GB2186409A - Vehicle identity detection system - Google Patents

Abstract

The data capture system is for the automatic charging of tolls to vehicular users of roads. The system comprises a plurality of vehicle identity data transmitting means mounted on respective vehicles, a plurality of roadside vehicle identity data interrogating means connected to sensors and linked to a central control which includes a number of validating processors. Each validating processor is allocated a discrete subset of all vehicles handled by the system, so that each vehicle can be validated to enable the preparation of toll invoices. A correlator is provided in the interrogating means to allow a correlation process to be performed to identify signals produced by the same vehicle from more than one sensor, to quantify pulse ratio and pulse alignment values to produce a correlation factor.

Description

SPECIFICATION Data capture system This invention relates to a data capture system for the automatic charging of tolls to vehicular users of roads.

The invention provides a correlation process to identify detector signals produced by the same veh iclefrom more than onevehiclesensor.

According to the present invention there is provided a data capture system for the automatic char ging oftolls to vehicular users of roads, the capture system comprising, a plurality of vehicle identity data transmitting means each being individually attachable to vehicles, plurality of roadside vehicle identity data interrogating means connected to a plurality of vehicle sensors, and linked by a communications network with a central control which includes a plurality of communications control processors, and a plurality of vehicle identity data validating processors which communicate by means of a common inter-processor bus, wherein each data validating processor allocated a discrete subset of all vehicles handled by the system, and upon transmit- ted vehicle identity data being detected by any one roadside vehicle identity data interrogating means, the vehicle identity data is transmitted through the communications networkto a communications control processor and then by way of the common interprocessor bus to a particular data validating processor allocated to the subset of vehicles within which, the detected vehicle identity data is located, whereupon,the detected vehicle identity data isvalidated for use in enabling the preparation of toll invoices for despatch to the particular vehicle user concerned, and correlation means is provided by an outstation processor included in the plurality of roadside vehicle identity data interrogating means, whereby a correlation process is performed to iden tifydetectorsignalsproduced bythesamevehicle from morethan one sensorto quantify pulse ratio and pulse alignmentvalues to produce a correlation factor.

The invention will be better understood from the following description of an exemplary embodiment which should by read in conjunction with the accompanying drawings, in which: Figure 1 shows a block schematic of the data capture system.

Figure 2 shows two pulses detected by an induc- tive road loop.

Figure 3 shows a flow chart depicting the steps performed to calculate the pulse ratio.

Figure 4shows a flow chart depicting the steps performed to calculate the alignment ratio.

Figure 5shows a flow chart depicting the steps performed to calculate the correlation factor, and, Figure 6shows a flow chart of correlation factor values.

The data capture system comprises electronic number plates (EN Ps) fitted to road vehicles, roadside interrogators, data transmission equipment and central office equipmentto collect and validateveh- icle identity data before passing it on to an accounts processing system.

Electronic number plate (ENP) Each vehicle in the system is fitted with vehicle identity data transmitting means, e.g. an electronic number plate (ENP).

The ENP is a small sealed module approximately 200mm long x 75mm wide and 40mm deep. It is located by means of securing points beneath the vehicle body. It is easy to fit, but once fitted is difficultto remove.

Each ENP apparatus has a unique identifying serial numberwhich is converted into code and stored in the ENP apparatus during manufacture. All ENP apparatus codes are independent ofanyvehicle mechanical registration number, making it difficult to copy and defraud.

At the fitting station where the vehicle is equipped, the vehicle registration number is entered into the system by an operator via a keypad, whilstthe serial number is read automatically into the system by an interrogator. This serial number is not displayed to the operator, for security reasons. The ENP appar atus is equipped with two aerials which provide elec- tromagnetic coupling with inductive road loops (cables buried in the road). One aerial receives sufficient energy to power up the ENP apparatus when it is in the immediate vicinity of a power loop PL. This aerial also provides a clock inputforthe ENP circuits which generate the synchronous data to betransmitted via the other aerial backto a receive loop RXL.

The ENP apparatus receives its power and clock at 147kHz and transmits the data on a 73.5kHz carrier.

The data is 9.1 87kBaud, i.e. one sixteenth of the powering frequency.

The ENP apparatus contains three integrated circuits (IC's). One, a fuse-link PROM, is programmed with the serial number code during manufacture. Another, a CMOS custom IC performs all logicfunctions, and a special bipolar IC, measures signal thresholds and performs the linearfunctions. These IC's together with other components, are mounted on a printed circuit board.

The ENP apparatus is capable of transmitting the serial code (in phase modulated form), a security or check code for providing an extra protection against fraud, and (optionally) variable data set-u p by the driver of the vehicle on a variable data unit within the vehicle.

Various types of variable data unit's can be used.

Some of the data field being varied automatically by peripheral equipment connected via the unit. This may include such items as emergency vehicle status and priority code, bus identification, depot, fleet and route number. The remainder of the data field being varied by switches on the unit.

Outstations Along the roadside RS are located vehicle identity interrogating means oroutsations OS which comprise an interrogator, which is connected to the veh icle sensors in the form of inductive road loops (power PLand receive RXL),a processor, a transmission unit and a number ofinterfaces to local equipment, such as atoll display TD where charges are indicated, a closed ci rcuit television control CCTVC, a maintenancehandsetorterminalTMthroughwhich police and maintenance services gain access to information, and a priority controller PC for handling control signals relating to vehicles requiring priority.

System in general It is arranged for the interrogatorto demodulate signals received from each receive loop RXL and pass the identity data to the processor where the code is verified. Vehicle identity data is subsequently transmitted from the outstations OS by the transmission unit to the central control CC byway of a communications networkCN in the form of cable network. EachcommunicationscontrollerCCLhas control of a part of the complete cable network, with a number of outstations (e.g. ten) connected (via the network) to each of its communications channels.

The central control CC comprises a number of communications controllers CCL, a number of processors (accounts processor AP, supervisory processor SP, fleet location processor FLP, traffic statistics processorTSP, data validation processor or data validator DV, and a spare processor SPE), disc and tape storage, and operator communication facilities OC which include visual display units (VDU's) and a hard copy terminal or printer.

The communications controllers CCL, handle data transmission between the outstations and a high speed bus IPB to which all the central control processors are connected. The IPB is a local area network link arrangementtermed an ETHERNET bus which operates 10 Mbits over a single coaxial cable.

Processors tap into the cable at intervals allowing up to 100 stations (nodes) on a 500m cable with upto 1024 stations in any network.

Concerning the various processors mentioned above, the data validation processors or data validators DV checkthe security code (if used) and location (outstation) of each ENP againstthe last known interrogation data, an accounts processorAP, prepares road charge invoices and despatches them periodically to the vehicle owners and a supervisory processor SP oversees the operation of the data validators DV, co-ordinates fault detection and recovery, including checking if apparent errors in vehicle data can be explained by faults known to the system ('Anomaly Processing'), and handles operatorcommunications.

Data received from the outstation units OS are interrogated bytheassociatedcommunicationscon- troller CCL and passed to the appropriate data valida- tor DVvia the high speed bus (local area communications network IPB). Each data validator DV is allocated a discrete subset of all vehicles in the system, to enable vehicle location checking to be maintained as the vehicles move through the area, and are detected by the differetn outstation units OS and, hence, different communications controllers CCL.

Any apparent error in vehicle data is passed on the supervisory processor SP, which checks if the error can be explained by known faults in the system, such as a faulty upstream interrogator. Atthe same time, if the vehicle was detected at a manned or CCTV outstation, data is sent to that outstation for display on the local terminal or inclusion with display atthe central control. Valid vehicle data is output for use bythe accounts processor AP.

Data that fail the validity check and anomaly analysis causes that End to be marked as 'suspect' in the computer records. It is added to the 'Wanted List' in the supervisory processor SP and marked for special attention in the data validator DV responsible forthat ENP.

A data capture system is described in greater detail in co-pending UK patent application No. 21 54832A.

Correlation process fordetectorsignals In order to identify detector signals produced by the same vehicle from more than one inductive road loop a correlation process is performed by a processor in a particular outstation. To correlate the signals,the pulse ratio and alignment of pulses are defined and are quantified, and are used to calculate a correlation factor.

Referring to Figure 2, two pulses, pn and pn+1 are shown. Pn is the detector pulse from an inductive road loop n, tp(n) is the duration of the detector pulse from the loop n and d the time between the centres oftwo pulses. In Figures3to Sthetwo pulses are identified as A and B.

The pulse ratio P, is the ratio between the duration of two detector pulses.

P=(tp(n) -tp(n+1))/tp(n)wheretp(n)isgreaterthan tp(n+1) As tp(n+ 1) approaches zero, the pulse ratio P approaches 1,themaximumvalue.

As tp(n+ 1) approaches tp(n), the pulse ratio P approaches zero, the minimum value.

Referring to Figure 3, a flow chart of the steps performed bya microprocessor to calculate the pulse ratio is shown.

Step 1 The input consists of pulse length A and pulse length B.

Step 2 The length of pulse A is checked to see if it is greaterthan or equal to the length of pulse B. If it is, steps 3,4 and 7 are performed, if it is not, steps 5,6 and 7 are performed.

Step3 The difference between the length of pulse A and pulse B is calculated.

Step 4 The pulse length is determined as the length of pulse A.

Step 5 The difference between the length of pulse B and pulseAiscalculated.

Step 6 The pulse length is determined as the length of pulse B.

Step7 The pulse length is checked to see if it equals zero, if it does steps 8 and 12 are performed, if it does not, steps 9,10 and 12 are performed or steps 9,1 1 and 12 are performed.

Step8 The pulse ratio equals FFFFH where FFFFH is determined as a hexadecimal number.

Step 9 The difference between the pulse lengths is divided by the pulse length, to see if the value is greater than zero.

Step 10 The pulse ratio is determined as a hexadecimal number FFFFH.

Step 11 The pulse ratio is determined as the difference between the pulse lengths multiplied by the hexadecimal number FFFFH and divided by the pulse length.

Step 12 The pulse ratio is generated as an output.

The alignmentAofthe pulses, is the ratio ofthe time between the centres of two pulses and thedura- tion ofthe longest pulse, and is given byA = d/tp(n) wheretp(n) is greaterthantp(n+1).

As d approaches zero, A approaches zero; when d equalstp(n),Aequals 1.

As d approaches infinity, A approaches infinity.

Referring to Figure4, a flow chart of the steps performed buy a microprocessor to calculate the al ig n- ment ratio is shown.

Step 1 The input consists of the length of pulse A and pulse B and an offsettimevalue.

Step 2 The length of pulse A is checked to see if it is greaterthan or equal to the length of pulse B, if it is, steps 3 and 5 are performed, if it is not, steps4and 5 are performed.

Step3 The pulse length is determined as the length of pulse A.

Step 4 The pulse length, is determined as the length of pulse B.

Step 5 The pulse length is checked to see if it equals zero.

If it does, steps 6 and 10 are performed, if it does not, steps 7,8 and 10 or steps 7,9 and 10 are performed.

Step 6 The alignment ratio is determined as a hexa decimal number FFFFH.

Step 7 The offset time value is divided bythe pulse length to see ifit isgreaterthanzero.

Step8 The alignment ratio is determined as a hexadecimal number FFFFH.

Step 9 The alignment ratio is determined as the offset time value multiplied by the hexadecimal number FFFFH and divided by the pulse length.

Step 10 The alignment ratio is generated as an output.

Correlation algorithm The correlation algorithm for calculating the detector correlation factor CF, is given by CF = Alignment Ratio/(Pulse Ratio/K)+ 1. The constant K is greater than the correlation factor.

Referring to Figure 5, a flow chart of the steps performed by a microprocessorto calculate the correla- tion factor is shown.

Step 1 The input consists of the pulse ratio and alignment ratio.

Step 2 The correlation factor is calculated by dividing the alignment ratio by a divisor. The divisor is obtained by dividing the pulse ratio by a constant and then adding onetothe result.

Step 3 The correlation factor is generated as an output.

To include all smaller pulses which fall within the boundaries of the longest pulse,thevalue ofthe con- stant K must be divided by two, as shown in Figure 6 which depicts the correlation factor values. The vertical axis shows correlation factorvalues CF. The horizontal axis shows alignment ratio values AR, and five graphs are depicted having different pulse ratios PR.

The calculation of the pulse ratio values PR, align- ment ratio values AR and correlation factor values CF are performed as described above by the outstations OS by circuitry well known in the data processing art, such as a microprocessor.

Claims (5)

1. Adata capturesystem forthe automaticchar- ging of tolls to vehicular users of roads, the capture system comprising, a plurality of vehicle identity data transmitting means each being individually attachable to vehicles, a plurality of roadside vehicle identity data interrogating means connected to a plurality of vehicle sensors, and linked by a communications networkwith a central control which includes a plurality of communications control processors, and a plurality of vehicle identity data validating processors which communicate by means of a common inter-processor bus, wherein each data validating processor is allocated a discrete subset of all vehicles handled by the system, and upqn transmitted vehicle identity data being detected by any one roadside vehicle identity data interrogating means, the vehicle identity data is transmitted through the communications network to a communications control processor and then by way of the common inter-processor bus to a particular data validating processor allocated to the subset of vehicles within which, the detected vehicle identity data is located, whereupon, the detected vehicle identity data is validated for use in enabling the preparation oftoll invoices for despatch to the particular vehicle user concerned; and correlation means is provided by an outstation processor included in the plurality of roadside vehicle identity data interrogating means,wherebya correlation process is performed to identify detector signals produced by the same vehicle from more than one vehicle sensor to quantifypulseratioandpulsealignmentvaluesto produce a correlation factor.

2. A data capture system, as claimed in claim 1, wherein the pulse ratio, p is given by (tp(n) tp(n+ 1 ))/tpn, wheretp(n) is the duration of the pulse detected by the road loop and tp(n) is greaterthan tp(n+1).

3. A data capture system as claimed in claim 2 wherein the alignment ratio A of pulses is given by d/tp(n), where d is the time between the centres of two pulses.

4. A data capture system as claimed in claim 3, wherein the correlation factor is given by: A/(P/K)+1 whereAisthe alignment ratio,Fisthe pulse ratio and Kisaconstant.

5. A data capturesystem substantially as herein before described with reference to Figures 1 to 6 of the accompanying drawings.