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 [email protected]
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