Ciabatti Ph.D. final discussion

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Università degli Studi Di Firenze
Dipartimento di Elettronica e Telecomunicazioni
Ph.D. Thesis on RF Microwave and Electromagnetism (XX)
Supervisors:
Prof. G. Manes
Dr. G. Collodi
Coordinator:
Prof. G. Manes
Candidate:
Michele Ciabatti
Resource-Constrained Communication within
Wireless Sensor Network:
a new Cross Layer solution

Ph.D. thesis, Firenze June 6th 2008
1. Problem Statement
2. MAC protocols
Overview
3. Proposed MAC layer
STAR
Performance analysis
4. Directive antennas integration
5. Cross-Layer scheme
DSTAR
Performance evaluation
6. Conclusions
7. Future work
8. Research involvements
9. Publications
Outline

WSN: monitoring networking infrastructure with distributed sensing and
processing capability
Definition
large number of sensor nodes that are densely deployed
sink unit (gateway), acting as a interface among heterogeneous
networking infrastructures
Task Mng
IPvx
802.11-16
2G/3G
I
I
I
I I
I
I
I
I
I
G
I
G
sensor-node
gateway
1. Problem Satement
WSN

WSN protocols features
 Tasks:
• To realize a self-organizing network “infrastructure”
• To fairly and efficiently share communication resources
 Requirements:
• Unique destination (Sink)
• High nodes density
• Low nodes mobility
• Limited resources (bandwidth, battery, processing and storage)
• Data centric
• Application oriented
1. Problem Satement

WSN protocols features
 Tasks:
• To realize a self-organizing network “infrastructure”
• To fairly and efficiently share communication resources
 Requirements:
• Unique destination (Sink)
• High nodes density
• Low nodes mobility
• Limited resources (bandwidth, battery, processing and storage)
• Data centric
• Application oriented
Ad Hoc networks approaches are not merely applicable
1. Problem Satement

System requirements
Power consumption issues to make the system able to run unattended;
 Optimal energy management;
 Network life-time to avoid the whole network to get partitioned;
 Capability of quickly set-up an end-to-end communication infrastructure;
 Support both to synchronous (source-initiated) and asynchronous (event-
based) sensing;
 Quality of Service (QoS) provisioning;
Optimization ensuring that the spent energy is directly related to the amount of
traffic. Trade off between:
 performance (latency, throughput, fairness);
 cost (energy efficiency, algorithmic complexity, signaling overhead).
1. Problem Satement

Overview
MAC
Schedule
based
Contention
based
TDMA CDMAFDMA IEE802.11 DCF Low power list.
PAMAS WISE MAC
S-MAC
T-MAC
DMAC
2. MAC protocols

Overview
MAC
Schedule
based
Contention
based
PAMAS WISE MAC
S-MAC
T-MAC
DMAC
Resources reservation
energy conserving
lower scalability
2. MAC protocols

Overview
MAC
Schedule
based
Contention
based
PAMAS WISE MAC
S-MAC
T-MAC
DMAC
MACAW
widely applied
idle listening
2. MAC protocols

Overview
MAC
Schedule
based
Contention
based
PAMAS WISE MAC
S-MAC
T-MAC
DMACSchedule offset (phase)
adaptation s to traffic
ineffective broadcasting
2. MAC protocols

Overview
MAC
Schedule
based
Contention
based
PAMAS WISE MAC
S-MAC
T-MAC
DMACDuty cycle
RTS/CTS handshake
higher collision probability
Schedule offset (phase)
adaptation s to traffic
ineffective broadcasting
2. MAC protocols

STAR MAC
Synchronous Transmission Asynchronous Reception
1. Completely novel approach effectively joining:
• WISE MAC (phase based transmission scheduling)
• S-MAC (duty cycle)
2. Efficient power management (stable low power state + duty cycle)
Duty cycle
Sleep status (TS , csleep= 0.01 mA):
• RF OFF
• Node (Micro): power save mode
MAC frame period (Tf = Tl + TS)

STAR MAC
Synchronous Transmission Asynchronous Reception
Background:
• WISE MAC: nodes maintain the schedule offsets of their neighbors
• S-MAC: nodes regularly broadcast SYNC packets (duty cycle)
Drawbacks (related to our application):
• WISE MAC: offset information is transmitted within ACK messages, then
its update depends on traffic load
• S-MAC: clustered nodes are strictly synchronized and must have the
same duty cycle and frame time
Proposed approach:
STAR protocol does not require strict node synchronization: each node can adjust
its duty cycle and frame period independently.
Nodes periodically send their offsets to neighbors through a MAC layer signaling.
As a result, the network topology is flat.

1. Beacon broadcasting (starting from Gateway)
2. Neighbors list assessment within at least 1 period (Tf)
3. Duty cycle operation mode with semi duplex communications
(independently each other)
4. Node’s phase transmission (time to the next awakening)
5. Weak and distributed synchronization scheme (rendez vous like)
STAR MAC
Set-up Phase

Weak nodes synchronization (2 way handshake)
• Set up + recovery procedures
MAC PDU header
STAR MAC
Regime Phase

Period 1 Period KPeriod 2 …
kTf kTf kTf
Tswitch
time
• Orphanage management
• Beacon broadcasting
• Neighbors list assessment within K period (K Tf)
• Own HELLO messages broadcasting in search of connectivity
HELLO HELLO HELLO
STAR MAC
Recovery Phase

Enhanced STAR (STAR+)
Subset:
set of neighbor nodes jointly awake for a
time interval greater than the time
necessary for receiving a message (TRx)
Only one synchronization message is multicasted to all the neighbors
nodes belonging to a subset
Lower number of synchronization messages (multicasting gain)

Normalized Cost:
Parameter Value
Cost of receiving status
(cRx)
10 mA
Cost of transmitting status
(CTx)
30 mAh
Cost of sleep status (csleep) 0.01 mA
number of neighbor nodes
(N)
1-80
Synchronization period (TF) 5-30 s
STAR
STAR +
ATSR (≈S-MAC)

Normalized Cost vs NNormalized Cost vs Tf

Normalized Cost vs NNormalized Cost vs Tf
Cut-off time for TF (floor effect)

Normalized Cost vs Duty-Cycle%

Performance of STAR and STAR+ protocols is better than ATSR
Normalized Cost vs Duty-Cycle%
Duty-cycle dimensioning according to scenario and topology

Directive Antennas
Expected benefits
 Antenna gain maximization towards desired directions,
concentrating energy in smaller area:
Transmitted power decreasing
Power consumption reduction
Network life time increasing
Received power increasing
Receiver sensitivity increasing
Coverage range increasing
Error probability reduction

Directive Antennas
Expected benefits
 Radiation towards undesired directions minimization
Interference caused by other transmissions reduction
Co-channel interference mitigation
multiple-access problems mitigation
Collision probability reduction
 Adaptability to time varying communication conditions:
Node’s failure
Channel errors
Congestion

Directive Antennas
Criticalities
 Cost and size
 On board integration
 Beam switching management:
Set-up phase signaling overhead
Latency for end-to-end communications setting-up
Algorithm complexity
Switching agility
 Support both to synchronous (source-initiated) and
asynchronous (event-based) sensing

Node 2
Node 4
Node 1
Node 3
D-STAR
Directive STAR

Features:
Cross-layer protocol design (MAC+PHY)
Space-time synchronization
Suitable for flat topology
Scalable
D-STAR

Hypothesis
 Beam width = θ [rad]
 N possible angular sectors:
N = 2π/θ
 Quasi ideal switching
Tswitch << Tpkt
Es:
 θ = π/2 [rad]
 N = 4
 Tswitch ≈ µs << Tpkt ≈ ms
D-STAR: ideal pattern antennas
y
II sector I sector
III sector IV sector
x
R
θ

D-STAR: State Diagram

INIT

DISCOVERY
Switch on
INIT

DISCOVERY
Switch on
nf < Nfd
INIT

DISCOVERY
Switch on
nf < Nfd
REGIME
nf=Nfd
INIT

DISCOVERY
1 < EmptySectors < Ns
Switch on
nf < Nfd
REGIME
nf=Nfd
INIT

DISCOVERY
Emptysectors = Ns
Switch on
nf < Nfd
REGIME
nf=Nfd
INIT

DISCOVERY
Emptysectors = Ns
Switch on
nf < Nfd
Battery < Battery_low
REGIME
Battery < Battery_low
nf=Nfd
INIT
OFF

D-STAR: Discovery phase
1. Duty cycle δ = 100%
Listening mode for a time interval Tset-up
Beacon (HELLO) broadcasting:
 1 beacon ∀ angular sector
 Node ID and Phase (φ) transmission (time to the next awakening)
 Waiting for a fixed time duration τs in search of REPLY messages
 Switching to the following angular sector
Exit condition:
 (Tset-up is expired, i.e., Nfd frame periods)

D-STAR: Discovery phase
δ = 100%
Tset-up
time
HELLO HELLO HELLO HELLO
HELLO
…
HELLO
y
x
Tbroad
Ns=4

D-STAR: Regime phase
Each node sends:
 HELLO messages to known neighbors belonging to different angular sectors
according to the phase transmitted in previous HELLO messages;
 several HELLO messages in background with the proper period to unknown
neighbors in the empty angular sector empty angular sector.
Upon the replying of a node, a logical channel is established:
 The channel access is managed by means of a CSMA/CA (Carrier Sense
Multiple Access with Collision Avoidance) approach.
If the number of empty angular sector is equal to Ns each node re-enters the
discovery phase in search of connectivity.

D-STAR: Regime phase
Tf
time
listening sleep
δ Tf
HELLO
…
HELLO
HELLO
…
HELLOHELLO
Hypothesis
 ideal phase;
 ideal duty-cycle;
 ideal antenna switching.
no deafness problem

Regime phase
Orphanage management
Own HELLO messages broadcasting in search of connectivity
Beam 1 Beam NBeam 2 …
KTf KTf KTf
Tswitch
time
HELLO HELLOHELLO
1 HELLO
broadcasting per
empty sector

Operative hypothesis
FP6-IST-1-508744-IP ‘‘GoodFood’’ reference scenario
 Monitored area = 25 · 25 [m2]
 Number of WSN nodes: [10…50]
 N = 1, 2 ,4, 6, 8 angular sectors
IEEE 802.15.4 compliance
 Bit rate = 250 kbps
 HELLO pkt length = 8 bytes
 Number of channel sensing for CSMAC/CA algorithm = 6
 Frame period: 10,25,50,75,93 s
 Duty-cycle: [1…5]%
 Packet Error Rate = 5%

Network lifetime gain vs nodes (Tf=93 s; d = 3%)
4
16

Network lifetime vs duty-cycle (Tf = 93 s; 50 nodes)

Network lifetime vs frame period (d=3 %; 50 nodes)

Hidden node analysis

S
S'
R

S
S'
R
S S'
R
R'

Signaling Overhead
Resource Utilization
Efficiency and complexity

Four-Beam Directional Antenna (FBDA)
Antenna features:
 Four coaxially fed planar patch antennas;
 The patches operate in linear polarization (2.4 GHz ISM);
 Each face is realized on a two-layer RF4 substrate 56x56x2.4 [mm].
Two views of the antenna

 The patches gain are comprised between 8.3dBi and 7.5dBi;
 Loss are 1.5 dB (switch, distribution network and mismatches);
 Combined patterns ensure a uniform coverage of the 360 degree horizon
Radiation patterns of the FBDA

Network lifetime vs nodes

PCmax=2%
overhearing effect

Packet delivery latency vs nodes

Conclusions
• Energy efficient MAC protocols proposal
 STAR (duty cycle);
 STAR + (multicasting);
 Analytical modeling & rationales;
 Performance of STAR and STAR+ protocols is better than S-MAC.
6. Conclusions
 Energy consumption;
 Latency;
 Easy to implement.
• Cross-layer approach (MAC+PHY) D-STAR
 C++ simulations;
 Performance of D-STAR protocols is better than STAR
also in mobile node scenario;

Future work
DSTAR implementation on practical test cases:
 FP6-IST-4-027738-NoE “CRUISE”
 FP6-2006-045299-STREP “DustBot”
UWB PHY layer integration with STAR MAC protocol
7. Future Work

Research involvements
FP6-IST-1-507325-NoE NEWCOM
“Network of Excellence in Wireless COMmunications”
Project A is addressed to “Ad Hoc and Sensor networks” with regards to:
 Cross-layer design of sensor networks;
 Simulation models and architectures for cross-layered sensor networks.
FP6-IST-4-027738-NoE CRUISE
“CReating Ubiquitous Intelligent Sensing Environment”
• WP 122 leader “Platforms, test beds measurements”
• Task 220.1.4 leader “Cross Layer Optimization”

FP6-IST-1-508744-IP GoodFood
• Work Package 7 leader: integrated solutions according to the AmI concepts,
allowing full interconnection and communication of multi-sensing systems along
the wine chain.

IST call 6 - FP6-2005-IST-6 DustBot
• Work Package 6: Robot-remote station communication subsystems; communication
protocols design and development.

1. F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, R. Fantacci, A. Manes, “Design and Application of
Enhanced Communication Protocols for Wireless Sensor Networks operating in
Environmental Monitoring”, International Journal of Sensor Networks Special Issue on
Wireless Ad Hoc Networks and Sensor Networks, to be published.
2. F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, R. Fantacci, G. Manes, A. Manes, I. Nelli,
“DSTAR MAC Protocol: a Cross Layer Solution for Wireless Sensor Networks Endowed
with Directive Antennas”, COST289 Special Issue for Springer Journal of Wireless
Personal Communications, to be published.
3. G. Manes, R. Fantacci, F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, A. Manes, I. Nelli, “Efficient
Publications
JournalPapers
1. F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, A. Manes, "An Embedded GPRS Gateway for
Environmental Monitoring Wireless Sensor Networks“ in Proc. of EWSN’06, Zurich,
Switzerland, Feb. 2006.
2. G. Manes, F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, A. Manes, "Enhanced Design
Solutions for Wireless Sensor Networks applied to Distributed Environmental
Monitoring" in Proc. of GE’06, Ischia, Italy, June 2006.
3. F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, R. Fantacci, A. Manes, "Design and
Application of Enhanced Communication Protocols for Wireless Sensor Networks
operating in Environmental Monitoring" in Proc. of IEEE ICC’06, Istanbul, Turkey, June
2006, vol. 8, pag. 3390-3395.
4. F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, R. Fantacci, A. Manes, “Enhanced System
Design Solutions for Wireless Sensor Networks applied to Distributed Environmental
Monitoring”, Proceedings of The Second IEEE International Workshop on Practical
Issues In Building Sensor Network Applications (SenseApp 2007), Dublin, Ireland,
October 2007.
5. G. Manes, R. Fantacci, F. Chiti, M. Ciabatti, G. Collodi, D. Di Palma, A. Manes, “Energy
Efficient MAC Protocols for Wireless Sensor Networks Endowed with Directive
Antennas: a Cross-Layer Solution" in Proc. of RWS’08, Orlando, Florida, January 2008.
ConferencePapers
9. Pubblications

Thank you for your attention !!!

1
Università degli Studi Di Firenze
Dipartimento di Elettronica e Telecomunicazioni
Ph.D. Thesis on RF Microwave and Electromagnetism (XX)
Supervisors:
Prof. G. Manes
Dr. G. Collodi
Coordinator:
Prof. G. Manes
Candidate:
Michele Ciabatti
Resource-Constrained Communication within
Wireless Sensor Network:
a new Cross Layer solution

Ciabatti Ph.D. final discussion

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