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

Wireless Sensor Node

Wireless Sensor Node

http://today.cs.berkeley.edu/800demo/

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

Used for network startup and link-layer organization Forms a flat topology

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

Node topology

SMACS Protocol

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

Multi-Winner Election(SWE) Process

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

Single Winner Election (SWE) Process

Simulation

Network of 45 randomly scattered nodes having a density of 0.04 nodes/m2

1mW transmit power, Tframe = 8.0s

Simulation

Simulation

Simulation

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