RFID-Radar^TM

The Problem - How can you measure range using low cost transponders

Before the arrival of RFID-radar, readers have been able to read the identity of multiple transponders in a zone at one time, but they have not been able to locate where in the zone the transponders actually are physically.

As the performance of readers and transponders improve, operating ranges increase giving one reader the ability to monitor larger areas meaning location information in addition to the identity information becomes very important.

RFID-radar works with very low cost transponders and relatively cheap reader systems.

Trolley Scan's new RFID-radar kit with High gain patch antennas

The invention

This is a world first base technology, allowing companies involved in its development the ability to deliver very advanced low cost RFID systems for many years.

Trolley Scan's new RFID-radar front panel showing simple controls for 2D scanning

Twelve transponders are plotted. The yellow zone is the field of view of the radar. The axes are in meters.

The equipment

The reader

The reader provides an energy field to power up the transponders, and measures the distance the signal travels from the transponder back to the reader. For 2D and 3D applications, two or three receiver channels are included in the reader to allow angle of arrival to be determined at the reader site by comparing the range from each of the reader channels.

The reader contains a fast processor module making up to 10000 range measurements per second to allow the tracking of each of the tags in the zone with update rates at one second intervals.

The reader interfaces to other computer networks via RS232.

The reader has one array of adjacent antennas measuring range from that array to the tags. The array contains one transmit antenna for energising the passive transponders and one antenna for each receiver (2 antennas total for 1D,3 antennas for 2D and four for 3D).

The reader can be set to operate in any frequency range from 860 to 960 Mhz, using 10 kHz of spectrum for the energising signal. Two reader systems can operate within 4 meters of each other. The reader processor consolidates the huge amount of information retrieved by the reader sections. It can report

1. Identity of tags in the field.
2. Identity, range and pointing vector to the tag in 1D, 2D or 3D space
3. Identity and track of movement of tags in the reader zone, updated at 1 second intervals.

The tags

Typical transponders in a credit card sized format and stick format

These are passive backscatter Ecotag UHF transponders. They can be packaged in different antenna forms. Operating range depends on the sensitivity of the transponder, with the 5 uW versions operating up to 40 meters, and the 200uW versions working out to 10 meters.

Operating range is a function of two processes

• The ability of the computer algorithms in the radar to determine the range
• The ability to power a tag at a distance and to detect the weak signal returning

Specification

Accuracy range

50 centimeter in absolute mode & millimeter resolution in relative mode

Max no of dimensions

3 (2 in evaluation version)

Pointing accuracy

0.2 degree

Maximum range of reader

40 meters (practical) Energising dependant on transponder type- 40 meters for current 5uW tags

Transponder technology

Passive TTF (Tag talks first) protocol

Multiple transponders

Up to 50 in the energising zone

Interfacing to computer network

RS232

Field of view

64 degrees- 80 degrees

Operating frequency of reader

860 to 960 MHz

Operating bandwidth of reader

10kHz

Interference zone with second reader on close frequency

4 meters

Multipath discrepancies

Range corrected for multipath

Competitive technologies

Ranging beacons

These are very sophisticated transponders that are attached to expensive military hardware in warehouses for locating where the "Military tank is parked". The transponders cost more than US$1000 each and the warehouse has to be fitted with ranging beacons all over the warehouse to provide triangulation.

WiFi/Bluetooth

GPS units fitted in each transponder with the position data communicated via WiFi networks. Transponders are very expensive and are major user of battery energy for the communication and position location.

Fingerprinting/Multilateration

The site where the transponders are to be used has to be mapped before use showing power fluctuations of signals on multiple receivers caused by a single source. Susceptible to other objects being moved into the site after survey impacting the survey, multipath variation due to reflections and needing multiple receivers. Very crude positioning technique.

Functionality

The radar measures the distance the signal travels from the various transponders to the radar antenna. By comparing the range on two receivers, the angle of arrival can be measured and so a direction and range can be shown. The reader can process about 50 transponders in a zone at a time, at the rate of 10000 range measurements per second, and can operate up to ranges of 40 meters with suitable transponders. Only one set of antennas is needed for a full fix with one reader. A third receiver channel can be added to give 3D coverage rather than 2D coverage (or a second evaluation system fixing the same transponders from a slightly different position and solving mathematically). A major feature of the system, besides its accuracy in measuring the range, is that the interference generated by this radar for other similar users and for other RF users, such as cell phones, is very low. Many RFIDradar systems can operate in close proximity without interfering with each other.

Another feature of the radar system is the ability to track moving targets. By measuring the range many times per second of each transponder, the reader can plot the path of a moving object in its field of view.

The reader outputs location and identity information at regular intervals, which can be displayed on a laptop running a Visual Basic program to show a radar type display.

The radar can also locate and process transponders attached to wood and metal.

Importance of this invention

When read ranges of RFID systems are small, then location information is not important as it is always in close proximity to the reader. As technology improves and the transponders need less and less power to operate, so the read range starts increasing, meaning the uncertainty in the exact location of the transponder increases. This improved sensitivity transponder technology needs increased information from the reader to assist in the speedy location of the transponder and here the technology detailed in this brochure becomes important.

This invention is the only solution to the RFID-Radar problem that uses low cost transponders.

The arrival of RFID-radar has stimulated the development of lower powered UHF backscatter transponders to increase operating range. While conventional RFID readers typically would want maximum read ranges of about ten meters, RFID-radars ability to report location means that ranges of 40 meters from one reader are being requested.

Commercialising

Trolley Scan are one of the world leaders in UHF RFID developments and manufacture leading edge designs which they export currently to 53 countries.

Trolley Scan are now delivering

• Commercial models to companies wanting to evaluate the technology.

• The commercial versions have a DSP processor onboard for performing the calculations, make 10000 measurements per second, and able to handle 50 targets in the zone at one time.
• "OEM versions" for including in the clients hardware are now being delivered. Trolley Scan provide the RFID-radar module and the client handles the interfacing of the data to the operator.

Specifications of commercial version now being supplied

• 2 D scanning
• Dual receiver, single energiser with three high gain patch antennas
• Supplied with 20 5uW transponders (operating range of 35 meters) and 5 200uW credit card sized transponders.
• Uses single board computer with embedded software for computation
• Interfaces to a user supplied computer for display of data communicating via RS232 link
• Software (source and executable code) supplied for display computer allowing client to adjust display software to their requirements. The display software runs on any Windows based (Win32) operating system in DOS console mode.
• Radar outputs position at one second interval for each transponder in the zone
  • Identity of transponder (within a few milliseconds of entering the field)
  • Range and angle of transponder(takes a few seconds for accurate readings as has to obtain a lock first)
  • Predicted path based on historical measurements for transponders that are moving and pass through null zones.
• The radar in 2D format weights 12kg and is shipped in a 32 by 32 by 45 cm box
• The operating frequency can be factory set to any frequency betwen 860-960Mhz with a 10kHz bandwidth.
• Operating power adjustable by the operator between 0.5 and 3.5 watts.

How does RFID-radar work?

Light and radio waves travel at the speed of light, namely 300 000 000 meters per second. RFID systems need to operate in a crowded RF spectrum, where other RFID systems, cell phones, radio stations and other communication users have to share the available radio spectrum. RFID-radar uses just 10 kilohertz of bandwidth to operate, meaning it can detect time differences only as small as 0.1 milliseconds, or 0.0001 seconds. In this time the radio wave will travel 30 kilometers, or 30 000 meters or 3 000 000 centimeters Yet the radar is able to determine the range of the transponder based on its received transmission to an accuracy of a few centimeters, or nearly 1 million times better than its basic time measuring properties. If we used a conventional military radar approach and wanted to get centimeter precision, then we would have to measure the time of flight to 0.3pico seconds (.3*10-12) which would use 300GHz of radio spectrum.

RFID-radar pay for this million times improvement in the timing accuracy of the basic system by taking a longer time to determine the exact position. As a result it is well suited to a static situations where transponders are relatively stationary. However developments are in progress to address the accurate tracking of movement by adapting some of the principles of operation.

We have also now added features that allow movements as small as one millimeter to be measured in static situations.This allows simultaneous measurements from the reader to up to 50 transponders and can be used to detect movement in structures such as bridges, dam walls, buildings, mine walls and roofs, and other fixed structures that might be stressed by weather, traffic, water pressure, wind etc. Here one lowcost instrument can be installed to permanently monitor the integrity of structures and send warnings before damage or failure. These measurements are instantaneous.

The angle of arrival measurement is virtually instantaneous and used in conjunction with range gives a 2D positioning system from a single measuring location.

"RFID-radar^TM", "Claymore^TM" and "Better than a tape measure!^TM" are the trademarks of Trolley Scan (Pty) Ltd

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