JP2010239227A - Host device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a host device which is coupled via a wireless network to n pieces of client device groups, constitutted of a first client device and i-th client device (i is an integer of 2≤i≤n, n is an integer of ≥2) which respectively send sensor data at sensing intervals Ts, in a steady state. <P>SOLUTION: A host device calculates a waiting term Twi, based on a first time t1 at which sensor data from a first client device are received in an initial state, an i-th time ti (the time ti is later than the time t1), at which the sensor data from the i-th client device are received in an initial state, the sensing intervals Ts and a number n, and instructs the i-th client device to send sensor data, after waiting for the waiting term Twi, and thus, in a steady state, sensor data from the first client device and the i-th client device can be received, at equal intervals on the time base by a host device. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates generally to a network optimization method, and more particularly to an apparatus and method for reducing network traffic bias by a host device on a wireless sensor network.

  There is a need to wirelessly collect data from client devices (also referred to as clients, slave units, and end nodes, for example, measurement devices) using a wireless sensor network. As an example, there is a measuring device network in which N clients (N is a natural number) are connected to one host device (also referred to as host, base unit, or base station node) via a wireless network. In the present specification, for simplicity, the client device is referred to as a “client” and the host device is referred to as a “host”.

The client typically sends sensor data to the host.
JP 2008-34945 A

  Assume that each client sends sensor data to the host at the same sensing interval. When the client is turned on, the client starts sending sensor data to the host at a constant sensing interval. In general, the timing at which the client is turned on is arbitrary. For this reason, the timings at which a plurality of clients send sensor data are often not equally spaced on the time axis. In other words, the timing at which the client sends sensor data tends to be biased.

  The present invention has been made in view of this point, and an object of the present invention is to provide a host device that reduces the unevenness of traffic of sensor data on a network.

  According to the present invention, in a steady state, the number n of first client devices and i-th client devices (i is an integer satisfying 2 ≦ i ≦ n and n is an integer satisfying n ≧ 2) each transmitting sensor data at a sensing interval Ts. A host device coupled to a group of client devices via a wireless network receives a first time t1 when the sensor data from the first client device is received in an initial state, and the sensor data from the i-th client device. Is calculated based on the i-th time ti (time ti is later than the time t1), the sensing interval Ts, and the number n, and the i-th client device receives the standby period Twi. By instructing to send the sensor data after waiting for Twi, in the steady state, the first client machine And said sensor data from said i-client device to be received by substantially the host device at regular intervals on the time axis.

  In one embodiment, the waiting period Twi is expressed as Twi = Ts− (ti−t1) + Ts · (i−1) / n.

  In one embodiment, when a command for the i-th client device is generated, the host device stores the command, and substantially responds to the sensor data sent from the i-th client device and substantially acknowledges the sensor data. At the same time, the command is sent to the i-th client device.

  In one embodiment, the host device deletes the stored command in response to an acknowledgment for the command sent from the i-th client device.

  According to the present invention, the number n of the first client device and the i-th client device (i is an integer of 2 ≦ i ≦ n and n is an integer of n ≧ 2) that sends sensor data at the sensing interval Ts in a steady state. A host device coupled to a group of client devices via a wireless network includes a first time t1 when sensor data from the first client device is received in an initial state during a waiting period Twi, and the i-th client device. From the i-th time ti (time ti is later than the time t1) at which the sensor data from the device is received in the initial state, the sensing interval Ts, and the number n, In the steady state, the first client is instructed to send the sensor data after waiting for a waiting period Twi. And a step of vessels and said sensor data from said i-client device to be received by the host device at regular intervals on the time axis.

  In accordance with the present invention, a host is coupled to a plurality of clients via a wireless network. The host sends a wait request instructing each client to wait for a waiting period before sending sensor data during the initial state. After waiting for a predetermined waiting period (that is, in a steady state), the client sends sensor data to the host at a constant sensing interval. The timing at which the client sends the sensor data is arranged at substantially equal intervals on the time axis by the host. Therefore, the network traffic resulting from sensor data from the client to the host is eliminated or at least reduced. In other words, network traffic is evenly distributed. This can reduce the possibility of packet loss due to packet collision.

  According to an embodiment of the present invention, the host that has received the sensor data sends the stored command to the client along with an acknowledgment for the sensor data. As a result, a command can be sent to a client (also called a terminal node) within a sensing interval at the longest, although not in real time. Here, since the client is normally in the sleep state, the influence on the battery life of the client can be minimized.

  Exemplary embodiments of the invention are described in detail below with reference to the drawings. The same reference signs represent the same component or corresponding components in different embodiments.

(System overview)
FIG. 1 is a schematic diagram of a system 100 using an exemplary embodiment of the present invention. System 100 is an ad hoc wireless sensor network. This system 100 is configured such that a small wireless sensor terminal in the vicinity spontaneously constructs a network. The system 100 includes a host 110, a PC (personal computer) 120, and clients 130, 140, 150, and 160. In this embodiment, four clients are provided, but the number of clients is not limited to this. The host 110 is also called a base station node, and the clients 130, 140, 150, 160 are also called end nodes.

  The client 130 includes an RF (High Frequency) unit 134 and a sensor 135. The client 140 includes an RF unit 144 and a sensor 145. The client 150 includes an RF unit 154 and a sensor 155. The client 160 includes an RF unit 164 and a sensor 165.

  Host 110 is coupled to RF unit 134 via wireless link 133. Host 110 is coupled to RF unit 144 via wireless link 143. Host 110 is coupled to RF unit 154 via wireless link 153. Host 110 is coupled to RF unit 164 via wireless link 163.

  The wireless links 133, 143, 153, and 163 may be, for example, a short-range wireless network that conforms to IEEE 802.15.4 using the 2.4 GHz band. This IEEE 802.15.4 is one of wireless communication standards called PAN (Personal Area Network) or WPAN (Wireless Personal Area Network), and has low cost, low power consumption, high reliability and security. The wireless links 133, 143, 153, and 163 are not limited to the specific wireless networks described above, and can be any suitable network that can typically exchange information in the form of packets.

  According to an embodiment, a wireless network comprised of wireless links 133, 143, 153, 163 may communicate between host 110 and RF units 134, 144, 154, 164 via intermediate nodes. The intermediate node may be realized by the RF units 134, 144, 154, 164. That is, each RF unit also has an automatic relay function, and can detect a communication environment and configure a network spontaneously. The exemplary network is a true mesh and the number of hops is virtually unlimited. In other words, embodiments of the present invention can use multi-hop wireless networks.

  The RF units 134, 144, 154, 164 can be coupled to the sensors 135, 145, 155, 165, respectively, for example by wire. Specifically, the RF units 134, 144, 154, and 164 can be connected to the sensors 135, 145, 155, and 165, respectively, by a UART (Universal Asynchronous Receiver Transmitter) or the like.

  The sensors 135, 145, 155, 165 can be any suitable sensor. Such sensors include, but are not limited to, temperature sensors, humidity sensors, acceleration (impact) sensors, optical sensors, and the like. The sensors 135, 145, 155, and 165 output data (“sensor data”) representing mechanical, electromagnetic, thermal, acoustic, and chemical parameters (eg, temperature).

  Sensor data can be represented by analog or digital signals. For example, sensor data representing temperature, which is a thermal parameter, can be expressed by a 10-bit (1024 step) digital signal. The sensors 135, 145, 155, and 165 send sensor data to the RF units 134, 144, 154, and 164, respectively. When the sensor data is an analog signal, an A / D (analog-digital) converter provided in the RF units 134, 144, 154, and 164 may convert the analog sensor data into digital sensor data.

  The RF units 134, 144, 154, and 164 generate wireless signals by encoding and modulating sensor data received from the sensors 135, 145, 155, and 165, respectively. The RF units 134, 144, 154, and 164 send the wireless signals to the host 110 via the wireless links 133, 143, 153, and 163, respectively. There are various schemes for encoding and modulating a radio signal. In a specific embodiment, a scheme conforming to the above-mentioned IEEE 802.15.4 is used.

  The host 110 obtains sensor data by demodulating and decoding the radio signals received from the RF units 134, 144, 154, 164. The host 110 sends the obtained sensor data to the PC 120. The PC 120 is coupled to the host 110 by, for example, a wired connection. Specifically, the PC 120 can be connected to the host 110 via a USB (Universal Serial Bus) or the like.

  The PC 120 can visually display or statistically process sensor data using, for example, software including a GUI (graphical user interface). Such software can perform, for example, confirmation of communication status, numerical display of sensor data, graph display, distribution color mapping of sensor values, recording of sensor data, export of sensor data, change of terminal settings, and the like.

(Waiting request)
FIG. 2 is a diagram illustrating a procedure 200 employed by an exemplary embodiment of the present invention. In this specification, the terms “sensor data”, “waiting request (also called a wait request)”, “ACK (acknowledge)”, and “command” indicating the type of a packet refer to messages representing the respective types. These messages can be composed of single or multiple packets. Packets can be transmitted over a wireless or wired network. In this specification, for example, “the host sends a standby request to the client” means “the host device sends a packet indicating a“ standby request ”to the client device”.

  Such a packet may represent each packet type using, for example, two bits of one byte in its header. For example, the “standby request” can be expressed by setting the first 2 bits representing the packet type to “11” in the packet header.

(Timing adjustment in the initial state)
In the initial state S1, the host 110 adjusts the timing at which the clients 140, 150, and 160 send sensor data to the host 110. Once the timing adjustment is made for each client, in the subsequent steady state S2, each of the clients 130, 140, 150, 160 sends sensor data to the host 110 at a constant sensing interval Ts. By adjusting the timing in the initial state S1, in the steady state S2, the sensor data that the clients 130, 140, 150, and 160 send to the host 110 are arranged at equal intervals on the time axis. The periods P12, P23, P34, and P41 are all equal. In other words, among the times when the host 110 receives sensor data from the clients 130, 140, 150, and 160, the time period between two adjacent times on the time axis is equal.

  Ideally, once the timing at which the client 140, 150, 160 sends sensor data to the host 110 is adjusted in the initial state S1, the sensor that the client 130, 140, 150, 160 sends to the host 110 in the subsequent steady state S2. Data is always arranged at equal intervals on the time axis. However, in actuality, the timing at which sensor data is sent may deviate with time. In such a case, the timing adjustment in the initial state S1 may be performed periodically (that is, at regular intervals).

  The timing adjustment interval may be appropriately determined according to the amount of deviation of the transmission time of the sensor data. Specifically, when the timing at which sensor data is transmitted is likely to be shifted, for example, the host 110 may generate the initial state S1 once a day to adjust the timing. On the other hand, if the timing at which the sensor data is transmitted is difficult to shift, the host 110 may generate the initial state S1 once a week, for example, and adjust the timing.

  Alternatively, the timing adjustment in the initial state S1 may be performed at any time when the host 110 determines that the timing of the sensor data sent by the clients 130, 140, 150, and 160 is no longer equidistant on the time axis. . Specifically, it may be determined whether or not the difference between any two periods P12, P23, P34, and P41 is greater than a predetermined threshold. When it is larger than the predetermined threshold value, timing adjustment is necessary. Therefore, the initial state S1 is provided and the timing adjustment is executed. This threshold value can be appropriately determined according to how much traffic concentration the network of the system 100 allows.

  Clients 130, 140, 150, and 160 are also referred to as a first node, a second node, a third node, and a fourth node, respectively. The number of clients is arbitrary, and in general, the host device 110 can be connected to n client devices from the first client device to the nth client device (n is an integer of n ≧ 2). In this case, an arbitrary client device can be expressed as an i-th client device (i is an integer of 2 ≦ i ≦ n and n is an integer of n ≧ 2). The i-th client device is also simply called an i-th node.

(Calculation of client waiting period)
In procedure 200, host 110 receives sensor data from first client 130 at time t1. The host 110 receives the sensor data from the second client 140 at time t2. The host 110 receives the sensor data from the third client 150 at time t3. The host 110 receives the sensor data from the fourth client 160 at time t4.

  Using time t1 as a reference, period p2 = time t2−time t1 (≧ 0), period p3 = time t3−time t1 (≧ 0), and period p4 = time t4−time t1 (≧ 0). As will be described later, the host 110 determines the waiting period 140Tw of the client 140 based on the period p2. The host 110 determines the waiting period 150Tw of the client 150 based on the period p3. The host 110 determines the waiting period 160Tw of the client 160 based on the period p4.

  In order to adjust the timing, the host 110 sends back a standby request 140w to the client 140 in response to the sensor data 140d1 from the client 140. Based on this standby request 140w, the client 140 waits for the standby period 140Tw before sending the next sensor data 140d2 to the host 110.

  The host 110 performs the same timing adjustment for other nodes. That is, the host 110 sends back a standby request 150 w to the client 150 in response to the sensor data 150 d 1 from the client 150. Based on this standby request 150w, the client 150 waits for the standby period 150Tw and then sends the next sensor data 150d2 to the host 110. In response to the sensor data 160 d 1 from the client 160, the host 110 sends back a standby request 160 w to the client 160. Based on this standby request 160w, the client 160 waits for the standby period 160Tw before sending the next sensor data 160d2 to the host 110.

The waiting period Tw (for example, 140 Tw, 150 Tw, 160 Tw)
Tw = Ts−pi + Ts · (i−1) / n
It can be expressed as. Here, Ts is a sensing interval, pi is a reception time difference of the i-th node, i is a node number, and n is the number of nodes (that is, the number of client devices).

More generally, the waiting period Twi of the i-th client device is
Twi = Ts− (ti−t1) + Ts · (i−1) / n
It can be expressed as. Here, t1 is the first time when sensor data from the first client device is received in the initial state, and ti is the i time when sensor data from the i-th client device is received in the initial state.

  For example, when the sensing interval is 60 seconds, the reception time difference p2 is 20 seconds, and the number of nodes is 4, the waiting period 140Tw for the client 140 (that is, the second node) as the second client device is 140Tw = 60 seconds−20 seconds + 60 seconds · (2-1) / 4 = 60 seconds−20 seconds + 15 seconds · 1 = 55 seconds. That is, the client 140 may wait for 55 seconds after sending the sensor data 140d1 and send the next sensor data 140d2.

  Similarly, the host 110 instructs the clients 150 and 160 to wait for waiting periods 150 Tw and 160 Tw, respectively. If the reception time difference p3 of the client 150 is 40 seconds, the waiting period 150Tw is 150Tw = 60 seconds−40 seconds + 60 seconds · (3-1) / 4 = 60 seconds−40 seconds + 15 seconds · 2 = 50 seconds. . If the reception time difference p4 of the client 160 is 35 seconds, the waiting period 160Tw is 160Tw = 60 seconds−35 seconds + 60 seconds · (4-1) / 4 = 60 seconds−35 seconds + 15 seconds · 3 = 70 seconds. . That is, the clients 150 and 160 may wait for 50 seconds and 70 seconds after sending the sensor data 150d1 and 160d1, respectively, and send the next sensor data 150d2 and 160d2.

  With the timing adjustment described above, the clients 130, 140, 150, and 160 can send sensor data to the host 110 at regular intervals on the time axis. In the above example, the periods P12, P23, P34, and P41 are all (sensing interval Ts) / (number of nodes n) = 60 seconds / 4 = 15 seconds.

  More generally, the waiting period is not limited to the above equation. The host 110 may set the standby period so that sensor data from each node is arranged at equal intervals on the time axis.

  In FIG. 2, for convenience of illustration, it is illustrated that it takes a considerable time from when the client 140 sends the sensor data 140 d 1 to when it receives the standby request 140 w from the host 110. For example, it is assumed that the sensing interval Ts is 1 minute and the time required for one round trip between the client 140 and the host 110 is, for example, on the order of several tens of ms. In such a case, it can be said that the period from when the client 140 sends the sensor data 140d1 until it receives the standby request 140w from the host 110 is negligibly small compared to the sensing interval Ts.

(Send command to client)
FIG. 3 is a diagram illustrating an example of a procedure in which the host sends a command to the client in the embodiment of FIGS. 1 and 2. The host 110 according to the embodiment of FIGS. 1 and 2 may send a command to the client (eg, client 130 in FIG. 3) by the procedure 300 of FIG. 3, but is not limited to this particular procedure and other procedures. May send the command to the client. Alternatively, the host 110 according to the embodiment of FIGS. 1 and 2 may not send commands to the client. The client 130 of FIG. 3 is an example, and may be any of the other clients 140, 150, 160 of FIG.

  In the procedure 300, the power source of the host 110, which is a base station node, is normally on. That is, in the period PonB, the host 110 is kept on.

  The power supply of the client 130 which is a terminal node transmits sensor data until receiving an ACK (for example, Pon1 in FIG. 3), or receives sensor command and then receives an ACK command and transmits ACK data. (For example, Pon2 in FIG. 3) is in an on state. The time axes PonB, Pon1, and Pon2 drawn boldly in FIG. 3 indicate that the host or client is powered on. A time axis Poff1 illustrated in a thin line in FIG. 3 indicates that the power supply of the client is in an off state (sleep state).

  The sleep state is provided to increase the battery duration by reducing power consumption. Normally, the host 110 is supplied with power from an outlet that is an AC (alternating current) power supply or an AC adapter connected to the outlet. However, the present invention is not limited to this, and the host 110 may provide a sleep state.

  Clients 130, 140, 150, and 160, which are end nodes, are usually driven by batteries, and in this case, a sleep state is usually provided. However, the clients 130, 140, 150, and 160 are not limited to this, and the sleep state may not be provided if a power source other than the battery (for example, AC power source) is used.

  The client 130 sends the sensor data 130D1 to the host 110. The host 110 sends an acknowledgment (ACK) 130A1 indicating that the sensor data 130D1 has been received to the client 130. The client 130 turns off the power after receiving the ACK 130A1. Therefore, the client 130 is in the power-on state during the period Pon1, and is in the off-state during the period Poff1 until the next power-on.

  A command CMD is generated in the host 110 at time tc. Examples of the command CMD include a command for requesting to change the transmission interval, a command for requesting to change the routing of the wireless network (that is, the path of the communication path), and the status of the end node (battery voltage, etc.). The command to request is listed. When the command CMD is generated, the host 110 associates the command CMD with the destination node 130 and stores the command CMD in a storage unit that forms a command queue in the host 110, for example. The command queue can be constituted by, for example, a RAM (Random Access Memory).

  After the time tc, after the period Poff1 in the sleep state ends, the power of the client 130 is turned on again during the period Pon2.

  The client 130 sends the sensor data 130D2 to the host 110. At this time, the host 110 sends the ACK 130A2 for the sensor data 130D2 and the stored command CMD to the client 130. The ACK 130A2 and the stored command CMD are typically sent over the wireless network by being included in a single packet. However, the present invention is not limited to this, and can be sent on the network by any appropriate method as long as they are sent substantially simultaneously.

  Specifically, the command CMD may be a command ID (identifier) representing one of various commands. Such a command ID can be expressed by, for example, 1-byte data. The ACK 130A2 only needs to be able to indicate whether or not the host 110 has received the sensor data 130D2, and can be expressed by, for example, 1-bit data (also referred to as a flag).

  Upon receiving the ACK 130A2 and the command CMD, the client 130 sends an ACK 130A3 for the command CMD to the host 110. The ACK 130A3 only needs to be able to indicate that the client 130 has received the command CMD, and can be expressed by, for example, 1-bit data.

  The command CMD may not require a response to it. For example, if the command CMD requests to change the sensor data transmission interval, the client 130 only changes the setting of the timer, for example, in order to change the sensor data transmission interval, and does not send a response to the host.

  On the other hand, the command CMD may require a response to it. For example, if the command CMD requests to notify the battery voltage, the client 130 sends data 130D3 representing the battery voltage to the host 110. Data 130D3 is not limited to this, and may generally be any suitable response corresponding to command CMD. The data 130D3 only needs to be able to represent a response (for example, data corresponding to a variable such as a physical quantity) corresponding to the command CMD, and can be represented by, for example, 1-byte data. ACK 130A3 and data 130D3 are typically sent in a single packet, but are not limited to this and can be sent in any suitable manner as long as they are sent substantially simultaneously.

  When the command CMD is sent from the host 110 to the client 130, the client 130 sends at least an ACK 130A3. However, data 130D3 may or may not be sent depending on the type of command CMD.

  At time td, host 110 receives ACK 130A3 (and possibly data 130D3). Since ACK 130A3 indicates that the client 130 has received the command CMD, the host 110 recognizes that the processing of the command CMD has been completed. Specifically, the host 110 deletes the command CMD from the command queue in which the command CMD is stored.

  When the command for the client 130 is not generated, the client 130 does not send the ACK 130A3 and the data 130D3 to the host 110. In this case, the client 130 does not need to secure time for sending the ACK 130A3 and the data 130D3 to the host 110. Therefore, the period Pon1 is generally shorter than the period Pon2.

  According to the procedure 300, the client 130 can send a response to the command CMD to the host at the sensing interval at the longest. Such a response to the host is not necessarily real time, but it can respond to the host at the sensing interval at the longest. Therefore, the client 130 can periodically respond to the host while realizing power saving.

  For example, the periods Pon1 and Pon2 are on the order of 10 ms to 1 s, depending on the embodiment. When a relay node exists between the client 130 and the host 110 (for example, a few hops), the periods Pon1 and Pon2 are on the order of several tens of ms. When there is heavy traffic, the periods Pon1 and Pon2 can be on the order of 1 second. The period Poff1 may be on the order of 1 s, for example, but may be set to an appropriate value according to a specific implementation example.

  If the procedure 300 is used, for example, it is possible to operate the client device with two AA batteries for six months.

(Client hardware)
FIG. 4 is a block diagram of a client 130 used for an exemplary embodiment of the invention. The client 130 includes an RF unit 134, a sensor 135, and an antenna 430. The sensor 135 outputs sensor data to the RF unit 134. The RF unit 134 converts the sensor data output from the sensor 135 into a radio signal and sends the radio signal to the host 110 from the antenna 430. The sensor 135 may be a measuring device.

  The RF unit 134 includes a sensor interface 440, a DC (direct current) power supply 445, an MCU (micro controller unit) 450, a ROM (read only memory) 452, a RAM (random access memory) 454, a timer 456, a wireless transmission / reception unit 458, and an RF. An interface 460 is included. The sensor interface 440 converts the sensor signal output by the sensor 135 into an appropriate signal (for example, a 10-bit digital signal) that can be processed by the MCU 450. The DC power source 445 supplies a DC power source to each functional block of the RF unit 134. The DC power source 445 can be, for example, a lithium battery that supplies a direct current of 3V.

  The MCU 450 is a microprocessor that is used to realize the functions of the client 130. The MCU 450 stores a program and data necessary for realizing the function of the client 130 in the ROM 452 or the RAM 454. The timer 456 measures the timing of turning off the power, for example, and triggers the MCU 450 to cut off the power supply from the DC power supply 445 when a predetermined time has elapsed. MCU 450 may include peripheral elements such as ROM 452, RAM 454, and timer 456 therein. In this case, the cost for constructing the system can be reduced as compared with the case where a ROM or the like is mounted as an independent component.

  The wireless transmission / reception unit 458 converts data from the MCU 450 into a response packet to be sent to the host 110 or converts a request packet received from the host into data. The RF interface 460 converts the packet output from the wireless transmission / reception unit 458 into an RF signal and outputs the RF signal to the antenna, reproduces the packet from the RF signal received by the antenna, and outputs the packet to the wireless transmission / reception unit 458.

  The clients 140, 150 and 160 have the same configuration as the client 130 shown in FIG.

(Host hardware)
FIG. 5 is a block diagram of a host 110 used for an exemplary embodiment of the invention. The host 110 includes an RF unit 510 and an antenna 530. In general, the host 110 may communicate with any of a plurality of clients. In the following description of the present specification, it is assumed that the host 110 communicates with the client 130. However, communication may be performed with the clients 140, 150, and 160 which are other clients.

  The RF unit 510 converts a request for the client 130 into a radio signal and sends the request to the client 130 from the antenna 530. The RF unit 510 converts the response from the client 130 received by the antenna 530 into data, and sends the data to the PC 120 via the interface 540.

  The RF unit 510 includes an interface 540, a power supply 545, an MCU 550, a ROM 552, a RAM 554, a timer 556, a wireless transmission / reception unit 558, and an RF interface 560. The interface 540 converts various signals output by the PC 120 into appropriate signals (for example, 8-bit digital signals) that can be processed by the MCU 550. The power source 545 supplies DC power to each functional block of the host 110. The power source 545 receives, for example, 100V AC supplied from a household AC (AC) power outlet, converts it to DC 3V, and supplies DC voltage to each block.

  The MCU 550 is a microprocessor that is used to realize the functions of the host 110. The MCU 550 stores programs and data necessary for realizing the functions of the host 110 in the ROM 552 or the RAM 554. The timer 556 measures a timeout time 230, for example, and triggers the MCU 550 to transmit a request cancellation when a predetermined time has elapsed. MCU 550 may include peripheral elements such as ROM 552, RAM 554, and timer 556 therein. In this case, the cost for constructing the system can be reduced as compared with the case where a ROM or the like is mounted as an independent component.

  The wireless transmission / reception unit 558 converts data from the MCU 550 into a request packet or a request cancellation packet to be sent to the client, or converts a response packet received from the client into data. The RF interface 560 converts the packet output from the wireless transmission / reception unit 558 into an RF signal and outputs the RF signal to the antenna, reproduces the packet from the RF signal received by the antenna, and outputs the packet to the wireless transmission / reception unit 558.

  The embodiments of the present invention have been described in detail above.

  Hosts and clients according to embodiments of the present invention can typically be realized by a group of circuit elements including semiconductor elements mounted on a substrate. Typically, the host 110 and the clients 130, 140, 150, and 160 are realized by a combination of an analog circuit that handles an analog signal from a sensor and a high-frequency signal for a wireless network, and a digital circuit whose main element is an MCU. Can be done.

  The control of the host device according to the present invention can typically be realized by software. That is, the procedure shown in FIG. 2 can typically be implemented by software stored on a computer readable medium. Examples of the computer readable medium include a hard disk drive and a semiconductor memory. Alternatively, procedures according to embodiments of the present invention may be implemented by a combination of software and hardware, or only by hardware. Control of client devices according to embodiments of the present invention may also typically be implemented by software.

  A part or all of the functional block groups shown in FIGS. 4 and 5 may be integrated and realized by being appropriately combined. For example, the RF unit 134 may be realized as a hybrid IC (integrated circuit). Further, for example, the client 130 may be realized by integrating the RF unit 134, the sensor 135, and the antenna 430 on one substrate.

  The present invention is not limited to the embodiments, and can be implemented in various other forms without departing from the spirit or main features thereof.

  As described above, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. The scope of the present invention is defined by the claims, and is not limited by the specification. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the present invention is particularly useful for a host / client system using a wireless sensor network.

1 is a schematic diagram of a system using an exemplary embodiment of the present invention. FIG. 6 illustrates a procedure employed by an exemplary embodiment of the present invention. FIG. 3 is a diagram illustrating an example of a procedure in which a host sends a command to a client in the embodiment of FIGS. 1 and 2. FIG. 4 is a block diagram of a client used for an exemplary embodiment of the present invention. FIG. 4 is a block diagram of a host used for an exemplary embodiment of the invention.

200 Procedure 110 Host 130, 140, 150, 160 Client 130d1, 140d1, 150d1, 160d1 Sensor data 140w, 150w, 160w Standby request S1 Initial state S2 Steady state Ts Sensing interval 140Tw, 150Tw, 160Tw Standby period

Claims (5)

In a steady state, the number n of client devices each composed of a first client device and an i-th client device (i is an integer of 2 ≦ i ≦ n and n is an integer of n ≧ 2) each sending sensor data at a sensing interval Ts. A host device coupled to a group via a wireless network,
The host device is
A first time t1 when the sensor data from the first client device is received in an initial state;
I-th time ti (time ti is later than time t1) when the sensor data from the i-th client device is received in the initial state;
The sensing interval Ts;
A waiting period Twi is calculated based on the number n,
Instructing the i-th client device to send the sensor data after waiting for the waiting period Twi, in the steady state, the sensor data from the first client device and the i-th client device is A host device that is received by the host device at substantially equal intervals above.   The host device according to claim 1, wherein the waiting period Twi is represented by Twi = Ts− (ti−t1) + Ts · (i−1) / n. The host device is
When a command for the i-th client device is generated, the command is stored,
3. The command according to claim 1, wherein, in response to sensor data sent from the i-th client device, the command is sent to the i-th client device substantially simultaneously with an acknowledgment of the sensor data. 4. Host equipment. The host device is
4. The host device according to claim 3, wherein the stored command is deleted in response to an acknowledge for the command sent from the i-th client device. In a steady state, wirelessly transmits a group of n client devices including a first client device and an i-th client device (i is an integer of 2 ≦ i ≦ n and n is an integer of n ≧ 2) that sends sensor data at a sensing interval Ts. A method of controlling a host device coupled via a network,
The waiting time Twi is a first time t1 when sensor data from the first client device is received in an initial state, and
I-th time ti (time ti is later than time t1) when sensor data from the i-th client device is received in the initial state;
The sensing interval Ts;
Calculating based on the number n;
Instructing the i-th client device to send the sensor data after waiting for the waiting period Twi, in the steady state, the sensor data from the first client device and the i-th client device is And receiving at a regular interval by the host device.

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