US20060103533A1

US20060103533A1 - Radio frequency tag and reader with asymmetric communication bandwidth

Info

Publication number: US20060103533A1
Application number: US10/988,271
Authority: US
Inventors: Kourosh Pahlavan; Farokh Hassanzadeh Eskafi
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-11-15
Filing date: 2004-11-15
Publication date: 2006-05-18
Also published as: US7180421B2; CN101160608A; CN101160608B; JP2008521287A; JP4934050B2; US20060103535A1

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS



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

N/A

BACKGROUND OF THE INVENTION

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.
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.
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.
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.
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.
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.
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.
In the second approach, transmitting the data back to the reader requires power like any other RF transmission.
Regardless of the approach, the logic engine of the tag that processes and transports the stored ID or data still needs power.
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.
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.
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.
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.
Generally, there are a number of problems associated to currently available narrowband RFID technologies. These are:

- Low data rate and lack of noise immunity, limiting an item-level tagging and high simultaneous number of interrogations by the reader.
- 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.
- Any attempt to remedy the above problems or additional functionality results in a complexity in the circuitry that opposes the cost and power constraints.

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.
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.
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.
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.
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

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.
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.
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.
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.
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

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”.
FIG. 2 is the block diagram of the main components of a responder or tag in one embodiment of the invention.
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.
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.
FIG. 5 depicts an embodiment of the front-end of a multi-band energizing design in a tag.
FIG. 6 depicts the high-level architecture of an RFID network as suggested by one embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION

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:

- 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.
- 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.
- 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.

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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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:

- Power Recovery & Supply Generation: a section for capturing electromagnetic energy and converting it to useful current and voltage levels.
- 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.
- Receiver: a section that detects and extracts the data and commands modulated on the incoming signal.

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.

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.