Presently, wireless sensor networks most challenging applications are related to mobile sinks or even nodes, monitoring and intervening in critical areas. To this end, proper communications protocols design plays a crucial role in fulfilling user requirements. In the following, the benefits of adopting directive antennas, both in terms of energy saving and targets tracking are presented by integrating this feature into a novel MAC protocol (MD-STAR). Simulation results are also deeply provided, underlining higher performance of MD-STAR with respect to existing solutions, for different directive main lobe width and node density values.

1. Slide 12009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
Energy Efficient Communications Solutions for NomadicEnergy Efficient Communications Solutions for Nomadic
NodesNodes
Within a Wireless Sensor NetworksWithin a Wireless Sensor Networks
Luca Bencini, Francesco Chiti, Giovanni Collodi, Davide Di Palma,
Romano Fantacci, Antonio Manes, Gianfranco Manes
Department of Electronics and Telecommunications – University of Florence

2. Slide 22009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
OUTLINEOUTLINE
• Introduction
• Application area
• System Requirement
• Mobile Directive Synchronous Transmission Asynchronous
Reception Protocol
• Proposed MAC Protocol
• State Diagram
• Discovery phase
• Regime phase
• Performance Analysis
• Relative lifetime gain
• Collision probability
• Latency
• Conclusion and future development

3. Slide 32009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
APPLICATION AREAAPPLICATION AREA
• habitat monitoring
• healthcare applications
• home automation
• traffic control
• robot applications (DustBot)
nomadic Wireless Sensor
Network application areas

4. Slide 42009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
SYSTEM REQUIREMENTSYSTEM REQUIREMENT
• low power consumption
• low latency
• low collision probability
• good synchronization between nodes and
nomadic nodes
cross-layer protocol
MD-STAR

5. Slide 52009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
Mobile Directive Synchronous Transmission Asynchronous Reception Protocol
MD-STAR protocol:
• is a novel cross-layer protocol
• allows the managements of smart antennas
• takes into the account the antenna capabilities (directivity)
• allows achievement of space-time synchronization for mobile nodes
in mesh topology networks
MD-STAR PROTOCOLMD-STAR PROTOCOL

6. Slide 62009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
STATE DIAGRAMSTATE DIAGRAM
INIT
OFF
DISCOVER
Y
REGIME
Switch on
fdf Nn <
fdf Nn = sNremptysecto =
lowbatterybattery _<
lowbatterybattery _<
sNremptysecto =≤1

7. Slide 72009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
DISCOVERY PHASEDISCOVERY PHASE
init
off
discove
y
regime
Switch on
fdf Nn <
fdf Nn = sNremptysecto =
lowbatterybattery _<
lowbatterybattery _<
sNremptysecto =≤1
time
fupset TT 2≥−
slf TTT += slf TTT +=
2
4
5
3 2
4 1
ID-node phase secto
r
2 T-phase 3
ID-node phase secto
r
2 T-phase 3
3
ID-node phase secto
r
2 T-phase 4

8. Slide 82009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
REGIME PHASEREGIME PHASE
init
off
discove
y
regime
Switch on
fdf Nn <
fdf Nn = sNremptysecto =
lowbatterybattery _<
lowbatterybattery _<
sNremptysecto =≤1
time
fT
lT
fT
lTsT sT
4
2
3
5
ID-node phase secto
r
4 T-phase 3
1
23
42
3 2
4 1
ID-node phase secto
r
2 T-phase 2
ID-node phase secto
r
2 T-phase 2
ID-node phase secto
r
2 T-phase 2

9. Slide 92009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
Rate 250 Kbps
Number of nodes [10, 15, …., 50]
Number of angular
sector
[1, 2, 4, 6, 8]
Monitored area 25 m x 25 m
Velocity of mobile node [4,1 : 5,1] m/s
PERFORMANCE ANALYSISPERFORMANCE ANALYSIS
• mobility model: Random Waypoint
Model (RWM)
• antenna model: ideal Switched Beam
antenna
Parameter considered to evaluate the performance of MD-STAR:
• relative lifetime gain
• collision probability
• latency

10. Slide 102009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
RELATIVE LIFETIME GAINRELATIVE LIFETIME GAIN

11. Slide 112009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
COLLISION PROBABILITYCOLLISION PROBABILITY

12. Slide 122009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
LATENCYLATENCY

13. Slide 132009 Radio & Wireless Symposium, San Diego, CA.2009 Radio & Wireless Symposium, San Diego, CA.
CONCLUSION AND FUTURECONCLUSION AND FUTURE
DEVELOPMENTDEVELOPMENT
CONCLUSION:
• MD-STAR protocol is suitable for the management of mesh
topology networks in presence of nomadic nodes.
• MD-STAR protocol satisfies the system requirement of low
power consumption, low latency and low collision probability.
FUTURE DEVELOPMENT:
• modify MD-STAR algorithm to manage mobile nodes using a
phased array antenna model.