Abstract:
A low duty cycle wireless device is disclosed. The low duty cycle wireless device includes a high data rate transceiver, a low data rate receiver, and a microprocessor. The low data rate receiver receives a command to receive a large amount of information. The display information far exceeds the capacity for reception through the low data rate receiver. In response to the received command, the microprocessor wakes up from a sleep mode and activates the high data rate transceiver to receive the display information. The microprocessor deactivates the high data rate transceiver once the display information has been received.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to apparatus and methods for communicating with a low duty cycle wireless battery powered device, and more particularly, to advantageous apparatus and methods for reducing the amount of time the wireless device is powered on in order to receive updates of new information and, consequently, reducing average power consumption and conserving power. 
     BACKGROUND OF THE INVENTION 
     Battery powered electronic shelf labels (ESLs) often must operate several years on one battery charge. Typically, conventional ESLs include a dedicated segmented liquid crystal display (LCD) which displays limited information such as the price of an item and the item&#39;s unit cost. As a result of displaying limited information, conventional ESLs include a low duty cycle, low power and low data rate receiver to receive a few hundred bits at a time in order to update the information at an ESL. To conserve power, the low data rate receiver typically remains powered off and periodically wakes up to receive a beacon signal at which point it determines whether to remain powered in order to receive subsequent updated information. 
     Due to the limited amount of displayable information of a segmented LCD, a conventional ESL has limited use for displaying advertising information such as specials, graphics, and the like. Conventional dot matrix displays, on the other hand, are capable of displaying more information which would be more suitable for advertising. For example, dot matrix displays may display graphics, colored graphics, colored text of varying styles and fonts, and other attractive information. However, the amount of information that is required to update a dot matrix display may require tens of thousands of bits for one update. For example, a low end, 320×240 pixel video graphics array (VGA) single color dot matrix display presently requires 76,800 bits for one update whereas a segmented LCD only requires a few hundred bits for one update. Utilizing the low data receiver approach to updating, the dot matrix display would have to be powered on for periods of time much longer than a conventional LCD, resulting in a high amount of power consumption. 
     One approach to satisfying large data rates of transmission required by a dot matrix display in an ESL or an advertising display may include employing a conventional high bandwidth transceiver such as I.E.E.E. 802.11, Bluetooth®, and Zigbee® transceivers. To conserve power in order for the ESL or advertising display to operate a long time on one battery charge, the conventional high bandwidth transceivers would have to operate at a very low duty cycle, for example, awaking from a sleep mode once every ten minutes. Retailers, who deploy ESLs and advertising displays, require that the response time for updating information be performed preferably within seconds of initiating an update. As a result, an ESL or advertising display utilizing the conventional high bandwidth transceiver must wake up periodically in small second increments to determine whether an update has been initiated. Conventional high bandwidth transceivers are burdened by multiple packet exchanges to determine whether an update has been initiated. Furthermore, multiple packet exchanges are also required by conventional high bandwidth transceivers to remain synchronized with a far end device to which it communicates. Thus, conventional high bandwidth transceivers, employed in this way, waste considerable power as compared to a conventional ESL. 
     SUMMARY OF THE INVENTION 
     The present invention recognizes the need to address problems of integrating a dot matrix display to a low duty cycle wireless device such as an electronic shelf label or advertising display. To such ends, a dual mode low duty cycle wireless device to drive a dot matrix display is disclosed. In one mode of communication, the low duty cycle wireless device utilizes a low power and low data rate receiver to determine whether display information is to be received from a host system such as a point of sale (POS) system. Once this determination has been made, the low duty cycle wireless device operates in a second mode of communication. In the second mode of communication, the low duty cycle wireless device utilizes a conventional higher data rate transceiver to receive the display information required by the dot matrix display. The present invention advantageously has the power conservation benefits of a low data rate receiver for passively acknowledging commands, as well as, with the throughput benefits of receiving large amounts of information as required by a dot matrix display with a high data rate transceiver. 
     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  shows a block diagram of a transaction management system in which the present invention may be advantageously employed; 
         FIG. 2  shows a low duty cycle wireless device in accordance with the present invention; 
         FIG. 3  shows an external view of an advertising display containing the components of  FIG. 2  in accordance with the present invention; and 
         FIG. 4  shows a flow chart illustrating a method for communicating with a low duty cycle wireless device of  FIG. 2  in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a transaction management system  100  employing ESLs  122  in accordance with the present invention. The system  100  includes an ESL host computer system  102  and a point-of-sale (POS) terminal  114 . Here, components  102  and  114  are shown as separate components that are networked together, but they and their subcomponents may also be combined or divided in various ways to compose a POS system  116 . 
     The system  100  also includes communication base stations (CBSs)  120  and ESLs  122 . ESLs  122  are an example of a low duty cycle wireless device in accordance with the present invention and described in further detail in connection with the discussion of  FIG. 2 . The CBSs  120  may be suitably mounted in or near the ceiling of the retail establishment. ESLs  122  are typically attached to store shelving adjacent to items. In one aspect, the system  100  includes a plurality of groups of ESLs  122  and a plurality of CBSs  120 , with each group of ESLs  122  preferably assigned to one of the CBSs  120 . 
     The system  100  also includes access point (AP)  128 . As will be described in further detail in connection with the discussion  FIG. 2 , ESLs  122  have a high data rate transceiver which communicates with host computer  102  over a different protocol, such as I.E.E.E. 802.11, than a passive backscatter technique conventionally employed in a conventional ESL. AP  128  supports the high data rate protocol and communicates with host computer  102  over a wireless local area network (LAN)  130 . Alternatively, AP  128  may communicate with host computer  102  over either wired network  124 , a wired LAN, or a separate wired network. Alternatively, the teachings of the invention contemplate integrating the access point functionality in a CBS. 
     The host computer system  102  records and schedules messages, such as price updates, to ESLs  122 . The ESL host computer system  102  monitors and maintains an action list for the ESLs  122 . Items or records on the action list may be provided from a user of the POS system  114  or host computer  102 . Based on the messages the ESL host computer system  102  has scheduled for an ESL  122 , the ESL host computer system  102  creates the appropriate message and sends the message to an appropriate CBS  120 . The message may originate from one of two classes of messages. The first class includes a beacon message to synchronize the clocks of the ESLs or to inform a particular ESL that display information requires updating. The second class includes display information updates. 
     The messages are sent to the CBSs  120  through communication links  124 . The communication links  124  may suitably utilize radio frequency (RF) communication, infrared (IR) communication, or some combination of communication techniques. Groups of ESLs  122  are assigned to a particular CBS for communication. After receiving a message from the host system  102 , a particular CBS  120  which has been assigned to an ESL  122  then transmits the message to the ESL  122  utilizing communication link  126 , which may suitably utilize RF communication, IR communication, or some combination of communication techniques. Processing of the two classes of messages will be described in further detail in connection with the discussion of  FIG. 2 . 
       FIG. 2  shows a low duty cycle wireless device  200  in accordance with the present invention. Low duty cycle wireless device  200  may suitably be used as one or more of the ESLs  122 . Low duty cycle wireless device  200  includes a low data rate receiver  210 , a high data rate transceiver  230 , a microprocessor  220 , a persistent memory  250 , a dot matrix display  240 , and a battery  260 . The low data rate receiver  210  may be a conventional low duty cycle, low power receiver which employs a conventional passive backscatter technique. The high data rate transceiver  230  may be a conventional high data rate transceiver such as an IEEE 802.11 receiver modified according to the teachings of the present invention. The microprocessor  220  may be any suitable microprocessor having a stand by mode in which it consumes a few microamperes (μA) and can be activated or awakened in a few microseconds. One microprocessor family suitable for this kind of operation is the Texas Instruments MSP430 series of microprocessors, for example. The battery  260  is coupled to the microprocessor  220  and the low data rate receiver  210 . The microprocessor  220  applies power to the high data rate transceiver  230 , display  240 , and memory  250  over communication bus  225  as needed. 
     The persistent memory  250  is random access memory (RAM). Flash memory and any other memory types which can persistently store data without having power applied are preferable. The display  240  may be any suitable bi-stable display such as cholesteric LCD (ChLCD) manufactured by Kent Displays Inc., bi-stable displays manufactured by ZBD Displays Ltd, Plastic Logic&#39;s electronic paper, or the like, which require a high rate of data for achieving an update, or any suitable type of low power consumption dot matrix display. A bi-stable display continues to display information such as on-screen images and text even after the power has been turned off to the display. The display utilizes power only when display information changes. 
     In a normal mode of operation, the low data rate receiver  210  wakes up from a sleep mode approximately every 1.45 seconds to receive a beacon message. In this mode, the low data rate receiver  210  consumes little power on the order of 2 μper cycle or 6 μwatts (μW) on average. The beacon message normally serves as a time synchronization point where the low data rate receiver  210  wakes up, synchronizes its internal logic, and returns to sleep mode. The instantaneous data rate for the low data rate receiver  210  is approximately 16 kilobits per second. However, considering that the low data rate receiver  210  is awaken every 1.45 seconds, the effective data rate is approximately 300 kilobits per second. 
     If there is an action to be performed such as updating display  240  with display information, such as an update of text, graphics, fonts, styles, colors, and the like, the beacon message will contain address and data components. The address component identifies the particular ESL for which the data components are destined. The data component includes a command and data portion relating to the command. The low data rate receiver  210  utilizes a conventional passive backscatter technique to acknowledge the command. When an action is to be performed, the low data rate receiver  210  communicates a clock or any suitable type of interrupt signal to microprocessor  220  over link  218 . 
     The low data rate receiver also forwards the command and data portions over serial port  215  to microprocessor  220 . Microprocessor  220  wakes up from sleep mode, synchronizes its clock, and processes the command portion accordingly. For a command indicating that display  240  is to be updated, for example, the command portion directs data in the beacon message to serial output  215  of the low data rate receiver  210 . In an alternative embodiment, link  218  may combine with serial output  215  into one signal wire. In this alternative, a change in state or signal transition can be used to activate microprocessor  220  until the command is received. 
     Microprocessor  220  wakes up and processes the command portion. When processing the command portion, microprocessor  220  recognizes that an update to display  240  is being requested from host computer  102 . Microprocessor  220  signals the high data rate transceiver  230  over communication bus  225  to wake up and start communication with host computer  102  to receive display information. The high data rate transceiver  230  may utilize any communication protocol as long as its data rate is substantially higher than the low data rate receiver  210  and serves the purpose of conserving the average power consumption of the low duty cycle wireless device  200 . The lowest communication rate for transceiver  230  is dependent on the amount of information needed to update display  240  and being able to update display  240  with that amount of information in a few milliseconds. On smaller screen sizes, such as 320×240 pixel display, a transceiver operating at least at 250 kilobits per second and consuming approximately 0.5-1 Watts of power would be sufficient. To consume less power when receiving display information, data rates in the order of megabits per second are preferable. One exemplary protocol meeting these criteria is the I.E.E.E. 802.11 protocol. 
     The high data rate transceiver  230  receives the display information from host computer such as host computer  102  through network  130  and forwards the display information to persistent memory  250  for storage. The persistent memory  250  stores display information so that it can be subsequently retrieved without having to re-receive the same display information. Upon completion of receiving the display information, microprocessor  220  awakes display  240  and updates display  240  with the display information stored in persistent memory  250 . Display  240  displays the updated display information. Once the display information is displayed, microprocessor  220  signals display  240  to power off and places itself into sleep mode to await the next command. Since display  240  is a bi-stable display, the information displayed remains displayed even after power to display  240  is turned off. 
     Although the low data rate receiver  210  and the high data rate transceiver  230  are depicted as separate components, it should be recognized that these components may be integrated into a single component consistent with the teachings of the present invention. 
     To enhance the advertising aspect, display  240  may have a larger screen size than a conventional LCD ESL. For example, the screen size of display  240  may measure 5″×7″ as compared to 1″×2″ of the conventional LCD ESL. With this sized screen, more attractive advertising information may be displayed and can be viewed from larger distances. Another example of a low duty cycle wireless device  200  in accordance with the present invention includes an advertising display. 
       FIG. 3  shows an external view of an advertising display  300  containing the components of  FIG. 2  in accordance with the present invention. Advertising display  300  may be free standing or may mount onto a shelf. As shown in  FIG. 3 , although not drawn to scale, the display area is approximately 4×5 inches. The display may be suitably implemented with a dot matrix display having approximately 50-100 pixels/inch. 
       FIG. 4  shows a flow chart illustrating a method for communicating with a low duty cycle wireless device  200  of  FIG. 2  in accordance with the present invention. At step  410 , a command is received by a low data rate receiver to update the wireless device&#39;s display such as display  240 . For example, a host computer of a POS system such as computer  102  of POS system  116  may transmit a command to update the wireless device&#39;s display information. At step  420 , a high data rate transceiver, such as high data rate transceiver  230 , is activated to communicate with the POS system, for example. For example, microprocessor  220  may awake from a sleep state to signal the high data rate transceiver to communicate with the POS system. At step  430 , display information is received over the high data rate transceiver. At step  440 , a display, such as display  240 , is activated to display the received display information. At step  450 , the received display information is displayed. At step  460 , the display and the high data rate transceiver are deactivated. Method  400  proceeds to a wait state  470  until the next command is received. During wait state  470 , the display draws no power while the high data rate transceiver, low data rate receiver, and microprocessor draw minimal power while in sleep mode. Alternatively, the high data rate transceiver may be completely powered off during wait state  470 . When the next command arrives, the method proceeds to step  410 . 
     While the present invention has been disclosed in the context of various aspects of presently preferred embodiments, it will be recognized that the invention may be suitably applied to other environments consistent with the claims which follow.