1 4 th Workshop COST289 – April 11 th 2007 D-STAR MAC Protocol: a Cross Layer Solution for...

14th Workshop COST289 – April 11th 2007

D-STAR MAC Protocol: a Cross Layer D-STAR MAC Protocol: a Cross Layer

Solution for Wireless Sensor Networks Solution for Wireless Sensor Networks

Endowed with Directive AntennasEndowed with Directive Antennas

Gianfranco Manes, Romano Fantacci, Francesco Chiti, Michele Ciabatti, Giovanni Collodi, Davide Di Palma, Ilaria Nelli, and Antonio

Manes

Department of Electronics and Telecommunications

University of Florence


OutlineOutline

1. Motivations WSNs

Directive antennas

2. Proposed protocol Discovery phase

Regime phase

3. Performance analysis

4. Conclusions

Outline Outline


Wireless Sensor NetworkingWireless Sensor Networking

Enabling technology to the aim of intelligent environments instrumenting

Affordable solution to some challenging problems: environmental sensing, productive chains control, real-time phenomena monitoring, safety and rescue application.

WSNs represent a special case of the more general wireless Ad Hoc networking paradigm with additional constraints: limited energetic, storage, processing and communication

capabilities low degree of mobility presence of a small number of sinks

1. Motivations 1. Motivations


Wireless Sensor NetworkingWireless Sensor Networking

This challenge might be got over through careful system design with particular regard to the communications protocols:

MAC layer:

management of both sleep and active power states

PHY layer:

introduction of directional antennas and their integration within the communications framework



Directive AntennasDirective Antennas

Expected benefits Antenna gain maximization towards desired directions,

concentrating energy in smaller area:

Transmitted power decreasing

Power consumption reduction

Network life time increasing

Received power increasing

Coverage range increasing

Error probability reduction




Expected benefits Radiation towards undesired directions minimization

Interference caused by other transmissions reduction

Co-channel interference mitigation

multiple-access problems mitigation

Collision probability reduction

Adaptability to time varying communication conditions: Mote’s failure

Channel errors

Congestion




Criticalities Cost and size

On board integration

Beam switching management: Set-up phase signaling overhead

Latency for end-to-end communications setting-up

Algorithm complexity

Switching agility

Support both to synchronous (source-initiated) and asynchronous (event-based) sensing



Directive-Synchronous Transmission Directive-Synchronous Transmission Asynchronous Reception (D-STAR)Asynchronous Reception (D-STAR)

STAR MAC concept for time synchronization [Chiti et al. in Proc. of IEEE ICC’06]

Cross-layer protocol design (MAC+PHY) Space-time synchronization Suitable for flat topology Scalable

2. Proposal2. Proposal


Directive-Synchronous Transmission Directive-Synchronous Transmission Asynchronous Reception (D-STAR)Asynchronous Reception (D-STAR)

Hypothesis

Beam width = θ [rad]

N possible angular sectors:

N = 2π/θ

Quasi ideal switching

Tswitch << Tpkt


θ = π/2 [rad]

N = 4

Tswitch ≈ μs << Tpkt ≈ ms


D-STAR: State DiagramD-STAR: State Diagram

DISCOVERY

1 < EmptySectors < Ns

Emptysectors = Ns

Switch on

nf < Nfd

Battery < Battery_low

REGIME

Battery < Battery_low

nf=Nfd

INIT

OFF



D-STAR: Discovery phaseD-STAR: Discovery phase

1. Duty cycle δ = 100% Listening mode for a time interval Tset-up

Beacon (HELLO) broadcasting: 1 beacon angular sector Node ID and Phase (φ) transmission (time to the next awakening)

Waiting for a fixed time duration τs in search of reply messages Switching to the following angular sector

Exit condition: (Tset-up is expired, i.e., Nfd frame periods)



D-STAR: Discovery phaseD-STAR: Discovery phase


δ = 100%

Tset-up

time

HELLO HELLO HELLO HELLO

HELLO

…

HELLO


D-STAR: Regime phaseD-STAR: Regime phase

Each node sends: HELLO messages to known neighbors belonging to different angular

sectors according to the phase transmitted in previous HELLO messages, several HELLO messages in background with the proper period to unknown

neighbors in the empty angular sector.

Upon the replying of a node, a logical channel is established: The channel access is managed by means of a CSMA/CA (Carrier Sense

Multiple Access with Collision Avoidance) approach.

Each node remains in the regime phase until there is at least one neighbor, otherwise if the number of empty angular sector is equal to Ns it re-enters the discovery phase in search of connectivity.



D-STAR: Regime phaseD-STAR: Regime phase


Tf

time

listening sleep

δ Tf

HELLO HELLO HELLO

…

HELLO + FWD

…

HELLO * FWD

HELLO

…HELLO HELLO

1 HELLO broadcasting

per sector


Operative hypothesisOperative hypothesis

FP6-IST-1-508744-IP ‘‘GoodFood’’ reference scenario Monitored area = 25 ∙ 25 [m2] Number of WSN nodes: [10…50] N = 1, 2 ,4, 6, 8 angular sectors HELLO pkt length = 8 bytes Bit rate = 250 kbps Packet Error Rate = 5% Number of channel sensing for CSMAC/CA algorithm = 6 Frame period: 10,25,50,75,93 s Duty-cycle: [1…5]%

3. Performance3. Performance


Università degli Studi di Firenze

Normalized Lifetime Gain (Tf=93 s d=3%)

0

5

10

15

20

25

10 15 20 25 30 35 40 45 50

Number of nodes

No

rma

lize

d L

ife

tim

e G

ain

omni

N=2/omni

N=4/omni

N=6/omni

N=8/omni


Network lifetime vs nodesNetwork lifetime vs nodes


Normalized Lifetime Gain (Tf=93 s; 50 nodes)

0

5

10

15

20

25

0,01 0,02 0,03 0,04 0,05

Dutycycle

No

rma

lize

d L

ife

tim

e G

ain

omni

N=2/omni

N=4/omni

N=6/omni

N=8/omni

Network lifetime vs duty-cycleNetwork lifetime vs duty-cycle



Normalized Lifetime Gain (d=3%; 50 nodes)

0

5

10

15

20

25

30

35

10 20 30 40 50 60 70 80 90

Frame period [s]

No

rma

lize

d L

ife

tim

e G

ain

omni

N=2/omni

N=4/omni

N=6/omni

N=8/omni

Network lifetime vs frame periodNetwork lifetime vs frame period



Occupied Channel Probability (Tf=93s; d=3%)

0

0,01

0,02

0,03

0,04

0,05

0,06

10 15 20 25 30 35 40 45 50

omni

N=2

N=4

N=6

N=8

Number of nodes

Occ

up

ied

Ch

ann

el P

rob

abil

ity

Collision Probability (Tf=93 s; d=3%)

0

0,005

0,01

0,015

0,02

0,025

10 15 20 25 30 35 40 45 50

omni

N=2

N=4

N=6

N=8

Number of nodes

Co

llis

ion

Pro

bab

ilit

y

SS'

R

S S'

RR'

Hidden node analysisHidden node analysis



Normalized Throughput (Tf=93 s; d=3%)

0,92

0,93

0,94

0,95

0,96

0,97

0,98

0,99

1

10 15 20 25 30 35 40 45 50

omni

N=2

N=4

N=6

N=8

Number of nodes

No

rma

lize

d T

hro

ug

hp

ut

Signaling Overhead (Tf=93 s; d=3%)

0

500

1000

1500

2000

2500

10 15 20 25 30 35 40 45 50

omni

N=2

N=4

N=6

N=8

Number of nodes

Ov

erh

ea

d [

pk

t/T

f]Signaling Overhead

Resource Utilization

Efficiency and complexityEfficiency and complexity



ConclusionsConclusions

Energy efficient WSN protocol design Cross-layer approach (MAC+PHY) Performance:

Energetic consumption Lifetime Latency Collision probability Signaling overhead

Good tradeoff Easy to implement

4. Conclusions4. Conclusions

1 4 th Workshop COST289 – April 11 th 2007 D-STAR MAC Protocol: a Cross Layer Solution for...

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