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Document Sample
Design of an energy efficient Medium Access
Control protocol for wireless sensor networks
Masters Thesis Defense
Kiran Tatapudi
Thesis Committee
Dr. Chansu Yu, Dr. Wenbing Zhao, Dr. Yongjian Fu
Organization
Introduction
Related Work
Bulk Synchronous Medium Access
Performance Evaluation
Conclusion
1
Introduction
What is a Wireless Sensor Network ?
Introduction
What is a Wireless Sensor Network ?
a collection of cheap, low power wireless devices with limited
processing and communication capabilities, which collectively help
monitor physical or environmental conditions
2
Introduction
What is a Wireless Sensor Network ?
a collection of cheap, low power wireless devices with limited
processing and communication capabilities, which collectively help
monitor physical or environmental conditions
Applications
•Habitat Monitoring
•Home Automation
SINK
•Surveillance
BASE STATION
Introduction
Key Aspects
•Sink based
SINK
BASE STATION
3
Introduction
Key Aspects
•Sink based
•Multi-hop communication
SINK
BASE STATION
Introduction
Key Aspects
•Sink based
•Multi-hop communication
•Time and space correlated
SINK
BASE STATION
4
Introduction
Key Aspects
•Sink based
•Multi-hop communication
•Time and space correlated (Message bursts)
How to Arbitrate the
medium !!
SINK
BASE STATION
Introduction
Medium Access Control
5
Introduction
Medium Access Control
arbitrate the shared communication medium among competing nodes and
thus provide a robust communication channel to applications
Introduction
Medium Access Control
arbitrate the shared communication medium among competing nodes and
thus provide a robust communication channel to applications
802.11 ??
6
Introduction
Medium Access Control
arbitrate the shared communication medium among competing nodes and
thus provide a robust communication channel to applications
802.11 ??
Unique requirements of Sensor networks
•Energy Efficiency
•Handle traffic bursts
Related Work
Two classes of protocols :
Contention based protocols
Time Division Multiple Access protocols
7
Related Work
Contention based protocols
CSMA for collision avoidance
Drawbacks
Higher number of Collisions
Re-transmissions
Non-deterministic
Related Work
Contention based protocols
CSMA for collision avoidance
ACK packets for collision detection
Drawbacks
Higher number of Collisions
Re-transmissions
Non-deterministic
8
Related Work
Contention based protocols
CSMA for collision avoidance
ACK packets for collision detection
Sleep schedules for energy conservation
Drawbacks
Higher number of Collisions
Re-transmissions
Non-deterministic
Related Work
Time Division Multiple Access
Exclusive slot assignment
9
Related Work
Time Division Multiple Access
Exclusive slot assignment
Collision free
Related Work
Time Division Multiple Access
Exclusive slot assignment
Collision free
Automatic duty cycle
10
Related Work
Time Division Multiple Access
Exclusive slot assignment
Collision free
Automatic duty cycle
Deterministic
Related Work
Time Division Multiple Access
Exclusive slot assignment
Collision free
Automatic duty cycle
Deterministic
Drawbacks
Synchronization Overhead
Improper schedule formation
11
Related Work
Two-hop graph coloring for slot scheduling in TDMA
Communications within two-hops interfere with each other, but
beyond that the communications are safe
Allot different slots for nodes within two-hop neighborhood and reuse
the slots for other nodes
Example:
1 2 3 4 1 2 3 1
Related Work
Two-hop coloring is not always correct
u b
a v
Exploit the unique feature of sink-based sensor net to simplify the
message exchange procedure while achieving collision-free slot
schedule !!!
12
Bulk Synchronous Medium Access
Key Aspects
Optimized for sink-based networks
Tree structure (rooted at sink and
grouped as non-interfering sets
based on hop-count from sink)
Parent child relationship between
two sets of nodes
Slot-based scheduling for tree
links
Automatic Routing
Bulk Synchronous Medium Access
Key Aspects
Optimized for sink-based networks
Tree structure (rooted at sink and
grouped as non-interfering sets
based on hop-count from sink)
Parent child relationship between
two sets of nodes
Slot-based scheduling for tree
links
Automatic Routing
BG0 BG1 BG2
13
Bulk Synchronous Medium Access
GG GG GG GG receives
G P1 receives G receives G
Data flow G
P1&P2 P2 receives
P2 P1
BIGSLOT
P1 P2 D1&D2 D1 D2 D1 receives
Three-way Handshaking
PADV, PSEL, SCH GD GD
D1 D2
messages slot sD1 slot sP1 slot sG
GD BIGSLOT0 BIGSLOT1 BIGSLOT 2
A TDMA frame in data phase
(a) 7-node scenario (b) TDMA schedule in BSMA
Bulk Synchronous Medium Access
Parameters for evaluating performance
Message Latency = (hop-count) * BIGSLOT
Energy Efficiency = ((TX slot) + (‘n’ RX slots)) / (BIGSLOT * 3)
14
Bulk Synchronous Medium Access
Parameters for evaluating performance
Message Latency = (hop-count) * BIGSLOT
Energy Efficiency = ((TX slot) + (‘n’ RX slots)) / (BIGSLOT * 3)
How to form such a tree !!
Bulk Synchronous Medium Access
Tree formation & slot scheduling
G can start (upstream)
communication at frame F3.
PADV
PSEL P1 & P2 can start (upstream)
communication at frame F4.
SCH
G
P1&P2
D1&D2
GD
Frame F0 Frame F1 Frame F2 Frame F3 Frame F4
Sleep
schedule
Receive PADV’s Send SCH
of D1
Send PSEL Receive PSEL’s
Receive SCH Send PADV
15
Bulk Synchronous Medium Access
Design Issues
Orphan Nodes
Bulk Synchronous Medium Access
Design Issues
Orphan Nodes
Tree Convergence
16
Performance Evaluation
90
Number of orphan nodes
80
70
60
50
40
30
20
10
0
10dB
8dB
6dB
4dB
2dB
Scheduling
10dB
(Z0)
8dB
6dB
4dB
2dB
phases (15)
10dB
SD=6dB
8dB
6dB
4dB
2dB
SD=4dB
SD=0dB
BIGSLOT size = 25
Conclusion
TDMA schemes based on two-hop graph coloring algorithm fail to provide
collision-free medium access and to utilize available transmission opportunities
BSMA is a simple, robust and energy efficient MAC protocol
Our simulation study based on ns-2 network simulator shows that BSMA
constructs a proper tree and collision-free schedule in reasonable number of
scheduling phases
17
Q&A
THANK YOU
18
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