Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Traffic analysis or control of surface vehicle
Reexamination Certificate
2001-11-30
2003-04-01
Beaulieu, Yonel (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Traffic analysis or control of surface vehicle
C701S118000, C340S934000
Reexamination Certificate
active
06542808
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to a method and system for mapping traffic congestion and in particular to a method for improving the accuracy of said mapping when a relatively small percentage of vehicles are used as traffic probes. In particular, this method provided also for using existing radio networks such as Public Land Mobile Networks (PLMN) and land mobile Private/Public Data Networks (PDN).
BACKGROUND OF THE INVENTION
Traffic congestion is an increasingly serious problem in cities.
One way to identify and map such congestion in real time (the first step to relieving it) is to identify and map the positions of vehicles that are stopped or moving slowly. Such systems are often referred to traffic control and car navigation in the field of Intelligent Transport Systems (ITS).
PCT publication WO 96/14586, published May 17, 1996, the disclosure of which is incorporated herein by reference, describes, inter alia, a system for mapping of vehicles in congestion.
In one embodiment described in the above publication, a central station broadcasts a call to the vehicles which requests tho se vehicles which are stopped or which have an average velocity below a given value to broadcast a signal indicative of their position. Such signals are broadcast in slots, each of which represent one bit (yes or no) which relates to a position. Preferably, only one logical slot (that may be represented by more than one actual slot) is used to define the related position. Such signals are then used to generate a map of those regions for which traffic is delayed or otherwise moving slowly.
Preferably, an additional call is sent to the vehicles requesting transmission of indication signals which locate the slow moving or delayed vehicles at a higher resolution than that of the first call. Further calls may be made to allow for transmission of additional information on the status of the vehicles and/or to provide further characterization of the delays.
FIG. 1
shows an initial map generated by such a method, wherein the area represented by a pixel (slot) may, for example, be of the order of 250 to 1000 meters square. In a preferred embodiment of the invention described, the system then determines, based, inter alia, on the extent of the various contiguous areas which shows positive responses, a smaller area or areas for further study. Preferably, the system broadcasts a further query requesting those vehicles within the smaller area that have at least a given delay (which may be the same as or different from that used in the first query) to broadcast in slots, each representing a position, using a finer resolution, for example, 100 to 250 meters square. Based on the responses to this query a second map such as that shown in
FIG. 2
is generated. As can be seen from
FIG. 2
, various branches of a road network radiating from an intersection, designated as A-F in
FIG. 2
, can be identified. To improve the usefulness of the display, a background map, such as a road map, may be displayed underlying the displays of any of
FIGS. 1
,
2
or
4
(described infra).
In the event that additional information relating to the delay is desired, further queries can be made. For example, vehicles which are traveling toward the intersection can be requested to broadcast in a slot which corresponds to the slot they are in and to their velocity toward the intersection. This allows for generation of the graph shown in the lower portion of FIG.
3
. Additional slots may be used for the acquisition of other information regarding the responding vehicles. Such information may also be graphed as shown in the upper portion of FIG.
3
.
Alternatively or additionally, a map which shows the average velocity of the vehicles toward the intersection as a function of the position can be generated. Such a map is shown in FIG.
4
. To acquire the information needed for generating such a map, a number of queries may be made, each requesting an indication from all vehicles within the area of interest having a given average velocity toward the intersection. The responding vehicles would broadcast their indication signals in slots corresponding to their position. In the map of
FIG. 4
, the velocity for a given pixel is determined, for example, as the average velocity of the reporting slots for that position. In a display of the map of
FIG. 4
, the velocity or delay toward the intersection can, for example, be displayed as a gray scale value or as a color, with for example red being the highest velocity or delay and blue being a minimum displayed velocity or delay.
FIG. 5
is a generalized block diagram for a system useful for performing the ITS function described above (and which is also useful for the method of the present invention).
FIG. 5
shows a base station or control center
91
having a control center transmitter
79
which broadcasts queries and optionally other signals to vehicles on command from a control computer
80
. A remote vehicle
85
(only one vehicle is shown for simplicity) receives the query at a vehicle receiver
84
and transmits commands to a microprocessor
86
, based on the queries it receives from the control center.
Microprocessor
86
also receives information regarding the status of the vehicle from one or more information generators and sensors indicated by reference numeral
88
. This information may be sent by the sensors on a regular basis or may be sent on command from the microprocessor.
Microprocessor
86
is then operative to command vehicle transmitter
90
to transmit indication signals (or if required, information bearing signals) in a suitable slot in accordance with the information received by microprocessor
86
.
The indication (or other) signals are received by a control center receiver
92
and processed by receiver
92
and computer
80
. While the operation and construction of the apparatus designated by reference numerals
82
,
84
,
86
and
90
is straightforward and needs no further explanation, the operation of receiver
92
is usefully expanded upon with reference to FIG.
6
.
Generally speaking, the RF signals transmitted by the vehicle may be at any frequency slot. It is to be expected that there will a certain amount of frequency diversity caused by the imperfect accuracy and stability of the vehicle transmitters
90
. The slots are wide enough to accommodate this diversity.
Furthermore, often the system utilizes very large numbers of vehicles. If too many of these vehicles (in some particular situation) transmit in the same slot, then the total power transmitted may exceed authorized ERP or dynamic range restrictions. To overcome this problem longer, lower power, pulses may be used for indication signals. Furthermore, if a single receiver is used for receiving signals for all of the slots, intermodulation effects may cause spurious signals to appear in slots for which no actual signals have been received.
These problems as well as near-end to far-end transmission problems are substantially solved by the system shown in FIG.
6
and by certain constraints placed on the system which are not shown in FIG.
6
. The problems and constraints but are described in the above referenced PCT publication, which should be consulted for a more complete exposition of the method and apparatus shown in
FIGS. 1-6
.
FIG. 6
shows a receiver system corresponding generally to reference number
92
and to a portion of computer
80
of FIG.
5
. While the system of
FIG. 6
is suitable for the prior art ITS system of the PCT publication, it is also suitable for use with the ITS system of the present invention.
An antenna
94
(or an array of antennas) receives signals from a plurality of vehicles simultaneously and passes them to a receiver and (optionally) AGC
96
. Receiver and AGC
96
, which may be of conventional design, down converts the received signals from RF to IF frequencies. The threshold levels of the detection process may be dependent on the AGC process. Alternatively, the system is operated in a closed loop mode in which the power radiated by the vehicl
Beaulieu Yonel
Norris Mclaughlin & Marcus P.A.
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