fairly simple, only consider the driving condition coming self, calculation is as follows, wherein Len_ARefer to the vehicle commander of corresponding car.

${\mathrm{DST}}_{rough}\left(A\right)=N_0\&CenterDot;(\frac{36}{161}\&CenterDot;|{\stackrel{r}{V}}_A|+1)\&CenterDot;{\mathrm{Len}}_A---\left(2\right)$

When traffic density is smaller, the number of vehicle A surrounding vehicles possibly even less than, result of calculation at this moment will less than zero.

Consider factors above, provide the computation model of vehicle A:

RNG_near(A)=max{DST_close(A),DST_rough(A)}(3)

We are by being modeled fence coverage intelligent driving model.In intelligent driving model, there is intended safe distance between rear car and front guide-car, the driving behavior of rear car is according to present speed and desired speed, and current inter-vehicular determines the behavior of subsequent time vehicle from the relativeness between expectation accident-free vehicle spacing.

RNG_warn(A)=s^*(υ_a,Δυ_a)(4)

The computational methods of fence coverage are as follows, whereinRepresent the speed of A car；T_aRepresent the response time；a_aRepresent the forward acceleration that vehicle is maximum；b_aRepresent maximum backward acceleration；υ_maxRepresent the maximal rate that current road segment allows.

$s^{*}({\mathrm{\&upsi;}}_a,{\mathrm{\&Delta;\&upsi;}}_a)=s_{0,a}+s_{1,a}\&CenterDot;\sqrt{\frac{{\mathrm{\&upsi;}}_a}{{\mathrm{\&upsi;}}_{0,a}}}+T_a\&CenterDot;{\mathrm{\&upsi;}}_a+\frac{{\mathrm{\&upsi;}}_a{\mathrm{\&Delta;\&upsi;}}_a}{2\sqrt{a_a{b}_a}}---\left(5\right)$

${\mathrm{\&upsi;}}_a={\mathrm{\&upsi;}}_{\max },{\mathrm{\&Delta;\&upsi;}}_a={\mathrm{\&upsi;}}_a-\left|{\stackrel{\&RightArrow;}{V}}_A\right|---\left(6\right)$

3) according to electromagnetic wave definitiveness propagation model and safety range, the power that message sends is calculated:

When the recipient of message requires electromagnetic wave propagation to this position, power is not less than P_min(general value-100dbm), message its is possible to be identified.If transmit power takes the minima that can meet safety range, then there is following relation:

P_track=PL_LOS(RNG_near)+P_min(7)

P_aware=PL_LOS(RNG_warn)+P_min(8)

Wherein PL_LOSIt is the energy loss in electromagnetic wave propagation process, has following relation with transmitting node and receiving node spacing:

${\mathrm{PL}}_{los}\left(d\&lsqb;m\&rsqb;\right)=\left\{\begin{array}{c}22.7{\log }_{10}\left(d\&lsqb;m\&rsqb;\right)+41+20{\log }_{10}\left(f\&lsqb;GHz\&rsqb;/5\right)\\ \begin{array}{cc}if& d<R_{bp}\end{array}\\ 40{\log }_{10}\left(d\&lsqb;m\&rsqb;\right)+41-17.3{\log }_{10}\left(R_{bp}\right)+20{\log }_{10}\left(f\&lsqb;GHz\&rsqb;/5\right)\\ \begin{array}{cc}if& d\&GreaterEqual;R_{bp}\end{array}\end{array}\right.---\left(9\right)$

$R_{bp}=4\frac{(h_A-1)(h_B-1)}{\mathrm{\&lambda;}}---\left(10\right)$

Wherein, d is the air line distance between sender and recipient, h_AAnd h_BBeing send the antenna height with recipient respectively, λ is electromagnetic wavelength, and f is electromagnetic frequency.

Formula (9) and (10) are substituted into respectively in formula (7) and (8), then can obtain respectively and follow the trail of Beacon and find the transmit power of Beacon, wherein tight confines RNG_nearWith fence coverage RNG_warnObtained by step (2).

4) Markov model of channel and the state of surrounding vehicles are controlled according to VANET, it is determined that during message transmission, successfully obtain the probability sending window, and according to safety index and the speed successfully obtaining the probability calculation outbound message transmission sending window:

VANET controls the Markov model of channel and meets following state transition equation:

$\mathrm{\&tau;}\left(p\right)=\frac{2{(1-p)}^2}{2-3p+{\mathrm{pW}}_s}---\left(11\right)$

${\mathrm{\&tau;}}^{*}\left(p\right)=1-{(1-p)}^{\frac{1}{N}}---\left(12\right)$

Wherein τ (p) represents the probability successfully obtaining channel resource, the probability that namely single is successfully transmitted, and p transfers to down with shape probability of state, W_sRepresenting the size of competition window, N is the interstitial content that communication range covers present node, is similar to the interstitial content in present node communication range.

By formula (11) and (12) it can be seen that when window size is fixing, the probability being successfully transmitted is determined by the interstitial content in communication range.Tight confines RNG_nearWith fence coverage RNG_warnInterior number of vehicles substitutes in equation (11) and (12), and the single obtained is successfully transmitted probability and corresponds to p respectively_trackAnd p_aware。

It addition, according to demand for security model it can be seen that reach safety index and must meet the following conditions:

$p_{t\_desire}\&le;1-{(1-p_{track})}^{t_{track}}---\left(13\right)$

$p_{a\_desire}\&le;1-{(1-p_{aware})}^{N_{aware}\&CenterDot;t_{aware}}---\left(14\right)$

Wherein, N_awareFor being positioned at vehicle A rear and being in RNG_warnNumber of vehicles in scope, t_trackRepresent that vehicle is at τ_trackThe number of times of Beacon message, t is sent in time_awareFor at τ_awareThe number of times finding Beacon is sent in time:

$R_{track}=\frac{t_{track}}{{\mathrm{\&tau;}}_{track}}---\left(15\right)$

$R_{aware}=\frac{t_{aware}}{{\mathrm{\&tau;}}_{aware}}---\left(16\right)$

The step calculating the transmission rate following the trail of Beacon and discovery Beacon is as follows:

41) initialize: according to adjacent vehicle state table Tab, calculate current time t_cIn table, all vehicles are gathered with the distance of Current vehicle AWhereinIt is at t_riThe displacement of the vehicle i that moment A obtains from Beacon message and speed,It it is the displacement of A car；

42) set of computations D_ATwo subset V_nearAnd V_warn, wherein V_nearMiddle vehicle distances D_Ai(i ∈ Tab) is less than RNG_near, V_warnMiddle vehicle distances D_Ai(i ∈ Tab) is less than RNG_warn, set sizes is designated as N respectively_nearAnd N_warn；

43) by N_nearAnd N_warnSubstitute in state transition equation (11) and (12), obtain now sending and follow the trail of Beacon and find that Beacon successfully obtains the probability respectively p sending window_trackAnd p_aware；

44) send the probability of window according to the successful acquisition of safety index and two kinds of Beacon, calculate the transmission rate R of two kinds of Beacon message_trackAnd R_aware。

Step 44) calculate transmission rate according to demand for security index, concrete steps include:

441) according to formula (13) and formula (15), obtain following the trail of the lower limit of the transmission rate of Beacon:

$R_{track}\&GreaterEqual;\frac{1}{{\mathrm{\&tau;}}_{track}}\&CenterDot;\frac{ln(1-p_{t\_desire})}{ln(1-p_{track})}---\left(17\right)$

By safety index p_{t_desire}And τ_trackAnd follow the trail of the Probability p of Beacon acquisition transmission window_trackBring formula (17) into and obtain rate limit as the transmission rate following the trail of Beacon；

442)VB_warnRepresent and be positioned at vehicle A rear and be in RNG_warnThe set of the vehicle composition in scope,Filter out set VB_warn；

443) according to formula (14) and formula (16), obtain finding the lower limit of the transmission rate of Beacon:

$R_{aware}\&GreaterEqual;\frac{1}{{\mathrm{\&tau;}}_{aware}\&CenterDot;N_{aware}}\&CenterDot;\frac{ln(1-p_{a\_desire})}{ln(1-p_{aware})}---\left(18\right)$

Wherein N_aware=| VB_warn|, by safety index p_{a_desire}And τ_awareAnd find that Beacon obtains the Probability p sending window_awareSubstitute into formula (17) and obtain rate limit as the transmission rate finding Beacon.

5) coordination system of the double; two Beacon sending mode of foundation, the power of the message transmission that before coordination, step obtains and speed, obtain final transmission parameter

Because it is found that surrounding vehicles is indiscriminate broadcast by Beacon, adjacent vehicle also can receive the discovery Beacon that this car sends, namely find that Beacon has actually shared the part of functions following the trail of Beacon, therefore by finding that Beacon converts to follow the trail of, Beacon can reduce the actual transmission rate following the trail of Beacon, reduce network burden further.

$R_{equal}=R_{aware}\frac{p_{aware}}{p_{track}}$

The primary condition of conversion is to find that the range of transmission of Beacon can cover the range of transmission following the trail of Beacon, i.e. P_trackLess than P_aware, to consider the conversion border issue that different wagon flow environment brings simultaneously, propose to send parameter conversion algorithm accordingly and be corrected sending parameter, to obtain final transmission parameter [P_{crct_t}, P_{crct_a}, R_{crct_t}, R_{crct_a}]。

It can be seen that when vehicle density ratio is sparse, wagon flow is close to when freely flowing, double; two Beacon send mechanism will deteriorate to the transmission mechanism only following the trail of Beacon.Due to the dynamic of vehicle communication topology, the power that Beacon message sends and speed are required for dynamically adjusting to adapt to new topological structure.The microcosmic traffic environment considered around Adjacent vehicles has relatively larger similarity, the transmission parameter making Beacon message is also more similar, so we about fix on preferential transmission in the fixed cycle (herein for 1s) follows the trail of Beacon, finding that Beacon sends in the latter stage in cycle, the independence ensureing two kinds of Beacon message of trying one's best is to weaken the impact of concealed terminal.

Above content is in conjunction with concrete optimal technical scheme further description made for the present invention, it is impossible to assert that specific embodiment of the invention is confined to these explanations.For general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, it is also possible to make some simple deduction or replace, protection scope of the present invention all should be considered as belonging to.

Claims (8)

1. the VANET channel congestion combination control method towards safety index, it is characterised in that comprise the following steps:

S1, the double; two Beacon transmission pattern of foundation: setting up double; two Beacon transmission pattern according to wagon flow demand for security characteristic, the Beacon message that vehicle sends includes tracking Beacon information and finds Beacon information, every T_adaptTime flows through topology according to microcosmic traffic at that time and calculates the transmit power and speed [P that obtain following the trail of Beacon information and discovery Beacon information at that time_{crct_t}, P_{crct_a}, R_{crct_t}, R_{crct_a}], wherein, P_{crct_t}For following the trail of the transmit power of Beacon information, P_{crct_a}For finding the transmit power of Beacon information；R_{crct_t}For following the trail of the speed of Beacon information, R_{crct_a}For finding the speed of Beacon information；The parameter adjusting double; two Beacon transmission pattern makes it meet safety requirements model；

S2, set up traffic safety model, calculate tight confines and fence coverage: utilize the Beacon message constructing adjacent vehicle state table received from surrounding vehicles, and utilization state table calculates the parameter relevant to safety range: traffic safety model is made up of relation between vehicle and demand for security model two parts, the tight confines RNG of traffic safety model_nearWith fence coverage RNG_warnComputational methods as follows, wherein A for send vehicle:

RNG_near(A)=max{DST_close(A),DST_rough(A)}(1)

RNG_warn(A)=s^*(υ_a,Δυ_a)(2)

Wherein the computational methods of continuous item are as follows:

DST_close(A)=max{PICK (FN (A), A, N₀),PICK(BN(A),A,N₀)}(3)

${\mathrm{DST}}_{rough}\left(A\right)=N_0\&CenterDot;(\frac{36}{161}\&CenterDot;|{\stackrel{r}{V}}_A|+1)\&CenterDot;{\mathrm{Len}}_A---\left(4\right)$

$s^{*}({\mathrm{\&upsi;}}_a,{\mathrm{\&Delta;\&upsi;}}_a)=s_{0,a}+s_{1,a}\&CenterDot;\sqrt{\frac{{\mathrm{\&upsi;}}_a}{{\mathrm{\&upsi;}}_{0,a}}}+T_a\&CenterDot;{\mathrm{\&upsi;}}_a+\frac{{\mathrm{\&upsi;}}_a{\mathrm{\&Delta;\&upsi;}}_a}{2\sqrt{a_a{b}_a}}---\left(5\right)$

${\mathrm{\&upsi;}}_a={\mathrm{\&upsi;}}_{\max },{\mathrm{\&Delta;\&upsi;}}_a={\mathrm{\&upsi;}}_a-\left|{\stackrel{\&RightArrow;}{V}}_A\right|---\left(6\right)$

Wherein N₀For the constant that is closely related, general value is 3；Len_ARepresent the length of A car；Represent the speed of A car；T_aRepresent the response time；a_aRepresent the forward acceleration that vehicle is maximum；b_aRepresent maximum backward acceleration；υ_maxRepresent the maximal rate that current road segment allows；Function PICK (S, A, N) represents and according to the distance of A, the vehicle in set S is ranked up, and exports the distance of the car little with A distance N, if number of vehicles is less than N, output-1 in set S；FN (A) be all directions identical and be positioned at A front side neighboring trace vehicle composition set；BN (A) be all directions identical and be positioned at A front side neighboring trace vehicle composition set；

Transmit power determined by S3, foundation electromagnetic wave definitiveness propagation model: the transmit power of described tracking Beacon information and discovery Beacon information is tried to achieve according to electromagnetic wave definitiveness propagation model:

P_track=PL_LOS(RNG_near)+P_min(7)

P_aware=PL_LOS(RNG_warn)+P_min(8)

Wherein P_minIt is the lowest power that can recognise that, PL_LOSIt is the energy loss in electromagnetic wave propagation process, has following relation with transmitting node and receiving node spacing:

${\mathrm{PL}}_{los}(d\&lsqb;m\&rsqb;)=\left\{\begin{array}{c}22.7{\log }_{10}(d\&lsqb;m\&rsqb;)+41+20{\log }_{10}(f\&lsqb;GHz\&rsqb;/5)\\ \begin{array}{cc}if& d<R_{bp}\end{array}\\ 40{\log }_{10}(d\&lsqb;m\&rsqb;)+41-17.3{\log }_{10}\left(R_{bp}\right)+20{\log }_{10}(f\&lsqb;GHz\&rsqb;/5)\\ \begin{array}{cc}if& d\&GreaterEqual;R_{bp}\end{array}\end{array}\right.---\left(9\right)$

$R_{bp}=4\frac{(h_A-1)(h_B-1)}{\mathrm{\&lambda;}}---\left(10\right)$

Wherein, d is the air line distance between sender and recipient, h_AAnd h_BBeing send the antenna height with recipient respectively, λ is electromagnetic wavelength, and f is electromagnetic frequency；Formula (9) and (10) are substituted into respectively in formula (7) and (8), then can obtain respectively and follow the trail of Beacon and find the transmit power of Beacon, wherein tight confines RNG_nearWith fence coverage RNG_warnObtained by step S2.

S4, foundation VANET control the Markov model of channel and calculate transmission rate: described VANET controls the Markov model of channel and meets following state transition equation:

$\mathrm{\&tau;}\left(p\right)=\frac{2{(1-p)}^2}{2-3p+{\mathrm{pW}}_s}---\left(11\right)$

${\mathrm{\&tau;}}^{*}\left(p\right)=1-{(1-p)}^{\frac{1}{N}}---\left(12\right)$

Wherein, τ (p) represents the probability successfully obtaining channel resource, the probability that namely single is successfully transmitted, W_sRepresenting the size of competition window, N is the interstitial content that communication range covers present node, is similar to the interstitial content in present node communication range, tight confines RNG_nearWith fence coverage RNG_warnInterior number of vehicles substitutes in equation (11) and (12), and the single obtained is successfully transmitted probability and corresponds to p respectively_trackAnd p_aware。

S5, determine final transmission parameter according to conversion algorithm: set up the coordination system of double; two Beacon sending mode, power that the message that before coordination, step obtains sends and speed, obtain final transmission parameter:

$R_{equal}=R_{aware}\frac{p_{aware}}{p_{track}}---\left(19\right)$

The primary condition of conversion is to find that the range of transmission of Beacon can cover the range of transmission following the trail of Beacon, i.e. P_trackLess than P_aware, to consider the conversion border issue that different wagon flow environment brings simultaneously, propose to send parameter conversion algorithm accordingly and be corrected sending parameter, to obtain final transmission parameter [P_{crct_t}, P_{crct_a}, R_{crct_t}, R_{crct_a}]。

2. a kind of VANET channel congestion combination control method towards safety index according to claim 1, it is characterised in that the safety requirements model in step S1 is:

A. for being in tight confines RNG_nearInterior vehicle, at τ_trackThe probability of the Beacon message being at least successfully received a vehicle transmission in the time reaches p_{t_desire}

B. for being in fence coverage RNG_warnOutside vehicle, at entry time τ_awareInside at least it is successfully received a fence coverage RNG_warnWithin the probability of Beacon message that sends of vehicle reach p_{a_desire}。

3. a kind of VANET channel congestion combination control method towards safety index according to claim 1, it is characterized in that, between described vehicle, relation includes correlation between the accumulation rate and speed, neighboring trace relation, forward direction relation, backward relation, same forwards neighboring trace vehicle relation, in the same direction front vehicle relation and same rearward neighboring trace vehicle relation.

4. a kind of VANET channel congestion combination control method towards safety index according to claim 1, it is characterised in that described correlation between the accumulation rate and speed is: symbol A ≡ B represents vehicle B and vehicle A in the same direction, when A and B meetsTime, it is in the same direction, whereinIt is the speed of A,It is the speed of B；

Neighboring trace relation is: it is adjacent with track, vehicle A place or in identical track that symbol A ≌ B represents track, vehicle B place, when A and B meets | L_B-L_A| during < 2, the two is neighboring trace relation, wherein L_AIt is ID, the L in track, A car place_BIt is the ID in track, B car place；

Forward direction relation is: symbol B ← A represents the B front at A, when A and B meetsTime, vehicle B and A is forward direction relation, whereinIt is the displacement of A,It it is the displacement of B；

Backward relation is: symbol B → A represents the B rear at A, when A and B meetsTime, vehicle B and A is backward relation；

With forwards neighboring trace vehicle relation it is: identical and the neighboring trace vehicle composition that is positioned at A front side the relation of set FN (A) and A in all directions is:

Front vehicle relation in the same direction: identical and the neighboring trace vehicle composition that is positioned at A front side the relation of set B (A) and A in all directions is:

With rearward neighboring trace vehicle relation it is: identical and the neighboring trace vehicle composition that is positioned at A front side the relation of set BN (A) and A in all directions is:

5. a kind of VANET channel congestion combination control method towards safety index according to claim 1, it is characterised in that step S4 specifically includes step:

S41, initialization: according to adjacent vehicle state table Tab, calculate current time t_cIn table, all vehicles are gathered with the distance of Current vehicle AWhereinIt is at t_riThe displacement of the vehicle i that moment A obtains from Beacon message and speed,It it is the displacement of A car；

S42, set of computations D_ATwo subset V_nearAnd V_warn, wherein V_nearMiddle vehicle distances D_Ai(i ∈ Tab) is less than RNG_near, V_warnMiddle vehicle distances D_Ai(i ∈ Tab) is less than RNG_warn, set sizes is designated as N respectively_nearAnd N_warn；

S43, by N_nearAnd N_warnSubstitute in state transition equation (11) and (12), obtain now sending and follow the trail of Beacon and find that Beacon successfully obtains the probability respectively p sending window_trackAnd p_aware；

The successful acquisition of S44, foundation safety index and two kinds of Beacon sends the probability of window, calculates the transmission rate R of two kinds of Beacon message_trackAnd R_aware。

6. a kind of VANET channel congestion combination control method towards safety index according to claim 1, it is characterised in that described safety requirements model meets the following conditions:

$p_{t\_desire}\&le;1-{(1-p_{track})}^{t_{track}}---\left(13\right)$

$p_{a\_desire}\&le;1-{(1-p_{aware})}^{N_{aware}\&CenterDot;t_{aware}}---\left(14\right)$

Wherein, N_awareFor being positioned at vehicle A rear and being in RNG_warnNumber of vehicles in scope, t_trackRepresent that vehicle is at τ_trackThe number of times of Beacon message, t is sent in time_awareFor at τ_awareThe number of times finding Beacon is sent in time:

$R_{track}=\frac{t_{track}}{{\mathrm{\&tau;}}_{track}}---\left(15\right)$

$R_{aware}=\frac{t_{aware}}{{\mathrm{\&tau;}}_{aware}}---\left(16\right).$

7. a kind of VANET channel congestion combination control method towards safety index according to claim 1, it is characterised in that described step S44) specifically include step:

S441, according to formula (13) and formula (15), obtain following the trail of the lower limit of the transmission rate of Beacon:

$R_{track}\&GreaterEqual;\frac{1}{{\mathrm{\&tau;}}_{track}}\&CenterDot;\frac{ln(1-p_{t\_desire})}{ln(1-p_{track})}---\left(17\right)$

By safety index p_{t_desire}And τ_trackAnd follow the trail of the Probability p of Beacon acquisition transmission window_trackBring formula (17) into and obtain rate limit as the transmission rate following the trail of Beacon；

S442、VB_warnRepresent and be positioned at vehicle A rear and be in RNG_warnThe set of the vehicle composition in scope,Filter out set VB_warn；

S443, according to formula (14) and formula (16), obtain finding the lower limit of the transmission rate of Beacon:

$R_{aware}\&GreaterEqual;\frac{1}{{\mathrm{\&tau;}}_{aware}\&CenterDot;N_{aware}}\&CenterDot;\frac{ln(1-p_{a\_desire})}{ln(1-p_{aware})}---\left(18\right)$

Wherein N_aware=| VB_warn|, by safety index p_{a_desire}And τ_awareAnd find that Beacon obtains the Probability p sending window_awareBring formula (18) into and obtain rate limit as the transmission rate finding Beacon.

8. a kind of VANET channel congestion combination control method towards safety index according to claim 1, it is characterised in that described T_adaptIt it is 5 seconds.