This document discusses several key concepts in wireless sensor networks: 1) The critical transmitting range problem and how to compute the minimum common range for network connectivity. 2) The advantages of clustering for efficient resource usage and network monitoring. 3) The need for time synchronization between sensor nodes and the challenges involved. 4) Methods for sensor self-localization including range-based algorithms and localization services like GLS.

1. PRESENTED BY,
M. JUNO ISABEL SUSINTHRA

3. • How to set the radio range for each node to use
minimize energy ,while still ensuring that the
communication graph of the nodes remains
connected and satisfies other desirable
communication properties.
• Simple case :all nodes must use the same
transmission range

4. The critical transmitting range (CTR) problem
define:
•Simple case :
All nodes ignore all effects of interference or multi-path and use the
same transmission range „This homogeneous topology
•control setting: how to compute the minimum common transmitting
range r such that the network is connected

5. Clustering allows hierarchical structures to be built on the nodes and
enables more efficient use of scare resources ,such as frequency
spectrum ,bandwidth ,and power
Clustering

6. The advantage of clustering „:
Frequency division multiplexing can be reused
across non-overlapping cluster „Clustering allows the
health of the network to be monitored and
misbehaving node to be identified (watchdog roles
in some nodes) „
Network can be comprised of mixtures nodes
,including more powerful or have special capability.

7. „cluster head:
A node declares itself a cluster-head if it has a higher ID
than all its” uncovered ” neighbors-neighbors that have not
been already claimed by another cluster-head „
Each node nominates as a cluster-head the highest ID node
it can communicate with (including itself) „Nominated
nodes then form clusters with their nominators

8. Time Synchronization:
 „Since the nodes in a sensor network operate
independently ,their clock may not be, or stay
synchronization with one another. „
This can cause difficulties when trying to integrate
and interpret information sensed at different nodes

9. Need for time synchronization:
 „Configuring a beam-forming array „Setting a TDMA
radio schedule „.
Synchronization is need for time-of-flight
measurements that are then transformed into distances
by multiplying with the medium propagation speed for
the type of signal used (radio frequency or ultrasonic)

10. Time Synchronization is difficult :
In sensor network „No special master clocks are available „
connections are ephemeral „communication delays are
inconsistent and unpredictable.

11. Localization and Localization Services:
 „For several sensor network applications ,including Target
tracking and habitat monitoring knowing the exact
location where information was collected is critical „
The value of the information collected can be enhanced if
the location of the sensors where readings were made is
also available

12. Self-localization:
That is methods that allow the nodes in a network to
determine their geographic positions on their own during
the network initialization
process „Location service algorithms-methods that allow
the nodes in a network to obtain the location of a desired
node

13. Localization and Localization Services:
GPS build nodes localize themselves within a few meter’s
accuracy by listening to signals emitted by a number of
satellites „GPS’s cons „Expensive „Difficult to incorporate
into every sensor node „Power consumption

14. Ranging Techniques:
 Ranging methods aim at estimating the distance of a
receiver to a transmitter „The first way Use RSS (received
signal strength) along with for signal strength as a
function of distance to estimate its distance from sender
to receiver „Localization to within a few meters is the
best that can currently be attained with RSS method

15. Ranging Techniques uses RSS:
The distance to estimate not very accurate „fading „
Shadowing „Multi-path effect „Not well-RF component

16. Range-Based Localization Algorithms:
 „Initial nodes 1,2,8,9,15 are landmarks „Node 10 can estimate its location
using Landmarks 8,9,15 „Node 7 can estimate its position using Nodes
8,9,10 as landmarks „This process terminates when no unlocalized node
has enough landmarks to determine its position „its always first localize
the nodes with the most landmarks

17. Other Localization Algorithms:
 „If sensor nodes are densely and uniformly deployed ,we
can use hop counts to landmarks as a substitute to
physical distance estimates „In order to transform hop
counts into approximate distance ,the system must
estimate the average distance corresponding to a hop

18. GLS( geographic location service):
The key idea of GLS is distribute the load so that each
network nodes acts as a location server for a relatively
small number of other nodes „GLS accomplish this by
organizing the nodes into a hierarchical structure
according to a spatial quad-tree, plus exploiting the ID
assigned to each node

19. GLS:
The one selected to be the location service for B is always
the node” close to B” „The node with least ID greater than
B „If no nodes greater than B in the tile ,select the node
with the smallest ID less than B