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Protocols for Self-Organization of a Wireless Sensor Network
K. Sohrabi, J. Gao, V. Ailawadhi, and G. J. Pottie
IEEE Personal Comm., Oct. 2000.Presented By: earl
Introduction
Self-Organization Wireless Sensor Network --wireless sensing + data networking Group of sensors (nodes) linked by wireless
medium to perform distributed sensing tasks.
Example: surveillance, security, health monitoring
systems, etc
Goals
Operate under dynamic condition: startup, steady state, failure operate unattended
Energy-efficiency
Design Challenges
Hardware: digital circuit design
Wireless networking: modulation, channel access, robust &
energy efficient protocols, routing, mobility etc.
Applications: detection and data collection, data diffusion,
notification
Main difference
Conventional Wireless Networks High QoS (high throughput/low delay) & High ba
ndwidth efficiency
Sensor Network Length of network’s lifetime need to conserve
energy Performance highly depends on energy efficienc
y of algorithms
Energy-Conserving
Energy consumptions: Sensing Data processing Communications
Communications is the major energy consumerTherefore, local processing is key
ORM concept
O -Organization of nodes to access shared medium network formation R -Routing in the network M -Mobility management
Protocols Self-Organization Medium Access Control for Sensor Networks (SMACS)
Network startup and link layer
Eavesdrop-And-Register (EAR) Algorithm Seamless interconnection of mobile nodes in the field
of stationary wireless nodes (mobility management)
Sequential Assignment Routing (SAR) Facilitates multi-hop routing
Single Winner Election (SWE) and Multi-Winner Election (MWE)
Facilitates local cooperative information processing
SMACS Protocol
SMACS Operation Discover neighbors Assign a channel to a links between
neighboring nodes Channel (time slot) = pair of time intervals
(transmission/reception pattern) Each link operates on a different frequency
(which is randomly chosen) Only local knowledge quick energy saving
Node turns on/off communication according to its timeslots
a
e
b
d
c
f
g
h
i
SMACS Protocol
Type1: invitation [to B 、 G] (node’s id and number of attached neighbors)Type2: response to Type1 [from B 、 G] (inviter and invitee’ addresses and invitee’s attached state)
SMACS Protocol
Type3: response to Type2 to notify chosen node [to B]•Inviter not attached : none•Inviter, invitee, attached : inviter’s schedule and frame epoch•Invitee not attached, inviter attached: proposed channel for the link, calculated by inviter
SMACS Protocol
Type4: response to Type3 [from B]•Invitee not attached, inviter not attached: channel determined by the invitee•Invitee not attached, inviter attached: none•Invitee attached, inviter not attached: channel determined by the invitee
EAR Protocol
The Ear algorithm’s motivation Designed to provide continuous
communication capability between mobile and stationary nodes
Mobile nodes join stationary wireless nodesMobile node is “eavesdropping” on control signalsBoth side keep a “registry” of neighbors’ information
EAR ProtocolEAR algorithm
Broadcast Invite (BI): The stationary node
invites other nodes to join Mobile Invite (MI):
The mobile responds to BI to request a connection
Mobile Response (MR): The stationary node
accepts the MI response Mobile Disconnect (MD):
The mobile informs the stationary response is needed node of a disconnect; no
BI triggers EARBI:{SNR, node ID, Tx Power,…}If MI info. possible, assign slot in TDMA frameConnect and disconnect thresholds
stationary node
mobilenode
BI
[MI/MD]
MR
Mobile nodes have the onus to manage connections/disconnections with stationary nodes based on the received signal-to-noise (SNR) ratioConnection and disconnection thresholds determine connectivity: Connection Threshold (CT) : minimum level
where connectivity is enabled (SNR > CT) Disconnection Threshold (DT) : maximum level
of connectivity (SNR < DT)
EAR Protocol
1 3
6 5
2
1 2 6 5
EAR is an adaptable protocol that allows stationary and mobile nodes to self-organize and establish connectivity
Mobile Connectivity List:
[ SNR > CT ] MI MessageMR MessageBI Message
MOBILE
EAR Protocol
SAR Protocol
Supports multi-hop routing Route must be robust to failureIt takes into consideration the energy resource and QoS on each path
SAR for Multi-hop routing
Failure Protection Creates multiple trees where the root of
each tree is a one-hop neighbor from the sink sink
Consider power,QoS
Backup route
SWE & MWE Protocols
Handle signaling and data transfer in local cooperative signal processing: Noncoherent Processing SWE Coherent Processing MWE
Elect Central Node (CN) for sophisticated information processing Sufficient energy reserve, computational capabi
lity, high SNR
Noncoherent Cooperative FunctionNo need for path optimality 3-Phase process: Phase I: Target detection, data collection,
and preprocessing Phase II: Membership declaration Phase III: Central node election
CN Election
2 components SWE algorithm —handle signaling for candidate
information “Elecmessage” Each node can announce itself as a CN candidate Compare information, keep record of 1 best candi
date Disseminate information throughout the network
Spanning Tree (ST) algorithm —compute a min-hop ST rooted at the CN
Coherent Cooperative Function
Differ from noncoherent algorithm Explicit computation of minimum energy path:
Path optimality for energy efficiency Limited number of sensor source nodes (SNs)
MWE Select SNs Calculate minimum energy paths from sensor n
ode to each SNUse SWE to select CN from minimum energy consumption
Simulation
Network of 45 randomly scattered nodes having a density of 0.04 nodes/m2
1mW transmit power, Tframe = 8.0s
ConclusionWireless Sensor Network Protocols
Low mobility, enough BW, energy-constrained Self-Organization Medium Access Control for Sensor
Networks (SMACS) Eavesdrop-And-Register (EAR) Algorithm Sequential Assignment Routing (SAR) Single Winner Election (SWE) and Multi-Winner
Election (MWE)
Future work Determine Min energy bound for network formation Higher mobility