25-08-2017, 09:32 PM
An Application-Specific Protocol Architecture for Wireless Microsensor Networks
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Introduction
Sensor Network Challenges
Limited communication bandwidth
Limited energy
Parameters (Design goals)
Ease of deployment
System lifetime
Latency
Quality
Neighboring nodes may have same data
End user cares about a higher-level description of events
LEACH (Low-Energy Adaptive Clustering Hierarchy)
Techniques (to achieve the design goals)
Randomized, adaptive, self-configuring cluster formation.
Localized control of data transfers
Low energy media access control (MAC)
Application specific data processing, such as data aggregation
and compression.
Background
Some application-specific protocols developed for MSN
Time division multiple-access(TDMA) MAC protocol for low-energy operation.
“Power-aware” routing protocols for wireless networks.
“Minimum transmission energy”(MTE) routing
Clustering
Nodes send data to central cluster head
Cluster head forwards data
Cluster head has to be high energy node
Fixed Infrastructure
LEACH Protocol Architecture
LEACH in brief
Randomized rotation of cluster heads among the sensors
All non-cluster head nodes transmit data to their cluster head
CH receives this data and performs signal processing
functions on the data and transmits data to the BS
Cluster Head Selection Algorithms
Pi(t) is the probability with which node i elects itself to be Cluster Head at the
beginning of the round r+1 (which starts at time t) such that expected number of
cluster-head nodes for this round is k.
k= # of clusters during each round
(1) N= # of nodes in the network
Each node will be Cluster Head once in N/k rounds.
Probability for each node i to be a cluster-head at time t
(2)
Ci(t) = it determines whether node i has been a cluster
head in most recent (r mod(N/k)) rounds.
Cluster Head Selection Algorithms (cont.)
This ensures energy at each node to be approx. equal after every N/k rounds.
Using (2) and (3), expected # of Cluster Heads per round is,
Steady State Phase
To reduce inter-cluster interference, each cluster in LEACH communicates using direct-sequence spread spectrum (DSSS).
Data is sent from the cluster head nodes to the BS using a fixed spreading code and CSMA.
LEACH-C: BS Cluster Formation
Uses a central control algorithm to form clusters
During setup phase each node sends its location and energy level to BS
BS assigns cluster heads and clusters
BS broadcasts this information
The steady-state phase is same as LEACH
Conclusion
Microsensor network protocols must be designed for
Bandwidth efficiency
Energy efficiency
High quality
LEACH
Better energy utilization and system lifetime
Load balancing is achieved
All nodes die at a time