Background ArDeZ - Overview Communication Sensor Networks period - - PDF document

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ArDeZ: An Asymmetric Rendezvous Based MAC for Sensor Networks

Kwan-Wu Chin and Raad Raad

Telecommunications and Information Technology Research Institute University of Wollongong Australia

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Outline

• Background
• ArDeZ

– Overview – Channel Setup – Generating Pseudo-random Rendezvous Periods – Transmissions: broadcast and unicast

• Results
• Conclusion and on-going work

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Background

• Sensor Networks

– Low cost nodes equipped with a processor, a low data rate transceiver, modest memory, and one or more sensors – Precision agriculture, bush fire monitoring, etc. – Energy constrained

• Medium Access Control (MAC)

– Coordinating channel access in an energy efficient manner. – Issues:

• collisions, idle-listening, overhearing, synchronization, and

control overheads.

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ArDeZ - Overview

• Pair-Wise Time Hoping

– Seed pseudo random rendezvous periods

• Mean rendezvous period (MRP)

12 12 12 23 23 Time 1 2 3

S1 S2 S3 S4 Communication period

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ArDeZ – Channel Setup

• Invite message

– Frequency dictated by Invite’s Mean Rendezvous Period (MRP)

• Scan for a maximum WaitNeighbor time
• Upon receiving an Invite message, a

sensor selects an invite slot randomly.

Invite Message Sleep

Time

Invite Slots

Part 1

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ArDeZ – Channel Setup

Sleep Time

Node-A’s Invite Message

• Node address
• Sensor capabilities
• Uplink and Downlink seeds

Us and Ds

• Constants Ca and Cb

Neighbors == N? Channel exist with node-A? Node-A meets criteria?

Channel Request Message

(Su, Sd, Duration)

Node-A

Channel ACK Message (CAM)

Node-B (Invitee) (Inviter)

Part II

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ArDeZ – Generation Rendezvous Periods

255 )% ( 255 )% (

b i seed a i d b i seed a i u

C D C S C U C S + = + =

MRP S D MRP S U

i d wake i i u wake i

× = × = 255 255

d i seed u i seed

S D S U = =

Advertise in Invite Messages, and selected by an invitee Ca and Cb are constants Jump offset MRP controls how “far” we jump into the future

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ArDeZ – Generation Rendezvous Periods

) ( ) (

wake i rx i wake i rx i

D IM Downlink U IM Uplink + = + =

i d i seed i u i seed

S D S U = =

+ + 1 1 IMrx is the timestamp

• f the Invite Message

Update the seed for next iteration

• First rendezvous period is relative to the reception time of the Invite
• Message. Subsequent periods are relative to the last rendezvous

period’s end time.

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ArDeZ – Supporting Broadcast

1 2 3 4 S1 S2 S3 S4 S5 S6 1 2 3 4 B2 B2 B2 B2 – Broadcast seed. Node-2 transmits, all other neighbors listen.

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ArDeZ – Transmitting and Receiving

DATA/ACK Time

Frame Hdr

Time DATA/ACK

Frame Hdr

Wakeup Wakeup MaxWait

Sender Receiver

• MaxWait – minimize idle listening
• Send a packet every z rendezvous periods to avoid losing

synchronization

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Analysis – Overlapping periods

8-bit 16-bit

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Analysis – Channel Setup

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Simulation

• ns-2 (ns-allinone-2.1b9)
• CBR – 100 packets, 50 bytes
• Only establish channels to a neighbor that has a

path to the sink

• Data rate – 20 Kb/s
• Rendezvous period length, 30ms
• Random number range, 0 … 255
• Energy

– Tx (12 mAh), Rx (1.8 mAh), asleep (5 μAh)

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Results – Channel Setup

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Results – Network Setup Time (36 nodes)

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Results – Node Density vs. Packet

Delivery Ratio

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Results – Throughput vs. Network Sizes

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Results – Energy Drain vs MRP

8-months

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Conclusion

• ArDeZ – An asymmetric MAC that uses

pseudo-random sleep/wake periods.

– Uplink and downlink channels with different duty cycles

• Simple setup procedure

– Low signaling overheads

• No global synchronization or superframe
• Duty Cycle controlled by adjusting each

link’s Mean Rendezvous Period (MRP)

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Current Work

• Comparisons with other MACs

– SMAC, TRAMA, WiseMAC, etc…

• Design and implementation of routing and

transport protocols that make use of MRP

• Collision free extensions

– Listening to neighbors’ seeds

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Questions? kwanwu@uow.edu.au