A+MAC: A+MAC: A Streamlined Variable Duty-Cycle A Streamlined Variable Duty-Cycle MAC Protocol for Wireless Sensor NetworksMAC Protocol for Wireless Sensor Networks

1Sang Hoon Lee, 2Byung Joon Park and 1Lynn Choi1School of Electrical Engineering, Korea University

{smile97, lchoi}@korea.ac.kr2Department of Computer Science, Kwangwoon University

bjpark@kw.ac.kr

In Proc. Computer and Applications (CCA) 2012To appear International Journal of Distributed Sensor Networks (SCIE)

MotivationMotivationTwo motivations

Control packets contain unnecessary information.Active period is still long.

IdeasSimplification of CSMA/CA

We eliminate unnecessary information from control packets.

Combined SYNC/RTS PeriodWakeup preamble period

A short wakeup period is designated to announce the presence of traffic.

Receiver(Busy cycle)

CTS/ Sleep/ ReceivePeriodfor SYNC for RTS

Receiver(Idle cycle)

Active Period

Sleep Periodfor SYNC

Active Period

SenderCS CS Send Data

Tx SYNC Tx RTS Rx CTS

<AMAC>

Idea 1: Simplification of CSMA/CAIdea 1: Simplification of CSMA/CARemove the unnecessary information from control packets

No virtual carrier sensingNodes, which don’t participate in a communication, sleep until the next cycle timeWe need no duration field in control packets.

No transmitter address field in CTS and ACK packetsThe destination of CTS and ACK already knows who will send the control packet.

SMAC versus A+MAC: control packet formats

Idea 2: Combined SYNC/RTS PeriodIdea 2: Combined SYNC/RTS PeriodReduce the length of an active period

Each node seldom transmits a SYNC packet.The contention between a SYNC packet and a RTS packet may be very light.

Nodes overuse energy to prevent the contention.

SMAC versus A+MAC

Idea 3: Wakeup Preamble PeriodIdea 3: Wakeup Preamble PeriodRemove the unnecessary long idle listening during idle cycle

Exploit a complementary cooperation between preamble sampling and CSMA/CAContention resolution ability and synchronized schedules of CSMA/CA based MACShort idle listening of preamble sampling

Wakeup preambleA sender transmits it to notify only the presence of traffic.Contains no information. Therefore, A+MAC tolerates collisions between multiple wakeup preambles.

If a node receives a wakeup preamble or detects a collision during a wakeup preamble period, it extends its active period.

Since each node coordinates wakeup schedule with neighbor nodes, a sender can send a short preamble just at the receiver’s wakeup preamble period.

A+MAC vs. AMACA+MAC vs. AMACA+MAC

AMAC

Receiver(Busy cycle)

CTS/ Sleep/ ReceivePeriodfor SYNC for RTS

Receiver(Idle cycle)

Active Period

Sleep Periodfor SYNC

Active Period

SenderCS CS Send Data

Tx SYNC Tx RTS Rx CTS

S-MAC vs. AMAC vs. A+MACS-MAC vs. AMAC vs. A+MACS-MAC AMAC A+MAC

Control packets All packets are 9B.

Same to S-MAC Simplified formatRTS: 7BCTS, ACK: 5BSYNC: 9BWakeup preamble: 1B

Notifying the presence of traffic

RTS Communication SYNC Wakeup preamble

The length of idle listening

Separate SYNC/RTS(64ms in NS2)

SYNC period(32ms in NS2)

Slot time(1ms in NS2)

Receiver’s active period

Separate SYNC/RTS(64ms in NS2)

Separate SYNC/RTS(64ms in NS2)

Combined SYNC/RTS(32ms in NS2)

Dynamic duty cycling

None Adaptive Active PeriodAdaptive Cycle Time

Wakeup Preamble PeriodAdaptive Cycle Time

ExperimentationExperimentationThe network topology and design parameters used for NS-2 simulations

Simulated protocolsS-MACA-MAC

Our previous study for an energy efficient MAC protocolDynamic duty cycling

A+MAC

Parameter Value

Number of nodes 200 random nodes

Number of messages 100 messages per a source

Message size 100 bytes

Packet generation interval 0 to 10 seconds

Duty cycle of S-MAC 11% (4T)

Maximum duty cycle of A+MAC 0.04% to 0.31% (32T to 4T)

Average Packet LatencyAverage Packet LatencyThe average latency of 100 packets

The longer the packet inter-arrival time, the shorter the latencyThe delay due to the contention diminishes.

The cycle time reduction can effectively alleviate the impact of contention in burst traffic patterns.

The operation of busy nodes do not collide with the operation of slow nodes.

When the packet inter-arrival time is long enoughThe latency of A+MAC becomes higher due to the long hop delay incurred by a larger maximum cycle time.

Energy ConsumptionEnergy ConsumptionThe average per-node energy consumption in delivering 100 packets

AMAC can almost halve the energy consumption of S-MAC.AMAC removes the unnecessary wakeups due to the RTS/CTS.

A+MAC more aggressively reduces the energy consumption due to idle listening.By eliminating idle listening due to SYNC/RTS period from active period, A+MAC4T can reduce the energy by more than 98% compared to SMAC although it can also substantially reduce the packet latency.

Empirical EvaluationEmpirical EvaluationThe network topology and design parameters used for MICA2 motes simulations

Simulated protocolsS-MACA+MAC

Parameter Value

Sensor nodes MICA2 motes with CC1000 transceiver

Topology 14 linear nodesA sink and a source are located at both ends.

Number of messages 20 messages

Message size 100 bytes

Packet generation interval 1 to 10 seconds

Duty cycle of S-MAC 11% (4T)

Maximum duty cycle of A+MAC 0.04% to 0.31% (32T to 4T)

Average Packet LatencyAverage Packet LatencyThe average latency of 20 packets

A+MAC4T has the highest communication performance.It enhances the performance up to 13.5% from SMAC since the adaptive cycle time can decrease the impact of sleep delay on the message latency.

As the packet inter-arrival time increases, SMAC catches up A+MAC8T. In other words, A+MAC8T can reduce the number of nodes’ wakeup while it provides comparable communication performance with S-MAC.

Energy ConsumptionEnergy ConsumptionThe average per-node energy consumption in delivering 20 packets

We simulated the energy consumption of a node with AEON tool.The energy model of AEON is based on measurements of node current draw and the execution of real code.

A+MAC4T can decrease 90% of energy consumption of SMAC. The diminution in the energy consumption of A+MAC is smaller than that in the result of NS-2 simulation. The impact of overhearing on the energy consumption is not observed

ConclusionConclusionA+MAC is fundamentally different from the existing MAC protocols

A complementary cooperation between preamble sampling and CSMA/CAEach node can dynamically adjust the operation of MAC protocol.

Duration of an active periodDuration of a periodic interval (cycle time)

Variable duty-cycle operation with wakeup preamble allows us to achieve both high performance and low energy consumption at the same time.

Busy nodes can work with the highest duty-cycle.Idle nodes can work with the lowest duty-cycle and minimize the idle listening.

Q&AQ&A