DOF: Duplicate Detectable Opportunistic Forwarding in Duty-Cycled Wireless Sensor Networks

Daibo Liu1, Zhichao Cao2, Jiliang Wang3, Yuan He3 Mengshu Hou1, Yunhao Liu3

1 University of Electronic Science and Technology of China

2 Hong Kong University of Science and Technology 3 Tsinghua University

1

CitySee

2

Protocols

• Routing – Collection Tree Protocol (CTP) (SenSys’09)

• Duty-cycled media access – X-MAC

3

t …… ……

I wake up periodically. If I hear nothing, I will go back to sleep!

…… ……

I prepare send a packet. I will not stop sending until the ACK comes!

Drawback

• Waiting long time for the deterministic forwarder wake-up – Longer delay

– Energy waste

4

Opportunistic Forwarding S

R1R4

R3R2

Reliable Link

Bursty Link

5

t S

R1

R2

R3

R4 Take first wake-up and successfully received opportunity.

Drawback

6 6

S

R1R4

R3R2

Reliable Link

Bursty Link

S

R1

R2

R3

R4

Data Data A

Data

Data

Data

A

A

A

R1, R2, and R3 are all active

R1

R2 R3

Shorten the lifetime Traffic jam

Existing Techniques

• Overhearing – Not scalable

– Lossy link

• Coordination – Extra control overhead

7

How to mitigate the influence of the duplicate in a light-weight and efficient way?

Temporal Diversity of ACK

• Split the Acknowledgment (ACK) waiting interval into multiple slot

• Distinguish all potential forwarders by their different ACK time slot

8

0 1 2 3 4 5 6 7

t

ACK Waiting Interval

Probe

DOF Overview

9

S

R1

R2

R3

R4

p p A A0 1 2 3 Data

Data0 A

A

p

p

p

A

A

A

04 1 2 3 S

R1R4

R3R2

Reliable Link

Bursty Link

• Probe (P): detecting available forwarders

• ACK (A): acknowledge the probe in different time slot

• Data: send the data to the forwarder R2

R1

R2 R3

Slot Assignment

10

0 1

0 1 2 ... 9 10 11 12 ... 19 20 21 22 ... 29

Zone 0 Zone 1 Zone 2

Hash

Priority

sequence

Routing progress: D

ACK slot 2 3 4 5 6 7 8 9

Routing progress

Mapping to priority sequence

Mapping to an ACK slot with randomness

Slot Inference

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• The slot Ks of the received ACK as :

- : preconfigured slot size

slotbasersTTTK /)(

slotT

P Sender P

1T

P A

2T

A

3T

12TTT

base

13TTT

r

the earliest ACK at slot 0 the received ACK

Slot Size

• Large Slot Size – Less ACK slots

– Robust

• Small Slot Size – More ACK slots

– Vulnerable

• Experiments in office environment – Tslot = 0.2ms

12 12

Retransmission

• Data transmission failure – Link failure

– Mismatch of slot information

• Experiments in office environment – link failure is rare

• Link initiated by probe is temporally available

– Maximum number of data transmission is 2

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Tunnel Transmission

14

S

R1R4

R3R2

Send

Queue

Take the benefit of the probe transmission of the first packet.

Evaluation

• Indoor Testbed with 20

Telosb nodes

• Different traffic loads – Inter Packet Interval (IPI) of

each node is set as 1s, 2s, 4s,

8s and 16s.

• ORW (IPSN’12) – Opportunistic Routing in Wireless

sensor networks

• A-MAC (SenSys’10) + CTP – Receiver initiated duty-cycled

media access

15 15

Duplicate

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IPI <= 2s, the duplicate ratio ORW: > 80% DOF: < 10%

Packet Reception Ratio

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IPI <= 2s, the average PRR DOF: > 46.5% improvement

Energy and Delay

18 18

Energy: radio duty cycle DOF : > 21.4% improvement

Delay: average preamble count DOF : as low as ORW

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DOF is a practical opportunistic forwarding technique tailored

to duty-cycled WSNs.

Conclusion

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• Exploiting the temporal diversity of ACK

Key design

• Indoor testbeds

• Good performance under various traffic loads

Evaluation

• Large-scale test

• Different hardware

Future works

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Thank you! Question?

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Slot Assignment Function

• Fixed slot assignment – Avoid the ACK slot collision

– Extra control overhead

– Lose some opportunities

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