2. System overview
The block diagram of the WGSN for the monitoring of combustible
gas concentration is presented in Fig. 1. The system consists
of a number of sensor and relay nodes, a network coordinator, and
possibly one or more wireless actuators.
The sensor node monitors the combustible gas concentration in
the environment. It is set up for several ranges of gas concentration,
as we discuss below. Wireless communication between the sensor
node and the network coordinator is implemented via the relay
node.
The network coordinator is responsible for creating and controlling
the network, indicating the current situation and alerting the
external and emergency services. Alerting the emergency services
may be implemented through the GSM cellular network by sending
an SMS or with the TCP/IP protocol over Ethernet or GSM/GPRS.
Apart from alerting of the potential emergency, the coordinator is
able to carry out preventive actions by seating the valve controlling
the gas delivery and deactivating electrical devices. These emergency
preventive measures are the responsibility of the wireless
actuators, which are part of the network and communicate with
the coordinator over the wireless link.
Communication within the network is implemented using the
IEEE 802.15.4 standard [14], while data are transmitted over the
ZigBee protocol stack [15]. Among the known data wireless transmission
standards, such as Bluetooth, WiFi, etc., we have found
ZigBee the most acceptable in terms of the trade-off between bandwidth
and power consumption, to ensure long autonomous battery
operation of the device. In addition, the modems which use the
ZigBee standard have the option to self-organize the whole sensor
network.
2. System overviewThe block diagram of the WGSN for the monitoring of combustiblegas concentration is presented in Fig. 1. The system consistsof a number of sensor and relay nodes, a network coordinator, andpossibly one or more wireless actuators.The sensor node monitors the combustible gas concentration inthe environment. It is set up for several ranges of gas concentration,as we discuss below. Wireless communication between the sensornode and the network coordinator is implemented via the relaynode.The network coordinator is responsible for creating and controllingthe network, indicating the current situation and alerting theexternal and emergency services. Alerting the emergency servicesmay be implemented through the GSM cellular network by sendingan SMS or with the TCP/IP protocol over Ethernet or GSM/GPRS.Apart from alerting of the potential emergency, the coordinator isable to carry out preventive actions by seating the valve controllingthe gas delivery and deactivating electrical devices. These emergencypreventive measures are the responsibility of the wirelessactuators, which are part of the network and communicate withthe coordinator over the wireless link.Communication within the network is implemented using theIEEE 802.15.4 standard [14], while data are transmitted over theZigBee protocol stack [15]. Among the known data wireless transmissionstandards, such as Bluetooth, WiFi, etc., we have foundZigBee the most acceptable in terms of the trade-off between bandwidthand power consumption, to ensure long autonomous batteryoperation of the device. In addition, the modems which use theZigBee standard have the option to self-organize the whole sensornetwork.
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