Energy and Latency Control in Low Duty Cycle MAC Protocols Yuan Li, Wei Ye, John Heidemann...

Energy and Latency Control in Energy and Latency Control in Low Duty Cycle MAC ProtocolsLow Duty Cycle MAC Protocols

Yuan Li, Wei Ye, John HeidemannYuan Li, Wei Ye, John HeidemannInformation Sciences Institute, Information Sciences Institute,

University of Southern CaliforniaUniversity of Southern California

WCNC 2005WCNC 2005

SpeakerSpeaker ：： Shih-Yun HsuShih-Yun Hsu

OutlineOutline

IntroductionMotivationGlobal Schedule Algorithm (GSA)Fast Path Algorithm (FPA)Experimental ResultsConclusion

IntroductionIntroduction

A

B

C

Wake up

Sleep


Sensor networksChanging batteries is difficultEnergy efficiency is important

Using sleep/wakeup MAC protocol S-MAC T-MAC ZigBee

Schedule-based MAC can increase latency in a multi-hop network


Sleep/wakeup MAC protocolMultiple schedules can occur in large networksNodes that share the same schedule are in the same

virtual clusterBorder nodes spend more time listening or sending

data and therefore consume more energyAlthough some optimizations schedule such as S-

MAC and T-MAC reduce latency, the sleep/wakeup cycle still incurs additional delay

MotivationMotivation

Allows all nodes to converge on a single global schedule to saving energy

Reduce the additional delay with schedule-based MAC

Global Schedule Algorithm Global Schedule Algorithm (GSA)(GSA)To converge on a single schedule

Uniquely identifyPropagate new schedules to other nodesDiscover new schedules

Assume it handle by the basic of sleep/wakeup MAC

GSAGSA

Uniquely identifyA node may start a new schedule with the same ID

when it rebootsAssigned a random identifier each time when it reboots

Combination of the schedule originator’s ID and the age of the schedule

GSAGSA

Propagate schedulesA node discover a new schedule, it compare the

age of the new schedule to its own scheduleChange schedule to the older one

If has the same ageCompare the schedule ID

Change schedule to the lower one

When change to the new schedule, it will update its neighbor

The new schedule will propagate through its virtual cluster

GSAGSA

A CB A

Schedule ID : 1Schedule Age : 0

AdoptA C

Schedule ID :1Schedule Age : 0 + t

GSAGSA

A CB A


AdoptA


B’s Schedule Age : 50 > A’s Schedule Age : 0

C


Schedule ID : 1Schedule Age : 50 + t

C’s Schedule Age : 0 < A’s Schedule Age : 50

Fast Path Algorithm (FPA)Fast Path Algorithm (FPA)

When a packet travels over multiple hops it can be delayed when its next-hop node is sleeping

FPA adds additional wakeup periods called fast path schedules along the path of source to sink

FPAFPA

Node 1

Node 2

Node 3

Node 4

Regular listen Fast path schedule

Data transmission S-MAC

FPAFPA

Node 1

Node 2

Node 3

Node 4


Data transmission S-MAC

TtxTcs d = Tcs + Ttx

d

2d

FPAFPA

The request of FPA is piggybacked on the routing packetAODVDSR

The time needed to transfer each following data packet in a n hop network over a fast path is approximately nd

FPAFPA

Node 1

Node 2

Node 3

Node 4


Data transmission

Node 5

FPAFPA

When the fast path schedule overlaps with the regular listen time, data is transferred during regular listen time instead

No explicit mechanism to remove fast path schedulesWhen the routing path changes, another fast path is

established along with the new pathThe old fast path will expire

FPAFPA

Many fast paths may exist at the same timeAssume each node can support a small number of

active pathseach node maintained fast path independently

If fast path slots from different paths overlap in time at a nodeThis slot could be lengthened

Experimental Results - GSAExperimental Results - GSA

Multiple schedules with GSAUsing S-MAC without global scheduling in an

outdoor network of 50 sensor nodeSchedule are identified by the initializing nodes

IDsSchedule 1 is initialized by node 1


With linear topology50 Mica2Dot motes with TinyOSS-MAC based10% duty cycleEach nodes are placed about 90cm apart, maki

ng a line about 45m long.Set transmission power to the lowest level

RF output power, -20dBm; PA POW, 01Transmission range : 2m


Schedule adoption is based on which nodes hear each other, the order in which nodes are activated is importantRandomly activate each mote at the start

Each nodes turned on manually, in pre-experiment state, and listens continuously

Broadcast a message from a central node to make all nodes to begin

Collect sleep schedule information in the networkRepeat the test for 4 times


Trigger packet was not always received by the nodes and in most experiments, 18 ～ 36% failed to participate

Experimental Results - GSAExperimental Results - GSA- : failed to active * : initial the scheduleX : use the primary schedule o : use the secondary schedule


Fail Wake 1 2 3 4 Change

18 32 16% 84% 37.5%

13 37 22% 49% 29% 67.6%

9 41 29% 37% 27% 7% 100%

16 34 21% 48% 24% 8% 91.2%


Expected that schedule boundaries would be relatively distinctOnly a few nodes on the border knowing multiple

schedulesShort-range radio reception is quite good to some

distance

Experimental Results - FPAExperimental Results - FPA

With linear topology10 Mica2 motes with TinyOSS-MAC based5% duty cycleEach motes are placed about 2m apartTransmission range : 3m


Source sent 10 unicast messages, each 100B long

Each message is sent 25s after the previousMeasure the arrival time of the message at eac

h node Repeat the experiment 5 times each with and

without fast paths enabled.


In the 100 packets transmitted in all the experiments, 2 packets are lost and not successfully retransmitted after 7 retriesThese packets will be ignored

6 packets were lost and then successfully retransmitted by the MAC layerThe effect of these packets will be discussed

ConclusionConclusion

Global Schedule Algorithm (GSA) allows all nodes to converge on a single global schedule to conserve energy

Fast Path Algorithm (FPA) allocate additional slots to avoid schedule misses and reduce latency

GSA and FPA both are experiment with actual networks

Energy and Latency Control in Low Duty Cycle MAC Protocols Yuan Li, Wei Ye, John Heidemann...

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