Mncs 16-08-3주-변승규-opportunistic flooding in low-duty-cycle wireless sensor networks with...

Intelligence Networking and Computing Lab.

IntroductionLow-Duty-Cycle Wireless Sensor Networks

Flooding in Low-Duty-cycle Networks

Review: Typical Issues in Flooding

MotivationFit for Intermittent Receivers

Traditional methods with Low-Duty-Cycle

PreliminariesNetwork Model

Assumptions

Performance Metrics

Main DesignDesign Overview

Flooding Energy Cost and Delay

The Delay pmf of the Energy-Optimal Tree

Decision Making Process

Decision Conflict Resolution

Shape of Opportunistic Flooding

2

Practical IssuesOn Node Failures

On Link Quality Change

EvaluationSimulation Setup

Baseline I : Optimal Performance Bounds

Baseline II : Improved Traditional Flooding

Performance Comparison

Investigation on System Parameters

Evaluation of Practical Issues

Overhead Analysis

Implementation and EvaluationExperiment Setup

Performance Comparison

Why Opportunistic Flooding is Better

Conclusion


Duty Cycle ofHumans

Lions

Sensors

4

6:00 7:00 8:00 17:00 00:00

: 75%

: 5%


Why low-duty-cycle?A cubic centimeter package

Limited amount of energy

Need for sustainable deployment of sensor systemTo reduce operational cost and ensure service continuity

5


Different wake-up timeIf its receivers do not wake up at the same time

A sender has to transmit the same packet multiple times

6

Sender

On

Off

Unreliable wireless linkdue to wireless loss

A transmission is repeated if the previous transmissions are not successful

Combination of the two featuresMake the problem more difficult

… …


Efficiency or Reliability

7

Source

Relay

Destination

Tradeoff RelationshipIf # of the relay nodes is increased, Broadcast Storm occurs

If # of the relay nodes is reduced, the next node could fail to receive a broadcast packet

Blind flooding Routing tree

in always-wake networks

In low-duty-cycle networksIf # of the relay nodes is increased, they cost of high energy consumption

If # of the relay nodes is reduced, the cost of long delays


Major Energy Drain1.3 ms to transmit a TinyOS packet using a CC2420 radio

3 ~ 4 orders of magnitude longer duration waiting for reception

9

17.4

19.7

16

17

18

19

20

Energy Consumption of CC2420 Radio

Transmission Idle Listening / Receiving

mA

Energy Consumption of Zigbee

Need for Low-Duty-Cycle OperationTo reduce the energy penalty in idle listening


If applied directly① A node broadcasts a packet as soon as it receives it

② Becomes even worse when unreliable links

③ Collisions are taken into account

10

①

②

③

Possible ArgumentsMultiple transmissions based on the neighbor schedules

ARQ-based mechanism to deal with unreliable links

Not suitable for low-duty-cycle networks,If used directly

Sender

On

Off

Collision Redundant

Need for a New Flooding DesignTo address these limitations


Two Possible Sensor StatesActive

Dormant

A node can only receive a packet when it is active, but can transmit a packet at any time

12

10 : Turning off all its modules except a timer to wake itself up

: Able to sense an event, or receive a packet

Working Schedules: 𝑤𝑖 , 𝜏T : working period of the whole network

𝑤𝑖 : string of ‘1’ and ‘0’s denoting the schedule

𝜏 : time units of length, T can be divided into

Each node picks one or more time units as its active state


Only one flooding will be in process at any time

Working schedules are shared with all its neighbors when joining the network

Unreliable links and collision are existLink quality is measured using probe-based method and updated infrequently

Do not consider “capture effect”

Local synchronization can be achieved in an accuracy of 2.24 usas described in Flooding Time Synchronization Protocol (FTSP), SenSys ‘04

Hop count is to denote the minimum number from a node to the source

13


Flooding delayDue to the imperfection of the links, the flooding delay exhibits inherent randomness

The average flooding delay is used

Energy consumptionAs the receiver-side energy is determined by their predefined working schedules

Only the sender-side energy

14


Directed Acyclic Graph (DAG)Edge weight : link quality

Energy-Optimal Tree : Default path in SOAR

Smaller hop count larger ones,

16

Opportunistic Flooding (this study defines)To utilize links outside an energy-optimal tree

If these links have a high chance of receiving the packet “statistically earlier” than its parent

not specified only 1-hop anywhere in this paper


About Energy OptimalityFlooding in low-duty-cycle is realized by multiple unicasts

The probability that a node has two neighbors with identical schedules?

Combination with repetition

Energy-optimal tree’s Energy optimality

Proof by contradiction

If multiple nodes wake up simultaneously

MCDS problem, NP hard

But is rare

17


About Delay Optimality

18

F

D

E

D and E receives the packet at time t

F wake up at time instances t +4, t +8, …

4 × 0.8

0.8

0.7

+8 × 1 − 0.8 × 0.8 +12 × 1 − 0.8 2 × 0.8 = 𝑡 + 4.999⋯

4 × 0.7 +8 × 1 − 0.7 × 0.7 +12 × 1 − 0.7 2 × 0.7 = 𝑡 + 5.71⋯

Delay in the case DF

Delay in the case EF

Delay in the case DF | EF

𝑡 +

𝑡 +

𝑡 + 4 × 1 − 1 − 0.8 1 − 0.7 +8 × 1 − 0.8 1 − 0.7 × 1 − 1 − 0.8 1 − 0.7

+12 × 1 − 0.8 1 − 0.72× 1 − 1 − 0.8 1 − 0.7

= 𝑡 + 4.26⋯


0.9

0.8

D

A

Computation of pmfSource S generates a packet at time slot 0

Intermediate A wakes up at every 10t time slot

Intermediate D wakes up at every 10t +5 time slot

19

S

E

C

D

G

B A

F

S

0

1.00

0

0.90

10

0.09

20

0.009

30

…

t

t

35

0.05 …

t5

0.72

15

0.22

25

𝑖:𝑡𝑙 𝑖 <𝑡𝑙+1(𝑗)

𝑝𝑙 𝑖 𝑞 1 − 𝑞 𝑛𝑖𝑗

The probability that it receives the flooding packet at its j-th active time slot

𝑝𝑙+1 𝑗 = (1)


Complexity AnalysisTheoretically, the delay pmf may have infinitely many entries

The Eq. (1) takes quadratic time 𝑂 𝑛2

But linear time is achievable

20

𝑝𝑙+1 𝑗 =

𝑖:𝑡𝑙 𝑖 <𝑡𝑙+1(𝑗)

𝑝𝑙 𝑖 𝑞 1 − 𝑞 𝑛𝑖𝑗

=

𝑖:𝑡𝑙 𝑖 <𝑡𝑙+1(𝑗−1)

𝑝𝑙 𝑖 1 − 𝑞 𝑛𝑖,𝑗−1(1 − 𝑞) +

𝑖:𝑡𝑙+1 𝑗−1 ≤𝑡𝑙 𝑖 <𝑡𝑙+1(𝑗)

𝑝𝑙 𝑖 𝑞

= 𝑝𝑙 𝑗 − 1 (1 − 𝑞) +

𝑖:𝑡𝑙+1 𝑗−1 ≤𝑡𝑙 𝑖 <𝑡𝑙+1(𝑗)

𝑝𝑙 𝑖 𝑞

2) = +0.009 × 0.8

= 0.512 ≈ 0.535

0.09

D

0.009A

0

0.90

10 20 30

…

t

0.05

0

0.72

0.22 …

t5 15 25

D

A0.8

(2)

1) = +0.09 × 0.8

= 0.216 ≈ 0.22

1) 2)

0.72 × 1 − 0.8

0.22 × 1 − 0.8


2) If ,

10

To judge Need or Redundantopportunistically early packets are forwarded

A node finds its 𝑝-quantile delay based on its pmf, 𝐷𝑝, shared with its parents

21

Expected Packet Delay (EPD)

A level-𝑙 node A receives a packet at its 𝑖 th active time unit with delay 𝑡𝑙(𝑖)

For a link quality 𝑞, 1

𝑞transmission are expected

1

𝑞-th time slot after 𝑡𝑙(𝑖)

𝐸𝑃𝐷 =

𝑗:𝑡𝑙+1 𝑗 >𝑡𝑙(𝑖)

𝑞 1 − 𝑞 𝑛𝑖𝑗𝑡𝑙+1 𝑗 (3)

18 22 26 Time

0.5

0.1 0.04

0.3

14

B’spmf

1) If 𝑝 = 0.8, then 𝐷𝑝 = ?

Received by A

1st try to B 2nd try to B

D𝑝 = 18𝐸𝑃𝐷 = 22

BA0.5

then 𝐸𝑃𝐷 = ?

3) If node A received at 9,

Did node A judge the packetNeed or Redundant?

…1 0 0 0 1 0 0 0 1 0 0 0 1 0 0 0 1…

3)

BA


Need for Selection of Flooding SendersTo avoid Collision caused by HTP

More likely to occur in a low-duty-cycle-networks

TDMA or RTS/CTS based solutions are not suitable

22

Reduced Sender SetLink quality threshold 𝑙𝑡ℎ

The best link quality is always included, the rest are selected inductively

All the candidates are tested one-by-one in descending order

Computation ComplexityDenote 𝐻 as the total number of sender candidates

A node consumes 𝑂 𝐻 time

To construct a sender set, totally, 𝑂 𝐻2 time is consumed

Sender

On

Off

Best Candidate

Candidate


Link-Quality-Based BackoffTo resolve collisions

To reduces redundant transmissions

A node with better link quality a higher priority to grab the channel : Ideal

Backoff DurationBackoff Time bound : 𝑇𝑏𝑎𝑐𝑘𝑜𝑓𝑓

Maximum Size of Sender Set : 𝑊

Random period of time : 𝑋

23

𝑡𝑏𝑎𝑐𝑘𝑜𝑓𝑓 = 𝑊 1 − 𝑞𝑇𝑏𝑎𝑐𝑘𝑜𝑓𝑓

𝑊+ 𝑋

0 ~ 𝑊 − 1Transmission Priority

RandomnessTo reduce collision

−𝑇𝑏𝑎𝑐𝑘𝑜𝑓𝑓

𝑊, 𝑇𝑏𝑎𝑐𝑘𝑜𝑓𝑓

𝑊

After BackoffThe one with the best link quality starts first

Best-link node can keep occupying the channel until the current time slot is passed

Intelligence Networking and Computing Lab. 24

Source

Candidates

S

A

B

C

D

E

F

H

G

(a) Original Network

S

A

B

C

D

E

F

H

G

(b) Sender Selection

S

A

B

C

D

E

F

H

G

(c) B receives the packet early

S

A

B

C

D

E

F

H

G

(d) B receives the packet late

Intelligence Networking and Computing Lab. 25

Source

Candidates

S

A

B

C

D

E

F

H

G

(c) B receives the packet early

S

A

B

C

D

E

F

H

G

(d) B receives the packet late

S

A

B

C

D

E

F

H

G

(g) B receives the packet late

S

A

B

C

D

E

F

H

G

(e) B sends the packet earlier than the others

S

A

B

C

D

E

F

H

G

(f) B sends the packet later than A


Just makes the use of Elementary mathematicsFirst and last

Nothing to waste

The 2nd half of this studyTreats the practical issues in the protocol

Evaluates it in diversified ways

Future workThe second half of Opportunistic Flooding in Low-Duty-Cycle Wireless Sensor Networks with Unreliable Links

Flooding Time Synchronization Protocol, SenSys ‘04

26

Mncs 16-08-3주-변승규-opportunistic flooding in low-duty-cycle wireless sensor networks with...

Engineering

Transcript of Mncs 16-08-3주-변승규-opportunistic flooding in low-duty-cycle wireless sensor networks with...