Cross-Layer Protocol Design and Optimization for Delay/Fault-Tolerant Mobile Sensor Networks IEEE Journal of Selected Areas in Communications, 2008 Yu.

Cross-Layer Protocol Design and Optimization for Delay/Fault-Tolerant Mobile Sensor Networks

IEEE Journal of Selected Areas in Communications, 2008

Yu Wang, Hongyi Wu, Feng Lin, and Nian-Feng Tzeng

Presented by Hanjin Park (September 16, 2008)Computer Network Lab.

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Contents

• Introduction• Problem definition• Solution

– Cross-Layer Data Delivery Protocol for DFT-MSN• Protocol Parameters• Asynchronous Phase• Synchronous Phase

– Protocol Optimization

• Performance Evaluation• Conclusion

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Introduction

• Delay/Fault-Tolerant Mobile Sensor Networks(DFT-MSN)– Extremely low and intermittent connectivity

• Sparse network density and dynamic mobility

– Without end-to-end connection• Convention routing for MSN do not work effectively

– Always end-to-end connected

– limited buffer• Save messages temporally to relay• Store and forward

A

BE

D

F

C

13

6 7

4

11

2

89

5

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Introduction

• Applications of DFT-MSN– Air quality sensor– Military sensor– Wildlife tracking

• ZebraNet at Princeton Univ.

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Introduction

• Problem of DFT-MSN– Work aggressively in order to catch every possible

opportunity for data transmission– But, working aggressively means DFT-MSN has power

consumption problem– More important power than conventional MSN– Because the conventional MSN has stable connectivity

and channel bandwidth– Tradeoff between link utilization and energy efficiency

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Problem definition

• How to make efficient use of the transmission opportunities whenever they are available, while keeping the energy consumption at the lowest possible level?

• Cross-Layer data delivery protocol– Asynchronous phase / Synchronous phase– Optimization

Layer 2Data Link Layer

One hop transmission

Layer 3Network Layer

Routing

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Preliminary

• Protocol Parameters– Nodal Delivery Probability

• Probability that a sensor can deliver message to sink• Decision on data transmission is based on delivery

probability

iSink

k

If there is no transmission during a certain period, reduce the delivery probability

When Whenever sensor i transmits a data message to another node k, deliveryprobability will be updated

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Preliminary

• Protocol Parameters– Message Fault Tolerance

• Multiple copies of the messages create/maintain by diff sensor

redundancy• Fault tolerant degree(FTD), amount of redundancy• Data queue management

0.98

j0.010.3

0.450.56

0.86

Sort the messages based on FTD. The smaller FTD, the more importantWhen a new Message come to queue with already full, then drop the bottommessage in the queueIf FTD of a message is larger than threshold, then drop it to reduce transmissioncost

0.580.780.86

Threshold = 0.57

M1,M2,M3,M4,M5,M6,M7

New Message M8Drop M5, M6, M8

M1,M2,M3,M4,M5,M6,M8

10

2

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Proposed Scheme

• Cross-Layer Data Delivery protocol for DFT-MSN– Asynchronous Phase

ASend RTS pkt.RTS pkt. contains nodal delivery probability, FTD of msg, and length of contention window(W)

Receive RTS.Only qualified receiver send back CTS.

Qualified receiver means which nodes with higher delivery probability than sender and available buffer space.

Receive CTS.Sender makes a neighboring table to control central arrangement for data transmission

Enter Synchronous phase

Collision may happens in two situations1)Multiple nodes may try to grasp the channel by sending preamble pkt.2)Multiple qualified neighbor nodes may reply with CTS pkts. simultaneously

A

B

C

D

E

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A

B

C

D

E

Proposed Scheme

• Cross-Layer Data Delivery protocol for DFT-MSN– Synchronous Phase

After obtaining information of qualified receivers, Node A decides which of them areto be selected(outgoing message M’s FTD and receiver’s delivery probability)

Send SCHEDULE pkt.

SCHEDULE pkt. includes list of receiver’s IDs and corresponding FTD of the message.

Receive SCHEDULE pkt.

If a receiver finds its ID in SCHED pkt. then accept the following message M, insert M to its queue with FTD.

Qualified receivers reply with an ACK pkt. At a specific time slot which predefined in the SCHED pkt.

Collision Free

After receiving the ACK pkt. the node A recalculates the FTD of its local copy of message M.

A

B

C

D

E

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A

B

C

D

E

Proposed Scheme

• Protocol Optimization– Periodic Sleeping

• Due to sparse connectivity of DFT-MSN, sensor nodes want to be mostly in the listening state power management problem

S cycles periodsi transmission cycles

# of Msg with FTD smaller than F at node i

total # of Msg at node i

Sleeping period of node i Minimum sleeping period

Threshold

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Proposed Scheme

• Protocol Optimization– Collision Avoidance During RTS Transmission

• Node i dynamically select a listening period between 1 to reduce overall collision prob.• node with a lower delivery probability to have a better

chance to grasp the channel high channel efficiency• The larger (maximum listening period), the less likely

collision will happen, but less link utilization(power efficiency problem)

• Find a minimum which keeps the collision prob.( ) under predefined threshold ( )

node i

node j

node i

node j

listen

listen

Send preamble pkt. simultaneously

preamble RTS

time slot

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Proposed Scheme

• Protocol Optimization– Collision Avoidance During CTS Transmission

• RTS pkt. has CW for that receiver can select randomly from the CW

• No fixed CW, adaptively changes the size of CW for efficiency

• Two schemes to optimized CW1. Minimizing overall collision probability2. Minimizing collision probability for nodes with high delivery

probabilities* (Appendix 2-A, 2-B)

node j

node i

listen

listen

RTS contains common CW size (W)

preamble RTS

node k listen

CW of node j

CW of node k

CTS

CTS

time slot

Send CTS pkt. simultaneously

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Proposed Scheme

• Protocol Optimization– 1) Minimizing overall collision probability

• Node i send RTS to its neighbor( )• Every qualified neighbor randomly selected a time slot

between 1 and • Probability that every CTS pkt.s is transmitted in a collision-

free

• Overall collision probability

• Find

node i

neighbor of node i ( )

0min( | )W H

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Proposed Scheme

• Protocol Optimization– Summary

• For channel efficiency, – Lower NDP is given a larger sleeping period because of lack of

delivery probability– To get the channel easily, Lower NDP, smaller listening period

• To reduce collision probability– Higher NDP, more likely selected as relay node.

Higher Delivery Prob.

Lower DeliveryProb.

Sleeping period shorter longer

Listening period(preamble/RTS)

longer shorter

Contention Window(CTS)

longer shorter

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Performance Evaluation

• OPT– Proposed protocol that employs all optimization

schemes– (sleeping period), (maximum listening period)

– (contention window)

• NOOPT– Basic protocol without parameter optimization

• NOSLEEP– Similar to OPT, except that nodes do not perform

periodic sleeping

• ZBR– Differs from OPT only in the message transmission

scheme– ZebraNet’s history-based scheme

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Performance Evaluation (# of sinks)

• More sink, fewer hops

• NOSLEEP – low delay, but highest energy consumption

• ZBR – low delay?

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Performance Evaluation (# of nodes)

• More node limited bandwidth, queue size most msg are drop lower delivery ratio

• ZBR’s transmission control is bad

• More node delay decrease (better chance to meet nodes

with HDP) 18 / 22

Performance Evaluation (Max queue size)

• Bigger queue size, increase delivery ratio

• Queue size does not affect the number of data transmission, and power consumption

• Because of waiting in queue, delay slightly increased 19 / 22

Performance Evaluation (Avg. speed)

• More speed, delivery ratio is increased?

• More speed, power consumption is decreased slightly due to less transmission

• More speed, delay is decreased (better chance to meet nodes with

HDP) 20 / 22

Conclusion

• DFT-MSN – Low and intermittent connection– No guarantee end to end connection– Limited buffer / store and forward

• Cross-Layer data delivery protocol– Asynchronous phase, synchronous phase– Employ layer 2’s information for working related layer 3

• Nodal delivery probability, Message fault tolerance

• Optimization – Sleeping period– Maximum Listening period– Contention window

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Discussion

• The lack of mentions about– Definition of some notation

• No consideration about– Impact of threshold– Parameters’ sensitivity– Synchronization– Recursive transmission

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Q & A

Thank you

[email protected]

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Reference• [1] Y. Wang and H. Wu, “The Delay Fault Tolerant

Mobile Sensor Network(DFT-MSN) : A New Paradigm for Pervasive Information Gathering,” IEEE Trans. Mobile Computing, vol. 6, no. 9, pp. 1021-1034, 2007.

• [2] http://www.princeton.edu/~mrm/zebranet.html

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Appendix 1• Message Transmission Process

i j

M

M7

MM1M

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Appendix 2-A

• Protocol Optimization– 2) Minimizing overall probability for nodes with high

delivery probability• Node with high delivery probability(DP) are better

candidates as dada relay nodes, so high collision prob.• Reduce collision probability according to DP• If sender is node i, RTS of sender(CW( ), maximum DP of

neighbors( ), DP of sender( )• Qualified neighbor node j receive RTS, select a timeslot

from 0 to to transmit CTS

• The larger (receiver DP), close to whole contention window W, otherwise if is small, it may have few choices.

sink

node i

node j

neighbor node

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Appendix 2-B

• Protocol Optimization– 2) Minimizing overall probability for nodes with high

delivery probability(cont.)• :prob. that node k doesn’t choose slot s

• :prob. that no other node select slot s except node j

•

neighbor node j ‘s collision probability (delivery probability )

• Find

slot s

kt

min( | )jW H

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