Abstract:
Techniques for a wireless electronic shelf label (ESL) system including a relay unit having multiple transmit antennae connected to a single RF transmitter. The transmitter is connected to the multiple transmit antennae through an impedance matched power splitter which uniformly splits the transmitter power output and allows each transmit antennae to transmit a fraction of the total transmit power produced by the transmitter. By locating the transmit antennae in multiple locations in a retail establishment, an improved pattern of RF coverage can be provided for ESLs, when compared to the traditional single transmit antenna. Additionally, the cost of the ESL system is low since fewer RF transmitters are required.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to improvements in electronic shelf label (ESL) systems used in transaction establishments. More specifically, the present invention relates to advantageous aspects of a wireless ESL communication system having multiple transmit antennae. 
     BACKGROUND OF THE INVENTION 
     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. The ESLs are coupled to a central server where information about the ESLs is typically maintained in an ESL data file which contains ESL identification information and ESL merchandise item information. Price information displayed by the ESLs is obtained from a price look-up (PLU) data file. The central server sends messages, including price change messages, to the ESLs through a relay unit which may be mounted in the ceiling of the retail establishment. 
     The communications link from the relay unit to an ESL, known as the “downlink”, typically uses radio frequency (RF) technology. To ensure that a message transmitted to the ESL was properly received, the ESL transmits a positive acknowledgement over an “uplink” communication path to the relay, which then relays the acknowledgment to the central server. The downlink communications path is separate from and may employ different technology than the uplink communication path, since the uplink path transmits much less data than the downlink path. 
     ESLs may be installed in a variety of premises presenting many RF barriers which may hinder the transmission of messages along the downlink. Previously, these barriers to RF transmission were overcome by including additional relay units, each having a single transmit antenna, at multiple locations throughout the retail establishment in order to ensure reliable transmission and coverage. While it is important for the communication links to be reliable, for ESL systems to be cost effective the ESLs must be inexpensive and the cost of the infrastructure, such as the relay units, kept to a minimum. Adding additional relay units to the retail establishments to overcome the RF barriers can significantly increase the cost of an ESL system, as each of the relay units includes a relatively expensive transceiver or transmitter. 
     Thus, it would be desirable to provide an ESL system having a relay unit which includes a single transmitter connected to multiple transmit antennae to provide improved RF transmission while maintaining lower costs. 
     SUMMARY OF THE INVENTION 
     The present invention advantageously provides methods and apparatus for a wireless ESL communication system including a relay unit having multiple transmit antennae connected to a single RF transmitter. The transmitter is connected to the multiple transmit antennae through an impedance matched power splitter which uniformly splits the transmitter power output and allows each transmit antennae to transmit a fraction of the total transmit power produced by the transmitter. By locating the transmit antennae in multiple locations in a retail establishment, an improved pattern of RF coverage can be provided for ESLs, when compared to the traditional single transmit antenna. Additionally, the cost of the ESL system is low since fewer RF transmitters are required. 
     A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following detailed description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a transaction management system in accordance with the present invention; 
     FIG. 2 is a block diagram of an ESL in accordance with the present invention; 
     FIG. 3 is a block diagram of a relay unit in accordance with the present invention; and 
     FIG. 4 shows a method of communicating with an ESL in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention now will be described more fully with reference to the accompanying drawings, in which several presently preferred embodiments of the invention are shown. This invention may, however, be embodied in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
     FIG. 1 shows a transaction management system  100  in accordance with the present invention. The system  100  includes a host computer system  102  and a point-of-service (POS) system  104 . Here, components  102  and  104  are shown as separate components that are networked together, but they and their subcomponents may also be combined or divided in various ways. Thus, host computer system  102  may be a POS terminal which doubles as a host computer for a network of other POS terminals. 
     The host computer system  102  includes a storage medium  106 , system software  108 , ESL software  110 , a display  112  and an input device  114 . The storage medium  106  includes a PLU data file  107  which stores item prices which are available for distribution to a POS terminal  116  by the host system  102 . Alternatively, provision may be made for a bar code scanner  118  to directly access the PLU data file  107 . The storage medium  106  also includes ESL data file  109  which contains item information, such as a PLU number and ESL identification information for each of the ESLs  122 . The system  102  executes system software  108  which updates the contents of storage medium  106  and performs other system functions, as described in greater detail below. Input device  114  is preferably a keyboard, but it will be recognized that data can be entered in a variety of alternative manners. 
     POS system  104  includes bar code scanner  118  and POS terminal  116 . 
     The system  100  also includes relay units  120  and ESLs  122 . The relay units  120  may be suitably mounted in or near the ceiling of the retail establishment. 
     ESL software  110  records, schedules, and transmits all messages to ESLs  122 . ESL software  110  controls the transmission of messages, including price change messages, to ESLs  122  utilizing relay units  120  which are placed periodically across a retail establishment. These messages are sent to the relay array units  120  through communications link  124 . Communications link  124  may suitably utilize radio frequency (RF) communication, infrared (IR) communication, a wired link, or some combination of communication techniques. After receiving a message from the host system  102 , the relay units  120  then transmit the message to the ESLs  122  utilizing an RF communication link  126 . 
     After receiving a message, the ESLs  122  may respond with an acknowledgement which is transmitted to the relay units  120  over communication link  127 , which may suitably utilize RF communication, IR communication, a wired link or some combination of communication techniques. The relay units  120  would then retransmit the acknowledgement message to the host system  102  over communication link  124 . 
     FIG. 2 shows a block diagram of the ESL  122  in accordance with the present invention. A liquid crystal display (LCD)  202  displays information, such as item price and related data. ESL  122  includes an RF receiver  206  for receiving messages from the relay unit  120 , and a transmitter  205  for transmitting messages to the relay unit  120 . The transmitter  205  may utilize RF communication, IR communication, a wired link or some combination of communication techniques. A power source  208  provides power for the operation of ESL  122 . The operation of ESL  122  is controlled by ESL circuitry  204  which decodes incoming messages received and performs any actions indicated by the messages. For example, if a price change message is received, the ESL circuitry  204  would cause the display  202  to be updated with the new price information. Volatile RAM  210  stores the ESL identification number and the displayed message. ESL circuitry  204  may also include a variety of components such as timers and other electronic components. 
     FIG. 3 shows a block diagram of the relay unit  120  in accordance with the present invention. A host communication system  302  provides an interface to the host system  102 . Messages to the ESLs  122  are transmitted by an RF transmitter  304  which is controlled by an RF transmitter control unit  306 . A transmitter output signal is fed into an impedance matcher and power splitter  308  which splits the signal between a plurality of transmit antennae  310  and maintains the characteristic impedance between the antennae  310  and the transmitter output. A receiver receives acknowledgement messages from the ESLs  122  and passes the messages to the host communication system  302 , which in turn forwards the messages to the host system  102 . While the transmitter  304  and the receiver  312  are shown as separate blocks, as would be understood by one of ordinary skill in the art, these devices may be combined into a single transceiver. 
     ESLs  122  are installed in a variety of retail establishments which present many RF barriers, such as shelves and columns, for example, which hinder the transmission of RF messages to the ESLs  122 . The relay unit  120  advantageously includes the RF transmitter  308  connected to the plurality of transmit antennae  310  through the impedance matcher and power splitter  308 . The transmit antennae  310  broadcast the RF signals from multiple sources in order to provide an improved pattern of RF coverage. Each antennae  310  transmits a fraction of the total transmit power into a physical area not reachable by a centrally located transmit antenna. Multiple relay units, each having multiple transmit antennae, may be installed throughout a retail establishment to provide improved RF coverage. 
     In one aspect, the impedance matcher and power splitter  308  may allow up to a predetermined number of transmit antennae  310  to be connected. Unused transmit antennae outputs are terminated in such a manner as to maintain a proper impedance match, ensuring that no power will be distributed to the unused outputs. 
     In another aspect, the impedance matcher and power splitter  308  may include connections for only the number of transmit antennae  310  to be connected. For example, if four transmit antennae are required, then the impedance matcher and power splitter would include connections for only four antennae. 
     FIG. 4 shows a method  500  of communicating with an ESL in accordance with the present invention. In step  502 , a relay unit, such as relay unit  120 , receives a message from a host system. The relay unit includes an RF transmitter, such as RF transmitter  304 , and an impedance matcher and power splitter, such as impedance matcher and power splitter  308 . In step  504 , the RF transmitter outputs an RF signal containing the message to the impedance matcher and power splitter. In step  506 , the impedance matcher and power splitter uniformly splits the RF signal between a plurality of transmit antennae, such as transmit antennae  310 . In step  508 , the split RF signal is transmitted by the plurality of transmit antennae to the ESL. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the present invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.