Solar-aware Clustering in Wireless Sensor Networks
Thiemo Voigt
Swedish Institute of Computer Science (SICS)
thiemo@sics.se
Adam Dunkels
SICS
adam@sics.se
Juan Alonso
SICS
alsonso@sics.se
Hartmut Ritter
Freie Universit
¨
at Berlin
hritter@inf.fu-berlin.de
Jochen Schiller
Freie Universit
¨
at Berlin
schiller@inf.fu-berlin.de
Abstract
Energy conservation plays a crucial in wireless sensor
networks since such networks are designed to be placed in
hostile and non-accessible areas. While battery-driven sen-
sors will run out of battery sooner or later, the use of re-
newable energy sources such as solar power or gravitation
may extend the lifetime of a sensor network. We propose to
utilize solar power in wireless sensor networks and extend
LEACH a well-known cluster-based protocol for sensor net-
works to become solar-aware. The presented simulation
results show that making LEACH solar-aware significantly
extends the lifetime of sensor networks.
1 Introduction
Wireless sensor networks have to take into account the
very limited resources of the nodes [1]. While many re-
searchers assume that all nodes in a sensor network are
battery-driven [7, 14, 15] nodes can also be powered by
other energy sources such as gravitation or solar power.
Nodes powered by such a source can process data, receive
and transmit packets as well as perform other tasks with-
out consuming battery energy. Therefore, it is attractive to
let nodes driven by solar energy perform the most energy-
demanding tasks. In cluster-based networks, the cluster
heads are responsible for performing the main and most
energy-intensive tasks. Hence, choosing solar-powered
nodes as cluster heads is attractive. It is, however, com-
plicated by the fact that the energy source is not permanent.
In the lab at FU Berlin, we have developed sensor boards
equipped with solar cells. This motivated us to investigate
if preferably choosing solar-powered nodes as cluster heads
is feasible and can provide energy savings.
Giving the already huge number of routing protocols in
wireless sensor networks, we decided to extend an exist-
ing cluster-based protocol rather than defining a new pro-
tocol from scratch. Towards this end, we extend LEACH
(low-energy adaptive clustering hierarchy) [7, 8], proba-
bly the best-known cluster-based protocol, to become solar-
aware. In a new version of LEACH [8], the base station
chooses the cluster heads. The cluster heads selected by the
base station remain cluster heads for a certain time called
round. We present two solar-aware extensions to LEACH
and present simulation results comparing the increased sen-
sor network lifetime with the standard centralized LEACH
protocol. Both solar-aware extensions provide significant
benefits in many scenarios. The reason for this improve-
ment is that solar-driven nodes have a higher probability to
become cluster heads and perform the energy-intensive du-
ties of a cluster head without consuming battery power.
However, in some scenarios, it is not sufficient to keep
the cluster head selected by the base station for an entire
round. We present a handover mechanism that allows a
cluster head to choose another, solar-powered node, as a
new cluster head. We show that this handover provides ad-
ditional benefits in these scenarios.
We have also extended a distributed version of
LEACH [7] to become solar-aware and demonstrate that
solar-awareness also in this case prolongs the lifetime of
the sensor network.
Our paper is outlined as follows. The following two
sections present some background on our hardware and on
LEACH. Section 4 explains the solar-aware versions of the
centralized LEACH protocol. Section 5 presents a set of
carefully chosen experiments. In the following section we
present the distributed version of LEACH and discuss and
evaluate solar-aware extensions. After presenting related
work in Section 7, we summarize our results and discuss
items of future work.
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