Inter-vehicle Communications for Merging Control

Transcription

1 Inter-vehice Communications for Merging Contro Takeshi Sakaguchi tsuya Uno Sadayuki Tsugawa Mechanica Eng. Lab. University of Tsukuba Mechanica Eng. Lab. IST, MITI Graduate Schoo IST, MITI Namiki 1-2, Tsukuba, Ibaraki, Namiki 1-2, Tsukuba, Ibaraki, Namiki 1-2, Tsukuba, Ibaraki, , JPN , JPN , JPN bstract This paper proposes a data transmission agorithm over inter-vehice communications and a merging contro agorithm, and describes the simuation studies and experiments using autonomous mobie robots with wireess LN for the evauation of the feasibiity of the data transmission and merging contro agorithms. The merging contro agorithm uses a virtua vehice which is generated by mapping a vehice on a main ane or a ramp in order to achieve ongitudina contro between a vehice at a ramp and one on a main ane. The resuts of the simuations show the efficiency of the data transmission and the feasibiity of the merging contro using this agorithm. This agorithm was impemented in autonomous mobie robots with a contro system and an on-board communications system using wireess LN for the evauation. I. INTRODUCTION Merging contro of vehices on highways woud contribute greaty to increase safety and to decrease congestion. Vehice contro is needed when a vehice merges into a patoon or changes anes. Inter-vehice communications is a indispensabe technoogy when the driver support and vehice contro probems are deat with under transitiona states incuding cooperative driving between more than one ane, cutting in a patoon and merging at a ramp. Much research on intervehice communications has been conducted from a communications point of view, but there is few research from a vehice contro point of view [1]. This paper proposes a data transmission agorithm over inter-vehice communications and a merging contro agorithm, and describes the simuation studies and experiments using autonomous mobie robots with wireess LN for the evauation of the feasibiity of the data transmission and merging contro agorithms. The merging contro agorithm uses a virtua vehice which is generated by mapping a vehice on a main ane or a ramp in order to achieve ongitudina contro between a vehice at a ramp and one on a main ane [2]. Vehice-vehice communications or vehice-road-vehice communications is necessary for this method. This paper aso deas with communications among vehices in an ony patoon. pure LOH method can be utiized for data transmission among vehices in a patoon, but a fast transmission rate is needed in order to transmit precise information among vehices in the vicinity taking account of vehice contro into consideration. In genera it is effective to use a timedivision mutipexing (TDM) method [3] or a round robin method in order to avoid coision and interference of packets during the communications. Each method transmits data sequentiay between two vehices. In the TDM method the maximum number of vehices in a patoon has to be fixed in advance to design the sots. This is a probem from the communications efficiency point of view. This paper proposes a data transmission agorithm that the sequence of transmission changes dynamicay adapting the number of vehices in a patoon based on a round robin method. This method can be appied to when another vehice breaks in the patoon. When the number of vehices increases, the channes for the vehice-vehice communications aso increase. This is a probem from a traffic point of view. When there are many patoons, patoon-patoon communications are effective, because it wi reduce the channes. twoayer system for inter-vehice communications is aso proposed in this paper. This system has the intrapatoon communications (vehice-vehice communications in a patoon) and the inter-patoon communications L C Fig.1. Communications of merging

2 (patoon-patoon communications). The resuts of the simuations show the efficiency of the data transmission and the feasibiity of the merging contro, when a patoon consists of ten vehices, the transmission rate is three times as efficient as a conventiona method. This agorithm was impemented in autonomous mobie robots with a contro system and an on-board communications system using wireess LN for the evauation. II. COMMUNICTIONS LGORITHM Inter-vehice communications that is essentia in merging contro can be cassified into vehice-vehice communications in a patoon (intra-patoon communications) and patoon-patoon communications (inter-patoon communications). data transmission agorithm in the intrapatoon communications is presented here, foowed by some consideration on the inter-patoon communications.. Intra-patoon communications The transmission rate must be fast enough in order to contro vehices with precise information on vehices in the neighborhood. pure LOH method can be utiized for data transmission among vehices in a patoon, but generay it is more effective to use a time-division mutipexing (TDM) method or a round robin method than the pure LOH method in order to avoid coision and interference of packets during communications. Each of the TDM method and the round robin method sequentiay transmits data between two vehices. TDM method, however, requires to decide the maximum number of vehices in a patoon in advance to prepare the sots. This may cause a probem from a communications efficiency point of view. In order to avoid the probem, a new data transmission agorithm for the inter-vehice communications is proposed here. It is assumed that an omni-directiona medium is empoyed. The agorithm is featured by that the sequence of data transmission from a vehice to another one is not based on the physica sequence of vehices in a patoon but on the identification numbering to vehices in a patoon. It is a round-robin method. The agorithm appied to vehices in a patoon under a steady state wi be expained, foowed by that when a new vehice joins the patoon. gorithm under steady state Data transmission under steady state is performed aong a ring of the vehices in a patoon. Here the patoon is defined as vehices inked with the inter-vehice communications. Each vehice in a patoon is assigned a transmission sequence which is not based on its position within a patoon. In addition, each vehice recognizes its own vehice identification (ID) number and the number of vehices in a patoon (Fig.2). t time j, Vehice i transmits data to Vehice i + 1 for data transmission and to Vehice i 1 for acknowedgement. t time j + 1, in tern, Vehice i +1 transmits data received from Vehice i and modified at Vehice i + 1 to Vehice i + 2 and aso to Vehice i. The ast Vehice n transmits data to Vehice 1 and to Vehice n 1. The data transmission is efficient when compared with the TDM method, and has foowing advantages: Each Vehice does not need to synchronize with every other vehice. There is no deay in waiting to transmit data. Transmitting time is not fixed, but in proportion to data ength. gorithm on vehice joining When vehices are transmitting data under steady state, if a new vehice joined the ring, a data transmission coision woud occur. The agorithm wi be extended to appy to such a situation when there exists another vehice that wants to join the ring. fter Vehice i finishes the transmission and before Vehice i + 1 starts one, there is a gap named an interruption detective gap as shown in Fig.3, where a the vehices in the patoon are under a receiving mode and the joining vehice has a chance to join the patoon. fter the joining vehice detects a gap, it transmits its request to Vehices i and i+1, when Vehices i and i + 1 identify the joining vehice, a new ring starts and the sequence of the transmission wi be atered to the new sequence of Vehice i, the joining vehice, then Vehice i + 1. fter the joining vehice, whose new ID is i + 1, transmits data to Vehice i + 2, whose od ID was i+1, the new ring starts. The data transmission is fexibe enough to change the ring depending on the number of vehices and to accommodate a newy joining vehice with ease. i-1 i i+2 i+1 Fig.2. Transmission of data under a steady state 1 cyce (variabe) n interruption detective gap Fig.3. Interruption detective gap

3 Inter-Patoon Communication Intra-Patoon Communication Patoon Patoon Patoon C Fig.4: Two-ayer system for inter-vehice communications. Inter-patoon communications Patoons in the neighborhood can merge using ony the intra-patoon communications, but the necessary number of channes for inter-vehice communications rapidy increases as the number of vehices increases. When there are many patoons, each patoon needs to recognize the dynamic information of the other patoons. These may cause a probem from a traffic point of view. In order to avoid the probem, a method using inter-patoon communications is proposed here. The necessary number of channes When a patoon consisted of n vehices merges into another patoon consisted of m vehices, 2m n at the maximum channes are needed for inter-vehice communications in the two patoons. To reduce the number of the channes, the communications between patoons wi be repaced by that between the ead vehices in each patoon, which wi need ony 2 channes. In the merging contro of two patoons, the ead vehice in a patoon is controed with the merging contro agorithm as a singe vehice. When the ead vehice predicts the merging, it commands the foowing vehices in the patoon to secure the necessary headway. In this case, the inter-patoon communications can be repaced by the inter-ead-vehice communications. Two-ayer system for inter-vehice communications In the inter-ead-vehice communications on the merging contro, the data transmission rate among patoons can be sower than that among vehices in a patoon, because the positions of vehices in a patoon can be estimated from the position of a ead vehice in the patoon. The inter-vehice communications system in the merging contro agorithm can be expressed as shown in Fig.4. In the figure, the ines among vehices show routes of communications. This system has two ayers of communications; one is the intra-patoon communications and the other is the inter-patoon communications. The vehice-road-vehice communications can be aso incuded as another communications among patoons. III. MERGING CONTROL LGORITHM This probem deat here is how to ongitudinay contro a vehice on a ramp or on ane changing to merge to through traffic. For simpicity, it is assumed that a vehices are moving at the same speed.. Merging at a Ramp The cases of merging are cassified into three ones as foows: Case 1: vehice at the ramp merges after the ast vehice in a patoon on the main ane. Case 2: vehice at the ramp merges before the ead vehice in a patoon on the main ane. Case 3: vehice at the ramp merges between vehices in a patoon on the main ane. It is necessary to secure the headway sufficienty unti passing the merging point in order to merge smoothy without crash. The merging contro agorithm is based on ongitudina contro between vehices at a ramp and on a highway. In a case of merging at a ramp, each vehice must compete the merging preparedness before arriving at a ramp because of a structura restriction. It requires transmission of the competion of the merging preparedness from a merged side to a merging side using inter-vehice communications.. Merging on Lane Changing When it is assumed that vehices change the ane between adjoined anes, the merging cases can be cassified into three ones as foows: Case 1: vehice on the ane merges after the ast vehice in a patoon on the next ane. Case 2: vehice on the ane merges before the ead vehice in a patoon on the next ane. Case 3: vehice on the ane merges between vehices in a patoon on the next ane. Case 1 Case 2 Fig.5. Merging at a ramp C 1 Case 3 Case 1 Case 2 Case 3 Fig.6. Merging on ane changing C 1 2 2

4 In a case of merging on ane changing, each vehice is going to merge after competing the merging preparedness because of no structura restriction. C. Merging gorithm for Each Case The merging contro agorithm proposed here empoys a contro of a virtua vehice, which is generated by mapping a vehice onto an object ane. The preset headway is L. Each merging in Fig.5 and 6 that has the same number is identica: in the case 1, a virtua vehice is generated ahead of a merging vehice, and in the case 2, a virtua vehice is generated ahead of a merged patoon. Here, the mergingatarampandonanechangingareconsidered to be identica. The merging contro in each Pattern is described as foows: In the case 1, since Vehice is to be foowed by Vehice after merging, Vehice is mapped onto the ramp or the next ane to ongitudinay contro Vehice. In the case 2, since Vehice is to be foowed by Vehice after merging, Vehice is mapped onto the ramp or the next ane to ongitudinay contro Vehice. Ineither of the cases 1 and 2, the headway between the vehices are controed to be L with norma acceeration. In the case 3, there are two reations among vehices: Vehice and Vehice C, and Vehice and Vehice. In terms of the reation between Vehice and Vehice C, the merging of Vehice C after Vehice is the same as in the case 1. In terms of the reation between Vehice and Vehice, the ongitudina contro aims at the headway 2L. D. Longitudina Contro gorithm For simpicity of the simuation studies, the dynamics of a vehice i in a patoon are described by a simpe mode ẍ i = u i (1) where x i is a position of a vehice and u i is a contro input to the vehice, as shown in Fig.7. Then, the error e i in the Vehice i+1 Vehicei headway from the predetermined L is described as e i = x i x i+1 L (2) and the dynamics of the error wi be ë i = u i u i+1. (3) With the poe assignment technique [5], the contro aw is found as u i+1 = u i + k 1 e i + k 2 ė i, (4) where k 1 and k 2 are the contro gains. The contro system is shown in Fig.8. The contro aw suggests that the position, speed and contro input of the ead vehice shoud be transmitted to the foowing vehice, or some of the data shoud be measured on the foowing vehice, in addition to that each vehice shoud have data on the geometry of the ramp. IV. SIMULTIONS Simuation studies have been conducted to show the feasibiity of the data transmission agorithm and the merging contro agorithm.. The evauation of the data transmission agorithm The performance of the communications agorithm is evauated to compare with the TDM method. Tabe I shows the conditions. It is assumed that no error occurs in the communications. Fig.9 shows the maximum throughput rates of the TDM method and the communications agorithm proposed here. This resut indicates that the agorithm presented here has arger throughput rate than the TDM method, and it is about TLE I. SIMULTION CONDITIONS Packet Length Guard its it Rate Coision Detective Gap Maximum Vehices 100 1,024 [its/sec] 32 [bits] 1.544M [its/sec] Packet transmitting/10 30 [cars] 0 + x i+1 x i Fig.7. Patooning of vehices k + k s 1 2 u u i i+1 1 e i s 2 Maximum Throughput Rate 10 1 TDM method Merging agorithm Number of Vehices Fig.8. Longitudina contro system Fig.9. Maximum throughput rate

5 twice as high as the TDM method [3] when there are 15 vehices in a patoon.. Merging contro simuation Simuation studies have been conducted to show the feasibiity of the merging contro agorithm. Two patoons, each of which consists of five vehices, are aternatey merging at a ramp or on ane changing using the communications agorithm. The assumptions are as foows: Each vehice can ocate its absoute position accuratey. Each vehice can communicate with any other vehice within a range where the own vehice centered. Each vehice can transmit and receive both the absoute position and the veocity (the moving direction and the speed). Each vehice has the same communications range and receiving capabiity. TLE II. MERGING SIMULTION CONDITIONS Initia Speed cceeration Headway Samping Time Communications Range Communications Cyce (a) at a ramp [m/sec] within ±0.1G 20[m] 0.01[sec] 300[m] 0.01[sec] (b) on ane changing Fig.10. Simuation resut of merging There is ony one ramp at a merging point. highway does not have more than two anes. Each vehice does not change anes in the vicinity of the ramp. The ramp joins the highways at 30 [degrees]. cceeration of each vehice is bounded. TLE II shows the conditions. Fig.10 shows the resuts of the simuation studies. The resuts indicate that smooth merging is possibe with the merging contro and data transmission agorithms presented here. V. EXPERIMENT The experiment has been conducted to show the feasibiity of the communications agorithm and the merging agorithm presented here. In this experiment, three autonomous indoor mobie robots were empoyed in order to demonstrate the merging contro. Each robot is two whee-differentia drive type, and can drive ateray and ongitudinay, and moves autonomousy with dead reckoning. Each robot is equipped with the same communications system. The communications data is transmitted with a dipoe antenna. The range is about 50[m]. The carrier frequency is 2.4[GHz] and the bit rate is 1.6[Mbps]. The size of the robot is 0.5[m] 0.4[m], and the headway is set to 1.0[m] and the maximum speed is to 0.1[m/sec]. The packet in the communications consists of the position x i,theveocityv i, the acceeration u i,andtheid number i. The ID number and x i are used to recognize the absoute position of each vehice, the veocity, v i,is used to recognize whether the ead vehice is stopped, and the input, u i, is used for the ongitudina contro. Fig.11 shows the merging scene in the experiment. efore merging, a patoon (Vehices, ) weremoving on the main ane and a robot (Vehice C) was moving on another ane at a distance of 0.9[m] from the patoon. Vehice was foowing to Vehice. Vehice was communicating with Vehice using the intra-patoon communications. When Vehice C reached at a ramp, Vehice began to communicate with Vehice C using the inter-patoon communications. Vehice was supposed to merge after 2.0[m] drive. fter the communications, Vehice sowed down and the ongitudina contro started to make the headway 2L with the acceeration. The speed of Vehice C and the headway were controed to make the headway L to a virtua vehice. Vehice C adjusted the speed and merged between Vehice and Vehice C. Vehice and Vehice C secured the headway sufficienty before passing the merging point. Each robot merged smoothy without stop and crash. When Vehice merged between Vehice and Vehice, the headway between Vehice and Vehice C was onger than L. It may have caused by time deay in the communications.

6 VI. CONCLUSIONS This paper deat with the inter-vehice communications for merging contro on highways, and proposed a merging contro agorithm with a concept of virtua vehices. The data transmission agorithm over the inter-vehice communications deat here is featured by the efficiency and fexibiity when compared with the conventiona agorithm. The agorithm purposed here has been impemented in autonomous mobie robots with a contro system and an on-board communications system using wireess LN for the evauation. This paper aso described the simuation studies and experiments to show the feasibiity of the data transmission and merging contro agorithms. VII. REFERENCES [1] Markos Papageorgiou (Ed.): Merging Contro, Concise Encycopedia of traffic & Transportation Systems, Pergamon Press, pp , [2] T. Sakaguchi,. Uno, S. Tsugawa: n gorithm for Merging Contro of Vehices on Highways, JSE Spring Convention Proceedings, pp.85 88, May [3] H. Fujii, O. Hayashi, Y. Hirao: Experimenta Research on Protoco of Inter-Vehice Communication for Mutipe Vehices, 3rd nnua Word Congress on ITS (CD-ROM), October 15, [4]. Cochran: HS Communications Overview, Proceedings of 1997 IEEE Inteigent Transportation Systems Conference (CD-ROM), [5] S. Tsugawa, S. Murata: Veocity Contro for Vehice Foowing through Vehice/Vehice Communication, 22nd Internationa Symposium on utomotive Technoogy & utomation, Vo.I, pp , Itay, May [6] S.Tsugawa: n Overview on Contro gorithm for utomated Highway Systems, Proceedings of 1999 IEEE Inteigent Transportation Systems Conference (CD-ROM), [7] Pravin Varaiya: Precursor Systems naysis of utomated Highway Systems ctivity rea J-Entry/Exit Impementation Fina Report, 4 December Fig.11. Merging scene of an experiment