Abstract:
A single antenna may be powered to illuminate or transmit to a receiver such as an RFID tag. That tag may then provide a responsive signal to a plurality of antennas, each of which are active. The signals from those antennas may be analyzed to determine which signal has the highest quality. This may be used to select a particular signal for future analysis or to select a particular antenna for use as both a transmission and reception antenna for future operations. For example, the antenna which provides the strongest signal may be utilized to further illuminate a given RFID tag.

Description:
BACKGROUND  
       [0001]     This invention relates generally to wireless transceivers that transmit and receive radio frequency information.  
         [0002]     Generally, a wireless transceiver transmits information and receives information. It may use common components for some aspects of the receive and transmit operation.  
         [0003]     One radio frequency transceiver is called a radio frequency identification (RFID) reader/writer (to be referred to as simply an RFID reader). A radio frequency identification tag may be an integrated circuit with a tag insert or inlay including an integrated circuit attached to an antenna. An RFID reader communicates with the tag. The RFID reader may be a fixed antenna or a portable device such as a barcode scanner.  
         [0004]     RFID systems may be utilized to determine the current location of articles of interest. A conventional RFID application is a dock door device. It determines which components, which have RFID tags on them, pass through a loading dock door. Many other applications may also be envisioned including electronic toll collection, sensor applications, inventory control and tracking, asset tracking and recovery, tracking manufacturing parts, tracking goods in supply chains, and payment systems, to mention a few examples.  
         [0005]     RFID systems may be active systems which are battery powered or passive systems that are powered by the reader. Active systems may be used, for example, in toll booths, while passive systems may be for asset management, as one example.  
         [0006]     Generally, RFID systems use one of four frequencies including a low frequency of 125 or 134.2 kilohertz, a high frequency of 13.56 megaHertz, an ultrahigh frequency (UHF) of 868 to 960 megahertz, and a microwave at 2450 megahertz. Each tag may be tuned to work with the material it is mounted on. Thus, depending on what the tag is mounted on, the tag may require a slightly different antenna design.  
         [0007]     Conventional passive full duplex RFID systems utilize multiple antenna ports, but not at the same time. Each RFID reader ‘port’ may consist of either one antenna that both transmits and receives or two antenna elements, each of which only transmits or receives but are switched in tandem as a pair. For clarity, these examples will focus on the particular reader design whose ports consist of a single antenna element each which both transmits and receives. The four port RFID reader would then have four antenna elements and one active set of transmit and receive circuitry and a multiplexer which would, at any given time, leave several antennas unused.  
         [0008]     Thus, there is a need for better ways to provide wireless transceivers, including those used in RFID systems. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a schematic depiction of one embodiment of the present invention;  
         [0010]      FIG. 2  is a flow chart for software which may be provided on the diversity controller shown in  FIG. 1  in accordance with one embodiment of the present invention; and  
         [0011]      FIG. 3  is a system depiction for one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]     Referring to  FIG. 1 , a transceiver  10  may communicate with a device  26  which, in one embodiment, may be a radio frequency identification (RFID) tag  26 . The system  10  may include multiple antennas. In the embodiment depicted, four antennas  24   a ,  24   b ,  24   c , and  24   d  are used, but any number of antennas may be utilized.  
         [0013]     Following the transmit path, a reference clock  12  develops a clock signal which powers a local oscillator  14 . The output of the local oscillator  14  is power divided by a power divider  16  to reduce the power as supplied to a transmission modulator  18 . The transmission modulator  18  provides an output signal to illuminate or power a tag  26 , in one embodiment of the present invention, using a passive system.  
         [0014]     The output from the modulator  18  is passed to one of the magnetic circulators  22   a - 22   d . In one embodiment, a circulator  22  may be provided for each antenna  24 . Other embodiments may using directional couplers or high isolation power dividers. The switching of the output of the modulator  18  may be accomplished by a switch  20  which may include three 1×2 switches in one embodiment of the present invention. Thus, a movable contact  36  may select one of the fixed contacts  38 , as a simple example. Each of the contacts  38  may provide a signal to one of the circulators  22  and, ultimately, to one and only one of the antennas  24 . Thus, a single antenna  24  may be selected for transmission. The switching may also be performed with solid state switches (e.g. Pseudomorphic High Electron Mobility Transistor Field Effect Transistor (PHEMT FET) switches or PIN diode switches) for increased switching speed and decreased cost.  
         [0015]     Following the receive path, each of the antennas  24   a - 24   d  may receive a signal back from the tag  26  in one embodiment of the present invention. Thus, while one antenna  24  may be selected for transmission, all four antennas  24 , which may be positioned in different locations, at least potentially receive a responsive signal from the tag  26 . In the case of a passively illuminated tag  26 , the antennas  24  receive back scattered radio frequency energy from the tag resulting from the illumination by the transceiver  10 .  
         [0016]     A received signal is provided from each antenna  24  to its associated circulator  22   a - 22   d . The circulators  22  may have three ports and operate as directional couplers. Each circulator  22  isolates at least one of the input or output paths from the other of the input or output paths. The circulators  22  may also include integral power dividers. Any signal coming into a circulator  22  on a particular port can only go out on a particular output port with high isolation provided on the prohibited output port.  
         [0017]     Each circulator  22  then communicates with a receive chain  28   a - 28   d . Each receive chain  28  is coupled to a digital correlator  30   a - 30   d . The correlators  30  are responsible for clock and data recovery from each receive chain  28 . There may be no inherent synchronicity between the received signals and the data recovery and processing. As a result, it may be necessary in some embodiments to correlate the incoming data to recover the clock. Once the clock is recovered, the data is necessarily recovered.  
         [0018]     After the data is recovered, the data may be provided to a diversity controller and final data extractor  500 . In one embodiment, the controller  500  may be a programmable controller such as an embedded microcontroller. The diversity controller controls the transmission through a selected one of the antennas  24  and decides, in some cases, which received signal is the most useful signal. For example, the diversity controller  500 , in one embodiment, may determine which of the received signals is the strongest and, therefore, is the best candidate for subsequent analysis. In other embodiments, the diversity controller  500  may correct for errors and even take votes between different potential channels.  
         [0019]     As indicated in  FIG. 1 , the diversity controller  500  may communicate with the switch  20  to select the desired transmission path. Thus, in one embodiment, one antenna after another may be powered to provide an output signal to the tag  26  and each of the antennas  24  may be polled to determine what signal is received back on those antennas  24 . Once the most appropriate transmission antenna is determined, that antenna may be permanently selected for one data recovery cycle. Thereafter, a new most suitable antenna may be determined for changed circumstances.  
         [0020]     Referring to  FIG. 2 , in accordance with one embodiment of the present invention, the software  40  determines whether a selection command has been received in diamond  42 . The selection command may be the result of the diversity controller&#39;s analysis of the outputs from the digital correlators  30  to  30   d , for example to determine which of the received signals is the strongest. If a selection command has been developed, an output may be provided by the controller  500  to select a particular antenna X which may be one of the antennas  24   a  through  24   d , as indicated in block  44 .  
         [0021]     Then, after the antenna  24  is powered up, the back scattered radio frequency energy from a tag  26  is received (block  46 ) by each of the antennas  24   a  through  24   d . The received signal strength or amplitude is measured and stored as determined in block  48  and, then, the next antenna  24  may be powered up by incrementing the antenna number variable as indicated in block  50 . Once all of the antennas have been analyzed as determined in diamond  52 , the various amplitudes may be compared as indicated in block  54 . Then, the diversity controller  500  may select a particular antenna  24  for subsequent transmission as indicated in block  56 .  
         [0022]     Thus, while only one antenna may transmit, in some embodiments of the present invention, multiple antennas may be listening. This may increase the read capability because there may be some tags that can be illuminated with one antenna but still cannot be heard well with that antenna. Because the same local oscillator may be utilized in some embodiments for both the transmission and receive paths, different receive chains may be enabled to function efficiently. For example, if there were independent radio frequency identification readers around a dock door they could all listen but, since they do not use the same local oscillator, their phase noise may be incoherent.  
         [0023]     In accordance with some embodiments of the present invention, adaptive antenna switching may be based on antenna specific received power amplitude. In some embodiments, multi-path distortion may be mitigated through simultaneous tag reads. In other embodiments, interference mitigation may be achieved through the use of multiple active spatially diverse antennas and receive chains. Since it may be unlikely that all of the receive chains get desensitized by the same interferer, interference may be reduced with such an arrangement in some cases.  
         [0024]     System  510  may include the controller  500 , an input/output (I/O) device  520  (e.g. a keypad, display), a memory  530 , a wireless interface  540 , and a static random access memory (SRAM)  560 , coupled to each other via a bus  550 . It should be noted that the scope of the present invention is not limited to embodiments having any or all of these components.  
         [0025]     Controller  500  may comprise, for example, one or more microprocessors, digital signal processors, microcontrollers, or the like. Memory  530  may be used to store messages transmitted to or by system  500 . Memory  530  may also optionally be used to store instructions that are executed by controller  500  during the operation of system  510 , and may be used to store user data. Memory  530  may be provided by one or more different types of memory. For example, memory  530  may comprise any type of random access memory, a volatile memory, or a non-volatile memory. The memory  530  may store the antenna selections  40 .  
         [0026]     I/O device  520  may be used by system inputs to the controller  500 , for example, from the user to switch  20  via the control  34  ( FIG. 1 ) and the receive user inputs and system inputs from the antennas  24  via the correlators  30  ( FIG. 1 ). System  510  may use wireless interface  540  to transmit and receive messages to and from wireless tags with a radio frequency (RF) signal. Examples of a wireless interface  540  may include an antenna or a wireless transceiver, although the scope of the present invention is not limited in this respect.  
         [0027]     While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.