Wireless and Mobile Network
547 Mobile Ad-hoc Networks...
transmission range, and adaptive transmission period. A duty cycling in MAC layer involves the
sensor node to sleep/wake up mechanisms to conserve energy. Sleep/wake up mechanisms
involves in putting the radio transceiver in the (low-power) sleep mode whenever
communication is not required, Ideally, the radio should be switched off as soon as there is no
more data to send/receive, and should be resumed as soon as a new data packet becomes ready.
The mechanism which makes the sensor nodes to alternate between active and sleep periods
depending on network activity can be referred as duty cycling.
Network Layer: Routing is the process which finds the path between the source to destination
while initiating data communication in the network. Routing is much more important than any
other networks compared to WSNs.
Table 5.1: Radio characteristics
Radio Mode Energy Consumption
Transmitter Electronics (ElecTx)
Receiver Electronics (E-elecRx) 50nj/bit
(Eelec = EelecRx = EelectTx)
Transmit Amplifier (camp) 100 pJ/bit/m* |
Idle (Eidle) 40nj/bit /
Sleep
The energy spent in communication (transmission and reception) is much higher than Idle and sleep
state of the sensor node. Energy efficient routing can be done through Cluster based hierarchical
Routing, flat routing, multipath routing, and geographical routing.
LEACH Protocol is a kind of cluster-based routing protocols, which includes distributed cluster
formation. LEACH randomly selects a few sensor nodes as cluster heads (CHs) and rotates this role to
evenly distribute the energy load among the sensors in the network. The idea is to form clusters of
the sensor nodes based on the received signal strength and use local cluster heads as routers to the
sink. In LEACH, the CH nodes compress data arriving from nodes that belong to the respective
cluster, and send an aggregated packet to the BS in order to reduce the amount of information that
must be transmitted to the BS. LEACH uses a Time division multiple access (TDMA) and code-division
multiple access (CDMA) MAC to reduce inter-cluster and intra-cluster collisions. Cluster heads
change randomly over time in order to balance the energy dissipation of nodes
4. Transport Layer: When multiple nodes want to transmit data through the same channel at a time or
when the routing node fails to forward the received data to the next routing nodes congestion
occurs. Congestion and data loss occurs at nodes which are nearer to the sink nodes. Energy saving
can be achieved in transport layer of WSNs through energy aware congestion avoidance, energy
efficient load sharing and energy efficient reliable mechanisms between end to end communication
in WSNs.
. Application layer: Energy saving in the application layer is achieved through application service
which aims at energy conservation, by caching mutable data obtained from data-retrieval at
locations that minimize the sum of request and update traffic § asynchronously multicasting
updates from sensors to observers reduces the total number of packet transmissions in the network.
WSN Based Techniques
¢ Energy Efficient Deployment in WSN : The optimal deployment of nodes adds to the lifetime of the
network, along with determination of deployment cost, coverage, connectivity, etc. A good
deployment is important to achieve load balance and prolong the network lifetime
