Cooperative Localization Protocols for Wireless Sensor Networks

1
Cooperative Localization Protocolsfor Wireless
Sensor Networks

• Francesco Chiti, Romano Fantacci, Simone Menci,
  Alessandro Zappoli
• Dipartimento di Elettronica e Telecomunicazioni
• Università degli Studi di Firenze
• via di S. Marta, 3 - 50139 Firenze, Italy
• francesco.chiti_at_unifi.it

2
Overview
0. Summary

• Introduction
• Motivations
• Proposed protocols
• Galileo Alone (GA)
• Galileo In-Ranging (GIR)
• Update Procedure (UP)
• Performance evaluation
• Conclusions
• Future developments

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Wireless Sensor Networking
1. Introduction

• WSNs introduced a novel communications paradigm
• compact, autonomous and cooperative nodes
  integrating
• Sensing modules
• Processing and communications capabilities,
• under limited energetic resources.
• widely applied to various fields
• environmental monitoring,
• health care,
• infrastructures management,
• safety of public buildings and homes,
• transportation
• military operations.

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Motivations
1. Introduction

• Location Based Services (LBSs)
• gathered data are labeled with their coordinates
  (absolute or relative)
• detecting and tracking several phenomena
• improving the interaction among people and
  intelligent environments.
• Examples
• In Situ (static events)
• Precision agriculture / smart warehouse
• Real-time (time-constrained events)
• Monitoring of buildings or critical areas
• Decision-support system
• condition-based human intervention

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Galileo Alone (GA)
2. Proposed protocols

• Galileo Node (GN)
• is equipped with GALILEO satellite receiver on
  board,
• has enhanced processing capabilities
• moves within an operative area according to a
  Random WayPoint (RWP) model
• The remaining nodes are able to self localize
  themselves by means of
• Ranging packets sent from mobile GN,
• over which they measure the relative SSR.

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GA scheme (1)
2. Proposed protocols
Galileo Pos Acquired
Node 5
Node 4
Galileo Pos Acquired
Galileo Pos Acquired
Node 2
Galileo Pos Acquired

• Localization procedure continues until the
  maximum number of received ranging packets for
  each node has been reached
• GA nodes is notified by means of ACK packets

Galileo Pos Acquired
Mobile Galileo node
Node 1
Node 3
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GA scheme (2)
2. Proposed protocols

• GN stops
• acquires its own position
• broadcasts ranging packets (with TTL1)
• Node N upon reception of the ranging packet
• estimates the received power level
• evaluates though SSR the estimated distance from
  GN
• N sends a ranging ACK to GN
• GN upon ranging ACK reception update its
  Positioning Table
• After the last ACK reception (or timeout
  expiring), GN moves to the next waypoint
• As N has received at least 4 ranging packets (or
  3 for 2D case), it evaluates its own position by
  applying a trilateration algorithm
• more than 4 packets are needed to achieve a fixed
  localization accuracy if SSR measures is affected
  by errors
• N sends a localization ACK
• NLAN ? LAN (Location Aware Node)

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Galileo In-ranging (GIR)
2. Proposed protocols

• GN could experiences coverage limitations
• Constrained paths
• Out-of-Service
• GALILEO signal outage
• Critical applications often require a coarse
  grain localization
• GN complexity might be reduced (especially in
  terms of mobility)

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GIR scheme
2. Proposed protocols
Nodo mobile Galileo
No ACK is required for GIR
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Update Profile (UP)
2. Proposed protocols

• RWP mobility pattern of GN is modified basing on
  LANs in each quarter (nXY)
• The directions N-S and E-O are randomly selected
  according with the following weighting factors
• Tradeoff between
• Localization latency
• Localization probability
• Overhead is accordingly reduced

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Scenarios characterization
3. Results

• Common parameters
• PT 0 dBm
• Psens -90 dBm
• fc 5 GHz
• GT GR 0.5
• Tmove 100 tu
• nIR-pkts 10
• ?H-GALILEO 2 m

• Outdoor-2D scenario
• Pth 74.7 dBm (RSSI threshold)
• m0 4.1 dB (m Nakagami)
• m? 2.5 dB (m Nakagami)
• ?V-GALILEO 0 m
• Area 150?150 m2

• Indoor-3D scenario
• Pth 75.8 dBm (RSSI threshold)
• m0 2.5 dB (m Nakagami)
• m? 0.25 dB (m Nakagami)
• ?V-GALILEO 4 m
• Area 30?30?30 m3

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3. Results
Accuracy vs Latency

• GA points out a greater accuracy
• GN exhibits a lower latency

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3. Results
Latency vs density

• ? density ? nodes get closer
• each ranging pkt is received by more nodes
• ? localization latency
• GIR is better suited for high density regime,
  providing low localization latency

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3. Results
Overhead vs density

• pkt towards GN increases linearly
• In ranging signaling follows a truncated
  exponential law
• ? density ? ? GIR overhead

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Comparison
3. Results

• GA
• Better accuracy
• High precision background applications, as in
  situ monitoring of stationary phenomena
• Environmental monitoring
• Risks prevention
• Deploy-and-Leave applications

• GIR
• Lower latency (for high density regime)
• Real time applications
• Seamless
• Decision support systems
• Safety-and-rescue
• Fault/outage prone applications
• Seamless operations

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3. Results
Latency (GAUP)

• UP procedure allows the latency halving
• Overhead is accordingly cut by half

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3. Results
Accuracy (GIR _at_ Indoor-3D)

• Indoor 3D criticalities
• strong multipath
• marked DOP
• Dependence on initial position estimation

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Indoor-3D
20
15
Localization error m
10
Modified scenario (Outdoor 3D)
5
0
0
0,001
0,002
0,003
0,004
0,005
Density node/m3
GIR is inefficient for sparse WSN

• Almost all nodes are localized at the increasing
  of density but
• more DOP for edge nodes
• more overhead (more IR pkts)

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Conclusions

• Localization error
• GA 1.2 m
• GIR 1.8 m
• Localization latency
• GIR is quicker but requires more overhead (IR
  pkts)
• UP optimizes RWP mobility model cutting latency
  by half

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Future developments

• ToA ranging with UWB transmissions
  (IEEE802.15.4a)
• more accurate channel modeling
• impact of multipath fading (due to ultra-wide
  bandwidth)
• NLOS regime affects the performance
• NLOS paths rejection

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Cooperative Localization Protocolsfor Wireless
Sensor Networks

• Francesco Chiti, Romano Fantacci, Simone Menci,
  Alessandro Zappoli
• Dipartimento di Elettronica e Telecomunicazioni
• Università degli Studi di Firenze
• via di S. Marta, 3 - 50139 Firenze, Italy
• francesco.chiti_at_unifi.it

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Risultati
Accuratezza Vs Multipath
Accuratezza Vs Galileo
Floor determinato dalle altre
tipologie di errore
Scarsa accuratezza determinata dalleffetto
multipath più deciso
Floor determinato dalle altre tipologie di errore
Ricevitori più performanti (quindi più costosi)
non aumentano significativamente le prestazioni

• Accuratezza ricevitori Galileo o GPS con
  tecniche
• evolute / augmentations

Ulteriore giustificazione per scelta sistema
Galileo

• Accuratezza ricevitori GPS poco sofisticati