2011 International Conference on Network and Electronics Engineering
IPCSIT vol.11 (2011) © (2011) IACSIT Press, Singapore
POWER AWARE HETEROGENEOUS WIRELESS SENSOR
NETWORK
S.Barani 1, C.Gomathy 2
1
2
Research Scholar, Sathyabama University
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
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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
Remote Monitoring
Unit
Sensing, Transmitting
and computational unit
TX / RX
TX / RX
Zigbee Module
Temperature
pressure Sensors
Remote Host
Zigbee Module
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
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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
Transmitter Current Tx_Ct
Reciever Current Rx_Ct
Power down current Pd_Ct
Operating Voltage of Zigbee
Operating Voltage of Sensors
Specification
27mA
27mA
0.5 µA
3.6 V
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
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