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POWER AWARE HETEROGENEOUS WIRELESS SENSOR NETWORK

S.Barani 1, C.Gomathy 2 1 Research Scholar, Sathyabama University

2 Department of E&C, Sathyabama University

Abstract. The requirement of lesser power consumption is essential in wireless sensor network due to its limited battery power. In real time, the power consumption cannot be reduced, as the power consumed is dependent on the application and the protocol implemented. Instead, the power consumption could be managed to increase the life time of the network. This paper focuses majorly on power management. Network with three nodes are established and the nodes connected in the network, are made to switch off if the power consumption is high. Power consumed by the entire network is analyzed based on the total battery power of the node at various scenarios. The lifetime of the entire network is calculated based on the power consumed by the network at the end of each transmission. The node conducting higher power is made idle and alternate nodes are turned on to increase lifetime.

Keywords: Homogeneous Network, Power management, Sensor network, Zigbee protocol

1. Introduction The wireless sensor network is made significant as it collects and transmits the sensory data at various

locations to the remote host for further processing where the risk factor for human intervention is high. The network is applied for applications like habitat monitoring, Temperature, pressure and various other parametric monitoring in industries, Automation of appliances, health monitoring, military applications, environmental monitoring etc...The deployed network can be homogeneous or heterogeneous network. The network comprises of huge sensors connected in a single mote where the data is transmitted to a remote host via a common gateway. Working on wireless sensor network in the simulation environment at various layers, though gives better performance implementation of real time generates many practical difficulties. When sensor nodes are deployed at different regions the very first difficulty faced is the condition of the node. The node should be under proper condition without any damage. The nodes should be as rugged as it withstands for different environmental and climatic condition. Hence we decided to work for a real time application. Implementation of real time sensor network is competent when it is proved to be energy efficient. Hence as a first module we analyze the power consumption of the network. Initially sensors connected in the network is considered as homogeneous network Two temperature sensors are connected in the network using Zigbee device.

In this paper we focus our work where the connected two temperature sensors in the network are made to sense at regular interval. The power consumption of each node is measured and hence the lifetime of the entire network is analyzed. The flow of the remaining paper is organized as follows Section II the work based on zigbee and wireless sensor network section III basic model of the system Section IV power estimation section V results and discussions.

+ S.Barani, 91- 44- 23664519, 91- 44 – 24503165, Email ID: baraniselvaraj77@gmail.com Dr.C.Gomathy, Email ID: cgomathy@yahoo.co.uk

2011 International Conference on Network and Electronics Engineering IPCSIT vol.11 (2011) © (2011) IACSIT Press, Singapore

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2. Existing Work on Network In this section we discuss about the existing work in sensor networks based on zigbee protocol stack. Y

W Zhu et al [1] proposed a wireless sensor network system to apply in the field of agricultural for green house. The author claims that the wireless technology used is cost effective and also supports mobility. Shizhuang Lin et al takes over the MAC layer and network layer completely, implemented hardware and software and analyzed the industrial applications of wireless sensor network system [2] the zigbee is also used in the field of medicine for patient health monitoring applications. It can be used to identify various several diseases [3] Michal VARCHOLA et al describes the features of the ZigBee standard that is great solution for wireless sensor network. The workplace for wireless sensors networking was prepared and tried out within works at DEMC.[4] Zulhani Rasin et al suggested to monitor temperature , PH value and turbidity of water . The claims the network to be cost effective.[5] From the related work discussed so for the network implemented with zigbee are application specific and not an open ended application.

2.1 Problem Identified

The inference made after the surveys are, the network should be cost effective, energy efficient and application specific. To make the system energy efficient the power consumed by the entire network should be estimated. Once the power consumed by the network is known power management could be implemented to increase the life span of the node. Power consumed by the entire network is estimated when the node senses, transmits and receives at regular interval.

3. Proposed Model of the Heterogeneous System

Fig 1: Flow diagram of system model

Figure 1 demonstrates the basic flow of system model. In the proposed model the sensors are connected to the zigbee module .The sensing module senses the data and the sensed data are acquired using the controller. The acquired data are transmitted to the remote unit in the interval of every 2 seconds. The power is estimated at the end of each transmission. The node that has highest power consumption is switched of using the relay and transmission from the highest power consuming node is cut off. Figure 2 describes the complete flow of the process .Three zigbee modules are used. The first module is used as receiver and the second and third module as transmitter. Current and potential transformers are used to calculate power in the circuit. The arm controller is used for manipulation of data. The power consumption of the devices used in the network are monitored for their power consumption continuously and controlled. The temperature sensors and pressure sensor are used to measure temperature and pressure respectively. Their power consumption based on their sensed values. When they reach certain set-point values, then they are automatically switched OFF when their power consumption exceeds the set-point

Temperature pressure Sensors

Zigbee Module

Sensing, Transmitting and computational unit

TX / RX TX / RX

Remote Monitoring Unit

Zigbee Module

Remote Host

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Fig 2: Complete Schematic of the network

Power Supply Unit consists of a 9V step down transformer, this supply is fed to the filter circuit and bridge rectifier for obtaining a steady DC output voltage. It is then fed to the voltage regulator 7912 and 7805. IC 7912 outputs a voltage of -12V to +12V which is given as input supply for the MEMS pressure sensor board .IC voltage regulator 7805 takes the input voltage from the transformer and outputs a voltage of +5V to both the temperature sensors. It also has a heat sink attached to it to cool the IC from runaway effects. Current Transformer provides an output of +5A to the sensor circuits for optimum usage. It steps down the current in a known ratio. The current transformer measures the current then it is given to the full wave precision rectifier, which normally converts ac signal into dc signal without conduction losses. Voltage transformer provides an output of +5V to the sensing circuit. The voltage-measured by the potential transformer is fed to the full wave precision rectifier, which normally converts the incoming ac signal into dc signal without any conduction losses. The temperature sensors are subject to varying temperatures and measure the temperatures and send them to the base station for further processing and monitoring. But when their power consumption exceeds their limit, they end up consuming more power than available to them through the battery. To avoid the over-consumption, whenever the set-point values of temperatures and pressure which indicates an increase in power consumption are obtained, the control signal from the ARM7 controller is directed to the Relay that is connected to the sensors. This relay automatically switches OFF the voltage supply to the sensors thus switching them to sleep mode. The measured values from the sensors are amplified through the op-amps present on the sensor boards, and the signal conditioning circuits. The signal conditioning circuits also isolate the measured values from noise. The sensed values are communicated through the Zigbee which transmit these values to the controller Zigbee. The controller Zigbee allocates the input signals from the two Zigbee connected to the ARM board, and used to transmit the values from the temperature and pressure sensors.

The ARM7 has been pre-programmed to -switch OFF the sensors that involve high power consumption, data communication through hardware interfaces of UART, serial and parallel communication. It also has an interfaced LCD screen to display the current consumption of the sensors that are measured. The temperature sensor is a thermistor that has varying values in its resistance according to the change in temperature. This change can be calculated into current consumption. The pressure sensor is a piezo-resistive micro diaphragm pressure sensor whose resistivity changes according to the force experienced on the piezo-resistive surface. Whenever the relays obtain a switch signal to switch the sensors from ON to OFF, the Vcc and GND (ground) connections are cut resulting in switching OFF of the devices. The signal conditioning circuit is used to provide 5V supplies to the sensors from the potentiometer transformers, as well as isolate the output signals of the sensors and give them as input to the ARM processor for processing and transmission through the Zigbee.

4. Power Estimation of the Proposed Network

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The initial specifications identified for calculating the power consumption are

SPECIFICATION OF ZIGBEE NODE

Parameter SpecificationTransmitter Current Tx_Ct 27mA Reciever Current Rx_Ct 27mA Power down current Pd_Ct 0.5 µA Operating Voltage of Zigbee 3.6 V Operating Voltage of Sensors 5.0 V

The battery used in the network is, Duracell battery of 1.5 v and 2500 mAh specification. Two batteries are used in a single node. Then total energy of a node (node with 2 AA Battery) [6][7]

(1.5+1.5) * 2500* 3600 = 27000 Joules

The node is programmed to operate as a transmitter or receiver in the interval of 3 seconds with a transmission or receiving time of 1 second. Hence totally for 28,800 seconds the node acts as a receiver / transmitter. The energy estimation for receiving and transmission are

Receiving energy of a node Rx_E =3.6V*27mA*28,800 = 2799.36 Joules / day Transmission energy of a node Tx_E =3.6V*27mA*. 28,800= 2799.36 Joules / day The node is programmed to sense in the interval of 4 seconds and hence Sensing energy of a temperature node = 5.0 * .097A * 21600 = 10,476 joules / day Sensing energy of a pressure node = 5.0 * .001 A * 21600 = 108 Joules / day Power down energy of a node = 3.6 * 0.000005 * 7200= 0.1296 Joules / day Total energy consumed by a single node (temperature) is 16,074.85 joules / day Total energy consumed by a single node (Pressure) is 5706.85 joules / day Lifetime of temperature node = 27000 / 16,074.85 = 1.6 Hours Lifetime of pressure node = 27000 / 5706.85 = 4.73 Hours Hence as per the circuit connected and programmed a single node (Temperature) should long last for 1.6hours and 4.73 hours for pressure node.

5. Results and Discussion The following observation has been made from figure 3 and figure 4. ‘C’ denotes the current

consumption of the three sensors together, ‘T1’ denotes the temperature in °C measured by temperature sensor 1, ‘T2’ denotes the temperature in °C measured by temperature sensor 2, ‘p’ denotes pressure measured in Pascal by pressure sensor .The energy calculation in section 4 describes clearly for a node to transmit the data, for 28,800 seconds per day the transmission and sensing energy alone consumes 2799.36 Joules / day and 10,476 joules / day. For a single transmission the energy consumed by the node is .0972 joules of transmission energy and 0.485 joules of sensing energy. Hence the network is managed to make the node alive. In this work a set point of 100 transmissions are taken. The data being acquired and transmitted for 100 seconds (100 transmissions) the temperature node is forced to power down mode. In the network two temperature nodes are connected .Immediately after one node is forced to power down node, the other node is made to conduct. Similarly for pressure node also acts in the same manner with a threshold of same 100 seconds / 100 transmissions.

Since the energy of the could be estimated based on the battery used, the network is energy aware and the nodes are alternatively forced to power down mode to save energy. In the entire network, temperature node should long last for 1.6 hours and pressure node for 4.73 hours. When tested practically temperature node is forced to work under idle condition for every 9.72 Joules for temperature nodes .Hence each temperature node worked well for an average of 0.6 hours and 3.2 hours for pressure node with an average lifetime of 4.4 hours. When more nodes are connected in the network all nodes can be made to sleep alternatively and the network life is increased.

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Fig 3: Acquired data from the network Fig 4: Photocopy of the entire network

6. References

[1] Y W Zhu, X X Zhong and J F Shi,” The Design of Wireless Sensor Network System Based on ZigBee Technology for Greenhouse” in the Journal of Physics: Conference Series 48, 2006, 1195–1199

[2] Shizhuang Lin, ingyu Liu,Yanjun Fang,Wuhan Univ., Wuhan ,” ZigBee Based Wireless Sensor Networks and Its Applications in Industrial” in the proceedings of Automation and Logistics, 2007 IEEE International Conference - 18-21 Aug. 2007 , 1979 - 1983

[3] Zigbee Alliance 2009

[4] Michal Varchola, Miloš Drutarovský ,” Zigbee Based Home Automation Wireless Sensor Network” in Acta Electrotechnica et Informatica No. 4, Vol. 7, 2007 – PP 1-8

[5] Zulhani Rasin, Mohd Rizal Abdullah “Water Quality Monitoring System Using Zigbee Based Wireless Sensor Network “ in the International Journal of Engineering & Technology IJET Vol: 9 No: 10 PP 24-28

[6] Datasheet 223C40

[7] Datasheet AD590