JP5227867B2 - Host device - Google Patents

Description

  The present invention relates to a host device, and more specifically to a host device used on a wireless sensor network.

  There is a need to wirelessly collect data from client devices using a wireless sensor network. An example is a measuring device network in which N clients (N: natural number) are connected to one host device 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 host requests measurement data from the client. The client responds to this request and sends measurement data to the host. The host does not request data to all clients at the same time, but sends a request message to each client in turn.
JP 2008-61227 A

  When wireless communication is performed between measurement devices, wireless packet loss may occur unlike wired communication. If packet loss occurs, the client resends the same packet. However, this retransmission packet increases traffic on the wireless network. As a result, it may cause further packet loss. The host must process more messages for the retransmitted packet. This increases the power consumed by the host processor.

  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 prevents an increase in retransmission packets on a wireless sensor network.

  A host device coupled to a client device via a wireless network according to the present invention includes an RF (high frequency) unit that sends a request packet to the client device, and the RF unit has a predetermined time from the time when the request packet is sent. If a response packet corresponding to the request packet is not received from the client device before the timeout time elapses, a packet for prohibiting transmission of the response packet is transmitted to the client device.

  In a host device according to an embodiment of the present invention, the timeout period is determined according to the number of client devices.

  In the host device according to an embodiment of the present invention, the timeout period is determined according to the number of intermediate nodes existing between the host device and the client device.

  In the host device according to an embodiment of the present invention, the timeout period is determined according to the task type of the client device.

  In accordance with the present invention, a host is coupled to a plurality of clients via a wireless network. In an embodiment, the host collects measurement data from a client connected to a measurement device (or sensor) or the like using communication application software. There may be a case where the host cannot receive a response from the client for a certain period of time (referred to as “timeout period”) after the host sends a request message to the client. In this case, according to the present invention, when the timeout time elapses, a packet for canceling the request (that is, requesting the stop / stop of the response to the already sent request) is transmitted to the client. The client that has received the request stops the response operation to the host when the response packet is being transmitted or is not yet transmitted. This eliminates the need for the client to send a retransmission packet that can be a load on the wireless network. As a result, it is possible to prevent an increase in message traffic due to retransmission packets, packet congestion due to traffic increase, and further packet loss.

  Exemplary embodiments of the invention are described in detail below with reference to the drawings.

(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 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.

(Request cancellation)
FIG. 2 is a diagram illustrating a procedure 200 employed by an exemplary embodiment of the present invention. In this specification, the words “request”, “request cancel”, “response”, and “ACK (acknowledge)” indicating the type of 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. Therefore, in this specification, “the host sends a request to the client” means “the host device sends a packet indicating“ 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, “request cancellation” can be expressed by setting the first 2 bits representing the packet type to “11” in the packet header.

  At time 0, the host 110 sends a request 210 to the client 130. The request 210 is, for example, a request “send sensor data indicating temperature to the host”. In an ideal communication situation, the client 130 receives the request 210 and immediately sends a response 220 to the host 110. In the above example, the response 220 is a packet describing sensor data representing temperature, but is not limited thereto. The response 220 can generally be any response packet that includes sensor data corresponding to a request packet from the host 110.

  The host 110 provides a timeout time 230. If the host 110 cannot receive a response 220 to the request 210 from the client 130 due to some situation (eg, packet loss) within the time-out period 230, the request cancellation 240 is sent to the client 130. In other words, when a response is not obtained from the client, a request cancellation 240 is sent from the host 110 to the client 130 at a time after the timeout time 230 from the request 210 (time 0 in FIG. 2). This request cancellation 240 is generated by the OS (operating system) of the host 110, for example. The request cancellation 240 is sent to the client (in this case, the client 130) that has received the already sent request (in this case, the request 210).

  An example of a situation in which the host 110 cannot receive a response from the client within the time-out period 230 is a case where traffic on the wireless network increases and is congested. There are various reasons for increased traffic. In general, the response 220 may include a number of packets depending on the sensor. Alternatively, when the wireless link (eg, 133) between the host 110 and the client (eg, 130) includes a plurality of hops (ie, multi-hop), packet loss (loss) may occur depending on the communication status. When packet loss occurs, the client generally tries to retransmit the same packet. Therefore, even if the host 110 sends a single request 210 to the client 130, there may be a situation where a large number of response packets are sent from the client 130. Under such circumstances, a response from a client (eg, client 140) different from the client 130 may be blocked by a large number of response packets from the client 130 and not reach the host 110.

  The timeout time 230 varies depending on the specifications of each system. Typically the timeout time is 5 seconds. In this case, if the response 220 is not received from the client 130 within 5 seconds after the request 210 is sent, the host 110 sends a request cancellation 240 to the client 130. As an example, if the client sends data from the sensor to the host every second (ie, the sampling time is 1 second), the timeout time is on the order of a few seconds.

  In a specific embodiment, the timeout period is set longer when the number of hops of the radio links 133, 143, 153, and 163 is large. That is, when there are many intermediate nodes between the host 110 and the clients 130, 140, 150, and 160, the timeout time is set longer. In other words, the timeout period can be determined according to the number of intermediate nodes existing between the host 110 and the clients 130, 140, 150, and 160.

  The request cancellation packet 240 is a packet that prohibits the client 130 from sending a response packet. The client 130 that has received the request cancellation 240 removes the task “send response packet 220” from the current task queue. Therefore, the client 130 does not send a response to the host 110 unless there is a new request.

  After the host 110 sends a request cancellation 240 to the client 130, the host 110 may send a new request 250 to the client 140, which is a different client. As in the case of the client 130 described above, if the host 110 does not receive a response to the request 250 from the client 140 within the time-out period 230, the request cancellation 260 is sent to the client 140.

  In accordance with an exemplary embodiment of the present invention, by sending request cancellations 240 and 260 to clients 130 and 140, respectively, an appropriately timed response (ie, a timeout period has been exceeded) from client 130 and 140 to host 110. To be sent to. Even if packet loss occurs, if the timeout period is exceeded, the host instructs the client not to retransmit the packet.

  FIG. 3 is a diagram illustrating the operation of the system when it is assumed that the host 110 does not send the request cancellation 240 to the client 130. Assume that the host 110 sends a request 250 to the client 140 without a response from the client 130 to the request 210. In other words, it sends a request to another client at the same time without knowing when a response from one client will reach the host. As a result, responses sent from a plurality of clients may be congested.

  Specifically, as shown in FIG. 3, after the host 110 sends a request 250 to the client 140, responses 310, 320, 330, 340, 350 from the client 130 are continuously sent to the host 110. To do. That is, in time period 360, host 110 cannot receive response 370 from client 140 due to the presence of responses 310, 320, 330, 340, 350 from client 130 (ie, due to network congestion). There can be.

  As an example of the case where a plurality of responses are sent in response to the same request, an ACK (acknowledge) from the host may not reach the client. Generally, the client sends a response to the host in response to a request from the host. When the host receives the response, it sends ACK, which is a message indicating that the response has been received, to the client. When the ACK does not reach the client, the client determines that the host has not received the response and resends the response to the host. In such a case, a plurality of responses are sent to the same request.

  The more clients, the greater the effect of this request cancellation. That is, compared to the case where the host 110 has only four clients 130, 140, 150, and 160, when the host 110 has a group of 100 clients, congestion due to concentration of many responses is avoided by canceling requests. The effect is high. This is because every time the timeout period elapses, the amount of potential traffic due to a large number of response packets from the client is reset to zero. As a result, congestion due to an excessive increase in response packets from the client can be alleviated.

  In a specific embodiment, the timeout period 230 is determined according to the number of clients connected to the host 110. For example, when the client is less than 5, the timeout time is set to 5 seconds, and when the client is 5 or more, the timeout time is set to 3 seconds. By making the timeout time variable in this way, it is possible to prevent a situation where the traffic volume rapidly increases in a short time when there are many clients. The time-out time is set short when real-time data is required, for example, when measuring the instantaneous value of electric energy, and the time-out time is set long when real-time data is not required. be able to.

(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 source 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.

(Task-dependent timeout period)
FIG. 6 is a diagram illustrating a procedure 600 employed by another exemplary embodiment of the present invention. In this embodiment, the host 110 may send different types of requests to the same client (eg, 130). For example, the host 110 sends a temperature request 610 at time 0 to send temperature sensor data to the client 130. The host 110 sends a voltage request 650 to the client 130 at time t1 to send the sensor data of the battery voltage of the client 130. In order to discriminate between different types of requests (here temperature and battery voltage) sent to the same client, the header of the request packet may contain data representing the type.

  Here, the interval at which the host 110 sends the temperature request 610 is relatively short. On the other hand, the interval at which the host 110 sends the voltage request 650 is relatively long. That is, the host 110 wants to check the temperature sensor data relatively frequently, but the battery voltage does not change abruptly.

  In this embodiment, the timeout time varies depending on the frequency of requests. That is, the time-out time of the temperature request 610 frequently checked is 630, and the time-out time of the voltage request 650 checked at a certain interval is 670. Accordingly, the temperature request cancellation 620 is sent from the host 110 to the client 130 at time t2 when the timeout time 630 has elapsed from time 0. On the other hand, the voltage request cancellation 660 is sent from the host 110 to the client 130 at time t3 when the timeout time 670 has elapsed from time t1. Here, (timeout time 630)> (timeout time 670).

  According to this embodiment, the timeout period varies depending on the type of request that the host issues to the client (specifically, depending on the frequency of requests). By adopting the timeout time depending on the task as described above, the timeout time can be changed according to the frequency of occurrence of the task. This has the advantage that the request can be canceled relatively quickly for tasks that can occur frequently. Furthermore, this embodiment can be suitably used when real-time data is required. This is because when real-time data is required, old data retransmitted from the client is unnecessary and congests the network.

  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 procedures shown in FIGS. 2 and 6 can be typically 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. It is a figure which shows operation | movement of a system when it is assumed that a host does not send request cancellation to a client. 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. FIG. 6 illustrates a procedure employed by another exemplary embodiment of the present invention.

200 Procedure 110 Host 130, 140 Client 210, 250 Request 220 Response 230 Timeout 240, 260 Request cancellation

Claims (4)

A host device coupled to a client device via a wireless network,
An RF (radio frequency) unit for sending a request packet to the client device;
If a response packet corresponding to the request packet is not received from the client device before a predetermined timeout period elapses from the time when the request packet is transmitted, the RF unit sends the response to the client device. A host device that sends packets that prohibit sending packets.   The host device according to claim 1, wherein the timeout time is determined according to the number of the client devices.   The host device according to claim 1, wherein the timeout time is determined according to the number of intermediate nodes existing between the host device and the client device.   The host device according to claim 1, wherein the timeout period is determined according to a task type of the client device.

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