Image Processing Reference
In-Depth Information
Next TDMA
schedule
Cluster members CH
CH BS
Direct transmission
(a)
Next setup
phase
Cluster members CH
Multi-hop forwarding
(b)
Next TDMA
schedule
CH higher level
or
CH BS
Sleeping
nodes
Idle nodes
BS nodes
(c)
FIGURE .
Super-frame comparisons between LEACH, MECH, and APTEEN. (a) LEACH transmission schedule.
(b) MECH transmission and forwarding phases. (c) APTEEN transmission schedule.
after all the data transmissions of low duty-cycle nodes. As in TEEN, forwarding is always to the
next-level cluster head, or directly to the sink node for the uppermost-level cluster head. But here
the sink node can communicate directly with any node, and hence, in addition to a time slot
for communication between cluster head and sink, the TDMA schedule also has a data time slot
for transmissions between the sink node and other non-cluster-head nodes.
Regarding energy efficiency, APTEEN performs slightly worse than TEEN, as non-cluster-head
nodes that are listening for incoming queries cannot go to sleep. his increased energy consumption
is partially balanced by the reactive operating mode. here is a trade-off between energy consump-
tion and response time, since the use of periodic transmissions can reduce the response time for
the queries (the BS always has updated data, so it does not need to wait for the sensed data), but it
also increases energy consumption. Nevertheless, APTEEN improves on LEACH, as it transmits data
basedonthethresholdvalues,whileLEACHtransmitsdataallthetime.
7.5.2.6 Power-Efficient Gathering in Sensor Information Systems (PEGASIS) Protocol
The PEGASIS protocol is a LEACH-inspired protocol proposed in [Lin]. PEGASIS is not exactly a
cluster-based protocol, as nodes are not explicitly grouped into clusters. PEGASIS is instead a chain-
based approach, in which each node only communicates with a close neighbor and takes turns to
transmit to the BS, thus reducing the amount of energy spent per round. his approach distributes
the energy load evenly among the sensor nodes in the network.
The PEGASIS protocol is designed for a WSN containing homogeneous and energy-constrained
nodes, with no mobility. The BS (sink) is fixed and far away from nodes. The radio model adopted
here is the same as the one presented in [Hei], i.e., the first-order radio model. Using this model,
energy efficiency can be improved by minimizing the amount of direct transmissions to the sink
node. This idea is common to the LEACH protocol, in which clustering is used to reduce both the
duty cycle of the nodes and direct transmissions to the BS. A way in which energy efficiency can be
further improved is to decrease the number of nodes that perform long-range direct transmissions.
So the basic idea of PEGASIS is to have only one designated node that directly transmits to the BS
in each round. his can be achieved with a linear chain-based approach, where sensor nodes form a
