for Wireless Sensor Networks

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FBRT: A Feedback
-
Based

Reliable Transport Protocol

for Wireless Sensor Networks

Yangfan Zhou

November, 2004

Supervisors: Dr. Michael Lyu and Dr. Jiangchuan Liu

1
st

Year MPhil Presentation

Presentation Outlines


1. Introduction


2. Design Considerations


3. Protocol Implementation


4. Simulation Results


5. Conclusion

Presentation Outlines


1.
Introduction


2. Design Considerations


3. Protocol Implementation


4. Simulation Results


5. Conclusion


Introduction


Wireless Sensor Networks (WSN)


Sensors nodes measure physical phenomena.


Target tracking


Environment data measurement


Engineering measurement


Sensor nodes form an ad
-
hoc multi
-
hop wireless
network to convey data to a sink.

Introduction


WSN Challenges


WSN suffers from energy constraint


WSN condition


Unreliable wireless link


High packet loss rate


Network Dynamics


Node failures


Link failures


Dynamic traffic load

Introduction


Reliable sensor
-
to
-
sink data transport for WSN


It is Important


Objective


to assure that the sink can receive desired
information is very important.


The work presented here is to address this problem.



Introduction


Reliable sensor
-
to
-
sink data transport for WSN


100% reliable data transport is not necessary.


Reliability means desired information has been
achieved


Source sensors might have different
contributions

Introduction


Reliable sensor
-
to
-
sink data transport for WSN


Bias the transport scheme

Introduction


Current Approaches on WSN data transport


RMST: Reliable Multi
-
Segment Transport

by Heidemann et al,
SNPA’03


PSFQ: Pump Slowly, Fetch Quickly

by C. Wan et al, W
SNA’02




Not applicable for sensor
-
to
-
sink data transport

Introduction



ESRT: Event to Sink Reliable Transport

by Sankarasubramaniam et al,
MobiHoc’03


Congestion detection


Queue Length


Reliability consideration


Receiving rate of the incoming packets


Rate adjustment


Unbiased adjustment


Introduction



CODA: Congestion Detection and Avoidance by
C. Wan, S
enSys'03
,



Congestion detection


channel sampling



Congestion avoidance


Slowing down the sending rate


It has not addressed the reliability issues.





Presentation Outlines


1. Introduction


2.
Design Considerations


3. Protocol Implementation


4. Simulation Results


5. Conclusion


Motivations


Issues to be addressed to provide reliable
sensor
-
to
-
sink data transport


Source reporting rate adjustment scheme


Routing scheme



Design Considerations


Reporting Rate Control


Relationship between receiving rates and distortion


Different contributions of source nodes.


Different energy costs for communication.


Rate control scheme should employ an optimization
approach to minimize energy consumption of the WSN.


Adjust the rates so that energy consumption is minimized
subjected to that the distortion is in a given range.


Design Considerations


Distortion and Sensor Contribution


Application Specific, should be determined by
applications.



Rate Control


Cooperation of the application and the
transport protocol.

Figure

Design Considerations


Communication cost estimation


Hop number from the source to the sink


Simple


Inaccurate


Node Price


Our metrics: Total number of packets sent by the in
-
network
nodes for per packet received by the sink


Accurate


Physical layer overhead


But hard to implement


Design Considerations


Node Price

NP(x): Node price of X


= node n’s downstream neighbors

Perc(i): the percentage of traffic that is routed to node i


The hop loss rate between node n and node i


The loss rate of the path from node i to the sink

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HopLossRat
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PathLossRa
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Perc
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PathLossRa
Perc(2)

2

3

Perc(3)

1

PathLossRate(2)

PathLossRate(3)

HopLossRate(2)

HopLossRate(3)

NP(3)

NP(2)

Sink

NP(sink) = 0

PathLossRate(Sink) = 0

Design Considerations


Node Price Estimation


Each node can calculate its NP and PathLossRate based on


The feedback of NP and PathLossRate of its downstream
neighbors


The HopLossRate to each of its downstream neighbors


The routing scheme: Perc(i)


Two unknowns


The HopLossRate


The routing scheme (Discussed Later)

Design Considerations


Hop Loss Rate


mainly caused by three factors


Congestion


Signal Interference


Fading.


packet loss rate will exhibit graceful increasing
behavior as the communication load increases (IEEE
802.11 MAC)


reasonable to estimate the packet loss rate based on
an exponential weighted moving average (EWMA)
estimation approach.


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HopLossRat
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HopLossRat







Design Considerations


Accurate and Current Hop Loss Rate Estimation


Indicates the congestion condition well


Indicates the weak link well


Node Price: based on loss rate estimation


Indicates the dynamic wireless communication
condition from the node to the sink well


can help to determine the reporting rates


can help to determine the routing scheme




Design Considerations


Routing Schemes


Minimizing local NP.


Locally optimal energy consumption, minimizing the energy
consumed for the sink to receive per packet from me)



Perc(2)

2

3

Perc(3)

1

HopLossRate(2)

HopLossRate(3)

NP(3)

NP(2)

Design Considerations


Routing Schemes: Oscillation Avoidance



Analysis


Routing Schemes: Oscillation Avoidance


Gradually shift traffic to best path


Adaptive to downstream dynamics



higher
lowest
higher
higher
NP
NP
NP
Perc


high
low
high
high
NP
NP
NP
Perc


Perc(2)

2

3

Perc(3)

1

HopLossRate(2)

HopLossRate(3)

NP(3)

NP(2)

Presentation Outlines


1. Introduction


2. Motivations and Design Considerations


3.
Protocol Implementation


4. Simulation Results


5. Conclusion


Protocol Implementation


Task assignment: Broadcast
interest

packet


Get possible downstream neighbor information


Select path with the lowest hop number to the sink as
tentative best path


Low reporting rate requirement tentatively



Protocol Implementation


Link loss rate estimation


Measured according to packet serial numbers holes


Estimated with an EWMA approach.


Protocol Implementation


Feedback of communication condition


Checking the following parameters in a given interval


A node


NP


A node

s path loss rate to the sink


Link loss rate from upstream neighbors



If they are changed, feed back the new value to
upstream nodes


higher priority.

Protocol Implementation


Feedback of newly desired reporting rates


FBRT

Application

Sensor Data

& Source NP

Rate adjustment

feedback

The Sink

FBRT

Node

FBRT

Encapsulate

my NP into

data packets

Rate adjustment

Sensor

Data

Application

Source

Presentation Outlines


1. Introduction


2. Motivations and Design Considerations


3. Protocol Implementation


4.
Simulation Results


5. Conclusion


Simulation results


Coding FBRT over NS
-
2



Setting of the network














Scheme 1: Based on directed diffusion with ESRT scheme. (*)


Scheme 2: FBRT (o)

Area of sensor field

1500m*1500m

Number of sensor nodes

100

MAC

IEEE 802.11 without
CTS/RTS and ACK

Radio power

0.2818

Packet length

36 bytes

Transmit Power

0.660 W

Receive Power

0.395 W

Feedback interval

1 second

IFQ length

50 packets

Simulation Time

1000 seconds

Simulation results


Simulation Network

Simulation results


Results



Energy consumed of the WSN (J)

Simulation results


Results



Presentation Outlines


1. Introduction


2. Motivations and Design Considerations


3. Protocol Implementation


4. Simulation Results


5
. Conclusion


Conclusion


we propose FBRP, a feedback
-
based protocol to
address reliable sensor
-
to
-
sink data transport
issue


FBRP optimizes the energy consumptions with
two schemes.


the sink's rate control scheme that feeds back the
optimal reporting rate of each source.


the locally optimal routing scheme for in
-
network nodes
according to the feedback of downstream
communication conditions.


Simulation results verify its effectiveness for
reducing energy consumption.


Thank You