Abstract:
Disclosed is a telemetering system that comprises a wireless base station and a number of wireless sensor nodes. Each wireless sensor node includes a solar cell, a sensor for producing observation data indicating a quantity being measured, a wireless interface for receiving the observation data from the sensor when the node is activated, and a time-schedule memory for storing time-schedule data. Control circuitry briefly activates its own node by supplying power from the solar cell to the wireless interface at periodic intervals according to the time-schedule data of the memory and briefly establishes a wireless link to the base station. During the time the wireless link is briefly established, the control circuitry of each node transmits the observation data to the base station and updates its time-schedule memory if it receives time-schedule data from the base station.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to telemetering systems, and more specifically to a wireless telemetering system in which observation data from remote sensor nodes are wirelessly collected at a central location at periodic intervals for power saving purposes. 
   2. Description of the Related Art 
   A known telemetering system comprises a plurality of wireless modules to perform measurement of physical quantities at remote locations. For power saving purposes, each sensor module is provided with a time-keeping device and the current time supplied from the device is constantly compared to power saving time-schedule. When the current time of day coincides with each successive instant of the time schedule, the sensor module is activated briefly and transmits a signal indicating a quantity being measured. Since the prior art sensor modules were designed to meet strict specifications that they must be of small design for less power consumption and be as less complex as possible for unattended operation, the power saving time schedule were manually set in each of the sensor modules at the time the system is initially started. Once the telemetering system became operational, it was impossible to update the time schedule of the remote sensor modules. 
   However, there is a need to control the power saving time schedule of each remote sensor module from a central location in a flexible manner. Further, there exists a need for controlling the sensor module to alter its process of measurement from the central location. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a telemetering system in which the power saving time schedules of a plurality of wireless sensor nodes are set and controlled by a wireless base station when each sensor node is briefly activated. 
   According to a first aspect of the present invention, there is provided a telemetering system comprising a wireless base station and a plurality of wireless sensor nodes, each wireless sensor node including a power source, a sensor for producing observation data indicating a quantity being measured, a wireless interface for receiving the observation data from the sensor when the wireless sensor node is activated, a time-schedule memory for storing time-schedule data, and control circuitry for briefly activating the wireless sensor node by supplying power from the power source to the wireless interface at periodic intervals according to the time-schedule data of the memory to establish a wireless link to the base station, and updating the time-schedule memory according to time-schedule data received through the briefly established wireless link and transmitting the observation data from the activated wireless interface to the base station. 
   According to a second aspect of the present invention, there is provided a method of operating a plurality of wireless sensor nodes from a wireless base station, wherein each of the wireless sensor nodes includes a sensor for producing observation data indicating a quantity being measured, a wireless interface for establishing an individual wireless link to the base station when the wireless interface is activated, and a time-schedule memory, the method comprising, in each of the wireless sensor nodes, (a) establishing a wireless link between the wireless base station and the sensor node and setting time-schedule data from the base station into the time-schedule memory, (b) briefly activating the wireless sensor node by supplying power from a power source to the wireless interface at periodic intervals according to the time-schedule data of the time-schedule memory to establish a wireless link to the base station, (c) determining, at the briefly activated sensor node, whether time-schedule data is received from the base station, (d) if time-schedule data is received from the base station, updating the time-schedule memory with the received time-schedule data, (e) transmitting the observation data from the briefly activated sensor node to the base station, and (f) receiving the transmitted observation data at the base station. 
   According to a third aspect of the present invention, there is provided a method of operating a plurality of wireless sensor nodes from a wireless base station, wherein each of the wireless sensor nodes includes a sensor for producing observation data indicating a quantity being measured, a wireless interface for establishing an individual wireless link to the base station when the wireless interface is activated, and a time-schedule memory, the method comprising, in each of the sensor nodes, the steps of (a) establishing a wireless link between the wireless base station and the sensor node and setting time-schedule data from the base station into the time-schedule memory of the sensor node, (b) briefly activating the sensor node by supplying power from a power source to the wireless interface at periodic intervals according to the time-schedule data of the time-schedule memory to establish a wireless link to the base station, (c) transmitting a command packet from the base station to each of the briefly activated the sensor nodes, (d) receiving the command packet at each of the briefly activated sensor nodes, (e) determining, in each of the briefly activated sensor nodes, whether the command packet contains time-schedule data, (f) if the time-schedule data is contained in the command packet, updating the time-schedule memory of each the sensor node, (g) transmitting the observation data from each of the briefly activated sensor nodes to the base station, and (h) receiving, at the base station, the observation data transmitted from each of the briefly activated sensor nodes. 
   Preferably, each of the wireless sensor nodes comprises a node memory for storing an upstream node identifier and at least one downstream node identifier, and wherein the method further comprises, in each of the wireless sensor nodes, the steps of (1) determining whether the command packet is destined for a downstream wireless sensor node, (2) if the command packet is destined for the downstream wireless sensor node, (3) determining whether the command packet contains node identifiers corresponding to the node identifiers stored in the node memory, and (4) if the command packet contains the corresponding node identifiers, forwarding the command packet to the downstream wireless sensor node. 
   According to a fourth aspect of the present invention, there is provided a wireless sensor node for a telemetering system including a wireless base station which transmits power saving time-schedule data to a plurality of wireless sensor nodes, wherein the wireless sensor node is one of the plurality of wireless sensor nodes, the sensor node comprising a power source, a sensor for producing observation data indicating a quantity being measured, a wireless interface for receiving the observation data from the sensor when the wireless interface is activated, a time-schedule memory for storing time-schedule data, and control circuitry for briefly activating the wireless sensor node by supplying power from the power source to the wireless interface at periodic intervals according to the time-schedule data of the memory to establish a wireless link to the base station, and updating the time-schedule memory according to time-schedule data received from the base station through the established wireless link and transmitting the observation data from the activated wireless interface to the base station through the established wireless link. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in detail further with reference to the following drawings, in which: 
       FIG. 1  is a block diagram of a wireless telemetering system of the present invention; 
       FIG. 2  is a block diagram of each of the wireless sensor nodes of the present invention; 
       FIG. 3  is an illustration of the data structures of packets of different types transmitted from the base station; 
       FIG. 4  is a flowchart of the operation of the packet processor of  FIG. 2  during the time the system is initialized; 
       FIG. 5  is a flowchart of the operation of the power controller of  FIG. 2  for briefly activating the associated packet processor and the wireless interface for power saving purposes; 
       FIG. 6  is a timing diagram of the telemetering system when each sensor node is activated according to one embodiment of the present invention; 
       FIG. 7  is a timing diagram of the telemetering system when each sensor node is activated according to another embodiment of the present invention; 
       FIG. 8  is a flowchart of the operation of the packet processor when activated by the power controller to receive a command packet from the base station and transmit observation data to the base station; 
       FIG. 9  is a block diagram of the wireless base station; and 
       FIG. 10  is a flowchart of the operation of the wireless base station. 
   

   DETAILED DESCRIPTION 
   In  FIG. 1 , a wireless telemetering network of the present invention comprises a wireless base station or data collection center  10  and a plurality of groups  11 ,  12 ,  13  and  14  of wireless sensor nodes located at distances from the base station. The sensor nodes of each group are indicated by the letters A, B and C appended to their group number. In each of the groups  11  to  14 , the sensor node A is nearest to the base station and the transmit power of the base station  10  is reachable only to these nearest sensor nodes  11 A,  12 A,  13 A and  14 A. Therefore, the base station  10  operates as an upstream node in the direction of its packet transmission, and in each group, the sensor node A operates as a repeater node for repeating the packet to the other nodes, or downstream nodes B and C. Likewise, in the opposite direction of transmission, the sensor node A repeats packets from the nodes B and C to the base station  10 . 
   As shown in detail in  FIG. 2 , each of the wireless sensor nodes includes a wireless transceiver or interface  20  that operates with an antenna  21  to establish a wireless link with a node that is within the reachable extent of the wireless interface  20 . A packet processor  22  is connected to the wireless interface  20  for routing the packet according to topology data transmitted from the base station  10  and setting node identifiers of upstream and downstream nodes in a node memory  23 . Additionally, the packet processor  22  provides the setting of power saving time-schedule data into a time-schedule memory  26 . Packet processor  22  is connected to a sensor  25  that processes the readings of a measurement instrument into a digital signal according to a measurement command from the base station. Packet processor  22  transmits the digital signal from the sensor  25  to the base station  10 . The measurement instrument may be a sunshine meter, a thermometer, an anemometer, and so on. For the purpose of disclosure, the following description proceeds with the assumption that the measurement instrument is a sunshine meter and the base station  10  is a data collection center for collecting the readings of the instruments and using the collected data for agricultural fieldwork. 
   Power saving controller  24  constantly compares current time of day supplied from a time-keeping device  27  to the time-schedule data stored in the time-schedule memory  26 . Preferably, the time-keeping device  27  is tuned to a radio channel broadcasting the local standard time, or configured to receive GPS (global positioning system) signals from GPS satellites to produce a high-precision time-of-day data. 
   The time-schedule data indicates the timing offset from a reference timing (the beginning of the day, for example) for initially activating the wireless interface  20  and the packet processor  22  via power lines  28  and  29 , respectively. The power saving time-schedule data further indicates a period between successive times at which both of the packet processor and the wireless interface are activated. Power saving controller  24  activates the packet processor and the interface for a predetermined interval sufficient to establish and maintain communication with the base station as well as with downstream nodes. 
   A power supply unit  30  is provided for receiving power from a solar cell  31  and supplies regulated power voltages to the power saving controller  24  and the time-keeping device  27  via power lines  32  and  33 , respectively. Depending on the type of measurement instrument used, the sensor  25  is constantly powered by the power supply unit  30  via a power line  34  or intermittently powered via a power line  35  under control of the power saving controller  24 . 
     FIG. 3  shows details of packets used in the telemetering system of the present invention. A routing packet and a power saving packet are used for transmission from the base station  10  at the time the network is initialized, and a command packet is used for transmission from the base station when each of the sensor nodes is briefly activated under control of its power saving controller  24 . Each of these packets includes a destination address (DA) field  41 , a source address (SA) field  42 , a packet type field  43 , and a payload field. The payload field of the routing packet contains topology data  44  indicating the topology of the network necessary for routing packets to and from the base station  10 . The payload field of the power saving packet contains timing offset data (T OFF )  45  and a period (T PER ) data  46 . The payload field of the command packet contains timing offset update data  47 , period update data  48  and measurement command data  49 . 
   The operation of packet processor  22  during the initialization of the system proceeds according to the flowchart of  FIG. 4 . 
   When all the wireless sensor nodes are deployed within the area of the system, the base station  10  transmits a routing packet and each sensor node is set in an active state to receive packets. In response to a routing packet (step  401 ), each of the repeater nodes  11 A,  12 A,  13 A,  14 A reads and examines topology data contained in it and sets the identifiers of its upstream nodes and its downstream nodes into the respective fields of the node memory  23  (step  402 ) and returns to the starting point of the routine. If no routing packet is received, the packet processor  22  checks to see if a power saving packet has been received (step  403 ). If so, the packet processor proceeds to decision step  404  to determine if the received packet is destined for the local node itself. If the decision is affirmative at step  404 , flow proceeds to step  407  to read the power saving data of the local node from the power saving packet (see  FIG. 3 ) and sets the timing offset value T OFF  and the period value T PER  into the time-schedule memory  26 . 
   If the received power saving packet is destined for a downstream node, the decision is negative at step  404  and flow proceeds to decision step  405  to determine whether the source and destination addresses of the received packet are respectively stored in the upstream and downstream fields of the node memory  23 . If this is the case, it is determined that the local node is a repeater node. Since the repeater node is responsible for timely activating itself for repeating packets between its upstream and downstream nodes, the packet processor proceeds from step  405  to step  406  to forward the packet to the downstream node and then at step  407  to read the power saving data of the downstream node from the packet and sets it into the time-schedule memory  26 . After executing step  407 , flow returns to the starting point of the routine. 
   After the telemetering system is initialized, the power controller  24  operates according to the flowchart of  FIG. 5 . 
   At step  501 , the power controller  24  reads the power saving data of its own node from the time-schedule memory  26  and determines the initial start timing “T” of the node by adding the timing offset value T OFF  to the timing reference T REF . At step  502 , the current time supplied from the time-keeping device  27  is compared to the determined initial start timing. When the current time becomes equal to the initial start timing, the decision at step  502  is affirmative and the power controller  24  proceeds to step  503  to activate the packet processor  22  and the wireless interface  20  and starts up a timer (step  504 ). When a predefined time-out period expires (step  505 ), the power controller  24  deactivates the packet processor and the wireless interface (step  506 ). At step  507 , the power controller  24  determines whether the activation of its own node is the last for the day. If the decision is negative, flow proceeds to step  508  to read the power saving data from the time-schedule memory  26  and the power controller determines the next start timing T by adding the period T PER  to the previous start timing T, and flow returns to step  502  to repeat the process for the next activation cycle. 
   If the current activation is the last one, flow proceeds from step  507  to decision step  509  to determine if the current time is equal to the reference timing T REF . If this is the case, flow returns to step  501  to repeat the routine all over again. 
   In this way, each sensor node is periodically activated for power saving purposes. If the timing offset is five minutes and the period between activations is one hour, the power saving controller  24  starts activating its packet processor and wireless interface at times of day 00:05, 01:05, 02:05, . . . , and so on. 
   When a sensor node is activated, it establishes communication with the base station for transmitting its measurement result and updating the power saving timing schedule if necessary, as will be described in detail later. Since each repeater node ( 11 A,  12 A,  13 A,  14 A) is required to forward a packet downstream when one of its downstream nodes is activated, the repeater node goes active simultaneously with the downstream node, as illustrated in  FIG. 6 . 
   Since sunshine meters are used in the illustrated embodiment, they are rendered inactive during the nighttime. To this end, the period data T PER  of each sensor node is updated by lengthening its value at the beginning of the nighttime so that each node is rendered inactive until the next early morning, whereupon the period data is updated again by shortening its value. 
   If there is no signal interference between adjacent groups, the sensor nodes of each group can be activated independently of those of adjacent groups. In this case, the sensor nodes of all groups can be operated in substantially the same activation time schedules. Specifically, all groups of sensor nodes use the same set of timing offset values as illustrated in  FIG. 6 . 
   However, if interference is likely to occur between adjacent groups, collisions may occur between transmitted packets. In such instances, it is preferable that all or adjacent groups use a different set of timing offset values as illustrated in  FIG. 7 . Specifically, the start timings of groups  11 ,  12 ,  13  and  14  are offset by 0, T1, T2 and T3, respectively. 
   When a sensor node is activated, the packet processor  22  of this node operates according to the flowchart of  FIG. 8 . 
   Since the base station  10  maintains the time-schedules of all sensor nodes of the system, it timely transmits a command packet to each sensor node during the time this sensor node is activated. 
   When a sensor node receives a command packet (step  801 ), the packet processor  22  checks to see if the packet is destined for the local node (step  802 ). If the packet is destined for the local node, flow proceeds to step  803  to determine whether the received packet contains a power saving update command or not. If the received packet contains a power saving update command, flow proceeds to step  804  to update the time-schedule memory  26  according to the power saving update command and proceeds to step  805  to read a measurement command from the received packet (step  805 ). At step  806 , the packet processor  22  instructs the sensor  25  to process the measured data according to the measurement command from the base station. More specifically, the sunshine meter produces an analog output signal, which is sampled at intervals and each sample value is then converted to a corresponding digital signal. Digital signals generated during a given interval of time are integrated, and then an average value is calculated by dividing the integrated value by the number of sample values generated in that given interval. The measurement command specifies the sampling interval, for example. 
   The processed observation data is transmitted to the base station  10  at step  807 . 
   If the received command packet is destined for another node, flow proceeds from step  802  to step  808  to look up the node memory  23  to determine whether the source and destination addresses of the received command packet are respectively stored in the upstream and downstream fields of the node memory  23 . If this is the case, it is determined that the local node is responsible for transmitting the packet to a downstream node and flow proceeds to step  809  to check to see if the packet contains a power saving update command. If so, flow proceeds to step  810  to update the time-schedule memory  26  according to the update command of the downstream node. At step  811 , the packet processor  22  transmits the received command packet to the downstream node. If no power saving update command is contained in the received command packet, step  810  is skipped. 
   If the decision at step  801  is negative, the packet processor proceeds to step  812  to determine whether an observation packet is received from a downstream node. If not, it returns to step  801  to monitor incoming packets. If an observation packet is received from a downstream node, the packet processor proceeds from step  812  to step  813  to forward a copy of the observation packet to the upstream node of the local node and returns to step  801 . 
   Details of the wireless base station  10  are shown in  FIG. 9 . The base station comprises a wireless interface  50  that operates with an antenna  51  to establish wireless links with all the wireless sensor nodes of the telemetering system. A control unit  52  is connected to the wireless interface  50  for transmitting and receiving packets to and from the remote sensor nodes. Connected to the control unit  52  is a time-schedule memory  53  in which a plurality of time-schedule data are mapped to the node identifiers of all wireless sensor nodes in respective entries. Where necessary, a plurality of time-schedule update data are additionally mapped to the node identifiers. A time-keeping device  54 , a display unit  55  and a keyboard  56  are connected to the control unit  52 . Time-schedule data and measurement commands are manually entered through the keyboard  56  and stored in respective entries of the memory  53 . 
   As shown in  FIG. 10 , the operation of the base station begins with step  1001  in which the control unit  52  reads time-schedule data from the first entry of the memory  53 . 
   At step  1002 , the control unit compares the current time supplied from the time-keeping device  54  to the read time-schedule data of the first node in the memory  53  for detecting a match (step  1003 ). When they coincide, flow proceeds to step  1004  to determine if time-schedule update data is present. If so, flow proceeds to step  1005  to transmit a command packet to the sensor node of the current entry, containing a measurement command and time-schedule update data. At step  1006 , the previous time-schedule data is replaced with the update data. At step  1007 , the base station receives an observation packet from the sensor node. At step  1008 , the control unit  52  checks to see if the last entry is reached in the memory  53 . If not, flow proceeds to step  1009  to read time-schedule data from the next entry of the memory  53  and returns to comparison step  1002 . 
   If no time-schedule update data is present, flow proceeds from step  1004  to step  1010  to transmit a command packet containing a measurement command, and proceeds to step  1007  to receive the returning observation packet. If the last entry is reached (step  1008 ), flow returns to step  1001 .