CA2103910A1 - Identification apparatus and method - Google Patents
Identification apparatus and methodInfo
- Publication number
- CA2103910A1 CA2103910A1 CA002103910A CA2103910A CA2103910A1 CA 2103910 A1 CA2103910 A1 CA 2103910A1 CA 002103910 A CA002103910 A CA 002103910A CA 2103910 A CA2103910 A CA 2103910A CA 2103910 A1 CA2103910 A1 CA 2103910A1
- Authority
- CA
- Canada
- Prior art keywords
- modulation
- signal
- modulations
- sequence
- interrogator
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
- G01S13/75—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors
- G01S13/751—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal
- G01S13/758—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems using transponders powered from received waves, e.g. using passive transponders, or using passive reflectors wherein the responder or reflector radiates a coded signal using a signal generator powered by the interrogation signal
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
- G01S13/82—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein continuous-type signals are transmitted
- G01S13/825—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein continuous-type signals are transmitted with exchange of information between interrogator and responder
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/0008—General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J13/00—Code division multiplex systems
- H04J13/10—Code generation
Landscapes
- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Signal Processing (AREA)
- Artificial Intelligence (AREA)
- Computer Vision & Pattern Recognition (AREA)
- Theoretical Computer Science (AREA)
- Radar Systems Or Details Thereof (AREA)
- Near-Field Transmission Systems (AREA)
Abstract
The present invention relates to a device, identification apparatus and method where a single carrier frequency is used by any number of remote device(s) upon which data or information is modulated for transmission to an interrogator, the modulation being selected arbitarily from a larger group of possible modulations available; and being any type of modulation for example AM, FM, PWM, etc. or being in accordance with a Pn-sequence or a number of different Pn-sequences.
Description
2103~1~
~0 92/17947 PCI/AU92/00~23 IDENTIFICATI~N APP~RATUS AND METHC3D
R~LATE12 APPLICAIIQN . . .
Applicant(s) have disclosed a related invention in PCT Application N~.
PCT/AU88/00469 or its equivalent in Australia, Australian Patent Application No.5 26093/88. The disclosure of this related application is herein incorporated by reference.
FIEI~[~ O~ INVENTION
The present invention relates to the field of identification of and/or communication between a number of remote objects or devices and an interrogator or 10 receiver simultaneously. In particular, the present invention deals with communication and/or identification of one or more remote devices, such as transponders. The present invention also relates to a modification of the invention disclosed in the above related patent application.
BACKGROUND ART
The related application disclosed a system adapted to identify one or more remote transponders simultaneoùsly.
The system disclosed utilized a number of remote transponders, each of which transmit a data or information signal at a carrier frequency selected randomly from a group of possible carrier frequencies. At each transmission a newly selected carrier 2 0 frequency is used.
Furthermore, applicants are aware of "frequency-hoppingn utilized in radar systems, where the remote transponder and interrogator are synchronised in theircommunication, and the data transmission occurs at a number of different carrierfrequencies (frequency-hopping), the hopping between or selection of frequencies25 occurring in accordance with a predetermined sequence to which both transponder and interrogator are synchronised. This type of system is not adapted to communicate with a number of remote transponders simultaneously in a reliable manner.
SUMMARY OF INVENTION
The present invention relates to a device in which communication is provided 3 0 between the device and a receiver or interrogator by use of a single carrier frequency in conjunction with a selected modulation, such as a Direct-Sequence Sprsad Spectrum modulation technique.
2lo39l~ ,hlT~, , The present invention provides a device comprising:
transmitter means adapted to transmit an information, code or identification - signal;
- selection means adapted to select a moclulation for transmission of said signal from a set of predetermined modulations;
wherein the signal is transmitted using the selected modulation.
The present invention also provides a communica~ion system comprising:
at least one remote device each adapted to transmit a signal at a modulation selected from a set of predetermined modulations; and a receiver adapted to receive transmissions from at least one remote device.
The present invention preferably includes generating means for generation a set of predetermined modula~ions.
Preferably, transmission of each signal at the newly selected modulation occurs sequentially or cyclically. The device may also include means for eXtracting timing 15 information or powering energy from an impinging electro-magnetic field.
Preferably, controi means is provided to select a modulation. The control means may also reselect the same or another modulation for the next transmission. The selection or reselection may occur in accordance with a probability weighting, pseudo-random binary sequence or may be random.
The present invention also provides a system for simultaneously identifying a first and second device, each device comprising code storage means, modulation means and an inductive receiver/transmitter means, the system comprising:
magnetic field generator/radiator means for generating a magnetic field from which said first and second devices are adapted to exlract power using said inductive 2 5 means;
each of said first and second devices, when so powered, respectively providing at least one unique code from the code storage means to the modulation means, said modulation means being adapted to provide at least one modulated code to the inductive means for transmission to a device identifying receiver;
3 0 each device adapted to modulate said at least one code at at least one modulation randomly selected from a predetermined finite set of modulations, while each device remains powered;
~o 92tl7947 210 3 ~1 Q rcr/Au92/ool23 each device being embodied in a single (IC) chip.
The present invention further provides a method of communication between an interrogator and at least two remote receiving devices, said method comprising the steps of:
radiating an interrogation signal from said interrogator to each remote device;
generating a reply signal at a modulation selected from a predetermined set of modulations in each remote device;
transmitting said reply signal from each remote device to the interrogator; and serially generating and transmitting the reply signal at a newly selected 10 modulation from said predetermined set of modulations.
The interrogator of the communication system may also be adapted to receive a number of lransmissions from any number of remote devices simultaneously, and demodulate the received transmissions to recover a signal from each remote device.
This is made possible by having an interrogator adapted to receive a number of different 1~ modulations simultaneously. Preferably, the interrogator comprises a number of modulation receiving channels, the number of channels corresponding to the number ot modulations avaiiable for selection for transmission of data by a remote device. The signal may be an identification, code andlor information signal. The signal is preferably RF.
A preferred embodiment of the present invention will now be described with reference to the accompanying-drawings, wherein:
Figure 1 shows a prior art DSSS transmitter;
Figure 2 shows a prior art DSSS receiver;
Figure 3 shows a device incorporating a transmitt0r according to the present invention;
Figure 4 shows a preferred form of PN generator; and Figure 5 shows a receiver according to the present invention.
The preferred embodiment to be described operates on principles similar to 3 0 those described in the aforementioned related application.
Although the specification refers to the term ~devicen. any communication apparatus is also encompassed, including transponders and transmitter/receiver 2 1 0 3 9 ~ ,~:,?~.
WO 92~17947 PCI/AV92/00123 systems. The term ~device" should therefore be given a broad interpretation the Udevice'' may be passive or active. The term "modulation" is also intended to beconstrued broadly and encompass many forms~of communication mediums, including aPN sequence. The term "interrogator" should also be interrupted broadly to include at 5 least devices adapted to receive transmissions from and/or communicate with one or more remote devices.
The present invention in one form represents a modification or enhancement of the applicants related invention, whereby a single carrier frequency is used, inconjunction with a "Direct-Sequent Spread Spectrum" mociulation technique.
1 û A transmitter for a Direct-Sequence Spread Spectrum (DSSS) system includes a source of pseudo-random data (usually binary), such data being generated at a rate considerably in excess of the system communication speed. Because of its similarity to natural noise, this data is commonly termed ~Pseudo-Noise" (PN). This PN data is then mix2d with the "real" data, so greatly increasing the requisite bandwidth, and 1 5 transmitted.
The receiver or interro~ator of the present invention must include, on each channel means to ~enerate a Pn-sequence identical to that used by a remote device. That is, the interrogator includes a separate channel for each possible Pn-sequence which can be selected by a remote device. The Pn-sequence of each channel needs to be accurately 20 synchronised with that of the transmitting remote device. Means for achieving such synchronisation are known (see, inter alia, Sklar, UDigitals Communications:
Fundamentals ~ Applications", Prentice-Hall, 1988). To be effective, synchronisation needs to be very precise (within a fraction of the period of the clock driving the PN
generator). When this occurs, the desired signal is greatly increased in amplitude, 25 while other, un-synchronized signals are greatly attenuated. Of course, should the receivet's PN generator produce a PN sequenced different to that at the transmitter, synchronisation will be impossible. It is this selective amplification property which provides the basis for the present invention. A correlation operation is performed between the received signal and this local PN source, leaving the required data or signal.
Unlike the prior art where a number of different carrier frequencies can be used, as shown in Figures 1 and 2 the present invention contemplates the use of a single carrier frequency for use by all remote devices, upon which a data or information signal ~ 2103~0 ~'0 92/17947 PCI'/AU~2/00123 is modulated in accordance with a particular type of modulation (AM, FM. etc) or in accordance with a particular pn-sequence.
Such a system is relatively highly resistant to interference (whether intentional or not), in that any received signal which does not correspond exactly to the local PN
5 signal, will be converted into wideband noise, which may readily be filtered out.
~E~ RlPTlON OF_TH~lNv~~
The invention provides a device and an object-identification system, characterised by the ability to identify (read signals from) several different objects simultaneously. Prior art systems employ a plurality of carrier radio frequencies, 10 was described in the applicants related invention. The related invention provided an identifying device (lltransponder", or utag") to be attached to the object to beidentified, said tag being adapted to transmit an identifying message at one of a plurality of radio frequencies. In use, the message is repeatedly transmitted, with the same or a new radio frequency being selacted at each transmission. The receiving equipment15 provides a plurality of channels, each sensitive to one of the plurality of frequencies, and can receive message on all frequencies simultaneously. Separation of messages transmitted by a plurality of tags is provided by limiting the bandwidth of the rece;ver channels, such that each receives messages on one radio frequency only. The system is characterised by the ability to identify a plurality of tags at once, such plurality being 20 randomly selected from an extremely large (quasi-infinite) total population of possible tags.
The present in~ention may be regarded as an improvement over or a modification of the related invention. In the present invention, a single radio frequency is used, and the tags are prevented from co-interfering by employing a plurality of PN sequences 25 and/or a plurality of types of modulation and likewise a plurality of corresponding receivers, each such receiver adapted to synchronise to only one of the said plurality of PN sequences or types of modulation.
- The transmitting portion of a device according to the present invention is shown conceptually in Fig. 3. Comparison with the prior art Fig. 1 will disclose the novelty, 3 0 which resides in the provision of a plurality of PN or modulation sources, and a selection means (which said means operates identically to that of the cited prior invention) to choose one of the PN or modulation sources.
2ln3sl~
WO 92/17947 PCI'/AU92/00123 The 1ag selects a PN or type of modulation source, transmits the message, selects a new (or the same) PN or type of modulation source, and repeats.
Rather than employing a plurality of separate PN generators, it will be advantageous to employ a single PN generator, adapteci to receive as inputs, certain 5 quantities ("co-efficients") which determine the generated sequence. An exemplary embodiment of such a circuit is shown in Fig. 4. The device comprises a shift register A, whose input is fed from the Exclusive-OR (XOR) function of two or more taps on the said shift register. Adroitly chosen taps will yield a plurality of long sequences, having good PN qualities. The exemplary embodiment employs two taps, implemented by the10 multiplexers B and C, which select two bits from the said register, and present them to the XOR gate D~ The output of this gate is presented to the serial data input of register A.
By changing the selection inputs to the multiplexers B and C, a plurality of PN sequences may be produced. In the exemplary embodiment, a plurality of such selections are pre-15 determined, and stored in the Read-Only-Memory (ROM) E. When a value is presented to the address inputs of E, its outputs direct multiplexers B and C to select taps on the register A, and a PN sequence is generated. In the complete tag, a Uselection means" is provided to select from the plurality of possible PN sequences.
A preferred receiving means are shown in Fig. 5. Each of the several PN or 2 0 modulation generators generates a different member of the plurality of PN sequences or modulations available in the device.
SUITABLE PN SEQUENCES
Suitable PN sequences can be characterised by 3 qualities:
1. Their auto-correlation function will approximate to a "spike" or mathematical 2 5 delta function. That is to say, if two copies of the same PN sequence are correlated together, a significant output will occur only when the two copies are in exact alignment. Any mutual misalignment will result in an essentially zero output.
2. The cross-correlation function between any two (different) PN sequences wiil be 3 0 essentially flatl i.e. there will be minimal output for any possible relative alignment of the two seciuences.
3. The PN sequence shall comprise approximately equal numbers of ONE and ZERO
21~10 WO 92/17947 PCI'/AU92/00123 bits.
The present system utilises the interference-resistant quality of a DSSS channelto identify or communicate with specific devices such as transponders.
According to the invention, each device is adapted to hold a plurality of dis~inct 5 PN sequences as a set of predetermined modulations. Alternatively, the device may hold a table of suitable coefficients, which may be passed to a digital logic circuit, such circuit being adapted to (when the said coefficients are presented as inputs) generate the required PN sequences or modulations.
A random or predetermined choice is made amongst these modulations and the 10 randomly chosen modulation is used to transmit a signal which is to form the communication.
Before the signal is transmitted again, a new choice (from the avaiiable PN
sequences) is made on a random or predetermined basis. Each bit of the message data is mixed with the chosen PN sequence, and transmitted. In practice this may imply that 15 what is transmitted is either a selected modulation or in the case of a stored sequence, its complement, depending on whether signal is a logic signal and the data bit is a zero or one. The transmission bandwidth has been increased in proportion to ~he number of bits in the PN sequence. In an alternative system, in which only alternate bits of the PN
sequence, rather than all bits, are reversed to suit the data polarity. Other schemes are 2 0 also possible.
The complete message is transmitted preferably using a single modulation PN
sequence. The PN sequence may extend over the entire message, or a shorter PN
sequence may be used repeatedly for each message bit. When the entire message has been sent, a new sequence is then selected, from a group of available sequences, and the 2~ message is retransmitted. In the present system, the radio carrier frequency remains substantially constant.
Conveniently, the receiver or interrogator may operate on the homodyne principle as described on pages 14-15 and Figure 9 of the related application. In the case of a plurality o~ devices transmitting simultaneously, an interrogator will yield as 30 output a wideband data stream, comprising the sum of messages received from all devices within range. Such messages will have been encoded using the plurality of PN
sequences as previously described.
2iO331~
This stream is passed simultaneously to a plurality of matched filters, each adapted to match one of the original, stored PN sequences. These filters may be cf the class of "Transversal Filters~, wherein the filter coefficients take the values +1 and -1, following the bit-sequence of the original PN pattern. The auto-correlation property of the PN sequences (as above-described) implies that when a data pattern matching the original sequence is presented to such a filter, a sharp positive voltage spike appears at the output, as the received data passes (momentarily) into alignment with the filter coefficients. Similarly the complement of the given sequence will develop a sharp negative pulse~ Non-matched data will merely generate low-level noise, which 10 may be filtered out by a simple amplitude "window~, or other circuitry.
The pulses so obtained represent one and zero bits of the original data.
The above-described cross-correlation property of the PN sequences enables messages encoded with a given PN sequence to be tecovered by the appropriate matched filter, and no other. This property serves to separate out the various transmissions 15 from one or more devices.
In a most preferred form, these transversal filters may be implemented by converting the receiver output to a sampled digital representation, and employing onc of the many "digital signal processor~ VLSl chips now available, to perform the filtering function in the digital domain. Many such chips are sufficiently powerful to 2 0 simultaneously filter a plurality of channels ~i.e. using different PN sequences).
An interrogator as described above is suitable for a PN sequence, however, the interrogator may be suitably constructed or adapted to receive and demodulate any type of modulation, depending on the form of modulation selected to transmit lhe signal from the remote device(s) to the interrogator, as would be understood by those of the art.
In yet another alternative, it is possible to combine the transponder and systemsimilar to that disclosed in the related application and the present invention, thus providing a plurality of remote devices, each modulated by a plurality of modulations or PN sequences andtor frequencies. This will require a plurality of receivers in the interrogator (one for each carrier frequency), each being adapted to demodulate a 30 number of received transmissions at a selected modulation. Such a system could simultaneously identify very large numbers of transponders, in that it provides a system utilising a plurality P1 of radio frequencies, with a second plurality P2 of PN
- 2103~10 ~0 92/17947 PCI`/AU92/00123 sequences employed upon each of the said frequencies, so obtaining a largar plurality (up to P1~P2) of simultaneously useable channels. While such a system would require a more elaborate receiver means (having up to P1~P2 receiving sections) than either of the description above~ it would permit rapid, simultaneous identification of very large 5 numbers of objections.
It may also be possible to utilise various forms of modulation (AM, FM, PWM and others as is known in the art). By selecting one modulation ~say AM) for the first transmission, then selecting another modulation say (FM) for the second modulation, etc. Selection may be carried out in a random or predetermined sequence.
2~
.~., ~-` 4 ''t~
. . , .
~0 92/17947 PCI/AU92/00~23 IDENTIFICATI~N APP~RATUS AND METHC3D
R~LATE12 APPLICAIIQN . . .
Applicant(s) have disclosed a related invention in PCT Application N~.
PCT/AU88/00469 or its equivalent in Australia, Australian Patent Application No.5 26093/88. The disclosure of this related application is herein incorporated by reference.
FIEI~[~ O~ INVENTION
The present invention relates to the field of identification of and/or communication between a number of remote objects or devices and an interrogator or 10 receiver simultaneously. In particular, the present invention deals with communication and/or identification of one or more remote devices, such as transponders. The present invention also relates to a modification of the invention disclosed in the above related patent application.
BACKGROUND ART
The related application disclosed a system adapted to identify one or more remote transponders simultaneoùsly.
The system disclosed utilized a number of remote transponders, each of which transmit a data or information signal at a carrier frequency selected randomly from a group of possible carrier frequencies. At each transmission a newly selected carrier 2 0 frequency is used.
Furthermore, applicants are aware of "frequency-hoppingn utilized in radar systems, where the remote transponder and interrogator are synchronised in theircommunication, and the data transmission occurs at a number of different carrierfrequencies (frequency-hopping), the hopping between or selection of frequencies25 occurring in accordance with a predetermined sequence to which both transponder and interrogator are synchronised. This type of system is not adapted to communicate with a number of remote transponders simultaneously in a reliable manner.
SUMMARY OF INVENTION
The present invention relates to a device in which communication is provided 3 0 between the device and a receiver or interrogator by use of a single carrier frequency in conjunction with a selected modulation, such as a Direct-Sequence Sprsad Spectrum modulation technique.
2lo39l~ ,hlT~, , The present invention provides a device comprising:
transmitter means adapted to transmit an information, code or identification - signal;
- selection means adapted to select a moclulation for transmission of said signal from a set of predetermined modulations;
wherein the signal is transmitted using the selected modulation.
The present invention also provides a communica~ion system comprising:
at least one remote device each adapted to transmit a signal at a modulation selected from a set of predetermined modulations; and a receiver adapted to receive transmissions from at least one remote device.
The present invention preferably includes generating means for generation a set of predetermined modula~ions.
Preferably, transmission of each signal at the newly selected modulation occurs sequentially or cyclically. The device may also include means for eXtracting timing 15 information or powering energy from an impinging electro-magnetic field.
Preferably, controi means is provided to select a modulation. The control means may also reselect the same or another modulation for the next transmission. The selection or reselection may occur in accordance with a probability weighting, pseudo-random binary sequence or may be random.
The present invention also provides a system for simultaneously identifying a first and second device, each device comprising code storage means, modulation means and an inductive receiver/transmitter means, the system comprising:
magnetic field generator/radiator means for generating a magnetic field from which said first and second devices are adapted to exlract power using said inductive 2 5 means;
each of said first and second devices, when so powered, respectively providing at least one unique code from the code storage means to the modulation means, said modulation means being adapted to provide at least one modulated code to the inductive means for transmission to a device identifying receiver;
3 0 each device adapted to modulate said at least one code at at least one modulation randomly selected from a predetermined finite set of modulations, while each device remains powered;
~o 92tl7947 210 3 ~1 Q rcr/Au92/ool23 each device being embodied in a single (IC) chip.
The present invention further provides a method of communication between an interrogator and at least two remote receiving devices, said method comprising the steps of:
radiating an interrogation signal from said interrogator to each remote device;
generating a reply signal at a modulation selected from a predetermined set of modulations in each remote device;
transmitting said reply signal from each remote device to the interrogator; and serially generating and transmitting the reply signal at a newly selected 10 modulation from said predetermined set of modulations.
The interrogator of the communication system may also be adapted to receive a number of lransmissions from any number of remote devices simultaneously, and demodulate the received transmissions to recover a signal from each remote device.
This is made possible by having an interrogator adapted to receive a number of different 1~ modulations simultaneously. Preferably, the interrogator comprises a number of modulation receiving channels, the number of channels corresponding to the number ot modulations avaiiable for selection for transmission of data by a remote device. The signal may be an identification, code andlor information signal. The signal is preferably RF.
A preferred embodiment of the present invention will now be described with reference to the accompanying-drawings, wherein:
Figure 1 shows a prior art DSSS transmitter;
Figure 2 shows a prior art DSSS receiver;
Figure 3 shows a device incorporating a transmitt0r according to the present invention;
Figure 4 shows a preferred form of PN generator; and Figure 5 shows a receiver according to the present invention.
The preferred embodiment to be described operates on principles similar to 3 0 those described in the aforementioned related application.
Although the specification refers to the term ~devicen. any communication apparatus is also encompassed, including transponders and transmitter/receiver 2 1 0 3 9 ~ ,~:,?~.
WO 92~17947 PCI/AV92/00123 systems. The term ~device" should therefore be given a broad interpretation the Udevice'' may be passive or active. The term "modulation" is also intended to beconstrued broadly and encompass many forms~of communication mediums, including aPN sequence. The term "interrogator" should also be interrupted broadly to include at 5 least devices adapted to receive transmissions from and/or communicate with one or more remote devices.
The present invention in one form represents a modification or enhancement of the applicants related invention, whereby a single carrier frequency is used, inconjunction with a "Direct-Sequent Spread Spectrum" mociulation technique.
1 û A transmitter for a Direct-Sequence Spread Spectrum (DSSS) system includes a source of pseudo-random data (usually binary), such data being generated at a rate considerably in excess of the system communication speed. Because of its similarity to natural noise, this data is commonly termed ~Pseudo-Noise" (PN). This PN data is then mix2d with the "real" data, so greatly increasing the requisite bandwidth, and 1 5 transmitted.
The receiver or interro~ator of the present invention must include, on each channel means to ~enerate a Pn-sequence identical to that used by a remote device. That is, the interrogator includes a separate channel for each possible Pn-sequence which can be selected by a remote device. The Pn-sequence of each channel needs to be accurately 20 synchronised with that of the transmitting remote device. Means for achieving such synchronisation are known (see, inter alia, Sklar, UDigitals Communications:
Fundamentals ~ Applications", Prentice-Hall, 1988). To be effective, synchronisation needs to be very precise (within a fraction of the period of the clock driving the PN
generator). When this occurs, the desired signal is greatly increased in amplitude, 25 while other, un-synchronized signals are greatly attenuated. Of course, should the receivet's PN generator produce a PN sequenced different to that at the transmitter, synchronisation will be impossible. It is this selective amplification property which provides the basis for the present invention. A correlation operation is performed between the received signal and this local PN source, leaving the required data or signal.
Unlike the prior art where a number of different carrier frequencies can be used, as shown in Figures 1 and 2 the present invention contemplates the use of a single carrier frequency for use by all remote devices, upon which a data or information signal ~ 2103~0 ~'0 92/17947 PCI'/AU~2/00123 is modulated in accordance with a particular type of modulation (AM, FM. etc) or in accordance with a particular pn-sequence.
Such a system is relatively highly resistant to interference (whether intentional or not), in that any received signal which does not correspond exactly to the local PN
5 signal, will be converted into wideband noise, which may readily be filtered out.
~E~ RlPTlON OF_TH~lNv~~
The invention provides a device and an object-identification system, characterised by the ability to identify (read signals from) several different objects simultaneously. Prior art systems employ a plurality of carrier radio frequencies, 10 was described in the applicants related invention. The related invention provided an identifying device (lltransponder", or utag") to be attached to the object to beidentified, said tag being adapted to transmit an identifying message at one of a plurality of radio frequencies. In use, the message is repeatedly transmitted, with the same or a new radio frequency being selacted at each transmission. The receiving equipment15 provides a plurality of channels, each sensitive to one of the plurality of frequencies, and can receive message on all frequencies simultaneously. Separation of messages transmitted by a plurality of tags is provided by limiting the bandwidth of the rece;ver channels, such that each receives messages on one radio frequency only. The system is characterised by the ability to identify a plurality of tags at once, such plurality being 20 randomly selected from an extremely large (quasi-infinite) total population of possible tags.
The present in~ention may be regarded as an improvement over or a modification of the related invention. In the present invention, a single radio frequency is used, and the tags are prevented from co-interfering by employing a plurality of PN sequences 25 and/or a plurality of types of modulation and likewise a plurality of corresponding receivers, each such receiver adapted to synchronise to only one of the said plurality of PN sequences or types of modulation.
- The transmitting portion of a device according to the present invention is shown conceptually in Fig. 3. Comparison with the prior art Fig. 1 will disclose the novelty, 3 0 which resides in the provision of a plurality of PN or modulation sources, and a selection means (which said means operates identically to that of the cited prior invention) to choose one of the PN or modulation sources.
2ln3sl~
WO 92/17947 PCI'/AU92/00123 The 1ag selects a PN or type of modulation source, transmits the message, selects a new (or the same) PN or type of modulation source, and repeats.
Rather than employing a plurality of separate PN generators, it will be advantageous to employ a single PN generator, adapteci to receive as inputs, certain 5 quantities ("co-efficients") which determine the generated sequence. An exemplary embodiment of such a circuit is shown in Fig. 4. The device comprises a shift register A, whose input is fed from the Exclusive-OR (XOR) function of two or more taps on the said shift register. Adroitly chosen taps will yield a plurality of long sequences, having good PN qualities. The exemplary embodiment employs two taps, implemented by the10 multiplexers B and C, which select two bits from the said register, and present them to the XOR gate D~ The output of this gate is presented to the serial data input of register A.
By changing the selection inputs to the multiplexers B and C, a plurality of PN sequences may be produced. In the exemplary embodiment, a plurality of such selections are pre-15 determined, and stored in the Read-Only-Memory (ROM) E. When a value is presented to the address inputs of E, its outputs direct multiplexers B and C to select taps on the register A, and a PN sequence is generated. In the complete tag, a Uselection means" is provided to select from the plurality of possible PN sequences.
A preferred receiving means are shown in Fig. 5. Each of the several PN or 2 0 modulation generators generates a different member of the plurality of PN sequences or modulations available in the device.
SUITABLE PN SEQUENCES
Suitable PN sequences can be characterised by 3 qualities:
1. Their auto-correlation function will approximate to a "spike" or mathematical 2 5 delta function. That is to say, if two copies of the same PN sequence are correlated together, a significant output will occur only when the two copies are in exact alignment. Any mutual misalignment will result in an essentially zero output.
2. The cross-correlation function between any two (different) PN sequences wiil be 3 0 essentially flatl i.e. there will be minimal output for any possible relative alignment of the two seciuences.
3. The PN sequence shall comprise approximately equal numbers of ONE and ZERO
21~10 WO 92/17947 PCI'/AU92/00123 bits.
The present system utilises the interference-resistant quality of a DSSS channelto identify or communicate with specific devices such as transponders.
According to the invention, each device is adapted to hold a plurality of dis~inct 5 PN sequences as a set of predetermined modulations. Alternatively, the device may hold a table of suitable coefficients, which may be passed to a digital logic circuit, such circuit being adapted to (when the said coefficients are presented as inputs) generate the required PN sequences or modulations.
A random or predetermined choice is made amongst these modulations and the 10 randomly chosen modulation is used to transmit a signal which is to form the communication.
Before the signal is transmitted again, a new choice (from the avaiiable PN
sequences) is made on a random or predetermined basis. Each bit of the message data is mixed with the chosen PN sequence, and transmitted. In practice this may imply that 15 what is transmitted is either a selected modulation or in the case of a stored sequence, its complement, depending on whether signal is a logic signal and the data bit is a zero or one. The transmission bandwidth has been increased in proportion to ~he number of bits in the PN sequence. In an alternative system, in which only alternate bits of the PN
sequence, rather than all bits, are reversed to suit the data polarity. Other schemes are 2 0 also possible.
The complete message is transmitted preferably using a single modulation PN
sequence. The PN sequence may extend over the entire message, or a shorter PN
sequence may be used repeatedly for each message bit. When the entire message has been sent, a new sequence is then selected, from a group of available sequences, and the 2~ message is retransmitted. In the present system, the radio carrier frequency remains substantially constant.
Conveniently, the receiver or interrogator may operate on the homodyne principle as described on pages 14-15 and Figure 9 of the related application. In the case of a plurality o~ devices transmitting simultaneously, an interrogator will yield as 30 output a wideband data stream, comprising the sum of messages received from all devices within range. Such messages will have been encoded using the plurality of PN
sequences as previously described.
2iO331~
This stream is passed simultaneously to a plurality of matched filters, each adapted to match one of the original, stored PN sequences. These filters may be cf the class of "Transversal Filters~, wherein the filter coefficients take the values +1 and -1, following the bit-sequence of the original PN pattern. The auto-correlation property of the PN sequences (as above-described) implies that when a data pattern matching the original sequence is presented to such a filter, a sharp positive voltage spike appears at the output, as the received data passes (momentarily) into alignment with the filter coefficients. Similarly the complement of the given sequence will develop a sharp negative pulse~ Non-matched data will merely generate low-level noise, which 10 may be filtered out by a simple amplitude "window~, or other circuitry.
The pulses so obtained represent one and zero bits of the original data.
The above-described cross-correlation property of the PN sequences enables messages encoded with a given PN sequence to be tecovered by the appropriate matched filter, and no other. This property serves to separate out the various transmissions 15 from one or more devices.
In a most preferred form, these transversal filters may be implemented by converting the receiver output to a sampled digital representation, and employing onc of the many "digital signal processor~ VLSl chips now available, to perform the filtering function in the digital domain. Many such chips are sufficiently powerful to 2 0 simultaneously filter a plurality of channels ~i.e. using different PN sequences).
An interrogator as described above is suitable for a PN sequence, however, the interrogator may be suitably constructed or adapted to receive and demodulate any type of modulation, depending on the form of modulation selected to transmit lhe signal from the remote device(s) to the interrogator, as would be understood by those of the art.
In yet another alternative, it is possible to combine the transponder and systemsimilar to that disclosed in the related application and the present invention, thus providing a plurality of remote devices, each modulated by a plurality of modulations or PN sequences andtor frequencies. This will require a plurality of receivers in the interrogator (one for each carrier frequency), each being adapted to demodulate a 30 number of received transmissions at a selected modulation. Such a system could simultaneously identify very large numbers of transponders, in that it provides a system utilising a plurality P1 of radio frequencies, with a second plurality P2 of PN
- 2103~10 ~0 92/17947 PCI`/AU92/00123 sequences employed upon each of the said frequencies, so obtaining a largar plurality (up to P1~P2) of simultaneously useable channels. While such a system would require a more elaborate receiver means (having up to P1~P2 receiving sections) than either of the description above~ it would permit rapid, simultaneous identification of very large 5 numbers of objections.
It may also be possible to utilise various forms of modulation (AM, FM, PWM and others as is known in the art). By selecting one modulation ~say AM) for the first transmission, then selecting another modulation say (FM) for the second modulation, etc. Selection may be carried out in a random or predetermined sequence.
2~
.~., ~-` 4 ''t~
. . , .
Claims (7)
1. A device comprising:
transmitter means adapted to transmit an information, code or identification signal;
selection means adapted to select, in a predetermined manner, a type of modulation for transmission of said signal from a set of predetermined type of modulations;
wherein the signal is transmitted using the selected modulation.
transmitter means adapted to transmit an information, code or identification signal;
selection means adapted to select, in a predetermined manner, a type of modulation for transmission of said signal from a set of predetermined type of modulations;
wherein the signal is transmitted using the selected modulation.
2. A device as claimed in Claim 1, wherein selection of said modulation is random.
3. A device as claimed in Claim 1 or 2, wherein the signal is successively orrepetitively transmitted at each transmission at a newly selected modulation from the set of modulations.
4. A device as claimed in Claim 1, 2 or 3, wherein each modulation comprised PN sequence selected from a group of possible Pn-sequences.
5. A device as claimed in Claim 1, wherein the modulation is one of DSSS, AM,FM or PWM.
6. A communication system comprising:
at least one remote device each adapted to transmit a signal at a modulation selected from a set of predetermined modulations; and an interrogator adapted to receive transmissions from at least one remote device.
at least one remote device each adapted to transmit a signal at a modulation selected from a set of predetermined modulations; and an interrogator adapted to receive transmissions from at least one remote device.
7. A system as claimed in Claim 6 wherein the interrogator includes a number of receiver channels adapted to receive transmissions from the remote devices, the number of channels corresponding to the number of modulations available for use by each remote device in the set of predetermined modulations.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPK5366 | 1991-03-28 | ||
| AUPK536691 | 1991-03-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2103910A1 true CA2103910A1 (en) | 1992-09-29 |
Family
ID=3775306
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002103910A Abandoned CA2103910A1 (en) | 1991-03-28 | 1992-03-24 | Identification apparatus and method |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0577687A1 (en) |
| CA (1) | CA2103910A1 (en) |
| WO (1) | WO1992017947A1 (en) |
| ZA (1) | ZA922184B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4242973C2 (en) * | 1992-12-18 | 1995-01-05 | Grundig Emv | Radio alarm system with a large number of message channels formed by the code multiplex method |
| DE4337637A1 (en) * | 1993-11-04 | 1995-05-11 | Licentia Gmbh | Transponder and data communication system |
| EP1335550A3 (en) * | 1994-09-09 | 2004-05-19 | XIRCOM Wireless, Inc. | Differential phase encoding apparatus |
| US5649295A (en) * | 1995-06-19 | 1997-07-15 | Lucent Technologies Inc. | Dual mode modulated backscatter system |
| US5649296A (en) * | 1995-06-19 | 1997-07-15 | Lucent Technologies Inc. | Full duplex modulated backscatter system |
| US5940006A (en) * | 1995-12-12 | 1999-08-17 | Lucent Technologies Inc. | Enhanced uplink modulated backscatter system |
| US6130602A (en) | 1996-05-13 | 2000-10-10 | Micron Technology, Inc. | Radio frequency data communications device |
| KR20000049066A (en) * | 1996-10-17 | 2000-07-25 | 핀포인트 코포레이션 | Article tracking system |
| KR100326182B1 (en) * | 1998-03-23 | 2002-07-02 | 윤종용 | Method and apparatus for generating pn sequence in cdma communication system |
| JP4259746B2 (en) * | 2000-12-15 | 2009-04-30 | イビデン株式会社 | Received wave transmitter and moving object identification system |
| FR2871312B1 (en) * | 2004-06-03 | 2006-08-11 | St Microelectronics Sa | CHARGE MODULATION IN AN ELECTROMAGNETIC TRANSPONDER |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4218680A (en) * | 1979-01-12 | 1980-08-19 | Motorola, Inc. | Coded coherent transponder |
| IL78972A (en) * | 1985-06-14 | 1991-04-15 | Mitsubishi Electric Sales Amer | Video optimized modulator-demodulator |
| US4746880A (en) * | 1987-02-06 | 1988-05-24 | Digital Rf Solutions Corporation | Number controlled modulated oscillator |
| WO1989005549A1 (en) * | 1987-12-04 | 1989-06-15 | Magellan Corporation (Australia) Pty. Ltd. | Identification apparatus and methods |
-
1992
- 1992-03-24 EP EP92907634A patent/EP0577687A1/en not_active Withdrawn
- 1992-03-24 WO PCT/AU1992/000123 patent/WO1992017947A1/en not_active Application Discontinuation
- 1992-03-24 CA CA002103910A patent/CA2103910A1/en not_active Abandoned
- 1992-03-25 ZA ZA922184A patent/ZA922184B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| WO1992017947A1 (en) | 1992-10-15 |
| EP0577687A1 (en) | 1994-01-12 |
| ZA922184B (en) | 1992-12-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 19960924 |