Toll collection system and its communication method

Information

  • Patent Grant
  • 6437706
  • Patent Number
    6,437,706
  • Date Filed
    Tuesday, February 27, 2001
    23 years ago
  • Date Issued
    Tuesday, August 20, 2002
    22 years ago
Abstract
An electronic toll collection system (ETCS) for use in a tollgate for charging a car without the need for the car to stop, in which communication failures or errors due to reflected waves from a structure or a passing car are prevented. A roadside communication antenna which communicates with a vehicle-mounted communication antenna for charging, and a car sensor which detects a car (cars) in an area wider than a designed communication area are installed at the tollgate. As an electromagnetic wave path judgment section obtains data on the profile and position of a car which has entered the tollgate, from a car data detector, it calculates electromagnetic wave paths of direct and reflected waves which connect the roadside communication antenna 21 and the vehicle-mounted antenna in each of the cars, and calculates the receiving electric field strength for each of the paths. The direction of the path which has the highest field strength among the paths to the car in the communication area is selected as radiation direction and the direction of the other paths as radiation direction; then the directional pattern which makes the radiant intensity in radiation direction the maximum and that in radiation direction null is determined to control the radiation direction of the antenna unit through a directivity controller.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




This invention relates to an electronic toll collection system based on radio communications for a tollgate, and particularly relates to a communication method suitable for the radio environment of a tollgate.




2. Description of Related Art




An electronic toll collection system (ETCS) is an electronic system that enables drivers at a tollgate on a turnpike such as an expressway to receive tickets or pay their tolls without stopping their cars.





FIGS. 2A and 2B

show an outline of a tollgate which uses an ETCS.

FIG. 2A

is a perspective view and

FIG. 2B

is a top view. The tollgate


300


is demarcated from the neighboring gate zone by an island


311


. A roadside communication antenna


21


is installed on the tollgate


300


. As a car


31


with a vehicle-mounted communication antenna enters a designed communication area


350


, necessary information for charging is exchanged between the roadside communication antenna


21


and the vehicle-mounted communication antenna


22


through radio signals and the car


31


can pass through the tollgate without a stop.




If a car which has no vehicle-mounted communication antenna


22


enters the tollgate area, a car sensor


321


detects its entry and, if no communication with the roadside communication antenna


21


occurs, the car is considered as having no vehicle-mounted communication antenna


22


and the driver must receive a ticket from toll collection personnel in the tollgate booth


301


or pay the toll to him or her.




In this system, if a car with a vehicle-mounted communication antenna enters the tollgate area and no communication is established, the car must stop temporarily. Conversely, if a car without a vehicle-mounted communication antenna enters the zone and a communication between the roadside antenna and the vehicle-mounted communication antenna of another car is established, the former car can pass through the tollgate without paying the toll. Therefore, in order to ensure that tolls are collected without fail, it is proposed that the designed communication area should be set to allow only one car to enter it and there should be a means to enable communication only with the vehicle-mounted communication antenna which is present in it, or disable communication with any vehicle-mounted communication antenna outside it.




For example, the toll collection system disclosed in J-P-A-No.40433/1998 uses a roadside communication antenna which irradiates electromagnetic wave beams with high directivity; and J-P-A-No. 214359/1998 discloses a system in which a car type detector is installed at the front of the tollgate and the directional pattern of electromagnetic wave beams of the roadside communication antenna is varied depending on the car type for the purpose of suppressing communication area variation caused by variation in the position (vertical) of a vehicle-mounted communication antenna.




Another type of proposal is that the roadside antenna should be selected depending on the car's position or height, or depending on the car's height and speed (J-P-A-No.315283, 5/1992 and J-P-A-No.239954/1995).




In the conventional toll collection systems, in order to ensure that each communication is established with only one car at a tollgate, attention is paid only to the directional range of direct electromagnetic wave beams but the influence of reflected waves in the communication area is not taken into consideration.




As shown in

FIG. 2A

, actually there are structures such as a sound-proof wall


201


and a roof


221


in the tollgate area. As the roadside communication antenna


21


irradiates an electromagnetic wave beam, not only direct radio wave


210


which comes directly from the antenna


21


reaches the vehicle-mounted communication antenna


22


in the car


31


, but also reflected wave


211


from the roof


221


and reflected wave


212


from the sound-proof wall


201


may be generated. Since the vehicle-mounted communication antenna


22


receives a radio signal as the direct wave combined with the reflected waves, the direct wave


210


may be offset by the reflected waves


211


and


212


even within the directional range of the electromagnetic wave beam and thus there may be a zone where the radio signal cannot be received. Such a zone momentarily changes depending on the position, speed and other factors of the car


31


and the next car


32


.




Besides, even when the vehicle-mounted communication antenna


23


in the next car


32


is outside the directional range of the roadside communication antenna


21


, the next car


32


may receive reflected waves from the structures in the tollgate area and/or the car


31


ahead, generating a path of reflected waves


213


, which means establishment of communication with a car outside the designed communication area. In this case, because the roadside communication equipment cannot distinguish between the car


31


and the next car


32


, if the communication with the latter is established before establishment of communication with the former, the equipment would mistake the communicating car


32


for the car


31


and, therefore, may allow the car


31


to pass through the gate without communication with it or without charging it. The frequency of such mistakes will be higher if there are more cars without vehicle-mounted communication antennas which enter the designed communication area.




As mentioned above, the communication area in conventional ETCSs is designed on the premise of transmission and reception of direct radio waves or at most once reflected wave from the ground, so reflected waves which vary depending on the entering car or other factors may make communication in the designed communication area impossible or make communication outside the area possible. This leads to the problem of low stability and low reliability in radio wave transmission and reception for toll collection.




Also, a special tollgate structure and a wide gate are required to decrease reflected waves. In addition, a specific communication means for each tollgate may be needed because different tollgates have different electromagnetic field environments. This results in a higher construction or operating cost.




SUMMARY OF THE INVENTION




The present invention has been made in view of the above circumstances and provides a toll collection system which electronically collects tolls with accuracy using special software to ensure stable communication with a car in the designed communication area while the radio environment in the tollgate area varies depending on the car position, and also provides its communication method.




The present invention concerns a toll collection system which charges cars which pass through a tollgate without a stop, by means of radio communication. The system is composed of the following devices installed at the tollgate: a roadside antenna whose directional pattern is variable; roadside communication equipment including a communication controller, which communicates with cars and the host system; and a car sensor which detects the position and profile of the car going to pass through the gate. In the system, taking it into consideration that the radio communication environment as mentioned above is influenced by reflected waves which vary depending on the car's position and profile, the environment for communication between the roadside antenna and the vehicle-mounted antenna in the designed communication area is maintained suitable for automatic toll collection.




For this purpose, the system is characterized in that plural paths of direct and reflected waves which connect the roadside antenna with the antenna in the car present in a given area (car detection area) including the communication area are found and one path which maximizes the sensitivity of communication with the car in the communication area is selected from among them, then the directional pattern of the roadside antenna is so adjusted as to suit the direction of radiation (radiation direction 1) for the selected radio wave path. Also the directional pattern is controlled so that radio communication is impossible with respect to a wave path radiation direction (radiation direction 2) other than radiation direction 1, namely so that the radiant intensity for radiation direction 1 is maximized (or more than intensity 1) and that for radiation direction 2 is null.




If the presence of more than one car in the car detection area is detected, plural paths of direct and indirect radio waves for each car are calculated and all paths of radio waves from/to any car outside the car detection area are treated as having the radiation direction 2.




Regarding the radio wave paths, the system calculates paths of direct waves and all reflected waves available for communication that connect the roadside antenna with the vehicle-mounted antenna whose position depends on the position of the detected car, according to the known reflecting surface data based on the tollgate structure and the reflecting surface data which varies depending on the car profile. A radio wave path for direct waves can be geometrically calculated from data on both the antennas and the reflecting surface data, while ones for reflected waves can be calculated by a numerical method based on radio wave data. Alternatively, it is also possible to calculate paths for different car profiles in advance on the assumption that a car is in the position of one of plural path points which are preset in the car detection area.




The process for calculating the radio wave paths begins when a car enters the communication area, and is repeated for every cycle of detection of the car or every path point. As radio communication with the car in the communication area is over, the process may be once ended.




If radio communication with the car in the communication area is not established, the system considers the car as not having a vehicle-mounted antenna adequately. This means that if communication is impossible even though the communication environment is good, the system considers that the car has no vehicle-mounted antenna or the vehicle-mounted antenna is not ON, judges the car unsuitable for automatic toll collection, and treats it as such, for example, by giving a warning.




As described above, according to the present invention, toll collection can be performed with accuracy because the influence of reflected waves from a tollgate structure or an approaching car on radio waves between the roadside antenna and vehicle-mounted antenna is avoided and a desirable radio wave path for communication with a car in the designed communication area is thus obtained with stability. Since the influence of reflected waves is avoided by adjusting the antenna directivity, restrictions on the tollgate structure can be relaxed and the tollgate construction or operating cost can be reduced.











BRIEF DESCRIPTION OF THE DRAWINGS




Preferred embodiments of the present invention will be described in detail based on the followings, wherein:





FIG. 1

is a block diagram for a toll collection system according to one embodiment of the present invention;





FIGS. 2A and 2B

illustrate the outline of a conventional ETCS and its problems;





FIGS. 3A and 3B

illustrate the outline of a tollgate to which the present invention is applied;





FIG. 4

shows one example of a roadside communication antenna as a unit which consists of an array antenna and a directivity controller;





FIG. 5

shows another example of a roadside communication antenna as a unit which consists of plural pencil beam antennas and a directivity controller;





FIG. 6

is a flowchart showing an example of an operational sequence for the electromagnetic wave path judgment section;





FIG. 7

illustrates a directional pattern, radiation direction 1 and radiation direction 2;





FIG. 8

illustrates the structure of an array antenna and a radiation direction;





FIGS. 9A

,


9


B, and


9


C are tables showing the data structures for the car type data memory and





FIG. 9D

illustrates car patterns;





FIGS. 10A and 10B

are tables showing the data structures for the path memory; and





FIG. 11

is the data structure for a directional pattern table.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS





FIG. 3

shows one example of a tollgate system to which the present invention is applied. In a tollgate


300


, a roadside antenna


101


and a car sensor


320


are installed overhead or on either side in the tollgate area and the other constituent parts are the same as shown in FIG.


2


. Plural such tollgates are installed in the tollgate zone.





FIG. 1

shows the structure of a toll collection system according to one embodiment of the present invention. The toll collection system has the following: a roadside communication antenna


21


composed of an antenna unit


101


and a directivity controller


111


for controlling its directional pattern; a communication controller


25


for communication of necessary information for charging with a vehicle-mounted communication antenna


22


by radio signals; a car sensor


320


which detects a car entering the tollgate; a car data detector


130


which determines the position and profile of the detected car; an electromagnetic wave path judgment section


150


which selects an electromagnetic wave path between the antenna unit


101


and the vehicle-mounted antenna


22


and decides the directional pattern for the beam emitted from the antenna unit


101


; and a storage


153


which stores car type data


1531


which is referred to for electromagnetic wave path judgment, and contains a path memory


1531


and a directional pattern memory


1532


. It is also possible that the roadside communication equipment


20


has a roadside communication antenna


21


, a communication controller


25


and a car sensor


320


and the other components are mounted on the host system which interconnects tollgates at different locations.




The roadside communication antenna


21


communicates with the vehicle-mounted antenna


22


in the car approaching the tollgate


300


through radio signals under the control of the communication controller


25


. The car sensor


320


detects not only the car present in the designed communication area


350


of the tollgate but also another car in a given area (car detection area) behind the communication area


350


, as shown in FIG.


3


B. The sensor uses a TV camera to take images of an approaching car periodically. The car data detector


130


is an image processor which processes images from the TV camera to determine the profile, position and speed of the car; it may be integrated with the car sensor


320


into a unit. In place of the TV camera, a laser sensor device may be used to detect the car profile and position.




Car profile data is used to calculate reflecting surface data and determine the position of a vehicle-mounted communication antenna, though it takes time to determine it accurately. In this embodiment, only rough car profile data including the length, height and width of the car is calculated and, according to this rough data, reference is made to the car type data


1530


stored in the storage


153


and the profile data nearest to the rough car profile data is sought and obtained. Here, it is assumed that the position of the vehicle-mounted communication antenna


22


is predetermined for each car type.





FIGS. 9A

,


9


B and


9


C show car type data structures.

FIG. 9A

is a car type data table


1530


-


1


which contains such data for each car type as length, height, width and profile.

FIG. 9B

is a data table which shows an example of profile data, where the vertexes for each of the planes (surfaces) which make up a car profile are designated by x, y and z coordinates. At least three vertexes should be designated for each plane. When four or more vertexes are designated, the profile data should be determined so as to have all these vertexes on the same plane. Here, car profile data for all planes of a car are not required; only profile data for the reflecting planes (surfaces) which is used as reflecting surface data in calculation of electromagnetic wave paths is required.





FIG. 9C

is a car type data table


1530


-


2


whose data structure is different from that of


1530


-


1


. This data structure consists of pattern data and profile data for each car type, where profile data is the same as the data shown in


9


B. Pattern data refers to image files as shown in

FIG. 9D

, which represent car type templates (i), (ii), (iii) and so on for different car types. The car data detector


130


extracts the car profile part from an image taken by the TV camera and checks its correlation with different types of car pattern data to choose the most correlative car type and accordingly refer to profile data.




The electromagnetic wave path judgment section


150


receives data on the position and profile of the detected car from the car data detector


130


, distinguishes between the car in the communication area and the car outside it and defines the former as car 1 and the latter as car 2. The explanation given below assumes that only one car can be present in each of the communication area and the car detection area as an area outside it.




The electromagnetic wave path judgment section


150


calculates electromagnetic wave paths between the antenna


101


and the vehicle-mounted communication antenna


22


using reflecting surface data based on the structure of the tollgate


300


and the profile of the detected car. As shown in

FIG. 3B

, electromagnetic wave paths include a direct wave between the antennas which reaches either antenna directly, and reflected waves which reach either antenna after reflection from a structure or a car.




The electromagnetic wave path judgment section


150


calculates the electric field strength for each calculated electromagnetic wave path upon reception by the antenna unit


101


, and selects the wave path whose field strength is the highest, among the calculated wave paths for car 1 and car 2 as described above. In other words, the electromagnetic wave path that enables the vehicle-mounted antenna to deliver the highest receiving sensitivity.




In addition, for all the calculated electromagnetic wave paths, the electromagnetic wave path judgment section


150


calculates the direction of radiation in the 3D space where radio waves are irradiated from the antenna unit


101


. It defines the direction of radiation for the chosen electromagnetic wave path with the highest field strength for car 1, as radiation direction 1, and the direction of radiation for the other electromagnetic wave paths as radiation direction 2. Then, it determines the directional pattern of the electromagnetic wave beam irradiated from the antenna unit


101


so that radiation is made in radiation direction 1 with a radiant intensity of over intensity 1, and in radiation direction 2 with a radiant intensity of below intensity 2 which is well below intensity 1, and controls the directivity controller


111


in the roadside antenna


21


according to this determined pattern.




The directivity controller


111


adjusts the feed power level or radiation angle for the antenna unit


101


, or makes an antenna selection in order to obtain the directional pattern as determined by the electromagnetic wave path judgment section


150


. As a result, the directional beam profile for the antenna unit


101


is adjusted so that the maximum radiation is directed toward the vehicle-mounted communication antenna in the communication area and the directional beam radiation null point is directed toward the vehicle-mounted communication antenna outside the communication area.




Next, the constituent parts of the system and their operations will be described in detail. The antenna unit


101


is either an array antenna composed of plural antenna elements, or a unit antenna composed of pencil beam antennas. In case of the former, the directivity controller


111


controls the power feed according to the directional pattern determined by the electromagnetic wave path judgment section


150


or the feed factor (amplitude and phase of electric power) for each antenna element. In case of the latter, the directivity controller


111


adjusts the directional pattern to the one determined by the electromagnetic wave path judgment section


150


, by changing the pencil beam antenna to be connected with the communication controller


25


.





FIG. 4

shows the structure of the array antenna combined with the directivity controller. The antenna unit


101


is composed of plural antenna elements


102


while the directivity controller


111


consists of plural phase/amplitude controllers


112


. When a radio signal is sent, the phase/amplitude controller


112


feeds electric power with the feed factor specified by the electromagnetic wave path judgment section


150


to excite the antenna elements


102


to control the directional beam profile so that radiation is made in radiation direction 1 with over intensity 1 and in radiation direction 2 with below intensity 2. For a signal that is received by the antenna unit


101


, the beam profile is also controlled in the same way.





FIG. 5

shows the structure of the pencil beam antenna unit. The antenna unit


101


is composed of plural pencil beam directional antennas


711


to


714


. The directivity controller


111


is composed of an antenna selector


701


and angle adjusters


721


to


724


. The antenna selector


701


selects the pencil beam antenna nearest to radiation direction 1 and makes a fine adjustment of its radiation direction with the corresponding angle adjuster.





FIG. 6

is a flowchart showing the operational sequence for the electromagnetic wave path judgment section. First, reflecting surface data for the structures of the tollgate and that for the detected car are obtained by reference to the storage


153


(S


11


, S


12


). The reflecting surface data for the structures is fixed for each tollgate and pre-analyzed and the analysis data is stored in the reflecting surface data memory (invisible in the figure) of the storage


153


.




The car reflecting surface data can be obtained by extracting the same normal from the profile data of the detected car. In this embodiment, regarding car reflecting surface data, analysis has been made in advance for data on each car profile as stored in the car type data memory


1530


and stored in the reflecting surface data memory; so, when profile data for the detected car is obtained by reference to the profile data in the car type data memory


1530


, reflecting surface data corresponding to the profile data can also be obtained.




Then, the points for transmission and reception of reflected waves are set (S


13


). Here, the transmission point is the roadside communication antenna


21


, or its location in the tollgate. The position of the vehicle-mounted communication antenna


22


in the detected car is registered as the reception point for each car j (S


14


, S


141


). Data on the position of the vehicle-mounted communication antenna


22


can be obtained as supplementary data for the car type data memory


1530


.




Next, under the above conditions, electromagnetic wave paths Γ i for direct and reflected waves are calculated (S


15


). The path of direct wave can be easily found by connecting the position of the roadside antenna


21


and that of the vehicle-mounted communication antenna


22


of the detected car in its detected position by a straight line, and geometrically checking whether there is no obstacle which blocks the line between the two positions.




On the other hand, paths of reflected waves can be calculated by a typical numerical method for electromagnetic waves. One example of such a calculation method is to use an algorithm that a reflecting surface is broken down into meshes and the current which flows in each mesh is calculated from the electromagnetic wave beam emitted from the array antenna to determine a reflected wave path. It is also possible to use the ray tracing method based on geometrical optics in which an electromagnetic wave path is determined on the assumption of specular reflection of electromagnetic waves on each reflecting surface. It should be noted that, taking into radio wave attenuation into account, a path of waves which undergo a smaller number of reflections than a given number of reflections, or a wave path effective for communication, is sought.




Then, for every calculated electromagnetic wave path, steps S


161


and


162


are taken (S


12


). At step S


161


, receiving field strength Pi is calculated, and at step S


162


, the direction in which each wave path is emitted from the antenna unit


101


is calculated and it is expressed as a radiation direction (θ,φ) which will be defined later.




The receiving field strength Pi for each path is calculated from the following parameters: transmitting power and antenna gain for the antenna unit


101


, propagation loss in the path space, loss at the reflection point, and antenna gain and receiving power for the vehicle-mounted communication antenna


22


. The antenna gain for the antenna unit


101


should be such gain that enables the designed basic directional pattern in the communication area


350


to get a sufficient field strength in the communication area. For the antenna gain and receiving power for the vehicle-mounted communication antenna


22


, standard values are used. A basic directional pattern refers to a radiation pattern which permits stable communication in a given position in the car detection area. This pattern involves only a direct wave or both direct and reflected waves from a structure of the tollgate.




Next, steps S


171


to S


176


are taken for each car j (S


17


). At step S


171


, from among receiving field strengths Pi calculated at step S


161


, the ones related to car j are extracted and expressed as Pji. At step S


172


, the Pji values are sorted in descending order and the maximum such value is expressed as MaxPji. At step


173


, the radiation direction (θi, φi) which corresponds to MaxPji is selected as radiation direction 1 (θi1,φi1). At step S


174


, radiation directions which do not correspond to MaxPji are all defined as radiation direction 2 (θki,φki).




At step S


175


, whether or not there is a car j in the communication area is checked to decide the step which follows. If there is not a car j in the area, step S


176


is carried out; if there is a car j in it, the process goes back to step S


17


and the steps for the next car (j=j+1) are started. Step


176


is carried out to redefine, as radiation direction 2, radiation direction (θi,φi) which has been defined as radiation direction 1 at step S


173


when there has been no car j in the communication area.




As discussed above, the electromagnetic wave path judgment section


150


distinguishes radiation direction 1 from radiation direction 2 and selects them as such with regard to each of electromagnetic wave paths Γi of direct and reflected waves, where radiation direction 1 refers to a direction that maximizes receiving filed strength Pji while radiation direction 2 refers to the other radiation directions.




Then, according to the selection of radiation direction 1 and radiation direction 2, the directional pattern for the antenna


101


is decided (S


18


). As mentioned later, after the electromagnetic wave path judgment section


150


determines the directional pattern so that the beam intensity in radiation direction 1 is maximized or over intensity 1 and that in radiation direction 2 is zero or below intensity 2, it gives the directivity controller


111


an instruction for the determined directional pattern.




In the above sequence, electromagnetic wave paths must be calculated repeatedly according to car profiles and positions. However, it is also possible that, if electromagnetic wave paths have been pre-calculated using car type data and car position data (path point in

FIG. 3

) as parameters, the calculation result data can be referred to later. Namely, a detection window is provided for each path point on the image, and in a real communication scene, the moment the car (image) comes into a detection window, the path memory


1531


is referred to for the path for the car. Car type data is obtained from the image taken at the first path point. This saves path calculation time in the electromagnetic wave path judgment section


150


and permits quick antenna directivity control which follows movements of successive cars entering the tollgate.





FIGS. 10A and 10B

show the data structures of the path memory. As seen in

FIG. 10A

, the path memory stores a path data file (path i, j) and a directional pattern file (dipat i, j) for each of path points x1, x2 and so on with respect to each car type. According to

FIG. 10B

, regarding electromagnetic wave paths 1 to 5, their radiation directions, whether the wave is direct or reflected, and receiving field strengths are calculated in advance, for instance, for a car of car type 1 at path point x1, and stored in path data file (path1,1).




Thus, the results of pre-calculations for plural combinations of car type and position data parameters by the electromagnetic wave path judgment section


150


are stored in the path memory


1531


as data available for reference in order to simplify the calculation of electromagnetic wave path Γi. In actual communication, it is also acceptable that, without relying on predetermined path points, the data for the car position closest to the car position detected by the car data detector


130


is searched from the path memory


1531


to select radiation direction 1 or 2.




Although only path data for the current car (car in the communication area) is shown in

FIGS. 10A and 10B

, it is also possible to add car type data and car position data (distance from the current car) for the next car as parameters and get path data for the next car beforehand. Since the next car is outside the communication area and the path calculation for the next car is only intended to prevent erroneous communication, it is sufficient to make a path calculation for just one next car or so and a relatively short distance from the current car (such a distance that the field strength for direct or reflected waves reaching the next car may be larger than that in radiation direction 1 for the current car); therefore the number of possible parameter combinations can be reduced to the extent that the calculation is possible.




FIG. 7 illustrates the basic directional pattern, radiation direction 1 and radiation direction 2. As indicated here, a car


31


which has been detected in the car detection area


130


is in the communication area


350


while a car


32


is outside the communication area. There are three electromagnetic wave paths for the roadside communication antenna


21


, the vehicle-mounted communication antenna


23


in the car


32


, and the vehicle-mounted communication antenna


22


in the car


31


: direct wave 1, direct wave 2 and reflected wave 1. In this case, the basic directional pattern for the roadside communication antenna


21


with respect to the communication area


350


is assumed to be as expressed by the dotted line in the figure.




Direct wave 1 represents a direct path between the roadside communication antenna


21


and the vehicle-mounted communication antenna


22


and runs in the main radiation direction for the directional pattern of the roadside communication antenna


21


. Direct wave 2 represents a direct path between the roadside communication antenna


21


and the vehicle-mounted communication antenna


23


and runs in the sub radiation direction for the directional pattern of the roadside communication antenna


21


. Reflected wave 1 represents a wave path from the roadside communication antenna


21


which is reflected from the car


31


and reaches the vehicle-mounted communication antenna


23


, and runs in the main or sub radiation direction for the directional pattern of the roadside communication antenna


21


.




The electromagnetic wave path judgment section


150


selects direct wave 1 for radiation direction 1 for the car


31


, and direct wave 2 for radiation direction 1 for the car


32


at step S


173


. At step S


174


, it selects indirect wave 1 for radiation direction 2 for the car


32


. However, if the receiving field strength for indirect wave 1 is larger than that for direct wave 2, radiation direction 1 for the car


32


is indirect wave 1. At step S


176


, for the car


32


, radiation direction 1 becomes radiation direction 2 because the car


32


is outside the communication area. As a consequence, direct wave 1 is selected for radiation direction 1 in the situation shown in FIG.


7


.




Next, the step of directional pattern determination by the electromagnetic wave path judgment section


150


(S


18


) will be explained, assuming that an array antenna or a pencil beam antenna unit is used.





FIG. 8

shows the structure of an array antenna composed of plane elements. A dielectric substrate


104


and antenna elements


102


which are mounted on a grounding board


103


constitutes an array antenna


101


. The feed factor (amplitude and phase) for power to be fed to each antenna element is adjusted by a corresponding phase/amplitude controller


112


shown in FIG.


4


.




Assume that:




x and y coordinate axes is taken with a desired point as the origin of coordinates on the antenna plane on which the antenna elements are arranged;




a z axis is vertically taken to the antenna plane in a manner that it extends through the dielectric substrate


104


from the grounding board


103


; and




power is irradiated from the array antenna


101


in a certain transmission direction


1000


on the x, y and z coordinate axes, the direction


1000


is expressed by angle θ from the x axis on the x/y coordinate plane and angle θ from the z axis. Radiation direction 1 and radiation direction 2 as mentioned above can also be defined by angles θ and φ (θ,φ).




Supposing that M antenna elements and N antenna elements are arranged in the x and y axis directions on the antenna plane, with element intervals d


x


and d


y


, respectively, the x and y coordinates for each antenna element


102


are expressed as (md


x


, nd


y


), where m=0, 1, 2, . . . , M-1; and n=0, 1, 2, . . . , N-1. When the feed factor for each antenna element is expressed as V


mn


and the power radiation from the array antenna unit


101


in the transmission direction


1000


is observed from far away enough, the power irradiated in the direction expressed as (θ,φ) or radiation pattern E (θ,φ) is represented by equation 1.










E


(

θ
,
φ

)


=




n
=
0


N
-
1







m
=
0


M
-
1





V
mn


exp






{


jk
0



(

mu
+
nv

)


}








Eq.  1













where u=k


0


sinθcosφ, v=k


0


sinθcosφ, k


0


is a carrier frequency wave number and j is an imaginary number. Equation 1 suggests that the electromagnetic wave emitted from each antenna element excited with a specified feed factor, with its phase changing according to the radiation angle, is combined with other such waves to form a radiation pattern.




Equation 1 takes the form of Fourier transform. Conversely, as a method using a Fourier transform pair, the feed factor V


mn


can be found by giving as many radiation patterns E (θ,φ) as antenna elements (M×N). Therefore, if radiation patterns E (θk,φl) are given (where k=0, 1, 2, . . . , M-1; and l=0, 1, 2, . . . , N-1), feed factor V


mn


can be calculated from the following equation 2:










V
mn

=


1
NM






l
=
1


N
-
1







k
=
0


M
-
1




exp






{


jk
0



(


mu
k

+

nv
1


)


}




E
k1



(

θ
,
φ

)










Equation  2













suggests that feed factor V


mn


is determined by the absolute value and phase angle calculated by giving radiant intensity Kkl (θk,φ1) with regard to M×N directions(θk,φ1).




This means that, when Ekl(θ,φ) is determined given E1 for radiation direction 1 (θi,φi) and E2 for radiation direction 2 (θh,φh), the feed factor of power irradiated with E1 for radiation direction 1 and E2 for radiation direction 2 can be calculated using equation 2. In this case, the intensity 1 and intensity 2 correspond to E1 and E2, respectively. Practically, 10×10 or a similar quantity of antenna elements are sufficient.




The directivity controller


111


supplies power with the amplitude and phase specified by feed factor V


mn


calculated using equation 2, to each antenna element


102


through the corresponding phase/amplitude controller


112


and changes the directional beam emitted from the array antenna


101


from the basic directional pattern to such a pattern that makes the intensity in radiation direction 1 over intensity 1 and that in radiation direction 2 below intensity 2.




In this embodiment, feed factors V


mn


for plural directional beam profiles are pre-calculated with radiation directions 1 and 2 as parameters and stored in the directional pattern memory


1532


of the storage


153


. After the electromagnetic wave path judgment section


150


selects radiation direction 1 and radiation direction 2, it reads out, from the memory, the directional pattern which provides radiation directions 1 and 2 most similar to the selected ones and sends its feed factor to the directivity controller


111


.





FIG. 11

shows the data structure of the directional pattern table. In this embodiment, the directional pattern table


1532


contains feed factors V


mn


(amplitude and phase) for the respective antenna elements which are pre-calculated for the respective path data files concerning car type and position x, as directional pattern files (dipat i, j) in the path memory


1531


shown in FIG.


10


A.




The structures of the array antenna


101


and directivity controller


111


or the method for finding V


mn


from a specified directional beam profile, as used in this embodiment, can be realized, for example, by using the array antenna and directivity synthesis method as stated on pages 80 through 92 of “Shin antena kogaku” (new antenna engineering) authored by Hiroyuki Arai (published by Sogo Denshi Shuppan in 1996) or the method or the like as stated in Chapter 9 of “Antena no kisoriron to sekkeiho” (basic theory and design method of antennas) authored by Kohei Hongo (published by Realize in 1993).




Next, how to control the directional pattern using pencil beam antennas as shown in

FIG. 5

will be explained. As the electromagnetic wave path judgment section


150


selects radiation direction 1 (θi,φi) and radiation direction 2 (θh,φh), it refers to the directional pattern memory


1532


in which basic directional patterns for pencil beam antennas in the array antenna unit


101


are stored in advance, and specifies the pencil beam antenna whose radiation direction (θl,φt) is most similar to the selected ones (step S


18


) and sends the relevant directional pattern data together with data on radiation directions 1 and 2 to the directivity controller


111


.




The antenna selector


701


in the directivity controller


111


connects the specified pencil beam antenna t with the communication controller


25


. The angle adjuster for the specified pencil beam antenna t is adjusted so that radiation direction 1 (θi,φi) coincides with the radiation direction (θt,φt) of the antenna t. Or, the angle adjuster for the specified antenna t is adjusted so that the intensity in radiation direction 2 (θh,φh) is null or below intensity 2.




As discussed so far, according to this embodiment, as a car approaching the tollgate is detected, the above-mentioned operational sequence is effectively followed to ensure stable communication with the car in the communication area while suppressing interference by reflected waves, and thereby perform automatic charging with accuracy. The sequence is as follows: all direct and indirect paths of electromagnetic waves between the roadside antenna and the vehicle-mounted antenna are calculated; the radiation direction which provides the highest electric field strength and corresponds to the path of radio waves to the car in the communication area is defined as radiation direction 1 and the direction which corresponds to other radio wave paths as radiation direction 2; and then the roadside antenna directional pattern is adjusted so that radiation power E (θ,φ) in radiation direction 1 is maximized or over intensity 1 and radiation power E (θk,φk) in radiation direction 2 is 0 or below intensity 2.




As a variation of this embodiment, the system may allow more than one car j to be present in the designed communication area and enable communication with plural cars concurrently. In this case, consequently the electromagnetic wave path judgment section


150


selects more than one radiation direction 1 (θji,φji), and the directivity controller


111


connects more than one pencil beam antenna for the radiation directions 1 with the communication controller


25


and adjusts the angle adjuster for each connected antenna to suppress the radiation power in radiation direction 2.




In this embodiment, the communication controller


25


starts communication just after control is performed by the electromagnetic wave path judgment section


150


and directivity controller


111


. In other words, at each time of periodic sampling by the car sensor


320


or the moment the head of the detected car passes each path point in the communication area


350


as shown in

FIG. 3B

, the electromagnetic wave path judgment section


150


and the directivity controller


111


begin operating; then upon optimization of the radiation pattern of the antenna unit


110


, the communication controller


25


starts communication with the car and the communication continues at least until the process of charging the car is finished.




At the next sampling time, or at the next path point, since the car's position has been changed, again the electromagnetic wave path judgment section is activated to readjust the radiation pattern of the antenna unit


110


. Although the communication continues during this readjustment, no communication trouble can occur because an once optimized radiation pattern can only undergo a fine adjustment.




The communication controller


25


and the electromagnetic wave path judgment section


150


are connected by a binary signal line


160


. The communication controller


25


sends the electromagnetic wave path judgment section


150


, through the binary signal line


160


, a high voltage signal during its communication with the vehicle-mounted communication antenna, and a low voltage signal while they are not communicating with each other, thereby enabling the judgement section


150


to stop its operation after the communication is over.




According to this embodiment, after a desirable electromagnetic wave path to a car in the communication area is acquired, if radio communication with the car in the communication area is not established, it is thought that the car has no vehicle-mounted antenna or the vehicle-mounted antenna is not ON. In this case, the system considers the car as not having a vehicle-mounted antenna properly and judges it unsuitable for automatic toll collection, and treats it as such, for example, by giving a warning.




Thus, the present invention produces the effect that the roadside communication antenna is controlled so as to obtain the required sensitivity for communication only with one car present in the designed communication area, while suppressing reflected radio waves from a structure or a car in the tollgate area, so that communication failures or errors can be prevented and charging or toll collection at the tollgate can be accurately performed through radio waves.




Also, the radiation pattern of the roadside antenna is adjusted so as to prioritize a required electromagnetic wave path and suppress unrequired electromagnetic wave paths, so restrictions on the structure of a tollgate as placed so far can be relaxed and the construction or operating cost can be reduced.




The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to appraise the public of the scope of the present invention, the following claims are made.



Claims
  • 1. A toll collection system communication method which charges a car passing through a communication area in a tollgate without a stop, by radio communication between a roadside antenna in the tollgate and a vehicle-mounted antenna in the car, the method comprising the steps of:detecting a car passing through a detection area including a communication area and a given area just before the communication area; calculating, when a car is present in the communication area, a plurality of electromagnetic wave beam paths of direct and reflected waves which connect the roadside antenna and the vehicle-mounted antenna; selecting a radiation direction of the wave beam paths whose communication sensitivity is the highest among the wave beam paths as radiation direction 1; defining the radiation direction of the wave beam paths other than the beam paths in the radiation direction 1 to cars outside the communication area as radiation direction 2; and controlling a directional pattern of the roadside antenna so that the intensity of the beam in the radiation direction 1 is over a first intensity, and that of the beam in the radiation direction 2 is below a second intensity of an intensity which disables communication.
  • 2. The toll collection system communication method according to claim 1, further comprising the steps of:calculating, when two or more cars are detected in the detection area, a plurality of wave beam paths of direct and indirect waves for the respective cars; and selecting all wave beam paths other than the wave beam paths to the cars outside the communication area as ones for the radiation direction 2.
  • 3. The toll collection system communication method according to claim 1, further comprising:obtaining data regarding a car profile of the detected car in the detection area; and calculating the wave beam paths by reference to car reflecting surface data for the car profile concerned and reflecting syrface data for the tollgate.
  • 4. The toll collection system communication method according to claim 1, wherein the process of calculating the wave beam paths begins when a car enters the communication area.
  • 5. The collection system communication method according to claim 1, wherein if no radio communication with a car which enters the communication area is established, the car is considered as not having a proper vehicle-mounted antenna.
  • 6. A toll collection system comprising:a car sensor for detection of a car in a given area including a designed communication area at a tollgate; and roadside communication antenna equipment having a roadside antenna and a directional pattern controller for changing its directional pattern, wherein charging is performed by radio communication between the roadside antenna and a vehicle-mounted antenna in an entering car without a stop, the system further comprising: an electromagnetic wave path judgement section: for calculating wave beam paths between the roadside antenna and the vehicle-mounted antenna according to data regarding a structure of the tollgate, a car profile and car position detected by the car sensor, and for selecting a radiation direction of the wave beam paths whose communication sensitivity is the highest among the wave beam paths as a radiation direction 1, and selecting all wave beam paths other than the wave beam paths to cars outside the communication area as the wave beam paths in a radiation direction 2 of disabled communication.
  • 7. The toll collection system according to claim 6, whereinthe car sensor is provided with a TV camera and images taken by the camera are processed to determine the profile of the car.
  • 8. The toll collection system according to claim 6, further comprising:a storage for storing gate reflecting surface data based on the structure of the tollgate and different types of car reflecting surface data for different vehicle profiles, wherein the electromagnetic path judgment sections obtains, from the storage, the gate reflecting surface data and the car reflecting surface data corresponding to the detected car profile, to calculate both a path of a direct wave between the roadside antenna and the vehicle-mounted antenna and a plurality of wave beam paths of reflected waves.
  • 9. The toll collection system according to claim 6, comprising:a storage for storing pre-calculated wave beam paths concerning a plurality car profiles, wherein the electromagnetic wave beam path judgment ssection obtains, from the storage, precalculated wave beam paths appropriate to the profiles.
  • 10. The toll collection system according to claim 6, whereinthe electromagnetic wave path judgement section: calculates the radiant intensities of the plurality of wave beam paths selects a radiation direction of the wave beam paths which has the highest radiant intensity as radiation direction 1, and determines a directional pattern which enables communication in the radiation direction 1 only.
  • 11. The toll collection system according to claim 10, further comprising:a storage for storing pre-calculated directional patterns as a plurality of combinations of variations of the radiation directions 1 and 2, wherein the electromagnetic wave path judgment section obtains a directional pattern appropriate to the selected radiation directions 1 and 2 from the storage.
  • 12. The toll collection system according to claim 6, whereinthe roadside antenna is an array antenna having a plurality of antenna elements, and the directional pattern is changed by controlling the amplitude and phase of power fed to the array elements.
  • 13. The toll collection system according to claim 6, wherein:the roadside antenna is an antenna unit which has a plurality of selectable pencil beam antennas arranged so as to emit beams in different directions, and the directional pattern is changed by selecting the pencil beam antenna whose radiation direction is nearest to the radiation direction of the prioritized wave beam path.
  • 14. A toll collection system communication method which charges a car passing through a communication area in a tollgate, by radio communication between a roadside antenna in the tollgate and a vehicle-mounted antenna in the car, the method comprising the steps of:detecting a car passing through a detection area including the communication area and a given area just before the communication area; calculating, when a car is present in the communication area, a plurality of electromagnetic wave beam paths of direct and reflected waves which connect the roadside antenna and the vehicle-mounted antenna; calculating, when two or more cars in the detection area are detected, a plurality of the wave beam paths for the respective cars; selecting a radiation direction of the wave beam paths whose communication sensitivity is the highest among the wave beam paths as radiation direction 1; and selecting the radiation of all wave beam paths other than the wave beam paths to the cars outside the communication area as a radiation direction 2 of disabled communication.
Priority Claims (1)
Number Date Country Kind
2000-055995 Feb 2000 JP
US Referenced Citations (6)
Number Name Date Kind
5227803 O'Connor et al. Jul 1993 A
5710556 Nishimura et al. Jan 1998 A
5751227 Yoshida et al. May 1998 A
5805082 Hassett Sep 1998 A
6081718 Ando et al. Jun 2000 A
6109525 Blomqvist et al. Aug 2000 A
Foreign Referenced Citations (2)
Number Date Country
7-239954 Sep 1995 JP
10-214359 Aug 1998 JP