08-02-2013, 12:59 PM
DETERMINATION OF RF SOURCE POWER IN WPSN USING MODULATED BACKSCATTERING
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ABSTRACT
A wireless sen sor network (WSN) is a wireless network consisting of spatially distributed autonomous devices
using sensors to cooperatively monito r physical or environmental conditions, such as temperature, sound,
vibration, pressure, motion or pollutants, at different locations. During RF transmission energy consumed by
critically energy-constrained sensor nodes in a WSN is related to the life time system, but the life time of the
system is inversely proportional to the energy consumed by sensor n odes. In tha t regard, modulated
backscattering (MB) is a promising design choice, in which sensor nodes send their data just by switching
their antenna impedance and reflecting the incident sign al coming from an RF source. Hence wireless passive
sensor networks (WPSN) designed to operate using MB do not have the lifetime co nstraints. In this we are
going to investigate the system analytically. To obtain interference-free communication connectivity with the
WPSN nodes n umber of RF sources is determined and analyzed in terms of output power and the transmission
frequency of RF sources, network size, RF source and WPSN node characteristics
INTRODUCTION
WSN:
The de velop men t of wir e le ss se nsor ne tw or ks wa s originally motivated by
military applications such as battlefield surveillance [7], [8]. However, wireless sensor
networks are now used in many industrial and civilian application areas, including industrial
process monitoring and control, machine health monitoring, environment and habitat
monitoring, healthcare applications, home automation, and traffic control [1]. In addition to one
or more sensors, each node in a sensor network is typically equipped with a radio transceiver or
other wireless communications device, a small microcontroller, and an energy source, usually a
battery.
MODEL OF WPSN
WPSN WITH MB:
Wireless passive sensor network proposed in this study is based on MB. The
source of energy is an RF power source which is assumed to have unlimited power. The source
transmits RF power to run the passive nodes, and it transmits and receives information from WPSN
nodes simultaneously. A typical WPSN node hardware is represented in Figure 1.
The WPSN node
hardware differs from the conventional WSN hardware basically on the power unit and the
transceiver. In a conventional WSN node, the power unit is a battery. The power generator, which
is an RF to- DC converter is an inherent part of the power unit and is the unique power source of
the sensor node.
Carrier Frequency
As in Figure 5), for a given network dimension and RF out-put power, increasing carrier frequency
mandates an increase in the number of RF sources. This is mainly because WPSN nodes become
able to use a higher data switching frequency, hence a higher data rate, and the energy consumption
for data communication increases. Furthermore, k can be reduced by increasing the output power at
a given RF frequency. When output power is increased, the range of RF sources increases, and they
start to transmit with higher energy. As a result, each RF source is able to communicate with more
WPSN nodes, and a smaller number of RF sources are required for communication connectivity
over the event field. On the other hand, the dependence of the required RF output power on
frequency and number of RF sources is illustrated in Figure7