RFID readers and systems with antenna switching upon detecting too few tags and methods

RFID readers, reader systems, and methods are provided that utilize smart antenna switching. A first signal is transmitted from a first antenna estimating presence of tags within the antennas field of view. If fewer than a predefined number of tags are estimated, the system switches to a second antenna. Otherwise, the tags found in the field of view of the first antenna are inventoried before switching to the second antenna.

BACKGROUND

Radio Frequency IDentification (RFID) systems typically include RFID tags and RFID readers (the latter are also known as RFID reader/writers or RFID interrogators). RFID systems can be used in many ways for locating and identifying objects to which the tags are attached. RFID systems are particularly useful in product-related and service-related industries for tracking large numbers of objects being processed, inventoried, or handled. In such cases, an RFID tag is usually attached to an individual item, or to its package.

In principle, RFID techniques entail using an RFID reader to interrogate one or more RFID tags. The reader transmitting a Radio Frequency (RF) wave performs the interrogation. A tag that senses the interrogating RF wave responds by transmitting back another RF wave. The tag generates the transmitted back RF wave either originally, or by reflecting back a portion of the interrogating RF wave in a process known as backscatter. Backscatter may take place in a number of ways.

The reflected-back RF wave may further encode data stored internally in the tag, such as a number. The response is demodulated and decoded by the reader, which thereby identifies, counts, or otherwise interacts with the associated item. The decoded data can denote a serial number, a price, a date, a destination, other attribute(s), any combination of attributes, and so on.

An RFID tag typically includes an antenna system, a power management section, a radio section, and frequently a logical section, a memory, or both. In earlier RFID tags, the power management section included an energy storage device, such as a battery. RFID tags with an energy storage device are known as active tags. Advances in semiconductor technology have miniaturized the electronics so much that an RFID tag can be powered solely by the RF signal it receives. Such RFID tags do not include an energy storage device, and are called passive tags.

A single RFID reader system may have several antennas. Due to the Tx/Rx chain, the RFID reader system selects, drives, and listens from only one of its antennas at any given time. A further complication arises when a combination of RFID systems is typically deployed and they need to coordinate antennas between themselves to limit interference.

Commonly used static antenna driving techniques may result in wasted time on antennas where no tags are in the field of view, not enough time on antennas where many tags are in their respective fields of view, and increased interference in multiple reader systems where transmission is caused through antennas even when no tags are in the field of view.

SUMMARY

Embodiments are directed to switching antennas in an RFID reader system while performing tag population checks instead of inventorying of all tags within one antennas field of view. Presence of tags is first detected through one antenna. If the number of tags is smaller than a predefined threshold, the system switches to another antenna without inventorying the tags detected in the field of view of the first antenna.

This and other features and advantages of the invention will be better understood in view of the Detailed Description and the Drawings, in which:

DETAILED DESCRIPTION

Throughout the specification and claims, the following terms take at least the meanings explicitly associated herein, unless the context clearly dictates otherwise. The meanings identified below are not intended to limit the terms, but merely provide illustrative examples for the terms. The meaning of “a,” “an,” and “the” includes plural reference, the meaning of “in” includes “in” and “on.” The term “connected” means a direct electrical connection between the items connected, without any intermediate devices. The term “coupled” means either a direct electrical connection between the items connected or an indirect connection through one or more passive or active intermediary devices. The term “circuit” means either a single component or a multiplicity of components, either active and/or passive, that are coupled together to provide a desired function. The term “signal” means at least one current, voltage, charge, temperature, data, or other measurable quantity. The terms “RFID reader” and “RFID tag” are used interchangeably with the terms “reader” and “tag”, respectively, throughout the text and claims.

All of the circuits described in this document may be implemented as circuits in the traditional sense, such as with integrated circuits etc. All or some of them can also be implemented equivalently by other ways known in the art, such as by using one or more processors, Digital Signal Processing (DSP), a Floating Point Gate Array (FPGA), a general purpose micro processor, etc.

FIG. 1is a diagram of components of a typical RFID system100, incorporating aspects of the invention. An RFID reader110transmits an interrogating Radio Frequency (RF) wave112. RFID tag120in the vicinity of RFID reader110may sense interrogating RF wave112, and generate wave126in response. RFID reader110senses and interprets wave126.

Reader110and tag120exchange data via wave112and wave126. In a session of such an exchange, each encodes, modulates, and transmits data to the other, and each receives, demodulates, and decodes data from the other. The data is modulated onto, and decoded from, RF waveforms.

Encoding the data in waveforms can be performed in a number of different ways. For example, protocols are devised to communicate in terms of symbols, also called RFID symbols. A symbol for communicating can be a delimiter, a calibration symbol, and so on. Further symbols can be implemented for ultimately exchanging binary data, such as “0” and “1”, if that is desired. In turn, when the waveforms are processed internally by reader110and tag120, they can be equivalently considered and treated as numbers having corresponding values, and so on.

Tag120can be a passive tag or an active tag, i.e. having its own power source. Where tag120is a passive tag, it is powered from wave112.

FIG. 2is a diagram of an RFID tag220, which can be the same as tag120ofFIG. 1. Tag220is implemented as a passive tag, meaning it does not have its own power source. Much of what is described in this document, however, applies also to active tags.

Tag220is formed on a substantially planar inlay222, which can be made in many ways known in the art. Tag220includes an electrical circuit, which is preferably implemented in an integrated circuit (IC)224. IC224is arranged on inlay222.

Tag220also includes an antenna for exchanging wireless signals with its environment. The antenna is usually flat and attached to inlay222. IC224is electrically coupled to the antenna via suitable antenna ports (not shown inFIG. 2).

The antenna may be made in a number of ways, as is well known in the art. In the example ofFIG. 2, the antenna is made from two distinct antenna segments227, which are shown here forming a dipole. Many other embodiments are possible, using any number of antenna segments.

In some embodiments, an antenna can be made with even a single segment. Different places of the segment can be coupled to one or more of the antenna ports of IC224. For example, the antenna can form a single loop, with its ends coupled to the ports. When the single segment has more complex shapes, it should be remembered that, at the frequencies of RFID wireless communication, even a single segment could behave like multiple segments.

In operation, a signal is received by the antenna, and communicated to IC224. IC224both harvests power, and responds if appropriate, based on the incoming signal and its internal state. In order to respond by replying, IC224modulates the reflectance of the antenna, which generates the backscatter from a wave transmitted by the reader. Coupling together and uncoupling the antenna ports of IC224can modulate the reflectance, as can a variety of other means.

In the embodiment ofFIG. 2, antenna segments227are separate from IC224. In other embodiments, antenna segments may alternately be formed on IC224, and so on.

The components of the RFID system ofFIG. 1may communicate with each other in any number of modes. One such mode is called full duplex. Another such mode is called half-duplex, and is described below.

FIG. 3is a conceptual diagram300for explaining the half-duplex mode of communication between the components of the RFID system ofFIG. 1, especially when tag120is implemented as passive tag220ofFIG. 2. The explanation is made with reference to a TIME axis, and also to a human metaphor of “talking” and “listening”. The actual technical implementations for “talking” and “listening” are now described.

RFID reader110and RFID tag120talk and listen to each other by taking turns. As seen on axis TIME, when reader110talks to tag120the communication session is designated as “R→T”, and when tag120talks to reader110the communication session is designated as “T→R”. Along the TIME axis, a sample R→T communication session occurs during a time interval312, and a following sample T→R communication session occurs during a time interval326. Of course interval312is typically of a different duration than interval326—here the durations are shown approximately equal only for purposes of illustration.

In terms of actual technical behavior, during interval312, reader110talks to tag120as follows. According to block352, reader110transmits wave112, which was first described inFIG. 1. At the same time, according to block362, tag120receives wave112and processes it, to extract data and so on. Meanwhile, according to block372, tag120does not backscatter with its antenna, and according to block382, reader110has no wave to receive from tag120.

During interval326, tag120talks to reader110as follows. According to block356, reader110transmits a Continuous Wave (CW), which can be thought of as a carrier signal that ideally encodes no information. As discussed before, this carrier signal serves both to be harvested by tag120for its own internal power needs, and also as a wave that tag120can backscatter. Indeed, during interval326, according to block366, tag120does not receive a signal for processing. Instead, according to block376, tag120modulates the CW emitted according to block356, so as to generate backscatter wave126. Concurrently, according to block386, reader110receives backscatter wave126and processes it.

In the above, an RFID reader/interrogator may communicate with one or more RFID tags in any number of ways. Some such ways are called protocols. A protocol is a specification that calls for specific manners of signaling between the reader and the tags.

One such protocol is called the Specification for RFID Air Interface—EPC™ Radio-Frequency Identity Protocols Class-1 Generation-2 UHF RFID Protocol for Communications at 860 MHz-960 MHz, which is also colloquially known as “the Gen2 Spec”. The Gen2 Spec has been ratified by EPCglobal, which is an organization that maintains a website at: <http://www.epcglobalinc.org/> at the time this document is initially filed with the USPTO.

It was described above how reader110and tag120communicate in terms of time. In addition, communications between reader110and tag120may be restricted according to frequency. One such restriction is that the available frequency spectrum may be partitioned into divisions that are called channels. Different partitioning manners may be specified by different regulatory jurisdictions and authorities (e.g. FCC in North America, CEPT in Europe, etc.).

The reader110typically transmits with a transmission spectrum that lies within one channel. In some regulatory jurisdictions the authorities permit aggregating multiple channels into one or more larger channels, but for all practical purposes an aggregate channel can again be considered a single, albeit larger, individual channel. Tag120can respond with a backscatter that is modulated directly onto the frequency of the reader's emitted CW, also called baseband backscatter. Alternatively, Tag120can respond with a backscatter that is modulated onto a frequency, developed by Tag120, that is different from the reader's emitted CW, and this modulated tag frequency is then impressed upon the reader's emitted CW. This second type of backscatter is called subcarrier backscatter. The subcarrier frequency can be within the reader's channel, can straddle the boundaries with the adjacent channel, or can be wholly outside the reader's channel.

A number of jurisdictions require a reader to hop to a new channel on a regular basis. When a reader hops to a new channel it may encounter RF energy there that could interfere with communications.

Embodiments of the present disclosure can be useful in different RFID environments, for example, in the deployment of RFID readers in sparse- or dense-reader environments, in environments with networked and disconnected readers such as where a hand-held reader may enter the field of networked readers, in environments with mobile readers, or in environments with other interference sources. It will be understood that the present embodiments are not limited to operation in the above environments, but may provide improved operation in such environments.

FIG. 4is a block diagram showing a detail of an RFID reader system410, which can be the same as reader110shown inFIG. 1. A unit420is also known as a box420, and has at least one antenna driver430. In typical embodiments it has four drivers430. For each driver430there is an output, which is typically a coaxial cable plug. Accordingly cables435can be attached to the outputs of the provided respective drivers430, and then the cables435can be attached to respective antennas440.

A driver430can send a driving signal, to cause its respective antennas440to transmit an RF wave412, which is analogous to RF wave112ofFIG. 1. In addition, RF wave426can be backscattered from the RFID tags, analogous to RF wave126ofFIG. 1. Backscattered RF wave426becomes a signal sensed by driver430.

Unit420also has other components450, such as hardware and software, which may be described in more detail later in this document. Components450control drivers430, and as such cause RF wave412to be sent, and interpret the sensed backscattered RF wave426. Optionally and preferably there is a communication link425to other equipment, such as computers and the like, for remote operation of system410.

FIG. 5is a block diagram of a whole RFID reader system500according to embodiments. System500includes a local block510, and optionally remote components570. Local block510and remote components570can be implemented in any number of ways. It will be recognized that reader110ofFIG. 1is the same as local block510, if remote components570are not provided. Alternately, reader110can be implemented instead by system500, of which only the local block510is shown inFIG. 1. Plus, local block510may be unit420ofFIG. 4.

Local block510is responsible for communicating with the tags. Local block510includes a block551of an antenna and a driver of the antenna for communicating with the tags. Some readers, like that shown in local block510, contain a single antenna and driver. Some readers contain multiple antennas and drivers and a method to switch signals among them, including sometimes using different antennas for transmitting and for receiving. And some readers contain multiple antennas and drivers that can operate simultaneously. A demodulator/decoder block553demodulates and decodes backscattered waves received from the tags via antenna block551. Modulator/encoder block554encodes and modulates an RF wave that is to be transmitted to the tags via antenna block551.

Local block510additionally includes an optional local processor556. Processor556may be implemented in any number of ways known in the art. Such ways include, by way of examples and not of limitation, digital and/or analog processors such as microprocessors and digital-signal processors (DSPs); controllers such as microcontrollers; software running in a machine such as a general purpose computer; programmable circuits such as Field Programmable Gate Arrays (FPGAs), Field-Programmable Analog Arrays (FPAAs), Programmable Logic Devices (PLDs), Application Specific Integrated Circuits (ASIC), any combination of one or more of these; and so on. In some cases some or all of the decoding function in block553, the encoding function in block554, or both, may be performed instead by processor556.

Local block510additionally includes an optional local memory557. Memory557may be implemented in any number of ways known in the art. Such ways include, by way of examples and not of limitation, nonvolatile memories (NVM), read-only memories (ROM), random access memories (RAM), any combination of one or more of these, and so on. Memory557, if provided, can include programs for processor556to run, if provided.

In some embodiments, memory557stores data read from tags, or data to be written to tags, such as Electronic Product Codes (EPCs), Tag Identifiers (TIDs) and other data. Memory557can also include reference data that is to be compared to the EPC codes, instructions and/or rules for how to encode commands for the tags, modes for controlling antenna551, and so on. In some of these embodiments, local memory557is provided as a database.

Some components of local block510typically treat the data as analog, such as the antenna/driver block551. Other components such as memory557typically treat the data as digital. At some point there is a conversion between analog and digital. Based on where this conversion occurs, a whole reader may be characterized as “analog” or “digital”, but most readers contain a mix of analog and digital functionality.

If remote components570are indeed provided, they are coupled to local block510via an electronic communications network580. Network580can be a Local Area Network (LAN), a Metropolitan Area Network (MAN), a Wide Area Network (WAN), a network of networks such as the internet, and so on. In turn, local block510then includes a local network connection559for communicating with network580.

There can be one or more remote component(s)570. If more than one, they can be located at the same place with each other, or in different places. They can access each other and local block510via network580, or via other similar networks, and so on. Accordingly, remote component(s)570can use respective remote network connections. Only one such remote network connection579is shown, which is similar to local network connection559, etc.

Remote component(s)570can also include a remote processor576. Processor576can be made in any way known in the art, such as was described with reference to local processor556.

Remote component(s)570can also include a remote memory577. Memory577can be made in any way known in the art, such as was described with reference to local memory557. Memory577may include a local database, and a different database of a Standards Organization, such as one that can reference EPCs.

Of the above-described elements, it is advantageous to consider a combination of these components, designated as operational processing block590. Block590includes those that are provided of the following: local processor556, remote processor576, local network connection559, remote network connection579, and by extension an applicable portion of network580that links connection559with connection579. The portion can be dynamically changeable, etc. In addition, block590can receive and decode RF waves received via antenna551, and cause antenna551to transmit RF waves according to what it has processed.

Block590includes either local processor556, or remote processor576, or both. If both are provided, remote processor576can be made such that it operates in a way complementary with that of local processor556. In fact, the two can cooperate. It will be appreciated that block590, as defined this way, is in communication with both local memory557and remote memory577, if both are present.

Accordingly, block590is location agnostic, in that its functions can be implemented either by local processor556, or by remote processor576, or by a combination of both. Some of these functions are preferably implemented by local processor556, and some by remote processor576. Block590accesses local memory557, or remote memory577, or both for storing and/or retrieving data.

Reader system500operates by block590generating communications for RFID tags. These communications are ultimately transmitted by antenna block551, with modulator/encoder block554encoding and modulating the information on an RF wave. Then data is received from the tags via antenna block551, demodulated and decoded by demodulator/decoder block553, and processed by processing block590.

FIG. 6is a block diagram illustrating an overall architecture of a RFID reader system600according to embodiments. It will be appreciated that system600is considered subdivided into modules or components. Each of these modules may be implemented by itself, or in combination with others. It will be recognized that some aspects are parallel with those ofFIG. 5. In addition, some of them may be present more than once.

RFID reader system600includes one or more antennas610, and an RF Front End620, for interfacing with antenna(s)610. These can be made as described above. In addition, Front End620typically includes analog components.

System600also includes a Signal Processing module630. In this embodiment, module630exchanges waveforms with Front End620, such as I and Q waveform pairs. In some embodiments, signal processing module630is implemented by itself in an FPGA.

System600also includes a Physical Driver module640, which is also known as Data Link. In this embodiment, module640exchanges bits with module630. Data Link640can be the stage associated with framing of data. In one embodiment, module640is implemented by a Digital Signal Processor.

System600additionally includes a Media Access Control module650, which is also known as MAC layer. In this embodiment, module650exchanges packets of bits with module640. MAC layer650can be the stage for making decisions for sharing the medium of wireless communication, which in this case is the air interface. Sharing can be between reader system600and tags, or between system600with another reader, or between tags, or a combination. In one embodiment, module650is implemented by a Digital Signal Processor.

System600moreover includes an Application Programming Interface module660, which is also known as API, Modem API, and MAPI. In some embodiments, module660is itself an interface for a user.

System600further includes a host processor670. Processor670exchanges signals with MAC layer650via module660. In some embodiments, host processor670is not considered as a separate module, but one that includes some of the above-mentioned modules of system600. A user interface680is coupled to processor670, and it can be manual, automatic, or both.

Host processor670can include applications for system600. In some embodiments, elements of module660may be distributed between processor670and MAC layer650.

It will be observed that the modules of system600form something of a chain. Adjacent modules in the chain can be coupled by the appropriate instrumentalities for exchanging signals. These instrumentalities include conductors, buses, interfaces, and so on. These instrumentalities can be local, e.g. to connect modules that are physically close to each other, or over a network, for remote communication.

The chain is used in opposite directions for receiving and transmitting. In a receiving mode, wireless waves are received by antenna(s)610as signals, which are in turn processed successively by the various modules in the chain. Processing can terminate in any one of the modules. In a transmitting mode, initiation can be in any one of these modules. That, which is to be transmitted becomes ultimately signals for antenna(s)610to transmit as wireless waves.

The architecture of system600is presented for purposes of explanation, and not of limitation. Its particular subdivision into modules need not be followed for creating embodiments according to the invention. Furthermore, the features of the invention can be performed either within a single one of the modules, or by a combination of them.

As mentioned previously, a single RFID reader system may have several antennas. Due to the Tx/Rx chain, the RFID reader system selects, drives, and listens from only one of its antennas at any given time. Furthermore, a combination of RFID systems is typically deployed and they need to coordinate antennas between themselves to limit interference.

To complicate the design of multiple antenna reader systems, antennas may be facing different directions. Time spent on an antenna that views no tags (while the other antenna has tags in view) represents missed performance (missed opportunity to identify tags). Even though the antennas could all be facing at the same location, different ones view different groups of tags, and may have differential effectiveness. For example, a dock door with two antennas at different heights on same side of the door connected to the same reader. In such a scenario, tag placement in the pallet would define which antenna is more likely to find which tags. Some tags may only be read by one of the antennas.

Moreover, synchronizing antennas between readers requires precision to limit system downtime. Synchronizing clocks accurately on separate processors is a complex problem. In addition, readers that view no tags and still transmit using their antennas increase the noise floor in a system deployment unnecessarily. This may cause degradation in the performance of other readers in the deployment which do view tags. Finally, antenna switching may need to be controlled at the speed of the air protocol. With the increased speed of new generation air protocols, increased demands are put on antenna switching.

Some of the solutions to challenges of static antenna switching mechanisms include user specifying time spent per antenna, user specifying order in which to cycle through antennas, or user specifying external triggers to start antenna operation. These approaches have their own limitations such as users or installers having to configure the reader(s) at time of deployment for a specific scenario, which may be costly and require tuning if scenario changes (e.g. conveyor belt speed changes, use of humans or forklifts for pushing pallets through the field of view of readers, etc.).

Additionally, tags may not be rapidly detected in a particular antenna read zone causing delay in seeing tags for the first time. Antennas may be grouped into “sources” (e.g. in a symmetrical deployment like a dock door, each of the 2 sources may be given same amount of time to see tags). This effectively gives a 50% duty cycle per door even if no tags are in that door. External triggers are also challenging to deploy and may break easily.

FIG. 7Ais a diagram illustrating an operation of an RFID reader system with multiple antennas and a conventional antenna switching algorithm which, however, can delay sensing tag presence.

Diagram700A illustrates one of the problems with conventional antenna switching methods, where commonly a predetermined time is allocated to each antenna associated with the RFID reader system.

It should be noted, while the term antenna is used throughout this document, the principles described herein are applicable to reader systems where multiple antennas are used in connection with RF ports. For example, a reader may employ four RF ports with two antennas attached to each RF port. In that scenario (and similar ones) the same principles described for the embodiments below apply to the RF ports as they would to the antennas.

Referring back to diagram700A, a conventional RFID reader system allocates equal periods of time to four antennas (712for antenna1,714for antenna2,716for antenna3,718for antenna4, and so on). Thus, period712is dedicated to inventorying of tags in the field of view of antenna1. The reader switches to antenna2from antenna1regardless of whether any tags are found or whether the inventorying of found tags is completed.

As discussed previously, tags are not always stationary. In applications such as dock doors, tags may be moving in and out of the field of view of one of the antennas constantly. Hence, a problem of latency is encountered. As shown by reference numeral704, in a worst case latency scenario, a tag may arrive in the field of view of antenna1(702) shortly after the reader switches from antenna1to antenna2. The arriving tag may be inventoried (706) only after the reader completes checking all other antennas and switches back to antenna1(712). Thus, the inventorying of the tag is delayed by almost the period it takes the reader to check three antennas.

FIG. 7Bis a diagram illustrating an operation of an RFID reader system with multiple antennas and a conventional antenna switching algorithm which, however, might allocate time poorly among two of them.

Diagram700B illustrates another aspect of the problem(s) with conventional antenna switching mechanisms at antenna level. Upon turning on the RF signal, a first fixed period712is dedicated to inventorying tags within the field of view of antenna1. However, a few tags may be found at the beginning of the fixed period712as shown by reference numeral702and the inventory process completed before period712ends. If no additional tags are found (704), the remainder of period712is wasted time on antenna1as illustrated by reference numeral722.

Furthermore, a number of tags may be found in the field of view of antenna2during period714. If the number of tags is such that their inventory cannot be completed within period714, the inventory process is cut off at the end of714and the reader switches to another antenna forcing the inventory process to begin either from the start. Some readers may implement complicated algorithms to remember the tags during the first attempt to inventory through antenna2, but that approach is not only expensive in terms of processing resources, but may not be reliable when tags are constantly moving in and out of the field of view.

The invention also includes methods. Some are methods of operation of an RFID reader or RFID reader system. Others are methods for controlling an RFID reader or RFID reader system.

The invention additionally includes programs, and methods of operation of the programs. A program is generally defined as a group of steps or operations leading to a desired result, due to the nature of the elements in the steps and their sequence. A program is usually advantageously implemented as a sequence of steps or operations for a processor, such as the structures described above.

Performing the steps, instructions, or operations of a program requires manipulation of physical quantities. Usually, though not necessarily, these quantities may be transferred, combined, compared, and otherwise manipulated or processed according to the steps or instructions, and they may also be stored in a computer-readable medium. These quantities include, for example, electrical, magnetic, and electromagnetic charges or particles, states of matter, and in the more general case can include the states of any physical devices or elements. It is convenient at times, principally for reasons of common usage, to refer to information represented by the states of these quantities as bits, data bits, samples, values, symbols, characters, terms, numbers, or the like. It should be borne in mind, however, that all of these and similar terms are associated with the appropriate physical quantities, and that these terms are merely convenient labels applied to these physical quantities, individually or in groups.

The invention furthermore includes storage media. Such media, individually or in combination with others, have stored thereon instructions of a program made according to the invention. A storage medium according to the invention is a computer-readable medium, such as a memory, and is read by a processor of the type mentioned above. If a memory, it can be implemented in a number of ways, such as Read Only Memory (ROM), Random Access Memory (RAM), etc., some of which are volatile and some non-volatile.

Even though it is said that the program may be stored in a computer-readable medium, it should be clear to a person skilled in the art that it need not be a single memory, or even a single machine. Various portions, modules or features of it may reside in separate memories, or even separate machines. The separate machines may be connected directly, or through a network such as a local access network (LAN) or a global network such as the Internet.

Often, for the sake of convenience only, it is desirable to implement and describe a program as software. The software can be unitary, or thought in terms of various interconnected distinct software modules.

This detailed description is presented largely in terms of flowcharts, algorithms, and symbolic representations of operations on data bits on and/or within at least one medium that allows computational operations, such as a computer with memory. Indeed, such descriptions and representations are the type of convenient labels used by those skilled in programming and/or the data processing arts to effectively convey the substance of their work to others skilled in the art. A person skilled in the art of programming may use these descriptions to readily generate specific instructions for implementing a program according to the present invention.

Embodiments of an RFID reader system can be implemented as a combination of hardware and software. It is advantageous to consider such a system as subdivided into components or modules. A person skilled in the art will recognize that some of these components or modules can be implemented as hardware, some as software, some as firmware, and some as a combination.

Methods are now described more particularly according to embodiments.

FIG. 8is a flowchart of an antenna port switching process by estimating how many tags are in an RFID reader system antenna's field of view according to embodiments.

Process800begins at operation810, where an estimate of how many tags there are in an antenna's field of view is performed by the reader. This may be performed by tag population check which includes transmitting a signal and listening to determine if any tags are responding to the signal or not.

The number of present tags may also be estimated by determining a power of the tag response signals and comparing that to an expected power of a single tag response.

According to a next decision operation820, a determination is made whether fewer than a predefined number of expected tag replies are detected. If more than the expected number of tags are detected, processing advances to operation830, where tags in the field of view of the antenna are inventoried.

According to a next operation850following fewer than the expected number of tags having been detected at decision operation820or operation830, another antenna is selected for further operations.

After completing operation850, the process may return to operation810for performing another tag population estimate through the selected other antenna. As discussed below, a reader system may include a plurality of antennas and the antenna selection may be based on an order of antennas, a pseudo-random algorithm, user specification, and the like.

FIG. 9Ais a flowchart of a further antenna port switching process by detecting tag presence in an RFID reader system employing a non-persistent session according to embodiments.

Some of the operations of process900A are similar to likewise numbered operations of process800. Process900A begins with two operations grouped together as905representing the tag population check employing a non-persistent session.

According to operation910, a number of tags within the antenna's field of view is estimated.

According to a next decision operation920, a determination is made whether fewer than an expected number of tags are detected.

If more than the expected number of tag responses are detected, those tags are inventoried at operation930.

According to a next operation950following fewer than expected number of tag detection at decision operation920or operation930, another antenna is selected for further operations. After completing operation950, the process may return to operation910for performing another tag population estimate through the selected other antenna.

FIG. 9Bis a flowchart of another antenna port switching process by detecting tag presence in an RFID reader system employing a persistent session according to embodiments.

Some of the operations of process900B are similar to likewise numbered operations of processes800and900A. Process900B begins with four operations grouped together as906representing the tag population check employing a persistent session. The persistent session is the same session as the inventory process.

According to a first operation912, a query command with a Q-parameter of “0” value is transmitted for detecting tags. In a persistent session, tag responses may be directed to target session flag state A or B. Therefore, the first query command is directed at target session flag state A.

According to a next decision operation914, a determination is made whether fewer than an expected number of tag replies are detected for target session flag state A. If more tag replies than the expected number are detected, the tags may be inventoried at next operation930. Otherwise, processing advances to operation916.

According to a next operation916, another query command with a Q-parameter of “0” value is transmitted for target session flag state B.

According to a next decision operation918, a determination is made whether less than the expected number of tag replies were detected for target session flag state B. If more tag replies than the expected number were detected, the tags may be inventoried at next operation930. Otherwise, processing advances to operation950.

According to a next operation950following detection of fewer than expected tags at decision operation918or operation930, another antenna is selected for further operations. After completing operation950, the process may return to operation910for performing another tag population estimate through the selected other antenna.

The operations included in processes800,900A, and900B are for illustration purposes. Antenna switching upon detecting fewer than an expected number of tags may be implemented by similar processes with fewer or additional steps, as well as in different order of operations using the principles described herein.

According to some embodiments, a method for an RFID reader system coupled to at least a first antenna and a second antenna includes causing the first antenna to radiate a first signal for estimating whether any tags are present in the first antenna's field of view, and causing the second antenna to radiate a second signal for estimating whether any tags are present in the second antenna's field of view if fewer than a preset number of tags are estimated in the first antenna's field of view. Otherwise the method includes inventorying tags estimated in the first antenna's field of view.

The preset number may be learned by the reader based on tag responses. If fewer than the preset number of tags are estimated in the second antenna's field of view, the reader system may cause a third antenna coupled to the RFID reader system to radiate a third signal for estimating whether any tags are present in the third antenna's field of view. Otherwise, the reader system may inventory tags estimated in the second antenna's field of view.

The second signal may be radiated regardless of whether any tags are estimated as present in the first antenna's field of view or responsive to estimating that no tags are present in the first antenna's field of view. The first tags may also be estimated as present in the first antenna's field of view, and the second signal radiated without addressing individually the first tags.

The second antenna may be selected before completing causing the first antenna to radiate such that no signal is radiated from the first antenna beyond the first signal. Also, selecting the second antenna may be delayed until an operation for a specific tag is completed.

According to another embodiment, the tag operation may be completed when a predefined criterion is satisfied. The predefined criterion may include one or more of a decision based on completion of an inventory operation, a decision based on an expiration of a time out period, or a decision based on a predefined Q parameter value. The Q parameter value may be learned by the RFID reader system based on tag responses or dictated by the first signal and have a value of at least 2.

According to further embodiments, the first signal may be for performing a partial query operation to detect the presence of the tags such that if one of a valid preamble and a collision is detected, a tag is estimated, else no tag is estimated. The second signal may be radiated regardless of whether any tags are estimated as present in the first antenna's field of view. The second signal may also be radiated responsive to estimating that no tags are present in the first antenna's field of view.

According to yet other embodiments, first tags, fewer than the preset number, may be estimated as present in the first antenna's field of view, and the second signal may be radiated without addressing individually the first tags.

The second antenna may be selected among a plurality of antennas associated with the RFID reader system based on a first predefined algorithm, an order of available antennas, or by random selection, in which the selection is different depending on whether any tags are sensed through the first antenna. If no tags are estimated, a third antenna may be selected according to the first algorithm or a second algorithm.

FIG. 10is a diagram illustrating an operation of an RFID reader system with multiple antennas and an antenna switching algorithm according to embodiments.

When tag population check is performed for each antenna instead of statically assigned time for inventorying tags regardless of whether any tags are estimated, time spent on each antenna is significantly reduced in the absence of tags in each antenna's field of view.

In diagram1000, the reduction in time spent on each antenna is illustrated by the TPC periods1002through1008. In periods1002through1008, the TPC may determine to tags have replied or fewer than an expected number have replied. Thus the reader system switches to another antenna.

Following the worst case latency scenario discussed inFIG. 7A, a tag may arrive in antenna1's field of view (1022) shortly after the reader has switched to antenna2. The arriving tag is detected when the reader completes checks through the other antennas per its antenna selection algorithm and returns to antenna1as shown by reference numeral1024. The tag is then inventoried through antenna1(1026), when the reader switches from tag population check mode to inventory mode (1012) on antenna1. The worst case latency as illustrated by reference numeral1014is significantly reduced compared to the scenario shown inFIG. 7A.

FIG. 11is a diagram illustrating an operation of an RFID reader system with multiple antennas and an antenna switching algorithm for two of its antennas that switches antennas based on detection of too few tags according to embodiments.

According to the example scenario shown in diagram1100, during a TPC process through a first antenna too few tags are found (1102). So, the reader switches to another antenna (1106) reducing time wasted on the first antenna significantly (1122). Following a TPC or query process, sufficient tags are found (1104) in the field of view of the second antenna.

The tags found in the field of view of the second antenna may then be inventoried. According to some embodiments, the time allocated to the second antenna may be adjusted (1124) to allow completion of the inventorying of all tags found in the field of view of the second antenna.

In this description, numerous details have been set forth in order to provide a thorough understanding. In other instances, well-known features have not been described in detail in order to not obscure unnecessarily the description.

A person skilled in the art will be able to practice the embodiments in view of this description, which is to be taken as a whole. The specific embodiments as disclosed and illustrated herein are not to be considered in a limiting sense. Indeed, it should be readily apparent to those skilled in the art that what is described herein may be modified in numerous ways. Such ways can include equivalents to what is described herein.

The following claims define certain combinations and sub-combinations of elements, features, steps, and/or functions, which are regarded as novel and non-obvious. Additional claims for other combinations and sub-combinations may be presented in this or a related document.