Conference Paper

Design and Application of Enhanced Communication Protocols for Wireless Sensor Networks operating in Environmental MonitorinDg

Dipartimento di Elettronica e Telecomunicazioni, Universitá degli Studi di Firenze - Via di S. Marta, 3 - 50139, Italy. Email:
DOI: 10.1109/ICC.2006.255596 Conference: Communications, 2006. ICC '06. IEEE International Conference on, Volume: 8
Source: IEEE Xplore

ABSTRACT

The adoption of Wireless Sensor Networks (WSN) for wide area environmental monitoring is currently considered one of the most challenging application scenario for this emerging technology. The promise of an unmanaged, self-configuring and self-powered wireless infrastructure attracts the attention of both final users and system integrators, replacing previously deployed wired solutions and opening new business opportunities. Even if many habitat monitoring applications usually do not provide for strictly real-time performances, however, smart power saving procedures have to be adopted, especially to increase the network lifetime. A common approach is to introduce a low power sleep mode, in which the node's radio section is switched off. In adhoc networking scenarios, this definitely requires the adoption of synchronization procedures, properly scheduling the packet transmission time and avoiding both overhearing effects and collisions. In this paper, a novel class of MAC layer protocols, named STAR MAC, that aims at efficiently managing the node's low power mode, is presented, and properly integrated within a routing scheme, according to the cross-layer design for minimizing the signaling overhead. The proposed solution is applied to a realistic user defined scenario oriented to agro-food production phase monitoring, highlighting remarkable advantages both in terms of cost and complexity reduction and QoS enhancement as well and, consequently, validating the WSN technology adoption.

Full-text

Available from: R. Fantacci
Design and Application of Enhanced
Communication Protocols for Wireless Sensor
Networks operating in Environmental MonitorinDg
Francesco Chiti
, Michele Ciabatti
, Giovanni Collodi
,DavideDiPalma
, Romano Fantacci
, Antonio Manes
Dipartimento di Elettronica e Telecomunicazioni,
Dipartimento di Energetica,
Universit
´
a degli Studi di Firenze -Via di S. Marta, 3 - 50139, Italy
Email: chiti@lenst.det.unifi.it, michele.ciabatti@unifi.it, collodi@ing.unifi.it,
davide.dipalma@unifi.it, romano.fantacci@unifi.it, antonio.manes@unifi.it
Abstract The adoption of Wireless Sensor Networks (WSN)
for wide area environmental monitoring is currently considered
one of the most challenging application scenario for this emerging
technology. The promise of an unmanaged, self-configuring and
self-powered wireless infrastructure attracts the attention of both
final users and system integrators, replacing previously deployed
wired solutions and opening new business opportunities. Even
if many habitat monitoring applications usually do not provide
for strictly real-time performances, however, smart power saving
procedures have to be adopted, especially to increase the network
lifetime. A common approach is to introduce a low power sleep
mode, in which the node’s radio section is switched off. In ad-
hoc networking scenarios, this definitely requires the adoption
of synchronization procedures, properly scheduling the packet
transmission time and avoiding both overhearing effects and
collisions. In this paper, a novel class of MAC layer protocols,
named STAR MAC, that aims at efficiently managing the node’s
low power mode, is presented, and properly integrated within a
routing scheme, according to the cross-layer design for minimiz-
ing the signaling overhead. The proposed solution is applied to a
realistic user defined scenario oriented to agro-food production
phase monitoring, highlighting remarkable advantages both in
terms of cost and complexity reduction and QoS enhancement as
well and, consequently, validating the WSN technology adoption.
I. INTRODUCTION
In the recent years, the availability of on-field monitoring
became a key issue for the assessment of environmental
processes and parameters. In this context, the application
of Wireless Sensor Networks (WSNs) technology represents
a significant advance over traditional invasive methods of
monitoring [1], [2]. As a matter of fact, instrumenting nat-
ural spaces with networked microsensors might enable long-
term data collection with enhanced accurateness. Further,
the communication capabilities allow nodes to cooperate in
performing more complex tasks, like statistical sampling or
data aggregation, not feasible with a point-to-point telemetry.
Finally, the computing and networking capabilities permits
both the reprogramming or even the autoreconfiguring of the
whole system.
The increasing need for products controlling at different
critical steps of the agro-food chain open a novel application
field for WSN. Among the related initiatives founded by public
institutions, the GoodFood Integrated Project [3], presented
within the IST thematic area of EC VI FP, aims at developing
the new generation of analytical methods based on Micro and
Nanotechnology (MST and M&NT) solutions for the safety
and quality assurance along the food chain in the agrofood
industry. GoodFood approach will comply, through the de-
velopment of innovative M&NT solutions, with the needs
of ubiquity, low cost and low power, fast response, simple
use and fully interconnection to the decisional bodies. The
project’s WorkPackage 7, aimed at implementing intelligent
and innovative communication solutions for food safety and
quality traceability, is developing a Pilot Site, oriented to the
wine production phase monitoring; this Pilot Site is being
deployed at the Montepaldi Farm (in the Chianti region, Italy),
and is expected to be fully operative by the end of 2005.
The requirements that WSN adoption is expected to satisfy
in performing an effective agro-food monitoring are mainly
concerned with the operating period. In particular, a large
number of battery operated nodes, deployed in outdoor en-
vironments, is expected to operate at least for a farming
season (usually 3-6 months), without maintenance. Besides,
since node are usually unattended, they might cope with node
fails or network congestion by means of adapting or even
autoreconfiguring their functionalities and protocols. Finally,
correct data delivering to remote user via gateway is to be
guaranteed to allow a proper monitoring.
The afore mentioned requirements compels the WSN com-
munications protocols to be carefully designed and optimized
for the case study under consideration. In this paper, a cross-
layer solution is presented, joining the MAC and Network
layers operations. The MAC layer protocol features are de-
scribed in Section II together with the performance analysis
as to the network synchronization capabilities. In Section III
the cross-layer routing protocol is highlighted and the overall
communications performance is presented for the practical
test case offered by the GoodFood project. Finally, some
conclusions are drawn explaining the future directions of the
present research activity.
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2006 proceedings.
1-4244-0355-3/06/$20.00 (c) 2006 IEEE
Page 1
II. MAC LAYER PROTOCOL
A. System Requirements
The most relevant system requirements leading the design
of an efficient Medium Access Control (MAC) protocol for an
environmental monitoring WSN, as to GoodFood project, are
mainly concerned with the power consumption issues and the
capability of quickly set-up an end-to-end communication in-
frastructure that supports both synchronous and asynchronous
queries. In particular, the most relevant challenge is to make
a system able to run unattended for a long period, as nodes
are expected to be deployed in zones hardly manageable for
maintenance. This calls for an optimal energy management,
since it is anyhow a limited resource and the failure of a
nodes may compromise WSN connectivity, as the network
gets partitioned. Therefore the MAC layer is to be optimized
ensuring that the energy it spends is directly related to the
amount of traffic that it handles and not to the overall working
time.
Other important properties are scalability and adaptability
of network topology, in terms of number of nodes and their
density. As a matter of fact, some nodes may either be turned
off or join the network afterward or, finally, they could be
moved to a different location. Thus, the MAC layer protocol
might be able to face these events with an higher degree of
responsiveness and reconfigurability.
Finally, several user-oriented attributes, including fairness,
latency, throughput and bandwidth utilization, need to be taken
into account even if they could be considered secondary with
respect to our application purposes, since, in contrast to typical
WLAN protocols, MAC protocols designed for WSN usually
trade off performance for cost [4].
Taking the IEEE 802.11 distributed coordination function
(DCF) [5] as a starting point, several more energy efficient
techniques have been proposed in literature to avoid excessive
power wasting when a node are in the so called idle mode, i.e.
a state in which it continuously sample the channels waiting
for a message. their circuitry. They are based on the receiver
periodical turning on the radio to detect the presence of a
packet preamble and if no signal is sensed the radio is turned-
off again until the next sample. As a consequence, a low
power state, in which the transceiver is disabled and only a
low level clock is active, might be introduced, duty cycling
the radio. Furthermore, the sender can simply wait until the
moment the receiver is about to sample the channel, and send
a packet with an ordinary preamble, this saving energy both at
the sender and at the receiver. In particular, according to the
WiseMAC protocol [6] nodes maintain the schedule offsets of
their neighbors through piggy backed information on the ACK
of the underlying CSMA protocol. However, WiseMAC suffers
the disadvantages of being subject to traffic fluctuations and,
moreover, to not efficiently managing message broadcasting
due to the absence of synchronization procedures.
Deriving from the classical contention-based scheme, sev-
eral protocols (S-MAC [7], T-MAC [8], and DMAC [9])
have been proposed to address the idle listening overhead
by synchronizing the nodes, and implementing a duty cycle
within each slot. At the beginning of a slot, all nodes wakeup
and any node wishing to transmit a message must contend
for the channel. This increases the probability of collision in
comparison to the random organization of the energy-efficient
CSMA protocols. To mitigate the increased collision overheads
S-MAC and T-MAC include an RTS/CTS handshake, while
DMAC avoids this protocol overhead.
Resorting to the above considerations, a class of MAC
protocols, particularly suited for a flat network topology, as
that considered in [3], has been derived, taking the benefits
of both WiseMAC and S-MAC schemes. In particular, it joins
the power saving capability, due to the introduction of a duty-
cycle, together with the advantages provided by the offset
scheduling, without an excessive signaling overhead. More
details about protocol issues, related TinyOS modules for the
implementation, and the provided advantages are given within
the next Section.
B. Proposed Scheme
1) Synchronous Transmission Asynchronous Reception
(STAR) MAC: An alternative approach to the problem of
providing an energy efficient MAC solution is represented
by the proposed scheme that is characterized as it follows.
Following [6], each node might be either into an idle mode,
in which it remains for a time interval T
l
(listening time), or
in an energy saving sleeping state for a T
s
(sleeping time).
The transitions between states are synchronous with a period
called frame equal to T
f
= T
l
+ T
s
partitioned in two sub-
intervals; as a consequence, a duty-cycle function can be also
introduced:
d =
T
l
T
l
+ T
s
(1)
Though the protocol is able to manage a specific duty cycle
for each node, it has been assumed to be the same for all the
nodes as so it usually happens. To provide full communication
capabilities to the network, all the nodes need to be weakly
synchronized, or, equivalently, to be aware at least of the
awakening time of all their neighbors. To this end, a node
sends frame by frame one synchronization message to each
of its neighbor nodes known to be in the listening mode
(Synchronous Transmission), as explained in Figure 1. Instead,
during the set up phase in which each node is discovering the
network topology, the control messages are asynchronously
broadcasted. On the other hand, its neighbors periodically
awake and enter the listening state independently (Asynchro-
nous Reception), as it is again presented in Figure 1. The
header of the synchronization message contains the following
fields: a node unique identifier, the message sequence number
and the phase, that is, the time interval after which the sender
claims to be in the listening status waiting for both the
synchronization and data messages from its neighbors. The
phase φ is evaluated according to the Figure 2 as it follows:
φ
1
= τ T
l
(2)
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Page 2
Parameter Value
c
Rx
=
10 mA
c
sleep
=
0.01 mA
C
Tx
=
30 mAh
c
Tx
=
0.001 mA
TAB LE I
P
OWER CONSUMPTION PARAMETERS FOR THE CONSIDERED PLATFORM.
if the node is in the sleeping mode, where τ is the time
remaining to the next frame beginning. Conversely, if the mote
is in the listening status, φ is calculated as:
φ
2
= τ + T
S
(3)
In order to fully characterize the STAR MAC approach, the
related energy cost can be evaluated as it follows:
C = c
Rx
dT
f
+c
sleep
[T
f
(1 d) NT
pkt
]+NC
Tx
[mAh]
(4)
where c
sleep
and c
Rx
represent the sleeping and the receiv-
ing costs [mAh] and C
Tx
is the single packet transmission
costs [mA], while T
Rx
and T
s
are the receiving and sleeping
times [s], T
pkt
is the synchronization packet time length [s]
and finally N is the number of neighbors. When the following
inequality hold:
NT
pkt
T
f
then:
C
=
c
Rx
dT
f
+ c
sleep
T
f
(1 d)+NC
Tx
[mAh] (5)
The protocol cost normalized to the synchronization time is
finally:
C
T
f
= c
Rx
d + c
sleep
(1 d)+
NC
Tx
T
f
[mA] (6)
As highlighted in Table I, it usually happens that c
Tx
<<
c
sleep
<< c
Rx
, in where c
Tx
= C
Tx
/T
pkt
and T
pkt
is the packet
transmission time [s], assumed equal to 100 ms as worst case.
This means that the major contribution to the overall cost
is represented by the listening period that the STAR MAC
protocol tries to suitably minimize. Nevertheless, an advanced
approach is presented below, aiming at minimizing also the
cost of packet transmission for densely deployed WSN or with
a high traffic load factor.
2) Enhanced STAR (STAR+) MAC: This approach intro-
duces an improvement in the STAR MAC as only one syn-
chronization packet is multicasted to all the neighbor nodes
belonging to a subset, i.e., such that they are jointly awake for
a time interval greater than T
Rx
. This leads to an additional
advantage, as the number of neighbors increases allowing
better performance with respect to scalability and a power
saving too. Besides, the synchronization overhead is reduced
with a consequent collisions lowering. Under this hypothesis
and, moreover, supposing that the number of subsets is K,
then the normalized cost might be expressed as:
C
T
f
= c
Rx
d + c
sleep
(1 d)+
KC
Tx
T
f
[mA] (7)
Since K N, the normalized cost results to be remarkably
lowered, especially if number of nodes and duty-cycle get
higher, even if the latter case is inherently power consuming.
C. STAR MAC Protocol Performance Analysis
A distributed network, in which nodes continuously switch
on and off, involves the considerable task of synchronism
maintaining among neighboring nodes: small hardware tol-
erances that are negligible in an isolated device become
relevant in long life networks, where motes have to preserve
mutual communication. In particular, nodes might face timing
misalignments (drift) arising from several reasons: different
FSMs, technologies and implementations for each node or in
addition not equal dynamic behaviors due to different sensing
messages handling. As a result, within a short period, it is
likely the lack of synchronization for the nodes to occur.
STAR MAC protocol effectively overcomes this problem,
since it does not rely upon a strict distributed synchro-
nization: the nodes are not expected to behave exactly in
the same way for what time issues are concerned, but the
capabilities provided by the communication protocol permit
to evaluate when and whom a message might be transmitted
to. The dynamic phase estimation, performed every MAC
period according to (2) or (3), allows each node to track and
compensate the time drifts of its neighbors without additional
complexity. Finally, it is worth noticing that the randomness
of the awakening times of all the nodes, due to the deployment
procedures, is able to reduce the collision probability over the
shared medium.
To highlight the benefits yielded by the STAR MAC, two
different test cases are presented. In the first case, two similar
nodes with the same FSM and moreover with the same T
f
and duty cycle equal to 60 s and 10%, respectively, are
investigated. In Fig. 3 the time diagram concerning the values
of the phase φ transmitted by each node is presented, pointing
out the presence of a phase drift for each node due to a
not ideal duty cycle. However, this is upper bounded by
the communication protocol, since the neighbor node upon
the reception of a synchronization message is able to com-
pensate for it by anticipating or delaying the sending of its
next synchronization message to that neighbor. Besides, this
positive attitude is better highlighted in Figure 4 where the
drift statistics for the nodes are compared. In particular, it is
shown that these random variables are both Gaussian with zero
mean and the same variance, thus proving the goodness of our
approach.
To fully characterize the system performance, a scenario
comprised of two nodes with different behaviors was also
investigated. In particular, an ordinary node with T
f
and duty
cycle equal to 60 s and 10%, respectively, and a master node
always in listening mode (i.e., with null duty cycle) have been
taken into account. In this case, the transmitted phase values
show a greater variation range, as it is pointed out in Fig. 5,
since the switching to the high power state from the low power
state considerably effects the accurateness of the duty cycle.
Nevertheless, the STAR MAC protocol is again able to limit
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Page 3
its negative impact through a compensation performed by each
node every synchronization period. This is fully presented in
Fig.s 6 where the statistics of the phase drifts for the master
node and the Node are depicted. In particular, it is possible
to notice that the ordinary node is effected by a remarkable
phase drift, whose mean value is about 500 ms, whilst the
master node mean phase drift is on the opposite equal to -
500 ms, thus pointing out the time compensation provided by
the STAR MAC protocol. These advantages is more evident
by noticing that a complete phase rotation takes about 6000 s
for an ordinary node (see Figure 5, while, basing on the above
mentioned mean value, a phase rotation period would be equal
to 300 s if this node was completely isolated, i.e., without the
time synchronization provided by the master node.
III. N
ETWORK LAY E R PROTOCOL
A. Application Requirements
The provisioning of remote environmental monitoring ca-
pabilities, as expected within the GoodFood project, estab-
lishes several requirements that communications protocols
may satisfy. Some of them are related with the end user
applications characteristics, while the others depend on the
node’s hardware restrictions. First of all, the data reporting
method is essentially time-driven [10] as applications require
periodic data monitoring. In future system releases it will
be likely to support also query-driven scheme in which the
gateway or another node in the network is able to generate a
specific query to another node, to acquire a certain parameter
value.
An additional requirement is represented by the need of fault
tolerance, since a node may fail for several reasons. In this
case, MAC and routing protocols might cooperate to quickly
set up a new end-to-end path.
Besides a certain amount of redundancy might be introduced
to allow data delivery even in the case of node’s trouble due
to physical damage, or environmental interference since the
communication protocol is unreliable, meaning that no explicit
acknowledgment is provided to lower the signaling overhead
and not to reduce the available bandwidth.
Finally, scalability issues may be addressed to make the
routing scheme able to operate in the correct way despite
the number of deployed nodes that can be on the order of
hundreds to sense a wide area. Moreover, the routing protocol
might cope with contemporaneous transmissions, occurring
when several nodes jointly enter the listening state trying to
control the network congestion.
To end with, the power consumption is to be deeply
considered in designing routing protocol, as usually nodes
have limited energy supply and limited computing power. In a
multihop WSN, each node plays a dual role as data sender and
data router: the energy needed to perform computations and
delivering information might dramatically reduce the node’s
lifetime, thus impacting on the network lifetime. As a results,
energy-conserving forms of communication and computation
are of primary importance.
B. Proposed Solutions
In order to evaluate the capability of the proposed MAC
scheme in establishing effective end-to-end communications
within a WSN, a routing protocol has been introduced and
integrated according to the cross layer design principle [11].
In particular, we refer to a proactive algorithm belonging to
the class of link-state protocol that enhance the capabilities of
the Link Estimation Parent Selection (LEPS) protocol [12].
It is based on periodically sending a control message to
neighbor nodes to carry on information needed for building
and maintaining the local routing table, depicted in Figure 7.
However, our approach resorts both to the signaling introduced
by the MAC layer, i.e., the synchronization message, and by
the Network layer, i.e., the ping message, with the aim of min-
imizing the overhead and make the system more adaptive in
a cross-layer fashion. In particular, the parameters transmitted
along a MAC synchronization message, with period T
f
,are
the following:
next hop to reach the the gateway, that is, the MAC
address of the one hop neighbor;
distance to the gateway in terms of number of needed
hops;
phase the schedule time at which the neighbor become
listening evaluated according to (2) or (3) in order to
minimize the time latency;
link quality estimation as the ratio of correctly received
and the expected synchronization messages from a certain
neighbor.
On the other hand, the parameters related to long-term phe-
nomena are carried out by the Network layer messages (ping),
with period T
p
>> T
f
, in order to avoid unnecessary control
traffics and, thus, reducing congestion. Particularly, they are:
battery level, i.e., an estimation of the energy available
at that node;
congestion level in terms of the ratio between the number
of packets present in the local buffer and the maximum
number of packets to be store in.
Once, the routing table has been filled with these parame-
ters, it is possible to derive the proper metric by means of a
weighted summation of them.
C. Overall Performance Analysis
1) Test-case Scenario: The reference scenario considered
in performing the simulations is related to the vineyard area
selected for the exploitation of the Good-Food project Pilot
Side at the University of Florence’s owned Montepaldi farm.
In this site, 15 nodes will be deployed in 10000 m
2
area by
the end of 2005, and at the present 9 nodes are fully operative.
Each node could be endowed with sensors monitoring three
different environments: plant, root soil and canopy atmosphere.
In Table II, the characteristics of each sensed environment in
terms of involved sensors and acquisition period are presented.
On the whole nodes, the sensors for soil temperature and
moisture, leaf temperature, and air temperature/humidity will
be implemented.
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2006 proceedings.
Page 4
Subsystem Monitored parameters T
Q
[min]
Root Soil Soil temperature 15
Soil moisture 15
Canopy atmosphere Air temperature 15
Air humidity 15
Plant Leaf temperature 15
Shoot diametric growth 15
TAB LE I I
C
HARACTERISTICS OF EACH SUBSYSTEM COMPOSING THE VINEYARD.
The power consumption values for the adopted optimized
platform are those reported in Table I; besides, T
l
=4s, T
S
=
56 s and, consequently, d =6.7%, moreover, the deployed
batteries are C-type primary lithium batteries. Finally, the
applied communications protocol is described in III-B.
The whole system is still running unattended beginning
from the summer season; packets are collected by the master
node and their correct delivering is monitored by a specific
application hosted within the remote server ( logger) that
stores and processes data.
2) Experimental Results: First of all, it has been measured
the node’s energetic consumption by averaging it over the
whole network: it results to be equal to 1.44 mAh. On
the other hand, its estimated value, based on modeling the
network behavior as a FSM and considering the practical
power consumption values as in Table I, is equal to 1.15
mAh, pointing out a good agreement with the experimental
results. As a consequence, the node life time is greater than 7
months in the case of above mentioned battery adoption, that
allows the network to operate for a farming season without
maintenance, as it is claimed by the user requirements.
Then the packet delivery ratio (PDR), i.e., the ratio between
the number of data packets correctly received by the master
node and the number of sent packets, has been verified to
be equal to 0.948. It could be due to link failures or the
residual packet collisions rate, not correctly handled by the
STAR MAC protocol, as packets are retransmitted when the
receiver is the sleeping mode. This allow the WSN utilization
for accurate environmental monitoring and, implicitly, validate
the efficiency of the adopted communication protocol.
To the purpose of evaluate the Quality of Service (QoS)
of the cross-layer solution, it has been measured the average
number of hops needed to deliver a packet to its destination.
It has been made feasible by concatenating the identifier of
intermediate nodes in a proper field of the packet header. It
is equal to 2.83; this circumstance implies that almost all the
data packets are not subject to loops that involve at least 4
hops and the routing functionalities are preserved. Finally, the
measured mean delivery delay, that is the difference between
the packet delivering time and the instant of its first sending,
results to be equal to 60.1 s, as the phase is randomly selected
with uniform distribution. This value represents a reasonable
latency for the considered application in which slow varying
phenomena are monitored.
IV. C
ONCLUSIONS
This paper deals with the proposal of an efficient cross-layer
communication protocol, allowing remarkable performance, in
terms of low power consumption and QoS, for a WSN oper-
ating in a critical scenario like outdoor environmental moni-
toring. At this aim an energy efficient MAC protocol, namely
STAR MAC, has been proposed and properly integrated within
a routing scheme, minimizing the signaling overhead. The
performance of the overall multi-hop communication solution
has been evaluated, by implementing it on motes operating
in the operative scenario related to the EU Integrated Project
GoodFood. In particular, it has been also described a practical
implementation of the Pilot Site, in terms of adopted platforms
and architectures on which the testing procedure has been
performed. The experimental results highlighted a noticeable
performance as far as energetic consumption, the node life
time, the data delivering efficiency and latency are concerned.
This allows the application of the WSN under investigation to
the field of environmental monitoring.
A
CKNOWLEDGMENT
The authors would like to express their gratitude to Prof.
Gianfranco Manes for his fruitful comments and discus-
sions. A particular thank the members of the EU Integrated
Project FP6-IST-1-508774-IP ”GoodFood” WorkPackage 7 for
their supporting in this research.
R
EFERENCES
[1] Akyldiz, I., F., Su, W., Sankarasubramaniam, Y., Cayirci, E. : A Survey
on Sensor Networks. IEEE Comm. Mag., (August 2002) 102–114.
[2] Ha
´
c, A. : Wireless Sensor Networks Designs. John Wiley & Sons, (2003).
[3] GoodFood Project. http://www.goodfood-project.org.
[4] Langendoen, K., Halkes, G. : Energy-Efficient Medium Access Control.
Tech. Rep. Delft University of Technology.
[5] IEEE standard 802.11: Wireless LAN Medium Access Control (MAC)
and Physical Layer (PHY) Specifications. (1999).
[6] El-Hoiydi, A., Decotignie, J.-D., Enz, C., Le Roux, E. : WiseMAC,
an Ultra Low Power MAC Protocol for the WiseNET Wireless Sensor
Network. in Proc. of SenSys’03, (November 2003).
[7] Ye, W., Heidemann, J., Estrin, D. : An Energy-Efficient MAC Protocol
for Wireless Sensor Networks. in Proc. of INFOCOM’02, 3 (June 2002)
1567–1576.
[8] van Dam, T., Langendoen, K. : An Adaptive Energy-Efficient MAC Proto-
col for Wireless Sensor Networks. in Proc. of SenSys’03, (November 2003)
171–180.
[9] Lu, G., Krishnamachari, B., Raghavendra, C. : An Adaptive Energy-
Efficient and Low-Latency MAC for Data Gathering in Sensor Networks.
in Proc. of WMAN’04, (April 2004).
[10] Al-Karaki, J., N., Kamal, A., E. : Routing Techniques in Wireless Sensor
Networks: a Survey. IEEE Comm. Mag. 6 (2004) 6–28.
[11] Shakkottai, S., Rappaport, T., S., Karlsson, P., C. : Cross-layer Design
for Wireless Networks. IEEE Comm. Mag., 41 (October 2003).
[12] TinyOS. http://www.tinyos.net.
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2006 proceedings.
Page 5
T
l
sleep
sleep
T
f
t
Tx
1
Tx
N
T
l
T
f
sleep
sleep
Tx
1
Tx
N
t
Fig. 1. STAR MAC functional characterization for two different nodes.
T
l
T
f
Tx
t
T
l
Tx
T
s
F
1
F
2
t
t
Fig. 2. Phase evaluation procedure for two different cases.
0
10000
20000
30000
40000
50000
60000
70000
0.00.00 1.12.00 2.24.00 3.36.00 4.48.00 6.00.00
Time [hh/mm/ss]
Transmitted Phase
Phase Node 1
Phase Node 2
Fig. 3. Time diagram of the transmitted phase for a couple of similar nodes.
−500 −400 −300 −200 −100 0 100 200 300 400 500
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
Phase drift values [ms]
Relative Frequency
(a) Node 1.
−1000 −500 0 500
0
0.01
0.02
0.03
0.04
0.05
0.06
Relative Frequency
Phase drift values [ms]
(b) Node 2.
Fig. 4. Statistics of the phase drift for homogeneous nodes.
0
10000
20000
30000
40000
50000
60000
70000
9.36.00 10.48.00 12.00.00 13.12.00 14.24.00 15.36.00
Time [hh/mm/ss]
Transmitted Phase
Phase Master Node
Phase Ordinary Node
Fig. 5. Time diagram of the transmitted phase for a couple of different
nodes.
−2500 −2000 −1500 −1000 −500 0 500 1000 1500 2000
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Phase drift values [ms]
Relative Frequency
(a) Master node.
0 500 1000 1500 2000 2500 3000 3500
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Phase drift values [ms]
Relative Frequency
(b) Ordinary node.
Fig. 6. Statistics of the phase drift for inhomogeneous nodes.
Fig. 7. Routing table general structure.
This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2006 proceedings.
Page 6
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    • "This paper deals with both the sleep/active states power management, as well as the introduction of directional antennas and their integration within the communications framework, following a cross-layer design. A novel MAC layer protocol, namely, D-STAR is proposed, aiming at expanding the capabilities of previously introduced STAR MAC approach [6] toward the management of directive antennas, without increasing the signaling overhead or affecting the setup latency, but by achieving a reduction in energy con- sumption.Figure 8 : Channel occupation probability as a function of the number of nodes in the case of omnidirectional and directive antennas with π and π/2 main lobes for T f = 93 seconds and δ = 3%. "
    [Show abstract] [Hide abstract] ABSTRACT: This paper deals with a novel MAC layer protocol, namely directive synchronous transmission asynchronous reception (D-STAR) able to space-time synchronize a wireless sensor network (WSN). To this end, D-STAR integrates directional antennas within the communications framework, while taking into account both sleep/active states, according to a cross-layer design. After characterizing the D-STAR protocol in terms of functional characteristics and antenna model, the related performance is presented, in terms of network lifetime gain, latency and collision probability. It has shown a remarkable gain in terms of energy consumption reduction with respect to the basic approach endowed with omnidirectional antennas, without increasing the signaling overhead nor affecting the set up latency.
    Full-text · Conference Paper · Feb 2008
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    • "We will focus on environmental monitoring [10, 11] as our basic application scenario. The characteristics of the scenario are: periodic traffic with low generation rate, delay insensitive communication , spatial and temporal redundancy of the data and sensor deaths being tolerable to some extent. "
    [Show abstract] [Hide abstract] ABSTRACT: Wireless Sensor Networks (WSNs) give rise to a new networking paradigm in which energy efficiency is a high priority goal. A direct measure of the energy efficiency is the network lifetime which WSN proposals strive to extend. To correctly quantify the lifetime, the metric must be defined in an application dependent manner. In this paper, we propose a generic lifetime measurement framework called Weighted Cumulative Operational Time (WCOT) for the performance evaluation of the WSNs. Novelty brought by WCOT is twofold: First, it defines a utility based interface for the diverse WSN applications to incorporate their scenario specific requirements into the metric itself. Second, WCOT assigns different weights to the operational durations that have different utilities and perform a weighted summation to calculate the cumulative lifetime thereafter. With this mechanism, a more representative lifetime metric which maps the complete network behavior into a numeric value is obtained. This is in contrast with metrics which focus solely on certain milestones of the network functionality to quantify the lifetime which include the first node death, the last node death.
    Full-text · Conference Paper · Oct 2007
  • Source
    [Show abstract] [Hide abstract] ABSTRACT: This paper deals with a novel MAC layer protocol, namely, directive synchronous transmission asynchronous reception (D-STAR) able to space-time synchronize a wireless sensor network (WSN). To this end, D-STAR integrates directional antennas within the communications framework, while taking into account both sleep/active states, according to a cross-layer design. After characterizing the D-STAR protocol in terms of functional characteristics, the related performance is presented, in terms of network lifetime gain, setup latency, and collision probability. It has shown a remarkable gain in terms of energy consumption reduction with respect to the basic approach endowed with omnidirectional antennas, without increasing the signaling overhead nor affecting the setup latency.
    Full-text · Article · Jan 2007 · EURASIP Journal on Wireless Communications and Networking
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