Abstract:
An apparatus for use in an RFID data collection system includes an antenna portion for wirelessly exchanging signals and a memory portion for storing RFID data. A signal processing portion is coupled among the antenna portion and the memory portion. The signal processing portion is configured to receive RFID data and to at least encode or decode the received RFID data via at least one spreading code, such as a mutually orthogonal code. Other configurations are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Continuation of Application No. 12/446,439 filed Apr. 21, 2010, which in turn is a U.S. National Phase application of International Application Serial No. PCT/US2007/065875, filed on Apr. 3, 2007, which claims the benefit of U.S. Provisional Application No. 60/841,775 filed Sep. 1, 2006. The disclosure of the prior applications is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    RFID (radio frequency identification) technology has gained momentum in the last decade as a solution for tracking resources in supply chain logistics. The ever increasing demands for data have drawn the attention to the search of new approaches for communication between RFID tags and. readers to decrease the communication time between every particular tag and reader. For example, Hewlett Packard Corp. has unveiled a new wireless chip capable to communicate with the speed up to 10 Megabits per second. See,  HP Unveils Revolutionary Wireless Chip that Links the Digital and Physical Worlds—Grain - sized chip could be attached to almost any object, making information more ubiquitous , HP Press Release from Jul 17, 2006. However, the communication distance for this device is limited to a few inches due to the employment of inductive coupling for harvesting energy and communication. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0003]      FIG. 1  is a block diagram showing an example of a RFID tag and associated reader employing aspects of the invention. 
           [0004]      FIG. 2  is a flow diagram illustrating an example of a routine performed by the reader for reading the RFID tag of  FIG. 1 . 
           [0005]      FIG. 3  is showing a general view of MIMO communication between RFID tag and reader. 
           [0006]      FIG. 4  is showing a general view of Code Division Multiple Access (“CDMA”) paradigm. 
           [0007]      FIG. 5  is showing a general view of the CDMA communication model. 
           [0008]      FIG. 6  is showing a general view of RFID tag implementing a parallel transmission of independent CDMA sequences from two tag antennas. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Benefits in RFID technology can be realized by employing multiplexing, spread-spectrum and other communication techniques described herein to increase the communication range and robustness with RFID tags, while decreasing communication time so that more tags can be read within a given period of time. By using, for example, multiplexing communication techniques at the tag, and employing more sophisticated processing at the RFID reader, these and other benefits may be realized with R″FID data collection. Briefly, and in general terms, aspects of the present invention provide a new approach for communications between RFID tags and readers based on the application of CDMA paradigms for communications between tags and readers, including using multiple antennas. As a result, a reader can read multiple tags simultaneously, with each tag having a different, mutually orthogonal code. (While the terms “CDMA communications”, “CDMA techniques”, and the like are used below, they generally relate to the use of spread spectrum communications, but not necessarily using orthogonal codes.) 
         [0010]    Various embodiments or examples of the invention will now be described. The following description provides specific details for a thorough understanding and enabling description of these embodiments. One skilled in the art will understand, however, that the invention may be practiced without many of these details. Additionally, some well-known structures or functions may not be shown or described in detail, so as to avoid unnecessarily obscuring the relevant description of the various embodiments. 
         [0011]    The terminology used in the description presented below is intended to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific embodiments of the invention. Certain terms may even be emphasized below; however, any terminology intended to be interpreted in any restricted manner will be overtly and specifically defined as such in this Detailed Description section. 
         [0012]    Referring to  FIG. 1 , an example of an RFID tag  100  and reader  102  is shown. The tag  100  includes two tag antennas  104  which receive signals from and transmit signals to the reader  102 . The antennas may be formed on a substrate for the tag, and be of any known form. For example, each antenna may be tuned to a different frequency. Tag analog circuitry  108 , coupled to the tag antennas, provides for data transfer with the reader by modulating a signal for transmission and receiving signals from the reader. Digital circuitry  110 , coupled to the tag analog circuitry, can be of many types, including dedicated logic devices, gate arrays, a microprocessor, or other digital signal processing circuitry, together with any necessary software/firmware. The digital circuitry communicates with memory  112 , which can be of any form, such as read-only memory (ROM), random access memory (RAM), non-volatile memory such as EEPROM, Flash, etc. The memory may store one or more spreading codes or chip sequences to spread transmitted data signals, or even store orthogonal codes to uniquely identify one or more channel codes associated with the tag. The analog circuitry  108 , digital circuitry  110  and memory  112  may be formed on a single semiconductor chip or device. 
         [0013]    A power supply  114  defines a type of tag. For example, the power supply can be a battery, making the tag  100  an active tag. Alternatively, the power supply can be energy storage circuitry to permit the tag to passively harvest and store electromagnetic energy received from the reader  102 . The tag  100  can also be a hybrid tag that employs both passive and active features. 
         [0014]    The reader  102  includes an antenna  116  coupled to a radio  118 . A memory  122  of the reader  102  stores data received from the tag, as well as instructions for operating the reader. A processor or digital circuitry  120  communicates with the radio to provide appropriate signals to the tag  100 , and receive data therefrom. For example, as described herein, the processor/digital circuitry  120  may include a despreader and detector or decoder (or associated software or firmware to perform detector/decoding functions) so as to process received CDMA signals from the tag  100 . The reader may employ any known receiver and decoder, such as a maximum likelihood detector, Viterbi decoder, feedback decoder, block/convolutional decoder, de-interleaver, and other known detectors/decoders, as well as any receiver, such as a rake receiver that employs multiple correlators. If, for example, the system employs direct sequence spread spectrum (DSSS) techniques, then the reader may process (e.g. XOR) the received spread spectrum signal with one or more locally stored/generated chipping sequence(s) (e.g. orthogonal code(s)), and then employ an integrator/correlator with decision unit to retrieve the transmitted tag data. 
         [0015]    Since RFID readers may employ synchronization under existing RFID technology, synchronization with tags employing CDMA communications can be readily implemented. Overall, the reader may be considerably more sophisticated in terms of processing capabilities (signal reception and decoding) as compared to the tags, which may be designed with much simpler data processing capabilities. 
         [0016]    The reader  102  may employ input/output circuitry  124 , which can be any of a variety of devices or circuitry. For example, the reader may include a trigger or button when employed as a hand-held reader (often with a portable power source), as well as include a display, speakers and/or output port for wired connection with an external computer or network. Alternatively, the reader could include any of a variety of sensors to cause the reader to automatically enter a reading or interrogation mode based on a signal from one or more sensors. 
         [0017]    The reader  102  can, of course, be of any possible configuration known in the RFID field. The reader may also employ CDMA encoding circuitry or instructions to encode and transmit data using CDMA encoding to tags or external receivers. While the system of  FIG. 1  is shown with a tag having two antennas and a reader having a single antenna, other alternatives are possible, so long as the tag or the reader employ code division multiplexing or spread spectrum transmissions, such as using encoding using orthogonal or spreading codes. In other words, the system uses spreading sequences (e.g., pseudo-random codes) for the tags/reader to provide spread-spectrum communications, where the modulated coded signal has a much higher bandwidth than the data being communicated. 
         [0018]    In operation, the tag  100  can operate normally using existing RFID standards, but can also operate under an alternative communication node employing CDMA coding, as described herein. Thus, the tag can provide an initial communication to the reader indicating that the tag is capable of CDMA communications, and thus the reader can begin using CDMA communication techniques with the tag (e.g., with appropriate decoding). Alternatively, the tag can have no standard operating protocol, and work only in a CDMA mode. 
         [0019]    Referring to  FIG. 2 , an example of a routine  200  stored in the memory  112  of the reader  102  is shown for handling RFID tags employing two or more forms of alternate coding or modulation. The routine  200  can be created as computer-executable instructions that may be interpreted not only by the reader or other specialized device, but also a general-purpose computer. The routine may be not only stored in the memory  122 , but also stored and distributed on computer-readable media, including magnetically or optically readable computer disks, hard-wired or preprogrammed chips (e.g., EEPROM semiconductor chips), nanotechnology memory, biological memory, or any other data storage media. Indeed, computer implemented instructions, and other aspects of the invention may be distributed over the Internet or over other networks (including wireless networks), or on a propagated signal on a propagation medium (e.g., an electromagnetic wave, sound wave, etc.) over a period of time, or they may be provided on any analog or digital network (packet switched, circuit switched, or other scheme). Thus, aspects of the routine may be not necessarily performed on a single device (e.g., the reader), but be distributed among two or more networked devices. 
         [0020]    Beginning in block  202 , the reader  102  polls or interrogates an area to identify any nearby RFID tags. If any tags are present (block  204 ), then the reader receives some initial information from the tag (e.g., a flag or header data), such as the tag  100  (block  206 ). The reader then determines from this initial information whether the tag is capable of any alternate transmission mode (block  208 ), and if not, employs standard decoding techniques known in the RFID field (block  210 ). 
         [0021]    However, if the tag employs an alternate transmission mode, then the reader may employ alternate decoding techniques, such as the CDMA communication techniques as well as associated functions, such as Viterbi decoding, maximum likelihood detecting functions, etc., as described herein (block  212 ). As noted above, the tags may be relatively unsophisticated relative to the reader, which may employ much more sophisticated and complex processing for signal acquisition and decoding. If any more tags are present (block  214 ), then the process loops back to block  202 , otherwise, the process ends. 
         [0022]    Importantly, by using COMA communication techniques, the reader may simultaneously, or substantially simultaneously, read multiple tags. An approach to further boost the communication rate between the RFID tag and the reader is to employ multiple-transmit and multiple-receive antennas, i.e., multiple-input multiple-output (MIMO) techniques.  FIG. 3  shows an example of such a MIMO alternative. As shown in this example, both the tag and the reader have three antennas each. Alternative embodiments may include more or less antennas for each component. 
         [0023]    The MIMO system with N T  transmitting antennas and N R  receiving antennas may be described as follow: 
         [0000]        r ( t )= Gs ( t )+ n ( t ),  (1)
 
         [0000]    where r(t) is a (N R ,l) vector of received signal; G is a (N T ,N R ) channel transfer matrix; n(t) is a (N R ,l) vector describing noise and interference; and s(t) is a (N T ,l) vector or transmitted signal. For an RFID tag with two antennas and a reader with two antennas, (1) will be in the form of 
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         [0024]    Since RFID tags (active or passive) are typically designed to be relatively simple and inexpensive devices, their processing capability should also be limited. Implementation of CDMA paradigm for communication between a RFID tag and a reader may provide substantial increase in the capacity of the exploited frequency band and good interference suppression (especially from narrowband interference). 
         [0025]    Since RFID tags are communicating with readers in close proximity, the communication channels are slow frequency-selective fading channels. In general terms, the Code Division Multiple Access (CDMA) or Code Division Multiplexing (CDM) paradigm may be presented as follows. Referring to  FIG. 4 , an information signal a i (t) with period T is combined with a spreading sequence s i (t) having a chip period T/N, where N is a spreading factor, 
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         [0026]    The CDMA communication model may be presented as follows, see  FIG. 5 , where E i  is an amplitude of an i th  information signal, and n(t) represents channel noise. 
         [0027]    The spreading sequence may be selected from any of the following:
       Pseudo-noise or m-sequences;   Gold codes;   Kasami sequences;   Walsh codes;   Other known spreading sequences/codes.       
 
         [0033]    Some desired properties of spreading sequences that may be achieved are as follows:
       Good correlation properties;   Narrow zero-delay peak;   Low nonzero-delay values;   Low cross-correlation with other codes;   A family of sequences that is sufficiently large.       
 
         [0039]    Aspects of the present invention contemplate a parallel transmission of independent CDMA sequences x i (t) from each tag&#39;s antenna or antennas. For example, in the case of two antennas on a single tag, the block diagram of the communication is shown on  FIG. 6 . While the same spreading code is shown as being applied to each of the two transmit channels, the tag could apply a different code to each channel. 
         [0040]    Since a single tag&#39;s antenna(s) are generally located in very close proximity, there is no need to implement a power control scheme for communication of a single tag with the reader. In the case of parallel communications of multiple tags with a reader, a power control scheme may be required. With multiple passive tags all located in close proximity to each other, a power control scheme may not be required (where a sophisticated reader is employed), since most passive tags have low transmission power. However, with spatially distributed tags, as well as with higher transmit power of active tags, a simple power control scheme may be employed, coordinated by the reader, to moderate transmit power of individual tags during reading sequences. 
         [0041]    A benefit of CDMA is the inherent security when using orthogonal or other codes. By employing a sufficiently large code set, data within each tag can be sufficiently secure against tapping or eavesdropping, assuming that the code is not known outside of the authorized user. Indeed, the reader can employ security techniques so that access to the codes is inhibited, such as through the use of smart cards, SIMs and other tamper-resistant memory devices having onboard processing capabilities. Of course, encryption or other security techniques may also be employed. 
         [0042]    While the system is generally described above as employing DSSS techniques, and alternative system may use frequency hopping spread spectrum (FHSS), where the tags/reader use appropriate hopping sequences. A drawback for FHSS is that it requires greater complexity at the tag. 
       CONCLUSION 
       [0043]    Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” As used herein, the terms “connected,” “coupled,” or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling of connection between the elements can be physical, logical, or a combination thereof. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or,” in reference to a list of two or more items, covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
         [0044]    The above detailed description of embodiments of the invention is not intended to be exhaustive or to limit the invention to the precise form disclosed above. While specific embodiments of, and examples for, the invention are described above for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. For example, while processes or blocks are presented in a given order, alternative embodiments may perform routines having steps, or employ systems having blocks, in a different order, and some processes or blocks may be deleted, moved, added, subdivided, combined, and/or modified to provide alternative or subcombinations. Each of these processes or blocks may be implemented in a variety of different ways. Also, while processes or blocks are at times shown as being performed in series, these processes or blocks may instead be performed in parallel, or may be performed at different times. Further any specific numbers noted herein are only examples: alternative implementations may employ differing values or ranges. 
         [0045]    The teachings of the invention provided herein can be applied to other systems, not necessarily the system described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments. 
         [0046]    Any patents and applications and other references noted above, including any that may be listed in accompanying filing papers, are incorporated herein by reference. Aspects of the invention can be modified, if necessary, to employ the systems, functions, and concepts of the various references described above to provide yet further embodiments of the invention. 
         [0047]    These and other changes can be made to the invention in light of the above Detailed Description. While the above description describes certain embodiments of the invention, and describes the best mode contemplated, no matter how detailed the above appears in text, the invention can be practiced in many ways. Details of the system may vary considerably in its implementation details, while still being encompassed by the invention disclosed herein. As noted above, particular terminology used when describing certain features or aspects of the invention should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the invention with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed in the specification, unless the above Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the invention encompasses not only the disclosed embodiments, but also all equivalent ways of practicing or implementing the invention under the claims. 
         [0048]    While certain aspects of the invention are presented below in certain claim forms, the inventors contemplate the various aspects of the invention in any number of claim forms. For example, while only one aspect of the invention is recited as a means-plus-function claim under 35 U.S.C §112, sixth paragraph, other aspects may likewise be embodied as a means-plus-function claim. (Any claims intended to be treated under 35 U.S.C. §112, sixth paragraph will begin with the words “means for”.) Accordingly, the inventors reserve the right to add additional claims after filing the application to pursue such additional claim forms for other aspects of the invention.