U.S. patent application number 10/988271 was filed with the patent office on 2006-05-18 for radio frequency tag and reader with asymmetric communication bandwidth.
Invention is credited to Farokh Hassanzadeh Eskafi, Kourosh Pahlavan.
Application Number | 20060103533 10/988271 |
Document ID | / |
Family ID | 36385709 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060103533 |
Kind Code |
A1 |
Pahlavan; Kourosh ; et
al. |
May 18, 2006 |
Radio frequency tag and reader with asymmetric communication
bandwidth
Abstract
A method and apparatus to overcome fundamental shortcomings in
narrow band as well as wide band RFID solutions through offering a
hybrid solution that utilizes benefits of narrow band in the
downlink direction with the benefits of ultra wide band in the
uplink. The invention encompasses a multitude of methods, including
an approach to increase the ability to capture electromagnetic
energy from the reader.
Inventors: |
Pahlavan; Kourosh; (Palo
Alto, CA) ; Hassanzadeh Eskafi; Farokh; (Brooklyn,
NY) |
Correspondence
Address: |
KOUROSH PAHLAVAN
2456 INDIAN DRIVE
PALO ALTO
CA
94303
US
|
Family ID: |
36385709 |
Appl. No.: |
10/988271 |
Filed: |
November 15, 2004 |
Current U.S.
Class: |
340/572.1 |
Current CPC
Class: |
G06K 7/0008 20130101;
G06K 7/10306 20130101 |
Class at
Publication: |
340/572.1 |
International
Class: |
G08B 13/14 20060101
G08B013/14 |
Claims
1. A system with a multitude of radio transceivers called readers
and a multitude of radio transceivers called tags, wherein the
readers transmit radio frequency signals to the said tags in a
narrow frequency band and receive radio frequency signals from the
said tags in an ultra wide frequency band. Conversely, the said
tags transmit in narrow band and receive in ultra wide band.
2. A system as in 1 where each individual tag maintains the
capability to store, erase, update and process local and incoming
data.
3. A system as in 1 and 2, where the signal energy transmitted from
the reader in narrow band also electrically and remotely energizes
the circuitry in the tags individually or collectively over the air
to wholly or partially substitute battery or other sources of power
in the tag.
4. A system as in 1 to 3, where the relationship between tag and
reader is reversed, i.e. the tag transmits in narrow band and
receives in ultra wide band, while the reader transmits in ultra
wide band and receives in narrow band.
5. A system as in 1 to 4 whereas the network of the multitude of
tags and readers can be organized and supervised by a multitude of
central or distributed servers that can control, process and store
the information flowing in the network of tags and readers.
6. A system such as in 1 to 5 where readers and tags are both
capable of using ultra wide band radio for both transmission and
reception of data, while the tags are still powered by narrowband
signals from the readers.
7. A system as in 1 to 6 where individual tags and readers can
listen to other propagating units, including other tags and readers
in order to organize their activity in the total network.
8. An RFID system that utilizes several circuits each tuned for
different frequencies in the receiving front-end so as to enable
the tag to simultaneously capture electromagnetic energy in the
said frequencies.
9. A system such as in 1-8 where the narrowband receivers and the
narrowband transmitters are completed with such functionality to
enable them to be compatible with legacy narrowband methods and
devices.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] TABLE-US-00001 3,516,575 Muffitt et al. June 1967 3,199,424
Vinding, J. January 1967 3,541,995 Fathauer, H. George November
1968 3,689,885 Kaplan et al. September 1972 3,713,148 Carelullo et
al. January 1973 6,550,674 Neumark, Yoram April 2003
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] N/A
BACKGROUND OF THE INVENTION
[0003] This invention relates generally to object and inventory
identification and control systems and more particularly to a
system using inventory identity labels mounted adjacent to
inventory items. These labels provide identification information
relative to the inventory, wherein the labels are enabled for
communication with a computerized inventory management system, and
wherein the labels' location and status is known at any time from a
remote location.
[0004] Radio Frequency Identification (RFID) refers to utilization
of RF signals as means of communication between responders,
normally tags or similar modules, and interrogators, normally
called readers. See e.g. U.S. Pat. Nos. 3,299,424 and
3,689,885.
[0005] The simplest RFID tags comprise an ID, normally in a digital
binary form, that is modulated on an RF carrier signal propagated
by the tag as described in e.g. U.S. Pat. No. 3,713,148.
[0006] Radio communication between a tag and a reader can be done
in two principally different ways. One way is using a tuned
circuitry in the tag such that when exposed to the electromagnetic
field generated by the reader, the tag comes into oscillation and
interacts with the reader field. The tag can use the effect of this
self-oscillation, which manifests itself as an inhibition of the
original field generated by the reader to present its ID or data.
This self-oscillation can be used to connect the reader and the tag
by means of magnetic coupling or backscattering. Under these
circumstances the reader can sense the presence of the tag and
demodulate the data that the tag has modulated into the field
inhibition pattern caused by magnetic coupling or backscattering by
the tag; see e.g. U.S. Pat. Nos. 3,516,575 and 3,541,995.
[0007] The second approach is to have a set-up like the one in
normal RF communication, i.e. the readers transmit signals that are
received by the tags and the tags transmit signals that can be
detected and decoded by the readers. In this approach, the
structure of the signal transmitted by the tag is inherently
independent of the signal received by it. Thereby, the tag can,
e.g. receive information from the reader in one band and transmit
it in a completely unrelated band and with a different signal
structure and technology.
[0008] There are variations of the first approach that use
backscattering in a band that is an integer multiple or fraction of
the original received signal, but this flexibility is limited to
this frequency multiplication/division only. There are also other
approaches using Surface Acoustic Wave, Acoustomagnetic and
electrical coupling as means of responding to the reader. However,
these approaches can all be classified in the same category of
devices that generate a reaction to the original field created by
the reader and inhibit the same through this reaction.
[0009] In the first approach, the tag can be a completely passive
element in that it does not require any source of power to inhibit
the electromagnetic field created by the reader and thereby convey
its data. The tag responds by presenting its ID or other data
through the inhibition pattern that is in turn sensed by the reader
monitoring its own transmitted signal.
[0010] In the second approach, transmitting the data back to the
reader requires power like any other RF transmission.
[0011] Regardless of the approach, the logic engine of the tag that
processes and transports the stored ID or data still needs
power.
[0012] This power can be provided by a source of energy that is
integrated with the tag, e.g. a battery or an accumulator of some
kind. But it can also be generated by other means, e.g. by
capturing the electromagnetic energy propagated by the reader or
similar sources of emitting such signals. This process requires a
circuitry that can convert electromagnetic energy to such current
and voltage levels that can satisfy the power needs of the tag
circuitry. A tag in the first approach will not need this recovered
data for its transmission stage, because it transmits as a reaction
to the field that is exciting it. In the second approach, a tag can
however use this electrical energy to power up its transmission
stage and transmit its data back to the reader or other units
prepared to communicate with it.
[0013] Magnetic coupling works only at very short distances and
backscattering relies on small signal reflections that only offer a
limited range and a low bandwidth for data exchange between the tag
and the reader. However, tags made with this approach are simple
and cheap to manufacture, because their transmission stages are
passive and their active control and data processing stages are
simple and low power so that, at least at short range, they can
supply their needed power by capturing electromagnetic energy
through simple and affordable power rectification circuitry on the
tag.
[0014] Using a RF transmission stage, in accordance with the second
approach, offers more flexibility, longer range and higher data
rate at higher complexity and power consumption due to the
complexity of the baseband and addition of an independent
transmission stage. Therefore, such tags are quite often battery
powered active tags. Active RF tags tend to be larger in size and
more expensive than corresponding passive ones.
[0015] Regardless of whether the tag acts as an active transmitter
or backscatters passively, all the communication between a tag and
a reader is performed in certain regulated frequency bands. The
amount of output power in each band is regulated to ensure the
integrity of the neighboring spectrum against signal pollution.
These bands are normally narrow bands in LF, HF, UHF and Microwave
portions of the RF spectrum.
[0016] Generally, there are a number of problems associated to
currently available narrowband RFID technologies. These are: [0017]
Low data rate and lack of noise immunity, limiting an item-level
tagging and high simultaneous number of interrogations by the
reader. [0018] The tags are nearly useless on metal or such
containers that contain conductive material, dielectric liquids and
in general such material that can cause detuning of the signal
through reflection and absorption. [0019] Any attempt to remedy the
above problems or additional functionality results in a complexity
in the circuitry that opposes the cost and power constraints.
[0020] These issues are mostly addressed by deploying Ultra Wide
Band (UWB) radio. Recent attention to UWB radio and its application
to RFID have brought about new possibilities in terms of higher
data rate, lower power consumption, location determination,
resilience to multi-path distortion and media penetration and
reflection.
[0021] UWB or Impulse Radio is a carrier-less radio whose signal is
in simple terms only an extremely short pulse in the time domain.
This very short pulse in the time domain corresponds to an
extremely wide bandwidth in the frequency domain.
[0022] Due to its impulse nature, the transmitter stage in the UWB
radio is very simple. The requirements of the UWB receiver stage on
filters, amplifiers and detection circuits that can handle the
extremely wide bandwidth, among other factors, make its design more
challenging. In comparison, a narrow band radio can be more
challenging in the transmitter stage and less challenging in the
constraints imposed on the amplification and detection stages of
the receiver.
[0023] UWB radio is extremely low power while it offers a very high
data rate. Due to its very wide frequency content, impulses can
penetrate material with an unprecedented performance and they are
very resilient to multi-path limitations imposed on narrowband
radio. These qualities have made UWB a natural choice for high
performance Radars and mine detectors.
[0024] Narrow band RFID techniques are invented and utilized across
a broad range of applications. UWB radio communication is also
applied to RFID in several embodiments for different applications;
see e.g. U.S. Pat. No. 6,550,674. The embodiments are normally
larger tags that deploy internal batteries and complex
transceivers.
A BRIEF SUMMARY OF THE INVENTION
[0025] It is an objective of the present invention to provide a
solution to the shortcomings of the currently available RFID
designs by combining narrowband and Ultra Wide Band technologies.
The system, methods and apparatuses provided by the present
invention alleviates these shortcomings by exploiting the benefits
of narrow and wide band communication between tags (responders) and
readers (interrogators). Using a narrowband link from the reader to
the tag warrants for the ability to transmit powerful signals that
can in the frame of allowed power envelopes set by regulatory
authorities energize passive tags in a way that their internal
circuitry can be powered up wholly or partially by the received
signals. Conversely, using an Ultra Wide Band link from the tag to
the user warrants for high data rate, low power, massive
simultaneous communications between the tags and the readers that
are resilient to multipath, penetration and reflection problems
that the currently available narrow band RFID technologies suffer
from.
[0026] It is another objective of this invention to alleviate the
problems that currently available UWB technologies suffer from. A
regular UWB radio transmits low power signals over a very wide
band. Transmitting high power over such a broad band would pollute
the RF spectrum and interfere with other wireless devices in those
bands. Furthermore, the UWB transmitter is extremely simple to
design, whereas the receiver stage could be more complex and power
consuming. Conversely a narrowband receiver is low power and
simple. By using UWB as means of transmitting data from the tag to
the reader only, all the benefits of UWB and all the benefits of
narrow band can be achieved simultaneously.
[0027] It is yet another objective of this invention to enable
design of an RFID tag that deploys separate transmitter and
receiver stages, whereby the transmitter function can be completely
decoupled from the limitations that the receiver design can impose
on the transmitter. The ability to combine narrow band and UWB
radios on receiver and transmitter stages respectively is a lucid
example of benefits from such decoupling.
[0028] It is yet another objective of this invention to create tags
and readers that are according to the said asymmetric bandwidth
also maintains backward compatibility with legacy RFID systems; see
FIG. 3.
[0029] It is yet another objective of this invention to provide yet
another technique to transmit more power to an RFID tag by
deploying multiple tuned circuits in the front-end of the tag so as
to capture energy from different bands simultaneously; see FIG.
5.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 illustrates the direction of communication and the
radio technology of the transmitter and receiver units in a tag and
a reader respectively. It also elucidates the directions called
"uplink" and "downlink".
[0031] FIG. 2 is the block diagram of the main components of a
responder or tag in one embodiment of the invention.
[0032] FIG. 3 is the block diagram of another embodiment of the
invention. In this embodiment, the tag and the reader are designed
such that they can function in a legacy network as well as the
network of responders (tags) and interrogators (readers) as
described by this invention.
[0033] FIG. 4 explains the direction of the signals and the
continuous overlapping nature of the energizing signal with respect
to the data exchange between the tags and a reader that is capable
of multiple simultaneous narrow band radio transmissions. Signals
on different channels or bands can energize the same tag
simultaneously and thereby enhance its ability to gain electrical
energy. The capability of the tags to listen to and to be energized
by the reader signals in different bands can also enhance location
determination, multi-access techniques, bit-rate and the overall
system performance.
[0034] FIG. 5 depicts an embodiment of the front-end of a
multi-band energizing design in a tag.
[0035] FIG. 6 depicts the high-level architecture of an RFID
network as suggested by one embodiment of this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0036] As illustrated in FIG. 1, the invented reader uses narrow
band channels to interrogate the tag. This direction of
communication is called a downlink communication. The used band can
be in any portion of the spectrum where radio communication is
possible. The receivers of these narrowband signals, i.e. the tags,
transmit their responses back to the readers in a stream of UWB
impulses. The direction of communication in this case is called
uplink (see FIG. 1). This means that each reader uses at least a
narrowband transmitter and a UWB receiver, while each tag utilizes
a UWB transmitter and a narrowband receiver. This asymmetric
utilization of the bandwidth, which is the core of this invention,
has many benefits, among them: [0037] A UWB transmitter is very
simple, low power, easy to design and cheap. This is true for a
narrowband receiver as well. By deploying these two simplest
combinations of the UWB and narrowband technologies, the tag which
is the most critical element of an RFID network, will end up having
a simple and cheap solution. [0038] The Ultra Wide Band transmitter
offers nearly all the benefits of a UWB radio in an RFID network.
It offers an RFID tag that is resilient to multipath, penetration
and reflection problems that narrowband RFID tags normally suffer
from. Furthermore, UWB provides an RFID system with unique
capabilities in terms of location determination that are not
offered by narrowband radio. The narrowband receiver of the tag can
be tuned to listen to a very narrow channel, which in turn can
enhance detection ability. The virtue of having a narrow band
receiver in the tag also enables the reader to exploit the maximum
allowable power output in the allowed band without interfering with
other radio systems. Thereby the reader can provide enough signal
strength to power up the tag through its narrow band receiver. A
reader with a UWB transmitter would not be able to output enough RF
energy to power up the tag, without polluting its utilized
spectrum. [0039] Since the transmitter stage of the tag is a very
low power UWB radio and its receiver stage can provide it with more
power through the strong incoming narrow band signals, a tag that
can be completely passive and still offer long range, high
bandwidth location determination and immunity to reflection,
multipath and penetration can be realized.
[0040] Magnetically coupled or backscattering RFID tags can also
use an embedded source of power to assist their digital circuitry
when enough power is not recycled from the reader signal. However,
this internal source of power--normally a battery--cannot easily
participate in the process of radio transmission, because the
transmitted signals are reflections or inhibitions of the original
reader signal. Deploying a stand-alone transmitter stage, as is the
case with the present invention, entails a capability to use the
internal or external power in any way needed. In this particular
case, it can be used to increase the power output of the
transmitter to achieve a longer range and better signal
quality.
[0041] A reader signal is normally a carrier on which the reader
command and data are modulated. This carrier signal also provides
the power for the tag. The signal from the reader to the tag can be
continuous or sequentially pulsed, depending on the way the tags
need to be powered up, the number of the tags, and the multi-access
method used for simultaneous access of multiple tags. If the
network deploys a TDMA (Time Division Multiple Access) scheme, the
tags will respond sequentially in accordance with the timing
protocol. However, the duration and the band in which the signal is
transmitted by the reader can cause different tags or subnets of
tags to be powered up and respond, simultaneously or sequentially.
FIG. 4 illustrates another embodiment of the invention in which
case the carrier signal is continuously broadcast over all tags in
the network in channel P, while the same reader also transmits a
narrow band signal in band Q, but only for a specific subnet of
tags, which can, e.g. need the extra power because of being far
from the reader. In this embodiment, the tag is equipped with
additional circuitry that allows the tag to capture electromagnetic
power from different bands of the spectrum. FIG. 5 illustrates this
detail in the "Power Recovery, Supply and Generation" module
depicted in FIG. 2.
[0042] The multi-band energizing scheme can be used as a
multi-access facilitator, but it can also provide increased
bit-rate from the reader to the tags, enhance location
determination, and in general increase the system performance.
[0043] In one embodiment of the present invention, the narrowband
receiver of the tag can behave like a legacy RFID tag, e.g. perform
magnetic coupling or backscattering. In this embodiment, the tag
will have the additional circuitry to create the return signal in
accordance with the technology in use (e.g. inductive coupling,
backscattering, etc.) and modulate its ID and data on this returned
signal. FIG. 3 illustrates this embodiment in the case of using
magnetic coupling. As depicted in the figure, a reader that is an
embodiment of this invention with said backward compatibility can
communicate with legacy tags as well as those in accordance with
this invention. Furthermore, tags of this invention that comply
with this said backward compatibility can communicate with legacy
readers and systems.
[0044] A typical network architecture for different embodiments of
this invention is illustrated in FIG. 6. A multitude of readers can
be present in a network, each serving a number of tags that may be
members of different subnets of different readers simultaneously.
These tags could be passive, active or legacy tags that do not
comply with the technology described in this invention, but still
accessible to the readers, because of the backward compatibility of
the readers to the legacy RFID tags.
[0045] Readers communicate with the tags wirelessly. However, they
can communicate with each other through a wired or wireless
communication. This flexibility in connection is also true about
the communication between readers and local servers and gateways.
The readers and other elements of the network such as local
servers, gateways, databases, and storage units can share or create
a Local Area Network (LAN) that can internally be interconnected
with wires or wirelessly. Finally, the network can connect to
external networks and the Internet through its gateways or other
computers in the LAN that are capable of external
communication.
[0046] FIG. 6 illustrates the high-level architecture of the system
that is an embodiment of this invention. At the lowest level of the
hierarchy, there are a considerable number of items with active and
passive tags mounted on them. The presence of a UWB transmitter
stage in the tags warrants for the system's capability to reach a
massive item-level deployment; the high data rate and thereby a
large system capacity allows for mass interrogations in short time
intervals.
[0047] Due to their very simple design, the passive tags are very
low cost. They are composed of a very small CMOS chip mounted on a
substrate that carries the narrow band antenna (or a wound loop)
for the receiver and the UWB antenna for the transmitter.
[0048] An active tag has an integrated battery. This battery could
be in similar embodiments substituted by a rechargeable accumulator
or a capacitor. The active tag exploits the reader signal in the
extent it can. When the distance to the reader is too far for the
passive solution to overcome, the battery power is switched on to
boost performance. Such a tag is often called a semi-active
tag.
[0049] The active tag can also solely rely on its battery resource;
thereby it does not need to be a continuous slave of one particular
reader and can initiate communication sessions and scheduled
processings on its own.
[0050] The second element of the system in the hierarchy is the
reader. The reader is designed so as to be backward compatible with
the traditional narrow band RFID systems as well as UWB tags (see
FIG. 3). Thereby, it can function across different standards and
solutions. However, the basic function of the reader in this system
will be to fulfill the subject of this invention, i.e. communicate
with the tags over a narrow band channel in downlink and UWB in
uplink. The reader is a node in a larger network of readers that
can be scattered over a local or wide area network.
[0051] The network of readers is intertwined and integrated with
the network of the third element of the system, i.e. the server
node. The server nodes are local control, communication and
management units of the system. However, they can work as gateways
to other networks or subsystems of tags and readers or other
computational and communication units, e.g. enterprise servers and
databases.
[0052] FIG. 2 depicts the internal architecture of the passive tag
in this embodiment. Upon a session initiation, the reader
broadcasts a signal that powers up all the tags in its reach. The
receiver front-end of the passive tags is divided into three
parallel sections. These are: [0053] Power Recovery & Supply
Generation: a section for capturing electromagnetic energy and
converting it to useful current and voltage levels. [0054] Clock
Recovery: a section that has the task of creating a system clock
for different blocks on the chip. This clock also provides the
basic building block for the UWB impulse generation circuitry.
[0055] Receiver: a section that detects and extracts the data and
commands modulated on the incoming signal.
[0056] The main processing unit onboard takes care of baseband
processing as well as control and system management of the entire
chip. The code for this work as well as encryption, decryption and
identification codes are stored in any non-volatile memory
compatible with the processing used for the rest of the tag chip
(e.g. CMOS, BiCMOS, etc.). This memory can be mask ROM, PROM,
EPROM, EEPRM, Flash, FeRAM, MRAM, etc. depending on the custom
needs and cost constraints. The working memory of the processor is
a RAM block.
* * * * *