Transcript Chapter 8 Asynchronous System Model

Energy-Efficient
Communication Protocol for
Wireless Microsensor
Networks
Wendi Rabiner Heinzelman, Anantha
Chandrakasan, and Hari Balakrishnan
by Mikhail Nesterenko
Outline
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I/O automaton definition
examples of I/O automata
execution
operations on I/O automata
– composition
– hiding
fairness
properties and proof methods
– invariants
– trace properties
– compositional reasoning
– hierarchical proofs
complexity
randomization
Radio and CommunicationModel
• nodes have sensors and limited energy supply
• nodes sense data and send it to centralized location – base
station; base station has large energy supply
• transmitter and receiver dissipate (use) the same amount of
energy (50nJ/bit)
– plus transmitter (amplifier) is using additional amount
proportional to square of distance to transmit
• radio channel is symmetric
• constant bit rate data generation (every node is sensing
and always ready to transmit)
Energy Analysis of Routing Protocols
• two models
– direct communication to base station
• drains the power of transmitters
• since only base station receives no sensor’s energy is
spent on the receivers
• hence if base station is close to the nodes or energy to
receive message is large, this strategy may be optimal
– “minimum energy” multihop routing – in addition to
sensing nodes act as routers to other nodes’ data
• conventional protocol optimize transmitter’s energy
minimum transmitter’s energy – MTE) but not
receiver’s
• see Figs. 3, 4, 5
More Problems with MTE
• MTE quickly drains the energy of nodes closest to base
station (and they die) which, in turn, drains even more energy
from nodes that are slightly off the base station – cascading
effect
• simulation
– MTE – nodes closest to base station die first
– direct – nodes furthest from bases station dies first
• see Fig. 6
Clustering
• conventional clustering assumes that there is a cluster head
(local base station) that collects the sensor data and
transmits to base station
– cluster head is close to the sensors so their energy is
conserved
– cluster head routes all messages from the cluster and
quickly dies
Low-Energy Adaptive Clustering
Hierarchy (LEACH)
• to conserve energy a cluster head LEACH includes randomized
rotation of a cluster head
• cluster head “compresses” (aggregates) the data before sending to
base station
• node randomly (proportional to the amount of remaining energy
remaining) elects itself cluster head (independently of other nodes in
the network)
– informs neighbors about it
– gives schedule as two when the neighbors send their data to
cluster head
– aggregates the sent data and sends it to base station
• the number of clusters is determined in advance to conserve overall
energy (see Figs 7, 8, 9, 10)
– there exists an optimum number of cluster heads (~5%)
– with this optimum LEACH reduces energy dissipation up to 7
times
– less cluster heads, less detailed picture
System Lifetime in LEACH
• besides decreasing energy dissipation, LEACH increases
system lifetime
– under LEACH it takes approx 8 times longer for the first
node to die and 3 times longer for the last node to die
(compared to any other protocol) – see Table 1
– the pattern of nodes deaths is uniform which increases
usability of the system as nodes dies; see Fig 12,
compare to Fig 6
LEACH Details
• functioning is in rounds, each round has two phases
– setup phase (short) – clusters are organized
– steady phase (long) – data is transferred to the base station
• phases
– advertisement – each node probabilistically elects to be a
cluster head and sends a “cluster-head-advertisement”
message with the same energy, a non-head node picks the
head on the basis of received signal strength
– cluster setup – the nodes inform cluster heads about their
choice
– schedule creation – cluster head creates TDMA schedule and
broadcasts it to the cluster
– data transmission – each node sends data to cluster head,
cluster head aggregates and forwards to base station
• to reduce interference between clusters CDMA spreading codes
are used (different frequencies?)
• LEACH can be extended to hierarchy