Energy-Efficient and Reliable Medium Access in Sensor Networks

Authors: Vivek Jain, Ratnabali Biswas and Dharma P. AgrawalDepartment of Computer Science

University of Cincinnati{jainvk, biswasr, dpa}@ececs.uc.edu

Presenter: Dr. Younghwan YooDepartment of Computer Science

University of Cincinnatiymomo@ececs.uc.edu

Outline Wireless Sensor Network Reliable Sensor MAC Hidden Node Problem Energy Efficient Sensor MAC Protocol Design Performance Evaluation Summary Future Work

Wireless Sensor Network (WSN)

Usually a set of small immobile nodes referred as motes

Generally static topology Cheap alternative to monitor inaccessible or

inhospitable terrains Applications

Medical Applications – wireless bio-sensors Nuclear and chemical plants Environmental monitoring Industrial Automation Ocean monitoring Battlefields

Good Reliable MAC

ControlOverhead

CollisionCongestionTransmissionRate Control

Idle Listening

Hidden Node

Overhearing

Error Recovery

Latency

Node receives more than one packet at

same time

Leads to packet loss due to buffer

overflow

Wastes energy listening to idle

channel

Wastes energy receiving packets for other nodes

Recover packets corrupted at physical

layerWastes energy

transmitting control packets

Carrier-sense, backoff, transmission, propagation,

processing, queuing

Reliable Sensor MAC

Hidden Node Problem

Data

Data

Data

Data

A B C D

Random

Backoff

Collision

Random

Backoff

Hidden node problem exists between every other pair nodes along a route

RTS/CTS packets constitute large overhead

Transmission rate control mechanism employed

Efficient-Efficient Sensor MAC

Energy-Efficient MAC

Adaptive DutyCycling

WakeupOn-Demand

Overemitting: Node transmits when receiver not ready for reception

Reduces ThroughputIncreases Latency

E2RMAC - Design Two radio solution

A Main radio for actual data transmission/reception A low power pico radio to detect and transmit busy tones

CSMA/CA based Skip Backoff mechanism: Intermediate receiving

node skips random backoff after successful reception

Implicit/Explicit Ack Transmission rate control: After receiving implicit

Ack refrain from transmitting for 2communication_duration

Adaptive retransmission attempts

ep11

Retransmission Attempts = Tx_Attempts + , where pe is packet error rate

Protocol for always-on requirement, e.g. automotive, telematics

E2RMAC – Basic Operation A B C D

Wakeup

Random Backoff

Filter

Data

Backoff Skipped

Processing Delay

Transmission Backoff (2xCommunication_Duratio

n + Random_Duration)

WakeupImplicit Ack

Propagation and Processing

DelaysFilter

Data

WakeupFilter

Data

Wakeup Explicit Ack

E2RMAC – Handling False Wakeups

WakeupFilter

Set ReceiveTimer = 2xCommunication_Duration

Data Wakeup

Set ReceiveTimer = Communication_Duration

Filter

Set ReceiveTimer = 2xCommunication_Duration

Data

Set ReceiveTimer = Communication_Duration

A B C

X Y Z

E2RMAC – Simulation Parameters

Parameter Value

Packet size 77 bytes

Filter/CTS size 19 bytes

RTS size 27 bytes

Ack size 11 bytes

Transmission rate 250 kbps

slotTime 1200 µs

TSIFS 200 µs

CWmin 1

CWmax 4

Tx_Attempts 5

Psensing= PTx= PRx 41 mW

Psleep 0.015 mW

PTx_on = PTx_off 35 mW

TTx_on 580 µs

Pwakeup_sensing= Pwakeup_Tx= Pwakeup_Rx 0.015 mW

Performance Evaluation – Linear Topology

All schemes are equally reliable Latency of E2RMAC is higher

than RMAC due to latency involved in transmitting filter packets and switching on/off the main radio

STEM and E2RMAC are the only energy efficient protocols

pe=0.4

Performance Evaluation – 8-hop Linear Topology

PDR of RTS-CTS based protocols is higher than E2RMAC as it alleviates the hidden terminal problem

pe=0.4

Performance Evaluation Transmission of control messages by STEM leads to better PDR,

poor latency and more energy consumption Due to adaptive retransmissions, E2RMAC tries to deliver old

packets first, leading to buffer overflow at source nodes and thus dropping newly generated packet less PDR when pe=0.4

Performance Evaluation

Energy expended by the common intermediate node

Energy Expended by the route nodes

E2RMAC consumes less energy by avoiding control overhead, and false wakeup

Performance Evaluation E2RMAC and STEM protocol have comparable

performances. We can conclude that transmission rate control and other optimizations successfully mitigates the hidden terminal problem

Summary – E2RMAC Best suited for dual radio architecture Energy savings largely depends on power consumption of

low-power pico radio Minimizing energy consumption

Minimum control messages Implicit Ack by wakeup radio Timers to avoid false wakeup

Ensuring reliability Adaptive retransmission attempts Implicit/explicit Ack Transmission rate control

Minimizing latency Skip backoff mechanism Minimum control overhead

Future Work Energy Consumption Analysis for

the proposed and existing protocols To be energy-efficient than single radio

solution (no sleep cycles), preliminary results suggests that pico-radio should consume less than

25% of Main radio power for E2RMAC 17% of Main radio power for STEM-T

8% improvement over STEM-T

Thank You!!!For further queries, please contact the authors

Backup Slides

Energy Consumption Analysis

RMAC – Design

Data

Data

Data

Data

A B C D

Random Backoff

Transmission Backoff

Implicit Ack

Ack

Propagation and Processing

DelaysBackoff Skipped

Explicit Ack

Processing Delay

CSMA/CA based Intermediate receiving

node skips random backoff after successful reception

Implicit Ack After receiving implicit Ack

refrain from transmitting for transmission backoff duration = 2communication_duration

RMAC – Performance Evaluation

Linear topology, Packet arrival rate = 5 and 10 pkts/sec respectively

Ack-based schemes have better PDR MultiPath and MultiPacket schemes have constant latency per hop

as no retransmissions are involved at any node

pe=0.2

RMAC – Performance Evaluation

Even at higher packet error rate, RMAC delivers more than 80% of packets

Also, latency per hop of RMAC is less than its Ack-based counterpart

pe=0.4

RMAC – Performance Evaluation

RMAC and CSMA-Ack schemes are compared for 6-hop linear topology by varying pe from 0 to 0.6

RMAC performs better than CSMA-Ack in all scenarios

RMAC – Performance Evaluation

Two 6-hop routes intersecting at the center node

At pe=0.6, RMAC uses slightly more retransmission attempts than CSMA-ACK but delivers more packets with same latency