Event Reliability in Wireless Sensor Networks

PhD Student: Muhammad Adeel Mahmood

Supervised by: Winston Seah

Network Engineering Research GroupVictoria University of Wellington

Wellington, New Zealand

Outline• Motivation• Introduction• Background• Related Work• Proposed Solution• Preliminary Work• Research Objectives• Contributions• Summary

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Motivation• Sink is only interested in a single packet containing

event’s information

• Identification of redundant packets

• Reliable event delivery

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Introduction• Wireless Sensor Networks

– Sensor Nodes• Large number

• Limited sensing, processing & communication capabilities

• Collaborate with each other

– Sink Nodes• More powerful

• Relays data

from network

to end user

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Introduction

• Distinctive Features:– Unique topology– Diverse application– Traffic characteristics– Resource constraints

• Challenges– Accurate event detection– Reliability event delivery– Network scalability & Event coverage– Energy conservation

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Background

• Reliability in WSNs– Packet Reliability– Event Reliability

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Background

• Reliability in WSNs– Hop-by-hop/End-to-end Packet Reliability– Hop-by-hop/End-to-end Event Reliability

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Reliability in WSNs• Retransmission / Redundancy-based Reliability

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Retransmission-based Reliability• Explicit Acknowledgementd (eACKs)

• Implicit Acknowledgements (iACKs)

–Implicit Acknowledgements (iACKs)

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Retransmission-based Reliability

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• Challenges– Packets need to be cached– Causes delay– Immediate retransmissions required– Network congestion

• Proposed solutions– Intelligent retransmission mechanism– Information redundancy

Redundancy-based Reliability• Information Redundancy (Coding Schemes)

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Redundancy-based Reliability

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• Challenges – Increased data transmission– Low performance in high loss environment– End-to-end coding– Limited no. of bits can be recovered

• Proposed solutions– Hop-by-hop coding– Incorporating with retransmissions

Existing solutions• Retransmission-based reliability

– End-to-end packet reliability • Packet reliability is good for traditional networks not for WSNs

– Event reliability• Event reliability is good, but all are sink-centric which consumes more energy

and traffic

– ACK/NACK • Does not exploit the broadcast nature of wireless networks

• Does not emphasize on spatial locality and overlapping regions of densely deployed nodes

• Redundancy-based Reliability – End-to-end encoding/coding– Only focused on packet reliability

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Existing Research

• Retransmission-based Schemes

Protocols Traffic FlowReliability

LevelLoss

RecoveryLoss Detection & Notification

Sink Centric

Redundancy

ERP Up Event Hop-by-hop iACK No No

SWIA [1] Up/Down Packet Hop-by-hop iACK - No

ESRT [2] Up Event End-to-end - Yes No

DST [] Up Event End-to-end - Yes No

STCP [3] Up Packet/Event End-to-end ACK/NACK Yes No

PORT [4] Up Event Hop-by-hop  - Yes No

ART [5] Up/Down Event End-to-end ACK/NACK Yes No

LTRES [6] Up Event End-to-end ACK/NACK Yes No

ERTP [7] Up Packet Hop-by-hop iACK/ACK Yes No

DTSN [8] Up Packet End-to-end ACK/NACK Yes -

RBC [9] Up Packet Hop-by-hop iACK Yes No

RMST [10] Up Packet Hop-by-hop NACK Yes No

PSFQ [11] Down Packet Hop-by-hop NACK Yes No

GARUDA [12] Down Packet Hop-by-hop NACK Yes No

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Existing Research

• Redundancy-based Schemes

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REDUNDANCY-BASED SCHEMES

ProtocolsTraffic Flow

Reliability Level

Encoding / Decoding

Coding Scheme

Performance Evaluation

Supportive Mechanisms

Wen et al. [7]

Up Packet End-to-end Erasure CodesTheoretical

AnalysisULP

Ali et al. [9]

Up Packet End-to-end Erasure CodesTheoretical

AnalysisGenetic

AlgorithmsMarchi et al.

[10]Up Packet End-to-end Erasure Codes Simulations

Enhansement Flow

Kim et al. [11]

Up Packet End-to-endErasure & Systematic

CodesReal test beds

Alternate Route-Fix

Srouji et al. [12]

Up Packet Hop-by-hop Erasure Codes Simulations Partial Coding

Kumar et al. [13]

Down Packet Hop-by-hop Erasure Codes Simulations FB Cast

Proposed Solution• This thesis aims to focus on the issues of event reliability

in a resource constrained WSN by proposing an distributed approach, where

– In-node decisions are made based on spatio-temporal correlation instead of relying on the sink

– Reliable transmission of a unique event is guaranteed while minimising unnecessary transmission of redundant events

– Overall network lifetime would be increased in terms of energy, traffic overhead, congestion, data flow and Coverage

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Preliminary Work

• We Proposed ERP, an event-to-sink reliability protocol that builds on a condition that only a single packet carrying the information about a particular event of interest to reach the sink

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Preliminary Work

• We Propose ERP, an event-to-sink reliability protocol that builds on a condition that only a single packet carrying the information about a particular event of interest to reach the sink

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Preliminary Work

• We Propose ERP, an event-to-sink reliability protocol that builds on a condition that only a single packet carrying the information about a particular event of interest to reach the sink

– Region-based selective retransmissions mechanism

– Reduced energy consumption through in-network data

processing

– Improved coverage of events in the network

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Preliminary Work

Basic Flow of ERP

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Preliminary Work

Basic Flow of ERP

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Experimental Design

• Simulation Setup– GloMoSim simulator– Set of nodes {200, 250, 300, 350, 400, 450, 500}– 200m X 200m area (Random node deployment)– 10m sensing range– 30m communication range– 40byte packets– Periodic packet transmission by nodes at regular intervals are

uniformly distributed between 3secs and 10secs– Simulation time 10secs up till 3600secs

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Results & Discussion

• ERP vs. SWIA

– Coverage with increasing node density

– Events successfully reported at the sink

– Number of duplicate packets transmitted

– Energy consumption in terms of packets

transmission by individual nodes

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Results & Discussion• ERP Vs. SWIA Vs. No-retransmissions

– Number of event detections reported at the sink

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Results & Discussion• ERP Vs. SWIA

– Number of duplicate events reported at the sink

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Results & Discussion• ERP Vs. SWIA

– Energy efficiency(Avg. transmission per node)

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Research Objectives

• This thesis aims to address the problem of reliable event delivery in resource constrained WSNs by– Accurate identification of duplicate events

– Guarantee reliable event delivery from the source to the sink

– Investigate coding schemes to further bolster guaranteed event reliability

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Goals Achieved So Far

• Development of an event-to-sink reliability protocol that serves to improve the scalability of event detection in a WSN [ERP]

• A survey on existing data transport reliability protocols in WSNs has been performed that reviews and analyse the existing research on data transport reliability in WSNs.

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Project Plan

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Summary

• The overall goal is to investigate a new approach to ensure reliable event delivery in a resource constrained WSN

• The preliminary work has shown that event reliability is more suitable than packet reliability in WSNs

• Incorporating information redundancy in order to guarantee reliable event delivery while improving overall network cost

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Thanks!

Questions?

Muhammad Adeel MahmoodNetwork Engineering Research Group

Victoria University of WellingtonWellington, New Zealand

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