WO2010029502A1

WO2010029502A1 - A radio frequency system

Info

Publication number: WO2010029502A1
Application number: PCT/IB2009/053935
Authority: WO
Inventors: Abraham Gert Willem Du Plooy; Albertus Jacobus Pretoriius
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-09-09
Filing date: 2009-09-09
Publication date: 2010-03-18
Anticipated expiration: 2011-03-09
Also published as: ZA201101616B

Abstract

A radio frequency system comprising a radio frequency identification (RFID) tag mounted in or on a road surface. An RFID tag reader for reading the tag is located above the RFID tag so that when a vehicle is traveling along the road surface and the tag is at least partially located between the RFID tag reader and the RFID tag, the RFID tag reader is then unable to read the RFID tag but when there is no vehicle located between the RFID tag reader and the RFID tag the RFID tag reader is able to read the tag.

Description

A RADIO FREQUENCY SYSTEM

BACKGROUND OF THE INVENTION

THIS invention relates to a radio frequency system, specifically to a system which is able to calculate amongst others the presence of a vehicle, the length of the vehicle, the number of vehicles passing along a specific road surface and the speed at which the vehicles travel.

At present some of these calculations are achieved through the use of radar toward the license plates, while other calculations are achieved manually.

The present invention provides an alternative radio frequency system for calculating the above-mentioned parameters. SUMMARY OF THE INVENTION

A radio frequency system comprising:

a radio frequency identification (RFID) tag mounted in or on a road surface; and

an RFID tag reader for reading the tag, the RFID tag reader being located above the RFID tag so that when a vehicle is traveling along the road surface and the tag is at least partially located between the RFID tag reader and the RFID tag, the RFID tag reader is then unable to read the RFID tag but when there is no vehicle located between the RFID tag reader and the RFID tag the RFID tag reader is able to read the tag.

A radio frequency system wherein the RFID tag re-radiates a signal and the RFID tag reader receives and reads the signal from the RFID tag.

The system may include an RFID tag reader mounting structure to which the RFID tag reader is mounted.

The RFID tag reader mounting structure may be one of an advertising billboard, a road sign, a lamp pole and a bridge.

The RFID tag reader may be a passive tag or an active tag reader.

The system may determine the presence of a vehicle when the re-radiated, back-scattered, signal received by the RFID tag reader, disappears when the vehicle travels along the road surface and it is at least partially located between the RFID tag and the RFID tag reader. When there is no vehicle located between the RFID tag reader and the RFID tag, the tag reader will be able to receive the re-radiated, back-scattered signal from the tag. In one example embodiment, the system includes at least two RFID tags and at least one RFID tag reader and the speed and length of the vehicle may then be calculated from the difference in time when the re-radiated, back-scattered, signals received by the reader, disappears. In another example embodiment, the system could include at least two RFID tags and at least two RFID tag readers and the speed and length of the vehicle may then be calculated from the difference in time when the re-radiated, back- scattered, signals received by the readers, disappear.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an example embodiment of a system with a vehicle not located between an RFID tag and an RFID tag reader;

Figure 2 shows the example embodiment of Figure 1 with the vehicle partially located between the RFID tag and the RFID tag reader; and

Figure 3 is a perspective view of an example embodiment of an RFID tag located in a tag housing.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the accompanying drawings, an example embodiment of a radio frequency system 10 shows a vehicle 12 traveling on a road surface 14.

An RFID tag 18 is mounted on or in a road surface 14 and an RFID tag reader 16 is mounted above the RFID tag 18 at a distance that is high enough to allow vehicles to pass between the reader and the tag. -A-

Each tag has a unique ID thus it is know exactly where it is placed in the road surface.

The RFID tag reader 16 is mounted on a mounting structure 22 which could take any form as long as it allows the RFID tag to be mounted at the correct orientation and distance in relation to the road surface.

Examples of such a mounting structure 22 could be a lamp pole, an advertising billboard, a road sign or a bridge over the road. However, it will be appreciated that the mounting structure could take any other suitable form.

Referring to Figure 1 , when the vehicle 12 is not located between the RFID tag 18 and the RFID tag reader 16, the RFID tag reader 16 transmits a signal 22a while the RFID tag 18 re-radiates the back-scattered signal. The tag reader 16 receives and reads this back-scattered signal 22b.

It is envisaged that the RFID tags will be passive RFID tags which will re- radiates (signal 20b) in response to being subjected to an energy field at the appropriate frequency, or polled (signal 20a) by the reader 16. However, an active tag system where the tags transmit at predetermined intervals will also be suitable although battery life considerations for the tag will need to be carefully taken into account in this case.

In either case, a radio frequency system is required wherein the RFID air protocol supports reading of multiple tags responding.

It is also envisaged that the frequency used is such that reading of the tag by the reader requires near line of sight. The Ultra High Frequency (UHF) band is a good example of such a frequency.

Let us consider the case where one tag is in the beam of one reader. The tag may transmit/respond in a predictable manner where T is the time period between transmissions/responses from the tag and R is the time to send the unique identification of the tag to the reader. It is clear that the most accurate tag disappearance time can be obtained when T and R is constant. It should also be noted that a lower T value will increase the accuracy of the system but will negatively influence the ability to read multiple tags. Also, R should be as short as possible and should be a fixed length.

To perform the speed and length calculations we require two tags in the road. Often these two tags will be simultaneous in the beam of the reader, which will influence the values of mostly T to allow for the reading of multiple tags in the beam.

RFID uses two general types of multi read protocols. A reader-talk-first protocol will interrogate tags in the field whereby a tag is selected and polled. A tag-talk-first protocol uses a method where the tag will transmit all the time when power is beamed at it.

It is acknowledged that in the tag-talk-first protocol, the tag often transmits with a random T value to allow for the reading of multiple tags in the beam and this will influence the accuracy of the speed measurements. However, within the scope of the purpose of traffic flow and speed indications the accuracy achievable is adequate.

The reader-talk-first protocols will interrogate tags in the field whereby a tag is selected to communicate with obtaining the identification code of the tag. With only one tag in the beam both R and thus T can be very deterministic and constant. With more tags and with the un-deterministic nature of RF, R will become less constant and predictable. However, within the scope of the purpose of traffic flow and speed indications the accuracy achievable is adequate.

A third method is by combining the two above protocols in the following manner: • All tags transmit with a fixed T and R in tag-talk-first mode.

• T is random between an upper and lower value, but fixed per tag. Each time a tag powers up a new random T may be selected. The reader can detect each tags T value easily.

• Each tag will also have a W value, which is smaller than T, to spread tag transmission where T is close. W may also be randomly selected when the tag is powered.

• It is clear that some crosstalk will happen. This crosstalk can then be managed by the reader setting the T and W values on each tag in a reader-talk-first protocol. The reader may also switch the randomization of T and R off where two readers are used with only one tag is in the beam of each reader.

An example of the above using two tags, T1 and T2 in the beam of one reader. T is set at 5ms, R is set at 1 ms and W is set at zero. When the reader switches on, both tags will transmit at the same time and the reader will not be able to decode the tag responses. The reader, with knowledge of the T1 and T2 identification code, may instruct for example T1 to set its W value to 3. Thus T1 and T2 will now transmit at different times. It is clear that the situation can be improved by having T, R and/or W set randomly by the tag at power on, thus allowing the reader to discover the T1 and T2 and from then on be able to optimise the tag transmissions.

In Figure2 the vehicle 12 is at least partially located between the RFID tag 18 and the RFID tag reader 16 so the RFID tag reader 16 is unable to read the tag 18. Thus, the reader 16 assumes that there is a vehicle located between the reader 16 and the tag 18.

In this manner the reader 16 can calculate a number of factors.

Firstly, as the presence of a vehicle is known the number of vehicles passing under the reader 16 can be calculated. This can be accomplished as the reader 16 will not receive a re-radiated, back-scattered signal from the tag 18 for a given time period and will then once again receive a signal from the tag which means that a vehicle has completely passed between the reader 16 and the tag 18.

Secondly, the length of the vehicle can be calculated using the amount of time that has elapsed between the last reading that the reader read the tag and the next reading that it is able to read the tag again, after a short interval.

In addition, the speed of the vehicle can be calculated. For this the system includes at least two RFID tags 18, each RFID tag 18 mounted in or on a road surface at a known distance between each other. Nominally one RFID tag reader 16 is mounted above the RFID tags 18. Thus the speed of the vehicle can be calculated using the time elapsed between when the vehicle passes over the first tag and when the vehicle passes over the second tag. Two RFID readers can be used to create a longer distance between measurement points. The time stamp (real time) can be used to calculate the elapsed time over the given distance. With elapsed time and distance, the speed can be calculated.

In another example embodiment, the system could include one RFID reader, with at least two external antenna sets and at least two RFID tags and the speed and the length of the vehicle may then be calculated from the difference in time when the re-radiated, back-scattered, signals received by the readers disappear. In the latter embodiment the accuracy is improved by placing the antenna sets and tags at such an angle to cater for the variation in vehicle shapes. I should be appreciated the vehicle height and from will break the reader tag beam at different times when the tag is at an angle below the antenna of the reader. The best position for the tag is directly below the antenna of the reader. With two tags we thus require two sets of antenna or readers to achieve tags directly below the antennas. In yet another example embodiment, the vehicle may carry a tag, for example in the windscreen, which is read whilst the measurement tags responses disappear. In this case the vehicle may be associated with the speed and length calculated.

In yet another embodiment the tags are place in the road in such a manner that the line and width of the vehicle may be calculated. In this example, the tags may be placed also on the verge of the road to detect when a vehicle is illegally traveling on the verge of the road.

Further, where vehicles are required to be fitted with vehicle identification tags, the system can be used to identify vehicles not fitted with such a tag. This is implemented in that if the reader 16 is unable to read the tag 18 located below, it should then be able to read a tag located on the motor vehicle. If it cannot read the tag 18 located below it and at the same time cannot read a tag located on the motor vehicle then the system assumes that there is either no tag on the vehicle or that the tag on the vehicle is faulty.

The tag reader 16 either includes a processor to make the necessary calculations for the above applications or alternatively the data is transmitted from the tag reader 16 to another computer to use the same data to make the necessary calculations.

In either case the tag reader is typically connected via a communications network to a central controller for the transmission of raw or calculated data to the central controller and for the central controller to transmit control commands to the tag reader 16.

The communications network may be a hard wired or wireless communications network.

Referring to Figure 3, the figure illustrates a perspective view of an example embodiment of an RFID tag 18 located in a tag housing 24. In this embodiment, the tag housing 24 is of the type of housing that is used for reflectors that are placed in the road surface and are commonly referred to as "cat's eyes".

The housing 24 illustrated in Figure 2 does not include a reflective hump and is solely used to house the tag 18. However, it will be appreciated that the housing could in addition include reflective material so that its function doubles as a tag housing and reflector.

Even without the double function it is advantageous to include the tag 18 in such a housing as machines used to cut the correct sized hole in a road surface already exist and these can be used to cut holes for the tag housing 24.

In any event the housing is typically made from a strengthened glass would the tag located as deep as required in a cutout in the glass. In this way the tag is protected from a vehicle driving over the housing. The tag antenna and the embodiment will form an integral unit.

Claims

CLAIMS:

1. A radio frequency system comprising:

2. A radio frequency system according to claim 1 wherein the RFID tag re-radiates a signal and the RFID tag reader receives and reads the signal from the RFID tag.

3. A radio frequency system according to claim 1 or claim 2 wherein the system include an RFID tag reader mounting structure to which the RFID tag reader is mounted.

4. A radio frequency system according to claim 3 wherein the RFID tag reader mounting structure is one of an advertising billboard, a road sign, a lamp pole and a bridge.

5. A radio frequency system according to any preceding claim wherein the RFID tag reader is a passive tag or an active tag reader.

6. A radio frequency system according to any preceding claim wherein the system includes at least two RFID tags and at least one RFID tag reader and the speed and length of the vehicle are calculated from the difference in time when the signal received by the reader disappears.

7. A radio frequency system according to any preceding claim wherein the system includes at least two RFID tags and at least two RFID tag readers and the speed and length of the vehicle is then calculated from the difference in time when the signals received by the readers disappear.