Relevance Estimation of Cooperative Awareness Messages in VANETs

Transcription

1 Relevance Etiation of Cooperative Awarene Meage in VANET Jakob Breu Reearch and Developent Dailer AG Böblingen, Gerany Eail: Michael Menth Departent of Coputer Science Univerity of Tübingen Tübingen, Gerany Eail: Abtract In Vehicular Ad-Hoc Network (VANET) a vehicle receive ultiple Cooperative Awarene Meage (CAM) fro neighboring node which infor it about their tatu A the rate of received CAM ay be high, their proceing ay be a challenge epecially in erie vehicle becaue their reource are contrained for econoic reaon In thi work, we aue that only a fraction of the received CAM can be handled We ugget that ot relevant eage hould be preferably proceed Thi require a iple function that calculate with little effort an etiate of the relevance of CAM baed on inforation uch a location and peed of the ender that i contained in any CAM We propoe a function that roughly peaking calculate the relevance of a CAM for it receiver That value increae with the potential of colliion with the ender of the CAM The function ha only a few paraeter Another contribution of the paper i the receiver-centric analyi of the choen relevance function It illutrate the effect of the function paraeter on the relevance of CAM originating fro vehicle in different poition and oveent relative to the receiver Index Ter Vehicular Ad-Hoc Network, Relevance Etiation, Scalability I INTRODUCTION In the lat year counication between vehicle and road ide infratructure received a lot of attention by the car indutry and reearch intitute Under ter like Car-to-X- Counication (Car2X, C2X) or Vehicular Ad-Hoc Network (VANET) the correponding activitie are uarized Thi technology enable a vat nuber of new function to increae afety, iprove driving cofort, and raie econoic and ecological efficiency in daily traffic [1] Worldwide tandardization and haronization between the vehicle anufacturer, upplier and the public ector i taking place [2] The European tandardization proce produced the Cooperative Awarene Meage (CAM) forat to continuouly dieinate tatu inforation about a vehicle [3] A CAM i broadcated to all nearby vehicle when a et of rule i et, and the eage broadcat frequency lie between 1 and 10 Hz [3, Appendix B] CAM have to be proceed by each receiving vehicle and allow to track the oveent and tate of the ender of thee CAM Many application rely on creating vehicle trajectorie fro ucceive CAM and on recognizing traffic pattern out of thee trajectorie In today tetbed, vehicle are well capable to proce the rate of received CAM for two reaon Firt, the current penetration rate of VANET technology i low o that tet vehicle receive only low rate of CAM Second, tet vehicle are equipped with powerful hardware that i able to proce uch ore eage than reource-contrained hardware of future erie vehicle In cae of high traffic denity and high percentage of vehicle being able to end CAM, a vehicle can receive a large rate of CAM eage, requiring lot of proceing power Initial iulation reult indicate high eage rate in variou realitic cenario for receiver We oit the preentation of thee reult due to lack of pace We propoe to deal with thi challenging ituation by proceing only the ot relevant eage If the rate of received CAM i larger than the proceing rate, the leat relevant eage are poibly dicarded Thi concept require a function that aign a relevance value to each received CAM; baed thee value the ot relevant CAM i elected for proceing The relevance function ut reflect the view of typical ue cae and ha to be coputable with an effort that i ignificantly lower than the proceing of the CAM itelf The reainder of thi paper i organized a follow Section II briefly review related work and ention the ue cae cluter we focu on In Section III we dicu how CAM ay be filtered baed on relevance etiate to cope with overload ituation Section IV preent the derivation of the propoed relevance function We illutrate the ipact of tunable paraeter of thi function on the relevance of CAM ent by vehicle with different location and peed relative to the receiving vehicle in Section V Finally, Section VI uarize thi work and provide an outlook on further reearch II RELATED WORK Delot et al propoed a relevance etiation echani to claify event and other inforation by their relevance to the driver [4] They ue obility and direction vector to copute a o-called encounter probability a a bae for the relevance calculation Alo they develop a eage dieination protocol for uch value Their work gave u oe valuable input, but ha a different focu Thi propoal alo incorporate paraeter we find difficult to deterine and there are proble with oving entitie of (alot) the ae heading

2 Zhou et al propoe a Layer of Interet (LoI) for publihubcribe yte to avoid congetion They ugget to ue different clae for eage of no interet, high interet, ediu interet, and regular interet Their approach give oe input for VANET a the different application clae have alo a different range of interet [5] Boll et al developed an adaptive prefetching algorith for the treaing of MPEG ovie [6] Their algorith pull frae over a network according to their relevance value Thee value repect the iportance of the frae for decoding of group of picture that are likely to be viewed in the near future A global relevance function i propoed which cobine tatic and dynaic relevance function to provide a ingle overall relevance value There i a vat nuber of application for VANET which cannot be covered in thi work We concentrate on afety application which try to avoid colliion with other object, otly other vehicle Therefore, they need the ae CAM a their inforation bae Exaple are: Overtaking Vehicle Warning, Interection Colliion Warning, Lane Change Aitant, Co-Operative Forward Colliion Warning, Pre-Crah Sening Warning, Co-Operative Merging Aitance [7] III ARCHITECTURE FOR MESSAGE PROCESSING The European Telecounication Standard Intitute (ETSI) paed an architectural layer odel to decribe the odule neceary for VANET technology deployent [8] The facilitie layer i located between the networking & tranport layer and the application layer It contain eleent of the ISO/OSI layer application, preentation, and eion, and erve a an inforation aggregation block Inforation fro different ource i collected here and acceible by the application A central part in the facilitie layer i the Local Dynaic Map (LDM) which i a repreentation of the vehicle urrounding baed on received inforation uch a CAM Therefore, the facilitie layer ha to provide central function for CAM aggregation With high incoing eage rate the load can increae ignificantly in the aggregation echani and in the data exchange between the facilitie and application layer It i an open challenge to deign the inforation flow and torage inide and between thee layer to avoid redundant tak We propoe that CAM received by a vehicle are firt proceed by a odule which aign a relevance value to the and baed on that value it inert the into a orted queue with liited pace Thi i illutrated in Figure 1 Then, the LDM or application can pull thee CAM according to their relevance for proceing If the queue i full and a new CAM i received, that CAM diplace the leat iportant CAM fro the queue if it i ore iportant A a conequence, ot relevant eage are preferably proceed and leat relevant eage are likely to be dropped Thi baic concept ay be augented by feedback fro application When an application, eg, a forward colliion avoidance application, i tracking a pecific vehicle becaue of it poibly dangerou oveent, new CAM fro thi Fig 1 Preferred proceing of ot relevant CAM by a vehicle vehicle have to get proceed with high priority Thu, rule are needed to override relevance etiate by feedback of greedy application Thi, however, i not in the focu of thi work and ubject to further reearch IV DERIVATION OF THE RELEVANCE FUNCTION In thi ection, we firt ketch how the relevance of other vehicle for potential colliion could be etiated in a relatively accurate way, but alo conclude that thi approach i coputationally deanding o that it i infeaible under reource contraint Then, we derive a relevance function in three tep and how that it i eay to calculate A Coplex Relevance Calculation of CAM Meage A CAM ( eage ) contain inforation about the poition p x p =, the peed v p y, and the heading ψ of it ender The peed ay be negative if the vehicle i oving backward The relevance etiation odule ue thee value and ha acce to the correponding value p r, v r and ψ r of the receiver By chooing colliion-related application the encounter probability ugget itelf a a relevance eaure A calculation of thi probability i poible in variou way With the help of a treet ap and by uing the ot probable path one could deterine whether ender and receiver can eet in the near future Although thi approach ay yield quite good etiate, there are everal reaon why it i not uitable for our propoed concept: A treet ap ha to be available for the current area However, often vehicle are only equipped with ap for one country or a certain region Map data require huge available torage pace Street ap are tatic while the real road yte i changing teadily Change exit teporarily or on a longter bai Map acce, ot probable path calculation, and ap atching, ie, deterining the exact own location in a ap by a atch of the driven trajectory with ap data, are CPU-intenive B A Siple Relevance Function for CAM Meage We derive a iple relevance function for CAM eage It decreae with increaing ditance between counicating vehicle, extrapolate their oveent, and add a penalty factor when the vehicle eet only in the future The function excel by it iple calculation

3 1) Ditance-Baed Relevance Etiation: A the probability for a colliion of two vehicle decreae with their ditance, we propoe the bae relevance function ( ) α d(, r) (1) A we conider afety application, we propoe that the relevance of a CAM decreae with increaing traight-line ditance d(, r) between ( ) the ender and the receiver r of α a CAM We ue d(,r) a a bae where the ditance i noralized by the unit eter and the paraeter α allow to control the decreae of the relevance with increaing ditance We argue that all vehicle within a radiu of d in are equally iportant for variou reaon It i hard to exactly deterine poition of vehicle and their ditance uing GPS, the CAM inforation ay not be accurate anyore ince tie ha paed between the eaureent of the data and the reception of the CAM eage, and vehicle can quickly change their oveent, eg, through acceleration, braking, or teering A a reult, all vehicle within a radiu of d in around the receiver can uddenly becoe very relevant or are already highly relevant Therefore, we ugget ( ) α ax(d(, r), din ) (2) a a iple relevance function The axiu relevance i liited to R ax = ( d in ) α 2) Mobility-Baed Relevance Etiation: Equation (2) decribe the relevance of a CAM for the tie it i received However, CAM of vehicle departing fro the receiver tend to becoe le relevant over tie while CAM of vehicle approaching the receiver tend to becoe ore relevant To predict the poition of the ender and the receiver of a CAM in the near future, we aue that they do not change their oveent We firt derive the obility vector fro the velocity v and heading ψ of the ender by ( ) ( ) v x v co(ψ v = = ) (3) v y v in(ψ ) Then, we calculate the tie-dependent ditance d(, r, t) between ender and receiver by d(, r, t) = p r + (t t now ) v r (p + (t t now ) v ) where variable t now repreent the current tie On thi bai we propoe the tie-dependent relevance function ( ) α ax(d(, r, t), din ) (4) Thi equation doe not yet repect the fact that vehicle eeting in the far future hould yield a lower relevance value than vehicle eeting very oon We achieve that by adding a penalty ter to the forula: ( ) α ( ax(d(, r, t), din ) 1 + t t ) β now (5) Paraeter β allow to control the penalty factor over tie and the tie i noralized by the unit econd Finally, we define the axiu tie-dependent relevance a the new relevance value: ax (R(r,, t)) (6) t now t t now+d ax We perfor thi axiization only over an interval of duration D ax ince the auption of a contant obility vector ay be valid only for liited tie 3) Eliination of the α-paraeter: Equation (5) ue the two paraeter α and β which both need to be tuned However, we can tranfor the equation by exponentiating both ide by 1 α A the relative order induced by the value propoed in Equation (5) doe not change by thi tranforation, we adopt the reult a a iplified relevance function with γ = β α : ( ) 1 ( ax(d(, r, t), din ) 1 + t t ) γ now (7) 4) Efficient Calculation of the Relevance Function: We calculate the relevance value uing Equation (6) and (7) in an efficient way If the ditance between ender and receiver i at ot d in when the CAM i received, then the relevance i et to the axiu value R ax Otherwie, the axiu of the tie-dependent relevance value in [t now ; t now +D ax ] need to be deterined There i a et T of at ot four potential intance for that axiu: 1) the beginning of the conidered interval, naely t now, 2) the tie t ax which i either the intance t in when the tie-dependent ditance becoe d in for the firt tie or the end of the interval t now + D ax when no point t in doe exit within that interval, 3) potential extree value of R(, r, t) within [t now ; t ax ] at ot two uch value t 1,2 inide can exit Thu, the relevance value can be calculated by ax t T (R(, r, t)) Two challenge reain: the calculation of t in and the calculation of t 1,2 inide a) Calculation of t in : We deterine t in by calculating with 4z(x + d t 1,2 2 in = t now ± in ) + y 2 y 2z (8) x =(p r x p x) 2 + (p r y p y) 2 (9) y =2(p r x p x)(v r x v x) + 2(p r y p y)(v r y v y) (10) z =(v r x v x) 2 + (v r y v y) 2 (11) and et t in to the allet one of thee value t 1,2 in in the range [t now ; t now + D ax ] if uch value exit Otherwie, t in i et to t now + D ax

4 b) Calculation of t 1,2 inide : A d(, r, t now) > d in hold, the ditance cannot becoe zero before t in Therefore, extree value of R(, r, t) within [t now ; t ax ] are alo extree value of it invere f(t) = ax(d(,r,t),din) (1 ) γ + t tnow Zero of the derivative of f are inide =t y + 2γy + 2z now (12) 4z(1 + γ) (2γy + y + 2z)2 8z(γ + 1)(2γx + y) ± 4z(1 + γ) t 1,2 They exit only if the dicriinant under the quare root in Equation (12) i not negative V EVALUATION In thi ection we illutrate the ipact of the poition and peed of the CAM ender relative to the CAM receiver on the relevance value Moreover, we how how the paraeter of the relevance function d in, D ax, and γ influence the reult A Receiver-Centric Analyi For evaluation purpoe we ue a receiver-centric analyi The receiver i till and located at the origin of a coordinate yte Potential ender ove fro the right to the left with a certain peed Any other point in the coordinate yte repreent the poition of a potential ender Fro any uch ender we evaluate the relevance of CAM for our conidered receiver Any pair of real ender and receiver can be apped into the coordinate yte of the receiver-centric analyi uch that the poition and peed of the ender relative to the receiver do not change The receiver i oved to the origin and the ender take an interediate poition p p r and obility vector v v r The ender find it final poition by a rotation around the origin uch that it obility vector point fro right to the left Since the relevance function depend only on the relative poition and peed of a ender and receiver, the tranlation of ender and receiver into the receiver-centric coordinate yte doe not change the relevance value of CAM B Ipact of Relative Speed v In the upper part of Figure 2(a) 2(f), we ue the receivercentric analyi and color point in a coordinate yte according to the relevance value of CAM originating fro the under the auption that the ender ha a certain (relative) peed v Darker point repreent higher relevance value a indicated in the legend Thi preentation eaily allow u to ee which relative poition and obility vector are conidered iportant by the relevance function The lower part of the figure indicate the abolute relevance value in a cro ection for Y = 0 If not entioned differently, we et v = 5, d in = 10, and D ax = 120 To avoid an abrupt tranition of the relevance for ditant oving ender, we et γ uch that we get (1 + Dax ) γ = 01, ie, γ = ln(01) ln(1+ Dax ) Figure 2(a) how the relevance function for a relative peed of v = 0, ie, ender and receiver are not necearily till, but they have the ae obility vector According to the contruction of the function, the relevance i highet within a radiu of d in and decreae with ditance fro the origin in all direction Figure 2(b) change the relative peed to v = 5 We can interpret the horizontal line at Y = 0 a a ituation where the ender and the receiver are approaching to each other The poitive obility vector of the ender effect that the area of ae relevance value are tretched to the right when coparing it to the figure with v = 0 We oberve that for v = 5 the ender poition fro which ender can eventually collide with the receiver alo yield large relevance value Thee large value lowly fade out with ditance fro the origin Increaing the relative peed to v = 10 lead to Figure 2(c) The area of high relevance for approaching vehicle now get higher value than with v = 5 We ee that by the darker color in the tail to the right The fater a vehicle ove toward the receiver, the earlier it reache the receiver cloe vicinity o that a lower penalty factor i applied Thi eentially caue the difference between Figure 2(c) and 2(b) C Ipact of the Miniu Ditance d in We now et the iniu ditance to d in = 20 for which the reult are given in Figure 2(d) Copared to Figure 2(b), the axiu relevance R ax = 1 d in i lower and o the value in the vicinity of the receiver are lower The relevance value of poition fro where vehicle can collide with the receiver are alo affected by thi change We choe thee value for d in baed on our experience with vehicle dynaic; higher value of d in are poible but lead to le differentiation in relevance value aong eage D Ipact of the Maxiu Tie D ax We et the axiu tie D ax = 15 but leave γ the ae value a for D ax = 120 and preent the correponding relevance value in Figure 2(e) Copared to Figure 2(b), we ee in the lower plot that there i now a clear dicontinuity at the edge between vehicle getting into the cloe vicinity of the receiver and other vehicle Therefore, we ugget to ue a higher value of D ax = 120 in order to dap the dicontinuity and hift it to the far right E Ipact of the Control Factor γ We initially decided to et γ = ln(01) ln(1+ Dax In Figure 2(f) ) ) γ = 02 In we et D ax = 15 and γ uch that (1 + Dax coparion to Figure 2(e) we ee that a lower γ value lead to a le harh dicontinuity On the other hand the tail to the right i alot inviible, which depict a neutralization of our approach of conidering the vehicle obility Therefore, we ugget to ue (1 + Dax ) γ = 01 in cobination with a large value of D ax = 120 VI CONCLUSION AND FUTURE WORK In a widely deployed VANET, vehicle have to proce a large aount of Cooperative Awarene Meage (CAM) A

5 (a) v = 0, d in = 10, D ax = 120 (b) v = 5, d in = 10, D ax = 120 (c) v = 10, d in = 10, D ax = 120 (d) v = 0, d in = 20, D ax = 120 (e) v = 5, d in = 10, D ax = 15 (f) v = 5, d in = 10, D ax = 15, odified γ Fig 2 Relevance value for ender oving fro right to left depending on poition and peed relative to a ender at the origin hardware in erie vehicle will be liited, only ot relevant CAM can be handled To that ai, we propoed a function to etiate the relevance of CAM for a receiver It ue only the poition, velocity, and heading of the ender which are contained in the CAM, and it can be eaily calculated The function ue the paraeter d in, D ax, and γ Paraeter d in i rather intuitive and we provided recoendation on how to et D ax and γ We developed a receiver-centric analyi and ued it to illutrate the effect of the ender poition, velocity, and heading relative to the receiver in a coprehenive way Moreover, we depicted the ipact of the tunable paraeter of the function Our propoal for relevance etiation and CAM election i only a firt tep in bringing VANET into erie vehicle In future work we will provide a ore elaborate relevance function that allow changing the obility vector of ender and receiver over tie Thi will widen the area of ender with high relevance value and i needed to capture vehicle driving curve The quality of the pre-elected CAM need to be aeed with regard to the requireent of variou application Experience fro currently conducted field operational tet ay be helpful The integration of application overriding relevance value by giving direct feedback to the facilitie layer i an open reearch iue ACKNOWLEDGMENT The author thank Dr Brakeeier and Dr Wei for fruitful dicuion and upport REFERENCES [1] M Sichitiu and M Kihl, Inter-Vehicle Counication Syte: A Survey, IEEE Counication Survey & Tutorial, vol 10, no 2, pp , 2008 [2] C Weiß, V2X Counication in Europe Fro Reearch Project Toward Standardization and Field Teting of Vehicle Counication Technology, Coputer Network, vol 55, no 14, pp , 2011 [3] European Telecounication Standard Intitute (ETSI), Intelligent Tranport Syte (ITS); Vehicular Counication; Baic Set of Application; Part 2: Specification of Cooperative Awarene Baic Service, Technical Specification, no , 2011 [4] T Delot, N Cenerario, and S Ilarri, Etiating the Relevance of Inforation in Inter-Vehicle Ad Hoc Network, in Proceeding of the Ninth International Conference on Mobile Data Manageent Workhop, 2008, pp [5] Z Zhou and W Wu, LoI: Efficient Relevance Evaluation and Filtering for Ditributed Siulation, Science in China Serie F: Inforation Science, vol 52, no 3, pp , 2009 [6] S Boll, C Heinlein, W Kla, and M Menth, MPEG-L/MRP: Ipleenting Adaptive Streaing of MPEG Video for Interactive Internet Application, Proceeding of ACM Multiedia 2001, 2001 [7] G e a Karagianni, Vehicular Networking: A Survey and Tutorial on Requireent, Architecture, Challenge, Standard and Solution, IEEE Counication Survey & Tutorial, vol 13, no 4, pp , 2011 [8] European Telecounication Standard Intitute (ETSI), Intelligent Tranport Syte (ITS); Counication Architecture, European Standard, no , 2010