Abstract:
An electronic shelf label with a modulated backscatter communication system which can actively transmit signals. The electronic shelf label includes a modulated backscatter receiver for receiving a first modulated radio frequency (RF) carrier signal, and a transmitter powered by the first modulated RF carrier signal for transmitting a second modulated RF carrier signal.

Description:
BACKGROUND OF THE INVENTION  
   The present invention relates to electronic shelf label (ESL) systems or electronic signage, and more specifically to an electronic shelf label. 
   ESL systems typically include a plurality of ESLs for each merchandise item in a store. ESLs display the price of corresponding merchandise items on store shelves and are typically attached to a rail along the leading edge of the shelves. A store may contain thousands of ESLs to display the prices of the merchandise items. 
   One type of ESL is disclosed in commonly assigned to U.S. Pat. No. 5,510,602. This type of ESL takes advantage of modulated backscatter communication techniques disclosed in commonly assigned U.S. Pat. No. 5,640,683. These patents are hereby incorporated by reference. 
   ESLs may be required to display information in many retail environments, including coolers and freezers where specially coated glass doors can reduce signal strength from wireless ESLs. Communication difficulties often require additional RF communication equipment to be installed to compensate for the loss. For example, in the system disclosed in the referenced U.S. Patent, a communication base station (CBS) must be dedicated and in close proximity to a cooler or freezer in order to communicate with ESLs in that cooler or freezer. In addition, noise generated by devices or reflected from devices can severely impact the ability of a CBS to receive a response (acknowledgement) from the ESL following successful execution of a command by the ESL. 
   Therefore, it would be desirable to provide an ESL with enhanced communication capability to avoid installation of the additional RF communication equipment, such as CBSs and antennae. 
   SUMMARY OF THE INVENTION 
   In accordance with the teachings of the present invention, an electronic shelf label is provided. 
   The electronic shelf label includes a modulated backscatter receiver for receiving a first modulated radio frequency (RF) carrier signal, and a transmitter powered by the first modulated RF carrier signal for transmitting a second modulated RF carrier signal. 
   It is accordingly an object of the present invention to provide an electronic shelf label. 
   It is another object of the present invention to provide an electronic shelf label which receives signals using protocols designed for modulated backscatter techniques and which sends responses using a semi-active transmitter powered by a received carrier signal, 
   It is another object of the present invention to provide an electronic shelf label which provides a passive uplink response by using energy in a received signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram of a transaction management system; and 
       FIG. 2  is a circuit diagram of control circuitry within the electronic shelf label. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , store system  10  primarily includes host computer system  12 , point-of-sale (POS) system  14 , and electronic shelf label (ESL) system  16 . 
   POS system  14  includes bar code scanner  18  and terminal  20 . 
   ESL system  16  primarily includes ESLs  22 , host ESL terminal  24 , ESL storage medium  26 , and communication base stations (CBSs)  28 . 
   ESLs  22  are typically attached to shelf units within a store. Each ESL  22  includes control circuitry  52 , a number of data registers  54 , a display  56 , and power source  58 . 
   Control circuitry  52  preferably includes all circuitry necessary for wireless communication with host ESL terminal  24 . Control circuitry  52  may include an application specific integrated circuit (ASIC) and an antenna. Communication between control circuitry  52  and host ESL terminal  24  may include modulated backscatter radio frequency (RF) communication and active communication for both downlink and uplink transmissions. 
   Data registers  54  contain data, usually the prices of items on the shelf. The data may also include symbols and phrases, such as promotional information associated with the items. 
   Display  56  may include a liquid crystal display (LCD) or electronic paper type display. 
   Power source  58  is preferably one or more batteries. 
   Host ESL terminal  24  executes ESL software  30 , which controls storage and display of ESL data  32 . ESL software  30  sends data from ESL data  32  to ESLs  22  and determines whether correct information is being displayed by ESLs  22  when an acknowledgement is received from ESLs  22 . Additionally, ESL software  30  may improve statistical accuracy by checking the displayed information against a checksum calculated from information in PLU data file  44 . 
   ESL storage medium  26  stores ESL data  32  and is preferably a fixed disk drive. 
   CBSs  28  send messages from host ESL terminal  24  to ESLs  22  and receive messages to host ESL terminal  24  from ESLs  22 . CBSs  28  are typically mounted to ceilings. The number and locations of CBSs  28  are determined by reception quality readings throughout a store. CBSs  28  are typically connected to host ESL terminal  24  through wire cables. 
   Host computer system  12  includes transaction server  42  and storage medium  44 . 
   Transaction server  42  distributes price and other information to POS terminals  20  and host ESL terminal  24 . 
   Storage medium  44  stores PLU data file  44 . PLU file  44  is preferably a primary location for storing item prices and other information. 
   Here, terminals  20 ,  24 , and  42  are shown as separate components that are networked together, but they may also be combined in different ways. For example, ESL terminal  24  and transaction server  42  may be combined to form a single host computer. POS terminal  20  and transaction server  42  may be combined to form a POS terminal which doubles as a host computer for a network of other POS terminals. 
   Turning now to  FIG. 2 , control circuitry  52  is shown in more detail. 
   Control circuitry  52  includes antenna  60 , detector  62 , signal processing circuitry  64 , and microcontroller  66 . 
   Antenna  60  receives and transmits modulated RF signals. Antenna  60  is preferably a quarter-wave folded planar conductor which operates around a carrier frequency of 2.45 GHz. 
   Reception of downlink signals is similar to the method disclosed in the previously incorporated U.S. Pat. No. 5,668,560. A downlink signal includes a modulated 2.45 carrier signal. 
   Detector  62  extracts an information signal from the downlink signal. Detector  62  is preferably a Schottky barrier-type silicon diode. 
   Signal processing circuitry  64  amplifies and demodulates the detected downlink signal to produce a downlink information signal. 
   Microcontroller  66  identifies on/off keyed data bits in the downlink information signal to generate data for display by display  14 . Microcontroller  66  also provides an uplink information signal. 
   Under the present invention, control circuitry  62  additionally includes switch  68 , amplifier  70 , and digital modulator  72 . 
   Switch  68  routes the downlink signal to amplifier  70 . Switch  68  is controlled by microcontroller  66 . 
   Amplifier  70  amplifies an uplink signal from digital modulator  72 . Amplifier  70  is powered by energy in the 2.45 carrier signal of the downlink signal. 
   Digital modulator  72  produces the uplink signal from an uplink information signal provided by microcontroller  66 . Microcontroller  66  activates switch  68  to cause amplification and transmission of the uplink signal from digital modulator  72 . Microcontroller  66  may be programmed to activate switch  68  if ESL  22  is placed in a location where unamplified passive communication is difficult. 
   For example, ESL  22  may be located in a freezer. Instead of attempting to return an acknowledgment using passive modulated backscatter techniques, microcontroller  66  is programmed to activate switch  68  to amplify the uplink signal before transmitting it. If microcontroller  66  does not cause switch  68  to route the incoming downlink signal to amplifier  70 , the uplink signal goes to antenna  60  unamplified. 
   Advantageously, transmission of amplified uplink signals uses energy in the downlink carrier signal, with little or no power from power source  58 . 
   Although the present invention has been described with particular reference to certain preferred embodiments thereof, variations and modifications of the present invention can be effected within the spirit and scope of the following claims.