18-02-2013, 10:30 AM
Bluetooth Based Smart Sensor Networks
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ABSTRACT
“Dragging the world towards wireless galaxy”
Various sensors are already in a broad use today as part of
different devices or as standalone devices connected to a network
usually to monitor industrial processes, equipments or installations.
The advancements in technology, wireless communications have
enhanced development of small, low power and low cost devices. Such
devices when organized into a network, present a powerful platform
that can be used in many interesting applications.
Bluetooth is a low cost, short-range, wireless technology with
small footprint, low power consumption and reasonable throughput.
Bluetooth wireless technology has become global technology
specification for “always on” wireless communication not just as a
point-to-point but was a network technology as well.
Introduction
The communications capability of devices and continuous transparent
information routes are indispensable components of future oriented automation
concepts. Communication is increasing rapidly in industrial environment even at
field level.
In any industry the process can be realized through sensors and can be
controlled through actuators. The process is monitored on the central control room
by getting signals through a pair of wires from each field device in Distributed
Control Systems (DCS). With advent in networking concept, the cost of wiring is
saved by networking the field devices. But the latest trend is elimination of wires
i.e., wireless networks.
Wireless sensor networks - networks of small devices equipped with
sensors, microprocessor and wireless communication interfaces.
In 1994, Ericsson Mobile communications, the global telecommunication
company based in Sweden, initiated a study to investigate, the feasibility of a low
power, low cost ratio interface, and to find a way to eliminate cables between
devices. Finally, the engineers at the Ericsson named the new wireless technology
as “Blue tooth” to honour the 10th century king if Denmark, Harald Blue tooth
(940 to 985 A.D).
The goals of blue tooth are unification and harmony as well, specifically
enabling different devices to communicate through a commonly accepted standard
for wire less connectivity.
Blue Tooth
Blue tooth operates in the unlicensed ISM band at 2.4 GHZ frequency band
and use frequency hopping spread spectrum technique. A typical Blue tooth device
has a range of about 10 meters and can be extended to 100meters. Communication
channels supports total bandwidth of 1 Mb / sec. A single connection supports a
maximum asymmetric data transfer rate of 721 KBPS maximum of three channels.
BLUE TOOTH – NETWORKS
In bluetooth, a Piconet is a collection of up to 8 devices that frequency hop
together. Each Piconet has one master usually a device that initiated establishment
of the Piconet, and up to 7 slave devices. Master’s Blue tooth address is used for
definition of the frequency hopping sequence. Slave devices use the master’s clock
to synchronize their clocks to be able to hop simultaneously.
Smart Sensor Node Architecture
The architecture shown in figure can easily be developed for specific sensor
configurations such as thermocouples, strain gauges, and other sensor technologies
and can include sensor signal conditioning as well as communications functions.
Conditioned along sensor signal is digitized and digital data is then processed
using stored TEDS data. The pressure sensor node collects data from multiple
sensors and transmits the data via bluetooth wireless communications in the
2.4 GHZ base band to a network hub or other internet appliance such as a
computer.
The node can supply excitation to each sensor, or external sensor power can
be supplied. Up to eight channels are available on each node for analog inputs as
well as digital output. The sensor signal is digitized with 16-bit A/D resolution for
transmission along with the TEDS for each sensor. This allows each channel to
identify itself to the host system. The node can operate from either an external
power supply or an attached battery. The maximum transmission distance is 10
meters with an optional capability to 100 meters.
The IEEE 1451 family of standards are used for definition of functional
boundaries and interfaces that are necessary to enable smart transducer to be easily
connected to a variety of networks.
Discovery Of The Smart Sensor Nodes
Smart sensor node discovery is the first procedure that is executed upon the
gateway installation. It goals to discover all sensor nodes in the area and to build a
list of sensor’s characteristics and network topology. Afterwards, it is executed
periodically to facilitate addition of new or removal of the existing sensors. The
following algorithm is proposed.
When the gateway is initialized, it performs bluetooth inquiry procedure.
When the blue tooth device is discovered, the major and minor device classes are
checked. These parameters are set by each smart node to define type of the device
and type of the attached sensors. Service class field can be used to give some
additional description of offered services. if discovered device is not smart node it
is discarded. Otherwise service database of the discovered smart node is searched
for sensor services. As currently there is no specific sensor profile, then database is
searched for the serial port profile connection parameters. Once connection strings
is obtained from the device. Blue tooth link is established and data exchange with
smart mode can start.
CONCLUSION
Blue tooth represents a great chance for sensor-networked architecture.
This architecture heralds wireless future for home and also for industrial
implementation. With a blue tooth RF link, users only need to bring the devices
with in range, and the devices will automatically link up and exchange
information.
Thus implementation of blue tooth technology for sensor networks not only
cuts wiring cost but also integrates the industrial environment to smarter
environment.
Today, with a broader specifications and a renewed concentration on
interoperability, manufacturers are ready to forge ahead and take blue tooth
products to the market place. Embedded design can incorporate the blue tooth
wireless technology into a range of new products to meet the growing demand for
connected information appliances.