Topology Control in Wireless Ad Hoc Networks phần 1 pdf

Istituto di Informatica e Telematica Topology Control in Wireless Ad Hoc Networks Paolo Santi Istituto di Informatica e Telematica del CNR, Pisa, ITALY paolo.santi@iit.cnr.it... Tutorial

Istituto di Informatica

e Telematica

Topology Control in Wireless Ad Hoc Networks

Paolo Santi

Istituto di Informatica e Telematica del CNR, Pisa, ITALY

paolo.santi@iit.cnr.it

Tutorial outline

 Introduction

– Motivation: the need for Topology Control (TC) in ad hoc networks

– An ad hoc network model

– Topology control: a taxonomy

 Stationary networks

– The critical transmitting range for connectivity

– Energy efficient communications: unicast/broadcast

– TC protocols: “ideal” properties and state-of-the-art solutions

 Mobile networks

– Mobility models

– The mobile critical transmitting range

– Topology control with mobility

 Open issues

– More realistic network and energy models

– Is mobility beneficial or detrimental for TC?

– Multi-hop data traffic

– Topology control in the protocol stack

 Towards and implementation of TC: the CLUSTERPOW and NTC-PL protocols

Istituto di Informatica

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Motivations for topology control

 Both energy and capacity are limited resources in ad hoc networks

 In case of Wireless Sensor Networks (WSN), energy consumption is

especially critical

 The ad hoc network designer should strive for reducing node energy

consumption and providing sufficient network capacity

 The answer: Topology Control (TC) — maintain a topology with certain properties (e.g., connectivity) while reducing energy consumption and/or increasing network capacity

Introduction: 1/7

Topology control: an informal definition

Topology control:

the art of coordinating nodes’ decisions regarding their

transmitting ranges, in order to generate a network with the

desired properties

A remark on terminology:

– Topology control: a system-level perspective — optimize the choice

of the nodes’ transmit power levels to achieve a certain global

property – Power control: a wireless channel perspective — optimize the choice

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An ad hoc network model

Introduction: 3/7

 The power p i required by node i to transmit data to node j must satisfy

p i /δ(i,j)α≥β,

where δ(i,j) is the distance between i and j, β is the transmission quality

parameter, and α is the distance-power gradient

 Nodes are represented by points in d-dimensional space (d=1,2,3)

 A range assignment is a function RA that assigns to every node u a

transmitting range RA(u) in (0,r max ], where r max is the maximum

transmitting range (common to all the nodes)

 Assuming β =1, the energy cost of a range assignment is defined as

∑u (RA(u))α

The communication graph

 Given node positions and a range assignment RA, the communication

graph contains a directed edge (u,v) if and only if v is within u’s

transmitting range, i.e RA(u) ≥ δ(u,v)

 A range assignment is said to be connecting if it generates a strongly

connected communication graph

 Note: if nodes are mobile, a range assignment which is connecting at

time t1 might become disconnected at a later time t2

 In mobile networks, we have in general a sequence of range

assignments RA1, RA2, , where the transition between the range

assignments is determined by the TC protocol

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The symmetric communication graph

Introduction: 5/7

 Often, we are only interested in bi-directional (symmetric) links

communication graph by deleting unidirectional wireless links

An example (Point Graph)

Comm graph

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Topology control: a taxonomy

Introduction: 7/7

Topology control

Homogeneous

(the CTR)

Non homogeneous

per-packet TC periodical TC

routing graphs level-based

The Critical Transmitting Range (CTR)

 A range assignment RA is said to be homogeneous if all the

nodes have the same transmitting range r, i.e RA(u)=r for all u, for some r∈(0,rmax]

R; what is the minimum value of r such that the r-homogeneous

range assignment is connecting?

 This minimum value of r is called the critical transmitting range for

connectivity