Enhanced Slotted Aloha Protocols for Underwater Sensor Networks with Large Propagation Delay Kai...
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Transcript of Enhanced Slotted Aloha Protocols for Underwater Sensor Networks with Large Propagation Delay Kai...
Enhanced Slotted Aloha Protocols for Underwater Sensor Networks with Large Propagation Delay
Kai Chen† Jianhua He§
Yi Zhou‡ Haibing Guan‡
†School of Information Security and Engineering,
Shanghai Jiaotong University, China.
‡School of Electronic, Information and Electrical Engineering,
Shanghai Jiaotong University, China.
§School of Engineering, Swansea University, UK.
IEEE VTC 2011
Outline
• Introduction• System model• SA-ALOHA• ISA-ALOHA• Simulation• Conclusion
Introduction
• Underwater sensor networks(UWSNs) have attracted large research interests from both academy and industry
• Due to the importance of MAC protocols for UWSNs– Design and analysis of MAC protocols
Introduction
• Among the existing MAC protocols in shared wireless medium– ALOHA protocols
Pure-ALOHA
Time
A
B
C
DATA
DATA
DATA
DATA
DATA
Slotted-ALOHA
Time
A
B
C
DATA
DATA
DATA
DATA
DATA
Introduction
• This frame can be received successfully– There are no other frames arrival at node in
conflict free period (Pcf)
],[ ,,,, fAikifAikicf TTtTTtP
ti,k: node i send the kth frame to node ATi,A: actual propagation delayTf: frame transmission time
Introduction
• Conflict free for two different frame transmission
fijij TTt
∆tij: the difference of start for two frame transmission∆Tij: the difference between propagation delay Ni to NA and that Nj to NA
Tf: frame transmission time
Introduction
• RF network scenarios
fij Tt
Pure-ALOHA Slotted-ALOHA
protocol
∆tij Any value Multiple of Tf
throughput 0.18 0.36
Time Time
A
B
C
A
B
C
DATA
DATA
DATA
DATA
DATA
DATA
DATA
DATA
DATA
DATA
TIME
Sender
Receiver
Radio wavePropagation speed : 3*108 m/s
Pure-ALOHA Slotted-ALOHA
protocol
∆tij random Multiple of Tf
∆Tij random random
throughput 0.18 0.18
Introduction
• UWSN scenarios
fijij TTt Pure-ALOHA Slotted-ALOHA
protocol
∆tij random Multiple of Tf
∆Tij random random
Time Time
A
B
C
A
B
C
DATA DATA
DATADATA
DATA
collisionDATA
DATA
DATA
collision
TIMEPropagation delay
UnderwaterSender
Receiver
Acoustic wavePropagation speed : 1500 m/s
Introduction-motivation
• The performance of Aloha in UWSNs can drop quickly with increasing propagation delay
Goal
• Reuse the idea of synchronous transmission in S-Aloha protocol– SA-ALOHA– ISA-ALOHA• Improvement for the SA-ALOHA
System model & Assumption
• Single hop star topology with a central control node A
• Fixed N ordinary nodes• Position information• Time synchronized• Each ordinary nodes may occasionally send
data frames to the central control node
SA-ALOHA
• Example of frame transmission and reception
SA-protocol
• Calculation of Tpre
slotAiipre TTT mod,,
Ti,A: propagation delat of node i to node ATslot: slot size
SA-protocol
• Problem– Propagation delay is not accurate
AiAierrAi TTT ,,,
~
Terr: Estimation error of Ti,j
T~i,A: estimated value of Ti,j
Tslot,isa: Tslot for ISA protocol
ISA-protocol
• Solution
]),1[(),max( , NiT errAi
max* ef TkT
maxeT
isaslotT , incslot TT
Tinc: the increment of time from Tslot for Tslot,isa
ISA-protocol
• Solution
Sender , N1
Sender , N2
Receiver , NA
Tslot,isa
=Tf+k*Temax
Frame1 Tx
Frame2 Tx
Frame1 Rec
Frame2 Rec
Tolerant of the error of estimation
Simulation
parameter value
Ordinary node 50
Transmission range 1000
RF UWSN
Propagation speed 3*108 m/s 1500 m/s
Frame length 512 bytes 50 bytes
Data rate 2 Mbps 2 kbps
Tf 2.048 ms 200 ms
Tslot = 1.01*Tf 2.06848 ms 202 ms
1000 mCenter node
Simulation result
Simulation result
Simulation result
Simulation results
Simulation result
Temax = 33 ms
Conclusion
• In this paper, the authors investigated the performances of Aloha protocols in (UWSN)– Long propagation delay• SA-protocol• ISA-protocol
• Simulation results demonstrate the effectiveness of our proposed protocols
24
Thanks for your at tention