challenges and node architecture

1. Unit-2
Sensor Network-Introduction
& Architecture
Dr.DEEPA.D
Asst Professor
Electronics and communication
R.M.K College of Engineering and Technology

2. What is a sensor
A sensor is a tiny electronic device that measures physical
input from its environment and converts it into data that can
be interpreted by either a human or a machine.
senorPhysical qty
observable
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3. Wireless Sensor Networks (WSNs) can be defined
as a self-configured and infrastructure less
wireless networks to monitor physical or
environmental conditions, such as temperature,
sound, vibration, pressure, motion or pollutants
A sink or base station acts like an interface
between users and the network. One can
retrieve required information from the
network by injecting queries and gathering
results from the sink.
A wireless sensor network contains hundreds
of thousands of sensor nodes. The sensor
nodes can communicate among themselves
using radio signals.

4. A wireless sensor node is equipped with
sensing and computing devices, radio
transceivers and power components.
The individual nodes in a wireless sensor
network (WSN) are inherently resource
constrained:
they have limited processing speed, storage
capacity, and communication bandwidth.
After the sensor nodes are deployed, they
are responsible for self-organizing an
appropriate network infrastructure often
with multi-hop communication with them.

5. Challenges for Wireless Sensor Network
 Characteristic requirements
 Type of service :The service type rendered by a conventional
communication network is evident – it moves bits from one place to
another.
A WSN is expected to provide meaningful information and/or actions about a
given task
 Quality of Service : Delay or minimum bandwidth are irrelevant when
applications are tolerant to latency or the bandwidth
 fault Tolerance: To tolerate node failure, redundant deployment is
necessary, using more nodes than would be strictly necessary if all nodes
functioned correctly.

6.  lifetime: WSN must operate at least for a given mission time or as long
as possible. Hence, the lifetime of a WSN becomes a very important
figure of merit. Evidently, an energy-efficient way of operation of the
WSN is necessary.
 Scalability Since a WSN might include a large number of nodes, the
employed architectures and protocols must be able scale to these
numbers.
 Wide range of densities : In a WSN, the number of nodes per unit area –
the density of the network – can vary considerably. Different applications
will have very different node densities.
 Programmability:These nodes should be programmable, and their
programming must be changeable during operation when new tasks
become important

7.  Maintainability :As both the environment of a
WSN and the WSN itself change (depleted
batteries, failing nodes, new tasks), the system
has to adapt. It has to monitor its own health and
status to change operational parameters or to
choose different tradeoffs

8. Required mechanisms
 To realize these requirements, innovative mechanisms for
a communication network have to be found, as well as
new architectures, and protocol concepts. A particular
challenge here is the need to find mechanisms that are
sufficiently specific to the idiosyncrasies of a given
application to support the specific quality of service,
lifetime, and maintainability requirements

9. Required mechanisms
 Multihop: A direct communication between a sender and a receiver
of WSN is difficult for long distance since it needs high
transmission power. The use of intermediate nodes as relays can
reduce the total required power.
 Energy-efficient operation: To support long lifetimes, energy-
efficient operation is a key technique.
Energy-efficient data transport between two nodes and energy-
efficient computation of a requested information are to be used.

10.  Auto-configuration: A WSN has to configure its operational
parameters autonomously, independent of external
configuration.
 Collaboration and in-network processing: In some
applications, a single sensor node is not able to decide
whether an event has happened. Several sensor nodes
have to collaborate to detect an event and only the joint
data of many sensors provides enough information.
 Information is processed in the network itself in various
forms to achieve this collaboration.

11. Data centric:
Address-centric: Transfer of data between two specific
devices, each with one network address as in traditional
communication networks.
In WSN, where nodes are deployed redundantly to protect
against node failures the identity of the node supplying data
is not important. Importance is given only to the data. Hence
a data-centric paradigm is necessary in designing WSN.

12. Locality:
Nodes which are very limited in resources like memory,
should limit the state of information processing with their
direct neighbors only. This will allow the network to scale to
large numbers of nodes without having to rely on powerful
processing at each single node.
.

13. 1.6 Enabling technologies for wireless
sensor networks
 MINIATURIZATION OF HARDWARE:. Smaller sizes in chips
have driven down the power consumption of the basic
components of a sensor node such as microcontrollers
and memory chips, the radio modems, responsible for
wireless communication, have become much more energy
efficient
 Reduced chip size and improved energy efficiency is
accompanied by reduced cost, which is necessary to make
redundant deployment of nodes affordable
.

14. Enabling technologies for wireless sensor
networks
Processing and communication:
Communication between sensor nodes is the most energy consuming
operation
 The primary objective of protocols is to minimize energy consumption
for communication.
 For efficiently communicate between sensor nodes, medium access
control (MAC) should be designed to minimize energy consumption.
 Another major communication method in WSNs is broadcasting.
A broadcast protocol for WSNs must be designed to minimize the factors
of energy waste, such as redundant transmissions of identical broadcast
packets and collisions.

15. Enabling technologies for wireless sensor
networks
Sensing equipment:
It is difficult to generalize because of the vast range of possible sensors.
 The three basic parts of a sensor node have to be accompanied by power
supply. This requires, high capacity batteries that last for long times.
 The counterpart to the basic hardware technologies is software..

16. APPLICATION TYPES
 Event detection
 Periodic measurements
 Function approximation and edge detection:
 Tracking:
 Deployment options

17. Single Node Architecture-Hardware
components
 Application’s requirements play a decisive factor with regard mostly to
size, costs, and energy consumption of the nodes –
 Communication and computation facilities as such are often considered to
be of acceptable quality,
 The trade-offs between features and costs is crucial.

18.  In some extreme cases, an entire sensor node should be
smaller than 1 cc, weigh (considerably) less than 100 g, be
substantially cheaper than US$1, and dissipate less than
100 µW.
 In even more extreme visions, the nodes are sometimes
claimed to have to be reduced to the size of grains of
dust. In more realistic applications, the mere size of a
node is not so important; rather, convenience, simple
power supply, and cost are more important

19. Hardware components
 Sensor node hardware overview
 Controller
 Memory
 Communication device
 Sensors and actuators
 Power supply of sensor nodes

20.  Controller : It is the Central processing unit of
the node
 It collects data from sensor and processes and
decides when and where to send
 Its capable of executing arbitrary code.
 Example : General purpose processor, DSP and
microcontollers
 Memory are used to store programs and
intermediate data; usually, different types of
memory are used for programs and data.
 RAM- for intermediate data
 ROM- for storing the program code
 Flash Memory- for storage of data if RAM gets
affected

21. Sensors and actuators
 Sensors:The actual interface to the physical world: devices that can
observe or control physical parameters of the environment
 Passive, Omindirectional sensor:- The Sensor measure the physical
quantity without manipulating the environment and also obtain energy
from environment to amplify their analog signal
 Passive narrow-beam sensor:- These are Passive Sensor and as well
defined notion of direction of measurement
 Active Sensor:- There are quite specific and plays a special attention for
sensing the shock waves from explosion. It requires external source of
power
 Actuators: These are for wireless sensor network that convers Electrical
signals into physical phenomenon

22. Communication device:
Turning nodes into a network requires a
device for sending and receiving
information over a wireless channel.
Here it uses Radio frequencies
Transceiver:- It is a device for both
transmitting and receiving operations that
convert bit stream coming from a micro
controller and convert them to and from
radio waves
Usually, half-duplex operation is realized
since transmitting and receiving at the
same time on a wireless medium is
impractical in most cases

23. Power Amplifier: it takes signal from IF and
amplifies them for Transmission over
antenna
Low noise amplifier: Amplifier incoming
signals without reducing the signal to noise
ratio
Elements:- Local oscillator(or) Voltage
Controlled Oscillator are used for freq
conversion from RF to IF or Baseband

24. Transceiver Tasks and characteristics
 Service to upper Layer:- Receiver has to offer some services to the MAC layer
 Power consumption: power required to transmit single bit and receiving the
same bit
 State change time and energy: operated in different modes and different
power safe states
 Data rate: Carriers freq and bandwidth will determine the data rate
 Modulation: It supports On/OFF Keying, ASK, FSk or similar modulation
 Coding:- various coding schemes are used
 Noise figure: (S/N)i/(S/N)o
 Gain: Its is the ratio of output signal to input signal power
 Frequency Stability: Denotes the degree of variations from centre
frequencies when temp/pressure changes
 Voltage range: It should operate reliably over a range of supply voltage

25. Power supply
As usually no tethered power supply is available, some
form of batteries are necessary to provide energy.
Sometimes, some form of recharging by obtaining energy
from the environment is available as well (e.g. solar
cells).
Energy Scavenging: The process of recharging the battery
with energy gathered fromm the environment is called
energy scavenging
Photovoltaics:- Power obtained from solar cells
Temperature gradient: Difference in temperature
Vibrations : due to vehicles
Pressure Vibrations
Flow of liquid /air : in wind mills or turbines