Patent Publication Number: US-2011051641-A1

Title: Low Power Consumption Wireless Sensory and Data Transmission System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to the application Ser. No. 12/534,108. 
    
    
     BACKGROUND 
     1. Field of Invention 
     This invention relates to an information collecting system, specifically to a low power consumption wireless sensory and data transmission network. 
     2. Description of Prior Art 
     Recently, much work has been directed towards the building of networks of distributed wireless sensor nodes. Sensor nodes in such networks conduct measurements at distributed locations and relay the measurements, via other data collection points. Wireless sensor networks, generally are envisioned as encompassing a large number of sensor nodes, with traffic flowing from the sensor nodes into a much smaller number of measurement data collection points through information collection apparatus. Sensor nodes are commonly equipped, for example, with sensors, a local storage unit, a processor and wireless communication devices. Such sensor nodes are typically small and the communication devices are typically short range communication transceivers that form an ad hoc communication network. 
     Generally, the sensor nodes have one or more of the following characteristics: a) the nodes are desired to operate for extended periods of time on battery power; b) the nodes have limited computation, memory and communication capability often due to power constraints; c) the nodes typically communicate using a short range ad hoc communication network; d) the nodes are commonly installed in remote or other environments that preclude normal communication and control of the devices; and e) the nodes are often inexpensive. Sensor nodes are generally expected to be long-lived (deployed for years), un-tethered (both in terms of communication and power), and unattended (and so are capable of self configuring and self-adapting). 
     Sensor nodes may have capability of measuring at least one characteristic in their environment, such as detecting ambient conditions (e.g., temperature, humidity, movement, sound, light, or the presence or absence of certain objects). Many potential applications of wireless sensor networks exist, including as example of physiological monitoring, environmental monitoring, condition-based maintenance, military surveillance, precision agriculture, geophysical monitoring, and/or monitoring various other types of events. 
     While individual sensor nodes may have limited functionality, the global behavior of the wireless sensor network can be quite complex. The information collection apparatus may be a mobile station connectable to an existing communication network such as the Internet. 
     Typically, the primary resource constraint of sensor nodes in sensor networks is energy. Because many sensor networks deploy sensor nodes that are battery powered and that can scavenge only a small amount of energy from their surroundings, limited battery power is one of major hurdles in achieving desired longevity of network operation. Reducing power consumption of the wireless sensor networks has been a topic of extensive study. The problem has not been completed resolved. 
     In some applications, it is required that the information collection network comprising sensor nodes with a local storage capability. In some other applications, the information collection system may comprise nodes with local storage capability only. A RFID system is an exemplary case of such applications. It is therefore desired that the information collection system has the flexibility for all such applications. 
     It is therefore an object of the present invention to provide a low power consumption wireless information collection system comprising wireless sensor nodes that achieves longevity of the operation with a conventional battery. 
     It is another object of the present invention to provide a low power consumption wireless information collection system comprising nodes with local storage unit that achieves longevity of the operation with a conventional battery. 
     It is yet another object of the present invention to provide a novel power management method for the wireless information collection system comprising a plurality of data collection devices (nodes) and an information collection apparatus. The devices are in a “switch-off” status until they receive the RF energy transmitted from the information collection apparatus. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment, a sensor node comprises a sensor, a processor, a transceiver, a RF energy receiver, and a switch. The sensor node may be powered by a battery. A plurality of sensor nodes may be deployed in an area of interests. The sensor nodes are at a “switch-off” status to reserve the battery power until the nodes are activated by an information collection apparatus. 
     The apparatus may comprise a RF energy generator and a transceiver conforming to the same communication standards as the sensor nodes. The apparatus may also comprise second transceiver for communicating with an existing communication network such as the Internet. The apparatus may be installed in a vehicle. 
     To activate the information collection system, the RF (radio-frequency) energy generated by the apparatus is transmitted in the area of the interests with pre-deployed sensor nodes. The RF energy receiver in the sensor nodes receives the electromagnetic energy by an antenna and converts the energy into a DC (direct-current) voltage. If the DC voltage is in exceeding of a threshold voltage of a switch, the battery power is directed to supply the operation of the sensor nodes. The nodes are activated. The sensor nodes will remain at the “switch-on” status even after the RF energy from the apparatus is switched off. A switch controller is used to maintain the switch at the “switch-on” status by drawing a current from the power supply to maintain the input voltage for the switch. 
     An ad hoc communication network comprising sensor nodes and information collection apparatus is then established. The data collected by sensors is sent to the information collection apparatus through the ad hoc network. The apparatus may send an instruction to sensor nodes to switch off the battery power after the completion of an information collection task. The apparatus may also send the collected data to a server through the existing communication network. 
     In another embodiment, the information collection system comprises at least a node without a sensor. The node may comprise a data storage unit with pre-stored data. After the node is activated, the data stored may be read out and be sent to the apparatus through the ad hoc communication network. 
     In yet another embodiment, the node may comprise a sensor and a storage unit with pre-loaded data. Data collected by the sensor and the data read out from the local storage unit may be sent in combination to the apparatus after the ad hoc communication network is established. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present invention and its various embodiments, and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a schematic diagram of a data collection device (node of the network) in three different embodiments. 
         FIG. 2  is a schematic diagram of an exemplary information collection apparatus. 
         FIG. 3  is a schematic diagram of depicting functional blocks for converting a received RF energy into a DC voltage and for supplying the battery power to the data collection devices. 
         FIG. 4  is a schematic functional block diagram of the information collection system. 
         FIG. 5  is a flow diagram depicting steps of the operation of the information collection system. 
         FIG. 6  is a flow diagram depicting steps of the power management method of the information collection system. 
         FIG. 7  is a schematic functional block diagram of the information collection system in one embodiment as a wireless sensor network. 
         FIG. 8  is a schematic functional block diagram of the information collection system in another embodiment as an active RFID system with low power consumption. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention will now be described in detail with references to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order not to unnecessarily obscure the present invention. 
       FIG. 1  is a schematic diagram of a data collection device (node of network) in three different embodiments. Type-I device  101  comprises a sensor unit  104 , a transceiver  106 , a processor  108 , a RF energy receiver  110 , a switch  112 , and a power supply  114 .  104  may comprise one sensor for measuring a characteristic of its environment such as temperature, humidity, movement, sound, light, or the presence or absence of certain objects.  104  may comprise a plurality of sensors for measuring different characteristic of their environment. The transceiver  106  is for the data collection device  101  to communicate with another device or with an information collection apparatus.  106  may conform to a short range communication standard such as the Bluetooth (IEEE 802.11b and its amendments), or the ZigBee (IEEE 802.15.4 and its amendments), or the WiFi (IEEE 802.11 and its amendments). The processor  108  may comprise an analog-to-digital converting circuits for converting an analog signal from the sensor to a digital signal, a digital signal processor and/or a CPU (central processing unit). The RF energy receiver  110  receives an external RF energy and converts the received energy into a DC voltage. The switch  112  with a “switch-on” threshold voltage is used to control the power supply  114 . If the DC voltage resulting from the received RF energy is in exceeding of the threshold voltage, the switch  112  directs the power supply  114  to provide energy for the operation of the device  101 . According to one implementation, the power supply  114  is a battery. The power supply  114  may be a solar panel in another implementation. The power supply  114  may be an energy harvesting device in yet another implementation. 
     As illustrated in  FIG. 1 , type-II device  102  is similar to the type-I device  101  except that the sensor unit  104  is replaced by a data storage unit  105 .  105  may be a semiconductor memory such as a flash memory or a plurality of flash memories.  105  may be pre-loaded with data before it is deployed to the field (an area of interest). 
     As further illustrated in  FIG. 1 , type-III device  103  comprises a sensor unit  104  and a storage unit  105 .  103  may be used to collect data via the sensor unit  104 . The collected data from the sensor unit  104  and the data read out from the storage unit  105  may be sent in combination through the ad hoc communication network to the information collection apparatus. 
       FIG. 2  is a schematic diagram of the information collection apparatus  200 . The apparatus  200  collects information from data collection devices after the devices and the apparatus form an ad hoc communication network. The apparatus  200  comprises a RF energy generator  202 , a first communication unit  204 , a second communication unit  206 , and a power supply unit  208 . The apparatus  200  may be installed in a mobile carrier  210  such as for example, in a vehicle. 
     The RF energy generator  202  generates an electromagnetic energy in RF band. The generated RF energy is transmitted to the area of interests with the pre-deployed data collection devices. The first communication unit  204  may conform to the same short range communication standard as the transceiver  106  in the data collection devices. The second communication unit  206  may be another transceiver for communicating with an existing communication network such as for example, the Internet. The power supply unit  208  may be a battery. 
       FIG. 3  is a schematic diagram of depicting functional blocks for converting received RF energy into a DC voltage and for controlling the battery power to provide energy for the operations of the data collection device. The RF energy generator  202  generates the RF energy and transmits the energy into the area of interests. A plurality of devices may have already been deployed in the area. The antenna  302  may be of inductive type or be of a dipole type depending on the frequency of the RF energy. The high frequency RF energy requires a dipole type of antenna. The rectifier  304  converts at least a portion of the received RF energy into a DC component. The voltage regulator  306  converts the DC component into a DC voltage. The DC voltage turns on the switch  112  if it is in exceeding of its “switch-on” threshold. A switch controller  308  is used to ensure the switch  112  to be maintained at the “switch-on” status even after the RF energy is switched off. In one implementation, the controller  308  may draw a current from the power supply  114  to assist to charge up an output capacitor of the voltage regulator  306  after the switch  112  is switched on. After the external RF energy source  202  is switched off, the voltage regulator  306  ceases to provide a stable output voltage. However, the current source controlled by the controller  308  will provide a current and a stable voltage to maintain the switch at the “switch-on” status. The power supply  114  provides power for the operation of the sensor  104 , the transceiver  106  and the processor  108  in an exemplary implementation as illustrated in  FIG. 3 . 
       FIG. 4  is a schematic functional block diagram of the information collection system  400 . The system  400  comprises the information collection apparatus  200 , a type-I device  101 , type-II devices  102  and  102   a , and a type-III device  103 . The devices may be connected to the apparatus  200  directly. The device may also be connected to the apparatus  200  through another device in the ad hoc communication network  402 . The information collection system  400  may comprise one type of devices and the system may also comprise all three types of devices. The apparatus  200  with the second communication unit  206  may be connected to an existing communication network  404 .  404  may be the Internet in an exemplary case. The data collected from each device (node) by the apparatus  200  may be sent to a server in the communication network  404 . Although one information collection apparatus is depicted in  FIG. 4 , the system  400  may comprise a plurality of apparatus and many devices. It should be noted that devices (nodes) are kept at the status of “switch-off” until the apparatus  200  sends out the RF energy as a triggering signal. The apparatus  200  has the capability of switching on and off the devices (nodes) of the information collection system. 
       FIG. 5  is a flow diagram depicting steps of the operation of the information collection system. Process  500  starts with a step  502  that a device (node) receives RF energy generated from an information collection apparatus  200 . The RF receiver  110  in the device converts the received RF energy into a DC voltage in step  504 . The device is switched on in step  506  if the DC voltage resulting from the received RF energy is in exceeding of the threshold voltage of the switch  112 . An ad hoc communication network (link)  402  is formed in step  508  if at least one device is switched on. In step  510 , data is collected by the sensor unit  104  and/or read out from the storage unit  105 . The collected and/or readout data are transmitted to the information collecting apparatus  200  through the ad hoc communication network  402  in step  512 . 
       FIG. 6  is a flow diagram depicting steps of the power management method of the information collection system  400 . Process  600  starts with step  602  that all devices (nodes) are at “switch-off” status. In step  604 , an electromagnetic energy in RF band is generated by the information collection apparatus  200 . The RF energy is received by a device (node) in step  606 . The power supply  114  (battery) is switched on in step  608  if the received RF energy generates a DC voltage in exceeding of the threshold voltage of the switch  112 . The RF energy generator is switched off in step  610 . The device (node) will maintain at the “switch-on” status by using the switch controller  308  as described. 
       FIG. 7  is a schematic functional block diagram of the information collection system  400  in one embodiment as a wireless sensor network  700 . The network  700  comprises a plurality of type-I devices ( 101   a ,  101   b ,  101   c  and  101   d ). Each device comprises at least one type of sensor. The devices are connected through an ad hoc communication network  702 . At least some of the devices are connected to the information collection apparatus  200  directly. The wireless sensor devices ( 101   a ,  101   b ,  101   c  and  101   d ) are at the “switch-off” status until the information collection apparatus  200  sends out the RF energy. The present invention provides a low power consumption sensor network. The sensor units will only start to collect data after the apparatus sends out the RF energy. The sensor units will be at the “switch-off” status when the measurement data is not required. By implementing the present invention, the wireless sensors powered by a battery have the capability to be used for a very long period of time. Therefore, the replacement of the battery, which may be a costly and difficult task, can be avoided. 
       FIG. 8  is a schematic functional block diagram of the information collection system  200  in another embodiment as an active RFID system  800  with low power consumption. The system  800  comprises a plurality of type-II devices ( 102   a ,  102   b ,  102   c , and  102   d ). Each device has a storage unit  105 . All devices are at the “switch-off” status until the RF energy is received. The RF energy may be generated from the information collection apparatus  200 . After receiving the energy and converting the energy into a DV voltage in exceeding of the threshold voltage of the switch  112 , the battery power is directed by the switch to provide power for the operations of the devices (nodes). The devices may form an ad hoc communication network  802 . At least some devices are connected to the apparatus  200  directly. The data stored in the devices may be read out and be transmitted to the apparatus  200 . Although a battery is used, the battery lifetime may be extremely long since the battery power is consumed only when it is triggered by an external RF power. The ad hoc communication network  702  provides additional communication capability and flexibility in comparison to a conventional RFID system. 
     While the invention has been disclosed with respect to a limited number of embodiments, numerous modifications and variations will be appreciated by those skilled in the art. It is intended that all such variations and modifications fall within the scope of the following claims: