Energy-Efficient, Application-Aware Medium Access for Sensor Networks

Venkatesh Rajenfran, J. J. Garcia-Luna-Aceves, and Katia ObraczkaComputer Engineering Department

University of California at Santa Cruz

The IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS 2005)

Wang, Sheng-ShihWang, Sheng-ShihSeptember 29, 2005September 29, 2005

Outline

Introduction FLow-Aware Medium Access (FLAMA) Simulation Test-bed Experiment Conclusions

Introduction --- MAC protocols for WSNs Main goal

Energy efficiency Category

Contention-based S-MAC, T-MAC, BMAC, DSMAC, WiseMAC, … Collision increases with the traffic load Degrade channel utilization and waste energy

Schedule-based TRAMA, LMAC, E-MAC, … Requirement of time synchronization Longer delay

FLAMA --- Overview

Main goal Energy efficiency

Features Data gathering application Collision-free Low transmission delay

FLAMA --- Time Organization

• neighbor discovery• time synchronization• traffic information exchange

• data transmission

…

Random access period(contention-based channel access)

Schedule access period(time-slotted channel access)

FLAMA --- Application

sinkQuery dissemination

FLAMA --- Application (cont’d)

sink

Forwarding Tree Formation Each node knows the incoming and outgoing flow

FLAMA --- Flow Model

c, d, and e respectively denote the fractions of the flows that are forwarded

B

AE

C

D

Fb

Fc

Fd

Fe

Node weights are directly proportional to the outgoing flow rate

FLAMA --- Random Access Period

Main tasks Time synchronization Data forwarding tree formation Traffic flow information exchange and

weight computation Two-hop neighborhood information and

corresponding node weight exchange

FLAMA --- Random Access Period

Length Based on the time required to complete

synchronization and tree formation SYNC_INTERVAL

Random access period

…

SYNC_INTERVAL

FLAMA --- Time Synchronization

The sink initiates the time synchronization

A node synchronizes with its parentsender receiver

SYNC

SYNC

SYNC_REQ

T1T2T3

T4

Calculate

T2 = T1 + +

T4 = T3 - +

clock drift

propagation delay

= (T2 – T1 + T3 – T4)/2

FLAMA --- Scheduled-Access Period

Goal Collision-free transmission scheduling

Solution Distributed election algorithm

Decide the state of each node at every slot

Priority

n: node id t: slot id C: constant multiplier

FLAMA --- Distributed Election Algorithm

Calculate my priority.ifif ((I have the highest two-hop priority) AND (I have data to send)) thenthen Transmit the data.elseelse ifif (the node with the highest one-hop priority is my child) thenthen Keep in the received mode. endifendif Go to sleep.end ifend if

B

A

C

D

20

10

5

25Tx

TxRx

Sl

Simulation Setup

Simulation platform: Qualnet Physical layer model: Mica2 motes’ Chipc

on CC1000 Number of nodes: 16 Grid topology: Node distance=75m Radio data rate: 19.2 Kbps Radio range: 300 feet 90m Simulation time: 2000 secs Data packet size: 128 bytes

Comparison

S-MAC Duty cycle=10% Adaptive listening is

allowed Contention window for

synchronization packets: 15 slots

Contention window for data packets: 31 slots

Topology for S-MAC and TRAMA

Simulation Results --- Average Delivery Ratio

FLAMA

TRAMA

S-MAC

FLAMA/TRAMA vs. S-MAC- Collision- Contention

FLAMA vs. TRAMA- Less overhead (no schedule packets)

Simulation Results --- Energy Saving

FLAMA

TRAMA

S-MAC

FLAMA vs. TRAMA- Less overhead (no schedule packets)

S-MAC- Fixed duty cycle

Simulation Results --- Average Queuing Delay

FLAMA

TRAMA

S-MAC

TRAMA vs. others- Schedule announcement- Random schedule

Test-Bed Experiments --- Setup

Platform: TinyOS for Mica2 motes No MAC buffer for frame queuing All sensors are directed to the sink Data payload: 128 bytes S-MAC duty cycle: 10%

Test-Bed Experiments --- Results

• average delivery ratio

• percentage sleep time

• average drops

RTS/CTS failure

- No buffer- Collision

Conclusions

FLAMA: An energy-efficient, schedule-based, MAC protocol Simple Application-aware (data gathering) Collision-free Outperform TRAMA and S-MAC in terms of

reliability and energy saving