EP1468394A1

EP1468394A1 - Method and system for periodically sampling a plurality of transponders

Info

Publication number: EP1468394A1
Application number: EP02782413A
Authority: EP
Inventors: John Mcmurray; Marthinus Jacobus Rudolph Oosthuizen
Original assignee: Supersensor Pty Ltd
Current assignee: ZIH Corp
Priority date: 2001-11-07
Filing date: 2002-11-07
Publication date: 2004-10-20
Also published as: WO2003040998A1

Abstract

A method of reading a plurality of transponders of an electronic radio frequency identification system comprises the steps of transmitting from a reader a pulsed energizing signal (114) having on and off parts. During on parts of the signal, energizing the transponders and receiving response signals transmitted by at least some of the transponders (trans #1). The method further comprises the steps of manipulating data in the system to compensate for the off parts. In one embodiment the data is manipulated by continuing to process random intertransmission intervals (63, 64.1 and 64.2) between response signals originating from a transponder, by utilizing power provided by an energy store on the transponder, to power an intertransmission interval generator on the transponder.

Description

METHOD AND SYSTEM FOR PERIODICALLY SAMPLING A PLURALITY

OF TRANSPONDERS

TECHNICAL FIELD

THIS invention relates to electronic identification (ID) systems and more

particularly to radio frequency (RF) ID systems.

BACKGROUND ART

Systems of the aforementioned kind are known in the art and comprise a

reader or interrogator and a plurality of transponders or tags forming a

transponder population. In use, each transponder is mounted on a

respective article to be identified or counted electronically with the

system.

The reader broadcasts an energizing signal towards the transponders.

The transponders derive power from the energizing signal and respond by

backscatter modulating the energizing signal with respective identification

(ID) code data. The reader reads this data sequentially and identifies the

transponders and hence identifies or counts the articles.

To avoid collisions between responses, it is known to use randomly

generated hold off times before a transponder would commence with a

response and also to use randomly generated intertransmission intervals between transmissions in a response by a transponder.

Should it be necessary to sample a transponder population, for example

by periodically switching the energizing signal on and off instead of using

a continuous energizing signal, it may be possible that some transponders

would not respond while the energizing signal is on, so that they would

not be read. One instance where sampling may be required and where

the hitherto known methods and systems would not work satisfactorily,

is when regulatory authorities dictate that the energizing signal be

switched on and off, for example with a 10% on/off duty cycle.

OBJECT OF THE INVENTION

Accordingly it is an object of the present invention to provide a method,

system, transponder and reader with which the applicants believe that

the aforementioned disadvantages may at least be alleviated.

SUMMARY OF THE INVENTION

According to the invention there is provided a method of reading a

plurality of transponders of an electronic identification system utilizing a

pulsed radio frequency energizing signal having on and off parts, the

method comprising the steps of:

broadcasting the energizing signal towards the transponders which derive power from the signal;

during on parts of the signal, energizing the transponders utilizing

the energizing signal and receiving response signals transmitted by

at least some of the transponders; and

- compensating for the off parts by manipulating data in the system.

The energizing signal may have an on to off duty cycle of less than 30%,

typically 10%.

The data may be manipulated by, during the off parts, continuing to

process data relating to intervals between response signals from a

transponder by utilizing power provided by an energy store on the

transponder to power data processing means on the transponder for

processing the data.

The energy store may comprise a capacitor.

The data processing means may comprise a random number generator

(RNG), counter, counter adjustment means and clock and wherein the

capacitor is connected to at least the RNG, counter and clock.

In another form the data may be manipulated by, during the off parts, stopping a clock on a transponder, saving present data relating to

intervals between response signals in data processing means on the

transponder, and at the start of a next on part, resuming processing of

the data with said present data.

In a slotted Aloha system the data may be manipulated by, during the off

parts, saving at least data relating to a last slot selected by a transponder

in data processing means on the transponder, and at the start of a next

on part, resuming processing with said data relating to a last slot

selected.

In yet another form of the method wherein the at least some of the

transponders are read according to a binary search procedure, the data

may be manipulated by saving in a reader of the transponders present

data relating to the procedure before an off part of the energizing signal

commences, and when a next on part commences, resuming the

procedure with said present data.

The data may further be manipulated by saving in data processing means

of a transponder, data relating to the procedure before an off part of the

energizing signal commences and when the next on part commences,

resuming the procedure on the transponder with the data saved in the data processing means of the transponder.

The data may be saved in a non-volatile memory arrangement of the

transponder for example EEPROM.

In still another form the data may be manipulated by, during the on parts,

transmitting to at least one of said transponders data relating to an

updated start value for data processing means of the transponder for

processing data relating to intervals between successive response signals

from the transponder.

The data relating to an updated start value may relate to one of a seed

for a random number generator (RNG) and a start count for a

transmission slot counter.

Further included within the scope of the present invention is an electronic

identification system comprising:

a reader for broadcasting a pulsed energizing signal having on and

off parts;

- a plurality of transponders each comprising means for generating

respective output data to be transmitted;

the reader comprising means for reading output data transmitted by the transponders; and

the system comprising data manipulating means for manipulating

data, to compensate for the off parts of the energizing signal.

In some embodiments, the data manipulating means may form part of a

transponder and may be means for manipulating data generated by

respective data processing means for processing intertransmission

interval data to cause the transponder at the end of respective successive

intervals to generate the output data. The data manipulating means may

comprise power storage means for providing power to the data

processing means during the off parts. The data processing means may

comprise a random number generator (RNG), a counter connected to

receive input data from the RNG and counter adjustment means and may

be driven by a local clock.

In some of these embodiments, the power storage means may be

connected to cause the clock, counter and counter adjustment means to

continue processing during the off parts. In other of these embodiments

there may be provided means for stopping the clock during the off parts

and the power storage means being operative to cause the RNG and

counter to save present data during the off parts. The data manipulating

means may further comprise means for, at the commencement of an on period, to restart the clock and to cause the counter and counter

adjustment means to proceed processing with said present data.

In other embodiments, such as those wherein the modulated data from a

transponder is read by a binary count procedure, the data manipulating

means may form part of the reader. In these embodiments the data

manipulating means may comprise means for saving during the off parts

present data relating to the procedure generated immediately before an

end of an on part and means for causing the reader to resume the

procedure with said present data when a next on part starts.

Yet further included within the scope of the present invention is an

electronic identification system comprising:

a reader for broadcasting a pulsed energizing signal having on

parts and off parts;

a plurality of transponders comprising respective data processing

means for processing intertransmission data to cause the

transponders at the end of respective successive intervals to

generate output data for transmission to the reader;

- the reader comprising means for reading transmitted output data;

and

the reader further comprising means for adjusting the interval data of selected transponders during on parts of the energizing signal.

Still further included within the scope of the present invention is a reader

or interrogator and a transponder as herein defined and/or described.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The invention will now further be described, by way of example only,

with reference to the accompanying diagrams wherein:

figure 1 is a block diagram of an electronic radio frequency

identification system according to the invention;

figure 2 is a typical time diagram of a known system;

figure 3 is a block diagram of a first embodiment of a transponder

according to the invention;

figure 4 is a flow diagram of the operation of the transponder in

figure 3;

figure 5 is a time diagram of a pulsed sampling system comprising

transponders of the kind in figure 3;

figure 6 is a block diagram of a second embodiment of a transponder

according to the invention;

figure 7 is a flow diagram of the operation of the transponder in

figure 6;

figure 8 is a time diagram of a pulsed sampling identification system comprising transponders of the kind in figure 6;

figure 9 is a block diagram of a third embodiment of a transponder

according to the invention;

figure 10 is a flow diagram of the operation of the transponder in

figure 9;

figure 1 1 is a flow diagram of the operation of a reader cooperating

with the transponder in figure 9;

figure 12 is a time diagram of the operation of a pulsed sampling

system comprising the transponders of figure 9;

figure 13 is a flow diagram of the operation according to the invention

of a transponder in a slotted Aloha system utilizing a pulsed

energizing signal;

figure 14 is a flow diagram of relevant parts of the operation

according to the invention of a transponder read by a binary

search procedure and utilizing a pulsed energizing signal;

and

figure 15 is a flow diagram of relevant parts of the operation

according to the invention of a reader cooperating with the

transponder the operation of which is shown in figure 14.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

An electronic radio frequency (RF) identification (ID) system according to the invention is generally designated by the reference numeral 10 in

figure 1 .

The system comprises a reader or interrogator 12 which broadcasts an

RF interrogation or energizing signal 14 towards a transponder population

16 comprising a plurality of transponders 18.1 to 18.n. Each

transponder is mounted on a respective article 20.1 to 20. n to be

counted and/or identified. In so-called Aloha systems, each transponder

intermittently backscatter modulates the impinging energizing signal 14 to

transmit back to the reader a respective response 22.1 to 22. n. As

shown in figure 2, each transponder transmits a first response signal a

respective random hold off period 24.1 to 24. n after a power on reset

(POR) signal 26. Subsequent response signals from the same

transponder are spaced at random intertransmission intervals 28 between

one another. The signals shown in figure 2 are for a continuous

energizing signal 14.

The hold off periods 24.1 to 24. n and intertransmission intervals 28 are

determined by respective random interval determining arrangements or

generators, such as random number generators (RNG) and associated up

or down counters forming part of the transponders. After a power on

reset (POR) signal, the RNG of a transponder is normally loaded with seed data pre-stored in a memory arrangement of the transponder. It will be

appreciated that in such cases the hold off period 24 after a power on

reset (POR) signal for a particular transponder would be constant.

It will further be appreciated that if it is necessary to sample the

transponder population by broadcasting a pulsed energizing signal and the

energizing signal is switched off before the end of the hold off periods

24.2 and 24. n shown in figure 2, transponders #2 and #n will never be

read.

In figure 3 there is shown a first embodiment of a transponder according

to the invention designated 18.1 . The transponder comprises a logic

control circuit 40, a Power on Reset (POR) signal generator circuit 42, a

memory arrangement 44, an intermission interval generator or data

processing means 43 comprising a local clock 46, an RNG and associated

counter 48, a shift register 50 and a modulator 52. A charge storage

device in the form of a capacitor 54 is connected to at least the

generator 43 comprising the RNG and associated counter 48 and clock

46, to power same. The logic control circuit 40 is sensitive to charge on

the capacitor via point 56 connected to the logic control circuit.

Operation of the transponder is illustrated in the flow diagram in figure 4

and a time diagram of operation of a pulsed sampling system comprising the aforementioned transponders is shown in figure 5.

A pulsed energizing signal is shown at 1 14 in figure 5. The on/off duty

cycle of the energizing signal is smaller than 30% and typically in the

order of 1 :9. Whereas the RNG and associated counter of the known

transponders would stop when power is removed from the known prior

art transponders, with the transponder 18.1 according to the invention,

the capacitor 54 provides power to enable the RNG and counter 48 and

clock 46 to proceed with the processing of intervals as hereinafter

described. The charge on the capacitor meets the power requirements of

the RNG and counter 48 and clock 46 during an "off" part of the

energizing signal 1 14.

The operation of the transponder is illustrated in figure 4 and indicates at

60 that while there is enough charge on the capacitor, the RNG and

counter proceed at 62 to process the hold off period 63 and the random

intertransmission intervals 64.1 and 64.2 (shown in figure 5) for

transponder #2. At the end of the hold off period 63 and first

intertransmission interval 64.1 at 68.1 and 68.2 respectively, no

backscatter modulation and hence transmission is possible due to the

fact that the energizing signal is "off". However, at the end of the next

intertransmission interval 64.2 at 68.3, the energizing signal is "on" so that backscatter modulation is possible, takes place and transponder #2

is read as hereinbefore described. It is only when the charge on the

capacitor 54 has fallen below a threshold value, as shown at 66 (shown

in figure 4), that the logic circuit loads the RNG with the original seed

data to start afresh to process the hold off time 63. This would typically

happen when the transponder is completely removed from the energizing

field 1 14.

A second embodiment of the transponder according to the invention is

shown at 1 18 in figure 6. The transponder 1 18 comprises substantially

the same functional elements as the transponder 18.1 plus a radio

frequency signal detection circuit 70.

The operation of the system is illustrated in figure 7. At 72 the circuit

70 detects if the transponder 1 18 is illuminated by the energizing signal

1 14. If not, the clock 46 of the transponder is stopped at 74. This puts

the transponder in an ultra low power consumption mode. However,

due to the power supplied by capacitor 54, the RNG and counter 48 act

as a non-volatile memory arrangement which retains present data, when

the clock is stopped. When the transponder is illuminated again, the

logic controller tests at 76 the voltage at point 56. If lower than a

threshold value, the RNG is loaded from memory 44, so that the RNG starts processing with the original seed data. However, if the voltage is

higher than the threshold value, the logic controller 40 assumes that the

RNG and counter values have been saved as aforesaid and the RNG and

counter then continue processing with the saved data, as shown at 78 in

figure 7. It will be appreciated that this operation in effect means that

the RNG and counter are freezed with their present data saved when the

energizing signal is in an off part of its cycle and that they resume

processing with that data when the energizing signal is switched on

again. As far as the RNG and associated counter 48 are concerned, the

energizing signal 1 14 would appear to be continuous.

A time diagram of the operation of a system comprising transponders

1 18 is shown in figure 8. In a system utilizing a continuous energizing

signal, transponder #2 would have responded with signal 80 shown in

broken lines a period 82.1 after the power down (PD) point of switched

energizing signal 1 14. However, due to the freezing of the clock 46 and

saving of the RNG and associated counter data, that signal is now

transmitted at 84, a period 82.2 after power on (PO) equal to period

82.1 . Since it overlaps with the second pulse of the energizing signal

1 14, the signal 1 14 is backscatter modulated with the ID data of

transponder #2, so that it may be read by reader 12 in conventional

manner. Another solution for the problems hereinbefore described presented by

intermittent or periodic sampling of the transponder population is

illustrated in figures 9 to 12. A third embodiment of the transponder

according to the invention is illustrated in figure 9 designated 218. It is

substantially similar to the transponder 18.1 except that it does not

comprise the capacitor 54, but comprises a data decoder 90 connected

to the logic controller 40.

The data decoder 90 enables a reader 12 (shown in figure 1 ) to change

(typically at the start of each "on" part of the energizing signal 1 14) the

RNG seed data in a selected transponder or selected transponders. In

this manner small seeds for short hold off periods may be loaded into the

RNG's of certain possibly yet unread transponders. As shown in figure

12, during the first pulse 1 14.1 of energizing signal T14, transponder #2

has a small seed value corresponding to a short hold off period and is

read during that pulse. However, transponder #1 has a bigger seed value

corresponding to a larger hold off period. At the start 92 of the second

pulse 1 14.2, a new or updated and smaller seed value is substituted in

transponder #1 by reader 12 via decoder 90 as shown at 91 in figure 1 1 .

The RNG and associated counter 48 now utilize as shown at 93 in figure

10 this new seed value to process a random, but short hold off period 94

shown in figure 12, to ensure that transponder #1 is read during pulse 1 14.2. The relevant operations of the transponder and reader are clearly

illustrated in figures 10 and 1 1 respectively.

In figure 13, there is illustrated operation of a transponder in a known so-

called slotted Aloha system 10, when used in a sampling method of

operation in which the energizing signal is intermittently or periodically

switched on and off as hereinbefore described during a read operation. In

the known slotted Aloha systems, when the reader 12 commands a new

round in the read operation, each transponder, by a random selection

method, selects a slot of a plurality of sequential slots in the round in

which to transmit its data. In the method according to the invention,

each transponder is further configured to save during off parts of the

energizing signal in a non-volatile memory arrangement of the

transponder, at least data relating to a last slot selected by the

transponder. When the energizing signal is switched on again at 120

and the saved data is in order at 122, the transponder proceeds with its

local processing utilizing that saved data. When at 124 the slot so

selected corresponds to a slot dictated by the reader, the transponder

transmits at 120 its data to be received by the reader.

In known so-called binary search procedures, the reader 12 cooperates

with the transponders 18.1 to 18.n in data processing during the read procedure of the data transmitted by the transponders.

Figure 14 illustrates operation of a reader 12 using binary search

principles in the sampling mode of operation hereinbefore described. At

130 the read operation starts. A sample or on part timer is initialized at

132 to the required on part time, the determination of the value of which

is subject to regulatory and system considerations. The value in the

timer is checked at 134 to determine whether time-out has occurred. If

not, operation continues at 1 36 with identification and reading of

transponders using binary search principles. The on part timer continues

to time the on part and when the on part has timed out, operation

continues at 138 by switching the energizing signal 1 14 off at 140 and

then saving at 142 the search data or status in the reader in a suitable

memory arrangement of the reader. This will allow the reader to continue

reading transponders as though the energizing signal has been on

continuously, as shown at 14 in figure 2, for example. At 144 an off

part timer is set up, typically with a value nine times that of the on part

timer. The off part is timed out at 146 and when time-out has occurred

at 148, the operation continues with retrieval at 150 of the

aforementioned saved data. The read cycle is then resumed at 132 with

initialization of the on part timer as hereinbefore described. Figure 15 illustrates operation of a transponder 18.1 to 18.n using binary

search principles and which cooperates with the reader 12 referred to

with reference to figure 14. At 152 the transponder receives an on part

of the energizing signal 1 14. If the reader 12 initiates a new search

procedure at 153, the transponder operation continues at 1 54 and

pointers and memory arrangements of data processing means of the

transponder are reset at 156. The transponder then continues to

cooperate at 158 with the reader 12 in the binary search procedure. The

procedure will continue until the energizing signal enters an off part at

160 or the reader stops the search procedure at which point the

transponder becomes dormant and waits at 162 for power to be

reapplied or the search to be started or restarted. If at 153 the reader

has not started a new search, operation continues at 164. The validity of

the saved pointer data and memory status are verified by the transponder

at 166 by some form of test, examples of which are a minimum capacitor

voltage test and a so-called "lazy-bit" test in which one or more bits in a

non-volatile memory arrangement of the transponder will change state at

a slightly higher capacitor voltage than the other bits, to act as an early

indicator of the local memory arrangement supply voltage approaching a

dangerously low level at which data status could be corrupted. If the

lazy bit or bits have reverted to their normal power off state due to

excessively long illuminating power removal, the memory status is uncertain and the transponder will continue at 1 54 as if a new search

had been started by the reader. If however the lazy bit or bits have

stayed in an initialized state, it would indicate that the memory

arrangement has not lost data saved therein, causing the transponder to

continue at 168 and 158 with the saved data, as if there had been no

power interruption.

Claims

1 . A method of reading a plurality of transponders of an electronic

identification system, utilizing a pulsed radio frequency energizing

signal having on and off parts, the method comprising the steps

of:

broadcasting the energizing signal towards the transponders

which derive power from the signal;

during on parts of the signal, energizing the transponders

utilizing the energizing signal and receiving response signals

transmitted by at least some of the transponders; and

compensating for the off parts by manipulating data in the

system.

2. A method as claimed in claim 1 wherein the energizing signal has

an on to off duty cycle of less than 30%.

3. A method as claimed in claim 1 or claim 2 wherein the data is

manipulated by, during the off parts, continuing to process data

relating to intervals between response signals from a transponder

by utilizing power provided by an energy store on the transponder

to power data processing means on the transponder for processing

the data.

4. A method as claimed in claim 3 wherein the energy store

comprises a capacitor.

5. A method as claimed in claim 3 or claim 4 wherein the data

processing means comprises a random number generator (RNG),

counter, counter adjustment means and clock and wherein the

capacitor is connected to at least the RNG, counter and clock.

6. A method as claimed in claim 1 or claim 2 wherein the data is

manipulated by, during the off parts, stopping a clock on a

transponder, saving present data relating to intervals between

response signals in data processing means on the transponder, and

at the start of a next on part, resuming processing of the data with

said present data.

7. A method as claimed in claim 1 or claim 2 for use in a slotted

Aloha system wherein the data is manipulated by, during the off

parts, saving at least data relating to a last slot selected by a

transponder in data processing means on the transponder, and at

the start of a next on part, resuming processing with said data

relating to a last slot selected.

8. A method as claimed in claim 1 or claim 2 for use in a method

wherein the at least some of the transponders are read according

to a binary search procedure, wherein the data is manipulated by

saving in a reader of the transponders present data relating to the

procedure before an off part of the energizing signal commences,

and when a next on part commences, resuming the procedure with

said present data.

9. A method as claimed in claim 8 wherein the data is manipulated by

saving in data processing means of a transponder data relating to

the procedure before an off part of the energizing signal

commences.

10. A method as claimed in claim 9 comprising the step of when the

next on part commences, resuming the procedure on the

transponder with the data saved in the data processing means of

the transponder.

1 1 . A method as claimed in any one of claims 6, 7, 9 and 10 wherein

the data is saved in a non-volatile memory arrangement of the

transponder.

12. A method as claimed in claim 1 or claim 2 wherein the data is

manipulated by, during the on parts, transmitting to at least one of

said transponders data relating to an updated start value for data

processing means of the transponder for processing data relating

to intervals between successive response signals from the

transponder.

13. A method as claimed in claim 12 wherein the data relating to an

updated start value relates to one of a seed for a random number

generator (RNG) and a start count for a transmission slot counter.

14. An electronic identification system comprising:

a reader for broadcasting a pulsed energizing signal having

on parts and off parts;

- a plurality of transponders energizable by the on parts of the

signal and each comprising means for generating respective

output data to be transmitted;

the reader comprising means for reading output data

transmitted by the transponders; and

the system comprising data manipulating means for

manipulating data, to compensate for the off parts of the

interrogation signal.

15. A system as claimed in claim 14 wherein the data manipulating

means forms part of a transponder and comprises data processing

means for processing intermission interval data to cause the

transponder at the end of respective successive intervals to

generate the output data.

16. A system as claimed in claim 15 wherein the data processing

means comprises random number generating (RNG) means, a

counter connected to receive input data from the RNG means and

counter adjustment means driven by a clock.

17. A system as claimed in claim 15 or claim 16 wherein the data

manipulating means comprises local power storage means for

providing power to the data processing means and clock during the

off parts.

18. A system as claimed in claim 17 wherein the power storage means

comprises a capacitor.

19. A system as claimed in claim 1 5 or claim 16 wherein the data

processing means comprises non-volatile memory means for

enabling the data processing means to save present data during off parts of the energizing signal.

20. A system as claimed in claim 14 wherein the manipulating means

forms part of the reader and may comprise means for saving

during off parts of the energizing signal present data relating to a

binary search procedure generated immediately before an end of

an on part and means for causing the reader to resume the

procedure with said saved present data when a next on part

starts.

21 . A reader for an electronic radio frequency identification system,

the reader comprising means for broadcasting an energizing signal

having on parts and off parts and data manipulating means for

saving during off parts of the energizing signal present data

relating to a binary search procedure generated immediately before

an end of an on part and means for causing the reader to resume

the procedure with said saved data when a next on part starts.

22. A transponder for an electronic radio frequency identification

system utilizing a pulsed radio frequency energizing signal having

on parts and off parts, the transponder comprising means for

generating output data to be transmitted during on parts of the energizing signal and data manipulating means for manipulating

data, to compensate for the off parts of the energizing signal.