an adaptive energy-efficient and low- latency mac for data gathering in wireless sensor networks...
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An Adaptive Energy-Efficient and Low-Latency MAC for Data Gathering in Wireless Sensor Networks
Gang Lu, Bhaskar Krishnamachari, and Cauligi S. RaghavendraDepartment of Electrical Engineering
University of Southern California
18th Intl. Parallel and Distributed Processing Symposium (IPDPS’04)
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Outline
Introduction DMAC Protocol Performance Evaluation Conclusions
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Main Concern
Primary goal: Energy efficiency Limited battery power
Secondary goal: Latency, throughput, fairness Source of energy consumption
Idle listening Collisions Overhearing Control packet overheads
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Issues in S-MAC
Main idea Eliminate idle listening
Major shortcoming Long delay Fixed duty cycle
Unadapted to the traffic variation Improvement
Adaptive listening Challenge
Data Forwarding Interruption (DFI) problem
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DFI Problem
Data forwarding process will stop at the node whose next hop is out of the overhearing range because it is in sleep mode
Packets are queued until the next active period, which increases latency
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DMAC Protocol
Application Data gathering
Motivation DFI problem
Objective Design of a MAC protocol, where nodes can
dynamically increase duty cycles and their nearby nodes keep asleep
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DMAC Overview
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
…… sleep
…… sleep
…… sleep
…… sleep
data ack
data ack
data ack
data ack
data ack
data ack
time
duty cycleadaptation
dataprediction more-to-send
staggered wakeup schedule
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Staggered Wakeup Schedule
Nodes wake up sequentially like a chain reaction An interval comprises receiving, sending, and sleep
periods
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
Rx Tx
…… sleep
…… sleep
…… sleep
…… sleep
data ack
data ack
data ack
data ack
data ack
data ack
time
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Staggered Wakeup Schedule (cont’d)
Tx period = Rx period = Tx: transmit data packet, receive ack packet Rx: receive data packet, transmit ack packet
Collision avoidance = BP + CW + DATA + SP + ACK
BP: backoff period (like DIFS in IEEE 802.11) CW: contention window SP: short period (like SIFS in IEEE 802.11) BP > SP
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Duty Cycle Adaptation
Scenario A node has multiple packets to send at a sending slot
Idea Increase own duty cycle Request other nodes on the multihop path to increase the
ir duty cycles Solution
slot-by-slot renewal mechanism More data flag (piggybacked in both data and ack packets)
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Tx
time
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Tx
Multiple packets
time
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Tx
data(more data)
Multiple packets
time
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Rxack(more data)
time
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Rx
Tx
data(more data)
time
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Rx
Tx
Rxack(more data)
time
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Rx Rx
time
data
Tx Tx
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Rx Rx
time
ack
Tx Tx
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Duty Cycle Adaptation (cont’d)
Rx Tx
Rx Rx
Tx
Tx
sleep
time
Rx
Tx
data
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Data Prediction
A
B C
S S S Rx Tx ……Rx
S S S S S ……Rx Tx
S S S Tx S ……Rx Tx
A
B
C1 packet 1 packet
additional sending
slot
additional receiving
slot
data
data ack
ack
3
3
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A
More-to-Send Packet
MTS packet Explicit control packet
Dest. local ID and a flag Request MTS (flag=1) /clear MTS (flag=0)
The MTS packet incurs small increase in slot length, and energy consumption
B
A
D
C
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More-to-Send Packet (cont’d)
A node sends a request MTS when Channel is busy Receives a request MTS from its children
A node sends a clear MTS when Buffer is empty All request MTSs received from children are cleared It sends a request MTS to its parent before and has not se
nt a clear MTS
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Performance Evaluation --- Model
Energy cost The total energy cost of
deliver a certain number of packets from sources to the sink
Latency End-to-end delay of a
packet Delivery ratio
The ratio of the successfully delivered packets to the total packets originating from all sources
Radio bandwidth 100 Kbps
Radio transmission range 250 m
Radio interference range 550 m
Data packet length 100 bytes
Transmit power 0.66 W
Receive power 0.395 W
Idle power 0.35 W
MTS packet length 3 bytes
Receiving/sending slot (w/ MTS)
10 ms (11 ms)
Active period in SMAC 20 ms
Duty cycle 10%
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Multihop Chain Evaluation
source
• Scenario (11 nodes)
sink
200 m
Increase linearly
Increaselinearly
Non-next hop nodes haveadditional active periods
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Traffic Load Evaluation --- Random Data Gathering Tree
Sensor field: 1000m 500m area 50 nodes randomly deployed Sink is at the right bottom corner 5 sources are at the margin
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Traffic Load Evaluation --- Latency
• full active CSMA/CA has the smallest delay for all traffic loads• DMAC/MTS handle the highest traffic load with the smallest delay
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Traffic Load Evaluation --- Energy
• DMAC and DMAC/MTS are two most energy efficient MAC protocols• DMAC outperforms DMAC/MTS because of less overheads requested by MTS packets
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Traffic Load Evaluation --- Delivery Ratio
• DMAC/MTS is better than other protocols• SMAC and DMAC have lower delivery ratio when the traffic load is heavy
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Scalability Evaluation
100 nodes randomly deployed in a 100m 500m area
Traffic generation: 1 message per 3 seconds Sink: at the right bottom corner Sources: at the margin
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Scalability Evaluation --- Latency and Energy
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Energy Latency
SMAC: a general-purpose energy-efficient MAC protocolDMAC: not suitable for applications that require data exchange between arbitrary sensor nodes
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Conclusions
Techniques in DMAC protocol Staggered active/sleep schedule Duty cycle adaptation Data prediction More-to-send packet
Advantages in DMAC protocol Tree-based data gathering Energy-efficient Low latency